WO2009037261A1

WO2009037261A1 - Rolling bearing device, in particular for medical apparatus

Info

Publication number: WO2009037261A1
Application number: PCT/EP2008/062313
Authority: WO
Inventors: Jesko-Henning Tanke; Pascal Ovize; Volker Wendt
Original assignee: Aktiebolaget Skf
Priority date: 2007-09-19
Filing date: 2008-09-16
Publication date: 2009-03-26
Also published as: FR2921140A1; FR2921140B1

Abstract

The rolling bearing device comprises at least one bearing 4, a fixed ring gear 2 and a rotating ring gear 3 mounted so as to rotate on the fixed ring gear about an axis 4a of the device by means of the said bearing. The device comprises a self-balancing means 15 mounted on the rotating ring gear and furnished with at least one row of rolling elements 43 capable of moving freely about the axis 4a inside at least one guide means 41, 42. The fixed ring gear 2 comprises a first portion 21 for the mounting of the bearing, a second portion 22 for the attachment of the device to an outside element, and means 23 for connecting the said portions capable of allowing at least one relative movement between the first and second portions, at least in the radial direction.

Description

Rolling bearing device, in particular for medical apparatus.

The present invention relates to the field of rolling bearings, particularly used in medical imaging devices such as scanners. In such applications, the rolling bearings usually have a considerable diameter, of the order of one metre, and often rotate at a high speed of several hundred revolutions per minute, for example between 200 and 300.

The requirements of accuracy and robustness demand the use o f sufficiently rigid antifriction bearings comprising a large number of rolling elements. However, because of their large diameter, such antifriction bearings tend to transmit vibrations to the gantry on which they are mounted during the use of the device. Through the resonance and amplification effect, the gantry in its turn generates a noise that is frequently ill received by the patient and the medical staff.

In the devices of the prior art, an attempt has been made to reduce the noise by placing layers of flexible damping material, for example made of elastomer, between the raceways and the rings of the bearings. Reference may be made to document US 2005/0008274 which proposes a resilient annular cushion in contact with the annular wire forming the raceway of the bearing.

In another technical field, in order to reduce the generation o f vibrations and noises, rolling bearings are known that are fitted with self-balancing means with balls. For more detail, it is possible for example to refer to the Italian utility model No. 239 275 or else to document DE-A1 - 103 33 672.

Such systems help to reduce the level of noise and vibrations. However, a further search is ongoing to reduce these sound and vibration levels particularly for medical imaging applications. In this field, the rolling bearings also incorporate ancillary systems such as electric motors and detection devices.

The multiplicity of rotating elements and the relatively large radii of gyration can cause unbalances capable of promoting the generation of additional vibrations.

The object of the present invention is to remedy these disadvantages.

The object of the present invention is to provide a rolling bearing with a very high vibration-damping effect, of relatively simple shape and economical to manufacture.

The subject of the invention is a rolling bearing comprising at least one bearing, a fixed ring gear and a rotating ring gear mounted so as to rotate on the fixed ring gear about an axis of the device by means of the said bearing. The device comprises a self-balancing means mounted on the rotating ring gear and furnished with at least one row of rolling elements capable of moving freely about the axis of the device inside at least one guide means.

The fixed ring gear comprises a first portion for the mounting of the bearing, a second portion for the attachment of the device to an outside element, and means for connecting the said portions capable o f allowing at least one relative radial movement between the said first and second portions, at least in the radial direction.

The use of a self-balancing means mounted on the rotating ring gear combined with the existence of a fixed ring gear in two portions connected together by means adapted to allow slight relative radial movements of the portions promotes the reduction in a significant manner of the vibrations that may be generated.

Specifically, the means of flexible connection between the two portions of the fixed ring gear make it possible to obtain good operating efficiency of the self-balancing means, which limits the vibrations that may be felt.

Advantageously, the connecting means tend to exert a return force from one portion of the fixed ring gear to the other portion. Advantageously, the device comprises a motor provided with a stator mounted on the fixed ring gear and a rotor mounted on the rotating ring gear. The device may also comprise means for detecting the angular position of the rotating ring gear.

