Design and Validation of a Motion Capture System for use on the ESA Short-Radius Human Centrifuge in Cologne, Germany
Short-radius human centrifuge (SRHC) systems are being evaluated for their potential to provide efficient multi-system integrated countermeasures for astronauts exposed to microgravity for prolonged periods. It is thought that exercise in an artificial gravity environment might efficiently mitigate the negative effects of gravity unloading on the musculo-skeletal and cardiovascular systems. As the equations of motion for rotating environments are more complex than those governing normal terrestrial situations, it is essential to develop an ability to analyze and study the kinematics and dynamics of movement on a short-radius human centrifuge.
By utilizing motion capture (Vicon Bonita) technology, it will be possible to track the dynamic movements of subjects during centrifugation. The effects of camera mounting, placement and vibration on the quality of data collected were the primary focuses of this study. A camera mounting structure was designed to attach to the ESA short-radius human centrifuge (2.7m in radius). The design was intended to maximize the available viewing area of the SRHC nacelle (bed) and minimize the effects of vibration.
Three tri-axial accelerometers were mounted, two on the mounting frame, one on the nacelle to capture vibration effects throughout the testing. Motion capture data was recorded in static and dynamic trials at acceleration profiles of 0g (static), 0.5g, 1g, 1.6g, 2.3g, 3.7g and 4g in the Z direction (towards the feet). Dynamic marker capture was performed up to 2.3g on a Lego Mindstorms NXT robotic structure with pre-programmed motion profiles. Camera positioning allowed for the successful observation of the lower body area of the SRHC nacelle, necessary during squat exercises.
Vibration observed throughout the SRHC nacelle and camera mounting structure increased proportionally with acceleration profiles, primarily in the sway (X) direction, up to very high acceleration profiles. At the extreme acceleration profiles (3.7g and 4g) vibration was diminished — dampened under the consistent deflection of the mounting structure during rotation. Nevertheless, motion capture marker reconstruction for all trials was performed successfully, including all static trials and the dynamic marker trials available. The magnitude of vibration-induced displacement observed in the markers was identified to be minimal in comparison to the displacement of the pre-programmed motion profiles.
As a study of feasibility, motion capture and reconstruction was successful using the designed mounting apparatus in this experiment. Affixation of the camera mounting apparatus could have been improved if modifications to the SRHC were possible, however this configuration can be considered a worst-case scenario for vibration interference to motion capture. These results lend well to the notion that large movement dynamic motion, such as squat exercises, can be adequately captured on a short-radius human centrifuge for biomechanical analysis and modeling purposes.