Development of instrumented insoles for biometric parameters monitoring

Abstract

The study of the plantar pressure distribution is becoming a very important tool to obtain information about any type of foot or gait disorders in many fields such as medicine, rehabilitation and sport. This work describes the design and development of an instrumented insoles named ECnsole to measure not only the plantar pressure distribution, but also many others variables related to gait such as time support, centre of pressure, position of the foot in swing phase, etc. Four different version of the ECnsole are presented. Version 1.0 consist of two datalogger devices that sample and send the data to aMiWi™ receiver at a personal computer (PC) (or store it into ¹SD memory card) connected two a pair of insoles which contains four pressure sensors located at big toe, 1st and 5th metatarsal heads, and heel, and one analogue accelerometer placed in the arch of the foot. In the next version the two dataloggerwere joint into just one placed at thewaist in order to reduce both complexity in communications and costs, this version was enumerated as 1.2. In ECnsole version 1.5 the analogue accelerometer was replaced by a digital inertial measurement unit (IMU), integrated by a 3D gyroscope, 3D accelerometer, and 3D magnetometer, placed in the arch of the foot. The location of the datalogger unit was also the waist. In the last prototype described, the whole electronic system is embedded inside the insole. ¹SD memory card socket is removed andMiWi™is replaced by a Bluetooth transceiver. Moreover, a pair of additional pressure sensors are added to the 3rd metatarsal and to the midfoot area. An android application have been designed also to plot the data obtained by the instrumented insoles. The prototypes have been validated both for the pressure sensors and for the IMU. To validate the pressure sensors a commercial in-shoe system F-Scan was used together with ECnsole. In case of the IMU, an algorithm to obtain the foot orientation during the swing phase have been used, comparing the resulting euler’s angles with the angles measured using an infrared video camera system, obtaining very good agreement in both cases.