Showing papers on "Compliant mechanism published in 2015"

A methodology for transferring principles of plant movements to elastic systems in architecture

Abstract: In architecture, kinetic structures enable buildings to react specifically to internal and external stimuli through spatial adjustments. These mechanical devices come in all shapes and sizes and are traditionally conceptualized as uniform and compatible modules. Typically, these systems gain their adjustability by connecting rigid elements with highly strained hinges. Though this construction principle may be generally beneficial, for architectural applications that increasingly demand custom-made solutions, it has some major drawbacks. Adaptation to irregular geometries, for example, can only be achieved with additional mechanical complexity, which makes these devices often very expensive, prone to failure, and maintenance-intensive.Searching for a promising alternative to the still persisting paradigm of rigid-body mechanics, the authors found inspiration in flexible and elastic plant movements. In this paper, they will showcase how today's computational modeling and simulation techniques can help to reveal motion principles in plants and to integrate the underlying mechanisms in flexible kinetic structures. By using three case studies, the authors will present key motion principles and discuss their scaling, distortion, and optimization. Finally, the acquired knowledge on bio-inspired kinetic structures will be applied to a representative application in architecture, in this case as flexible shading devices for double curved facades. Plant movements.Kinetic structures.Biomimetics.Facade shading.Compliant mechanisms.

Stress-constrained topology optimization for compliant mechanism design

Abstract: This article presents an application of stress-constrained topology optimization to compliant mechanism design. An output displacement maximization formulation is used, together with the SIMP approach and a projection method to ensure convergence to nearly discrete designs. The maximum stress is approximated using a normalized version of the commonly-used p-norm of the effective von Mises stresses. The usual problems associated with topology optimization for compliant mechanism design: one-node and/or intermediate density hinges are alleviated by the stress constraint. However, it is also shown that the stress constraint alone does not ensure mesh-independency.

A comparative analysis of joint clearance effects on articulated and partly compliant mechanisms

Abstract: Clearance is inevitable in the articulated mechanisms due primarily to the design, manufacturing and assembly processes or a wear effect. This phenomenon affects the kinematic and dynamic performances of mechanism negatively. Compliant mechanism, which consists of at least one flexible member along with the conventional rigid links, becomes a favorable choice to decrease the number of movable joints and also their clearance effects. In this study, conventional and compliant slider–crank mechanisms having joints with clearance are used to investigate and compare the effects of joint clearance. Pseudo-rigid-body model of compliant mechanism is constituted. For the case of different clearance sizes and running speeds, kinematic and dynamic performances of mechanisms are compared to each other. The results show that the joint clearance leads to chaotic behavior on kinematic and dynamic outputs of mechanism. The flexibility of small-length flexural pivot, that is, pseudo-joint, has clear suspension effects to decrease the undesired reflections of joints clearance on the system outputs. Also, this pseudo-joint constitutes a force-closed kinematic pair behavior between journal and bearing in joint having clearance. This leads to continuous contact mode by preventing the separation of journal and bearing parts.

Variable Camber Compliant Wing - Design

Abstract: This paper describes the design process and design validation of the US Air Force Research Laboratory developed Variable Camber Compliant Wing. The Variable Camber Compliant Wing was designed and fabricated based on compliant mechanisms and advanced manufacturing technologies, enabling a solution that is light weight, requires low power, and is low cost. The Air Force Research Laboratory demonstrates a new capability and technology for an active wing camber change without discrete control surfaces under realistic aerodynamic conditions. In this particular study, the wing was designed to target, but does not exactly resemble airfoil shapes between the NACA 2410 and NACA 8410, but the design is not only limited to these airfoils. The entire skin is seamless and continuous, constructed from a single piece of non-stretchable composite skin. The smooth elastic deformation of the Variable Camber Compliant Wing is obtained through the underlying compliant mechanism. 2D camber change is achieved by linear actuation to control both leading and trailing edge deflection. 3D shape change is also capable through camber variation along the span using a distributed actuation system. Proving the capability of a smooth 2D and 3D shape change would allow aircraft to significantly reduce fuel burn by continuously optimizing the wing L/D throughout the mission, as well as reduce airframe noise caused by holes and gaps existing on a conventional wing. Future aerodynamic applications and testing plans are discussed in this paper.

Direct Design of an Energy Landscape with Bistable DNA Origami Mechanisms

Abstract: Structural DNA nanotechnology provides a feasible technique for the design and fabrication of complex geometries even exhibiting controllable dynamic behavior. Recently we have demonstrated the possibility of implementing macroscopic engineering design approaches to construct DNA origami mechanisms (DOM) with programmable motion and tunable flexibility. Here, we implement the design of compliant DNA origami mechanisms to extend from prescribing motion to prescribing an energy landscape. Compliant mechanisms facilitate motion via deformation of components with tunable stiffness resulting in well-defined mechanical energy stored in the structure. We design, fabricate, and characterize a DNA origami nanostructure with an energy landscape defined by two stable states (local energy minima) separated by a designed energy barrier. This nanostructure is a four-bar bistable mechanism with two undeformed states. Traversing between those states requires deformation, and hence mechanical energy storage, in a complian...

