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Vision sensors bridge the gap between photoelectrics and vision systems


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Bob Tremblay, 09-11-2011

As the product manager for Checker, I am often asked the difference between a vision sensor and a vision system. Vision sensors bridge the gap between photoelectric sensors and vision systems. Photoelectric sensors have been around in factory automation for many years.  They are a proven technology, are accepted on the factory floor, and are very affordable. They are also easy to understand and can be deployed by factory personnel. However, they are not the best answer for every inspection application, as they often require frequent adjustment and costly mechanical fixturing to ensure that the product under inspection is being accurately presented to the sensor array.

Machine vision systems are able to solve many inspection tasks that photoelectric sensors cannot. They are powerful devices capable of providing a wealth of information about the quality of the product being manufactured.  They can guide robots, inspect for the presence of components, measure critical dimensions, and even read printed bar codes on products. However, they are typically a more expensive solution, and they often require advance training and/or the services of a third party to deploy the system on the line. 

A vision sensor bridges the gap between these two by combining the simplicity and ease of use of a photoelectric sensor with the power of a machine vision system, providing a product that is easily deployed and maintained by factory engineers and technicians at a price point well below that of a vision system. Vision sensors can detect objects regardless of their speed and position, eliminating the need for both a trigger signal and costly mechanical fixturing.  They adapt to the production environment, not the other way around.  Vision sensors can simplify inspections that would be troublesome for photoelectric sensors, such as the presence of tapped threads or weld nuts in an automotive assembly.  They can inspect multiple features on a product—for example, the presence of a cap and a label on a package.  They can even tell you if the correct label has been applied to the product, by identifying a unique pattern such as a company logo.  A photoelectric sensor can’t do this.  Inspections can be accurately placed over areas of interest, because the user sees a picture of what is being inspected; but unlike in a full vision system, only one or two parameters can be adjusted, much like with a photoelectric sensor.

In sum, a vision sensor is a dynamic device that is easy to use right out of the box for operators on the factory floor, at a very low cost.

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