Electricity: motive power systems – Positional servo systems – Program- or pattern-controlled systems
Patent
1991-11-21
1993-04-20
Ip, Paul
Electricity: motive power systems
Positional servo systems
Program- or pattern-controlled systems
318565, 318563, 3644742, 901 9, B25J 1906
Patent
active
052045986
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of stopping an industrial robot after the industrial robot collides with an object, and more particularly to a method of stopping an industrial robot for increased safety.
2. Description of the Related Art
When an industrial robot (hereinafter referred to as a "robot") collides with foreign matter due to a teaching process error or the like, it is necessary to stop the operation of the robot for the safety of the operator and the protection of the robot. It is customary to apply a speed command of nil to the servomotor associated with each axis with respect to which the collision has been detected, thereby producing a reverse torque to stop the operation of the robot in as short a period of time as possible. For an axis with respect to which no collision is detected, an alarm is issued after a position deviation or error, which is the difference between a position command for the servomotor and an actual position thereof, takes a value greater than a predetermined value, thus cutting off the drive current supplied to the servomotor.
According to the above conventional process, since a collision is detected with respect to each axis, and a reverse torque is applied to any axis with respect to which a collision is detected, the operation of the axis is stopped in a short period of time. For an axis with respect to which no collision is detected, however, its operation based on a motion command is continued until the position command for the axis exceeds a predetermined value and an alarm is issued. Therefore, the robot moves along a path different from a taught path, resulting in a safety failure. Inasmuch as the de-energization of the servomotor for the axis with respect to which no collision is detected is delayed, the complete stoppage of the robot is also delayed.
SUMMARY OF THE INVENTION
In view of the aforesaid drawbacks of the conventional industrial robots, it an object of the present invention to provide a method of stopping an industrial robot within a short period of time for an axis with respect to which no collision is detected.
To accomplish the above object, there is provided in accordance with the present invention a method of stopping an industrial robot having a plurality of axes drivable by respective servomotors after a collision of the industrial robot with foreign matter is detected, the method comprising the steps of, after the collision is detected, setting a speed command for the servomotor for the axis with respect to which the collision is detected, to "0", thereby producing a reverse torque to stop rotation of the servomotor, calculating a position error as the difference between a position command applied to the servomotor and an actual position thereof after elapse of a predetermined period of time, activating an alarm if the position error of the servomotor exceeds a predetermined value, or if the position error of another servomotor exceeds the predetermined value, and cutting off currents supplied to all the servomotors for thereby stopping movement of the industrial robot.
According to the present invention, there is also provided a method of stopping an industrial robot after a collision of the industrial robot with foreign matter is detected, the method comprising the steps of, after the collision is detected, informing a host processor of the collision, setting a speed command for the servomotor for the axis with respect to which the collision is detected, to "0", thereby producing a reverse torque to stop rotation of the servomotor, cutting off a current supplied to the servomotor after elapse of a predetermined period of time, cutting off currents supplied to all the servomotors under the control of the host processor in response to the informed collision, for thereby stopping movement of the industrial robot.
The monitoring of a position error of a servomotor for the axis with respect to which the collision is detected is stopped, and a speed command is set to "0". A rev
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Hamura Masayuki
Ito Susumu
Sakai Tamotsu
Torii Nobutoshi
Fanuc Ltd.
Ip Paul
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