Machine tool

Abstract

To provide a machine tool making it possible to upgrade the precision in a halt position of an object of drive in the case where semi-closed loop control is implemented.SOLUTION: A machine tool 1 includes a guide mechanism 30 that guides an object of drive which is at least one of a tool TO1 and a workpiece W1, a servo motor 40 that moves the object of drive to be guided by the guide mechanism 30, and a control unit U1 that performs semi-closed loop control on the servo motor 40 so that the object of drive is moved from an initial position P1 to a target position P2. The control unit U1 performs the semi-closed loop control so that a vibrational component Vc, which repeats an advancement motion M1 of heading for the target position P2 and a retreat motion M2 opposite to the advancement motion M1 from an intermediate position P3 between the initial position P1 and target position P2 to the target position P2 is added to the motions of the object of drive.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a machine tool that performs semi-closed loop control. [Background technology]

[0002] As a machine tool, a numerically controlled (NC) lathe is known that cuts a workpiece held by a spindle with a tool. The NC lathe is equipped with a guide mechanism for the tool and workpiece to be driven, a servomotor having an internal encoder, a servo amplifier, an NC device, etc. The servo amplifier performs semi-closed loop control on the servomotor based on a position command from the NC device and a feedback signal from the internal encoder (for example, see Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2023-25474 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, even though the output of the internal encoder indicates that the driven object has reached the target position, the driven object may actually stop slightly off from the target position. Adding a sensor to detect the position of the driven object in order to improve the accuracy of the stop position of the driven object leads to increased costs. Therefore, it is desirable to improve the accuracy of the stop position of the driven object when semi-closed loop control is performed without adding a position detection sensor. The above-mentioned problems are not limited to lathes, but exist in various machine tools such as machining centers.

[0005] The present invention discloses a machine tool capable of improving the accuracy of the stopping position of a driven object when semi-closed loop control is performed. [Means for solving the problem]

[0006] The machine tool of the present invention is a machine tool that processes a workpiece with a tool, A guide mechanism for guiding at least one of the drive targets of the tool and the workpiece; A servo motor for moving the driven object guided by the guide mechanism; a control unit that performs semi-closed loop control on the servo motor so as to move the driven object from an initial position to a target position; The control unit has an aspect of controlling the semi-closed loop so as to add a vibration component to the movement of the driven object, which repeats a forward movement toward the target position from an intermediate position between the initial position and the target position to the target position and a backward movement opposite to the forward movement. Effect of the Invention

[0007] According to the present invention, it is possible to provide a machine tool capable of improving the accuracy of the stopping position of a driven object when semi-closed loop control is performed. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram illustrating a configuration example of a machine tool. [Diagram 2] FIG. 2 is a block diagram illustrating a schematic configuration example of an electric circuit of a machine tool. [Diagram 3] FIG. 1 is a block diagram illustrating a schematic example of a semi-closed loop control system. [Figure 4] 2 is a diagram showing a schematic example of a relationship between a control position x1 and an actual position x2 of a driven object. FIG. [Diagram 5] FIG. 2 is a diagram showing an example of dividing a control position x1 into regions centered on a reference position 0 in semi-closed loop control. [Figure 6] 11A and 11B are diagrams illustrating an example in which a vibration component is added to the movement of a drive target from an intermediate position to a target position. [Figure 7]FIG. 10 is a diagram illustrating an example of a vibration component. [Figure 8] 13A and 13B are diagrams illustrating an example in which vibration is continued for a set period after the driven object reaches a target position. [Figure 9] 10 is a flowchart illustrating an example of a vibration condition determination process. [Figure 10] FIG. 13 is a diagram illustrating a current command having a variation in sweep frequency. [Figure 11] 10 is a diagram showing a schematic example of an amplitude magnification M with respect to a frequency f. FIG. [Figure 12] FIG. 2 is a diagram illustrating an example of a phase delay φ with respect to a frequency f. [Figure 13] 11 is a flowchart illustrating an example of a frequency determination process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following embodiments of the present invention will be described. Of course, the following embodiments are merely illustrative of the present invention, and not all of the features shown in the embodiments are necessarily essential to the solution of the invention.

[0010] (1) Overview of the technology included in this invention: First, the outline of the technology included in the present invention will be described with reference to the examples shown in Figures 1 to 13. Note that the figures in the present application are diagrams showing examples in a schematic manner, and the magnification ratios in each direction shown in these figures may differ, and each figure may not be consistent. Of course, each element of the present technology is not limited to the specific example shown by the symbol. In addition, in the present application, a numerical range "Min to Max" means equal to or greater than the minimum value Min and equal to or less than the maximum value Max.

[0011] [Aspect 1] As illustrated in FIGS. 1 to 3, a machine tool 1 according to an embodiment of the present technology is a machine tool 1 that processes a workpiece W1 with a tool TO1, and includes a guide mechanism 30, a servo motor 40, and a control unit U1. The guide mechanism 30 guides at least one of the tool TO1 and the workpiece W1 as a driven object. The servo motor 40 moves the driven object guided by the guide mechanism 30. The control unit U1 performs semi-closed loop control (see FIG. 3, for example) on the servo motor 40 so as to move the driven object from an initial position P1 to a target position P2. The control unit U1 performs semi-closed loop control so as to add a vibration component Vc to the movement M0 of the driven object, which repeats a forward movement M1 from an intermediate position P3 between the initial position P1 and the target position P2 to the target position P2 and a backward movement M2 opposite to the forward movement M1, as illustrated in FIG. 6 and the like.

[0012] If the semi-closed loop control is performed without adding the vibration component Vc to the movement M0 of the driven object, the structure from the servo motor 40 to the driven object will be distorted, causing internal stress to remain in the structure, and the stop position of the driven object may actually deviate from the target position P2. In the semi-closed loop control of the above embodiment, the vibration component Vc is added to the movement M0 of the driven object from the intermediate position P3 to the target position P2, so that the driven object reaches the target position P2 while releasing the internal stress generated in the structure. This reduces the internal stress remaining in the structure, and the actual stop position of the driven object approaches the target position P2. Therefore, the above embodiment can improve the accuracy of the stop position of the driven object while suppressing an increase in the cycle time of the command to move the driven object. In addition, by reducing the internal stress remaining in the structure, the torque generated by the servo motor when the driven object is stopped is reduced, and standby power is reduced.

