GB2235330A

GB2235330A - Magnetic disc apparatus

Info

Publication number: GB2235330A
Application number: GB9013382A
Authority: GB
Inventors: Junichi Ikeda; Akiyuki Ogawa; Tsuneharu Ogasawara
Original assignee: Tokico Ltd
Current assignee: Tokico Ltd
Priority date: 1989-06-20
Filing date: 1990-06-15
Publication date: 1991-02-27
Also published as: JPH0386978A; DE4019654A1; GB9013382D0

Abstract

The invention is directed to a magnetic-head support structure in a magnetic disc apparatus, in which at least one magnetic head for writing and reading magnetic information with respect to at least one disc is mounted to a forward end of an arm which moves over a side of the disc. A pivot shaft is provided out of a rotational range of the disc, substantially in parallel with the disc. An elastic element in the form of a belt is wound about the pivot shaft. The elastic element is fixedly mounted to a part of the arm at a region except for a range within which the elastic element is wound about the pivot shaft, so that the elastic element is prevented from slipping in a circumferential direction of the pivot shaft. Rotation of the pivot shaft causes the arm, via the elastic element, to move in an angular motion over the disc surface. <IMAGE>

Description

MAGNETIC DISC APPARATUS

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a magnetic disc apparatus and, more particularly, to a structure of an arm for supporting a magnetic head. Background Art

Fig. 12 shows the conventional example of a magnetic disc apparatus. The reference numeral 10 denotes a base in the form of a box. A spindle motor (not Shown) is accommodated in the base 10. The spindle motor has a rotational shaft 12 which is oriented in a direction perpendicular to the drawing sheet of Fig. 12. A plurality of discs 14 are mounted to the rotational shaft 12 in a superimposed manner. Each of the discs 14 has a discoidal configuration as a whole, and at least front surface the disc 14 has a strong or intensive magnetism. The disc 14 is fixedly mounted to the rotational shaft 12 at a location adjacent a central axis of the disc 14. The disc 14 has its front and rear sides which are provided with a magnetized points and non-magnetized points, so that the disc 14 can record information in magnetically.

Recording of the magnetically written to the discs 14 and reading of recorded magnetically written from the discs 14 are practiced by a plurality of magnetic heads 16. Two magnetic heads 16 are provided at a corresponding each one of the discs 14, for the front side and for the rear side thereof. The plurality of magnetic heads 16 are mounted to one end of an arm 18. The arm 18 is supported for angular movement about a pivot shaft 20. Rotation moment is given to the arm 18 so that the arm 18 is operated about the pivot shaft 20 by a voice coil motor 22. The voice coil motor 20 comprises a coil 24 provided at the other end of the arm 18, and a pair of magnets 26 and 26 fixedly mounted to the base 10. The voice coil motor 22 can move the magnetic heads 16 along the surfaces of the respective discs 14 by a force acting between the coil 24 and the magnets 26.

1 In the magnetic disc apparatus, normally, one recording side (front side or rear side) of one of the plurality of discs 14 is utilized as a servo side, and position data are written to the servo side. A system, in which positions of the magnetic heads 16 are controlled on the basis of the position data written to the servo side, is called a servo-side servocontrol.

The servo control utilizing the position data written to the servo side is practiced on the assumption that the magnetic heads 16 provided for the servo side and the magnetic heads 16 for a data side provided on a disc side except for the servo side are in a predetermined positional relationship as viewed from the direction along the rotational shaft 12. Accordingly, in order to maintain the positional relationship, it is required that central axes of the angular movement of the respective arm 18 and pivot shaft 20 are strictly in agreement with each other.

Fig. 13 shows the conventional example of a support structure between the arm 18 and the pivot shaft 20. The arm 18 is supported by the pivot shaft 20 at two locations including a p#ir of bearings 24 and 24 which are provided respectively at upper and lower portions of the pivot shaft 20.

Each of the bearings 24 is composed of an inner ring 26, an outer ring 28 and a plurality of steel balls 30. The inner ring 26 is fixedly mounted to the pivot shaft 20. The outer ring 28 is fixedly mounted to the arm 18. The steel balls 30 are interposed between the inner ring 26 and the outer ring 28, and are rotated during relative rotation between the inner ring 26 and the outer ring 28.

