Ricoh FT8780, FT880 Service Manual FT8780

RICOH FT8780

SERVICE MANUAL

IMPORTANT SAFETY NOTICES

PREVENTION OF PHYSICAL INJURY

1. While the machine warms up, it will suddenly start turning to perform the process control data initialization. Keep hands away from any mechanical and electrical components during this period.

2. Before disassembling or assembling parts of the copier and peripherals, make sure that the copier and the second sorter power cord is unplugged.

3. The wall outlet should be near the copier and easily accessible.

4. Note that some components of the copier, the paper tray unit, and the 2nd sorter are supplied with electrical voltage even if the main switch is turned off.

5. If any adjustment or operation check has to be made with exterior covers off or open while the main switch is turned on, keep hands away from electrified or mechanically driven components.

6. The inside and the metal parts of the fusing unit become extremely hot while the copier is operating. Be careful to avoid touching those components with your bare hands.

HEALTH SAFETY CONDITIONS

1. Never operate the copier without the ozone filters installed.

2. Always replace the ozone filters with the specified ones at the specified intervals.

3. Toner and developer are non-toxic, but if you get either of them in your eyes by accident, it may cause temporary eye discomfort. Try to remove with eye drops or flush with water as first aid. If unsuccessful, get medical attention.

OBSERVANCE OF ELECTRICAL SAFETY STANDARDS

1. The copier and its peripherals must be installed and maintained by a customer service representative who has completed the training course on those models.

2. The RAM board on the main control board has a lithium battery which can explode if replaced incorrectly. Replace the battery only with an identical one. The manufacturer recommends replacing the entire RAM board. Do not recharge or burn this battery. Used batteries must be handled in accordance with local regulations.

SAFETY AND ECOLOGICAL NOTES FOR DISPOSAL

1. Do not incinerate the toner cartridge or the used toner. Toner dust may ignite suddenly when exposed to open flame.

2. Dispose of used toner, developer, and photoconductors according to local regulations.

3. Dispose of replaced parts in accordance with local regulations.

4. When keeping used lithium batteries in order to dispose of them later, do not put more than 100 batteries per sealed box. Storing larger numbers or not sealing them apart may lead to chemical reactions and heat build-up.

SECTION 1

OVERALL MACHINE

INFORMATION

Overall

Information

6 March 1992 SPECIFICATIONS

1. SPECIFICATIONS

Main Copier

Copier

Configuration: Console Copy Process: Dry Electrostatic Transfer System Originals: Sheet/Book Original Size: Maximum: 11" x 17", A3 Copy Paper Size: Maximum: 1st and 2nd tray 8

1/2" x 14", A4

3rd tray 11" x 17", A3

Minimum: 1st and 3rd tray 5

2nd tray 8

1/2" x 81/2", A5 1/2" x 11", A4

Copy Paper Weight: Standard Copying: 14 ~ 42 lb, 52 ~ 157 g/m

Duplex Copying: 17 ~ 28 lb, 64 ~ 105 g/m Warm Up Time: Within 8.0 minutes (room temp. 68°F, 20°C) First Copy Time: 3.9 seconds (8 Copying Speed: 80 copies/minute (8

1/2" x 11", A4, feed from 3rd tray)

1/2" x 11", A4)

Optional Equipment: 20 Bin Sorter 1

20 Bin Sorter 2

Menu Reader

Key Counter

Receiving Tray

Guidance ROM Kit

2 2

1-1

SPECIFICATIONS 6 March 1992

Reproduction Ratios: See the following table:

LT/DLT version A4/A3 version

200% 200%

Enlargement

155% 141% 129% 122% 121% 115%

Full Size 100% 100%

93% 93% 77% 82%

Reduction

74% 71% 65% 65% 50% 50%

Zoom: 50 ~ 200% Copy Exit Tray Capacity: 250 Sheets Toner Replenishment: Cartridge exchange (1500 g) Paper Feed: 1st tray (550 sheets)

