JPH0549234U - Lead screw device - Google Patents

Abstract

(57) [Summary] [Structure] The bearing 4 supporting the screw shaft 1 in the feed screw device is movable in a direction perpendicular to the axis of the screw shaft 1. [Effect] Since the whirling phenomenon occurring when the screw shaft 1 rotates can be absorbed by the bearing 4 part, the whirling phenomenon is transmitted to the nut screwed to the screw shaft 1 and the linear slide connected to the nut. It is difficult and the straightness of the linear slide can be improved.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a lead screw device used in semiconductor manufacturing equipment, precision processing machines, precision measuring equipment, and the like.

[0002]

[Prior Art]

 Conventionally, in a hydrostatic bearing device, a feed screw device has been used to drive a linear motion slide supported on a guide shaft. As shown in FIG. 3, the structure of the feed screw device is composed of a screw shaft 1, a nut 2 screwed to the screw shaft 1, and a linear slide 3 connected to the nut 2. Then, the screw shaft 1 is rotated by a motor (not shown), this rotational movement is converted into a linear movement of the nut 2, and the linear motion slide 3 connected to the nut 2 is driven. Although not shown, the linear motion slide 3 is supported by hydrostatic pressure fluid on the guide shaft to form a hydrostatic fluid bearing, and smooth and precise driving can be performed.

Both ends of the screw shaft 1 are connected to an inner ring 4 a of a bearing 4 which is a ball bearing by a tightening nut 5, and an outer ring 4 b of the bearing 4 is a bearing housing by tightening a plate 6 with a bolt 8. It is connected to 7. In other words, the screw shaft 1 is supported by the bearing 4 in a state in which it has a degree of freedom in the rotation direction, but is otherwise constrained.

[0004]

[Problems to be solved by the device]

 However, in the above feed screw device, when the screw shaft 1 is rotated, a whirling phenomenon occurs as shown in FIG. 4, and the central portion of the screw shaft 1 is greatly swollen by the whirling amount δ to rotate. It was inevitable. Since this whirling phenomenon is transmitted to the linear slide 3 through the nut 2, the linear slide 3 is designed to move slightly in a direction perpendicular to the original moving direction. When the straightness of motion of the linear motion slide 3 was actually measured, as shown in the chart of FIG. 5, a deflection phenomenon was observed at a cycle that coincides with the lead of the screw shaft 1 and the straightness performance was degraded. There was a problem that

The amount of the deflection amount δ is determined by the ratio between the rigidity of the screw shaft 1 and the supporting rigidity of the linear slide 3 in the direction perpendicular to the moving direction of the linear slide 3, and The lower the supporting rigidity of the linear motion slide 3 compared to the rigidity of 1, the larger the amount of deflection δ becomes. Further, when the linear motion slide 3 is supported by the hydrostatic bearing, the supporting rigidity becomes low, so that there has been a problem that the above-mentioned whirling phenomenon becomes remarkable.

Further, when the feed screw device is assembled, it is necessary to completely match the moving axis of the screw shaft 1 with the moving direction of the direct-acting slide 3, but it is difficult to actually match the both. However, there is a problem in that an error of about several tens of μm cannot be avoided, and thus the straightness performance of the linear motion slide 3 itself is deteriorated.

[0007]

[Means for Solving the Problems]

 In view of the above, the present invention makes the bearing portion supporting the screw shaft in the feed screw device movable in a direction perpendicular to the axis of the screw shaft.

[0008]

[Action]

 According to the present invention, since the bearing portions at both ends can move in the direction perpendicular to the shaft core, even if a whirling phenomenon occurs when the screw shaft rotates, the bearing portions at both ends move in the whirling direction. By doing so, it is possible to reduce the amount of deflection that is transmitted to the nut.

[0009]

【Example】

 Hereinafter, the present invention will be described in detail based on embodiments (the same portions as those in the conventional example are denoted by the same reference numerals).

