Vision for Steel Mill - High Speed Visual Inspection

Online Inspection Hits the Steel Industry
Surface inspection is widely being used in the aluminium, plastics, paper and steel industries. In the case of the later, the quality of the surface determines the quality of the entire product and as such, top quality surfaces result in increased value. As the need for thinner and thinner sheets of metal increases, the requirements for the surface of such products has become ever more important. This article explains how one company uses machine vision technology to perform high speed visual inspection of strip steel for defects such as roll marks, imprints, scale or slip marks with outstanding results.

PCVision Frame Grabber speeds surface inspection
The HTS-2W system from Parsytec is recognized as a major breakthrough within the steel industry because of its ability to automatically detect and classify defects on strips of steel to millimeter scale. The system is in use today around the world, saving steel producers millions of dollars in reduced scrap and improved efficiency. Coreco Imaging's PCVision image capture board is playing a key role as part of this innovative machine vision solution that inspects strips of red-hot steel moving at high speed.

An issue of quality
The quality of the surface determines the value of strip steel used in automobile production and countless other applications. Nicks, cracks, and other blemishes can turn a beautiful piece of sheet metal suitable for a Mercedes into virtually worthless scrap metal. Parsytec, a German company with U.S. headquarters in Chicago, specializes in the analysis of defects on high speed production lines. Before the new system was unveiled, automatic detection and classification of surface defects on hot strip steel had been an urgent, but intractable problem. Visual inspection of the hot strip was impossible because of high strip speeds and temperatures that can exceed 1200oC. Steel mills were forced to rely on visual inspection after production was completed which meant that by the time inspection occurred, the damage was done.

Automatic defect detection
Now all of that is history. Parsytec's HTS-2W system is the first in the world to be able to automatically detect and classify hot strip defects online for steel producers, a business "must". Manufacturers can now tune mill setup online as the steel rolls out, rather than waiting the usual 4-6 days for feedback on product quality. The system examines and analyzes the entire strip surface, top and bottom, as the strip passes through the mill at up to 20 meters per second. Results are available in real-time at an operator station, where a user-friendly screen display provides a detailed examination of the molten steel with millimeter precision. If subprime quality strips are found, they can immediately be rescheduled, rather than sent to a customer who's demands for surface quality are greater than that available in a particular coil.

Inspection system features
The solution combines cutting edge hardware, software, and communications technology to redefine inspection quality for the steel industry. A bank of CCD video cameras with synchronized strobe lights captures the entire strip surface, using overlapping viewing fields to ensure complete coverage. High performance frame grabbers from Coreco Imaging are installed in the central PC, where they capture images from multiple cameras for analysis by Parsytec's sophisticated inspection software. The Parsytec application processes the images to provide meticulous detection and classification of defects, even those that are difficult for experienced inspectors to distinguish. The heart of the HTS-2W hot strip quality system is Coreco Imaging's PCVision, "all-in-one" machine vision board that combines a high performance frame grabber and digital I/O on one half-size PCI-bus card. PCVision provides state-of-the-art frame capture capabilities that support the demanding requirements of the Parsytec solution.

Significant to PCVision is 4MB of high-speed, on-board memory for buffering image data between the camera and host PC system. This feature, unavailable in other low-cost machine vision boards, transfers a 512 x 512 image to the host CPU in less than 4 ms, 10 times faster than competitors. This allows for simultaneous acquisition and processing of data. The on-board memory also assures that image information will not be lost during transfer to system memory. Fully programmable timing and extensive trigger, strobe, and asynchronous reset options provide industrial-strength frame capture flexibility.

Unprecedented viewing options
For viewing the hot strip steel, the HTS-2W provides extensive options. Operators can display an overview of defect locations, zoom in on a section of the strip to identify defects by type and severity, even zoom in further to review individual defects in detail. Other features include size measurement, area marks, contrast optimization, and 3D views to help users check defects. Resolution can be set to the minimum defect size to be analyzed, all the way down to one-half millimeter.

Automatic defect classification makes use of neural networks, artificial intelligence-based software that can be trained to distinguish between a variety of defects: fire cracks, seams, scrap marks, indentations, roll marks, and a host of others. Every defect is documented by its particular image along with type, size, severity code, and location on the strip. The system is even smart enough to offer suggestions on how to fine-tune production procedures.

Return of Investment
The new Parsytec system provides steel manufacturers with an early return on investment by catching defects quickly, saving product that would otherwise have to be scrapped. The solution also eliminates the costly delays and bottlenecks of traditional tail-end inspection. In addition, by recognizing patterns of repetitive defects, the HTS-2W allows steel mills to assess and track the effectiveness of their production processes.

Reference
Eye on Imaging, Coreco Imaging

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