Intrinsic contact based sensing aims to resolve the locations of soft-body contact, forces at the interface, and the moment about the contact normals using internal force and torque measurements [2]. It is assumed to involve contact between a rigid apparatus and an object (here, a foot) in the environ- ment. It has mainly been applied to problems in robotic ma- nipulation, but we have adapted it to foot-ground interaction sensing. This approach can be viewed as an alternative to sensing foot-floor contact via dense surface mounted trans- ducer arrays, relative to which far fewer sensors are required. The method is based on resolving the contact centroid xc as- sociated with a pressure distribution pR(x) distributed over an area R. xc is a unique point on the floor such that there is a normal force Fc that gives rise to the same intrinsic force measurements as pR(x) does [2]. The sensing problem is simple to formulate for a single floor tile (Fig. 2), with force sensor locations x j where internal force measurements f j are taken and j indexes the tile sensors. The contact cen- troid xc and normal force Fc = (0, 0, Fc) can be recovered from scalar force measurements F j = (0, 0, f j ) via force and torque equilibrium equations,
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