Maximum Efficiencies of Conventional Mechanical Paradox Planetary Gears for Reduction Drive.

Abstract

Mechanical paradox planetary gears are suitable for power transmissions of current robots, such as space manipulators, which drive large-inertia loads, because the gears offer high reduction ratio, small size, light weight and high reliability. However, mechanical paradox planetary gears are subject to a drawback in that their efficiencies are lower than those of conventional planetary gears. The efficiencies of mechanical paradox planetary gears are hence theoretically analyzed and evaluated by defining the tooth number modification of a planet gear to deal with all the possible combinations of tooth numbers. The following results are obtained : the efficiencies are greatly influenced by the efficiencies of the planet and internal gear pairs ; the maximum efficiencies are minimally influenced by the reduction ratio, and they are obtained when the factors of the contact ratio of the gear pairs are approximately equal ; the maximum efficiency is approximately 78% if the tooth surface friction coefficients are 0.1.