Magnetic recording/reproducing apparatus

Abstract: A magnetic recording/reproducing apparatus of serpentine system capable of recording/reproducing a large amount of high density data at high speed with a tracking control for precisely positioning a combination head includes a combination head having a magnetic head corresponding to a magnetic tape formed by a plurality of tracks arranged in parallel to one another in a direction in which the magnetic tape runs, and a light emitting unit disposed at a position confronting one side of the magnetic tape for emitting light in a widthwise direction of the magnetic tape. The appratus also includes a light receiving unit having a plurality of light receiving elements disposed at a position confronting the other side of the magnetic tape for receiving the light emitted from the light emitting unit such that the light receiving unit are so disposed that outputs from the light receiving elements have a predetermined relation which governs the feedback control at a time when the magnetic head moved to a predetermined track position, and a head operating unit capable of moving the combination head in the widthwise direction of the magnetic tape. The apparatus further has a slit plate formed integrally with the combination head and having openings whose number is the same as the number of a plurality of tracks confronting the magnetic head in the widthwise end portion and the the other end portion of the magnetic tape.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-track magnetic recording/reproducing apparatus which uses a magnetic tape having a reduced width as a recording medium. More particularly, the present invention relates to a magnetic recording/reproducing apparatus capable of precisely recording/reproducing a large amount of data at high speed and the precise recording/reproducing being performed with a precise tracking control maintained. 2. Description of the Related Art The inventors know that a magnetic recording/reproducing apparatus, except the one having a rotary head, used for an audio device has the same numbers of the tracks and the recording heads or the same numbers of the reproducing heads and the recording heads in pairs. The above-described term "the number of the tracks" means the total number of data tracks formed in parallel to the direction in which the tape runs. The magnetic recording/reproducing apparatus of the above described type includes a device for restricting the relative positions between the magnetic tape and the magnetic head. The restricting device has generally a guide post or the like, having a pair of flanges for guiding the two vertical ends of the magnetic tape so as to make it run toward the fixed magnetic head, is formed in a passage through which the magnetic tape runs. Thus, the vertical movement of the magnetic tape is restricted. On the other hand, a multi-track magnetic recording/reproducing apparatus used for a backup storage of an information processing system, so-called "a cassette streamer", employs a recording/reproducing system known as "a serpentine system". A conventional serpentine system has a pair of a recording head for recording and a reproducing head for reproducing the contents when a magnetic tape is run in one direction and another pair of a recording head for recording and a reproducing head for reproducing the contents when the magnetic tape is run in the other direction so that it is capable of corresponding to a plurality of tracks. In this system, information is successively recorded or reproduced from tracks during the running of the magnetic tape in one direction or in the other direction instead of recording information on a plurality of tracks of the magnetic tape simultaneously. At the time of the above-described operation, the tracks are switched by moving the above-described two pairs of the recording heads and the reproducing heads, and the positioning of the magnetic tape to the position of a desired track is simultaneously performed. There is a known device for restricting the relative positions between the head and the magnetic tape as disclosed in JP-A-62-183019 in which the positioning of the head is achieved in accordance with an open loop control method with a stepping motor provided in which the restricting flanges are used in addition to the above-described structure. Recently, a combination head having multiple heads has been developed in accordance with an advancement of a thin film magnetic head. Therefore, multi-track magnetic recording/reproducing apparatus enabling higher density storage have been developed. The apparatus of the type described above is capable of recording information in a narrow track width, reducing the allowable offtrack distance.Therefore, in order to operate a precise tracking control, the device for restricting the relative positions between the tape and the head has an additional structure which followup-controls the magnetic head with respect to the waving movement of the magnetic tape. The added structure is a head moving device for moving the magnetic head in the widthwise direction of a tape in addition to the above-described mechanism in which the flanges are provided for the purpose of restricting the vertical movement of the magnetic tape. The apparatus of the type described above is exemplified by a fixed-head digital audio tape recorder which has the same numbers of the recording heads and the tracks or the same numbers of the reproducing heads each of which forms a pair with the above-described recording heads and the tracks. The apparatus of the type described above is arranged, as disclosed in the Trans. IECE Japan EA83-56, Trans. IECE Japan EA81-64 and the Sharp Engineering Report 1984-28, a servo-only track formed on the magnetic tape is traced by two parallel reproducing heads disposed in the widthwise direction of the tape so as to compare and followup-control the reproduction output therefrom for restricting the relative positions between the magnetic head and the magnetic tape. Another device for restricting the relative positions between the tape and the head has been disclosed in Japanese Patent Publication No. 63-64811 in which a structure for magnetically detecting the relative positions between an end portion of the magnetic tape and the magnetic head is provided for a magnetic recording/reproducing apparatus arranged to have the same number of the heads and the tracks. However, the device for restricting the relative positions between the tape and the head has a guide post having flanges which restrict the vertical movement of the magnetic tape by contacting the vertical ends of the magnetic tape with the flanges of the guide post. Therefore, if a magnetic tape having a width which is larger than the distance between the upper flange and the lower flange is driven, the mechanical stresses act upon the two vertical ends of the magnetic tape and cause the two vertical ends of the magnetic tape to be damaged. Therefore, the restriction width in the above-described restricting device is limited to several tens of µm, because the end portions of the magnetic tape must be protected from the damage. Consequently, in a high density magnetic recording/reproducing apparatus in which the allowable offtrack is arranged in the range from ten and several µm to several tens of µm, the above-described structure in which the movement of the magnetic tape is restricted by the flanges or the like cannot correspond to the above-described allowable offtrack. When a higher recording density is desired, the width of the track of the magnetic tape can be reduced by reducing the width of the track of the magnetic head. However, the reduction in the track pitch involves a certain limit since the integration of the thin film head is limited to a certain degree. Furthermore, an increase in the number of the heads causes the size of the circuit to be enlarged and the overall cost is thereby risen. Therefore, a high density magnetic recording/reproducing apparatus which is provided with the pitch of the tracks is several tens of µm and the several tens to hundreds of tracks cannot employ the same number of the heads and the tracks. On the other hand, the multi-track magnetic recording/reproducing apparatus so-called a cassette streamer and employing the conventional serpentine system is arranged to record/reproduce information on the multiplicity of the tracks by moving the magnetic head in the widthwise direction of the magnetic tape. Therefore, the recording/reproducing can be operated by moving the magnetic head in several times even if the track pitch is reduced and the number of the tracks is increased. Therefore, the integration of the thin film head does not encounter a problem. However, the track width necessarily becomes several tens of µm when the track pitch is made several tens of µm. Therefore, the allowable offtrack also becomes ten and several µm to several tens of µm. It leads a fact that the device for restricting the relative positions between the tape and the head, in which the restriction by means of the flanges or the like and the open loop control by using the stepping motor are performed, does not correspond to the above-described allowable offtrack. It might therefore be considered feasible to employ a structure for overcoming the above-described problem in terms of the allowable offtrack, the structure being arranged such that the relative positions between the magnetic head and the magnetic tape is detected by a sensor and the head operating device is feed-back controlled by a detection signal so that the magnetic head is tracking-controlled. However, if the above-described tracking control of several µm is desired to be achieved, a mechanism for supporting the magnetic head, a power source for the magnetic head, a mechanism for transmitting power to the magnetic head, and a sensor for detecting the relative positions between the magnetic tape and the magnetic head must be constituted precisely. However, the conventional head operating device has a complicated structure and a large dead zone since it includes the power source utilizing a rotary motor such as the stepping motor, a mechanism for converting the rotational motion of the rotary motor into a linear motion, a bearing supporting mechanism and the like. Therefore, a desired control accuracy cannot be obtained. Furthermore, since a mechanism for supporting the magnetic head by means of parallel leaf springs is employed in the conventional structure, a feedback control with an excellent gain cannot be obtained easily due to an influence of the secondary resonance. The secondary resonance takes place because the magnetic head is secured to either of the leaf springs or because the mechanism for supporting the magnetic head is connected to the above-described mechanism for converting the rotational motion of the power source for the magnetic head into the linear motion. Furthermore, if the tracking control by means of the servo track of the type employed in the above-described fixed-head digital audio tape recorder is operated in accordance with the serpentine method, a multi-servo tracks must be provided and problems in terms of a recording density on the servo track arise. Therefore, even if the method of this type is employed, high density recording cannot be obtained satisfactorily. SUMMARY OF THE INVENTION An object of the present invention is to provide a magnetic recording/reproducing apparatus system capable of recording/reproducing a large amount of high density data at high speed with a tracking control for precisely positioning a combination head. The apparatus of the present invention is capable of recording/reproducing the data without providing flanges for restricting the relative positions between the magnetic tape and the magnetic head and without a servo track on the magnetic tape. Accordingly the invention provides a magnetic recording/reproducing apparatus comprising a composite magnetic head having a number of recording/reproducing heads less than the number of tracks provided on a magnetic tape in parallel with each other and with the direction (X) in which the tape runs, said composite head being movable relative to the magnetic tape in the widthwise direction (Y) of the tape to a number of operational positions at each of which said heads are aligned with a respective set of desired ones of said tracks, characterised by control means for setting and maintaining said composite head at a selected one of said positions, said control means including an optical system having a light emitting means and a multi-element light receiving means disposed on opposite sides of the tape, and arranged to transmit light