JPH07117137B2 - Hydrostatic screw and manufacturing method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a hydrostatic screw for supporting between a male screw and a female screw by fluid pressure in a non-contact manner.

[Conventional technology]

As one of the means to achieve high speed and high accuracy of screw feed that converts rotation into linear motion, pressurized fluid is supplied to the clearance between male and female threads (hereinafter referred to as thread clearance), and male thread is fed via fluid pressure. There is a static pressure screw that supports between the female and female threads in a non-contact manner.

This hydrostatic screw has many technical problems such as complicated design of internal thread due to supply and recovery of fluid, which is not easy to design or requires high-precision machining, but high-speed and high-precision screw feed. The friction loss, which is the main cause that prevents the change, can be made extremely small, and the wear can be eliminated altogether. Therefore, it is applied to manufacturing equipment that requires high-speed and high-precision such as ultra-precision machining, semiconductor elements, optical elements, and electronic devices in recent years. Is being considered.

FIG. 4 is a sectional view showing the structure of a conventional hydrostatic screw. The male screw 1 is a normal feed screw. On the other hand, the female screw has a complicated structure because it supplies and recovers the fluid in the screw gap. That is, it is composed of the case 2 and the nut 3, and the nut 3
A fluid supply groove 4 and a recovery groove 5 are spirally engraved on the outer periphery of the cylinder in accordance with the pitch of the male screw 1, and the supply groove 4 and the recovery groove 5 are guided to the supply hole 6 and the recovery hole 7, respectively, and the screw gap 8 is formed. The fluid is supplied to and recovered from the fluid. The case 2 has a fluid supply / recovery hole 21.

FIG. 5 is an enlarged sectional view of the screw portion. The conventional hydrostatic screw has a slope between the ridge and the valley of the screw (hereinafter referred to as a flank),
That is, a trapezoidal screw whose angle of thread between the left and right flanks 9 is around 60 ° is mainly used. The reason for this is the supply groove 4
From the relation that the feed hole 6 for guiding the fluid from the to the screw gap 8 is processed, if the flank surface 9 is not inclined, that is, if the angle of the screw thread is vertical, the supply hole 6 is inclined and processed. This is very difficult and almost impossible due to processing technology. Further, since the recovery hole 7 is merely a passageway for the fluid, it may be located anywhere other than the flank surface, for example, in the valley portion of the female screw, and the machining hole is not required to be so precise, but the supply hole 6 has the flank surface 9. Since it exists on the left and right of the thread, it is necessary to process more than twice the number of recovery holes 7. Further, the supply hole 6 directly influences the amount of fluid supplied to the screw gap 8 and the uniformity of the flow, and controls the performance of the hydrostatic screw, so that precision of processing is required. In particular, in the case of miniaturizing the hydrostatic screw, the supply hole 6 also becomes relatively thin, which makes it more difficult to perform precision machining, and it is not easy to miniaturize the hydrostatic screw.

On the other hand, hydrostatic screws follow the same principle as hydrostatic bearings,
If the clearance between the male and female threads or the shaft and the bearing decreases, the fluid pressure in the clearance increases and the fluid pressure increases. Conversely, if the clearance increases, the fluid pressure decreases. Configured to be kept. The greater the rate of increase or decrease in fluid pressure due to this gap change, the higher the rigidity between the male and female threads or the shaft and bearing.
The performance will be good. However, since the rigidity cannot be increased so much only by the resistance of the flow path in the gap, it is usual to add a flow resistance such as a self-made diaphragm, a surface diaphragm, or an orifice diaphragm to improve the rigidity efficiently. It However, if an orifice diaphragm is applied to the static pressure screw,
Further, since it becomes difficult to process the supply hole 6, a self-made diaphragm or a surface diaphragm is often used.

FIG. 6 is a flank surface of a self-drawing type static pressure screw viewed from the screw feeding direction. Although it is helically tight in the direction perpendicular to the paper surface, the cut surface is not shown. The self-made throttle uses the change in the cross-sectional area of the flow path from the supply hole 6 to the screw gap as the flow path resistance. In this case, the fluid discharged from the supply hole 6 through the flank surface 9 to the screw gap is the flow path. Most flows in the radial direction of the flank 9 so that the resistance is minimized.
Therefore, in order to uniformly supply the fluid to all the portions on the circumference of the flank surface 9, a large number of supply holes 6 that require precision machining must be formed on the flank surface 9, which is a high cost of the hydrostatic screw. It is the biggest drawback that leads to

