JPH0835522A - Hydrostatic bearing - Google Patents

Abstract

PURPOSE:To provide a hydrostatic bearing excellent in a characteristic such as a vibration damping characteristic or a load characteristic by using electric rheology for pressure fluid. CONSTITUTION:This bearing has a rotation shaft 1, a bearing wedge 4 for journaling the journal of this rotation shaft 1, electric rheology fluid for filling the gap between the journal and the bearing wedge 4, a pump 11 for pressure- supplying the electric rheology fluid into the gap, and a power source 12 for applying voltage to the rotation shaft 1 and the bearing wedge 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrostatic bearing, and by using an electrorheological fluid (hereinafter abbreviated as ER fluid) as a pressurized fluid, its static and dynamic characteristics can be controlled. The present invention relates to a hydrostatic bearing that achieves high performance.

[0002]

2. Description of the Related Art A hydrostatic bearing supplies a pressurized fluid such as pressurized oil to a gap between a journal of a rotary shaft and a metal holder that supports the journal, and applies a load to the rotary shaft by the pressurized fluid. It is designed to be supported.Because it has extremely low starting friction and low speed friction compared to sliding bearings, etc., it does not cause wear and seizure due to it, has high motion accuracy, and has good vibration damping performance. Widely used in machine tools and precision measuring instruments that require motion characteristics.

By the way, when such a hydrostatic bearing is applied to an ultra-precision processing machine or the like, further improvement in performance is required. For example, it is desired to improve the load characteristics of the bearing, easily cope with load fluctuations, and further improve vibration damping performance.

[0004]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to obtain a hydrostatic bearing having further excellent vibration damping characteristics and load characteristics.

[0005]

This problem is solved by using an ER fluid as the pressurized fluid of the hydrostatic bearing and applying a voltage between the rotary shaft and the receiving metal. Further, as the ER fluid, used is one in which inorganic / organic composite particles formed by a core made of an organic polymer compound and a surface layer made of an inorganic ion exchanger or an inorganic substance having an ER effect are dispersed in an electrically insulating medium. It is preferable.

The present invention will be described below with reference to the embodiments shown in the drawings. 1 and 2 show an example of a thrust bearing as an example of a hydrostatic bearing according to the present invention.
Is a rotating shaft made of a conductive material. This rotary shaft 1
The cylindrical base 2 is rotatably supported by a static pressure air bearing 3 in the radial direction of the cylindrical base 2 in an upright state such that its axial direction is vertical. A portion of the lower end of the rotary shaft 1 which becomes the journal 1a has the same diameter as the main body 1b of the rotary shaft 1. The rotating shaft 1 also functions as one electrode for applying a voltage to the ER fluid described later.

A receiving member 4 made of an electrically insulating material is provided so as to face the journal 1a of the rotating shaft 1. The receiving metal 4 is attached to the base 2, and an annular land 5 is formed at the center of the receiving metal 4 so as to project upward.
A circular pond-shaped recess 6 is formed inside the land 5. An annular outer land 7 is provided outside the land 5 so as to be in contact therewith. The outer land 7 is made of a conductive material and functions as the other electrode for applying a voltage to the ER fluid, and the upper surface thereof is about 0.1 to 0.5 mm from the upper surface of the land 5. When the lower end surface of the journal 1a of the rotary shaft 1 contacts the upper surface of the land 5, the rotary shaft 1 and the outer land 7 are not electrically short-circuited.

A channel 8 communicating with the bottom of the recess 6 is formed inside the receiving metal 4. The channel 8 is connected to a pump 11 via a throttle 9 and a pipe 10, and the pump 1
The ER fluid is supplied to the recess 6 under pressure by means of 1.

Reference numeral 12 in the drawing denotes a DC power source, and a DC voltage is applied from the DC power source 12 to the rotary shaft 1 and the outer land 7 by the lead wires 13 and 14. In addition, a discharge port 15 is formed in the base 2,
The ER fluid overflowing from the recess 6 is discharged from here, and is collected by the pump 11 by a pipe (not shown).

