Abstract:
A rotational bearing system incorporates a ball bearing to support a freely rotatable shaft or housing through rolling contact with the ball bearing, the rotational bearing system comprises: vibratory elements adapted to excite in resonant vibration a fixed shaft or a fixed housing in rolling contact with the ball bearings to lower the frictional resistance of the ball bearing.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a rotational bearing system which is suitably applicable, for example, to a hard disk head access mechanism or the like. 
     More specifically, this invention concerns a rotational bearing system using ball bearings for rotatably supporting a shaft or a housing, the bearing system including means to vibrate a shaft or a housing, whichever is stationary to reduce the frictional resistance of the bearing to a marked degree. 
     2. Description of the Prior Art 
     Shown in FIG. 18 is the construction of a head access mechanism in a conventional hard disk device, including a swing arm 5 rotatably mounted on an arm bearing assembly 4 for rotational movements relative to a magnetic memory medium or a hard disk 3 mounted on a base 2. A magnetic head 7 is mounted on the fore distal end of the swing arm 5 through a head suspension 6. 
     A voice coil motor 8 is mounted on the rear end of the swing arm 5 away from the magnetic head 7. The swing arm 5 is rotationally driven according to a tracking control signal which is supplied to the voice coil motor 8, moving the magnetic head 7 across the recording tracks formed on the magnetic memory medium 3, to access track information recorded on the magnetic memory medium 3. 
     As shown in FIG. 19, the arm bearing 4 has its housing 15 rotatably supported on a fixed shaft 13 which is planted on a base member 11 by means of a fitting screw 12, through ball bearings 14 which are arranged around the fixed shaft 13. The swing arm 5 is fixedly mounted, for example, on the upper end of the housing 15. 
     With the hard disk head access mechanism of the above-described construction, in case the track pitch between the respective recording tracks on the magnetic memory medium 3 is minimized to increase the recording density, the accuracy of controlling the position of the magnetic head 7 has to be improved to a range of fine movements on the order of submicrons. 
     For fine and high-speed control of the position of the magnetic head 7, it is important to reduce the frictional resistance of the ball bearings 14 of the arm bearing 4. For instance, if the ball bearings 14 have a large frictional resistance, correct tracking control of the magnetic head 7 becomes difficult due to lack of linearity between the tracking servo signal which is supplied to the voice coil motor 8 for a fine displacement of the magnetic head 7 and the actual magnetic head displacement. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, the present invention has as its object the provision of a rotational bearing system of the type employing ball bearings for supporting a rotational shaft or a rotatable housing and which is arranged to reduce the frictional resistance of the bearing markedly to realize high-speed servo characteristics. 
     In accordance with the present invention, there is provided a rotational bearing system incorporating ball bearings to support a shaft or housing in freely rotatable state through rolling contact with the ball bearing, the rotational bearing system comprising: vibratory elements adapted to excite in resonant vibration a fixed shaft or a fixed housing in rolling contact with the ball bearings thereby lowering the frictional resistance of the ball bearing. 
     By exciting in a predetermined resonance mode a fixed shaft or a fixed housing, which forms a stationary member in rolling contact with the ball bearings, the frictional resistance of the bearings relative to the rotatable housing or rotational shaft can be markedly lowered, permitting accurate control of fine movements of an object of control with satisfactory linearity. 
     The above and other objects, features and advantages of the invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings which show by way of example preferred embodiments of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings: 
     FIG. 1 is a schematic plan view of a bearing system embodying the present invention; 
     FIG. 2 is a sectional view of an arm bearing assembly, taken on line II--II of FIG. 1; 
     FIG. 3 is a plan view of the fixed shaft shown in FIG. 2; 
     FIG. 4 is a perspective view of the fixed shaft shown in FIG. 2; 
     FIG. 5 is a diagrammatic illustration of a drive circuit for piezoelectric members; 
     FIG. 6 is a sectional view of the fixed shaft, employed for explanation of a resonant excitation mode of the fixed shaft; 
     FIG. 7 is a sectional view of the fixed shaft, employed for explanation of a resonant excitation mode of the fixed shaft; 
     FIGS. 8A-B are signal waveform diagrams showing results of experiments; 
     FIGS. 9A-B are signal waveform diagrams showing results of experiments; 
     FIG. 10 is a schematic plan view showing another embodiment of the rotational bearing system according to the present invention; 
     FIG. 11 is a sectional view of the bearing system, taken on line XI--XI of FIG. 10; 
     FIGS. 12A-B are signal waveform diagram showing results of experiments; 
     FIGS. 13A-B are signal waveform diagram showing results of experiments; 
     FIG. 14 is a sectional view of a modification of the fixed shaft for an internally excited type bearing system; 
     FIG. 15 is a sectional view of a modification of the fixed shaft for an internally excited type bearing system; 
     FIG. 16 is a diagrammatic plan view of a modification of the externally excited type bearing system; 
     FIG. 17 is an exploded perspective view of a modification of fulcrum projections; 
     FIG. 18 is a schematic plan view of a hard disk head access mechanism; and 
     FIG. 19 is a schematic plan view of a conventional bearing system. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Hereafter, the invention is described more particularly by way of the preferred embodiments shown in the drawings. 
