Machine tool

Abstract

To provide a machine tool which can reduce a load applied to a driving system for moving a drive object when the drive object starts moving toward a target position.SOLUTION: A machine tool 1 includes: a guide mechanism 30 for guiding at least one drive object of a tool TO1 and a workpiece W1; a servo motor 40 which moves the drive object to be guided by the guide mechanism 30; and a control section U1 which controls the servo motor 40 so as to move the drive object from an initial position P1 up to a target position P2. The control section U1 controls the servo motor 40 so as to apply vibration Vc repeating a progress motion M1 directing to the target position P2 and a regression motion M2 opposite to the progress motion M1 to the drive object in a set period 202 until starting the movement of the drive object from the initial position P1 to the target position P2.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a machine tool that machines a workpiece with a tool. [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 servo motor, a servo amplifier, an NC device, etc. (For example, see Patent Document 1). The guide mechanism may be a sliding guide mechanism such as a combination of a dovetail and a dovetail groove, or a rolling guide mechanism such as a ball screw or a linear guide. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2022-177508 A Summary of the Invention [Problem to be solved by the invention]

[0004] Since friction occurs due to the guide surfaces of the guide mechanism and O-rings for sealing, lubricating oil is supplied to the guide surfaces of the guide mechanism. When the driven object is stopped, the lubricating oil film on the guide surfaces may disappear, causing an "oil film break." For example, when the oil film breaks on the guide surface, the guide surface sticks, and the servo motor generates a large torque to start the movement of the driven object. Then, when the driven object starts to move toward the target position, a large load is applied to the drive system that moves the driven object, for example, the drive shaft of the servo motor, which may cause the drive system to deteriorate. Therefore, it is desirable to reduce the load applied to the drive system when the driven object starts to move toward the target position. 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 reducing the load applied to a drive system that moves a driven object when the driven object starts to move toward a target position. [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 controls the servo motor so as to move the driven object from an initial position to a target position, The control unit has an aspect in which it controls the servo motor to apply vibrations to the driven object that repeat a forward movement toward the target position and a backward movement opposite to the forward movement during a set period until the driven object starts to move from the initial position toward the target position. Effect of the Invention

[0007] According to the present invention, it is possible to provide a machine tool that is capable of reducing the load applied to a drive system that moves a driven object when the driven object starts to move toward a target position. [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] FIG. 1 is a diagram illustrating an example of a Stribeck curve. [Diagram 5] 5A to 5C are diagrams illustrating examples of lubrication states of guide surfaces. [Figure 6]11A and 11B are diagrams illustrating an example in which vibration is applied to a drive target during a set period until the drive target starts to move from an initial position toward a target position. [Figure 7] FIG. 10 is a diagram illustrating an example of vibration. [Figure 8] 10A and 10B are diagrams illustrating an example in which a vibration component is added to the movement of a driven object from when the driven object starts to move toward a target position until the moving object reaches an intermediate position. [Figure 9] 13 is a flowchart illustrating an example of a vibration condition confirmation 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 and 2, 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 controls the servo motor 40 to move the driven object from an initial position P1 to a target position P2. The control unit U1 controls the servo motor 40 to apply vibration Vc to the driven object, which repeats a forward movement M1 toward the target position P2 and a backward movement M2 opposite to the forward movement M1, during a set period 202 until the driven object starts to move from the initial position P1 toward the target position P2.

[0012] When the driven object stops for a while, friction of the guide surfaces 33, 34 (see FIG. 5) increases due to oil film breakdown or the like. When the servo motor 40 starts to move the driven object from the initial position P1 toward the target position P2 without applying vibration Vc to the driven object, the servo motor 40 generates a large torque to move the driven object against the initial large friction. Since the initial large friction is applied to the guide surfaces 33, 34 for a relatively long distance from the start of the movement, a large torque continues to be generated, and a high load is applied to the drive system that moves the driven object, for example, the drive shaft of the servo motor 40. In the above embodiment, the vibration Vc is applied to the driven object during the set period 202 until the driven object starts to move toward the target position P2, so that the lubricating oil 35 spreads over the guide surfaces 33, 34 by the vibration Vc before the start of the movement, and the initial large friction is applied to the guide surfaces 33, 34 over a short distance due to the vibration. By spreading the lubricating oil 35 over the guide surfaces 33, 34, friction between the guide surfaces 33, 34 is reduced, the torque generated when the servo motor 40 starts to move the driven object from the initial position P1 toward the target position P2 is reduced, and the load applied to the drive system that moves the driven object is reduced. Therefore, the above embodiment can reduce the load applied to the drive system that moves the driven object when the driven object starts to move toward the target position. As a result, deterioration of the drive system is suppressed.

