JPH07281758A - Control system for servo motor - Google Patents

Abstract

PURPOSE:To provide the control system for servo motor with which the vibration of a controlled system can be suppressed and input follow-up ability can be improved by extending the band of a speed loop. CONSTITUTION:Concerning the control of the controlled system due to a servo motor, an acceleration loop is formed by feeding the acceleration of the controlled system back to the torque command of the servo motor. Concerning that acceleration loop, a control term H(s) is contained serially with a term G(s) of the controlled system at a gap from the torque command of the servo motor to the output of the acceleration loop, and this control term is defined as a function for the term of the controlled system and the desired characteristic of the acceleration loop. Further, that desired output characteristic is decided so as not to generate any vibration. Thus, the vibration of the controlled system is suppressed by preventing the output of the acceleration loop from being vibrated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servomotor control method, and more particularly to a servomotor control method used as a drive source for machine tools, robots and the like.

[0002]

2. Description of the Related Art A feed shaft of a machine tool, an arm of a robot and the like are driven by a servo motor, and conventionally, the servo motor has been subjected to speed loop control and position loop control. In the control of this servomotor, the gain of the speed loop is always kept constant and set to a value with a certain margin with respect to the gain level that causes mechanical resonance. FIG. 2 is a block diagram showing an example of a servo motor position control system, where 1 is a position control unit and Kp is a position loop gain. Further, 2 is a speed control unit, K1 is an integral gain, and K2 is a proportional gain. 3 is a motor and mechanical system,
Reference numeral 4 denotes a term for integrating the speed to obtain the position. The position detected by the position detector is subtracted from the position command to obtain the position deviation, the position deviation is multiplied by the position loop gain to obtain the speed command, and the actual speed detected by the speed detector etc. is calculated from the speed command. Calculate the speed deviation by subtracting, integrate the speed deviation,
It is generally performed to add a value obtained by multiplying the integral value by the integral gain K1 to obtain a torque command (current command), and drive the servo motor based on the torque command (and further by performing current loop control). ing.

Further, control of a servomotor only by speed loop control without position loop control is generally performed. Further, FIG. 13 and FIG. 14 show an example of a control method for improving the disturbance suppressing property and the vibration suppressing property by feeding back some state quantity to the torque command in addition to the position loop control and the speed loop control. . In the control method shown in FIG. 13, the torque applied to the mechanical system such as the arm is obtained by differentiating the motor speed detected by the speed detector and multiplying it by the inertia term of the mechanical system, and the difference between the value and the torque command is obtained. That is, the disturbance suppression property is improved by returning the disturbance to the torque command. Further, in the control system shown in FIG. 14, the observer changes a speed component in a mechanical system such as an arm, and the difference between the value and the motor speed is returned to the torque command as a twist amount to change the apparent mechanical characteristic. ing. Then, the disturbance suppression property and the vibration suppression property are improved by the feedback of the speed by the above speed loop.

[0004]

The conventional control of the servomotor by the speed loop control has a problem that mechanical resonance occurs at the resonance frequency, for example, when the rigidity of the mechanical system connected to the motor is low. That is,
In the command to the servo motor, there is a problem that the frequency has to be lower than the resonance frequency. For example,
In the block diagram showing the relationship between the arm command and the torque command in FIG. 15, the relationship between the arm command y and the torque command u in the conventional speed loop control is, for example,
G (s) = {1 / (Jm + Jl)} · {(Bs + C) /
Mechanical system transfer function G represented by (As ² + Bs + C)}
(S) (hereinafter, referred to as a controlled object term G (s)). Here, Jm is the inertia (inertia moment) of the motor, Jl is the inertia of the load, and A, B, and C are coefficients representing the transfer function.
Then, in the term G (s) to be controlled, G
When a command with a frequency such that (As ² + Bs + C) in the denominator of (s) becomes small is input, resonance occurs and G
The value of (s) has a characteristic of becoming a large value, and the torque command u
The arm acceleration y with respect to increases and mechanical resonance is generated. FIG. 16 shows a graph of the above-mentioned characteristic of arm acceleration with respect to frequency, and shows that large arm acceleration occurs at the resonance point. Therefore, an object of the present invention is to solve the above-mentioned problems of the conventional servo motor control method and to provide a servo motor control method capable of suppressing the vibration of the controlled object. Another object of the present invention is to extend the band of the speed loop and provide a control method of a servo motor having a good input following property.

