JPH10274521A - Contour measurement data correction method and contour measuring machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and a contour measuring machine therewith, by which the narrow range of a linear encoder can be corrected easily, which has difficulty in generating a difference depending upon a worker, and has minimum possibility to cause a secular change in the contour measuring machine which detects a displacement amount in the moving direction (X-direction) of a stylus and a perpendicular direction (Z-direction) to it, using the linear encoder. SOLUTION: A reference gauge having a high flatness surface is measured, a least square straight line is calculated for the measurement data of the one corresponding to the narrow range of a linear encoder to obtain the variation in the respective measurement data from the least square straight line, and the variation is taken as a narrow range correction value. The measurement data are outputted from the two linear encoders in Z-direction and X- direction, therefore, the reference gauge is first measured in a condition as inclined by a small angle to such a degree as the output of the X-direction is negligible, and the correction value of the Z-direction is calculated from the measurement data. Next, it is measured in a condition as inclined by a large angle within a range of such a degree as a stylus can trace the reference gauge accurately. After the measurement data are corrected by the correction value in the Z-direction, the correction value in the X-direction is calculated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a contour shape measuring device for determining a contour shape of a workpiece, and more particularly to a contour shape measuring device for detecting a moving direction of a stylus and a displacement amount in a direction perpendicular thereto with a linear encoder. The present invention relates to a method for correcting measurement data and a contour shape measuring instrument provided with the method.

[Prior art]

FIG. 7 shows a measuring section 4 of a general contour shape measuring machine.
Indicates 0. As shown in FIG. 7, the measuring unit 40
A feed device 43 is provided on a column 42 erected at 1
A detector 44 having the stylus 49 and detecting the amount of displacement of the stylus 49 in the Z direction (vertical direction) is provided on the feed device 43 so as to be movable in the X direction (horizontal direction). The moving amount of the detector 44 (in order to unify the name with the Z direction,
In this specification, a linear encoder that detects the “displacement amount” in the X direction is also built in. Accordingly, when the detector 44 is moved in the X direction in a state where the stylus 49 is in contact with the measurement position of the workpiece W, the amount of displacement of the stylus 49 in the Z direction is detected by the detector 44. The amount of displacement in the X direction is detected by the scale of the feed device 43, and measurement data (displacement data of the stylus 49 in the X and Z directions) is obtained. Then, the contour shape of the work W is calculated from the measurement data, and the result is output to a CRT or an XY recorder.

As a detecting method of the detector 44, a differential transformer or the like may be used. However, since the measuring error of the differential transformer or the like is proportional to the detecting range, the measuring range is relatively wide like the contour shape measurement. In such a case, a linear encoder is often used as in the case of detecting the displacement amount in the X direction.

In general, photoelectric encoders are generally used as linear encoders. In the photoelectric linear encoder, the displacement is detected by counting the scale with a read head based on the scale on which the scale is precisely engraved, but the displacement between the scales (narrow range) is also minute. Can be detected. In other words, the read head is also provided with precisely engraved scales,
If the displacement is made within a narrow range, the relative position between the scale of the scale and the scale of the read head changes, and the light quantity changes sinusoidally. This is electrically divided to obtain a fine displacement. For example, the narrow range is 10 to 20 μm, which is divided into 50 to 100.

[0005]

In this case, the accuracy of the distance between the scales in the wide range depends on the manufacturing accuracy of the scale because the accuracy of the distance between the scales appears directly as the measurement accuracy. (Eg, the relative inclination between the scales of the read head and the gap between the scale and the read head). That is, if the positional relationship between the scale and the read head is not correctly adjusted,
Since a correct sine waveform cannot be obtained, an error occurs in the detected value. Usually, as a method for adjusting the narrow range, the outputs of two photoelectric sensors provided in the read head are plotted on an XY graph so that the outputs are 90 ° out of phase with each other, and plotted (Lissajous waveform) Is adjusted so that is a perfect circle. FIG. 8 shows an example in which the Lissajous waveform K is elliptical with respect to the perfect circle J, and the difference δ with respect to the perfect circle J represents an error.

[0006] However, it takes a lot of time to perform such an adjustment, and the adjustment accuracy is likely to vary from individual to individual. Further, since the positional relationship between the scale and the read head is mechanically adjusted, even if it is correctly adjusted once, the possibility of aging due to temperature change, vibration, or the like is inevitable.

The present invention has been made in view of such circumstances, and a contour shape measuring device for detecting a displacement amount of a moving direction (X direction) of a stylus 49 and a direction perpendicular to the direction (Z direction) by a linear encoder. In the above, it is an object of the present invention to provide a method capable of easily correcting a narrow range of a linear encoder, hardly causing a difference between operators, and having a very small possibility of aging, and a contour shape measuring instrument provided with the method. .

[0008]

According to the present invention, in order to achieve the above object, a reference gauge having a high flatness surface is measured obliquely, and the obtained measurement data corresponds to a narrow range of a linear encoder. For the measured data of the minute, a least-square straight line is calculated, a deviation of each measured data from the least-square straight line is obtained, and the obtained deviation is used as a narrow range correction value of the linear encoder.

