CN102322882A - Absolute shaft angle encoding system based on array detector - Google Patents

Abstract

The invention discloses an absolute shaft angle encoding system based on an array detector. It includes a light source, a rotating shaft, a code disc, an objective lens, an array detector and a data processing circuit; The installation of the disc, imaging objective lens and array detector needs to meet the positional relationship of the object image. After the array detector obtains the enlarged local image information of the encoding disc, it is transmitted to the data processing circuit. After the data processing circuit analyzes and processes the image information, it outputs the angle information. . The encoder disc adopts single-turn absolute encoding method, which reduces the number of code channels and the size of the encoder disc; uses array detectors as receiving elements to meet the requirements of high response frequency; adopts hardware circuits as data processing units, which has good real-time performance and fast response speed. Fast, small size and other characteristics. An imaging objective lens is added to magnify the partial image of the code disc to improve the resolution of the system.

Description

Absolute Shaft Angle Encoding System Based on Array Detector

technical field

The invention relates to a precision angle measurement system, in particular to an absolute shaft angle encoding system based on an array detector.

Background technique

According to different encoding methods, traditional shaft encoders can be divided into two types: incremental and absolute. The advantages of incremental encoders are fast response, simple structure, and small size. The disadvantages are that they are greatly affected by the environment. It is easy to cause data loss after power failure, and there is error accumulation. Compared with the incremental encoder, the absolute shaft encoder has the advantages of strong anti-interference ability, no need to re-calibrate after power failure, and no cumulative error.

At present, there are many companies and research institutions that develop shaft encoders in the world, mainly German Heidenhain Company, Opton Company, etc.; Japan's Tamagawa Company, Nikon Company, Canon Company, etc.; American Itek Company, Renco Company, etc., and British , Switzerland and Russia and other countries' research institutions and manufacturers. The Goddard Space Center of NASA in the United States developed a 27-bit ultra-high resolution absolute shaft encoder for the Cartesian coordinates of the vehicle. It uses a new encoding method and image recognition technology to meet the needs of aerospace technology. my country's encoder research probably started in the 1960s. The Changchun Institute of Optics and Mechanics of the Chinese Academy of Sciences developed the first encoder disc and circular grating in 1964, and successfully applied them to photoelectric theodolites and measuring radars. The unit has also successively carried out the development and research of photoelectric encoders, and achieved certain results. In the late 1980s, Chengdu Institute of Optics and Mechanics developed a 26-bit absolute shaft angle encoder <±10″; in 2001, Changchun Institute of Optics and Mechanics developed Produced a 15-bit ultra-small absolute photoelectric encoder with a diameter of 40mm.

For the existing absolute shaft encoders, there is a contradiction between resolution and system size. High-resolution encoders tend to have larger system sizes, while miniaturized encoders often have low angular resolution. In addition, the low response frequency is also a major problem in the existing shaft encoders.

The absolute shaft-angle encoder described in the utility model patent "Absolute Position Shaft-Angle Encoder" (patent application number: 200620115789.6) has similarities with the present invention, and its main features are introduced below:

1. The proposed system uses the linear array CCD to collect the local information of the code disc, and then uses the electronic subdivision technology to improve the angular resolution, which overcomes the contradiction between the encoder size and the angular resolution to a certain extent.

2. In the proposed system, in order to reduce the size of the code disc and improve the resolution of the coarse code at the same time, it is necessary to reduce the size of the engraved line of the code disc within the diffraction limit range. Since the pixel size of the array detector has a limit minimum size, the engraved line of the code disc needs to be reduced. Too small line size is not conducive to electronic subdivision to obtain fine codes, so there is a contradiction between improving the resolution of coarse codes and improving the resolution of fine codes, that is, there are still certain problems in improving the resolution while reducing the size of the encoder.