[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 servo motor 40 to add the vibration Vc as a component to the movement M0 of the driven object, from when the driven object starts to move from the initial position P1 toward the target position P2, to an intermediate position P3 between the initial position P1 and the target position P2. When the driven object starts to move from the initial position P1 toward the target position P2, the oil film in the guide mechanism 30 may not have been completely removed, and therefore the above embodiment can further reduce the load applied to the drive system that moves the driven object when the driven object starts to move toward the target position.

[0015] [Aspect 3] As illustrated in FIG. 8, the control unit U1 may control the servo motor 40 to continuously add the vibration Vc as a component to the movement M0 of the driven object for a second set period 203 after starting to move the driven object from the initial position P1 toward the target position P2. When the driven object starts to move from the initial position P1 toward the target position P2, the oil film in the guide mechanism 30 may not have been completely removed, and therefore the above embodiment can further reduce the load on the drive system that moves the driven object when it starts to move toward the target position.

[0016] [Aspect 4] The frequency of the vibration Vc may be included in a resonance frequency band including frequencies at which resonance occurs 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 Vc in the resonant frequency band is applied to the driven object in the set period 202 until the driven object starts to move from the initial position P1, the lubricant oil 35 is likely to spread over the guide surfaces 33, 34 before the driven object starts to move. Therefore, the above embodiment can provide a suitable example for reducing the load applied to the drive system that moves the driven object when the driven object starts to move toward the target position.

[0017] [Aspect 5] The control unit U1 may perform closed-loop control (see, for example, FIG. 3) on the servo motor 40 so as to move the object to be driven from the initial position P1 to the target position P2. As illustrated in FIG. 13, in a frequency determination mode for determining the frequency of the vibration Vc, the control unit U1 may input a current command 300 having a fluctuation of a sweep frequency to the closed loop to detect a resonance frequency fr generated in a portion that holds the object to be driven in the machine tool 1, and may determine the detected resonance frequency fr as the frequency of the vibration Vc.

[0018] When a current command 300 having a variation in the sweep frequency is input to a 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 occurring in the portion is detected, the detected resonant frequency fr is determined as the frequency of the vibration Vc. When the vibration Vc of the resonant frequency fr is applied to the object to be driven during a set period 202 until the object to be driven, which is in the initial position P1, starts to move, the lubricant oil 35 is more likely to spread over the guide surfaces 33, 34 by the time the object to be driven starts to move toward the target position P2. Therefore, the above embodiment can provide a suitable example for reducing the load applied to the drive system that moves the object to be driven when the object to be driven starts to move toward the target position. Here, the closed loop control means control having a feedback loop. The closed loop may be a semi-closed loop or a full-closed loop.

[0019] (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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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).

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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 .

[0031] 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.

[0032] 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.

[0033] Since friction occurs due to the guide surfaces of the guide mechanism 30 and the sealing O-rings, a lubricant is supplied to the guide surfaces of the guide mechanism 30. In sliding guideways such as a combination of a dovetail and a dovetail groove, and rolling guideways such as a ball screw and a linear guide, the relationship of the Stribeck curve shown in FIG. As shown in FIG. 4, the Stribeck curve shows the relationship between the parameter H=ηV / W and the friction coefficient μ. Here, η is the viscosity of the lubricant, V is the speed of the moving body, and W is the load applied between the guideways. The moving body corresponds to a dovetail that can move along a fixed dovetail groove. The larger the friction coefficient μ, the greater the friction between the guideways. The Stribeck curve is divided into a boundary lubrication region AR1, a mixed lubrication region AR2, and a liquid lubrication region AR3 according to the parameter H. FIG. 4 shows that the parameter H of the boundary between the boundary lubrication region AR1 and the mixed lubrication region AR2 is H1 (H1>0), and the parameter H of the boundary between the mixed lubrication region AR2 and the liquid lubrication region AR3 is H2 (H2>H1).

