In most of the gear drives, when the driving torque is suddenly reduced as a result of power off, torsional
vibration, power outage or any mechanical failure at the transmission input side, then gears will be rotating
either in the same direction driven by the system inertia, or in the opposite direction driven by the resistant
output load due to gravity, spring load, etc. The latter condition is known as backdriving. During inertial motion
or backdriving, the driven output shaft (load) becomes the driving one and the driving input shaft (load)
becomes the driven one. There are many gear drive applications where the output shaft driving is less
desirable. In order to prevent it, different types of brake or clutch devices are used. However, there are also
solutions in gear transmission that prevent inertial motion or backdriving using self-locking gears without any
additional devices. The most common one is a worm gear with a low lead angle. In selflocking worm gears,
torque applied from the load side (worm gear) is blocked, i.e. cannot drive the worm. However, their
application comes with some limitations: the crossed axis shafts’ arrangement, relatively high gear ratio, low
speed, low gear mesh efficiency, increased heat generation, etc.

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