Machine tool, contact detection method between grinding wheel of machine tool and workpiece, and storage medium

Abstract

The present invention provides a machine tool, a method for detecting contact between a grinding wheel of a machine tool and a workpiece, and a computer program. The method for detecting contact between a grinding wheel of a machine tool and a workpiece controls at least one actuator so that a tool holder that holds a grinding wheel rotatable around a tool rotation axis moves relative to a workpiece holder that holds the workpiece in a moving direction. The method controls a motor different from at least one actuator that enables a holder of one of the tool holder and the workpiece holder to move along a control axis that intersects the tool rotation axis and the moving direction, so that the holder of one of the tool holder and the workpiece holder is stationary in a direction along the control axis. The method further detects contact between the grinding wheel and the workpiece based on changes in a control value of the motor.

Description

Technical Field

[0001] The invention relates to a machine tool, a contact detection method between a grinding wheel of the machine tool and a workpiece, and a computer program. Background Art

[0002] Patent document 1 records a technique for detecting the moment when a grinding wheel contacts a workpiece in a machine tool for grinding a raw material with a grinding wheel. In the technique, the current of a motor that rotates the grinding wheel is monitored, and the moment when the grinding wheel contacts the workpiece is detected by utilizing the change in the current when the workpiece moves toward the grinding wheel and contacts the grinding wheel.

[0003] Patent Document 1: Japanese Patent Application Laid-Open No. 11-077491

[0004] If you want to rotate the grinding wheel at a specified speed, you need to apply a large amount of power to the motor at the beginning. If you reach the predetermined rotation speed, the power of the motor will drop. Since it takes a predetermined time for the power to stabilize, the threshold for detecting the moment when the grinding wheel contacts the workpiece cannot be set during this period, and it takes time to detect the contact. In addition, since the power of the motor is unstable even in the non-contact state, it is easy to misdetect. Summary of the invention

[0005] The technology disclosed in the present application aims to provide a machine tool, a method for detecting contact between a grinding wheel and a workpiece in a machine tool, and a computer program that can detect with high accuracy the moment when a grinding wheel contacts a workpiece.

[0006] The method for detecting contact between a grinding wheel and a workpiece of a machine tool of the first embodiment of the present disclosure controls at least one actuator so that a tool holder that holds the grinding wheel so as to be rotatable around a tool rotation axis moves relative to a workpiece holder that holds the workpiece in a moving direction. A motor different from at least one actuator is controlled to move one of the tool holder and the workpiece holder along a control axis that intersects the tool rotation axis and the moving direction so that the holder of one of the tool holder and the workpiece holder is stationary in a direction along the control axis. The contact between the grinding wheel and the workpiece is detected based on changes in a control value of the motor. Preferably, the motor is a servo motor. More preferably, the motor is an AC servo motor.

[0007] According to a second aspect of the present disclosure, in addition to the contact detection method of the first aspect, the control axis is perpendicular to the tool rotation axis.

[0008] According to a third aspect of the present disclosure, in the contact detection method of the first aspect or the second aspect, the control axis is perpendicular to a straight line extending in the moving direction.

[0009] According to the fourth embodiment of the present disclosure, based on the contact detection methods of the first to third embodiments, the electric machine is configured to move the tool holder along a control axis, and at least one actuator is at least one additional motor, and the at least one additional electric machine is configured to move the tool holder along each of at least one additional control axis perpendicular to the control axis.

[0010] According to the 5th mode of the present disclosure, on the basis of the contact detection methods of the 1st to 4th modes, the workpiece holder supports the workpiece so that it can rotate around the workpiece rotation axis. When the tool rotation axis and the workpiece rotation axis are on the same plane, the moving direction is parallel to the same plane. When the tool rotation axis and the workpiece rotation axis are lines in a twisted position, the moving direction is along a line perpendicular to the tool rotation axis and the workpiece rotation axis.

[0011] According to a sixth aspect of the present disclosure, based on the contact detection method of the first aspect to the fifth aspect, the control value includes at least one of a current command value for the motor, a current feedback value from the motor, a position feedback value, and a speed feedback value. The position feedback value is obtained by integrating the rotation speed obtained from the speed detector of the motor, obtained from the output value of the angle detector of the motor, or obtained from the position detector of the tool holder or the workpiece holder. The speed feedback value is obtained from the speed detector of the motor, or obtained by converting the output value of the angle detector of the motor.

[0012] According to a seventh aspect of the present disclosure, based on the contact detection method of the sixth aspect, when the value representing the central tendency of the current command value for each constant time width deviates from a predetermined range, it is determined that the grinding wheel is in contact with the workpiece. The value representing the central tendency refers to the central value of a numerical group in a statistical distribution, such as an average value, a median value, or a mode. Preferably, the range is determined based on the value representing the central tendency of the current command value for each constant time width when the grinding wheel rotates at a rotational speed at which the grinding wheel rotates during grinding processing, when the grinding wheel is not in contact with the workpiece.

[0013] According to an eighth aspect of the present disclosure, based on the contact detection method of the sixth aspect, when the value of the statistical dispersion of the current feedback value for each constant time width deviates from a predetermined range, it is determined that the grinding wheel and the workpiece are in contact. The value representing the statistical dispersion represents the extent of spread of the statistical distribution, and refers to, for example, dispersion, standard deviation, mean absolute deviation, mean deviation, etc. Preferably, the range is determined based on the value of the statistical dispersion of the current feedback value for each constant time width when the grinding wheel rotates at a rotational speed of the grinding wheel during grinding processing in a state where the grinding wheel does not contact the workpiece.

[0014] According to a ninth aspect of the present disclosure, in addition to the contact detection method of the sixth aspect, when the value of the statistical deviation of the position feedback value for each constant time width deviates from a predetermined range, it is determined that the grinding wheel and the workpiece are in contact. Preferably, the range is determined based on the value of the statistical deviation of the position feedback value for each constant time width when the grinding wheel rotates at a rotational speed at which the grinding wheel rotates during grinding processing, when the grinding wheel is not in contact with the workpiece.

[0015] According to a tenth aspect of the present disclosure, in addition to the contact detection method of the sixth aspect, when at least one of a velocity feedback value and a value indicating a statistical dispersion of velocity feedback values ​​for each certain time width deviates from a predetermined range, it is determined that the grinding wheel is in contact with the workpiece. Preferably, the range is determined based on the at least one value when the grinding wheel is rotating at a rotational speed at which the grinding wheel rotates during grinding processing, when the grinding wheel is not in contact with the workpiece.

[0016] According to an eleventh aspect of the present disclosure, in the contact detection method of the seventh aspect, the value indicating the central tendency is represented by at least one of an average value and a valid value.

[0017] According to a twelfth aspect of the present disclosure, in the contact detection method of any one of the eighth aspect to the tenth aspect, the value indicating the statistical dispersion is represented by at least one value including a standard deviation.

[0018] According to a 13th aspect of the present disclosure, in the contact detection method of the 9th aspect or the 10th aspect, the value indicating the statistical dispersion is represented by at least one value including a valid value.

[0019] The machine tool of the 14th mode of the present disclosure includes a component for executing the contact detection method of any one of the 1st to 13th modes. Preferably, the machine tool includes: a tool holder that holds the grinding wheel so that it can rotate around the tool rotation axis; a workpiece holder that holds the workpiece; at least one actuator that is configured to move one of the tool holder and the workpiece holder relative to the other of the tool holder and the workpiece holder in a moving direction; a motor that is configured to move the tool holder or the workpiece holder along a control axis; and an electronic circuit that detects at least one actuator and monitors the control value of the motor to determine whether the grinding wheel is in contact with the workpiece. The electronic circuit is configured to execute the contact detection method of any one of the 1st to 13th modes.

[0020] A computer program according to a fifteenth aspect of the present disclosure includes instructions for causing a computer to execute the contact detection method according to any one of the first to thirteenth aspects.

[0021] A computer-readable storage medium according to a sixteenth aspect of the present disclosure stores the computer program according to the fifteenth aspect.