[0013] Here, the machine tool includes a lathe, a machining center, and the like. The guide mechanism may guide the driven object so that the driven object moves in a predetermined direction, or may guide the driven object so that the driven object rotates about a predetermined axis. Moving a driven object includes moving the driven object in a commanded moving direction, turning the driven object in a commanded direction, and the like. The servo motor may move a tool as a driven object, may move a workpiece as a driven object, or may move both the tool and the workpiece as driven objects. When both the tool and the workpiece are driven, the guide mechanism guides both the tool and the workpiece. The above remarks also apply to the following aspects.

[0014] [Aspect 2] As illustrated in FIG. 8, the control unit U1 may control the semi-closed loop so as to apply the vibration component Vc to the drive object during a set period 202 within a period (e.g., a stop period 201) during which the drive object reaches the target position P2 and remains at the target position P2. In the above case, the internal stress remaining in the structure from the servo motor 40 to the driven object is further reduced, thereby making it possible to further improve the accuracy of the stopping position of the driven object.

[0015] [Aspect 3] 9, in a vibration condition determination mode for determining the vibration condition (e.g., frequency or amplitude) of the vibration component Vc, the control unit U1 may perform the semi-closed loop control with each of a plurality of candidates i (e.g., frequency fi or amplitude Ai) of the vibration condition as the vibration condition to detect the torque (e.g., torque value TR1i) generated by the servo motor 40 when the driven object stops at the target position P2. The control unit U1 may determine, as the vibration condition, a candidate among the plurality of candidates i when the torque (TR1i) falls below a reference torque (e.g., reference torque value TR0). If internal stress remains in the structure from the servo motor 40 to the driven object, the servo motor 40 generates a torque (TR1i) corresponding to the internal stress of the structure when the driven object stops at the target position P2 in semi-closed loop control. Therefore, if the vibration conditions of the vibration component Vc are determined so that the torque (TR1i) generated by the servo motor 40 when the driven object stops is lower than the reference torque (TR0), the internal stress remaining in the structure when the driven object stops is reduced. Therefore, the above embodiment can provide a suitable example for improving the accuracy of the stop position of the driven object.

[0016] [Aspect 4] The frequency of the vibration component Vc may be included in a resonance frequency band that can cause resonance in a portion of the machine tool 1 that holds the driven object (e.g., the tool rest 20 or the headstock 10). Since there is a range of frequencies measured when resonance occurs, the resonance frequency band means a range of frequencies in which resonance may occur. The resonance frequency fr shown in FIG. 13 is included in the resonance frequency band. In the above case, since the vibration component Vc in the resonant frequency band is applied to the movement M0 of the driven object from the intermediate position P3 to the target position P2 in the semi-closed loop control, the internal stress generated in the structure from the servo motor 40 to the driven object is easily released, and the internal stress remaining in the structure is further reduced. Therefore, the above embodiment can provide a suitable example for improving the accuracy of the stop position of the driven object.

[0017] [Aspect 5] As illustrated in FIG. 13, in a vibration condition determination mode for determining the frequency of the vibration component Vc, the control unit U1 may input a current command 300 having a sweep frequency fluctuation to the semi-closed loop to detect a resonant frequency fr generated in a part of the machine tool 1 that holds the object to be driven, and determine the detected resonant frequency fr as the frequency of the vibration component Vc. When a current command 300 having a fluctuation in the sweep frequency is input to the semi-closed loop, a portion of the machine tool 1 that holds the object to be driven vibrates at the sweep frequency of the current command 300. When a resonant frequency fr generated in the portion is detected, the detected resonant frequency fr is determined to be the frequency of the vibration component Vc. This further reduces the internal stress remaining in the structure from the servo motor 40 to the object to be driven. Therefore, the above embodiment can provide a suitable example for improving the accuracy of the stop position of the object to be driven.

[0018] (2) Specific examples of machine tool configurations: Fig. 1 illustrates a schematic configuration of a lathe as an example of machine tool 1. Fig. 2 illustrates a schematic configuration of an electric circuit of a lathe as an example of machine tool 1. Machine tool 1 shown in Figs. 1 and 2 is an NC automatic lathe equipped with an NC (numerical control) device 70 that performs numerical control of machining of workpiece W1 held by spindle 11. Since computer 100 is not an essential element in machine tool 1, an external computer 100 may not be connected to machine body 2.

[0019] The machine tool 1 shown in FIG. 1 is an NC machine tool including a headstock 10 incorporating a spindle 11, a tool rest 20 directly or indirectly holding a tool TO1, a guide mechanism 30 for the headstock 10 or tool rest 20, a servo motor 40, an NC device 70, and the like. Here, the headstock 10 collectively refers to a front headstock 10A and a back headstock 10B also called an opposed headstock. The spindle 11 collectively refers to a front spindle 11A and a back spindle 11B also called an opposed spindle. The headstock 10 shown in FIG. 1 is provided with a motor 13, for example a built-in motor, which rotates the spindle 11 around the spindle center line AX1. The spindle 11 shown in FIG. 1 has a gripping portion 12 such as a collet. The tool rest 20 collectively refers to a comb tool rest 21 and a turret tool rest 22. The comb tool rest 21 shown in Fig. 1 is provided with a swivel unit 25 incorporating a plurality of tools TO1. The guide mechanism 30 collectively refers to a guide mechanism 31 that guides the headstock 10 and a guide mechanism 32 that guides the tool rest 20. The guide mechanism 32 includes a swivel guide mechanism that guides the swivel of the swivel unit 25. The servo motor 40 collectively refers to a servo motor 41 that moves the headstock 10 and a servo motor 42 that moves the tools TO1. The servo motor 42 includes not only a servo motor that moves the tool rest 20 but also a servo motor that rotates the swivel unit 25.

