Showing papers on "Compliant mechanism published in 2011"
TL;DR: In this paper, a flexure-based compound bridge-type (CBT) displacement amplifier for piezoelectric drives is investigated, and the derived models are utilized to optimize the amplifier structure through particle swarm optimization (PSO).
206 citations
01 Jan 2011
133 citations
TL;DR: In this article, the authors explored the deflection and buckling of fixed-guided beams used in compliant mechanisms and developed a model for the axial deflection of the buckling beam.
Abstract: 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.
114 citations
TL;DR: In this article, four flat folding paper mechanisms are presented with their corresponding kinematic and graph models, and principles from graph theory are used to abstract the mechanisms to show them as coupled, or inter-connected, mechanisms.
Abstract: . Origami is the art of folding paper. In the context of engineering, orimimetics is the application of folding to solve problems. Kinetic origami behavior can be modeled with the pseudo-rigid-body model since the origami are compliant mechanisms. These compliant mechanisms, when having a flat initial state and motion emerging out of the fabrication plane, are classified as lamina emergent mechanisms (LEMs). To demonstrate the feasibility of identifying links between origami and compliant mechanism analysis and design methods, four flat folding paper mechanisms are presented with their corresponding kinematic and graph models. Principles from graph theory are used to abstract the mechanisms to show them as coupled, or inter-connected, mechanisms. It is anticipated that this work lays a foundation for exploring methods for LEM synthesis based on the analogy between flat-folding origami models and linkage assembly.
104 citations
TL;DR: Two new approaches for synthesizing compliant multistable mechanisms are proposed, which enable designers to achieve multistability through the use of a single bistable mechanism.
Abstract: A compliant multistable mechanism is capable of steadily staying at multiple distinct positions without power input. Many applications including switches, valves, relays, positioners, and reconfigurable robots may benefit from multistability. In this paper, two new approaches for synthesizing compliant multistable mechanisms are proposed, which enable designers to achieve multistability through the use of a single bistable mechanism. The synthesis approaches are described and illustrated by several design examples. Compound use of both approaches is also discussed. The design potential of the synthesis approaches is demonstrated by the successful operation of several instantiations of designs that exhibit three, four, five, and nine stable equilibrium positions, respectively. The equations for determining the actuation force required to move a multistable mechanism are provided. The synthesis approaches enable us to design a compliant mechanism with a desired number of stable positions.
85 citations
TL;DR: In this article, an analytical model and an operational procedure are presented, which make it possible to optimize conically shaped dielectric-elastomer linear actuators for known materials and desired force/stroke requirements.
Abstract: An analytical model and an operational procedure are presented, which make it possible to optimize conically shaped dielectric-elastomer linear actuators for known materials and desired force/stroke requirements. The actuators are obtained by coupling a dielectric elastomer film with a compliant frame which is sized by means of a pseudorigid body model. Depending on the frame design, the actuators can work monodirectionally or bidirectionally. Simulation and experimental results are provided which demonstrate the efficacy of the proposed design procedure and show that well-behaved conically shaped actuators can be conceived and produced.
76 citations
01 Jul 2011-Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology
TL;DR: In this article, the 3R pseudo-rigid-body model (PRBM) was used to model the nonlinear deflection by approximating it as motion of rigid links, and a six-dimensional objective function was formulated by combining the approximation errors of both tip point and tip slope for the two extreme load cases.
Abstract: Compliant mechanisms have been used in many engineering areas where high precision and sensitivity are required. One of the major challenges of designing compliant mechanisms lies in understanding and analyzing the nonlinear deflections of flexible members. The pseudo-rigid-body model (PRBM) method, which simplifies the modeling of the nonlinear deflection by approximating it as motion of rigid links, has been accepted as one of the most important tools for synthesis and analysis of compliant mechanisms. In this paper, a review of various PRBMs is presented. The 3R PRBM whose characteristic parameters are independent of external loads is discussed in detail. For the purpose of finding the optimal set of the characteristic parameters for the 3R PRBM, a six-dimensional objective function is formulated by combining the approximation errors of both tip point and tip slope for the two extreme load cases, i.e., pure moment load and pure vertical force load. A particle swarm optimizer was employed to conduct a continuous search on the objective function. The resulting 3R PRBM with the optimized characteristic parameters shows better performance in predicting large deflections of cantilever beams over the original 3R PRBM.