past at least one edge of the tape in such a way that the pattern of light transmitted to said multi-element light receiving means is dependent upon said operational position of the composite head relative to the tape. According to a first embodiment the light receiving means comprises first and second light receiving elements which are arranged so that the output of the second light receiving element is a multiple of the output of the first light element and dependent upon the operational position of the composite magnetic head. Preferably in each operational position of the composite magnetic head a constant area of said first light receiving element is exposed to light from said light emitting means whilst the area of the second light receiving element exposed to light from the light emitting means varies in dependence upon the operational position of the composite magnetic head. In a preferred embodiment the quantity of light received by the second light receiving element in each operational position of the composite magnetic head is an integer multiple of the light received by the first element, where the integer multiple corresponds to the respective operational position. In one aspect of the first embodiment the light receiving means is mounted to and movable with the composite magnetic head. In a second aspect a slit plate is mounted to the composite magnetic head and is movable therewith, the slit plate being movable between the light emitting means and the light receiving means and having aperture means therein which controls the pattern of light transmitted to the first and second light receiving elements in dependence upon the operational position of the composite magnetic head. According to this second aspect of the first embodiment the aperture means may comprise a first aperture allowing a constant area of the first light receiving element to be illuminated by the light emitting means and a second aperture illuminating an area of the second element in dependence upon the operational position of the composite magnetic head. According to a second embodiment a plurality of spaced apart light receiving elements may be provided adjacent an edge of the tape, the arrangement being such that outputs of selected ones of said light receiving elements have predetermined relationships in each of the operational positions. Preferably for each operational position the output of a selected light receiving element equals the sum of the output of two other selected light receiving elements. According to a first aspect of the second embodiment the light receiving elements are mounted to and movable with the composite magnetic head. Preferably the light receiving elements are in operation displaced by differing amounts from an edge of the tape. The pitch d i between the ends of adjacent light receiving elements Da i , Da i+1 in the lateral direction to the tape is preferably determined according to: d i = d when i ≦ 2 and d i = (i - 2) d when 3 ≦ i ≦ n - 1 where d is the pitch of the tracks on the magnetic tape and n is the number of light receiving elements. According to a second aspect of the second embodiment a slit plate is mounted to the composite magnetic head and movable therewith, the slit plate being movable between the light emitting means and the light receiving means and having aperture means which selectively allows light to pass from the light emitting means to selected ones of the light receiving elements in a pattern dependent upon the operating position of the composite magnetic head. Preferably the aperture means comprises a plurality of slits wherein each slit is arranged to allow light to pass from the light emitting means to a respective light receiving element and selected ones of the operational positions of the composite magnetic head. The pitch d i between the ends of adjacent slits A i and A i+1 of the slit plate in the lateral direction of the magnetic tape is preferably determined according to d i = d when i ≦ 2 and d i = (i - 2) d when 3 ≦ i ≦ n - 1 where d is the pitch of the tracks on the magnetic tape and n is the number of slits. According to a third embodiment a plurality of light receiving elements are provided adjacent each edge of the magnetic tape. The number of light receiving elements adjacent each edge of the tape is preferably equal to the number of operational positions. The pairs of light receiving elements are preferably arranged with one element of each pair adjacent each edge of the magnetic tape, the arrangement being such that the outputs of each pair of light receiving elements satisfy a predetermined relationship when the composite magnetic head is in a respect one of the operational positions. Preferably the predetermined relationship is that the outputs of the light receiving elements of a pair of light receiving elements are balanced. According to a first aspect of the third embodiment the light receiving means is mounted to the composite magnetic head and movable therewith, the light receiving elements being positioned so that light receiving elements of respective pairs of light receiving elements are substantially aligned with respective edges of the magnetic tape in each respective operational position. According to a second aspect of the third embodiment a slit plate is mounted to the composite magnetic head and movable between the light emitting means and the light receiving means having aperture means therein which allows light to pass through respective pairs of light emitting elements in each respective operational position. Preferably the light receiving elements are arranged along the edges of the magnetic tape and the aperture means comprises a plurality of apertures which permit light to pass to a respective pair of light receiving elements in each respective operational position. The composite magnetic head of the foregoing embodiments is preferably supported between free ends of two parallel leaf springs. The control means preferably includes a voice coil type linear motor for setting and maintaining the composite head at a selected one of the operational positions. The voice coil type linear motor preferably has a magnetic circuit which is closed in the direction of the composite magnetic head and in the direction of the magnetic tape. Preferably the composite magnetic head is mounted on a support means which is disposed between the free ends of the parallel leaf springs. The support means being responsive to movement of the coil of the voice coil type linear motor to set and maintain the operational position of the composite magnetic head. The voice coil is preferably connected to the support means in such a manner that force from the voice coil is applied in the vicinity of the centre of gravity of the support means. The light receiving elements may be manufactured using semiconductor technology to enable the composite magnetic head to be positioned with sufficient accuracy. The apertures of the slit plates may be produced using etching technology to ensure that sufficient accuracy is achieved. The use of a voice coil type linear motor overcomes the dead zone and frictional load problems previously encountered. The leakage flux from the voice coil type linear motor is reduced by closing the magnetic circuit of the voice coil type linear motor in the direction of the combination head and the magnetic tape. The composite magnetic head is preferably mounted to a support member which is disposed between the free ends of two parallel leaf springs. The voice coil type linear motor is arranged to transmit force to the support member in the vicinity of the centre of gravity thereof. This arrangement allows a reduction of secondary resonance and increases the precision of the servo control. The optical system of the invention enables the combination head to be accurately positioned without the need for a servo track. Furthermore, the arrangement of light receiving elements ensures that the system is temperature compensated. The recording/reproducing apparatus of the invention enables a composite magnetic head to be accurately positioned on the magnetic tape to allow a large amount of data to be recorded at high speed. The apparatus is particularly suitable for use in a serpentine type system. The present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic front elevational view of the magnetic tape and the combination head for a magnetic recording/reproducing apparatus according to the present invention: Fig. 2 is a front elevational view which illustrates the relative positions among a magnetic tape, a combination head and a light receiving device; Fig. 3a is a schematic plan view which illustrates the relative positions among the magnetic tape, the combination head and the light-receiving device; Fig. 3b is a front elevational view which illustrates the relative positions among the magnetic tape, the combination head and the light-receiving device; Fig. 4 is a front elevational view which illustrates the relative positions among the magnetic tape, the light receiving device of the combination head, the reference opening and an opening for detecting the positional relationship; Fig. 5a is a schematic plan view which illustrates the relative positions among the magnetic tape, the combination head, a light-receiving device and a slit plate; Fig. 5b is a front elevational view which illustrates the relative positions among the magnetic tape, the combination head, a light-receiving device and a slit plate; Fig. 6 is a front elevational view which illustrates the relative positions among the magnetic tape, the combination head and the light receiving device; Fig. 7a is a schematic plan view which illustrates the relative positions among the magnetic tape, the combination head and the light-receiving device; Fig. 7b is a front elevational view which illustrates the relative positions among the magnetic tape, the combination head and the light-receiving device; Fig. 8 is a front elevational view which illustrates the relative positions among the magnetic tape, the combination head, the light receiving device and openings formed in the slit plate; Fig. 9a is a schematic plan view which illustrates the relative positions among the magnetic tape, the combination head, the light-receiving device holding member and the slit plate; Fig. 9b is a front elevational view which illustrates the relative positions among the magnetic tape, the combination head, the light-receiving device holding member and the slit plate; Fig. 10 is a front elevational view which illustrates the relative positions among the magnetic tape, the combination head and the light receiving device; Fig. 11a is a schematic plan view which illustrates the relative positions among the magnetic tape, the combination head and the light-receiving device holding member; Fig. 11b is a front elevational view which illustrates the relative positions among the magnetic tape, the combination head and the light-receiving device holding member; Fig. 12 is a front elevational view which illustrates the relative positions among the magnetic tape, the combination head, the light-receiving device and openings formed in the slit plate; Fig. 13a is a schematic plan view which illustrates the relative positions among the magnetic tape, the combination head, the light-receiving device holding member and the slit plate; Fig. 13b is a front elevational view which illustrates the relative positions among the magnetic tape, the combination head, the light-receiving device holding member and the slit plate; Fig. 14 is a perspective view which illustrates the magnetic tape in non-loaded state; Fig. 15 is a perspective view which illustrates the magnetic tape in loaded state; Fig. 16 illustrates the structure of a tracking control; Fig. 17 illustrates the transfer function of the spring system of the parallel leaf spring supporting structure shown in Figs. 14 and 15; and Fig. 18 illustrates the transfer function of the spring system when the combination head and the holder are not disposed between the parallel leaf springs with the axis of abscissa representing frequencies and the axis of ordinate representing gains. DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will now be described with reference to Figs. 1 to 3. A magnetic recording/reproducing apparatus according to the present invention is suitable for recording and reproducing data in accordance with a serpentine method in which magnetic heads whose number is smaller than the number of the tracks of the magnetic tape used. First, the serpentine method which is used for the recording/reproducing apparatus according to the present invention will be described with reference to Fig. 1. Referring to Fig. 1, it is