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3-8

(3)

Developer unit

1)

Construction of the developer unit

• The developer unit consists of the magnet roller, sleeve, transport screw and

mixing mill.

• The developer is mixed and charged by the transport screw and the mixing mill

and is transferred on the developer sleeve. The developer on the sleeve

forms a brush by the magnetic force of the magnetic roller, and makes contact

with the electrostatic latent image on the drum. Toner sticks to the areas of

charge on the drum.

• The doctor blade controls the thickness of developer on the sleeve.

• The TDC sensor is an inductance type sensor used to measure the ratio

toner to developer.

• A twin field magnet roller forms 2 pole  peaks facing the drum, to enhance

developing performance.

• A dust collector vacuum duct is provided under the developer unit to prevent

toner dusting. The dust collector ducts connected with the dust collector fan

mounted on the machine frame which vacuums the scattered toner to prevent

toner dusting under the developer unit.

Drum

Corona

Part description

Function

1

Magnet roller

Transport developer to photo receptor.

2

Doctor blade

Control height of developer on sleeve.

3

Mixing mill

Mix and charge developer and transport it to magnet

roller.

4

Transport screw

Mix developer and transport to mixing mill.

5

TDC sensor

Measure toner density.

6

Dust collector duct

Collect scattered toner dust.

7

Spacer ring

Keep the distance between the magnet roller and

photo receptor.

Sub Assemblies

3-9

2)

Developing

• The developer mixing unit contains developer which is a mixture of fine powder

(non-magnetic toner) and fine ferrite carrier.

• The developer is mixed by the transport screw and the mixing mill. The toner

becomes charged  ( + ) and the carrier becomes charged ( – ). The developer
is magnetically stuck on the aluminum sleeve of the magnet roller, and the
magnetic brush is formed.
The developer is transfered counterclockwise in the rotating direction of the
sleeve.
The height of magnetic brush is controlled by the gap between the doctor
blade and the sleeve surface.

• The drum with an electrostatic latent image (negative charge) is rotating

clockwise and makes contact with the magnetic brush.

• The sleeve is charged opposite of the drum and an electric field is formed.

The positive toner is stuck on the electrostatic latent image on the drum.

• The sleeve has applied ( – ) bias voltage, which prevents the drum from

covering with toner. The distance between the drum and the sleeve is controlled
with the spacer rings.

Amount of developer

Approx. 650 g

Initial toner density

4.0 %

Sleeve revolution

476 rpm  Drum revolution

108 rpm (FP-7750)

Magnet roller diameter

30 mm

DSD

0.8 mm

BSD

0.61 mm

Developing bias voltage

–250 V reference

N3

N1

S1

S2

S3

N2

Reference:

• The twin field magnet roller presents enhanced developing performance by

a wider developing area which results from two pole peaks (S1 and S2 pole)
facing the drum surface.

• N2 through S3: Attract the developer to the sleeve from the mixing mill.
• S3 pole:

Raise the head of developer and control the head height with

the doctor blade.

• N2 through S1: Transfer the developer to the developing position.
• N1 through N2: Separate the developer from the sleeve.

3-10

3)

Driving developer

• The revolution of the main motor is transmitted to the developer drive gear via

respective gears and belt. The developer is connected to the main body with

the gear. The sleeve gear is connected with the mixing mill gear and the

transport screw gear to mix and transfer the developer.

Drum

Main motor

Magnetic
roller

Developer unit

Sub Assemblies

3-11

4)

Installing/removing the developer unit

• Turning the developer release lever on the right side of  the main body, the

cam rotates  which  presses the spacer ring of developer to the drum surface.

Accordingly, the developer is separated from the drum.