AN ELECTRIC MOTOR DRIVEN TOOL

The present invention relates to a tool designed for high speeds and with a structure according to the preamble of Patent Claim 1.

The tool according to the invention is designed for speeds of up to 500,000 revolutions per minute and higher, for which reason the tool has a unique design. It is also possible for the tool to be made small, for example with a shaft diameter of as little as 2 mm or less.

By virtue of its high speeds but relatively low torques, the tool is especially suitable for use in nanotechnology, for example for grinding, drilling, milling, engraving, etc.

The tool has a novel design, and the special features that distinguish it from the prior art in this field are set forth in the characterizing parts of the patent claims.

The invention will be described below on the basis of examples and with reference to the drawing, in which Figure 1 is a schematic view of the tool in one position, and Figure 2 is a schematic view of the tool in a position different than the first position, Figures IA and 2 A show alternative embodiments of the tool according to Figures 1 and 2, Figures IB and 2B show further variations of the tool according to Figures 1 and 2, Figure 3 shows a cross section along the line III-III in Figure 4 with pressure distribution around the radial fluid bearing, Figure 4 shows a longitudinal section through the tool according to a variant, Figure 5 is a schematic view of a cross section along the line V-V in Figure 6 with the pressure distribution

around the radial fluid bearing, Figure 6 shows a longitudinal section through the tool according to the invention and Figures 7 and 8 show alternative embodiments of the invention.

In the figures, reference number 1 designates a shaft of a rotatably driven tool, whose machining tool end is designated by reference number 2. The machining tool 2 can be integrated in or releasably connected to the shaft 1. In a first embodiment according to Figures 1 and 2, the tool is mounted with its shaft in a radial fluid bearing 3 formed by an axial bore 4 in a housing 5. Adjacent to the machining end 2 of the shaft 1, the latter is provided with a rotor 6 driven by a rotating magnetic field generated by a stator 6', which rotor is received freely in the stator 6' in the housing 5, as is shown. The stator 6' can of course be arranged instead in a separate part, fastened to the housing. Adjacent to the rotor 6, an axial bearing 8 is arranged for cooperation with a bottom end surface 9 of a cavity 7 receiving the stator 6'. The axial bearing 8 is fed with the same bearing fluid as the radial bearing. Figures IB and 2B show how the tool according to the invention is also provided with an axial bearing 30, for example in the form of a ceramic ball, acting against the inner end surfaces of the shaft 1 and movable in the axial direction. Within the scope of the invention, it is of course possible to exclude the axial fluid bearing 8 and to only use the axial bearing 30 for the axial displacement of the shaft 1 and of the tool. With the tool fully inserted, the axial fluid bearing 8 can take up the axial forces and the axial bearing 30 can be unloaded.

Fluid, liquid or gas (for example water or air), for the fluid bearing of the tool shaft 1 is introduced into an inlet 11, as is indicated by an arrow 12, and distributes itself in the radial bearing 3 on the one hand towards the axial bearing 8 and on the other hand towards the inner end of the shaft located in

the housing. The introduced bearing fluid is conveyed away via outlet channels 13 and 14. To secure the axial position of the tool in the housing with the axial bearing 8 cooperating with the end surface 9, or when the axle according to Fig. 2B rests against the ball 30, a counter- force acting against the axial bearing is generated by means of the bearing fluid being exposed to underpressure, i.e. forced out with underpressure via the outlet channels 13 and 14. The bearing fluid that reaches the axial bearing 8, 9 is prevented from leaking out in the turbine wheel end on account of an underpressure prevailing in the space round the axial bearing.

In order to increase the mass inertia of the tool, the rotor 6 can be dimensioned, or the material thereof chosen, such that its mass inertia increases the rotation energy and thereby increases the machining capacity of the tool.

During machining operations, the housing 5, with the tool located therein in the position shown in Figure 1, can be displaced to and away from the workpiece. However, it is also possible to only displace the tool in the axial bore 4 instead. This can be done (see Figure 1) by a liquid column 15 being formed between the end of the shaft 1 in the housing 5 and a piston 16 that is displaceable axially in the bore 4. In the fully inserted position of the tool, the liquid column which is located between the end of the shaft 1 and the piston 16, and which (when the bearing medium is a liquid) is formed by the bearing fluid flowing from the inlet 11 to the outlet 14, is at all times fully developed, this by virtue of the fact that the piston 16 in the starting position keeps the outlet line 14 open. If the tool is to be displaced axially outwards, the piston 16 is quickly forced in by the desired distance, which means that the shaft 1 and thus the tool are displaced by said distance. When the piston 16 is drawn back

