Compensation value checking system and compensation value checking method for a probe

Abstract

A verification system for a compensation value of a probe (8) includes an initial offset value estimation unit (11), an offset value during verification estimation unit (13), and a compensation value error estimation unit (14). The offset value during verification estimation unit (13) calculates a value of an offset shift amount during verification based on a verification measurement result before turning over and a verification measurement result after turning over. The verification measurement result before turning over is obtained by measuring a measurement object during verification at the first reference measurement angle. The verification measurement result after turning over is obtained by measuring the measurement object during verification at the measurement angle that is 180° different from the first reference measurement angle.The compensation value error estimation unit (14) estimates an error of a compensation value of the probe (8) based on the initial value of the offset shift amount and the value of the offset shift amount during a check.

Description

[0001] The invention relates to a compensation value verification system and a compensation value verification method for verifying a compensation value of a probe head used, for example, for measuring a workpiece origin position.

[0002] Typically, a probe is brought into contact with a workpiece or a reference sphere while being rotated through multiple angles. This is done, for example, when measuring the workpiece's initial position, measuring workpiece dimensions after machining, or calibrating machine accuracy. Additionally, a compensation value is set for the probe to compensate for variations in the distance between the main spindle's reference point and a measurement point, such as the radius of a stylus ball or the probe's length. However, if the probe changes over time, for example, due to thermal deformation caused by temperature changes in the operating environment, a discrepancy arises between the set compensation value and the actual error, and this discrepancy becomes a measurement error.

[0003] As a method to avoid the measurement error caused by the temperature change of a probe, as described above, there is a method for performing a calibration activity to periodically reset the compensation value. For example, JP 2016-083729A discloses a method for calibrating a compensation value in a radial direction of a remote end section of a probe by measuring a reference sphere that serves as a calibration reference using the probe.

[0004] As another method to avoid measurement errors caused by temperature changes in a probe, a method for eliminating the influence of measurement errors exists by developing a measurement procedure. For example, JP 2020-196 051 A discloses a method for eliminating the influence of a measurement error in a radial direction of a remote end section of a probe by changing the feed angle of a main spindle on which the probe is mounted, according to a measurement target. Specifically, when the coordinates of a predetermined measuring point are measured, the main spindle is reversed to measure the coordinates twice, and the measurement results before and after the reversal are averaged to eliminate the influence of a measurement error.

[0005] However, the method disclosed in JP 2016-083729A presents a problem with the calibration of the probe head, as it tends to be performed more often than necessary, making the calibration process cumbersome. Additionally, if a calibration reference is always installed inside a machine tool, problems arise due to the increasingly limited space for workpiece mounting and a deterioration in calibration accuracy caused by the influence of chips and cutting fluids. Consequently, it can be difficult to always mount the calibration reference inside the machine tool. Therefore, it is conceivable that by designing the calibration reference to be removable, it would be possible to install the calibration reference each time the calibration process is performed.However, the problem arises that the workload on an operator increases depending on the frequency of the calibration activity if the calibration reference is attached and removed each time the calibration activity is performed.

[0006] On the other hand, the method disclosed in JP 2020-196 051 A can reduce the frequency of probe calibration. However, it is necessary to perform the coordinate measurement of a predetermined measuring point twice, namely before and after reversing the main spindle, and therefore a problem arises with regard to the time required for the coordinate measurement.

[0007] Therefore, the invention addresses the problems described above, and it is an object of the invention to provide a compensation value verification system and a compensation value verification method for a probe that can easily verify a compensation value of a probe, in order to minimize the frequency of an activity associated with calibrating to reset the compensation value of the probe and to ensure the measurement accuracy of a position by the probe at all times.

[0008] The problem is solved by a verification system for a compensation value of a probe head with the features according to claim 1 and a compensation value verification method for verifying an error in a compensation value of a probe head with the features according to claim 5. Advantageous further developments are included in the dependent claims.

[0009] To solve the problems described above, the invention, according to a first aspect, provides a verification system for the compensation value of a probe head, which checks for errors in the compensation value of a probe head mounted on a main spindle in a machine tool. The machine tool has translational axes with three or more axes and a main spindle rotatable with a tool mounted thereon, wherein an angle between a feed direction of the main spindle, on which the probe head is mounted, and a contact direction is set as a measuring angle. The contact direction is a direction in which the probe head is brought into contact with a predetermined object by a movement of the main spindle in a plane perpendicular to an axis line of the main spindle. Furthermore, the object can be measured with the probe head at a plurality of measuring angles. A predetermined measuring angle is also set as a first reference measuring angle.The probe compensation value verification system includes an initial offset value estimation unit, an offset value during verification estimation unit, and a compensation value error estimation unit. The initial offset value estimation unit calculates an initial offset displacement value as a deviation of the center position of a probe stylus ball relative to the center of the main spindle, based on an initial measurement before inversion and an initial measurement after inversion. The initial measurement before inversion is obtained by measuring an initial object at a first reference measurement angle. The initial measurement after inversion is obtained by measuring the initial object at a measurement angle that differs by 180° from the first reference measurement angle.Furthermore, the Offset Value During Inspection Estimation Unit calculates an Offset Displacement Extent During Inspection value based on an Inspection Measurement Before Inspection and an Inspection Measurement After Inspection. The Inspection Measurement Before Inspection is obtained by measuring the object during an inspection at the initial measurement angle. The Inspection Measurement After Inspection is obtained by measuring the object at a measurement angle that differs from the initial reference measurement angle by 180°. Additionally, the Compensation Value Error Estimation Unit estimates an error in a probe compensation value based on the initial Offset Displacement Extent value and the Offset Displacement Extent During Inspection value.

[0010] In the invention according to a second aspect, which is included in the invention according to the first aspect, the initial offset value estimation unit obtains the initial measurement result-after-reversing by changing the switching direction of the main spindle by 180°, while the contact direction for obtaining the initial measurement result-before-reversing remains unchanged.

[0011] In the invention according to a third aspect, which is included in the invention according to the first aspect, the first measuring object is an annular, spherical or cylindrical calibration reference and the initial offset value estimation unit obtains the initial measurement result-after reversal by changing the contact direction by 180°, while the switching direction of the main spindle to obtain the initial measurement result-before reversal remains unchanged.

