Machine tool, measurement method, and measurement program

Abstract

This machine tool includes a table driving unit that turning-drives a table around a turning axis; a main shaft to which a touch probe can be attached; a main-shaft drive unit that feeding-drives the main shaft relative to the table; and a control unit. The control unit executes: driving processing for turning-driving the table within an angle range determined in advance; first measurement processing for measuring a position of a reference object at first and second reference positions when the table is driven to a first turning angle; second measurement processing for measuring the position of the reference object at the first to third reference positions when the table is driven to a second turning angle; third measurement processing for measuring the position of the reference object at the second and third reference positions when the table is driven to a third turning angle; and output processing for outputting each position measured by the first to third measurement processing. The second turning angle is an angle between the first and third turning angles.

Description

Machine tool, measurement method, and measurement program

[0001] The present disclosure relates to a machine tool, a measurement method, and a measurement program.

[0002] Japanese Patent Application Laid-Open Publication No. 2016-155185 (Patent Document 1) discloses "an error identification method capable of simultaneously identifying all center position errors of the rotation axes, inclination errors of the rotation axes, and squareness of the linear axes among the geometric errors of a five-axis controlled machine tool that has one rotation axis on the table side and one rotation axis on the spindle head side relative to the translation axes" (see abstract).

[0003] The machine tool disclosed in Patent Document 1 uses a touch probe attached to the spindle head to measure the position of a target sphere (reference object) fixed to the table. The machine tool measures the position of one reference object while rotating the table. The machine tool then identifies a geometric error based on the difference between the measured value and the command value.

[0004] JP 2016-155185 A

[0005] To more accurately identify geometric errors related to the table's rotation axis, it is preferable to place multiple reference objects on the table. In this case, if the reference objects are spaced farther apart on the table, the table's motion can be captured more accurately, improving the accuracy of measuring geometric errors. However, in this case, depending on the table's rotation angle, the spindle may interfere with other components, and the machine tool can only measure the table's posture within a narrow range of rotation angles.

[0006] On the other hand, if the distance between the reference objects on the table is short, interference between the spindle and other members can be avoided and the machine tool can measure the table orientation over a wider range of rotation angles. However, in this case, the machine tool cannot accurately measure the table orientation.

[0007] In view of the above, there is a need for a technique for accurately capturing the movement of the table over a wider range of rotation angles in order to calculate the geometric error associated with the rotation axis of the table.

[0008] One example of the present disclosure provides a machine tool capable of measuring actual values ​​used in error correction processing for a rotation axis of a table on which a workpiece can be placed. The table is configured to allow a reference object to be attached. The attachment position of the reference object on the table includes one or more first reference positions that belong to a first region on the table but not to a second region on the table, one or more second reference positions that belong to an overlapping region between the first region and the second region, and one or more third reference positions that belong to the second region but not to the first region. The machine tool further includes a table drive unit that drives the table to rotate about the rotation axis, a spindle to which a touch probe can be attached, a spindle drive unit that drives the spindle to feed relative to the table, and a control unit that controls the machine tool. The control unit executes a drive process for driving the table to rotate around the rotation axis within a predetermined angular range, a first measurement process for measuring the position of the reference object at the first reference position and the second reference position with the touch probe when the table is driven to a first rotation angle within the predetermined angular range, a second measurement process for measuring the position of the reference object at the first reference position, the second reference position, and a third reference position with the touch probe when the table is driven to a second rotation angle within the predetermined angular range, a third measurement process for measuring the position of the reference object at the second reference position and the third reference position with the touch probe when the table is driven to a third rotation angle within the predetermined angular range, and an output process for outputting each of the positions measured in the first to third measurement processes as the actual measurement value. The second rotation angle is an angle between the first rotation angle and the third rotation angle.

[0009] In one example of the present disclosure, the control unit further performs the error correction process based on the actual measurement value, wherein the error correction process calculates a rotation center related to the rotation axis and a geometric error related to the rotation axis.

[0010] In one example of the present disclosure, the number of the first reference positions is 2 or more, and the number of the third reference positions is 2 or more.

[0011] In one example of the present disclosure, the number of the second reference positions is two or more.

[0012] In one example of the present disclosure, when a distance from the touch probe to the first reference position in the axial direction of the spindle is defined as a first distance, a distance from the touch probe to the second reference position in the axial direction of the spindle is defined as a second distance, and a distance from the touch probe to the third reference position in the axial direction of the spindle is defined as a third distance, when the table is at the first pivot angle, the first distance is shorter than the second distance and the second distance is shorter than the third distance. When the table is at the third pivot angle, the third distance is shorter than the second distance and the second distance is shorter than the first distance.

[0013] Another example of the present disclosure provides a measurement method for measuring, by a machine tool, actual measurement values ​​used in error correction processing for a rotation axis of a table on which a workpiece can be placed. The table is configured to allow attachment of a plurality of reference objects. The attachment positions of the reference objects on the table include one or more first reference positions that belong to a first region on the table and do not belong to a second region on the table, one or more second reference positions that belong to an overlapping region between the first region and the second region, and one or more third reference positions that belong to the second region and do not belong to the first region. The machine tool includes a table drive unit that drives the table to rotate around the rotation axis, a spindle to which a touch probe can be attached, and a spindle drive unit that drives the spindle to feed relative to the table. The measurement method includes a driving step of driving the table to rotate around the rotation axis within a predetermined angular range, a first measurement step of measuring the position of the reference object at the first reference position and the second reference position with the touch probe when the table is driven to a first rotation angle within the predetermined angular range, a second measurement step of measuring the position of the reference object at the first reference position, the second reference position, and a third reference position with the touch probe when the table is driven to a second rotation angle within the predetermined angular range, a third measurement step of measuring the position of the reference object at the second reference position and the third reference position with the touch probe when the table is driven to a third rotation angle within the predetermined angular range, and an output step of outputting each of the positions measured in the first to third measurement steps as the actual measurement value. The second rotation angle is an angle between the first rotation angle and the third rotation angle.

