N. Tolou

Bistable vibration energy harvesters: A review

Powering electronics without depending on batteries is an open research field. Mechanical vibrations prove to be a reliable energy source, but low-frequency broadband vibrations cannot be harvested effectively using linear oscillators. This article discusses an alternative for harvesting such vibrations, with energy harvesters with two stable configurations. The challenges related to nonlinear dynamics are briefly discussed. Different existing designs of bistable energy harvesters are presented and classified, according to their feasibility for miniaturization. A general dynamic model for those designs is described. Finally, an extensive discussion on quantitative measures of evaluating the effectiveness of energy harvesters is accomplished, resulting in the proposition of a new dimensionless metric suited for a broadband analysis.

Statically Balanced Compliant Micro Mechanisms (SB-MEMS): Concepts and Simulation

Compliant mechanisms play an important role in micro mechanical structures for MEMS applications. However, the positive stiffness of these mechanisms remains a significant drawback. This stiffness can be compensated by including a static balancing mechanism (SBM), resulting in a statically balanced compliant micro mechanism (SB-CMM). This paper presents concepts and simulation results of such mechanisms, which could be applied to MEMS (SB-MEMS). Two categories of SB-CMMs are presented for different situations: the balancing force and travel path are either (1) perpendicular to each other, or (2) parallel to each other. The presented concepts provide compliant mechanisms with a finite zero stiffness range at the start or at a further predefined position of the overall mechanism travel range, respectively. The simulation results confirm the validity and performance of the presented concepts, which have been optimized for further evaluation. Incorporation of these concepts can ultimately result in a reliable, smaller, and energy efficient microsystem, having a larger useful travel range.Copyright

CONCEPT AND MODELING OF A STATICALLY BALANCED COMPLIANT LAPAROSCOPIC GRASPER

The objective of this investigation is to present a concept as well as mathematical modeling and finite element modeling of a statically balanced compliant laparoscopic grasper. To obtain force feedback, the positive stiffness of the compliant grasper was statically balanced by a negative-stiffness compensation mechanism. The negative stiffness has been produced by pairs of pre-stressed initially-curved pinned-pinned beams out of linear elastic material, arranged perpendicular to the link driving the grasper. First, the conceptual design is explained. Subsequently, its behavior is mathematically formulated and then finite element modeling is implemented using a commercially available finite element modeling package. Finally, a stress-optimized design of a negative-stiffness compensation mechanism and the effect of parameter changes on the accuracy are obtained. The results illustrate the efficiency of the applied analysis methods for the case of statically balancing the laparoscopic grasper. It also demonstrates the efficiency of the balancer concept. The proposed procedure is found to be convenient for this set of problems, and can probably be applied to other similar practical problems.Copyright

Comparative Vibration Analysis of a Parametrically Nonlinear Excited Oscillator Using HPM and Numerical Method

The objective of this paper is to present an analytical investigation to analyze the vibration of parametrically excited oscillator with strong cubic negative nonlinearity based on Mathieu-Duffing equation. The analytic investigation was conducted by using Hes homotopy-perturbation method (HPM). In order to obtain the analytical solution of Mathieu-Duffing equation, homotopy-perturbation method has been utilized. The Runge-Kuttas (RK) algorithm was used to solve the governing equation via numerical solution. Finally, to demonstrate the validity of the proposed method, the response of the oscillator, which was obtained from approximate solution, has been shown graphically and compared with that of numerical solution. Afterward, the effects of variation of the parameters on the accuracy of the homotopy-perturbation method were studied.

Bistable Compliant Mechanisms: Corrected Finite Element Modeling for Stiffness Tuning and Preloading Incorporation

Bistable straight-guided buckling beams are essential mechanisms for precision engineering, compliant mechanisms, and MEMS. However, a straightforward and accurate numerical modeling have not been available. When preloading effects must be included, numerical modeling becomes an even more challenging problem. This article presents a straightforward numerical model for bistable straight-guided buckling beams, which includes preloading effects as well. Adjusting the bistable force–displacement characteristic by variation of design parameters and preloading is also investigated. Both lumped compliance and distributed compliance are considered in this work. In order to validate the model, measurements have been performed. It was shown that a small precurvature of bistable straight-guided buckling beams is crucial to avoid convergence into higher order buckling modes in nonlinear analysis of ANSYS™ and to obtain reliable results. Transient analysis using ANSYS™ with subsequent preloading and motion displacements can incorporate preloading effects. Moreover, the model correction allows accurate description of the increased symmetry and energy efficiency of the bistable behavior in case of increasing (in order of effectiveness) the initial angle and preloading for the case of distributed compliance. This behavior was observed by increasing the initial angle, thickness, and length of the rigid segment for the case of lumped compliance.

