Application of Nonlinear Integrated Design Process to Assistive Device Product Development: Electric Wheelchairs for Seniors

With the advancement of technology, lifestyle, and diversification of user and market demands, and product design and development processes have been complex. Additionally, challenges for interdisciplinary collaboration have intensified. Identifying and addressing problems at an early stage can reduce costs in the development process. Consequently, the objective for manufacturers and design teams is systematic development as an operational framework. We created products to meet market demands while minimizing research and development costs and maximizing operational efficiency. In current electric wheelchairs, flaws are found in a hard-to-use folding mechanism, increased friction owing to side folding, and a large size post-folding leading to poor mobility. This study was conducted to meet the needs of senior wheelchair users and enhance practicality, aesthetics, and cost-effectiveness in product development. The nonlinear integrated design (NLID) process was used as an operational model to develop an electric wheelchair with a one-touch automatic open and fold for seniors. The NLID process was developed referring to the Double Diamond design process proposed by the British Design Council and the Five-Step Design Thinking Model proposed by Stanford University. Based on user needs, the NLID process with innovative and practical concepts was developed for interdisciplinary product design and development, and interdisciplinary integration. The process was based on four core principles: eight operational steps, three convergence processs, and the cyclical operation of the four feedback loops. With the process, a systematic nonlinear integrated design method was created for product development. The designed electric wheelchair exhibited the following features: (1) Front and rear quick folding mechanism: Unlike traditional left-right folding wheelchairs, this model incorporates a parallel four-bar connecting system. By pressing a button on the right-hand side of the back armrest, the electric pushrod beneath the seat swiftly retracts, facilitating rapid folding without the need for excessive preliminary actions; (2) Reduced size: The wheelchair’s folded size was decreased by 50%, enabling easy placement in a 1200-cc car trunk and allowing seniors to easily carry it; (3) small wheels: The folded electric wheelchair was equipped with two small auxiliary wheels on the handlebar, simplifying the process of pushing it into and out of a car’s trunk. The research results provide a reference for assistive product designers using the NLID process.