Multivariate Parameter Sets for Optimal Synthesis of Compliant Mechanisms

2005 ◽  
Author(s):  
Alexander Shibakov ◽  
Stephen L. Canfield ◽  
Patrick V. Hull
Keyword(s):  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Mesh Size ◽  
Synthesis Process ◽  
Design Parameters ◽  
Control Points ◽  
Computationally Efficient ◽  
Alternative Approach ◽  
Multivariate Parameter ◽  
Simple Mapping

This paper will propose the use of control maps along with discretized elements or meshes in the design parameter set for optimizing compliant mechanisms. The use of control maps will be demonstrated to encode the motion of groups of nodes or control points defining the mesh with simple mapping rules. The technique will serve as an alternative to increased mesh size or node wandering techniques that have been proposed to increase the number of alternative design shapes that may be considered. As an alternative approach, the proposed control map parameterization has the significant benefit that it minimizes the number of design parameters necessary (parameters increase linearly with the mesh size) in describing a given design making it computationally efficient. A limited number of tiles can produce a map that has a significant effect on the final shape. If the tiles are chosen appropriately, the problems such as material overlap and non-convex mesh elements are avoided automatically. This paper will describe the implementation of these control maps and provide several examples showing their implementation in the compliant mechanism topology synthesis process.

Optimal Synthesis of Compliant Mechanisms Using Subdivision and Commercial FEA

2004 ◽  
Author(s):  
Patrick V. Hull ◽  
Stephen Canfield
Keyword(s):  
Topology Optimization ◽  
Mechanism Design ◽  
Compliant Mechanism ◽  
Rapid Prototype ◽  
Optimization Procedure ◽  
Design Tool ◽  
Design Parameters ◽  
Solid Model ◽  
Control Points ◽  
Numerical Instabilities

The field of distributed-compliance mechanisms has seen significant work in developing suitable topology optimization tools for their design. These optimal design tools have grown out of the techniques of structural optimization. This paper will build on the previous work in topology optimization and compliant mechanism design by proposing an alternative design space parameterization through control points and adding another step to the process, that of subdivision. The control points assist a specific design to be represented as a solid model during the optimization process. The process of subdivision creates an additional number of control points that help smooth the surface (for example a C2 continuous surface depending on the method of subdivision chosen) creating a manufacturable design free of traditional numerical instabilities. Note that these additional control points do not add to the number of design parameters. This alternative parameterization and description as a solid model effectively and completely separates the design variables from the analysis variables during the optimization procedure. The motivation behind this work is to avoid several of the numerical instabilities that occur in topology optimization and to create an automated design tool from task definition to functional prototype created on a CNC or rapid-prototype machine. This paper will describe the complaint mechanism design process including subdivision and will demonstrate the procedure on several common examples.

Constant Force Compliant Mechanisms Without Preloading

2021 ◽  
Author(s):  
Premkumar Pujali ◽  
Hong Zhou
Keyword(s):  
Compliant Mechanisms ◽  
Large Range ◽  
Compliant Mechanism ◽  
Experimental Results ◽  
Design Parameters ◽  
Constant Force ◽  
Spline Curves ◽  
Output Force

Abstract A constant force compliant mechanism generates an output force that keeps invariant in a large range of input displacement. Because of the constant force feature and the merits of compliant mechanisms, they are utilized in many applications. A problem in the current constant force compliant mechanisms is their preloading range that is a certain starting range of the input displacement. In the preloading displacement, the output force of a constant force compliant mechanism does not have the desired value. It goes up from zero value. The preloading displacement often occupies one quarter or more of the entire input displacement range, which weakens the performance of constant force compliant mechanisms. The preloading issue is eradicated in this research by using prebuckled beams as components for constructing constant force compliant mechanisms. It is difficult to synthesize constant force compliant mechanisms that are composed of prebuckled beams because of the intertwined force, buckling and deflection characteristics. In this research, the undeformed beams are represented by spline curves and controlled by its interpolation points. The synthesis of constant force compliant mechanisms is systemized as optimizing the design parameters of the composed prebuckled beams. Fully compliant constant force compliant mechanisms are synthesized without preloading. The synthesis solutions are validated by experimental results.

