Integrated Design Of A Novel Electro-Hydraulic Loading Device

Loading devices play important roles in dynamic load simulations and performance tests of marine shafting under laboratory conditions,which help reduce the cost of experiments on real ships and improve the reliability of marine shafting.However,the existing loading devices are mostly driven by valve-controlled cylinders.These systems cannot avoid the problem of low energy efficiency resulted from the throttle loss.Meanwhile,the high-frequency self-excited noise generated by the valves diminishes the system stability and control performance.To overcome the weakness of valve-controlled loading systems,a novel electro-hydraulic force tracking actuator based on Pasca l's Principle is developed.An electric cylinder is utilized to change the volume of the enclosed oil and generate the desired loading pressure.In order to obtain the optimal designed parameters form the perspectives of both mechanism and control performa nce,an integrated design methodology is presented in this paper,which overcomes the limitations of conventional design methods.The design results are verified through experiments.Specific research details are as summarized follows.Firstly,the components and the main principle of the proposed electro-hydraulic actuator are presented.The complete mathematical model of the novel actuator is established.To avoid the difficulties of force measurement in the loading process,a semi-closed-loop force control structure with hydraulic pressure feedback is constructed.The feasibility of the control system is analyzed on frequency domain.The nonlinear element due to the entrained air in hydraulic oil is replaced by a bounded time-varying coefficient.Thus,the original model is translated into linear time-varying model.The effect of the time-varying parameter on system's frequency characteristic is studied.A compound double-closed-loop control system including a motor velocity controller,a hydraulic pressure controller and a feedforward compensator is designed.Secondly,the purpose and requirements of control system is presented.A series of performance indexes such as stability criteria,bandwidth,control errors and continuous operation capability of the proposed actuator are established based on the mathematical model.The complicated interactions of design parameters are analyzed through numerical simulations.To minimize the force control error and the motor power simultaneously,a multi-objective nonlinear constrained optimization problem including both mechanical and control parameters is formulated.The problem is solved by a particle swarm algorithm to obtain the optimal parameters.Finally,the main components are selected according to the design results,and a test bench of the novel electro-hydraulic actuator is established.The control program and the human-machine interface are developed.Experimental results verify the feasibility of the proposed semi-closed-loop force control structure.Meanwhile,the novel force loading device meets all the design requirements,which demonstrates the effectiveness of the integrated design.