An IMU-to-Body Alignment Method Applied to Human Gait Analysis

This paper presents a novel calibration procedure as a simple, yet powerful, method to place and align inertial sensors with body segments. The calibration can be easily replicated without the need of any additional tools. The proposed method is validated in three different applications: a computer mathematical simulation; a simplified joint composed of two semi-spheres interconnected by a universal goniometer; and a real gait test with five able-bodied subjects. Simulation results demonstrate that, after the calibration method is applied, the joint angles are correctly measured independently of previous sensor placement on the joint, thus validating the proposed procedure. In the cases of a simplified joint and a real gait test with human volunteers, the method also performs correctly, although secondary plane errors appear when compared with the simulation results. We believe that such errors are caused by limitations of the current inertial measurement unit (IMU) technology and fusion algorithms. In conclusion, the presented calibration procedure is an interesting option to solve the alignment problem when using IMUs for gait analysis.The work presented in this paper has been carried out with the financial support from: (i) the Commission of the European Union, within H2020, specific RTD programee “ICT 24 A. Research & Innovation Actions to Advance Key Technologies Relevant for Industrial and Service Robotics”, under contract H2020-ICT24-2016-688175, “XoSoft, Soft Modular Biomimetic Exoskeleton to Assist People with Mobility Impairments”; (ii) Brazilian funding agencies CNPq (308529/2013-8), CAPES (PGPTA 3457/2014, PVE A126/2013) and FAPES (67566480, 72982608). We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI)