40
Principles of Operation
NOTE:
6400–004/04P
hammer bank shown.
Tungsten
Carbide
Hammer Tip
Hammer Bank Assembly:
Coils, Magnet, Pole Pieces,
Hammer Spring Assemblies
Alignment Pin
Hammer Spring Assembly
Figure 12. 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 the hammer must print a dot, a current pulse
energizes the coils. 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 a dot
impression of the hammer tip on the paper.
While the hammer is in flight the coil is de-energized and its 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.
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