Sensors simplify vision systems
By Jon Titus, Contributing Technical Editor -- Test & Measurement World, 6/1/2006 2:00:00 AM
Many engineers think a vision system requires a big budget and a lot of headaches to get cameras, lights, and software working together. Powerful microprocessors and dense memory chips now let vendors offer small, inexpensive vision sensors that handle sophisticated inspection tasks with ease. These sensors can take over for older, expensive equipment that requires regular maintenance and programming.
In addition, small inexpensive sensors let engineers add inspection equipment to a production line where high costs previously prevented its use. Adding inspection stations along a production line helps catch defects quickly and prevents defective products from going through additional processing steps. Rejects get swept off a line—and accounted for—as soon as sensors detect them.
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| The PresencePLUS P4 Edge 1.3 sensor from Banner Engineering provides a 1280x1024-pixel image detector that lets the unit capture many regions of interest. Internal memory saves as many as 12 inspection “recipes” for different products. Courtesy of Banner Engineering. |
Companies such as Cognex and Banner Engineering offer a variety of vision sensors that vary in their capabilities. Buyers can choose simple absence/presence detectors or sophisticated vision systems that match geometrical patterns and detect image features. Sensor prices start in the $1000 to $2000 range.
Vision sensors provide a graphical user interface (GUI) that lets you enter information about what you want to inspect and the features you want to look for on an object. A laptop computer, connected through an Ethernet cable, serves as a GUI display and data-entry terminal. A vision sensor requires no knowledge of machine-vision algorithms.
For the most part, sensor "learning" involves the capture of one or more images of known-good products as well as products that get close to the known-bad category. Then, you identify regions of interest.
"Say you must inspect a cell-phone keypad," said Jeff Schmitz, corporate business manager for vision sensors at Banner Engineering. "You'd image a known 'good' cell keypad, and draw a boundary around the keys you wish to verify. Then, the software will match the image of each keypad inspected with the stored pattern to give a percent match."
Vision sensors make pass/fail decisions and generate an output that causes immediate action. But they also can communicate with other equipment.
"The DVT sensors offer communication tools," said Conner Henry, product marketing manager for the DVT product line at Cognex. "Those tools control the Ethernet port to communicate with most devices—from programmable logic controllers to robots—that use a standard protocol. A uniform series of setup steps for each protocol makes it easy for new users to communicate vision information to other equipment."
An Ethernet port also lets vision sensors communicate with a host computer that can pass inspection results to statistical process-control software available from third parties. And some sensor networks let you simultaneously monitor the images from each connected sensor. These products prove good things really do come in small packages.
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