Pivoting rotor ratchet mechanism for worm gear potentiometer

Abstract

A ratcheting mechanism for a multiturn variable resistance device, of the worm screw-actuated type, has mutually engageable stopping members on the rotor and in the housing, limiting rotor travel beyond first and second limits. The stopping member in the housing has an inclined surface on one side which pivotally lifts the rotor against the force of the electrical contact spring (carried on one side of the rotor in contact with a resistive element), when the rotor reaches the first limit of travel. The pivoting action compresses the contact spring while allowing the spur gears on the rotor momentarily to disengage from the worm gear. This disengagement releases the spring, which then urges the rotor back into a gear-engaging position. The rotor is provided with at least one axially-shortened spur gear tooth positioned so as to be engageable with the worm gear when the rotor is at the second limit of travel. The further rotation of the rotor beyond the second limit of travel being inhibited by the engagement of the stopping member, the engagement of the shortened tooth with the worm gear pivotally lifts the rotor, thereby compressing the spring and momentarily disengaging the spur and worm gears. Following the momentary disengagement, the spring is released, thereby urging the rotor back into a gear-engaging position.