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Combining the resolution of conventional gas chromatography systems with the size factor of microGC systems is important for improving the affordability and portability of high performance gas analysis. Recent work has demonstrated the feasibility of high resolution separation of gases in a benchtopscale short column system by controlling thermal gradients through the column. This work reports a microfabricated thermally controllable gas chromatographic column with a small footprint (approximately 6.25 cm2). The design of the 20 cm column utilizes 21 individually controllable thin film heaters and conduction cooling to produce a desired temperature profile. The reported device is capable of heating and cooling rates exceeding 8000 °C/min and can reach temperatures of 350 °C. The control methods allow for excellent disturbance rejection and precision to within +/− 1 °C. Each length of the column between heaters was demonstrated to be individually controllable and displayed quadratic temperature profiles. This paper focuses on the fabrication process and implementation of the thermal control strategy. [2019–0113]

This paper presents the development of an origami-inspired support system (the OriGuide) that enables the insertion of flexible instruments using medical robots. Varying parameters of a triangulated cylindrical origami pattern were combined to create an effective highly compressible anti-buckling system that maintains a constant inner diameter for supporting an instrument and a constant outer diameter throughout actuation. The proposed origami pattern is composed of two repeated patterns: a bistable pattern to create support points to mitigate flexible shaft buckling and a monostable pattern to enable axial extension and compression of the support system. The origami-based portion of the device is combined with two rigid mounts for interfacing with the medical robot. The origami-based portion of the device is fabricated from a single sheet of polyethylene terephthalate. The length, outer diameter, and inner diameter that emerge from the fold pattern can be customized to accommodate various robot designs and flexible instrument geometries without increasing the part count. The support system also adds protection to the instrument from external contamination.

The cylindrical cross-axis flexural pivot (CCAFP) is proposed as an ultra-compact flexure capable of being integrated into hollow cylindrical shafts, enabling shaft motion without inhibiting cables or other components inside the shaft. Mechanism geometry, materials, and manufacturing are proposed and the results analyzed and tested. A parametric finite element model of the CCAFP was created to analyze the force-deflection and strain-deflection relationships and the predicted behavior was verified by experiment. Analytic models of stress-limiting cam-surfaces suggest even larger motions may be possible when not limited by current practical constraints. The CCAFP is demonstrated and tested at multiple size scales and in multiple materials, ranging from 28.6 mm diameter 4130 steel (achieving 9 degrees of angular deflection) to 3 mm diameter NiTi (achieving an angular deflection of 85 degrees). The results are generalized to apply to a range of applications, and the CCAFP particularly shows promise for implementation in minimally invasive surgical instruments to decrease instrument size while maintaining instrument performance.

This work presents two novel support systems used to help mitigate flexible device buckling during insertion such as the insertion of medical device into the body. These systems are collapsible to accommodate the changing length of the flexible device as it is inserted. They use tension in wires or geometry to provide systems with lateral stiffness used to support the device. Through modeling, the performance of these systems can be predicted and they can be designed to a desired performance. This was validated in the geometry-based support system. They provide systems with small operating volumes and part counts.

The Zipper Tube Reinforcement (ZTR) is a novel support system developed to mitigate buckling in thin flexible devices used in robotic surgery. The ZTR was inspired by a construction technique called a Buckling Restrained Braced Frame (BRBF) and deployable booms for space applications. It utilizes a zipper function to allow a rolled sheet to deploy into a variable-length tube and stow in a small volume spooled on a mandrel. The tube envelops the device and allows it to support a much higher compressive load before buckling failure through the insertion stroke. The ZTR also enables the possibility of smaller, more flexible devices due to its design for continuous support and could find application in other fields.

This paper reports on the design, fabrication, and testing of a fully-compliant mechanism designed for precise parallel guidance. The mechanism is designed to guide arrays of micro-scale needles for straight-line injections of thousands of culture cells simultaneously. During injection, the needle array is to be lowered into the cell culture dish. It must be guided carefully during insertion of the needles into the cells because any rotation or transverse motion of the needles during insertion can lead to tearing of the delicate cell membranes, leading to cell death. The injection system consists of a fully-compliant mechanism designed for straight-line motion, while resisting motions in other direction. Successive prototypes are shown to illustrate the process of design, and to illustrate the benefits of the final system. Prototypes were demonstrated using deep reactive ion etching of silicon wafers, as well as rapid prototyping using a three-dimensional printer in ABS polymer. The final system consists of a single, 3-D-printed part that incorporates compliance to guide the needle array over a distance of about 1.5 mm while restraining transverse deflections or rotations. Testing shows that injections performed using the system result in high cell viability, suggesting that the system appropriately restrains off-axis motions. While the system demonstrated here is designed specifically for biological research, it may be adapted to manufacturing, position control, or any other application requiring straight-line motion while minimizing transverse deflections or rotations.

