Motor control device and motor control system

Abstract

To more effectively suppress positional deviation between a plurality of motors.SOLUTION: A motor control device performing synchronization control between a main driving shaft motor driving a main driving shaft and a driven shaft motor driving a driven shaft so as to follow the main driving shaft, includes: an estimation unit for estimating an ideal position of the driven shaft motor based on a shift command value provided to the driven shaft motor; a detection unit for detecting an actual position of the driven shaft motor; a calculation unit for calculating an error between the ideal position and the actual position in the driven shaft motor based on the ideal position estimated by the estimation unit and the actual position of the driven shaft motor detected by the detection unit; and a motor control unit for performing current control to the driven shaft motor based on the error calculated by the calculation unit and a torque command provided to the main driving shaft motor.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a motor control device and a motor control system. [Background technology]

[0002] Patent Document 1 discloses a double-supported positioner having a first member and a second member erected on a base, with a first lifting frame mounted on the first member so as to be able to rise and fall freely, and a second lifting frame mounted on the second member so as to be able to be raised and lowered freely, and supporting a workpiece between the first lifting frame and the second lifting frame. The double-supported positioner includes a first lifting mechanism for lifting and lowering a first lifting frame, a first servo motor for driving the first lifting mechanism to position the first lifting frame at a predetermined height, a second lifting mechanism for lifting and lowering a second lifting frame, a second servo motor for driving the second lifting mechanism to position the second lifting frame at a predetermined height, a first position detector for detecting an actual position of the first lifting frame, a second position detector for detecting an actual position of the second lifting frame, and a lifting drive monitoring unit for stopping the first servo motor and the second servo motor when a difference between the actual position detected by the first position detector and the actual position detected by the second position detector exceeds a predetermined threshold. A servo control method applied to a feed drive mechanism that drives one driven object with multiple motors is disclosed.

[0003] In Patent Document 2, a servo control method controls the speed of a driven object using a signal that combines the speed feedback of each motor, and uses a torque command obtained by the speed control to drive all of the motors. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-055377 A [Patent Document 2] JP 2011-217530 A Summary of the Invention [Problem to be solved by the invention]

[0005] The present disclosure has been devised in view of the above-mentioned conventional situation, and has an object to more effectively suppress positional deviations between multiple motors. [Means for solving the problem]

[0006] The present disclosure provides a motor control device that synchronously controls a main drive shaft motor that drives a main drive shaft and a driven shaft motor that drives a driven shaft to follow the main drive shaft, comprising: an estimation unit that estimates an ideal position of the driven shaft motor based on a movement command value given to the driven shaft motor; a detection unit that detects an actual position of the driven shaft motor; a calculation unit that calculates an error between the ideal position and the actual position of the driven shaft motor based on the ideal position estimated by the estimation unit and the actual position of the driven shaft motor detected by the detection unit; and a motor control unit that controls the current of the driven shaft motor based on the error calculated by the calculation unit and a torque command given to the main drive shaft motor.

[0007] The present disclosure also provides a motor control system including a positioner having a main drive shaft motor that drives a main drive shaft and a driven shaft motor that drives a driven shaft to follow the main drive shaft, and a motor control device that synchronously controls the main drive shaft motor and the driven shaft motor, wherein the motor control device estimates an ideal position of the driven shaft motor based on a movement command value given to the driven shaft motor, detects an actual position of the driven shaft motor, calculates an error between the ideal position and the actual position of the driven shaft motor based on the estimated ideal position and the detected actual position of the driven shaft motor, and controls the current of the driven shaft motor based on the calculated error and a torque command given to the main drive shaft motor. Effect of the Invention

[0008] According to the present disclosure, positional deviation between multiple motors can be more effectively suppressed. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram showing a configuration example of a motor control system according to an embodiment; [Diagram 2] A block diagram showing an example of the internal configuration of a position control unit. [Diagram 3] Block diagram showing an example of the internal configuration of the position control simulation unit DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] (Background to this disclosure) In the servo control method of Patent Document 1, position control of multiple motors is performed. However, due to twisting of the workpiece, etc., the positions of these motor shafts may be shifted. In such a case, when correcting the positions of the multiple motor shafts in the servo control method of Patent Document 1, control is performed to correct the position shift of the multiple motor shafts without considering the position shift caused by the workpiece, which causes problems such as the motor torque of each motor shaft not being uniform and excessive force being generated on each motor shaft.

