Photo-eye pulse detection logic

Hello,
I work for a beverage company that uses a laser coder to print date codes on bottles. We have a problem where occasionally the photo-eye that is used for bottle detection gets dirty and stops sensing bottles, which in turn causes the printer to stop printing the date codes on the bottles. Since we have a 100% traceability policy, we end up having to rework the product when this happens. Im looking for any help or advice on how to resolve this issue. Ive considered adding an additional eye and programming some type of "heartbeat" logic, but Id have to add a PLC and an additional sensor to the system first. Does anyone know if there is an easier way to do this?

So is the photoeye connected directly to the marking equipment?


If so I'd look at

a) perhaps addressing the cause of the sensor fouling [as a PM, give it a wipe between runs or a hood of some sort?] or

b) changing the sensor out for one that is less sensitive or prone to getting dirty in the first place (ultrasonic, capacitive, blue light, fiber optic, laser distance positioned far enough away to avoid getting dirty etc.)

The eye is directly connected to the laser printer. There is a fume extractor immediately after and above the laser head, and the eye is located a couple of inches upstream and below the printer head. I think a big part of the problem is that it isnt getting cleaned often enough, but if ask the operators they'll all tell you that it is....

We've tried a few different sensors and continue to have trouble. We are currently using a fiber optic sensor.

Can you interlock the conveyor if the sensor stays high for x millliseconds. As you mentioned bottles i imagine its running at high speed.


Barry.

If the emitter is far enough away from the sensor, I would consider a concentrated air hose to keep contaminates from building up on the sensor, otherwise a backup is possible, but expensive. At that point, should probably create a maintenance PM that they have to attend to it at whatever interval is necessary for cleaning to ensure no breakdown. Adding an additional cover to calibrate looking through would still require cleaning, so you're probably smoked on that idea. May indeed be best to get operators use to a daily cleaning of it to ensure efficiency.

I can interlock the conveyor, but would still have to tell the system when there are bottles present and the eye should be pulsing on and off. The conveyor runs constantly but there may or may not be bottles on it depending on whether the filler is running.

I agree there should be a better PM plan to keep the eye clean. I will take a closer look at the system and see about repositioning the eye in relation to the print head and possibly a blow-off system for it as well.

If the NO is wired to the laser printer, then use the NC wire to PLC and monitor its inputs changing, if not changing then stop the line.

I did this using a through beam sensor that output a normally high signal, It went low when the beam was broken. I had the PLC raise an error if the sensor stayed low for more than x milliseconds, to indicate if it was blocked/dirty/disconnected.

But we have a pretty clean environment aside from the laser fumes.

Edit: It was an ultrasonic through beam sensor, not a photo-type.

woody400 said:

The eye is directly connected to the laser printer. There is a fume extractor immediately after and above the laser head, and the eye is located a couple of inches upstream and below the printer head. I think a big part of the problem is that it isnt getting cleaned often enough, but if ask the operators they'll all tell you that it is....

We've tried a few different sensors and continue to have trouble. We are currently using a fiber optic sensor.

Click to expand...

Banner's t30 and s30 lines of dc photos both have an alarm output if the excess gain is 1 to 1.5. They may also have it available on other styles. To get the alarm function you have to hook up the DC in reverse - to brown, + to blue.

Hook up the alarm output to a annoying buzzer or tattle tale counter