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The increasing demand for innovative grippers and actuators for the automation sector encourages the development of new and innovative functional principles. Intelligent materials are particularly suitable for this purpose based on their high energy density. In this study, a two-finger gripper driven by shape memory alloys (SMA) for use in automation technology is presented. Previous grippers driven by SMA can only be found in the field of micro gripping due to the limited stroke generated by SMA. Based on a methodical product development, a new type of gripper was developed and is presented in this study, which can achieve an opening width comparable to conventional grippers based on transmission mechanisms. Two different variants of the gripper are shown and compared aiming to minimize the installation space and weight of the gripper. In addition to the design presentation, a prototype is built, and the functionality is demonstrated through various test series. [ABSTRACT FROM AUTHOR]

The increasing demand for innovative grippers and actuators for the automation sector encourages the development of new and innovative functional principles. Intelligent materials are particularly suitable for this purpose based on their high energy density. In this study, a two-finger gripper driven by shape memory alloys (SMA) for use in automation technology is presented. Previous grippers driven by SMA can only be found in the field of micro gripping due to the limited stroke generated by SMA. Based on a methodical product development, a new type of gripper was developed and is presented in this study, which can achieve an opening width comparable to conventional grippers based on transmission mechanisms. Two different variants of the gripper are shown and compared aiming to minimize the installation space and weight of the gripper. In addition to the design presentation, a prototype is built, and the functionality is demonstrated through various test series.

Novel miniature-scale bistable actuators are developed, which consist of two antagonistically coupled buckling shape memory alloy (SMA) beams. Two SMA films are designed as buckling SMA beams, whose memory shapes are adjusted to have opposing buckling states. Coupling the SMA beams in their center leads to a compact bistable actuator, which exhibits a bi-directional snap-through motion by selectively heating the SMA beams. Fabrication involves magnetron sputtering of SMA films, subsequent micromachining by lithography, and systems integration. The stationary force–displacement characteristics of monostable actuators consisting of single buckling SMA beams and bistable actuators are characterized with respect to their geometrical parameters. The dynamic performance of bistable actuation is investigated by selectively heating the SMA beams via direct mechanical contact to a low-temperature heat source in the range of 130–190 °C. The bistable actuation is characterized by a large stroke up to 3.65 mm corresponding to more than 30% of the SMA beam length. Operation frequencies are in the order of 1 Hz depending on geometrical parameters and heat source temperature. The bistable actuation at low-temperature differences provides a route for waste heat recovery. [ABSTRACT FROM AUTHOR]

This paper aims to implement the controllable deformation of a structure using Shape Memory Alloys (SMA) actuators. A sensorless displacement estimation method is proposed. This method is tested on a prototype composed of a disc, beams, and SMA actuators. By measuring the variation of electrical resistivity in SMA springs, as a feedback signal in the closed-loop position control, the surface displacement is obtained without any external displacement sensor. The proposed method is validated by comparing the displacement values estimated by the electrical resistivity measurement with those measured by a laser sensor. The estimated displacement and the measured displacement follow the reference displacement with steady-state errors, respectively of 1.14% and 0.42%. [ABSTRACT FROM AUTHOR]

Novel miniature-scale bistable actuators are developed, which consist of two antagonistically coupled buckling shape memory alloy (SMA) beams. Two SMA films are designed as buckling SMA beams, whose memory shapes are adjusted to have opposing buckling states. Coupling the SMA beams in their center leads to a compact bistable actuator, which exhibits a bi-directional snap-through motion by selectively heating the SMA beams. Fabrication involves magnetron sputtering of SMA films, subsequent micromachining by lithography, and systems integration. The stationary force–displacement characteristics of monostable actuators consisting of single buckling SMA beams and bistable actuators are characterized with respect to their geometrical parameters. The dynamic performance of bistable actuation is investigated by selectively heating the SMA beams via direct mechanical contact to a low-temperature heat source in the range of 130–190 °C. The bistable actuation is characterized by a large stroke up to 3.65 mm corresponding to more than 30% of the SMA beam length. Operation frequencies are in the order of 1 Hz depending on geometrical parameters and heat source temperature. The bistable actuation at low-temperature differences provides a route for waste heat recovery.

