Gradient banding.. Ink starvation? Suggested causes?

[websnail]

Had a bit of a weird one here:

This is what I get when I try to print with a number of my CIS kits which I've built myself.. I've got about 4 or 5 systems that work pretty well with minimal banding (if any) while another 3 kits and printers are showing this sort of banding or worse..

The image above shows a section of the printout and as you can see it's running "full" when it starts the sweep and then starves or something as it gets to the end of its run then repeats as it heads back the other way.


To date I've tried a plethora of variables from different tubing, fittings, cartridges (new/empty->refilled) and so on and so far can't figure out what the heck is going on.

So, rather than concentrate on the CIS side of things I'm wondering if the usual gurus can point to anything obvious relating to possibly the cartridge, ink, etc.. that I may have missed.

Cheers

 

[mikling]

Pop in some normal carts. If it goes away. I would guess at ink starvation. Also you have an air break for damping don't you?

 

[ghwellsjr]

It's rather hard to tell what your image represents. Is it supposed to be one solid color? Are there just seven passes of the print head and is this bi-directional printing? If so, are the lighter ones going from right to left or the other way around and are the darker ones normal?

If it is bi-directional printing, what happens when you try uni-directional printing? What happens with other colors?

Also, I can see two or three large diagonal bands. Are these an artifact of the scanning or display process and not visible on your printout?

 

[websnail]

Pop in some normal carts. If it goes away. I would guess at ink starvation.

Of course I completely forgot to try this!... Doh!.. the simplest things.. (will report back on results).

Also you have an air break for damping don't you?

The air break is provided in the top of the cartridge (ie: there are bubbles and/or an air space at the top of the cartridge.. There definitely isn't a completely full cartridge in any instance.

 

[websnail]

It's rather hard to tell what your image represents. Is it supposed to be one solid color?

Yes

Are there just seven passes of the print head and is this bi-directional printing?

This is only the top left quarter of a full A4 printout so essentially if you saw the whole thing you'd see it starting full colour then fading in a gradient to the far side and then it starts back the other way with full colour to start and then fading again to the far side.. So yes it is bidirectional.

If so, are the lighter ones going from right to left or the other way around and are the darker ones normal?

Copy, paste and flip the image and you'd get a more complete picture of what's happening (the description above should help).

If it is bi-directional printing, what happens when you try uni-directional printing? What happens with other colors?

Not sure how I could get it to go uni-directional but I can tell you that when I set the paper setting to photo-pro it has a similar affect but less pronounced due to the denser placement of dots. It is still there though.

Also, I can see two or three large diagonal bands. Are these an artifact of the scanning or display process and not visible on your printout?

That's the paper warp..

 

[mikling]

One thing is that I feel your printhead hurting as you try this during testing. The bad or hidden side is that if a user doesn't do this testing on a periodic basis, but just prints continuously, it is unlikely they will not know there is a problem.

In a way this thread should shed light on when users of CIS are asked if they have problems. Sometimes there is, but they are not aware of them so they answer there is none. Many pop a CIS in, think it is heaven since there are no more carts to worry about and then believe that it couldn't be better until some problems slowly creep in. Eventually the toll on the head is too great and bad things happen.

No marketer of a CIS would warn customers about the potential problems and periodic testing should be carried out to determine if there is one. The whole premise of the CIS sale is printing is now worry free.

Back to your problem. It certainly looks like as ink is being starved ,slowly reintroduced, used up, starved, reintroduced etc.

To test if it is mechanical related, change your test pattern. Print a column solely on the left. Then solely on the right and see if there is any correlation to head position and it would point to whether it is printed area related as well with respect to its periodicity.

If the left column and right column on separate sheets appear similar. Then it is solely cart related. Do keep in mind that 99% of the colors you print are always blended so the problem could be with any of the cart or carts.

 

[ghwellsjr]

I'm not sure if all Canon printers behave the same way but I have created a table of how the different paper types for the i9900 result in different printing modes:

http://www.nifty-stuff.com/forum/viewtopic.php?pid=9079#p9079

If your printer behaves the same way, you could select standard for plain paper or select the default for Matte Photo Paper.

You could also select the 1-pass settings for plain paper (print quality of 5 or 4).

 

[websnail]

Right... Well after additional testing, me very nearly punching a hole in a convenient wall and finally biting the bullet and getting out a new printhead I've reached the following conclusions.

1. Never use used cartridges as part of a CIS
2. If you do use "used" cartridges you must mark them so you know which they are in case you hit problems
3. Don't use very thin tubing unless you absolutely have to!
4. Take your time

I'll update this later but suffice to say I've narrowed down the problems to a mixture of cartridge foam, lack of a decent pull through mechanism (unlike MIS's bottom fill adaptor) and a few other things...

Pretty hacked off though...

 

[websnail]

Right... My other half has just had a good "I told you so moment" as I've been too busy to deal with one of the problem printers for a few days and had left it sitting with a complete change of tubing (wider bore ID) and a new magenta cartridge along with some home made thin silicon grommets (courtesy of my new hollow punch tool set).

3 days I left it and after finding yet another problem printer at a client school I was having a bad day, so I opted to compound it by trying some new ideas (re: grommets).

So, imagine my surprise and delight when one of the problem printers printed out fine with no problems at all after having had a chance to sit and settle.



Of course the other one is still causing problems but it would seem that the cartridge sponge condition along with a decent inner diameter tubing may well be the fault.. I'll let you know how the other printer works out in a few days when I rejig the cartridges and tubing to match the other one.

 

[mikling]

This feed issue is again related to the thread where I stated In my opinion, the problems start as soon as the peristaltic pump starts drawing from the head at an accelerated rate. i.e cleaning Don't ignore the fact that programmed into the firmware of the printer is the aspect that even during printing, the printer will go though a set of cleaing procedures after a certain duration of elapsed printing.

If the feed line has too much resistance, the vacuum generated will be high enough that the cartridge seal will leak. So I'm not terribly surprised that this problem pops up now and then. Now going back to the feed lines, some variables which contribute to the level of resistance are diameter, wall smoothness, #bends, radii of bends and physical properties of the ink. All these are also components of the variables of the Mariotte bottle principle as well.

I don't know the tolerance of the Canon printheads but it appears to me that Epson piezo printheads actually generate greater vacuum while printing and appear more tolerant of feed resistances. The aspect of insufficient ink flow causing bad printing due to old cartridges/sponges probably gives a hint as to how less tolerant the newer Canon printhead is to ink feed issues and its unfriendly nature to CISs is revealed. I suspect that the tiny microdroplet nozzles and extremely small print chambers correlate with sensitivity.