ERROR IDENTIFICATION METHOD OF MACHINE TOOL AND ERROR IDENTIFICATION SYSTEM OF THE SAME

Abstract

An error identification method includes a tool sensor position acquisition stage, a reference block position acquisition stage, a relative position calculation stage, a reference tool position acquisition stage, a position measurement sensor measurement stage, a length compensation value calculation stage, a diameter compensation value acquisition stage, a position measurement stage, a position compensation stage, and a geometric error identification stage. The diameter compensation value acquisition stage acquires a radial direction compensation value of the position measurement sensor with the measured jig. The position measurement stage indexes the rotation axis to a plurality of any given angles and measures respective positions of the measured jig. The position compensation stage compensates the position measurement value at the position measurement stage using the length direction compensation value and the radial direction compensation value. The geometric error identification stage identifies the geometric error from the plurality of position measurement values.

Claims

1. An error identification method for measuring a position of a measured jig in a three-dimensional space and identifying a geometric error in a machine tool from a value of the measured position, in which the measured jig is secured on a table by a position measurement sensor installed to a main spindle in the machine tool, the machine tool including three or more translational axes, one or more rotation axes, the rotatable main spindle to which a tool is to be installed, the table, and a control device configured to control the respective translational axes, rotation axis, and main spindle, the error identification method comprising: a tool sensor position acquisition stage of installing a reference tool for a length reference of the tool to the main spindle and acquiring a sensing position of a distal end of the reference tool with a tool sensor; a reference block position acquisition stage of acquiring positions of the translational axes when the reference tool installed to the main spindle is directly or indirectly brought into contact with a reference block disposed at the tool sensor side; a relative position calculation stage of calculating a relative position of the reference block with respect to the sensing position from the sensing position acquired in the tool sensor position acquisition stage and the positions of the translational axes acquired in the reference block position acquisition stage; a reference tool position acquisition stage of installing the reference tool to the main spindle and acquiring a reference tool position with the tool sensor, the reference tool position being a distal end position of the reference tool; a position measurement sensor measurement stage of installing the position measurement sensor to the main spindle and measuring a position of the reference block with the position measurement sensor; a length compensation value calculation stage of calculating a length direction compensation value of the position measurement sensor from the reference tool position acquired in the reference tool position acquisition stage, the position of the reference block measured in the position measurement sensor measurement stage, the relative position calculated in the relative position calculation stage, and the length of the reference tool; a diameter compensation value acquisition stage of acquiring a radial direction compensation value of the position measurement sensor with the measured jig; a position measurement stage of indexing the rotation axis to a plurality of any given angles and measuring respective positions of the measured jig by the position measurement sensor; a position compensation stage of compensating the value of the measured position at the position measurement stage using the length direction compensation value and the radial direction compensation value; and a geometric error identification stage of identifying the geometric error from the plurality of the value of the measured position compensated in the position compensation stage.

2. The error identification method according to claim 1, wherein the tool sensor position acquisition stage to the relative position calculation stage are configured to be executed once, the reference tool position acquisition stage to the geometric error identification stage being configured to be executed several times.

3. The error identification method according to claim 1, wherein the positions measured by the position measurement sensor are positions of the translational axes when the position measurement sensor senses a contact with measurement object.

4. The error identification method according to claim 1, wherein the positions measured by the tool sensor are positions of the translational axes when the tool installed to the main spindle moves in the translational axes and the tool sensor senses a contact with the tool or passing of the tool.

5. The error identification method according to claim 1, wherein the measured jig has a spherical shape.

6. The error identification method according to claim 5, wherein the diameter value acquisition stage includes measuring an initial position of the measured jig by the position measurement sensor, the diameter compensation value acquisition stage includes acquiring a compensation value of the position measurement sensor in radial direction.

7. An error identification system for measuring a position of a measured jig in a three-dimensional space and identifying a geometric error in a machine tool from a value of the measured position, in which the measured jig is secured on a table by a position measurement sensor installed to a main spindle in the machine tool, the machine tool including three or more translational axes, one or more rotation axes, the rotatable main spindle to which a tool is to be installed, the table, and a control device configured to control the respective translational axes, rotation axis, and main spindle, the error identification system comprising: a reference tool for a length reference of the tool; a tool sensor configured to detect a distal end position of the reference tool installed to the main spindle; a reference block installed to the tool sensor side; a tool sensor position acquisition unit configured to move the reference tool installed to the main spindle in the translational axes and acquire and store a sensing position of the distal end of the reference tool with the tool sensor; a reference block position acquisition unit configured to a move the reference tool installed to the main spindle in the translational axes to directly or indirectly bring the reference tool into contact with the reference block, the reference block position acquisition unit being configured to acquire and store positions of the translational axes at the contact; a relative position calculation unit configured to calculate and store a relative position of the reference block with respect to the sensing position from the sensing position acquired in the tool sensor position acquisition unit and the positions of the translational axes acquired in the reference block position acquisition unit; a reference tool position acquisition unit configured to move the reference tool installed to the main spindle in the translational axes, the reference tool position acquisition unit being configured to acquire and store a reference tool position with the tool sensor, the reference tool position being the distal end position of the reference tool; a measurement position acquisition unit configured to measure and store a position of the reference block with the position measurement sensor installed to the main spindle; a length compensation value calculation unit configured to calculate and store a length direction compensation value of the position measurement sensor from the reference tool position acquired in the reference tool position acquisition unit, the position of the reference block acquired in the measurement position acquisition unit, the relative position acquired in the relative position calculation unit, and the length of the reference tool; a diameter compensation value acquisition unit configured to acquire and store a radial direction compensation value of the position measurement sensor with the measured jig; a position compensation unit configured to index the rotation axis to a plurality of any given angles and compensate and store the respective values of the measured position of the measured jig measured by the position measurement sensor using the length direction compensation value and the radial direction compensation value; and a geometric error identification unit configured to identify the geometric error from the plurality of the values of the measured position compensated in the position compensation unit.

