a perfect focus on all objects, and this is not possible with a common lens’ field of view.” In this case, the cavity inspection can be performed from the outside, without inserting the probe. “These optical lenses can help you inspect defects in caps and objects at a range of ten to 120mm.”
Inspecting the bottom inner surfaces and inner sidewalls at the same time Common in the food and beverage industry, this lens can inspect caps from the inside to check for defects in the cap’s form or seal, and can also be used to inspect paper cups, checking the cups’ shape and integrity or to identify any impurities or contaminants that could be present inside. The metal industry can also benefit from inner inspection lenses as complex mechanical parts need to be inspected for internal features or structural defects.
Boroscopic probes for panoramic imaging from inside cavities Boroscopic probes are special lenses that allow you to get panoramic images from inside a cavity. They need to be inserted inside the cavity, but you get a view of the entire interior surface in high resolution. “A wide range of samples can be inspected using boroscopic probes,” says Danese, with diameters ranging from five to 100mm, and integrated illumination is used to highlight the features. These probes are useful to find residuals
or thread defects in mechanical parts such as engine cylinders, as well as in the food and beverage industry, where drink cans or bottles can be inspected simply, by inserting the optics into the sample to check for impurities, surface defects, dents or any other feature the user wants to find.
Multi-angle inspection using mirrors Featuring a bi-telecentric lens and an array of mirrors, multi-view lenses “allow you to get four different outer views of a sample,” says Danese. “The views are equally spaced at 90 degrees so you can get a complete image of the sample in just one shot.” It’s also possible to “insert another optic on the top, to inspect the top part”, and you have the option to “perform both inspections and measurements, to look for different defects in angles or alignments.” Examples for which these multi-view
lenses are widely used include for vial inspection in the pharmaceutical industry.
Four different outer views in one shot Poly-view lenses are another type of multi- view lens. These include a “fixed focal length lens and an array of mirrors that allow you to get eight different images of the sample in one shot. [By] adjusting the optics’ working distance, it’s possible to inspect the inner and outer surface at the same time, getting a trapezoidal view of the sample.” Examples of poly-view lens inspection applications include identifying cuts, scratches or contaminants on flip-off caps and cracks or other defects on syringe tubes.
The latest in 360-degree imaging “Because many applications require the inspection of the tops and outer surfaces of larger samples, large field-of-view catadioptric lenses cover samples up to 110mm in diameter, with an extra-wide lateral viewing angle,” said Danese. Again used in the food and beverage industry, these catadioptric lenses are used for code reading, identification and the detection of dents, deformations and defects in food cans and cap grooves.
“Another important [innovation] is
hypercentric lenses,” said Danese. “These feature a unique design that allows you to simultaneously inspect the inner walls and bottom of cavities with one camera.” By positioning the entrance pupil in front of the lens in a convergence point with crossing rays, the lens can collect rays that pass through bottlenecks and narrow openings, making it possible to image the inside of tight containers in high resolution, and making it compatible for high-speed beverage applications.”
Liquid lens technology “Liquid lenses are special lenses that are able to change optical power when electronically driven,” explained Danese. “They are composed of a special liquid with optical properties, enclosed in a container and sealed off with a thin polymer elastic membrane that’s able to modify its shape – changing the optical properties of the lens itself – when it’s electronically driven.
Focusing in a few milliseconds “This adjustment of optical properties [can be] useful for machine vision,” said Danese, “because it ensures a series of advantages versus mechanical focusing.” With the ability to change focus very quickly, electronically driven liquid lenses can have a focusing speed of just a few milliseconds. With a compact, robust and reliable
system – “guaranteed for more than a million cycles”, claims Danese – liquid lenses can also be highly cost-effective. The ability to perform “fast, precise and reliable refocusing in milliseconds is ideal for robotic applications that inspect cavities with different diameters.i
AUGUST/SEPTEMBER 2024 IMAGING AND MACHINE VISION EUROPE 33
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