Passive Compliance Control of a Weld Inspection Manipulator for Intersecting Pipes

To inspect the welded joint of intersecting pipes in a nuclear power station, a weld inspection manipulator with a passive compliant end-effector was designed and manufactured, and a corresponding control strategy was realized based on a simple novel geometric method. The manipulator was composed of five observable articulations in series. The first three are controllable active articulations driven by servo motors and the other two are uncontrollable passive articulations preloaded by torsion springs. All of them were measured by rotary encoders. The geometrical analysis indicated that passive articulations could be controlled indirectly by adjusting the active articulations. The inverse kinematics question was resolved by the geometrical method in order to determine the relationship between the active articulation variables and the required position force of the end-effector. Then a method of cascaded position-force control was presented and a Matlab simulation was made to verify its validity. The simulation result proved that the control algorithm was of rapid convergence with high precision. To evaluate the quality of inspection, scanning experiments are implemented, which proved that the inspection task was successfully finished. The outcome of this study would provide an automatic manipulator for the welded joint inspection of numerous intersecting pipes in a nuclear power station.