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Dotty Spotty. Issue
2, March 1999
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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: |
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Short
Index........................
HP's PhotoRET
Epson's
MicroPiezo
HP's
Cooling Mechanism
Canon's
Plain paper optimisation
Alps
Dye-subs
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 Canon
US 4740796 |
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 |
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 |
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 |
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 |
Same as above, describing the piezo inkjet head used in Epso>
| HP
US 5650808 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
| Epson
US 5795082 |
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 |
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.
I leave you with the patent for
the Colgate Tartar Control Toothpaste with Micro Crystals (copper
colored box).
| Colgate
US 4889712 |
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.
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