2nd tray (3,000 sheets) 3rd tray (1,500 Sheets)

Power Source: 120 V, more than 20 A (LT/DLT version)

220, 230, 240 V, more than 10 A (A4/A3 version)

Power Consumption:

Maximum during LT/DLT version A4/A3 version

Stand-by 1.90 kw 2.00 kw

Copying Cycle 1.71 kw 1.75 kw

Dimensions: Copier Only: 49.3" x 29.9" x 56.9"

(1253 x 760 x 1444.5 mm)

With Sorter: 81.5" x 34.4" x 56.9"

(2070 x 873 x 1444.5 mm)

Weight: Copier Only: 892 lb (405 kg)

With 2 Sorters: 1308 lb (593 kg)

Noise Emission: Copier Only: 63 dB

With Sorter: 64 dB

1-2

Overall

Information

6 March 1992 SPECIFICATIONS

Document Feeder

Original Size:

Stack feed mode Single feed mode Duplex mode

Maximum 11" x 17", A3 11" x 17", A3 11" x 17", A3

Minimum 8

1/2" x 11", A4 51/2" x 81/2", A5 81/2" x 11", A4

Original Weight:

Stack feed mode Single feed mode Duplex mode

Maximum 34 lb, 128 g/m

Minimum 14 lb, 52 g/m

43 lb, 157 g/m

11 lb, 35 g/m

Feed-in Unit Capacity: 50 Sheets (80 g/m2, 20 lb) CFF Original Stack Height:Maximum: 50 mm Original Set: First sheet on top, stack face down

25 lb, 93g/m

14 lb, 52 g/m

1-3

COPY PROCESSES AROUND THE DRUM 6 March 1992

2. COPY PROCESSES AROUND THE DRUM

1-4

Overall

Information

6 March 1992 COPY PROCESSES AROUND THE DRUM

1. DRUM CHARGE In the dark, the charge corona unit gives a uniform positive charge to the selenium drum. The charge remains on the surface of the drum because the photoconductive selenium has electrical resistance in the dark.

2. EXPOSURE An image of the original is reflected to the selenium drum surface via the optics assembly. The charge on the drum surface is dissipated in direct proportion to the intensity of the reflected light, thus producing an electrical latent image on the drum surface.

3. ERASE The erase lamp illuminates the areas of the charged drum surface that will not be used for the copy image. The resistance of the drum in the illuminated areas drops and the charge on those areas dissipates.

4. DRUM POTENTIAL SENSOR The drum potential sensor detects the electric lines of force from the electric potential on the drum to compensate image processing elements.

5. DEVELOPMENT Negatively charged toner is attracted to the positively charged areas of the drum, thus developing the latent image. (The negative triboelectric charge is caused by friction between the carrier and toner particles.)

6. PRE-TRANSFER The pre-transfer corona (PTC) applies a negative dc charge and an ac charge to the drum. The dc charge increases the negative potential of the toner to improve toner transfer to paper. The ac charge decreases positive charge on the drum and makes paper separation easier. The pre-transfer lamp (PTL) also makes paper separation easier by illuminating the drum and decreasing the positive charge on the drum.

7. IMAGE TRANSFER Paper is fed to the drum surface at the proper time so as to align the copy paper and the developed image on the drum surface. Then, a strong positive charge is applied to the back side of the copy paper, providing an electrical force which causes the copy paper to be attracted to the drum’s surface. At the same time, the toner particles are pulled to the copy paper from the drum’s surface.

8. PAPER SEPARATION A strong ac corona discharge is applied to the back side of the copy paper, reducing the positive charge on the copy paper and breaking the electrical attraction between the paper and the drum. Then, the stiffness of the copy paper causes it to separate from the drum surface. The pick-off pawls help to separate paper which has low stiffness.

9. CLEANING The cleaning brush first removes remaining toner on the drum surface. Then, the cleaning blade which is angled against drum rotation (counter blade system) removes the rest of the toner. The flick roller mechanically removes the toner on the cleaning brush.

