JP2979952B2 - Ball screw device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a ball screw device used for a transfer device such as a semiconductor chip mounter or a woodworking machine which requires a long stroke operation and a high speed operation.

[0002]

2. Description of the Related Art A ball screw device is used as a feeder suitable for a case where a long stroke and a high speed operation are required.
The ball screw device has the advantages of not only compactness and good transfer accuracy, but also less problems such as friction and heat generation.On the other hand, the longer the screw shaft, the longer the support span and the inherent radial There is a fatal disadvantage that the frequency becomes extremely low and high-speed operation cannot be performed.
This is because the allowable maximum speed of the ball screw device is limited so as not to reach a so-called critical speed that causes a resonance phenomenon between the natural frequency of the screw shaft in the radial direction and the rotational vibration force.

In order to avoid such large vibrations due to the resonance of the screw shaft, there has been proposed a method of fixing the screw shaft at both ends and moving the ball nut in the axial direction while rotating the ball nut. However, even in the case of a ball screw device that rotates a ball nut, the natural frequency itself of the screw shaft remains low because the support span of the screw shaft remains long. If the vibration frequency is in the critical speed range, even if whirling due to eccentric mass does not occur as in the case of the screw shaft rotation method,
Eventually, a resonance phenomenon occurs and large vibration occurs. For this reason, in a table driving device or the like using a ball screw device, it is common to use the screw shaft at a rotation speed lower than the critical speed.

[0004] On the other hand, the present applicant has disclosed in Japanese Patent Application Laid-Open No. Hei 6-11009 that a long middle shaft is coaxially held as a vibration damping mass in a screw shaft having a hollow hole. To propose a ball screw device that can be operated beyond the critical speed by configuring the center shaft to collide with the inner surface of the hollow hole when the screw shaft vibrates and suppressing the vibration at the resonance point by the collision. I have. In the same application, when the screw shaft and the middle shaft come into contact due to the processing accuracy of the hollow hole of the screw shaft and the bending of the middle shaft, and a uniform gap between the screw shaft and the middle shaft cannot be secured, the vicinity of the center of the middle shaft is An example in which one portion is fixed with an annular bush is also disclosed.

[0005] Also, the applicant of the present invention disclosed in Japanese Patent Application No. Hei 6-003773, a long vibration damping mass inserted into a hollow hole of a screw shaft, and an outer surface of the vibration damping mass. And a rubber material or a synthetic resin material functioning as a cushioning material that prevents contact between the screw shaft and the inner surface of the hollow hole of the screw shaft. A ball screw device has been proposed which attenuates the combined vibration and indirectly attenuates the vibration also by the friction generated between the screw shaft and the damping mass, thereby enabling operation exceeding the critical speed.

[0006]

SUMMARY OF THE INVENTION The aforementioned Japanese Patent Application No. Hei 6-003.
In the ball screw device proposed in No. 773, a shock absorber made of a rubber material or a synthetic resin material is interposed between the damping mass body and the inner diameter surface of the hollow screw shaft. Basically, vibration energy is attenuated by a damping effect due to collision and a friction effect between the damping mass body, the hollow screw shaft and the cushioning material. However, there is a problem that such a vibration damping effect due to collision or friction does not occur when the screw shaft is excited at a low frequency of less than tens of Hz (see experimental data described later). This is because the vibration acceleration transmitted through the screw shaft becomes very small in low frequency vibration, and the vibration suppression mass is restrained due to the gravity of the vibration suppression mass and the viscous force between the vibration suppression mass and the screw shaft. As a result, relative motion between the screw shaft and the damping mass body does not occur.

On the other hand, in the case of the ball screw device proposed in the above-mentioned Japanese Patent Application Laid-Open No. Hei 6-11009, a long vibration damping mass body held coaxially with the screw shaft collides with the inner surface of the hollow screw shaft during vibration. However, when excited at a low frequency, the screw shaft and the damping mass body do not always move relative to each other. However, regarding the vibration suppression of the screw shaft at a low frequency, although the relative movement between the two needs to be performed efficiently, Japanese Unexamined Patent Publication No. Hei 6-11009 does not consider any specific means. There is a problem that it cannot be expected that a great damping effect can be expected.

