JP7737186B1 - Absolute position detection device and absolute position detection method - Google Patents

Abstract

An absolute position is detected with high resolution using only a magnetic scale having a magnetized pattern consisting of one non-repeating code pattern.
[Solution] The absolute position detecting device includes a magnetic scale having one magnetic track on which a magnetization pattern consisting of a non-repeating code pattern is recorded, and a detecting device. The detecting device has two sets of detecting element groups, each consisting of a plurality of detecting elements, arranged opposite to each other on the magnetic scale, calculates a code section position calculation value corresponding to the code section position based on code information of the magnetic scale obtained from the magnetization pattern, calculates a section interpolation value of the magnetic scale using a difference value between the detection values of each detecting element in a plurality of detecting element pairs selected from the two detecting element groups, and obtains the absolute position over the entire length of the magnetic scale from the code section position calculation value and the section interpolation value.
[Selected Figure] Figure 1

Description

The present invention relates to an absolute position detection device and a position detection method.

Magnetic scale devices used for measurement, positioning control, etc. are known to be absolute value magnetic scale devices and incremental value magnetic scale devices. Incremental value magnetic scale devices output one unit pulse for each unit displacement as the moving object moves, while absolute value magnetic scale devices output an output value that corresponds to the absolute position of the moving object from the origin.

Unlike incremental magnetic scale devices, absolute value magnetic scale devices do not need to be returned to the origin when the power is turned off, and no cumulative errors occur due to the influence of external noise. Furthermore, even if the detection head comes off the scale, the absolute position of the returned point can be instantly obtained by returning it to the scale. Therefore, absolute value magnetic scale devices are widely used in various industrial machines to measure the position or absolute position of linearly moving objects.

For example, Patent Document 1 discloses an absolute value magnetic scale device that includes a magnetic scale in which a first magnetic track recording a magnetization pattern in which no identical bit combination codes are generated is juxtaposed with a second magnetic track recording an alternating magnetization pattern whose period is one bit length of the magnetization pattern. The absolute value magnetic scale device generates a high-resolution digital absolute position signal by interpolating a section absolute position signal over one period based on a two-phase signal obtained from the second magnetic track into a code position signal obtained from the magnetization pattern of the first magnetic track.

Patent No. 2571394

The absolute value magnetic scale device disclosed in Patent Document 1 requires that two magnetic tracks be arranged adjacent to each other on the magnetic scale: an absolute value track as the first magnetic track and an alternating magnetic track as the second magnetic track. This makes the magnetic scale structure complex and increases manufacturing costs. Furthermore, the magnetic scale width must be wide, and the detection head must be sized to match the magnetic scale, making it difficult to miniaturize the absolute value magnetic scale device.

The present invention was made in consideration of these circumstances, and its purpose is to provide an absolute position detection device and method that can detect high-resolution absolute position using only a magnetic scale with a magnetized pattern consisting of a single non-repeating code pattern, without using an alternating magnetic track, and that allows for the device to be made smaller and less expensive.

In order to solve the above problem, the first technical means of the present invention comprises a magnetic scale on which a magnetization pattern having a non-repeating code pattern of n bits (n is an integer of 2 or more) magnetized at a predetermined pitch is recorded, the magnetization pattern having both at least one portion where the pole changes from south to north and one portion where the pole changes from north to south within a continuous (n+1) pitch, a detection device having a first detection element group consisting of at least n detection elements arranged at one pitch intervals facing the magnetic scale, and a second detection element group consisting of at least n detection elements arranged at a half pitch offset from each of the detection elements of the first detection element group, The magnetic scale is characterized by comprising a code section position calculation unit that calculates a code section position calculation value at a code section position corresponding to n-bit code information obtained from the detection values of each detection element of the first detection element group or the second detection element group, based on the code information; an interpolated value calculation detection element identification unit that identifies an interpolated value calculation detection element of the first detection element group or the second detection element group that corresponds to the code section position; an interval interpolated value calculation unit that calculates an interval interpolated value at the code section position from the detection values of the interpolated value calculation detection elements; and an absolute position calculation unit that obtains an absolute position signal over the entire length of the magnetic scale from the code section position calculation value and the interval interpolated value.

A second technical means of the present invention is the first technical means, wherein the detection device has a lookup table that stores, for each code section position of the first detection element group, two pairs of detection element pairs, each consisting of one detection element of the first detection element group and one detection element of the second detection element group, as detection elements for calculating first detection element group interpolated values, and, for each code section position of the second detection element group, two pairs of detection element pairs, each consisting of one detection element of the first detection element group and one detection element of the second detection element group, as detection elements for calculating second detection element group interpolated values, and the interpolated value calculation detection element identification unit selects and stores the two pairs of detection element pairs in the lookup table according to the code section position of the first detection element group or the second detection element group. The interval interpolation value calculation unit identifies either the first detection element group interpolation value calculation detector element or the second detection element group interpolation value calculation detector element as the detector element for calculating the interval interpolation value based on the magnitude of the difference in detection values between the detector elements of the pair of detector elements in the first detection element group interpolation value calculation detector element or the second detection element group interpolation value calculation detector element stored in a file, and the interval interpolation value calculation unit calculates the interval interpolation value at the code interval position based on the ratio of the difference in detection values between the detector elements of each of the two pairs of detector elements in the first detection element group interpolation value calculation detector element or the second detection element group interpolation value calculation detector element identified by the interpolation value calculation detector element identification unit.

A third technical means of the present invention is the first technical means, wherein the detection device has a lookup table that stores, for each code section position of the first detection element group, two pairs of detection element pairs, each consisting of one detection element of the first detection element group and one detection element of the second detection element group, as detection elements for calculating an interpolated value for the first detection element group, and two pairs of detection element pairs, each consisting of one detection element of the first detection element group and one detection element of the second detection element group, as detection elements for calculating an interpolated value for the second detection element group, for each code section position of the second detection element group; and the detection element specification unit for calculating an interpolated value determines the minimum absolute value of the detection values of each detection element of the first detection element group and the minimum absolute value of each detection element of the second detection element group. The section interpolation value calculation unit compares the minimum absolute value of the detection values of the output elements with the minimum absolute value of the detection values of the output elements, and identifies the first detection element group interpolation value calculation detection element or the second detection element group interpolation value calculation detection element stored in the lookup table with the larger absolute minimum value as the detection element for calculating the section interpolation value at the code section position of the first detection element group or the second detection element group, and calculates the section interpolation value at the code section position based on the ratio of the difference values between the detection values of each of the detection elements in each of the two detection element pairs for the first detection element group interpolation value calculation detection element or the second detection element group interpolation value calculation detection element identified by the interpolation value calculation detection element identification unit.

A fourth technical means of the present invention is the first technical means, wherein the detection device has a memory unit that stores code information obtained from a non-repeating code pattern of the magnetic scale, and the interpolation value calculation detection element identification unit references the code information stored in the memory unit according to the code section positions of the first detection element group and the second detection element group, and selects two pairs of detection element pairs, each pair consisting of one detection element of the first detection element group and one detection element of the second detection element group, that satisfy the selection conditions as detection elements for first detection element group interpolation value calculation corresponding to the code section position of the first detection element group, and one detection element of the second detection element group. One of two pairs of detector elements, each consisting of one detector element of the first detector element group and one detector element of the second detector element group, that meets the selection conditions for the detector elements for calculating the interpolated value of the second detector element group corresponding to the code section position is identified, and the section interpolation value calculation unit calculates the section interpolation value at the code section position based on the ratio of the difference values between the detection values of each of the two pairs of detector elements, for the detector elements for calculating the interpolated value of the first detector element group or the detector elements for calculating the interpolated value of the second detector element group identified by the detector element identification unit for calculating the interpolated value of the interpolated value.

A fifth technical means of the present invention is that the interpolation value calculation detection element identification unit identifies one detection element of the first detection element group and one detection element of the second detection element group as a detection element pair, which satisfy the selection conditions as a first detection element group interpolation value calculation detection element corresponding to the code section position of the first detection element group, in accordance with the code section positions of the first detection element group and the second detection element group, based on n-bit code information acquired from the detection value of each detection element of the first detection element group or the second detection element group, and the polarity of the front and rear magnetic poles estimated from the magnetization pattern of the magnetic scale to which each detection element of the first detection element group or the second detection element group faces. Two pairs of detector elements are identified, each pair consisting of one detector element of the first detector element group and one detector element of the second detector element group, which satisfy the selection conditions for the detector elements for calculating the interpolated value of the second detector element group corresponding to the code section position of the second detector element group. The interval interpolation value calculation unit calculates the interval interpolation value at the code section position based on the ratio of the difference values between the detection values of the respective detector elements of the two pairs of detector elements for calculating the interpolated value of the first detector element group or the second detector element group identified by the interpolation value calculation detector element identification unit.