In another embodiment, the guide means is or are fitted to the rotating ring gear.

In one embodiment, the guide means is an annular element having a U-profile or O-profile section. As a variant, the guide means may comprise a ring provided with a groove forming a raceway and a collar. In one embodiment, the device comprises a guide path for the rolling elements formed directly on the rotating ring gear.

In one embodiment, the connecting means comprise at least one block made of synthetic material. As a variant, the connecting means may comprise a wavy metal collar. Preferably, the device comprises a damping hoop isolating inner and outer rings of the bearing from the corresponding ring gears. This therefore increases the vibration-damping effect.

The invention also relates to an apparatus for medical imaging, for example a scanner or a nuclear magnetic resonance apparatus, comprising a rolling bearing device as described above.

Thanks to this, the operating noises of the apparatus are considerably reduced. The operating noise reduction increases comfort and reduces the fatigue of the patient and the medical staff. The present invention will be better understood on studying the detailed description of embodiments taken as nonlimiting examples and illustrated by the appended drawings in which:

- Figures 1 to 6 are half-views in axial section of a rolling bearing device according to the first, second, third, fourth, fifth and sixth embodiments of the invention, and

- Figure 7 is a view in perspective of rolling bearing device connecting means according to the sixth embodiment of the invention.

Figure 1 shows a rolling bearing, indicated by the general reference number 1 , and provided with means for reducing vibrations and noises.

The rolling bearing 1 comprises an outer ring gear 2, an inner ring gear 3 , an antifriction bearing 4, with an axis 4a, placed between the outer ring gear 2 and inner ring gear 3. The inner ring gear 3 is in this instance rotating, the outer ring gear 2 being fixed. The antifriction bearing 4 comprises a row of rolling elements 5 , in this instance balls, an outer ring 6 and an inner ring 7. The antifriction bearing 4 also comprises a cage 8 for maintaining an even circumferential spacing between the rolling elements 5. The outer ring 6 is annular and has an axial outer surface, two radial lateral surfaces and a bore from which a raceway 6a of torroidal shape is formed. The raceway 6a is symmetrical relative to a radial plane passing through the centre of the rolling elements 5. The inner ring 7 is in the shape of a collar open at one point (not shown) of its circumference. The inner ring 7 has a cylindrical bore, two radial lateral surfaces and an axial outer surface from which a raceway 7a o f torroidal shape is formed. The raceway 7a may be symmetrical relative to a radial plane passing through the centre of the rolling elements 5. The inner ring 7 may be made from a wire whose initial circular or rectangular cross section is modified by wire drawing until the final profile is obtained and is then cut to length and rolled on itself with the ends placed end-to-end in order to finally obtain a circular race open at a point of its circumference. The material, for example steel, naturally undergoes heat treatment in order to give it the required hardness. The raceway 7a may undergo slight lapping in order to give it a correct roughness. This manufacturing method is particularly economical because one and the same section of wire may be used to manufacture rolled rings of final section and diameters that are very different from one another.

The outer ring 6 may also be an open ring as an alternative. The outer ring 6 may therefore also be manufactured from a blank in the shape of a circumferentially continuous ring. Otherwise, the outer ring 6 may be manufactured from a portion of tube. The raceway 6a may also undergo a slight lapping in order to give it a correct roughness.