Estimating Stress Bounds in Early-Stage Design of Distributed Compliant Mechanisms

2016 ◽  
Author(s):  
Sreekalyan Patiballa ◽  
John Francis Shanley ◽  
Girish Krishnan
Keyword(s):  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Early Stage ◽  
Functional Characterization ◽  
Stress Constraints ◽  
Design Stage ◽  
Synthesis Process ◽  
Early Design Stage ◽  
Computationally Intensive ◽  
Early Stage Design

Synthesis of distributed compliant mechanisms is often a two-stage process involving (a) conceptual topology synthesis, and a subsequent (b) refinement stage to meet stress and manufacturing specifications. The usefulness of a solution is ascertained only after the sequential completion of these two steps, which are in general computationally intensive. This paper presents a strategy to rapidly estimate final operating stresses even before the actual refinement process. This strategy is based on the uniform stress distribution metric, and a functional characterization of the different members that constitute the compliant mechanism topology. It enables selecting the best conceptual solution for further optimization, thus maximally avoiding refinement of topologies that inherently may not meet the stress constraints. Furthermore this strategy enables modifying topologies at the early design stage to meet final stress specifications, thus greatly accelerating the overall synthesis process.

Synthesizing Bidirectional Constant Torque Compliant Mechanisms Using Precompressed Beams

2018 ◽  
Author(s):  
Monik Thanaki ◽  
Hong Zhou
Keyword(s):  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Building Blocks ◽  
Design Parameters ◽  
Input Shaft ◽  
Rotation Direction ◽  
Constant Torque ◽  
A Value ◽  
Output Torque ◽  
Large Scope

A constant torque compliant mechanism has its output torque invariant in a large scope of input rotation. Different from conventional constant torque compliant mechanisms in which the input shaft can only rotate in one direction, the input shaft of a bidirectional constant torque compliant mechanism can rotate either clockwise or counter-clockwise. The direction of the output or resisting torque changes with the input rotation direction. A common problem in the current bidirectional constant torque compliant mechanisms is that they require a preloading range that is a certain starting range of the input rotation. Within the preloading range, the output torque does not have the desired torque, and it increases from zero to a value. The preloading range weakens the performance of bidirectional constant torque compliant mechanisms. In this paper, precompressed beams are used as building blocks for bidirectional constant torque compliant mechanisms to surmount the preloading problem. Bidirectional constant torque compliant mechanisms are synthesized through optimizing the design parameters of the composed precompressed beams. The introduced synthesis approach is demonstrated by synthesizing bidirectional constant torque compliant mechanisms that have different numbers of precompressed beams.

Compliant Mechanism Synthesis Using Degree of Genus and Variable Width Curves

2014 ◽  
Author(s):  
Hong Zhou ◽  
Azher Hussain Naser Mohammed
Keyword(s):  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Structural Complexity ◽  
Joint Effect ◽  
Synthesis Process ◽  
Mechanism Synthesis ◽  
Shape Morphing ◽  
Optimizing Control ◽  
Material Layout ◽  
Shape And Size

Compliant mechanisms (CMs) utilize elastic deformations for mechanism functions. Their merits primarily come from jointless structures. The structure of a fully CM is a piece of elastic material and is defined by its topology, shape and size. Topology is the overarching material layout of a CM while shape and size are on its structural details, but topology is entangled with shape and size in the synthesis process of a CM because its elastic deformation is from the joint effect of topology, shape and size. Degree of freedom (DOF) and number of links used in rigid mechanism synthesis are not effective to guide the synthesis of CMs since any point of a fully CM can deform and its whole structure forms a single piece. Without effective synthesis guidance, the structural complexity of a synthesized CM can be undesirably high. In this paper, degree of genus (DOG) is introduced for topology guidance of CM synthesis. DOG of a CM is the number of holes and is actively controlled during its synthesis process. With DOG guidance, a synthesized CM will not have overcomplicated topology. Variable width curves (VWCs) are introduced in this paper for shape and size description. Any connection in a CM is defined as a VWC and the entire CM is modeled as a network of VWCs. With VWC description, a synthesized CM will not have unsmooth connection. Under DOG and VWC strategies, CM synthesis is systematized as optimizing control parameters of networks of VWCs. The proposed CM synthesis using DOG and VWC strategies is demonstrated by synthesizing shape morphing compliant mechanisms.