76 citations
TL;DR: In this article, a stochastic formulation for the design variations results in nearly black and white mechanism designs, robust with respect to uncertainties in the production process, i.e. without any hinges or small details which can create manufacturing difficulties.
Abstract: . The aim of this article is to introduce a new topology optimisation formulation for optimal robust design of Micro Electro Mechanical Systems. Mesh independence in topology optimisation is most often ensured by using filtering techniques, which result in transition grey regions difficult to interpret in practical realisations. This problem has been alleviated recently by projection techniques, but these destroy the mesh independence introduced by the filters and result in single node connected hinges. Such features in the design are undesirable as they are not robust with respect to geometric manufacturing errors (such as under/over etching). They can be avoided by optimising for several design realisations which take into account the possible geometry errors. The design variations are modelled with the help of random variables. The proposed stochastic formulation for the design variations results in nearly black and white mechanism designs, robust with respect to uncertainties in the production process, i.e. without any hinges or small details which can create manufacturing difficulties.
65 citations
TL;DR: A new unified formalism for modeling the mechanical interactions between medical devices and anatomical structures and for computing accurately the haptic force feedback is presented and is demonstrated in interactive simulation of flexible needle insertion through soft anatomical structures with force feedback.
Abstract: The paper is dedicated to haptic rendering of complex physics-based environment in the context of surgical simulation. A new unified formalism for modeling the mechanical interactions between medical devices and anatomical structures and for computing accurately the haptic force feedback is presented. The approach deals with the mechanical interactions using appropriate force and/or motion transmission models named compliant mechanisms. These mechanisms are formulated as a constraint-based problem that is solved in two separate threads running at different frequencies. The first thread processes the whole simulation including the soft-tissue deformations, whereas the second one only deals with computer haptics. This method builds a bridge between the so-called virtual mechanisms (that were proposed for haptic rendering of rigid bodies) and intermediate representations (used for rendering of complex simulations). With this approach, it is possible to describe the specific behavior of various medical devices while relying on a unified method for solving the mechanical interactions between deformable objects and haptic rendering. The technique is demonstrated in interactive simulation of flexible needle insertion through soft anatomical structures with force feedback.
65 citations
TL;DR: In this paper, the authors present new concepts for designing fully compliant statically-balanced compliant mechanisms without prestressing assembly, which can ideally provide zero stiffness and energy free motion like a traditional rigid-body mechanism.
Abstract: . The purpose of this paper is to present new concepts for designing fully-compliant statically-balanced mechanisms without prestressing assembly. A statically-balanced compliant mechanism can ideally provide zero stiffness and energy free motion like a traditional rigid-body mechanism. These characteristics are important in design of compliant mechanisms where low actuation force, accurate force transmission or high-fidelity force feedback are primary concerns. Typically, static balancing of compliant mechanisms has been achieved by means of prestressing assembly. However, this can often lead to creep and stress relaxation arising in the flexible members. In this paper two concepts are presented which eliminate the need for prestressing assembly of compliant mechanisms: (1) a weight compensator which employs a constant-force compliant mechanism, (2) a near-zero-stiffness mechanism which combines two multistable mechanisms. In addition to the advantages provided by statically-balanced compliant mechanisms, two other notable features of these statically-balanced mechanisms are their ability to be monolithically fabricated and to return to their as-fabricated position without any disassembly when not in use.
60 citations
TL;DR: In this article, the authors presented normalized, nonlinear and analytical models of spatial compliant parallel modules, which addressed the nonlinearity of load-equilibrium equations, applied in the deformed configuration, under small deflection hypothesis.
TL;DR: In this article, the structural analysis and the computation of the necessary actuation voltage to initiate the snap-through of bistable composite structures with piezoceramic actuators are elaborated.