Accordingly, the present invention has been made in view of the above-mentioned conventional problems, and has provided a ball screw device having a long screw shaft capable of always exhibiting an excellent damping effect even in a low frequency range. The purpose is to provide. Another object of the present invention is to provide a ball screw device capable of suppressing vibrations in a wide range of frequencies in accordance with the natural frequency of the screw shaft that changes depending on the position of the ball nut.

[0009]

A ball screw device according to the present invention comprises a long screw shaft having a ball screw groove on its outer peripheral surface and having a hollow hole, and a ball screw opposed to the ball screw groove of the screw shaft. A ball nut having a groove on the inner peripheral surface, and a number of fittings between the ball screw groove of the screw shaft and the ball screw groove of the ball nut to allow the screw shaft and the ball nut to perform a relative spiral movement. A ball screw device having a ball and a vibration damping mass inserted into the hollow hole of the screw shaft with a gap in the radial direction, wherein an outer surface of the vibration damping mass and an inner surface of the hollow hole of the screw shaft are provided. And a vibration-damping mass holding ring constituting two or more support points spaced apart in the axial direction, at least between an outer diameter surface of the holding ring and an inner diameter surface of the hollow hole. Characterized by having a slight gap.

In the above-mentioned ball screw device, the axial spacing of a plurality of support points of the vibration-damping mass holding ring is made different so as to increase the natural frequency of the vibration-damping mass. Things.

[0011]

According to the ball screw device of the present invention, the radial natural frequency of the damping mass is changed by changing the axial spacing of the holding ring holding the damping mass, thereby changing the screw shaft. By approaching the natural frequency, a resonance state of the damping mass body can be generated even when the excitation force (excitation acceleration) becomes small. When the resonance state occurs, the damping mass body starts to vibrate independently, and as a result, a large relative motion occurs between the damping mass body and the screw shaft. Even if the spring rigidity of the damping mass is not so large, there is a small gap between the screw shaft and the damping mass, so the relative motion of the screw shaft and the damping mass causes impact and friction. Power comes.

In this manner, at a low frequency, even if the excitation force from the screw shaft is small, a large damping effect is produced, and the vibration of the screw shaft is suppressed. However, the above-described vibration suppression effect is exhibited only in a certain frequency range. Since the natural frequency of the screw shaft changes constantly depending on the position of the ball nut, the vibration damping effects of the vibration damping masses overlap each other by inserting them into the hollow holes with different supporting spans by the retaining ring of the vibration damping mass. The frequency range having a vibration damping effect is expanded, and vibration of the screw shaft due to a wide range of frequencies is also suppressed.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a longitudinal sectional view of an embodiment in which the ball screw device of the present invention is applied to a table driving device. First, the configuration will be described. The illustrated table drive device is configured to feed-drive a table 2 movably supported along a base 1 that is long in the axial direction by a ball screw device 10. It is mounted on a U-shaped base 1 via a linear guide bearing (linear guide device) (not shown) so as to be able to move smoothly.

The ball screw device 10 is a long hollow screw shaft 11 having a helical ball screw groove 11a on the outer peripheral surface.
And a ball nut 12 having a ball screw groove 12a facing the ball screw groove 11a of the screw shaft on the inner peripheral surface, and the ball shaft 11 fitted between the two ball screw grooves 11a, 12a.
And a number of balls 13 enabling relative spiral movement between the ball nut 12 and the ball nut 12.

The ball screw of this embodiment is of a so-called end cap type. Although not shown, for example, an approximately donut shape for guiding and circulating a ball moving to a through hole provided in the body of the ball nut 12 is shown. End caps having a curved path are mounted on both ends of the nut body, and the ball that has moved from the ball screw groove 11a of the screw shaft and made a U-turn on one curved path and advanced through the through-hole is reversed on the other curved path. The U-turn is repeated to return between the ball screw groove 11a and the ball screw groove 12a of the ball nut.