8. An error identification method for measuring a position of a measured jig in a three-dimensional space and identifying a geometric error in a machine tool from a value of the measured position, in which the measured jig is secured on a table by a position measurement sensor installed to a main spindle in the machine tool, the machine tool including three or more translational axes, one or more rotation axes, the rotatable main spindle to which a tool is to be installed, the table, and a control device configured to control the respective translational axes, rotation axis, and main spindle, the error identification method comprising: a tool sensor position acquisition stage of installing a reference tool for a length reference of the tool to the main spindle and acquiring a sensing position of a distal end of the reference tool with a tool sensor; a reference tool measurement position acquisition stage of acquiring any given tool measurement position with the reference tool installed to the main spindle; a position measurement sensor measurement position acquisition stage of acquiring any given sensor measurement position with the position measurement sensor installed to the main spindle; a position measurement sensor length calculation stage of acquiring a difference between the tool measurement position and the sensor measurement position and acquiring a length of the position measurement sensor based on the difference and the length of the reference tool; a first reference block position acquisition stage of measuring a position of a reference block disposed at the tool sensor side with the position measurement sensor installed to the main spindle; a relative position calculation stage of calculating a relative position of the reference block with respect to the sensing position from the sensing position acquired in the tool sensor position acquisition stage, the position of the reference block acquired in the first reference block position acquisition stage, the length of the position measurement sensor calculated in the position measurement sensor length calculation stage, and the length of the reference tool; a reference tool position acquisition stage of installing the reference tool to the main spindle and acquiring a reference tool position with the tool sensor, the reference tool position being a distal end position of the reference tool; a second reference block position acquisition stage of installing the position measurement sensor to the main spindle and measuring a position of the reference block with the position measurement sensor; a length compensation value calculation stage of calculating a length direction compensation value of the position measurement sensor from the reference tool position acquired in the reference tool position acquisition stage, the position of the reference block measured in the second reference block position acquisition stage, the relative position calculated in the relative position calculation stage, and the length of the reference tool; a diameter compensation value acquisition stage of acquiring a radial direction compensation value of the position measurement sensor with the measured jig; a position measurement stage of indexing the rotation axis to a plurality of any given angles and measuring respective positions of the measured jig by the position measurement sensor; a position compensation stage of compensating the values of the measured position at the position measurement stage using the length direction compensation value and the radial direction compensation value; and a geometric error identification stage of identifying the geometric error from the plurality of the values of the measured position compensated in the position compensation stage.

9. The error identification method according to claim 8, wherein the tool sensor position acquisition stage to the relative position calculation stage are configured to be executed once, the reference tool position acquisition stage to the geometric error identification stage being configured to be executed several times.

10. The error identification method according to claim 8, wherein the positions measured by the position measurement sensor are positions of the translational axes when the position measurement sensor senses a contact with a measurement object.

11. The error identification method according to claim 8, wherein the positions measured by the tool sensor are positions of the translational axes when the tool installed to the main spindle moves in the translational axes and the tool sensor senses a contact with the tool or passing of the tool.

12. The error identification method according to claim 8, wherein the measured jig has a spherical shape.

13. The error identification method according to claim 12, wherein the diameter compensation value acquisition stage includes measuring an initial position of the measured jig by the position measurement sensor, the diameter compensation value acquisition stage including acquiring a compensation value of the position measurement sensor in a radial direction.

