heat tunnel alarm

We have a heat tunnel the shrinks plastic over the rugs per a customers request. We have a banner retroreflective photoeye mounted before and after the heat tunnel. Their is a one shot rising bit that starts a timer and the after eye stops the timer. The problem we are having is the the rug blocks the second eye which in turn stops the timer but the rug is still physcially in the tunnel. The tunnel conveyors down stream can jam and has a good chance of burning up a rug before the operator can remove it.


here is the part of the program i am having issues with

p.s would i need to use the one shot falling bit to look for a made not made before turning the timer off.

thanks ahead of time

I think you answered on your own quastion.

if you use the one shot falling bit you would stop the timer after the part will be out of the tunnel.
or move the sensor away from the tunnel exit to rise when the part arrived.

An OSF would do the trick.

Try this:
Delete Rung two and put the follwing two rungs in its place:

XIC I:0.0/10 OSF B3/70 B3/71
XIC B3/70 BST OTU B3/59 NXB RES T4:10 BND

would this cause problem id the rugs are not all the same length. I am thinking about timing the rug using the first eye and subtacting it from the timer value. would this work

You make it complicated.

The OSF would fit to every rug size if the sensor located in the exit of the tunnle.
When the rug go out the heat keep working until the rug pass the sensor.it would fit for every length.

The rugs teat I am talking about vary in size. We might run a small then an extra large right after it. If you are using the 2nd eye to locate the back of the rug then your timer would have to be different. Say i set a 25 ms timer . On the big rugs it might take 25 sec to make it through the tunnel and another 5 or so to move the rug far enougth so the 2nd pe is unblocked. This would cause the alarm to go off which everyone know if their is alot of false alarms people on the floor will ignore the alarm all together.

I guess you use a constant length for certain batch.

and you have small gap btween the rugs.and the conveyor have constant speed for this batch.
So when the first sensor go on run a timer to count to length of the rud add 10% for safety and put thids time in the alarm time.
In that way the system will upgate according to the rug lentgh.

All the best

Alaric usually offers working suggestions so I would try it.

I started a reply but got slightly confused so need to verify something. If the conveyor is a constant speed then the length will not be relevant to the entry and exit time, in other words it should take the same amount of time from entry to exit regardless of length. One timer initiated on entry can do this.

With that said and assuming more than 1 rug can enter the heat tunnel at one time then you can use a counter UP and DOWN instruction to determine if a rug is within the heat tunnel and initiate a timer that will reset everytime a product exits the tunnel, if the count is greater than 1 it will always time, if timer done bit is reached it sets an alarm bit. If count is too high then alarm bit is set. This is a pdf of an RSLogix example I did http://www.plctalk.net/qanda/attachment.php?attachmentid=4355

Since the rugs are at different lengths I would have the EXIT PE at a distance slightly greater than the maximum rug length and determine the time to go from entry PE to exit PE.

rsdoran said:

Alaric usually offers working suggestions so I would try it.

Click to expand...

I appreciate the sentiments Ron, especially coming from you. Unfortunately, all too often I get into the field and find that what I thought was going to work doesnt.


As for different length rugs:
Are there a few fairly consistent size ranges to the rugs? Then just add a couple of extra photo sensors. PE1 is at the tunnel Connection: closeentrance. PE2 is 1 meter back from the tunnel entrance. PE3 is at 2 meters. Then as soon as the rug enters the tunnel, ie PE1 turns on, look at the other photo eyes. If Only PE1 is on, then you have a very short rug, if PE1 and two are on you have a medium rug, if all three are on, you have a long rug. Then with a one shot, MOV a value into the T4:10.PRE according to the rug size range.

Alaric

Why to make it complicated?
PE1 (entrance side) go on and run a timer T1 when it go off move the value from T1 to any register and add 10%(for saftey) then move this value to another timer T2 which run by PE2 (exit side) so if the rug stuck PE2 is on the timer T2 exceede his value it mean something stuck on the tunnel.

Arik I thought of that too but I dont think it will work like you think it would. I am not sure how you are taking into consideration the time the rug is in the tunnel and clearing the tunnel. I think that method would require 3 timers and compare instructions.

Another issue, if tunnel is long like I think it is, would be a second rug could enter...ie short then medium/long. The medium rug would reset TIMER2 creating the possibility they jam in the tunnel and heat is on too long.

The hardware idea sounds good but I have class now so no time to state my thoughts except I might extend it to use 3 exit PE if possible. One timer could do tunnel time which entry to exit would be the same and a second timer to verify the rug has left the tunnel.

Actually I like my example in the pdf above.

One problem with your last idea, Arik. There are long rungs that don't clear the entrance eye before reaching the exit eye. So far, I'm liking Ron and Alaric's ideas.

I'll add my thoughts...

4 timers:

• Timer #1 starts at the leading edge of the entrance eye, and resets at the leading edge of the exit eye. Preset is slightly higher than the time to travel from entrance to exit.
  
  
• Timer #2 starts at the trailing edge of the entrance eye, and resets at the trailing edge of the exit eye. Preset is slightly higher than the time to travel from entrance to exit.
  
  
• Timer #3 runs whenever the entrance eye is blocked. Preset is slightly higher that the time it takes the longest rung to pass.
  
  
• Timer #4 runs whenever the exit eye is blocked. Preset is slightly higher that the time it takes the longest rung to pass.
  
  
• Alarm latches when any timer expires.

Timers 1 and 2 should make up for the lowered effectiveness of timer 3 and 4 when running short rugs. Or, similar to Alaric's idea, you could add an additional eye upstream to 'pre-measure' each rung and use that value to preset timer 3. A lot depends on how much of a difference between there is between longest and shortest.

Of course, this wouldn't work if there is the possibility that more than 2 rugs can be in the tunnel at the at the same time. We don't know if this is the case.

Of course, a shift register would probably be the best solution, but I don't know if it needs to be that fancy...



-Eric

ArikBY said:

Alaric

Why to make it complicated?
PE1 (entrance side) go on and run a timer T1 when it go off move the value from T1 to any register and add 10%(for saftey) then move this value to another timer T2 which run by PE2 (exit side) so if the rug stuck PE2 is on the timer T2 exceede his value it mean something stuck on the tunnel.

Click to expand...

So what happens if you do it that way and the rug gets stuck near the tunnel entrance with some rug still protruding out, and the operator walks away? Then the timer keeps on counting up - meanwhile the PLC just thinks that this is a really mongo rug.


I really like the solution suggested by Eric. No extra hardware, and I believe it will work. It will pick up rugs stuck halfway at the entrance, or exit as well as anywhere in the tunnel.

Eric


I took in my consideration that the rug can not cover the 2 sensor at the same time.
if not my method will work.
The first rug will set the alarm time if PE2 exceed the alarm will work.if the rug is longer then the tunnel.then yo need to add another sensor in order to measure the lentgh befor the tunnel.
it depend on the length of the conveyor befor the tunnel.
I cannot show my ladder on this board.
I hope you will understand my idea.
I hope in 23 day it will be easy with the new simulator.

Alaric

I did not took in my consideration that the rug might stuck in the entrance.
So I think Eric idea is the best.it cover both option.