Elastic Hinges Research Articles

Design and Validation of a Carbon-Fiber Collapsible Hinge for Space Applications: A Deployable Boom

This work presents an analysis and validation of a foldable boom actuated by tape-spring foldable elastic hinges for space applications. The analytical equations of tape-springs are described, extending the classical equations for isotropic materials to orthotropic carbon-fiber composite materials. The analytical equations which describe the buckling of the hinge have been implemented in a multibody simulation software where the hinge was modeled as a nonlinear elastic bushing and the boom as a rigid body. In the experimental phase, the boom was fabricated using a thin layer carbon-fiber composite tube, and the residual vibrations after deployment were experimentally tested with a triaxial accelerometer. A direct comparison of the simulation with the physical prototype pointed out the dangerous effect of higher order vibrations which are difficult to capture in simulation. We observed that while the vibrational spectra of simulations and experiments were compatible at low frequencies during deployment, a marked difference was observed at frequencies beyond 30 Hz. While difficult to model, higher order frequencies should be carefully accounted for in the design of self-deployable space structures. Indeed, if tape-springs are used as a self-locking mechanism, the higher vibrational modes could have enough energy to unlock the structure during operation.

衛星搭載用大型光学系向け低歪み鏡支持機構の開発

A novel design of mirror support mechanism for space telescopes is presented, which uses ball bearings for the stress relief devices instead of using elastic hinges on the kinematic truss-like structural members. By using this mechanism, disturbance moment applied to the mirror is limited within the small friction torque regardless to the mounting error or distortion of base structures. The point of the design is to bring out the excellent stress relief performance of the mechanism without degrading the linearity of the stiffness and mechanical strength. The experimental model of the proposed support mechanism is produced, and its mechanical performances are investigated. Those results show that the expected characteristics of the support system can be realized.

弾性ヒンジを用いたアクティブ制御型油静圧スラスト軸受に関する研究

弾性ヒンジを用いたアクティブ制御型油静圧スラスト軸受に関する研究

A Foldable Antagonistic Actuator

We report on an actuator based on dielectric elastomers that is capable of antagonistic actuation and passive folding. This actuator enables foldability in robots with simple structures. Unlike other antagonistic dielectric elastomer devices, our concept uses elastic hinges to allow the folding of the structure, which also provides an additional design parameter. To validate the actuator concept through a specific application test, a foldable elevon actuator with outline size of 70 mm × 130 mm is developed with angular displacement range and torque specifications matched to a 400-mm wingspan micro-air vehicle (MAV) of mass 130 g. A closed-form analytical model of the actuator is constructed, which was used to guide the actuator design. The actuator consists of 125-μm-thick silicone membranes as the dielectric elastomers, 0.2mm-thick fiberglass plate as the frame structure, and 50-μm-thick polyimide as the elastic hinge. We measured voltage-controllable angular displacement up to ±26° and torque of 2720 mN · mm at 5 kV, with good agreement between the model and the measured data. Two elevon actuators are integrated into the MAV, which was successfully flown, with the foldable actuators providing stable and well-controlled flight. The controllability was quantitatively evaluated by calculating the correlation between the control signal and the MAV motion, with a correlation in roll axis of over 0.7 measured during the flights, illustrating the high performance of this foldable actuator.

The stability of a flexibly mounted rotating cylinder in turbulent annular fluid flow

In this paper, we determine the inviscid linear stability with respect to two-dimensional disturbances of a fluid flow between two concentric cylinders. The inner rigid cylinder rotates with the angular velocity Ω0 and is fixed on elastic hinges at each end in the transverse direction. The outer cylinder does not rotate and is rigidly fixed. We assume that the fluid flow has an inner core that rotates as a solid body with angular velocity Ω0/2 and outside the core there are turbulent boundary layers. The velocity profile of the turbulent boundary layers satisfies the viscous Camassa−Holm equations. The perturbed fluid flow is derived from Rayleigh’s equation. The analysis yields an equation of motion of the cylinder equivalent to previous work without boundary layers and a basic flow of constant angular vorticity. The analysis is not restricted to a small gap between the cylinders. The results are compared with the results by Antunes et al. (1996), who consider a similar problem with uniform velocity profile and the limit of small gap. For ρc/ρf<1 the results disagree in that the present analysis shows stability whereas Antunes et al. find instability. For ρc/ρf>1 both theories predict stability and for larger values of ρc/ρf the agreement is good especially for small gap.

