JPS6256381B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a movable body guided by a feed screw, a nut screwed into the feed screw, and a guide means that allows movement only in a straight direction, and driven in a straight line by the feed screw and the nut. The present invention relates to a screw feeding device equipped with a screw feeding device, and particularly relates to an improvement in the coupling structure between a nut and a movable body.

Conventionally, the nut of the feed screw and the movable body were usually rigidly connected, and the radial runout of the screw was faithfully transmitted to the movable body. Therefore, in the combination of the movable body and its guide means, even if the movable body has good straight-line accuracy, the combination of screws deteriorates the straight-line accuracy of the movable body.

In recent years, air bearing-type linear guides have been used in locations that require high linear accuracy for movable objects, but while air bearings provide higher linear accuracy than rolling guides or sliding guides, they have low rigidity. Even a slight radial runout of the screw significantly deteriorates the linear accuracy of the movable body, often halving the value of using an air bearing.

Conventionally, the following four methods have been considered to solve these problems. That is, the first method is to manufacture and use screws with small runout, and the second method is to manufacture and use screws with small runout.
The second method is to reduce the screw diameter to lower the bending rigidity of the screw so that it follows the movement of the movable body even if there is runout in the screw, the third method is to increase the rigidity of the air bearing, and the fourth method is The method used was to connect the nut and the movable body using an elastic body.

However, all of the above methods have advantages and disadvantages, and are not perfect. In other words, with the first method, since the screw is thin and long, there is a limit to reducing radial runout in terms of machining accuracy.If the screw diameter is increased, it is easier to reduce runout during machining, but it can be dramatically reduced. Moreover, increasing the screw diameter causes problems such as increased screw driving force.

The second method is the opposite of the first method; even if the screw diameter is made thinner, the rigidity will not drop dramatically.If the screw diameter is made thinner, it will become difficult to work, the radial runout will increase, and the pitch accuracy of the screw will become more difficult. It also tends to decrease.

The third method is disadvantageous in terms of miniaturization of the device because the size of the guide portion becomes large and the power required for driving becomes large.

The fourth method and its problems will be explained with reference to a specific example shown in FIGS. 1 to 3. 1 is a known linear air bearing, 2 is a guide body having a rectangular cross section, and 3 is a guide body that surrounds this guide body 2. It is a movable body configured in a similar manner. Although not shown, high-pressure air is pumped between the movable body 3 and the guide body, and the movable body 3 floats above the guide body 2 without contacting it, and is movable only in the direction of arrow A. Reference numeral 4 denotes a leaf spring having circular arc portions 5 on both sides, and a flat portion 6 between the circular arc portions 5 is fixed to the movable body 3 with a screw or the like. Further, the plate spring 4 has a flat portion 7 extending from the free end of each arcuate portion 5, and this flat portion 7
is fixed with a screw 8 to a nut 10 which is screwed into a feed screw 9.

According to such a configuration, the leaf spring 4 is moved in the feeding direction,
That is, it has relatively high rigidity in the direction of arrow A, and has relatively low rigidity in directions perpendicular to the direction of arrow A, that is, in the directions of arrows B and D, because the arc portion 5 is easily bent. Therefore, even if the feed screw 9 undergoes radial deflection in the direction of arrow B and deflection in the direction of arrow D, the forces applied to the movable body 3 in the B and D directions are reduced due to the bending of the circular arc portion 5.

However, since the rigidity in the direction of arrow C also decreases, the nut 10 becomes easier to rotate in the direction of arrow C.
This has the disadvantage that it is difficult to faithfully transmit the drive by the feed screw 9 to the movable body 3. Therefore, the basic principle is that the smaller the rigidity of the arc portion 5 is made so that the vibration of the feed screw 9 does not affect the movable body 3, the more difficult it becomes to accurately transmit the drive of the feed screw 9 to the movable body 3. It has some disadvantages. Furthermore, it is difficult to form the leaf spring 4 accurately, and errors in shape as shown in FIGS. 2 and 3 are likely to occur. When the shape error becomes large, an unreasonable force acts between the movable body 3 and the nut 10, which may even deteriorate the straight-line accuracy of the movable body 3.

As mentioned above, both methods were incomplete.

In view of these problems, the present invention prevents radial runout from being transmitted to the movable body and degrades the linear accuracy of the movable body even if there is radial runout in the feed screw, and also prevents the axial movement of the nut. It is an object of the present invention to provide a screw feeding device that can faithfully transmit data to a movable body.

