Observer-Based Complementary Filter Design for a Hexapod-Based Calibration Device With High-Bandwidth and Large Stroke

To ensure that multi-axis vibration sensors provide accurate and reliable measurements, a hexapod-based calibration device (HBCD) with high-bandwidth and large stroke needs to be developed. The high-bandwidth motion provided by the HBCD can reach up to hundreds of millimeters at low frequencies and drop to only micrometer level at high frequencies. The decline of the feedback quality with the increasing frequency severely deteriorates the control performance of the HBCD. This study presents the design of an observer-based complementary filter (OBCF) to estimate the high-bandwidth motion state of the HBCD, addressing both low-frequency, large-stroke and high-frequency, small-stroke motion. A model-based nonlinear observer is constructed to remedy the position measurement by employing the control force. And a complementary filter is formed to combine the best frequency ranges of the control force and the position measurement. Stability of the feedback control system when implementing the OBCF is analyzed. Comparison experiments are conducted to evaluate the effectiveness of the proposed OBCF in achieving the high-bandwidth motion. The experimental results demonstrate that the testing capabilities of the HBCD are enhanced at high frequencies. The repeatability of the circular motion at 100 Hz and the harmonic distortion of the sine motion at 100 Hz can be enhanced from 0.46 to 0.22 m/s2 and 25.2% to 6.2%, respectively.