Zhao Jiangbo

Friction compensation using dual observer for 3-axis turntable servo system

Friction and load disturbance are important factors in high resolution control for 3-axis turntable servo system. LuGre dynamic friction model is adopted to describe the mathematic model of the pitch axis servo system with friction. Due to the dynamic LuGre model is built on three unknown parameters. Besides, system torque and inertia are also uncertain due to the motor torque ripple or disturbance. A dual sliding mode observer is adopted to estimate these parameters, and Lyapunov function is used to design the update laws. Based on these estimated parameters, adaptive control law is designed to compensate the unknown friction and load disturbance. Simulation suggest that the proposed method is global asymptotically convergent, which guarantee the position and speed signals track the desired trajectories asymptotically.

A robust fault detection and isolation method via sliding mode observer

A robust fault detection and isolation (FDI) approach for a class of nonlinear systems with uncertainty was presented. The FDI scheme was based on sliding mode observer, which was robust against system uncertainty. Fault detection can be realized by use of sliding boundary size. When the fault had been detected, the estimate part in the observer for the fault can be enabled. A radial basis function (RBF) neural network was used to approximate the fault, so making the fault isolation a simple task. The theoretic analysis guaranteed the convergence of the observer. Simulation results show the feasibility of the proposed approach.

The fractional order PI control for an energy saving electro-hydraulic system

In an electro-hydraulic system (EHS), the throttling phenomenon of the hydraulic valve leads to the problem of low utilization efficiency of hydraulic energy and severe increases in temperature. To alleviate this problem, this paper presents a type of one-chamber-controlled hydraulic circuit. In some applications where elastic load is dominant, this hydraulic circuit can achieve a significant energy-saving effect. For a valve-controlled system, the orifice non-linearity and the slowly varying parameter significantly influence the control performance of the electro-hydraulic system. With this aim in mind, the orifice compensation method is proposed to deal with the orifice non-linearity. Based on the compensation, the fractional order proportional–integral (FOPI) controller is adopted to deal with the problem of fluid parameter variation. In the controller designing process, this paper proposes a controller parameter tuning method based on system frequency characteristic data. Simulation and experiment results show that the strategy presented in this paper can reduce the energy losses dramatically and, at the same time, the control performance of electro-hydraulic system can be guaranteed.

Cross-Coupled Control for Three-Axis Turntable Target Tracking System

Cross-coupled control (CCC) is an efficient method for decreasing contouring error, which has been used widely in multi-axes motion systems. The contour error transfer function (CETF), constituted by the response of contouring error between with and without the multi-axis CCC, was introduced to simplify the MIMO system to SISO system. In this paper, the CCC algorithm was introduced to the three-axis stable tracking system, and a biaxial CCC controller was built. Analyses and experiments results suggest that the CCC controller raised target tracking accuracy compared with traditional P controller. In which, the pitch direction tracking error decreased 35%, and the yaw direction error decreased 31%.

A calculation method of braking torque for eddy current dynamometer using least square method based on assumption of cylindrical ring

For engineering applications, the existing method of calculating the braking torque is more complex. Furthermore, the calculation method depends on the internal structure parameters which are often difficult to obtain. Hence, the calculational method of braking torque using least square method based on assumption of cylindrical ring (CR-LS) is proposed in this paper. Referring to calculation methods of eddy current braking devices, The CR-LS assumes that the eddy current is distributed as a cylindrical ring with the same width as the tooth tip of the inductor. Eddy current values are worked out by conversion coefficient. With the employ of LS, unknown internal structure parameters of dynamometer in formula are fitted. It makes the formula use in industrial control with easy. By experimental verification, the formula obtained by CR-LS was simple and available, and calculation results had minor errors in contrast with output values of actual system. Therefore CR-LS can be applied in actual engineering calculations of dynamometer.

Controller parameters optimization of large inertia and time-varying load system based on extremum seeking algorithm

It is difficult to tune controller parameters for large inertia and time-varying load system. To solve this problem, a new controller parameters optimization strategy based on extremum seeking algorithm is proposed. This novel method is model-free. It utilizes data of experiments to get the gradient information of performance to control parameters, so as to tune the controller parameters. This paper analyzes the convergence of extremum seeking algorithm and proposes the high-pass filter parameters selection principles. Simulation and experimental results show that the system control performance is significantly improved using extremum seeking algorithm compared to traditional methods.