Silverace - dottyspotty
Issue 2: Patents: The Technology and Science Behind Printers

March 1999

Many years ago, in a pre electronic, pre-PC age, patents were received, read, then issued by hand. They covered many inventions now used by man - a better detergent for mom, longer wearing shoe rubber for the kids, and even longer lasting diamond tipped blades for dad. Some of these inventions have gone on to fame, while others sit idle, collecting dust in the closets of their inventors and in the long halls of storage drawers in the patent offices around the world.

Patents are a man-made agreement -- one that establishes the original author and creator of an invention was this person, and gives to that person the exclusive right to capitalize on their invention in the marketplace. Naturally, patents came about far after the various laws of the land, at a time when people attempted to strive for some 'civility' among each other that was governed by something more than just the 'arbitrary' finger on the trigger of a gun barrel, or the quick stab of the knife into an unlucky competitor. Patents arrived when people truly began to 'believe' in the universal laws espoused by their peers, but only agreed upon after much harsh argument and debate.

Patents are, in fact, an evil, an arbitrary limit on the capitalist marketplace placed by man so that the inventor can have time to bring their inventions to market to make some profit before the other lions arrive. Because of this allowance given to the receiver of the patent, they are hotly contested for and many people will apply for patents the moment they have something new and innovative at hand to gain the advantage.

Due to the differences in patents laws in different countries, some patents that are valid in one country will not be valid in a neighboring country. In short, there are two significant ways of determining the lawful and 'original creator' of an invention. The first way is by the time of application -- thus, the person who gets his patent application into the hands of the patent officer wins, even if he did not 'invent' first. The second way is by the original date an invention was first created -- thus, even if the original creator files last, he still gets the patent.

Well, if you want to know why this point is of vital note: Japan and United States, the two largest manufacturers and creators of ink jet printing devices in the world, use different methods, the two described above. Naturally, this has made some creators in one country extremely wary of filing a patent in the other for fear that another competitor will look over the application, then file the winning patent in the home country.

In any case, let's get on with the show.

After the age of the TRS-80, the age of the Apple II, the age of the Commodore 64, XT, Apple, and PC, we have arrived in the age of the Internet. And unlike days past when the only way to look at a patent was to either visit the Patent Office in person, or to request a copy by mail after submitting some fee, patents can now be viewed online courtesy of IBM, one of the world's most prolific applicants of patents (but surprisingly, not #1 -- a Japanese company has this title).

The IBM Patent Server is located at:

Scanned pages of almost all issued US Patents from the 1970s are available for browsing online for free.

What this means is you, the average person, now has access to the storehouse of human innovations throughout the past two decades! (unfortunately, there are some bad patents as well; ideas so absurd or obtuse, they will never be used)

And what follows is a walk through some of the various patents that accompany our ink jet printers home with us, to allow us to produce high quality output in a matter of minutes. (You can retrieve the full patent application of the patents described in this article directly from the IBM Patent Server yourself as you read.)

This is my brief journey through 760 pages of more than fifty patents related to modern ink jet printers.

Short Index........................
HP's PhotoRET
Epson's MicroPiezo
HP's Cooling Mechanism
Canon's Plain paper optimisation
Alps Dye-subs

Patent Owner, US Patent #
[Search Field] (Patent Issued Date, Patent Application Date)

Canon US 4740796

[346/001.1] (1988, 1986)

Ever a mouthful, this title simply describes what is to follow a complete description of the Canon Bubblejet concept -- bubbles forcing dots out of the nozzle -- and their use in a printer.

There are three major methods of forcing inkjet dots onto a paper in use today in the home inkjet market - bubblejet, thermal, and piezo -- each respectively used and patented by Canon, HP, and Epson. In the bubblejet method, a resistive element heats the ink (a liquid) until it changes phase and becomes gas, thus creating an expanded bubble in the nozzle tubes which forces some ink out the tip and onto the paper. The patent covers some items of other interest: Dot size is primarily controlled by ink pressure or pulse width of the electrical signal driving the heating resistor. They describe how up to 6 resistor can be placed in line to generate different dot sizes when fired and controlled in parallel. The ink they use has a basic composition of water (68%), ethylene glycol (30%) and black pigment/colorant (2%).

