JPS58186545A - Feed screw drive - Google Patents

Abstract

PURPOSE:To realize restraint of thermal expansion of a screw shaft by putting preparatory tension, corresponding to only portion of the rising temperature of the screw shaft unrestrainable by cooling fluid, on a feed screw and having said preparatory tension absorbed. CONSTITUTION:A feed screw shaft 2 of a feed screw device, for accurately moving a mobile table and the like of a machine tool, is supported at its both ends by one pair of bearings 8 and 10 inserted in brackets 4 and 6 fixed on a basic stand 100 and its middle part is screwed in a ball nut 26. The screw shaft 2 is maintained at about desired temperature (for example, at 18-22 deg.C when desired temperature is 20 deg.), therefore, preparatory tension corresponding to temperature dispersion, that is, about + or -2 deg.C is enough as said preparatory tension to be given to the screw shaft 2 by nuts 12 and 16. Thus, thermal expansion of the screw shaft can be restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a feed screw device that prevents deterioration of positional accuracy due to heat generation of the feed screw.

Feed screw devices are widely used to accurately move moving tables of machine tools, etc., but in recent years, their feed speeds have increased significantly, and at rapid feed speeds of 10 m/min or more, they are not diagnostic and may not work properly. This is becoming more frequent and often used under harsh conditions.As the feed speed increases, even if a ball screw with low friction is used as the feed screw means, The influence that thermal expansion of the feed screw shaft has on positioning accuracy cannot be ignored.

Various measures have been considered to counter this problem, and one of them is to apply pre-tension to the screw shaft in advance. In other words, pre-tension is applied to the feed screw shaft in advance to stretch it.

Even if the temperature of the screw shaft increases due to heat generation, only the pretension changes, and the length of the screw shaft itself does not change.

By the way, it is not uncommon for the temperature rise of the feed screw shaft to exceed 10°0 when the feed screw is operated continuously at rapid speed. If the temperature of a screw shaft with a length of 1 m rises by 10°O, the coefficient of linear expansion is -5 1,2 x 10 /°o because the screw shaft is usually made of steel, and the amount of elongation is 120μ. It also becomes. On the other hand, a screw shaft with a shaft diameter of 4 [] am and a length of 1 nL is
K to stretch by 20 μm is approximately 3200 as pretension.
It is necessary to apply a load of 4 to the screw shaft.

Applying such a large load to the feed screw shaft is undesirable because the same load is also applied to the bearings supporting the screw shaft, leading to heat generation and damage to the bearings.

That is, it is extremely difficult to control the thermal expansion of the screw shaft using only pretension.

Another means of suppressing the elongation of the screw shaft is to forcibly cool the screw shaft. For example, a hollow hole is made in the screw shaft and a cooling fluid is passed through the hole. According to this means, the heat generated by the screw shaft is cooled by the fluid, and the thermal expansion of the screw shaft is suppressed. However, in the case of fluid cooling, it is unavoidable that the temperature of the screw shaft will deviate from the intended temperature by about ±1°0, and when considering the performance of the temperature detection part, the error will be about ±2°0. I have to look forward to it.

However, for the above-mentioned reason, the amount of elongation of the screw shaft when the temperature change is 20 is 24 μm, but this thermal expansion is a serious problem in positioning in precision machine tools.

In view of the above circumstances, it is an object of the present invention to provide a feed screw device that can suppress thermal expansion of a screw shaft by simultaneously employing the above two means. That is 8
In the present invention, the temperature rise of the screw shaft is suppressed mainly by cooling fluid to minimize thermal expansion.

This pretension is applied to the feed screw shaft to absorb the amount that cannot be suppressed completely.In this way, as mentioned above, the screw shaft can be brought to almost the desired temperature by the cooling fluid. Since the pretension can be regulated, it is only necessary to apply a relatively small load corresponding to this temperature variation.

Hereinafter, one embodiment of the present invention will be described in more detail based on the drawings.

