Seek Mechanism; Write Protect Detection; Track 00 Detection; Index Detection - Fujitsu M255XK Customer Engineering Manual

3.1.5 Seek Mechanism
The seek mechanism is built around a stepping motor with a capstan (pulley). This
mechanism includes a steel band, guide shaft and read/write head carriage. The
carriage slides along two guide shafts and is connected to the capstan of the
stepping motor via the steel band.
The stepping motor utilizes a 4-phase construction. This stepping motor is driven
by single-phase excitation and it rotates one step (1.8
0 )
to move the carriage one
track.
Parallelism and distance between the shaft and disk center lines, as well as the
shaft and capstan, are assembled to close tolerances. Temperature expansion of
the chassis, steel band, carriage, and associated items have been carefully studied
and designed to counteract the expansion of the disk.
3.1.6 Write Protect Detection
This detector is comprised of a Light Emitting Diode (LED) and photo-transistor.
They detect the presence or absence of a wri te enable notch on the disk jacket.
When a disk with a covered notch is inserted, the light path is broken and any
operation of the write circuits is prevented. Previously written data is thereby
protected, even if a write command is given.
The LED is mounted on the spindle motor circuit card and the photo-transistor
sensor is mounted on the write protect circuit card assembly.
3.1.7 Track 00 Detection
The Track 00 detector is comprised of an LED and photo transistor assembly
(photo-interrupter) and a mechanical stop. The photo-interrupter provides a signal
to the drive's circuitry whenever the head carriage is at the outermost track
position (Track 00). The mechanical stop prevents the head carriage from moving
beyond Track 00 during a seek operation or when power is initially turned on.
If the head carriage is at its innermost track position, and a step-in command is
received, there is enough margin provided to ensure that the heads will not reach
the edge of the opening in the disk.
To calibrate the head carriage (return it to Track 00), command the carriage to
move several steps beyond the maximum track number. For example, command a
M255XK, which has 80 cylinders, to move outward 84 to 86 steps to have it
calibrate at track 00.
3.1.8 Index Detection
An LED and photo-transistor are mounted in the drive to detect the Index hole in
the disk each time the hole passes the detector. The LED is mounted on the
spindle motor circuit board and the photo-transistor is mounted on the sensor block
assembly.
TS-021-013087 ••• 01 3-3