FIG. 7 shows a flank surface of a surface-drawing type. The cut surface is not shown as in FIG. The surface restrictor is provided with a flow path groove 10 on the flank surface 9, and the change in the cross-sectional area of the flow path from the flow path groove 10 to the screw gap is used as the flow path resistance. In this case, since the channel groove 10 is provided in the circumferential direction of the flank surface 9, the supply hole 6
The fluid discharged from flows through the flow channel 10 having a small flow resistance and then reaches the flank 9 (screw gap). For this reason, it is not necessary to machine a large number of supply holes 6 unlike the self-drawing, but it is not easy to move the machining tool into and out of the machining position, so that the flank surface of the female screw is required to be as precise as the supply holes. Forming the flow path groove 10 to be formed is a drawback that leads to cost increase of the hydrostatic screw. As a conventional example that solves this problem and does not require the flow passage holes and the flow passage grooves on the flank surface, there is a hydrostatic screw using a porous body. Since the porous throttle has high air supply efficiency, it has an advantage that it can have higher rigidity than other throttle types. FIG. 8 shows an example of a conventional hydrostatic screw using a porous body, which is disclosed in Japanese Patent Laid-Open No. 59-113360.
Are disclosed in. In the figure, 38 is a male thread, 39 is a nut made of a porous material corresponding to the male thread 38, 40 is an outer cylinder that maintains airtightness on the outer peripheral surface of the nut 39, and 41 is an outer cylinder 40.
Is a side plate that is airtightly fitted to the inner peripheral surface of and is in close contact with the side surface of the nut 39. In this example, gas is supplied from the flow path 43 to the nut 39 through the circumferential step portion 42, and the gas is injected from the entire surface of the nut 39. Since the porous body is used as the gas supply path, there is an advantage that it is not necessary to provide a flow path hole or a flow path groove on the flank surface. However, since the gas supply area is large, there is a drawback that the rigidity cannot be obtained unless the gas flow rate is increased. Also, since there is a gas supply hole in addition to the flank surface, unless it is machined with high accuracy so that the entire gap between the male and female threads is uniform, the gas will be washed away from the wide gap, which is extremely dangerous. There is a drawback that the rigidity cannot be obtained unless a large flow rate of gas is supplied.

As an example of improving the defect that the gas ejection area is large, as shown in FIG. 9, there is a hydrostatic screw in which the porous body surface of the gas ejection portion is crushed. This example is disclosed in Japanese Laid-Open Patent Publication No. 60-241566, and is shown in FIG.
Is a male screw, 52 is a screw because it is made of a porous body, and 56 is a blind portion. Since the ejection area is reduced in this way, there are advantages that the above problems can be solved and the gas supply amount can be reduced. However, there is a problem that a complicated process of selectively forming the blinds at a predetermined position is required. In particular, the pressure of the supplied gas is often high in order to increase the rigidity, and it is difficult to perform a strong crushing process that exhibits a crushing effect against this high pressure. Further, there is a problem that it is difficult to exhaust gas. Since the structure is such that the porous body is arranged over the entire surface of the male screw, the exhaust passage has only the screw gap. Therefore, since the exhaust resistance is large, there is a problem that the pressure in the screw gap portion increases and the rigidity decreases.

[Problems to be solved by the invention]

An object of the present invention is to provide a compact, high-performance, low-cost hydrostatic screw that solves the above problems.

[Means for solving problems]

In the hydrostatic screw according to the present invention, at least a part of the flank surface is formed of a porous body having a fluid supply path, and a through hole for supplying a fluid into the porous body is connected to the porous body. Further, the method for producing a hydrostatic screw according to the present invention, the tubular base material having at least a porous hollow cylinder fixed to the inside of a multi-wheel cylinder is processed from the inside, and at least a part of the flank surface is processed. A step of forming a screw thread and a thread trough so as to be composed of the porous body, and a step of processing the tubular base material from the outside to form a through hole reaching the porous body. To do.

[Action]

According to the present invention, by using the porous body for the fluid supply path to the flank surface of the hydrostatic screw, the porous body also functions as the flow path resistance. Also, since the porous itself becomes the flow path,
It is not necessary to process the supply hole or the flow channel on the flank surface. Further, it is possible to easily realize a hydrostatic screw having a vertical thread angle, which is almost impossible in the past, and a hydrostatic screw made of ceramic. Further, the hydrostatic screw can be downsized.

