The handheld device could be a smartphone or even a custom piece of hardware for First Responders. This device collects the sensor data and combines with any additional sensor data of its own, to pass over a High Frequency radio link, to a basestation.
Other technology that we're investigating the potential of:
- Energy harvesting, from sole deflection, has the potential to significantly improve the life of the product
Accelerometers and gyroscopes provide high sample rate inertial measurements, however inertial measurements must be integrated multiple times to obtain the displacement. This leads to exponential growth in positioning error.
These errors can be reduced through:
- Data-fusion with slower, but more accurate sensors
Filtering is implemented in our algorithms to reduce noise propagation, prior to integration. Initially we are using a basic Kalman filter, but higher order filters will be explored throughout the project.
Zero Update is effectively live calibration, thanks to the mechanics of the human foot - each foot is held stationary for a significant period of the step cycle. This is illustrated in the figure left.
As the device undergoes high accelerations during steps, stationary periods can be detected to remove accumulated errors, improving the acccuracy of positioning. The detected stationary period is highlighted on the figure also.