Note: Descriptions are shown in the official language in which they were submitted.
--`` 21~937~
-2- ~
. .
Summary of the Invention:
The above-discussed and other problems and
deficiencies of the prior art are overcome or
alleviated by the high capacity, high speed memory
, 5 system of the present invention. In accordance with
i; the present invention the system comprises a disk drive
3 cartridge and an electronics unit. The disk drive
cartridge comprises five magnetic hard disks having 300
megabytes of usable capacity housed in a hermetically -~
sealed, self-contained unit suitable for use in extreme
environments of vibration, shock and temperature. The
~ electronics unit comprises a metal structure wherein
I the electronics for the system are housed.
The disk drive cartridge has a stationary spindle
to which a motor stator assembly is attached. A motor
1 rotor assembly is constituted by a rotary hub mounted
t around the stator, the hub having a motor magnet
-~ mounted therein. Upper and lower bearing assemblies ~-~
are positioned between the stator and the rotor. This
assembly is preloaded by a pair of canted springs which
are disposed about the spindle and bear against the ~
' floating race of the upper bearing assembly. - ~i
Preloading the assembly in this manner avoids abrupt
contact between the bearing and the spindle shaft ;~
j 25 during vibrations. These abrupt contacts have been -
;i found to generate head position errors during
`~ vibration. These head position errors are outside the
bandwidth of typical prior art closed loop servos. -
~owever, due to the increased capacity of the present
`J 30 invention a higher bandwidth is utilized. Accordingly,
`1 the canted springs of the present invention prohibit
, the abrupt contacts, thereby eliminating the head
`! errors that would otherwise result.
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21~937~
-3-
The disk drive cartridge also includes a
temperature sensor mounted on a circuit board of the
spindle assembly. The temperature sensor measures
internal temperature of the disk drive cartridge. This
temperature information is used to modify a seek
1 algorithm. More specifically, to modify drive current
J levels to the voice coil (since voice coil resistance
changes with temperature), to modify head load/unload
operation, to modify temperature drift for readings of
1 10 Hall effect devices, and to better account for flex
bias of capton flex circuits.
The disk drive cartridge further includes a head
loading sensor assembly. A magnetic flux sensor is
i disposed on a circuit board which extends over a ~ -
portion of an arm assembly. The arm assembly has a
permanent magnet therein position to pass under the
magnetic flux sensor (e.g., a Hall effect sensor).
Accordingly, as the arm assembly moves the magnetic
flux from the permanent magnet detected by the flux
~; 20 sensor will vary. This has been determined to be a
~t generally linear relationship. Therefore, the positionof the arm assembly (more particularly, the permanent
magnet in the arm assembly) is tracked by the flux
sensor. Further, the arm assembly as does prior art
arm assemblies has a park or stop position. However,
unlike the prior art arm assemblies, the arm assembly
of the present invention is completely moved away
(fully retracted) from the disk in its park position.
In this fully retracted position the heads and disk are
immune to induced shock and vibration.
The electronics unit has a novel peak detection
circuit. In the rrior art individual peak detectors
were used to recover each servo burst (for head
positioning, i.e., track location and center). The use
of a single peak detector, as in the present invention,
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2~0937~
.:,
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j requires high speed operation. With a single circuit,
I temperature induced variations are consistent for each
servo. The circuit comprises a precision rectifier for
rectifying a servo burst. The rectified signal is then
integrated by an integrator. The integrated signal -
~` passes through a multiplexer and is converted to an
eight bit word by a high speed A/D converter.
The above-discussed and other features and
, advantages of the present invention will be appreciated
;1 10 and understood by those skilled in the art from the
following detailed description and drawings.
~' Brief Description of the Drawin~s~
l Referring now to the drawings wherein like
sl elements are numbered alike in the several FIGURES:
j 15 FIGURE l is a perspective view of a disk drive -~
cartridge and associated electronics unit in accordance
with the present invention;
FIGURE 2 is a block diagram illustrating
~, interconnection of the disk drive cartridge and the -
electronics unit of FIGURE l;
FIGURE 3 is an exploded perspective view of the ;
disk drive cartridge of FIGURE l with the cover removed; ~ -~
FIGURE 4A is a top view of the disk drive
. cartridge of FIGURE l with the cover removed;
`i 25 FIGURE 4B is a side elevational view partly cut -~
l away of the disk drive cartridge of FIGURE l;
;'t ` FIGURE 4C is a rear elevational view partly cut
: .~ . .
away of the disk drive cartridge of FIGURE l;
, FIGURE 4D is a view taken along the line 4D-4D
`~ 30 with the arm and sensor removed for clarity;
, FIGURE 4E is a top diagramatic view of flexible
circuitry used in the disk drive cartridge of FIGURE l; ~-
`-~ FIGURE 5 is a side elevational view partially in
~-, cross-section of the spindle motor assembly used in the
35 disk drive of FIGURE l;
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FIGURES 6A-B are views of a canted spring used in
the spindle motor assembly of FIGURE 5 wherein, FIGURE
6Ais a top view thereof and FIGURE 6BiS a
~ cross-sectional view taken along the line 6B-6B in
::~ 5 FIGURE 6A; -
FIGURES 7A-B are views of a circuit board assembly .