[0014] In another example of the present disclosure, there is provided a measurement program for measuring, by a machine tool, actual measurement values ​​used in error correction processing for a rotation axis of a table on which a workpiece can be placed. The table is configured to allow attachment of a plurality of reference objects. The attachment positions of the reference objects on the table include one or more first reference positions that belong to a first region on the table and do not belong to a second region on the table, one or more second reference positions that belong to an overlapping region between the first region and the second region, and one or more third reference positions that belong to the second region and do not belong to the first region. The machine tool includes a table drive unit that drives the table to rotate around the rotation axis, a spindle to which a touch probe can be attached, and a spindle drive unit that drives the spindle to feed relative to the table. The measurement program is programmed in a computer and includes a drive process for driving the table to rotate around the rotation axis within a predetermined angular range, a first measurement process for measuring the position of the reference object at the first reference position and the second reference position with the touch probe when the table is driven to a first rotation angle within the predetermined angular range, a second measurement process for measuring the position of the reference object at the first reference position, the second reference position, and a third reference position with the touch probe when the table is driven to a second rotation angle within the predetermined angular range, a third measurement process for measuring the position of the reference object at the second reference position and the third reference position with the touch probe when the table is driven to a third rotation angle within the predetermined angular range, and an output process for outputting each of the positions measured in the first to third measurement processes as the actual measurement value. The second rotation angle is an angle between the first rotation angle and the third rotation angle.

[0015] The above and other objects, features, aspects and advantages of the present invention will become apparent from the following detailed description of the invention taken in conjunction with the accompanying drawings.

[0016] 1 is a diagram showing an example of the appearance of a machine tool. FIG. 2 is a diagram showing an example of an apparatus configuration for realizing five-axis machining. FIG. 3 is a diagram showing an example of an arrangement pattern of a reference object on a table. FIG. 4 is a diagram showing an example of a spindle interfering with the table. FIG. 5 is a diagram showing another example of an arrangement pattern of a reference object on a table. FIG. 6 is a diagram showing, in tabular form, a reference object T to be measured and a reference object T not to be measured, sorted by the rotation angle of the table. FIG. 7 is a diagram for explaining a measurement process when a reference object is attached to a first reference position. FIG. 8 is a diagram for explaining a measurement process when a reference object is attached to a second reference position. FIG. 9 is a diagram for explaining a measurement process when a reference object is attached to a third reference position. FIG. 10 is a diagram showing an example of a drive mechanism of a machine tool. FIG. 11 is a diagram showing an example of a hardware configuration of a control unit. FIG. 12 is a flowchart showing the flow of a measurement process. FIG. 13 is a diagram showing a change in the position of the reference object due to rotation.

[0017] Hereinafter, each embodiment according to the present invention will be described with reference to the drawings. In the following description, the same parts and components are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated. Note that each embodiment and each modified example described below may be selectively combined as appropriate.

[0018] <A. Appearance of Machine Tool 100> First, a machine tool 100 according to an embodiment will be described with reference to Fig. 1. Fig. 1 is a diagram showing an example of the appearance of machine tool 100.

[0019] The term "machine tool" as used herein is a concept that encompasses various devices that have the function of machining a workpiece. Machine tool 100 may be a horizontal machining center or a vertical machining center. Alternatively, machine tool 100 may be a lathe, or other cutting machine, grinding machine, multi-tasking machine, five-axis machine, or the like. Furthermore, machine tool 100 is not limited to one that performs only subtractive machining, but may also perform additive machining in addition to subtractive machining.

[0020] Machine tool 100 includes, for example, a cover body 130 and an operation panel 200 .

[0021] Cover body 130 is a mechanism for protecting components provided inside machine tool 100. Cover body 130 is provided with a door DR. Door DR is, for example, a sliding door. Door DR may be configured to be openable and closable by a drive source such as a motor, or may be configured to be openable and closable manually.

[0022] Control panel 200 is a general-purpose computer and has a display for displaying various pieces of information related to machining. The display may be, for example, a liquid crystal display, an organic electroluminescence (EL) display, or other display device. The display also has a touch panel that accepts various operations for machine tool 100 by touch operation.

[0023] <B. Device Configuration of Machine Tool 100> Machine tool 100 according to the embodiment is, for example, a five-axis machining center. A five-axis machining center is a machine that can machine a workpiece by combining three linear axis drives, a rotational axis drive, and a tilt axis drive.

[0024] The device configuration of machine tool 100 as a five-axis machining device will be described below with reference to Fig. 2. Fig. 2 is a diagram showing an example of a device configuration for realizing five-axis machining.

[0025] 2, the machine tool 100 includes a spindle head 140 and a table mechanism 150. The spindle head 140 includes a spindle 142 and a housing 143.

[0026] The spindle 142 is provided inside a housing 143. A tool TL for machining a workpiece W can be attached to the spindle 142. In the example of Fig. 2, a tool TL for milling is attached to the spindle 142.

[0027] For ease of explanation, the coordinate system based on the main axis 142 will be represented by the X-axis, Y-axis, and Z-axis below. The Z-axis is an axis parallel to the axial direction of the main axis 142. The X-axis is an axis on a plane perpendicular to the Z-axis. The Y-axis is an axis perpendicular to both the X-axis and the Z-axis. In the example of FIG. 2, the Y-axis is shown as an axis parallel to the vertical direction.

[0028] The axis that rotates around the X-axis is also called the A-axis, the axis that rotates around the Y-axis is also called the B-axis, and the axis that rotates around the Z-axis is also called the C-axis.

[0029] The spindle head 140 is configured to be movable relative to the workpiece W. As an example, the spindle head 140 is configured to be feed-drivable in the X-axis direction and the Y-axis direction.

[0030] More specifically, a bed (not shown) serving as a base is provided inside machine tool 100. A column (not shown) extending in the XY plane is provided on the bed. A first saddle (not shown) is provided on the side of the column. The first saddle is configured to be drivable in the X-axis direction relative to the column via a drive mechanism such as a ball screw or a servo motor. A spindle head 140 is provided on the side of the first saddle. The spindle head 140 is configured to be drivable in the Y-axis direction relative to the first saddle via a drive mechanism such as a ball screw or a servo motor. This allows the spindle head 140 to be driven to any position in the X-axis and Y-axis directions.

