Note: Descriptions are shown in the official language in which they were submitted.
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DISCLOSURE
Background of the Invention
The present invention relates to a linear actuator for a random access
memory apparatus or the like and, more particularly, to such a linear actuator
S which provides highly accurnte and fast positioning of a data transfer head with
respect to a disc recording surface.
Direct access memories of the type ernploying one or more magnetic
discs for recording and storing data are widely used as peripheral memories for
computers and other data processing units. Memories of this nature have the
10 advantage of enabling information to be either transferred to, or removed from,
randomly selected address locations or tracks on the disc without the necessity of
the memory having to serially seek the desired location as is necessary, for ex-
ample, when magnetic tape memories are employed.
The read/write recording head or other data transfer device associated
15 with each disc recording surface for transferring data to and from such surfacla is
typically movable translationally with respect to the disc between the various
~dress locations. It will be recognized that the speed at which data can be applied
or removed from a disc will depend in a large measure on the speed with which
the transfer head Is movable between various ones of the locations. It is also
20 necessary that the transfer head be quile accurately positioned with respect to
each address location, not only to assure that data is either applied to or removed
from the proper address, but to enable address locations to be closely spaced to
one another to provide adequate storage capacity on the disc surface.
Typically, the transfer head or heads are mounted on a carriage which
25 is, in turn, mounted upon a track for
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travel on a translational path which will provide the desired
movement of -the heads between the radially spaced address
locations. The carriage can be driven by various mechanisms,
the most satisfactory of which to date is basically a voice
coil, i.e., a solenoid of the type used to drive an audio
speakerO While linear actua~ors of this type have been gen-
erally satisfactory, they do have certain disadvantages.
For one, it will be apprecia~ed that every time it is desired
to move a transfer head and, hence, the carriage supporting
the same, it is necessary that the momentum of the carriage
be changed from essentially zero to a high value in a very
short time in order to achieve a realistic access time.
The electrical power required to cause a voice coil to
provide the accelerations required is of a high order of
magnitude. Moreover, a voice coil actuator is relatively
inefficient in terms of the amount of electrical power that
must be delivered to it relative to the mechanical power out-
put. Also, complicated drive and control circuitry has been
required to provide the necessary power and yet enable quite `
accurate positioning of the head or heads at address locations.
Summary of the Invention
In accordance with one aspect o this invention
there is provided a linear actuator for transmitting motion
separately to two different carriages comprising: (a) a drive
shaft having a cylindrical surface; (b) a support mounting
said drive shaft for rotation thereof about the axis of said
cylindrical surface; (c) two separate carriages to be driven;
~d) coupling means associated with each of said carriages for
converting rotary motion of saia drive shaft into translational
motion of said respective carriages, said coupling means
including for each of said carriages: (1) a roller; (2) means
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carried by said carriage for supporting said roller and main-
taining the same in driving frictional engagement with said
cylindrical surEace of said drive shaft; and (3) roller control
means for selectively changing angular orientation of the axis
of rotation of each of said rollers between an orientation
parallel to the axis of rotation of said cylindrical surface
to one obli~ue with respect thereto in which rotation of said
drive shaft and roller causes relative translational motion
between said roller and said drive shaft, the roller control ~`
10 means for each of said rollers changing the angular orienta-
tion of the axis of its associated roller independently of
the angular orientation of the axis of the other roller where- :
by the coaction of a single drive shaft with two separate
carriages provides separate and independent motion of said
two carriages; and (e) power means connected to one of said
drive shafts and said rollers for rotating the same. ~ :
In accordance with another aspect of this inven-
tion there is provided a linear actuator for transmitting : :
motion separately to two different carriages comprising: (a)
20 a drive shaft having a cylindrical surface; (b) a support :
mounting said drive shaft for rotation thereof about the axis
o said cylindrical surface; (c) power means connected to
said drive shaft for rotating the same about said axis of
said cylindrical surface; (d) two separate carriages to be -
driven; and (e) coupling means associated with each of said
carriages for converting rotary motion of said drive shaft
into translational motion of said respective carriages, sald
coupling means including for each of said carriages; (1) a
roller; (2) means carried by said carriage for supporting
said roller and maintaining the same in frictional engagement
with said cylindrical surface of said drive shaft to be
driven into xotation thereby; and (3) roller control .
