Presence detection of dowel pins
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Table of Contents
Challenge:
- Differentiate between two different heigths of dowel pins → 30mm difference
- Detection must be made from above
- Sensor should be smaller than our W12 PowerProx Housingstyle (see below)
- The solution should have two hard wired switching outputs
Solution:
Sensor -> Background suppression sensor with laser autocollimation WTT4SLC-3B2262A00 1097190 which comes with a MF (multifunction output) and a standard output.
You can set up the MF as a second switching output in our free sensor engineering tool "SopasET" https://www.sick.com/ag/en/p/p367244.
Solution conditions -> Distance between sensor and the bigger dowel was around 160mm from top
-> The dowels were guided standing and very precise - otherwise we would have a jumping signal (see explanation below the pictures).
Side view:
Long dowel:
Short dowel:
possible Problems -> The WTT4 calculates the received light runtime and evaluates a distance value. This system is very precise but comes with several susceptibility to sharp edges (for example the edge of the dowel head).
We could have an inaccurate measurement value which can be higher or lower than the actual real distance value! This may lead to failure switching!
The reason is the high amount of light that comes back to the sensor from the direct reflex of the shiny dowel head.
Our proposal: Tilt the sensor a few degrees horizontally to prevent the direct reflex , the switching signal becomes way more stable.
Additional information:
To prevent such failure switching at short distances, a special version of PowerProx is created with a polarizing filter on the front screen to filter out such reflexes and to reduce the laser power.
These versions are available as shiny versions.
application example, presence detection, dowel pins, powerprox