Fuzzy controller scheduling for robotic manipulator force control

Force control of robotic manipulators is becoming more and more important in applications that involve interaction with the environment. Depending on the nature of the task at hand, different control algorithms can be suitable to be implemented. In this paper the task of reaching an object by the robot tool and applying a constant force on it is considered as a case study. This task is one of the typical manipulation operations. A fuzzy logic scheduling approach, which smoothly changes the control action between two force control schemes, is proposed. The first force control method is admittance control, which is suitable to be used in the phase of approaching the work piece. The second one is an explicit force control strategy, integral force control, suitable for force regulation when the manipulator tool is in contact with the work piece. The fuzzy controller scheduling approach is tested via experimental work on a direct drive SCARA-type manipulator. It is also compared with a crisp controller switching method. Experiments are carried out with fixed and free-to-move work pieces. The results validate that the proposed fuzzy transition has advantages over a crisp switching between controllers.