of these main sections. For example, the tape heads are identified according to their functions of
erasing, recording, or playback.
a. All of the tape machines require some type of mechanism to move the tape past the record
and playback heads. Such mechanisms have been given various names, but "tape transport" seems to be
generally accepted as standard. "Tape handlers" is the term used to designate machines designed for
fast start-stop operation. These fast start-stop machines are usually a type of computer or laboratory
tape transport which require the tape to start or stop instantaneously. In contrast, the standard machine
requires about 1 second to reach full spied and perhaps 5 to 10 seconds to fully stabilize.
(1) A good quality tape transport has the features of the mechanism illustrated in Figure 3-1.
These features include the tape supply reel, which is provided with either a friction brake or an active
back torque. The back torque is supplied by the drive system or a torque motor. Back tension (torque)
is necessary to keep the tape from becoming tangled due to the inertia of the tape reel. The tension idler
holds a certain amount of tape in its loop; this spare amount of tape is temporarily let out during quick
starts. A slight delay in time is allowed for the supply reel, which has appreciable inertia, to start turning
at operating speed. The tension idler and back torque work together to smooth out irregularities caused
by the rubbing of the tape against the supply reel sides, sticking together of tape layers, or other causes.
(2) Again looking at Figure 3-1, note that the tape is drawn from the tension idler, across the
rolling tape guide erase head, tape guide, record head, tape guide, and reproduce head. The force, which
draws the tape across the heads at a constant speed, is provided by the capstan and the capstan pressure
roller. The combination of the capstan, the tension idler, and reverse torque of the supply reel keeps the
tape under constant tension. There is friction between the tape and the stationary heads. This friction is
a source of vibration. Attempts to eliminate this vibration are included in the design of the transport
mechanism by using a rigid base on which to mount the transport components. Other causes of
vibration are the amount of wrap around the head, smoothness of head faces, tape tensions, tape
condition, tape composition, temperature, and humidity. The capstan may be either the shaft of the drive
motor or a shaft driven through a speed-reducing mechanism. The capstan and any associated
mechanism must be made with precision, or it causes problems during both record and playback. This
requirement for precision components includes the drive motor, as it must drive the capstan mechanism
at a constant speed.
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