A Semianalytical Approach to Large Deflections in Compliant Beams under Point Load

The deflection of compliant mechanism (CM) which involves geometrical nonlinearity due to large deflection of members continues to be an interesting problem in mechanical systems. This paper deals with an analytical investigation of large deflections in compliant mechanisms. The main objective is to propose a convenient method of solution for the large deflection problem in CMs in order to overcome the difficulty and inaccuracy of conventional methods, as well as for the purpose of mathematical modeling and optimization. For simplicity, an element is considered which is a cantilever beam out of linear elastic material under vertical end point load. This can further be used as a building block inmore complex compliant mechanisms. First, the governing equation has been obtained for the cantilever beam; subsequently, the Adomian decomposition method (ADM) has been utilized to obtain a semianalytical solution. The vertical and horizontal displacements of a cantilever beam can conveniently be obtained in an explicit analytical form. In addition, variations of the parameters that affect the characteristics of the deflection have been examined. The results reveal that the proposed procedure is very accurate, efficient, and convenient for cantilever beams, and can probably be applied to a large class of practical problems for the purpose of analysis and optimization.

Collinear-Type Statically Balanced Compliant Micro Mechanism (SB-CMM): Experimental Comparison Between Pre-Curved and Straight Beams

The feasibility of collinear-type statically balanced compliant micro mechanism (SB-CMM) with pre-curved beams has been studied experimentally and compares to those with initially straight beams. The collinear-type SB-CMM is a near zero stiffness micro mechanism with a near zero actuation force in a finite range of motion. However, from the experimental data, it was found that the collinear-type SB-CMM are sensitive to fabrication errors, as a results negative or positive constant force instead of zero actuation force maybe obtained. For the case of pre-curved beams, the curvature can be tuned for better zero stiffness behavior. Further improvements in the concept are considered towards a robust design and reliable prototypes, such as optimization and accurate dimensioning and fabrication.Copyright

Comparison of Methods for Large Deflection Analysis of a Cantilever Beam Under Free End Point Load Cases

The objective of this paper is to present a comparative analysis for large deflections of a cantilever beam under free end point load. pseudo rigid body model (PRBM), non-linear beam theory numerically solved with integration (NLBT-NUM), linear beam theory (LBT), finite element modeling (FEM) using an available commercially FEM package, non-linear beam theory solved with direct nonlinear solution (NLBT-DNS) and experimental evaluation (EXP), have been implemented. For the purpose of comparison, the relation between the displacements, rotating angle of the tip and applied force were calculated and shown graphically. The accuracy of the path of the tip as a function of the force is compared with the NLBT-NUM, which is taken as a reference. In addition, computation times and implementation convenience were recorded. In the case of a perpendicular load, the PRBM is accurate and has little computation time. The NLBT-NUM, NLBT-DNS and FEM analysis are accurate, but the computation time is longer. The NLBT-DNS has been introduced for the first time and provides semi-exact closed form solutions for both horizontal and vertical position. In case of a non-perpendicular load, the NLBT-NUM and FEM analysis are the only accurate methods while computation time is less for the numerical solution. In conclusion, the PRBM and the FEM are recommended for the cases of perpendicular load and non-perpendicular load respectively. Finally, it can be concluded that the more accurate methods take more computation time, and that the accuracy is affected by load cases.Copyright

The Scope for a Compliant Homokinetic Coupling Based on Review of Compliant Joints and Rigid-Body Constant Velocity Universal Joints

Many applications require a compliant mechanism to transmit rotation from one direct to another direct with constant velocity. This paper presents a literature survey towards the design of compliant constant velocity universal joints. The traditional constant velocity universal joints available from the literature were studied, classified and their mechanical efficiencies were compared. Also the graph representation of them was studied. In the same manner, literature review for different kind of compliant joints suitable for the Rigid-Body-Replacement of constant velocity universal joints was also performed. For the first time a comparison with analytical data of compliant joints was performed. All of compliant universal joints are non-constant velocity and designed based on rigid Hooke’s universal joint. Also we show there are no equivalent compliant joints for some rigid-body joints such as cylindrical joint, planar joint, spherical fork joint and spherical parallelogram quadrilateral joint. However, we may achieve them by combining numbers of available compliant joints. The universal joints found are non-compliant non-constant velocity universal joint, non-compliant constant velocity universal joint or compliant non-constant velocity universal joint. A compliant constant velocity universal joint has a great horizon for developments, for instance in medical or rehabilitation devices.Copyright

A Compliant On/Off Connection Mechanism for Preloading Statically Balanced Compliant Mechanisms

Static balancing is an important contribution to compliant mechanisms enabling low operating force, thus allowing high mechanical efficiency. Preloading is generally needed in statically balanced compliant mechanisms, which at smaller scales presents a significant challenge. Physical handling of zero-force structures without causing damage also becomes difficult. This paper presents a solution to both of these issues. A novel compliant connection mechanism based on bistable beams was used to precisely preload the system in the direction of motion without backlash. Once this bistable mechanism is engaged by loading beyond its threshold, the system is in operating condition, i.e. the ON position. When the connection mechanism is disengaged (OFF position), it is much stiffer than it is in the statically balanced state and therefore more robust for handling purposes. As a demonstrator, we present the first statically balanced gripper with a fully compliant ON/OFF-connection mechanism allowing pre-loading collinear with the direction of motion. The combination of a pre-loaded bistable mechanism (i.e. negative stiffness) and a voluntary closing gripper (i.e. positive stiffness) is used for static balancing (i.e. zero stiffness and zero actuation force). The results show that the actuation force is reduced by at least 91% when the preload is engaged. The proposed ON/OFF connection shows a promising method for pre-loading compliant mechanisms or related devices.Copyright