JP3023970B2 - Servo control system - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo control system for controlling the driving of a servo motor, and more particularly to a servo control system capable of compensating for a position deviation in a servo control loop and a steady-state deviation of speed. Related to a servo control system.

(Prior art)

Conventionally, a servo control system counts a position deviation between a position command signal for commanding a target position and a feedback position signal from a position detector provided on a servomotor by a deviation counter, and determines a speed command speed according to the deviation. Is generated, and the servomotor is driven and controlled according to the speed deviation between the speed command signal and the feedback speed signal of the servomotor. by the way,
In the servo control system, there is a problem that a steady deviation occurs due to the mechanical load of the control target, which causes the control target to follow with a delay when the position command signal changes. For this reason, for example, there has been a problem that the contour accuracy at the time of control is reduced, and the radius is reduced even in perfect circular cutting.

In order to solve such a problem, there is a servo control system that employs feedforward control. The feedforward control includes a method for compensating for a steady-state deviation caused by a controlled object following the command signal with a delay when the command signal changes, and a method for compensating for a disturbance input.

FIG. 7 is a block diagram showing a schematic configuration of a conventional servo control system in which a feed-forward compensation loop for compensating deviation is added to a normal feedback control system.

The servo motor 8 is, for example, an AC servo motor. A position detector 9 for detecting the current position is connected to the servomotor 8. The current position signal PF is output from the position detector 9 to the subtractor 1 and the speed calculator 10. The speed calculation unit 10 calculates a current speed signal VF indicating the rotation speed of the servo motor 8 based on the current position signal PF,
Output to Instead of the speed calculation unit 10, there is a speed sensor (pulse generator) for detecting the current speed which is connected to the servo motor 8.

The subtractor 1 receives a position command signal Pc indicating the target position of the servo motor 8 and the current position signal PF from a host controller (not shown), subtracts the current position signal PF from the position command signal Pc, Position control unit 3 as signal εp
Output to The position control unit 3 outputs a speed command signal Vcl corresponding to the position deviation signal εp to the adder 42. At this time, the feed forward loop 41 performs a predetermined operation (such as differentiating the position command signal Pc and multiplying it by a predetermined coefficient) on the position command signal Pc to remove a steady-state position deviation.
Vc2 is output to the adder 42. Therefore, the adder 42 outputs the speed command signal Vc3 obtained by adding the speed compensation signal Vc2 for compensating the position steady-state deviation to the normal speed command signal Vc1. The subtractor 4 has a speed command signal Vc3 and a current speed signal VF
, The current speed signal VF is subtracted from the speed command signal Vc3, and a speed deviation signal εv is output to the speed control unit 6. The speed controller 6 outputs a torque command signal (current command signal) Tc of the servo motor 8 corresponding to the speed deviation signal εv to the current controller 7. The current control unit 7 drives the power transistor,
A drive current is supplied to the servo motor 8.

Since the steady-state error that causes the control delay depends on the mechanical load of the control target, the speed command signal Vc1 must be adjusted in advance to advance the control so that the predicted steady-state error can be compensated. The compensation signal Vc2 is fed back positively.

[Problems to be solved by the invention]

The above-described prior art attempts to achieve a high-speed response of servo control by removing the first-order lag element of the position loop by variably setting the coefficient of the feedforward loop 41 according to the predicted steady-state deviation. Such compensation is effective when the mechanical load does not fluctuate and the steady-state deviation is constant.

However, in a normal servo control system, this steady-state deviation is not constant, and the inertia fluctuation of the mechanical load and the fluctuation of the friction torque of the controlled object (during different cutting operations of a machine tool or lifting a different heavy object with a robot arm, for example). Fluctuates as needed. Therefore, in a feedback loop in which the steady-state deviation fluctuates as needed,
If a constant positive feedback compensation as in the related art is applied, the fluctuation of the steady-state error cannot be compensated for, and unexpected nonlinear phenomena may occur or vibration may occur.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a servo control system having a high-speed response characteristic capable of performing deviation compensation according to a fluctuation of a steady-state deviation.

