Underactuated Three Gymnastics Robot Control Strategy Study

Underactuated three-link gymnastic robot is a typical model of underactuated mechanical system, which possesses high-nonlinear property and is very complex. This robot can realize gymnastic appearance, such as body's rotating, swing-up and handstand etc, by the means of driving underactuated joints through actuated joints with the dynamic coupling relation. Due to the underactuated property of this system, it's difficult to realize the swing-up and balance control of the robot. To solve the control problems of three-link gymnastic robot, swing-up and balance strategies are studied in this paper. Moreover, the real model of three-link gymnastic robot is also designed in order to demonstrate the validity of control strategies.Firstly, the dynamic model of the three-link gymnastic robot system is obtained based on Lagrange equation, and then the division of the swing-up area and the balance area are simplified by analyzing the dynamic characteristic of this system.Secondly, a swing-up control law is designed based on a quadratic positive definite function, which guarantees the three links swing up into balance area with a desired posture. Afterwards, a balance control law based on LQR could realize the control target successfully.Moreover, in order to improve the control performance, a swing-up control law based on partial feedback linearization and balance control law based on LQR is proposed. This strategy has the merits of swinging up quickly and switching smoothly between the controllers. At the same time, the configuration of swing-up controller is simple.At last, the real model of three-link gymnastic robot is designed in this paper. And the type of motors, encoders and control box are chosen based on the control experiments of the robot model.