JPS6256382B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a feed screw, a nut screwed into the feed screw, a guide means having a straight guide path, and a nut movable along the guide path and coupled to the nut. The present invention relates to a screw feeding device equipped with a movable body driven by a screw, and particularly relates to an improvement that increases the feeding accuracy thereof.

Conventionally, in order to improve the feed accuracy, that is, the positioning accuracy, using open-loop control in screw feeding devices, it is necessary to use a screw with a small cumulative lead error, or to make the cumulative lead slightly shorter than the target value, and to apply tension to the screw. Methods such as adjusting the screw by stretching it to a target value have been used. However, the former method not only requires highly accurate and expensive screws, but also has a limit in accuracy. In addition, the latter method requires a large tension, which not only requires a screw-supported bearing with a large thrust load capacity, but also requires the body that supports the bearing to have great rigidity so that it will not deform even under the tension. However, this method had disadvantages such as the overall size of the device.

Additionally, in the past, since the nut of the feed screw and the movable body were rigidly connected, radial runout caused by bending of the feed screw affected the movable body, resulting in a disadvantage such as deterioration of the linear accuracy of the movable body. It was hot.

In view of the above-mentioned problems, the present invention makes it possible to effectively change the cumulative lead of the feed screw and change the amount of feed of the movable body per fixed number of rotations without impairing the linear accuracy of the movable body. The purpose is to provide a screw feeding device that can.

For this reason, the present invention provides means for changing the parallelism between the feed screw and the guide path, and by actively changing the parallelism, the cumulative lead of the feed screw can be effectively changed, and the feed screw and the guide path can be effectively changed. In order to prevent deterioration of the linear accuracy of the movable body even when the two are not parallel, one of the nut screwed onto the feed screw and the movable body should have a shaft extending perpendicular to the guiding direction, and the other should have a shaft that extends concentrically with the movable body. A member having a hole to be fitted into the shaft is provided, and a plurality of rolling elements are arranged in a single row between the outer circumference of the shaft and the inner circumference of the hole so as to be able to roll in the axial direction of the shaft and to surround the shaft. To provide a screw feeding device which allows relative displacement between a nut and a movable body in a direction orthogonal to the axis of the feed screw without resistance.

An embodiment of the present invention will be described below based on the drawings. In FIGS. 1 and 2, 1 and 2 are respectively known straight air bearings, and 3 and 4 are guide means each forming a straight guide path. 5 and 6 are the guide bodies 3 and 4, respectively, with a rectangular cross section.
It is a movable body configured to surround the Although not shown, high-pressure air is pumped between the movable bodies 5, 6 and the guide bodies 3, 4, and the movable bodies 5,
6 floats from the guide bodies 3 and 4 without contacting them and is movable only in the direction of arrow D. Further, each of the guide bodies 3 and 4 is fixed to the body 11 at both ends thereof via pedestals 7 and 8 with screws 9 and 10. 12
1 is a feed screw supported at both ends by ball bearings 13 and 14, and 15 is a nut for applying preload to the ball bearing 19. 16 is a motor that drives the feed screw 12, and 17 is a shaft coupling that connects the motor 16 and the feed screw 12. 18, 19, and 20 are brackets fixed to the adjustment member 21 with set screws 22, 23, and 24, respectively;
20 supports the motor 16 and the ball bearing 14, respectively. The adjustment member 21 is attached to the fuselage 11
It is rotatably supported by a pivot shaft 25 implanted in the body 11, and is fixed to the body 11 by a set screw 28. A beam 27 connects the movable bodies 5 and 6, and is fixed to each movable body by a set screw 28. 29 is a nut screwed onto the feed screw 12, 30 is a movable body 5,
6 is a table that is fixedly placed on top of the table.

The connection structure between the nut 29 and the beam 27 will be explained with reference to FIG. 3. 31 is a hard shaft in the shape of a round bar installed in the nut 29 in a direction extending perpendicular to the direction of movement of the nut 29; is a hard bushing having a cylindrical hole 33 press-fitted into the beam 27, and the shaft 31 is fitted concentrically into the hole 33. 34 is a plurality of steel balls as rolling elements interposed between the outer periphery of the shaft 31 and the inner periphery of the hole 33;
They are held by a retainer 35 that loosely fits into the hole 33 and the steel balls 34, and are arranged in a single row at a predetermined position. Further, the dimensions of each element are set so that the fit between the shaft 31, the hole 33, and the steel ball 34 has a negative clearance. 36 is a compression spring provided in the retainer 35. By setting the length of the compression spring 36 to a predetermined length, when the shaft 31 and the retainer 35 are assembled into the bush 32, the retainer 35 can be easily positioned. In addition, when the shaft 31 is mounted in the vertical direction, that is, in the direction of gravity, as shown in Fig. 3, a preload is applied to the steel balls 34, and although they do not slip, they gradually fall downward and the cage is removed. 35
However, by using the compression spring 36, this phenomenon can be reliably prevented. In this way, the nut 29 and the beam 27 are connected via the shaft 31, the plurality of steel balls 34, and the bush 32.

