Magnetic Head Assembly Having Consistent Track Pitch

1. Field of the Invention

This invention relates to a magnetic head assembly to be used with a magnetic disc drive device for writing and reading data to and from both sides of a flexible magnetic disc such as so called a floppy disc.

2. Prior Art

External data storage devices using flexible magnetic discs such as so called floppy discs as recording media are widely used for data processing equipments including word processors and personal computers. Recently magnetic discs whose both sides can be used for storing data have become popular.

FIG. 5 of the accompanying drawings shows the configuration of a typical drive device that can be used with two-sides recording magnetic discs. As shown in FIG. 5, the device comprises a magnetic head assembly 101, which further comprises magnetic head carriage 102 and an arm, said magnetic head assembly 101 being moved radially to the two sided recording magnetic disc 105 being used along a guide shaft 104 by a pulse motor which is not shown.

Said magnetic head carriage 102 is made of electrically non-conductive synthetic resin and provided with a magnetic head fitting member 102a at its front end and a support member 102b projecting upward magnetic head fitting member 102a provided at its rear end. In FIG. 5, reference numeral 107 denotes a lower magnetic head 107 which is fitted to said magnetic head fitting member 102a by way of a mold case 108. Reference numeral 109 denotes a lead wire extending from said lower magnetic head 107, said lead wire 109 being connected with another lead wire 111 for external connection via a junction terminal 110.

An arm 103 is realized by molding electrically non-conductive synthetic resin in the form of a plate which is shorter than the magnetic head carriage 102 and comprises a portion of a leaf hinge spring 112 which is integrally buried therein. The arm 103 is swingably fitted to said magnetic head carriage 102 by screwing the tip of said leaf hinge spring 112 to said support member 102b. In FIG. 5, reference numeral 113 denotes a screw for screwing said leaf hinge spring 112 and reference numeral 115 a spacer while reference numeral 116 denotes a metal fixture.

Reference numeral 117 denotes a upper magnetic head which is fitted to a gimbals spring 118 which is securely fitted to the arm 103 so that it faces vis-a-vis the lower magnetic head 107 mounted on said magnetic head carriage 102. Reference numeral 119 denotes a pivot that comes to be engaged with said gimbals spring 118 from behind and reference numeral 120 denotes a lead wire extending from said upper magnetic head 117 and connected with a lead wire 122 for external connection by way of a flexible print substrate 121. Reference numeral 123 denotes a pusher spring provided between said metal fixture 116 and the arm 103 to elastically and constantly bias said arm 103 toward the magnetic head carriage 102 so that the magnetic disc 105 is held by said upper magnetic head 107 and lower magnetic head 117 from both sides.

With a magnetic head assembly 101 which is configured as described above, if it is not loaded with a magnetic disc, the arm 103 is moved upward by a lifting mechanism which is not shown and held at a position which it reaches when it is pivoted around the leaf hinge spring 112 in the direction indicated by arrow F so that the upper magnetic head 117 is separated from the lower magnetic head 107 by a predetermined distance.

On the other hand, when a magnetic disc 105 is loaded between the upper magnetic head 117 and the lower magnetic head 107 and clamped there, consequently the arm 103 is released from the lifted and held condition and pushed downward by the resilient force of the pusher spring 123. The magnetic disc 105 is held by the upper magnetic head 117 and the lower magnetic head 107 on both sides and becomes ready for recording and reading data to and from the magnetic disc 105.

In order to ensure stable recording and reading operations with a magnetic head assembly of this type, it may be needless to say that the pressure applied to a magnetic disc 105 by the upper magnetic head 117 and the lower magnetic head 107 to hold the magnetic head 105 has to be maintained at a constant level.

However, with a magnetic head assembly 101 of the prior art as described above, since the arm 103 is held only by the leaf hinge spring 112 at its one end, if the magnetic head assembly 101 is subjected to a force of vibration or shock, the vertical element of the force (along line Z--Z in FIG. 5) effects a large moment of inertia to the arm 103 with its fulcrum located at the leaf hinge spring 112 so that the pressure applied to the magnetic disc 105 by the upper magnetic head 107 and the lower magnetic head 117 can significantly fluctuate.

If the upward inertia of the arm 103 is greater than the pressure applied to the magnetic disc 105 by the upper magnetic head 117 and the lower magnetic head 107, the magnetic disc 105 separates from the magnetic heads 107 and 117 which interferes with the recording or reading operation which is going on. Moreover, if the pressure applied to the magnetic disc 105 by the upper magnetic head 117 and the lower magnetic head 107 fluctuates for any reason, the recording or reading operation at hand will be adversely affected as the magnetic disc 105 can vibrate in the direction of rotation or rotate at varied speeds because of a variation in the friction between the magnetic disc 105 and the magnetic heads 107 and 117 even when the heads are securely pressed against the disc.

