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5
Functional Overview
Contents
Basic Printer Functions . . . . . . . . . . . DC Controller/Power System . . . . . . . . Print Engine Control System . . . . . . . Power System (on DC Controller PCA) . Formatter System . . . . . . . . . . . . . . CPU . . . . . . . . . . . . . . . . . . . . Read Only Memory (ROM) . . . . . . . Random Access Memory (RAM) . . . . Parallel Interface . . . . . . . . . . . . . Control Panel . . . . . . . . . . . . . . . Resolution Enhancement (REt) . . . . . . EconoMode . . . . . . . . . . . . . . . . Memory Enhancement technology (MEt) Enhanced I/O . . . . . . . . . . . . . . . Page Protect . . . . . . . . . . . . . . . . PJL Overview . . . . . . . . . . . . . . Image Formation System . . . . . . . . . . Toner Cartridge . . . . . . . . . . . . . . Step 1: Drum Cleaning . . . . . . . . . . Step 2: Drum Conditioning . . . . . . . . Step 3: Image Writing . . . . . . . . . . Step 4: Image Developing . . . . . . . . Step 5: Image Transferring . . . . . . . . Step 6: Image Fusing . . . . . . . . . . . Paper Feed System . . . . . . . . . . . . . . Paper Jam Detection . . . . . . . . . . . Basic Sequence of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3 5-4 5-5 5-6 5-8 5-8 5-8 5-8 5-8 5-9 5-9 5-10 5-10 5-11 5-11 5-11 5-12 5-13 5-13 5-13 5-13 5-14 5-14 5-14 5-15 5-18 5-19
Functional Overview
5-1
5-2
Functional Overview
Basic Printer Functions
This chapter presents a generalized functional overview of the printer and the printing processes. The following printer systems are discussed:
· · · · ·
DC Controller System/ Power System Formatter System Image Formation System Paper Feed System Laser/Scanner System Figure 5-1 is a generalized block diagram of the printer:
Figure 5-1
Printer Functional Block Diagram
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Functional Overview
5-3
DC Controller/Power System
The DC Controller PCA coordinates all print engine activities, drives the laser, and coordinates print data from the Formatter PCA with the image formation process. The DC Controller also includes both AC and DC power supply and distribution circuitry. The DC Controller controls the following systems and functions:
· Print Engine Control · Laser and Scanner Drive · Paper Motion Photosensors (Paper Out, Paper Registration, and Paper Exit · Power System · AC Power Distribution · DC Power Distribution · Overcurrent/Undervoltage Protection · SleepMode · High Voltage Power Distribution
Figure 5-2 shows the various DC controller loads.
Figure 5-2
· Motor
Sensors)
AC Driver
Low-Voltage Supply
+5V +12V
DC Controller Loads
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Functional Overview
Print Engine Control System
Laser and Scanner Drive
Based on information received from the Formatter, the DC Controller sends signals to the Laser/Scanner Assembly to modulate the laser diode ON and OFF and to drive the Laser/Scanner motor. Refer to "Image Formation System," later in this chapter for more information.
Paper Motion Monitoring and Control
The DC Controller PCA controls paper motion by continuously monitoring the various paper sensors and coordinating the timing with the other print processes. For a detailed explanation of paper movement, and the interaction of photosensors and solenoid with the paper movement process, refer to the section "Paper Feed System," later in this chapter.
+12 V Shutoff Switch
The 12 volt DC power shutoff switch, Switch 101, located on the top of the printer, is activated by the printer door. The front door must be closed before the printer can resume printing.
Engine Test Switch
The Test Print, Switch 201, located on the DC Controller, is activated manually through an access hole at the front of the printer. This switch causes the print engine to perform a self-test diagnostic which bypasses the Formatter PCA and prints a full page of black vertical lines. This test is useful for troubleshooting printer problems because it isolates the print engine from the Formatter PCA. (See Chapter 7, "Troubleshooting," to learn more about how to perform an engine test.)
