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Inkjet Printer

The Inkjet Printer has some characteristics of dot matrix printer (DMP) and some characteristics of laser printer.
Similarities in DMP and Inkjet

1. Like the print head of the DMP printer, the inkjet printer use an “Ink Cartridge”.
2. The inkjet has a carriage mechanism to move the ink cartridge.
3. The inkjet has paper fee motor (stepper) to move the paper as it is in a DMP.
Similarities in Inkjet and Laser
1. Cut sheet paper are used in both the printers.
2. Printing quality of the inkjet is similar to that of the laser printer.
3. Inkjet and Laser are non-impact printers as there is no direct contact between paper and the print head.

Types of Inkjet Printer

There are basically two types of Inkjet printers
1. Thermal/Bubble Jet
2. Mechanical/Peizo Electric Crystal

Thermal/Bubble Jet Technology

This technology is used in Canon and HP Inkjet printers. The Canon printers are sold as Bubble Jet and HP printers are sold as DeskJet printers.

The ink filled in cartridge is heated at high temperature as such that bubbles are generate in the liquid ink. This bubble pushes the ink out from holes in the nozzle on print cartridge.
This ink drop pushed from the nozzle is printed as dots on the paper.
This process is repeated 5000 to 8000 times in one second.
This ink is kept in what is called a firing chamber. The firing chamber has layer of thin film resistor to heat the ink.
One silicon layer is pasted on the firing chamber to rapidly cool down the resistor.

Thermal Controlling

The cartridge has one thermal control to regulate the ink temperature by controlling the speed of firing.
This is called as frame wear control. The thermal sense resistor is attached to the cartridge body (shell), which supplies the feedback to keep the temperature in operating range.
This process is called as pulse warming.
Thus to keep the resistor of each nozzle at a thermal operating range, two processes are used:

1. OFF DOT PULSE WARMING

These low energy pulses are supplied to the resistor, not for firing, but to keep the resistor warm. These signal pulses are supplied till the correct operating temperature is not reached. These pulses can be switched off at any time.

2. FAST PULSE WARMING

This process is used when there is no printing. These pulses are applied before printing to heat cartridge. After this process the Off Dot Pulse warming process is starte.
Both the processes are done separately.

MACHANICAL/PEIZO ELECTRIC CRYSTAL TECHNOLOGY

This technology is used in Epson printers. These are high quality printers but costly.
In this printers the head and ink cartridge are separate.
The print head use peizo electric crystal in place of the resistor to force the ink out of the chamber.
when the electronic current is applied to these crystal, it twitches, forcing the ink out of the chamber.

Printer Speed

The speed of inkjet printer is measured in PPM (Pages Per Minute).
Following parts are required in a high speed inkjet printer.

Print Head

1. The number of nozzles are increased to 128 for printing two lines at once and for color cartridge 64 nozzles are used for each color.
2. High response frequency is used for faster ink injection.

Printer Control

1. High speed CPU is used.
2. High speed/high capacity RAM (Memory) is used.

Printer Engine

1. High-speed carriage and paper feed motor.
2. Extra motor to service the ink cartridge. This is called as pumping/service station motor.

TYPES OF CARTRIDGE

Following types of ink cartridges are used with the inkjet printers:

1. Only Black.
2. Only color (Cyan, yellow and magenta colors in a single color cartridge).
3. Black and Color (Cyan, yellow and magenta colors in a single color cartridge).
4. Black and color (Cyan, Yellow and Magenta colors in separate color cartridges).

(i) Only Black

This cartridge is used only in black and white inkjet printers.

(ii) Only Color (CMY)

This cartridge is used in color inkjet printers. In this printer the black color is printed by combining CMY colors from the color cartridge.
This generate a washed out black color.

(iii) Black & Color Ink Cartridge

This cartridge has two parts for black, and color inks.

When B & W printing job is supplied then black cartridge is used and for color printing color cartridge is used.

(iv) Black & Three Separate Color Cartridges

This allows individual cartridges to be changes/refilled when a particular ink gets exhausted.

Color Conversion Process

The picture on the color monitor is made of RGB (Red, Green and Blue) Colors.
When printing a color job this RGB color is converted to CMYK (Cyan, Magenta, Yellow and black) by printer CPU and supplied to the ink cartridge for printing.

Section Of Inkjet Printer

1. Logic Board

This section has logic ASIC (application specific IC), RAM, ROM, supply regulator IC’s.

2. Power Supply

The supply to inkjet printer is supplied from adapter of 12, 18, 24 or 30v. This voltage is supplied to regulator IC for 5V, 17V and 19V supply to different sections.
In some printers have power supply section on the logic board.

3. Control Panel

The front panel has indicator LED’s and operating switches.

4. Mechanical Unit

The parts in this unit are:

  • Head
  • Motor
    • CR Motor
    • PF Motor (Paper Feed/Pumping Motor)

In Some printers separate motor is used for pumping (cleaning) of the ink cartridge head. In some printers PF motor is to lock and free the cartridge.
The locking position is also called as cap position.
This motor also performs the wiping and spitting operations. This operation is performed when printer is swtiched on, after printing first page or when the ink overflows.

