Exploiting Implicit Kinematic Kernel for Controlling a Wearable Robotic Extra-finger

In the last decades, wearable robots have been proposed as technological aids for rehabilitation, assistance, and functional substitution for patients suffering from motor disorders and impairments. Robotic extra-limbs and extra-fingers are representative examples of the technological and scientific achievements in this field. However, successful and intuitive strategies to control and cooperate with the aforementioned wearable aids are still not well established. Against this background, this work introduces an innovative control strategy based on the exploitation of the residual motor capacity of impaired limbs. We aim at helping subjects with a limited mobility and/or physical impairments to control wearable extra-fingers in a natural, comfortable, and intuitive way. The novel idea here presented lies on taking advantage of the redundancy of the human kinematic chain involved in a task to control an extra degree of actuation (DoA). This concept is summarized in the definition of the Implicit Kinematic Kernel (IKK). As first investigation, we developed a procedure for the real time analysis of the body posture and the consequent computation of the IKK-based control signal in the case of single-arm tasks. We considered both bio-mechanical and physiological human features and constraints to allow for an efficient and intuitive control approach. Towards a complete evaluation of the proposed control system, we studied the users' capability of exploiting the Implicit Kinematic Kernel both in virtual and real environments, asking subjects to track different reference signals and to control a robotic extra-finger to accomplish pick-and-place tasks. Obtained results demonstrated that the proposed approach is suitable for controlling a wearable robotic extra-finger in a user-friendly way.