assumed that the direction in which a magnetic tape 11 runs is X and that the widthwise direction of the magnetic tape 11 is Y. A track group 12 is formed on the magnetic tape 11, the track group 12 having 16 tracks T₁ to T₁₆ in the direction Y at the same pitch a. A combination head 13 has four recording heads W₁ to W₄ and reproducing heads R₁ to R₄ which are integrally formed and disposed so as to correspond to the above-described track group 12. The recording heads W₁ to W₄ are in parallel provided in the direction Y at the same pitch b (b = 4a), while the reproducing heads R₁ to R₄ are disposed in parallel in direction X or - X in such a manner that they form pairs with the corresponding recording heads W₁ to W₄. The recording heads W₁ to W₄ and the reproducing heads R₁ to R₄ which form the pairs are alternately disposed in the direction Y. When data is recorded or reproduced, the above-described combination head 13 is first moved to a position shown in Fig. 1. That is, it is moved to a position so as to make the center of the recording head W₁ and that of the reproducing head R₁ coincide with the center of the track T₁, the center of the recording head W₂ and that of the reproducing head R₂ coincide with the center of the track T₅, the center of the recording head W₃ and that of the reproducing head R₃ coincide with the center of the track T₉, and the center of the recording head W₄ and that of the reproducing head R₄ coincide with the center of the track T₁₃. Then, while maintaining the established relative positions, the magnetic tape 11 is allowed to run in the direction X when data is recorded so that data is simultaneously recorded on the tracks T₁ and T₉ by using the recording heads W₁ and W₃. When the recording to the tape-end has been completed, the magnetic tape 11 is allowed to run in the - X direction so that data is simultaneously recorded on the tracks T₅ and T₁₃ by using the recording heads W₂ and W₄. After the recording to the tape-end has been completed, the combination head 13 is moved in the - Y direction by a distance a so that the center of the recording head W₁ and that of the reproducing head R₁ coincide with the center of the track T₂. With the established relative positions maintained, the magnetic tape 11 is again allowed to run in the direction X so that data is recorded on the tracks T₂ and T₁₀ by using the recording heads W₁ and W₃. After recording to the tape-end has been completed, the magnetic tape 11 is then allowed to run in the direction - X so that data is recorded on the tracks T₆ and T₁₄ by using the recording heads W₂ and W₄. Similarly, data is recorded on all of the tracks T₁ to T₁₆. According to this embodiment, since the number of the reproducing heads and the number of the recording heads are respectively arranged to be four with respect to the 16 tracks, the relative positions between the magnetic tape 11 and the combination head 13 become four positions. Now, a tracking control device of the magnetic recording/reproducing apparatus according to the present invention will be described with reference to Figs. 2 and 3. As shown in Figs. 2, 3a and 3b, the magnetic recording/reproducing apparatus includes the combination head 21 having a light-receiving device holding member 22 formed integrally with the combination head 21. A magnetic tape 23 has a track group 24 constituted by the 48 tracks T₁ to T₄₈ formed in the direction Y at the same pitch as shown in Fig. 2. According to this embodiment, width C of the magnetic tape 23 is arranged to be 6,35 mm (1/4 inch) and the track pitch is arranged to be 120 µm. The combination head 21 includes 8 recording heads W₁ to W₈ and reproducing heads R₁ to R₈ which are integrally formed with the combination head 21. The recording heads W₁ to W₈ are disposed in the direction Y at a pitch of 720 µm, while the reproducing heads R₁ to R₈ are disposed in the direction X or - X forming pairs with the corresponding recording heads W₁ to W₈. The recording heads W₁ to W₈ and the reproducing heads R₁ to R₈ which form pairs are alternately disposed in the direction Y. When the magnetic tape 23 is allowed to run in the direction X, the four recording heads W₁, W₃, W₅ and W₇ of the combination head 21 perform the recording When the magnetic tape 23 is allowed to run in the direction - X, the four recording heads W₂, W₄, W₆ and W₈ perform the recording. Furthermore, whenever the magnetic tape 23 reciprocates once, the combination head 21 is moved in the direction - Y so that the combination head 21 is positioned at 6 relative positions with respect to the magnetic tape 23. As a result, all of the 48 tracks T₁ to T₄₈ are subjected to the data recording/reproducing. Furthermore, the light-receiving device holding member 22 has a reference outputting light receiving device 25a serving as a first light receiving device and a light receiving device 25b for detecting the relative position and serving as a second light receiving device, which are formed at positions adjacent to the - Y directional edge of the magnetic tape 23. The light receiving devices 25a and 25b can be moved in accordance with the movement of the combination head 21 in the ± Y directions since the light-receiving device holding member 22 is integrally formed with the combination head 21. The light receiving surface of the light receiving device 25a is arranged such that its Y directional width el is 120 µm which is the same width as that of the tracks T₁ to T₄₈ while its X directional width is f with which a sufficient output level can be obtained. The light receiving device 25b is formed near the light receiving device 25a and the light receiving device 25b has a light receiving surface whose X directional width is arranged to be f and whose Y directional width e₂ is arranged be a proper value holding the relationship e₂ ≧ 720 µm. The output level for a unit area of the two light receiving devices 25a and 25b are arranged to be the same. The reference-outputting light receiving device 25a is positioned such that it is not concealed by the magnetic tape 23. The light receiving device 25b for detecting the relative positions is provided such that its - Y directional end is not covered by the -Y directional edge of the magnetic tape 23 when the recording head W₁ and the reproducing head R₁ are at the track position T₁. Furthermore, it is structured such that its light receiving area exposed from under the magnetic tape 23 becomes enlarged in accordance with the movement of the combination head 21 in the direction - Y. When the combination head 21 moved to each of the relative positions with respect to the magnetic tape 23, output Ea₁ from the light receiving device 25a and output Eb₁ from the light receiving device 25b hold the following relationship: Eb₁ = m × Ea₁ (1 ≦ m, where m represents a positive integer) The above-described numeral m represents each of the relative positions between the reproducing head R₁ of the combination head 21 and the plurality of tracks T₁ to T₆ positioned in a range in which the reproducing head R₁ can move, the numeral m can be a different value in accordance with each of the relative positions. That is, according to this embodiment, for example, when the recording head W₁ moved to the positions of the tracks T₁, T₂, T₃, T₄, T₅ and T₆, the each of the following relationships is established: Eb₁ = Ea₁, Eb₁ = 2Ea₁, Eb₁ = 3Ea₁, Eb₁ = 4Ea₁, Eb₁ = 5Ea₁ and Eb₁ = 6Ea₁. The light receiving devices 25a and 25b are connected to a head operating unit (omitted from illustration). The head operating unit feedback-controls the combination head 21 in the ± Y directions so as to make outputs Ea1 and Eb1 from the light receiving devices 25a and 25b to hold the relationship Eb1 = m × Ea1. As a result, the relative positions between the magnetic tape 23 and the combination head 21 are held at predetermined positions as described above. As shown in Figs. 3a, 3b, light emitting unit 26 capable of emitting light of a sufficient quantity to the light receiving devices 25a and 25b is disposed in a portion confronting the light receiving devices 25a and 25b with the - Y directional end of the magnetic tape 23 disposed therebetween. When all of the tracks T₁ to T₄₈ including the tracks T₁, T₁₃, T₂₅, and T₃₇ are subjected to the data reproduction operation of the magnetic recording/reproducing apparatus structured as described above, the combination head 21 is operated by the head operating unit so that the reproducing head R₁ and the track T₁, the reproducing head R₃ and the track T₁₃, the reproducing head R₅ and the track T₂₅ and the reproducing head R₇ and the track T₃₇ are moved to the corresponding relative positions with respect to the magnetic tape 23. At this time, the head operating unit moves the combination head 21 so as to make the output Ea₁ from the light receiving device 25a and the output Eb₁ from the light receiving device 25b hold the following relationship: Eb₁ = Ea₁ Furthermore, the head operating unit makes the combination head 21 follow the weaving of the magnetic tape 23 so that the relative positions between the magnetic tape 23 and the combination head 21 are maintained. Therefore, the relative position between the combination head 21 and the magnetic tape 23 can be held correctly. In this state,when the magnetic tape 23 is allowed to run in the X direction, the data on the tracks T₁, T₁₃, T₂₅ and T₃₇ are reproduced by the reproducing heads R₁, R₃, R₅ and R₇. When the reproduction to the end portion of the magnetic tape 23 has been completed, the magnetic tape 23 is allowed to run in the - X direction so that the each data on the tracks T₇, T₁₉, T₃₁ and T₄₃ is reproduced by the reproducing heads R₂, R₄, R₆ and R₈ respectively. When data reproduction for one reciprocation has been completed, the combination head 21 is moved by the head operating unit to the relative position of the magnetic tape 23 at which the reproduction head R₁ corresponds to the track T₂, the reproduction head R₃ corresponds to the track T₁₄, the reproduction head R₅ corresponds to the track T₂₆ and the reproduction head R₇ corresponds to the track T₃₈. At this time, the head operating unit moves the combination head 21 so as to make the output Ea1 from the light receiving device 25a and the output Eb₁ from the light receiving device 25b to hold the following relationship: Eb₁ = 2Ea₁ When the magnetic tape 23 is allowed to run in the X direction, data on the tracks T₂, T₁₄, T₂₆ and T₃₈ is reproduced by the reproducing heads R₁, R₃, R₅ and R₇. Then, the magnetic tape 23 is allowed to run in the - X direction so that each data on the tracks T₈, T₂₀, T₃₂ and T₄₄ is reproduced respectively. Then, the similar operation is repeated until the magnetic tape 23 is reciprocated 6 times so that data on all of the tracks T₁ to T₄₈ is reproduced. The above-described operation is similarly applied to the recording operation. In general, the output from the light receiving device such as a photo-diode and that from the light emitting unit such as a light emitting diode can be easily changed due to the influence of the ambient temperature. However, the tracking control device according to this embodiment is structured such that the output Eb₁ from the light receiving device 25b for detecting the relative position is an integer multiple of the output Ea₁ from the reference-outputting light receiving device 25a at each of the relative positions between the magnetic tape 23 and the combination head 21. Therefore, the position control can be stably controlled without an influence of temperature. The positions of the light receiving devices 25a and 25b are not limited to the above-described description in which they are disposed at the - Y directional edge of the magnetic tape 23. Another structure may be employed in which they are disposed at the + Y directional edge of the magnetic tape 23. In this case, the area of appearance of the light receiving surface of the light receiving device 25b is decreased in accordance with the movement of the combination head 21 in the direction - Y. This structure may also be applied to the following embodiments. A second embodiment of the present invention will be described with reference to Figs. 4 and 5. The elements having the same functions as those shown in the aforesaid embodiment are given the same reference numerals and their descriptions are omitted. As shown in Figs. 4, 5a and 5b, the magnetic recording/reproducing apparatus according to this embodiment includes a combination head 21 for recording/reproducing data from the magnetic tape 23, the combination head 21 having a slit plate 27 integrally formed with the combination head 21. The structure of the magnetic tape 23 and that of the combination head 21 can