An Empirically Determined Design Guideline for Rectangular Cross Section Nitinol Flexure Hinges With the Focus on Flexibility-Strength Trade-Off

2018 ◽  
Author(s):  
S. Coemert ◽  
M. Olmeda ◽  
J. Fuckner ◽  
C. Rehekampff ◽  
S. V. Brecht ◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Cross Section ◽  
Electrical Discharge Machining ◽  
Rectangular Cross Section ◽  
Flexure Hinge ◽  
Element Analysis ◽  
Design Guideline ◽  
Trade Off ◽  
Flexure Hinges ◽  
Compliance Modeling

In our group, we are developing flexure hinge based manipulators made of nitinol for minimally invasive surgery. On the one hand, sufficient flexibility is required from flexure hinges to be able to cover the surgical workspace. On the other hand, the bending amount of the flexure hinges has to be limited below the yielding point to ensure a safe operation. As a result of these considerations, it has to be questioned how much bending angle a nitinol flexure hinge with given geometric dimensions can provide without being subject to plastic deformation. Due to the nonlinearities resulting from large deflections and the material itself, the applicability of the suggested approaches in the literature regarding compliance modeling of flexure hinges is doubtful. Therefore, a series of experiments was conducted in order to characterize the rectangular cross section nitinol flexure hinges regarding the flexibility-strength trade-off. The nitinol flexure hinge samples were fabricated by wire electrical discharge machining in varying thicknesses while keeping the length constant and in varying lengths while keeping the thickness constant. The samples were loaded and unloaded incrementally until deflections beyond visible plastic deformation occured. Each pose in loaded and unloaded states was recorded by means of a digital microscope. The deflection angles yielding to permanent set values corresponding to 0.1% strain were measured and considered as elastic limit. A quasilinear correlation between maximum elastic deflection angle and length-to-thickness ratio was identified. Based on this correlation, a minimal model was determined to be a limit for a secure design. The proposed guideline was verified by additional measurements with additional samples of random dimensions and finite element analysis.

scholarly journals Empirical Compliance Equations for Constant Rectangular Cross Section Flexure Hinges and Their Applications

2016 ◽  
Vol 2016 ◽  
pp. 1-11 ◽  
Author(s):  
Tiemin Li ◽  
Yunsong Du ◽  
Yao Jiang ◽  
Jinglei Zhang
Keyword(s):  
Finite Element ◽  
Stress Concentration ◽  
Cross Section ◽  
Rectangular Cross Section ◽  
Great Influence ◽  
Exponential Model ◽  
Geometrical Parameters ◽  
Element Analysis ◽  
Flexure Hinges ◽  
Wide Range

This paper presents the derivation of empirical compliance equations of the constant rectangular cross section flexure hinge. The stress concentration caused by changes in cross section is analyzed based on finite element analysis results for the purpose of overcoming compliance calculation errors. It shows that the stress concentration has great influence on axial compliance calculation, while it has little influence on shear and bending compliance calculation. Then empirical compliance equations with a relative wide range ofh/Landt/Lare derived based on the exponential model in conjunction with consideration of all geometrical parameters of flexure hinges and the influence of the stress concentration on axial compliance calculation. Finally, in order to verify the validity of the empirical equations, the input/output compliance and displacement amplification ratios of bridge-type microdisplacement amplification mechanisms are analyzed. Meanwhile, an experimental platform of displacement amplification mechanisms is set up. The experimental results and finite element method (FEM) values are in good agreement with the theoretical arithmetic, which demonstrates the accuracy of the empirical compliance equations. It provides a reference point for further studies on the design and optimization of flexure hinges and compliant mechanisms.

scholarly journals Multi-objective optimization of a type of ellipse-parabola shaped superelastic flexure hinge

2016 ◽  
Vol 7 (1) ◽  
pp. 127-134 ◽  
Author(s):  
Zhijiang Du ◽  
Miao Yang ◽  
Wei Dong
Keyword(s):  
Compliant Mechanisms ◽  
Pareto Frontier ◽  
Flexure Hinge ◽  
Multi Objective Optimization ◽  
Nsga Ii ◽  
Element Analysis ◽  
Multi Objective ◽  
Flexure Hinges ◽  
Static Responses ◽  
Motion Range