This paper investigates the design of a nano-injection system that can deliver genetic material to cells within live tissue. The approach to creating such a system was to create candidate designs that meet all the requirements for successful in vivo injection and can be fabricated using silicon etching. The designs were tested through large-scale prototyping and through models that describe the systems’ behavior on the micrometer scale. One design consists of an array of lances on a rigid backing. The other design consists of an array of lances grouped in sets of three on a backing that can conform to the shape of the tissue being injected. Each design was prototyped in 3D printed ABS plastic. Preliminary results were qualitative and showed that the rigid and flexible designs performed similarly on mostly flat and irregular surfaces. On convex surfaces with a strong curvature (radius of curvature of about 2 cm), the flexible array gave slightly better results. Final testing gave a quantitative comparison of the two designs’ efficiencies on strongly curved convex surfaces. These results supported the preliminary results that the flexible array is more efficient in reaching points on the tissue than the rigid array is. As the applied force increased, each array performed more efficiently.Copyright © 2016 by ASME

This paper presents a performance-based comparison of quadratic shell elements with shear deformation and 3-D quadratic solid elements for modeling geometrically non-linear coupled in-plane and out-of-plane deflection of thin-film compliant microelectromechanical systems. A mesh density study of a single out-of-plane torsional compliant element indicates that a relatively coarse shell element mesh can produce force, displacement, and stress results very similar to those predicted by a much larger and computationally costly 3-D solid element model for out-of-plane loading. Shell and 3-D solid element models of a macro-scale prototype of a MEMS compliant lamina emergent constant-force mechanism are shown to agree very well with experientially acquired force displacement data, and to agree well in their estimates of Von Mises stresses. Close agreement of shell element and 3-D solid element models is also demonstrated for models of a thin-film MEMS constant-force mechanism and a thin-film MEMS cellular lance mechanism. Both of these mechanisms exhibit highly non-linear mechanism stiffness, and large, coupled in and out-of-plane displacements. Together, these results strongly suggest that quadratic shell elements with shear deformation can be used to model the coupled in-plane and out-of-plane motion of thin-film compliant mechanisms.

This paper introduces piezoresistive encoders that can provide information on the performance of ratcheting actuation systems, and may be useful in future applications that require position determination. One unique feature of the encoders is that they gain their piezoresistance from the bulk properties of polycrystalline silicon without additional fabrication steps. In this study, two encoders are considered: a parallel-guiding encoder in an on-chip Wheatstone bridge, and a piezoresistive microdisplacement transducer (PMT) encoder in an on-chip Wheatstone bridge. In tests, the encoders each generated measurable signals, with the PMT encoder providing the best sensitivity. The PMT encoder operated at actuation frequencies up to 920 Hz and produced a signal between 2 V and 3.2 V (applied gain of 1000). The PMT encoder produced unique signals corresponding to distinct ideal and non-ideal behaviors of a ratchet wheel actuation system.

This paper presents a microelectromechanical test device and calibration method for finding torsional piezoresistive coefficients for micro sensing applications. The test device consists of a slider-crank connected to two torsional legs. The slider-crank creates torsional stress in the legs which causes a change in the electrical resistance through the legs. A model that predicts the effects of a scissor hinge on the slider-crank is presented. Torsional stresses in the legs are calculated and the legs are discretized into long parallel resistors and the stresses applied to each resistor. Assuming a second-order piezoresistance, an optimization is then done to find the piezoresistive coefficients by changing them until the model prediction fits the test data. These coefficients can be used to predict angular displacement from resistance measurements in fully integrated torsional sensors.

This paper describes a battery-free threshold shock sensor with wireless readout via RFID circuitry. The entire package is designed to provide low-cost sensors for monitoring shock loads in applications such as shipping. The sensor is based on a mechanical bistable mechanism laser-cut from a single Delrin layer which switches states when exposed to accelerations above a threshold. The sensor was tested using quasi-static accelerations in a centrifuge, pulsed accelerations from an impact event, and vibration (sinusoidal) accelerations on a shaker table. Measured threshold accelerations were similar in magnitude for the three load types, although they varied slightly due to dynamic effects. This phenomenon was further explored using a dynamic model of the sensor. Threshold accelerations in the range of 30-50 G's were measured, and these values can be varied by changing the mass of the accelerometer's outer frame. Wireless readout was successfully demonstrated by using the mechanical accelerometer as an electrical switch connected to the sensor input of an RFID chip.