The feed screw device of the present invention is similar to the conventional example shown in FIG. 3, in which a screw shaft 1 having a spiral groove, a nut 2 screwed into the screw shaft 1, and a linear motion slide connected to the nut 2 are provided. 3, the linear slide 3 is supported on the guide shaft by hydrostatic bearings. Then, as shown in FIG. 1 which is a sectional view of the bearing portion of the screw shaft 1, the end portion of the screw shaft 1 is connected to an inner ring 4a of a bearing 4 which is a ball bearing by a tightening nut 5. On the other hand, the outer ring 4b of the bearing 4 is mounted in the space formed by the bearing housing 7 and the plate 6 mounted on the bearing housing 7 with bolts 8. A gap d of about 0.2 to 0.3 mm is formed between them, and spheres 9 are evenly distributed on the circumference between both end surfaces of the outer ring 4b and the bearing housing 7 and the plate 6. A carrier 10 for positioning and positioning the sphere 9 is provided. Then, by tightening the plate 6 with the bolts 8, the outer ring 4b of the bearing 4 is held via the balls 9.

Therefore, the outer ring 4b of the bearing 4 is not completely fixed to the bearing housing 7, and the ball 9 rolls, so that the gap d is formed in the direction perpendicular to the axis of the screw shaft 1. It is possible to move within the range. Further, if the tightening force of the bolt 8 is increased, the force of holding the outer ring 4b through the ball 9 by the plate 6 is increased, so that the bearing 4 becomes difficult to move in the direction perpendicular to the axis. In other words, the tightening force of the bolt 8 can adjust the support rigidity in the direction perpendicular to the axis of the bearing 4.

Now, when the screw shaft 1 is rotated in this feed screw device, the nut 2 screwed into the spiral groove and the direct-acting slide 3 connected thereto can be linearly moved. At this time, a whirling phenomenon occurs in the screw shaft 1, but since the bearing 4 of the screw shaft 1 is movable in the direction perpendicular to the shaft core as described above, this bearing 4 is not perpendicular to the shaft core. By moving in the direction, the whirling phenomenon is absorbed, and it is possible to prevent the whirling phenomenon from being transmitted to the nut 2 and the linear motion slide 3. When the feed screw device is assembled, an error of about several tens of μm occurs between the moving direction of the linear motion slide 3 and the axis of the screw shaft 1. The clearance d absorbs this error and does not deteriorate the straightness performance of the linear motion slide 3.

Next, another embodiment of the present invention will be described. As shown in the cross section of the bearing portion in FIG. 2, the end of the shaft 1 is connected to the inner ring 4a of the bearing 4 by a tightening nut 5, while the outer circumference of the outer ring 4b of the bearing 4 and the inner circumference of the bearing housing 7 are A gap d of about 0.2 to 0.3 mm is formed between them, and a slide bearing member 11 is interposed between both end surfaces of the outer ring 4b and the bearing housing 7 and the plate 6. .. Then, the plate 6 is fastened to the bearing housing 7 with bolts 8 to hold the outer ring 4 b of the bearing 4 via the plain bearing member 11.

The sliding bearing member 11 is made of a material having excellent slidability such as carbon or fluorine resin, and has a friction coefficient with the bearing housing 7 or the plate 6 of 0.2 or less. Therefore, in this feed screw device, the outer ring 4b of the bearing 4 is not completely fixed to the bearing housing 7, but slides through the slide bearing member 11, whereby the outer ring 4b moves relative to the axis of the screw shaft 1. It is possible to move vertically in the vertical direction, and it is possible to absorb the whirling phenomenon of the screw shaft 1 as in the above-described embodiment.

The supporting structure for the bearing 4 as shown in FIGS. 1 and 2 may be formed only on one end of the screw shaft 1. However, if both ends are formed into such a supporting structure, the effect is further enhanced. it can . Further, in the above embodiment, various materials such as metal and ceramics can be used as the material of each member. Particularly, if the members such as the inner ring 4a, the outer ring 4b and the ball 9 of the bearing 4 are made of ceramics, wear resistance is improved. Can be higher.