As you can see, most of the inkjet droplets are wasted carrier -- water and glycol, and just a small percentage is colorant. This naturally leads to many of the deficiencies of inkjet printing vs. other methods of printing such as fading (when light hits the colorant, the UV and IR rays tend to break down the chemical bonds and cause fading), lack of density (dark colors can not be made darker than a certain level because the amount of colorant is not very high), and the small color gamut of the output (the colors that can be created are limited due to the limited amount of colorant applied).

Yet, this point aside, we see that the 'idea' of a variable dot inkjet printer has been around for more than a decade (1986, invention made before the application date). Both methods described push a larger volume of ink out the nozzles as they increase.

Canon US 5826333

[29/890] (1998, 1995)
Method of Manufacturing an Ink Jet Head

In detail, you can read about how inkjet heads are actually made using standard and microelectronic manufacturing techniques. Needless to say, only the technically inclined will want to read this in detail; others may pass for the pretty pictures.

HP US 5359353

[347/086] (1994, 1991)
Spring-Bag Printer Cartridge With Volume Indicator

In the early days (eg. HP 1200 models), inkjet printers simply printed until they were out of ink, and continued to do so unless the operator realized this condition and changed the cartridge. Early cartridges had no clear ink level windows, so it was a guessing game to determine how many pages of life were left in each cartridge. One of the early innoventions was to create a inkjet cartridge which had a visible ink level indicator so you can quickly and reliably check the ink level with a glance at the cartridge. In this HP design, a bag of ink has two colored strips attached to the sides. As the bag collapses as the ink runs out, the strips move relative to each other and is visible through a small window. One strip is colored differently from the other so you can determine just how much ink is left inside.

HP US 5721573

[347/007] (1997, 1994)
Cooldown Timing System Montiors Inkjet Cartridge Ink Levels

Despite the above invention, people are lazy and often do not want to open the cover of their printers to check their printers. Also, printers may be networked and located far away from the operator. Finally, mechanical indicators are 'expensive' to produce and incorportate into an inkjet cartridge, and they do not tell the computer nor the printer that the ink has run out. Print jobs can still run without ink in the printer. By HP's second generation of inkjet printers (eg. HP 6xx series), their engineers had thought of a novel way of measuring the amount of ink in a cartridge. They measured the time it takes for the ink head to cool down from the operating temperature to another preset point. The time difference reflected the amount of ink in the cartridge and how fast heat was pulled away from the ink head into the ink liquid itself. With this invention, the printer could simply gauge the temperature difference during page feeds, or during lengthy head cleaning cycles, to let the computer know how much ink was left, without slowing down the regular print process. Printers never do rest...

Various Epson Patents

Epson US 5748214
[347/70] (1998, 1995)
Inkjet Recording Head ( click here for the patent )
Epson US 5818472
[347/10] (1998, 1995)
Inkjet Recording Apparatus

Same as above, describing the piezo inkjet head used in Epson printers. The piezo inkjet method is that no bubbles of gas or air are introduced into the nozzles. In piezo printing, a small piezo element temporarily moves inward when an electrical signal is applied, thus constricting the nozzle and forcing ink out the end. Clean, simple, and the epitome of solid-state with no heating elements to wear or burn out, or gas bubbles to clog the nozzles. The second patent goes into technical detail as to how the piezo head is driven by circuitry.

HP US 5650808

[347/043] (1997, 1995)
Color Ink Jet Pen Having Nozzle Group Spacing to Prevent Color Bleed

Besides the basic method used to force ink out of the nozzle, much study and research has been made to improve their design to improve output quality. Here, we see that on method of improving the output is to leave enough space between nozzles on the printhead so that the colors to not mix on the head itself. Since all liquids tend to adhere to a surface, it is natural to assume that if nozzles are spaced too closely to one another, the liquid that comes out of each will flow by way of their surface tension together. This is one limit of inkjet head sizes and may prevent ultra-thin or -small devices from being capable of rapid output using inkjet heads.