TL;DR: In this article, a new material representation model is developed to implicitly describe material usage in a given design domain in terms of one implicit design variable, the iso-line/surface threshold of a characteristic response function.
TL;DR: In this paper, a variable stiffness actuator based on the use of flexures is investigated, which allows the implementation of a desired stiffness profile and range, and a preliminary prototype of the overall joint is depicted.
Abstract: Variable stiffness actuators can be used in order to achieve a suitable trade-off between performance and safety in robotic devices for physical human―robot interaction. With the aim of improving the compactness and the flexibility of existing mechanical solutions, a variable stiffness actuator based on the use of flexures is investigated. The proposed concept allows the implementation of a desired stiffness profile and range. In particular, this paper reports a procedure for the synthesis of a fully compliant mechanism used as a nonlinear transmission element, together with its experimental characterization. Finally, a preliminary prototype of the overall joint is depicted.
TL;DR: In this article, a new systematic design and optimization procedure used for the microgrippers driven by a chevron electrothermal actuator is presented, which includes three steps: first, a suitable rigid-body gripper mechanism is selected using the type synthesis of the kinematic chain method; then, the rigid body mechanism is transferred into a compliant micro gripper; finally, by the stiffness matrix model and the genetic algorithm, a geometry parametric optimization with the high output stiffness objective is carried out.
Abstract: This paper presents a new systematic design and optimization procedure used for the microgrippers driven by a chevron electrothermal actuator. The procedure includes three steps: first, a suitable rigid-body gripper mechanism is selected using the type synthesis of the kinematic chain method; then, the rigid-body mechanism is transferred into a compliant microgripper; finally, by the stiffness matrix model and the genetic algorithm, a geometry parametric optimization with the high output stiffness objective is carried out. Using this procedure, a novel SU-8 electrothermal microgripper is obtained. According to the FEM simulation, the microgripper meets the design requirements and satisfies the constraints. To eliminate the out-of-plane actuation, a novel processing technology is implemented to fabricate the microgripper with a sandwich structure actuator. The experimental results demonstrate that a jaw gap change of 107.5 µm requires only 73.6 mV, 25.61 mW and only 44.92 °C temperature increase at the actuator and the out-of-plane actuation is almost eliminated. A micromanipulation of a micro blood vessel specimen and a micro-assembly for micro-tensile testing studies of fine hair are demonstrated. Hence, the design procedure is valid to generate novel compliant micro mechanisms. The fabrication process can be used in the fabrication of other SU-8 MEMS devices actuated by the electrothermal actuator.
TL;DR: In this article, the authors propose the merger of the fields of compliant mechanisms and space mechanisms as a future direction of research in compliant mechanisms, discusses in detail the motivation to do so, and addresses the key factors of applying compliant mechanism technology to space mechanisms.
Abstract: . Compliant mechanisms offer distinct advantages for use in space that can address many of the issues encountered with current rigid-link space mechanisms. Compliant space mechanisms are defined as moveable mechanical assemblies that achieve their desired motion, force, or displacement by means of the deflection of flexible members and can perform a necessary function in the environments of launch and space. Many current space mechanisms are already highly optimized, yet they still experience inherent challenges, and it is unclear if significant improvements in performance can be made by continuing to refine current designs. Compliant space mechanisms offer a promising opportunity to change the fundamental approach to achieving controlled motion in space systems and have potential for dramatic increases in mechanism performance given the constraints of the space environment. This paper proposes the merger of the fields of compliant mechanisms and space mechanisms as a future direction of research in compliant mechanisms, discusses in detail the motivation to do so, and addresses the key factors of applying compliant mechanism technology to space mechanisms.
01 Jan 2011
TL;DR: The paper gives an overview on the developments at the German Aerospace Center DLR towards anthropomorphic robots which not only try to approach the force and velocity performance of humans, but also have similar safety and robustness features based on a compliant behaviour.
