Research On Robust Control Of Electro-Hydrostatic Actuators And Secondary Controlled Systems Based On Quantitative Feedback Theory

Recently,faced with challenges posed by fuel consumption and exhaust emissions,energy-efficient hydrostatic actuation has attracted increasing attention.Among the techniques,electro-hydrostatic actuation and secondary control stand out for their excellent energy efficiency and control performance.It becomes a significant topic to improve control performance,maneuverability as well as their facilitation while maintaining a good energy efficiency.Though numerous studies have been done,there is still a gap between a theory and practice.Challenges such as uncertainties and unknown nonlinearities in both system and environment,and control complexity stop those advanced control techniques from implementation.Therefore,to improve tracking accuracy and robustness,reduce control complexity and facilitate industrial applications,it is required to research on certain control issues in energy-efficient hydrostatic actuation.Quantitative feedback theory(QFT)is a frequency domain method to design a low-bandwidth robust controller to achieve desired performance,in the presence of plant uncertainty and unknown nonlinearity.As it is based on Nichols chart,designers are allowed to have an insight into the trade-offs among the performance,thus to simplify the control scheme and avoid over-design.Given the aforementioned research background and the prospect of QFT,focused on eletro-hydrostatic actuatiors(EHAs)and secondary controlled systems,the author carries out research as follows based on QFT.(1)In occasions with requirements of high accuracy and repeatability,in the presence of parametric uncertainty and unknown nonlinearity,the author proposed a robust position control scheme combined with leakage and friction compensation applied to a typical EHA.QFT is employed to design a robust controller as to the uncertainties caused by load variation or model inaccuracy.In this way,the prescribed specifications of robust margin,sensitivity reduction and tracking performance are satisfied transparently with no over-design.Furthermore,the author identified the internal leakage based on experimental data and constructed a compensation scheme proportional to the load pressure.Without introducing an integrator into the controller,limit cycle is avoided and the response speed is improved.At last,the friction parameters in the actuator are identified based on LuGre friction model and then compensated through an observer in the loop.The variations in friction and loads are considered as output disturbances and have been constrained during the QFT controller design.Based on the EH A test rig,the proposed robust position control scheme combined with leakage and friction compensation is examined.It shows that both transient and steady-state position tracking performance are greatly improved.(2)Aimed at remote,hazardous or other inaccessible situations,given the benefit of tele-presence and high energy efficiency,the author studies EHA-based teleoperator for the first time.Considering the difficulties in modeling human arm,haptic device and environment,the author proposes a quantitative analysis approach for bilateral control schemes applied to EHA-based teleoperator.Enabled by QFT,parametric uncertainties in human arm,haptic device and environment are described in plant templates to calculate open-loop bounds on a Nichols chart.Thus,the design process and also trade-offs between robust stability and transparency are visualized.Within the analysis framework,controller parameters are tuned for four commonly used bilateral control schemes,i.e.,FR,PE,SCC and FRP.They are verified and evaluated on an EHA-based teleoperator through contact tests with both soft and hard environment.Furthermore,the aforementioned QFT position controller is introduced to the slave manipulator to improve the tracking performance in bilateral control.(3)Secondary controlled hydrostatic actuation is ideal to be applied to a swing system on a hydraulic excavator,which submits to large inertial load and cyclical operation.Faced with parametric uncertainties in load,viscous friction and bulk modulus,and output disturbances from environment,the author proposes a diagonal control scheme based on multi-input multi-output quantitative feedback theory(MIMO QFT),to satisfy the prescribed specifications defined by robust margin,sensitivity reduction and tracking performance.Through verification and evaluation based on Simulink and also Simhydraulics models,both the pressure and velocity channels exhibit excellent tracking performance and robustness against parametric uncertainty,unknown disturbance and nonlinear friction.The visualized synthesis approach reduces the complexity of the two-input two-output control scheme,and thus facilitate the implementation of the secondary controlled hydrostatic actuation.