Design Of Compliant Mechanisms Research Articles

Design of a Compliant Sternum Prosthesis for Improving Respiratory Dynamics

This study presents a novel approach to sternum prosthesis design, aiming to address the limitations of the current solutions by employing compliant mechanisms. The research focuses on developing a prosthetic design capable of generating lifting movements on ribs during breathing. First, a videogrammetry experimental test and virtual simulations were conducted to ascertain the vertical forces applied to each sternum joint. Subsequently, a compliant mechanism design was initiated, involving optimization and finite element analysis (FEM). A comprehensive kinematic performance analysis was performed to evaluate the prosthetic design. The results indicate that the obtained displacements of each rib closely align with those reported in the existing literature, demonstrating the effectiveness of the proposed solution. In conclusion, the developed sternum prosthesis exhibits the capability to recover approximately 56% of the ribs’ natural movements, highlighting its potential as an innovative and promising solution in the field of chest prosthetics.

Topology Design of Compliant Mechanism Design With Multiple Component Modeling Connected by Various Joints

Abstract This study presents a novel framework for the optimal design of compliant mechanisms, specifically addressing the structural drawbacks of conventional single-point or de facto hinges. The hinges often lead to structural instability and stress concentration while deriving maximum motion. To overcome these issues, we introduce a new method that can design stable and elastic domains connected by either revolute or prismatic joints. The new method, called sequential analysis based on the reaction force, can successfully eliminate weak hinge points while optimizing joint locations. The efficiency of developed methodology is validated through several numerical examples, yielding compliant mechanisms with suppressed hinges.

Design of a large stroke compliant gripping mechanism for constant-force applications

Design of a large stroke compliant gripping mechanism for constant-force applications

Compliant mechanism design of combined aircraft wing for stable separation

Abstract Stable separation is a crucial condition that must be met in order for combined aircraft to successfully engage in cooperative flight. In order to achieve the desired fast and controlled separation, this paper proposes a novel design for a torque-driven compliant separation mechanism. By taking into account the compliance characteristics of a sinusoidal acceleration function curve, a mechanical model for the separation mechanism is developed. By utilising the Coulomb friction law, an accurate determination of the aerodynamic load distribution under various conditions is achieved. Subsequently, the relationship between the unlocking moment and the aerodynamic load is derived based on these findings. Through the utilisation of the finite element method, a model of the separation mechanism is generated. To ensure the safety and reliability of the compliant separation mechanism, the mechanical properties of the structural materials are thoroughly analysed under the maximum aerodynamic load. Subsequently, the separation mechanism structure is constructed and subjected to testing in order to showcase the compliance characteristics. In addition, this paper conducts a simulation to analyse the impact of flight speed and angle-of-attack on the separation process. By doing so, the optimal conditions for separation are determined. The methods and findings presented in this study have the potential to contribute valuable insights to the design of combined aircraft.

Curved-Crease Origami for Morphing Metamaterials.

We find a closed-form expression for the Poisson's coefficient of curved-crease variants of the "Miura ori" origami tessellation. This is done by explicitly constructing a continuous one-parameter family of isometric piecewise-smooth surfaces that describes the action of folding out of a reference state. The response of the tessellations in bending is investigated as well: using a numerical convergence scheme, the effective normal curvatures under infinitesimal bending are found to occur in a ratio equal and opposite to the Poisson's coefficient. These results are the first of their kind and, by their simplicity, should provide a fruitful benchmark for the design and modeling of curved-crease origami and compliant shell mechanisms. The developed methods are used to design a curved-crease 3D morphing solid with a tunable self-locked state.

An Analytical Model for Nonlinear-Elastic Compliant Mechanisms with Tension-Compression Asymmetry

Abstract While nonlinear-elastic materials demonstrate potential in enhancing the performance of compliant mechanisms, their behavior still needs to be captured in a generalized mechanical model. To inform new designs and functionality of compliant mechanisms, a better understanding of nonlinear-elastic materials is necessary and, in particular, their mechanical properties that often differ in tension and compression. In the current work, a beam-based analytical model incorporating nonlinear-elastic material behavior is defined for a folding compliant mechanism geometry. Exact equations are derived capturing the nonlinear curvature profile and shift in the neutral axis due to the material asymmetry. The deflection and curvature profile are compared with finite element analysis along with stress-distribution across the beam thickness. The analytical model is shown to be a good approximation of the behavior of nonlinear-elastic materials with tension-compression asymmetry under the assumptions of the von Kármán strain theory. Through a segmentation approach, the geometries of a semicircular arc and folding compliant mechanism design are defined. The deflection of the folding compliant mechanism due to an applied tip load is then evaluated against finite element analysis and experimental results. The generalized methods presented highlight the utility of the model for designing and predicting the behavior of other compliant mechanism geometries and different nonlinear-elastic materials.