Between the inner ring gear 3 and the inner ring 7 a damping hoop 9 is provided. The hoop 9 is made of an elastic material with a U-shaped cross section. The hoop 9 may be of annular shape or else open at a point of its circumference, which makes it possible to both place it on the inner ring 7 and to place it in the inner ring gear 3 before or after it is installed on the inner ring 7. Similarly, a damping hoop 10 made of elastic material having a U-shaped cross section is placed between the outer ring gear 2 and the outer ring 6. The damping hoop 10 may be manufactured from an elastomer having good vibration-damping characteristics, for example an acrylonitrile butadiene rubber NBR 70. The inner ring gear 3 is made in two portions 1 1 , 12 mounted axially fixedly one against the other by any appropriate means, for example by screwing. The portion 1 1 comprises an axial outer surface l l a from which is made an annular groove l ib of substantially rectangular section in which the inner ring 7 is placed and the inner hoop 9. The axial dimension of the annular groove l ib is adjusted to ensure a housing with insignificant or no clearance of the inner ring 7 and the hoop 9 because of the elasticity of the said hoop 9. In the vicinity of the groove l ib, axially on the side opposite to the portion 12, the axial outer surface l l a is extended inwards by a radial surface l i e, and then by an axial surface l i d of smaller diameter than the axial surface l l a, and then by an end radial surface l i e extending up to a bore 1 I f.

The portion 12 of the inner ring gear 3 comprises an outer surface 12a axially extending the outer surface l l a and comprising, at one axial end, an annular radial surface 12b and then a substantially axial annular surface 12c with a smaller diameter than the axial surface 12a, and an end radial surface 12d connecting the substantially axial surface 12c and a bore 12e. Axially on the side opposite to the end radial surface l i e, the bore l l f of the portion 1 1 is delimited by an end radial surface l l g extended from a large diameter edge by an axial surface l l h, itself extended to a free end by a radial surface l l i connecting to the outer surface l l a. The radial surface l l i rests against an end radial surface 12f of the portion 12 delimiting the bore 12e, on the side opposite to the radial surface 12d. Axial drill holes 13 and 14 may be provided from the end surfaces l i e and 12d for the attachment of rotating parts.

As will be described in greater detail below, the device 1 comprises a self-balancing means 15 mounted between the portions 1 1 and 12 of the inner ring gear 3 so as to limit the vibrations and noises in operation.

The outer ring gear 2 comprises an inner portion 21 , an outer portion 22 and elastic flexible connecting means 23 connecting the said portions. The inner portion 21 comprises a bore 21 a and a shoulder 21b extending radially inwards from the bore 21 a. The outer hoop 10 is in contact with the bore 21 a and the shoulder 21 b. The remaining free length of the bore 21 a is furnished with an annular spacer 24. The spacer 24 may be made of a rigid material, for example of steel or a synthetic material. It rests on the outer ring 6 of the antifriction bearing via the hoop 10 in order to hold it against the shoulder 21b.

The inner portion 21 of the outer ring gear 2 comprises a radial end surface 21 c extending outwards from the bore 21 a on the side opposite to the shoulder 21b, and then an outer surface 21 d axially delimited on the opposite side to the radial surface 21 c by a radial surface 2 I e, itself extended from a small-diameter edge by an axial surface 21 f extending outwards. Beyond the shoulder 21 b, the inner portion 21 comprises a bore 21 g with a smaller diameter than the bore 21 a and then an annular protrusion 2 I h extending radially inwards and terminating in a radial surface 2 Ii connecting at a large-diameter edge to the axial surface 2 I f.

The inner portion 21 of the outer ring gear 2 is associated with an intermediate plate 25 of annular shape and rectangular section in contact with the end radial surface 21 c and extending inwards beyond the bore 21 a of the inner portion 21. The intermediate plate 25 is also in contact with the spacer 1 1 in order to hold it in position.

The device 1 also comprises a motor 26 comprising a rotor 27 mounted on the portion 12 of the inner ring gear 3 and in contact with the radial surface 12b and axial surface 12c of the said portion 12. The rotor 27 is attached to the portion 12 of the inner ring gear 3 by means not shown, for example by bonding or screwing. The motor 18 also comprises a stator 28 placed around the rotor 27 with a slight radial air gap. The stator 28 is attached to the inner portion 21 of the outer ring gear 2. The attachment may be provided by screws 29 engaging in blind holes 29a arranged on the radial surface 21 c of the inner portion 21 of the outer ring gear 2. The screws 29 pass through a portion o f the stator 28 and the intermediate plate 25 which they also attach. The through holes for the screws 29 are therefore provided through the intermediate plate 25. A spacer 30 ensures a slight spacing between the stator 28 and the intermediate plate 25.

