Abstract-Underactuated mechanism is a nonlinear system which dimension of input is less than one of state. There are still some problems to be explorations in underactuated mechanism control, especially in ones with multi-DOF. The model reference adaptive control is proposed to solve the control problem of a novel underactuated spring-coupling mechanism with multi-DOF in this paper. Firstly, dynamics model is established and linearized. Then, an adjustable gain adaptive controller based on Lyapunov stability theory is presented. Finally, simulations are presented to illustrate the superior performance of the proposed method through theoretical analysis and design. The results show that the stability, accuracy and rapid response are fine, and the adaptive steady holding problem of multi-DOF underactuated mechanism is solved.

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