1998 IEEE International Conference on Robotics and Automation

Motion Planning for a 3-DOF Robot with a Passive Joint

K. M. Lynch, N. Shiroma, H. Arai, and K. Tanie

Abstract

This paper studies motion planning from one zero velocity state to another for a three-joint robot in a horizontal plane with a passive revolute third joint. Such a robot is small-time locally controllable on an open subset of its zero velocity section, allowing it to follow any path in this subset arbitrarily closely. However, some paths are ``preferred'' by the dynamics of the manipulator in that they can be followed at higher speeds. We describe an algorithm that plans collision-free paths in the robot's configuration space, where the motions correspond to dynamically preferred robot motions. Thus the problem of planning fast trajectories in the robot's six-dimensional state space is reduced to the computationally simpler problems of planning paths in the three-dimensional configuration space and time-scaling the paths according to the manipulator dynamics.
Available as postscript (706 K) and pdf (161 K)

See the video of a 3 DOF robot with a passive (unactuated) joint navigating through an obstacle field.


Figure 1: A collision-free motion for a 3R robot with a passive third joint. This motion was successfully implemented on the MEL experimental underactuated manipulator of Figure 2.


Figure 2: The experimental underactuated manipulator at the Mechanical Engineering Laboratory in Tsukuba, Japan.

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