Manipulation of polygonal objects with two wheeled-tip fingers: Planning in the presence of contact position error

This paper addresses the planning problem of object manipulation using wheeled-tip robots considering the wheel–object contact positioning error. The term wheeled-tip refers to a new mechanism that incorporates active wheels at robot’s fingertips and allows the grasp contact-point to move along the object’s surface. The benefits of unlimited rolling contact is achieved at the cost of contact positioning error that may cause the manipulation to fail. We propose a probabilistic based algorithm for robot motion planning that in addition to being collision free, guarantees the stability of the grasp throughout the planned path. To do so, first we introduce an algorithm that ensures the kinematical stability of the grasp during manipulation by respecting the force closure constraint. Further we extend the algorithm to address the practical uncertainties involved in the position of wheel–object contact points. The proposed algorithms can be employed for manipulators with limited rolling contacts, as well. The algorithms have been tested and the results prove that the planned path can be trusted in uncertain situations.

Research highlights
► In a wheeled-tip finger, an active wheel is incorporated at the robot’s fingertip.
► It allows the grasp contact-point to move along the object’s surface, unlimitedly.
► Contact-point motion results in contact-positioning error and may cause the manipulation to fail.
► Our PRM-based algorithm guarantees the stability of the grasp throughout the planned path.
► The algorithm is developed for polygonal objects with two wheeled-tip fingers.