Electricity: motive power systems – Positional servo systems – Adaptive or optimizing systems including 'bang-bang' servos
Patent
1990-08-28
1993-10-19
Ip, Paul
Electricity: motive power systems
Positional servo systems
Adaptive or optimizing systems including 'bang-bang' servos
318610, 318611, 318616, G05D 300
Patent
active
052549216
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an abnormality detecting method for a servo system which is capable of quickly detecting an occurrence of an abnormal condition over a wide range of motor rotation speed.
BACKGROUND ART
In servo systems, generally, the difference (actual position deviation) between a command amount of movement and an actual amount of movement is periodically detected, and the drive of a servomotor is controlled in accordance with a torque command determined based on the difference (speed deviation) between a command speed, corresponding to the position deviation, and an actual speed. When the actual position deviation becomes larger than an allowable value, it is determined that the servomotor has been unable to follow the command for some reasons and hence an excessive error has occurred, and therefore, an alarm is generated to inform the occurrence of an abnormal condition.
Conventionally, the allowable position deviation for discriminating an excessive error is set to a large value, i.e., about 1.3 times the position deviation that can normally occur when the servomotor is rotated at a maximum speed. Therefore, when the motor is driven at a low speed, or when a currently stopped operating part (axis) of a direct drive robot is rotated at a low speed due to an interference torque generated by the movement of another operating part, a considerably long time elapses from the occurrence of an abnormal condition, e.g., a collision of a robot arm with an obstacle during a low-speed operation, until the position deviation reaches the allowable position deviation and thus the occurrence of abnormality is detected. As a result, a machine provided with the servomotor, such as a robot, may be damaged, or a workpiece may be excessively cut.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide an abnormality detecting method for a servo system which is capable of quickly detecting an occurrence of an abnormal condition over a wide range of motor rotation speed, particularly, in a low rotational speed range.
To achieve the above object, an abnormality detecting method of the present invention comprises the steps of: (a) simulatively effecting a response operation corresponding to a normal servo control during an execution of a servo control; and (b) determining an occurrence of an abnormal condition when a difference between an actual position deviation occurring in the servo control and a position deviation occurring in the simulated servo control becomes larger than a predetermined value.
As described above, according to the present invention, an occurrence of an abnormal condition in the servo system is determined when the difference between an actual position deviation occurring in the servo control and a position deviation occurring in the simulated servo control corresponding to a normal servo control becomes larger than the predetermined value. This makes it possible to quickly detect an occurrence of an abnormal condition over a wide range of motor rotation, particularly, in a low-speed rotation range. Accordingly, a damage to the machine, an excessive cutting of a workpiece, etc. can be positively prevented.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a functional block diagram showing a digital servo control device for carrying out an abnormality detecting method according to one embodiment of the present invention;
FIG. 2 is a block diagram illustrating the servo control device of FIG. 1 by using transfer functions; and
FIG. 3 is a flowchart of an excessive error detecting process executed by the servo control device of FIG. 1.
BEST MODE OF CARRYING OUT THE INVENTION
A digital servo control device for embodying an abnormality detecting method of an embodiment of the present invention comprises a microcomputer (not shown) which is arranged to achieve a function of a conventional digital servo circuit section 1 (FIGS. 1 and 2), and a function of an alarm generating section 2 (FIGS. 1 and 2) forming a principal part of the present invention.
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Fanuc Ltd.
Ip Paul
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