JPH08194542A - Automatic overshootless tuning method - Google Patents

Abstract

PURPOSE: To execute the automatic tuning of a positioning servo system without causing the overshoot. CONSTITUTION: In the case of performing the automatic tuning, the control structure of a system is turned to sliding mode control, the number (m) of times of the changeover of a variable gain is obtained (a step 106), the number (m) of times of the gain changeover is used as a feature amount for tuning and the ratio Jn /KTn of the set value Jn of the moment of inertia to the set value KTn of a torque constant is adjusted (the step 107). Other than the time of executing the automatic tuning, normal control, that is a proportional integral control is typically executed (the step 109).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a servo system auto-tuning method, and more particularly to a positioning servo system auto-tuning method in which the occurrence of overshoot is suppressed.

[0002]

2. Description of the Related Art As an automatic tuning method for a servo system, the amount of overshoot of a response waveform when a step waveform or the like is input to the system is used as a characteristic amount, and various methods are used based on the extracted characteristic amount to determine the gain. There have been methods for adjustment and identification of the moment of inertia, etc. (For example, refer to: Japan Society of Electrical Engineers National Conference Proceedings Vol. 1991, No.
6,9.10.1, pp.5-18), this method is commonly used because it is easy to implement. FIG. 7 shows an example of the step response waveform. By obtaining the values e ₁ , a, b, T from the response waveform for the command value e ₀ , the overshoot amount E, the amplitude damping ratio D, the settling time ratio R, etc. Are obtained, and tuning is performed based on these characteristic amounts.

Further, Japanese Patent Laid-Open No. 5-324081 discloses a positioning method which suppresses the occurrence of overshoot by utilizing sliding mode control.

[0004]

However, in the above-described conventional auto-tuning method, since the feature amount is extracted from the step response, the amount of overshoot is large at the initial stage of auto-tuning in which the gain is not sufficiently tuned, and the positioning servo When it is applied to the actual process of the system, there is a problem that it may cause great damage such as collision with peripheral devices. In addition, JP-A-5
The technology disclosed in Japanese Patent No. 324081 uses two types of sliding curves, which makes control complicated,
Also, since the control in the sliding mode is always performed,
There is a problem that the amount of calculation becomes huge. An object of the present invention is to provide an auto tuning method that suppresses the occurrence of overshoot.

[0005]

The overshoot-less auto-tuning method of the present invention is an auto-tuning method for performing auto-tuning of a servo system based on a feature amount extracted from a response waveform. The servo system has a sliding mode control structure, and the number of times of variable gain switching is adopted as the characteristic amount. In the present invention, the servo system can be controlled by proportional-plus-integral control except when auto-tuning is executed.

[0006]

[Operation] As a control structure during auto-tuning operation,
Since sliding mode control, which is highly robust to the response of the load system, is adopted, overshoot does not occur even at the beginning of auto tuning.
Therefore, when the positioning servo system is automatically tuned in an actual process, problems such as collision of peripheral devices do not occur. Although gain switching occurs in the sliding mode control, as will be apparent from an embodiment described later, in the present invention, the number of times of gain switching is used as a characteristic amount for automatic tuning, and various characteristics of the system, such as servo, are used. The characteristics of the motor and load system are estimated. Further, in the present invention, the auto tuning of the servo system can be performed offline or during online operation.

[0007]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a control block diagram showing a control system to which an automatic tuning method according to an embodiment of the present invention is applied, and FIG. 2 is a flowchart showing a processing procedure of this automatic tuning method. First, the control system will be described. This control system is a servo system that positions the position x of the controlled object 8 by the torque generated by the servo motor torque generation mechanism 6. 11 shows a servomotor and an inertial load, and a servomotor torque generating mechanism 6 that generates a torque with a torque constant K _T according to an output current i _ref , a servomotor driven by this torque, and an inertial moment of the load. And the inertia element 7 of J. The controlled object 8 has a function of converting the angular acceleration u of the servo motor and the inertial load into the position x, and its transfer function is represented by 1 / S ² (two-fold integral element). This control system uses PI (proportional integration) during normal operation.
It is configured to perform control by control and shift to a sliding mode control structure during auto tuning. That is, the speed command generator 1 that generates a speed command value corresponding to the position deviation with the position loop gain K _P
And the speed loop gain is K _V , the integral gain is K _i , and PI that generates the proportional control manipulated _{variable UPID} according to the speed deviation.
The control unit 2, the correction unit 5 that outputs the output current i _ref according to the manipulated variable U _ref , and the servo motor + inertial load 11 described above.
And the speed of the controlled object 8 and the controlled object by inputting the position x