[0031] The table mechanism 150 includes drive mechanisms 152 A and 152 B, a swivel base 154 , and a table 156 .

[0032] The table mechanism 150 is configured to be capable of being driven and fed in the Z-axis direction. More specifically, a second saddle (not shown) is provided on the bed. The second saddle is configured to be capable of being driven and fed in the Z-axis direction via a drive mechanism such as a ball screw or a servo motor. The second saddle is also provided with the table mechanism 150. This allows the spindle head 140 to be driven to any position in the Z-axis direction.

[0033] The table mechanism 150 is configured to be rotatable about a rotation axis AXA parallel to the X-axis. More specifically, the drive mechanisms 152A and 152B are fixed to the second saddle so as to face each other in the X-axis direction. A swivel base 154 is provided between the drive mechanisms 152A and 152B. A motor is provided inside each of the drive mechanisms 152A and 152B. Each motor is connected to the swivel base 154 and is synchronously controlled. As a result, the drive mechanisms 152A and 152B are configured to drive the swivel base 154 to rotate about the rotation axis AXA.

[0034] Various motors can be used for the drive mechanisms 152A, 152B. As an example, the motors may be servo motors or direct drive motors. The direct drive motor directly drives and rotates the swivel base 154 without using a reduction mechanism. By using a direct drive motor, the driving force of the motor is directly transmitted to the swivel base 154, improving the efficiency of force transmission.

[0035] The swivel base 154 is provided with a table 156 on which the workpiece W is placed. The table 156 is configured to be rotatable about a rotation axis AXB. The rotation axis AXB is an axis that is perpendicular to the contact surface of the workpiece W on the table 156, and is an axis that rotates together with the swivel base 154. A motor is provided inside the swivel base 154, and the table 156 is connected to this motor. This motor drives the table 156 to rotate about the rotation axis AXB.

[0036] <C. Measurement Processing> Machine tool 100 controls the driving of spindle 142 and table 156 by outputting command values ​​for each of the X-axis, Y-axis, Z-axis, A-axis, and B-axis in accordance with a pre-designed machining program. This allows machine tool 100 to machine workpiece W into any desired shape.

[0037] At this time, the actual positions of spindle 142 and table 156 may deviate from the positions recognized by machine tool 100. Such geometric deviation errors occur due to various factors, such as the device configuration of machine tool 100 and the shape of the workpiece. For this reason, some machine tools 100 are equipped with a function to correct such geometric errors. This correction function corrects the internal parameters of machine tool 100 so that the recognized position approaches the actual measurement position of the reference object.

[0038] It is necessary to measure the positions of reference objects at a plurality of reference positions in order to accurately identify the geometric error associated with the rotation axis of the table 156. Figure 3 shows an example of an arrangement pattern of reference objects on the table 156.

[0039] 3, reference object T is placed at reference positions PX1 to PX4 on table 156. The reference object T is, for example, a steel ball. The reference object T may be placed manually on table 156, or may be placed automatically on table 156. Furthermore, one reference object T may be placed sequentially at reference positions PX1 to PX4, or four reference objects T may be placed at reference positions PX1 to PX4.

[0040] Machine tool 100 rotates table 156 at predetermined rotation angles and measures the position of reference object T at each rotation angle at reference positions PX1 to PX4. The position of reference object T is measured by touch probe TP. Touch probe TP is a contact-type position measurement sensor.

[0041] The touch probe TP is configured to be detachable from the spindle 142. The touch probe TP can be attached to and detached from the spindle 142 by, for example, an automatic tool changer (ATC). The machine tool 100 mounts the touch probe TP on the spindle 142 when performing geometric error correction processing.

[0042] 3, when the intervals between reference positions PX1 to PX4 are long, machine tool 100 can more accurately capture the movement of table 156. As a result, the accuracy of geometric error correction improves. However, in this case, depending on the rotation angle of table 156, there is a possibility that spindle 142 may interfere with other members.

[0043] FIG. 4 is a diagram showing an example in which spindle 142 interferes with table 156. In state (B) of FIG. 4, table 156 has rotated 180° around rotation axis AXA, compared to state (A) of FIG. 4. In state (A) of FIG. 4, machine tool 100 can measure the position of reference object T at reference position PX1 without causing spindle 142 to interfere with table 156. On the other hand, in state (B) of FIG. 4, spindle 142 interferes with table 156, so machine tool 100 cannot measure the position of reference object T at reference position PX1. Therefore, in arrangement pattern (A) of FIG. 3, machine tool 100 can only measure the attitude of table 156 within a narrow range of rotation angles.

[0044] On the other hand, as shown in arrangement pattern (B) in Figure 3, when the intervals between reference positions PX1' to PX4' on table 156 are short, machine tool 100 can avoid interference between spindle 142 and other members. As a result, machine tool 100 can measure the attitude of table 156 over a wider range of swing angles. However, when the intervals between reference positions PX1' to PX4' are short, machine tool 100 cannot accurately capture the movement of table 156 at each swing angle.

[0045] Therefore, in machine tool 100 according to the embodiment, the position of reference object T is measured at more reference positions than in the example of Fig. 3. Fig. 5 is a diagram showing another example of the arrangement pattern of reference objects on table 156.

[0046] The mounting area of ​​the reference object T on the table 156 includes a mounting area R1 (first area) and a mounting area R2 (second area). The mounting areas R1 and R2 are areas on the table 156. The mounting area R1 and the mounting area R2 partially overlap.

[0047] The mounting positions of the reference object T on the table 156 include reference positions P1 and P2 (first reference positions) that belong to the mounting region R1 but not to the mounting region R2, reference positions P3 and P4 (second reference positions) that belong to the overlapping region of the mounting region R1 and the mounting region R2, and reference positions P5 and P6 (third reference positions) that belong to the mounting region R2 but not to the mounting region R1. The reference positions P1 to P6 on the table 156 are determined in advance.

[0048] Machine tool 100 changes reference positions P1 to P6 to be measured depending on the rotation angle of table 156. The manner in which reference object T is measured will be described below.