For this reason, the present invention provides a member having a shaft extending in a direction perpendicular to the moving direction of the nut on one of the nut and the movable body, and a hole into which the shaft is fitted concentrically on the other, and the outer periphery of the shaft. By interposing a plurality of rolling elements arranged in a single row surrounding the shaft and capable of rolling in the axial direction of the shaft, the direction of movement of the nut is And to provide a screw feeding device which has large rigidity in the rotational direction and can be displaced with almost no resistance against radial runout of the feeding screw.

An embodiment of the present invention will be described below with reference to FIGS. 4 to 6. Components that are substantially the same as those explained in FIG. 1 are designated with the same reference numerals.
Also, the same symbols indicating the directions are used, and the explanation thereof will be omitted. 20 is the nut 1 to the nut 10
A round bar-shaped shaft 21 is installed in a direction extending perpendicularly to the moving direction of 0, and 21 is a bush having a cylindrical hole 22 into which the shaft 20 is fitted, and is fixed to the movable body 3 with a bolt 23. . Reference numeral 24 denotes a plurality of steel balls, which are held by a retainer 25 that loosely fits into the shaft 20, the hole 22, and the steel balls 24, and are arranged in a single row at a predetermined position between the shaft 20 and the hole 22. ing. Furthermore, the dimensions of the fit between the shaft 20, the hole 22, and the steel ball 24 are set so that there is a negative clearance. Therefore, the nut 10 and the movable body 3 are connected to each other by the connection between the shaft 20 and the bush 21 via the steel ball 24.

Due to the above configuration, force is applied in the direction of compressing the steel balls 24 in the movement direction of the nut 10, that is, in the direction of arrow A, and in the rotation direction of the nut 10, that is, in the direction of arrow C, so that the steel ball 24 has a large rigidity.
If I had to pick a factor that could reduce the rigidity, it would be the deformation of the contact area between the steel ball 24, the shaft 20, and the hole 22, but if the fit between them is increased by increasing the negative clearance and increasing the preload, the rigidity can be easily reduced. can be raised. On the other hand, the nut 10 can be displaced in the direction of arrow B, that is, in the radial deflection direction of the feed screw 9, with almost no resistance due to the rolling of the steel balls 24, as shown in FIG. 6, for example. For example, if the diameter of the shaft 20 is 10 mm, the diameter of the steel ball 24 is 3 mm, and the preload amount is 6 μm in diameter, in FIG. 6, the angle θ=
It can be displaced within a range of ±5° with almost no resistance. Needless to say, displacement in the direction of arrow B' and the direction of arrow D can be made without resistance only by rolling of the steel ball 24. Therefore, the nut 10 faithfully transmits the motion to the movable body 3 without rotating, and the radial runout of the feed screw 9 is hardly transmitted to the movable body 3, so that the movement is extremely accurate without impairing the linear accuracy of the movable body 3. High precision screw feeding is achieved.

In the above example, a combination of a round bar-shaped shaft, a cylindrical hole, and a steel ball was shown, but it is not necessary to use a round bar-shaped shaft.
The rolling elements do not need to be spheres, and various other modifications are possible.

In FIG. 7, rolling grooves 32 and 33 for steel balls 24 are provided on the shaft 30 and bush 31, respectively. 3
4 is a holder for the steel balls 24. the rolling groove 32,
The groove 33 may be an arcuate groove or a groove in which two arcuate surfaces are combined in a V-shape called a gochiku arc.

Further, as shown in FIG. 8, a shaft 35 having a rectangular cross section
, a roller or needle-like roller 36 , and a rectangular hole 3
The shaft and hole may have a polygonal cross section, such as by combining a bush 38 having a diameter of 7. 39 is a holder for the roller 36.

In both of the configurations shown in FIGS. 7 and 8, the contact area of the rolling portion between the rolling element and the shaft and hole increases, so the rigidity in the directions of arrows B and C shown in FIGS. 4 and 5 is It is larger and suitable for more precise motion transmission. On the other hand, in this case, the rigidity against displacement in the direction of arrow D becomes large, but the displacement component in the direction of arrow D is much smaller than the displacement component in the direction of B, so even if the rigidity in the D direction is large, there is no practical problem. There isn't.

