Electricity: motive power systems – Positional servo systems – 'reset' systems
Patent
1994-03-14
1997-11-25
Cabeca, John W.
Electricity: motive power systems
Positional servo systems
'reset' systems
318432, 388809, 364161, H02M 112
Patent
active
056916159
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a motor control method for driving a control object, such as a robot or a machine tool, and more particularly to a robust adaptive PI (proportional-plus-integral) control method which executes adaptation of parameters, such as inertia, coefficient of dynamic friction, gravitational disturbance, or Coulomb's friction, so as to stabilize the characteristics of the control object against variation of these parameters.
2. Description of the Related Art
The control of a machine driven by a servomotor, such as a robot or a machine tool, is generally performed by a P control (proportional control) for position control and an PI control (proportional-plus-integral control) for speed control. FIG. 2 is a block diagram showing a motor speed control system using a PI control method. In this drawing, a command speed r is subtracted by an actual motor speed y to obtain a speed deviation, which is multiplied by a proportional gain K2 in a proportional element 1. On the other hand, the speed deviation is integrated in an integral element 2 and multiplied by a integral gain K1 therein. An output of the proportional element 1 is added to an output of the integral element 2 to obtain a torque command Tcmd, which is thereafter outputted to a motor 7, i.e. a control object, so as to drive the motor 7. In this case, the gains K1 and K2 for the PI control are normally fixed at predetermined constant values.
However, when values of proportional gains K1 and K2 are constant, if parameters such as inertia, dynamic friction, gravitational disturbance or Coulomb's friction of the machine or the like as a control object change, then control characteristics may also change, thereby lowering control efficiency.
For example, as shown in FIG. 3, in the case where the integral gain K1 and the proportional gain K2 are fixed values and the control object has a certain inertia, the gain and phase of an entire control system being G and f respectively with respect to frequency, if the inertia of the control object increases to a 5 times larger value, then the gain and phase change from G and f to G' and f', respectively, thereby causing the change of characteristic of the entire control system. Thus, in the conventional control system, the integral gain K1 and proportional gain K2 must be selected so as to always stabilize the control system against possible variations of parameters within a predetermined range.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a robust adaptive proportional-plus-integral control (PI control) method capable of stabilizing the characteristics of a control system against fluctuation of the parameters, such as inertia, coefficient of dynamic friction, gravitational disturbance, which may raise a problem in the control of a motor.
In order to accomplish the above purpose, a first aspect of the present invention provides an adaptive proportional-plus-integral control method for a motor control system including a proportional-plus-integral loop as a speed loop, comprising steps of: from a motor speed command, as a state variable, for the purpose of equalizing the actual motor speed to the motor speed command; and of an equation of motion of a control object, so as to converge said state variable at zero and converge estimated values of parameters to be adapted at their true values, said parameters including inertia, coefficient of dynamic friction, gravitational disturbance, and Coulomb's friction.
Furthermore, a second aspect of the present invention provides an adaptive PI control method for a motor control system including a proportional-plus-integral loop as a speed loop, comprising steps of: actual motor speed from a speed command; of a control object to be controlled by a motor, using said state variable; of said estimated values and its actual value; and a processing of said proportional-plus-integral loop, thereby producing a torque command to be supplied to said motor for driving.
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Arita Soichi
Kato Tetsuaki
Nakamura Masaru
Yoshida Osamu
Cabeca John W.
Fanuc Ltd.
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