[0012] In the invention according to a fourth aspect, which is included in the invention according to each of the first to third aspects, a measurement angle perpendicular to the first reference measurement angle is selected as a second reference measurement angle. The initial offset value estimation unit calculates an initial value of the offset displacement magnitude based on a measurement result at the second reference measurement angle and a measurement angle that differs by 180° from the second reference measurement angle. The offset value-during-verification estimation unit calculates the value of the offset displacement magnitude-during-verification based on a measurement result at the second reference measurement angle and the measurement angle that differs by 180° from the second reference measurement angle.

[0013] To solve the problem described above, the invention, according to a fifth aspect, provides a compensation value verification method for checking for errors in the compensation value of a probe head in a machine tool. The machine tool has translation axes with three or more axes and a rotatable main spindle with a tool mounted thereon, wherein an angle between a forward direction of the main spindle on which the probe head is mounted and a contact direction is defined as a measuring angle. The contact direction is a directionin which the probe head is brought into contact with a predetermined measuring object by a movement of the main spindle in a plane perpendicular to an axis of the main spindle. Furthermore, the measuring object can be measured with the probe head at a plurality of measuring angles. A predetermined measuring angle is also set as a first reference measuring angle. The verification procedure for the compensation value of the probe head includes: A first step to calculate an initial value of an offset displacement magnitude as a deviation from the center position of a stylus ball of the probe head with respect to a center of the main spindle, based on an initial measurement result before reversal and an initial measurement result after reversal, wherein the initial measurement result before reversal is obtained by measuring an initial measuring object at a first reference measuring angle, and the initial measurement result after reversal is obtained by measuring the initial measuring object at a measuring angle.a second step to calculate a value of the offset displacement magnitude-during-verification based on a verification measurement result-before-inversion and a verification measurement result-after-inversion, wherein the verification measurement result-before-inversion is obtained by measuring a test object during a verification at the first reference measurement angle and the verification measurement result-after-inversion is obtained by measuring the test object during a verification at the measurement angle that differs by 180° from the first reference measurement angle; and a third step to estimate an error of a compensation value of the measuring probe based on the initial value of the offset displacement magnitude and the value of the offset displacement magnitude-during-verification.

[0014] According to the invention, the initial value of the offset displacement magnitude is calculated based on the initial measurement result before and after inversion. Additionally, the value of the offset displacement magnitude during verification is calculated based on the verification measurement result before and after inversion. Furthermore, an error in the probe's compensation value is calculated based on the initial offset displacement magnitude and the offset displacement magnitude during verification. Therefore, probe calibration can be performed only when necessary, according to the estimated error of the probe's compensation value. This minimizes the frequency of probe calibration without compromising accuracy.

[0015] Furthermore, it is not necessary to upgrade a calibration reference for each check. Also, an operation required to change the measuring angle by 180° from the initial reference measuring angle, such as reversing the main spindle, is only performed once. Therefore, the check can be completed quickly. Fig. Figure 1 is an explanatory perspective view depicting a machine tool. Fig. Figure 2 is a block diagram that represents a configuration in an NC unit associated with a compensation value check for a probe. Fig. 3A and Fig. 3B are explanatory views showing the probe head in a state where an offset displacement occurs due to the inclination of a stylus. Fig. 3A represents the state from above and Fig. 3B represents the state of one side. Fig. 4A to Fig. Figure 4C shows illustrative views of an initial measurement object and a stylus ball of the probe head seen from above when an initial value of an offset displacement magnitude is calculated. Fig. Figure 5 is an illustrative view of a reference sphere and the stylus sphere of the probe head seen from above when the initial value of the offset displacement magnitude is calculated. Fig. 6A to Fig. 6C are explanatory views of a measured object during an inspection and the stylus ball of the probe head seen from above when a value of the offset displacement magnitude-during-inspection is calculated. Fig. Figure 7 is a flowchart that illustrates a process associated with a compensation value check for the probe.

[0016] The following describes a compensation value verification system and a compensation value verification method for a probe as an embodiment according to the invention based on the drawings in detail.

[0017] First, based on Fig. 1 a machine tool 1 described. Fig. Figure 1 is an explanatory perspective view depicting machine tool 1. The X-axis, Y-axis, and Z-axis in Fig. The three axes are perpendicular, namely translation axes provided in the machine tool 1. The Y-axis direction is a front-back direction, the X-axis direction is a left-right direction, and the Z-axis direction is an up-down direction of the machine tool 1.

[0018] The machine tool 1 is a three-axis machining center. A Y-axis guide is formed on the upper surface of a bed 2. A table 3 is movably mounted on the Y-axis guide in the Y-axis direction. This means that the table 3 is movable with respect to the bed 2 with one translational degree of freedom. Additionally, a column 4 is mounted upright on a rear section of the bed 2, and an X-axis guide is formed on a front surface of the column 4. A main spindle head 6 is installed on the X-axis guide via a longitudinal slide 5, and the main spindle head 6 is movable in the X-axis and Z-axis directions. This means that the main spindle head 6 is movable with respect to the bed 2 with two translational degrees of freedom, and by combining this with the movement of the table 3, the main spindle head 6 is movable with respect to the bed 2 with three translational degrees of freedom.

[0019] Furthermore, the machine tool 1 includes an NC unit 10 to control the operations of a main spindle 7 and each translation axis. The NC unit 10 is configured to include a CPU and memory connected to the CPU. In the machine tool 1, for example, a tool (not shown) mounted on the main spindle 7 of the main spindle head 6 is rotated by the control of the NC unit 10 in response to a machining program stored in the NC unit 10 or to the operation of a button by the operator. The NC unit 10 then controls a relative position and orientation between the workpiece (not shown) fixed on the table 3 and the tool, thereby machining the workpiece.

[0020] The following describes a verification system of a compensation value of a probe 8 and a verification method of a compensation value of a probe 8 as the main parts of the invention. Fig. Figure 2 is a block diagram that represents a configuration in the NC unit 10 associated with a compensation value check for the probe 8.

[0021] The main spindle 7 can be equipped with the probe 8 used for a calibration operation described later. Additionally, a reference sphere 9, which serves as a calibration reference for calibrating the probe 8, can be installed on the table 3. Meanwhile, the NC unit 10 contains an initial offset value estimation unit 11, a The NC unit 10 comprises a verification measurement application determination unit 12, an offset value-during-verification estimation unit 13, a compensation value error estimation unit 14, and a compensation value error display unit 15. The estimation units and the determination units are provided in the NC unit 10 as memory for storing information such as operating instructions of the machine tool 1 and programs to calculate measured values ​​and calculation results.

