Metrics for Evaluation and Design of Large-Displacement Linear-Motion Compliant Mechanisms

2012 ◽  
Vol 134 (1) ◽  
Author(s):  
Allen B. Mackay ◽  
David G. Smith ◽  
Spencer P. Magleby ◽  
Brian D. Jensen ◽  
Larry L. Howell
Keyword(s):  
Performance Characteristic ◽  
Microelectromechanical Systems ◽  
Compliant Mechanisms ◽  
Large Displacement ◽  
Torsional Stiffness ◽  
Axial Stiffness ◽  
Linear Motion ◽  
Transverse Stiffness ◽  
Actuation Force ◽  
Performance Tradeoff

This work introduces metrics for large-displacement linear-motion compliant mechanisms (LLCMs) that evaluate the performance tradeoff between displacement and off-axis stiffness. These metrics are nondimensionalized, consisting of relevant characteristics used to describe displacement, off-axis stiffness, actuation force, and size. Displacement is normalized by the footprint of the device, transverse stiffness by a new performance characteristic called virtual axial stiffness, and torsional stiffness by the characteristic torque. These metrics account for the variation of both axial and off-axis stiffness over the range of displacement. The metrics are demonstrated for several microelectromechanical systems (MEMS) that are sensitive to size because of high cost and off-axis stiffness because of function. The use of metrics in design is demonstrated in the design of an LLCM; the resulting design shows increased values for both the travel and transverse-stiffness metrics.

scholarly journals Study on the large-displacement behaviour of a spiral spring with variations of cross-section, orthotropy and prestress

2018 ◽  
Vol 9 (2) ◽  
pp. 337-348 ◽  
Author(s):  
Giuseppe Radaelli ◽  
Just L. Herder
Keyword(s):  
Graphical Representation ◽  
Compliant Mechanisms ◽  
Large Displacement ◽  
Torsional Stiffness ◽  
Nonlinear Behaviour ◽  
Cross Sectional ◽  
Energy Field ◽  
Spiral Spring ◽  
Out Of Plane ◽  
Torsion Stiffness

Abstract. This work is dedicated to the study of the large-displacement behaviour of a spiral spring. Parameters that influence the local torsion stiffness of the beam that constitutes the spiral are varied and their effect is studied. Cross-sectional shape, orthotropic material orientation and prestress are the three classes of parameters that are varied. The effect that the local change in torsional stiffness has on the overall behaviour is illustrated in a linearised way by comparing in-plane and out-of-plane stiffnesses, and nonlinearly, by inspecting a graphical representation of the potential energy field of the system. Several embodiments composed of multiple spirals are showed to illustrate how the understanding of the nonlinear behaviour could be exploited in conceptual design of compliant mechanisms.

A Proximally-Adjustable Variable Length Intramedullary Nail: Ex Vivo Quasi-Static and Cyclic Loading Evaluation

2017 ◽  
Vol 11 (4) ◽  
Author(s):  
Mark J. Hedgeland ◽  
Alexander Martin Clark ◽  
Mario J. Ciani ◽  
Arthur J. Michalek ◽  
Laurel Kuxhaus
Keyword(s):  
Cyclic Loading ◽  
Mechanical Performance ◽  
Ex Vivo ◽  
Healing Process ◽  
Axial Loading ◽  
Torsional Stiffness ◽  
Axial Stiffness ◽  
Four Point Bending ◽  
Point Bend ◽  
Static And Cyclic Loading

An adjustable-length intramedullary (IM) nail may reduce both complications secondary to fracture fixation and manufacturing costs. We hypothesized that our novel nail would have suitable mechanical performance. To test this hypothesis, we manufactured three prototypes and evaluated them in quasi-static axial compression and torsion and quasi-static four-point bending. Prototypes were dynamically evaluated in both cyclic axial loading and four-point bending and torsion-to-failure. The prototypes exceeded expectations; they were comparable in both quasi-static axial stiffness (1.41 ± 0.37 N/m in cervine tibiae and 2.30 ± 0.63 in cadaver tibiae) and torsional stiffness (1.05 ± 0.26 N·m/deg in cervine tibiae) to currently used nails. The quasi-static four-point bending stiffness was 80.11 ± 09.360, greater than reported for currently used nails. A length-variance analysis indicates that moderate changes in length do not unacceptably alter bone-implant axial stiffness. After 103,000 cycles of axial loading, the prototype failed at the locking screws, comparable to locking screw failures seen clinically. The prototypes survived 1,000,000 cycles of four-point bend cyclic loading, as indicated by a consistent phase angle throughout cyclic loading. The torsion-to-failure test suggests that the prototype has adequate resistance to applied torques that might occur during the healing process. Together, these results suggest that our novel IM nail performs sufficiently well to merit further development. If brought to market, this adjustable-length IM nail could reduce both patient complications and healthcare costs.