[0011] Therefore, in the servo control method of Patent Document 2, a torque command is output only to the driving shaft among the multiple motors, and the driven shaft is torque-controlled (current-controlled), thereby synchronously controlling the multiple motors. In this servo control method, the driven shaft plays the role of a torque assistant, and by omitting position control of the motor shaft, it is possible to release relative positional deviation to the driven shaft side. However, since this method is premised on the driving shaft and the driven shaft being mechanically connected via a moving object (hereinafter referred to as "work"), there is a problem that when the work is not held, that is, when the driving shaft and the driven shaft are not mechanically connected, the driven shaft goes into a runaway state.

[0012] Hereinafter, with reference to the drawings as appropriate, an embodiment specifically disclosing a motor control device and a motor control system according to the present disclosure will be described in detail. However, more detailed description than necessary may be omitted. For example, detailed description of already well-known matters and duplicated description of substantially the same configuration may be omitted. This is to avoid the following description becoming unnecessarily redundant and to facilitate understanding by those skilled in the art. Note that the attached drawings and the following description are provided to enable those skilled in the art to fully understand the present disclosure, and are not intended to limit the subject matter described in the claims.

[0013] First, the configuration of a motor control system 100 according to an embodiment will be described with reference to Fig. 1. Fig. 1 is a block diagram showing an example of the configuration of a motor control system 100 according to an embodiment.

[0014] The motor control system 100 includes a controller CON and a positioner PG. The motor control system 100 controls the positioner PG, which includes a first servo motor SM1 and a second servo motor SM2, by the controller CON.

[0015] The control device CON executes current control for driving a motor shaft of a first servo motor SM1 (hereinafter referred to as a “main shaft”) and a motor shaft of a second servo motor SM2 (hereinafter referred to as a “driven shaft”) provided in the positioner PG. The control device CON includes a movement control command unit 10, a first current control unit 15, a position control simulation unit 21, and a second current control unit 22.

[0016] The movement control command unit 10 generates the difference in the position (motor rotation angle θm) of the drive shaft per unit time (control period Tp) (θm(t+Tp)-θm(t) where θm(t) is the motor rotation angle at time t), as a movement command value Δθm*, based on an operation program for the driven body of the motor MT created by a user (for example, a person who controls or manages the motor control system 100 or the control device CON). The movement control command unit 10 outputs the movement command value Δθm* to the position control unit 13 as a movement command value that indicates the movement amount of the drive shaft (amount of motor rotation).

[0017] In addition, when adjusting the relative position of the driven shaft with respect to the main shaft, the movement control command unit 10 may generate the movement amount (motor rotation amount) of the driven shaft per unit time (control period), generate a movement command value Δθe* that indicates the movement amount (motor rotation amount) of the driven shaft, and output it to the position control simulation unit 21.

[0018] The movement amount calculation unit 11 acquires information on the current motor rotation angle θm of the main drive shaft detected by the encoder ENC1 capable of detecting the rotation angle of the main drive shaft. The movement amount calculation unit 11 calculates the difference in the actual motor position (rotation angle) of the first servo motor SM1 per unit time (control period Tp) as the current motor movement amount Δθm and outputs it to the position control unit 13.

[0019] The speed calculation unit 12 acquires information on the current motor rotation angle θm of the main drive shaft detected by the encoder ENC1 capable of detecting the rotation angle of the main drive shaft. The speed calculation unit 12 calculates the current rotation speed ωm of the motor shaft of the first servo motor SM1 and outputs it to the speed control unit 14.

[0020] The position control unit 13 calculates the current position of the drive shaft of the first servo motor SM1 (i.e., the actual position of the drive shaft) based on the current motor movement amount Δθm. The position control unit 13 calculates the rotation speed of the first servo motor SM1 for moving the position of the drive shaft from the current position of the drive shaft to a position indicated by the movement command value Δθm* based on the current position of the drive shaft of the first servo motor SM1. The position control unit 13 generates a speed command value ωm* that indicates the rotation speed of the first servo motor SM1 and outputs it to the speed control unit 14.