Notched CFRP laminates under vibration

This paper deals with the experimental and theoretical analysis of damaged and undamaged Carbon Fiber Reinforced Polymer (CFRP) laminate elements under free vibration. CFRP laminate specimens were experimentally investigated using a mechanical apparatus capable of simulating hinge conditions at the edges of simply supported laminate beams. Damage in the CFRP laminates subjected to testing was due to double rectangular notches on different sections of the specimens with varying increases in width determining local reduction of bending stiffness with effects on dynamic response. Shown herein are the envelope of Frequency Response Functions (FRFs) obtained through dynamic testing and the changes of natural frequency values are related to the damage degree of CFRP laminates. A theoretical model, based on the assumption that an elastic rotational hinge concentrated at the axis of a notch may be assumed to describe damage analytically, was developed for an analytical study of damaged CFRP laminates under vibration. Theoretical frequency values are compared with those obtained through tests and finite element analysis. The availability of the theoretical model on the basis of the data collected is discussed.

Vibration of CFRP cantilever beam with damage

The aim of this paper is the analysis of vibration of undamaged and damaged Carbon Fibre Reinforced Polymer (CFRP) beam elements. Experimental free vibration of CFRP cantilever beam elements were investigated by dynamic tests; damage of CFRP specimens were locally due to double notches close to the fixed end with different reduction of section and bending stiffness. Frequency values were extracted by transformed signals in frequency domain using the Fast Fourier Transform (FFT) technique. A comparison was made of the experimentally extracted frequencies at each damage level and in relation to the single positions of the accelerometer. The present paper illustrates the envelope of Frequency Response Functions (FRFs) obtained by the experimental dynamic tests and the changes of natural frequency values correlated to the damage degree of CFRP beam element.Theoretically, the dynamic behavior of damaged CFRP cantilever beam is studied with an appraisal model adopting an elastic hinge as equivalent concentrated damage. Theoretical data is defined and discussed in comparison to the experimental results.

Wind turbine blade vibration at standstill conditions—the effect of imposing lag on the aerodynamic response of an elastically mounted airfoil

AbstractThe present study investigated physical phenomena related to stall‐induced vibrations potentially existing on wind turbine blades at standstill conditions. The study considered two‐dimensional airfoil sections while it omitted three‐dimensional effects. In the study, a new engineering‐type computational model for the aeroelastic response of an elastically mounted airfoil was used to investigate the influence of temporal lag in the aerodynamic response on the aeroelastic stability in deep stall. The study indicated that even a relatively low lag significantly increases the damping of the model. A comparison between the results from a model with lag imposed on all force components with the results from a model with lag imposed exclusively on the lift showed only marginal difference between the damping in the two cases. A parameter study involving positions of the elastic hinge point and the center of gravity indicated that the stability is relatively independent of these parameters. Another parameter study involving spring constants showed that the stability of each mode is dependent only on the spring constant acting in the direction of the leading motion of the mode. An investigation of the influence of the added mass terms showed that only the pitch‐rate and flapwise‐acceleration terms have any influence on the stability. An investigation of three different profiles showed that the stability is heavily dependent on the aerodynamic characteristics of the profiles—mainly on the lift. It was also shown that only the edgewise mode is unstable in deep stall. Moreover, independent of the amount of temporal lag in the aerodynamic response of the model, the inflow‐angle region in the vicinity of 180° remains unstable in the edgewise mode. Therefore, this inflow‐angle region may create stability problems in real life. The other type of vibrations potentially present at standstill conditions is vortex‐induced, being outside the scope of the present study. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Determination of dynamic accuracy of manipulation systems of robots with elastic hinges

Two mathematical models for determining the dynamic accuracy of manipulation systems of robots with elastic hinges are considered. Mathematical models are the implementation of the method based on the Lagrange equation and using the transformation matrices of elastic coordinates. Mathematical models make it possible to determine the elastic deviations of manipulation systems of robots from programmed motion trajectories caused by elastic deformations in hinges, which are taken into account in directions of change of the corresponding generalized coordinates. One model is the exact implementation of the Lagrange method and makes it possible to determine the total elastic deviation of the manipulation system from the programmed motion trajectory. Another mathematical model is approximated and makes it possible to determine small elastic quasi-static deviations and elastic vibrations. The results of modeling the dynamics by two models are compared to the example of a three-link manipulation system. The considered models can be used when performing investigations of the mathematical accuracy of the manipulation systems of robots.

Analysis of the flexural mode response of a novel trimaran by segmented model test

A novel ship concept design is significantly an adhoc process. In the preliminary design stage of novel vessels, it is very important to be able to develop an initial estimate of the effects of stiffness and mass distribution on the longitudinal flexural natural frequencies due to different general arrangements in still water at zero speed to satisfy design specifications. For new emerging designs, this estimate has to be made based on a model test. The experiments should also be planned so that scales effects and other features that are not present in full scale case, are minimized. A model with a length of 1.5 meter has been selected. The model was cut into four segments longitudinally and connected by a backbone beam with three elastic hinges joining the four segments. Wet vibration tests were conducted on the model, showed significant influences on the flexural natural frequencies through variations in stiffness and different mass distributions. The whipping frequency was calculated with four degrees of freedom theoretical model to compare with the experimental results. The theoretical model shows a good agreement with the experimental results.