[0022] In the initial offset value estimation unit 11, a side face of an initial measurement object is first measured by the probe 8 mounted on the main spindle 7, according to a measurement procedure described later. The initial measurement object is, for example, a side face of the reference sphere 9 installed on the table 3 or a side face of the table 3 itself. Next, a calculation is performed based on the measurement result, and an initial offset displacement value 16 is calculated and set. The initial offset displacement value 16 is normally set when the probe 8 is calibrated.

[0023] In the offset value-during-verification estimation unit 13, during a verification according to a measurement procedure described later, a side face of a test object is first measured by the probe 8 mounted on the main spindle 7. The test object during the verification is, for example, a side face of the reference sphere 9 installed on the table 3 or a side face of the table 3 itself. Next, a calculation is performed based on the measurement result, and a value 17 of the offset displacement magnitude-during-verification is calculated and set.

[0024] In the compensation value error estimation unit 14, a compensation value error estimation magnitude 18 is calculated based on the initial value 16 of the offset displacement magnitude and the value 17 of the offset displacement magnitude during verification.

[0025] Here, the error types assumed for measurements with the probe 8 in a radial direction are described. Three error types are assumed in the invention.

[0026] A first error is a positioning error of a feed axis of a machine tool. The positioning error of the machine tool is indicated by a reference symbol E. mAs illustrated, even when the feed axis of a machine tool is positioned in the same location, the backlash of a ball screw can cause an error to occur when the feed axis is positioned from the + (plus) side to the - (minus) side, and when it is positioned from the - (minus) side to the + (plus) side. This error changes as the feed axis wears from prolonged use of the machine tool. Conversely, the change in error over a usage period of a few days to a few weeks can be considered minor.

[0027] A second type of error is one caused by a signal output characteristic of a probe. The error caused by the signal output characteristic is indicated by a reference symbol E. pThe error is specifically described as follows: it is an error caused by the delay between when a probe stylus makes contact with a test object and when it outputs a contact signal, or an error caused by the characteristics of a contact pair arranged within the probe to detect the contact. In other cases, the error, which is an error caused by the characteristics of the contact pair, can vary depending on the direction of contact with the test object. The error caused by the probe's signal output characteristics is less likely to change over time than an error caused by the stylus bending described later. However, the error changes significantly if the probe is replaced or if the probe deteriorates over time due to factors such as wear of its internal structure.On the other hand, if the same probe is used continuously for a few days to a few weeks, the change is considered small.

[0028] A third error is one caused by the misalignment of the probe's stylus ball center relative to the main spindle center. Specifically, this error is caused by bending of the probe's stylus. The error caused by this misalignment is indicated by a reference symbol E. s The error caused by the offset displacement is due to factors such as thermal deformation and the force applied during contact with the object being measured. Therefore, the error has the characteristic of changing with temperature variations in the operating environment and with an increase in the number of contacts with the object being measured. Fig. 3A and Fig. Figure 3B shows the probe 8 in a state where the offset displacement occurs due to the inclination of the stylus. Fig. 3A represents the state from above and Fig. 3B represents the state from one side. Then the error E caused by the offset shift described above can be... s using an angle e s and a distance d s The position of the stylus ball center relative to the main spindle center can be expressed by the following formula (1). Es,θ=dscos(θs−θ) θ: Angle in a contact direction of the probe head with respect to a main spindle switching direction E s,θ : Error in the radial direction in the contact direction θ θ s : Angle of the stylus ball center position relative to the main spindle center d s : Distance relative to the main spindle center to the stylus ball center position

[0029] A first method for calculating the initial value 16 of the offset displacement extent using the initial offset value estimation unit 11 is based on Fig. 4A to Fig. 4C described. Fig. 4A to Fig. Figure 4C shows explanatory views of an initial measurement object and the stylus ball of the probe head 8, viewed from above, when the initial value 16 of the offset displacement magnitude is calculated. Fig. 4A to Fig. Figure 4C represents the initial measurement object, a measuring point, and the stylus ball with radius r, respectively, represented by a hatched area, a black circle, and a small circle. Additionally, a white triangle attached to the stylus ball indicates the advance direction of the main spindle 7, on which the probe head 8 is mounted. Furthermore, a white arrow indicates the contact direction in which the stylus ball, i.e., the probe head, is brought into contact with the initial measurement object. Finally, the angle between the advance direction and the contact direction is defined as a measuring angle θ.

[0030] In the first procedure, as in Fig. 4A to Fig. As shown in Figure 4B, the measurement is performed while the switching direction of the main spindle 7, on which the probe 8 is mounted, is changed. The initial value 16 of the offset displacement is then calculated from the measurement results. Specifically, a predetermined measuring angle is set as a reference measuring angle in the initial offset value estimation unit 11. Subsequently, a predetermined measuring point of the initial measurement object is measured at two measuring angles: the reference measuring angle and the measuring angle reversed by 180° with respect to the reference measuring angle. For example, as shown in Fig. Figure 4A shows a first reference measurement angle set to 0°. Then a measurement point X is set. A The measurement was taken on a measuring surface of the initial measurement object at 0° and 180°. At this point, an initial measurement result before turning over can be obtained. 1,The measurement result at 0° can be expressed by the following formula (2). On the other hand, an initial measurement result after inverting Â1' can be expressed by the following formula (3). A^1=xA+r+E^m,x++E^p,θ=0+E^s,θ=0A^1=xA+r+E^m,x++E^p,θ=0+d^scosθ^s A^1'=xA+r+E^m,x++E^p,θ=180+E^s,θ=180A^1=xA+r+E^m,x++E^p,θ=180−d^scosθ^s 1: Initial measurement result before turning over with respect to the first reference measurement angle Â1': Initial measurement result after reversing with respect to the first reference measurement angle θ: Measuring angle x A : Actual X-coordinate of measurement point X A in the initial measurement r: Radius of the stylus ball Ê m,x+ : Initial value of the positioning error on the X-axis + side of the machine tool Ê p,θ : Initial value of the error caused by the probe characteristics E s,θ: Initial value of the error caused by stylus bending θ̂ s : Initial value of the angle of the stylus ball center position relative to the main spindle center d̂ s : Initial value of the distance to the stylus ball center position with respect to the main spindle center

