Abstract

To aid in the design of future wearable health devices (WHDs), contact pressure between the distal forearm (wrist) and two different wrist-worn devices was investigated in this work. The first device included eight force sensors arranged in series along the length of a wristband to measure the pressure profile. The band also included a tensioner device for manually tightening the band while on a wrist. Testing was done on dummy wrists and the results were statistically significant supporting the hypothesis that areas of the wrist with lower radius of curvature will experience higher contact pressures generally and a faster rate of change in pressure as the band is tightened. The second band included a controller, actuator, and force sensors for actively controlling the contact pressure of a photoplethysmography (PPG) sensor on the wrist during user motion. A total of eight tests were performed on six human subjects to estimate previously unknown design parameters related to contact pressure control of a wrist-worn device. Participants were asked to perform several actions including tapping their finger at different rates, tossing a ball, wrist flexion and extension, and making a fist. The design parameters investigated were system stiffness, range in contact pressure caused by motion, range of motion in the radial direction required to maintain a desired pressure, arterial pulse pressure amplitude and its relation to pressure tolerance, and system response time required to maintain a constant pressure. System stiffness was observed to be greater during motion (dynamic) than during rest (static) and to increase with increasing contact pressure. The change in contact pressure caused by motion was around 18 kPa in some cases and the maximum range of motion to maintain a contact pressure was about 7 mm. The arterial pulse pressure amplitude ranged between 0.05 to 0.3 kPa. It was estimated that a maximum sensor platform speed of 30 mm/s or greater is required to maintain a constant contact pressure during large motion actions such as flexing the wrist up and down. Finally, no significant differences were observed in the PPG signal between states in which the contact pressure was controlled vs. not controlled.

Degree

College and Department

Ira A. Fulton College of Engineering; Mechanical Engineering

Rights

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