JP3748168B2 - Ball screw device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a ball screw device, and more particularly, to a ball screw device that is used for driving a high-speed feed of a machine tool and realizes high speed and high accuracy.
[0002]
[Prior art]
Conventionally, as a ball screw device, for example, as disclosed in Japanese Utility Model Publication No. 6-11433, a tube type in which a nut is screwed to a screw shaft having a spiral groove via a rolling element such as a steel ball. One using a ball screw 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 nut rotates, the ball moves while rolling in both spiral grooves, and the nut moves linearly along the screw shaft.
[0003]
In the ball screw device as described above, when feeding is performed at high speed, the amount of heat generation increases, causing a temperature rise, the screw shaft expands, and the accuracy in the feeding direction is adversely affected. Further, in the case of nut rotation and shaft fixing (not rotating), there is a problem that the heat dissipation effect from the screw shaft is small and the temperature rise is large compared to the shaft rotation. Furthermore, 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 that can slide one end in the axial direction There are many. This support structure has a problem that the rigidity in the feed direction is lowered. For this reason, it was difficult to use the ball screw device at high speed rotation.
[0004]
In addition, when a ball made of a ceramic material is used as a rolling element, the linear expansion coefficient is small, so the expansion due to temperature rise is small, and the specific gravity is small, so the preload to increase the axial positioning accuracy is increased. Not enough. In addition, since the linear expansion coefficient of the rolling element is smaller than that of metal ball screw shafts and ball nuts, there is a problem that if high-speed feeding is performed, 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 deteriorate.
[0005]
Furthermore, recently, machine tools have been increased in speed, and it has become possible to set the feed rate to 60 m / min and the 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, as shown in Fig. 1, the stroke is full with the rise and fall of the rotation, and the time during which the feed rate is high is not much. Since it cannot be made longer, if the effective stroke is short, the advantage of high speed cannot be fully utilized. When the stroke is long, the time ratio of the high feed rate increases as shown in Fig. 2, and the benefits of higher speed come into play. However, if the stroke is lengthened, 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]
[Problems to be solved by the invention]
An object of the present invention is to solve the problems as described above, and to prevent a temperature increase at high speed rotation and to achieve high accuracy and high rigidity at high speed rotation in a ball screw device. It is another object of the present invention to provide a ball screw device capable of high-speed rotation even when the stroke can be made long so as to exhibit the effect of high-speed rotation and the natural frequency is reduced by extending the stroke. .
[0007]
[Means for Solving the Problems]
In order to achieve these objects, a ball screw device of the present invention has a screw shaft having a spiral ball screw groove on the outer peripheral surface and a ball screw groove facing the ball screw groove of the screw shaft on the inner peripheral surface. And a ball nut that rotates around the screw shaft, and a rolling element that is movably fitted between the ball screw groove of the screw shaft and the ball screw groove of the ball nut. A nut rotation type ball screw device having a cooling mechanism on a 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.
[0009]
Moreover, a hollow may be provided in the screw shaft, and a damper may be inserted into the hollow.
[0010]
Further, the damper may have a radial gap between the damper and a hollow inner wall of the screw shaft, and the cooling mechanism may be characterized in that a coolant passes through the gap in the axial direction.
[0011]
Furthermore, 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.
[0012]
The present invention provides a cooling mechanism for the screw shaft in the nut rotating ball screw device, so that the screw shaft can be hollow cooled with a simple structure, preventing thermal expansion of the screw shaft due to a temperature rise at high speed rotation, Accurate feeding is possible. In addition, by adding a damper to the hollow part of the shaft, it is possible to avoid the problem of the critical speed of the screw shaft even in a long stroke that demonstrates the effect of high-speed rotation, and further increase the speed of machine tool feed and cutting feed. It became.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be specifically described. 3 is a partial front sectional view of a nut rotating ball screw device according to an embodiment of the present invention. FIG. 4 is a partial front sectional view of a nut rotating ball screw device according to another embodiment of the present invention. 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.