[0031] The initial value 16 (Ê1) of the offset displacement magnitude with respect to the first reference measurement angle, which here is the initial value 16 (Ê1) of the offset displacement magnitude in the X-axis direction, is calculated, as shown in the following formula (4), by dividing the difference between the initial measurement result before turning over and the initial measurement result after turning over by two. E^1=A^1−A^1'2=E^p,θ=0−E^p,θ=1802+d^scosθ^s Ê1: Initial value of the offset displacement magnitude with respect to the first reference measuring angle

[0032] Additionally, a measuring angle perpendicular to the first reference measuring angle is set as a second reference measuring angle. In the Fig. 4A to Fig. The example shown in 4C is as described in Fig. 4B is shown, since the first reference measurement angle is in Fig. 4A 0°, the second reference measurement angle is 90°. Accordingly, at this time the measurement point X AMeasurements are taken on the measuring surface of the initial measurement object at 90° and 270°. At this point, an initial measurement result before turning Â2, which is the measurement result at 90°, can be calculated in the same way as the initial measurement result before turning Â1. Conversely, an initial measurement result after turning Â2', which is the measurement result at 270°, can be calculated in the same way as the initial measurement result before turning Â1'. Thus, the initial value 16 (Ê2) of the offset displacement extent with respect to the second reference measurement angle, which here is the initial value 16 (Ê2) of the offset displacement extent in the Y-axis direction, is calculated, as shown in the following formula (5), by dividing the difference between the initial measurement result-before-turning Â2 and the initial measurement result-after-turning Â2' by two. E^2=A^2−A^2'2=E^p,θ=90−E^p,θ=2702−d^ssinθ^s 2: Initial measurement result before turning over with respect to the second reference measurement angle Â2': Initial measurement result after reversing with respect to the second reference measurement angle Ê2: Initial value of the offset displacement magnitude with respect to the second reference measuring angle

[0033] This is the first procedure to calculate the initial value 16 of the offset displacement magnitude.

[0034] Next, a second procedure is described to calculate the initial value 16 of the offset displacement magnitude using the initial offset value estimation unit 11, based on Fig. 5 described. Fig. Figure 5 is an explanatory view of the reference sphere 9, which is an initial measurement object when the initial value 16 of the offset displacement magnitude is calculated, and the stylus sphere of the probe head 8 seen from above. The large circle in the center of Fig. Figure 5, a black circle, and a small circle each represent the reference sphere 9 with radius R, a measuring point, and a stylus sphere with radius r, respectively. Additionally, a white triangle attached to the stylus sphere indicates the direction of advancement of the main spindle 7, on which the probe head 8 is mounted. Furthermore, a white arrow indicates the direction of contact in which the stylus sphere, i.e., the probe head, is brought into contact with the reference sphere 9.

[0035] In the second procedure, for example, as in Fig. Figure 5 shows a diameter compensation value for the probe 8 obtained using the reference sphere 9. The reference sphere 9 is an example of a calibration reference. The initial value 16 of the offset displacement magnitude is calculated based on the diameter compensation value.

[0036] To obtain the diameter compensation value of the probe 8 using the reference sphere 9, measurements are taken at measuring points of X. + , Y + , X - and Y - Nine measurements were performed on the reference sphere. Measurements at measuring points X correspond to... + , Y + , X - and Y - on reference sphere 9, as in Fig. Figure 5 shows each measurement at angles of 0°, 90°, 180°, and 270°. This means that measurements in the second method at measuring points of X + , Y + , X_ and Y_ on the reference sphere 9 measurements at the same measuring angles as in the first method. Specifically, the measurements at the first reference measuring angle and a measuring angle reversed by 180° with respect to the first reference measuring angle correspond to the measuring points of X in the first method. + and X -in the second method. On the other hand, the measurements at the second reference measurement angle and a measurement angle reversed by 180° with respect to the second reference measurement angle in the first method correspond to the measurements at measurement points of Y. + and Y - in the second procedure.

[0037] Therefore, the case in which the first reference measurement angle is set to 0° and the measurement is performed at 0° and 180° is considered. The coordinates X + and X - , which are determined by measuring X + -Side vertex of the reference sphere 9 at θ = 0° and of the X - The lateral vertex of the reference sphere 9 at θ = 180° are each expressed by formulas (6) and (7). X+=x0+R+r+E^m,x++E^p,θ=0+E^s,θ=0 X−=x0−R−r+E^m,x−−E^p,θ=180−E^s,θ=180 X + : Measurement result of X + -Side parting X_: Measurement result of the X - -Side parting x0: X-coordinate of the center of the reference sphere R: Radius of the reference sphere Ê m,x+ : Initial value of the positioning error on the X-axis + side of the machine tool Ê m,x- : Initial value of the positioning error on the X-axis side of the machine tool

[0038] An X-coordinate x0 of the center of the reference sphere 9 is assumed to have been obtained in advance using known measuring instruments. Similarly, the radius R of the reference sphere 9 is also assumed to be known. At this point, when the X + -side surface is measured, the diameter compensation value C x+ of the probe 8, and, if the X - -side surface is measured, the diameter compensation value C x- of the probe 8, as expressed by the following formulas (8) and (9). Cx+=X+−(x0+R)=+r+E^m,x+E^p,θ=0+E^s,θ=0Cx+=+r+E^m,x++E^p,θ=0+d^scosθ^s Cx−=X−−(x0−R)=−r+E^m,x−E^p,θ=180−E^s,θ=180Cx−=−r+E^m,x−−E^p,θ=180+d^scosθ^s C x+ : Diameter compensation value of the probe when the X + - Side surface is measured C x- : Diameter compensation value of the probe when the X - - Side surface is measured Ê m,x+ : Initial value of the positioning error on the X-axis + side of the machine tool Ê m,x- : Initial value of the positioning error on the X-axis side of the machine tool

[0039] Furthermore, the sum of the diameter compensation value C divided by two x+ of probe 8, when the X + -side surface is measured, and the diameter compensation value C x- of probe 8, when the X - -side area is measured, expressed by the following formula (10). Cx++Cx−2=E^m,x++E^m,x−2+E^p,θ=0−E^p,θ=1802+d^scosθ^s