Motor
The Motor is controlled by the DC Controller PCA. The Motor provides all of the printer's paper movement.
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Functional Overview
5-5
Power System (on DC Controller PCA)
The AC, DC, and high voltage power supply circuits are all contained within the DC Controller PCA.
AC Power Distribution
The AC power circuitry supplies AC voltage whenever the power cord is connected to the AC power source. AC voltage is distributed to the DC power supply circuitry and to the AC driver circuitry, which controls AC voltage to the fusing assembly's heating element.
DC Power Distribution
The DC power distribution circuitry, located on the DC Controller PCA, distributes +5 V DC and +12 V DC as follows: +5 V DC: Formatter PCA Photosensors DC Controller Circuitry Laser/Beam Detect Circuitry Motor Scanner Motor Solenoid High Voltage Power Supply
+12 V DC:
+12VA DC:
Overcurrent/Overvoltage Protection
There are two overvoltage /overcurrent devices in this printer:
· Fuse F101 provides overcurrent protection for the fusing system circuitry. To
check or replace the fuse requires the removal of the DC Controller. Fuse 102 (found only on 110V units) provides overcurrent protection to the printer DC power supply circuitry. · In addition, the +12V DC and +5V DC power circuitry contains an overcurrent protection circuit which automatically shuts off the output voltage when an overcurrent condition occurs due to a short or abnormal voltage on the load side.
SleepMode
Instead of a power switch, the printer has a SleepMode function. After the printer has been idle for 15 minutes, it turns itself off by shifting to SleepMode. The front panel lights remain off, and the printer retains all printer settings and downloaded fonts and macros while in SleepMode.
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Functional Overview
The printer exits SleepMode and all of the lights power on when any of the following occur:
· A job is received. · The Front Panel Button is pressed. · The printer front door is opened.
Note
The printer will not enter SleepMode if there is a printer error.
High Voltage Power Distribution
The High Voltage Power Supply PCA applies an overlap of DC and AC voltage to the primary charging roller and the developing roller. This circuit also applies a positive or negative DC voltage to the transfer charging roller according to the instructions from the CPU on the DC Controller PCA. This circuit also controls the image density by changing the primary AC voltage and the developing AC bias according to the setting of the print density dial. High voltage is disabled when the printer's EP Door is open (i.e., switch SW101 is open).
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Functional Overview
5-7
Formatter System
The Formatter PCA is responsible for the following:
· · · · ·
Receiving and processing print data from the printer interface. Monitoring Front Panel Button and relaying printer status information. Developing and coordinating data placement and timing with the print engine. Storing font information. Communicating with the host computer through the Bi-Directional Interface. The Formatter PCA receives print data from the Bi-Tronics Interface and converts it into a dot image. The DC Controller synchronizes the Image Formation System with the Paper Feed System and signals the Formatter to send the print image data. The Formatter sends the print image data (dots) in the form of a VIDEO signal and the printing process begins. The Formatter PCA also provides mounting locations for additional memory.
CPU
The Formatter PCA incorporates a Motorola 68030 custom-built microprocessor operating at 24 MHz.
Read Only Memory (ROM)
Besides storing microprocessor control programs, the ROM stores dot patterns of internal character sets (fonts).
Random Access Memory (RAM)
The RAM stores printing and downloaded font information received from the host system and temporarily stores a full page of print image data before the data is sent to the print engine. (See "Page Protect" later in this chapter.) Memory capacity can be increased by adding a DRAM memory card to the Formatter PCA. Note that adding memory may also increase print speed when printing complex graphics.
Parallel Interface
The Formatter PCA receives incoming data through its Bi-Tronics interface. The Bi-Tronics I/O provides high speed and two-way communication between the printer and the host, allowing the user to change printer settings and monitor printer status from the host computer. This interface is IEEE-1284 compliant.
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Functional Overview
Control Panel
Status LED Lights
The Formatter uses three LEDs mounted under the printer cover to communicate printer status to the user. Refer to "Using the Control Panel" in Chapter 3 and "Printer Error Troubleshooting" in Chapter 7 for more information on the lights.