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means for selectively changing the angular orientation of the
axis of rotation of each of said rollers between an orienta-
tional parallel to the axis of rotation of said cylindrical
surface to one oblique with respect thereto in which rotation
of said drive shaft causes translational motion of said
roller and hence of said carriages; said roller control means
including for each of said rollers; (a) a lever arm secured
to its associated roller having means spaced from said roller
for generating a first magnetic field; (b) means for generating
a second magnetic field at a location at which it will interact
with said first magnetic field, the interaction of said
magnetic fields applying sufficient force to said lever to
pivot the same and thereby change the angle of orientation of
the axis of rotation of its associated roller; and (c) means
for changing the direction of one of said first and second
magnetic fields o said roller control means for each of said
rollers relative to the other to correspondingly change the
airection of the force applied to said lever of each by the
interaction of said magnetic fields.
The present invention in one o~ its aspects
provides a linear actuator which is capable of providing
highly accurate and fast positioning of a transfer head with
respect to a record surface of a magnetic recording disc
without the high electrical power requirements of more con-
ventional arrangements. It further includes a power drive
circuit for such a linear actuator which is quite simple and
yet substantially reduces the amount of power required to
control the positioning of a transfer head carriage.
In its basic aspects, a random access memory
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apparatus which includes the linear ac~uator of the
invention has, as is typical, a carriage on which the
transfer head or heads are mounted and a track on which
the carriage is mounted for travel on a translational
path proviaing movement of the transfer head between
radially spaced address locations on a recording disc.
In addition, it includes a drive shaft having a
cylindrical peripheral surface and a support mounting
such drive shaft for rotation about the axis or such
cylindrical surface. The drive shaft is oriented
with its axis generally parallel to the translational
path that the carriage travels; and a power source,
such as a motor, is provided for rotating the drive
shaft about the axis of such cylindrical surface.
Coupling means are also provided for converting the
rotary motion of the drive shaft into translational
motion of the carriàge. Such coupling means includes
a roller, and means carried by the carriage for
supporting the roller and maintaining the same in
frictional enga~ement with the cylindrical sur~ace
o~ the drive shaft. Rotation of the drive shaft
will therefore cause the roller to be similarly
rotated. ~ `
Roller control means are provided for selec-
tively changing the angular orientation of the axis of
rotation of the roller with respect to the axis of
rotation "
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~076254
of the eylindrical surface, That is, the roller control means acts to turn the axis
of the roller relative to the axis of the drive shaft cylindrical surface between an
orientation in which such axes are parallel to one another and one or more in which
they are oblique with respect to one another. It will be recognized that when the
axes are parallel to one another, the roller will trace a path on the drive shaft which
is in a plane normal to the drive shaft's axis. However, when the axis of the roller
is oblique with respect to the axis of rotation of the cylindrical surface, the roller
will trace, assuming a good frictional engagement between the roller and the cy-lindrical surface, a helix along the cylindrical surface. That is, the roller will not
only be rotated by the drive shaft, but it wil1 also be moved translationally with
respect thereto in a direction paraUel to the drive shaft's axis of rotation. Since
the roller is carried by the carriage, the carriage will also be moved translationally.
It will be appreciated from the above that a desired translational
motion of the carriage can be obtained merely by varying the angle between the
axis of rotation of the roller and the axis of rotation of the drive shaft. Moreparticularly, the power of the rotating drive shaft is transmitted through the
roller to the carriage to cause translational movement of the latter whenever the
angular orientation of the axis of the roller is oblique with respect to the axis of
the drive shaft. Because the drive shaft continuously rotates, it is not necessary
to ac~elerate the power source itself, i.e., the drive shaft, from zero momentumto a high momentum each time it is desired to move the carriage. Moreover,
neglecting friction losses, all of the power extracted by the carriage from the
drive shaft is converted into carriage acceleration. The high electrical drivingpower required by conventional linear actuators is therefore not needed.
The apparatus further includes a position sensor for determining the
position at any given time of the transfer head relative to a desired address loca-
tion. A position servo system responds to a difference between the desired and
actual position of the head by regulating the roller con~rol means to make a cor-
respvnding adjustment in the angular orientation of the roller axis to cause thecarriage to move in a direction moving the transfer head to the desired address ~ -~
location. As another salient feature of the invention, the position servo system
4.
