Electrical rotating machine

Abstract: A bearing apparatus for use in an floppy disc drive device motor having a sleeve bearing and a thrust bearing is provided which is characterized in that there is provided a thrust bearing having such a convex portion, a projection, or a concave portion that makes the rotation shaft of the motor inclined with respect to the center axis of the sleeve bearing. Therefore, the rotation shaft ofa motor can be forcibly inclined with the rotation shaft and the sleeve bearing being kept in contact with each other. In addition, it is possible to reduce deviation in inclination of the motor rotation shaft and to ensure electric conductance between the motor rotation shaft and the motor body. These advantages areattained by a specific structure in which a projection, a convex portion, or a concave portion is provided at the thrust bearing, and therefore, the structure is simple and requires low costs.

Description: The present invention relates to a bearing apparatus in, particularly, a motor for a floppy disc drive device. A floppy disc drive device has been widely used for a computer external memory device, since it allows flexible replacements of floppy discs and easy treatment. Recently, there has been a tendency to down-sizing computers, and therefore, the floppy disc drive devices is included in microcomputers have come to follow this tendency. In addition, as the size of a floppy disc drive device is reduced, the motor for driving a floppy disc must be formed to have a small and thin size. Although conventional bearings for driving a floppy disc drive device have been of ball bearing type, bearings of the type as shown in FIG. 5 have been recently used for reasons as stated above. In a conventional bearing apparatus for a floppy disc drive motor used in the floppy disc drive device, a rotation shaft 1 is supported by a sleeve bearing 7 and a thrust bearing 6, as shown in FIG. 5, and therefore, there is a small gap in the radial direction. So that, when an external force is applied to a rotor yoke or when a magnetic unbalance occurs, inclination of the rotation shaft 1 changes, As a result, read/write characteristics of the floppy disc drive device are deteriorated in some cases. Therefore, a concept of a dynamic pressure type bearing using a fluid such as an oil or the like has been proposed as a method of filling the radial gap. The rotation speed of floppy disc drive device drive motor is about 300 rpm, so that sufficient effects cannot be obtained by a dynamic pressure type bearing using a fluid like an oil. When the dynamic pressure type bearing has been used, and even if the rotation shaft 1 can be supported to stand vertically and stable rotation can be obtained, floppy disc drive device chassis is electrically isolated from the rotation shaft 1, so that it is not possible to form a circuit for discharging static electricity of a floppy disc, which is necessary for floppy disc drive device drive motor. The present invention has been made to improve drawbacks of a conventional apparatus as stated above, and an object of the present invention is to provide a bearing apparatus in an electrical rotating machine especially floppy disc drive device motor which has a simple structure, which ensures a sufficient rotational accuracy of a rotation shaft to prevent deterioration in read/write characteristics of floppy disc drive device, and which can discharge static electricity of an floppy disc. EP-A-0589514 discloses a rotating machine having a rotor and stator rotatable relatively to one another, the machine comprising a frame mounting a stator yoke which forms part of the stator; a cylindrical shaped sleeve mounted on the frame; a rotation shaft supporting the rotor and having a curve shaped end and a diameter which is smaller than the inside diameter of the sleeve bearing and rotatably supported in said sleeve bearing, and a thrust bearing supporting the curve shaped end of the rotation shaft and, according to the present invention, such a machine is characterised by the upper surface of the thrust bearing being shaped to provide a concave portion, which is offset from the centre line of the sleeve bearing, whereby the curve shaped end of the rotation shaft rests in the concave portion with the rotation shaft inclined to the centre line of, and in contact with, the sleeve bearing, the inclination being stabilised by magnetic attraction between the stator and the rotor; and by a conductive path for static electricity from the rotor to the frame via the rotation shaft and sleeve bearing. Since the rotation shaft of the rotating machine is actively inclined, swinging movements of the rotation shaft are reduced and rotation of the rotating machine is stabilized, so that effective reading/writing operation of floppy disc drive device is realized. Further, electric conductance is ensured between the rotation shaft and the sleeve bearing, so that static electricity is discharged from a floppy disc. In the accompanying drawings: FIG. 1 is a cross-sectional view showing a first embodiment of the present invention. FIG. 2 is an enlarged view showing a bearing portion according to the first embodiment of the present invention. FIG. 3 is an enlarged view showing a bearing portion according to a second embodiment of the present invention. FIG. 4 is a cross-sectional view showing a part of an other embodiment. FIG. 5 is an enlarged view showing a bearing