Integrated design of a novel force tracking electro-hydraulic actuator

Abstract

Conventional hydraulic actuators in which the output force is regulated through servo-valves or variable pumps usually suffer from great noise and low efficiency. To overcome this hurdle, a novel force tracking electro-hydraulic actuator based on Pascal's principle is developed. The novel device uses an electric cylinder to change the volume of enclosed fluid and generate the desired loading pressure. In order to further improve the performance of the novel actuator, an integrated design procedure in which the mechanisms and control structure are designed simultaneously is studied. Firstly, the complete mathematical model of the novel actuator is established. The nonlinear system is translated into a linear time-varying model by replacing the effective bulk modulus of hydraulic oil with a time-varying coefficient. The feasibility of the semi-closed control structure with pressure feedback is analyzed on frequency domain and a compound controller is given. Secondly, performance indexes such as stability criteria, bandwidth, control errors and continuous operation capability of the novel actuator are presented in detail. Interactions of the design variables are analyzed through numerical simulations. Afterwards, a nonlinear constrained multi-objective optimization problem including both mechanical and control parameters is formulated. To prevent the optimization progress from falling into local minimum point, a particle swarm algorithm is employed to carry out the optimization design. Experiment results demonstrate the effectiveness of the proposed integrated design method. And simulations are executed to verify the higher efficiency of the proposed novel electro-hydraulic actuator which is compared with the valve-controlled counterpart.