Showing papers on "Compliant mechanism published in 2007"

Characteristics of Beam-Based Flexure Modules

Abstract: The beam flexure is an important constraint element in flexure mechanism design. Nonlinearities arising from the force equilibrium conditions in a beam significantly affect its properties as a constraint element. Consequently, beam-based flexure mechanisms suffer from performance tradeoffs in terms of motion range, accuracy and stiffness, while benefiting from elastic averaging. This paper presents simple yet accurate approximations that capture the effects of load-stiffening and elastokinematic nonlinearities in beams. A general analytical framework is developed that enables a designer to parametrically predict the performance characteristics such as mobility, over-constraint, stiffness variation, and error motions, of beam-based flexure mechanisms without resorting to tedious numerical or computational methods. To illustrate their effectiveness, these approximations and analysis approach are used in deriving the force-displacement relationships of several important beam-based flexure constraint modules, and the results are validated using finite element analysis. Effects of variations in shape and geometry are also analytically quantified.

Constraint-based design of parallel kinematic XY flexure mechanisms

Abstract: This paper presents parallel kinematic XY flexure mechanism designs based on systematic constraint patterns that allow large ranges of motion without causing over-constraint or significant error motions. Key performance characteristics of XY mechanisms such as mobility, cross-axis coupling, parasitic errors, actuator isolation, drive stiffness, lost motion, and geometric sensitivity, are discussed. The standard double parallelogram flexure module is used as a constraint building-block and its nonlinear force-displacement characteristics are employed in analytically predicting the performance characteristics of two proposed XY flexure mechanism designs. Fundamental performance tradeoffs, including those resulting from the nonlinear load-stiffening and elastokinematic effects, in flexure mechanisms are highlighted. Comparisons between closed-form linear and nonlinear analyses are presented to emphasize the inadequacy of the former. It is shown that geometric symmetry in the constraint arrangement relaxes some of the design tradeoffs, resulting in improved performance. The nonlinear analytical predictions are validated by means of computational finite element analysis and experimental measurements.

Synthesis of Multistable Equilibrium Compliant Mechanisms Using Combinations of Bistable Mechanisms

Abstract: In this paper, we present a mathematical approach to synthesize multistable compliant mechanisms by combining multiple bistable equilibrium mechanisms. More specifically, we identify and categorize various types of bistabilities by characterizing the essential elements of their complicated deformation pattern. The behavior of a bistable compliant mechanism, in general, is highly nonlinear. Using combinations of such nonlinearities to capture the behavior of multistable (more than two stable positions) mechanisms can be quite challenging. To determine multistable behavior, our simplified mathematical scheme captures the essential parameters of bistability, such as the load-thresholds that cause the jump to the next stable position. This mathematical simplification enables us to characterize bistable mechanisms by using piecewise lower-order polynomials and, in turn, synthesize multistable mechanisms. Three case studies involving combinations of two, three, and four bistable behaviors are presented for the purpose of generating multistable mechanisms with up to 16 stable positions. The methodology enables us to design a compliant mechanism with a desired number of stable positions. A design example of a quadristable equilibrium rotational compliant mechanism consisting of two bistable submechanisms is presented to demonstrate the effectiveness of the approach. DOI: 10.1115/1.3013316

Plastic latching accelerometer based on bistable compliant mechanisms

Abstract: 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.

Design, Simulation, and Fabrication of a Quadstable Monolithic Mechanism With X- and Y-Directional Bistable Curved Beams

Abstract: This paper demonstrates a novel quadstable monolithic mechanism (QsMM), which provides four stable equilibrium positions within its planar operation range. The QsMM has been realized from the use of both X- and Y-directional bistable structures, which utilize curved snapping beams. Two pairs of curved beams were attached to an inner frame in both X and Y directions to present an independent bistable behavior in the directions. It was found out that the design of the inner frame is crucial for the quadstability and dynamic responses of the mechanism. A millimeter-scale brass mechanism was actually fabricated by ultraprecision milling to test the quadstability and the force-displacement behavior. The prototype clearly demonstrates four distinct stable positions in its millimeter-scale operation range. The design concept, finite element simulation, fabrication, and experimental measurement of the proposed multistable mechanism have been presented. The mechanical multistability of the proposed QsMM can be utilized for multiple switching and optical networking applications, yielding low power consumption operations.

