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Chapter 4 Printing Mechanism
connecting rod attaches to a counterweight frame surrounding the hammer
bank. (The hammer bank and the counterweight constitute the shuttle
assembly.) The rotary motion of the shuttle drive motor converts to linear and
opposing motion of the hammer bank assembly and the counterweight, in an
arrangement similar to that of a horizontally-opposed gasoline engine.
Mechanically, this design achieves the same benefits as this type of engine:
perfect primary balance, low vibration, and durability.
Each hammer spring is a stiff leaf spring with a cylindrical tungsten carbide tip
on the free end. (See Figure 12.) A permanent magnet is imbedded along the
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 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.
NOTE: 6400-004 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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