Design of Bend-and-Sweep Compliant Mechanism for Passive Shape Change

2012 ◽  
Author(s):  
Yashwanth Tummala ◽  
Mary Frecker ◽  
Aimy Wissa ◽  
James E. Hubbard
Keyword(s):  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Shape Change ◽  
Stress Relief ◽  
Von Mises Stress ◽  
Nonlinear Stiffness ◽  
Compliant Joints ◽  
Stiffness Properties ◽  
Von Mises ◽  
Wing Morphing

Contact aided compliant mechanisms are a class of compliant mechanisms where parts of the mechanism come into contact with one another during motion. Such mechanisms can have nonlinear stiffness, cause stress-relief, or generate non-smooth paths. New contact aided compliant mechanisms called bend-and-sweep compliant mechanisms are presented in this paper. These bend-and-sweep mechanisms are made up of compliant joints which are alternately located in two orthogonal directions, and they also exhibit nonlinear stiffness in two orthogonal directions. The stiffness properties of these mechanisms, in each direction, can be tailored by varying the geometry of the compliant joints. One application of these mechanisms is in the passive wing morphing of flapping wing UAVs or ornithopters. A design study is conducted to understand the effect of hinge geometry on the deflections and maximum von Mises stress during upstroke and downstroke. It is shown that the bend-and-sweep compliant elements deflect as desired in both the bending and sweep directions.

Design and Optimization of a Bend-and-Sweep Compliant Mechanism

2013 ◽  
Author(s):  
Yashwanth Tummala ◽  
Mary Frecker ◽  
Aimy Wissa ◽  
James E. Hubbard
Keyword(s):  
Optimization Problem ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Leading Edge ◽  
Von Mises Stress ◽  
Nsga Ii ◽  
Design And Optimization ◽  
Compliant Joint ◽  
Von Mises ◽  
Wing Morphing

A novel contact aided compliant mechanism called a bend-and-sweep compliant mechanism is presented. This mechanism has tailorable nonlinear stiffness properties in two orthogonal directions. The fundamental element of this compliant mechanism is the Angled Compliant Joint (ACJ), and the geometric parameters determine the stiffness. This paper presents the design and optimization of such a compliant mechanism. A multi-objective optimization problem was formulated for design optimization of the bend-and-sweep compliant mechanism. The objectives of the optimization problem were to maximize the bending and sweep displacements while minimizing the von Mises stress and mass of each mechanism. This optimization problem was solved using NSGA-II (a genetic algorithm). The results of this optimization for a single ACJ during upstroke and downstroke are presented. Results of two different loading conditions used during optimization of a single ACJ for upstroke are presented. Finally, optimization results comparing the performance of compliant mechanisms with one and two ACJs are also presented. It can be inferred from these results that the number of ACJs and the design of each ACJ determines the stiffness of the bend-and-sweep compliant mechanism. These mechanisms can be used in various applications. Ornithopters or flapping wing unmanned aerial vehicles have unique potential to revolutionize both civil and military applications. The overall goal of this research is to improve the performance of such ornithopters by passively morphing their wings. Passive wing morphing of ornithopters can be achieved by inserting contact-aided compliant mechanisms in the leading edge wing spar. Previously the authors have shown that bending of ornithopter wings can be achieved by integrating a one degree of freedom contact aided compliant mechanism called a compliant spine. The spine was inserted into the leading edge spar and successful flight testing has shown that passive wing bending in ornithopters is feasible and results in significant improvements in lift and thrust. In order to achieve a bio-inspired wing gait called continuous vortex gait, the wings of the ornithopter need to bend, sweep, and twist simultaneously. This can be achieved by using the bend-and-sweep compliant presented in this paper.

scholarly journals Force Diverting Helmet Liner Achieved Through a Lattice of Multi-Material Compliant Mechanisms