[0049] In the following description, the rotation angle of the table 156 is set to 0° when the surface on the table 156 on which the workpiece W is placed is parallel to the horizontal plane and the workpiece W is positioned above the table 156. The rotation angle of the table 156 is set to -180° when the surface on the table 156 on which the workpiece W is placed is parallel to the horizontal plane and the workpiece W is positioned below the table 156.

[0050] Fig. 6 is a diagram showing, in tabular form, the reference positions of measurement objects and reference positions of non-measurement objects for each rotation angle of the table 156. Fig. 7 is a diagram for explaining the measurement process when the reference object T is attached at the reference positions P1 and P2.

[0051] When measuring the position of the reference object T, the machine tool 100 rotates the table 156 around the rotation axis AXA within a predetermined angular range Δθ.

[0052] More specifically, first, the operator attaches the reference object T to the reference position P1 within the attachment region R1. Thereafter, the machine tool 100 starts the process of rotating the reference object T.

[0053] In step S1, it is assumed that the rotation angle of table 156 reaches rotation angle θ1 (first rotation angle). When table 156 is driven to rotation angle θ1 within a predetermined angle range Δθ, machine tool 100 measures the position of reference object T in mounting region R1 with touch probe TP. That is, in step S1, machine tool 100 does not measure the position of reference object T that does not belong to mounting region R1.

[0054] The rotation angle θ1 is, for example, "0°" or "-30°". More specifically, machine tool 100 first maintains the rotation angle of table 156 at "0°". Then, machine tool 100 measures the position of reference object T in mounting area R1 with touch probe TP. Next, machine tool 100 maintains the rotation angle of table 156 at "-30°". Then, machine tool 100 measures the position of reference object T in mounting area R1 with touch probe TP.

[0055] In this way, when the rotation angle of table 156 is rotation angle θ1, machine tool 100 measures mounting region R1, which is located closer to spindle 142.

[0056] Next, in step S2, it is assumed that the rotation angle of table 156 reaches rotation angle θ2 (second rotation angle). Rotation angle θ2 is an angle between rotation angle θ1 described above and rotation angle θ3 described below. When table 156 is driven to rotation angle θ2 within a predetermined angle range Δθ, machine tool 100 measures the position of reference object T in mounting areas R1 and R2 with touch probe TP. That is, in step S2, machine tool 100 targets the entire area for measurement.

[0057] Swivel angle θ2 is, for example, "-60°", "-90°", or "-120°". As a more specific measurement process of step S2, machine tool 100 first maintains the swivel angle of table 156 at "-60°". Then, machine tool 100 measures the position of reference object T with touch probe TP. Next, machine tool 100 maintains the swivel angle of table 156 at "-90°". Then, machine tool 100 measures the position of reference object T with touch probe TP. Next, machine tool 100 maintains the swivel angle of table 156 at "-120°". Then, machine tool 100 measures the position of reference object T with touch probe TP.

[0058] In this way, when the rotation angle of table 156 is rotation angle θ2, machine tool 100 measures the entire mounting areas R1 and R2.

[0059] Next, in step S3, it is assumed that the rotation angle of table 156 reaches rotation angle θ3 (third rotation angle). When table 156 is driven to rotation angle θ3 within the predetermined angle range Δθ, machine tool 100 sets reference object T belonging to mounting region R2 as the measurement target. In the example of Figure 7, there is no reference object T belonging to mounting region R2, so machine tool 100 does not measure the position of reference object T in step S3.

[0060] The rotation of the table 156 between step S2 and step S3 may or may not be performed.

[0061] Based on the completion of the measurement process of steps S1 to S3, the operator changes the mounting position of reference object T from reference position P1 to reference position P2. Then, machine tool 100 executes the measurement process of steps S1 to S3 again.

[0062] Next, the operator changes the mounting position of reference object T from reference position P2 to reference position P3. Thereafter, machine tool 100 starts the measurement process shown in Fig. 8. Fig. 8 is a diagram for explaining the measurement process when reference object T is mounted at reference positions P3 and P4.

[0063] In step S4, it is assumed that the rotation angle of table 156 reaches rotation angle θ1 (first rotation angle). When table 156 is driven to rotation angle θ1 within the predetermined angle range Δθ, machine tool 100 measures the position of reference object T in mounting region R1 with touch probe TP. That is, in step S4, machine tool 100 does not measure the position of reference object T that does not belong to mounting region R1.

[0064] The rotation angle θ1 is, for example, "0°" or "-30°". More specifically, machine tool 100 first maintains the rotation angle of table 156 at "0°". Then, machine tool 100 measures the position of reference object T in mounting area R1 with touch probe TP. Next, machine tool 100 maintains the rotation angle of table 156 at "-30°". Then, machine tool 100 measures the position of reference object T in mounting area R1 with touch probe TP.

[0065] Next, in step S5, it is assumed that the rotation angle of table 156 reaches rotation angle θ2 (second rotation angle). When table 156 is driven to rotation angle θ2 within the predetermined angle range Δθ, machine tool 100 measures the position of reference object T in mounting areas R1, R2 with touch probe TP. That is, in step S5, machine tool 100 targets the entire area for measurement.

[0066] Swivel angle θ2 is, for example, "-60°", "-90°", or "-120°". As a more specific measurement process of step S5, machine tool 100 first maintains the swivel angle of table 156 at "-60°". Then, machine tool 100 measures the position of reference object T with touch probe TP. Next, machine tool 100 maintains the swivel angle of table 156 at "-90°". Then, machine tool 100 measures the position of reference object T with touch probe TP. Next, machine tool 100 maintains the swivel angle of table 156 at "-120°". Then, machine tool 100 measures the position of reference object T with touch probe TP.

[0067] Next, in step S6, it is assumed that the rotation angle of table 156 reaches rotation angle θ3 (third rotation angle). When table 156 is driven to rotation angle θ3 within the predetermined angle range Δθ, machine tool 100 sets reference object T belonging to mounting region R2 as the measurement target. That is, in step S6, machine tool 100 does not measure the position of reference object T that does not belong to mounting region R2.

