Printer and Photocopier Troubleshooting and Repair Collection : Ink-jet printer basics                  
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Ink-jet printer basics

(From: Tony Hardman (AHED_CIJ@f54x19.demon.co.uk).)

There is a US publication called 'The Hard Copy OBSERVER' from Lyra Research Inc. Tel: (617) 322-0708.

This discusses the latest technologies and who does what. It may not cover the print head technology very much but is a good read if you are into print technology in general.

There are many companies that sell variable print processes. One I have heard of is RALFLATAC. They do a brochure that does an excellent brief of most technologies available for printing. They have UK (and many other sites in europe) and US sites. UK Tel 01732-583661, US Tel (704) 684-3931.

I have no idea if you can easily get copies of either publication from them so here goes a very very brief description.

Ink jet printing has two main types, continuous ink jet (CIJ) and impulse printing (DOD) (drop on demand). Each of these can be a single jet, or an array of jets.

A primer on priming

The priming station of a typical ink-jet printer (e.g., HP DeskJet 500C) includes a rubber seal ('boot') and small pump to actually suck on the end of the print cartridge to free up nozzles (there are 50 or more in a typical print cartridge) that have dried up or become clogged. It may fire all the nozzles at some point during this process as well. It also includes rubber 'flappers' which the end of the cartridge pass over to wipe off excess ink.

Priming and cleaning are normally done automatically upon power-on and possibly between pages. However, additional cycles may be needed at times.

With the water based ink, even if the printer is powered off properly which seats the cartridge(s) on a rubber seal, some evaporation occurs so priming will often be needed after it sits idle for a while. Note: Don't kill power to an ink-jet printer as soon as your printout pops free - it needs to position the printhead and cartridge(s) on the rubber boots. Wait until the printhead stops moving and clunking. Some (older) printers don't even have a seal in which case letting it sit idle is even more likely to result in problems.

If there has been ink spilled into the priming area, it may clog up the little hose connecting the priming station to the pump - I have used a wooden toothpick to clear the hole though this may be risky if it should break off. With care, a wire rounded off at the end so as not to puncture the tubing can also be used. Complete disassembly and washing of the parts is probably the best but is probably a pain.

A bit of ink-jet history?

(From: John Nagle (nagle@netcom.com).)

The original ink jet printer of this type was the Teletype Inktronic, which introduced the concept of video-type distortions to printing. It appeared around 1970, and was so bad nobody tried again for years.

(From: Tony Hardman (AHED_CIJ@f54x19.demon.co.uk).)

I guess that is why it was used in industrial applications I guess. Were the 'video-type distortions' a deliberate feature or just a coincidence of how they turned out?

Who are/were Inktronic???(apologies to anyone connected with them) I guess that may have been spin off development from some work contracted out by IBM, but it was so....?? (costly/low res/unreliable - choose one) they lost interest. Although one of the very early machines still runs well on a textile mill. It had a large number of jets side by side, and may be multi color too. I've only seen the patents so don't know exactly what it looks like.

I thought original ink jet printer was a chart recorder developed in the last century. It was just a nozzle on deflection mechanism, and was not modulated so it was always printing. It was a lighter mechanism than actually trying to move a pen and so had some performance advantages over other technology available at the time...

The same reason CIJ still sells world wide, even when high resolution DOD is biting at its heals.

Inkjet types (at least from a Xerox perspective)

(From: Peter (hedgieus@yahoo.com).)

Here are history/trivia. (I used to work at Xerox marking technology group, working on ink-jets and daisy printers.)

Response times of resistance heater elements in ink jet printers

The ink drops that make up the 'image' on the paper from an ink jet printer are expelled by microscopic resistance (thin film or the like) heaters with response times in the 10s of microseconds if I recall correctly. When living in the macro world, it is often counterintuitive to realize that a resistance element can have such a fast thermal response.

(From: John Eaton (johne@vcd.hp.com).)

The trick is that a lot of the energy that you pump into the resistor leaves the printhead with the fired dot. One way to detect Out_of_Ink is to mount a thermistor on the printhead and watch for a sudden rise in temperature as you are firing.

How many colors can an ink-jet printer can produce?

"I use a HP680C in the office, and it have two cartridges, one for black and one for color (yellow/cian/magenta?). If the printer fire one drop of each ink at a given point, we can have only 6 different colors (ignoring white and black). If it can fire two or more drops at a given point, maybe we can have more colors, but I suspect that the printer use this to control quality of the presentation, not the number of colors. Anybody knows for sure? With dithering it can make more colors, with reduced resolution."

Like most print processes you only have a limited selection of inks to use. Full colour can be derived from three primary colors, just like a monitor. For monitors, these are Red, Green, and Blue because monitors emit light resulting in an additive color process. Inks, on the other hand, absorb light so printing is a subtractive process. The resulting inks should then be cyan (blue+green or -red), magenta (red+blue or -green), and yellow (red+green or -blue).

