Desktops make inspection more accessible

AOI systems with small footprints offer the capabilities of inline equipment while permitting companies to perform inspection at multiple locations around the factory.

Ann R. Thryft, Contributing Technical Editor -- Test & Measurement World, 6/1/2010 12:00:00 AM

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The future of inspection may be mobile

Read more articles from the June issue.

Like most electronic systems, inspection systems have become more compact and more capable as processors and other components have become smaller, faster, and more powerful. A class of inspection systems, called desktops or benchtops, has arisen with smaller footprints and lower costs, yet with most of the capabilities of their larger counterparts. They are often used in labs or other offline locations for testing samples taken from the production line. Now, some EMS (electronic manufacturing services) providers and electronics OEMs are asking for even smaller systems.

There is definitely a trend toward smaller AOI (automated optical inspection) systems in assembled PCB (printed-circuit board) inspection, said Henk Biemans, GM of Marantz Business Electronics. "We developed our first desktop AOI machine in 1996 for internal use in our audio-visual production lines," he said. "We needed something to replace manual inspection, which was done mostly offline for through-hole and surface-mount components, because they had become too small and too many to inspect reliably with the human eye."

Users occasionally want to test their products post-print or post-placement in addition to post-reflow, said Biemans. With a desktop AOI machine or an offline AOI system, they can put in a batch of boards and run them without holding up the production line. This flexibility is especially important for EMS providers, which represent 80% of Marantz' customers for desktop AOI systems.

Desktop machines' prices, at around $50,000 or so, are about one-quarter to one-third of inline machine prices, making AOI more accessible to smaller companies, Biemans explained. Instead of buying a couple of inline systems, some customers purchase many desktop machines and install them in multiple places around the factory, not only in the surface-mount line.

When desktop AOI systems were new, they were slower than the big inline AOI machines, but they could be programmed more quickly, so they were used for simpler tasks, said Biemans. Large inline AOI machines are usually still faster at top speed, but desktop machines have become almost as powerful, while still being easier to program. And desktop AOI technology is now used for a wider range of applications.

"Because they can be so difficult to program and it takes so much time to get them up and running, inline AOI systems can be line-stoppers," explained Biemans. "If you're an ODM [original design manufacturer] with a huge factory producing a board that takes a couple of months to develop, maybe that's no problem. But in the EMS world, that won't work: You need to run some products in the morning, entirely different ones in the afternoon, and they all have to be inspected and shipped that same day."

Desktop AOI machines cost less than their larger inline cousins because they are less complex, so there's less need for mechanics such as conveyors for manipulating the board, said Don Miller, CEO and president of Nordson YesTech, which manufactures inline and benchtop AOI systems. Benchtops are often used in lower-cost areas where you might not want to place optical inspection inline, and they offer more flexibility because you can also use them to inspect boards throughout the various process steps. "Because of their lower price, benchtop units used to be viewed as less capable, but that's not necessarily the case today," he said. "Our benchtop AOI unit runs the same software as our inline unit, and the programs are interchangeable, so for all practical purposes, it has the same capabilities."

A large inline machine takes up more floor space, can be difficult to move, and may be committed to a production line, said Nordson YesTech's international manager Josh Petras. But a benchtop system can be moved easily from one line to another or from the production floor to a different area for test or failure analysis of the board. Some of the company's EMS customers place its benchtop AOI system next to the production line and emulate inline operation in a method Nordson YesTech calls "human automation." The AOI operator pulls each board from the line as it exits the reflow oven, inspects the board in the benchtop AOI, and then places the board back on the conveyor to continue the process.

According to Biemans, "If you find a problem in an inline system, you can flag it immediately and prevent a larger number of boards from being produced incorrectly before finding the defect. That's the true advantage of inline AOI: You find defects on the spot."

In contrast, with an offline system, you can inspect batch lots while the line is still going, although defects aren't discovered as quickly. Using an offline desktop or AOI system prevents the risk of holding up the entire production line while the inspection program for a new product is still being created or debugged to run the inline AOI system.

One difference between desktop and inline machines that's being erased is in how they are programmed, said Biemans. Many of the big high-volume AOI machines use rule-based programming—-inspecting each item on a board, such as a solder joint, requires multiple rules. Image-based programming, more common in desktop machines, uses the actual image to set base targets. To program a specific board on a big inline system could take up to two days, versus two hours for a desktop system. Some of the rule-based systems now have better libraries. In addition, rule-based programming can be added to the Marantz desktop system for certain inspection tasks while keeping the advantages of its original image-based inspection for tasks where that is more efficient and effective.

"In the past five years, we've seen an increase in demand for desktop AOI systems," Biemans said. "They've became more prevalent, cheaper, and much more powerful by combining image-based and rule-based programming architectures. You can now get the same quality in desktop AOI as in inline machines, although their speeds may not have caught up with the fastest inline systems."

The future of inspection may be mobile

Some machine-vision systems are smaller than traditional benchtops or PCs because they are built on open platforms, not dedicated components, and because embedded and PC architecture, components, and software are becoming more similar. Increasingly powerful components in compact, off-the-shelf systems make it easier to bring machine vision to places where there's less space, said Kamalina Srikant, National Instruments' vision product manager.

"Smart cameras, for example, can now do what it took a desktop PC to do in the past," Srikant said. "Compact machine-vision hardware ranges from smart cameras with integrated image sensors to embedded vision systems with external camera connectivity." For example, NI's Embedded Vision System is a dedicated machine-vision controller with a multicore processor, a real-time OS, FPGAs, and isolated I/O lines. It can be used with multiple IEEE 1394a or GigE Vision tethered cameras.

Since laptops are becoming more powerful, their hardware no longer limits their use as a vision-system controller, said Nathan Cohen, sales manager for Imperx. He added that the only thing you can't get for laptops are image-processing boards that do real-time high-performance processing in an onboard FPGA, because such boards cannot fit into a laptop. On the other hand, Imperx' laptop frame-grabber card contains drivers for using most software packages. "Now, you can base a machine-vision system on a laptop with two digital camera inputs," said Cohen. One type of portable system in which a laptop and multiple cameras are commonly used is a 3-D data-acquisition system for stereo photogrammetry of large objects.

Because hardware platforms are made in such a compatible way, which one you select for machine vision has become almost transparent, said Endre Toth, director of business development for Vision Components. And you can port an in-house, embedded application based on C or C++ to many different hardware platforms. "So, when you go to design the next generation of inspection or metrology equipment, you can choose a different platform, such as embedded or portable hardware, because it's lower cost, more integrated, and more rugged than earlier hardware generations," he said.

An example of this principle occurred when MVTec ported its Halcon machine-vision software library to the Nokia N900 cellphone and ran a machine-vision application on the phone. Although the relatively poor quality of the optics makes cellphones unsuitable for many industrial machine-vision applications, tasks such as scanning bar codes and data codes, OCR (optical character recognition), and to some extent pattern recognition are feasible, said Heiko Eisele, president of the Germany-based MVTec's US subsidiary.

Traditionally, most machine-vision applications developed with third-party, hardware-independent software have been created for PCs, but in principle these applications can be run on any hardware. "We've made our Halcon machine-vision software available on smart cameras," said Eisele, "and we are getting requests to port it to other embedded platforms, such as compact image-processing systems without all the usual PC peripherals or motherboards, which will be assembled into finished products by our customers."—Ann R. Thryft

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