[0014]
(1) First Embodiment A ball screw device 3 shown in FIG. 3 includes a screw shaft 1, a ball nut 2 rotatable around the screw shaft 1, and a cooling mechanism including a cooling device R1. The screw shaft 1 is fixed to the base 5 near both ends thereof. The slide table 6 is supported by 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.
[0015]
The screw shaft 1 has a spiral 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 fitted between the ball screw groove 7 of the screw shaft 1 and the ball screw groove of the ball nut 2 so as to roll freely. A drive motor 9 that rotates 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.
[0016]
The screw shaft 1 is provided with a hollow 1s penetrating in the axial direction. 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 through the conducting pipe 1t. The hollow 1s of the screw shaft 1, the inflow pipe 1i, the discharge pipe 1o, the conducting pipe 1t, and the cooling device R1 constitute a cooling mechanism.
[0017]
The ball, screw shaft 1 and ball nut 2 are each made of steel. However, the ball can be made of ceramic having a small specific gravity and a small linear expansion coefficient.
[0018]
In such a nut rotation type ball screw device, when the ball nut 2 is rotated around the screw shaft 1 by the drive motor 9, the ball advances while rolling in the ball screw grooves of the screw shaft 1 and the ball nut 2. When the ball goes around the ball screw groove a predetermined number of times, the ball is picked 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. When the ball nut 2 rotates, the ball nut 2 and the slide table 6 supported by the ball nut 2 move linearly in the process of rolling while moving in the ball screw groove.
[0019]
The cooling mechanism of the present embodiment cools the entire ball screw device by passing a coolant made of water, oil or the like through the hollow 1 s 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 screw shaft, cools the entire ball screw, and is discharged from the discharge pipe 1o. Returning to R1, it is recycled again.
[0020]
Here, the driving method of the ball nut is configured such that the driving motor 9 is connected to the ball nut 2 and driven by its power, but the present invention is not limited to this, and the rotor of the hollow motor is used. The ball nut itself may be configured with and driven directly.
[0021]
In the present embodiment, by passing a coolant through the hollow of the screw shaft 1, it is possible to suppress a temperature rise of the entire ball screw device, suppress a thermal displacement of the screw shaft, and improve the accuracy of the ball screw device. In this embodiment, the ball is made of steel. However, when the ball is made of ceramic, the change in the internal clearance of the ball screw device that occurs due to the small coefficient of linear expansion of the ceramic material is suppressed, and high positioning accuracy is achieved. Can be achieved.
[0022]
Further, according to the present embodiment, the cooling mechanism is provided on the screw shaft of the ball nut rotating type ball screw device, and therefore the cooling device can be provided with a simple structure.
[0023]
(2) Second Embodiment FIG. 4 shows a ball screw device 3 'according to a second embodiment of the present invention. 4, the schematic configuration of the ball screw device is substantially the same as that of the first embodiment shown in FIG. 3. However, in this embodiment, a damper (or vibration damping) is further provided in the hollow 1 s of the screw shaft 1. (Mass body) 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 is omitted as appropriate.
[0024]
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, 4b, whereby the damper 4 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. The coolant can pass through the gap between the damper 4 and the screw shaft 1 in the axial direction.
[0025]
The holding means 4a and 4b are made of, for example, an annular material such as metal or rubber, and are provided with a plurality of passage holes (not shown) in the axial direction of the screw shaft 1 so that the coolant can pass therethrough.
[0026]
Three or more holding means including both ends of the damper 4 can be provided, and by making the support span adjustable, the natural frequency of the damper 4 is brought close to the natural frequency of the screw shaft 1 and has a great damping effect. Can be demonstrated. Further, by providing the damper 4 with holding means at various intervals, the damper 4 has a plurality of natural frequencies, and even if the radial frequency of the screw shaft 2 changes in the radial direction as the ball nut 2 moves. Therefore, it is possible to cope with a wide frequency range by being close to one of the natural frequencies of the damper 4.
