Rotary actuator for positioning magnetic heads in a disk drive

Abstract: A rotary actuator for positioning magnetic heads in a disk drive, comprising a stator assembly and a rotor assembly. An arm assembly (9, 10) having magnetic heads (11) is fixed to the rotor assembly (4, 5, 9), which rotates back and forth within a limited angle range around a fixed axis (5) of the rotary actuator due to the forces between plural magnets (6, 7, 8) and a driving current which flows through flat coils (2, 3). Two flat coils (2, 3) are arranged on a arcuate inner surface (1s) of the stator such that two adjacent vertical parallel portions (2a, 3a) thereof closely contact with each other. The two flat coils (2, 3) have an electrical connection with a drive source such that the currents through the two adjacently parallel portions (2a, 3a) flow in the same di­ rection. Three permanent magnets (6, 7, 8) are disposed on the rotor surface, the central magnet (7) having a greater lateral width than that of other two side magnets (6, 8), and a polarity of the central magnet (7) is opposite to that of other magnets (6, 8). In another embodiment, each of flat coils (2, 3) comprises an inner coil (2B, 3B) and an outer coil (2A, 3A) resulting in enhancing the torque of the rotary actuator. Several modifications of coil and permanent magnet arrangement, and other related improvements in the structure thereof are also disclosed.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a rotary actuator for a disk drive used as external storage in a computer system. More particularly, this invention relates to a rotary actuator for positioning a read/write head onto the target track in a disk drive. This invention is intended to provide a rotary actuator having an increased access speed and high reliability. 2. Description of the Related Art A magnetic disk drive or an optical disk drive has made a remarkable progress in storage capacity in recent years. For example, a storage capacity of 1 giga-bytes per spindle can be obtained in a hard magnetic disk drive. There are two types in positioning the magnetic heads: (1) linear actuator type and (2) rotary actuator type. This invention relates to the latter type and an example of the prior art technology is disclosed in Japanese Unexamined Patent Publication SHO-56-88663 by I. Kitamura etal. dated on July 18, 1981. Figures 1 and 2 show schematically a fundamental structure of the rotary actuator and a disk assembly DA, and a disk drive respectively. Figure 1 shows a perspective view, in which the stacked magnetic disk assembly DA and the rotary actuator assembly OM with magnetic heads are separated. Figure 2 shows a plan view of the disk drive, in which these component units are assembled. A spindle 36 having a plurality of disks 37 at equal intervals (in Figure 1, 10 disks are shown) rotates at a speed of 3600 rpm. The data are recorded on both surfaces of the disk 37, and a magnetic head 31, two magnetic heads being arranged on each arm 32, is positioned on a specified track on the disk surface by an actuator movement and perform a read/write operation. In the rotary actuator type, the arm 32 of the actuator assembly can move or rotate within a specified angle ϑ as shown in Figure 2, and the movement thereof is precisely controlled by a rotary actuator OM. The rotary actuator OM cannot rotate continuously but rotate within a limited angle range, therefore, the motor OM is hereinafter called a rotary actuator in the present invention. The rotary actuator OM includes a stator assembly 34 and a rotor assembly 33. The stator assembly 34 comprises a stator housing 39 and a yoke and coils (these are not shown). The rotor assembly 33 comprises a plurality of arms 32 fixed to a rotor yoke (not shown) in a projecting way. A number of arms is equal to that of disks or in a range between number of disks plus one and minus one (9 arms are shown in Figure 1). At each far end of arms 32, a head assembly 30 is disposed having two magnetic heads 31. As shown in Figure 2, the rotary actuator OM is arranged at a corner of a disk enclosure 38, and the stator housing 39 forms a part of a completed disk enclosure. The rotary actuator OM is positioned in such a way that, when the rotor 33 rotates within the angle ϑ, the magnetic head 31 located at far end of the combination of arm 32 and head assembly 30, can sweep the entire recording region on the disk surface. In order to reduce an access time in the disk drive, it is desirable that the rotary actuator OM has a high torque performance. As a structure of the rotary actuator, two types have been known and utilized; (1) moving coil type and (2) moving magnet type. The moving coil type comprises a stator with permanent magnets and a rotor with coils, and the moving magnet type comprises a stator with coils and a rotor with permanent magnets. An example of the latter type