JPH09264324A - Feed screw mechanism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a feed screw mechanism in which the suction flow rate necessary for the dust proof is reduced to prevent turbulence of the air flow in the vicinity of a device 11, and the dustproof shield of a maximum source of generating dust is performed as the acceleration is increased. SOLUTION: In a feed screw mechanism, scattered metallic powder to be generated by rubbing of metals with each other such as a ball 3 and a nut 2, or oil (or grease) is scattered only from each side of the nut 2, and the effective dust proof can be achieved by sucking the metal powder or oil (grease) by vacuum in the vicinity of each end part of the nut 2. Because only suction is wasteful even if the suction flow rate is abundant, shielding members 5, 6 are fitted with a space therebetween. Dust generated between the ball 3 in the nut 2, a threaded shaft 1 and the nut 2 is spun out in a space between the end in the nut 2, and sucked into a suction port (on the opposite side to the fitting side) provided in the vicinity of the shielding members 5, 6 earlier than being discharged from the clearance between the shielding members 5, 6 and the threaded shaft 1 into a pneumatic piping. The amount of dust to be scattered outside the nut 2 is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus having a drive mechanism section using a uniaxial or more feed screw, which is used in an environment where dust is not desired.

[0002]

2. Description of the Related Art For example, in an exposure apparatus for printing a minute semiconductor circuit pattern on a wafer or a glass plate, dust is likely to adhere to the wafer or the glass plate during an exposure operation, resulting in a defective product. Therefore, various dust countermeasures are taken with great care.

As measures against such dust generation, it is necessary to install an exposure device in a clean room which prevents dust from entering the outside world, and to wear special clothes, hats, gloves, masks, etc. It is actually being done.

On the other hand, the exposure apparatus has a drive unit for driving the stage and the like, and this drive unit can also serve as a dust source. Therefore, in order to prevent dust generated from the drive unit from reaching the wafer or the like, a measure is taken to cover the entire drive unit with a bellows type cover or the like.

More specifically, taking the conventional exposure apparatus as an example, the process of dust generation in the drive unit and its countermeasure will be described. In a stage that supports a wafer or a glass plate, a linear drive mechanism that drives the stage using a ball screw is generally provided. FIG. 1a is a top view of such a ball screw, FIG. 1b is a partial cross-sectional perspective view of the ball screw, and FIG. 1c is an enlarged axial cross-sectional view of the ball screw near the circulating ball.

As is well known in the art, a ball screw has a cylindrical nut 2 having a female screw on its inner circumference, provided around a screw shaft 1 formed with a male screw, and a screw formed between both screws. A plurality of balls 3 are arranged in the groove, and when the screw shaft 1 is rotated, the nut 2 linearly moves according to the rotation. As shown in FIG. 1b, the nut 2 is provided with a return tube 4 through which the balls 3 are circulated. That is, the ball 3 that rolls around the screw shaft 1 as it rotates
Is returned to its original position by the return tube, so that the nut 2 can make a linear motion indefinitely as long as it is along the screw shaft 1.

By the way, in order to prevent a clearance (play) of the nut 2 with respect to the screw 1 shaft and to increase the rigidity, a constant preload is applied, whereby the ball 3 is placed on the nut side and the screw shaft. The contact portions 1a and 2a are in contact with the contact portions 1a and 2a at two locations on each side. Such preload can be performed by adjusting the diameter of the ball in units of microns.

However, the preload applied to the screw shaft 1 causes the following problems. For example, considering the ball screw of FIG. 1c as an example, a force is always applied between the screw shaft 1 and the ball 3 (steel ball) provided between the nut 2 and the screw shaft 1 by the preload, and the screw shaft 1 and the nut 2 The groove portion 2 has slight elastic deformation at the contact portions 1a and 2a (contact points) with the ball 3.

When the feed screw under such a condition is given an arbitrary acceleration to move the movable portion fixed to the nut 2 of the feed screw, the ball 3 inside the nut 2 is proportional to the acceleration. Then, rolling friction occurs between the screw shaft 1 and the nut 2. If this rolling friction is large, slippage occurs between the ball 3 and the screw shaft 1 and the nut 2. It is considered that the sliding causes the metals to rub against each other to generate dust.

Therefore, conventionally, the entire threaded portion is covered with, for example, a bellows type cover which expands and contracts as the nut moves.
In addition, measures were taken to prevent dust from scattering by sucking in the vicinity of the nut on the cover.

