Motion Planning for Non-Holonomic Mobile Manipulator Based Visual Servo under Large Platform Movement Errors at Low Velocity

Abstract

A non-holonomic mobile manipulator (NMM) is termed here as a robotic system in which a manipulator is mounted on a non-holonomic mobile platform. This paper presents a method for planning a motion of NMM for effectively performing eye-on-hand visual servo especially when there are excessive errors in platform movement at low velocity due to friction, slippage, backlash, or flexibility. Due to excessive errors in platform movement at low velocity, direct application of a conventional method for manipulator based visual servo to an NMM may not be effective for generating servo motions. In this paper, we propose a method of generating servo motions for an NMM based visual servo, which is not affected by the excessive platform movement errors at low velocity. We achieve this by generating a series of discrete optimal poses of NMM on-line as a higher level plan for servo motion. More specifically, NMM is to move successively to the chosen poses while maintaining a proper velocity for avoiding excessive movement errors and satisfying non-holonomic constraints until it reaches the final poses where the manipulator alone can servo to the target object while the platform can be kept stationary. We use the virtual visual servo by E. Marchand and F. Chaumette to make sure that the manipulator is able to reach a target object without violating its joint limits, its boundary of workspace and singularities. The on-line selection of local mobile platform poses is based on a local random search. Finally, simulations on a redundant NMM are carried out to demonstrate the effectiveness of the proposed method.