Leakage flux shielding structure of disk unit
This application is a file wrapper continuation of application Ser. No. 07/799,360 filed Nov. 27, 1991, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the leakage flux shielding structure of a flexible disk unit having a reduced thickness. 
     2. Description of the Prior Art 
     FIG. 8 is a diagram showing the positional relationship of the spindle motor, carriage assembly and stepping motor of a flexible disk unit of the prior art. FIG. 9 is a sectional view illustrating the positional relationship between the spindle motor and the carriage of the flexible disk unit. FIG. 10 is a diagram showing the whole configuration of the flexible disk unit. In these figures, reference numeral 1 represents a spindle motor for rotating a magnetic recording medium (unshown), 1a driving magnet, 1b starer, 1c coil, 1d spindle motor substrate, 1e chucking hub, 1f rotation axis, 2 frame, 3 carriage assembly, 3a carriage for mounting a magnetic head 3c, 3b arm for mounting a magnetic head 3d, 4 stepping motor for positioning the carriage assembly 3 in the radial direction of the medium, 5 sensor, 4a lead screw directly connected to the rotation axis of the stepping motor 4, 6 slide cam, 7 cartridge holder, 8 lever, 9 substrate, 10 shield cover and 11 front panel. 
     The operation of the flexible disk unit will be described next. In FIG. 10, when the magnetic recording medium (unshown) is inserted into the unit, the medium is loaded onto the read-write position by a loading mechanism consisting of the slide cam 6, the cartridge holder 7 and the lever 8. The detailed explanation of the loading mechanism is omitted here. When the medium is placed in the loading position, the hub of the medium is chucked by the chucking hub 1e of the spindle motor 1 fixed to the frame 2, and the medium rotates by the rotation of the spindle motor. 
     A projection (unshown) provided on the carriage assembly 3 is engaged with a groove in the lead screw 4a directly connected to the axis of the stepping motor 4 so that the rotary motion of the stepping motor is changed into the motion in the radial direction of the medium of the carriage assembly 3. Therefore, the magnetic heads 3c and 3d mounted on the carriage assembly 3 are moved in the radial direction of the magnetic recording medium by means of the stepping motor 4, and are positioned above the target truck. The flexible disk unit of the prior art is configured as shown in FIG. 8 and FIG. 9. That is, an outer rotor type spindle motor wherein the driving magnet 1a is located outside the stator 1b and the coil 1c is used, and the carriage assembly 3 is located above the stator 1b, the coil 1c and the driving magnet 1a as shown in FIG. 9. 
     Since the flexible disk unit of the prior art is configured as described above, the carriage 3 must be made thin to reduce the thickness of the flexible disk unit. However, the magnetic heads 3c and 3d can be made thin to a certain degree in connection with the unshown medium. Furthermore, there is a limit to a reduction in the thicknesses of the driving magnet 1a, the coil 1c and the case 1n of the spindle motor 1 in order to maintain performance. Similarly, the thicknesses of the IC 1h and the connector 1j on the motor substrate 1d cannot be reduced. Thus the disk unit of the prior art is difficult to be made thin. 
     SUMMARY OF THE INVENTION 
     In view of the problem of the prior art, it is an object of the present invention to achieve a high-performance flexible disk unit having a structure which permits reduction of its thickness. 
     In the present invention, a recess is formed by denting a part of the stator toward the inside thereof or by cutting a part of the stator and is free from a coil. The carriage is positioned so that the magnetic heads of the carriage go into the recess. At the same time, a head shield edge (bent portion) for shielding leakage flux in the direction of the above magnetic heads are provided on the side of the spindle motor. 
     The magnetic heads at the tip of the carriage are positioned in such a way that they can enter the recess of the stator. As a result, the position of the carriage is lowered, thus reducing the thickness of the unit. Furthermore, the influence of leakage flux from the spindle motor on the magnetic heads can be prevented by the head shield portion. 
     The above and other objects, features, and advantages of the invention will become more apparent from the following description when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1 to 5 are plan, side, perspective and exploded perspective views of the leakage flux shielding structure of a disk unit according to an embodiment of the present invention. 
     FIGS. 6 and 7 are plan and perspective views of the leakage flux shielding structure of a disk unit according to another embodiment of the present invention. 
     Figs. 8 to 10 are plan, side and exploded perspective views of a flexible disk unit of the prior art. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the accompanying drawings, an embodiment of the present invention will be described. 
