Abstract: Based on fuzzy control theory, the joints position control of 2R underactuated robot is studyed. a electromagnetic brake is fixed into the passive joint to control the coupling state between joints. The process to control the robot position can be divided into two phases. The brake is released during the first phase. Depending on the dynamic coupling effect between the angle acceleration of passive joint and the torque of active joint, passive joint can be controlled indirectlly to the desired position along the desired trajectory. The fuzzy control rules during the first phase are described and fuzzy controller are designed to control the motion of passive joint. The brake is locked during the second phase, then active joint is controlled to the desired position. The experimental control system based on PMAC controller is designed and developped. Finally, the position control of the 2R underactuated robot is achieved successfully by experiments. The experimental data indicates that the fuzzy control method presented has high precision and good robust character for position control of the passive joints. Furthermore, this method doesn’t rely on the dynamic modle of the robot and the calculation during real-time control is very few, which shows the advantage of intelligent control.

Key words: Control system, Fuzzy control, Position control, Underactuated robot