Picture: Fraunhofer IWU
The Fraunhofer Institute for Machine Tools and Forming Technology (IWU) is currently developing an adaptive exoskeleton system for hand rehabilitation, which can be customized to individual patients using 3D printing technologies and shape memory alloys. The goal is to create lightweight and compact support systems that specifically promote finger and wrist movements without restricting them.
At the heart of the project is the combination of parametrically modeled CAD designs and additive manufacturing using selective laser sintering (SLS). By integrating 3D scan data of the patient’s hand, the geometry of the exoskeleton can be precisely adapted to the individual’s anatomy. Differences in hand size, finger orientation, or joint positions can thus be directly incorporated into the design. 3D printing enables the production of complex geometries that would be nearly impossible to achieve with conventional manufacturing methods.
In addition to the outer fit, the actuation mechanism plays a key role. A novel step actuator has been developed, based on a bidirectional stepper motor and shape memory alloys (SMA). These wires change their length in a controlled manner when heated, enabling precise movement of artificial tendons. According to Alina Carabello, a research associate at Fraunhofer IWU and TU Chemnitz, this solution allows both the force and range of motion to be individually adjusted for each hand. Thanks to its feedback capability, even dynamic gripping processes — such as holding a plastic bottle — can be supported.
The system is designed for therapeutic applications in cases of tendon injuries, paralysis, or post-stroke rehabilitation. Since the movements can also be performed automatically without continuous supervision by medical personnel, the exoskeleton is particularly well-suited for intensive rehabilitation phases that require high repetition rates.
