Recording and/or reproducing apparatus for longitudinal recording

Abstract: A recording and/or reproducing apparatus employs azimuth-pair-head (41, 42, 43, 44) in a rotary head drum. The rotary head drum is axially shifted by a head shifting means. First tracks (No. 1, No. 2, No. 3, No. 4) are formed on a magnetic tape (10) during forward driving of the magnetic tape across the rotary head drum. On the other hand, second tracks (No. 5, No. 6, No. 7, No. 8) are formed adjacent to the first tracks during reverse driving across the rotary head drum. Since the first and second tracks are formed by means of the azimuth-pair-head, azimuth gaps thereof will have different or symmetrical obliquity to each other. This successfully avoids cross-talk between adjacent tracks to allow formation of the first and second tracks in a tightly arranged fashion. As a consequence, high-density longitudinal recording without cross-talk between adjacent tracks becomes possible.

Description: The present invention relates generally to a recording and/or reproducing apparatus for recording and/or reproducing information on longitudinal tracks formed on a magnetic tape, such as video tape, pulse-code modulated (PCM) audio tape and so forth. More specifically, the invention relates to a recording and/or reproducing apparatus for longitudinal recording, which allows high-density recording. In the conventional recording and/or reproducing apparatus having a rotary head drum, such as a video tape recorder (VTR), PCM audio player (R-DAT) and so forth, helical recording systems have been employed. As is well known, magnetic tapes are wrapped around the rotary head drums in helical fashion for recording and/or reproducing information on helical tracks formed on the magnetic tapes. In order to wrap the magnetic tape onto the rotary head drum in helical fashion, tape paths upstream and downstream of the rotary head drum have to lie in different planes. This makes the structure of the tape paths complicated. Tape loading mechanisms also become complicated. Furthermore, conventional recording and/or reproducing apparatus allows only one-way recording and limits recording capacity of the magnetic tape. Also rewinding of the tape is necessary when a different track is to be used for recording or reproducing. Thus requiring an inconveniently long access period. For eliminating such defects inherent in the helical scanning-type recording system, there has been proposed a longitudinal recording system. Such a system has been disclosed in the United States Patent 4,040,109, issued on August 2, 1977, to Igor Alexervich Kryltosov. In the shown longitudinal recording system, signal processing on the time base can freely performed by a digitizing signal processing system. In addition, it becomes possible to harmonise the operation of the mechanical system and signal processing system for cooperation therewith. On the other hand, in the conventional longitudinal recording system, cross-talk between adjacent recording tracks raises problems. Such problems become more and more serious when high-density recording is attempted. Conventionally, a guard-band is formed between adjacent tracks for avoiding cross-talk. This however prevents high-density longitudinal recording. On the other hand, the requirement for more compact magnetic tape cassettes, such as VTR tape cassettes, PCM audio cassettes and so forth with substantially high-density longitudinal recording capacity and/or reproducing apparatus is becoming higher. IBM Technical Disclosure Bulletin Volume 22, No 4 discloses an apparatus for recording a plurality of parallel longitudinally extending tracks on a magnetic tape using a head which is stepped transverse to the direction of tape motion between recording tracks. JP-A-59/104703 discloses a helically scanning video recorder using multiple heads with different azimuth angles. JP-A-59/70230 discloses a helically scanning video recorder in which time compressed information signals are recorded in separate areas divided in the direction of the width of the medium by a guard band. IBM Technical Disclosure Bulletin Volume 15, No 11 discloses a system for recording mutually perpendicular sets of tracks on opposite sides of a magnetic tape. EP-A-197,333, which is prior art to this application by virtue of Art. 54(3) EPC only, discloses an apparatus for recording digital signals on a magnetic tape in tracks approximately parallel to the tape edge. Therefore, it is an object of the present invention to provide a recording and/or reproducing apparatus, which can perform high-density longitudinal recording. Another object of the invention is to provide a longitudinal recording and/or reproducing apparatus which eliminates the requirement for or significantly narrows the width of the guard-band between longitudinal tracks but still successfully avoids cross-talk between