[0011]

By the way, in such a linear drive mechanism using a feed screw, the demand for high-speed movement and high-speed alignment (abrupt stop) of the movable portion is becoming severer year by year. Since such a feed screw is preloaded, the amount of dust generated further increases when it is moved at high speed, etc., and it is not possible to effectively prevent dust generation with conventional measures that cover the entire screw portion. is there.
This is because even if it covers the entire screw part, the nut moves with respect to the screw shaft, so that the dust source cannot be completely shielded.

Further, the conventional bellows type dust-collecting cover can itself become a dust-generating source by repeating expansion and contraction of the cover itself, so it cannot be said that it is a very effective measure against the speeding up of the feed screw. . Further, if the suction amount is not the minimum necessary amount, the air flow around the device may be disturbed, and eventually all the dust may be collected from around the device.

Therefore, according to the present invention, the suction flow rate required for dust prevention is reduced as much as possible so as not to disturb the air flow around the apparatus, and the maximum dust source associated with the increase in acceleration is shielded against dust. It is intended to provide a screw mechanism.

[0014]

In order to achieve the above object,
The feed screw mechanism of the present invention has a shaft having a male screw formed on the outer periphery thereof, a nut having a hole inserted into the shaft, and a nut having a female screw formed on the inner periphery of the hole so as to face the male screw. A plurality of balls rollably arranged in a thread groove space formed between the male screw and the female screw, and a shield provided at the entrance of the hole of the nut for shielding the screw shaft space The nut has a suction opening that is connectable to an external suction means for sucking air in the thread groove space.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, attention is paid particularly to the two points that the amount of dust generation increases with an increase in acceleration and that rolling friction occurs between the ball inside the nut and the screw shaft and the nut.

It will be described below that the amount of dust generated increases with an increase in acceleration. In a linear drive mechanism that uses a feed screw, in order to improve the tracking of the screw shaft with respect to the drive command,
Although the feed screw is preloaded, the contact surface is slightly elastically deformed. In such a case, when the feed screw suddenly starts rotating from the stopped state, rolling friction occurs between the ball inside the nut, the screw shaft, and the nut. This rolling friction causes rubbing between the metals.

Metal powder scattered by such rubbing,
Alternatively, oil (or grease) or the like scatters from both sides of the nut to the outside, so dust can be effectively achieved by suctioning near both ends of the nut. However, even if only suction is performed, no matter how much the suction flow rate is, it is useless, so a shield member is attached to form a closed space. It is preferable that this shield member is arranged inside the nut and the clearance with the outer diameter of the screw shaft is made as small as possible within the range where interference with the screw shaft does not occur. Needless to say, it is more effective to cover the thread groove portion of the screw shaft. It is preferable that the length of the portion of the shield member that has a small clearance with the screw shaft is longer than one lead.

With the above-mentioned structure, the dust generated between the ball inside the nut, the screw shaft and the nut is
Once it is repelled into the space at both ends inside the nut, it is sucked into the pneumatic piping through the suction port (mounting side and the opposite side) provided near the shield member faster than it is ejected from the gap between the shield member and the screw shaft. Be done. As a result, the amount of dust generated outside the nut is reduced.

[0019]

Embodiments of the present invention will now be described in detail with reference to the drawings. 2a is a front view of a lead screw mechanism according to the present invention, and FIG. 2b is a front view of the lead screw mechanism of FIG. 2a.
FIG. 2c is a view taken along line A-IIA and viewed in the direction of the arrow.
[Fig. 2] is a view of the lead screw mechanism of Fig. 2a taken along line IIB-IIB and viewed in the direction of the arrow.

In the figure, the nut 2 has a flange portion 2a.
And a cylindrical portion 2b are connected to each other, and has a hole 2c penetrating the center thereof in the axial direction. A female screw 2d is provided inside the hole 2c.
Are formed. A screw shaft 1 having a male screw 1a is inserted into the hole 2c, and a screw groove space is formed between the male screw 1a and the female screw 2d.

Disc-shaped resin shield members 5 and 6 are provided near both ends of the hole 2c of the nut 2, respectively.
The shield member 6 on the cylindrical portion 2b side is attached to the cylindrical portion 2b with three screws 7. On the other hand, the flange portion 2
The shield member 5 on the a side is, for example, press-fitted to the flange 2
Although it is attached to a, it can of course be attached using other attachment means.