Further, in this example, various sensors are provided for measuring experimental data described later. First, a first pressure sensor 16 that measures the pressure of the ER fluid in the recess is attached to the bottom of the recess 6. Further, a second pressure sensor 17 for measuring the supply pressure of the ER fluid supplied from the pump 11 is attached to the pipe 10, and signals from these two pressure sensors 16 and 17 are amplified by an amplifier 18 and recorded. A total of 19 items are input and recorded.

Further, in order to obtain the vertical displacement of the rotary shaft 1, that is, the variation of the gap h (hereinafter referred to as a bearing gap) between the lower end surface of the journal 1a of the rotary shaft 1 and the upper surface of the land 5, a gap is obtained. A sensor 20 is attached to the base 2, and a signal from the gap sensor 20 is sent to the amplifier 2
It is configured to be input to the recorder 19 via 1.

The ER fluid used here is not particularly limited, and conventionally known ones may be used. Among them, the applicant of the present invention first applied for a patent (Japanese Patent Laid-Open No. 5-3.
No. 24102, Japanese Patent Application No. 5-175706) are preferable. This ER fluid is a dispersion of inorganic / organic composite particles formed of an organic polymer compound core and an inorganic ion exchanger or a surface layer of an electrically semiconductive inorganic material in an electrically insulating medium, or Inorganic / organic composite particles are dispersed in an electrically insulating medium,
In addition, the surface of the inorganic / organic composite particles is polished.

Examples of the inorganic ion exchanger include hydroxides of polyvalent metals, hydrotalcites, acid salts of polyvalent metals, hydroxyapatite, Nasicon type compounds, clay minerals, potassium titanates, heteropolyacid salts, or At least one selected from insoluble ferrocyanide is used, and the inorganic substance having the electrorheological effect is
Polyvalent metal hydroxides, hydrotalcites, polyvalent metal acid salts, hydroxyapatite, Nasicon type compounds,
At least one selected from clay minerals, potassium titanates, inorganic ion exchangers composed of heteropolyacid salts or insoluble ferrocyanides, and silica gel is used.
The electrically semiconductive inorganic substance may be a metal oxide, a metal hydroxide, a metal oxide hydroxide, or one obtained by subjecting at least one of these to metal doping, or the presence or absence of metal doping. At least one selected from the group consisting of at least one selected from the above as an electric semiconductor layer on another support is used.

Further, examples of the organic polymer compound used as the core of the inorganic / organic composite particles include poly (meth)
Acrylic ester, (meth) acrylic ester-styrene copolymer, polystyrene, polyethylene, polypropylene, nitrile rubber, butyl rubber, ABS resin, nylon, polyvinyl butyrate, ionomer, ethylene-vinyl acetate copolymer, vinyl acetate resin, Examples thereof include one kind or a mixture or copolymer of two or more kinds such as a polycarbonate resin. Further, as the electric insulating medium, all those used in the conventional ER fluid can be used. For example, diphenyl chloride, butyl sebacate, aromatic polycarboxylic acid higher alcohol ester, halophenyl alkyl ether, trans oil, chlorinated paraffin, fluorine-based oil, or silicon-based oil, etc., electrical insulation and electrical insulation and electrical breakdown Any fluid can be used as long as it has high strength, is chemically stable, and can stably disperse the inorganic / organic composite particles, and a mixture thereof can also be used.

Further, in order to produce the above-mentioned inorganic / organic composite particles, for example, core particles made of an organic polymer compound and an inorganic ion exchanger or an inorganic substance having an electrorheological effect (hereinafter referred to as ER inorganic substance). There is a method of carrying fine particles by a jet stream and causing them to collide. In this case, the fine particles of the ER inorganic material collide with the surface of the core particles at a high speed and are fixed to form a surface layer. Another example of the manufacturing method is a method in which the core particles are suspended in a gas and a solution of the ER inorganic material is atomized and sprayed on the surface. In this case, the surface layer is formed by the solution adhering to the surface of the core particles and drying.

