Simplified approach for modelling and control a 3-DOF RRR type robotic manipulator using squirrel-cage induction motors

Worldwide there are currently over 800,000 industrial robots in operation, mostly in Japan, the European Union and North America. Most of the robots use DC motors, driving the manipulator´s maintenance very expensive. This is the main reason for changing, whenever it´s possible, a dc motor for an ac motor. For such tasks, vector control enables the control of induction motors in similar way used in dc motors. Vector control, also called field oriented control, enhances the dynamic performance of ac motors, and is becoming an industrial standard. So, to check possibility of using induction motors in manipulators, this paper proposes a control of 3-DOF manipulator driven by induction motors. For this we have modeled the manipulator mechanical coupling as a load applied at induction motor shaft, so it has direct influence on both dq currents, which were chosen as ours state variables to be controlled. This simplification provides not only an easy design procedure, but also a computational implementation of low complexity, allowing system to be implemented on a digital signal processing and thus motivating its application in industrial environments. Experimental tests on a built manipulator are shown validating simulation results and shown certain degree of robustness on currents´ control as expected for vector control and also giving a low error at steady-state for manipulator position.