Xerox 4090 - Manual (Page 34)

SETTING UP PRINT JOB SOURCES
5a and 5b Air bearings
Two air bearing sensor assemblies (upper [b] and lower [a] air
bearings) are used to guide the tape across the magnetic
head on an air cushion and to measure air pressure
reflection. The pressure signal is processed by the control
system, which maintains constant tape velocity and air
pressure by changing the reel motor speed whenever
appropriate.
6 Magnetic head assembly
This assembly consists of a read/write head and an erase
head. The dual-gap read/write head unit is designed to
perform the read/write functions in a 9-track format. It allows
a write-to-tape operation, a read-only operation, or a read-
after-write operation. During a write operation, a full-width
erase head erases the tape while it moves forward before the
tape passes over the write head.
7 Erase head
8 BOT/EOT assembly
Located next to the magnetic head assembly, this assembly
optically detects the beginning-of-tape (BOT) and the end-of-
tape (EOT) markets. Photosensors detect light reflected from
the BOT and EOT markers on the tape so that the tape drive
can recognize starting and stopping areas.
9 Tape cleaner
The cleaner consists of two blades and a vacuum port to strip
unwanted particles off the tape surface. It is designed so
that the first blade cleans the tape in the forward direction
and the second cleans it in the reverse direction. The
vacuum port removes the unwanted particles from that area.
10 File protect sensor (not shown)
This sensor consists of a reflective ring around the file
(supply) hub and a photosensor next to it that are used to
detect the presence or absence of the write-enable ring on
the file reel.
11 Cover interlock (not shown)
There is an interlock associated with the door latch as a
safety device. The tape unit can be operated only when the
door is closed.
Control panel switches
Two types of functions are controlled by the switches on the
control panel: operator and maintenance. Switches to the left
of the two-digit LED display are the operator functions, and
switches to the right of the display are for maintenance
functions. When the magnetic tape drive is online to the printer,
maintenance functions do not work. Figure 3-4 shows the
control panel switches.
3-6 XEROX 4050/4090/4450/4650 LPS OPERATOR GUIDE