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FLOATING ARM
UNFLEXED PROFILE
~:::::;::~i.o--liiiiiiiiiiiiiiii=====7====
OF HEAD ASSEMBLY
\
DUAL SURFACE DISK
(PART OF DISK PACK)
;,
READ/WRITE
HEAD
~1'--"
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II I
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FIXED ARM
CARRIAGE
CAM
(PART OF HEAD CAM)
\
~---'"'......,
HEADS UNLOADED- CAM
SURFACE ON EACH HEAD
ASSEMBLY RIDES ON CAM
WHEN CARRIAGE IS
RETRACTED. READ/WRITE
HEAD FACE MOVES CLEAR
OF DISK SURFACE.
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SECURED TO
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~--~
CUSHIONING LAYER OF AIR
EXISTS ON SURFACE OF
SPINNING DISK. HEAD GIMBALS
COMPENSATE FOR DISK VARIATIONS.
Figure 3-9.
To prevent damage to the heads and/or the
disk pack during automatic operation, load-
ing occurs only after the disk pack is up to
speed and the heads are over the disk sur-
faces.
For the same reason, the heads un-
load automatically and are retracted if the
disk pack rpm drops out of tolerance. During
manual operations, heads should never be
loaded on a disk pack that is not rotating.
Head loading is part of the Power On/First
Seek function.
As power to the deck is se-
quenced up, the drive motor starts.
This
initiates disk pack rotation and a first
seek interlock delay.
Actual delay is ap-
proximately 15 seconds.
When the disk pack rpm reaches 3000, the
power supply speed relay energizes to es-
tablish the ability to continue the operation.
Upon completion of the first seek interlock
delay, the logic specifies a forward seek
and the carriage moves forward toward track
O.
Head loading occurs during this forward
motion.
The carriage continues toward the
spindle until the servo detects ,track
o.
The floating arm (Figure 3-9)
is designed
to maintain a
~onstant
loading force.
While
the heads are retracted, head cams on the
actuator housing bear
agains~
the floating
arm cam surfaces.
The cams support the load-
ing force and hold the heads in unloaded
position.
As the carriage moves forward, the
83318200
A
-
r-"
-
-
~
--
Head Loading
HEADS LOADED - CAM SURFACE
ON EACH HEAD ASSEMBLY RIDES
OFF CAM AS CARRIAGE EXTENDS.
SPRING FORCE OF FLOATING ARM
MOVES READ/WRITE HEAD TCWARD
DISK SURFACE UNTIL OPPOSING
FORCE OF AIR LAYER CANCELS
FORCE OF FLOATING ARM.
floating arm cam surface rides off the head
cam just after the read/write heads move out
over the disk surface.
The loading force
moves the head face toward the air layer on
the surface of the spinning disk until the
opposing forces balance.
The heads loaded switch status reflects the
state of the read/write heads (loaded or
unloaded).
This status is used in the logic
chassis and power supply.
The switch mounts
on the carriage track and is transferred by
carriage motion.
Whenever the carriage is
fully retracted, the switch state reflects
the unloaded status of the heads.
As the
carriage moves forward during a Power On/
First Seek,_the switch transfers at a point
within about 0.1 to 0.2 inch forward of the
retracted stop.
This switch status remains
unchanged until the carriage is retracted to
the same position and, as such, does not
precisely indicate the loaded/unloaded
status
of the heads.
Precise status is determined
by the logic when the servo track head
~es
dibits.
Head unloading occurs whenever power to the
unit is removed or disk pack rpm drops below
tolerance.
Either event drops a speed
~le
signal to the logic.
This causes the voice
coil to drive the carriage in reverse from
its current location toward the retracted
3-15
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