On the opposite side, the device 1 comprises means 31 for detecting the rotation parameters, for example the angular position or the speed of one ring gear relative to the other. In this respect, the detection means 31 comprise an encoder collar 32 and a sensor block 33. The encoder collar 32 may be of the magnetic type and be in the shape of a tape made of polymer material filled with magnetic or magnetized particles, and attached to the axial surface l i d of the portion 1 1 of the inner ring gear 3 , for example by bonding. The sensor block 33 may comprise one or more detection elements, for example Hall effect cells, placed around the multipole encoder collar 32 with a slight radial air gap. The sensor block 33 is attached against the radial surface 21 i of the inner portion 21 of the outer ring gear 2. The outer portion 22 of the outer ring gear 2 comprises an annular flange 22a provided for the attachment of the device to a support that is outside the device and is furnished for this purpose with drill holes 34. The flange 22a comprises a bore 22b partially radially surrounding the axial surface 21 f of the inner portion 21 and the sensor block 33. The outer portion 22 comprises a radial end surface 22c extending, from one end of the bore 22b, towards the outside and extended at a large-diameter edge by an annular protrusion 22d extending axially towards the inner portion 21. The protrusion 22d has a larger radial dimension than the diameter of the outer surface

21 d of the inner portion 21. An axial space 35 is arranged between the radial surface 22c of the outer portion 22 and the radial surface 21 e o f the inner portion 21 of the outer ring gear 2.

The connecting means 23 are mounted between the inner portion 21 and the outer portion 22, resting against the radial surfaces

21 e and 22c. The connecting means 23 comprise a plurality of elastic mounts 36, each mount being connected to the inner portion 21 and the outer portion 22 by appropriate means (not shown), for example by screwing or bonding. The mounts 36 may be of the silent block type. The connecting means 23 make it possible to elastically connect the inner portion 21 and the outer portion 22.

The elastic connecting means 23 provide a mechanical connection between the two portions 21 , 22 of the outer ring gear 2 while allowing a slight relative movement between them, in the axial and radial directions. In addition, the connecting means 23 make it possible to obtain an excellent damping of the vibrations between the inner portion 21 and the outer portion 22 of the outer ring gear 2.

As a variant, the mounts 36 could be replaced by a circumferentially continuous circular collar made of a flexible material and attached by one of its faces to the radial surface 21 e and by its other face to the radial surface 22c.

As indicated above, in order to limit the vibrations and noises in operation of the device, the self-balancing means 15 is provided at the inner ring gear 3. The self-balancing means 15 comprises an outer ring 41 , an inner ring 42 and an a row of rolling elements 43 , in this instance balls, placed between the said rings.

The outer rings 41 is annular and has an axial outer surface mounted resting against the axial surface l l h, two radial lateral surfaces resting against the radial surface l l g and the radial surface

12f, and a bore from which a torroidal-shaped raceway 41 a is formed for the rolling elements 43. The outer ring 41 may be circumferentially continuous or open at a point of its circumference.

The inner ring 42 is in the shape of a collar whose lateral edges engage in the corresponding lateral grooves (not referenced) made on the radial surface l l g and on the radial surface 12f of the first and second portions 1 1 , 12 of the inner ring gear 2. The inner ring 42 may be made of steel sheet or of a thin plastic relative to its diameter. It may be circumferentially continuous or open at a point of its circumference. In the latter case, the inner ring 42 is rolled on itself with the ends placed end-to-end. The inner ring 42 and the outer ring 41 are clamped axially between the first portion 1 1 and the second portion 12 of the inner ring gear 2. The said rings form guide means for the rolling elements 43. The said rolling elements 43 are capable o f moving freely about the axis 4a inside the space delimited between the rings 41 and 42. Accordingly, a radial clearance is arranged between the rings 41 , 42 and the rolling elements 43 such that they are able to travel freely between the said rings irrespective of the relative speeds of the latter. The number of rolling elements 43 is such that, when they are placed in contact side by side, they cover an angular sector of less than 180° .