10. QUENCHING

Light from the quenching lamp electrically neutralizes the drum surface.

1-5

MECHANICAL COMPONENT LAYOUT 6 March 1992

3. MECHANICAL COMPONENT LAYOUT

3.1 COPIER

18 19

22 23 24 25 26 27 28 29 30 31 1 2

3 4

7891011121314151617

1. First Mirror

2. Second Mirror

3. Third Mirror

4. Inverter Guide Plates

5. Duplex Tray

6. Third Tray

7. Pick-up Roller

8. Separation Roller

9. Paper Feed Roller

10. Vertical Transport Unit

11. Relay Rollers

12. Pick-off Pawls

13. Transfer and Separation Corona Unit

14. Horizontal Transport Unit

15. Registration Rollers

16. Pre-transfer Corona Unit

17. Second Tray

18. First Tray

19. Toner Hopper

20. Development Unit

21. Drum Thermistor and Drum Potential Sensor

22. Erase Lamp

23. Fifth Mirror

24. Fourth Mirror

25. Sixth Mirror

26. Charge Corona Unit

27. Quenching Lamp

28. Cleaning Unit

29. Transport Unit

30. Pressure Roller

31. Hot Roller

1-6

Overall

Information

6 March 1992 MECHANICAL COMPONENT LAYOUT

3.2 ARDF

1 2 3 4 5 6 7 8 9

12131415161718

1. Original Tray Extension

2. Upper Exit Rollers

3. Upper Inverter Gate

4. Lower Inverter Rollers

5. Upper Inverter Rollers

6. Switch Back Gate

7. Switch Back Tray

8. Upper Relay Roller

9. Friction Tab

10. 1st Pick-up Rollers

11. 2nd Pick-up Rollers

12. Separation Rollers

13. Lower Relay Roller

14. Pressure Rollers

15. Transport Belt

16. Lower Inverter Gate

17. Lower Exit Rollers

18. CFF Guide

1-7

ELECTRICAL COMPONENT DESCRIPTIONS 6 March 1992

4. ELECTRICAL COMPONENT DESCRIPTIONS

Refer to the electrical component layout on the reverse side of the Point to Point (Water proof paper) index numbers.

4.1 COPIER

Name Function Index. No.

Motors

1st Tray Drive Drives the bottom plate in the 1st tray. 132 2nd Tray Drive Drives the bottom plate in the 2nd tray. 139 3rd Tray Drive Drives the bottom plate in the 3rd tray. 65 Charge Wire Cleaner Drives the charge corona wire cleaner. 74 Development Drives the development unit. 51 Fusing Cooling Fan Cools fins of the de-curling roller. 58 Fusing Exhaust Fan Removes the heat in the de-curling unit. 56 Lens Horizontal Drive Shifts the lens horizontal position. 54 Lens Vertical Drive Shifts the lens vertical position. 57 Main Drives the main unit components. 73 Mirror Unit Drive Positions the mirror unit. 78 Optics Cooling Removes the heat from the optics unit. 77 Scanner Drive Drive the 1st and 2nd scanners. 55 T & S Wire Cleaner Drives the transfer and separation wire cleaner. 72 Toner Supply Rotates the toner supply roller. 75 Vaccum Fan Removes the heat and dust in the machine. 52

Clutches

LCT Drive Transmits the main copier drive to the 1st and 2nd

feed sections. Paper Feed - 1st Tray Drives the paper feed roller of the 1st tray. 134 Paper Feed - 2nd Tray Drives the paper feed roller of the 2nd tray. 159 Paper Feed - 3rd Tray Drives the paper feed roller of the 3rd tray. 66 Paper Feed - Duplex Drives the paper feed roller of the duplex unit. 67 Vertical Transport Unit

Drive Registration Drives the registration roller. 79

PCBs

DC Drive Drives dc components. 116 Drum Current Detection Measures the corona current. 106 Main Controls overall machine operation. 122 Motor Control Controls the dc motors. 123 DC Motor Drive Drives the dc motors. 101 Operation Unit Controls the monitor display. 124 PTL Controls the pre-transfer lamp operation. 121 Quenching Lamp Controls the quenching lamp operation. 120

Transmits the main copier drive to the vertical

transport unit and the 3rd tray.