According to the above-described coupling structure, a force is applied in the direction of movement of the nut 29, that is, the arrow D direction, and in the rotation direction of the nut 29, that is, the E direction, in a direction that compresses the steel ball 34, so that the steel ball 34 has a large rigidity. The main factor that reduces rigidity is the steel ball 3.
4, the shaft 31, and the hole 33.
Rigidity can be easily increased by making these fits with a negative clearance and increasing the preload, or by the method described in other embodiments. On the other hand, with respect to the radial runout of the feed screw 12 in the directions of arrows F and G and the rotational runout in the direction of arrow J, the nut 29 can be displaced with almost no resistance in the state shown in FIG. 5, for example. For example, shaft 31
When the diameter of the steel ball 34 is 10 mm, the diameter of the steel ball 34 is 3 mm, and the amount of preload is 6 μm in diameter, displacement can be made with almost no resistance within the range of angle θ=±5° in FIG. Further, it goes without saying that the steel ball 34 can be displaced in the directions of the arrows H and K without resistance due to rolling of the steel ball 34.

Therefore, the nut 29 faithfully transmits motion to the movable bodies 5 and 6 without rotating, and also prevents radial runout from occurring in the feed screw 12 and
When the axis of the nut 29 and the guide bodies 3, 4 are not parallel, displacement of the nut 29 in a direction other than the drive direction is hardly transmitted to the movable bodies 5, 6. Therefore, even if a guide means such as an air bearing which has high straightness but has low guide rigidity is used, the original straight-line accuracy will not be impaired at all.

By adopting the above-mentioned coupling structure between the nut 29 and the beam 27, as shown in FIG.
There is no problem in driving the movable bodies 5 and 6 even if the feed screw 12 is arranged at an angle with respect to the moving direction of
By arranging them at an angle, the cumulative lead can be effectively changed. To install the feed screw 12 at an angle in this manner, as shown in FIG. 1, the set screw 26 is loosened, the adjustment member 21 is rotated about the pivot 25, and the set screw 26 is tightened and fixed.

Now, in FIG. 7, the feed screw 12 of lead l
is installed at an angle a degree in the positive direction from the direction of arrow D, and when the feed screw 12 is driven N rotations by the motor 16 and the nut 29 is moved by a distance L to the position 29' shown by the broken line, the movable body 5,6
The distance over which is sent is L′ = Lseca. On the other hand, when the nut 29 is fed a distance L, the nut 29 is tilted at an angle b° as shown in FIG.
More lb/360 is sent than Nl, L=l(N+
b/360). Therefore, L'-Nl=l・sec a・(N+b/360)-Nl... If the angle a° is negative, the nut 29 will be fed lb/360 less than Nl due to the inclination of the angle b°, so L'-Nl=l・sec a・(N-b/360)-Nl... becomes.

Also, from tan b=M/P, tan|a|=M/L, b=tan ^-1 (L/P・tan|a|)... In other words, in Fig. 7 and Fig. 8, feed screw 1
When the feed screw 12 is rotated N times, the cumulative lead Nl changes to L', and the difference L'-Nl is the amount of change in the cumulative lead due to tilting the feed screw 12 by a degree. For example, let Nl = 150mm, l = 2mm, P = 30mm, and in order to simplify the calculation, L≒
When Nl is assumed, the relationship between angle a° and L'-Nl is
~From the formula, it becomes as shown in Figure 9. That is, the angle a
By changing ±0.4°, the cumulative lead can be increased to 150
It is possible to change it by approximately +14.8 μm to −7.5 μm with respect to mm. In this case angle |a|=
Even at 0.4°, the angle b is at most 2°, so the above-mentioned coupling structure of the nut 29 and beam 27 will not hinder operation at all, and M at that time will be 1.05mm, so M should be reduced to 1/10 to 1. By adjusting with an accuracy of /20 mm, the cumulative lead can be easily changed with an accuracy of 1 μm or less.

