Turning – Process of turning
Reexamination Certificate
1999-03-05
2001-05-01
Scherbel, David A. (Department: 3722)
Turning
Process of turning
C082S046000, C082S047000, C076S101100
Reexamination Certificate
active
06223635
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for polishing balls for use in a ball bearing or the like, as well as to a method of forming an annular groove for guiding a ball when it is abraded.
As illustrated in
FIG. 1
, in this type of conventional ball polishing apparatus, a plurality of annular grooves (ball grooves)
4
having a size substantially equal to the diametrical size of a ball
3
to be polished are concentrically formed in a rotary plate
1
which rotates and in a fixed plate
2
which is stationary and opposite to the rotary plate
1
. A rotary conveyor
5
which rotates conveys and introduces the balls
3
to be polished to the annular grooves
4
where they are polished so as to comply with predetermined standards.
In actually polishing the balls
3
, some ball polishing apparatuses contain tens of thousands of balls
3
which are stored in the conveyor
5
at one time, and they are repeatedly polished by through feed. These “tens of thousands of balls
3
” stored in the conveyor
5
at one time will hereinafter be referred to as one lot. After the balls
3
of one lot have undergone all the processing steps, the next lot will be processed.
As illustrated in
FIGS. 2A and 2B
, the polishing process required for one lot usually includes several stages (e.g. three stages; i.e., a roughing stage, a semi-finishing stage, and a finishing stage). Machining pressures are controlled so as to ensure the accuracy of a machining speed and a diametrical size corresponding to each stage.
FIG. 2A
illustrates the relationship between machining pressures and the corresponding machining stages; and
FIG. 2B
illustrates the relationship between the amount of variations in the diametrical size of the ball and the respective machining stages.
As illustrated in
FIG. 2A
, the largest machining pressure is preset for the roughing stage, and a middle degree of machining pressure is preset for the semi-finishing stage. Then, the least machining pressure is preset for the finishing stage. In this way, the machining pressure is changed according to the machining stage, thereby increasing the amount of polishing of the ball
3
in the roughing stage and bringing the ball
3
close to a desired ball in terms of the accuracy of the surface and finished size (the diametrical size of the ball) in the finishing stage.
FIG. 2B
illustrates the amounts of scheduled polishing allowance for the ball
3
in the respective machining stages, indicating the difference between the purposes of machining.
FIG. 3
is a longitudinal cross section illustrating the configuration of the conventional ball polishing apparatus. In the drawing, supports
7
a,
7
b
are provided on a bed
6
. A rotary plate
1
is supported by the support
7
a
(on the left-hand side of the drawing) so as to be rotatable and movable in the longitudinal direction of the bed
6
. In other words, the support
7
a
doubles as a guide member. The rotary plate
1
is fixed to a flange
9
which is integrally formed at one end of a rotary shaft S. The rotary shaft
8
is rotatively inserted into the center hole formed in a piston rod
10
which is fitted into the center hole of the support
7
a
in a slidable manner. The rotary shaft
8
is supported at both ends by the piston rod
10
via rolling bearings
11
a
and
11
b,
such as ball bearings or taper-roller bearings, so as to be rotatable and to be slidable together with the piston rod
10
. A pulley
12
is fitted to the other end of the rotary shaft
8
via a spline so as to be slidable. The pulley
12
is connected to the drive shaft of a motor by way of an endless belt (not shown). The rotary plate
1
is rotated together with the rotary shaft
8
by means of a drive force of the motor.
Two oil chambers
13
a
and
13
b
are formed between the internal circumferential surface of the center hole of the support
7
a
and the external circumferential surface of the piston rod
10
, and liquid-operated (hydraulic) ports
14
a
and
14
b
are bored in the support
7
a
so as to communicate with the respective oil chambers
13
a
and
13
b.
These hydraulic ports
14
a
and
14
b
are connected to a hydraulic circuit (not shown). The rotary plate
1
slides over the bed
6
in its longitudinal direction in the drawing together with the piston rod
10
by alternate influx or efflux of a working (hydraulic) fluid into or out of the respective hydraulic chambers
13
a
and
13
b.
The rotary plate
1
is pressed against the surface of the fixed plate
2
mounted on the support
7
b
by feeding the hydraulic fluid into the hydraulic chamber
13
a,
and by discharging the hydraulic fluid out of the hydraulic chamber
13
b.
The pressing force is regulated by a pressure regulation mechanism provided in the hydraulic circuit. In
FIG. 3
, a bellows cover
15
prevents exposure of a portion of the piston rod
10
in the vicinity of one end of the support
7
a.
With the balls
3
to be polished being sandwiches between the rotary plate
1
and the fixed plate
2
(that is, between the annular grooves
4
), the rotary plate
1
is rotated while it is pressed against the fixed plate
2
. As a result, the balls
3
repeatedly pass along the annular grooves
4
, whereby the balls
3
are polished so as to achieve desired size and quality. This polishing process is usually carried out while machining pressures (the machining pressures of the rotary disk
1
) and the rotational speed of the rotary disk
1
, or the like, are regulated. Further, the polishing process is comprised of two or three steps; i.e., roughing and finishing steps or of three steps; i.e., roughing, semi-finishing, and finishing steps. In this case, it is desirable to control the machining load imposed on the ball
3
(a load imposed on the rotary plate
1
) in the final finishing process to ensure as small a force as possible with as high accuracy as possible.
In a case where annular grooves are formed in both plates of the conventional ball polishing apparatus, annular grooves are previously formed in the fixed plate by a lathe or the like, and this fixed plate is attached to a fixed plate mount on the main body of the polishing apparatus.
Subsequently, a so-called “plate conditioning” is carried out; namely, balls to be polished are introduced into the space between a plane rotary plate without annular grooves which has a grindstone fitted and the fixed plate having the annular grooves formed therein, and then the polishing of the balls is repeated, so that annular grooves are formed in the rotary plate. The “plate conditioning operation” is continued until the annular grooves of the rotary disk are formed to a predetermined depth, and uniform contact is ensured between the balls and the annular grooves formed in both plates.
The previously described conventional ball polishing apparatus presents the following problems:
A sliding guide mechanism is of high frictional resistance, and a rolling guide is usually subjected to an increase in frictional force due to a pre-load or resistance in it's sealing section. The frictional force or resistance is not negligible as compared to a pressure required to polish the ball
3
. For this reason, as illustrated in
FIG. 4
, hysteresis develops in the regulated machining pressure during the course of polishing of the balls
3
when the machining pressure is regulated according to the machining process. Further, since the frictional force changes even during stable machining operations, it is difficult to control the machining pressure with a high degree of accuracy.
In the conventional ball polishing apparatus illustrated in
FIG. 3
which uses the sliding guide, if the balls
3
are polished under the polishing pressures in the respective three machining steps; namely, the roughing step, the semi-finishing step, and the finishing step, as illustrated in
FIGS. 2A and 2B
, actual machining pressures in the respective machining steps change to become higher or lower due to the previously-described hysteresis with reference to preset
Jibu Shoji
Nojima Hiroyuki
Sato Chuichi
Sumita Yuichi
Tonooka Katsuhisa
Nguyen George
NSK Ltd.
Scherbel David A.
Sughrue Mion Zinn Macpeak & Seas, PLLC
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