HP LaserJet Enterprise 500 Maintenance Manual - Page 219

Shuttle Frame Assembly, Hammer Springs and Hammer Bank Detail

Page 219 highlights

Shuttle Frame Assembly attaches to the hammer bank; the small end of the other 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 46.) 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. NOTE: LineJet 500Q hammer bank shown. Hammer Bank Assembly: Coils, Magnet, Pole Pieces, Hammer Spring Assemblies Tungsten Carbide Hammer Tip Hammer Spring Assembly Alignment Pin Figure 46. 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. 219

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Shuttle Frame Assembly
219
attaches to the hammer bank; the small end of the other 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 46.) 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 46. 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
: LineJet 500
Q
hammer bank
shown.
Hammer Bank Assembly:
Coils, Magnet, Pole Pieces,
Hammer Spring Assemblies
Alignment Pin
Hammer Spring
Assembly
Tungsten
Carbide
Hammer Tip