[Means for solving the problem]

A servo control system according to the present invention negatively feeds back a feedback position signal indicating a current position of a servo motor to a position command signal, and generates a position deviation calculating means for obtaining a position deviation, and a speed command signal according to the position deviation. Generating a position deviation compensation signal according to the position deviation obtained by the position deviation calculation means, and generating the position deviation compensation signal according to the position deviation according to a predetermined compensation function. Position deviation compensation signal generation means, and compensates for the position deviation by positively feeding back the position deviation compensation signal to at least one of the input side and the output side of the position control means,
First correcting means for correcting the speed command signal, negative feedback of a feedback speed signal indicating the current speed of the servo motor to the speed command signal, and speed deviation calculating means for obtaining a speed deviation. Speed control means for generating a current command signal, a speed deviation compensation signal generating means for generating a speed deviation compensation signal in accordance with the speed deviation obtained by the speed deviation calculation means, and the speed control means A second correction means for compensating for a speed deviation by positively feeding back at least one of an input side and an output side of the input signal, thereby correcting a current command signal, and a current control means for generating a drive current according to the current command signal And a servo motor driven by the drive current, and the current position and speed of the servo motor are detected, and the feedback position signal and the feedback speed signal are output. Output means, wherein the position deviation compensation signal generation means variably controls the characteristic of the predetermined compensation function using the speed deviation compensation signal generated from the speed deviation compensation signal generation means as a parameter, and is variably controlled. And generating the position deviation compensation signal in accordance with the position deviation in accordance with the compensation function.

[Action]

The position deviation obtained by the position deviation calculation means is a feedback loop including a mechanical load (position control loop).
System. The position deviation compensation signal generating means generates a position deviation compensation signal in accordance with the position deviation, and the correcting means feeds back the position deviation compensation signal to at least one of the input side and the output side of the position control means. Therefore, when the position deviation compensation signal is positively fed back to the input side of the position control means, the position control means inputs a signal obtained by adding the position deviation compensation signal to the position deviation as a new deviation signal, and a speed command signal based on the signal. Will occur. At this time, the new position deviation input to the position control means is a signal in which the position steady deviation has been compensated, so the position control means outputs the speed command signal in which the position steady deviation in the position control loop system has been compensated. As a result, even if the position steady-state deviation fluctuates due to the influence of a mechanical load or the like, the position deviation compensation signal also fluctuates, so that the fluctuation of the position steady-state deviation can be effectively compensated.

Further, when the position deviation compensation signal is fed back to the output side of the position control means, a speed command signal corresponding to the position deviation compensation signal is added to the speed command signal output from the position control means, and the speed control of the next stage is performed. It will be input to the means. At this time, the new speed command signal input to the speed control means is a speed command signal in which the position steady deviation is compensated, so that the position control means outputs a speed command signal in which the position steady deviation in the position control loop system is compensated. Looks as if you are. Accordingly, even if the position steady-state deviation fluctuates due to the influence of a mechanical load or the like, the position deviation compensating signal also fluctuates, and a speed command signal based on the fluctuation is output. Can compensate.

Further, the speed deviation obtained by the speed deviation calculating means is of a feedback loop (speed control loop) system including a mechanical load. The speed deviation compensation signal generating means generates a speed deviation compensation signal according to the speed deviation, and the correcting means feeds back the speed deviation compensation signal to at least one of the input side and the output side of the speed control means. Therefore,
When the speed deviation compensation signal is fed back to the input side of the speed control means, the speed control means inputs a signal obtained by adding the speed deviation compensation signal to the speed deviation as a new deviation signal, and generates a current command signal based on the signal. I will be. At this time, since the new speed deviation input to the speed control means is a signal in which the steady-state speed deviation is compensated, the speed control means
The current command signal in which the speed steady-state deviation is compensated in the speed control loop system is output. Even if the speed steady-state deviation fluctuates due to the influence of a mechanical load or the like, the speed deviation compensating signal also fluctuates. Fluctuations in the steady-state deviation can be effectively compensated.

When the speed deviation compensation signal is positively fed back to the output side of the speed control means, a current command signal corresponding to the speed deviation compensation signal is added to the current command signal output from the speed control means, and the current control of the next stage is performed. It will be input to the means. At this time, the new current command signal input to the current control means is a current command signal in which the speed steady deviation is compensated, so that the speed control means outputs a current command signal in which the speed steady deviation is compensated in the speed control loop system. Looks as if you are. Therefore, even if the speed steady-state deviation fluctuates due to the influence of a mechanical load or the like, the speed deviation compensation signal also fluctuates, and a current command signal based on the fluctuation is output. Can compensate.

