Disk apparatus

Abstract: For a balance adjustment due to a reduction in size and weight of an actuator, an arm portion, an axis attaching portion, and a coil supporting portion are arranged so that the centers of gravity on the coil side are located on a straight line connecting a rotational center and the center of gravity on the head side. Further, the improvement of an assembling efficiency of a VCM, an increase in torque, a one-touch fixing of an FPC connecting band, a noise prevention of a read pattern, and an insulation between the base and cover due to a bias of an MR read head are accomplished. A sector mark is detected by comparing a peak detection pulse and its reference polarity signal. A redundancy is provided to a reference detection polarity signal so that a read signal can be detected even if any one of the read signals of the sector marks is dropped out. A gray code detecting section for recognizing a cylinder address also detects on the basis of a peak detection pulse and a polarity signal due to the reading of a gray code. A memory space to store a program is divided into an ROM space of a small electric power consumption and an RAM space of a large electric power consumption and stores each peculiar program. When the CPU doesn't execute a program in the RAM space, the execution of an idle program in the ROM space is allocated, thereby reducing an electric power consumption in an idle state by using an ROM.

Description: BACKGROUND OF THE INVENTION The present invention relates to a disk apparatus which can increase a memory capacity and can realize a small and thin shape and, more particularly, to a small disk apparatus using a disk medium of 2.5 inches. The invention relates to a disk apparatus of a sector servo system for positioning a head on the basis of servo information recorded on a data surface and, more particularly, to a disk apparatus which accurately detects a sector mark and a gray code indicative of a cylinder address which have been recorded in a servo frame at the head of a sector together with servo information. Further, the invention relates to a data processing apparatus including a disk apparatus which is controlled by a microprocessor and to a power saving method of such an apparatus. More particularly, the invention relates to a data processing apparatus in which a program memory is constructed by an ROM and an RAM of different electric power consumptions and to a power saving method of such an apparatus. In recent years, a small hard disk has been installed as an external memory apparatus of a notebook type computer or a portable communication terminal. As such a small hard disk, for example, a hard disk having therein two or three small disk media of 2.5 inches is used. In such a small disk apparatus, in addition to an enlargement of a memory capacity, a miniaturization, a light weight, and a thin shape of the apparatus are further requested. The miniaturization, light weight, and thin shape of the disk apparatus reduce an installation space when the apparatus is installed in a notebook type computer or the like. The whole computer including a magnetic disk apparatus is miniaturized and can be easily carried. Further, drive loads of a spindle motor and a voice coil motor are reduced, so that the electric power consumption can be saved. The notebook type computer or portable communication terminal can operate by a battery power source. The performance is, therefore, decided by a period of time during which the computer or terminal can be used without charging the battery. Thus, when the electric power consumption of the disk apparatus decreases, the battery usable time increases by a time corresponding to such a decreased power consumption and the performance is improved. In order to further accomplish a small size, light weight, and thin shape of the disk apparatus, however, there are the following various problems. In an actuator of the in-line type for positioning a head, an arm portion for supporting the head is provided at one end of a rotary shaft and a movable coil of a voice coil motor is provided at the other end of the rotary shaft. The actuator must accomplish both of the light weight and a balance between the head side and the coil side. Particularly, in recent years, the actuator has an asymmetrical arm shape in which the front edge of the arm is bent to the disk center side in a manner such that even if the rotational position of the actuator changes, the head direction does not largely deviate from the track tangent line. Thus, in addition to a balance adjustment in the front/rear direction, a balance in the right/left direction in association with the asymmetrical arm shape has to be obtained. Hitherto, such a balance adjustment is performed by a weight adjustment such as to change the thicknesses of the right and left portions of the movable coil on the installation side, or the like. However, designing works to simultaneously adjust both of the balance in the front/rear direction and the balance in the right/left direction of the actuator by adjusting the thicknesses are complicated. There is a problem such that even if the weight balance is obtained, the shape balance is largely lost, or the like. In the voice coil motor for driving the actuator of the head, a yoke having a permanent magnet is fixed and arranged to a casing base for the movable coil on the actuator side. Hitherto, the yoke side having the permanent magnet is assembled and fixed by screws, an adhesive agent, caulking, or the like. Therefore, the number of parts and the number of assembling steps increase and the assembling works are complicated. In the conventional voice coil motor, the magnet on the yoke side is set to the same size as that of each of the coil portions on the right and left sides of the rectangular movable coil on the actuator side, thereby allowing a magnetic flux to pass through the coil effective portion to generate a rotational torque. A magnetic flux density of the coil at the edge portion of the magnet decreases, however, due to a leakage magnetic flux and the coil effective length is not fully used. SUMMARY OF THE INVENTION According to the invention, there is provided a disk apparatus which can eliminate a spatial vain due to an arrangement of parts and can be miniaturized and can maintain a high quality in spite of the miniaturization. It is an object of the present invention to realize a disk apparatus comprising: a disk medium which is rotated by a spindle motor; an actuator for movably