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Ashok Midha - One of the best experts on this subject based on the ideXlab platform.
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A Methodology for Determining Static Mode Shapes of a Compliant Mechanism Using the Pseudo-Rigid-Body Model Concept and the Degrees-Of-Freedom Analysis
Journal of Mechanisms and Robotics, 2020Co-Authors: Pratheek Bagivalu Prasanna, Ashok Midha, Sushrut G. Bapat, Vamsi LodagalaAbstract:Abstract Traditionally, the deflected configuration of compliant segments is determined through rigorous mathematical analysis using Newtonian mechanics. Application of this approach in evaluating the deformed configuration of compliant mechanisms, containing a variety of segment types, becomes cumbersome. This paper introduces a methodology to determine the possible deflected configuration(s) of a compliant mechanism, for a given set of load and/or displacement boundary conditions. The methodology utilizes the principle of minimum potential energy, in conjunction with the degrees-of-freedom analysis and the pseudo-Rigid-Body Model concept. The static mode shape(s) of compliant segments are integrated in identifying the possible deflected configuration(s) of a given compliant mechanism. The methodology facilitates the in situ determination of the possible deformed configuration(s) of the compliant mechanism and its constituent segments. This, in turn, assists in the important task of identifying an appropriate pseudo-Rigid-Body Model for the design and analysis of a compliant mechanism. The proposed methodology is illustrated with examples, and supported with experimental validation.
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A Methodology for Determining Static Mode Shapes of a Compliant Mechanism Using the Pseudo-Rigid-Body Model (PRBM) Concept and the Degrees-of-Freedom Analysis
Volume 5A: 43rd Mechanisms and Robotics Conference, 2019Co-Authors: Sushrut G. Bapat, Pratheek Bagivalu Prasanna, Ashok MidhaAbstract:Abstract Traditionally, the deflected configuration of compliant segments is determined through rigorous mathematical analysis using Newtonian mechanics. Application of these principles in evaluating the deformed configuration of compliant mechanisms, containing a variety of segment types, becomes cumbersome. This paper introduces a methodology to determine the expected deflected configuration(s) of a compliant mechanism, for a given set of load and/or displacement boundary conditions. The method utilizes the principle of minimum total potential energy, in conjunction with the degrees-of-freedom analysis and the pseudo-Rigid-Body Model concept. The static mode shape(s) of compliant segments are integrated in identifying the possible functional configuration(s) of a given compliant mechanism’s structural configuration. The methodology, in turn, also facilitates the in situ determination of the deformed configuration of the constituent compliant segments. It thus assists in the identification of an appropriate pseudo-Rigid-Body Model for design and analysis of a compliant mechanism.
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Classification of Compliant Mechanisms and Determination of the Degrees of Freedom Using the Concepts of Compliance Number and Pseudo-Rigid-Body Model
Volume 5A: 43rd Mechanisms and Robotics Conference, 2019Co-Authors: Pratheek Bagivalu Prasanna, Ashok Midha, Sushrut G. BapatAbstract:Abstract Understanding the kinematic properties of a compliant mechanism has always proved to be a challenge. A concept of compliance number offered earlier emphasized the development of terminology that aided in its determination. A method to evaluate the elastic degrees of freedom associated with the flexible segments/links of a compliant mechanism using the pseudo-Rigid-Body Model (PRBM) concept is provided. In this process, two distinct classes of compliant mechanisms are developed involving: (i) Active Compliance and (ii) Passive Compliance. Furthermore, these also aid in a better characterization of the kinematic behavior of a compliant mechanism. A more lucid interpretation of the significance of compliance number is provided. Applications of this method to both active and passive compliant mechanisms are exemplified. Finally, an experimental procedure that aids in visualizing the degrees of freedom as calculated is presented.
