Ball separator assembly

A ball bearing separator assembly comprising an annular ball separator having partitions extending axially from one side thereof, which partitions are abuttable with an annular retention ring, thus forming a circumferential array of ball pockets for bearings. The retention ring may have an axial array of fingers which snap into channels or voids in the partitions to lock them together. The ball separator in another embodiment may have pins which extend from the distal end of the molded separator partitions, which pins may mate with corresponding orifii in the retention ring. The pins may be distorted after mating with their respective orifii to secure the retention ring to the distal ends of the partitions on the ball separator. The annular body portions of the separator and its associated retention ring may be of reduced radial dimension adjacent the ball pockets thereof, to permit flexure of the separator assembly during rotation with a bearing about non-circular harmonic drive-type wave generator mechanisms.

BACKGROUND OF THE INVENTION 
(1) Field of the Invention 
This invention relates to the provision of separators for antifriction 
rolling elements, and is more especially concerned with providing improved 
ball separators for use in radially flexible bearings. The invention is 
thus particularly well adapted for use in transmissions or actuators of 
the type employing generators for imparting a radial wave of deflection, 
commonly known as harmonic drive transmissions or strain wave gearing. 
(2) Prior Art 
Harmonic drive actuators customarily include in concentric relation three 
elements: a circular spline, a flexspline engaging externally or 
internally with the circular spline, and a wave generator for radially 
deflecting the flexspline to effect such engagement at spaced 
circumferential points. One element in this compact transmission assembly 
may serve as input and another may function as the output. The present 
invention has particular application to a novel bearing assembly to be 
interposed between the flexspline and the wave generator to render 
generation of the wave shaping more efficient. 
In conventional annular ball bearings a separator is usually journalled on 
one of a pair of concentric race rings or may ride on the balls confined 
thereby. These commercially available separators may be formed with 
closely fitting, circumferentially spaced ball pockets for receiving and 
guiding the respective balls in raceways of the rings. While experience 
indicates that reasonably good performance may be expected of such 
bearings in some harmonic drive transmissions, the tendency is for the 
radially moving rolling elements in the load region of their 
circumferential travel to pinch or bind the separator, and provide undue 
wear. This problem is acknowledged in U.S. Pat. No. 3,285,099, which is 
assigned to the assignee of the present invention. This design however, 
shows a retaining ridge or platen for holding the separator axially in 
position. These components add inertia to the high speed rolling elements, 
which inertia is undesirable, because inertia slows down the response time 
of the components comprising the system in which they operate. 
Since the wave generator bearing may be elliptical (or trichoidal) in 
shape, the rolling elements thereabout move at varying radii and having a 
varying angular velocity. The prior art bearing separators have not 
minimized the inertia in strain wave gearing systems, nor have they 
provided a simple, inexpensive rolling element ring which is easy to 
assembly which provides long service life for motion in a non-circular 
path. 
In view of the foregoing, it is an object of the present invention, to 
provide, for use in a deflectable, out-of-round bearing, a more economical 
rolling element separator which shall be capable of reducing friction 
losses, and reduce the inertia over current bearing assemblies. 
It is a further object of the present invention, to provide a moldable 
separator, which permits mid-assembly inspection, which separator itself 
is easily assembled, and which readily adapts to a non-circular locus of 
motion. 
BRIEF SUMMARY OF THE INVENTION 
The present invention relates to ball bearing separators in radially 
flexible ball bearing assemblies. 
Harmonic drive actuators as aforementioned, may have an elliptoidal wave 
generator around which the ball bearing assembly is arranged. The ball 
bearing assembly is also arranged in relation to a flexspline having gear 
teeth which are radially deflectable into contact with gear teeth of a 
stationary spline. The ball bearing assembly comprises an inner race, an 
outer race, and a plurality of rolling elements, preferably balls, held by 
a separator assembly, thereinbetween. 
The separator assembly may be comprised of a ball separator and an axial 
retention ring. The ball separator comprises an annular body member having 
a plurality of axially arranged partitions disposed in a radially directed 
array spaced on one side thereof. Each pair of adjacent partitions has an 
arrangement of curved walls sufficient to maintain a ball therebetween, 
and which, with the annular body and retention ring defines a ball pocket. 
