Showing papers on "Compliant mechanism published in 2003"

An element removal and reintroduction strategy for the topology optimization of structures and compliant mechanisms

Abstract: A method is developed to systematically remove and reintroduce low density elements from and into the finite element mesh on which the structural topology optimization problem is defined. The material density field which defines the topology and the local ‘stiffness’ of the structure is optimally distributed via non-linear programming techniques. To prevent elements from having zero stiffness, an arbitrarily small lower bound on the material density is typically imposed to ensure that the global stiffness matrix does not become singular. While this approach works well for most minimum compliance problems, the presence of low density elements can cause computational problems, particularly in structures that exhibit geometric non-linearities, e.g. in compliant mechanisms. To resolve this problem, a systematic approach for removing and reintroducing low density elements is presented, and the substantial performance improvements both in design and computational efficiency of the method over current methods are discussed. Several structures and compliant mechanisms are designed to demonstrate the method. Copyright © 2003 John Wiley & Sons, Ltd.

A new scheme for imposing a minimum length scale in topology optimization

Abstract: A new scheme for imposing a minimum length scale in topology optimization is presented. It guarantees the existence of an optimal design for a large class of topology optimization problems of practical interest. It is formulated as one constraint that is computationally cheap and for which sensitivities are also cheap to compute. The constraint value is ideally zero, but it can be relaxed to a positive value. The effect of the method is illustrated in topology optimization for minimum compliance and design of compliant mechanisms. Notably, the method produces compliant mechanisms with distributed flexibility, something that has previously been difficult to obtain using topology optimization for the design of compliant mechanisms. The term ‘MOLE method’ is suggested for the method. Copyright © 2003 John Wiley & Sons, Ltd.

Design of Compliant Mechanisms for Morphing Structural Shapes

Abstract: Various compliant mechanism synthesis methods have been developed over the past decade; however, very little attention has been directed towards adaptive shape change problems. In this paper, we present a systematic method for synthesizing compliant mechanisms to morph a given curve or profile into a target curve utilizing minimum number of actuators (typically one). Two objective functions are formulated, using Least Square Errors and a modified Fourier Transformation, to capture the shape differences. The topology and dimensions of the optimal compliant mechanism are generated using Genetic Algorithms. Applications of this synthesis approach are demonstrated through two adaptive antenna design examples.

Design and application of compliant mechanisms for morphing aircraft structures

Abstract: Morphing aircraft structures can significantly enhance air vehicle performance. This paper highlights ongoing work to design novel compliant mechanisms that efficiently morph aircraft structures in order to exploit aerodynamic benefits. Computational tools are being developed to design structures that deform into specified shapes given simple actuator inputs. In addition, these synthesis methods seek to optimize the stiffness of the structure to minimize actuator effort and maximize the stiffness with respect to the environment (external loading). These tools have been used to study two different types of morphing systems: (i) variable geometry wings and (ii) high-frequency vortex generators for active flow control. Several case studies are presented which highlight the design approach and computational and experimental results of these morphing aircraft systems.

Tubular compliant mechanisms for ultrasonic imaging systems and intravascular interventional devices

Abstract: A micromanipulator comprising a tubular structure and a structural compliance mechanism that are formed from a tube made of an elastic and/or superelastic material. Fabricated with laser machining and has no mechanical joints, the micromanipulator can be manipulated in various motions and degree-of-freedoms without permanent deformation. Shape Memory Alloys (SMAs) in one embodiment are implemented as main actuators of the micromanipulator. The micromanipulator can be implemented with multiple SMAs to manipulate the mechanism with multiple degree-of-freedom. In another implementation, multiple segments of the mechanisms are formed and arranged in various configurations, including a “double-helix”-like configuration, for enabling intricate motions of the micromanipulator. The micromanipulator is useful for intravascular interventional applications and particularly ultrasonic imaging when coupled with an ultrasound transducer.