In the hollow hole 11b of the screw shaft 11, a central shaft 1 as a vibration damping mass made of a long iron bar having an outer diameter smaller than the diameter of the hollow hole and having a length somewhat shorter than the entire length of the screw shaft 11 is provided.
5 are inserted one by one through a gap 14 in the radial direction. In addition, between the outer surface of the center shaft 15 and the inner surface of the hollow hole 11b of the screw shaft 11, there is provided a vibration damping mass holding ring (hereinafter simply referred to as a holding ring) forming three support points spaced apart in the axial direction. Bush 25 is interposed, and the center shaft 1
5 is held. In the case of this embodiment, as shown in FIG. 2, a gap C1 is provided between the outer diameter surface of the bush 25 and the inner diameter surface of the hollow hole 11b.
A gap C2 is also provided between the inner diameter surface of the inner shaft 15 and the outer diameter surface of the central shaft 15. Therefore, the bush 25 can be moved within the hollow hole 11b, whereby the axial position of the bush 25 can be freely adjusted to change the support interval (support span) of the center shaft 15.

The clearances C1 and C2 are formed in the bush 25.
May be small enough to slide on the inner surface of the hollow hole and the outer surface of the central shaft. Screw covers 16 are attached to the openings at both ends of the hollow hole 11b of the screw shaft 11 to prevent the center shaft 15 and the bush 25 from falling off. The screw shaft 11 of the ball screw device 10 having such a structure is disposed on the base 1 through directly above the central concave portion of the base 1, and both ends thereof cannot be rotated via the screw shaft fixing members 17, respectively. Are fixedly supported by the base 1.

On the other hand, the ball nut 12 screwed to the screw shaft 11 is rotatably fitted via a ball bearing 18 to a lower portion of the table 2 running on the base 1. A pulley 19 is attached to an end face of the ball nut 12 so as to be integrally rotatable. A driving motor 20 is mounted on the upper surface of the table 2, and a pulley 21 attached to the motor output shaft and the pulley 19
2 are connected so as to be synchronously rotatable.

Next, the operation will be described. When the driving motor 20 is driven to rotate, the driving torque is transmitted to the pulley 21, the timing belt 22, and the pulley 19, and the ball nut 12 of the ball screw device 10 rotates. Then, the ball 13 fitted between the screw shaft 11 and the ball nut 12
Is the ball screw groove 11 of the screw shaft 11 and the ball nut 12
a and 12a while rolling and moving infinitely within the ball nut 12 via a circulation path (not shown).
As a result, the ball nut 12 is guided by the screw shaft 11 that is fixedly supported in a non-rotating manner, and moves in the axial direction. At the same time, the table 2 smoothly moves on the base 1 in the axial direction while being guided by the linear guide device.

At this time, since the screw shaft 11 does not rotate,
Whirling vibration due to eccentric mass as in the case of use with shaft rotation does not occur, but vibration occurs because minute vibration due to rotation of the ball nut 12 is applied. Since the support span of the long screw shaft 11 is long and the natural frequency is low,
When the ball nut 12 is rotated at a high speed, the frequency of the minute vibration may become a critical speed range of the screw shaft 11. In this case, if the screw shaft 11 is a general solid shaft, a resonance phenomenon occurs and large vibrations are likely to occur in the screw shaft 11.

