Importance

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Abstract

A linear actuator having an output shaft having a pair of driven wheels mounted thereon. One of the driven wheels is rotatably mounted in a fixed plane and has a drive nut for an associated thread on the output shaft. The other drive wheel is rotatably fixed to the output shaft. An input shaft is in side-by-side relationship with the output shaft and adapted to be rotated by a suitable power source. The input shaft provides a drive wheel for each of the driven wheels, with the ratio between each drive and driven wheel set being chosen to rotate the driven wheels at different speeds in the same rotational direction and thereby produce a controlled axial movement of the output shaft in a direction depending upon the relative rotation of the driven wheels. The other driven wheel and the drive wheel of its set are in the form of meshing helical gear wheels. A fail-safe arrangement is provided and has a clutch between the drive wheels of the input shaft, a back-drive for the output shaft, and biasing means for effecting a back-drive. The arrangement is such that the meshing helical gears impart an axial force to engage the clutch only while power is supplied, and the biasing means are operative to back-drive the output shaft to a fail-safe position when the power is terminated.

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First Claim