Each pocket is also of sufficient size to permit ball precession to occur 
without the ball binding with the ball separator, when the separator 
assembly is used in conjunction with an elliptoidal or trichoidal wave 
generator member in a harmonic drive assembly. 
The axially arranged partitions extending off the annular member, may each 
have a notch arranged near their proximal end on their radially innermost 
side thereof. A channel or void is formed in the partition, from the 
distal side of the notch, axially towards the distal end of the partition. 
The axial retention ring has a plurality of axially arranged fingers 
spaced on one side thereof, in juxtaposition with the partitions on the 
ball separator. The axial retention ring is coaxially matable with the 
ball separator, to form the separator assembly. The fingers on the axial 
retention ring mate respectively with the channels on the radially 
innermost side of the partitions. A lip is arranged radially outwardly on 
the distal end of each finger. The lip is shaped in an inverted "V" form 
to mate with the notch in the partition. Rotation of the bearing and 
corresponding rotation of the separator assembly causes centrifugal forces 
in the finger to "lock-in" the lip into the notch. 
The bearing unit may be assembled with the ball separator spaced between 
the inner and outer bearing races of the bearing assembly. The ball 
bearings may then be placed into the bearing pockets defined by the 
adjacent partitions. At this juncture in the assembly process, the proper 
clearances between the inner and outer races and the ball bearings and 
maybe even the unit on which the bearing assembly mates, may be observed 
and evaluated. Satisfactory inspection and pre-assembly will then permit 
the axial retention ring to be placed onto the ball separator, and snapped 
into place. 
The separator assembly, in a further embodiment, may be adaptable to ball 
bearing assemblies in which the separators themselves are radially 
deflectable. That is, those assemblies in harmonic-drive type units, 
wherein the inner or outer race would be engagable with an elliptoidal or 
trichoidal generator to cause an advancing deflection wave therein, as 
shown in U.S. Pat. No. 3,285,099. The separator assembly, in such an 
embodiment, would include the ball separator and the axial retention ring, 
as aforementioned. The ball separator and axial retention ring however, 
may each have circumferentially spaced portions of their annular bodies, 
cyclically tapering to reduced radial dimensions, from radially thicker 
dimensions and tapering back again to thicker portions, to allow flexing 
at those spaced thinner portions. The portions of pinched or reduced 
radial dimensions would be arranged between adjacent partitions. The 
radial dimension of the reduced portions would be less than the axial 
dimension of those reduced portions, that is, the width, of the annular 
body portions of the ball separator and the axial retention ring. The 
partitions in this embodiment, would still have concave surfaces to define 
a ball pocket, but the ball pockets need only be large enough to permit 
entrance of the ball during assembly, because precession does not occur in 
these embodiments, due to the radial flexing of the separator assembly in 
the radially flexible bearing assembly permitted by the circumferentially 
spaced pinched annular body portions by virtue of engagement of the 
partition walls with the balls. 
A further embodiment of a ball bearing separator assembly includes a 
separator member having axially arranged partitions on one side thereof, 
as well as a separate retention ring which butts against the distal ends 
of the partitions. There are however, axially arranged pins extending from 
the distal ends of the partitions which mate with corresponding spaced 
axially arranged orifii on the retention ring. The pins are molded with 
the entire separator member, from a thermoplastic material. After the ball 
members have been assembled in their appropriate pockets and the pins have 
mated with their corresponding openings or orifii in the retention ring, 
the distal ends of the pins may be distorted by heating means, or the 
like, to prevent the retention ring from separating from or loosening from 
the ball separator. The body portions of the ball separator and the 
retention ring in this embodiment may also have pinched segments of 
reduced radial dimension between adjacent partitions and their 
corresponding segments on the retention ring, as did one of the 
aforementioned embodiments, to permit flexing or bending of the separator 
assembly during motion thereof, thus accommodating the non-circular 
curvature of a harmonic drive type wave generator.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to the drawings in detail, and particularly to FIG. 1, there 
is shown a ball bearing separator assembly 10, rotatable about an axis, 
not shown, transverse thereto, which assembly 10 includes, a ball 
separator 12, and an axial retention ring 14. The ball separator 12 
comprises an annular body member 16 with a plurality of axially arranged 
partitions 18 circumferentially spaced on one side thereof. A ball pocket 
20 is defined as the generally cubically shaped volume disposed between 
adjacent partitions 18. Each partition 18 has a generally radially 
directed wall surface 22 on each side thereof. Each wall surface 22 
however, is concave in shape, and when paired together with a facing wall 
surface 22 of an adjacent partion, prevents radial excursion of a ball 24 
therefrom. Each concave wall surface 22 is of sufficient radial dimension, 
depending on the size of the particular balls 24 used, and each ball 
pocket 20 is of sufficient arcuate dimension to permit ball precession to 
occur, without allowing the ball to bind with respect to the ball 
separator 12. This was discussed in U.S. Pat. No. 3,285,099, and is herein 
incorporated by reference. 
