Spring Actuator Research Articles

Thermomechanical behavior of NiTiPdPt high temperature shape memory alloy springs

Transformation strains in high temperature shape memory alloys (HTSMAs) are generally smaller than for conventional NiTi alloys and can be purposefully limited in cases where stability and repeatability at elevated temperatures are desired. Yet such alloys can still be used in actuator applications that require large strokes when used in the form of springs. Thus there is a need to understand the thermomechanical behavior of shape memory alloy spring actuators, particularly those consisting of alternative alloys. In this work, a modular test setup was assembled with the objective of acquiring stroke, stress, temperature, and moment data in real time during joule heating and forced convective cooling of Ni19.5Ti50.5Pd25Pt5 HTSMA springs. The spring actuators were subjected to both monotonic axial loading and thermomechanical cycling. The role of rotational constraints (i.e., by restricting rotation or allowing for free rotation at the ends of the springs) on stroke performance was also assessed. Finally, recognizing that evolution in the material microstructure can result in changes in HTSMA spring geometry, the effect of material microstructural evolution on spring performance was examined. This was done by taking into consideration the changes in geometry that occurred during thermomechanical cycling. This work thus provides insight into designing with HTSMA springs and predicting their thermomechanical performance.

Robust optimisation of the spring actuator in a vacuum circuit breaker

We present a concept of robust optimisation design for the spring actuator in a 10 kV/12.5 kA vacuum circuit breaker. We assume the breaking and closing velocity characteristics, which are derived form the technical data of the interrupter, as the specifications for the problem, and take the lengths of the connecting rods of the actuator and the stiffness coefficients of the breaking and closing springs as the optimisation variables. The variance between the specifications and the velocities calculated at each breaking and closing point and the maximal variation allowed by the design variables within acceptable tolerances make up the multiple objective function. The optimal parameters for the spring actuator are given by solving a non-linear programming problem with multiple targets and two-level optimisation.

Design and implementation of shape memory alloy-actuated nanotweezers for nanoassembly

Reliable and accurate tools for nanoscale manipulation are constantly sought to complement new breakthroughs in nanomaterials and nanotechnology. In this study, a new design of electrically actuated nanotweezers was developed for manipulation of individual nanowires. The design featured two chemically etched tungsten tips attached to a carbon fiber-reinforced polymer and two shape memory alloy actuators. The shape recovery effect of the spring actuators was exploited as a control mechanism for the bending and relaxation modes of the nanotweezers. This was activated by driving a potential difference of less than 1 V across the coils, which was considerably lower than for electromechanical micro/nanotweezers previously developed. To demonstrate the pick-and-place capability of the system, experiments were implemented inside the vacuum chamber of a JEOL-JSM 6300 SEM. Individual Au nanowires averaging 5–10 µm in length and 200 nm in diameter were assembled on silicon substrates using the tungsten tips to draw initials out of various nanowire shapes such as curls, loops, crosses, and zigzags. With such capability, the nanotweezers may find applications in the manufacturing of complex nanostructures or modification of surface properties of materials.

