Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1996-07-08
1998-05-12
Ro, Bentsu
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
3185682, G05B 1918
Patent
active
057511306
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for determining time constant for acceleration and decelerations of a servomotor for driving the axes of an industrial robot, which are to be determined when a track program is performed for the robot.
BACKGROUND ART
In preparing a modern track program for an industrial robot (hereinafter referred to simply as "robot"), a commonly employed system is designed so that a definite time constant is set with every motion, and servomotors (hereinafter referred to simply as "motors") for driving the axes of the robot are made to be accelerated and decelerated smoothly with a filter of the time constant applied. In setting the time constant, the concept of maximum acceleration control is usually applied in order to shorten cycle times of robot operation.
In the conventional maximum acceleration control, the maximum acceleration is determined by separately calculating moments and inertias that act on the motors of the individual axes at various points of time during the operation, and, based on the result of the calculation, time constants are set so that the servomotors can generate their respective maximum torques.
In general, however, a robot moves on a target track as a plurality of axes thereof are actuated simultaneously, so that torques (interference torques) attributable to the motions of other axes act on each axis of the robot. According to the conventional method, however, even though the time constants are set so that the motors of the individual axes can generate their maximum torques on calculation, the torques may possibly be saturated on account of the interference torques, or on the contrary, the robot sometimes may be actuated with a small torque generated therein.
If the torques are saturated, the accuracy of the robot track worsens. If the robot is operated with a small working torque, then it implies that the cycle times are not satisfactorily shortened by making the robot operate to its capacity. Thus, according to the conventional method for the robot track programming, problems are inevitable because the time constants are not settled in consideration of interference torque components.
DISCLOSURE OF THE INVENTION
The object of the present invention is to improve the track accuracy and to shorten the cycle time of a robot by setting, in consideration of the interference torques attributable to the motions of other axes, the time constants for acceleration and deceleration, which are to be determined when programming for the track of a robot having a plurality of axes to be driven individually by servomotors.
In order to achieve the above object, according to an aspect of the present invention, there is provided a time constant setting method for a track program for a robot having a plurality of axes driven individually by servomotors, comprising steps of: least two axes out of said plurality of axes, which are shortest as far as torques generated will not saturate, at the start point and end point of a motion section where the speed of each axis at the start point and end point can be regarded as zero, taking into consideration the effects of interference torques exerted between said at least two axes, by online software processings of a robot controller which controls said robot; and which controls said robot.
According to another aspect of the present invention, there is provided a time constant setting method for a track program for a robot having a plurality of axes driven individually by servomotors, comprising steps of: least two axes out of said plurality of axes, which are shortest as far as torques generated will not saturate, at the start point and end point of a motion section where the speed of each axis at the start point and end point can be regarded as zero, taking into consideration the effects of interference torques exerted between said at least two axes, by online software processings of a robot controller which controls said robot; and axes in the robot controller which controls said robot.
Preferably, the sof
REFERENCES:
patent: 5004968 (1991-04-01), Mizuno et al.
patent: 5325467 (1994-06-01), Torii et al.
English language Patent Abstract & JP 4-306711, filed Oct. 29, 1992, letoshi ITOU.
Hara Ryuichi
Nagayama Atsuo
Fanuc Ltd.
Ro Bentsu
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