Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
2000-11-09
2001-10-16
Estremsky, Sherry (Department: 3681)
Bearings
Rotary bearing
Antifriction bearing
C384S462000
Reexamination Certificate
active
06302588
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a rotary ball bearing. It relates especially to a bearing used to facilitate reciprocating rotary motion of a shaft or the like and to a method of distributing or replenishing lubricant in such a bearing.
Typically, a rotary ball bearing for a reciprocating rotary shaft or the like is constructed with two rings, namely an inner ring mounted to the shaft and an outer ring mounted to a stationary support or housing. The two rings define opposing races and are separated by a circular array of balls. Relative rotation of the rings results in the rolling of the balls along the races in the rings. In order to reduce rolling friction and to minimize wear of the bearing parts, the bearing is normally lubricated with a viscous lubricant such as oil or grease which occupies the spaces between the balls and the walls of the races. If the bearing is pre-loaded axially so that the internal clearances between the parts of the bearing are more or less removed, the balls are constrained against “skidding” in their races during normal operation of the bearing. In other words, the initial relationship between the balls and the races is fixed. Thus, if one bearing ring is rotated relative to the other back and forth through a small angle in reciprocation, each ball of the bearing rolls over a definite portion of the race in each ring and is constrained to roll over these same small areas of the races as long as the bearing remains in use.
Reciprocating rotary shafts with bearings such as this are often used to move a mirror used in beam scanning or steering applications. These applications include electronic manufacturing and repair operations in which a laser beam is directed to perform tasks such as the profiling, marking, cutting, drilling, and trimming of silicon and other semiconducting materials, the trimming and cutting of thick and thin films on semiconductors, the drilling of via holes in printed circuit boards, and the inspection of solder paste and component placement on printed circuit boards and infrared beam scanning among many others.
FIG. 3
shows a conventional rotary bearing as might be used in a reciprocating device such as a galvanometer. The bearing comprises an inner ring
2
and a concentric outer ring
4
, the two rings being separated radially by balls
6
which roll in races defined by the opposing surfaces of the rings. In cross section, those races may have cylindrical or, more often, elliptical curvature so stresses are highest where the radially inner and outer poles of the balls contact the bottoms of the races. A lubricant is invariably provided between the rings to minimize wear of the bearing parts. In a typical application, e.g., a shaft bearing for a galvanometer, the inner ring
2
may be angularly reciprocated relative to outer ring
4
about an axis A through a small angle &thgr; of, say, 0°-15°. Since the balls
6
roll along the same small segments of the races, after only a few minutes of operation, the lubricant present in the reciprocating ball bearing is squeezed out of the high-pressure regions between the balls and the races, primarily at the ball poles which contact the bottoms of the races. After only a relatively few reciprocations of the bearing ring
2
through an angle &thgr; of, say, 8°, small lubricant “hills”
8
build up in the races at the extreme ends of each ball's excursion along the races. Since the angle &thgr; through which the bearing rings
2
and
4
rotate relatively is always the same, there is no mechanism to return the lubricant
8
to the high-pressure areas of the bearing between the ball poles and bottoms of the races where it is needed. Resultantly, those areas tend to wear excessively.
If now the bearing rings
2
and
4
are caused to rotate relatively through a larger angle &thgr; of, say 10° for one reason or another, the lubricant hills
8
deposited as aforesaid will increase the torque required to rotate the bearing momentarily. Of course, once the new angular excursion of the bearing ring
2
is established, the original lubricant hills
8
will disappear and reform on the races at the new extremes of ball travel. This process goes on continuously for the life of the lubricant in a bearing used in a random reciprocating application and may not be noticed. Eventually however, all of the excess lubricant is “parked” at the extremes of the allowed bearing ball travel and thereafter has no great affect on day-to-day bearing operation. However, as noted above, the lubricant is not present in the high-pressure areas of the bearing where it is most needed. Consequently, excessive wear occurs at those locations so that the bearing has a relatively short useful life. In fact, the aforesaid lubricant parking phenomenon is the main cause of bearing failure in most reciprocating bearings since, unless one bearing ring can rotate completely around relative to the other, the excess lubricant is effectively lost to the lubricant replenishment process. This is why many failed bearings seem to have plenty of lubricant remaining in them. The lubricant is in fact there, but it is not available at the high-pressure areas of the bearings where it is most needed.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a long-lived ball bearing for reciprocating applications.
Another object of the invention is to provide an improved ball bearing for the reciprocating shaft of a galvanometer.
Another object of the invention is to provide a bearing of this type which has improved wear characteristics.
A further object of the invention is to provide a method of prolonging the life of a rotary ball bearing used in reciprocating applications.
Yet another object of the invention is to provide a method of redistributing the lubricant in a rotary shaft bearing.
Other objects will, in part, be obvious and will, in part, appear hereinafter.
The invention accordingly comprises several steps and the relation of one or more of said steps with respect to each of the others, and the article processing the features, properties and relation of elements which are exemplified in the following detailed description, and the scope of the invention will be indicated in the claims.
Briefly, my rotary bearing comprises at least three radially spaced concentric rings separated by at least two circular arrays of balls located between adjacent rings. The opposing faces of the rings define races and the balls in each array are separated by a cage enabling the balls to roll along the races defined by those rings. Typically, balls in the inner array are fewer and smaller than those in the outer array and the race crossections may have various shapes depending upon the particular application. In any event, the intermediate ring acts as the outer ring with respect to the inner array of balls and as the inner ring with respect to the outer array of balls.
Thus, the relationship between the rings and balls is no longer fixed because the intermediate ring can roll on both sets of balls independently of the inner and outer ring. As we shall see, this enables each ball to travel around the circumferences of its races or tracks even though the inner and outer rings only reciprocate relatively. To put it another way, if the inner and outer rings are fixed relatively, the intermediate ring is still free to rotate about the axis of the bearing thereby allowing the balls in each array to roll along their respective races independently of the angular relationship of the inner and outer rings.
It will be appreciated from the foregoing that as long as each array of balls can roll along the entire circumference of the track defined by the corresponding pair of adjacent rings, there will be no build-up of lubricant hills along the races defining that track. Because the recirculating arrays of balls will constantly redistribute or replenish the lubricant along the races, particularly at the bottoms of the races where it is most needed, bearing wear will be minimized.
An important aspect of th
Cesari and McKenna
Estremsky Sherry
GSI Lumonics Inc.
Lewis Tisha D.
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