VOL. 3, NO. 6, JUNE 2019 6001004 Sensor applications A Novel Approach for Real-Time Gait Events Detection Using Developed Wireless Foot Sensor Module Ratan Das 1,2, , Neha Hooda 1,2 , and Neelesh Kumar 1,2 1 CSIR-Central Scientific Instruments Organisation, Chandigarh 160030, India 2 Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India Manuscript received March 16, 2019; revised April 5, 2019; accepted April 29, 2019. Date of publication May 3, 2019; date of current version June 3, 2019. Abstract—This article presents a method for the detection of heel strike (HS) and toe off (TO) for overground walking using developed wireless foot sensor module (WFSM). The proposed algorithm uses variation of foot angle measured from WFSM for estimating stance and swing phase during human gait. The significance and novelty of the developed work lies in the fact that the method validates an approach for detecting gait events using foot angle variation alone, computed from a single inertial sensor. For 11 479 steps recorded from 34 healthy volunteers, it showed 100% true positive detection rate with a mean error of –12.9 ± 30.6 ms and 7.9 ± 10.8 ms for HS and TO, respectively, referenced against foot switches. One-way analysis of variance (ANOVA) test for gait cycle time computed from a force sensitive resistor and WFMS showed no significant difference (p > 0.01) between the two sensor methods. The developed system was benchmarked against Zebris FDM system (Zebris medical GMBH, Germany) and Kistler Force Platform (Kistler Inc., Colorado, USA) for comparing temporal gait parameters. The proposed work also reports an improvement in terms of detection latency and, thus, shows potential for real-time control applications. Index Terms—Sensor applications, gait, heel strike (HS), inertial sensor, sensor applications. I. INTRODUCTION Human gait is the way locomotion which is achieved using limbs. The analysis of gait involves assessment and measurement of param- eters related to human locomotion. One of the key components of gait analysis is the true detection of heel strike (HS) and toe off (TO). Both these events represent the phase shift between the stance and swing phase of a gait cycle and are crucial in estimating gait temporal parameters [1]. Inertial measurement units (IMUs) have been widely used for application in motion analysis owing to its light weight, small size, low power consumption, portability, and low cost. Many techniques for gait event detection such as thresholding [2], peak de- tection [3], zero crossing [4], [5], and rule-based state machines [6] have been reported for identifying gait events from inertial sensor data. Both accelerometers and gyroscopes have inherent noise char- acteristics such as drifts, multiple peaks, and thresholds, and thus, they yield poor detection when there is alteration of gait [7]–[9]. In this work, we considered variation of foot angle as a gait feature for identifying HS and TO. The foot angle variation is computed from acceleration and angular rate parameter obtained from the wireless foot sensor module (WFSM) using a complementary filter. There are several studies that computed human joint angles, including foot an- gle using inertial systems [2], [8], [10]–[15]. However, to the best of our knowledge, there is no reported work on HS and TO detection using foot angle variation as a standalone parameter, computed from a single IMU. Corresponding author: Ratan Das (e-mail: ratans16@gmail.com). Associate Editor: J. M. Corres. Digital Object Identifier 10.1109/LSENS.2019.2914719 Fig. 1. (a) Developed WFSM. (b) WFSM’s plane of measurement. (c) Placement on subject. II. MATERIALS AND METHOD A. Wireless Foot Sensor Module (WFSM) An IMU (GY-80) board, with a digital tri-axis Accelerometer (ADXL345) and a Gyroscope (L3G4200D), is used for measuring the acceleration as well as angular rate. Three types of footwear (U.K. size 6, 8, and 9) of same brand and design were fitted with force sensi- tive resistor (FSR) at identified positions beneath the Heel (FSR H ) and Toe (FSR T ) with an extra layer of insole on top. The top insole pre- vents damage of FSR and connecting wires from direct contact while providing physical and electrical insulation to the wearer. For data acquisition, preprocessing, and wireless communication, an Arduino Nano board coupled with a Bluetooth transceiver module (HC-05) is used. Data are seamlessly transmitted by the module at a baud rate of 38 400 and processed using an application developed in LabVIEW. A Lithium ion battery (3.7 V, 1500 mAh) and a dc–dc converter are used for powering the WFSM at 5 V with a current consumption of 80 mA. Fig. 1 shows the prototype of the developed WFSM and its plane of measurement. 1949-307X C  2019 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information.