14. An error identification system for measuring a position of a measured jig in a three-dimensional space and identifying a geometric error in a machine tool from a value of the measured position, in which the measured jig is secured on a table by a position measurement sensor installed to a main spindle in the machine tool, the machine tool including three or more translational axes, one or more rotation axes, the rotatable main spindle to which a tool is to be installed, the table, and a control device configured to control the respective translational axes, rotation axis, and main spindle, the error identification system comprising: a reference tool for a length reference of the tool; a tool sensor configured to detect a distal end position of the reference tool installed to the main spindle; a reference block installed to the tool sensor side; a tool sensor position acquisition unit configured to move the reference tool installed to the main spindle in the translational axes and acquire and store a sensing position of the distal end of the reference tool with the tool sensor; a reference tool measurement position acquisition unit configured to acquire and store any given tool measurement position with the reference tool installed to the main spindle; a position measurement sensor measurement position acquisition unit configured to acquire and store any given sensor measurement position with the position measurement sensor installed to the main spindle; a position measurement sensor length calculation unit configured to acquire a difference between the tool measurement position and the sensor measurement position, the position measurement sensor length calculation unit being configured to calculate and store a length of the position measurement sensor based on the difference and the length of the reference tool; a first reference block position acquisition unit configured to measure and store a position of the reference block with the position measurement sensor installed to the main spindle; a relative position calculation unit configured to calculate and store a relative position of the reference block with respect to the sensing position from the sensing position acquired in the tool sensor position acquisition unit, the position of the reference block acquired in the first reference block position acquisition unit, the length of the position measurement sensor calculated in the position measurement sensor length calculation unit, and the length of the reference tool; a reference tool position acquisition unit configured to move the reference tool installed to the main spindle in the translational axes, the reference tool position acquisition unit being configured to acquire and store a reference tool position with the tool sensor, the reference tool position being the distal end position of the reference tool; a second reference block position acquisition unit configured to measure and store a position of the reference block with the position measurement sensor installed to the main spindle; a length compensation value calculation unit configured to calculate and store a length direction compensation value of the position measurement sensor from the reference tool position acquired in the reference tool position acquisition unit, the position of the reference block acquired in the second reference block position acquisition unit, the relative position calculated in the relative position calculation unit, and the length of the reference tool; a diameter compensation value acquisition unit configured to acquire and store a radial direction compensation value of the position measurement sensor with the measured jig; a position compensation unit configured to index the rotation axis to a plurality of any given angles and compensate and store the respective values of the measured position of the measured jig measured by the position measurement sensor using the length direction compensation value and the radial direction compensation value; and a geometric error identification unit configured to identify the geometric error from the plurality of the values of the measured position compensated in the position compensation unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] FIG. 1 is a schematic diagram of a machining center.

[0039] FIG. 2 is a schematic diagram illustrating one example of a laser sensor.

[0040] FIG. 3 is a schematic diagram illustrating a modification example of the laser sensor.

[0041] FIG. 4 is a schematic diagram of the laser sensor of the disclosure mounted to the machining center.

[0042] FIG. 5 is a schematic diagram illustrating one example of a touch sensor.

[0043] FIG. 6 is a schematic diagram illustrating a modification example of the touch sensor.

[0044] FIG. 7 is a flowchart for measurement preparation work.

[0045] FIG. 8 is an explanatory view for Step SR1 in the measurement preparation work.

[0046] FIG. 9 is an explanatory view for Step SR2 in the measurement preparation work.

[0047] FIG. 10 is an explanatory view for Step S1-2 for an error identification method of the disclosure.

[0048] FIG. 11 is a flowchart for the error identification method of the disclosure.

[0049] FIG. 12 is a schematic diagram of a touch trigger probe and a target ball.

[0050] FIG. 13 is a flowchart for S1 in the error identification method of the disclosure.

[0051] FIG. 14 is a flowchart for S2 in the error identification method of the disclosure.

[0052] FIG. 15 is a schematic diagram of a relationship between a measurement value at an initial position measurement of the target ball of the disclosure and a sphere center.

[0053] FIG. 16 is a schematic diagram of a relationship between the measurement values and touch trigger probe diameter compensation values at the initial position measurement of the target hall of the disclosure.

[0054] FIG. 17 is a flowchart for measurement preparation work of a modification example.

[0055] FIG. 18 is an explanatory view for Step SQ2 in the measurement preparation work of the modification example.

[0056] FIG. 19 is an explanatory view for Step SQ3 in the measurement preparation work of the modification example.

DETAILED DESCRIPTION

[0057] The following describes embodiments of the disclosure based on the drawings.

[0058] FIG. 1 is a schematic diagram of a machining center, which is one configuration of a machine tool, that includes three translational axes orthogonal to one another and two rotation axes orthogonal to one another. A motion of two degrees of freedom for translation of a main spindle 2 in an X-axis and a Z-axis, which are the translational axes and are orthogonal to one another, is possible with respect to a bed 1. A motion of one degree of freedom for rotation of a table 3 in a C-axis, which is the rotation axis, is possible with respect to a cradle 4. A motion of one degree of freedom for rotation of the cradle 4 in an A-axis, which is the rotation axis orthogonal to the C-axis, is possible with respect to a trunnion 5. A motion of one degree of freedom for translation of the trunnion 5 in a Y-axis, which is the translational axis and orthogonal to the X-axis and the Z-axis, is possible with respect to the bed 1. Accordingly, the motions of the three degrees of freedom for translation and the two degrees of freedom for rotation of the main spindle 2 are possible with respect to the table 3. Servo motors, which are controlled by a numerical control unit (not illustrated), drive respective feed axes. A workpiece is secured to the table 3, a tool is installed to the main spindle 2 and rotated, and a relative position and a relative posture between the workpiece and the tool are controlled, thus ensuring processes of the workpiece.

