This article presents some results of an ongoing research project to investigate the components and modules that are necessary to equip a robot with exploratory capabilities. Of particular interest is the recovery of certain material properties from a surface, given minimal a priori information, with the intent to use this information to enable a robot to stand and walk stably on a surface that is unknown and unconstrained. To this end, exploratory procedures (EPs) have been designed and implemented to recover penetrability, compliance, and surface roughness by exploring the surface using a compliant wrist sensor. A six-degree-of-freedom compliant wrist sensor that combines passive compliance and active sensing has been developed to provide the necessary flexibility for force and con tact control, as well as accurate position control. This article describes the compliant wrist and sensing mechanism design along with a hybrid control algorithm that utilizes the sensed information from the wrist to adjust the apparent stiffness of the end effector as desired.
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