JP2018128345A - Temperature correction method, temperature correction program, and coordinate measuring machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a temperature correction method, a temperature correction program, and a coordinate measuring machine capable of further reducing a scale error. SOLUTION: A plurality of measurement values Lw of works having different nominal dimensions L with known thermal expansion coefficients are measured, the thermal expansion coefficient of the scale is as, the temperature of the scale is ts, the thermal expansion coefficient of the work is aw, and the thermal expansion coefficient of the work is A graph showing the change in the scale error Es2 for each nominal dimension L, where the temperature is tw, the scale reading Ls is calculated, and the scale error Es obtained from the scale reading Ls is replaced with the scale error Es2 at 20 ° C. The equivalent scale temperature coefficient error dKs is calculated using the slope asc and a specific expression, the scale error Ec2 is calculated using asc as the correction value of the thermal expansion coefficient of the scale, and the change of the scale error Ec2 for each nominal dimension L is calculated. The scale offset error dts0 is calculated by using the slope as0 of the graph and the specific expression. [Selection diagram] Figure 2

Description

  The present invention relates to a temperature correction method, a temperature correction program, and a coordinate measuring machine.

ISO 1 defines a standard reference temperature for work geometry specification and verification, and the standard reference temperature is set to 20 ° C. When there is a deviation between the temperature at the time of measurement and the standard reference temperature, an error occurs in the measured length even if the temperature of the workpiece and the measuring machine is equal. As a coordinate measuring machine that measures the length of such a workpiece, for example, in a three-dimensional measuring machine, temperature correction is performed in order to maintain measurement accuracy (for example, Patent Documents 1 to 3). In order to perform temperature correction, the CTE (Coefficient of Thermal Expansion) and the temperature of the scale arranged along each axis constituting the three-dimensional space in the CMM and the workpiece to be measured are known. There is a need. For example, when measuring a 1000 mm steel workpiece at 23 ° C., the CTE of the workpiece is about (10 ± 1) × 10 ⁻⁶ / ° C., but CTE uncertainty is about ± 1 × 10 ⁻⁶ / ° C. To do. For this reason, the measurement dimension uncertainty due to CTE uncertainty is 3 μm. This uncertainty cannot be corrected as long as it is measured at 23 ° C., and increases as the deviation from 20 ° C. increases.

  Patent Document 1 discloses a temperature correction method in which a temperature is monitored by a temperature sensor mounted on each axis scale and a temperature sensor that measures a workpiece, and a measurement result is converted into a value at 20 ° C. and output. ing. In Patent Documents 2 and 3, temperature correction is performed on the basis of the measured length of a workpiece having a low thermal expansion coefficient and a workpiece that thermally expands, and the reference length and the thermal expansion coefficient of the workpiece stored in advance in the control unit.

Also scale the error E by the conventional method, usually using the work, such as gauge blocks or steps gauge (made of steel), the value L _w and the work length of the measurement of the length of the workpiece as shown in the following formula (100) it represents a ratio of the difference between the calibration value L _c.
E = (L _w −L _c ) / L _c (100)

JP-A-11-190617 Japanese Patent Laid-Open No. 06-229705 Japanese Patent Laid-Open No. 06-229706

  However, in the temperature correction method according to the above-mentioned patent document, since the thermal expansion coefficient of the scale and the temperature of the scale and the workpiece are corrected as being correct, it cannot be said that the measured length is the length at the standard reference temperature. There is a problem that the scale error is large when converted into a height.

  An object of the present invention is to provide a temperature correction method, a temperature correction program, and a coordinate measuring machine that can further reduce a scale error.

Temperature correction method of the coordinate measuring machine according to the present invention, the thermal expansion coefficient measures the plurality of measurement values L _w of known nominal dimension L is different work, the thermal expansion coefficient of the scale a _s, a temperature scale t _s, wherein the thermal expansion coefficient of the workpiece a _w, if the temperature of the workpiece was t _w, and calculating the scale reading L _s using the following equation (1), obtained from reading the scale L _s and replacing the scale error E _s to scale the error E _s2 when the 20 ° C. was equivalent with the slope a _sc of a graph showing a change in the scale error E _s2 for each nominal dimension L, the following equation (2) A step of calculating the scale temperature coefficient error dK _s , a step of calculating the scale error E _c2 from the measured value L _w calculated using the a _sc as a correction value of the thermal expansion coefficient of the scale, Scale error _Ec2 The gradient a _s0 graph showing a change in, characterized in that it comprises the step of calculating a scaled offset error dt _s0 using the following equation (3).
_{L s = L w -L (a} s (t s -20) -a w (t w -20)) ··· (1)
dK _s = (a _s −a _sc ) / a _s (2)
_{dt s0 = a s0 / a s} ··· (3)

