IBM 727, Руководство по инструкции

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source and the cell. However, if the tape breaks, the light source strikes the cell
and stops the machine.
4. 5 REEL DRIVE CLUTCHES
Each tape reel is mounted on a hub protruding from the upper front plate of the
machine. This hub contains an expansion rim that grips the reel tightly when the
locking screw in the center of the hub is tightened. The hub is mounted on a shaft
extending through the upper front plate and to the rear. This shaft is driven by two
continuously running three-phase motors through two magnetic powder type clutches;
one for forward motion and one for reverse motion. A third clutch is used as a
brake.
Figure 10 shows a single clutch unit. The innermost part is the rotor that is
keyed to the shaft. Surrounding this part is the clutch housing with pulley grooves
cut in its circum ference to make it free to turn on the shaft. Within the clutch hous­
ing is embedded a coil, the connections for which are brought out to slip rings on one
end of the housing. In the space between the rotor and the housing is a mixture of
magnetic iron powder and graphite.
When current flows through the coil in the housing, flux is produced. It solidifies
the iron and graphite mixture and causes the rotor and housing to be essentially locked
together. Therefore, if the housing is made to turn continuously through pulley action
from the m otors, the rotor does not move with it unless current is flowing through the
coil. As soon as current is caused to flow through the coil, the rotor begins to move
with the housing and to turn the hub and reel at the front of the machine.
Because of the inductance of the coil, current in it builds up gradually and, b e­
cause torque transmitted is proportional to current (and flux), a quite smooth a ccel­
eration is produced. This smoothness is essential because shock in the reel causes
slippage of the tape on the reel, and eventual breakage. The magnetic powder clutch
was selected here for its ability to produce quite smooth accelerations and large
torques with relatively small control currents. The iron-graphite mixture does not
wear the clutch parts but only tends to polish them. To hold the iron-graphite mixture
in the vicinity of the flux gap, a series of labyrinth type ridges were designed into the
clutch parts. These ridges assist centrifugal force to return the powder back to the
magnetic gap.
All three clutches are mounted on the same shaft with all rotors keyed to it. The
front clutch has a stationary housing and thus serves as a brake when necessary. The
middle clutch housing is driven in a clockwise direction and serves as a forward drive.
The rear clutch housing is driven in a counterclockwise direction and serves as a
reverse drive.
Control of the clutch energization is discussed under section 7. 0.
Each brake may be released when the machine is unloaded by depressing the r e ­
lease button located below and to the left of the file reel. The left button causes d e-
energization of the left brake clutch and the right button causes de-energization of the
right brake clutch.
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