Challenge: The Pathlock device provides a means for manual wheelchairs users to propel themselves forward in a straight line over uneven surfaces or cross slopes without the need to continually correct the direction of travel. I was tasked with developing a concept that relied entirely on magnets to provide a variable strength locking function to the caster.
Process: I began this project with research into the cost, weight and strength of various magnets, since they would perform the main function of the device. After developing and quickly prototyping a range of locking devices, such as a low friction mock-up pictured to the right, I performed quantitative testing, measuring the strength and angle of attraction across various concepts.
From this point, I refined a concept that allowed for variable strength via three magnets that interfaced with a steel plate mounted to the caster, as pictured below. I also designed a robust handle and cable operated remote lever to provide mechanical advantage to the user and precisely select the desired setting.
Using this fully functional prototype, I developed a series of criteria for evaluation. This testing pushed the concept to include larger, more powerful magnets that had to be carefully shaped to interface with their counterparts. The resulting device was strong enough to provide enough resistance to keep the user in a straight line, at the cost of an increase in the overall weight of the chair.
At this point in testing, it was determined that a spring loaded mechanism provided a better solution at lower cost and weight.
Challenge: The Single Motor Propelled Wheelchair (SiMPL-WC) is a modular powered mobility device developed at the Human Engineering Research Laboratories. This adjustable four bar linkage hard stop was design to support the novel suspension system, to guarantee the device would not reach an unsafe angle of deflection.
Process: To integrate fluidly with the existing system, I modified the original linkage to interface with a hard stop bolted to the frame. The hard stop was designed with wide fillets to increase overall strength and a hard resin insert which allows for variable thicknesses, which are extrapolated from the weight of the user. The insert also provides cushion during impact, reducing noise and vibration.
After the system was modeled in Solidworks, FEA ensured the design was mechanically sound. The parts were wire EDM cut and finished on a manual mill, welded, and hand mounted on the existing prototype chair.