Publications

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The purpose of this report is to provide an overview of Micro-System technology as it applies to inertial sensing. Transduction methods are reviewed with capacitance and piezoresistive being the most often used in COTS Micro-electro-mechanical system (MEMS) inertial sensors. Optical transduction is the most recent transduction method having significant impact on improving sensor resolution. A few other methods are motioned which are in a R&D status to hopefully allow MEMS inertial sensors to become viable as a navigation grade sensor. The accelerometer, gyroscope and gravity gradiometer are the type of inertial sensors which are reviewed in this report. Their method of operation and a sampling of COTS sensors and grade are reviewed as well.

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One of the challenges facing microrobotic manufacturing is the ability to sense interactions for force-guided assembly of small devices. There is a need for a force transducer with the ability to sense forces in multiple degrees-of-freedom in the mN range with resolution on the order of 10 μN for microassembly applications. This paper presents theoretical studies for developing a surface micromachined piezoresistive force transducer that can measure normal force in the z-direction and moments about the x and y-axes. The devices proposed here are based on a compliant platform design with integrated piezoresistive sensing elements fabricated in a modified SUMMiT process. Various configurations and sensor element layouts are explored to determine the relationship of the applied forces and moments experienced during assembly and the corresponding strain. Structural and finite element analysis is used to determine the elastic response of the device and establish the best locations and orientations of the sensing elements to effectively utilize the piezoresistive effect of the polysilicon sensors. Initial experiments show the polysilicon piezoresistors to have a gauge factor of approximately 25. The expected sensitivities for these devices are presented. Copyright © 2005 by ASME.

The objective of this LDRD project was to develop a programmable diffraction grating fabricated in SUMMiT V{trademark}. Two types of grating elements (vertical and rotational) were designed and demonstrated. The vertical grating element utilized compound leveraged bending and the rotational grating element used vertical comb drive actuation. This work resulted in two technical advances and one patent application. Also a new optical configuration of the Polychromator was demonstrated. The new optical configuration improved the optical efficiency of the system without degrading any other aspect of the system. The new configuration also relaxes some constraint on the programmable diffraction grating.

Micro mirrors have emerged as key components for optical microelectromechanical system (MEMS) applications. Electrostatic vertical comb drives are attractive because they can be fabricated underneath the mirror, allowing for arrays with a high fill factor. Also, vertical comb drives are more easily controlled than parallel plate actuators, making them the better choice for analog scanning devices. The device presented in this paper is a one-degree of freedom vertical comb drive fabricated using Sandia National Laboratories SUMMiT™ five-level surface micromachining process. The electrostatic performance of the device is investigated using finite element analysis to determine the capacitance for a unit cell of the comb drive as the position of the device is varied. This information is then used to design a progressive linkage that will seek to alleviate or eliminate the effects of instability. The goal of this research is to develop an electrostatic model for the behavior of the vertical comb drive mirror and then use this to design a progressive-linkage that can delay or eliminate the pull-in instability. Copyright © 2005 by ASME.

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Electrostatic comb drives are widely used in microelectromechanical devices. These comb drives often employ rectangular fingers which produce a stable, constant force output as they engage. This paper explores the use of shapes other than the common rectangular fingers. Such shaped comb fingers allow customized force-displacement response for a variety of applications. In order to simplify analysis and design of shaped fingers, a simple model is developed to predict the force generated by shaped comb fingers. This model is tested using numerical simulation on several different sample shaped comb designs. Finally, the model is further tested, and the use of shaped comb fingers is demonstrated, through the design, fabrication, and testing of tunable resonators which allow both up and down shifts of the resonant frequency. The simulation and testing results demonstrate the usefulness and accuracy of the simple model. Finally, other applications for shaped comb fingers are described, including tunable sensors, low-voltage actuators, multistable actuators, or actuators with linear voltage-displacement behavior.

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The three-year LDRD ''CNC Micromachines'' was successfully completed at the end of FY02. The project had four major breakthroughs in spatial motion control in MEMS: (1) A unified method for designing scalable planar and spatial on-chip motion control systems was developed. The method relies on the use of parallel kinematic mechanisms (PKMs) that when properly designed provide different types of motion on-chip without the need for post-fabrication assembly, (2) A new type of actuator was developed--the linear stepping track drive (LSTD) that provides open loop linear position control that is scalable in displacement, output force and step size. Several versions of this actuator were designed, fabricated and successfully tested. (3) Different versions of XYZ translation only and PTT motion stages were designed, successfully fabricated and successfully tested demonstrating absolutely that on-chip spatial motion control systems are not only possible, but are a reality. (4) Control algorithms, software and infrastructure based on MATLAB were created and successfully implemented to drive the XYZ and PTT motion platforms in a controlled manner. The control software is capable of reading an M/G code machine tool language file, decode the instructions and correctly calculate and apply position and velocity trajectories to the motion devices linear drive inputs to position the device platform along the trajectory as specified by the input file. A full and detailed account of design methodology, theory and experimental results (failures and successes) is provided.

