Validation of an Inertial Sensor System for Quantifying Knee Function

Gait analysis has become a useful tool for clinicians in evaluating the progression of pathologies through functional analysis. The high cost and dedicated laboratories associated with the traditional camera-based motion analysis systems present the need for an alternative system. Direct measurement of kinetic parameters using inertial sensors (gyroscopes and accelerometers), in place of indirect calculations from position data obtained using cameras, has been shown effective in resolving important gait parameters. In order to directly compare gait parameters obtained using inertial sensors and a camera system, data was simultaneously collected from both systems for seven test subjects during normal gait. Three uni-axial gyroscopes and one tri-axial accelerometer were mounted on each subject\u27s right leg, as well as the reflective markers needed for the camera-based system. Knee flexion angle, angular velocities, and linear and angular accelerations were compared between the two systems. The similarities between the two methods validate the accuracy of the inertial sensor system with respect to the currently accepted camera-based method for some parameters. The errors found when comparing the two systems can be minimized by altering the number of sensitive axes of the sensors, as well as improving the accuracy of their placement. Such an inertial sensor system may provide an alternative that is suitable for use in a clinical setting

Signal Quality and Compactness of a Dual-Accelerometer System for Gyro-Free Human Motion Analysis

There is a growing interest in measuring human activities via worn inertial sensors, and situating two accelerometers on a body segment allows accessing rotational kinematic information, at a significantly lower energy cost when compared with gyroscopes. However, the placement of sensors has not been widely considered in the literature. In practice, dual-accelerometer systems should be built as compact as possible to ensure long-term wearability. In this paper, the impact of sensor placement and nature of human activity on signal quality is quantified by individual and differential signal-to-noise ratios (SNRs). To do so, noise-free signals are described by a 2-D kinematic model of a body segment as a function of kinematic variables and sensor location on the segment. Measurements are modelled as kinematic signals disturbed by zero mean additive Gaussian noise. Depending on the accuracy needed, one can choose a minimal SNR to achieve, with such dual-accelerometer arrangement. We estimate SNR and minimal sensor separations for three data sets, two from the public domain and one collected for this paper. The data sets give arm motion profiles for reaching, inertial data collected during locomotion on a treadmill and during activities of daily life. With a dual-accelerometer arrangement, we show that it is possible to achieve a good differential SNR for the analysis of various human activities if the separation between the two sensors and their placement is well chosen

Doctor of Philosophy

dissertationMotion capture has applications in many fields. A need has arisen for motion capture systems that are low-cost, mobile, and intuitive. An attitude heading reference system (AHRS) calculates the global orientation of a rigid body by synthesizing the output from an array of sensors. A complete motion capture system utilizing gyroscopes, accelerometers, and magnetometers attached to the main body segments of a human is proposed. This is accomplished by providind a low-cost calibration procedure for micro electro-mechanical system (MEMS) gyroscopes, accelerometers, and magnetometers in order to create a custom AHRS unit. The accuracy of reproducing global orientations using these AHRS units is analyzed for individual modules as well as redundant groups of AHRS nodes for increased accuracy. In order to make the system intuitive, a localization procedure for finding the locations of all AHRS units attached to the body is proposed. Sensors were successfully calibrated to an accuracy sufficient for AHRS development. The accuracy of the AHRS units was verified and led to a functioning motion capture system. The localization procedure was verified with volunteer subjects and successfully finds the location of all attached AHRS units

Measurement of Railway Track Geometry: A State-of-the-Art Review

The worldwide increase in frequency of traffic for passenger trains and the rise of freight trains over the recent years necessitate the more intense deployment of track monitoring and rail inspection procedures. The wheel-rail contact forces, induced by the static axle loads of the vehicle and the dynamic effects of ground-borne vibration coming from the track superstructure, have been a significant factor contributing to the degradation of the railway track system. Measurements of track irregularities have been applied since the early days of railway engineering to reveal the current condition and quality of railway lines. Track geometry is a term used to collectively refer to the measurable parameters including the faults of railway tracks and rails. This paper is aiming to review the characteristics of compact inertial measurement systems (IMUs), their components, installation, the basic measures of the quality of the track using motion sensors, like accelerometers, gyroscopes and other sensing devices mounted on different places of the vehicle. Additionally, the paper briefly discusses the fundamentals of inertial navigation, the kinematics of the translational and rotational train motions to obtain orientation, velocity and position information