is disclosed in U.S. Pat. No. 4,346,416, issued on Aug. 24, 1982 to C.M. Riggle etal., and the same is also disclosed in Japanese Patent Publication SHO-62-35181 dated on July 31, 1987. Figure 3 shows a schematic cross section of the rotary actuator OM of the prior art, the cross section being vertical to the longitudinal axis thereof. A stator includes a yoke 61 and a flat coil 64 arranged on an inside surface of the yoke 61 and further includes an axis 63 fixed to the stator. The coil 64 has a shape as shown in Figure 4. A rotor 62 can move around the axis 63 and holds two permanent magnets 65 and 66, which are elongated in a direction vertical to the sheet and facing parallel windings 64a and 64b in a longitudinal direction. The polarity arrangements of two permanent magnets 65 and 66 are reversed. The permanent magnet 65 has an S pole facing the coil winding 64a and the permanent magnet 66 has an N pole facing the other coil winding 64b. When the rotary actuator OM is actuated, an electrical current flows along the coil winding. The directions of the current flow along the coil windings 64a and 64b are opposite and further the directions of magnetic flux in the gap regions are also opposite, therefore, the rotor is subjected to two torques working additively. The movement of the rotor 62 can be precisely controlled by the direction and the magnitude of the electrical current. The structure of the rotary actuator OM shown in Figure 3 develops a comparatively small torque because it has only one pair of poles (two pole type). In order to obtain a larger torque, a structure having two pair of poles (four pole type) and two coils, is disclosed in Japanese Unexamined Patent Publication SHO-60-5480 dated on Jan. 12, 1985 and EP-A-0 127 058. The four pole type of a rotary actuator OM is schematically shown in Figure 5. Two flat coils 74 are arranged on an inside surface of a yoke 71, and four permanent magnets 75 to 78 are fixed on a rotor 72. This type of the rotary actuator OM has a capacity to develop a larger torque and an effect to reduce the magnitude of the magnetic flux compared with the two pole type, resulting in making a thickness of the coil thin. In designing a rotary actuator having a rotor with four magnetic poles, it becomes a problem to arrange plural permanent magnets in a limited area of the rotor surface. In Figure 5, the details of a mechanical structure for supporting a plurality of arms are not shown for simplicity, each arm having a head assembly. The arm assembly restricts utilization of the entire surface of the rotor, and further, the radius of the rotor is smaller than that of the yoke. Therefore, a circumferential width of each permanent magnet is inevitably reduced. This fact reduces the intensity of the magnetic flux in the gap between the permanent magnet and the coil, resulting in reducing the torque of the rotary actuator. SUMMARY OF THE INVENTION It is a general object of the invention, therefore to provide a rotary actuator having a larger motor torque within a limited space of a specified outline. It is a more specific object of the invention to provide a rotary actuator of a multipole type having a larger motor torque. It is another object of the invention to provide a rotary actuator having a uniform motor torque over a whole range of rotation thereof. It is still another object of the invention to provide a rotor and arm assembly comprised in a rotary actuator, a natural vibration frequency thereof being as high as possible. Foregoing and related objects for obtaining a rotary actuator with a larger motor torque are accomplished by the rotary actuator of the present invention as defined in claim 1 and depending claims which comprises a stator having a yoke, an inside surface thereof being substantially of an arcuate shape in a longitudinal direction, a rotor arranged in a region defined by the arcuate shape of the yoke and supported rotatably around a fixed axis to the stator, an arm assembly fixed to the rotor projecting therefrom in an opposite direction toward the yoke, three permanent magnets disposed on an outer surface of the rotor, a width of the central magnet being larger than those of other two magnets, and two flat coils, each coil being arranged on an inside surface of the yoke and having two parallel portions and two turning portions, adjacent parallel portions of the two flat coils closely contacting with each other, and the two flat coils having connection to a power source that electric currents along the above two adjacent vertical parallel portions are in the same direction. The motor torque and a uniformity thereof in the whole rotation range can be further improved by a rotary actuator in which the following features are added to the above structure. Each of two flat coils has an outer coil and an inner coil, the inner coil being arranged inside the outer