The primary goal of this portion of the LDRD is to develop a vertical programmable diffraction grating that can be fabricated with Sandia's Ultra-planar Multi-level MEMS Technology, the SUMMiT V{trademark} process. This grating is targeted for use in a chemical detection system dubbed the Polychromator. A secondary goal is to design diffraction grating structures with additional degrees of freedom (DOF). Gratings with 2.5 microns of vertical stroke have been realized. In addition, rotational DOF grating structures have been successfully actuated, and a structure has been developed that minimizes residual stress effects.

In this paper we describe a high amplitude electrostatic drive for surface micromachined mechanical oscillators that may be suitable for vibratory gyroscopes. It is an advanced design of a previously reported dual mass oscillator (Dyck, et. al., 1999). The structure is a 2 degree-of-freedom, parallel-plate driven motion amplifier, termed the secondary mass drive oscillator (SMD oscillator). During each cycle the device contacts the drive plates, generating large electrostatic forces. Peak-to-peak amplitudes of 54 μm have been obtained by operating the structure in air with an applied voltage of 11 V. We describe the structure, present the analysis and design equations, and show recent results that have been obtained, including frequency response data, power dissipation, and out-of-plane motion.

This paper describes the configuration space representation of mechanical function and shows how it supports the design of micro-mechanisms. The domain characteristics of curved geometry, joint play, and custom joints render traditional design tools inappropriate, but configuration spaces can model these characteristics. They represent the quantitative and the qualitative aspects of kinematic function in a concise geometric format that helps designers visualize system function under a range of operating conditions, find and correct design flaws, study joint play, and optimize performance. The approach is demonstrated on a surface micromachined counter meshing gear discrimination device developed at Sandia National Laboratories.

Electronic sensing circuitry and micro electro mechanical sense elements can be integrated to produce inertial instruments for applications unheard of a few years ago. This paper will describe the Sandia M3EMS fabrication process, inertial instruments that have been fabricated, and the results of initial characterization tests of micro-machined accelerometers.

Active control of structures has been under intensive development for the last ten years. Reference 2 reviews much of the identification and control technology for structural control developed during this time. The technology was initially focused on space structure and weapon applications; however, recently the technology is also being directed toward applications in manufacturing and transportation. Much of this technology focused on multiple-input/multiple-output (MIMO) identification and control methodology because many of the applications require a coordinated control involving multiple disturbances and control objectives where multiple actuators and sensors are necessary for high performance. There have been many optimal robust control methods developed for the design of MIMO robust control laws; however, there appears to be a significant gap between the theoretical development and experimental evaluation of control and identification methods to address structural control applications. Many methods have been developed for MIMO identification and control of structures, such as the Eigensystem Realization Algorithm (ERA), Q-Markov Covariance Equivalent Realization (Q-Markov COVER) for identification; and, Linear Quadratic Gaussian (LQG), Frequency Weighted LQG and H-/ii-synthesis methods for control. Upon implementation, many of the identification and control methods have shown limitations such as the excitation of unmodelled dynamics and sensitivity to system parameter variations. As a result, research on methods which address these problems have been conducted.

This paper studied the behavior of retained system poles and transmission zeros in a control design model when the model is truncated. The sensitivity of the transmission zeros due to the tuncation of system dynamics was analytically obtained. The sensitivity of system poles to the truncation of system dynamics was shown to be zero as expected. The effects of actuator-sensor type and location was also studied. The results were illustrated with two example problems. The effect of transmission zero shifts in control design models and the controllers designed from them was illustrated with an example.

Structural system identification methods are analytical techniques for reconciling test data with analytical models. However, for system identification to become a practical tool for engineering analysis, the estimation techniques/codes must communicate with finite element software packages without intensive analyst intervention and supervision. This paper presents a technique used to integrate commercial software packages for finite element modeling (MSC/NASTRAN), mathematical programming techniques (ADS), and linear system analysis (PRO-MATLAB). The parameter estimation techniques and the software for controlling the overall system were programmed in PRO-MATLAB. Two examples of application of this software using measured data are presented. The examples consist of a truss structure in which the model form is well defined, and an electronics package whose model form is ill-defined since it is difficult to model with finite elements. A comparison of the resulting updated models with the experimental data showed significant improvement. 22 refs.

The winding process is encountered frequently in manufacturing, such as winding of polymer films and paper, laminated pressure vessel construction, and the manufacture of wound capacitors. The winding of capacitors will typically involve hundreds of plies of conductor and dielectric wound over a core. Due to the large number of layers, the calculation of the mechanical studies within a wound capacitor is a significant computational task. The focus of Part II of this paper is the formulation and application of optimization techniques for the design of wound capacitors. The design criteria to be achieved is a specified uniform wound tension in a capacitor. The paper will formulate an optimization statement of the wound capacitor design problem, develop a technique for reducing the numerical calculation required to repeatedly analyze the capacitor as required by the optimization algorithm, and apply the technique to an example. 4 refs., 13 figs., 4 tabs.