Joint coupling design of underactuated hands for unstructured environments

This paper examines joint coupling in underactuated robotic grippers for unstructured environments where object properties and location may not be well known. A simplified grasper consisting of a pair of two-link planar fingers with compliant revolute joints was simulated as it grasped a target object. The joint coupling configuration of the gripper was varied in order to maximize successful grasp range and minimize contact forces for a wide range of target object sizes and positions. The number of actuators was also varied in order to test performance for varying degrees of underactuation. A normal distribution of object position was used to model sensing uncertainty and weight the results accordingly. There are three main results: distal/proximal joint torque ratios of around 1.0 produced the best results, both for cases in which sensory information available for the task was poor and when sensing was good; an actuator for each gripper finger performs no better than a single actuator for both fingers; and that for good sensing, the gripper should be positioned off-center from the object, resulting in an increased lever arm and lower unbalanced contact forces on the object.