[0059] A machine related to the disclosure is not limited to the machining center but may be a machine tool such as a lathe, a multitasking machine, and a grinder. The number of axes is not limited to five axes but may be four axes and six axes. Further, the mechanism is not limited to one that the table 3 has the two degrees of freedom for rotation or more in the rotation axes, but a mechanism where the min spindle 2 has the two degrees of freedom for rotation or more and a mechanism where the main spindle 2 and the table 3 each have the one degree of freedom for rotation or more may be employed.

[0060] FIG. 2 is a schematic diagram of a laser sensor 40 as one example of a tool sensor of the disclosure. While the laser sensor 40 includes a light emitting portion 11, a light receiving portion 12, and a base portion 13, the laser sensor 40 here includes a reference block 42 between the light emitting portion 11 and the light receiving portion 12. The light emitting portion 11, the light receiving portion 12, and the reference block 42 are each secured to the base portion 13. Note that, as illustrated in FIG. 3, the reference block 42 may he separately disposed near the laser sensor 40.

[0061] As illustrated in FIG. 4, the laser sensor 40 is mounted to the trunnion 5 of the machining center in FIG. 1 via a sensor mounting block 41.

[0062] With the laser sensor 40, the light emitting portion 11 outputs laser light 14, and the light receiving portion 12 receives the laser light 14, When the laser light 14 is obstructed by a substance and therefore a light-receiving rate becomes a certain rate or less, the laser sensor 40 generates a signal. A control device (not illustrated) receives this signal and determines positions of feed axes at a time point of a reception of the signal or a time point considering the delay as measurement values. For example, the tool is mounted to the main spindle 2 and is caused to approach a laser light in the Z-axis to acquire a Z-axis position Zt at a time point of the tool cutting off the laser light. A Z-axis position Zb of a reference tool is similarly acquired. A length, of the tool with respect to the reference tool can be acquired from a difference between Zt and Zb. A subtraction of a length Td of the reference tool as well can acquire an absolute length of the tool.

[0063] FIG. 5 is a schematic diagram of a touch sensor 50 as one example of the tool sensor of the disclosure. The touch sensor 50 includes a base portion 51, a touch sensor portion 52, and a reference block 53. The touch sensor portion 52 and the reference block 53 are secured on the base portion 51. The touch sensor 50 is mourned to the trunnion 5 of the machining center in FIG. 1 similar to the laser sensor 40. As illustrated in FIG. 6, the reference block 53 may be separately disposed near the touch sensor 50.

[0064] The following describes an error identification method and an error identification system in the case of using the laser sensor 40 as the tool sensor (corresponding to claims 1 to 7). It should be noted that the case of the use of the touch sensor 50 differs only in a sensing method and is substantially identical.

[0065] First, the following describes a procedure for measurement preparation work based on a flowchart in FIG. 7. The measurement preparation work needs to be performed in advance before a measurement of a target ball (measured jig) and geometric error identification by a touch trigger probe as a position measurement sensor are made, which will be described later. It is only necessary to perform the measurement preparation work at a low frequency in the cases such as deterioration of a laser sensor and exchange due to a failure of the laser sensor.

[0066] At Step SR1, as illustrated in FIG. 8, a reference tool 8 is installed to the main spindle 2 and is measured by the laser sensor 40. Here, the Z-axis is moved such that the reference tool 8 approaches the laser light 14 and the Z-axis position at a time point of a distal end of the reference tool 8 cutting off the laser light 14 and a light-receiving rate being a threshold or less or a time point considering a signal delay is acquired. A storage unit (not illustrated) in the control device stores the acquired Z-axis position Z1 (a tool sensor position acquisition stage and tool sensor position acquisition means. Here, the control device functions as means that performs respective stages of the disclosure). The storage unit also preliminarily stores the length Td of the reference tool 8. Here, a reference tool distal end position Z1′ may be calculated from Z1 and Td (=Z1−Td) and stored.

[0067] Next, at Step SR2, the position of the reference block 42 is acquired using the reference tool 8. Here, as illustrated in FIG. 9, with the reference tool 8 installed to the main spindle 2, the reference tool 8 is brought into contact with the reference block 42 via a block gauge 43 to acquire the Z-axis position Zb at the time. The storage unit (not illustrated) in the control device stores a value Zb′ found by subtracting a thickness Hb of the block gauge 43 (=Zb−Hb) (a reference block position acquisition stage and reference block position acquisition means). Here, a reference block top surface position Zb″ may be calculated and stored also using Td (=Zb−Hb−Td). The block gauge 43 may be a block with already-known thickness dimension or a similar block.

[0068] At Step SR3, a relative position dZb (=Z1−Zb′) of the reference block 42 with respect to a sensing position of the laser sensor 40 is calculated from the Z-axis position Z1, which is stored at Step SR1, and the Z-axis position Zb′, which is stored at Step SR2, and is stored in the storage unit in the control device (a relative position calculation stage and relative position calculation means). Here, the storage unit also stores the block gauge thickness Hb, and dZb may be calculated from Z1, Zb, and Hb (dZb=Z1−Zb−Hb). Note that, the storage of Z1′ and Zb″ allows the calculation by dZb=Z1′−Zb″.