This operation is performed by service sled mechanism. The service sled is moved up/down by homing lever.

The steps to homing lever are supplied by service station motor.

The number of steps and other information is stored in Non-Volatile RAM (NVRAM).

When printer is switched on station motor receives the step signal information from NVRAM.

The motor operates to unlock the service sled and move the cartridge to the left.

When printer is switched off, step signals from NVRAM are supplied to bring the cartridge in locking position.

5. Sensor

Sensors used in inkjet printers are:

  • Top Door Sensor
  • PCA Sensor (Temp Sensor).
  • Paper Sensor.

Logic Board Components

Logic ASIC

This is special type of circuit designed by printer company. This circuit has CPU logic, control logic, interface host computer, control of motor, firing print cartridge etc.

CPU

The 68 series CPU from Motorola is used for controlling and other functions.
This CPU has 16 bit data and 18 bit address bus. The processor interface block is used to connect RAM and ROM to CPU.

Crystal Oscillator

15.975MHz crystal is connected to CPU clock frequency.

Timer

This block is not used in this model.

Motor Control

This block is not used in this model.

Register

This block converts serial output data into parallel input data.

DMA (Direct Memory Access)

This block is used for data transfer at high speed.

GPIO (General Purpose Input Output)

This block is used for communication between ASIC and other components.

Memory Controller

This block generates location in RAM for reading/writing information by CPU.

I/O Function

This block connects printer to computer for communication.

I/O Driver/Receiver

This block is not used in the model.

PCMCIA Block

This block is not use in this model.

Memory Block

This block has four sections to connect different capacity memory.

DRAM

This is used to temporarily hold the data received from computer.

ROM

The BIOS and internal fonts are stored in ROM.

EEPROM

This IC has program stored for general purpose input output.

Flash EEPROM

This is special IC in which the user can feed different language fonts without program IC.

Power Supply

The SMPS power supply is used that generates digital 5V supply for logic board, 17V for motor, 19V fir black cartridge, 17V for color cartridge and 12V for different sections.

Paper Feed Motor

The PF motor operates on 17V. The PWM (Pulse Width Modulation0 is used for motor drive.

Carriage Motor Driver

Simple DC motor is used that operates on 17V. The PWM is used for motor driver.

Power on Reset

This block checks the I/O voltage. If voltage is low or temperature of cartridge is high then it generates reset signal.

Keypad Assembly

The keypad assembly is on front panel.
This panel has two LED’s and two switches.

Sensor PCA

The cartridge shell has one PCA sensor (temp sensor), which is connected to main board through 4 wires. This is optical sensor.

Door Sensor

This sensor has one switch to sense the open/close door.
If the door is open then printing is not possible and user can disconnect the cartridge.

Page Sensor

Optical sensor is used to sense the paper in/out.

Carriage Encoder Strip

This strip has magnetic bar, which is used for carriage control i.e. position of printing on paper.

IDE sense

This block has two circuits-first circuit checks the presence of cartridge and second circuit check whether cartridge is OK/damaged.

Printer Cartridge Driver

This block supplies firing signals to the nozzles on print cartridge.

Functional Block Components

Electronic Printed Circuit Array (Elec. PCA)

Head Driver

This logic section supplies the firing signals to cartridge nozzles through adjuster in cartridge to heat the ink.
Heat boils the ink and the air bubble due to boiling drops the ink from nozzle on paper for image printing.
This section also checks the presence/absence of cartridge and condition off cartridge. OK/damaged.

Logic Section

ASIC

The 68 series CPU from Motorola Company is used.
This ASIC is used for head control, motor control, data input, output control, keypad I/O control etc.

ROM

This IC has BIOS and fonts stored.

DRAM

This IC is used for data buffering from computer.

NVRAM

This IC has instructions stored. According to step signal, the control signals are supplied to motor driver, carriage positioning and service station position sensing circuit.

Power Supply

The DC supply form regulator is supplied to different sections.

Sensor assembly/PCA sensor

Three sensors are used in this section:

Temperature sensor

This sensor is placed in cartridge shell to control the temperature of ink.

Access door switch

When the door is open or closed, signal is supplied to ASIC to inicate the condition.
This condition is indicated by indicator LED on front panel.

Media sensor

This sensor indicates the presence/absence of paper in printer.

Mechanical Assembly

Paper Motor

This motor is used to feed/load, paper to printer or ejects the paper.

Carriage Motor

This motor is used to move the cartridge from left to right or righ to left.

Service station motor

This is called as purge unit in HP printers. The main function of this motor is to service the cartridge.
One ink on nozzle and clean it.
This motor performs three operations:

  • Wiping – clean the nozzle.
  • Spitting – absorbs the overflow ink from nozzle.
  • Capping – lock/unlock the cartridge.

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