[0020] The control axes of the machine tool 1 shown in FIG. 1 include the X-axis indicated by "X", the Y-axis indicated by "Y", the Z-axis indicated by "Z", and the B-axis indicated by "B". The Z-axis direction is a horizontal direction along the spindle center line AX1 which is the rotation center of the workpiece W1. The X-axis direction is a horizontal direction perpendicular to the Z-axis. The Y-axis direction is a vertical direction perpendicular to the Z-axis. The B-axis is a reference axis for controlling the rotation angle of the turning unit 25, and is, for example, a vertical control axis along the Y-axis. Note that the Z-axis and the X-axis do not have to be perpendicular as long as they intersect, the Z-axis and the Y-axis do not have to be perpendicular as long as they intersect, and the X-axis and the Y-axis do not have to be perpendicular as long as they intersect. In addition, the drawings referred to in this specification merely show examples for explaining the present technology, and do not limit the present technology. In addition, the explanation of the positional relationship of each part is merely an example. Therefore, reversing the left and right, reversing the rotation direction, etc. are also included in the present technology. Furthermore, the identity of the direction, position, etc. is not limited to an exact match, but includes deviations from an exact match due to errors.

[0021] The machine tool 1 shown in FIG. 1 is a movable spindle type lathe, in which both the front headstock 10A and the back headstock 10B move in the Z-axis direction. The guide mechanism 31 guides the headstock 10 along the Z-axis. When the gripper 12 grips the workpiece W1, the guide mechanism 31 guides the workpiece W1 along the Z-axis. Note that the machine tool 1 may be a fixed spindle type lathe in which the front headstock 10A does not move, or the front headstock 10A may move in the Z-axis direction without moving the back headstock 10B. Of course, the headstock 10 may also move in the X-axis direction, etc. The spindle 11 releasably holds the workpiece W1 with the gripper 12. The motor 13 rotates the spindle 11 together with the workpiece W1 around the spindle center line AX1. When the workpiece W1 before machining is, for example, a cylindrical (rod-shaped) long material, the workpiece W1 may be supplied to the gripper 12 from the rear end (left end in FIG. 1) of the front spindle 11A. In this case, a guide bush that supports the workpiece W1 slidably in the Z-axis direction may be disposed on the front side (right side in FIG. 1) of the front spindle 11A. When the workpiece W1 before machining is a short material, the workpiece W1 may be supplied to the gripper 12 from the front end of the front spindle 11A. After the front machining, the workpiece W1 is transferred from the front spindle 11A to the back spindle 11B, and becomes a product by back machining.

[0022] The tool rest 20 has a plurality of tools TO1 for machining the workpiece W1 attached directly or indirectly, and is movable in the X-axis direction and the Y-axis direction. The guide mechanism 32 guides the tool rest 20 along the X-axis and the Y-axis together with the tools TO1. Of course, the tool rest 20 may move in the Z-axis direction. The tools TO1 include tools including cut-off tools, rotary tools such as rotary drills and end mills, and the like. The swivel unit 25 provided on the comb tool rest 21 is swivelable around the B-axis together with the tools TO1. It can be said that the comb tool rest 21 includes a guide mechanism 32 that guides the swivel unit 25 around the B-axis together with the tools TO1. The turret tool rest 22 indexes the tool TO1 by rotating around a rotation axis AX2 along the Z-axis. The guide mechanism 30 may be a rolling guide mechanism such as a ball screw or a linear guide, or a sliding guide mechanism such as a combination of a dovetail and a dovetail groove.

[0023] As shown in FIG. 2, the NC device 70 is connected to an operation unit 80, a servo amplifier 50, a rotation drive unit (not shown) for the spindle 11, a drive unit (not shown) for the gripper 12, and the like. Here, the servo amplifier 50 collectively refers to a servo amplifier 51 for the headstock 10 and a servo amplifier 52 for the tool rest 20. The servo amplifier 50 and the NC device 70 are examples of a control unit U1. The servo amplifier 50 is connected to a servo motor 40 having an internal encoder 43. The NC device 70 includes a CPU (Central Processing Unit) 71, which is a processor, a ROM (Read Only Memory) 72, which is a semiconductor memory, a RAM (Random Access Memory) 73, which is a semiconductor memory, a clock circuit 74, an I / F (interface) 75, and the like. Therefore, the NC device 70 is a kind of computer. In FIG. 2, the I / Fs for the operation unit 80, the servo amplifier 50, the external computer 100, and the like are collectively referred to as an I / F 75.

[0024] The ROM 72 stores a control program PR1 for interpreting and executing a machining program PR2 including a plurality of commands CM1. The ROM 72 may be a semiconductor memory capable of rewriting data. The RAM 73 stores the machining program PR2 created by an operator in a rewritable manner. The machining program is also called an NC program. The CPU 71 uses the RAM 73 as a work area and executes the control program PR1 stored in the ROM 72 to realize the functions of the NC device 70. Of course, some or all of the functions realized by the control program PR1 may be realized by other means such as an ASIC (Application Specific Integrated Circuit).

[0025] The operation unit 80 includes an input unit 81 and a display unit 82, and functions as a user interface for the NC device 70. The input unit 81 is configured, for example, from buttons and a touch panel for receiving operation input from an operator. The display unit 82 is configured, for example, from a display for displaying the contents of various settings received as operation input from the operator and various information related to the machine tool 1. The operator can store the machining program PR2 in the RAM 73 using the operation unit 80 and the computer 100.

[0026] The servo amplifier 51 controls the position and movement speed of the headstock 10 together with the workpiece W1 as a driven object according to a command 57 from the NC device 70. The servo motor 41 controlled by the servo amplifier 51 rotates according to a torque command 59 from the servo amplifier 51, and moves the headstock 10 together with the workpiece W1 via the guide mechanism 31. For example, when the headstock 10 is a headstock 10A that can move along the Z axis, the servo amplifier 51 controls the position and movement speed of the headstock 10A in the Z axis direction according to a command 57 from the NC device 70. The servo motor 41 moves the headstock 10A in the Z axis direction via the guide mechanism 31 according to the torque command 59 from the servo amplifier 51.