2017 ◽  
Author(s):  
Vaibhav Gokhale ◽  
Prasad Tapkir ◽  
Andres Tovar
Keyword(s):  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Radial Force ◽  
Von Mises Stress ◽  
Element Analysis ◽  
Linear Force ◽  
The One ◽  
Von Mises ◽  
Energy Absorbing ◽  
The Impact

This work introduces the design of a lattice array of multi-material compliant mechanisms (LCM) that diverts the impact radial force into tangential forces through the action of elastic hinges and connecting springs. When used as the helmet liner, the LCM liner design has the potential to reduce the risk of head injury through improved impact energy attenuation. The compliant mechanism array in the liner is optimized using a multi-material topology optimization algorithm. The performance of the LCM liner design is compared with the one obtained by expanded polypropylene (EPP) foam, which is traditionally used in sport helmets. An impact test is carried out using explicit, dynamic, nonlinear finite element analysis. The parameters under consideration include the internal energy, the peak linear force, as well as von Mises stress and effective plastic strain distributions. Although there is a small increase in stress and strain values, the simulations show that the maximum internal of the LCM liner design is four times the one of the foam design while the peak linear force is reduced to about half. While the use of the LCM liner design is intended for sports helmets, this design may find application in other energy absorbing structures such as crashworthy vehicle components, blast mitigating structures, and protective gear.

scholarly journals Design of Compliant Joints for Large Scale Structures

2020 ◽  
Author(s):  
Angela Nastevska ◽  
Jovana Jovanova ◽  
Mary Frecker
Keyword(s):  
Large Scale ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Small Scale ◽  
Nonlinear Bending ◽  
Large Scale Structures ◽  
Compliant Joints ◽  
Scale Structures ◽  
High Level ◽  
Novel Design

Abstract Large scale structures can benefit from the design of compliant joints that can provide flexibility and adaptability. A high level of deformation is achieved locally with the design of flexures in compliant mechanisms. Additionally, by introducing contact-aided compliant mechanisms, nonlinear bending stiffness is achieved to make the joints flexible in one direction and stiff in the opposite one. All these concepts have been explored in small scale engineering design, but they have not been applied to large scale structures. In this paper the design of a large scale compliant mechanism is proposed for novel design of a foldable shipping container. The superelasticity of nickel titanium is shown to be beneficial in designing the joints of the compliant mechanism.

Kinematic Synthesis of Planar, Shape-Changing Compliant Mechanisms Using Pseudo-Rigid-Body Models

2012 ◽  
Author(s):  
Kai Zhao ◽  
James P. Schmiedeler ◽  
Andrew P. Murray
Keyword(s):  
Rigid Body ◽  
Shape Matching ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Shape Change ◽  
Flexible Beam ◽  
Beam Model ◽  
Flexible Beams ◽  
Multi Objective Genetic Algorithm ◽  
Optimization Loop

This paper presents a procedure using Pseudo-Rigid-Body Models (PRBMs) to synthesize partially compliant mechanisms capable of approximating a shape change defined by a set of morphing curves in different positions. To generate a single-piece compliant mechanism, flexural pivots and flexible beams are both utilized in the mechanism. New topologies defined by compliant mechanism matrices are enumerated by modifying the components that make up a single degree-of-freedom (DOF) rigid-body mechanism. Because of the introduction of the PRBM for flexural pivots and the simplified PRBM for flexible beams, torsional springs are attached at the characteristic pivots of the 1-DOF rigid-body mechanism in order to generate a corresponding pseudo-rigid-body mechanism. A multi-objective genetic algorithm is employed to find a group of viable compliant mechanisms in the form of candidate pseudo-rigid-body mechanisms that tradeoff minimizing shape matching error with minimizing actuator energy. Since the simplified beam model is not accurate, an optimization loop is established to find the position and shape of the flexible beam using a finite link beam model. The optimal flexible beams together with the pseudo-rigid-body mechanism define the solution mechanism. The procedure is demonstrated with an example in which a partially compliant mechanism approximating two closed-curve profiles is synthesized.