Temperature correction program of the coordinate measuring machine according to the present invention, the computer, the thermal expansion coefficient measures the plurality of measurement values L _w of known nominal dimension L is different work, the thermal expansion coefficient of the scale a _s, the temperature scale t _s, the thermal expansion coefficient of a _w of the _workpiece, if the temperature of the workpiece was t _w, and calculating the scale reading L _s using the above equation (1), reading of the scale and replacing the scale error _{E s} obtained from L _s the scale error _{E s2} when the 20 ° C., and the gradient _{a sc} of a graph showing a change in the scale error _{E s2} for each nominal dimension L, the equation (2 ) To calculate the equivalent scale temperature coefficient error dK _s, to calculate the scale error E _c2 from the measured value L _w calculated using the a _sc as the correction value of the thermal expansion coefficient of the scale, Call The gradient a _s0 of a graph showing a change in the scale error E _c2 for each dimension L, thereby forming characterized by and a step of calculating the scale offset error dt _s0 using the above equation (3).

Coordinate measuring machine according to the present invention, the thermal expansion coefficient of the known nominal dimension L measures the plurality of measurement values L _w of different work, the thermal expansion coefficient of the scale a _s, a temperature scale t _s, the work the thermal expansion coefficient of a _w, if the temperature of the workpiece was t _w, and calculates a scale reading L _s by using equation (1), the scale error E _s obtained from readings L _s of the scale The scale error E _s2 at 20 ° C. is substituted, and the equivalent scale temperature coefficient error dK _s is calculated using the slope a _{sc of the} graph representing the change in the scale error E _s2 for each nominal dimension L and the above equation (2). Then, the scale error E _c2 is calculated from the measurement value L _w calculated using the a _sc as the correction value of the thermal expansion coefficient of the scale, and the slope a of the graph representing the change in the scale error E _c2 for each nominal dimension L scale using the _s0, the above equation (3) And calculates the offset error _{dt s0.}

According to the present invention, based on the scale error E _s reading of a plurality of scales nominal dimension L are different, by obtaining the thermal expansion coefficient of more accurate scale, the equivalent scale temperature coefficient of the temperature sensor error dK _s and scale offset Since the error dt _s0 can be separated, each temperature sensor can be corrected more accurately.

It is a perspective view which shows typically the structure of the measuring machine main body which concerns on this embodiment. It is a block diagram which shows the structure of the control apparatus which concerns on this embodiment. It is a graph with which it uses for description of a magnification error and an offset error. It is a graph which shows the scale error computed based on the measured value which measured the length of the step gauge. It is a graph which shows the scale error of scale reading. It is a graph which shows the result of having calculated the scale error at the time of 20 ° C based on the result of Drawing 5. The thermal expansion coefficient of the scale is a graph showing the scale error calculated by substituting a _sc. Further is a graph showing the scale error calculated by substituting the temperature t _s of the scale corrected temperature t _s-corr. It is a graph which shows the correlation of the result measured with the temperature sensor attached to the coordinate measuring machine, and the calibrated temperature sensor. It is a graph which shows the result of having performed temperature correction of a scale and a work thermometer.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

1. Embodiment (1) Overall Configuration A three-dimensional measuring machine as a coordinate measuring machine includes a measuring machine main body 10 shown in FIG. 1 and a control device to be described later. The measuring machine body 10 includes a base 12, a Y-axis rail 14, a Y-axis moving body 16, an X-axis moving body 18, and a Z-axis moving body 19. The Y-axis rail 14 is provided along the Y-axis on the base 12. The Y-axis moving body 16 has a pair of leg portions 15 and a beam portion 17 spanned between the upper ends of the leg portions 15, and the leg portion 15 travels along the Y-axis rail 14. The stage 12 can be moved in the Y-axis direction. The X-axis moving body 18 is supported by the beam portion 17 of the Y-axis moving body 16 so as to be movable in the X-axis direction orthogonal to the Y-axis. The Z-axis moving body 19 is supported by the X-axis moving body 18 so as to be movable in the Z-axis direction orthogonal to the X-axis and the Y-axis. The Z-axis moving body 19 holds the probe 20 at the tip.