[0034] FIG. 5 shows a schematic example of the lubrication state of the guide surface. 5, lubricating oil 35 is supplied between guide surfaces 33, 34. Here, guide surface 33 is a guide surface for a moving body such as a dovetail, and guide surface 34 is a guide surface for a fixed body such as a dovetail groove. In general, the moving body and the fixed body are made of metal, and although guide surfaces 33, 34 are formed to be smooth macroscopically, guide surfaces 33, 34 have irregularities microscopically.

[0035] In the boundary lubrication region AR1 shown in Figs. 4 and 5, the guideways 33 and 34 are in a lubricated state where the oil film is thin and many parts are in contact. Since there are many contact parts, the guideways 33 and 34 in the boundary lubrication region AR1 can be said to be in an "oil film break" state. Therefore, the friction coefficient μ in the boundary lubrication region AR1 is large. When the guideway 33 of the moving body starts to move, the parameter H increases and the region transitions from the boundary lubrication region AR1 to the mixed lubrication region AR2. In the mixed lubrication region AR2, the guideways 33 and 34 are in a lubricated state where the lubricant 35 increases and the number of contact parts decreases but the contact parts remain. Therefore, the friction coefficient μ in the mixed lubrication region AR2 generally decreases as the parameter H increases. When the speed V of the moving body increases, the parameter H further increases and the region transitions from the mixed lubrication region AR2 to the liquid lubrication region AR3. In the liquid lubrication region AR3 shown in Figs. 4 and 5, the lubricant 35 increases further and the region transitions from the mixed lubrication region AR2 to the liquid lubrication region AR3 where the lubricant 35 increases and the contact parts disappear due to the oil film.

[0036] From the above, when the driven object stops for a while, the boundary lubrication area AR1, which can be said to be an oil film break, is formed between the guide surfaces 33 and 34, and the friction between the guide surfaces 33 and 34 increases. When the servo motor 40 starts to move the driven object toward the target position without applying vibration to the driven object, the servo motor 40 generates a large torque to move the driven object against the large friction of the boundary lubrication area AR1. For a relatively long distance from the start of the movement of the driven object, the large friction of the boundary lubrication area AR1 is applied to the guide surfaces 33 and 34, so that a large torque continues to be generated and a high load is applied to the drive system that moves the driven object, for example, the drive shaft of the servo motor 40. The high load applied to the drive system may lead to damage to the drive system. In particular, when the guide mechanism 30 is a sliding guide mechanism such as a combination of a dovetail and a dovetail groove, the friction of the boundary lubrication area AR1 is large, so that the drive system is likely to be subjected to a high load. In addition, when the command CM1 is a fast-forward command that does not involve cutting the workpiece W1, the movement of the driven object is high speed, so that a high load is likely to be applied to the drive system.

[0037] In this specific example, before the driven object starts to move toward the target position, micro-vibrations are applied to the driven object so that the lubricating oil 35 enters between the guide surfaces 33, 34, and the area between the guide surfaces 33, 34 is shifted from the boundary lubrication area AR1 to the mixed lubrication area AR2. As a result, when the driven object starts to move toward the target position, the load applied to the drive system that moves the driven object is reduced, and deterioration of the drive system is suppressed.

[0038] FIG. 6 shows a schematic example of a state in which vibration Vc is applied to the driven object during a set period 202 until the driven object starts to move from an initial position P1 toward a target position P2. FIG. 7 shows a schematic example of vibration Vc. In FIGS. 6 and 7, the horizontal axis is time t, and the vertical axis is the control position x1 of the driven object. 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 time t is the movement stop timing t3. t=0 shown in FIG. 7 is different from t=0 shown in FIG. 6. The control position x1 is a semi-closed loop control position that receives feedback signals (SG1, SG3) based on the output of the encoder 43 shown in Fig. 3. 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.

