Dacheng Cong

Adaptive inverse control of time waveform replication for electrohydraulic shaking table

A combined control strategy with an adaptive inverse control (AIC) and an inverse frequency response function (IFRF) equalization technique is proposed for the electrohydraulic shaking table (EST) system. The control purpose is to improve the accuracy of time waveform replication. In contrast to the iterative compensation through repetitive excitations control approach of industrial EST controllers, the proposed control strategy utilizes an IFRF of the EST system for extending the EST system frequency bandwidth and obtaining asymptotic reference tracking, and employs a variable tap-length filtered-x least-mean-squares algorithm to adaptively tune the time-domain drive signal and further improve the position and acceleration tracking performance of the EST system. Thus, the proposed combined control strategy is designed to combine the merits of IFRF and AIC. The procedures of the proposed control strategy are programmed in MATLAB/Simulink, and then compiled to a real-time PC with Microsoft Visual Studio.NET for implementation. The simulated and experimental results show that this control strategy achieves satisfactory position and acceleration waveform replication accuracy.

A Survey on Control of Parallel Manipulator

Based on extensive study on literatures of control of parallel manipulators and serial manipulators, control strategies such as computed torque control, PD+ control, PD with feedforward compensation, nonlinear adaptive control are classified into two categories: model-based control and performance-based control. Besides, as advanced control strategies, robust control and passivity-based control for the parallel manipulators are also introduced. Comparative study in view of computation burden and tracking performance are performed. It turned out that the physical structure properties of parallel manipulators’ dynamics are similar with that of serial ones, and this constitutes a common foundation for the two kinds of manipulators to develop together that control design of parallel manipulators can start with ever established control methods of serial manipulators.

Time Problems in HIL Simulation for On-orbit Docking and Compensation

The research work in this paper is oriented to establish a real hardware-in-the-loop (HIL) simulation system to reappear the on-orbit docking process on the ground. The docking frequency is discussed based on the analyzing the characteristics of docking mechanism. The time delay and time lag problems in the HIL simulation for on-orbit docking are quantitatively discussed. Furthermore, the compensation scheme to each of them is discussed and a compensator to all above time problems of them is presented. To verify the effectiveness of the compensator or to check the dynamic characteristics of the HIL simulation system, a verification idea and a validation model are presented. To do prophase research, a prototype of the HIL simulation system is established. Finally simulation was made on the virtual prototype of HIL simulation system with the validation model.

Feed-forward inverse control for transient waveform replication on electro-hydraulic shaking table

In this paper, an improved feed-forward inverse control scheme is proposed for transient waveform replication (TWR) on an electro-hydraulic shaking table (EHST). TWR is to determine whether a test article can remain operational and retain its structural integrity when subjected to a specific shock and vibration environment. Feed-forward inverse transfer function compensation is a useful technique to improve the tracking accuracy of the TWR on the EHST system due to their inherent hydraulic dynamics. Whenever a feed-forward inverse transfer function is employed, it is critical to design the identification accuracy of the inverse transfer function. A combined control strategy, which combines a feed-forward inverse transfer function compensation approach with a simple internal model control (IMC) and a real-time feedback controller, is proposed to minimize the effect of the system uncertainty and modeling error, and further to improve the tracking accuracy of the TWR. Thus, the proposed control strategy combines the merits of feed-forward inverse transfer function compensation and IMC. The procedure of the proposed control strategy is programmed in MATLAB/Simulink, and then is compiled to a real-time PC with Microsoft Visual Studio.NET for implementation. Simulation and experimental results demonstrated the viability of the proposed combined control strategy.

Interface Issues in Hardware-In-the-Loop Simulation for Spacecraft On-orbit Docking

This paper presents an idea on the simulation/hardware interface of hardware-in-the-loop (HIL) simulation for spacecraft on-orbit docking. The obstacles that hinder the design of the HIL simulation system are discussed. Then the design criteria of the HIL simulation system are presented based on them. Since the practical HIL simulation system for on-orbit docking is very complicated, the verification about the criteria was done on 1 degree-of-freedom (DOF) case with the nonlinear docking mechanism model. To put the design criteria into practice, the two-degree-of-freedom control structure is required as a control structure for the HIL simulation system for on-orbit docking. The relation ship between the distortion of the HIL simulation and the transfer characteristics of the simulation/hardware interface is qualitatively discussed. The simulation results on 1 DOF case demonstrated that the ideas and the methods discussed above are feasible and practical.

