Nonlinear Compensation Control And Applications For Servo Systems

Backlash,friction and mechanical resonance are the inherent characteristics of servo systems,which may severely degrade the system control performance,especially for the large servo systems with high precision.Therefore,it is important to investigate compensation methods for these nonlinearities and mechanical resonance in design of servo systems.In this thesis,the compensation control of servo systems in presence of backlash,friction and mechanical resonance is discussed based on the background of the large radar servo systems with high precision.First,the backlash and friction compensation schemes are designed in terms of single motor driving servo systems,and then the mechanical resonance suppression is studied for dual-motor driving systems.Finally,an extended state observer based adaptive robust control algorithm is proposed to deal with the uncertain nonlinearities and disturbances for multi-motor driving servo systems,which will be finally applied in the design of radar servo systems.The main contents of this thesis are summarized as follows:(1)According to the Wiener-Hammerstein servo systems with asymmetric backlash,a novel composite control strategy is proposed by incorporating the output feedback and the dynamic inverse compensation of backlash.First,the parameter estimation model of the system is established by the parameterized piecewise linear expression,which is employed to derive a novel dynamic inverse model of backlash with bounded error.Besides,the reversing time of intermediate state can be shortened by adjusting the inverse model parameter,such that the driving signal can achieve rapid transition between the different linear segments of the backlash,which guarantees the backlash compensation in the sense of physical mechanism.Based on the dynamic inverse model,the output feedback is employed to design the robust compensation scheme,which can maintain the satisfactory dynamic response and steady-state accuracy.The simulation results show that the proposed algorithm can effectively eliminate the hysteresis error caused by the backlash and further improve the system tracking accuracy.(2)Considering the friction nonlinearity in servo systems,an adaptive dynamic surface controller is designed based on the improved LuGre model of which the discontinuous term is modified using a continuous hyperbolic tangent function.Besides,the high order neural network is utilized to approximate the uncertain nonlinearity in the system.While the residual reconstruction error and other bounded disturbance are compensated by using robust integral of the sign of the error(RISE)term,an adaptive dynamic surface controller is proposed for servo system,which can yield asymptotic tracking error convergence.Experimental results illustrate that the proposed method provides much smaller steady-state errors,and improves the convergence rate and tracking performance.(3)Considering the dual-motor driving servo systems with different resonance points,a composite control based on the multi-strategy is presented to suppress the mechanical resonance in different frequency ranges.The four inertia model is firstly conducted for the dual-motor driving servo system.According to the low frequency resonance,two kinds of disturbance observer-based compensation schemes are proposed,where the compensation parameter design and its effect on the resonance suppression are provided and analyzed,respectively.For the high frequency resonance,the notch filter-based scheme is studied to suppress resonance,in which the notch filter design and the parameter adjustment rules are both mentioned.From the simulation results,it is demonstrated that the proposed strategies give the preferable performances and effectively attain the mechanical resonance suppression.(4)An extended state observer based adaptive robust controller is investigated for dual-motor driving servo systems,where the backlash,friction and uncertain disturbance are all taken into consideration.First,the complicated nonlinearities(e.g.,backlash,friction)and the uncertain disturbance are analyzed.Then the nonlinearities and uncertain disturbances are merged into the lumped disturbance,which is estimated using the extended state observer.Based on the estimation results,an adaptive robust controller is proposed to guarantee the system stability and the transient performance in the sense of L_?norm,where the adaptive law is employed to estimate and compensate the upper boundary of observer error.The simulation results validate that the proposed method can compensate the nonlinearities and uncertain disturbances to improve the control performance.(5)The experiments on dual-motor driving radar servo systems verify the effectiveness of the extended state observer based adaptive robust scheme.The results illustrate that the proposed methods provide satisfactory performances of the compensation for nonlinear factors and uncertain disturbances,which can satisfy the tracking performance and steady state accuracy in the design of the system.Therefore,the proposed algorithms have the applicable value in practical engineering.