组完整编码，其中N为码道的等分数，n组完整编码对应的码道宽度为

为了提高粗码分辨率，需要增大N，而N越大，

越大，细分能够提高的分辨率越小，这形成一对矛盾。3. The proposed encoding disc adopts a pseudo-random encoding method. In order to carry out electronic subdivision, the partial image of the encoding disc formed by the array CCD needs to contain at least

group of complete codes, where N is the equal fraction of the code channel, and the code channel width corresponding to n groups of complete codes is

In order to improve the coarse code resolution, N needs to be increased, and the larger N is,

The larger , the smaller the resolution that can be improved by subdivision, which forms a pair of contradictions.

4. The proposed encoding disk is encoded by pseudo-random encoding, and it is more complicated to decode angle information from image information.

With the development of industries and fields such as national defense and automation, the requirements for the miniaturization, intelligence and integration of shaft encoders are getting higher and higher. There are many factors restricting the development of shaft encoders, among which the encoding method and detector They are two key factors. Changing the traditional coding method and developing a small-sized code disc that is conducive to electronic subdivision is an important way to promote the development of shaft angle encoders. For the requirements of the detector, on the one hand, it must cooperate with the code disc to effectively Resolving the partial image of the encoding disc is convenient for electronic subdivision. On the other hand, it requires good real-time performance, that is, high response frequency, which is more conducive to real-time processing. Reducing the size of the system, increasing the resolution, and reducing the response time are the development trends of photoelectric shaft encoders.

Contents of the invention

In order to overcome the problems in the background technology, the object of the present invention is to provide an absolute shaft angle encoding system based on an array detector.

The technical scheme that the present invention solves its technical problem to take is:

The invention includes a light source, a rotating shaft, an encoding disc, an objective lens, an array detector and a data processing circuit; the encoding disc is installed in the rotating shaft, the light source is placed on one side of the encoding disc, and the other side of the encoding disc is provided with an imaging objective lens and an array detector in sequence , the installation of the encoder disc, imaging objective lens and array detector needs to meet the positional relationship of the object image. After the array detector obtains the enlarged local image information of the encoder disc, it is transmitted to the data processing circuit. After the data processing circuit analyzes and processes the image information, it outputs angle information.

它由n位编码刻线和1位分隔刻线组成。分隔刻线是角宽度为θ₁的透光窗口，它作为标志，用来区分相邻两组编码，分隔刻线与左右两边的编码刻线均相距角宽度为θ₂的角间隔，编码刻线由n个窗口组成，每个窗口有两种可能的状态：透光和遮光，分别代表二进制“1”和“0”，每个窗口的角宽度为θ₃，整个码道2ⁿ组编码刻线采用n位自然二进制码进行编码。每组编码的角度关系满足

θ₁、θ₂和θ₃三者均不相等。The said code disk is based on the binary code, and uses light-transmitting and light-shielding windows to respectively represent "1" and "0" in the binary code. , divided into 2 ⁿ areas equally along the circumferential direction, that is, 2 ⁿ groups of codes. The angular width of each group of codes is

It consists of n-bit coding lines and 1-bit separating lines. The separation reticle is a light _- transmitting window with an angular width of θ _1. It is used as a sign to distinguish two adjacent groups of codes. The line is composed of n windows, and each window has two possible states: light-transmitting and light-shielding, representing binary "1" and "0" respectively, the angular width of each window is θ ₃ , and the entire code channel is 2 ⁿ groups of codes The engraved line is coded with n-bit natural binary code. The angular relationship of each group of codes satisfies

None of θ ₁ , θ ₂ and θ ₃ are equal.

The data processing circuit includes an array detector control module, a data receiving module, a coarse code decoding module, a fine code decoding module, an angle information acquisition module and a data output module; the array detector control module for outputting control signals and the The data receiving module receiving array detector data is connected with the array detector respectively, and the data receiving module is respectively connected with the angle information acquisition module after the coarse code decoding module and the fine code decoding module, and the angle information acquisition module is connected with the data output module connect.

The beneficial effects that the present invention has are:

1. A single-turn absolute encoding method is adopted, which can achieve the purpose of reducing the code track and reducing the size of the encoding disc.

2. The array detector is used as the receiving element. On the one hand, it can subdivide the received coarse code information. On the other hand, its response frequency is high, which can well meet the requirement of high response frequency.

3. The hardware circuit is used as the data processing unit, which has the characteristics of good real-time performance, fast response speed and small size.

