Analysis and evaluation of bundled SMA actuator wires

The attractive properties of shape memory alloys (SMA), especially their high energy density, steadily expand the range of applications in which SMA wires represent attractive alternative actuator components. Industrial applications in particular, oftentimes require large forces, which scale with the diameter of SMA actuator wires. The higher the required actuator force, the larger the total effective cross-sectional area of the SMA wires is needed. Increasing the SMA wire diameter results in worse actuator dynamics due to a decreasing surface-to-volume ratio and thus slower convective cooling. Instead of simply increasing the wire diameter, the bundling of several thin wires offers a suitable alternative to generate higher forces. This results in an increased surface-to-volume ratio and thus permits higher dynamic system performance. This paper discusses the mechanical and thermal behavior of SMA wire bundles and shows the influence of contact resistance inside the clamps, which is important to optimize for a long-lasting functionality of SMA bundles. In addition, the experiments show an indirect heating between single SMA wires inside a bundle, which leads to an energy saving capability up to 60%. Two electro-mechanical experiments show the behavior of SMA bundles in a constant force and a constant strain measurement. The experimental results show a maximum stroke of 4–4.5% and a generated maximum force of 1200 N. The results are discussed to provide an understanding of the mechanical characteristics of SMA bundles. In addition, an infrared (IR)-Camera provides an insight into the thermal behavior

High-Power Shape Memory Alloy Catapult Actuator for High-Speed and High-Force Applications

Nickel-Titanium (NiTi) based shape memory alloy (SMA) wires are already often used in industrial actuator applications. Their high energy density allows the building of light-weight actuator systems with high forces using small installation spaces. Combined with the biocompatibility of NiTi, a huge field of applications can be covered by SMA actuated systems. In systems like emergency brakes or switch disconnectors, which require high forces as well as high actuation speed, the high-power capability of NiTi actuators is exploited. The presented work details the development and characterization of a giant power catapult demonstrator, that combines the high-speed and high-force capability of SMA wires. To illustrate the vast force, speed, and power potential of SMA wires, a bowling ball is launched from its resting position vertically into the air using SMA wires. For demonstration purposes, a target altitude for the bowling ball of 500 mm is chosen. With the height and the overall accelerated mass given, an actuation force F≅ 920 N is needed. The instantaneous energy release from the designed power source results in the targeted flight height and an overall peak power of P≅ 0.5 MW

First-Century Sources for the Life of Muhammad? A Debate

This article proposes to interpret Surah 97 based on research undertaken in the framework of the Corpus Coranicum, project. The first part scrutinizes Christopn LUXENBERG'S seriously flawed argument that Surah 97 can be understood as a Qur'anic hymn on the Nativity of Jesus if some of its key expressions are read against the semantic background of Syriac, while the remainder of the article endeavours to develop a more tenable understanding of the text. This involves an attempt to date Surah 97 relative to other Qur'anic texts and to detect possible additions to it. In addition, the article discusses the meaning and reference of its most central term, laylat al-qadr. Finally special attention is given to the question whether the text might not, in spite of the circularity of LUXENBERG'S reading, contain implicit references to the Nativity. © Walter de Gruyter 2012

High‐Speed Antagonistic Shape Memory Actuator for High Ambient Temperatures

This work presents the development of an innovative shape memory alloy (SMA) actuator principle, which allows high-speed switching cycles through the decoupling of antagonistically arranged SMA wires. Being optimized for the use at high ambient temperatures up to 65 °C, a possible application area is the active venting of injection molds where it can be used to expel air, which is trapped during the injection mold process. The patented actuator principle is based on a decoupled agonist–antagonist SMA-spring system and allows a high-speed closing movement by a compact and lightweight design. Another innovation compared to conventional antagonistic SMA actuator systems is the integrated fail-safe mechanism, which guarantees a defined closed state in case of power failure. Subsequently, in the motivation the need for active venting valves for injection molding is first described. Second, the novel actuator principle is introduced, and the development of an electronics concept is discussed. Finally, the design process, assembly, and validation of two iterations of the actuator prototype are presented. The final prototype validation measurements showcase high performance by valve strokes of 1 mm within 100 ms at ambient temperature of 65 °C

