Linear actuator for memory storage device

A linear actuator for translating accessing transducers such as read/write heads along a straight line path of travel relative to a rotating magnetic disk includes a carriage, a flat coil mounted to the disk and having an effective winding extending transversely at the rear end of the carriage, one pair of rollers mounted at right angles to each other at one side of the carriage in rolling engagement upon a cylindrical guide rail, two pairs of rollers similarly mounted at the other side of the carriage in rolling engagement upon a second guide rail. The second guide rail is fixedly mounted to a base frame; the other guide rail is pivotally mounted parallel to the other rail and is biased by a spring to preload the single pair of rollers against the pivotal rail. A pair of block magnets are mounted at the rear end of the base frame with a gap therebetween that is aligned with the path of travel of the effective winding. The pairs of rollers are symmetrical about the plane of the coil to minimize bending moments and thus enable rapid accessing without inducing vibrations.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention generally relates to an electromagnetic actuator assembly 
for moving an accessing transducer relative to media, such as a disk, upon 
which information is stored for magnetic or optical accession and more 
particularly to an actuator assembly for moving an accessing transducer 
along a straight line extending radially of the media, the assembly being 
hereinafter called a linear actuator. 
2. Description of the Prior Art 
U.S. Pat. No. 3,838,445 to Barnard discloses a linear actuator for a 
magnetic disk storage apparatus that utilizes a cylindrical rod to guide a 
carriage assembly along the desired straight line path of travel relative 
to a rotating magnetic disk. Assessing transducers are mounted in a 
cantilevered manner to the carriage assembly directly overhead the guide 
rod, the guide rod being mounted to a baseplate to extend radially under 
the rotating disk along the desired path of travel. The carriage is driven 
by a cylindrical voice coil motor coupled to the carriage assembly. 
According to this patent, the mass of the carriage is concentrated about 
an axis that is coincident with, or closely adjacent to, the so-called 
axis of frictional resistance and also the axis of drive force input, 
which axes are aligned with the voice coil motor. Two pairs of bearings 
are mounted in a balanced geometry at opposite sides of the carriage 
assembly to keep the carriage upright on the guide rod, and one of the 
bearings rides against a so-called swung way to preload or bias such 
bearing downwardly. 
Another linear actuator for use in a magnetic disk storage apparatus is 
disclosed in U.S. Pat. No. 3,587,075 to Brown and MacArthur. As in the 
Barnard patent, the actuator includes a carriage assembly, and such 
assembly is guided in a precise linear path by a cylindrical guide rail. A 
cylindrical voice coil motor is provided for exerting a bidirectional 
drive force at the center of mass of the entire carriage assembly. 
Bearings are included in the carriage assembly to contact the guide rail 
at three points in the same vertical plane, and such bearings are 
spring-biased to keep the carriage aligned with the rail. A further pair 
of bearings is provided at one side of the carriage to ride along a flat 
support rail. 
SUMMARY OF THE INVENTION 
According to the present invention, an actuator for moving an accessing 
transducer along a linear path, that is, a linear actuator, includes a 
pair of precision cylindrical guide rails mounted parallel to the desired 
linear path of travel of the accessing transducer and a carriage having 
roller bearings mounted on opposite sides thereof to engage the guide 
rails. A generally flat coil member is mounted upon the carriage between 
bearings. At least one pair of permanent magnets of rectangular 
cross-section are fixedly mounted to a rigid base to provide an effective 
gap therebetween that is aligned with the path of travel of the effective 
coil section to bidirectionally drive the carriage in a direction and 
speed corresponding to the polarity and voltage of the direct current 
applied to the coil. Preferably, the coil member is mounted upon the 
carriage such that the effective coil section is located approximately 
coincident with the center of gravity of the carriage as a whole, and the 
roller bearings are arranged in pairs at each side of the carriage to 
engage the guide rails approximately equidistantly above and below the 
center of gravity of the carriage. With such a symmetrical relationship 
between the roller bearings and the flat effective coil section, 
practically all bending moments are eliminated in the plane that extends 
parallel to the coil section, thereby eliminating a potential source of 
vibration. 