[0022] In the contact detection method of the first mode, the machine tool of the 14th mode including a component for executing the contact detection method of the first mode, the computer program of the 15th mode including instructions for causing a computer to execute the contact detection method of the first mode, and the storage medium of the 16th mode storing the computer program, it is not necessary to apply a large amount of electric power, and the contact between the grinding wheel and the workpiece is detected according to the change of the control value of the motor that performs the control that is easy to stably control the electric power. Therefore, the setting for detecting the contact between the grinding wheel and the workpiece does not require time, and the signal is stable when non-contact, so the contact can be detected with high precision. Moreover, the control axis intersects with the tool rotation axis and the moving direction, so the component of the control axis direction of the resistance generated by the contact between the grinding wheel and the workpiece becomes larger. Therefore, the contact can be detected according to the control value of the motor. In addition, when the motor is a servo motor, the feedback signal can be used as the control value, and the contact can be detected with high precision without setting another sensor for detecting the contact. Moreover, by using an AC motor, the motor life can be extended.

[0023] In the contact detection method of the second aspect, the machine tool of the 14th aspect including a component for executing the contact detection method of the second aspect, the computer program of the 15th aspect including an instruction for causing a computer to execute the contact detection method of the second aspect, and the storage medium of the 16th aspect storing the computer program, since the control axis is perpendicular to the tool rotation axis, the component of the control axis direction of the resistance generated by the contact between the grinding wheel and the workpiece becomes larger. Therefore, the contact can be detected with higher accuracy.

[0024] In the contact detection method of the third aspect, the machine tool of the fourth aspect including a component for executing the contact detection method of the third aspect, the computer program of the fifth aspect including an instruction for causing a computer to execute the contact detection method of the third aspect, and the storage medium of the sixth aspect storing the computer program, since the control axis is perpendicular to the straight line extending in the moving direction, the component of the control axis direction of the resistance generated by the contact between the grinding wheel and the workpiece becomes larger. Therefore, the contact can be detected with higher accuracy.

[0025] In the contact detection method of the fourth mode, the machine tool of the 14th mode including a component for executing the contact detection method of the fourth mode, the computer program of the 15th mode including an instruction for causing a computer to execute the contact detection method of the fourth mode, and the storage medium of the 16th mode storing the computer program, the control value of the motor for controlling the movement of the grinding wheel having a smaller moment of inertia than the workpiece is usually applied to the detection of the contact. Therefore, the change of the control value caused by the resistance generated by the contact becomes larger. Therefore, the contact can be detected with higher accuracy.

[0026] In the contact detection method of the fifth mode, the machine tool of the fourteenth mode including a component for executing the contact detection method of the fifth mode, the computer program of the fifteenth mode including instructions for causing a computer to execute the contact detection method of the fifth mode, and the storage medium of the sixteenth mode storing the computer program, when the workpiece has a shape of a rotating surface relative to the workpiece rotation axis and the grinding wheel has a shape of a rotating surface relative to the tool rotation axis, the grinding wheel can approach the workpiece in a direction of the shortest distance, and a desired portion can be ground.

[0027] In the contact detection method of the sixth mode, the machine tool of the fourteenth mode including a component for executing the contact detection method of the sixth mode, the computer program of the fifteenth mode including instructions for causing a computer to execute the contact detection method of the sixth mode, and the storage medium of the sixteenth mode storing the computer program, since the control value includes at least one of a current command value to the motor that changes when the grinding wheel contacts the workpiece, a current feedback value from the motor, a position feedback value, and a speed feedback value, contact can be detected with high precision.

[0028] Since the maximum and minimum values ​​of the current command value in the contact state when the grinding wheel and the workpiece are in minute contact of several μm are difficult to be different from the maximum and minimum values ​​of the current command value in the non-contact state when the grinding wheel and the workpiece are not in contact, it is difficult to detect by threshold value. However, since the current command value in the contact state tends to be biased toward the vicinity of the maximum or minimum value, the value representing the concentration trend of the current command value for each certain time width is easy to be different. In the contact detection method of the seventh mode, the machine tool of the fourteenth mode including a component for executing the contact detection method of the seventh mode, the computer program of the fifteenth mode including instructions for causing a computer to execute the contact detection method of the seventh mode, and the storage medium of the sixteenth mode storing the computer program, this property of the current command value can be used to detect minute contacts of several μm or the like.

[0029] Since the current feedback value in the contact state when the grinding wheel and the workpiece are in minute contact of several μm is difficult to be different from the current feedback value in the non-contact state when the grinding wheel and the workpiece are not in contact, or the current feedback value changes in the non-contact state before and after the contact state, it is difficult to pass the threshold detection. However, in the contact state, the deviation of the current feedback value for each certain time width tends to increase, so the value representing the statistical deviation of the current feedback value for each certain time width is easy to be different. In the contact detection method of the eighth mode, the machine tool of the fourteenth mode including a component for executing the contact detection method of the eighth mode, the computer program of the fifteenth mode including instructions for causing a computer to execute the contact detection method of the eighth mode, and the storage medium of the sixteenth mode storing the computer program, this property of the current feedback value can be used to detect minute contacts of several μm or the like.

[0030] Since the maximum and minimum values ​​of the position feedback value in the contact state when the grinding wheel and the workpiece are in minute contact of several μm are difficult to be different from the maximum and minimum values ​​of the position feedback value in the non-contact state when the grinding wheel and the workpiece are not in contact, it is difficult to pass the threshold detection. However, in the contact state, the deviation of the position feedback value for each certain time width tends to increase, so the value representing the statistical deviation of the position feedback value for each certain time width is easy to be different. In the contact detection method of the 9th mode, the machine tool of the 14th mode including a component for executing the contact detection method of the 9th mode, the computer program of the 15th mode including instructions for causing a computer to execute the contact detection method of the 9th mode, and the storage medium of the 16th mode storing the computer program, this property of the position feedback value can be used to detect minute contacts of several μm or the like.

[0031] Even in the contact state when the grinding wheel and the workpiece are in minute contact of a few μm, the speed feedback value is significantly different from the maximum and minimum values ​​of the speed feedback value in the non-contact state when the grinding wheel and the workpiece are not in contact. Thus, in the contact state, the deviation of the speed feedback value for each certain time width tends to increase, so the value representing the statistical deviation of the speed feedback value for each certain time width is also prone to difference. In the contact detection method of the tenth mode, the machine tool of the fourteenth mode including a component for executing the contact detection method of the tenth mode, the computer program of the fifteenth mode including instructions for causing a computer to execute the contact detection method of the tenth mode, and the storage medium of the sixteenth mode storing the computer program, this property of the speed feedback value can be used to detect minute contacts of a few μm or the like.

[0032] In the contact detection method of the 11th aspect, the machine tool of the 14th aspect including a component for executing the contact detection method of the 11th aspect, the computer program of the 15th aspect including instructions for causing a computer to execute the contact detection method of the 11th aspect, and the storage medium of the 16th aspect storing the computer program, since the absolute value of the value indicating the central tendency of the current command value for each certain time width is much larger than the value of the statistical deviation of the current command value, the effective value including both the central tendency of the current command value for each certain time width and the statistical deviation of the current command value also changes in the same manner as the value indicating the central tendency of the current command value for each certain time width. Therefore, it is possible to detect micro contacts of several μm or the like using the average value and the effective value supported by a large amount of hardware.

[0033] In the contact detection method of the 12th aspect, the machine tool of the 14th aspect including a component for executing the contact detection method of the 12th aspect, the computer program of the 15th aspect including instructions for causing a computer to execute the contact detection method of the 12th aspect, and the storage medium of the 16th aspect storing the computer program, it is easy to install because it utilizes standard deviation supported by a large amount of hardware.

[0034] In the contact detection method of the 13th aspect, the machine tool of the 14th aspect including a component for executing the contact detection method of the 13th aspect, the computer program of the 15th aspect including an instruction for causing a computer to execute the contact detection method of the 13th aspect, and the storage medium of the 16th aspect storing the computer program, since the absolute value of the value indicating the central tendency of the speed feedback value / position feedback value is a value close to 0, the effective value including both the central tendency of the speed feedback value / position feedback value for each constant time width and the statistical deviation of the speed feedback value / position feedback value for each constant time width also changes in the same manner as the statistical deviation. Therefore, even with the effective value supported by a large amount of hardware, it is possible to detect a micro contact of several μm or the like.

[0035] According to the technology disclosed in the present application, the moment when the grinding wheel contacts the workpiece can be detected with high precision. More specifically, the minute contact when the grinding wheel contacts the workpiece with a minute amount of several μm can be detected. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a structural diagram showing the structure of the machine tool according to the embodiment.

