Mechanical Operation - OKIDATA Microline 395 Service Handbook

%2.2 Mechanical Operation

2.2 MECHANICAL OPERATION
2.2.01 The Printhead Mechanism
The Microline 395 uses a highly efficient stored energy type printhead. Power is not consumed until the
printwires are activated, thereby extending the printhead life to approximately 200 million characters.
The printhead uses 24 printwires (two columns of 12 wires each). Each wire is welded to an armature.
Behind this armature is a spacer ring.
Each of the 24 printwire armatures have a permanent magnet behind them. The magnets attract the
armatures, drawing the printwires into the wire guide, thus keeping the wires inside the printhead. A coil is
wrapped around each of the permanent magnets.
When a dot is to be printed, current is passed through the appropriate coil. This creates an
electromagnetic field which opposes the magnetic field of the permanent magnet. The armature can then
spring forward and the print wire (which is attached to the armature) strikes the ribbon and imprints a dot
on the paper.
When current is removed from the coil, the magnetic field of the permanent magnet attracts the armature,
causing the printwire to retract into the wire guide once again.
The printhead contains a built-in thermistor used to monitor the printhead temperature.
The parts listed below make up the printhead.
Wire Guide
Print Wires
Armature Assembly
Spacer
Permanent Magnet Assembly
Thermistor
Printed Circuit Board with Coils
Head Gap Adjusting
The head gap adjusting mechanism adjusts the gap between the platen and printhead. This is
accomplished by moving the adjusting lever on the left side of the printer mechanism. When the lever is
moved the carriage shaft rotates. Since the carriage shaft is attached to the printer mechanism with
eccentric collars, as the carriage shaft rotates, the distance between the platen and carriage shaft
changes.
ML395 ( 96-02-03 )