[0005]

The present invention achieves the above object by forming an acceleration loop by feeding back the acceleration of the controlled object to the torque command of the servo motor in the control of the controlled object by the servo motor. It is a thing. Further, the acceleration loop formed in the servo motor control method of the present invention includes a control term in series with the term of the control target between the torque command of the servo motor and the output of the acceleration loop. As a function of the term and the desired output characteristic of the acceleration loop, and by making the desired output characteristic an output characteristic in which vibration does not occur,
The vibration of the output of the acceleration loop is prevented to suppress the vibration of the controlled object. Further, the acceleration loop formed in the servo motor control method of the present invention includes a feedback term between the output of the acceleration loop and the torque command of the servo motor, and by adjusting this feedback term, the output gain of the acceleration loop can be adjusted. Determine the absolute value. Furthermore, in the acceleration loop of the servo motor control method of the present invention, the acceleration of the feedback control target can be determined by the acceleration sensor connected to the control target, and can be determined by the observer in the acceleration loop.

[0006]

According to the present invention, as described above, the acceleration loop is formed in the position control system of the servo motor to feed back the acceleration of the controlled object to the torque command of the servo motor, and the acceleration loop is fed back by this feedback of the acceleration. The output vibration is prevented and the band of the speed loop is extended. Then, by improving the characteristics of the acceleration loop, it is possible to suppress the vibration of the controlled object and improve the input following ability. FIG. 1 is a block diagram of an acceleration loop formed in the servomotor control method of the present invention. In FIG. 1, only the period from the torque command u to the arm tip acceleration y is shown, and the term G to be controlled is indicated.
(S) is a transfer function of the mechanical system from the torque command u to the arm tip acceleration y, and H (s) is a control term to be incorporated in the acceleration loop of the present invention, which is in series with the term G (s) to be controlled. F (s) is a feedback term of the acceleration loop of the present invention, and is inserted between the arm tip acceleration y and the torque command u, and its output is added with the opposite sign to the torque command u. ing.

The transfer function from the torque command u to the arm tip acceleration y by this acceleration loop is expressed by the following equation (1). y / u = G · H / (1 + G · H · F) (1) Here, in the transfer function of Expression (1), the term G to be controlled is
(S) is a transfer function of the mechanical system from the torque command u to the arm tip acceleration y, which is unique to the mechanical system and is automatically set when a certain mechanical system is determined. On the other hand, the control term H (s) and the feedback term F (s)
Is a configurable term. Therefore, in order to realize the desired input / output characteristic y / u of the acceleration loop, the control term H (s) and the feedback term F (s) are set by the mechanical system so as to achieve the desired input / output characteristic y / u. This can be performed by setting the term G (s) to be controlled, which is a given transfer function. Whether or not the acceleration loop in the formula (1) causes vibration is determined by, for example, the above formula (1).
It can be determined by whether or not there is s in which the term (1 + G · H · F) of the denominator of is zero. At this time, as the desired input / output characteristic y / u on the left side of the equation (1), there is no s such that the denominator when expressed in the s region is zero, and there is no input that prevents vibration. Set the output characteristics, and set the input / output characteristics to the right side {G · H /
Control term H (s) that satisfies (1 + G · H · F)}
And the feedback term F (s) is set. With this setting, the denominator term (1 + G · H ·
There is no s that makes F) zero, and there is no vibration state.