Kinematic Representations of Pop-Up Paper Mechanisms

Abstract: Pop-up paper mechanisms use techniques very similar to the well-studied paper folding techniques of origami. However, popups differ in both the manner of construction and the target uses, warranting further study. This paper outlines the use of planar and spherical kinematics to model commonly used pop-up paper mechanisms. A survey of common joint types is given, including folds, interlocking slots, bends, pivots, sliders and rotating sliders. Also included is an overview of common onepiece and layered mechanisms, including single-slit, double-slit, V-fold, tent, tube strap and arch mechanisms. Each mechanism or joint is described using a kinematic or compliant mechanism representation. In addition, it is shown that more complex mechanisms may be created by combining simple mechanisms in various ways. The principles presented are applied to the creation of new pop-up joints and mechanisms. The new mechanisms employ both spherical and spatial kinematic chains. Various other applications are also mentioned which could benefit from the use of pop-up mechanism principles. Possible applications include deployable structures, packaging and instruments for minimally invasive surgery.Copyright © 2007 by ASME

Distributed Shape Optimization of Compliant Mechanisms Using Intrinsic Functions

Abstract: A compliant mechanism transmits motion and force by deformation of its flexible members. It has no relative moving parts and thus involves no wear, lubrication, noise, or backlash. Compliant mechanisms aim to maximize flexibility while maintaining sufficient stiffness so that satisfactory output motion may be achieved. When designing compliant mechanisms, the resulting shapes sometimes lead to rigid-body type linkages where compliance and rotation is lumped at a few flexural pivots. These flexural pivots are prone to stress concentration and thus limit compliant mechanisms to applications that only require small-deflected motion. To overcome this problem, a systematic design method is presented to synthesize the shape of a compliant mechanism so that compliance is distributed more uniformly over the mechanism. With a selected topology and load conditions, this method characterizes the free geometric shape of a compliant segment by its rotation and thickness functions. These two are referred as intrinsic functions and they describe the shape continuously within the segment so there is no abrupt change in geometry. Optimization problems can be conveniently formulated with cusps and intersecting loops naturally circumvented. To facilitate the optimization process, a numerical algorithm based on the generalized shooting method will be presented to solve for the deflected shape. Illustrative examples will demonstrate that through the proposed design method, compliant mechanisms with distributed compliance will lessen stress concentration so they are more robust and have a larger deflected range. It is expected that the method can be applied to design compliant mechanisms for a wide variety of applications.

Synthesis of Bistable Compliant Four-Bar Mechanisms Using Polynomial Homotopy

Abstract: In this paper we formulate and solve the synthesis equations for a compliant four-bar linkage with three specified equilibrium configurations in the plane. The kinematic synthesis equations as for rigid-body mechanisms are combined with equilibrium constraints at the flexure pivots to form design equations. These equations are simplified by modeling the joint angle variables in the equilibrium equations using sine and cosine functions. Polynomial homotopy continuation is applied to compute all of the design candidates that satisfy these design equations, which are refined using a Newton-Raphson technique. A numerical example demonstrates design methodology in which the homotopy solver obtained eight real solutions. Two of them provide two stable and one unstable equilibrium, and hence, can be used as the prototype of bistable compliant mechanisms.

Synthesis of Path Generating Compliant Mechanisms Using Initially Curved Frame Elements

Abstract: Initially curved frame elements are used in this paper within an optimization-based framework for the systematic synthesis of compliant mechanisms (CMs) that can trace nonlinear paths. These elements exhibit a significantly wider range of mechanical responses to applied loads than the initially straight frame elements, which have been widely used in the past for the synthesis of CMs. As a consequence, fewer elements are required in the design discretization to obtain a CM with a desired mechanical response. The initial slopes at the two nodes of each element are treated as design variables that influence not only the shape of the members in a CM, but also the mechanical response of the latter. Building on our prior work, the proposed synthesis approach uses genetic algorithms with both binary (i.e., 0/1) and continuous design variables in conjunction with a co-rotational total Lagrangian finite element formulation and a Fourier shape descriptors-based objective function. This objective function is chosen for its ability to provide a robust comparison between the actual path traced by a candidate CM design and the desired path. Two synthesis examples are presented to demonstrate the synthesis procedure. The resulting designs are fabricated as is, without any postprocessing, and tested. The fabricated prototypes show good agreement with the design intent.