1-8

Overall

Information

6 March 1992 ELECTRICAL COMPONENT DESCRIPTIONS

Name Function Index. No.

Interface Interface between the main PCB and other PCBs. 115 Vaccum Motor Controls the vacuum fan motor operation. 108

Power Packs

Charge Provides power for the charge corona wire. 103 Development Bias Provides power for the development bias. 104 PTC Provides power for the pre-transfer corona wire. 107 Separation Provides power for the separation corona wire. 105 Transfer Provides power for the transfer corona wire. 102 Power Supply Unit Provides dc power to dc components. 119

Relays

Anticondensation Heater Provides power to the anticondensation heater. 113 Drum Heater 1 Provides power to the drum heater. 114 Drum Heater 2 Provides power to the drum heater. 110 Fusing SSR (16 A) Provides power to the 720 W fusing lamp. 111 Fusing SSR (20 A) Provides power to the 900/950 W fusing lamp. 112 Relay Unit Provides ac power to ac components. 118

Sensor

Auto Responce Turns on the display from the screen saver condition. 93 Drum Potential Detects the drum surface voltage. 95 Duplex Entrance Detects misfeeds. 12 Exit Detects misfeeds. 10 Fusing Unit Detects misfeeds. 9 Image Density Measures the density of the image on the drum. 87 Jogger Home Position Detects when the duplex side plate is at the home

position. Lens Horizontal Encoder Detects the lens horizontal drive motor operation. 5 Lens Horizontal Home

Position Lens Vertical Encoder Detects the lens vertical drive motor operation. 7 Lens Vertical Home

Position Lower Limit - 1st Tray Turns off the 1st tray motor when the tray reaches

Lower Limit - 2nd Tray Turns off the 2nd tray motor when the tray reaches

Lower Limit - 3rd Tray Turns off the 3rd tray motor when the tray reaches

Mirror Unit Encoder Detects the mirror drive motor operation. 29 Mirror Unit Home

Position Paper End - 1st Tray Detects the presence of paper in the 1st tray. 159 Paper End - 2nd Tray Detects the presence of paper in the 2nd tray. 146

Detects when the lens is at the horizontal home

position.

Detects when the lens is at the vertical home

position.

the down position.

Detects when the mirror unit is at the home position.

138

140

1-9

ELECTRICAL COMPONENT DESCRIPTIONS 6 March 1992

Name Function Index. No.

Paper End - 3rd Tray Detects the presence of paper in the 3rd tray. 42 Paper End - Duplex Detects the presence of paper in the duplex tray. 13 Paper Feed - 1st Tray Turn off the 1st tray paper feed clutch. 154 Paper Feed - 2nd Tray Turn off the 2nd tray paper feed clutch. 147 Paper Feed - 3rd Tray Turns off the 3rd tray paper feed clutch. 16 Paper Feed - Duplex Turns off the duplex paper feed clutch. 18 Paper Size 1 - 1st Tray Determines what paper size is in the 1st tray. 133 Paper Size 1 - 2nd Tray Determines what paper size is in the 2nd tray. 142 Paper Size 1 - 3rd Tray Determines what paper size is in the 3rd tray. 35 Paper Size 2 - 1st Tray Determines what paper size is in the 1st tray. 157 Paper Size 2 - 2nd Tray Determines what paper size is in the 2nd tray. 143 Paper Size 2 - 3rd Tray Determines what paper size is in the 3rd tray. 34 Paper Size 3 - 1st Tray Determines what paper size is in the 1st tray. 137 Paper Size 3 - 2nd Tray Determines what paper size is in the 2nd tray. 144 Paper Size 3 - 3rd Tray Determines what paper size is in the 3rd tray. 33 Paper Size 4 - 1st Tray Determines what paper size is in the 1st tray. 135 Paper Size 4 - 3rd Tray Determines what paper size is in the 3rd tray. 32 Paper Size 5 - 3rd Tray Determines what paper size is in the 3rd tray. 39 Paper Size 6 - 3rd Tray Determines what paper size is in the 3rd tray. 38 Paper Size 7 - 3rd Tray Determines what paper size is in the 3rd tray. 37 Paper Size 8 - 3rd Tray Determines what paper size is in the 3rd tray. 36 Paper Volume - 1st Tray Detects the amount of paper in the 1st tray. 131 Paper Volume - 2nd

