Less Drive A Three-link Robot Control Strategy

This thesis studies on the control strategy of three-link underactuated robot aims to develop new methods for underactuated mechanical systems. The three-link underactuated robot has many advantages such as light weight, low cost and low energy consumption; illustrating its good prospect of application in industrial robots, space robots and extraterrestrial exploration. Considering the exist problem of controlling the three-link underactuated robot, three new control strategies are proposed based on the system characteristic analysis. They are fuzzy control based on energy, control strategy based on energy decoupling, control strategy based on energy decoupling and posture regulating, respectively.Firstly, the dynamic model of the three-link underactuated robot is obtained based on the Lagrange equation, and some system character-istics are analyzed. The motion place is divided into swing up area and attractive area based on the system characteristics.Secondly, two control laws are designed for each actuated joint to control energy and posture of actuated link, respectively; meanwhile, a fuzzy controller is employed to regulate the control parameters of the energy control law, so the energy of the system can converge to the potential energy on the upright unstable equilibrium point, and the system can move into the attractive area. In attractive area, a balance control law based on LQR is designed to stabilize the system on the upright unstable equilibrium point.Then, for removing the coupling among the energy and the system states and the control torque of one link of the three-link underactuated robot, the swing up area is divided into swing up subarea 1 and subarea 2. In swing up subarea 1, a control law is designed to control the posture of one link until it stretch in a natural way, so the energy and the states of the link can be controlled independently; in swing up subarea 2, a control law is designed to increase the energy until the potential energy on the upright unstable equilibrium point, so the system can enter the attractive area smoothly.Finally, a control strategy based on the energy decoupling and posture regulating is presented for making the robot enter the attractive area more rapidly. Since the energy control and the decoupling control are carried out simultaneously, the robot can satisfy the conditions of attractive area more rapidly, and the total control period is shortened.