Steerability in Planar Dissipative Passive Robots

Steerability is intuitively the ability to change directions. In this paper, a formal definition is given for the steerability of a robot achieved either passively or actively. A dissipative passive robot uses only passive actuators such as brakes and clutches (a clutch is essentially a brake plus a gearbox) to redirect or steer operator-imposed motion by dissipating energy. While it has safety and ergonomic advantages, which are essential for human interactions, it also has difficulties in redirecting certain motions since passive actuators cannot add energy. The force generated from a passive actuator is used to measure the steerability. A steerability theorem was then developed for a manipulator with generalized passive actuators. The steerability analysis for an example diamond-shaped manipulator shows the difference in steerability when using only brakes or a combination of brakes and clutches. Further analyses show the difference comes from the ability of a clutch to change the direction of the generated force in the subject robot by altering the effective gear ratios.