A laser printer can be a challenging device to manage and troubleshoot. In this video, you’ll learn about the internal components of a laser printer and the process used when printing a page of output on a laser printer.
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Laser printers are a remarkable piece of technology. You’re literally using laser beams to provide output on a piece of paper. You combine that laser with high voltage, charged ions, powdered ink, heat, and paper, and you get some very high quality output from that combination. One of the advantages also of laser printing is that you can print very, very fast relative to other types of printing.
But this laser printing also has some negatives associated with it. For example, there are many moving parts inside of this printer, which means there are many opportunities for things to go wrong with those moving parts. A the laser printer also has memory inside of it where the page is stored before it’s printed. Other printer types don’t need that memory, so laser printers might cost a little more because of the additional memory installed.
These printers can also get pretty messy on the inside, especially if one of those toner cartridges leaks and that toner gets to the inside of the printer. That toner is relatively difficult to clean out, and it tends to get everywhere once it leaks out of the toner cartridge.
The imaging drum that’s inside of your laser printer is the middleman between the laser and the printed image on the page. The laser draws out what it would like to print on that imaging drum. The imaging drum is then put through toner, and the toner sticks to the area where that particular laser was hit. That toner is transferred to the paper where it is heated and permanently affixed to the output that you receive on the outside of the printer.
Often, this imaging drum is part of the toner cartridge itself, but there are laser printers that separate these into separate components so that you can replace the toner cartridge without necessarily replacing the imaging drum. Here’s a view of the imaging drum inside of my laser printer. There’s usually a protected cover because this is a photosensitive drum, and you want to be sure the only thing that is marking anything onto this drum is the laser itself.
The process of permanently attaching that toner to the printed page is done using heat and pressure, and that is using a fuser assembly to complete that process. This is effectively melting the toner and permanently affixing it to the page. This fuser assembly usually is the same size as the paper that’s going through the printer so that the entire page can be fused as it passes by.
Here’s a shot of the fuser assembly on my printer. There are connections here so that you can pop out the fuser assembly and replace it. There’s also warning signs on the printer telling you that that fuser assembly is going to be very hot.
Color laser printers usually have four different colors that they use to be able to print. Those colors are cyan, yellow, magenta, and black. So there might be four different toner cartridges inside of this printer, each with a different color. Those four separate cartridges provide the color needed to print a color image, but instead of printing them one at a time to the paper, it prints them onto a single transfer belt. That transfer belt then transfers all four of those colors to a single transfer roller, which finally then makes it onto your printed page.
Here’s another shot of the transfer belt inside of this laser printer. You can see the place where the cartridges would go. Those toner cartridges would then provide the colors. Those colors would be put onto the same belt. That belt would then transfer them to a transfer roller, which then finally puts the image on the page.
Inside of your laser printer is a stack of blank paper, and your laser printer is responsible for grabbing the top sheet off of the top of that stack and then sending that through the printing process. To be able to do that, it uses pickup rollers. Those pickup rollers are designed to pick up a single page at a time.
If there are problems with your pickup rollers, you may find that your laser printer isn’t picking up any pages to send through the printer, or it may be picking up more than one page at a time, which could potentially cause jams inside of the laser printer. It’s very common when performing maintenance of the printer to be able to clean or even replace those pickup rollers if they become worn.
Here’s a close-up view of the pickup rollers on my laser printer. These haven’t really been worn very much. You can still see the ridges that are inside of these pickup rollers. And these are pretty clean as well, and there shouldn’t be any problem having those pickup rollers perform properly inside of this laser printer.
Another component that works in conjunction with those pickup rollers is the separation pad. The separation pad helps pick up that single page from the top of the paper tray. This is usually right on the paper tray. It’s relatively inexpensive if you have to replace it, and it’s very small. It’s easy to clean off and make sure that it’s working properly. If you look carefully at the separation pad, you’ll be able to see if there’s any wear or if anything’s dirty, it’s very easy to clean off and make sure that it’s able to pick up those pages from your paper tray.
The vast majority of your printers are going to print on a single side of the paper as that paper passes through the system. But on some printers, you’re able to turn that paper over inside of the printer, send it back through, and print on the other side of the paper. We call that process duplexing, and your printer has to be specifically designed to provide that duplexing process.
If you print a document in this duplex mode, you’ll often hear the first page go through the printer, you’ll hear it turn around inside the printer and then be sent back through the printer to print on the other side. This means that somewhere in the printer there is a mechanism that is used to flip that page over to the other side and send it back through. This is the duplexing assembly. It might be built into your paper tray, or it might be built into some other part that’s inside of your printer.
Not all printers are able to provide this duplexing functions, and some printers allow you to add on this function after you’ve purchased the printer as an add-on. On my printer, the duplexing function is part of the paper tray, so it sends it into the paper tray to flip it around and send it back through the laser printer.
Let’s look at a cross-section of a laser printer and go through all seven steps of printing a page, from the very beginning to the very end when that paper comes out of the printer. Inside the printer is a photosensitive drum that is rotating around, and this is where your paper tray is. And the paper is going through the printer from one end to the other.
The first step in this process is the processing. The printer is not moving. There’s nothing happening inside of the printer other than the data and the pages being sent into the memory of the printer. The printer is then processing all of those images, and it’s building out in memory exactly how that page is going to look when it’s printed.
An important aspect of this processing phase is that the entire page has to be rendered in memory before the laser printer ever begins printing. The laser printer can’t print half the page, process more information, and print the other half of the page. It had to print the entire page in one single pass.
The second step is charging the photosensitive drum with negative ions. This is done on older laser printers with a corona wire or newer printers with a primary charging roller. This means the entire photosensitive drum will have a negative set of ions associated with the entire printing area.
Now that this charging process has effectively created a blank slate for the laser, the Step 3 of exposing is going to use the laser to write out the image that it would like to appear on the printed output. That laser is effectively neutralizing that negative charge at every point that it would like to have toner appear on the printed page.
Step 4 is the developing process. This is the process of getting toner from the toner cartridge onto the sections of the photosensitive drum that have been neutralized. To do this, the toner has a negative charge associated with it, so it’s not going to stick to any of the areas that have been negatively charged during our phase 2 charging process. The only place, then, that the toner will be able to stick are those areas that have been neutralized by the laser.
Those areas that have the toner stuck to them continue rotating by the transfer roller, which is Step 5. This is going to transfer the toner from the photosensitive drum onto the paper that’s passing by. Now we need some way to permanently fasten the toner to the paper. And to do that, we go through Step 6, the fusing process that will use heat and pressure to effectively melt the toner and permanently fastened it to the paper.
That’s the reason that when you retrieve a freshly printed paper from a laser printer that the entire paper is warm, because it’s gone through that fusing process. There will still be a little bit of toner left onto the photosensitive drum, so our final step is to clean that toner off of the photosensitive drum and prepare it for another cycle of that drum through the seven steps.
To summarize those steps again, we start with Step 1 processing, where we’re building the entire page of the output in memory. We’re then beginning the charging process, where we’re preparing that drum with that negative electrostatic charge. In Step 3, we’re going to write the image with the laser that’s inside of that laser printer.
And in Step 4, we take the negatively charged toner and have that stick to those areas that were written to with the laser. Step 5 is transferring, where we’re taking the toner from the drum and transferring it to the paper. Step 6 is the fusing process that permanently adheres that toner to the paper using heat and pressure. And lastly, in Step 7, the cleaning process will remove any excess toner from the photosensitive drum.
Category: CompTIA A+ 220-1001