Tray

Detects the amount of paper in the 2nd tray.

149

Paper Volume - 3rd Tray Detects the amount of paper in the 3rd tray. 31 Pick-up Position -

Duplex Registration Sensor Detects the lead edge of paper to determine the stop

Return Home Position Detects when the 1st scanner is at the return

Scanner Home Position Detects when the 1st scanner is at the home

Detects the duplex pick-up roller position.

timing of a feed clutch and detects misfeeds.

position.

Toner Cartridge Detects when a toner cartridge is in the machine. 2 Toner Coil Overload Detects the toner collection coil drive gear operation. 1 Toner Near End Detects toner near end condition. 28 Transport Detects misfeeds. 20 Tray Paper Position Detects the top sheet position in the 2nd tray. 141 Upper Limit - 1st Tray Sends signal to stop lifting up the 1st tray bottom

plate. Upper Limit - 2nd Tray Sends signal to stop lifting up the 2nd tray bottom

plate. Upper Limit - 3rd Tray Sends signal to stop lifting up the 3rd tray bottom

plate.

161

158

1-10

Overall

Information

6 March 1992 ELECTRICAL COMPONENT DESCRIPTIONS

Name Function Index. No.

Solenoids

2nd Tray Lock Locks the 2nd tray. 136 Cleaning Brings the cleaning blade into contact with the drum. 53 Fork Gate 1 Varies the paper path in the duplex unit depending

on paper size. Fork Gate 2 Varies the paper path in the duplex unit depending

on paper size. Inverter Gate Drives the inverter gate up and down. 61 Junction Gate Drives the junction gate up and down. 60 Pick-up - 1st Tray Lifts the pick-up roller of the 1st tray. 155 Pick-up - 2nd Tray Lifts the pick-up roller of the 2nd tray. 148 Pick-up - 3rd Tray Lifts the pick-up roller of the 3rd tray. 70 Pinch Roller Brings the return pinch rollers into contact with a

paper. Pressure Plate Brings the pressure plate on papers in the duplex

unit. Positioning Lowers the positioning roller in the duplex unit. 64 Duplex Paper Stopper Lowers the paper stopper in the duplex unit. 71

Switches

1st Tray Down Lowers the 1st tray bottom plate. 151 1st Tray Set De-energizes power when the 1st tray is slided to

the left. 2nd Tray Down Lowers the 2nd tray bottom plate. 150 3rd Tray Down Lowers the 3rd tray bottom plate. 40 Anticondensation Turns on the tray heaters. 23 Error Reset Resets error condition. 11 Left Door 1 Turns off the main motor when the left door is open. 25 Left Door 2 Turns off dc 24 volts lines when the left door is open. 24 Main Supplies power to the copier. 26 Right Door 1 Turns off dc 24 volts lines when the right door is

open. Right Door 2 Turns off the main motor when the right door is open. 19 Tray Cover Turns off components when the tray left top cover is

open.

Heaters

1st Tray Removes humidity from the paper in the 1st tray. 156 2nd Tray Removes humidity from the paper in the 2nd tray. 145 3rd Tray Removes humidity from the paper in the 3rd tray. 92 Anticondensation Prevents moisture from forming on the lens and

mirrors. Drum Warms the drum when it gets too cool. 96 Exposure Lamp Warms the exposure lamp when it gets too cool. 86

160

153

1-11

ELECTRICAL COMPONENT DESCRIPTIONS 6 March 1992

Name Function Index. No.