Therefore, by forming an acceleration loop as in the present invention, it is possible to prevent the vibration of the arm tip acceleration y with respect to the input torque command u, and control by vibrating the arm tip acceleration y. Vibration of the target can be suppressed. In addition, input followability can be improved by suppressing vibration. Further, in a mechanical system in which mechanical resonance occurs, the term G (s) to be controlled, which is the transfer function of the mechanical system of the equation (1), becomes large. When the term G (s) to be controlled is sufficiently large in the equation (1), the input / output characteristic y / u becomes y / u → 1 / F (2), and the magnitude of the arm tip acceleration y is , Can be limited by the feedback term F in the acceleration loop.
Therefore, by adjusting this feedback term F, the absolute value of the output gain of the acceleration loop can be suppressed. Further, as described above, the desired input / output characteristic y / u and the term G of the controlled object which is the transfer function of the mechanical system
By setting the control term H (s) and the feedback term F (s) corresponding to (s), the desired input / output characteristic y / u of the acceleration loop can be realized.
By setting the time constant of the desired input / output characteristic y / u to a desired value, the frequency characteristic can be made a desired characteristic and the input followability can be improved.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. (Servo Motor Control System for Implementing the Present Invention) First, a servo motor position control system for implementing the present invention will be described. The servo motor position control system embodying the present invention is the same as the servo motor position control system shown in the block diagram showing an example of the servo motor position control system in FIG. Therefore, detailed description of FIG. 2 will be omitted. The servo motor control system of the present invention forms an acceleration loop by adapting to the section of the motor mechanical system in the servo motor position control system shown in FIG. Also, FIG.
FIG. 3 is a block diagram of a main part of servo motor control of a machine according to an embodiment that implements the servo motor control system of the present invention. In the figure, 10 is a control device such as a numerical control device for controlling the machine, 11 is a digital servo circuit 12 that receives various commands and the like output from the control device 10 to the servo motor.
The shared memory 12 to be delivered to the processor is a digital servo circuit, which is composed of a processor, a ROM, a RAM, and the like, and the processor performs position, speed, and current control processing of the servomotor 14. Reference numeral 13 is a servo amplifier composed of an inverter or the like, 14 is a servo motor, and 15 is a position / speed detector for detecting the rotational position and speed of the servo motor 14 and feeding back the position / speed to the digital servo circuit 12.

(Structure of Acceleration Loop of the Present Invention) Next, the acceleration loop of the servo motor control method of the present invention will be described. First, the term of the motor mechanical system in the servo motor position control system to which the acceleration loop of the present invention is applied is determined using the model diagram of the motor mechanical system of FIG. The model diagram of FIG. 4 is, for example, a mechanical system model in which a robot that transmits the driving force of a motor to an arm for driving is formed by regarding the motor and the arm as a spring / damper system. J in the figure
m is the motor inertia, Jl is the load inertia, Dm is the damping constant, and Km is the spring constant. In this mechanical system model, if the term to be controlled, which is the transfer function from the motor torque to the arm tip acceleration, is G (s), this G (s) is expressed by the following equation (3). G (s) = {1 / (Jm + Jl)} · {(Dms + Km) / {(Jm · Jl) s ² / (Jm + Jl) + Dms + Km} (3) Therefore, using this control target term G (s) The term of the motor mechanical system in the servo motor position control system is shown in FIG.
Is a block diagram of. In FIG. 5, the input torque command u is a term G to be controlled which is a term of the motor mechanical system.
The arm tip acceleration y is output by (s), and is represented by the relational expression of y / u = G. The arm tip acceleration y is directly influenced by the term G (s) to be controlled. Become.

The control method of the servo motor of the present invention includes a control term H (s) and a feedback term F as shown in FIG. 1 in the section of the motor mechanical system in the servo motor position control system.
(S) is added to form an acceleration loop.
In FIG. 1, the acceleration loop includes a control term H (s) connected in series to a control target term G (s) which is a transfer function of a mechanical system from a torque command u to an arm tip acceleration y, and , Feedback term F of acceleration loop
(S) between the arm tip acceleration y and the torque command u,
It is formed by inserting the output by adding the output with the opposite sign to the torque command u. When the acceleration loop shown in FIG. 1 is implemented by the mechanical system model shown in FIGS. 4 and 5, the transfer function G (s) from the torque command u to the arm tip acceleration y by this acceleration loop is, for example, a feedback term. F (s) can be expressed as (Jm + Jl) by the following equation (4). In this case, a block diagram of the acceleration loop in the servomotor control method of the present invention is as shown in FIG. y / u = GH · (1 + GH · (Jm + Jl)) (4) Therefore, the input / output characteristic y / of the desired acceleration loop is obtained.
In order to realize u, in Expression (4), the control term H (corresponding to the term G (s) of the control target given by the mechanical system is obtained so that the desired input / output characteristic y / u is obtained. s) is set. Then, by using this set control term H (s), an acceleration loop is formed in the term of the motor mechanical system in the servo motor position control system to obtain the desired input / output characteristic y / u of the acceleration loop. Obtainable.

