Question How is Ink Delivered to a Printhead?

[David40]

I was just curious about how the ink is delivered to the printhead on my Mutoh 1204? Is there a pump for each color? If pressurized what is the psi. on those lines? Does the head suck the ink from the lines, or does it merely act as a valve that opens and closes?
Please enlighten me.

Thanks

 

[Solventinkjet]

The ink cartridges are filled with ink and then any air is sucked out. That way when you install a new cartridge there are no air bubbles introduced but it also means the cartridge will not naturally fill the ink lines. A rubber seal called a cap top seals up with the bottom of the head and a single pump pulls a vacuum on the entire system at the same time. This vacuum sucks the air out of the lines and ink replaces it. Once the ink gets to the dampers on top of the head, they prevent the ink from flowing back to the cartridge which it will want to do naturally.

So now you have ink in the system and the dampers are holding the ink in place. When you go to print, the head fires and depletes the ink in the dampers. As ink leaves the damper, the damper collapses but the flexible plastic and spring metal resist the contraction which pulls new ink into the damper and thus, the head. The head is never truly closed like a valve. Fluid can flow through at any time. The damper is what does all the magic of keeping ink flowing and also from simply falling out of the head. The pump simply gets the process started.

 

[David40]

So, if there is no pressure pushing the ink and no suction from the head, then it's basically gravity fed? I know that's how my desktop printer works because the heads are right below the ink cartridges, but on this printer the ink cartridges are actually below the level of the printhead and the tubing goes up well above the head, so it just seems like it defies physics to be gravity fed.

 

[Solventinkjet]

Not gravity fed but negative pressure. Think of it like dipping a straw in a cup of water, blocking the top opening with your finger, and then lifting it out of the water. The water stays in the straw. The pump pulls the ink down through the dampers and the head. Once it hits the damper, it's like blocking that open end of the straw. If you take a damper off the ink line, the ink will flow back to the cartridge against gravity.

 

[David40]

So the damper has some sort of a one way check valve incorporated into it? Seems like such a delicate balance to maintain, with the dampers playing a critical role in the process. I imagine if the check valve part of that fails the ink cartridge would suck all the ink out of the damper and you would see some sort of ink starvation in the printed output?

 

[Solventinkjet]

So the damper has some sort of a one way check valve incorporated into it? Seems like such a delicate balance to maintain, with the dampers playing a critical role in the process. I imagine if the check valve part of that fails the ink cartridge would suck all the ink out of the damper and you would see some sort of ink starvation in the printed output?

Exactly. Older dampers don't have the valve and simply pull back on the system enough keep the balance but because of issues related to that, most new dampers do have the valve or there is an external one added in the machine design. It is a delicate balance which is why bad dampers tend to cause drop out as you stated. I have seen a single bad o-ring cause a channel to drop. But it's a lot cheaper than making a positive pressure system which is why they use it on these machines.