coil, the turning portions of the inner coil being bent outwardly and overlapped over the turning portion of the outer coil and fitted in a recess or groove formed into the inside surface of the yoke. Both two flat coils have connection with a power source that current flowing through the centrally located parallel portions of a pair of the outer and inner coils are all in the same direction. Details of these modifications will become clear from a reading of the detailed description of the invention with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of a stacked magnetic disk assembly and a rotary actuator assembly with magnetic heads, Figure 2 shows a schematic plan view a disk drive in which the disk assembly and the rotary actuator assembly are combined forming a disk drive, Figure 3 is a schematic cross section of a rotary actuator having two poles of the prior art, Figure 4 shows a flat coil used in Figure 3, Figure 5 is a schematic cross section of a rotary actuator having four poles of the prior arts, Figure 6 is a schematic cross section of a first embodiment of a rotary actuator of the present invention using two flat coils and three permanent magnets, Figure 7 is a plan view of the two flat coils of the first embodiment, Figure 8 shows a perspective view of the rotary actuator of the first embodiment, in which a yoke cover and a rotor and arm assembly are removed and separately shown, Figure 9 is a cross section of the rotary actuator of the first embodiment for explaining the principle of the invention, in which directions of magnetic flux are illustrated, Figure 11 is a schematic cross section of a rotary actuator of a third embodiment of the present invention using two flat coils and three permanent magnets, each of the flat coils having an outer and an inner coil, Figure 12 is a plan view of the two flat coils of the third embodiment, Figure 13 is a perspective view of the outer and inner coils of the third embodiment, Figure 14 shows a perspective view of the rotary actuator of the third embodiment, in which a yoke cover and a rotor and arm assembly are removed and separately shown, Figure 15 is a cross section of the rotary actuator of the third embodiment for explaining the principle of the invention, in which lateral widths of coils and permanent magnets and directions of magnetic flux are shown, Figure 16 is a graph illustrating a magnetic flux density measured in the gap region along the periphery of the inner surface of the yoke of the third embodiment, Figure 17 is a graph illustrating a force constant curve in the rotation range, in which the gap d in the third embodiment is changed, and Figures 24(a) and 24(b) show a plan view of a disk drive and a cross sectional view of a rotary actuator respectively, in which the rotary actuator of the present invention as well as the disk assembly is directly fixed to the same disk enclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Figures 6 and 8 show a schematic cross section and a perspective view of a rotary actuator OM of a first embodiment respectively, in which arrangements of permanent magnets and coils of the present invention are clearly shown. Other parts such as arms 9 and head assemblies 10 are illustrated in a simplified form. Two flat coils 2 and 3 are fixed to an inside surface of a yoke core 1a, and these components are forming a main portion of a stator. As shown in Figure 8, the stator comprises the yoke core 1a and a yoke cover 1b, however the yoke core 1a may be a combination of an outer member of aluminum alloy and an inner member of soft iron to reduce the weight thereof. The yoke core 1a has an arcuate inner surface 1s extending in a longitudinal direction, or the yoke core may be substantially a part of a semicylinder. A central axis 5 of a rotor 4 is fixed to the stator. In Figure 8, both ends 5c and 5d of the axis 5 are shown. The rotor 4 can rotate back and forth around the axis 5. Three permanent magnets 6, 7, and 8 are fixed on one side 4a of a cylindrical surface of the rotor 4, facing the coils 2 and 3 on the yoke core 1a. The rotor 4 and permanent magnets 6 to 8 form a rotor assembly. A plurality of arms 9 are fixed to the rotor 4 projecting from an opposite side 4b of the rotor surface. A magnetic head assembly 10 with two magnetic heads 11 is attached on a far end of the arm 9. In the embodiment, the core 1a constitutes a part of the disk enclosure of a disk drive, which makes it easy to cool the flat coils 2 and 3. The yoke core 1a is made of soft iron such as low carbon steel. Two flat coils 2 and 3 have substantially the same shape as shown in a plan view of Figure 7. Substantial vertical parallel portions 2a, 2c, 3a and 3c of flat coils 2 and 3 are effective work zones for driving the rotor assembly, and horizontal portions 2b, 2d, 3b and 3d are turning portions of coil windings and do not contribute to