Free Vibrations of Beam System Structures with Elastic Boundary Conditions and an Internal Elastic Hinge

The study of the dynamic properties of beam structures is extremely important for proper structural design. This present paper deals with the free in-plane vibrations of a system of two orthogonal beam members with an internal elastic hinge. The system is clamped at one end and is elastically connected at the other. Vibrations are analyzed for different boundary conditions at the elastically connected end, including classical conditions such as clamped, simply supported, and free. The beam system is assumed to behave according to the Bernoulli-Euler theory. The governing equations of motion of the structural system in free bending vibration are derived using Hamilton's principle. The exact expression for natural frequencies is obtained using the calculus of variations technique and the method of separation of variables. In the frequency analysis, special attention is paid to the influence of the flexibility and location of the elastic hinge. Results are very similar with those obtained using the finite element method, with values of particular cases of the model available in the literature, and with measurements in an experimental device.

Incorporation of flexural hinge fatigue-life cycle criteria into the topological design of compliant small-scale devices

The design synthesis of compliant mechanisms yields optimized topologies that combine several stiff parts with highly elastic flexural hinges. The hinges are often represented in a finite element analysis by a single node (one-node hinge), which leaves the actual physical meaning of the hinge (to be fabricated) ambiguous. In order to circumvent this problem, in this work, one-noded hinges have the fatigue-life incorporated into them during the design synthesis by embedding analytical expressions accounting for stress concentration, surface finish, non-zero mean stresses and superposed multiple loading conditions into the formulation. Various flexural hinges with rectangular, circular and parabolic profile geometries are investigated. By incorporating the hinge geometry and fatigue behavior into the design process, unclear interpretation issues that would be encountered during any later manufacturing stage of a compliant mechanism design are removed. Examples are provided to illustrate the overall process.

C25 空気圧ベローズを用いた多自由度微動ステージのためのアクチュエータユニットとその位置決め特性(M-OS5-1 空気圧制御の高度化,M-OS5 フルードパワーの基礎と応用,「海を越え,国を越え,世代を超えて!」)

The demand for ultra precise positioning of nanometer-order is increasing with the progress of nanotechnology in semiconductor industry. Previously we developed the one axis stage driven by pneumatic bellows for such a demand, and realized ultra precise positioning and long stroke. However, not only a one axis stage, but also a stage with multiple degrees of freedom is often demanded in semiconductor industry. In this paper, we proposed the actuator unit composed a bellows and elastic hinge guide, and show the fine movement stage with 3 degree of freedom applying proposed actuator units. The characteristics of the pneumatic bellows actuator unit are also evaluated and the positioning accuracy of the actuator unit is 50 [nm] or less, which is same level with the accuracy of one axis stage. It is found that the actuator unit can also realizes ultra precise positioning and long stroke though we must improve the control of the stage to eliminate the small vibration in the transient response.

Establishment and Development of Torque Metrology in CSIR-NPL for Providing the Traceability in Torque Measurements to User Industries

Torque primary standard machines are established at CSIR-NPL, India to realize the torque scale and to disseminate the same for user industries for providing the traceability in torque measurement. Two torque machines, a primary standard machine comprising of elastic hinge supported load lever with scale pan having an uncertainty of ±0.01 % and a secondary standard machine comprising of an unsupported lever arm with a scale pan suspended by a knife edge having an uncertainty of ±0.05 %, are established. The uncertainty of these machines are estimated theoretically by considering the uncertainty contributions of various input quantities which is also reaffirmed through the inter-comparison carried out on these machines.

Precision Control of Magnetic Drive Actuator Used for Laser Cutting with Compensation of Zero Point of Displacement Sensor

This paper describes a precision control method for a magnetic drive actuator used for the laser cutting to realize high speed and high accuracy machining. Firstly, a zero bias current method is applied to drive the electromagnets to achieve a high-precision and long-stroke of the actuator. Secondly, a compensation method of the zero point of the displacement sensors is presented to prevent the generation of the disturbance force produced by the elastic hinges. Finally, the positioning performance of the actuator is evaluated through experiments and the experimental results show that the actuator has a positioning resolution of the order of micrometer, a bandwidth greater than 130Hz, and a positioning stroke of 1mm.

