In order to simplify hardware system work effort and concentrate more on HCI system design and construction about HCI system research work, comparing the cost and performance of these sensor toolkits, CHR-6dm AHRS that is a cost-effective orientation effective sensor system is chosen in our research work. CHR-6dm is an IMU and AHRS from CH Robotics combining tri-axis rate gyros, tri-axis accelerometers, tri-axis magnetic sensors, and a 32-bit ARM Cortex processor all on one small and tiny board as the picture above, combining with an onboard EKF that handles the tricky data fusion problem, and outputs yaw, pitch, and roll angles at up to 300 Hz over a single TTL(3.3V) UART interface. These three angles informations are attitude estimation results calculated by embedded EKF module that needs 3-axis gyroscope, accelerometers and magnetometers all together. It provides built-in routines for gyro bias calibration, and downloadable Personal in Computer (PC) software with convenient functions for system configuration, automatic soft and hard iron magnetometer calibration, data visualization, and also data output as log file for data analysis as well . In the log data output by CHR-6dm PC software, attitude estimation result calculated by EKF, accelerometers, magnetic, and gyroscope sensors measurement data are included for data processing.
To improve the quality of sensor signal, the combination of median filter and mean filter with the data window size as 7 was practiced and tested to output better signal with less noise and outlier signal of sensor to preprocess sensor signal for further information acquirement and estimation. A high pass filter was also integrated to remove gravity element from measured signal. Furthermore, the coordinate transformation from measurements in the body frame to absolute coordinate and integral algorithm realization could help to get movement trajectory information that could be understood by machine and realize gesture interaction. Some related observation and measurement experiments are implemented and experiment data exhibits that our developed and integrated sensor systems could work normally and measure accelerator and rotate angular rate together for movement. The static measurement of EKF result and the trajectory display of the movement measurement of CHR-6dm also prove the scientific feasibility of statusinformation acquirement and gesture interaction of this HCI hardware system.
