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 with linear guides and bearings. These parts are prone to wear, especially in abrasive environments. This can be overcome 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 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.

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.

Most relevant to predicting the behavior of shape-memory-alloy (SMA)-based actuator-sensor applications activated by Joule heating are the electro-mechanical characteristics of the material under consideration. For a comprehensive characterization, a single setup that is able to provide all relevant data and information is desirable. This work covers the design, implementation and validation of such a high-end test bench for the holistic characterization of SMA micro-wires. In addition, the setup provides the possibility of application simulation experiments. Key elements of the design are the clamping mechanism guided on air bearings, a linear direct drive, a high-resolution load cell, a high-precision constant current source and a stress-controlled in-line wire sample installation. All measurements take place inside an isolated, temperature-controlled chamber. With the presented setup, the electro-mechanical and thermal characteristics of SMA wire samples with diameters from 20 µm to 100 µm can be determined. Via hardware-in-the-loop (HiL) implementation, the outputs with different biasing mechanisms and additional end-stops can be simulated even at high ambient temperatures. The generated results facilitate the prediction of the exact characteristics of SMA-driven actuator-sensor systems in a variety of applications and lead to a better general understanding of the alloy’s properties. All functionalities and features of the setup are presented by discussing the results of exemplary experiments.

Shape Memory Alloys (SMAs) are a class of smart materials that exhibit a macroscopic contraction of up to 5% when heated via an electric current. This effect can be exploited for the development of novel unconventional actuators. Despite having many features such as compactness, lightweight, and high energy density, commercial SMA wires are characterized by a highly nonlinear behavior, which manifests itself as a load-, temperature-, and rate-dependent hysteresis exhibiting a complex shape and minor loops. Accurate modeling and compensation of such hysteresis are fundamental for the development of highperformance SMA applications. In this work, we propose a new dynamical model to describe the complex hysteresis of polycrystalline SMA wires. The approach is based on a reformulation of the M üller-Achenbach-Seelecke model for uniaxial SMA wires within a hybrid dynamical framework. In this way, we can significantly reduce the numerical complexity and computation time without losing accuracy and physical interpretability. After describing the model, an extensive experimental validation campaign is carried out on a 75 µm diameter SMA wire specimen. The new hybrid model will pave the development of hybrid controllers and observers for SMA actuators.

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.