Further, a preferred example of the method for producing the inorganic / organic composite particles is a method of forming the surface layer at the same time as the core body. In this method, for example, when emulsion-polymerizing, suspension-polymerizing or dispersion-polymerizing a monomer of an organic polymer compound forming a core in a polymerization medium, fine particles of an ER inorganic substance are present in the monomer or in the polymerization medium. This is what you do. Water is preferred as the polymerization medium, but a mixture of water and a water-soluble organic medium can also be used, and an organic poor solvent can also be used. According to this method, the monomers are polymerized in the polymerization medium to form core particles, and at the same time, the ER
The inorganic fine particles are oriented on the surface of the core particles in a layered form to cover the core particles and form a surface layer. According to the simultaneous formation method of the core body and the surface layer, the ER inorganic particles are densely and firmly adhered to the surface of the core body particles made of the organic polymer compound to form the robust inorganic / organic composite particles.

The shape of the inorganic / organic composite particles is not necessarily spherical, but the emulsified / adjusted core particles
When produced by the suspension polymerization method, the resulting inorganic / organic composite particles have a substantially spherical shape. The particle size of the inorganic / organic composite particles is not particularly limited, but is 0.1
The thickness is preferably about 500 μm, and more preferably about 5 to 200 μm. The particle size of the ER inorganic fine particles at this time is not particularly limited, but is preferably 0.005 to 100.
μm, and more preferably 0.01 to 10 μm.

In such an inorganic / organic composite particle,
The weight ratio of the ER inorganic substance forming the surface layer to the organic polymer compound forming the core is not particularly limited, but ER
The inorganic substance: organic polymer compound ratio is preferably in the range of 1 to 60:99 to 40, and particularly preferably in the range of 4 to 30:96 to 70. E obtained when the weight ratio of ER inorganic substance is less than 1%
The ER effect of the R fluid composition is insufficient, and if it exceeds 60%, an excessive current will flow to the obtained fluid composition.

Inorganic / organic composite particles produced by various methods as described above, particularly a method of simultaneously forming a core body and a surface layer, are generally used in an organic polymer substance or in a manufacturing process for all or part of the surface layer. Since the ER effect of the ER inorganic fine particles is not sufficiently exhibited because it is covered with a thin film of the dispersant, the emulsifier and other additive substances, it is preferable to use the inorganic / organic composite particles whose surface is polished. However, when the inorganic / organic composite particles are produced by the method of forming the surface layer after forming the core, there is no inert substance on the surface of the surface layer, and the ER effect of the inorganic ion exchanger is sufficient. Since it is large, polishing is not always necessary.

The surface of the particles can be polished by various methods. For example, the inorganic / organic composite particles may be dispersed in a dispersion medium such as water and the mixture may be stirred. At this time, it is also possible to carry out by a method of mixing abrasives such as sand particles or balls in the dispersion medium and stirring with inorganic / organic composite particles, or by a method using a grinding wheel. Also, without using a dispersion medium,
It is also possible to carry out dry stirring using the inorganic / organic composite particles and the above-mentioned abrasives and grinding wheels.

A more preferable polishing method is a method of stirring the inorganic / organic composite particles by a jet stream or the like. This is a method of polishing the particles themselves by violently colliding with each other in the gas phase, and does not require any other abrasive,
This is a preferable method because the inactive substance separated from the surface of the particles can be easily dispersed by classification. In the above jet stream agitation, it is difficult to specify the polishing conditions depending on the type of equipment used, the agitation speed, the material of the inorganic / organic composite particles, etc., but generally 0.5- It is preferable to stir in a jet stream for about 15 minutes.

This ER fluid can be produced by uniformly stirring and mixing the above-mentioned inorganic / organic composite particles with other components such as a dispersant in an electrically insulating medium. As this agitator, any agitator that is usually used for dispersing solid particles in a liquid dispersion medium can be used. This ER
The content of the inorganic / organic composite particles in the fluid is not particularly limited, but is 1 to 75% by weight, and particularly 10 to 60% by weight.
It is preferably in the weight%. If the content is less than 1%, a sufficient ER effect cannot be obtained, and if it is more than 75%, the initial viscosity of the composition when a voltage is not applied becomes too large, which makes it difficult to use.