[0040] Similarly, the diameter compensation value C y+ of probe 8 when the Y+ side surface is measured, and the diameter compensation value C y- of the probe 8, when the Y-side surface is measured, which are the compensation values ​​in the Y-axis direction, as expressed in the following formulas (11) and (12). Cy++=+r+E^m,y++E^p,θ=90−d^ssinθ^s Cy−=−r+E^m,y−−E^p,θ=270−d^ssinθ^s C y+ : Probe diameter compensation value when the Y + - Side surface is measured C y- : Probe diameter compensation value when the Y - -side surface is measured Ê m,y+ : Initial value of the positioning error on the Y-axis + side of the machine tool Ê m,y- : Initial value of the positioning error on the Y-axis side of the machine tool

[0041] The sum of the diameter compensation value C, divided by two, is then calculated. y+ of probe 8, when the Y + -side surface is measured, and the diameter compensation value C y- of probe 8, when the Y - -side area is measured, expressed by the following formula (13). Cy+Cy−2=E^m,y++E^m,y−2+E^p,θ=90−E^p,θ=2702−d^ssinθ^s

[0042] Here, the first terms on the right-hand side of formula (10) are the sum of the initial value Ê. m,x+ of the positioning error on the X-axis + side of machine tool 1 and the initial value Ê m,x- of the positioning error on the X-axis side of the machine tool 1. Similarly, the first terms on the right-hand side of formula (13) are the sum of the initial value Ê m,y+ of the positioning error on the Y-axis + side of machine tool 1 and the initial value Ê m,y-of the positioning error on the Y-axis - side of the machine tool 1. As described above, in the invention, an error due to backlash of a ball screw is assumed to be the positioning error of the machine tool 1. Accordingly, the positioning error on the + side and the positioning error on the - side normally have a relationship in which the signs are reversed. Therefore, if the absolute value of the positioning error on the + side and the absolute value of the positioning error on the - side are considered to be the same, based on the characteristics of the machine tool 1 used, the first terms on the right-hand sides of formulas (10) and (13) become 0. At this point, the right-hand sides of formulas (10) and (13) correspond to the right-hand sides of formulas (4) and (5).In other words, in the second procedure, if the absolute value of the positioning error on the + side and the absolute value of the positioning error on the - side are assumed to be the same, the formula, expressed as the sum of the diameter compensation value of probe 8 when the + side area is measured and the diameter compensation value of probe 8 when the - side area is measured, divided by two, is the same as the formula for calculating the initial value 16 of the offset displacement extent in the first procedure. Consequently, the procedure for obtaining the diameter compensation value of probe 8 using a calibration reference becomes the second procedure for calculating the initial value 16 of the offset displacement extent. That is, by using the second procedure, the initial value 16 of the offset displacement extent can be easily calculated from the diameter compensation value of probe 8.

[0043] It should be noted that the initial value 16 of the calculated offset displacement magnitude is stored in the initial offset value estimation unit 11 in both the first and second procedures.

[0044] Next, based on Fig. 6A to Fig. Section 6C describes a procedure for calculating the value 17 of the offset displacement magnitude during verification. This is described in Fig. 6A to Fig. The method shown in 6C is the same as the one using Fig. 4A to Fig. 4C described the first method to calculate the initial value 16 of the offset displacement magnitude. Fig. 6A to Fig. Figure 6C shows explanatory views of a measurement object during an inspection and the stylus ball of the probe head 8 seen from above when the value 17 of the offset displacement magnitude during inspection is calculated. Fig. 6A to Fig. Figure 6C represents the object being measured during an inspection, a measuring point, and the stylus ball with radius r, respectively, as shown by a hatched area, a black circle, and a small circle. Additionally, a white triangle attached to the stylus ball indicates the direction of advancement of the main spindle 7, on which the probe head 8 is mounted. Furthermore, a white arrow indicates the direction of contact in which the stylus ball, i.e., the probe head, is brought into contact with the object being measured during an inspection. Finally, the angle between the direction of advancement and the direction of contact is defined as a measuring angle θ.

[0045] The measurement to calculate value 17 of the offset displacement magnitude during verification is performed at the same reference measurement angles as those used to calculate the initial value 16 of the offset displacement magnitude. Accordingly, for example, if the measurements are taken as described in Fig. 4A and Fig. 4B is shown, to calculate the initial values ​​16 of the offset displacement extent, a measurement to measure a measuring point X B by setting the first reference measurement angle to 0°, as in Fig. 6A shown, and the second reference measurement angle at 90°, as shown in Fig. 6B shown, carried out.

[0046] First, as in Fig. 6A is shown, the first reference measurement angle is set to 0° and the measurement point X B On a measuring surface of the object being measured during an inspection, measurements are taken at 0° and 180°. At this point, an inspection measurement result before inverting, which is the measurement result at 0°, can be expressed by the following formula (14). Furthermore, an inspection measurement result after inverting, which is the measurement result at 180°, can be expressed by the following formula (15). As is evident from formulas (14) and (15), the measurement results are 1,A1' these, in which the diameter compensation value C x+ , when the X+ side area is measured, which is the diameter compensation value of the probe 8, is subtracted from the actual measured values. A1=xB+r+Em,x++Ep,θ=0+Es,θ=0−Cx+A1=xB+(Em,x+−E^m,x+)+(Ep,θ=0−E^p,θ=0)+(dscosθs−d^scosθ^s) A1'=xB+r+Em,x++Ep,θ=180+Es,θ=180−Cx+A1'=xB+(Em,x+−E^m,x+)+(Ep,θ=180−E^p,θ=0)+(−dscosθs−d^scosθ^s) A1: Verification measurement result before turning over with respect to the first reference measurement angle A1': Verification measurement result after turning over with respect to the first reference measurement angle x B : Actual X-coordinate of measurement point X B in the verification measurement E m,x+ : Current value of the positioning error on the X-axis + side of the machine tool E p,θ : Current value of the error caused by the probe characteristics E s,θ: Current value of the error caused by bending the stylus θ s : Current value of the angle of the stylus ball center position relative to the main spindle center d s : Current value of the distance to the stylus ball center position with respect to the main spindle center