Here, the position deviation compensation signal generating means generates the position deviation compensation signal according to the position deviation according to a predetermined compensation function, and the speed deviation compensation signal generated from the speed deviation compensation signal generating means. Is used as a parameter to variably control the characteristics of the predetermined compensation function, and the position deviation compensation signal is generated according to the position deviation according to the variably controlled compensation function. As a result, there is an excellent effect that optimal position deviation compensation control can be performed according to the compensation control state based on the speed deviation compensation signal.

〔Example〕

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a diagram showing one embodiment of the servo control system of the present invention.

The servo motor 8 is, for example, a synchronous AC servo motor. A position detector 9 for absolutely detecting the current position is connected to the servomotor 8. Further, although not shown, a mechanical load such as a machine tool is connected to the servomotor 8. Therefore, the position detector 9 is coupled to the servomotor 8, and is coupled to the mechanical load of the machine tool or the like, and the current position of the machine tool or the like is fed back even in a semi-closed loop configuration in which the current position of the servomotor 8 is fed back. A fully closed loop configuration may be used.

As the position detector 9, for example, Japanese Patent Application Laid-Open No. 57-70406
An inductive type phase shift type position sensor as disclosed in Japanese Patent Application Laid-Open Publication No. H10-260, may be used. In that case, the output of the position detector 9 is composed of an AC signal that is electrically phase-shifted according to the current position, and this output is input to the conversion means 13 and converted into a digital current position signal PF. 10 and subtractor 1
Is output to

The speed calculation unit 10 calculates a current speed signal VF indicating the rotation speed of the servomotor 8 based on the current position signal PF, and outputs the current speed signal VF to the subtractor 4. A speed sensor (pulse generator) for detecting the current speed instead of the speed calculation unit 10
May be coupled to the servo motor 8.

The subtracter 1 receives a position command signal Pc indicating the target position of the servomotor 8 and a current position signal PF indicating the current position of the servomotor 8 from a host controller (not shown),
The current position signal PF is subtracted from the position command signal Pc, and the position deviation signal εp is converted to the position control unit 3 and the position steady deviation compensation calculation unit 11.
Output to

The position steady deviation compensation calculation unit 11 receives the position deviation signal εp and outputs a position steady deviation compensation signal αp to the adder 2.
The position steady-state deviation compensation calculation unit 11 is configured as shown in FIG.
In accordance with a predetermined correction function f (εp), a position steady deviation compensation signal αp is output in response to the input of the position deviation signal εp. The speed steady-state error compensation signal αv of the speed steady-state error compensation operation unit 12 may be input to the position steady-state error compensation operation unit 11. In this case, the characteristic of the correction function shown in FIG. It may be changed according to the magnitude of the compensation signal αv. That is, the position steady-state deviation compensation signal αp is given by the equation αp
= K (αv) · f (εp). K (α
v) is a constant for changing the gradient of the correction function f (εp) according to the magnitude of the speed steady-state deviation compensation signal αv, and is the rated output of the servo motor 8, the inertia, and the state of the mechanical load coupled to the servo motor 8. Can be appropriately selected according to the conditions. For example, K (αv) is a constant value when the speed steady-state deviation compensation signal αv is equal to or less than a predetermined value, and is set to a value that decreases in accordance with a linear function characteristic when the speed steady deviation compensation signal αv is equal to or more than the predetermined value. As a result, optimal position steady deviation compensation control can be performed according to the control state of the speed steady deviation compensation calculation unit 12.

Note that the characteristics of the correction function of the position steady-state error compensation calculation unit 11 change in a cubic function near zero where the position error signal εp is small, and become saturated as the position error signal εp becomes larger than a predetermined value. Composed of joins.

The adder 2 inputs the position deviation signal εp and the position steady deviation compensation signal αp, and outputs a new position deviation signal (εp + αp) obtained by adding both signals to the position control unit 3. Since the new position deviation signal (εp + αp) is a signal for removing a position steady deviation in the position control loop system of the servo control system, the position control unit 3 controls the inertia fluctuation of the mechanical load to be controlled and the friction torque. Even if the position steady-state deviation fluctuates as needed due to fluctuations and the like, the position steady-state deviation can be compensated according to the fluctuation, and the high-speed response characteristics of the position control loop system can be improved.

The position control unit 3 calculates the speed command signal Vc according to the position deviation signal (εp + αp) and outputs it to the subtractor 4. Therefore, the position control unit 3 outputs to the subtractor 4 a speed command signal Vc from which the position steady-state deviation of the position control loop system has been removed.

