Disk drive

Abstract: A retracting assembly produces a constant torque, in a data zone of a magnetic disk, which is greater than static friction of a bearing for a rotary actuator. However, in a parking zone on an outer portion of the magnetic disk, the retracting assembly generates a torque which suddenly increases so that a large holding torque is obtained and a magnetic head is reliably locked.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a disk drive that can be utilized as an external memory of a computer system, such as a magnetic disk or a magneto-optical disk. More specifically, it relates to a whole construction of a disk drive having a housing of a credit card type, a circuit assembly thereof and the structure of each of the various mechanical components within the above housing. 2. Description of the Related Art Generally, disk drives, e.g., magnetic disk drives, having at least one magnetic disk utilized as a recording medium, have been in practical use in various areas including computer systems as non-volatile memory devices. Further, in recent years, improvements in the technology of the magnetic disk drives, such as increasing the magnetic recording density of the magnetic disk, have been realized, leading to down-sizing of magnetic disk drives per se. On the other hand, computer systems, etc., have been becoming more compact, lighter in weight and lower in power consumption, as represented by a portable personal computer, owing to recent rapid development of microelectronics. Though down-sizing of the technology of the magnetic disk drive has progressed recently as described above, the dimensions are still too large, the weight too heavy and the power consumption too high if a magnetic disk having a diameter of 2.5 inches is utilized. Therefore, it may be difficult for the current magnetic disk drives to be applied to the above portable personal computer for which compactness, lighter weight and lower power consumption are required. To meet this requirement, a magnetic disk drive utilizing a magnetic disk with a diameter of 1.89 inches has been announced in public recently. This magnetic disk drive surely has smaller dimensions than the magnetic disk drive with a diameter of 2.5 inches. However, in such a magnetic disk drive comprising a magnetic disk with a diameter of 1.89 inches, down-sizing of the magnetic disk drive has been attempted by using the prior art without making any improvements. Therefore, a problem occurs in that the dimensions of the above magnetic disk drive, especially the thickness or height, are still too large for the disk drive to be practically used as a portable device (nowadays, it is generally well known that the lower limit of the thickness thereof is as large as 10 mm). Moreover, another problem occurs in that such a magnetic disk drive cannot have sufficient durability against mechanical shock caused by external factors, such as a fall of the portable device, even if the disk drive is applied to a portable device. Further, a modular unitary disk file subsystem has been disclosed in U.S. Pat. Nos. 4639863 & 4860194, wherein an elongated printed circuit board is directly attached to the side of a housing including a head and disk assembly so as to attain thinner dimensions. However, a concrete thickness value in such a construction is not described in these prior arts. Moreover, even though the thickness of the disk drive can be reduced successfully, a new problem would occur in that the area of the disk drive including the printed circuit board and the housing is enlarged more than usual. Taking these conditions into account, in a known portable personal computer or the like that is currently in use, an integrated circuit(IC) memory card is provisionally utilized, rather than a magnetic disk, so that the required dimensions and weight can be attained. The specifications of this IC memory card have been standardized recently {the standard specification of JEIDA (Japan Electronic Industry Development Association) and PCMCIA (Personal Computer Memory Card International Association)}, where the thickness or height of the card is defined as 5 mm or 3.3 mm. A card satisfying these standard specifications is sufficiently thin and sufficiently light, and therefore the above card can be suitable for application to a portable personal computer, etc., in view of dimensions and weight. However, presently, there are two significant disadvantages in the above IC memory card as follows. First, computer systems utilizing the IC memory card are extremely expensive. More concretely, the cost per megabyte thereof is several tens of thousands of yen/MByte, which is several hundred times higher than a computer system utilizing flexible disk drive and is several tens of times higher than that of hard disk drive (i.e., magnetic disk drive). Second, the whole storage capacity of a computer system utilizing the above IC memory card is not always sufficient to comply with the current requests of users. Nowadays, an IC memory card having a storage capacity of approximately 1 MByte is mainly used. The storage capacity of the IC memory card will be increased up to the order of several MBytes to 10 MBytes in the future. On the other hand, presently, in the ideal portable personal computer, a memory system having more than 40 MBytes is actually required. Accordingly, the computer system utilizing the above IC memory card cannot substantially satisfy the current requirements for storage capacity. Moreover, in the near future, the above storage capacity that is required by users will be expected to be increased more and more. Therefore, it will be difficult for the storage capacity of the IC memory card to catch up with the required storage capacity, even with the progress of IC memory technology taken into account. As described above, if a magnetic disk drive according to the prior art is to be utilized for a portable personal computer, it will be sufficient in respect to the cost and storage capacity, but it is not sufficient in respect to the dimensions, weight, power consumption and durability against mechanical shock. On the contrary, the IC memory card currently utilized for portable personal computers is sufficient in respect to the dimensions, weight, power consumption and durability against mechanical shock, however, the cost of the IC memory card is too expensive and the storage capacity thereof is not always satisfactory for the users. Therefore, in order to realize a suitable portable personal computer, a memory device that has both the advantages of the magnetic disk drive and the IC memory card is strongly desired. As a strategy for overcoming the above-mentioned difficulties, it is considered to be effective to utilize the specifications of a type III of PCMCIA. In this type III of PCMCIA, the same dimensions as type I and type II are defined in respect to plane directions, while the thickness dimensions are allowed to be a maximum value of 10.5 mm. If one connectors conforming to the type III of PCMCIA is provided, a cord having the thickness of 10.5 mm can be inserted into two different kinds of slots of the type I and type II arranged in a vertical direction. As described above, if the specification of the thickness dimension is defined as 10.5 mm, a disk drive of a card type can be realized by using the prior art without any improvements. Actually, a device having a thickness of 10.5 mm has already been announced. However, the down-sizing of the device is necessitated in personal computers, particularly notebook type personal computers, and therefore, a structure such that the two slots are arranged in a vertical direction may be disadvantageous in terms of down-sizing. On the other hand, in palm top type personal computers, only one slot can be provided in each personal computer. In other words, it is now difficult for memory devices in all areas that IC memory cards are utilized to be replaced with magnetic disk drives. Therefore, it is strongly desired that magnetic disk drives having outer dimensions conforming to the type I or type II, i.e., disk drives with a thickness equal to or less than 5 mm, be realized. WO-A-90/05359 discloses a disk dive according to the preamble of each independent claim, in which the retraction mechanism (locking means) comprise a magnetically permeable capture member attached to the rotary arm. The capture member is attracted by a stationary magnet which is mounted in a member for containing the magnetic field, this latter member having a gap substantially parallel to the magnet flux lines. The attraction takes only place when the capture member is in the direct vicinity of the gap. SUMMARY OF THE INVENTION According to a first aspect of the invention, there is provided a disk drive comprising, inside a rectangular housing: at least one disk that stores information; and a head assembly that performs read/write operations on said disk, wherein said head assembly has a head that executes reproducing/recording operations corresponding to read/write operations of said information in a predetermined position on said disk; a rotary type actuator that forces said head to move through a stroke to said predetermined position on said disk; and a retraction mechanism which forces said head to move and retract from an arbitrary position above a data zone of said disk to a predetermined position for parking the head; characterised in that said retraction mechanism comprises: a retraction magnet provided in an outer fringe part of said actuator; and a retraction yoke provided with a first portion above a path of movement of said retraction magnet and a second portion below said path such that the height of a gap between said first and second portions decreases in the direction along said path toward said predetermined position, wherein the interaction between said retraction magnet and said retraction yoke produces a substantially constant retraction force throughout the full stroke of the head. According to a second aspect of the invention, there is provided a disk drive comprising, inside a rectangular housing: at least one disk that stores information; and a head assembly that performs read/write operations on said disk, wherein said head assembly has a head that executes reproducing/recording operations corresponding to read/write operations of said information in