Evaluation of Spatial Isotropy of Output of Robotic Mechanisms.

Abstract

First, new constraints on the manipulating force/moment and the translatory/angular velocity at the end effector of robots are proposed, in which the values with different dimensions such as force and moment and such as translatory velocity and angular velocity can be treated as numerically equivalent. Under those constraints, the maximum output power at the end effector can be calculated. And the power transmission index which is defined as the ratio of the maximum output power at the end effector mentioned just above to the sum of the maximum power of all actuators in the mechanism is proposed as a new quantitative measure of spatial isotropy of output of robotic mechanisms. The main characteristics of the power transmission index is summerized as follows : (1) it is a nondimensional quantity that varies between zero and one, (2) its value equals zero at a singular point which is commonly observed in both in-parallel actuated mechanisms and serial mechanisms and is also peculiarly observed in in-parallel actuated mechanisms. Illustrative examples on a planar in-parallel actuated mechanism and a serial mechanism with three degrees of freedom are shown and relationships between the power transmission index and conventional evaluation values for robotic mechanisms such as transmission index and manipulability are discussed.