However, in the case of this embodiment, the screw shaft 11
Is hollow, and a long center shaft 15 is inserted therein, and is supported by three bushes 25 at three locations with an axial interval, that is, a support span. Since the supporting span can be easily changed by moving the bush 25 in the axial direction, it is possible to make the radial natural frequency of the center shaft 15 close to the natural frequency of the screw shaft 11. Thus, even if the screw shaft 11 is excited at a low frequency of, for example, tens of Hz or less, if the natural frequency of the center shaft 15 is close to the natural frequency of the screw shaft 11, the exciting force (excitation force) due to the rotation of the ball nut 12 is obtained. The resonance state of the center shaft 15 can be generated even with a small vibration having a small acceleration. Due to the occurrence of this resonance, the center shaft 15 starts to independently vibrate asynchronously with the screw shaft 11, and as a result, a large relative movement occurs between the center shaft 15 and the screw shaft 11.
Bush 2 supporting hollow shaft diameter of screw shaft 11 and center shaft 15
Since a slight gap C1 is provided between the screw shaft 11 and the outer diameter of the screw shaft 5, the relative motion of the screw shaft 11 and the center shaft 15 generates an impact or a frictional force, and the vibration energy of the screw shaft 11 is canceled out. The vibration of the shaft 11 is damped.

As described above, according to the ball screw device of the present embodiment, even if the frequency is low and the excitation force from the screw shaft 11 is small, the support span of the bush 25 is adjusted to adjust the characteristic of the central shaft 15 in the radial direction. The vibration frequency is made closer to the natural frequency of the screw shaft 11 to produce a large vibration damping effect, thereby suppressing the vibration of the screw shaft. FIG. 3 shows the result of the impulse response of the screw shaft 11 by the experiment performed to confirm the above-described vibration damping effect.
6 to FIG.

In this experiment, a length of 3630 mm and an outer diameter of 40
The attenuation state of the vibration when impact vibration is applied to a long hollow screw shaft having a natural frequency of about 11 Hz is recorded. FIG. 3 shows a case where the subject has only a hollow screw shaft. FIG. 4 shows a case where the subject is a screw shaft used in a ball screw device proposed in Japanese Patent Application No. 6-003773, in which a long vibration damping mass body is inserted into a hollow hole of a hollow screw shaft, and Between the vibration damping mass and the inner diameter surface of the hollow screw shaft, a cushioning material made of a rubber material or a synthetic resin material having a length substantially covering the entire length of the vibration damping mass is interposed.

FIG. 5 shows the case of the screw shaft 11 of the present invention shown in FIG. In each graph, the horizontal axis is time (1 scale 1 sec), and the vertical axis is the amplitude of vibration of the screw axis (1 scale is 0.
5 mm). As is clear from the comparison of each graph,
If the natural frequency of the screw shaft is such a low frequency,
Although the vibration damping effect was not recognized to the extent of anything other than those of the present invention, the remarkable vibration damping effect was obvious at a glance in the case of the screw shaft 11 of this embodiment in FIG. .

FIG. 6 shows a comparison of the results of plotting the displacement of the screw shaft due to the impact excitation in the above experiment. From this result, in the case of the screw shaft of Japanese Patent Application No. 6-003773, no effect is recognized unless the natural frequency of the screw shaft becomes a certain high frequency, whereas in the case of the screw shaft of the present invention. It is evident that the natural frequency of the screw shaft exhibits a remarkable vibration damping effect in a wide range from a low frequency to a high frequency.

FIGS. 7 and 8 show a modification of the structure for mounting the bush 25. FIG. 7 is such that the bush 25 is screwed from outside of the hollow screw shaft 11 with a set screw 30 so that the bush 25 does not move in the hollow hole 11b in the axial direction when the ball screw device is operated. 11 fixed. In the fixed state, a gap C1 is interposed between the outer diameter surface of the bush 25 and the inner diameter surface of the hollow hole 11b, and a gap C2 is formed between the inner diameter surface of the bush 25 and the outer diameter surface of the center shaft 15. Intervening. The center shaft 15 is formed by the clearance C2.
Can vibrate independently of the screw shaft 11, the center shaft 15 and the screw shaft 1
A large relative movement between them is possible.

