Patent Application
20170297160
This application claims the benefit of Japanese Patent Application Numbers 2016-083860 filed on Apr. 19, 2016 and 2017-019723 filed on Feb. 6, 2017, the entirety of which is incorporated by reference.
The disclosure relates to a method that identifies a geometric error in a machine tool from a measurement result of a position of an object in the machine and a system that identifies the geometric error.
There is a geometric error between the respective axes such as an error in center position of the rotation axis (a displacement from an assumed position) and a tilt error of the rotation axes (squareness and parallelism between the axes) as a major factor of affecting motion accuracy of the five-axis-control machining center. For example, in the five-axis-control machining center in
The geometric errors deteriorate the motion accuracy of the machine, deteriorating process accuracy of the workpiece. In view of this, the geometric errors need to be reduced through adjustment but it is difficult to zero the geometric errors. Performing a control to compensate the geometric error makes highly-accurate processes possible.
Such compensation control requires measuring, or identifying the geometric error in the machine. The inventor has proposed a method to identify the geometric error in the machine as disclosed in Japanese Unexamined Patent Application Publication No. 2011-38902. In the method of the disclosure, a table is rotated and indexed at a plurality of angles in rotation axes. Respective center positions of a ball secured on the table are measured using a touch trigger probe mounted to a main spindle so that a geometric error in the machine is identified from the acquired measurement values.
The touch trigger probe includes a sensor that senses a contact with a measurement target. At the moment of sensing the contact, the sensor transmits a signal over, for example, infrared light and radio wave. A receiver coupled to a numeral value control unit acquires current positions of respective axes (skip values) at the moment of the reception of the signal or a time point considering the delay, and these values are determined as the measurement values.
However, the measurement by the touch trigger probe requires compensations of the acquired positions. This is because, since contact points of control points as references of the positions of the feed axes (X and Y-axes are a main spindle center and the Z-axis is a main spindle end surface) with the touch trigger probe differ from the positions of the feed axes when the touch trigger probe contacts the measurement target. For example, the X- and Y-axis directions are shifted by a radius of a stylus ball of the touch trigger probe. The shift occurs due to, for example, a displacement between the main spindle center and a core of the touch trigger probe, the delay of the signal in contact, and directional dependency of the sensor in the touch trigger probe. The X- and Y-axis directions are shifted by amounts of lengths of the touch trigger probe body and the stylus in the Z-axis direction, and the shift occurs due to, for example, the signal delay in contact Accordingly, a calibration to acquire compensation values to compensate these shifts is required.
As disclosed in Japanese Unexamined Patent Application Publication No. 4-63664 and Japanese Unexamined Patent Application Publication No. 58-82649, there are known as calibration methods of a radial direction compensation value of the touch trigger probe.
In the method disclosed in JP-A-4-63664, a main spindle center position is adjusted so as to match a center of a ring gauge as a reference with the main spindle center using a dial gauge. A diameter compensation value of the touch trigger probe is acquired from a skip value when the touch trigger probe is brought into contact with the inner diameter of the ring gauge and an inner diameter value of the ring gauge.
In the method disclosed in JP-A-58-82649, the touch trigger probe is brought into contact with a bore inner diameter as a reference in one direction. When the touch trigger probe contacts the bore inner diameter in the opposite direction, a main spindle is rotated by 180° and a bore center position is acquired from an average value of both skip values and then compensation values in the respective directions are acquired.
On the other hand, a method using a reference tool (hereinafter referred to as a “method 1”) has been known as a calibration method of a length compensation value. In the method 1, the reference tool is installed to a main spindle, and a position at which a clearance between a block gauge and the reference tool becomes almost 0 is found and recorded. The position is determined from a resistance when the block gauge is manually moved while a Z-axis is manually operated such that the reference tool contacts a reference surface such as a table top surface via the block gauge. Next, a touch trigger probe measures the reference surface, that is, acquires a Z-axis position when the touch trigger probe is in contact. A length of the touch trigger probe in contact, namely, the length compensation value of the touch trigger probe is acquired from a value found by subtracting the recorded Z-axis position of the reference tool and a thickness of the block gauge from the Z-axis position acquired by the touch trigger probe.