The self-balancing means 15 and the connecting means 23 make it possible to obtain an excellent damping of the vibrations and noises of the device. Specifically, the self-balancing means 15 is particularly effective because it is associated with the connecting means 23 which allow a certain capacity of movement in the radial direction of the inner portion 21 relative to the outer portion 22 of the outer ring gear 2. The self-balancing means 15 may therefore operate efficiently. The embodiment illustrated in Figure 2 in which the reference numbers of the identical elements have been retained differs mainly in that the rotating inner ring gear 3 is made in one piece. This simplifies the construction of the device 1 and increases its rigidity. The inner ring gear 3 may be obtained by machining a piece of steel. The inner ring gear 3 has a profile similar to that of the previously described embodiment. The inner ring gear comprises a bore 3a from which an annular groove or crank 3b is made situated substantially in a radial mid-plane of the ring gear 3. At the crank 3b, a recess 3c is arranged, for example by machining, forming a raceway of torroidal shape for the rolling elements 43.

In this embodiment, the guide means of the rolling elements 43 are therefore partly directly constituted by the inner ring gear 3. The inner ring 42 may preferably be made of plastic for example in the shape of a strip rolled up on itself with the ends 42a and 42b end-to- end, the said strip being inserted by deformation into the side grooves of the crank 3b. The ring 42, the ring gear 3 and the rolling elements 43 form a self-balancing means 45.

The variant embodiment illustrated in Figure 3 differs mainly from the previously described embodiment in that an annular duct 46 in the shape of a tube rolled on itself is placed in the crank 3b in contact against the walls of the latter. The duct 46 has in cross section an O-profile and forms a guide means for the rolling elements 43. The duct 46 and the said rolling elements 43 constitute a self-balancing means 47. The crank 3b in this instance has an axial dimension that is slightly less than that of the preceding embodiment in order to hold the duct 45 in position while making it possible to arrange a radial clearance between the said duct and the rolling elements 43.

The embodiment illustrated in Figure 4 in which the reference numbers of the similar elements have been repeated, differs mainly from the first embodiment in that the design of the outer ring gear 2 is slightly different. The outer surface 21 d of the inner portion 21 in this instance comprises a slightly greater axial dimension and is delimited axially, on the side opposite to the radial surface 21 c, by a substantially radial surface 2 Ij which extends inwards and is connected to the radial surface 21 i by means of a axial surface 21k. The sensor block 33 is mounted against the axial surface 21k.

The annular outer portion 22 for its part comprises a general L shape. The flange 22a is extended at a small-diameter end by an axial portion 22e radially surrounding the outer surface 2 I d of the inner portion 21 . The axial portion 22e comprises a bore 22f facing the said outer surface 2 I d. A radial space 50 is therefore arranged between the inner portion 21 and the outer portion 22.

In this embodiment, connecting means 51 making it possible to elastically connect the inner portion 21 and the outer portion 22 are housed in grooves 53 , 54 made respectively on the outer surface 21 d o f the inner portion 21 and the bore 22f of the outer portion 22 of the outer ring gear 2. The connecting means 51 are made in the form of an annular block 52 of synthetic material extending radially between the said grooves in the radial space 50. The block may for example be made of rubber.

As a variant, the connecting means could have the form of a plurality of segments partially housed both in the groove 53 and in the groove 54, and spaced in the circumferential direction relative to one another. It could also be possible to fill with elastomer foam the radial space 50 situated between the grooves 53 and 54.

The embodiment illustrated in Figure 5 , in which the reference numbers of the similar elements have been retained differs in that a self-balancing means 55 comprises a collar 56 having a U profile in cross section, and the rolling elements 43. Two branches of the U of the collar 56 come into contact against the radial surface l l g and axial surface l l h of the portion 1 1 of the inner ring gear 3. The last branch of the U makes it possible to hold the rolling elements 43 in position axially between the portions 1 1 and 12. In this embodiment, the axial distance separating the radial surface l l g of the portion 1 1 and the radial surface 12f of the portion 12 is slightly reduced.

