Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
'i s v '.3 ~ 4
. ,
D~]~L ~ DISI~ DRIV~
Iackg uncd of_the Invention
The present invention rela-tes to magne-tic storage
systems such as clisk clrive systems as used for digital computers.
Rotatiny maqnetic data storage devices have been used
in computer systems for over 25 years. Rotatable fixed and
removable hard disks having magnetic surfaces have been employed
for the recording and retrieval of data. The disk drives have
a magne-tic read/write head attached -to a movable arm used to
position the head over a selected concen-tric track. More
recent developments have included utilization of removable
flexible disks being comprised of a magnetically coated circular
disk of mylar or other flexible material having a diameter of
approximately 20.3 centime-ters. Devices incorporating these
flexible disks are more compact and have a much lower cost per
lS drive than their predecessors using hard disks. One of the most
recent developments in magnetic storage devices is the develop-
ment of flexible mini-disks, the disks comprising a magnetically
coated circular flexible plastic disk contained within a rigid
envelope having cutouts for accessing the magnetic medium, the
mini-disk having an outside diameter of approximately 13.3
centimeters. While these devices offer a
L~ ~
1~575/LT~ -2-
1 further improvement in co~pactness and reduction in
cost per disk drive, the cost per bit stored remains
relatively high due to the fact that only a single
mini-disk is driven by a mini-disk drive. Furthermore,
the recording density of the mini-disk is restricted
due to the fact that the number of concentric tracks
or track density, is limited. This limitation results
from error inherent in the means utilized in seeking
the selected tracks. Finally, because the mini-disks
are removable, the head-load pressure pad for contacting
the surface of the mini-disk with the magnetic read/write
head must be positioned a considerable distance from
the disk in order to allow the disk to be inserted
and removed without interference. This distance between
the pressure pad and the disk results in significant
delays in head-load time with concomitant increases in
the mean time to seek a selected track. To summarize,
currently available flexible mini-disk drives have inher-
ent limitations in storage capacity and track seeking
speed-
~ ~v9~ ~l
- 3
mm~ry o~ the :Invention
_ _ . _ _ _ _ _ _ _ _ _ _ _
In accordance wit:h the present invention there is
provided a magnetic storage systeln com~)risin(i:
a rotatable member hclving a track with a circular
component disposed about an axis and a translational component
perpendicular to the circular component to define a pitch, the
pitch of the track having alternating rest zones and transition
zones, the pitch of the transition zones gradually decreasing
from the middle to the adjacent rest zones;
means for rotatably driving the member about the axis;
a magnetic head support including means for engaging
the track such that the head support translates parallel to the
translational component as the member rotates;
a magnetic transducer head mounted on the head support;
and
means for transporting a magnetic storage medium past
the head transverse to the translational component, the medium
having a magnetic surface parallel to the translational component,
the magnetic surfaces having data tracks transverse to the trans-
lational component that correspond in position to the rest zones.
The said rotatable member may be a lead screw having agenerally helical track with a circumferential component and an
axial component.
The said driving means may comprise a motor coupled to
the lead screw to rotatably drive the same.
In apparatus having a specified head alignment error when
the motor has a given angular error the circumferential component
of t~ach ramE) iS equal to approY~imately twice the motor angular
crror and the axial component o~ each ramp is approximately equal
to the specifiecl head alignment error. The driving means may
comprise a stepper motor rotating the lead screw incrementally
from one rest position to another and the track engaging means
engayes the ramps when ~he motor is in the rest positions and
enyages the transition zones when the motor is rotating from
one rest position to the other.
A specific embodiment of the invention is magnetic disk
drive apparatus comprising a housing having a disk receiving a
slot, a disk drive spindle disposed in the housing adjacent to
the slot, a clamp to position a disk received by the slot onto
the spindle to lie in a disk plane and first and second elements
disposed in alignment with each other on opposite sides of the
disk plane within the housing. The first element is movable
transverse to the disk plane between a rest position and a
position in the disk plane and the second element is stationary.
