Fast and accurate vision-based positioning control employing multi-rate Kalman filter

To achieve fast and accurate positioning control, a controller based on a visual servo employing a multi-rate Kalman filter was implemented and experimentally evaluated. Although a visual servo is expected to achieve robust positioning control by eliminating positional errors due to operation environments, applying visual information to positioning control faces three challenges, namely, lower sampling speed, longer delay, and lower positional accuracy than those possible by using a conventional position encoder. To overcome these problems, a multi-rate Kalman filter with a time-delay compensation technique is employed to combine visual information with encoder-based positional information. Two models describing a positioning-control experimental system using a one-axis linear stage with a camera were investigated to determine the optimum structure of the Kalman filter. Evaluation of the experimental system showed that the designed controller achieves high-precision (±10 μm) positioning control within approximately 10-ms settling time while simultaneously adjusting the environmental positional errors.