Abstract: The paper gives an overview on the developments at the German Aerospace Center DLR towards anthropomorphic robots which not only try to approach the force and velocity performance of humans, but also have similar safety and robustness features based on a compliant behaviourWe achieve this compliance either by joint torque sensing and impedance control, or, in our newest systems, by compliant mechanisms (so called VIA - variable impedance actuators), whose intrinsic compliance can be adjusted by an additional actuator Both approaches required highly integrated mechatronic design and advanced, nonlinear control and planning strategies, which are presented in this paper
TL;DR: In this paper, several common types of planar flexure hinges with different geometries are characterized and categorized, providing a comprehensive guide with explicit analytical expressions to replace one-node hinges effectively.
Abstract: . The synthesis of compliant mechanisms yield optimized topologies that combine several stiff parts with highly elastic flexure hinges. The hinges are often represented in finite element analysis by a single node (one-node hinge) leaving doubts on the physical meaning as well as an uncertainty in the manufacturing process. To overcome this one-node hinge problem of optimized compliant mechanisms' topologies, one-node hinges need to be replaced by real flexure hinges providing desired deflection range and the ability to bear internal loads without failure. Therefore, several common types of planar flexure hinges with different geometries are characterized and categorized in this work providing a comprehensive guide with explicit analytical expressions to replace one-node hinges effectively. Analytical expressions on displacements, stresses, maximum elastic deformations, bending stiffness, center of rotation and first natural frequencies are derived in this work. Numerical simulations and experimental studies are performed validating the analytical results. More importance is given to practice-oriented flexure hinge types in terms of cost-saving manufacturability, i.e. circular notch type hinges and rectangular leaf type hinges.
TL;DR: Dong et al. as mentioned in this paper showed that the cup is essentially a compliant mechanism with the unique feature of transforming a set of different tooth rotations into a single rigid body rotation and demonstrates how the cup affects tooth conjugation and the conjugate tooth profiles.
Abstract: The paper and its companion [Dong et al., 2011, "Kinematic Fundamentals of Planar Harmonic Drives," ASME J. Mech. Des., 133(1), p. 011007], which treats a harmonic drive without a cup, present the geometry-relevant operation of harmonic drives under an ideal little or no-load condition. This paper shows that the cup is essentially a compliant mechanism with the unique feature of transforming a set of different tooth rotations into a single rigid body rotation and demonstrates how the cup affects tooth conjugation and the conjugate tooth profiles. It proves and demonstrates that the conjugating tooth profile should be a three-dimensional surface because of the cup deformation. The use of spur gears on both flexspline and circular spline will cause excessive interference and excessive deformation will become necessary to overcome the interference. Since no-load geometry is clearly identified, excessive deformation and errors due to incorrect geometry can be removed or filtered and the loading effects can be identified. Contact ratio of a harmonic drive is also obtained through the range of conjugate positions. Although loading is not considered, the geometric error is. Eliminating or reducing geometric error will improve the performance.
TL;DR: A domain-specific initial population strategy is developed that generates geometrically feasible structures for path generating compliant mechanisms (PGCMs) and is coupled with the elitist non-dominated sorting genetic algorithm (NSGA-II) which has been customized for structural topology optimization.
Abstract: Genetic algorithms (GAs) can precisely handle the discrete structural topology optimization of single-piece elastic structures called compliant mechanisms. The initial population of these elastic structures is mostly generated by assigning the material at random. This causes disconnected or unfeasible designs and further rule-based repairing can result in representation degeneracy. However, the problem-specific initial population can affect the performance of GAs like other operators. In this paper, a domain-specific initial population strategy is developed that generates geometrically feasible structures for path generating compliant mechanisms (PGCMs). It is coupled with the elitist non-dominated sorting genetic algorithm (NSGA-II) which has been customized for structural topology optimization. The performance of initial population strategy over random initialization using customized NSGA-II is checked on single and bi-objective optimization problems. Based on the results, it is observed that the custom initialization outperforms the random initialization by dominating all the solutions and exploring larger area of posed objectives. The elastic structures obtained by solving two examples of PGCMs using domain specific initial population strategy are also presented.
TL;DR: A characterization based on eigentwists and eigenwrenches for the synthesis of a compliant mechanism at a given point involves characterizing the compliance matrix at a unique point called the center of elasticity, where translational and rotational compliances are decoupled.