     FIGS. 1 to 5 are diagrams showing the embodiment. FIG. 1 is a diagram showing the positional relationship of the spindle motor, carriage, stepping motor and magnetic recording medium. FIG. 2 is a diagram showing the positional relationship of the stator, coil and carriage. FIG. 3 is a sectional view showing the positional relationship between the spindle motor and the carriage. FIG.4 is a diagram showing the shape of the shield plate of the spindle motor. FIG. 5 is a diagram showing the whole configuration of the disk unit. In these figures, reference numeral 1 represents a spindle motor which includes a rotor 1q for rotating a magnetic recording medium 12, 1a driving magnet provided on the outside periphery of the rotor 1q, 1b ring-shaped stator, 1c coil provided on the inside periphery of the stator 1b, and 1d spindle motor substrate. The magnet 1a described above is opposed to the coil 1c. 1e represents a chucking hub, 1f rotation axis, 1g recess free from the coil 1c and formed by denting (recessing) a part of the outside periphery of the stator 1b, which is the feature of the present invention, 1h IC for the spindle motor 1, 1j connector for connecting the substrate 9, and 1k a bent edge of the shield plate which is located at the recess of the shield plate 1m and constitutes a head shield portion. Reference numeral 2 represents a frame, 3 carriage assembly, 3a carriage for mounting a magnetic head 3c, 3b arm for mounting a magnetic head 3d, 4 stepping motor for seeking and positioning the carriage assembly 3 in the radial direction of the medium, 4a lead screw attached to the rotation axis of the stepping motor 4, 5 sensor, 6 slide cam, 7 cartridge holder, 8 lever, 9 substrate, 10 shield cover, and 11 front panel. The shield plate 1m described above is wide enough to cover the coil 1c and shaped like a ring. It has a projection 1y on the outside periphery thereof and fixed on top of the stator 1b, and a recess 1r corresponding to the recess 1g described previously is formed on the shield plate. In this case, a bent portion 1k is formed as a head shield edge by folding the rim of the shield plate 1m where the recess 1r is formed in the direction of the motor substrate 1d. 
     The operation of the disk unit will be described next. In FIG. 5, when the magnetic recording medium (unshown) is inserted into the unit, the medium is loaded onto the read-write position by a loading mechanism consisting of the slide cam 6, the cartridge holder 7 and the lever 8. The detailed explanation of the loading mechanism is omitted here. When the medium is placed in the loading position, the hub of the medium is chucked by the chucking hub 1e of the spindle motor 1 fixed to the frame 2, and the medium rotates by the rotation of the spindle motor. 
     A projection (unshown) provided on the carriage assembly 3 is engaged with a groove in the lead screw 4a directly connected to the axis of the stepping motor 4 so that the rotary motion of the stepping motor is changed into the motion in the radial direction of the medium of the carriage assembly 3. Therefore, the magnetic heads 3c and 3d mounted on the carriage assembly 3 can go into the recesses 1g and 1k and move in the radial direction of the magnetic recording medium by means of the stepping motor 4 so that they are positioned above the target truck. 
     The disk unit according to the present invention is configured as shown in FIG. 1, FIG. 2 and FIG. 3. That is, an inner rotor type spindle motor wherein the driving magnet 1a is located inside the stator 1b and the coil 1c is used, and furthermore a recess 1g  free from the coil 1c is formed by denting a part of the outside periphery of the stator 1b toward the inside periphery thereof. When the carriage 3 is positioned on the inside periphery, it goes into the recess 1g described above and is located on the same plane with the stator 1b, the coil 1c and the driving magnet 1a. 
     Since the bent edge 1k is provided on the carriage 3 side of the shield plate 1m as shown in FIGS. 3 and 4, leakage flux from the motor to the magnetic heads 3c and 3d can be shielded, thus preventing the bad influence of the magnetic heads 3c and 3d on the recording and reproduction of information, 
     It has been explained that the head shield edge is the bent portion formed by folding a part of the shield plate 1m, but an object separate from the shield plate 1m may be attached to the motor substrate 1d to form this. 
     In the above embodiment, the recess 1g free from the coil 1c is formed by denting a part of the outside periphery of the stator 1b as shown in FIG. 2, but as shown in FIG. 6, an opening free from the coil 1c may be made in the portion of the stator 1b corresponding to the recess 1g. 
     In addition, as shown in FIG. 7, if a bent portion is provided on the carriage side of the shield plate, the same effect can be achieved without shaping the shield plate like a ring. 
     As described in the foregoing, according to the present invention, in a disk unit comprising a ring-shaped stator having a coil on the inside periphery thereof, &amp; spindle motor supported by a rotation axis and including a rotor for rotating a magnetic recording medium and having a magnet opposed to the coil and provided on the outside periphery of the motor, a carriage having a magnetic head at the tip thereof and supported in such a way that it can move in the radial direction of the magnetic recording medium on the rotor, a recess free from a coil is formed by denting a part of the stator toward the inside thereof or opening it, and the carriage is positioned in such a way that the head of the carriage enters the recess. Furthermore, a head shield portion for shielding leakage flux in the direction of the magnetic head is provided on the side of the spindle motor with the result that flux leaked to the magnetic head of the carriage can be prevented, thus making it effectively possible to achieve a highly reliable disk unit.