Inertia-based angle measurement unit for gait assistive device

Abstract

The study and estimation of various joint angles in humans has important significance in medical treatment, rehabilitation, physical training and so forth. Exoskeleton devices that can enhance human’s performance or assist disabled people have been developed in recent years. This paper describes a developed measurement system to estimate various human joint angles during a human gait using a MEMS bases low-g three-axis accelerometer (ADXL 335). A LabVIEW-based measurement system is developed to calculate the tilt angles of the accelerometer, based on the physical model of three acceleration components of the same. With the developed algorithm based on tri-axis tilt sensing, an ADXL 335 IC is used for measuring roll and pitch components, which are of numerous use in rehabilitation robotics. A combination of three sensor assembly is used per leg to calculate various joint angles viz. hip, knee and ankle. NI cDAQ-9172 with NI 9205 I/O module is used for acquiring signal from the accelerometer and the algorithm is implemented in LabVIEW-2012. Data for individuals from different age groups were recorded for different gait speed with this measurement system and dynamically tested against standard Biometrics Ltd. goniometer assembly. An accuracy of ±1 degree was achieved with this measurement system.