  The measuring machine main body 10 includes a Y-axis scale 22 that measures the amount of movement of the probe 20 in the Y-axis direction, an X-axis scale 24 that measures the amount of movement of the probe 20 in the X-axis direction, and the movement of the probe 20 in the Z-axis direction. And a Z-axis scale 26 for measuring the quantity. The Y axis scale 22 is provided on the Y axis rail 14, the X axis scale 24 is provided on the beam portion 17, and the Z axis scale 26 is provided on the Z axis moving body 19. Actually, the measuring instrument main body 10 includes a detector (not shown) that reads the values of the X-axis scale 24, the Y-axis scale 22, and the Z-axis scale 26, respectively. The detector outputs a coordinate signal indicating the read result to the control device 30.

  The measuring machine main body 10 is provided with an X-axis scale 24, a Y-axis scale 22, a Z-axis scale 26, and a temperature sensor 28 as a thermometer for measuring the temperature of the workpiece W. The temperature sensor 28x is provided on the X-axis scale 24, the temperature sensor 28y is provided on the Y-axis scale 22, the temperature sensor 28z is provided on the Z-axis scale 26, and the temperature sensor 28w is provided on the workpiece W. Each temperature sensor 28 outputs the detected temperature signal to the control device 30.

  FIG. 2 is a block diagram showing the configuration of the control device 30. The control device 30 includes a temperature calculation unit 32, a temperature correction unit 34, a displacement calculation unit 36, and a basic temperature correction unit 35. The control device 30 reads various programs such as a basic program and a temperature correction processing program stored in advance, and controls the whole according to these various programs.

  Each temperature sensor 28 and the measuring machine main body 10 are electrically connected to the control device 30. The controller 30 receives the temperature signal output from each temperature sensor 28 and the coordinate signal output from the measuring machine main body 10. As shown in the figure, the coordinate measuring machine 1 includes a measuring machine main body 10, a control device 30, and each temperature sensor 28. The temperature correction device 38 includes each temperature sensor 28, a temperature calculation unit 32, a temperature correction unit 34, and a basic temperature correction unit 35.

Temperature calculating unit 32 converts the input temperature signal to the temperature data to calculate the temperature t _w of the temperature t _s and the workpiece W of the scale. The displacement calculation unit 36 calculates the displacement amount, that is, the length (hereinafter also referred to as “scale reading”) L _s of the probe 20 based on the input coordinate signal. For example, when measuring the length of the workpiece W in the X-axis direction, that is, the distance between two points, when the contact portion at the tip of the probe 20 comes into contact with the workpiece W, a coordinate signal related to the coordinates of the contact portion is measured. The main body 10 outputs. The control device 30 calculates the length in the X-axis direction of the workpiece W, which is the displacement amount of the probe 20, based on the coordinate signals of the two points obtained in this way.

Temperature t _s of the scale can be used the measured temperature by the temperature sensor 28 installed in the measuring unit.

The basic temperature correction unit 35 performs a basic temperature correction process on the scale reading L _s based on the temperature data of each part obtained by the temperature calculation unit 32. Base temperature correction process is calculated for scale reading L _s, the thermal expansion coefficient of a _s, a measured value L _w of the length of the workpiece W subjected to basic temperature correction based on a _w. Measurements L _w of the length of the workpiece W, the thermal expansion coefficient of the scale a _s, a thermal expansion coefficient of the workpiece W a _w, a temperature scale t _s, the temperature of the workpiece W and t _w, the following formula (10).
_{L w = L s (1 +} a s (t s -20) -a w (t w -20)) ··· (10)

The temperature correction unit 34 corrects the temperature sensor 28 based on the temperature data at each location obtained by the temperature calculation unit 32. First, the temperature correction unit 34 is a temperature sensor provided on each scale from scale errors E _c at a plurality of lengths of a step gauge having a small thermal expansion coefficient (hereinafter referred to as “step gauge having a low thermal expansion coefficient”) as the workpiece W. 28x, 28y, and 28z are corrected, and then the temperature sensor 28w of the workpiece W is corrected using a separately prepared temperature sensor.

First, a case where the temperature sensors 28x, 28y, and 28z are corrected will be described. When the calibration value of the length of the workpiece W and L _c, the scale error E can be expressed by the following equation (11).
_{E = L w -L c = L} s (1 + a s (t s -20) -a w (t w -20)) - L c ··· (11)

In this embodiment, the error included in the measured value L _w is provided as an error of the X-axis scale 24, Y-axis scale 22, and Z-axis scale 26, the error of each scale intrinsic thermal expansion coefficient a _s, in each scale temperatures sensors 28x, 28y, the error of the temperature _{t s} measured by 28z, believed to include the magnification error of each scale reading _{L s.} Further error in the measured temperature t _s of the scale, the magnification error, and a offset error.

