Importance

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Abstract

A linear drive, particularly useful for locking or unlocking a door lock mechanism or the like permits manual operation by providing an output shaft that can move freely regardless whether the output shaft is in extended or retracted positions without back driving the motor. The output shaft is coaxially slideably situated over a screw which moves a nut that is theadingly engaged therewith and moves inside the output shaft along the axial direction of the screw. The output shaft is not threadingly engaged with the screw. The output shaft thus is freely movable relative to the screw, which results in essentially zero back drive of the screw and the motor. To provide for manual operation, the nut is automatically moved back to its neutral position every tie the output shaft is extended or retracted by a torsion spring or the like which can store energy therein. Whenever the motor is operated to drive the screw, the spring gear is also rotated, which causes the spring to store energy therein. As soon as the motor is turned off, the energy stored in the spring causes the worm gear to rotate in the direction opposite to the last motor driven direction to move the nut to the neutral position it was in prior to energization of the motor.

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First Claim