[0037] Figure 2 This is a block diagram of a peripheral circuit of a motor according to an embodiment.

[0038] Figure 3 It is a control block diagram of the motor control in a semi-closed loop mode.

[0039] Figure 4This is a control block diagram of the motor in a fully closed loop mode.

[0040] Figure 5 An example of a method of moving a grinding wheel toward a workpiece is shown.

[0041] Figure 6 An example of a method of moving a grinding wheel toward a workpiece is shown.

[0042] Figure 7 An example of a method of moving a grinding wheel toward a workpiece is shown.

[0043] Figure 8 An example of a method of moving a grinding wheel toward a workpiece is shown.

[0044] Fig. 9 An example of a method of moving a grinding wheel toward a workpiece is shown.

[0045] Fig.10 An example of a change in the current command value of the second motor when the position control of the second motor is performed is shown.

[0046] Fig.11 An example of a change in the average value of the current command value for the second motor when the position control is performed on the second motor is shown.

[0047] Fig.12 An example of change in the standard deviation of the current command value of the second motor when the position control is performed on the second motor is shown.

[0048] Fig.13 An example of a change in the effective value of the current command value of the second motor when the position control of the second motor is performed is shown.

[0049] Fig.14 An example of a change in the current feedback value of the second motor when the position control of the second motor is performed is shown.

[0050] Fig.15 An example of a change in the average value of the current feedback value of the second motor when the position control of the second motor is performed is shown.

[0051] Fig.16 An example of change in the standard deviation of the current feedback value of the second motor when the position control of the second motor is performed is shown.

[0052] Fig.17 An example of a change in the effective value of the current feedback value of the second motor when the position control of the second motor is performed is shown.

[0053] Fig.18 An example of a change in the speed feedback value of the second motor when the position control of the second motor is performed is shown.

[0054] Fig.19 An example of a change in the average value of the speed feedback value of the second motor when the position control of the second motor is performed is shown.

[0055] Fig. 20 An example of a change in the standard deviation of the speed feedback value of the second motor when the position control of the second motor is performed is shown.

[0056] Fig.21 An example of a change in the effective value of the speed feedback value of the second motor when the position control of the second motor is performed is shown.

[0057] Fig. 22 An example of a change in the position feedback value of the second motor when the position control of the second motor is performed is shown.

[0058] Fig.23 An example of changes in the average value of the position feedback value of the second motor when the position control of the second motor is performed is shown.

[0059] Fig.24 An example of a change in the standard deviation of the position feedback value of the second motor when the position control of the second motor is performed is shown.

[0060] Fig.25 An example of a change in the effective value of the position feedback value of the second motor when the position control of the second motor is performed is shown.

[0061] Fig.26 This is a flowchart showing the processing flow of the method for detecting contact between the grinding wheel and the workpiece according to the present embodiment. DETAILED DESCRIPTION

[0062] Hereinafter, the present invention will be described in detail based on the accompanying drawings showing the embodiments. In addition, the same reference numerals in the drawings represent corresponding or substantially the same structures.

[0063] (Implementation Method)

[0064] (Structure of Machine Tool 1)

[0065] Figure 11 is a block diagram showing the structure of a machine tool 1 according to an embodiment of the present invention. The machine tool 1 includes a base 10, a workpiece spindle table 11, a workpiece holder 12, a carriage 13, a saddle 14, a tool spindle table 15, a tool holder 16, a first motor 21, a second motor 22, a third motor 23, a fourth motor 24, a first ball screw 31, a second ball screw 32, and a third ball screw 33. The base 10 supports the workpiece spindle table 11, the workpiece holder 12, the carriage 13, the saddle 14, the tool spindle table 15, the tool holder 16, the first motor 21, the second motor 22, the third motor 23, the fourth motor 24, the first ball screw 31, the second ball screw 32, and the third ball screw 33. Here, it is assumed that the workpiece rotates along the workpiece rotation axis A described later. XW The axis of the base 10 is the Z axis, the axis perpendicular to the Z axis and along the upper surface of the base 10 is the Y axis, and the axis perpendicular to the Y axis and the Z axis is the X axis.

[0066] The workpiece spindle 11 supports the workpiece holder 12 so as to be rotatable about the workpiece axis A. XW For example, a motor (not shown) is mounted on the workpiece spindle 11, and the motor is configured to rotate the workpiece holder 12 around the workpiece rotation axis A. XW The workpiece holder 12 is, for example, a workpiece spindle. The workpiece holder 12 holds the workpiece W so that it can rotate around the workpiece rotation axis A. XW The support 13 is connected to the second motor 22 by means of a second ball screw 32. The second motor 22 is configured to move the saddle 14, the tool spindle table 15, and the tool holder 16 in the Y-axis direction. The support 13 supports the first motor 21, and supports the saddle 14, the tool spindle table 15, and the tool holder 16 to be slidable. The saddle 14 is connected to the first motor 21 by means of a first ball screw 31. The first motor 21 is configured to move the saddle 14 in the X-axis direction.

[0067] The saddle 14 supports the third motor 23 and supports the tool spindle 15 and the tool holder 16 so that they can slide in the Z-axis direction. The third motor 23 is configured to move the tool spindle 15 and the tool holder 16 in the Z-axis direction. The tool spindle 15 supports the tool holder 16 so that it can move around the B-axis A. XB The fourth motor 24 is configured to rotate the tool holder 16 about the B axis A. XB Furthermore, a motor (not shown) is mounted on the tool spindle 15, and the motor is configured to rotate the tool holder 16 around the tool rotation axis A. XT The tool holder 16 is, for example, a tool spindle. The tool holder 16 holds the grinding wheel GS so that it can rotate around the tool rotation axis A. XT Rotate.

[0068] In addition, the workpiece spindle table 11 includes the same structure as the support 13 and the saddle 14 as the tool spindle table 15, and the machine tool 1 may also include a fifth motor 25, a sixth motor 26 and a seventh motor 27 for driving the workpiece spindle table 11 in the X-axis direction, the Y-axis direction and the Z-axis direction, and a fifth ball screw 35, a sixth ball screw 36 and a seventh ball screw 37 connecting these motors to the workpiece spindle table 11. In the following embodiments, the first motor 21, the second motor 22, the third motor 23, the fourth motor 24, the fifth motor 25, the sixth motor 26 and the seventh motor 27 may also be collectively referred to as a plurality of motors 20. The plurality of motors 20 are preferably servo motors. In addition, the plurality of motors 20 are more preferably AC servo motors.

[0069] In addition, the first motor 21, the second motor 22, the third motor 23, the fifth motor 25, the sixth motor 26 and the seventh motor 27 are respectively configured to move the tool holder 16 or the workpiece holder 12 along the control axis. The control axis of the first motor 21 and the control axis of the fifth motor 25 are the X axis. The control axis of the second motor 22 and the control axis of the sixth motor 26 are the Y axis. The control axis of the third motor 23 and the control axis of the seventh motor 27 are the Z axis.

[0070] The machine tool 1 further includes a numerical control device 5, an input / output interface 6, a servo driver device 7, and a monitoring device 8. The numerical control device 5 is configured to control the rotation of a plurality of motors 20, a workpiece holder 12, and a tool holder 16, etc., to process the workpiece W into a desired shape. The input / output interface 6 includes an input device such as a button and a display device such as a display. The input / output interface 6 is preferably a touch panel display. The servo driver device 7 outputs an optimal current or voltage to the motor 20 according to the command value from the numerical control device 5. The monitoring device 8 monitors the signal sent by the feedback control of the motor 20, and sends a signal to the numerical control device 5 when a predetermined condition is met. For example, the monitoring device 8 determines the contact between the grinding wheel GS and the workpiece W according to the signal, and sends a signal indicating whether there is contact to the numerical control device 5. If the numerical control device 5 receives a signal indicating that the grinding wheel GS is in contact with the workpiece W, the relative movement of the grinding wheel GS and the workpiece W is stopped, and the position of the grinding wheel GS or the workpiece W is returned to a predetermined position.

