Supernumerary Robotic Fingers for Assistance in Cylindrical and Pinch Grasps

Grasping impairments constitute a major limitation that affects the performance in many activities of daily life. Current assistive devices, such as hand exoskeletons, are designed to aid patients by giving them the additional assistance force necessary to close the hand and grip objects. However, this often results in improvement of only power grasps (such as cylindrical and spherical grasps), but not precision grasps. Another alternative for assisting hand function is to 'augment' the hand with additional robotic fingers. These supernumerary robotic fingers can assist the hand grasping function by performing a grip in coordination with the palm (analogous to an extra thumb) or by performing grasps on their own when there are two or more extra fingers. This work presents an assistive device comprising two supernumerary robotic fingers aimed for people with hand grasping limitations. The extra fingers can assist in performing power grasps such as cylindrical in conjunction with the user's palm or performing precision grasps such as pinch grasp. The fingers are actuated by servomotors and their positions are controlled by commands derived from the wearer's wrist movements. Hence, this new design seeks to assist people through an easy-to-operate interface that avoids the use of joints unrelated to the motor task and thus provides natural control for the patient.