Publication
Comparison of two upper limb active exoskeletons for simulating microgravity by analyzing muscle activity in dynamic arm movements
Julia Habenicht; Marc Tabie; Mathias Trampler; Elsa Andrea Kirchner
In: 2025 3rd International Conference on Integrated Systems in Medical Technologies (ISMT) - Conference Proceedings. International Conference on Integrated Systems in Medical Technologies (ISMT-2025), December 4-5, Erlangen, Germany, IEEE Xplore, 2025.
Abstract
The use of active exoskeletons in rehabilitation or for specific physical work is increasing. Supporting movements continuously is feasible by dynamically compensating for the weight of the wearer's limbs. Such an approach can also be used to simulate weightlessness, as the weight of limbs is not felt in space. This study compares two upper limb active exoskeletons regarding their ability to simulate weightlessness. One is actuated by brushless drives combined with a high gear ratio harmonic drive, and one is actuated by quasi direct drives (QDDs). To this end, 11 subjects per system performed simple dynamic arm movements wearing the exoskeleton in gravity compensation mode (GCM) (weight of the exoskeleton is dynamically compensated) and controlled with a dynamic arm model (DAM) to simulate microgravity (system's weight and weight of the user's arm is compensated). Muscle activity under both conditions were analyzed and compared within each system. In both systems, the analyzed muscle activity during movements under DAM was lower than the muscle activity under GCM. However, these differences were only significant for the system actuated by QDDs, suggesting that the new exoskeleton is better able to simulate weightlessness for this type of movement due to its higher transparency, lower friction and higher dynamics in control compared to an exoskeleton actuated by high gear ratio harmonic drives.