Abstract: In this paper, we implement a characterization based on eigentwists and eigenwrenches for the synthesis of a compliant mechanism at a given point. For 2D mechanisms, this involves characterizing the compliance matrix at a unique point called the center of elasticity, where translational and rotational compliances are decoupled. Furthermore, the translational compliance may be represented graphically as an ellipse and the coupling between the translational and rotational components as vectors. These representations facilitate geometric insight into the operations of serial and parallel concatenations. Parametric trends are ascertained for the compliant dyad building block and are utilized in example problems involving serial concatenation of building blocks. The synthesis technique is also extended to combination of series and parallel concatenation to achieve any compliance requirements.
TL;DR: This paper proposes a hybrid position/force control algorithm for a closed-chain planar manipulator with the last link flexible that is optimized for kinematic and force manipulability in the region of interest.
Abstract: In this paper, simultaneous position/force control of a closed-chain planar manipulator with the last link flexible is studied when the manipulator is in contact with an environment. The proposed manipulator consists of a flexible link connected to three rigid linkages whichare optimized for kinematic and force manipulability in the region of interest. The flexible link is modeled as a series of rigid links connected by virtual torsion springs. A hybrid position/force control algorithm is developed and implemented on the manipulator. Experimental results are presented to verify the performance of the controller.
TL;DR: In this paper, a compliant spatial four-bar (RSSR) mechanism is proposed for the pseudo-rigid-body model (PRBM) with out-of-plane motions.
TL;DR: In this article, a spatial hybrid motion mechanism with 3-DOF is developed that integrates two types of motion through only one compliant mechanism: a macro motion driven by DC servomotors for large workspace and a micro motion driven via PZT actuators for high precision.
TL;DR: In this article, the authors present an approach for design and fabrication of miniature compliant hinges in multi-material compliant mechanisms, which allows for the concurrent design of the part and the manufacturing process.
Abstract: Multi-material molding (MMM) enables the creation of multi-material mechanisms that combine compliant hinges, serving as revolute joints, and rigid links in a single part. There are three important challenges in creating these structures: (1) bonding between the materials used, (2) the ability of the hinge to transfer the required loads in the mechanism while allowing for the prescribed degree(s) of freedom, and (3) incorporating the process-specific requirements in the design stage. This paper presents the approach for design and fabrication of miniature compliant hinges in multi-material compliant mechanisms. The methodology described in this paper allows for the concurrent design of the part and the manufacturing process. For the first challenge, mechanical interlocking strategies are presented. For the second challenge, the development of a simulation-based optimization model of the hinge is presented, involving functional and manufacturing constrains. For the third challenge, the development of hinge positioning features and gate positioning constraints is presented. The developed MMM process is described, along with the main constraints and performance measures. This includes the process sequence, the mold cavity design, gate selection, and runner system development. A case study is presented to demonstrate the feasibility of creating multi-material mechanisms with miniature hinges serving as joints through MMM process. The approach described in this paper was utilized to design a drive mechanism for a flapping wing micro air vehicle. The methods described in this paper are applicable to any lightweight, load-bearing compliant mechanism manufactured using multi-material injection molding.
TL;DR: In this paper, a quadristable compliant mechanism with a bistable structure embedded in a surrounding beam structure is developed, which can be easily miniaturized, offering a significant advantage for application in micro actuators, micro sensors and microelectromechanical systems.
Abstract: A quadristable mechanism with a bistable structure embedded in a surrounding beam structure is developed. Three stable equilibrium positions are within the range of the forward motion of the mechanism, and the fourth stable equilibrium position can only be reached on the backward motion. The quadristability of the mechanism originates from combined compression and bending of the beam structures. Finite element analyses are used to characterize the quadristable behavior of the mechanism under static loading. A design formulation is proposed to find the shape of beams of the mechanism. Prototypes of the mechanism are fabricated and tested. The characteristics of the mechanism predicted by theory are verified by experiments. The design example presented in this investigation demonstrates the effectiveness of the optimization approach for the design of the quadristable compliant mechanism. The proposed mechanism has no movable joints and gains its mobility from the deflection of flexible members. This compliant mechanism can be easily miniaturized, offering a significant advantage for application in micro actuators, micro sensors and microelectromechanical systems.
