A Machine Vision System For Real Time Inspection Of Moving Web

A machine vision system for real time inspection of moving web is discussed. The system is for use in detecting, locating, identifying, classifying and sizing defects on a moving sheet of web and, mapping the defects detected on the roll of web being inspected on a printer. On the latter, the precise location on the X and Y axes on the roll of web for each defect detected is recorded using a code whereby the type of defect is identified and it's size reported. The system's unique configuration of hardware components includes a novel Time Delay and Integration (TDI) type camera as the sensors, a novel image processing board directly coupled to the TDI camera forming a camera-image processing board subassembly and, a novel master timing and synchronization board subsystem. The latter being capable of synchronizing the triggering, timing and sampling time of multiple channels within the TDI sensor and multiple TDI camera-image processing board subassemblies, in parallel within the same time frame, by controlling a novel master clocking scheme within a TDI logic circuit, contained within each camera, wherein the clocks' speed for data output, in Megahertz (MHZ), remains constant regardless of web speed whereas, the imager clocks' speed and signal format varies with web speed. This allows a high level of stop motion at any web speed including high speeds, that is, motion within the defined pixel size on the web during sampling time being less than 0.00002" (0.02 mils) and, renders the system immune to process vibrations. Furthermore, through routines in firmware, the system's performance and abilities are not affected by web speed variations. The system is integrated on a 20 slots AT2 compatible backplane having a PC bus single board AT2 compatible computer system wherein is contained various routines to generate data by processing various types of defects on various types of webs which are downloaded on to each of the image processing boards' programmable chips at system start-up by a master program. Contained therein is an expert system master program especially conceived and designed for the purpose of this system having routines to operate the boards, render logical decisions based on the data generated by the image processing boards, and generate the required reports. The system also comprises a subsystem, controlled by routines contained in the master program, which maintains the intensity and uniformity of web illumination within 0.5%, according to the type and thickness of the web being inspected, and controls the various positions of the illumination source's components. The standard configuration of the system developed produces a pixel size on the moving web of 0.0025" (2.5 mils) but can be configured to have a smaller or larger pixel size, the latter being proportional to the number of camera-image processing board subassemblies used.