Abstract
We developed an experimental device to measure the coefficient of friction of human finger pulp and investigated the influence of three factors (angle of contact with the friction surface, moisture condition of the fingertip, and roughness of the friction surface) on the coefficient of friction. Ten male subjects who had no hand injuries (average age : 23.8 years) were selected. Each subject was instructed to touch the friction plate (acryl plate) using the right index fingertip while applying a vertical force of approximately 20 N and then to slide the right index fingertip at a speed of approximately 5 mm/s. The angle of contact with the friction surface was defined as the angle between the central axis of the finger and the friction plate, and was set to 30, 45, and 60 degrees. In order to investigate the influence of the moisture condition, artificial sweat was applied to the fingertip to simulate three conditions (dry, appropriate moisture, and excess moisture conditions). In order to investigate the influence of the roughness of the friction surface, four aluminum plates processed by straight knurling under different conditions were used as friction plates to produce different surface roughnesses. The maximum coefficient of friction at the start of finger sliding was taken as the maximum coefficient of static friction μs, while the average coefficient of friction during sliding was taken as the coefficient of dynamic friction μk of the subject. As the angle of contact increased, μs and, μs tended to decrease, and μs at an angle of contact of 30 degrees was significantly greater than that at 60 degrees. No significant difference was observed for μk. With respect to the influence of the moisture condition, μk for the appropriate moisture condition was significantly greater than that for the dry condition. In addition, μk for the excess moisture condition did not differ from that for the dry condition. In the case of μs, there was no significant difference between the three conditions. With respect to the influence of the roughness of the friction surface, as the surface roughness increased, μs increased, and when the surface roughness exceeded a certain fixed level, it did not affect μs or μk.
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