[0021] The speed control unit 14 calculates a torque required to rotate the first servo motor SM1, which is currently rotating at a rotation speed ωm, at the speed command value ωm* based on the difference between the speed command value ωm* of the first servo motor SM1 and the current rotation speed ωm of the first servo motor SM1. The speed control unit 14 generates a first torque command for rotating the main drive shaft at the speed command value ωm* based on the calculated torque, and outputs the first torque command to each of the first current control unit 15 and the second current control unit 22. The first torque command is a current command that indicates a current value for rotating the main drive shaft at the speed command value ωm*. Of the first torque commands output from the speed control unit 14, the first torque command input to the second current control unit 22 is multiplied by a gain K1.

[0022] The first current control unit 15 includes an amplifier (not shown) and controls the first servo motor SM1 to flow with a current proportional to the torque command (current command) output from the speed control unit 14. The amplifier (not shown) supplies a current to be flowed from a power source (not shown) to the first servo motor SM1. The first servo motor SM1 generates a rotational torque proportional to the current flowing therethrough.

[0023] The position control simulation unit 21 acquires a movement command value Δθs* based on the movement command value Δθm*, which is the motor rotation amount of the first servo motor SM1 output from the movement control command unit 10, and the movement command value, which is the motor rotation amount of the second servo motor SM2. Note that the movement command value, which is the motor rotation amount of the second servo motor SM2, is not essential and may be omitted if position adjustment of the driven shaft is not required. The position control simulation unit 21 outputs an estimated position of the driven shaft, which is an estimate of the current position of the driven shaft (i.e., the actual position of the driven shaft, which is ideally equal to the actual position of the drive shaft) based on the movement command value Δθs*.

[0024] The control device CON generates a restoration torque command by multiplying a difference between the estimated position (motor rotation angle θs') of the driven shaft and the current motor rotation angle θs of the driven shaft detected by an encoder ENC2 capable of detecting the rotation angle of the driven shaft (i.e., the positional deviation amount of the driven shaft) by a gain K2. This restoration torque command is for causing the second servo motor SM2 to generate a torque (restoring force) for restoring (adjusting) the current motor rotation angle θs of the driven shaft to the estimated position (motor rotation angle θs') of the driven shaft based on the positional deviation amount of the driven shaft, and is provided to the second current control unit 22.

[0025] The control device CON generates an assist torque command by multiplying the first torque command output by the speed control unit 14 by a gain K1, adds this assist torque command to the restoration torque command, and outputs the result as a second torque command to the second current control unit 22.

[0026] The second current control unit 22 includes an amplifier (not shown) and controls so that a current proportional to a second torque command (current command) flows to the second servo motor SM2. The amplifier (not shown) supplies a current to be flowed from a power source (not shown) to the second servo motor SM2. The second servo motor SM2 generates a rotational torque proportional to the current flowing therethrough.

[0027] The positioner PG adjusts the posture of the workpiece Wk placed on the workpiece tables STD1, STD2 and gripped by the clamps CMP1, CMP2 by controlling the first servo motor SM1 and second servo motor SM2 by the control device CON. The positioner PG includes encoders ENC1, ENC2, a first servo motor SM1, a second servo motor SM2, reducers DEC1, DEC2, the workpiece tables STD1, STD2, and clamps CMP1, CMP2.

[0028] The encoder ENC1 detects the amount of rotation (motor rotation angle θm) of the motor shaft (main drive shaft) of the first servo motor SM1. The encoder ENC1 outputs the detected motor rotation angle θm to the control device CON.

[0029] The encoder ENC2 detects the amount of rotation (motor rotation angle θs) of the motor shaft (driven shaft) of the second servo motor SM2. The encoder ENC2 outputs the detected motor rotation angle θs to the control device CON.

[0030] The first servo motor SM1 is driven by a current supplied from a first current control unit 15, and adjusts the gripping height, gripping posture, etc. of the workpiece Wk by the workpiece stand STD1 and the clamp CMP1 on the drive shaft side, respectively.

[0031] The second servo motor SM2 is driven by a current supplied from a second current control unit 22, and adjusts the gripping height, gripping posture, etc. of the workpiece Wk by the workpiece stand STD2 and the clamp CMP2 on the driven shaft side, respectively.

[0032] The reducer DEC1 converts (decelerates and increases torque) the rotation speed and generated torque of the first servo motor SM1 and outputs them. The reducer DEC2 converts (decelerates and increases torque) the rotation speed and generated torque of the second servo motor SM2 and outputs them.