A sixth technical means of the present invention is the first technical means, wherein the detection device further includes one auxiliary detection element each shifted by half a pitch outside the detection elements located at both ends of the first detection element group and the second detection element group, and the interpolation value calculation detection element identification unit identifies one detection element of the first detection element group and one detection element of the second detection element group that meets the selection conditions as a first detection element group interpolation value calculation detection element corresponding to the code section position of the first detection element group based on the magnetization pattern of the magnetic scale acquired from the detection values of each detection element and auxiliary detection element of the first detection element group and the second detection element group, depending on the code section position of the first detection element group and the second detection element group. and two pairs of detector elements, each pair consisting of one detector element of the first detector element group and one detector element of the second detector element group, that satisfy the selection conditions for the detector elements for calculating the interpolated value of the second detector element group corresponding to the code section position of the second detector element group. The interval interpolation value calculation unit calculates the interval interpolation value at the code section position based on the ratio of the difference values between the detection values of the detector elements of each of the two pairs of detector elements, for the detector elements for calculating the interpolated value of the first detector element group or the detector elements for calculating the interpolated value of the second detector element group identified by the detector element identification unit for calculating the interpolated value of the first detector element group or the detector elements for calculating the interpolated value of the second detector element group.

The seventh technical means of the present invention is characterized in that, in the first to sixth technical means, the two pairs of detection elements serving as the detection elements for calculating the first detection element group interpolated value and the detection elements for calculating the second detection element group interpolated value are a combination of detection elements in which the difference in detection values of the detection elements of one of the detection element pairs is zero when the magnetic scale displacement is in the vicinity of (m-1) pitches (m is a positive integer), and a combination of detection elements in which the difference in detection values of the detection elements of the other detection element pair is zero when the magnetic scale displacement is in the vicinity of (m-1/2) pitches.

An eighth technical means of the present invention is an absolute position detection device comprising: a magnetic scale having one magnetic track on which a magnetization pattern is recorded, the magnetization pattern having a non-repeating code pattern of n (n is an integer of 2 or more) bits magnetized at a predetermined pitch, the magnetization pattern having both at least one portion where the pole changes from south to north and one portion where the pole changes from north to south within consecutive ( n+1) pitches; and a detection device having two detection element groups, a first detection element group consisting of at least n detection elements arranged at one pitch interval facing the magnetic scale, and a second detection element group consisting of at least n detection elements arranged at a half pitch offset from each of the detection elements in the first detection element group,
The detection device calculates a code section position calculation value corresponding to a code section position based on code information obtained from the magnetization pattern of the magnetic scale, calculates a section interpolation value at the code section position using a difference value between detection values of each detection element in a plurality of detection element pairs selected from the two detection element groups, and obtains an absolute position over the entire length of the magnetic scale from the code section position calculation value and the section interpolation value.

A ninth technical means of the present invention is an absolute position detection method using a magnetic scale having one magnetic track on which a magnetization pattern is recorded, the magnetization pattern having a non-repeating code pattern of n (n is an integer of 2 or more) bits magnetized at a predetermined pitch, the magnetization pattern having both at least one portion where the pole changes from south to north and one portion where the pole changes from north to south within consecutive ( n+1) pitches, and a detection device having two detection element groups, i.e., a first detection element group consisting of at least n detection elements arranged at one pitch interval facing the magnetic scale, and a second detection element group consisting of at least n detection elements arranged at a half pitch offset from each of the detection elements in the first detection element group ,
code information of the magnetization pattern of the magnetic scale is obtained from detection values of the two groups of detection elements, a code section position calculation value corresponding to a code section position of the magnetic scale is calculated based on the code information, and an interval interpolation value at the code section position is calculated based on a difference value between detection values of each detection element in a plurality of pairs of detection elements selected from the two groups of detection elements, and an absolute position over the entire length of the magnetic scale is obtained from the position calculation value based on the code section position and the interval interpolation value.

The present invention provides an absolute position detection device and absolute position detection method that can detect high-resolution digital absolute position using only a magnetic scale with a magnetized pattern consisting of a single non-repeating code pattern, thereby enabling the device to be made smaller and less expensive.

1 is a diagram illustrating an example of the configuration of an absolute position detection device according to an embodiment of the present invention. 10A and 10B are diagrams illustrating an example of a 6-bit non-repeating code pattern and the relationship between the code position number. FIG. 1 is a diagram illustrating an example of a magnetic scale having a 6-bit non-repeating code pattern, but outside the scope of the present invention. FIG. 10 is a diagram for explaining an example of a "code information-code position number correspondence table" showing code position numbers corresponding to code information obtained from a detection element. 10 is an example of a "code position number-detector element for calculating interpolated value correspondence table" in which the detector element for calculating interpolated value to be used corresponds to the code position number. FIG. 10 is a process flow diagram showing an example of absolute position calculation in a position calculation unit. FIG. 10 is a process flow diagram showing an example of absolute position calculation in a position calculation unit. 10 is a diagram for explaining the positional relationship between each of the detection elements of groups A and B and the magnetic scale. FIG. FIG. 10 is a diagram showing the detection values obtained from each detection element of group A at code position numbers 0 to 1. FIG. 10 is a diagram showing the detection values obtained from each detection element of group B at code position numbers 0 to 1. 10 is a diagram showing the detection values of detection elements selected from each detection element of group A for calculating an interpolated value at code position numbers 0 to 1. FIG. 10 is a diagram showing the detection values of detection elements selected from each detection element of group B for calculating an interpolated value at code position numbers 0 to 1. FIG. 10 is a diagram showing the difference values of the detection values of each detection element of the detection element pairs of group A at code position numbers 0 to 1. FIG. 10 is a diagram showing the difference values of the detection values of each detection element of the detection element pairs of group B at code position numbers 0 to 1. FIG. 10 is a diagram for explaining which difference value of the interpolation value calculation detection element of group A or group B is used to calculate the interval interpolation value at code position numbers 0 to 1. FIG. 10 is a diagram showing the change in the minimum absolute value of the detected values of the detecting elements of groups A and B at code position numbers 0 to 1. FIG. 10A and 10B are diagrams for explaining a method of calculating an interval interpolation value using a difference value between detection values of each detection element of a detection element pair of group B. FIG. 10A and 10B are diagrams for explaining a method of calculating an interval interpolation value using a difference value between detection values of each detection element of a detection element pair in group A. 10A and 10B are diagrams illustrating results when an absolute position is calculated from a chord section position calculation value and a section interpolation value. FIG. 10 is a diagram showing the detection values of all the detection elements when group A is at code position number 0. 10 is a table showing selection conditions for detecting elements for calculating interpolated values when group A is at code position number 0. 10 is a table showing selection conditions for detecting elements for calculating interpolated values when group A is at code position number 0. FIG. 10 is a diagram showing the detection values of each detection element of a detection element pair that satisfies the selection conditions for a detection element for calculating an interpolated value when group A is at code position number 0. FIG. 10 is a diagram showing the detection values of each detection element of a detection element pair that satisfies the selection conditions for a detection element for calculating an interpolated value when group A is at code position number 0. 10 is a diagram showing the polarity of the magnetization pattern when the magnetization pattern of the magnetic scale is read when group A is at code position numbers 0 to 54, including one pitch before and after. FIG. 10 is a diagram showing the polarity of the magnetization pattern when the magnetization pattern of the magnetic scale is read when group B is at code position number 0, including one pitch before and after the magnetization pattern. 1 is a diagram showing an ideal position where group A and group B switch with respect to the magnetic scale 10. FIG. 10 is a diagram showing the magnetization patterns of each detection element group A or B and the magnetic scale in the vicinity of code position number 29. FIG. FIG. 10 is a diagram showing a change in polarity of the magnetization pattern of the magnetic scale in the vicinity of code position number 29. This figure shows an example in which a change in polarity of the magnetization pattern of the magnetic scale detected by each detection element of group A or group B occurs only once in six pitches near code position number 29. 3A and 3B are diagrams showing an example of a magnetization pattern of a magnetic scale in the absolute position detection device according to the embodiment of the present invention. FIG. 10 is a diagram showing an example of a configuration of an absolute position detection device according to an embodiment of the present invention, which includes an auxiliary detection element.

Preferred embodiments of the absolute position detection device and absolute position detection method of the present invention will be described below with reference to the drawings. In the following description, components with the same reference numerals in different drawings are considered to be similar, and their description may be omitted. Note that the present invention is not limited to the examples of these embodiments, and includes all modifications within the scope of the claims and equivalents. Furthermore, to the extent that multiple embodiments can be combined, the present invention includes any combination of embodiments.

[First embodiment]
FIG. 1 is a diagram showing an example of the configuration of an absolute position detection device according to an embodiment of the present invention. The absolute position detection device 1 includes a magnetic scale 10 having one magnetic track magnetized at a predetermined pitch P, and a detection device 20. The magnetic scale 10 has a magnetization pattern that forms a non-repeating code pattern such as an M series (Maximum Length Sequence) when a north pole is designated as "0" and a south pole is designated as "1." Hereinafter, the parameters of the magnetic scale 10 described in this embodiment will be explained assuming that the number of bits is 6 and the pitch P is 6 mm. In this case, the total length is 360 mm and the effective length is 330 mm. Details of the magnetic scale 10 and the relationship between the total length and the effective length will be described later.

(Code position number)
2 is a diagram illustrating the relationship between an example of a 6-bit non-repeating code pattern and the code position number. In this embodiment, numbers are assigned sequentially for each pitch of the magnetic scale 10 within the detection device 20, and these numbers are called code position numbers. As shown in FIG. 2, the code position numbers are assigned sequentially from left to right, starting from 0, and the total length is 0 to 59, with an effective range of 0 to 54, corresponding to the total length and effective length of the magnetic scale 10. The starting point of the code position number with respect to the magnetic scale 10 will be described later.