The shield members 5 and 6 have openings 5a,
6a. Since the inner diameters of the openings 5a and 6a are slightly larger than the outer diameter of the male screw 1a of the screw shaft 1,
A minute gap is formed between the shield members 5 and 6 and the screw shaft 1. This is because if this gap is large, the dust will be scattered to the outside, and if there is no gap, the dust will come into contact and generate dust from this part. The shield members 5 and 6 have openings 5
a and 6a have thick proximity portions 5b and 6b, and the lengths of the proximity portions 5b and 6b in the axial direction are the male screw 1a of the screw shaft 1.
Longer than the lead length to improve the dustproof effect.

In the flange portion 2a and the cylindrical portion 2b, passages 2e and 2f which are suction openings extending radially outward from the holes 2c near the shield members 5 and 6 are formed. Joints 8 and 9 are screwed and attached at the outer ends of the passages 2e and 2f.

A plurality of balls 3 are arranged between the screw shaft 1 and the nut 2 so that they can roll in the screw groove. The return tube 4 is provided for ball circulation as in the conventional case.

FIG. 3 is a schematic diagram of an XY stage using the feed screw mechanism according to the present invention. In FIG. 3, a Y stage 200 that is in charge of driving in the Y direction is placed on the base 100, and an X stage is further mounted on the Y stage 200.
An X stage 300 that is in charge of driving in the direction is mounted. Feed screw mechanisms having the same structure are provided to drive both stages.

A step motor 202 is attached to a post 201 fixed to the base 100, and a rotation shaft (not shown) of the step motor 202 is connected to the screw shaft 1. The nut 2 screwed onto the screw shaft 1 is used for the Y stage 20.
It is fixed to 0. The step motor 202 rotates precisely according to a signal from a control circuit (not shown).

On the other hand, a step motor 302 is attached to the post 301 fixed to the Y stage 200, and a rotation shaft (not shown) of the step motor 302 is connected to the screw shaft 1. The nut 2 screwed onto the screw shaft 1 is fixed to the X stage 300. The step motor 302 also rotates precisely according to a signal from a control circuit (not shown).

Pneumatic piping AL for vacuum suction
Extends from the pneumatic control unit 400 on the factory side and is once relayed by the main pneumatic relay unit 500. It is preferable that the pneumatic pipe AL is independently connected to the pneumatic control unit 400 so as not to affect the operation of other pneumatic equipment and efficiently achieve the suction action. Here, the pneumatic piping AL is 2
One of the branches AL1 passes through the flow controller 501 on the Y stage side and extends to the sub air pressure relay unit 601. Further, in the sub-pneumatic relay section 601, the pneumatic piping is divided into two, one of which AL11 is the nut 2
To the fitting 8 (Fig. 1c) attached to the other one AL1
2 is connected to a joint 9 attached to the nut 2. As a result, both ends of the nut 2 can be sucked with the same flow rate.

On the other hand, of the pneumatic pipes AL branched in the main pneumatic relay section 500, the other one AL2 passes through the flow controller 502 on the X stage side and extends to the sub pneumatic relay section 602. Further, in the sub-pneumatic relay section 602, the pneumatic piping is divided into two, one of which is AL21 and the nut is two.
To the fitting 8 (Fig. 1c) attached to the other one AL2
2 is connected to a joint 9 attached to the nut 2.

The main air pressure relay section 500 is provided with an acceleration information detecting device 503 which is a detecting means. The acceleration information detecting device 503 detects the input signals of the step motors 202 and 302, detects which acceleration acts on the X and Y stages based on the input signals, converts the accelerations into an electric signal, and controls the flow rate as a control means. Controller 50
It has a function of transmitting to the 1 and 502.

Next, the operation of the feed screw mechanism of this embodiment will be described. In FIG. 3, it is assumed that a predetermined negative pressure is constantly generated in the pneumatic piping AL by the pneumatic control unit 400 on the factory side. Further, when the feed screw mechanism is not operating, the flow rate controllers 501 and 502 are the pneumatic piping AL.
1. Keep AL2 fully closed. This is because dust is hardly generated when the feed screw mechanism does not operate, and thereby the load on the pneumatic control unit 400 can be reduced. Here, the step motor 2 is controlled by a control circuit (not shown).
It is assumed that the rotation command is generated in 02 or 302.

When the step motor 202 or 302 rotates, the screw shaft 1 rapidly starts to rotate from the stopped state, and as described above, the metal scraped between the ball 3 and the screw shaft 1 and the nut 2 rubs against each other. The metal powder or oil (or grease) that has been peeled off due to (slip)
An attempt is made to scatter from both sides of the nut 2 through the thread groove space formed between the male screw 1a and the female screw 2d.