The error of the workpiece W, an error in the thermal expansion coefficient a _w of the workpiece W, an error of the temperature t _w, which is measured by the temperature sensor 28w provided on the workpiece W, is believed to include error calibration values L _c. Further, errors in the measured temperature t _w of the workpiece W includes a magnification error, and a offset error.

  Here, the magnification error and the offset error will be described with reference to FIG. FIG. 3 is a graph showing errors included in the temperature data measured by the temperature sensor. The horizontal axis shows the deviation from 20 ° C. when measured by the temperature sensor provided in the coordinate measuring machine 1, and the vertical axis Deviation from 20 ° C. when measured with a temperature sensor calibrated in the same environment with the axis. In the case of an ideal temperature sensor having no error, the result measured by the temperature sensor provided in the coordinate measuring machine 1 coincides with the result measured by the calibrated temperature sensor. It becomes a straight line with an inclination of 1. On the other hand, when there is an error in the temperature sensor provided in the coordinate measuring machine 1, the measurement result is a straight line with a different inclination or a straight line that does not pass through the origin. Among these, an error appearing in the slope of the straight line is called a magnification error. An error that appears in the deviation of the origin is called an offset error. The actual error is a combination of the magnification error and the offset error.

X-axis scale 24, Y-axis scale 22, and out of the error in the Z-axis scale 26, error and magnification error in temperature t _s of the scale of the thermal expansion coefficient a _s of each scale when the temperature changes, in the same way It is indistinguishable because it occurs. Offset error of the magnification error and the temperature t _s of the scale of each scale reading L _s indistinguishable as well. Of error for the workpiece W, the offset error of the temperature t _w of the error and the workpiece W magnification errors, and calibration values L _c of the temperature t _w of the error and the workpiece W in the thermal expansion coefficient a _w of the workpiece W also indistinguishable. In addition, when the calibration value _Lc and the value of the thermal expansion coefficient _aw of the workpiece W can be regarded as known with high accuracy, it can be assumed that there is no error. Therefore, there are four possible temperature sensor errors. That is, the magnification error and the scale of the temperature t _s of the scale consists of error in the thermal expansion coefficient a _s error dK s _{(hereinafter,} referred to as "equivalent scale Temperature factor error"), the temperature t _s of the scale consists of offset error and the magnification error of each scale error dt s0 _{(hereinafter,} referred to as "scale offset error"), is constructed with an error of the thermal expansion coefficients a _w magnification error and the workpiece W in the temperature t _w of the workpiece W that error dk w _{(hereinafter,} referred to as "equivalent work temperature factor error"), and the error correction value L _c of the offset error and the workpiece W in the temperature t _w of the workpiece W error dt w0 _{(hereinafter,} "work offset Called "error").

When the temperature _{t w} of the temperature _{t s} and the workpiece W of each scale to the correct temperature of each scale and the workpiece W, the measured temperature _t ^w of the measured temperature _t ^{s *} and the workpiece W of each scale ^* is represented by the following formula (12), (13).
t _s ^* = (1 + dK _s ) t _s + dt _s0 (12)
t _w ^* = (1 + dk _w ) t _w + dt _w0 (13)

Thus, the scale error E can be expressed by the following equation (14), where L _{w is} the measured value of the workpiece W and P ₀ is the probing error.
_{E = L w -L c = L} s (1 + a s (t s * -20) -a w (t w * -20)) - L c
_{≒ a s dt s0 + a s} dK s (t s -20) L w -a w dt w0 -a w dk w (t w -20) L w + P 0 ··· (14)

When using the step gage of the low thermal expansion coefficient as the work W, since the thermal expansion coefficient a _w of the workpiece W is 0, the scale error E _c can be represented by the following formula (15).
_{E c = L w -L c =} L s (1 + a s (t s * -20)) - L c
_{= A s dt s0 + a s} dK s (t s -20) L w ··· (15)

The scale reading L _s can be expressed by the following equation (16) from the equation (10).
_{L s = L w -L (a} s (t s -20) -a w (t w -20)) ··· (16)

When using the step gage of the low thermal expansion coefficient as the work W, since the thermal expansion coefficient a _w of the workpiece W is 0, the scale error E _s reading L _s of scale formula (17), reading of the scale is below It can represent with Formula (18). Incidentally, a _s can be used notarized value of the thermal expansion coefficients of the scale.
_{L s = L w -La s (} t s -20) ··· (17)
_{E s = L s -L c =} L w -La s (t s -20) -L c (18)

Replacing the scale error E _s to scale the error E _s2 when the 20 ° C., the gradient a _sc when the graph representing the change in the scale error E _s2 for each nominal dimension L is, in a more correct thermal expansion coefficient of the scale is there. Scale error _{E s2,} by dividing the scale error _{E s} in deviation from 20 ° C., can be calculated.