In the support structure for the arm 18, in order for smooth rotation, slight clearances are required among the inner ring 26, the outer ring 28 and the steel balls 30. By presence of the clearances, however, there is a case where a central axis of the inner ring 26 and a central axis of the outer ring 28 are slightly shifted or deviated from each other. This shift or deviation causes shift or deviation between the central axis of the angular movement of the pivot 2 shaft 20 and the central axis of the angular movement of the arm 18, and damages the positional relationship between the magnetic head for the servo side and the magnetic head for the data side.

In order to avoid occurrence of the deviation due to presence of the clearances in the support structure, the following consideration has been made.

Resilient or elastic elemtints 32 are embedded in the outer periphery of the pivot shaft 20, and an elastic force acts upon each of the inner rings 26 in oneradial direction by a corresponding one of the elastic elements 32, to deform the inner ring 26 in the radial direction. A wave washer 34, which is bent as a whole into a corrugated configuration and which is capable of being elastically deformed in a thickness direction, is provided between the outer rings 28 and 28 of the respective upper and lower bearings 24 and 24. As shown in Fig. 14, forces Fr in the radial direction are applied respectively to the inner rings 26 by the elastic elements 32, while forces Fa in the thrust direction are applied respectively to the outer rings 28. Accordingly, the inner rings Z6, the balls 30 and the outer rings 28 are in point contact with each other at four locations.

However, the above-described support structure has the following problems:

(1) Since points of contact P, between the inner rings 26 and the balls 30 and points of contact P2 between the balls 30 and the outer rings 28 are deviated in the direction along the central axis of the pivot shaft 20, it cannot be avoided that the frictional resistance during rotation increases.

(2) If an external force is applied which is opposed to the forces Fr in the radial direction or to the forces Fa in the thrust direction, deviation occurs at the points of contact P, or P2, so that the arm 18 is going to fall down in accordance with the deviation. Accordingly, deviation occurs between the arm 18 and the central axis of the pivot shaft 20. Particularly, when the strong or powerful voice coil 3 motor is used in order to increase the moving velocity of the heads, large acceleration is applied to the arm 20 so that the aforementioned deviation increases.

The invention has been proposed in view of the above circumstances, and it is an object of the invention to provide a magnetic disc apparatus in which resistance during rotation is small, and it is possible to prevent positional deviation the pivot shaft and the arm.

SUMMARY OF THE INVENTION

In the invention, an elastic element in the form of a belt Is wound about a circumference of a pivot shaft, and the elastic element in the form of the belt is fixedly mounted to the pivot shaft at a part of a range within which the elastic element is wound about the pivot shaft, so that both ends of the elastic element in the form of the belt are fixedly mounted to a back plate. Accordingly, when the back plate tends to be moved angularly about the circumference of the pivot shaft, the elastic element does not slide in a circumferential direction with respect to the pivot shaft. Thus, the range, within which the elastic element is wound about the pivot shaft, moves. As a result, angular movement of the back plate is permitted. Such angular movement of the back plate is permitted by winding of the elastic element or by unwinding of the wound elastic element. Such angular movement differs from rotational movement like a ball bearing, but does not require clearances between various constitutional elements. Accordingly, deviation of a central axis of the angular movement is extremely small. When rotation moment is given to the back plate by driving means, at least one magnetic head supported by the back plate can be moved along a side of at least one disc.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a view as viewed from an axial direction of a pivot shaft according to a first embodiment of the invention; Fig. 2 is a view as viewed from the arrows II - II 4 1 in Fig.