Design of Compliant Mechanisms by Topology Optimization Based on Isogeometric Analysis

Design of Compliant Mechanisms by Topology Optimization Based on Isogeometric Analysis

Innovative design of self-locking avoidance compliant mechanism of traction type coal baffle

Innovative design of self-locking avoidance compliant mechanism of traction type coal baffle

A novel bridge-type compliant displacement amplification mechanism under compound loads based on the topology optimisation of flexure hinge and its application in micro-force sensing

The design and modelling of bridge-type compliant displacement amplification mechanisms (CDAMs) are key components in precision engineering. In this study, a bridge-type CDAM under compound loads with an optimum flexure hinge configuration is designed, analysed, and tested. For the case when the flexure hinge configuration is unknown, the internal force distribution for a bridge-type CDAM under compound loads is analysed, and the topology of the flexure hinge is optimised. By applying different volume constraints, the optimised flexure hinge configurations are all V-shaped. Subsequently, a static model of the V-shaped flexure hinge is established. For a bridge-type CDAM with V-shaped flexure hinges, the compliance matrix of the flexure hinge is combined with the relationship among the local compliance matrices in a serial mechanism; consequently, the analytical relationship between the output displacement, output force, and input force is derived. The CDAM is parametrically optimised to further improve the output performance. Simulations and experiments verify the topology optimisation result, static model, and parametric optimisation result. Finally, the CDAM and its static model are applied to the tensile manipulation and micro-force sensing in a microfiber tensile test.

Inerter-based Building Mass Damper: Optimization and experimental study

The Building Mass Damper is a design concept for vibration control of structures where the upper substructure effectively behaves as a Tuned Mass Damper (TMD) for the lower one. Unfortunately, its tuning usually requires softening or partial isolation of the upper substructure; limiting its applicability for retrofitting. The recently proposed Inerter-based Building Mass Damper (IBMD) is an in-parallel intervention on the upper substructure with an inerter and a damper. Thus, the inerter allows correct Tuning, the upper substructure provides the Mass, and the damper adds the Damping. Therefore, a very large mass-ratio TMD is obtained with marginal additional weight and minimal practical impact. In the present work, experimental tests supported by numerical simulations on a small two-story structure model quantitatively confirm the effectiveness of the IBMD. Besides, an innovative compliant mechanism design is introduced for the implementation of the translation-rotational converter that drives the inerter; which has minimal backlash and friction, still allowing large strokes. The experiments involved a frictional damper, which performed comparable to a linear viscous damper considered in the simulations.

The Design and Testing of an Additive Manufacturing-Obtained Compliant Mechanism for the Complex Personalisation of Lenses in Clinical Optometry

The Design and Testing of an Additive Manufacturing-Obtained Compliant Mechanism for the Complex Personalisation of Lenses in Clinical Optometry

A new cockroach-like compliant mechanism with SLA-3D printing for micromanipulation and micropolishing of biomaterials

The traditional compliant mechanisms often employ displacement amplification mechanisms to magnitude the workspace but their displacements are still smaller than 1 mm. Unlike previous studies, the present paper proposes a new conceptual design of compliant mechanism which is inspired from biomechanics of cockroach animal. The developed compliant mechanism for two specific functions, such as microgripper and micropositioner which can handle biomaterials. It can permit a large stroke over 1 mm. Modeling of the performances of the proposed mechanism are built by a couple of adaptive neuro fuzzy inference system (ANIFS) and particle swarm optimization (PSO) where PSO is to optimize the ANFIS. To enhance the performances of the mechanism, accelerated particle swarm optimization (APSO) is utilized to search the optimal design parameters. Lastly, the optimized mechanism is printed by Stereolithography (SLA) 3D technique, and the experimental verifications are performed. The results indicated that circumstance #1, the stroke is about 1.5279 mm, the frequency is 49.02103 Hz, the crosstalk error is 0.01108 mm, and the stress is 8.50514 MPa. In circumstance #2, the stroke is 1.44544 mm, the frequency is 54.51361 Hz, the crosstalk error is 0.0248 mm, and the stress is 8.35604 MPa. In last circumstance, the optimized results are achieved the stroke of 1.62369 mm, frequency of 51.62278 Hz, crosstalk of 0.028141 mm, and stress of 7.71713 MPa. The results indicated that the safety factor of three cases are over 2.5 to ensure a safe operation. The tested results are well satisfied with the simulated results.