A self-retracting fully compliant bistable micromechanism

Abstract: A new class of fully compliant bistable mechanisms with the added benefit of integrated self-retraction has been developed (hereafter identified as Self-Retracting Fully compliant Bistable Mechanism or SRFBM). A technique using tensural pivots to manage compressive loading in compliant mechanisms is introduced and implemented in the SRFBM. The elimination of traditional kinematic joints and their associated clearance allows a total displacement between stable positions of 8.5 /spl mu/m, and the mechanism size is less than 300 /spl mu/m square when using 2.0 /spl mu/m minimum line widths. Maximum actuation force is approximately 500 /spl mu/N. The SRFBM's small linear displacement and reasonable actuation force facilitate integration with efficient thermal actuators. Furthermore, fully compliant mechanisms allow greater freedom in fabrication as only one mechanical layer is needed. Systems with on-chip actuation have been fabricated and tested, demonstrating bistability and on-chip actuation, which requires approximately 150 mW. A single fatigue test has been completed, during which the SRFBM endured approximately 2 million duty cycles without failure.

Design of Distributed Compliant Mechanisms

Abstract: The optimization problem formulations currently used to synthesize compliant mechanism topologies aim to maximize the flexibility for obtaining the desired output motion while maximizing the overall stiffness for satisfactorily bearing the applied loads. The best solution to this problem, as posed, is a linkage consisting of rigid members connected together with revolute joints. The current elastic mechanics-based formulations do generate compliant topologies that closely imitate a rigid-body linkage by means of lumped compliance as in flexural pivots. Systematically generating such topology solutions could serve as a creative aid in the conceptual design of mechanisms, especially when the force-deflection specifications are nonintuitive to human designers. However, flexural pivot-based compliant designs are not useful in most applications when large displacements and/or high strength are desired. Ideally, compliant designs should distribute flexibility uniformly throughout the structure rather t...

Piezoelectrically actuated four-bar mechanism with two flexible links for micromechanical flying insect thorax

Abstract: In this paper, a piezoelectrically actuated four-bar mechanism with two flexible links is proposed to be used in a micromechanical flying insect robot wing thorax for stroke amplification. PZT-5H- and PZN-PT-based unimorph actuators are utilized at the input link of the four-bar for a compact and lightweight thorax transmission mechanism. The kinematics and dynamics of the proposed wing structure with two parallel four-bar mechanisms are analyzed, optimal four-bar link size selection method is introduced, and quasistatic forces generated at the wing are computed for evaluating the feasibility of the design. Using laser micromachining and folding techniques, prototype four-bar structures are constructed. In the experiments, for a 10/spl times/1/spl times/0.12 mm/sup 3/ PZT-5H actuator-based four-bar mechanism, the stroke amplification of around 20 - 25 is held, and an attached polyester wing is resonated at 29 Hz with around 90/spl deg/ flapping motion. These results match closely with the predicted theoretical values.

Freeform Skeletal Shape Optimization of Compliant Mechanisms

Abstract: Compliant mechanisms are elastic continua used to transmit or transform force and motion mechanically. The topology optimization methods developed for compliant mechanisms also give the shape for a chosen parameterization of the design domain with a fixed mesh. However, in these methods, the shapes of the flexible segments in the resulting optimal solutions are restricted either by the type or the resolution of the design parameterization. This limitation is overcome in this paper by focusing on optimizing the skeletal shape of the compliant segments in a given topology. It is accomplished by identifying such segments in the topology and representing them using Bezier curves. The vertices of the Bezier control polygon are used to parameterize the shape-design space. Uniform parameter steps of the Bezier curves naturally enable adaptive finite element discretization of the segments as their shapes change. Practical constraints such as avoiding intersections with other segments, self-intersections, and restrictions on the available space and material, are incorporated into the formulation. A multi-criteria function from our prior work is used as the objective. Analytical sensitivity analysis for the objective and constraints is presented and is used in the numerical optimization. Examples are included to illustrate the shape optimization method.

Optimized binary modular reconfigurable robotic devices

Abstract: Binary robotic devices with large degrees of freedom have been proposed by a number of researchers. However, experimental implementations of these concepts have been built with conventional components. These physical systems are heavy, complex and far from being practical devices. In this paper, a lightweight, compliant mechanism driven by optimized magnet-coil actuators is proposed and developed as an element for modular hyper-redundant degrees of freedom robotic systems. Such elements could be used in a number of applications and would replace conventional, complex, and heavy components. The device has a parallel kinematic structure. Its binary actuation simplifies its control architecture.