Compliant piezoresistive MEMS sensors exhibit great promise for improved on-chip sensing. As compliant sensors may experience complex loads, their design and implementation require a greater understanding of the piezoresistive effect of polysilicon in bending and combined loads. This paper presents experimental results showing the piezoresistive effect for these complex loads. Several n-type polysilicon test structures, fabricated in MUMPs and SUMMiT processes, were tested. Results show that, while tensile stresses cause a linear decrease in resistance, bending stresses induce a nonlinear rise in resistance, contrary to the effect predicted by linear models. In addition, tensile, compresive, and bending loads combine in their effects on resistance. The experimental data illustrates the inability of linear piezoresistance models to predict the piezoresistive trends of polysilicon in bending and combined loads, indicating the need for more complete nonlinear models appropriate for these loading conditions.

This paper proposes a model for predicting the piezoresistive effect in microflexures experiencing bending stresses. Linear models have long existed for describing piezoresistivity for members in pure tension and compression. However, extensions of linear models to more complex loading conditions do not match with experimental results. A second-order model to predict piezoresistive effects in tension, compression, and more complex loading conditions is proposed. A reduced form of the general second-order model is presented for thin flexures in bending. A three-step approach is used to determine the piezoresistive coefficients for this reduced-form model. The approach is demonstrated for two sets of -type polysilicon. The predictive ability of the model is investigated by comparing the results to the experimental results using the new piezoresistive model and coefficients. One of the ways to implement the model is with multiphysics finite element analysis (FEA). The piezoresistive FEA for flexures algorithm is a FEA implementation of the unidirectional form of the model for flexures. The results presented in this paper are for the simplified cases of long thin flexures experiencing bending and axial loads. This new model could contribute to optimized sensors and feedback control of microdevices, nanopositioning, and self-sensing microdevices.

This paper presents the design, fabrication, and testing of a miniature latching accelerometer that does not require electrical power. Latching is attained by using a bistable compliant mechanism that switches from one mechanical position to another when the force on the accelerometer exceeds a threshold value. Accelerometers were fabricated by laser cutting the compliant mechanism switch out of both ABS and Delrin plastic sheets. Packaging consisted of gluing the single compliant layer to a supporting substrate. The switching thresholds of the accelerometers were varied from 10g to 800g by varying the surface area of the free moving section between 100 and 500 mm2.

A new, compact 2 degree-of-freedom mechanism 4.1 mm in diameter suitable for robotically controlled surgical operations is presented. Current commercially available robotically controlled instruments achieve high dexterity defined by three degrees of freedom and relatively confined swept volume at just under 1 cm in diameter. Current smaller diameter instruments result in high part count and large swept volumes (less dexterity). A meso-scale rolling contact gripping mechanism is proposed as an alternative. The manufacturing of the parts is made feasible by Metal Laser Sintering, which can produce parts that are difficult to replicate with traditional manufacturing methods. The resulting instrument has only 6 parts and a small swept volume. Instrument actuation and control by a surgical robotic system is demonstrated.Copyright © 2015 by ASME

This paper describes the design and fabrication of a 2-DOF wrist mechanism suitable for fabrication with maximum dimension on the order of 2–4 mm. The design is based on the idea of 2 half-cylinders in contact such that their axes lie orthogonal to each other. In that way, each cylinder can roll parallel to the other cylinder’s axis, giving 2 rotational degrees of freedom. To constrain the cylinders’ motion, unique gear teeth are designed that allow rolling motion in either orthogonal direction, but constrain all other motions. Contact can be guaranteed using a compressive force acting to push the cylinders together. We first demonstrate the design at centimeter scale using FDM 3D printing. Based on the smooth motion achieved, we fabricate a wrist with maximum dimension of 3 mm using layered sheets of carbon nanotube composite material. Each sheet is individually patterned using photolithography.

Air-suspension of transmission-line structures using microelectromechanical systems (MEMS) technology provides the effective means to suppress substrate losses for radio-frequency (RF) signals. However, heating of these lines augmented by skin effects can be a major concern for RF MEMS reliability. To understand this phenomenon, a thermal energy transport model is developed in a simple analytical form. The model accounts for skin effects that cause Joule heating to be localized near the surface of the RF transmission line. Here, the model is validated through experimental data by measuring the temperature rise in an air-suspended MEMS coplanar waveguide (CPW). For this measurement, a new experimental methodology is also developed allowing direct current (dc) electrical resistance thermometry to be adopted in an RF setup. The modeling and experimental work presented in this paper allow us to provide design rules for preventing thermal and structural failures unique to the RF operation of suspended MEMS transmission-line components. For example, increasing the thickness from 1 to 3 mum for a typical transmission line design enhances power handling from 5 to 125 W at 20 GHz, 3.3 to 80 W at 50 GHz, and 2.3 to 56 W at 100 GHz (a 25-fold increase in RF power handling)

We propose an extended finite element-boundary integral method (EFE-BI) to model the electromagnetic (EM) behavior of RF-MEMS switches over a wide frequency range from UHF to terahertz. Our new method integrates EM with finite element heat transfer analysis to extract heat dissipation on the micrometer-scale switch beam due to the non-uniform radio frequency (RF) current distribution. The developed EFE-BI technique is an extension of the standard finite element-boundary integral (FE-BI) method to allow for accurate characterization of RF-MEMS structures whose entire size is a small fraction of a wavelength (λ/250 or less) and may contain dimensions in the order of λ/50 000 or less. Our model predictions exhibit good agreement with experimental results obtained independent of the current study.

