Troubleshooting HP Laser Printer Paper Paper Path Problems
Fully half of all customer complaints are about paper path problems. Moving paper is the most difficult, if not the most complicated, thing the average laser printer has to do. Compounding this problem is the mix of media available to the user envelopes.
Beyond the standard 8-1/2" x 11" paper, customers need to print on card stock, microfilm cards, transparencies-just about everything but napkins are specified out, and baseball caps. While many of the more exotic choices are specified out, printers are expected to perform acceptably for a wide variety of media.
In this article, we'll look at paper path problems true mechanical wear and failure problems (not bad sensors or error messages). While we will discuss the role sensors play in troubleshooting jams, most of what we will deal with here is simple mechanics. We're concerned here with real jams, not fake or phantom ones.
Moving paper through office machines is a task that manufacturers have been wrestling with for the last 40 years. Through that period, a lot has been learned about the mechanics of moving individual sheets of paper.
Surprisingly, the technology for doing so so remains largely unchanged from year to year. There are only so many ways to move paper. The problems remain the same, as well. There are essentially six problems involved in moving paper through a laser printer:
Separate and control a single sheet of paper.
Align the paper so that the image will be properly registered on the page.
Feed the paper through the machine at a constant speed, synchronized with the image system.
Prevent static charges from affecting the movement of the paper.
Use heat and pressure to melt the toner-cast image into the fibers of the paper.
Eject the paper from the machine in the desired fashion.
While all this is happening, the system must not deform the paper in any way and must protect it from vagrant debris in the paper path.
Laser Printer Paper Separation Characteristics
The first challenge is to acquire control of a single sheet of paper. The earliest machines accomplished this by having the operator insert single sheets of paper sequentially. Today's environment requires machines to feed paper at high speeds up to 30 sheets per minute. The difficulty this presents is that paper sheet tend to Cling together. Push on one piece, and you automatically put pressure on the paper beneath it. Getting one sheet of paper al a tme turns out to be a demanding technical problem. Separating the top sheet of paper from the pages beneath it is accomplished in one of three ways:
1. Pressure Between a D-Roller and a Separation Pad
The stacked paper is presented to the machine with no impediment on the leading edge. The paper is held to the top of the tray With firm pressure from below. When the D-shaped roller grasps the top sheet, sheets beneath are carried forward by a combined friction/static adhesion to the top sheet by the same pressure from the D-Roller. Lying in the path of the D-Roller's asymmetrical tum is a cork-covered Separation Pad.
The pressure between the Separation Pad and the leading edge of the D-Roller provides resistance against any paper being fed through, separating the top sheet from any sheets tagging along beneath it. The requirement is that the coefficient of friction must be greater between the Separation Pad and a sheet of paper, than exists between two sheets of paper. If the pad is worn smooth, or if a strong static bond exists between the individual sheets, multiple feeds are possible. If the D-Roller is worn, the pad can prevent any paper feed.
Separation Pad or Sep Pad. This serves to separate paper by having a higher coefficient of friction between the pad and a piece of paper than between any two pieces of paper. Eventually, it gets worn slick and the Coefficient of friction is reduced below the threshold for holding the underneath side of paper.
2. Pressure Between a D-Roller and an In-line Clip
The stacked paper is presented to the machine with an impeding corner clip. The impact of the D-Roller snaps one shect out of the clip and forces it into the feed.
3. Back Pressure From a Separation Roller
For higher-speed feeds, grouped rollers are used. Some, uses three Pickup/Separation Rollers to accomplish pickup, feed and separation. The first roller engages the paper, propelling it into the machine. The second roller, mounted below, back-feeds the paper under the object sheet, preventing multiple feeds, while the third roller continues the feed into the machine.
Printer Paper Separation Failures
Multiple feeds do sometimes occur, most commonly due to worn Separation Pads, for printers that have them. In the other two separation systems, multiple feeds are relatively uncommon.
Failure to feed at all is a more common problem. Jams at the Pickup Assembly çan usually be attributed to a worn Pickup Roller. In the Canon SX engine, the D-Roller acquires a crescent shape at its leading edge. The more pronounced the crescent shapc, the more likely the roller is to fail. Before a permanent failure, D-Rollers may fail intermittently, because they have accumulated dust and debris. On a service call for pickup jams, you would routinely change the Pickup Assembly, even though it might have considerable life left.
The duplex version of the many laser printers engine uses an identical roller on a similar axle for lower feed. However, this roller must work twice as hard in the printer. For every page fed, the Lower Roller must make two revolutions. Compounding this problem is that many firms use the Lower Tray for letterhead.
Since bond paper wears a roller down more than twice as quickly as short-fiber copy paper, it will cut the life span of the Lower Pickup to one-fourth that of the upper one, or about 25,000 prints. Worse, the cotton-rag bond papers sacrifice much more dust and debris during the process.
Some laser printers may have two other feed problems. The guide tab at the left forward top of the paper tray become bent down ove