be the same as those according to the first embodiment. A light-receiving device holding member 22 is disposed to the side of the slit plate 27 opposite to the side confronting the magnetic tape 23, the light-receiving device holding member 22 being formed independently from the combination head 21 and the slit plate 27. The light-receiving device holding member 22 has a reference-outputting light receiving device 28a serving as the first light receiving device and a light receiving device 28b for detecting the relative position and serving as the second light receiving device at a position corresponding to the - Y directional end of the magnetic tape 23, the light receiving devices 28a and 28b being disposed in the direction X. The large portion of the light receiving surface of the light receiving device 28a and that of 28b are positioned in the direction - Y by larger degrees than the - Y directional edge of the magnetic tape 23. The light receiving surface of the light receiving device 28a and that of 28b are arranged such that the X directional width ℓ H is larger than the X directional width f of a reference opening 27a and that of an opening 27b for detecting the relative position. On the other hand, the Y directional width ℓ v , is larger than the Y directional width e₂ of an opening 27b for detecting the relative position. The output levels for a unit area of the two light receiving devices 28a and 28b are arranged to be the same. The above-described slit plate 27 has the reference opening 27a serving as the first opening and an opening 27b for detecting the relative position and serving as the second opening. The reference opening 27a is arranged such that its Y directional opening width e1 is 120 µm which is the same width as that of the tracks T₁ to T₄₈ while its X directional opening width is f with which a sufficient output level can be obtained. The opening 27b for detecting the relative position is formed near the reference opening 27a and it has the X directional width of f and whose Y directional width e₂ has a proper value holding the relationship e₂ ≧ 720 µm. The reference opening 27a is positioned such that it is not obstructed by the magnetic tape 23. Furthermore, when the reference opening 27a is moved in the direction Y in accordance with the movement of the combination head 21 in the direction Y, it is arranged so as to allow a predetermined area of the light receiving surface of the light receiving device 28a to be illuminated for all of the movement range of the reference opening 27a. The opening 27b for detecting the relative positions . is provided such that its- Y directional end appears from the - Y directional edge of the magnetic tape 23 when the recording head W₁ and the reproducing head R₁ are at the track position T₁. Furthermore, the opening 27b is structured such that its opening area appearing from the magnetic tape 23 becomes enlarged and the illuminated area of the light receiving surface of the light receiving device 28b is increased in accordance with the movement of the combination head 21 in the direction - Y . When the combination head 21 moves to each of the relative positions with respect to the magnetic tape 23, output Ea₂ from the light receiving device 28a due to light which passed through the reference opening 27a and output Eb₂ from the light receiving device 28b due to light which passed through the opening 27b for detecting the relative position have the following relationship: Eb₂ = m × Ea₂ (1 ≦ m, where m represents a positive integer) The above-described numeral m represents the each of the relative positions between, for example, the reproducing head R₁ of the combination head 21 and the plurality of tracks T₁ to T₆ positioned in a range in which the reproducing head R₁ can move, the numeral m can be a different value in accordance with each of the relative positions. That is, according to this embodiment, when the recording head W₁ moved to, for example, the positions of the tracks T₁, T₂, T₃, T₄, T₅ and T₆, each of the following relationships is established: Eb₂ = Ea₂, Eb₂ = 2Ea₂, Eb₂ = 3Ea₂, Eb₂ = 4Ea₂, Eb₂ = 5Ea₂ and Eb₂ = 6Ea₂. The light receiving devices 28a and 28b are connected to head operating unit (omitted from illustration). The head operating unit feedback-controls the combination head 21 in the ± Y directions so as to make the outputs Ea₂ and Eb₂ from the light receiving devices 28a and 28b to hold the relationship Eb₂ = m × Ea₂. As a result, the relative positions between the magnetic tape 23 and the combination head 21 are held at a predetermined positions as described above. As shown in Figs. 5a, 5b, the light emitting unit 26 is disposed in a portion confronting the reference opening 27a and the opening 27b for detecting the relative position in the slit plate 27 with the Y directional edge of the magnetic tape 23 disposed therebetween. When all of the tracks T₁ to T₄₈ including the tracks T₁, T₁₃, T₂₅, and T₃₇ are subjected to the data reproduction operation of the magnetic recording/reproducing apparatus structured as described above, the combination head 21 is operated by the head operating unit so that the reproducing head R₁ and the track T₁, the reproducing head R₃ and the track T₁₃, the reproducing head R₅ and the track T₂₅ and the reproducing head R₇ and the track T₃₇ are moved to the corresponding relative positions with respect to the magnetic tape 23. At this time, the head operating unit moves the combination head 21 so as to make the output Ea₂ from the light receiving device 28a and the output Eb₂ from the light receiving device 28b hold the following relationship: Eb₂ = Ea₂ Furthermore, the head operating unit makes the combination head 21 follow the weaving of the magnetic tape 23 so that the relative positions between the magnetic tape 23 and the combination head 21 are maintained. In this case, when the magnetic tape 23 is allowed to run in the X direction, the data on the tracks T₁, T₁₃, T₂₅ and T₃₇ are reproduced. On the other hand, when the magnetic tape 23 is allowed to run in the - X direction, the data on the tracks T₇, T₁₉, T₃₁ and T₄₃ are reproduced. When data reproduction for one reciprocation has been completed, the head operating unit feedback-controls to move the combination head 21 so as to make the output Ea₂ from the light receiving device 28a and the output Eb₂ from the light receiving device 28 establish the following relationship: Eb₂ = 2 Ea₂ When the magnetic tape 23 is allowed to run in the X direction, each data on the tracks T₂, T₁₄, T₂₅ and T₃₈ is reproduced respectively. Then, the magnetic tape 23 is allowed to run in the - X direction so that each data on the tracks T₈, T₂₀, T₃₂ and T₄₄ is reproduced respectively. Then, the similar operation is repeated so that data on all of the tracks T₁ to T₄₈ is reproduced. The above-described operation is similarly applied to the recording operation. According to this embodiment, the control is performed such that the quantity of light made incident upon the light receiving devices 28a and 28b after it passed through the - Y directional end of the magnetic tape 23, the reference opening 27a and the opening 27b for detecting the relative position is detected and the output Eb₂ from the light receiving device 28b becomes an integer multiple of the output Ea₂ from the light receiving device 28a. Therefore, the tracking control similar to the first embodiment can be performed. According to this embodiment, since the structure is arranged such that the slit plate 27 is moved together with the combination head 21, the weight of the movable portion can be reduced in comparison to the first embodiment. Similarly to the first embodiment, the position control can be stably controlled without an influence of temperature. Then, a third embodiment of the tracking control device of a magnetic recording/reproducing apparatus according to the present invention will be described with reference to Figs. 6 and 7. As shown in Figs. 6, 7a and 7b, the magnetic recording/reproducing apparatus includes a combination head 21 for recording/reproducing data from a magnetic tape 23, the combination head 21 having a light-receiving device holding member 29 formed integrally with the combination head 21. The above-described magnetic tape 23 has the track group 24 constituted by the 48 tracks T₁ to T₄₈ formed in the Y direction at the same pitch as shown in Fig. 6. According to this embodiment, width C of the magnetic tape 23 is arranged to be 1/4 inch and the track pitch is arranged to be 120 µm. The combination head 21 includes 8 recording heads W₁ to W₈ and reproducing heads R₁ to R₈ which are integrally formed with the combination head 21. The recording heads W₁ to W₈ are disposed in the Y direction at a pitch of 720 µm, while the reproducing heads R₁ to R₈ are disposed in the X or - X direction forming pairs with the corresponding recording heads W₁ to W₈. The recording heads W₁ to W₈ and the reproducing heads R₁ to R₈ which form pairs are alternately disposed in the Y direction. When the magnetic tape 23 is allowed to run in the X direction, the four recording heads W₁, W₃, W₅ and W₇ of the combination head 21 perform the recording, while the magnetic tape 23 is allowed to run in the - X direction, the four recording heads W₂, W₄, W₆ and W₈ perform the recording. Furthermore, whenever the magnetic tape 23 reciprocates once, the combination head 21 is moved in the - Y direction so that the combination head 21 is positioned at 6 relative positions with respect to the magnetic tape 23. As a result, all of the 48 tracks T₁ to T₄₈ are subjected to the data recording/reproducing. Furthermore, the light-receiving device holding member 29 has light receiving device group 30 consisting of five light receiving devices Da₁ to Da₅ at positions corresponding to the - Y directional end portion of the magnetic tape 23. The light receiving devices Da1 to Da5 are arranged to have the same output level per unit area and to be moved in accordance with the movement of the combination head 21 in the ± Y directions since the light-receiving device holding member 29 is integrally formed with the combination head 21. The light receiving surface of each of the light receiving devices Da1 to Da5 is arranged such that its X directional width is f with which a sufficient output level can be obtained. The light receiving device Da₁ is positioned at the largest degree in the - Y direction. The light receiving devices Da2 to Da4 are respectively positioned such that their - Y directional ends are successively shifted by 120 µm in the + Y direction which corresponds to the width of the each of the tracks T₁ to T₄₈. The light receiving device Da₅ is positioned from the - Y directional end by 240 µm in the + Y direction. That is, pitch d₁ between the light receiving devices Da₁ and Da₂, pitch d₂ between the light receiving devices Da₂ and Da₃ and pitch d₃ between the light receiving devices Da₃ and Da₄ are respectively arranged to be 120 µm. On the other hand, pitch d₄ between the light receiving devices Da₄ and Da₅ is arranged to be 240 µm. The relationship among the light receiving devices Da₁ to Da₅ and the pitches d₁ to d₅ are arranged as follows assuming that the i-th pitch in the + Y direction is d i and the pitch of each of the tracks T₁ to T₄₈ is d: d i = d when i ≦ 2 d i = (i - 2) × d when 3 ≦ i ≦ n - 1 (where i and n respectively represent positive integers) According to this embodiment, the structure is arranged such that when, for example, the recording head W₁ and the reproducing head R₁ of the combination head 21 are at the track position T₁, the light receiving device Da₁ is positioned at a pitch 3d from the - Y directional edge of the magnetic tape 23. According to this embodiment, when the recording head W₁ moved to, for example, the positions of the tracks T₁, T₂, T₃, T₄, T₅ and T₆, the following relationships among the outputs Ea₁ to Ea₅ from the light receiving devices Da₁ to Da₅ are established: Ea₃ = Ea₁ - Ea₂; Ea₄ = Ea₁ - Ea₂; Ea₄ = Ea₁ - Ea₃; Ea₅ = Ea₁ - Ea₂; Ea₅ = Ea₁ - Ea₃; Ea₅ = Ea₁ - Ea₄. The light receiving devices Da₁ to Da₅ are connected to head operating unit (omitted from illustration). The head operating unit feedback-controls the combination head 21 in the ± Y directions so as to make the outputs Ea₁ and Ea₅ from the light receiving devices Da₁ to Da₅ to hold the above-described relationship when the combination head 21 moved to the relative positions among the recording heads W₁ to W₈, the reproducing heads R₁ to R₈ and the tracks T₁ to T₄₈. As a result, the relative positions between the magnetic tape 23 and the combination head 21 are held at a predetermined positions as described above. As shown in Figs. 7a, 7b, light emitting unit 