One of the greatest challenges in the design of shape-memory elements (mostly binary Nickel-Titanium wires) is to ensure that the required travel (stroke) is achieved, as this is subject to variation due to various influencing factors. One way of predicting the stroke is to use a suitable energy model. In the past, for example, a model was developed by Oelschläger with which the stroke can be calculated on the basis of the electrical energy. However, so far no model takes into account the change of the phase transformation temperature. In this study, the model of Oelschläger is extended and verified to consider the degradation behavior over the whole lifetime. For this purpose, fatigue tests of 52 wires (2 different load scenarios) were performed. Based on these tests and the application of statistical methods (distribution models, goodnes-of-fit tests etc.), a target model was developed for each load scenario, which is used to verify the extended energy model. The energy model was applied to wires of both load scenarios to simulate the stroke progression. The verification of the extended simulation model shows that it is possible to simulate the longterm behavior of the stroke for one of the two load scenarios. The second load scenario shows deviations between the target model and the simulation, which is due to problems in the area of measurement equipment, convection, and temperature distribution in the wire. Nevertheless, a decisive modeling approach could be developed, which can be used to consider the long-term behavior of the phase transformation temperature of wires in simulations. [ABSTRACT FROM AUTHOR]

The rapid changes in industry during the past decade, have started to greatly affect the manufacturing environment and production facilities. Traditional production facilities are being replaced by smart factories that are based on high technological aspects using smart machines to produce smart products. Due to the shortening of products life cycle, the need for a rapid design process has become an emerging issue.However, the rapid design process is not the only challenge but also, speed and efficiency of the assembly process, after sale services and disassembly operations. Thus, design for disassembly has become an important sub-topic for the design process. As a result, product designers are now concerned with designing products that can be disassembled easily to avoid destructive separation of products, in order to minimize waste and scrap of products at their end of life. This can be done by allowing recovery of reusable components and materials so that they can be used in later generations of products, remanufacturing or recycling processes.Design for disassembly offers different disassembly techniques that can facilitate the disassembly process greatly. Active disassembly is considered as one of the most important disassembly techniques. This is due to the fact; active disassembly can provide a more generic solution for most of disassembly problems as well be discussed in the present research. As a result, the present research aims to present an overview of design for disassembly discussing its different techniques with emphasis on active disassembly focusing on its importance and advances in detail.

One of the greatest challenges in the design of shape-memory elements (mostly binary Nickel-Titanium wires) is to ensure that the required travel (stroke) is achieved, as this is subject to variation due to various influencing factors. One way of predicting the stroke is to use a suitable energy model. In the past, for example, a model was developed by Oelschläger with which the stroke can be calculated on the basis of the electrical energy. However, so far no model takes into account the change of the phase transformation temperature. In this study, the model of Oelschläger is extended and verified to consider the degradation behavior over the whole lifetime. For this purpose, fatigue tests of 52 wires (2 different load scenarios) were performed. Based on these tests and the application of statistical methods (distribution models, goodnes-of-fit tests etc.), a target model was developed for each load scenario, which is used to verify the extended energy model. The energy model was applied to wires of both load scenarios to simulate the stroke progression. The verification of the extended simulation model shows that it is possible to simulate the longterm behavior of the stroke for one of the two load scenarios. The second load scenario shows deviations between the target model and the simulation, which is due to problems in the area of measurement equipment, convection, and temperature distribution in the wire. Nevertheless, a decisive modeling approach could be developed, which can be used to consider the long-term behavior of the phase transformation temperature of wires in simulations.