At least one of the elements is a magnetic head. The first
element is moved from the rest position to an intermediate position
spaced closer to the disk plane than the rest position, pre-
ferably responsive to engagement of the clamp. Responsive to a
disk access command, the first element is then moved from the
intermediate position to the position in the disk plane to clamp
a disk on the spindle between the first and seoond elements to
2S enable recording or retrieving of magnetically stored information.
Another specific embodiment of the invention is drive
apparatus for two magnetic disks. First and second spindles are
i 1 V '~
-- 5
mounted on a chassis for ,independent ro-tation about aligned
axes. A motor is mounted on the chassis. The motor has an
output shaft rotatable about an axis nonparallel to the spindle
axes. ~ direction changing pulley is ~ounted on the chassis
for rotation about an axis nonparallel to the spindle axis and
an endless belt extends in a path around the output shaft, the
pulley and the first and second spindles so as to rotatably
drive the spindles in opposite directions of rotation.
Another specific embodiment of the invention is drive
apparatus for two magnetic dis]cs in which first and second
spindles are mounted on a chassis for independent rotation about
aligned axes and magnetic transducer heads are cantilevered
outwardly from the ends of a magnetic head transport block
facing toward the spindles to permit the heads to move closer to
the spindle axes than the block. The spindles have large
diameter belt engaging portions adjacent to each other and small
diameter disk engaging portions opposite to each other. The
magnetic head transport block is translatable along the disk
planes in a radial direction relative to the spindle axes in
line with the belt engaging portions. The heads are in line
with the respective disk engaging portion.
1 15~ 14
13575/l,TR -6-
1 Brief Descri~ n of the Draw~s
The features of specific embodiments of the best
mode contemplated of carrying out the invention are
illustrated in ~he drawings, in which:
FIG. 1 is a front elevation view of a dual mini-disk
drive incorporating the principles of the invention;
FIG. LA is a perspective.view of part of the dual
mini-disk dri.ve having the bezel removed;
FIG. 2 is a fragmentary perspective view depicting the
apparatus for rotating the disks in opposite directions:
FIG. 3 is a side elevation view of the dual mini-disk
drive;
FIG. 4 is a side view of a magnetic read/write h~ead
and associated plate in the open position;
FIG. S is a side view of the magnetic read/write
head and associated plate in the closed position;
FIG. 6 i9 a perspective view depicting the magnetic
read/write head loading mechanism of the invention;
FIG. 7 is a plan view on line 7-7 of FIG. 3;
FIG. 8 is a perspective view of the lead screw of a
disk drive incorporating principles of the invention;
FIG. 9 is a detail of the lead screw thread of the
invention; and
FIG. lO is a schematic end view of a portion of
25 the lead screw of the invention.
~ 159~'~4
13575/ITR -7-
1 Detai_ed Description of the Specific Embodiments
The present invention greatly increases the storage
capacity of a flexible disk drive without increasing
its outside dimensions. Furthermore, increases in track
seeki~g speed are also achieved while track seeking
error is reduced and interchangeability of the removable
disks is improved.
According to the invention, a drive apparatus fGr
magnetically coated information storage disks comprising
a chassis having a bezel attached perpendicularly to
one end of the chassis, the bezel having first and
second adjacent disk receiving slots aligned in planes
parallel to the chassis; first and second spindles
attached to either side of the chassis, the rotational
axes of the spindles being substantially perpendicular
to the plane of the chassis; a motor; means for coupling
the motor to the spindles to rotatably drive the spindles
in opposite directions of rotation and means for clamping
disks received by the respective slots to the respective
spindles to rotate such disks in opposite directions.
Interposed between the parallel planes of the disk
receiving slots is a head carriage assembly having a
first magnetic read/write head and a second magnetic
read/write head mounted on the carriage assembly in
a back-to-back relationship to face disks received by
the respective slots; means for intermittently loading
the heads onto the surface of the disks received by
the respective slots for the purpose of reading information
from and writing information onto the received disks.