26 capable of emitting light of a sufficient quantity to the light receiving devices Da₁ to Da₅ is disposed in a portion confronting the light receiving devices Da₁ to Da₅ with the - Y directional end of the magnetic tape 23 disposed therebetween. When all of the tracks T₁ to T₄₈ including the tracks T₁, T₁₃, T₂₅, and T₃₇ are subjected to the data reproduction operation of the magnetic recording/reproducing apparatus structured as described above, the combination head 21 is operated by the head operating unit so that the reproducing head R₁ and the track T₁, the reproducing head R₃ and the track T₁₃, the reproducing head R₅ and the track T₂₅ and the reproducing head R₇ and the track T₃₇ are moved to the corresponding relative positions with respect to the magnetic tape 23. At this time, the head operating unit moves the combination head 21 so as to make the output Ea₁ from the light receiving device Da₁ and the output Ea₂ from the light receiving device Da₂ hold the following relationship by the feedback control: Ea₃ = Ea₁ - Ea₂ Furthermore, the head operating unit makes the combination head 21 follow the weaving of the magnetic tape 23 so that the relative positions between the magnetic tape 23 and the combination head 21 are maintained. Therefore, the relative position between the combination head 21 and the magnetic tape 23 can be held correctly. In this case, when the magnetic tape 23 is allowed to run in the direction X, the data on the tracks T₁, T₁₃, T₂₅ and T₃₇ are reproduced by the reproducing heads R₁, R₃, R₅ and R₇. When the reproduction to the end portion of the magnetic tape 23 has been completed, the magnetic tape 23 is allowed to run in the direction - X so that the data on the tracks T₇, T₁₉, T₃₁ and T₄₃ is reproduced by the reproducing heads R₂, R₄, R₆ and R₈. When data reproduction for one reciprocation has been completed, the combination head 21 is moved by the head operating unit to the relative position of the magnetic tape 23 at which the reproduction head R₁ corresponds to the track T₂, the reproduction head R₃ corresponds to the track T₁₄, the reproduction head R₅ corresponds to the track T₂₆ and the reproduction head R₇ corresponds to the track T₃₈. At this time, the head operating unit moves the combination head 21 so as to make the output Ea₁ from the light receiving device Da₁ and the output Ea₂ from the light receiving device Da₂ and the output Ea₄ from the light receiving device Da₄ establish the following relationship by the feedback control: Ea₄ = Ea₁ - Ea₂ When the magnetic tape 23 is allowed to run in the direction X in this state, data on the tracks T₂, T₁₄, T₂₆ and T₃₈ is reproduced by the reproducing heads R1, R3, R5 and R7. Then, the magnetic tape 23 is allowed to run in the direction - X so that data on the tracks T₈, T₂₀, T₃₂ and T₄₄ is reproduced. Similarly, the combination head 21 is moved after the one reciprocation at each of the track positions so as to hold the following relationships: when data on tracks T₃, T₁₅, T₂₇, T₃₉ and tracks T₉, T₂₁, T₃₃, T₄₅ are reproduced, Ea₄ = Ea₁ - Ea₃ when data on tracks T₄, T₁₆, T₂₈, T₄₀ and the tracks T₁₀, T₂₂, T₃₄, T₄₆ are reproduced , Ea₅ = Ea₁ - Ea₂ when data on tracks T₅, T₁₇, T₂₉, T₄₁ and tracks T₁₁, T₂₃, T₃₅, T₄₇ are reproduced , Ea₅ = Ea₁ - Ea₃ when data on tracks T₆, T₁₈, T₃₀, T₄₂ and tracks T₁₂, T₂₄, T₃₆, T₄₈ are reproduced, Ea₅ = Ea₁ - Ea₄ As a result, the track switching operation and the track followup operation are executed so that the data on all of the tracks T₁ to T₄₈ are reproduced. The above-described operation is applied to the data recording operation. According to this embodiment, since the structure is arranged such that the difference in output between two predetermined light receiving devices becomes the same as the output from a predetermined light receiving device, the position control can be stably obtained without an influence of temperatue. According to this embodiment, the numbers of the relative positions between the magnetic tape 23 and the combination head 21 are arranged to be six. The number of the light receiving devices for detecting a plurality of relative positions can be reduced by increasing the number of the relative positions. The positions of the light receiving devices Da₁ to Da₅ are not limited to the above-described structure in which they are positioned at the - Y directional end of the magnetic tape 23. A structure may be employed in which they are positioned at the + Y directional end of the magnetic tape 23 and the appearance area of the light receiving surface of each of the light receiving devices Da₁ to Da₅ decreases in accordance with the movement of the combination head 21 in the - Y direction. The above-described structure may be applied to the following embodiments. Then, a fourth embodiment of the present invention will be described with reference to Figs. 8 and 9. In order to make the description easier, the elements having the same function as those in the above-described embodiments are given the same reference numerals and their descriptions are omitted. As shown in Figs. 8, 9a and 9b, the magnetic recording/reproducing apparatus according to this embodiment includes a combination head 21 for recording/reproducing data from the magnetic tape 23, the combination head 21 having a slit plate 31 integrally formed with the combination head 21. The structure of the magnetic tape 23 and that of the combination head 21 are arranged to be the same as those according to the third embodiment. A light-receiving device holding member 32 is disposed to the side of the slit plate 31 opposite to the side confronting the magnetic tape 23, the light receiving device holding member 32 being formed independently from the combination head 21 and the slit plate 31. The light-receiving device holding member 32 has five light receiving devices Db₁ to Db₅ at positions corresponding to the - Y directional end of the magnetic tape 23, the light receiving devices Db₁ to Db₅ being disposed in the X direction. The light receiving devices Db₁ to Db₅ are arranged to independently receive light which passes the - Y directional edge of the magnetic tape 23 and openings A₁ to A₅ to be described later, The light receiving surface of each of the light receiving devices Db₁ to Db₅ is arranged to be elongated in the Y direction, and the large portion of the light receiving surface of them are positioned in the - Y direction by larger degrees than the - Y directional edge of the magnetic tape 23. The light receiving surface of each of light receiving devices Db₁ to Db₅ are arranged such that the X directional width ℓ H is larger than the X directional width f of each of openings A₁ to A₅. Furthermore, the Y-directional width ℓ v is arranged to be a value which corresponds to the Y-directional movement of the openings A₁ to A₅. The output levels for a unit area of the light receiving devices Db₁ to Db₅ are arranged to be the same. The above-described slit plate 31 has the openings A₁ to A₅. The openings A₁ to A₅ are arranged such that its directional opening width is f with which a sufficient output level can be obtained from the light receiving devices Db₁ to Db₅. The opening A₁ is positioned at the largest degree in the - Y direction. The openings A₂ to A₄ are respectively positioned such that their - Y directional ends are successively shifted by 120 µm in the + Y direction which corresponds to the width of the each of the tracks T₁ to T₄₈ from the - Y directional end of the opening A₁. The opening A₅ is positioned from the - Y directional end by 240 µm in the + Y direction. That is, pitch d₁ between the openings A₁ and A₂, pitch d₂ between the openings A₂ and A₃ and pitch d₃ between the openings A₃ and A₄ are respectively arranged to be 120 µm. On the other hand, pitch d₄ between the openings A₄ and A₅ is arranged to be 240 µm. The relationship among the openings A₁ to A₅ and the pitches d₁ to d₅ are arranged as follows assuming that the i-th pitch in the + Y direction is d i and the width of each of the tracks T₁ to T₄₈ is d: d i = d when i ≦ 2 d i = (i - 2) × d when 3 ≦ i ≦ n - 1 (where i and n respectively represent positive integers) According to this embodiment, the structure is arranged such that when, for example, the recording head W₁ and the reproducing head R₁ of the combination head 21 are at the track position T₁, the opening A₁ is positioned at which it appears by 3d from the - Y directional edge the magnetic tape 23. According to this embodiment, when the recording head W₁ moved to, for example, the positions of the tracks T₁, T₂, T₃, T₄, T₅ and T₆, the following relationships among the outputs Eb₁ to Eb₅ from the light receiving devices Db₁ to Db₅ due to light which passed through the openings A₁ to A₅ and the - Y directional edge of the magnetic tape 23 are established: Eb₃ = Eb₁- Eb₂; E b4 = Eb₁ - Eb₂; Eb₄ = Eb₁ - Eb₃; Eb₅ = Eb₁- Eb₂; Eb₅ = Eb₁ - Eb₃; Eb₅ = Eb₁- Eb₄. The light receiving devices Db₁ to Db₅ are connected to an operating unit (omitted from illustration). The head operating unit feedback-controls the combination head 21 in the ± Y directions so as to make the outputs Eb₁ and Eb₅ from the light receiving devices Db₁ to Db₅ hold the above-described relationships when the combination head 12 is moved to the relative positions among the recording heads W₁ to W₈ and the reproducing heads R₁ to R₈ and the tracks T₁ to T₄₈. As a result, the relative positions between the magnetic tape 23 and the combination head 21 are held at a predetermined positions as described above. As shown in Figs. 9a, 9b, light emitting unit 26 capable of emitting light of a sufficient quantity to the light receiving devices Db₁ to Db₅ is disposed in a portion confronting the light receiving devices Db₁ to Db₅ with the - Y directional end of the magnetic tape 23 and the openings A₁ to A₅ formed in the slit plate 31 disposed therebetween. When all of the tracks T₁ to T₄₈ including the tracks T₁, T₁₃, T₂₅, and T₃₇ are subjected to the data reproduction operation of the magnetic recording/reproducing apparatus structured as described above, the combination head 21 is operated by the head operating unit so that the reproducing head R₁ and the track T₁, the reproducing head R₃ and the track T₁₃, the reproducing head R₅ and the track T₂₅ and the reproducing head R₇ and the track T₃₇ are moved to the corresponding relative positions with respect to the magnetic tape 23. At this time, the head operating unit moves the combination head 21 so as to make the output Eb₁ from the light receiving device Db₁, the output Eb₂ from the light receiving device Db₂ and the output Eb₃ from the light receiving device Db₃ hold the following relationship by the feedback control: Eb₃ = Eb₁ - Eb₂ Therefore, the head operating unit makes the combination head 21 follow the weaving of the magnetic tape 23 so that the relative positions between the magnetic tape 23 and the combination head 21 are maintained. In this case, when the magnetic tape 23 is allowed to run in the X direction, the data on the tracks T₁, T₁₃, T₂₅ and T₃₇ are reproduced by the reproducing heads R₁, R₃, R₅ and R₇. When the magnetic tape 23 is allowed to run in the X direction, the data on the tracks T₇, T₁₉, T₃₁ and T₄₃ are reproduced by the reproducing heads R₂, R₄, R₆ and R₈. Similarly, the combination head 21 is moved after the one reciprocation at each of the track positions so as to hold the following relationships: When data on the tracks T₂, T₁₄, T₂₆, T₃₈ and the tracks T₈, T₂₀, T₃₂, T₄₄ are reproduced, Eb₄ = Eb₁ - Eb₂ When data on tracks T₃, T₁₅, T₂₇, T₃₉ and tracks T₉, T₂₁, T₃₃, T₄₅ are reproduced, Eb₄ = Eb₁ - Eb₃ When data on tracks T₄, T₁₆, T₂₈, T₄₀ and the tracks T₁₀, T₂₂, T₃₄, T₄₆ are reproduced Eb₅ = Eb₁ - Eb₂ When data on tracks T₅, T₁₇, T₂₉, T₄₁ and tracks T₁₁, T₂₃, T₃₅, T₄₇ is reproduced Eb₅ = Eb₁ - Eb₃ When data on tracks T₆, T₁₈, T₃₀, T₄₂ and tracks T₁₂, T₂₄, T₃₆, T₄₈ is reproduced Eb₅ = Eb₁ - Eb₄ As a result, the track switching operation and the track followup operation are executed so that the data on all of the tracks T₁ to T₄₈ is reproduced. The above-described operation is applied to the data recording operation. As described above, since the structure according to this embodiment is arranged such that the slit plate 31 is moved together with the combination head 21, the weight of the movable portion can be reduced in comparison to the structure according to the third embodiment. Similarly to the first embodiment, a stable position control can be obtained without an influence of temperature. Then a fifth embodiment of the tracking control device of a magnetic recording/reproducing apparatus will be described with reference to Figs. 10 and 11. As shown in Figs. 10, 11a and 11b, the magnetic