Bearings – Linear bearing – Recirculating
Reexamination Certificate
2000-09-20
2002-07-02
Footland, Lenard A. (Department: 3682)
Bearings
Linear bearing
Recirculating
Reexamination Certificate
active
06412983
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a linear motion guide unit in which a slider is movable on an elongated track rail by virtue of rolling elements running through recirculating passages where separating elements are each arranged between any adjacent rolling elements to keep the rolling elements against coming in engagement with each other.
2. Description of the Prior Art
In most linear motion guide units, the rolling elements run through the recirculating passages in the slider to allow the slider to move on the track rail. Nevertheless, any adjacent rolling elements can sometimes come into contact with each other when they run through the load areas provided between the track rail and the slider. Especially, the rolling elements in the linear motion guide units, as having neared each other, can sometimes come into contact or engagement with each other because a distance of the centers of adjacent rolling elements changes subtly owing to the eccentricity of each rolling element, the skew and deformation of the track rail, which might arise from external loads applied unevenly. As the rolling elements turn in the same direction, the contact forces at contact areas on one rolling element are opposite the contact forces on the other. Thus, the frictional forces arising from the contact or engagement of the adjacent rolling elements results in impeding the smooth running of the rolling elements. During sliding motion of the slider on the track rail, the rolling elements in the recirculating passages are subjected to the repeated collisions against one another as well as the raceways, and moreover the rolling is substituted frequently for sliding motion. This causes noise or vibration considerably high in frequency and consequently premature wear of the rolling elements as well as the recirculating passages, thus reducing the operating accuracy and the acceptable service life of the linear motion guide unit.
A linear motion guide unit has been conventionally proposed, in which separators are each arranged between any two adjacent rolling elements to keep the rolling elements from coming into direct contact with each other in the recirculating passages. Referring to
FIG. 10
, there is shown an example of the prior separators. A separator
50
in
FIG. 10
is made in a substantially cylindrical form and provided in axially opposite faces thereof with semi-spherical concavities
51
, which are arranged in symmetry to each accommodate a part of the sphere of any rolling element
20
. Any separator
50
has to be accepted commonly to isolate any two adjacent rolling elements
20
apart from each other, so that an axial distance between the centers of the semi-spherical concavities
51
is preselected to a fixed thickness t.
When the slider moves on the track rail, the rolling elements run through the recirculating passages, which are composed of non-loaded areas formed in the slider and load areas provided between first raceway grooves on the track rail and second raceway grooves on the slider. Most recirculating passages usually show some variance in length. Thus, when each of the separators
50
shown in
FIG. 5
is in turn interposed between any two adjacent rolling elements or balls
20
, the last separator can be sometimes interposed either too tightly or too loosely. Nevertheless, it is very tough to make the recirculating passage match in length with a circular string of the combined rolling elements and separators. Any separator cramped tightly can afford no play to the associated adjacent rolling elements, thereby increasing remarkably the sliding friction applied to the slider. To cope with this, it may be propose to prepare other types of the separators for the last separator, which are different in thickness t from the major separators to compensate for the variance in length of the recirculating passage. However, this needs to reserve many types of the separators differing in their axial thickness, resulting in disadvantages of complicated production and management of parts or components, which might cause the increase of production cost of the linear motion guide unit.
With the use of the separators having a fixed axial thickness, the rolling elements can sometimes dent the track rail with pitches nearly equal to that of the rolling elements. Thus, the slider can get scratched thereby resulting in causing noise, unacceptable vibration and badly premature wear. To deal with the disadvantage mentioned just above, a linear motion guide unit is disclosed in, for example, Japanese Patent Laid-Open No. 281154/1998, in which the separators to be interposed between any two adjacent rolling elements are made varied each other in their axial thickness to render unlike the pitches of the dents that might arise on the track rail, thereby to help ensure the slider moves smoothly with less noise. With this prior linear motion guide unit, many types of the separators, which are varied individually in axial thickness, are prepared previously and any desired type of the separator is selected depending on the interval between the adjacent rolling elements.
In another linear motion guide unit disclosed in Japanese Patent Laid-Open No. 126148/1993, in which the separators are also interposed between any two adjacent rolling elements, two types of separators are employed; many separators of a fixed axial thickness, and at least one of another type composed of halves adjustable relatively in position to make easy the production and assemblage of the linear motion guide unit. The separators are made less in size than the rolling elements and, therefore, the halves come to be produced in further small in size.
Japanese Utility Model Publication No. 10286/1976, moreover, discloses a ball bearing with separators, in which the separators interposed between the adjacent steel balls are each made with semi-spherical concavities that are less in the radius of curvature than the steel balls. In addition, the separators are elastic and also made with annular groove extending around the radially outer periphery thereof, thereby to allow freely adjusting the interval between any two adjacent balls.
Although but it may be considered to make the overall separator elastic, such separator is easily subjected to much deformation dependently on the force occurring between the adjacent rolling elements, so that the control of the interval between the adjacent balls becomes very complex. As will be seen from the above discussions, it may be worthwhile considering a recirculating-ball linear motion guide unit in which a separator is partly made ready to undergo elastic deformation so that the separator may not only absorb most variations in an interval between any two adjacent rolling elements with the deformation occurring in its elastic parts so far as the interval between the adjacent rolling elements remains within a preselected value, but also keep the interval between the adjacent rolling elements from becoming less than a preselected critical value, thereby making it possible to compensate for the variances in length of recirculating passages with the separator.
SUMMARY OF THE INVENTION
The present invention, therefore, has as its primary object to overcome the major problem in the prior linear motion guide unit where it is very tough to make a recirculating passage agree in length with a recirculating-ball string composed of rolling elements and separators disposed between any two adjacent rolling elements. More particular, it relates to a linear motion guide unit in which a separator is partly made ready to undergo elastic deformation so as to compensate for the variance in length of recirculating passage with the elastic performance, thereby making assembly operation easy and helping ensure smooth sliding motion with low noise.
The present invention is concerned with a linear motion guide unit comprising; a track rail having first raceway grooves on lengthwise side surfaces thereof; a slider riding astride on the track rail for movement in a sliding
Browdy and Neimark
Footland Lenard A.
Nippon Thompson Co. Ltd.
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