Optimal Design and Hybrid Control for the Electro-Hydraulic Dual-Shaking Table System

Atomic force microscope(AFM) is a very important instrument with atomistic level resolution, which has been widely employed in the field of micro/nano technology. As a critical part of AFM system, the piezoelectric scanner exists many defects such as hysteresis, creep, and ease of vibration effects, which has become a bottleneck in its further development and application. In this paper, an image-based method by using polar coordinate is presented to model the piezoelectric scanner utilized in AFM, which can effectively avoid the troubles of data acquisition in AFM system. The parameters of its inverse model are identified by the Least-square method(LSM) and an inverse feedforward control strategy is developed. To verify the performance of this strategy, Being CSPM5500 AFM has been employed, the analysis and performance evaluation have been conducted in detail, which demonstrates that the novel hysteresis model and the image-based inverse feedforward control strategy presented in this paper possess a good performance for AFM nano imaging.

Research of Compound Controller for Flight Simulator with Disturbance Observer

This paper proposes a new high speed robust control system based on both zero phase error tracking (ZPET) control system and disturbance observer for an optical disk recording system. In optical disk recording systems (for example CD-R), the servo system must have a precise response whose error is less than 0.1 [/spl mu/m] for a reference input signal with an amplitude of 100 [/spl mu/m]. Moreover, the servo system can detect only the error, i.e. the position difference between the optical spot and the track to be followed. For this purpose, the servo system proposed in this paper estimates the reference input signal from the error, and realizes the high speed robust control based on ZPET control. Numerical simulation results point out that the proposed system has a quick and robust response.

This paper presents a 2-link, 2-DOF flexible manipulator control using an inverse feedforward controller and an adaptive notch filter with a direct strain feedback controller. In the flexible manipulator, transient and residue vibrations inhibit the full potential of the manipulator. Vibrations caused by abrupt changes in the direction of the links are referred to as transient vibrations, whereas residual vibrations occur when the arm takes too long to settle after engaging in the intended task. The feedforward adaptive notch filter will reduce transient vibration caused by the manipulator arm beginning and halting suddenly, while the strain feedback will assure the quick decay of leftover vibrations. Maple, Maplesim, and MATLAB tools were used to model the manipulator and create the inverse controller and adaptive notch filter. The experiments took place in the dSPACE control desk environment. The experimental results of the spectral power of strain resulting from the two strategies are compared. From the results, the adaptive notch filter control had over an 80% improvement in the reduction in resonant frequencies that contribute to vibration. The results confirmed the feasibility of the approach, characterized by very minimal transient vibrations and a quick settling of the end effector.

Using VSC-MTDC for wind farm integration is considered to be a promising solution. In order to provide a stable ac voltage control and avoid active power control conflicts, the amplitude-phase control strategy, rather than the active/reactive power decoupled control strategy, is generally applied for the VSC connected to wind farms. However, using such a control strategy, the flexibility of power flow control will be partly lost. As the positive and negative pole dc networks in the bipolar VSC-MTDC can operate independently, a novel hybrid control strategy is proposed in this paper. In the proposed hybrid control strategy, the amplitude-phase control and active/reactive power decoupled control can be applied to the positive and negative poles, respectively. Hence, the hybrid strategy combines the advantages of the amplitude-phase control and active/reactive power decoupled control and can be adapted to bipolar VSC-MTDC for large-scale wind farm integration. Simulation results using PSCAD show that the hybrid control strategy can provide the stable ac voltage control and active/reactive power flow control for the integration of wind farms; moreover, such a hybrid control strategy is helpful to avoid the overload of dc lines, stabilize the dc voltage, and enhance the power transfer capability.

In this paper, a novel 2-DOF high-speed/high-accuracy robotic system is proposed, which consists of two permanent linear DC servomotors and a planar parallel mechanism. Analysis of robotic dynamical model verifies that load variation is violent. Due to the direct-drive principle of a linear motor, the load disturbance can have a significant effect on position accuracy. For this purpose, a discrete-time disturbance observer, feedback controller and ZPECT feedforward controller is presented. The disturbance observer, which is applied to the plant velocity loop, provides robustness for design of both the feedback controller and the feedforward controller. The feedback controller is intended to make the command following properties fast, and the feedforward term realized as a Zero Phase Error Tracking Controller improves tracking. In the experiment, robotic max acceleration is equal to 20m/s2, max velocity is more than 1 m/s, and resolution is 0.5 μm. While the tracking errors are less than 50 μm, the steady-state errors are less than 1 μm, and steady time is less then 42 ms. Experiment results show that: high-performance motion system can be obtained with this discrete-time controller, even in large load variance motion system.

