阅读说明：本技术 伺服控制装置 (Servo control device ) 是由 森桥谅 山本健太 园田直人 于 2020-03-12 设计创作，主要内容包括：本发明提供一种能够在摆动加工中稳定地进行加工的伺服控制装置。伺服控制装置(20)具备：摆动指令生成部(23),其生成用于使工件(W)与工具(14)相对地摆动的摆动指令；位置控制部(22)、速度控制部(24)以及电流控制部(25)中的任意一方,所述位置控制部(22)生成使工件(W)与工具(14)相对地移动的位置指令,所述速度控制部(24)生成使工件(W)与工具(14)相对地移动的速度指令所述电流控制部(25)生成使多个轴驱动的转矩指令；以及增益变更部,其变更控制增益,其中,摆动指令生成部(23)将在摆动动作开始时输出的信号发送到增益变更部,增益变更部变更控制增益。(The invention provides a servo control device capable of stably processing in swing processing. A servo control device (20) is provided with: a swing command generation unit (23) that generates a swing command for swinging the workpiece (W) and the tool (14) relative to each other; any one of a position control unit (22), a speed control unit (24), and a current control unit (25), wherein the position control unit (22) generates a position command for moving the workpiece (W) and the tool (14) relative to each other, the speed control unit (24) generates a speed command for moving the workpiece (W) and the tool (14) relative to each other, and the current control unit (25) generates a torque command for driving a plurality of axes; and a gain changing unit that changes the control gain, wherein the wobble command generating unit (23) transmits a signal output at the start of the wobble operation to the gain changing unit, and the gain changing unit changes the control gain.)

1. A servo control device for controlling a machine tool for performing a turning process on a workpiece by a cooperative operation of a plurality of axes,

the servo control device includes:

a swing command generating unit that generates a swing command for swinging the workpiece and the tool relative to each other;

at least one of a position control unit that generates a position command for moving the workpiece and the tool relative to each other, a speed control unit that generates a speed command for moving the workpiece and the tool relative to each other, and a current control unit that generates a torque command for driving the plurality of axes; and

a gain changing unit for changing the control gain,

wherein the swing command generating unit transmits a signal output at the start of a swing operation to the gain changing unit, and the gain changing unit changes the control gain.

2. Servo control device according to claim 1,

the execution state of the wobbling motion is represented by a frequency or an amplitude.

3. Servo control device according to claim 1 or 2,

the gain changing unit changes at least one of a position gain of the position control unit, a speed gain of the speed control unit, and a current gain of the current control unit, which is the control gain.

4. Servo control device according to claim 3,

the gain changing unit changes only the speed gain of the speed control unit.

5. Servo control device according to any of claims 1 to 4,

the gain changing unit changes the control gain so that a gain value at the wobble frequency approaches 0 dB.

Technical Field

The present invention relates to a servo control device.

Background

Conventionally, there is known an oscillating machining method for crushing chips by relatively oscillating (oscillating) a tool and a workpiece in a machining direction (see, for example, patent documents 1 and 2).

Patent document 1 describes that "in the cutting edge trajectory of the cutting tool 130, the cutting portion in the present forward movement overlaps with the cutting portion in the next return movement, and for example, the circumferential surface shape of the workpiece W in the n-th rotation of the spindle 110 is included in the circumferential surface shape of the workpiece W in the n + 1-th rotation of the spindle 110, and therefore the cutting tool 130 generates a wobbling operation that does not machine the workpiece W. During this lost motion, chips generated from the workpiece W are cut off. The machine tool 100 smoothly processes the outer shape and the like of the workpiece W while cutting chips. ".

Patent document 2 describes "the control device 8 will be described in detail with reference to fig. 2 and 3. As shown in fig. 2, the control device 8 includes: a central control unit 80 configured by a CPU or the like; an input unit 81 configured by a touch panel or the like; a program information storage unit 82 that stores program information programmed by the user using the input unit 81; a vibration cutting information storage unit 83 that stores data for causing the cutting tool 4 to vibrate at a low frequency according to mechanical characteristics such as mass on the machining table and motor characteristics, the data being data that enables a non-oscillating operation even if a gain value of a high gain is set; a motor control unit 84 for controlling the operation of the cutting tool feed drive motor 7a via the servo amplifier 9; and a display unit 85 configured by a liquid crystal monitor or the like. ".

Disclosure of Invention

Problems to be solved by the invention

It is desirable to stably perform machining in the swing machining.

