Understanding Laser Printers – CompTIA A+ 220-901 – 1.14

Laser printers are very complex mechanical devices that combine technology with a high resolution output device. In this video, you’ll learn about the internals of a laser printer and the steps of the laser printing process.

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Laser printers are a testament to our modern technology. We can literally print with laser beams. We’re grabbing a laser, were using high voltage, some charged ions, some powdered ink, toner. We apply some heat and some paper, and you finally have your output. This provides us with a very high quality output. We’re able to use this for many different purposes. It also is a very fast printer. We aren’t usually waiting on laser printers these days, but it is a very complex piece of machinery. There are a lot of moving parts inside of it. It requires this high voltage, and a lot of memory. On the inside, the toner can get pretty messy. And whenever you have to work inside of a laser printer, you have to deal with this mess and this heat, to be able to resolve whatever problem might be inside the device.

One of the major components inside of our laser printer is this imaging drum. This is a photosensitive drum that the laser is effectively painting the image onto, as it cycles through in the printer. As this imaging drum spins around, it’s also picking up toner, and that toner is then transferred to the paper that will ultimately display our image. This imaging drum might be separate from the toner cartridge, like the one that you see here on my laser printer. Or it might be combined with the toner cartridge, so that every time you’re swapping out the toner cartridge, you’re also swapping out the imaging drum.

Here’s a bigger view of my laser printer. You can see that the imaging drum is right here in the middle. The toner is up in the higher part of the printer, and there’s a mechanism to pull the paper down from the bottom. You normally don’t want to expose your imaging drum to light like this. The only reason you would do this is if you needed to get into the back of the printer to replace it. The toner that’s inside of our laser printers does not stick to paper and stay there by itself. We have to melt these tiny toner particles to the paper, and press them onto the paper with heat. This is something that is handled through the fuser assembling.

This fuser assembly is a device that gets pretty warm inside of our printer, and it’s applying both the pressure and applying the heat at the same time, to make sure that toner sticks to the paper permanently. Here’s the back of my laser printer. You can see the fusing assembly is right here. The paper is coming out of the back, and it’s going towards the top of the printer, to the output tray. But it has to pass by this fuser assembly to apply that heat and that pressure, to permanently affix those toner particles to the paper.

If you have a color laser printer, these are usually using four different colors: the cyan, the yellow, the magenta, and the black, to be able to produce the vibrant colors that you see on your laser printer output. This means that we have to have four separate toner cartridges, and so we have to have some way to take all of the toner from all of those different cartridges, and have them all show up on the same place. And we do that with a transfer belt and roller. We take the image that we’re printing from all of those colors of the toner cartridges, and we put them all transferred to this single belt. This belt is then going to transfer the image onto the paper itself. It’s a very easy way to get all of these different colors to one central place, so that we can get output on our paper.

The paper is pulled through the printer using these pickup rollers. You can see there’s pickup rollers here, in the center of the picture. These pickup rollers should pick a single page at a time, and send it all the way through the printer. If the paper is coming through multiple sheets at a time, or it’s jamming because it’s not able to pull the paper properly, them we may want to clean the rollers or make sure we can replace the rollers, so they’re able to work optimally. Here’s a close-up of the pickup rollers. They’re usually a rubbery substance, and they have some resistance to them, so that they’re able to grab that paper and send it through the printer.

If you look on the paper tray of your laser printer, there is probably a separation pad right where the paper is going into the printer. It’s the job of the separation pad to pull just the top sheet of paper from the stack of paper that’s in your paper tray, and send that through the printer. You don’t want multiple sheets going through the laser printer when you’re trying to print. Fortunately, the separation pad is relatively inexpensive. So if you’re having problems with the separation pad, or it’s getting worn out, it’s a very easy and inexpensive thing to replace.

Most of the commercial laser printers that we have in our offices will print on one side of the page, and one side only. There’s not two printing mechanisms inside of the printer, to print on both sides. So to be able to do that, we use a duplexing assembly inside of the printer that does allow us to print on both sides of the paper. Its job is usually send the paper through, and then to flip the paper over inside the printer, so that it can then print on the other side of the paper. Usually, it is using a mechanism like this that is able to flip the paper over, and send it back through the printing mechanism. This could be something that is built into the printer, comes as a feature of the printer itself, or it may be something that you can add on to the printer at a later time.

This is a view of the duplexing assembly inside of my laser printer. It’s built into the bottom of the paper tray. So it sends through the paper, and it flips it over by sending it through and flipping it back onto the paper feed. If we were to cut a laser printer in half and look at it from the side, we’d have a view that looks something like this, as the paper is going through the printer. The first step when laser printing is called the processing. This is where we’re taking the entire page that’s to be printed, and constructing it in the memory of the printer. The printer does not move until the entire processing phase is complete.

Laser printers have to print entire pages at a time; they can’t print half the page and then wait and print the other half. Once you start the photosensitive drum turning, and all of the process occurring, you have to go all the way through, for the entire page, at one time. That’s why, if you’re printing some very large graphical types of output, you will need more printer memory inside of your printer, to be able to perform the processing. The next step is the charging phase. There is a wire inside of your printer whose job it is to set a negative electrical charge to this photosensitive drum that’s inside of our printer. And as the drum is rotating around, it’s charging that part of the drum. This charge is going to be very important when we get to phase three, which is the exposing phase.

That’s where we have a laser that is actually writing the image of what we want onto the photosensitive drum. It’s effectively removing those negative ions every place the laser is touching. This becomes important during the developing phase. This is where we take the toner from our toner cartridge, and apply it to the photosensitive drum. We’re also charging our toner with a negative charge. So we have a photosensitive drum that has a negative charge, and we have a toner with the negative charge. And obviously, a negative is not going to attract to a negative. They’re going to repel each other. But every place that we’ve touched with the laser no longer has the negative charge.

So every place that we have these tiny little dots of toner are going to stick to every place the laser has touched on this photosensitive drum. Now that we have toner onto the drum, we now need to transfer the toner to the paper, and this is the transferring phase. As the paper is going through the laser printer, this toner is being placed onto the paper, as it’s passing by the photosensitive drum, and it continues to rotate around. At that point, we have to make sure that the toner particles are going to stick to the paper, so we go through the fusing phase. We apply heat and pressure, to be able to melt that toner right onto the page itself, and there it will sit permanently when it comes out of the printer.

There’s usually a little bit of toner left on the photosensitive drum, so we need to make sure we clean that off completely in phase seven. This cleaning phase will make sure that the photosensitive drum has no more toner on it, and we can begin the process over again. It usually takes a number of cycles of the photosensitive drum going around to transfer an entire page of information. So this entire process is taking place multiple times, just to be able to get a single page of output.

So here’s a summary of that laser printing process. In step one, we are processing the image and building the entire page in the memory of the laser printer. In step two, we’re going to prepare the drum by putting a negative electrostatic charge on the outside of the drum itself. In step three, we need to expose that drum with the laser. And that effectively removes that negative charge, so that our negatively charged toner can then connect and place the toner onto the imaging drum in step four, the developing phase. In step five, we need to transfer the toner off of the drum and onto the paper where, in phase six, we will fuse that, with heat and pressure, onto the page itself. And finally, we clean the photosensitive drum and begin the process all over again.