a predetermined position on said disk; a rotary type actuator that forces said head to move through a stroke to said predetermined position on said disk; and a retraction mechanism which forces said head to move and retract from an arbitrary position above a data zone of said disk to a predetermined position for parking the head; characterised in that said retraction mechanism comprises: a retraction magnet provided in an outer fringe part of said actuator; and a retraction yoke provided with a first portion above a path of movement of said retraction magnet and a second portion below said path, wherein a region of overlap between said retraction magnet and said retraction yoke includes a first subregion corresponding to the head being positioned above said data zone and a second subregion corresponding to the head being parked in said predetermined position, the region having a thickness in a radial direction relative to a rotational axis of said actuator, which thickness increases along said path of movement of said retraction magnet in the direction toward said predetermined position, and wherein the interaction between said retraction magnet and said retraction yoke produces a substantially constant retraction force throughout the full stroke of the head. According to the third aspect of the invention, there is provided a disk drive comprising, inside a rectangular housing: at least one disk that stores information; and a head assembly that performs read/write operations on said disk, wherein said head assembly has a head that executes reproducing/recording operations corresponding to read/write operations of said information in a predetermined position on said disk; a rotary type actuator that forces said head to move through a stroke to said predetermined position on said disk; and a retraction mechanism which forces said head to move and retract from an arbitrary position above a data zone of said disk to a predetermined position for parking the head, the retraction mechanism comprising a soft magnetic element mounted on a moving portion of the actuator, and a stationary retraction magnet; characterised in that said retraction mechanism further comprises: a retraction yoke provided with a first portion above a path of movement of said soft magnetic element, a second portion below said path, and said retraction magnet, such that the height of a gap between said first and second portions decreases in the direction along said path toward said predetermined position, wherein the interaction between said soft magnetic element, said retraction magnet, and said retraction yoke produces a substantially constant retraction force throughout the full stroke of the head. An embodiment of the present invention can provide a magnetic disk drive of lower cost and sufficient storage capacity simultaneously having advantages of IC memory card of compactness, lighter weight, lower power consumption and sufficient durability against mechanical shock. An embodiment of the present invention can also provide a magnetic disk drive that has the same thickness as the IC memory card, e.g., 5 mm, a weight lighter than 70g, stability against mechanical shock of more than 200G and resistance to external magnetic field of more than 1 kGauss. A disk drive embodying the present invention comprises a rectangular housing, inside which are contained at least one disk that stores information, a disk driving means that forces the disk to rotate, a head assembly that performs read/write operations on the disk, and electronic circuitry. Also, at least one connector that is connected to the electronic circuitry is fixed outside the housing. Further, the above electronic circuitry includes an interface circuit that allows communication with an external host system, a read/write circuit that receives read signals from the head assembly and provides write signals to the head assembly, a servo circuit that controls the operation of the magnetic disk and head assembly, and a control circuit that receives control signals from the host system via the interface circuit and provides the control signals to the read/write circuit and the servo circuit. Further, the above head assembly includes a magnetic head that executes reproducing/recording operations corresponding to read/write operations of information at a predetermined position on the magnetic disk, a supporting spring mechanism that supports the magnetic head, an arm that supports the spring mechanism, and a rotary type actuator that forces the arm to rotate in either direction and the magnetic head to move to a predetermined position on the magnetic disk. Preferably, the above housing has a base at the lower side and a cover at the upper side, and electronic components that constitute the above electronic circuitry are assembled on at least one printed circuit board which is located along either one inner wall surface or both of respective inner wall surfaces of the base and cover. More concretely, the above printed circuit board is composed of a flexible printed circuit board. Alternatively, both the base and cover are made of metal and are also used as metal based printed circuit boards. Further, preferably, the disk drive according to the present invention has outer dimensions in plane directions of approximately 85.6 mm × 54 mm and has a thickness of less than 8 mm, typically 5 mm. Further, preferably, a plurality of insertion guide portions, which allow said housing to be inserted into a slot of a host device so that the disk drive can be in an operative condition, are provided on predetermined portions of the respective sides having longer dimensions of the housing. Further, preferably, only one connector is attached to a portion of one of the sides with shorter dimensions of the housing. Furthermore, the connector is located in an approximately central position in respect to the thickness direction of the housing, and is attached to either one of the sides having the shorter dimensions of the housing, in a position opposite to the head assembly across the magnetic disk. Further, preferably, the base and cover of the housing have coupling flanges, respectively, that extend outward at the outer peripheral portion thereof, excluding the portion where the connector is located, the housing being formed by jointing the above coupling flanges together. In this case, the base and cover are made of a metal including iron, a metal including aluminum or resin material. Furthermore, the jointed coupling flanges are preferably covered with at least one frame, that is constructed so that it serves as an insertion guide rail, a sealing means for ensuring that the inside of the housing remains closed, or a buffer means that protects the housing from a mechanical shock. Further, preferably, the disk driving means includes a spindle motor that is located at the inner portion of the disk so that the disk can rotate. Further, the above spindle motor has a first fixed shaft that is fixed in a predetermined position within the housing so as to support the disk rotatably, and has a pair of first bearing means that are fixed at the upper side and lower side of the first fixed shaft, respectively, so as to hold the disk. The above head assembly has at least one magnetic head that executes reproducing/recording operations corresponding to read/write operations of the information on either surface of the upper and lower surfaces of the magnetic disk, at least one arm that supports the magnetic head, and an actuator that forces the arm to rotate in either direction and the magnetic head to move to the predetermined track on the magnetic disk. The head assembly further has a rotary type actuator that forces the arm to rotate in either direction and the head to move to the predetermined track on the magnetic disk, a second fixed shaft that is fixed in a predetermined position within the housing, and has a pair of second bearing means that are fixed at the upper side and lower side of the second fixed shaft, respectively. Furthermore, the above first fixed shaft and second fixed shaft are constructed to be fastened to the base by fitting them into the base. Further, preferably, the first fixed shaft and second fixed shaft have flange portions on one portion of the first fixed shaft and second fixed shaft, respectively, wherein the flange portion of the first fixed shaft has a diameter approximately equal to or larger than the average span between the pair of first bearing means, and the flange portion of the second fixed shaft has a diameter approximately equal to or larger than the average span between the pair of second bearing means. Further, preferably, the first fixed shaft at the disk and second fixed shaft at the actuator are rigidly coupled with the cover in respect to the thickness direction of the housing. More concretely, one end of the fixed shaft at the disk and the fixed shaft at the actuator are fixed to the cover by spot welding or by adhesion. Further, preferably, the spindle motor has a fixed shaft that fixes the spindle motor per se in a predetermined position within the housing, a pair of bearing means that are fixed around the fixed shaft, a spindle hub that has an outer portion engaged with the central hole of the magnetic disk and has an inner portion mounted in the first fixed shaft rotatably via the bearing means, at least one rotor magnet that is fixed to the spindle hub, and at least one stator coil that is fixed to the base. In this case, the rotor magnet is located between the position of the inside diameter of the magnetic disk and the position of the outer peripheral portion of the bearing means in respect to the radial direction of the rotor magnet. More concretely, the spindle motor is an outer ring rotating type motor, and the rotor magnet has a thickness larger than the average distance between the pair of bearing means at the upper and lower sides, and the respective centers of the magnetic disk, the rotor magnet and the pair of bearing means are located in the approximately same position in respect to the thickness direction of the housing. Alternatively, the spindle motor is a flat type motor with an axial gap in which a magnetic gap is formed in the axial direction of the fixed shaft of the spindle, and the magnetic disk is engaged with the outer peripheral portion of the rotor magnet, and the