Abstract. Flexure hinges made of superelastic materials is a promising candidate to enhance the movability of compliant mechanisms. In this paper, we focus on the multi-objective optimization of a type of ellipse-parabola shaped superelastic flexure hinge. The objective is to determine a set of optimal geometric parameters that maximizes the motion range and the relative compliance of the flexure hinge and minimizes the relative rotation error during the deformation as well. Firstly, the paper presents a new type of ellipse-parabola shaped flexure hinge which is constructed by an ellipse arc and a parabola curve. Then, the static responses of superelastic flexure hinges are solved via non-prismatic beam elements derived by the co-rotational approach. Finite element analysis (FEA) and experiment tests are performed to verify the modeling method. Finally, a multi-objective optimization is performed and the Pareto frontier is found via the NSGA-II algorithm.

Experimental and FEM-Based Payload Analysis of Ti-6Al-4V Flexure Hinges

2019 ◽  
Author(s):  
S. Coemert ◽  
L. G. Wegener ◽  
B. Yalvac ◽  
J. Fuckner ◽  
T. C. Lueth
Keyword(s):  
Rectangular Cross Section ◽  
Dimensional Accuracy ◽  
Vertical Axis ◽  
Geometric Parameters ◽  
Design Guideline ◽  
Flexure Hinges ◽  
Payload Capacity ◽  
To Come ◽  
Experimental Values ◽  
The Individual

Abstract In this work, we investigated the effect of geometric parameters on the payload capacity of Ti-6Al-4V flexure hinges taking plastic deformation as a boundary failure criterion into account. Finite element and experimental analysis were performed in combination to increase the significance of the findings. For both simulations and experiments rectangular cross section flexure hinges were designed with varying thickness, length and width. While varying one of the parameters, the others were kept constant in order to see the individual influence of that particular parameter. The samples were fabricated using laser cutting of Ti-6Al-4V (Grade 5) metal sheets to ensure optimum dimensional accuracy. In the experimental procedure, the samples were fixed at the proximal end and exposed to gradually increasing vertical loads at the distal end by using weights. Simultaneously, they were exposed to a counteracting moment by pull-wire actuation attached on the tip to simulate the realistic actuation-loading behavior. For the sake of a uniform comparison of the samples with different dimensions, a state of equilibrium was defined such that the proximal and distal ends of the hinge were parallel. As soon as this state was achieved, the poses in each loading state were documented by a digital microscope for later postprocessing. On the other hand, the simulations were constructed in a way that permitted the experimental approach to be reflected in the simulation environment as realistically as possible. While performing a deformation-based simulation, the surface on which the payload was acting was blocked against rotation around the lateral axis so that the state of equilibrium could be maintained. The hinges were deflected with gradually increasing deformation in the vertical axis until 0.2% plastic strain occurred in the unloaded state. At this point the deformations in the vertical axis for both loaded and unloaded states were recorded to be compared with the experimental values. The forces leading to the deformation in the loaded state were calculated as output of the simulation and recorded as payload capacity. Consequently, the deformations obtained by analyzing the images captured during the experiments were compared and matched with the ones obtained from the simulations. The experimental loads leading to these deformations were recorded as experimental payload values. In the first step towards the evaluation of the results, payload values obtained from experiments and simulations were compared to check the consistency of the process. Subsequent to verifying the consistency, the effect of the geometric parameters on the payload progression was analyzed based on the simulation results. Nonlinear multidimensional regression was performed to come up with a design guideline which approximates the payload capacity based on the dimensional parameters. The proposed guideline estimates the payload value as proportional to width, inversely proportional to length and proportional to the 1.6th power of thickness.