Synthesis of contact‐aided compliant mechanisms for non‐smooth path generation

Abstract: Topology optimization is used in this paper for the systematic synthesis of contact-aided compliant mechanisms that trace prescribed, non-smooth paths in response to a single, monotonically increasing input force. Intermittent contact interactions that enable these mechanisms to exhibit non-smooth responses also lead to algorithmic difficulties when the techniques from the synthesis of ordinary compliant mechanisms are used to design contact-aided compliant mechanisms. A sequential optimization approach based on a regularized normal contact model for large displacements is used in this work to circumvent these difficulties and to enable the use of computationally efficient, gradient-based optimization methods. We use an objective function based on Fourier shape descriptors, which allows the designer to emphasize different aspects of the design intent (such as the shape, the size and the orientation of the output path) separately. A variable-stiffness input spring is used to allow the synthesis procedure to choose the appropriate magnitude of the input force. An arc-length finite element solver and heuristic measures that guard against local and global instabilities add to the robustness of the synthesis procedure as demonstrated by the two design examples presented in this paper.

Designing Distributed Compliant Mechanisms With Characteristic Stiffness

Abstract: A novel method is proposed in this paper to address the cutting-edge problem of topology optimization of distributed compliant mechanisms, which requires the design to possess both large output displacements and evenly distributed compliance simultaneously. The design is represented by a level-set model that precisely specifies the distinct material regions and their sharp interfaces as well as the geometric boundary of the structure, capable of performing topological changes and capturing geometric evolutions at the interface and the boundary. Existing techniques for eliminating de facto hinges in the design are reviewed. Further, the intrinsic deficiencies in the widely used “spring model” are discussed and a new formulation considering the “characteristic stiffness” of the mechanism is proposed. The proposed method is demonstrated with benchmark examples of compliant mechanism optimization. The result is a design with evenly distributed compliance and a more desirable characteristic, which uniquely distinguishes our method.Copyright © 2007 by ASME

Methodology of Compliant Mechanisms and its Current Developments in Applications: A Review

Abstract: Traditional rigid-body mechanisms consist of a number of components to implement their functions. Therefore they face problems such as backlash, wear, increase in part-count, weight, assembly cost and time, regular maintenance. Reducing these problems will help in increasing mechanism performance and cost reduction. Recently, there are several examples of compliant mechanisms that have been designed and widely used in various fields such as for adaptive structures, biomedical, hand-held tools, components in transportations, MEMS and robotics. However, the largest challenge was relative difficulty in analyzing and designing compliant mechanisms. Two approaches known in the literature for the systematic synthesis of compliant mechanisms are the kinematics-based approach and the structural optimisation based approach.

Introduction to Compliant Long Dwell Mechanism Designs Using Buckling Beams and Arcs

Abstract: New classes of compliant long dwell mechanism designs are introduced, formulated, and simulated. These classes of compliant dwell mechanisms incorporate the buckling motion of flexible members. Long dwell motion is obtained throughout the buckling motion of a flexible follower. Flexible buckling members are modeled using polynomial functions fitted to nonlinear inextensible exact elastica theory. The displacement analysis of the mechanisms is done quasi-statically using loop closure theory, static equilibrium of flexible parts represented by polynomial load deflections. One example of each new mechanism and its simulation results are presented.

Components for the Design of Lamina Emergent Mechanisms

Abstract: This paper presents components for lamina emergent mechanism (LEM) that can be used as building blocks to create mechanisms capable of more complex motion As the name suggests, lamina emergent mechanisms are fabricated out of planar materials (the lamina) but their motion is out of that plane (emergent) Lamina emergent mechanisms can provide benefits that include reduced manufacturing costs and minimal volume when in the planar state The compact initial state of LEMs is beneficial in reducing shipping costs, especially in volume critical applications LEMs also exhibit the potential benefits of compliant mechanisms, namely increased precision, reduced weight, reduced wear, and part count reduction Due to the deflection of their members, compliant mechanisms have the ability to store energy, and the resulting effect can be used to perform the function of springs The LEM components presented in this paper include flexible segments, and mechanisms with behaviors similar to planar change-point four-bar and six-bar mechanisms, and spherical change-point mechanismsCopyright © 2007 by ASME