     Referring to FIGS. 1 through 4, there is shown a first embodiment incorporating the invention into an internally excited type bearing system, wherein the component parts common to the conventional counterpart of FIG. 18 are designated by common reference numerals. In this embodiment, the arm bearing 4 assembly which rotatably supports the swing arm 5 on the base 2 includes a fixed shaft 21 which is fixed on the base 2, and a rotatable housing 23 which is rotatably mounted on the fixed shaft 21 through ball bearings 22H and 22L which are provided at the upper and lower ends of the fixed shaft 21. 
     In this embodiment, the swing arm is fixedly mounted by screws 25 on a flange portion 24 which is extended outward from the upper end of the rotatable housing 23. 
     The fixed shaft 21 is fixedly planted on the base 2 by threading a screw 29 into a tapped hole 31 in the base 2 through a bore 30 in the fixed shaft 21, interposing a pair of spacers 26H and 26L in abutting engagement with the upper and lower end faces of the fixed shaft 21, respectively, and a ring washer 27 and a spring washer 28 under the screw head. 
     As shown in FIG. 3, the fixed shaft 21 is formed with an axial center bore 30 substantially of a square shape in section, and has piezoelectric members 31A to 31D bonded on the inner surfaces of the four side walls of the bore 30, for example, by the use of an epoxy adhesive. 
     The piezoelectric members 31A to 31D are each formed of a strip-like piezoelectric material with a silver electrode bonded on each side by a baking treatment, and are inversely polarized relative to the adjacent piezoelectric members as shown in FIG. 5. 
     The outer silver electrode surfaces of the piezoelectric members 31A to 31D are bonded to the inner wall surface of the fixed shaft 21 by an epoxy adhesive to form equivalent circuits (FIG. 5) which are electrically commonly connected to the fixed shaft 21. 
     The silver electrodes on the inner side of the piezoelectric members 31A to 31D are commonly connected to a lead wire 32. The oscillating output of a resonance drive power source 33 (e.g., of a frequency of 90 kHz) is supplied between the lead wire 32 and the fixed shaft 21 through a drive control circuit 36 which is controlled by drive control signal S1 applied from a system control circuit (not shown), thereby causing the piezoelectric members 31A to 31D to vibrate at the resonance frequency. 
     In this particular embodiment, a spring 35 which is interposed between the ball bearings 22H and 22L permits the latter to deviate in the upward and downward directions upon imposition of pressure, thereby suppressing the so-called &#34;fluttering&#34; of the ball bearings 22H and 22L. 
     With the foregoing construction, as the piezoelectric members 31A to 31D are driven at a high frequency by the oscillating output of the resonance drive power source 33, each pair of the opposingly located piezoelectric members, 31A and 31C, 31B and 31D, which are polarized in the opposite directions (in the outward or inward direction) are put in electrostrictive actions in these directions. As a result, as shown in FIG. 7 the wall surfaces 37A to 37D which are bonded respectively to the piezoelectric members 31A to 31D resonate, generating standing waves of double wavelength with a node at junction points 38. 
     In such a state of resonant excitation, as shown schematically in FIG. 7, the fixed shaft 21 can be put in resonant vibrations having alternately a first deformation mode indicated by the solid line where the it tends to expand in the direction of a pair of opposing piezoelectric members 31A and 31C, and a second deformation mode indicated by a broken line where it tends to expand in the direction of the other pair of piezoelectric members 31B and 31D. 
     If a tracking servo signal is supplied to the voice coil motor 8 while vibrating the arm bearing assembly 4 in such vibration modes, the frictional resistance of the ball bearings 22H and 22L relative to the swing arm 5 is reduced markedly, thereby significantly improving the linearity of fine movements of the swing arm 5 and thus of the magnetic head 7 relative to the tracking servo signal, as compared with the conventional counterpart. 
