Design and validation of Vicon Bonita motion capture system for use on the ESA short-radius human centrifuge in Cologne, Germany

Abstract

Background: Short-radius human centrifuge (SRHC) technology is being considered as a multi-system integrated microgravity countermeasure for our astronauts. To design SRHC countermeasures, it is essential to develop the ability to analyze and study the kinematics and dynamics of movement on a SRHC. Aims: By utilizing motion capture (Vicon Bonita) technology, subject movement can be tracked during centrifugation. The effects of camera mounting and vibration on the quality of data collected were the primary focus of this study. Methods: A camera mounting structure (cage) was designed to attach to the ESA short-radius human centrifuge (r=2.7m), to maximize available viewing area, and to minimize effects of vibration. Three tri-axial accelerometers were mounted, two on the cage and one on the nacelle (bed) to capture vibration effects. Motion capture and accelerometer data were taken at acceleration profiles of 0g (no movement), 0.5g, 1g, 1.6g, 2.3g, 3.7g and 4g in the Z direction (towards the feet). Fourier spectral analysis and FFT filtering were used to analyze frequency power spectra and estimate displacement of the cage. Root mean square error (RMSE) of the marker positions was analyzed across acceleration profiles. Results: Camera positioning allowed for the observation of the lower body area of the SRHC nacelle. Vibration related displacement of the cage increased proportionally with acceleration to a maximum of 5.1±0.87mm (90% peak to peak) at 3.7g, primarily in the sway (X) direction. At 4g, this vibration reduced to 3.3±1mm. Frequency analysis of vibration profiles of the nacelle and cage showed maximal power spectra at 13Hz in sway and 38Hz in surge (Z) directions at 3.7g. Mean RMSE values across acceleration profiles showed a maximum position variation of 2.37±1.18mm.Conclusion: Motion capture and reconstruction were successful for static markers using the designed mounting apparatus. Vibration was minimized at the highest acceleration profile, hypothesized to be dampened under deflection during rotation. Mounting of the apparatus could be improved if modifications to the SRHC are possible. This configuration should be considered a worst-case scenario for vibration interference to motion capture. These results suggest the feasibility of capturing large movement dynamic motion, such as squat exercises, on a short-radius human centrifuge for analysis and modeling purposes.