Powered Arm Orthosis to Augment Arm Function in Persons with Disabilities Daniel Abramovich Michael Scarsella Steven Toddes Advisor: Professor Allen Hoffman | Mechanical Engineering Department Overview Duchenne’s Muscular Dystrophy (DMD) is a degenerative genetic disease occurring primarily in adolescent males. DMD results in a deterioration of muscle tissue causing afflicted persons to be wheelchair bound. Those afflicted with DMD typically lose muscle function in their limbs proximally to distally, leaving them with only minor tactile function in their hands by their teenage years, resulting in limited independence. Patients will generally require assistance in completing activities of daily living (ADL’s), such as brushing teeth, fork feeding, and combing hair. Orthotic devices have helped DMD patients regain small levels of independence by helping to recreate movements within their arms. By designing a powered arm orthosis with a comprehensive control system, DMD patients could operate a mechanism that would allow them to complete ADL’s with minimal assistance, thereby restoring their independence. Abstract Muscular Dystrophy, and other similar afflictions, where articulation of arm muscles is hindered, can severely impact the quality of life. By creating a wearable, electromechanically powered arm orthosis, strength no longer available to the arm muscles is augmented and controlled by the user, thereby restoring arm function. In the design produced, a wearable orthosis controlled by joystick allowed the user to lift his own arm plus an additional 3 lbs in weight. The device incorporated 2 degrees of freedom or DOF (elbow flexion and humeral rotation) that can be controlled independently or simultaneously. With the use of the powered orthosis, daily tasks were achieved at a rate that was only 70% slower than that of a normally functioning person. Project Objectives The goal of this project was to develop and build a powered arm orthosis for clients with symptoms of or similar to Muscular Dystrophy, in order to aid in tasks of daily living; improving independence and quality of life. To obtain the desired level of quality, the design would have to meet specifications in the following categories: ● Comfort ● Safety ● Aesthetics ● Ease of use ● Functionality ● Durability Results 1.Succeeded in powered, 2 - DOF motion in both independent and coupled motion. Humeral Rotation: 95° Elbow Flexion:110° 2. Prototype Load Capacity vs. Original Task Specifications: Humeral rotation : 166% Elbow flexion :120% 3.With the feature of coupled motion, the device achieved a 41% speed increase in motions that would be completed by each degree of freedom independently. 4.Orthosis weighs 5.2 lb, a 48% improvement in weight reduction over previous design. 5.Activities of Daily Living (brushing teeth, combing hair, drinking, blowing nose, washing face) completed at a rate of only 70% slower than that of a normally functioning person. Frame Subassembly Elbow Flexion Subassembly Humeral Rotation Subassembly Mechanical Analysis Prior to manufacturing, stress analyses were conducted to ensure the prevention of failure under the maximum loading conditions. A Finite Element Analysis was performed on the elbow joint sprocket and other critical components to see how they would perform under the maximum loading conditions. Stress calculations on the elbow flexion worm determined the relationship between safety factor and applied torque on the worm under maximum loading. Final Design The orthosis consists of three subassemblies: frame, elbow flexion, and humeral rotation. The frame provides rigid support to the user’s arm and allows for fluid motions in each degree of freedom. The elbow flexion subassembly utilizes a gear train assembly, driven by a DC motor, which applies a torque to a sprocket that is affixed to the forearm portion of the frame. By driving the motor in either direction, the forearm portion of the frame articulates up or down. The gearing system amplifies the motor’s torque by 54x and incorporates an inline slip clutch. The humeral rotation subassembly includes a circular track around the upper arm, which creates humeral rotation by rotating the frame and lower arm, while stabilizing the upper arm. The humeral rotation is driven by a bevel gear set and a worm which translates circumferentially around the circular track on a custom delrin slider. Recommendations Lighten design by use of more lightweight materials that do not compromise strength or structural integrity Lighter/Higher torque motors for increased power and lighter overall design weight Adjustable humeral bars to fit a wider range of clientele Condensed circuitry for increased portability Special Thanks:Gary and Andy of the Massachusetts Hospital School User Controls The orthosis is controlled by the user through a joystick interface, and is powered by a 12 volt source. The joystick control works by sending a signal through a dual H-bridge circuit, which drives the intended motor in the appropriate direction through polarity switching. The electronics are neatly arranged within a box with connections for the joystick, power cables to the 12 volt source, motor cables, as well as a battery meter display for protection in the event that the orthosis is being run by a portable battery source. Humeral Rotation Elbow Flexion Final Design Prototype Control System