EP1045996A1

EP1045996A1 - Hydrostatic bearing for absorbing axial and radial forces

Info

Publication number: EP1045996A1
Application number: EP98900061A
Authority: EP
Inventors: Ulrich Raess
Original assignee: Individual
Current assignee: Individual
Priority date: 1998-01-06
Filing date: 1998-01-06
Publication date: 2000-10-25
Also published as: AU5305298A; JP2002500328A; US6419396B1; WO1999035413A1

Abstract

The invention relates to a bearing for a shaft with a high speed characteristic which absorbs external forces acting on the shaft, and provides for a single-piece hydrostatic bearing (2) for absorbing axial and radial forces at high speed characteristics. According to the invention a shaft (3) to be mounted is mounted in a contact-free manner using water as hydraulic medium, a bearing body has several grooves (17, 20, 21) which end in nozzles (18, 22, 23) and a gap (19, 24, 25) having various heights (H, h) is situated between the nozzles (18, 22, 23) and a shaft (3) to be mounted and/or additional elements. Water flows through said nozzles and supports the shaft (3) to be mounted on a film of water. The full force of the bearing is supported by a flange screwed to the machine tool.

Description

HYDROSTATIC BEARING TO ACCEPT AXIALS AND RADIALS

POWERS

The prior invention relates to bearings and in particular it relates to bearings for grinding and milling spindles in machine tools for machining technology as defined in the claims.

As is well known, machine tools are used, among other things, for machining components such as metal components. Such machine tools often have a grinding or milling spindle which is driven by a high-speed motor and which work spindle can be connected to an adapter for receiving a workpiece or a tool

Such work spindles of machine tools are guided over bearings. These bearings perform a variety of tasks. The bearings give the components 5 that are used to perform the cutting and feed movements an exact path of movement, they also bear the weight of the spindle shaft and surrounding components, and the bearings also take any stresses that arise - exert vibration-free forces. A high degree of rigidity and a high level of damping are therefore required, perpendicular and parallel to the guideway. 0 To ensure high long-term accuracy when grinding and milling To maintain movement, there are also demands on the guidance of the spindle shaft for low friction forces, little wear, good playability and protection against chips, cooling water, dirt and damage.

In practice, high-speed spindles work in the cutting technology in the range of 20-1000000 revolutions per minute. Such work spindles are guided on conventional ball and roller bearings, magnetic bearings and hydrostatic bearings. Usually the speed indicators, formed from diameter in mm times speed in rpm (D * n), give a better insight into the prevailing speed conditions. The area of the rolling bearings with a speed index is rather less than 2.5 million and the area of the hydrostatic bearings is more than 2.5 million.

Ball bearing bearings are less suitable for the work area at high speeds. They are quite voluminous and therefore limit their inclusion in the machine tool. In order to meet the requirements for low friction at high revolutions with ball and roller bearings and to absorb axial and radial forces, several small ball bearings are often arranged to accommodate an axial or radial force component.

Such ball or roller bearings have point and line pressure contact with the work spindle. They therefore have a line stiffness, which can lead to tilting and deflection and further, consequent disadvantages under moment loads. This shock sensitivity essentially determines the relatively short lifespan of the ball or Bearings. In order to reduce the sensitivity to impact, additional stabilizing bearings are arranged. All of these disadvantages make the use of ball and roller bearings uneconomical with today's ever increasing demands on cutting speeds.

Magnetic bearings can only be used to a limited extent for use in a milling tool. High forces are generated during milling, which requires a high load capacity and high radial and axial rigidity of the bearing. A disadvantage of magnetic bearings is that they are relatively soft and only lightly resilient. In addition, they are quite expensive and can only be controlled by electronics.

Hydrostatic bearings with hydraulic oil are preferred in machine tools that operate in the lower speed range. A disadvantage of an application in high-speed machine tools is that the oil generates frictional heat due to its high viscosity and the resulting frictional heat is poorly transported away. In addition, hydrostatic bearings only accept force components in one direction.

It is therefore an object of the present invention to provide a bearing, for example for use in machine tools for machining technology, which overcomes the aforementioned disadvantages. In particular, the warehouse should have a simple and compact structure and it should be economical to purchase and maintain. The warehouse should be compatible and integrable with common processes in the tool industry. This object is achieved by the invention as defined in the claims.

