Oki Microline 390, Maintenance Manual, Page: 39 / 174

3.2 Mechanical Operation
3.2.1 The printhead mechanism and its operation (See Figure 3.3.)
The printhead is a spring charged type driving head utilizing a permanent magnet. It is
attached to the carriage and moves parallel with the platen.
Figure 3-2 Arrangement of the head pins
(View
from the tip of the printhead)
The printhead is composed of the following parts:
(a) Wire guide
Print wires
Armature assembly
(d) Yoke
S p r i n g
S p a c e r
(g) Magnet assembly
Thermistor
Printed circuit board
Operation of printhead
When the printhead is inactive, the armature is attracted to a permanent magnet and the
spring attached to the armature is compressed. The print wires attached to each armature are
thus concealed inside the wire guide.
When a signal for a character to be printed is detected, current flows through the coil. The
magnetic fluxes (caused by the permanent magnet which is situated between the armature
and the poles) are canceled, removing the attracting force. The armature is driven in the
direction of the platen by the force of the armature spring expanding. The print wire attached
to the armature protrudes from the tip of the wire guide, striking the ribbon and prints a dot
on the paper.
After the character has been printed, the armature is attracted to the permanent magnet
again and the print wires are concealed inside the wire guide.
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