KM 6501 Ink-coverage related registration issue

[Copycats]

We have a KM 6501 with a Creo RIP.

When we have heavy coverage and we are printing on Cover-weight stock in 11x17,12x18 or 13x19 sizes, we get inconsistent shifting of the image of up to 1" in a direction parallel to the feed direction of the sheet. It varies form sheet to sheet and it makes it impossible to run jobs with these characteristics on the machine.

Does anyone know of a fix, or has anyone come across this before? I am wondering if we have a defective box.

Thanks in advance.

 

[pq man]

We have the same setup and the same problem I am in the pressroom but I see this happening.Our km guy has not been able to come up with a fix.

 

[alu]

pq man... you see this happening and your km guy has no fix? doesn't sound right....

copycats, sounds like your stock is being pushed past the registration roller..
see if the tray settings has the loop increased.. you can try to decrease it.

the system registers by having it bump up against a registration roller for a certain period of time to straighten the stock and to have it 'start' from a known position (it's all about timing the sheet to meet up with the image sitting on the transfer belt..) If your stock is pushed past the reg roller during this process.. your sheet will be early and the image will be shifted towards the trailing edge.

I would say you need to have your reg roller cleaned or replaced, but look at the loop settings in the meantime.

(I don't think this has anything to do with heavy or light coverage)

 

[Copycats]

copycats, sounds like your stock is being pushed past the registration roller..
see if the tray settings has the loop increased.. you can try to decrease it.

the system registers by having it bump up against a registration roller for a certain period of time to straighten the stock and to have it 'start' from a known position (it's all about timing the sheet to meet up with the image sitting on the transfer belt..) If your stock is pushed past the reg roller during this process.. your sheet will be early and the image will be shifted towards the trailing edge.

I would say you need to have your reg roller cleaned or replaced, but look at the loop settings in the meantime.

(I don't think this has anything to do with heavy or light coverage)

Alu,
- What are the loop settings?
- We have not seen this kind of level of mis-registration except with heavy coverage on cover weight stock.

Thanks!

 

[OkiTech]

It is also called - paper buckle setting. What happens is - feed rollers that deliver paper out of tray to registration roller, than reg. roller takes over, makes stop to register while feed rollers give the paper a little extra push which creates a paper buckle before registration roller. In large machines lake this the registration roller is usually driven by it's own Stepping motor which is really precise but some rollers in the paper path could be driven via electromagnetic clutch which could get sluggish or worn-out and do not engage or dis-engage on time creating a problem you had described. If I were to trouble shoot this, I'd jig the covers, take flashlight and watch the machine print trying to catch where the problem is coming from.

 

[Copycats]

It is also called - paper buckle setting. What happens is - feed rollers that deliver paper out of tray to registration roller, than reg. roller takes over, makes stop to register while feed rollers give the paper a little extra push which creates a paper buckle before registration roller. In large machines lake this the registration roller is usually driven by it's own Stepping motor which is really precise but some rollers in the paper path could be driven via electromagnetic clutch which could get sluggish or worn-out and do not engage or dis-engage on time creating a problem you had described. If I were to trouble shoot this, I'd jig the covers, take flashlight and watch the machine print trying to catch where the problem is coming from.

Thank you for the suggestion.
Our service rep replaced the motors and rollers about two months ago and we still have the issue.