1 1 ~9 ~ ~4
1 3 5 7 5 /LT i~ - 8 -
1 Beca~se the disks are rotated in opposite direc-
tions, the ~irst disk may be interchanged with the second
disk and vice-versa withou~ a~Eecting the integrity of
the data retrieved from the disk. ~urthermore, by posi-
tioning the magnetic read/write heads between the
adjacent sur~ace~s of the parallel disks, the disk drive
of the invention is rnore compact than drives where the
disks are rotated in the same direction with the magnetic
read/write heads being positioned on alternate surfaces.
Additionally, a single motor located between the
the slots adjacent to the spindles, is utilized to drive
the first and second spindles and the respective disks,
thus a more compact drive is achieved compared to drives
where each spindle has its own motor. The motor output
shaft located at one end of the motor, has an axis
of rotation substantially perpendicular to the axis of
rotation of the spindles. At the other end of the motor
is located a rotatable direction-changing pulley having
an axis of rotation approximately parallel to the axis
of rotation of the motor. An endless belt extends in
a path around the output shaft, the pulley and the first
and second spindles. This method of driving the spindles
permits them to be rotated in opposite directions while
being driven by the same motor.
The addition of the second drive spindle for the
second disk, without increasing the external dimensions
of the drive, doubles the storage capacity of the disk
drive of the present invention when compared to previous
drives employing a single spindle.
;~0
13575/LTR -9-
1 A cylindrical lead screw is employed for reproduci-
bly selecting tracks on the disks. According to the
invention, the lead screw design permits a substantial
increase in storage capacity of the invention by substan-
tially increa~ing the track density of the disks. The
head carriage assembly has a cam follower which rides
in a helical groove on the lead screw. The lead screw
is attached to a stepper motor via a shaft. As the
s~epper motor is incremented about its rotational axis,
the shaft rotates the lead screw thus causing the head
carriage assembly to be repositioned radially with
respect to the plane of the received circular disks.
Angular error which is inherent in this type of
track seeking mechanism is compensated for by the design
of the groove. The helical groove is comprised of
a plurality of ramps of a constant pitch, adjacent ramps
being connected by transition zones. The pitch of the
ramps is dependent upon variable factors including the
maximum ansular error of the stepper motor, the desired
track density, the inertial mass of the head carriage
assembly and the diameter of the lead screw. As the
lead screw rotates, the head carriage assembly is posi-
tioned radially by the transition zones while the ramps
function to compensate for angular error of the stepper
motor. Thus, any angular error will not result in track
seeking error beyond a preselected limit.
Utilization of the alternating ramps and transition
zones permits a higher track density because reduced
track seeking error is achieved, thus the tracks can
be located in closer proximity to one another than in
~1~391~1'1
l3575/LT~l -10-
l previous drives where the lead screw did not incorporate
a groove design according to the invention. Uniformity
o track selection among drives is also improved by the
reduction of track seekin~ error, thus the interchange-
ability of disks from one drive of the invention toanother drive of the invention is improved. Finally,
track see)cing latency is reduced because the lead screw
of the invention can be rotated at a greater angular
velocity while simultaneously compensating for the
proportionally greater track seeking error that is
inherent as the stepper motor speed increases.
~ ccording to the invention, tracX seeking latency is
also reduced by permitting the head-load pressure pad to
be maintained in close proximity to the disk prior to
loading the magnetic read/write head onto the surface of
the disk. As the disk is removed, however, the pad is
repositioned a substantial distance from the disk to
permit the disk to be removed or inserted without inter-
ference from the head or the head-load pressure pad.
This aspect of the invention is accomplished by mechani-
cally linking a disk clamping mechanism to its
associated head-load pressure pad. Upon inserting a disk,
a plate having a rotatable disk clamp attached is posi-
tioned over the center of the disk so that pressure
from the clamp frictionally mates the disk to the spindle.
