Cam mechanism

Details Cam mechanism Cam mechanism

2001-10-22

2003-04-15

Hannon, Thomas R. (Department: 3682)

Bearings

Rotary bearing

Antifriction bearing

C074S425000

Reexamination Certificate

active

06547441

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a cam mechanism that incorporates a highly precise bearing assembly capable of significantly improving the dynamic and static positional stability of the cam mechanism's output shaft.
2. Description of the Current Art
Various types of intermittent indexing-type cam mechanisms are currently known in the art. These cam mechanisms incorporate input and output shafts as means of transferring torque into and out of the cam mechanism, and two bearings, axially aligned with and located at each of the input and output shafts as means of supporting both thrust and radial loads applied during operation of the cam mechanism. Tapered roller bearings are generally used in cases where the input and output shafts must operate with a high degree of precision.
FIGS. 20 and 21
show cam mechanism
1
a
in which input shaft
4
is rotatably supported at both ends by tapered roller bearings
3
mounted in housing
2
. Globoid cam
5
is axially formed on input shaft
4
. Output shaft
7
, whose rotating axis is offset 90-degrees in relation to that of input shaft
4
, is rotatably supported by tapered roller bearings
6
mounted at both ends of the shaft and supported by housing
2
. Turret
9
is installed to or integrally formed as part of output shaft
7
and incorporates cam followers
8
installed in a radial pattern on the axial perimeter of shaft
7
. Turret
9
and cam followers
8
are dimensioned so as to allow cam followers
8
to mesh with spiral channel
10
of globoid cam
5
. The rotation of input shaft
4
results in the rotation of output shaft
7
by means of cam followers
8
following the transverse movement of globoid cam valley
10
.
FIGS. 22 and 23
illustrate the structure of cam mechanism
1
b
which, similar to cam mechanism
1
a,
incorporates input shaft
4
and output shaft
7
. In cam mechanism
1
b
, output shaft
7
is formed as a ring-type structure that radially encompasses hollow cylindrical part
11
integrally formed at the center of housing
2
. Radial and thrust loads applied to output shaft
7
are born by housing
2
as will be explained. Multiple first cam followers
12
are installed in a radial pattern on the perimeter of the inwardly facing radial surface of input shaft
7
. First cam followers
12
slide along cylindrical surface
13
provided by housing
2
as means of bearing radial loads applied to input shaft
7
. Second cam followers
8
are installed to the outwardly facing perimeter of output shaft
7
and are located so as to mesh with cam valley
10
of globoid cam
5
. Support piece
15
, structured so as not to interfere with the rotation of globoid cam
5
, is installed within housing
2
, and ring flange
16
, formed as part of housing
2
, is located radially opposite to support piece
15
. Second cam followers
8
pass through the space provided between support piece
15
and ring flange
16
, thus forming a structure whereby support piece
15
and ring flange
15
are able to bear the thrust loads applied to output shaft
7
. Torque applied to input shaft
4
is transferred to output shaft
7
through the rotation of globoid cam
5
driving cam followers
8
, thus providing a mechanism through which the desired rotational position of output shaft
7
is controlled through the rotation of input shaft
4
.
Modern industry is being called upon to produce various types of components that must be made smaller and to more precise dimensions. This requirement has resulted in a demand for cam mechanisms that are able to operate with an extremely high degree of precision. It is proving difficult to make conventional cam mechanism structures operate with the degree of precision now required by many industrial applications. Even with the use of precision tapered roller bearings, conventional cam mechanisms cannot provide the high degree of operating precision called for in certain applications. This problem is the result of using standard commercial grade bearings in the construction of the cam mechanism, the difficulty of machining the housing, turret, and output shaft flanges to extremely tight tolerances, the difficulty of maintaining the required dimensions during assembly, and a general fall-off in dimensional accuracy that results from a combination of problems encountered during the manufacturing process. As a result, manufacturers often need to disassemble cam mechanisms that don't perform to specification, check and re-machine components, and re-assemble the cam mechanism to ascertain if the required operational specifications have been met.
A major problem encountered with the use of standard roller bearings is that the bearing is unable to deliver adequate performance after being installed as a component of the cam mechanism. The following discussion will explain some of the shortcomings that can be encountered when installing a roller bearing into the cam mechanism.
1: One problem is that gap can be generated between the axial surface of output shaft (a) and the inner circumference of the bearing race. Although the perimeter of output shaft (a) and the inner diameter of race (c) may be fabricated to perfectly concentric shapes, gap (d) can exist, as illustrated in
FIG. 24
, after the cam mechanism is assembled as a result of the diameter of inner race (c) being fabricated to a slightly large diameter. The operating precision of the cam mechanism is thus adversely affected due to gap (d) causing the misalignment of centerline (e) of output shaft (a) with centerline (f) of bearing (b). Moreover, variations in the radial load may continually change the position of gap (d), thus creating abrasion between output shaft (a) and inner race (c), a problem that results in a shortened service life for the cam mechanism.
2: There is also a problem in that the perimeter of output shaft (a) cannot always be made to a perfectly concentric shape. In order to prevent a gap from forming between the output shaft and bearing race (see the preceding paragraph), some cam mechanisms utilize press fit tolerances in the assembly of output shaft (a) to bearing (b). As shown in
FIG. 25
, an eccentrically shaped cross section of output shaft (a) can be transferred the inner race (c) of bearing (b) as a result of the press fit, thus distorting bearing race surface (h) that was fabricated to the specified shape and tolerances. As a result of the distorted contours of bearing race surface (h), excessive pressure is applied to some rollers (g) while others fail to contact the race surface, thus creating an eccentric roller path that degrades the bearing's rotating accuracy and makes it difficult for the cam mechanism to operate with a high degree of precision. Moreover, excessive pressure applied between rollers (g) and race surface (h) causes excessive wear that shortens the service life of the cam mechanism.
3: Another problem that can arise is an eccentric shape of the inner surface of race (c) that results in the inner contour of the race not accurately matching the perimeter contour of output shaft (a).
FIG. 26
provides a view of bearing (b) before (FIG. a) and after (FIG. b) insertion of output shaft (a) into the bearing race. Even though output shaft (a) may be formed to perfect concentricity, inserting the output shaft into the eccentrically shaped internal diameter of race (c) will transfer the eccentric shape to the race surface (h) and thereby distort the race and bearing surface on which the rollers ride (FIG. b).
4: Furthermore, it can prove difficult to maintain an accurate 90-degree angle between output shaft (a) and seating surface (i) of bearing (b). As shown in
FIG. 27
, radial flange (j) is provided on output shaft (a) as means of locating bearing (b). In cases where the machining process utilized to form flange (j) leaves metal particles or other debris on the flange surface, bearing (b) will not seat completely by becoming slightly cocked on the shaft, a problem that will result in a falloff of the rotating precision of the cam mechanism's ou

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