5-6
Phaser 480 Color Printer
5
Theory of Operation
Engine control board block description
The engine control board receives color bitmaps from the image processor
board. It also controls the print engine's printing process, including all motors,
sensors, and the thermal head. The block diagram shown in Figure 5-1
illustrates the functional operation of the print engine control board. The block
diagram consists of five major functions:
■
Central processing unit (CPU)
■
Interface
■
Thermal Head controller
■
Thermal Head
■
Mechanical controller with motors, solenoids, and sensors
CPU
The print engine CPU consists of a microprocessor, ROM, RAM and a clock
circuit. The CPU is the heart of the print engine. It controls the timing
controller, the mechanical controller, and print engine diagnostics.
Interface buffers
The interface buffers receive data from the image processor board, where the
image data was received from the host computer and processed into data for the
print engine. The interface buffer routes received data signals to the data
controller.
Thermal Head controller
Each thermal heating element must receive sufficient energy to sublime dye
properly. Too much energy and the dot smears when printed. Too little energy,
and the dye dot is ill-formed and does not achieve the correct color. In the
thermal head controller, the data of the current raster line to be printed is
compared with the previously printed lines. Using an algorithm the thermal
head controller determines when, and for how long, the individual thermal head
elements should be energized to properly sublime dye onto the paper. This
comparison accounts for the thermal energy stored in each heating element from
its previous dot printing action as well as the thermal energy picked up from
adjacent heating elements.
Using this information, in conjunction with timing signals, the thermal head
controller drives the thermal heads with the data stored in the line memory
buffer. The head controller generates variable length strobes. During printing,
the strobe length is varied, based on the overall thermal head temperature and
the volume of dots printed in a line. The voltage level of the pulse is fixed at
about 24 VDC.
