JPH02309046A - Ball screw rotation stopping mechanism - Google Patents

Abstract

PURPOSE:To stop a traveling stage in place accurately by furnishing two press ing plates, which use the slide friction force of sliding members to stop that unstable rotating condition of a ball screw remaining when the driving current to a DC motor is shut off. CONSTITUTION:No.2 pressing plate 62 is installed with a certain gap reserved relative to No.1 pressing plate 61, and sliding members 71, 72 of fluoric resin are affixed to their inner surfaces, and these two places are coupled together resiliently using coil springs 81, 82 and a bolt 9. A slide disc 3 secured to a ball screw is inserted into this gap, and the front and rear surfaces are put in contact with the sliding members 71, 72, wherein the contact pressure is adjusted by the coil springs 81, 82 properly. Stopping the ball screw in rotation can be accomplished by the method wherein its unstable rotation arising when the driving current is shut off is suppressed by the slide friction force due to the contact pressure between the sliding members 71, 72 and slide disc 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a rotation stop mechanism for a ball screw in a moving stage.

[Prior Art] As the density of semiconductor products increases, extremely high precision is required for the movement of a stage on which products are mounted and moved. For this purpose, a ball screw is used in the moving stage. The structure and operation of the ball screw moving stage 1 will be explained with reference to FIG. Both ends of the ball screw 11 are equipped with bearings 121,1.
22, and a drive motor 13 is coupled to one end.

A movable part 14 is fitted into the ball screw H, and the movable body 2 is fixed to this, and the movable body is moved by rotation of the drive motor. As the drive motor, a pulse motor whose rotation can be controlled with high precision is suitable, but a DC motor is used when high-speed movement is required.

[Problem to be solved] In the above, when a DC motor is used as the drive motor, the drive current is set so that the speed is low at the start and end and high in the middle, in order to make the moving object move smoothly. A method is used to control the rotational speed of the ball screw as a trapezoid. Furthermore, if the drive current is simply cut off when stopping the rotation, the rotational force will remain unstable due to the inertia of the ball screw. There is a method of asymptotic control (±0 asymptotic control), but such a control method is somewhat troublesome.

There is also a method of providing a brake means and operating it at the same time as the cutting off of the drive current, but there is no guarantee that the brake means can stop accurately.

This invention has been made in view of the above, and is a simple and simple method that prevents the unstable rotation state that occurs when the rotation of a ball screw driven by a DC motor stops and accurately stops a moving stage at a predetermined position. The purpose of this invention is to provide a mechanism for stopping the rotation of the structure.

[Means for Solving the Problems] The present invention is a rotation stop mechanism for a ball screw in a ball screw moving stage driven by a DC motor, in which a steel sliding disk is fixed to the tip of the ball screw. In addition, sliding material made of fluororesin is attached to the surfaces of the two suppression plates, and the springs are used to constantly contact the front and back surfaces of the sliding disks with appropriate contact pressure, so that the balls that remain when the drive current of the DC motor is cut off The unstable rotation of the screw is stopped by the sliding friction force of the sliding material.

[Operation] In the above-mentioned rotation stop mechanism, the key point is to use a fluororesin sliding member in place of the braking member. The properties of this sliding material are such that both static and dynamic friction coefficients generally decrease with load, and the higher the contact pressure, the smaller the friction coefficient becomes. Therefore, in the above rotation stop mechanism,
The sliding member is kept in constant contact with the sliding disk by an appropriate contact pressure by a spring, and the mW of friction against the rotation of the ball screw is made as small as possible. Thereby, the rotation of the ball screw in the driven state is performed smoothly. When stopping rotation, the ball screw shifts from low-speed rotation according to the above-mentioned trapezoid with the drive current of the DC motor, but when the current is cut off, the ball screw shifts to inertial rotation with a small rotational force, and the inertial rotation is smaller than the sliding friction force of the sliding material. When the force becomes small, the rotation is stopped, the unstable rotation state is suppressed, and the moving stage is stopped at a predetermined position. Here, the sliding friction force is appropriately set by adjusting the strength of the spring relative to the suppression plate. Note that in this case, the above-described ±0 asymptotic control of the drive current is not necessarily required.

[Embodiment] Figures 1 (a), (b), (c) and (d) show the structure of an embodiment of the ball screw rotation stop mechanism according to the present invention. Figure (a) is a central sectional view of the ball screw H in the axial direction.
Figure (b) is a front view in a direction perpendicular to the axis, figure (c) is a partially detailed view, and figure (d) is a perspective external view. In each figure, the ball screw II for the moving stage 1 in FIG. 2 is a bearing! 2, and a steel sliding disk 3 is fixed to its tip. One end of each of the two leaf springs 51 and 52 is fixed to the fixture 4 that fixes the bearing 12,
A first pressing plate 81 having the shape shown is attached to each other end so that it can respond to the axial movement of the ball screw 11.

A second pressing plate 82 is provided with a constant gap with respect to the first pressing plate 61, and sliding materials 71 and 72 made of fluororesin are pasted on the inner surfaces of each, and coil springs 81 are attached to these 2yA points. .82 and are elastically connected by bolts 91 and 92. The sliding disc 3 is inserted into the gap, and the front and back surfaces contact the sliding material 71.72, and the contact pressure is applied to the coil spring 81.82 (Fig. (representatively shown). When the rotation of the ball screw 11 is stopped 1-, as described above, the sliding friction force caused by the contact pressure between the sliding members 71 and 72 and the sliding disk 3 prevents the ball screw from becoming unstable when the drive current is cut off. Rotation is inhibited and stops.

[Effects of the Invention] As is clear from the above explanation, the rotation of the ball screw according to the present invention is stopped. It is a simple mechanism that stops rotation when the rotational force becomes larger than a stable rotational force, and does not require ±0 asymptotic control of the drive current for the drive motor as in the past, or a brake means (such as a ball screw). Accurately stops the rotation of!・,
However, the effect of contributing to highly accurate position control of the moving stage using a ball screw is significant.

[Brief explanation of drawings]

Figures 1 (a), (b), (c) and (d) are structural diagrams of rotating nodes of the ball screw according to the present invention [Fig. FIG. DESCRIPTION OF SYMBOLS 1... Movement stage by ball screw, 11... Ball screw, 12... Bearing, 13... Drive motor,
14... Moving unit, 2... Moving object,
3...Sliding disk, 4...Fixing tool,
5... Temporary spring, 61... First suppression plate, 62.
...Second pressing plate, 71.72...Sliding material, 8,81.
82...Coil spring, 9.91.92...Bolt.

Claims (1)

[Claims] In a ball screw moving stage driven by a DC motor, a steel sliding disk is fixed to the tip of the ball screw, and a fluororesin sliding material is pasted on the surface, and the pasted sliding material is The spring constantly contacts the front and back surfaces of the sliding disk with an appropriate contact pressure, and the sliding friction force of the sliding material prevents the unstable rotation of the ball screw that remains when the drive current of the DC motor is cut off. A rotation stop mechanism for a ball screw, characterized in that it is provided with two pressing plates that stop the rotation.