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Limitations in the Use of Small-Length Flexural Pivot in a Pseudo-Rigid-Body Model
Volume 5A: 39th Mechanisms and Robotics Conference, 2015Co-Authors: Vamsi Lodagala, Krutika Karthik, Ashok MidhaAbstract:This paper investigates the effective use of the pseudo-Rigid-Body Model (PRBM) of a small-length flexural pivot (SLFP), examining its very definition, and providing helpful guidelines in the context of a compound compliant beam composed of both compliant and Rigid segments. Traditionally, for convenience in Modeling, the pseudo-Rigid-Body Model of the small-length flexural pivot assumes the characteristic pivot to be placed at the center of the SLFP. It is also suggested that the length of the adjacent Rigid segment is ten or more times larger than the length of the compliant segment. In recent times, a growing interest has been expressed to test this assumption and learn more about its limitations. This paper investigates the performance of the PRBM of the SLFP, for initially straight and initially curved compound compliant beams by varying the compliant to Rigid segment length ratio. The error, defined by comparing the PRBM deflections with those obtained from the closed-form elliptic integral method, may be assigned an acceptable value in determining the limit value of the segment length ratio. Plots of the maximum deflection that may be obtained within an error limit of 3%, for various segment length ratios of a fixed-free, compound compliant beam are provided.Copyright © 2015 by ASME
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Mechanical Advantage of a Compliant Mechanism and Significant Factors Affecting it, Using the Pseudo-Rigid-Body Model Approach
Volume 5A: 39th Mechanisms and Robotics Conference, 2015Co-Authors: Ashok Midha, Sushrut G. Bapat, Prem A. MidhaAbstract:Although work related to mechanical advantage of compliant mechanisms has been presented almost two decades ago, unlike many Rigid-Body mechanism systems, this performance measure has seldom been used. In great part, the reasons are attributed to, one, the relatively recent development of and a lack of familiarity with this technology and, two, the complexity of the understanding and evaluation of mechanical advantage of compliant systems. In an effort to simplify the evaluation, this work uses the pseudo-Rigid-Body Model (PRBM) of a compliant mechanism, along with traditional notions of power conservation and angular velocity ratios using instant centers. As a first step, the inherent compliance in the mechanism is neglected in determining its mechanical advantage, followed by considerations to optimize its structural configuration for enhancing its mechanical advantage. The PRBM methodology, which offers us a way to estimate the characteristic compliance of the mechanism, now enables its inclusion in determining the mechanical advantage of the compliant mechanism. Two significant factors affecting it are i) the structural configuration of the PRBM, and ii) the energy stored in compliant elements of the mechanism. Several case studies are presented, which suggest that minimizing the latter contribution relative to that of an optimized structural configuration may improve the mechanical advantage of a compliant mechanism. Nonetheless, its effect on the mechanical advantage cannot be neglected.Copyright © 2015 by ASME
Larry L. Howell - One of the best experts on this subject based on the ideXlab platform.
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a pseudo Rigid Body Model of the human spine to predict implant induced changes on motion
Journal of Mechanisms and Robotics, 2011Co-Authors: Peter A Halverson, Anton E. Bowden, Larry L. HowellAbstract:Injury, instrumentation, or surgery may change the functional biomechanics of the spine. Adverse changes at one level may affect the adjacent levels. Modeling these changes can increase the understanding of adjacent-level effects and may help in the creation of devices that minimize adverse outcomes. The current Modeling techniques (e.g., animal Models, in vitro testing, and finite element analysis) used to analyze these effects are costly and are not readily accessible to the clinician. It is proposed that the pseudo-Rigid-Body Model(PRBM) may be used to accurately predict adjacent level effects in a quick and cost effective manner that may lend itself to a clinically relevant tool for identifying the adjacent-level effects of various treatment options for patients with complex surgical indications. A PRBM of the lumbar spine (lower back) was developed using a compliant mechanism analysis approach. The global moment-rotation response, relative motion, and local moment-rotation response of a cadaveric specimen were determined through experimental testing under three conditions: intact, fused, and implanted with a prototype total disc replacement. The spine was Modeled using the PRBM and compared with the values obtained through in-vitro testing for the three cases. The PRBM accurately predicted the moment-rotation response of the entire specimen. Additionally, the PRBM predicted changes in relative motion patterns of the specimen. The resulting Models show particular promise in evaluating various procedures and implants in a clinical setting and in the early stage design process.
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A 3-D Chain Algorithm with Pseudo-Rigid-Body Model Elements
Mechanics Based Design of Structures and Machines, 2011Co-Authors: Robert Parley Chase, Larry L. Howell, Robert H. Todd, Spencer P MaglebyAbstract:A chain algorithm element is created from pseudo-Rigid-Body segments and used in a chain calculation that accurately predicts the force deflection relationship of beams with large 3-D deflections. Each chain element is made up of three superimposed pseudo-Rigid-Body Models acting orthogonally in relation to each other. The chain algorithm can accurately and quickly predict large displacements and the force-deflection relationship of lateral torsional buckled beams. This approach is not intended to compete with finite element analysis, but rather is a supplement tool that may prove particularly useful in the early phases of design when many analysis iterations are required. The 3-D chain algorithm is demonstrated and compared to the finite element analysis for the nonlinear large-deflection, post-buckling path of a flexible beam undergoing lateral-torsional buckling.