Two-Step Design of Multicontact-Aided Cellular Compliant Mechanisms for Stress Relief

2012 ◽  
Vol 134 (12) ◽  
Author(s):  
Vipul Mehta ◽  
Mary Frecker ◽  
George A. Lesieutre
Keyword(s):  
Compliant Mechanisms ◽  
Effective Properties ◽  
Compliant Mechanism ◽  
Stress Relief ◽  
Homogenization Method ◽  
Computationally Efficient ◽  
Cellular Mechanisms ◽  
Linear Elastic ◽  
Step Procedure ◽  
Contact Mechanism

A methodology for topology optimization to the design of compliant cellular mechanisms with and without internal contact is presented. A two-step procedure is pursued. First, a baseline noncontact mechanism is developed and optimized via an inverse homogenization method using the “solid isotropic material with penalization” approach. This compliant mechanism is optimized to yield specified elasticity coefficients, with the capability to sustain large effective strains by minimizing local linear elastic strain. In the second step, a system of internal contacts is designed. The initial continuum model of a noncontact mechanism is converted into a frame model, and possible contact links are defined. A computationally efficient algorithm is employed to eliminate those mechanisms having overlapping contact links. The remaining nonoverlapping designs are exhaustively investigated for stress relief. A differential evolution optimizer is used to maximize the stress relief. The results generated for a range of specified elasticity coefficients include a honeycomb-like cell, an auxetic cell, and a diamond-shaped cell. These various cell topologies have different effective properties corresponding to different structural requirements. For each such topology, a contact mechanism is devised that demonstrates stress relief. In one such case, the contact mechanism increases the strain magnification ratio by about 30%.

Geometric Modeling and Synthesis of Spatial Multimaterial Compliant Mechanisms and Structures Using Three-Dimensional Multilayer Wide Curves

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
Hong Zhou ◽  
Kwun-Lon Ting
Keyword(s):  
Cross Sections ◽  
Geometric Modeling ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Three Dimensional ◽  
Modeling Method ◽  
Synthesis Process ◽  
Variable Cross ◽  
Finite Element Procedure ◽  
Multiple Materials

A 3D multilayer wide curve is a spatial curve with variable cross sections and multiple materials. The performance of multimaterial compliant mechanisms and structures is enhanced by integrating multiple materials into one-piece configurations. This paper introduces a geometric modeling method for spatial multimaterial compliant mechanisms and structures by using 3D multilayer wide curves. Based on the introduced modeling method, a geometric synthesis approach is proposed. In this paper, every connection in a spatial multimaterial compliant mechanism or structure is represented by a 3D multilayer wide curve and the whole compliant mechanism or structure is modeled as a set of connected wide curves. The geometric modeling and synthesis are considered as the generation and optimization of the control parameters of the corresponding 3D multilayer wide curves. The performance of spatial multimaterial compliant mechanisms and structures is evaluated by the isoparametric degenerate-continuum nonlinear finite element procedure. The problem-dependent objectives are optimized and the practical constraints are imposed during the synthesis process. The effectiveness of the proposed geometric modeling and synthesis procedures is verified by the demonstrated examples.

Optimal Synthesis of Compliant Mechanisms Using Subdivision and Commercial FEA

2005 ◽  
Vol 128 (2) ◽  
pp. 337-348 ◽  
Author(s):  
Patrick V. Hull ◽  
Stephen Canfield
Keyword(s):  
Topology Optimization ◽  
Mechanism Design ◽  
Compliant Mechanism ◽  
Rapid Prototype ◽  
Optimization Procedure ◽  
Design Tool ◽  
Design Parameters ◽  
Solid Model ◽  
Control Points ◽  
Compliant Mechanism Design

The field of distributed-compliance mechanisms has seen significant work in developing suitable topology optimization tools for their design. These optimal design tools have grown out of the techniques of structural optimization. This paper will build on the previous work in topology optimization and compliant mechanism design by proposing an alternative design space parametrization through control points and adding another step to the process, that of subdivision. The control points allow a specific design to be represented as a solid model during the optimization process. The process of subdivision creates an additional number of control points that help smooth the surface (for example a C2 continuous surface depending on the method of subdivision chosen) creating a manufacturable design free of some traditional numerical instabilities. Note that these additional control points do not add to the number of design parameters. This alternative parametrization and description as a solid model effectively and completely separates the design variables from the analysis variables during the optimization procedure. The motivation behind this work is to create an automated design tool from task definition to functional prototype created on a CNC or rapid-prototype machine. This paper will describe the proposed compliant mechanism design process and will demonstrate the procedure on several examples common in the literature.