drive the rotor assembly. Two flat coils 2 and 3 are arranged closely contacting with each other, and fixed on the arcuate inner surface of the yoke core 1a in a manner that a coil back surface closely contacts to the curved arcuate surface of the yoke core. Two adjacent vertical parallel portions 2a and 3a contact tightly with each other and face the central permanent magnet 7. Other vertical parallel portions 2c and 3c are positioned facing magnets 6 and 8 respectively. Two pairs of terminals of the flat coils are connected to a power source which is driven by a servo system such that, when the coils are excited, electric currents flowing through two adjacent parallel portions 2a and 3a are in the same direction. Three permanent magnets 6, 7, and 8 are made of samarium cobalt (SmCo), preferably, neodymium iron boron (NdFeB) which is an alloy magnet with rare earth metal, and these magnets are attached on a semicylindrical surface 4a of the rotor 4. Polarities of the permanent magnets 6, 7, and 8 are selected such that two side magnets 6 and 8 have the same polarity and the center magnet 7 has a reversed polarity. The rotor 4 is rotatable around the axis 5 via bearings (not shown). A longitudinal length of three magnets is substantially the same as or not greater than that of the effective parallel portions of the flat coils. In the first embodiment, a lateral width of the center magnet 7 is about twice that of the other two side magnets 6 and 8. Each lateral width of the side magnets 6 and 8 is less than that of parallel portions 2c and 3c, and also a lateral width of the center magnet 7 is less than that of a combination of adjacent parallel portions 2a and 3a. On the opposite surface 4b of the rotor 4, a plurality of arms 9, e.g., nine arms when ten disks are used, are fixed, maintaining an equal distance between adjacent two arms and projecting in an opposite direction toward the yoke core 1a. At a far end of each arm 9, a head assembly 10 is fixed with two magnetic heads 11. When the arms are actuated, a magnetic head 11 can be positioned on a target track on either a bottom or upper surface of of one of adjacent disks. When the rotary actuator OM is excited, in other words, the servo current flows through the flat coils 2 and 3, then permanent magnets 6, 7, and 8 are subjected to circumferential forces in the same direction, resulting in rotating the rotor 4 around the axis 5 with the arms 9 and positioning the magnetic head 11. In the first embodiment, the flat coils 2 and 3 are disposed closely contacting with each other. Because there is no gap between two flat coils, a circumferential width of two parallel portions 2a and 3a can be increased. And further, because the directions of electric current in both parallel portions 2a and 3a are the same, the single integrated center permanent magnet 7 can be utilized. This is a strong advantage over the prior art in which four magnets are needed shown in Figure 5. In Figure 6, flat coils 2 and 3 are shown schematically of a single layer winding, however, in an actual application, a multi-layer coil is utilized. The second, third and so forth layers of the coil winding are laminated on the first layer in the order. In Figure 8, the yoke cover 1b and the rotor 4 with permanent magnets 6 to 8 and arms 9 are dismantled and illustrated separately. The yoke cover 1b is fastened to the yoke core 1a by three bolts 12, and end portions 5c and 5d of the axis 5 (not shown) are inserted in holes 1c and 1d and fixed by bolts 13. The fixing method of the axis 5 shown in the Figure 8 is conventional for simplicity, other method thereof of the present invention is disclosed later. Figure 8 mainly aims to show clearly the actual arrangements of the flat coils 2 and 3 and the permanent magnets 6 to 8. Figure 9 is a schematic cross section for explaining the principle of the first embodiment. The main differences from Figures 3 and 5 are that: (1) three permanent magnets are used contrary to two magnets of Figure 3 and four magnets of Figure 5; (2) the center magnet 7 of the embodiment has a wider width than those used in Figures 3 and 5; (3) the current directions of two adjacent parallel portions 2a and 3a of coil windings of the embodiment are the same, however, the current directions of two adjacent coil windings of Figure 5 are opposite; and (4) there is no gap between two coils in the embodiment. The magnetic flux penetrating through yoke 1a, the gap, permanent magnets 6 to 8 and the rotor 4 are shown by the arrows in Figure 9. The combination of two parallel portions 2a and 3a and the single center permanent magnet 7 may be regarded as forming a single pole in a multipole motor, therefore, the rotary actuator of the first embodiment may be called a three-pole motor, contrary to the two-pole motor of Figure 3 and the four-pole motor of Figure 5 in the prior art. When an electric