Printer Faults - Vertical Distortion

Vertical distortion will stretch or squash the page.

Most laser printers produce the page vertically making 300, 600 or 1200 horizontal lines for each inch of vertical movement and feeding the paper at an appropriate rate. Paper is driven forward by feed rollers, the registration station and then by the fuser. By design the cogs driving those rollers move in lock-step.

The implication of vertical distortion is that there is some difference in movement between the paper and the print-process. Superficially that looks difficult to achieve as the registration rollers grip paper quite firmly and are usually driven by the same motor that is driving the print cartridge.

Registration roller timing is quite critical but a failure there would lead to pages being misregistered - and indeed vertical distortion and registration issues can go together.

Generally the print process turns once or twice as the machine ensures rollers are clean and toner is evenly distributed on the developer. At that point the paper is released and just before it passes the transfer roller the laser begins to write the latent image.

It isn't impossible for a clutch to slip in a laser printer just as it does in a car. There is usually no driving force other than momentum that would fight the registration rollers acting on the paper. One possibility might be a pickup roller wrongly positioned so that it is still dragging on the paper when it should have disengaged (although that might more likely cause a misfeed).

The fuser rollers normally move in lock-step with the print process. The fuser might cause a change in paper movement if the pressure roller is crushed. In use the fuser pressure roller is held hard up against the heated roller or foil. If the fuser is idle for a long time the pressure roller rubber distorts and there is a ridge left in the material; the roller then makes thumping noises as it turns and the page might feed unevenly. Normally a pressure roller will pretty largely recover if it is run a bit so that the pressures are equalised around it.

When some models of fuser are shipped the pressure is removed using locking levers. Some printer manuals recommend storing printers with the fuser removed and the levers put in the disengaged position. Some Printers (the HP LJ 5100 for instance) have lock levers that are determined to move back to the engaged position.

So for vertical distortions check:

• Fuser rollers rotate freely and evenly.
• The registration rollers have an even grip on the paper
• No obstruction interferes with smooth paper advance.