〔Example〕

(Embodiment 1) FIG. 1A is a first embodiment of the present invention, in which 11 is a porous body, and 12 is a conduction hole between the supply groove 4 and the porous body 11. In the figure, the same numbers are used for the same parts as the conventional example. Reference numeral 19 is the tip of the thread, and is the inner ring cylinder of FIG. 3 (a) described later.
It is made of 15 materials, and 20 is a screw base, which is made of the material of the outer ring cylinder 16 of FIG. 3 (a) described later. The fluid passes from the supply groove 4 through the through hole 12 and reaches the porous body 11,
It is supplied to the left and right screw gaps 8.

Further, FIG. 1 (b) schematically shows the vicinity of the flank surface of the hydrostatic screw of FIG. 1 viewed from the screw feeding direction. The cut surface is not shown in the drawing although it is helically tightened in the direction perpendicular to the paper surface. Note that the conductive hole 12 behind the flank surface is indicated by a broken line. The through hole 12 is located at a position corresponding to the screw thread.

Normally, the porous body 11 is composed of innumerable minute spaces that are continuously connected, so that the fluid passing through it has a channel resistance due to a change in cross-sectional area and a channel resistance due to viscous friction with the wall surface of the minute space. Will be received. For this reason, the cross-sectional area change has a dominant flow path resistance compared to the self-made diaphragm and the surface diaphragm, which are the main constituents of the flow path resistance. That is, the flow rate of the fluid is proportional to the cube of the screw clearance and the bearing clearance, and the viscous resistance is proportional to the flow velocity and the flow rate. Since the flow passage in the porous has a very thin viscous resistance, the screw clearance becomes large in the porous throttle. If the flow velocity increases, the viscous resistance in the porous medium increases, so that the flow rate does not increase, and the screw gap decreases, and if the flow velocity decreases, the viscous resistance in the porous medium decreases, so that the flow rate does not decrease. This means that, compared to a conventional throttle with only a change in cross-sectional area, a porous throttle with viscous resistance in addition to a change in cross-sectional area reduces the pressure inside the gap more as the gap increases, and decreases the gap more as the gap decreases. It will have the effect of increasing the pressure. This increases the rigidity of the hydrostatic screw as compared with the conventional one.

With such a structure, in the hydrostatic screw of the present invention, the porous body 11 serves both as a fluid supply path and as a flow path resistance addition. As an effect of this, it is not necessary to precisely process the supply hole and the flow path groove which are indispensable for the self-drawing or surface-drawing type static pressure screw, and the processing is facilitated, so that the cost of the static pressure screw can be reduced. In addition, in the conventional hydrostatic screw, it was necessary to provide the supply holes on the left and right flanks 9 of the thread, but the hydrostatic screw of the present invention has one conduction hole 12 for fluid of the left and right flanks 9. Can be supplied. Further, since the conduction hole 12 is provided at a position where the conventional static pressure screw is not effectively used at all, the screw thread can be reduced by the amount that the supply hole 6 is not required, and the static pressure screw can be downsized. Becomes

Incidentally, the hydrostatic screw of the present invention can be applied to any fluid of gas or liquid, and the viscosity is greatly different between gas and liquid, if the porous body 11 having an appropriate flow path resistance is selected to match this Not to mention good things. The proper flow rate of the fluid depends on the ratio between the screw clearance and the porosity of the porous material. If the gap is made large, the porosity is made large, and if the gap is made small, the porosity is made small, so that an appropriate design value is obtained. The porosity can be adjusted by, for example, the particle size of the raw material before sintering.

(Embodiment 2) FIG. 2 shows a second embodiment of the present invention. In the conventional hydrostatic screw, it is almost impossible to provide the feed hole unless the flank 9 is inclined. However, since the hydrostatic screw of the present invention does not require the feed hole, the thread shown in FIG. A hydrostatic screw whose angle is vertical can be easily realized.

Generally, a screw thread with an inclined thread has many advantages such as being able to receive a load in the direction perpendicular to the feed direction, the flank surface serving as a feed guide, and the fact that it has an automatic centripetal property, but it is a machine tool. It is not easy to form a flank surface with high accuracy because the method of creating a screw thread by means of precision has a difficulty in precision, and processing with a mold molded into the screw thread is the main, especially in the radial direction of the screw. Since the processing component force becomes large, in the processing of the male screw that determines the screw feed accuracy, the bending moment component acts to induce the deflection of the male screw, which hinders high-precision machining. In this respect, a screw with a vertical thread angle has exactly the opposite advantages and disadvantages, and it is difficult for deflection to occur during processing.Therefore, a precision feed screw used for machine tool lead screws, etc. This is the reason why a trapezoidal screw with a vertical mountain angle is used. In the hydrostatic screw of the present invention, the angle of the screw thread can be made vertical as in the present embodiment, and higher precision of screw feeding, which is the main purpose of the hydrostatic screw, can be achieved more easily than before. However, since the hydrostatic screw of the present invention does not need to limit the angle of the thread to the vertical and can be freely selected, it can be applied to a wide range of applications.

