JPH0780757A - Position displacement measuring method and device in machine tool - Google Patents

Abstract

PURPOSE:To realize a precise position control by measuring the position displacement of a tool or a work in the main axial direction at a high accuracy, during the operation of a machine tool. CONSTITUTION:A position displacement measuring device applied to the main shaft part of a machine tool 1 to carry out a cutting process in a fly cutting method includes an interferometer 20 loaded on a movable table mechnism 40 together with a machine main body, a laser beam source device 30, a laser beam passage formed of a transparent material formed to the core 27 of the main shaft 3, and a reflecting mirror 26 installed to the rear surface of a tool installing part 4, and the position displacement of a processing point P is measured by making the incident point Q of the measuring beam 32 on the reflecting mirror 26 as the measuring point. A signal detected by the beam detector 23 of the interferometer 20 is delivered to an FB signal operation member through a cable 24, and a signal to indicate the position displacement of the processing point P in the Z axial direction is produced. This signal is utilized as a signal to correct the input of the position loop of a position control system of the position in the axial direction of the movable table mechanism 40.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement measuring method and a displacement measuring apparatus in a machine tool, and more specifically, to a positional displacement of a tool or a work in a machine tool for performing precision machining, particularly ultra precision machining. The present invention relates to a method for precisely measuring the vicinity of a processing point as a measurement point and a displacement measuring device for carrying out the method. INDUSTRIAL APPLICABILITY The displacement measuring method and device of the present invention can be utilized to improve the accuracy of feedback control of the tool or work position in a machine tool.

[0002]

2. Description of the Related Art Machine tools that require precise machining accuracy,
Particularly in the ultra-precision machine, it is necessary to continuously measure a machining error during machining and perform automatic correction control of the machine so that the tool or the work always takes a correct position. The so-called in-process method has been conventionally known as a method for measuring the position error during processing, but the conventional in-process method attaches a measuring element to the measurement point near the processing part and occurs during processing. Since it is necessary to perform measurement under adverse conditions such as cutting chips, cutting oil, mechanical vibration, heat, etc., it is true that ultra-precision measurement, for example, in the nanometer unit, is performed with high reliability. It was difficult. In addition, the life of the measuring element could not be kept long.

As a method of measuring the relative position between tool workpieces during machining without attaching a measuring element to the measuring point, there is a method called a machining surface reference control machining method. In this method, an object to be measured is measured. It is not possible to avoid the problem of Abbe error that occurs when the measurement point and the measurement scale are not on the same line, and it is a method suitable for performing precise position control based on highly accurate measurement. It was hard to say.

[0004]

Therefore, the first aspect of the present invention is to be solved.
One purpose is the point where processing is actually performed (processing point)
Displacement measurement method and displacement measurement for machine tools that can measure the positional displacement of the object to be measured (tool or work) with the measurement point near the It is another object of the present invention to provide an apparatus, and a method and an apparatus capable of performing in-process measurement without being affected by adverse conditions such as cutting chips, cutting oil, mechanical vibration, and heat. To provide.

Still another object of the present invention is to
An object of the present invention is to provide the above method and device capable of improving the position control accuracy in a machine tool controlled by an NC device (numerical control device).

[0006]

According to the present invention, "a light reflecting means is arranged on the back surface of a tool mounting means or a work mounting means of a machine tool, and an optical path formed by penetrating a spindle of the machine tool is used. The above technical problem is solved by "a position displacement measuring method in a machine tool, characterized in that the position displacement along the main axis direction of the tool or the work is measured by reciprocally propagating a measurement light beam of an interferometer means". In order to improve the position control accuracy in the machine tool controlled by the NC device, the above method further provides a basic method for achieving the above (configuration according to claim 1). "While the measurement of the positional displacement is continuously performed while the machine tool is operating,
The measurement result of the position displacement is used to perform position correction control of the movable portion in the spindle direction of the machine tool so that the position of the machining point along the spindle direction is corrected. " (The structure according to claim 2).

Further, as a constitution of a position displacement measuring apparatus for carrying out each of the above-mentioned methods, "an interferometer means arranged at a position relatively distant from a machining point on a spindle of a machine tool, and the machine tool A light reflecting means arranged on the back surface of the tool mounting means or the work mounting means, a measurement light beam reciprocating propagation optical path means formed penetrating the main axis of the machine tool, and a coherent light beam to the interferometer means. A position displacement measuring device in a machine tool, characterized in that it is provided with a light source means for making the light incident (the structure according to claim 3), and in the device, "position control of a movable portion in the main axis direction of the machine tool. And a means for supplying a correction signal for correcting the position of the machining point along the main axis direction to the control means to be executed "(structure according to claim 4).

