Machine tool and machine tool control device

Abstract

To control the movement of a mobile body with high accuracy.SOLUTION: A machine tool includes a feed drive unit, a friction compensation unit, and a step input unit. The feed drive unit is for moving a mobile body in the machine tool. The friction compensation unit adds a friction compensation value obtained from rolling friction measurement data or a friction compensation value calculated using a rolling friction model in advance to a current value input into the feed drive unit to compensate for the rolling friction generated in the feed drive unit. The step input unit adds a predetermined step input value to the friction compensation value to reduce the inverse response generated by the addition of the friction compensation value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a machine tool and a machine tool control device. [Background technology]

[0002] In the above technical field, Patent Document 1 discloses a technique for estimating frictional force to control the movement of an object. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 5560068 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the technique described in the above document, an inverse response occurs due to friction compensation, and the accuracy of the movement of the object may be low.

[0005] An object of the present invention is to provide a technique for solving the above-mentioned problems. [Means for solving the problem]

[0006] In order to achieve the above object, the machine tool according to the present invention comprises: a feed drive unit for moving a moving body in the machine tool; a friction compensation unit that adds, in advance, a friction compensation value obtained from measurement data of rolling friction or a friction compensation value calculated using a rolling friction model to a current value input to the feed drive unit in order to compensate for rolling friction occurring in the feed drive unit; a step input unit that adds a predetermined step input value to the friction compensation value in order to reduce an inverse response caused by adding the friction compensation value; It is a machine tool equipped with In order to achieve the above object, another machine tool according to the present invention comprises: a feed drive unit for moving a moving body in the machine tool; a friction compensation unit that adds, in advance, a friction compensation value obtained from measurement data of rolling friction or a friction compensation value calculated using a rolling friction model to a current value input to the feed drive unit in order to compensate for rolling friction occurring in the feed drive unit; a step input unit that adds a predetermined step input value to the friction compensation value in order to reduce an inverse response caused by adding the friction compensation value; Equipped with the step input unit includes a calculation unit that calculates timing and magnitude of the step input value from a tracking error when the friction compensation value before adding the step input value is used, Addition of the step input value is started between the timing when the absolute value of the tracking error becomes maximum before the sign of the tracking error in the case where the friction compensation value before adding the step input value is used is first reversed and the timing when the sign of the tracking error is first reversed. R It is a machine tool. In order to achieve the above object, the present invention provides a machine tool control device comprising: In order to compensate for rolling friction that occurs in a feed drive unit for moving a moving body in a machine tool, a friction coefficient obtained from measurement data of rolling friction is calculated for the current value input to the feed drive unit. compensation a friction compensation unit that adds in advance a friction compensation value calculated using a rolling friction model or a rolling friction model; The aforementioned Rolling friction of a step input unit that adds a predetermined step input value to the friction compensation value in order to reduce an inverse response caused by the compensation; Equipped with The step input unit is a machine tool control device that includes a calculation unit that calculates the timing and magnitude of the step input value from a tracking error when the friction compensation value before adding the step input value is used. [Effects of the Invention]

[0007] According to the present invention, the movement of a moving body can be controlled with high precision. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a block diagram showing the configuration of a machine tool according to a first embodiment. [Figure 2] FIG. 10 is a block diagram showing the hardware configuration of a machine tool according to a second embodiment. [Figure 3]FIG. 10 is a block diagram showing the functional configuration of a machine tool according to a second embodiment. [Figure 4] 10 is a flowchart showing the flow of processing in a machine tool according to a second embodiment. [Figure 5] FIG. 10 is a diagram showing a table of friction characteristics of the machine tool according to the second embodiment. [Figure 6] FIG. 10 is a block diagram showing a control system of a machine tool according to a second embodiment. [Figure 7] FIG. 10 is a diagram showing changes in various values ​​of the machine tool according to the second embodiment. [Figure 8] 10A to 10C are diagrams illustrating suppression of an inverse response of a machine tool according to a second embodiment. [Figure 9] 10 is a flowchart showing a process for suppressing an inverse response of a machine tool according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. However, the components described in the following embodiments are merely examples and are not intended to limit the technical scope of the present invention.

[0010] [First embodiment] An object moving device 100 according to a first embodiment of the present invention will be described with reference to Fig. 1. The object moving device 100 is incorporated into a machine tool and is a device for moving a workpiece placed on a stage.

[0011] As shown in FIG. 1, the machine tool 100 includes a feed drive unit 101, a friction compensation unit 102, and a step input unit 103.