portion of a conventional motor. An embodiment of the present invention will be described below with reference to the drawings. FIG.1 is a cross-sectional view of floppy disc drive device motor according to the present invention . In this figure, reference 1 denotes a rotation shaft of a motor, and reference 2 denotes a rotor yoke. The rotor yoke 2 is formed in a disc-like shape by punching a permeable soft iron plate by press-processing, and a hole for allowing the rotation shaft 1 to penetrate is formed in the center of the yoke. The rotation shaft 1 is forcibly engaged in the hole, and thus, the rotor yoke 2 is finally fixed to the rotation shaft 1. When the floppy disc drive device motor is incorporated in the floppy disc drive device, floppy disc is mounted on the upper surface of the rotor yoke 2, so that the floppy disc rotates as the rotor yoke 2 rotates. A magnet 3 formed of hard ferrite or hard rubber and hard ferrite particles mixed and kneaded there into is inside the peripheral portion of the rotor yoke 2. This magnet 3 is magnetized such that N- and S-poles alternately appears along the circumferential direction of the rotor yoke 2. Reference 4 denotes a stator coil, and reference 5 denotes a stator yoke. References 6, 7 and 8 respectively denote a thrust bearing, a sleeve bearing, and a motor frame. Further, the stator yoke 5 is fixed on the motor frame 8. A sleeve bearing 7 is installed in the center of the stator yoke 5, and the rotation shaft 1 is rotatably supported by the bearing 7, which will be described in more detail later. The stator yoke 5 is provided with a plurality of magnetic poles formed in a star-like arrangement, in the direction from the center towards the magnet 3. A stator coil 4 is wound near the tops of the star-like arrangement. Moreover specific explanation will be omitted except for the bearing structure described below, since the structure and operation of the motor shown in FIG. 1 are well-known. FIG. 2 is an enlarged cross-sectional view showing a part of bearing portion (i.e., portion A shown in FIG. 1). As can be seen from FIG. 2, a thrust bearing 6 is provided on the internal bottom surface of the sleeve bearing 7 having a sleeve shape whose bottom portion is fixed to the motor frame 8. A projection 6c is provided at the bottom portion of the thrust bearing 6, and this projection 6c is engaged in a hole formed in the motor frame. The end of the bottom portion of the rotation shaft 1 has a hemispheric shape. A conical projection 6a, forming to the side thereof a concavity, is provided on the upper surface of the thrust bearing 6 at a deviated portion thereof, i.e., at a position offset from the center line of the sleeve bearing 7 indicated by one-dot-dashed line in the figure. Operation of the above embodiment will now be explained. At first, if a rotation shaft 1 is inserted in a sleeve bearing 7 in an floppy disc drive device motor, as shown in FIG. 1, the magnet 3 and fixed magnetic poles at ends of the stator yoke 5 attract each other, so that the rotor yoke 2 is attracted in the direction towards the motor frame 8 until the end of the rotation shaft 1 is brought into contact with the thrust bearing 6. When the floppy disc drive device motor is rotated in this condition, the rotor yoke 2 rotates, maintaining this condition. However, since there is an actual clearance between the rotation shaft 1 and the sleeve bearing 7, the rotor yoke 2 rotates with itself slightly inclined in a particular direction due to lack of uniformity in the sizes of the gaps between the magnet 3 of the rotor yoke 2 and the fixed magnetic poles 5a, and in the magnetomotive force of the stator coil 4. Therefore, according to the present invention, in order to previously incline the rotation shaft 1 at a predetermined angle  ° the bottom portion of the rotation shaft 1 is formed in a hemispherical shape and the projection 6a is provided on the upper surface of the thrust bearing 6 at a portion offset from the center thereof,so that the rotation shaft 1 is inclined with a gap between the rotation shaft 1 and the sleeve bearing 7. Consequently, as shown in FIG. 2, the end of the bottom portion of the rotation shaft 1 is in contact with the thrust bearing 6, and the side wall of the rotation shaft 1 is in contact with the sleeve bearing 7. The rotation shaft thus attains three contact points and is stably supported by these contact points. In addition, since the cylindrical bearing 7 is thus continuously kept in direct contact with the rotation shaft 1, static electricity charged in the rotor yoke 2 from an attached floppy disc escapes in the direction towards the motor frame 8 through the rotation shaft 1 and the sleeve bearing 7. Therefore, static electricity is not charged in the rotor yoke 2. FIG. 3 is a partial enlarged cross-sectional view showing another embodiment of the present invention. In this embodiment, a conical concave portion 6b is formed in the upper surface of a thrust bearing 6, and the end of the bottom portion of this concave portion 6b is situated at a deviated portion, i.e., a position offset from the center line of the sleeve bearing 7 indicated by one-dot-dashed line. Moreover those portions which are common to the portions of FIG. 1 are referred to by the same reference symbols, and explanation thereof will be omitted herefrom. Thus, in the second embodiment, a concave portion 6b is formed at a deviated portion offset from the