Electricity: motive power systems – Positional servo systems – Digital or numerical systems
Patent
1984-12-07
1986-09-09
Dobeck, B.
Electricity: motive power systems
Positional servo systems
Digital or numerical systems
318636, 318677, G05B 1928
Patent
active
046111557
DESCRIPTION:
BRIEF SUMMARY
CROSS REFERENCES TO RELATED APPLICATIONS
This application is related to U.S. application Ser. No. 673,741.
1. Field of the Invention
This invention relates to a servo control circuit for controlling the position, velocity and torque of a servomotor. More particularly, the invention relates to a servo control circuit applicable to control of a servomotor and adapted so as to enable execution of position and velocity loop control and current control on the basis of an output from a single counter which counts pulses of a number corresponding to the rpm of a servomotor.
2. Description of the Related Art
To move an object and position it at a predetermined location, a servomotor and servo control circuit are required as motive sources for obtaining a rotational position, velocity, torque and the like which are in accordance with commanded data. Servo control is executed to produce an output based on a comparison between an externally applied command signal input and a feedback signal indicative of the state of the servomotor.
As shown in FIG. 1, such a servo control system performs position, velocity and current control by feeding back rotation pulses PC from a rotary encoder connected to the shaft of a servomotor 101 (each pulse being generated whenever the servomotor 101 rotates through a predetermined angle of rotation), as well as an armature current I which flows into the servomotor 101.
Specifically, SVU denotes a servoamplifier constituting a current control loop and consisting of a microprocessor 108a which performs processing for current control, an interface circuit 108d for input/output coordination between the servoamplifier SVU and a main amplifier. Also included are set forth below, a counter 108g for counting pulses corresponding to the rpm of the servomotor 101, an analog-to-digital converter circuit (referred to as an A/D converter) 108f for digitizing the armature current of the servomotor 101, and an inverter (voltage supply circuit) 115 for producing as an output a voltage for driving the servomotor 101.
A main processor 150 calculates the difference between a position command PCMD and information indicative of the present position of the servomotor 101, obtains a velocity command VCMD by performing a predetermined position loop calculation, then senses the actual velocity Va of the servomotor 101 based on the present position information. Based on the above data the main processor 150 calculates the difference between the commanded velocity VCMD and the actual velocity Va, and produces as an output a current ICMD which will provide a predetermined servomotor drive torque.
The current command ICMD is delivered to the servoamplifier SVU via an interface circuit 151. In the servoamplifier SVU, the processor 108a calculates the difference between the current command ICMD and the actual current of the servomotor 101 obtained via the AD converter 108f. In other words, the processor performs a predetermined current loop calculation and produces an inverter drive signal as an output. The inverter 115, which is a power amplifier, amplifies the inverter drive signal into a predetermined armature current which is supplied to the servomotor 101. Thus, servomotor control is carried out in such a manner that the servomotor 101 will be rotated to a designated position and at a designated velocity and torque.
In a case where the servomotor 101 is an AC motor such as a synchronous motor, the counter 108g is used to sense the rotational position of the servomotor 101 in order to exercise armature current phase control.
In servo control, the response required for the current control loop is considerably quicker than the response required of the velocity control loop, with the result that the sampling period T.sub.1 of the current control loop is short in comparison with the sampling period T.sub.2 of the velocity control loop. Accordingly, the position of the rotor of servomotor 101 is sensed by counting the output pulses of the rotary encoder 102 with the counter 108g and processing these output pulses by
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patent: 4525658 (1985-06-01), Yamagida
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Dobeck B.
Fanuc Ltd.
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