[0027] The servo amplifier 52 controls the position and movement speed of the tool rest 20 together with the tool TO1 as a driven object in accordance with a command 57 from the NC device 70. The servo motor 42 controlled by the servo amplifier 52 rotates in accordance with a torque command 59 from the servo amplifier 52, and moves the tool rest 20 together with the tool TO1 via the guide mechanism 32. For example, when the tool rest 20 is a comb tool rest 21 that is movable along the X-axis and Y-axis, the X-axis servo amplifier 52 controls the position and movement speed of the comb tool rest 21 in the X-axis direction in accordance with the command 57 from the NC device 70, and the Y-axis servo amplifier 52 controls the position and movement speed of the comb tool rest 21 in the Y-axis direction in accordance with the command 57 from the NC device 70. The X-axis servo motor 42 moves the comb tool rest 21 in the X-axis direction via the guide mechanism 32 in accordance with a torque command 59 from the servo amplifier 52, and the Y-axis servo motor 42 moves the comb tool rest 21 in the Y-axis direction via the guide mechanism 32 in accordance with a torque command 59 from the servo amplifier 52. The B-axis servo amplifier 52 controls the position and rotation speed of the turning unit 25 together with the tool TO1 as a driven object in accordance with a command 57 from the NC device 70. The B-axis servo motor 42 rotates in accordance with the torque command 59 from the servo amplifier 52, and turns the turning unit 25 together with the tool TO1 via the guide mechanism 32.

[0028] 3 is a schematic diagram illustrating a semi-closed loop control system. The semi-closed loop control system has a loop that feeds back a position detected by an encoder 43 provided in a servo motor 40. Since the encoder 43 is inside the servo motor 40, the semi-closed loop control system does not feed back a position obtained by detecting the actual position of the driven object. The control system shown in FIG. 3 is provided for each of the Z-axis movement of the front headstock 10A, the Z-axis movement of the rear headstock 10B, the X-axis movement of the comb tool rest 21, the Y-axis movement of the comb tool rest 21, the B-axis rotation of the swivel unit 25, the X-axis movement of the turret tool rest 22, the Y-axis movement of the turret tool rest 22, etc.

[0029] The NC device 70 can output a command 57 to the servo amplifier 50. When the command 57 is a position command for a driven object (tool TO1 or workpiece W1), the subtraction unit 55 of the servo amplifier 50 inputs the position command from the NC device 70, inputs the position feedback signal SG1 based on the output from the encoder 43 of the servo motor 40, and outputs a position deviation SG2 to the position gain 53. The position deviation SG2 is a difference signal between the position command for the driven object and the position feedback signal SG1. The position gain 53 inputs the position deviation SG2 from the subtraction unit 55, and outputs a speed command 58 to the subtraction unit 56 based on the position deviation SG2. The subtraction unit 56 inputs the speed command 58 from the position gain 53, inputs the speed feedback signal SG3 based on the output from the encoder 43, corrects the speed command 58 based on the speed feedback signal SG3, and inputs it to the speed gain 54. The speed gain 54 inputs the corrected speed command from the subtraction unit 56, and outputs a torque command 59 to the servo motor 40 based on the corrected speed command. Since the torque of the servo motor 40 is proportional to the current flowing through the servo motor 40 , the torque command 59 corresponds to the value of the current flowing through the servo motor 40 .

[0030] As described above, the NC device 70 and the servo amplifier 50 perform semi-closed loop control on the servo motor 40 so as to move the driven object from the initial position to the target position according to the command CM1 for moving the driven object. For example, if the command CM1 is a fast-forward command for moving the tool TO1 along the X-axis, the NC device 70 and the servo amplifier 52 for the tool perform semi-closed loop control on the servo motor 42 so as to linearly move the tool TO1 along the X-axis from the initial position to the target position. Note that the fast-forward command is a command for moving the tool TO1 without cutting the workpiece W1, unlike a cutting feed command that involves cutting the workpiece W1. The command CM1 may be a command for moving the tool TO1 along multiple axes, for example, the X-axis and the Y-axis. If the command CM1 is a fast-forward command for rotating the tool TO1 around the B-axis, the NC device 70 and the servo amplifier 52 perform semi-closed loop control on the servo motor 42 so as to rotate the tool TO1 around the B-axis from the initial position to the target position. When the command CM1 is a command to move the workpiece W1 along the Z axis, the NC device 70 and the servo amplifier 51 for the headstock perform semi-closed loop control on the servo motor 41 to move the workpiece W1 in a straight line along the Z axis from the initial position to the target position.

[0031] Furthermore, the NC device 70 can output a current command as a command value for current control to the servo amplifier 50 as a command 57. This current command means an input value that has not received feedback of the current control, and a torque command 59 input to the servo amplifier 50 means an output value that has received feedback of the current control. If there are no feedback signals (SG1, SG3), the torque command 59 becomes a current command. Furthermore, the servo amplifier 50 can output a torque value corresponding to the torque command 59 to the NC device 70. The torque value corresponds to the value of a current flowing through the servo motor 40. The NC device 70 can output a torque value acquisition command to the servo amplifier 50 for acquiring the torque value from the servo amplifier 50. The servo amplifier 50 that has received the torque value acquisition command outputs the torque value to the NC device 70.

[0032] The above-mentioned encoder 43 is inside the servo motor 40 and indirectly detects the position of the driven object. Because friction occurs due to the guide surface of the guide mechanism 30, the sealing O-ring, etc., if the structure from the servo motor 40 to the driven object is distorted and internal stress remains, the detected position based on the encoder 43 will deviate from the actual position of the driven object. The above-mentioned structures are the guide mechanism 30, the headstock 10, the tool rest 20, etc. As a result, even though the output of the encoder 43 in the servo motor 40 indicates that the driven object has reached the target position, the driven object may actually stop slightly deviating from the target position.

[0033] Fig. 4 shows a schematic example of the relationship between the control position x1 based on the output of the encoder 43 and the actual position x2 of the driven object when the control unit U1 performs semi-closed loop control to move the driven object from the initial position P1 to the target position P2. The control position x1 is the semi-closed loop control position that receives the position feedback signal SG1 shown in Fig. 3. For example, when the driven object is moved along the X axis, the control position x1 indicates the control position on the X axis, and the position x2 indicates the actual position on the X axis. It is assumed that no internal stress remains in the above-mentioned structure at the initial position P1.