Optimal design of a compliant mechanism with circular notch flexure hinges

Abstract: This paper presents an optimal design of a compliant mechanism with circular notch flexure hinges as well as a performance evaluation of a two-axes ultra-precision stage using the compliant mechanism. The compliant mechanism consists of two double-symmetric four-link mechanisms for two translational motions. As the circular notch flexure hinge can produce rotation as well as axial translation via its deformation, the double symmetric four-link mechanism can translate along one direction in a small range. In the optimal design, a composite global design index based on Min-Max principle is applied for the design of the compliant mechanism with circular notch flexure hinges owing to its simplicity and compactness. The designed compliant mechanism, piezoelectric elements for actuation, and capacitance-type displacement sensors for position measurement are assembled into an ultra-precision stage. The experimental results show that the stage implemented by the compliant mechanism will be applicable to t...

Redesign of the MMOC microgripper piezoactuator using a new topological optimization method

Abstract: This paper presents a new method developed for the optimal design of piezoactive compliant mechanisms. It is based on a flexible building blocks method, called Flexln, which uses an evolutionary approach, to optimize a truss-like structure made of passive and active piezoelectric building blocks. An electromechanical approach, based on a mixed finite element method, is used to establish the model of the piezoelectric blocks. A planar monolithic compliant micro-actuator is synthesized by the optimization method, based on the specifications drawn from a piezoelectric microgripper prototype (MMOC). Finally, some performances comparisons between the optimally Flexln synthetized gripper and the previous gripping system demonstrate the interests of the proposed optimization method for the design of micro-actuators, microrobots, and more generally for adaptronic structures.

Compliant Mechanical Amplifier Design using Multiple Optimally Placed Actuators

Abstract: This article discusses a methodology for designing compliant mechanisms with piezoelectric actuation to obtain maximum deflection and force at the output point. The focus is on design of compliant mechanisms with multiple piezoelectric actuators. The number, size, and position of the actuators within the compliant mechanism are optimized for the maximum output deflection. Predicted results demonstrate that compliant mechanisms with multiple, optimally placed actuators outperform those with a single actuator placed at a predetermined location.

Flexible bearings for high-precision mechanisms in accelerator facilities

Abstract: While in conventional mechanical bearings motion is obtained by sliding or rolling between solid bodies with the resulting mechanical non-linearities, flexible bearings rely on the elastic properties of matter allowing several advantages to be obtained. Combining flexible bearings with adequate actuators and sensors allows thus nanometric positioning resolutions to be obtained. In this paper, the basic principles of compliant mechanisms design methodology are presented. To illustrate the approach, some examples taken from aerospace and astronomical applications are described. Several compliant mechanisms used at the Swiss Light Source synchrotron facility are then presented.

MEMS Optical Force Sensor Enhancement Via Compliant Mechanism

Abstract: Although there are capacitive surface micromachined force sensors with adequate resolution for cell manipulation and microneedle injections, it comes with the sacrifice of dynamic range and linearity In contrast, optical based force sensors can provide the desired resolution and maintain relatively large sensing ranges compared to similar capacitive sensors Plus, optical interferometry provides a sensing method that uncouples the conflicting design parameters, such as sensitivity and linearity The current drawback to optical interferometry is the large off-chip equipment that is currently used in the operation of optical sensors However, innovative techniques are being applied to surface micromachined microphones that allow off-chip components to be integrated onto the sensing chip These same techniques can easily translate to the force sensor presented in this research, due to the similarities in the sensing methods The thrust of this work is to explore a mechanism approach for enhancing the performance of a surface micromachined optical force sensor A new design is presented which introduces a special mechanism, known as the Robert’s mechanism, as an alternate means in which the device is structurally supported The new design’s implementation is achievable using an equivalent compliant mechanism Initially, an analytical set of pseudo-rigid-body-model equations were developed to model the compliant design A more accurate model was then constructed using FEA methods The geometric parameters of the compliant Robert’s mechanism were then optimized to obtain a sensor with improved linearity and sensitivity Overall, the force sensor provides higher sensitivity, larger dynamic range and higher linearity compared to a similar optical force sensor that uses a simple structural supporting scheme In summary, this paper demonstrates the effectiveness of using a mechanism approach for enhancing the performance of MEMS sensors The expected impact is to improve biomedical experiments and help further advance research that can improve quality of lifeCopyright © 2007 by ASME