In times of smart products and systems, the Internet of Things (IoT) plays an increasingly important role. IoT combines the digital world (internet) with the physical world (sensors, actuators, robots, smartphones, connected cars etc.). The autonomous operation and remote control of smart systems (e.g. smart home, production hall or line) requires efficient and specially reliable actuators and control mechanisms. Shape memory actuators are particularly suitable for this application due to their properties as they are lightweight, small, energy-efficient and can also be used as sensors at the same time. Many shape memory actuators have been developed for various applications over the past years. Despite great interest, there are no standardized test programs available. The complexity of the shape memory technology is a major challenge in testing fatigue and degradation behavior of components to determine reliability. This article presents fatigue test results of a laboratory test rig of a case study for a shape memory actuator, including all boundary conditions and test requirements. The measurement data consists of different parameters e.g. the stroke of the actuator, the electrical voltage and current (to activate the actuator) as well as the ambient temperature. Since the study comprises only a few prototypes, parametric methods are not suitable for a comprehensive evaluation, therefore parameter-free methods are used as well. The analysis regarding the description of dependencies between the recorded signals and the detection of degradation of the shape memory actuators is discussed in detail. The main objective is the development of a prognosis algorithm in order to be able to predict the failure behaviour of the actuators at an early stage. The methodical approach includes various methods and procedures, which are applied in a logical order. The statistical analytics used in this study are focusing on nonparametric significance tests, such as the Levene’s test and the u-test by Wilcoxon and Mann-Whitney. Further methods are the correlation analysis and the regression analysis as well as multivariate 3D-plots. The fundamentals of shape memory alloys, as well as the used statistical nonparametric methods, are described briefly. Finally, the realization (application of the analysis methods) based on the real test rig data of a case study consisting of 18 actuators is shown and discussed in detail.

The bend and free recovery (BFR) test according to ASTM F2082 is a standard method to determine the transition temperatures of Nitinol shape memory alloys (SMAs). Unfortunately, this standard method is limited to SMA wires which are straight in its trained shape. Thus, the standard BFR test is not suitable for thermomechanical characterization of curved Nitinol SMA wires which should serve as actuators in cochlear implants in future. We developed a modified BFR measurement setup to determine the active austenite finish (AF) temperature of these very thin wires (Ø100 μm). The active AF temperature specifies the completion of the shape recovery upon heating. A parametric study of the measurement setup was carried out to investigate the influence of the heating rate on the observed active AF temperature and to verify the repeatability of the measurement setup. First, the curved wire was straightened in a cold water bath before inserting it into a water bath that is gradually heated from 5 °C to 45 °C. The shape change of the previously straightened wire was then recorded throughout the experiment using a digital microscope. Five different heating rates were employed: 0.25 K/min, 0.33 K/min, 0.5 K/min, 1 K/min as well as an unregulated maximum heating rate achievable of approximately 1.5 K/min. Furthermore, an investigation on the test-retest reliability was performed with three wires by repeating the experiment ten times with each wire. The results of this study revealed no influence of the heating rate on the thermomechanical response of the wires. Based on data from this study, a regulated heating rate of 1 K/min is suggested for future investigations, as this reduces the duration of the measurement from four hours to less than an hour. The values obtained from each wire through the test-retest reliability investigation showed a standard deviation of 1.9 K, 1.1 K and 2.1 K respectively. Our developed measurement setup demonstrates appropriate repeatability of the measurements.

Shape memory alloy actuators (SMAA) are attractive for lightweight construction applications such as in the fields of e-mobility and aerospace due to their properties (high actuator performance, low weight, silent operation). Used force-fit and firmly bonded connections (crimping, casting) can only be released again non-destructively to a limited extent. Combined with the complex material behavior of NiTi-SMAA, the development of standardized SMAA is limited. In this paper, a novel approach based on a form-fit connection is presented. [ABSTRACT FROM AUTHOR]

The influence of fraction of the forward and reverse martensitic transformations on the variations in the recoverable strain, recovery stress, work output and irreversible strain was studied during thermal cycling of the equiatomic NiTi alloy under torque stress. The samples pre-deformed by various strain (3–7%) were subjected to thermal cycling in two regimes: in the temperature range of 450 K÷T c , where M f

Actuators based on the shape memory effect have recently become more and more economically important due to the many advantages of shape memory alloys (SMAs), such as their high energy density. SMAs are usually used to control the end/maximum positions, thus the actuators always move between two positions. The repeatable control of intermediate positions has so far proven difficult, because in most cases, external sensors are necessary to determine the length of the SMA element. Additionally control strategies for SMA actuators are rather complex due to the non-linear behavior of this material. The SMA actuator presented here is able to control intermediate positions with repeatable accuracy without the need of a separate control technology. The integrated control unit is based on a mechanical principle using a shaft with a circumference groove. This groove has a height profile that turns the shafts rotation, generated by the SMA, into a translational movement. Therefore, the SMA wire generates a partial stroke at each complete activation, turning the shaft partially. With several activation cycles in a row, the stroke adds up until reaching the maximum. A further activation cycle of the wire resets the actuators stroke to its initial position. Each part of the stroke can, thereby, be controlled precisely and repeatedly within the scope of each complete cycle of the actuator. Based on an integrated ratchet, each stroke of the actuator can hold energy free.