In the preferred embodiment, one of the cylindrical guide rails is fixedly 
mounted to the base (or frame of the assembly in which the linear actuator 
is used), and the other rail is mounted for pivoting about an axis that is 
parallel to the fixed rail. Such pivotable rail is biased by a spring 
toward the fixed rail to thereby preload the carriage between both rails 
with controlled or preselected low-friction rolling resistance. 
Another preferred feature of the linear actuator of the present invention 
is that the actuator is of the long-gap/short-coil type, and the coil 
(more particularly, the flat effective coil section) is situated between 
the foremost and rearmost roller bearings. With this geometrical 
relationship, no significant bending moments are applied to the carriage 
in the plane parallel to the direction of travel, even when the carriage 
is moved to the extremities of its travel, that is, when the carriage is 
fully extended toward the media (e.g., the rotating disk) or fully 
retracted therefrom. 
A principal advantage of the present invention is that the linear actuator 
of this invention is that the aforementioned symmetry of the bearings and 
flat coil section affords a high degree of stability so that when caused 
to move swiftly back and forth across the disk or other media, minimal 
vibrations and thus undesirable resonances will occur. Also, the flat coil 
member has a relatively low mass, thus providing rapid accessing time. 
Also, the flat coil section may be fabricated according to 
state-of-the-art techniques from printed circuit material, thus minimizing 
its potential cost of manufacture. The preferred spring-biased pivotal 
guide rail arrangement provides for precise low-friction guidance of the 
carriage, while yet reducing the complexity of assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Now referring more particularly to FIGS. 1-3, it will be seen that a 
preferred embodiment of a linear actuator 10 includes a carriage 12 that 
is received for linear travel upon a base 14. The carriage includes a 
U-shaped frame 16 cast from a material of low or non-magnetic permeability 
such as aluminum. Transducers 18, in this embodiment, read/write heads are 
affixed to the leading of the carriage frame upon flexible support arms 20 
(such arms being commonly referred to and hereinafter called flexures). 
The flexures 20 support the transducers in vertically spaced, parallel 
relationships above and below the two rotating magnetic disks DK (FIGS. 2 
and 5) of a magnetic disk storage apparatus (not shown). The actuator 10, 
as previously discussed in connection with the prior art U.S. Pat. Nos. 
3,838,455 and 3,587,075, serves to accurately and very rapidly position 
the transducers relative to the tracks of the disks. 
The aforementioned stability of the linear actuator 10 is provided by 
supporting the carriage 12 for movement upon a pair of parallel, 
transversely spaced, precision cylindrical guide rails 22 and 24 further 
by utilizing a generally flat coil member 26 having a rectangular winding 
28, and by mounting the coil upon the carriage so that the effective 
winding section 28a of the winding 28 lies in a plane aligned with the 
axes of the cylindrical guide rails 22 and 24. The actuator includes a 
pair of block shaped (rectangular) permanent magnets 30 and 32 mounted in 
parallel spaced apart relation upon a U-shaped bracket 34 so that the air 
gap between the magnets is aligned with the path of travel of the flat 
coil member. The bracket is made of high magnetic permeability material so 
that it provides a flux return path. The magnets are preferably formed 
from ceramic material. The magnet bracket 34 is affixed at the rear end 
(relative to the disks or other media) of the base frame 14. It is noted 
at this point that although in this embodiment the magnets and guide rails 
are secured upon an integral base frame, such parts could also be directly 
mounted to the frame of the apparatus in which the actuator is used, that 
is, to the frame a direct access, magnetic or optic memory drive unit. 
The coil member is secured upon the carriage in a plane extending through 
the center of gravity thereof and the carriage is mounted for movement on 
the cylindrical guide rails 22 and 24 in a manner that assures that 
minimal bending moments (cantilevering action) will be induced upon the 
carriage by the electromagnetic forces to rapidly access the transducers 
18. The carriage 16 includes roller bearings or rollers, as specified 
hereinafter, that are arranged in pairs at the sides of the carriage frame 
16 to engage the rails 22 and 24. The lines of rolling contact of each 
pair of rollers are symmetrically disposed relative to the plane of the 
coil member indicted by the line A--A in FIG. 5 so that the point of 
application of force by the coil on the carriage--the center of the 
effective section 28a of the coil winding 28--is midway between the upper 
and lower rollers of each pair. It is, of course, understood the rollers 
maintain the carriage, and thus also the coil member 28, aligned with the 
parallel axes of the guide rails. 