supporting a head in the radial direction for a recording surface of the disk medium; and a voice coil motor (VCM) for rotating the actuator in a range of a predetermined rotational angle. According to the invention, a disk apparatus having an actuator which has a relatively simple shape and is balanced is provided. The actuator comprises: an arm portion having a head at a front edge; an axis attaching portion integrally formed at a root portion of the arm portion; and a coil supporting portion which is integrally formed in the rear portion of the axis attaching portion and which supports a movable coil of the voice coil motor. The arm portion, axis attaching portion, and coil supporting portion are arranged so that the position of the center of gravity is located on the coil side on the straight line connecting the rotational center of the actuator and the position of the center of gravity on the head side. In this instance, the arm portion of the actuator has an asymmetrical shape such that the front edge side to which the head is attached is bent to the disk center side. The coil side is rotated and positioned so that the position of the center of gravity on the coil side is located on the straight line for the position of the center of gravity calculated on the head side so as to sandwich the rotational center of the actuator while setting such a rotational center to a boundary. Consequently, even in the actuator having an asymmetrical shape with respect to the right and left, an actuator having a relatively simple shape and a preferable balance in the right/left direction and the front/rear direction is obtained. A structure which is highly stable against an external vibration or an impact is realized. According to the invention, there is provided a disk apparatus which can easily assemble the yoke side of a voice coil motor by a small number of parts. The yoke side of the voice coil motor is assembled by using an adsorbing force of a magnet. The voice coil motor first comprises: a flat movable coil supported on the actuator side; a pair of permanent magnets which are fixedly arranged at positions so as to sandwich the movable coil; and a pair of yoke members for supporting each of the permanent magnets and forming a magnetic circuit. The pair of yoke members are assembled and fixed by an absorption of the permanent magnets, thereby forming an assembly structure for forming an enclosing space of the movable coil. Specifically speaking, flat plate members are used for the pair of yoke members. A plurality of upright members to decide a coil enclosing interval between the pair of permanent magnets are provided for one of the plate members and a projection for positioning is provided at a front edge of at least one of the upright members. Further, a reception hole for positioning is formed at the position of the other plate member which faces the projection. Since the yokes are assembled and fixed by using an attracting force of the magnet, screws, an adhesive agent, caulking, or the like is unnecessary to assemble the yokes. The number of parts and the number of assembling steps can be reduced and the assembling works can be simplified. According to the invention, there is provided a disk apparatus which makes the most of an effective length of the coil so as to increase a generation torque of the magnetic circuit. The front and rear outer edges of the pair of permanent magnets are slightly overlapped to the inner edges of the front and rear portions of the coil in the radial direction of the arm in the movable coil. A magnetic flux of the permanent magnet is allowed to pass while exceeding right and left torque generation effective portions of the movable coil. A magnetic flux density in an edge portion of the magnet decreases by the generation of a leakage magnetic flux which does not pass the coil. However, the edge portions of the magnet are enlarged up to the front and rear portions of the coil exceeding the right and left torque generation effective portions of the coil. Thus, with respect to the magnet edge portions as well, by allowing a uniform magnet flux to pass through the right and left torque generation effective portions of the coil, the coil effective length is fully used. Consequently, the effective length of the coil can be substantially increased and the rotational torque which is generated by the magnetic circuit can be increased. That is, in association with the enlargement of the magnet in the front/rear direction, the rotational torque and a thrust force of the actuator are also simultaneously increased by the magnetic flux which passes through the front and rear portions of the coil. Therefore, the widths to overlap the front and rear portions of the coil of the magnet are decided so as to increase the rotational torque in a range such that the thrust force does not exceed a specified value. The present invention will become more apparent from the following detailed description with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an explanatory diagram of an internal structure of a disk apparatus of the invention; Fig. 2 is a cross sectional view taken along the line I-I in Fig. 1; Fig. 3 is an assembly exploded diagram of the disk apparatus of the invention; Fig. 4 is a circuit block diagram of the disk apparatus of the invention; Fig. 5 is an explanatory diagram of a balance adjustment in an actuator of the invention; Fig. 6 is an explanatory diagram of an actuator which is balance adjusted irrespective of the invention; Fig. 7 is a cross sectional view of a rotary shaft of the actuator; Fig. 8 is a cross sectional view taken along the line II-II in Fig. 7; Fig. 9 is an explanatory diagram of a manufacturing of an actuator block by a pull-out work; Fig. 10 is an assembly exploded diagram on the fixing side of a VCM; Fig. 11 is an explanatory diagram of an assembly state on the fixing side of the VCM; Figs. 12A to 12C are explanatory diagrams of a lower yoke having a lower magnet; Figs. 13A and 13B are explanatory diagrams of an upper yoke having an upper magnet; Fig. 14 is an explanatory diagram of the relation between a magnet and a movable coil; Fig. 15 is an explanatory diagram of an overlap in the front/rear direction of the magnet for the movable coil; Fig. 16 is an explanatory diagram of the operation by the overlap of the magnet; Figs. 17A and 17B are characteristics graph showing the relation of a thrust force of a rotational force for the overlap; Fig. 18 is a cross sectional view of an integrated