[0033] A workpiece Wk is placed on each of the workpiece tables STD1 and STD2. The workpiece table STD1 supports one end of the placed workpiece Wk. The workpiece table STD2 supports the other end of the placed workpiece Wk. The clamp CMP1 is disposed opposite the workpiece table STD1. The clamp CMP2 is disposed opposite the workpiece table STD2. Each of the workpiece table STD1 and the clamp CMP1 clamps and holds one end of the workpiece Wk. Each of the workpiece table STD2 and the clamp CMP2 clamps and holds the other end of the workpiece Wk.

[0034] Next, the position control unit 13 will be described with reference to Fig. 2. Fig. 2 is a block diagram showing an example of the internal configuration of the position control unit 13.

[0035] The position control unit 13 generates and outputs a speed command ωm* for the main drive shaft based on the input movement command value Δθm* for the first servo motor SM1. The position control unit 13 includes a deviation counter unit 13A.

[0036] The deviation counter section 13A adds the movement command value Δθm*, which is the amount of change in the motor rotation angle of the first servo motor SM1 per unit time (control cycle Tp), to the deviation counter section 13A, and subtracts the amount of change Δθm in the motor rotation angle of the first servo motor SM1 per unit time (control cycle Tp) (i.e., the actual movement amount of the main drive shaft) output from the movement amount calculation section 11 from the deviation counter section 13A. The value of the deviation counter section 13A obtained in this way is the difference between the command position (motor rotation angle θm*) and the actual position (motor rotation angle θm) of the first servo motor SM1, which is the main drive shaft, in other words, the position deviation of the main drive shaft.

[0037] The position control unit 13 multiplies the position deviation held by the deviation counter unit 13A by a position proportional gain Kp to calculate a proportional term, and multiplies the drive shaft movement command value Δθm* by a feedforward gain Kf to calculate a feedforward term. The position control unit 13 adds the proportional term and the feedforward term described above to generate a rotation speed command.

[0038] Next, the position control simulation unit 21 will be described with reference to Fig. 3. Fig. 3 is a block diagram showing an example of the internal configuration of the position control simulation unit 21.

[0039] The position control simulation unit 21 obtains the sum of the input movement command value Δθm* of the first servo motor SM1 and the movement command value Δθe* for changing the relative position of the second servo motor SM2 with respect to the first servo motor SM1 as a movement command value Δθs* of the second servo motor SM2, and estimates and outputs an estimated position of the driven shaft. The position control simulation unit 21 includes a deviation counter unit 21A. Note that the input movement command value Δθs* may be only the movement command value Δθm* of the first servo motor SM1.

[0040] The deviation counter unit 21A adds here the movement command value Δθs* of the second servo motor SM2 given for each input control period Tp, and subtracts here the estimated movement amount Δθs' of the driven shaft (the difference value of the estimated position θs' for each control period Tp). The value calculated here is the difference between the command position θs* of the driven shaft and the current motor rotation angle position (motor rotation angle θs) of the driven shaft, i.e., the position deviation of the driven shaft.

[0041] The position control simulation unit 21 multiplies the position deviation by a position proportional gain Kp to calculate a proportional term, and multiplies the movement command value Δθs* of the second servo motor SM2 by a feedforward gain Kf to calculate a feedforward term. The position control simulation unit 21 adds the proportional term and the feedforward term to generate a virtual speed command ωs*'.

[0042] The position control simulation unit 21 calculates the virtual speed command ωs*' of the driven shaft by approximating the value n (n: integer, n=1 to 2) samples earlier as an estimated value of the speed of the driven shaft. The position control simulation unit 21 integrates (Σ) the estimated speeds of the driven shaft to output an estimated position of the driven shaft, which is an estimate of the current position of the driven shaft. Note that the estimated speed of the driven shaft estimated here is ideally synchronized with the actual speed of the drive shaft. Also, the estimated position of the driven shaft estimated here is ideally synchronized with the actual position of the drive shaft.

[0043] The position control simulation unit 21 may calculate an average value between the latest virtual speed command for the driven shaft and the immediately preceding virtual speed command for the driven shaft, and use this as the estimated speed of the driven shaft.