recording/reproducing apparatus includes the combination head 21 for recording and reproducing data from the magnetic tape 23 and having a light-receiving device holding member 34 formed integrally with the combination head 21. The above-described magnetic tape 23 has a track group 24 constituted by the 48 tracks T₁ to T₄₈ formed in the direction Y at the same pitch as shown in Fig. 10. According to this embodiment, width C of the magnetic tape 23 is arranged to be 6,35 mm (1/4 inch) and the track pitch is arranged to be 120 µm. The weaving taken place in the magnetic tape 23 is restricted to smaller than ± 50 µm by flanges or the like (omitted from illustration) for ± Y directional edge of the magnetic tape 23. The combination head 21 includes 8 recording heads W₁ to W₈ and reproducing heads R₁ to R₈ which are integrally formed with the combination head 21. The recording heads W₁ to W₈ are disposed in the Y direction at a pitch of 720 µm, while the reproducing heads R₁ to R₈ are disposed in the X or - X direction forming pairs with the corresponding recording heads W₁ to W₈. The recording heads W₁ to W₈ and the reproducing heads R₁ to R₈ which form pairs are alternately disposed in the Y direction. When the magnetic tape 23 is allowed to run in the X direction, the four recording heads W₁, W₃, W₅ and W₇ of the combination head 21 perform the recording, while the magnetic tape 23 is allowed to run in the direction - X, the four recording heads W₂, W₄, W₆ and W₈ perform the recording. Furthermore, whenever the magnetic tape 23 reciprocates once, the combination head 21 is moved in the - Y direction so that the combination head 21 is positioned at 6 relative positions with respect to the magnetic tape 23. As a result, all of the 48 tracks T₁ to T₄₈ are subjected to the data recording/reproducing. Furthermore, light receiving device group 34 serving as a light receiving device group on one end and consisting of six light receiving devices Da₁ to Da₆ is provided in a portion corresponding to the portion in the vicinity of the + Y directional end of the magnetic tape 23. Similarly, light receiving device group 35 serving as a light receiving device group on another end and consisting of six light receiving devices Db₁ to Db₆ is provided in a portion corresponding to the portion in the vicinity of the - Y directional end of the magnetic tape 23. The number of the light receiving devices of the light receiving device groups 34 and 35 is arranged to be six which is the same as the number of the tracks T₁ to T₆ in a range in which, for example, the recording head W₁ and the reproducing head R₁ of the combination head 21 can be moved. The light receiving devices Da₁ to Da₆ and Db₁ to Db₆ are arranged to have the same output level. Furthermore, the light-receiving device holding member 33 is integrally formed with the combination head 21. As a result, the light receiving devices Da₁ to Da₆ and Db₁ to Db₆ can be moved in accordance with the movement of the combination head 21 in the ± Y directions. The light receiving surface of each of the light receiving devices Da₁ to Da₆ and Db₁ to Db₆ is arranged to have the Y-directional width e which can correspond to the weaving of the magnetic tape 23. The X-directional width is arranged to be f with which a sufficient output can be obtained. According to this embodiment, the above-described width e is 100 µm. The light receiving devices Da₁ to Da₆ and Db₁ to Db₆ are arranged such that the light receiving devices Da₁ and Db₁ are disposed at the - Y directional end and the light receiving devices Da₂ to Da₆ and Db₂ to Db₆ are formed in the + Y direction to form a line at the same pitch d (d = 120 µm) as the track pitch of the magnetic tape 23. The light receiving devices Da₁ and Db₁ are shifted by 6,35 mm (1/4 inch) in the direction Y of the magnetic tape 23. Furthermore, when, for example, the recording head W₁ and the reproducing head R₁ of the combination head 21 is at the track position T₁, the center of the light receiving devices Da₁ and that of Db₁ coincide with the ± Y directional edge of the magnetic tape 23. The above-described light receiving devices Da₁ to Da₆ and Db₁ to Db₆ are connected to the head operating unit (omitted from illustration). The head operating unit feedback controls the combination head 21 so as to move it to each of the relative positions between the recording heads W₁ to W₈, the reproducing heads R₁ to R₈ and the tracks T₁ to T₄₈ such that the difference in the output from the corresponding light receiving devices becomes zero, the combination head 21 being moved in the ± Y direction. As a result, the relative position between the magnetic tape 23 and the combination head 21 can be held at a predetermined position. As shown in Figs. 11a, 11b, light emitting unit 36 capable of emitting a sufficient quantity of light to the light receiving devices 34 and 35 are disposed at positions corresponding to the light receiving device groups 34 and 35 with the ± Y directional edge of the magnetic tape 23 disposed therebetween. At this time, the head operating unit feedback controls the combination head 21 so as to move it such that the difference in the output between the light receiving device Da₁ and the light receiving device Db₁ becomes zero. Furthermore, the head operating unit make the combination head 21 follow the weaving of the magnetic tape 23 so as to maintain the relative position between the magnetic tape 23 and the combination head 21. When the reproduction of data for one reciprocation has been completed, the combination head 21 is moved to the relative position with the magnetic tape 23 at which the reproducing head R₁ and the track T₂ correspond to each other, the reproducing head R₃ and the track T₁₄ correspond to each other, the reproducing head R₅ and the track T₂₆ correspond. to each other and the reproducing head R₇ and the track T₃₈ correspond to each other. At this time, the head operating unit feedback-controls the combination head 21 so as to move it such that the difference in the output between the light receiving device Da₂ and that of the light receiving device Db₂ becomes zero. When the magnetic tape 23 is allowed to run in the X direction, data on the tracks T₂, T₁₄, T₂₆ and T₃₈ is reproduced by the reproducing heads R₁, R₃, R₅ and R₇. Then, when the magnetic tape 23 is allowed to run in the direction - X so that the tracks T₈, T₂₀, T₃₂ and T₄₄ are subjected to the reproduction. Similarly, when data on the tracks T₃, T₁₅, T₂₇ and T₃₉ and data on the tracks T₉, T₂₁, T₃₃ and T₄₅ is reproduced, the combination head 21 is moved so as to make the difference in the output between the light receiving devices Da3 and Db3 become zero. When data on the tracks T₄, T₁₆, T₂₈ and T₄₀ and data on the tracks T₁₀, T₂₂, T₃₄ and T₄₆ is reproduced, the difference in the output between the light receiving devices Da₄ and Db4 is made zero. When data on the tracks T₅, T₁₇, T₂₉ and T₄₁ and data on the tracks T₁₁, T₂₃, T₃₅ and T₄₇ is reproduced, the difference in the output between the light receiving devices Da₅ and Db₅ is made zero. When data on the tracks T₆, T₁₈, T₃₀ and T₄₂ and data on the tracks T₁₂, T₂₄, T₃₆ and T₄₈ is reproduced, the difference in the output between the light receiving devices Da₆ and Db₆ is made zero. The combination head 21 is moved after one reciprocation at each track position has been completed. Thus, the track switching operation and the track following-up operation are executed until data on all of the tracks T₁ to T₄₈ is reproduced. The above-described operation is applied to the recording operation. Then, a sixth embodiment of the present invention will be described with reference to Figs. 12 and 13. In order to make the description easy, the elements having the same functions as those according to the aforesaid embodiments are given the same reference numerals and their descriptions are omitted. As shown in Figs. 12, 13a and 13b, the magnetic recording/reproducing apparatus includes the combination head for recording and reproducing data from the magnetic tape 23, the combination head 21 having a slit plate 37 integrally formed with the combination head 21. The structures of the magnetic tape 23 and the combination head 21 are the same as those according to the fifth embodiment. The weaving of the magnetic tape 21 is restricted to ± 50 µm or less by flanges or the like (omitted from illustration) for restricting the ± Y directional end of the magnetic tape 21. The light-receiving device holding member 38 is disposed to the side of the slit plate 37 opposite to the side which confronts the magnetic tape 23, the light-receiving device holding member 38 being independently formed from the combination head 21 and the slit plate 37. The light-receiving device holding member 38 has light receiving device groups 39 and 40 which respectively consist of six light receiving devices Di₁ to Di₆ and Dj₁ to Dj₆ at the positions corresponding to the ± Y directional ends of the magnetic tape 23. The light receiving devices Di1 to Di₆ and Dj₁ to Dj₆ are arranged such that the light receiving devices Di₁ and Dj₁ are disposed at the + X directional end and the other light receiving devices are successively disposed in the - X direction to form a line at a pitch g. Furthermore, their Y-directional centers coincide with the ± Y- directional end of the magnetic tape 23. The above-described light receiving devices Di₁ to Di₆ and Dj₁ to Dj₆ are respectively arranged to independently receive light which passed through the ± Y-directional end of the magnetic tape 23 and openings Si₁ to Si₆ and Sj₁ to Sj₆ to be described later. The light receiving surfaces of the light receiving devices Di₁ to Di₆ and those Dj₁ to Dj₆ are arranged such that the Y directional width ℓ v is larger than the Y directional width e of openings Si₁ to Si₆ and Sj₁ to Sj₆, and the X directional width ℓ H is smaller than the above-described pitch g. The output levels for a unit area of the light receiving devices Di₁ to Di₆ and Dj₁ to Dj₆ are arranged to be the same. The above-described slit plate 37 has an opening group 41 consisting of six openings Si₁ to Si₆ and serving as an opening group at an end portion at positions corresponding to the light receiving devices Di₁ to Di₆. On the other hand, opening group 42 consisting of six openings Sj₁ to Sj₆ and serving as an opening group at another end portion at positions corresponding to the light receiving devices Dj₁ to Dj₆. The openings are provided by six so as to correspond to the number of the tracks T₁ to T₆ in a range in which, for example, the recording head W1 and the reproducing head R1 can move which form pairs. The openings Si₁ to Si₆ and Sj1 to Sj₆ move. in accordance with the ± Y directional movement of the combination head 21 since the slit plate 37 is integrally formed with the combination head 21. Each of the openings Si₁ to Si₆ is arranged to have a Y-directional width e (e = 100 µm) so as to correspond to the weaving of the magnetic tape 23. On the other hand, their X-directional width is arranged to be a width f with which a sufficient output can be obtained from the light receiving devices Di₁ to Di₆ and Dj₁ to Dj₆. The openings Si₁ to Si₆ and Sj₁ to Sj₆ are arranged such that the openings Si₁ and Sj₁ are disposed at the + X directional end and at the - Y directional end and the openings Si₂ to Si₆ and Sj₂ to Sj₆ are respectively and successively disposed in the + Y direction at the same pitch d (d = 120 µm) as the track pitch of the magnetic tape 23 and at a pitch g in the - X direction. Furthermore, the light receiving devices Di₁ to Di₆ and the light receiving devices Dj₁ to Dj₆ are shifted by 6,35 mm (1/4 inch) which corresponding to the width of the magnetic tape 23 in the direction Y. According to this embodiment, when for example, the recording head W₁ and the reproducing head R₁ of the combination head 21 are at the track position T1, the Y-directional centers of the openings Si₁ and Sj₁ coincide with the centers of the light receiving devices Di₁ and Dj₁, that is, the ± Y directional ends of the magnetic tape 23. The above-described light receiving devices Di₁ to Di₆ and Dj₁ to Dj₆ are connected to the head operating unit (omitted from illustration). The head operating unit feedback-controls the combination head 21 to move it in the ± Y direction of the magnetic tape 23 such that the difference in the output between light receiving devices Di₁ to Di₆ and Dj₁ to Dj₆ which form pairs becomes zero when the combination head 21 has been shifted to each of the relative positions between the recording heads W₁ to W₈ and the reproducing heads R₁ to R₈ and the tracks T₁ to T₄₈. As a result, the relative position between the magnetic tape 23 and the combination head 