[0027]
Here, the example in which the ball screw device 3 is cooled by passing the coolant through the gap between the inner wall surface of the hollow 1 s of the screw shaft 1 and the damper 4 has been described. However, the present invention is not limited to this example. An axial hollow hole may be provided in 4 to form a cylindrical shape, and a coolant may be passed through the hollow hole.
[0028]
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. High speed operation became possible. In particular, even if the screw shaft is lengthened to reduce the critical speed, the vibration can be reduced so that the operation at the critical speed or higher is possible. In addition, according to the second embodiment, since a longer stroke is possible, it is possible to take a longer time for high-speed driving as shown in FIG. 2, so that the effect of high-speed driving can be further enhanced. It was.
[0029]
In addition, as shown in FIG. 5, it is possible to provide a cooling device as described above also in a screw shaft rotation type ball screw device. 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 the nut rotation type ball screw device as in the present invention, since the screw shaft 1 does not rotate, 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.
[0030]
Further, in the present invention, cooling is performed from the screw shaft side, but it is also possible to cool from the ball nut side. However, in the present invention, since the ball nut side rotates around the screw shaft, a simpler structure can be obtained by providing a cooling mechanism only on the screw shaft side. In addition, from the ball nut side, a cooling effect can be imparted by oil air or oil mist lubrication.
[0031]
【The invention's effect】
As described above in detail, since the present invention provides a cooling mechanism for the screw shaft in the nut rotary ball screw device, the screw shaft can be hollow cooled with a simple structure, and a highly accurate and highly rigid feed can be achieved. Became possible. In addition, it is possible to achieve a long stroke that exhibits the effect of high-speed rotation, and high-speed rotation is possible even if the stroke is lengthened to lower the natural frequency.
[Brief description of the drawings]
FIG. 1 is a graph showing a high-speed startup pattern when a stroke is short.
FIG. 2 is a graph showing a high-speed startup pattern when the stroke is long.
FIG. 3 is a partial front sectional view of a nut rotating ball screw device according to an embodiment of the present invention.
FIG. 4 is a partial front sectional view of a nut rotating ball screw device according to another embodiment of the present invention.
FIG. 5 is a partial cross-sectional view of the front surface when hollow shaft cooling is performed in a screw shaft drive type ball screw device.

Claims (3)

A screw shaft having a helical ball screw groove on the outer peripheral surface, a ball nut having a ball screw groove facing the ball screw groove of the screw shaft on the inner peripheral surface and rotating around the screw shaft; and the screw A rolling element that is movably fitted between a ball screw groove of the shaft and a ball screw groove of the ball nut, and a cooling mechanism is provided in the screw shaft, and a hollow portion is provided in the screw shaft , The damper is inserted into the hollow portion, and the damper has a gap between the inner wall of the hollow portion and is held concentrically with the screw shaft, and the cooling mechanism is configured so that a coolant passes through the gap. A nut rotation type ball screw device characterized by being configured to pass in the axial direction of a screw shaft . A screw shaft having a helical ball screw groove on the outer peripheral surface, a ball nut having a ball screw groove facing the ball screw groove of the screw shaft on the inner peripheral surface and rotating around the screw shaft; and the screw A rolling element that is movably fitted between a ball screw groove of the shaft and a ball screw groove of the ball nut, and a cooling mechanism is provided in the screw shaft, and a hollow portion is provided in the screw shaft , The damper is inserted into the hollow portion, the damper has a hollow hole in the axial direction of the screw shaft, and the cooling mechanism allows the coolant to pass through the hollow hole in the axial direction of the screw shaft. A nut rotation type ball screw device characterized by the above-mentioned. A plurality of holding means for holding the damper on the screw shaft are provided, and the holding means is provided with a plurality of passage holes in the direction of the screw shaft so that the coolant can pass, and the holding means supports the damper. The nut rotation type ball screw device according to claim 1 or 2 , wherein the support span for adjusting is adjusted so that the natural frequency of the damper is close to the natural frequency of the screw shaft.

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