Electricity: motive power systems – Positional servo systems – With protective or reliability increasing features
Patent
1996-12-13
1998-06-16
IP, Paul
Electricity: motive power systems
Positional servo systems
With protective or reliability increasing features
318560, 318603, 318613, 318618, H02P 500
Patent
active
057676461
DESCRIPTION:
BRIEF SUMMARY
This application is a 371 of PCT/JP96/01076 filed on Apr. 19, 1996.
TECHNICAL FIELD
The present invention relates to control of a servomotor, and more particularly to a method of and an apparatus for detecting an anomalous running of a motor controlled by a software servo control system.
BACKGROUND ART
FIG. 8 is a block diagram of a conventional servomotor control system. In FIG. 8, a control of the servomotor is generally performed in the following manner. The position of a mechanical system 6 detected by a position detector 8, such as an encoder, is fed back and the position feedback value is subtracted from a position command to obtain a position deviation by an error register 1. This position deviation is multiplied by a position gain Kp of an element 2 to obtain a speed command by a position loop process. A speed of a motor 5 detected by a speed detector 7 is fed back and the speed feedback value is subtracted from the speed command to obtain a speed deviation, so that a torque command (an electric current command) is obtained by a speed loop process such as a proportion-integration control. Further, an electric current feedback value is subtracted from the torque command to obtain a voltage command by a current loop process, and the electric current is fed to a motor 5 by a servo amplifier 4 based on the voltage command. In FIG. 8, an element 3 performs a speed loop process and a current loop process. In this control system, the position to be fed back is a position of a mechanical system 6 driven by the motor 5.
FIGS. 9a-9c and 10a-10c respectively show relation between the position deviation and the speed command in the control system as shown in FIG. 8.
FIGS. 9a-9c show a case in which the motor 5, the speed detector 7 and the position detector 8 operate in a normal condition. In FIG. 9a, the position of the mechanical system, which is detected by the position detector 8, is fed back to a position command to obtain a position deviation, as shown in FIG. 9b. The speed command (FIG. 9c) is determined based on this position deviation and the motor is driven on the basis of the speed command to thereby reduce the position deviation.
FIGS. 10a-10c show a case in which the motor 5, the speed detector 7 and the position detector 8 do not operate normally, to cause an anomalous running of the motor 5. In FIG. 10a, the negative or positive sign of the feedback value, which indicates the moving direction of the position of the mechanical system, is opposite to the sign indicating the direction of the position command. As shown in FIG. 10b, although the actual position of the mechanical system approximates to the position command so that the actual position deviation decreases, a position deviation obtained by the error register 1 increases. The speed command increases in accordance with the increased position deviation, as shown in FIG. 10c, so that the motor is driven in accordance with the speed command. Thereby the motor is accelerated to cause an anomalous running.
A cause for such anomalous running is exemplified by a misconnection of cables in attaching the speed detector and the position detector, by which the sign of detection signals output from the speed detector or the position detector is opposite to the direction of the position command.
So as to prevent the anomalous running of the motor, there is conventionally provided an anomalous running detector 10 which detects an anomalous running when the position deviation between the position command and the position feedback value exceeds a set value. Upon detection of an anomalous running, the anomalous running detector 10 issues an alarm or shuts off the energization of the motor. FIGS. 11a and 11b show the conventional anomalous running detecting method in which the position deviation is compared with a predetermined reference value a and the speed command is made zero when the position deviation exceeds the reference value .alpha..
The control system generally utilizes a pulse control. In FIGS. 9 to 11, however, the pulse signals are depic
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patent: 4743822 (1988-05-01), Futami et al.
patent: 4965504 (1990-10-01), Ueda et al.
Fanuc Ltd.
Ip Paul
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