Laser Printers

Laser Printers

Laser printers have been around since the 1960's when Canon patented a process called electrophotography. Electrophotography is the process using static and metallic toner to produce images on a piece of paper. It was originally meant for photocopier technology, but became well-suited in the mid-1970's for commercial large-scale printing.

Currently Canon produces about 75% of all the laser printer engines used in the world. Hewlett Packard and many other large-scale laser printer manufacturers use Canon's engines due to their many innovations.

The Parts

There are 10 major parts to a laser printer. Some are contained within the printer itself, and some are contained within a removable cartridge that contains the toner the printer uses to produce the images. Here are the common parts;

The Drum - The drum is the photosensitive cylinder that is charged by the laser beam. It is contained most often within the toner cartridge, although some printers do contain drums that are separate from the toner cartridge. By holding varying electrostatic charges, it can attract and repel metallic toner in the pattern produced on a screen.
Toner - The toner cartridge is where the toner is stored. Toner is a plastic that melts when heated, allowing it to melt right on to the paper. It also may contain iron oxide, which helps it maintain it's static charge. Some methods also use silica sand, wax, and/or charged dye, all to help regulate the charge held by the toner.
Doctor Blade - The Doctor Blade is also contained within the toner cartridge. It scrapes away excess toner from the drum after it passed the transfer roller. The excess toner is stored in a special compartment away from the new toner, as it has already been exposed to the electrostatic charge. After the doctor blade removes excess toner, the drum is ready to be re-charged.
Primary Corona - After the toner is removed by the doctor blade, the primary corona, or corona wire, charges the drum to an even -600V. The drum must have an even charge before being exposed to the laser or the image will not be created properly.
Transfer Corona - This wire charges the paper with a positive charge in order to attract the negatively-charged toner. After the toner is transferred to the paper, the paper passes over a static charge eliminator strip so that the paper does not stick to the drum.
Fusing Roller - These rollers melt the toner to the paper by producing a heat between 160 and 185 degrees Celsius. It also applies a pressure to the paper in order to maintain a sharper cleaner image. The fusing roller is why a page comes out hot from a laser printer.
Paper Transport - There are four paper transport mechanisms that move paper through the laser printer. They are the feed roller, the registration roller, the fuser roller, and the exit roller. (The fuser roller mechanism is considered part of the printing process as well as a paper feeding mechanism.)
Power Supplies - There are two separate power systems in a Laser Printer. There is the low-voltage power supply that feeds the electronic control circuits in the printer and the roller motors. The other power system runs a high-voltage system to charge, clean, and fuse toner and the drum.
Controller Circuits - These are the brains of the printer. Controllers run from simplistic circuits that run the bare essentials of the printer to motherboards with large RAM, font script, and monitoring technology.

The Laser

The 10th an most important component of the laser printer is the laser itself. The laser mechanism is actually several parts that work hand-in-hand, and their function is determined by a couple of differences in the process used by different manufacturers.

The laser itself is simply that, a laser that emits of concentrated beam of light. This light is bounced off a 6 or 8 sided mirror at the image drum. The laser is turned on and off in a specific sequence, which works with the spinning mirror to produce on and off bits on the drum. The laser can be turned on and off up to 30,000 times per second. Depending on the process used, hitting the drum with the laser can either tell it to attract or repel toner. Most lasers use a system where the drum loses it's charge to attract toner, but some laser printers use the opposite system.

Another system doesn't use a laser at all. Instead, it uses LEDs, or Light Emitting Diodes. LEDs are cheaper than a laser mechanism, but produce lower-quality results. Instead of a single laser, a row of LEDs manipulate the charge on the drum. The more LEDs in a row, the higher the quality of the print.

As I stated last week, the process of printing is a continual process. The drum rotates and can be cleaned on one section of it's surface, written on by the laser, and transferring the toner on another all at the same time. A whole sheet of paper isn't printed at once; it is a line-by-line process. This can make laser printers faster than other printers, but remember that the first page of a laser printer is always slow because the systems in printer need to charge, clean, and heat up in order to prepare for the print job.