Effect of Matching Buckling Loads on Post-Buckling Behavior in Compliant Mechanisms

2021 ◽  
Author(s):  
A. Numić ◽  
T. W. A. Blad ◽  
F. van Keulen
Keyword(s):  
Compliant Mechanisms ◽  
Relative Length ◽  
Optimal Designs ◽  
Element Analysis ◽  
Buckling Loads ◽  
Actuation Force ◽  
Stepped Beam ◽  
Buckling Behavior ◽  
Post Buckling ◽  
Novel Method

Abstract In this paper, a novel method for stiffness compensation in compliant mechanisms is investigated. This method involves tuning the ratio between the first two critical buckling loads. To this end, the relative length and width of flexures in two architectures, a stepped beam and parallel guidance, are adjusted. Using finite element analysis, it is shown that by maximizing this ratio, the actuation force for transversal deflection in post-buckling is reduced. These results were validated experimentally by identifying the optimal designs in a given space and capturing the force-deflection characteristics of these mechanisms.

Topology Synthesis of Large-Displacement Compliant Mechanisms

1999 ◽  
Author(s):  
Claus B. W. Pedersen ◽  
Thomas Buhl ◽  
Ole Sigmund
Keyword(s):  
Sensitivity Analysis ◽  
Optimization Problem ◽  
Adjoint Method ◽  
Compliant Mechanisms ◽  
Large Displacement ◽  
Element Formulation ◽  
Method Of Moving Asymptotes ◽  
Synthesis Tool ◽  
Lagrangian Finite Element ◽  
Moving Asymptotes

Abstract This paper describes the use of topology optimization as a synthesis tool for the design of large-displacement compliant mechanisms. An objective function for the synthesis of large-displacement mechanisms is proposed together with a formulation for synthesis of path-generating compliant mechanisms. The responses of the compliant mechanisms are modelled using a Total Lagrangian finite element formulation, the sensitivity analysis is performed using the adjoint method and the optimization problem is solved using the Method of Moving Asymptotes. Procedures to circumvent some numerical problems are discussed.

scholarly journals Biomechanical comparison of medial sustainable nail and proximal femoral nail antirotation in the treatment of an unstable intertrochanteric fracture

2020 ◽  
Vol 9 (12) ◽  
pp. 840-847
Author(s):  
Shaobo Nie ◽  
Ming Li ◽  
Hui Ji ◽  
Zhirui Li ◽  
Wenwen Li ◽  
...  
Keyword(s):  
Cyclic Loading ◽  
Torsional Stiffness ◽  
Proximal Femoral Nail ◽  
Axial Stiffness ◽  
Intertrochanteric Fractures ◽  
Loading Test ◽  
Cyclic Loading Test ◽  
Femoral Nail ◽  
Unstable Intertrochanteric Fracture ◽  
The Mean

Aims Restoration of proximal medial femoral support is the keystone in the treatment of intertrochanteric fractures. None of the available implants are effective in constructing the medial femoral support. Medial sustainable nail (MSN-II) is a novel cephalomedullary nail designed for this. In this study, biomechanical difference between MSN-II and proximal femoral nail anti-rotation (PFNA-II) was compared to determine whether or not MSN-II can effectively reconstruct the medial femoral support. Methods A total of 36 synthetic femur models with simulated intertrochanteric fractures without medial support (AO/OTA 31-A2.3) were assigned to two groups with 18 specimens each for stabilization with MSN-II or PFNA-II. Each group was further divided into three subgroups of six specimens according to different experimental conditions respectively as follows: axial loading test; static torsional test; and cyclic loading test. Results The mean axial stiffness, vertical displacement, and maximum failure load of MSN-II were 258.47 N/mm (SD 42.27), 2.99 mm (SD 0.56), and 4,886 N (SD 525.31), respectively, while those of PFNA-II were 170.28 N/mm (SD 64.63), 4.86 mm (SD 1.66), and 3,870.87 N (SD 552.21), respectively. The mean torsional stiffness and failure torque of MSN-II were 1.72 N m/° (SD 0.61) and 16.54 N m (SD 7.06), respectively, while those of PFNA-II were 0.61 N m/° (SD 0.39) and 6.6 N m (SD 6.65), respectively. The displacement of MSN-II in each cycle point was less than that of PFNA-II in cyclic loading test. Significantly higher stiffness and less displacement were detected in the MSN-II group (p < 0.05). Conclusion The biomechanical performance of MSN-II was better than that of PFNA-II, suggesting that MSN-II may provide more effective mechanical support in the treatment of unstable intertrochanteric fractures. Cite this article: Bone Joint Res 2020;9(12):840–847.