Fig. 3 is a perspective view under a wound condition of an elastic element which is used in Fig. 1; Fig. 4 is a top plan view under a developed condition of the elastic element illustrated in Fig. 3; Fig. 5 is a view for explanation of equilibrium between a tension force and a support force of the elastic element illustrated in Fig. 3; Fig. 6 is a view as viewed from an axial direction of a pivot shaft section according to a second embodiment of the invention; Fig. 7 is a view of the second embodiment according to the invention, as viewed in the same direction as that in Fig. 2; Fig. 8 is a view as viewed from the arrows VIII VIII in Fig. 7; Fig. 9 is a top plan view of the entire arm supporting a magnetic head of a magnetic disc apparatus to which the support structure according to the invention is applied; Fig. 10 is a top plan view of a back plate used in the arm illustrated in Fig. 9; Fig. 11 is a side elevational view of the back plate illustrated in Fig. 10; Fig. 12 is a top plan view of the conventional magnetic disc apparatus; Fig. 13 is a longitudinal cross-sectional view of a pivot shaft section of the magnetic disc apparatus illustrated in Fig. 12; and Fig. 14 is a view for explanation of a deviation preventing system for bearings in the pivot shaft illustrated in Fig. 13.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Various embodiments of the invention will be described below with reference to the drawings. In this connection, in the drawings, components or parts common to those in the conventional example are designated by the same reference numerals, and the description of the common components or parts will be simplified.

Figs. 1 through 5 show a first embodiment of the invention.

An elastic element for supporting an arm of a magnetic disc apparatus will first be described with reference to Figs. 3 and 4.

The elastic element 40 has its top plan configuration as shown in Fig. 4, and is made of a thin metallic plate rich in spring characteristic such as, for example, stainless steel. The elastic element 40'is composed of a narrow-width section 42 and a wide-width section 44. The narrow-wIdth section 42 and the wide-width section 44 are arranged with their respective centers identical with each other. The wide-width section 44 is provided with a window 46 whose width dimension is slightly larger than the width of the narrow-width section 42. The window 46 is used such that the elastic element 40 is bent or flexed as shown in Fig. 3 to pass, through the window 46, the narrow-width section 42 from one side of the wide-width section 44 toward the other side thereof. Ends of the respective narrow-width and widewidth sections 42 and 44, and substantially a central portion of the elastic element 40 are formed respectively with bores 48, 50 and 52 through which bolts and so on pass when the elastic element 40 is fixedly mounted to other elements. Stuck to peripheral regions of the respective locations where the bores 48 and 50 are formed respectively in both ends of the elastic element 40 are a pair of reinforcing plates 54 and 56 for reinforcing the peripheral regions.

The elastic element 40 constructed as above is wound about the circumference of a pivot shaft 58 which is fixedly mounted vertically onto the base 10, as shown in Figs. 1 and 2. A bolt 60 is inserted through the bore 52 which is provided in the elastic element 40. Further, the bolt 60 is screwed into the pivot shaft 58. Accordingly, the elastic element 40 is fixedly mounted to the pivot shaft 58 by the bolt 60 at a single location substantially at the central area of the elastic element 40 in the longitudinal 6 1 1 i direction, whereby no slip occurs between the elastic element 40 and the pivot shaft 58.

The narrow-width section 42 has its forward end which passes through the window 46 and which is pulled out toward the opposite side of the elastic element 40. The pulled-out forward end of the narrow-width section 42 is fixedly mounted to a back plate 62. The back plate 62 has Its top plan configuration, that is, a configuration as shown in Fig. 2, which is a Cshaped configuration. The pulled-out forward end of the narrow-width section 42 is fixedly mounted to the rear side of the back plate 62, that is, to the side thereof opposite to the side thereof in contact with the pivot shaft 58. An engaging element 64 is fixedly mounted to the rear side of the back plate 62 by bolts 66. The engaging element 64 has its forward end which is provided with a spring element 67 capable of being elastically deformed. The spring element 67 is inserted through the bore 48 in the narrow-width section 42 and is hooked to the end of the narrowwidth section 42 under the elastically deformed condition. On the other hand, the wide-width section 44 has Its end which Is fixedly mounted to the front side of the back plate 62 by bolts 68.

In the support structure constructed as above, a tension force T acts upon the elastic element 40 by elastic deformation of the spring element 67. Accordingly, the elastic element 40 is wound about the pivot shaft 58 by the tension force T. At this time, as shown in Fig. 5, if it is assumed that an angle defined between the front side of the back plate 62 and the direction of the tension force T, that is, the direction of the narrow-width section 44 is B &AA, the force Fr, by which the back plate 62 is urged against the pivot shaft 58 is given by the following equation:

Fr T x sin 0 Further, it is assumed that a force generated by acceleration, that is, by the sum of acceleration of the voice coil motor, acceleration due to variation from the 7 outside and gravitational acceleration, acting upon the sum of masses of various components, for example, the arm, the magnetic head, the back plate, the elastic element, a post and so on, which are supported by the elastic element 40, is F 9 It is also assumed that a restoring force generated by the elastic element 40 under the bent or flexed condition is Fe Then, as far as the following equation holds, the elastic element 40 is maintained wound about the pivot shaft 58:

Fr > F 9 + Fe Accordingly, the back plate 62 is supported for pivotal movement about the pivot shaft 58.