Using Rigid-Body Mechanism Topologies to Design Shape-Changing Compliant Mechanisms

2015 ◽  
Vol 8 (1) ◽  
Author(s):  
Kai Zhao ◽  
James P. Schmiedeler
Keyword(s):  
Rigid Body ◽  
Shape Matching ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Shape Change ◽  
Mesh Network ◽  
Adaptive Antenna ◽  
Optimal Size ◽  
Dimensional Synthesis ◽  
Element Analysis

This paper uses rigid-body mechanism topologies to synthesize fully distributed compliant mechanisms that approximate a shape change defined by a set of morphing curves in different positions. For a shape-change problem, a rigid-body mechanism solution is generated first to provide the base topology. This base topology defines a preselected design space for the structural optimization in one of two ways so as to obtain a compliant mechanism solution that is typically superior to the local minimum solutions obtained from searching more expansive design spaces. In the first strategy, the dimensional synthesis directly determines the optimal size and shape of the distributed compliant mechanism having exactly the base topology. In the second strategy, an initial mesh network established from the base topology is used to generate different topologies (in addition to the base), and an improved design domain parameterization scheme ensures that only topologies with well-connected structures are evaluated. The deformation of each generated compliant mechanism is evaluated using geometrically nonlinear finite element analysis (FEA). A two-objective genetic algorithm (GA) is employed to find a group of viable designs that trade off minimizing shape matching error with minimizing maximum stress. The procedure's utility is demonstrated with three practical examples—the first two approximating open-curve profiles of an adaptive antenna and the third approximating closed-curve profiles of a morphing wing.

Optimization of a Forward-Swept Compliant Mechanism

2017 ◽  
Author(s):  
Joseph Calogero ◽  
Mary Frecker ◽  
Zohaib Hasnain ◽  
James E. Hubbard
Keyword(s):  
Compliant Mechanism ◽  
Shape Change ◽  
Translational Motion ◽  
Peak Stress ◽  
Axial Rotation ◽  
Degree Of Freedom ◽  
Data Set ◽  
Multi Objective ◽  
Multi Objective Genetic Algorithm ◽  
Wing Morphing

A coupled 3 degree-of-freedom contact-aided compliant mechanism called the Forward Swept Compliant Mechanism (FSCM) is designed optimized for coupling orthogonal translational motion. The purpose of this mechanism is to allow desirable wing morphing passively in an ornithopter wing structure to improve free flight pitch agility via sweeping the wing tip forward during downstroke. This new contact-aided compliant mechanism design, based on the coupled three degree of freedom Bend-Twist-and-Sweep Compliant Mechanism, was developed to couple motion in bending to forward sweep during downstroke to destabilize the downstroke, and thereby increasing pitch agility. This is made possible due to an axial rotation of the mechanism, positioning the angled compliant joint such that the axis of deformation is skewed from the lifting direction. A multi-objective optimization problem was formulated and solved using a multi-objective genetic algorithm. The objectives of this optimization were to maximize forward sweep while minimizing bending, twist, peak stress, and mass. During the optimization, 3084 designs were simulated throughout 37 generations. The complete data set from the optimization was used to understand the relationship between each design variable and each objective, as well as in a random forest of regression trees to determine each variable’s importance to each objective. Two designs were chosen and compared for performance tradeoffs, where additional shape change is achieved at the expense of higher peak stress. The first design achieved the desired 2 degrees of forward sweep, and the second design achieved 5 degrees of forward sweep at the expense of larger bending and a higher peak stress.