[0008]

In the position displacement measuring method and apparatus of the present invention, the interferometer is arranged on the main axis of the machine tool at a position relatively distant from the machining point, and the light beam from the coherent light source (laser) is emitted. It is incident. The measurement light beam generated in the interferometer passes through the optical path formed through the main axis of the machine tool, is reflected by the light reflecting means arranged on the back surface of the tool mounting means or the work mounting means, and the optical path is formed. In the reverse direction to re-enter the interferometer. In the interferometer, wavefront superposition with the reference light beam is performed by an optical system according to the type of interferometer used, and light and darkness due to interference is observed at the photodetector. The detection output obtained by the photodetector is converted into a signal indicating the displacement amount of the light reflecting means in the main axis direction through signal processing suitable for the interferometer used (for example, a phase compensation interferometer is used. In that case, the signal representing the amount of phase compensation is treated as a signal representing the amount of position displacement).

Further, the signal representing the displacement amount of the light reflecting means in the main axis direction is converted into a signal representing the displacement amount of the machining point in the main axis direction through a relationship determined by an appropriate evaluation method, and the signal of the machining point position is converted. Used for precision control. That is, the position displacement of the machining point during machining is continuously monitored, the position correction signal is supplied to the position control system of the moving element of the machine tool in real time, the limit of the motion accuracy of the machine and the heat generated during cutting. Position correction control for compensating the influence of machining point position drift caused by various factors such as thermal displacement of each part due to temperature change due to the like, displacement due to cutting resistance, etc. is executed.
As a result, extremely high-precision position control that suppresses the influence of these drift factors is realized.

According to the present invention, the interferometer means having the measuring light beam optical path penetrating the main axis of the machine tool is utilized,
Since the position displacement of the tool or the workpiece in which the measurement point is set on the spindle is measured, a highly accurate measurement signal that does not include the Abbe error can be obtained without being hindered by the rotational movement of the spindle. Also, since the measurement point can be set at a position where there is no risk of cutting chips and cutting oil scattering without moving away from the processing point, in-process measurement under much better conditions than the conventional in-process method can be performed. Will be possible.

Further, since the measuring device main body (interferometer main body) which is likely to cause an error due to heat or mechanical vibration can be installed at a position separated from the processing point, the reliability of the measuring accuracy can be kept higher and the measuring device can be improved. It is extremely advantageous in extending the life of the device and reducing the burden of maintenance work such as cleaning.

[0012]

FIG. 1 is a schematic diagram for explaining a schematic configuration example in the case where the displacement measuring method or device according to the present invention is applied to a spindle portion of a precision machine tool for cutting by a fly cutting method. In FIG. 1, a precision machine tool generally designated by reference numeral 1 is provided with a machine body moving and mounting section and a work mounting section on a bed 70. The work placement part has a work attachment column 61 installed on a base 60 whose height is adjustable, and a work 62 to be processed is attached to the column 61.

On the other hand, the machine main body moving / placing section is provided with a guide mechanism 50, whose internal structure is omitted, and is illustrated in a lump. A moving table mechanism 40 driven in the Y direction (vertical direction on the paper surface) and the Z direction (horizontal direction on the paper surface),
In addition, it is composed of a machine body and a displacement measuring device placed on the moving table mechanism 40.

The machine body is supported by a spindle housing 2 fixedly mounted on the moving table mechanism 40 (in the figure, the upper half portion is shown broken) and a bearing portion 9 attached to the spindle housing 2. In this state, the main shaft 3 is rotated and driven by the main shaft motor 10. The bearing portion 9 includes an air bearing mechanism (detailed structure is omitted), and an air jet that fulfills a thrust bearing function is supplied to the gap 7 between the main shaft 3 and the main shaft 3, while a key coupling (not shown in the drawings) is made to the main shaft 3. The air jet that fulfills the radial bearing function is supplied to the gap 8 between the rotary member 12 and the rotary member 12.

A cutting tool 5 is mounted on the tip of the spindle 3 via a tool mounting portion 4. Cutting edge 6 of tool 5 and spindle 3
A small offset distance is provided between the axis of rotation and the axis of rotation. Therefore, when the spindle 3 rotates in a state in which the cutting edge portion 6 is pressed against the work 62, the cutting edge portion 6 has an offset distance centered on the intersection point P (hereinafter, referred to as a processing point) between the rotation axis of the spindle 3 and the workpiece machining surface. Then, the orbiting motion is performed with the radius as the radius, and the cutting process is executed according to the depth of cut (position on the Z axis).