[0012] The driving unit 101 moves the moving body 120 in the machine tool 100 .

[0013] In order to compensate for the rolling friction that occurs in the feed drive unit 101, the friction compensation unit 102 adds in advance to the current value 121 input to the feed drive unit 101 a friction compensation value 122 obtained from measurement data of the rolling friction or a friction compensation value 122 calculated using a rolling friction model.

[0014] The step input unit 103 adds a predetermined step input value 123 to the friction compensation value 122 in order to reduce the inverse response caused by the friction compensation.

[0015] According to this embodiment, the moving body can be moved with higher precision.

[0016] [Second embodiment] Next, a machine tool 200 according to a second embodiment of the present invention will be described with reference to Figure 2 and subsequent figures. Figure 2 is a diagram for explaining the configuration of the machine tool 200 according to this embodiment. The machine tool 200 is equipped with a ball screw 202 as a feed drive unit that moves a stage 201 as a moving body. Such ball screw-driven stages have high energy conversion efficiency, little wear, and a long life, and are therefore often used as feed devices for industrial machinery such as machine tools.

[0017] The ball screw 202 is connected to a motor 204 via a coupling 203, and is journaled by a bearing 205. As the ball screw 202 rotates, a nut 206 moves left and right in the figure, which causes the stage 201 to move in the X-axis direction while being guided by a linear guide 207.

[0018] The machine tool 200 is equipped with a tool 208 and processes a workpiece 209 that is a workpiece fixed to a stage 201 .

[0019] 3 is a diagram illustrating the configuration for drive control of stage 201 in machine tool 200. Stage 201 moves back and forth within movement area 330. In such a ball screw-driven stage 201, rolling friction reduces tracking performance. Rolling friction is generated by the balls between ball screw 202 and nut 206 and the balls in linear guide 207.

[0020] Graph 350 shows the relationship between the stage position and the rolling friction of the ball screw. The rolling friction depends on the displacement from the velocity reversal point. For example, suppose the stage 201 starts moving from a starting position 351, the velocity reverses at a velocity reversal point 352, and the stage 201 returns to the original starting position 351. In a region 353 from the starting position 351 until the stage 201 moves a predetermined distance, the rolling friction exhibits nonlinear spring characteristics. On the other hand, in a region 354 from the time the stage 201 moves a predetermined distance from the starting position 351 until the velocity reversal point 352, the rolling friction is a constant value.

[0021] Furthermore, in region 355 from when the velocity reverses at velocity reversal position 352 until stage 201 moves a predetermined distance, rolling friction exhibits nonlinear spring characteristics, and thereafter, in region 356 up to start position 351, rolling friction has a constant value. Therefore, machine tool 200 controls the movement of stage 201 taking into account such rolling friction characteristics.

[0022] Rolling friction causes a large spike-like tracking error near the velocity reversal point. This tracking error is sometimes called a quadrant spur. To perform high-precision tracking control of the stage 201, it is necessary to compensate for the rolling friction and suppress the quadrant spur.

[0023] As a method for compensating for rolling friction, a model-based or learning-based feedforward approach is more effective than a feedback approach such as a disturbance observer.

[0024] Many rolling friction models have been proposed and evaluated, including the LuGre model, generalized Maxwell-slip model, rheology-based model, database-based friction model, and elastic-plasticity-based model. Model-based friction compensation approaches precisely measure rolling friction and generate a model through curve fitting. Then, the rolling friction is compensated for with a control input calculated based on the obtained model. In contrast, learning-based approaches, such as iterative learning control, do not use a rolling friction model, but instead suppress quadrant projections by gradually shaping the friction compensation input over multiple iterations of movement control.

[0025] To compensate for rolling friction in this manner, machine tool 200 has a data acquisition unit 302 , a derivation unit 303 , a friction compensation unit 304 , a storage unit 305 , a control unit 306 , an update unit 307 , and a determination unit 308 .

[0026] The data acquisition unit 302 acquires current data 322 (=f np j+1 ), and command data 321 (displacement data r j ) and get.

[0027] The data acquisition unit 302 acquires the displacement data r j The velocity reversal positions 352 and 351 are detected based on the velocity derived from the velocity, and it is determined whether the stage 201 is in a linear region 354 or 356 or a nonlinear region 353 or 355 based on the amount of displacement from the velocity reversal positions 351 and 352.

