Dual Optimization of Contact-Aided Compliant Mechanisms for Passive Dynamic Shape Change

Compliant four-bar mechanisms treated in previous works consisted of at least one rigid moving link, and such mechanisms synthesized for motion generation tasks have always comprised a rigid coupler link, bearing with the conventional definition of motion generation for rigid-link mechanisms. This paper introduces a new task called compliant-segment motion generation where the coupler is a flexible segment and requires a prescribed shape change along with a rigid-body motion. The paper presents a systematic procedure for synthesis of single-loop compliant mechanisms with no moving rigid-links for compliant-segment motion generation task. Such compliant mechanisms have potential applications in adaptive structures. The synthesis method presented involves an atypical inverse elastica problem that is not reported in the literature. This inverse problem is solved by extending the loop-closure equation used in the synthesis of rigid-links to the flexible segments, and then combining it with elastic equilibrium equation in an optimization scheme. The method is illustrated by a numerical example.

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Synthesis of Distributed Compliant Mechanisms for Adaptive Structures Application: An Elasto-Kinematic Approach

Volume 2: 23rd Design Automation Conference ◽

10.1115/detc97/dac-3861 ◽

1997 ◽

Author(s):

Laxminarayana Saggere ◽

Sridhar Kota

Keyword(s):

Smart Materials ◽

High Performance ◽

Compliant Mechanisms ◽

Shape Change ◽

Current Trend ◽

Adaptive Structures ◽

Topology Generation ◽

Synthesis Procedure ◽

Actuation Scheme ◽

Kinematic Approach

Abstract Compliant mechanisms are a class of mechanisms that achieve desired force and motion transmission tasks by undergoing elastic deformations as opposed to rigid-body displacements in the conventional rigid-link mechanisms. Most of the previously reported synthesis studies in compliant mechanisms related to either partially-compliant mechanisms or fully-compliant mechanisms with joint compliance. Methods developed for fully-compliant mechanisms with link compliance addressed the issue of topology generation for desired deflections at discrete points on the mechanism. This paper presents a new, first-principles based synthesis procedure for fully-compliant mechanisms with link compliance — that is, distributed-compliant mechanisms — for continuous shape change requirements in a particular segment of a mechanism. The general approach presented in this paper for the synthesis of distributed compliant mechanisms is shown to be well suited for application in the design of adaptive structures, an emerging class of high-performance structural systems. The current trend in the design of adaptive structures is to embed structures with force or strain inducing “smart” materials to serve as distributed actuators. Potential advantages of using the distributed compliance scheme over the distributed actuation scheme in the design of adaptive structures include a significant reduction in the number of required actuators and controls.

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Shape Recovery Model of a Curved Beam Using Piezoelectric Actuation

Volume 6: Materials and Fabrication, Parts A and B ◽

10.1115/pvp2012-78382 ◽

2012 ◽

Author(s):

Amit Maha ◽

Su-Seng Pang

Keyword(s):

Shape Recovery ◽

Shape Change ◽

Optimal Placement ◽

External Loading ◽

Curved Beam ◽

Recovery Model ◽

Curved Structures ◽

Beam Geometry ◽

Circular Beam ◽

Dynamic Shape

A thin composite curved beam under external loading is used to simulate different structures such as pressurized pipes, O-Rings etc. These products can undergo dynamic shape change and warping. A piezoelectric actuator is to be used to design for thin curved structures. Simple thin quarter circular beam geometry is analyzed with external loading at the free end. The orientation and placement of the piezoelectric material on a composite curved beam directly affects the deflection and stress applied to that beam. The optimal placement for an actuator for shape recovery was estimated.

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Dynamic Shape Change of an Aortic Valve Cusp Perforation on 3D Transesophageal Echocardiogram

Heart Research - Open Journal ◽

10.17140/hroj-7-152 ◽

2020 ◽

Vol 7 (1) ◽

pp. 1-2

Author(s):

Maedeh Ganji ◽

◽

Jose Ruiz ◽

Robert Percy ◽

Emil Missov ◽

...