current i flows through the coil windings, the total torque T is generated, which is given by the following equation. T = B L i r, where B is a magnetic flux density at the coil winding; L is an effective total length of the coil winding; and r is a distance from the pivotal center of the rotor to a surface of the permanent magnet. When the structure of Figure 9 is compared with that of Figure 3 of the prior art, the effective total coil length L of the embodiment is about twice the length of the latter. Therefore, the first embodiment of Figure 9 can obtain the torque T of two times the torque of Figure 3. When the first embodiment is compared with four-pole motor type of Figure 5 of the prior art, two gaps between permanent magnets are necessary in the embodiment, but three gaps are needed in the prior art, and further, the embodiment can increase the number of turns of the flat coil more than that of the prior art. A distribution of magnetic flux of Figure 9 has a wider uniform zone in a lateral direction than that of Figure 5, in which a comparatively sharp polarity change occurs over the two parallel portions 74a of coil windings. These factors results in increasing the torque of the rotary actuator of the present invention by the increased magnetic flux density B and the increased effective coil length L. Three permanent magnets 6 to 8 are subjected to the magnetic attractive force toward the yoke core 1a, however, the attractive forces caused by two permanent magnets 6 and 8 are almost opposite in direction and the effects thereof are canceled. The resultant attractive force, which causes a load to the bearings (not shown) in supporting the rotor 4 around the axis 5, does not increase so much as the torque increase. In the above explanation, the flat coils are arranged on the stator side and the permanent magnets are arranged on the rotor side in the first embodiment of the present invention. However, these arrangements can be reversed. In the first embodiment explained using Figures 6 through 9, the flat coils 2 and 3 provide the turning portions 2b, 2d, 3b and 3d of coil windings, and these portions do not contribute to generate torque. In order to get more torque within a limited height of a rotary actuator, it is desirable to increase the number of turns of each flat coil and increase an effective vertical parallel portions of coil windings 2a, 2c, 3a and 3c. However, turning portions 2b, 2d, 3b and 3d occupy a considerable part of the vertical height of the flat coil. A second embodiment of the present invention aims to improve the above problem and increase the effective parallel portions of the coil winding. Figures 11 through 14 are related to the third embodiment. Figure 11 shows a cross section of the third embodiment of a rotary actuator OM, and Figures 12 and 13 show respectively a plan view of two flat coils and a perspective view of each flat coil. Figure 14 shows a perspective view of the rotary actuator OM of the third embodiment. As the rotary actuator, the principal structures of first and third embodiments are the same except those of flat coil 2 and 3. Same or like reference numerals used in Figures 11 through 14 designate same or like parts used in Figures 6 to 8. Therefore, the detailed explanations of the similar parts of the third embodiment are omitted. Two flat coils 2 and 3 of the third embodiment have the same design, however, each flat coil consists of an outer coil and inner coil. As shown in Figures 12 and 13, the fiat coil 2 consists of outer coil 2A and inner coil 2B, and the flat coil 3 consists of outer coil 3A and inner coil 3B. Each of outer and inner coils has four portions such that the outer coil 2A has two parallel portions 2Aa and 2Ac and two turning portions 2Ab and 2Ad and that the inner coil 2B has parallel portions 2Ba and 2Bc and turning portions 2Bb and 2Bd. The terminals of two pair coils 2 and 3 are connected to the driving source such that the directions of electric current flowing four coil portions 2Aa, 2Ba, 3Aa and 3Ba are the same as in the first embodiment. The special features of the second embodiment exist in that each of flat coils 2 and 3 consists of the outer and inner coils. The inner coil, e.g., 2B is arranged and fitted into the outer coil 2A when assembled, and further as shown in Figure 13, the turning portions 2Bb and 2Bd of the inner coil 2B are bent outwardly such that portions 2Bb and 2Bd respectively are disposed over and overlapped on the curved turning portions 2Ab and 2Ad. In order to fit two flat coils 2 and 3 on a yoke core 1a of Figure 14, the yoke core 1a provides a recess or a groove 15 at upper and lower portions of the inner surface thereof. The outwardly protruding portions (turning portions 2Bb, 2Bd, 3Bb and 3Bd) of inner coils 2B and 3B are received in the recess or groove 15. As shown in Figure 12, two flat coils 2 and 3 