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A Pseudo-Rigid-Body Model for Large Deflections of Fixed-Clamped Carbon Nanotubes
Journal of Mechanisms and Robotics, 2010Co-Authors: Larry L. Howell, Christopher Dibiasio, Michael A. Cullinan, Robert M. Panas, Martin L. CulpepperAbstract:Carbon nanotubes (CNTs) may be used to create nanoscale compliant mechanisms that possess large ranges of motion relative to their device size. Many macroscale compliant mechanisms contain compliant elements that are subjected to fixed-clamped boundary conditions, indicating that they may be of value in nanoscale design. The combination of boundary conditions and large strains yield deformations at the tube ends and strain stiffening along the length of the tube, which are not observed in macroscale analogs. The large-deflection behavior of a fixedclamped CNT is not well-predicted by macroscale large-deflection beam bending Models or truss Models. Herein, we show that a pseudo-Rigid-Body Model may be adapted to capture the strain stiffening behavior and, thereby, predict a CNT’s fixed-clamped behavior with less than 3% error from molecular simulations. The resulting pseudo-Rigid-Body Model may be used to set initial design parameters for CNT-based compliant mechanisms. This removes the need for iterative, time-intensive molecular simulations during initial design phases. DOI: 10.1115/1.4001726
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Force-Displacement Model of the FlexSuRe™ Spinal Implant
Volume 2: 34th Annual Mechanisms and Robotics Conference Parts A and B, 2010Co-Authors: Eric M. Stratton, Larry L. Howell, Anton E. BowdenAbstract:This paper presents Modeling of a novel compliant spinal implant designed to reduce back pain and restore function to degenerate spinal disc tissues as well as provide a mechanical environment conducive to healing of the tissues. Modeling was done through the use of the pseudo-Rigid-Body Model. The pseudo-Rigid-Body Model is a 3 DOF mechanism for flexion-extension (forward-backward bending) and a 5 DOF mechanism for lateral bending (side-to-side). These Models were analyzed using the principle of virtual work to obtain the force-deflection response of the device. The Model showed good correlation to finite element analysis and experimental results. The implant may be particularly useful in the early phases of implant design and when designing for particular biological parameters.Copyright © 2010 by ASME
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comparison of molecular simulation and pseudo Rigid Body Model predictions for a carbon nanotube based compliant parallel guiding mechanism
Journal of Mechanical Design, 2008Co-Authors: Christopher Dibiasio, Larry L. Howell, Robert M. Panas, Martin L. Culpepper, Spencer P MaglebyAbstract:We report on the accuracy of the pseudo-Rigid-Body Model (PRBM) in predicting the behavior of a nanoscale parallel-guiding mechanism (nPGM) that uses two single-walled (5,5) carbon nanotubes (CNTs) as the flexural guiding elements. The nPGM has two regions of behavior: region I is governed by the bulk deformation of the nanotubes, and region 2 is characterized by hingelike flexing of four "kinks" that occur due to buckling of the nanotube walls. PRBM parameters for (5,5) CNTs are proposed. Molecular simulation results of region I behavior match PRBM predictions of (I) kinematic behavior with less than 7.3% error and (2) elastomechanic behavior with less than 5.7% error. Although region I is of more interest because of its well-defined and stable nature, region 2 motion is also investigated. We show that the PRBM parameters are dependent on the selection of the effective tube thickness and moment of inertia, the lesson being that designers must take care to consider the thickness and moment of inertia values when deriving PRBM constants.
Mohammad H. Dado - One of the best experts on this subject based on the ideXlab platform.
