Feed calibration chart

[DesireeM]

Does anyone know of or have a chart or diagram that shows the media thickness=feed calibration for Versaworks? I have most of our media calibrated and written on my own chart near the printer but if there's a way to bypass the test print and just use the micrometer to check the media thickness and change the feed calibration accordingly that would be so much better and faster.

 

[BIG EASY DOES IT]

Does feed rate go specifically on media thickness? I thought it was more the weight/ texture that created drag on the surfaces in the printer and you would have to account for that when setting up the feed rate. The HP does it auto so just a thought.

 

[DesireeM]

Does feed rate go specifically on media thickness? I thought it was more the weight/ texture that created drag on the surfaces in the printer and you would have to account for that when setting up the feed rate. The HP does it auto so just a thought.

Good point. It's just that when you do the test print for the feed calibration it prints horizontally and doesn't really feed the material through; just the couple inches of the test print so I thought it must be a thickness thing. Weight must factor in it too though...that would make sense but then how would the test print account for that if it only moves the media by about an inch?

 

[BIG EASY DOES IT]

Excellent question. The printheads fire at the same spot everytime if the media doesn't move enough you should be able to see that it missed the area it was firing or the test print would be short. There are some other people that might be able to explain this further.

 

[DesireeM]

Excellent question. The printheads fire at the same spot everytime if the media doesn't move enough you should be able to see that it missed the area it was firing or the test print would be short. There are some other people that might be able to explain this further.

Maybe I didn't explain it properly. It's not an error. That's just how the test print works. Have you ever seen the Roland calibration? Here's a pic of the final result and an explanation in case you've never seen it.
The printhead shoots left once, printing all of the bottom rectangles in one shot. Then the media moves forward an inch and the printhead shoots out and prints each of the top squares individually starting with the one on the right, then returns to starting point then shoots out and prints the 2nd one, then back to start point and so on.

 

[BIG EASY DOES IT]

So afterwards you pick one that is printed with zero gap?

 

[DesireeM]

So afterwards you pick one that is printed with zero gap?

Right. No gap but no overlap.

 

[BIG EASY DOES IT]

When it moves that inch it is testing the drag on the material. If there is more drag then the media won't move as much and thus you will be farther to the right hand side of the calibration. If it has almost no drag then it might move to far and then your farther to the left of the calibration chart. It doesn't have to move 10 feet to know that every inch it is off by a tenth of and inch.

 

[DesireeM]

When it moves that inch it is testing the drag on the material. If there is more drag then the media won't move as much and thus you will be farther to the right hand side of the calibration. If it has almost no drag then it might move to far and then your farther to the left of the calibration chart. It doesn't have to move 10 feet to know that every inch it is off by a tenth of and inch.

Yes, I'm aware of the mechanics behind it. Hoping for some kind of reference sheet though just to make life easier....

 

[BIG EASY DOES IT]

That's what I am trying to say though you will find no such thing. Every printer depending on the amount of gunk on the rollers or how old the plastic on the platen is will be different even on the same media. There will be no chart where just by measuring thickness you can get a compensation number. Depending on the media each roll could be different. Like a more natural canvas no two rolls are the same.

 

[P Wagner]

OP is correct, the calibration is principally based on the thickness of the media that is being printed on.

The weight of the roll is another variable, and that obviously changes as the media roll is gradually consumed. Each machine is unique, and thus, for best results the calibration really should be performed on the device, rather than an educated guess.

 

[BIG EASY DOES IT]

I'm more talking about the weight of the material after it comes off the roll? The weight/drag that the roll has traveling to the platen. How does the thickness matter? If by thicker you mean heavier?

 

[P Wagner]

I'm more talking about the weight of the material after it comes off the roll? The weight/drag that the roll has traveling to the platen. How does the thickness matter? If by thicker you mean heavier?

On a drum-based plotter (printer), the media is being transported by the drum. The amount of distance that one rotation of the drum covers is based on the thickness of the media, in much the same fashion as a snow tire (high profile tire) cover more distance per rotation versus a normal diameter tire, thus throwing off the accuracy of the speedometer & odometer.

The feed calibration adjusts the distance of the media advance to the media so the printer minimizes banding.

 

[BIG EASY DOES IT]

This would change with every rotation then because he drum becomes smaller and smaller with each turn. So wouldn't you need to calibrate every roll every time you put it on. Or if you cut off a 10 foot section while in between prints it would completely change the diameter of the roll making it even smaller.

 

[P Wagner]

This would change with every rotation then because he drum becomes smaller and smaller with each turn. So wouldn't you need to calibrate every roll every time you put it on. Or if you cut off a 10 foot section while in between prints it would completely change the diameter of the roll making it even smaller.

You are referring the diameter of the feed roll of media (I think). The drum I am speaking of is the circular drum that the pinch rollers press the media against to advance the media through the printer. The diameter of the drum is fixed and does not change. The media thickness is the variable.

 

[BIG EASY DOES IT]

Gotcha. So basically just changing the thickness of the top of the drum between the pinch rollers. So the immediate calibration comes from this and then you have to run a test to change it if stuff doesn't match up? It seems like this is not the greatest method. Since some materials range in thickness slightly throughout the roll, Ill take it back to a natural canvas. Didn't know different printers do it differently because the HP latex have the OMAS sensor that looks at the backing fiber as it moves and auto adjusts. Even though it also has a drum below the pinch rollers.

 

[P Wagner]

Gotcha. So basically just changing the thickness of the top of the drum between the pinch rollers. So the immediate calibration comes from this and then you have to run a test to change it if stuff doesn't match up? It seems like this is not the greatest method. Since some materials range in thickness slightly throughout the roll, Ill take it back to a natural canvas. Didn't know different printers do it differently because the HP latex have the OMAS sensor that looks at the backing fiber as it moves and auto adjusts. Even though it also has a drum below the pinch rollers.

That's the cool thing about the HP OMAS camera system, it automates the process of feed calibrations, and it constantly performs the calibration adjustments as the device is printing. The superior image quality of the HP Latex machines is directly attributable to this type of on-board intelligence and automation that is built into the printer.