Spring Actuator Research Articles

Modified PID like fuzzy servo control applied to smart actuator based miniature Parallel Robot

Miniature flexible parallel robots, popularly used for micro positioning application demands the use of non conventional actuators. Shape memory alloys (SMA) are popular smart actuators because of its light weight, integration compatibility, ease of actuation and high power density. Inclusion of shape memory alloy actuators to the parallel robot brings in control challenges due to its nonlinearity, coupling effects and cocontraction of antagonistic pair of actuators in the mechanism in order to achieve bi directional motion. In this paper, a PID like fuzzy controller is designed and applied to a nonlinear SMA spring actuator connected to a symmetric 2 DOF miniature parallel robot. The fuzzy rules are designed from the general response plot and modified to be applied to a parallel mechanism which involves cocontraction of antagonistic actuators. The paper has also presented the control and electrical circuit design used in the experimental set up. The fuzzy control is implemented in the hardware controller with model based position feedback and tested for the trajectory tracking characteristics of the end effector with disturbances. Experimental results are presented with quantitative analysis to show the effectiveness of the proposed controller in handling nonlinearities and disturbances compared to the conventional PID control and nonlinear Sliding mode control (NSMC). The test results has demonstrated the superior nature of proposed control over other controllers in the trajectory tracking with disturbances and also linearizing the hysteresis of controlled system.

An Extended Three-Dimensional Finite Strain Constitutive Model for Shape Memory Alloys

AbstractA 3D finite-strain constitutive model for shape memory alloys (SMAs) is proposed. The model can efficiently describe reversible phase transformation from austenite to self-accommodated and/or oriented martensite, (re)orientation of martensite variants, minor loops, latent heat effects, and tension–compression asymmetry based on the Eulerian logarithmic strain and the corotational logarithmic objective rate. It further accounts for smooth thermomechanical response; temperature dependence of the critical force required for (re)orientation, temperature, and load dependence of the hysteresis width; and asymmetry between forward and reverse phase transformation, and it is flexible enough to address the deformation response in the concurrent presence of several phases, i.e., when austenite, self-accommodated, and oriented martensite co-exist in the microstructure. The ability of the proposed model to describe the aforementioned deformation response characteristics of SMAs under multiaxial, thermomechanical, and nonproportional loading relies on the set of three independent internal variables, i.e., the average volume fraction of martensite variants, their preferred direction, and the magnitude of the induced inelastic strain, which further allow for an implicit description of a fourth internal variable, the volume fraction of oriented as opposed to self-accommodated martensite. The calibration of the model and its numerical implementation in an efficient scheme are presented. The model is validated against experimental results associated with complex thermomechanical paths, including tension/compression/torsion experiments, and the efficiency of its numerical implementation is verified with simulations of the response of a biomedical superelastic SMA stent and an SMA spring actuator.

Dynamic Liquid Crystalline Networks for Twisted Fiber and Spring Actuators Capable of Fast Light-Driven Movement with Enhanced Environment Adaptability

Dynamic Liquid Crystalline Networks for Twisted Fiber and Spring Actuators Capable of Fast Light-Driven Movement with Enhanced Environment Adaptability

Optimization of capacity control of reciprocating compressor using multi-system coupling model

The actuator of the stepless capacity control system of a reciprocating compressor directly controls the action characteristics of the suction valve, thus changing the regulation system energy-saving effect and the operating performance of the compressor. Optimizing the structural and control parameters of the actuator can reduce the withdrawal impact of the valve plate and improve valve performance. As a mechatronic hydraulic system, the capacity control system has the characteristics of multi-system coupling, system structure and interrelated control parameters. This paper improves the operating model of the reciprocating compressor under the condition of capacity control and integrates the coupling effect between mechanical and hydraulic systems and the valve. The solution was solved using a multi-software co-simulation method and the correctness was verified through comparisons with experimental data. The effects of reset spring stiffness, actuator stroke, and return oil pressure on valve action characteristics, compressor performance, and energy-saving effect were analysed. The valve plate withdrawal speed, and the compressor performance parameters, such as operating pressure, standard capacity, indicated work, and indicated specific work as evaluation indexes, and the optimum design scheme of reset spring stiffness, actuator stroke, and return pressure is proposed. The results indicated that, under the premise of guaranteeing control effect and compressor performance, the capacity control system of the reciprocating compressor with optimized parameters reduces valve plate withdrawal speed by 10.8%, improves valve performance, saves energy, and reduces unit maintenance costs.