The equivalent scale temperature coefficient error dK _s can be calculated from the following equation (19) based on the more accurate thermal expansion coefficient a _sc of the scale.
dK _s = (a _s −a _sc ) / a _s (19)

A value obtained by correcting the thermal expansion coefficient of the scale using the thermal expansion coefficient a _{s of} the scale and the more accurate thermal expansion coefficient a _sc of the scale can be calculated using the following equation (20).
_{L asc = L w + L (} a s -a sc) (t s -20) ··· (20)
_Assuming that the scale error obtained from L _asc is E _c2 , the scale offset error dt _s0 is calculated from the slope a _s0 (offset error of the scale thermometer) of the graph representing the change in the scale error E _c2 for each nominal dimension L. It can be calculated using equation (21).
_{dt s0 = a s0 / a s} ··· (21)

In this way, the temperature correction unit 34 from the scale error E _s in a plurality of nominal dimension L of different steps gauge low thermal expansion coefficient, to obtain an equivalent scale temperature coefficient error dK _s and scale offset error dt _s0. The resulting equivalent scale temperature coefficient errors dK _s, calculates the temperature _{t s} from the scale offset error _{dt s0,} and the equation (12). The temperature calculated in this way is referred to as a corrected temperature _ts-corr . By calculating the corrected temperature ts _-corr for each scale, the temperature sensors 28x, 28y, and 28z of each scale can be corrected. Specifically, the temperature sensor 28x, 28y, 28z can be corrected by changing the setting to the corrected temperature ts _-corr .

Further, the control unit 30 changes the thermal expansion coefficient a _s of scale in the formula (10), more correct thermal expansion coefficient a _sc scales determined for each scale.

Incidentally, the error of thermal expansion coefficients a _w of the workpiece W contained in the equivalent work temperature coefficient errors dk _w Since vary workpiece W of interest to be able separated magnification error of the workpiece W, the equivalent of the temperature sensor 28w work Correction by the temperature coefficient error dk _w is not possible. Therefore, in this embodiment, the equivalent work temperature coefficient error dk _w is ignored.

Uncertainty of the calibration value L _c of the workpiece W included in the workpiece offset error dt _w0 is 0.3 μm for a 500 mm step gauge (Takamitsu Osawa et al., Synthesiology Vol 2 No. 2 pp.101-112 Jun. 2009) Therefore, it is considered that the influence on the work offset error dt _w0 is small. Thus in the present embodiment, the error of the calibration values L _c of the work W is to be ignored. As described above, the temperature correction unit 34 calculates the workpiece offset error dt _w0 , that is, the corrected temperature tw _−corr by comparing the temperature sensor 28 _w that measures the temperature tw of the workpiece W with the calibrated temperature sensor. The temperature sensor 28w is corrected.

Controller 30, the correction temperature sensor 28 the temperature t _s of the scale as measured _by, based on the temperature t _w of the workpiece W, the measured value of the workpiece W subjected to temperature correction for scale reading L _{s Lw} is calculated.

(2) Operation and Effect Using the coordinate measuring machine 1 configured as described above, the temperature sensors 28x, 28y, and 28z are corrected, the temperature sensor 28w is corrected using the calibrated temperature sensor, and these corrections are made. A procedure for correcting the temperature of the scale reading L _s at the temperature measured using each temperature sensor 28 will be described.

First, two or more lengths having different nominal dimensions L of the step gauge having a low thermal expansion coefficient as the workpiece W are measured under a plurality of temperature conditions. Specifically, the step gauge is installed on the base 12 in parallel with the X axis, and the coordinates of two points in the X axis direction of the step gauge are detected under two conditions with different temperatures, for example. The detection result is output from the measuring machine body 10 to the control device 30 as a coordinate signal. Controller 30, based on the coordinate signal of the resulting two points, by the base temperature correction, calculates the measured value L _w in the X-axis direction of the step gage.

Next, the control device 30 calculates a scale reading L _s for each obtained measurement value L _{w according} to the above equation (17). Furthermore, the control device 30, by the above formula (18), calculates the scale error _{E s} of scale reading _{L s.} Since the work W used is a step gauge having a low thermal expansion coefficient, the scale error E _c can be said to be an error caused by the X-axis scale 24 when it is considered that the workpiece W does not thermally expand regardless of the temperature.