With a view to eliminate these problems, the applicant of the present invention has proposed in the Japanese Patent Application No. 62-62559 a magnetic head assembly that operates stably for data recording and reading even when it is subjected to a vibration or shock force. This proposed magnetic head assembly comprises an arm which is provided to support an upper head device and other upper members in such a manner that it can swingably move relative to a magnetic head carriage, that its fulcrum of swinging movement of the arm is positioned approximately at its middle point, a balancer is provided on the arm at a position nearer to the rear end than the fulcrum in order to balance the front and rear portions of the arm and a biasing means such as a spring is provided to maintain the pressure applied to the magnetic disc by the magnetic head assembly.

With a magnetic head assembly having an arrangement as described above, the vibration of the arm caused by an external force can be minimized, however, the assembly is accompanied by certain drawbacks.

More specifically with such a magnetic head assembly, the upper and lower magnetic heads have to be so arranged that a gap which is equal to the width of four or eight tracks is accurately provided therebetween. When the two heads are assembled, the upper magnetic head is correctly positioned by moving it relative to the lower magnetic head and utilizing positioning bores prepared on the upper magnetic head. Now, during the operation of the positioning, the upper magnetic head is subjected to a force which pushes it to the lower magnetic head and is greater than the force which is normally exerted on the upper magnetic head to push it toward the lower magnetic head so that the track pitch between the upper and lower heads can be varied from that of normal reading and reproducing operations. Moreover, if the pressure applied to the magnetic head is varied in the course of time due to variation in rotational friction of the fulcrum of the arm, it can result in variation of the track pitch between the upper and lower heads. Particularly if the fulcrum of the arm is located above the upper magnetic head with a view to avoid interference between the arm and a case of the magnetic disc at the time of loading the magnetic disc, there can occur a large positional deviation of the upper magnetic head in the radial direction of the magnetic disc in response to the rotation of the arm and consequently the above mentioned deviation of the track of the upper magnetic head can become significant even when the swinging displacement of the arm is very small.

Therefore, it is an object of the present invention to provide a magnetic head assembly which is free from any variation of track pitch between the upper and lower magnetic heads during assembling and normal recording and reading operations.

The above described problems of the prior art are solved and the above object and other objects of the present invention are achieved by providing a magnetic head assembly, wherein an arm for supporting an upper magnetic head is connected to a magnetic head carriage for supporting a lower magnetic head by way of a fulcrum of the arm so that said arm and the upper magnetic head fitted thereto can be swingably displaced to move toward or away from said lower magnetic head and said arm is provided with a biasing means to bias said upper magnetic head toward said lower magnetic head and a stopper means to define the position of the upper magnetic head nearest to the lower magnetic head.

With such an arrangement as described above, the upper magnetic head is secured against any undesired downward displacement from the defined lowest position due to a force applied to the movable arm and the upper magnetic head upper magnetic head attached thereto by means of a stopper. Therefore, if the position of the upper magnetic head closest to the lower magnetic head is accurately defined, any displacement of the upper magnetic head relative to the lower magnetic head after adjustment of the track pitch and/or during normal operation of the assembly is completely eliminated.

Now the invention will be described by referring to the accompanying drawings that illustrate a preferred embodiment of the invention.

FIG. 1 is a perspective view of a magnetic disc drive apparatus using a magnetic head assembly according to the invention;

FIG. 2 is a lateral view of the magnetic disc drive apparatus of FIG. 1;

FIG. 3 is a plan view of an upper magnetic head unit;

FIG. 4 is a sectional side view of the upper magnetic head unit of FIG. 3; and

FIG. 5 is a sectional side view of a magnetic disc drive apparatus of the prior art.

Referring to FIGS. 1 and 2, reference numeral 1 denotes a magnetic head assembly, said magnetic head assembly 1 being provided with a lower magnetic head unit 2 and a carriage 5 that can be linearly moved along a guide shaft 3 in the radial direction of the magnetic disc 4, said carriage 5 being provided with upper magnetic head unit 6 and an arm 8 which is supported by a swing shaft 7 being swingably supported relative to the carriage 5.

Said carriage 5 is realized in the form of a thin plate made of an aluminum alloy and comprises a fitting member 10 realized by forming an opening at the front end thereof for fitting lower magnetic head unit 2 thereto. Reference numeral 9 denotes a substrate of the assembly having arm fitting plate members 11a, 11b which are formed by folding up the two lateral end portions of the substrate. Shaft bearing bores 12a, 12b are respectively provided on the arm fitting plate members 11a, 11b for bearing the swing shaft 7.

On the other hand, the arm 8 comprises a fitting member 13 at its front end for the upper magnetic head unit 6 realized by forming an opening similar to the fitting member 10 of said carriage 5, an upwardly inclined portion 14 at its center and a horizontal portion 15 whose level is higher than that of said fitting member 13 nearer to its base. The inclined portion 14 comprises plate members for fitting 16a, 16b which are formed by folding up its corresponding areas and said plate members for fitting 16a, 16b are also provided respectively with shaft bearing bores 17a, 17b for bearing swing shaft 7. It should be noted that the shaft bearing bores 17a, 17b are located near the center of gravity of the arm 8. The swing shaft 7 is passed through the shaft bearing bores 12a, 12b provided on the arm fitting plate members 11a, 11b by way of the shaft bearing bores 17a, 17b so that the arm 8 is swingably supported by the carriage 5.