~:~ used in the spindle assembly of the disk drive ~ :
cartridge of FIGURE 1 wherein, FIGURE 7AiS a top view
thereof and FIGURE 7Bis a cross-sectional view taken
along the line 7B-7B in FIGURE 7A; :
~ FIGURE 8 is a block diagram of the spindle servo
~ circuit used in the electronics unit of FIGURE l; :
~i FIGURES 9A-B are views of the arm assembly used in
:~ the disk drive cartridge of FIGURE l wherein, FIGURE 9A .
is a top view thereof and FIGURE 9BiS a side
elevational view thereof;
dl FIGURES lOA-B are views of the magnet assembly in :
the arm assembly of FIGURES 9A-B wherein, FIGURE lOAis
a top view thereof and FIGURE lOBis an elevatlonal
view thereof;
FIGURES llA-D are views of the sensor assembly
.1 used in the disk drive cartridge of FIGURE 1 wherein,
FIGURE llAiS a bottom view thereof, FIGURE llBis an
end view thereof, FIGURE llC is a top view thereof and
FIGURE llD is a view taken along the line llD-llD in
FIGURE llA;
FIGuRE 12 is a block diagram of a closed loop
3 system used by the electronics unit of FIGURE l;
!~ FIGURE 13 is a block diagram of the circuitry of
the electronics unit of FIGURE l;
FIGURE 14 is a diagram of embedded servo bust
information used for track centering and location in
;;~
accordance with the present invention;
FIGURE 15 is a timing diagram for the embedded
servo burst information of FIGURE 14;
'
21~937~
,
:`
FIGU~ES 16A-C are a schematic diagram of the servo
recovery circuit in accordance with the present
invention; and
FIGURE 17 is a top level structure chart of the
` 5 software in accordance with the present invention.
Description of the Preferred Embodiment:
Referring to FIGURES 1 and 2, a disk memory system
is shown generally at 50. Disk memory system is a high
capacity, high speed memory system which is designed to
operate in severe environments (e.g., a military `~
aircraft). Disk memory system 50 comprise a disk drive ` ~
cartridge 52 and an electronics unit 54. Disk drive `
cartridge 52 comprises five magnetic hard disks
providing 300 megabytes of usable capacity. The disks -~
utilize Winchester disk technology and are housed in a
~-i hermetically sealed, self-contained unit which is `~--
configured as a plug-in module. Accordingly, disk ~ -
drive cartridge 52 is fully interchangeable and capable
~ of rough handling, transportation and operation in -
;~ 20 extreme environments of vibration, shock and -
d~! temperature.
Disk drive cartridge 52 comprises a housing 58 -
which has a main housing section 60 with a removable
~ cover plate 62 which is fastened to main housing
;vl 25 section 60 with a plurality of screw fasteners 64. `
Housing section 60 and cover plate 62 are of metal,
` preferably aluminum. A front cover 66 has a release
latch mechanism 68 for locking the housing into or
~! :: -:
-~ releasing it from a vibration cradle (not shown)
, 30 equipped with shock mounts in which the unit would be
~ mounted. Housing section 60 has a mounting slot 70
i~ along the length of its two opposite sides, and these
grooves mate with corresponding runners or guides in
the cradle. To insure that the unit is properly -~
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3 ~ ~
-7-
mounted in the cradle (and to insure proper alignment
with electrical connectors on the back end of the
unit), the grooves are offset on the two sides of the
unit (as are the mating guides in the cradle). Since
i, 5 the grooves and mating guides are asymmetric, the unit
il can only be mounted in one position (i.e., the proper
one) in the cradle.
, Electronics unit 54 comprises a sealed metal
structure 72 wherein the electronics for the system are
housed. Structure 72 comprises a main housing section
74 with a removable cover plate 76 which is fastened to
housing section 74 with a plurality of screw fasteners
73. Housing section 74 and cover plate 76 are of
metal, preferably aluminum. A plurality of connectors
78 are mounted at a front end of housing section 74 to
provide a means for interfacing electronics unit 54
with disk drive cartridge 52, a host computer~85
(FIGURE 2) and a power source. Electronics unit 54
also includes an elapsed time indicator 75, a bit
initiate switch 77 and bit indicator 79.
Disk drive cartridge 52 is interconnected with
electronics unit 54, m~re particularly disk drive
,; control electronics 80, by signal lines 82 (i.e.,
cables). Disk drive control electronics 80
communicates with interface electronics 84 (described
hereinafter) within electronics unit 54 by signal lines
86. Electronics unit 54, more particularly interface
electronics 84, communicates with host computer 85 via
a small computer system interface (SCSI) bus 88 (i.e.,
cables).
Referring to FIGURES 3 and 4A-E, disk drive
cartridge 52 includes a spindle assembly 90 (described
. hereinafter). Spindle assembly 90 includes a circuit
! board 96 at its lower end. An actuator plate 100 is
mounted within housing section 60 adjacent spindle
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1 `-` 2iO9370
-8-
assembly 90. An arrn pivot shaft 102 extends upwardly
from actuator plate 100. A field assembly 104 having a
head loading assembly 106 mounted thereon is mounted on
actuator plate 100. Field assembly comprises a core
104a, an upper field 104b and a lower field 104c. A
pair of adjustable arm stroke limiters 108 are mounted -
- at opposing ends of field assembly 104 by fasteners 109.
A first bearing assembly 110 is disposed on shaft
102 and is supported by plate 100. An arm assembly 111
comprises a center arm 112 having upper and lower arms d
, 116 attached thereto by fasteners 117. Arm
assembly lll is disposed on shaft 102 and is supported`
by bearing 110 to allow the arm assembly 111 to rotate
relative to shaft 102. Center arm assembly 112
, 15 includes a housing portion 118 wherein a voice coil
;l unit 120 is housed. Voice coil 120 includes a central
f opening 120a wherein motor core 104a is disposed. The ;
! current through voice coil unit 120 in cooperation withfield assembly 104 drives the arm assembly in a linear
il 20 fashion. A landing zone flag 117 and landed position
flag 119 are mounted to housing 118. Flags 117 and 119
`,1 ::.: .:
are detected by an optical assembly 115. Each arm 112,
~' 114, 116 includes a plurality of flextures 121.
Flextures 121 have a raised or button feature 122 on at
; 25 least one surface thereof and a head assembly 124
disposed at one end thereof. A second bearing assembly
126 is disposed on shaft 102 above the arm assembly.