Optimization of a Bend-Twist-and-Sweep Compliant Mechanism

2014 ◽  
Author(s):  
Joseph Calogero ◽  
Mary Frecker ◽  
Aimy Wissa ◽  
James E. Hubbard
Keyword(s):  
Compliant Mechanism ◽  
Twist Angle ◽  
High Stress ◽  
Peak Stress ◽  
The Other ◽  
Optimal Designs ◽  
Von Mises Stress ◽  
Loading Conditions ◽  
Objective Functions ◽  
Von Mises

The overall goal of this research is to develop design optimization methodologies for compliant mechanisms that will provide passive shape change. Our previous work has focused on designing two separate contact-aided compliant elements (CCE): one for bend-and-sweep deflections, called the bend-and-sweep compliant element (BSCE), and another for twist deflection, called the twist compliant element (TCE). In the current paper, all three degrees of freedom, namely bending, twist, and sweep, are achieved simultaneously using a single passive contact-aided compliant mechanism. A new objective function for a contact-aided compliant mechanism is introduced and the results of the optimization procedure are presented. A bend-twist-and-sweep compliant element (BTSCE) can be inserted into the leading edge spar of an ornithopter, which is an avian-scale flapping wing un-manned air vehicle. The multiple objective functions of the optimization problem presented in this paper are: for upstroke, maximize tip bending and sweep deflections, maximize twist angle, and minimize the mass and peak von Mises stress in the BTSCE, and for downstroke, minimize tip bending and sweep deflections, minimize twist angle, and minimize the mass and peak von Mises stress in the BTSCE. This allows a designer to select a CCE from a set of optimal designs to accomplish all three displacement goals. The BTSCE was modeled using a commercial finite element program and optimized using NSGA-II, a genetic algorithm. The results for a single angled compliant joint (ACJ) for quasi-static upstroke loading conditions are presented. Two optimal designs are discussed and compared, one with a moderate peak stress and moderate deflections, the other with a high peak stress and large deflections. The optimization results are then compared to the previous results for the two independent CCEs. A design study showed that the angle of the ACJ needs to be obtuse to achieve a positive twist angle during upstroke, and an acute contact angle reduces peak stress. The deflection objective functions were relatively insensitive to eccentricity for upstroke and downstroke compared to the other parameters, and a high stress penalty was paid for any gains in deflection. The downstroke objective functions were relatively insensitive to all parameters compared to the upstroke objective functions, and were much smaller in magnitude. The optimization showed that under simplified upstroke loading conditions, the BTSCE with a single ACJ allowed bending deflection near 30% of the length of the BTSCE, twist angle near 0.14 radians, and sweep deflection near 5% of the length of the BTSCE.

A Conceptual Design Tool for Synthesis of Spatial Compliant and Shape Morphing Mechanisms

2018 ◽  
Author(s):  
Sreekalyan Patiballa ◽  
Kazuhiro Uchikata ◽  
Ramkumar Komanduri Ranganath ◽  
Girish Krishnan
Keyword(s):  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Shape Change ◽  
Design Guidelines ◽  
Design Tool ◽  
Three Dimensions ◽  
Shape Morphing ◽  
Compliant Surfaces ◽  
Flow Through ◽  
External Loads

Synthesis of spatial compliant mechanisms for morphing surfaces in three dimensions is challenging as it not only involves meeting the kinematic requirement for spatial shape change, but also providing support against external loads. In three dimensions, there are no existing insightful techniques for synthesis, and the computational approaches are rendered complex. This paper builds on a new insightful technique to synthesize compliant mechanism topologies by visualizing a kinetostatic field of forces that flow through the mechanism geometry. Such a framework when extended to three dimensions, enables a maximally decoupled synthesis framework of shape morphing compliant surfaces, where a primary mechanism meets the shape change requirement, and an auxiliary mechanism provides the required support under external loads. The preliminary design guidelines are implemented using an immersive Virtual Reality based design tool, and verified using finite element simulations for several spatial compliant mechanisms. This design framework is deemed useful for a larger class of shape morphing structures beyond the examples presented in the paper.