Japanese Unexamined Patent Application Publication No. 2012-61570 discloses a measuring method for a length of a touch trigger probe in contact using a CCD camera. With the method, the touch trigger probe is brought in contact with a top surface of a holding block, a position of a main spindle is acquired when a signal is output, and a distal end of the touch trigger probe in contact is photographed by the CCD camera to measure a distal end position. Next, the holding block is removed to recover the length when the touch trigger probe is not in contact and measures the distal end position by the CCD camera. An amount of shrinkage in contact is calculated from a difference between both distal end positions. A distal end position of a reference tool is measured by the CCD camera so that a position of the main spindle is acquired at the time as well. A length of the touch trigger probe in contact, namely, a length compensation value of the touch trigger probe is acquired from a relationship between the acquired amount of shrinkage in contact, distal end position of the touch trigger probe in contact, main spindle position while the touch trigger probe is in contact, distal end position of the reference tool, and main spindle position with the reference tool.
Furthermore, Japanese Unexamined Patent Application Publication No. 2001-105279 discloses a compensation method of a workpiece position using a laser sensor and a reference block. When laser light is obstructed by a tool distal end and therefore a light-receiving rate becomes a certain rate or less, the laser sensor generates a signal. Positions of feed axes at a time point when a control device of a machine tool receives the signal are determined as measurement values. With the method, the reference block is prepared near the laser sensor and a position of the laser light is matched with a position (height) of a top surface of the reference block. The laser sensor stores a position with the reference tool installed. Next, the touch trigger probe is brought into contact with the reference block and the position is stored, and the touch, trigger probe is also brought into contact with the workpiece and the position is stored. The workpiece position with respect to the reference tool is measured and compensated from a difference between both positions and the position of the reference tool. In the method, the workpiece position is measured without acquiring the length compensation value of the touch trigger probe.
The calibration of the touch trigger probe needs to be performed before the measurement for identification of geometric error. Moreover, a state of the touch trigger probe changes due to, for example, a thermal displacement due to such as a heat, generation in the main spindle and a secular change, thus a required compensation value changes. In view of this, the calibration is preferably performed immediately before the measurement.
However, the methods in JP-A-4-63664 and JP-A-58-82649 have a problem of the necessity of additionally preparing another measuring device such as a dial gauge and a reference of, for example, a workpiece with a ring gauge and a bore.
Furthermore, since JP-A-4-63664, JP-A-58-82649, and the method 1 require hand work, this makes the work troublesome. Accordingly, once performed, the calibration is not performed thereafter in many cases. In this case, if the state of the touch trigger probe changes due to such as the thermal distortion, the measurement accuracy of the touch trigger probe deteriorates, causing a problem of failing to highly accurately identify the geometric error in the machine.
The method of JP-A-2012-61570 has a problem of requiring the measuring device, the expensive CCD camera. Additionally, since the holding block needs to be moved, this causes a problem of a reduction in work frequency due to hand working. To automatically remove the holding block, a mechanism for driving the holding block and an actuator are required, causing a problem of cost increase.
Further, JP-A-2001-105279 discloses the method for measuring the position of the workpiece without the use of the length compensation value of the touch trigger probe. However, the method requires matching the laser light position of the laser sensor with the reference block position or knowing a positional relationship between both in advance, The required information in the method of JP-A-2001-105279 means that a relationship between the length of the reference tool measured by the laser sensor and the length of the touch trigger probe with which the reference block is brought into contact, that is, the length compensation value of the touch trigger probe needs to be known in advance. However, JP-A-2001-105279 does not disclose the method of knowing the positional relationship between both in advance.
Therefore, an object of the disclosure is to provide an error identification method and an error identification system that can concurrently perform calibrations of diameter/length compensation values of a position measurement sensor when a measured jig such as a target ball is measured with the position measurement sensor such as a touch trigger probe to identify a geometric error in a machine tool that includes three translational axes and at least one rotation axis from a position of the measured jig.
In order to achieve the above-described object, there is provided an error identification method according to a first aspect of the disclosure. The error identification method may be for measuring a position of a measured jig in a three-dimensional space, the measured jig being secured on a table by a position measurement sensor installed to a main spindle in a machine tool. The machine tool may include three or more translational axes, one or more rotation axes, the rotatable main spindle to which a tool is to he installed, the table, and a control device configured to control the respective translational axes, rotation axis, and main spindle. The error identification method may identify a geometric error in the machine tool from a value of the measured position (position measurement value). The error identification method may execute 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 tool sensor position acquisition stage may install a reference tool for a length reference of the tool to the main spindle and acquire a sensing position of a distal end of the reference tool with a tool sensor. The reference block position acquisition stage may acquire 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. The relative position calculation stage may calculate 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. The reference tool position acquisition stage may install the reference tool to the main spindle and acquire a reference tool position with the tool sensor. The reference tool position may be a distal end position of the reference tool. The position measurement sensor measurement stage may install the position measurement sensor to the main spindle and measure a position of the reference block with the position measurement sensor. The length compensation value calculation stage may calculate 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. The diameter compensation value acquisition stage may acquire a radial direction compensation value of the position measurement sensor with the measured jig. The position measurement stage may index the rotation axis to a plurality of any given angles and measure respective positions of the measured, jig by the position measurement sensor. The position compensation stage may compensate 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 may identify the geometric error from the plurality of position measurement values compensated in the position compensation stage.