[0039] 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 servo amplifier 52 for the tool performs semi-closed loop control on the servo motor 42 so as to move the tool TO1 from the initial position P1 to the target position P2. The servo amplifier 52 of this specific example controls the servo motor 42 to apply vibration Vc to the tool TO1, which repeats a forward movement M1 toward the target position P2 and a backward movement M2 opposite to the forward movement M1, during a set period 202 until the tool TO1 starts moving from the initial position P1 toward the target position P2. The set period 202 means a period from a set vibration start timing t1 to a timing t=0 at which the driven object starts moving toward the target position P2, and is connected to a period in which the driven object moves from the initial position P1 toward the target position P2. The set period 202 is shorter than a stop period 201 during which the driven object stops at the initial position P1. The set period 202 is not particularly limited, and may be 1 to 10,000 milliseconds.

[0040] As shown in FIG. 6, the vibration Vc is not applied to the movement of the tool TO1 from the initial position P1 to the target position P2 (movement M0 of the driven object), but the vibration Vc is applied to the tool TO1 until it starts moving toward the target position P2. Due to the vibration Vc, the lubricant 35 enters between the guide surfaces 33, 34 before the tool TO1 starts moving toward the target position P2, and the area between the guide surfaces 33, 34 transitions from the boundary lubrication area AR1 to the mixed lubrication area AR2. Although the large friction of the boundary lubrication area AR1 is applied to the guide surfaces 33, 34 during vibration, the large friction is applied to the guide surfaces 33, 34 only over a short distance due to the vibration. The torque generated by the servo motor 42 is reduced by causing the servo motor 42 to start moving the tool TO1 from the initial position P1 to the target position P2 after the friction of the guide surfaces 33, 34 is reduced. This reduces the load applied to the drive system that moves the tool TO1, and suppresses deterioration of the drive system. The vibration Vc can be said to be a micro-vibration that reduces friction generated in the guide mechanism 30 until the driven object starts to move from the initial position P1 toward the target position P2. In addition, since the vibration Vc is not applied to the movement of the tool TO1 from the initial position P1 to the target position P2, 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.

[0041] 7 is a sine wave with a period T and an amplitude A. Therefore, among t=0 to T, the tool TO1 performs an advance motion M1 between 0 to (1 / 4)T and between (3 / 4)T and T, and the tool TO1 performs a retreat motion M2 between (1 / 4)T and (3 / 4)T. Note that the vibration Vc is not limited to a sine wave, and may be a triangular wave, a square wave, or the like. It is presumed that the triangular wave and square wave contain harmonic components, which makes it easier for the lubricating oil 35 to enter between the guide surfaces 33 and 34. The NC device 70 can output the amplitude A and frequency (f) of the vibration 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 apply the vibration Vc of the amplitude A and frequency f to the driven object.

[0042] The amplitude A of the vibration Vc as the control position x1 is preferably 1 to 100 μm. When the amplitude A is 1 μm or more, the driven object actually vibrates against the friction between the guide surfaces 33, 34, which makes it easier for the lubricating oil 35 to enter between the guide surfaces 33, 34. When the amplitude A is 100 μm or less, the vibration distance that the guide surface 33 of the moving body moves against the large friction in the boundary lubrication area AR1 during vibration is prevented from becoming excessive. When the amplitude A is 100 μm or less, the vibration Vc as the control position x1 can be said to be a micro-vibration, and the vibration that actually occurs can be said to be a micro-vibration. The frequency f=1 / T of the vibration Vc is preferably 1 to 1000 Hz. When the frequency f is 1 Hz or more, the number of vibrations in the set period 202 increases, so that the lubricating oil 35 easily enters between the guide surfaces 33, 34. When the frequency f is 1000 Hz or less, the vibration of the driven object easily follows the control, so that the lubricating oil 35 easily enters between the guide surfaces 33, 34.