21 is maintained at a predetermined position. As shown in Figs. 13a, 13b, the light emitting unit 43 capable of emitting light to the light receiving devices 39 and 40 is provided at the positions confronting the above-described light receiving device groups 39 and 40 with the ± Y directional end of the magnetic tape 23 and the slit plate 37 disposed therebetween. At this time, the head operating unit feedback-controls to calculate the difference in the output between the light receiving device Di1 and the light receiving device Dj₁ due to incident light from the light emitting unit 43 via the openings Si₁ and Sj₁ formed in the slit plate 37 and the ± Y directional end of the magnetic tape 23. The combination head 21 is operated such that the difference in the output becomes zero. Therefore, the combination head 21 moves so as to follow the weaving of the magnetic tape 23. As a result, the relative positions between the combination head 21 and the magnetic tape 23 can be maintained correctly. When the magnetic tape 23 is allowed to run in the direction X in this state, data on the tracks T₁, T₁₃, T₂₅ and T₃₇ is reproduced by the reproducing heads R₁, R₃, R₅ and R₇. When the magnetic tape 23 is allowed to run in the - X direction, data on the tracks T₇, T₁₉, T₃₁ and T₄₃ is reproduced by the reproducing heads R₂, R₄, R₆ and R₈. When the reproduction of data for one reciprocation has been completed, the combination head 21 is moved so as to make the following differences in the following outputs zero: when data on the tracks T₂, T₁₄, T₂₆ and T₃₈ and data on the tracks T₈, T₂₀, T₃₂ and T₄₄ is reproduced, the output difference between the light receiving devices Di₂ and Dj₂ due to incident light via the openings Si₂ and Sj₂ and the edges of the magnetic tape 23; when data on the tracks T₃, T₁₅, T₂₇ and T₃₉ and data on the tracks T₉, T₂₁, T₃₃ and T₄₅ is reproduced, the output difference between the light receiving devices Di₃ and Dj₃ due to incidental light via the openings Si₃ and Sj₃ and the edges of the magnetic tape 23; when data on the tracks T₄, T₁₆, T₂₈ and T₄₀ and data on the tracks T₁₀, T₂₂, T₃₄ and T₄₆ is reproduced, the output difference between the light receiving devices Di₄ and Dj₄ due to incident light via the openings Si₄ and Sj₄ and the edges of the magnetic tape 23; when data on the tracks T₅, T₁₇, T₂₉ and T₄₁ and data on the tracks T₁₁, T₂₃, T₃₅ and T₄₇ is reproduced, output difference between the light receiving devices Di₅ and Dj₅ due to incidental light via the openings Si₅ and Sj₅ and the edges of the magnetic tape 23; when data on the tracks T₆, T₁₈, T₃₀ and T₄₂ and data on the tracks T₁₂, T₂₄, T₃₆ and T₄₈ is reproduced, the output difference between the light receiving devices Di6 and Dj₆ due to incident light via the openings Si₆, Sj₆ and the edges of the magnetic tape 23. As a result, the track switching operation and the track following up operation can be performed and the data reproduction from all of the tracks T₁ to T₄₈ is completed. The above-described operation is applied to the recording operation. Then, a seventh embodiment of the present invention will be described. According to this embodiment, an example of a serpentine magnetic recording/reproducing apparatus is provided. The magnetic recording/reproducing apparatus according to this embodiment is structured such that a combination head having recording heads and the reproducing heads whose number is smaller than the number of the tracks of the magnetic tape is allowed to run once in the direction of the magnetic tape on which a plurality of tracks are formed in parallel in the direction in which the tape runs. As a result, a plurality of tracks are simultaneously subjected to the recording or the reproducing. Furthermore, the combination head is moved by the head operating means in the widthwise direction of the magnetic tape by the track switching operation. As a result, data is recorded/reproduced from all of the tracks. Then, the magnetic recording/reproducing apparatus according to this embodiment will be described with reference to Figs. 14, 15 and 16. Fig. 14 is a perspective view which illustrates the magnetic recording/reproducing apparatus to which no magnetic tape has been loaded. Fig. 15 illustrates a state in which the magnetic tape has been loaded. A combination head 51 for recording or reproducing data from a magnetic tape 52 is fastened to a holder 53 serving as a member for holding the combination head 51. Light-receiving groups 54 and 55 for detecting the vertical two ends of the magnetic tape 52 are secured to a portion in the vicinity of the combination head 51. That is, a movable portion 56 is constituted by combining the combination head 51, the light receiving device groups 54 and 55 and the holder 53. The holder 53 is fastened between the free ends of parallel leaf springs 57a and 57b whose one ends are secured to a fastening portion 58. The fastening portion 58 is fastened to a main frame (omitted from illustration) of the magnetic recording/reproducing apparatus. As head moving unit for moving the combination head 51 to the widthwise direction of the magnetic tape 52, a voice coil type linear motor 59 having no friction loss and dead zone is employed. The voice coil type linear motor 59 includes a square yoke type magnetic circuit 60 secured to the main frame and a coil 61 for generating moving force. The above-described movable portion 56 is connected to the coil 61 by the bobbin 62 which connects the movable portion 56 and the coil 61 such that it acts in synchronization with the movement of the coil 61 and the power generated by the coil 61 passes through a portion in the vicinity of the center of gravity of the movable portion 56. As a result of the above-described structure, precise servo control can be performed in the operation of the combination head 51. Reference numerals 60a and 60b represent magnets of the voice coil type linear motor 59. Reference numeral 60C represents a central magnet into which the coil 61 is inserted from outside. Reference numeral 60d represents an outside magnetic pole,60e represents a common magnetic pole positioned in close contact with the terminals of each of outer magnetic poles confronting the central magnetic pole 60C and outer magnetic poles 60d. Thus, a closed circuit of the magnetic circuit 60 is constituted so that the combination head 51 does not receive an influence of a leaked flux from the magnetic circuit 60. Therefore, the influence of the leaked flux from the voice coil type linear motor 59 upon the combination head 51 and the magnetic tape 52 can be reduced to ten and several Oes. Furthermore, the main frame is provided with a light emitting device 63 position in the opposite direction to the light receiving devices 54 and 55 with the magnetic tape 52 is disposed therebetween and fixed guides 64a and 64b disposed on the both sides of the combination head 51 and guiding the magnetic tape 52. Fig. 16 illustrates the structure of the tracking control according to this embodiment. As shown in Fig. 16, the magnetic tape 65 has a track group 66 consisting of 48 tracks T₁ to T₄₈ at the same pitch in the direction Y. According to this embodiment, the width C of the magnetic tape 65 is arranged to be 6,35 mm (1/4 inch) and the track pitch is arranged to be 120 µm. The combination head 67 includes 16 recording heads W₁ to W₁₆ and reproducing heads R₁ to R16 which are formed integrally. The recording heads W₁ to W₁₆ are disposed in the direction Y at a pitch of 360 µm. The reproducing heads R₁ to R₁₆ form a pair with the corresponding recording heads W₁ to W₁₆ in the X or - X direction. The recording heads W₁ to W₁₆ and the reproducing heads R₁ to R₁₆ each forming a pair are alternately disposed in the direction Y. In the combination head 67 thus structured, when the magnetic tape 65 is allowed to run in the direction X, 8 recording heads W 2n-1 (n = 1 to 8) perform the recording operation, while when the magnetic tape 65 is allowed to run in the direction- X, 8 recording heads W 2n (n = 1 to 8) perform the recording. Furthermore, the combination head 67 is moved in the direction - Y whenever the magnetic tape reciprocates. Therefore, the relative position with respect to the magnetic tape 65 is changed three times. As a result, all of the 48 tracks T₁ to T₄₈ are subjected to the data recording/reproducing. The holder 68 has, at its portion corresponding to the + Y directional end of the magnetic tape 65, a light-receiving device group 69 consisting of three light receiving devices Da₁ to Da₃ and disposed at an end. Furthermore, a light-receiving device group 70 consisting of three light receiving devices Db₁ to Db₃ and disposed at the other end is provided in a portion corresponding to the - Y directional end. The number of the provided light receiving devices 69 and 70 corresponds to the number of the tracks T₁ to T₃ in a range in which, for example, the pair of the recording head W₁ and the reproducing head R₁ of the combination head 67 operate. The light receiving devices Da₁ to Da₃ and Db₁ to Db₃ are arranged to have the same output level for a unit light receiving area. Furthermore, they are integrally formed with the combination head 67 by the holder 68. As a result, they can be moved in accordance with the movement of the combination head 67 in the ± Y direction. The light receiving devices Da₁ to Da₃ and Db₁ to Db₃ are disposed at the same pitch (120 µm) as the track pitch of the magnetic tape 65, and the light receiving devices Da₁ and Db1 are shifted from each other in the direction Y by the width 6,35 mm (1/4 inch) of the magnetic tape 65. Furthermore, when, for example, the recording head W₁ and the reproducing head R₁ of the combination head 67 are at the track position T₁, the centers of the light receiving devices Da₁ and Db₁ coincide with the ± Y directional ends of the magnetic tape 65. As a result of the above-described structure, when data on all of the tracks T₁ to T48 is reproduced, the head operating unit is feedback-controlled so as to make the output difference between the light receiving devices Da₁ and Db₁ becomes zero when the magnetic tape 65 is allowed to run in the direction X. With the thus realized precise tracking control performed, data on 8 tracks T 6n-5 (n = 1 to 8) is reproduced by 8 reproducing heads R 2n-1 (n = 1 to 8). When the reproduction to the end portion of the magnetic tape 65 has been ended, the magnetic tape 65 is allowed to run in the direction - X. During this, the feedback control is maintained such that the output difference between the light receiving devices Da₁ and Db₁ is made zero is conducted so that the data on 8 tracks T₆ n-2 (n = 1 to 8) is reproduced by 8 reproducing heads R 2n (n = 1 to 8). Similarly, the track switching operation and the track follow-up operation are conducted. Thus, data on all of the tracks T₁ to T₄₈ is ended. The above-described operation is also applied to the recording operation. Although the combination head 67 is held by a parallel leaf spring according to this embodiment, the present invention is not limited to the description above. A structure may be employed in which it is held by a shaft and a bearing in a sliding method. Fig. 17 illustrates the transfer function of the spring system of the parallel leaf spring supporting structure shown in Figs. 14 and 15. As shown in Fig. 17, the second resonance frequency becomes 1.2 kHz with respect to the first resonance frequency 30 Hz. With the characteristics described above, the closed loop servo with the cutoff frequency of about 500 Hz can be obtained by performing a servo control such as the phase compensation. Therefore, the tape weaving of, for example, 100 Hz can be followup controlled at a compression ratio of about -20 to -30 dB. Fig. 18 illustrates the transfer function for a structure in which the combination head 51 and the holder 53 are not supported between the parallel leaf springs 57a and 57b Figs. 14 and 15. Since the second resonant frequency is about 450 Hz, the cutoff frequency becomes lowered excessively and the servo gain reduction becomes too lowered to conduct the closed loop servo. Therefore, a tracking control with a satisfactory followup characteristics cannot be conducted. Since the voice coil type linear motor 59 is used to operate the combination head 51 and since the power generated by the linear motor 59 is arranged to pass through a portion in the vicinity of the center of gravity of the movable portion 56, the operation of the combination head 51 can be precisely servo-controlled. It should be understood that the present invention is not limited to the specific embodiments described in this specification, except as defined in the appended claims.