Here, “the tool sensor side” obviously may include the case of directly disposing the reference block to the tool sensor and also includes the case of disposing the reference block separately near the tool sensor. The same applies to the following disclosure.
With the error identification method according to a second aspect of the disclosure, which is in the first aspect of the disclosure, the tool sensor position acquisition stage to the relative position calculation stage may be configured to be executed once. The reference tool position acquisition stage to the geometric error identification stage may be configured to be executed several times.
With the error identification method according to a third aspect of the disclosure, which is in the first aspect of the disclosure, the positions measured by the position measurement sensor may be positions of the translational axes when the position measurement sensor senses a contact with a measurement object.
With the error identification method according to a fourth aspect of the disclosure, which is in the first aspect of the disclosure, the positions measured by the tool, sensor may be 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.
With the error identification method according to a fifth aspect of the disclosure, which is in the first aspect of the disclosure, the measured jig may have a spherical shape.
With the error identification method according to a sixth aspect of the disclosure, which is in the fifth, aspect of the disclosure, the diameter compensation value acquisition stage may measure an initial position of the measured jig by the position measurement, sensor. The diameter compensation value acquisition state may acquire a compensation value of the position measurement sensor in a radial direction.
In order to achieve the above-described object, there is provided an error identification system according to a seventh aspect of the disclosure. The error identification system may be tor measuring a position of a measured jig in a three-dimensional space, the measured jig being secured on a table by a position measurement sensor installed to a main spindle in a machine tool. The machine tool may include 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 may identify a geometric error in the machine tool from, a value of the measured position (the position measurement value). The error identification system may include a reference tool, a tool sensor, a reference block, a tool sensor position acquisition means, a reference block position acquisition means, a relative position calculation means, a reference tool position acquisition means, a measurement position acquisition means, a length compensation value calculation means, a diameter compensation value acquisition means, a position compensation means, and a geometric error identification means. The reference tool may be for a length reference of the tool. The tool sensor may be configured to detect a distal end position of the reference tool installed to the main spindle. The reference block may be installed to the tool sensor side. The tool sensor position acquisition means may be configured to move the reference tool installed to the main spindle in the translational axes to acquire and store a sensing position of the distal end of the reference tool with the tool sensor. The reference block position acquisition means may be configured to 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 means may be configured to acquire and store positions of the translational axes at the contact. The relative position calculation means may be 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 means and the positions of the translational axes acquired in the reference block position acquisition means. The reference tool position acquisition means may be configured to move the reference tool installed to the main spindle in the translational axes. The reference tool position acquisition means may be configured to acquire and store a reference tool position with the tool sensor. The reference tool position may be the distal end position of the reference tool. The measurement position acquisition means may be configured to measure and store a position of the reference block with the position measurement sensor installed to the main spindle. The length compensation value calculation means may be 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 means, the position of the reference block acquired in the measurement position acquisition means, the relative position acquired in the relative position calculation means, and the length of the reference tool. The diameter compensation value acquisition means may be configured to acquire and store a radial direction compensation value of the position measurement sensor with the measured jig. The position compensation means may be configured to index the rotation axis to a plurality of any given angles to compensate and store the respective position measurement values of the measured jig measured by the position measurement sensor using the length direction compensation value and the radial direction compensation value. The geometric error identification means may be configured to identify the geometric error from the plurality of position measurement values compensated in the position compensation means.