The ER fluid of this prior invention has an extremely high E
It has an R effect, excellent stability over time, and little scratching, so it does not wear the electrode surface or equipment wall, and the current that flows during voltage application is small, so there is no danger of heat generation and low power consumption. Therefore, it is highly practical and is particularly suitable for the hydrostatic bearing of the present invention.

In the hydrostatic bearing having such a structure, the recess 6 of the receiving plate 4 is supplied with ER fluid from the pump 11 at a pressure of 0.1 to 0.7M.
It is supplied at a flow rate of about 30 to 90 ml / min at about Pa and a DC voltage of 0.01 to 20 kV from the DC power supply 12 is applied to the rotary shaft 1 and the outer land 7 for various applications as a hydrostatic bearing. Be used for. However, this condition is a preferred example in the present invention, and the present invention is not limited to this. It is necessary to use a special pump having good wear resistance as the pump 11, and it is necessary to prevent the impeller and the like inside the pump from being worn by the ER fluid in which solid particles are dispersed.

In such a hydrostatic bearing,
By applying a DC voltage between the rotating shaft 1 and the outer land 7, the apparent viscosity of the ER fluid existing in the bearing gap increases, which strengthens the squeeze film effect that acts on the bearing gap and reduces vibration. Performance is improved and rotation accuracy is improved. Further, the load capacity and the load characteristic of the bearing change due to the voltage application, whereby the load characteristic of the bearing can be easily controlled by adjusting the applied voltage.

The characteristics of the hydrostatic bearing of the above example will be described below based on experimental results. In this experiment, E
As the R fluid, 5% by weight of inorganic / organic composite particles having an average particle size of 15 to 20 μm in which the surface of the above polymer particles is coated with particles of special titanium oxide (C-II manufactured by Ishihara Sangyo Co., Ltd.) It was dispersed in. Further, the inner diameter of the recess 6 was 15 mm, the inner diameter of the outer land 7 was 40 mm, the outer diameter was 50 mm, and the difference between the upper surfaces of the land 5 and the outer land 7 was 225 μm.

Further, the outer diameter of the journal 1a of the rotary shaft 1 is 50 mm, and the own weight of the rotary shaft 1 is 22.4 N (2.27).
kgf), and if necessary, a weight was placed on the upper part of the rotary shaft 1 to make the bearing load variable. The receiving pad 4 was made of hard vinyl chloride, and the outer land 7 was made of stainless steel. Furthermore, the first pressure sensor 1
6 and the second pressure sensor 17 are strain type pressure transducers,
An eddy current type non-contact displacement gauge was used for the gap sensor 20.

FIG. 3 shows the results of measuring the response characteristics of the bearing gap and the recess pressure when the flow rate of the ER fluid and the bearing load are constant and a DC voltage of 500 V is instantaneously applied and disconnected. From this graph, it can be seen that it takes about 50 seconds for the axial displacement to stabilize. Further, it can be seen that when a voltage is applied, the bearing gap widens and the recess pressure decreases. It is considered that this is because the pressure distribution applied to the bearing surface changes as shown in FIG. 2 (b) as the apparent viscosity of the ER fluid between the electrodes increases. In FIG. 2B, the total pressure in the pressure distribution before and after the voltage application is equal because the load applied to the rotating shaft is constant.

FIG. 4 shows that the compression pressure of the ER fluid is 0.4MP.
6 is a graph showing the relationship between the bearing load and the bearing gap when the applied voltage is changed while a is kept constant. From this graph, when the bearing load is constant, the bearing gap is widened by applying the voltage, and the tendency becomes stronger as the bearing load is smaller. The bearing gap is considered to be around 25 μm minimum because of the presence of ER fluid there. Also, from this graph, it can be seen that the bearing load can be increased by the applied voltage in the case of a constant bearing gap. Therefore, if the voltage is adjusted appropriately for the fluctuation of the bearing load, the bearing gap can be kept constant. I see what I can do.