New developments and operation of the MX beamline XALOC at ALBA synchrotron

BL13-XALOC is a Macromolecular Crystallography beamline at the 3-GeV ALBA synchrotron near Barcelona, and is operating with users since 2012. Currently being the only MX beamline at the site, XALOC has been designed to deal not only with easily automatable x-ray diffraction experiments of medium-sized crystals, but also with more complex ones that include a variety of crystal sizes and unit-cell length dimensions, crystals with high mosaic spread, and/or poorly diffracting crystals. The aim for a reliable all-in-one beamline contrasts with the trend observed lately, i.e. MX beamlines target specific characteristics of the crystals (microcrystals, large unit cells), techniques (tunability, small or large wavelengths), or to the status of the MX projects (crystal screening). The flexibility of the beamline is achieved by providing a very stable photon beam in an enery range of 5-22 keV and by changing the beam size at the sample position without loosing flux through defocusing to accomodate the dimensions of the beam to those of the sample. The beam dimensions at the sample position range from 57×5.5 µm2 FWHM (H×V) when focused to ~300×300 µm2. The dimensions of the beam are changed without varying the beam path. The beamline optics that allows this flexibility is based on an in-vacuum undulator, a Si(111) channel-cut monochromator, and a pair of KB mirrors. The defocused beam is severely affected by the slope errors of the mirrors, which produce striations on the beam profile at the sample position, mainly in the vertical direction. To minimize these striations, we have developed a new method that corrects mirror profiles by using spring actuators. The process resulted in a 4-fold reduction of the mirror slope errors, and in striations of the beam that amount only for ~10% of the nominal defocused beam profile. We expect that this uniform, tailored beam will improve the estimation of the radiation dose onto the sample, and will help in establishing a better data collection strategy. The end station includes a high accuracy single-axis diffractometer, a removable mini-kappa stage, an automated sample mounting robot, and a Pilatus6M, photon-counting detector. A new TANGO-based beamline control system (Sardana) has also been developed. Statistics of usage of the beamline and some relevant examples will be given.

Saddle-shaped, bistable morphing panel with shape memory alloy spring actuator

Bistable structures are attractive morphing components because they can transform from one stable state to another simply through the application of an external force or moment. Each stable state is preserved despite the absence of a continuous energy supply. However, its competency is quite limited because most bistable composites (unsymmetric laminated bistable composites) have limited equilibrium shape configurations after curing. Most of them are cylindrical in shape. In this paper, for the first time, we present a saddle-shaped bistable panel that can be used for various soft-morphing applications. The mechanics of the saddle-shaped, bistable panel are investigated using the Rayleigh–Ritz approximation. A simple analytical model is proposed to obtain saddle bistability and deformations. Finite element (FE) numerical analysis is also performed to validate the analytical model approach. The numerical FE analysis shows good correlation with simple analytical solutions. Furthermore, for practical, smart-structure applications of the saddle-shaped bistable panel, the FE method simulated a snap-through action induced by a shape memory alloy (SMA) spring actuator. A simple design criterion for the snap-through action of a saddle composite panel actuated by an SMA spring component is suggested, based on the FE analysis.

Low Voltage Rf Mems Capacitive Shunt Switches

Micro-electro-mechanical-systems(MEMS) switches have low resistive loss, negligible power consumption, good isolation and high power handling capability compared with semiconductor switches. Lifetime of capacitive shunt switches strongly depends on the actuation voltage so low voltage switches is necessary to enhance its performance as well as to broaden its application area. This paper presents the design and simulation of low voltage capacitive shunt MEMS switches together with its RF performance for high frequency applications. The low voltage switches are realized by lowering the spring constant of the beam using serpentine spring designs together with large capacitive area so as to achieve the good RF performance as well. The pull-in voltage is analyzed with commercial CAD finite element analysis software CoventorWare. The electromagnetic performance in terms of scattering parameters, insertion loss, and isolation are analyzed with software Ansoft HFSS10. The switches achieved insertion loss $$<$$ < 0.47 dB in on state from 2 to 40 GHz; it provided better than 25 dB isolation in off state with a capacitance ratio of 94---96. The actuation voltage as low as 1.5 V with actuation area $$110\,\times \,100\,\upmu \mathrm{m^2}$$ 110 × 100 μ m 2 along with good RF performance is reported. The design parameter optimization including selection of appropriate number of meanders and its width found to be one of the most sensitive factors affecting the spring stiffness and actuation voltage.

A room-temperature processed parylene-patterned helical ionic polymer–metal composite spring actuator with selectable active region

