Development of a wearable plantar force measurement device for gait analysis in remote conditions

Flexible sensor matrix film-based wearable plantar pressure force measurement and analysis system

Plantar pressure force data derived from gait and posture are commonly used as health indicators for foot diagnosis, injury prevention, and rehabilitation. This study developed a wearable plantar pressure force measurement and analysis (WPPFMA) system based on a flexible sensor matrix film to monitor plantar pressure force in real time. The developed system comprised a flexible sensor matrix film embedded in the insole of the shoe, a wearable data acquisition (DAQ) device with a Bluetooth module, and dedicated software with an intuitive graphical user interface for displaying the plantar pressure force data from receivers by using a terminal unit (laptop or smart-phone). The flexible sensor matrix film integrated 16 piezoresistive cell sensors to detect pressure force at different anatomical zones of the plantar and under different body positions. The signals from the flexible sensor matrix film were collected using the DAQ module embedded in the shoe and transmitted to the receivers through Bluetooth. The real-time display and analysis software can monitor, visualize, and record the detailed plantar pressure force data, such as average pressure force, maximum pressure force, and pressure force distributions and variations over time. The outcomes of the trials in which the system was worn revealed the applicability of the developed WPPFMA system for monitoring plantar pressure force under static and dynamic wearing conditions. The plantar pressure force data derived from this system provide valuable insights for personal foot care, gait analysis, and clinical diagnosis.

PI-Sole: A Low-Cost Solution for Gait Monitoring Using Off-The-Shelf Piezoelectric Sensors and IMU

In this paper, viability of low-cost off-the-shelf Piezoelectric ceramic disc elements is explored for an insole-based gait monitoring system, `PI-Sole' (Piezo In-Sole). Piezoelectric elements can sense dynamic changes in pressure in a closed-loop environment with good sensitivity and a wide measurement range. In this paper, method to enable these elements to continuously sense plantar pressure while walking is proposed, making them a very cost-efficient alternative to the widely used Force Sensing Resistors (FSR) and pressure plates for monitoring human gait. However, piezoelectric elements show hysteresis in their force response, inducing a drift in calculated pressure which increases with time. A novel and effective method to perform detrending of the signal is also presented utilizing stride contexts from a 6-DoF Inertial Measurement Unit (IMU) and the same is utilized to perform zero-correction in the pressure data. 3-D trajectories of strides are calculated using the IMU, and parameters like stride length, stride height etc. are further derived. In order to test the validity of our proposed methods, important kinetic parameters like Vertical Ground Reaction Force (VGRF) and Center of Pressure (CoP) are calculated using PI-Sole and compared to the ones calculated using FSR's in multiple prior works. Applicability of PI-Sole is demonstrated further by depicting and analysing characteristic differences between a heel-strike toe-off stance type, and a flat-strike stance type, the latter being one of the primary symptoms in many cases of pathological gait, including Parkinsonian gait. Important artefacts from foot's height profile while walking are analysed for both stance types in context of standard gait events. We report a mean error of 2.8cm in stride length calculation, and a mean accuracy of 94.5% in calculating swing/stance duration of gait cycles.