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Compact System 3D Inspects Surfaces With Micron-Scale Precision

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Researchers at The Optical Society have developed a lightweight optical system that can carry out 3D inspection of surfaces with micron-scale precision. According to the team, this technology could be used to enhance quality control inspection for high-tech products like semiconductor chips, solar panels and consumer electronics.

The research was published in The Optical Society (OSA) journal Applied Optics. 

Capturing 3D Measurements

One of the challenges of capturing precision 3D measurements on the production line is caused by vibrations, so samples must be periodically taken for analysis in a lab. During this process, defective products that are developed must be discarded. 

To get around this, the team set out to develop a system that could operate in such an environment, like an industrial manufacturing plant. The research team was led by Georg Schitter from Technische Universität Wien in Austria, and they combined a compact 2D fast steering mirror with a high precision 1D confocal chromatic sensor. 

Ernst Csencsics co-led the research team with Daniel Wertjanz. 

“Robot-based inline inspection and measurement systems such as what we developed can enable 100% quality control in industrial production, replacing current sample-based methods,” Csensics said. 

The newly developed system is designed to be mounted on a tracking platform that is placed on a robotic arm, and this enables contactless 3D measurements of arbitrary shapes and surfaces. Weighing in at 300 grams and measuring 75 X 63 X 55 millimeters cubed, the system is impressively small.

“Our system can measure 3D surface topographies with unprecedented combination of flexibility, precision, and speed,” said Wertjanz. “This creates less waste because manufacturing problems can be identified in real-time, and processes can be quickly adapted and optimized.”

Existing systems often rely on bulky instruments to carry out precision measurements. In order to enable this on the production floor, the team created the system based on a 1D confocal chromatic distance sensor developed by Micro-Epsilon, and these can measure displacement, distance and thickness extremely accurately while using the same principles as confocal microscopes. However, they are much smaller.

The team combined the confocal sensor with a fast steering mirror, with the later measuring just 32 millimeters in diameter. Besides this, they also developed a reconstruction process which can create a 3D image of the sample’s surface topography by using the measurement data.

The system can fit on a metrology platform, with the latter serving as a connection to a robotic arm. This is what uses active feedback control to compensate for vibrations between sample and measurement system.

“By manipulating the optical path of the sensor with the fast-steering mirror, the measurement spot is scanned quickly and precisely across the surface area of interest,” said Wertjanz. “Because only the small mirror needs to be moved, the scan can be performed at high speeds without compromising precision.”

Testing the New System

The researchers tested the new system by using various calibration standards that are structured with defined lateral sizes and heights. The experiments showed that it can measure with a lateral of 2.5 microns and axial resolution of 76 nanometers.

“This system could eventually bring a variety of benefits to high-tech manufacturing,” said Wertjanz. “In-line measurements could enable zero-failure production processes, which are especially useful for low-volume fabrication. The information could also be used to optimize the manufacturing process and machine tools settings, which can increase overall throughput.”

The team will now try to implement the system on the metrology platform, as well as incorporate it with robotic arms. If they can achieve this, they will be able to test robot-based precision 3D measurement on freeform surfaces in environments like the industrial production line, which are often full of vibrations.

Alex McFarland is a historian and journalist covering the newest developments in artificial intelligence.