(Detection device)
The detection device 20 includes a detection element group S consisting of a plurality of detection elements, and a microcomputer M that performs position calculations based on analog output data from the detection element group S and outputs the absolute position to the outside. In the configuration example shown in Fig. 1, the microcomputer M is depicted as a functional block, but the microcomputer M also includes hardware such as a CPU, ROM, and RAM (not shown). Details of the detection device 20 will be described later.

(Detection element group)
Each detection element in the detection element group S in the exemplary configuration shown in FIG. 1 is disposed facing the magnetic scale 10 and outputs an analog value corresponding to each magnetic field of the magnetic scale 10. A Hall sensor, for example, using the Hall effect, capable of detecting the magnitude and direction of a static magnetic field can be used. In this embodiment, two detection element groups, group A and group B, are provided to avoid inaccurate reading of code information at polarity change points in the non-repeating code pattern of the magnetic scale 10. Each of the detection element groups A and B has six detection elements, the same number as the number of bits in the non-repeating code. The six detection elements A1 to A6 in group A are disposed at one-pitch intervals, and the six detection elements B1 to B6 in group B are disposed at one-pitch intervals, offset by half a scale pitch from each of the detection elements in group A. Therefore, the detection elements A1, B1, A2, B2, etc., and the detection elements in group A and the detection elements in group B are alternately disposed at half-scale pitch intervals.

Here, the detector element group A and the detector element group B correspond to the first detector element group and the second detector element group, respectively, in this invention. Furthermore, in the following explanation, the detector element group A will sometimes be referred to simply as group A, and the detector element group B will sometimes be referred to simply as group B. Furthermore, the detector elements A1 to A6 and B1 to B6 themselves, as well as the detection values of these detector elements, will sometimes be referred to simply as A1 to A6 and B1 to B6. The direction in which the code position number increases is considered forward. Therefore, the detector element group B is located half a pitch ahead of the detector element group A.

Figure 7 is a diagram illustrating the positional relationship between each detection element in groups A and B and the magnetic scale. In Figure 7, the point 1.5 mm to the left of the position where detection element A1 of group A, the leftmost element on the page, overlaps the left edge of magnetic scale 10 (on the code position number 0 side), is set to point 0 on magnetic scale 10, and the effective range is from point 0 for detection element A1 to the point where detection element B6 is 363 mm away (the point where A1 is 330 mm away). Furthermore, the effective range for relative movement of detection elements A1 and B1 of detection device 20 to calculate absolute position is code position numbers 0 to 54.

(microcomputer)
Returning to the configuration example shown in Fig. 1, the microcomputer M uses a multiplexer 21 to select analog detection values output by each detection element of the detection element group S, converts them into digital values in an A/D converter 22, and sends them to the RAM of the microcomputer M. The CPU of the microcomputer M operates in accordance with various programs stored in the ROM to realize various functions for calculating the absolute position shown in the position calculation unit 30, and outputs the absolute position by internally calculating the detection values of each detection element sent to the RAM. In addition to the programs, the ROM of the microcomputer M also stores a lookup table 36 used for position calculations, etc.

The position calculation unit 30 includes the following functional units: a code information acquisition unit 31, a code interval position calculation unit 32, a detection element identification unit for calculating interpolated values 33, an interval interpolated value calculation unit 34, and an absolute position calculation unit 35. These functional units will be explained in detail in the explanation of the operation of the detection device. The code information acquisition unit 31 is used to acquire code information, etc. of the magnetic scale 10 from the detection values of each detection element group A and B. The code interval position calculation unit 32 is used to calculate a code interval position calculation value, which is a displacement determined by the code of the magnetic scale 10, based on the code information of groups A and B acquired by the code information acquisition unit 31.

The interpolated value calculation detection element identification unit 33 is used to identify detection elements for calculating interpolated values for each code interval position. In this embodiment, the detection elements for calculating interpolated values corresponding to code information are stored in advance as a lookup table in a storage unit (not shown). The interval interpolated value calculation unit 34 is used to calculate an interpolated value for the corresponding code interval position based on the detection values of the detection elements identified by the interpolated value calculation detection element identification unit 33. The absolute position calculation unit 35 is used to calculate the absolute position of the magnetic scale 10 by adding the interval interpolated value calculated by the interval interpolated value calculation unit 34 to the code interval position calculated by the code interval position calculation unit 32.

(External output section)
The microcomputer M is provided with a communication means for outputting the absolute position data calculated by the absolute position calculation unit 35 to the external output unit 23, and includes, for example, an interface for SPI communication. The external output unit 23 uses SPI communication to send the absolute position data calculated by the microcomputer M to a D/A converter, and outputs the absolute position to the outside as a voltage output.

(Magnetic scale magnetization pattern conditions)
As described above, the magnetic scale 10 is magnetized with a non-repeating code pattern. In order to detect a position with high resolution, the following conditions must be satisfied in addition to the non-repeating code pattern.
(Magnetic pattern condition) In all parts of the magnetic scale's magnetization pattern, there must be both parts that change from south pole to north pole and parts that change from north pole to south pole within the pattern for (number of bits + 1) pitches.

Therefore, the magnetic scale of the present invention is a magnetization pattern having an n-bit non-repeating code pattern magnetized at a predetermined pitch, and within each of (n+1) consecutive pitches (n is a positive integer), there is at least one portion where the pole changes from south to north and one portion where the pole changes from north to south. This is a necessary condition for identifying pairs of detecting elements in group A and group B, each of which satisfies the predetermined conditions described below, in order to calculate the interpolated value of the code section position.

In the case of this embodiment, since the code is a 6-bit non-repeating code, both "south pole to north pole" and "north pole to south pole" sections must exist within the entire seven pitch length. The magnetization pattern shown in Figure 2 is an example of a pattern that meets the above conditions; it is part of a 6-bit non-repeating code pattern, and both "south pole to north pole" and "north pole to south pole" sections exist within all seven pitches of the pattern. Such a magnetization pattern enables high-resolution position detection.

On the other hand, Figure 3 is a diagram illustrating an example of a magnetic scale that has a 6-bit non-repeating code pattern but is outside the scope of the present invention. The magnetization pattern shown in Figure 3 has a 6-bit non-repeating code pattern, but although there is a section in the pattern for the 7 pitches on the left side that goes from "N pole to S pole," there is no section that goes from "S pole to N pole." Therefore, high-resolution position detection is not possible with this magnetization pattern.

For a 6-bit full-scale magnetic scale, the effective length is 64 x 6 mm, or 384 mm, and the total length is (64 + 5) x 6 mm, or 414 mm. However, in this embodiment, in order to meet the above conditions, the effective length is 55 x 6 mm, or 330 mm, and the total length is (55 + 5) x 6 mm, or 360 mm.

(Preparation required for processing operations)
The following describes the preparations required for the processing operations of the absolute position detection device in this embodiment. First, an interpolated value for one pitch of the magnetic scale 10 is set. The resolution is determined by the size of this interpolated value. In this embodiment, one pitch of 6 mm is divided into 120 parts to achieve a resolution of 0.05 mm. Next, the detection values of each detection element in a magnetic field-free environment are acquired and recorded as offset values in the detection device 20. These offset values are used to correct the magnetic field detection values of each detection element when the absolute position detection device is in operation. Furthermore, a "code information-code position number correspondence table" and a "code position number-detection element correspondence table for calculating interpolated values" are recorded in the lookup table 36.

Figure 4 is a diagram illustrating an example of a "code information-code position number correspondence table" showing the code position numbers corresponding to the code information obtained from the detection elements. The "code information-code position number correspondence table" is used to convert the code information obtained from the 6-bit values acquired by each of the detection element groups A and B into a code position number. Table I in Figure 4 shows the correspondence between the polarity of each detection element (where north pole is "0" and south pole is "1"), the corresponding 6-digit binary number, the code information converted to decimal, the code position number corresponding to the code information, and the displacement of detection element A1 or B1 with the displacement of the magnetic scale corresponding to the code position number.

In this embodiment, the polarities of the detection elements with code position numbers 55 to 63 shown in Table 1 of Figure 4 (when the displacement of detection element A1 is between 330 mm and 384 mm) do not match the magnetization pattern conditions of the magnetic scale described above, and are therefore not used and are not magnetized on the magnetic scale 10. Table II also sorts the code information and code position numbers in code information order, and the information in Table II is recorded in the lookup table. For convenience, the value "255" is entered for code position numbers corresponding to code information that does not exist on the magnetic scale 10 of this embodiment.

Figure 5 is an example of a "Code Position Number - Detector Element for Calculating Interpolated Values Correspondence Table" that associates the detector element for calculating interpolated values to be used with the code position number. The "Code Position Number - Detector Element for Calculating Interpolated Values Correspondence Table" records multiple detector elements (detector elements A1 to B6) used to calculate the interpolated value at the code position number when the detection device 20 reads code information and obtains the code position number. In this embodiment, there is a table α corresponding to the code position numbers of group A, and a table β corresponding to the code position numbers of group B. Four detector elements Aw, Ax, Ay, Az, and Bw, Bx, By, and Bz are recorded according to the code position number. Aw and Ax, Ay and Az, Bw and Bx, and By and Bz are the detector elements selected as pairs to calculate the interpolated value. The criteria for selecting these detector elements will be described later.

(Processing flow)
The following describes the process in this embodiment in which the detection device 20 acquires the detection value of the magnetic field of the magnetic scale from the detection elements and calculates the absolute position using the microcomputer based on that data. Figures 6A and 6B are processing flow diagrams showing an example of absolute position calculation in the position calculation unit.