structure of the VCM and the actuator; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT [Whole structure and circuit block] Fig. 1 is a plan view of an internal structure of a disk apparatus of the present invention. Fig. 2 shows a cross sectional view taken along the line I-I in Fig. 1. A casing of the disk apparatus of the invention has a two-split structure comprising a base plate 12 and a cover 10. An actuator 26 is rotatably provided in the corner portion of the base plate 12. The actuator 26 has a VCM 20 in the rear portion of the rotational center. A head 14-1 is attached on the front edge side of the actuator 26. A disk as a recording medium that is rotated by a spindle motor 22 is provided for the actuator 26. In the embodiment, three disks 30-1 to 30-3 are attached. Since both of the front and back surfaces of each of the three disks 30-1 to 30-3 are used as data surfaces, the total number of data surfaces is equal to 6. In correspondence to the data surfaces, six head portions 14-1 to 14-6 are supported at the front edge of the actuator 26 by independent arm portions. In Fig. 2, only the top head portion 14-1 and the lowest head portion 14-6 are shown by reference numerals and the head portions 14-2 to 14-5 are sequentially arranged between them in accordance with the order from the upper position as shown in the diagram. In the embodiment, a write head and a read head are provided for each of the head portions 14-1 to 14-6 as will be obviously explained hereinlater. A magnetic head using a coil is used as a write head. An MR head using a magnetoresistive device is used as a read head. A circuit board 60 using FPC is arranged in the base plate 12 adjacent to the actuator 26. An FPC connecting band 62 is led out from the FPC board 60 and is fixed to the side surface of the actuator 26. Patterns to connect between an installation circuit including a head IC circuit 18 installed on the FPC board 60 and the six head portions 14-1 to 14-6 supported at the front edge of the actuator 26 are formed on the FPC connecting band 62. As patterns on the FPC connecting band 62, total four connecting patterns comprising a pair of patterns for the read head and a pair of patterns for the write head are formed per one head portion. Further, a pair of patterns for supplying a drive current to a movable coil of the VCM 20 are formed on the FPC connecting band 62. Further, a bias supply pattern to apply a bias voltage to the disks 30-1 to 30-3 through the actuator 26 is formed on the band 62. The details of each portion of the disk apparatus of the invention shown in Figs. 1 and 2 will be obviously explained hereinlater. Fig. 3 is an exploded assembly diagram of the disk apparatus of the invention. The spindle motor 22 which rotatably supports the three disks 30-1 to 30-3 is assembled onto the base plate 12. A circulating filter 55 is arranged near the disks 30-1 to 30-3 and removes the dust in the air flowing in association with the rotation of the disk. For example, a paper filter is used as a circulating filter 55. The actuator 26 is assembled together with the VCM 20 and the FPC board 60 coupled by the FPC connecting band 62. The VCM 20 is fixed to screw holes 56 and 58 of the base plate 12 by screws 52 and 54. The FPC board 60 is fixed to screw holes 68 and 70 of the base plate 12 by screws 64 and 66. The cover 10 is attached to the upper portion of the base plate 12 through a packing 28. The cover 10 is fixed to screw holes 37, 40, 42, and 44 of the base plate 12 by four screws 32, 34, 36, and 38. Vis through holes 72, 74, and 76 and, further, a screw hole (not shown) at the right rear position are formed in the cover 10. A lower portion of a fixing axis of the spindle motor 22 is screwed and fixed to the base plate 12. The spindle motor 22 is attached and fixed to an upper screw hole 50 by a screw 46 inserted through a screw through hole 48 of the cover 10. Namely, the spindle motor 22 has a twin-supporting structure that is fixed on both sides of the base plate 12 and the cover 10. Owing to the twin-supporting structure of the spindle motor 22, an attaching rigidity for the base plate 12 and cover 10 is remarkably improved. When the attaching rigidity of the spindle motor 22 is improved, the oscillation of the rotary shaft of the multilayer disk to which the disks 30-1 to 30-3 are attached is prevented. An offtrack amount which causes an on-track error can be extremely reduced. Fig. 4 is a whole circuit block diagram of the disk apparatus of the invention. The disk apparatus of the invention comprises: a disk enclosure 1000 having a structure shown in Figs. 1 and 2; and a drive controller 1012 installed to the printed circuit board which is enclosed from the lower side into an opening portion of the base plate 12 of the lower portion of the disk enclosure 1000. The head portions 14-1 to 14-6 are provided in the disk enclosure 1000 in correspondence to the six data surfaces of the three disks 30-1 to 30-3. Read heads 15-1 to 15-6 and write heads 16-1 to 16-6 are integrally provided for the head portions 14-1 to 14-6, respectively. Magnetic heads are used as write heads 16-1 to 16-6. MR heads using the magnetoresistive devices are used as read heads 15-1 to 15-6. In the MR head, it is necessary to allow a specific bias current to flow in the reading operation. The read heads 15-1 to 15-6 and write heads 16-1 to 16-6 are connected to the head IC circuit 18, by which the head switching operation and the supply of the bias voltage to the read heads 15-1 to 15-6 using the MR heads are executed. The spindle motor 22 to rotate the disk and the VCM 20 to position the head are provided in the disk enclosure 1000. An MPU 1024 which functions as a control unit is provided for the drive controller 1012. A readable and rewritable EPROM 1026 which is used as a program memory and a writable DRAM 1028 are connected to a bus 1058 of the MPU 1024. A leading program (boot program) which is used at the time of the leading operation in association with the turn-on of the power source of the disk apparatus has fixedly been stored in the EPROM 1026. A control program (micro program) which was downloaded from the disk on the disk enclosure 1000 side after completion of the leading operation of the disk apparatus by the leading program in the EPROM 1026 is stored in the DRAM 1028. Further, an interface circuit 1030 and a buffer memory 1032 for data transfer are connected to the bus 1058 of the MPU 1024. For instance, an SCSI is used as an interface circuit 1030. For