Impact of vibrating devices on the hand-arm system when using exoskeletons at the same time

Status:

completed 11/2025

Aims:

Since exoskeletons for the upper extremities are also intended to support the use of hand-held machines, the question arises as to what effect exoskeletons have on users when working with vibrating machines and tools. For this reason, an experimental study was conducted to clarify whether the use of passive exoskeletons in conjunction with vibrating machines and tools could critically increase the vibration exposure for employees. The aim was to draw up a recommendation or preventive guidelines for the use of passive exoskeletons in connection with working with vibrating hand-held tools, if this proved necessary based on the results.

Activities/Methods:

In order to close the gaps in knowledge outlined above, a comprehensive laboratory study was conducted to identify acute physiological changes that occur when working with exoskeletons and, where possible, to attribute these changes to mechanical factors. The study examined two passive exoskeletons worn on the body (ShoulderX and Paexo) which, according to the manufacturer's specifications, are designed to support the shoulder-arm system. With 30 participants, the laboratory study examined the influence of the exoskeletons on physiological reactions during activities involving vibrating tools in two work processes – drilling and sanding on a wooden plate at shoulder level and above – in a vertical upward direction and in a horizontal forward direction, and compared with the activities without the use of exoskeletons.

Mechanical and physiological parameters were considered in order to obtain a comprehensive picture of human-machine interaction. The mechanical parameters measured were the vibration exposure at the handles of the machines, the vibration transmission to the wrists and the resulting feed force. Physiologically, the change in vibration perception at the fingertips, the blood circulation behaviour of the hands, the muscle activity in the shoulders, upper and lower arms, the posture and the subjective strain were recorded using a questionnaire.

Results:

The results suggest that the influence of the working direction and the exoskeletons is machine-specific. When using the exoskeleton with a high support torque (ShoulderX), increased vibration exposure was measured with the drilling machine in both directions of work. Activities in a horizontal working direction caused higher vibration exposure with and without exoskeletons on the sanding machine than in a vertical direction. The known positive effect of a reduction in muscular activity through exoskeletons in the shoulder area was also observed under the conditions presented. The other acute physiological effects could be linked to the wearing exoskeletons in isolated cases, but did not follow a uniform pattern. For example, only with one exoskeleton (ShoulderX) in the horizontal working direction was vibration perception reduced on both machines compared to performing the activity without an exoskeleton. No systematic effect of the exoskeletons on blood circulation in the hands was observed. Both exoskeletons mainly caused a higher posture of the right upper arm, which was used to grip the main handle of the power tools. Subjectively, the support provided by ShoulderX was perceived as slightly stronger than that provided by Paexo, but the activities were not assessed as being any less strenuous.

The study shows that the use of an exoskeleton with a high support torque can result in increased vibration exposure. At the same time, wearing an exoskeleton reduces vibration transmission in the lower frequency range between 5 Hz and 90 Hz, so that this unfavourable effect is largely relativised. Vibration exposure can also vary depending on the working direction. Taking these factors into account, it is not possible to formulate general recommendations for the use of vibrating machines and exoskeletons. Regardless of the exoskeletons, the effects of vibration are more strongly influenced by other factors such as the coupling forces applied, the user's handling of the machine and the working method, as well as the person themselves. It must be examined on a case-by-case basis whether the vibration exposure changes with a specific device. However, no positive effects in terms of vibration exposure or the associated physiological response in the hand-arm system in the sense of prevention through exoskeletons are to be expected.

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