Touch probe correction value inspection system and correction value inspection method

Abstract

To provide a touch probe correction value inspection system and a correction value inspection method that can simply inspect a correction value of a touch probe in order to minimize a performance frequency of a work concerning calibration for re-setting the correction value of the touch probe and constantly ensure positional measurement accuracy using the touch probe.SOLUTION: A correction value error estimation amount, which is an error of a correction value of a touch probe, is calculated on the basis of an initial value of an offset displacement magnitude and a value of the offset displacement magnitude during inspection. Therefore, according the calculated correction value error estimation amount, the touch probe can be calibrated only when necessary, a performance frequency of a calibration work for the touch probe can be minimized while maintaining accuracy.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a correction value inspection system and a correction value inspection method for inspecting the correction value of a touch probe used for measuring the origin position of a workpiece, etc. [Background technology]

[0002] Conventionally, a touch probe is attached to a spindle and indexed through multiple rotation angles while contacting a workpiece or a reference sphere to measure the workpiece's origin position, measure the workpiece's dimensions after machining, and calibrate machine accuracy. Such touch probes are equipped with a compensation value to correct for deviations in the distance from the spindle's reference point to the measurement point, such as the radius of the stylus ball or the length of the touch probe. However, if the touch probe changes over time, such as thermal deformation due to temperature changes in the operating environment, a deviation will occur between the preset compensation value and the actual error, resulting in a measurement error.

[0003] One method for preventing measurement errors due to the above-mentioned deterioration of the touch probe over time is to periodically perform calibration to reset the correction value. For example, Patent Document 1 discloses a method for calibrating the correction value in the radial direction of the tip of the touch probe by measuring a reference sphere that serves as a calibration reference using the touch probe.

[0004] Another method for preventing measurement errors due to changes in the touch probe over time is to cancel the effects of measurement errors by devising a measurement method. For example, Patent Document 2 discloses a method for canceling the effects of measurement errors in the radial direction of the tip of the touch probe by changing the indexing angle of the spindle to which the touch probe is attached depending on the measurement target. Specifically, when measuring the coordinates of a specified measurement point, the spindle is reversed and measurements are taken twice, and the measurement results before and after the reversal are averaged to cancel the effects of measurement errors. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-83729 [Patent Document 2] Japanese Patent Publication No. 2020-196051 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the method described in Patent Document 1 has the problem that the calibration work of the touch probe tends to be performed more than necessary, making the calibration work cumbersome. Furthermore, if the calibration standard is permanently installed inside the machine tool, problems arise such as a reduced space for installing the workpiece and a deterioration in calibration accuracy due to the influence of cutting chips and cutting fluid, making it difficult to permanently install the calibration standard inside the machine. Therefore, one possible solution is to make the calibration standard detachable and install the calibration standard each time calibration work is performed. However, if the calibration standard must be attached and detached every time calibration work is performed, this can increase the burden on the operator depending on the frequency of calibration work. On the other hand, the method described in Patent Document 2 can reduce the frequency of touch probe calibration work, but it requires that the main axis be reversed and measurements be taken twice each time to measure the coordinates of a specified measurement point, which results in a problem that coordinate measurement takes time and the work required to calibrate the machine precision becomes longer.

[0007] Therefore, the present invention has been made in consideration of the above problems, and aims to provide a touch probe correction value inspection system and correction value inspection method that can easily inspect the touch probe correction value, minimizing the frequency of calibration work for resetting the touch probe correction value and always ensuring the accuracy of position measurement by the touch probe. [Means for solving the problem]

[0008] In order to achieve the above object, the invention of claim 1 of the present invention provides a compensation value inspection system for inspecting an error in a compensation value of a touch probe attached to a spindle of a machine tool having three or more translation axes and a rotatable spindle on which a tool is attached, the system being configured to measure the workpiece with the touch probe at a plurality of measurement angles, where the angle between the indexing direction of the spindle to which the touch probe is attached and a contact direction in which the spindle is moved in a plane perpendicular to the axis of the spindle to bring the touch probe into contact with a predetermined workpiece, the system being configured to measure the workpiece with the touch probe at a plurality of measurement angles, the predetermined measurement angle being a first reference measurement angle, and the system being configured to measure an initial measurement result before reversal obtained by measuring an initial workpiece at the first reference measurement angle and a measurement result at a position 180° different from the first reference measurement angle. and an initial offset value estimation means for calculating an initial value of an offset displacement amount, which is a deviation in the position of the center of the stylus ball of the touch probe from the center of the spindle, based on an initial measurement result after inversion in which the initial measured object is measured at the measurement angle changed by 180° from the first reference measurement angle; an inspection offset value estimation means for calculating a value at the time of inspection of the offset displacement amount, based on a pre-inversion inspection measurement result in which the test object is measured at the first reference measurement angle and a post-inversion inspection measurement result in which the test object is measured at the measurement angle changed by 180° from the first reference measurement angle; and a correction value error estimation means for estimating an error in a correction value of the touch probe, based on the initial value of the offset displacement amount and the value at the time of inspection of the offset displacement amount.

