IBM 727, Руководство по инструкции

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4. 0 PHYSICAL DESCRIPTION
The 727 magnetic tape unit is built on a frame about 2f x 2T2" x 5f3 -3 /4 M. Mounted
on the front of the frame are the reels, vacuum columns, read-w rite and erase heads
and the tape driving pulleys and capstans. The buttons and lights used to control the
unit manually are mounted on a door form ing part of the cover over the front. Fig­
ure 4 is a sketch of the machine front without covers and Figure 5 is a sketch of the
configuration of the panel buttons and lights.
4 .1 TAPE MOTION
Tape is transported from the left or file reel through the read-write and erase
heads to the right or machine reel. Because the reels containing the tape are rela ­
tively sluggish in action, it would be practically impossible to start and stop the tape
efficiently if it were driven directly from the reels. Therefore, a buffer storage area
is provided in the form of vacuum columns below the reels. In each of these columns
a loop of tape is retained and the tape is driven through the read-w rite and erase heads
by a friction drive and pulley combination. As tape is drawn from one column, it is
replenished periodically by rotating the associated reel in the proper direction. As
tape is driven into the opposite column, the associated reel is periodically caused to
turn in the correct direction to wind up the tape. The control of the reel motion and
the reel drive will be discussed further on. Figure 6 illustrates the path of the tape
from one reel to the other. The next paragraphs describe the mechanics of the tape
transportation mechanism.
The right and left drive capstans turn continuously in the direction shown. To
drive from left to right (forward), the right moving pulley fork pivots to the right
squeezing the tape between the moving pulley and the rotating drive capstan. At the
same time, the left moving pulley fork pivots toward the left drive capstan, but does
not strike it.
To drive from right to left (backward), the left moving pulley fork pivots to the
left causing the tape to be squeezed between the left moving pulley and the left drive
capstan. At the same time, the right moving pulley moves toward the right drive
capstan but does not strike it.
To stop tape motion, the moving pulley forks pivot in the opposite direction caus­
ing the tape to be squeezed between either the right or left moving pulley and the right
or left stop capstan, respectively. If the tape is moving from left to right, it is
stopped at the left stop capstan. If the tape is moving from right to left, it is stopped
at the right stop capstan.
4 .2 MOVING COIL ASSEMBLY
Figure 7 is a sketch of the linkage operating the moving pulley assem blies. The
basic motion is imparted to the system by the moving coil. This coil is suspended in
the field of a permanent magnet. Passing current through it causes it to move very
rapidly either up or down, depending on the direction of current flow.
If the coil is caused to move upward, called the "start" position, the linkage
causes both moving pulley forks to pivot toward their respective drive capstans. If
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