The invention aims to provide a servo control device capable of stably processing in swing processing.

Means for solving the problems

(1) One embodiment of the present disclosure is a servo control device for controlling a machine tool that performs a turning process on a workpiece by a cooperative operation of a plurality of axes, the servo control device including: a swing command generating unit that generates a swing command for swinging the workpiece and the tool relative to each other; at least one of a position control unit that generates a position command for moving the workpiece and the tool relative to each other, a speed control unit that generates a speed command for moving the workpiece and the tool relative to each other, and a current control unit that generates a torque command for driving the plurality of axes; and a gain changing unit that changes a control gain, wherein the wobble command generating unit transmits a signal output at the start of a wobble operation to the gain changing unit, and the gain changing unit changes the control gain.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, it is possible to provide a servo control device capable of stably performing machining in wobbling.

Drawings

Fig. 1 is a diagram illustrating a configuration of a machining system including a servo control device of a machine tool according to the present embodiment.

Fig. 2 is a diagram showing a relationship between a feed amount and a rotation angle in a swing operation.

Fig. 3 is a graph showing the gain before switching the control gain in the wobbling operation.

Fig. 4 is a graph showing the gain in a state where the control gain is switched during the wobbling operation.

Description of the reference numerals

14: a tool; 20: a servo control device; 21: a gain setting section; 22: a position control unit; 23: a swing command generating unit; 24: a speed control unit; 25: a current control unit; w: and (5) a workpiece.

Detailed Description

An example of an embodiment of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding portions are denoted by the same reference numerals.

Fig. 1 is a diagram illustrating a configuration of a machining system 1 including a servo controller 20 of a machine tool 10. The machining system 1 shown in fig. 1 includes: a machine tool 10 and a servo control device 20 for controlling the machine tool 10.

Machine tool 10 has a tool 14. The tool 14 performs a turning process on a workpiece W having a shape such as a cylindrical shape, a conical shape, or a truncated cone shape. In the example of fig. 1, the tool 14 performs a turning process on the outer peripheral surface of the workpiece W. In the example of fig. 1, the central axis of the workpiece W, which is the rotation axis of the workpiece W, is defined as the Z axis, and an axis perpendicular to the Z axis is defined as the X axis.

The machine tool 10 is not limited to machining a workpiece W having a linear shape in the direction along the Z axis, and may machine a workpiece W having a tapered shape or an arc shape. Further, the machine tool 10 is not limited to machining the outer peripheral surface of the workpiece W, and may machine the inner peripheral surface of the workpiece W in a cylindrical shape, for example. The machine tool 10 is not limited to performing turning, and may perform machining such as cutting, grinding, or polishing.

The machine tool 10 includes a main spindle M0 as a motor 12 and two feed axes M1 and M2 that operate in cooperation with the main spindle M0. The main shaft M0 includes a main shaft motor, and the feed shafts M1, M2 include servo motors. The main shaft M0 and the feed shafts M1 and M2 are controlled by the servo control device 20.

The main shaft M0 rotates the workpiece W around the central axis (Z axis) of the workpiece W. The feed shaft M1 enables the tool 14 to be fed in the Z-axis direction (first direction) and the tool 14 to be reciprocated, i.e., oscillated, in the Z-axis direction. The feed shaft M2 is capable of feeding the tool 14 in the X-axis direction (second direction) and reciprocating, i.e., swinging, the tool 14 in the X-axis direction.

In the case of performing the turning process on the workpiece W in a cylindrical or cylindrical shape, the workpiece W is rotated about the central axis (Z axis) of the workpiece W, and the tool 14 is fed only in the Z axis direction (the processing direction in this case) along the generatrix of the outer peripheral surface of the workpiece W.

On the other hand, when performing the turning process on a workpiece W having a different outer diameter in the Z-axis direction, such as a circular arc-shaped workpiece W, the workpiece W is rotated around the central axis (Z-axis) of the workpiece W, and the tool 14 is fed in an oblique direction (a direction in which the Z-axis direction and the X-axis direction are combined) along a generatrix of the outer peripheral surface of the workpiece W (a processing direction in this case). In this case, at least two feed shafts M1, M2 are required to feed the tool 14 in an oblique direction along a generatrix of the outer peripheral surface of the workpiece W. The tool 14 is fed in an oblique direction along a generatrix of the outer peripheral surface of the workpiece W by controlling both the feed shaft M1 and the feed shaft M2.

