scholarly journals Fully-compliant statically-balanced mechanisms without prestressing assembly: concepts and case studies

2011 ◽  
Vol 2 (2) ◽  
pp. 169-174 ◽  
Author(s):  
G. Chen ◽  
S. Zhang
Keyword(s):  
Stress Relaxation ◽  
Force Feedback ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
High Fidelity ◽  
Constant Force ◽  
Force Transmission ◽  
Actuation Force ◽  
New Concepts ◽  
Creep And Stress Relaxation

Abstract. The purpose of this paper is to present new concepts for designing fully-compliant statically-balanced mechanisms without prestressing assembly. A statically-balanced compliant mechanism can ideally provide zero stiffness and energy free motion like a traditional rigid-body mechanism. These characteristics are important in design of compliant mechanisms where low actuation force, accurate force transmission or high-fidelity force feedback are primary concerns. Typically, static balancing of compliant mechanisms has been achieved by means of prestressing assembly. However, this can often lead to creep and stress relaxation arising in the flexible members. In this paper two concepts are presented which eliminate the need for prestressing assembly of compliant mechanisms: (1) a weight compensator which employs a constant-force compliant mechanism, (2) a near-zero-stiffness mechanism which combines two multistable mechanisms. In addition to the advantages provided by statically-balanced compliant mechanisms, two other notable features of these statically-balanced mechanisms are their ability to be monolithically fabricated and to return to their as-fabricated position without any disassembly when not in use.

Negative Stiffness Building Blocks for Statically Balanced Compliant Mechanisms: Design and Testing

2010 ◽  
Vol 2 (4) ◽  
Author(s):  
Karin Hoetmer ◽  
Geoffrey Woo ◽  
Charles Kim ◽  
Just Herder
Keyword(s):  
Force Feedback ◽  
High Efficiency ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Building Blocks ◽  
Negative Stiffness ◽  
High Fidelity ◽  
Proof Of Concept ◽  
Design Considerations ◽  
Design And Testing

In some applications, nonconstant energy storage in the flexible segments of compliant mechanisms is undesired, particularly when high efficiency or high-fidelity force feedback is required. In these cases, the principle of static balancing can be applied, where a balancing segment with a negative stiffness is added to cancel the positive stiffness of the compliant mechanism. This paper presents a strategy for the design of statically balanced compliant mechanisms and validates it through the fabrication and testing of proof-of-concept prototypes. Three compliant mechanisms are statically balanced by the use of compressed plate springs. All three balanced mechanisms have approximately zero stiffness but suffer from a noticeable hysteresis loop and finite offset from zero force. Design considerations are given for the design and fabrication of statically balanced compliant mechanisms.

A Building Block Approach for the Design of Statically Balanced Compliant Mechanisms

2009 ◽  
Author(s):  
Karin Hoetmer ◽  
Just L. Herder ◽  
Charles J. Kim
Keyword(s):  
Building Block ◽  
Force Feedback ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Building Blocks ◽  
Negative Stiffness ◽  
High Fidelity ◽  
Input Output ◽  
Input And Output ◽  
Block Approach

Particularly when high-fidelity force feedback is required, such as in surgical forceps, the energy loss between input and output in compliant mechanisms is undesired. To restore the force feedback, the principle of static balancing can be applied, where a balancing segment with a negative stiffness is added to a compliant mechanism. Currently there are no mature methods for the design of statically balanced compliant mechanisms (SBCM). The goal of this paper is to investigate the possibility of extending the Building Block Approach for the design of statically balanced compliant mechanisms. To this end, the Building Block Approach is extended with negative stiffness balancing building blocks that can be added to a designed compliant mechanism. To demonstrate the feasibility of the method, a statically balanced compliant gripper was designed by this Extended Building Block Approach. The maximum operating force of the unbalanced gripper of 3.5 N was reduced to −1 N for the balanced gripper. Thus, the gripper is slightly overbalanced. The gripper example demonstrates the functionality of the proposed method; the input-output stiffness of a compliant mechanism can be severely reduced by a balancing segment.