Determination of Isospectral Nonuniform Rotating Beams

In this paper we look for nonuniform rotating beams that are isospectral to a given uniform nonrotating beam. A rotating nonuniform beam is isospectral to the given uniform nonrotating beam if both the beams have the same spectral properties, i.e., both the beams have the same set of natural frequencies under a given boundary condition. The Barcilon-Gottlieb type transformation is proposed that converts the governing equation of a rotating beam to that of a uniform nonrotating beam. We show that there exist rotating beams isospectral to a given uniform nonrotating beam under some special conditions. The boundary conditions we consider are clamped-free and hinged-free with an elastic hinge spring. An upper bound on the rotation speed for which isospectral beams exist is proposed. The mass and stiffness distributions for these nonuniform rotating beams which are isospectral to the given uniform nonrotating beam are obtained. We use these mass and stiffness distributions in a finite element analysis to show that the obtained beams are isospectral to the given uniform nonrotating beam. A numerical example of a beam having a rectangular cross section is presented to show the application of our analysis.

콘크리트 회전형 기둥의 비선형 횡방향 거동 및 단면응력 분포 분석

Fixed connection is generally used for beam and column connections of concrete structures, but significant damages at the connection due to severe earthquakes have been reported. In order to reduce damages of the connection and improve seismic performance of the connection, several innovative connections have been suggested. One newly proposed connection type allows a rotation of the connection for applications in rotating or rocking beams, columns, and shear walls. Such structural elements would provide a nonlinear lateral force-displacement response since their contact depth developed during rotation is gradually reduced and the stress across the sections of the elements is non-linearly distributed around a contact area, which is called an elastic hinge region in the present study. The purpose of the present study is to define the elastic hinge region or length for the rocking columns, through investigating the cross-sectional stress distribution during their lateral behavior. Performing a finite element analysis (FEA), several parameters are considered including axial load levels (5% and 10% of nominal strength), different boundary conditions (confined-ends and cantilever types), and slenderness ratios (length/depth

Generation of nanometer displacement using reduction mechanism consisting of torsional leaf spring hinges

Displacement reduction mechanisms based on the leverage provided by elastic leaf springs and flexure hinges are widely used due to the high positioning repeatability and the capability of linear motion. One application is to provide the precise motion needed for use as a standard for nanometer displacement. However, a large reduction ratio exceeding 1/1000 has not yet been achieved because the fulcrum cannot withstand the large stress induced by the accumulated force produced by the mechanism. We have developed a displacement reduction mechanism based on torsional leaf spring hinges that can provide a reduction ratio of over 1/1000. The hinge is of solid construction and consists of four leaf springs arranged radially around an axis with a circular platecapping each end. The hinge provides accurate twisting around the centralaxis and accurate reduction without deformation of the fulcrum. This paper describes the characteristics of the displacement reduction system, which can demonstrably producea 1-nm step displacement. The dynamic characteristics were examined by analyzing the transfer function of the system for a nanometer displacement. Furthermore, the motionalcapability of the mechanism was demonstrated by producing sinusoidal, triangular, and rectangular wave nanometer-scale displacements.

Free transverse vibration of rotating blades in a bladed disk assembly

This paper investigates the natural frequency of free transverse vibration of blades in rotating disks to examine the relationship of natural frequencies, blade stiffness and nodal diameters to study how neighboring blades react upon each other and affect blade natural frequency. With the use of elastic hinge theory and a cantilever beam model subjected to either a transverse concentrated force or a bending moment at the free end, the force-deflection stiffness/moment-rotation stiffness of the beam have been developed. Thereafter, the reaction forces and moments from the neighboring blades have been determined without the need for an exact solution of large deformation of cantilever beams including geometrical nonlinearity effects. With the use of the energy conservation principle and modal theory, the natural frequency of free transverse vibration of blades in rotating disks has been determined for any nodal diameter. A comparison of the analytical and finite element solutions for a bladed disk with uniform aerofoils shows that the analytical method presented in this paper is accurate.

Nano positioning control for dual stage using minimum order observer

A nano positioning control is developed using the ultra-precision positioning apparatus such as actuator, sensor, guide, power transmission element with an appropriate control method. Using established procedures, a single plane X-Y stage with ultra-precision positioning is manufactured. A global stage for materialization with robust system is combined by using an AC servo motor with a ball screw and rolling guide. An ultra-precision positioning system is developed using a micro stage with an elastic hinge and piezo element. Global and micro servos for positioning with nanometer accuracy are controlled simultaneously using an incremental encoder and a laser interferometer to measure displacement. Using established procedures, an ultra-precision positioning system (100 mm stroke and ±10 nm positioning accuracy) with a single plane X-Y stage is fabricated. Its performance is evaluated through simulation using Matlab. After analyzing previous control algorithms and adapting modern control theory, a dual servo algorithm is developed for a minimum order observer to secure the stability and priority on the controller. The simulations and experiments on the ultra precision positioning and the stability of the ultra-precision positioning system with single plane X-Y stage and the priority of the control algorithm are secured by using Matlab with Simulink and ControlDesk made in dSPACE.