In the accompanying drawings, a feed screw shaft 2 is pivotally supported at both ends by a pair of bearings 8 and 10 fitted into brackets 4 and 6 fixed to a base 100, and a pole nut 26 is screwed into the intermediate portion thereof. are combined. The bearings 8 and 10 are fixed by screwing the nuts 12 and 14 or the nut 16.1B onto the screw shaft 2 and the brackets 4 and 6, respectively.

The screw shaft 2 is rotatably supported by the brackets 4 and 6, which will be explained in detail later. One end of the screw shaft 2 is connected to a motor 22 via a coupling 20, and by driving the motor 22, the screw shaft 2 rotates and the table 2 fixed to the pole nut 26 is rotated.
4 is movable, but this is known, so
I will not mention it further here.

A hollow hole 3o is bored in the center of the feed screw shaft 2 along its entire length in the direction of the -c axis.

The openings at both ends are closed by plugs 32 and 34.

The feed screw shaft 2 is also formed with a pair of diametrical through holes 36 and 38 near each end so as to communicate with the hollow hole 30.

Caps 46 and 4 are fixed to the bracket 4 and B via seal members 42 and 44 in the through holes 36 and 3, respectively.
It is connected to 8. One cap 46 is for fluid discharge, and the other cap 48 is for fluid supply.

In this embodiment, before the feed screw device is assembled, the length of the screw large diameter portion 2a is shorter than the distance between the bearings 8 and 10.

The stepped portion 2c between the large diameter portion 2a and the small diameter portion 2b is a bearing @=
It's slightly off from 10. Then, when assembling, the small diameter part 2b
Natsuto 12. Each dimension is selected so that the stepped portion 2c abuts the bearings 8, 1o when the nut 16 is screwed together and pretension is applied to the screw shaft 2.

In this case, nuts 12. The load applied to the screw shaft 2K by the 16° nut is relatively small, so that the bearings 8 and 10 will not be damaged due to overload during assembly. The reason for this will be explained below.

During operation of the device, cooling fluid is forced from the cap 48 through the through hole 38 into the hollow hole 30, and after flowing through the hollow hole 30, is discharged from the cap 46 through the through hole 36.

Therefore.

The screw shaft 2 is brought to approximately the desired temperature by this cooling fluid (for example, when the desired temperature is 20°0).

18-22°0). Therefore.

Natsu 12. The pretension applied to the screw shaft 2 by the nut 16 is equal to the temperature variation described above.

In other words, it is sufficient to add an amount corresponding to approximately ±2°0.

For example, if the screw shaft 2 has a shaft diameter of 40 layers and a length of one shoulder, the screw shaft 2 will elongate by about 24 μm if only the cooling fluid is used for cooling.

It is sufficient to apply pre-tension by applying a load of about 600 kg. This is a much smaller value than the conventional example, and it is possible to prevent overload from being applied to the bearings 8, 10, etc.

The device is also easy to assemble. This allows the feed screw device to maintain stable feed accuracy.

It should be noted that the above-described embodiment is one embodiment of the present invention, and the present invention should not be interpreted as being limited thereto, and it goes without saying that details can be changed and improved as appropriate.

[Brief explanation of drawings]

The accompanying drawing is a cross-sectional view showing an embodiment of a feed screw device according to the present invention. [Explanation of symbols of main parts] 2--------One feed screw 4.6---Bracket s, 1o---One bearing 12.14; 16, 1B---Nut

Claims (1)

[Scope of Claims] A feed screw device in which a nut screwed onto a feed screw shaft is moved when the feed screw shaft is rotated. A hollow hole in the axial direction is made in the screw shaft, and a fluid is circulated through the hollow hole to cool the screw shaft. At the same time, the screw shaft is pretensioned by a nut at both ends, and the magnitude of the pretension is (1) A feed screw device characterized by having a size corresponding to the variation in temperature control by the fluid.