The servo control device 20 is configured by using a computer including a memory such as a ROM (read only memory) and a RAM (random access memory) connected to each other via a bus, a CPU (control processing unit), and a communication control unit. The servo control device 20 includes a position control unit 22, a swing command generation unit 23, a speed control unit 24, a current control unit 25, and a storage unit, not shown, and the functions or operations of these units are realized by cooperation of a CPU mounted on the computer, a memory, and a control program stored in the memory.

The storage unit, not shown, stores machining conditions and the like of the workpiece W. The machining conditions of the workpiece W include a relative rotation speed of the workpiece W and the tool 14 around the central axis of the workpiece W, a relative feed speed of the tool 14 and the workpiece W, position commands of the feed shafts M1, M2, and the like.

A host Computer (not shown) such as a CNC (Computer Numerical Controller) or a PLC (Programmable Logic Controller) is connected to the servo Controller 20, and the above-described rotational speed or feed speed can be input from the host Computer to a storage unit (not shown). The storage unit or the position control unit 22, which is not shown, may be provided not only in the servo control device 20 but also in the upper computer.

Further, a storage unit (not shown) may store a machining program executed by the machine tool 10, and a CPU (not shown) in the servo control device 20 may read the above-described rotation speed and feed speed from the machining program as machining conditions and output the machining conditions to the position control unit 22 and the swing command generating unit 23.

The position control unit 22 generates a position command for moving the workpiece W and the tool 14 relative to each other. Specifically, the position control unit 22 has a function of generating position commands of the feed axes M1, M2 based on the relative rotational speed of the workpiece W and the tool 14 around the center axis of the workpiece W and the relative feed speed of the tool 14 and the workpiece W. The position command is a command indicating a target position when the tool 14 and the workpiece W are relatively fed in a direction (machining direction) along a generatrix of the outer circumferential surface of the workpiece W.

The swing command generating unit 23 generates a swing command for swinging the workpiece W relative to the tool 14, using the position command from the position control unit 22. Specifically, the swing command generating unit 23 generates a swing command of the feed shaft M1 based on the aforementioned rotation speed and feed speed, and causes the tool 14 to intermittently cut the workpiece W at a swing frequency that is a positive non-integral multiple of the rotation speed. The swing command is a periodic command created asynchronously with respect to the rotational speed around the central axis, and includes a swing frequency and a swing amplitude. That is, the execution state of the wobbling motion is represented by the wobbling frequency or the wobbling amplitude. The value of the S/60 × I term in expression (1) of the wobble command described later corresponds to the wobble frequency, and the value of the K × F/2 term in expression (1) corresponds to the wobble amplitude.

Here, the intermittent cutting means that the tool 14 performs a turning process on the workpiece W while periodically contacting and separating from the workpiece W, and is also referred to as swing cutting or vibration cutting. In addition, in fig. 1, the workpiece W is rotated and the tool 14 is swung with respect to the workpiece W, but a configuration may be adopted in which the tool 14 is rotated about the central axis of the workpiece W and the workpiece W is swung with respect to the tool 14. In fig. 1, the feed operation and the swing operation of the workpiece W are both performed by one feed shaft M1, M2, but the feed operation and the swing operation of the workpiece W may be performed by the respective feed shafts.

The subtractor 26 obtains a positional deviation between the position command from the position command unit and the position feedback detected by the detector 13. The adder 27 adds the positional deviation to the weaving command from the weaving command generating unit 23 to calculate a composite command. The synthesized command is supplied to the speed control unit 24.

The speed control unit 24 generates a speed command from the synthesized command. The subtractor 28 generates a speed deviation by subtracting a speed feedback detected by an encoder, not shown, of the motor from the speed command from the speed control unit 24, and supplies the speed deviation to the current control unit 25.

The current control unit 25 generates a torque command from the speed command and the speed deviation, and inputs the torque command to the amplifier. The amplifier supplies the torque command converted by the current control unit 25 to the feed shaft M1. The feed shaft M1 is controlled based on such a command. The feed shaft M1 is provided with a detector 13 formed of an encoder, and when the feed shaft M1 rotates, the detector 13 feeds back the actual position of the feed shaft M1 to the subtractor 26. When the difference between the position command value and the position feedback value based on the combined command disappears, the actual position of the feed shaft M1 reaches the position command value.