4. An imaging objective lens is added between the code disk and the array detector to enlarge the partial image of the code disk. On the one hand, under the same system size, the system resolution can be effectively improved. On the other hand, it solves the problem of improving the resolution of coarse codes. The contradiction between the high rate and the improvement of fine code resolution.

Description of drawings

Fig. 1 is a schematic diagram of the general structure principle of the present invention;

Fig. 2 is an overall schematic diagram of an encoding disc;

Fig. 3 is a partially enlarged schematic diagram of the code disc;

Fig. 4 is the local size of the code disc;

Fig. 5 is the reading principle of the subdivision code;

Fig. 6 is a block diagram of a data processing circuit.

In the figure: 1. Light source, 2. Rotating shaft, 3. Coding disc, 31. Each group of codes, 32. Separation line, 33. n-bit coding line, 34. Angle interval, 35. Pixel scale, 36. Reference line , 4, objective lens, 5, array detector, 6, data processing circuit, 61, array detector control module, 62, data receiving module, 63, coarse code decoding module, 64, fine code decoding module, 65, angle information acquisition module, 66, a data output module.

Detailed ways

Below in conjunction with accompanying drawing and embodiment the present invention will be further described:

As shown in Figure 1, the present invention comprises a light source 1, a rotating shaft 2, an encoding disc 3, an objective lens 4, an array detector 5 and a data processing circuit 6; an encoding disc 3 is installed in the rotating shaft 2, and the light source 1 is placed on one side of the encoding disc 3 , the other side of the encoding disc 3 is provided with an imaging objective lens 4 and an array detector 5 in turn, the installation of the encoding disc 3, the imaging objective lens 4 and the array detector 5 needs to meet the positional relationship of the object image, and the array detector 5 obtains the enlarged code After the partial image information of the disc is transmitted to the data processing circuit 6, the data processing circuit 6 analyzes and processes the image information, and then outputs the angle information.

The light source 1 uses LED as the lighting source to illuminate the part of the code disk 3 to ensure that the code disk 3 is clearly imaged on the array detector 5. The code disk 3 is coded by a single-turn absolute coding method, and the imaging objective 4 is located 5 and the code disk 3, its function is to enlarge the code disk image, so that the array detector 5 can receive the appropriate code disk 3 image, and ensure the accuracy of subsequent decoding. The data processing circuit 6 receives the image information, then decodes it, and finally outputs the angle result through the USB interface. The following is a further detailed introduction to several important parts of the system.

1. Encoding disk

As shown in Fig. 2, Fig. 3, and Fig. 4, the whole code disc has only one circle of code track, which is equally divided into 128 areas along the circumferential direction, that is, 128 groups of codes, and the angular width of each group of codes 31 is 168′45″, which is composed of 7 The coding engraved line 33 of one bit and 1 spaced engraved line 32 are made up of, and the engraved line 32 of separating is the light-transmitting window that angular width is 8 ', and it is used for distinguishing two adjacent codes, and engraved line 32 is separated from the engraved engraving on left and right sides. The lines 33 are all separated by an angular interval 34 with an angular width of 20'. The coded line 33 is composed of 7 windows, and each window has two possible states: light-transmitting and light-shielding, representing binary "1" and "0" respectively, The angular width of each window is 17'15", and 128 groups of 7-bit coded engraved lines are coded with natural binary codes.

Second, the principle of angle measurement

The code disk 3 is enlarged by the objective lens 4, and its partial image is imaged on the array detector 5. In order to ensure that at least two dividing lines appear in the array detector, and at the same time facilitate the subsequent pixel subdivision, the selected size is Two regions (the entire circumference is divided into 128 regions) are imaged on the detector.

First, A/D conversion is performed on the information obtained from the array detector 5 to obtain binarized data.

