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Purvis Industries

Backdriving A Gearbox

Posted on Monday Oct 28, 2019 at 08:29PM in General

Where Self Locking is the inability to drive the output shaft of a gearbox, backdriving is the ability to drive the output shaft.

This essentially makes the gearbox become a speed increasing device.  This can be done intentionally or unintentionally and can occur in various ways.  Backdriving can occur when the applied load overcomes the frictional resistance or holding power of the rotating elements in the gearbox, causing the output shaft to speed up.  This is more common in lifting and inclined applications because gravity assists the force pulling the load down.

A gearbox that is backdriving may cause the motor to overspeed, which may lead to damage to the gearbox, motor or other system components. 

Intentionally using the gearbox as a speed increaser will also cause backdriving.  Not all worm gears can be backdriven because of their tendency to lock when driven in reverse rotation.  Worm gear sets generate more heat than other gear types due to the amount of sliding friction produced while rotating.  Spur and helical gears are commonly used as speed increasers.  Under a backdriving or speed increasing operation, increased noise and temperature levels may become undesirable. 

If an application has a sufficient amount of reverse momentum that may cause the load to overhaul the frictional resistance of the gear set in a reducer, a “backstopping” or “one direction” mechanical clutch should be used to prevent backdriving.  If the application requires the speed to be increased, carefully review and select a gearbox suitable for that type service. 

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