Realization of Pseudo Mechanism Function Using a Worm Gear

Abstract

A conceptional idea of the pseudo mechanism is proposed. This concept means that a different mechanical feature from the natural one appears on the mechanism by means of control method. For example, a worm gear behaves like an one-way clutch. Generally, worm gears cannot be driven by load torque because of its mechanical stop feature. But the worm gear of this concept can be driven by load in specified direction, and the rotation to the other direction is prohibited. This asymmetrical motion is achieved by a switching operation of a force feedback control. The applied load torque is detected and fed back positively to a position servo control system in order to achieve power assist control. The worm gear seems to be driven by the load torque and it resembles to a spring motion. If the force feedback line is cut off, the drive system cannot be driven by a load. The switching operation of the force feedback line causes to a selection of back drivable feature or mechanical stop feature. The switching condition is set by a direction and threshold value according to the required mechanical feature. The pseudo mechanical worm gear also pretends as a torque limiter or a ratchet.

Worm gear mechanism with switchable backdrivability

“…The equation of motion can be described as shown in Eq. (11), and the displacement z can be calculated.…”

“…To provide the worm gear with backdrivability, a technique that uses a feedback control based on the measured torque was proposed [11]. However, if back-drivability is provided mechanically, the response and the reliability can be enhanced.…”