Ankle Exoskeleton - added Stability/Mobility (Biomechatronics Lab) Mechanical Engineering Capstone

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As humans age, many will develop mobility impairments and different types of gait disorders, including hemiplegic and neuropathic gait. Some medical conditions including head trauma, stroke, cerebral palsy, and arthritis may cause the development of walking and stability impairments, which overall affects the quality of life. In order to minimize the effect gait disorders have on the human population, the goal of this project is to develop an external, attachable, lightweight device that will augment the mobility and stability capabilities of the user. To develop such a device, it is expected to be energy efficient, assist/adjust the gait of the user, lightweight, cost-effective, and support a variety of people with various medical conditions. Design considerations including the total weight of the device, energy storage capacity, maximum and control ability of supplying torque to the ankle as well as pressure to the foot, as well as surface finish were explored. Two modes of assistance, passive and active, were suggested in the design stages. A passive device would store and release energy without the usage of electronics to assist the gait of the user while an active device supplies energy for assistance through electronics. Literature review and function decomposition were conducted in order to aid in the development of a design. Several full designs were created and analyzed through a Pugh Chart and Morphological Matrix, resulting in the chosen design termed the Strawberry. The Strawberry featured an aluminum infrastructure with an Arduino-controlled motor-spring and lithium-ion battery system, with pressure sensors embedded within the baseplate to detect when a person is lifting or lowering their feet. After discussing this design with the client Dr. Lerner, some alterations were created. Due to the frailty of aluminum, carbon fiber would be utilized as the infrastructure of the Strawberry due to its strength and elastic properties. The original motor specifications did not provide enough energy to the electrical system. Two alternative options were suggested, which includes a Maxon Cylinder Motor or a Maxon Semispherical Motor. The current design utilizes a lead screw linear actuator to transform the rotational motion of the Maxon Cylinder Motor to linear motion that will apply a pressure gradient across the baseplate, assisting with the upward and downward motion of the ankle and foot. For bilateral support, two of these mechanisms are placed on the sides of the foot for both even weight distribution and to execute more control in the device’s operation. The modifications to the Strawberry design will provide valuable insight on the efficiency of a fully contained ankle exoskeleton compared to the current designs where the motors are attached to the back of the individual. Potential risks of failure of the device were analyzed and mitigated through a variety of safety and warning mechanisms to the user, including internal failure detection and an automatic/manual off switch for active elements. DAQ system and stress analysis were conducted in order to ensure that prototype specifications are within the desired safe operational ranges. The Strawberry will undergo a series of level ground, incline, and staircase testing on human subjects in order to record and analyze the energy reduction the user is required to move in the different modes of ambulation as well as examine the form modifications to the user’s gait patterns when wearing the device through DAQ systems and motions capturing. The newest version of the model now called the Kiwi is pictured. To find out more information: www.ceias.nau.edu/capstone/pr...