[0069] The following describes a procedure of the geometric error identification of the disclosure based on a flowchart in FIG. 11.

[0070] First, at Step S1, a calibration of a length compensation value of a touch trigger probe 30 is performed. The details will be described later.

[0071] Next, at Step S2, as illustrated in FIG. 12, an initial position of a target ball 32 secured on the table 3 is measured. A diameter compensation value calibration of the touch trigger probe 30 is performed with the target ball 32 (a diameter compensation value acquisition stage and diameter compensation value acquisition means). The details will be described later.

[0072] At Step S3, respective expected center positions of the target ball and touch trigger probe distal end positions after a movement by a rotation and an inclination of the rotation axes under preset measurement conditions (such as index angles of the respective rotation axes) are calculated using the target hall initial position measured at Step S2 and the length of the touch trigger probe 30 (length compensation value) (a position measurement stage and position compensation means).

[0073] Furthermore, three-dimensional position coordinate values calculated in the respective index angles are set as instruction values of the respective X-, Y-, and Z-axes. An instruction value list that sets the respective index angles as the instruction values of the rotation axes is created.

[0074] At Step S4 the touch trigger probe 30 is brought into contact with a surface of the target ball 32 at four points or more on the basis of the respective feed axis instruction values in the instruction value list created at Step S3. The compensation is performed using the length compensation value acquired at Step S1 and the diameter compensation value acquired at Step S2 to acquire the center position and the diameter of the target ball 32 to position compensation stage and position compensation means). Here, the use of a diameter calibration value of the target ball 32 preliminarily measured by a coordinate measuring machine or a similar machine allows acquiring the center position of the target ball 32 through the measurement at the three-point contact.

[0075] At Step S5, the identification calculation of the geometric error in the machine is performed on the basis of the acquired center position coordinate values of the target ball 32 and the instruction values at the respective positions (a geometric error identification stage and geometric error identification means). The details will be described later.

[0076] Here, the following describes a length compensation value calibration at Step S1 based on a flowchart in FIG. 13.

[0077] First, at Step S1-1, similar to Step SR1 described in FIG. 8, the reference tool 8 is installed to the main spindle 2, and the laser sensor 40 performs the measurement. The storage unit in the control, device (not illustrated) stores a Z-axis position Zd (a reference tool position acquisition stage and reference tool position acquisition means). Using Td, Zd′=Zd−Td may be stored.

[0078] Next, at Step S1-2, as illustrated in FIG. 10, the touch trigger probe 30 is installed to the main spindle 2 to measure the reference block 4 by the touch trigger probe 30. Here, the Z-axis is moved such that the touch trigger probe 30 approaches the reference block 42, and a Z-axis position Zp at a time point of a stylus at a distal end of the touch trigger probe 30 contacting the reference block 42 and the touch trigger probe 30 transmitting a trigger signal or a time point considering the signal delay is acquired. The storage unit in the control device (not illustrated) stores the acquired Z-axis position Zp to position measurement sensor measurement stage and measurement position acquisition means).

[0079] At Step S1-3, the length of the touch trigger probe 30 in contact, which is the length direction compensation value of the touch trigger probe 30, is calculated. That is, the length direction, compensation value (length in contact) Tp (=Zp−Zd+dZb+Td) is acquired from Zd stored at Step S1-1, Zp stored at Step S1-2, and the relative position dZb of the reference block 42 and the reference tool length Td, which are stored in the storage unit in the control device. The storage unit stores the length direction compensation value Tp (a length compensation value calculation stage and length compensation value calculation means). Here, Tp (=Zp−Zd′−dZb) may be acquired from Zd′, Zp, and dZb.

[0080] The following describes details of Step S2 based on a flowchart in FIG. 14.

[0081] First, before executing Step S2, as illustrated in FIG. 12, the touch trigger probe 30 with a stylus ball at a distal end is mounted to the main spindle 2 of the five-axis-control machining center, and the target ball 32 is installed and secured on the table 3.

[0082] At Step S2-1, the touch trigger probe 30 is moved in the Z-direction to bring the touch trigger probe 30 into contact with a site near an apex in the +Z-direction of the target ball 32, and a Z-axis coordinate value zm1 in contact is stored.

[0083] Next, at Step S2-2, a temporary Z-carter position zt is acquired from the following formula 1 using a diameter d0 of the target ball 32 preliminarily measured by the coordinate measuring machine or a similar machine and a preliminarily acquired touch trigger probe diameter compensation value t1.

zt=zm1−d0/2−t1  [Formula 1]

[0084] At Step S2-3, the main spindle 2 is indexed to 0°, and the touch trigger probe 30 is moved to a site near the apex on the +X-side of the target ball 32. After that, the touch trigger probe 30 is moved in the −X-direction to bring the touch trigger probe 30 into contact with a site near the apex on the +X-side of the target hall 32, and an X-axis coordinate value xml in contact is stored.

