Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1993-10-06
1995-08-15
Shoop, Jr., William M.
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
318610, G05B 19405
Patent
active
054422701
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a control method for object of control including spring system, such as a robot driven by a servomotor, more particularly to an adaptive sliding mode control method for object of control.
BACKGROUND ART
In controlling a machine or the like driven by a servomotor, linear control, such as PI (proportional-plus-integral) control, is employed assuming the machine, as an object of control, to be a non-spring system such as a rigid body.
However, since a robot is generally constructed in the form of a cantilever, it undergoes a large variation of inertia depending on the attitude of the robot, accompanying the change in the response of a servo system. Moreover, a robot has a low rigidity and resulting low resonance frequency due to the effects of the spring element such as the speed reducer and others, and so, in positioning the distal end (tool center point) of a robot, the end of the robot tends to sway even after positioning by servomotor. Conventionally, therefore, variations in the spring system and inertia due to the low rigidity of the robot have been ignored, and instead, the servo gain is reduced for the control, or a timer is activated after the positioning so that operation is performed after the vibration of the distal end of the robot is stopped following the passage of a predetermined period of time.
Thus, the present inventors have proposed inventions in which sliding mode control is applied to a control object driven by a servomotor, in order to prevent a moving part of a machine from vibrating (See Publication JP-A-3-92911 and JP-A-3-118618).
It is known that a combination of the sliding mode control and adaptive control is highly useful, since it provides very high robust properties (i.e., high resistance to parameter variations and high disturbance restraining capability). If this technique is applied to a machine of flexible structure such as a robot, however, estimated parameters (inertia, coefficient of dynamic friction, gravity term, etc. of the control object) will not converge properly, thereby causing the vibration of machine's moving parts.
DISCLOSURE OF THE INVENTION
Thus, the object of the present invention is to provide an adaptive sliding mode control method capable of improving the convergence of the aforesaid estimated parameters, as well as capable of providing an excellent vibration-damping effect.
In order to achieve the above object, an adaptive sliding mode control method according to the present invention is arranged so that the difference between the position of a servomotor and the position of a moving part of an object of control driven by the servomotor is fed back to a phase plane for sliding mode control, and a torque command for the servomotor is controlled so that the value of the phase plane converges to 0.
Preferably, in an adaptive sliding mode control method, a phase plane Suf for sliding mode control is given by position of a servomotor; .epsilon. is a speed deviation; .epsilon.t is the difference between the position of the servomotor and the position of a moving part of an object of control driven by the servomotor; Kp is a position loop gain; and K1 is a feedback gain of the difference between the position of the servomotor and the position of the moving part of the object of control driven by the servomotor.
A torque command .tau. for the servomotor is obtained in accordance with .epsilon.+Kp.multidot.K1.multidot..epsilon.t-K1.multidot..epsilon.t)+Ahat. multidot..theta.+Grhat+.tau.1, coefficient of dynamic friction, and a gravity term, respectively; .theta.r and .theta.r are a position command speed and acceleration, respectively; .epsilon.t is the differential of the difference between the position of the servomotor and the position of the moving part of the control object driven by the servomotor; and .tau.1 is a switching input, the switching input being adjusted to the maximum value of a disturbance when the value of the phase plane Suf is not smaller than 0, and to the minimum value of the disturb
REFERENCES:
patent: 5216342 (1993-06-01), Torii et al.
patent: 5341078 (1994-08-01), Torii et al.
Fanuc Ltd.
Shoop Jr. William M.
Sircus Brian
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