According to this modification, there is an advantage that the support span of the center shaft 15 can be kept constant. FIG. 8 shows that the bush 25 has the hollow hole 1 when the ball screw device is operated.
A bush 25 is fixed to the center shaft 15 with a tight fit so that the bush 25 does not move freely in the axial direction in the inside 1b. In this case, the center shaft 15 can vibrate independently of the screw shaft 11 by the gap C1 between the outer diameter surface of the bush 25 and the inner diameter surface of the hollow hole 11b.
A large relative movement is possible between.

This modified example also has the advantage that the support span of the center shaft 15 can be kept constant as described above. FIG. 9 shows another embodiment of the ball screw device of the present invention. This embodiment is different from the embodiment shown in FIG. 1 in that the long center shaft 15 is divided into a plurality (in this case, two, but may be more). Thereby, there is an advantage that the insertion of the center shaft 15 into the hollow hole 11b of the screw shaft 11 becomes easy.

FIG. 10 shows still another embodiment. This embodiment has a configuration in which a plurality of bushes 25 are used to support the center shaft 15 with a plurality of support spans having different lengths. Since the natural frequency in the radial direction of the center shaft 15 varies depending on the length of the support span, the center shaft 15 in this case has a plurality of natural frequencies. As a result, even if the radial natural frequency of the screw shaft 11 changes with the movement of the ball nut, the screw shaft 11 comes close to any one of the plurality of radial natural frequencies of the center shaft 15.
There is an advantage that the vibration of is more effectively suppressed.

FIG. 11 shows another embodiment. In this embodiment, the center shaft 15 into which the hollow hole 11b of the screw shaft 11 is inserted is used.
Is axially constrained by a long set screw 31 screwed into the hollow hole 11b from both sides of the screw shaft 11. Central axis 1
In the case where the length of the screw shaft 11 is extremely shorter than the length of the screw shaft 11, the center shaft 15 supported by the bush 25 moves in one of the axial directions when the ball screw device 10 is operated. There is a possibility that the characteristics of the damping effect set in the above may change. In order to prevent such a phenomenon, it is desirable to keep the center shaft 15 supported by the bush 25 in the initial state. According to this embodiment, the center shaft 15 is axially moved from the screw shaft end by the set screw 31.
There is an advantage that the position can be adjusted and easily fixed and maintained at that position.

FIG. 12 shows another embodiment. This embodiment differs from that of FIG. 1 in that most of the length of the center shaft 15 in the length direction is covered with a resin tube 32 except for a portion supported by a bush 25. The resin tube 32 has an advantage that the noise generated by the collision between the inner diameter surface of the screw shaft 11 and the center shaft 15 is reduced, so that the quiet operation can be performed, and the generation of new vibration due to the collision is suppressed.

FIG. 13 shows another embodiment. In this embodiment, the outer diameter surface of the central shaft 15 is covered with a resin coating 33 instead of the resin tube 32 shown in FIG. This resin coating 33 is screw shaft 1
There is an advantage that noise generated by a collision between the inner diameter surface of the inner shaft 15 and the center shaft 15 can be reduced to achieve quiet operation, and that new vibration due to the collision can be suppressed.

FIG. 14 shows still another embodiment. In this embodiment, a cushioning member 34 made of a rubber material or the like is attached to an inner end surface of a lid 16 screwed into an end of a hollow hole 11b of a screw shaft 11 into which a center shaft 15 is inserted. The cushioning member 34 has an advantage that the noise generated by the collision between the center shaft 15 and the lid 16 can be reduced and quiet operation can be performed, and the generation of new vibration due to the collision can be suppressed.

In each of the above embodiments, the driving method of the ball nut 12 is performed by belt driving by the driving motor 20 installed on the upper surface of the table 2. However, the present invention is not limited to this. A system in which the inserted hollow motor is mounted on the table 2 with a bracket and the ball nut 12 is connected to the motor output portion to drive the motor may be used.