Nut and preload washers 128 are secured to shaft 102 to
- retain and provide a preloading force on the arm
~ 30 assembly. A clock plate 130, preferably comprised of ~;
`-' metal, is secured to housing section 60, spindle
; assembly 90 and shaft 102 by a plurality of screw ~ m
fasteners 132.
A landing pad and ramp bracket 13~ is mounted to
,~ 35 actuato_ plate 100. A landing pad and ramp sllde 136
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~09370
,, 9
I
~, is mounted to bracket 134 by fasteners 137. Landing
`~ pad and ramp slide 136 includes a plurality of landing
ramps 138 and landing pads 142. Landing ramps 138
include recesses 140 which are configured to accept
buttons 122 on flextures 120. ~
A voice coil flex circuit 144 is secured to a flex
mounting bracket 146 by a pair of fasteners 148.
Bracket 146 is mounted to plate 100 by fasteners 150.
Circuit 144 provides connection to voice coil 120.
;;~ 10 A hybrid circuit board 152 is mounted on a
mounting bracket 154 which is secured to the inside
surface of housing section 60. A head flex circuit 15
~1 is connected to board 152 and is retained by a flex
retainer 154 attached to board 152 by fasteners 156.
Circuit 151 is connected at the other end to the arm
!~ assembly. Fasteners 156 also secure one end of board
~ 152 to bracket 154. The other end of board 152 is
,~i secured to bracket 154 by fasteners 158. Flex circuit
151 includes a stiffener 160. Another flex circuit 162
provides connection between board 152 and a connector
164 through a rear end of housing section 60. A
spindle motor flex circuit assembly 166 provides
connection between board 96 and connector 164.
Spindle assembly 90 comprises a plurality of
magnetic recording disk 168 (e.g., five disk) disposed
about a spindle motor assembly 170. Disk 168 are
spaced apart by a plurality of disk spacers 172. Disk
168 and spacers 172 are retained on assembly 170 by a
disk retainer 174.
Spindle motor assembly 170 spins the disks 168 in
a precise rotary path so that the magnetic tracks on
the disks remain in an established concentric location
through the operating environment of extreme
'f temperature and vibration. This degree of accuracy
ultimately limits the minimum track width that can be
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9 3 ~ 0
-10-
.
used and the related maximum tracks per inch which is
directly related to data capacity (described ~ ~
hereinafter). ~ -
Prior art commercial disk drives are susceptible
~ 5 to vibration and temperature. For example, during
j exposure to low levels of vibration, the disk platters
begin to wobble as the spindle bearings are overloaded
by g forces and, in some instances, the shaft itself
can bend and contribute to this effect. Displacements
as small as 300 minches will cause track -~
mispositioning and data errors. Further, when exposed ~-
to the temperature range of -55C to +71C, severe `
track mispositioning occurs due to both the design of
the disk clamp and the disk media itself. In the case
of the disk clamp, a mismatch of temperature
coefficients resulting from a steel spindle shaft
" (required for the bearing load) and an aluminum platter
~ causes the platter to expand and contract around one of`~ the clamp~fastening screws, rather than the center lineof the spindle. This causes a 'one time around' wobble
of the platter resulting in track mispositioning and
l data errors. Also, a second temperature induced effect
`l is caused by the non-uniform coefficient of thermal
expansion around the circumference of the platter.
.d, 25 This lack of concentric expansion and contraction over
temperature of anisotropy also caused track
t mispositioning and data errors. The spindle assembly
~ 90 of the present invention has resolved these
; vibration problems.
Referring now to FIGURE 5, spindle motor assembly
l 170 comprises a hub 176 with a shaft 178 at about the ;
-t center thereof. Shaft 178 (preferably a steel shaft)
t is mounted on a support plate 180. Spindle shaft 178
is attached to support plate 180 by screw threads 182,
and spindle shaft 178 has a hollow interior defining a
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.
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; central passageway 185. Support plate 180 is, in turn,
fastened to the bottom of outer case 60 by a plurality
of screws (not shown). The upper end of spindle shaft
178 is held by plate 130 via screw 132' (FIGURE 4B?.
Thus, both the upper and lower ends of spindle shaft
178 are rigidly held.
An annular motor winding 184, which forms the
stator of an electric motor is mounted on shaft 178 via
upper and lower sleeves 186, 188. Sleeves 186 and 188
are secured about shaft 178. Sleeve 186 is secured to
shaft 178 by a locking bar 189 and set screw 190. A
washer 191 sits on a shoulder 192 of shaft 178. Washer
191 and shoulder 192 support sleeve 188 and stop it
from downward movement along the axis of spindle shaft
178.
3, The rotor structure of the motor has an annular
magnet 194 which is adhesively bonded to a steel sleeve
196 which, in turn, is locked to rotary outer steel hub
176. An annular cap 198 is fit within the inside
diameter of hub 176 at the upper end thereof.
Magnet 194, sleeve 196, hub 176 and cap 198
constitute a rotor structure which rotates around the
stator structure mounted on the spindle shaft 178, so
this rotor structure must be mounted on bearings.
According, the rotor structure is mounted on lower and
upper bearings 200 and 202. The inner race of lower
bearing 200 is trapped and locked against rotation
between a shoulder 204 on spindle shaft 178 and a ~-~
shoulder 206 on base plate 180. A radially inwardly
extending flange 208 from hub 176 engages the rotating
outer race of bearing 200.
The floating inner race 209 of upper bearing 202
is held at spindle shaft 178 by a pair of canted -~
springs 210 which are disposed within a recess or -~
groove 211 about shaft 178. Canted springs 210 are
. . :
21~370
-12-
. .
preferably comprised of 302 stainless steel wire per
ASTM-A580. Canted springs 210 eliminate abrupt metal
to metal contact (due to external vibration/shock
environments) between race 209 of bearing 202 and
5 spindle shaft 178. The abrupt contact generates head
position errors which are outside the bandwidth of
typical closed loop servos ~e.g., a normal bandwidth
for a closed loop servo is 250 Hz). However, the
present invention has track densities of about 2075 -~-~
10 tracks per inch with center spacing of about 476
minches. This is a much higher capacity than taught
by the prior art (e.g., about 875 tracks per inch).