adjacent longitudinal tracks. In order to accomplish the aforementioned and other objects, a recording and/or reproducing apparatus, according to the present invention, employs an azimuth-pair-head in a rotary head drum. The rotary head drum is axially shifted by a head shifting means. First tracks are formed on a magnetic tape during forward driving of the magnetic tape across the rotary head drum. On the other hand, second tracks are formed adjacent to the first tracks during reverse driving across the rotary head drum. Since the first and second tracks are formed by means of the azimuth-pair-head, azimuth gaps thereof will have different or symmetrical obliquity to each other. This successfully avoids cross-talk between adjacent tracks to allow formation of the first and second tracks in a tightly arranged fashion. As a consequence, high-density longitudinal recording without cross-talk between adjacent tracks becomes possible. According to the present invention, there is provided a parallel scanning tape recording and/or reproducing apparatus for a magnetic tape, characterised in that it comprises: a rotary head drum carrying first and second magnetic heads, said first magnetic head being formed with a first gap and said second magnetic head being formed with a second gap with an azimuth angle different from that of said first gap, said first and second magnetic heads are associated so as to form a block of two heads constituting an azimuth-pair-head and being cooperative in forming a portion of a single longitudinally extending track on a magnetic tape in one cycle of a recording operation, said track portion having a first section formed by means of said first magnetic head and having a first azimuth pattern and a second section formed by means of said second magnetic head and having a second azimuth pattern which is different from said first azimuth pattern of said first section; means for guiding said magnetic tape onto said rotary head drum for recording and reproduction, said guiding means, in use, wrapping said magnetic tape on the periphery of said rotary head drum so that the longitudinal axis of said magnetic tape lies perpendicular to the axis of rotation of said rotary head drum and that said magnetic tape mates with the periphery of said rotary head drum over a predetermined angular range around the axis of the head; means, cooperating with said pair of magnetic heads for shifting said pair of magnetic heads relative to the tape in a direction parallel to said axis of rotation of said rotary head drum for switching tracks scanned by said pair of magnetic heads and adjusting means which, when said apparatus performs recording and reproducing both in forward and reverse driving of said magnetic tape, increases a scanning angular range over which said pair of magnetic heads scan the magnetic tape when the driving direction of said tape coincides with the direction of rotation of said rotary head drawn and decreases said scanning angular range when said driving direction and said direction of rotation do not coincide to form longitudinal tracks of equal longitudinal length both in forward and reverse recording and reproducing. The shifting means shifts the azimuth-pair-head in a first direction to form a first group of longitudinal tracks and in a second direction opposite to the first direction to form a second group of longitudinal tracks, each of the longitudinal tracks of the first group being formed in spaced apart relationship to the other for leaving a given clearance therebetween, and each of the longitudinal tracks of the second group being formed in the clearances between the longitudinal tracks of the first group. Each of the longitudinal tracks of the first group has the first section opposing the second section of adjacent longitudinal tracks of the second group. In one embodiment, the shifting means is operative in synchronizm with rotation of the rotary head drum for shifting the azimuth-pair-head to next track after eacn scanning cycle. The shifting means is operative to shift the azimuth-pair-head during a period in which the azimuth-pair-head is out of the predetermined angular range. The given clearance between the longitudinal tracks of the first group corresponds the lateral width of the longitaudinal track of the second group to be formed therein. The parallel scanning tape recording and/or reproducing apparatus performs recording and reproducing both in forward and reverse driving of the magnetic tape, and a scanning angular range over which the azimuth-pair-head scans the magnetic tape, is so adjusted as to form longitudinal tracks of equal longitudinal length both in forward recording and reverse recording. In this case, the magnetic tape may be separated into first and second halves by the longitudinal axis thereof, the first half being scanned by the azimuth-pair-head for recording