In this study, to enhance the system reliability under false data injection (FDI) attacks and DC-link voltage (DCLV) sensor failures, a hybrid control strategy for a DC microgrid (DCMG) based on the Lagrange extrapolation and voltage observer is proposed. Under normal conditions without FDI attacks or DCLV sensor failures, the DCMG system works in a distributed control scheme. To enhance the reliability of the system under the DCLV sensor failure or FDI attack, the DCMG system utilizes a hybrid control strategy that combines distributed control with decentralized control. The hybrid control strategy is achieved by the proposed detection algorithms for FDI attacks and DCLV sensor failures. The detection of FDI attacks is accomplished by comparing the predicted secondary controller output based on the Lagrange extrapolation with the actual one. When a power agent detects an FDI attack, its control mode is switched to decentralized control by using the proposed hybrid control strategy. The DCLV sensor failure detection algorithm to enhance system reliability against DCLV sensor failures is achieved by comparing the estimated DCLV with the measured one from the voltage observer. Upon detecting a DCLV sensor failure, the operation of the power agent is switched to the current control mode to sustain the system operation even under DCLV sensor failures. The proposed detection algorithms are simple, effective, and precise, operating without mutual interference that deteriorates the detection accuracy. Simulation and experiments are carried out under various uncertain test conditions to validate the reliability and effectiveness of the proposed control strategy.

The quality of the final prints in electronic-shaft paper-folding machinesseriously influenced by the mechanical periodic disturbance. This paper takes the periodic shock-disturbance and sinusoidal disturbance in the electronic-shaft paper-folding machineas as the research objects. Disturbance observer is designed based on Propotional Integral Diffrential (PID) control algorithm. Firstly this paper establishes a model of the system with MTALAB system identification tools in the process of establishing the control system. Secondly,the paper inverses this established model. In order to approximate the mode and guarantee the stability of the inversed model, zero-phase error-tracking controller (ZPETC) has been designed to remove the instable zero-point of the original model. Finally, the paper constructs the disturbance observer of the established reversed model based on PID control algorithm. The simulation on experimental platform shows that the resistivity of paper-folding machine to the external disturbance has been improved impressively and the proposed PID algorithm disturbance observer has been proved can be used in periodic disturbance suppression in the electronic-shaft paper-folding machine.

An optimal discrete controller is presented in this paper for contour error control using the standard linear quadratic (LQ) method, upon which the offset loss function and the control loss function were considered to attain a relatively good compromise. The weight coefficient for the control loss and the optimal discrete sampling period are garnered, then a zero phase error tracking controller (ZPETC) is designed with the disturbance observer (DOB) to improve the anti-interference capability and the robustness of the system. The proposed methods are capable of enhancing the stability and rapidity of the discrete controller and reducing the contour error of the system. The results may be valuable for various trajectory tracking control applications.

Inverse optimal control for autonomous carrier landing with disturbances

To aimed at the synchronous control for dual-cylinder with unbalanced and uncertainty loading, this paper proposes a hybrid control method that consists of feed-forward control and fuzzy feedback control. In the first, a feed-forward controller of each cylinder based on trajectory restrains is developed to limit the motion and synchronous error to a certain extent, and also smooth the piston motion. Then, two fuzzy controllers are specified to improve the tracking performance of cylinder and compensate the synchronous error. The simulation experimental results show that the proposed hybrid control strategy can control the maximum synchronous error of the total system to be within ±10mm under the consideration of large load imbalance, and has the system motion of a good smoothness.