Upon clamping the disk onto the spindle, the plate to
which the clamp is attached is displaced about a fulcrum
~oint toward the plane of the chassis and surface of
the associated received disk. This displacement not only
clamps the disk onto the spindle, but permits a head-load
arm to which the head pressure pad is attached to be
lowered in close proximity to the disk. Thus, while
1lSg~4
13575/I.T~
1 the disk is clamped in place, its associated magnetic
read/write head and pressure pad are located in close
proximity to the opposite surfaces of the disk. Upon
commancl, the he~d-load pressure pad can be loaded onto
the disk th~s allowing recording or retrieval of informa-
tion by the head with a reduced latency due to the
close proximity of the pressure pad and magnetic read/
write head to the opposite surfaces of their associ-
ated disks. Additionally head wear and disk wear are
reduced by the selective loading and unloading of the
pressure pad as compared to those systems where the
head is continually in contact with the received disk.
Upon removal of the disk, the plate to which the
rotatable clamp is attached is displaced away from the
plane of the chassis and concomitantly the head-load
arm and pressure pad are lifted away from the surface
of the disk to permit easy removal without interference
from the pressure pad or magnetic head.
With initial reference to FIGS. 1, LA, 2 and 3, a
dual flexible mini-disk drive 10 incorporating the princi-
ples of the invention is shown. The drive has a chassis
16 having a first side panel 13 and a second side panel
14 of equal dimensions each being perpendicular to the
plane of the chassis. In the preferred embodiment, the
side panel height H and the chassis width W conform to
established industry standards for a single mini-disk
drive, the height H being 8.25+ .02 centimeters and
the width W being 14.60 + .00, -.05 centimeters. The
side panels have pairs of guides 91 and 92 for positioning
received mini-disks.
11~9~1 1
13575/LT~ -12-
1 ~ bezel 17 is attached to one end of the chassis,
the plane of the bezel being approximately perpendicular
to the plane of the chassis. The bezel 17 has a first
slot 18 and a second slot 19 lying in planes parallel to
the chassis 16 for receiving selectively removable mini-
disks 42. The received mini-disks also lie in planes
parallel to the plane of the chassis. A first spindle
21 and a second spindle 22 are disposed on either side of
the chassis and are journaled by bearings for independent
10 rotation on a shaft 25~ which is press fit into the chassis.
The spindles are thus aligned on an axis traverse to the
plane of the chassis. A first movable plate 23 and a second
movable plate 24 are attached to chassis supports 26 and 27,
respectively, the supports being located at the end of the
15 chassis opposite the end to which the bezel is attached.
The plates 23 and 24 are pivotally mounted to the chassis
supports by means of flat springs 28 and 29, respectively,
which urge plates 23 and 24 away from the plane of the
chassis 16, i.e., away from each other.
A mini-disk 42 has a central circular opening, the
periphery of which is selectively clamped to the first
spindle 21 or the second spindle 22 by a first rotatable
disk clamp 33 or a second rotatable disk clamp 34, respec-
tively. The clamps are attached to the movable plates 23
25 and 24, respectively, and have a periphery that is elasti-
cally compressible hy virtue of the slots formed therein.
A first locking door 31 and a second locking door 32
are rotatably coupled to the end of the movable plates, 23
and 24 respectively. Each door is pivotally attached by means
30 of pins 30 which connect the end of the plates 23 and 24 to
I ~9'~
13575/L'I'R -13-
I tabs 35 protrudill~J from the surface of the doors. Upon
insertioll, a mini-disk is clamped onto its respective
spindle by tlle user liftincJ the end of the door extending
away ~rom the plane of the hezel while simultaneously
rotating it to a position flush with the bezel. This
operation locks the plate and clamp into a fixed position
which results in the frictional mating of the mini-disk to
its respective spindle. The mini-disk may be removed by
rotating the respective door to a position appro~imately
lO perpendicular to the plane of the bezel, thus allowing
the tension created in the flat springs 28 and 29 t~
reposition the plates 23 and 24 away from the plane of
the chassis and permit removal of the received mini-disk.