The embodiment illustrated in Figure 6 in which the similar reference numbers have been retained differs from the embodiment of Figure 4 in that a connecting means 60 placed in the grooves 53 and 54 of the first portion 21 and the second portion 22 of the outer ring gear 2 comprise a wavy collar 61.

As illustrated more visibly in Figure 7, the collar 61 is continuous in the circumferential direction and comprises a succession of undulations formed so that a summit in contact with the groove 54 is directed inwards in the direction of the groove 53 and an immediately following summit in contact with the groove 53 is directed outwards in the direction of the groove 54. The undulations are radially prestressed between the inner portion 21 and the outer portion 22 but by elastic deformation allow a slight relative radial movement between these two portions. The lateral edges of the collar 60 bear against the lateral edges of the grooves 53 , 54 thereby providing the axial connection between the portions 21 , 22 of the outer ring gear 2. Naturally, the collar 61 could be open and formed from a wavy strip rolled on itself with the two ends of the strip placed end-to- end to form the said collar.

Although, in all of the embodiments previously described, the device comprises a self-balancing means furnished with a single array of balls housed with a radial clearance between the inner and outer rings, it is easy to conceive that it could also be possible, without departing from the context of the invention, to provide several arrays of balls for the self-balancing. It could also be possible to use several antifriction bearings between the rotating inner ring gear and the fixed outer ring gear.

Thanks to the invention, this gives a rolling bearing provided with a self-balancing means mounted on the rotating ring gear and elastically deformable connecting means connecting an inner portion and an outer portion of the fixed ring gear, the connecting means being capable of allowing a relative movement between these portions in a radial direction and of exerting a return force in an opposite radial direction. The rolling bearing makes it possible to provide particularly effective damping of the vibrations.

Claims

1 -Rolling bearing device comprising at least one bearing (4), a fixed ring gear (2) and a rotating ring gear (3) mounted so as to rotate on the fixed ring gear about an axis (4a) of the device by means of the said bearing, characterized in that it comprises a self-balancing means

( 15 ; 45 ; 47; 55) mounted on the rotating ring gear and furnished with at least one row of rolling elements (43) capable of moving freely about the axis (4a) inside at least one guide means (41 , 42; 3c, 42; 46; 56), and in that the fixed ring gear (2) comprises a first portion (21 ) for the mounting of the bearing, a second portion (22) for the attachment of the device to an outside element, and means (23 ; 51 ; 60) for connecting the said portions capable of allowing a relative movement between the first and second portions, at least in the radial direction. 2-Device according to Claim 1 , wherein the connecting means

(23 ; 5 1 ; 60) tend to exert a return force from one portion of the fixed ring gear to the other portion.

3-Device according to Claim 1 or 2, comprising a motor (26) provided with a stator (28) mounted on the fixed ring gear and a rotor (27) mounted on the rotating ring gear.

4-Device according to any one of the preceding claims, comprising means (31) for detecting the angular position of the rotating ring gear.

5-Device according to any one of the preceding claims, wherein the guide means (41 , 42; 3c, 42; 46; 56) is or are fitted to the rotating ring gear.

6-Device according to Claim 5 , wherein the guide means (46 ; 56) is an annular element having a U-profile or O-profile section. 7-Device according to Claim 5 , wherein the guide means comprise a ring (41 ) provided with a groove forming a raceway and a collar (42).

8-Device according to any one of Claims 1 to 5 , comprising a guide path (3c) for the rolling elements formed directly on the rotating ring gear.

9-Device according to any one of the preceding claims, wherein the connecting means (23 ; 51 ) comprise at least one block (36; 52) made of synthetic material. 10-Device according to any one of Claims 1 to 8, wherein the connecting means (60) comprise a wavy metal collar (61).

1 1 -Device according to any one of the preceding claims, comprising a damping hoop (9, 10) isolating inner and outer races (6, 7) of the bearing from the corresponding ring gears. 12-Apparatus for medical imaging comprising a rolling bearing device according to any one of the preceding claims, placed between a fixed portion and a rotating portion.