are arranged such that two parallel portions 2Aa and 3Aa of coil windings are closely contacting with each other and further two inner coils 2B and 3B are arranged such that no gap is left between portions 2Aa and 2Ba, and 3Aa and 3Ba. As a result, a gap d remains between portions 2Ac and 2Bc, and between portions 3Ac and 3Bc. In Figure 12, an inside width Y of the outer coil 3A is larger than an outside width X of inner coil 3B, therefore, the gap d remains on both sides. The relative arrangements of the flat coils 2, 3 to a rotor 4 with three permanent magnets 6, 7, 8 fixed thereon, are schematically illustrated in Figure 11. The magnetic flux penetrating through yoke core 1a, permanent magnets 6 to 8 and rotor 4 are shown in Figure 15, which is similar as Figure 9. There is one difference that gap d is provided between parallel coil portions 2Ac and 2Bc, and portions 3Ac and 3Bc. As explained in the first embodiment, the motor torque is proportional to BL (called a force constant), in which B is a magnetic flux density and L is an effective total length of the flat coil winding. The provision of the gap d alleviates a change in BL value when the rotor 4 rotates. Figure 16 shows a graph illustrating a distribution of the magnetic flux density along the periphery of the inner surface of the yoke core 1a. Position C on the abscissa shows the center of the yoke core 1a and positions A and B show circumferentially right and left ends of the effective coil zone respectively. When the rotor 4 is positioned at the center of an oscillatory movement, the relative widths of magnets and coils are also shown in Figure 16, where M₆, M₇ and M₈ designate lateral widths of permanent magnets 6, 7 and 8 respectively, and C₆, C₇ and C₈ designate the effective lateral widths corresponding to (2Ac+d+2Bc), (2Aa+2Ba+3Aa+3Ba), and (3Ac+d+3Bc) respectively as illustrated in Figure 15. If the gap d is not provided, two side magnets 6 and 8 have a smaller travel range, in which the torque to each magnet is almost uniform, than that for the center magnet 7. In the embodiment, therefore, the gap d is provided in C₆ and C₈. Thus, the difference between widths C₇ and M₇ is brought substantially equal to each difference between widths C₆ and M₆ and between widths C₈ and M₈. When the rotor 4 rotates, the relative positions of coils, shown by C₆, C₇ and C₈ in Figure 16, move to left and right sides. A torque change is remarkably reduced, because the gap d is provided between coil portions 2Ac and 2Bc, and between portions 3Ac and 3Bc. The third embodiment of the invention has effects of increasing the effective lateral widths C₆ and C₈ and reducing the sharp torque change. Figure 17 is a graph illustrating a force constant BL curve for two cases by simulation. Curve A shows a case in which the inner coils 2B and 3B are wound large enough such that there is no gap left between parallel portions 2Ac and 2Bc, and 3Ac and 3Bc, and curve B shows a case in which the gaps d are provided as shown in Figure 15. A peak value BL of curve A is higher than that of curve B by a few percents, however, curve B shows a flat characteristic compared with curve A. The final embodiment relates to a more detailed structure of a rotary actuator, in which a fixing method of the center axis thereof to a disk drive, a connecting method of an arm assembly with a head assembly and a stator structure are disclosed. Figure 24(a) show a top view of the disk drive comprising a rotary actuator, cover portions of enclosure parts being removed, and Figure 24(b) shows a cross section of the rotary actuator OM. A disk enclosure 38 has two separable parts 38a and 38b. A disk assembly DA including disks 37, a spindle 36, and a spindle motor (not shown) in fastened to upper and lower cover portions of the main disk enclosure 38a. A rotary actuator OM is arranged at a corner of the disk enclosure 38a, and a stator housing 28, in which a yoke core 1a and coils 2 and 3 are fixed, and the stator housing 28 also serves as a part of the enclosure. Coil and magnet structures are similar as those of the first or second embodiments, therefore, details are omitted. Same or like reference numerals designate same or corresponding parts previously explained. In Figure 24(a), the disk drive has two rotary units, one being the disk assembly DA having disks 37 and spindle 36 and the other, the rotary actuator OM. The spindle 36 with disks is made to rotate by a spindle motor (not shown). In order to get a precise positioning of a magnetic head onto the disk surface and to obtain further a high reliability throughout a life of the disk drive, it is very important that both directions of the central axis 5 (5a and 5b) of the rotary actuator OM and center axis of the spindle 36, are maintained in a precise parallel alignment with each other. In Figures 24(a) and 24(b), both axes are firmly fixed to a