The gain setting unit 21 sets the servo gains of the servo motors of the feed shafts M1 and M2. The setting of the servo gain may be performed by receiving a signal output at the start of the wobbling operation from the wobble command generating unit 23 when switching from normal cutting to wobble cutting, and changing at least one of a position gain of the position control unit 22, a speed gain of the speed control unit 24, and a current gain of the current control unit 25, which are control gains to be described later. The gain setting unit 21 changes the value of the gain by changing the magnification (control gain) by which the gain (japanese: gain ゲイン) described later is multiplied. The magnification factor is calculated by using a preset parameter as the magnification factor, or by the gain setting unit 21, considering how much the swing motion is to be multiplied based on both the execution state of the swing motion and the gain after the change. At this time, the execution state of the wobbling motion is recognized by referring to a value indicated by the wobbling frequency or the amplitude of the wobbling, for example.

Next, the swing command generating unit 23 will be described. Fig. 2 is a diagram showing a relationship between a feed amount and a rotation angle in a swing operation.

The horizontal axis in fig. 2 represents the rotation angle of the workpiece W, and the vertical axis represents the feed amount of the tool 14 in the machining direction (i.e., the direction along the generatrix of the outer peripheral surface of the workpiece W in fig. 1). Fig. 2 shows a plurality of straight broken lines C1, C2, C3 … extending in an oblique direction.

As shown in fig. 2, the vertical axis coordinate of the intersection point between the broken line C1 and the vertical axis corresponds to the vertical axis coordinate of the starting point of the next broken line C2. Similarly, the ordinate of the intersection point between the broken line C2 and the ordinate corresponds to the ordinate of the start point of the next broken line C3. The plurality of straight broken lines C1, C2, and C3 … indicate the trajectory of the tool 14 on the workpiece W in the absence of the swing command. On the other hand, curves a1, a2, A3 … shown in fig. 2 represent the trajectory of the tool 14 on the workpiece W in the presence of the swing command. That is, the broken lines C1, C2, C3, and the like represent only the position commands (original command values) before the addition of the weaving command, and the curves a1, a2, A3, and the like represent the position commands after the addition of the weaving command. Therefore, the curves a1, a2, and A3 represent commands obtained by adding the position commands indicated by the dotted lines C1, C2, and C3 to the cosine-wave wobble command.

In addition, a curve a1 is a trajectory of the tool 14 at the time of the first revolution of the workpiece W, a curve a2 is a trajectory of the tool 14 at the time of the second revolution of the workpiece W, and a curve A3 is a trajectory of the tool 14 at the time of the third revolution of the workpiece W. For the sake of brevity, the trajectory of the tool 14 after the fourth rotation of the workpiece W is not shown.

The swing command generating unit 23 generates the swing command as described below. The swing command generating unit 23 determines the swing frequency to create commands such as the position commands of the feed shafts M1 and M2 created by the position control unit 22, i.e., the curves a1, a2, and A3 having the broken lines of the broken lines C1, C2, and C3 as reference axes. S/60 × I in the formula (1) described later is a wobble frequency.

In determining the above-described wobble frequency, it is preferable that the initial phase of the cosine wave-shaped curve a2 having a broken line, for example, a broken line C2, as a reference axis is shifted by half a period from the cosine wave-shaped curve a1 having a broken line, for example, a broken line C1, as a reference axis, as shown in fig. 2. The reason is that: when the half cycle is shifted, the oscillation amplitude of the oscillation command can be minimized, and as a result, the chips can be crushed most efficiently.

The swing command generating unit 23 determines the swing amplitude of the swing command, and generates commands such as curves a1, a2, and A3 having broken lines C1, C2, and C3 as reference axes. The value of K × F/2 in the equation (1) described later is the wobble amplitude. The curve a1 and the curve a2 shown in fig. 2 overlap each other at a location B1 rotated by about 0 degrees and a location B2 rotated by about 240 degrees. As can be seen from fig. 2, at the positions B1 and B2, the maximum value of the curve a1 with respect to the broken line C1 is larger than the minimum value of the curve a2 with respect to the broken line C2. In other words, the swing command generating unit 23 preferably determines the swing amplitude so that the previous curve a1 and the next curve a2 partially overlap each other. Since the feed speed is fixed, the swing amplitudes of the swing commands in the curves a1, a2, and A3 are all the same.

In the overlap portions B1 and B2, the tool 14 is separated from the workpiece W when processing is performed along the trajectory of the curve a2, and thus the workpiece W is not processed. In the present embodiment, such overlapped portions B1 and B2 are generated periodically, and therefore so-called intermittent cutting can be performed. In the example shown in fig. 2, chips are generated at the positions B1 and B2 by the operation corresponding to the curve a 2. That is, two chips are generated in the curve a2 of the second revolution. Since such intermittent cutting is periodically performed, vibration cutting can be performed.