[0085] At Step S2-4, the main spindle 2 is indexed to 180° such that the touch trigger probe 30 contacts the target ball 32 at the point identical to the point on the stylus ball in contact at Step S2-3. After the touch trigger probe 30 is moved to the site near the apex on the −X-side of the target ball 32, the touch trigger probe 30 is moved in the +X-direction to bring the touch trigger probe 30 into contact with the site near the apex on the X-side of the target ball 32, and an X-axis coordinate value xp1 in contact in stored.

[0086] At Step S2-5, an X-center position xo is acquired from the following formula 2 using the stored xm1 and xp1.

[0087] Here, at Step S2-3 and Step S2-4 as illustrated in FIG. 15, the touch trigger probe 30 contacts the target ball 32 at the identical point on the stylus ball of the touch trigger probe 30. This ensures accurately acquiring xo without being affected by a difference in property due to a difference in the contact direction of the touch trigger probe 30 and a swing of the touch trigger probe 30 and the main spindle 2.

xo=(xp1+xm1)/2  [Formula 2]

[0088] At Step S2-6, similar to the above-described operations, the main spindle 2 is indexed to 270° and the touch trigger probe 30 is moved to the site near the apex on the +Y-side of the target ball 32. After that, the touch trigger probe 30 is moved in the −Y-direction to bring the touch trigger probe 30 into contact with the site near the apex on the +Y-side of the target hall 32, and a Y-axis coordinate value pill in contact is stored.

[0089] At Step S2-7, similar to the above-described operations, the main spindle 2 is indexed to 90° and the touch trigger probe 30 is moved to the site near the apex On the −Y-side of the target ball 32. After that, the touch trigger probe 30 is moved in the +Y-direction to bring the touch trigger probe 30 into contact with the site near the apex on the −Y-side of the target ball 32, and a Y-axis coordinate value yp1 in contact is stored.

[0090] At Step S2-8, a Y-center position yo is acquired from the following formula 3 using the stored ym1 and yp1.

yo=(yp1+ym1)/2  [Formula 3]

[0091] At Step S2-9, similar to Step S2-3, the main spindle 2 is indexed to 0°. The apex on the +X-side of the target hall 32 is measured to update the X-axis coordinate value xm1.

[0092] At Step S2-10, similar to Step S2-4, the main spindle 2 is indexed to 180°. The apex on the −X-side of the target ball 32 is measured to update the X-axis coordinate value xp1.

[0093] At Step S2-11, the X-center position xo is calculated again from the formula 2 using the updated xm1 and xp1.

[0094] At Step S2-12, the main spindle 2 is indexed to 0° (an angle indexed at the usual measurement).

[0095] At Step S2-13, the touch trigger probe 30 is positioned at the X-coordinate xo, the Y-coordinate yo, and the right above the apex of the target hall 32 in the Z-axis direction. The touch trigger probe 30 in moved in the −Z-direction to bring the touch trigger probe 30 into contact with a site near the apex in the positive direction of +Z of the target ball 32 and a Z-axis coordinate value zm2 in contact is stored.

[0096] At Step S2-14, a Z-center position zo is acquired from the following formula 4.

zo=zm2−d0/2−t1  [Formula 4]

[0097] At Step S2-15, the touch trigger probe 30 is moved to the site near the apex on the +X-side of the target ball 32. After that, the touch trigger probe 30 is moved in the −X-direction to bring the touch trigger probe 30 into contact with the site near the apex on the +X-side of the target ball 32, and an X-axis coordinate value xm2 in contact is stored.

[0098] At Step S2-16, the touch trigger probe 30 is moved to the site near the apex on the −X-side of the target ball 32. After that, the touch trigger probe 30 is moved in the +X-direction to bring the touch trigger probe 30 into contact with the site near the apex on the −X-side of the target ball 32, and an X-axis coordinate value xp2 in contact is stored.

[0099] At Step S2-17, the touch trigger probe 30 is moved to the site near the apex on the +Y-side of the target hall 32. After that, the touch trigger probe 30 is moved in the −Y-direction to bring the touch trigger probe 30 into contact with the site near the apex on the +Y-side of the target ball 32, and a Y-axis coordinate value ym2 in contact is stored.

[0100] At Step S2-18, the touch trigger probe 30 is moved to the site near the apex on the −Y-side of the target ball 32. After that, the touch trigger probe 30 is moved in the +Y-direction to bring the touch trigger probe 30 into contact with the site hear the apex on the −Y-side of the target ball 32, and a Y-axis coordinate value yp2 in contact is stored.

[0101] At Step S2-19, contact touch trigger probe diameter compensation values tc1, tc2, tc3, and tc4 in the +X, −X, +Y, and −Y-directions are acquired using the following formula 5. Here, the main spindle center when the target ball 32 is positioned at the position (xo, yo) matches the target ball center. Therefore, as illustrated in FIG. 16, the respective compensation values can be acquired from a movement distance from the center, position and the target ball diameter.

tc1=x0−xp2−d0/2

tc2=xo−xm2+d0/2

tc3=yo−yp2−d0/2

tc4=yo−ym2+d0/2  [Formula 5]

[0102] As described above, at Step S2, the center position (xo, yo, zo) of the target ball 32 is measured together with the acquisition of the touch trigger probe diameter compensation values tc1, tc2, tc3, and tc4.