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includes a power drive circuit which minimizes the power required to change the
axis of rotation of the roller. In this connection, the interaction of a magnetic
field developed by an induction coil with another magnetic field is used to develop
the force which changes the angular orientation of the roller axis. In its basic
S aspects, the power drive circuit inclwdes a power source connected to the induc-
tion coil through a first switch which is responsive to receipt of a control signal
by applying power from the power source to the coil. A second switch is providèd
which is responsive to receipt of an information signal indicating a difference
between the position desired for a transfer head and its actual position by gene~
10 ating a control signal for application to the first switch which is pulsed to altern-
ately switch ON and O~F the application of power from the source to the coil.
The time delay between pulses of the pulse control signal is selected to be shorter
than the decay time for current in the coil, and means are provided for continuing
current flow through the coil between pulses. The result is that the coil will re-
lS main energized during the full duration of an information signal, even though thefirst switch is discontinuously operating during such duration. The continuous
energization of the eoil by a discontinuous application of power thereto will pr~
vide a significant power saving.
The invention includes many other features which are important and
2~ will be described in more detail hereinafter. For one, an especially compact drive
apparatus can be provided for two or more separate discs or disc packs by driving
a plurali~y of carriages from a single drive shaft. That is, the rollers of a plurality
of carriages are made to frictîonally engage the same drive shaft for independent
driving. Other features of the invention, som~ of which are independently usable :
25 in linear actuators designed for ma~hines other than disc pack drives, will be de-
scribed or will become apparent from the following more detailed description of `
the preferred embodiments.
Brief Description of the Drawings
With reference to the aceompanying three sheets of drawing:
311 PIGo 1 is a partial and broken side elevation view illustrating the
pertinent portions of a preferred embodiment of a random access memory appa-
ratus incorporating th~ invention;
~71~jZ5~
FIG. 2 is a bottom plan view of the apparatus of FIG. 1;
FIC;. 3 is a sectional view taken generally on a plane indicated by the
lines 3-3 in FIG. 2 and illustrating details of the apparatus;
FIG. 4 is a sectional view taken on a plane indicated by the lines 4-4
5 in FIG. 3 illustrating details of the roller mech~nism;
FIGs. 5 ~nd 6 are views similar to FIG. 4 illustrating different orienta-
tions of the roller with respect to the drive shaft;
FIG. 7 is a partial sectional view illustrating details of the mounting
of the drive shaft;
FIG. 8 is an enlarged sectional view illustrating details of the mount-
ing of the roller;
FIG. 9 is an enlarged sectional view similar to FIG. 8 illustrating an
alternate mounting of the roller with respect to the remainder of the carriage;
FIC:. 10 is a schematic electrical diagram of the power drive circuit
15 of the invention; and
~ IG. 11 is a sectional view somewhat similar to FIG. 3 illustrating
another preferred embodiment of the invention.
Detailed ~
With reference first to ~ . 1, the pertinent portion 11 of a recording
20 disc drive apparatus is illustrated. Such apparatus includes a recording disc 12
mounted axially on a spindle 13 for rotation therewith. The opposite planar sur-
faces 14 of the disc 12 are coated with a magnetically recordable material mak-
ing the same into data storage record surfaces.
Associated with each record surface 14 is a data transfer device in
25 the form of a read/write head 16. As illustrated, each of the heads 16 is supported
ViA a cantilevered arm 17 extending from a carriage which is generally referred
to by the reference numeral 18. The carriage 18 is, in turn, mounted for travel
back and forth on ~ translational path defined by a track. In general, the track
consists of a pair OI spaced apart guide rails 19 and 21 ~FIG. 2) which are mounted
30 on opposite sides of the carriage via en~ fl~nges 22 which, in turn, project from
a stationary baseplate 23. Although the details of the track will be discussed in
more detRil hereinafter, it will be seen from FIG~ 2 that the carriage includes a
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pair of bearing projections 24 which are slidably received via sleeve bearings 26
on the r~il 21 at positions which are spaced a substantial distance apart to pro-
vide stability. On the opposite side of the carriage, a support roller 27 is main-
tained in engagement as will be discussed with the rail 19. The result is that the
5 carriage is supported on its opposite sides for movement back and forth on a
translational path indicated by the arrow 28 (~IG. 2). Such movement will resultin the read/write heads 16 being translationally moved across their associated
disc record surfaces between radially spaced address locations.