[0035]

As described above, according to the first aspect of the present invention,
According to the invention, a hollow hole penetrating the screw shaft is provided, and a long damping mass body is inserted into the hollow hole, and the outer surface of the damping mass body and the inner surface of the hollow hole of the screw shaft are formed. In between, there is provided a damping mass body holding ring constituting two or more support points spaced apart in the axial direction, at least a small gap between the outer diameter surface of the holding ring and the inner diameter surface of the hollow hole Configuration. Therefore, by adjusting the support span of the damping mass body, the radial natural frequency of the damping mass body can be made closer to the natural frequency of the screw shaft. Relative motion is generated, and the vibration of the screw shaft is effectively suppressed by the impact and frictional force generated by this, and the effect that a large vibration suppression effect can be exhibited even at a low frequency even when the excitation force from the screw shaft is small. .

According to the second aspect of the present invention, since the axial spacing of the plurality of support points of the vibration suppression mass holding ring is made different, the vibration suppression mass has a plurality of natural frequencies, As a result, even if the natural frequency in the radial direction of the screw shaft constantly changes with the movement of the ball nut, it comes close to one of the multiple radial natural frequencies of the damping mass, and Can handle the area,
This has the effect of further suppressing vibration of the screw shaft.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of one embodiment of the present invention.

FIG. 2 is an enlarged cross-sectional view of a holding structure of the damping mass body in FIG.

FIG. 3 is a graph showing an impulse response of a single hollow screw shaft.

FIG. 4 is a graph showing an impulse response when a vibration damping mass body is inserted into a hollow screw shaft and rubber or a synthetic resin material is interposed between the hollow screw shaft and a hollow hole of the screw shaft.

FIG. 5 is a graph showing an impulse response in the case of the present invention shown in FIG.

6 is a graph showing vibration displacement values during impact excitation of the screw shaft of the present invention shown in FIG. 1 and other screw shafts.

FIG. 7 is an enlarged cross-sectional view of another holding structure of the damping mass body of the present invention.

FIG. 8 is an enlarged sectional view of still another holding structure of the vibration damping mass body of the present invention.

FIG. 9 is a longitudinal sectional view of another embodiment of the screw shaft of the present invention.

FIG. 10 is a longitudinal sectional view of another embodiment of the screw shaft of the present invention.

FIG. 11 is a longitudinal sectional view of another embodiment of the screw shaft of the present invention.

FIG. 12 is a longitudinal sectional view of another embodiment of the screw shaft of the present invention.

FIG. 13 is a longitudinal sectional view of another embodiment of the screw shaft of the present invention.

FIG. 14 is a partially enlarged sectional view of another embodiment of the screw shaft of the present invention.

[Explanation of symbols]

 Reference Signs List 10 ball screw device 11 screw shaft 11a ball screw groove (of screw shaft) 11b hollow hole 12 ball nut 12a ball screw groove (of ball nut) 13 ball 15 damping mass body 20 driving means (drive motor) 25 damping mass body Retaining ring (Bushing)

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) F16H 25/00-25/24 F16F 15/00-15/36 F16C 3/00-3/02

Claims (2)

(57) [Claims] 1. A long screw shaft having a ball screw groove on its outer peripheral surface and having a hollow hole, a ball nut having an inner peripheral surface with a ball screw groove facing the ball screw groove of the screw shaft,
A number of balls fitted between the ball screw groove of the screw shaft and the ball screw groove of the ball nut to allow the screw shaft and the ball nut to perform a relative helical movement, In a ball screw device having a vibration damping mass inserted with a gap in the radial direction, the ball screw device is interposed between an outer surface of the vibration damping mass and an inner surface of a hollow hole of the screw shaft, and is axially spaced. And a vibration control mass body holding ring constituting two or more support points, and having a small gap between at least an outer diameter surface of the holding ring and an inner diameter surface of the hollow hole. Ball screw device. 2. The ball screw device according to claim 1, wherein axial distances between a plurality of support points of the damping mass holding ring are made different so as to increase the natural frequency of the damping mass. And ball screw device.