CCD-based on-line thickness measurement system for calender

Abstract

An on-line calender thickness measurement system based on linear CCD is proposed. In this system, an optical projection method based on collimated light and CCD is used to realize the thickness measurement for sheet product. To test the accurate position of the edge of the sheet projection, a quadratic differentiating circuit and an accurate pulse width measurement method based on programmable counter array are used to deal with the CCD signals, which make the resolution up to 0.5μm for a linear CCD with 14 μm image sensing element size. Based on microcontroller, the integrated CCD sensor module and 2-D coordinate data acquisition module are developed to record the values of thickness and position coordinates. A distributed automatic data acquisition and control system is established by using the USB and RS485 serial bus to connect the host computer and measuring modules. In addition, to eliminate the factors that influence the on-line measurement accuracy, such as the roundness tolerance of roller, the irregularities of guide rail, an error compensation method based on multilayer feedforward neural network is used. The in situ experiments show that the on-line measurement standard deviation is 10μm within the measuring range of 10 mm.