In this case, since the measurement data is output from the two linear encoders in the Z direction and the X direction, the calculation of the correction value is performed separately in the Z direction and the X direction. That is, first, measurement is performed with the high flatness surface of the reference gauge inclined at a small angle with respect to the horizontal plane so that the output in the X direction is negligibly small, and a correction value in the Z direction is calculated from the measurement data. . Next, measurement is performed in a state in which the stylus is inclined at a large angle within a range where the stylus can accurately trace the reference gauge, and the measurement data is corrected by a correction value in the Z direction, and then a correction value in the X direction is calculated.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 3 is a block diagram showing an embodiment of a contour shape measuring machine according to the present invention. As shown in FIG. 3, the measuring unit 40 makes the stylus 4 contact the stylus 49 against the surface of the workpiece W as described in the related art (FIG. 7).
9 relative to the workpiece W, and
The displacement amount in the direction and the X direction is detected by a linear encoder.

The Z-correction value calculating section 31 calculates a Z-correction value of the Z-level data contained in the detector 44 from the measurement data obtained by measuring the high flatness plane Ga of the reference gauge G at a small angle with respect to the horizontal plane.
For the measurement data corresponding to the narrow range of the linear encoder, a least-square straight line is calculated, and the deviation of each measurement data from the least-square straight line is obtained. The obtained deviation is used as the narrow-range correction value δz of the Z linear encoder. . The Z correction value storage unit 32 stores the narrow range correction value δz.

Similarly, the X correction value calculating section 33 calculates the narrowness of the X linear encoder built in the feeder 43 from the measurement data obtained by measuring the high flatness surface Ga by inclining the reference gauge G by a large angle. For the measurement data corresponding to the range,
After correcting with the narrow range correction value δz previously obtained, the least square line is calculated, and the deviation of each measurement data from the least square line is obtained. The obtained deviation is used as the narrow range correction value δx of the X linear encoder. And X correction value storage unit 34
Stores the narrow range correction value δx.

The above is the calculation of the correction value. When the workpiece is measured after the narrow-range correction values δz and δx are set and stored, the Z-measurement data correction unit 35
Is corrected using the narrow-range correction value δz output from the Z-correction-value storage unit 32. Further, the X measurement data correction unit 36 includes a detector 44.
Is corrected using the narrow range correction value δx output from the X correction value storage unit 34. Then, the contour shape calculation unit 37 calculates the contour shape of the workpiece based on the measurement data corrected by the Z measurement data correction unit 35 and the X measurement data correction unit 36.

The flowchart shown in FIG. 1 is a procedure for calculating the narrow range correction value δz and the narrow range correction value δx.
3 is an explanatory diagram of a reference gauge measurement for calculating a narrow range correction value δz, FIG. 4 is an explanatory diagram of a calculation of a narrow range correction value δz, and FIG. 5 is an explanatory diagram of a reference gauge measurement for calculating a narrow range correction value δx. FIG. 6 is an explanatory diagram for calculating the narrow range correction value δx.

First, a surface having high flatness accuracy (high flatness surface G)
The reference gauge G having (a) is set in the measuring unit 40 at a small angle (for example, θa = 2.5 °) at which the output in the X direction can be ignored (step 11), and the high flatness surface Ga is measured (step 11). Step 12). Then, a correction section Ma in which measurement data for the narrow range Za (for example, Za = 10 μm) of the Z linear encoder is obtained from all the obtained measurement data (La in FIG. 3) (step 13), and the correction section A least-squares straight line Ba is calculated for the measurement data in Ma (step 14), a Z-direction deviation from the least-squares straight line Ba is determined for each individual measurement data, and the obtained deviation is calculated as Z
A narrow range correction value δz of the linear encoder is set (step 15). Then, the narrow range correction value δz is stored (step 16). When θa = 2.5 ° and Za = 10 μm, the necessary amount of displacement of the stylus 49 in the X direction (same as the correction section Ma) is about 250 μm.

Next, the reference gauge G is set in the measuring section 40 at a large angle (eg, θb = 45 °) within a range where the stylus 49 can accurately trace the reference gauge G (step 17). The flatness plane Ga is measured (step 18). Then, all the obtained measurement data (Lb in FIG. 5)
, The narrow range Xa of the X linear encoder (for example, Xa
= 10 μm) is set (step 19), and the measurement data in the correction section Mb is corrected with the narrow range correction value δz (step 2).
0), a least-squares straight line Bb is calculated (step 21), an X-direction deviation from the least-squares straight line Bb is obtained for each measurement data, and the obtained deviation is used as a narrow range correction value δx of the X linear encoder. (Step 22). Then, the narrow range correction value δx is stored (step 23).

Although the reference gauge G may be manufactured exclusively, an optical flat or a block gauge may be used. In any case, the length that requires a high-precision flatness plane may be about several mm.

The narrow range detection method of the linear encoder includes a moiré fringe method and an optical interference method, and the present invention can be applied to any case.