example, a notebook type computer in which the disk apparatus of the invention has been installed is used as a host computer and commands and data which are necessary for an external memory are transmitted and received. Further, a cache controller 1031 and a cache memory 1033 are provided. The spindle motor 22 provided in the disk enclosure 1000 is controlled by a PWM circuit 1034 and a driver 1036. A head positioning control of the VCM 20 provided in the disk enclosure 1000 is performed by a D/A converter 1038 and a driver 1040. In any of the above cases, the driving of the spindle motor 22 and the positioning control of the VCM 20 are executed by a program control by the MPU 1024. As a read/write system, an AGC amplifier 1042, an equalizing circuit 1044, a most likelihood detecting circuit 1046, an encoder/decoder 1050, and a hard disk controller 1052 are provided for the drive controller 1012. Further, as a servo system of the head positioning control, a peak holding circuit 1054, an A/D converter 1055, and a servo frame demodulating circuit 1056 are provided. In the reading operation, the head IC circuit 18 is switched to, for example, the read head 15-1 side of the head portion 14-1 by a switching signal from the hard disk controller 1052. An analog read signal (read signal) from the read head 15-1 is supplied to the AGC amplifier 1042. The analog read signal is amplified by the AGC amplifier 1042 and, after that, it is waveform equalized by the equalizing circuit 1044 and is supplied to the most likelihood detecting circuit 1046 and a VFO circuit 1048. In the reading operation, the VFO circuit 1048 generates a reference clock synchronized with the read signal. Outputs of the most likelihood detecting circuit 1046 and VFO circuit 1048 are supplied to the encoder/decoder 1050 which has been switched to the decoder side in the reading mode. Read data is reconstructed while performing a clock synchronization and is subjected to a formatting process by the hard disk controller 1052. After that, it is transferred to the buffer memory 1032. Subsequently, the read data is transmitted to an upper apparatus through the interface circuit 1030. In the writing operation, on the other hand, write data transferred to the buffer memory 1032 through the interface circuit 1030 is supplied through the hard disk controller 1052 to the encoder/decoder which has been switched to the encoder side in the writing operation. The encoder/decoder executes a conversion to convert, for instance, the write data to the 2-7 run length code or the like, an addition of an ECC check code, and the like and, after that, supplies the resultant data to, for example, the write head 16-1 via the head IC circuit 18. Servo information according to the sector servo system has been recorded on each of the data surfaces provided for the disk enclosure 1000. [Actuator] Fig. 5 relates to an embodiment of the actuator which is used in the disk apparatus of the invention and has been balance adjusted to the optimum state. Fig. 6 shows the actuator before the balance adjustment of the invention is used. In Fig. 5, the actuator 26 of the invention has an elongated arm portion 80-1 on the disk side around an axis attaching portion 85, as a center, to which a cylindrical rotary shaft 86 is attached. The head portion 14-1 is attached to the front edge of the arm portion 80-1 through a gimbal spring 82-1 coupled by a pin 84. A point 94 of the head portion 14-1 is set to a reference position (head center) which gives a head gap. A coil supporting plate 88 which integrally has a movable coil 90 of the VCM 20 is attached behind the axis attaching portion 85. In the invention, the axis attaching portion 85 and arm portion 80-1 of the actuator 26 are formed by a machine work of an aluminum extruded block. The coil supporting plate 88 attached behind the axis attaching portion 85 is molded integrally with the movable coil 90 by using liquid polymer. The arm portion 80-1 is the top arm portion in the actuator 26 in Fig. 2. The remaining three arm portions 80-2 to 80-4 are formed below the arm portion 80-1. Among them, with respect to the lowest arm portion 80-4, the head portion 14-6 is supported through a gimbal spring 82-6 in a manner similar to the top arm portion 80-1. However, with regard to the intermediate two arm portions 80-2 and 80-3, gimbal springs 82-2 and 82-3 and gimbal springs 82-4 and 82-5 are provided on both sides and the head portions 14-2 to 14-5 are attached to the front edges, respectively. Further, in the actuator 26 of the invention of Fig. 5, in the front edge portion of the arm portion 80-1, the attaching portion of the gimbal spring 82-1 is bent to the center side of the disk 30-1, thereby providing an angle as will be obviously understood from Fig. 1. Thus, the actuator 26 has an asymmetrical shape with respect to the right and left when it is seen from the movable coil 90 side. The asymmetrical shape with an angle at the edge of the arm portion 80-1 suppresses a fall-down of the write head and read head for the track direction of the circumferential direction of the disk in association with the rotation of the actuator 26, thereby maintaining an orthogonal relation as much as possible. As shown in Fig. 6, hitherto, the actuator 26 with such an asymmetrical shape has a shape such that a rotational center 92, a center 96 in the shape of the movable coil 90, and further the head center 94 as a head gap position of the head portion 14-1 are arranged so as to be located on a straight line 95. A balance of the actuator 26 in the conventional shape of Fig. 6 is adjusted so as to make the whole center of gravity of the actuator 26 coincide with the rotational center 92. In order to make the whole center of gravity of the actuator 26 coincide with the rotational center 92, a thick portion for providing a weight for balance adjustment is formed in each member on the head side and coil side. Thus, a weight of the whole actuator 26 increases, thereby increasing an inertia of the actuator 26 by the VCM 20. On the other hand, in the actuator 26 of the invention of Fig. 5, a position 98 of the center of gravity on the head 14-1 side and a position 100 of the center of gravity on the movable coil 90 side are obtained around the rotational center 92 as a center. When the position 98 of the center of gravity on the head side and the position 100 of the center of gravity on the coil side are obtained as mentioned above, the position of the coil supporting plate 88 for the rotary bearing