This paper presents a novel helical ionic polymer metal composite (IPMC) spring actuator. A room-temperature fabrication process is developed to selectively grow in situ nickel metal electrode on a coiled Nafion strip, which is patterned with parylene as a masking layer to delineate the inactive region. This method allows the helical spring actuator to be shaped in a near-constant temperature environment and minimizes the residual stress effect on the Nafion polymer, compared to other processes using thermal treatment. The developed process ensures that short-circuiting never occurs between the outer and inner electrodes of the actuator, and the active region can be designed via parylene patterning. The motion of the fabricated spring actuator is measured, and the maximal displacement reaches 1 mm at the endpoint of the spring under a 0.1 Hz 6 V square wave actuation. A microtensile experiment is performed for characterizing the stress and strain relation. The resulting Young’s moduli of the Nafion and fabricated IPMC strips are 183 and 227 MPa, respectively. Analysis based on Castigliano’s theorem is executed to derive equations related to the moment, force output, strain energy, and displacement of an arbitrary point of the fabricated spring actuator. Results show the produced moment, force, and strain energy of the operated spring actuator are in the level of 1.5 μN m, 300 mN, and 20−100 μJ, respectively.

Reducing the seat vibration of vehicle by semi active force control technique

This article focusses on reducing the axis acceleration and minimizing the vertical displacement by using an air spring actuator and active force control as a main control element. In active force control loop track the developed force of an air spring actuator is fed as a feedback to the actuator. Mamdani and sugeno type fuzzy interference system are used to develop a desired force and to estimate mass of the system respectively. The performance of the system is analyzed for both time and frequency domains and contrasted with passive suspension due to the irregular road disturbances. While developing the simulation model, quarter car suspension with seat as three degree of freedom and an air spring actuator acting as a force generator are modeled as non-linear system. The simulation result shows the effectiveness of the proposed control scheme in suppressing the undesirable effects of the suspension system.

Study of the Complex Stiffness of a Vibratory Mechanical System with Shape Memory Alloy Coil Spring Actuator

The vibration control is an important area in the dynamic of structures that seeks to reduce the amplitude of structural responses in certain critical frequency ranges. Currently, the scientific development leads to the application of some actuators and sensors technologically superior comparing to the same features available on the market. For developing these advanced sensors and actuators, smart materials that can change their mechanical properties when subjected to certain thermomechanical loads can be employed. In this context, Shape memory alloys (SMAs) may be used for developing dynamic vibration dampers which are capable of acting on the system providing proper tuning of the excitation frequency and the natural frequency. This paper aims to analyze the behavior of the stiffness and damping of a SMA helical coil spring actuator coupled to a mechanical system of one degree of freedom (1 DOF) subjected to an unbalanced excitement force and a temperature control system. By analyzing the effect of these parameters on the structural response and considering the concept of complex stiffness, it can be possible to predict the system's behavior within certain acceptable ranges of vibration, already in the design phase.

OS0903 ベルト駆動による渦巻きばね型SMA熱エンジンの試作および動作特性

OS0903 ベルト駆動による渦巻きばね型SMA熱エンジンの試作および動作特性

Mathematical Description and Static Characteristics of the Spring Actuator with Pneumatic Artificial Muscle

The article is focused on the actuator with one pneumatic artificial muscle and spring which counteracts the tensile force of the artificial muscle. Such a solution requires only one inlet and one outlet electromechanical pneumatic valve. It is suitable for the synthesis of so-called low cost bioservosystems. The paper presents mathematical description and static characteristics of individual parts of the actuator and also characteristics of the all mechanism.

Identification and Control of Shape Memory Alloys

In recent years, shape memory alloys have been used widely as actuators in microelectromechanical systems. Shape memory alloys have non-linear hysteresis behaviours and parameter uncertainties that include electrical properties such as resistance. These behavioural uncertainties limit the control accuracy of shape memory alloy actuators using mathematical models. In this article, a new method is proposed for force control of shape memory alloy spring actuators. An artificial neural network is used to identify and control the shape memory alloy actuator. The shape memory alloy spring under test is a product of the Toki Corporation; its coil diameter is 0.62 mm, the diameter of the wire is 0.15 mm, and this type of shape memory alloy actuator can produce 40 gf. The results obtained are verified by an experimental set-up, which is also used to train the artificial neural network as an identifier and a controller of the system.