Simultaneous measurements for the interlink of electro-thermo-mechano-electro characteristics in shape memory springs

This experimental study aimed to obtain the actuation properties of Shape Memory Alloy (SMA) spring actuators available under the commercial names of Biometal® NiTiCu and KRL® NiTi NiTiCu, NiTiFe. An objective is to characterize the electro-thermo-mechano-electro behavior of shape memory spring through experimentation via simultaneous measurement techniques. These measurements are synchronized by embedding an impedance analyzer and data acquisition module through a unique program. Moreover, to obtain the mathematical model by parts of the SMA spring and equivalent circuit analysis of active spring through their electro-thermo-mechano-electro characteristics exhibited during shape memory effect. Based on the experimental results, the SMA spring’s equivalent circuit is considered a series resistance – inductance circuit. It was found from the experimental results that the Biometal® actuator produced more resistance, inductance variation and offered more displacement as compared to KRL® actuators.

Effect of biasing conditions on the performance of a SMA spring actuator under thermo-mechanical loading

This paper presents an extension of the existing phase kinetics model of shape memory alloy (SMA) wire on a SMA spring actuator. The phenomenological modeling of an SMA spring under two different bias conditions – SMA spring with (A) normal spring (B) SMA wire along with the computing algorithm is addressed. The results of Case A are found in close agreement with the published literature. Whereas, the results of Case B are reported for the first time and outperform the results of Case A in terms of equal deflection, more controllability, and degrees of freedom as compared with Case A.

Fine resolution smart force sensor based on lever arm mechanism using shape memory alloy spring

SummaryA novel force measurement technique using the variable resistance property of shape memory alloy (SMA) spring is presented. The unique abilities of SMA, a smart material make it a potential candidate to construct actuators and dampers and of late is added to the domain of sensing technology in the design of creative sensing systems. The sensing mechanism is realized using a lever arm made of less stiff acrylic material; one of the links of the lever arm is integrated with an SMA spring actuator that is connected perpendicular to the stationary base, and the unknown load is placed at the other link; the force due to the measurand and the transmitted force act on the arms of the lever. The displacement due to the application of force on one of the flexible arms causes a variation in the strain that leads to resistance variation of the Joule‐heated SMA spring attached at the other arm. The active sensor possesses static and dynamic sensing capabilities and can detect force in the range of a few millinewtons, and the sensor design is validated from the experimental measurements and analytical results. The performance of the sensor is evaluated from its static and dynamic characteristics and depicts promising results. The design methodology of the sensor mechanism and selection of material suitable to offer flexible transformation of force leads to the development of a force sensor with fine resolution.

Laboratory-Scale Processing and Performance Assessment of Ti\u2013Ta High-Temperature Shape Memory Spring Actuators

Ti75Ta25 high-temperature shape memory alloys exhibit a number of features which make it difficult to use them as spring actuators. These include the high melting point of Ta (close to 3000 °C), the affinity of Ti to oxygen which leads to the formation of brittle α-case layers and the tendency to precipitate the ω-phase, which suppresses the martensitic transformation. The present work represents a case study which shows how one can overcome these issues and manufacture high quality Ti75Ta25 tensile spring actuators. The work focusses on processing (arc melting, arc welding, wire drawing, surface treatments and actuator spring geometry setting) and on cyclic actuator testing. It is shown how one can minimize the detrimental effect of ω-phase formation and ensure stable high-temperature actuation by fast heating and cooling and by intermediate rejuvenation anneals. The results are discussed on the basis of fundamental Ti–Ta metallurgy and in the light of Ni–Ti spring actuator performance.

Scaling and development of elastic mechanisms: the tiny strikes of larval mantis shrimp.

Latch-mediated spring actuation (LaMSA) is used by small organisms to produce high acceleration movements. Mathematical models predict that acceleration increases as LaMSA systems decrease in size. Adult mantis shrimp use a LaMSA mechanism in their raptorial appendages to produce extremely fast strikes. Until now, however, it was unclear whether mantis shrimp at earlier life-history stages also strike using elastic recoil and latch mediation. We tested whether larval mantis shrimp (Gonodactylaceus falcatus) use LaMSA and, because of their smaller size, achieve higher strike accelerations than adults of other mantis shrimp species. Based on microscopy and kinematic analyses, we discovered that larval G. falcatus possess the components of, and actively use, LaMSA during their fourth larval stage, which is the stage of development when larvae begin feeding. Larvae performed strikes at high acceleration and speed (mean: 4.133×105rads-2, 292.7 rad s-1; 12 individuals, 25 strikes), which are of the same order of magnitude as for adults - even though adult appendages are up to two orders of magnitude longer. Larval strike speed (mean: 0.385 m s-1) exceeded the maximum swimming speed of similarly sized organisms from other species by several orders of magnitude. These findings establish the developmental timing and scaling of the mantis shrimp LaMSA mechanism and provide insights into the kinematic consequences of scaling limits in tiny elastic mechanisms.

