Abstract

A safety interlock circuit for a vacuum cleaner system is disclosed for interrupting the flow of current through conductors of a vacuum hose and handle assembly whenever an electrical attachment accessory is disconnected from the handle assembly during operation of the vacuum. A pulse-type reset circuit is also disclosed for re-enabling current flow through the conductors of the vacuum hose and handle assembly after the electrical attachment accessory has been reattached to the handle assembly. The safety interlock circuit of the preferred embodiment comprises a relay coil, a plurality of normally open relay contacts, and a current sensing resistor, all connected in series with an AC power source and a motor of the electrical attachment accessory. A voltage doubler is also connected in parallel with the current sensing resistor for supplying a DC voltage to the relay coil. The safety interlock circuit operates to interrupt current flow by opening the normally open relay contacts whenever the relay coil is de-energized. The pulse-type reset circuit comprises a momentary contact pushbutton reset switch, a plurality of transistors, a capacitor, and a plurality of optical-electrical coupling devices. The pulse-type reset circuit operates to supply a pulse of current to the relay coil to temporarily energize the relay coil to thereby close the normally open relay contacts, thereby allowing current flow through the current sensing resistor and allowing the voltage doubler to apply a voltage across the relay coil to sustain operation of the motor.