Subproject: Development of actuators/sensors in textile structures
PowerGrasp aims to realise an arm-hand orthosis with soft kinematics to support workers of all ages with regard to manual, musculoskeletally stressful activities, which can be used without restricting the user in his or her own movement and without being hindered by the system itself, which responds promptly and adaptively to changes in the work process and the user's abilities and which can be used independently of constitution, age and gender. The sub-project of TITV Greiz was primarily concerned with the development of pneumaticbsoft actuators to support hand and finger movement, and with the integration of actuator and sensor modules of all partners as well as their wiring in a sleeve and a glove.
The main focus of the work at TITV Greiz is on the development and production of pneumatic actuators that can support the movement of the hand and finger apparatus. Basic textile materials are to be used and pneumatic deformations are to be converted into a directed movement by means of air-tight and yet stretchable coatings or tubes. In addition, a
methodology is to be developed that comparably evaluates the suitability of the novel actuators and their working capacity. In addition to the actuators of the TITV Greiz, further modules are to be built by the project partners and connected with suitable sensors as control variables. The integration technologies at TITV Greiz play a major role in this and are combined into a complete system through the competences in assembly and prototyping. The goal is the integration of several actuators for fingers, hand and arm as well as the sensor integration in the glove to control the hand actuators and the textile-based wiring of further inertial sensors to control the arm actuators.
Finally, the task is to produce a functional demonstrator in the form of a glove with sufficient finger actuators.
The generation of textile-based actuators will initially be further advanced with the pneumatic spacer fabric developed at TITV Greiz. In the process, the known textile structures
measuring at least 10 cm × 10 cm are being examined for their suitability in smaller, approx. 8 cm × 2 cm bending actuators. The textile structure and its bonding will be considered as well as the subsequent airtight coating with silicone on all sides and edges of the spacer fabric.
As further functional approaches, a textile-coated silicone tube and a textile-reinforced silicone cast in finger form are investigated. The silicone tube changes its circumference and
length when pressure is applied. Depending on the textile coating, it can be used as a push actuator or - with a special knitted structure from the project partner WarmX - also as a pull actuator. The finger-shaped silicone cast, on the other hand, functions again as a bending actuator by introducing a textile reinforcement on one side into the cast. The textile acts as a directional element for the actuator.
In the course of the work, a new methodology is also being developed that can reproducibly inflate the pneumatic patterns and determine the force effect by means of contact pressure measurement, as well as testing the load-bearing capacity of the actuator and the adhesive strength of the coatings by increasing the internal pressure. Further work in the project includes the assembly of the gloves and sleeves with the corresponding actuators and the cabling for the measurement data acquisition. For this, soutage embroidery with insulated cable strands is used, the sensor foils of the project partner Würth Elektronik are sewn onto the fingertips, and pockets, fastening tabs and tension straps for the actuators are attached. Concepts for force transmission are being developed.
Results and Applications
For each of the actuator principles mentioned
- pneumatic spacer fabric
- textile-coated silicone hose
- textile-reinforced silicone cast
functional modules have been constructed. The general feasibility of such modules was proven in the project and reproduced several times. From the derivation of the use cases in
the project and on the basis of the requirements for force transmission, working capacity, internal pressure and repeat cycles for the movement, the textile-reinforced, cast silicone
finger could be selected as the optimal functional principle. This can withstand internal pressures of more than 4 bar and can thus perform very large movements of up to 5 cm with
an actuator length of 8 cm. The high pressure also makes it possible to generate a clearly noticeable force effect on the finger.
In addition to various actuators, the project has also produced the assembly solutions for the gloves and sleeves, which include the bus-like wiring pattern structure for sensor evaluation as well as the fastenings for actuators and sensors.
Fig. 1: Illustration of 3 different actuator principles (from left to right: pneumatic spacer fabric, textile-covered silicone tube, textile-reinforced silicone cast)
Fig. 2: Sensor integration of foil sensors (Würth Elektronik) on the glove
Fig. 3: Example of the complete set-up without actuators (left: Pull-over sleeve, right: top with sleeve and glove)
Dipl.-Ing. (FH) Kay Ullrich