US 4,904,909 A · Controller for electric clamp

Abstract

A controller for an electric clamp closes the clamp rapidly at first, then runs at a slower speed while contacting the workpiece, and speeds up again after contacting it, to close with full clamping force. Arrival of the clamp at the position for slowing down is directly detected by means of a proximity sensor, as are arrivals at other positions. The speed of operation is relatively insensitive to the voltage of its AC electrical power source because an open-loop compensating signal controls the pulse duration of rectified DC pulses that drive the motor. The controller has dynamic braking that is applied between individual pulses of pulse trains of motor current; this results in sigfificant increase in swings of current values for a given motor speed, that reduces harmful effects of mechanical friction. Two jogging speeds are selectable.

Claims13

Dependent claims

A controller for an electric clamp which is driven open and closed by an electric motor to which power is connected upon commands, comprising in combination:

(a) means responsive to a command to close the clamp, for providing high-speed travel during a run-up in the closing direction;
(b) proximity sensing means for directly detecting when the clamp reaches a predetermined position, and for initiating thereupon an interval during which the speed of travel is lower;
(c) means for terminating the lower-speed travel after a predetermined time;
(d) means for providing higher power to the clamp thereafter during completion of its closing;
(e) sensing means for directly sensing that the clamp has reached a closed position and for interrupting power flow to the motor thereupon.

2 more elements

A controller for an electric clamp having a DC electric motor powered by unidirectional rippling voltage derived by unregulated rectification of an AC power source, and having apparatus for open-loop compensation to reduce the effects of AC variations of source voltage on motor speed, comprising:

(a) sensing means for sensing unregulated voltage and producing a control signal in response thereto;
(b) comparator means for comparing the instantaneous value of the rippling voltage with a threshold based upon said control signal and for providing an output dependent upon whether the rippling voltage or the threshold is greater;
(c) control means for producing, in response to said output of said comparator means, a train of pulses that are applied to the motor, said pulses having widths that are determined by the time that the instantaneous value of the rippling voltage exceeds the threshold.

Dependencies are inferred from the claim text.

Controller for electric clamp

Life of this patent

Controller for electric clamp

Life of this patent

Abstract

Claims13