[0008]

[Outside 1] A control loop for PI control is configured by the differential element 9 that outputs Further, in order to perform auto tuning, a sliding mode controller 3 that generates a manipulated variable U _S for generating a sliding mode with a switching gain (variable gain) of K _S.
Further, a gain switching determination mechanism 10 for determining gain switching in the sliding mode and performing gain switching in the sliding mode controller 3, and a number calculation unit 4 for counting the number of times of gain switching m are provided. The deviation (position deviation) x _ref −x between the position command x _ref and the actual position x of the controlled object 8 is input to the speed command generator 1 and also to the sliding mode controller 3 and the gain switching determination mechanism 10. ing. Speed command generator 1
Generates a speed command value represented by _{K P (x r ef -x)} . Then, the deviation between the speed command value and the actual speed (speed deviation)

[0009]

[Outside 2] Is input to the gain switching determination mechanism 10 together with the PI control unit 2. The PI control unit 2

[0010]

[Equation 1] The proportional control manipulated _{variable UPID} is output as represented by. The correction unit 5 has a ratio J _n between the torque constant setting value K _Tn (torque constant model value) and the inertia moment setting value (inertia moment model value) J _n with respect to the input operation amount U _ref.
/ K _Tn is corrected and the output current i _ref for the servo motor is output. This ratio J _n
/ K _Tn is a parameter representing the characteristics of the servo motor and the load system (control target 8). Here, the operation amount U _ref is a difference U _PID −U _S between the proportional control operation amount U _PID and the operation amount U _S for generating the sliding mode. Also, the ratio J _n
/ K _Tn changes according to the output of the number-of-times calculating unit 4. Next, the control operation in the control system will be described with reference to FIG. First, it is determined whether or not it is an auto tuning operation (step 101). If it is not the auto tuning operation, normal control (PI control) is executed according to a well-known procedure (step 10).
9) Output the output current i _ref to drive the servo motor (step 108) and return to step 101. In case of auto tuning operation, speed command value x _ref , position x, speed

[0011]

[Outside 3] Is input (step 102), and the speed command value K _P (x _ref −
After calculating x), the gain switching determination mechanism 10 determines the gain switching (step 103), the PI control unit 2 calculates the proportional control manipulated _{variable UPID} (step 104), and the sliding mode controller 3 generates the sliding mode. The manipulated variable U _S for is calculated. Then, the number-of-times calculating unit 4 calculates the number of times m of gain switching (step 106), and the ratio J _n / K _Tn of the correcting unit 5 is adjusted according to the number of times of switching m (step 10).
7). Then, the set value element 5 outputs the output current i _ref based on the adjusted ratio J _n / K _Tn (step 108),
Return to step 101. Next, the auto tuning operation performed by the control structure as the sliding mode control will be described in more detail.

The gain changeover determination mechanism 10 has a speed deviation.

[0013]

[Outside 4] The state is determined by the sign of the product of the position deviation x _ref −x, the switching gain K _S of the sliding mode controller 3 is switched, and the sliding mode is executed. In particular,

[0014]

[Equation 2] And Here, reference [1]: IEEJ Transactions on Volume D, Volume 107
Volume 11, Nos. 1403-1410 (1987) and Reference [2]: Proceedings of the 1993 National Conference of the Institute of Electrical Engineers, No. 871 (1993),

[0015]

(Equation 3) Then, in equation (2),

[0016]

[Equation 4] And, in equation (3),

[0017]

(Equation 5) Becomes The model is correct,

[0018]

(Equation 6) If, that is, if the ratio of model values to the ratio of actual values of torque constant and moment of inertia are equal,

[0019]

(Equation 7) Thus, positioning is completed without switching the gain. As described above, the number-of-times calculating unit 4 receives the number of times of gain switching m as an input and tunes the ratio J _n / K _Tn of the correcting unit 5. In the present embodiment, the number of times of switching from state 2 to state 3 is m ₁ , the number of times of switching from state 2 to state 1 is m ₂ , and the number of times of gain switching m is defined by m = m ₁ −m ₂ (5) did. Also, let δ be a positive number,

[0020]