As the locking door rotates from a plane parallel to its
15 respective movable plate, i.e., in the open position to
a plane perpendicular to its respective movable plate,
i.e., in the closed position, the movable plate pivots
toward the plane of the chassis and the clamp engages the
disk.
A motor 36 for driving the spindles in opposite
directions is mounted on the chassis between the slots
18 and 19 and adjacent to the spindles 21 and 22, thè
output shaft 37 of the motor having an axis of rotation
substantially perpendicular to the axis oE the spindles.
25 A drive pulley 38 is attached to the output shaft 37
of the motor 36. Mounted on the chassis near the other
end of the motor is a rotatable, direction-changing pulley
39 having an axis of rotation lying in the same plane
as the axis of rotation of the output shaft 37. An endless
30 drive belt 41 passes over the drive pulley 38, second
1 l ~ 9 L '1 '1
13575/LTR -14-
1 spindle 22, direction-cha~ging pulley 39, andfirst spindle
2l. The clir~ction of the belt is reversed by the drive
pulley and the direction-changing pulley such that the
first spindle and the second spindle are driven in o~posite
directions; thus, mini-disks clamped to the first and
second spindles also rotate in opposite directions.
Maynetic read/write heads 63 and 64 are positioned
~ack-to-back between the planes of the slots 18 and 19
so, as seen by heads 63 and 64, the mini-disks clamped
10 to spindles 21 and 22 rotate in the same direction, i.e.,
cloc~wise. As a result, both mini-disks can be ad-
dressedfor reading and writing purposes in the same
manner, i.e., by the same electronic circuitry, because
the disks are moving past the heads in the same direc-
15 tion relative to the heads.
FIG. 3 depicts mini-disk 42 clamped onto the
first spindle 21 by the first disk clamp 33 with
plate 23 in a "closed" position. As plate 23 moves
into the closed position, clamp 33 moves into the
20 central opening of the mini-disk with a force fit,
thereby compressing the periphery of clamp 33 and
centering the mini-disk thereon. When plate 23 is
in the closed position, the end of clamp 33 lies in-
side the center opening of spindle 21. The faces of
25 the mini-disk are clamped between the surfaces of
clamp 33 and spindle 2~ parallel thereto. The second
plate 24 is shown in an "open" position. When in the
closed position, the plate 23 or 24 is repositioned to
a plane parallel with that of the chassis 16. In the
30 open position, the plate 23 or 24 is urged away from
a plane parallel to that of the chassis 16 by tension
in the springs 28 and 29, respectively.
1 1 5 ~
13575/LTR -15-
l A first reference plane 44 and a second reference
plane 46 are aLtached to the chassis 16 by means of sup-
ports~47 and 48, respectively. The reference planes
serve to maintain the flexil)le disk in a plane parallel
to the axis of radial displacement of the magnetic heads.
In FIGS. 4, 5, 6, and 7, the head-load mechanism
according to the invention is shown. FIG. 6 depicts a
perspective of the essential elements of the head-load
mechanism associated with the first spindle 21. Th~se
10 elements associated with the second spindle 22 are
substantially identical; therefore, the description is
limited to those elements associated with the first
spindle. A solenoid 52 is attached to t~e chassis 16.
