The Future of Photoelectric Sensors Lies in Distance Measurement

 

Optical sensors have always used the options available with a light-sensitive component (photodiode or transistor) to measure the intensity of the incident light. This principle is simple, effective, and is ideal for the design of photoelectric sensors. However, it is always difficult if the reflection characteristics of the object to be detected alter the light incidence at the diode. In principle, a thru-beam sensor detects any object, but a reflector in the beam of a retro-reflective sensor remains undetected.

 

These theoretical considerations indicate that the majority of conventional photoelectric measuring methods only lead indirectly to the result. The only way to reliably measure the distance to an object where the reflection characteristics are constantly changing is by direct measurement. Whereas this is nothing new, it has rarely been implemented in the industrial sensor sector due to high costs. In addition to distance sensor VDM28 with Pulse Ranging Technology (PRT) principle  for larger measuring ranges,  Pepperl+Fuchs has now added the RL31-8-H, a triangulation sensor with multi-pixel array (MPA), as a cost-effective sensor with background suppression for medium distances (up to 800 mm).

Both sensors have a measuring principle that directly measures the distance to the object and is not dependent on the reflection characteristics of the object. The user is free to configure both sensors by using the IO-Link interface. Put simply, a measuring sensor is a sensor with defined switching properties. Both the PRT principle and triangulation, via MPA, provide the opportunity to read the measured values by IO-Link for processing in real time. Detection by position is common to both sensors.

Pepperl+Fuchs is continuing along this path to include vision sensors. The majority of smart cameras available on the market only evaluate a contrast image, which essentially depends upon the reflection characteristics of the object and the lighting conditions. The LineRunner400 transfers the technology, triangulation, to the vision sensors.  One or more laser lines projected onto the object enable the distance measurement to the object for each pixel of the captured image. This is completely independent of the surface characteristics and the lighting conditions. The use of vision sensors is just as simple and reliable as the use of a photoelectric sensor. Sensing by ranging is also the future trend for vision sensors.

Technology that was previously reserved for metrology is now a measuring principle for standard photoelectric sensors from Pepperl+Fuchs.