A Computational Approach to the Number of Synthesis of Linkages

Abstract: This paper presents a number of systematically designed compliant topologies and discusses how the intrinsic kinematic behavior can be extracted from them. This is then applied to the number synthesis of linkages. Many techniques developed for number synthesis of linkages enumerate numerous possible kinematic chains, but few can select the best configuration among them. A systematic computational approach that can select the best configuration based on kinetostatic design specifications is presented here. This is a serendipitous result that transpired when two well-developed design techniques for compliant mechanisms were combined. A number of examples with nonintuitive design specifications are included to illustrate the new approach to the number synthesis. The examples also illustrate that the kinematic behavior is aptly captured in the elastic mechanics-based topology optimization method to compliant mechanism design. Dimensional synthesis is also accomplished in the same procedure, which is an added benefit of this approach.

Biomimetic Compliant System for Smart Actuator-Driven Aquatic Propulsion: Preliminary Results

Abstract: Biomimetic design takes principles from nature to employ in engineering problems. Such designs are hoped to be quiet, efficient, robust, and versatile, having taken advantage of optimization via natural selection. However, the emulation of specific biological devices poses a great challenge because of complicated, arbitrary, and over-redundant designs. Compliant mechanisms are of immediate appeal in addressing the problem of complex, biomimetic deformation because of their inherent flexibility and distributed compliance. The goal of this research is to develop a biologically-inspired hydrofoil for aquatic propulsion, by assembling planar compliant mechanism building blocks to generate complex 3-D deformations. The building block is a rib structure generated from topology optimization. An ADAMS model is then created to quickly visualize motion and estimate system characteristics. System refinement is achieved through further size and shape optimization of individual ribs. Testing of a single-rib and dual-actuator system is currently in progress. The preliminary results have demonstrated the potential of this combined approach to quickly identify and evaluate new applications that may result from building blocks.Copyright © 2003 by ASME

Identification of Macro- and Micro-Compliant Mechanism Configurations Resulting in Bistable Behavior

Abstract: IDENTIFICATION OF MACROAND MICROCOMPLIANT MECHANISM CONFIGURATIONS RESULTING IN BISTABLE BEHAVIOR Brian D. Jensen Department of Mechanical Engineering Master of Science The purpose of this research is to identify the configurations of several mechanism classes which result in bistable behavior. Bistable mechanisms have use in many applications, such as switches, clasps, closures, hinges, and so on. A powerful method for the design of such mechanisms would allow the realization of working designs much more easily than has been possible in the past. A method for the design of bistable mechanisms is especially needed for micro-electro-mechanical systems (MEMS) because fabrication and material constraints often prevent the use of simple, well-known bistable mechanism configurations. In addition, this knowledge allows designers to take advantage of the many benefits of compliant mechanisms, especially their ability to store and release energy in their moving segments. Therefore, an analysis of a variety of mechanism classes has been performed to determine the configurations of compliant segments or rigid-body springs in a mechanism which result in bistable behavior. The analysis revealed a relationship between the placement of compliant segments and the stability characteristics of the mechanism which allows either analysis or synthesis of bistable mechanisms to be performed very easily. Using this knowledge, a method of type synthesis for bistable mechanisms has been developed which allows bistable mechanisms to be easily synthesized. Several design examples have been presented which demonstrate the method. The theory has also been applied to the design of several bistable micromechanisms. In the process of searching for usable designs for micro-bistable mechanisms, a mechanism class was defined, known as “Young” mechanisms, which represent a feasible and useful way of achieving micro-mechanism motion similar to that of any four-bar mechanism. Based on this class, several bistable micro-mechanisms were designed and fabricated. Testing demonstrated the ability of the mechanisms to snap between the two stable states. In addition, the mechanisms showed a high degree of repeatability in their stable positions. COMMITTEE APPROVAL: Larry L. Howell, Committee Chair Linton G. Salmon, Committee Member Timothy W. McLain, Committee Member Craig C. Smith, Graduate Coordinator

Parameterization strategy for optimization of shape morphing compliant mechanisms using load path representation

Abstract: The distributed compliance and smooth deformation field of compliant mechanisms provide a viable means to achieve shape morphing in many systems, such as flexible antenna reflectors and morphing aircraft wings. We previously developed a systematic synthesis approach to design shape morphing compliant mechanisms using Genetic Algorithm (GA). However, the design variable definition, in fact, allows the generation of invalid designs (disconnected structures) within the GA. In this research, we developed a load path representation to include the structure connectivity information into the design variables, thus improving the GA efficiency. The number of design variables is also independent of the number of elements in the finite element model that is used to solve for the structural deformation. The shape morphing synthesis approach, incorporating this path representation, is demonstrated through two examples, followed by discussions on further refinements.