This paper explores contact heating in microelectromechanical systems (MEMS) switches with contact spot sizes less than 100 nm in diameter. Experiments are conducted to demonstrate that contact heating causes a drop in contact resistance. However, existing theory is shown to over-predict heating for MEMS switch contacts because it does not consider ballistic transport of electrons in the contact. Therefore, we extend the theory and develop a predictive model that shows excellent agreement with the experimental results. It is also observed that mechanical cycling causes an increase in contact resistance. We identify this effect as related to the build-up of an insulating film and demonstrate operational conditions to prevent an increase in contact resistance. The improved understanding of contact behavior gained through our modeling and experiments allows switch performance to be improved.

Bistable mechanical devices remain stable in two distinct positions without power input. They find application in valves, switches, closures, and clasps. Mechanically bistable behavior results from the storage and release of energy, typically in springs, with stable positions occurring at local minima of stored energy. Compliant mechanisms offer an elegant way to achieve this behavior by incorporating both motion and energy storage into the same flexible element. Interest in compliant bistable mechanisms has also recently increased because of the advantages of bistable behavior in many micro-electro-mechanical systems (MEMS). Design of compliant or rigid-body bistable mechanisms typically requires simultaneous consideration of both energy storage and motion requirements. This paper simplifies this process by developing theory that provides prior knowledge of mechanism configurations that guarantee bistable behavior. Configurations which include one or more translational, or slider, joints are studied in this work. Several different mechanism types are analyzed to determine compliant segment placement that will ensure bistable mechanism operation. Examples demonstrate the power of the theory in design.

Bistable mechanisms, which have two stable equilibria within their range of motion, are important parts of a wide variety of systems, such as closures, valves, switches, and clasps. Compliant bistable mechanisms present design challenges because the mechanism’s energy storage and motion characteristics are strongly coupled and must be considered simultaneously. This paper studies compliant bistable mechanisms which may be modeled as four-link mechanisms with a torsional spring at one joint. Theory is developed to predict compliant and rigid-body mechanism configurations which guarantee bistable behavior. With this knowledge, designers can largely uncouple the motion and energy storage requirements of a bistable mechanism design problem. Examples demonstrate the power of the theory in bistable mechanism design.

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.

Cross-axis flexural pivots, formed by crossing two flexible beams at their midpoints, have been used in compliant mechanisms for many years. However, their load–deflection behavior has yet to be appropriately modeled to allow easy analysis and synthesis of mechanisms containing them. This paper uses results of non-linear finite element analysis to investigate this behavior. Based on the analysis, two models for the pivots are presented – one simple and one more complex. The accuracy of the models is demonstrated by comparing results to those measured for pivots made from polypropylene and steel.

By integrating interferometric deflection data from electrostatically actuated microcantilevers with a numerical finite difference model, we have developed a step-by-step procedure to determine values of Young's modulus while simultaneously quantifying nonidealities. The central concept in the methodology is that nonidealities affect the long-range deflections of the beams, which can be determined to near nanometer accuracy. Beam take-off angle, curvature and support post compliance are systematically determined. Young's modulus is then the only unknown parameter, and is directly found. We find an average value of Young's modulus for polycrystalline silicon of 164.3 GPa and a standard deviation of 3.2 GPa (/spl plusmn/2%), reflecting data from three different support post designs. Systematic errors were assessed and may alter the average value by /spl plusmn/5%. An independent estimate from grain orientation measurements yielded 163.4-164.4 GPa (the Voigt and Reuss bounds), in agreement with the step-by-step procedure. Other features of the test procedure include that it is rapid, nondestructive, verifiable and requires only a small area on the test chip.

A bistable mechanism has two stable states within its range of motion. Its advantages include the ability to stay in two positions without power input and despite small external disturbances. Therefore, bistable micro-mechanisms could allow the creation of MEMS with improved energy efficiency and positioning accuracy. This paper presents bistable micro-mechanisms which function within the plane of fabrication. These bistable mechanisms, called “Young” bistable mechanisms, obtain their energy storage characteristics from the deflection of two compliant members. They have two pin joints connected to the substrate, and can be constructed of two layers of polysilicon. The pseudo-rigid-body model is used to analyze and design these mechanisms. This approach allows greater freedom and flexibility in the design process. The mechanisms were fabricated and tested to demonstrate their bistable behavior and to determine the repeatability of their stable positions.