As mentioned previously, the access speed of a disc type storage de-
10 vice is dependent in a major way on the speed with which the carriage can mo-ve
the head 16 between address locations. Drives provided in the past for effect-
ing the carriage movement have, in general, certain deficiencies. ~or one, in
moving the carriage from one essentially stationary location to another, it is
necessary that a high power input be initially delivered to the drive mechanism
15 in order to overcome both its own inertia and that of the carriage. Moreover,most have not been able to provide the accuracy which is desired for loca1ing
and maintaining the heads at a particular location with respe~t to the record
surfaces. As a particularly salient feature of ~he instant invention, it includes
a linear actuator for driving the carriage which substantially alleviates such
20 problems. The mechanical power for moving the carriage is provided by a driveshaft 29 which has a cylindrical peripheral surface 31 and is mounted for rotation
about the axis of such cylindrical surface. More particularly, a pair of spaced
apart uprights 32 project upwardly from the baseplate 23 on the side thereof
opposite the carriage 18 and rotatably receive the shaft 29. As illustrated, the25 drive shaft 29 is supported with its axis of rotation generally parallel to the rails
19 and 21, and hence, parallel to the translational path of the carriage.
Motive power means are connected to the drive shaft 2g for rotating
the same about its axis. That is, an electric motor 33 is also mounted to the base- -
plate 23 on the same side thereof as the shaft 29. As is best shown in ~IG. 2~ the
30 drive shaft of the motor is drivingly ~onnected via suitable pulleys (not visible)
and a drive belt 34 with one end of the shaft 29. The motor 33 is therefore ar-
ranged to rotatably drive such shaft.
" : - .
~7~Z54
~ rhe rotary motion of the drive shaft 29 is also usable eO drive the
spindle 13 and, hence, rotate the recording disc 12. More particularly, as illustrated
in FIG. l, the drive shaft is connected through a bevel gear train 35 to the shaft
for such rotation. Thus, the single power source represented by the motor 33 can5 be used to perform two functions, i.e., both drive the carriage and to rotate the
recording disc.
Coupling means are provided for convertin~ rotary motion of the drive
shaft into translational motion of the carriage. As is best il1ustrated in ~IG. 3,
for this purpose a roller 36 mounted for rotation between the legs 37 of a yoke 38
10 is maintained in frictional engagement with the cylindrical surface of the drive
shaft. The roller 36 is positioned within an elongated slot 39 extending throughthe baseplate 23, and a support rod 40 is rigidly secured to the base end of theyoke. As is shown, the rod 40 is journalled for ro~ation within the plate 41 (FIG. 3)
of the carriage about an axis which passes through the center of rotation of 1heroller 36. The rod 40 passes beyond the plate 41 into a chamber 42 of the carri-age wherein a coiled compression spring 43 axially surrounding the end of the rod
bears against a thrust bearing 44 thereon to resiliently urge the rod and, hence,
the roller 36 toward the drive shaft 29. Spring 43 is selected to not only provide
sufficient force to maintain the wheel 36 in engagement with the drive shaft with
20 $he ~rictional force necessary for the acceleration desired as will be described,
but also to urge the carriage 18 pivotally sbout the guide rail 21 to maintain the
carriage roller 27 in engagement with the rail l9 which acts, in effect, as a trans-
verse restraint rail. Thus, the means for maintaining the roller 36 in engagement
with the drive shaft 29 also forms a part of the structure defining the relation-
25 ship between the carriage and its track.
Control means are provided for selectively changing the angular
- - orientation of the roller's axis of orientation. In this ~onnection, as best illus-
trated in FIG. 3, the legs 37 of the roller yoke 38 extend beyond the roller and~re angled outward to be clear of the drive shaft 29. Such legs form, in effect,30 a lever arm 45 which extends in a direction having a component transverse to the
axis of the support rod 4Q. Thus, pivoting of such arm about the axis of the rod40 will result in changing the angular orientation of the axis of rotation of the
roller 36.
8.
~IL07625~
The interaction of magnetic fields are used to pivot the lever arm and
thereby change the angle or orientation of the roller axis. More particularly, ap~ir of spaced apart permanent magnets 46 and 47 are supported on opposite sidesof an elongated, soft iron rnagnetic core 48, all of which are supported by a frame
5 49 secured tothebaseplate adjacent drive shaft 29. The free end of the lever arm
45 has a bobbin 50 which axially surrounds the core 48 secured thereto, and an
induction coil arrangement 51 is wrapped around ~he bobbin.