In FIGS. 1 and 2, the porous body 11 is provided in a part of the ridges and valleys of the screw, but the gap between the ridges and valleys of the screw may be a porous body. The through hole 12 is a porous body.
It only needs to reach 11 and need not be opened in the porous body. It goes without saying that various changes can be made without departing from the spirit of the present invention.

(Embodiment 3) FIGS. 3 (a), (b) and (c) are a third embodiment for explaining a method for manufacturing a hydrostatic screw according to the present invention. FIG. 3 (a) is a manufacturing process of the processed base material 13 constituting the nut portion of the hydrostatic screw of the present invention, in which 14 is a porous hollow cylinder, 15 is an inner ring cylinder, and 16
Is the outer ring cylinder. The processed base material 13 is arranged integrally on the inner surface and the outer surface of the porous hollow cylinder 14 so that the inner ring cylinder 15 and the outer ring cylinder 16 are coaxial with each other. The integration is done by fitting the individually manufactured inner ring cylinder 15, outer ring cylinder 16 and porous hollow cylinder 14 and then joining them by heat diffusion, pouring a porous material into the gap between the inner ring cylinder 15 and the outer ring cylinder 16. Firing method or inner ring cylinder
Various methods such as a method in which a porous portion is formed on the outer surface of 15 or the inner surface of the outer ring cylinder by plasma spraying and then the inner ring cylinder 15 or the outer ring tube 16 is fitted and coupled thereto can be applied. Also, the processed base material 13
Any of (14 or 14 to 16) may be used as long as it has a porous body such as metal or ceramic.

FIG. 3 (b) shows the processed base material 13 thus manufactured.
In addition, the internal thread portion 17 is manufactured by known cutting and grinding, and the fluid supply groove 4 and the discharge groove 5 are spirally manufactured by cutting or grinding, and the through hole 1 is formed by drilling.
2 shows the nut 18 of the hydrostatic screw of the present invention in which the discharge hole 7 and the discharge hole 7 are manufactured. FIG. 3 (c) shows the nut 18 of the present invention assembled in the case 2 by press fitting or shrink fitting.
Due to this manufacturing method, it is not necessary to make many precise supply holes and flow passage grooves as in the past, and precision machining is required only for the flank surface of the screw, which is unavoidable because it is a hydrostatic screw. Therefore, it is possible to reduce the influence of the processing accuracy on the performance and facilitate the processing, so that it is possible to improve the performance and cost of the hydrostatic screw. Further, in the conventional hydrostatic screw, the material of the nut 18 is limited to metal because of the precision machining of the supply hole and the flow path groove, but the machining base material 13 is made of ceramic, and the material of the present invention is used in the calcination stage. After adjusting the form of the hydrostatic screw, it is possible to perform main firing by normal machining and finally grind or lap only the flank surface of the screw with high accuracy, so that a hydrostatic screw made of ceramic can be realized. Become.
Compared to metal, ceramic is suitable for high precision processing such as high rigidity and low processing strain, and because it does not plastically deform, there is no need to clog the porous body due to processing, etc. It is an advantageous material for realizing. Needless to say, the material has a low coefficient of thermal expansion, is lightweight, and is compatible with high speed and high accuracy, which is the main purpose of hydrostatic screws.

In the embodiment shown in FIG. 3, the case where the inner ring cylinder is provided is described, but the hydrostatic screw shown in FIG. 3C can be manufactured without the inner ring tube.

〔The invention's effect〕

As described above, the porous throttle type hydrostatic screw of the present invention shown in the first and second embodiments has a precise supply hole and flow which are indispensable for the conventional self-drawn throttle and surface throttle type hydrostatic screw. Since the processing of the groove is not required, not only the processing is easy, but also the angle of the thread can be selected, so that the application is wide range. In particular, the realization of a screw whose thread angle is vertical, which was almost impossible in the past, can further advance the precision of screw feed, which is the main purpose of a hydrostatic screw. Further, the hydrostatic screw of the present invention does not need to have at least two supply holes (one on each flank face of the thread) for each thread as in the prior art, and each thread has a corresponding thread. Since it is only necessary to provide one (one for the flank surfaces on both sides) conduction hole, the size of the screw can be easily reduced. In addition, the porous throttle is superior to the conventional throttle because it has an automatic flow rate controllability, which is effective in increasing the rigidity of the hydrostatic screw. There are various advantages directly connected to.

