Abstract
This paper presents the design and testing of a wrist-worn Wearable Health Device (WHD) with an integrated compliant Constant-Force Mechanism (CFM) as part of the wrist band, acting to keep the band tension constant. An integrated CFM can keep pressure on the wrist constant or near-constant, thereby solving one of the main difficulties (movement of and varying force on the sensor area) that wrist-worn WHDs face. The design requirements for a constant-force wristband were narrowed down to seven critical requirements. Multiple CFMs were explored with two main concepts (buckling beams and tape springs) prototyped and evaluated against the key requirements. The tape spring concept was chosen for human subject trials testing due to the mechanism’s better performance compared to the buckling beams concept. The human subject testing (IRB2020-268) compares pressure on the wrist for both a band with and without an integrated CFM for eight different movement activities. The band with the integrated CFM produced reduced variation in the pressure on the wrist, but the difference was not significant. In addition, it was found that, even with the CFM, the band’s sensor location shifted during human motion. Future work will focus on alternative ways of reducing pressure variation, including constant force mechanisms that apply force directly to the sensor package, rather than acting to keep band tension constant.