Mechanical Operation - Printhead Mechanism - OKIDATA ML380 Service Manual

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Service Guide ML380
Chapter 2 Principles of Operation
2.2 MECHANICAL OPERATION
2.2.01 Printhead Mechanism
The Microline 380 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 a magnetic field
which counters 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 printhead is composed of the following parts.
Wire Guide
Print Wires
Armature Assembly
Yoke
Spring
Spacer
Magnet Assembly
Thermistor
Printed Circuit Board