Major techniques currently available to implement typical shape memory materials (such as shape memory alloys and polymers) for three basic types of shape switching actuations-one-time shape memory actuation, cyclic shape memory actuation and cyclic shape change actuation-were explored in detail. Typical actuators corresponding to these three types of actuations are systematically discussed. Possible combination of different types of shape memory materials/shape change materials and/or different stimuli for actuators with novel functions, which are not easily achievable, in particular at small scale, using conventional approaches, is presented to reveal the great potential of shape memory material based actuators in engineering applications. We provide a road map to guide engineers in the process of evaluation and selection of the right type of mechanism to meet the requirement(s) of a particular application. [ABSTRACT FROM AUTHOR]

This study introduces the development of a thermally responsive shape-morphing fabric using low-melting-point polyamide shape memory actuators. To facilitate the blending of biomaterials, we report the synthesis and characterization of a biopolyamide with a relatively low melting point. Additionally, we present a straightforward and solvent-free method for the compatibilization of starch particles with the synthesized biopolyamide, aiming to enhance the sustainability of polyamide and customize the actuation temperature. Subsequently, homogeneous dispersion of up to 70 wt % compatibilized starch particles into the matrix is achieved. The resulting composites exhibit excellent mechanical properties comparable to those reported for soft and tough materials, making them well suited for textile integration. Furthermore, cyclic thermomechanical tests were conducted to evaluate the shape memory and shape recovery of both plain polyamide and composites. The results confirmed their remarkable shape recovery properties. To demonstrate the potential application of biocomposites in textiles, a heat-responsive fabric was created using thermoresponsive shape memory polymer actuators composed of a biocomposite containing 50 wt % compatibilized starch. This fabric demonstrates the ability to repeatedly undergo significant heat-induced deformations by opening and closing pores, thereby exposing hidden functionalities through heat stimulation. This innovative approach provides a convenient pathway for designing heat-responsive textiles, adding value to state-of-the-art smart textiles.

Fascinating properties of shape memory alloys, being shape memory effect and super-elasticity, make them unique in comparison to other materials. One of the most common applications of these materials is in actuators as an actuation mechanism. In this research, a shape memory actuator is presented and modeled. The Souza et al. constitutive model is employed in finite element analysis software in order to simulate the shape memory behavior of Nitinol. Ti-49.8%Ni was selected according to the proper characteristics, and its mechanical properties are characterized through experimental tests to the calibrated model for this alloy. The simulation results were further verified by empirical evaluation of a Nitinol actuator. [ABSTRACT FROM AUTHOR]

Abstract: A thin film actuator of a ferromagnetic shape memory alloy (FSMA) is presented allowing two degrees of freedom (2D) control of a bulk micromirror. The actuation mechanism is based on a simultaneous ferromagnetic and martensitic transformation. The movable parts of the actuator are designed as a monolithic device with two thermally and magnetically decoupled actuation units, which is demonstrated by coupled finite element simulations. The problem of FSMA thin film integration is solved by a novel transfer bonding process. First demonstrators of the FSMA actuator show a highly nonlinear response at low actuation voltage allowing large optical scanning angles up to 65° at tuneable frequencies. [Copyright &y& Elsevier]

A novel actuation mechanism is presented, which makes use of the antagonism of intrinsic magnetic and shape recovery forces acting on a ferromagnetic shape memory alloy (SMA) microactuator in a magnetic field. This mechanism is associated with large actuation and small biasing forces in each actuation direction resulting in a large stroke. Since no additional biasing elements are required, extremely compact designs are possible. As a demonstrator, an optical microscanner of 7 mm×3 mm×5 mm size is presented showing large scanning angles up to 120° in off-resonance mode. The scanning performance keeps frequency independent below a critical frequency, which is determined by heat transfer times. [Copyright &y& Elsevier]