The configuration of the carriage frame 16 and the attachment of the 
rollers thereto will now be particularly described in connection with 
FIGS. 2-4. Frame 16 is generally U-shaped in top plane (FIG. 2) and 
includes side arms 36 and 38 that extend perpendicularly from a cross 
member 40. The frame is received on the rails 22 and 24 with the arms 
projecting away from the disks DK. The frame is of an integral 
construction which, as stated hereinbefore, is cast from a non-ferrous 
material. Side arms 36 and 38 are recessed (FIG. 4) to provide a cavity 
into which the coil member 26 is affixed. The arms are spaced from each 
other by a distance greater than the width of the magnets 30, 32 to allow 
the carriage frame to be retracted and extended with the side arms being 
disposed at opposite sides of the magnets (i.e., to register with the gap 
between the magnets) and with the coil member extending through such gap 
between the magnets. FIG. 5 shows the extended position of the carriage; 
the effective winding section 28a of the coil winding is then disposed 
near the front ends of the magnets (relative to the rotating disks DK). 
As best seen in FIG. 4, the side arms 36 and 38 of the carriage frame 16 
are cut away to provide upper flat surfaces or lands and lower lands. Such 
lands extend at 45.degree. angles with the plane of the coil member 26, 
and thus the upper lands would, if projected, respectively perpendicularly 
intersect the planes of the lower lands. These lands provide surfaces for 
mounting the pairs of rollers at right angles with each other, as shall 
now be described. 
A single pair of rollers 42 and 44 are mounted at the center of the left 
side arm 36 on pins or shafts extending perpendicularly from the upper and 
lower lands thereof. Two pairs of rollers are mounted to the other or 
right side arm 38. The front or leading pair of rollers 46 and 48 (FIGS. 
2, 4 and 5) is mounted adjacent the front end of the right arm, and the 
trailing or rear pair of rollers 47 and 49 is mounted adjacent the rear 
end of the arm (FIGS. 2, 3 and 5). Such two pairs of rollers are also 
mounted similarly to rollers 42 and 44 so that the axes of rotation of the 
upper rollers are perpendicular to the axes of rotation of the underlying 
lower rollers. Such symmetry of the upper and lower rollers about the 
plane of the flat coil member 28 is such that the roller pairs engage the 
respective cylindrical guide rails, with two lines of rolling contact 
equidistantly spaced at opposite sides of (above and below in the 
illustrated arrangement) the plane through the axes of the guide rails 22 
and 24 (i.e., the plane through line A--A in FIG. 5). 
There is always some significant play in each of the rollers 42-49, that 
is, some limited looseness between the roller member in contact with the 
guide rails 22, 24 and the shafts thereof that are mounted to the side 
arms 36, 38 of the carriage frame 16. Another aspect of the present 
invention relates to the means for biasing (or preloading as it is 
popularly known) the rollers with a controlled relatively firm spring 
force against the cylindrical guide rails or rods 22 and 24 so that such 
play will not result in vibrations, particularly resonant vibrations. 
Vibrations may potentially be caused from such play when the carriage is 
rapidly accelerated or decelerated. In the preferred embodiment, 
preloading of the rollers is accomplished by fixedly mounting the guide 
rail 24 to a base frame 50 (FIGS. 1-4) and pivotally mounting the other 
guide rail 22 to base frame 50 for pivoting about an axis that is parallel 
to rail 24. The pivotal rail 24 is biased toward the fixed rail and is so 
mounted to the base frame that when it is firmly engaged between the 
single pair of rollers 42 and 44, the rails are aligned with the gap 
between the magnets and the coil member 26 is parallel to and 
equidistantly spaced between the magnets 30 and 32. The fixed rail 24 is 
secured upon pedestals 52 (FIGS. 1, 3 and 4). These pedestals hold the 
rail in elevated position to provide adequate clearance for movement of 
the lower rollers 44 and 48. The pivotal rail 22 is secured upon a 
Y-shaped pivotal pedestal structure 54, which as may be best seen in FIGS. 
1 and 4, provides clearance for movement of the lower roller 44. 