Functional morphology of the raptorial forelegs in Mantispa styriaca (Insecta: Neuroptera)

The insect leg is a multifunctional device, varying tremendously in form and function within Insecta: from a common walking leg, to burrowing, swimming or jumping devices, up to spinning apparatuses or tools for prey capturing. Raptorial forelegs, as predatory striking and grasping devices, represent a prominent example for convergent evolution within insects showing strong morphological and behavioural adaptations for a lifestyle as an ambush predator. However, apart from praying mantises (Mantodea)—the most prominent example of this lifestyle—the knowledge on morphology, anatomy, and the functionality of insect raptorial forelegs, in general, is scarce. Here, we show a detailed morphological description of raptorial forelegs of Mantispa styriaca (Neuroptera), including musculature and the material composition in their cuticle; further, we will discuss the mechanism of the predatory strike. We could confirm all 15 muscles previously described for mantis lacewings, regarding extrinsic and intrinsic musculature, expanding it for one important new muscle—M24c. Combining the information from all of our results, we were able to identify a possible catapult mechanism (latch-mediated spring actuation system) as a driving force of the predatory strike, never proposed for mantis lacewings before. Our results lead to a better understanding of the biomechanical aspects of the predatory strike in Mantispidae. This study further represents a starting point for a comprehensive biomechanical investigation of the convergently evolved raptorial forelegs in insects.

Development of Subcarangiform Bionic Robotic Fish Propelled by Shape Memory Alloy Actuators

In this paper, a shape memory alloy (SMA) actuated subcarangiform robotic fish has been demonstrated using a spring based propulsion mechanism. The bionic robotic fish developed using SMA spring actuators and light weight 3D printed components can be employed for under water applications. The proposed SMA spring-based design without conventional motor and other rotary actuators was able to achieve two-way shape memory effect and has reproduced the subcarangiform locomotion pattern. The positional kinematic model has been developed and the dynamics of the proposed mechanism were analysed and simulated using Automated Dynamic Analysis of Mechanical Systems (ADAMS). An open loop Arduino-relay based switching control has been adopted to control the periodic actuation of the SMA spring mechanism. The undulation of caudal fin in air and water medium has been analysed. The caudal fin and posterior body of the developed fish prototype have taken part in undulation resembling subcarangiform locomotion pattern and steady swimming was achieved in water with a forward velocity of 24.5 mm/s. The proposed design is scalable, light weight and cost effective which may be suitable for underwater surveillance application.

Towards Gut Microbiota Sampling Using an Untethered Sampling Device

Recent studies suggest that human gut microbiota can act as a bio-marker for human health. Also, it can function as a potential tool to understand stress and anxiety. However, the conventional tools have limitations acquiring samples of gut microbiota without contamination. In this work, an untethered robotic capsule prototype is developed that can actively collect the microbiota from the mucosa layer of the small intestine for the first time with the potential to avoid the upstream and downstream contamination. An analytical model for quantifying the peristaltic forces and developing two-way shape memory alloy spring actuator is presented. For the first time, a novel two-way shape memory alloy spring actuator (5 mm x $\phi ~4$ mm) is used to perform the sampling inside the gut. The spring actuator can apply 675 mN force, which is sufficient to perform in vivo sampling. A specialised experimental setup that can keep the freshly dissected intestine alive for 6 hours is utilised to test the robotic capsule. The robotic capsule prototype has collected an average of $200~\mu L$ and $112~\mu L$ sample from living pig duodenal and ileal tissues respectively i.e. in the presence of peristaltic forces. The robotic capsule was also tested on intestine of other species including cow and sheep and collected an average of $160~\mu L$ and $185~\mu L$ of content respectively from the living post-mortem tissues. The collected sample size for all the species is feasible to analyse the microbiota through next generation sequencing techniques. The experimental setup is a reliable proxy to in-vivo behaviour and the robotic capsule experimental result is promising in terms of in situ collection of microbiota.

산업 노동자의 들기 작업 시 허리 통증을 예방하기 위한 수동 모듈형 외골격 시스템 개발

This paper deals with the development of a passive modular hip exoskeleton system aimed at preventing musculoskeletal low back pain, which commonly occurs in heavy weight transport workers, by improving back muscle strength. The passive exoskeleton system has the advantage of being lightweight, making it suitable for modular exoskeleton systems. The cam and spring actuator designed in this study was applied to the passive modular exoskeleton system to build human hip and lumbar muscle strength. In order to evaluate the effectiveness of the passive modular exoskeleton system, a test was performed in which a subject lifted a 15 kg weight three times in a stoop posture, using heart rate measurement and Borg scale recording. According to the results, all subjects showed 26.83% lower maximum heart rate and 34.73% lower average heart rate than those who did not wear the system, and Borg scale evaluation result was lower. All subjects wore this system and did not experience back pain during the experiment. Through this study, we validated the effectiveness of the passive modular exoskeleton system and proved that this system can build the strength of industrial workers and be a solution to prevent musculoskeletal lumbar disease.

