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

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 i n principle limited to the pixel size, the output data from the CCD usually have been interpolated in some way for better resolution measurement. Howe ver, the ordinary digital method is difficult to apply to high-speed measur ement because of the extra processing time required for analogue-digital co nversion, memory storage and calculation. Our proposed analogue method real izes position measurement with subpixel resolution, leaving the analogue hi gh-speed performance unchanged. The proposed method features realization of an interpolation algorithm exclusively with analogue circuitry, which calc ulates an actual peak position using the peak value and the values of the t wo pixels adjacent to the pixel that produced the peak value. We have desig ned and constructed the prototype circuitry for this system and experimenta l 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 i s effective for real-time, in-line and low-cost position measurement with s ubpixel resolution for a measurement system using a CCD.