Lamps

Exposure Exposes the original with high intensity light. 85 Fusing 1 Provides heat to the hot roller and keeps the roller at

the operating temperature.

Fusing 2 Provides heat to the hot roller during warm-up. 90 Pre-Transfer Removes excessive positive charge from the drum

surface to the transfer and separation process. Quenching Electrically neutralizes the drum surface prior to

charging.

Thermistors

Drum Monitors the drum temperature. 94 Fusing Monitors the hot roller temperature. 88

Other Components

Total Counter Keeps a count of the number of copies made. 117 FL Stabilizer Stabilizes power to the exposure lamp. 109 Thermofuse Provides back-up overheat protection in the fusing

unit. Anticondensation

Turns off the anticondensation and drum heaters. Thermoswitch

1-12

Overall

Information

6 March 1992 ELECTRICAL COMPONENT DESCRIPTIONS

4.2 ARDF

Symbol Name Function Index. No.

Motors

M1 M2 Belt Drives the transport belt. 16

M3 Inverter Drives the inverter rollers and the exit rollers. 17 M4 Job Separation Drives the job separator. 5

Circuit Boards

PCB1 DF Main Controls overall ARDF functions. 3 PCB2

Solenoids

SOL1

SOL2 Inverter Gate Opens the inverter gate. 23

Feed-in Drives the pick-up rollers, separation rollers

and relay rollers.

Indicator Indicates the Insert Original indicator and the

Auto Feed indicator.

Switch Back Switches the switch back gate position to

directs the original to the switch back tray or onto the exposure glass.

Sensors

S1 Entrance Cover Detects if the entrance cover is open. 4 S2 Lift Detects if the transport unit is open. 14 S3 Inverter Cover Detects if the inverter cover is open. 22

S8 S9 Inverter Jam Detects paper jams in switch back operation. 18

S10

S11

S12 Exit Detects paper jams. 21

S13

S14 Original Width Detects the original width. 13 S15 Timing Supplies timing pulses to the DF main board. 10

Pick-up Roller H.P. Detects if the pick-up roller is in the home

position.

Job Separation H.P.

Job Completion Detects that last original of the first job is fed

Original Detects if the original is set on the original

Registration Sets the feed-in motor, belt motor and inverter

Inverter Registration

Inverter Entrance Sets the inverter motor and the belt motor off,

CFF Detects if the computer form is set in the CFF

Detects if the job separator is in the home position.

from the original table.

table.

motor off timing. Detects original misfeed.

Sets the inverter motor and the belt motor off, reversing timing. Detects original jams.

reversing timing, inverter solenoid and switch back solenoid off timing.

guide. Counts the holes lined up on the computer form.

1-13

DRIVE LAYOUT 6 March 1992

5. DRIVE LAYOUT

1. Main Motor

2. Development Drive Motor

A : Development Unit B : Cleaning Unit C : Relay Transport Unit (to 1st & 2nd Tray) D : Fusing Unit E : Vertical Transport Unit F : Duplex Unit

1-14

Overall

Information

6 March 1992 PAPER PATH

6. PAPER PATH

6.1 SINGLE SIDED COPY -- COPY FACE DOWN

6.2 DUPLEX MODE (1ST SIDE)

1-15

PAPER PATH 6 March 1992

6.3 DUPLEX MODE (2ND SIDE)

6.4 IMAGE OVERLAY MODE (1ST SIDE)

1-16

Overall

Information

6 March 1992 PAPER PATH

6.5 IMAGE OVERLAY MODE (2ND SIDE)

1-17

SECTION 2

DETAILED SECTION

DESCRIPTIONS

6 March 1992 PROCESS CONTROL

1. PROCESS CONTROL

1.1 OVERVIEW

The characteristics of each unit which is related to the copy image reproduction are changed by various factors. To get stable images over long periods and in continuous copy runs, these characteristic changes have to be compensated. The following figure and table show how these factors are compensated on this copier.