The shape of the curve A3 formed with respect to the broken line C3 is the same as the curve a 1. Curve a2 and curve A3 overlap at a point B3 at an angle of about 120 ° and a point B4 at an angle of about 360 °. By the action corresponding to the curve a3, chips are generated at the positions B3 and B4, respectively. That is, two chips are generated in the curve a3 of the third revolution. Thereafter, the workpiece W generates two chips per one rotation. Wherein no chips are generated in the first revolution.

By determining the wobble frequency and the wobble amplitude in this manner, the wobble command generating unit 23 generates a wobble command.

For example, the swing command is expressed by the following equation (1).

[ number 1 ]

In the formula (1), K is the swing amplitude multiplying power, and F is the workThe amount of movement of the tool 14 per revolution of the workpiece W, i.e., the feed per revolution [ mm/rev ]]And S is the rotation speed [ min ] of the workpiece W around the central axis^-1]Or [ rpm ]]Here, the wobble frequency corresponds to the term S/60 × I in equation (1), and the wobble amplitude corresponds to the term K × F/2 in equation (1), where the wobble amplitude magnification K is a number of 1 or more, and the wobble frequency magnification I is a non-integer greater than zero (e.g., a positive non-integer such as 0.5, 0.8, 1.2, 1.5, 1.9, 2.3, or 2.5, …). the wobble amplitude magnification K and the wobble frequency magnification I are constants (in the example of fig. 2, I is 1.5).

The reason why the wobble frequency magnification I is not set to an integer is as follows: in the case of a wobbling frequency that is exactly the same as the rotational speed of the workpiece W about the central axis, the aforementioned overlapping portions B1, B2, B3, B4, etc. cannot be generated, and the effect of crushing chips by wobbling cutting cannot be obtained.

In addition, according to the equation (1), the weaving command is a command obtained by subtracting the term (K × F/2) as an offset value from a cosine wave having the broken lines C1, C2, and C3 indicating the position command as reference axes. Therefore, the position trajectory of the tool 14 based on the combined command value obtained by adding the position command and the swing command can be controlled with the position based on the position command as the upper limit in the machining direction of the tool 14. Therefore, the curves a1, a2, A3, etc. of fig. 2 do not exceed the broken lines C1, C2, C3, etc. in the + direction (i.e., the machine direction of the tool 14).

Further, by setting the swing command expressed by the equation (1), it is understood from the curve a1 of fig. 2 that, at the start point of the machining of the tool 14 (position of 0 ° on the horizontal axis), no large swing occurs initially in the feeding direction of the tool 14.

The initial values of the parameters (K, I in expression (1)) adjusted when determining the wobble frequency and the wobble amplitude are values stored in a storage unit (not shown) before the operation of the machine tool 10. The rotation speed (S) of the workpiece W is stored in advance as a machining condition in a storage unit (not shown). The weekly feed amount F is obtained from the rotational speed (S) and the position command generated by the position control unit 22.

For example, when the workpiece is cylindrical or cylindrical in shape, the workpiece W is oscillated in the machining direction, which is the direction of the feed axis M1(Z axis) along the generatrix of the outer peripheral surface of the workpiece W.

On the other hand, when the workpiece machining shape is a cone shape, a truncated cone shape (tapered shape), or a circular arc shape, for example, the workpiece machining shape is oscillated in a direction along an inclination of a generatrix of the outer peripheral surface of the workpiece W, that is, in a machining direction which is a direction of a combination of the direction of the feed axis M1(Z axis) and the direction of the feed axis M2(X axis).

Next, the gain change performed by the gain setting unit 21 will be described.

Here, the gain refers to a control gain. Specifically, in order to calculate the operation amount for eliminating the speed deviation in the speed control, the speed deviation is amplified by a compensator, not shown, and the control gain is calculated by multiplication or integration in the compensator when the amplification is performed. Then, after the operation amount is calculated, the calculated operation amount is input to the control target. The feedback obtained in this way can be used as a response. In the following description, the ratio of the input to the response at each frequency is referred to as a gain, and in order to calculate the above-described operation amount, the amplification factor used in amplifying the deviation is referred to as a control gain. If the control gain is made too large, oscillation and overshoot tend to occur.