single enclosure body. The central axis of the rotary actuator OM has a middle portion 5a having a larger diameter and two end portions 5b having a smaller diameter. At the end portions, a hole is formed vertically to the direction of the axes 5a and 5b. Two end portions 5b of the axis are firmly fixed to side walls of the upper and lower covers of the main disk enclosure 38a using a bolt 20 and a tapped hole formed in the side walls, the side walls being formed for an opening to install the rotary actuator OM. Therefore, the main disk enclosure 38a supports both rotary actuator OM and disk assembly DA. The stator housing 28 is made of aluminum alloy to reduce the weight of the disk drive and the yoke core 1a of soft iron is fixed firmly to the inner surface of the stator housing 28, and further flat coils 2 and 3 are fixed firmly on an inner surface of the yoke core 1a. In Figure 24(b), the space portions between the inner surface of stator housing 28 and upper and lower portions of the flat coil 2 or 3 are utilized as a recess for receiving the turning portion for the inner coil as previously explained. The above stator structure having the stator housing 28 and yoke core 1a is very efficient to remove heat generated in the flat coils, resulting in reducing overall dimensions of the rotary actuator. In Figure 24(b), the rotor comprises a rotor body 24 of aluminum alloy, a rotor yoke 22 of soft magnetic material having a semicylindrical shape and permanent magnets 6 to 8. In the embodiment, the rotor body 24 is machined as an integral part with arms 9 and rotatably supported by the fixed axis 5 using a bearing 26. The integrally machined part of rotor body 24 and arm 9 reduces a moment of inertia of the arm and rotor assembly, and increases reliability. An end portion of the arm 9 is machined such that a wall is formed such that the wall surface has a first direction parallel to the longitudinal direction of the center axis of the rotary actuator and a second direction which is vertical to the first direction and oblique to that of the disk rotation. A head assembly 10 is first assembled with a connector 25 having a wall surface, which mates with another wall surface of the arm 9. The connector 25 with the head assembly 10 is thereafter fixed to the arm 9 using two bolts 23a and 23b. The direction of the center line CL of head assembly 10 is maintained almost in the same direction of the arm 9. Two tapped hole are formed, each on the wall surface of the arm 9 and connector 25 respectively, and the arm and connector are bolted together by two bolts 23a and 23b. Directions of bolts are opposite, therefore, it is easy to assemble the head assembly 10 with the arm 9. The above head and arm assemblies are easy in assembling and have effects of enhancing a mechanical stiffness of the combined structure resulting in raising a resonant frequency and reducing a moment of inertia thereof.

Claims: A rotary actuator for positioning a read/write magnetic head (11) on the target track on a disk assembly (DA), the disk assembly (DA) having spindle means (36) for rotating disks (37) around a spindle axis, the spindle means (36) being supported by upper and lower portions of a disk enclosure (38), the rotary actuator (OM) being positioned at one corner of the disk enclosure (38), having arm means (32, 9) for moving the magnetic head (31, 11) back and forth in a radial direction of the disk (37) with the rotation of the rotary actuator (OM), said rotary actuator comprising: a stator including a yoke (1) having an arcuate inner surface (1s) extending in a longitudinal direction, and two flat coils (2, 3), each coil (2, 3) being arranged on the inner surface (1s) of said yoke (1) and formed of two substantially parallel portions (2a, 2c, 3a, 3c) and two turning portions (2b, 2d, 3b, 3d), two parallel portions (2a, 3a) of said two flat coils (2, 3) being adjacently arranged and having electrical connection to a power source such that electric currents flowing through said two adjacently arranged parallel portions (2a, 3a) are in the same direction, a rotor (4) supported rotatably within a limited angle range (ϑ) around a fixed axis (5), the axis (5) being arranged in a region defined by said arcuate inner surface (1s) and parallel to said longitudinal direction, wherein permanent magnets (6, 7, 8) are arranged on an outer surface of said rotor (4) an arm (9), one end thereof being fixed to said rotor (4) and the other end projecting in an opposite direction toward said yoke (1), characterized in that there are three permanent magnets (6, 7, 8), the center magnet (7) having a lateral width larger than that of said other two magnets (6, 8) and having substantially an equal distance from each of said other two magnets (6, 8) and a polarity of the central magnet (7) being opposite to that of said other two magnets (6, 8), and the adjacent