HP US 5673069

[347/015] (1997, 1994)
Method and Apparatus for Reducing the Size of Drops Ejected From A Thermal Ink Jet Printhead

One ever popular method of achieving better output from an inkjet printer is through the use of smaller dots and higher resolution. Reducing the dots is necessary as resolution increases; otherwise, the dot will be too big and overflow into the next. We see here that one of the issues that is dealt with is the uniformity of drop sizes. The temperature of the print head changes the viscosity of the ink, thus creating variations in drop sizes. In this patent, it is noted that it is better to keep the temperature at a steady 'reference' value by firing non-printing pulses of the thermal resistors in the nozzles to keep the temperature high. By using two different reference temperatures for 300x300 dpi and 300x600 dpi printing, two dot sizes are available for the two print modes -- a larger dot for the former, a smaller dot for the latter. This idea is introduced in the early HP printers, such as the 6xx line of inkjets years ago.

Various HP Patents

HP US 5726690
[347/015] (1998, 1994) ( Click here for the Patent )
Control of Ink Drop Volume In Thermal Inkjet Printheads By Varying The Pulse Width of the Firing Pulses HP US 5642142
[347/015] (1997, 1995)
Variable Halftone Operation Inkjet Printheads
HP US 5381166
[346/140.1] (1995, 1992)
Ink Dot Size Control For Ink Transfer Printing

Yet another mouthful, we see in this patent that the early HP inkjet printers (6xx line, RET series) could vary the dot sizes between ~66 and ~84 picolitres by varying the width of the electrical pulse sent to the thermal resistor(s) in the nozzles. This allows for the use of larger dots at 300x300 dpi, smaller ones at 300x600 dpi. Pulse width modulation is a very popular idea used to control dot sizes and you'll see Canon and Epson using this idea, albeit patented for their respective inkjet technologies.

The second patent introduces timings for the pulses. eg. 1.9 microsecond for a 66 pl. drop size. Also, the RET (resolution enhancement technology) concept is introduced. To reduce the banding problems often seen in older inkjet printers, micro stepping and multi-pass printing is introduced along with 4 dot sizes vs. 2. (a precursor to the 16 dot sizes found in today's RET II printers) In short, a subset of dots for each particular line is printed in one pass of the head. The paper is fed a small amount, not quite enough to go to a completely new line, and the head again passes over the area and applies another subset of dots missing from the first pass. The ability to produce multi-sized dots along with the ability to place dots in between other dots enhances the output in the HP printers with RET.

The third patent introduces the idea of rings around the nozzle to control ink spread across the head. One way of preventing ink dropplets from spreading on the nozzle and resulting in distorted output is to etch rings around the nozzle. When a volume of ink forms on the head during droplet formation, it will expand until it reaches the first ring and stop -- similar to a moat around a castle. Only when the volume is great enough to overcome the barrier of the first ring does it expand further, only to stop on the second ring, and so forth. Various methods are used to coat the surface to head and rings to further control the spread of ink. As a result, a better formed ink drop is produced by the inkhead.

As you can read, these three patents together let anyone understand how the HP RET technology, introduced many years ago, led to better inkjet printers on the marketplace that what had been previously been made available (not anymore however).

Canon US 5748207

[347/043] (1998, 1993)
Ink Jet Recording System for Preventing Blurring at Color Boundary Portion Canon US 5831642
[347/9] (1998, 1997)
Ink Jet Recording Method and Apparatus

One of the problems that was occurring frequently back when inkjet printers were starting out was bleeding. You see, paper is made of fibers. These fibers draw water and other liquids into them as well as ink. Although many Chinese artists have made a name for themselves with their classical images of bamboo and landscapes with bleeding brushstrokes, almost everyone dislikes inkjet output that has bled to some degree. This not only makes images blurred, text characters are also ruined by ink bleed. When inks of the same color bleed into each other, you notice the effect less. But when colors of differing colors bleed into each other, you will immediately notice the rainbow of colors that are created by the mixture. Inkjet printer often use a slightly larger dot than the resolution they are printing at. Why? Dots are round, not square like the grid they are to print to, thus there are four areas at each corner where no ink is. If dots were the same size as the grid, images would appear poor as areas of white paper show through past each dot. Thus, overlapping dots that are slightly larger than the resolution of the print is used. Unfortunately, this allows adjacent dots to touch each other, and bleed if wet. Since all inks take some time to dry, one method that has been extensively used to prevent this is to print a subset of dots in one pass, the others in subsequent pass(es) for each line. And you wonder why some printers take so many passes over each line.... All of this is done to reduce the warping of paper due to being too wet, while reducing intradot bleeding. As you can see in Canon patent 5831642, a lot of work and thought goes behind the scenes to figure out how a solid pattern is to be broken up into multi-pass patterns -- you can view the patterns yourself in this patent.