The pseudo-rigid-body model concept allows compliant mechanisms to be analyzed using well-known rigid-body kinematics. This paper presents a pseudo-rigid-body model for initially curved pinned-pinned segments that undergo large, nonlinear deflections. The model approximates the segment as three rigid members joined by pin joints. Torsional springs placed at the joints model the segment’s stiffness. This model has been validated by fabricating several such segments from a variety of different materials. Testing of the force-deflection behavior of these segments verified the accuracy of the model.

RF MEMS switches have demonstrated excellent performance. However, before such switches can be fully implemented, they must demonstrate high reliability and robust power-handling capability. Numerical simulation is a vital part of design to meet these goals. This paper demonstrates a fully integrated electrothermal model of an RF MEMS switch which solves for RF current and switch temperature. The results show that the beam temperature increases with either higher input power or increased frequency. The simulation data are used to predict switch failure due to temperature-related creep and self pull-in over a wide range of operating frequency (0.1-40 GHz) and power input (0-10 W). Self pull-in is found to be the dominant failure mechanism for an example geometry.

This paper explores the effects of two parameters—operation voltage and the distance between the lance and electrode—on the repulsion process of a Stand-Alone Lance, a second-generation Nanoinjection tool used to inject DNA into egg cells for genetic purposes. Using a mathematical computer model to simulate the motion of the DNA during repulsion from the lance and into the cell, the results are quantified by the average DNA travel time and the electric field strength, which relates to the electroporation envelope. It is found that voltage has a very strong effect, while changing distance yields much less dramatic results. Specific ideal values are recommended for the magnitude and duration of the voltage pulse to successfully repel DNA into the cell.Copyright © 2012 by ASME

This paper introduces a metamorphic erectable cell restraint (MECR) to provide cell restraint in genetic research. A micro-electromechanical systems (MEMS) metamorphic mechanism with two phases of motion was designed to grasp individual embryos about their midplane. The first phase of motion lifts a compliant gripper approximately 40 μm (about half the diameter of an embryo). The gripper then closes in the second phase to grasp the embryo. The metamorphic mechanism includes compliant mechanism components which are analyzed here. A microscale prototype was fabricated from polysilicon and used to demonstrate the mechanism’s two phase motion.Copyright © 2012 by ASME

This paper describes a fully compliant constant-force micro-mechanism that enables dual-stage motion for nanoinjection. Nanoinjection is a recently developed process for delivering DNA into mouse zygotes via electrostatic accumulation and release of the DNA onto a microelectromechanical system (MEMS) lance. The fully compliant constant-force nanoinjector is a concatenation of two separate mechanisms: a six-bar mechanism with compliant lamina-emergent torsional (LET) joints to raise the lance, and a pair of constant-force crank-sliders with LET joints positioned on either side of the six-bar mechanism to drive the lance forward. The fully compliant nanoinjector exhibits self-reconfiguring metamorphic motion to first raise the lance to the midline of the zygote and then translate the lance forward with a controlled motion. This dual-stage motion is necessary for the lance to pierce the zygote without causing damage to the cell membrane. The device achieves two sequential displacement behaviors in a compliant mechanism fabricated from a single, continuous piece of material.

A nanoinjection lance array has been developed to inject foreign genetic material into thousands of cells at once using electrophoresis to attract and repel particles to and from the lances. A unique combination of isotropic and anisotropic etch processes are used to fabricate the four million 1 μm by 8 μm solid lances on a 2 cm by 2 cm chip. Initial studies show high cell viability when the lance array is used to pierce through a culture of HeLa cancer cells, often used for genetic research. A mathematical computer model simulating motion of attracted or repelled particles informs the design of the nanoinjection lance array system. The nanoinjection lance array provides an efficient, convenient, and quick way to simultaneously inject thousands of cells for a wide range of genetic research applications.Copyright © 2012 by ASME

Static balancing is an important contribution to compliant mechanisms enabling low operating force, thus allowing high mechanical efficiency. Preloading is generally needed in statically balanced compliant mechanisms, which at smaller scales presents a significant challenge. Physical handling of zero-force structures without causing damage also becomes difficult. This paper presents a solution to both of these issues. A novel compliant connection mechanism based on bistable beams was used to precisely preload the system in the direction of motion without backlash. Once this bistable mechanism is engaged by loading beyond its threshold, the system is in operating condition, i.e. the ON position. When the connection mechanism is disengaged (OFF position), it is much stiffer than it is in the statically balanced state and therefore more robust for handling purposes. As a demonstrator, we present the first statically balanced gripper with a fully compliant ON/OFF-connection mechanism allowing pre-loading collinear with the direction of motion. The combination of a pre-loaded bistable mechanism (i.e. negative stiffness) and a voluntary closing gripper (i.e. positive stiffness) is used for static balancing (i.e. zero stiffness and zero actuation force). The results show that the actuation force is reduced by at least 91% when the preload is engaged. The proposed ON/OFF connection shows a promising method for pre-loading compliant mechanisms or related devices.Copyright © 2012 by ASME