First, in step S1, the detection values of the magnetic field of the magnetic scale for all detection elements in groups A and B are obtained. In this embodiment, a total of 12 detection values are obtained: six in group A (A1-A6) and six in group B (B1-B6). Figure 8A is a diagram showing example detection values obtained from each detection element in group A at code position numbers 0-1 (displacement 0-12 mm), and Figure 8B is a diagram showing example detection values obtained from each detection element in group B at code position numbers 0-1. Figure 7 shows the positional relationship between the magnetic scale and each detection element when the detection values shown in Figures 8A and 8B were obtained. For example, detection element A1 is located in the displacement range of 0-12 mm, and detection element B6 is located in the displacement range of 33-45 mm.

Next, in step S2, the absolute values of the detection values of all detection elements in groups A and B are calculated. In this process, the minimum absolute value of the detection values of the detection elements in group A and the minimum absolute value of the detection elements in group B are found.

Next, proceed to step S3, where the detected values from both groups A and B are converted into code information. As shown in Table I of Figure 4, the code information is first converted into a six-digit binary number, with north poles represented as "0" and south poles represented as "1," and then converted back to decimal to obtain the code information. When the detection element is located at the boundary between the north and south poles, the detected value approaches 0 (zero), and accurate code information may not be read. However, in this embodiment, groups A and B are offset by half a pitch. Therefore, when the detection element in group A is located at the boundary between the north and south poles, the detection element in group B is away from the boundary, and when the detection element in group B is located at the boundary between the north and south poles, the detection element in group A is away from the boundary. Therefore, the correct code information can be read from either group. The question of which code information from group A or group B to use will be discussed later.

Next, proceed to step S4, where the chord position numbers for groups A and B are obtained from the chord information for groups A and B using a pre-recorded lookup table 36. In this embodiment, the chord position numbers are obtained by referencing Table II in Figure 4, which is recorded in the lookup table 36. Note that in this embodiment, the obtained chord position numbers may be the same for group A and group B, or may be one greater than the chord position number for group A because the position of group B is half a pitch ahead of the position of group A. The processing from steps S1 to S4 is performed by the chord information acquisition unit 31 of the position calculation unit 30.

Next, proceed to step S5, where it is determined whether the code position number for group A is outside the range of the magnetic scale being used. If it is outside the range (if "YES"), proceed to step S6, set the invalid flag for group A, and then proceed to step S9. In this embodiment, the valid range for code position numbers is 0 to 54, and as shown in Table II in Figure 4, "255" is assigned to code position numbers outside the valid range.

If the code position number for group A is within the range in step S5 ("NO"), proceed to step S7, where the four detection elements to be used for position calculation based on the acquired code position number for group A are obtained from the pre-recorded lookup table 36. In this embodiment, the four detection elements Aw, Ax, Ay, and Az corresponding to each code position number shown in Table α in Figure 5 are selected. For example, when the code position number for group A is 1, A5, B3, A6, and B3 are selected as the four detection elements Aw, Ax, Ay, and Az, respectively. Hereinafter, the detection values of the four detection elements Aw, Ax, Ay, and Az will also be simply referred to as Aw, Ax, Ay, and Az. Figure 9A shows the detection values of the detection elements selected from each detection element in group A for calculating the interpolated value for code position numbers 0 to 1.

The process proceeds from step S7 to step S8, where the difference values of the detection values of each detection element of the detection element pair in group A are calculated. In this embodiment, two difference values are calculated from the detection values of the four detection elements to reduce the influence of geomagnetism, temperature changes, etc. If the two difference values are Au and Av, respectively, they can be calculated using the following equation.
Au=Ax-Aw...Formula 1
Av=Az-Ay...Formula 2
10A is a diagram showing the difference between the detection values of each detection element of the detection element pair in group A at code position numbers 0 to 1. As shown in Fig. 10A, it can be seen that the difference value Au crosses zero at a position where the displacement is 3 mm, and the difference value Av crosses zero at a position where the displacement is 6 mm.

The process proceeds from step S6 or step S8 to step S9, where it is determined whether the code position number for group B is outside the range of the magnetic scale being used. If it is outside the range (if "YES"), it proceeds to step S10, where an invalid flag for group B is set, and then processing proceeds to step S13. As with the determination in step S5, the valid range for code position numbers for group B is 0 to 54, and as shown in Table II in Figure 4, "255" is assigned to code position numbers outside the valid range.

If the code position number for group B is within the range in step S9 ("NO"), proceed to step S11, where the four detection elements to be used for position calculation are retrieved from the pre-recorded lookup table 36 based on the retrieved code position number for group B. In this embodiment, the four detection elements Bw, Bx, By, and Bz are selected as the four corresponding code position numbers shown in Table β of Figure 5. For example, when the code position number for group B is 0, A6, B5, A6, and B4 are selected as the four detection elements Bw, Bx, By, and Bz, respectively. Hereinafter, the detection values of the four detection elements Bw, Bx, By, and Bz are simply referred to as Bw, Bx, By, and Bz. Note that the processing of step S11 is performed by the detection element identification unit 33 for interpolated value calculation in the position calculation unit 30. Figure 9B shows the detection values of the detection elements Bw, Bx, By, and Bz selected from the detection elements of group B for interpolated value calculation at code position numbers 0 to 1.

Next, the process proceeds from step S11 to step S12, where the difference values of the detection values of each detection element of the detection element pair of group B are calculated. In this embodiment, two difference values are calculated from the detection values of the four detection elements to reduce the influence of geomagnetism, temperature changes, etc. If the two difference values are Au and Av, respectively, they can be calculated using the following equation.
Bu=Bx-Bw...Formula 3
Bv=Bz-By...Formula 4
10B is a diagram showing the difference between the detection values of each detection element of the detection element pair in group B at code position numbers 0 to 1. As shown in FIG. 10B, it can be seen that the difference value Bu crosses zero at displacement positions of 0 mm and 6 mm, and the difference value Bv crosses zero at displacement positions of 3 mm and 9 mm. Note that the processing from step S5 to step S12 is mainly performed by the interpolation value calculation detection element identification unit 33 of the position calculation unit 30.

Next, the process moves to step S13, where it is determined whether both the invalid flags for group A and group B are set. If they are set (YES), the process moves to step S14, where an error is output and the calculation of the absolute position is terminated. This process mainly occurs when the detection element group S of the detection device is outside the effective range of the magnetic scale.

If neither the invalid flag for group A nor the invalid flag for group B is set in step S13 (if "NO"), the process proceeds to step S15 and subsequent steps, where it is determined whether the difference value of the code position number of group A or group B should be used to calculate the interval interpolation value used in the absolute position calculation. First, in step S15, it is determined whether the invalid flag for group A is set. If the invalid flag for group A is set (if "YES"), the process proceeds to step S20, where the interval interpolation value is calculated using the difference values Bu and Bv of group B. Also, if the invalid flag for group A is not set (if "NO") in step S15, the process proceeds to step S16, where it is determined whether the invalid flag for group B is set. If the invalid flag for group B is set (if "YES") in step S16, the process proceeds to step S19, where the interval interpolation value is calculated using the difference values Au and Av of group A.

Also, if the invalid flag for group B is not set in step S16 (if "NO"), that is, if the invalid flags for both group A and group B are not set, proceed to step S17, where it is determined whether the code position number for group A and the code position number for group B are the same. If the code position number for group A and the code position number for group B are the same (if "YES"), proceed to processing in step S18. If the magnitude of the difference value Bv is negative (if "YES") in step S18, proceed to step S19, where the interval interpolation value is calculated using the difference values Au and Av for group A. If the magnitude of the difference value Bv is not negative (if "NO"), proceed to step S20, where the interval interpolation value is calculated using the difference values Bu and Bv for group B.

If the code position number of group A and the code position number of group B are different in step S17 (if "NO"), proceed to step S21. If the code position number of group B is one greater than the code position number of group A (if "YES"), proceed to step S22. If the magnitude of the difference value Av is negative in step S22 (if "YES"), proceed to step S20, where the interval interpolation value is calculated using the difference values Bu and Bv of group B. If the magnitude of the difference value Av is not negative (if "NO"), proceed to step S19, where the interval interpolation value is calculated using the difference values Au and Av of group A.

In step S21, if the code position number of group B is not one greater than the code position number of group A (if "NO"), proceed to step S23, where it is determined whether the minimum absolute value of the detected values of group A is greater than the minimum absolute value of the detected values of group B. If the minimum absolute value of the detected values of group A is greater than the minimum absolute value of the detected values of group B (if "YES"), proceed to step S19, where the interval interpolation value is calculated using the difference values Au and Av of group A. If the minimum absolute value of the detected values of group A is not greater than the minimum absolute value of the detected values of group B (if "NO"), proceed to step S20, where the interval interpolation value is calculated using the difference values Bu and Bv of group B.

After calculating the interval interpolation value in step S19 or step S20, the process proceeds to step S24, where the absolute position is calculated by adding the interval interpolation value to the code interval position calculated using the code position number. The processing of step S24 is performed by the absolute position calculation unit 35 of the position calculation unit 30.