[0044] Furthermore, the position control simulation unit 21 calculates an estimated movement amount Δθs′ based on the difference between the latest estimated position of the driven shaft and the immediately previous estimated position of the driven shaft, and inputs it to the deviation counter unit 21A.

[0045] In addition, calculations at each point in the position control simulation section are performed every control period Tp, and z -nrepresents a delay of n cycles (outputs the value n times before). Also, 1-z -1 represents the difference between the current value and the previous value (that is, the amount of change in the current value from the previous value).

[0046] As described above, even if torque is generated in the drive shaft and the driven shaft when no workpiece Wk is placed on the positioner PG, the control device CON in the embodiment generates a restoring torque command that applies a restoring force to the driven shaft targeting the estimated position of the driven shaft (i.e., the actual position of the drive shaft), thereby preventing the driven shaft from freely rotating (running out of control) due to the torque generated by the driven shaft, which is not subject to position control.

[0047] (Additional Note) The above description of the present embodiment discloses the following techniques.

[0048] (Technology 1) A motor control device that synchronously controls a main drive shaft motor (first servo motor SM1) that drives a main drive shaft and a driven shaft motor (second servo motor SM2) that drives a driven shaft so as to follow the main drive shaft, an estimation unit (position control simulation unit 21) that estimates an ideal position (estimated position) of the driven shaft motor (second servo motor SM2) based on a movement command value Δθm* given to the driven shaft motor (second servo motor SM2); A detection unit (deviation counter unit 21A) for detecting an actual position of the driven shaft motor (second servo motor SM2); a calculation unit (gain K2) that calculates an error between the ideal position (estimated position) of the driven shaft motor (second servo motor SM2) and the actual position of the driven shaft motor (second servo motor SM2) based on the ideal position (estimated position) estimated by the estimation unit (position control simulation unit 21) and the actual position of the driven shaft motor (second servo motor SM2) detected by the detection unit (deviation counter unit 21A); and a motor control unit (second current control unit 22) that controls a current of the driven shaft motor (second servo motor SM2) based on the error calculated by the calculation unit (gain K2) and a torque command given to the main drive shaft motor (first servo motor SM1). Motor control device (control device CON). With this configuration, the control device CON according to the embodiment can calculate the difference (error) between the estimated position of the driven shaft (i.e., the position of the drive shaft) and the current position of the driven shaft (i.e., the actual position of the driven shaft) by executing a position simulation for estimating the position of the driven shaft by the position control simulation unit 21. Therefore, the control device CON can more effectively suppress the positional deviation between the drive shaft and the driven shaft without executing position control on the driven shaft by controlling the current of the driven shaft so as to eliminate the calculated difference (error).

[0049] (Technology 2) The estimation unit (position control simulation unit 21) A movement amount (estimated movement amount) of the driven shaft motor (second servo motor SM2) is estimated, estimating a speed of the driven shaft motor (second servo motor SM2) corresponding to the movement command value based on the movement command value and the estimated movement amount of the driven shaft motor (second servo motor SM2); estimating the ideal position (estimated position) of the driven shaft motor (second servo motor SM2) based on the estimated speed of the driven shaft motor (second servo motor SM2); A motor control device according to (Technical 1). With this configuration, the control device CON according to the embodiment can obtain an estimated speed of the driven shaft (i.e., the actual speed of the drive shaft) having a smaller response delay compared to position control by simulating the speed control to estimate the estimated speed of the driven shaft. As a result, the control device CON can estimate the estimated position of the driven shaft with higher accuracy by integrating the obtained estimated speed of the driven shaft.

[0050] (Technology 3) The estimation unit (position control simulation unit 21) generating a speed command (virtual speed command) for the driven shaft based on the movement command value and the estimated movement amount of the driven shaft motor (second servo motor SM2); The estimated speed of the driven shaft motor (second servo motor SM2) is estimated by approximating the speed command one or two samples before. The motor control device according to (Technology 1) or (Technology 2). With this configuration, the control device CON according to the embodiment can obtain an estimated speed of the driven shaft (i.e., the actual speed of the drive shaft) with a sufficiently small response delay by simulating the speed control and estimating the estimated speed of the driven shaft. As a result, the control device CON can estimate the estimated position of the driven shaft with high accuracy by integrating the obtained estimated speed of the driven shaft.