Further, the control unit 30 replaces the calculated scale error E _s to scale the error E _s2 when the 20 ° C., to a graph showing changes in the scale error E _s2 for each nominal dimension L. In the graph, a plurality of straight lines equal to the number of temperature conditions are obtained. Based on the plurality of straight lines, for example, an approximate line is obtained by the least square method, and a more accurate thermal expansion coefficient _asc of the scale is obtained from the inclination of the graph. Controller 30 changes the thermal expansion coefficient a _s of scale in the formula (10), more correct thermal expansion coefficient a _sc scales determined for each scale.

Subsequently, the control device 30 calculates the equivalent scale temperature coefficient error dK _s using the above equation (19).

Further, the control unit 30 obtains the scale error _{E c2} to change the formula of thermal expansion coefficient _{a s} of scale in (15) in _{a sc,} gradient a graph showing a change in the scale error _{E c2} for each nominal dimension L _{From s0} , the scale offset error dt _s0 is calculated using the above equation (20).

The temperature sensor 28x is corrected by calculating the corrected temperature t _s-corr from the obtained equivalent scale temperature coefficient error dK _s , scale offset error dt _s0 , and the above equation (12). Similarly, the temperature sensors 28y and 28z are corrected for the Y-axis scale 22 and the Z-axis scale 26.

Next, the control device 30 receives temperature signals from a calibrated temperature sensor different from the temperature sensor 28 attached to the coordinate measuring machine 1 and a temperature sensor 28 w that measures the temperature of the workpiece W. In this way, the control device 30 compares the temperature data of the calibrated temperature sensor with the temperature data of the temperature sensor 28w of the workpiece W, and calculates the workpiece offset error dt _w0 , that is, the corrected temperature tw _-corr . Thus, the control unit 30, based on the work offset error _{dt w0,} it is possible to correct the temperature sensor 28w.

Coordinate measuring machine 1, used as the corrected temperature sensors 28x, 28y, 28z, the 28w, a _{t s} a corrected temperature _{t s-corr,} and _{t w} is the corrected temperature _{t w-corr} Using the above equation (10), temperature correction is performed on the reading L _{s of} each scale, and the thermal expansion coefficient a _s of the scale is replaced with a more accurate thermal expansion coefficient a _s0 , thereby making measurement without errors. it is possible to calculate the value L _w.

The temperature correction device 38 according to the present embodiment separates the equivalent scale temperature coefficient error dK _s and the scale offset error dt _s0 of the temperature sensor 28 by obtaining a more accurate thermal expansion coefficient of the scale from the scale reading L _s. Therefore, each temperature sensor 28 can be corrected more accurately. Coordinate measuring machine 1, by performing the temperature correction at temperature measured using the temperature sensor 28 is corrected as described above, it is possible to further reduce the scale error E _c.

The equivalent scale temperature coefficient error dK _s and the scale offset error dt _s0 are caused by deviations from the standard reference temperature, and include various errors (magnification error and offset error shown in FIG. 3). Therefore, the temperature correction device 38 can remove the error included in the scale reading L _s by temperature correction by calculating the equivalent scale temperature coefficient error dK _s and the scale offset error dt _s0 .

2. Example In fact, using a step gauge low coefficient of thermal expansion as the work W, was calculated with the more correct thermal expansion coefficient a _s scale, equivalent scale temperature coefficient errors dK _s, the scale offset error dt _s0. The step gauge has nominal dimensions of 20 mm, 120 mm, 220 mm, 320 mm, 420 mm, 520 mm, and 620 mm. The measurement temperature by changing the measurement date are different two conditions, to measure the length of the X-axis direction was calculated scale error E _c. Scale temperature t _s was the temperature measured by temperature sensor 28x. The result is shown in FIG. In FIG. 4, the horizontal axis is the nominal size (mm) of the step gauge, and the vertical axis is the scale error E _c (μm). Scale error _{E c} is the calibration value of the step gauge _{L c,} when the measured value is _{L w,} can be expressed by E _{c =} L w -L _c.

Figure 5 is a graph showing the relationship between the nominal dimension of the scale error E _s and the workpiece W. Scale error _{E s} is the calibration value _{L c} of the step gauge, the scale reading When _{L s,} can be expressed by E _{s =} L _s -L _c.

