Myoelectric prosthetic hand users are severely hampered in their ability to grasp and manipulate fragile objects. In these systems, electromyography (EMG) signals recorded from an amputee's residual muscles are processed to produce an electrical voltage proportional to muscle activation to drive the DC motors of a prosthetic hand. With training, users can voluntarily open, close and stop the hand with proportional control over the speed of the fingertips. If the user applies a continuous EMG signal to grasp an object, the motors driving the fingertips will stall on the object, producing high grasping forces of 30-100N depending on the EMG amplitude. Such high forces make it very challenging to grasp fragile objects without damaging them. Careful control and timing of EMG signals can be used to move the fingers at very slow speeds, stopping them before a fragile object is crushed;however, this approach requires direct vision, intense concentration, and has inconsistent success. As a result, most prosthesis users avoid handling fragile objects, restricting the utility of their prosthesis, particularly in bimanual tasks. In research to date, w have developed biologically inspired strategies to solve this problem. A tactile sensor on each fingertip detects when contact is made and modulates the control signals to the motors, similar to an inhibitory biological reflex. For a range of low to medium amplitude EMG signals, this reflex will cause the grasp closure to stop at low forces, preventing fragile objects from being crushed. This approach does not restrict a subject's ability to produce higher forces with larger EMG signals for grasping heavier objects, or even to crush objects if this is the desired outcome. This approach gives the user proportional control over a wider range of grasping forces with virtually no cognitive burden. Preliminary research has demonstrated that this feature offers substantial improvement in activities of daily living that involve fragile or deformable objects. In this research we will develop a low-cost and robust tactile sensor that meets design requirements proposed by a commercial partner and integrate these sensors with a commercially available prosthetic hand. Outcome measures to evaluate this and alternative technologies will be developed and evaluated with third-party clinical research partners. This research and development will focus on demonstrating feasibility of this technology and reducing or eliminating risks prior to commercialization. Phase I endpoints will result in a low-cost sensor ready for larger scale integration and clinical trials to demonstrate benefits to upper extremity amputees, clinicians and third-party payers.
Each year there are approximately 1,400 births with congenital defects resulting in upper limb loss and a growing number of veterans returning from the war with traumatic upper-limb loss. The young, ambitious and otherwise physically capable and motivated individuals who have suffered from such misfortune expect to benefit from the high tech world in which they are raised, only to find that rehabilitation has not advanced much beyond early cable-driven hook systems while state-of-the-art technology is costly and mostly ineffective. This research seeks to commercialize a relatively simple and useful approach to incorporate tactile sensing that will provide greater ease in grasping deformable objects, thereby providing myoelectric prostheses that are simpler and more intuitive to use while bringing performance closer to that of the human hand.