Toward a Unified Design Approach for Both Compliant Mechanisms and Rigid-Body Mechanisms: Module Optimization

Abstract: Rigid-body mechanisms (RBMs) and compliant mechanisms (CMs) are traditionally treated in significantly different ways. In this paper, we present a synthesis approach that is appropriate for both RBMs and CMs. In this approach, RBMs and CMs are generalized into modularized mechanisms that consist of five basic modules, including compliant links (CLs), rigid links (RLs), pin joints (PJs), compliant joints (CJs), and rigid joints (RJs). The link modules and joint modules are modeled through beam elements and hinge elements, respectively, in a geometrically nonlinear finite-element solver, and subsequently a beam-hinge ground structure model is proposed. Based on this new model, a link and joint determination approach—module optimization—is developed for the type and dimensional synthesis of both RBMs and CMs. In the module optimization approach, the states (both presence or absence and sizes) of joints and links are all design variables, and one may obtain an RBM, a partially CM, or a fully CM for a given mechanical task. Three design examples of path generators are used to demonstrate the effectiveness of the proposed approach to the type and dimensional synthesis of RBMs and CMs.

Modeling Large Spatial Deflections of Slender Bisymmetric Beams in Compliant Mechanisms Using Chained Spatial-Beam Constraint Model

Abstract: Modeling large spatial deflections of flexible beams has been one of the most challenging problems in the research community of compliant mechanisms. This work presents a method called chained spatial-beam-constraint-model (CSBCM) for modeling large spatial deflections of flexible bisymmetric beams in compliant mechanisms. CSBCM is based on the spatial beam constraint model (SBCM), which was developed for the purpose of accurately predicting the nonlinear constraint characteristics of bisymmetric spatial beams in their intermediate deflection range. CSBCM deals with large spatial deflections by dividing a spatial beam into several elements, modeling each element with SBCM, and then assembling the deflected elements using the transformation defined by Tait-Bryan angles to form the whole deflection. It is demonstrated that CSBCM is capable of solving various large spatial deflection problems whether the tip loads are known or the tip deflections are known. The examples show that CSBCM can accurately predict the large spatial deflections of flexible beams, as compared to the available nonlinear FEA results obtained by ANSYS. The results also demonstrated the unique capabilities of CSBCM to solve large spatial deflection problems that are outside the range of ANSYS.Copyright © 2015 by ASME

Effect of flexure hinge type on a 3D printed fully compliant prosthetic finger

Abstract: Soft robotics, as a new dimension in robotics, is an rapidly growing research area. Fully compliant mechanisms and structures can be built using soft materials. Having a fully compliant system -a monolithic body- will reduce the manufacturing and assembly costs and show a whole-body bending performance similar to its natural counter-parts. Current prosthetics, particularly fingers and hands, require significant manufacturing and assembly operations. Using additive manufacturing (aka 3D printing), low cost and high performance prosthetic devices can be established. In this study, we report on a fully compliant finger which is 3D printed with a modified low-cost 3D printer based on the Fused Deposition Modelling (FDM) technique. Prior to the finger fabrication, the bending behavior of some well-known flexure hinges were modelled and experimentally evaluated to find the most suitable design for a fully compliant prosthetic finger. Experimental and numerical results from the finite element analysis for the hinges and the complaint finger are in good correlation, encouraging us to establish a single piece prosthetic hand in the near future.

Structural optimization for flexure-based parallel mechanisms – Towards achieving optimal dynamic and stiffness properties

Abstract: Flexure-based parallel mechanisms (FPMs) are a type of compliant mechanisms that consist of a rigid end-effector that is articulated by several parallel, flexible limbs (a.k.a. sub-chains). Existing design methods can enhance the FPMs’ dynamic and stiffness properties by conducting a size optimization on their sub-chains. A similar optimization process, however, was not performed for their sub-chains’ topology, and this may severely limit the benefits of a size optimization. Thus, this paper proposes to use a structural optimization approach to synthesize and optimize the topology, shape and size of the FPMs’ sub-chains. The benefits of this approach are demonstrated via the design and development of a planar X − Y − θ z FPM. A prototype of this FPM was evaluated experimentally to have a large workspace of 1.2 mm × 1.2 mm × 6°, a fundamental natural frequency of 102 Hz, and stiffness ratios that are greater than 120. The achieved properties show significant improvement over existing 3-degrees-of-freedom compliant mechanisms that can deflect more than 0.5 mm and 0.5°. These compliant mechanisms typically have stiffness ratios that are less than 60 and a fundamental natural frequency that is less than 45 Hz.

