Floating magnetic head

Abstract: A floating magnetic head (1) which suppresses the effects of an external magnetic head and has rails (3,4) of good flatness. The winding of the head can be wound at high efficiency. The number of turns n₁ of the coil (31) on the side of the leading end (9) is set less than the number of turns n₂ of the coil (32) on the side of the trailing end (5). The product of the number of turns n₁ of the coil (31) and the cross-sectional area A₁ of the core leg (30a) is set substantially equal to the product of the number of turns n₂ of the coil (32) and the cross-sectional area A₂ of the core leg (30b). That is, n₁ · A₁ = n₂ · A₂ . The magnitude of the noise voltage induced across the coil (31) is substantially equal to the magnitude of the noise voltage induced across the coil (32). Furthermore, the two coils (31,32) are wound in opposite senses. Therefore, noise voltage produced in the whole floating magnetic (1) head is null. In this manner, the generation of noise due to an external magnetic field is prevented. Since the number of turns n₁ of the coil (31) is smaller, the whole groove (10) is not required to be made deep. Hence, the amount of the overhang of one rail (3) can be reduced, whereby the flatness can be improved. Furthermore, the interference with the bottom (24) of the groove (10) can be avoided. This improves the efficiency of the operation to wind the coils (31,32).

Description: FIELD OF THE INVENTION The present invention relates to a floating magnetic head used in a magnetic disk drive and, more particularly, to a floating magnetic head of the composite type. BACKGROUND OF THE INVENTION A floating magnetic head of the composite type which has been heretofore frequently used (US 4,870,521) is generally indicated by reference numeral 1 in Fig. 5. This head 1 has a substantially rectangular slider 2 made of a ceramic such as calcium titanate. Rails 3 and 4 for producing a floating force are mounted on the top surface of the slider 2 which is opposite to a magnetic recording medium. One rail 3 has a slit 6 of a given depth, the slit 6 extending longitudinally of the rail 3 on the side of its trailing end 5 at which the medium exits from the head. A head core 8 having a read/write gap 7 and made of a ferromagnetic substance such as a ferrite is inserted in the slit 6. The core 8 is rigidly mounted by sealing of glass or other bonding material. A groove 10 which increases gradually in depth from its leading end 9 toward its trailing end 5 is formed at one corner of the slider 2. The groove 10 extends to the trailing end 5. The head core 8 has a leg 8a mounted in the groove 10 on the side of the trailing end 5. A coil 11 is wound around the leg 8a of the core. In this floating magnetic head 1, the coil 11 is wound only on the core leg 8a disposed on the side of the trailing end 5. Therefore, if an external magnetic field which is perpendicular to the floating surfaces of the rails 3 and 4 acts on the floating surfaces, an electromotive force may be induced in the coil 11, whereby noise is produced. It is sometimes necessary that the coil 11 is composed of a number of turns. In this case, the coil 11 is required to form multiplex winding because the width of the groove 10 is limited. However, where the coil 11 is built in multiplex winding, the outer portion of the coil 11 is inferior in sensitivity to the inner portion. Also, there is the possibility that the outer portion of the coil 11 is disarranged toward the rail 3 and makes contact with the magnetic recording medium, thus creating a breakage. SUMMARY OF THE INVENTION It is an object of the present invention to provide a floating magnetic head which suppresses the effects of an external magnetic field, has rails having good flatness, and has coils capable of being wound at improved efficiency. This object is achieved in accordance with the teachings of the invention by a floating magnetic head comprising: a substantially rectangular slider made of a nonmagnetic material and provided with a groove which gradually increases in depth from its entrance end toward its trailing end, the groove extending to the trailing end; rails mounted on the surface of the slider which is opposite to a magnetic recording medium to produce a floating force; a head core having legs located in the groove on the side of the entrance end of the groove and on the side of the trailing end of the groove, respectively, the core having a read/write gap; two coils wound in opposite senses around the legs, respectively, of the head core, the coils facing the groove, the coils being located on the side of the leading end and on the side of the trailing end, respectively. The number of turns of the coil on the side of the leading end is less than the number of turns of the coil on the side of the exit end. The cross-sectional area of the leg of the core on the side of the leading end is larger than the cross-sectional area of the leg of the core on the side of the exit end. The product of the number of turns of the coil on the side of the leading