inner peripheral portion of the rotor magnet is rotatably supported by the fixed shaft of the spindle via the bearing means, and the rotor magnet is constructed such that it also serves as a spindle hub. In both of the above two kinds of spindle motors, the magnetic disk is preferably fixed to the spindle hub by adhesion. Further, preferably, a load/unload assembly is provided inside the housing that allows the magnetic head to be loaded in a predetermined position on the magnetic disk and the magnetic head to be unloaded from the position thereon in connection with inserting/removing operations for inserting the housing into a slot of a host device and for removing the housing from the slot thereof. Furthermore, a locking assembly is provided inside the housing that forces the magnetic disk and actuator to be locked mechanically in a predetermined position in connection with the above inserting/removing operations. Further preferably, the actuator includes a flat coil that is located in one end of a moving part of the arm (carriage) opposite to the magnetic head in respect to the second fixed shaft of the actuator; an upper yoke, a lower yoke and side yokes that are located around the flat coil; and a permanent magnet that is located in either one or both of the upper and lower yokes. In this case, a magnetic circuit is constituted from the upper yoke, lower yoke, side yokes and permanent magnet. Furthermore, either one or both of the upper and lower yokes are constructed such that the width of each central portion of the upper and lower yokes is larger than the width of each remaining portion thereof. Further preferably, the actuator is a moving coil type actuator that includes an upper yoke element having a plurality of first bent portions that are bent downward at approximately right angles, respectively, and a lower yoke element having a plurality of second bent portions that are bent upward at approximately right angles, respectively. Furthermore, a closed magnetic path is formed by combining the upper and lower yoke elements with each other. Further preferably, the disk drive according to the present invention further comprises a retraction magnet that is provided in the outer fringe part of the actuator to force the magnetic head to be in retraction, and a retracting yoke that is located around the retraction magnet and has a gap in which the retraction magnet is placed. More concretely, the thickness of the gap is changed in the direction of displacement of the magnetic head so as to retract the magnetic head toward a predetermined position. Typically, the thickness value g of the gap is changed approximately with a relation of approximately 1/(× + × 0 ) in respect to the displacement value × of the magnetic head. Alternatively, the area of the portion, where the retraction magnet and retraction yoke overlap with each other in the plane included in a space therebetween, is changed in the direction of displacement of the magnetic head so as to retract the magnetic head toward a predetermined position. Additionally preferably, the disk drive according to the present invention comprises a rectangular housing which includes one magnetic disk that is equal to or less than 4.8 cm (1.89 inches), a head assembly having two magnetic heads that execute read/write operations, and further comprises one connector that is connected to the electronic circuitry outside the housing, and has outer dimensions in plane directions of approximately 85.6 mm × 54 mm. In such a construction, the magnetic disk and two magnetic heads are constructed such that perpendicular magnetic recording can be executed. Typically, each of the two magnetic heads is a unitary magnetic head that has a body comprised of flexible thin sheet. Alternatively, the magnetic disk and two magnetic heads are constructed such that longitudinal magnetic recording can be executed, and each of the two magnetic heads includes a head slider with a predetermined flying height. BRIEF DESCRIPTION OF THE DRAWINGS The above object and features of the present invention will be more apparent from the following description of the preferred embodiments with reference to the accompanying drawings, wherein: Figs. 1, 2 are views showing an example of a disk drive structure according to a prior art; Figs. 3, 4, 5, 6, 7, 8 and 9 are views showing a disk drive structure useful for understanding the present invention; Fig. 10 is a view showing a whole spindle motor construction of a disk drive useful for understanding the present invention; Fig. 11 is a view showing an actuator construction of a disk drive useful for understanding the present invention; Figs. 12, 13, 14 and 15 are views showing one improved example of a whole spindle motor construction as in Fig. 10; Fig. 16 is a view showing a preferred embodiment of a whole spindle motor construction as in Fig. 10; Figs. 17 and 18 are views showing one preferred embodiment of a head retracting construction of a disk drive according to the present invention; Fig. 19 is a graph for explaining the relationship between the displacement of a magnetic head and the gap value in Fig. 18; Fig. 20 is an enlarged perspective view of Fig. 18; Fig. 21 is a model of rotation utilizing magnetic force for explaining the principle of a head retracting mechanism in a disk drive according to the present invention; Fig. 22 is a graph showing the result of actual measurement of torque in a head retracting mechanism of gap changing type; Fig. 23 is a view showing an example of a head retracting mechanism of area changing type; and Fig. 24 is a view showing still an other example of a head retracting mechanism in a disk drive according to the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing the embodiments of the present invention, the related art and the disadvantage therein will be described with reference to the related figures. Figs. 1 and 2 are views showing an example of a disk drive structure according to a prior art. To be more specific, Fig. 1 is a front view showing the whole structure of a disk drive according to a prior art, and Fig. 2 is a schematic diagram showing separately a circuit assembly and a mechanical assembly of the disk drive in Fig. 1. In this case, a magnetic disk drive 1 has two housings, i.e., an inner housing 6 and an outer housing 7. As shown in Figs. 1 and 2, a magnetic disk 2, a spindle motor 3, a magnetic head mechanism 4, a head IC 5 constituting an amplifying circuit 5a and the like are contained in the inner housing 6, which is enclosed in the outer housing 7. Further, in a space between the outer housing 7 and the inner housing 6, an IC 8 constituting a read/write circuit 8a, an IC 9 constituting a control circuit 8b, an IC 10 constituting a positioning circuit 8c and an IC 10' constituting an interface circuit 8d are incorporated. Furthermore, a connector 7' is attached in the outer housing 7. Such a magnetic disk drive 1 is usually stored in a predetermined place, and is carried and connected to an external host system, such as a host computer (not illustrated) by utilizing the connector 7', as occasion demands. Further, information can be read (reproduced) off the magnetic disk 2 and the information can be written (recorded) on the above magnetic disk 2, utilizing the read/write circuit 8a. More specifically, in the above circuit configuration, control signals S c and address signals S a are sent from the host computer to the interface circuit 8d via the connector 7'. Further, the control signals S c are input to the control circuit 8b, and status signals S s indicating the current status of the magnetic disk drive 1 are issued from the control circuit 8b to the interface circuit 8d. Also, the interface circuit 8d is coupled to the positioning circuit 8c, which determines the position of the magnetic head mechanism 4 on the magnetic disk 2 in accordance with instructions from the host computer. The information of the above position read by the magnetic head mechanism 4 is sent back to the positioning circuit 8c as position signals S p , via the amplifying circuit 5a, so that accurate positioning can be performed by means of servo control. Further, power is supplied to all the above circuits, together with any other associated circuits. In the above-mentioned prior art, the inner and outer housings 6, 7 form a double structure, where the disk drive 1 has the inner housing 6 that incudes main mechanical components, and has the outer housing 7 that surrounds the inner housing 6 and that includes mainly electronic circuitry. Owing to such a double structure, the lower limit of the thickness H 1 (Fig. 1) of the outer housing 7, i.e., the height dimension of the disk drive 1 is likely to be limited to a certain minimum value. Consequently, it becomes difficult to realize a disk drive having a thickness as small as that of an IC memory card and having overall dimensions that conform to those of the IC memory card, according to the prior art as illustrated in Figs. 1 and 2. Therefore, a disk drive in which the outer dimensions thereof, the whole thickness in particular, can be reduced remarkably by providing a housing of a single structure, is highly desired. Figs. 3, 4, 5, 6, 7, 8 and 9 are views showing a disk drive structure useful for understanding the present invention. To be more specific, Fig. 3 is a perspective view showing an outer appearance of a magnetic disk drive and the dimensions thereof; Fig. 4 is a perspective view partially showing the construction within a housing; Fig. 5 is a schematic diagram separately showing a circuit assembly and a mechanical assembly illustrated in Fig. 4 separately; Fig. 6 is an exploded perspective view showing the construction of Fig. 4 in more detail; Fig. 7 is a sectional front view of Fig. 4; Fig. 8 is an enlarged sectional view taken along a line I-I of Fig. 4; and Fig. 9 is an enlarged sectional view taken along a line II-II of Fig. 6. As illustrated in these figures, a magnetic disk drive 20 comprises a single rectangular housing 21 that is constituted from a base at the lower side and a cover at the upper side. Further, the housing 21 has outer dimensions in plane directions of approximately 85.6 mm × 54 mm and has a thickness of less than 8 mm, typically 5 mm or 3.3 mm; namely, the above magnetic disk drive 20 can have the same size as that of the currently used IC memory