Design and verification of auxetic microstructures using topology optimization and homogenization

Abstract: The design of mechanical microstructures having auxetic behaviour is proposed in this paper using techniques of topology optimization for compliant mechanisms. A robust hybrid algorithm based on evolutionary algorithms and local search steps is used. The result may need verification in order to accommodate needs not taken into account in the topology optimization. Therefore, a numerical homogenization scheme is used in order to show that the final design still has the wished negative Poisson’s property.

Robust design for a flexible bearing with 1-DOF translation using the Taguchi method and the utility concept

Abstract: A flexible bearing with compliant mechanisms for high-precision mechanism applications has been established as an efficient structure. We have attempted to realize a novel robust design of a flexible bearing with one degree of freedom (1-DOF) translation for highprecision mechanisms. First, the relationship between five design variables and the stress of the displacement responses is illustrated using the response surface method. Next, the Taguchi method, combined with a utility concept, is adopted to determine the optimal parameter combination to minimize stress while simultaneously maximizing displacement. An orthogonal array L27 is used in the experimental work. The experimental results show that displacement and stress values measured 0.11332 mm and 37.625 MPa, respectively. The confirmation results fall within 95% of the CICE. The proposed methodology is useful for the robust design of flexible bearings and related mechanisms.

Conceptual designs of multi-degree of freedom compliant parallel manipulators composed of wire-beam based compliant mechanisms:

Abstract: This paper proposes conceptual designs of multi-degree(s) of freedom (DOF) compliant parallel manipulators (CPMs) including 3-DOF translational CPMs and 6-DOF CPMs using a building block based pseu...

Fluid-Structure Interaction of a Variable Camber Compliant Wing

Abstract: This paper presents results for a loosely-coupled fluid-structure interaction (FSI) of a flexible wing using FUN3D to compute the aerodynamic flow-field and Abaqus to calculate the structural deformation. NASA Langley also provides a general 3D algorithm to interpolate between dissimilar meshes which is used here to map pressures and displacements between the aerodynamic and structural codes. This method is applied to the AFRL developed “Variable Camber Compliant Wing” (VCCW), which is an adaptable wing designed target airfoil shapes between a NACA 2410 and 8410. Results will be compared to experiments conducted in the AFRL Vertical Wind Tunnel.

Dynamic modeling and model order reduction of compliant mechanisms

Abstract: In this work, a novel approach towards statical and dynamical modeling of compliant mechanisms is presented which serves as an origin for model order reduction procedures to provide small, efficient and accurate approximations. As 3D finite element modeling of compliant mechanisms results in very large-scale systems, both model reduction and real-time controlling of the mechanism are not possible. This and the fact that in compliant mechanisms mostly the flexure hinges contribute to the overall performance motivates a procedure which is based on partitioning the structure into elastically deformable hinges and rigid linkages. Unlike common modeling techniques, the reproduction of the non-negligible nonlinear behavior is assured and contributes to precise approximation as well as the fact that not only the flexure itself deforms but also adjacent structures. Furthermore, the proposed methodology is applicable to all kinds of flexure hinges with concentrated compliances and compliant mechanisms of complex geometric shape as well as spatial loading cases. First, an analysis of the inserted flexure hinges yields the significantly deformed region of which corresponding master models with connecting nodes are created. With their geometric properties the mechanism is further divided into remaining stiff sections. Their spatial centroid location and moments of inertia about mass centroid are calculated and according point masses are generated. A finite element model of the mechanism is then developed by rigidly linking the master models with the point masses. Therewith, an accurate 3D model with appreciable less degrees of freedom arises, named significant region model. The system matrices K, M in combination with the input matrix B and the output matrix C yield a closed-form description of the mechanism. In a second step, a considerable decrease of system size is performed by applying modern model order reduction techniques, namely Krylov subspace reduction. A comparison of the new two step approach with full 3D finite element modeling reveals only marginal deviations of less than 6% regarding the static displacements and less than 0.0001% relating to the frequency response of an exemplary mechanism with a substantial lower number of degrees of freedom.

Nonlinear modeling of compliant mechanisms incorporating circular flexure hinges with finite beam elements

Abstract: Modeling of compliant mechanisms incorporating flexure hinges is mainly focused on linear methods. However, geometrically nonlinear effects cannot be ignored generally. This work shows that nonlinear behavior plays an important role in the deformation and stress analysis, which consequently impacts the design of compliant mechanisms. In this study a nonlinear higher order finite beam element based modeling approach is presented strongly reducing the computation time of nonlinear models. Planar deformation and mechanical stress of a single circular flexure hinge under a wide range of loads is modeled and computed with the proposed approach. A comparison with a 3D-nonlinear finite element model shows very good agreement and validates the beam model. It is shown that the linear and nonlinear deformation behavior of a single flexure hinge deviate marginally so that linear modeling approaches are sufficient. Furthermore a planar displacement amplification mechanism incorporating circular flexure hinges is studied by means of the same method highlighting the distinct deviation of the behavior of the geometrically nonlinear model from its linear prediction. In conclusion the nonlinear behavior at the system level can not longer be neglected. Finally, a study shows that different designs of the displacement amplification mechanism are achieved when linear or nonlinear modeling approaches are applied.

