Bearings – Linear bearing – Recirculating
Reexamination Certificate
2001-11-15
2004-02-03
Footland, Lenard A. (Department: 3682)
Bearings
Linear bearing
Recirculating
Reexamination Certificate
active
06685354
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a guide apparatus which is used in a linear guide section of, e.g., a machine tool or a like tool, for the purpose of guiding a movable member, such as a table, over a stationary section, such as a bed, and in which a slider equipped with a plurality of rolling elements, which elements circulate endlessly, freely travels back and forth along a track rail. More specifically, the present invention relates to an improvement for effecting high-speed movement of a slider on the raceway rail.
2. Description of the Related Art
As a guide apparatus of this type, there has hitherto been known a guide apparatus comprising a track rail which is disposed on a stationary section, such as a bed, and has a raceway surface for rolling members, such as rollers, formed therein; and a slider which is attached to the track rail by way of a plurality of rolling elements and travels along the track rail while supporting a movable element such as a table.
The slider has a load raceway surface opposing a raceway surface of a track rail via rolling elements, and a return path disposed parallel to the load raceway surface. Further, the slider comprises a slide block that is movable along the track rail in association with rolling action of the rolling elements, and a pair of end caps. The end caps are fixed to respective end faces of the slide blocks and have a U-shaped turning path (called a “U-turn path). The U-turn path guides, toward the return path, rolling elements which have passed by a position between the load raceway surface of the slide block and the raceway surface of the track rail. The end caps are fixed to the respective end faces of the slide block, as a result of which the load raceway surface is connected to the end of the return path by way of the U-turn path. Thus, an endless circulation path is completed within the slider.
The rolling elements circulating through the endless circulation path of the slider roll through a position between the load raceway surface of the slide block and the raceway of the track rail. More specifically, the rolling elements roll through a load area while receiving the load exerted on the slide block. In a non-load area, the rolling elements are released from load and roll in a non-load state in which no load is exerted on the rolling elements.
FIG. 7
is an enlarged cross-sectional view showing a junction between the non-load area and the load area. More specifically, the drawing shows that rolling elements
101
having rolled through a U-turn path
100
without receiving load enter a position between a raceway surface
103
of a track rail
102
and a load raceway
105
of a slide block
104
. The load raceway surface
105
of the slide block
104
and the rolling elements
101
, such as balls or rollers, are made of steel but are not completely rigid bodies and have slight elasticity. In the load area, the load raceway surface
105
and the rolling elements
101
are susceptible to slight elastic deformation due to load, and in the non-load area the rolling elements are restored to their original shapes upon being released from the load. For these reasons, the inner diameter of the return path and that of the U-turn path
100
, which constitute the non-load area, are greater than the diameter of the rolling element
101
. However, an interval between the load raceway surface
105
of the slide block
104
in the load area and the raceway surface
103
of the track rail
102
is smaller than the diameter of the rolling element
101
. Hence, if the rolling elements
101
having rolled through the non-load area abruptly enter the load area, the rolling elements
101
are subjected to abrupt compression at the entrance of the load area. As a result, large resistance is imposed on circulation of the rolling elements
101
, and noise associated with circulation of the rolling elements
101
becomes greater. For these reasons, in order to smoothly and resiliently deform the rolling elements
101
which enter the load area from the non-load area, each longitudinal end of the load raceway surface
105
has hitherto been subjected to crowning. Each end of the load area is slightly broadened, in the form of a bell bottom, toward the non-load area. By means of such broadening of the load area, the rolling elements
101
that have rolled into the load area from the non-load area roll to the depth of the load area, thereby diminishing circulation resistance and noise of the rolling elements
101
.
As mentioned above, the U-turn path
100
constituting the non-load area is defined by the end cap
107
differing from the slide block
104
that has the load raceway surface
105
formed thereon. In order to effect smooth transfer of the rolling elements
101
between the non-load area and the load area, the end cap
107
must be positioned accurately in relation to the slide block
104
. In the related art, an attempt has been made to increase positional accuracy in attaching the end cap
107
to the slide block
104
, by means of fitting a boss projecting from the end cap
107
into a recessed hole formed in the end face of the slide block
104
, thereby completely matching the edge of the crowned load raceway surface
105
to a sidewall surface
106
at the interior diameter of the U-turn path
100
.
Even when positional accuracy in mounting the end cap
107
relative to the slide block
104
has been increased, the sidewall surface
106
at the interior diameter of the U-turn path
100
becomes lower than the edge of the load raceway surface
105
, by virtue of the relationship between accuracy in formation of the load raceway surface
105
and accuracy in formation of the plastic end cap
107
, as indicated by broken lines shown in FIG.
7
. Eventually, there may arise a case where the edge of the load raceway surface
105
projects slightly at a junction between the load raceway surface
105
and the U-turn path
100
. In this way, if the rolling elements
101
enter the load area from the U-turn path
100
, the rolling elements
101
collide with the edge of the thus-projecting load raceway surface
105
. Such a collision does not pose a serious problem when the slider travels along the track rail at a low speed; however, the collision poses a noticeable problem when there is a necessity of increasing the speed at which the slider is to travel along the track rail. Hence, if the speed at which the slider travels along the track rail is increased, within a given period of time a larger number of balls come to collision with the load raceway surface. As a result, resistance imposed on circulation of the rolling elements or noise becomes noticeable. Further, since impact energy is proportional to the square of speed, the edge of the projecting load raceway surface becomes vulnerable to damage.
A semi-circular guide section situated at the interior diameter of the U-turn path
100
has hitherto been attached to an end cap or a slide block. However, in order to increase an accuracy in formation of an endless circulation path, there has recently been practiced direct formation of the semi-circular guide section at the end face of the slide block by means of injection molding of synthetic resin (as described in Japanese Patent Application Laid-Open No. 317762/1995). Even in that case, difficulty is encountered in matching the edge of the load raceway surface to the inner side surface of the U-turn path having a semi-circular guide section provided thereon, without involvement of formation of a step. High-speed circulation of rolling elements has encountered the previous problems.
SUMMARY OF THE INVENTION
The present invention has been conceived in light of the drawbacks and aims at providing a linear guide apparatus which avoids occurrence of collision of rolling elements, which would otherwise arise when the rolling elements roll into a load area from a non-load area, thereby diminishing slide resistance and noise, which would otherwise arise when a slider moves at high speed rela
Michioka Hidekazu
Murata Tomozumi
Footland Lenard A.
THK Co. Ltd.
Westerman Hattori Daniels & Adrian LLP
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