Keyword(s):

Aortic Valve ◽

Shape Change ◽

Transesophageal Echocardiogram ◽

Dynamic Shape

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

Volume 4: 36th Mechanisms and Robotics Conference, Parts A and B ◽

10.1115/detc2012-70359 ◽

2012 ◽

Cited By ~ 2

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.

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

Journal of Mechanisms and Robotics ◽

10.1115/1.4030585 ◽

2015 ◽

Vol 8 (1) ◽

Cited By ~ 4

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.

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Constraint-Based Synthesis of Shape-Morphing Structures in Virtual Reality

Volume 2: 34th Annual Mechanisms and Robotics Conference, Parts A and B ◽

10.1115/detc2010-29017 ◽

2010 ◽

Author(s):

Judy M. Vance ◽

Denis Dorozhkin

Keyword(s):

Virtual Reality ◽

Rigid Body ◽

Method Development ◽

Compliant Mechanisms ◽

Design Method ◽

Shape Change ◽

The Body ◽

Motion Path ◽

Primary Methods ◽

Shape Morphing

This manuscript outlines a novel approach to the design of compliant shape-morphing structures using constraint-based design method. Development of robust methods for designing shape-morphing structures is the focus of multiple current research projects, since the ability to modify geometric shapes of the individual system components, such as aircraft wings and antenna reflectors, provides the means to affect the performance of the corresponding mechanical systems. Of particular interest is the utilization of compliant mechanisms to achieve the desired adaptive shape change characteristics. Compliant mechanisms, as opposed to the traditional rigid link mechanisms, achieve motion guidance via the compliance and deformation of the mechanism’s members. The goal is to design a single-piece flexible structure capable of morphing a given curve or profile into a target curve or profile while utilizing the minimum number of actuators. The two primary methods prevalent in the design community at this time are the pseudo-rigid body method (PRBM) and the topological synthesis. Unfortunately these methods either tend to suffer from a poor ability to generate potential solutions (being more suitable for the analysis of existing structures) or are susceptible to overly-complex solutions. By utilizing the constraint-based design method (CBDM) we aim to address those shortcomings. The concept of CBDM has generally been confined to the Precision Engineering community and is based on the fundamental premise that all motions of a rigid body are determined by the position and orientation of the constraints (constraint topology) which are placed upon the body. Any mechanism motion path may then be defined by the proper combination of constraints. In order to apply the CBDM concepts to the design and analysis of shape-morphing compliant structures we propose a tiered design method that relies on kinematics, finite element analysis, and optimization. By discretizing the flexible element that comprises the active shape surface at multiple points in both the initial and the target configurations and treating the resulting individual elements as rigid bodies that undergo a planar or general spatial displacement we are able to apply the traditional kinematics theory to rapidly generate sets of potential solutions. The final design is then established via an FEA-augmented optimization sequence. Coupled with a virtual reality interface and a force-feedback device this approach provides the ability to quickly specify and evaluate multiple design problems in order to arrive at the desired solution.

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Design and Prototyping of a Shape-Changing Rigid-Body Human Foot in Gait

Volume 5B: 42nd Mechanisms and Robotics Conference ◽

10.1115/detc2018-85630 ◽

2018 ◽

Author(s):

Tanner N. Rolfe ◽

Andrew P. Murray ◽

David H. Myszka

Keyword(s):

Rigid Body ◽

Compliant Mechanisms ◽

Shape Change ◽

Dynamic Change ◽

A Priori ◽

External Loading ◽

Loading Conditions ◽

Kinematic Synthesis ◽

Human Foot

Traditional ankle-foot devices such as prostheses or robotic feet seek to replicate the physiological change in shape of the foot during gait using compliant mechanisms. In comparison, rigid-body feet tend to be simplistic and largely incapable of accurately representing the geometry of the human foot. Rigidbody mechanisms offer certain advantages over compliant mechanisms which may be desirable in the design of ankle-foot devices, including the ability to withstand greater loading, the ability to achieve more drastic shape-change, and the ability to be synthesized from their kinematics, allowing for realistic functionality without a priori characterization of the external loading conditions of the foot. This work focuses on applying the methodology of shape-changing kinematic synthesis to design and prototype a multi-segment rigid-body foot device capable of matching the dynamic change in shape of the human foot in gait.