Next, the setting of the control term H (s) will be described. For example, the output of the desired acceleration loop is u
When the time constant is T, the input / output characteristic is expressed by the following equation (5). y / u = 1 / {(Jm + Jl) · (Ts + 1)} (5) In this case, the control term H (s) that satisfies the following equation (6) obtained from the equations (4) and (5). ) Is obtained corresponding to the term G (s) to be controlled given by the mechanical system. G · H · (Jm + Jl) / {1 + G · H · (Jm + Jl)} = 1 / (Ts + 1) (6) In this case, the control term H (s) is represented by Formula (3).
It is expressed by the following equation (7) using (s). H (s) = Jm.Jls / {(Jm + Jl) .Dm.Ts + (Jm + Jl) .Km.T} + 1 / Ts (7) Therefore, the mechanical system of the transfer function G (s) as shown in FIG. If the feedback term is (Jm + Jl) and an acceleration loop is formed by using the control term H (s) shown in the above equation (7), the input / output characteristic shown in the above equation (5) where the time constant is T Can be obtained. The input / output characteristic y / u obtained by this acceleration loop has no resonance point and the output gain is suppressed, and the time constant can be set to T to obtain a desired frequency characteristic.

FIG. 7 is a Bode diagram from the acceleration command to the arm tip acceleration when the time constant T is 4 ms in the input / output characteristic shown by the equation (5). The magnitude in decibels with respect to the frequency is shown, and FIG. 7B shows the phase with respect to the frequency.
FIG. 8 is a Bode diagram from the motor torque to the arm tip acceleration when only the term G (s) to be controlled is used without configuring the acceleration loop of the present invention, and is similar to FIG. 8A shows the size in decibels with respect to the frequency, and FIG. 8B shows the phase with respect to the frequency. When FIG. 7 and FIG. 8 are compared, 9 [H
z] The swelling and the abrupt change of the phase due to the resonance before and after are eliminated when the acceleration loop of the present invention is configured as shown in FIG. 7, and it is shown that the vibration of the tip of the arm is prevented.

Next, a configuration example of the control term H (s) will be described. FIG. 9 is a configuration example of the control term H (s) in the acceleration loop represented by the equation (4), and the feedback term F (s) is the sum of the values of the motor inertia and the load inertia in the mechanical system (Jm + Jl). )age,
In the case of realizing the desired output u of the acceleration loop with the time constant T, the two terms represented in the form of the sum in the equation (7) are configured by parallel blocks, and the acceleration command u is set for each of them. It inputs and adds each output. Further, FIG. 10 is another example of the configuration of the control term H (s), which is the control term H in the acceleration loop represented by the equation (4).
(S) is a configuration example in which the feedback term F (s) is set to 1 in (s) and the desired output u of the acceleration loop is realized with the time constant T, and the control term H corresponding to the equation (7) is given.
(S) is represented by the following equation (8). H (s) = Jm · Jls / {(Dm · Ts + Km · T) + (Jm + Jl) / Ts} (8) Then, in this formula (8), two terms expressed in the form of sum are connected in parallel. It is configured by blocks, the acceleration command u is input to each, and each output is added. This control term H (s) can be executed by software calculation processing.
The transfer function of the coefficient as shown by is calculated. Note that in FIG. 9 and FIG. 10, the control term H (s) is represented by the alternate long and short dash line.

Next, regarding the incorporation of the acceleration loop constituted by the control term H (s) and the feedback term F (s) into the position control system of the servomotor, the configuration examples of FIGS. 11 and 12 are used. Explain. FIG. 11 shows
It is a configuration example in the case of detecting the arm acceleration used in the acceleration loop by an accelerometer, and shows only the inner portion of the velocity loop in FIG. In the acceleration loop in the figure, the control term H (s) is used as a control target term G that is a transfer function of the mechanical system.
(S) is serially incorporated, and the output of the term G (s) to be controlled is inverted and fed back to the input side of the control term H (s) with its sign inverted. The feedback term is omitted in the figure. The speed loop in the figure is constructed by feeding back the motor speed from item 5.

