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The aim of the present study was to fi nd and describe the relationship between damping properties and both the number of layers and the fi ber orientation in woodveneer-composite specimens. The testing apparatus was a simple torsional pendulum in which the frequencies of the resulting free vibrations were maintained between 13 and 23 Hz. Cross-sectional (30 × 30 mm) specimens with a total length of 250 mm were used. The specimens were cut from manufactured wood-veneer-composite panels (both 0°/90° and 0°/0° oriented) with up to 13 layers. Existing problems such as nonlinearities, which are often responsible for weighting results, were taken into account by using several mathematical approaches. The results led to a consistent picture of the damping properties across the measured range. We found that the damping ratio increased for the 0°/90° orientation with increasing numbers of layers in a cross-sectional specimen of constant outer dimensions. This effect could not be reproduced for specimens oriented 0°/0°.

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Influence of an active hand exoskeleton on muscle activity of the forearm in industrial assembly grip types Objective: The study aims to identify the effects of the soft exoskeleton Bioservo IronHand® on muscle activity of the forearm flexor muscles in the following gripping tasks relevant to automotive assembly: 2-finger grip (2Finger), 5-finger grip (5Finger), full-hand grip (HandUmf). Methods: Twelve subjects were included in the study. The following exoskeleton conditions were applied to each subject for each grip task: Exoskeleton off (Off), Exoskeleton on, Locking Tendency 0 % (On_LT0) and Exoskeleton on, Locking Tendency 85 % (On_LT85) in order to examine their effects on the myoelectrical muscle activity of the forearm flexors at 50 % of the individual maximum hand strength (measured at M. flexor digitorum superficialis). Results: In the 2Finger condition, mean muscle activity, normalised to maximal muscle activation (MVE), increased significantly in On_LT0 (22.84 %MVE) compared to Off (18.51 %MVE, +4.33 %MVE, 95% CI [+1.88 %MVE; +6.78 %MVE]). No significant differences in muscle activity were observed for the 5Finger condition (Off: 19.38 %MVE, On_LT0: 20.37 %MVE, and On_LT85: 18.80 %MVE). For 2Finger and 5Finger conditions, clear intraindividual increases of muscle activity (> Root Mean Square Error) were observed for one-third and one-quarter of all subjects respectively. In the HandUmf condition, mean muscle activity decreased significantly in both On_LT0 (28.87 %MVE, –4.35 %MVE, 95% CI [–1.36 %MVE; –7.35 %MVE]) and On_LT85 (26.98 %MVE, –6.24 %MVE, 95% CI [–3.25 %MVE ; –9.24 %MVE]) compared to Off (33.23 %MVE). Conclusion: The soft exoskeleton Bioservo IronHand® may reduce myoelectrical muscle activity of the forearm flexor muscles at 50 % of the maximum hand strength during HandUmf by 13 % (95% CI [4 %; 22 %]) for On_LT0 and 19 % (95% CI [10 %; 28 %]) for On_LT85 conditions. However, in 2Finger and 5Finger grip tasks, up to one third of the subjects showed increases in muscle activity of up to 120 % (reference level without support). Based on these results, the suitability of the exoskeleton remains questionable at least for these specific grip tasks at 50 % of the maximum hand strength. Keywords: exoskeleton – hand – work – grip – electromyography (EMG)