portion 85 of the actuator 26 is adjusted and positioned, for example, in a manner such that the position 100 of the center of gravity on the coil side is located on a straight line 102 connecting the rotational center 92 and the position 98 of the center of gravity on the head side. When the actuator of Fig. 5 according to the present invention is compared with the conventional actuator of Fig. 6, it will be understood that the actuator has a shape such that the coil supporting plate 88 having the movable coil 90 is rotated in a manner such that the position 100 of the center of gravity on the coil side is located on the straight line 102 (connecting the rotational center 92 and head side center position 98) which was rotated clockwise from the position on the conventional straight line 95. Loose holes 87-1 and 87-2 are formed in the coil supporting plate 88. The loose hole 87-1 locating on the straight line 102 is provided for balance adjustment in the longitudinal direction of the actuator for the rotational center 92. Since the coil supporting plate 88 has an asymmetrical shape in the embodiment, the loose hole 87-2 is formed to adjust in a manner such that the position 100 of the center of gravity on the coil side in association with the asymmetrical shape is located on the straight line 102 passing through the center of the movable coil 90. More specifically speaking, a weight on the head side having the arm 80-1 and gimbal spring 82-2 is first decided. A weight on the coil side is subsequently set so as to be equal to the weight on the head side in a state in which the loose holes 87-1 and 87-2 are formed. The position 98 of the center of gravity on the head side and the position 100 of the center of gravity on the coil side are obtained. The above component elements are arranged so as to be located on the straight line 102 passing the rotational center 92. As mentioned above, the conventional actuator 26 in Fig. 6 is constructed in a manner such that the head center 94 of the core of the head 14-1, the center 92 of the rotation, and the center 96 of the shape of the coil 90 are located in a line. Moreover, a balance weight is attached or cut out as necessary so that the center of gravity is located at the rotation center 92 and a balance is adjusted at the initial stage to assemble the actuator. Therefore, when the parts such as an FPC and the like are attached later, the balance is lost due to such an attachment. Another weight is further attached in order to get a proper balance. Consequently, an inertia of the actuator is large. On the other hand, the actuator 26 of the invention in Fig. 5 is constructed such that when the parts such as an FPC and the like are attached later, a line connecting the center 100 of gravity of the coil, the rotation center 92, and the center 98 of gravity on the head side becomes the straight line 102 so that the center of gravity is located at the rotation center 92. Therefore, when the actuator is assembled, there is no need to use a weight for balance adjustment. The weight can be reduced and a high speed access can be performed. Actually, the access time can be reduced from the conventional average time 15 msec to 12 msec. The inertia and weight after the FPC and the like were attached in this case are as follows. Conventional (Fig. 6) Invention (Fig. 5) Inertia 2.39g-cm 2 9.44g-cm 2 Weight (with FPC) 5.49g 4.70g A method of assembling the actuator 26 in Fig. 5 will now be described. First, the head portion 14-1 is mounted to a gimbal spring (suspension) 82-1 and is caulking fixed to the arm portion 80-1 having integratedly the axis attaching portion 85. The other head portions 14-2 to 14-6 are also similarly constructed. A head assembly is formed as mentioned above. Subsequently, the head assembly and the coil 90 are set into a die and the coil supporting plate 88 having the coil 90 is integratedly formed behind the axis attaching portion 85 by a insertion molding of a resin, thereby completing the actuator 26. In this case, a material which decides a specific gravity of the molding resin is selected so as to obtain a weight balance. Therefore, the adhesion of the coil supporting plate 88 and the attachment of the weight to obtain a weight balance after completion of the actuator which were executed hitherto are unnecessary. The actuator can be easily assembled. Fig. 7 shows an embodiment of the rotary shaft 86 provided in the axis attaching portion 85 of the actuator 26 of the invention of Fig. 5. The rotary shaft 86 is a cylindrical member and has therein a fixed axis 104. A shaft portion 110 provided in the lower portion of the fixed axis 104 is pressed and fixed into a lower yoke 24 which functions as a bottom plate shown in Fig. 2. A screw hole 112 is formed in the upper portion of the fixed axis 104 and is screwed and fixed through a yoke which forms an upper portion of the VCM 20. Grooves 106 and 108 are formed at two positions of the upper portion of the fixed axis 104. A plurality of bearings 114 and 116 are arranged in the grooves 106 and 108. An outer lace 118 is provided in the outside of the bearing 114. An outer lace 120 is provided in the outside of the bearing 116. When assembling, the outer laces 118 and 120 are fixed to the rotary shaft 86 by vises 122, 124, 126, and 128, respectively, as shown in the diagram. A spring 130 is assembled between the outer laces 118 and 120. Further, seal plates 132 and 134 are fixed to the outside of the bearings 114 and 116. In a state in which the assembly of the shaft portion shown in Fig. 7 was completed, the vises 122, 124, 126, and 128 are removed. Consequently, the outer laces 118 and 120 are pressed in the vertical direction by the spring 130, thereby pressing the inner tapered surfaces of the outer laces to the ball bearings 114 and 116 by specified preloads. Fig. 8 is a cross sectional view taken along the line II-II in Fig. 7. The ball bearing 116 is arranged in the groove 108 of the lower portion of the fixed axis 104 like a ring without a gap, thereby constructing a full ball structure. The bearing structure of Fig. 7 is characterized in that no inner lace is provided for the ball bearings 114 and 116. That is, in the bearing structure of the conventional disk apparatus, a bearing structure having an inner lace and an outer lace is used. However, in association with a miniaturization of the disk apparatus, the bearing structure of the actuator 26 also becomes a motor. In the bearing using both of the inner lace and the outer lace, since