When the oscillating operation is started by starting the oscillating cutting while the position gain of the position control unit 22, the speed gain of the speed control unit 24, and the current gain of the current control unit 25 are maintained at the control gain at the time of normal cutting, the position accuracy of the tool 14 is likely to be unstable, and the operation is likely to be unstable. This is because, in general, a high control gain is often set at the time of normal cutting in order to improve the responsiveness of a highly accurate servo, and therefore, the value of the gain at the wobble frequency is an absolute value that is shifted from 0dB (decibel).

When the machine tool 10 is switched from the normal cutting to the weaving cutting, that is, when the weaving operation is started, the weaving command generating unit 23 transmits a signal notifying that the weaving operation is started to the gain setting unit 21. Specifically, as shown in fig. 3, in order to maintain accuracy even when the cutting is performed at a high frequency during normal cutting, the frequency of the point P at which the gain of good follow-up performance is 0dB is set to a high value. Here, in the case of the frequency characteristic in the velocity gain, the good following performance means that the value of the gain reaches-3 dB, and the following performance is good by setting the value of the gain as close to 0dB as possible.

Fig. 3 is a graph showing a state before switching the control gain in the wobbling operation.

However, in the state where the normal cutting is performed, as shown in fig. 3, the gain value is deviated from 0dB at the wobble frequency for performing the wobble cutting. In the machine tool 10, when switching from normal cutting to swing cutting, a signal for notifying the start of the swing operation is transmitted from the swing command generating unit 23 to the gain setting unit 21. Thus, the gain setting unit 21 changes the value of the speed gain so as to be close to 0dB after decreasing as shown in fig. 4, and supplies the speed gain to the speed control unit 24. This makes the gain value at the wobble frequency about 0dB, improves the following ability of the tool 14 during the wobble operation, and stabilizes the position accuracy of the tool 14 and the operation.

Fig. 4 is a graph showing a state after switching the control gain during the wobbling operation.

The present embodiment described above achieves the following effects.

In the present embodiment, the weaving command generating unit 23 transmits a signal output at the start of the weaving operation to the gain setting unit 21 constituting the gain changing unit, and the gain setting unit 21 changes the control gain. This makes it possible to set the gain value at the wobble frequency to a value as close to 0dB as possible.

In the present embodiment, the execution state of the swing motion is represented by a frequency or an amplitude. Thus, by changing the control gain so that the gain value at the wobble frequency becomes close to 0dB, the ability of the wobble amplitude to follow can be improved.

In the present embodiment, the gain changing unit changes at least one of the position gain of the position control unit 22, the speed gain of the speed control unit 24, and the current gain of the current control unit 25, which is a control gain, and for example, the gain changing unit changes only the speed gain of the speed control unit 24.

Thus, for example, when the current gain is changed to perform current control, there is almost no communication delay from the motor, and therefore, the frequency band in which the gain value responds at 0dB is wide and is not limited. However, it is possible to easily perform control by changing only the speed gain without performing such current control which is difficult to handle.

In the present embodiment, the gain changing unit changes the control gain so that the gain value at the wobble frequency approaches 0 dB. This improves the following performance of the tool 14 for performing the swing cutting, and enables stable machining during the swing cutting.

The present embodiment has been described above. The above-described embodiment is a preferred embodiment, but is not limited to the above-described embodiment, and various modifications may be made. For example, the present invention can be modified as in the modification example described below.

That is, the configurations of the wobble command generation unit, the position control unit, the speed control unit, the current control unit, the gain change unit, and the like are not limited to the configurations of the wobble command generation unit 23, the position control unit 22, the speed control unit 24, the current control unit 25, the gain setting unit 21, and the like in the above embodiment.

In the above embodiment, the gain setting unit 21 changes the speed gain of the speed control unit 24, but the configuration is not limited thereto. The gain changing unit having the gain setting unit 21 may change at least one of the position gain of the position control unit 22, the speed gain of the speed control unit 24, and the current gain of the current control unit 25, or may change the three.

In the above embodiment, the gain setting unit 21 constituting the gain changing unit changes the gain so as to decrease the value of the velocity gain in order to make the value of the gain at the wobble frequency as close to 0dB as possible, but the present invention is not limited to this configuration. For example, when the gain value at the wobble frequency is low or when high accuracy is required for cutting, the gain changing unit may change at least one of the position gain, the velocity gain, and the current gain so that the gain value at the wobble frequency is as close to 0dB as possible.