Screen Printed Large Area Sensors for Pressure Distribution Monitoring in Wheelchairs
Sammanfattning: A sedentary lifestyle can induce health related problems including pressure ulcers. Prolonged sitting inadequacies constitute a risk for pressure ulcer to many individuals, in particular people with disabilities and reduced mobility. The measurement of distributed pressure and detection of irregular sitting postures are essential in prevention of the risk of developing pressure ulcers.In this thesis, a screen-printed pressure sensor for a large area is presented, with the objective of measuring the distributed pressure of a seated person in a wheelchair. The conductors and interdigital patterns are printed with silver-based ink. A blend of a non-conductive and a low resistive ink is used for customized resistance for an optimal sensing range of the pressure sensor. The effect of moisture and temperature are realized in an environment chamber. For characterization, other key performance tests such as repeatability, drift and flexibility are carried out. The surface morphology is carried out for structural analysis of printed samples. The sensor data is acquired and processed using an 8-bit ATmega-2560 microcontroller and wirelessly transmitted to a PC for post-processing, storage and analysis. For real-time data presentation of distributed pressure points, a GUI has been developed to display the values obtained from the large area sensor. The detection of four sitting postures; forward leaning, backward leaning, left leaning and right leaning along with a normal sitting posture is attained. An analysis for stretchable printed tracks has been conducted to investigate the changes in electrical resistance using elongation tests, surface morphology and EDS. The optimal curing time and temperature were investigated to manufacture stretchable conductive tracks.In summary, the contributions in this thesis provides an effective approach regarding pressure distribution measurement and recognizing irregular sitting postures for wheelchair users.
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