xerographic grey

several photocopic pieces
(different from the ones above)
featured on one of my favorite blogs:

t o n e r w o r k s

3 kommentarer:

corona wire sa...

nähdä näkyjä


Toner is sometimes referred to as dry ink, but toner isn't actually ink at all! Ink is a pigmented liquid. Toner is a fine, negatively charged, plastic-based powder. The black color in photocopier toner comes from pigments blended into the plastic particles while they are being made.

In your photocopier, toner is stuck on larger, positively charged beads and stored inside a toner cartridge. When toner-coated beads are rolled over the drum, the toner particles find the positively charged ions on the unexposed areas on the drum's surface much more attractive than the weakly charged bead. The same particles are subsequently even more drawn to the electrostatically charged paper. The plastic in the toner lets you keep it from jumping ship once you've finally got it on the paper; all you have to do is apply heat to the toner, and the plastic particles melt and fuse the pigment to the paper.

The Fuser
The fuser provides the finishing touches that make the toner image on a sheet of paper permanent. The fuser has to do two things:

* Melt and press the toner image into the paper
* Prevent the melted toner and/or the paper from sticking to the fuser

All that's required to accomplish these tasks is quartz tube lamps and Teflon-coated rollers. The sheet of paper is sent between two of the rollers. Then, the rollers gently press down on the page to embed the toner in the paper fiber. Meanwhile, inside the rollers, the lamps are on, generating enough heat to melt the toner. Why doesn't the toner melt onto the rollers instead? Just like non-stick coating prevents your dinner from becoming glued to the bottom of your frying pan, the Teflon coating the rollers keeps the toner and paper from sticking to them.

- - -

mike cannell sa...

ah, a fellow xerophilliac!

troylloyd sa...

warm photocopies
almost better than
sniffin' mimeo


analog machines get better greys than digital, i think the tech descrip below may illustrate why:

Unlike an analog copier, toner sticks to the drum surface where the light strikes (1s) and does not stick where there is no light (0s.) This is what is known as the “Black-Write” system, and is created by utilizing different polarities of (+/-) charge and toner than in an analog (“White-Write”) system. Printed areas are described digitally as “1” and non-print areas are “0.” This is the latent image on the drum. However, this latent image is not as powerful as the equivalent analog latent image. For this reason, bias voltage is used to enhance the image. Bias voltage is applied through the mag roller and causes a greater potential (voltage) difference between the black and white areas of the latent image. Toner sticks to the printed areas (1s) and not to the non-printed areas (0s.) At that point, we have a toned image on the drum.
An exposure lamp lights and scans the original, as in an analog copier. However, the exposure lamp is usually Xenon, not quartz-halogen. These lamps usually run cooler and do not require as much ventilation as the lamps used in analog copiers. The image is reflected off the original, to a set of mirrors and to a lens, as in an analog copier. However, unlike an analog copier, the image does not reflect to the drum. After the image leaves the lens, it strikes the Charge Coupled Device (CCD.) This device converts the optical image into digital electronic pulses (1s and 0s.) These signals are carried by wire harness to circuit boards in the machine, where they are converted to a string of 1s and 0s, each one representing a tiny portion of the image. 1 is print. 0 is no print. An easy way to understand this is to visualize an old dot matrix printer. As the image is laid on the paper, it is rather easy to see how everything is made up of rows of dots. No dots = blank areas. If printer resolution is 300 dpi (dots per inch), then there are 300 dots (dots of black or white) in one inch of print. These 1s and 0s are sent to the laser unit.

2. The laser unit consists of a laser diode (which creates the laser beam) and a polygon motor. The polygon motor is rotating at about 20,000 rpm. It has multiple surfaces; usually at least 5. The laser beam is aimed at it. As the motor/mirrors rotate, the laser beam shoots a row of 1s and 0s onto the mirror. The laser beam is firing its dots (it is pulsing on & off as determined by the 1s and 0s; if it were printing a black line, it would be all 1s and the laser beam would be on constantly for the length of the line.) Since the laser beam is traveling at the speed of light (186,000 miles per second), the mirror surface, is, in effect, practically standing still. An entire row of dots, the width of the page being copied (or printed) is fired on to that mirror surface and reflected to the drum. The next mirror surface (which rotates past at 20,000 rpm, remember) receives the next row of dots. Thus, for an image being copied at 300 dpi, 300 mirror surfaces will pass and add their row of dots to the drum for one inch of drum travel. Since the drum is turning relatively slowly, it is, in effect, standing still, compared to the speed of the laser polygon motor. As these dots are placed on the drum, they will affect the charge that has already been placed there by the charge corona. Unlike an analog copier, however, the charge will not attract toner. It will repel the toner. So, during exposure, wherever the 1s are present, the charge will be removed from the drum surface, causing toner to stick. If you have trouble remembering this, think of this silly little model. The pointy “1” punches a hole in the surface, which the toner then falls into. Sorry, if that sounds condescending or juvenile, but it makes it easier for me to remember it. The important thing to remember about exposure is that it is divided into two separate sections, before and after the CCD. Because of the “Black-Write” system, exposure effects and problems in a digital imager (copier, fax, printer) are exactly opposite those of an analog copier, if they occur after the CCD.

Reduction & Enlargement: In order to reduce or enlarge, the speed of scan has to change, as in an analog copier. The scan motor and the first set of mirrors are pretty much identical. To reduce, the machine scans faster than when it is in 1:1. To enlarge, it scans slower than 1:1. Unlike an analog copier, the digital copier’s lens does not move; the width of the image is changed electronically. The entire image enters the CCD, and is then adjusted in size before it gets to the laser beam. The laser beam can only be on (1s) or off (0s.) Its size cannot be reduced or increased. In enlargement, there are more 1s than there would have been. This creates a problem in reduction. Since 1s cannot be reduced, some of them (some dots) must be eliminated. Theoretically, very fine lines, running parallel to paper path (lead edge to trail edge) may disappear, or copy too light. I have never seen this be a problem. In most cases the human eye cannot see the difference. In an analog copier, the image was reduced. In a digital, it is broken down and created all over again in the form of 1s and 0s.

* Blanking Lamps: There are none in a digital copier. This is because there is no image to erase in the black-write system. The laser beam writes only the image on the drum. Unlike an analog copier, the unused area of the drum surface does not have to have charge removed from it.