Detailed

Descriptions

Potential Sensor

Toner Supply

Development Bias

Exposure Lamp

PTC

Main PCB

Transfer Corona

Charge Corona

ID Sensor

Drum Current Detection PCB

Separation Corona

: Sensing Item : Controlled Item

2-1

PROCESS CONTROL 6 March 1992

Section Characteristics Causes of Change Compensation Method

Drum Charge

Potential

Sensitivity Repeat Stress

Residual Voltage

Charge Corona

Exposure Lamp Intensity Repeat Stress Measure the drum potential of a part

Development Amount of

Charge Potential

Mirror Reflectivity Lens Clearness

Toner Charge

Repeat Stress Temperature Humidity

Temperature Humidity Repeat Stress Temperature Humidity

Dirtiness Temperature Humidity

Dirtiness

Repeat Stress Temperature Humidity

Measure the drum potential of a part that was not exposed (Dark Potential) with the potential sensor and adjust the charge corona output.

Measure the drum potential of a part that was exposed (Light Potential) and adjust the exposure lamp voltage.

Measure the drum potential of a part that was erased by the erase lamp (residual voltage) and adjust the development bias, light potential, and dark potential

Measure the drum potential of a part that was not exposed (dark potential) and adjust the charge corona output.

that was exposed (light potential) and adjust the exposure lamp voltage.

Measure the reflected light intensity of the ID sensor pattern and adjust the toner density in the development unit.

2-2

6 March 1992 PROCESS CONTROL

1.2 IMAGE CONTROL

1.2.1 Latent Image Control

Charge

Exposure

Black White

Erase

Potential Sensor

Drum

The figure shows the changes of the drum potential during the copy process. V0: The drum potential just after charging the drum. Vd (Dark Potential): The drum potential just after exposing the black

pattern (Vd pattern)

Detailed

Descriptions

VL (Light Potential): The drum potential just after exposing the white

pattern (VL pattern)

Vr (Residual Voltage): The drum potential just after the exposure of the

erase lamp.

2-3

PROCESS CONTROL 6 March 1992

[V]

Drum Potential

LightOriginal DensityDark

The above figure shows the relationship between the drum potential and the original density (exposing light intensity). To get constant copy quality, this relationship must be maintained.

Since this relationship tends to change to the one represented by the dotted line by various factors, compensations are required as follows:

A decrease in dark voltage (Vd) is compensated for by increasing the charge corona output. A increase in light voltage (VL) is compensated for by increasing the exposure lamp voltage. Since the residual voltage (Vr) increase cannot be compensated for by increasing the lamp voltage, it is compensated by increasing the development bias voltage and changing the Vd and VL standard value.

1.2.2 Image Density Control

To maintain constant copy image density, the ID sensor detects the toner amount of the ID sensor pattern. From this, it is understood that drum potential is stabilized with the above compensations. According to the detection results, the toner density in the development unit is controlled so that the toner amount on the sensor pattern is constant.

The following sections explain the details of these compensations.

2-4

6 March 1992 PROCESS CONTROL

1.3 PROCESS CONTROL DATA INITIALIZATION

The following flow chart shows all the steps that will be performed whenever the main switch is turned on while the hot roller temperature is below 100°C. This initializes all the process control settings.

Main SW On (Fusing Temp. < 100°C)

Drum Potential Sensor Calibration

Drum Conditioning Start (Fusing Temp. = 160°C)

• Exposure lamp ON

Vsg Adjustment

Lamp Intensity Sensor Calibration

Detailed

Descriptions

Charge Corona Current Adjustment

Vr Measurement

• Lens position shift

• Exposure lamp OFF

• Scanner moves to return position (Vd Pattern)

• Exposure lamp ON

Vd Correction

• Exposure lamp OFF

• Scanner returns to home position (VL Pattern)

• Exposure lamp ON

VL Correction

• Exposure lamp OFF

V01 Detection

• Scanner moves to return position (ADS Pattern)

• Exposure lamp ON

ADS Adjustment

2-5

PROCESS CONTROL 6 March 1992

1.3.1 Drum Potential Sensor Calibration

[A]

Potential Sensor

Bias P.P.