Further, although the linear motion slide 3 is supported by the hydrostatic fluid in the above-mentioned embodiment, the feed screw device of the present invention is not limited to the drive of the hydrostatic bearing device, and various linear lines are used. It can be used as a guide device.

Experimental Example In the feed screw device of the present invention, in order to absorb the whirling phenomenon, the supporting rigidity A (kgf / μm) in the direction perpendicular to the moving direction of the linear slide 3 and the bearing 4 are used. The ratio B / A between the shaft center of and the supporting rigidity B (kgf / μm) in the vertical direction is important. Then, the feed screw device of the present invention shown in FIG. 1 was prototyped, and an experiment was conducted to compare the straightness performance by changing the values of the support stiffnesses A and B. The dimensions of each part are as shown in Table 1, and the linear motion slide 3 was supported by static pressure air, and the supporting rigidity A was determined by this air pressure. On the other hand, the support rigidity B of the bearing 4 was adjusted by the tightening force of the bolt 8 for mounting the plate 6 in FIG. The results are shown in Table 2.

[0018]

[Table 1]

[0019]

[Table 2]

It is apparent from Table 2 that the smaller the ratio B / A of the supporting rigidity A of the linear motion slide 3 and the supporting rigidity B of the bearing 4, the better the straightness performance. This is because the smaller the supporting rigidity ratio B / A is, the easier the bearing 4 is to move in the direction perpendicular to the shaft core, and the larger the absorption amount of the swinging phenomenon is. Further, the straightness normally required for a hydrostatic bearing is 0.2 μm or less per 100 mm, but it can be seen that this required characteristic is satisfied if the ratio B / A of the supporting rigidity is 1/5 or less.

Further, in Table 2, No. When the straightness of motion of the linear slide 3 was examined for the example of No. 5, as shown in the chart diagram of FIG. 6, almost no fringing phenomenon was observed, and in comparison with the conventional example shown in FIG. It can be seen that the straightness performance is far superior.

Further, in the above experimental example, the structure in which the sphere 9 shown in FIG. 1 is arranged is shown, but the structure in which the sliding bearing member 11 shown in FIG. By setting the ratio B / A of the support rigidity A of No. 3 and the support rigidity B of the bearing 4 to be 1/5 or less, the straightness could be 0.2 μm or less per 100 mm.

[0023]

[Effect of the device]

 As described above, according to the present invention, the bearing that supports the screw shaft in the feed screw device is movable in the direction perpendicular to the axis of the screw shaft, so that the whirling phenomenon that occurs when the screw shaft rotates is prevented. It can be absorbed by the bearing portion. Therefore, it is difficult to transmit the whirling phenomenon to the nut screwed to the screw shaft and the linear motion slide connected to the nut, and the straightness performance of the linear motion slide can be improved. It can be suitably used for driving a dynamic slide.

[Brief description of drawings]

FIG. 1 is a sectional view showing a bearing portion of a screw shaft in a feed screw device of the present invention.

FIG. 2 is a cross-sectional view showing another embodiment of the present invention.

FIG. 3 is a schematic view showing a conventional feed screw device.

FIG. 4 is a diagram for explaining a whirling phenomenon in a conventional feed screw device.

FIG. 5 is a chart showing the straightness of motion of a linear slide driven by a conventional feed screw device.

FIG. 6 is a chart showing the straightness of motion of a linear slide driven by the feed screw device of the present invention.

[Explanation of symbols]

 1 ... Screw shaft 2 ... Nut 3 ... Linear slide 4 ... Bearing 4a ... Inner ring 4b ... Outer ring 5 ... Tightening nut 6 ... Plate 7 ... Bearing housing 8 ... ..Bolts 9 ... Spheres 10 ... Carriers 11 ... Slide bearing members

Claims (1)

[Scope of utility model registration request] 1. A feed screw device in which a nut screwed on a screw shaft is moved in a linear direction by rotating the screw shaft, and a bearing portion for supporting an end portion of the screw shaft is provided in the feed screw device. A feed screw device characterized in that it is movable in a direction perpendicular to the axis of the.