[0071] Figure 2 2 is a block diagram of a peripheral circuit of the motor 20 according to the embodiment. The numerical control device 5 includes an electronic circuit 51 and a memory 52. Figure 2The electronic circuit 51 is a processor such as an ECU. The memory 52 is configured to store a processing program for processing the workpiece W. The electronic circuit 51 executes the processing program to control the rotation of the motor 20, the workpiece holder 12, and the tool holder 16. The monitoring device 8 includes an electronic circuit 81 as a hardware processor such as an ECU and a memory 82. The memory 82 stores a logic for determining contact. The electronic circuit 81 executes the logic.

[0072] Moreover, refer to Figure 2 ,exist Figure 1 The first motor 21 to the fourth motor 24 shown are each provided with at least one of the speed detectors VD1 to VD4 and the position detectors (angle detectors) PD1 to PD4. In addition, although not shown, the servo drive device 7 may also include a speed detector and a position detector (angle detector) for controlling the fifth motor 25, the sixth motor 26, and the seventh motor 27, respectively. In the following embodiments, these speed detectors are collectively referred to as speed detectors VD. These position detectors (angle detectors) are collectively referred to as position detectors (angle detectors) PD.

[0073] The speed detector VD is, for example, an incremental encoder E connected to the motor 20. Figure 1 In the figure, the encoder E2 connected to the second motor 22 is shown as the speed detector VD2. The angle detector PD is, for example, an incremental encoder E connected to the motor 20. The rotation angle of the motor 20 detected by the angle detector PD is obtained by integrating the output of the encoder E. In addition, the encoder E can also be set as an absolute encoder, the output value of the encoder E is used as the output of the angle detector PD, and the displacement of the output value is used as the output of the speed detector VD. Figure 1 In FIG. 1 , the encoder E2 connected to the second motor 22 is shown as the speed detector PD2. The position detector PD is, for example, a linear scale L for measuring the position of the workpiece holder 12 or the tool holder 16. Figure 1 2 shows a linear scale L2 for detecting the position of the bracket 13 in the Y-axis direction.

[0074] Reference Figure 2The servo driver device 7 includes a first servo driver 71, a second servo driver 72, a third servo driver 73, and a fourth servo driver 74 for respectively controlling the first motor 21, the second motor 22, the third motor 23, and the fourth motor 24. In addition, although not shown in the figure, the servo driver device 7 may also include a servo driver for respectively controlling the fifth motor 25, the sixth motor 26, and the seventh motor 27. Since the fourth motor 24 does not have a position detector PD equivalent to a linear scale, the fourth servo driver 74 has the same basic functions as the above-mentioned servo driver except that it does not process information from the linear scale, and is collectively referred to as a servo driver 70.

[0075] The monitoring device 8 is electrically connected to the numerical control device 5 , the servo driver device 7 , the speed detector VD, and the position detector (angle detector) PD. Figure 3 and Figure 4 1 is a control block diagram for explaining the details of these signals and controlling the motor 20 . Figure 3 This is a control block diagram of feedback control of a system (semi-closed loop method) when an encoder E is used as a position detector (angle detector) PD. Figure 4 This is a control block diagram of feedback control of a system (full closed loop method) when a linear scale L is used as the position detector PD. Figure 3 and Figure 4 The servo driver 70 includes a position controller 70a, a speed controller 70b, a current controller 70c and a voltage regulator 70d.

[0076] Reference Figure 3 When position control is performed in a semi-closed loop mode, the position command value θ from the numerical control device 5 is r The position feedback value θ obtained by integrating the output value of encoder E c The deviation e o The position controller 70a usually outputs a speed command value ω using proportional control (P control). r . Reference Figure 4 When position control is performed in a fully closed loop mode, the position command value P from the numerical control device 5 is r The position feedback value P obtained from the linear scale L c The deviation e o The position controller 70a usually outputs a speed command value ω using proportional control (P control). r When the speed control for controlling the speed of the workpiece holder 12 or the tool holder 16 is performed, a speed command value ω is input from the numerical control device 5 to the speed controller 70b. r .

[0077] The subsequent processing is common to all methods, whether it is semi-closed loop, full-closed loop or speed control. Speed ​​command value ω r and the speed feedback value ω obtained from encoder E c The deviation e u The speed controller 70b usually uses proportional integral control (PI control) to output the current command value i r . Current command value i r The current feedback value i obtained as the output of the voltage regulator 70d c The deviation e i The current controller 70c usually outputs a voltage command value E using proportional integral control (PI control). r The voltage regulator 70d is usually a power amplifier, which adjusts the voltage according to the voltage command value E r The driving current i for controlling the motor 20 is output to the motor 20. c .

[0078] return Figure 2 The monitoring device 8 is configured to monitor the position command value θ output from the numerical control device 5. r , P r Or speed command value ω r , the speed command value ω output from the position controller 70a r , the current command value i output from the speed controller 70b r , the current feedback value i output from the voltage regulator 70d c , the speed feedback value ω output from encoder E c , and the position feedback value θ obtained by integrating the value output from encoder E c (Or, the position feedback value P output from the linear scale L c ). In the following embodiments, these values ​​monitored by the monitoring device 8 are referred to as control values. The monitoring device 8 includes an electronic circuit 81 configured to calculate the average, standard deviation, effective value, etc. of these values, and can output a signal to the numerical control device 5 when these values ​​or the calculated values ​​meet predetermined conditions. The numerical control device 5 can set parameters (threshold values) for determining predetermined conditions in the memory 82 of the monitoring device 8.

[0079] Figures 5 to 9 Examples of methods for moving the grinding wheel GS toward the workpiece W are shown respectively. Figures 5 to 9 In FIG, the grinding wheel GS is shown as being larger than the workpiece W, but in reality the workpiece W is usually larger than the grinding wheel GS. Figure 5 Indicates the tool rotation axis A XT and workpiece rotation axis A XWThis is an example of moving the grinding wheel GS in the X-axis direction in a direction parallel to the Z-axis. Figure 6 Indicates the tool rotation axis A XT With workpiece rotation axis A XW In the same plane, the tool rotation axis A XT Rotate the workpiece along axis A in a direction parallel to the X axis. XW This is an example of moving the grinding wheel GS in the Z-axis direction in a direction parallel to the Z-axis. Figure 7 The figure shows that when the grinding wheel GS has a conical shape, the tool rotation axis A is rotated so that the side surface of the cone is parallel to the grinding target surface of the workpiece W. XT Tilt to the workpiece rotation axis A XW An example of moving the grinding wheel GS along the X axis on the same plane. Figure 8 Indicates the tool rotation axis A XT and workpiece rotation axis A XW This is an example of moving the grinding wheel GS in the Z-axis direction in a direction parallel to the Z-axis. Fig. 9 Indicates the tool rotation axis A XT Rotate the workpiece along axis A in a direction parallel to the X axis. XW This is an example of moving the grinding wheel GS in the Y-axis direction in a direction parallel to the Z-axis.

[0080] In the following description, Figures 5 to 9 The arrow outside the coordinate axis indicates the moving direction MD of the grinding wheel GS. Figures 5 to 8 As shown in the example, in the tool rotation axis A XT and workpiece rotation axis A XW When the two components are on the same plane, the moving direction MD is parallel to the same plane. Fig. 9 As shown in the example, in the tool rotation axis A XT and workpiece rotation axis A XW When the line is in a twisted position, the moving direction MD is along the tool rotation axis A. XT and workpiece rotation axis A XW In addition, the motor 20 involved in the movement of the grinding wheel GS can be called at least one actuator. The motor 20 involved in the movement of the grinding wheel GS can also be called an additional motor. Figure 5 In the example, the first motor 21 is at least one actuator. Figure 6 In the example, the third motor 23 is at least one actuator. Figure 7 In the example, the first motor 21 and the third motor 23 are at least one actuator. Figure 8 In the example, the third motor 23 is at least one actuator. Fig. 9 In the example, the second motor 22 is at least one actuator.

[0081] In addition, Figures 5 to 9 In the example of , it is also possible to move the workpiece W instead of the grinding wheel GS. In particular, when the desired surface cannot be ground without moving the workpiece W, it is preferable to move the workpiece W. In this case, Figure 5 In the example, the fifth motor 25 is at least one actuator. Figure 6 In the example, the seventh motor 27 is at least one actuator. Figure 7 In the example, the fifth motor 25 and the seventh motor 27 are at least one actuator. Figure 8 In the example, the seventh motor 27 is at least one actuator. Fig. 9 In the example of FIG. 1 , the sixth motor 26 is at least one actuator. The control axis of at least one actuator may also be referred to as an additional control axis.