Scalable Bi-Directional SMA-Based Rotational Actuator

In industrial applications, rotatory motions and torques are often needed. State-of-the-art actuators are based on either combustion engines, electro-motors, hydraulic, or pneumatic machines. The main disadvantages are the construction space, the high weight, and a large amount of needed peripheral devices. To overcome these limitations, compact and light-weight actuator systems can be built by using shape memory alloys (SMAs), which are known for their superior energy density. In this paper, the development of a scalable bi-directional rotational actuator based on SMA wires is presented. The scalability was based on a modular design, which allowed the actuator to be adapted to various application specifications by customizing the rotational angle and the output torque. On the mechanical side, each module enabled a small rotatory motion, which added up to the total angle of the actuator. The SMA wires were arranged in an agonist-antagonist configuration to provide active rotation in both directions. The presented prototype achieved a total rotation of 100°. The modularity of the mechanical concept is also reflected in the electronics, which is discussed in this paper as well. This consideration allows the electronics to be adapted to the mechanics with minimal changes. As a result, a prototype, including the presented mechanical and electronic design, is reported in this study

Advanced design and control concepts for actuators based on shape memory alloy wires

Intelligente Materialien eröffnen durch ihre einzigartigen Formfaktoren ganz neue Designmöglichkeiten und ihre Eigenschaft, Aktorik mit Sensorik zu kombinieren, kann in multifunktionalen Systemen zu bisher ungenutzten Mehrwerten führen. Gleichzeitig führt die hiermit verbundene Komplexität zu neuen Herausforderungen bei der Entwicklung und Ansteuerung von Systemen, sodass es bisher trotz der Vielzahl an Vorteilen noch vergleichsweise wenige kommerzielle Produkte gibt. Diese Dissertation setzt sich als Ziel, diese Herausforderungen zum einen durch die Entwicklung einer systematischen Konstruktionsmethodik als auch durch die beispielhafte Illustration von Konstruktionslösungen anzugehen. Sie konzentriert sich dabei speziell auf das Technologiefeld der Formgedächtnislegierungen (FGL) und erläutert nach einer grundlegenden Einführung in den Entwurf von FGL-Aktorsystemen die intelligente Kopplung von FGL-Aktordrähten mit bistabilen, nichtlinearen Federelementen. Durch diese Kombination lassen sich die oft zitierten Nachteile von FGL – langsame Aktuierung und Energieineffizienz – für viele Anwendungen eliminieren. Ein zweiter Weg zu hoher Geschwindigkeit und Energieeffizienz liegt in der Ansteuerung mit Pulsen bei hohen elektrischen Spannungen. Zusammenfassend zeigt diese Arbeit innovative und gleichzeitig systematische Konzepte zur Entwicklung von FGL-Aktoranwendungen auf und möchte damit einen Beitrag zur weiteren zukünftigen Verbreitung dieser noch jungen Technologie leisten.Versatility and variability in form factor of smart materials, combined with their actuation and sensing abilities, allow for the design and construction of multifunctional systems. These systems add value to industrial and consumer products. Despite the considerable number of advantages, only a few smart-material-based actuator-sensor-systems are commercially available, mainly due to challenges in design, fabrication, and control of these materials. This dissertation attacks these challenges by providing a systematic design framework, as well as exemplary illustrations of design solutions. Special focus of this work is on the technological field of shape memory alloys (SMA). After a basic introduction to the design of SMA actuator systems, the intelligent combination of SMA actuator wires with bi-stable, nonlinear spring elements is described. This combination eliminates oftentimes-quoted disadvantages of SMAs – slow actuation and energy-inefficiency – for a wide range of applications. A second approach for the realization of high-speed actuation and energy-efficiency is the activation of SMA wires with high voltage pulses, which leads to actuation times in the millisecond-range and energy-savings up to 80 % in comparison to the suppliers’ recommendations. In summary, this thesis demonstrates innovative, and at the same time systematic concepts for the design and control of SMA actuator systems. Thus, it aims at contributing to future spreading of this still young technology