Design of Circular Cross-Section Corner-Filleted Flexure Hinges for Three-Dimensional Compliant Mechanisms

2002 ◽  
Vol 124 (3) ◽  
pp. 479-484 ◽  
Author(s):  
Nicolae Lobontiu ◽  
Jeffrey S. N. Paine
Keyword(s):  
Cross Section ◽  
Compliant Mechanisms ◽  
Compliant Mechanism ◽  
Three Dimensional ◽  
Circular Cross Section ◽  
Axial Loading ◽  
Flexure Hinge ◽  
Flexure Hinges ◽  
Element Simulation ◽  
The Right

The paper introduces the circular cross-section corner-filleted flexure hinges as connectors in three-dimensional compliant mechanism applications. Compliance factors are derived analytically for bending, axial loading and torsion. A circular cross-section corner-filleted flexure hinge belongs to a domain delimited by the cylinder (no fillet) and the right circular cross-section flexure hinge (maximum fillet radius). The analytical model predictions are confirmed by finite element simulation and experimental measurements. The circular cross-section corner-filleted flexure hinges are characterized in terms of their compliance, precision of rotation and stress levels.

Design of Contact-aided Compliant Flexure Hinge Mechanism Using Superelastic Nitinol

2021 ◽  
pp. 1-19
Author(s):  
Zhongyuan Ping ◽  
Tianci Zhang ◽  
Chi Zhang ◽  
Jianbin Liu ◽  
Siyang Zuo
Keyword(s):  
Compliant Mechanism ◽  
Nickel Titanium ◽  
Flexure Hinge ◽  
Maximum Strain ◽  
Clinical Value ◽  
Element Analysis ◽  
Flexure Hinges ◽  
Static Models ◽  
Flexible Instruments ◽  
Bending Behaviour

Abstract This paper presents a novel miniature contact-aided compliant mechanism (CCM) that includes flexure hinges and contact-aided structures. This continuum mechanism comprises a nickel–titanium alloy (Nitinol) tube with CCM cut via laser micromachining and actuated using wires bending from −80° to +80° in four directions. The proposed CCM has the following merits: perfect capacity for deflection around the centroid, a self-backbone, and improved torsional as well as tensile strengths. Further, it is pre-assembled. First, kinematic and static models are used to predict the bending behaviour of the mechanism. Thereafter, the maximum strain is evaluated using finite element analysis (FEA) then compared with the static models. Finally, the performances of the mechanism are characterized by experiments. The results validate the proposed models and demonstrate that the torsional and tensile strengths of the proposed CCM increased by more than 100% and 30%, respectively, compared with those of conventional non-CCMs with a similar fatigue life. Moreover, with the integrated forceps and probe, the proposed mechanism can achieve object transfer and square trajectory scanning of the targeted location. These experimental results demonstrate the potential clinical value of the proposed mechanism and provide important insights into the design of long and flexible instruments for endoscopic surgery.

Design and Analysis of a Contact-Aided Variable Stiffness Flexure Hinge (CVSFH)

2021 ◽  
Author(s):  
Shenyuan Dai ◽  
Lifang Qiu ◽  
Qichao Chen ◽  
Yanlin Li
Keyword(s):  
Contact Interaction ◽  
Compliant Mechanisms ◽  
Rectangular Cross Section ◽  
Variable Stiffness ◽  
Theoretical Equation ◽  
Flexure Hinge ◽  
Element Analysis ◽  
Equivalent Mechanical Model ◽  
Different Dimensions ◽  
Motion Characteristics

Abstract Flexure hinges are the basis of compliant mechanisms. The stiffness is one of the important indexes to evaluate the performance of a flexure hinge, and the rotation angle when the stiffness changes affects its motion characteristics. Thus, based on the constant rectangular cross-section flexure hinge and contact interaction, this paper proposed a contact-aided variable stiffness flexure hinge (CVSFH). With the deformation under an external load, the contact interaction with different parts of the CVSFH itself can achieve the purpose of variable stiffness. The equivalent mechanical model is built and the theoretical equation of the stiffness is given. CVSFHs with different dimensions are designed, and a finite element analysis (FEA) is done. The FEA results of the design examples are coincide with the theoretical results, which verifies the feasibility of the design and the correctness of the theoretical equation.

