Development of a transfer function for DML's IMU

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DML's GaitSmart system uses Inertial Measurement Units (IMUs) to measure how a person's limbs move when they walk. This data is then presented in a simple to read report and can also be used to determine a personalised exercise plan. There are many conditions that affect the way a person walks, including osteoarthritis, frailty, stroke and Parkinson's Disease.With the early onset of conditions, changes from a normal gait pattern are small, and therefore it is essential that the measurement system is accurate to within a degree. And for a Medical Device this accuracy should be referenced back to SI Units.DML has already ascertained the accuracy from steady state cyclic motion through a previous successful A4i project with NPL. The aim of this project is to extend this so that it includes the accuracy when natural interferences are introduced as a result of medical conditions and gait events such as heel strike.In order to do this the IMU needs to be subjected to an impulse response during cyclic movement in the different planes. The orientation measured using a metrology system and the IMU response will then be used to determine the transfer function. This transfer function can then be used to determine the expected accuracy under any motion that the IMU may be exposed to.This approach will be applicable for any company with an IMU based system and will provide a reference standard back to SI units. As wearable technology becomes more widespread the need for a reference standard becomes essential. This project will enable NPL to offer the solution developed in this project.