Smart camera cuts the cost of web inspection
Web inspection involves examining vast quantities of material at extremely high speeds. Often, multiple line-scan cameras feed data into multiple frame grabbers or image processors where data are operated on in a parallel fashion. Not only is this expensive, it is unnecessary in situations where only known defects must be detected. This was the case at DuPont (Circleville, OH), where defects on thin films needed to be examined at speeds up to 200 feet per minute.
To reduce the cost of image-processing hardware, the system uses 12 time-delay-and-integration cameras with embedded digital video-processing algorithms from Dalsa (Waterloo, Ont., Canada). DuPont chose the 8-tap, 2048 x 96 CCD camera because of the data-reduction algorithms embedded in it, says Jim Roberts, manager of advanced cameras at Dalsa.
By developing a custom module for the camera, algorithms such as thresholding, run-length encoding, and edge detection can be performed at video rates up to 20 MHz. Because of this, says Roberts, multiple frame grabbers are no longer required, as preprocessing data reduces camera output data rates by up to 99% over conventional cameras. In the system supplied to DuPont, 12 of the company`s cameras were multiplexed using Dalsa`s hub multiplexer and the resulting data fed to a PC-based frame grabber from Coreco (Montreal, Que., Canada).
By using on-the-fly gray-scale thresholding, the cameras look for products that exceed a specific gray-scale threshold. In this way, film defects are detected. By doing so, says Roberts, systems integrators can tackle systems that were previously cost-prohibitive and technically infeasible due to system bandwidth limitations.
Contact Jim Roberts at (519) 886-6270 for more information.