[0019]

As described above, according to the present invention, a reference gauge having a high flatness surface is provided in a contour shape measuring instrument for detecting the moving direction of a stylus and the amount of displacement in a direction perpendicular thereto with a linear encoder. A narrow range correction value of the linear encoder is calculated from the measurement data obtained by the measurement, and the measurement data is corrected using the correction value when measuring the workpiece. Therefore, the precise positional relationship between the scale and the read head does not need to be mechanically adjusted, so that the narrow range of the linear encoder can be easily corrected, and the adjustment accuracy may vary between workers, It is possible to provide a contour shape measuring instrument which is once correctly adjusted and is not likely to change over time.

[Brief description of the drawings]

FIG. 1 is a flowchart of an embodiment of a contour shape measurement data correction method according to the present invention.

FIG. 2 is a block diagram of an embodiment of a contour shape measuring apparatus according to the present invention.

FIG. 3 is an explanatory diagram of reference gauge measurement for calculating a correction value of a narrow range in the Z direction in the embodiment of the contour shape measurement data correction method according to the present invention.

FIG. 4 is an explanatory diagram of a Z-direction narrow range correction value calculation according to the embodiment of the contour shape measurement data correction method according to the present invention.

FIG. 5 is an explanatory diagram of measurement of a reference gauge for calculating a correction value in a narrow range in the X direction in the embodiment of the contour shape measurement data correction method according to the present invention.

FIG. 6 is an explanatory diagram for calculating an X-direction narrow range correction value in the embodiment of the contour shape measurement data correction method according to the present invention.

FIG. 7 is an external view of a measuring unit of a general contour shape measuring instrument.

FIG. 8 shows an example of a Lissajous waveform of a linear encoder.

[Explanation of symbols]

 11: Reference gauge setting step 12: Reference gauge measurement step 13: Z correction section setting step 14: Z reference straight line calculation step 15: Z correction value calculation step 16: Z correction value storage step 17: Reference Gauge setting step 18 Reference gauge measuring step 19 X correction section setting step 20 Z data correction step 21 X reference straight line calculation step 22 X correction value calculation step 23 X correction value storage step

Claims (6)

[Claims] An X linear encoder for detecting an amount of displacement of a stylus in a moving direction and a Z linear encoder for detecting an amount of displacement of the stylus in a direction perpendicular to the moving direction; The stylus is relatively moved with respect to the work while the stylus is in contact with the work, and the X linear encoder and the Z linear encoder detect a moving direction of the stylus and a displacement amount in a direction perpendicular to the moving direction. In a contour shape measuring machine for measuring the contour shape of the reference gauge, the high flatness surface of the reference gauge having a high flatness surface is measured at a small angle with respect to the moving direction of the stylus, and the obtained measurement data A least-squares straight line is calculated for the measurement data corresponding to the narrow range of the Z linear encoder, and deviations of individual measurement data from the least-square line are determined. The narrow range correction value of the Z linear encoder is used. The high flatness surface of the reference gauge is measured at a large angle within a range where the stylus can accurately trace the reference gauge. After correcting the measurement data corresponding to the narrow range of the X linear encoder with the narrow range correction value of the Z linear encoder, a least square line is calculated, and the deviation of each measurement data from the least square line is calculated. Wherein the obtained deviation is used as a narrow range correction value of the X linear encoder. 2. The contour shape measurement data correction method according to claim 1, wherein the Z linear encoder and the X linear encoder are photoelectric and have a narrow range output having a sine waveform. 3. The method according to claim 1, wherein the small angle is 2.5 ° and the large angle is 45 °. 4. An X-linear encoder for detecting a displacement amount of a stylus in a moving direction and a Z-linear encoder for detecting a displacement amount of the stylus in a direction perpendicular to the moving direction. A measuring unit that moves the stylus relative to the workpiece while abutting the stylus, and detects a moving direction of the stylus and a displacement amount in a direction perpendicular thereto with the X linear encoder and the Z linear encoder; A reference gauge having a high flatness surface, and the measurement data obtained by measuring the high flatness surface of the reference gauge at a small angle with respect to the moving direction of the stylus by the measurement unit, and For the measurement data corresponding to the narrow range of the linear encoder, a least-square straight line is calculated, a deviation of each measurement data from the least-square line is obtained, and the obtained deviation is referred to as the Z linear encoder. A Z correction value calculating unit that sets a narrow range correction value of the Z linear encoder; a Z correction value storage unit that stores a narrow range correction value of the Z linear encoder; Of the measurement data obtained by measuring at a large angle tilt within a range that can accurately trace the reference gauge,
For the measurement data corresponding to the narrow range of the X linear encoder, after correcting with the narrow range correction value of the Z linear encoder, calculate the least square line and determine the deviation of individual measurement data from the least square line, The obtained deviation is used as a narrow range correction value of the X linear encoder.
A contour shape measuring device comprising: a correction value calculation unit; and an X correction value storage unit that stores a narrow range correction value of the X linear encoder. 5. The contour shape measuring apparatus according to claim 4, wherein the Z linear encoder and the X linear encoder are photoelectric and have a narrow range output having a sinusoidal waveform. 6. The contour shape measuring machine according to claim 4, wherein the small angle is 2.5 ° and the large angle is 45 °.