A Vision-Based Positioning System with Inverse Dead-Zone Control for Dual-Hydraulic Manipulators

The robotic platform in this study is being used for research into assisted tele-operation for common nuclear decommissioning tasks, such as remote pipe cutting. It has dual, seven-function, hydraulically actuated manipulators mounted on a mobile base unit. For the new visual servoing system, the user selects an object from an on-screen image, whilst the computer control system determines the required position and orientation of the manipulators; and controls the joint angles for one of these to grasp the pipe and the second to position for a cut. Preliminary testing shows that the new system reduces task completion time for both inexperienced and experienced operators, in comparison to tele-operation. In a second contribution, a novel state-dependent parameter (SDP) control system is developed, for improved resolved motion of the manipulators. Compared to earlier SDP analysis of the same device, which used a rather ad hoc scaling method to address the dead-zone, a state-dependent gain is used to implement inverse dead-zone control. The new approach integrates input signal calibration, system identification and nonlinear control design, allowing for straightforward recalibration when the dynamic characteristics have changed or the actuators have deteriorated due to age.