HP US 5821957

[347/43] (1998, 1997)
Method of Ink Jet Printing Using Color Fortification of Black Regions

An older idea of the above, HP tries to reduce bleeding by first printing the color dots, then the black dots later. While this reduces bleeding by letting inks dry between passes, it is not as advanced as the later Canon patent above. So, as you can see, a simple idea can be extended in a novel way and patented.

Epson US 5748208

[347/43] (1998, 1993)
Color Inkjet Recording Method

You'd be surprised, but even the order dots are placed on the paper, and even the colors used affect the amount of blurring across colors. When you print color dots next to black dots on paper, the black ink will tend to bleed into the color dots while both are still wet. Since it takes far longer for the ink to dry on the page than a couple seconds, it doesn't make sense to wait several seconds on each pass. HP has taken the route of adding a heater to some of their faster printers (eg. HP 1200, HP 2000/2500) to have the ink dry quicker, but it still doesn't directly address the bleeding of black into adjacent color areas. Epson notes that the paper fibers naturally pull ink sideways during the normal process of inkjet printing. Dots falling on dry paper next to wet areas already covered with dots lead to the natural migration of inks across the two boundaries. Surprisingly, the fix is to first print a color dot in the same area as where the black dot is to go adjacent to a color area! When a black dot is then printing into this pre-saturated area, the ink does not migrate sideways, but rather only vertically into the paper. As a result, bleeding between the black/color boundary is significantly reduced and rapid printing can occur with the page still wet.

Various Patents/different owners

Canon US 5832185
[395/109] (1998, 1997)
Alteration of Dither Matrix Size For Full Color Dithering
Epson US 5557709
[395/109] (1996, 1994)
Method And Apparatus For Dither Array Generation To Reduce Artifacts in Halftones Images
Epson US 5796929
[395/109] (1998, 1996)
Banding And Ink-Bleeding Reduction In Cluster Dither By Screen Displacement
Epson US 5675716
[395/109] (1997, 1994)
Method And Apparatus For Vivid Color Correction In Binary Printing Devices
Epson US 5838885
[395/109] (1998, 1996)
Salt-And-Pepper Noise Reduction

One of the initial, and most visible, problems that occurred with early inkjet printers was the banding of colors between different lines/passes of the inkjet head. The mechanical feed mechanism is simply not accurate enough to provide exact pixel feed on each pass, nor can there be any guarantees that the print head itself is perfectly accurate. As a result, the pixels on one row slightly overlap those of another pass, and banding results. The slight differences that occur chemically and physically in the paper and inks as they dry also contribute to this effect. To minimize or eliminate these effects, a variety of dithering patterns are used. As a quick backgrounder, dithering is used in printing whenever a limited number of original colors are used to create the entire gamut of intermediate colors on paper. One would think that if you had only four colored crayons, you would have a hard time creating other colors. Luckily, at the resolution used in printing (100 dots per inch or higher), the human eye makes up for this lack of colors by blending patterns of colors together. Thus, a pattern of 50% cyan and 50% yellow appears to be green to the human eye at the usual hand held distances. This mixing of patterns of colors also applies to monitors, TVs, LCD panels, and other devices which use a limited set of colors to display images.

The easiest way one can create a pattern is to simply assign them by percentage. Lets say we have a two by two pixel pattern grid -- with each pixel assigned to any one of the four CYMK colors (in 4-color printers). If we wanted green, we could simply color two dots cyan and two yellow. However, if we simply did this across a large area of green, we would see that these grids aligned side-by-side suddenly create an even pattern of lines alternating between cyan and yellow. Since this isn't the desired effect, we can introduce 'random' dithering patterns which mix up the way we color a grid to reduce the 'patterned' effect we would otherwise expect to see. One common method is the diffusion array which, by its randomness of dot placement, reduces banding significantly. However, even with the diffusion array, unexpected groups of whirls and other defects can appear because the randomizing process introduces 'unwanted' patterns by chance.