scholarly journals A Wear Simulation Method for Mechanical Face Seals under Friction Instability Conditions

2020 ◽  
Vol 10 (8) ◽  
pp. 2875
Author(s):  
Wentao He ◽  
Shaoping Wang ◽  
Chao Zhang ◽  
Xi Wang ◽  
Di Liu
Keyword(s):  
Contact Pressure ◽  
Torsional Stiffness ◽  
Frictional Heat ◽  
Axial Stiffness ◽  
Asperity Contact ◽  
Wear Simulation ◽  
Time Rate ◽  
Wear Time ◽  
Face Seals ◽  
Non Gaussian

Mechanical face seals are crucial components of automotive cooling water pumps and affect the safe operation of the pump. This article focuses on the effect of friction instabilities on the wear of the seals. Friction instabilities, such as stick-slip, occur when the axle is decelerated or operated at a low speed. Based on previous studies, a simulation model is proposed of a mechanical face seal that considers the interaction of asperities of non-Gaussian surfaces and the heat transfer between the sealing rings. According to the Archard wear equation, a numerical wear simulation is performed, and the wear distance rate and wear time rate are obtained. A comparison of the contact pressure of the Gaussian and non-Gaussian surfaces indicates that the latter is more likely to generate high contact pressure, thereby producing more significant wear. The viscous shear heat and frictional heat due to asperity contact decrease with an increase in the thickness of the tapered film. As the shaft decelerates, the wear distance rate increases with an increase in the axial stiffness. The axial damping only affects the duration of the oscillations. The wear time rate decreases with an increase in the torsional stiffness and torsional damping. The results of this research provide guidelines for estimating the wear of mechanical seals when friction instabilities occur.

Design and Comparative Analysis of Linear Guides for Refreshable Braille Displays

2017 ◽  
Author(s):  
Varan Gupta ◽  
Pulkit Sapra ◽  
Suman Muralikrishnan ◽  
M. Balakrishnan ◽  
P. V. M. Rao
Keyword(s):  
Comparative Analysis ◽  
Cost Efficiency ◽  
Compliant Mechanisms ◽  
Low Cost ◽  
Industrial Applications ◽  
Linear Motion ◽  
Motion System ◽  
Friction Cost ◽  
Cost Feasibility

Linear guides are extensively employed in several industrial applications. Miniaturization, minimal friction, cost efficiency and low maintenance are the major challenges faced while developing a linear motion system. This paper presents design and realization of such systems, overcoming the aforementioned challenges. Linear guidance mechanisms, suitable for implementing latching in Refreshable Braille Displays are proposed, where uniform behavior under eccentric loading is required. Several low cost, reliable and efficient guide mechanisms with predetermined dimensional constraints have been designed. Seven mechanisms are illustrated and analyzed in this paper, which includes both, traditional contact-based mechanisms and compliant mechanisms that offer contact-less motion. The paper further compares the functionality, cost feasibility and ease of manufacturing and assembly of these mechanisms.

The Effect of Lateral Cortex Disruption and Repair on the Stability of the Medial Opening Wedge High Tibial Osteotomy

2005 ◽  
Vol 33 (10) ◽  
pp. 1552-1557 ◽  
Author(s):  
Bruce S. Miller ◽  
William O. P. Dorsey ◽  
Cari R. Bryant ◽  
John C. Austin
Keyword(s):  
High Tibial Osteotomy ◽  
Torsional Stiffness ◽  
Osteotomy Site ◽  
Axial Stiffness ◽  
Control Group ◽  
Tibial Osteotomy ◽  
Opening Wedge ◽  
Lateral Cortex ◽  
Wedge High Tibial Osteotomy ◽  
Tibial Cortex

