Conventionally, as a linear guide device for guiding a movable body such as a table or the like along a fixed unit such as a bed or the like, there has been known a bearing for linear sliding in which a sliding base carrying a movable body such as a table or the like is moved along a track rail arranged on a fixed unit such as a bed, a saddle or the like, or a ball spline device in which a cylindrical nut member fitted to a spline shaft is moved along the spline shaft via balls.
Among them, as a former bearing for linear sliding, there has been known a constitution comprising a track rail having a ball rolling groove, a sliding base having a load rolling groove opposed to the ball rolling groove as well as a ball return hole in parallel therewith, having a direction change path for guiding balls from the load rolling groove to the ball return hole and moved along the track rail, and a number of balls rolling between the sliding base and the track rail while carrying a load and circulating an endless track constituted by the load rolling groove, the ball return hole and the direction change path of the sliding base.
Further, as a latter ball spline device, there has been known a constitution comprising a spline shaft having a ball rolling groove along the axial direction and a nut member having a load rolling groove opposed to the ball rolling groove and fitted to the outer periphery of the spline shaft via balls, where the nut member is moved along the spline shaft similarly in accordance with endless circulation of the balls and which is used by transmitting torque mutually between the nut member and the spline shaft.
According to the conventional linear guide device constituted as described above, the endless track of a sliding member such as the sliding base or the nut member is filled with the balls and accordingly, when the sliding member is moved along the track rail or a guide shaft such as the spline shaft, the balls contiguous to each other are circulated in the endless track while colliding with each other or rubbing each other and there poses a problem where the balls are worn at an early stage and the device life is shortened.
Hence, as means for resolving such a problem, there has been proposed a bearing for linear sliding in which a ball connector where a number of balls are aligned and held is integrated to the endless track (Japanese Unexamined Patent Publication No. JP-A-5-52217). As shown by FIG. 25 and FIG. 26, according to such a ball connector 200, spacers 202 are interposed among respective balls 201 contiguous to each other, the spacers 202 are connected by a pair of strip-like connecting members 203 along a direction of arranging the balls by which the balls 201 are connected in a rosary-like shape and the ball connector is fabricated by molding flexible resin by injection molding in which the balls 201 are arranged in a die as cores.
According to the conventional bearing for linear sliding constituted as described above, as shown by FIG. 27, the above-described ball connector 200 is integrated to a ball return hole 205 and direction change paths 206 of a sliding base 204 and circulated in the endless track and in this case, the spacers 202 are interposed among the balls 201 contiguous to each other and accordingly, mutual friction or collision among the balls is prevented and wear of the balls 201 can be prevented as less as possible.
Meanwhile, in circulating the balls in the endless track, the ball relieved of a load needs to be scooped up from the ball rolling groove of the track rail to the direction change path of the sliding base and in such a scoop-up operation, as shown by FIG. 28, it is preferable to guide the ball 201 in a direction where a ball rolling groove 208 of the track rail 207 and a load rolling groove 209 of the sliding base 204 are opposed to each other (hereinafter, described as ball contact direction). Because when the ball 201 is guided in such a direction, meandering of the ball 201 in the direction change path 206 is prevented and circulation of the ball 201 in the endless track of the sliding base 204 is carried out smoothly.
Meanwhile, from a standpoint of avoiding magnifying of the sliding base 204, there is a case where formation of the ball return hole 205 in the ball contact direction is not necessarily proper and there is a case where the ball return hole 205 cannot be formed in the ball contact direction for avoiding interference with a tap hole since the tap hole is formed at the sliding base 204 to fix a movable body such as a table or the like.
Accordingly, in order to promote the degree of freedom of a position of forming the ball return hole 205 in respect of the sliding base 204 while achieving smooth formation of circulation of the balls 201 in the endless track, as shown by FIG. 29, the direction change path 206 for guiding the balls from the load rolling groove 209 to the ball return hole 205 needs to form to bend from the ball contact direction.
Further, in the case of considering the inherent role of the direction change path where the direction of rolling the balls is reversed, it is preferable that the swirl radius of the balls in such a direction change path is large and for that purpose, the length of the direction change path needs to set long. However, in the case where the ball return hole is positioned in the ball contact direction in view from the load rolling groove, when the length of the direction change path is set long, an interval between the load rolling groove and the ball return hole is naturally widened and magnification of the sliding base cannot be avoided.
Accordingly, also in view thereof, the ball return hole needs to form at an arbitrary position of the sliding base and the direction change path for communicating and connecting the ball return hole with the load rolling groove needs to form to bend.
However, according to such a conventional ball connector 200, side edges of the strip-like connecting members 203 for connecting the respective spacers 202 are linearly formed and therefore, there poses a problem in which although the ball connector 200 is easy to bend in a direction intersecting with the faces of the connecting members 203 (arrow line A direction in FIG. 26), the ball connector 200 is difficult to bend in a direction in parallel with the faces of the connecting members 203 (arrow line B direction in FIG. 25), when the direction change path 206 is bent to deviate from the ball contact direction as mentioned above, the ball connector 200 is obliged to integrate into the endless track by forcibly bending it and therefore, smooth circulation of the ball connector 200 cannot be expected.
Therefore, according to the conventional linear guide device using the ball connector, when smoothness of circulation of the ball connector in the endless track is considered, the ball return hole is obliged to form in the ball contact direction in view from the load rolling groove which constitutes one factor for magnifying the sliding base.
Further, according to the conventional ball spline device described above, from a standpoint of achieving to downsize the nut member, the ball return hole needs to install as near to the inner diameter of the nut member as possible and it is difficult to form the ball return hole in the ball contact direction in view from the load rolling groove similar to the bearing for linear sliding mentioned above.
Therefore, when the conventional ball chain shown by FIG. 25 is integrated to the endless track of the ball spline device, smooth circulation of the ball chain cannot be expected.
Meanwhile, according to a ball screw device which is used with a purpose of converting rotational movement of a motor into linear movement and which constitutes a linear guide unit of a machine tool or the like by being used along with the linear guide device mentioned above, a screw shaft and a nut member are in mesh with each other via balls and the nut member is similarly provided with an endless track for the balls. Accordingly, from a standpoint of preventing wear of the balls circulating at inside of the nut member, it is preferable also for the ball screw device to integrate a ball connector to the endless track. However, as already has been explained, the conventional ball connector is provided with a structure where it is easy to bend only in specific directions and accordingly, it is difficult to integrate the ball connector to the ball endless track of the ball screw device.
That is, in integrating the ball connector to the ball endless track of the ball screw device, the ball connector needs to wind spirally in respect of the screw shaft. Accordingly, the ball connector needs to circulate not planarly but sterically and in the case of the conventional ball connector having small degree of freedom in respect of the bending direction, smooth circulation of the ball connector in the endless track cannot be expected. Further, when the ball connector is integrated to the ball screw device, the ball connector is obliged to circulate in the endless track in a state accompanied by more or less twist and when the conventional ball connector having a low degree of freedom in respect of the bending performance is used by forcibly twisting it, there is a concern where the balls are detached from the ball connector per se.