Front Panel Button
The Formatter PCA is connected to a microswitch located on the control panel PCA. The single button is used for such functions as self test, reset, and to display error codes. Refer to "Using the Control Panel" in Chapter 3 for more information on the Front Panel Button.
Resolution Enhancement (REt)
The Formatter PCA contains circuitry for Resolution Enhancement technology (REt), which modifies the standard video dot data on its way to the DC Controller to produce "smoothed" black-to-white boundaries. REt is user-adjustable from some software applications. Available settings are On or Off.
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Functional Overview
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EconoMode
The EconoMode setting uses approximately 50% less toner than standard mode printing by reducing the dot density. However, EconoMode does not extend toner cartridge component life. EconoMode, which can also be thought of as "draft mode," is user-selectable through some software applications. The default setting is Off.
Figure 5-3
EconoMode vs Normal Mode Note
EconoMode does not affect print speed or memory usage.
Memory Enhancement technology (MEt)
The Hewlett-Packard Memory Enhancement technology (Met) effectively doubles the standard memory through a variety of font and data compression methods. MEt is only available in PCL mode and is not customer selectable. When using the host-based driver, your PC handles memory management.
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Functional Overview
Enhanced I/O
The Enhanced I/O feature allows printer memory to be used for storing data received from the host computer. When Enhanced I/O is enabled, you can send more data to your printer in shorter amounts of time, which allows you to return to your application sooner. Enhanced I/O has the following options:
· Auto--allows the printer to use Enhanced I/O memory allocation to increase the
speed of data transfer from the host computer to the printer, if necessary. · Off--uses the minimum amount of printer memory for storing data sent from the host computer. Enhanced I/O is only available in PCL mode. When using the host-based driver, your PC handles memory management.
Page Protect
Page complexity (rules, complex graphics, or dense text) may exceed the printer's ability to create the page image fast enough to keep pace with the Image Formation process. If Page Protect is disabled and a page is too complex, the page may print in parts (for example, the top half on one page and the bottom half on the next page). Some print data loss is likely in these instances, and the printer will display an error message. Page Protect allows the Formatter to create the entire page image in page buffer memory before physically moving the paper through the printer. This process ensures that the entire page will be printed. Page Protect applies only to PCL printing. The default setting is Auto.
PJL Overview
Printer Job Language (PJL) is an integral part of configuration, in addition to the standard Printer Command Language (PCL). With standard Centronics cabling, PJL allows the printer to perform functions such as:
· Two-way communication with the host computer through a Bi-directional Parallel · Isolation of print environment settings from one print job to the next. For
connection. The printer can tell the host such things as the control panel status. example, if a print job is sent to the printer in landscape mode, the subsequent print jobs print in landscape only if they are formatted for landscape printing.
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Functional Overview
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Image Formation System
Laser printing requires the interaction of several different technologies (such as electronics, optics, and electrophotographics) to provide a printed page. Each process functions independently and must be coordinated with the other printer processes. Image formation consists of six processes:
· · · · · ·
Figure 5-4
Step 1. Drum Cleaning Step 2. Drum Conditioning Step 3. Image Writing Step 4. Image Developing Step 5. Image Transferring Step 6. Image Fusing
Electrostatic Latent Image Formation Block Flow Of Paper
2. Scanning Exposure
Direction Of Drum Rotation
Manual Feeding Slot
3. Developing
Developing Block
Drum Cleaning Block
Paper Delivery
7. Drum Cleaning
Fuser Block
5. Separation 4. Transfer 6. Fusing Registration
Transfer Block
Image Formation Block Diagram
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Functional Overview
Multi-Purpose Tray
1. Primary Charging
Toner Cartridge
As the "heart" of the Image Formation System, the toner cartridge houses the cleaning, conditioning, and developing steps of the process. The toner cartridge contains the photosensitive drum, primary charging roller, developing station, toner cavity, and cleaning station. Including these components, which wear, degrade, or are consumed in the replaceable toner cartridge, eliminates the need for a service call when replacement is required. The special photosensitive properties of the drum allow an image to be formed on the drum surface and then transferred to paper.
