There are conveyor application scenarios that require the detection of untagged or unread product in order to enable corrective action. These scenarios typically revolve around the verification of tags to ensure that they are properly placed and encoded. Using a photo eye and two simple business rules, this condition is inferable:
- Business Rule #1: If the photo eye tripped and there was no tag detected within a configured period, then it can be inferred that there is an untagged or unreadable product on the conveyor.
- Business Rule #2: If a photo eye is tripped and then tripped a second time without any tags being detected, then it can be inferred that the first product to trip the photo eye is untagged or unreadable.
These rules work perfectly so long the product that passes the photo eye breaks the beam just one time. When the beam is broken more than once for a single item, business rule #2 takes effect and causes unexpected behavior. Unfortunately, this is not uncommon in deployment scenarios so here are a couple of gotchas and ways to mitigate them:
- Reflective Photo Eyes with Reflective Material on Product
- Problem: You are using a reflective photo eye that uses a mirror to detect beam breaks and have packages with reflective material such as clear tape or shrink- wrap that cause multiple physical beam breaks for a single item.
- Steps to mitigate the problem:
- Physically adjust your photo eye’s sensitivity so that it is less sensitive to reflective material.
- Use the Stable Set Interval within your B-ALE specification to smooth double detections.
- If there is non-reflective material at a consistent height across all packages then consider adjusting the height of the photo eye mounts so that it misses the reflective material.
- Irregular Shaped Product that Causes Multiple Beam Breaks
- Problem: You have irregular shaped packages that cause multiple breaks for a single item.
- Steps to mitigate the problem:
- Use the Stable Set Interval within your B-ALE specification to smooth double detections.
- If there are consistent solid sections of the package then consider adjusting the height of the photo eye mounts so that the photo eye is targeted at solid sections.