[0009] The invention described in claim 2 is the invention described in claim 1, wherein the initial offset value estimation means obtains the initial measurement result after reversal by changing the indexing direction of the spindle by 180° while keeping the contact direction the same as when the initial measurement result before reversal was obtained. The invention described in claim 3 is the invention described in claim 1, wherein the initial measured object is a ring-shaped, spherical, or cylindrical calibration standard, and the initial offset value estimation means obtains the initial measurement result after reversal by changing the contact direction by 180° while keeping the indexing direction of the spindle the same as when the initial measurement result before reversal was obtained. The invention described in claim 4 is characterized in that, in the invention described in any one of claims 1 to 3, a measurement angle perpendicular to the first reference measurement angle is set as a second reference measurement angle, the initial offset value estimation means calculates an initial value of the offset displacement amount based on measurement results at the second reference measurement angle and the measurement angle that is 180° different from the second reference measurement angle, and the inspection-time offset value estimation means calculates an inspection-time value of the offset displacement amount based on measurement results at the second reference measurement angle and the measurement angle that is 180° different from the second reference measurement angle.

[0010] Furthermore, in order to achieve the above object, the invention of claim 5 of the present invention provides a correction value inspection method for inspecting an error in the correction value of a touch probe in a machine tool having three or more translation axes and a rotatable main spindle to which a tool is attached, the method being capable of measuring the workpiece with the touch probe at a plurality of measurement angles, where the measurement angle is an angle between an indexing direction of the main spindle to which a touch probe is attached and a contact direction in which the main spindle is moved in a plane perpendicular to the axis of the main spindle to bring the touch probe into contact with a predetermined workpiece, the method comprising: defining a predetermined measurement angle as a first reference measurement angle; and comparing a pre-reversal initial measurement result obtained by measuring an initial workpiece at the first reference measurement angle with a correction value inspection method that inspects an error in the correction value of the touch probe in a machine tool having a rotatable main spindle to which a tool is attached, the method being capable of measuring the workpiece with the touch probe at a plurality of measurement angles, the method comprising: a first step of calculating an initial value of an offset displacement amount, which is a deviation in position of the center of the stylus ball of the touch probe from the center of the spindle, based on an initial measurement result after inversion in which the initial object to be measured is measured at the measurement angle changed by 180° from the first reference measurement angle; a second step of calculating a value at the time of inspection of the offset displacement amount, based on an inspection measurement result before inversion in which the object to be measured is measured at the first reference measurement angle and a post-inversion inspection measurement result in which the object to be measured is measured at the measurement angle changed by 180° from the first reference measurement angle; and a third step of estimating an error in the correction value of the touch probe, based on the initial value of the offset displacement amount and the value at the time of inspection of the offset displacement amount. [Effects of the Invention]

[0011] According to the present invention, a predetermined measurement angle is defined as a first reference measurement angle, and an initial value of an offset displacement, which is the deviation of the position of the center of the stylus ball of the touch probe from the center of the spindle, is calculated based on a pre-inversion initial measurement result obtained by measuring an initial object to be measured at the first reference measurement angle and a post-inversion initial measurement result obtained by measuring the initial object to be measured at a measurement angle 180° different from the first reference measurement angle. Furthermore, a test value of the offset displacement is calculated based on a pre-inversion inspection measurement result obtained by measuring an object to be tested at the first reference measurement angle and a post-inversion inspection measurement result obtained by measuring the object to be tested at a measurement angle 180° different from the first reference measurement angle. Furthermore, an error in the touch probe correction value is estimated based on the initial value of the offset displacement and the test value of the offset displacement. This makes it possible to calibrate the touch probe only when necessary based on the estimated error in the touch probe correction value, minimizing the frequency of touch probe calibration without sacrificing accuracy. Furthermore, there is no need to set up a calibration standard each time an inspection is performed, and the spindle reversal required to change the measurement angle by 180° from the first reference measurement angle only needs to be performed once, thereby reducing the time required for the calibration process. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a perspective explanatory view showing a machine tool. [Figure 2] FIG. 2 is a block diagram showing a configuration relating to a correction value inspection of a touch probe in an NC device. [Figure 3] 1A and 1B are explanatory diagrams showing a touch probe in a state in which an offset displacement has occurred due to tilting of the stylus, with FIG. 1A showing the probe from above and FIG. 1B showing the probe from the side. [Figure 4] 10 is an explanatory diagram showing an initial object to be measured and a stylus ball of a touch probe viewed from above when an initial value of an offset displacement amount is calculated; FIG. [Figure 5] 10 is an explanatory diagram showing a reference sphere and a stylus ball of a touch probe viewed from above when an initial value of an offset displacement amount is calculated; FIG. [Figure 6]10 is an explanatory diagram showing an object to be inspected and a stylus ball of a touch probe viewed from above when calculating an offset displacement amount during inspection. FIG. [Figure 7] 10 is a flowchart showing a process relating to inspection of a correction value of a touch probe. DETAILED DESCRIPTION OF THE INVENTION