The abrupt contact does cause head errors within the
j bandwidth of the closed loop servo of the present -1
15 invention. Accordingly, the canted springs 210 avoid
the abrupt contact and, therefore, eliminate head
position errors caused by such contact. The canted
springs 210 are an important feature of the present
' invention, since they provide a high axial and radial
20 stiffness in the spindle motor assembly which, in turn,
provides high vibration/shock/temperature resistant
performance. The canted springs 210 also provide -~
adequate axial movement allowing for bearing preload.
~'~ This movement is required for a constant bearing -
preload to be applied as materials expand and contract
with temperature variations. One of ~e two identical
~, canted springs 210 is shown in FIGURES 6A-B. Spring
` 210 comprises a plurality of continuous coils 212
', configured to form a ring shape having an inner
diameter for engaging the recessed portion of shaft
178. The inner race 209 of bearing 202 is also held by
a washer 213.
~`j Washer Z13 is held in place by a spring washer
214, a washer 215 and a nut 216 which is threaded onto
the top of spindle shaft 178. The rotary outer race of
.
~ :
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-!
-`~ 21~937~
~ -13-.
bearing 202 engages a radially inwardly projecting
j flange 218 on cap 198. Thus, the rotor structure of
?j magnet 194, sleeve 196, hub 176 and cap 198 are
supported for rotation by bearings 200 and 202.
A preload force also is imposed on bearings 202 by
, nut 216 acting through washer 210, spring washer 214
and washer 213 to impose a lead on the inner race
which, in turn, is transferred through to the balls of
, bearing 202 to load the outer race against the flange
218 on cap 198. The preload is also imposed on bearing
200 by being transmitted from cap 198 through sleeve
~1 196 and outer hub 176 to load the outer race of bearing
,'2~ ' 200, and thence through the balls of bearing 200 to
react against plate 180. The preload operates to
maintain contact throughout the bearing pack to reduce
the effects of shock load and vibration.
Wires 220 from the windings of stator 184 pass
into central passage 185 in spindle shaft 178 through a
pair of opposed openings 222 in spindle shaft 178. The
wires 220 pass through a passage 224 in plate 180 and
,2~ are connected to printed circuit board 96. Board 96 is
,~ spaced from and attached to plate 180 by a plurality of
spacers 226 and screws 228 which thread into plate
180. Current is delivered through wires 220 to the
windings of stator 184 to drive the rotor and discs 168
3 Referring to FIGURES 7A-B, spindle motor circuit
board 96 includes a plurality of Hall effect circuits
230, 232 and 234, each comprising a Hall effect sensor
236, resistors 238, 240 and a concentrator 241.
Circuit 234 also includes a capacitor 242. Sensors 236
and capacitor 242 are secured to board 96 by a suitable
adhesive. Circuit board 96 is generally round and has
an outside diameter about the same as disks 168. Board
96 also has an opening 244 at about the cènter thereof
where shaft 178 passes. Hall effect sensors 236 are
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2~L093~f 0
-14-
used to provide rotating magnet position information
' which is fed into a spindle servo circuit 245 (FIGURE
8). The disk spindle rotation speed is controlled by
the closed-loop velocity servo circuit 245 and the
motor (described hereinbefore). A phase-locked loop
` 246 on the spindle servo circuit uses the Hall signals
to lock the spindle speed. The spindle servo circuit
245 includes a predriver 247 which regulates the amount
, of drive current set regardless of temperature induced
gain variations. This results in predictable and
repeatable spindle start times throughout the operating
~', temperature extremes. ;
A temperature sensor 247 is mounted on circuit
board 96. A mounting pad 248 is disposed between
sensor 247 and board 96. Temperature sensor 246 is an
; important feature of the present invention. The output
`1 of temperature sensor 247 is used to modify the seek
-} algorithm. More specifically; drive current levels to
the voice coil 120 are adjusted for temperature
variations (since voice coil resistance changes with
` temperature), to adjust head load/unload operation, to
,,~ modify temperature drift for readings of Hall effect
devices, and to better account for flex bias of capton ~-~
`1, flex circuits.
The output of temperature sensor 247 is used to
modify servo parameters during head load/unload and
seeking operations. The output of temperature sensor
247 is converted by an A/D converter 456 (FIGURE 13
`! described hereinafter in conjunction with the novel
peak detection circuitry) which is controlled by the
,? drive controller 350. The corresponding temperature
dependent servo parameters are stored in a ROM lookup
`l :
~ table. The following servo parameters are temperature
,~ dependent for head load/unload operation~
-..
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`7
.! --15--
) Hall effect position sensor gain; and
, (2) driving current necessary to drive the
l actuator arm in an open loop fashion at a constant
acceleration.
The following servo parameters are temperature
dependent for seeking operation:
(l) flexible head cable compliance; and
(2) driving current necessary to accelerate
actuator arm at constant acceleration.
Typical commercial disk drives are susceptible to
what is commonly known as 'head crashes' when exposed
to vibration. The flying head is supported by an air `
bearing which is stable and stiff enough tojresist
contact with the disk surface due to the exponential
, 15 nature of the air bearing force vs. displacement
curve. It has been determined that head crashes and
media,damage generally occur when the disk drives are ~;
exposed to vibration during the following operations.
Rapidly positioning the head laterally track to track
which tends to tilt or roll the head causing the air ` ~;
bearing to become unstable, particularly under
vibration. By optimizing the head flexure attachment --
point to the center of gravity of the head the tendency
to tilt or roll the head under rapid positioning is
eliminated, whereby air bearing stability is increased
and tolerance to operating vibration is improved.
