Panasonic FP-7742 / FP-7750 (serv.man2) Service Manual ▷ View online
3-12
5)
TDC sensor
• TDC sensor which is installed under the developer transport screw is an
inductance type sensor is used to detect the ratio of toner to carrier in the
developer. The sensor measures changes of magnetic flux density, and
monitors the toner density in this way.
• The developer is a mixture of carrier which is a magnetic substance and
toner which is not a magnetic substance. When the amount of toner is over the
standard, the magnetic flux density reduces. The TDC sensor output drops
below the standard voltage as a result. When the amount of toner is less than
the standard, the carrier percentage is high and the magnetic flux density is
also high, resulting in a lower TDC sensor output voltage than the standard.
• The lower density of toner causes the increase of TDC sensor output. Being
over the standard, the toner hopper motor drives and toner is supplied to the
developer mixing unit to keep the toner density constant.
6)
Manual supply of toner
• The toner in the developer unit can be manually increased by supplying toner
from the toner hopper to the developer unit to get higher copy density.
To manually supply toner: Choose "Toner supply" in the "User mode".
In so doing, approx. 2.8 g is supplied to the developer mixing unit.
<CPU>
<Developer Unit>
Sensor output
Gain adjustment
Sensor Area
2
V
p
TDSN
TDREF
GND
V
p
TDSN
CN7
TDREF
GND
3
1
4
4
3
5
2
7
8
6
9
Sub Assemblies
3-13
SV405
1
2
7)
Drum cleaning
• After developing and transferring, the toner remaining on the drum is cleaned
away by the cleaning blade.
• The cleaning blade touches the drum surface with a specific pressure using
the blade pressure spring, and cleans the toner off of the drum surface.
• This toner is transferred to the front of the drum unit by the revolution of the
toner collecting screw.
• The toner receiving sheet touches the drum surface and prevents the toner
scraped away with the cleaning blade from dropping out of the drive unit.
8)
Toner transporting
• The toner cleaned from the drum by the cleaning blade is transported to the
front of main body with toner transport screw.
• The toner recycle transport screw and the waste toner screw and connect
with the developer mixing unit and the waste toner bottle respectively.
• Usually the aperture to the recycle unit is opened. The toner transferred with
the toner transport coil spring falls down through this hole and is transferred
to the deveoper mixing unit by the recycle screw.
to the deveoper mixing unit by the recycle screw.
• When in "Refresh" mode, the recycled solenoid actuates and the toner is
transferred to the toner screw and is contained in the waste toner bottle.
Sheet
Corona
Grid
Drum
3
4
Part description
Function
1
Cleaning blade
Clean toner off of the drum.
2
Toner transport screw
Transfer toner scraped from photo receptor to the
front side of the main body.
3
Toner recycle transport
Transfer collected toner to developer mixing unit.
screw
4
Waste toner screw
Transfer collected toner to waste toner bottle.
Waste toner bottle
Recycle pipe
Refresh pipe
Copy density
sensor
sensor
3-14
4
6
7
1
2
3
5
(4)
Toner hopper unit
1)
Construction of the toner hopper
• The construction of the toner hopper is as follows.
Part description
Function
1
Toner bottle
Supply toner.
2
Home position sensor
Detect the home position of toner bottle.
3
Reserve tank
After storing toner in toner hopper, supply to
developer mixing unit.
4
Toner volume sensor
Detect toner level in reserve tank.
5
Hopper motor
Drive toner bottle and toner supply roller.
6
Toner supply roller
Supply toner to developer mixing unit.
7
Toner supply shutter
Connect toner hopper unit with developer mixing
unit.
Bottle holder
Sensor plate
Supply roller gear
Agitator
Agitator gear
Bottle drive gear
Spring clutch
Agitator
Sub Assemblies
3-15
2)
Supplying toner
The toner hopper unit supplies toner to the reserve tank by turning the toner
bottle.
• When the TDC sensor in the developer unit detects lower toner density the
toner hopper motor (stepping motor)operates and rotates the toner supply roller
to supply toner to the developer mixing unit, from the reserve tank.
• The revolution of the hopper motor is transmitted via respective gears. When
the hopper motor rotates in reverse it drives the toner supply roller via spring
clutch and supplies toner from the reserve tank in the hopper unit to the
developer mixing unit. When the motor rotates forward the revolution turns
the toner bottle via spring clutch to supply toner to the reserve tank.
• Controlling toner level
The toner volume sensor installed in the hopper detects the volume of toner in
the reserve tank in the hopper.
When detecting too much toner the toner supply roller only rotates in reverse
and transfers toner in the reserve tank to the developer mixing unit.
When detecting low toner, the toner bottle is rotated via spring clutch and
bottle driving gear after finishing toner supply(normal revolution for the hopper
motor),and toner is supplied to the reserve tank to keep the toner volume in
the reserve tank constant.
• A toner supply by the toner supply roller (approx. 16 seconds) can supply
1.4 g of toner of to the hopper.
• Separating the developer mixing unit from the toner supply unit of toner hopper,
the toner supply shutter is closed to prevent toner drop.
TDC sensor output Toner empty Hopper
Toner
Toner supply Add toner
sensor
motor
bottle
roller
High (Lower toner density)
Detect
Reverse rotation
—
Rotate
Supply toner to developer unit
High
Non detect Forward rotation Rotate
—
Supply toner to sub-hopper
Low (Higher toner density)
Detect
Stop
—
—
—
Low
Not detect
Stop
—
—
—
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