Claims: A magnetic recording/reproducing apparatus comprising a composite magnetic head (13; 21; 51; 67) having a number of recording/reproducing heads (W₁₋₈, R 1-8; W 1-16, R₁₋₁₆) less than the number of tracks (24; 66; T₁₋₄₈) which are provided on a magnetic tape (11; 23; 52; 65) in parallel with each other and with the direction (X) in which the tape runs, said composite head being movable relative to the magnetic tape in the widthwise direction (Y) of the tape to a number of operational positions at each of which said heads are aligned with a respective set of desired ones of said tracks, characterised by control means for setting and maintaining said composite head at a selected one of said positions, said control means including an optical system (26, 22; 26, 27, 22; 26, 29; 26, 31, 32; 36, 33; 43, 37, 38; 63, 68) having a light emitting means (26; 36; 43; 63) and a multi-element light receiving means (25a, 25b; 28a, 28b; 30; Db₁₋₅; 34, 35; 39, 40; 69, 70) disposed on opposite sides of the tape, and arranged to transmit light past at least one edge of the tape in such a way that the pattern of light transmitted to said multi-element light receiving means is dependent upon said operational position of the composite head relative to the tape. An apparatus as claimed in claim 1, wherein the light receiving means comprises first (25a; 28a) and second (25b; 28b) light receiving elements, the arrangement being such that the output of the second light receiving element is a multiple of the output of the first light receiving element in dependence upon the operational position of the composite magnetic head. An apparatus as claimed in claim 2, wherein in each operational position of the composite magnetic head a constant area of the first light receiving element is exposed to light from the light emitting means (26) whilst the area of the second light receiving element exposed to light from the light emitting means varies in dependence upon the operational position of the composite magnetic head. An apparatus as claimed in claim 3, wherein the first light receiving element is positioned so that the tape does not obstruct light from the light emitting means, whereas the second element is positioned so that an edge of the tape obstructs light passing to the second element in dependence upon the operational position of the composite magnetic head. An apparatus as claimed in claim 4, wherein the quantity of light received by the second light receiving element at each operational position of the composite magnetic head is an integer multiple of the light received by the first element, wherein the integer multiple corresponds to the respective operational position. An apparatus as claimed in any one of the preceding claims, wherein the light receiving means (25a, 25b) is mounted to and movable with the composite magnetic head. An apparatus as claimed in any one of claims 1-5, wherein the optical system includes a slit plate (27) mounted to the composite magnetic head and movable therewith, the slit plate being movable between the light emitting means (26) and light receiving means (28a, 28b) and having aperture means (27a, 27b) therein which controls the pattern of light transmitted to the first and second light receiving elements in dependence upon the operational position of the composite magnetic head. An apparatus as claimed in claim 7, wherein the aperture means comprises a first aperture (27a) allowing a constant area of said first light receiving element (28a) to be illuminated by said light emitting means (26) and a second aperture (27b) illuminating an area of the second element (28b) in dependence upon the operational position of the composite magnetic head. An apparatus as claimed in claim 1, wherein three or more spaced apart light receiving elements (Da₁-Da₅, Db₁-Db₅) are provided adjacent an edge of the tape, the arrangement being such that outputs of selected ones of the light receiving elements have predetermined relationships in each of the operational positions. An apparatus as claimed in claim 9, wherein for each operational position the output of a selected light receiving element (Da₁-Da₅, Db₁-Db₅) equals the sum of the outputs of two other selected light receiving elements (Da₁-Da₅, Db₁-Db₅). An apparatus as claimed in claim 9 or claim 10, wherein the light receiving elements are mounted to and movable with the composite magnetic head. An apparatus as claimed in claim 11, wherein the light receiving elements are in operation displaced by differing amounts from an edge of the tape. An apparatus as claimed in claim 12, wherein the pitch d i between the ends of adjacent light receiving elements Da i and Da i+1 in the lateral (Y) direction of the tape is determined according to: d i = d when i ≦ 2 and d i = (i - 2) d when 3 ≦ i ≦ n - 1 where d is the pitch of the tracks on the magnetic tape and n is the number of light receiving elements. An apparatus as claimed in any one of claims 9 to 12, wherein the light receiving elements are of constant width in the longitudinal direction (X) of said tape. An apparatus as claimed in claim 9 or claim 10 wherein the optical system includes a slit plate (31) mounted to the composite magnetic head and movable therewith, the slit plate (31) being movable between the light emitting means (26) and the light receiving elements (Db₁ - Db₅) and having aperture means (A₁ - A₅) which selectively allows light to pass from the light emitting means (26) to selected ones of the light receiving elements (Db₁ - Db₅, 32) in a pattern dependent upon the operational position of the composite magnetic head. An apparatus as claimed in claim 15, wherein the aperture means (A₁-A₅) comprises a plurality of slits (A₁-A₅), each said slit being arranged to allow light to pass from the light emitting means (26) to a respective light receiving element (Db₁ - Db₅) in selected ones of the operational positions of the composite magnetic head. An apparatus as claimed in claim 16, wherein the pitch d i between the ends of the adjacent slits A i and A i+1 of the slit plate (31) in the lateral direction (Y) of the magnetic tape is determined according to: d i = d when i ≦ 2 d i = (i - 2d) when 3 ≦ i ≦ n - 1 where d is the pitch of the tracks on the magnetic tape and n is the number of slits in the slit plate. Apparatus according to any one of claims 15 to 17, wherein the slits (A₁ - A₅) are all of constant width (f) in the longitudinal (X) direction of said tape. An apparatus as claimed in claim 1, wherein a plurality of light receiving elements (Da₁ - Da₆, Db₁ - Db₆; Di₁ - Di₆, Dj₁ - Dj₆; Db₁ - Db₃, Da₁ - Da₃) are provided adjacent each edge of the magnetic tape. An apparatus as claimed in claim 19, wherein the number of light receiving elements adjacent each edge of the tape is equal to the number of operational positions. An apparatus as claimed in claim 20 or claim 21, wherein pairs of light receiving elements (Da₁ - Da₆, Db₁ - Db₆; Di₁ - Di₆, Dj₁ -Dj₆; Db₁ - Db₃, Da₁ - Da₃ ) are arranged with one element of each pair adjacent each side of the magnetic tape, the arrangement being such that the outputs of each pair of light receiving elements satisfy a predetermined relationship when the composite magnetic head is in a respective one of the operational positions. An apparatus as claimed in claim 21, wherein the predetermined relationship is that the outputs of the light receiving elements of a pair of light receiving elements are balanced. An apparatus as claimed in claim 21 or 22, wherein the light receiving elements are mounted to said composite magnetic head and movable therewith, the light receiving elements being positioned so that light receiving elements of respective pairs of light receiving elements are substantially aligned with respective edges of the magnetic tape in each respective operational position. An apparatus as claimed in claim 21 or claim 22, wherein the optical system includes a slit plate (37) mounted to the composite magnetic head and movable between the light emitting means (43) and the light receiving elements (Di₁ - Di₆, Dj₁ - Dj₆) having aperture means (Si₁ - Si₆, Sj₁ - Sj₆) therein which allows light to pass to respective pairs of the light emitting elements in each respective operational position. An apparatus as claimed in claim 24, wherein the light receiving elements are arranged along the edges of said magnetic tape and the aperture means comprises a plurality of apertures (Si₁ - Si₆, Sj₁ - Sj₆) which permit light to pass to a respective pair of light receiving elements in each respective operational position. An apparatus as claimed in any one of claims 1 and 23 to 25 wherein said light emitting means transmits light past both edges of the tape. An apparatus as claimed in any one of the preceding claims wherein said light receiving means are so disposed that outputs from said light receiving elements have a predetermined relation which governs said control means when said composite magnetic head is in each operational position. An apparatus as claimed in any one of the preceding claims including head operating means capable of moving said combination head in the widthwise direction of said tape. An apparatus according to any one of the preceding claims, wherein said composite magnetic head is supported between free ends of two parallel leaf springs (57a, 57b). An apparatus as claimed in any one of the preceding claims, wherein the control means includes a voice coil type linear motor (59) for setting and maintaining the composite head at a selected one of said operational positions. An apparatus as claimed in claim 30, wherein the voice coil type linear motor has a magnetic circuit which is closed in the direction of the composite magnetic head and in the direction of the magnetic tape. An apparatus according to claim 30 or claim 31, when dependent on claim 29 further including a support means (53) disposed between the free ends of the parallel leaf springs (57a, 57b), the support means supporting the composite magnetic head and being responsive to movement of the coil of the voice coil type linear motor to set and maintain the operational position of the composite magnetic head. An apparatus as claimed in claim 32, wherein the voice coil is connected to the support means in such a manner that force from the voice coil is applied in the vicinity of the centre of gravity of the support means. A serpentine type magnetic recording/reproducing system incorporating the apparatus of any one of the preceding claims.

Inventors: IWAMATSU TADASHI, OKUDA TOHRU, IWAMATSU, TADASHI, OKUDA, TOHRU
Applicants: SHARP KK, SHARP KABUSHIKI KAISHA
Application year: 1990
Main classification: G11B5
IPC codes: G11B5