The X-axis position and the Y-axis position of the moving table mechanism 40 are controlled by a control unit including an NC device, an encoder and the like in accordance with a machining program in a semi-closed system similar to the conventional one. For the directional position), position control is performed based on the detection output of the displacement measuring device according to the present invention. The displacement measuring device incorporated to apply the invention of the present application to the main spindle portion includes an interferometer 20, a laser light source device 30, and a core portion 27 of the main spindle 3, which are placed on the moving table mechanism 40 along with the machine body. And a reflection mirror 26 attached to the back surface of the tool mounting portion 4, and the processing is performed with an incident point (reflection point) Q of the measurement light beam 32 on the reflection mirror 26 as a measurement point. The position displacement of the point P is measured.

The laser light source device 30 includes an emitted light beam 31.
Is installed on the base 33 in such a manner that the optical axis can be adjusted so as to make the light incident on the interferometer 20 accurately. In order to simplify the optical axis adjustment, it may be possible to connect the laser light source device 30 and the light incident part of the interferometer 20 with a coherency-preserving optical transmission medium (for example, a single mode optical fiber). There are no particular restrictions on the type of laser oscillator used (gas laser, semiconductor laser, etc.), but if the oscillation frequency fluctuates, it may cause a decrease in measurement accuracy. Therefore, a laser device equipped with means for stabilizing the oscillation frequency (wavelength) should be used. It is preferable to use.

During the processing, the reflecting mirror 26 rotates together with the main axis, so that the incident point (reflecting point) Q of the measuring light beam 32 is changed.
Should be coincident with the center of rotation of the main shaft 3, or the reflecting surface should be made to be exactly orthogonal to the main shaft. Therefore, it may be considered that a mechanism for finely adjusting the direction of the reflecting surface of the reflecting mirror 26 is additionally provided at the place where the reflecting mirror is attached.

The main-axis core portion 27, which serves as a round-trip optical path for the measurement light beam between the interferometer 20 and the reflection mirror 26, is a cavity (air).
However, in order to suppress fluctuations in the refractive index of the medium due to temperature rise and to prevent optical path length fluctuations that cause measurement errors, a material transparent to the laser beam (for example,
Acrylic resin) is preferable. If a more accurate measurement is intended, a high vacuum may be considered.

In the figure, an interferometer 20 having a Michelson-type basic arrangement consisting of a half mirror 21, a reference mirror 22, and a photodetector 23 is illustrated.
Any type can be used as long as it can be arranged to set a measuring light beam optical path that passes through and reciprocates the main shaft 3. For example, by using a known phase compensation type interferometer, it is possible to perform position displacement measurement with extremely high accuracy (resolution of about several nm).

The signal detected by the light detecting section 23 of the interferometer 20 is sent to the FB signal calculating section (see FIGS. 2 and 3 to be described later) via the cable 24, and the position of the moving table mechanism 40 in the main axis direction ( It is used for position correction (position on Z axis). FB
In the signal calculation unit, signal processing suitable for the adopted interferometer is performed, and a signal representing the positional displacement of the processing point P in the Z-axis direction is generated through the signal representing the positional displacement of the reflecting mirror 27. When the phase compensation type interferometer is used, the signal representing the phase compensation amount is processed as the signal representing the reflection mirror position displacement amount.

Since the quantity measured by the interferometer 20 is a change in the round-trip optical path length of the measurement light beam 32, the reflection point Q of the measurement light beam 32 is directly measured with the position of the interferometer 20 as a reference. Positional displacement measurement with points will be performed. In this case, it is clear that both the measurement point Q and the measurement light beam 32 corresponding to the measurement scale are on the main axis, and thus the possibility of the above-mentioned Abbe error occurring is avoided in principle.

Since the measuring point Q is set on the back surface of the tool mounting portion 4 not far from the machining point P, the interferometer 20
It is sufficiently possible to evaluate the position displacement of the processing point P in the main axis direction based on the measurement result of. For example, the relationship between the position displacement Δq in the main axis direction at the point Q and the position displacement Δp in the main axis direction at the point P can be calculated using a method such as comparing the position displacement amount measurement data at the point Q with the actual measurement data of the cut amount, and Δq = αΔp It may be possible to obtain it in advance in a format such as (α is a conversion coefficient).
When the conversion coefficient α is considered to change under other conditions such as the temperature T, the output of the temperature sensor arranged at an appropriate position is used to evaluate α as a function of a variable indicating the conditions such as the temperature. Just do it. Further, even when it is necessary to correct the temperature of the interferometer according to the change in the refractive index due to the change in the temperature of the material forming the optical path 27, it is conceivable to use the output of the temperature sensor to perform the calculation in consideration of this. The simplest evaluation method is to always consider α = 1 (displacement Δq of reflecting mirror = displacement Δp of processing point).