Design of 3-legged XYZ compliant parallel manipulators with minimised parasitic rotations

Abstract: Enterprise Ireland (CF20122748Y); University College Cork (UCC 2013 Strategic Research Fund)

Synthesis of Constant Torque Compliant Mechanisms

Abstract: Constant torque compliant mechanisms produce an output torque that does not change in a large range of input rotation. They have wide applications in aerospace, automobile, timing, gardening, medical and healthcare devices. Unlike constant force compliant mechanisms, the synthesis of constant torque compliant mechanisms has not been extensively investigated yet. In this paper, a method is presented for synthesizing constant torque compliant mechanisms that have coaxial input rotation and output torque. The same shaft is employed for both input rotation and output torque. A synthesized constant torque compliant mechanism is modeled as a set of variable width spline curves within an annular design domain formed between a rotation shaft and a fixed ring. Interpolation circles are used to define variable width spline curves. The synthesis of constant torque compliant mechanisms is systematized as optimizing the control parameters of the interpolation circles of the variable width spline curves. The presented method is demonstrated by the synthesis of constant torque compliant mechanisms that have different number of variable width spline curves in the paper.Copyright © 2015 by ASME

Extended nonlinear analytical models of compliant parallelogram mechanisms: third-order models

Abstract: This paper proposes extended nonlinear analytical models, third-order models, of compliant parallelogram mechanisms. These models are capable of capturing the accurate effects from the very large a...

Performance analysis and optimization of a five-degrees-of-freedom compliant hybrid parallel micromanipulator

Abstract: There are generally two main directions for the investigation and development of parallel manipulators, namely macro/meso stream and micro/nano stream, in which the former one has been thoroughly investigated in recent decades, while the latter one still remains many performance related open issues that significantly affect their application potentials in critical situations such as high-precision automated cell manipulation. Improving the overall performance of parallel manipulators is the bridge to connect the academia and industry for the great development and real-world application. This research is to develop a novel methodology called performance decomposition and integration for governing the design optimization process of complicated micromanipulator. A new five degrees-of-freedom (DOF) compliant hybrid parallel micromanipulator which is configured with five identical PSS limbs and one constraining UPU limb is proposed as a case study. The performance visualization, finite element analysis, and dimensional optimization are implemented. The proposed methodology is applicable for the design improvement of different kinds of compliant/parallel mechanisms. Performance is a critical topic for the further improvement of compliant parallel mechanisms.The research attempts to propose a paradigm called performance decomposition and integration to manage the overall performance of these mechanisms in a higher level.A CHPMM is proposed as an example to showcase part of the principle of PDI in the process of design and optimization.The proposed method can be well integrated with the methodology of system hybridization through the specific methods of mechanism hybridization, actuation hybridization and optimization hybridization.For the future work, a physical prototype will be manufactured to further improve the overall performance in aspects of manipulation and control under the guidance of the proposed methods.

Pseudorigid-Body Models of Compliant DNA Origami Mechanisms

Abstract: In this paper, we introduce a strategy for the design and computational analysis of compliant DNA origami mechanism (CDOM), which are compliant nanomechanisms fabricated with DNA origami self-assembly. The rigid, compliant and flexible parts are constructed by bundles of many double-stranded DNA (dsDNA) helices, bundles of a few dsDNA helices or a single dsDNA helix, and single-stranded DNA (ssDNA) strands respectively. Just like in macroscopic compliant mechanisms, a CDOM generates its motion via deformation of at least one structural member. During the motion, strain energy is stored and released in the compliant components. Therefore, these CDOM have the advantage of suppressing thermal fluctuations due to the internal mechanical energy barrier for motion. Here we show that classic Pseudo-rigid-body (PRB) models for compliant mechanism are successfully employed to the analysis of these DNA origami nanomechanisms and can serve to guide the design and analysis method, an example of compliant hinge joint and a bistable four-bar CDOM fabricated with DNA origami are presented.

New phenomena in nonlinear elastic structures: from tensile buckling to configurational forces

Abstract: The theory of the planar elastica is presented in detail and is used to illustrate problems of buckling of a slender structure under tensile dead loading, of buckling as related to constraint’s curvature, and of configurational forces. These problems are important tools in the design of compliant mechanisms, in the emergent field of soft robotics and for the understanding of snake and fish locomotion.