Reduction of Stress in Plastic Compliant Mechanisms by Introducing Metallic Reinforcement

2017 ◽  
Author(s):  
Joshua Crews ◽  
Ashok Midha ◽  
Lokeswarappa R. Dharani
Keyword(s):  
Stress Relaxation ◽  
Compliant Mechanisms ◽  
Experimental Testing ◽  
Testing Device ◽  
Bending Stress ◽  
New Class ◽  
Metallic Reinforcement ◽  
Creep And Stress Relaxation

A method is provided and validated for redesigning compliant segments to improve their fatigue, creep, and stress relaxation performance. The method reduces the bending stress in the polymer portion of the compliant segment without the need for overall mechanism redesign, by introducing metallic reinforcement and by matching the force-deflection response of the redesigned segment to that of the baseline segment. An example redesign case study is presented and validated with experimental testing using a unique deflection testing device designed for fixed-free compliant mechanisms. This vein of research is undertaken using metallic reinforcement (inserts) toward the development of a new class of compliant mechanisms with significantly greater performance, particularly insofar as the problems of fatigue and creep are concerned.

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.

Statically Balanced Compliant Mechanisms (SBCM’S): An Example and Prospects

2000 ◽  
Author(s):  
Just L. Herder ◽  
Fred P. A. van den Berg
Keyword(s):  
Force Feedback ◽  
Compliant Mechanisms ◽  
Compensation Mechanism ◽  
Force Transmission ◽  
Low Friction ◽  
Transmission Process ◽  
Transmission Quality ◽  
Gripping Force ◽  
Elastic Elements

Abstract In some applications of compliant mechanisms, the fact that energy is stored in the elastic members presents a problem. For instance, in manually operated instruments, such as surgical forceps, the operating force should preferably be proportional to the gripping force, while forces introduced by the bending of elastic elements would disturb this force transmission process. To restore the force transmission quality, compliant mechanisms may be statically balanced, resulting in statically balanced compliant mechanisms (SBCM’s). This paper presents an example of a compliant surgical forceps mechanism, which is statically balanced by a low-friction rolling-link compensation mechanism. Force feedback is restored to the extent that the pulse in an artificial artery can be perceived clearly.

Towards the Design of a Statically Balanced Compliant Laparoscopic Grasper Using Topology Optimization

2008 ◽  
Author(s):  
Ditske J. B. A. de Lange ◽  
Matthijs Langelaar ◽  
Just L. Herder
Keyword(s):  
Topology Optimization ◽  
Force Feedback ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Negative Stiffness ◽  
Compensation Mechanism ◽  
Laparoscopic Grasper ◽  
The Difference ◽  
Force Displacement ◽  
Compliant Mechanism Design

This paper presents the design of a grasping instrument for minimally invasive surgery. Due to its small dimensions a compliant mechanism seems promising. To obtain force feedback, the positive stiffness of the compliant grasper must be statically balanced by a negative-stiffness compensation mechanism. For the design of compliant mechanisms, topology optimization can be used. The goal of this paper is to investigate the applicability of topology optimization to the design of a compliant laparoscopic grasper and particularly a compliant negative-stiffness compensation mechanism. In this study, the problem is subdivided in the grasper part and the compensation part. In the grasper part the deflection at the tip of the grasper is optimized. This results in a design that has a virtually linear force-displacement characteristic that forms the input for the compensation part. In the compensation part the difference between the force-displacement characteristic of the grasper part and the characteristic of the compensation part is minimized. An optimization problem is formulated enabling a pre-stress to be incorporated, which is required to obtain the negative stiffness in the compensation part. We can conclude that topology optimization is a promising approach in the field of statically balanced compliant mechanism design, even though there is great scope improvement of the method.

scholarly journals Review Article: Inventory of platforms towards the design of a statically balanced six degrees of freedom compliant precision stage

2011 ◽  
Vol 2 (2) ◽  
pp. 157-168 ◽  
Author(s):  
A. G. Dunning ◽  
N. Tolou ◽  
J. L. Herder
Keyword(s):  
Degrees Of Freedom ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Compensation Mechanism ◽  
Precision Engineering ◽  
Six Degrees Of Freedom ◽  
Actuation Force ◽  
Precision Stage ◽  
Compliant Parts ◽  
Great Scope

Abstract. For many applications in precision engineering, a six degrees of freedom (DoF) compliant stage (CS) with zero stiffness is desirable, to deal with problems like backlash, friction, lubrication, and at the same time, reduce the actuation force. To this end, the compliant stage (also known as compliant mechanism) can be statically balanced with a stiffness compensation mechanism, to compensate the energy stored in the compliant parts, resulting in a statically balanced compliant stage (SBCS). Statically balanced compliant stages can be a breakthrough in precision engineering. This paper presents an inventory of platforms suitable for the design of a 6 DoF compliant stage for precision engineering. A literature review on 3–6 DoF compliant stages, static balancing strategies and statically balanced compliant mechanisms (SBCMs) has been performed. A classification from the inventory has been made and followed up by discussion. An obviously superior architecture for a 6 DoF compliant stage was not found. All the 6 DoF stages are either non-statically balanced compliant structures or statically balanced non-compliant structures. The statically balanced non-compliant structures can be transformed into compliant structures using lumped compliance, while all SBCMs had distributed compliance. A 6 DoF SBCS is a great scope for improvements in precision engineering stages.