By using the relationship (Δp = αΔq) determined by such an evaluation method and measuring the machining point position displacement in real time during machining, position correction for realizing a more desirable machining point position is executed. You can do it.
This will be described below.

What is controlled by the NC device is usually
Since it is the position (semi-closed system) detected by the encoder mounted on the rotary shaft of the motor as a position detector (rotary position of the encoder mounting shaft), the position control in the spindle direction by the NC controller is ideal. However, the position of the processing point P that determines the depth of cut of the workpiece 62 does not always change as desired.

Various factors such as the limit of the motion accuracy of the machine, thermal displacement of each part due to temperature change due to heat generated during cutting, displacement due to cutting resistance, and the like can be considered as causes for changing the position of the processing point P. However, according to the measuring method or the assumed device of the present invention, most of the various factors that cause the processing point position error are measured, and therefore the measurement result is incorporated in the position control system as a position correction amount in real time. As a result, it becomes possible to realize position control in which the effects of the above factors are suppressed.

FIG. 2 is a block diagram showing an essential part of a machine tool control system used for this purpose. Further, FIG. 3 is a simplified description of a control loop of Z-axis control executed by the system shown in FIG.

2, the CPU incorporated in the CNC denoted by reference numeral 100 sequentially reads the program data stored in the memory in the CNC 100 and performs the necessary interpolation calculation on the XYZ axis data. A movement command signal for each axis is sent to the shared RAM 101 every predetermined period.

On the other hand, the CPU of the digital servo circuit 102 which drives each axis motor 103 reads out this movement command from the shared memory 101 in a predetermined cycle and generates a position command signal for each of the XYZ axes. Regarding the X-axis and the Y-axis, the deviation between the position command value and the current position detected by the encoder of each axis is used as the position loop input as in the past, but regarding the Z-axis, as shown in each figure, Interferometer 20
FB generated by the FB signal calculator 25 based on the output of
The position loop input is determined in consideration of the signal (a signal indicating the amount of positional displacement of the machining point P or the amount of correction required).

That is, the CP in the digital servo circuit 102
By U, the calculation corresponding to the deviation of the position command Pz of the Z-axis position pulse and the current position Pf detected by the Z-axis encoder 104 corrected by the FB signal is performed in a predetermined cycle,
It is input to the Z-axis position loop. For example, when the FB signal represents the required correction amount as it is, a deviation calculation is performed using Pz and the FB signal as an addition term and Pf as a subtraction term. When the FB signal represents an error amount, deviation calculation is performed using Pz as the addition term and Pf and the FB signal as the subtraction term.

The velocity command signal Vz generated by the position loop processing PL based on the input thus determined
Is calculated as a deviation from the current speed Vf corresponding to the differential value of the position detection output of the encoder 104, and the speed loop processing V
It is input as L. In the speed loop processing VL, the torque command Tz is generated, the drive current corresponding to the torque command Tz is supplied to the motor M through the servo amplifier, and the motor rotates, whereby the desired position correction control is realized. .

In the embodiment described above, in the machine tool of the type in which the work is fixed and the main body part carrying the tool on the rotating main spindle moves XYZ, the reflection mirror is attached to the back side of the tool mounting part and the measuring point. Although the example in which Q is set has been described, the machine tool to which the displacement measuring method or device of the present invention is applied is not limited to that of the above embodiment, and
The position of the measurement point (mirror mounting position) is not limited to the tool side, but may be set on the work support side spindle.

For example, based on a movement command programmed on the Cartesian coordinate system, by combining the rotational movement on the workpiece rotation C-axis and the movement on the X-axis, the fly-cutting type machining including the movement in the virtual Y-axis direction is performed. If a precision machine tool of a type that executes a process (for example, see the attached specification of Japanese Patent Application No. 5-158093 of the present applicant), on the rotary spindle on the back surface of the tool mounting portion, as in the present embodiment. It is possible to set the measurement point Q at and correct the position in the direction of the main axis to realize precise control of the depth of cut.