Crashes also occur when the disk is spinning up or
down, whereby the head air bearing is weakened and, ;~
under vibration, the head may come into contact with ~i
the disk. Also when the disk is stopped, the head will
rest on the disk surface. Normally, during spin down,
most commercial disks allow the head to come in contact
with the disk surface until the disk is spun up again
and the air bearing re-established. This condition is
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-- 2109370
-16-
not suitable in a military type product which is
' subject to operational shock, vibration and rough
handling.
Accordingly, at the first onset of spin down, the
head must be removed away from the disk surface. The
arm assembly 111 of the present invention provides for
; the heads to be completely removed away from the disk.
Referring to FIGURES 9A-B, the actuator arm
~- assembly is shown generally at 111. Arm assembly
il 10 comprises center arm assembly 112, upper arm 114 and
lower arm 116. Center arm assembly includes housing
portion 118. Arm assembly 111 is dynamically balanced`
around its pivot axis so that inputs of shock,
vibration and load factors to the cartridge do not
induce torsional effects in the arm. This results in
the head staying on track during high acceleration
input disturbances. Housing 118 has a cylindrical
opening 250 therethrough having a diameter sufficient
~, for accepting bearings 110 and 126. Housing 118 also
` 20 has opposing pairs of rectangular opening 252, 254 ;
which define a cavity within housing 118 whereln voice
q coil 120 is mounted. Housing 118 further includes yet
another opening 256 wherein a magnet assembly 258 is
mounted by fasteners 260 to housing 118. Also,
J 25 referring to FIGURES lOA-B magnet assembly 258
comprises a block assembly 262 having an accurate front
`~ surface 264, opposing side surfaces 266, 268, a rear
surface 270 including extensions 272 at each side 266,
~`l 268 and opposing top and bottom surfaces 274, 276. A
, 30 mounting hole 278 is provided at each extension 272. ~;~
'-~ Fasteners 260 pass through mounting holes 278. Surface
274 includes a platform 280 having a channel or slot
282 therein. A permanent magnet 284 is secured in
channel 282 by a suitable adhesive. Magnet 284
includes opposing accurate front and rear surfaces 286,
., . ,.
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'' ''` 2109370
1 -17-
,.; ,
287, side surfaces 288, 290, and top and bottom
`I surfaces 292, 294. Magnet 284 has a north pole 296,
;j designated (N), at end 288 and an opposing south pole
298, designated (S), at end 290.
Referring to FIGURES 4A and llA-D, head loading
sensor assembly is shown at 106. Assembly 106
,, comprises a printed wiring board 300 having opposing
~ bottom and top surfaces 302 and 304. A magnetic flux
,`~ sensor 306 (i.e., a Hall effect sensor) having leads
10 308 is mounted at surface 302 by a suitable adhesive.
Sensor 306 is positioned over a Hall effect
concentrator 310 disposed within an opening 312 throug~
board 300. A plurality of contact pins 314 extend
through board 300. Pins 314 provide connection means i~
15 with spindle motor flex circuit assembly 166. ~;
Resistors 316, 318 and a capacitor 320 are mounted at
surface 304 of board 300. Sensor 306 is preferably a
Hall effect type magnetic flux sensor having a ceramic
substrate with a hermetically sealed element. Sensor ~ --
20 306 senses magnetic flux from magnet 284 in the
actuator arm assembly 111. Assembly 111 is shown in
the parked or fully retracted position in FIGURE 4A,
whereby buttons 122 on flextures 121 are disposed
within recesses 140 of landing ramps 138 with heads 124
25 disposed between corresponding landing pads 142. In
this position the heads and disks are immune to induced
shock and vibration. This fully retracted position of
the arm/head assembly is an important feature of the
present invention. In this fully retracted position - -
30 the magnetic flux from magnet 284 sensed by sensor 306 ~-
is greatest. As the arm assembly 111 is rotated to
position heads 124 over corresponding disks 168, magnet -~
284 will move away from sensor 306 reducing the
magnetic flux ~rom magnet 284 sensed by sènsor 306. It
35 has been determined that the;output of sensor ~06
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2109370
-18- ~-
. , .
relates to arm assembly lll position (i.e., head
position) in a linear manner. Accordingly, sensor 306
~` senses magnetic flux from magnet 284 to determine head
:' position.
Also, automatic head retraction is accomplished in
both the normal and abnormal operating situations. For
normal operation, the heads are retracted off the media
whenever the spindle is turned off. Retraction is
accomplished in less than lO0 m seconds so it does not
add appreciable time to an orderly shutdown. The
abnormal operations occur when the primary system power
~`~ is lost or when the operator inadvertently removes the
~I cartridge while the spindle is still spinning. In
i'l response to a primary power failure which would cause -
~ 15 the disk to stop rotating, electronics senses power ~ ~
i¦ failure and utilizes the back EMF of the spinning -
1 spindle motor to generate the power required for
retracting the heads off the disk and onto the resting
pads. Thus the energy in the rotating inertia of the
motor and disk assembly is converted to retraction -~
' motion unloading the heads, and protecting both them
and the media from exposure to shock and vibration.
The second abnormal sequence occurs if the operator ~`~
removes the cartridge while the spindle is spinning.
In this case a sensor in the cartridge handle senses
that the handle release has been activated. The
electronics respond to this signal by rapidly -~
retracting the heads to the resting pad. Here again,
this is accomplished in less than lO0 m seconds, which
is before the cartridge has disengaged the connector.
The use of magnetic flux sensor 308 and magnet 284 -~
as a position sensor is an important feature of the
present invention. This position information can be
used to correct position errors.
:
`'; 2109370
~ --1 9--
.