(Equation 8) The ratio J _n / K _Tn was tuned as represented by According to the tuning of the equation (6), when J _n / K _Tn is smaller than the actual value (actual J / K _T ), the ratio J _n / K _Tn increases by δ · m, and when it is larger than the actual value, δ・ Reduce by m. And finally,

[0021]

[Equation 9] Tuning is performed until Next, the results of simulation of the tuning method of this embodiment will be described. Here, in the initial state,

[0022]

[Equation 10] The tuning method of the present embodiment is applied to the positioning system that has become. FIG. 3 shows a step response waveform in the case where normal control (PI control) is performed in the initial state, by the relationship between time and displacement. As shown in this figure, when auto tuning is performed by normal control, a considerable overshoot occurs at the beginning of auto tuning. FIG.
FIG. 4 shows a step response waveform in the initial state (before the start of auto-tuning) when the control structure is set to the sliding mode control according to the present embodiment. FIG. 4A is a position response waveform, and FIG. 4B is a phase plane locus waveform. As shown in FIG. 4A, the sliding mode control does not cause overshoot in the initial state. Note that Fig. 4 (b)
In, there is a portion having a sawtooth-shaped locus, which indicates that the gain was switched there. In this embodiment, each time a step waveform is input, the ratio J _n / K _Tn changes in accordance with the number of times m the gain is switched, whereby tuning proceeds.

As the auto tuning progresses as described above, the number of times m the gain is switched when the step waveform is input gradually decreases. FIG. 5 shows a step response waveform when the number of gain changes m is 2 immediately before the end of tuning. 5A and 5B show the position response waveform and the phase plane locus waveform, respectively, as in the case of FIG. Since the number of times m the gain is switched is 2, the sawtooth-like portion is hardly seen in the phase surface locus waveform shown in FIG. 5 (b). Then, FIG. 6 shows a step response waveform at the time of returning to the normal control after the end of the auto tuning, by the relationship between time and displacement. The unit p.u. in FIGS. 4 and 5 is the unit of the position defined in the system. As is clear from the above simulation results, according to the auto-tuning method of the present invention, it is possible to consistently tune the positioning system from the beginning to the end of tuning without causing overshoot.

[0024]

As described above, the overshoot-less auto-tuning method of the present invention does not cause an overshoot during auto-tuning, and therefore can be performed quickly without causing an accident such as a collision with peripheral devices. It is possible to tune and it is easy to apply to an actual process.

[Brief description of drawings]

FIG. 1 is a control block diagram showing a control system to which an overshootless auto-tuning method according to an embodiment of the present invention is applied.

FIG. 2 is a flowchart showing a processing procedure of an overshootless auto tuning method according to an embodiment of the present invention.

FIG. 3 is a graph showing a step response waveform of a normal control system in an initial state.

4A and 4B are diagrams showing a step response waveform in an initial state when a sliding mode is applied, in which FIG. 4A is a graph showing a position response waveform, and FIG. 4B is a graph showing a phase surface locus waveform.

FIG. 5 is a diagram showing a step response waveform immediately before the end of auto tuning when a sliding mode is applied,
(a) is a graph showing a position response waveform, and (b) is a graph showing a phase surface locus waveform.

FIG. 6 is a graph showing a step response waveform after completion of auto tuning.

FIG. 7 is a diagram showing an example of a step response waveform.

[Explanation of symbols]

1 Speed command generation part 2 PI control part 3 Sliding mode controller 4 Number of times calculation part 5 Correction part 6 Servo motor torque generation mechanism 7 Inertia element 8 Controlled object 9 Differentiation element 10 Gain switching determination mechanism 11 Servo motor + inertial load 101 to 109 steps i _ref Output current J Inertia moment J _n Inertia moment setting value K _i Integral gain K _P Position loop gain K _S Switching gain K _T Torque constant K _Tn Torque constant setting value K _V Velocity loop gain m Number of switching times x Position x _ref Position command value

Claims (3)

[Claims] 1. An auto-tuning method for performing auto-tuning of a servo system based on a feature amount extracted from a response waveform, wherein during the execution of auto-tuning, the servo system has a sliding mode control structure, and the feature amount is a variable gain. Overshoot-less auto tuning method characterized by adopting the number of times of switching. 2. The servo system is controlled by proportional-plus-integral control except when auto-tuning is executed.
Overshoot-less auto-tuning method described in. 3. The overshootless auto-tuning method according to claim 1, wherein the servo system is a positioning servo system.