Other Information

There are a couple of safety and operational facts you must know. First of all, never plug a laser printer into a UPS. UPS systems are designed to provide a limited amount of power to the computer, and laser printers require high power levels at start-up that most UPS systems can not provide.

Secondly, toner is a (excuse my language) pain in the butt. Because it melts easily, it's hard to remove from your skin. Because it's so fine, you can't vacuum it up with a standard vacuum. And no matter how hard you try, you can't brush the stuff off your skin. Remember these few hints;

Wash your hands in cold water when you get toner on your skin, and never try licking your fingers and rubbing it. It's messy stuff. There's no way around it.
The primary and transfer corona wires will get dirty over time. In order to clean them, run a dry cotton swab across them. Don't press too hard on the wires, as they are extremely thin and will snap. (Replacing a corona wire is as hard as replacing your left hand.)
There are several filters inside the printer to trap gasses and excess toner. If you don't clean these filters every so often, they'll plug and you'll notice a foul smell (ozone) or excess toner buildup inside the printer and on the paper. The fuser cleaning pad is the worst offender, as it will leave blobs of toner on your paper if it gets dirty.
If you EVER need to clean the laser (Which you should NEVER have to), make sure you clean the laser lenses AND the mirrors with a lint-free cloth. If you have to use a cleaner, rubbing alcohol is always the best because it evaporates without reside.
Don't vacuum up spilt toner with a normal vacuum. Toner is normally 15 microns wide, and can pass through the vacuum bag. The first place it's going to go after it escaped the bag is the motor, where it will melt and make a HUGE mess. There are special vacuums and bags for this job, but most of the time you'll have to be inventive. (A magnet works wonders in this case, but remember not to keep a magnet close to your computer or your back-up disks)
There are special roller cleaning products that can clean rollers that don't pick up paper any more. Don't use normal cleaners, as they leave residues that compound this problem. A wire brush and these rubber conditioners are the best tools you can find.

Printer Problems

There are a few common problems that can occur with printers. The first problem that every technician dreads is the "It won't print" syndrome. This occurs when a computer novice is trying to use a computer and has no idea how the system works. So the problem is "It won't print". If you're not on-site, this can be a real headache. Here are some easy steps to try to eliminate printer problems.

Ask if the printer is on. I know, this sounds idiotic, but it happens. I've spent too much time on the phone asking about problems that could have been solved by asking this simple question. It does two things; It ensures the printer is on and plugged in, and gets the person looking for other flashing buttons that can be a sign of the problem.
Make sure the printer is on-line. An off-line printer won't print, no matter how much you kick, punch, and scream at it. An on-line printer will either have a light off or on depending on the model, so if you can read the manual.
Make sure the paper is in straight, and that there's enough paper to reach the paper feed rollers. Some printers can't print when they get down to 2 or 3 sheets because the paper won't press hard enough on the paper feed roller to grab.
Check the toner levels, ribbon wear, and ink levels. Common symptoms of these problems are pages that only print in streaks or are faded, or the computer warning you the levels are low.
Make sure the right drivers are installed, and are working properly.
If it is a new printer, make sure the cable is a bi-directional (IEEE 1284) cable.
Ensure that no small pieces of paper are jamming up rollers or jets.

If all of these fail, you've probably got a more serious problem that will involve opening, cleaning, and repairing the printer. Consult the manual for details on these issues.

In Conclusion

Please review the methods of installing Printer Drivers and printers by going to Start - Settings and clicking Printers. This system is automated, so I have not covered it here. Do a quick review to make sure you know how to install a local and a network printer using this wizard.

Most printers are so cheap, they aren't serviceable and are replaced more often than serviced. Others are so complex, only specifically trained individuals should even open them up. Most of the time, the problems you will see have nothing to do with what I have talked about here. I've seen bent paper trays, dead motors, snapped corona wires, and every other problem that has nothing to do with any of the information I have given. Essentially, for every part in a printer there is a new and unique problem. Spend as much time as you can reading and watching printers, and when the problems occur, think them out logically and rationally.