~ Referring to FIGURE 12, an example of such a
`~! closed-loop system is shown generally at 322. A ~ :
~!l , commanded positio~ signal is presented on a line 324 to
a summing junction 326. The output of junction 326 on
~ 5 a line 328 is a position error and is utilized by
',! actuator arm dynamics 330 to position the heads. The
3 position of the heads is sensed by a position sensor
(i.e., sensor 308 and magnet 284~ at 332. A signal
indicative of head position is presented on a line 334
~ 10 to junction 326. The actuator arm position 322
`~ determined by the Hall effect sensor 332 (e.g. sensor
306) is fed back at 334 and subtracted from the
commanded position at 324 to provide the position error
signal at line 328.
Referring to FIGURE 13, controller interface
electronics 84 comprises an I/O controller 336, e.g.,
an Intel 80C186 microprocessor (operating at 12.5 MHz)
as the main control element. The Intel 80C186 is a ;
, highly integrated 16 bit microprocessor with chip
select logic, two channel DMA controllers, three timers -~
and an interrupt controller contained on-board. A ~ -
control program is stored in memory 338 of electronics
84, e.g., a 64K x 16 bit EPROM or E PROM. There are
also two 32K x 8 static RAMs (SRAM) 340 for scratch pad
and variable storage. Further, twelve discrete system
input signals and sixteen discrete output signals are
used for various functions from control of the ready
light, to I/O controller, to drive controller
i~ communications. A combination I/O an disk data
controller 342 (e.g. an 8496 from National
Semiconductor3 is in electronics 84. The I/O section
344 of this device is implemented as a state machine
sequencer that receives commands from the processor.
These commands execute various functions such as data
in phase and status phase. When an operation is
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complete an interrupt to the I/O controller is
activated. Various control status registers are used
to store error status conditions. The disk data
controller 346 section is also a state machine
sequencer that executes commands issued by the I/O
controller. The commands control the reading and
writing to the disk. Again, various control, status
and error registers give the ability to correct errors
or determine if a retry is necessary. The combination
i 10 I/O and disk data controller utilizes its own dedicated`~ data buffer which consists of two high speed 32K x 8
SRAMs. Three disk channels into the data buffer are `
, controlled by the I/O and disk data controller. The
l three channels are I/O, disk and processor. The disk
,i 15 channel has the highest priority and the processor
channel the lowest. This scheme allows for concurrent
`', data transfer between the I/O and disk interfaces.
Thirty-one analog voltage channels monitor various
system functions for self test. An eight bit A/D 348
i~ 20 measures these channels and the BIT software determines
if there is a fault in the system.
Disk drive cartridge 52 utilizes both a dedicated ~ ;
surface and embedded servo system. This means that one
of the five media platters is totally dedicated to
track servo information. Servo information is also
embedded on all other surfaces at the beginning of
every sector on every track. This servo system
provides the best combination of coarse and fine
positioning necessary for high speed operations in
extreme environments.
Disk drive circuitry 80 implements the critical
s drive level functions necessary for high speed disk
drive operations. Disk drive circuitry provides
~; read/write head positioning (control of the rotary
actuator motor, i.e., movement of voice coil 120 in
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~3 field assembly 104), read/write head selection, spindle
~ motor start/stop, BIT functions, and power interruption
i~ and transient recovery control.
~¦ A drive controller 350 is the main controlling
element of the disk drive circuitry 80. The drive
controller utilizes a high speed digital signal
.~ processor (e.g., Texas Instruments TMS 320C30
state-of-the-art 32 bit digital signal processor) to
control the position of the heads through the
10 implementation of a closed-loop digital control
`!.~ algorithm.
The disk drive control scheme utilizes a
complimentary system of dedicated and embedded servo
information to insure optimum control of read/write
15 head position during track seek, read and write
operations. -
Track acquisition is accomplished via closed loop ~ ~
control 352 of the rotary actuator. Coarse position ~ -
information is written on a dedicated surface (i.e.,
;,~ 20 one surface of one of the five disks 168) and is
comprised of alternating tracks 0.70 MHz and 1.00 MHz
signals. The mid point between each of these tracks
defines the center of each cylinder and consequently
the data tracks located on the remaining disk
~; ~ 25 surfaces. When a seek command is received, the drive
; controller utilizes the coarse position information to
control head actuator acceleration and velocity during
' the seek operation.
Once track acquisition is complete, the embedded
30 servg 354 information on the acquired track is utilized
to perform track centering and following. Referring to
FIGURES 14 and 15 a novel peak detector (described
hereinafter) is utilized to recover amplitude
``3 information for each of four servo bursts, designated
~`~ 35 A, B, C, D respectively. This information is processed
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, by the drive controller 350 to determine exact head
position and the amount of current to apply to the
rotary actuator (i.e., voice coil 120) to correct and
maintain head position.
~' 5 Tracks Al, Bl, A2, B2, A3 and B3 are
shown in FIGURE 14. The embedded servo information is
designated A, B, C and D respectively. The amplitude
i peak information indicated at 356 is detected by the
-1 novel peak detector circuitry described hereinafter.
This servo information is a quad burst of time
~, displaced pulses (e.g., a burst may compromise a 2.5
~ MHz sine wave for 4 m sec.). The heads can be `
"!, maintained on track centers by e~ualizing, the
¦ amplitude between overlapping servo burst. For
example, burst 358 designated A and burst 360
designated B overlap track center line 362 of track
Al. Line 362 corresponds to equal amplitudes for
both A and B as designated by VA and VB (i.e.,
VA=VB). Accordingly, the heads can be maintained
on track center by adjusting head position so that
amplitudes between overlapping servo bust are equal
(e.g., VA = VB). The quad burst provides for
linear track-to-track ~ositioning with a tolerance of
+/- one track. Also, these embedded servo burst are
used for track to track positioning and fine
positioning, as described hereinbefore.