[0028] The derivation unit 303 derives a basis function Ψ(r j ) and current data 322 (=f np j+1 ) and the linear relationship 333(=(f p j+1 =Ψ(r j )θ j+1 )) is estimated. θ in the linear relation 333 j+1corresponds to the physical properties of the stage 201.

[0029] The calculation unit 304 calculates the parameter θ estimated by the derivation unit 303 in the nonlinear regions 353 and 355. j+1 Among them, the inertia J, the viscous friction coefficient D, and the basis function Ψ(r j ) and calculates the current data 341 using the acceleration and velocity.

[0030] The current data 322 (=f np j+1 ) and current data 341 calculated by the calculation unit 304, the correction data 391 is derived. The accumulation unit 309 then accumulates the derived correction data 391 in association with the displacement of the stage 201 from a velocity reversal position 352. Note that if the start position 351 or the velocity reversal position 352 changes along with a change in the command position, there may be a case where the corresponding correction data 391 does not exist, and therefore the following measures are taken.

[0031] (1) Use the closest correction data 391 (2) Linear interpolation from the correction data 391 of the previous and next positions (3) Average the data for each location and store it in one table. In (1), for example, if the rolling friction is −3 Nm 1 μm from the speed reversal position 240 and −2 Nm 2 μm from the speed reversal position 240, then inputting 1.2 μm will output −3 Nm. In (3), for example, if there are multiple speed reversal positions 240, a table is created by averaging multiple pieces of rolling friction data.

[0032] That is, in the nonlinear regions 353 and 355 , the storage unit 309 derives correction data 391 representing rolling friction from the current data 341 calculated by the calculation unit 304 and the current data 322 acquired by the data acquisition unit 302 .

[0033] The control unit 306 calculates the current data 363 for driving the motor 204 in the linear regions 354 and 356 based on the command value trajectory data r for the next operation. j+1 Basis functions Ψ(r j+1 ) and the linear relational expression 333 (=(f p j+1 Ψ(r j )θ j+1 )). The control unit 306 also derives current data 364 for driving the motor 204 in the nonlinear regions 353 and 355 using the current data 322 and correction data 391. At this time, the step input unit 362 adds a predetermined step input value to the friction compensation value calculated using the linear relational expression 333 and correction data 391 in order to reduce the inverse response (control in the opposite direction to the command). The control unit 306 then drives the motor 204 using the calculated current data 363 and the derived current data 364.

[0034] Update unit 307 sequentially updates at least one of linear relational expression 333 and correction data 391. Update unit 307 also performs update processing based on the latest current data 322 and command data 321 acquired by data acquisition unit 302 at predetermined timings. Here, the predetermined timings include, for example, timing when the tool of machine tool 200 is separated from the workpiece to be machined, timing during tool replacement, and timing when the internal temperature of machine tool 200 reaches or exceeds a predetermined value. Other timings include timing when machine tool 200 has been in use for a certain period of time, timing when the movement distance of stage 201 caused by motor 204 exceeds a certain value, and timing when the cumulative driving time of motor 204 has exceeded a certain period of time. Furthermore, the timings include timing when the internal temperature of machine tool 200 falls below a certain value, and timing when the amount of change in the internal temperature of machine tool 200 since the last update processing was performed exceeds a certain amount of change. Update unit 307 performs update processing at at least one of the above-mentioned predetermined timings.

[0035] FIG. 4 is a diagram illustrating the flow of the friction compensation process. In STEP 1, a normal ILC (Standard-ILC) is used to calculate current data 322 (=f np j+1 =Q(f j +Le j Here, f is the FF (Feedforward) input (current data 322), e is the tracking error, L is the learning filter, and Q is the robust filter. np The superscript np on the right side of the symbol indicates that the FF input is obtained by Standard-ILC. That is, the command data 321 (=r j ) for FF input f j The motor 204 is operated with a current (initial value of which is zero at the start of learning) according to the current. Displacement data of the stage 201 moved by the operation of the motor 204 is obtained.

[0036] Tracking error e j = Command data 321 - Calculate displacement data. FF input f j and the tracking error e j and current data 322(f np j+1 =Q(fj+Lej)) is calculated (FF input by normal ILC). The linear relational expression 333 and friction model of the motor 204 are reflected in the current data 322 through the tracking error. The command data 321 represents the command value trajectory (target trajectory) of the stage 201, that is, the input of the position at which the stage 201 is desired to move.

