Zhendong Sun

Second-order sliding mode control of a 2D torsional MEMS micromirror with sidewall electrodes

A second-order sliding mode control (2-SMC) scheme with a proportional integral derivative (PID) sliding surface, to achieve enhanced transient response, accurate positioning and precise tracking performance of a 2-degree-of-freedom (2D) torsional MEMS micromirror with sidewall electrodes, is developed in this paper. The PID sliding surface is chosen to achieve a zero steady-state error of the closed-loop system. The 2-SMC is able to reduce the chattering phenomena, which comprises of an equivalent control and switching control to dominate model uncertainty and external disturbances leading to an enhanced performance of the controlled system. Finite-time convergence of the closed-loop system in the presence of bounded parameter uncertainties and external disturbances is guaranteed through Lyapunov stability analysis. The proposed 2-SMC is programmed in a LABVIEW environment and implemented based on National Instrument (NI) field-programmable gate array hardware to verify the effectiveness and robustness. The experimental results of set-point regulation and sinusoidal trajectory tacking demonstrate that the closed-loop system with the proposed control scheme significantly improves the transient performance, accurate positioning and trajectory tracking with robustness against external disturbance. The 95% settling time is shortened from 70 to 3 ms for the X-axis and from 60 to 3 ms for the Y-axis respectively, the overshoots and steady-state errors are eliminated in both axes, and less than 5% maximum positioning error is achieved in the presence of external disturbance.

Nonlinear control of an electromagnetic polymer MEMS hard-magnetic micromirror and its imaging application

In this paper, a nonlinear feedback control algorithm is proposed to improve the performance of an electromagnetic actuated polymer MEMS hard-magnetic micromirror. The enhanced performance and effectiveness of the proposed algorithm are verified experimentally through National Instrument Field-Programmable Gate Array hardware. Considering the critical requirements in the micromirror-based optical switching applications, the set-point regulation tests are performed to investigate the transient and positioning performance of the system. The proposed scheme provides enhanced transient response when compared to traditional proportional-integral-derivative control. Compared with open loop control, the experimental results of set-point regulation have demonstrated that the 95% setting time is shortened from 50 to 10 ms while the 30% overshoot is eliminated with high positioning performance by using the proposed scheme. A magnetic micromirror-based laser scanning system is developed to verify the tracking and imaging performance of the closed-loop system with the proposed scheme. The results confirm that the closed-loop controlled magnetic micromirror follows the given sinusoidal and triangle trajectories precisely with the proposed scheme and an image of the scanned target is obtained.

Effect of CNTs alignment on electrical conductivity of PDMS/MWCNTs composites

A new 3D percolation network model is proposed to analyze the effects of CNTs alignment on electrical conductivity of polydimethylsiloxane (PDMS)/CNTs composites, wherein the polymer-type dependent formula is employed to adjust data in comprehensive experiments. In the Monte Carlo simulation, the percolation threshold of multi-walled CNTs (MWCNTS) filled PDMS composites at each given alignment is compared with existing experiment results. The results show that for a fixed measurement direction, perfectly aligned MWCNTs results in a worse conductivity; while for a fixed volume fraction and partially aligned CNTs, with alignment angle of 30°, can achieve the best electrical conductivity for PDMS/MWCNTs composites.

Tracking control of an electrostatic torsional micromirror beyond the pull-in limit with enhanced performance

In this paper, we will study the output-error-constrained tracking control problem of an electrostatic torsional micromirror beyond the pull-in limit. We will first show that this problem can be formulated as a robust output regulation problem and it further boils down to a robust regulation problem with output-constrained by adaptive internal model design, the solution of which would in turn lead to the solution of the original problem. Then we design a regulation controller for such a regulation problem by using the barrier Lyapunov function technique. Our adaptive control law ensures the electrostatic torsional micromirror with a enhanced tracking performance in the sense that the moveable micromirror can achieve the sinusoidal wave scanning of any frequency up to a full gap operation without contacts of the fixed bottom electrode, and furthermore, the estimated sinusoidal wave frequency converges to its real value.

