Development of an actively compliant underwater manipulator

Abstract

This thesis describes the design, construction, and evaluation of an actively compliant underwater manipulator for installation on the underwater remotely operated vehicle (ROV) JASON. The goal of this work has been to produce a high fidelity force-controllable manipulator exhibiting no backlash, low stiction/friction, high backdriveability, wide dynamic range, and possessing a large work envelope. By reducing the inherent dynamic nonlineari ties, a wide range of joint compliances can realistically be achieved. This feature is important when implementing various force control schemes, particularly impedance control. In addition, a mechanically "clean" transmission reduces the need for sensors and allows the user to rely on integral motor sensors to provide torque, position, and velocity information. A three axis manipulator rated to full ocean depth was built. Each of the revolute joints is driven by a DC brushless sensorimotor working through a multi-stage cable/pulley transmission. The manipulator mechanism and wiring is fully enclosed by cast aluminum housings filled with mineral oil. Mineral oil functions to pressure compensate and lubricate the system. Exterior surfaces of the manipulator are smooth and continuous, and were designed to act as work surfaces. Joints one and two have a 240° range of motion, while joint three can rotate 380°. The manipulator transmissions are modeled and predictions of manipulator stiffness, dynamic range, payload capacity, and hysteresis are compared with the results of tests conducted on the actual system. Operation of the cable/pulley transmissions are evaluated and suggestions for improvements are given.