[0103] The touch trigger probe is moved toward the center of the target ball 32, such that the touch trigger probe is brought into contact with the target ball 32. Assume that the measurement values of the respective axes at any given point on the surface of the target ball 32 as (xs, ys, zs). Then, the following formula 6 can also be used to acquire touch trigger probe compensation values (tax, tay, taz) at the any given point.

tax=xo−xs−d0/2

tay=yo−ys+d0/2

taz=zo−zs+d0/2  [Formula 6]

[0104] Next, the following describes details of Step S5.

[0105] In one measurement condition, one of the rotation axes is secured and the other is indexed to a plurality of angles, and the center position of the target ball is measured. Difference vectors of the measurement values at the ball center position with respect to the instruction values under the measurement condition can be distributed to radial direction, axial direction, and tangent direction components of an index axis. These respective components can be approximated as Fourier series of a zero-order component (radius error), a first-order component (a center deviation), and a second-order component (elliptical shape), namely, an arc with error by, for example, least-square method.

[0106] A radial direction component dRr.sub.i, an axial direction component dRa.sub.i, and a radial direction component dRt.sub.i of the measurement values at a k-th index angle θ.sub.ijk of a j-th rotation axis under a measurement condition i can be expressed as the following formula 7.

dRr.sub.i=ra0.sub.i+ra1.sub.i*cos (θ.sub.ijk)+rb1.sub.i*cos (θ.sub.ijk)+ra2.sub.i cos (2θ.sub.ijk)+rb2.sub.i sin (2θ.sub.ijk)

dRa.sub.i=aa0.sub.i+aa1.sub.i*cos (θ.sub.ijk)+ab1.sub.i*cos (θ.sub.ijk)+aa2.sub.i cos (2θ.sub.ijk)+ab2.sub.i sin (2θ.sub.ijk)

dRt.sub.i=ta0.sub.i+ta1.sub.i*cos (θ.sub.ijk)+tb1.sub.i*cos (θ.sub.ijk)+ta2.sub.i cos (2θ.sub.ijk)+tb2.sub.i sin (2θ.sub.ijk)  [Formula 7]

[0107] As the geometric error in the five-axis-control machining center in FIG. 1, the squareness between the X and Y axes is denoted as dCyx, the squareness between the Y and Z axes as dAxz, the squareness between the Z and X axes as dBxz, the X-direction error of the C-axis center position as dXca, the offset error between the C and A axes as dYca, the angular offset error of the A-axis as dAca the squareness between the C and A axes as dBca, the Y-direction error of the A-axis center position as dYay, the Z-direction error of the A-axis center position as dZay, the squareness between the A and Z axes as dBay, and the squareness between the A and Y axes as dCay.

[0108] When a first measurement condition is determined as the A-axis of 0° and the C-axis of 0′ to 360°, a second measurement condition is determined as the C-axis of −90° and the A-axis of −90° to +90°, and a third measurement condition is determined as the A-axis of −90° and the C-axis of 0° to 180°, relationships between the respective coefficients in the formula 7 and the geometric errors are the following formula 8. Here, each of R.sub.1, R.sub.2, and R.sub.3 are distances from a rotational center to a ball center position on a plane where all the ball center positions instructed under the first, second and third measurement conditions are placed, namely, a radius of an arc trajectory. A modification of the formula 8 can acquire the respective geometric errors.

ra1.sub.1=−dXca−(dBca+dBay+dBxz)*H

rb1.sub.1=dYca+dYay−(dAca+dAxz)*H

rb2.sub.1=dCyx*R.sub.1/2

aa1.sub.1=dBca+dBay

ab1.sub.1=dAca

ra1.sub.2=−dYay

rb1.sub.2=dZay

rb2.sub.2=−dAxz*R.sub.2/2

aa1.sub.2=dCay

ab1.sub.2=−(dBay+dBxz)

rb2.sub.3=dBxz*R.sub.3/2  [Formula 8]

[0109] The error identification method and the error identification system with the above-described configuration allows the calibration of the length and diameter compensation values of the touch trigger probe 30 during a sequence of respective measurements for the geometric error identification. The need for hand work except for the preparation work in advance is eliminated. Accordingly, the preparation of additional jig or a similar preparation is not required ensuring, a reduction in a load of an operator of the machine—and reliably performing the calibration of the touch trigger probe 30 at the geometric error identification. This does not deteriorate the measurement accuracy of the touch trigger probe 30 even, if the state of the touch trigger probe 30 changes due to such as the heat displacement, ensuring highly accurately identifying the geometric error.

[0110] Further, the measurement system with the CCD camera or a similar system is not required, thus achieving a comparatively low price.

