I have a laser printer and sometimes I have continued using a toner cartridge until it is literally out of toner - ignoring the messages that the printer gives me.
Can this damage the printer in any way? For instance, the drum or the fuser unit? How does the toner being low specifically affect the other components?
Just look at how the laser printer works. http://computer.howstuffworks.com/laser-printer3.htm A laser beam create an electrical charge on a drum, this charge attract small particles of toner that are then transferred to the paper. Then the paper goes trough the oven that cook the toner to make it stick to paper. I see no reason why no toner can do any damage to the printer. It will just stay blank.
Do not believe printer sellers. They make no money on the printer but only on cartridge. So they will tell you to change them more often than necessary.
Short answer: No.
A laser printer will have a mixture of toner and developer in its developer housing. The physical interaction between the particles of toner and developer are what gives the toner an electrical charge. The polarity of this charge will depend on the development system being used in your specific printer.
The printer will either have a Toner Concentration (TC) sensor, or use an algorithm to determine how much toner is in the housing, and how much to dispense.
In many home and small office printers, when you replace the toner you also replace the developer as well, starting you with a known TC. If you are actually adding toner, only, then the printer will dispense toner to reach the working TC. I suppose it might take longer to tone up if you really ran it down.
In no case would you run into a permanent damage situation.
The answer is no. The printing device will let you know when it can no longer print because of toner.
Now to discuss this further: A little knowledge first on how it works. Simple language here. Toner is added to a developer unit which sits real close to the image unit, but the toner does not rub on the drum (imaging unit).
An image that you want to print is placed on the drum by usually a laser beam. The drum has a specific charge of electricity and now even different where the image is because of the laser beam. The image is such that it attracts the toner from the developer unit to electrically stick to the image. Just a note here if you run out of toner it wont print anyway. Why print an image with no toner? There wont be any image.
Next step is to get the image onto the paper. As the drum rotates in time it meets with the paper to be printed. The paper will pass under the drum so the image will go onto the paper. Under the paper but directly under the drum is another electrical charge unit that is much stronger than that of the toner stuck to the drum. It now is pulled to the paper, and now on the paper. The paper now makes its way to what is called a fuser or fixing assembly (same thing). The fuser now melts the toner and presses it into the fibers of the paper and then your print is done.
The process I explained is a little more involved and has a few methods it can produce the same effect but all the processes have toner a developer unit, a drum, transfer unit and fuser.
Now to answer your question. How can it matter if you are out of toner or not? The toner is not a lubricant for any component and no damage can occur with no toner. You wont get any print on your paper for one thing. The other thing is your printing device knows when it is low and out. The reason is not because it will harm your machine but because if your out of toner why would want to continue printing if blanks comes out? Waste of paper.