     According to the results of experiments, the resonance frequency of the fixed shaft 21 was 86 kHz in a case employing, as the fixed shaft 21, a 6 mm (diameter)×15 mm (length) metal cylinder internally formed with the bore 30 and having 2.7 mm×15 mm×0.2 mm piezoelectric members 31A to 31D bonded on the inner wall surfaces thereof. 
     It has also been confirmed that, as a driving force is applied by the voice coil motor 8 for a fine drive of the swing arm 5 which is supported on the arm bearing assembly 4 with the fixed shaft 21, the frictional resistance can be significantly lowered by the resonant excitation of the fixed shaft 21 as compared with operations without the resonant excitation. 
     Specifically, it has been confirmed that the magnetic head 7 is displaced by a distance L 1  as shown in FIG. 8(B) when a drive signal S2 in the form of a stepwise varying current I T1  is applied to the voice coil motor 8, as shown in FIG. 8(A), without the resonant excitation of the fixed shaft 21, while the magnetic head 7 is displaced by an about three times greater distance L 2  as shown in FIG. 9(B) when the same drive signal S2 of the stepwise varying current I T1  is applied as shown in FIG. 9(B), to put the fixed shaft 21 in resonant excitation. 
     This implies that the resonant excitation of the fixed shaft 21 by the internal excitation has an effect of reducing to about 1/3 the frictional resistance of the fixed shaft 21 and the rotatable housing 23 which are in rolling contact with the ball bearings 22H and 22L. 
     As seen particularly in FIGS. 2 to 4, the fixed shaft 21 is provided with four fulcrum projections 39H or 39L on the upper and lower end faces in positions corresponding to the nodes 32, thereby spacing apart the vibratory portions of the wall surfaces 37A to 37D from the spacers 26L or 26H, which would otherwise interfere with the resonant actions of the wall portions 37A to 37D. 
     Referring to FIGS. 10 and 11, there is shown a second embodiment in which the invention is applied to an externally excited type bearing system and wherein the component parts common to FIG. 18 are designated by common reference numerals. In this embodiment, the arm bearing assembly 4 is arranged to drive a swing arm 5 by a rotational shaft which is rotatable relative to the base 2. 
     More specifically, a hexagonal shaped fixed housing 44 with a bore 43 of a circular shape in section is erected on a base member 42 which is fixed on the base 2 by set screws 41. The upper end of the housing 44 is fixed in position by means of a stationary member 45 which is fixed to the base 2 by set screws 46. 
     Received in the bore 43 of the fixed housing 44 is a rotational shaft 47 which is rotatably supported by ball bearings 47H and 47L at the upper and lower ends of the bore 43. The swing arm 5 is integrally fixed to outwardly projected end 47X of the rotational shaft 47 by a set screw 49 through a spacer 48. Indicated at 50 is a spring which is interposed between the ball bearings 47H and 47L to suppress fluttering of the ball bearings. 
     Piezoelectric members 55A to 55F are bonded on outer surfaces of the six side walls of the fixed housing 44 to excite the wall surface portions 56A to 56F in resonance. 
     In this case, the adjacent piezoelectric members 55A and 55B, 55B and 55C, 55C and 55D, 55D and 55E, 55E and 55F and 55F and 55A are polarized opposite each other by a polarization treatment to excite the fixed housing 44 in resonance in a mode in which standing or stationary waves of triple wavelength are generated in the wall surface portions 56A to 56F with a node at junctions 57 between the adjacent piezoelectric members. 
     With the arrangement of FIGS. 10 and 11, the frictional force of the ball bearings 47H and 47L which are inserted between the fixed housing 44 and rotational shaft 47 can be reduced in the same manner as in the first embodiment of FIGS. 1 through 9, except that the resonant excitation is induced from outside of the fixed housing 44. It follows that the frictional resistance of the bearings can be lowered markedly as compared with the conventional counterpart. 
     In this embodiment, six fulcrum projections 58H or 58L are provided on the upper and lower end faces of the fixed housing 44 in positions corresponding to the nodes 56. These fulcrum projections 58H and 58L are abutted against the stationary member 45 and base member 42, spacing the wall surface portions 56A to 56F from the stationary member 45 and base member 42 to excite the wall surface portions 56A to 56F efficiently in resonance free of interference by the stationary and base members 45 and 42. 
     According to the results of experiments, in case of a hard disk device 1 employing the arm bearing assembly 4 with a fixed housing 44 of a resonance frequency of 64 kHz, the magnetic head 7 showed a response action as shown in FIG. 12(B), namely, a displacement by a distance L 11  when a drive signal S2 with a drive current value of I T2  was supplied to the voice coil motor 8 as shown in FIG. 12(A) without external resonant excitation by the piezoelectric members 55A to 55F on the fixed housing 44. In contrast, when the same drive signal S2 with a drive current value of I T2  was supplied to the voice coil motor 8 as shown in FIG. 13(A) with resonant excitation of the piezoelectric members 55A to 55F on the fixed housing 44, the distance of displacement L 12  of the magnetic head 7 became about 4.5 times greater than the distance L 11  in an unexcited state, as shown in FIG. 13(B). 
     The above-described embodiments of the invention are open to various modifications and alterations as follows. 
     (1) In the first embodiment shown in FIGS. 1 to 4, the fixed shaft 21 is shown as having a bore of a substantially equilateral square shape in cross-section. However, it may be replaced by a bore of a substantially equilateral hexagonal shape as shown in FIG. 14 or of other polygonal shape with a larger number of angles. 
     In the embodiment of FIG. 14, six piezoelectric members 61A to 61F are bonded on the six surfaces 61A to 61F of the hexagonal side walls to excite the wall surface portions 61A to 61F in resonant state generating stationary waves of a triple wavelength with nodes at the junctions 62 between the respective adjacent piezoelectric members. 
     The arrangement of FIG. 14 produces the same effects as described hereinbefore in connection with the embodiment of FIGS. 1 to 4. 
     (2) In place of the square bore 30 of FIGS. 1 to 4, the fixed shaft 21 may be provided with a circular bore as shown in FIG. 15. In this case, four piezoelectric members 65A to 65D are mounted on the circular inner wall surface symmetrically in 90° angular positions such that each piezoelectric member faces another piezoelectric member, to excite the wall surface portions 66A to 66D in resonance generating standing waves of double wavelength with nodes at the joints 67 between the respective adjacent piezoelectric members. 
     The arrangement of FIG. 15 can also produce the same effects as the embodiment of FIGS. 1 to 4. 
     (3) If desired, the fixed housing 44 of FIGS. 10 and 11 with a substantially equilateral hexagonal outer shape may be replaced by a housing of a square shape as shown in FIG. 16 or of other shapes. In case of the square housing of FIG. 16, four piezoelectric members 71A to 71D are bonded on the surfaces of the four side walls thereby to excite the contacting wall surface portions 72A to 72D in resonance generating standing waves of double wavelength having a node at the junctions between the respective adjacent piezoelectric members. 
     The arrangement of FIG. 16 likewise produces the same effects as described hereinbefore in connection with FIGS. 10 and 11. 
     (4) In the embodiment of FIGS. 1 to 4, the fulcrum projections 39H and 39L are provided on the upper and lower end faces of the fixed shaft 21 in the positions corresponding to the nodes 38. Alternatively, the same effects can be obtained by providing the fulcrum projections 71H and 71L on the surfaces of the spacers 26H and 26L which are in abutting engagement with the upper and lower end faces of the fixed shaft 21 as shown in FIG. 17, instead of providing them on the fixed shaft 21. 
     With regard to the alternative location of the fulcrum projections, the same applies to the fulcrum projections 58H and 58L for the fixed housing 44 of FIGS. 10 and 11 to be excited in resonance. Namely, instead of providing the fulcrum projections 58H and 58L on the fixed housing 44, they may be provided on the part of the stationary member 45 and base member 42 to be held in abutting engagement with the upper and lower end faces of the fixed housing 44. 
     (5) Although the present invention is applied to a bearing system for a hard disk magnetic head access mechanism in the foregoing embodiments, the invention is applicable to ball bearing type rotational bearings in general. 
     (6) In the foregoing embodiments, the fixed shaft 21 or the fixed housing 44 is excited into resonance regardless of whether the rotational drive of the swing arm 5 is activated. However, if necessary, the excitation may be caused by conventional means to cease when the swing arm 5 is at rest. 
     (7) There may be employed vibratory elements other than the piezoelectric members of the above-described embodiments. 
     (8) Irrespective of the particular number of the piezoelectric members used in the foregoing embodiments, similar effects of resonance can be obtained by the use of one or more piezoelectric members. 
     (9) Although the resonant excitation is a method of high power efficiency in driving the vibratory elements, the effects of the invention can be produced by excitation other than at the resonant mode. 
     It will be appreciated from the foregoing description that, according to the present invention, a ball bearing type rotational bearing system with a markedly reduced frictional resistance can be realized by exciting in resonance a shaft or housing which is formed of a stationary member in rolling contact with the ball bearing.