[0013] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A touch probe compensation value inspection system and compensation value inspection method according to an embodiment of the present invention will be described in detail below with reference to the accompanying drawings. First, the machine tool 1 will be described with reference to Fig. 1. Fig. 1 is an explanatory perspective view showing the machine tool 1. Note that the X-axis, Y-axis, and Z-axis in Fig. 1 are three orthogonal axes (translation axes of the machine tool 1), with the Y-axis direction being the front-to-rear direction of the machine tool 1, the X-axis direction being the left-to-right direction, and the Z-axis direction being the up-to-down direction.

[0014] Machine tool 1 is a three-axis machining center, and a Y-axis guide is formed on the upper surface of bed 2, with table 3 mounted on this Y-axis guide so that it can move in the Y-axis direction. That is, table 3 is capable of translational movement with one degree of freedom relative to bed 2. Also, a column 4 is erected at the rear of bed 2, with an X-axis guide formed on the front surface of column 4. A spindle head 6 is mounted on the X-axis guide via a saddle 5, and this spindle head 6 is capable of movement in the X-axis and Z-axis directions. That is, spindle head 6 is capable of translational movement with two degrees of freedom relative to bed 2, and by combining this with the movement of table 3, it is possible to achieve translational movement with three degrees of freedom relative to bed 2.

[0015] The machine tool 1 is also provided with an NC device 10 for controlling the operation of the spindle 7 and each translation axis. The NC device 10 is configured to include a CPU and a memory connected to the CPU. The machine tool 1 is controlled by the NC device 10 in response to, for example, an operating program stored in the NC device 10 or button operations by an operator, and processes a workpiece (not shown) fixed on the table 3 by rotating a tool (not shown) attached to the spindle 7 of the spindle head 6 and controlling the relative position and attitude between the workpiece and the tool.

[0016] The following describes the system and method for inspecting the compensation value of the touch probe 8, which are essential parts of the present invention. Fig. 2 is a block diagram showing the configuration for inspecting the compensation value of the touch probe 8 in the NC device 10. A touch probe 8 used for calibration work, which will be described later, can be attached to the spindle 7. A reference sphere 9 that serves as a calibration reference when calibrating the touch probe 8 can be installed on the table 3. Meanwhile, the NC device 10 is equipped with an initial offset value estimating means 11, an inspection / measurement implementation determining means 12, an inspection offset value estimating means 13, a correction value error estimating means 14, and a correction value error display means 15. These estimating means and determining means are provided in the NC device 10 as a memory that stores programs for calculating operation commands and measurement values ​​for the machine tool 1, as well as calculation results, etc.

[0017] The initial offset value estimation means 11 measures the side of the initial object to be measured, for example, the side of a reference sphere 9 placed on the table 3 or the side of the table 3, using the touch probe 8 attached to the spindle 7, according to a measurement procedure that will be described later. Then, calculations are performed based on the measurement results to calculate and set an initial value 16 of the offset displacement amount. Setting of this initial value 16 of the offset displacement amount is normally performed at the same time that calibration of the touch probe 8 is performed.

[0018] Similarly, inspection offset value estimation means 13 measures the side of the object to be inspected, for example, the side of a reference sphere 9 placed on table 3 or the side of table 3, using a touch probe 8 attached to spindle 7, according to a measurement procedure described below. Next, calculations are performed based on the measurement results to calculate and set an inspection-time value 17 of the offset displacement amount. Furthermore, correction value error estimation means 14 calculates a correction value error estimate 18 based on an initial value 16 of the offset displacement amount and the inspection-time value 17 of the offset displacement amount.

[0019] Here, the types of errors that are assumed when measuring the diameter direction with the touch probe 8, and the three types of errors that are assumed in the present invention will be described. The first error is the positioning error of the feed axis of the machine tool. This positioning error of the machine tool is represented by the symbol E m In the feed axis of a machine tool, due to backlash in the ball screw, an error can occur even when the position is the same when positioned from the + side to the - side and when positioned from the - side to the + side. This error changes when the feed axis wears out after using the machine for an extended period of time, but the change over a period of several days to several weeks can be considered small.