[0047] Here, the changes in the positioning error E are m of machine tool 1 and the change in the error E caused by the signal output characteristic p of the probe 8, as described above, is small. In this case, formulas (14) and (15) can be approximated as formulas (16) and (17) described below. A1≅xB+(dscosθs−d^scosθ^s) A1'≅xB+(−dscosθs−d^scosθ^s)

[0048] In formulas (16) and (17) the actual coordinate value X B of measuring point X Ban unknown number. However, as is evident from formulas (16) and (17), the actual coordinate value X can be used. B of measuring point X B based influence by using the difference between the verification measurement result-before-turning A1 with respect to the first reference measurement angle and the verification measurement result-after-turning A 1' with respect to the first reference measurement angle. Accordingly, the value 17 (E1) of the offset displacement magnitude during verification in the X-axis direction (at the first reference measurement angle) is calculated according to the following formula (18). E1=A1−A1'2≅E^p,θ=0−E^p,θ=1802+dscosθs E1: Value of the offset displacement magnitude during verification with respect to the first reference measurement angle

[0049] On the other hand, if the same calculations as in the X-axis direction are performed in the Y-axis direction, the value 17 (E2) of the offset displacement extent-during-verification in the Y-axis direction (at the second reference measurement angle) is calculated according to the following formula (19). E2=A2−A2'2≅E^p,θ=90−E^p,θ=2702−dssinθs A2: Verification measurement result before turning over with respect to the second reference measurement angle A2': Verification measurement result after turning over with respect to the second reference measurement angle E2: Value of the offset displacement magnitude during verification with respect to the second reference measuring angle

[0050] As described above, a predetermined measurement point of the object is measured during a verification at two measurement angles: the reference measurement angle and a measurement angle inverted by 180° relative to the reference measurement angle. The measurement error component can then be extracted by taking the difference between the verification measurement result before inversion (A1, A2) and the verification measurement result after inversion (A1', A2').

[0051] Finally, in the compensation value error estimation unit 14, an error of the compensation value in the radial direction of the probe 8, namely the compensation value error estimation magnitude 18, is calculated. To calculate the compensation value error estimation magnitude 18, as expressed in the following formulas (20) and (21), the difference between the initial value 16 (Ê1, Ê2) of the offset displacement magnitude, obtained according to formulas (4) and (5), and the values ​​17 (E1, E2) of the offset displacement magnitude-during-verification, obtained according to formulas (18) and (19), is taken. ΔE1=E1−E^1≅dscosθs−d^scosθ^s ΔE2=E2−E^2≅−(dssinθs−d^ssinθ^s) ΔE1: Error of the compensation value in the radial direction in the first reference measurement angle direction ΔE2: Error of the compensation value in the radial direction in the second reference measurement angle direction

[0052] Here, the error of the compensation values ​​ΔE1 and ΔE2 in the radial direction of the probe 8, which are obtained according to formulas (20) and (21), is described.

[0053] In formula (16), the verification measurement result before turning over with respect to the first reference measurement angle A1 is the measurement result of the measuring point X. B at the first reference measurement angle. Therefore, in formula (16) the measurement error with respect to the actual coordinate value x B of measuring point X B (d s cosθ s - d̂ s cosθ̂ sThe measurement error is an error associated with a deviation that arises between the displacement of the probe 8 when the compensation value is set in the radial direction and the displacement of the probe 8 when the measurement is performed, since the displacement of the probe 8 changes over time. Furthermore, the measurement error corresponds to the right-hand side of formula (20). Additionally, if the same calculation as in the first reference measurement direction is performed in the second reference measurement direction, the measurement error (-d) s sinθ s + d̂ s sinθ̂ s ) regarding the actual coordinate value x B of measuring point X Bcalculated, and the measurement error corresponds to the right-hand side of formula (21). Therefore, using the method of the invention, it is possible to estimate the compensation value error estimation extent 18, namely the error of the compensation value in the radial direction of the probe 8 in a predetermined measurement angle direction.

[0054] In the embodiment described above, the offset displacement dimensions with respect to the first reference measuring angle and the second reference measuring angle are calculated by measuring the same measuring point in the X-axis direction while the advance angle of the main spindle 7 is changing. However, in both the measurement by the initial offset value estimation unit 11 and the measurement by the offset value-during-verification estimation unit 13, a measuring point and a measuring direction can differ between the measurement with respect to the first reference measuring angle and the measurement with respect to the second reference measuring angle. For example, as in Fig. 4C and Fig. Figure 6C shows that the measurement in the X-axis direction can be performed at 0°, which is the first reference measuring angle, while the measurement in the Y-axis direction can be performed at 90°, which is the second reference measuring angle. In this case, the measurement result before reversing is obtained with respect to the first reference measuring angle, based on the measurement performed at 0° in the X-axis direction. Similarly, the measurement result before reversing is obtained with respect to the second reference measuring angle, based on the measurement performed at 90° in the Y-axis direction, while the switching direction of the main spindle 7 remains unchanged. Next, after the switching direction of the main spindle 7 has been reversed, the measurement is carried out at the measuring angle of 180° in the X-axis direction in order to obtain the measurement result-after reversal with respect to the first reference measuring angle.The measurement result after reversing the second reference measuring angle is also obtained according to the measurement performed at a measuring angle of 270° in the Y-axis direction while the switching direction of the main spindle 7 remains unchanged. Thus, even if the measuring point and the measuring direction are different, as long as the first reference measuring angle is perpendicular to the second reference measuring angle, the same initial values ​​16 of the offset displacement extent as those according to formulas (4) and (5), or the same values ​​17 of the offset displacement extent during verification as those according to formulas (18) and (19) can be obtained.

[0055] In addition, the process flow associated with checking the compensation value of the probe 8 is described by the compensation value verification system for the probe 8 of the embodiment using the flowchart in Fig. 7 described. Checking the compensation value of the probe 8 is a check to see whether a calibration activity is necessary to reset the compensation value of the probe 8, or not, and it can be said that it is a check of the measurement accuracy with the probe 8.

[0056] S1: Refer to verification measurement application condition parameters. For the verification measurement application condition parameters, it is only necessary to use, for example, the temperature information from at least one of the machine tool and the surrounding area, the elapsed time since the previous verification measurement, and the count of the number of measurements using the probe. Depending on the parameters to be used, systems for measuring and storing information such as temperature values, elapsed time, and the number of measurements, as well as temperature sensors, are pre-installed in the machine tool 1 and the NC unit 10.

