Preliminary Study of 3-D Dynamic Interactions Between Backpack and Bearer for Health Monitoring Using a Multiple Sensor Method

During loading carriage, the pack interaction forces exerted on the human torso directly relate to perceived discomfort and the risk of injury. Understanding these interactions will help to assess human health in real-world scenarios. However, 3-D interaction forces between the pack and torso are challenging to be directly measured from single-function sensors. In this article, we proposed a sensor-fused method integrating multiple 3-D accelerometers and gyroscopes to estimate the dynamic interactions between them. This method uses linear and angular accelerations from multiple sensors to derive 3-D dynamic pack forces and moments, without requiring numerical differentiation or integration of the signals. We validated the calculated 3-D pack forces with the measurements from the multicamera motion analysis system at three walking speeds while carrying a 24.5-kg backpack. Time traces of the predicted pack forces showed good agreement with the measured data, especially for the two major pack forces (tangential and normal), with relative root mean square errors (RMSEs) well below 3.5% and 6.8%, respectively. Peak pack force can reach up to 500 N, more than twice the pack weight during load carriage. Sensitivity analysis showed that redundancy from an increased number of sensors could be used to improve calculation accuracy and pack mass center estimation error had only moderate effect on predicted results. The proposed multisensor method can effectively evaluate 3-D dynamic interaction forces between backpack and bearer while carrying a load and provide insights to improve the design of load carriage systems.