A lifter arm 53 is attached to an armature 50, which has
15 one end pivotally attached to the solenoid, the lifter
arm being urged away from the plane of the chassis 16 by
by a lifter arm spring 54 up against a set screw 62 mounted
on plate 23. A head-load arm 56 is pivotally attached by
an axle 57 to a head carriage assembly described below. A
20 head-load arm spring 58 urges a pressure pad 59 on arm
56 toward the plane of the chassis. While solenoid 52 is
not activated, spring 58 urges arm 56 against lifter arm
53, which is spaced a predetermined distance from the plate
23 by set screw 62. A first magnetic read/write head 63
25 and a second magnetic read/write head 64 are mounted on the
ends of respective head support brackets 65 and 75, which
are attached to a lead screw follower block 66. Heads 63
and 64, brackets 55 and 75, and block 66 comprise a head
carriage assembly which moves parallel to the plane of the
30 received mini-disk in a radial direction relative to the
13575/LTR -16-
1 a~is of tl~e spindLes 21 ~nd 22 on carriage rails 67 (FIG. 7)
which are anchored to the ch~ssis. Carriage rails 67 extend
throu~3h passag~s, not shown, in block 66 or a separate member
attached thereto. ~leads 63 and 64 are cantilevered off the
elld of block 66 faciny spindles 21 and 22 by brackets 65 and
75 in line with the disk engaging portions of the spindles
as shown in FIG. 3. The hidden line labeled 66 in FIG. 7
designates the end of the b]ock facing spindles 21 and 22,
which is in line with the belt engaging portions of the
10 5pindles. Thus, although the radial progress of block 66
toward the axis of the spindles is limited by the large
diameter of the belt engaging portions of spindles 21 and
22 (see FIGS. 2 and 7), heads 63 and 64 are able to move
closer to the axis of the spindles than block 66 by virtue
15 Of the cantilevered construction, thereby permitting access
by heads 63 and 64 to the full data storage surface of the
disks.
In an alternative preferred embodiment third and fourth
magnetic read/write heads replace the pressure pads 59 and
20 61, respectively. These additional heads permit recording
and retrieval of information from both sides of a mini-disk
without the necessity of removing, turning over and reinsert-
ing the mini-disk into the drive.
In FIG. 4, the plate 23 is shown in the open position.
25 The pressure pad 59 is urged by spring 54 away from the
plane of the chassis 16 thus permitting easy insertion and
removal of the mini-disk 42 without interference from the
pressure pad 59 or the magnetic read/write head 63. FIG. 5
depicts the plate 23 in the closed position, in which the
30 pressure pad 59 lies in close proximity to the surface of the
mini-disk 42.
13575/L~r~ -17-
I Lll ~he oi~e~ osition, the plate 23 is urged away from
the plarle of tlle chassis 16 by the force created in the
spri.ngs 28 attachincJ the plate to the chassis supports 26;
the liEter arm 53 under tension from the solenoid spring
54 lifts the head-load arm 56 away from the plane of the
chassis thus overcoming the lesser opposing force of
spring 56. In the closed posi-tion, the plate 23 is moved
toward the plane of the chassis and locked in that position
by the user rotating the locking door 31 into a posi-tion
10 flush with the bezel 17. As the plate is moved into the
closed position, this motion is transferred by set screw
62 to lifter arm 53. As a result, the head-load arm 56
and the lifter arm 53 are also moved toward the plane of
the chassis which causes the head-load arm to position the
15 attached head-load pressure pad into closely spaced proximity
to the plane of an inserted mini-disk. When the mini-disk
is clamped onto its respective spindle by positioning the
plate to the closed position, the gap between the head and
the mini-disk is maintained at a minimum by adjustment
20 of set screw 62. Upon command, the solenoid 52 is activated..
to draw the armature 50 toward the solenoid and position
the lifter arm 53 to a point in closer proximity to the
plane of the received mini-disk than the position deter-
mined by the plate 23 and the set screw 62~ This reposi-
25 tioning upon command permits the head-load arm 56 to transmit
the force of the spring 58 through the pressure pad 59 unto
the surface 79 of the mini-disk opposite the surface 81 in
proximity to the magnetic read/write head 63. Thereupon,
the magnetic read/write head contacts the surface 81 of the
30 mini-disk to enable either recording or retrieval of
magnetic information.