[0020] The second error is due to the signal output characteristics of the touch probe. This error due to the signal output characteristics is represented by the symbol E p Specifically, this error is due to the delay between when the touch probe stylus comes into contact with the workpiece and when a contact signal is issued, and due to the characteristics of the contact pair inside the touch probe for detecting contact. Furthermore, errors due to the characteristics of the contact pair may differ depending on the direction of contact with the workpiece. Such errors due to the signal output characteristics of the touch probe are less likely to change over time than errors due to bending of the touch probe stylus, which will be described later. Although errors can change significantly when the touch probe is replaced or when the internal structure of the touch probe deteriorates over time due to wear, the change can be considered small if the same touch probe is used continuously for several days to several weeks.

[0021] The third error is an error caused by the offset displacement of the center of the stylus ball of the touch probe relative to the center of the spindle. This error caused by offset displacement is caused by factors such as thermal deformation and the force received when contacting the workpiece, and therefore has the property of changing with changes in the temperature of the operating environment and an increase in the number of contacts with the workpiece. Figure 3 shows the touch probe 8 in a state in which offset displacement has occurred due to the stylus being tilted, with Figure 3a shown from above and Figure 3b shown from the side. The error caused by the offset displacement as described above is the angle θ of the stylus ball center position relative to the spindle center. s and distance d s By using the above, it can be expressed by the following equation (1).

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[0022] Next, a first method for calculating the initial offset displacement amount initial value 16 by the initial offset value estimating means 11 will be described with reference to Fig. 4. Fig. 4 is an explanatory diagram showing the initial workpiece to be measured and the stylus ball of the touch probe 8 as viewed from above when the initial offset displacement amount initial value 16 is calculated. In Fig. 4, the hatched area represents the initial workpiece to be measured, the black circles represent measurement points, and the small circles represent the stylus ball with radius r. The open triangle attached to the stylus ball represents the indexing direction of the spindle 7 to which the touch probe 8 is attached, and the open arrow represents the contact direction when the stylus ball comes into contact with the initial workpiece to be measured. The angle between the indexing direction and the contact direction is defined as the measurement angle θ.

[0023] In the first method, as shown in Fig. 4, measurements are taken while changing the indexing direction of the spindle 7 to which the touch probe 8 is attached, and an initial value 16 of the offset displacement amount is calculated from the measurement results. That is, the initial offset value estimation means 11 takes a predetermined measurement angle as a reference measurement angle, and performs measurements at two measurement angles, the reference measurement angle and a measurement angle 180° inverted from the reference measurement angle, for a predetermined measurement point on the initial measurement object. For example, as shown in Fig. 4a, the first reference measurement angle is taken as 0°, and measurements are taken at measurement point X on the measurement surface of the initial measurement object at 0° and 180°. A At this time, the initial measurement result before inversion, which is the measurement result at 0°, can be expressed by the following formula (2), and the initial measurement result after inversion, which is the measurement result at 180°, can be expressed by the following formula (3).

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[0024] Also, the measurement angle perpendicular to the first reference measurement angle is set as the second reference measurement angle. In the example shown in Fig. 4, since the first reference measurement angle is set as 0° in Fig. 4a, the second reference measurement angle is set as 90° as shown in Fig. 4b. Therefore, this time, the measurement point X on the measurement surface of the initial measurement object is set at 90° and 270°. A The initial value 16 of the offset displacement amount relative to the second reference measurement angle, in this case the initial value 16 of the offset displacement amount in the Y-axis direction, is calculated using the following equation (5) from the initial measurement result before inversion, which is the measurement result at 90°, and the initial measurement result after inversion, which is the measurement result at 270°.

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[0025] Next, a second method for calculating the initial value 16 of the offset displacement amount by the initial offset value estimation means 11 will be described with reference to Fig. 5. Fig. 5 is an explanatory diagram showing a reference sphere 9, which is the initial object to be measured when calculating the initial value 16 of the offset displacement amount, and the stylus ball of the touch probe 8, viewed from above, in which the large circle in the center of Fig. 5 represents the reference sphere 9 with radius R, the black circles represent measurement points, and the small circle represents the stylus ball with radius r. In addition, the open triangle attached to the stylus ball represents the indexing direction of the spindle 7 to which the touch probe 8 is attached, and the open arrow represents the contact direction when the stylus ball comes into contact with the reference sphere 9.