[0068] Swivel angle θ3 is, for example, "-150°" or "-180°". More specifically, machine tool 100 first maintains the swivel angle of table 156 at "-150°". Then, machine tool 100 measures the position of reference object T with touch probe TP. Next, machine tool 100 maintains the swivel angle of table 156 at "-180°". Then, machine tool 100 measures the position of reference object T with touch probe TP.

[0069] In this way, when the rotation angle of table 156 is rotation angle θ3, machine tool 100 sets mounting region R2, which is located closer to spindle 142, as the measurement target.

[0070] Based on the completion of the measurement process of steps S4 to S6, the operator changes the mounting position of reference object T from reference position P3 to reference position P4. Then, machine tool 100 executes the measurement process of steps S4 to S6 again.

[0071] Next, the operator changes the mounting position of reference object T from reference position P4 to reference position P5. Thereafter, machine tool 100 starts the measurement process shown in Fig. 9. Fig. 9 is a diagram for explaining the measurement process when reference object T is mounted at reference positions P5 and P6.

[0072] In step S7, it is assumed that the rotation angle of table 156 reaches rotation angle θ1 (first rotation angle). When table 156 is driven to rotation angle θ1 within the predetermined angle range Δθ, machine tool 100 measures the position of reference object T in mounting region R1 with touch probe TP. That is, in step S7, machine tool 100 does not measure the position of reference object T.

[0073] Next, in step S8, it is assumed that the rotation angle of table 156 reaches rotation angle θ2 (second rotation angle). When table 156 is driven to rotation angle θ2 within the predetermined angle range Δθ, machine tool 100 measures the position of reference object T in mounting areas R1, R2 with touch probe TP. That is, in step S8, machine tool 100 targets the entire area for measurement.

[0074] Swivel angle θ2 is, for example, "-60°", "-90°", or "-120°". As a more specific measurement process of step S8, machine tool 100 first maintains the swivel angle of table 156 at "-60°". Then, machine tool 100 measures the position of reference object T with touch probe TP. Next, machine tool 100 maintains the swivel angle of table 156 at "-90°". Then, machine tool 100 measures the position of reference object T with touch probe TP. Next, machine tool 100 maintains the swivel angle of table 156 at "-120°". Then, machine tool 100 measures the position of reference object T with touch probe TP.

[0075] Next, in step S9, it is assumed that the rotation angle of table 156 reaches rotation angle θ3 (third rotation angle). When table 156 is driven to rotation angle θ3 within the predetermined angle range Δθ, machine tool 100 sets reference object T belonging to mounting region R2 as the measurement target. That is, in step S9, machine tool 100 does not measure the position of reference object T that does not belong to mounting region R2.

[0076] Swivel angle θ3 is, for example, "-150°" or "-180°". More specifically, machine tool 100 first maintains the swivel angle of table 156 at "-150°". Then, machine tool 100 measures the position of reference object T with touch probe TP. Next, machine tool 100 maintains the swivel angle of table 156 at "-180°". Then, machine tool 100 measures the position of reference object T with touch probe TP.

[0077] In this way, when the rotation angle of table 156 is rotation angle θ3, machine tool 100 sets mounting region R2, which is located closer to spindle 142, as the measurement target.

[0078] Based on the completion of the measurement process of steps S7 to S9, the operator changes the mounting position of reference object T from reference position P5 to reference position P6. Then, machine tool 100 executes the measurement process of steps S7 to S9 again.

[0079] As described above, machine tool 100 changes the measurement range of reference object T depending on the rotation angle of table 156. This allows machine tool 100 to avoid interference between spindle 142 and other members, and to measure the attitude of table 156 over a wider rotation angle range. Furthermore, machine tool 100 can measure the positions of sets of reference objects T arranged over a wider range at each rotation angle, and can measure the attitude of table 156 more accurately. As a result, geometric errors related to the rotation axis of table 156 can be corrected more accurately.

[0080] In the above description, two reference positions P1 and P2 are given as examples of first reference positions belonging to the mounting area R1 excluding the mounting area R2, but the number of first reference positions may be one or three or more.

[0081] In addition, in the above description, two reference positions P3 and P4 are given as examples of second reference positions belonging to the overlapping area of ​​the mounting areas R1 and R2, but the number of second reference positions may be one or three or more.

[0082] Furthermore, in the above description, two reference positions P5 and P6 are given as examples of third reference positions belonging to the mounting area R2 excluding the mounting area R1, but the number of third reference positions may be one or three or more.

[0083] Furthermore, the first to third reference positions relative to the rotation angle of the table 156 can be determined based on any reference. As an example, if the distance from the touch probe TP to the first reference position in the axial direction (Z-axis direction) of the main shaft 142 is defined as a "first distance," the distance from the touch probe TP to the second reference position in the axial direction of the main shaft 142 is defined as a "second distance," and the distance from the touch probe TP to the third reference position in the axial direction of the main shaft 142 is defined as a "third distance," when the table 156 is at a rotation angle θ1, the first distance is shorter than the second distance, and the second distance is shorter than the third distance. Furthermore, when the table 156 is at a rotation angle θ3, the third distance is shorter than the second distance, and the second distance is shorter than the first distance.

[0084] Furthermore, although the above description has been given of an example in which measurement processing is performed while the mounting position of one reference object T is sequentially changed among reference positions P1 to P6, measurement processing may also be performed with multiple reference objects T mounted at their reference positions. In this case, machine tool 100 measures the positions of the multiple reference objects T at each rotation angle of table 156.

[0085] Although the above description has been given of an example in which the reference positions P1 to P6 are divided into two mounting areas R1 and G2, the reference positions may be divided into three or more mounting areas. In this case, the overlapping area between the first and second mounting areas is different from the overlapping area between the second and third mounting areas.

[0086] <D. Drive Mechanism of Machine Tool 100> Next, the drive mechanism of machine tool 100 will be described with reference to Fig. 10. Fig. 10 is a diagram showing an example of the drive mechanism of machine tool 100.

[0087] As shown in FIG. 10 , machine tool 100 includes a control unit 50 , a spindle drive unit 230 , and a table drive unit 240 .