parallel portions (2a, 3a) of said two flat coils (2, 3) being closely contacting with each other facing said center magnet (7). A rotary actuator according to claim 1, characterized in that a total lateral width of said two adjacently arranged parallel portions (2a, 3a) is larger than a lateral width of said center magnet (7), and each lateral width of the remaining parallel portions (2c, 3c) of said two flat coils (2, 3) is larger than each lateral width of said remaining two magnets (6, 8). A rotary actuator according to claim 1 or 2, characterized in that a longitudinal length of said parallel portions (2a, 2c, 3a, 3c) of said two flat coils (2, 3) is larger than that of said three permanent magnets (6, 7, 8). A rotary actuator according to claim 2, characterized in that said lateral width of said center magnet (7) is substantially twice that of said other two magnets (6, 8). A rotary actuator according to anyone of claims 1 to 4, characterized in that each of said two flat coils (2, 3) comprises an inner coil (2B, 3B) and an outer coil (2A, 3A), each of said inner and outer coils having two parallel portions (2Aa, 2Ac, 2Ba, 2Bc, 3Aa, 3Ac, 3Ba, 3Bc) and two turning portions (2Ab, 2Ad, 2Bb, 2Bd, 3Ab, 3Ad, 3Bb, 3Bd), said inner coil being arranged inside said outer coil, and having electrical connection to the power source such that currents flowing through said inner and outer coils (2B, 3B, 2A, 3A) are in the same direction. A rotary actuator according to claim 5, characterized in that said arrangement of said inner coil (2B, 3B) includes that one parallel portion (2Ba, 3Ba) of each of said innner coils (2B, 3B) on the center side closely contacts with the respective parallel portion (2Aa, 3Aa) of the outer coils (2A, 3A) on the center side, and a gap remains between the other parallel portion (2Bc, 3Bc) of each of said inner coils (2B, 3B) and the other respective parallel portion (2Ac, 3Ac) of said outer coils (2A, 3A). A rotary actuator according to claim 5 or 6, characterized in that two turning portions (2Bb, 2Bd) of said inner coil (2B) are bent outwardly and disposed on the turning portions (2Ab, 2Ad) of said outer coil (2A). A rotary actuator according to claim 7, characterized in that a recess (15) is formed on the inner surface (1s) of said yoke (1), the recess being located at a corresponding position of said outwardly bent turning portion (2Bb, 2Bd, 3Bb, 3Bd) of said inner coil (2B, 3B) and having a sufficient size for receiving it when said flat coil (2, 3) is arranged on the inner surface (1s) of said yoke (1). A rotary actuator according to anyone of claims 1 to 8, characterized in that said fixed axis (5) of said rotor provides means for fixing both end portions (5b) of said rotor to the side walls of the upper and lower portions of the disk enclosure (38), said side walls being formed for an opening to install the rotary actuator (OM) to the disk enclosure. A rotary actuator according to claim 9, characterized in that said fixing means comprises a hole formed at both end portions of said axis (5), the direction of said hole being vertical to the direction of said axis, whereby the rotary actuator (OM) is fixed to the disk enclosure using said hole and a bolt (20). A rotary actuator according to anyone of claims 1 to 10, characterized in that said stator further comprises a stator housing (28, 39), the stator housing (28, 39) being fixed to the disk enclosure (38) at said one corner and forming a part of a completed disk enclosure, said yoke (1) being fixed to an inner wall surface of said stator housing (28, 39), and said two flat coils (2, 3) are fastened to the inner surface of said yoke (1), whereby heat generated in the flat coils (2, 3) is removed from an outer surface of the stator housing (28, 39) by thermal conduction through said yoke (1) and said stator housing (28, 39). A rotary actuator according to anyone of claims 1 to 11, characterized in that said other end of said arm (9) has a first wall surface, said first wall surface having a first direction parallel to said longitudinl direction and a second direction vertical to said first direction and oblique to that of the disk rotation, and a connector (23, 25) is provided, said connector being assembled with a head assembly (10) at one end and having a second wall surface at the other end, said second wall surface mating with said first wall surface of said arm (9) and being assembled therewith, and the center line (CL) of a combination of said head assembly (1) and said connector (23, 25) is substantially in the same direction as that of said arm (9).

Inventors: ARUGA KEIJI, IMAMURA TAKAHIRO, MAEDA HIROSHI, SUZUKI NORIHIKO, YAMADA TOMOYOSHI, ARUGA, KEIJI, IMAMURA, TAKAHIRO, MAEDA, HIROSHI, SUZUKI, NORIHIKO, YAMADA, TOMOYOSHI
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1989
Main classification: G11B5
IPC codes: G11B5, H01F7