Figure 11 is a diagram explaining which difference value of the interpolation value calculation detection element in group A or group B is used to calculate the interval interpolation value for code position numbers 0 to 1. Interval A indicates the range where the code position number in group A and the code position number in group B are the same, and interval B indicates the range where the code position number in group B is one greater than the code position number in group A. Additionally, interval C1 indicates the range around where the code position number in group A changes, and interval C2 indicates the range around where the code position number in group B changes.

Figure 12 shows the change in the minimum absolute value of the detection values of each detection element in groups A and B for code position numbers 0 to 1. When the displacement of detection element group S is within range C1 or C2 shown in Figure 11, step S23 is performed according to the data shown in Figure 12. In range C1, the difference values Bu and Bv of group B are used to calculate the interval interpolation value, and in range C2, the difference values Au and Av of group A are used to calculate the interval interpolation value. In range D shown in Figure 11, the code position number of group A is outside the range, so step S15 determines that the difference values Bu and Bv of group B are used to calculate the interval interpolation value.

(interval interpolation calculation)
13 is a diagram illustrating a method for calculating an interval interpolation value using the difference between the detection values of each detection element in the detection element pair of group B. When the displacement between the magnetic scale 10 and the detection device 20 is between 0 and 3 mm, the interval interpolation value is calculated using the code position number of group B and the difference values Bu and Bv of group B. The difference value Bu is 0 at a displacement of 0 mm, and the difference value Bv is 0 at a displacement of 3 mm. In the range of displacement between 0 and 3 mm, the difference value Bu is always negative, and the difference Bv is always positive. Assuming that the changes in the difference values Bu and Bv are parallel, the magnitude of the displacement L can be calculated by the following equation, based on a proportional relationship, where P is the length of one pitch.
L=Bu/(Bu-Bv)×P/2...Formula 3

FIG. 14 is a diagram illustrating a method for calculating an interval interpolation value using the difference between the detection values of each detection element of a detection element pair in group A. When the displacement between the magnetic scale 10 and the detection device 20 is between 3 and 6 mm, the interval interpolation value is calculated using the code position number of group A and the difference values Au and Av of group A. The difference value Au is 0 at a displacement of 3 mm, and the difference value Av is 0 at a displacement of 6 mm. Furthermore, in the range of 3 to 6 mm of displacement, the difference value Au is always negative, and the difference Av is always positive. Assuming that the changes in the difference values Au and Av are parallel, the magnitude of L, starting from the position of 3 mm of displacement (P/2), can be calculated using the following proportional relationship:
L=Au/(Au-Av)×P/2...Formula 4

Therefore, within the range of displacement of 0 to 6 mm,
If the code position number of group B is referenced, the interval interpolation value is
Bu/(Bu-Bv)×P/2...Equation 5
If the code position number of group A is referenced, the interval interpolation value is
Au/(Au-Av)×P/2+P/2...Formula 6
can be calculated using the formula:

In addition, since the interpolated value for one pitch of 6 mm is 120, when the code position number of group B is referenced, the section interpolated value is
Bu/(Bu-Bv)×60...Formula 7
If the code position number of group A is referenced, the interval interpolation value is
Au/(Au-Av)×60+60...Formula 8
can be calculated using the formula:

The absolute position is found by adding the interval interpolation value to the chord interval position calculated from the chord position number. In this case, if a chord position number from group A was referenced, the chord position number from group A is used, and if a chord position number from group B was referenced, the chord position number from group B is used. In this embodiment, one pitch is set to 6 mm, so the chord interval position calculated from the chord position number is the value obtained by multiplying the chord position number, which takes values from 0 to 54, by 6 mm. The chord interval position calculation value is calculated by the chord interval position calculation unit 32 of the position calculation unit 30.

Figure 15 shows the results of calculating absolute position from the calculated code section position value and the section interpolation value. Figure 15(A) shows the change in the section interpolation value obtained from the above processing flow, and Figure 15(B) shows the change in the calculated code section position value corresponding to the code position number. Figure 15(C) shows the calculated absolute position value obtained by adding the section interpolation value shown in Figure 15(A) and the calculated code section position value shown in Figure 15(B). It can be seen that the absolute position value changes almost linearly with displacement. Figure 15 only shows the range of displacement from 0 to 12 mm and code position numbers 0 and 1, but absolute position can also be calculated for code position numbers 2 to 54 according to the above processing flow.

(Continuity of absolute position at the detection element group switching part)
In order to continuously detect the absolute position of the magnetic scale 10, in this embodiment, it is necessary to eliminate jumps in the calculated absolute position value at the switching portion between the detecting element groups A and B. At the switching portion between the detecting element groups A and B, i.e., at the switching portion between the case where the detected values of the detecting elements for calculating interpolated values obtained from the code position numbers of group A are used and the case where the detected values of the detecting elements for calculating interpolated values obtained from the code position numbers of group B are used, the formula for calculating the position changes, but if the calculated values for the position at the switching portion match, no jumps have occurred. Below, in this embodiment, it will be verified whether the calculated values at one of the switching portions of the detecting element groups match.

As a premise, as shown in Figure 11, the code position number is switched sequentially from the end of the magnetic scale 10, starting from code position number 0 in group B, code position number 0 in group A, code position number 1 in group B, and continuing until code position number 54 in group A at the end of the scale. Regarding the detection value of the detector element selected for each code position number, referring to the code position number - detector element correspondence table for calculating interpolated values in Figure 5, if the code position number in group B and the code position number in group A are the same, the detector element in the By, Bz detector pair in group B matches the detector element in the Aw, Ax detector pair in group A. If the code position number in group B is one greater than the code position number in group A, the detector element in the Bw, Bx detector pair in group B matches the detector element in the Ay, Az detector pair in group A.

Here, referring to Equations 1 to 4,
Au=Ax-Aw...Formula 1
Av=Az-Ay...Formula 2
Bu=Bx-Bw...Formula 3
Bv=Bz-By...Formula 4
Therefore, when the code position numbers of group A and group B are the same, the difference values Bv and Au are equal, and when the code position number of group B is one greater than the code position number of group A, the difference values Av and Bu are equal. As shown in Figure 11, the switching point between the detection element groups of group A and group B is the point where the difference value Bv or difference value Av becomes 0. This does not change even if the code position number increases, and at the point where the code position number switches from group B code position number k (0 to 54) to group A code position number k, the difference values Bv and Au are both 0.

Based on the above assumptions, when the calculations in steps S19, S20, and S24 of the processing flow shown in FIG. 6B are performed, the calculated absolute position value of the portion where code position number k (0 to 54) in group B switches to code position number k in group A is as follows:
In the position calculation using the interval interpolation value of group B according to Equation 5,
Bu/(Bu-Bv)×P/2+k×P=Bu/(Bu-0)×P/2+k×P=P/2+k×P,
In the position calculation using the section interpolation value of group A according to Equation 6,
Au/(Au-Av)×P/2+P/2+k×P=0/(0-Av)×P/2+P/2+k×P=P/2+k×P,
Here, the value of k×P corresponds to the chord section position calculation value, and the same applies below.

Here, when the interpolation value of 120 for one pitch is used, at the point where the chord position number of the B group is switched to the chord position number of the A group in this embodiment,
In the position calculation using the interval interpolation value of group B according to Equation 5,
Bu/(Bu-0)×60+0×120=60+0×120=60,
In the position calculation using the section interpolation value of group A according to Equation 6,
0/(0-Av)×60+60+0×120=0+60+0×120=60,
and the values match.

Similarly, at the portion where code position number k (0 to 53) in group A switches to code position number k+1 in group B, difference values Av and Bu are both 0. When the calculations in steps S19, S20, and S24 shown in Figure 6B are performed, the position at which code position number k (0 to 53) in group A switches to code position number k+1 in group B is determined as follows:
In the position calculation using the section interpolation value of group A according to Equation 6, Au/(Au-0)×P/2+P/2+k×P=Au/(Au-0)×P/2+P/2+k×P=P+k×P,
In the position calculation using the section interpolation value of group B according to Equation 5, Bu/(Bu-Bv) x P/2 = 0/(0-Bv) x P/2 + (k+1) x P = P + k x P,
and the values are the same.

Similarly, when the interpolation value 120 of one pitch is used, at the point where the chord position number 0 of group A switches to the chord position number 1 of group B in this embodiment,
In the position calculation using the section interpolation value of group A according to Equation 6, Au/(Au-0) x 60 + 60 + 0 x 120 = 60 + 60 + 0 x 120 = 120,
In the position calculation using the section interpolation value of group B according to Equation 5, 0/(0-Bv) x 60 + (0 + 1) x 120 = 0 + 1 x 120 = 120,
and the values match.
As described above, in this embodiment, the calculated position values are the same at the switching point from group A to group B and at the switching point from group B to group A, so there is no jump in the calculated position value at the switching point between the detection element groups, ensuring continuity of the absolute position.

(Code position number - detection element correspondence table for calculating interpolated values)
A method for creating the code position number-detector element correspondence table for calculating interpolated values shown in Fig. 5 will be described. First, as a premise, when the code position number of group B and the code position number of group A are the same value, the pair of detector elements By and Bz in group B matches the pair of detector elements Aw and Ax in group A, as shown by light hatching in Fig. 5. When the code position number of group B is one greater than the code position number of group A, the pair of detector elements Bw and Bx in group B matches the pair of detector elements Ay and Az in group A, as shown by thick hatching in Fig. 5. The only locations where they do not match are the pair of detector elements Bw and Bx at code position number 0 in group B and the pair of detector elements Ay and Az at code position number 54 in group A, which correspond to both ends of the magnetic scale 10. Therefore, the code position number - detection element correspondence table for calculating interpolated values created in this embodiment can be created by selecting detection elements Aw, Ax, Ay, and Az at code position numbers 0 to 54 in group A, and detection elements Bw and Bx at code position number 0 in group B.

