Force sharing strategies.

<p>The plane represents all possible combinations of interaction forces (<i>f</i>_R, <i>f</i>_L). The dotted line intersecting the horizontal and vertical axes at <i>f</i>_ext. represents all force combinations corresponding to the same external force <i>f</i>_ext. The intersection of this line with the <i>f</i>_R = <i>f</i>_L line is the point at which the two participants split the external force equally. Parameter d is a measure of the distance from equal force sharing. The quadrants highlighted in grey are those in which internal forces are present. <i>Insets</i>: The insets illustrate the direction of the forces applied by the two participants (-<i>f</i>_R, and–<i>f</i>_<i>L</i>) and the haptic device (<i>f</i>_ext) to the object in the first and second quadrants.