Experimental analysis of an innovative prosthetic hand with proprioceptive sensors

This paper presents an underactuated artificial hand intended for functional replacement of the natural hand in upper limb amputees. The natural hand has three basic functionalities: grasping, manipulation and exploration. To accomplish the goal of restoring these capabilities by implanting an artificial hand, two fundamental steps are necessary: to develop an artificial hand equipped with artificial proprioceptive and exteroceptive sensors and to fabricate an appropriate interface able to exchange sensory-motor signals with the amputee’s body and the central nervous system. In order to address these objectives, we have studied an underactuated hand according to a biomimetic approach, and we have exploited robotic and microengineering technologies to design and fabricate its building blocks. The architecture of the hand comprises the following modules: an actuator system embedded in the underactuated mechanical structure (artificial muscoskeletal system), a proprioceptive sensory system (position and force sensors), an exteroceptive sensory system (3D force sensors distributed on the cosmetic glove), an embedded control unit (low level control loop dedicated to control incipient slippage and grasping), and a human/machine interface (a EMG control unit to enable the amputee to control the artificial hand). The first prototype of the artificial hand has been designed and fabricated. The hand is underactuated (9 degrees of freedom controlled by two actuators), and is equipped with opposable thumb and a proprioceptive sensory system. This paper presents the fabrication and experimental characterization of the hand, focusing on the mechanical structure, the actuator system and the proprioceptive sensory system. The grasping and sensing capabilities of the first prototype have been experimentally tested with an innovative method to estimate the grasping force, and preliminary results are presented and analyzed.