[0034] A frictional force acts on the guide surface of the guide mechanism 30. When the servo motor 40 starts to move the driven object, the above-mentioned structure is distorted, so that the driven object actually starts to move at the motion start point Ps, which is slightly delayed from the initial position P1 in terms of control. Even when the driven object is moving, a frictional force acts on the guide surface of the guide mechanism 30, and distortion of the structure remains. Even if the controlled position of the driven object reaches the target position P2, internal stress remains due to distortion of the structure, and an error Er occurs between the actual position of the driven object and the exact target position P2. Adding a sensor to detect the actual position of the driven object in order to eliminate the error Er leads to increased costs. The same can be said about the B-axis rotation of the rotating unit 25.

[0035] 5 is a schematic diagram showing an example of division of a control position x1 in semi-closed loop control, centered on a reference position 0. The control position x1 indicates the target position of the driven object in the direction of movement of the driven object, with the right side of the reference position 0 indicating a positive position and the left side of the reference position 0 indicating a negative position. Since a frictional force acts on the guide surface of the guide mechanism 30, even if control is performed to move the driven object within the range of the first region AR1 in which only a force less than the frictional force is applied to the driven object around the reference position 0 in the direction of movement of the driven object, the actual position of the driven object does not change. This is because the distortion of the structure from the servo motor 40 to the driven object does not exceed the friction of the guide surface. The plus side boundary of the first region AR1 corresponds to the operation start point Ps shown in FIG. 4. The second regions AR2 and AR3 on both sides of the first region AR1 in the direction of movement of the driven object are regions in which the actual position of the driven object changes due to control to move the driven object in the direction of movement of the driven object, and distortion of the structure is reduced due to vibration around the reference position 0. The third regions AR4 and AR5 on both sides of the second regions AR2 and AR3 in the direction of movement of the driven object are regions in which the change in the position of the driven object in the direction of movement of the driven object is large, so that much distortion remains in the structure due to the movements in the plus and minus directions in the vibration around the reference position 0. It can also be said that a large amount of internal stress remains due to the movement from the positive third region AR4 to the negative third region AR5, and a large amount of internal stress remains due to the movement from the negative third region AR5 to the positive third region AR4. Therefore, it is preferable that the vibration that reduces the residual stress of the structure repeats a movement from the positive second region AR2 to the negative second region AR3 and a movement from the negative second region AR3 to the positive second region AR2 in the direction of the movement of the driven object.

[0036] In this specific example, a slight vibration component is added to the movement of the driven object such that the moving driven object moves back and forth between the second areas AR2 and AR3 before reaching the target position P2, thereby reducing the residual stress of the structure while suppressing an increase in the cycle time of the command CM1. As a result, when semi-closed loop control is performed, the actual stop position of the driven object approaches the target position P2, improving the accuracy of the stop position of the driven object.

[0037] FIG. 6 shows a schematic example of a state where a vibration component Vc is added to the movement of the driven object from an intermediate position P3 between the initial position P1 and the target position P2 to the target position P2. FIG. 7 shows a schematic example of the vibration component Vc. In FIGS. 6 and 7, the horizontal axis is time t, and the vertical axis is the control position x1. FIG. 6 shows that control is performed to start moving the driven object from the initial position P1 when t=0, and that control is performed to stop the driven object at the target position P2 when the time t is the movement stop timing t1. t=0 shown in FIG. 7 is different from t=0 shown in FIG. 6. For example, when the tool TO1 moves linearly along the X-axis, the control position x1 indicates the control position of the tool TO1 (particularly the cutting edge) along the X-axis.

[0038] Assume that the command CM1 is a fast-forward command to move the tool TO1 from the initial position P1 to the target position P2. In this case, the tool servo amplifier 52 performs semi-closed loop control on the servo motor 42 so as to add a vibration component Vc to the movement of the tool TO1 (movement M0 of the driven object) that repeats a forward movement M1 from an intermediate position P3 toward the target position P2 and a backward movement M2 opposite to the forward movement M1. As shown in FIG. 6, the vibration component Vc is not added to the movement of the tool TO1 from the initial position P1 to the intermediate position P3, but the vibration component Vc is added to the movement of the tool TO1 from the intermediate position P3 to the target position P2. By adding the vibration component Vc, the tool TO1 reaches the target position P2 while releasing the internal stress generated in the structure from the tool servo motor 42 to the tool TO1, and the internal stress remaining in the structure is reduced. As a result, the actual movement stop position of the tool TO1 approaches the target position P2, improving the accuracy of the movement stop position of the tool TO1. The vibration component Vc can be said to be a micro-vibration component that releases the internal stress generated in the structure from the servo motor 40 to the driven object when the driven object stops at the target position P2. By reducing the internal stress remaining in the structure, the torque generated by the servo motor 42 when the tool TO1 stops moving is reduced, and standby power is reduced. Also, since the vibration component Vc is not applied to the movement of the tool TO1 from the initial position P1 to the intermediate position P3, power consumption is reduced. The same can be said for the B-axis rotation of the swivel unit 25, the Z-axis movement of the workpiece W1, etc.

[0039] The intermediate position P3 may be a position at a predetermined distance from the target position P2, such as a position where the target position P2 is used as a reference and the target position P2 is in-position. The in-position means a set position where the driven object is treated as having reached the target position. The intermediate position P3 may be a position when the rotation speed of the servo motor 40 becomes equal to or lower than a predetermined rotation speed, or may be a position at a timing a predetermined period before the motion stop timing t1 when the target position P2 is expected to be reached.

[0040] The vibration component Vc shown in FIG. 7 is a sine wave with a period T and an amplitude A. Therefore, among t=0 to T, a component of forward motion M1 is added to the movement of the tool TO1 between 0 to (1 / 4)T and (3 / 4)T to T, and a component of backward motion M2 is added to the movement of the tool TO1 between (1 / 4)T to (3 / 4)T. Note that the vibration component Vc is not limited to a sine wave, and may be a triangular wave, square wave, etc. Triangular waves and square waves contain harmonic components, and therefore are presumed to be more effective in releasing the internal stress generated in the structure when the driven object stops. The NC device 70 can output the amplitude A and frequency (assumed to be f) of the vibration component Vc as arguments to the servo amplifier 50. The servo amplifier 50, which receives the amplitude A and frequency f, performs semi-closed loop control so as to add the vibration component Vc of the amplitude A and frequency f to the movement M0 of the driven object.