[0088] Control unit 50 controls various devices within machine tool 100. The device configuration of control unit 50 is arbitrary. Control unit 50 may be configured as a single control unit, or may be configured as multiple control units. As an example, control unit 50 includes at least one of a CNC (Computer Numerical Control) and a PLC (Programmable Logic Controller).

[0089] The spindle drive unit 230 is a drive mechanism for directly or indirectly driving the spindle 142. The spindle drive unit 230 may be composed of a single drive unit or multiple drive units. In the example of Fig. 10, the spindle drive unit 230 is composed of motor drivers 231C, 231X, and 231Z and motors 232C, 232X, and 232Y.

[0090] The motor driver 231C sequentially receives input of a target rotation angle or a target rotation speed of the main shaft 142 about the axial direction of the main shaft 142 as a rotation center from the control unit 50, and outputs a current corresponding to the target rotation angle or the target rotation speed to the motor 232C. The motor 232C drives the main shaft 142 to rotate about the axial direction of the main shaft 142 as a rotation center. The motor 232C may be an AC motor, a stepping motor, a servo motor, or any other type of motor.

[0091] The motor driver 231X sequentially receives input of target positions of the spindle 142 in the X-axis direction from the control unit 50, and outputs a current corresponding to the target position to the motor 232X. This causes the motor 232X to drive the spindle 142 to any position in the X-axis direction. The motor 232X may be an AC motor, a stepping motor, a servo motor, or any other type of motor.

[0092] The motor driver 231Y sequentially receives input of target positions of the spindle 142 in the Y-axis direction from the control unit 50, and outputs a current corresponding to the target position to the motor 232Y. This causes the motor 232Y to drive the spindle 142 to any position in the Y-axis direction. The motor 232Y may be an AC motor, a stepping motor, a servo motor, or any other type of motor.

[0093] Table driving unit 240 is a driving mechanism for directly or indirectly driving table 156. Table driving unit 240 may be composed of a single driving unit or multiple driving units. In the example of Fig. 10, table driving unit 240 is composed of motor drivers 241A, 241B, and 241Z and motors 242A, 242B, and 242Z.

[0094] The motor driver 241A receives an input of a target value for the rotation angle of the table 156 about the above-mentioned rotation axis AXA (see FIG. 2), and outputs a current corresponding to the target value to the motor 242A. In this way, the motor driver 241A controls the rotation angle of the table 156 about the rotation axis AXA. The motor 242C may be an AC motor, a stepping motor, a servo motor, or any other type of motor.

[0095] Motor driver 241B receives a target value for the rotation angle of table 156 about the above-mentioned rotation axis AXB (see FIG. 2) and outputs a current corresponding to the target value to motor 242B. In this way, motor driver 241B controls the rotation angle of table 156 about rotation axis AXB. Motor 242C may be an AC motor, a stepping motor, a servo motor, or any other type of motor.

[0096] The motor driver 241Z sequentially receives input of target positions of the table 156 in the Z-axis direction from the control unit 50, and outputs a current corresponding to the target position to the motor 242Z. This causes the motor 242Z to move the table 156 to any position in the Z-axis direction. The motor 242Z may be an AC motor, a stepping motor, a servo motor, or any other type of motor.

[0097] <E. Hardware Configuration of Control Unit 50> Next, the hardware configuration of the control unit 50 shown in Fig. 10 will be described with reference to Fig. 11. Fig. 11 is a diagram showing an example of the hardware configuration of the control unit 50.

[0098] As described above, the control unit 50 may be a CNC or a PLC. Fig. 11 shows the hardware configuration of the control unit 50 as a CNC.

[0099] The control unit 50 includes, for example, a control circuit 101, a read only memory (ROM) 102, a random access memory (RAM) 103, a communication interface 104, and an auxiliary storage device 120. These components are connected to an internal bus 109.

[0100] The control circuit 101 is configured, for example, by at least one integrated circuit, which may be configured, for example, by at least one central processing unit (CPU), at least one graphics processing unit (GPU), at least one application specific integrated circuit (ASIC), at least one field programmable gate array (FPGA), or a combination thereof.

[0101] The control circuit 101 controls the operation of the control unit 50 by executing various programs such as a measurement program 122 and a correction program 124. The measurement program 122 is a program for implementing the measurement process shown in Fig. 7. The correction program 124 is a program for correcting geometric errors related to the rotation axis of the table 156 based on actual measurement values ​​measured in the measurement process shown in Fig. 7.

[0102] Upon receiving a program execution command, the control circuit 101 reads the program from the ROM 102 to the RAM 103. The RAM 103 functions as a working memory and temporarily stores various data necessary for executing the program.

[0103] Communication interface 104 is an interface for realizing communication with various devices. Machine tool 100 communicates with various drive units (such as the above-mentioned spindle drive unit 230 and the above-mentioned table drive unit 240) for realizing additional machining of a workpiece, for example, via communication interface 104.

[0104] The auxiliary storage device 120 is a storage medium such as a hard disk or a flash memory. The auxiliary storage device 120 stores a measurement program 122, a correction program 124, etc. The measurement program 122 and the correction program 124 may not be stored in the auxiliary storage device 120, but may be stored in a storage area of ​​the control circuit 101 (e.g., cache memory), the ROM 102, the RAM 103, an external device (e.g., a server), etc.

[0105] Furthermore, the measurement program 122 may be provided not as a standalone program but as part of an arbitrary program. In this case, various processes according to this embodiment are realized in cooperation with the arbitrary program. Even a program that does not include some of these modules does not deviate from the spirit of the measurement program 122 according to this embodiment. Furthermore, some or all of the functions provided by the measurement program 122 may be realized by dedicated hardware. Furthermore, the control unit 50 may be configured in the form of a so-called cloud service in which at least one server executes part of the processes of the measurement program 122.

[0106] <F. Control Flow> Next, the control flow of the measurement process described above with reference to Fig. 7 will be described with reference to Fig. 12. Fig. 12 is a flowchart showing the flow of the measurement process.

[0107] 12 is realized, for example, by control unit 50 of machine tool 100 executing the above-described measurement program 122. In another aspect, some or all of the processing may be performed by circuit elements or other hardware.