[0026] In the second method, for example, as shown in FIG. 5, a calibration standard such as a reference sphere 9 is used to determine the diameter correction value of the touch probe 8, and an initial value 16 of the offset displacement amount is calculated based on the diameter correction value. + , Y + , X - , Y - The measurement at each measurement point corresponds to measurement angles of 0°, 90°, 180°, and 270° as shown in FIG. 5, and is the same measurement angle as the first method. Specifically, the measurement at the first reference measurement angle in the first method is X + and X - The measurement at the second reference measurement angle corresponds to measuring Y + and Y - This corresponds to measuring the following:

[0027] Therefore, first, let us consider the case where the first reference measurement angle is set to 0° and measurements are performed at 0° and 180°. When θ=0°, the X of the reference sphere 9 is + side, θ=180°, X of reference sphere 9 - The coordinates when measuring each side are given by the following equations (6) and (7).

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[0028] Similarly, the diameter correction value of the touch probe 8 when measuring the Y+ side surface and the diameter correction value of the touch probe 8 when measuring the Y- side surface, which are correction values ​​in the Y-axis direction, can be calculated using the following equations (11) and (12).

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[0029] Here, the first term on the right-hand side of Equation (10) and Equation (13) is the sum of the initial value of the positive-side positioning error and the initial value of the negative-side positioning error of the machine tool. As mentioned above, the positioning error of the machine tool is expected to be an error due to ball screw backlash. Therefore, the positive-side positioning error and the negative-side positioning error usually have opposite signs. If the absolute values ​​of the positive-side positioning error and the negative-side positioning error can be considered to be the same based on the characteristics of the machine tool used, the first term on the right-hand side of Equation (10) and Equation (13) will be 0, matching the right-hand side of Equation (4) and Equation (5). In other words, if the absolute values ​​can be considered to be the same, the initial value 16 of the offset displacement obtained by the second method will be the same as the initial value 16 of the offset displacement obtained by the first method. Therefore, the method of calculating the radius correction value of the touch probe 8 using a calibration standard is the second method for calculating the initial value 16 of the offset displacement. With this second method, the initial value 16 of the offset displacement can be easily calculated from the radius correction value of the touch probe 8. Whether the first method or the second method is used, the calculated initial value 16 of the offset displacement amount is stored in the initial offset value estimation means 11 .

[0030] Next, a method for calculating the inspection offset displacement value 17 by the inspection offset value estimation means 13 will be described with reference to FIG. 6. The method shown in FIG. 6 is the same as the first method for calculating the initial offset displacement value 16 described with reference to FIG. 4. FIG. 6 is an explanatory diagram showing the inspection object and the stylus ball of the touch probe 8 as viewed from above when calculating the inspection offset displacement value 17. The hatched area in FIG. 6 represents the inspection object, the black circles represent measurement points, and the small circles represent the stylus ball with radius r. The open triangle attached to the stylus ball represents the indexing direction of the spindle 7 to which the touch probe 8 is attached, and the open arrow represents the contact direction when the stylus ball comes into contact with the inspection object. Furthermore, the angle between the indexing direction and the contact direction is defined as the measurement angle θ.

[0031] The measurement for calculating the inspection value 17 of the offset displacement amount is performed at the same reference measurement angle as when the initial value 16 of the offset displacement amount was calculated. Therefore, if the measurements shown in Figs. 4a and 4b were performed for calculating the initial value 16 of the offset displacement amount, the first reference measurement angle is set to 0° as shown in Fig. 6a, and the second reference measurement angle is set to 90° as shown in Fig. 6b, and the measurement points X B can be measured. That is, as shown in FIG. 6a, the first reference measurement angle is set to 0°, and the measurement point X on the measurement surface of the test object is measured at 0° and 180°. B In this case, the pre-reversal inspection measurement result, which is the measurement result at 0°, can be expressed by the following formula (14), and the post-reversal inspection measurement result, which is the measurement result at 180°, can be expressed by the following formula (15). Note that, as is clear from formulas (14) and (15), the measurement result is obtained by subtracting the diameter correction value at the time of X+side measurement, which is the diameter correction value of the touch probe 8.

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[0032] Here, as mentioned above, the positioning error E m The error due to the signal output characteristics of the touch probe is represented by the symbol E p Assuming that the change between σ and σ is small, Equations (14) and (15) can be approximated as Equations (16) and (17) below.

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[0033] In equations (16) and (17), the measurement point X B The true coordinate value x B is an unknown quantity, but its influence can be canceled by taking the difference between the two. Therefore, the value 17 of the offset displacement amount in the X-axis direction at the time of inspection is calculated by the following equation (18).