[0041] The amplitude A of the vibration component Vc as the control position x1 is preferably 1 to 100 μm. When the amplitude A is 1 μm or more, the vibration component Vc passes through the first region AR1 in FIG. 5 and tends to enter the second regions AR2 and AR3. When the amplitude A is 100 μm or less, the vibration component Vc tends to enter the second regions AR2 and AR3 without reaching the third regions AR4 and AR5 in FIG. 5. When the amplitude A is 100 μm or less, the vibration component Vc can be said to be a micro-vibration component, and the vibration that actually occurs can be said to be a micro-vibration. The frequency f=1 / T of the vibration component Vc is preferably 100 to 1000 Hz. When the frequency f is 100 Hz or more, the number of vibrations from the intermediate position P3 to the target position P2 increases, so that the internal stress generated in the structure when the driven object stops is easily released. When the frequency f is 1000 Hz or less, the vibration of the driven object easily follows the control, so that the internal stress generated in the structure when the driven object stops is easily released.

[0042] In addition, in order to facilitate the release of the internal stress occurring in the structure, a semi-closed loop control may be performed to move the driven object by changing the vibration conditions including the frequency f and the amplitude A, and a vibration condition that releases as much as possible the internal stress occurring in the structure when the driven object stops may be searched for. If internal stress remains in the structure when the driven object stops, the servo amplifier 50 controls the servo motor 40 to generate a torque that cancels the internal stress of the structure. Therefore, the magnitude of the torque generated by the servo motor 40 when the driven object stops corresponds to the magnitude of the residual stress in the structure. Therefore, a semi-closed loop control may be performed to move the driven object by changing the vibration conditions, and the vibration condition that minimizes the torque value acquired from the servo amplifier 50 when the driven object stops may be set as the vibration condition of the vibration component Vc. For example, when the vibration conditions are stored in the ROM 72 shown in FIG. 2, the NC device 70 can output the vibration conditions stored in the ROM 72 to the servo amplifier 50 as arguments. As a result, the vibration component Vc is added to the movement M0 of the driven object so that the internal stress occurring in the structure when the driven object stops is released as much as possible. The vibration conditions may be searched for within a range of a guide amplitude A=1 to 100 μm and a guide frequency f=100 to 1000 Hz. The vibration conditions explored may include waveforms such as triangular waves and square waves.

[0043] As shown in FIG. 8, the servo amplifier 50 may perform semi-closed loop control so as to add the vibration component Vc to the driven object during a set period 202 within a stop period 201 during which the driven object stops at the target position P2 after reaching the target position P2. The set period 202 means a period during which the addition of the vibration component Vc continues from the motion stop timing t1 at which the driven object reaches the target position P2 to the vibration stop timing t2, and is shorter than the stop period 201. The set period 202 is not particularly limited, such as 1 to 1000 milliseconds. By continuing the vibration during the set period 202 after the driven object reaches the target position P2, it is possible to further reduce the internal stress remaining in the structure from the servo motor 40 to the driven object when the driven object is at the target position P2. This makes it possible to further improve the accuracy of the stop position of the driven object.

[0044] The machine tool 1 shown in FIG. 2 may have a vibration condition determination mode for determining the vibration conditions of the vibration component Vc, in addition to a machining mode for machining a workpiece W1 with a tool TO1 in accordance with a machining program PR2. 9 is a schematic diagram illustrating a vibration condition determination process performed by the NC device 70 in the vibration condition determination mode. When the operation unit 80 accepts an operation to select the vibration condition determination mode, the NC device 70 starts the vibration condition determination process. Hereinafter, the vibration condition determination process will be described using the movement of the tool TO1 as an example.

[0045] When the vibration condition determination process starts, the NC device 70 sets a candidate i for acquiring a torque value TR1i when the tool TO1 stops moving from among multiple candidates i for the vibration condition (step S102). The candidate i for the vibration condition is, for example, a combination of a frequency fi and an amplitude Ai. The factors of the candidate i may include a waveform such as a triangular wave or a rectangular wave, a set period 202 shown in FIG. 8, and the like. Next, the NC device 70 causes the servo amplifier 52 for the tool to execute semi-closed loop control so as to add a vibration component of the candidate i from an intermediate position P3 to the movement of the tool TO1 from the initial position P1 to the target position P2 (movement M0 of the driven target) (step S104). After the movement of the tool TO1 stops and the addition of the vibration component is also stopped, the NC device 70 acquires the torque value TR1i from the servo amplifier 52 (step S106). In this manner, the NC device 70 and the servo amplifier 52 perform semi-closed loop control using the candidate i as the vibration condition, and detect the torque generated by the servo motor 42 when the tool TO1 stops at the target position P2.

[0046] After acquiring the torque value TR1i, the NC device 70 judges whether or not to end the search for vibration conditions (step S108). For example, the NC device 70 may judge the search to be ended when the torque value TR1i falls below the reference torque value TR0 corresponding to the reference torque, or may judge the search to be ended when the torque values ​​TR1i are acquired for all candidates i. If the NC device 70 judges not to end the search for vibration conditions, it repeats the processes of steps S102 to S108. If the NC device 70 judges to end the search for vibration conditions, it determines the candidate i whose torque value TR1i falls below the reference torque value TR0 as the vibration condition for the vibration component Vc (step S110) and ends the vibration condition determination process. In step S110, the NC device 70 may determine the candidate i whose torque value TR1i is the smallest among the acquired torque values ​​TR1i as the vibration condition for the vibration component Vc. In this manner, the NC device 70 and the servo amplifier 52 determine, from among the multiple candidates i, the candidate in which the torque generated by the servo motor 42 when the movement of the tool TO1 stops falls below the reference torque as the vibration condition of the vibration component Vc.