card of type II of PCMCIA. In this case, unlike the prior art as shown in Figs. 1 and 2, one magnetic disk 24 preferably having a diameter of 48 mm or 1.89 inches that stores information, a disk driving means 15 that forces the magnetic disk to rotate, a head assembly that performs read/write operations on the magnetic disk 24, and electronic circuitry that is composed of electronic components 70 are contained in a closed space within the above single housing 21. Further, the above disk driving means 15 has a spindle motor 26 that is located at the inner portion of the magnetic disk 24 so that the magnetic disk can rotate and a fixed shaft 25 of spindle that is fixed in a predetermined position within the housing 21 so as to support the magnetic disk 24 rotatably. Furthermore, the above head assembly has at least one magnetic head 27 that executes reproducing/recording operations corresponding to read/write operations of the information on either surface of the upper and lower surfaces of the magnetic disk 24, at least one arm 28 that supports the magnetic head 27, and an actuator 29 that forces the arm 28 to rotate in either direction and the magnetic head 27 to move to the predetermined track on the magnetic disk 24. Further, in some disk drives, a head with a small pressing load is utilized as the above magnetic head. For example, when the contact type magnetic head, disclosed in Japanese Unexamined Patent Publication (Kokai) No. 3-178017 is utilized as the magnetic head 27, an extremely small load of several tens of mg can be used. On the other hand, in the flying type head as shown in Figs. 4 to 7, it is possible for a head with a relatively small load of several hundreds of mg to be utilized. Further, by applying the negative pressure type head slider and load/unload mechanism to the disk drive according to the present invention, the friction of the head, caused when a spindle motor starts up, can be substantially neglected. By virtue of such advantages, a spindle motor, that starts up with a relatively low power voltage, can be realized. Furthermore, the above electronic circuitry includes an interface circuit 39 that allows communication with an external host computer, a read/write circuit 36 that receives read signals from the head assembly and provides write signals to the head assembly, a servo circuit that is comprised of a positioning circuit 37 and an amplifying circuit (head IC) 35 to control the operations of the magnetic disk 24 and the head assembly, and a control circuit 38 that receives control signals S c from the external host computer via the interface circuit 39 and provides the control signals S c to the read/write circuit 36 and the servo circuit. More specifically, the control signals S c and address signals S a are sent from the host computer to the interface circuit 39 via the connector 42. Further, the control signals S c are input into the control circuit 38, and status signals S s indicating the current status of the magnetic disk drive 20 are issued from the control circuit 38 to the interface circuit 39. Also, the interface circuit 39 is coupled to the positioning circuit 37, which determines the position of the magnetic head 27 on the magnetic disk 24 in accordance with instructions from the host computer. Here, the information of the above position read by the magnetic head 24 is sent back to the positioning circuit 37 as position signals S p , via the amplifying circuit 35, so that accurate positioning can be performed by means of servo control. Further, power is supplied to all the above circuits via the connector 42, together with any other associated circuits. Hereinafter, with regard to the various signals in the interface circuit in the disk drive, some additional explanation will be given. As the specifications of the interface utilized for the connector 42, the following specifications can be used; namely, SCSI (Small Computer System Interface), IDE (or PC/AT) and PCMCIA-ATA(AT Attachment) that will be standardized in the near future. Among these interface specifications, with regard to SCSI and IDE, in particular, their electrical specifications are different from the electrical specifications of the IC memory card fabricated in accordance with PCMCIA. Accordingly, it is impossible for a disk drive fabricated in accordance with SCSI or IDE, and the above IC memory card to be used in common. On the other hand, since PCMCIA-ATA provides an extended function of PCMCIA PC Card Standard, a disk drive fabricated in accordance with PCMCIA-ATA and a disk drive fabricated in accordance with usual PCMIA can be inserted into the same slot of a host computer. Therefore, the PCMCIA-ATA can be recommended as the interface of choice. Furthermore, a power supply voltage of preferably 3 - 3.3V, should be used. In conventional electronic circuits, power consumption can be reduced by operating the circuits at a relatively low voltage. An IC memory operative at a lower voltage can be obtained due to the recent progress in the design of electronic circuits. However, the decreasing of a voltage supplied to mechanical components does not always lead to a reduction in power consumption. On the contrary, in such a case, the ratio of power consumption of electronic circuits for driving the mechanical components to power consumption of the mechanical components per se is likely to be rather increased. The main designs for effectively decreasing applied voltage are as follows. First, a spindle motor can be improved and therefore the start-up operation at a lower voltage can be realized. Second, the diameter of bearing means can be made smaller and therefore a load torque can be reduced. Third, a head with a lower pressure load can be adopted and therefore a load torque during start-up operation can be reduced. Fourth, a housing made of metal including iron can be adopted and therefore shielding against various electrical noises can be improved. Furthermore, as shown in Fig. 6, a plurality of insertion guide portions 50 are provided on predetermined portions of the respective sides having longer dimensions of the housing 21. The above insertion guide portions 50 are intended to allow the housing 21 to be inserted into a slot of a host computer so that the disk drive can be placed in an operative condition, if the respective connectors of the host computer and disk drive are connected with each other. These insertion guide portions 50 are constructed to have a thickness of less than the whole thickness of the housing 21. As apparent from Fig. 7, the disk 24 is located approximately in the central position in respect to the thickness direction of the housing 21. Accordingly, there exists a flat space 30 between the disk 24 and the base 22, and another flat space 31 between the disk 24 and the cover 23. In the vicinity of the arm 28 in the space 30, an IC 35a is incorporated, that constitutes a first stage amplifying circuit 35 for amplifying very small read signals reproduced by the magnetic head 27. Further, in the space 30, ICs for processing analog signals, e.g., an IC 36a that constitutes a part of the read/write circuit 36 and an IC 37a that constitutes a part of the positioning circuit 37, are also incorporated. On the other hand, in a space 31 that is positioned on the opposite side of the space 30 with respect to the disk 24 and is separated from the space 30 by the disk 24, ICs for processing digital signals, e.g., an IC 36b that constitutes the remaining part of the read/write circuit 36, an IC 36b that constitutes the remaining part of the positioning circuits 37, an IC 38a that constitutes the control circuit 38 and an IC 39a that constitutes the interface circuit 38 are incorporated. All the electronic components 70 that include the above-mentioned ICs 36a - 39a are assembled on the respective surfaces of a first body portion 40a and a second body portion 40b of a printed circuit board 14, which are attached close to the inner wall surfaces of the base 22 and cover 23, respectively, and the above electronic components 70 are contained within the housing 21, together with the printed circuit board 14. Preferably, the above printed circuit board (PCB) 14 is a flexible printed circuit board (FPC) 40 that is bent into the lower first body portion 40a and the upper second body portion 40b. In this case, the above flexible printed circuit board 40 has two bands of connecting portions 40c, 40d by which the lower first body portion 40a and the upper second body portion 40b are coupled with each other. Hereinafter the reason why the longer side of the housing 21 is selected as the bent portions (the connecting portions) of the FPC40 in which the upper and lower portions thereof are integrated with each other, will be explained in detail. As illustrated in Figs. 4 and 6, FPC circuit patterns at the upper and lower sides are connected on the FPC. The signals flow from the magnetic head through the connector, via the head IC, demodulation circuit (analog) in the read/write circuit and digital processing circuit. As described above, in view of the analog circuit portion and digital circuit portion being separated between the lower side and upper side of the FPC., respectively, the signals output from the demodulation circuit and the control signals are arranged to pass through the connecting portions. As the position where these connecting portions are located, both the shorter sides and longer sides of the housing may be selected. Also as described above, the connector is attached to one of the shorter sides, while the head actuator is located in the vicinity of one of the shorter sides. Accordingly, if the upper and lower sides of the FPC are connected with each other in the shorter side, they must be connected at the side of the head actuator. Such a connecting structure is disadvantageous in that the overall path for the signals becomes longer. On the contrary, if the upper and lower sides of the FPC are connected with each other in the longer side, the above-mentioned signal flow can be realized without any difficulties in arranging circuit patterns. However, when a disk with a diameter of 4.8 cm (1.87 inches) is incorporated inside a housing of memory card size, the disk is likely to protrude outside the housing and strike the longer sides of the housing. To avoid this problem, a part of the connecting