Preliminary results of Robo-Mate lab tests

The first tests are over: To assess usability, effectiveness and efficiency, eight persons have performed 3 tasks with and without exoskeleton modules in the Robo-Mate labs in Switzerland. The main result: The modules are effective and efficient, but usability has to be improved.

During and after the three tasks, we have collected data on muscle activity, perceived physical exertion, perceived musculoskeletal pressure and usability. For the following report on preliminary results, we focus on perceived physical exertion and usability.

The tested modules
We have tested two modules: the trunk module and the passive arms. The passive arms provide a constant supporting force to the arms, while the trunk module supports the trunk during flexion and extension.

The tasks
Each of our eight test participants performed three tasks:

• Dynamic lifting | with trunk module: the participant was required to lift a load (7.5 and 15kg) with straight arms from knee height to waist height with and without the trunk module.
• Static overhead task | with passive arms: the participant was required to hold a load (0kg and 2kg) in their dominant hand overhead for 30 seconds with and without the passive arm module.
• Bending task | with trunk module: the participant was required to maintain 6 static spinal flexion postures (spinal flexion: 0, 10, 20, 30, 40, 50) for 5 seconds with and without the trunk module. During this task the arms were relaxed and hanging downwards.

Measures for perceived exertion and usability

• Physical exertion was measured by a subjective rating scale measured from zero (no physical exertion) to ten. It was rated for three musculoskeletal areas: legs, arms and trunk.
• Usability of the exoskeleton modules was obtained via a System Usability Scale. This subjective rating scale consists of ten questions rated from one (strongly disagree) to five (strongly agree). Using these answers, a usability score is calculated where a value of 70 is deemed acceptable.

Results
The trunk module seems to be effective with regard to physical exertion, especially for dynamic lifting: Our participants reported reduced physical exertion for both the trunk and the legs. When they had to only bend over and hold their position, the trunk module reduced physical exertion of the trunk only at a flexion angle of more than 20°. For less than 20°, the negative effect of the weight of the trunk module seemed to outweigh the positive effect of the supporting torque.
While the trunk module was effective at reducing perceived physical exertion for angles of more than 20°, it also increased physical exertion for the legs.

Usability is clearly the area where the trunk module needs most improvement: For both dynamic lifting and static bending, our participants did not reach an acceptable usability score.
The passive arms were effective at reducing perceived exertion for the arms, but slightly increased exertion for legs and trunk. Usability scores for the passive arms were significantly higher than for the trunk module: Half of our participants reached an acceptable usability score.

Consequences
The lab tests have shown that the trunk module is very promising in terms of reducing physical workload on the trunk and thus has a potential to prevent musculoskeletal disorders of the lower back. What we need to clearly improve is usability. The passive arms have a potential to reduce fatigue for overhead tasks, and if they are built in a more light-weight manner, the negative impact on trunk and leg exertion may be reduced.
The results also highlight the importance of an expert analysis of tasks performed in industry, because an exoskeleton may be beneficial for certain tasks and certain body regions, but may not be so for other tasks and increase workload on other parts of the body.
Following the tests, we have made adjustments to the modules and we will now move out of the lab and test the modules on the shop floors of our industry partners CRF (Italy), INDRA (France) and COMPA (Romania). More details on the results of lab tests and tests on the shop floor will be published in journals – and on this website.