Sensing subsystems and force control of the AMADEUS dextrous underwater gripper

This paper presents the design of the fingertip sensing subsystem constructed for use in a dextrous underwater gripper. Two distinct types of sensor were developed specifically for this application, a fingertip force sensor and a slip sensor. The force sensor is used to determine the force exerted by the gripper on the target object, and hence allow the force loop closure required for carrying out dextrous manipulation and the handling of delicate marine samples. The function of the slip sensor is to detect the occurrence of slippage between the fingertip and the target, and this information can be used in a variety of ways, for example providing a warning system to the force control loop or enhancing the gripper's exploratory capabilities in areas of poor visibility. The force sensor is a simple robust device based on strain gauge technology and is incorporated on an artificial finger tip mounted at the extremity of the gripper finger. The slip sensor is an extremely small piezoelectric-based device capable of being shaped to suit the curvature of the fingertip. The novel nature of the gripper's technology and construction means that its dynamic characteristics were previously poorly understood. Closed loop control requires that identification of the manipulator dynamics be established, and these are presented along with the first results for closed loop control.