Design of a Monolithic Constant-Force Compliant Mechanism for Extended Range of Motion and Minimal Force Variation

2021 ◽  
Author(s):  
Ching-Wei Lo ◽  
Yuan Chang ◽  
Mien-Li Wang ◽  
Cian-Ru Lin ◽  
Jyh-Jone Lee
Keyword(s):  
Finite Element ◽  
Range Of Motion ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Synthesis Method ◽  
Structural Deformation ◽  
Constant Force ◽  
Wide Range ◽  
Extended Range ◽  
Force Variation

Abstract Compliant mechanisms enable passive force control through induction of strain energy during deformation. This has been perceived as a desired factor for developing precise handling equipment of limited size where additional sensors and controls are inessential to its operation. In this paper, our objective is to design a monolithic constant-force compliant mechanism to be integrated in a constant-force gripper for extended range of bidirectional motion. A topology synthesis method has been proposed by means of domain definition, discrete parameterization, topology optimization, and nonlinear structural deformation evaluation. This article adapts a compliant topology of a homogeneous beam configuration that exhibits zero stiffness behavior over a pre-established effective region. The optimization by genetic algorithm generates discrete shaping parameters for formation of an optimal geometry. The structural deformation computation via vector form intrinsic finite element that accounts for large displacement motion quantifies an iterative series of load-displacement relations in the optimization. Results have been verified using a conventional finite element method. A conceptual gripper has been proposed with a pair of embedded constant-force compliant mechanisms. This procedure has prepared a general guideline for future development of passive compliant devices that require accurate force regulation over a wide range of motion.

A Parametric Approach to the Optimization-Based Design of Compliant Mechanisms

1997 ◽  
Author(s):  
Matthew B. Parkinson ◽  
Larry L. Howell ◽  
Jordan J. Cox
Keyword(s):  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Topological Optimization ◽  
Constant Force ◽  
Parametric Approach ◽  
Element Analysis ◽  
Analysis Package ◽  
Generation Mechanisms ◽  
Compliant Mechanism Design ◽  
Nonlinear Nature

Abstract Several optimization-based strategies have been proposed for compliant mechanism design that do not rely on the experience or intuition of the designer. This paper demonstrates an optimization-based method wherein compliant mechanisms are modeled parametrically within an optimization and a finite element analysis package. Topological optimization is performed to minimize an objective function representing the fitness of the design. This methodology exploits the nonlinear nature of compliant mechanisms and augments optimization-based methods previously proposed. Using this method, constant-force mechanisms optimized for a displacement from 4% to 25% of the mechanism’s total length were predicted to remain within 3.58% of constant force. Results from the testing of fabricated mechanisms are: for 4–25% displacement, within 7.5% constant force; for 18–65% displacement, within 2.3%. Path generation mechanisms were designed with similarly encouraging results.

Creep and Stress Relaxation Behavior of Homogeneous and Reinforced Compliant Mechanisms and Segments

2018 ◽  
Author(s):  
Joshua Crews ◽  
Lokeswarappa R. Dharani ◽  
Ashok Midha
Keyword(s):  
Stress Relaxation ◽  
Compliant Mechanisms ◽  
Test Results ◽  
Stress Relaxation Behavior ◽  
Relaxation Resistance ◽  
New Class ◽  
Engineering Plastics ◽  
Physical Tests ◽  
Metallic Reinforcement ◽  
Creep And Stress Relaxation

Two critical disadvantages of compliant mechanisms constructed of engineering plastics are poor creep and stress relaxation resistance. Metallic reinforcement is investigated as a method to improve the creep and stress relaxation behaviors of compliant mechanisms and compliant segments. The stress relaxation and creep behaviors of homogeneous compliant segments are compared to those of metallic reinforced compliant segments. Special specimens and fixtures were designed for conducting physical tests. Test results show that metallic reinforced compliant segments significantly outperform homogeneous compliant segments with respect to both creep and stress relaxation. This vein of research is undertaken using metallic reinforcement (inserts) toward the development of a new class of compliant mechanisms with significantly greater performance, particularly insofar as the problems of fatigue and creep are concerned.

Sign in / Sign up

Export Citation Format

Share Document