[0108] In step S110, the control unit 50 determines whether or not it has received an instruction to measure the actual measurement value used for the geometric error associated with the rotation axis of the table 156. The measurement instruction is issued, for example, in response to an operation on the operation panel 200 described above. If the control unit 50 determines that the measurement instruction has been received (YES in step S110), it switches control to step S112. If not (NO in step S110), the control unit 50 executes the process of step S110 again.

[0109] In step S112, the control unit 50 starts the process of rotating the table 156 around the rotation axis AXA within a predetermined angular range Δθ.

[0110] In step S114, it is assumed that the rotation angle of the table 156 has reached a predetermined rotation angle θ1. Based on this, the control unit 50 maintains the rotation angle of the table 156 at the rotation angle θ1 and measures the position of the reference object T that belongs to the mounting region R1. Thereafter, the control unit 50 resumes the rotation driving of the table 156.

[0111] In step S116, it is assumed that the rotation angle of the table 156 has reached the predetermined rotation angle θ2. Based on this, the control unit 50 maintains the rotation angle of the table 156 at the rotation angle θ2 and measures the reference object T belonging to the mounting regions R1 and R2. Thereafter, the control unit 50 resumes the rotation driving of the table 156.

[0112] In step S118, the control unit 50 determines that the rotation angle of the table 156 has reached the predetermined rotation angle θ3. Based on this, the control unit 50 maintains the rotation angle of the table 156 at the rotation angle θ3 and measures the position of the reference object T that belongs to the mounting region R2.

[0113] In step S119, the control unit 50 determines whether the measurement process has been completed for all of the reference positions P1 to P6. If the control unit 50 determines that the measurement process has been completed for all of the reference positions P1 to P6 (YES in step S119), the control unit 50 switches control to step S120. If not (NO in step S119), the control unit 50 prompts the operator to change the reference object to a different reference position. Based on the completion of the reference object change operation, the control unit 50 returns control to step S112.

[0114] In step S120, the control unit 50 outputs the measurement results from the processes of steps S114, S116, and S118. As an example, the control unit 50 outputs each position of the reference object T in association with each rotation angle of the table 156 in steps S114, S116, and S118 and the reference positions P1 to P6. Each position of the reference object T is represented, for example, by three-dimensional coordinate values.

[0115] The positions of the reference object T output in step S120 are used in the correction process for the rotation axis of the table 156. Various correction algorithms are used in this correction process. Some CNCs have this correction process installed as a standard function. When such a CNC receives input of the positions of the reference object T at each rotation angle, it automatically corrects the drive parameters of the machine tool 100 through internal processing. In other words, the user only needs to input the measured positions of the reference object T at each rotation angle into the correction algorithm installed as a standard function.

[0116] <G. Error Correction Processing> Next, an example of error correction processing using the measurement position output in step S120 (see FIG. 12) described above will be described.

[0117] As described above, the machine tool 100 uses the touch probe TP to measure the center of the reference object T on the machine coordinate system. This measurement is performed at multiple rotation angles around the A axis. The reference object T is placed at multiple locations on the table 156. FIG. 13 is a diagram showing the change in position of the reference object T due to rotation around the A axis. Note that the rotation angle of the table 156 around the B axis is fixed. When the A axis is determined at a rotation angle of a [deg], the position of the reference object T in the coordinate system of the machine tool 100 is ｉ The i-th position is expressed by the following formula (1).

[0118] If there is no geometric error, the reference object T ｉ is the center of rotation of the A axis ｒ P ｃ (= [ ｒ X ｃ , ｒ Y ｃ , ｒ Z ｃ ]) and rotates around it.

[0119] When the A axis is rotated ideally and the A axis is indexed by an angle a, the reference object T ｉ The position is expressed by the following formula (2).

[0120] The "α" shown in the above formula (2) ｉ " is the reference object T ｉThe reference angle may be different for each reference object T. Also, the reference object T at the reference angle and the center of rotation of the A axis ｉ The distance between the position of ｉ (= [u ｉ , v ｉ , w ｉ ]) is represented by the following formula (3).

[0121] When the geometric error of the linear axis is corrected in advance, the reference object T ｉ The position deviation is expressed by the following formula (4).

[0122] In the above formula (4), the geometric error regarding the A axis is "E ＸＡ (a)" and "E ＹＡ (a)" and "E ＺＡ (a)" and "E ＡＡ (a)" and "E ＢＡ (a)" and "E ＣＡ (a)" is shown. ＸＡ (a) shows the axial error motion of the A axis in the X direction. ＹＡ (a) shows the radial error motion of the A axis in the Y direction. ＺＡ (a) shows the radial error motion of the A axis in the Z direction. ＡＡ (a) shows the angular positioning error motion of the A axis about the X axis. ＢＡ (a) shows the tilt error motion of the A axis around the Y axis. ＣＡ (a)) shows the tilt direction error motion of the A axis around the Z axis.

[0123] Reference object T including geometric errors ｉ The position of is expressed by the following formula (5) from the above formulas (3) and (4).

[0124] Finally, the geometric error "E" of the table 156 in the A axis is calculated by solving the following equation (6): ＸＡ (a)," "E ＢＡ (a)," "E ＣＡ (a)," "E ＹＡ (a)," "E ＡＡ (a)," "E ＺＡ(a)) and the center of rotation of the table 156 on the A axis " ｒ P ｃ " is identified.

[0125] Here, "ΔP" shown in equation (6) ｉ (a) is the error between the estimated position and the measured position, and is expressed by the following equation (7).

[0126] Machine tool 100 substitutes the measured position output in step S120 (see FIG. 12) above into equation (7) above, and calculates the geometric error regarding the A-axis and the center of rotation so that the sum of the errors shown in equation (6) above is minimized. The geometric error and the center of rotation are calculated, for example, by the least squares method. In this way, machine tool 100 can simultaneously calculate the geometric error regarding the A-axis and the center of rotation of the A-axis.