portions where the disk protrudes outside the housing is cut out. In such a construction, the connecting portions can be reasonably located at the longer side of the housing. In this case, it is advantageous that the connecting portions are separated into two parts as shown in Fig. 6, so that the elastic force that is generated in the connecting portions when the FPC is bent back, can be reduced. As illustrated in Fig. 8, the above connecting portions 40c (40d) are located across the base 22 and cover 23. Further, when the housing 21 is in a closed condition such that the cover 23 covers over the base 22, the connecting portions 40c (40d) are curved so that they protrude inside the housing 21 as shown in Fig. 9. As apparent from Fig. 9, since the connecting portions are constructed to have excess length, it becomes possible for the base 22 and cover 23 to be arranged in plane directions and for the various components to be incorporated inside the housing 21. As the excess length of the connecting portions becomes large, the components can be incorporated more easily, while the protruding parts formed by this excess length are likely to interfere with the disk 24 and the other mounted components. To avoid this difficulty, it is proposed that these protruding parts be bent back further so that they are folded together in multiple layers. More concretely, in the condition that the base 22 and cover 23 are arranged in plane directions, such a folded structure can be realized by forcing down the center of the bridge portion of the FPC40 with a wire. In the condition that the base 22 is overlaid with the cover 23, the cover 23 adheres closely to the base 22 via a packing 41, and therefore the whole space within the housing 21 where the disk, etc., are contained is closed up tightly. In this case, to reduce the pressure difference between the inside and outside of the housing caused by the temperature rise during operation of the disk drive, an air filter for circulation is attached to the housing. In that sense, it cannot always be said that the space within the housing is perfectly closed up. However, dust in the air can be prevented from entering the housing. Therefore, the structure, in which the air filter is provided, is also usually referred to as a tightly closed structure. Further, the connector 42 is attached to either one of two sides having shorter dimensions of the housing 21. Here, the above connector 42 is located in a position opposite to the actuator 29 across the disk 24 and is located in the approximately central position in respect to the thickness direction of the housing 21, so that mechanical support of the whole disk drive can be achieved by means of the connector 42 with good balance of weight. The magnetic disk drive of the present invention does not incorporate a vibration-free support mechanism that is employed in general devices, but employs a mechanical support using a connector which makes a feature. The connector which has as many as 68 pins produces a considerably large holding force but still consideration must be given to cope with the disturbance. The disturbance which is internally generated stems from (1) vibration due to the unbalanced spindle and (2) seek reaction of the actuator. Furthermore, external vibration and shocks are added thereto. Here, first, countermeasure is taken against the above two causes of internal generation. First, vibration due to the unbalanced spindle generates while the spindle is revolving and becomes a cause of error in position. Therefore, attention is given in an effort to minimize the amount of residual imbalance, and support conditions are contrived too to reduce the effect. Generally speaking, the vibration due to imbalance is determined by a moment of the center of rotation of the spindle and the center of gravity or the distance of the fulcrum. In the present invention which accomplishes the support using the connector, therefore, the spindle is disposed on a side close to the connector and the actuator is disposed on a side remote from the connector. The moment that is generated can be decreased by about 40% compared with that of the constitution fabricated in an opposite manner, and the error in position due to the vibration of imbalance can be decreased by 40%. When completely balanced, only the moment of rotation generates which does not change irrespective of the position of the actuator. In principle, therefore, there arises no adverse effect even when the actuator is disposed on the side remote from the connector. To cope with the reaction of the actuator, first, the connector accomplishes the linear support; i.e., considerably rigid support is accomplished in the direction of rotation to suppress the rotary motion of the whole drive caused by the moment generated by the actuator thereby to suppress the error in position caused by the turn of the drive. The connector is disposed at the center in the thickness direction of the drive and, further, the center of gravity of the actuator is brought into this position, so that there takes place no motion due to the seek reaction (moment) in the up-and-down direction or in the twisting direction. This makes it possible to suppress error in position, fluctuation of floatation, etc. caused by the motion in the directions outside the planes. More concretely, the connector 42 is fixed on the cover 23 of the housing 21 and is connected to the second body portion 40b of the FPC 40, on which the digital electronic components such as the IC 39a of the interface circuit 39 are assembled. Further, a par o of the second body portion 40b, that is connected to the connector 42, is covered with the packing 41. A similar construction of the above-mentioned disk drive has been disclosed in Japanese Unexamined Patent Publication (Kokai) No. 60-242568. However, in such a known construction, it is not described clearly that all the electronic components including analog and digital components are incorporated within a single housing, unlike the above-described disk drive. On the contrary, the disk drive explained above is intended to accommodate all the electronic components, as well as the disk and various mechanical components by utilizing the spaces within a single housing effectively. Consequently, the disk drive 20 can have a single housing structure and can have a thickness dimension of approximately 5 mm which is the same as that of an IC memory card of the above-mentioned type II of PCMCIA. Therefore, the disk drive 20 becomes thinner and more compact than any disk drive according to a prior art, and it can be more easily used for a portable computer than the prior art disk drive. Furthermore, since the connecting portions 40c, 40d are previously formed in the above-mentioned FPC 40, it becomes unnecessary to provide a connector component for connecting two body portions 40a, 40b to each other. Owing to the above advantage, the disk drive 20 can have an even thinner dimension as desired for a suitable and portable memory device. The construction of the disk drive as described above has also the following features. First, an analog circuit portion for processing analog signals and a digital circuit portion for processing digital signals are separated from each other at the lower side and upper side of the housing, respectively. Second, a substrate of the disk, that is generally made of metal including aluminum, is located between the above two separated circuit portions; namely, the disk substrate has a function of electromagnetically shielding the above two circuit portions from each other. In such a construction, it becomes possible for analog signals in the analog circuit portion to be prevented from suffering negative influence due to electromagnetic waves generated by the digital circuit portion. In other words, the disk drive has a structure in which a counter measure against various electric noises cab be taken without increasing the thickness dimension of the disk drive. In this case, it will be also possible in the future for the thickness of the disk drive to be reduced to 3.3 mm which is the same as that of the type I of PCMCIA IC memory card. Further, since the structure of such a disk drive is resistant to electric noises, a disk drive operative at a lower power supply voltage can be realized and power consumption in the disk drive can be reduced. Hereinafter, a whole spindle motor construction of a disk drive will be described with reference to Fig. 10. Fig. 10 is a view showing a first preferred a whole spindle motor construction of a disk drive useful for understanding the present invention. In Fig. 10, the main part of the spindle motor construction is illustrated. As shown in Fig. 10, a fixed shaft 25 is fastened to the base 22 and cover 23 in order to hold the spindle motor 26 per se in a predetermined position within the housing 21 so that one magnetic disk 24 can rotate therein. A pair of first bearing means 26-2 (from now on, "first" will be omitted) are fixed around the spindle 25 in order to support the fixed shaft 25. Further, a spindle hub 11 has an outer portion engaged with the central hole of the magnetic disk 24 and has an inner portion rotatably mounted on said fixed shaft 25 via the bearing means 26-2. In this case, a rotor magnet 26-3 is composed of a permanent magnet having the form of a flat plate that is magnetized in the axial direction of the fixed shaft 25, and is fitted into a recessed portion of the bottom surface of the spindle hub 11 and is finally adhered thereto. The spindle hub 11 is made of a soft magnetic material that can be utilized as a yoke. Alternatively, if a nonmagnetic material is used for the spindle hub 11, the rotor magnet 26-3 is adhered to this spindle hub 11 via another yoke. In this case, preferably, an outer ring rotating motor in which the outer ring portion of the bearing means 26-2 rotates is utilized as the spindle motor 26. Further, a stator coil 26-4 is fixed on the upper wall surface of the base 22 inside the housing 21, so that the stator coil 26-4 faces the rotor magnet 26-3, close to the rotor magnet 26-3 with a certain axial gap. To be more specific, the rotor magnet 26-3 is located between the position of the inside diameter of the magnetic disk 24 and the position of an outer peripheral portion of the bearing means in respect to the radial direction