Furthermore, a component force Fe in the tangent direction of the tension force T as indicated by F in Fig. 5 can be expressed as follows:

F e = T x cos d\ The component force FO acts equally upon both elements 70 and 72, shown in Fig. 4, which constitute the wide-width section 44, if the elements 70 and 72 are equal in width dimension to each other, because the elements 70 and 72 are equal in cross-sectional area to each other on the assumption that the elastic-element 40 is uniform in thickness.

Accordingly, tension forces Tl and T2 of the respective elements 70 and 72 satisfy the following equation:

T1 = T2 = F() Moreover, if consideration is made to in-plane moment M, that is, moment occurring in a plane at which the back plate 62 is in contact with the pivot shaft 58, the following equations hold:

T1 = 1/2F6 + M/a T2 = 1/2F E? - M/a 8 1 p where a is 1/2 of a center distance 2a between the elements 70 and 72 in Fig. 4. If, of T, and T2, any one taking a small value is positive, displacement of the back plate 62 in the aforesaid plane is due only to elastic deformation such as elongation of the elastic element 40, or deflection of the pivot shaft 58. Accordingly, relative displacement in the clockwise or counterclockwise direction between the back plate 62 and the pivot shaft 58 in Fig. 2 is brought to a minute value resulting from the elongation of the elastic elemdnt 40 and the deflection of the pivot shaft 58.

Fig. 6 shows a second embodiment of the invention.

A pivot shaft 80, which is applied to the second embodiment, has its cross-sectional configuration as shown in Fig. 6. That is, a part of an outer periphery of the pivot shaft 80 is formed into a planar surface section 82, and the remaining part of the outer periphery of the pivot shaft 80 is formed into a curved surface section 84 which is in the form of a curved surface whose radius of curvature is larger than an arc whose diameter is defined by the planar surface section 82. An elastic element 40 constructed similarly to the previous first embodiment is wound about the pivot shaft 80. The elastic element 40 is fixedly secured to the outer periphery of the pivot shaft 80 through a pair of welding sections which are designated respectively the reference numerals 86 and 88 in Fig. 6. In this connection, the welding sections 86 and 88 are provided out of a region in the outer peripheral surface of the pivot shaft 80, within which unwinding or winding of the elastic element 40 is practiced. Accordingly, the presence of the welding sections 86 and 88 does not hinder the winding and unwinding. The elastic element 40 is clamped between the pivot shaft 80 and the arm 18, and a bolt 90 is screwed into the planar surface section 82, whereby the pivot shaft 80 is fixedly mounted to the arm 18. Accordingly, the arm 18 can be moved angularly together with the pivot shaft 80. Further, in this second embodiment, the top plan configuration of the back plate 62 is formed into a rectangular configuration, and a reinforcing 9 rib 92 is fixedly secured to one side of the back plate 62, that Is, to a side thereof opposite to a side thereof where the pivot shaft 80 exists, whereby the rigidity of the back plate 62 Is raised.

in the second embodiment constructed as described above, the elastic element 40 is wound about or unwound from the curved surface section 84 of the pivot shaft 80, whereby the pivot shaft 80 and the arm 18 can be moved together angularly. Moreover, since the pivot shaft 80 is fixedly mounted to the arm 18 through the planar surface section 82, it can be ensured to connect the pivot shaft 80 and the arm 18 to each other. Further, since the elastic element 40 is deformed along the curved surface section 84 which is relatively large in radius of curvature, the bending stress generated in the elastic element 40 is small. Thus, it is possible to prevent fatigue destruction of the elastic element 40, and it is possible to reduce the force required for operating the arm 18.

Figs. 7 and 8 show a third embodiment of the invention.