[0082] In the present embodiment, a motor different from at least one actuator among the first motor 21 to the seventh motor 27 is controlled so that one of the tool holder 16 and the workpiece holder 12 is stationary in a direction along the control axis of the motor. Furthermore, the contact between the grinding wheel GS and the workpiece W is detected based on the change in the control value of the motor whose control axis is not perpendicular to the direction of the friction torque generated by the contact between the grinding wheel GS and the workpiece W. Specifically, the control axis of the motor used to detect the contact between the grinding wheel GS and the workpiece W is perpendicular to the tool rotation axis A. XT More preferably, a motor having a control axis substantially parallel to the direction of the friction torque generated by the contact between the grinding wheel GS and the workpiece W is used to detect the contact between the grinding wheel GS and the workpiece W. That is, the control axis is preferably parallel to the tool rotation axis A. XT Vertical. Preferably, the control axis is perpendicular to a straight line extending in the moving direction MD.

[0083] Figure 5 In the example, the second motor 22 or the sixth motor 26 is preferably used to detect the contact between the grinding wheel GS and the workpiece W. Figure 6 In the example, the second motor 22 or the sixth motor 26 is preferably used to detect the contact between the grinding wheel GS and the workpiece W. Figure 7 In the example, the second motor 22 or the sixth motor 26 is preferably used to detect the contact between the grinding wheel GS and the workpiece W. Figure 8 In the example, the second motor 22 or the sixth motor 26 is preferably used to detect the contact between the grinding wheel GS and the workpiece W. Fig. 9 In the example, the third motor 23 or the seventh motor 27 is preferably used to detect the contact between the grinding wheel GS and the workpiece W.

[0084] Furthermore, it is more preferable that, in a motor having a control axis which is not perpendicular to the direction of the friction torque generated by the contact between the grinding wheel GS and the workpiece W, the motor for controlling the movement of the grinding wheel GS is used to detect the contact between the grinding wheel GS and the workpiece W. This is because, generally, since the inertia (moment of inertia) of the grinding wheel GS is smaller than the inertia (moment of inertia) of the workpiece W, the acceleration generated by the friction torque shows a larger value, and the control value becomes larger. Figures 5 to 8 In the example, the second motor 22 is preferably used to detect the contact between the grinding wheel GS and the workpiece W. In this case, the at least one actuator is at least one additional motor configured to move the tool holder 16 along each of at least one additional control axis perpendicular to the control axis of the second motor 22. Fig. 9 In the example of , the third motor 23 is preferably used. In this case, at least one actuator is at least one additional motor, and the at least one additional motor is configured to move the tool holder 16 along each of at least one additional control axis perpendicular to the control axis of the third motor 23. However, in the case where the inertia (moment of inertia) of the grinding wheel GS is greater than the inertia (moment of inertia) of the workpiece W, the motor that controls the movement of the workpiece W can also be used to detect the contact between the grinding wheel GS and the workpiece W.

[0085] Figure 10 to Figure 25 It is shown that the period T in the figure c The first motor 21 is controlled to stop the grinding wheel GS in a state where the grinding wheel GS is in slight contact with the workpiece W by a few μm. Figure 5 1 and 10. The second motor 22 is moved as shown in FIG. 1 and the second motor 22 is positionally controlled at a predetermined position. In addition, the second motor 22 is controlled by a semi-closed loop method. Even when the second motor 22 is controlled by a fully closed loop method, a signal change in the control system of the second motor 22 is detected. Figure 10 to Figure 25 In addition, when the second motor is speed-controlled to a speed of 0, a signal similar to the Figure 10 to Figure 21 Signals of roughly the same nature.

[0086] Specifically, Figure 10 to Figure 13 are current command values ​​i and i of the second motor 22 when the second motor 22 is position controlled. r , current command value i r The average value of the current command value i r The standard deviation of the current command value i r Examples of changes in effective values. Figure 14 to Figure 17 are current feedback values ​​i of the second motor 22 when the position of the second motor 22 is controlled. c , current feedback value i c The average value of the current feedback value ic The standard deviation of the current feedback value i c Examples of changes in effective values. Figure 18 to Figure 21 are speed feedback values ​​ω of the second motor 22 when the position of the second motor 22 is controlled. c , speed feedback value ω c The average value of speed feedback value ω c The standard deviation of speed feedback value ω c Examples of changes in effective values. Figure 22 to Figure 25 are the position feedback values ​​θ of the second motor 22 when the position of the second motor 22 is controlled. c , position feedback value θ c The average value of the position feedback value θ c The standard deviation of the position feedback value θ c Examples of changes in effective values.

[0087] These average values, standard deviations, and effective values ​​are the average values, standard deviations, and effective values ​​of each control value within a certain time width before and after the corresponding time. Fig.11 , 15 The average values ​​in , 19, and 23 are moving averages of a certain time width. Fig.12 , 16 The standard deviations in , 20, and 24 are the standard deviations for each certain time width. Fig.13 , 17 The valid values ​​in , 21, and 25 are valid values ​​for each certain time width.

[0088] Reference Fig.10 , the current command value i in the contact state when the grinding wheel GS and the workpiece W are in minute contact with each other at a level of several μm r The maximum and minimum values ​​of the current command value i when the grinding wheel GS does not contact the workpiece W r The maximum value of i rMAX , minimum value i rMIN Difficult to differentiate. Fig.10 In the period T c The current command value i in part r Slightly above the maximum value i rMAX Therefore, even if the current command value i is used as it is r , it is also difficult to pass the threshold detection. This is because, from the current command value i r The maximum value of i rMAX , minimum value i rMIN A margin M is added to remove the influence of noise, etc. ir The resulting range R ir [i rMIN -M ir ,irMAX +M ir ]When in contact, the current command value i r Less likely to deviate.

[0089] However, in the contact state, due to the existence of the current command value i r Biased towards the maximum value i rMAX or minimum value i rMIN Therefore, it indicates that the current command value i for each certain time width r The value of the central tendency of the current command value i for each certain time width is likely to be different. r The value of the central tendency is calculated based on the multiple current command values ​​i in the time width including the corresponding time. r To obtain. Fig.10 In the contact state, the current command value i r Biased towards maximum value i rMAX Therefore, if Fig.11 As shown, the current command value i for each certain time width r The average value of is greater than that of the non-contact state. Therefore, when the current command value i r The average value of each fixed time width deviates from the current command value i in the non-contact state. r The maximum value of the average value of each given time width i rAVMAX , minimum value i rAVMIN Additional margin M irAV The resulting range R irAV [i rAVMIN -M irAV ,i rAVMAX +M irAV ], it can be determined that the grinding wheel GS is in contact with the workpiece W.

[0090] On the other hand, Fig.10 As shown in the enlarged area P and Q of r in i rMAX 、i rMIN The current command value i for each certain time width vibrates at almost the same frequency and the main amplitude does not change greatly. r The statistical dispersion of will not change significantly. Fig.12 As shown, the current command value i r The standard deviation of is unlikely to differ between the contact state and the non-contact state. r The maximum value of the standard deviation of rSDMAX , minimum value i rSDMIN A margin M is added to remove the influence of noise, etc. irSD The resulting range R irSD [irSDMIN -M irSD ,i rSDMAX +M irSD ]When in contact, the current command value i r The possibility of deviation from the standard deviation is small, and it is difficult to apply it to detect the contact between the grinding wheel GS and the workpiece W.

[0091] Since the current command value i r The effective value of is equal to the square root of the value averaged over a period of the square of the instantaneous value of the current, so it contains the current command value i for each certain time width. r The central tendency and current command value i r In an AC servo motor, since current is generated even when stationary, the current command value i is expressed as the value of the current command value at a certain time width. r The absolute value of the central tendency of the value is much larger than the current command value i r Therefore, when the current command value i r In the effective value, the current command value i r The central tendency ratio of the current command value i r Therefore, if Fig.13 As shown, the current command value i for each certain time width r The effective value of is greater than that of the non-contact state. r The effective value of the current command value i in the time width including the corresponding time is calculated according to the multiple current command values ​​i r Therefore, when the current command value i r The effective value of each fixed time width deviates from the current command value i in the non-contact state. r The maximum value of the effective value of each given time width i rRMMAX , minimum value i rRMMIN Additional margin M irRM The resulting range R irRM [i rRMMIN -M irRM ,i rRMMAX +M irRM ], it can be determined that the grinding wheel GS is in contact with the workpiece W.