a diameter of ball bearing is extremely small, an abrasion resistance and a rigidity for a shock of the ball bearing deteriorate. In the invention, therefore, as shown in Fig. 7, no inner lace is provided but the grooves 106 and 108 are directly provided for the fixed axis 104 and are used in place of the inner lace. Since no inner lace is provided as mentioned above, even when the axial structure is miniaturized, ball bearings of large diameters can be used as ball bearings 114 and 116 which are used. Therefore, the abrasion resistances of the ball bearings 114 and 116 and the rigidity for a shock remarkably increase as compared with the case of using the inner lace. Further, as shown in Fig. 8, since the ball bearings 114 and 116 have the full ball structure, a load that is applied to each ball bearing is reduced and an impact resistance can be improved. Fig. 9 shows a manufacturing state of an arm block having the axis attaching portion 85 and arm portions 80-1 to 80-4 in the actuator 26 of the present invention of Fig. 5. In the conventional disk apparatus, the arm block of the actuator is molded by an aluminum die-cast. Therefore, there is a problem such that a nest easily occurs in the block and a deformation occurs due to the heat by the occurrence of the nest and a deformation due to an aging change occurs and an offtrack is likely to occur. In the actuator of the disk apparatus of the invention, as shown in Fig. 9, a die material 136 having an axis hole 138 and a hollow portion 140 is derived by an extrusion molding of aluminum. After the die material was cut out as shown by imaginary lines, an arm block 142 is formed by a machine work and the actuator 26 of Fig. 5 is assembled. By using the arm block 142 by the extrusion molding as mentioned above, the offtrack depending on the thermal deformation or aging deformation by the nest which occurs in the conventional aluminum die-cast hardly occurs. In the blocks obtained by the extrusion molding and machine work, there is hardly a variation of the shape as parts, so that the stable performance of the actuator can be realized. [Assembly structure on the fixed side of voice coil motor] Fig. 10 is an assembly exploded diagram on the fixed side of the VCM 20 that is used for driving the actuator. Fig. 11 shows an assembling state. The fixed-side that is used in the VCM 20 of the invention comprises: the lower yoke 24 to which a lower magnet 154 is fixed; and an upper yoke 152 to which an upper magnet 156 is fixed. As shown in Fig. 12A, the lower magnet 154 formed like a fan is adhered and fixed to the upper surface of the lower yoke 24. Through holes 162 and 164 of screws are formed at two positions of the lower yoke 24. The through holes 162 and 164 are used to attach a stopper portion and has a hole shape such that two corners are chamferred in order to prevent the rotation. A reception hole 168 for positioning by coming into engagement with the upper yoke 152 is opened on the through hole 164. Further, a latch member 200 is formed on the left side of the lower magnet 154 by bending by a cut-out of the lower yoke 24. A latch magnet 198 is attached to the inside of the latch member 200. The latch member 200 and latch magnet 198 latch the head portion provided at the front edge of the actuator to the innermost position of the disk and will be obviously explained hereinlater. Fig. 12B is a side elevational view of a lower yoke 150. Fig. 12C is a bottom view of the lower yoke 24. Fig. 13A shows a bottom view of the upper yoke 152 in Fig. 10. Fig. 13B shows a side elevational view thereof. The upper magnet 156 is fixed to the lower surface of the upper yoke 152 by an adhesive agent or the like. The upper magnet 156 is arranged so as to overlap to the lower magnet 154 in Fig. 12A through a predetermined gap. Working holes 158 and 160 which are used when the lower yoke 24 locating on the lower side is fixed to the base plate 12 side by the screws are formed in the upper yoke 152 on both sides of the upper magnet 156. A through hole 170 to fix with a vis at the rotational center of the actuator is also formed in the upper yoke 152. Standing members 174, 176, and 178 which are bent downward are formed at three positions of the upper yoke 152. Among them, a projection 166 which is fitted into the reception hole 168 of the lower yoke 24 in Figs. 12A to 12C is formed in the lower portion of the standing member 176. A height of the standing member 176 excluding the standing members 174 and 178 and projection 166 decides a gap interval in which the movable coil 90 on the actuator side between the lower magnet 154 and the upper magnet 156 when the upper yoke 152 is assembled to the lower yoke 24 is enclosed. When the VCM 20 is assembled to the base plate 12 as mentioned above, first, an assembly of the lower yoke 24 and upper yoke 152 is prepared. Namely, since the lower magnet 154 is provided for the lower yoke 24 and the upper magnet 156 is provided for the upper yoke 152, as shown in Fig. 10, the projection 166 at the edge of the standing member 176 of the upper yoke 152 is positioned and fitted into the reception hole 168 of the lower yoke 24. The lower yoke 24 and upper yoke 152 are set into a state in which they are integrally assembled and fixed as shown in Fig. 11 by an adsorbing force of the lower magnet 154 and upper magnet 156. Therefore, when a magnetic circuit is formed by assembling the yoke, screws, adhesive agent, caulking, or the like as in the conventional apparatus is unnecessary. The lower yoke 24 and upper yoke 152 can be fixed into an assembling state by only an attracting force of the magnets. After the upper and lower yokes were assembled, as shown in Fig. 11, the screws 52 and 54 are inserted from the working holes 158 and 160 of the upper yoke 152 into the screw holes 56 and 58 of the base plate 12 via the through holes 162 and 164 of the lower yoke 24 and are fixed by using a driver or the like. [Enlargement of effective length of coil of voice coil motor] Fig. 14 shows the arrangement relation between the magnet and the movable coil in the VCM of the present invention and shows a state in which the upper yoke in the VCM is removed. The movable coil 90 of the actuator 26 is installed to the coil supporting plate 88 provided in the rear portion of the rotary shaft 86. In the movable coil 90, right and left coil portions 90-1 and 90-2 for the longitudinal direction of the actuator 26 become the portions of the coil effective length to obtain a rotational torque for a