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Changing shapes and implied viscosities of suspended submicron particles

Atmospheric Chemistry and Physics ◽

10.5194/acp-15-7819-2015 ◽

2015 ◽

Vol 15 (14) ◽

pp. 7819-7829 ◽

Cited By ~ 68

Author(s):

Y. Zhang ◽

M. S. Sanchez ◽

C. Douet ◽

Y. Wang ◽

A. P. Bateman ◽

...

Keyword(s):

Relative Humidity ◽

Gas Phase ◽

Shape Change ◽

Particle Diameter ◽

Submicron Particles ◽

Flow Tube ◽

Shape Factors ◽

Tube Reactor ◽

Organic Particles ◽

Dynamic Shape

Abstract. The change in shape of atmospherically relevant organic particles is used to estimate the viscosity of the particle material without the need for removal from aerosol suspension. The dynamic shape factors χ of particles produced by α-pinene ozonolysis in a flow tube reactor, under conditions of particle coagulation, were measured while altering the relative humidity (RH) downstream of the flow tube. As relative humidity was increased, the results showed that χ could change from 1.27 to 1.02, corresponding to a transition from aspherical to nearly spherical shapes. The shape change could occur at elevated RH because the organic material had decreased viscosity and was therefore able to flow to form spherical shapes, as favored by the minimization of surface area. Numerical modeling was used to estimate the particle viscosity associated with this flow. Based on particle diameter and RH exposure time, the viscosity dropped from 10(8.7±2.0) to 10(7.0±2.0) Pa s (two sigma) for an increase in RH from < 5 to 58 % at 293 K. These results imply that the equilibration of the chemical composition of the particle phase with the gas phase can shift from hours at mid-range RH to days at low RH.

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Understanding the Relationship Between Pitch Agility and Propulsive Aerodynamic Forces in Bio-Inspired Flapping Wing Vehicles

Volume 2: Integrated System Design and Implementation; Structural Health Monitoring; Bioinspired Smart Materials and Systems; Energy Harvesting ◽

10.1115/smasis2015-8835 ◽

2015 ◽

Cited By ~ 1

Author(s):

Zohaib Hasnain ◽

James E. Hubbard ◽

Joseph Calogero ◽

Mary I. Frecker ◽

Aimy A. Wissa

Keyword(s):

Motion Tracking ◽

Compliant Mechanisms ◽

Shape Change ◽

Tracking System ◽

Fold Increase ◽

Flapping Wing ◽

Small Scale ◽

Propulsive Force ◽

Aerodynamic Forces ◽

The Relationship

Ornithopters, or flapping wing mechanical birds, represent a unique category of aerial vehicles that fill a need for small-scale, agile, long range, and payload-capable flight vehicles. This study focuses on understanding the relationship between the propulsive aerodynamic forces and pitch agility in these flapping wing vehicles. Using analytical methods, the aerodynamic moment acting upon a wing undergoing elastic flapping was calculated. A method to determine the pitch stiffness of the vehicle was then derived using a preexisting stability analysis. This method was used to demonstrate that pitch agility in flapping wing birds is intricately tied to the flapping cycle with different parts of the cycle creating stabilizing and destabilizing effects. The results indicated that pitch agility, and propulsive force generation, have a dependency on the shape of the wing, and that deformations such as bend and sweep are capable of making the vehicle more agile. Contact-aided compliant mechanisms with nonlinear stiffness were designed and inserted into the wing of an ornithopter to induce controlled morphing. These elements have varying stiffness during the upstroke and downstroke parts of the cycle which introduces an asymmetry between the two halves of the flapping cycle. The resulting flapping motion exhibited a two fold increase in horizontal propulsive force over the baseline case. A motion tracking system was used to capture the free flight response of the ornithopter in steady level flight. This information was then used to calculate the pitch stiffness of the ornithopter with a rigid spar, and, one with a nonlinear compliant element inserted into the spar to induce a desired shape change. The results revealed that an upstroke in which the aerodynamic forces are similar in magnitude to that of the downstroke, may be necessary to make the vehicle more agile, and, that there is a compromise between vehicle agility and flight propulsive forces.

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