Self-shaping building skin: Comparative environmental performance investigation of shape-memory-alloy (SMA) response and artificial-intelligence (AI) kinetic control

This paper presents the first controlled experimental investigation on the environmental performance of self-shaping adaptive façade, which is a kinetically-responsive building skin activated by smart material. Although adaptive façade is an emerging subject in architectural design and research, its effectiveness has been rarely addressed in terms of building performance. Thus, in this study, we investigated indoor temperature and daylight illuminance of a thermo-responsive skin actuated by shape-memory alloy (SMA). For comparative analysis in a controlled situation, two identical lab-scale (1:20) building models with kinetic louver shading were designed, representing a south-oriented living room of 3.4 m✕5.2 m. The shadings were climate-adaptively operated by a conventional electromagnetic motor (baseline) and an SMA actuator (test case), respectively, for the same time period. The mechanical characterization and simulation of SMA-bias coil spring actuation were studied, and an artificial neural networks (ANNs) model was employed for the baseline's optimal dynamic control to approximate the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) Standard for thermal comfort (19.4–27.8 °C) and a minimum illuminance level of 500 lx. The study's findings indicate that SMA actuation is effective for controlling indoor daylight intensity, thereby improving overall indoor environmental conditions. Nevertheless, the climate-responsive self-shaping was not as instantaneous as the optimal kinetic control. Average performance was probabilistically different; however, a significant correlation was found in illuminance variation.

Two‐Dimensional Electromechanically Transformable Metasurface with Beam Scanning Capability Using Four Independently Controllable Shape Memory Alloy Axes

AbstractThe advancements in wireless technology, especially in radar detection, where accurate target information is critically needed, have set new standards for antenna subsystems that demand higher gain and full scanning coverage in both the azimuth and elevation planes while maintaining lower cost and design simplicity. The conventional phased array usually requires complex feeding circuitry with large spatial occupancy that renders the system bulky and expensive; therefore, a reconfigurable metasurface may be a suitable alternative. Earlier research outcomes have shown different kinds of reconfigurability in designing metasurfaces for beam steering. Designing electrically reconfigurable metasurfaces using PIN diodes, varactor diodes, etc., is a well‐known approach; however, these methods suffer from poor isolation of switches, limited power handling due to nonlinearities, high cost, and complicated biasing networks. This work proposes a novel electromechanically transformable metasurface working as a beam‐steering surface with a wider tuning range in the azimuth plane and a simplified independent switching mechanism. The incorporation of four shape memory alloy (SMA) actuator springs allows swift movements in eight different directions. The electrical control of the pitches of the four springs oriented along the four different SMA axes enables adequate mechanical transformation of the 2D metasurface to obtain beam coverage capability.

Dual adaptive robust control for uncertain nonlinear active suspension systems actuated by asymmetric electrohydraulic actuators

This study investigates the vibration control issue of active suspension systems. Unlike previous results that neglect the actuator dynamics or consider the impractical symmetrical hydraulic cylinder model, this paper incorporates more reasonable asymmetric electrohydraulic actuator into active suspension system and derives its dynamic model. However, whether active suspension or electrohydraulic actuator suffers from nonlinearities (e.g. nonlinear spring, nonlinear damper and nonlinear actuator dynamics) and parameters uncertainties (e.g. the variations of sprung mass and hydraulic fluid’s bulk modulus as well as hydraulic cylinder original control volumes) , which were rarely synthetically considered in the existing researches.To address these issues, we develop a novel dual adaptive robust controller (ARC). An ARC is firstly designed for main-loop system for stabilizing the car body and improving ride comfort in the presence of nonlinearities and parameter uncertainties as well as road disturbances. In order to meet the constraints requirements of suspension system, the tunable parameters in main-loop control law are optimized by solving linear matrix inequality with kidney-inspired algorithm. Another ARC is further synthesized for sub-loop system to deal with the nonlinear and uncertain dynamics in electrohydraulic actuator for ensuring the force tracking performance. Meanwhile, the uncertain parameters are estimated online to compensate the model deviation. The terminal control law is able to guarantee the asymptotic stability of close-loop system within Lyapunov framework. Finally, the effectiveness and robustness of the proposed controller are demonstrated via excessive simulation experiments over different road conditions.

