Electricity: motive power systems – Positional servo systems – With particular 'error-detecting' means
Patent
1984-12-11
1986-03-11
Dobeck, B.
Electricity: motive power systems
Positional servo systems
With particular 'error-detecting' means
318602, G05B 106
Patent
active
045756660
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a system for detecting the absolute position of an operating shaft by way of servocontrol of a servomotor, and more particularly to an absolute position detecting system for a servocontrol system, for detecting the absolute position of an operating shaft based on a detected output produced on rotation at a preset r.p.m. ratio of a resolver and an absolute encoder which rotate with a servomotor.
Servomotors are widely used for positioning a movable portion of an industrial robot or the like with a high accuracy, the servomotors being subjected to servocontrol.
FIG. 1 is a block diagram for explaining such servocontrol, showing an example in which the operating shaft of an industrial robot or the like is positionally controlled by an NC (numerical control) apparatus. Designated in FIG. 1 at 101 is a paper tape punched with NC command data such as positioning information for machining, M, S, T function information, etc., and 102 an NC apparatus for enabling a tape reader, described later, to read NC data from the paper tape 101, encoding the read NC data, feeding M, S, T function commands, etc. to the machine through a driver, not shown, and feeding a movement command Zc to a following pulse distributor. The NC apparatus 102 is composed of a processor 102a for effecting arithmetic operations according to a control program, a program memory 102b for storing the control program, a data memory 102c for storing data, an operator's console 102d for effecting control, a tape reader/puncher 102e, a display unit 102f, an input/output port 102g, a current position counter 102h, and an address/data bus 102 interconnecting the above components.
Denoted at 103 is a pulse distributor for effecting a known pulse distributing arithmetic operation based on the movement command Zc, to generate distributed pulses Ps having a frequency dependent on a command speed. A known acceleration and deceleration circuit 104 produces a pulse train Pi by rectilinearly increasing the pulse rate of the distributed pulse train Ps at the time it is generated, and by rectilinearly reducing the pulse trai at the time it is ended. A motor 105 drives an operating shaft, and a pulse coder 106 generates one feedback pulse FP each time the motor 105 rotates through a prescribed interval an error calculating and storing unit 107 is composed of a reversible counter for storing the difference Er between the number of input pulses Pi generated by the acceleration and deceleration circuit 104 and the number of feedback pulses FP. The error calculating and storing unit 107 comprises, as shown, an arithmetic circuit 107a for calculating the difference Er between Pi and FP, and an error register 107b for storing Er. More specifically, in the event that the motor 105 is commanded to rotate and hence is rotating in a normal direction, the error calculating and storing unit 107 counts up the pulse Pi each time it is generated, counts down the feedback pulse FP each time it is generated, and stores the difference Er between the number of the input pulses and the number of the feedback pulse in the error register 107b. 108 denotes a digital-to-analog (DA) converter for generating an analog voltage in proportion to the content of the error register 107b, and 109 denotes a speed control circuit. The error calculating and storing unit 107 and the DA converter 108 constitute a motor position control circuit.
Operation of the conventional apparatus shown in FIG. 1 will be described.
Prior to machining, the NC data on the paper tape 101 is read by the tape reader/puncher 102e and stored through the bus 102j in the data memory 102c. A start command is applied, via the bus 102j, to the processor 102a in response to operation of the operator's console 102d. Then, the operator's console 102d is operated upon to successively read the machining control program out of the program memory 102b and execute the machining control program. More specifically, the NC data is read from the data memory 102c and at the same t
REFERENCES:
patent: 3904944 (1975-09-01), Carrick et al.
patent: 4023085 (1977-05-01), Bishop et al.
patent: 4529922 (1985-07-01), Ono
Nakashima Seiichiro
Sakakibara Shinsuke
Toyoda Kenichi
Dobeck B.
Fanuc Ltd.
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