magnetic flux which is generated between the lower magnet 154 and the upper magnet 156 locating in the upper portion. On the other hand, with respect to front and rear coil portions 90-3 and 90-4 of the movable coil 90, even if a magnetic flux passes through such portions, no rotational torque is derived and a thrust force in the longitudinal direction of the actuator 26 is generated. Therefore, the front and rear coil portions 90-3 and 90-4 become the coil portions which don't generate any rotational torque. In the conventional VCM, magnet outer edges 179 and 184 in the front/rear direction of the lower magnet 154 and upper magnet 156 are made coincide with coil inner edges 180 and 182 in the front/rear direction of the movable coil 90, thereby preventing that the magnet enters the coil portions 90-3 and 90-4 which don't contribute to the generation of the rotational torque. On the other hand, in the VCM 20 of the present invention, as shown in Fig. 14, as compared with the col inner edges 180 and 182 in the front/rear direction of the movable coil 90, the magnet outer edges 179 and 184 of the lower magnet 154 and upper magnet 156 (not shown) are enlarged so as to slightly overlap to the front and rear coil portions 90-3 and 90-4 as shown by broken lines. Fig. 15 is a cross sectional view in the longitudinal direction of the actuator in Fig. 14. As will be obviously understood from the cross sectional view, as compared with the coil inner edge 180 in the outside of the movable coil 90, the magnet outer edges 179 and 186 of the lower magnet 154 and upper magnet 156 are fitted into the front and rear coil portions by only ΔL. With respect to the coil inner edge 182 on the inside, magnet outer edges 184 and 188 of the lower magnet 154 and upper magnet 156 are fitted by only ΔL. Fig. 16 shows a function in the case where the magnet edge portions are slightly overlapped to the front and rear coil portions. A magnetic flux density which is caused by the lower magnet 154 and upper magnet 156 and which passes through the right and left portions of the coil effective length of the movable coil 90 is reduced at the magnet outer edge which reaches the front and rear portions of the coil due to an external leakage magnetic flux. Thus, even if the front/rear magnet width physically coincides with the length of the right and left coil portions, the effective length is substantially reduced due to a decrease in magnetic flux density at the edge portion. On the other hand, as shown in Fig. 16, in case of enlarging the magnet outer edges 179 and 186 so as to overlap in excess of the coil inner edge 180, a magnetic flux leakage to the outside between the magnets is generated at the position exceeding the coil effective length of the right and left coil portions. A uniform magnetic flux density is obtained with respect to the whole physical effective length of the right and left coil portions. Thus, the physical coil effective length almost coincides with the coil effective length at which the magnetic flux density becomes constant. The effective length of the coil can be substantially increased as compared with the conventional one. A rotational torque which is generated in the VCM can be also increased. On the other hand, an amount ΔL in which the magnet outer edge is overlapped to the front and rear coil portions is determined in consideration of the thrust force of the actuator which is generated when the magnetic flux passes in the front and rear coil portions. Fig. 17A shows the relation between an overlap amount (L) of the magnet outer edge for the coil portion and a rotational force F. Fig. 17B shows the relation of a thrust force F2 for the overlap amount (L). The rotational force F1 of the VCM is equal to F11 in the case where the overlap amount (L) = 0, namely, in the same case as the conventional one. When the overlap amount of the magnet outer edge is increased, however, the rotational force increases and is saturated at a certain position as shown by a curve 190. On the other hand, the thrust force F2 has characteristics such that, as shown by a curve 192, when the overlap amount (L) = 0 is set to an initial value, the thrust force F2 also increases in association with an increase in overlap amount (L) and is finally saturated. When the thrust force F2 is too large, a twist occurs in the rotation of the actuator 26 and an inertia increases. Therefore, the overlap amount ΔL is decided at a position such as to suppress the thrust force F2 to a specified threshold value Fth. When the thrust force F2 is suppressed to the threshold value Fth, the overlap amount ΔL that is decided at a point 194 on the curve 192 is derived. The rotational force at the overlap amount ΔL is set to F12 that is given at a point 195A on the characteristics curve 190, so that the rotational force of the VCM can be increased. [Assembling structure with actuator] Fig. 18 shows an assembling structure of the actuator 26 to the lower yoke 24 which functions as a bottom plate in Fig. 2. The lower yoke 24 of the VCM 20 is extended up to the portion of the rotary shaft 86 of the actuator 26. A hole 172 is formed in such an extended portion of the lower yoke 24. The shaft portion 110 in the lower portion of the fixed axis 104 provided on the inside of the rotary shaft 86 of the actuator 26 through the ball bearings 114 and 116 is inserted and fixed into the hole 172 with a pressure. Further, a stopper 196 for positioning the coil supporting plate 88 of the movable coil 90 of the rear portion of the actuator 26 is also integrally provided by screwing on the lower yoke 24 which functions as a bottom plate. Further, the latch magnet 198 is arranged at the position of a latch member which is lifted up by cutting out a part of the lower yoke 24. The screw 54 to fix the stopper portion 196 to the lower yoke 24 passes through the through hole 164 and is screwed and fixed into the screw hole 58 of the base plate 12 in Fig. 2 that is located on the lower side. Thus, the screw 54 has a function to fix the lower yoke 24 which functions as a bottom plate to the base plate 12. By installing the actuator 26 and, further, the stopper portion 196 by using the lower yoke 24 on the fixed side of the VCM 20 as a bottom plate, a positional accuracy of the fixed side of the VCM 20 and the actuator 26 can be remarkably improved as compared with the case where the fixed side of the VCM 20 and the actuator 26 are separately formed and are individually assembled and fixed onto, for example, the base plate 12.

