Fig. 1.

Schematic drawing of the handle and an object-based system of coordinates (left panel) and the moment arms of the digit forces (right panel). Force components in the X direction are called the normal forces, in the Y direction—tangential forces. The magnitude of r is the same for all the digits. The sense of r’s is different for the thumb and finger forces. d^s is the projected distance from a center of the finger sensor to the center of the thumb center. d_th is the distance between the point of application of the thumb force and the center of the thumb sensor. The moment arm of the normal force of finger f with respect to the point of the thumb force exertion is $d_f=d_f^{\mathrm{s}}+d_f^{\mathrm{c}}-d_{\text{th}}\text{where}{d}_f^{\mathrm{c}}$ is the distance between the point of application of the finger force and the center of the finger sensor (not shown in the figure). The figure is not to scale.