[0043] As shown in FIG. 8, the servo amplifier 50 may control the servo motor 40 so that the vibration Vc is added as a component to the movement M0 of the driven object from the start of moving the driven object from the initial position P1 toward the target position P2 to an intermediate position P3 between the initial position P1 and the target position P2. The intermediate position P3 may be a position at a predetermined distance from the initial position P1, a position when the rotation speed of the servo motor 40 becomes equal to or greater than a predetermined rotation speed, or a position at a timing after a predetermined period from t=0. The period from the timing t=0 to the vibration stop timing t2 means a period during which the addition of the vibration Vc continues from the set period 202, and is shorter than the period from the timing t=0 to the movement stop timing t3. The period from the timing t=0 to the vibration stop timing t2 is not particularly limited and may be 1 to 1000 milliseconds. When the driven object starts to move from the initial position P1 toward the target position P2, the lubricating oil 35 may not have sufficiently penetrated between the guide surfaces 33, 34. In this case, as the vibration Vc continues to be applied, more lubricating oil 35 penetrates between the guide surfaces 33, 34, and the load applied to the drive system that moves the driven object when the driven object starts to move toward the target position P2 becomes even smaller.

[0044] Here, the period from timing t=0 to vibration stop timing t2 is set as the second set period 203. The servo amplifier 50 may control the servo motor 40 so as to continuously add the vibration Vc as a component to the movement M0 of the driven object during the second set period 203 after the driven object starts to move from the initial position P1 toward the target position P2. The second set period 203 may be a predetermined period set in the machine body 2 from the beginning, or may be a period designated by an operator. The second set period 203 as a designated period may be designated in the machining program PR2. When the second set period 203 is designated, the NC device 70 may pass the second set period 203 to the servo amplifier 50. The servo amplifier 50 may control the servo motor 40 so as to add the vibration Vc as a component to the movement M0 of the driven object during the second set period 203 received from the NC device 70.

[0045] In order to minimize the load on the drive system that moves the driven object, the vibration conditions including the frequency f and the amplitude A may be changed to add the vibration Vc to the stopped driven object, and a vibration condition that minimizes the friction between the guide surfaces 33 and 34 may be searched for. The friction between the guide surfaces 33 and 34 corresponds to the starting torque, which is the torque when the stopped driven object starts to move. Therefore, as illustrated in FIG. 9, a candidate i for the vibration condition of the vibration Vc may be set, and the vibration Vc may be applied to the driven object under the vibration condition of the set candidate i, and it may be confirmed that the detected starting torque is lower than the reference torque. The machine tool 1 shown in FIG. 2 has a manual mode in which the vibration condition confirmation process shown in FIG. 9 can be executed, in addition to a machining mode in which the workpiece W1 is machined by the tool TO1 according to the machining program PR2.

[0046] 9 is a schematic diagram illustrating the vibration condition confirmation process performed by the NC device 70 in the manual mode. When the operation unit 80 receives an operation to detect the starting torque in the manual mode, the NC device 70 starts the vibration condition confirmation process. The vibration condition confirmation process will be described below using the movement of the tool TO1 as an example. Whether or not the tool TO1 has actually moved can be determined, for example, by placing the probe of a dial gauge against the tool rest 20 on which the tool TO1 is mounted and checking whether or not the long hand of the dial gauge has moved.

[0047] When the vibration condition confirmation process starts, the NC device 70 sets a candidate i for the vibration condition of the vibration Vc (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. 6, and the like. The candidate i may be set from among a plurality of candidates i for the vibration condition. Next, the NC device 70 causes the servo amplifier 52 for the tool to execute semi-closed loop control so as to apply the vibration of the candidate i to the tool TO1 stopped at the initial position P1 for the set period 202 (step S104). After the vibration of the candidate i is stopped, the NC device 70 causes the servo amplifier 52 to execute semi-closed loop control so as to move the tool TO1 by a minute amount ΔX (step S106). Immediately, the NC device 70 acquires a torque value TR1 from the servo amplifier 52 (step S108). Next, the NC device 70 causes the operation unit 80 to accept an operation as to whether or not the tool TO1 has actually moved, and determines whether or not the tool TO1 has actually moved (step S110).

