Weijie 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.

Internal Model-Based Robust Tracking Control Design for the MEMS Electromagnetic Micromirror

The micromirror based on micro-electro-mechanical systems (MEMS) technology is widely employed in different areas, such as scanning, imaging and optical switching. This paper studies the MEMS electromagnetic micromirror for scanning or imaging application. In these application scenarios, the micromirror is required to track the command sinusoidal signal, which can be converted to an output regulation problem theoretically. In this paper, based on the internal model principle, the output regulation problem is solved by designing a robust controller that is able to force the micromirror to track the command signal accurately. The proposed controller relies little on the accuracy of the model. Further, the proposed controller is implemented, and its effectiveness is examined by experiments. The experimental results demonstrate that the performance of the proposed controller is satisfying.

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.

Modelling and adaptive dynamic sliding mode control of dielectrophoresis-based micromanipulation

Automated, precise single particle manipulation in the microscale is in great demand and is one of the great challenges in biomedical and biochemical engineering. Automatic micromanipulation has also become a microrobotics challenge. Following this challenge, control technology is integrated with dielectrophoresis (DEP)-based micromanipulation technology in this paper to construct automatic DEP-based micromanipulation systems. DEP micromanipulation systems with electrodes of quadrupole polynomial geometry are developed as controllable microactuators. A semianalytical modelling method is proposed to formulate the analytical models of the DEP manipulation systems, which manifests that the DEP manipulation systems are non-affine non-linear systems. Then, taking the parameter uncertainties, unmodelled dynamics and external disturbances into account, an adaptive law combined with a dynamic sliding mode controller is designed for two-dimensional trajectory tracking control of a DEP micromanipulation system. The closed-loop system is proved stable in the presence of bounded lumped uncertainty based on the Lyapunov theorem. Finally, simulation results show the validity of the proposed control design.

An Enhanced Robust Control Algorithm Based on CNF and ISM for the MEMS Micromirror against Input Saturation and Disturbance

Input saturation is a widespread phenomenon in the field of instrumentation, and is harmful to performance and robustness. In this paper, a control design framework based on composite nonlinear feedback (CNF) and integral sliding mode (ISM) technique is proposed for a MEMS micromirror to improve its performance under input saturation. To make the framework more effective, some essential improvements are supplied. With the application of the proposed design framework, the micromirror under input saturation and time-varying disturbances can achieve precise positioning with satisfactory transient performance compared with the open-loop performance.

Constraint robust adaptive stabilization for a class of lower triangular systems with unknown control direction

This paper studies the constrained robust adaptive stabilization problem for a class of lower triangular systems with unknown control direction. A robust adaptive feedback control law for the systems is proposed by incorporating the technique of Barrier Lyapunov Function with Nussbaum gain. Such a controlled system arises from the study of the constrained robust output regulation problem for a class of output feedback systems with the unknown control direction and a nonlinear exosystem. An application of the constrained robust adaptive stabilization design leads to the solution of the constrained robust output regulation problem in the sense that the output tracking error is constrained within the prescribed barrier limit while asymptotically approaching to zero and the closed loop signals are all bounded for all the time. A numerical example is provided to illustrate the performance of the proposed control.

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.

A robust control approach for MEMS capacitive micromachined ultrasonic transducer

An optimal composite nonlinear feedback control method with integral sliding mode is presented in this paper. The controller extends the travel range of the micro-electromechanical system capacitive micromachined ultrasonic transducer (CMUT). Moreover, enhanced transient response and precise tracking performance is achieved. It is known that CMUT is inherently unstable which results in pull-in phenomenon and it is very sensitive to small perturbations, so one of the major problems is to stabilize the CMUT beyond the pull-in limit with the external disturbances. In addition, the input saturation problem is significant to CMUT. Based on that, a robust control scheme is derived using composite nonlinear feedback control law combined with integral sliding mode control law. Then all the tuning parameters for the proposed control method are converted into a minimization problem and solved by particle swarm optimization algorithm automatically. We verified the effectiveness through extending the travel range of the CMUT gap by three control methods which are proportional integral derivative, composite nonlinear feedback and the method we proposed. The stability and small range tracking performance with three control methods is compared on the pull-in position of CMUT. The simulations show that the proposed control method has desired tracking performance and robustness to external disturbance with input saturation.