The lever arm 45 will travel translationally of the drive shaft with the
roller 36, and the induc$ion coil arrangement 51 provides means for generating a10 first magnetic field at a location on such lever arm spaced from the roller. The
permanent magnets generate a second magnetic field along the path travelled by
the coil arrangement upon translational motion OI the roller. The permanent mag- -
nets are chosen relative to the power with which the coil arrangement 51 will beexcited to apply sufficient force to the lever to pivot the same as necessary to15 cause the desired pivoting of the roller axis. In this connection, a sufficient gap
must exist between the bobbin 50 and the iron core 48 to permit the bobbin to
pivot with the lever a desired amount without binding. It will be recognized that
the direction of current flow in the coil arrangement will control the directionof the magnetic field produced by the coil relative to that produced by the per-
20 manent magnets and, hence, the direction of the force applied to the lever. Thus,control sf the direction of current flow in the coil arrangement will provide con-
trol of the direction of the carriage on its translational path.
PIGs. 4-6 illustrate differing relationships of the roller to the shaft
providing carriage trRnslation. FIG. 4 first shows the axis of the roller parallel
a5 to the axis of the peripheral surface of the drive shaft. It will be recognized that
as the shaft rota1 es, the roller will be caused to rotate because of its frictional
engagement therewith. The roller will not be moved translationally, however,
but will merely continuously travel over a circular path of the surface o~ the
drive shaft, the plane of such path being normal to both the axis of the drive shaft
30 and the axis of the roller. FIG. 5 shows the r oller turned clockwise so that its
axis is now oblique to that of the drive shaft's peripheral surface. The roller will
now describe a helical path Oll the surface of the shaft, Assuming the shaft is
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rotating in the direction indicated by arrow 52, the roller and, hence, the carriage,
will be moved translationally in the direction indicated by arrow 53. FIG. 6 illus-
trates the roller turned counterclockwise with the shaft continuing to rotate inthe direction indicated by the arrow 54.
As another salient feature of the invention, it includes a power drive
circuit for energizing the coil arrangement 51 in a manner minimizing the amountof power required for such energization. Reference is made to FIG. 10 for a de-
tailed description of such power drive circuit. The coil arrangement 51 is actu-ally made up of two separate inductiorl coils represented in FIG. 10 at 55 and 56.
The power drive circuit is arranged to separately energize each of the coils 55
and 56 in opposite directions. In this connection, the circuitry for energizing each
is basically a duplication of that for energizing the other. Such circuitry will be
described in detail only, therefore~ in connection with energization of the coil 55.
As illustrated, a power voltage source as represented at 57 is con-
nected through a saturating power transistor driver 58 with the coil 55. The
transistor driver 58 acts, in effect, as a switch which responds to receipt o acontrol signal by applying power from the power source to the coil. That is, theapplication of an appropriate signal to its base will result in its saturation and a
consequent ~low OI power from the power source 57 through the coil 54.
Operation of the transistor 59 is controlled by a high gain operational
amplifier 59. The inverting input of the amplifier 59 is ~onnected to the outputof a position servo control 61. The output generated by the servo control 61 is
indicative at any time of the difference between the actual position of the trans-
fer head and the desired address location therefore. In this connection, such
position servo control receive input as to a desired address location as schem-
atically indicated by the address signal generator 62. It also receives an inputfrom a position sensor 63 which ~an be, for example, a position transducer 64
(FIG. ~) OI a type commonly used. The position servo control compares the sig-
nals received from the address signal generator and the position sensor and re- -
sponds to a difference by issuing a position information signal indicative of the
difference and app~ying it either on line 66 or ~7 depending upon the direction the
~arriage must travel to reach a desired address location.
., : ' .
10. " '
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The coil 55 is connected in series with the output of the driver 58 in a
feedback connection to the non-inverting inpu~ of the amplifier 59. This arrange-
ment will result in the output of the arnplifier 59 applied to t~e base of the tran-
sistor 58 being a pulse control signal whenever the information signal on line 68
5 indicates a difference between an actual position of the carriage and a desired
position. That is, when an information signal Iirst appears at the inverting ter-
minal of the amplifier s9, the trans;stor will be turned ON to apply the potentiAl
supplied by source 57 through coil 55, Such potential will be applied to the non-
inverting terminal o~ the high gain amplifier because of the feedback connection.