of the rotor magnet 26-3. The base 22 that constitutes a part of the housing 21 is made of a soft magnetic material and also serves as a stator yoke. Here, the stator coil 26-4 is located in a such a manner that it protrudes toward the space near the magnetic disk 24 inside the housing 21. In this construction of the spindle motor, a face-to-face type motor, i.e., a flat type motor, utilizing the magnetic flux in the axial direction of the spindle 25 between the rotor magnet 26-3 and stator coil 26-4, can be formed, and the spindle hub 11 and the magnetic disk 24 rotate in an integrated form with the rotor magnet 26-3 in accordance with the rotation thereof. In this case, the thickness of the spindle motor per se can become remarkably small. By using the face-to-face type (axial gap) motor, the almost inside of the motor can be covered with the bearing, and also the outer diameter of the motor can be smaller than the inner diameter, and thereby the drive having a thickness of lower than 5 mm can be realized. Further, since at least the base 22 is made of a soft magnetic material and acts as a yoke simultaneously, a disk drive, in which excellent characteristics can be ensured with smaller size and lower weight than a prior art disk drive, can be provided. In particular, the above structure can be effectively applied to a disk drive utilizing a small number of magnetic disks. Fig. 11 is a perspective view illustrating the structure of the actuator in a magnetic disk drive useful for understanding the present invention. In Fig. 11, the arm 28 has an arm end 28-1 for holding at its end the magnetic head 27 as mentioned earlier, and is disposed to rotate in the direction of arrow B with a second fixed shaft 45 as a center, and has a flat coil 67 attached to the rear end thereof. A pair of permanent magnets 29-5 and 29-6 are arranged near the flat coil 67. Furthermore, an edge portion on the side of the arm 28 is curved in the direction of width, and a central portion of an edge portion on the side opposite to the above edge portion is protruded in a cornered shape to form a lower yoke 29-2 which can be arranged at the corner of the disk drive efficiently utilizing the space in the magnetic disk drive. There is further provided an upper yoke 29-1 of a curved shape having ordinary width. The upper and lower yokes 29-1 and 29-2 are magnetically coupled together at their both sides by using side yokes 29-3 and 29-4 maintaining a predetermined distance. The flat coil 67 moves in a gap between the upper yoke 29-1 and the pair of permanent magnets 29-5, 29-6 in a magnetic circuit 65 constituted by the above yokes, and thus a drive coil motor (DCM) is constituted. In the actuator of this disk drive as mentioned above, the lower yoke 29-2 has a broad central portion in which the magnetic flux density becomes great as the magnetic flux directly passes from one permanent magnet 29-5 to the other neighboring permanent magnet 29-6 in the magnetic circuit 67. Furthermore, the sectional area is increased by increasing the area of the lower yoke 29-2. Therefore, the problem of magnetic flux saturation is eliminated even when the thicknesses of the lower yoke 29-2 and the upper yoke 29-1 are decreased, making it possible to suppress the drop in the magnetic flux density across the gap which is caused by the leakage of magnetic flux due to magnetic flux saturation. The lower yoke 29-2 having the above-mentioned shape enables the actuator 29 to be installed at the corner in the magnetic disk drive to efficiently utilize the space, and the disk drive as a whole can be constructed in a compact size. Figs. 12, 13, 14 and 15 are diagrams illustrating an improvement from the structure of the spindle motor shown in Fig. 10. If described in further detail, Fig. 12 is a sectional view of the spindle motor of the axial flux type according to the above improved example. Aventurine portions 75 denote a magnetic path auxiliary means which according to this embodiment is formed together with a rotor yoke 76 as a unitary structure. Figs. 13 to 15 illustrate in detail the structure of the spindle motor of the axial flux type, wherein Fig. 13 is a perspective view of a constituent block, Fig. 14 is a sectional view along the line IV-IV of the constituent block of Fig. 13, and Fig. 15 is a sectional view along the line V-V of the constituent block of Fig. 13. Aventurine portions 75 denote a magnetic path auxiliary means which is formed together with the rotor yoke 76 as a unitary structure. In Fig. 13 , an annular magnetic path auxiliary means 75 made of a magnetic material is disposed at a position near the magnet 26-3 and the stator 26-4 to trap the leakage magnetic flux. That is, the annular magnetic path auxiliary means 75 is formed together with the rotor yoke 76 as a unitary structure so as to include therein the magnets 26-3 and stator coils 26-4 that are annularly arranged. The gap between the magnetic path auxiliary means 75 and the stator yoke 77 is set to be smaller than the gap between the magnets 26-3 and the stator yoke 77. When the spindle motor 26 is rotating, therefore, a closed magnetic path is formed in the circumferential direction as indicated by a broken line with arrow in Fig. 14. As shown in Fig. 15, furthermore, the leakage magnetic flux is trapped by the magnetic path auxiliary means 75 which exhibits properties of the magnetic material, and auxiliary closed magnetic paths are formed in the radial direction passing through the magnetic path auxiliary means 75. That is, when there is no magnetic path auxiliary means, the magnetic flux passes through the closed magnetic path of the circumferential direction only. In this structure , however, the magnetic flux disperses in the auxiliary closed magnetic paths of the radial direction. Therefore, the magnetic flux density decreases in the rotor yoke 76 and in the stator yoke 77; i.e., the magnetic flux is not saturated in the rotor yoke 76 and in the stator yoke 77, resulting in a decrease in the leakage magnetic flux density. On the other hand, the magnetic flux density increases across the gap for rotating the rotor yoke 76 compared with that of when there is no magnetic path auxiliary means. Therefore, even when the rotor yoke 76 and the stator yoke 77 are machined to have thicknesses smaller than those of the prior art, the electric current flowing into the stator coils 26-4 can be efficiently converted into a torque. At the same time, the magnetic head, recording disk and like portions that deal with recording signals are less affected by the leakage magnetic flux density. Fig. 16 is a sectional view illustrating a preferred embodiment of the whole structure of the spindle motor of Fig. 10, and wherein the same constituent portions as those of Fig. 12 are denoted by the same reference numerals but are not described. In this embodiment, the magnetic path auxiliary means 75' is formed integrally with the stator yoke 77. Even this constitution makes it possible to obtain the same effects as those of the embodiment of Figs. 12 to 15. In addition to the above, though not diagramed, the magnetic path auxiliary means 75 (75') may be split and are formed integrally with the rotor yoke 76 and the stator yoke 77, and the thus split magnetic path auxiliary means 75 are opposed to each other to obtain the same effects. In Figs. 12 and 16, the magnetic path auxiliary means 75 is arranged so as to include the magnet 26-3 consisting of a plurality of magnet elements and the stator coil 26-4 consisting of a plurality of coil elements that are annularly and contiguously arranged from both the inner and outer peripheral sides. However, the leakage magnetic flux density can be decreased to be smaller than that of the prior art even when the magnetic path auxiliary means 75 is arranged on either the inner peripheral side or the outer peripheral side only. According to the above improved embodiments shown in Figs. 12 to 16, the magnetic path auxiliary means helps decrease the leakage magnetic flux density that is caused by saturation in the rotor yoke and in the stator yoke, and the electric current flowing into the coil is efficiently converted into a torque and, besides, the portions such as the magnetic head and the recording disk that deal with recording signals are less affected by the leakage magnetic flux density. It is therefore allowed to easily provide a spindle motor having a size and a thickness which are smaller than those of the prior art. Figs. 17 and 18 are diagrams illustrating a preferred embodiment of a magnetic head retracting assembly in the magnetic disk drive of the present invention. If described in further detail, Fig. 17 is a plan view which illustrates a portion of the magnetic head retracting assembly in an emphasizing manner, and Fig. 18 is a side view which schematically illustrates the magnetic head retracting assembly. The magnetic disk drive and the IC memory card used for personal computers require a high degree of durability with respect to not only shocks but also external magnetic field. The IC cards must not permit data to become abnormal even in a magnetic field which is as strong as 1 KGauss (1000 Gauss). However, equipment having an aluminum base/cover are not generally capable of withstanding such an intense magnetic field. In the magnetic disk drives, in general, the magnetic head and the medium portion (magnetic disk) must be placed in a magnetic field which is weaker than 5 Gauss. Therefore, a steel base/cover is employed as mentioned earlier to completely shield the magnetism. A steel plate having a thickness of about 0.4 mm exhibits a shielding effect to a degree sufficient to meet the above demand. However, the problem exists in that the steel plate that is press-worked often has a residual magnetization of as great as about several tens of gausses. As required, therefore, the magnetic annealing is effected to cope with the problem. To minimize the effect caused by the external magnetic field, it is important that the magnetic head is retracted to the data zone when the power source is turned off. This is because, the magnetic head has a large effect for concentrating the magnetic flux and just under the magnetic head, the data is affected by a magnetic field of the order of 10 Gauss and is likely to be erased in a magnetic field of the order of 100 Gauss. In the