to the starting position, the tool naturally follows it. It must be understood that these displacements of the tool backwards and forwards in the housing 1 take place within a very short time, for which reason the liquid column is not influenced to any appreciable degree by the bearing fluid that flows towards the end of the shaft and the liquid column. When the bearing medium is instead composed of a gas (air) (see Figures IA and 2A), a liquid is delivered without any appreciable pressure via a channel 28 in order to ensure the liquid column 15. In the case (see Figures IB and 2B) where the axle 1 only rests against the axial bearing, the ball 30, which acts against the end surface of the shaft 1, the ball constitutes the only axial bearing (not shown), and the axial displacement of the tool takes place by means of the part 16', on which the ball is arranged, being displaced axially. In the case shown in Figures IB and 2B, where the axial fluid bearing 8 is combined with the axial bearing 30 (ball), the shaft 1 in the inserted end position will bear against the axial fluid bearing 8, and the bearing 30 can be relieved, which bearing has a bearing function only during outward displacement of the shaft 1 by means of the part 16'.

By designing the rotor 6 with a certain axial extent, the action of the stator 6', and thus of the rotating magnetic field, on the rotor 6 can remain essentially the same, even when the tool is displaced outwards from the housing 5.

When the tool is to be removed from the housing, for example for replacement, an overpressure is applied in the outlet channel 13 instead of an underpressure, and this overpressure directly "pushes" the tool out of the housing 5. During tool replacement, the turbine wheel is removed from the shaft and is mounted on a new shaft with a new machining tool end.

To achieve the high speeds intended for the invention and to generate a stable

movement of the tool, an aim is to eliminate pressure variations in the bearings. Figures 3-6 show schematic views of a tool according to the invention, which differs from the tool described in connection with Figures 1 and 2 only in that the radial fluid bearings have been given a special design. Figure 4 thus shows two radial fluid bearings 17 and 18. In the example shown, the non-bearing outer side of each bearing is provided with three axial channels 19 (see Fig. 3) which at one end comprise a radial channel 20 in the bearing, opening into the bearing surface, and which at the other end open into a space 21 present between the two bearings. As will be appreciated, the space 21 is filled with bearing fluid, which flows on the one hand into the gap between the shaft 1 and the bearing surface and on the other hand via the channels 19 and the radial channels 20 to the bearing gap. The supply of bearing fluid also through the channels 20 means that a pressure distribution curve is formed in the bearing gap between each radial bearing 17 and 18 and the shaft 1, as shown in Figure 3. By delivering bearing fluid through the channels 20, a controlled pressure distribution (according to the arrows in Figure 3) is obtained in the bearing, which effectively prevents incorrect functioning of the bearing at high speeds.

Figure 5 shows another embodiment for solving the problems mentioned earlier. Here, the arrangement differs from Figures 3 and 4 in that the bearing surface of each bearing 17 and 18 supporting the shaft 1 has regular radial formations deviating from the purely circular shape. In the example shown in Figure 5, the bearing surface has three radially widened, axial parts 22, which means that the bearing fluid flowing between the fluid bearing and the shaft is compressed in the "narrower" areas during rotation of the shaft, for which reason a pressure curve is also obtained corresponding to the one in Figure 5.

The preferred embodiment of the invention described above can be modified in accordance with what is shown in Figures 7 and 8.

Instead of operating with underpressure in the bearing fluid in order to use a force to maintain the position of the axial bearing 8; 30 with respect to the end surface 9, this force can, as shown in Figure 7, instead be generated by applying an external force component generated, for example, by an air stream 25 directed more or less axially towards the rotor 6 (see Figure 7).

Finally, Figure 8 shows the axially inwardly directed force generated by a magnet 27, attracting the rotor 6. Alternatively, this magnet 27 can be replaced by or supplemented with a magnet 27 placed at the inner end of the shaft 1 and attracting the axle 1.

The modifications described above in connection with Figures 7 and 8 thus presuppose the same tools as shown in and described with reference to Figures 1-6, except that an underpressure is not necessary in the outlet channels 13, 14, since the tool's axial movement controlled by the piston 16 and the liquid column 15 is generated in the manner described earlier.

The above-described tool according to the invention can of course be combined to form a tool with several rotating shafts provided with machining tools and operating, if necessary, at different speeds.