FIG. 9 shows a cage 40 with compression springs 41 and 42 attached, with the structure of the cage 25 in FIG. 4 slightly changed.
This is an example using . Only one of the compression springs may be used. By using a spring in this way and setting the length of the spring to a predetermined length, when the shaft, rolling element, and bush are assembled, the positioning of the rolling element in the axial direction of the shaft can be easily controlled. It can be done easily. Furthermore, if the shafts 20, 30, 35, etc. are mounted in the vertical direction, that is, in the direction of gravity, the rolling elements will be preloaded, and although they will not slip, they will gradually fall downward and the cage 40 may come into contact with the nut 10 or the movable body 3, and the rolling motion of the rolling elements in the axial direction may be hindered and the rolling elements may not operate properly, but this phenomenon can be reliably prevented by using a spring.

FIG. 10 shows an example of a structure in which a preload can be applied during assembly and the preload can be easily adjusted according to the load. In this case, a slot 43 is provided at one location of the bush 31 in FIG. 7, and the bush 31 is fitted into a housing 45 which also has a slot 44. By tightening a bolt 46, the bush 31 is fixed to the housing 45. , the preload can be adjusted by further tightening. This configuration is the seventh
In addition to the configuration shown in the figure, the configuration shown in FIG. It also becomes easier to process the inner surface of 38.

In all of the above embodiments, preload is applied to the rolling elements, but depending on the purpose, some play in the A direction and C direction may be allowed.
In this case, there is no need to apply preload.

In addition, in the above embodiments, the shaft is a nut,
Although the bush is shown attached to the movable body, the shaft may be attached to the movable body and the bush to the nut, and the mounting direction may be as shown in Fig. 4.
Even if it is not horizontal, as long as it extends perpendicular to the direction of movement of the nut, there will be no problem whether it is vertical or diagonal.

According to the screw feeding device of the present invention, as is clear from the above description, one of the nut and the movable body has a shaft extending perpendicularly to the direction of movement of the nut, and the other has this shaft concentrically. A member having a hole to be fitted is provided, and 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. Because of this, the nut faithfully transmits motion to the movable body without rotating, and the radial runout of the feed screw is hardly transmitted to the movable body, which impairs the original linear accuracy of the movable body. An extremely high-precision screw feeding device with no problems can be realized with a very simple configuration.

Therefore, as guide bearings for movable objects, it is possible to use air bearings that have low rigidity but high linear accuracy without sacrificing their features, and can absorb radial runout without resistance, making them expensive and large in diameter. Since there is no need to use a feed screw with small radial runout, it is possible to realize a screw feed device that is inexpensive and requires less power, and it is also possible to easily correct deviations in parallelism between the guide means of the movable body and the feed screw. Because it can be absorbed,
Assembling can be done easily and in a short time without requiring any skill, and it has many effects.

[Brief explanation of the drawing]

Figures 1 to 3 show an example of a conventional screw feeding device, Figure 1 is a partially exploded perspective view showing the schematic configuration, and Figures 2 and 3 explain the shape error of the leaf spring. 4 to 6 show an embodiment of the present invention, FIG. 4 is a vertical cross-sectional view of the main part, and FIG. 5 is a cross section taken along line E-E' in FIG. 6 are longitudinal sectional views of essential parts for functional explanation, and FIGS. 7 to 10 are longitudinal sectional views of essential parts of other embodiments. 2 is a guide body (guiding means), 3 is a movable body, 9 is a feed screw, 10 is a nut, 20, 30, 35 are shafts,
21, 31, 38 are bushes (members with holes), 22, 27 are holes, 24 are steel balls (rolling elements), 2
5, 34, 39, 40 are cages, 36 are rollers (rolling elements), 41, 42 are compression springs, 43, 44 are slots, and 45 is a housing.

Claims (1)

[Scope of Claims] 1. A feed screw, a nut screwed into the feed screw, and a movable body guided by a guide means that allows movement only in a straight direction and driven straight by the feed screw and nut, One of the nut and the movable body is provided with a shaft extending perpendicularly to the linear direction, and the other is provided with a member having a hole into which the shaft is fitted concentrically, and between the outer periphery of the shaft and the inner periphery of the hole. . A screw feeding device including a plurality of rolling elements that are movable in the axial direction of the shaft and arranged in a short row surrounding the shaft. 2. The screw feeding device according to claim 1, wherein the rolling elements are disposed between the shaft and the member by a retainer that loosely fits into the shaft, the hole, and these rolling elements. 3. The screw feeding device according to claim 1, further comprising an elastic body that supports the retainer at a predetermined position in the axial direction of the shaft. 4. The screw feeding device according to claim 1, wherein the shaft, the hole, and the rolling element are fitted with a negative clearance.