disk medium without the magnetic head, on the other hand, the data is not erased even in a magnetic field which is as strong as about 1000 Gauss. In view of the fact that a portable disk is affected by the magnetic field disturbance particularly when it is being carried, it is essential to employ a mechanical retracting assembly which does not rely upon the VCM (voice coil motor) drive. In a magnetic disk drive having a floating magnetic head, in particular, it is essential to provide a magnetic head retracting assembly which forces the magnetic head to retract to the parking zone when the disk is stopped in order to avoid damage to the data zone during the CSS (contact start stop) operation, and an actuator locking assembly for holding the retracted magnetic head. Even in the magnetic disk drive using a negative-pressure slider (zero-load slider) that does not perform the CSS operation, it is necessary to employ the retracting and locking operations in view of the fact that the magnetic head comes into collision with the medium when a shock is imparted thereto from the external side. Moreover, the magnetic disk drive having the unloading mechanism requires a mechanism which reliably moves the magnetic head to the unloading position and holds it at that position when the power source is cut off. Usually, the magnetic head retracting assembly: (1) utilizes a return spring, (2) utilizes a counter electromotive force of the spindle motor to force the actuator to retract, or (3) utilizes the gravity. Further, the actuator locking assembly: (1) utilizes a ratchet mechanism, (2) utilizes the frictional force, or (3) utilizes the magnetic force. So far as a linear spring is used, however, the return spring in the ordinary magnetic head retracting assembly (1) exhibits a change in the offset force depending upon a position on the data zone, and greatly affects the control system. Moreover, an excessively great offset force is applied at a position opposite to the retracted zone, and becomes a cause of an increase in the consumption of electric power. Even in the case of the retracting assembly (2), the electromotive force of the spindle motor decreases with a decrease in the size of the magnetic disk drive, and a sufficiently large retracting force is not obtained. Furthermore, the magnetic head retracting assembly (3) which utilizes the gravity is not applicable to the balanced rotary actuator which nowadays is chiefly used. In the modern small disk drives, furthermore, it is not allowed to determine the direction of installation, and the assembly (3) is not utilizable. Further, the actuator locking assembly (1) requires a solenoid or the like for liberating or holding the actuator. The actuator locking assembly (2) requires a fine and cumbersome setting. Even in the case of the locking assembly (3) which performs the so-called catching using the magnetic force of a magnet, the effective range is limited to near the parking zone. The retracting assembly which uses the return spring has the locking ability, but its locking force is weaker than the retracting force unless a magnetic spring is used, and is not practicable. The present invention therefore employs a retracting assembly by using a magnet as shown in Figs. 17 and 18. Here, the head assembly has a rotary actuator 29 (see, for example, Fig. 11), and has a retraction magnet 85 at the outer edge of a flat coil 86 of the actuator 29 in order to maintain the magnetic head 29 under the retracted condition. Moreover, retraction yokes 87 are arranged under and over the retraction magnet 85 thereby to form a closed magnetic path. If concretely described with reference to a graph of Fig. 19 and a gap changing structure of Fig. 20, a gap G in the magnetic circuit is so set in the data zone that a gap value g will vary in proportion to an inverse number of a value X + X 0 which is obtained by adding a given integration constant X 0 to a moving distance X of the magnetic head. Moreover, a stepped portion 87-1 is formed in the yoke 87 so that the gap value g will abruptly decrease in the locking zone. With this formation, a constant torque is produced in the data zone which is greater than the static friction of the bearing means 46. In the locking zone on the outer portion of the magnetic disk, on the other hand, the torque suddenly increases. Therefore, a large holding torque is obtained and the magnetic head is reliably locked. Fig. 21 is a diagram showing a model of magnetic circuit for explaining the principle of the magnetic head retracting assembly according to the present invention. Generally, there are various methods for calculating magnetic attraction, and a method which uses a change ratio of magnetic energy and is used most conveniently will be hereby explained. Magnetic energy W of a system expressed by magnetomotive force NI, magnetic flux  and magnetic resistance R is given by: W = 1/2 2 R = 1/2NI = 1/2(NI) 2 /R The force generated is given as follows by differentiating magnetic energy in the moving direction: F = dW/dx = -1/2(NI) 2 /R 2 dR/dx = -1/2 2 dR/dx Let's consider a magnetic circuit model such as one shown in Fig. 21. In this case, magnetic energy is stored in the space, the magnet and the yoke. Here, ℓ g : air gap distance (inclusive-of thickness of magnet; g is a suffix) ℓ m : thickness of magnet (m is a suffix) S' : sectional area of magnet µ 0 : permeability in air µ r : permeability of recoil H e : intersection of tangent of demagnetization curve at operating point with B = 0 (linearized coercive force) B r : intersection of tangent of demagnetization curve at operating point with H = 0 (linearized residual magnetic flux density; B r = µ r H e ) Assuming in this case that the magnetic resistance inside the yoke can be neglected (or the magnetic energy does not exist), the magnetic resistance R of this magnetic circuit can be expressed as follows: R = { (ℓ g - ℓ m ) µ 0 + ℓ m µ r } 1 S' If µ 0 = µr in this case, R = ℓ g /(µ 0 S') On the other hand, the magnetomotive force NI is given as follows: NI = H e ℓ m Therefore, assuming that the area S' does not change,  = NI/R = µ 0 S'H e ℓ m /ℓ g dR/dx = 1/(µ 0 S')dℓ g /dx Accordingly, the generated force can be given as follows: F = - 1 2 µ 0 S'(H 0 ℓ m ℓ m ) 2 dℓ g dx (generated force due to gap change) As can be understood from the above explanation, a large generated force can be obtained when the magnet is thick relative to the gap and the gap change ratio is great. To obtain predetermined force irrespective of the position X, ℓ g = 1 2 µ 0 S'(H e ℓ m ) 2 1 F • 1 x+x 0 x 0 : integration constant Since it is practically difficult to produce the shape having such functions, a substantially constant torque can be obtained even by a linear change if the gap distance ℓ g is made sufficiently greater than the thickness ℓ m of the magnet. When the device is used as the lock, a step or steps may be provided so that this gap change becomes sufficiently great. Fig. 22 is a graph showing the actually measured result of the torque in the gap change type head retraction mechanism. According to the actually measured result, a substantially constant retraction force can be obtained throughout the full stroke of the head 27, and a torque about four to nine times the retraction force is generated at the lock position on the right side of the graph, so that sufficient performance as the lock mechanism can also be obtained. The holding torque at this lock position becomes greater with a greater thickness (ℓ m ) of the magnet 87 as can be appreciated clearly from the actually measured result of Fig. 22 and from the magnetic circuit model of Fig. 21. Fig. 23 is a perspective view of an example of the area change type retraction mechanism. In Fig. 23, the overlapping area of the retraction magnet 85 and the retraction yoke 87 is change inside the plane between them in the direction in which the magnetic head 29 undergoes displacement, so as to force the head 29 to retract. More in particular, the overlapping area between the magnet 85 and the yoke 87 becomes progressively greater linear-function-wise towards the right side, and the width of the yoke 28 is drastically increased by forming another step 87-2 with respect to the planar direction of the yoke 87. With such a construction, the change with respect to the moving distance X of the retraction force can be calculated using the magnetic circuit model shown in Fig. 21. Namely, this calculation provides: dR/dx = -ℓ g /(µ 0 S 2 ) dS/dx Accordingly, the generated force is given as: F = 1 2 µ 0 (H c ℓ m ) 2 ℓ g • dS dx (generated force due to area change) In other words, a predetermined force can be obtained by the linear change of the area S. In the lock area, a step portion is disposed in the same way as in Fig. 19 so that the holding torque is increased and the magnetic head can be locked reliably. Fig. 24 shows another example of the retraction mechanism for the magnetic head in the magnetic disk drive according to the present invention. In this example, the magnet 85 is not disposed at the moving portion but is assembled in a part of the yoke 87 at the fixed portion. An iron plate 85-1 as a soft magnetic substance is disposed at the moving portion. This arrangement provides the effect similar to that of other embodiments. In this example, however, a magnetic circuit other than the gap is likely to be formed and in such a case, a part of the magnetic flux generated by the permanent magnet does not contribute to the generation of the retraction force. For this reason, the design of the magnetic circuit becomes more difficult. In this embodiment, the yoke 87 is made of a sheet metal which is substantially concentric with the center of rotation, and the center shape and other groove shapes are finished to predetermined shapes. In any of the examples of the head retracting mechanism and the lock mechanism according to the present invention, the retracting force which is substantially constant throughout the full regions of the magnetic disk can be generated by the simple mechanism and a sufficiently large lock force can be generated at the lock position. Accordingly, a compact and high reliability magnetic disk drive can be accomplished. In these embodiments, the direction of the magnetic flux exists in the axial direction of the actuator pivot, but can be set in the radial direction.