For example, when the feed screw 12 with a lead of 2 mm is mounted parallel to the moving direction of the movable bodies 5 and 6 and driven 75 rotations, the moving distance of the movable bodies 5 and 6 is the target value.
If it is 149.990mm compared to 150.000mm, loosen the set screw 26 shown in Fig. 1 and rotate the adjusting plate 21 counterclockwise around the pivot 25 by 0.28° from Fig. 9 to fix it. , 6 is as per the target value,
It will be sent 150.000mm. In this way, the cumulative lead of the feed screw 12 can be easily and effectively changed by a minute amount, and even if there is a cumulative lead error in the feed screw, the feed amount of the movable body can be easily adjusted to the target value and within 1 μm. Can be adjusted precisely with precision.

In the connection structure between the nut 29 and the beam 27 in the above embodiment, a combination of a round rod-shaped shaft, a cylindrical hole, and a steel ball is shown. Its function can be achieved by combining it with rolling elements that can roll, and various modifications as described below are possible.

FIG. 6 shows an example in which the shaft 37 and the bush 38 are provided with rolling grooves 35 and 36 in the direction of rotation of the steel ball 34, respectively. 39 is a holder for the steel balls 34. The rolling grooves 35 and 36 may be arcuate grooves, or may be a groove in which two arcuate grooves called a gothic arm are combined in a V-shape.

Further, although not shown, the shaft and the hole may be polygonal, and rollers or needle-like rollers may be disposed therebetween.

This increases the contact area between the rolling elements and the rolling parts of the shaft and hole, increasing the rigidity in the direction of arrow D in Figure 1 and the direction of arrow E in Figure 3, resulting in more accurate motion transmission. suitable for By the way, in this case, the stiffness against displacement in the K direction also increases, but since the displacement component in the K direction is much smaller than the displacement components in the F, G, and H directions, there is no practical effect even if the stiffness in the K direction is large. There is no problem.

Further, in the embodiment shown in FIG. 1, an adjustment plate 21 is provided to adjust the inclination of the feed screw 12, and the adjustment plate 21 is rotated to adjust the inclination.
If the inclination adjustment frequency is infrequent, the bearing and motor supporting the feed screw may be directly attached to the body 11, and each may be adjusted independently. Further, if necessary, a driving means for rotating the adjusting plate 21 shown in FIG. 1 may be provided, and the driving means may be controlled by an external signal to change the inclination of the feed screw.

According to the screw feeding device of the present invention, as is clear from the above description, the cumulative lead of the feed screw can be effectively changed by changing the parallelism between the guide path of the movable body and the axis of the feed screw. Therefore, even if there is a large cumulative lead error in the feed screw, the amount of movement of the movable body can be easily adjusted to the target value. Moreover, even if the feed screw and the guide path are not parallel, or even if there is radial runout in the feed screw, the movable body can move straight due to the combination of the shaft, hole, and rolling element, which connects the nut and the movable body. No loss of accuracy. Therefore, it is possible to provide a small-sized screw feeding device that has high guiding accuracy and positioning accuracy even if an inexpensive feed screw that is not very accurate is used.

[Brief explanation of the drawing]

FIG. 1 is a partially sectional top view of an embodiment of the present invention;
Fig. 2 is a sectional view taken along line A-A in Fig. 1, Fig. 3 is an enlarged sectional view taken along line B-B in Fig. 1, Fig. 4 is a sectional view taken along C-C in Fig. 3, and Fig. 5 is a functional explanation. FIG. 6 is a cross-sectional view of the main parts of another embodiment, and FIGS. 7 and 8 are
The figure is a schematic diagram for explaining the operation, and FIG. 9 is a graph showing the relationship between the inclination angle of the feed screw and the amount of change in cumulative lead. 3 and 4 are guide bodies as guide means constituting a guide route; 5 and 6 are movable bodies; 12 is a feed screw;
3 and 14 are ball bearings, 16 is a motor, 21 is an adjustment member, 25 is a pivot, 27 is a beam, 29 is a nut, 31
32 is a shaft, 33 is a hole, 34 is a steel ball as a rolling element, and 35 is a cage.

Claims (1)

[Scope of Claims] 1. A feed screw having a nut screwed thereon is provided, and a guide means having a straight guide path for movably guiding the movable body is provided substantially parallel to the feed screw,
A means for changing the parallelism between the feed screw and the guide path is provided, and one of the nut and the movable body has a shaft extending perpendicular to the guide direction, and the other has a hole into which this shaft is fitted concentrically. A screw in which a plurality of rolling elements are provided between the outer periphery of the shaft and the inner periphery of the hole and are movable in the axial direction of the shaft and are arranged in a single row so as to surround the shaft. Feeding device. 2. The means for changing the parallelism includes an adjusting member that integrally connects the means for supporting the feed screw and the means for driving the feed screw, and supports the adjusting member so as to be rotatable in the direction in which the parallelism changes. 2. The screw feeding device according to claim 1, comprising means for fixing said adjusting member and means for fixing said adjusting member.