A microvalve with high operation temperature ranging up to 120 °C is presented, which is driven by a TiNiPd thin film microactuator. Fabrication is based on a hybrid integration concept. The main fabrication technologies are magnetron sputtering, photochemical micromachining, and thin film transfer. Infrared microscopy investigations of temperature profiles and force-deflection tests are performed to determine optimum operation conditions of the TiNiPd microactuator. Gas flow measurements demonstrate control of pressure differences up to 70 kPa. The high phase transformation temperatures allow a cooling time of the microactuator of 22 ms at room temperature resulting in a maximum operation frequency of the microvalve of 30 Hz. [Copyright &y& Elsevier]

A microgripper system is presented, which consists of a monolithic shape memory alloy (SMA) device of 2 mm×5.8 mm×0.23 mm size and an integrated optical position sensor. Gripper closing and opening is performed by two integrated actuators, which form an antagonistic pair. Investigations of temperature profiles by coupled finite-element simulations and infrared microscopy demonstrate a sufficient thermal insulation of the actuators for their selective control. The motion of gripping jaws is transmitted by an integrated gearing mechanism into a linear motion of an integrated optical slit, which is detected by change of optical transmission. The maximum stroke and force of the gripping jaws are 300 μm and 35 mN, respectively. In the range between 10 and 90% of the maximum stroke, positioning is achieved within 140 ms with an accuracy of about 2 μm. [Copyright &y& Elsevier]

• A new elastocaloric cooling system is proposed to harvest low-grade heat. • Transition temperature gradient facilitates cascade utilization of low-grade heat. • Transition temperature gradient improves system COP by a factor of more than 5. • Optimizing transition temperature profile can further boost performance for 20%. • Solar thermal air-conditioner and refrigerator are two potential applications. Unlike the conventional elastocaloric cooling system that depends on electricity, the coupled elastocaloric power and cooling cycle proposed in this study exploits low-grade thermal energy in a cascade manner, which opens a new paradigm for the caloric cooling community. Cascade utilization of heat relies on a gradient of transition temperature inside the shape memory alloy actuator that best matches the temperature profile of the material during operation. A transient numerical model is developed to simulate the performance of this new system, and the model is experimentally validated. The transition temperature gradient should exceed 60 K for optimum utilization of input heat. At the same gradient, the distribution of transition temperature can be optimized, where at least 10% improvement over linear profile can be expected in terms of efficiency and cooling power density. Based on the superior performance, this technology could be powered by solar thermal collectors working at 110 °C and could be applied to residential air-conditioners and off-grid refrigerators. The novel system proposed in this study not only complements the existing library of heat-activated cooling technologies, but also provides a new pathway for the expansion of caloric cooling at large. [ABSTRACT FROM AUTHOR]

• Counter body stiffness influences TiNi actuator performance. • SME, recovery stress and work output non-linearly depend on stiffness. • SME, recovery stress and work output decrease on thermal cycling. • The highest work output is achieved at a stiffness of 6.3 GPa. The influence of the counter-body stiffness on the recovery stress, recoverable strain and work output variations during the thermal cycling of NiTi cylindrical samples in the actuator regime has been studied. Pre-deformed samples were connected by one side to a pendulum dynamometer with variable stiffness, which played the role of elastic counter-body, and the other sample side was fixed. Two schemes of pre-deformation under torsion mode were used: active deformation in martensite state, or cooling under constant stress. It was shown that the shape memory effect and recovery stress value depended non-linearly on stiffness values. Work output was calculated for all samples. The optimal interval of stiffness, which provided maximum output, was found in both preliminary deformation schemes used. It was shown that for samples deformed by cooling under constant stress, the values of shape memory effect, maximum recovery stress and work output were higher than for the samples pre-deformed in the martensite state. The shape memory effect, maximum recovery stress and work output values decreased on thermal cycling. [ABSTRACT FROM AUTHOR]