13575/IIT~ -18-
l Bec~se plate 23 brings pressure pad 59 into close
proximity to the mini-disk as the user closes the loading
door 31, the latency between the he~d-load command to
the solenoid and the actual loading of the pressure pad
is substantial]y reduced. ~his reduction in latency permits
greater track seeking speed to be achieved as head-load
delay is minimized. Additionally because the gap 82 is
reduced by the invention, the pressure pad 59 strikes
the surface of the mini-disk 79 with less force thus
lO reducing bounce and head settling time.
With reference to FIGS. 7, 8 and lO, elements of
the track seeking mechanism according to the invention
are shown. Attached to the chassis 16 is a stepper motor
68 whose rotational axis is perpendicular to th~ rotational
15 axis of the first spindle 21 and the second spindle 22.
To the stepper motor's output shaft 69 is attached a lead
screw 71 having a helical track for example in the form of a V-groove
72. Vpon command, the stepper motor 68 rotates in equal
increments the shaft 69 and the lead screw 71. The head
20 carriage assembly 66 has the first magnetic read/write head
63 and the second magnetic read/write head 64 mounted coaxially
such that the heads are aligned on an axis substantially
parallel to the axis of the spindles 21 and 22. The head
carriage assembly is positioned between the planes of the
25 slots 18 and l9, the heads being mounted on the head carriage
assembly in a back-to-back relationship to face the adjacent
surfaces of the mini-disks received by the respective
slots fox selectively recording and retrieving information.
The head carriage assembly is positioned radially with
30 respect to the axis of the mini-disks in order to reproduci-
bly position the heads over selected tracks of the mini-
3~
l3s7s/r.rl~ -19-
1 di~ks. ~ follower such as a ~ll 78 (FIG. 3) is attached to lead screw
~ollo~r bloe~ 66 byl~ans of a flat spring 70 or other means to link
the head-block assembly to the lead screw 71. The lead
screw has a helical V-groove 7~ for radially positioning
the head carriage assembly. BaLl 78 is spring loaded by
spring 70 to ride in V-groove 72 as the lead screw rotates.
As the stepper motor rotates, the shaft and lead screw
cause the head carriage assembly to be repositioned
radially. The head carriage assembly slides freely along
lQ carriage rails 67 such that movement of the head carriage
assembly is limited along an axis radial to the disks and
is bi-directional depending upon the direction of rotation
of the stepper motor; thereby, any concentric track on the
surface of either mini-disk may be selected.
With reference to FIGS. 8 and 9, the details of the
lead screw 71 of a dual mini-disk drive incorporating
principles of the invention are shown. FIG. 8 is perspec-
tive view of a lead screw 71 having a helical V-groove
72 on its surface. In the preferred embodiment, the cross-
20 sectional profile of the V-groove has an angle of approxi-
mately 70. FIG. 9 depicts a portion of the V-groove
in detail.
According to the invention, the helical V-groove is o~,prised
of alternating rest zones 73 and transition zones 74 having dlfferent
25 pitches dependent in value upon variable factors including the
m~un~m stepper motor ang~ar error, the desired track density, the
inertial mass of the head carriage assembly and the diameter of the
lead screw. Rest zones 73 oorrespond in position to the tracks on the
disk and transition zones 74 correspond to the spacing between tracks
30 thereon. Preferably, the rest zones have zero pitch, i.e., they lie
in a plane perpendicular to the screw axis. But if the spacing between
tracks is too large, the rest zones may need to have a pitch larger than
zero, a~it still smaller than the pitch of the transition zones, to
prevent undue oscillation o~lead screw follcwer 78. For the following
35 example, it is assured the rest ~nes have a pitch larger than zero,
i.e., they are in the form of ramps.