Next, we will explain the conditions for the detector elements Aw, Ax, Ay, and Az used to calculate the interpolated value at each code position number. In the calculation of step S19 of the processing flow shown in Figure 6B, combinations of detector element pairs Aw, Ax, and Ay, Az are selected for each code position number to obtain appropriate difference values Au and Av for calculating the interpolated value. The detector elements Aw, Ax, Ay, and Az used to calculate the interpolated value that meet the conditions are selected from all detector elements A1 to B6 at the corresponding code position number.

Figure 16 shows the detection values of all detection elements when group A is at code position number 0. Figures 17 and 18 are tables showing the selection conditions for detection elements for calculating interpolated values when group A is at code position number 0. Figure 17 shows two examples, Tables A and B, of the conditions for detection elements Aw and Ax for calculating interpolated values, and Figure 18 shows two examples, Tables C and D, of the conditions for detection elements Ay and Az for calculating interpolated values. Figures 17 and 18 show the characteristics of the detection values on the left, center, and right sides within the range of code position numbers. Figures 19 and 20 show the detection values of each detection element in a detection element pair that meets the selection conditions for a detection element for calculating an interpolated value when group A is at code position number 0. (A) and (B) in Figure 19 show the detection elements that meet the conditions in Tables A and B shown in Figure 17, respectively, and (C) and (D) in Figure 20 show the detection values of the detection elements that meet the conditions in Tables C and D shown in Figure 18, respectively.

For example, a detection element that meets the Aw condition shown in Table A of Figure 17 has a detection value that is negative on the left, near 0 in the center, and positive on the right. When selecting a detection element from Figure 16 that has a detection value that meets this condition, detection element B5 is the one that fits. Furthermore, a detection element that meets the Ax condition shown in Table A of Figure 17 has a detection value that is near 0 on the left and negative in the center. When selecting a detection element from Figure 16 that has a detection value that meets this condition, detection element A5 is the one that fits. Therefore, under the conditions shown in Table A of Figure 17, Aw is B5 and Ax is A5, and the detection values are as shown in (A) of Figure 19.

Furthermore, detector elements that satisfy the Aw condition shown in Table B of Figure 17 have detection values that are near 0 on the left side and positive in the center. Selecting a detector element with a detection value that meets this condition from Figure 16 results in detector element A6. Also, detector elements that satisfy the Ax condition shown in Table B of Figure 17 have detection values that are positive on the left side, near 0 in the center, and negative on the right side. Selecting a detector element with a detection value that meets this condition from Figure 16 results in detector element B4. Therefore, under the conditions shown in Table B of Figure 17, Aw is A6 and Ax is B4, and the respective detection values are as shown in Figure 19 (B). Thus, there is not necessarily one pair of detector elements that meets the selection conditions for detector elements for interpolation value calculation. Multiple pairs of detector elements can be selected depending on the positional relationship between the detector element group and the magnetic scale. The code position number vs. detector element for interpolation value calculation correspondence table shown in Figure 5 indicates that the detector elements for interpolation value calculation when A group code position number is 0 have Aw=A6 and Ax=B4.

Next, we will explain the conditions for selecting detection elements for calculating interpolated values depending on the positional relationship between the detection element group S and the magnetic scale 10. Fig. 21 is a diagram showing the polarity of the magnetization pattern when group A reads the magnetization pattern of the magnetic scale at code position numbers 0 to 54, including one pitch before and after. When group A is at code position numbers 0 to 54, the conditions for the pair of detection elements Aw and Ax of group A are as follows:
Selection condition for Aw: A portion in group B that changes from a north pole to a south pole Selection condition for Ax: A portion in group A that has a north pole and the left side becomes a south pole Or selection condition for Aw: A portion in group A that has a south pole and the left side becomes a north pole Selection condition for Ax: A portion in group B that changes from a south pole to a north pole Hereinafter, these conditions will be referred to as "A group detection element selection condition 1".

Similarly, the selection conditions for the pair of detecting elements Ay and Az in group A are as follows:
Selection condition for Ay: A portion in group A where the north pole is located and the right side becomes the south pole Selection condition for Az: A portion in group B where the south pole becomes the north pole Selection condition for Ay: A portion in group B where the north pole becomes the south pole Selection condition for Az: A portion in group A where the right side becomes the north pole Hereinafter, these conditions will be referred to as "A group detection element selection condition 2".

Here, because the detection elements B1-B6 in group B are located half a pitch ahead of the detection elements A1-A6 in group A, when the code information read by group A is adopted, the conditions of the magnetization pattern dictate that at least one detection element in group B will be a detection element that changes from north to south pole or south to north pole. One of the detection elements Aw, Ax and one of the detection element pairs Ay, Az are selected as a detection element in group B that changes from north to south pole or south to north pole, and the other detection element is selected from the detection elements in group A that, at a specified position, has the same detection value as one of the detection elements in group B, as described below. This is also true when the code information read by group B is adopted.

22 is a diagram showing the polarity of the magnetization pattern, including one pitch before and after, when group B reads the magnetization pattern of the magnetic scale at code position number 0. When group B is at code position number 0, the selection conditions for the pair of detecting elements Bw and Bx of group B are as follows:
Selection condition for Bw: A portion in group A that changes from a north pole to a south pole Selection condition for Bx: A portion in group B that has a north pole and the left side becomes a south pole Selection condition for Bw: A portion in group B that has a south pole and the left side becomes a north pole Selection condition for Bx: A portion in group A that changes from a south pole to a north pole Hereinafter, these conditions will be referred to as "B group detection element selection condition 1."

The number of candidate detector element pairs that satisfy A-group detector element selection condition 1 and A-group detector element selection condition 2 varies depending on each code position number, but in practice, it is necessary to select the detector element pairs to be written to the lookup table from among multiple candidates. If the above selection conditions are met, it is possible to perform high-resolution absolute position detection. However, in order to perform accurate absolute position detection taking into account individual differences between detector elements, it is desirable to measure and determine the most ideal detector elements.

First, the necessary data is obtained from the detection values of all detection elements at the ideal point where group A and group B switch with respect to the magnetic scale 10. Fig. 23 is a diagram showing the ideal position where group A and group B switch with respect to the magnetic scale 10. As shown in Fig. 23, the ideal positions are 0 mm, which is the point where detection element A1 has moved 1.5 mm backward from the point at the end of the magnetic scale 10, and then points 3 mm, 6 mm, 9 mm, and so on, with the size of one pitch being P and the code position number being k, as follows:
Switching point from group B code position number k to group A code position number k: 1/2 × P + P × k
Switching point from group A code position number k to group B code position number k+1: P × (k+1)

At the point where switching from group B to group A is desired, Ax - Aw = Au = 0, so from all selection candidates, the pair of detection elements whose actual measured value of Ax - Aw is closest to 0 is adopted as the detection element pair. Also, at the point where switching from group A to group B is desired, Az - Ay = Av = 0, so from all selection candidates, the pair of detection elements whose actual measured value of Az - Ay is closest to 0 is adopted as the detection element pair.

Referring to Figure 11, it can be seen that the difference values Au and Bv are 0 at displacements of 3 mm and 9 mm, i.e., at a pitch of (m-1/2) where m is a positive integer, and the difference values Av and Bu are 0 at displacements of 6 mm and 12 mm, i.e., at a pitch of (m-1). Thus, one pair of detection elements of the two pairs of detection elements used for calculating interpolated values is a combination in which the difference value is 0 when the magnetic scale displacement is near a pitch of (m-1/2), and the other pair of detection elements is a combination in which the difference value is 0 when the displacement is at a pitch of (m-1).

Second Embodiment
In the first embodiment, in an absolute position detection device equipped with a magnetic scale having one magnetic track, the following means was employed to eliminate jumps at the switching point between group A and group B in order to continuously detect the absolute position.
(1) When the group B code position number and the group A code position number are the same value, By and Bz of group B are matched with Aw and Ax of group A.
(2) If the code position number of group B is one greater than the code position number of group A, Bw and Bx of group B are matched with Ay and Az of group A, and further,
(3) The switching point between group A and group B is set to the point where the difference values Au and Av become zero.

However, as shown in this embodiment, even if the difference values Au and Av at the switching point between groups A and B are not made to be exactly 0, it is possible to perform absolute position calculations with high resolution, although there is a possibility of jumps in the calculated value at the switching point between groups A and B. Specifically, the minimum absolute value of the detection values of the detection elements in group A is compared with the minimum absolute value of the detection values of the detection elements in group B, and the absolute position can be calculated using the code position number with the larger minimum absolute value and the detection element for calculating the interpolated value that corresponds to that code position number.

For example, the aforementioned Figure 12 shows the change in the minimum absolute value of the detection values of each detection element in Groups A and B for code position numbers 0 to 1. When the displacement is 3 to 6 mm, the minimum absolute value of the detection values of the detection elements in Group A is greater than the minimum absolute value of the detection values of the detection elements in Group B. Therefore, in the section where the displacement is 3 to 6 mm, the code section position calculation value is calculated according to the code position number in Group A, and the section interpolation value is calculated using the detection element corresponding to the code position number in Group A in the code position number - detection element correspondence table for calculating interpolated values shown in Figure 5. If the processing of this embodiment is explained using the processing flow shown in Figure 6B, this corresponds to omitting steps S17, S18, S21, and S22, and proceeding to step S23 if step S16 returns "NO."

