Drum unit charges the surface of the photosensitive drum to a negative potential to draw a static image; also, serves to rid the surface of the photosensitive drum of residual toner.

Drum Unit

Purpose: Here, you will study the construction of the drum unit and the functions associated with the unit.

1. Outline

a. Function

The drum unit serves to transfer the toner image developed on the photosensitive drum onto print paper and also to clean the surface of the photosensitive drum to prepare for the formation of the next image.

b. Construction

The drum unit consists of the photosensitive drum [1], primary charging roller [2], and cleaning blade [3].

The photosensitive drum receives drive from the main motor by way of the developing clutch, and the primary charging roller operates in keeping with the movement of the photosensitive drum. The cleaning blade remains in contact with the photosensitive drum at all times, and the toner scraped off by the blade is sent to the waste toner bottle by the work of the waste toner feedscrew. The machine is equipped with a brush [4] used to clean the primary charging roller.

See the following diagram to find out how the components of the drum unit are arranged:

○Drum Unit

[1] Photosensitive drum

[2] Cleaning blade

[3] Primary charging roller

[4] Primary charging roller cleaning brush

[5] Waste toner outlet

Next, we are going to study the functions of the drum unit.

2. Primary Charging Roller Cleaning Mechanism

a. Outline

As more and more prints are made, there will be a growing buildup of toner and paper lint on the primary charging roller, causing image faults if left unattended. The machine is designed to execute cleaning of the primary charging roller as follows:

b. Timing of Execution

The machine executes a cleaning run while the photosensitive drum is rotating.

c. Particulars of Operation

The cleaning brush [3] remains in contact with the primary charging roller [2] at all times. It slides to the right and left (reciprocating movement) because of the force of the cam gear [4] that rotates with the photosensitive drum [1], thereby cleaning the primary charging roller as long as the photosensitive drum rotates.