Large scale simulation of NiTi helical spring actuators under repeated thermomechanical cycles

As typically utilized in applications, a shape memory alloy (SMA) actuator operates under a large number of thermomechanical cycles, hence the importance of accounting for the cyclic behavior characteristics in modeling and numerical simulation of these actuators. To this end, the present work is focused on the characterization of the cyclic, evolutionary behavior of binary 55NiTi using a newly developed, multi-axial, material-modeling framework and its finite element analysis (FEA) implementation for use in the simulations of SMA actuators. In particular, two different geometric configurations of four- and two-coil helical springs subjected to axial end-forces are investigated under the effect of a large number of thermal cycles leading to the saturated deformation state of the coils. In addition, two different boundary conditions were examined, corresponding to: (a) the loading end cross section assumed to be free-to-twist, and (b) the loading end cross section assumed to be restrained against twist rotation. The study has led to the following five important conclusions: (i) the states of stresses and strains in the coils exhibited marked spatial non-homogeneities, both along the length as well as the cross section of the wires; (ii) the cyclic deformation response of the coils exhibits a similar evolutionary character to that of the 55NiTi material when tested under simple isobaric tensile stress conditions; (iii) the end boundary conditions affect the evolution of the deformation response; (iv) the magnitudes of the evolving nonlinear deformation states (i.e., axial displacements on the martensite and austenite sides, as well as the actuation displacement) were found to be proportional to the number of coils in an essentially linear manner, and (v) the change in coil diameter, while maintaining the pitch height, wire diameter and the number of coils fixed, has a significant effect on the response of the helical spring, both with regard to the resulting stress state and the evolutionary axial displacement behavior during the thermal cycles.

Design and Aerodynamic Characteristics Analysis of a Section Morphing Wing Based on Smart Materials

This paper discusses the design of a section morphing wing that permits a change in the wing section while simultaneously supporting structural wing loads. Section morphing wing allows for two discreet airfoil of the wing. The airfoil 1 is original airfoil maintained by NACA 4412 rib sections. The section morphing wing uses shape memory alloy spring actuator to drive wing section deformation. Skins of the section morphing wing uses shape memory polymer. Computational aerodynamics are used to estimate the performance and dynamic characteristics of each wing section of this section morphing wing as its wing section is changed. Results show that when angle of attach (AOA) is 0 deg, the lift-drag ratio decrease as the airfoil thickness decreases when mach number is less than 0.9 and the lift-drag ratio increase as the airfoil thickness decreases when mach number is greater than 0.9. When AOA is 5deg, the lift-drag ratio increase as the airfoil thickness decreases . The lift-drag ratio decrease as the airfoil thickness decreases when mach number is less than 0.7. When AOA is 10deg, the lift-drag ratio increase as the airfoil thickness decreases when mach number is greater than 0.7. We can chose airfoil 1 or airfoil 2 according to variation flight conditions.

Possible options for jointly deploying a ring provided with V-fold bars and a flexible pre-stressed center

The paper presents the detailed design of a conical ring constructed with V-fold bars. The discussed designs follow recent ESA patents and have been implemented in a demonstrator model, successfully manufactured and tested. The main options investigated include spring and electric motor actuation. Installation of springs in V-fold joints as well as a release cable was the first option investigated. The demonstrator model also contemplated the use of three electric motors as actuators instead of springs in all V-fold hinges. The latter deployment actuation method was shown at the large deployable antenna workshop in ESTEC, demonstrating the performances that can be achieved by this architecture, mainly low mass, high deployed stiffness, scalability to large dimensions and potential for modularity.

Analysis of the transformations temperatures of helicoidal Ti-Ni actuators using computational numerical methods

The development of shape memory actuators has enabled noteworthy applications in the mechanical engineering, robotics, aerospace, and oil industries and in medicine. These applications have been targeted on miniaturization and taking full advantage of spaces. This article analyses a Ti-Ni shape memory actuator used as part of a flow control system. A Ti-Ni spring actuator is subjected to thermomechanical training and parameters such as transformation temperature, thermal hysteresis and shape memory effect performance were investigated. These parameters were important for understanding the behavior of the actuator related to martensitic phase transformation during the heating and cooling cycles which it undergoes when in service. The multiple regression methodology was used as a computational tool for analysing data in order to simulate and predict the results for stress and cycles where the experimental data was not developed. The results obtained using the training cycles enable actuators to be characterized and the numerical simulation to be validated.