[Third embodiment]
In the first and second embodiments, after acquiring the code position number, the code position number-detection element for calculating interpolated values correspondence table stored in the lookup table is referenced, and detection values of four detection elements for calculating interpolated values are acquired according to the code position numbers of group A and group B,
These detected values are used to calculate the absolute position, but a method for calculating the absolute position without using the code position number - interpolated value calculation detection element correspondence table will be described below.

As mentioned above, there are two selection conditions for calculating the interpolated value of group A when the group A is at code position numbers 0 to 54: group A detector selection condition 1 and group A detector selection condition 2. Also, as mentioned above, in order to create the code position number - detector element for calculating interpolated values correspondence table shown in Figure 5, there is group B detector selection condition 1 for the selection condition of Bw and Bx when group B is at code position number 0. However, group B detector selection condition 1 also holds when group B is at code position numbers 1 to 54.

When group B is in the code position numbers 0 to 54, the selection conditions for the pair of detecting elements By and Bz of group B are as follows:
Selection condition for By: A portion in group B where the north pole is located and the right side becomes the south pole Selection condition for Bz: A portion in group A where the south pole is located and the north pole Selection condition for By: A portion in group A where the north pole is located and the south pole is located Selection condition for Bz: A portion in group B where the south pole is located and the right side becomes the north pole Hereinafter, these conditions will be referred to as "group B detection element selection condition 2."

Figure 24 shows the magnetization pattern of each detection element group A or B and the magnetic scale near code position number 29, with Figure 24 (A) showing the case where group A is at code position number 29, and Figure 24 (B) showing the case where group B is at code position number 29. When this positional relationship is met, selecting the detector elements Aw, Ax, Ay, Az, and Bw, Bx, By, Bz for calculating the interpolated value in accordance with the aforementioned "A group detector element selection condition 1," "A group detector element selection condition 2," "B group detector element selection condition 1," and "B group detector element selection condition 2" results in Aw=B6, Ax=A4, Ay=A6, Az=B3, Bw=A1, Bx=B4, By=B6, Bz=A4, or Aw=A1, Ax=B3, Ay=B6, Az=A3, Bw=B1, Bx=A4, By=A1, Bz=B3.

In this way, it is possible to identify the detection elements for calculating interpolated values from the polarity of the magnetic scale and the positional relationship of each detection element, without using a pre-stored code position number - detection element for calculating interpolated values correspondence table. Regarding the polarity of the magnetic scale, the polarity of the magnetic scale facing each detection element is determined from the positive/negative value of the detection value of each detection element in groups A and B. Then, based on the arrangement of the magnetic scale polarities, four detection elements for calculating interpolated values are selected for each of groups A and B in accordance with the above-mentioned "Group A Detection Element Selection Condition 1," "Group A Detection Element Selection Condition 2," "Group B Detection Element Selection Condition 1," and "Group B Detection Element Selection Condition 2." The interval interpolated value can then be calculated from these detection values, similar to the method described in the first or second embodiment. However, this method is valid when the magnetic pole pattern for six pitches of the magnetic scale facing each detection element in groups A and B is a magnetization pattern that has both a portion where the pole changes from south to north and a portion where the pole changes from north to south. It is not valid otherwise.

Figure 25 shows the change in polarity of the magnetization pattern of the magnetic scale near code position number 29, and Figure 26 shows an example where the change in polarity of the magnetization pattern of the magnetic scale detected by each detection element of group A or group B near code position number 29 occurs only once within six pitches. The magnetization pattern shown in Figure 25 has at least one portion where the pole changes from south to north and one portion where the pole changes from north to south within a range of seven consecutive pitches, and meets the conditions for the magnetization pattern of the present invention. However, at code position number 29, as shown in Figure 26, there is only one portion where the pole changes from south to north within a range of six pitches of the magnetic scale where each detection element of group A and group B faces.

For this reason, while the absolute position can be detected using the above method within the code position number range of 0 to 28, at code position number 29, it is not possible to select all of the detector elements Aw, Ax, Ay, Az, and Bw, Bx, By, Bz for calculating the interpolated values simply by using the 6-bit magnetic poles that each detector element in groups A and B faces. Incidentally, if the polarity of each detector element in groups A and B can only be determined for the 6 bits shown in Figure 26, even if four detector elements for calculating the interpolated values are selected for each of groups A and B according to "Group A Detector Element Selection Condition 1," "Group A Detector Element Selection Condition 2," "Group B Detector Element Selection Condition 1," and "Group B Detector Element Selection Condition 2," only one of the detector elements in the pair can be selected: Ax = A4, Az = B3, Bx = B4, Bz = A4, or Ax = B3, Az = A3, Bx = A4, Bz = B3.

On the other hand, the magnetic scale 10 satisfies the magnetization pattern condition of having at least one part that changes from a south pole to a north pole and one part that changes from a north pole to a south pole within a range of seven consecutive pitches. Therefore, based on this condition, even if the magnetization pattern for six pitches only has one part that changes from a south pole to a north pole or one part that changes from a north pole to a south pole, it is possible to estimate the polarity of the magnetic poles before and after six pitches.

Therefore, in this embodiment, when the six-pitch magnetic pole pattern of the magnetic scale, which the six detection elements of each of groups A and B face, contains both a portion where the pole changes from south to north and a portion where the pole changes from north to south, the detection element for calculating the interpolated value is selected based on the six-pitch magnetic pole pattern; otherwise, the polarity of the magnetic poles before and after the six-pitch magnetic pole pattern is estimated, and the detection element for calculating the interpolated value is selected without using the code position number - detection element for calculating the interpolated value correspondence table.

[Fourth embodiment]
In the third embodiment, when the 6-bit magnetic pole pattern detected by each of the detection elements in groups A and B does not include both a portion where the pole changes from south to north and a portion where the pole changes from north to south, the polarities of the magnetic poles before and after the detected magnetic pole are estimated to select a detection element for calculating an interpolated value. However, in this embodiment, code information indicating the magnetization pattern of the magnetic scale to be used is stored in advance in a lookup table.

Figure 27 is a diagram showing an example of the magnetization pattern of the magnetic scale in an absolute position detection device according to an embodiment of the present invention. As shown in Figure 27, if the polarity of the magnetic scale is stored in advance as code information in a lookup table, corresponding to the code position number, with, for example, a north pole being "0" and a south pole being "1," then by referencing this lookup table, it is possible to determine the polarity of the magnetic pole to the left of the magnetic pole detected by the leftmost detection elements A1 and B1 (the "north" pole at the left end of magnetic scale 10 in Figure 24) and the polarity of the magnetic pole to the right of the magnetic pole detected by the rightmost detection elements A6 and B6 (the "north" pole at the right end of magnetic scale 10 in Figure 24), as shown in Figure 24.

Specifically, after acquiring the code position number, the detection device 20 references a lookup table that stores the magnetization pattern, and references the polarity of the (code position number - 1) portion to determine the polarity of the magnetic poles in the left portion, and the polarity of the (code position number + number of bits) portion to determine the polarity of the magnetic poles in the right portion. Then, based on the polarities of the magnetic poles for the detected six pitches and the polarities of the magnetic poles before and after, it can select detection elements for calculating the interpolated value from the detection element selection conditions for groups A and B shown in the third embodiment.

Fifth Embodiment
In the third embodiment, the polarities of the magnetic poles before and after the 6-bit magnetic poles detected by each of the detection elements of groups A and B are estimated based on the magnetization pattern conditions, and in the fourth embodiment, the polarities of the magnetic poles before and after the 6-bit magnetic poles detected by each of the detection elements of groups A and B are identified by referring to a lookup table in which the magnetization pattern of the magnetic scale is recorded, and a detection element for calculating an interpolated value that meets the respective conditions is selected. However, in the present embodiment, the polarities of the magnetic poles before and after the 6-bit magnetic poles detected by each of the detection elements of groups A and B are determined by using auxiliary detection elements that are separately provided.

Figure 28 is a diagram showing an example configuration of an absolute position detection device according to an embodiment of the present invention, including auxiliary detection elements. As shown in Figure 28, in this embodiment, auxiliary detection elements C1 and C2 are arranged in front of and behind the A group detection elements A1 to A6 and the B group detection elements B1 to B6 as the detection element group S, i.e., to the left of detection element A1 and the right of detection element B6, respectively. Furthermore, the polarity of the magnetic poles in front of and behind the A group detection elements A1 to A6 and the B group detection elements B1 to B6 facing each other can be determined from the detection values of auxiliary detection elements C1 and C2, making it possible to select detection elements for calculating interpolated values according to the selection conditions shown in the third embodiment.

1... absolute position detection device, 10... magnetic scale, 20... detection device, 21... multiplexer,
22...A/D conversion unit, 23...external output unit, 30...position calculation unit, 31...code information acquisition unit, 32...code section position calculation unit, 33...detection element identification unit for interpolated value calculation, 34...section interpolated value calculation unit, 35...absolute position calculation unit, 36...lookup table, A1 to A6...detection elements (detection values) of group A, B1 to B6...detection elements (detection values) of group B, C1, C2...auxiliary detection elements, M...microcomputer, S...detection element group.