end and the cross-sectional area of the core leg on the side of the leading end is set substantially equal to the product of the number of turns of the coil on the side of the trailing end and the cross-sectional area of the core leg on the side of the trailing end. In such a structure, as is already known from JP-A-59 058 615, the product of the number of turns of the coil on the side of the leading end and the cross-sectional area of the core leg on the side of the leading end is set substantially equal to the product of the number of turns of the coil on the side of the trailing end and the cross-sectional area of the core leg on the side of the trailing end and, therefore, the magnitude of the noise voltage induced across the coil on the side of the leading end is substantially equal to the magnitude of the noise voltage induced across the coil on the side of the exit end. Furthermore, the coil on the side of the leading end and the coil on the side of the trailing end are wound in opposite senses. Therefore, the noise voltages induced across the two coils cancel out each other. The noise voltage produced in the whole floating magnetic head is null. Since the number of turns of the coil on the side of the leading end is less than the number of turns of the coil on the side of the trailing end, the clearance between the core on the side of the leading end and the bottom of the groove is balanced against the clearance between the core on the side of the trailing end and the bottom of the groove. This makes it unnecessary to render the whole groove deep. Also, because the number of turns of the coil wound around the core leg on the side of the leading end is less than the number of turns of the coil wound around the core leg on the side of the trailing end, the groove can be made shallow. Other objects and features of the invention will appear in the course of the description thereof which follows. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a floating magnetic head according to the invention; Fig. 2 is a schematic cross section of the floating magnetic head shown in Fig. 1; Fig. 3 is a perspective view of another floating magnetic head according to the invention; Fig. 4 is a schematic cross section of the floating magnetic head shown in Fig. 3; Fig. 5 is a perspective view of a conventional floating magnetic head. DETAILED DESCRIPTION OF THE INVENTION Referring to Fig. 1, a floating magnetic head according to the invention is generally indicated by reference numeral 1. The head 1 comprises a substantially rectangular slider 2 made of a ceramic such as calcium titanate. Rails 3 and 4 are mounted on the top surface of the slider 2 which is opposite to a magnetic recording medium (not shown) to produce a floating force. The slider 2 has a groove 10 at the corner located on the side of the exit end 5 from which the magnetic recording medium exits. The depth of the groove 10 gradually increases from the leading end 9 toward the trailing end 5, and the groove 10 extends to the trailing end 5. A head core 30 is bonded to this corner and faces the groove 10. The head core 30 has two core legs 30a and 30b of the same thickness. These legs 30a and 30b are located on the side of the leading end 9 and on the side of the trailing end 5, respectively, of the groove 10. Coils 31 and 32 are wound around these legs 30a and 30b, respectively. The width W 1 of the core leg 30a on the side of the leading end is set larger than the width W 2 of the core leg 30b on the side of the trailing end. The cross-sectional area A 1 of the core 30a is larger than the cross-sectional area A 2 of the core 30b. The coils 31 and 32 on the side of the leading end and on the side of the trailing end, respectively, are wound in opposite senses and connected together. The number of turns n 1 of the coil 31 on the side of the leading end is less than the number of turns n 2 of the coil 32 on the side of the trailing end. The product of the number of turns n 1 of the coil 31 and the cross-sectional area A 1 of the core leg 30a is set substantially equal to the product of the number of turns n 2 of the coil 32 and the cross-sectional area A 2 of the core leg 30b. Referring also to Fig. 2, since the number of turns n 1 of the coil 31 on the side of the leading end is less than the number of turns n 2 of the coil 32 on the side of the exit end, the clearance L 1 between the core leg 30a on the side of the leading end and the bottom 24 of the groove is balanced against the clearance L 2 between the core leg 30b on the side of the trailing end and the bottom 24 of the groove. This makes it unnecessary to render the whole groove 10 deep. Hence, the amount of the overhang of the rail 3 can be reduced, whereby the flatness can be improved. Furthermore, the interference with the bottom 24 of the groove can be avoided because the number of turns n 1 of the coil 31 on the side of the leading end is smaller as mentioned above. This improves the efficiency of the operation to wind the coils. In consequence, the cost of the finished floating magnetic