Then find out two adjacent separation lines 32 according to the different line widths of the separation line and the coding line, and then obtain the 7-bit coded data 33 between the two adjacent separation lines, so that the roughness of the absolute information of the angle can be obtained. Code, assuming that the decimal value corresponding to the obtained natural binary code is N, then the rough code reading is

As shown in Figure 5, the fine code acquisition method is as follows, assuming that the detected two adjacent separation lines cover m pixels on the array detector, respectively numbered according to 0, 1, 2, ..., m-1, if The pixel sequence number at the position of the detection line 36 is m', so the reading of the subdivision code is

Thus, the final measured angle can be expressed as:

3. Data processing circuit

The data processing circuit 6 selects Altera Company's EP2C5T144 FPGA as the main control processing chip to realize data acquisition and data processing functions. The basic framework of the hardware system is as follows:

As shown in Figure 6, described data processing circuit 6 comprises array detector control module 61, data receiving module 62, deciphers coarse code module 63, deciphers fine code module 64, obtains angle information module 65 and data output module 66; The array detector control module 61 for outputting control signals and the data receiving module 62 for receiving array detector data are connected to the array detector 5 respectively, and the data receiving module 62 passes through the coarse code decoding module 63 and the fine code decoding module respectively. After 64, it is connected with the acquisition angle information module 65, and the acquisition angle information module 65 is connected with the data output module 66.

The hardware system uses a programmable logic device FPGA as the main chip. According to the requirements of the array detector 5, the array detector control module 61 of the FPGA generates a control signal to drive the array detector 5 to work, and the partial code disc 3 collected by the array detector 5 Enlarged image information is received by the data receiving module 62 of FPGA, and according to the described encoding disc 3 characteristics of claim 2, FPGA decodes the received data by decoding the coarse code module 63 and the fine code module 64 respectively, and the obtained results of the two are similar. Combined with the angle result calculated by the angle information acquisition module 65 , the angle result can be output by the data output module 66 .

Claims (3)

1. the absolute shaft encode system based on detector array is characterized in that: comprise light source (1), rotating shaft (2), code-wheel (3), object lens (4), detector array (5) and data processing circuit (6); Code-wheel (3) is installed in the rotating shaft (2); Light source (1) places a side of code-wheel (3), and the opposite side of code-wheel (3) is provided with image-forming objective lens (4) and detector array (5) successively, and code-wheel (3), image-forming objective lens (4) and detector array (5) three install and need satisfy image position relation; After detector array (5) obtains the code-wheel topography information after the amplification; Pass to data processing circuit (6), data processing circuit (6) to the image information analyzing and processing after, output angle information.

2. a kind of absolute shaft encode system according to claim 1 based on detector array; It is characterized in that: described code-wheel (3); Is the basis with the binary code, with the window of printing opacity and shading represent respectively in the binary code " 1 with " 0 ", its coded system adopts single-ring absolute type to encode; whole code-disc has only one to enclose code channel, along the circumferential direction is divided into 2 ⁿIndividual zone, promptly 2 ⁿGroup coding.The angular breadth of every group coding (31) is

, and it is made up of n position coding groove (33) and 1 separation groove (32).Separating groove (32) is that angular breadth is θ ₁Optical transmission window, it as a token of is used for distinguishing two adjacent groups coding, coding groove (33) the homogeneous phase elongation width of separating groove (32) and the right and left is θ ₂Angular spacing (34), coding groove (33) is made up of n window, each window has two kinds of possible states: printing opacity and shading, represent binary one and " 0 " respectively, the angular breadth of each window is θ ₃, whole code channel 2 ⁿGroup coding groove (33) adopts n position natural binary code to encode.The angular relationship of every group coding satisfies

θ ₁, θ ₂And θ ₃The three is all unequal.

3. a kind of absolute shaft encode system according to claim 1 based on detector array; It is characterized in that: described data processing circuit (6) comprises detector array control module (61); Data reception module (62); Separate thick sign indicating number module (63), separate thin sign indicating number module (64), obtain angle information module (65) and data outputting module (66); Be used to export control signal detector array control module (61) and the data reception module that is used for the receiving array detector data (62) both be connected with detector array (5) respectively; Data reception module (62) is conciliate thin sign indicating number module (64) back and is obtained angle information module (65) and be connected through separating thick sign indicating number module (63) respectively, obtains angle information module (65) and is connected with data outputting module (66).

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