The ball separator 12 and the retention ring 14 have a radially outermost 
peripheral surface 26 and 28 respectively, and they each have a radially 
innermost peripheral surface 30 and 32, respectively. 
The retention ring 14 has a plurality of fingers 34 annularly arranged on 
one side thereof, as shown in FIG. 1, directed towards the ball separator 
12. The fingers 34 are generally parallel with the axis of rotation of the 
ball bearing separator assembly 10, and are each arranged to interdigitate 
respectively with one of the partitions 18 of the ball separator 12. Each 
finger 34 comprises a main body portion 36 extending from the side of the 
retention ring 14 and having a radially innermost surface which is 
coplanar with the innermost surface 32 of the retention ring 14. A lip or 
tab 38 of generally inverted "V" configuration extends generally radially 
outwardly from the distal end of the main body portion 36 of each finger 
34. 
Each partition 18 has a channel or void 40 on its radially innermost 
portion which may receive a finger 34. Each void 40 is defined by a 
radially innermost surface 42 having a stepwise configuration 44, as shown 
in FIGS. 1 and 2 and the radially outermost surface of an inner race 46 of 
a ball bearing unit 48, shown partially in FIG. 2. The stepwise 
configuration 44 of the innermost surface 42 of each partition 18 permits 
the interdigitable mating between each finger 34 and its respective 
partition 18. 
The ball bearing unit 48, shown with the retention ring 14 and separator 12 
assembled in FIG. 2, also comprises an outer race 50. The inner and outer 
races 46 and 50 each have a trough-shaped channel 52 in which the balls 24 
may run. The ball bearing unit 48 is shown arranged about a central member 
54. 
Assembly of a ball bearing unit 48, would comprise the steps of placing the 
ball separator 12 in coaxial alignment between the coaxially arranged 
inner and outer race 46 and 50, depositing seratum the ball bearings 24 in 
their respective ball pockets 20, then checking the pro forma assembly for 
proper fit and alignment, thus permitting quality inspection. The 
retention ring 14, would then be aligned with the ball separator 12, so 
that the fingers 34 are in axial and radial alignment with the partitions 
18, and the retention ring would then be pushed into place, the tabs 38 
mating with the stepped configuration 44 of the radially inner surface 42 
of each partition 18. The snapping interdigitation would insure the 
locking therebetween. 
During rotation of the ball bearing separator assembly 10, centrifugal 
force causes each of the fingers 34 to press more tightly against the 
radially innermost surface 42 of the partition, further increasing their 
interlocking capabilities. 