[0048] If the tool TO1 has not moved, the NC device 70 performs the processes of steps S106 to S110 again. Therefore, the movement amount of the tool TO1 as the control position x1 is a distance obtained by multiplying the number of times step S106 is executed by the minute amount ΔX. When the tool TO1 actually moves, the NC device 70 determines whether the candidate i is applicable to the vibration condition of vibration Vc based on the starting torque value TR1i, using the last acquired torque value TR1 as the starting torque value TR1i (step S112), and ends the vibration condition confirmation process. For example, the NC device 70 can determine that the candidate i is applicable to the vibration condition of vibration Vc when the starting torque value TR1i is below a reference torque value, and that the candidate i is not applicable to the vibration condition of vibration Vc in other cases. In step S112, the NC device 70 may display the determination result on the display unit 82, or may set the candidate i to the vibration condition of vibration Vc only when it is determined that the candidate i is applicable to the vibration condition of vibration Vc.

[0049] By performing the vibration condition confirmation process for a plurality of candidates i, the vibration condition of the vibration Vc is searched for and the vibration condition of the vibration Vc is set so that the starting torque is as small as possible. The vibration condition may be searched for in a standard amplitude A=1 to 100 μm and a standard frequency f=1 to 1000 Hz. For example, when the vibration condition is stored in the ROM 72 shown in FIG. 2, the NC device 70 can output the vibration condition stored in the ROM 72 as an argument to the servo amplifier 50. As a result, the vibration Vc is applied to the tool TO1 so that the load applied to the drive system that moves the driven object when the tool TO1 starts to move toward the target position is as small as possible. Of course, in the B-axis rotation of the swivel unit 25, the Z-axis movement of the workpiece W1, etc., the load applied to the drive system when the driven object starts to move toward the target position in the machining mode can be reduced by a similar action.

[0050] The frequency of the vibration Vc may be included in a resonant frequency band that may cause resonance in a portion of the machine tool 1 that holds the object to be driven. When the object to be driven is a tool TO1, the portion that holds the object to be driven 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 object to be driven is a workpiece W1, the portion that holds the object to be driven 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 resonant frequency (referred to as fr) that occurs in the portion that holds the object to be driven is measured, for example, by a hammering test before the machine tool 1 is shipped, and written to the ROM 72. Since the measured resonant frequency fr has a width, the width is ±Δf (Δf>0), and the resonant frequency band means a frequency range in which resonance may occur, such as (fr-Δf) to (fr+Δf).

[0051] When the frequency of the vibration Vc is included in the resonant frequency band, the vibration Vc of the resonant frequency band applied to the drive target at the initial position P1 vibrates the structure from the servo motor 40 to the drive target relatively strongly. The amplitude A of the vibration Vc is small, about 1 to 100 μm, and the vibration Vc is applied to the drive target only until the drive target starts to move or only up to the intermediate position P3, so that the deterioration of the position accuracy of the drive target due to the resonance itself occurring in the part holding the drive target 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 drive target. By vibrating the structure relatively strongly, the lubricating oil 35 is easily distributed on the guide surfaces 33, 34 before the drive target starts to move. Therefore, when the frequency of the vibration Vc is included in the resonant frequency band, the load applied to the drive system that moves the drive target when the drive target starts to move toward the target position P2 can be effectively reduced.

[0052] The machine tool 1 shown in Fig. 2 may have a frequency determination mode for determining the frequency of the vibration Vc in addition to the machining mode and the like, and in the frequency determination mode, the frequency of the vibration Vc may be determined to be a frequency within 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 represents time t and the vertical axis represents 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.

[0053] Fig. 11 schematically shows an example of the amplitude magnification M of the 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. Note that 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.

[0054] 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 it 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 frequency determination mode, the resonant frequency fr may be determined to be the frequency of the vibration Vc.

[0055] 13 is a schematic diagram illustrating a frequency determination process performed by the NC device 70 in the frequency determination mode. When the operation unit 80 accepts an operation to determine the frequency of the vibration Vc in the frequency 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.

[0056] 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.

[0057] 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.

