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Old December 13th, 2017, 09:36 PM   #1
backendcode
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Please give me troubleshooting tips

Hello All,

Currently, I am providing support at automation cells at my work. I know ABB robot programming and PLC (don't have much experience) and all the automation cell have ABB robots and Allen Bradley PLC.

Sometimes, a robot stops and wait for PLC signal and I find very challenging to find that bit or find what signal robot is waiting for.

for example, robot load the part in CNC machine and when a part gets clamp in CNC, CNC send a signal to Robot, you can go now because i have part clamped but somehow there is chip under the cnc clam and clamp signal won't ON then robot will stuck inside the machine wait for that signal and it would be so hard to for to find why robot stuck inside lol

I work in an automotive industry and some of you may know they die for production and if line stop they expect some kind of magic and make the line run in 10 seconds.

Please give me some troubleshooting tips which can help me to find the issue on the line.

I understand every production line is different so my post sounds stupid but I am sure you can give me something out of your years of experience.

Thank you,
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Last edited by backendcode; December 13th, 2017 at 09:43 PM.
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Old December 13th, 2017, 10:38 PM   #2
willxfmr
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I think your best course of action would be to spend as much time as you can with the operators when the cells are running. They are the ones that will know what has gone wrong in the past, and what was done to fix the problem. Not every operator is going to be open to the idea of you just hanging out in their area, but you can usually find at least one that is willing to share what they know. Of course a big box of doughnuts appearing at break time never hurts your chances of finding someone willing to help you. In the good old days it was a case of beer, but times have changed.... Remember, you want them to share the results of hard learned lessons, so be polite, and respectful. even if they are neither. Also try not to be asking work related questions constantly. You want to try and spend as much time talking about sports, beer, cars ect as you do work. That will improve your chances of developing a good working relationship with the operators.
The other thing I do when I start at a new place is to spend a lot of time going over prints and programs. Pick one piece of the process, such as moving the piece to the work table, and watch it in the program, and find the devices in the prints that are part of that one move. Once you know all of the parts involved with getting that one task done, move on to the next.
By and large, it really is about experience and spending time with the machines, but you can give yourself a leg up by studying what it does, when it does it, and what conditions have to be met before the machine moves on to the next step. None of this is really specific to your machines or process, it's just what has worked for me when I find myself being the junior Bubba once again.

Good luck.
Bubba.
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Old December 14th, 2017, 12:50 PM   #3
saultgeorge
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Another thing that I learned real quick was to make use of the cross reference feature in the logic. As per your example, if a part present sensor won't come on when you're just "sure" the clamp is down and the robot is still in pounce, then look in your logic at that sequence and see where the DI ("go to pick 1") for instance is (it will be an OUTPUT in your logic and cross reference that to the previous output that is driving it, etc. until you find the input in your logic that is not made (a part present for example.) The operator should be able to show you all the part present sensors and then you can determine which is not lit up, etc. Hope this helps.
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Old December 14th, 2017, 12:54 PM   #4
alive15
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Check the robot program on the teach pendant. Normally the program should stop on the line of code it's waiting on. So if it's waiting on Clamp open, then if you go to the teach pendant program, you should see a line that says "Waiting on Input clamp open = on" or something similar along those lines.
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Old December 14th, 2017, 01:55 PM   #5
Mispeld
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For the type of troubleshooting described, specifically work cell machine sequencing, my advice is to spend some time reviewing the PLC and other (e.g., robot) programs when you are not under the duress of getting a faulted machine back into operation. I would focus on understanding the sequence control logic, of which there are many different styles in practice. The better ones will quickly lead you to the step that the machine is "stuck" on. From there, it will be clear (in a good program) what conditions are needed to go into the next state.

Since it sounds like you have multiple machines to deal with, it may be the case there are different sequencer strategies across the plant. If you have access to the original programmer(s) or other knowledgeable individuals, maybe they will help describe where the sequence control is located in the program and how it works. If you are on your own, you will need to figure it out by code-reading and observation. In either case, you may want to start a notebook with critical information for each machine so you can quickly orient yourself to the sequencer code, external interfaces, system-wide interlocks, etc. when called out to troubleshoot. The challenge is to have enough well organized information to quickly locate the problem, but not too much that your notes become unwieldy.

As you get more familiar with each machine, one way to check your understanding is to describe the operation and sequence to a colleague. This is the next best thing to actually solving a problem with a particular machine.
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Old December 14th, 2017, 02:08 PM   #6
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Something I forgot to mention: become familiar with whatever information is readily available, such as Human-Machine-Interface (HMI) displays or robot teach pendants as already mentioned. In some cases a good machine designer may have included troubleshooting screens with machine state/transition conditions, system interlocks, device faults, etc. The only caution is to be careful because sometimes these HMI screens may not be kept up-to-date as the machine sequence is changed over time.
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Old December 14th, 2017, 02:27 PM   #7
Steve Bailey
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The best time to start troubleshooting is when everything is working right. Study the operation, get a feel for how long the individual steps take, even listen to how it sounds. Once you know the correct operation it's easier to spot what's different when there's trouble.
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Old December 14th, 2017, 04:29 PM   #8
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Quote:
Originally Posted by Steve Bailey View Post
The best time to start troubleshooting is when everything is working right. Study the operation, get a feel for how long the individual steps take, even listen to how it sounds. Once you know the correct operation it's easier to spot what's different when there's trouble.
Excellent words of wisdom. And if you can't, ask the operator. He/She can be a wealth of knowledge.
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Old December 14th, 2017, 05:00 PM   #9
bill4807
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Regarding troubleshooting and knowing your machines obviously do all the things others have stated here.

For this particular problem definitly look at the robot program on the teach pendant for the input that is waiting on..if there are no alarms then the program should be sitting at that line or at least looping at that particular input. Should be commented out "hopefully".
Then cross reference in your PLC for that output of the PLC.
Sounds like the sensor your referring to might be an APS. Sensor (air part seat) or air gap sensor. I assume this because you say chips are in the way of the part sit ting properly. Lots of fixtures and clamp jaws have through porting for air seating.
Make sure the CNC is flushing the fixture properly between part rotations to eliminate chips.
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Old December 14th, 2017, 07:31 PM   #10
backendcode
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Thank you so much, everyone! All the replies are very valuable!
Thank you once again,
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Old December 15th, 2017, 12:40 AM   #11
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All the above plus, deductive logic. Think of what signalthe PLC is waiting for. In your example above, there has to be a sensor/switch, maybe a prox or read switch if pneumatic, to indicate that the clamp is fully retracted or extended whichever the case maybe. Is there an encoder? Have a look at the robot itself and most importantly at the schematic as it will show the IOs , the sensors etc. Basically learn the machine.
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