or reproduction while the magnetic tape is driven in forward direction and the second half being scanned by the azimuth-pair-head while the magnetic tape is driven in reverse direction. The track pattern formed in the first half is symmetric to that formed in second half. In the alternative embodiment, the parallel scanning recording and/or reproducing apparatus further comprises auxiliary rotary head drum with an azimuth-pair-head, said auxiliary rotary head drum being designed and arranged for recording and reproducing on the back side of the magnetic tape. The tape guiding means is designed for guiding the magnetic tape onto both of rotary head drums for sequential operation of the rotary head drums. In another alternative, the rotary head drum is provided with first and second azimuth-pair-heads which are associated with the shifting means to be axially shifted in synchronism with each other. The shifting means comprises a linear motor and movement driven by the linear motor in parallel to the rotation axis of the rotary head drum, the movement carrying the first and second azimuth-pair-heads for simultaneously shifting both heads in axial directions for switching scanning tracks. According to another aspect of the invention, there is provided a parallel scanning tape recording and/or reproducing apparatus for magnetic tape, characterised in that it comprises a rotary head drum carrying an azimuth-pair-head having first and second head portions having differing azimuth angles and means for guiding said tape around part of the periphery said rotary head drum, for recording and reproduction of a signal, such that the longitudinal axis of said magnetic tape is perpendicular to the rotation axis of said rotary head drum, the arrangement being such that in use during rotation of said head a first group of longitudinal track portions are decoded with lateral clearances therebetween and thereafter a second group of longitudinal track portions are recorded in said clearances. Preferably, the appratus includes means, cooperative with said azimuth-pair-head, for shifting the latter in a direction parallel to said rotation axis of said rotary head drum, said shifting means shifting said azimuth-pair-head relative to the tape in a first axial direction for forming said first group of longitudinal track portions which are separated from each other by a predetermined clearance left therebetween, and in the opposite axial direction for forming said second group of longitudinal track portions in said clearances between adjacent first tracks. The shifting means intermittently shifts the azimuth-pair-head relative to the tape for switching scanning tracks in synchronism with rotation of the rotary head drum. Preferably, the intermittent shift of the azimuth-pair-head is caused in the first axial direction up to reaching a first end track and subsequently reversing shifting direction to shift the azimuth-pair-head in a second axial direction up to reaching a second end track. According to a further aspect of the invention, there is provided a method of recording and/or reproducing information on a plurality of tracks formed on a magnetic tape and extending parallel to the longitudinal axis of said magnetic tape using an apparatus according to any one of the preceding claims, comprising the steps of: guiding said magnetic tape on said rotary head drum in such a manner that said magnetic tape runs in parallel to the direction of motion of said azimuth-pair-head and is wrapped onto the periphery of said rotary head drum over a predetermined angular range, around the axis of the head; and shifting said azimuth-pair-head from one track to another track every cycle of rotation of said rotary head drum, the magnitude of the shift of said azimuth-pair-head in every shifting operation substantially corresponding to twice the axial width of a single track thereby to scan alternate tracks across the width of the tape driving said tape recording medium along a tape path in both forward and reverse directions; and increasing a scanning angular range over which said heads scan said tape when the driving direction of said tape coincides with the direction of rotation of said azimuth-pair-head and decreasing said scanning angular range when said driving and rotation directions do not coincide whereby the longitudinal length of each of said tracks formed by said heads per rotation of said rotary head drum is equal in both forward recording and reverse recording. In the method as set forth above, shifting is caused in the first axial direction and second axial direction opposite to the first axial direction, and in shifting in the first axial direction, the azimuth-pair-head scans the first group of track portions and in shifting in second axial direction, the azimuth-pair-head scans a second group of track portions located between the first group