[0057] S2: Determine whether a verification measurement application condition is met or not. Specifically, threshold values ​​for the verification measurement application condition parameters referenced in S1 are preset. Then, if the verification measurement application condition parameters exceed the threshold values, it is determined that the verification measurement application condition is met. For example, the threshold values ​​could be that the change in the ambient temperature of the machine tool since the previous calibration is 5°C or more, or that the elapsed time since the previous verification measurement is 2 hours or more. It should be noted that a setting screen for the above verification measurement application condition parameters and threshold values ​​may be located in NC unit 10, allowing an operator to conveniently adjust them.

[0058] The processing of the S1 and S2 described above is also carried out by the verification measurement application determination unit 12 arranged in the NC unit 10.

[0059] S3: Perform a verification measurement when determining that the verification measurement condition in S2 is satisfied, and calculate the values ​​17 of the offset displacement extent-during-verification. The values ​​17 of the offset displacement extent-during-verification are determined by the in Fig. 6A to Fig. The methods shown in 6C were measured and calculated according to formulas (14) to (19) as described above.

[0060] S4: Refer to initial values ​​16 of the offset displacement magnitude stored in advance in the initial offset value estimation unit 11. The initial values ​​16 of the offset displacement magnitude are determined by the in Fig. 4A to Fig. 4C and Fig.The 5 methods shown were measured and calculated according to formulas (4) and (5) or formulas (10) and (13) as described above.

[0061] S5: Calculating compensation value error estimation magnitudes 18, which are change magnitudes in the measurement error, based on the initial values ​​16 of the offset displacement magnitude and the values ​​17 of the offset displacement magnitude during verification. The compensation value error estimation magnitudes 18 are calculated according to formulas (20) and (21), as described above.

[0062] S6: Comparison of the compensation value error estimation values ​​18 calculated in S5 with threshold values ​​in the compensation value error display unit 15. At this point, the compensation value error estimation values ​​18 in the X-axis and Y-axis directions are compared with the corresponding threshold values. Note that the threshold values ​​in the compensation value error display unit 15 are preset. A setting screen for the threshold values ​​can be located in the NC unit 10 so that an operator can conveniently adjust them.

[0063] S7: Execute a warning action in the compensation value error display unit 15 if the compensation value error estimation parameters 18 exceed the threshold values. Specifically, an alarm is issued and a message indicating that an alarm has been issued is displayed. For example, a warning lamp and a buzzer can be installed and activated in the machine tool 1 to trigger the alarm. Additionally, the program of the machine tool 1 can be stopped simultaneously with the execution of the warning action, so that the measurement with the probe 8 is not performed while the compensation value error estimation parameters 18 exceed the threshold values.

[0064] In the processing of S6 and S7 described above, which is carried out by the compensation value error display unit 15, the compensation value error estimation values ​​18 calculated in S5 can, for example, be displayed on a screen so that an operator can see and determine whether the probe 8 needs to be calibrated or not. Furthermore, it can be configured to store the compensation value error estimation values ​​18 calculated from previous verification measurements, and their changes can be displayed as a graph.

[0065] Using the compensation value verification system and the compensation value verification procedure for the probe 8, which has the configuration described above, the initial values ​​16 of the offset displacement magnitude, which are deviations from the center position of the probe ball of the probe 8 with respect to the center of the main spindle 7, are calculated based on the initial measurements before and after reversal. The initial measurements before reversal are obtained by measuring an initial measurement object at the first reference angle and the second reference angle, with a predetermined measurement angle set as the first reference angle and a measurement angle perpendicular to the first reference angle set as the second reference angle.The initial measurement values ​​after inversion are obtained by measuring the initial object at a measurement angle that differs by 180° from the first reference measurement angle and at a measurement angle that differs by 180° from the second reference measurement angle. Additionally, the values ​​17 of the offset displacement magnitude during inspection are calculated based on the inspection measurement results before inversion and the inspection measurement results after inversion. The inspection measurement results before inversion are obtained by measuring an object during an inspection at the first reference measurement angle and the second reference measurement angle. The inspection measurement results after inversion are obtained by measuring the object during an inspection at the measurement angle that differs by 180° from the first reference measurement angle and at the measurement angle that differs by 180° from the second reference measurement angle.Furthermore, the compensation value error estimation amplitudes 18, which are the errors of the compensation values ​​of the probe 8, are calculated based on the initial values ​​16 of the offset displacement amplitude and the values ​​17 of the offset displacement amplitude during verification. Therefore, it is possible to perform a calibration of the probe 8 only when necessary according to the calculated compensation value error estimation amplitudes 18, and the frequency of the probe 8 calibration activity can be minimized without compromising accuracy. Moreover, it is not necessary to set up a calibration reference, such as the reference sphere 9, for each verification. Similarly, a smaller number of reversals of the main spindle 7 are required. Therefore, the working time for the calibration activity can be reduced.

[0066] It should be noted that the compensation value verification system and the compensation value verification method for the probe according to the invention are not limited to the aspects of the embodiments described above and can be modified appropriately if necessary without departing from the spirit of the invention.

[0067] For example, in the embodiments described above, the compensation value verification system is applied to a three-axis machining center, but the invention is applicable to other types of machine tools. For example, instead of a machining center, the machine tool could be a lathe, a multitasking machine, or a grinding machine. Furthermore, the number of axes is not limited to three. Thus, for example, a machine that has a rotatable and pivotable table and rotates the main spindle head around the axis in the front-back direction will not cause any problems.

[0068] In addition, although a reference sphere is used in the above embodiments, a cylindrical reference that can measure an outer circumferential area and a ring gauge that can measure an inner circumferential area can be used as a calibration reference.

[0069] Furthermore, the measuring point to be measured with the probe when the offset displacement magnitude value is calculated during verification may be the same or different from the measuring point to be measured when the initial value of the offset displacement magnitude is calculated.