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[0034] Finally, the correction value error estimation means 14 calculates the error in the radial correction value of the touch probe 8, i.e., the correction value error estimate 18. In calculating this correction value error estimate 18, the difference between the initial value 16 of the offset displacement amount calculated using equations (4) and (5) and the value 17 of the offset displacement amount at the time of inspection calculated using equations (18) and (19) is taken, as shown in the following equations (20) and (21).

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[0035] Here, the error of the radial correction value of the touch probe 8 obtained by the formulas (20) and (21) will be explained. The formula (16) is obtained by the first reference measurement angle at the measurement point X B This is the measurement result. Measurement point X B The true coordinate value x B On the other hand, the measurement error is as follows: In other words, the offset displacement of the touch probe changes over time, causing a discrepancy between when the radial correction value is set and when it is measured. This measurement error corresponds to the right-hand side of equation (20). Therefore, by using the method of the present invention, it is possible to estimate the correction value error estimate 18, i.e., the magnitude of the error in the radial correction value of the touch probe 8 in a specified measurement angular direction.

[0036] In the above-described embodiment, the offset displacement amounts at the first and second reference measurement angles are calculated by measuring the same measurement point in the X-axis direction while changing the index angle of the spindle 7. However, in both the measurement by the initial offset value estimation means 11 and the measurement by the inspection offset value estimation means 13, the measurement point and measurement direction may be different between the measurement at the first reference measurement angle and the measurement at the second reference measurement angle. For example, as shown in FIGS. 4c and 6c, measurement may be performed in the X-axis direction when measuring at the first reference measurement angle of 0°, and measurement may be performed in the Y-axis direction when measuring at the second reference measurement angle of 90°. In this example, the pre-reversal measurement result at the first reference measurement angle is obtained by measuring in the X-axis direction at a measurement angle of 0°, and the pre-reversal measurement result at the second reference measurement angle is obtained by measuring in the Y-axis direction at a measurement angle of 90° while keeping the index direction of the spindle 7 the same. Next, after reversing the indexing direction of spindle 7, measurement is made in the X-axis direction at a measurement angle of 180° to obtain the measurement result after reversal at the first reference measurement angle, and measurement is made in the Y-axis direction at a measurement angle of 270° while keeping the indexing direction of spindle 7 the same to obtain the measurement result after reversal at the second reference measurement angle. In this way, if the first reference measurement angle and the second reference measurement angle are orthogonal to each other, it is possible to obtain the initial value 16 of the offset displacement amount that is the same as equations (4) and (5), or the value 17 of the offset displacement amount during inspection that is the same as equations (18) and (19), even if the measurement point and measurement direction are different.

[0037] 7, the flow of processing related to inspection of the compensation value of the touch probe 8 by the compensation value inspection system for the touch probe 8 of this embodiment will be described. Inspection of the compensation value of the touch probe 8 is an inspection to determine whether calibration work is required to reset the compensation value of the touch probe 8, and can be said to be an inspection of the measurement accuracy of the touch probe 8.

[0038] S1: Refer to the inspection and measurement implementation condition parameters. The inspection and measurement implementation condition parameters may include temperature information on the machine tool and / or the surrounding area, the time elapsed since the previous inspection and measurement, and the count value of the number of measurements made by the touch probe. Depending on the parameters used, a program for measuring and storing the temperature sensor, temperature value, elapsed time, number of measurements, etc. is set in advance in the machine tool 1 or the NC device 10.

[0039] S2: Determine whether the inspection and measurement implementation conditions are met. Specifically, threshold values ​​are set in advance for the inspection and measurement implementation condition parameters referenced in S1, and it is determined that the inspection and measurement implementation conditions are met when the inspection and measurement implementation condition parameters exceed the threshold value. Possible threshold values ​​include, for example, a change in the ambient temperature of the machine tool from the time of calibration of 5°C or more, or an elapsed time of 2 hours or more since the previous inspection and measurement. The above inspection and measurement implementation condition parameters and threshold values ​​may be set arbitrarily by the operator by providing a setting screen on the NC device 10. The above-described processes of S1 and S2 are executed by the inspection / measurement execution determining means 12 provided in the NC device 10.

[0040] S3: If it is determined in S2 that the inspection and measurement conditions are met, inspection and measurement are carried out to calculate the inspection value 17 of the offset displacement amount. The inspection value 17 of the offset displacement amount is measured by the method shown in FIG. 6 as described above, and is calculated by equations (14) to (19). S4: Refer to the initial value 16 of the offset displacement amount stored in advance in the initial offset value estimation means 11. The initial value 16 of the offset displacement amount is measured by the method shown in Fig. 3 or Fig. 4 as described above, and is calculated by the formula (4), formula (5), formula (10), or formula (13). S5: Calculate the correction value error estimate 18, which is the amount of change in measurement error, based on the initial value 16 of the offset displacement amount and the value 17 of the offset displacement amount at the time of inspection. The correction value error estimate 18 is calculated using equations (20) and (21) as described above.

