On an Adaptive Mask Overlay Topology Synthesis Method

2010 ◽  
Author(s):  
Anupam Saxena
Keyword(s):  
Unique Feature ◽  
Compliant Mechanisms ◽  
Synthesis Method ◽  
Small Deformation ◽  
Computational Effort ◽  
Topology Design ◽  
Optimization Process ◽  
Post Processing ◽  
Contour Boundary ◽  
Effective Use

A stochastic topology design approach is presented that yields binary, well connected continua. Inspired by the well known photolithographic technique used in the fabrication of micro-components, a number of negative-masks are appropriately laid over the design region to simulate voids. A unique feature is the effective use of the masks. In addition to their position and sizes, the number of circular masks is adaptively determined in each step of the optimization process. Thus, not only the void shapes but also their number is varied. The proposed method is significantly efficient compared to the previous implementations [21] and [23] and requires much less computational effort to yield good solutions. The honeycomb parameterization employed eliminates all subregion connectivity anomalies by ensuring edge connectivity throughout. Boundary smoothening is performed as a preprocessing step to moderate the notches, and to obtain an honest evaluation of a candidate design. Thus, both material and contour boundary interpretation steps are no longer required when post-processing the synthesized solutions. Various features of the method are demonstrated through the synthesis examples of small deformation compliant mechanisms.

An Adaptive Material Mask Overlay Method: Modifications and Investigations on Binary, Well Connected Robust Compliant Continua

2011 ◽  
Vol 133 (4) ◽  
Author(s):  
Anupam Saxena
Keyword(s):  
Compliant Mechanisms ◽  
Search Algorithm ◽  
Reaction Force ◽  
Small Deformation ◽  
Mesh Dependency ◽  
Overlay Method ◽  
Contour Boundary ◽  
Mutation Strategies ◽  
Effective Use ◽  
Single Material

The material mask overlay strategy employs negative masks to create material voids within the design region to synthesize perfectly binary (0-1), well connected continua. Previous implementations use either a constant number of circular masks or increase the latter via a sequence of subsearches making the procedure computationally expensive. Here, a modified algorithm is presented wherein the number of masks is adaptively varied within a single search, in addition to their positions and sizes, thereby generating material voids, both efficiently and effectively. A stochastic, mutation-only search with different mutation strategies is employed. The honeycomb parameterization naturally eliminates all subregion connectivity anomalies without requiring additional suppression methods. Boundary smoothening as a new preprocessing step further facilitates accurate evaluations of intermediate and final designs with moderated notches. Thus, both material and contour boundary interpretation steps, that can alter the synthesized solutions, are avoided during postprocessing. Various features, e.g., (i) effective use of the negative masks, (ii) convergence, (iii) mesh dependency, (iv) solution dependence on the reaction force, and (v) parallel search are investigated through the synthesis of small deformation fully compliant mechanisms that are designed to be robust under the specified loads. The proposed topology search algorithm shows promise for design of single-material large deformation continua as well.

scholarly journals Design of Large-Displacement Compliant Mechanisms by Topology Optimization Incorporating Modified Additive Hyperelasticity Technique

2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Liying Liu ◽  
Jian Xing ◽  
Qingwei Yang ◽  
Yangjun Luo
Keyword(s):  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Previous Method ◽  
Large Displacement ◽  
Topology Design ◽  
Optimization Process ◽  
Response Analysis ◽  
Modified Technique ◽  
Element Analysis ◽  
Output Displacement

This paper is focused on the topology design of compliant mechanisms undergoing large displacement (over 20% of the structural dimension). Based on the artificial spring model and the geometrically nonlinear finite element analysis, the optimization problem is formulated so as to maximize the output displacement under a given material volume constraint. A modified additive hyperelasticity technique is proposed to circumvent numerical instabilities that occurred in the low-density or intermediate-density elements during the optimization process. Compared to the previous method, the modified technique is very effective and can provide more accurate response analysis for the large-displacement compliant mechanism. The whole optimization process is carried out by the gradient-based mathematical programming method. Numerical examples of a force-inverting mechanism and a microgripping mechanism are presented. The obtained optimal solutions verify the applicability of the proposed numerical techniques and show the necessity of considering large displacement in the design problem.