The subtracter 4 receives the speed command signal Vc and the current speed signal VF, subtracts the current speed signal VF from the speed command signal Vc, and adds the speed deviation signal εv to the adder 5 and the speed steady-state deviation compensation calculator 12.
Output to

The speed steady deviation compensation operation unit 12 receives the speed deviation signal εv, and outputs the speed steady deviation compensation signal αv to the adder 5 and the position steady deviation compensation operation unit 11. Speed steady deviation compensation calculation unit
Numeral 12 outputs a steady speed deviation compensation signal αv in response to the input of the speed deviation signal εv in accordance with a predetermined correction function f (εv) as shown in FIG. Note that this correction function f (εv)
Is composed of a combination of two functions such that the velocity deviation signal εv changes like a cubic function near zero where the velocity deviation signal εv is small, and saturates as the velocity deviation signal εv becomes larger than a predetermined value. The characteristics are substantially the same as those of the unit 11.

The adder 5 receives the speed deviation signal εv and the speed steady-state deviation compensation signal αv, and outputs a new speed deviation signal (εv + αv) obtained by adding both to the speed control unit 6. Since this new speed deviation signal response (εv + αv) is a signal for removing the steady speed deviation in the speed control loop system of the servo control system, the speed control unit 6 controls the inertia fluctuation and the friction torque of the mechanical load to be controlled. Even if the steady-state speed deviation fluctuates at any time due to fluctuations in speed, the speed steady-state deviation can be compensated according to the fluctuation, and the high-speed response characteristics of the speed control loop system can be improved.

The speed controller 6 controls the torque command signal (current command signal) of the servo motor 8 according to the speed deviation signal (εv + αv).
Tc is calculated and output to the current control unit 7. Therefore, the torque command signal Tc from which the steady-state speed deviation of the speed control loop system is removed is output from the speed control unit 6 to the current control unit 7.

The current control unit 7 drives a power transistor and supplies a drive current to the servo motor 8.

Note that the characteristics of the position steady-state deviation compensation calculation unit 11 and the speed steady-state deviation compensation calculation unit 12 shown in FIGS. 2 and 3 are merely examples, and may be appropriately changed depending on the servomotor 8 and the mechanical load connected thereto. For example, a linear function, a quadratic function, a tertiary or higher-order function, an exponential function, or a linear approximation thereof may be used.

Further, in the embodiment of FIG. 1, the case where the steady deviation of the position and the speed of both the position control loop system and the speed control loop system is compensated has been described. However, the present invention is not limited to this, and one of the steady deviations is compensated. It is needless to say that the effect of the present invention can be obtained even if the configuration is adopted.

FIG. 4 is a view showing an absolute type position sensor comprising an inductive type phase shift type position sensor which is an example of the position detector 9 shown in FIG. Since the details of the phase detector 4 are known in Japanese Patent Application Laid-Open No. 57-70406, a brief description will be given here.

The position detector 9 is inserted into a space between a stator 23 in which a plurality of poles A to D are provided at predetermined intervals (for example, 90 degrees) in a circumferential direction, and a stator 23 surrounded by the poles A to D. Rotor 24.

The rotor 24 is made of a shape and a material that changes the reluctance of each of the poles A to D according to the rotation angle, and has an eccentric cylindrical shape as an example. Primary coils 1A to 1D and secondary coils 2A to 2D are wound around the poles A to D of the stator 23, respectively. A first pair of two poles A and C, which are radially opposed, and a second pair of poles B and D are coiled so as to operate differentially, and It is configured to cause a reluctance change.

The primary coils 1A and 1C wound on the first pole pair A and C are excited with a sine signal sinωt and the second pole pair B
And D are wound by the primary coils 1B and 1C.
It is excited at sωt. As a result, the secondary coils 2A to 2D
Obtains the combined output signal Y from This combined output signal Y is supplied to the rotor 24 with respect to a primary AC signal (excitation signal of the primary coil) sinωt or cosωt serving as a reference signal.
Is a signal Y = sin (ωt−θ) that is phase-shifted by an electrical phase angle corresponding to the rotation angle θ.

Therefore, when the inductive phase shift type position sensor as described above is used, the primary AC signal sinωt or cosωt
, And phase difference measuring means for calculating the position data of the rotor that has measured the electrical phase shift θ of the combined output signal Y. The primary AC signal generating means and the phase difference measuring means are provided in the converting means 13.

FIG. 5 is a diagram showing an example of the conversion means 13 of FIG.
In the conversion means 13, a predetermined high-speed clock pulse CP is counted by a counter 26, and based on the output of the counter 26, a sine / sine signal sinω
t and a cosine signal cos ωt, respectively. Sign
The output of the cosine signal generating means 27 is applied to each of the primary coils 1A to 1D and the secondary coils 2A to 2D as described above.