Omega-Shaped Inchworm-Inspired Crawling Robot With Large-Index-and-Pitch (LIP) SMA Spring Actuators

This paper proposes three design concepts for developing a crawling robot inspired by an inchworm, called the Omegabot. First, for locomotion, the robot strides by bending its body into an omega shape; anisotropic friction pads enable the robot to move forward using this simple motion. Second, the robot body is made of a single part but has two four-bar mechanisms and one spherical six-bar mechanism; the mechanisms are 2-D patterned into a single piece of composite and folded to become a robot body that weighs less than 1 g and that can crawl and steer. This design does not require the assembly of various mechanisms of the body structure, thereby simplifying the fabrication process. Third, a new concept for using a shape-memory alloy (SMA) coil-spring actuator is proposed; the coil spring is designed to have a large spring index and to work over a large pitch-angle range. This large-index-and-pitch SMA spring actuator cools faster and requires less energy, without compromising the amount of force and displacement that it can produce. Therefore, the frequency and the efficiency of the actuator are improved. A prototype was used to demonstrate that the inchworm-inspired, novel, small-scale, lightweight robot manufactured on a single piece of composite can crawl and steer.

A Bio-Inspired Robot Using Electro-Conjugate Fluid

Electro-Conjugate Fluid (ECF) is a kind of functional fluid that produces a jet flow (ECF jet) when subjected to high DC voltage. A strong ECF jet is known to be generated in a nonuniform electric field, for example, a field with a pair of needle and ring electrodes. This study introduces the ECF jet in developing a novel bio-inspired robot. We first propose the concept of a robot driven by an ECF jet. The robot is mainly composed of ECF jet generators (a micro fluid pressure source), fiber-reinforced rubber actuators, a built-in spring actuator, and an ECF tank. We next investigate the characteristics of the ECF jet generator, the fiberreinforced rubber actuator, and the built-in spring actuator. As a result, we confirmed that the maximum pressure and flow rate of the ECF jet generator are 32.0 kPa and 27.0 ml/min, respectively, and that the actuators could be driven by the ECF jet. We then developed a bio-inspired robot and demonstrated that the robot could move in a 14 mm diameter acrylic half pipe with 0.6 mm/s, and in a 14 mm diameter acrylic pipe with 0.5 mm/s. The robot is 300 mm long with a mass of 26 g.

Robust control of vehicle suspension with electrohydraulic actuator

This paper presents a study on robust control of vehicle electrohydraulic suspension with parameter uncertainties. The change of sprung mass and the variation of spring stiffness, damping coefficient, and actuator parameters are considered as parameter uncertainties and described by different methods. A robust controller is then designed for the uncertain vehicle suspension model to optimise its performances on ride comfort, suspension deflection, and road holding ability considering suspension and actuator parameter uncertainties and actuator saturation. The sufficient conditions for designing such a controller are derived as linear matrix inequalities (LMIs) which can be solved using standard software. Numerical simulations are used to validate the effectiveness of the proposed approach. It is confirmed by the simulation results that the applied control strategy performs better than the passive suspension regardless of the parameter uncertainties.

복합 재료와 형상 기억 합금 코일 스프링 구동기를 이용한 유연하게 변형 가능한 바퀴 로봇의 설계 및 제작

In order to operate a search and rescue robot in hazardous area, the robot requires high mobility and adaptable locomotion for moving in unpredictable environments. In this paper, we propose the deformable soft wheel robot that can produce three kinds of driving modes; caterpillar driving mode, normal wheel driving mode, legged-wheel driving mode. The robot changes its driving mode as it faces the various obstacles such as a small gap, stairs etc. Soft film and composite materials are used for fabrication of deformable wheel structure and Shape Memory Alloy (SMA) coil spring actuators are attached on the structure as an artificial muscle. Film lamination and an composite manufacturing process is introduced and the robot design is required to be modified and compromised to applying the manufacturing process. The prototype is developed and tested for verifying feasibility of the deformable wheel locomotion.