Synthesizing Bidirectional Constant Torque Compliant Mechanisms

2017 ◽  
Author(s):  
Bhavanam Praveen Reddy ◽  
Hong Zhou
Keyword(s):  
Unique Feature ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Synthesis Method ◽  
Control Parameters ◽  
Curved Beams ◽  
Rotation Direction ◽  
Constant Torque ◽  
Output Torque ◽  
Spline Curves

The output or resisting torque from a constant torque compliant mechanism keeps invariant in a large range of input rotation. Unlike regular constant torque compliant mechanisms that have only one input rotation direction, the input rotation of a bidirectional constant torque compliant mechanism can be either clockwise or counter-clockwise. Its resisting or output torque reverses its direction with the change of the input rotation direction. The unique feature of bidirectional constant torque compliant mechanisms makes their synthesis challenging. In this paper, a synthesis method is introduced to surmount the synthesis challenges. The constant resisting torque is generated through a set of curved beams that are mounted within an annular design domain. Because of the bidirectional requirement, the two ends of each curved beam are aligned along radial direction before deformation to avoid rotational bias. Spline curves are employed to describe curved beams and defined by their control parameters. The synthesis of a bidirectional constant torque compliant mechanism is systematized as optimizing the control parameters of its curved beams. The presented method is demonstrated by the synthesis of bidirectional constant torque compliant mechanisms that have different arrangements of curved beams in the paper.

Topology Synthesis of Compliant Mechanisms for Nonlinear Force-Deflection and Curved Path Specifications

1999 ◽  
Vol 123 (1) ◽  
pp. 33-42 ◽  
Author(s):  
A. Saxena ◽  
G. K. Ananthasuresh
Keyword(s):  
Finite Element ◽  
Linear Models ◽  
Compliant Mechanisms ◽  
Synthesis Method ◽  
Design Sensitivity ◽  
Finite Element Models ◽  
Geometrically Nonlinear ◽  
Linear Elastic ◽  
Nonlinear Design ◽  
Nonlinear Force

Optimal design methods that use continuum mechanics models are capable of generating suitable topology, shape, and dimensions of compliant mechanisms for desired specifications. Synthesis procedures that use linear elastic finite element models are not quantitatively accurate for large displacement situations. Also, design specifications involving nonlinear force-deflection characteristics and generation of a curved path for the output port cannot be realized with linear models. In this paper, the synthesis of compliant mechanisms is performed using geometrically nonlinear finite element models that appropriately account for large displacements. Frame elements are chosen because of ease of implementation of the general approach and their ability to capture bending deformations. A method for nonlinear design sensitivity analysis is described. Examples are included to illustrate the usefulness of the synthesis method.

Synthesis of Planar, Compliant Four-Bar Mechanisms for Compliant-Segment Motion Generation

1999 ◽  
Vol 123 (4) ◽  
pp. 535-541 ◽  
Author(s):  
L. Saggere ◽  
S. Kota
Keyword(s):  
Compliant Mechanisms ◽  
Shape Change ◽  
Synthesis Method ◽  
Elastic Equilibrium ◽  
Body Motion ◽  
Motion Generation ◽  
Generation Task ◽  
Potential Applications ◽  
Flexible Segment ◽  
Definition Of

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.

On Optimization of 2D Compliant Mechanisms Using Honeycomb Discretization With Material-Mask Overlay Strategy

2007 ◽  
Author(s):  
Anupam Saxena
Keyword(s):  
Genetic Algorithm ◽  
Compliant Mechanisms ◽  
Optimal Solutions ◽  
Free Rotation ◽  
Post Processing ◽  
Hexagonal Cell ◽  
Rectangular Cell ◽  
New Material ◽  
Assignment Approach ◽  
The Continuum

Novel honeycomb tessellation and material mask overlay methods are proposed in this paper to obtain optimal planar compliant topologies free from checkerboard and point flexure pathologies. A cardinal reason, namely the presence of strain-free rotation regions in rectangular cell based discretization is identified to be a cause in appearance of such singularities. With each hexagonal cell sharing an edge with its neighboring cells, strain-free displacements are not permitted anywhere in the continuum. The new material assignment approach manipulates material within a group of cells as opposed to a single cell thereby reducing the number of variables making optimization efficient. Optimal solutions obtained are free from intermediate material states and can be manufactured directly after design, without requiring any post processing. The proposed procedure is illustrated using two classical examples in 2D compliant mechanisms solved using genetic algorithm.

