Machine element or mechanism – Elements – Cams
Reexamination Certificate
1999-09-22
2002-05-28
Luong, Vinh T. (Department: 3682)
Machine element or mechanism
Elements
Cams
C074S567000, C384S255000, C123S090500
Reexamination Certificate
active
06393938
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a cam follower which includes a bearing unit mounted on a head portion of a cantilevered stud and each having rollers and an outer ring so that the outer peripheral surface of the outer ring constitutes a follower surface driven by a cam or cam-like guide rail (hereinafter “cam-driven surface”). More particularly, the present invention relates to an improved cam follower suitable for use in indexing drive devices and the like.
2. Description of the Related Art
Among various known types of cam followers is one which, as illustrated in
FIG. 5
, includes a bearing unit mounted on a head portion of a cantilevered stud
51
. The bearing unit includes rollers
52
and an outer ring
53
provided around the outer periphery of a distal end portion of the stud
51
. In indexing drive devices, a plurality of such cam followers
50
are disposed at equal intervals or pitches around a driven shaft. Driving shaft is disposed orthogonally to the driven shaft, and the driving shaft has a helical cam formed on its outer periphery. The surface of the helical cam (hereinafter “cam surface”) is capable of being sequentially brought into contact with one cam-driven surface to another. Specifically, as the driving shaft makes one rotation, the cam followers are caused to turn with the driven shaft by an angle equal to one pitch between the cam followers. In this way, the driven shaft is driven to turn by a given angle corresponding to the number of rotations of the driving shaft.
With the conventionally-known cam follower, the cam surface and cam-driven surface must of course be processed with high precision in order to attain predetermined linear contact with each other. However, if an inclination occurs in the cantilevered stud of the cam follower, the cam-driven would be brought in so-called “uneven or biased contact” with the cam surface, even in the case where the cam and cam-driven surfaces are processed with sufficient precision. In the case of an indexing drive device or the like, the main cause for such biased contact is that the cam followers project radially outward from the outer periphery of the driven shaft with the respective studs supported in a cantilever fashion and including the bearing units mounted on their head portions and thus the studs are apt to resiliently bend or incline due to the pressing force applied from the cam. Under such conditions, mechanical stress acting on the cam-driven surface and the rolling-contacting surfaces of the rollers and stud's head portion in each of the cam followers would assume a distribution pattern such that it becomes greater in regions closer to the proximal end of the cantilevered stud.
The stud may be secured to the periphery of the driven shaft in a previously inclined posture at an initial stage of assemblage of the cam follower, taking into account the possible resilient bending or inclination; in this case too, however, if the stud is secured to the periphery of the driven shaft in more than or less than a predetermined initial inclination due to manufacturing and assembling errors, then the mechanical stress acting on the cam-driven surface and the rolling-contacting surfaces of the rollers and stud's head portion would assume a distribution pattern such that it becomes greater in regions closer to the free (i.e., distal) or proximal end of the stud.
According to a “rated cam follower lifetime” based on the Japanese Industrial Standards (JIS B 1518-1992), it is required that the mechanical stress acting on the rolling-contacting surfaces of the rollers and stud's head portion be distributed uniformly. In cases where greatest mechanical stress occurs in a local region proximate to the free or proximal end of the cantilevered stud and decreases abruptly in a direction toward the other end, the actual lifetime of the cam follower would be shortened to a significant degree.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provided a cam follower which includes a cantilevered stud and a bearing unit having rollers and an outer ring mounted on a head portion of the cantilevered stud so that the outer peripheral surface of the outer ring constitutes a cam-driven surface, and which can effectively alleviate a maximum intensity level of mechanical stress adversely affecting the lifetime of the bearing unit.
It is another object of the present invention to provide a cam follower which includes a cantilevered stud and a bearing unit having rollers and an outer ring mounted on a head portion of the cantilevered stud so that the outer peripheral surface of the outer ring constitutes a cam-driven surface, and which can effectively level off mechanical stress adversely affecting the lifetime of the bearing unit.
According to a first aspect the present invention, there is provided a cam follower of the type comprising a cantilevered stud and a bearing unit mounted on a head portion of the stud and including rollers and an outer ring, an outer peripheral surface of the outer ring constituting a cam-driven surface. The cam-driven surface includes a central load bearing region substantially parallel to an axis of the cantilevered stud and a couple of load-reducing regions indented radially inward from the central load-bearing region and located on axial opposite sides of the central load-bearing region axially symmetrically to each other.
Because the cam-driven surface includes two radially-indented load-reducing regions formed axially symmetrically about the central load-bearing region, its effective length of contact with a cam surface is shortened as compared to the cam-driven surface of the conventional cam followers, and the pressing force from the cam or cam-like guide rail acts only on the central load-bearing region located at a given distance from the axial opposite ends of the cam-driven surface, instead of acting intensively on the axial opposite ends of the cam-driven surface. Further, in the present invention, the mechanical contact stress applied to the cam driven surface is not transmitted, as is, to between the inner surface of the outer ring and the outer surface of the roller and between the outer surface of the roller and the outer surface of the stud's head portion; instead, the mechanical stress transmitted to between the inner surface of the outer ring and the outer surface of the roller and between the outer surface of the roller and the outer surface of the stud's head portion are caused to present a maximum intensity level at points corresponding to the proximal end of one of the load-reducing regions and then gradually decreases in the directions toward the axial opposite ends of the roller. The load-reducing bearing regions may be formed by partly cutting away axial opposite end portions of the outer ring.
When the cantilevered stud is resiliently bent or inclined by the pressing force from the cam or when the cantilevered stud is inclined in any direction due to an assembling or manufacturing error, the mechanical stress acting on the cam-driven surface becomes greatest at a boundary between the central load-bearing region and one of the load-reducing regions and gradually decreases over the load-bearing region in a direction toward one of the axial opposite ends of the outer ring.
In the cam follower, distribution of the mechanical stress acting on the roller differs from distribution of the mechanical stress acting on the cam-driven surface. The inner peripheral surface of the outer ring and the outer peripheral surface of the stud's head portion extend parallel to the axis of the stud, and each of the rollers has a central cylindrical portion parallel to the axis of the stud and a couple of crown portions extending axially from the axial opposite ends of the cylindrical portion while gradually decreasing in diameter in the directions toward the axial opposite ends of the roller. Although the outer ring and rollers are normally made of steel and have considerable
Kosugi Futoshi
Maeno Tatsuo
Sahara Shinsuke
Dann Dorfman Herrell and Skillman
Luong Vinh T.
Skillman Henry H.
Tsubakimoto Chain Co.
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