3D Displacement, Velocity, and Acceleration of Seated Operators in a Whole Body Vibration Environment using Optical Motion Capture Systems

Whole body vibration (WBV) is traditionally monitored using accelerometry, but optical motion analysis techniques may provide a means to investigate both vibration exposure and kinmatic joint motions simultaneously. While each method has strengths and weaknesses, the objective of this work is to combine these methods into an efficient and effective methodology to obtain three dimensional motion data for WBV. Optical motion capture systems and accelerometers have been used in this article to collect three dimensional (3D) motion data from three seated heavy machinery subjects under five rides that simulate off-road whole body vibration scenarios using a platform motion simulator. 3D displacement data obtained from markers are smoothed and then double differentiated using a five point central finite difference method to obtain linear acceleration values. A number of filtering and smoothing techniques have been implemented to obtain realistic linear acceleration from the markers data. These methods include low pass digital filtering (LPF), B-spline approximation (BSA), wavelet decomposition and reconstruction (WDR) and singular spectrum analysis (SSA). By using four markers and one accelerometer on each segment, the 3D angular velocity and angular acceleration values have been determined. The process of using markers has been designed to achieve two goals. The first goal was to obtain local coordinate system to guide the accelerometer throughout the trial, and the second, was to help in finding the angular velocity and angular acceleration of the segment. The goal of using accelerometers was to define a guide for subsequent filtering operations. The effectiveness of filtering was compared to the accelerometer data in the frequency domain in terms of 1/3-octave band-pass filtering and power spectrum. The results demonstrate the significance of using optical motion capture markers with a minimal number of accelerometers to obtain realistic 3D motion data in a whole body vibration environment. Keywords-component; motion capture; accelerometers; vibration; filtering.