2–39
Principles of Operation
Print Mechanisms
Hammer Bank, Shuttle, and MPU
Printing is synchronized with shuttle movement by signals from the magnetic
pickup unit (MPU). The MPU, located next to the flywheel timing disk, is so
oriented that timing signals relate precisely to the shuttle position. Variations
in magnetic reluctance are sensed by the MPU from apertures on the timing
disk as it rotates, generating SYNC pulses. Two aperture locations at
opposite ends of the disk are of double width (material between two adjacent
apertures is removed). These double width apertures separate the 284 single
width apertures into two groups and generate a RESYNC signal coincident
with the shuttle starting to move from left to right.
One rotation of the disk provides eight printing periods and four back and
forth shuttle cycles. Each printing period is followed by a turnaround period
when the shuttle movement is reversed, paper is advanced a distance
determined by the vertical dot density, and no printing occurs.
Typical signal levels received from the magnetic pickup are:
SYNC: 2.5 to 5.5 Vpp
RESYNC: 4 Vpp minimum
Operation of the hammer bank and shuttle is described on page 2–5.
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