head can be reduced. The effect of an external magnetic field is described next. If an external magnetic field acts on the surfaces of the rails 3 and 4 perpendicularly to these surfaces, the magnetic flux of the external magnetic flux is divided into two portions, which pass through the legs 30a and 30b, respectively, of the core. The portion excluding the core legs 30a and 30b, i.e., the portion opposite to the magnetic recording medium, has a short magnetic path length. Therefore, assuming that the magnetic resistance of this portion is sufficiently smaller than the magnetic resistances of the core legs 30a and 30b, the magnetic fluxes flowing through the cores 30a and 30b, respectively, are given by Φ 1 = H(t) / (ℓ 1 / µ · A 1 ) Φ 2 = H(t) / (ℓ 2 / µ · A 2 ) where ℓ 1 is the magnetic path length of the core leg 30a on the side of the leading end, µ is the magnetic permeability of the head core 30, and ℓ 2 is the magnetic path length of the core leg 30b on the side of the trailing end. The noise voltages induced across the coils 31 and 32 are respectively given by V 1 (t) = - n 1 · d Φ 1 / dt = - n 1 · (µ A 1 /ℓ 1 ) · dH(t) / dt V 2 (t) = - n 2 · d Φ 2 / dt = - n 2 · (µ A 2 /ℓ 2 ) · dH(t) / dt Assuming that ℓ 1 = ℓ 2 and n 1 · A 1 = n 2 · A 2 , we have V 1 (t) = V 2 (t) In this way, the noise voltages V 1 (t) and V 2 (t) are equal. Since the coils 31 and 32 are wound in opposite senses with respect to the external magnetic field, the noise voltages V 1 (t) and V 2 (t) cancel out each other. Therefore, the noise voltage produced in the whole floating magnetic head 1 is null. In this manner, the generation of noise due to an external magnetic field is prevented. In the above example, the core legs 30a and 30b have the same thickness. The width W 1 of the leg 30a is larger than the width W 2 of the leg 30b. The cross-sectional area A 1 of the leg 30a is larger than the cross-sectional area A 2 of the leg 30b. The cross-sectional area A 1 of the leg 30a can be made larger than the cross-sectional area A 2 of the leg 30b by making their thicknesses different while setting their widths equal to each other, by making their widths and thicknesses different, or by making their widths and thicknesses different. Another floating magnetic head according to the invention is next described by referring to Figs. 3 and 4. The head, indicated by numeral 1, comprises a substantially rectangular slider 2 made of a ceramic such as calcium titanate. Rails 3 and 4 are mounted on the top surface of the slider 2 which is opposite to a magnetic recording medium (not shown) to produce a floating force. One rail 3 is provided with a slit 6 of a given depth, the slit 6 extending parallel to this rail 3. The slit 6 is located on the side of the trailing end 5 from which the medium exits. A head core 40 having a read/write gap 20 and made of a ferromagnetic material such as a ferrite is inserted in the slit 6 and sealed by glass or other bonding material. The head core 40 has two core legs 40a and 40b of the same thickness. These legs 40a and 40b are located on the side of the leading end 9 of the groove 10 and on the side of the trailing end 5, respectively, of the groove 10. Coils 41 and 42 are wound around these legs 40a and 40b, respectively. The width of the core leg 40a on the side of the entrance end is set larger than the width of the core leg 40b on the side of the exit end. The cross-sectional area A 1 of the leg 40a is larger than the cross-sectional area A 2 of the leg 40b. The coils 41 and 42 on the side of the entrance end and on the side of the trailing end, respectively, are wound in opposite senses with respect to an external magnetic field and connected together. The number of turns n 1 of the coil 41 on the side of the entrance end is less than the number of turns n 2 of the coil 42 on the trailing end. The product of the number of turns n 1 of the coil 41 and the cross-sectional area A 1 of the core leg 40a on the side of the leading end is set substantially equal to the product of the number of turns n 2 of the coil 42 on the side of the leading end and the cross-sectional area A 2 of the core leg 40b on the side of the leading end. In this floating magnetic head 1, the number of turns n 1 of the coil 41 on the side of the leading end is less than the number of turns n 2 of the coil 42 on the side of the trailing end. The clearance L 1 between the core leg 40a on the side of the leading end and the bottom 24 of the groove is balanced against the clearance L 2 between the core leg 40b on the side of the exit end and the bottom 24 of the groove, in the same way as in the floating magnetic head 1 described previously in connection with Fig. 1. This makes it unnecessary to render the whole groove 10 deep. Hence, the amount of the overhang of the rail 3 can be reduced, whereby the flatness can be improved. Furthermore, the interference with the bottom 24 of the groove can be circumvented because the number of turns n 1 of the coil 41 on the side of the leading end is smaller as mentioned above. This improves the