[0092] Reference Fig.14 , the current feedback value i in the contact state when the grinding wheel GS and the workpiece W are in micro contact with each other at a level of several μm c The maximum and minimum values ​​of the current feedback value i when the grinding wheel GS does not contact the workpiece W c The maximum value of i cMAX , minimum value i cMIN Therefore, even if the current feedback value i is used as it is,c , it is also difficult to pass the threshold detection. This is because from the current feedback value i c The maximum value of i cMAX , minimum value i cMIN A margin M is added to remove the influence of noise, etc. ic The resulting range [i cMIN -M ic ,i cMAX +M ic ]When in contact, the current feedback value i c Less likely to deviate.

[0093] In addition, if Fig.15 As shown, the current feedback value i c The average value of changes before and after contact. In this way, since the current feedback value i representing each certain time width c The value of the central tendency of the contact changes before and after the contact, so the current feedback value i representing each certain time width is used. c It is difficult to determine contact based on the value of central tendency.

[0094] On the other hand, Fig.14 As shown in the enlarged area R and S, the current feedback value i c When in contact, the amplitude of the change increases, so the current feedback value i c The current feedback value i of each certain time width increases. c The statistical dispersion of the current feedback values ​​i in the time width including the corresponding time is c Therefore, if Fig.16 As shown, the current feedback value i c The standard deviation of is easy to produce differences in the contact state and the non-contact state. Therefore, when the current feedback value i c The standard deviation of each fixed time width deviates from the current feedback value i in the non-contact state. c The maximum value of the standard deviation of each given time width i cSDMAX , minimum value i cSDMIN Additional margin M icSD The resulting range R icSD [i cSDMIN -M icSD ,i cSDMAX +M icSD ], it can be determined that the grinding wheel GS is in contact with the workpiece W.

[0095] Moreover, since the current feedback value i representing each certain time width c The absolute value of the central tendency value is much larger than the current feedback value i c The statistical deviation value, so the current feedback value i cThe effective value of the current feedback value i c The central tendency of the current feedback value i c Therefore, if Fig.17 As shown, the current feedback value i of each certain time width c The effective value of does not change in a way that the value when in contact is distinguishable from the value when not in contact. The current feedback value i of each certain time width c The effective value of the current feedback value i in the time width including the corresponding time is c Therefore, it is difficult to determine contact using effective values.

[0096] Reference Fig.18 , the speed feedback value ω when the grinding wheel GS and the workpiece W are in contact with each other at a microscopic level of several μm c , the speed feedback value ω in the non-contact state where the grinding wheel GS does not contact the workpiece W c The maximum value of ω cMAX , minimum value ω cMIN Therefore, if Fig.18 As shown, when the speed feedback value ω c Deviation from the speed feedback value ω in the non-contact state c The maximum value of ω cMAX , minimum value ω cMIN Additional margin M ωc The resulting range R ωc [ω cMIN -M ωc ,ω cMAX +M ωc ], it can be determined that the grinding wheel GS is in contact with the workpiece W.

[0097] When the speed feedback value ω is calculated c The time width of the central tendency value and the speed feedback value ω c If the frequency of change is different, the value indicating the central tendency in the time width is calculated to be biased toward the maximum value ω. cMAX Or the minimum value ω cMIN For example, consider the case where the maximum value ω is exceeded in this time width. cMAX Speed ​​feedback value ω c The number of times is much greater than the minimum value ω in this time width. cMIN Speed ​​feedback value ω c In this case, if Fig.19 As shown, the speed feedback value ω for each certain time width is expressed by the presence or absence of contact. c The central tendency value of is easy to produce differences. The speed feedback value ω for each certain time width is representedc The value of the central tendency is calculated based on the multiple speed feedback values ​​ω in the time width including the corresponding time. c At this time, if Fig.19 As shown, when the speed feedback value ω c The average value of each fixed time width deviates from the speed feedback value ω in the non-contact state c The maximum value of the average value of each given time width ω cAVMAX , minimum value ω cAVMIN Additional margin M ωcAV The resulting range R ωcAV [ω cAVMIN -M ωcAV ,ω cAVMAX +M ωcAV ], it can be determined that the grinding wheel GS is in contact with the workpiece W. In addition, depending on the contact time and material of the grinding wheel GS and the workpiece W, there is also a speed feedback value ω indicating each certain time width. c The central tendency value of does not differ depending on the presence or absence of contact. In this case, it is difficult to express the speed feedback value ω c The value of central tendency is used to detect contacts.

[0098] In addition, if Fig.18 As shown, due to the speed feedback value ω c When in contact, the amplitude of the change increases, so the speed feedback value ω for each certain time width c The statistical deviation of each certain time width is increased. c The statistical deviation of the speed feedback value ω in the time width including the corresponding time c Therefore, if Fig. 20 As shown, the speed feedback value ω for each certain time width c The standard deviation of is easy to produce differences in contact state and non-contact state. Therefore, when the speed feedback value ω c The standard deviation of each fixed time width deviates from the speed feedback value ω in the non-contact state. c The maximum value of the standard deviation of each given time width ω cSDMAX , minimum value ω cSDMIN Additional margin M ωcSD The resulting range R ωcSD [ω cSDMIN -M ωcSD ,ω cSDMAX +M ωcSD ], it can be determined that the grinding wheel GS is in contact with the workpiece W.

[0099] Moreover, it represents the speed feedback value ω c The absolute value of the central tendency value is close to 0, and the speed feedback value ωc The statistical deviation of is much larger than the speed feedback value ω c The absolute value of the central tendency of the value. Therefore, in the speed feedback value ω c In the effective value of c The statistical deviation ratio of the speed feedback value ω c The value of the central tendency contributes more. Fig.21 As shown, the speed feedback value ω for each certain time width c The effective value of is greater than the value in the non-contact state. The speed feedback value ω for each certain time width c The effective value of is based on the multiple speed feedback values ​​ω in the time width including the corresponding time c Therefore, when the speed feedback value ω c The effective value of each certain time width deviates from the speed feedback value ω in the non-contact state c The maximum effective value of each given time width ω cRMMAX , minimum value ω cRMMIN Additional margin M ωcRM The resulting range R ωcRM [ω cRMMIN -M ωcRM ,ω cRMMAX +M ωcRM ], it can be determined that the grinding wheel GS is in contact with the workpiece W.

[0100] Reference Fig. 22 , the position feedback value θ when the grinding wheel GS and the workpiece W are in contact with each other at a microscopic level of several μm c The maximum and minimum values ​​of the position feedback value θ in the non-contact state where the grinding wheel GS does not contact the workpiece W c The maximum value of θ cMAX , minimum value θ cMIN Therefore, even if the position feedback value θ is used as it is, c , it is also difficult to pass the threshold detection. This is because from the position feedback value θ c The maximum value of θ cMAX , minimum value θ cMIN A margin M is added to remove the influence of noise, etc. θc The resulting range R θc [θ cMIN -M θc ,θ cMAX +M θc ]When in contact, the position feedback value θ c Less likely to deviate.

[0101] When the position feedback value θ c The time width of the central tendency value is related to the position feedback value θc If the frequency of change is different, the value indicating the central tendency in the time width is calculated to be biased toward the maximum value θ. cMAX Or the minimum value θ cMIN For example, consider the case where the maximum value θ is exceeded in this time width. cMAX Position feedback value θ c The number of times is much greater than the minimum value θ cMIN Position feedback value θ c In this case, if Fig.23 As shown, the position feedback value θ for each certain time width is expressed by the presence or absence of contact. c The central tendency value of θ is likely to be different. c The value of the central tendency is calculated based on the multiple position feedback values ​​θ in the time width including the corresponding time. c At this time, if Fig.23 As shown, when the position feedback value θ c The average value of each certain time width deviates from the position feedback value θ in the non-contact state c The maximum value of the average value of each given time width θ cAVMAX , minimum value θ cAVMIN Additional margin M θcAV The resulting range R θcAV [θ cAVMIN -M θcAV ,θ cAVMAX +M θcAV ], it can be determined that the grinding wheel GS is in contact with the workpiece W. In addition, depending on the contact time, material, etc. of the grinding wheel GS and the workpiece W, there is also a position feedback value θ indicating each certain time width. c The central tendency value of θ does not differ depending on the presence or absence of contact. In this case, it is difficult to use the position feedback value θ to represent the position feedback value. c The value of central tendency is used to detect contacts.

