Brother P-touch BB4, Service Manual

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II - 1
2.1 THEORY OF OPERATION
2.1.1 Print Mechanism
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Structure of Thermal Head
This machine uses direct thermal printing. The thermal print head has a heat generator
consisting of 64 heating elements which are vertically aligned as shown in Figure 2.1-1.
Each heating element is 0.136 mm wide by 0.106 mm high.
Figure 2.1-1 Heat Generator of Thermal Head
Printing Process
When the cylindrical rubber platen is pressed against the thermal print head with the
thermal tape sandwiched inbetween, the CPU applies electric power to the selected ones
of those 64 heating elements.
The selected heating element(s) generates heat that dissolves the metal deposit layer of
the thermal tape so as to reveal the substrate layer, producing a dot on the tape. The tape
is advanced and the next heating cycle is repeated, thus forming a character on the tape.
Character Formation
While the drive motor (DC motor) feeds the tape by 0.106 mm for 13.8 ms, the thermal
head generates heat once. The feed amount of 0.106 mm is smaller than the width (0.136
mm) of the heating elements so that the heat generated at one heating cycle will overlap
with the next heating cycle. This forms a character having no gap between adjacent
printed dots.
0.106 mm
6.784 mm
0.136 mm