A high-stroke, high-pressure electrostatic actuator for valve applications

This paper presents a novel large-stroke electrostatic valve actuator for high-pressure applications. The combination of pressure balancing and flexible electrode structures ensures large flow gaps at a low actuation voltage. A simulation tool was built to evaluate the design parameters. Design specific, as well as general optimisations are performed. The model shows a 5.6 times (theoretical) performance improvement compared to earlier designs. A micromachined test structure was fabricated and evaluated. Measurement results are presented and discussed.     

Electrostatic actuation as a self-testing method for silicon pressure sensors

The aim of this work is to investigate the possibility of using electrostatic forces to actuate the membrane of a pressure sensor in order to create self-testing features in the system. It is shown that the electrostatic pressure is small compared with the external pressure, unless large voltages or electrical charges are used. The interrelation between electrostatic forces and externally applied pressure is calculated for different electrical drive modes of the capacitor, in the case of a uniform membrane and for a MESA-type membrane.     

A novel bulk micromachined electrostatic microvalve with acurved-compliant structure applicable for a pneumatic tactile display

Recent success of microelectromechanical systems (MEMS) in projection displays have raised similar expectation for an efficient, low power, affordable, full-page and pneumatic tactile display. Such design has not been achieved by the conventional technology but could bring significant improvement to current refreshable Braille displays. This paper demonstrates a novel bulk-micromachined electrostatic microvalve suitable for a pneumatic tactile display. The microvalve, a silicon perforated diaphragm juxtaposed to a silicon inlet orifice, requires relatively low closing voltage against a large supply differential pressure and flow rate, i.e., 72.9 V-rms for 19.3 kPa and 85 mi/min. Such an attractive characteristic is due to its unique curved-compliant structure that has, unlike other electrostatic microvalves, no tolerance for any initial air gap between its electrodes. As a design tool, a mechanical model of the microvalve is introduced based on the lubrication theory and large plate deflection theory. The model is established on a steady-state coupled field problem of fluid-solid mechanics. Reynolds and von-Karman equations were simultaneously solved for the microvalve geometry by finite difference approximation and double Fourier series expansion. The results of the model and experiments are compared and found to be in good agreement with a relative error less than 10%     

A single crystal silicon 3 dimensional processing technique with applications in large displacement electrostatic actuation

 A new process has been developed to produce mechanical structures of multiple levels on a silicon substrate. The process lends itself to high aspect ratio bulk micromachining of single crystal silicon. Structures can be fabricated at multiple levels with a single lithography step and without alignment requirements. Any required difference in height between levels is defined precisely at intermediate etch steps. One application of this process utilizes the out of plane asymmetries produced by the multiple levels to create a large displacement, large force and highly linear out of plane actuator stage. This technique is easily combined with single level high aspect ratio MEMS processing methods. Received: 10 August 2001/Accepted: 24 September 2001     

A microvalve for lab-on-a-chip applications based on electrochemically actuated SU8 cantilevers

Increasing the complexity and functionality of Lab-on-a-Chip devices requires integrated valves for internal flow regulation. The device introduced in this work is an electrochemical SU8 microvalve, featuring a cantilevered structure that seals an adjacent channel under the action of a growing electrolysis bubble. The valve is based on previously reported movable microcantilevers embedded in microchannels. As opposed to membrane valves moving perpendicular to the substrate, the cantilever valve is patterned next to the channel and closes it by moving horizontally, dramatically reducing footprint. Its compact, monolithic and 2D construction reduces assembly problems and results in negligible increase in dead volume (14.5 nl). Besides, its location in the way of the channels avoids the need for auxiliary filling ports or separate working media for actuation. Effective sealing with negligible leakage at 20 kPa has been achieved. The valve also displays passive flow regulation induced by the pressure differential generated across the valve chamber under flow conditions (42-72% flow decrease).     

Bio-inspired backstepping adaptive sliding mode control for parallel mechanism with actuation redundancy

This paper presents a bio-inspired backstepping adaptive sliding mode control strategy for a novel 3 degree of freedom (3-DOF) parallel mechanism with actuation redundancy. Based on the kinematic model and the dynamic model, a sliding mode controller is designed to assure the tracking performance, and an adaptive law is introduced to approximate the system uncertainty including parameters’ variation, external disturbances and un-modeled part. Furthermore, a bio-inspired model is introduced to solve the inherent chattering problem of sliding mode control and provide a chattering free control. The simulation and experimental results testify that the proposed bio-inspired backstepping adaptive sliding mode control can achieve better performance (the tracking accuracy, robustness, response speed, etc.) than the conventional slide mode control.     

