Importance

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Abstract

A safety device for power driven equipment which mechanically locks an access door on the equipment in closed position until the power drive motor has coasted to a stop. A manually operated locking bolt for the access door is pivotally mounted on a housing in which the control components for the safety device are contained. A locking plate is rigidly mounted on the pivot shaft of the locking bolt within the housing for movement with the shaft and bolt. A solenoid operated locking lever is pivotally mounted in the housing and is engageable with the locking plate when the solenoid is energized to prevent movement of the locking bolt from its door locking position. A bolt mounted on the locking plate actuates a switch which is electrically connected in the drive motor control circuit to open the circuit when the lock bolt moves to an unlocked position. A voltage sensitive relay (ZVM) maintains the control solenoid energized even after the drive motor is deenergized by the voltage produced by the back EMF of the coasting motor rotor. Therefore, only when the motor rotor becomes or approaches a stationary condition will the ZVM deenergize the solenoid which disengages the locking lever from the locking plate to permit the locking bolt to be manually moved to unlocked position for opening of the access door of the equipment.

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First Claim