efficiency of the operation to wind the coils. In consequence, the cost of the finished floating magnetic head can be reduced. Since the product of the number of turns n 1 of the coil 41 on the side of the leading end and the cross-sectional area A 1 of the core leg 40a on the side of the leading end is set substantially equal to the product of the number of turns n 2 of the coil 42 on the side of the leading end and the cross-sectional area A 2 of the core leg 40b on the side of the trailing end, the magnitude of the noise voltage induced across the coil 41 is equal to the magnitude of the noise voltage induced across the coil 42. Furthermore, the coils 41 and 42 are wound in opposite senses. Therefore, the noise voltages induced across the coils 41 and 42 cancel out each other. Therefore, the noise voltage produced in the whole floating magnetic head 1 is null. In this manner, the generation of noise due to an external magnetic field is prevented. Because the novel floating magnetic head is constructed as described above, and because the product of the number of turns of the coil on the side of the entrance end and the cross-sectional area of the core leg on the side of the leading end is set substantially equal to the product of the number of turns of the coil on the side of the trailing end and the cross-sectional area of the core leg on the side of the trailing end, the magnitude of the noise voltage induced across the coil on the side of the leading end is substantially equal to the magnitude of the noise voltage induced across the coil on the side of the trailing end. Furthermore, the coil on the side of the leading end and the coil on the side of the trailing end are wound in opposite senses. Therefore, the noise voltages induced across the two coils cancel out each other. The noise voltage produced in the whole floating magnetic head is null. In this manner, the generation of noise due to an external magnetic field is prevented. Since the number of turns of the coil on the side of the leading end is less than the number of turns of the coil on the side of the trailing end, the clearance between the core leg on the side of the leading end and the bottom of the groove is balanced against the clearance between the core leg on the side of the trailing end and the bottom of the groove. This makes it unnecessary to render the whole groove deep. Hence, the amount of the overhang of the rail can be reduced, whereby the flatness can be improved. Furthermore, the interference with the bottom of the groove can be avoided because the number of turns of the coil on the side of the entrance end is smaller as mentioned above. This improves the efficiency of the operation to wind the coils. In consequence, the cost of the finished floating magnetic head can be reduced.

Claims: A floating magnetic head (1) comprising: a substantially rectangular slider (2) made of a nonmagnetic material having a leading end (9) and a trailing end (5); a groove (10) formed in the slider (2) gradually increasing in depth along one side of the slider (2) towards the trailing end (5) and opening at the trailing end (5); rails (3,4) mounted on a surface of the slider (2) which is opposite to a magnetic recording medium to produce a floating force; a head core (30;40) located on the one side of the slider (2), on which the groove (10) is formed, and having a first leg (30a;40a) and a second leg (30b;40b), the second leg (30b;40b) being located at the trailing end (5) of the slider such that the first leg (30a;40a) is located between the second leg (30b;40b) and the leading end (9) of the slider, the core having a read/write gap (20); a first coil (31;41) and a second coil (32;42) to be wound around the first leg (30a;40a) and the second leg (30b;40b) respectively in opposite sense, to connect them in balanced winding manner, the coils (31,32;41,42) being at least partially in the groove (10) ; the cross-sectional area of the first leg (30a;40a) being larger than that of the second leg (30b;40b), and the coils (31, 32; 41,42) being wound around the first and the second legs (30a, 30b; 40a,40b) in such conditions that the product of the number of turns of the first coil (31;41) and the cross-sectional area of the first leg (30a;40a) being set substantially equal to the product of the number of turns of the second coil (32;42) and the cross-sectional area of the second leg (30b;40b). A floating magnetic head according to claim 1, wherein the head core (30) is located within the groove (10) formed in the slider (2). A floating magnetic head according to claim 1, wherein the head core (30) is adhered to the one side of the slider (2). A floating magnetic head according to claim 1, 2 or 3, wherein the number of turns of the first coil (31;41) on the first leg (30a;40a) is less than the number of turns of the second coil (32;42) of the second leg (30b;40b).

Inventors: EGAWA MOTOJI, EGAWA, MOTOJI, EGAWA, MOTOJI, C/O MINEBEA CO., LTD.
Applicants: MINEBEA KK, MINEBEA CO.,LTD.
Application year: 1993
Main classification: G11B5
IPC codes: G11B5