Control circuit for hospital bed

Abstract

Beds, such as hospital beds, in which at least some portion of the bed is movably actuated by an electric motor (or motors) are provided with a control circuit to determine proper energization of the motor from an AC power source. Since the AC signal from the power source could be harmful to the person selecting a desired direction of travel of the movable portion of the bed, the selecting portion of the control circuit is isolated by appropriate transformers from the power portion that supplies the motor. Bidirectional switching devices, such as triacs, are utilized to convey the power to the motor. Other bidirectional switching devices, such as triacs, are used to gate the power handling triacs through appropriate gating transformers. A phase shifting arrangement is utilized in connection with the gating transformers to provide proper commutation of the power handling triacs. Supplemental features, such as additional locations of the control and limit switches to establish maximum distance of travel may be employed. When both head and knee movable portions are utilized, a contour circuit may be employed to automatically adjust the knee portion upon variation of the head portion, within certain limits of travel. A disconnect arrangement employing a self-gating triac is utilized to automatically open a hot line to the common of one of the motors unless the energizing circuit for that motor is completed.