Thus, many of these more advanced dithering patterns not only randomly form grids, by they also modify them based on neighboring grids to further eliminate dithering patterns and such. Dithering patterns also affect the 'relative' quality of the final pictures that are printed. As an example, since human skin is one of the flattest color areas in a photo, your mind expects to see little variation across the body and face. Using 'normal' dithering patterns, black dots may unexpectedly get placed in areas of skin. While this would be fine at matching the 'real' color closely if it were not skin, black dots mar skin areas and colors to the human eye. A modified dithering pattern that avoids placing black dots in skin tones 'improves' the picture. You can see this difference in Epson printer drivers as they have an option to select between photographic and other types of dithering array biases manually. Also, since the human eye notices bright colors and adjusts them automatically for slight hue mismatches, it is 'better' to reduce the presence of dark/black dots in bright/light color areas to enhance the apparent vividness of pictures. Yes, the colors may not match as closely, but the human eye loves and accepts slightly off bright 'eye candy' colors more than bright colors with annoying dark dots here and there -- quite simply because such artifacts of limited color printing does not occur in 'real' life where there are no such dithering effects at all.

Epson US 5844585

[347/43] (1998, 1996)
Apparatus And Method For Printing High-Quality Color At High Speed

Combine the two ideas of multi-pass line scanning and dithering with a novel idea of feeding the paper slightly at each pass and you get this patent. While one line is being passed over a second time, the inkjet head has already advanced far enough to begin printing the first pass for the next. With each pass, the paper is slightly advanced to give the printer a head-start on the following lines, while the prior lines are completed. No need for the nozzles of one color to sit idle after it has printed its share of dots for that line as the heads continues to pass over and over again to finish with the other colors. Open up any Epson color printer and you'll see this novel idea at work.

Epson US 5684932

[395/109] (1997, 1994)
Method And Apparatus For Dither Array Generation To Reduce Artifacts In Halftoned Image Data Utilizing Ink Reduction Processing

Novel dither matrixes also help when you have the fundamental problem faced by all inkjet printers -- round dots vs. square ones. This may take a moment to sink in, but when you realize that round dots do not cover the area of a square completely (it leaves the four corners untouched), you see that there's a problem. How do you create a dither array properly? Most inkjet printers of the past used slightly larger dots than the width of the square grid to adjust for this. Unfortunately, this also alters the image (eg. oversaturation of overlapping areas between dots) and this patent attempts to correct for these large dots when used in a dither matrix.

HP US 5764254

[347/70] (1998, 1995)
Alignment of Differently Sized Printheads in a Printer

In HP printers, especially early ones (eg. HP 1200), the black color cartridge was capable of printing at 600 dpi and the nozzles were accordingly as small. Color, unfortunately, printed at 300 dpi and used larger nozzles. Differences in ink composition also contributed to this. Well, what to do? This patent explains how they lined everything up to make it all work. Naturally, printers today can simply avoid this mess by using dots and nozzles of the same size regardless of color.

Canon US 5717448

[347/43] (1998, 1997)
Ink Jet Printing Apparatus And Ink Jet Printing Method

Highly variable dot technology can improve images by reducing the visible signs of dithering. If a smaller dot is used to correctly dither an image, the more natural it will appear. In this patent, we see how generating multiple pulses creates multiple dots. Placing many smaller dots on top of each other results in a larger final dot on the paper. This is a precursor to the 16 dot size technology in the latest HP 7xx/8xx/11xx/2xxx series printers. But, to avoid bleeding, dots of different colors placed next to each other are limited to a maximal size, one such that they just barely touch each other, but do not overlap. Mentioned are there dots sizes, 5, 7 and 10 picolitres for various implementations but have yet to see an implementation in a commercial, home Canon inkjet printer. (They do have dual dot size printers.)

Canon US 5805190

[347/100] (1998, 1996) ( Click here for the Patent )
Method and Apparatus For Ink Jet Printing with Ink and a Print Property Improving Liquid

Introduced in the BJC-7000, the idea behind this invention is to prevent bleeding by chemical reactions. Ink is 'wet' in that it will bleed into paper. To prevent this, a liquid chemical is first applied to an area of the paper just before ink is applied on top. Due to a chemical reaction between the liquid and ink, the ink 'dries' is made insoluble and permanent -- thus, it stays near the surface of the paper and does not migrate through the fibers of the paper. Of course, we've yet to see this idea work perfectly across a broad range of papers.

