Experimental investigations of sensor-based surface following tasks by a mobile manipulator.

摘要

This paper discusses experimental investigations of the feasibility and requirements of simultaneous external-sensor-based-control of the wheeled platform and the manipulator of a mobile robot. The experiments involve 3-D arbitrary surface following by the manipulator while the platform moves along a predefined trajectory. A variety of concave and convex surfaces were used in the experiments, during which target and measured values of the platform and arm positions and orientations, together with the surface absolute location and normal estimates, were logged at 10 Hz. For all experiments, the data logs showed significant noise, at high frequency, in the calculated surface normal values despite smooth tracking of their target values by the arm and the platform, with typical closed loop delays between target and achieved values of the order of 100 msec. This high-frequency noise in the calculated values is conjectured to result mainly from the arm's transmission cables compliance and backlash in the spherical wrist gears. On the other hand, the end-effector distance to the surface showed some low frequency errors of the order of (plus minus)20%The two major sources of these low frequency errors appeared to reside respectively in the low values of the velocity bound and gain parameters utilized to filter the high frequency noise in the calculated normal values prior to using them as input to the arm control, and in the rolling contact of the platform's rubber-coated wheels on the ground where significant errors in the platform's positions and orientations can accumulate.