FIG. 5 shows the situation where the area coefficient of the hydrostatic bearing of the above-mentioned example changes due to the electrorheological effect (ER effect) of the ER fluid, using the bearing load as a parameter. Generally, the area coefficient is determined only by the shape of the bearing surface, and it is known that a bearing with a large area coefficient requires a low fluid pressure in the recess necessary to support the same bearing load (Aoyama Fuji Jiro, "Hydraulic Bearing" (1990), 133, refer to Industrial Research Committee).

From the graph of FIG. 5, it can be seen that in this example, when the bearing load is constant, the area coefficient increases corresponding to the magnitude of the applied voltage, and the load characteristics of the bearing change. Further, when the applied voltage is 0 V and 400 V, the area coefficient is almost constant regardless of the increase in the bearing load. This point is similar to the conventional hydrostatic bearing, but the applied voltage is 800
In the case of V, the area coefficient decreases as the bearing load increases. It is considered that this is because the bearing gap is reduced as the bearing load is increased, and the flow velocity of the ER fluid between the electrodes is increased, so that the ER effect is reduced.

FIG. 6 is a graph showing the results of the frequency dependence of the dynamic compliance of the hydrostatic bearing obtained by the impulse hammer method with the applied voltage as a parameter.
This is a measurement of the dynamic compliance in the axial direction when the bearing gap is constant. From this graph, it can be seen that the compliance annuity value at the resonance point decreases as the voltage applied to the ER fluid increases, and the vibration damping performance improves. It is considered that this is because the viscoelasticity of the ER fluid between the electrodes changes due to the voltage application and the squeeze film action acting on the bearing gap becomes stronger. It is also understood that the attenuation characteristic can be controlled by changing the applied voltage.

The hydrostatic bearing of the present invention is not limited to the thrust bearing shown in the above-mentioned example, but includes other types of hydrostatic bearings such as radial bearings, and exhibits the same actions and effects. Is.

[0034]

As described above, in the hydrostatic bearing of the present invention, the ER fluid is used as the pressurizing fluid and the voltage is applied to the ER fluid to exert the ER effect. The vibration damping performance and load characteristics of the pressure bearing are greatly improved, and these characteristics can be easily controlled by adjusting the applied voltage.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an example of a hydrostatic bearing of the present invention.

FIG. 2 is an enlarged view of a main part of FIG. 1 and a view showing a pressure distribution of an ER fluid.

FIG. 3 is a graph showing the response characteristics of the bearing gap and the recess pressure in the example of the present invention.

FIG. 4 is a graph showing a relationship between a bearing gap and a bearing load in the example of the present invention.

FIG. 5 is a graph showing the relationship between the area coefficient and the bearing load in the example of the present invention.

FIG. 6 is a graph showing dynamic characteristics in an example of the present invention.

[Explanation of symbols]

1 ... Rotary axis, 1a ... Journal, 2 ... Base, 4 ... Receipt,
5 ... Land, 6 ... Recess, 7 ... Outer land, 11 ... Pump, 12 ... DC power supply

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Claims (4)

[Claims] 1. A rotary shaft, a support for pivotally supporting a journal of the rotary shaft, an electrorheological fluid filled in a gap between the journal and the support, and a pressure for pressurizing the electrorheological fluid in the gap. A hydrostatic bearing having a supply means and a power supply for applying a voltage between a rotating shaft and a receiving metal. 2. The hydrostatic bearing according to claim 1, which is a thrust bearing. 3. The inorganic-organic composite particle as defined in claim 1, wherein the electrorheological fluid comprises an inorganic-organic composite particle formed by a core body made of an organic polymer compound and a surface layer made of an inorganic ion exchanger or an electric semiconductor inorganic substance. Hydrostatic bearings that are dispersed in an insulating medium. 4. The inorganic-organic composite particle according to claim 1, wherein the electrorheological fluid is formed of a core body made of an organic polymer compound and a surface layer made of an inorganic ion exchanger or an electrically semiconductive inorganic material. A hydrostatic bearing which is dispersed in an electrically insulating medium and whose inorganic / organic composite particles are obtained by polishing the surface of the particles.