A Study of Conditions That Affect the Distribution of Compliance in Compliant Mechanisms

2008 ◽  
Author(s):  
Stephen L. Canfield ◽  
Daniel L. Chlarson ◽  
Alexander Shibakov ◽  
Joseph D. Richardson ◽  
Anupam Saxena
Keyword(s):  
Strain Energy ◽  
Compliant Mechanisms ◽  
Optimization Process ◽  
Objective Functions ◽  
Compatibility Analysis ◽  
Pareto Sets ◽  
Show Evidence ◽  
Final Design ◽  
Additional Constraints ◽  
Insight Into

Researchers in the field of optimal synthesis of compliant mechanisms have been working to develop design tools that yield distributed compliant devices from a continuum design domain. However, it has been demonstrated in the literature that much of this work has resulted in mechanisms that localize compliance rather than distribute it as desired. Inaccurate representation of the stiffness or strain energy due to the existence of point flexures in the mechanism was identified as the cause of this behavior by early researchers. To eliminate this cause, several approaches have been tried to improve the design of distributed mechanisms, for example additional constraints on the optimization process, alternate parameterization techniques that avoid point flexures and additional objective functions evaluated as Pareto sets. In this paper, the authors further investigate the fundamental reasons for the prevalence of lumped designs. Representative simple compliant mechanisms are investigated analytically and numerically and the influence of various additional objectives on the final design is evaluated. To extrapolate these results to more complex mechanisms, examples are constructed that show evidence that a preference remains for lumped compliance, despite the countermeasures that have been applied. Pareto compatibility analysis developed by the authors is used to analyze the influence of various objectives on the distributive nature of the final design. These conditions that influence the distribution of compliance fall into two basic categories: those specific to the numerical methods applied and those of purely mechanical (i.e. fundamental) nature. This work will examine conditions of the latter type and will demonstrate that such a preference for lumped compliance exists. This preference is shown to be contained in the classic objectives; flexibility and stiffness. Based on these results, greater insight into the optimization process is gained and applied to improve the search for distributed compliant mechanisms.

Are Circular Shaped Masks Adequate in Adaptive Mask Overlay Topology Synthesis Method?

2010 ◽  
Vol 133 (1) ◽  
Author(s):  
Anupam Saxena
Keyword(s):  
Resource Constraints ◽  
Synthesis Method ◽  
Design Procedure ◽  
Topology Design ◽  
Two Dimensional ◽  
Closed Curves ◽  
Compliance Minimization ◽  
Topological Features ◽  
Mean Compliance ◽  
Material Layout

Previous versions of the material mask overlay strategy (MMOS) for topology synthesis primarily employ circular masks to simulate voids within the design region. MMOS operates on the photolithographic principle by appropriately positioning and sizing a group of negative masks and thus iteratively improves the material layout to meet the desired objective. The fundamental notion is that a group of circular masks can represent a local void of any shape. The question whether masks of more general shapes (e.g., any two-dimensional closed, nonself intersecting polygon) would offer significant enhancements in efficiently attaining the appropriate topological features in a continuum remains. This paper investigates the performance of two other mask types; elliptical and rectangular masks are compared with that of the circular ones. These are the respective modest representatives of closed curves and their polygonal approximations. First, two mean compliance minimization examples under resource constraints are solved. Thereafter, compliant pliers are synthesized using the three mask types. It is observed that the use of elliptical or rectangular masks do not offer significant advantages over the use of circular ones. On the contrary, the examples suggest that less number of circular masks are adequate to model the topology design procedure more efficiently. Thus, it is postulated that using generic simple closed curves or polygonal masks will not introduce significant benefits over circular ones in the MMOS based topology design algorithms.

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