Service Manual
5-7
Theory of Operation
5
Thermal head
The thermal head is the device that sublimes wax dots onto the paper. It
contains a row of 3584 solid-state heating elements. The actual number of
elements used during a particular print depends on the paper size (A or A4, B or
A3) and the image to be printed. The thermal head prints raster lines parallel to
the short axis of the paper.
Earlier, in the topic “The print process,” we said that the print engine prints one
line at a time; this is not exactly the case, it just appears that way. To simplify its
electrical design, the print engine actually uses a drive signal multiplexing
scheme to energize the heating elements. During printing, the head controller
activates a pair of heating element segments from eight heating segments of the
thermal head. (Individual elements in the segments may or may not be
energized depending upon whether the element is to print a dot; it is just that
segments are printed as pairs.) Following the printing of the first pairs of
segments, the head controller energizes the second pair of segments from the
eight heating element segments, then the third pair. Energizing the fourth pair
of segments completes the raster line printing.
Mechanical controller
The mechanical controller interfaces the CPU to the print engine's motors,
sensors, solenoids and fans. By interpreting signals from the sensors, buffered
by the mechanical controller, the CPU keeps track of the paper position, transfer
roll position and paper position during printing. Based on this information the
CPU determines the proper time to transmit signals to the mechanical controller
to advance the paper, energize a solenoid, or check a sensor.