Background Medial opening wedge high tibial osteotomy is gaining popularity as a treatment option for medial compartment degenerative disease in the young, active patient. One of the potential technical pitfalls of this procedure is inadvertent disruption of the lateral tibial cortex during distraction at the osteotomy site. Purpose (1) To investigate the effect of lateral cortex disruption on stability during medial opening wedge high tibial osteotomy and (2) to evaluate 3 different methods of repair of the disrupted lateral cortex. Study Design Controlled laboratory study. Methods A total of 50 validated replicate tibias were evaluated in a medial opening wedge high tibial osteotomy model. Specimens were divided into 5 groups: (1) control, or intact lateral cortex (n = 10); (2) disrupted lateral cortex (n = 10); (3) lateral cortex repaired with 1 staple (n = 10); (4) lateral cortex repaired with 2 staples (n = 10); and (5) lateral cortex repaired with a periarticular plate and screws (n = 10). Specimens were placed in compression and torsion under physiologic loads, and stiffness and micromotion were calculated. Results Disruption of the lateral cortex resulted in a 58% reduction in axial stiffness and a 68% reduction in torsional stiffness compared to control specimens (P<. 05). Disruption of the lateral cortex also resulted in increased micromotion at the osteotomy site. All 3 methods of repair of the lateral cortex restored stiffness and micromotion values to those of the control group (P<. 05). Conclusions Instability at the osteotomy site may contribute to the high rate of delayed union or nonunion associated with medial opening wedge high tibial osteotomy. Repair of the lateral tibial cortex by each of these techniques restored stability to the osteotomy site in this replicate tibia model and might be effective in clinical use. However, more studies are needed to further explore the relationship between lateral cortex disruption and patient outcomes in the clinical setting before definitive conclusions can be drawn.

Straight-Line Mechanisms as One Building Element of Small Precise Robotic Devices

2014 ◽  
Vol 613 ◽  
pp. 96-101 ◽  
Author(s):  
Jaroslav Hricko
Keyword(s):  
Compliant Mechanisms ◽  
Building Blocks ◽  
Linear Motion ◽  
Kinematics Analysis ◽  
Positioning Accuracy ◽  
Building Element ◽  
Revolute Joints ◽  
Straight Line ◽  
Robotic Devices ◽  
Straight Line Mechanism

Small precise robotic devices, working on principle of compact compliant mechanisms, must meet the conditions to high positioning accuracy what mean moving in straight-line too. But, compliant mechanisms are usually produced by equivalent of revolute joints, therefore in design of small robotic devices is necessary apply knowledge from design of one type of specialized mechanisms – straight-line mechanisms. This paper presents some straight-line mechanism and its applications to design of some small precise robotic devices. According to kinematics analysis most known straight-line mechanisms are evaluated for their application in compliant mechanisms. Such devices are transformed to flexure structures. Consequently, these devices are important building blocks to design some linear-motion stages and/or micro-grippers.

The effect of load application rate on the biomechanics of synthetic femurs

2009 ◽  
Vol 224 (4) ◽  
pp. 599-605 ◽  
Author(s):  
R Zdero ◽  
S Shah ◽  
M Mosli ◽  
E H Schemitsch
Keyword(s):  
Linear Correlation ◽  
Loading Rate ◽  
Application Rate ◽  
Torsional Stiffness ◽  
Fourth Generation ◽  
Axial Stiffness ◽  
Average Value ◽  
Rate Effects ◽  
Strong Linear Correlation ◽  
Torsional Test

Biomechanical investigations are increasingly using commercially available synthetic femurs as surrogates for human cadaveric femurs. However, the rate of force application in testing these artificial femurs appears to be chosen arbitrarily without much consideration to their visco-elastic time-dependent nature. The aim of this study, therefore, was to examine the effect of loading rate on the mechanical behaviour of synthetic femurs. Ten left, medium, fourth-generation composite femurs (Model 3403, Pacific Research Laboratories, Vashon, WA, USA) were fixed distally into cement-filled steel cubic chambers for mounting into a mechanical tester. In randomized order, each of the ten femurs was loaded at rates of 1, 2.5, 5, 7.5, 10, 20, 30, 40, 50, and 60 mm/min to obtain axial, lateral, and torsional stiffness. Axial stiffness showed an aggregate average value of 1742.7 ± 174.7 N/mm with a high linear correlation with loading rate ( R2 = 0.80). Lateral stiffness yielded an aggregate average value of 56.9 ± 10.2 N/mm and was linearly correlated with loading rate ( R2 = 0.85). Torsional stiffness demonstrated an aggregate average value of 176.9 ± 14.5 N/mm with a strong linear correlation with loading rate ( R2 = 0.59). Despite the high correlations between stiffness and speed, practically this resulted in an overall average difference between the lowest and highest stiffness of only 4 per cent. Moreover, no statistical comparisons between loading rates for axial, lateral, or torsional test modes showed differences ( p ≤ 0.843). Future biomechanical investigators utilizing these synthetic femurs need not be concerned with loading rate effects over the range tested presently. This is the first study in the literature to perform such an assessment.

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