The method of manufacturing a hydrostatic screw of the present invention shown in Embodiment 3 has the advantage that a processed base material of a porous drawing hydrostatic screw can be obtained relatively easily by various methods, and also a hydrostatic screw made of a ceramic. Therefore, there is an advantage that high-speed and high-accuracy screw feed can be achieved by taking advantage of the characteristics of ceramics.

Therefore, precision feeding of samples and processing / measuring tools in equipment that requires ultra-precision machining or measurement accuracy, high-speed / precision drive of XY stages used for fine pattern transfer and inspection in semiconductor device manufacturing processes, or optical or magnetic disk devices When used for high-speed and high-accuracy feed positioning of the writing and reading heads in FIG.

Furthermore, although the case where a part of the flank surface of the internal thread is made of a porous body has been described in Examples 1 and 2, a part of the flank surface of the external thread is made of a porous body so that fluid can flow to the external thread side. It is also possible to provide holes.

In addition, in the first and second embodiments, an example in which a part of the flank surface is made of a porous body has been described, but the tip end portion 19 of the screw thread may be entirely made of a porous body. In that case, a tubular preform having a double structure without the inner ring cylinder 15 in FIG. 3 (a) may be used.

[Brief description of drawings]

FIG. 1 (a) is a sectional view of a first embodiment of the hydrostatic screw of the present invention using a porous restrictor, FIG. 1 (b) is a flank surface of the first embodiment, and FIG. 2 is a porous restrictor. 2 is a sectional view of a hydrostatic screw according to a second embodiment of the present invention, FIG. 3 is a sectional view of an embodiment showing a method for manufacturing a hydrostatic screw according to the present invention using a porous throttle,
FIG. 4 is a sectional view showing the structure of a conventional hydrostatic screw, FIG. 5 is an enlarged sectional view of the screw portion in FIG. 4, and FIG. 6 is a self-drawing flank surface of the conventional hydrostatic screw. FIG. 7 shows a flank surface of a conventional hydrostatic screw, which is a surface drawing type. 8 and 9 are cross-sectional views showing the structure of a conventional hydrostatic screw using a porous body. 1 is a male screw, 2 is a case for storing a nut, 3 is a nut, 4 is a supply groove, 5 is a recovery groove, 6 is a supply hole, 7 is a recovery hole, 8 is a screw gap, 9 is a flank surface, and 10 is a flow path. Grooves, 11 is a porous body, 12 is a through hole, 13 is a processed base material, 14 is a porous hollow cylinder, 15 is an inner ring cylinder, 16 is an outer ring cylinder, 17 is a female screw part, 18 is a nut, 19 is a thread Tip part, 20 is a screw base, 21 is a fluid supply / recovery hole of the case, 38 is an external thread, 39 is a nut made of a porous material corresponding to the external thread 38, and 40 is airtight on the outer peripheral surface of the nut 39. The outer cylinder, 41 is airtightly fitted to the inner peripheral surface of the outer cylinder 40,
And a side plate that is in close contact with the side surface of the nut 39, 42 is a peripheral step portion, 43 is a flow path, 51 is a male screw, and 52 is a screw because it is made of a porous body,
53 is an outer cylinder, 54 is a supply cylinder, 55 is a spiral air supply groove, 56 is a mesh, 57, 58 and 59 are gaps, and θ is a thread angle.

Claims (2)

[Claims] 1. A base portion made of a non-porous body having fluid passage holes, and a porous body in which at least a part of a flank between threads and valleys of the screw is joined to the base portion made of the non-porous body. A porous body portion, the porous body portion has a fluid supply path, and the conduction hole for supplying a fluid into the porous body portion is connected to the porous body portion. Hydrostatic screw characterized by having 2. A tubular base material in which at least a porous hollow cylinder is fixed to the inside of an outer ring cylinder is processed from the inside, and a thread is formed so that at least a part of a flank surface is constituted by the porous body portion. A method of manufacturing a hydrostatic screw, comprising: a step of forming a screw thread; and a step of processing the tubular base material from the outside to form a through hole reaching the porous body portion.