of track portions. In this case, adjacent first and second tracks are formed by means of the azimuth-pair-head in such a manner that the sections of tracks opposing to each other have different azimuth pattern. The method may further comprises steps of providing auxiliary rotary head drum with an azimuth-pair head and guiding the magnetic tape onto the auxiliary rotary head drum for scanning tracks on the back side of the magnetic tape. The method as set forth above may also comprise a step of reversing tape driving direction between forward and reverse directions. In the alternative, the method as set forth above may further comprise a step of reversing tape driving direction between forward and reverse directions, and a first group of the first and second tracks are formed in a first half of the magnetic tape during forward driving, a second group of first and second tracks are formed in a second half of the magnetic tape during tape driving in the reverse direction. The present invention will be understood more fully from the detailed description given herebelow and from the accompanying drawings of the preferred embodiment of the invention, which, however, should not be taken to limit the invention to the specific embodiments but are for explanation and understanding only. In the drawings: Fig. 1 is a diagramatic illustration of the preferred embodiment of a longitudinal recording and/or reproducing apparatus with a dual-drum arrangement, according to the present invention; Fig. 2 is a diagramatic illustration of the preferred embodiment of a longitudinal recording and/or reproducing apparatus with a single-drum arrangement, according to the present invention; Fig. 3 is a cross-section of a rotary head drum to be employed in he preferred embodiments of the longitudinal recording and/or reproducing apparatus of Figs. 1 and 2; Fig. 4 is a front elevation of an azimuth-pair-head to be employed in the preferred embodiment of the longitudinal recording and/or reproducing apparatus; Fig. 5 is a section taken along line IV - IV of Fig. 3; Fig. 6 is a block diagram of a converter circuit employed in the preferred embodiment of the longitudinal recording and/or reproducing apparatus; Fig. 7 is a block diagram of a recording circuit in the preferred embodiment of the longitudinal recording and/or reproducing apparatus; Fig. 8 is a block diagram of a reproducing circuit in the preferred embodiment of the longitudinal recording and/or reproducing apparatus; Fig. 9 is an illustration showing one example of longitudinal recording track pattern to be formed on a magnetic tape; Fig. 10 is an illustration showing another example of longitudinal recording track pattern to be formed on the magnetic tape; Figs. 11(A) and 11(B) show a graph showing relationship between the magnetic tape and a magnetic head positions in sequential tape feed; Figs. 12(A) and 12(B) show a graph showing relationship between the signal and tape head position, in intermittent tape feed; Figs. 13(A), 13(B), 13(C) and 13(D) show relationship between signals to be recorded by means of first and second heads respectively, and head positions of the first and second heads, in intermittent tape feed; and Figs. 14 to 19 respectively show head positions at tape start and tape stop in forward and reverse modes, and still start and stop. Referring now to the drawings, particularly to Figs. 1 and 2, there are diagramatically illustrated the preferred embodiments of a longitudinal recording and/or reproducing apparatus according to the present invention. The shown embodiment of the longitudinal recording and/or reproducing apparatus is employed in a VTR. A VTR tape cassette 11 containing a VTR tape 10 is used for longitudinal recording. The VTR tape cassette 11 has a supply reel 12 and take-up reel 13. The VTR tape is wound around the supply reel 12 and the take-up reel 13 at each end. When this VTR tape cassette 11 is loaded on the preferred embodiment of the longitudinal recording and/or reproducing apparatus, the VTR tape 10 is wrapped around the first and second head drums 15 and 16. For loading the VTR tape 10 onto the first and second head drums 15 and 16, and for defining the tape path, tape guides 17, 18, 19, 20 and 21 are provided. Adjacent to the tape path, tension levers 25 and 26 also are provided. The tension levers 25 and 26 are biased by means of coil springs 23 and 24 so as to provide tension for the VTR tape 10. The tension levers 25 and 26 are pivotable at one end and carry tape guides 27 and 28 at the other ends. Therefore, the tape guides 27 and 28 bias the tape for adjusting tension on the tape constant. In the vicinity of the tape path between the first and second head drums 15 and 16, capstans 29 and pinch roller 30 are provided for feeding the VTR tape. In this arrangement, the second head drum 16 mates with the front surface of the VTR tape 