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High-Performance Mechanical Transmissions

V. Yuen, C. Teng, G. Lam, A. González-Palacios (U. Iberoamericana at León, Mexico), J. Angeles Force-and-motion transmission at uniform speed is mostly done with gear trains and, to a much less extent, with harmonic drives. Direct drives are also gaining acceptance in robotics applications. Gear trains exhibit many drawbacks, namely, backlash, sliding, and the requirement of special-purpose machine tools for tooth generation. To be sure, the foregoing drawbacks have been alleviated to some extent with highly expensive manufacturing methods. Harmonic drives, on the other hand, solve the problem of backlash, but not the one of power losses due to sliding, for their operation relies on very flexible components that bring about important amounts of power dissipation and undesirable flexibility in the transmission mechanism. Direct drives, in turn, solve the problem by eliminating the transmission mechanism completely. Nevertheless, direct transmission is not always possible, for the motors capable of delivering the required torques at the rather low speeds required in robotics applications are extremely massive, which brings about an inadmissible dead load to the mechanism. Upon considering the foregoing alternatives to gears, we decided to try to replace gear trains with cam mechanisms, while using a novel methodology developed completely at CIM. This is how we ended up with a mechanical transmission based on cam mechanisms, whereby all parts in contact roll with respect to each other. The outcome is a novel transmission that produces high reduction rates, of the order of 1 to 20, in a rather compact space, with negligible power losses, high stiffness, and ease of manufacturability, for all parts can be produced on standard numerically-controlled machine tools.

Thierry Baron
Mon Apr 7 12:54:24 EDT 1997