TL;DR: In this paper, the multilayered nature of MLEMs and the interactions between these layers show how the capabilities of these layers can be enhanced and allow them to meet specific design objectives.
Abstract: Multiple-layer lamina emergent mechanisms (MLEMs) are the mechanisms made from multiple sheets (lamina) of material with motion that emerges out of the fabrication plane. Understanding how layers are used in existing products and in nature provides insight into how MLEMs can also use layers to achieve certain tasks. The multilayered nature of MLEMs and the interactions between these layers show how the capabilities of MLEMs are enhanced and allow them to meet specific design objectives. Layer separation is one objective for which MLEMs are well-suited. Layer separation can have a variety of applications and there are a number of different ways to design a MLEM to achieve this objective.
TL;DR: In this paper, the authors discuss the integration of two previously disparate research areas: topology optimization of compliant mechanisms and flapping wing vehicles and discuss the incorporation of these physics into a gradient-based topological optimization scheme, to design thrust-optimal compliant flapping mechanisms.
Abstract: This work discusses the integration of two previously disparate research areas: topology optimization of compliant mechanisms and flapping wing vehicles. The efficient actuation of the latter is considerably challenging, with competing weight, energy, and authority requirements; intuitive design strategies are not typically available for the aeroelastic physics that define the flapping system. We discuss the incorporation of these physics into a gradient-based topological optimization scheme, to design thrust-optimal compliant flapping mechanisms. This is done with a nonlinear dynamical finite element model incorporating both the mechanism and the wing structure, coupling elastic, inertial, aerodynamic, and actuator forces. Several optimal mechanism topologies are presented, along with a detailed discussion of the relevant flapping physics driving the design process.
01 Apr 2011-Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology
TL;DR: In this article, the rotational stiffness and center shift of a monolithic flexural pivot are modeled for parametric insight of the large deformation behavior of the cross-spring pivot.
Abstract: Manufacturing the cross-spring pivot is not an easy task because of the non-monolithic arrangement. This problem can be resolved by moving the intersection point of the pivot to a remote position. However, the in-plane configuration leads to nonlinear behavior for the monolithic flexural pivot. In this paper, the nonlinear models of stiffness and center shift are developed for parametric insight of the large deformation behavior. The influences of both two drive loads (the horizontal force and bending moment) on the rotational stiffness are characterized, and the load stiffening effect induced by the payload is analyzed. Meanwhile, the nonlinear relationships between center shift and angular displacement are investigated to provide reference for combination of the building blocks. In addition, the effect of loads on the center shift is also evaluated, which is an important consideration in the design of compliant mechanisms. Finally, the nonlinear characteristics, revealed by the analysis model, are validated by finite element analysis (FEA).
TL;DR: In this article, a unified approach to type synthesis of both rigid and compliant parallel mechanisms has been proposed, which is based on the state-of-the-art analysis for several major type synthesis approaches related to compliant and rigid mechanisms.
Abstract: Type synthesis of both rigid and compliant parallel mechanisms has become a hot issue in the field of mechanisms and robotics research in recent years. A unified approach to type synthesis of the two classes of mechanisms, however, has not been referred and investigated up to date. Based on the state-of-art analysis for several major type synthesis approaches related to rigid and compliant mechanisms, respectively, it proves feasible to establish a unified methodology for type synthesis of these two classes of mechanisms. That is a synthesis philosophy in terms of the hierarchy mapping between mathematic, physical, and mechanical building blocks in the framework of screw theory, as addressed in this paper. The key point of the proposed method lies in establishing the mapping among three different building blocks (i.e. geometric building block, kinematic or constraint building block, and mechanical building block). As a result, it makes the whole type synthesis process simple and visible. By using the proposed method, two examples are taken to verify the effectiveness for the type synthesis of both rigid and flexure mechanisms. The content of this paper may provide a theoretical frame for constructing a visualized algorithm or software about the unified type synthesis (or conceptual design) of both rigid and flexure parallel mechanisms.