Another embodiment of the above-identified ball bearing separator assembly 
78 is shown in FIG. 3, having a ball separator 60 which mates with a 
retention ring 62 as in one of the aforementioned embodiments. This 
embodiment however, includes a plurality of ball pockets 64 which mate 
more snugly with a ball 66 of a given size which will not allow 
significant ball precession during rotative travel around a harmonic drive 
type wave generator. The ball separator 60 comprises an annular body 
member 68 of reduced radial dimension at spaced circumferential 
localities, that is, between adjacent partitions 70. The retention ring 62 
is of corresponding reduced radial dimensions at corresponding spaced 
circumferential localities, that is between adjacent fingers 72. The ball 
separator 60 and the retention ring 62 have outer and an inner surfaces 74 
and 76 respectively, which define the reduced radial dimensions, those 
dimensions being stepped, curved or tapering from the radially thickest 
portions axially adjacent each partition 70 to the radially thinnest 
portions axially adjacent each ball pocket 64 and then being stepped, 
curved or tapering to the radially thickest portions axially adjacent each 
partion 70 (or finger 72) to begin the cycle anew. The radially smallest 
dimension r1 of the ball separator 60 and retention ring 62 being less 
than the axial dimensions a1 thereof, as shown in FIG. 3, (r1.gtoreq.a1). 
The reduced radial dimension of the ball separator 60 and the retention 
ring 62, which reduced radial dimensions are in axial alignment, permit a 
bearing assembly 78, which comprises the ball separator 60 and the 
retention ring 62 and balls 66, to bend at the points of reduced radial 
dimension, permitting their use in bearing assemblies around harmonic 
drive type wave generators of non-circular (elliptoidal or trichoidal) 
configuration exemplified by central members 54 of FIG. 2. The concavely 
curved walls of the partitions 70 by virtue of their snug engagement with 
the balls 24 as shown particularly in FIG. 5, cause the separator 60 and 
the ring to follow the non-circular path of the balls. 
A preferred further embodiment, is shown in FIG. 4, wherein a ball bearing 
separator assembly 80 comprises a ball separator 82, and a retaining ring 
84. The ball separator 82 includes a plurality of axially disposed 
partitions 86 extending off one side thereof, as shown in the 
aforementioned embodiments. The partitions 86 each have a pair of 
curvilinear sides 88 as the aforementioned embodiments, which define, 
along with an axially transverse wall 90 of the body of the ball separator 
82 and the retaining ring 84, a ball pocket 91, properly sufficient in 
size to retain a particular ball 92 therein, and of proper arcuate 
dimension to permit precession of each ball 92 with respect to the ball 
pocket 91 during rotation about a harmonic drive type wave generator. Each 
partition 86 may be of full radial dimension, (without the voids or 
channels of the aforementioned embodiments) which dimension is enough to 
secure the ball therebetween and be of the same radial dimension as the 
retention ring 84. A pin 94, molded from the same material and in the same 
mold as the ball separator 82, extends axially from the distal end of each 
partition 86, as shown in FIG. 4. An orifice or channel 96 is axially 
arranged and spaced circumferentially within the retention ring 84, 
corresponding to the positioning of each pin 94 molded into the ball 
separator 82. 
During assembly of the ball bearing separator assembly 80, after the 
particular balls 92 have been inserted into their respective ball pockets 
91, the retention ring 84 is fitted onto the ball separator 82 by 
insertion of the pins 94 through their respective channels 96 in the 
retention ring 84. The distal ends of the pins 94 which extend beyond the 
ring 84 may then be distorted or enlarged by known means, such as heating, 
to facilitate abuttable securement of the retention ring 84 against the 
distal ends of the partitions 86, thus completing assembly of the ball 
bearing separator assembly 80. 
The pinned ball separator 82 and retention ring 84, may have portions of 
their radial dimensions pinched or reduced at circumferentially spaced 
portions between their adjacent partitions 86, as shown in FIG. 5, and as 
was described in an earlier embodiment. If this configuration is chosen, 
the ball pockets 91 may be of the type described in the second embodiment, 
which is the close-fitting type, not permitting ball precession during 
movement around a harmonic drive-type wave generator, but which ball 
separator "bends" (with the pinched retention ring) to accommodate the 
non-circular contours of that particular non-circular wave generator and 
follow the path of the balls. 
Thus there has been shown several ball bearing separator assemblies which 
may be molded from plastic material, and which permit ball inspection 
prior to final assembly, and which separator assemblies minimize imbalance 
and torque problems in ball bearing assemblies which are undersirable in 
high speed harmonic drive type mechanisms. 
Though the invention has been described with a certain degree of 
particularity, it is intended that the appended claims be interpreted in a 
descriptive and not a limiting sense.