A pivot shaft 100 according to the third embodiment is provided, at its upper and lower portions, with respective larger-diameter sections 101 and 102. The larger-diameter sections 101 and 102 can be rotated respectively along upper and lower sides 103 and 104 of the back plate 62. The larger-diameter sections 101 and 102 have their respective outer peripheral surfaces which project radially outwardly from the outer peripheral surface of the remaining section of the pivot shaft 100, that is, from an outer peripheral surface of a smaller-diameter section between the largerdiameter sections 101 and 102, by a dimension larger than the thickness of the elastic element 40. Accordingly, a clearance or gap, through which the elastic element 40 can pass, occurs between the outer peripheral surface of the pivot shaft 100 and the back plate 62.

With the above arrangement, the elastic element 40 is prevented from being clamped between the back plate 62 and the pivot shaft 100. Accordingly, the elastic element 40 can -1 be prevented from being damaged, or from being fatiguedestructed, so that the service life of the elastic element 40 can be prolonged.

Figs. 9 through 11 show an example as to how the support structure described above is applied to the arm which supports the magnetic heads.

The reference numeral 106 designates a back plate which has its function equivalent to that of the back plate 62 applied to each of the aforementioned embodiments. As shown in Fig. 9, a head support element 108 is motnted to one end of the back plate 106. A gimbal 110 is mounted to the forward end of the head support element 108. The magnetic heads 16 are mounted to the forward end of the gimbal 110. Further, connection between the back plate 106 and the head support element 108 and connection between the head support element 108 and the gimbal 110 utilize bolts 112. A coil 24, which is a part of the voice coil motor, is mounted to the other end of the back plate 106 by the bolts 112.

The back plate 106 has its configuration as shown in Figs. 10 and 11.

The reference numeral 114 designates a section which is superimposed upon a part of the head support element 108, and the section 114 is formed with female threaded bores 116 with which the bolts 112 are engaged respectively. The reference numeral 118 denotes a section which is superimposed upon a part of the coil 24, and the section 118 is formed with the female threaded bores 116 with which the bolts 112 are engaged respectively.

The back plate 106 is mounted to the pivot shaft 58 by the elastic element 40, similarly to the case of each of the previous embodiments. Accordingly, female threaded bores 120 are provided such that the bolts 68 for mounting of one end of the elastic element 40 are threadedly engaged with the female threaded bores 120, respectively. Further, female threaded bores 122 are provided such that the bolts 66 for mounting of the engaging element 64 are threadedly engaged with the female threaded bores 122, respectively.

With the magnetic disc apparatus constructed as 11 above, a range or region within which the elastic element 40 is wound about the pivot shaft 58 moves, and the back plate 106 is supported for angular movement about the center of the pivot shaft 58. Accordingly, a magnetic force is applied to the coil 24 which is united together with the back plate 106, whereby it is possible to move the magnetic heads 16 which are supported by the back plate 106 through the head support element 108 and the gimbal 110.

In connection with the above, the configuration of the elastic element 40 should not be limited to t4ose used in the above-described embodiments. For instance, it will be effective to consider the following factor.

That is, if consideration is made to the amount of elastic deformation of the elastic element, it is desirable for the width dimension of the widewidth section that the sum of the widths of elements forming the widewidth section is made in agreement with the width of the narrow-width section. By slightly reducing the sum of the widths on the side of the wide-width section less than the width on the side of the narrow-width section, however, the bending moment (refer to Fig. 5) generated at the pivot shaft due to the difference in the direction of the tension force between the narrow-width section and the wide-width section as shown in Fig. 5 may be balanced. Further, it is of course that the basic or fundamental function of supporting the arm in place of the bearings can be fulfilled, even if, an asymmetric configuration is taken in which a range extending from a fixed location toward the one end side and an area toward the other end side are not superimposed upon each other, for example, a configuration is taken in which one of the two elements constituting the wide-width section is omitted.

12 1

Claims

What is claimed is:

1. A magnetic-head support structure in a magnetic disc apparatus, in which at least one magnetic head for writing and reading magnetic information with respect to at least one disc is mounted to a forward end of an arm which moves along a side of said disc, characterized by comprising: a pivot shaft provided out of a rotational range of said disc, substantially In parallel with said disc; and an elastic element in the form of a belt, wound about said pivot shaft, wherein said elastic element is fixedly mounted to a part of said arm at a region except for a range within which said elastic element is wound about said pivot shaft.

