Practical considerations on proprioceptive tactile sensing for underactuated fingers

Underactuated mechanisms are becoming more prevalent in new robotic graspers, partly because of the desire to reduce the complexity and associated costs of conventional fully actuated systems. With the same objective of reducing the costs of the components needed to provide a sensory feedback, several authors have worked on finding alternatives to external tactile sensors. This paper is about one of these methods, namely proprioceptive tactile sensing, especially designed for underactuated fingers. It focuses on certain practical considerations, such as the impact of the curvature of the grasped object and the reconfiguration of the finger after the contact, and proposes the analysis of their influence on the precision of the algorithm. To this aim, simulations and experimental data are provided for different grasping scenarios. It is shown that the effect of local curvature remains limited compared with other causes of imprecision such as friction in the system. It is also demonstrated that the reconfiguration, if within reasonable limits, does not cause significant variations on the estimation of the contact location.