Concurrent design of controller and passive elements for robots with impulsive actuation systems

There are some biological evidences showing that the actuation system in legged animals is impulsive; it is not continuous. As opposed to continuous control/actuation, the control actions occur in specific intervals, and from the instant of one actuation until the start of the next one, passive elements guarantee the stability of the robotic system and govern its natural dynamics. In this paper, we present an analytical method for concurrent design of impulsive controller and passive elements (compliance and damper) for robotic systems; e.g., manipulators and legged-robots. To optimize the force profiles of passive elements, three different cost functions are presented which optimize the natural dynamics and energy consumption of the robot. The presented method can be applied to both cyclic and non-cyclic (explosive) tasks so as to attain energy efficient and bio-inspired motions. The method is applied to three biological models: a simulated human arm for throwing an object, a swing leg for drawing an oval, and a 3D quadruped robot for performing walking gait. Our findings in the simulation studies are in line with the hypothesis of impulsive actuation in nature and show the applicability of our method in robotics.     

A duality principle for homogeneous vectorfields with applications

We introduce a duality principle for homogeneous vectorfields. As an application of this duality principle, stability and boundedness results for negative order homogeneous differential equations are obtained, starting from known results for positive order homogeneous differential equations.     

Energy-saving optimal control for a factual electrostatic precipitator with multiple electric-field stages based on GA

For energy-saving control of electrostatic precipitator with multiple electric-field stages, a new optimal control strategy to minimize the total power consumption by adjusting the secondary voltages subject to the dust outlet concentration requirement is suggested. The optimal problem is established on the basis of the proposed mathematical models on the secondary voltage relating to the outlet concentration, the secondary current, the primary voltage and the primary current, and is solved by the genetic algorithm. A practice application to an industrial precipitator is given as well.     

A stochastic maximum principle for systems with jumps, with applications to finance

We consider a stochastic control problem with linear dynamics with jumps, convex cost criterion, and convex state constraint, in which the control enters the drift, the diffusion, and the jump coefficients. We allow these coefficients to be random, and do not impose any L^p-bounds on the control.

We obtain a stochastic maximum principle for this model that provides both necessary and sufficient conditions of optimality. This is the first version of the stochastic maximum principle that covers the consumption–investment problem in which there are jumps in the price system.     

Fabrication and characterization of cantilevers with integrated sharp tips and piezoelectric elements for actuation and detection for parallel AFM applications

We have developed a new process to fabricate arrays of cantilevers with integrated tips for atomic force microscope (AFM) imaging and a piezoelectric layer for vertical actuation and detection. A good homogeneity of the tip shape is obtained thanks to a self-sharpening effect. The cantilevers have been characterized mechanically and electrically.     

A second-order maximum principle for discrete-time bilinear control systems with applications to discrete-time linear switched systems

A powerful approach for analyzing the stability of continuous-time switched systems is based on using optimal control theory to characterize the “most unstable” switching law. This reduces the problem of determining stability under arbitrary switching to analyzing stability for the specific “most unstable” switching law. For discrete-time switched systems, the variational approach received considerably less attention. This approach is based on using a first-order necessary optimality condition in the form of a maximum principle (MP), and typically this is not enough to completely characterize the “most unstable” switching law. In this paper, we provide a simple and self-contained derivation of a second-order necessary optimality condition for discrete-time bilinear control systems. This provides new information that cannot be derived using the first-order MP. We demonstrate several applications of this second-order MP to the stability analysis of discrete-time linear switched systems.     

A risk‐sensitive stochastic maximum principle for fully coupled forward‐backward stochastic differential equations with applications

In this paper, we are interested in the problem of optimal control where the system is given by a fully coupled forward‐backward stochastic differential equation with a risk‐sensitive performance functional. As a preliminary step, we use the risk neutral which is an extension of the initial control system where the admissible controls are convex, and an optimal solution exists.Then, we study the necessary as well as sufficient optimality conditions for risk sensitive performance. At the end of this work, we illustrate our main result by giving an example that deals with an optimal portfolio choice problem in financial market, specifically the model of control cash flow of a firm or project where, for instance, we can set the model of pricing and managing an insurance contract.