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Chapter 6 Printing Mechanism
length of the hammer bank and acts on the hammer springs through
individual pole pieces. The pole pieces magnetically attract and hold the free
end of the hammer spring under tension. This is called the retracted state.
Figure 51. Hammer Springs and Hammer Bank (Detail)
Two electromagnetic coils are mounted behind each hammer and wound
around each pole piece. The coils are normally de-energized. When hammer
driver logic determines that a hammer must print a dot, a current pulse
energizes the coils behind it. The polarity of the resulting magnetic field
opposes the field of the permanent magnet, canceling its effect and releasing
the hammer. The hammer springs forward, strikes the ribbon and paper, and
leaves an impression of its tip (a “dot”) on the paper.
While the hammer is in flight the coils are de-energized and their magnetic
field collapses. After striking the ribbon and paper, the hammer rebounds and
the permanent magnet recaptures it. When the shuttle reaches the end of a
sweep, it reverses direction, the paper is moved up one dot row, and the
hammer springs print the next row of dots as the shuttle sweeps in the
opposite direction.
NOTE: P5015 hammer bank shown.
Hammer Bank Assembly:
Coils, Magnet, Pole Pieces,
Hammer Spring
Assemblies
Alignment Pin
Hammer Spring
Assembly
Tungsten
Carbide
Hammer Tip
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