A coil spring 20 is resiliently positioned between the horizontal portion 15 of the arm 8 and the carriage 5 and the arm 8 is biased in the direction where the upper magnetic head unit 6 is pushed toward lower magnetic head unit 2. Thus, a predetermined pressure is always applied to the upper magnetic head unit 6 and the lower magnetic head unit 2 by the coil spring 20. Besides, a horizontal plate member 21 is connected to the arm fitting plate members 11b of arm 8 at its upper area and a rod screw 22 for the stopper is screwed into said horizontal area 21. The rod screw 22 comes to abut the arm 8 at a position which is directly opposite to the coil spring 20 so that the lowest position of the upper magnetic head unit 6 on the arm 8 is defined by said coil spring 20. Moreover, the lowest position of the upper magnetic head unit 6 can be redefined by appropriately rotating said rod screw 22.

As illustrated in FIGS. 3 and 4, said upper magnetic head unit 6 comprises a magnetic head 30 which consists of a head slider comprising a read/write core having a read/write gap and said magnetic head 30 is bonded to a flat spring plate located at the center of a circular gimbals spring 31, while the circular peripheral area of said gimbals spring 31 is welded to a semi-spherical main body 32 of the head by laser beam welding or some other appropriate technique. The main body 32 carries alignment recesses 35, 35 for engagedly receiving an alignment rod for aligning a magnetic head 34 of the lower magnetic head unit 2 having a configuration similar to that of the upper magnetic head unit 6.

The embodiment having a configuration as described above is basically not different from any magnetic head assembly of the prior art in terms of function. More specifically, when a magnetic disc is not loaded, the inclined portion 14 of the arm 8 is held horizontal. On the other hand, when a magnetic disc 4 is loaded, said disc is held at its both ends by the magnetic heads 30, 34 so that it is ready for data recording or reading.

To assembly the magnetic head assembly 1, the carriage 5 is bonded to the arm 8 and the shaft bearing bores 12a, 12b of the arm fitting plate members 11a, 11b of the carriage 8 and the shaft bearing bores 17a, 17b of the plate members for fitting 16a, 16b of the arm 8 are aligned so that the swinging shaft 7 can run through all the bores. At the same time, the coil spring 20 is loaded between the carriage 5 and the arm 8. Thereafter, the lower magnetic head unit 2 is mounted to the fitting member 10 of the carriage 5, while the upper magnetic head unit 6 is mounted to the fitting member 13 of the arm 8, At this stage, while the lower magnetic head unit 2 may be rigidly fitted to the carriage 5, the upper magnetic head unit 6 should be loosely fitted to the arm 8.

Then, the rod screw 22 is screwed until its tip gets to the read/write position sc, that a correct gap is realized for a magnetic head 2 to be loaded between the magnetic head 30 of the upper magnetic head unit 6 and the magnetic head 34 of the lower magnetic head unit 2.

Under this condition, the alignment rod is placed in the alignment recess 35 provided on the upper magnetic head unit 6 to adjust the track pitch of the magnetic head 30 of the upper magnetic head unit 6. Then, the magnetic head 30 is precisely positioned so that a distance equal to the width of four (4) or eight (8) tracks is accurately provided between itself and the magnetic head 34 of the lower magnetic head unit 2 in the radial direction of the magnetic disc 4. Although the upper magnetic head unit 6 is subjected to a force directed to the lower magnetic head unit 2 and exerted by the alignment rod during this positioning operation, the upper and lower magnetic heads 30 and 34 are free from any variation of the track pitch due to undesired movement of the upper magnetic head unit 6 after the positioning operation because any further vertical movement of the upper magnetic head unit 6 is prohibited by the rod screw 22.

After the correct adjustment of the track pitch between the upper and lower magnetic heads 30, 34, the force of rotational friction of the swinging shaft 7 may vary with time if the magnetic disc drive apparatus is run for a long time. However, even if such a condition arises, the track pitch can not be varied by the pressure of the upper magnetic head 30 because the lowest position of the upper magnetic head unit 6 is strictly defined by the rod screw 22.

As is apparent from the above description, in a magnetic head assembly according to the invention, the upper head device is biased toward the lower head device by a bias means while the lowest position of the upper head device where it comes closest to the lower head device is strictly defined by the stopper means so that a correct gap is realized between the two head devices. Consequently, even if the upper head devices is subjected to adjustment operations for the track pitch while it is under pressure, the upper head device is completely free from any displacement after the adjustment operations and variations of the track pitch due to variations of the pressure applied to the magnetic disc by the upper head device. As is apparent from the above description, in a magnetic head assembly according to the invention, the upper head device is biased toward the lower head device by a bias means while the lowest position of the upper head device where it comes closest to the lower head device is strictly defined by the stopper means so that a correct gap is realized between the two head devices. Consequently, even if the upper head devices is subjected to adjustment operations for the track pitch while it is under pressure, the upper head device is completely free from any displacement after the adjustment operations and variations of the track pitch due to variations of the pressure applied to the magnetic disc by the upper head device.