JP2000018364A - Ball screw device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ball screw device capable of rotation at high speed even if its natural frequency decreases as the result of extension of stroke, while achieving high accuracy for the rotation at high speed and enabling extension of the stroke whereby the effect of the rotation at high speed is highly exercised. SOLUTION: A nut rotation type ball screw device 3 includes a threaded shaft 1 having a helical ball thread groove on its outer peripheral surface, a ball nut 2 having a ball thread groove on its inner peripheral surface that is opposite to the ball thread groove in the threaded shaft 1 and being rotatable about the threaded shaft 1, and a rolling element freely rollingly fitted between the ball thread groove in the threaded shaft 1 and the ball thread groove in the ball nut 2. The threaded shaft 1 is provided with cooling mechanisms R1, 1t, 1i, 1o. The threaded shaft 1 is provided with a cavity 1s, in which a damper 4 is inserted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ball screw device, and more particularly, to a ball screw device used for driving a machine tool at high speed and realizing high speed and high precision.

[0002]

2. Description of the Related Art Conventionally, as a ball screw device, for example, as disclosed in Japanese Utility Model Publication No. 6-11433,
2. Description of the Related Art A tube-type ball screw in which a nut is screwed to a screw shaft having a spiral groove via a rolling element such as a steel ball is known. A spiral groove corresponding to the spiral groove of the screw shaft is provided on the inner surface of the nut. When the screw shaft or the nut rotates, the ball moves while rolling in the two spiral grooves, and the nut moves linearly along the screw shaft.

In the above-described ball screw device, when feeding is performed at a high speed, the amount of heat generated increases and the temperature rises, and the screw shaft expands, which adversely affects the accuracy of the feeding direction. In the case of nut rotation and fixed shaft (no rotation), the heat radiation effect from the screw shaft is smaller than that of shaft rotation.
There was a problem that the temperature rise was large. Further, if both ends of the screw shaft are fixed to the machine base, there is a problem that the machine base is deformed when the thermal expansion of the screw shaft is large, and an example of a support structure in which one end can slide in the axial direction is provided. There are many. This support structure has a problem that the rigidity in the feed direction is reduced. For this reason, it has been difficult to use the ball screw device at high speed.

When a ball made of a ceramic material is used as a rolling element, expansion due to a rise in temperature is reduced due to a small coefficient of linear expansion, and since its specific gravity is small, a preload for improving positioning accuracy in the axial direction is reduced. Increase is not enough. In addition, since the linear expansion coefficient of the rolling element is smaller than that of a metal ball screw shaft / ball nut, when high-speed feeding is performed, there is a problem that a clearance is easily generated inside the ball screw and preload is lost. As a result, the positioning accuracy of the ball screw device may be deteriorated.

Further, recently, the speed of a machine tool has been increased, and it has become possible to set a feed rate to 60 m / min and an acceleration to about 1 to 1.5 G. However, even if the speed can be increased, if the screw shaft is short and the stroke is short, FIG.
As shown in the figure above, the stroke becomes full when the rotation rises and falls, and the time during which the feed speed is high cannot be extended too much.If the effective stroke is short, the advantage of high speed can be fully utilized. Not done. When the stroke is long, as shown in FIG. 2, the time ratio of the high feed rate becomes large, and the advantage of high speed comes into play. However, when the stroke is long, the natural frequency of the screw shaft decreases, which is dangerous. There is a problem that the speed decreases and high-speed rotation cannot be performed.

[0006]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and realizes a ball screw device that prevents a temperature rise during high-speed rotation and that achieves high precision and high rigidity at high-speed rotation. The purpose is to: It is another object of the present invention to provide a ball screw device capable of achieving a long stroke that exhibits a high-speed rotation effect, and capable of high-speed rotation even if the natural frequency is reduced by increasing the stroke. .

[0007]

In order to achieve these objects, a ball screw device according to the present invention comprises: a screw shaft having a helical ball screw groove on its outer peripheral surface; A ball nut having a ball screw groove on its inner peripheral surface and rotating around the screw shaft; and a ball screw groove of the screw shaft and a ball screw groove of the ball nut rotatably fitted. And a cooling mechanism provided on the screw shaft.

[0008] The cooling mechanism may be characterized in that a hollow is provided in the screw shaft, and a coolant is passed through the hollow.

Further, a hollow may be provided in the screw shaft, and a damper may be inserted into the hollow.

Further, the damper has a gap in the radial direction between the damper and the hollow inner wall of the screw shaft, and the cooling mechanism allows the coolant to pass through the gap in the axial direction. Good.