[0041] S6: The correction value error display means 15 compares the correction value error estimate 18 calculated in S5 with a threshold value. At this time, the comparison is made with the threshold values ​​corresponding to the X-axis direction and the Y-axis direction, respectively. These threshold values ​​are set in advance in the correction value error display means 15. Alternatively, for example, a setting screen for the threshold value may be provided in the NC device 10 so that the operator can set it as desired.

[0042] S7: If the correction value error estimate 18 exceeds the threshold value, the correction value error display means 15 executes a warning operation. Specifically, an alarm is output and a message is displayed indicating that an alarm has been output. One method for outputting the alarm is to install a warning light or buzzer on the machine tool 1 and activate it. Furthermore, the program of the machine tool 1 may be stopped together with the execution of the warning operation so that measurement by the touch probe 8 is not performed while the correction value error estimate 18 remains above the threshold value. In relation to the processes of S6 and S7 executed by the compensation value error display means 15, for example, the compensation value error estimate 18 calculated in S5 may be displayed on a screen so that the operator can visually check and determine whether or not to calibrate the touch probe 8. It is also possible to store the compensation value error estimate 18 calculated in past inspection measurements and display its changes as a graph.

[0043] According to the correction value inspection system and correction value inspection method for a touch probe 8 having the above-described configuration, a predetermined measurement angle is set as a first reference measurement angle, and a measurement angle perpendicular to the first reference measurement angle is set as a second reference measurement angle, and an initial value 16 of the offset displacement amount, which is the deviation in position of the center of the stylus ball of the touch probe 8 from the center of the spindle 7, is calculated based on the pre-inversion initial measurement result in which the initial measured object is measured at the first reference measurement angle and the second reference measurement angle, and the post-inversion initial measurement result in which the initial measured object is measured at a measurement angle differing by 180° from the first reference measurement angle and a measurement angle differing by 180° from the second reference measurement angle. Furthermore, an offset displacement value 17 at the time of inspection is calculated based on pre-inversion inspection measurement results obtained by measuring the object to be inspected at the first and second reference measurement angles, and initial post-inversion measurement results obtained by measuring the object to be inspected at a measurement angle 180° different from the first reference measurement angle and a measurement angle 180° different from the second reference measurement angle. Furthermore, a correction value error estimate 18, which is an error in the correction value of the touch probe 8, is calculated based on the initial offset displacement value 16 and the offset displacement value 17 at the time of inspection. Therefore, it is possible to calibrate the touch probe 8 only when necessary in accordance with the calculated correction value error estimate 18, minimizing the frequency of calibration work for the touch probe 8 without sacrificing accuracy. Furthermore, since there is no need to install a calibration reference such as a reference sphere 9 each time an inspection is performed, and the number of times the spindle 7 is rotated is reduced, the calibration work time can be shortened.

[0044] The touch probe correction value inspection system and correction value inspection method according to the present invention are not limited to the above-described embodiments, and can be modified as needed without departing from the spirit of the present invention.

[0045] For example, while the above embodiment is directed to a correction value inspection system for a three-axis machining center, the present invention can also be applied to other types of machine tools. For example, instead of a machining center, it may be a lathe, a multi-tasking machine, a grinding machine, etc. Furthermore, the number of axes is not limited to three, and there is no problem if the table is rotatably supported or the spindle head rotates about an axis in the front-to-rear direction, etc. In addition, in the above embodiment, a reference sphere is used as the calibration standard, but it is also possible to use a cylindrical standard other than a reference sphere that can measure the outer circumferential surface, or a ring gauge that can measure the inner circumferential surface.

[0046] Furthermore, when calculating the inspection value of the offset displacement amount, the measurement points measured by the touch probe may be the same as or different from the measurement points measured when calculating the initial value of the offset displacement amount. Furthermore, the object to be measured for inspection used in calculating the value of the offset displacement amount at the time of inspection may be the same as or different from the initial object to be measured used in calculating the initial value of the offset displacement amount, provided that the measurement is performed at the same measurement angle when calculating the value of the offset displacement amount at the time of inspection and when calculating the initial value of the offset displacement amount.