Joining by Forming of Tubes to Sheets with Counterbored Holes

2018 ◽  
Vol 767 ◽  
pp. 421-428 ◽  
Author(s):  
Luis M. Alves ◽  
Rafael M. Afonso ◽  
Carlos M.A. Silva ◽  
Paulo A.F. Martins
Keyword(s):  
Analytical Model ◽  
Cross Section ◽  
Room Temperature ◽  
Tube Wall ◽  
Rectangular Cross Section ◽  
Dissimilar Materials ◽  
Forming Process ◽  
Element Analysis ◽  
Joining By Forming ◽  
Tube Wall Thickness

This paper presents a new joining by forming process for connecting tubes to sheets. The process consists of forming an annular flange with rectangular cross section by partial sheet-bulk of the tube wall thickness and performing the mechanical interlock by upsetting the free tube end against a flat-bottomed (counterbored) sheet hole. The presentation identifies the variables and the workability limits of the process and includes an analytical model to assist readers in the design of the new joints. The new proposed joining by forming process and the corresponding analytical model are validated by experimentation and numerical simulation using finite element analysis. The process allows connecting tubes to sheets made from dissimilar materials at room temperature, avoids the utilization of addition materials or adhesives and produces joints that are easy to disassembly at the end of live, allowing recyclability of the tubes and sheets.

scholarly journals Shape Optimization of Bone-Bonding Subperiosteal Devices with Finite Element Analysis

2017 ◽  
Vol 2017 ◽  
pp. 1-7
Author(s):  
Takeshi Ogasawara ◽  
Masayoshi Uezono ◽  
Kazuo Takakuda ◽  
Masanori Kikuchi ◽  
Shoichi Suzuki ◽  
...  
Keyword(s):  
Finite Element ◽  
Cross Section ◽  
Bonding Strength ◽  
Clinical Performance ◽  
Rectangular Cross Section ◽  
Optimum Shape ◽  
Bone Surface ◽  
Element Analysis ◽  
Cross Sectional ◽  
Rapid Acquisition

Subperiosteal bone-bonding devices have been proposed for less invasive treatments in orthodontics. The device is osseointegrated onto a bone surface without fixation screws and is expected to rapidly attain a bone-bonding strength that successfully meets clinical performance. Hence, the device’s optimum shape for rapid and strong bone bonding was examined in this study by finite element analyses. First, a stress analysis was performed for a circular rod device with an orthodontic force parallel to the bone surface, and the estimate of the bone-bonding strength based on the bone fracture criterion was verified with the results of an animal experiment. In total, four cross-sectional rod geometries were investigated: circular (Cr), elliptical (El), semicircular (Sc), and rectangular (Rc). By changing the height of the newly formed bone to mimic the progression of new bone formation, the estimation of the bone-bonding strength was repeated for each geometry. The rod with the Rc cross section exhibited the best performance, followed by those with the Sc, El, and Cr cross sections, from the aspects of the rapid acquisition of strength and the strength itself. Thus, the rectangular cross section is the best for rod-like subperiosteal devices for rapid bone bonding.

Comparison of Design by Analysis Methods

2006 ◽  
Author(s):  
Sebastian Schindler
Keyword(s):  
Cross Section ◽  
Rectangular Cross Section ◽  
Pressure Vessels ◽  
Element Analysis ◽  
Advantages And Disadvantages ◽  
Direct Route ◽  
Analysis Methods ◽  
Air Cooler ◽  
Section Viii ◽  
Division 2

The paper discusses the advantages and disadvantages of the two well known Design by Analysis methods for unfired pressure vessels: the stress categorisation method (as given e.g. in the 2004 ASME B&BV Code Section VIII Division 2 [1], and EN 13445-3 Annex C [2]) and the new Direct Route (using elastic-plastic finite-element analysis) as given in EN 13445-3 Annex B [2]. A comparison of results is given for examples of various degree of difficulty to show the principal ideas and the applicability of the two approaches: a dished end with a nozzle in the knuckle region, a cylindrical shell to flat end connection and a rather complex header of an air cooler with rectangular cross section. As shown by the considered examples, the Direct Route method gives unique solutions (which is not always the case for stress categorisation) and can be advantageous in some cases, but requires a more time consuming analysis. The questionable design limits given by the 3f-criterion of the stress categorisation method can be avoided by usage of the progressive plastic deformation design check of the Direct Route if the required number of action cycles is low.

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