Flexible building blocks method for the optimal design of compliant mechanisms using piezoelectric material

Abstract: This paper presents a new method to optimally design active compliant mechanisms. It is partly ba sed on a flexible building blocks method called FlexIn, whic h had been developed at the French Atomic Energy Commission (CEA ). This method uses an evolutionary algorithm approach to optimize a truss-like structure, made of an assembl y of passive and active piezoelectric building blocks from two sp ecific libraries. The mechanical approach used to establis h the actuator model of the piezoelectric block and its v alidation by a commercial finite element software are described. Th en, the optimization method is illustrated by the synthesis of a planar monolithic compliant microgripper device. Finally, the mechanical performances of a pseudo-optimal mechani sm are commented, and demonstrate the interests of the pro posed optimization method for the design of smart structu res.

Carbon nanotube based compliant mechanism

Abstract: A nano-scale compliant mechanism includes a coupler and a plurality of nanotubes disposed for nano-scale motion relative to a grounded component. The nanotubes are fastened at one end to the coupler and at the other end to ground, to guide motion of the coupler relative to the ground. Particular embodiments include a plurality of parallel carbon nanotubes. An exemplary embodiment exhibits first and second regions of mechanical behavior; a first region governed by bulk elastic deformation of the nanotubes and a second region governed by compliant, hinge-like bending of the buckled nanotubes.

Cartwheel flexure-based compliant stage for large displacement driven by a stack-type piezoelectric element

Abstract: When the short displacement of a piezoelectric element in a compliant stage with simple flexures is amplified for large motion range by an amplification mechanism, a large displacement causes an excessive stress in a simple flexure. Moreover the excessive stress has the possibility of a yielding failure. A cartwheel flexure hinge offers the compliant stage larger displacement than the simple flexures. In this study, a compliant stage for displacement driven by a stack-type piezoelectric element is proposed. For large displacement, rotational joints are implemented by cartwheel flexure hinges. A mathematical model for compliant stage with massless flexure node is derived, and then the proposed stage is analyzed. In addition, the proposed stage is designed and manufactured. Experiments demonstrate the performance of the proposed stage.

Development of Deployable Wings for Small Unmanned Aerial Vehicles Using Compliant Mechanisms

Abstract: DEVELOPMENT OF DEPLOYABLE WINGS FOR SMALL UNMANNED AERIAL VEHICLES USING COMPLIANT MECHANISMS Steven D. Landon Department of Mechanical Engineering Master of Science Unmanned Air Vehicles (UAVs) have recently gained attention due to their increased ability to perform sophisticated missions with less cost and/or risk than their manned counterparts. This thesis develops approaches to the use of compliant mechanisms in the design of deployable wings for small UAVs. Although deployable wings with rigid-link mechanisms have been used in the past to maintain flight endurance while minimizing required storage volume, compliant mechanisms offer many advantages in manufacturability and potential space savings due to function sharing of components. A number of compliant, deployable wing concepts are generated and a classification system for them is formed. The pool of generated concepts serves as a basis for stimulating future concept ideas. A methodology is also proposed for evaluating concepts for a given application. The approach to developing compliant designs for certain applications is illustrated through two example designs, which demonstrate key portions of the proposed design process. Each is modeled and analyzed to demonstrate viability.

Gramian-based optimal design of a dynamic stroke amplifier compliant micro-mechanism

Abstract: This paper presents a new method developed for the optimal design of microrobotic compliant mechanisms. It is based on a flexible building block method, called Flexln, which uses an evolutionary approach, to optimize a truss-like structure made of building blocks. From the first design step, in addition to conventional mechanical criteria, dynamic gramian- based metrics can be considered in the optimization procedure to fit expected frequency responses of the synthesized mechanisms. A planar monolithic compliant coupling structure is obtained by the optimal design method to act as a stroke amplifier for piezoelectric stacked actuators, to operate in both static and dynamic motions, and to passively filter out undesirable vibrations. Finally, performance comparisons between some of the pseudo-optimal Flexln synthetized compliant mechanisms demonstrate the interests of the proposed optimization method for the design of dynamic operating smart microrobotic structures.

Concepts for Achieving Multi-Stability in Compliant Rolling-Contact Elements

Abstract: 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