Still further, the damper may have a hollow hole in the axial direction, and the cooling mechanism may be characterized in that the coolant passes through the hollow hole of the damper in the axial direction.

According to the present invention, the cooling mechanism is provided on the screw shaft in the nut rotation type ball screw device, so that the screw shaft hollow cooling can be performed with a simple structure, and the thermal expansion of the screw shaft due to the temperature rise at high speed rotation is reduced. Prevention and high-precision feeding became possible. In addition, by adding a damper to the hollow part of the shaft, it is possible to avoid the problem of critical speed of the screw shaft even in long strokes, which exerts high speed rotation effect, and it is possible to further increase the speed of machine tool high speed feed and cutting feed. It became.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described specifically. FIG. 3 is a front partial cross-sectional view of a nut rotating ball screw device according to one embodiment of the present invention, and FIG. 4 is a front partial cross-sectional view of a nut rotating ball screw device according to another embodiment of the present invention. FIG. 5 is a partial front sectional view of an example in which shaft hollow cooling is performed in a screw shaft drive type ball screw device.

(1) First Embodiment A ball screw device 3 shown in FIG.
Nut 2 rotatable around the cooling device R
1 is provided. The screw shaft 1 is fixed to the base 5 near both ends thereof. The slide table 6 is connected to the ball nut 2 via the mounting housing 8.
And is movable in parallel with the axial direction of the screw shaft 1. The ball screw device 3, the base 5, and the slide table 6 constitute a table driving device.

The screw shaft 1 has a helical ball screw groove 7 on the outer peripheral surface. The ball nut 2 is formed in a substantially cylindrical shape, has a ball screw groove (not shown) facing the ball screw groove 7 of the screw shaft 1 on the inner peripheral surface, and is provided with a ball circulation tube 10. A large number of rolling elements (balls) are formed by the ball screw groove 7 of the screw shaft 1 and the ball nut 2.
Rollably fit between the ball screw groove of the head. A drive motor 9 for rotating the ball nut 2 is fixed to the mounting housing 8. The pulley of the motor 9 and the pulley of the ball nut 2 are connected by a belt 11.

The screw shaft 1 has a hollow 1s penetrating in the axial direction.
Is provided. One end of the hollow 1s is connected to the inflow pipe 1i, and the other end is connected to the discharge pipe 1o. The inflow pipe 1i and the discharge pipe 1o are connected to the cooling device R1 via the conduction pipe 1t. The hollow 1s of these screw shafts 1, the inflow pipe 1i, the discharge pipe 1o, the conduction pipe 1
t and the cooling device R1 constitute a cooling mechanism.

The ball, screw shaft 1, ball nut 2
Are made of steel. However, the ball may be made of ceramic having a small specific gravity and a small coefficient of linear expansion.

In such a nut rotating type ball screw device, when the ball nut 2 is rotated around the screw shaft 1 by the drive motor 9, the screw shaft 1 and the ball nut 2 are rotated.
The ball advances while rolling in the ball screw groove. When the ball goes around the ball screw groove a predetermined number of times, the ball is scooped up from one end of the ball circulation tube 10, passes through the tube 10, and returns to the ball screw groove from the other end of the tube 10. The ball nut 2 and the slide table 6 supported by the ball nut 2 move linearly in the process of moving the ball while rolling in the ball screw groove by the rotation of the ball nut 2.

The cooling mechanism of the present embodiment cools the entire ball screw device by passing a coolant such as water or oil through the hollow 1s of the screw shaft 1. That is,
The coolant supplied from the cooling device R1 is introduced into the hollow 1s of the screw shaft 1 from the inflow pipe 1i, passes through the inside of the screw shaft, cools the entire ball screw, is discharged from the discharge pipe 1o, and is discharged to the cooling device R1. Return is used again.

Here, the driving method of the ball nut is such that the driving motor 9 is connected to the ball nut 2 and the ball nut is driven by the power. However, the present invention is not limited to this. May constitute the ball nut itself and drive it directly.

In the present embodiment, by passing a coolant through the hollow of the screw shaft 1, it is possible to suppress the temperature rise of the entire ball screw device, suppress the thermal displacement of the screw shaft, and improve the precision of the ball screw device. it can. In the present embodiment, the ball is made of steel. However, when the ball is made of ceramic, a change in the internal clearance of the ball screw device caused by a small linear expansion coefficient of the ceramic material is suppressed, and high positioning accuracy is achieved. Can be achieved.

Further, according to the present embodiment, the cooling mechanism is provided on the screw shaft of the ball nut rotating ball screw device, so that the cooling device can be provided with a simple structure.

