Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1997-02-28
1998-09-22
Sircus, Brian
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
318561, 318566, 318574, G05B 1300
Patent
active
058119523
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method of setting an accelerating/decelerating motion of an industrial robot, and more particularly to an accelerating/decelerating motion setting method in which the maximum acceleration is determined in planing a target track, taking dynamic characteristics of the robot into consideration.
BACKGROUND ART
It is preferable to realize an accelerating/decelerating motion for generating the maximum value of a driving torque (maximum torque) in acceleration/deceleration in order to move the robot efficiently. However, a large interference torque would act on an axis of the robot due to the inertia fluctuation and the motion of other axes during movement from its inherent structure, and the effect of dynamical friction cannot be negligible. It is therefore difficult to perform an acceleration/deceleration control as to generate the maximum torque with precision.
Thus, in the maximum acceleration controlling method which has been popularly adopted in this field of art, an interference torque has not been taken into consideration in determining the maximum acceleration of an accelerating/decelerating motion when planing the target track. Further, it has been a common practice to evaluate the effect of dynamical friction at a fixed value and set the maximum torque of a motor smaller by an amount corresponding to the fixed value.
In the foregoing conventional method, since the interference torque is not taken into consideration, the necessary torque for actual motion occasionally exceeds the maximum torque which the motor can output, or otherwise the maximum torque of the motor is not fully outputted.
In the former case (torque saturation), since the robot cannot follow a motion command, precision of the track would become worse. In the latter case, adequate performance of the robot cannot be achieved to lower the operating efficiency. Further, since the effect of dynamical friction is considered unilaterally, a torque smaller than necessary is used during deceleration.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide a method of setting an accelerating/decelerating motion of a robot, in which an interference torque and effect of dynamical friction are properly taken into consideration, thereby improving the track precision and the operating efficiency.
In the present invention, a position at which a torque acting on the robot axis during accelerating or decelerating becomes maximal is estimated using a successive calculating process, and an accelerating/decelerating motion is set based on the estimated torque. Further, by considering the effect of dynamical friction in opposite directions during acceleration and deceleration, to achieve the maximum torque with more precision in the accelerating/decelerating motion.
According the present invention, a condition for the accelerating/decelerating motion is set, taking the following three conditions into account when planning a target track:
1) A constraint condition formula for each axis in order to realize the target track of the robot. Generally this formula is given as a Jacobean which defines a conversion relation between the position/posture of a tip point of a tool in an rectangular coordinate system and each axis value.
2) Motion equations of the robot, based on which the interference torque is calculated.
3) A constraint condition formula regarding the maximum torque of the robot. The effect of dynamical friction is evaluated in opposite directions in this constraint condition formula when taking the effect into consideration.
By executing the following processes A-F with respect to the accelerating and decelerating motions, a proper condition for the accelerating/decelerating motion is set.
A. A certain position in the target track is set, and an acceleration such as to generate the maximum torque is calculated based on the motion equations of the robot.
B. A position at which a command torque becomes maximal when the robot is moved (in an accelerated motion or a decelerated
REFERENCES:
patent: 3665493 (1972-05-01), Glowzewski et al.
patent: 4463297 (1984-07-01), Bennett et al.
patent: 4518909 (1985-05-01), Friedli et al.
patent: 4769583 (1988-09-01), Goor
patent: 4973895 (1990-11-01), Torii et al.
Kato Tetsuaki
Nagayama Atsuo
Fanuc Ltd.
Sircus Brian
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