Electricity: motive power systems – Positional servo systems – With stabilizing features
Patent
1987-08-20
1989-03-28
Shoop, Jr., William M.
Electricity: motive power systems
Positional servo systems
With stabilizing features
318561, 318618, 364174, G05B 501
Patent
active
048167347
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a system for controlling the speed of a servomotor, and more particularly to a speed control system for a servomotor suitable for driving a load of a low rigidity.
DESCRIPTION OF THE RELATED ART
Industrial robots have a plurality of arms coupled to provide high freedom for performing a variety of operations. Since the coupled arms are in the form of a long cantilever, or due to the characteristics of a power transmission mechanism between the arms and a servomotor, the arms are inevitably of a low degree of rigidity. Regardless of being such a mechanical load of low rigidity, the industrial robot is required to have an increased operation speed and an increased operation range and to effect highly accurate positioning in order to increase its working capability.
In order to ideally control a speed control system employing a DC motor for controlling a conventional mechanical load of low rigidity, e.g., robot arms, there has been proposed a speed control system as illustrated in FIG. 2 of the accompanying drawings. Denoted in FIG. 2 at K.sub.1 is an integration constant, K.sub.2, K.sub.3, K.sub.4 proportionality constants, Kt a power amplifier constant, Jm a rotor inertia, J.sub.l a load inertia, and K a spring constant of a rotor and load coupling. The ratio (transfer function) between an input signal Vr and an output signal, e.g., a speed Vl of the distal end of a robot hand, which is supplied as a feedback signal to a speed control integrator, is calculated by the following equation: ##EQU1##
According the equation (1), the coefficients of the terms of the linear differential S (=d/dt), the quadratic differential S.sup.2, the third differential S.sup.3 in the denominator are the products of only the proportionality constants K.sub.2, K.sub.3, K.sub.4. Therefore, it is easy to vary these coefficients freely thereby to stabilize the speed control system. In the DC term, too, only the integration constant K.sub.1 can freely be varied, independent of the proportionality constants K.sub.2, K.sub.3, K.sub.4, to increase response time and provide protect against disturbances applied to a position control system.
Actually, however, an observer is used when producing the displacement d of a mechanical feed system or a speed signal Vl at the distal end of the hand, and since the observer contains some error, it is difficult to obtain an accurate feedback signal. Heretofore, therefore, a motor speed Vm is usually fed back to the integrator. In this case, the relationship between the motor speed Vm and the speed Vl of the distal end of the hand is expressed, using the spring constant K, by: ##EQU2##
Consequently, the coefficients of the quadratic differential S.sup.2 include two coefficients, i.e., the proportionality constant K.sub.4 and the integration constant K.sub.1, thereby making it difficult to stably adjust the mechanical load of low rigidity.
More specifically, the time constant of the position control system is determined by the ratio of the coefficients of the term of the linear differential and the DC term, and is expressed by: 3-2) respect to (K.sub.2 +K.sub.3), the speed control system is allowed to effect accurate operation. However, since the proportionality constant K.sub.4 is included in the term of the quadratic differential, the position control system cannot be balanced when selecting the value of K.sub.1 in relation to (K.sub.2 +K.sub.3), resulting in the problem of impaired stability.
SUMMARY OF THE INVENTION
The present invention eliminates the problems of the conventional speed control system. It is an object of the present invention to provide a speed control system capable of stable positional control without impairing the response speed in a speed control loop by feeding back a speed signal issued as approximate data from a mechanical load, together with a motor speed, to a speed control integrator.
According to the present invention, there is provided a speed control system for controlling a servo control system with a comman
REFERENCES:
patent: 4581699 (1986-04-01), Delmege et al.
patent: 4680581 (1987-07-01), Kurakake et al.
patent: 4695780 (1987-09-01), Kurakake et al.
Kurakake Mitsuo
Sakamoto Keiji
Bergmann Saul M.
Fanuc Ltd
Shoop Jr. William M.
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