10 When the potential applied to the non-inverting terminal becomes equal to thepotential OI the positlon information signal potential, the output of the amplifier
will be turned OFF, with the result that the potential at the non-inverting input
terminal of the amplifier 59 will again differ from the information position signal,
and the amplifier 59 will again be turned ON to thereby again also turn ON driver ;
15 58. The high gain amplifier 59 will thus be responsive to receipt of an informa-
tion signal by generating a pulse control signal for application to the driver to
alternately switch ON and OFF the application from the source 57 to the coil 55.Means are provided to continue current flow through the coil S5 be-
tween pulses, i.e~, when the transistor driver 58 is OFF duringi an information
20 signal. More particularly, a pa$h 68 for such current flow is provided between
ground represented at 63 and the input end of the coil 55. A diod0 71 is inserted
in the path 68 to limit the back emf applied to the collector of the driver 58
whenever such driver i9 OFF between pulses.
It will be appreciflted that with this arrangement, the coil 55 will re-
25 main energized during the full duration of any information signal on the amplifier
59 even though the driver 58 is discontinuously operated during such duration. In
this connection, the time delay between pulses of the pulse control signal is se-
lected to be shorter than the decay ~ime for current in such coil. Means are in-cluded in the feedback connection for setting the repetition rate at which the
30 amplifier 59 prvvides the pulses of the control signal. More particularly, a resist-
ance divider network made up of a pair of resistances 71 and 72 having their
common connection connected through a capacitance 73 to ground as indicated
~ , . . . . ... ..
~al7625~
at 74 is included in the feedback circuit. The value of the resistances and the
capacitance 73 are chosen relative to the L/R time constant of the coil 5s to
provide both a repetition rate and current pulse width which assures full and con-
stant energization of the coil.
The acceleration of the carriage will depend on the angular velocity
at which the roller 36 is pivoting at any given time. Thus, once a desired earri-
age acceleration is achieved, energization of the coil can be terminated. Because
of the angular relationship OI the roller 36 to the axis of the drive shaft at such
time, however, the velocity of the carriage will be maintained. A further power
savings in the control circuitry is therefore achievable.
It will be recognized that because the roller 36 frictionally engages
the drive shaft 29, the frictional resistance to reorientation of the roller's axis
relative to the axis of the drive shaft must be overcome each $ime the roller isreoriented~ Means are provided for maintaining a eurrent flow through the coil
at all times to reduce or remove, as desired, the effect of this "deadband" on the
operation of the positioning mechanism. More particularly, a forward biased
diode 76 is included in the feedback connection having its input also connected
through a resistance 77 with ground as represented at 69. By selecting the diodeand the resistance to provide a diode voltage drop which equals the current which
~o must flow through the coil to overcome the ~riction times the value OI the resist-
ance 77, the deadband will be removed, It will be appreciated~ however, that in
those instances in which the deadband is of no consequence, the diode 76 need not
be provided. Moreover, a divider network can be substituted for the diode 76 to
perform the function of eliminating or reducing the deadband characteristics.
From the above, it will be seen thnt whenever ~n information signal
indicating that the carrîage must move in the direction represented by the coil 55
is applied to the switch represented by the amplifier 59, the coil will be energized
for the duration of such signal to cause the lever arm 46 to be pivoted in the
proper direction to c~use the carriage to move translationally ~o the desired
address lo~ation~
II it is necessary that the carriage move in the opposite ~irection to
rsach the address location, the output îrom the position servo ~ontrol will be
12.
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directed on line 67 to high gain amplifier 59' which is the duplicate of ~mplifier
59. Such amplifier will switch ON and OFF transistor driver 58' to drive the
coil 56 in the same manner as coil 55 is driven. As mentioned before, the cir-
cuitry for driving coil 56 is the same as that described for driving the coil 55,
and will not be described in detail. Primed reference numerals, however, are
used to indicate like components.
