Discrete Time Reference Model Following Frequency-Shaped Sliding Mode Control with Pre-Filter for Hydraulic Manipulator

In the position and trajectory tracking control of hydraulic manipulators, it is difficult to obtain desired performance due to its nonlinearity, for instance, variation of the moment of inertia, the unsymmetrical effect of single rod cylinders, dead zone of the hydraulic control valve, time delay of hydraulic system and mechanical resonances. Therefore, application of a robust control system to the nonlinearity and disturbance is desired. Sliding mode control has strong robustness to parameter change and disturbance. Moreover model following control prevents the dynamic characteristics of plant to follow a reference model which has ideal characteristics. Then, by feedback of estimated disturbance from VSS disturbance observer in the inner loop, the response of the system is improved. Moreover sliding mode control with frequency shaping suppresses spillover of mechanical resonances. Therefore, we design a discrete-time reference model following frequency-shaped sliding mode controller with pre-filter, which combines the advantages of these control theories. In this paper, it is shown that our control method can improve trajectory tracking performance and robustness of hydraulic manipulators in experiments and simulations.