[0047] Furthermore, in the above embodiment, the temperature information of the machine tool and / or the surroundings, the time elapsed since the previous inspection measurement, and the count value of the number of measurements made by the touch probe are presented as parameters for the inspection and measurement conditions, but it is also possible to use the amount of movement of the feed axis, the number of reversals of the feed axis, the cutting distance, the number of workpieces to be machined, etc. The amount of movement of the feed axis can also be rephrased as the distance traveled by the workpiece, etc., and the cutting distance is the amount of movement of the feed axis while the workpiece is being machined. Additionally, in the above embodiment, the first reference measurement angle is set to 0° and the second reference measurement angle is set to 90°, but the first and second reference measurement angles can be set freely as long as they are orthogonal to each other. Also, if the angle that requires inspection is only in one predetermined direction, only one reference measurement angle is required. For example, if only the X-axis direction is required, it is possible to configure the system so that the initial value of the offset displacement amount and the value during inspection are calculated only for 0°. [Explanation of symbols]

[0048] 1·· Machine tool, 7·· Spindle, 8·· Touch probe, 9·· Reference sphere (calibration standard), 10·· NC device (touch probe correction value inspection system), 11· Means for estimating initial offset value, 13·· Means for estimating offset value during inspection, 14·· Means for estimating correction value error.

Claims

1. 1. A compensation value inspection system for inspecting an error in a compensation value of a touch probe attached to a spindle in a machine tool having three or more translation axes and a rotatable spindle to which a tool is attached, comprising: If the angle between the indexing direction of the spindle to which the touch probe is attached and the contact direction in which the touch probe is brought into contact with a predetermined workpiece by moving the spindle in a plane perpendicular to the axis of the spindle is defined as a measurement angle, the workpiece can be measured by the touch probe at a plurality of measurement angles, an initial offset value estimating means for calculating an initial value of an offset displacement amount, which is a deviation of the position of the center of the stylus ball of the touch probe from the center of the spindle, based on a pre-inversion initial measurement result obtained by measuring an initial measured object at the first reference measurement angle, where the predetermined measurement angle is defined as a first reference measurement angle, and a post-inversion initial measurement result obtained by measuring the initial measured object at the measurement angle that is 180° different from the first reference measurement angle; an inspection offset value estimation means for calculating an inspection value of the offset displacement amount based on a pre-inversion inspection measurement result obtained by measuring the object to be measured during inspection at the first reference measurement angle and a post-inversion inspection measurement result obtained by measuring the object to be measured during inspection at the measurement angle that is 180° different from the first reference measurement angle; a correction value error estimation means for estimating an error in the correction value of the touch probe based on an initial value of the offset displacement amount and a value of the offset displacement amount at the time of inspection.

2. 2. The touch probe correction value inspection system according to claim 1, wherein the initial offset value estimation means obtains the initial measurement result after reversal by changing the indexing direction of the spindle by 180° while keeping the contact direction the same as when the initial measurement result before reversal was obtained.

3. the initial object to be measured is a ring-shaped, spherical, or cylindrical calibration standard; 2. The touch probe correction value inspection system according to claim 1, wherein the initial offset value estimation means obtains the initial measurement result after reversal by changing the contact direction by 180° while keeping the indexing direction of the spindle the same as when the initial measurement result before reversal was obtained.

4. a measurement angle orthogonal to the first reference measurement angle is defined as a second reference measurement angle; the initial offset value estimation means calculates an initial value of the offset displacement amount based on measurement results at the second reference measurement angle and the measurement angle that is 180° different from the second reference measurement angle; The touch probe correction value inspection system according to any one of claims 1 to 3, characterized in that the inspection offset value estimation means calculates the inspection value of the offset displacement amount based on measurement results at the second reference measurement angle and the measurement angle that is 180° different from the second reference measurement angle.

5. A correction value inspection method for inspecting an error in a correction value of a touch probe in a machine tool that has three or more translation axes and a rotatable main spindle to which a tool is attached, and that is capable of measuring the workpiece with the touch probe at a plurality of measurement angles, where the angle between the index direction of the main spindle to which a touch probe is attached and a contact direction in which the main spindle is moved in a plane perpendicular to the axis of the main spindle to bring the touch probe into contact with a predetermined workpiece, comprises: a first step of calculating an initial value of an offset displacement amount, which is a deviation of the position of the center of the stylus ball of the touch probe from the center of the spindle, based on a pre-inversion initial measurement result obtained by measuring an initial measured object at a predetermined measurement angle as a first reference measurement angle and a post-inversion initial measurement result obtained by measuring the initial measured object at the measurement angle that is 180° different from the first reference measurement angle; a second step of calculating a value of the offset displacement amount during inspection based on a pre-inversion inspection measurement result obtained by measuring the object to be measured during inspection at the first reference measurement angle and a post-inversion inspection measurement result obtained by measuring the object to be measured during inspection at the measurement angle that is 180° different from the first reference measurement angle; a third step of estimating an error in the correction value of the touch probe based on an initial value of the offset displacement amount and a value of the offset displacement amount at the time of inspection.

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