IGA-based topology optimization in the design of stress-constrained compliant mechanisms

Topology design of compliant mechanisms has gained wide popularity among the scientific community, and their use in the mechanical engineering field is being of upmost importance. In this paper, an isogeometric analysis (IGA) formulation is used to solve the topology optimization problem of compliant mechanisms. Stress constraints are introduced in the problem to guarantee the attainment of realistic solutions. For this purpose, an overweight constraint is considered for the design process, replacing the use of local stress constraints. The material distribution in the domain is modeled with quadratic B-splines and with a uniform relative density within each element of the mesh. These strategies to define the material layout are used to compare the IGA-based formulation with the finite element (FEM) formulation. The IGA formulation provides several advantages with respect to the classical FEM-based approaches that are shown and analyzed with an input-parameters sensitivity analysis. The sensitivity analysis and the assessment of the importance of introducing of stress constraints in the problem are developed by solving two benchmark problems. Regarding the sensitivity analysis of input parameters, the results show that the ratio between the material and the springs stiffnesses is the parameter with the largest influence on the solutions of the problem. Moreover, the advantages of the IGA formulations over FEM formulations are related with the computational time, the smoothness of the structural borders, and the non-appearance of the checkerboard patterns. With respect to the stress constraints, the results show that they have to be considered in order to avoid instability and structural integrity problems.

Enhancing the design space of bistable laminates by tailoring the attachment boundary conditions

Abstract Bi/Multi stable laminates are structural elements with more than one stable equilibrium configuration. The bistability makes them very interesting for the design of compliant mechanisms. However, these laminates are extremely sensitive to boundary conditions and attachment methods. It has been shown prior in the literature that restrictive boundary conditions can lead to the loss of bistability or unwanted deformation modes. This manuscript develops attachment concepts that leverage the structural behavior changes caused by boundary conditions to expand the design space of bistable elements for structural applications. A systematic means of using the boundary conditions to improve the stability margins and load introduction of bistable tape springs is demonstrated. The stability margins and the achievable angles have been quantified using an analytical model previously developed by Guest and Pellegrino. Subsequently, high-fidelity FE simulations are done in ABAQUS to determine the limits of the proposed method in terms of localization effects. Based on the analytical model and simulation outcomes, layup, size, and attachment points are determined, and two prototypes are fabricated, illustrating the effectiveness of the proposed method in expanding the design space of traditional bistable tape springs.

Modelling and performance analysis of a curvature-adjustable multiple-axis flexure hinge based on Bézier curve

In order to solve the uniqueness of the compliance equations and each notch profile, a curvature-adjustable multiple-axis flexure hinge with complex notch profiles is designed and investigated based on Bézier curve in this paper. The hinge can evolve into multiple-axis flexure hinges with single and hybrid, symmetric and asymmetric notch profiles composed of the ellipse, circle, hyperbola and parabola. In addition, analytical compliance equations in six degrees of freedom based on the Castigliano’s Second Theorem are proposed. Then, a simplified notch profile classification method based on a binary quadratic implicit equation is proposed. Moreover, analytical compliance equations are validated by finite element analysis. The maximum relative error between the finite element analysis and the analytical results is 6.07%. Finally, the compliance, precision of rotation and stress are investigated based on structural parameters. The results show that the change in the rotation centre does not significantly affect the axial and bending compliance for the flexure hinge with a specific single and flush Bézier curve notch profile. Moreover, the flexure hinge with a notch profile consisting of ellipse and hyperbola has the highest rotational precision. The proposed curvature-adjustable multiple-axis flexure hinge can provide more compliance options for the design of compliant mechanisms.

Design of a Novel Large-Stroke Compliant Constant-Torque Mechanism Based on Chained Beam-Constraint Model

Abstract This study addressed the development of a novel compliant constant-torque mechanism (CCTM) that utilizes Bezier curved beams to provide a large stroke in the constant-torque operating range. Previous CCTMs are limited by their working stroke, which reduces their applicability. The proposed mechanism is based on an analytical model using the chained beam-constraint model (CBCM), which captures the kinetostatic behavior of flexible segments. A genetic algorithm based on the CBCM was used to obtain the optimal structure, which was then verified through finite element analysis and experimental results. The results show that the proposed CCTM provides good flatness with a deviation of 3.7% and a large stroke of 80° in the constant-torque working range, while maintaining compactness. This novel CCTM has the potential to provide a simple and effective solution for torque regulators in various applications

