Stiffness Analysis of Underactuated Fingers and Its Application to Proprioceptive Tactile Sensing

Underactuation has become, in recent years, more and more prevalent in robotic fingers since it provides the latter with the ability to mechanically adapt to the shape of the objects seized. To improve the usually simplistic control schemes of these fingers, and possibly to provide force feedback or control, tactile sensors are typically used. However, another promising avenue, as presented in this paper, is rather to use information provided by proprioceptive (i.e., internal) sensors. Most interestingly, this can be done using only the torque and position sensors typically found attached to the actuator(s) of these fingers. Because a relationship exists between the stiffness of an underactuated finger as seen from its actuator and the contact locations on its phalanges, it is possible to estimate one from the other. In this paper, a proprioceptive tactile sensing algorithm based on this technique is presented. It is concluded that within certain theoretical and practical limits, it is possible to extract tactile data from a self-adaptive finger, namely position and magnitude of the contact forces, without actually using any physical tactile sensors.