It was then replaced the scale error _{E s} to scale the error _{E s2} when the 20 ° C.. Scale error E _s2, by dividing the scale error E _s in deviation from 20 ° C., was calculated. The result is shown in FIG. The graph shown in this figure shows one straight line obtained by the least square method from two graphs corresponding to two conditions of measured temperature. From the inclination of this figure, it was found that the more accurate thermal expansion coefficient of the X-axis scale in the coordinate measuring machine used in this example was 7.86 × 10 ⁻⁶ (/ ° C.). The catalog value of the thermal expansion coefficient of the scale of the coordinate measuring machine is 8.00 × 10 ⁻⁶ (/ ° C.). The equivalent scale temperature coefficient error dK _s calculated from the equation (19) was 0.018.

Subsequently, using the value corrected by 7.86 × 10 ⁻⁶ (/ ° C.) as the thermal expansion coefficient of the scale, the measured value was calculated from the above equation (10) to obtain the scale error E _c2 . The result is shown in FIG. The slope a _{s0 in} this figure was 0.0011, and the scale offset error dt _s0 calculated using the above equation (21) was 0.131.

FIG. 8 shows the corrected temperature t _s-corr from equation (12) using the more accurate thermal expansion coefficient of the scale obtained as described above, the equivalent scale temperature coefficient error dK _s, and the scale offset error dt _s0. It was. Further, FIG. 8 shows the result of recalculating the scale error E _c using the corrected temperature t _s-corr . From the figure, by correcting the temperature sensor 28x of the X-axis scale 24, it was confirmed that the scale error E _c is remarkably reduced. Note the scale error _{E c} shown in the figure, further subtracting the probing error (-0.6065μm).

Then, install a temperature sensor 28w for measuring the temperature t _w of the block gauge low thermal expansion coefficient is placed on the base 12, a calibrated temperature sensor next were obtained temperature data. FIG. 9 shows a correlation diagram between the temperature sensor 28w and the temperature data measured by the calibrated temperature sensor. FIG. 9 shows the deviation from 20 ° C. of the temperature sensor 28 w on the horizontal axis, and the deviation from 20 ° C. of the calibrated temperature sensor on the vertical axis. From this figure, it was confirmed that the offset error dt _w0 was 0.06 ° C.

Next, the effectiveness of the temperature sensor 28x corrected as described above was confirmed using a steel block gauge as the workpiece W. A block gauge having a nominal size of 500 mm was used, the length in the X-axis direction was measured under five conditions with different measurement temperatures by changing the measurement date, and the scale error was calculated. The result is shown in FIG. In FIG. 10, the horizontal axis indicates a deviation (° C.) from 20 ° C., and the vertical axis indicates a scale error (μm). Scale error _{E MX} is the calibration value _{L c,} the measured value as _{L w,} determined at E MX ₌ L w -L _c. Scale error _{E MX-s-corr} is a more correct thermal expansion coefficient, a result of the temperature correction using the corrected temperature sensor 28x of the X-axis scale 24, the correction to _{t s} of the above formula (10) the measurements were obtained using a rear temperature was calculated as L _w. Further scale error _{E MX-corr} is a more correct thermal expansion coefficient, a result of the temperature correction using the temperature sensor 28w of the corrected workpiece W, _{t s} of the above formula (10), and _{t w} the corrected temperature was calculated from the measured value L _w obtained using a _s a thermal expansion coefficient.

In the figure, ● represents a scale error E _MX , ▲ represents a scale error E _MX-s-corr , and ○ represents a scale error E _MX-corr . From this figure, it can be seen that the scale error changes according to the deviation from 20 ° C. The maximum scale error was -2.7 (μm) and the standard deviation was 0.59 (μm) before correcting the temperature sensors 28x and 28w of the X-axis scale 24 and the workpiece W. It was confirmed that the maximum graduation error was reduced to -0.7 (μm) and the standard deviation was reduced to 0.24 (μm).

3. The present invention is not limited to the above-described embodiment, and can be appropriately changed within the scope of the gist of the present invention.

In the above embodiment, the equivalent scale temperature coefficient error dK _s and the scale offset error dt _s0 are calculated by measuring a plurality of lengths using a block gauge having a low thermal expansion coefficient as the workpiece W. Is not limited to this. For example, the equivalent scale temperature coefficient error dK _s and the scale offset error dt _s0 may be calculated by measuring a plurality of lengths using a block gauge whose thermal expansion coefficient value is known with high accuracy.

