Sensitive Active Surfaces on the Velvet II Dexterous Gripper

The Velvet Fingers [1] is a dexterous under-actuated gripper for unstructured industrial environments. It offers enhanced manipulability by means of Active Surfaces (AS) on its fingers, i. e., surfaces able to emulate different levels of friction and to apply tangential thrusts to the contacted object. The usefulness of the AS (implemented by controlled conveyor belts) is discussed in [2]. Although their benefits are substantial, their main limitations are the lack of force feedback and missing information of the contact point location, as well as limitations on the fictitious friction range. In this article we discuss the employment of an intrinsic force/torque (F/T) sensor mounted between the frame of the phalanx and the AS which are henceforth referred to as Sensitive Active Surfaces (SAS). For this purpose the experimental device shown and described in Fig. 2 has been set up at the University of Pisa. Furthermore, we implemented and tested an algorithm for the determination of contact point locations, as well as a variable friction control algorithm. The geometrical portion of the belt involved in a possible contact with a grasped object is formed by a plane corresponding to the outer conveyor belt surface and two semicircles associated with the belt rollers (see indicators (3), (4) and (8) in Fig. 2). Since the sensing surface is convex, the