A CCD Camera-Based System for Slit Width Measurement of a Long Precision Slot Die

摘要

This paper describes a slit width measurement system for long precision slot dies. A CCD-camera with its optical axis in the Y-direction, is scanned along the slit length of the slot die in the X-direction to take the images of the slit. The Z-directional positions of the two edges forming the slit are determined from the binary image of the slit. The slit width in the Z-direction, can then be calculated from the edge positions. The system has advantages of non-contact, high speed and high resolution. A 1.4m long slot die with a designed slit width of 150μm is measured by the measurement system. The magnification of the objective is set to be 1000x to obtain a field of view of 310μm (Z) × 230pm (X). The pixel numbers of the CCD are 720 (Z) x 480 (X). A proper threshold for binarization of the CCD image is chosen for reducing the influence of the Y-directional straightness error of the scanning stage. The time for scanning the entire length of the slot die is 30 seconds. Experimental results have shown the measurement system can achieve sub-micrometer slit width measurement.