PLC trouble?

Hi,

I have been troubleshooting a machine, a carrier plating machine to be specific. This machine uses a FUJI F70 cpu (modular type plc) with a number of i/os. This plating is use to plate several types of material, including Cu, Sn & Ag. The client said that the problem started over 5 months ago, the machine is running well on Cu but having trouble with Sn & Ag. During this time, they would simply reset the system upon trouble & the machine would run for about an hour before having trouble again. For them, that was tolerable.

Around 4 months ago, this problem worsen. After resetting the system, it will run for around 2-3 cycles then the trouble arises. This time its no longer tolerable so they do not use the machine on Sn & Ag BUT still the machine is running good on Cu.

This is the problem:
1.) This machine has 5 carriers, among those only carrier 2 has apparent problem. Please see attachment
2.) Cu starts from no.9 whilst Sn (4-2) & Ag starts from no.8. During Sn & Ag the machine skips 1 position (ex. if the carrier should put the material @ no.11, it will load on 12) BUT this problem is not seen during Cu operation.
3.) I checked the program & i found out that the reason the machine skips 1 position is that there are times the limit switch on carrier2 is not detected. I thought of transferring this limit switch to another i/o BUT then again I thought, why this problem does not occur in Cu? All the process are the same except they start at different position.

Is this possibly a PLC trouble?

How long does Limit Sw 2 get held "ON"? Could it be that with Cu it is running slower at that point and making the switch for a longer period of time?

RussB said:

How long does Limit Sw 2 get held "ON"? Could it be that with Cu it is running slower at that point and making the switch for a longer period of time?

Click to expand...

Hi RussB,

I have thought of that also so I check the speed. Unfortunately, they are running on the same speed. What I did next is run Ag & Sn on a lower frequency, the problem still arises. Then I ran Cu on a much higher speed but there is no problem.

look for the difference in every aspect of the operation when running different materials and solutions. i used to work in a plating environment and with different materials ( size and shape ) and different plating material ( solution ). Does the problem persist with different material or solution?

What is the usual indication that plc itself has trouble?

The limit switch that is on carrier 2 that you say

i

I found out that the reason the machine skips 1 position is that there are times the limit switch on carrier2 is not detected.

Click to expand...

My money is on this switch being miss wired, with the live supply to this switch being now connected to a supply that is turned off by another switch.
Probably because of wiring alterations, or a terminal fell out and got connected to the one next to where it originally came from.

A matter of looking and testing at this switch seems to be the order of the day.