[0037] In STEP 2, the parameter θ j+1 Estimate Ψ(r j ) is a basis function. The FF input equation Ψ(r j )θ j+1 But, f np j+1 Use linear least squares to fit the parameters θ j+1 Here, the weighting matrix Wj is used to exclude the nonlinear regions 353 and 355, and the parameter θj+1 The accuracy of the

[0038] In STEP 3, the parameter θ j+1 Rolling friction T rf Find r j and T rf In other words, the parameter θ j+1 Among them, J and D and the basis function Ψ(r j ) and current data 341 is derived from the acceleration and velocity. np j+1 ) to calculate and store the correction data 391 for the nonlinear regions 353, 355. Then, a table 501 is created from the command data 321 and the correction data 391. Here, J is the inertia, D is the viscosity coefficient, R is the ball screw lead (the distance the nut advances in the axial direction with one rotation of the screw), K T indicates the torque constant. The current data 341 is rf =(f np j+1 -J / RK T < <r j >>-D / RK T <r j >)K T is equivalent to <r j > is r j Differential of, < <r j >> is, <r j > represents the derivative of

[0039] In STEP 4, the parameter θ estimated in STEP 2 is j+1 The FF input is recalculated from the table 501 created in STEP 3. In other words, in the linear region 354, 356, the next command r j+1 Based on Ψ(r j+1 ) and the θ we just calculated j+1 From this, Ψ(r j+1 )θ j+1 (J / (R×K t )×acceleration+D / (R×K T )×speed+Tc / K T ×b_rf) to calculate the FF input. Next, in the nonlinear regions 353 and 355, J / (R × KT )×acceleration+D / (R×K t ) × speed + (rolling friction stored in table 501) / K T The next FF input f j+1 Furthermore, a predetermined step input value is added to these FF inputs to reduce the inverse response.

[0040] Parameter θ j+1 is a part of the motor 204 that corresponds to the mechanical characteristics, and is a value independent of the command. j+1 ) according to the command, the current data becomes the appropriate FF input for any command. To calculate the FF input in the linear region 354, 356, T )×acceleration+D / (R×K T )×speed+Tc / K T × b_rf" is used. Note that b_rf is 1 in the linear regions 354, 356, and is between -1 and 1 in the nonlinear regions 353, 355 (depending on the distance from the velocity reversal position 240 and the friction model). By repeating the above steps 1 to 4, the tracking error e decreases (learning control). By saving the learned θ and the correction data 391, appropriate FF correction can be performed even if a different command is used. Although the processing flow for estimating parameters and performing friction compensation has been described above using FIG. 4, the present invention is not limited to this, and the parameters may be known.

[0041] 5 is a diagram illustrating a table 501 showing the relationship between displacement and rolling friction in the nonlinear regions 353 and 355. The table 501 is stored in the storage unit 309. In the nonlinear regions 353 and 355, the current data 364 is derived using the table 501, which associates the nonlinear characteristics of rolling friction with the displacement (position) of the stage 201 and the correction data 391 (rolling friction), without using any mathematical formulas. The table 501 stores the rolling friction in association with the displacement from the velocity reversal position 240.

[0042] The friction compensation approach using the linear relational expression 333 and the table 501 can effectively suppress the quadrant protrusion, but it may cause an inverse response, which is a tracking error in the opposite direction to the quadrant protrusion. In machining, this inverse response can cause overcutting and roughening of the workpiece surface.

[0043] Therefore, in this embodiment, the inverse response is analyzed and suppressed in the step input unit 362. Specifically, the step input unit 362 checks the inverse response through a simulation in the absence of a step input, analyzes the inverse response based on the results, and performs a step input with a timing and magnitude that suppresses the inverse response.

[0044] FIG. 6 is a diagram showing the above processing in this embodiment as a control system. The purpose of this control system is to reduce the tracking error e=rx between the position reference r and the output x. Because the tracking error (quadrant projection) increases when the velocity is reversed, feedforward friction compensation is considered effective. Therefore, a feedforward controller 601 is introduced as a stable inverse system of a nominal model P of the controlled object 607. The feedforward controller 601 achieves perfect tracking control if there are no modeling errors or disturbances. In addition, a proportional-integral-derivative (PID) controller is provided as a feedback controller 602 to suppress steady-state errors.

[0045] For correction of rolling friction by feedforward control, a friction model ^Trf as shown in graph 350 is used. Furthermore, a friction compensation unit 603 is provided to compensate for the rolling friction Trf using the rolling friction model ^Trf. For correction of rolling friction by feedforward control, a friction model ^Trf as shown in graph 350 is used. The friction compensation value is calculated based on the friction model and the position reference.