2. The magnetic-head support structure for the magnetic disc apparatus, according to claim 1, characterized in that, said arm has a back plate to which said elastic element is fixedly mounted; and said magnetic head is supported on one end of said back plate,

3. The magnetic-head support structure for the magnetic disc apparatus according to claim 2, characterized that, wherein drive means is provided on the other end of said back plate, for applying rotation moment to said back plate.

4. The magnetic-head support structure for the magnetic disc apparatus, according to claim 3, characterized in that said elastic element has its both ends which are fixedly mounted to said back plate.

5. The magnetic-head support structure for the magnetic disc apparatus, according to claim 4, characterized in that a pair of reinforcing plates larger in thickness than 13 1 said elastic element per e are superimposed respectively upon the both ends of said elastic element.

6. The magnetic-head support structure for the magnetic disc apparatus, according to claim 4, characterized in that means for applying a tension force to said back plate is provided at fixed locations between said elastic element and said back plate.

7. The magnetic-head support structure forxthe magnetic disc apparatus, according to claim 5, characterized in that means for applying a tension force to said back plate is provided at fixed locations between said elastic element and said back plate.

8. The magnetic-head support structure for the magnetic disc apparatus, according to any one of claim 6, characterized in that said back plate is composed of a narrow-width section and a wide-width section, said widewidth section being composed of a pair of elements which are arranged in pa'rallel relation to each other with a spacing larger than a width of said narrow-width section left therebetween.

9. The magnetic-head support structure for the magnetic disc apparatus, according to any one of claim 7, characterized in that said back plate is composed of a narrow-width section and a wide-width section, said widewidth section being composed of a pair of elements which are arranged in parallel relation to each other with a spacing larger than a width of said narrow-width section left therebetween.

10. The magnetic-head support structure for the magnetic disc apparatus, according to claim 8, characterized in that a portion of said pivot shaft, about which said elastic element is wound, has its circular crosssectional configuration.

14 t

1 1 11. The magnetic-head support structure for the magnetic disc apparatus, according to claim 9, characterized in that a portion of said pivot shaft, about which said elastic element is wound, has its circular cross- sectional configuration.

12. The magnetic-head support structure for the magnetic disc apparatus, according to claim 10, characterized In that portions of said pivot shaft, which are In contact with said pair of elements of said wide-width section of said elastic element, have their respective outer diameters which are larger than that of the remaining portion of said pivot shaft.

13. The magnetic-head support structure for the magnetic disc apparatus, according to claim 11 or 12, characterized in that a portion of said pivot shaft, about which said elastic element is wound, has its circular crosssectional configuration.

14. The magnetic-head support structure for the magnetic disc apparatus, according to claim 8, characterized in that a portion of said pivot shaft, about which said elastic element is wound, has a cross-sectional configuration which is composed by a straight section, and a curved section whose radius of curvature is larger than an arc whose diameter is defined by said straight section.

15. The magnetic-head support structure for the magnetic disc apparatus, according to claim 9, characterized in that a portion of said pivot shaft, about which said elastic element is wound, has a cross-sectional configuration which is composed by a straight section, and a curved section whose radius of curvature is larger than an arc whose diameter is defined by said straight section.

16.

The magnetic-head support structure for the magnetic disc apparatus, according to any one of claim 14, characterized in that said elastic element is made of a metallic plate.

17. The magnetic-head support structure for the magnetic disc apparatus, according to any one of claim 13, characterized in that said elastic element is made of a metallic plate.

18. The magnetic-head support structure for the magnetic disc apparatus, according to any one of ciaim 15, characterized in that said elastic element is made of a metallic plate.

19. The magnetic-head support structure substantially as herein described with reference to and as shown in the accompanying drawings.

16 Published 1991 at The Patent Office, State House, 66/71 High Holborn. LondonWCIR41P. Further copies may be obtained from Sales Branch. Unit 6. Nine Mile Point, Cwmfelinfach. Cross Keys. Newport. NPI 7HZ. Printed by Multiplex techniques ltd. St Mary Cray. Kent.