This work introduces metrics for large-displacement linear-motion compliant mechanisms (LLCMs) that evaluate the performance tradeoff between displacement and off-axis stiffness. These metrics are nondimensionalized, consisting of relevant characteristics used to describe displacement, off-axis stiffness, actuation force, and size. Displacement is normalized by the footprint of the device, transverse stiffness by a new performance characteristic called virtual axial stiffness, and torsional stiffness by the characteristic torque. These metrics account for the variation of both axial and off-axis stiffness over the range of displacement. The metrics are demonstrated for several microelectromechanical systems (MEMS) that are sensitive to size because of high cost and off-axis stiffness because of function. The use of metrics in design is demonstrated in the design of an LLCM; the resulting design shows increased values for both the travel and transverse-stiffness metrics.

This paper explores the deflection and buckling of fixed-guided beams used in compliant mechanisms. The paper’s main contributions include the addition of an axial deflection model to existing beam bending models, the exploration of the deflection domain of a fixed-guided beam, and the demonstration that nonlinear finite element models typically incorrectly predict a beam’s buckling mode unless unrealistic constraints are placed on the beam. It uses an analytical model for predicting the reaction forces, moments, and buckling modes of a fixed-guided beam undergoing large deflections. The model for the bending behavior of the beam is found using elliptic integrals. A model for the axial deflection of the buckling beam is also developed. These two models are combined to predict the performance of a beam undergoing large deflections including higher order buckling modes. The force versus displacement predictions of the model are compared to the experimental force versus deflection data of a bistable mechanism and a thermomechanical in-plane microactuator (TIM). The combined models show good agreement with the force versus deflection data for each device.

Electrophoretic systems commonly use metal electrodes in their construction. This paper explores and reports the differences in the electrophoretic motion of DNA (decomposition voltage, electrical field, etc.) when one electrode is constructed from a semiconductor, silicon, rather than metal. Experimental VI (voltage-current) curves for different electrode configurations (using steel and silicon) are presented. Experimental results are used to update and validate the mathematical model to reflect the differences in material selection. In addition, the model predicts large curved-field motion for DNA motion. The model helps to quantify the effect of parameters on DNA motion in biological microelectromechanical systems in order to improve device designs and protocols.

This paper presents an underwater, silicon, thermal microactuation system capable of moving a 200 μN load to a displacement of 110 μm. Its function relies on a thermal actuator capable of 9 μm of displacement in an aqueous environment. This actuator is combined with a ratcheting device to achieve the 110 μm of displacement. The system is a microelectromechanical system (MEMS) fabricated with a two layer surface-micromachining process, PolyMUMPS. The actuation system is designed to provide motion to biological microelectromechanical systems (BioMEMS) in aqueous environments. This paper presents the design and experimental demonstration of the actuation system. The in-depth analysis of the thermal, mechanical, and fabrication aspects of the actuation system are outlined, and the experimental procedure and test parameters are discussed.Copyright © 2011 by ASME

This paper outlines the adaptation of a mathematical computer model used to simulate the motion of DNA particles in order to determine the best geometry and setup for a prototype cell injection system. The model predicts DNA motion due to electrophoresis near micromachined electrodes. Ten key electrode parameters are identified to test for significance, and three key test measurements are identified to help compare the various setups. A simple design of experiment is used to organize and analyze the data collected from forty-one simulations of the DNA motion within the electric field. Based on the simulations of attracting DNA to the lance for injection, it is found that a compact ring electrode placed underneath an insulated lance will yield the optimal results. Two additional areas for research are recommended.Copyright © 2011 by ASME

This paper demonstrates a low stiffness compliant joint design obtained by balancing the energy stored within individual components of the mechanism. As a step toward a fully-compliant zero-stiffness joint, this paper presents the design of a partially-compliant joint. A wireform torsion bar partially compliant joint was optimized using a pseudo rigid body model. A low stiffness design was obtained by balancing the energy stored within individual components of the mechanism. The joint was then fabricated using piano wire, polypropylene and Delrin®. During testing it was found that friction in the joint was greater than any internal forces allowing the joint to be neutrally stable in all positions. Dynamic force deflection data on the joints was collected in order to investigate the friction characteristics. The Delrin® joint exhibited only Coulomb friction while the polypropylene model exhibited both Coulomb and viscous friction.Copyright © 2011 by ASME

