  Robotic hands with soft surfaces can perform stable grasping, but the high
friction of the soft surfaces makes it difficult to release objects, or to
perform operations that require sliding. To solve this issue, we previously
developed a contact area variable surface (CAVS), whose friction changed
according to the load. However, only our fundamental results were previously
presented, with detailed analyses not provided. In this study, we first
investigated the CAVS friction anisotropy, and demonstrated that the
longitudinal direction exhibited a larger ratio of friction change. Next, we
proposed a sensible CAVS, capable of providing a variable-friction mechanism,
and tested its sensing and control systems in operations requiring switching
between sliding and stable-grasping modes. Friction sensing was performed using
an embedded camera, and we developed a gripper using the sensible CAVS,
considering the CAVS friction anisotropy. In CAVS, the low-friction mode
corresponds to a small grasping force, while the high-friction mode corresponds
to a greater grasping force. Therefore, by controlling only the friction mode,
the gripper mode can be set to either the sliding or stable-grasping mode.
Based on this feature, a methodology for controlling the contact mode was
constructed. We demonstrated a manipulation involving sliding and stable
grasping, and thus verified the efficacy of the developed sensible CAVS.