FIG. 12 shows an example of the structure in which the arm acceleration used in the acceleration loop is detected by an observer, and only the inside of the velocity loop in FIG. 2 is shown.
The acceleration loop in the figure incorporates the control term H (s) in series with the term G (s) to be controlled, which is the transfer function of the mechanical system, and outputs the control term H (s) and the motor speed from the term 5. Is obtained by observing the arm acceleration by the observer 6 which receives as input and inverting the sign of the arm acceleration to the input side of the control term H (s) and feeding it back. The feedback term is omitted in the figure. The speed loop in the figure is constructed by feeding back the motor speed from item 5. According to the present invention, as described above, the transfer function from the torque command u by the acceleration loop to the arm tip acceleration y is y / u by forming the acceleration loop in the position control system of the servo motor.
= G · H / (1 + G · H · F), the control term H (corresponding to the term G (s) of the controlled object given by the mechanical system so that the desired input / output characteristic y / u is obtained. s) and the feedback term F (s). This control term H (s),
By setting the feedback term F (s), the vibration in the acceleration loop can be prevented to prevent the vibration of the controlled object, and the input / output characteristic y / which makes the control term H (s) desired.
By setting the frequency characteristic to correspond to u, it is possible to improve the input followability with a desired frequency characteristic.
Moreover, by adjusting the feedback term F, the absolute value of the output gain of the acceleration loop can be suppressed.

[0017]

As described above, according to the present invention, it is possible to provide a servomotor control system capable of suppressing the vibration of the controlled object. Further, the present invention can extend the band of the speed loop to provide a servomotor control system having a good input following property.

[Brief description of drawings]

FIG. 1 is a block diagram of an acceleration loop formed in a servo motor control method according to the present invention.

FIG. 2 is a block diagram showing an example of a servo motor position control system.

FIG. 3 is a block diagram of a main part of servo motor control of a machine according to an embodiment that implements the servo motor control method of the present invention.

FIG. 4 is a model diagram of a motor mechanical system.

FIG. 5 is a block diagram of a motor mechanical system in a servo motor position control system.

FIG. 6 is a block diagram of an acceleration loop in the servomotor control method of the present invention.

FIG. 7 is a Bode diagram from an acceleration command to an arm tip acceleration according to the servo motor control method of the present invention.

FIG. 8 is a Bode diagram from an acceleration command to an arm tip acceleration by a conventional servo motor control method.

FIG. 9 is a configuration example of a control term in an acceleration loop of the servo motor control method of the present invention.

FIG. 10 is another configuration example of the control term in the acceleration loop of the servomotor control method of the present invention.

FIG. 11 is a structural example of a servo motor position control system of the servo motor control system of the present invention.

FIG. 12 is another configuration example of the servo motor position control system of the servo motor control system of the present invention.

FIG. 13 is an example of a configuration of a conventional servo motor control method.

FIG. 14 is a configuration example of a conventional servo motor control method.

FIG. 15 is a block diagram showing a relationship between a conventional torque command and arm acceleration.

FIG. 16 is a characteristic diagram of a conventional servo motor control method.

[Explanation of symbols]

 3 Motor mechanical system Jm Motor inertia Jl Load inertia Km Spring constant Dm Damping constant G (s) Controlled term H (s) Control term F (s) Feedback term

Claims (6)

[Claims] 1. A control method of a servo motor, wherein in the control of a controlled object by a servo motor, an acceleration loop is formed by feeding back the acceleration of the controlled object to a torque command of the servo motor. 2. The acceleration loop includes a control term in series with a term to be controlled between the torque command of the servo motor and the output of the acceleration loop, and the control term controls the vibration of the output of the acceleration loop. The control method of the servomotor according to claim 1, wherein the control is performed. 3. The servo motor control method according to claim 2, wherein the control term of the acceleration loop is a function of a term to be controlled and a desired output characteristic of the acceleration loop. 4. The acceleration loop includes a feedback term between the output of the acceleration loop and the torque command of the servomotor, and the feedback term defines the absolute value of the output gain of the acceleration loop. Servo motor control method described. 5. The servomotor control method according to claim 1, wherein the acceleration of the controlled object is obtained by an acceleration sensor connected to the controlled object. 6. The acceleration of the controlled object is obtained by an observer in an acceleration loop.
Servo motor control method described.