Seat Backrest Morphing Using Nitinol Actuators

This thesis proposes a new method of seat cushion shape morphing. The proposed method is a flexible patch-based approach allowing localized morphing for areas of the back or neck that are often lack of support. The focus of this work is on the lumbar region to demonstrate cushion morphing to provide the needed support. The thesis introduces Nitinol, a shape memory alloy, and describes the process of making Nitinol springs as the actuators to bend a flexible panel behind the lumbar area for cushion morphing. An approximation theory has been developed to relate the human weight to the required stiffness for spring design and fabrication. The spring control issues have been studied to address, i) the blasting current for obtaining desired shape deformation, and ii) the holding current for maintaining deformation. Settling time and spring temperature have been studied to culminate in a final design. At last, the springs have been integrated with a cushion support panel in the lumbar area for a commercial chair. Along with a pressure sensing cover, a morphing chair backrest has been developed under a closed-loop control. It has been successfully tested that this chair can automatically adjust the lumbar profile according to an allowable sitting pressure.