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limit position synthesis and analysis of compliant 4 bar mechanisms with specified energy levels using variable parametric pseudo Rigid Body Model
Mechanism and Machine Theory, 2005Co-Authors: Mohammad H. DadoAbstract:This paper provides a synthesis and analysis procedure for the limit positions of compliant 4-bar mechanisms. The mechanism compliance is present at the output link which is considered to be fixed to the ground and can experience large non-linear elastic deflection at its pinned end. Under this condition, the mechanism mobility and its limit positions are dependent on the output link compliance. In addition, an elastic potential energy is stored at each limit position with a magnitude depending on the mechanism geometry and output link compliance properties. The developed procedure provides means of determining the complete mechanism geometry for (1) specified limit positions, or (2) specified energy level at each limit position. On the analysis side, the procedure provides the limit positions and energy levels for specified mechanism geometry. The compliant output link is Modeled using the variable parametric pseudo-Rigid-Body Model. In this Model, the pseudo-Rigid-Body parameters vary for different loading conditions, thus, providing a more accurate Model than that with fixed parameters. The procedure is presented in form of charts with minimum computational effort by the user. Illustrative examples are presented to prove the utility of the developed procedure.
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Variable parametric pseudo-Rigid-Body Model for large-deflection beams with end loads
International Journal of Non-Linear Mechanics, 2001Co-Authors: Mohammad H. DadoAbstract:Abstract This paper presents a variable parametric pseudo-Rigid-Body Model for large-deflection beams with end loads. The values of the applied load ( P ) and joint stiffness of pseudo-Rigid-Body Model ( k ) are expressed in terms of its kinematic parameters: the characteristic length ( γ ) and the “pseudo-Rigid-Body angle” (Θ). The expressions cover practical range of applications using a single equation for each variable. The accuracy of the expressions is excellent with correlation coefficients of (0.999) and (0.995). The accuracy of the end deflections generated by these expressions is shown to be much more greater than using the constant values for ( γ ) and ( k ). The new Model is used for the analysis of two compliant mechanisms with different modes of analysis. The advantages of the new Model and how it blends itself very smoothly in the analysis algorithm is illustrated through these examples.
Spencer P Magleby - One of the best experts on this subject based on the ideXlab platform.
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A 3-D Chain Algorithm with Pseudo-Rigid-Body Model Elements
Mechanics Based Design of Structures and Machines, 2011Co-Authors: Robert Parley Chase, Larry L. Howell, Robert H. Todd, Spencer P MaglebyAbstract:A chain algorithm element is created from pseudo-Rigid-Body segments and used in a chain calculation that accurately predicts the force deflection relationship of beams with large 3-D deflections. Each chain element is made up of three superimposed pseudo-Rigid-Body Models acting orthogonally in relation to each other. The chain algorithm can accurately and quickly predict large displacements and the force-deflection relationship of lateral torsional buckled beams. This approach is not intended to compete with finite element analysis, but rather is a supplement tool that may prove particularly useful in the early phases of design when many analysis iterations are required. The 3-D chain algorithm is demonstrated and compared to the finite element analysis for the nonlinear large-deflection, post-buckling path of a flexible beam undergoing lateral-torsional buckling.
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comparison of molecular simulation and pseudo Rigid Body Model predictions for a carbon nanotube based compliant parallel guiding mechanism
Journal of Mechanical Design, 2008Co-Authors: Christopher Dibiasio, Larry L. Howell, Robert M. Panas, Martin L. Culpepper, Spencer P MaglebyAbstract:We report on the accuracy of the pseudo-Rigid-Body Model (PRBM) in predicting the behavior of a nanoscale parallel-guiding mechanism (nPGM) that uses two single-walled (5,5) carbon nanotubes (CNTs) as the flexural guiding elements. The nPGM has two regions of behavior: region I is governed by the bulk deformation of the nanotubes, and region 2 is characterized by hingelike flexing of four "kinks" that occur due to buckling of the nanotube walls. PRBM parameters for (5,5) CNTs are proposed. Molecular simulation results of region I behavior match PRBM predictions of (I) kinematic behavior with less than 7.3% error and (2) elastomechanic behavior with less than 5.7% error. Although region I is of more interest because of its well-defined and stable nature, region 2 motion is also investigated. We show that the PRBM parameters are dependent on the selection of the effective tube thickness and moment of inertia, the lesson being that designers must take care to consider the thickness and moment of inertia values when deriving PRBM constants.