In order to achieve the above-described object, there is provided an error identification method according to an eighth aspect of the disclosure. The error identification method may be for measuring a position of a measured jig in a three-dimensional space, the measured jig being secured on a table by a position measurement sensor installed to a main spindle in a machine tool. The machine tool may include 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 may identify a geometric error in the machine tool from a value of the measured position (position measurement value). The error identification method may use a tool sensor and a reference block disposed at the tool sensor side. The error identification method may execute a tool sensor position acquisition stage, a reference tool measurement position acquisition stage, a position measurement sensor measurement position acquisition stage, a position measurement sensor length calculation stage, a first reference block position acquisition stage, a relative position calculation stage, a reference tool position acquisition stage, a second reference block position acquisition 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 tool sensor position acquisition stage may install a reference tool fir a length reference of the tool to the main spindle and acquire a sensing position of a distal end of the reference tool with the tool sensor. The reference tool measurement position acquisition stage may acquire any given tool measurement position with the reference tool installed to the main spindle. The position measurement sensor measurement position acquisition stage may acquire any given sensor measurement position with the position measurement sensor installed to the main spindle. The position measurement sensor length calculation stage may acquire a difference between the tool measurement position and the sensor measurement position and acquire a length of the position measurement sensor based on the difference and the length of the reference tool. The first reference block position acquisition stage may measure a position of the reference block with the position measurement sensor installed to the main spindle. The relative position calculation stage may calculate 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. The reference tool position acquisition stage may install the reference tool to the main spindle and acquire a reference tool position with the tool sensor. The reference tool position may be a distal end position of the reference tool. The second reference block position acquisition stage may install the position measurement sensor to the main spindle and measure a position of the reference block with the position measurement sensor. The length compensation value calculation stage may calculate 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. The diameter compensation value acquisition stage may acquire a radial direction compensation value of the position measurement sensor with the measured jig The position measurement stage may index the rotation axis to a plurality of any given angles and measure respective positions of the measured jig by the position measurement sensor. The position compensation stage may compensate 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 may identify the geometric error from the plurality of position measurement values compensated in the position compensation stage.
In the error identification method according to a ninth aspect of the disclosure, which is in the eighth aspect of the disclosure, the tool sensor position acquisition stage to the relative position calculation stage may be configured to be executed once. The reference tool position acquisition stage to the geometric error identification stage may be configured to be executed several times.
In the error identification method according to a tenth aspect of the disclosure, which is in the eighth aspect of the disclosure, the positions measured by the position measurement sensor may be positions of the translational axes when the position measurement sensor senses a contact with a measurement object.
In the error identification method according to an eleventh aspect of the disclosure, which is in the eighth aspect of the disclosure, the positions measured by the tool sensor may be 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.
In the error identification method according to a twelfth aspect of the disclosure, which is in the eighth aspect of the disclosure, the measured jig may have a spherical shape.
In the error identification method according to a thirteenth aspect of the disclosure, which is in the twelfth aspect of the disclosure, the diameter compensation value acquisition stage may measure an initial position of the measured jig by the position measurement sensor. The diameter compensation value acquisition stage may acquire a compensation value of the position measurement sensor in a radial direction.
In order to achieve the above-described object, there is provided an error identification system according to a fourteenth aspect of the disclosure. The error identification system may be for measuring a position of a measured jig in a three-dimensional space, the measured jig being secured on a table by a position measurement sensor installed to a main spindle in a machine tool. The machine tool may include 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 may identify a geometric error in the machine tool from a value of the measured position (position measurement value). The error identification system may include a reference tool, a tool sensor, a reference block, tool sensor position acquisition means, reference tool measurement position acquisition means, position measurement sensor measurement position acquisition means, position measurement sensor length calculation means, first reference block position acquisition means, relative position calculation means, reference tool position acquisition means, second reference block position acquisition means, length compensation value calculation means, diameter compensation value acquisition means, position compensation means, and geometric error identification means. The reference tool may be for a length reference of the tool. The tool sensor may be configured to detect a distal end position of the reference tool installed to the main spindle. The reference block may be installed to the tool sensor side. The tool sensor position acquisition means may be 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. The reference tool measurement position acquisition means may be configured to acquire and store any given tool measurement position with the reference tool installed to the main spindle. The position measurement sensor measurement position acquisition means may be configured to acquire and store any given sensor measurement position with the position measurement sensor installed to the main spindle. The position measurement sensor length calculation means may be configured to acquire a difference between the tool measurement position and the sensor measurement position. The position measurement sensor length calculation means may be configured to calculate and store a length of the position measurement sensor based on the difference and the length of the reference tool. The first reference block position acquisition means may be configured to measure and store a position of the reference block with the position measurement sensor installed to the main spindle. The relative position calculation means may be 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 means, the position of the reference block acquired in the first reference block position acquisition means, the length of the position measurement sensor calculated in the position measurement sensor length calculation means, and the length of the reference tool. The reference tool position acquisition means may be configured to move the reference tool installed to the main spindle in the translational axes. The reference tool position acquisition means may be configured to acquire and store a reference tool position with the tool sensor. The reference tool position may be the distal end position of the reference tool. The second reference block position acquisition means may be configured to measure and store a position of the reference block with the position measurement sensor installed to the main spindle. The length compensation value calculation means may be 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 means, the position of the reference block acquired in the second reference block position acquisition means, the relative position calculated in the relative position calculation means, and the length of the reference tool. The diameter compensation value acquisition means may be configured to acquire and store a radial direction compensation value of the position measurement sensor with the measured jig. The position compensation means may be configured to index the rotation axis to a plurality of any given angles and compensate and store the respective position measurement values of the measured jig measured by the position measurement sensor using the length direction compensation value and the radial direction compensation value. The geometric error identification means may be configured to identify the geometric error from the plurality of position measurement values compensated in the position compensation means.
