| Summary: | 碩士 === 國立成功大學 === 醫學工程研究所碩博士班 === 94 === Wheelchairs are main products within the market demand of the medical instruments nowadays. In the past years, either manual or powered wheelchairs had been designed to move on level ground. However it still has not been satisfied for the users to move in vertical direction. Consequently, an innovative design for a wheelchair with adjustable seat height will be an inevitable trend to establish a more functional wheelchair.
The drawbacks of modern designs for vertical movements of a powered-wheelchair include an excessive height of the chassis which results in difficult to access and a mal-planning of the mass centroids between the wheelchair and user which usually increases the risks of fall. Otherwise, an improper mechanical design for lifting and lowering the wheelchair may injure the user’s body segments.
This study presents a new mechanism design, Position Power Screw of 3-Stage Type, to achieve a safe seat-height adjustable function. The new design and analysis can overcome the above-described drawbacks, and do an accurate upward or downward motion of seat height. The system was divided into structural design and control simulation. The design rationale is that a power screw which is an element for precision positioning device providing up to different travel ranged will play an important role for the mechanism with variable seat height. Based on the different power screws combined, the mechanism efficiently overcomes the excessive height of the chassis when the seat lowers down to the lowest position. In order to assist the screw structure in supporting the external force and moment from the user or environment, the support mechanism was designed to improve the stability and strength for the whole structure. The whole designed structure was estimated the reliability and feasibility of structural strength in consideration of safe factors by FEM. Intelligent variable height system designed to solve the problem of mass mentroid was separated into static and dynamic system. Static system makes the seat height variable move in vertical direction by the user’s command when the wheelchair is stop. Dynamic system architecture modeled by combining inverted pendulum system and anatomical viewpoint can adjust the seat height automatically and keep the user stable without bending his/her trunk when the wheelchair detects different inclinations of a ramp. The two systems will be simulated via Simulink and estimated the validity and feasibility. And the designed system will not only detect the inclinations of a ramp and then adjust the seat height automatically but also keep the user stable from falling. According to the design and control system of this new mechanism, it can provide an excellent practicability and safety for a powered wheelchair. In the future, it may apply to other industrial applications.
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