Over the past few years, a new photoelectric sensor family has begun to take the forefront on the factory floor.  Unlike previous designs that included two or more different components, self-contained thru-beams combine both emitter and receiver elements into one housing.

 

There are two significant drawbacks to conventional thru-beam sensors: the two-piece architecture and the need to keep both the emitter and receiver in alignment.  Not so the self-contained thru-beam sensor.

Shaped in the letter C or L, these sensors send a beam of visible red or laser light across from one arm to the other.  Regardless of the gap between the arms, these sensors can offer pinpoint accuracy with resolutions down to 0.03 mm, both because of the tiny diameter of the light beam, and the rigidity of the housing. 

Because thru-beams exhibit high excess gain, they are extremely tolerant of dirt, moisture, and debris.  Moreover, the smaller the lens, the smaller the effective beam. This allows very small targets and part, package, or product configuration variations to selectively break the beam. 

Together, the combination of excess gain and small effective beam increases the utility and accuracy of self-contained thru-beams.  This allows them to be used for a wide variety of “error-proofing” functions such as part count, part presence, part or product feature verification, part size verification, edge detection, part location, tool size monitoring, part feed verification, part ejection verification, double hit elimination, gripper positioning, and so forth. 
As an added benefit, thru-beams can be ordered with hardened bodies to survive harsh environments that would destroy conventional sensors and unacceptably degrade sensor performance.

In this typical application, tension on sheet feed is monitored in a progressive die

 

L-shaped design is useful for detecting aspects of large objects, such as edge position detection.

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Fork Sensors at a Glance

Pros:
• Extremely tolerant of dirty environments
• Immune to target color, reflectivity, or surface condition
• Most repeatable non-contacsensing technology
• Highly accurate part variation detection
• High accuracy independent of beam length

Cons:
• May be confused by translucent objects
• Will not sense color variations

 

Information courtesy of Balluff.
www.balluff.com

: Design World :

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Filed Under: Sensors (position + other)

 

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