; Each sector (0-54, FIGURE 15) includes a data
~ segment 364 which is preceded by the embedded servo
; burst A, B, C and D. The timing sequence for the
embedded servo/sector is provided in FIGURE 15. This
includes timing or the following operations: zero;
dedicated surface index; sector mark detection window;
.~ read signal, data head; sector mark detected;
multiplexers Ao, Al, and A2; servos CS, WR, INT
and RD; and embedded servo reset.
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21~937Q
i -23-
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A rotary actuator drive circuit 365 comprises a
twelve bit D to A converter 366 and an amplifier 368.
The actuator drive 365 receives positioning data from
the drive controller 350 which is converted to analog
voltage for the rotary actuator motor drive. Velocity
profiles and rotary actuator drive currents are kept
constant regardless of variation in resistance to
provide optimum performance throughout the severe
il environments.
~ 10 The drive controller 350 is supported by a drive -~
`~ controller memory which utilizes both RAM 370 and PROM
372. The RAM 370 is a 64 Kbit CMOS static RAM `
;1~ organized as 2K x 32 and is on-board the drive
controller. It is used to temporarily store and
~l 15 manipulate program data elements. The PROM 372 is a l
,l Mbit CMOS EPROM organized as 32K x 32 which stores the
drive controller operating program.
The drive controller 350 communicates with the
disk data processor through a parallel communications
port. Input/output ports for discrete signals are also
provided. The discrete signals come from other parts
of the disk electronics 80 and cartridge 52 and include
~, "heads retracted", "handle closed", communication port
; flag, A/D converter status and power status. Output
; 25 signals are also incorporated and include spindle motor
enable, rotary actuator enable, head selection, A/D and
D/A converters.
The closed-loop spindle control circuit 374,
l described hereinbefore utilizes a Hall signal feedback
376 to control spindle speed.
Read/Write analog signal processing circuitry 378
~il provides the high density encoding/decoding for disk
~'; data read~write operations. The data is encoded ~rom
i NRZ and clock to run length limited by an encoder 380.
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During the write process, NRZ formatted data and
clocking information is encoded and supplied to the
write drivers. During the read operation, encoded data
~ stored on the disk is recovered by analog amplification
`I 5 and detection with subsequent clock recovery and
' decoding via a data synchronizer, phase lock loop (PLL)
381 and a run length limited (RLL) to NRZ decoder 382.
The first stage of the analog circuitry includes
an automatic gain control amplifier, which maintains a -
constant signal amplitude at the output of a Bessel
filter in the read string. The Bessel filter band
limits the read signal supplied to the equalizer and
~, detector. The equalizer restores critical amplitude
and phase information for detection of the data
transitions by the detector circuitry.
The output of the data detector is supplied to the
phase comparator of the phase-locked loop via a data
, synchronizer. The synchronizer is utilized to insure
fast acquisition of phase lock by running the PLL on a
reference clock when the system is not in the read
mode. The synchronized run length limited data and
phase-locked clock are supplied to a decoder 382 for
` conversion to NRZ data and clock.
Write interlocks and cartridge file protection
capabilities are incorporated into the circuits at 384
;~ to allow for user-selectable protection against loss of
stored information due to an inadvertant overwrite.
~,1; Referring to FIGURES 16 A-C, the novel peak
detection circuit is shown generally at 386. FIGUR~ 16
A-C are a schematic diagram of the track following
servo electronics 354 and the course position servo
.,
352. Accordingly, the schematic also shows a dedicated -
servo detection circuit 388, an index detection circuit
390 and a sector mark detection circuit 392. The peak
detection circuit 386 comprises a precision rectifier
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-- ~109370
25-
;~ 394 having an input on line 396 to an amplifier 398.
Amplifier 398 has a feed back loop comprising resistors
400, 402 and a diode 404. The output of amplifier 398
`l . :
i is connected to a diode 406. A capacitor 410 and an
i~ 5 inductor 412 are also connected to amplifier 398. An
`, output of rectifier 394 is presented on a line 408.
This output is a precision rectified signal of the
,j input signal (i.e., servo burst) presented at line
396. An integrator 414 receives the signal presented
at line 408. This signal is presented through a
3 resistor 416 to an input of an amplifier 418. A
:!1 resistor 420 is connected between ground and the other`
;! input of amplifier 418. A capacitor 422 and an
-~ inductor 424 are also connected to amplifier 418. The
output of amplifier 418 is pre~ented on a line 426.
This output is an integrated signal of the signal input
;, at line 408. ~
~1 An integration dump 428 receives the signal -
, presented at line 426. Dump 428 comprises a pair of
high speed analog switches 430, 432 and a resistor
~ 434. The integrated signal is then presented on a line
', 436 to an amplifier 438 having a feed back resistor
440. The other input of amplifier 438 is connected by
a resistor 442 to ground. The output of amplifier 438
on line 444 is presented to a multiplexer 446.
Capacitors 448 and inductors 450 are also connected to ;
multiplexer 446. A selected input of multiplexer 446
is presented at its output on a line 452. The signal
at line 452 is presented to an amplifier 454. Thf~ -
;i 30 output of amplifier 454 is converted from an analog
, signal to a digital signal (i.e., an eight bit word) by
an A/D converter 456. A voltage regulator 458 provides
, a reference voltage to converter 456. Capacitors 460, -
-~ 462 and resistor 464 are connected to regùlator 458.
Capacitors 466, 468 and inductor 470 are connected to
converter 456.
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This single high speed peak detection circuit 386
, is utilized in conjunction with high speed A/D
, converter 456 to recover the magnetically recorded,
`l
time division multiplexed, spacially displaced servo -
l lj
~1 5 information bursts. This method of recovery is in
`~ contrast to prior art commercial practice where
; individual detectors are utilized for recovery of each
servo burst. The benefit of a single recovery circuit
3 is in operation over extreme temperatures, where
parameter drift of individual circuits would have to be
accounted for. The single recovery circuit parameter
j variations over temperature will be identical for each`
i servo burst, and would therefore cancel any negative
effects.