Nanoinjection is an innovative approach for the electromechanical injection of DNA into cells, in which DNA is electrically attracted to a lance, inserted into a cell, and repelled by reversing the electrical polarity. In previous work, the lance has been micromachined as part of an on-chip microelectromechanical system. This work investigates a Stand-Alone Lance concept, where the lance and other components are independent of a common substrate. The Stand-Alone Lance may make nanoinjection more accessible to researchers and be more compatible with lab equipment commonly available in transgenic facilities. Required parameters for the electrode are investigated using a mathematical computer model. Different materials and fabrication processes for the metal lance are also considered. Additional testing was performed using tungsten probes, including mock injections on mouse egg cells. Based upon the optimistic cell viability rate, it is recommended to further investigate the use of the Stand-Alone Lance to perform nanoinjections.Copyright © 2011 by ASME

We present a new technique for fabricating compliant mechanisms from stamped metal sheets. The concept works by providing thinned segments to allow rotation of flexural beams 90 deg about their long axis, effectively providing a flexure as wide as the sheet’s thickness. The method is demonstrated with the design and fabrication of a metal bistable mechanism for use as a threshold accelerometer. A new model based on elliptic integral solutions is presented for bistable mechanisms incorporating long, thin flexures. The resulting metal bistable mechanisms are tested for acceleration threshold sensing using a drop test and a vibration test. The mechanisms demonstrate very little variation due to stress relaxation or temperature effects. The force-displacement behavior of a mechanism is also measured. The mechanisms’ switching force is less than the designed value because of out-of-plane motion and dynamic effects.

This paper explored the deflection and buckling of fixed-guided beams. It uses an analytical model for predicting the reaction forces, moments, and buckling modes of a fixed-guided beam undergoing large deflections. One of the strengths of the model is its ability to accurately predict buckling behavior and the buckled beam shape. The model for the bending behavior of the beam is found using elliptic integrals. A model for the axial deflection of the buckling beam is also developed based on the equations for stress and strain and the buckling profile of the beam calculated with the elliptic integral solution. These two models are combined to predict the performance of a beam undergoing large deflections including higher order buckling modes. The force vs. displacement predictions of the model are compared to the experimental force vs. deflection data of a bistable mechanism and a thermomechanical in-plane microactuator (TIM). The combined models show good agreement with the force vs. deflection data for each device. The paper’s main contributions include the addition of the axial buckling model to existing beam bending models, the exploration of the deflection domain of a fixed-guided beam, and the demonstration that nonlinear finite element models may incorrectly predict a beam’s buckling mode unless unrealistic constraints are placed on the beam.Copyright © 2010 by ASME

Tristable mechanisms, or devices with three distinct stable equilibrium positions, have promise for future applications, but the complexities of the tristable behavior have made it difficult to identify configurations that can achieve tristable behavior while meeting practical stress and fabrication constraints. This paper describes a new tristable configuration that employs orthogonally oriented compliant mechanisms that result in tristable mechanics that are readily visualized. The functional principles are described and design models are derived. Feasibility is conclusively demonstrated by the successful operation of four embodiments covering a range of size regimes, materials, and fabrication processes. Tested devices include an in-plane tristable macroscale mechanism, a tristable lamina emergent mechanism, a tristable micromechanism made using a carbon nanotube-based fabrication process, and a polycrystalline silicon micromechanism.

This paper presents an alternative to fabrication methods commonly used in compliant mechanisms research, resulting in a new class of compliant mechanisms called wireform mechanisms. This technique integrates torsional springs made of formed wire into compliant mechanisms. In this way the desired force, stiffness, and motion can be achieved from a single piece of formed wire. Two techniques of integrating torsion springs are fabricated and modeled: helical coil torsion springs and torsion bars. Because the mechanisms are more complex than ordinary springs, simplified models, which aid in design, are presented, which represent the wireform mechanisms as rigid-body mechanisms using the pseudo-rigid-body model. The method is demonstrated through the design of a mechanically tristable mechanism. The validity of the simplified models is discussed by comparison to finite element models and, in the case of the torsion-bar mechanism, to experimental measurements.

This paper presents the design, manufacture, and testing of a battery-free, wireless threshold accelerometer based on a fully compliant bistable mechanism (FCBM). The FCBM stores threshold acceleration measurements mechanically, eliminating the need for electrical power. The sensorpsilas state can be read wirelessly via a passive RFID tag. Because information can be stored in these tags for over 25 years, the sensor can be left unattended for long periods of time. The FCBM portion of the sensor is laser cut from a single sheet of plastic (Delrin) and integrated with an Atmel ATA5570 RFID chip. Both elements can be manufactured at low cost. The G-force needed to exceed the shock threshold can be varied by changing the mass of the FCBM. Multiple sensors were tested using three different methods. The first method was a centrifuge, providing a constant force input. The second method was a drop test that gave an impulse input to the sensor. The final method used a shaker table to provide a sinusoidal input. In each of these tests, it was found that the FCBM sensed the correct acceleration and retained its mechanical state. A number of prototype sensors were constructed with different masses resulting in threshold accelerations between 15 and 180 Gpsilas. The overall size of these sensors was approximately 28 mm x 26 mm. The RFID tags operate at 150 kHz and were read using a commercial off-the-shelf reader with a range of approximately 3 cm. Longer range readers are readily available at higher operating frequencies.

