Abstract
This paper addresses the trajectory tracking problem for constrained high dynamic electro-hydraulic actuator in the presence of time-varying parameters, high frequency external load interference, measurement noise and some unmeasurable states. An adaptive robust optimal control scheme is proposed for the electro-hydraulic actuator in legged robot. The framework of our presented scheme is based on a linear time-varying model predictive controller (LTV-MPC) embedded with a multi-scale online estimator (MEKF). With fast- varying and slow- varying time scales, the MEKF part is used not only for measurable states filtering and unmeasurable states estimation, but also for time-varying parameters and external load interference estimation, which will be integrated into the mpc model in real time. The LTV-MPC part is a trajectory tracking controller designed by constrained MPC with an approximate high-precision real-time model and a rapidly solved cost function, which guarantees that the input and output constraints are satisfied during the receding horizon and optimal control process. Finally, with a series of highly dynamic conditions, the comparison experiment results show that the proposed controller has a simple design process, strong adaptive robust performance and trajectory tracking performance, which verifies the effectiveness of the control scheme.
Highlights
Electro-hydraulic actuators are extensively used in heavyduty electromechanical systems and legged robots, for their high load capacity and large power density ratio [1]–[7]
(1) When the system is disturbed by high frequency and large external load, the adaptive method has the problem of high gain feedback.When system parameters change, the extended state observer (ESO)(Extended state observer)-based controller has poor estimated performance, and complicated parameter adjustment
Inspired by the above literatures, this paper proposes an adaptive robust Model Predictive Control (MPC) trajectory tracking control scheme for constrained high dynamic actuators in legged robot, which aims to achieve the following objectives
Summary
Electro-hydraulic actuators are extensively used in heavyduty electromechanical systems and legged robots, for their high load capacity and large power density ratio [1]–[7]. The designed control scheme required for the actuator can provide the suitable tracking performance by (a) effectively overcoming the time-varying parameters, external load interference and measurement noise, (b) solving the problem that some states are not measurable, (c) constraining the control input and system output within corresponding ranges, and (d) providing a real-time computational optimal control action. Through the comparison test results with high dynamic working conditions, We found that only the proposed MEKF-MPC scheme can simultaneously achieve effective suppression of parameter time-varying, high-frequency large-load interference and noise, at the same time, achieve the simplified system design and high-precision trajectory tracking control while satisfying the input and output constraints.
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