Force Sensor for Assisted Walking Exosuit
Development of a robust, low-profile tension sensor for webbing to be used in control and evaluation of suit that aids in walking.
At the Harvard Biodesign Lab, I have worked on designing, testing, and fabricating custom load cells for a soft, wearable "exo-suit" designed to reduce the metabolic cost of walking. One model is specifically designed to measure tensile forces in webbing.
Webbing is a strong, lightweight, and flexible material that experiences low extension. For these reasons, it is commonly used as an ergonomic interface for high-load uses, for instance, as seat belts or as straps for tote bags, suitcases, and backpacks. More recently, webbing has found an application in wearable robotics, a field that aims to assist or enhance human movement with devices worn on the body. One such device, the Warrior Web suit being developed at the Harvard Biodesign Lab, aims to decrease the body’s energy consumption during long or burdened walks. This goal is realized in a soft exo-suit design that pulls up at the heel, actuating the ankle, and communicating the reaction force to a network of webbing anchored to the hips and thighs. A low-profile tension sensor for webbing has the potential to provide information regarding the forces throughout the suit. In particular, an accurate measurement of force delivered at the ankle can be integrated into the suit to measure the force applied at the ankle joint.
I designed a load cell using conventional strain gauges to that could measure the tension in the webbing. I developed the circuit design and coded software-side calibration schemes to ensure stable and accurate signal from the sensor. The final prototype was less than 50 g and operated over a 25 to 350 N range with 5 N resolution and less than 3% hysteresis. The design was optimized for repeated manufacture and for interfacing with the electronics of future generations of the exo-suit.
Webbing is a strong, lightweight, and flexible material that experiences low extension. For these reasons, it is commonly used as an ergonomic interface for high-load uses, for instance, as seat belts or as straps for tote bags, suitcases, and backpacks. More recently, webbing has found an application in wearable robotics, a field that aims to assist or enhance human movement with devices worn on the body. One such device, the Warrior Web suit being developed at the Harvard Biodesign Lab, aims to decrease the body’s energy consumption during long or burdened walks. This goal is realized in a soft exo-suit design that pulls up at the heel, actuating the ankle, and communicating the reaction force to a network of webbing anchored to the hips and thighs. A low-profile tension sensor for webbing has the potential to provide information regarding the forces throughout the suit. In particular, an accurate measurement of force delivered at the ankle can be integrated into the suit to measure the force applied at the ankle joint.
I designed a load cell using conventional strain gauges to that could measure the tension in the webbing. I developed the circuit design and coded software-side calibration schemes to ensure stable and accurate signal from the sensor. The final prototype was less than 50 g and operated over a 25 to 350 N range with 5 N resolution and less than 3% hysteresis. The design was optimized for repeated manufacture and for interfacing with the electronics of future generations of the exo-suit.
Views of the webbing tension sensor
Figures demonstrating exo-suit design from A. Asbeck, R. Dyer, A. Larusson, and C.J. Walsh, ”Biologically-inspired soft exosuit,” Proceedings of the IEEE International Conference on Rehabilitation Robotics, Jun 2013:1-8, 2013, Link
Note: This material is based upon work supported by the Defense Advanced Research Projects Agency (DARPA), Warrior Web Program.
© Ishan Chatterjee 2020