Design of a rapid-prototyped smart robotic exoskeleton for power wheelchair users

Over 400,000 people in the United States use wheelchairs in their daily lives due to muscular diseases such as muscular dystrophy and cerebral palsy, injury, and stroke. Additionally, people with lower extremity weakness or paralysis due to these issues often have upper limb impairments as well, severely limiting their ability to do activities of daily living. There has been an increased interest in exoskeletons, particularly actively-actuated exoskeletons, to help augment activities of daily living for such persons; however, portability and accurately and intuitively deriving user intent have been limiting factors. We propose a compact, light-weight, and smart assistive 3 degrees of freedom wheelchair-mounted robotic upper arm exoskeleton to augment elbow and shoulder flexion/extension, as well as shoulder abduction/adduction joint movements. The novel smart controller system involves force sensing resistors to detect user intent, rotary encoders for joint feedback, and a user-interface system utilizing microcontroller technology to manipulate the wheelchair-mounted robotic upper arm exoskeleton. A prototype was designed and modeled using SolidWorks and fabricated using additive manufacturing, while stress and displacement were estimated using finite element analysis and end-effector workspace was calculated using Denavit-Hartenberg parameters in MATLAB. The current prototype uses joint angle limits based on biomechanical limitations and can be customized for particular user’s range of motion. Workspace results show total range for the end-effector of 10.42, 13.16, and 69.6 cm in the X, Y, Z directions with rotations from -30 to 25°, -40 to 50°, and -30 to 50° of the first (shoulder abduction/adduction), second (shoulder flexion/extension), and third (elbow flexion/extension) joints, respectively. The overall weight of the proposed exoskeleton is under 3 kg. Finite element analysis showed areas along links of high stress which will be reinforced. An institutional review board application was approved to conduct testing on participants without disability in order to determine efficiency of the proposed exoskeleton. The results of initial human subject testing showed promise for the smart, force-input controller with successful actuation of each exoskeleton joint.