Abstract: A skin friction balance uses a parallel linkage mechanism to avoid inaccuracies in skin friction measurement attributable to off-center normal forces. The parallel linkage mechanism includes a stationary plate mounted in a cage, and an upper and lower movable plate which are linked to each other and to the stationary plate through three vertical links. Flexure pivots are provided for pivotally connecting the links and the plates. A sensing element connected to the upper plate moves in response to skin friction, and the lower plate moves in the opposite direction of the upper plate. A force motor maintains a null position of the sensing element by exerting a restoring force in response to a signal generated by a linear variable differential transformer (LVDT).

Abstract: A skin friction force measuring device having a first pivoted 13 L-shaped arm 12, a second arm 16 pivoted 17 on one end of the L-shaped arm with a sensing element 20 attached to an end of the second arm. In response to skin friction forces on the sensing element 20 the arms are pivoted about the two pivots and two nulling means 23, 28 force the pivots back to their zero positions. The outputs of the two nulling means are indicative of the skin friction forces along two perpendicular axes, x and y, in the plane of the sensing element.