Stable posture tracking for modular spatial hyper-redundant serial arms using selective control points

Robotic arms with redundant degrees of freedom are known to exhibit characteristics that make them more suitable than their non-redundant counterparts in many manipulation tasks. These redundant degrees of freedom allow for multiple control objectives to be pursued simultaneously leading to increased efficiency, dexterity and versatility. Redundancy however brings about structural complexity, difficulties in tasks specification, challenging kinematics and dynamics and high computational cost. This work tackles kinematic hyper redundancy resolution in the context of posture (shape) control of a modular serial link arm by proposing a new take on formulating and solving the problem. In the proposed formulations, strategic points along the arm (termed control points) are explicitly controlled in such way that their overall motion steers the posture of the arm toward the desired target posture. These control points stem from the modular structure of the arm and are chosen in order to achieve specific control characteristics. Desired target posture outlines are specified intuitively and arbitrarily with continuous spline curves. The proposed method has demonstrated the ability to safely steer the arm towards intermediate postures which reduce the overall posture tracking error. It copes well with singularities and is capable of tracking target postures that are significantly distinct from the arm's initial posture. Numerical simulations on a 40 DOF arm are conducted to assess the validity and performance of the method.{GRAPHICAL ABSTRACT}