DESCRIPTION OF SYMBOLS 1 CMM 30 Control apparatus 32 Temperature calculation part 34 Temperature correction part 36 Displacement calculation part 38 Temperature correction apparatus W Workpiece

Claims (6)

Thermal expansion coefficient measures the plurality of measurement values L _w of the workpiece known nominal dimensions L are different, the thermal expansion coefficient of the scale a _s, a temperature scale t _s, the thermal expansion coefficient of the work a _w, a work If the temperature was t _w, and calculating the scale reading L _s using the following equation (1),
Replacing the scale error E _s obtained from the scale reading L _s with a scale error E _s2 at 20 ° C .;
A step of calculating an equivalent scale temperature coefficient error dK _s using a slope a _{sc of} a graph representing a change in the scale error E _s2 for each nominal dimension L and the following equation (2):
Calculating a scale error E _c2 from the measured value L _w calculated using the a _sc as a correction value of the thermal expansion coefficient of the scale;
The temperature of the coordinate measuring machine comprising: a slope a _{s0 of} a graph representing a change in the scale error E _c2 for each nominal dimension L; and a step of calculating a scale offset error dt _s0 using the following equation (3): Correction method.
_{L s = L w -L (a} s (t s -20) -a w (t w -20)) ··· (1)
dK _s = (a _s −a _sc ) / a _s (2)
_{dt s0 = a s0 / a s} ··· (3) Further corrected temperature t _s-corr of the temperature t _s of the scale was calculated using the following equation (4), characterized in that the thermal expansion coefficient a _s of scale in the gradient a _sc, comprising the step of changing each The temperature correction method for a coordinate measuring machine according to claim 1.
t _s ^* = (1 + dK _s ) t _s + dt _s0 (4) Against the computer,
Thermal expansion coefficient measures the plurality of measurement values L _w of the workpiece known nominal dimensions L are different, the thermal expansion coefficient of the scale a _s, a temperature scale t _s, the thermal expansion coefficient of the work a _w, a work If the temperature was t _w, and calculating the scale reading L _s using the following equation (1),
Replacing the scale error E _s obtained from the scale reading L _s with a scale error E _s2 at 20 ° C .;
A step of calculating an equivalent scale temperature coefficient error dK _s using a slope a _{sc of} a graph representing a change in the scale error E _s2 for each nominal dimension L and the following equation (2):
Calculating a scale error E _c2 from the measured value L _w calculated using the a _sc as a correction value of the thermal expansion coefficient of the scale;
A coordinate measuring machine characterized by executing a slope a _{s0 of} a graph representing a change in a scale error E _c2 for each nominal dimension L and a step of calculating a scale offset error dt _s0 using the following equation (3): Temperature correction program.
_{L s = L w -L (a} s (t s -20) -a w (t w -20)) ··· (1)
dK _s = (a _s −a _sc ) / a _s (2)
_{dt s0 = a s0 / a s} ··· (3) Further corrected temperature t _s-corr of the temperature t _s of the scale was calculated using the following equation (4), the thermal expansion coefficient a _s of scale in the gradient a _sc, that to perform the step of changing each The temperature correction program for a coordinate measuring machine according to claim 3.
t _s ^* = (1 + dK _s ) t _s + dt _s0 (4) Thermal expansion coefficient measures the plurality of measurement values L _w of the workpiece known nominal dimensions L are different, the thermal expansion coefficient of the scale a _s, a temperature scale t _s, the thermal expansion coefficient of the work a _w, a work When the temperature of tw is _tw , the scale reading L _s is calculated using the following formula (1),
Replacing the scale error E _s obtained from readings L _s of the scale graduation error E _s2 when the 20 ° C.,
The equivalent scale temperature coefficient error dK _s is calculated using the slope a _{sc of the} graph representing the change in the scale error E _s2 for each nominal dimension L and the following equation (2):
A scale error E _c2 is calculated from the measured value L _w calculated using the a _sc as a correction value of the thermal expansion coefficient of the scale,
A coordinate measuring machine with a temperature correction function, wherein a scale offset error dt _s0 is calculated using a slope a _{s0 of} a graph representing a change in the scale error E _c2 for each nominal dimension L and the following equation (3).
_{L s = L w -L (a} s (t s -20) -a w (t w -20)) ··· (1)
dK _s = (a _s −a _sc ) / a _s (2)
_{dt s0 = a s0 / a s} ··· (3) Further corrected temperature t _s-corr of the temperature t _s of the scale was calculated using the following equation (4), the thermal expansion coefficient a _s scale gradient a _sc, and changing each billing Item 6. A coordinate measuring machine with a temperature correction function according to Item 5.
t _s ^* = (1 + dK _s ) t _s + dt _s0 (4)

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