A novel position measurement with subpixel resolution using a charge-coupled device

Abstract

This paper describes a novel subpixel measuring method using analogue data processing for a position-measurement system using a charge-coupled device (CCD). Since the position-measuring resolution of a system using a CCD is in principle limited to the pixel size, the output data from the CCD usually have been interpolated in some way for better resolution measurement. However, the ordinary digital method is difficult to apply to high-speed measurement because of the extra processing time required for analogue-digital conversion, memory storage and calculation. Our proposed analogue method realizes position measurement with subpixel resolution, leaving the analogue high-speed performance unchanged. The proposed method features realization of an interpolation algorithm exclusively with analogue circuitry, which calculates an actual peak position using the peak value and the values of the two pixels adjacent to the pixel that produced the peak value. We have designed and constructed the prototype circuitry for this system and experimental results demonstrated that the prototype circuitry has a resolution of the order of 1/10 pixel. We conclude that the method described in this paper is effective for real-time, in-line and low-cost position measurement with subpixel resolution for a measurement system using a CCD.