The composite output signal Y of the secondary coils 2A to 2D Y = sin (ωt−
θ) is given to the zero-cross detecting means 28. The zero-cross detecting means 28 outputs a pulse L in synchronization with the timing when the electric phase angle of the combined output signal Y is zero. The pulse L is used as a latch pulse of the latch circuit 29. Therefore,
The latch circuit 29 sets the counter 26 in response to the rise of the pulse L.
Is latched. A period in which the count value of the counter 26 makes one cycle is synchronized with one cycle of the sine signal sinωt. Then, the latch circuit 29 latches the count value corresponding to the phase difference θ between the reference AC signal sinωt and the combined output signal Y = sin (ωt−θ). Therefore, the latched value is output as digital position data Dθ. Note that the latch pulse L can be appropriately used as a timing pulse.

Further, of the values latched by the latch circuit 29, a value indicating the absolute position within one rotation of the servo motor is output as digital phase data P3, and is used for field switching position control.

Since the combined output signal P1 of the phase shift type position sensor as shown in FIG. 4 uses the absolute position of the servo motor as the signal phase difference, it has a feature that it is hardly affected by noise. Therefore, as shown in FIG. 2, when the synthesized output signal P1 is fed back from the position detector 9 to the position / velocity control system 1, it is directly fed back without using a communication line and is affected by noise and the like. There is no, I can't do it. However, the combined output signal P1 of the position detector 9 may be fed back using a communication line such as a serial communication interface.

Although FIGS. 4 and 5 show the case where the range of one rotation is absolutely detected, it is preferable that a plurality of such absolutes are combined to detect the absolute position over multiple rotations.

Next, another embodiment of the present invention will be described with reference to FIG. 6, the same components as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted.

This embodiment is different from that of FIG. 1 in the following points. The position steady deviation compensation calculation unit 11 outputs a position steady deviation compensation speed signal Vc2 for compensating the position steady deviation to the position control unit 3.
Is output to an adder 61 provided at the subsequent stage. The characteristic of the correction function of the position steady deviation compensation calculating section 11 may be substantially the same as that shown in FIG. 2, but is configured to output a speed signal corresponding to the position deviation signal εp. The adder 61 adds the speed command signal Vc1 output from the position control unit 3 and the position steady deviation compensation speed signal Vc2, and outputs the result to the subtractor 4 as a new speed command signal Vc3. Therefore, a new speed command signal
Vc3 is a speed signal for removing the position steady-state deviation in the position control loop system of the servo control system. The position steady-state deviation can be compensated for according to the variation, and the high-speed response characteristic of the position control loop system can be improved.

The speed steady-state deviation compensation calculation unit 12 outputs a speed steady-state error compensation torque signal Tc2 for compensating the speed steady-state error to the speed control unit 6.
Is output to the adder 62 and the position steady-state deviation compensation calculation unit 11 provided at the subsequent stage. The characteristic of the correction function of the steady speed deviation compensation calculation unit 12 may be substantially the same as that shown in FIG. 3, but is configured to output a torque signal according to the speed deviation signal εv. The adder 62 includes a torque command signal Tc1 output from the speed control unit 6 and a speed steady-state deviation compensation torque signal Tc2.
And outputs the same to the current control unit 7 as a torque command signal Tc3. Since this new torque command signal Tc3 is a signal for removing the steady-state speed deviation in the speed control loop system of the servo control system, the steady-state speed deviation due to the inertia fluctuation of the mechanical load to be controlled or the fluctuation of the friction torque is reduced. The speed steady-state deviation can be compensated for according to the amount of the fluctuation, and the high-speed response characteristic of the speed control loop system can be improved.

With such a configuration, it is possible to compensate for the steady-state deviations of the respective positions and speeds in the position control loop system and the speed control loop system similarly to the embodiment of FIG. 1, and to perform the deviation compensation according to the fluctuation of the deviation. be able to.

The servomotor is not limited to a synchronous servomotor, but may be an induction AC servomotor. Further, it goes without saying that the present invention is not limited to the AC servomotor but may be another type such as a DC servomotor. Further, the position sensor is not limited to the inductive type phase shift type sensor, and an optical absolute encoder, an incremental encoder, or another type of sensor may be used.