Using Rigid-Body Mechanism Topologies to Design Shape-Changing Compliant Mechanisms

2013 ◽  
Author(s):  
Kai Zhao ◽  
James P. Schmiedeler
Keyword(s):  
Rigid Body ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Shape Change ◽  
Adaptive Antenna ◽  
Dimensional Synthesis ◽  
Element Analysis ◽  
Initial Element ◽  
Multi Objective Genetic Algorithm ◽  
Improved Design

This paper uses rigid-body mechanism topologies to synthesize distributed compliant mechanisms that approximate a shape change defined by a set of morphing curves in different positions. A single-actuator compliant mechanism is synthesized from a single degree-of-freedom rigid-body mechanism’s base topology in one of two ways. In one case, the base topology is directly evaluated through dimensional synthesis to determine the compliant mechanism’s optimal dimensions. In the second, the base topology establishes an initial element network for an optimization routine that determines topologies and dimensions simultaneously, and an improved design domain parameterization scheme ensures that only topologies with well-connected structures are evaluated. A multi-objective genetic algorithm is employed to search the design space, and the deformation is evaluated using geometrically nonlinear finite element analysis. The procedure’s utility is demonstrated with two practical examples — one approximating open-curve profiles of an adaptive antenna and the other closed-curve profiles of a morphing wing.

An Assessment of Fused Deposition Modeling for the Manufacturing of Flexural Pivots in an Anthropomorphic Robotic Hand Design

2016 ◽  
Author(s):  
Scott Hill ◽  
Stephen Canfield
Keyword(s):  
Additive Manufacturing ◽  
Fused Deposition Modeling ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Low Cost ◽  
High Mobility ◽  
Robotic Hand ◽  
Fused Deposition ◽  
Compliant Joints ◽  
Deposition Modeling

There is a significant rise in the design of robots performing ever-more complicated tasks. This has motivated more-anthropomorphic grasping hands for these robots. These hands or grippers are complex machines requiring numerous joints to provide high mobility within a relatively small device. Compliant mechanisms and grippers based on compliant joints provide a viable approach to design improved grippers. The use of compliant joints in the design of a hand yields a number of features that can potentially benefit the design; it allows for more lifelike mobility and can eliminate the need for traditional bearings that yield high contact stresses. This allows for much more variety in material choices. The freedom of choosing from a wider range of materials provides many benefits. For example, plastics can provide softer finger members, improved gripping characteristics and components that are less stiff, making them inherently safer for systems that operate in proximity to people. They can provide the flexibility to more naturally conform to the contour of a particular object when grasping it and reduce the necessary gripping forces to achieve reliable operation. Additionally, a solid-state design compliant mechanism design allows more freedom in designing mechanisms that will be constructed for high mobility and operating in a small space. This approach is further enhanced by the increased availability of additive manufacturing tools that enables ready implementation of compliant mechanism designs with almost any topology. This paper will examine the application additive manufacturing tools to create an anthropomorphic gripper based on compliant mechanism components. The primary contribution of this paper is the empirical evaluation of a set of compliant joints for use as the fingers in an anthropomorphic robotic hand produced using additive manufacturing. Three compliant joints will be considered: the simple straight-axis flexural pivot, cross-axis flexural pivot, and leaf-type isosceles-trapezoidal flexural pivot. Each joint type has demonstrated characteristics that may be suitable for fingers in gripping mechanism and are readily suited to be manufactured using low-cost fused deposition modeling techniques that allow for quick and low-cost production. Further, three materials are evaluated for application as the build material of each compliant joint individually and as a complete solid-state anthropomorphic gripper. These materials are: acrylonitrile butadiene styrene (ABS), Nylon 6, and thermoplastic polyurethane (TPU). Each joint and each material option is compared on the basis of their feasibility for rapid prototyping and suitability for substitution of the interphalangeal joints of the human hand. Deflection tests and finite element analysis are used to gather the empirical data for comparison. An evaluation of the tests is provided to determine which compliant joints are well suited for this application. The paper will also consider the as-built material characteristics relative to their application as gripper elements and will compare and contrast the suitability and any impact on the empirical testing and design. This work will provide information on the combination of joint topology, material and manufacturing processes and can be used to inform the design of soft or highly compliant mechanisms.

Sign in / Sign up

Export Citation Format

Share Document