Pulse driYing of the power transistor and each of the induction coils
will result in substantially less power being dissipated to drive the coil. More~
over, the simplicity and inexpensiveness of the electronics of the instant circuit
relative to bridge type circuits used in the past to drive carriages of random
access memory devices should be readily apparent. It will be appreciated that
although for a further minimization of the total power dissipated, a pair of power
drivers 58 and 58' are used to drive two separate eoils 55 and 56, an inverter
could be used to enable one power driver and coil to be employed in the circuitry
to obtain movement of the carriage in both directions.
As another salient feature of the invention, a simple and yet highly
effective means is provided for preventing translational travel of the carriage
with respect to the drive shaft beyond desired limits. More particularly, as is
best illustrated in ~IG. 1, a pair of resilient cushioning bumpers 81 and 82 areprovided at opposite ends OI the path of travel of the free end of the lever arm46. Upon the carriage approaching the limit of its travel in either direction, the
lever arm will engage a bumper and be pivoted in a direction resulting in the rol-
ler 36 being oriented transverse to the axis of the drive shaft as illustrated in
FIG. 4. Thus, the conversion of the rotary motion of the drive shaft 21 into trans-
2S lational motion of the carriage will be arrested. This safety limit on the travel of
the carriage is obtained without the necessity of including an impact bumper or
the like to absorb the momentum of the carriage itself. That is, merely by prop-erly positioning the stops in the path of the lever arm as aforesaid, the continuous
rotation of the drive shaft is used to automatically stop the carriage.
It is quite important in a disc drive memory apparatus that the trans-
fer heads be quite precisely located with respect to the record surface on the
disc. It is the relationship of the c~rriage 18 to its track which provides the
:,
13.
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~(~7~25~
desired exact positioning of the heads in the direction transverse to the carriage
path of travel. More particularly, at the time of manufacture the guide rail 21
is carefully aligned parallel to the desired translational path of the carriage and
rigidly fixed thereto. Because this is the only portion of the track which restrains
movement transverse to such path, the pla~ement of the guide rail relative to the
desired path is the only substantial critical portion of the manufacturing opera-
tion. The mounting of the carriage slideably on the guide rail at positions spaced
a substantial distance from one another along the direction of the translationalpath provides stability for the carriage in such direction.
1~ The apparatus includes several areas which could provide inaccuracies
in the positioning of the carriage in the direction of the carriage translational
path. As another salient feature of the invention, it includes means for prevent-
ing such inaccuracies. For one, the apparatus includes means for taking up play
between the drive shaft 29 and its supports in the direction of the drive shaft
axis. More particularly, as shown in FIG. 7, a keeper washer 86 is held in loca-tion by being seated within an annular groove in the bore through which the drive
shaft 29 extends in the support standard 32. The bearing 87 for the shaft is sand-
wiched between a shoulder 88 on the shaft and the keeper ring 86.
Resilien~ spring means are provided for urging ~he drive shaft against
the keeper ring 86. That is, as shown in FIG. 1, a second keeper ring 89 is pro-vided within an annular groove in the bore of the other support standard 32 to
maintain a compression spring 91 in eng~gement with the bearing 92 associated
with such standard. As illustrated, such bearing bears against a shoulder 93 on
the drive shaft to thereby impart the compression force of the spring to such
drive shaft.
It will be seen from the above that the compression spring 91 will act
to urge the drive shaft to the right as viewed in FIG. 1 in the direction of theaxis of rotatiorl of the cylindrical surface to thereby take up uly play in the dire~
tion of sueh axis, It is important that the compressive force provided by the
spring 91 be greater than the largest frictional force along the axis of rotation
expected between the cylindrical surface and tlle roller. That is, the force pro-
vided by the compression spring must be greater than the reac~ion force on the
~:
14.
~7~ S4
the drive shaft to the left when the carriage is moving with its greatest acceler-
ation to the right as viewed in FIG. 1. Any reaction force on the drive shaft tothe right will be opposed by the keeper ring 86. The above construction, there-
fore, will prevent unintended translational motion of the drive shaft and its cy-
5 lindrical surface in the direction of the drive shaft's axis.
Means are also provided for taking up play between the roller 36 whichengages the drive shaft, and its carriage. More partieularly, spring means in the
form of a leaf spring 96 ~FIGs. 3, 4 and 8) are mounted on the carriage and bearagainst a ball bearing 97 associated with the yoke 38. The leaf spring is positioned
10 to resiliently urge the yoke, and, hence, the roller 36 supported by such yoke in
one direction along the axis of rotation of the drive shaft. Again, the Iorce pr~
vided by the leaf sprin~ 96 must be greater than the component of the frictionalforce along such path between the roller and the drive shaft when the carriage is
undergoing its greatest acceleration.
