Human finger friction in contacts with ridged surfaces

Ridges are used on many objects to increase the friction and therefore improve the grip. Currently there has been one study investigating the effect of ridge dimensions, and this only examined four surfaces. Therefore, more work needs to be done to establish the effects of ridge height, width and spacing. In this study, 17 different rectangular ridged surfaces were manufactured from brass. The friction between these surfaces and the human finger were measured using a finger friction rig. It was found that as the finger moved over the ridged surfaces, the friction varied between maxima and minima, corresponding to the position of the finger. There was an increase in friction with increased ridge height and also increased spacing of the ridges. The friction decreased with the width of the ridges, up to 4 mm, after which no change was seen. It was concluded that the main mechanisms of skin friction, when sliding over rectangular ridges, are adhesion, ploughing friction and energy return from the reformation of the finger. The highest friction is achieved using high, narrow, widely spaced ridges. However, if consistent friction is required across the surface, the opposite should be used, at the expense of high friction.