[0070] Furthermore, the object being measured during a check, which is used when calculating the offset displacement extent value during a check, can be the same or different from the initial object being measured, which is used when calculating the initial offset displacement extent value. In the embodiment above, the side face of the table is taken as an example of both the initial and the object being measured during a check, but the initial and the object being measured during a check can be a section of the machine tool other than the table, or a clamping device or workpiece mounted on the table. However, it is necessary to perform the measurement when calculating the offset displacement extent value during a check and the measurement when calculating the initial offset displacement extent value at the same measuring angle.

[0071] Furthermore, in the embodiments described above, the temperature information from at least one area of ​​the machine tool and the surrounding area, the time elapsed since the previous verification measure, and the count of the number of probe measurements are presented as the verification measurement application condition parameters. However, for example, the movement range of the feed axis, the number of reversals of the feed axis, a cutting distance, and the number of workpieces to be machined can be used. It should be noted that the movement range of the feed axes can, for example, be expressed as the movement distance of a workpiece.

[0072] Additionally, in the embodiments described above, the first reference measurement angle is set to 0° and the second reference measurement angle is set to 90°. However, as long as both reference measurement angles are perpendicular to each other, the first and second reference measurement angles can be freely adjusted. Furthermore, if the angle required for verification is only in a predetermined direction, only one reference measurement angle is necessary. For example, if the angle required for verification is only in the X-axis direction, the initial value of the offset displacement magnitude and the value of the offset displacement magnitude during verification can be calculated only at 0°.

[0073] It is explicitly stated that all features disclosed in the description and / or claims are intended to be disclosed separately and independently of one another for the purpose of the original disclosure and for the purpose of limiting the claimed invention, irrespective of the combination of features in the embodiments and / or claims. It is explicitly stated that all ranges of values ​​or specifications of groups of units disclose every possible intermediate value or unit for the purpose of the original disclosure and for the purpose of limiting the claimed invention, in particular as limits of ranges of values. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2016 - 083 729 A [0003, 0005] JP 2020 - 196 051 A [0004, 0006]

Claims

A system for checking a compensation value of a probe (8) that checks an error in a compensation value of a probe (8) mounted on a main spindle (7) in a machine tool (1), wherein the machine tool (1) has translation axes with three or more axes and the main spindle (7) rotatable with a tool mounted thereon, wherein an angle between a stepping direction of the main spindle (7) on which the probe (8) is mounted and a contact direction is set as a measuring angle, and the contact direction is a direction in which the probe (8) is brought into contact with a predetermined measuring object by a movement of the main spindle (7) in a plane perpendicular to an axis line of the main spindle, the measuring object can be measured with the probe at a plurality of measuring angles, a predetermined measuring angle is set as a first reference measuring angle,and the verification system of the compensation value of the probe comprises: an initial offset value estimation unit (11) that calculates an initial value of an offset displacement amount as a deviation of a center position of a stylus ball of the probe (8) with respect to a center of the main spindle (7) based on an initial measurement result before turning over and an initial measurement result after turning over, wherein the initial measurement result before turning over is obtained by measuring an initial measurement object at the first reference measurement angle, and the initial measurement result after turning over is obtained by measuring the initial measurement object at a measurement angle different by 180° from the first reference measurement angle; an offset value during verification estimation unit (13) that calculates a value of an offset displacement amount during verification based on a verification measurement result before turning over and a Verification measurement result calculated after turning,wherein the inspection measurement result before turning is obtained by measuring a measurement object during inspection at the first reference measurement angle, and the inspection measurement result after turning is obtained by measuring the measurement object during inspection at the measurement angle different by 180° from the first reference measurement angle; and a compensation value error estimation unit (14) that estimates an error of a compensation value of the probe (8) based on the initial value of the offset shift amount and the value of the offset shift amount during inspection. A compensation value checking system of a probe (8) according to claim 1, wherein the initial offset value estimation unit (11) obtains the initial measurement result after inversion by changing the indexing direction of the main spindle (7) by 180° while keeping the contact direction unchanged for obtaining the initial measurement result before inversion. A compensation value checking system of a probe (8) according to claim 1, wherein the initial measurement object is an annular, spherical, or cylindrical calibration reference, and the initial offset value estimation unit (11) obtains the initial measurement result-after-inversion by changing the contact direction by 180° while the indexing direction of the main spindle (7) for obtaining the initial measurement result-before-inversion remains unchanged. A verification system of a compensation value of a probe (8) according to one of claims 1 to 3, wherein a measurement angle perpendicular to the first reference measurement angle is set as a second reference measurement angle, the initial offset value estimation unit (11) calculates an initial value of the offset shift amount with respect to the second reference measurement angle based on a measurement result at the second reference measurement angle and a measurement result at a measurement angle different by 180° from the second reference measurement angle, and the offset value-during-verification estimation unit (13) calculates the value of the offset shift amount-during-verification based on a measurement result at the second reference measurement angle and a measurement result at the measurement angle different by 180° from the second reference measurement angle. A compensation value verification method for verifying an error in a compensation value of a probe (8) in a machine tool (1), wherein the machine tool (1) has translation axes with three or more axes and a main spindle (7) rotatable with a tool mounted thereon, wherein an angle between a stepping direction of the main spindle (7) on which the probe (8) is mounted and a contact direction is set as a measurement angle, the contact direction is a direction in which the probe (8) is brought into contact with a predetermined measurement object by a movement of the main spindle (7) in a plane perpendicular to an axis line of the main spindle (7), the measurement object can be measured with the probe at a plurality of the measurement angles, a predetermined measurement angle is set as a first reference measurement angle,and the compensation value verification method comprises: a first step of calculating an initial value of an offset displacement amount as a deviation of a center position of a stylus ball of the probe (8) with respect to a center of the main spindle (7) based on an initial measurement result before turning and an initial measurement result after turning, wherein the initial measurement result before turning is obtained by measuring an initial measurement object at a first reference measurement angle, and the initial measurement result after turning is obtained by measuring the initial measurement object at a measurement angle different by 180° from the first reference measurement angle; a second step of calculating a value of the offset displacement amount during verification based on a verification measurement result before turning and a verification measurement result after turning,wherein the verification measurement result before turning is obtained by measuring a measurement object during verification at the first reference measurement angle, and the verification measurement result after turning is obtained by measuring the measurement object during verification at the measurement angle different by 180° from the first reference measurement angle; and a third step of estimating an error of a compensation value of the probe (8) based on the initial value of the offset shift amount and the value of the offset shift amount during verification.

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