[0058] After detecting the resonance frequency fr, the NC device 70 determines the resonance frequency fr to be the frequency of the vibration Vc (step S206), and ends the frequency determination process. By determining the detected resonance frequency fr as the frequency of the vibration Vc, the vibration Vc of the resonance frequency fr applied to the driven object at the initial position P1 vibrates the structure from the servo motor 42 to the tool TO1 relatively strongly. By vibrating the structure relatively strongly within a range in which the deterioration of the positional accuracy of the tool TO1 due to the resonance itself is suppressed, the lubricant 35 is easily spread to the guide surfaces 33, 34 before the driven object starts to move. Therefore, it is possible to effectively reduce the load applied to the drive system that moves the driven object when the driven object starts to move toward the target position P2. Of course, a similar action also improves the accuracy of the stop position of the driven object in the machining mode in the B-axis rotation of the swivel unit 25, the Z-axis movement of the workpiece W1, etc.

[0059] In order to check vibration conditions other than the frequency, such as the amplitude of the vibration Vc, the NC device 70 may perform a vibration condition checking process shown in FIG.

[0060] As described above, the vibration Vc is applied to the driven object during the set period 202 until the driven object starts to move toward the target position P2, so that the vibration Vc spreads the lubricant 35 over the guide surfaces 33, 34 before the movement starts. In addition, the initial large friction applied to the guide surfaces 33, 34 is only a short distance due to the vibration. By spreading the lubricant 35 over the guide surfaces 33, 34, the friction of the guide surfaces 33, 34 is reduced, and the torque generated when the servo motor 40 starts to move the driven object from the initial position P1 toward the target position P2 is reduced, and the load applied to the drive system that moves the driven object is reduced. Therefore, in this specific example, when the driven object starts to move toward the target position, the load applied to the drive system that moves the driven object can be reduced, and deterioration of the drive system can be suppressed.

[0061] (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 closed-loop control performed by the control unit U1 is not limited to semi-closed-loop control, and may be full-closed-loop control. The command CM1 for moving the driven object is not limited to a fast-forward command, and may be a cutting feed command for moving the driven object while cutting the workpiece W1, or the like.

[0062] (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 reduce the load applied to the drive system that moves the driven object when the driven object starts to move toward a target position through various aspects. Of course, even a technology that consists 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]

[0063] 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, 33, 34 ... guide surface, 35 ... lubricant, 40, 41, 42...Servo motor, 43...Encoder, 50, 51, 52...Servo amplifier, 57...command, 58...speed command, 59...torque command, 70...NC device, 201...stop period, 202...set period, 203...second set period, 300...Current command, A,Ai...amplitude, AR1...boundary lubrication area, AR2...mixed lubrication area, AR3...liquid lubrication area, CM1: Command, CV: command value, 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, PR1: Control program, PR2: Machining program, SG1: Position feedback signal, SG3: Speed ​​feedback signal, t1: vibration start timing, t2: vibration stop timing, t3: movement stop timing, TO1...Tools, TR1: torque value, TR1i: starting torque value, U1: control unit, Vc…vibration, W1: Work, x1…control 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 controls the servo motor so as to move the driven object from an initial position to a target position, The control unit controls the servo motor to apply vibration to the driven object that repeats a forward movement toward the target position and a backward movement opposite to the forward movement during a set period until the driven object starts to move from the initial position toward the target position.

2. 2. The machine tool according to claim 1, wherein the control unit controls the servo motor so as to add the vibration as a component to the movement of the driven object from when the driven object starts to move from the initial position toward the target position to an intermediate position between the initial position and the target position.

3. 2. The machine tool according to claim 1, wherein the control unit controls the servo motor so as to continuously add the vibration as a component to the movement of the driven object for a second set period from when the driven object starts to move from the initial position toward the target position.

4. 3. The machine tool according to claim 1, wherein a frequency of the vibration 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. The control unit is performing a closed-loop control on the servo motor so as to move the driven object from the initial position to the target position; 3. The machine tool according to claim 1 or claim 2, wherein, in a frequency determination mode for determining a frequency of the vibration, a current command having a fluctuation of a sweep frequency is input to the closed loop to detect a resonant frequency generated in a portion of the machine tool that holds the object to be driven, and the detected resonant frequency is determined as the frequency of the vibration.

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