Electricity: motive power systems – Positional servo systems – With stabilizing features
Patent
1989-09-11
1992-07-21
Ip, Paul
Electricity: motive power systems
Positional servo systems
With stabilizing features
318611, 318798, 318808, 318599, H02P 540
Patent
active
051325993
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
a. Field of the Invention
This invention relates to a velocity control apparatus for controlling the velocity of a servomotor by PWM (pulse-width modulation) control of an inverter.
b. Description of the Related Art
In recent years, microprocessors have come to be widely used in velocity control apparatuses for controlling the driving of the servomotor. With a motor drive circuit composed of digital circuitry using a microprocessor, table information such as amplitude characteristics decided in conformity with motor characteristics is created, and the velocity of a servomotor is controlled by PWM control of an inverter based on a set velocity signal.
In a conventional velocity control apparatus of this kind, the range of fluctuation allowed with regard to power supply voltage is set to be within a prescribed limit. The apparatus is provided with a function which protects the motor from overcurrents when the aforementioned limit is exceeded, and with a protective function which shuts down the system automatically when the voltage is too low. However, no particular consideration is given to fluctuations within the prescribed limit.
More specifically, a fixed current loop constant K is provided. Therefore, when power supply voltage Vdc becomes high, current loop gain K' (=K.multidot.Vdc/Pa, where Pa represents carrier wave amplitude) rises in proportion to the voltage value and there is the danger that the motor current will oscillate. Conversely, when the power supply voltage becomes low, current loop gain diminishes and the response of the velocity loop to a commanded velocity signal slows down. The result is a deterioration in the quick response of the control system.
SUMMARY OF THE INVENTION
The present invention has been devised to solve the foregoing problems and its object is to provide a velocity control apparatus which makes stable velocity control possible by compensating for fluctuation in power supply voltage and obtaining a constant current loop gain.
In accordance with the present invention, there is provided a velocity control apparatus for controlling the drive current of a servomotor by a PWM-controlled inverter circuit, thereby controlling velocity of the servomotor, the apparatus includes a power supply of the inverter circuit, voltage detecting means for detecting an output voltage value of the power supply, and gain control means for holding constant a current loop gain based on the detected voltage value. Further, there is provided a PWM control device for PWM-controlling the inverter circuit used in the velocity control apparatus, the device includes constant computing means for computing a current loop constant inversely proportional to the power supply voltage of the inverter circuit, and signal generating means for forming a PWM control signal from the current loop constant and a command current value in such a manner that the current loop gain becomes constant.
Thus, in accordance with the present invention, when the servomotor is PWM-controlled, the power supply voltage is detected at all times and the current loop gain is held constant to enhance the stability of the control system. Further, in accordance the PWM control device of the invention, it is possible to construct a control system stabilized with respect to fluctuations in the power supply voltage.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram illustrating an embodiment of the present invention,
FIG. 2 is a view illustrating an example of the construction of a motor control system,
FIG. 3 is a time chart for describing PWM control,
FIG. 4 is a view for describing computation with regard to current loop gain K', and
FIG. 5 is a flowchart illustrating a processing procedure for setting gain.
DESCRIPTION OF THE PREFERRED EMBODIMENT
An embodiment of the present invention will now be described in detail with reference to the drawings.
FIG. 2 is a view illustrating an example of the construction of a PWM-controlled motor control system. An inverter section 2 supplied with comm
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Kono Shinichi
Takahashi Hironobu
Fanuc Limited
Ip Paul
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