Strain wave gears for exoskeletons

Whether in medical technology, industry, logistics, or skilled trades, exoskeletons create new possibilities. They make movements easier or even possible in the first place, reduce physical strain, and ensure greater safety, stability, and endurance. However, replicating the human musculoskeletal system at the highest level is a real challenge and places high demands on gear technology—especially in terms of compactness, power density, backlash-free operation, safety, and robustness. Strain wave gears offer clear advantages here.

Backlash-free strain wave gears are an ideal solution for exoskeletons
Strain wave gears operate without backlash, respond dynamically, and offer high torque density. This allows for compact, lightweight, and powerful drive units, which is particularly advantageous for exoskeletons with limited installation space. Their smooth and quiet operation increases wearing comfort. The high overload capacity also increases operational reliability. In addition, their design with few wear-relevant contact points means they are low-maintenance.

Requirements and advantages of strain wave gears in exoskeletons

High torque density
Limited installation space and weight requirements call for compact gearboxes with high power density. Strain wave gears enable high transmission ratios and torques while maintaining a small size, thus supporting the implementation of lightweight, portable systems.

Backlash-free and high positioning accuracy
Since the gearbox acts directly on the hip, knee, or shoulder joints, it directly influences the accuracy of the movement. Backlash-free strain wave gears ensure precise positioning and high repeatability. This ensures stable and reproducible motion sequences, even with changes in direction and varying loads.

High torsional rigidity
High torsional rigidity minimizes twisting under load. This means that the force is transmitted directly even at high joint moments and the joint movement remains precise.

High overload protection
Dynamic movements or unexpected loads lead to load peaks. The high overload reserve helps to prevent damage and premature wear. This increases reliability in continuous use.

Defined backlash
Defined backlash allows torque to be transferred back from the joint to the drive system. Nabtesco strain wave gears offer adjustable backlash torque. This allows the interaction between the exoskeleton and the user to be specifically adjusted.

Long service life and maintenance-free
Exoskeletons are designed for high cycle counts. Nabtesco strain wave gears are designed for continuous use and are maintenance-free. This reduces downtime and simplifies operation.

Application example: RISE project at TU Berlin
For the active exoskeleton of the RISE student project at TU Berlin, we co-developed six actuators at our Limburg (Lahn) site – three on each side of the body: two on the hip (1x flexion/extension and 1x abduction/adduction) and one on the knee (flexion/extension). A total of three actuator types are used in two different designs (knee/hip) and with several different gear ratios. The project focused on short development times, low mass, and a compact design. 

The integrated electromechanical drives consist of a strain wave gear, electric motor, and position sensors. They enable high torques in limited installation space and meet the requirements for backlash-free operation, reversibility, and overload capacity. The strain wave gears are manufactured according to automotive standards and are designed for a long service life. The result is dynamic, precisely executed movements with maximum safety.

Would you like to learn more about the advantages of Nabtesco strain wave gears in exoskeletons, or do you have questions about a specific project? Our experts will assist you with design and integration. Contact us now!