Therefore, the colors used in common ink-jet printers are not really capable of producing true full spectrum photorealistic quality results since they are red (not magenta), blue (not cyan), and yellow. These are optimized for nice saturated primary colors when used independently. Also see the section: Why are red, blue, and yellow inkjet primaries?.

In addition, the combination of the three primary colors should be capable of being combined to produce black but due to misregistration and the pigments used, this black would be somewhat muddy and brown. Therefore, a separate black ink cartridge is normally used for black printing.

(From: Tony Hardman (AHED_CIJ@f54x19.demon.co.uk).)

With printing there are more problems than solutions and I do not know which method HP use in their printing.

If you can vary the drop size, you can change the drop spread on the paper. This can be done by firing bigger slugs of ink, or multiples of the drop at the same position. As you can figure the ink will either spread and make a bigger drop, or stay the same size and become denser. Depending on the resolution you want these could both improve colour density. This depends on two key components.. The ink, and the paper.

The problems with laying down multiple drops on paper is that if you do a large block the paper will curl up and the overall image becomes worse. This is why you can pay 1$ a sheet for 'quality' paper.

Another problem with this is speed. Firing two drops in the exact same place is difficult... Unless the head is stationary but that is not good either. You may notice that most DOD printers in high resolution mode do a number of passes over the same place. This does allow dithering and other techniques for resolution / colour enhancement. They usually only print while going in one direction for improved mechanical control.

In the 1600 printer there is a heater to assist with the drying times and reduce the curling problem.

Inks are a problem too. They can dry at different times because of the different dyes used, or they may not mix how you expect if you place two colours on top of each other. Its only ink ... but to get the best balance of surface tension, drying time, viscosity, colour, stability.... and more is not as straight forward as it might seam. I have noticed that the water based inks are improving, and there are some that do not run if they get wet (after drying on the paper).

I think the spec in your manual may suggest what method they use.. The printer resolution (best) is 600dpi (I guess), and I recon the best full colour resolution is lower. Also the print head is only 300dpi so you must do two passes to get 600dpi black (single black ink cartridge). This suggests a partial step of 1/600 inch between the passes. What happens when you print black using the colour head? How many passes, how much slower? The resolutions quoted may also be 600 * 300, or what ever. If they make blocks of colour from a potential 600dpi machine, the resultant image is probably only 75dpi (possibly less). This still might be called 600dpi, because the drop placement uses this resolution, but it is not 600dpi at full colour. The resolution of quality picturers / poster is several thousand dpi, but not a variable image (not ink jet).

In the Lyra publications they did publish the real print head specifications for the machines they review. They also include some of the methods of colour printing.

After all this I have noticed that I have not answered the question of how do HP et all get their colour resolutions. All I have mentioned is a few of the parameters that the designers have to deal with.

Why are red, blue, and yellow inkjet primaries?

For a subtractive printing process, the 'optimum' primary colors for a 3-ink system would be closer to magenta, cyan, and yellow. However, these are not generally used. Why?

I don't know the precise answer but it is no doubt a tradeoff between cost and which colors are used most often. For non-photo printing, the straight red, blue, and yellow are far more useful since they can be use by themselves or in simple combination to produce a wide range of vibrant, if not realistic colors. For example, pure red is far more likely to be used for simple graphics than magenta. To make something that looks like pure red using magenta and yellow requires a precise combination - not easy to do with an inkjet printer!

About inkjet printer ink

No, you can't refill your HP DeskJet cartridges with fountain pen ink!

(The following is from someone who also sells inkjet refill kits so this may not be an entirely unbiased writeup.)

(From: John Connolly (toner@idirect.com).)

There are at least 10 ingredients in inkjet ink, starting with triple distilled, de-ionized water, dye or pigment color of a known particle size, humectants such as glycol to minimize evaporation (and head clogging), surfactants to balance the surface tension and paper wetting, resins to get good paper adhesion, biocides and fungicides and buffering agents for the correct pH. These considerations ensure that properly reverse engineered inks not only work, but produce a print comparable to the OEM. For printers like Epson, with fixed permanent print heads in the printer, expensive repairs are also avoided.

To make matters worse HP has rigged their most popular black cartridges for the Deskjet 500 & 600 series to curb refilling, with air bladders, constantly changing maze/ venting assemblies at the bottom, and logic to change the signals to the micro-resistor jets on the 3rd or subsequent reinstallation of the cartridge. The color cartridges for these MUST be refilled before air locks occur, particularly in the yellow chamber.

Some people still manage to get an acceptable refilling success rate with these Deskjets, but we feel it is a bad introduction to refilling for the first time refiller. Deskjet series 700, 800 & 900 are better bets to refill.

But, the current Lexmark, Canon, Xerox and Epson cartridges are by far the easiest to refill.

Image Control's refill kits for the Canon 4000 series refill the BCI-21 black 40 times, or the BCI-21, 12 times EACH color.

More details on inkjet inks, a description of our refill kits which are larger than most offered, references and printer/cartridge tips are available at Image Control's Web Site.

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