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A Pseudo-Rigid-Body Model for Rolling-Contact Compliant Beams
Volume 8: 31st Mechanisms and Robotics Conference Parts A and B, 2007Co-Authors: Allen Boyd Mackay, Spencer P Magleby, Larry L. HowellAbstract:This paper presents a pseudo-Rigid-Body Model (PRBM) for rolling-contact compliant beams (RCCBs). The loading conditions and boundary conditions for the RCCB can be simplified to an equivalent cantilever beam that has the same force-deflection characteristics as the RCCB. Building on the PRBM for cantilever beams, this paper defines a Model for the force-deflection relationship for RCCBs. The definition of the RCCB PRBM includes the pseudo-Rigid-Body Model parameters that determine the shape of the beam, the length of the corresponding pseudo-Rigid-Body links and the stiffness of the equivalent torsional spring. The behavior of the RCCB is parameterized in terms of a single parameter defined as clearance, or the distance between the contact surfaces. RCCBs exhibit a unique force-displacement curve where the force is inversely proportional to the clearance squared.Copyright © 2007 by ASME
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A 3D Pseudo-Rigid-Body Model for Large Spatial Deflections of Rectangular Cantilever Beams
Volume 2: 30th Annual Mechanisms and Robotics Conference Parts A and B, 2006Co-Authors: Nathan O. Rasmussen, Larry L. Howell, Jonathan W. Wittwer, Robert H. Todd, Spencer P MaglebyAbstract:The design of compliant mechanisms has been aided by the development of pseudo-Rigid-Body Models to predict the motion of flexible members undergoing large displacements. Many of these Models are based on the fact that the end of a cantilever beam follows a near-circular path when planar loads are applied. This paper shows that the application of 3-dimensional end-loading causes a beam to follow a near-spherical path, even for beams with non-circular cross-sections. A 3D pseudo-Rigid-Body Model is presented that allows the motion of an end-loaded rectangular beam to be predicted using a Rigid link and a spherical joint. Two sets of deflection limits for 0.5% error are presented and shown to be dependent upon the aspect ratio of the cross-section of the beam. The Model has the potential for aiding in the design of spatial compliant mechanisms and analysis of planar compliant mechanisms undergoing large out-of-plane motions.
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Development of Commercially Viable Compliant Mechanisms Using the Pseudo-Rigid-Body Model: Case Studies of Parallel Mechanisms
Journal of Intelligent Material Systems and Structures, 2004Co-Authors: Christopher A. Mattson, Larry L. Howell, Spencer P MaglebyAbstract:Analysis and synthesis of compliant mechanisms has recently been the subject of significant study in the research community. This focus has led to a number of design approaches for developing compliant mechanisms. This paper describes the value of using the Pseudo-Rigid-Body Model (PRBM) to design compliant mechanisms for commercial products. Application of the PRBM is illustrated through the development of two parallel mechanisms: a bicycle derailleur and parallel-motion bicycle brakes. The PRBM allows compliant mechanisms to be Modeled and analyzed as Rigid-Body mechanisms and significantly reduces the complexity of analysis. Mechanisms with straightforward properties are used to demonstrate the use of the PRBM to design commercially viable compliant mechanisms for required motion and force-deflection characteristics.
Ilse Jonkers - One of the best experts on this subject based on the ideXlab platform.
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Implementation of physiological functional spinal units in a Rigid-Body Model of the thoracolumbar spine
Journal of biomechanics, 2019Co-Authors: Wei Wang, Dongmei Wang, Friedl De Groote, Lennart Scheys, Ilse JonkersAbstract:Abstract Most of the current Rigid-Body Models of the complete thoracolumbar spine do not properly Model the intervertebral joint as the highly nonlinear stiffness is not incorporated comprehensively and the effects of compressive load on stiffness is commonly being neglected. Based on published in vitro data of individual intervertebral joint flexibility, multi-level six degree-of-freedom nonlinear stiffness of functional spinal units was Modelled and incorporated in a Rigid-Body Model of the thoracolumbar spine. To estimate physiological in vivo conditions of the entire spine, stiffening effects caused by directly applied compressive loads, and contributions to mono-segmental stiffness from the rib cage as well as multi-segmental interactions in the thoracic spine were analysed and implemented. Forward dynamic simulations were performed to simulate in vitro tests that measured the load-displacement response of the spine under various loading conditions. The predicted kinematic responses of the Model were in agreement with in vitro measurements, with correlations between simulated and measured segmental displacements varying between 0.66 and 0.97 (p 1.6 °. Coupling relationships were found between lateral bending and axial rotation. Under compressive loads, the Model behaved stiffer and showed a decreased range of motion: The flexion/extension response of the full thoracolumbar spine under compressive loads up to 800 N was found to strongly correlate with the literature (r = 0.99, p