CAUTION
The printer's toner cartridge does not include a light-blocking shutter. Be careful to avoid exposing the drum to light, which can permanently damage the drum. Protect the cartridge whenever removing it from the printer.
Step 1: Drum Cleaning
The cleaning blade is in contact with the surface of the drum at all times. As the drum rotates during printing, excess toner wiped off and stored in the waste toner receptacle.
Step 2: Drum Conditioning
After the drum is physically cleaned, it must be conditioned. This process consists of applying a uniform negative charge on the surface of the drum with the primary charging roller, located in the toner cartridge. The primary charging roller is coated with conductive rubber. An AC bias is applied to the roller to erase any residual charges from any previous image. In addition, a negative DC bias is applied by the charging roller to create a uniform negative potential on the drum surface. The amount of DC voltage is modified by the print density setting.
Step 3: Image Writing
During the writing process, a modulated laser diode projects the beam onto a rotating scanning mirror. As the mirror rotates, the beam reflects off the mirror, first through a set of focusing lenses, off a mirror, and finally through a slot in the top of the toner cartridge, and onto the photosensitive drum. The beam sweeps the drum from left to right, discharging the negative potential wherever the beam strikes the surface. This creates a latent electrostatic image, which later is developed into a visible image.
Functional 5 Overview
Because the beam is sweeping the entire length of the drum and the drum is rotating, the entire surface area of the drum can be covered. At the end of each sweep, the beam strikes the beam detect lens, generating the Beam Detect Signal (BD). The BD signal is sent to the DC Controller, where it is converted to an electrical signal used to synchronize the output of the next scan line of data.
Functional Overview
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Step 4: Image Developing
At this stage of the process, the latent electrostatic image is present on the drum. The toner particles obtain a negative surface charge by rubbing against the developing cylinder which is connected to a negative DC supply. The negatively charged toner is attracted to the discharged (exposed, grounded) areas of the drum, and repelled from the negatively charged (non-exposed) areas.
Step 5: Image Transferring
During the transferring process, the toner image on the drum surface is transferred to the paper. A positive charge applied to the back of the paper by the transfer roller causes the negatively charged toner on the drum surface to be attracted to the paper. After separation, the drum is cleaned and conditioned for the next image.
Step 6: Image Fusing
During the fusing process, the toner is fused into the paper by heat and pressure to produce a permanent image. The paper passes between a heated fusing element and a soft pressure roller. This melts the toner and presses it into the paper.
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Functional Overview
Paper Feed System
Both the Paper Input Bin and the Single Sheet Input Slot merge into one, main input area. Paper placed in either of these areas enables the Paper Out Sensor (sensor 202), which informs the DC Controller that paper is present. When the printer receives a print job and is ready to print, the DC Controller enables the Laser/Scanner Assembly and the Motor. Paper motion begins when the DC Controller energizes solenoid SL1. This causes the paper pick up roller to rotate once. Two actions occur as a result of this rotation. First, the paper kick plate pushes the paper against the pick-up roller. Second, the pick-up roller grabs the top sheet and advances it to the Feed Assembly drive rollers. To ensure that only one sheet is fed, a main separation pad, along with two subpads, hold the remainder of the stack in place. The feed assembly drive rollers advance the paper to the Paper Registration photosensor (PS203). This sensor informs the DC Controller of the exact location of the paper's leading edge, so that the image being written on the photosensitive drum can be precisely positioned on the page. The feed assembly drive rollers then advance the paper to the transfer area where the toner image on the photosensitive drum is transferred to paper. After the image is transferred, the paper enters the fusing assembly where heat from the fuser and pressure from the Pressure Roller permanently bond the toner image to paper. The Paper Exit Sensor (PS201) determines that paper has successfully moved out of the fusing area. The fusing assembly exit rollers deliver paper to either the Output Paper Bin or the Front Output slot, depending upon the position of the Face-up/Face-down lever.
