Improving grasp robustness via in-hand manipulation with active surfaces

In this article, we discuss a strategy to employ and exploit the active surfaces of an articulated robotic grasping device for in-hand manipulation in order to achieve a robust enveloping grasp starting from an initially acquired dexterous fingertip grasp. The presented work was carried out within the scope of the EU-FP7 project RobLog (http://www. roblog.eu/), which is aimed at using the Parcelrobot platform shown in Fig. 1 for the autonomous unloading of shipment containers filled with geometrically simple objects (such as boxes, barrels or coffee sacks). Here, the underlying idea is to simplify the design and control of the necessary articulated grasping device and to tailor it to preserve specific desired features. To this end, the Velvet Fingers gripper [1], [2] was developed during the course of the RobLog project. Each of the gripper’s two fingers has a planar manipulator structure with two joints and active surfaces which are implemented by coupled conveyor belts on the inside of the two phalanges. The mechanical structure is underactuated and comprises only one actuated Degree of Freedom (DoF) for opening and closing and two DoF for the belt movements. If, during grasping, the proximal phalanges are blocked by an object, the gripper’s distal phalanges continue to “wrap around” and envelope it in a firm grasp.