JPH0449A - Ball screw shaft - Google Patents

Abstract

PURPOSE:To improve the efficiency of grinding work of an outer size such as shortening of an outer size grinding time, reduction of the degree of consumption of a grinding wheel, to reduce weight, and to decrease inertial moment by forming a clearance part for grinding of an outer size in the land part of the outer size part of a screw shaft to reduce a grinding area. CONSTITUTION:After the outer size of a shaft material is cut to a specified size, machining work for a ball screw groove 6 is effected. During machining work, a clearance part 4 having depth slightly deeper than a cut amount during grinding of an outer size is formed in the shape of a helical groove in an outer size part except the vicinity of a ball screw groove 6 of a land part 5. Thereafter, after surface hardening of a screw shaft through heat treatment is effected, finish grinding of the outer size of the land part 5 is effected. Finish groove grinding work is applied to the ball screw groove 6 located in the central position of the land part 5. During grinding of the groove, the ground surface of the land part 5 is used as a work reference surface. During cylinder grinding of the land part, an actual grinding area is sharply reduce, and by increasing the depth of a groove formed in the land part, a shaft weight is reduced on the whole, and inertial moment is reduced.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a ball screw shaft incorporated in a ball screw device, and in particular, in a large lead or extra large lead ball screw shaft with a large thread groove pinch, the shaft outer diameter grinding portion ( This invention relates to a ball screw shaft that reduces the grinding area (land part).

[Prior art]

In precision ball screw shafts, the outside diameter of the shaft is generally finished by cylindrical finish grinding, which is used as the processing standard for ball screw grooves. The same applies to the large lead or extra large lead ball screw shaft 1 in which the ball screw groove 2 has a large pinch as shown in Fig. 4, and the shaft outer diameter portion 3 and the ball screw groove 2 are first machined by turning the shaft material. After that, hardening treatment such as heat treatment is performed, and then the shaft outer diameter portion 3 is cylindrically ground, and the thread groove is finished by grinding based on this shaft outer diameter grinding portion. In the case of a large lead or extra large lead ball screw shaft, the width T of the shaft outer diameter portion 3 is wide;
Therefore, the outer diameter cylindrical grinding area also becomes large. In addition, in the case of a ball screw shaft l with a large lead or an extra-large lead, the diameter of the shaft outer diameter portion 3 may be increased in order to minimize the lead angle of the ball screw shaft 2 due to issues such as screw efficiency and ball circulation operation. However, in this case, although the width of the land portion on the outer diameter of the shaft does not change, the outer diameter increases and the amount of grinding increases, so it takes time to grind the outer diameter portion of the shaft with a grindstone.

[Problem to be solved by the invention]

As mentioned above, on the ball screw shaft of a precision ball screw device, cylindrical outer diameter grinding is performed on the land portion of the outer diameter of the screw shaft in order to use it as a reference surface for machining the ball screw groove. In this case, the width of the land portion is wider than that of the ball screw groove, and the cylindrical grinding area becomes correspondingly larger, which takes time for grinding and causes a decrease in productivity. Furthermore, since the grinding area is large, grinding resistance and heat generation are large, and there is a problem in that it is difficult to improve the bending accuracy during machining of the ball screw shaft. Furthermore, large lead and extra large lead ball screw shafts with a large outer diameter have a large moment of inertia during rotation, which is disadvantageous in terms of improving the precision of the ball screw device.

SUMMARY OF THE INVENTION In view of the above-mentioned problems, it is an object of the present invention to provide a ball screw shaft in which the grinding area of the outside diameter of the shaft and the moment of inertia are reduced without weakening the shaft rigidity.

[Means to solve the problem]

The ball screw shaft according to the present invention has a relief portion having a smaller diameter than the shaft outer diameter in the middle of the shaft outer diameter land between the ball screw grooves.

The depth of this relief part is determined so as not to exceed the rigidity of the ball screw shaft by t, but especially when the outer diameter of the land part is large, such as in a large lead or extra-large lead ball screw shaft, the depth of the relief part is set so as not to exceed the rigidity of the ball screw shaft. It is better to reduce the moment of inertia.

[Effect]

In the present invention, a spiral groove is formed in advance in the land portion between the ball screw grooves of the ball screw shaft at a midway position of the land portion by turning or the like as a pre-process of the grinding process. During cylindrical grinding of parts, the actual grinding area of the grindstone is significantly reduced.

In addition, by deepening the groove formed in the land portion,
Overall, the shaft weight is reduced and the moment of inertia is reduced.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

The first embodiment shown in the first example has one relief part 4 in the land part.
This is an example of a spiral shape. After cutting the outer diameter of the shaft material to the specified dimensions, the ball screw groove is turned, and the outer diameter portion of the land other than the vicinity of the ball screw groove is cut by the amount of cut during outer diameter grinding. Also, a slightly deep relief part 4 is formed in the shape of a spiral groove. Thereafter, the surface of the screw shaft is hardened by heat treatment, and then the outer diameter of the land portion 5 is finished ground. Then, the ball screw groove 6 located at the center of the land portion 5 is subjected to finishing groove grinding. Ball screw groove 6
When groove grinding is performed, the ground surface of the land portion 5 is used as a processing reference surface. On the other hand, the second embodiment shown in FIG.
2 on the land between the ball screw grooves 6 and 6.
This forms a book relief part 44'. As a result, the outer diameter grinding surface remains at the center of the land portion 5, so that the screw shaft can be stably supported during outer diameter grinding. This embodiment is particularly suitable for an extra-large lead ball screw shaft with a wide land portion.

The third embodiment shown in FIG. 3 is an example in which the depth of the relief part 7 of the land part is cut so that it is deeper than the groove bottom of the ball screw groove 6. This makes the ball screw shaft lightweight. The moment of inertia during operation of the ball screw device is reduced.

In each of the above embodiments, the outer diameter grinding area of the land portion 5 is reduced compared to the case without the relief portion, and since the outer diameter grinding surface of the land portion exists near the ball screw groove, the thread groove grinding finish is improved. It does not interfere with the standard chamfering of processing.

〔Effect of the invention〕

As explained above, according to the present invention, a relief part for outer diameter grinding is formed in the land part of the outer diameter part of the screw shaft, and the grinding area is reduced, so that the outer diameter grinding processing time is shortened and the grinding wheel is worn out. In addition to improving the efficiency of outer diameter grinding, such as reducing the
Grinding resistance and heat generation during machining are reduced, and machining accuracy such as bending is improved.

The present invention is particularly effective when applied to large leads with wide land portions and ultra-thick ball screw shafts - reducing the weight of screw shaft combinations,
Various effects are brought about, such as lowering the moment of inertia and increasing operational responsiveness.

[Brief explanation of the drawing]

FIG. 1 is a side view of a ball screw shaft according to a first embodiment of the present invention, FIG. 2 is a side view of a second embodiment of the present invention, and FIG. 3 is a side view of a ball screw shaft according to a third embodiment of the present invention. The fourth side view is a side view of a conventional ball screw shaft. 1... Ball screw shaft, 2, 6... Ball screw groove, 4
．． 4', 7...Escape part, 5...Land part.

Claims (2)

[Claims] (1) A ball screw shaft characterized in that a relief portion having a smaller diameter than the shaft outer diameter is formed in the middle of the land portion of the shaft outer diameter between the ball screw grooves. (2) The ball screw shaft according to claim 1, wherein the relief portion is formed to have a smaller diameter than the outer diameter of the groove bottom of the ball screw groove so that it also serves as a groove for reducing the moment of inertia.