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Smart Actuator-Sensor Systems
In this paper, the development process of a shape memory alloy (SMA) driven pinch valve is proposed. The features of SMA actuator wires like small installation space, small weight, and the high energy density, allow for designing compact systems with high force outputs. A functional prototype is presented, allowing for closing forces of up to 250 N and 3 mm of stroke, which enables pinching hoses up to a diameter of 5 mm. It is driven by four mechanically parallel 500 µm diameter wires to open the valve and two 300 µm diameter to close the valve and cut off the medium flow inside of the hose. This SMA driven pinch valve features a spring-loaded toggle mechanism. It leads to stable and energy free position holding in both, opened and closed state of the valve, compared to commonly used valves, which allow for only one energy free position. As the system can be built without using any ferromagnetic materials the valve is predestined to be used in Magnetic Resonance Imaging (MRI). Due to the higher energy efficiency and weight reduction in comparison to commonly used solenoid pinch valves, they can be a substitute in a variety of applications.
Within industrial manufacturing, most processing steps are accompanied by transporting and positioning of workpieces. The active interfaces between handling system and workpiece are industrial grippers, which often are driven by pneumatics. On the way to better energy efficiency and digitalization, companies are looking for new actuation technologies with more sensor integration and higher efficiencies. Commonly used actuators like solenoids and electric engines are in many cases too heavy and large for direct integration into the gripping system. Shape memory alloy (SMA) actuators are suited to overcome those drawbacks of conventional actuation systems, because of their high energy density. Additionally, they feature self-sensing abilities that lead to sensor-less monitoring and control of the actuator element. Another drawback of conventional grippers is their design, which is based on moving parts with linear guides and bearings. These parts are prone to wear, especially in abrasive environments. This can be improved by a compliant gripper design that is based on flexure hinges and thus dispenses with joints, bearings and guides. In the presented work, the development process of a functional prototype for a compliant gripper driven by a bistable SMA actuator for industrial applications is outlined. The focus lies on the development of the compliant kinematics, where first results of FEM simulation are discussed. As a result, a working gripper-prototype which is manufactured with modern 3D-printing technologies is introduced.
In der industriellen Fertigung sind die meisten Bearbeitungsschritte mit dem Transportieren und Positionieren von Werkstücken verbunden. Die aktiven Schnittstellen zwischen Handhabungssystem und Werkstück sind industrielle Greifer, die vor allem im kleinteiligen Bereich oft pneumatisch angetrieben werden. Auf dem Weg zu höherer Energieeffizienz und digitalen Fabriken sind Unternehmen auf der Suche nach neuen Antriebstechnologien mit mehr Sensorintegration und besseren Wirkungsgraden. Gängige Aktoren wie Magnete und Elektromotoren sind in vielen Fällen zu schwer und groß für eine direkte Integration in das Greifsystem. Aufgrund ihrer hohen Energiedichte sind Formgedächtnislegierungen (FGL) geeignet, diese Nachteile herkömmlicher Aktuatoren zu überwinden. Zusätzlich verfügen sie über sogenannte Self-Sensing Fähigkeiten, die zu einer sensorlosen Überwachung und Steuerung des Antriebssystems führen. Ein weiterer Nachteil konventioneller Greifer ist ihr Aufbau, der auf beweglichen Teilen, die besonders in abrasiven Umgebungen schnell verschleißen. Dies kann durch Festkörpergelenke, die konventionelle Gelenke ersetzen, vermieden werden. In der vorliegenden Arbeit wird der Entwicklungsprozess eines Funktionsprototyps für einen elastischen Greifer, der von einer bistabilen FGL-Antriebseinheit angetrieben wird, für industrielle Anwendungen umrissen. Der Schwerpunkt liegt auf der Entwicklung des FGL-Antriebs, während ein erster Designansatz für den nachgiebigen Greifmechanismus mit Festkörpergelenken vorgestellt wird. Das Ergebnis ist ein funktionierender Greifer-Prototyp, der hauptsächlich aus 3D-gedruckten Teilen besteht. Erste Ergebnisse von Validierungsversuchen werden diskutiert. Abstract Within industrial manufacturing most processing steps are accompanied by transporting and positioning of workpieces. The active interfaces between handling system and workpiece are industrial grippers, which often are driven by pneumatics, especially in small scale areas. On the way to higher energy efficiency and digital factories, companies are looking for new actuation technologies with more sensor integration and better efficiencies. Commonly used actuators like solenoids and electric engines are in many cases too heavy and large for direct integration into the gripping system. Due to their high energy density shape memory alloys (SMA) are suited to overcome those drawbacks of conventional actuators. Additionally, they feature self-sensing abilities that lead to sensor-less monitoring and control of the actuation system. Another drawback of conventional grippers is their design, which is based on moving parts, are prone to wear, especially in abrasive environments. This can be overcome by flexure hinges that dispense with bearings and guides. In the presented work, the development process of a functional prototype for a compliant gripper driven by a bistable SMA actuation unit for industrial applications is outlined. The focus lies on the development of the SMA actuator, while the first design approach for the compliant gripper mechanism with solid state joints is proposed. The result is a working gripper-prototype which is mainly made of 3D-printed parts. First results of validation experiments are discussed.
As a smart material thermal shape memory alloys (SMAs) feature actuator behavior combined with self-sensing capabilities. With their high energy density and design flexibility they are predestined to be used in soft robotics and the emerging field of morphing surfaces. Such shape changing surfaces can be used for novel human-machine interaction (HMI) elements based on mode-/situation-dependent interfaces that may be applied to all kind of machines, appliances and smart home devices as well as automotive interiors. Since many of those contain textile surfaces, it is of special interest to place SMA-based actuator-sensor-elements beneath a textile cover or integrated them in the textile itself. In this study, the unique features of SMAs are used to design a system which represents an active "morphing" button. It can lower into the surface it is integrated in, pops up to be used and shows a proportional signal output depending on the pushing stroke. The system is characterized concerning haptics and sensor technology. The button consists of a TPU structure, to which two NiTi wires are attached. When activated, the SMAs contract and the structure curves upwards. The user can now push on the device to use it as a button. In the future, the use of SMA wires and for example TPU fibers enables direct integration in the production process of a possible smart and functional textile.
Continuum robots are inspired by biological trunks, snakes and tentacles. Unlike conventional robot manipulators, there are no rigid structures or joints. Advantageous is the ease of miniaturization combined with high dexterity, since limiting components such as bearings or gears can be omitted. Most currently used actuation elements in continuum robots require a large drive unit with electric motors or similar mechanisms. Contrarily, shape memory alloys (SMAs) can be integrated into the actual robot. The actuation is realized by applying current to the wires, which eliminates the need of an additional outside drive unit. In the presented study, SMA actuator wires are used in variously scaled continuum robots. Diameters vary from 1 to 60 mm and the lengths of the SMA driven tentacles range from 75 to 220 mm. The SMAs are arranged on an annulus in a defined distance to the neutral fiber, whereby the used cores vary from superelastic NiTi rods to complex structures and also function as restoring unit. After outlining the theoretical basics for the design of an SMA actuated continuum robot, the design process is demonstrated exemplarily using a guidewire for cardiac catheterizations. Results regarding dynamics and bending angle are shown for the presented guidewire.