FREQUENCY-DOMAIN CONSEQUENCES OF LOW-VELOCITY FRICTION - THE NONMINIMUM-PHASE BEHAVIOR OF GEARED TRANSMISSIONS

We make several experimentally based observations that enhance the und erstanding of the dynamics of geared robot drives. We show that: (1) a t low velocities, a gear transmission can behave as a nonminimum-phase system; (2) this nonminimum phase behavior is intimately related to t he dynamics of friction at gear-tooth contact; and(3) by virtue of com pliance in bearings and supports, gear drives do nor have a constant t ransmission ratio overall frequencies, but instead show step changes i n transmission ratio. These findings guide the development of a new dy namic model of a gear transmission that captures these salient charact eristics and makes explicit the different torque-transmission modes. W e remark on the implications of these findings for robot force control .