Research On The Control Of Robot With Underactuated Joint

An underactuated mechanical system refers to a system with less number of actuators than the degree-of-freedom of the system considered. The major character is that the dimension of input space is less than dimension of output space. It is obvious that this kind of manipulator has many merits and becomes one of the major topics of the field of robotics recently. For example, underactuated manipulator maybe useful in particular instances to reduce weight, cost or energy consumption, while still maintaining an adequate degree of dexterity. It is suitable for working in hazardous areas or with dangerous materials. It is particularly important for a space robot working in outer space to have the ability to control the failed joint in the event of an actuator failure.The problem of position control is studied in this paper, and the results of my work are as follows:At first, the dynamical model of underactuated manipulator is established by using the way of Lagrange.The linearization problem is formulated and solved for nonlinear system. By using it, we can finish the first step of dealing with the underactuated manipulator. Then based on the result above, an open-loop way for underactuated mechanical systems using oscillatory inputs with amplitude and frequency modulations is investigated. In this way, we can deal with the model further by making use of averaging theory.Considering the last model, we propose the control strategy that has two steps. The first step is to enable the unactuated joint move to their desired position which can be attained by simple feedbackcontrol. The second step is to enable the actuated joint move the desired position. In this paper, we mainly focus on control to meet the second subgoal. We have acquired the way through analyzing the averaged system of the underactuated robot. Then the way is adopted in the original system. We can enable positioning to an arbitrary single equilibrium point from an arbitrary initial point by modulating the amplitude. All figures and the simulation results are showed. The result shows that the control way is feasible and valuable.Finally, the concept of chaos and chaos control based on periodic signal are presented. They establish the base for the subsequent and further study.