Measuring Behavior 2005: Roetenberg

3D motion analysis applying inertial sensing

D. Roetenberg

Twente University, Enschede, The Netherlands

Small inertial sensors like accelerometers and gyroscopes are more and more used in ambulatory motion analysis. Typically, angular orientation of a body segment is determined by integrating the output from the angular rate sensors strapped on the segment. Microelectromechanical (MEMS) gyroscopes are accurate for angular velocity measurements but can only be used for a short time to calculate angular orientation. A relatively small offset error due to temperature effects on the gyroscope signal and noise will introduce large integration errors. Linear accelerometers measure the vector sum of acceleration a of the sensor and the gravitational acceleration g. In most situations of human movement sensing, g is dominant, thus providing inclination information that can be used to correct the drifted orientation estimate from the gyroscopes. However, accelerometers cannot detect rotations around the vertical axis, therefore, additional magnetic sensing is required. The magnetometer is sensitive to the earth’s magnetic field. It gives information about the heading direction in order to correct drift of the gyroscope about the vertical axis. Several filters like Foxlin 1996 and Bachmann 2000 have been proposed to fuse gyroscopes, accelerometers and magnetometers for body segment orientation measurements. They work in real-time and seem accurate but they have an important limitation. Ferromagnetic materials, like iron, in the vicinity of the sensor will disturb the local magnetic field and will therefore distort the orientation measurement. This magnetic interference impedes many applications; especially the ones outside the lab like back load estimation for ergonomic purposes at assembly lines. In this study, a Kalman filter based on Luinge et al. 1999, is designed to fuse 3D gyroscope, accelerometers and magnetometer signals to estimate orientation and to compensate for magnetic interferences.

Paper presented at Measuring Behavior 2005 , 5^th International Conference on Methods and Techniques in Behavioral Research, 30 August - 2 September 2005, Wageningen, The Netherlands.