Frame grabbers thriving in inspection
By Ann R. Thryft, Contributing Technical Editor -- Test & Measurement World, 4/1/2009 2:00:00 AM
If a slew of new frame-grabber products is any indication, these image-acquisition boards are thriving in electronics and semiconductor inspection. Recent product introductions from Adlink, Dalsa, Euresys, Matrox Imaging, National Instruments, and Sensoray, among others, include interfaces such as PoCL (Power over Camera Link) or 1394b (FireWire), take advantage of PCI Express bandwidth, incorporate additional logic for image preprocessing, or take GigE Vision functions onboard. One frame grabber from Imperx resides on an ExpressCard in a notebook computer.
| SIDEBAR: 10 GigE may be coming to machine vision |
Although users may associate frame grabbers with older analog interfaces, engineers are actually using them widely with digital interfaces. “Most camera manufacturers are moving to standard digital buses like Camera Link, GigE Vision, and IEEE 1394a/b because of their lower implementation cost,” said Matt Slaughter, vision products manager for National Instruments. “With standard interfaces, the ease of combining cameras and frame grabbers from multiple vendors with a minor configuration effort means you can have a system up and running in a very short time.”
In particular, vendors say, frame grabbers are needed where either the combination of resolution and bandwidth or else bandwidth alone is very high. “In terms of imaging needs, the semiconductor/electronics segment can be divided into two major groups,” said Dwayne Crawford, product manager for Matrox Imaging. Wafer, LCD, and PCB (printed-circuit board) inspection constitute the first, high-end group, with similar data rates and image sizes. “The number of pixels you need to inspect an LCD panel or the larger dies is increasing exponentially,” he said. “Fine details are shrinking in semiconductor geometries, as well. In PCBs, geometries are also shrinking, but throughput is more of an issue.” In the second group, wafer bumping and wire-bonding inspection, large images are not a concern: Although frame rates are high, data throughput is not. But in these applications, image acquisition must be synchronized with motion-control I/O.
Because of its very high bandwidth, Camera Link has become the de facto serial digital standard for use with frame grabbers in machine vision, said Inder Kohli, Dalsa’s product manager for frame grabbers and vision processors. “Since FireWire and GigE Vision interfaces are ubiquitous in PCs, you can use them to bring in camera data,” he said. “But Camera Link is driving both the growth of, and many trends in, frame grabbers and vision processors.” In semiconductor and electronics inspection, users want more efficient, less costly production lines, reflected in better resolution and higher frame rates in cameras. GigE and FireWire rates are not high enough for every application in this segment, so frame grabbers are still needed here, he said.
One trend affecting frame grabbers is the evolution of the AIA’s Camera Link standard, as evidenced in the PoCL interface, said Kohli. In some semiconductor and electronics applications, such as wire-bonding inspection, small, lightweight, high-bandwidth cameras use single-cable connections incorporating power and data. He explained that although in-line power is native to FireWire, adding power to GigE lines could add cost and complexity to a vision system. “Power over Camera Link cameras cost-effectively deliver power and higher bandwidth data on the same cable,” he said. Crawford said that Matrox Imaging, like some other frame-grabber manufacturers, has added support for the interface to its newer product families because PoCL helps reduce camera size and simplify cabling.
Manufacturers are also adding onboard logic to handle a variety of processing tasks. As data rates increase, image data must be processed faster, so even more preprocessing tasks must be offloaded onto frame grabbers to reduce the load on the host computer’s CPU, said Kohli. Dalsa’s Xcelera-CL PX4 SE has a suite of onboard processing functions, such as color space conversion and defect analysis, that users previously performed with custom boards or a vision-processor board. “Combining onboard processing capability with PCI Express’s high transfer bandwidth, as we’ve done with the Xcelera SE, lets the frame grabber provide both raw images and processed data concurrently, making processing more efficient and cost effective,” he said.
Preprocessing functions can help correct optical artifacts such as distortion that are becoming a greater problem as sensors get larger and pixels shrink in geometry, said Crawford. “Preprocessing operations—such as optical and prospective distortion correction, flat-field correction for uniform sensitivity and responsivity across the sensor, and dead pixel replacement—are therefore more relevant,” he said. “Single FPGAs [field-programmable gate arrays] can handle these operations well, and correcting image artifacts must occur before you even begin processing the images, so we’ve put them on our frame grabbers, such as the Matrox Solios family.”
In some of its frame grabbers, National Instruments offers the option of onboard, user-programmable FPGAs for controlling timing, triggering, and I/O. The FPGA can also be used to synchronize multiple cameras and lights, or control hardware like actuators with precise timing, said Slaughter.
All of Imperx’s frame grabbers are made for notebook computers, said company sales manager Nathan Cohen. “Notebooks are entering machine-vision applications more and more as they come equipped with dual-core and quad-core processors, huge amounts of memory, and higher bus speeds” he said. “You can use them for a small production run, [for] simpler systems that do not need many I/O controls, or for more complex systems that sit on the production line but need to be contained in a compact space. We’re seeing a rise in inquiries for electronics applications because people are shrinking their systems.” Notebooks equipped with frame grabbers make machine vision portable, and they are becoming popular in situations where a full desktop computer is not needed, he said.
The company’s newest model, FrameLink Express, was originally designed for military applications. A Camera Link model for newer, faster ExpressCard laptops, it can simultaneously acquire images from two Camera Link cameras. Because it’s compliant with ExpressCard, it provides up to 235 Mbytes/s of bandwidth, which is fast enough to work with line-scan cameras on an electronics production line, Cohen said. The FrameLink Express can do histograms, look-up tables, and hex pixel dumps, and it also integrates a timing generator. “With two inputs on the frame grabber, you can designate one camera as a primary and one as a slave and synchronize imagery very precisely for 3-D inspection, or use multiple cameras at different points on a production line,” he said. “Multiple inputs in a laptop also let you overlay images for multispectral inspection such as IR, UV, and visible light.”
More trends in machine vision will affect frame grabbers in the near future. One of the most important is dealing with the high bandwidth and huge images resulting from the use of Camera Link, said Slaughter. “In PCB and component inspection, you might want a really high-resolution image of a board or wafer, but what do you do with it? Do you stream it to a RAID array, or try to do some kind of in-line processing? If you are doing in-line processing, you won’t be able to do it very fast, so do you do post-processing?”
PCs equipped with multicore processors may be one solution, according to Slaughter. “One machine with a multicore processor can chop up the image into smaller data sets that can be processed in parallel,” he said. “Our software makes this easy by automatically splitting up the images into the right number of pieces based on how many cores your PC has.”
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