  This paper introduces a pair of low-cost, light-weight and compliant
force-sensing gripping pads used for manipulating box-like objects with
smaller-sized humanoid robots. These pads measure normal gripping forces and
center of pressure (CoP). A calibration method is developed to improve the CoP
measurement accuracy. A hybrid force-alignment-position control framework is
proposed to regulate the gripping forces and to ensure the surface alignment
between the grippers and the object. Limit surface theory is incorporated as a
contact friction modeling approach to determine the magnitude of gripping
forces for slippage avoidance. The integrated hardware and software system is
demonstrated with a NAO humanoid robot. Experiments show the effectiveness of
the overall approach.