[0102] On the other hand, Fig. 22 As shown, the position feedback value θ c When in contact, the amplitude of the change increases, so the position feedback value θ c The statistical dispersion of Fig.24 As shown, the position feedback value θ c The standard deviation of is likely to differ between the contact state and the non-contact state. Fig.24 As shown, when the position feedback value θ c The standard deviation of each certain time width deviates from the position feedback value θ in the non-contact state. cThe maximum value of the standard deviation of each given time width θ cSDMAX , minimum value θ cSDMIN Additional margin M θcSD The resulting range R θcSD [θ cSDMIN -M θcSD ,θ cSDMAX +M θcSD ], it can be determined that the grinding wheel GS is in contact with the workpiece W.

[0103] In addition, the position feedback value θ c The absolute value of the central tendency of is close to 0. In this case, the position feedback value θ c The statistical deviation of is much larger than the position feedback value θ c The absolute value of the central tendency of the value. Therefore, in the position feedback value θ c In the effective value of c The statistical deviation ratio of the position feedback value θ c The value of the central tendency contributes more. Fig.25 As shown, the position feedback value θ for each certain time width c The effective value of is greater than the value in the non-contact state. The position feedback value θ for each certain time width c The effective value of is based on the multiple position feedback values ​​θ in the time width including the corresponding time c Therefore, when the position feedback value θ c The effective value of each certain time width deviates from the position feedback value θ in the non-contact state c The maximum effective value of each given time width θ cRMMAX , minimum value θ cRMMIN Additional margin M θcRM The resulting range R θcRM [θ cRMMIN -M θcRM ,θ cRMMAX +M θcRM ], it can be determined that the grinding wheel GS is in contact with the workpiece W.

[0104] If the monitoring device 8 inputs the information for specifying the range R obtained as above via the input / output interface 6 and the numerical control device 5 irAV , R irRM , R icSD , R ωc , R ωcAV , R ωcSD , R ωcRM , R θcAV , R θcSD , R θcRM The monitoring device 8 detects the current command value i r, current feedback value i c , speed feedback value ω c and position feedback value θ c , calculate the average value, standard deviation and effective value of each fixed time width. r , current feedback value i c , speed feedback value ω c and position feedback value θ c The average value, standard deviation, and effective value of the current command value i in the time width including the corresponding time are calculated. r , current feedback value i c , speed feedback value ω c and position feedback value θ c Obtain them separately.

[0105] (Contact detection method)

[0106] Next, use Fig.26 The contact detection method between the grinding wheel GS and the workpiece W according to the present embodiment will be described in detail. Fig.26 This is a flowchart showing the processing flow of the contact detection method of the grinding wheel GS and the workpiece W of this embodiment. In step S1, the method controls a motor other than at least one actuator to stop one of the tool holder 16 and the workpiece holder 12 in a direction along the control axis. Figures 5 to 8 In the example, the motor is, for example, the second motor 22 . Fig. 9 In the example, the motor is, for example, the third motor 23. The control may be position control to control one of the tool holder 16 and the workpiece holder 12 at a specific position, or may be speed control to make the (rotation) speed of the tool holder 16 and the workpiece holder 12 zero.

[0107] In step S2 , the method controls at least one actuator in order to move the tool holder relative to the workpiece holder along a movement direction MD. Figure 5 In the example, the first motor 21 or the fifth motor 25 is at least one actuator. Figure 6 In the example, the third motor 23 or the seventh motor 27 is at least one actuator. Figure 7 In the example, the first motor 21 and the third motor 23, or the fifth motor 25 and the seventh motor 27 are at least one actuator. Figure 8 In the example, the third motor 23 or the seventh motor 27 is at least one actuator. Fig. 9 In the example, the second motor 22 or the sixth motor 26 is at least one actuator.

[0108] In step S3, the method detects the contact between the grinding wheel GS and the workpiece W according to the change of the control value of the motor. The control value includes the current command value i r , the current feedback value i from the motor c , position feedback value θ c and speed feedback value ω c Specifically, when the current command value i for the motor at each certain time width is represented, r When the value of the concentration tendency of deviates from the predetermined range, the method determines that the grinding wheel GS is in contact with the workpiece W. Specifically, when the current command value i of the motor for each certain time width is r At least one of the average value and the effective value deviates from the predetermined range R irAV , R irRM When , this method determines that the grinding wheel GS and the workpiece W are in contact.

[0109] Or, in the current feedback value i representing each certain time width c When the statistical deviation value of deviates from the predetermined range, the method determines that the grinding wheel GS is in contact with the workpiece W. Specifically, when the current feedback value i c The standard deviation deviates from the predetermined range R icSD When , this method determines that the grinding wheel GS and the workpiece W are in contact.

[0110] Or, in the case of position control, when the position feedback value θ c When the statistical deviation of deviates from the predetermined range, the method determines that the grinding wheel GS is in contact with the workpiece W. Specifically, when the position feedback value θ of each certain time width c At least one of the standard deviation and the effective value deviates from the predetermined range R θcSD , R θcRM , this method determines that the grinding wheel GS is in contact with the workpiece W. The same is true in the fully closed loop method.

[0111] Or, at the speed feedback value ω c And the speed feedback value ω representing each certain time width c When at least one of the statistical deviations of the values ​​of ω deviates from a predetermined range, the method determines that the grinding wheel GS is in contact with the workpiece W. Specifically, when the speed feedback value ω c And the speed feedback value ω for each certain time width c At least one of the standard deviation and the effective value deviates from the predetermined range R ωc , R ωcSD , R ωcRMWhen , this method determines that the grinding wheel GS and the workpiece W are in contact.

[0112] In step S4, the method detects the position feedback value θ when contact is detected. c (P c ) is stored in the memory 52. ​​The value is used in the subsequent grinding process. Finally, in step S5, the method returns the tool holder 16 or the workpiece holder 12 to the original position. The original position is, for example, the origin position in the processing program. In addition, steps S4 or S5 can also be omitted.

[0113] The contact detection method described above may also be realized by simply executing a program stored in the memory 52 of the numerical control device 5. In this case, the monitoring device 8 may also be configured to set the current command value i r , current feedback value i c , position feedback value θ c , speed feedback value ω c The data are transferred to the numerical control device 5, which calculates a value indicating the central tendency of these values ​​for each constant time width and a value indicating the statistical deviation of these values ​​for each constant time width to determine whether the grinding wheel GS and the workpiece W are in contact.

[0114] Alternatively, the program stored in the memory 52 of the numerical control device 5 may be executed to determine only the contact between the grinding wheel GS and the workpiece W. In this case, the monitoring device 8 calculates the current command value i r , current feedback value i c , position feedback value θ c , speed feedback value ω c The value of the central tendency of each fixed time width is calculated, or the value of the statistical deviation of each fixed time width is calculated. In addition, the logic of the monitoring device 8 may be executed until the contact determination between the grinding wheel GS and the workpiece W, and only the processing of steps S4 and S5 may be executed by the program stored in the memory 52 of the numerical control device 5.

[0115] The functions of the program of the numerical control device 5 and the logic of the monitoring device 8 may be partially or entirely realized by a dedicated processor or integrated circuit. The program or logic is not limited to being recorded in the memory 52 or 82, but may be recorded in a storage medium such as a floppy disk, an optical disk, a CD-ROM, a magnetic disk, an SD card, a USB memory, an external hard disk, etc. that can be removed from the numerical control device 5 or the monitoring device 8 and can be read by the numerical control device 5 or the monitoring device 8. In addition, the numerical control device 5 or the monitoring device 8 is an example of a computer.