The combined contour control strategy of H_inf velocity feedback control, zero phase error tracking control (ZPETC) and normal cross-coupled control is proposed. It reduces the influences of load interference, mechanical time delay and parameter mismatch between two axes on the contour accuracy of XY table directly driven by two permanent magnet linear synchronous motors (PMLSM). H_inf velocity feedback control has the advantages of fast responding and suppressing interference. ZPETC implements precise tracking based on zero-pole and phase cancellations. With the contour error as the direct controlled variable, normal cross-coupled control improves the contour accuracy by real-time compensation between two axes. Compared with the conventional method, the contour error is decreased much and the controller design is simplified. Simulation results show that the designed control system possesses good tracking performance, strong robustness and high contour accuracy.

Multi-axis motion system is widely applied in commercial industrial machines such as precision CNC machine tools, Robot manipulator and laser cutting machines, etc. Contour accuracy plays a major role for the multi-axis servo motion system. The contour machining accuracy is related to the synthesis of single-axis position accuracy and multi-axis linkage accuracy. Only improving the single-axis tracking performance cannot effectively guarantee the machining accuracy of multi-axis system. The primary objective of this study was to design a contour control method to improve single-axis tracking accuracy and multi-axis contour accuracy. A control strategy that combines a sliding mode tracking controller, a disturbance observer and an adaptive fuzzy PID cross coupled controller is proposed. Sliding mode control is simple and has strong robustness to parameter changes and disturbance, which is especially suitable for control of such as non-linear multi-axis motion system. Besides, disturbance is inevitable in practical application, which degrades the motion accuracy. In order to eliminate the influence of external disturbance and uncertainty, disturbance observer is adopted to accurately estimate external disturbance and reduce the chattering phenomenon of sliding mode control, then improve the single-axis tracking accuracy. In order to further consider the coordination between different motion axes and improve the contour accuracy, the PID cross coupled control is used. Owing to conventional PID control cannot satisfy the multi-axis servo motion system with nonlinearity and uncertainty, an adaptive fuzzy method with on-line real-time PID parameters adjustment is proposed. The three-axis motion platform driven by PMLSM is used as the control object, to analysis the influence of disturbance observer on sliding mode control signal and analysis adaptive fuzzy PID cross coupled control performance respectively. The disturbance observer is used to observe the disturbance signal and estimate the disturbance well. The chattering of the sliding mode control signal is obviously improved. Next, compared with the conventional PID-CCC control, adaptive fuzzy PID- CCC control can significantly reduce the tracking error, the contour accuracy is also obviously improved. The disturbance observer can effectively eliminate the influence of external disturbance, reduce the chattering of sliding mode control, and ensure the single-axis accurate tracking. The self-adaptive fuzzy PID cross coupled controller can eliminate the influence of the dynamic characteristics mismatching and parameter difference of each axis, and improve contour accuracy. The simulation results clearly demonstrate the effectiveness of the proposed control method.

This paper presents a new control scheme to compensate for the amplitude- and rate-dependent hysteresis behavior of a piezo-driven parallel stage developed for the application of biological cell manipulation. A variable phase-delay model with variable gain is established to describe the nonlinear hysteresis of the system. The proposed controller integrates an inverse model-based preview feedforward control and a PID feedback control, which has a simple structure and is ease of real-time implementation. The effectiveness of the preview-based control is demonstrated through experimental studies. Results show that the combined control scheme suppresses the tracking error by more than 11 times compared to the stand-alone PID control. It provides a baseline of practical control of the piezostage system for biological cell manipulation.

This paper presents design and force-tracking impedance control of 2-degree-of-freedom (DOF) wall-cleaning manipulator equipped with disturbance observer (DOB) and sliding mode control (SMC). In order to keep in contact with various shapes of walls, the proposed manipulator is designed to ensure 2-DOF motions of translation and tilting by using ball screws. The position-based force tracking impedance control (FTIC) is first adopted for the proposed manipulator not only to interact with walls in a desired dynamic behavior but also to maintain a constant contact force. Also, to improve the force tracking capability of proposed manipulator against different walls and brushes for manipulator, the FTIC is combined with the disturbance observer (DOB) and the sliding mode control (SMC). Extensive experiments prove that although different brushes used for manipulator rotate against varying shapes of walls, the proposed manipulator can keep a constant contact force within a bound of ± 4.5 N by virtue of the proposed FTIC equipped with the DOB and the SMC.