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Subject: Re: How can a laser printer be converted to burning a pattern into polystyrene

Date: Thu Mar 12 04:43:00 1998
Posted by Ricky J. Sethi
Position: Phd

Hi Mel,

You bring up quite a few points and I'll try to deal with most of them. But let me warn you at the outset: the answers I'm going to give are probably not what you were looking for. From the way your question's phrased, it sounds like you're thinking of burning the styrofoam directly with a laser. But this isn't how a laser printer works at all. Although the laser printer does use a laser, it doesn't use it to burn an image directly on the paper. Instead, the laser printer works much like a copier. Because of this, I'll limit my discussion to laser printers rather than go into the specifics of lasers, also.

Before we jump into how a laser printer works, however, let me clarify that I'll be talking about write-black printers, as opposed to write-white printers. The difference between the two is that the write-white printers print the charged area of the drum (explained below) and the write-black printers print the uncharged areas of the drum (you guessed it: explained below as well). Btw, a good overview of a write-white printer (along with a nice picture to make all this clear) is available here. Also, since your question was pretty detailed, I'll try to cover all the basics below. Translation: this is a lenghty answer so please feel free to skip around and explore the links, especially Prof. Bloomfield's great site (link below) and the picture (linked above; in fact, you might want to refer to the picture to visualize the components and process as you read my answer).

Okay, with the warnings safely out of the way, let's get started. The whole process of printing starts off by first positively charging a photoconductor coated drum. Then, the laser (which is controlled by the printer controller via the print engine) is directed to various parts of the drum to form the image on this tube. The points of the photoconductor coating that are struck by the laser become conducting and the electric charge is "removed" from those points. This results in an inverse image of the print job being formed on the drum (i.e., the areas struck by the laser become neutral and form the image part whereas the points that weren't struck stay positively charged and represent the dark areas).

Next, positively charged toner particles are "sprayed" onto the drum and only "stick" to the uncharged areas on the drum. Thus, the toner particles are the "ink" which really form the image and only the uncharged portion is printed (the charged portion is the "white" background).

Finally, a sheet of paper is negatively charged by a wire. Then, as the drum rotates, the negatively charged paper is brought into contact with it and the positively charged toner particles are attracted to the paper, forming the desired image. The paper and toner are then fused by a combination of heat and applied pressure. As the finished page is being delivered, the drum is cleared of its electrical charge, cleaned, and recharged in anticipation of the next print job.

So that, in brief, is the printing process for a write-black printer. The physics of write-white printers is also covered at Prof. Louis Bloomfield's excellent site, How Things Work. The basic difference is that the drum is negatively charged and the paper is positively charged (and, of course, that one prints the charged areas (write-white) while the other prints the uncharged areas (write-black)).

As for the printer driver information, you don't really have to modify that. The printer driver is the program on the host computer that communicates with the printer. The printer has it's own computer that is controlled by the aptly named printer controller. This figures out how to move the laser (via the print engine, another, even smaller, computer), rasterize the image, how to talk with the host computer that's requesting the print job, etc. So you wouldn't really have to write a printer driver (which is doable) but you would have to make a printer controller, engine, and convert the actual mechanism! For a great reference to the more technical aspects of printers, you might want to check out A Laser Printer Book.

So that should cover the basics of printers and how they work. As to your specific project, I would guess that you want to print on polystyrene foam (and not some of the other forms of polystyrene, like cd cases, etc., which already have a well-established printing method). Quite honestly, I'm not sure how you might go about that. This would probably be something that you might want to ask some experts in this field, especially since I'm more of a theoretician than an experimentalist :) But I suspect that something like this hasn't been done because it most likely is not economically feasible using current technology. That's not to discourage you... not at all! Maybe you can be the first the discover a way to do this and become a billionaire. If you do succeed in this endeavour, might I suggest donating some of that new-found wealth to the arts and sciences?

Good luck!!!

Rick.


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