center line of the sleeve bearing 7, and therefore, the rotation shaft 1 is inclined. As a result, the rotation shaft 1 is in contact with the thrust and sleeve bearings 6 and 7 at three points and is stably supported by these contact points, so that the rotation shaft rotates stably. In the first and second embodiments, the thrust bearing 6 is press-fitted and fixed to the hole formed in the motor frame 8 when assembling the motor. Therefore, it is not possible to perform fine adjustment of the positional relationship between the thrust bearing and the rotation shaft after assembling the motor. In the Fig. 4 embodiment, for example, an engagement part 6c is provided in the bottom portion of the thrust bearing 6 to constitute a rotation portion, as shown in FIGS. 2 and 3, and the thrust bearing 6 is rotatably installed on the motor frame 8 when assembling the motor. After assembling the motor, the rotational position of the thrust bearing 6 is adjusted with a screw driver when testing rotation of a floppy disc drive device motor, to attain the position where the rotation shaft 1 rotates at the highest stability. Thereafter, the thrust bearing 6 is fixed to the motor frame 8 by means of an adhering or brazing method or the like. In case where the length of the shaft in the thrust direction requires a high accuracy, a screw portion 9 is provided on an engaging surface of the thrust bearing 6 to be engaged with the motor frame 8, thereby to fix the thrust bearing 6 to the motor frame 8. Otherwise, in case where the inclination direction of the rotation shaft 1 has already been decided before the assembling of the motor is started, the thrust bearing 6 can be fixed at a particular position to the motor frame 8. Therefore, the thrust bearing 6 is engaged in the motor frame 8 in such a manner in which the thrust bearing 6 does not rotate in relation to the motor frame 8. In this case, the cross-sections to be engaged with each other may be D- or I-shaped or may be of a convex shape or the like. In each of the first and second embodiments, the concave portion is provided on the upper surface of the thrust bearing at a position offset from the center line of the sleeve bearing and is thus deviated. However, if the concave portion is provided on the center line, it is possible to form a stable contact portion between the bottom end of the rotation shaft and the thrust bearing as well as a stable contact portion between the side wall of the rotation shaft and the sleeve bearing, by canting the rotation shaft relatively to the sleeve bearing. The above mentioned embodiments relate to a motor for a floppy disc drive device. But it is understood that the present invention is applicable to a bearing of a generator. According to the present invention, the rotation shaft of a motor can be forcibly inclined with the rotation shaft and the sleeve bearing being kept in contact with each other. Therefore, it is possible to reduce deviation in inclination of the motor rotation shaft and to ensure electric conductance between the motor rotation shaft and the motor body. These advantages are attained by a specific structure in which a concave portion is provided on the thrust bearing, and therefore, the structure is simple and requires low costs.

Claims: An electrical rotating machine having a rotor and stator rotatable relatively to one another, the machine comprising a frame (8) mounting a stator yoke (5) which forms part of the stator; a cylindrical shaped sleeve bearing (7) mounted on the frame (8); a rotation shaft (1) supporting the rotor and having a curve shaped end and a diameter which is smaller than the inside diameter of the sleeve bearing (7) and rotatably supported in said sleeve bearing (7), and a thrust bearing (6) supporting the curve shaped end of the rotation shaft (1); characterised by the upper surface of the thrust bearing (6) being shaped (6a,6b) to provide a concave portion, which is offset from the centre line of the sleeve bearing (7), whereby the curve shaped end of the rotation shaft (1) rests in the concave portion with the rotation shaft inclined to the centre line of, and in contact with, the sleeve bearing, the inclination being stabilised by magnetic attraction between the stator and the rotor; and by a conductive path for static electricity from the rotor to the frame via the rotation shaft (1) and sleeve bearing (7). A machine according to claim 1, characterised in that at least one of the sleeve bearing (7) and the thrust bearing (6) is made from metal and is electrically connected to the frame (8). A machine according to claim 1 or claim 2, characterised in that the thrust bearing (6) is rotatable relatively to the sleeve bearing (7) for changing the angular position of the concave portion. A machine according to any one of the preceding claims, characterised in that the thrust bearing (6) is movable in the thrust direction of the rotation shaft (7) for adjusting the axial position of the rotation shaft. A machine according to claim 1 or claim 2, characterised in that the thrust bearing (6) is tightly fixed to the sleeve bearing (7). A generator according to any one of the preceding claims. A motor according to any one of the preceding claims.

Inventors: FUJITANI SAKAE, HARADA NAOYUKI, SUZUKI YUZURU, FUJITANI, SAKAE, HARADA, NAOYUKI, SUZUKI, YUZURU
Applicants: MINEBEA KK, MINEBEA CO., LTD.
Application year: 1995
Main classification: H02K5
IPC codes: H02K5, F16C17