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Functional Overview
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Figure 5-5 shows a simplified paper path and the locations of the photosensors and rollers.
Figure 5-5
Simplified Paper Path
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Functional Overview
Figure 5-6 shows the locations of the photosensors, switches, solenoid, and other important printer elements. Table 5-1 describes the function of each photosensor and the solenoid.
Figure 5-6
Solenoid and Sensors Table 5-1
No. SL1 PS201 PS202
Solenoid and Photosensors
Name Paper Pick-up Solenoid Paper Exit Sensor Paper Out Sensor Description Enables the Paper Pickup Roller. Senses when paper has successfully moved out of the fusing area and the next sheet of paper can be fed. Senses no paper in either the Paper Input Bin or Manual Input Slot. If this sensor does not sense paper in the Input Paper Bin or the Single-Sheet Input Slot, the formatter displays the paper-out indication on the front panel. Paper must be reloaded before printing can resume. Detects the leading and trailing edges of the paper. Synchronizes the photosensitive drum and the top of the paper.
PS203
Paper Registration Sensor
PS204
Door Open/Cartridge Sensor (HP LaserJet 5L only) Detects whether printer door is open and cartridge is in In the HP LaserJet 6L, SW101 performs the place. If the door is open or the cartridge is not in place, the functions of 5L's PS204. control panel LEDs will display an error message. Printing cannot continue until the door is closed and the cartridge is in proper position.
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Functional Overview
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Paper Jam Detection
The Paper Out Sensor (PS202), Paper Registration Sensor (PS203), and the Paper Exit Sensor (PS201) detect when paper is moving through the printer. (See Figure 5-5 for roller and sensor locations.) If a paper jam is detected, the DC Controller immediately stops the printing process and causes a paper jam indication on the front panel. A paper jam can be detected under any of the following conditions:
· Power-On Jams. Paper is present under either PS201 or PS203 at power-on. · Pickup Jams. Paper does not reach and clear photosensor PS203 within a specified
period of time. The time period begins when the Paper Pickup Solenoid (SL1) is energized. · Delay Jams. Paper does not reach or clear a specific photosensor within a specified period of time.
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Functional Overview
Basic Sequence of Operation
The Formatter PCA and the DC Controller PCA share information during printer operation. The DC Controller-to-Formatter Connector (J201) forms a link which operates as a serial data bus. This allows printer status, command information, and dot-image data to be passed between the two PCAs. Figure 5-7 shows the general timing of the printer events. The following events take place during normal printer operation:
Table 5-2
Period WAIT
Printer Timing
Timing From when the paper is inserted to the end of Main Motor initial rotation. Purpose Clear the drum surface potential and clean the Transfer Roller. Maintain the printer in ready state.
STBY (standby) From the end of the WAIT or the LSTR period until the input of the PRNT signal from the Formatter. Or from the end of the LSTR period until power OFF. INTR (initial rotation) PRNT From the input of the PRNT signal from the Formatter until the laser diode intensity has been stabilized. From the end of initial rotation until the Scanner Motor stops. From the primary voltage (DC) OFF until the Main Motor stops. If another PRNT signal is sent from the Formatter, the printer returns to the INTR period. If not, it returns to the STBY period.
Stabilize the photosensitive drum sensitivity in preparation for printing. Also clean the Transfer Roller. Form images on the photosensitive drum based on the /VDO signal from the Formatter and transfer the image to paper. Deliver the last sheet of paper. Also clean the Transfer Roller.
LSTR (last rotation)
Refer to Timing Diagram on the next page
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Figure 5-7
General Timing Diagram - HP LaserJet 5L
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Functional Overview
Figure 5-8
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General Timing Diagram - HP LaserJet 6L
Functional Overview
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Functional Overview