Referring to FIGURE 17, a top level structure
chart of the software is provided. The software for
the I/O control 336 performs the following functions:
accepts commands from the I/O bus and generates the
required control signals to execute the commands;
controls data flow between the I/O bus and the disk
drive; monitors drive status and reports abnormalities
on the I/O bus; and generates and transmits disk status
on command. The software for drive control 350
controls the following functions: read/write head ~-
-~ 2~ positioning; spindle motor starting and stopping; head
retraction on power loss or cartridge removal;
read/write head selection; power interruption and
3 recovery control for both controllers; built-in-test
functions; and drive status monitoring and reporting to
the I/O controller. The functions performed by the
software are illustrated here by describing the read
operation, the write operation and the Built-In Test
(BIT) function.
A command is received on the I/O bus and is
decoded as a read command by the I/O control. The
',~
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~'~ :~ 2109370
:,`
,
-27-
:
status of~ the drive is checked for cartridge installed
~j and disk spinning. If these conditions are met, the
, command is determined to be valid and the read
;~ operation is started. The address information received
i 5 with the read command is translated into a head and -
~, cylinder number. This information is transmitted in a
~l seek command to the drive control which decodes the
seek command and selects the required head. The drive
, controller 350 then positions the heads on the required
~,, 10 cylinder by driving the rotary actuator. This motion
may involve acceleration and deceleration depending
.ii 5
l upon the number of cylinders the heads must be moved. `
After completion of this open-loop move, the servo
;~ error voltage is read and used to center the heads on
~ 15 the track by means of a closed-loop digital control
`! . algorithm. After the heads are centered a command
complete response is returned to I/O control.
The I/O control loads the disk data controller 346
, registers with the proper information to perform a read
`i 20 operation. This information includes the starting -
~' sector number on the track and the number of sectors to
be read. As part of the read operation, the I/O
, control checks the header information to determine if
;~ the heads were centered over the correct track by the
open-loop move. If the heads are on a:~ incorrect
track, the I/O control calculates the correction ;
'i required to position the heads. The I/O control sends
~`1 another seek command to the drive control to position
the heads correctly. Upon completion of this
operation, a command complete is sent from the drive
control to the I/O control again. Another read
operation is performed by the I/O control. During the ~;`
data transfer from disk to RAM, under the control of ~ i~
the disk data controller 346, error detection is
~i 35 active. If a data error occurs, the disk data
;, controllér 346 supplies syndrome bytes to the I/0
`: , ', ,,. : :
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,
- 210937~ `
-28-
control to enable it to correct the error. The I/O
control performs an 'exclusive or' operation on the
! data with these syndrome bytes to correct the data
error. After a sector of data has been loaded into
ram, the I/O control signals the drive control so that
its disk controller can transfer data from RAM to the
I/O bus. Thus, data transfers occur concurrently from
disk to RAM and RAM to the I/O bus.
~ It should be noted that the drive control cannot
!,' 10 determine actual head position. Upon receipt of a seek
command, it loads a cylinder address register with the
cylinder number and makes an open loop move. If the
I/O control determines an incorrect positioning, it
must send a special command to the drive control, which
repositions the heads without changing the contents of
its cylinder address register. This maintains
synchronization between the two controllers.
In the write operation, the same head positioning ;~
operations are performed as during the read operation. -
Data transfers from the I/O bus to RAM are performed
concurrently with the initial head positioning -
.~ operation.
During the execution of BIT some visual indication
is provided to indicate progress through the test.
Upon entering the test, both BIT indicators are set.
Next the disk drive cartridge ready led is lit to
indicate that both processors are operational. The led
is turned off upon completing the ROM checksum tests
regardless of the result of the tests. Upon completion
of the test, the I/O control processor will clear only
those BIT indicators representing a fully functional
line replaceable unit (LRU).
The system incorporates a BIT capability to
provide failure detection and location functions for
both on~aircraft and off-aircraft levels of
.~
,., .
-
~y ~` 210937~
-29-
1 maintenance. BIT features may be initiated by a
y~ combination of manual, automatic or remote commands;
self-monitoring of normal operating modes is also
included. Fault status indication is provided remotely
sl 5 via the bus or locally via the fault indicators.
A BIT power controller is used to control the BIT
indicators. This controller powers the BIT indicator
drivers directly from the +28V DC input and provides a
; power-up pulse to allow both BIT indicators to be set
upon power-up despite a power supply failure. The
power controller is power sequenced to prevent normal
power-up and power-down routines from generating false
BIT indications.
~, .
`~j Two BIT indicators 79 are provided to give a
visual indication of the functional condition of the
LRU they represent. One indicator represents the
~ electronics unit 54 and the other indicator represents
;, the disk drive cartridge 52. Both indicators are
j magnetically latched so that the last tested functional
condition will remain displayed after powering down. ~1
Once set, the indicators will remain set until the ` -
` indicated LRU successfully passes execution of the BIT ;~
program.
~ The BIT switch 77 is provided to allow manual
;¦ ~ 25 initiation of the BIT routine. This switch only
initiates BIT when the system is not performing a
commanded function.
Wrap functions are provided to test the data path
in expanding loops. These wrap tests loop the data -~
;i 3~ locally at the controller, at the encoder/decoder and ~-
finally at the disk itself.
The system contains the capability to monitor test
points during the BIT routine. Built in test circuits
consisting of an analog to digital converter with a
multiplexed input performs discrete measurement of key
.,
:'
.J
109370
~ -30-
~ ` .
~1 circuit test points located in the read/write data
3 channel, the spindle drive circuitry, the rotary
actuator drive and the power supply. The measured
values are compared to ROM stored values to determine
signal validity.
While preferred embodiments have been shown and
described, various modifications and substitutions may
~i be made thereto without departing from the spirit and
i scope of the invention. Accordingly, it is to be
y 10 understood that the present invention has been
described by way of illustrations and not limitation.
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