The idea of the invention is to provide a single bearing for receiving the force components that occur. The bearing is preferably designed in one piece and receives axial and / or radial force components which occur on a shaft and adjacent elements. This is a departure from known designs, where several separate bearings are used for such purposes.

By using a single bearing, the movement of the shaft in the bearing can be compared to a gyroscopic movement. The center of the shaft in the area of the bearing represents the stop point of the gyro, which is why gyro equations can be used to describe the movement and to take precession and nutation into account. As a result of movement analyzes, the bearing is provided with specially arranged bearing areas, which effectively compensate for shaft precession and nutation.

By using a single, preferably one-piece bearing, a compact design is made possible. This in turn permits use at high speed ratios> 2.5 million. The present invention can thus be used in a high-speed machine tool for machining technology, advantageously direct power transmission via a flange from the shaft to a machine tool. The camp is advantageously hydrostatic and is operated with water. It is thus possible to preload the bearing in the idle state of the shaft by means of turbulent flowing water which flows through nozzles into a bearing gap between the shaft and the bearing. The shaft is mounted on the water film so that it is flat. The bearing gap allows the external forces acting on the spindle shaft to be balanced with the preload of the bearing unit. This enables hydrostatically controlled compensation of the forces acting on the bearing from the outside. In particular, the gap width can be controlled in a simple and uncomplicated manner by means of pocket printing, without disturbing resonances and / or rocking of the shaft occurring during operation.

A preferred embodiment is explained in more detail using the example shown in the drawing below. Show:

Fig. 1 general view through part of a preferred embodiment of a machine tool with a work spindle and with a bearing in vertical section.

2 and 2a the outlined functional principle of the bearing according to FIG. 1st

3 shows the arrangement of opposite areas of a bearing according to FIGS. 1 and 2.

4 occurring force relationships depending on the gap height of two areas of a bearing according to FIGS. 1 to 3. 1 shows the overall view of part of an exemplary embodiment of a bearing 2 according to the invention in exemplary use in a machine tool with a spindle shaft 3, with a pressure feed flange 9, a housing 5 with a high-frequency motor 1 and a first flange 4. Of course, others are also Purposes of the bearing are possible, these are freely available to the person skilled in the art with knowledge of the present invention and are not further explained here.

The rotor of the motor 1, the bearing 2 and a first flange 4 adjoining the bearing 2 on the end face are connected to one another via the spindle shaft 3 with axis AA ′. On the side facing away from the flange, the pressure feed flange 9 is screwed onto the housing by means of screws 15. These screws are located in the outer area of the pressure feed flange 9.

The bearing 2 with axis BB 'is preferably a hydrostatic bearing. This bearing 2 absorbs radial and axial forces via the shaft 3 and axial forces via the element or first flange 4 adjoining the end of the bearing 2, which are transmitted during the generation of cutting and forming movements of the rotating components. Water is preferably used as the medium for operating the hydrostatic bearing 2.

The motor unit 1 is located in a motor housing 5, the rotor of which is connected directly to the spindle shaft 3, for example by means of a shrink fit, and later rotates it. The stator of the motor encloses the rotor. The pressure feed flange 9 enables the pressure medium to be fed in and out via the seal 10. The hydrostatic bearing 2 is sealed towards the motor housing and outwards via labyrinths 7 and 13. In particular, the hydrostatic bearing 2 consists of a one-piece body in the exemplary form of a flange with a feed channel 14 at the end of which there are several channels. A detailed description of the bearing 2 and its elements is given in the description according to FIGS. 2 and 2a. This one-piece body transmits the forces to the next assembly, for example to the machine tool 11, and is screwed onto the machine tool by means of screws 6. With knowledge of the present invention, the person skilled in the art is free to design the bearing body in several pieces; this may be necessary for assembly reasons, for example.

The diameter of the spindle shaft 3 is reinforced in the contact area between the bearing and the motor, so that on this surface the axial force which is generated in particular by the weight of the motor and can be absorbed by the bearing via the spindle shaft. A cover 8 sits on the flange 12, which is fastened to the housing 5 by means of screws 16 by the bearing flange 2.