Three-Dimensional Material Mask Overlay Topology Optimization Approach With Truncated Octahedron Elements

Abstract This paper presents a 3D material mask overlay topology optimization approach using truncated octahedron elements and spheroidal masks. Truncated octahedron elements provide face connectivity between two juxtaposed elements, thus eliminating singular solutions inherently. A novel meshing scheme with Tetra-Kai-Decaheral or TKD (generic case of truncated octahedron) elements is proposed. The scheme is extended to parameterized generic-shaped domains. Various benefits of implementing the elements are also highlighted, and the corresponding finite element is introduced. Spheroidal negative masks are employed to determine the material within the elements. Seven design variables define each mask. A material density formulation is proposed, and sensitivity analysis for gradient-based optimization is developed. fminconmatlab function is used for the optimization. The efficacy and success of the approach are demonstrated by solving structures and compliant mechanism design problems. Compliance is minimized for the former, whereas a multi-criteria arising due to flexibility and stiffness measures is extremized for optimizing the mechanisms. Convergence of the optimization is smooth. The volume constraint is satisfied and remains active at the end of the optimization.

Modelling of a general lumped-compliance beam for compliant mechanisms

Compliant mechanisms are crucial in a wide range of applications, and straight flexure beams with uniform thickness serve as their fundamental building blocks. While techniques and methods exist to estimate the sophisticated load-displacement behavior of these beams, dealing with the nonlinear large deformation and parametric design of complex compliant mechanisms using these beams remains a significant challenge. To address this challenge, an analytical model has been developed to integrate six independent geometric parameters into a general lumped-compliance beam, known as the general lumped-compliance beam model (GLBM). This approach enables the determinate synthesis of force-displacement characteristics in compliant mechanisms that feature any two flexure beams connected in series, such as the conventional lumped-compliance beam, distributed beam, inverted beam, and folded beam. The closed-form beam constraint model (BCM) is utilized to derive the GLBM that accurately captures geometric nonlinearity and load-dependent effects. To demonstrate the effectiveness of this modeling technique, we verified five specific configurations of the GLBM using nonlinear finite element analysis (FEA). In addition, we selected two representative compliant mechanisms, a revolute joint and a bistable mechanism, for nonlinear analysis and experimental validation, which further showcases the efficacy of this proposed GLBM.

Buckling-induced instability in topology optimization of compliant constant-force mechanisms

Compliant constant-force mechanisms are compliant mechanisms that provide a nearly constant force over a prescribed deflection range. Topology optimization is an effective method for compliant constant-force mechanism design. However, instabilities caused by buckling often cause the optimization algorithm to fail to converge. This study analyzes the causes of buckling-induced instability and proposes methods to avoid this instability. A mechanism with three torsional springs is proposed, and its three force–displacement curves are analyzed. These bifurcated force–displacement curves cause the optimization algorithm to be unstable. Several topology optimization models with buckling constraints are proposed for designing compliant constant-force mechanisms. Their effects are tested and analyzed in numerical examples with different target constant forces and constant-force strokes. Almost all optimization results have three hinges, corresponding to a proposed mechanism with three torsion springs. A slight change in their initial design causes a large change in the force–displacement curve, which eventually leads to buckling-induced instability. This instability can be avoided by constraining the buckling load calculated at the configuration near the start of the constant-force stroke.

An enhanced proportional topology optimization with virtual elements: Formulation and numerical implementation

This paper presents an improved non-sensitivity structural topology optimization method incorporating virtual elements with unstructured polygonal meshes. Specifically, we employ the recently developed gradient-free proportional topology optimization (PTO) approach, for the first time, together with a new material distribution formula suitable for both minimum compliance and compliant mechanism problems. In order to improve performance, we integrate a linear virtual element method (VEM) module into the PTO algorithm. The linear VEM has a desirable characteristic: it does not require numerical integration and, more importantly, is less sensitive to small-edge elements, thus, significantly reducing computational time. Additionally, we utilize virtual elements with unstructured polygonal meshes inside PTO to suppress one-node connection instabilities. Furthermore, the Heaviside-type operator in the main PTO algorithm loop enhances the optimized results by encouraging the density variables to approach discrete (0/1) solutions more effectively. We demonstrate the performance of our developed method in terms of computational speed, diversity of applications, and improved black-and-white (0/1) structures through several benchmark examples of compliance and compliant mechanism designs.