[0051] (Technology 4) a positioner including a main drive shaft motor (first servo motor SM1) that drives a main drive shaft, and a driven shaft motor (second servo motor SM2) that drives a driven shaft so as to follow the main drive shaft; A motor control system including a motor control device that synchronously controls the main shaft motor (first servo motor SM1) and the driven shaft motor (second servo motor SM2), The motor control device includes: An ideal position (estimated position) of the driven shaft motor (second servo motor SM2) is estimated based on a movement command value Δθm* given to the driven shaft motor (second servo motor SM2); Detecting the actual position of the driven shaft motor (second servo motor SM2); calculating an error between the ideal position (estimated position) and the actual position of the driven shaft motor (second servo motor SM2) based on the estimated ideal position (estimated position) and the detected actual position of the driven shaft motor (second servo motor SM2); current control of the driven shaft motor (second servo motor SM2) based on the calculated error and a torque command given to the main drive shaft motor (first servo motor SM1); The motor control system 100. With this configuration, the motor control system 100 according to the embodiment can calculate the difference (error) between the estimated position of the driven shaft (i.e., the position of the driving shaft) and the current position of the driven shaft (i.e., the actual position of the driven shaft) by executing a position simulation to estimate the position of the driven shaft by the position control simulation unit 21. Therefore, the motor control system 100 can more effectively suppress the position deviation between the driving shaft and the driven shaft without executing position control on the driven shaft by controlling the current of the driven shaft so as to eliminate the calculated difference (error).

[0052] Although the embodiments have been described above with reference to the accompanying drawings, the present disclosure is not limited to such examples. It is clear that a person skilled in the art can conceive of various modifications, corrections, substitutions, additions, deletions, and equivalents within the scope of the claims, and it is understood that these also belong to the technical scope of the present disclosure. In addition, the components in the above-mentioned embodiments may be arbitrarily combined within the scope of the invention. [Industrial Applicability]

[0053] The techniques disclosed herein are useful as motor control devices and motor control systems that more effectively suppress positional deviations between multiple motors. [Explanation of symbols]

[0054] 10. Movement Control Command Unit 11. Movement amount calculation section 12 Speed ​​calculation section 13 Position control section 13A Deviation counter section 14 Speed ​​control section 15 First current control section 21 Position control simulation section 21A Deviation counter section 22 Second current control section 100 Motor Control System CMP1, CMP2 clamp CON Control device DEC1,DEC2 Reducer MT motor PG Positioner SM1 First servo motor SM2 Second servo motor STD1, STD2 work table Wk Work

Claims

1. A motor control device that synchronously controls a main drive shaft motor that drives a main drive shaft and a driven shaft motor that drives a driven shaft so as to follow the main drive shaft, an estimation unit that estimates an ideal position of the driven shaft motor based on a movement command value given to the driven shaft motor; A detection unit for detecting an actual position of the driven shaft motor; a calculation unit that calculates an error between the ideal position and the actual position of the driven shaft motor based on the ideal position estimated by the estimation unit and the actual position of the driven shaft motor detected by the detection unit; a motor control unit that controls a current of the driven shaft motor based on the error calculated by the calculation unit and a torque command given to the main drive shaft motor. Motor control device.

2. The estimation unit is Estimating a movement amount of the driven shaft motor; estimating a speed of the driven shaft motor corresponding to the movement command value based on the movement command value and the estimated movement amount of the driven shaft motor; estimating the ideal position of the driven shaft motor based on the estimated speed of the driven shaft motor; The motor control device according to claim 1 .

3. The estimation unit is generating a speed command for the driven shaft based on the movement command value and the estimated movement amount of the driven shaft motor; estimating an estimated speed of the driven shaft motor by approximating the speed command one or two samples before; The motor control device according to claim 1 .

4. a positioner including a main drive shaft motor that drives a main drive shaft and a driven shaft motor that drives a driven shaft so as to follow the main drive shaft; A motor control system comprising: a motor control device that synchronously controls the main drive shaft motor and the driven shaft motor, The motor control device includes: Estimating an ideal position of the driven shaft motor based on a movement command value given to the driven shaft motor; Detecting an actual position of the driven shaft motor; calculating an error between the ideal position and the actual position of the driven shaft motor based on the estimated ideal position and the detected actual position of the driven shaft motor; a current control for the driven shaft motor based on the calculated error and a torque command given to the main drive shaft motor; Motor control system.

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