With the disclosure, the calibration of the length and diameter compensation values of the position measurement sensor is possible during a sequence of respective measurements for the geometric error identification. The need for hand work except fix the preparation work in advance is eliminated. Accordingly, the preparation of an 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 position measurement sensor at the geometric error identification. This does not deteriorate the measurement accuracy of the position measurement sensor even if the state of the position measurement sensor changes due to such as the heat displacement, ensuring highly accurately identifying the geometric error in the machine tool.
Further, the measurement system with the CCD camera or a similar system is not required, thus achieving a comparatively low price.
The following describes embodiments of the disclosure based on the drawings.
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.
As illustrated in
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.
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.
First, the following describes a procedure for measurement preparation work based on a flowchart in
At Step SR1, as illustrated in
Next, at Step SR2, the position of the reference block 42 is acquired using the reference tool 8. Here, as illustrated in
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″.
The following describes a procedure of the geometric error identification of the disclosure based on a flowchart in
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.
Next, at Step S2, as illustrated in
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).
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.
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.
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.
Here, the following describes a length compensation value calibration at Step S1 based on a flowchart in
First, at Step S1-1, similar to Step SR1 described in
Next, at Step S1-2, as illustrated in
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.
The following describes details of Step S2 based on a flowchart in
First, before executing Step S2, as illustrated in
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.
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]
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.
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.
At Step S2-5, an X-center position xo is acquired from the following formula 2 using the stored xm1 and xp1.
Here, at Step S2-3 and Step S2-4 as illustrated in
xo=(xp1+xm1)/2 [Formula 2]
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.
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.
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]
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.
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.
At Step S2-11, the X-center position xo is calculated again from the formula 2 using the updated xm1 and xp1.
At Step S2-12, the main spindle 2 is indexed to 0° (an angle indexed at the usual measurement).
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.
At Step S2-14, a Z-center position zo is acquired from the following formula 4.
zo=zm2−d0/2−t1 [Formula 4]
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.
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.
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.
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.
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
tc1=x0−xp2−d0/2
tc2=xo−xm2+d0/2
tc3=yo−yp2−d0/2
tc4=yo−ym2+d0/2 [Formula 5]
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.
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]
Next, the following describes details of Step S5.
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.
A radial direction component dRri, an axial direction component dRai, and a radial direction component dRti of the measurement values at a k-th index angle θijk of a j-th rotation axis under a measurement condition i can be expressed as the following formula 7.
dRr
i
=ra0i+ra1i*cos (θijk)+rb1i*cos (θijk)+ra2i cos (2θijk)+rb2i sin (2θijk)
dRai=aa0i+aa1i*cos (θijk)+ab1i*cos (θijk)+aa2i cos (2θijk)+ab2i sin (2θijk)
dRt
i
=ta0i+ta1i*cos (θijk)+tb1i*cos (θijk)+ta2i cos (2θijk)+tb2i sin (2θijk) [Formula 7]
As the geometric error in the five-axis-control machining center in
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 R1, R2, and R3 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.
ra11=−dXca−(dBca+dBay+dBxz)*H
rb11=dYca+dYay−(dAca+dAxz)*H
rb21=dCyx*R1/2
aa11=dBca+dBay
ab11=dAca
ra12=−dYay
rb12=dZay
rb22=−dAxz*R2/2
aa12=dCay
ab12=−(dBay+dBxz)
rb23=dBxz*R3/2 [Formula 8]
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.
Further, the measurement system with the CCD camera or a similar system is not required, thus achieving a comparatively low price.
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.
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.
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
First, Step SQ1 is identical to Step SR1 in
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
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
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).
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
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).
While the procedure of the geometric error identification after this is identical to the above-described configurations described in
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-083860 | Apr 2016 | JP | national |
| 2017-019723 | Feb 2017 | JP | national |