The simple and compact design of the bearing 2 ensures that a high-speed motor is connected directly to the spindle shaft and that the hydrostatic bearing 2 operates without contact in the area of high speed indicators. Non-contact means that the spindle shaft 3 has no contact with the bearing material. Since the shaft and bearing work without contact, a long service life can be expected. 2 and 2a show the functional principle of the hydrostatic bearing 2 according to FIG. 1. The feed channel 14 of the bearing 2 has several channels. A first channel 17 forms the continuation of the feed channel. This channel 17 ends in a nozzle 18. This nozzle is a fixed pre-throttle. Further channels 20, 21, which branch off from the first channel, end in nozzles 22, 23, which are also fixed pre-throttles. These nozzles 18, 22, 23 are open to the outside by means of known techniques, ie to the spindle 3 or to the first flange 4. There is a gap 19, 24, 25 with different widths H and h between nozzles 18, 22, 23 and spindle shaft 3 and / or other elements such as the first flange 4. This gap 19-24.25 is flowed through with the medium water during the operating phase. The water advantageously flows through these nozzles. The bearing of the spindle shaft 3 shown by way of example thus functions via a water film which is established in columns 19, 24, 25 between nozzles 18, 22, 23 and spindle shaft 3 and the first flange 4.

The high rigidity of this bearing 2 is advantageously ensured by the fact that bearing areas arranged in a ring in the bearing absorb the axial and radial forces. Advantageously, three to eight storage areas are arranged at a distance from one another and are advantageously made in one piece without separation channels. The missing separation channels counteract a loss of rigidity.

First bearing areas, which point largely perpendicular to the axis AA 'of the spindle shaft 3, absorb forces acting radially on the spindle shaft 3. Further bearing areas, which point largely parallel to the axis AA 'of the spindle shaft 3, absorb axially acting forces. This bearing 2 thus absorbs radial and axial forces from the spindle 3 via first bearing regions and absorbs and gives axial forces from the flange 4 via further bearing regions these forces again via the further flange 2, which is connected to the machine tool 11. As a result of the analysis of the equations of motion of the shaft, these bearing areas have been optimized.

A first channel 17 forms the continuation of the feed channel 14 in the direction of the spindle shaft 3 along the axis BB '. The other two channels 20, 21 protrude perpendicularly from the lower area of the feed channel. These channels also each end in columns 24, 25 via a nozzle opening 22, 23. One channel 21 is on the flange side, the other channel 20 is oriented on the motor side. These gaps 19, 24, 25 are filled with water and allow the absorption of the radial and axial forces which are transmitted to the flange on the one hand during tool machining and on the other hand absorb the axial forces which are transmitted via the spindle shaft. Due to the high forces that arise during the grinding or milling process, high surface stiffness of the bearing is required, which can be achieved via the pressure medium water. Water is characterized by a suitable E-module of approx. 2.1 10 * ⁵ N / cm ² and a suitable kinematic viscosity of 1.0 mm ² / s at 20 ° C. With knowledge of the present invention, the person skilled in the art is of course also free to use other printing media which have similar property values in terms of modulus of elasticity and viscosity to water, water, for example glycerin.

The bearing 2 is biased by water pressure in the idle state. The contact between shaft 3 and the solid material of the bearing 2 is only given over water and is referred to as non-contact and thus as frictionless. With constant pump pressure and a turbulent flow set by the fixed pre-throttle, the water reaches the main gap 19, 24, 25 with the exemplary height H (H = 100 * h) and flows over a largely to this standing gap h laterally, as can be seen in FIG. 2, again via a return channel. The flow speed and the amount of water are retained even when the bearing is working under load. With knowledge of the present invention, the person skilled in the art is free to choose other dimensions and ratios of gap height and pocket width.

During operation, the external axial and radial forces act on the bearing 2. The observation of the area of radial force shows, for example in FIG. 2a, how the bearing works under the action of force.

With the external force F _{r, the} shaft 3 presses on the small gap h ₀ along the axis BB '. Under the action of force, the gap h reduces its distance from the shaft 3 by delta h. This reduction in the gap height reduces the outflow of water and increases the pocket pressure in the larger gap area H. This pressure increase counteracts the external force F _r , which causes the gap to be reduced. The gap increases again automatically and the pocket pressure in the warehouse decreases. The described pressure compensation works smoothly and therefore hardly causes any heat to be generated. The temperature rise of the bearing is avoided by the circulation of the flowing water with turbulent flow.

