A Model-free Fine Position Control Method Using the Base- Sensor: with Application to a Hydraulic Manipulator

Manipulators are often required to perform small amplitude, slow motions with very high precision. For hydraulic manipulators these fine motions are difficult to execute due to high nonlinear joint friction found in these systems. Poor tracking, stick-slip behavior, and large static position errors often occur. Current methods proposed to improve the performance of hydraulic manipulators require complex modeling and identification and often produce marginal results. Here, a control scheme based on feedback from a basemounted force/torque sensor is presented. The theoretical background for the method is presented, and an easy to implement simplified form is developed, based on quasi-static equations. Experimental results for a Schilling Titan II industrial hydraulic manipulator performing fine-motion tasks under the simplified control algorithm are presented. It is shown that performance is significantly improved over traditional control methods. It is also shown that the control scheme is robust to changes in payload.