~ 1 5 ~
13575/L'rR -20-
1 The ramps are defined by two orthogonal components:
an axial or translational component 84 parallel to the
rotation axis 76 of the lead screw 71 and a circumferential
or circular component 86 perpendicular to the rotational
axis of the lead screw. The parallel component 84 repre-
sents the total permissible alignment error of the head
with respect to the selected track. As this component
is reduced, the angle 77 of the ramp approaches 90D.
However, the acceleration of the head carriage assembly
10 66 from a transition zone 74 to a ramp 73 also increases
as the angle 77 increases. As the acceleration increases,
the lead screw follower 78 may e~bit an undesirable oscillation
within the V-groove. Thus, the co~nent 84 of the ramp 73 parallel
to the rotational axis 76 is selected to be as small as possible,
15 preferably zero, to keep the lead screw follower oscillation to a
m~i~m. In one ~mxxL~ent, the ramp component 84 is approximately
0.003 centLmeter in order to achieve a track seeking error of
approximately ~ 0.0015 centimeter. The angle 77 in the
preferred embodiment is approximately 83.
The component 86 perpendicular to the rotational axis
76 is the chord distance 86, subtended by a radial angle
87 equal to approximately twice the maximum stepper motor
angular error. The radial angle 87 is the angle projected
on a plane perpendicular to the rotational axis of the
25 lead screw, the vertex of the angle being positioned on
the rotational axis of the screw. In one embodi-
ment, the radial angle 87 equals approximately two degrees
and the radius of the lead screw is approximately 1.15
centimeters. Thus, the resultant chord length 86 equals
30 0.02 centimeters.
~1~g'~
13575/LT~ -21-
1 The transition zones 74 alternate with and connect
the r~nps 73 clnd have an axial component 83 parallel to
the axis of rotation of thelead screw 76 which is approxi-
mately equal to the distance between the tracks of the
disk. In one embodiment, this component 83 is
approximately 0.025 centimeters. As shown in FIG. 9,
the pitch of transition zones 74 is steeper than the pitch
of ramps 73. The preferred embodiment has transition zones
which have a continually changing pitch, steeper in the
10 middle than at the ends, in order that the lead screw
follower may slow down as it approaches the ramps. Thus,
the head carriage assembly 66 smoothly makes the transition
between adjacent ramps while minimizing the acceleration
near the ramps. In summary, the use of different pitches
15 permits more accurate head-track alignment in the position-
ing of head carriage assembly 66 than a constant steep pitch
and permits faster positioning of head carriage assembly 66,
and thus shorter access time to the data on the disks than
a constant gradual pitch. In operation, while stepper motor
20 68 rotates incrementally from one rest position to another,
ball 78 engages ramps 73 when the motor is in the rest
positions and engages transition zones 74 when the motor is
rotating from one rest position to the other. The circum-
ferential component of transition zones 74 corresponds to
25 one or more angular increments of the stepper motor.
The described embodiments of the invention are only
considered to be preferred and illustrative of the inventive
concepts; the scope of the invention is not to be restricted
to such embodiment. Various and numerous other arrangements
30 may be devised by one skilled in the art without departing
from the spirit and scope of this invention. For example,
.
13575/LTR -22-
1 the track on the lead screw could be raised instead of a
qroove in which case the follower would have to be modified
to engagc the raised track. Furtller the track seeking
mechanism and the head loading mechanism could be employed
in a single disk drive packaged in the conventional manner.
The method of rotating the disks in opposite directions
or recording or retrieving information from their adjacent
suraces may be incorporated in data storage systems utili~
zing 20.3 centimeter flexible disks or fixed and removable
10 hard disks. The advantage of a more compact drive and
utilization of a single motor would be achieved in any
of these alternative embodiments. Additionally, the means
for reducing head-load delay described herein could be
incorporated in a number o storage systems having removable
15 media other than those utilizing mini-disks, including those
using magnetic heads on both sides of a disk or mini-disk
for removing the medium accessing both sides of the
medium without removing the medium.
, : !
~;