The pivotal mounting pedestal 54 includes posts at its forward and rearward 
ends upon which the rail 22 is supported. A pivot pin 56 is received in a 
bore extending longitudinally through its lower end (i.e., its end that is 
opposite from the rail 22). The front and rear ends of the pivot pin 56 
are engaged in V-shaped grooves formed in extensions 58 at the side of the 
base 18 (FIGS. 1 and 3). Such grooves are formed to enable the pedestal 54 
to pivot about an axis that is parallel to the fixed rail 24. The height 
of pivotal pedestal and the width of the base (particularly, the 
transverse distance between grooves for the pivot pin and fixed rail 24) 
are arranged to cause the flat coil 26 to be aligned with the axes of 
rails 22 and 24, thus properly in the magnet gap, when the rail 22 is 
preloaded or biased against the associated carriage rollers 42 and 44. 
The pivotal rail 22 is spring-biased toward the fixed rail 24 by a coil 
spring 60. Referring to FIGS. 1 and 4, the spring 60 is received in an 
outwardly facing, countersunk portion of a bore 62 formed in the base of 
the pivotal pedestal 54. The spring is engaged upon a pin 64 that extends 
transversely and outwardly from a base support portion 66. The pin 64 
extends through a smaller portion of bore 60 through the pedestal that is 
coaxial with the countersunk bore portions and a split ring or clip 70 is 
attached at the outer end of the pin to engage the spring in compression 
against the pedestal. It will be appreciated that manufacture and assembly 
of this preloading or spring-biasing arrangement is quite simple but yet 
the arrangement provides excellent preloading characteristics. 
The coil 28 is illustrated herein as a coil of copper wire having leads 
28c; such leads are only diagrammatically shown, it being understood by 
those of skill in this art that a flexible lead strip is provided for 
connection to the direct current power source of the associated memory 
accessing device (direct access storage device). The illustrated coil was 
formed on a removable rectangular coil form so that the longitudinal or 
side sections of the rectangular coil are sufficiently spaced from the 
sides of magnets 32, 34, thus making effective coil section 28a longer 
than the width of the magnets. Due to the comparatively small width of the 
effective coil section relative to the length of the magnets, the coil and 
magnet arrangement of the actuator 10 is of the so-called short coil/long 
gap type. 
The front end of the flat coil 26 abuts against the transverse portion 40 
of the carriage frame 16, and the coil has a length measured in its 
direction of travel such that its effective coil section 28a (at the rear 
end of the coil) is situated between the axes of the forward rollers 46 
and 48 and rearward rollers 48 and 49. That is, the straight flat 
effective coil section extends transversely of the carriage ahead of a 
transverse plane through the axes of the rear pair of rollers 48 and 49. 
This positioning minimizes any tendency for the coil to induce a bending 
moment on cantilevering action on the carriage about any of the rollers. 
It is noted, however, that the coil 28 may also be fabricated using 
state-of-the-art printed circuit board technology, such as, for example, 
shown in the U.S. Pat. No. 4,196,456 to Manzke et al. 
The connection of the flexures 20 to the carriage frame will now be briefly 
described. The integral transverse portion 40 at the front end of the 
carriage frame 16 extends substantially above and below the coil 26. The 
transverse frame portion is cut away at its corners to match the flats or 
lands on the side arms, thereby minimizing the weight of the frame. A 
center pair of flexures are affixed to flat projection 80 extending 
transversely at the center of the front face of the frame. An upper 
flexure is affixed to the underside of a removable plate 82 that is 
received in a recess formed in the upper edge of the transverse portion 
40. Similarly, a lower flexure is affixed upon the upper face of a plate 
84 that is removably received with a recess formed in the lower edge of 
the transverse portion of the frame. The plates 82 and 84 are each 
detachably secured by a screw to the frame. The particular flexure 
connection of this preferred embodiment facilitates precise assembly of 
flexures, while providing a compactness that reduces the overall length of 
the linear actuator 10. It is, however, understood that other means for 
mounting the accessing transducers to the carriage would also be suitable 
and that transducers other than those diagrammatically illustrated herein 
can be provided. It is, for example, intended that optical transducers can 
also be incorporated in the actuator. 
Although the best mode contemplated for carrying out the present invetion 
has been herein shown and described, it will be apparent that modification 
and variation may be made without departing from what is regarded to be 
the subject matter of the invention.