Mechanical parts basically serve a single purpose: to transfer force from one point to another. For example, a paper transport system must transfer the physical force of a paper advance motor to the paper itself to move it through the printer. This is accomplished through a series of gears, pulleys, rollers, and belts. Whenever mechanical parts are in contact with one another, they produce friction, which causes wear. Lubricants, bushings, and bearings work to minimize the damaging effects of friction on mechanical parts. The Various Mechanical Components in a Common Printer are as Follows:
Gear
A gear performs several important tasks. Their most common application is t£._transfer mechanical force from one rotating shaft !9 another. The simplest arrangement uses two gears in tandem as shown in 2-1. When two gears are used, the direction of secondary rotation is opposite that of the primary shaft. If secondary direction must be the same, a third gear might be added as shown in 2-2. It is possible to change the direction of applied force by using angled gears. By varying the angles of both gears, force can be directed just about anywhere. Several secondary gears can be run from a single drive gear to distribute force to multiple locations simultaneously, a common tactic in complex mechanical systems like the bubble jet printer in 2-3.
Pulley
Pulley sets are used commonly in many printers. Like gears, pulleys are used to transfer force from one point to another. Instead of direct contact, however, pulleys are joined together by a drive linkage, which is usually composed of a belt, wire, or chain (much the same way as a belt in your automobile). A basic pulley set is illustrated in 2-5. A motor turns a drive pulley, which is connected to a secondary pulley through a drive linkage under tension. As the drive pulley turns, force is transferred to the secondary pulley through the linkage, so the secondary pulley also turns. Notice that both pulleys turn in the same direction.
Rollers
For a printer to work at all, paper must be handled gently but firmly. Rubber-coated rollers are ideal for this purpose; they provide the high friction needed to carry paper through the printer reliably and consistently, yet the pressures applied by the rollers will not damage the paper. AB you might imagine, damaged, old, or dirty rollers can have an adverse effect on the paper transport system. There are three types of rollers found in most moving-carriage printers: a platen, pressure (or contact) roller(s), and bail rollers. All three rollers are illustrated in 2-6. Your main roller is the platen. It is driven by a paper advance motor, and it provides paper support in front of the print head. The rubber also serves as a firm but pliable surface for impact printing. Pressure rollers hold paper against the platen and ensure positive traction and even paper advance.
Reducing Friction
As with all mechanical systems, parts that are in contact with one another will wear while the system operates due to unavoidable friction that occurs between parts. It follows, then, that reducing friction will extend your printer's working life. Lubrication, bushings, and bearings are three commonly accepted methods of reducing friction. Oils or grease have always been one answer (and might prove quite effective in small doses), but this lubrication must be replaced on a regular basis for it to remain effective. Otherwise, it can wear away, dry out, or harden into thick sludge. Lubricants are also notorious for collecting dust and debris from the environment, which eventually defeats any benefits that the lubricant can provide. When applying lubricants, remember to apply them sparingly. Bushings are essentially "throw-away" wear surfaces as shown in 2-7. A bushing is made of softer materials than the parts it is separating, so any friction generated by moving parts will wear out the bushing before allowing the parts to make contact themselves. When a bushing wears out, simply replace it with a new one. Bushings are much less expensive and easier to replace than major mechanical parts such as slides or frames.
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