Sliding mode control of a 2D torsional MEMS micromirror with sidewall electrodes

In this paper, a first-order sliding mode controller is implemented to control the tilt angle of a 2-Degree-of-freedom (DOF) torsional MEMS micromirror with sidewall electrodes. Stability of the closed-loop system is proved by Lyapunov method. Furthermore, both the experimental and simulation results are shown to verify the effectiveness of the control scheme. It is demonstrated that the torsional MEMS micromirror with proposed sliding mode controller has good transient response and tracking performance.

Numerical and experimental study of radiation induced conductivity change of carbon nanotube filled polymers

Measuring the conductivity changes of sensing materials to detect a wide range of radiation energy and dosage is one of the major sensing mechanisms of radiation sensors. Carbon nanotube (CNT) filled composites are suitable for sensing radiation because of the extraordinary electrical properties of CNTs and the CNT-network formed inside the polymer matrix. Although the use of CNT-based nanocomposites as potential radiation sensing materials has been widely studied, there is still a lack of theoretical models to analyze the relationship between electrical conductivity and radiation dosages. In this article, we propose a 3D model to describe the electrical conductivity of CNT-based nanocomposites when being irradiated by ionizing radiation. The Monte Carlo method has been employed to calculate radiation intensity, CNT concentration and alignments influence on the electrical conductivity. Our simulation shows a better agreement when CNT loading is between the percolation threshold and 3% volume fraction. Radiation experiments have been performed to verify the reliability of our model to illustrate a power function relationship between the electrical conductivity of a CNT-filled polymer and radiation intensity. In addition, the predicted alignment to obtain the best sensitivity for radiation sensing has been discussed to help with CNT-network building in the fabrication process.

Twisting sliding mode control of an electrostatic MEMS micromirror for a laser scanning system

In this paper, we present a twisting control scheme with proportional-integral-derivative ( PID ) sliding surface for a two-axis electrostatic torsional micromirror, and the utilization of the proposed scheme in a laser scanning system. The experimental results of set-point regulation verify that the proposed scheme provides enhanced transient response and positioning performance as compared to traditional sliding mode control. To evaluate the tracking performance of the closed-loop system, triangular waves with different frequencies are used as desired traces. With the proposed scheme the experimental results verified that the closed-loop controlled micromirror follows the given triangular trajectories precisely. A micromirror-based laser scanning system is developed to obtain images. When compared with open-loop control, the experimental results demonstrated that the proposed scheme is able to reduce the distortion of the raster scan, and improve the imaging performance in the presence of cross-coupling effect.

Active Disturbance Rejection Control of a 2D MEMS Micromirror with Sidewall Electrodes

This study proposes the active disturbance rejection control (ADRC) for a second degree of freedom (2D) electrostatic torsional micromirror with sidewall electrodes. The main idea is to use the linear extended state observer (LESO) to estimate the external disturbance and the angular velocity of the micromirror, and a feedback controller is further applied to achieve the position control of the micromirror. The effectiveness of the LESO in the estimation of the external disturbance and angular velocity is demonstrated. The proposed novel control scheme provides the micromirror with high positioning accuracy and disturbance rejection.

High performance closed-loop control of a 2D MEMS micromirror with sidewall electrodes for a laser scanning microscope system

This paper presents the design and experimental implementation of an adaptive sliding mode control scheme for a 2D MEMS micromirror with sidewall electrodes(SW), a closed-loop controlled 2D micromirror-based laser scanning microscope system is developed based on NI field-programmable gate array (FPGA) hardware, 2D image of the scanned target are obtained. Controller implementation, image acquisition and display are performed with LABVIEW software through the FPGA card. Compared with open-loop control, the experimental results demonstrated that the proposed scheme is able to reduce the Y-to-X cross-axis effect and achieve accurate tracking of a reference triangular signal. The scanning performance is significantly improved, and better 2D image of target is obtained using the micromirror with the proposed scheme.

Application of twisting algorithm to a 2D electrostatic MEMS micromirror

In this paper, a second-order sliding mode control (2-SMC) scheme, called twisting algorithm, is applied to control an electrostatically actuated 2D torsional MEMS micromirror. The proposed twisting algorithm is able to improve the transient and positioning performance of the controlled 2D micromirror including robustness against model uncertainties and external disturbances. The main advantages of the proposed scheme over the first-order SMCare chattering attenuation and enhanced positional accuracy. The closed-loop stability and higher performance of the micromirror under closed-loop control is verified though numerical simulations and experiments.