Claims: A disk apparatus comprising: a head; an actuator supporting said head and movable in radial direction of a recording surface of a disk medium; and a motor (20) for rotating said actuator (26) in a predetermined range of a rotational angle, said motor having a flat movable coil supported by said actuator; characterized by a pair of permanent magnets (156, 154) fixedly arranged at positions which sandwich said movable coil (90), for imparting a driving force; and a pair of yoke members (24, 152) for supporting said permanent magnets (156, 154) and forming a magnetic circuit; wherein said pair of yoke members (24, 152) are fixed together by an attraction by said permanent magnets (156, 154), whereby said pair of yoke members (24, 152), when in their final operating positions, are held together primarily by magnetic attraction substantially without the use of any other fastening means. A disk apparatus according to claim 1, wherein the upper magnet (154) is attached to the lower side of the upper yoke member (152) and the lower magnet (154) is attached to the upper side of the lower yoke member (24). A disk apparatus according to claim 1 or 2, characterized by an upright member, formed integrally on said upper yoke member (152), for connection the upper yoke member and the lower yoke member (24) and defining a space between said upper and lower yoke members (24, 152). A disk apparatus according to claim 1 or 2, characterized by said first yoke member further (152) including a plurality of upright members extending toward said second yoke member (24), each said upright member having an end defining a front edge that faces said second yoke member (24), and each said upright member further defining sides of said space between said pair of permanent magnets, at least one of said front edges having a projection for positioning said pair of yokes, and said second yoke member (24) having a reception hole for positioning, wherein said reception hole engages said projection. A disk apparatus according to any of claims 1 to 4, wherein said movable coil (90) further defines a right coil (90-1) portion opposed to a left coil (90-2) portion, said left and right coil (90) portions attached through a front coil portion (90-3) and a back coil portion (90-4) that opposes the front coil portion, each said portion having an inner edge (182) and an outer edge (180), each said inner edge facing an opposing portion, and said permanent magnets (154, 156) further having front and rear outer edges respectively corresponding to said front and rear inner edges of said front and rear coil portions (90-3, 90-4), wherein said front (182) and rear (180) outer edges of said pair of permanent magnets are arranged so as to slightly overlap said front and rear inner edges of said movable coil (90) in a radial direction of said actuator (26), and a magnetic flux of said permanent magnet is allowed to pass outside of a torque generation valid portion defined by said right and left coil (90) portions of said movable coil (90).

Inventors: ENDO KENJI, GOFUKU TATSUYA, ISHIZAKI HIROKAZU, OHBA KAZUHIDE, OKAMURA EIJI, ONO CHIHIRO, ONO TAKAHIRO, SAIKI MASARU, SASAKI TSUTOMU, SATOH ATSUSHI, SUDA ISAO, SUZUKI HIROFUMI, SUZUKI NORIHIKO, TAKAHASHI EISAKU, TOHKAIRIN KOICHI, TOKAIRIN TAKASHI, ENDO, KENJI, GOFUKU, TATSUYA, ISHIZAKI, HIROKAZU, OHBA, KAZUHIDE, OKAMURA, EIJI, ONO, CHIHIRO, ONO, TAKAHIRO, SAIKI, MASARU, SASAKI, TSUTOMU, SATOH, ATSUSHI, SUDA, ISAO, SUZUKI, HIROFUMI, SUZUKI, NORIHIKO, TAKAHASHI, EISAKU, TOHKAIRIN, KOICHI, TOKAIRIN, TAKASHI, ENDO, KENJI, C/O YAMAGATA FUJITSU LIMITED, GOFUKU, TATSUYA, C/O FUJITSU LIMITED, ISHIZAKI, HIROKAZU, C/O FUJITSU LIMITED, OHBA, KAZUHIDE, C/O YAMAGATA FUJITSU LIMITED, OKAMURA, EIJI, C/O FUJITSU LIMITED, ONO, CHIHIRO, C/O YAMAGATA FUJITSU LIMITED, ONO, TAKAHIRO, C/O YAMAGATA FUJITSU LIMITED, SAIKI, MASARU, C/O FUJITSU LIMITED, SASAKI, TSUTOMU, C/O FUJITSU LIMITED, SATOH, ATSUSHI, C/O YAMAGATA FUJITSU LIMITED, SUDA, ISAO, C/O YAMAGATA FUJITSU LIMITED, SUZUKI, HIROFUMI, C/O YAMAGATA FUJITSU LIMITED, SUZUKI, NORIHIKO, C/O YAMAGATA FUJITSU LIMITED, TAKAHASHI, EISAKU, C/O YAMAGATA FUJITSU LIMITED, TOHKAIRIN, KOICHI, C/O YAMAGATA FUJITSU LIMITED, TOKAIRIN, TAKASHI, C/O YAMAGATA FUJITSU LIMITED
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1995
Main classification: G11B21
IPC codes: G11B5, G11B21, G11B33, G11B25