(2) Second Embodiment FIG. 4 shows a ball screw device 3 'according to a second embodiment of the present invention. In FIG. 4, the schematic configuration of the ball screw device is substantially the same as that of the first embodiment shown in FIG. 3, but in this embodiment, a damper (or vibration damper) is further provided in the hollow 1 s of the screw shaft 1. Mass 4) is inserted. In the following, portions common to the first embodiment shown in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted as appropriate.

The damper 4 has a length substantially close to the axial length of the hollow 1 s of the screw shaft 1. The damper 4 is provided with a plurality of holding means 4a and 4b.
Is held concentrically with the screw shaft 1 with a slight gap from the inner wall surface of the hollow 1s of the screw shaft. This damper 4 and screw shaft 1
The coolant can pass axially through the gap.

The holding means 4a, 4b are made of, for example, an annular material such as metal or rubber, and are provided with a plurality of through holes (not shown) in the axial direction of the screw shaft 1 so that the coolant can pass through.

It is also possible to provide three or more holding means including both ends of the damper 4. By making the supporting span adjustable, the natural frequency of the damper 4 is made closer to the natural frequency of the screw shaft 1 and large. The vibration damping effect can be exhibited. Further, by providing the damper 4 with holding means at various intervals, the damper 4 has a plurality of natural frequencies. Even if the radial natural frequency of the screw shaft 2 changes with the movement of the ball nut 2, And any one of the natural frequencies of the damper 4 so as to be able to cope with a wide frequency range.

Here, an example has been described in which the ball screw device 3 is cooled by passing the coolant through the gap between the inner wall surface of the hollow 1s of the screw shaft 1 and the damper 4, but the present invention is not limited to this. For example, the damper 4 may be provided with a hollow hole in the axial direction to form a cylindrical shape, and the coolant may pass through the hollow hole.

In the second embodiment described above, the temperature rise can be suppressed by providing the cooling system, and the vibration can be greatly reduced by providing the damper. A further high-speed operation in is now possible. In particular, even if the critical speed is lowered by lengthening the screw shaft, operation at a speed higher than the critical speed is possible by reducing the vibration. Further, according to the second embodiment, since a longer stroke can be achieved, as shown in FIG. 2, it is possible to take a longer time for high-speed driving.
The effect of high-speed driving has been enhanced.

As shown in FIG. 5, it is possible to provide the above-described cooling device also in a ball screw device of a screw shaft rotation type. However, in this case, it is necessary to connect the screw shaft to the inflow pipe and the discharge pipe in a watertight and rotatable manner. In the case of a nut-rotating ball screw device as in the present invention, the screw shaft 1 does not rotate, so that the inflow pipe 1i and the discharge pipe 1o may be fixed to the screw shaft 1 in a watertight manner. Therefore, a simple structure can be obtained in the case of the nut rotation type.

In the present invention, cooling is performed from the screw shaft side. However, cooling can be further performed from the ball nut side. However, in the present invention, since the ball nut side rotates around the screw shaft, it is simpler to provide a cooling mechanism only on the screw shaft side. The cooling effect can be provided from the ball nut side by oil air or oil mist lubrication.

[0031]

As described in detail above, the present invention provides
Since a cooling mechanism is provided on the screw shaft in the nut rotation type ball screw device, hollow cooling of the screw shaft can be performed with a simple structure, and high precision and high rigidity feed is possible. Further, it is possible to make the stroke longer so as to exhibit the effect of high-speed rotation, and to perform high-speed rotation even if the stroke is lengthened and the natural frequency decreases.

[Brief description of the drawings]

FIG. 1 is a graph showing a high-speed rising pattern when a stroke is short.

FIG. 2 is a graph showing a high-speed rising pattern when a stroke is long.

FIG. 3 is a partial front sectional view of a nut rotation type ball screw device according to an embodiment of the present invention.

FIG. 4 is a partial front sectional view of a nut rotation type ball screw device according to another embodiment of the present invention.

FIG. 5 is a partial front cross-sectional view of the case where shaft hollow cooling is performed in a screw shaft drive type ball screw device.

Claims (1)

[Claims] 1. A screw shaft having a helical ball screw groove on the outer peripheral surface, and a ball having a ball screw groove on the inner peripheral surface facing the ball screw groove of the screw shaft and rotating around the screw shaft. A nut rotating ball comprising: a nut; a rolling element rotatably fitted between a ball screw groove of the screw shaft and a ball screw groove of the ball nut; and a cooling mechanism provided on the screw shaft. Screw device.