Ending Conveyor Nuisance Stops at a Fortune 50 DC
Sensorless muting light curtains stopped wrapped pallets from tripping the safety system, without weakening safety for people.
A Fortune 50 consumer goods distribution center kept losing its outbound packaging line to false safety trips. Nothing was broken. A loose tail of stretch wrap or a half-peeled label was enough to make the light curtain think a person was walking through.
Han-Tek worked with Leuze to replace the old muting sensors with sensorless muting light curtains that recognize a pallet on their own. Daily nuisance stops went to zero, and the line now runs above 99.5% availability.
The line's number one fault wasn't a broken part
Pallets leave the building through guarded areas protected by safety light curtains: invisible fences of light that stop the conveyor if a person walks through. Pallets have to pass through too, so the system "mutes" the curtain for a moment as each load goes by. Here, that muting was done with separate sensors mounted in front of the curtain, and it was the line's most frequent fault.
Stretch-wrap tails
Film hanging past the pallet edge looked like a person to the curtain.
Loose labels
A half-peeled barcode label was enough to break the muting sequence.
Sensors knocked out of line
Conveyor vibration moved the external muting sensors out of alignment.
Every false trip meant a manual reset, a full system restart, lost throughput and people pulled off other work, often several times a day.
Let the light curtain recognize the pallet
Han-Tek worked with Leuze to replace the external-sensor muting with Leuze MLC 530 SPG-RR sensorless muting light curtains, then built the new logic into the conveyor PLC. Here is how it works, in three steps.
- 1
The PLC calls ahead
As a pallet approaches, the conveyor PLC sends the curtain a Control Signal: a load is coming.
- 2
The curtain sees the load
When the pallet breaks the beams, the curtain recognizes it and opens a short gate for that load only.
- 3
People still stop the line
Anyone who walks in without that signal trips the curtain, exactly as before.
- Removed the external muting sensors and brackets entirely: less wiring, a smaller footprint and nothing left to knock out of alignment.
- Integrated the curtains into the existing conveyor PLC logic as part of Han-Tek's integrated conveyor system.
- Leuze application engineers validated the installation on site.
The new curtains are Type 4, PL e and SIL 3, TÜV certified. The line got more uptime with the same level of protection for people.
From daily resets to no resets at all
| Metric | Before: sensor muting | After: sensorless muting |
|---|---|---|
| Nuisance stops | Frequent, daily | Eliminated |
| Downtime | High | Negligible |
| Operator intervention | Regular | None required |
| System availability | Inconsistent | Greater than 99.5% |
- Nuisance stops eliminated: stretch-wrap tails no longer trip the line, and operators no longer reset it.
- Less maintenance: no muting sensors to realign or recalibrate.
- Higher availability: the outbound line runs above 99.5%.
- A new standard: the facility standardized on this light curtain for future expansions and shared the results with other company sites.
"The new light curtains have completely changed the performance of our outbound loading."
Questions about light curtain nuisance stops
What is a light curtain nuisance stop?
A stop where the safety light curtain halts the conveyor even though no person entered the guarded area. Common causes are stretch-wrap tails, loose labels and muting sensors that have drifted out of alignment.
Does sensorless muting make the area less safe?
No. The curtains used here are Type 4, PL e and SIL 3, TÜV certified. They only open for a load the PLC has announced, so a person walking in still stops the line.
Can this be added to an existing conveyor line?
Yes. This project replaced the muting on a running outbound line. Han-Tek removed the old sensors and built the new logic into the existing conveyor PLC.
Who supplied the light curtains?
Leuze supplied the MLC 530 SPG-RR light curtains, and their application engineers validated the installation on site. Han-Tek handled the controls integration.
More outbound and conveyor projects
Does your line stop for no reason?
Tell us how often your light curtains trip and what your pallets look like. A Han-Tek engineer will tell you whether sensorless muting fits your line.
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