Koyu Nikoloff US 5660622

[160/287.34] (1997, 1996)
Coating for Ink Jet Recording Sheets

The easiest way to achieve high quality output from an inkjet printer today is to simply use specially coated inkjet paper. Vs. the other ideas for improving quality and reducing bleeding, using paper alone will give you the best improvements, especially when companies optimize their inks for use on their inkjet papers. The chemical composition of what goes into an inkjet paper is disclosed in this patent. In this presentation, hydricated silica, binder, optical brightner, water, cationic agent, leveling flow modifier, and dispensing agent are the main ingredients. I'll leave the chemical compound details in the patent for those who possess a good understanding of chemistry.

Canon US 5825377

[347/15] (1998, 1997)
Method and Apparatus for Ink-Jet Recording With Inks Having Different Densities

Epson US 5795082

[400/120.09] (1998, 1997)
Printing System Utilizing Inks of Different Densities, Cartridges Used Therefor, and Method of Recording Images

The best in inkjet printing today comes from 6-color printers. The wider gamut due to the expanded color set allows for more natural transitions between color areas and more subtle gradiants.You can read in both patents in detail how the various colors are patterned and combined for the best quality output. The Epson patent covers their Sylus Photo printer, and explains in detail how the color ranges are matched to the desired colors, how the software determines whether to use one color or the other, graphs the lightness of each color at various densities, provides the names of the dyes used for each color and percentages of total ink volume, etc.

You'll note that their colors do not reach full lightness (ie. the lightest shades possible) -- about 95% instead -- nor full darkness (ie. the darkest shades possible) -- even black applied at 100% coverage achieves between 20 and 25%. E.G. The ink composition chart lists four dyes used: Direct Blue 99, Acid Red 289, Direct Yellow 88, and Food Black 2 in ranges from 0.7 to 4.8%. The rest of the ink consists of Diethylene Glycol (20-30%), Surfinol 465 (1%), and Water (63.1-79%). This explains why black text from inkjet printers do not look as dark as black text from laser printers created from solid carbon. Also, this means that third-party inks which use the same composition as stated in this patent, have a very good chance of working just fine in your Epson Photo printer. (Naturally, it would be ideal to have the actual inks processed though a gas spectrometer and chemical analyzer...) A fine way of saving money. Mix your own if you have these components handy.

Thus, unlike a traditional print, the color gamut and dynamic range of a picture printed on these very best Epson Photo printers will not have the widest gamuts of colors possible through other means. This is due to the fact that 3-7% of inks used in inkjet printers are the actual color dyes/pigments. Still, for those Epson Stylus Photo owners, this patent provides a very interesting look behind the workings of your printer and reveals a lot of fascinating facts.

Alps US 5806995

[400/120.02] (1998, 1997)
Thermal Transfer Printer

For those who have or are interested in how the Alps 1300 (and similar Alps 5000) sub-dye printers operate, read this patent. The technology behind thermal printers is very simple. Simply heat a carrier of color, which melts and is transferred onto paper. These colors can mix during the melted stage and combine to form a seemless output characteristic of photo quality sub-dye prints. Today, the Alps 1300/5000 provide the very best photo output prints for under $500 US to consumers for use with their computers for general use, bettering even the best home photo inkjet printers available -- the Epson Photo Stylus series.

Unfortunately, patents do take a couple years to process, so the very latest technologies are not publicly available. But based on the prior works we have available to us, we can guess at the innovations being used and how their applied today. With the IBM Patent Server in hand, you'll soon be looking up patent numbers from a variety of products and surprise yourself when you learn what is and can be patented, as well the innovations involved.

I leave you with the patent for the Colgate Tartar Control Toothpaste with Micro Crystals (copper colored box).

Colgate US 4889712

[424/52] (1989, 1988)
'Anticalculus Composition for a Toothpaste'

Toothpaste can not be patented by itself. The product is of such universal importance that the FDA and government would prevent such from occurring if tried. But, better compositions than just fluoride and paste can be patented and here, we see that plaque form when it crystallizes on the surface of the teeth. The patent covers a polymeric polycarboxylate which doesn't dissolve in saliva that, when applied, prevents the crystallization of plaque. Thus, not all toothpastes are made equal and spending just a few pennies extra for better toothpastes can improve your oral health.