[0116] (Features and Effects of the Contact Detection Method of the Present Embodiment)

[0117] The machine tool 1 of this embodiment and the contact detection method of the grinding wheel GS and the workpiece W of this embodiment do not need to apply a large amount of power, and detect the contact between the grinding wheel GS and the workpiece W based on the change in the control value of the motor that performs the control of the power easily and stably. Therefore, the setting for detecting the contact between the grinding wheel GS and the workpiece W does not require time, and the signal is stable when there is no contact. In addition, the control axis and the tool rotation axis A are XT intersects with the moving direction MD, and more specifically, the control axis and the tool rotation axis A XT The control axis direction of the control axis is perpendicular to the moving direction MD. Therefore, the component of the resistance generated by the contact between the grinding wheel GS and the workpiece W becomes larger. Therefore, the contact between the grinding wheel GS and the workpiece W can be detected with high precision using the control value of the motor. As a result of the experiment conducted by the applicant according to the above method, it was confirmed that the contact between the grinding wheel GS and the workpiece W can be detected in the state of micro-contact of the grinding wheel GS grinding the workpiece W at a level of 3 μm. Using this contact detection method, high-precision coordinate positioning for grinding processing can be performed in a short time.

[0118] (Variation Example)

[0119] Figure 11 to Figure 25 The result of the change corresponds to the control method and the gain used in the position controller 70a, the speed controller 70b, the current controller 70c, and the voltage regulator 70d. Therefore, the threshold value for determining whether the grinding wheel GS contacts the workpiece W may also change according to the control method and the gain used by the servo driver 70. Figure 11 to Figure 25 The result also corresponds to the current command value i r , current feedback value i c , position feedback value θ c and speed feedback value ω c The resolution of the servo drive 70 may be changed, or the time width used as a reference for calculating the value indicating the central tendency and the value indicating the statistical deviation. The time width also depends on the sampling interval of the servo drive 70. Therefore, if the performance of the servo drive 70 is improved and the resolution and sampling interval are reduced, the threshold value for determining whether the grinding wheel GS and the workpiece W are in contact may change.

[0120] In the above-mentioned embodiment, the current command value i for the motor is represented by r The central tendency value, i, represents the current feedback value from the motor c The statistical deviation of the position feedback value θ c The statistical deviation of the value and the speed feedback value ω cThe grinding wheel GS is judged to be in contact with the workpiece W based on one of the values ​​of the statistical deviation of the above-mentioned values. However, a plurality of values ​​may be combined to judge that the grinding wheel GS is in contact with the workpiece W. For example, when a certain number of the plurality of values ​​exceeds the range determined as above, it may be judged that the grinding wheel GS is in contact with the workpiece W. Alternatively, when a value obtained by weighted addition of the plurality of values ​​exceeds a predetermined range, it may be judged that the grinding wheel GS is in contact with the workpiece W.

[0121] In the above-mentioned embodiment, at least one actuator may be an actuator other than a motor. For example, at least one actuator may be a hydraulic piston.

[0122] In the present application, "include" and its derivatives are non-restrictive terms that describe the presence of constituent elements, and do not exclude the presence of other constituent elements not described. This also applies to "have", "include" and their derivatives.

[0123] Terms such as "part," "section," "element," "body," and "structure" may have various meanings such as a single part or a plurality of parts.

[0124] Ordinal numbers such as "first" and "second" are only used to identify structures and do not have other meanings (such as a specific order, etc.). For example, although there is a "first element", it does not imply the existence of a "second element", and although there is a "second element", it does not imply the existence of a "first element".

[0125] Unless otherwise specified in the embodiments, the terms "substantially", "about" and "approximately" indicating the degree may mean that the final result does not have a reasonable deviation that varies greatly. All numerical values ​​recorded in this application may be interpreted as including the terms "substantially", "about" and "approximately".

[0126] In the present application, the term "at least one of A and B" should be interpreted as including only A, only B, and both A and B.

[0127] In view of the above disclosure, it is obvious that various changes and modifications of the present invention can be made. Therefore, the present invention can also be implemented in a manner different from the specific disclosure of this application without departing from the scope of the present invention.

Claims

1. A method for detecting contact between a grinding wheel of a machine tool and a workpiece, wherein: controlling at least one actuator so that a tool holder that holds a grinding wheel rotatably about a tool rotation axis moves relative to a workpiece holder that holds a workpiece in a moving direction, controlling a motor different from the at least one actuator that can move one of the tool holder and the workpiece holder along a control axis that intersects the tool rotation axis and the moving direction, so that the one holder is stationary in a direction along the control axis, The contact between the grinding wheel and the workpiece is detected according to the change of the control value of the motor, The control value includes a current command value for the motor. When the value indicating the concentration tendency of the current command value from the numerical control device at each constant time width deviates from a predetermined range, it is determined that the grinding wheel is in contact with the workpiece.

2. A method for detecting contact between a grinding wheel of a machine tool and a workpiece, wherein: controlling at least one actuator so that a tool holder that holds a grinding wheel rotatably about a tool rotation axis moves relative to a workpiece holder that holds a workpiece in a moving direction, controlling a motor different from the at least one actuator that can move one of the tool holder and the workpiece holder along a control axis that intersects the tool rotation axis and the moving direction, so that the one holder is stationary in a direction along the control axis, The contact between the grinding wheel and the workpiece is detected according to the change of the control value of the motor, The control value includes a current feedback value from the motor, When a value indicating the statistical dispersion of the current feedback value at each predetermined time width deviates from a predetermined range, it is determined that the grinding wheel is in contact with the workpiece.

3. A method for detecting contact between a grinding wheel of a machine tool and a workpiece, wherein: controlling at least one actuator so that a tool holder that holds a grinding wheel rotatably about a tool rotation axis moves relative to a workpiece holder that holds a workpiece in a moving direction, controlling a motor different from the at least one actuator that can move one of the tool holder and the workpiece holder along a control axis that intersects the tool rotation axis and the moving direction, so that the one holder is stationary in a direction along the control axis, The contact between the grinding wheel and the workpiece is detected according to the change of the control value of the motor, The control value includes a position feedback value, When a value indicating the statistical dispersion of the position feedback value for each predetermined time width deviates from a predetermined range, it is determined that the grinding wheel is in contact with the workpiece.

4. A method for detecting contact between a grinding wheel of a machine tool and a workpiece, wherein: controlling at least one actuator so that a tool holder that holds a grinding wheel rotatably about a tool rotation axis moves relative to a workpiece holder that holds a workpiece in a moving direction, controlling a motor different from the at least one actuator that can move one of the tool holder and the workpiece holder along a control axis that intersects the tool rotation axis and the moving direction, so that the one holder is stationary in a direction along the control axis, The contact between the grinding wheel and the workpiece is detected according to the change of the control value of the motor, The control value includes a speed feedback value, When at least one of the velocity feedback value and a value indicating a statistical dispersion of the velocity feedback value for each predetermined time width deviates from a predetermined range, it is determined that the grinding wheel is in contact with the workpiece.

5. The contact detection method according to any one of claims 1 to 4, wherein: The control axis is perpendicular to the tool rotation axis.

6. The contact detection method according to any one of claims 1 to 4, wherein: The control axis is perpendicular to a straight line extending in the moving direction.

7. The contact detection method according to any one of claims 1 to 4, wherein: The motor is configured to move the tool holder along the control axis, The at least one actuator is at least one additional motor configured to move the tool holder along each of at least one additional control axis perpendicular to the control axis.

8. The contact detection method according to any one of claims 1 to 4, wherein: The workpiece holder holds the workpiece so as to be rotatable about a workpiece rotation axis. When the tool rotation axis and the workpiece rotation axis exist on the same plane, the moving direction is parallel to the same plane. When the tool rotation axis and the workpiece rotation axis are lines in a twisted position, the moving direction is along a line perpendicular to the tool rotation axis and the workpiece rotation axis.

9. The contact detection method according to claim 1, wherein: The value representing the central tendency is represented by at least one of an average value and a valid value.

10. The contact detection method according to any one of claims 2 to 4, wherein: The value representing the statistical dispersion is represented by at least one value including a standard deviation.

11. The contact detection method according to claim 3 or 4, wherein: The value representing the statistical dispersion is represented by at least one value including a valid value.

12. A machine tool, wherein: The invention comprises components for executing the contact detection method according to any one of claims 1 to 11.

13. A storage medium storing a computer program, wherein: The computer program includes instructions for causing a computer to execute the contact detection method according to any one of claims 1 to 11 when the computer program is executed.

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