[0046] As described above, feedforward friction compensation can effectively reduce tracking errors, but friction compensation can sometimes result in an inverse response, which is a tracking error in the opposite direction to the quadrant projection. Therefore, in this embodiment, the inverse response is analyzed by simulation and suppressed based on the analysis results. Specifically, a step input unit 362 is provided that adds a step input value to cancel the inverse response.

[0047] Figure 7 shows the simulation results. For a typical movement command such as Figure 7(a), friction compensation suppresses the tracking error (causing quadrant projection) as shown in Figure 7(b), but an inverse response 701 may occur as shown in Figure 7(c). Figure 7(d) shows the rolling friction and its compensation input near the speed reversal timing. Figures 7(e) and 7(f) show the equivalent input disturbance, defined as the difference between the applied rolling friction and the friction compensation value. The equivalent input disturbance is small at the sample points, but becomes relatively large between sample points because the control input is discretized by the zero-order hold block 606. Figures 7(e) and 7(f) show that the characteristics of the equivalent input disturbance are determined by friction compensation. The friction compensation value is set to a step-like value by the zero-order hold block 606, resulting in a spike-like input disturbance. Without friction compensation, the input disturbance would be a step disturbance as shown in Figure 7(e) without comp.

[0048] It is generally known that in a closed loop system in which the control target P and feedback controller CFB are linear and time-invariant, the input disturbance and tracking error to the control target P satisfy the following equations. Let the number of integrals that the feedback controller 602 has be i. In this case, the error ei when an impulse disturbance enters the input terminal of the control target P satisfies the following equation (1).

number

number

[0049] 8, in order to reduce such an inverse response 701, a step input value Gs calculated based on the parameters calculated by the parameter calculation unit 605 is added to the friction compensation value from timing Ts (604). This makes it possible to suppress (803) the inverse response 701 without increasing the tracking error 801 due to friction.

[0050] The parameter calculation unit 605 calculates the timing and magnitude of the step input value from the tracking error when the friction compensation value before adding the step input value 604 is used.

[0051] FIG. 9 is a flowchart showing the flow of the parameter calculation process in parameter calculation section 605.

[0052] T represents time, and T=0 is the timing at which the stage speed reverses. First, in step S901, the tracking error Ec(T) due to friction compensation (without step input) is obtained.

[0053] Next, in step S902, the occurrence timing Tq and magnitude Eq of the quadrant projection and the zero cross timing Ti of the tracking error are obtained.

[0054] Furthermore, in step S903, Tq is input as the initial value for Ts, and the process proceeds to step S904 to calculate Eus(T-Ts), where Ts represents the timing at which the step input is added, and Eus(T) represents the tracking error due to the step input.

[0055] The feedback controller 602 is expressed by the following equation (3), where kp is the proportional gain, ki is the integral gain, kd is the differential gain, and Tf is the time constant of the pseudo differential.

number

number

number

number

[0056] Next, in step S907, it is determined whether the following formula is true: -Eq≦Minimum value of Ep(T)≦0 If this formula is true, the process ends.

[0057] If the above inequality does not hold, the process proceeds to step S908, where Ts is incremented, i.e., one sampling period is added to Ts. Then, in step S909, while it is determined that Ts≦Ti, the processes of steps S904 to S908 are repeated to determine Ts and Gs that satisfy the relationship -Eq≦Ep(T)≦0. That is, the step input unit 362 (parameter calculation unit 605) adds the step input value Gs while changing the timing between timing Tq, at which the absolute value of the tracking error when using the friction compensation value before adding the step input value Gs, is maximized, and timing Ti, at which that absolute value becomes 0, to determine the step input value Gs such that the absolute value of the negative error does not become greater than the maximum value Eq.

[0058] On the other hand, if Ts and Gs that satisfy the relationship -Eq≦Ep(T)≦0 cannot be determined within the timing up to Ti, a slight inverse response and a slight increase in the quadrant projection are allowed.

[0059] That is, the parameter calculation unit 605 starts adding the step input value Gs between the timing Tq when the absolute value of the tracking error reaches a maximum and the timing Ti when the sign of the tracking error is first reversed, before the sign of the tracking error is first reversed when the friction compensation value before adding the step input value is used. Also, the parameter calculation unit 605 determines the magnitude Gs of the step input value using the value of the tracking error when the friction compensation value before adding the step input value is used.