In the above-described embodiment, the case where the position steady-state deviation compensation calculation unit 11 and the high-speed steady-state deviation compensation calculation unit 12 are provided has been described. However, it is not always necessary to provide both, and the effect can be sufficiently achieved by providing only one of them. Can do it.
However, it is needless to say that the deviation can be removed more effectively by providing both as in the present embodiment and changing the control characteristic of the position steady-state deviation compensation calculation unit 11 according to the output of the speed steady-state deviation compensation calculation unit 12. Absent.

Further, in the embodiment shown in FIG.
Outputs the position steady-state error compensation signal αp, the speed steady-state error compensation operation unit 12 outputs the speed steady-state error compensation signal αv, and in the embodiment of FIG. 6, the position steady-state error compensation operation unit 11 outputs the position steady-state error compensation speed signal Vc2. The case where the speed steady-state deviation compensation calculation unit 12 outputs the speed steady-state deviation compensation torque signal Tc2 separately has been described, but the present invention is not limited to this. αp and the position steady-state error compensation speed signal Vc2, and the speed steady-state error compensation calculating unit 12 may output the speed steady-state error compensation signal αv and the speed steady-state error compensation torque signal Tc2. Absent.

〔The invention's effect〕

According to the present invention, even if the steady-state deviation in each of the position control loop system and the speed control loop system of the servo control system fluctuates, those steady-state deviations are effectively compensated,
There is an excellent effect that a servo control system excellent in high-speed response can be configured.

In particular, when generating the position deviation compensation signal, the position deviation compensation signal is generated according to the position deviation according to a predetermined compensation function, and the characteristic of the predetermined compensation function is varied using the speed deviation compensation signal as a parameter. Controlling and generating a position deviation compensation signal corresponding to the position deviation in accordance with the variably controlled compensation function, thereby performing optimal position deviation compensation control according to a compensation control state based on the speed deviation compensation signal. The effect is excellent.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a servo control system according to the present invention, FIG. 2 is a diagram showing output characteristics of a position steady-state deviation compensating operation unit in FIG. 1, and FIG. FIG. 4 is a cross-sectional view showing an absolute type position sensor including an inductive type phase shift type position sensor which is an example of the position sensor shown in FIG. 1, and FIG. 5 is a block diagram showing an example of the conversion means of FIG. 1, FIG. 6 is a block diagram showing another embodiment of the present invention, and FIG. 7 is a block diagram showing a schematic configuration of an example of a conventional servo control system. It is. 1 subtractor, 2 adder, 3 position control unit, 4
... Subtractor, 5 ... Adder, 6 ... Speed control unit, 7 ... Current control unit, 8 ... Servo motor, 9 ... Position detector, 10
…………………………………………………………………………………………………………………………………………………… ……… ………………………………… More
... Speed steady-state deviation compensation calculation unit, 13 ... Conversion means

──────────────────────────────────────────────────続 き Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G05D 3/00-3/20

Claims (1)

(57) [Claims] 1. A position deviation calculating means for obtaining a position deviation by negatively feeding back a feedback position signal indicating a current position of a servo motor with respect to a position command signal, and a position control means for generating a speed command signal according to the position deviation. A position deviation compensation signal for generating a position deviation compensation signal according to the position deviation calculated by the position deviation calculation means, and for generating the position deviation compensation signal according to the position deviation according to a predetermined compensation function. Generating means; first correction means for compensating the position deviation by positively feeding back the position deviation compensation signal to at least one of the input side and the output side of the position control means, thereby correcting the speed command signal; A speed deviation calculating means for obtaining a speed deviation by negatively feeding back a feedback speed signal indicating the current speed of the servomotor to the speed command signal, and a current command signal according to the speed deviation. Speed control means for generating, a speed deviation compensation signal generating means for generating a speed deviation compensation signal according to the speed deviation obtained by the speed deviation calculation means, an input side of the speed control means and an output of the speed deviation compensation signal. Second correction means for compensating for the speed deviation by positively feeding back to at least one of the two sides, thereby correcting the current command signal; current control means for generating a drive current in response to the current command signal; And a detecting means for detecting a current position and a speed of the servo motor and outputting the feedback position signal and the feedback speed signal. The position deviation compensation signal generating means includes: The characteristic of the predetermined compensation function is variably controlled by using the speed deviation compensation signal generated from the compensation signal generating means as a parameter, and the variably controlled compensation function is controlled. A servo control system wherein the position deviation compensation signal is generated according to the position deviation according to a compensation function.