[0127] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0128] 50 Control unit, 100 Machine tool, 101 Control circuit, 102 ROM, 103 RAM, 104 Communication interface, 109 Internal bus, 120 Auxiliary storage device, 122 Measurement program, 124 Correction program, 130 Cover body, 140 Spindle head, 142 Spindle, 143 Housing, 150 Table mechanism, 152A Drive mechanism, 152B Drive mechanism, 154 Swivel table, 156 Table, 200 Operation panel, 230 Spindle drive unit, 231C Motor driver, 231X Motor driver, 231Y Motor driver, 231Z Motor driver, 232C Motor, 232X Motor, 232Y Motor, 240 Table drive unit, 241A Motor driver, 241B Motor driver, 241Z Motor driver, 242A Motor, 242B Motor, 242C motor, 242Z motor, AXA rotation axis, AXB rotation axis, DR door, P1 reference position, P2 reference position, P3 reference position, P4 reference position, P5 reference position, P6 reference position, R1 mounting area, R2 mounting area, T reference object, TL tool, TP touch probe, W workpiece, Δθ angle range, θ1 rotation angle, θ2 rotation angle, θ3 rotation angle.

Claims

1. A machine tool capable of measuring actual values ​​used in error correction processing of a rotation axis of a table on which a workpiece can be placed, wherein the table is configured so that a reference object can be attached, and the attachment position of the reference object on the table includes one or more first reference positions that belong to a first area on the table and do not belong to a second area on the table, one or more second reference positions that belong to an overlapping area between the first area and the second area, and one or more third reference positions that belong to the second area and do not belong to the first area, and the machine tool is equipped with a table drive unit for driving the table to rotate around the rotation axis, a spindle to which a touch probe can be attached, a spindle drive unit for driving the spindle to feed relatively with respect to the table, and a control unit for controlling the machine tool, wherein the control unit is configured to perform a drive process for driving the table to rotate around the rotation axis within a predetermined angle range, a first measurement process for measuring the position of the reference object at the first reference position and the second reference position with the touch probe when the table is driven to a first rotation angle within the predetermined angular range; a second measurement process for measuring the position of the reference object at the first reference position, the second reference position, and the third reference position with the touch probe when the table is driven to a second rotation angle within the predetermined angular range; a third measurement process for measuring the position of the reference object at the second reference position and the third reference position with the touch probe when the table is driven to a third rotation angle within the predetermined angular range; and an output process for outputting each of the positions measured in the first to third measurement processes as the actual measurement value, wherein the second rotation angle is an angle between the first rotation angle and the third rotation angle.

2. The machine tool according to claim 1, wherein the control unit further executes the error correction process based on the actual measurement value, and the error correction process calculates the center of rotation related to the rotation axis and a geometric error related to the rotation axis.

3. A machine tool according to claim 1 or 2, wherein the number of said first reference positions is two or more, and the number of said third reference positions is two or more.

4. A machine tool according to claim 1 or 2, wherein the number of second reference positions is two or more.

5. A machine tool according to claim 1 or 2, wherein, when the distance from the touch probe to the first reference position in the axial direction of the spindle is defined as a first distance, the distance from the touch probe to the second reference position in the axial direction of the spindle is defined as a second distance, and the distance from the touch probe to the third reference position in the axial direction of the spindle is defined as a third distance, when the table is at the first swivel angle, the first distance is shorter than the second distance and the second distance is shorter than the third distance, and when the table is at the third swivel angle, the third distance is shorter than the second distance and the second distance is shorter than the first distance.

6. A measurement method for measuring, by a machine tool, actual measurement values ​​used in error correction processing of a rotation axis of a table on which a workpiece can be placed, wherein the table is configured so that a plurality of reference objects can be attached, and the attachment positions of the reference objects on the table include one or more first reference positions that belong to a first area on the table and do not belong to a second area on the table, one or more second reference positions that belong to an overlapping area between the first area and the second area, and one or more third reference positions that belong to the second area and do not belong to the first area, and the machine tool is equipped with: a table drive unit for driving the table to rotate around the rotation axis; a spindle to which a touch probe can be attached; and a spindle drive unit for driving the spindle to feed relatively with respect to the table, and the measurement method comprises: a driving step for driving the table to rotate around the rotation axis within a predetermined angular range; a first measuring step of measuring the position of the reference object at the first reference position and the second reference position with the touch probe when the table is driven to a first rotation angle within the predetermined angular range; a second measuring step of measuring the position of the reference object at the first reference position, the second reference position, and the third reference position with the touch probe when the table is driven to a second rotation angle within the predetermined angular range; a third measuring step of measuring the position of the reference object at the second reference position and the third reference position with the touch probe when the table is driven to a third rotation angle within the predetermined angular range; and an output step of outputting each of the positions measured in the first to third measuring steps as the actual measurement value, wherein the second rotation angle is the angle between the first rotation angle and the third rotation angle.

7. A measurement program for measuring, by a machine tool, actual measurement values ​​used in error correction processing of a rotation axis of a table on which a workpiece can be placed, wherein the table is configured so that a plurality of reference objects can be attached, and the attachment positions of the reference objects on the table include one or more first reference positions that belong to a first area on the table and do not belong to a second area on the table, one or more second reference positions that belong to an overlapping area between the first area and the second area, and one or more third reference positions that belong to the second area and do not belong to the first area, and the machine tool comprises: a table drive unit for driving the table to rotate around the rotation axis; a spindle to which a touch probe can be attached; and a spindle drive unit for driving the spindle to feed relatively with respect to the table, and the measurement program includes in a computer: a drive process for driving the table to rotate around the rotation axis within a predetermined angle range; a first measurement process for measuring the position of the reference object at the first reference position and the second reference position with the touch probe when the table is driven to a first rotation angle within the predetermined angular range; a second measurement process for measuring the position of the reference object at the first reference position, the second reference position, and the third reference position with the touch probe when the table is driven to a second rotation angle within the predetermined angular range; a third measurement process for measuring the position of the reference object at the second reference position and the third reference position with the touch probe when the table is driven to a third rotation angle within the predetermined angular range; and an output process for outputting each position measured in the first to third measurement processes as the actual measurement value, wherein the second rotation angle is an angle between the first rotation angle and the third rotation angle.

Images