Rice Lake Okidata 320-390-420 Turbo - Service Guide User Manual
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Service Guide ML320/321Turbo
Chapter 2 Operation Description
2.2 Mechanical Operation
2.2.1 Printhead Mechanism and Operation (See Figure 2-2 below).
The printhead is a spring charged 9-pin driving head using a permanent magnet. It is attached to the
carriage, which moves parallel to the platen. Electrically, this unit is connected to the control circuits
through the control board.
(1) The printhead configuration
The printhead is composed of the following parts:
(a) Wire guide
(b) Spring assembly (Wire, Armature, Spring, Yoke, Spacer)
(c) Magnet assembly (Magnet, Core, Coil, Yoke)
(d) Printed circuit board
(e) Fin
(2) Printhead Operation (See Figure 2-3 below).
(a) When the printhead is idle, the armature is attracted by a permanent magnet and the spring fixing the
armature is compressed. The print wires fixed to each armature are thus concealed under the wire guide.
(b) When a signal for a character to be printed is detected, a current flows through the coil. When the coil
is activated, the magnetic flux (caused by the permanent magnet between the armature and the core) is
canceled to eliminate the attracting force. The armature is driven in the direction of the platen by the force
of the armature spring. The print wire fixed to the armature protrudes from the tip of the wire guide, strikes
the paper through the ribbon and prints a dot on the paper.
(c) After the character has been printed, the armature is magnetically attracted again and the print wires
are again concealed under the wire guide.