Further, a reflection mirror is attached to the back surface of the work mounting portion of the lathe, a measurement point Q is set on the spindle, the work position displacement during machining is measured in real time, and the result is a tool moving table or a work moving table. It can also be used for position correction control in the direction of the main axis.

[0035]

According to the position displacement measuring method and apparatus of the present invention, by using the interferometer means having the measuring light beam optical path penetrating the main shaft of the machine tool, a tool or tool having a measuring point set on the main shaft is used. Since the position displacement of the workpiece is measured, it is possible to obtain a highly accurate measurement signal that does not include an Abbe error, without being hindered by the rotational movement of the spindle.
Also, since it is possible to set the measurement point at a position where there is no risk of cutting chips and cutting oil scattering without moving away from the processing point,
It has become possible to perform in-process measurements under much better conditions than conventional in-process methods.

Furthermore, since the measuring device main body (interferometer main body) which is likely to cause an error due to heat or mechanical vibration can be installed at a position separated from the processing point, the reliability of the measurement accuracy can be kept higher and the measuring device can be improved. It has become possible to extend the service life and reduce the burden of maintenance work such as cleaning.

Since the measurement point Q is set on the back surface of the tool or the mounting portion of the work which is not far from the machining point, it is sufficiently possible to properly evaluate the positional displacement of the machining point based on the measurement result. Based on this evaluation, it became possible to continuously monitor the position displacement of the machining point during machining and to supply the position correction signal to the position control system of the moving element of the machine tool in real time. This limits the machine's motion accuracy,
It is possible to perform position correction control that compensates for the influence of machining point position drift caused by various factors such as thermal displacement of each part due to temperature change due to heat generated during cutting, displacement due to cutting resistance, etc. A major factor that hinders the improvement of machining accuracy has been removed.

[Brief description of drawings]

FIG. 1 is a schematic diagram illustrating an example of a schematic configuration when a displacement measuring method or device according to the present invention is applied to a spindle portion of a machine tool that performs cutting by a fly cutting method.

FIG. 2 shows a machine tool control system used when the measurement result obtained by the position displacement measuring apparatus used in the embodiment shown in FIG. 1 is used for correction control of the Z-axis position of a machining point. It is the thing which illustrated the structure with the principal part block diagram.

FIG. 3 is a simplified block diagram showing a control loop of Z-axis control executed by the system shown in FIG.

[Explanation of symbols]

 1 Precision Machine Tool 2 Spindle Housing 3 Spindle 4 Tool Mounting Part 5 Tool 6 Blade Edge 7, 8 Gap 9 Bearing Part 10 Spindle Motor 11 Encoder (Spindle) 20 Interferometer 21 Beam Splitter 22 Reference Mirror 23 Photo Detector 24 Cable 25 FB Signal calculation unit 26 Reflection mirror 27 Spindle core unit 30 Laser light source device 31 Laser beam 32 Measuring light beam 40 Moving table mechanism 40 50 Guide mechanism 60 Base 61 Work mounting column 62 Work 70 bed 100 CNC 101 Shared memory 102 Digital servo circuit 103 Each axis drive motor 104 Encoder (Z axis) P Machining point Q Measurement point (measurement light beam incident point)

Claims (4)

[Claims] 1. A light reflecting means is arranged on the back surface of a tool mounting means or a work mounting means of a machine tool, and a measuring light beam of an interferometer means is reciprocated by using an optical path formed through a main shaft of the machine tool. A positional displacement measuring method in a machine tool, characterized in that the positional displacement of the tool or the work along the main axis direction is measured by propagating. 2. The position displacement measurement is continuously performed while the machine tool is operating, and the position displacement measurement result is corrected such that the position of the machining point along the spindle direction is corrected. 2. The position displacement measuring method in a machine tool according to claim 1, wherein the method is used to perform position correction control of the movable portion of the machine tool in the spindle direction. 3. An interferometer means arranged at a position relatively distant from a machining point on a spindle of a machine tool, and a light reflecting means arranged on a back surface of a tool mounting means or a work mounting means of the machine tool. A machine tool comprising: a measurement light beam reciprocating propagation optical path means formed penetrating a main axis of the machine tool; and a light source means for making a coherent light beam incident on the interferometer means. Position displacement measuring device. 4. A means for supplying a correction signal for correcting the position of a machining point along the main axis direction to a control means for controlling the position of a movable portion of the machine tool in the main axis direction. The position displacement measuring device in a machine tool according to claim 3, which is characterized in that.