Case

Sensor

Output

Amp.

Drum

RA2

RA1

Drum Current Detection PCB

Relay

TRIG 1 (800V) TRIG 2 (100V) PWM Sensor

Main PCB

The drum potential sensor [A] is located just above the development unit. The sensor has a detector which detects the electric lines of force from the electric potential on the drum. The output of the sensor depends of the number of electric lines of force.

Since the output of the sensor is affected by environmental conditions, such as temperature and humidity, the sensor output is calibrated during process control data initialization.

The drum current detection board has two relay contacts. Usually RA2 grounds the drum. However, during the initialization, the main PCB turns RA1 on and RA2 off and applies the development bias to the drum shaft.

By measuring the outputs of the drum potential sensor when +100 V and +800V are applied to the drum, the sensor output is calibrated automatically.

2-6

6 March 1992 PROCESS CONTROL

1.3.2 Drum Conditioning

When the drum temperature reaches 160°C, the machine starts the drum conditioning process. In this mode, all the coronas and lamps around the drum are activated and drum sensitivity is stabilized, as in continuous copy runs.

1.3.3 Vsg Adjustment

During drum conditioning, the ID sensor checks the bare drum’s reflectivity and calibrates the output of the ID sensor to +4 V.

1.3.4 Lamp Intensity Sensor Calibration

Detailed

Descriptions

Main PCB

PWM

FL Stabilizer

The exposure lamp intensity is monitored by the main PCB through the fiber optics cable. A photodiode on the main PCB converts the light intensity to a dc voltage. The main PCB sends a PWM signal with a 100% duty cycle to the FL stabilizer and checks the monitored voltage, adjusting it to +3 V. This +3 V is used as the light intensity standard.

2-7

PROCESS CONTROL 6 March 1992

1.3.5 Charge Corona Current Adjustment

+12V

GND

-12V

CN342-3

CN342-2 CN342-1

CN341-4

RA1

CN341

-1

CN341-2

Potential S.

CN103-B24

Id Set

CN103-A14

CN104-A28

CN104-B1

CN104-A1

RA2

RA1

HIC1

CN342

-4

T343

CN342

-5

-6

-7

-8

Drum Current Detect PCB MainPCB

PCL

The charge corona current is measured and adjusted automatically by the drum current detect PCB.

The charge corona current flows to the drum current detect PCB through the drum and the drum shaft. The drum shaft is grounded by the drum current detect PCB usually. However, during the process control data initialization, the main PCB activates the corona current circuit in the drum current detection PCB which converts the drum current to a voltage and separates it into ac and dc component outputs. Then, the main PCB reads them through A/D converters as digital data. The main PCB adjusts the corona current by controlling the PWM signal to the charge corona power pack.

When the auto drum current adjustment mode is selected by the SP mode, the drum current detect PCB is used to measure and adjust other corona outputs in the same way.

2-8

+ 343 hidden pages

Ricoh FT8780, FT880 Service Manual FT8780

Specifications and Main Features

Frequently Asked Questions

User Manual

6 March 1992 SPECIFICATIONS

COPY PROCESSES AROUND THE DRUM 6 March 1992

MECHANICAL COMPONENT LAYOUT 6 March 1992

3.1 COPIER

3.2 ARDF

ELECTRICAL COMPONENT DESCRIPTIONS 6 March 1992

4.1 COPIER

4.2 ARDF

DRIVE LAYOUT 6 March 1992

6 March 1992 PAPER PATH

6 March 1992 PROCESS CONTROL

1.1 OVERVIEW

1.2 IMAGE CONTROL

1.3 PROCESS CONTROL DATA INITIALIZATION