Claims (9)

a magnetic scale on which a magnetization pattern is recorded, the magnetization pattern having a non-repeating code pattern of n bits (n is an integer of 2 or more) magnetized at a predetermined pitch, the magnetization pattern having both at least one portion where a pole changes from south to north and one portion where a pole changes from north to south within a continuous (n+1) pitch;
a detection device including a first detection element group consisting of at least n detection elements arranged at one-pitch intervals facing the magnetic scale, and a second detection element group consisting of at least n detection elements arranged at half-pitch intervals from each of the detection elements in the first detection element group,
the detection device includes a code section position calculation unit that calculates, based on n-bit code information obtained from the detection values of each of the detection elements of the first detection element group or the second detection element group, a code section position calculation value at a code section position corresponding to the code information;
an interpolation-value-calculating detector element specifying unit that specifies an interpolation-value-calculating detector element corresponding to the code section position of the first detector element group or the second detector element group;
an interval interpolation value calculation unit that calculates an interval interpolation value at the code interval position from the detection value of the interpolation value calculation detection element;
an absolute position calculation unit that obtains an absolute position signal over the entire length of the magnetic scale from the code section position calculation value and the section interpolation value; the detection device includes a lookup table that stores, for each code section position of the first detector element group, two pairs of detector element pairs, each consisting of one detector element of the first detector element group and one detector element of the second detector element group, as detector elements for first detector element group interpolation value calculation, and, for each code section position of the second detector element group, two pairs of detector element pairs, each consisting of one detector element of the first detector element group and one detector element of the second detector element group, as detector elements for second detector element group interpolation value calculation,
the interpolated value calculation detector element specifying unit specifies either the first detector element group interpolated value calculation detector element or the second detector element group interpolated value calculation detector element as the detector element for calculating the interval interpolated value, based on a magnitude of a difference value between detection values of each of the detector elements in the pair of detector elements in the first detector element group interpolated value calculation detector element or the second detector element group interpolated value calculation detector element stored in the lookup table, in accordance with the code interval position of the first detector element group or the second detector element group;
2. The absolute position detection device according to claim 1, wherein the interval interpolation value calculation unit calculates the interval interpolation value at the code interval position based on a ratio of difference values between detection values of each of the detection elements of each of the two pairs of detection elements in the first detection element group interpolation value calculation detection elements or the second detection element group interpolation value calculation detection elements identified by the interpolation value calculation detection element identification unit. the detection device includes a lookup table that stores, for each code section position of the first detector element group, two pairs of detector element pairs, each consisting of one detector element of the first detector element group and one detector element of the second detector element group, as detector elements for first detector element group interpolation value calculation, and, for each code section position of the second detector element group, two pairs of detector element pairs, each consisting of one detector element of the first detector element group and one detector element of the second detector element group, as detector elements for second detector element group interpolation value calculation,
the interpolated value calculation detector element specifying unit compares the minimum absolute value of the detection value of each of the detector elements of the first detector element group with the minimum absolute value of the detection value of each of the detector elements of the second detector element group, and specifies the first detector element group interpolated value calculation detector element or the second detector element group interpolated value calculation detector element stored in the lookup table with the larger minimum absolute value as the detector element for calculating the section interpolated value at the code section position of the first detector element group or the second detector element group;
2. The absolute position detection device according to claim 1, wherein the interval interpolation value calculation unit calculates the interval interpolation value at the code interval position based on a ratio of difference values between detection values of each of the detection elements of each of the two pairs of detection elements in the first detection element group interpolation value calculation detection elements or the second detection element group interpolation value calculation detection elements identified by the interpolation value calculation detection element identification unit. the detection device has a storage unit that stores code information obtained from the non-repeating code pattern of the magnetic scale,
the interpolation value calculation detector element specifying unit refers to the code information stored in the storage unit in accordance with the code section positions of the first detector element group and the second detector element group, and specifies either one of two detector element pairs, each consisting of one detector element of the first detector element group and one detector element of the second detector element group, that satisfy a selection condition as a first detector element group interpolation value calculation detector element corresponding to the code section position of the first detector element group, or one of two detector element pairs, each consisting of one detector element of the first detector element group and one detector element of the second detector element group, that satisfy a selection condition as a second detector element group interpolation value calculation detector element corresponding to the code section position of the second detector element group;
2. The absolute position detection device according to claim 1, wherein the interval interpolation value calculation unit calculates the interval interpolation value at the code interval position based on a ratio of difference values between detection values of each of the detection elements of each of the two pairs of detection elements in the first detection element group interpolation value calculation detection elements or the second detection element group interpolation value calculation detection elements identified by the interpolation value calculation detection element identification unit. the interpolated value calculation detect element specifying unit specifies, in accordance with the code section positions of the first detect element group and the second detect element group, either one of two detect element pairs, each consisting of one detect element of the first detect element group and one detect element of the second detect element group, that satisfy a selection condition as a first detect element group interpolated value calculation detect element corresponding to the code section position of the first detect element group, or one of two detect element pairs, each consisting of one detect element of the first detect element group and one detect element of the second detect element group, that satisfy a selection condition as a second detect element group interpolated value calculation detect element corresponding to the code section position of the second detect element group, based on n-bit code information acquired from the detection value of each detect element of the first detect element group or the second detect element group, and the polarity of the front and rear magnetic poles estimated from the magnetization pattern of the magnetic scale that each detect element of the first detect element group or the second detect element group faces;
2. The absolute position detection device according to claim 1, wherein the interval interpolation value calculation unit calculates the interval interpolation value at the code interval position based on a ratio of difference values between detection values of each of the detection elements of each of the two pairs of detection elements in the first detection element group interpolation value calculation detection elements or the second detection element group interpolation value calculation detection elements identified by the interpolation value calculation detection element identification unit. the detection device further includes one auxiliary detection element shifted by half a pitch outside the detection elements located at both ends of the first detection element group and the second detection element group,
the interpolated value calculation detect element specifying unit specifies, in accordance with the code section positions of the first detect element group and the second detect element group, either one of two detect element pairs, each consisting of one detect element of the first detect element group and one detect element of the second detect element group, that satisfy a selection condition as a first detect element group interpolated value calculation detect element corresponding to the code section position of the first detect element group, or one of two detect element pairs, each consisting of one detect element of the first detect element group and one detect element of the second detect element group, that satisfy a selection condition as a second detect element group interpolated value calculation detect element corresponding to the code section position of the second detect element group,
2. The absolute position detection device according to claim 1, wherein the interval interpolation value calculation unit calculates the interval interpolation value at the code interval position based on a ratio of difference values between detection values of each of the detection elements of each of the two pairs of detection elements in the first detection element group interpolation value calculation detection elements or the second detection element group interpolation value calculation detection elements identified by the interpolation value calculation detection element identification unit. The absolute position detection device described in any one of claims 2 to 6, characterized in that the two pairs of detection elements serving as the first detection element group interpolated value calculation detection elements and the second detection element group interpolated value calculation detection elements are a combination of detection elements in which the difference in detection values of the detection elements of one of the detection element pairs is zero when the magnetic scale displacement is in the vicinity of (m-1) pitches (m is a positive integer), and a combination of detection elements in which the difference in detection values of the detection elements of the other detection element pair is zero when the magnetic scale displacement is in the vicinity of (m-1/2) pitches. an absolute position detection device comprising: a magnetic scale having one magnetic track on which a magnetization pattern is recorded, the magnetization pattern having a non-repeating code pattern of n (n is an integer of 2 or more) bits magnetized at a predetermined pitch, the magnetization pattern having both at least one portion where the pole changes from south to north and one portion where the pole changes from north to south within consecutive (n+1) pitches; and a detection device having two detection element groups: a first detection element group consisting of at least n detection elements arranged at one pitch interval facing the magnetic scale; and a second detection element group consisting of at least n detection elements arranged at a half pitch offset from each of the detection elements of the first detection element group ,
the detection device calculates a code section position calculation value corresponding to a code section position based on code information obtained from the magnetization pattern of the magnetic scale, calculates a section interpolation value at the code section position using a difference value between detection values of each detection element in a plurality of detection element pairs selected from two detection element groups, and obtains an absolute position over the entire length of the magnetic scale from the code section position calculation value and the section interpolation value. an absolute position detection method using a magnetic scale having one magnetic track on which a magnetization pattern is recorded, the magnetization pattern having a non-repeating code pattern of n (n is an integer of 2 or more) bits magnetized at a predetermined pitch, the magnetization pattern having both at least one portion where the pole changes from south to north and one portion where the pole changes from north to south within consecutive (n+ 1) pitches; and a detection device having two detection element groups, a first detection element group consisting of at least n detection elements arranged at one pitch interval facing the magnetic scale, and a second detection element group consisting of at least n detection elements arranged at a half pitch offset from each of the detection elements in the first detection element group ,
an absolute position detection method comprising: acquiring code information of the magnetization pattern of the magnetic scale from detection values of two sets of detection element groups; calculating a code section position calculation value corresponding to a code section position of the magnetic scale based on the code information; calculating a section interpolation value at the code section position based on a difference value between detection values of each detection element in a plurality of detection element pairs selected from the two sets of detection element groups; and obtaining an absolute position over the entire length of the magnetic scale from the position calculation value based on the code section position and the section interpolation value.