[0060] Instead of terminating the process when the minimum value of -Eq≦Ep(T)≦0 is met for the first time, the process may be repeated for all Ts in the range of 0≦Ts≦Ti, and then the Ts and Gs for which Ep(T)≦0 and the minimum value of Ep(T) are the largest may be adopted. Also, Ts may be changed in the decreasing direction from Ti to Tq. That is, Ts may be set to Ti in S903, one sampling period may be subtracted from Ts in S908, and the condition determination Ts≦Ti may be changed to Ts≧0. In each of the above cases, Ts may be changed by adding or subtracting multiple sampling periods. By performing the above process, it is possible to determine an appropriate step input value and its timing, thereby suppressing the inverse response without increasing the tracking error that can cause quadrantal spikes.

[0061] In the present embodiment, a ball screw has been described as an example of a feed drive unit, but the present invention is not limited to this. Also, in the above embodiment, a friction compensation value calculated using a rolling friction model is added to the current value, but the present invention is not limited to this, and a friction compensation value obtained from measurement data of rolling friction may be added to the current value.

[0062] Furthermore, a machine tool control device equipped with a friction compensation unit and a step input unit for realizing the above-mentioned control in a machine tool is also included in the scope of the present invention.

[0063] [Other embodiments] Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above embodiments. Various modifications can be made to the configuration and details of the present invention that are understandable to those skilled in the art within the technical scope of the present invention. Furthermore, systems or devices that combine the separate features included in each embodiment in any manner are also included in the technical scope of the present invention.

[0064] The present invention may also be applied to a system consisting of multiple devices or to a single device. Furthermore, the present invention may also be applied when an information processing program that realizes the functions of the embodiments is supplied to a system or device and executed by a built-in processor. The technical scope of the present invention also includes a program installed on a computer to realize the functions of the present invention, a medium storing the program, a server from which the program is downloaded, and a processor that executes the program. In particular, the technical scope of the present invention includes at least a non-transitory computer-readable medium storing a program that causes a computer to execute the processing steps included in the above-described embodiments.

Claims

1. a feed drive unit for moving a moving body in the machine tool; a friction compensation unit that adds, in advance, a friction compensation value obtained from measurement data of rolling friction or a friction compensation value calculated using a rolling friction model to a current value input to the feed drive unit in order to compensate for rolling friction occurring in the feed drive unit; a step input unit that adds a predetermined step input value to the friction compensation value in order to reduce an inverse response caused by adding the friction compensation value; A machine tool equipped with

2. 2. The machine tool according to claim 1, wherein the step input unit includes a calculation unit that calculates the timing and magnitude of the step input value from a tracking error when the friction compensation value before adding the step input value is used.

3. A feed drive unit for moving a moving body in a machine tool; a friction compensation unit that adds, in advance, a friction compensation value obtained from measurement data of rolling friction or a friction compensation value calculated using a rolling friction model to a current value input to the feed drive unit in order to compensate for rolling friction occurring in the feed drive unit; a step input unit that adds a predetermined step input value to the friction compensation value in order to reduce an inverse response caused by adding the friction compensation value; Equipped with the step input unit includes a calculation unit that calculates timing and magnitude of the step input value from a tracking error when the friction compensation value before adding the step input value is used, a machine tool that starts adding a step input value between the timing when the absolute value of the following error becomes maximum before the sign of the following error is first reversed when the friction compensation value before adding the step input value is used, and the timing when the sign of the following error is first reversed.

4. 4. The machine tool according to claim 3, wherein the step input unit determines the magnitude of the step input value using a value of a tracking error when the friction compensation value before adding the step input value is used.

5. 5. The machine tool according to claim 4, wherein the step input unit adds the step input value while changing the timing between a timing at which the absolute value of the tracking error becomes maximum when the friction compensation value before adding the step input value is used and a timing at which the absolute value becomes zero, and determines the step input value such that the absolute value of a negative error does not become larger than the maximum absolute value of the tracking error.

6. a friction compensation unit that adds in advance a friction compensation value obtained from measurement data of rolling friction or a friction compensation value calculated using a rolling friction model to a current value input to a feed drive unit for compensating for rolling friction that occurs in the feed drive unit for moving a moving body in a machine tool; a step input unit that adds a predetermined step input value to the friction compensation value in order to reduce an inverse response caused by the compensation for the rolling friction; Equipped with The step input unit includes a calculation unit that calculates the timing and magnitude of the step input value from a tracking error when the friction compensation value before adding the step input value is used.

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