Real-time Rendering of Large-scale Terrain in the Flight Simulator

Large terrain is an important component of the virtual visual environment in the flight simulator. This paper presents a view-dependent dynamic LOD algorithm which is inspired by the geometry clipmap, and has some supplement or improvement in data structure, refinement criterion, rendering way, etc. The algorithm treats the terrain data as vertex texture; carries out uniform management on the terrain geometry data sets, terrain color texture and normal vectors using a hierarchy like the clipmap; and applies the identical spatial partition, transition scheme and update method to these data. The experiment shows that the algorithm can have much smaller memory requirements, make full use of the advantage of GPU and produce realistic and continuous images with the interactive speed. Especially, virtual clipmap support can make sure the algorithm fit the applications which have gigantic terrain range or need higher precision, so it has great extensibility and broad application prospects.

New Modeling and Analysis of Three-Stage Electro-Hydraulic Servo Valve

To develop higher performance three-stage electro-hydraulic servo valve, a new modeling software, AMEsim, is used to develop its non-linear model according to the construction and principles presented in this paper. The results of simulation and experimental test about an existing valve are consistent, which proves the model is right. Based on the analysis of the model, the performances of three-stage electro-hydraulic servo valve are mainly affected by pilot valve performance, spool and sleeve performance, position transducer performance and servo controller performance. The methods of modeling and analysis possess universal significance to other similarity system.

Analysis of Performance Effect Factors of Three- Stage Electro-Hydraulic Servo Valve

A new modeling software, AMEsim is put forward in this paper to develop a nonlinear model for a higher performance three stage electro-hydraulic servo valve. The simulation results and experimental results on existing valve are consistent, which proves that the developed model is right. The analysis of the model shows that pilot valve bandwidth mainly affects the bandwidth of three-stage electro-hydraulic servo valve and is responsible for overshoot. The analysis also indicates that pilot valve resolution affects the resolution of three-stage electrohydraulic servo valve and pilot valve rated flow affects the bandwidth and overshoot. The result further reveal that the position transducer affects the bandwidth and overshoot, servo controller affects the bandwidth and stability, the spool diameter and mass affect the bandwidth and hydraulic natural frequency, flow force on spool affects the bandwidth, overlap distance of restriction edge affects the dead zone size of mid-position and resolution of midposition, coulomb friction force between spool and sleeve affects the resolution and radial clearance affects leakage flow and resolution. The analytical results are very useful because the methods can be applied to other similar systems.

Modeling and Key Technologies Study of Three-Stage Electro-Hydraulic Servo Valve

The modeling and study of three-stage electro-hydraulic servo valve are presented in this paper. According to its construction and principle, its model is built. The results of simulation and experimental test are consistent, which proves the validity of the model. Based on the study of the model, the performances of three-stage electro-hydraulic servo valve are mainly affected by pilot valve performance, spool and sleeve performance, position transducer performance and servo controller performance, which shows that there are four main key technologies. The study results have a guiding role for developing higher performance three-stage electro-hydraulic servo valve.

A New Procedural for the Integration of the HIL Simulation System for On-orbit Docking

This paper present a new method for the integration of the HIL simulation system for on-orbit docking. First, the problems, such as stability, in the integration of the HIL simulation system arc discussed. The HIL simulation tasks are discussed based on the analysis of the characteristics of the docking mechanism. A new idea and procedural to integrate the HIL simulation system is presented. The two-degree-of-freedom control structure is defined as a practical control structure for the HIL simulation system based on the analysis of the single degree-of-freedom (DOF) model of HIL simulation for on-orbit docking. The pre-filter of the two-degree-of-freedom control structure can be defined with several procedurals, for an example, QFT. By increasing the hydraulic spring rate, the sensitivity of the electro-hydraulic system to payload stiffness is reduced. The simulation results on single DOF case demonstrated that the ideas and the procedural for the HIL simulation system integration are feasible and practical.