On Honeycomb Parameterization for Topology Optimization of Compliant Mechanisms

Abstract: Discrete parameterization using full or partial ground structures of truss/frame elements is not appropriate for domain representation as they do not map all points in the continuum and can lead to dangling or overlapping elements in the optimal topology. Existing continuum parameterization using units cells with holes, ranked microstructures or penalized Young’s modulus (SIMP model) mainly have problems like the appearance of checkerboard patterns and stiffness singularity regions. This is probably due to point-contact between diagonally placed cells and such regions can be avoided by using higher order elements, perimeter constraints or filtering schemes which result in additional computational load on the optimization procedures. An edge connectivity throughout is ensured when using a honeycomb representation with staggered regular hexagonal cells. In this paper, such a parameterization is employed for topology synthesis of compliant mechanisms with flexibility-stiffness and flexibility-strength multi-criteria formulations. The material connectivity is well-defined, and checkerboard and zero-stiffness singularities are not seen in numerous examples solved with honeycomb parameterization.Copyright © 2003 by ASME

Synthesis of shape morphing compliant mechanisms using a load path representation method

Abstract: The performance of many mechanical systems is directly related to the geometric shapes of their components, such as aircraft wings and antenna reflectors. While the shapes of these components are mostly fixed, incorporating shape morphing into these systems can increase the flexibility and enhance the performance. A synthesis approach for shape morphing compliant mechanism is presented in this paper, using a load path representation method to efficiently exclude the invalid topologies (disconnected structures) from the Genetic Algorithm (GA) solution space. The synthesis approach is illustrated through a flexible antenna reflector design and a morphing aircraft trailing edge. The results demonstrate the capability of the load path representation method to create various designs with less design variables. The results also show that the use of compliant mechanisms can indeed provide a viable alternative for shape morphing applications. Methods to improve convergence such as employing a local search within or following the GA are also discussed.

Synthesis of shape morphing compliant mechanisms using load path representation

Abstract: Synthesis of shape morphing compliant mechanism is inherently different from typical single output problems, due to the multiple output points along the morphing boundary. Two synthesis approaches, using a fixed initial discretization mesh and using a load path representation, have been developed previously to simultaneously address the topology, size, and geometry aspects of a compliant mechanism. Due to insufficient diversity in later generations, pre-matured convergence to sub-optimal solution is observed in the load path approach. In this paper, additional genetic operation strategies are introduced to enhance the design diversity in each Genetic Algorithm population. The capabilities and limitations of the fixed mesh approach and the improved load path approach are studied through several examples. The results show that the load path approach can achieve better quality solution with less computation time than the fixed mesh approach. The load path representation can potentially lead to a fully systematic synthesis approach due to the absence of a prespecified initial discretization mesh. Boundary conditions are currently being incorporated into the design variable to understand their importance in structural topology.

On the design of compliant-based micro-motion manipulators with a nanometer range resolution

Abstract: In the last decades, there has been an increasing demand in the field of micromanipulation with high precision requirement. This motivated the development of a class of new devices, micro-motion manipulators or macromanipulators. This paper concerns some issues on designing a high-precision micromanipulator, which is based on "compliant mechanism" concept. The design rules for this kind of micromanipulators in terms of material, geometry, flexure hinges, actuators, motion and fabrication, are proposed in an imperative way. Based on these rules, the practical realization for the design of two compliant-based macromanipulators is described. The results of this paper are very useful for the design of compliant-based macro-motion systems.

Fabrication of micromachined TiNi-based microgripper with compliant structure

Abstract: One of the problems faced in the development of micro-gripper is that the actuation displacement or force is too small In this study, it is aimed to solve this problem with application of shape memory and compliant mechanisms TiNi film based micro-gripper with compliant structure was design, simulated and fabricated Some important issues regarding to the preparation of high performance shape memory TiNi films using sputtering methods were discussed

A Closed-Form Dynamic Model of the Compliant Constant-Force Mechanism Using the Pseudo-Rigid-Body Model