Load–Displacement Behavior of Helical Shape Memory Alloy Spring Actuators with Small Spring Diameter to Wire Diameter Ratios

A design methodology for fabricating and predicting the load–displacement behavior of shape memory alloy (SMA) spring actuators has been previously created and validated (Nicholson et al., Smart Mater Struct 23(12):13–23, 2014). However, it was found in this work that for springs with a spring index (ratio of spring diameter to wire diameter) below five, the load–displacement response of shape memory spring actuators no longer fits the previously established model. This paper explores the use of a correction factor in the governing equations to account for the plastic deformation that occurs when fabricating springs with very small spring indices. The plastic deformation induces an effective reduction in the volume of the transforming material, thus reducing the load-bearing and actuation capabilities of the spring. A semi-analytical solution to this problem is found which can be used to predict the load–displacement behavior. This is accomplished through a reduction in the effective wire diameter based on the approximate shear strain during loading. This approach is consistent with observations during thermomechanical cycling in SMAs, where the phase transformation remained mostly unhindered despite large residual inelastic and/or plastic strains, and has direct application in the design of actuators with small spring indices by quantifying the drop in actuation force and stroke.

Simulation of Shape Memory Alloy (SMA)-Bias Spring Actuation for Self-Shaping Architecture: Investigation of Parametric Sensitivity.

Parametric complexity of the thermomechanical shape memory alloy (SMA) model is one of the major barriers to advanced application of the SMA actuation in adaptive architecture. This article seeks to provide architectural practitioners with decision-making information about SMA actuator design parameters. Simulation-based global sensitivity analysis of an SMA-bias spring actuation model reveals that the SMA spring index (a spring’s outer diameter divided by its wire diameter) and stiffness of the bias spring are significant factors in both displacement and force exertion. Among all parameters, maximum output stroke and force largely depend on the temperature range at which the SMA spring operates. These findings also indicate a trade-off between the spring diameter and wire thickness, demonstrating that the output stroke and force tend to counter one another. Appropriate preloading and choice of an optimal spring index should be considered for desirable SMA motion.

Design and analysis of serpentine meander asymmetric cantilever RF-MEMS shunt capacitive switch

In this paper, the design of asymmetric cantilever radio frequency micro electromechanical system (RF-MEMS) capacitive shunt switch is presented. The analysis and design have considered for single meander, uniform serpentine and non-uniform serpentine asymmetric cantilever RF-MEMS capacitive shunt switches were proposed. The non-uniform serpentine meander cantilever structure shows better performance compared to other structures. The actuation voltage attained for the serpentine meander cantilever is 1.1 V, 3.2 V with the spring constants 0.03 N m, 0.32 N m for the left and right cantilevers respectively. The proposed model isolations observed in-off states at left, right and both side cantilevers are − 52 dB, − 61 dB, − 45 dB at frequency of 7 GHz, 11.1 GHz, 12 GHz respectively. The proposed device insertion loss is − 0.2 dB and return loss is − 44 dB over 12 GHz is observed at on-state of the proposed model. The performance parameters are also observed for spring constant, pull in voltage, quality factor, stress analysis, switching time, resistance, inductance, capacitance, stiction loss and variation of gap with respect to spring constants and actuation voltages are calculated and analysed.

Electromechanically Deployable High-Gain Pop-Up Antenna Using Shape Memory Alloy and Kirigami Technology

This article proposes a low-cost, high-gain, and vertically polarized deployable antenna utilizing kirigami pop-up geometry. It primarily utilizes a foldable polyethylene terephthalate sheet to produce kirigami geometry in association with a rectangular radiating monopole, two reflectors, and a parasitic strip director. The reflectors and director increase the antenna gain and provide a frequency-independent tilted radiated beam with a higher beamwidth in the azimuth plane. In addition, electromechanically excited shape memory alloy (SMA) actuators enable folding and unfolding, make the antenna easily transportable and swiftly deployable. We describe the step-by-step fabrication of the kirigami geometry and shape memory spring actuator characterization. The designed, fabricated, and tested antenna achieves a −10 dB reflection bandwidth of 48.8% (1.7–2.8 GHz) providing a peak gain of more than 10 dBi at 2.45 GHz. The tilted radiated beam has a significantly wider beamwidth (90°) in the azimuth plane, compared to 40° in the elevation plane. The measured results agree well with simulations, verifying the proposed design concept. The fabricated prototype offers cost-effectiveness, more rapid fabrication, unprecedented performance, and significant potential for use in a range of microwave applications.