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Scientist saves workers' eyes, cuts factory costs

By Zhang Zhihao | China Daily | Updated: 2017-10-16 07:10

In a giant, dark factory, thousands of young workers sat in separate booths, each staring through a small glass rectangle at a white lamp on their tables looking for defects.

Each had a pile of the smartphone screens and several large bottles of eyedrops, which they used often.

Zhang Zhengtao, 36, a scientist and Party representative from the Chinese Academy of Sciences' Institute of Automation, witnessed the scene at a quality inspection factory for smartphone screens in Dongguan, Guangdong province, two years ago.

"I tried the work once, and my eyes got sore within a minute," he said. "It broke my heart seeing those people in their early 20s doing such eye-scorching work for months, sacrificing their eyesight just so we can have new smartphones."

Zhang specializes in precision measurement and equipment assembly, which involves measuring, controlling or making extremely small equipment often in the scale of a millionth or even a billionth of a meter.

Most of his work is used in cutting-edge science projects, from spacecraft to nuclear energy, where accuracy is paramount. After seeing the factory, he wondered if he could use his skills to replace manual inspection with robotics.

"As a Party member, I have a duty to use my knowledge to help industry and its workers," he said.

But the problem was complicated. Machines don't have the thinking ability needed to detect the two dozen types of small defects, Zhang said.

"Tiny defects from previous production procedures can be pressed together with other defects, creating an illegible mess for computer scanners," he said.

And computers have difficulty distinguishing between easily fixable defects and serious ones "because to a computer camera, they look similar", he said.

Experienced workers see the complicated defects when they examine the glass screen under bright light, but they misjudge more than 5 percent of the products, he said.

Last year, China produced about 2.1 billion phone screens and employed more than 150,000 inspectors. Manufacturers spend more than 10 billion yuan ($1.5 billion) a year on personnel, Zhang said.

"If we can replace manpower with machine, not only can we decrease the fault rate and cut cost by hundreds of millions, we can also keep young adults from damaging their eyes," he said.

But creating a machine smart enough to detect various defects after the screen is finished is still too hard, Zhang said. So he decided to take it one step at a time, and in 2016, his team created China's first fully automated optical inspection machine for glass printing, a key step in making phone screens.

AOIs are most commonly used in checking for defects in printed circuit board. "It is essentially a highly sensitive camera that rapidly scans the object and then identifies various types of defects using its vast database," he said.

By focusing on defects found in a single manufacturing step, Zhang applied machine learning and artificial intelligence to analysis of a quantities of data, creating a "visual recognition database that can read glass printing defects like a human mind", he said.

This new machine has less than a 1 percent error rate in identifying defects. As glass printing is an early production procedure, the machine reduces the workload and difficulties of quality inspection in the final stage, he said.

During testing, a single machine can help a factory save more than 650,000 yuan annually on glass printing defects alone, Zhang said. The machine has recently passed all testing and is available for industrial use.

"We will build similar" AI+AOI' machines in the future and apply them to other phases of the phone screen production line, such as plain glass inspection, and possibly even branch out to other industries like electronics or energies," Zhang said.


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