Means are also provided Ior preventing axial movement of the roller
with respect to its yoke along the translational path. That is, as can be seen from
FIG. 8, the roller 36 is rnounted on its axle via a duplexed pair of ball be~rings 98
and 99. As is illustrated, the inner races of the bearings are sandwiched between
the shoulder of an enlarged end la1 of the roller axle and a spacer collar 102 on
such axle9 and the upper races are clamped within the roller by an annular side
plate ln3. As is known, such an arrangement will prevent axial movement of the
roller along the axle.
~IG. 9 illustrate~ an alternate embodiment of means for preventing
axial movement of the roller with respect to the yoke. In this arrangement, the
right-hand bearing 104 for the roller axle 106 is prevented from moving to the
right by a keeper washer 107, and a compression spring maintained by a keeper
washer 109 resiliently urging the be~ring 111 and, hence, the axle against whichit abutts, also to the right. This arrangement is basically the same arrangementas that provided for taking up slack in the drive shaft, and, again, the compressive
force provided by the spring 108 must be greater than the component along the
axis of the a2de 106 OI any frictional force between the roller and the drive sha~t
tending to move the roller to the left as viewed in the drawing.
,
15.
,
.~7~iZS~
The above described constructions for taking up play or otherwise
preventing relative movement will assure that the precise positioning of the heads
along the tr~nslational path of the carriage will not be affected by play in thedrive mechanism. They are therefore important in assuring that the drive mechan-
s ism of the invention is capable of accurately locating the transfer heads at ad-
dress locations on record surfaces with the accuracy required in modern disc
drive storage devices.
The linear actuator of the invention readily lends itself to providing
translational motion separately to two or more different carriages. Reference
10 is made to FIG. 11 which illustrates a preferred embodiment of a constructionfor separately driving two carriages. More particularly, a pair of carriages 121and 122 are shown on opposite sides of a single drive shaft 123. Each of the
carriages 121 and 122 is respectively provided with a roller 124 and 126 in en-
gagement with the drive shaft, and includes roller control means, generally refer-
red to by the reference numeralls 127 and 128 for selectively changing the annu-lar orientation of the axis of rotation of each of the rollers îndependently of the
angular orientation of the other. Each of the carriages 121 and 122 ~arries a
transfer head (not shown) for translational motion between different address
locations on respective data storage discs 129 and 131. The mechanism and power
20 driver circuitry for each of the carriages is the same as that described for the
single carriage embodiment. Because of this, the in~ividual parts of each of thecarriages are referred to by the same reference numerals utilized with the single
carriage embodiment, and will not be described in detail.
The power for both carriages is provided by the single ~rive shaft 123.
25 rhus~ a single power source enables each of the carriages ~o be driven, thereby
minimizing the number of power sources which must be provided. It is particu-
larly important to note that although a single drive shaft is used to drive bothcarriages, the positioning of each of the carriages is independent of the position- ;
ing of the other. Moreover, although the placement OI the earriages on opposite
30 sides of the drive shaft makes an especially compact arrangement, any number
of carriages greater than one can be provided along the drive shaft either AXially
thereof or on opposite sides as shown. The only limitation is with respect to the
16.
~9762~
amount of power which can be transmitted through the drive shaft 123, and the
complexity which might be associated with the driving of numerous ~arriages
from a single drive shaftO Also, the particular mechanism being transported by
each of the carriages is not limited. For example, one carriage could be trans-
5 lationally moving a transfer head as aforesaid, while the other might be provid-
ing movement of a printing head in a data read-out terminal.
From the above description of preferred embodiments, it will be seen
that the disc dsta storage drive apparatus of the invention includes many fea-
tures which are new and useful. Moreover, certain of the features are useful in
10 other environments in which a linear actuator is desired, e.g., printers for data
readoutO It is therefore in~ended that the coverage afforded applicant be limited
only by the terms of the claims and equivalent language. In this connection the
termins~logy "position sensor" is meant to include, of course, the electronics
which would separate position information from other data recorded on a record
15 surface, as well as the separate transducer mechanism of the preferred embodi-
ment.
17.
.,
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