[0047] In the semi-closed loop control, when the tool TO1 stops at the target position P2, the servo motor 42 generates a torque according to the internal stress of the structure up to the tool TO1. If the vibration conditions of the vibration component Vc are determined so that the torque generated by the servo motor 42 when the tool TO1 stops moving is lower than the reference torque, the internal stress remaining in the structure when the tool TO1 stops moving is reduced. Therefore, the vibration condition determination process improves the accuracy of the movement stop position of the tool TO1 in the machining mode. Of course, similar effects also improve the accuracy of the stop position of the driven object in the machining mode for the B-axis rotation of the swivel unit 25, the Z-axis movement of the workpiece W1, etc.

[0048] The frequency of the vibration component Vc may be included in a resonance frequency band that may cause resonance in a portion of the machine tool 1 that holds the driven object. When the driven object is a tool TO1, the portion that holds the driven object includes at least the tool rest 20, and may include at least a part of the guide mechanism 32 as a portion where resonance occurs. When the driven object is a workpiece W1, the portion that holds the driven object includes at least the headstock 10, and may include at least a part of the guide mechanism 31 as a portion where resonance occurs. The resonance frequency (referred to as fr) that occurs in the portion that holds the driven object is measured, for example, by a hammering test before the shipment of the machine tool 1, and written to the ROM 72. Since the measured resonance frequency fr has a width, the width is ±Δf (Δf>0), and the resonance frequency band means a frequency range in which resonance may occur, such as (fr-Δf) to (fr+Δf).

[0049] When the frequency of the vibration component Vc is included in the resonant frequency band, the vibration component Vc of the resonant frequency band applied to the driven object from the intermediate position P3 to the target position P2 vibrates the structure from the servo motor 40 to the driven object relatively strongly. The amplitude A of the vibration component Vc is small, about 1 to 100 μm, and the vibration component Vc is applied to the movement M0 of the driven object only from the intermediate position P3, so that the deterioration of the position accuracy of the driven object due to the resonance itself occurring in the part holding the driven object is suppressed. In particular, when the command CM1 is a fast-forward command that does not involve cutting the workpiece W1, the resonance does not lead to a deterioration of the position accuracy of the driven object. By vibrating the structure relatively strongly, the internal stress generated in the structure is easily released, and the internal stress remaining in the structure is further reduced. Therefore, when the frequency of the vibration component Vc is included in the resonant frequency band, the accuracy of the stop position of the driven object can be further improved.

[0050] In the machine tool 1 shown in FIG. 2, in the vibration condition determination mode, the frequency of the vibration component Vc may be determined to be the frequency in the resonance frequency band. The resonance frequency fr included in the resonance frequency band can be measured by inputting a current command 300 having a variation in the sweep frequency illustrated in FIG. 10 to the servo amplifier 50. In FIG. 10, the horizontal axis is the time t, and the vertical axis is the command value CV. The NC device 70 can output the current command 300 to the servo amplifier 50 as the command 57 shown in FIG. 3. The sweep frequency is a frequency that continuously changes from the start frequency to the stop frequency, and FIG. 10 shows a sweep frequency in which the frequency continuously increases. The amplitude Ac of the current command 300 is constant regardless of the frequency.

[0051] FIG. 11 schematically shows an example of the amplitude magnification M of vibration with respect to the frequency f when an external force for vibrating the mass point of the vibration system is applied. The amplitude magnification M is the ratio of the amplitude of the output vibration to the amplitude of the external force. FIG. 12 schematically shows an example of the phase lag φ of the output vibration with respect to the frequency f when an external force for vibrating the mass point of the vibration system is applied. The phase lag φ is the phase difference between the external force and the output vibration, and the lag of the phase of the output vibration with respect to the phase of the external force is shown as a negative value. The mass point corresponds to the part that holds the drive target in the machine tool 1, the external force corresponds to the current command 300 input to the servo amplifier 50, and the output vibration corresponds to the torque command 59 that has received feedback. Therefore, the amplitude magnification M corresponds to the ratio of the amplitude of the torque command 59 to the amplitude of the current command 300.

[0052] As shown in FIG. 11, the amplitude magnification M peaks near the natural vibration frequency fn of the mass point. This is because resonance occurs. The peak of the amplitude magnification M depends on the damping ratio of the vibration system, and becomes lower as the damping ratio increases. As shown in FIG. 12, the phase lag φ of the output vibration with respect to the frequency f is greater than -90° when f < fn, -90° when f = fn, and less than -90° and greater than -180° when f > fn. From the above, when the current command 300 having a fluctuation in the sweep frequency is input to the servo amplifier 50, the frequency at which the phase delay φ of the torque command 59 that vibrates upon receiving feedback becomes −90° becomes the resonant frequency fr. Therefore, in the vibration condition determination mode, the resonant frequency fr may be determined to be the frequency of the vibration component Vc.

[0053] 13 is a schematic diagram illustrating a frequency determination process performed by the NC device 70 in the vibration condition determination mode. When the operation unit 80 accepts an operation to determine the frequency of the vibration component Vc in the vibration condition determination mode, the NC device 70 starts the frequency determination process. Hereinafter, the frequency determination process will be described using the movement of the tool TO1 as an example.

[0054] When the frequency determination process starts, the NC device 70 outputs a current command 300 having a variation in the sweep frequency that changes continuously from the start frequency to the stop frequency as the command 57 shown in Fig. 3 to the servo amplifier 52 (step S202). The servo amplifier 52 inputs the current command 300 to a semi-closed loop, detects the phase lag φ of the oscillating torque command 59 upon receiving feedback, and outputs sweep information indicating the change in the phase lag φ relative to the frequency of the current command 300 to the NC device 70. The sweep information is information that shows a curve as shown in Fig. 12 in the range from the start frequency to the stop frequency. The NC device 70 that has received the sweep information acquires the frequency of the current command 300 when the phase lag φ becomes -90° as the resonant frequency fr (step S204). In this manner, NC device 70 and servo amplifier 52 input current command 300 to the semi-closed loop to detect resonance frequency fr generated in the portion of machine tool 1 that holds tool TO1.

