Method and apparatus for stopping an industrial robot

A method of stopping an industrial robot after a collision of the industrial robot with foreign matter is detected, said method comprising the steps of:

• after the collision is detected, informing a host processor of the collision;
• setting a speed command for a servomotor for an axis with respect to which the collision is detected, to "0", to produce a reverse torque to stop rotation of said servomotor;
• cutting off a current supplied to said servomotor after elapse of a predetermined period of time;
• and
• cutting off currents supplied to all the servomotors under control of said host processor in response to said informing of the collision, for thereby stopping movement of said industrial robot.

A robot control system for a robot having a plurality of axes drivable by servomotors corresponding thereto, comprising:

• position deviation means for receiving a position command and a detected position for each of the servomotors and for generating a position deviation corresponding to each of the servomotors;
• a read-only memory storing a control program for at least one axis;
• collision detection means for detecting a collision condition along one of the axes;
• speed command means, operating in accordance with the control program, for setting a speed command to zero for a servomotor corresponding to the one of the axes upon detection of the collision condition;
• and
• current supply means for cutting off current to all of the servomotors after a predetermined period of time has elapsed since setting of the speed command to zero if the position deviation for any of the servomotors exceeds a predetermined value.

A robot control system for a robot having a plurality of axes drivable by servomotors corresponding thereto, comprising:

• a read only memory storing a control program;
• a plurality of axis control circuits, each corresponding to one of the servomotors, to receive a position command, a speed command, an alarm signal and an actual position of the servomotor corresponding thereto, to generate a position error in dependence upon a difference between the position command and the actual position of the servomotor corresponding thereto and to control the servomotor in dependence upon the position error, the speed command and the alarm signal, including cutting off current supplied to the servomotor upon receipt of the alarm signal;
• and
• at least one digital signal processor, operatively connected to said axis control circuits and said read only memory, for executing the control program to set a speed command to zero for a servomotor producing movement along an axis when a collision condition is detected for movement along the axis and, after a predetermined period of time has elapsed since the speed command was set, to produce the alarm signal if the position error generated by any of said axis control circuits exceeds a predetermined value.