On the other hand, the acceleration information detecting device 503 detects the input signals of the step motors 202 and 302, detects what kind of acceleration is applied to the X and Y stages based on the input signals, converts the accelerations into an electric signal, and then the flow rate. It is transmitted to the controllers 501 and 502.

The flow rate controllers 501 and 502 open the flow rate adjusting valves of the pneumatic pipes AL1 and AL2 in accordance with the electric signal from the acceleration information detecting device 503 so that the air having a predetermined flow rate can pass therethrough. As a result, the sub air pressure relay unit 60
1, 602 and pneumatic piping AL11, AL12, AL2
1, the air in the hole 2c (FIG. 1c) of the nut 2 is sucked through the AL 22. As a result, the dusty metal powder,
It can be captured just before it is scattered to the outside of the nut 2 due to a slight clearance between the screw shaft 1 and the shield members 5 and 6.

The flow rate controllers 501 and 502 adjust the flow rate of the suctioned air. If the suction flow rate is too low, the dust trapping effect is weakened. On the other hand, if the suction flow rate is too high, all the dust from the factory is removed. , And the Y stage may be collected, and the load on the pneumatic control unit 400 that drives other pneumatic equipment (for example, a suction carrier) is also reduced.

Further, it is generally considered that the larger the acceleration is, the larger the amount of dust generation is. Therefore, the flow rate adjusted by the flow rate controllers 501 and 502 is proportional to the detected acceleration within a certain range. By increasing or decreasing the amount, dust can be captured efficiently even if the feed screw is driven at high speed, while the pneumatic control unit 4 on the factory side
The burden of 00 can be further reduced.

In consideration of maintenance, the shield member is not shaped like the labyrinth seal conventionally used by screw manufacturers, but the side opposite to the flange is removable as shown in FIG. Things are better.

In this embodiment, the driving acceleration is detected based on the driving command to the step motor, but the actual acceleration can be detected by mounting an acceleration pickup or the like on the stage. . Furthermore, in the present embodiment, an example in which the present invention is applied to an XY stage for an exposure apparatus is shown, but the feed screw mechanism of the present invention is not limited to this, and it can be applied to any machine used in an environment where dust is disliked. Is possible.

[0039]

As described above, the feed screw mechanism of the present invention can sufficiently withstand use in an environment where extremely high cleanliness is required by shielding and sucking the nut portion which is a dust source. Moreover, by adjusting the suction flow rate, it is possible to sufficiently cope with high-speed driving of the feed screw.

[Brief description of drawings]

FIG. 1A is a top view of a conventional ball screw. (B) A partial sectional perspective view of a conventional ball screw. (C) An enlarged sectional view in the axial direction near a circulating ball of a conventional ball screw.

FIG. 2A is a front view of a feed screw mechanism according to the present invention. (B) A view of the feed screw mechanism of FIG. 2a taken along line IIA-IIA and viewed in the direction of the arrow. (C) A view of the lead screw mechanism of FIG. 2a taken along line IIB-IIB and viewed in the direction of the arrow.

FIG. 3 is a schematic configuration diagram of an XY stage using a feed screw mechanism according to the present invention.

[Explanation of symbols]

 1 Screw axis of feed screw 2 Nut of feed screw 3 Circulation ball in nut 4 Return tube 5, 6 Shield member 7 Screw 8, 9 Joint 100 Base 200 Y stage 300 X stage 400 Pneumatic control unit 500 Pneumatic relay unit

Claims (4)

[Claims] 1. A nut having a male screw formed on the outer periphery thereof, a nut having a hole inserted through the shaft, and a female screw formed on the inner periphery of the hole facing the male screw, A plurality of balls rotatably arranged in a screw groove space formed between the screw and the female screw, and a shield member that is provided at the entrance of the hole of the nut and shields the screw shaft space. The feed screw mechanism, wherein the nut has a suction opening that can be connected to an external suction means in order to suck air in the thread groove space. 2. The feed screw mechanism according to claim 1,
The feed screw mechanism, wherein the nut has a circulation passage for circulating the balls. 3. The feed screw mechanism according to claim 1,
The feed screw mechanism, wherein the axial length of the shield member is longer than the lead length of the male screw of the shaft. 4. The feed screw mechanism according to claim 1,
Further, the feed screw mechanism is provided with a detection means for detecting information on the acceleration of the nut and a control means for controlling the flow rate of the sucked air based on the information on the acceleration detected by the detection means. .