[0111] To acquire the reference block position, the configuration indirectly brings the reference tool into contact with the reference block using the block gauge. However, the reference tool may be directly brought into contact with the reference block without the block gauge.

[0112] Furthermore, the tool sensor position acquisition stage to the geometric error identification stage are executed once in the configuration. However, the tool sensor position acquisition stage to the relative position calculation stage may be executed once, and the reference tool position acquisition stage to the geometric error identification stage may be executed several times.

[0113] The following describes the error identification method and the error identification system corresponding to claims 8 to 14. It should be noted that since the configurations are identical to the above-described configurations other than the measurement preparation work, the following describes the measurement preparation work based on the flowchart in FIG. 17.

[0114] First, Step SQ1 is identical to Step SR1 in FIG. 7. That is, as illustrated in FIG. 8, the reference tool 8 is installed to the main spindle 2 and is measured by the laser sensor 40. Here, the Z-axis is moved such that the reference tool 8 approaches the laser light 14 and the Z-axis position at the time point of the distal end of the reference tool 8 cutting off the laser, light 14 and the light-receiving rate being the threshold or less or the time point considering the signal delay is acquired. The storage unit (not illustrated) in the control device stores the acquired Z-axis position Z1 (the tool sensor position acquisition stage and the tool sensor position acquisition means). The storage unit also preliminarily stores the length Td, of the reference tool 8.

[0115] Next, at Step SQ2, a position of any given reference surface such as the top surface of the table or the jig is acquired with the reference tool 8 (a reference tool measurements position acquisition stage and reference tool measurement position acquisition means). For example, as illustrated in FIG. 18, with the reference tool 8 installed to the to spindle 2, the reference tool 8 is brought into contact with the top surface of the table 3 via the block gauge 43 to acquire a Z-axis position Ztt at the time. The storage unit (not illustrated) in the control device stores a value Za′ found by subtracting the thickness Hb of the block gauge 43 from the Z-axis position Za (=Za−Hb), The block gauge 43 may not be a block gauge but may be a block with already-known thickness dimension or a similar block.

[0116] At Step SQ3, the touch trigger probe 30 is installed to the main spindle 2 to measure the position of the any given reference surface identical to Step SQ2 by the touch trigger probe 30 (a position measurement sensor measurement position acquisition stage and position measurement sensor measurement position acquisition means). For example, as illustrated in FIG. 19, the Z-axis is moved such that the touch trigger probe 30 approaches the top surface of the table 3. The Z-axis position Zp at the time point of the stylus of the touch trigger probe 30 contacting the top surface and the touch trigger probe 30 transmitting the trigger signal or the time point considering the signal delay is acquired. The storage unit (not illustrated) in the control device stores the acquired Z-axis position Zp.

[0117] At Step SQ4, the length of the touch trigger probe in contact is calculated. A touch trigger probe length in contact Tp (=Zq−Za+Td) is acquired from Za, which is stored at Step SQ2, Zq, which is stored at Step SQ3, and the reference tool length Td, and, the storage unit stores the touch trigger probe length in contact Tp (a position measurement sensor length calculation stage and position measurement sensor length calculation means).

[0118] At Step SQ5, the reference block 42 is measured by the touch trigger probe 30 (a first reference block position acquisition stage and first reference block position acquisition means). That is, as illustrated in FIG. 10, the Z-axis is moved such that the touch trigger probe 30 approaches the reference block 42, and the Z-axis position Zp at the time point of the stylus of the touch trigger probe 30 contacting the reference block 42 and the touch trigger probe 30 transmitting the trigger signal or the time point considering the signal delay is acquired. The storage unit in the control device (not illustrated) stores the acquired Z-axis position Zp.

[0119] At Step SQ6, the relative position dZb (=Z1−Td−Zp+Tp) of the reference, block 42 with respect to the laser sensor 40 is calculated from the Z-axis position Z1, which is stored at Step SQ1, the touch trigger probe 30 length in contact Tp, which is, calculated at Step SQ4, the Z-axis position Zp, which is stored at Step SQ5 and the reference tool length Td, and is stored in the storage unit in the control device (the relative position calculation stage and the relative position calculation means).

[0120] While the procedure of the geometric error identification after this is identical to the above-described configurations described in FIG. 11 to FIG. 16, Step S1-2 in FIG. 13 becomes a second reference block position acquisition stage and second reference block position acquisition means corresponding to claim 8 and claim 14.

[0121] Furthermore, in the modification example as well, the tool sensor position acquisition stage at Step SQ1 to the relative position calculation stage at Step SQ6 may be executed once, and the subsequent reference tool position acquisition stave to the geometric error identification stage may be executed several times.

[0122] It is explicitly stated that all features disclosed in the description and/or the claims are intended to be disclosed separately and independently from each other for the purpose of original disclosure as well as for the purpose of restricting the claimed invention independent of the composition of the features in the embodiments and/or the claims. It is explicitly stated that all value ranges or indications of groups of entities disclose every possible intermediate value or intermediate entity for the purpose of original disclosure as well as for the purpose of restricting the claimed invention, in particular as limits of value ranges.