[0055] The detection of the resonance frequency fr is not limited to detection based on the phase delay φ. For example, the frequency at which the amplitude magnification factor M with respect to the frequency of the current command 300 is greatest may be detected as the resonance frequency fr. In addition, if a vibration sensor is provided in the tool rest 20, the vibration of the tool rest 20 with respect to the frequency of the current command 300 may be detected by the vibration sensor, and the frequency at which the amplitude of the tool rest 20 is most amplified may be detected as the resonance frequency fr.

[0056] After detecting the resonance frequency fr, the NC device 70 determines the resonance frequency fr to be the frequency of the vibration component Vc (step S206), and ends the frequency determination process. By determining the detected resonance frequency fr as the frequency of the vibration component Vc, the vibration component Vc of the resonance frequency fr applied to the driven object from the intermediate position P3 to the target position P2 vibrates the structure from the servo motor 42 to the tool TO1 relatively strongly. By vibrating the structure relatively strongly within a range where the deterioration of the positional accuracy of the tool TO1 due to the resonance itself is suppressed, the internal stress generated in the structure is easily released, and the internal stress remaining in the structure is further reduced. Therefore, the accuracy of the movement stop position of the tool TO1 is further improved. Of course, the accuracy of the stop position of the driven object in the machining mode is also improved by a similar action in the B-axis rotation of the swivel unit 25, the Z-axis movement of the workpiece W1, etc.

[0057] In order to determine vibration conditions other than the frequency, such as the amplitude of the vibration component Vc, the NC device 70 may perform the vibration condition determination process shown in FIG.

[0058] As described above, when the driven object moves from the intermediate position P3 to the target position P2 in the semi-closed loop control, the vibration component Vc is added to the movement M0 of the driven object, so that the driven object reaches the target position P2 while the internal stress generated in the structure from the servo motor 40 to the driven object is released. When the driven object stops, the residual stress of the structure is reduced, so that the actual stop position of the driven object approaches the target position P2, and the accuracy of the stop position of the driven object is improved. When the driven object moves, the internal stress of the structure is released, so that the increase in the cycle time of the command CM1 is suppressed. Therefore, this specific example can improve the accuracy of the stop position of the driven object while suppressing the increase in the cycle time of the command CM1. Furthermore, when the residual stress of the structure is reduced, the torque generated by the servo motor 40 when the driven object stops is reduced, and the standby power is reduced.

[0059] (3) Modification: The present invention contemplates various modifications. For example, the control unit U1 may be configured not only by the machine body 2, but also by the machine body 2 and the computer 100. The command CM1 for moving the driven object is preferably a fast-forward command for moving the driven object without cutting the workpiece W1, but may be a cutting feed command for moving the driven object while cutting the workpiece W1.

[0060] (4) Conclusion: As described above, according to the present invention, it is possible to provide a technology for a machine tool or the like that can improve the accuracy of the stopping position of a driven object when semi-closed loop control is performed through various aspects. Of course, even a technology consisting only of the constituent elements according to the independent claims can obtain the basic functions and effects described above. In addition, configurations in which the configurations disclosed in the above examples are substituted with each other or the combination is changed, configurations in which the configurations disclosed in the publicly known techniques and the above examples are substituted with each other or the combination is changed, etc. The present invention also includes these configurations. [Explanation of symbols]

[0061] 1...Machine tool, 2...Machine body, 10...headstock, 11...spindle, 12...gripping portion, 13...motor, 20...tool rest, 21...comb tool rest, 22...turret tool rest, 25...swivel unit, 30, 31, 32...Guide mechanism, 40, 41, 42...Servo motor, 43...Encoder, 50, 51, 52...Servo amplifier, 57...command, 58...speed command, 59...torque command, 70...NC device, 201... Suspension period, 202... Setting period, 300...Current command, A,Ai...amplitude, AR1...first area, AR2,AR3...second area, AR4,AR5...third area, CM1: Command, CV: command value, Er...error, f, fi...frequency, fn...natural frequency, fr...resonance frequency, M...amplitude magnification, M0: Movement of the driven object, M1: Forward motion, M2: Reverse motion, P1...Initial position, P2...Target position, P3...Intermediate position, Ps...Movement start point, PR1: Control program, PR2: Machining program, SG1: Position feedback signal, SG3: Speed ​​feedback signal, t1: timing when motion stops, t2: timing when vibration stops, TO1...Tools, TR0: Reference torque value, TR1i: Torque value, U1: control unit, Vc...vibration component, W1: Work, x1: Control position, x2: Actual position, φ...Phase lag.

Claims

1. A machine tool that processes a workpiece with a tool, A guide mechanism for guiding at least one of the drive targets of the tool and the workpiece; A servo motor for moving the driven object guided by the guide mechanism; A control unit that performs semi-closed loop control on the servo motor so as to move the driven object from an initial position to a target position, The control unit controls the semi-closed loop to add a vibration component to the movement of the driven object that repeats a forward movement from an intermediate position between the initial position and the target position to the target position and a backward movement opposite to the forward movement.

2. 2. The machine tool according to claim 1, wherein the control unit controls the semi-closed loop so as to apply the vibration component to the driven object during a set period within a period during which the driven object remains at the target position after reaching the target position.

3. 3. The machine tool according to claim 1 or claim 2, wherein in a vibration condition determination mode for determining a vibration condition of the vibration component, the control unit performs semi-closed loop control for each of a plurality of candidates for the vibration condition using the candidate as the vibration condition, detects the torque generated by the servo motor when the driven object stops at the target position, and determines as the vibration condition a candidate among the plurality of candidates when the torque falls below a reference torque.

4. 3. The machine tool according to claim 1, wherein a frequency of the vibration component is included in a resonance frequency band capable of causing resonance in a portion of the machine tool that holds the object to be driven.

5. 3. The machine tool according to claim 1 or claim 2, wherein, in a vibration condition determination mode for determining a frequency of the vibration component, the control unit inputs a current command having a sweep frequency fluctuation to the semi-closed loop to detect a resonant frequency generated in a portion of the machine tool that holds the object to be driven, and determines the detected resonant frequency as the frequency of the vibration component.

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