An exemplary arrangement of the bearing 2 around the work spindle 3 can be seen in FIG. 3. Fig. 3 is based on the previous description and refers to this. The bearing 2 lies in a ring around the working shaft 3. According to the section BB ', a radial force application F _r is compensated for via a plurality of first bearing areas which are largely radial to the axis AA' of the shaft 3. According to section AA ', a grain pensation of an axial force application F., over several other bearing areas, which are largely axial to the axis AA 'of the shaft 3.

FIG. 4 shows a diagram on which the force relationships of two exemplary regions of the bearing 2 lying opposite one another can be seen. Fig. 4 is based on the previous description and refers to this. The gap width h of the bearing areas changes depending on the external force F acting. The force axis points upwards and is designated by F. The axis of the gap height is drawn to the right and named with h. If the external force F ₁ rises in a first bearing area, for example, the force F ₂ drops to the same extent in an opposite bearing area, for example in a second bearing area. At the intersection of the two graphs, the central position of the gap h _{m can be} read, which occurs during the phase of the preload F _v in both areas of the bearing 2. An operating force F _B occurs during the operation of the rotating shaft 3 and is the sum of the external force and the pocket force that builds up in the bearing 2. With this operating force, the new column height deviates by a delta h from the central position of the gap h _m . To the same extent that the gap h of the first storage area becomes smaller, the opposite gap h of the second storage area becomes larger.

The machine tool and its elements are made, for example, from known and proven materials such as metal (Cr-Ni steel, etc.). Of course, other realizations of a machine tool and its elements with other materials are also available to the person skilled in the art with knowledge of the present invention.

Claims

PATENT CLAIMS

1. Bearing for a shaft, which bearing absorbs external forces acting on the shaft, characterized in that a single hydrostatic bearing (2) is provided for absorbing axial and radial forces.

2. Bearing according to claim 1, characterized in that the hydrostatic bearing (2) is compact and at a high speed index> 2.5 million. is operable.

3. Bearing according to claim 1 or 2, characterized in that the hydrostatic bearing (2) is integrally formed.

4. Bearing according to one of claims 1 to 3, characterized in that a shaft (3) to be supported is mounted contactlessly and with high rigidity via the pressure medium water.

5. Bearing according to one of claims 1 to 4, characterized in that a body of the hydrostatic bearing (2) has a plurality of channels (17, 20, 21), that these channels end in nozzles (18, 22-23) and that a gap (19, 24, 25) with between the nozzles (18, 22, 23) and a shaft (3) to be supported and / or other elements (4) adjacent on the end face different heights (H, h), water flows through these nozzles and the shaft (3) to be supported is supported by a film of water.

6. Bearing according to claim 5, characterized in that when axial and radial forces act, the gap spacing (H, h) varies and a pocket pressure is set which counteracts external forces in a compensating manner.

7. Bearing according to one of claims 1 to 7, characterized in that the hydrostatic bearing (2) is biased by a water pressure.

8. Bearing according to one of claims 1 to 8, characterized in that bearing areas which are oriented substantially perpendicular to the axis (AA ') of the shaft (3) absorb forces acting radially on the shaft (3) and that bearing areas which largely aligned parallel to the axis (AA '), absorb forces acting axially on the shaft (3).

9. Bearing according to one of claims 1 to 8, characterized in that bearing areas which are aligned substantially parallel to the axis (AA ') of the shaft (3) axially on an element (4) which is adjacent to the end of the hydrostatic bearing (2). absorb acting forces.

10. Machine tool with a bearing (2) according to one of claims 1 to 9, characterized in that a spindle shaft (3) at a high speed index> 2.5 million. is operable and that the hydrostatic Bearing (2) absorbs all forces and transmits them directly to the machine tool (11) via a flange.

11. Use of the bearing according to one of claims 1 to 9, characterized in that the bearing (2) supports a spindle shaft (3) of a machine tool for machining technology, that a motor rotor (1) is shrunk onto the spindle shaft (3) and that the spindle shaft (3) with speed indicators> 2.5 million is operable.