Claims: A disk drive comprising inside a rectangular housing: at least one disk (24) that stores information; and a head assembly that performs read/write operations on said disk, wherein said head assembly has a head (27) that executes reproducing/recording operations corresponding to read/write operations of said information in a predetermined position on said disk; a rotary type actuator (29) that forces said head (27) to move through a stroke to said predetermined position on said disk (24); and a retraction mechanism (85,87) which forces said head (27) to move and retract from an arbitrary position above a data zone of said disk (24) to a predetermined position for parking the head; characterised in that said retraction mechanism comprises: a retraction magnet (85) provided in an outer fringe part of said actuator; and a retraction yoke (87) provided with a first portion above a path of movement of said retraction magnet (85) and a second portion below said path such that the height of a gap between said first and second portions decreases in the direction along said path toward said predetermined position, wherein the interaction between said retraction magnet (85) and said retraction yoke (87) produces a substantially constant retraction force throughout the full stroke of the head (27). A disk drive as set forth in claim 1, wherein the height (g) of said gap is changed approximately with a relationship of 1/(X+Xo) in respect to a displacement value (X) of said head and integration constant (Xo) so as to retract said head to said predetermined position by means of a magnetic attraction. A disk drive as set forth in claim 1, wherein said retraction yoke (87) has an area in which the height of said gap becomes extremely small in the position where said head (27) is finally locked. A disk drive as set forth in claim 1, wherein said retraction force is increased abruptly in the position where said head (27) is finally locked by making the thickness value of said gap an extremely small value. A disk drive comprising, inside a rectangular housing: at least one disk (24) that stores information; and a head assembly that performs read/write operations on said disk, wherein said head assembly has a head (27) that executes reproducing/recording operations corresponding to read/write operations of said information in a predetermined position on said disk; a rotary type actuator (29) that forces said head (27) to move through a stroke to said predetermined position on said disk (24); and a retraction mechanism (85,87) which forces said head (27) to move and retract from an arbitrary position above a data zone of said disk (24) to a predetermined position for parking the head; characterised in that said retraction mechanism comprises: a retraction magnet (85) provided in an outer fringe part of said actuator; and a retraction yoke (87) provided with a first portion above a path of movement of said retraction magnet (85) and a second portion below said path, wherein a region of overlap between said retraction magnet and said retraction yoke includes a first subregion corresponding to the head being positioned above said data zone and a second subregion corresponding to the head being parked in said predetermined position, the region having a thickness in a radial direction relative to a rotational axis of said actuator, which thickness increases along said path of movement of said retraction magnet in the direction toward said predetermined position, and wherein the interaction between said retraction magnet (85) and said retraction yoke (87) produces a substantially constant retraction force throughout the full stroke of the head (27). A disk drive as set forth in claim 5, wherein the thickness of the region where said retraction magnet (85) and said retraction yoke (87) overlap upon each other varies as a linear function in the first subregion. A disk drive as set forth in claim 5, wherein said substantially constant retraction force is generated in the first subregion, by changing said thickness in the direction of displacement of said head (27) so that said thickness becomes large as the displacement of said head increases. A disk drive as set forth in claim 1, wherein said retraction yoke (87) is arranged proximate a first end of the path of movement of said retraction magnet (85). A disk drive as set forth in claim 1, wherein said retraction yoke (87) is arranged proximate a second end of the path of movement of said retraction magnet (85). A disk drive as set forth in claim 1, wherein one of said portions of said retraction yoke (87) is arranged on an upper part of the retraction magnet (85). A disk drive as set forth in claim 1, wherein one of said portions of said retraction yoke (87) is arranged on a lower part of-the retraction magnet (85). A disk drive as set forth in claim 1, wherein said gap is taper-shaped. A disk drive comprising, inside a rectangular housing: at least one disk (24) that stores information; and a head assembly that performs read/write operations on said disk, wherein said head assembly has a head (27) that executes reproducing/recording operations corresponding to read/write operations of said information in a predetermined position on said disk; a rotary type actuator (29) that forces said head (27) to move through a stroke to said predetermined position on said disk (24); and a retraction mechanism (85,87) which forces said head (27) to move and retract from an arbitrary position above a data zone of said disk (24) to a predetermined position for parking the head, the retraction mechanism comprising a soft magnetic element (85-1) mounted on a moving portion of the actuator, and a stationary retraction magnet (85); characterised in that said retraction mechanism further comprises: a retraction yoke (87) provided with a first portion above a path of movement of said soft magnetic element (85-1), a second portion below said path, and said retraction magnet, such that the height of a gap between said first and second portions decreases in the direction along said path toward said predetermined position, wherein the interaction between said soft magnetic element, said retraction magnet, and said retraction yoke (87) produces a substantially constant retraction force throughout the full stroke of the head (27).

Inventors: ARUGA KEIJI, KOGANEZAWA SHINJI, KOUHEI TORU, KUROBA YASUMASA, MASE HIROYUKI, MATSUMOTO MASARU, MIZOSHITA YOSHIFUMI, SUGAWARA TAKAO, TSUNEKAWA MASAO, YAMADA TOMOYOSHI, ARUGA, KEIJI, KOGANEZAWA, SHINJI, KOUHEI, TORU, KUROBA, YASUMASA, MASE, HIROYUKI, MATSUMOTO, MASARU, MIZOSHITA, YOSHIFUMI, SUGAWARA, TAKAO, TSUNEKAWA, MASAO, YAMADA, TOMOYOSHI
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1992
Main classification: G11B21
IPC codes: H02K41, H02K33, H02K7, G11B5, G11B19, G11B33, H02K21