Local Redesign for Additive Manufacturability of Compliant Mechanisms Using Topology Optimization

2021 ◽  
Author(s):  
Stijn Koppen ◽  
Emma Hoes ◽  
Matthijs Langelaar ◽  
Mary I. Frecker
Keyword(s):  
Topology Optimization ◽  
Additive Manufacturing ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Computational Effort ◽  
Manufacturing Constraints ◽  
Design For Additive Manufacturing ◽  
Computationally Efficient ◽  
Stress Levels ◽  
Overhang Angle

Abstract Compliant mechanisms are crucial components in current and future high-precision applications. Topology optimization and additive manufacturing offer freedom to design complex compliant mechanisms that were impossible to realize using conventional manufacturing. Design for additive manufacturing constraints, such as the maximum overhang angle and minimum feature size, tend to drastically decrease the performance of topology optimized compliant mechanisms. It is observed that, among others, design for additive manufacturing constraints are only dominant in the flexure regions. Flexures are most sensitive to manufacturing errors, experience the highest stress levels and removal of support material carries the highest risk of failure. It is crucial to impose these constraints on the flexure regions, while in others part of the compliant mechanism design, these constraints can be relaxed. We propose to first design the global compliant mechanism layout in the full domain without imposing any design for additive manufacturing constraints. Subsequently we redesign selected refined local redesign domains with design for additive manufacturing constraints, whilst simultaneously considering the mechanism performance. The method is applied to a single-input-multi-output compliant mechanism case study, limiting the maximum overhang angle, introducing manufacturing robustness and limiting the maximum stress levels of a selected refined redesign domain. The high resolution local redesigns are detailed and accurate, without a large additional computational effort or decrease in mechanism performance. Thereto, the method proves widely applicable, computationally efficient and effective in its purpose.

Exploiting the instability of eccentric tube robots for distal force control in minimally invasive cardiac ablation

2021 ◽  
pp. 095440622110075
Author(s):  
Hessa Alfalahi ◽  
Federico Renda ◽  
Conor Messer ◽  
Cesare Stefanini
Keyword(s):  
Minimally Invasive ◽  
Force Control ◽  
Motion Tracking ◽  
Heart Surgery ◽  
Compliant Mechanism ◽  
Heart Rhythm ◽  
Disease Recurrence ◽  
Optimal Level ◽  
Design Parameters ◽  
Cardiac Ablation

While the dilemma of motion tracking and force control in beating-heart surgery is previously addressed using active control architectures and rigid robotic actuators, this work leverages the highly controllable mechanical properties of concentric tube robots for intelligent, design-based force control in minimally invasive cardiac ablation. Briefly, cardiac ablation is the conventional procedure for treating arrhythmia patients, by which exposing the diseased cardiac tissue to Radio-Frequency (RF) energy restores the normal heart rhythm. Yet, the procedure suffers low success rate due to the inability of existing flexible catheters to maintain a consistent, optimal contact force between the tip electrode and the tissue, imposing the need for future repeat surgeries upon disease recurrence. The novelty of our work lies in the development of a statically-balanced compliant mechanism composed of (1) distal bi-stable concentric tubes and (2) a compliant, torsional spring mechanism that provides torque at tubes proximal extremity, resulting in an energy-free catheter with a zero-stiffness tip. This catheter is expected to maintain surgical efficacy and safety despite the chaotic displacement of the heart, by naturally keeping the tip force at an optimal level, not less and not more than the surgical requirement. The presented experimental results of the physical prototype, reflect the feasibility of the proposed design, as well as the robustness of the formulated catheter mathematical models which were uniquely deployed in the selection of the optimal design parameters.

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