1. Field of the Invention
The present invention relates to a ball linear guide and a method of manufacturing the ball linear guide.
2. Description of the Prior Art
Ball linear guides have been used for a variety of applications, for example, X, Y and Z axes of machine tools such as NC machines; and slide portions of other machines, automatic welding machine, injection molding machines, automatic carrying devices, industrial robots, and other general industrial machines.
Ball linear guides have a general configuration that a ball continuously runs cyclically through a ring-shaped ball-cyclic-running path. FIGS. 10, 11 and 12 show an example of a structure of a prior art ball linear guide, wherein FIG. 10 is a perspective view of the structure; FIG. 11 is a sectional view taken on line X--X of FIG. 10, showing a ball-cyclic-running path; and FIG. 12 is a perspective view showing a state in which the structure is assembled.
In these figures, reference numeral 1 indicates a bearing main body placed on a raceway base 2; 3, 4 are end plates, serving as ball returning U-shaped cages, mounted on both ends of the bearing main body 1; 5 is a mounting bolt for mounting the end plates 3, 4 to the bearing main body 1; 6 is a loaded ball groove in the form of a dovetail groove formed in a side surface portion, facing a running surface of the raceway base 2, of the bearing main body 1; 7 is a loaded ball running in the loaded ball groove 6; 8 is a non-loaded ball hole formed on the opposed side to the above side surface portion, facing the running surface of the raceway base 2, of the bearing main body 1; 9, 10 are direction changing U-shaped grooves formed in the end plates 3, 4, respectively; 7' is a non-loaded ball running in each of the non-loaded ball hole 8, and direction changing U-shaped grooves 9, 10; 11 is a ball guiding semi-circular portion; and 12 is a bolt hole for mounting the ball linear guide main body 1 to a mating machine or apparatus. In addition, reference numeral 13 indicates an oil leakage preventive plate mounted on an outer side of each of the end plates 3, 4 with a screw 14.
In such a ball linear guide, a ball runs as the loaded ball 7 in the loaded ball groove 6, turning 180.degree., as the non-loaded ball 7', in the direction changing U-shaped groove 9 formed in the end plate 3, and it runs through the non-loaded ball hole 8. Then, the ball, as the non-loaded ball 7' turns 180.degree. again in the direction changing U-shaped groove 10 formed in the end plate 4, and it returns, as the loaded ball 7, into the loaded ball groove 6.
In this way, the ball-cyclic-running path, which is composed of the loaded ball groove 6, non-loaded ball hole 8 and direction changing U-shaped grooves 9, 10, takes the form of a field track. Of these components of the ball-cyclic-running path, the loaded ball groove 6 is easy to machine from outside thereof, but each of the non-loaded ball hole 8 and direction changing U-shaped grooves 9, 10 is difficult to machine from outside thereof. For this reason, as shown in FIG. 12, the ball linear guide is manufactured by the steps of separately preparing the components, that is, the ball linear guide main body 1 in which the loaded ball groove 6 and the linear non-loaded ball hole 8 have been already formed, the end plates 3, 4 in which the direction changing U-shaped grooves 9, 10 to be connected to the linear non-loaded ball hole 8 have been already formed, and the ball guiding semi-circular portions 11; and assembling them in one body.
The ball linear guides of this type have been disclosed, for example, in Japanese Patent Publication No. Sho 62-27287.
At present, in general, the bearing main body 1 is formed of a metallic block, and each of the end plates 3, 4 is formed of a resin member having a semi-circular ball path.
Specifically, the end plates 3, 4 having the semi-circular ball paths are fixedly by means of the mounting bolts 5 at both the ends of the bearing main body 1 formed of a block having linear ball paths, to be thus assembled into the ball linear guide.
In the prior art ball linear guide in which the end plates are assembled with the block, there are split lines between the end plates and the block. More concretely, at a mating portion between the end plate and the block, there is formed a step along the circumference of the mating portion of the ball path. That is, there exists a chamfer structure based on the step between the bearing main body 1 and each of the end plates 3, 4. Such a structure tends to obstruct smooth running and rotation of balls through the ball-cyclic-running path. This presents a problem in making difficult high speed rotation of balls and in causing vibrational noise due to the step. For the ball linear guide having end plates made of resin, there arises another problem that it has a low wear resistance and it is low in service life for lack of smooth rotation.
From viewpoint of manufacture, the prior art ball linear guide is disadvantageous in that the number of parts is large due to the split structure. This increases the number of assembling steps, for example, for mounting the end plates using bolt mounting taps and holes, to require mating works for the bolts and parts, thereby increasing the number of working steps. Further, the assembly must be performed with great care. In addition, the prior art manufacturing method requires the expense of a mold for the end plate.