Customized exoskeletons with SMA drive

Exoskeletons as therapeutic aids for limited hand mobility

Tendon injuries or strokes can severely limit hand mobility. Exoskeletons, which are attached to the hand like a second skeleton, are increasingly being used in therapy. They enable targeted, slow movement of the wrist and fingers. For successful therapy, it is crucial that the exoskeleton is individually tailored to the patient's hand and meets key requirements such as low weight and compact design.

Customized exoskeletons

SMA stepper motors and 3D printing open up new possibilities for designing exoskeletons that fit perfectly and provide gentle support.  Human hands differ significantly from one another not only in size but also in proportions. The manufacture of exoskeletons using 3D printing offers almost unlimited geometric freedom. The manufacturing process can be made particularly efficient if a parametric CAD model is used as a basis. Ideally, a digital 3D scan of the patient's hand is available so that the geometric shape and the relationships between the individual elements of the hand can be mapped.

Individualized force assistance through SMA drive

In addition to anatomy, hand strength also varies from person to person. Therefore, it makes sense for most patients to individualize the force and stroke of the exoskeleton. A high dead weight of the device would be very burdensome. In addition to the fit of the shell, the drive is therefore particularly important. A combination of bidirectional kinematics driven by SMA wires is particularly suitable. This concept is based on only two artificial tendons, which are precisely controlled by the stepper motor for flexion and extension movements of the hand and fingers. Various positions can be set and held without energy. The result is a very precise and repeatable movement – supported by the smooth response of the SMA wires, which enable gentle movement steps.