Abstract: A CLOSED-FORM DYNAMIC MODEL OF THE COMPLIANT CONSTANT-FORCE MECHANISM USING THE PSEUDO-RIGID-BODY MODEL Cameron L. Boyle Department of Mechanical Engineering Master of Science A mathematical dynamic model is derived for the compliant constant-force mechanism, based on the pseudo-rigid-body model simplification of the device. The compliant constant-force mechanism is a slider mechanism incorporating large-deflection beams, which outputs near-constant-force across the range of its designed deflection. The equation of motion is successfully validated with empirical data from five separate mechanisms, comprising two configurations of compliant constant-force mechanism. The dynamic model is cast in generalized form to represent all possible configurations of compliant constant-force mechanism. Deriving the dynamic equation from the pseudo-rigidbody model is useful because every configuration is represented by the same model, so a separate treatment is not required for each configuration. An unexpected dynamic trait of the constant-force mechanism is discovered: there exists a range of frequencies for which the output force of the mechanism accords nearer to constant-force than does the output force at static levels.

Topology Optimization of a Compliant Gripper Using Hybrid Simulated Annealing and Direct Search

Abstract: The present work introduces a new methodology for solving the topology optimization problem of a compliant gripper. A hybrid optimization technique is developed using simulated annealing as a random search method, while the simplex method (Nelder-Mead) is used as a direct search method. A new modified technique of motion from one search point to another based on the discrete nature of adding and/or removing a structural member is proposed. The traditional continuous simulated annealing technique is used to find the members’ heights. A discrete uni-variant search method is adopted following the simulated annealing and before the simplex method. This corresponds to about 14% of the number used in the old method and in the previous work in the literature, and about 86% of the optimization time is saved. The optimum design of a compliant mechanism is conducted for maximum flexibility and stiffness using the developed hybrid optimization technique.Copyright © 2003 by ASME

Energy-based efficiency of mechanized solid state actuators

Abstract: The research in this study develops an analysis technique for mechanized solid-state actuators. The methodology's strength stems from the fact that it can be applied to a single solid-state actuator or an actuator that is coupled to a compliant mechanism (mechanized). The technique couples the actuator to any compliant mechanism and it takes into account interactions between the mechanized actuator and its load. Thus the methodology can be applied to a myriad of loaded systems. The analysis technique is rooted in thermodynamics and thus can be expanded to a wide range of systems (piezoelectric, electrohydraulic, electrostrictive, magnetostrictive, etc.). The methodology uses energy transfer as a medium to develop analytical relationships between input parameters and output parameters. Results of the technique are consistent with existing energy-based techniques and experimental data.

Maximum Energy-Efficiency Compliant Mechanism Design for Piezoelectric Stack Actuators

Abstract: Combined optimization of a compliant mechanism and a piezoelectric stack actuator for maximum energy conversion efficiency is considered. The paper presents a system level analysis in which the actuator and the compliant mechanism are mathematically described as linear two-port systems. The combination of stack and compliant mechanism is used to drive a structure, modeled as a mass-spring system. The analysis assumes all components to be free from dissipation, and the piezoelectric stack is driven by an ideal voltage source. Energy conversion efficiency is defined as the ratio of the output mechanical energy to the input electric energy. Theoretical bounds on the system efficiency are obtained. It is shown that the stack actuator can be optimized separately and matched to the specified structure and an optimally designed complaint mechanism. The optimization problem for the compliant mechanism is formulated to maximize a weighted objective function of energy efficiency and stroke amplification. Optimization results are presented for ground structures modeled using frame elements.Copyright © 2003 by ASME

Actuation Development and Evaluation for INSTAR - Inertially Stabilized Rifle

Abstract: In the use of piezoelectric actuators, it is a clear choice to use stack (or d 33 mode) architectures when very high force is required or bender (or d 31 mode) architectures when very high displacements are needed. However, the choice isn't as clear for applications that need simultaneously moderate to high force and displacement. This paper presents one such application, INSTAR, which is posed with this dilemma. INSTAR is a novel rifle system that has an inertially stabilized barrel via an active suspension based on piezoelectric actuation. While the frequency required for this application was low (∼10Hz), the displacement (± 200 to 400 microns) and the force (22-45 N) are moderate. Two very different actuation approaches were developed, modeled, fabricated and experimentally validated within the INSTAR demonstration platform: 1) a d 31 approach based on the Recurve architecture with focus on generating higher forces than is common for d 31 actuators and 2) a d 33 approach based upon a compliant mechanism designed using topology optimization with focus on providing more amplified strain than is common for d 33 actuators. Both approaches were successful in meeting the INSTAR requirements, but each had its own advantages and disadvantages.