Knowledge and control of residual strain is critical for device design in MEMS, and therefore it is important to establish standards for residual strain measurement. In this study, pointer, microring, bent-beam, and fixed-fixed beam test structures are used to evaluate residual strain both theoretically and experimentally. An equation that enables easier evaluation of bent- beam structures is derived. Also, a finite difference model that incorporates the non-idealities of fixed-fixed beams and determines an optimum fit to the measured deflection curve is presented. The model allows accurate residual strain evaluation of each buckled fixed-fixed beam. Experimentally, pointer structures were found to be susceptible to adhesion. Microrings, intended for residual tension assessment, also could not be evaluated because the residual strain was compressive. Bent-beam and fixed-fixed beams could both be evaluated. The main criterion for test structure effectiveness was taken to be the repeatability of residual strain on structures in close proximity; each should exhibit the same value. Using optical microscopy, the residual strain of bent-beams was determined with ± 13 µe repeatability based on standard deviation of adjacent structures of similar design. Using optical interferometry, the residual strain of fixed-fixed beams was determined with ± 2 µe repeatability based on standard deviation for adjacent beams of different lengths. The strain values obtained from the two structures are in reasonably good agreement. Cantilevers were also evaluated to obtain film curvature values.

Microelectromecahanical system (MEMS) actuation is a growing area of research. One obstacle for use of actuation in MEMS applications is the difficulty of proper sensing. Recent work has been done that shows the potential for thermomechanical in-plane microactuators (TIMs) to act as self-sensors by using the piezoresistive characteristic of silicon. However, in order to implement this technology a calibration method needs to be devised to account for variations between TIMs. This work presents an approach for this calibration consisting of two parts that compensate for variation in fabrication and material properties. Test structures are presented that will enable this calibration to be done on-chip, and validation is given for the usability of this approach. Two validation approaches are used. For the first approach, data previously gathered was analyzed using the TIM itself for calibration. This approach showed significant correlation with the model; however, this approach confounds any sensing signal and therefore was used only for general model validation. The second approach uses a novel calibration structure that decouples the mechanical and electrical characteristics. This approach showed correlation with test data within the bounds of experimental uncertainty in nearly all cases. Suggestions are given concerning implementation.Copyright © 2008 by ASME

This paper presents the design, fabrication, and testing of a force sensor for integrated use with thermomechanical in-plane microactuators. The force sensor is designed to be integrated with the actuator and fabricated in the same batch fabrication process. This sensor uses the piezoresistive property of silicon as a sensing signal by directing the actuation force through two thin legs, producing a tensile stress. This tensile load produces a resistance change in the thin legs by the piezoresistive effect. The resistance change is linearly correlated with the applied force. The device presented was designed by considering both its piezoresistive sensitivity and out-of- plane torsional stability. A design trade-off exists between these two objectives in that longer legs are more sensitive yet less stable. Fabrication of the sensor design was done using the MUMPs process. This paper presents experimental results from this device and a basic model for comparison with previously attained piezoresistive data. The results validate the concept of integral sensing using the piezoresistive property of silicon.

Compliant piezoresistive MEMS sensors exhibit great promise for improved on-chip sensing. As compliant sensors may experience complex loads, their design and implementation require a greater understanding of the piezoresistive effect of polysilicon in bending and combined loads. This paper presents experimental results showing the piezoresistive effect for these complex loads. Several n -type polysilicon test structures were tested. Results show that, while tensile stresses cause a linear decrease in resistance, bending stresses induce a nonlinear rise in resistance contrary to the effect predicted by available models. The experimental data illustrate the inability of published piezoresistance models to predict the piezoresistive trends of polysilicon in bending and combined loads, indicating the need for more complete models appropriate for these loading conditions and more complete understanding of the piezoresistive effect.

This paper describes the design of a novel multi-stable compliant mechanism capable of large angle deflections. The multi-stable COmpliant Rolling-contact Element (CORE), reduces friction, allows for large angular displacements, and requires no external force to remain in its multiple equilibrium positions. This paper develops and discusses seven methods to create multi-stable mechanisms from the CORE. These seven methods have different characteristics and advantages.Copyright © 2007 by ASME