Methods of Dating Muslim Traditions

There are hardly any sources available for the historically most important period of Islam, its first 150 years of existence. We only have at our disposal traditions that can be found in later written collections. The historical reliability of these traditions is doubtful because religious and political developments possibly - sometimes even demonstrably - have distorted, embellished or even created such traditions

A unified approach to thermo-mechano-caloric-characterization of elastocaloric materials

This paper presents a novel approach to characterizing the relevant mechanical, thermal and caloric properties of elastocalorics material in a single testing device. Usually, tensile experiments are performed to determine the rate- and process-depending stress/strain behavior of nickel-titanium-based shape memory alloys and potentially other elastocaloric materials made from metallic alloys. These tests are relevant for, e.g., characterization of hysteresis properties and subsequent calculation of mechanical work input. In addition, simultaneous observation with an infrared camera is useful to understand temperature evolution and maximum temperature changes achievable during the loading/unloading process. Characterization of the caloric properties of the materials determines latent heats and, together with the mechanical work, also the material coefficient of performance. It is typically carried out via differential scanning calorimetry (DSC), which is performed in a separate device and requires a second experiment with different types of samples. Furthermore, DSC measurements do not reflect the way mechanically induced phase transformations trigger the release and absorption of latent heats as it is the case for elastocalorics. In order to provide a more consistent understanding of the relevant elastocaloric material properties, we here present a novel method that (a) allows for a systematic determination of load-dependent latent heats and (b) introduces a comprehensive testing setup and suitable testing routine to determine the mechanical, thermal and caloric parameters in the same experimental device and with the same sample, thus greatly simplifying the overall procedure

Performance-Optimized Dielectric Elastomer Actuator System with Scalable Scissor Linkage Transmission

Thanks to their outstanding properties, in the last few years Dielectric Elastomer Actuators (DEAs) have increasingly attracted the interest of the scientific community and generated a surge in the effort devoted to their industrialization. Compared to conventional actuator systems, DEAs are based on inexpensive and widely available polymeric materials, which make them potentially attractive from a market perspective. However, DEA systems with a given layout and dimensions have a fixed force-stroke response that is only suitable for a specific load profile. This leads to a wide variety of designs combined with small production volumes and high costs, limiting the competitive advantage. This work addresses this issue by proposing a combination of DEA systems with compliant scissor linkage transmission mechanisms, which provide linear stroke and force scaling and simultaneously maintain performance optimization by leaving the convertible energy density of the DEA unaffected. For this purpose, three systems are designed, based on a same strip-shaped DEA combined with inclined buckled beam biasing mechanisms. Two of the systems are coupled with scissor linkages that offer transmission ratios of 3:1 and 1:3, respectively, to adapt the system to different load profiles. The system design is explained in detail, and the functional principle is validated through experiments

Tilman Nagels Kritik an der Isnad-cum-matn-Analyse. Eine Replik

In a recent issue of Arabica, Tilman Nagel published a fundamental critique of the isnād-cum-matn analysis. He claims that the method is a formalistic procedure that is incapable of producing any relevant results with regard to the life of Muḥammad and that is to be regarded as a step backwards in the study of the historical Muḥammad. He also criticises the proponents of this method – most notably Gregor Schoeler and Harald Motzki – and accuses them of methodological flaws and scholarly naïveté. In particular, he argues that the proponents of this method wrongly claim that it allows the identification of ‘authentic’ traditions about the life of Muḥammad. The following article offers a critical review of Nagel's arguments. It shows that Nagel's criticism is fraught with misunderstandings and misrepresentations of the works he discusses and that his accusations are thus unwarranted and untenable. The article also explains what the isnād-cum-matn analysis actually is and how it can be used for dating traditions, which is – in contrast to Nagel's claims – the method's primary objective