10 for recording or reproducing the video signal on the peripheral surface. On the other hand, the first head drum 15 mates the back side of the VTR tape 10 for performing recording and reproducing of the video signal on the back side. It should be appreciated that, when back side recording is unnecessary, single head drum can be used as shown in Fig. 2. In this case, the head drum 15 and the tape guide 17 can be omitted. Fig. 3 shows the detailed contruction of the rotary head drum 16 suitable to be employed in the preferred embodiments of the longitudinal recording and/or reproducing apparatus of Figs. 1 and 2, the construction of which is also suitable for the rotary head drum 15. The head drum 16 is sandwiched between flange guides 31 and 32. The flange guides 31 and 32 define the tape run path adjacent the rotary head drum 16. The rotary head drum 16 has an inner cylindrical section 16a fixedly mounted at the top of a hollow cylindrical rotary shaft 33. The rotary shaft 33 serves as an output shaft of a motor 34. The motor 34 has a motor housing 35. A boss 35a with a bearing 35b is formed at the bottom of the motor housing 35 in order to rotatably receive the rotary shaft 33. The motor housing 35 houses a stator coil 36 and a rotor magnet 37 in coaxial relationship to each other. The rotor magnet 37 is fixed to the rotary shaft 33 so as to rotate therewith. Therefore, the rotary shaft 33 is rotatingly driven by means of the motor 34 in order to rotate the rotary head drum 16. The rotary head drum 16 defines an annular groove 16b. A linear motor 38 is housed within the annular groove 16b. The linear motor 38 is fixedly mounted on the rotary head drum 16 by means of a mounting bracket 38a which is fixed to the bottom of the rotary head drum. The linear motor 38 comprises a a electromagnetic coil 39a and a stator core 39b. A movement 40 is also disposed within the annular groove 16b adjacent the linear motor 38. The movement 40 is coupled to the linear motor 38 so as to be driven by the latter to move with respect to the stator core. The movement 40 is mounted on a guide 40a which extends in parallel to the rotation axis of the rotary head drum 16. Therefore, the movement 40 is guided by the guide 40a to cause thrusting movement in the axial direction. A head support bracket 40b is fixedly mounted on the movement 40. The head support bracket 40b has a pair of radially extending legs 40c and 40d. A pair of magnetic heads 41 and 42 are mounted on the leg 40c and another pair of magnetic heads 43 and 44 are mounted on the leg 40d. Pairs of magnetic heads 41, 42 and 43 44 respectively forms azimuth-pair-heads. These two azimuth-pair-heads are axially aligned with each other. As shown in Fig. 4, the magnetic heads 41 and 42 forming one azimuth-pair-head have azimuth gaps 41a and 42a of mutually different azimuth angles. Similarly, the magnetic heads 43 and 44 form azimuth-pair-head of substantially identical construction as that of the azimuth-pair head formed by the magnetic heads 41 and 42. A pair of upper and lower circuit boards 45 and 46 are also disposed within the annular groove 16b. The upper circuit board 45 is connected to the magnetic heads 41, 42, 43 and 44 and contains serial-to-parallel converter circuit. On the other hand, the lower circuit board 46 contains a drive circuit for the aforementioned linear motor 38. A photo-coupling 47 formed of a light-conductive material, is inserted through the axially extending hollow space of the rotary shaft 33. This photo-coupling 47 is designed for transmitting video signal data therethrough. The photo-coupling 47 opposes prisms 48 and 49 at both ends thereof. A light emitting element 50 and a light sensing element 51 are provided in the vicinity of the the prism 48. Similarly, a light emitting element 52 and a light sensing element 53 are provided in the vicinity of the the prism 49. The light emitting element 52 and the light sensing element 53 are connected to amplifiers 54 and 55 respectively. Slip rings 56 are provided in the vicinity of the lower end of the rotary shaft 33. The slip rings 56 are connected to a power source to supply electric power to the circuit boards 45, 46, and the linear motor 38. Fig. 6 shows a diagram of the circuit associated with the rotary head drum 16. The light sensing element 51 is connected to a serial-to-parallel converter 60 via a light demodulator 59. The serial-to-parallel converter 60 is connected to the magnetic heads 41, 42, 43 and 44 via amplifiers 61 and recording terminals R of field switches 62. The light sensing element 51, the light demodulator 59, the serial-to-parallel converter 60, the amplifiers 61, and the field switches 62 constitute a recording circuit for recording data, such as a video signal, onto the magnetic tape. On the other hand, the field switches 62 have reproducing terminals P. The reproducing terminals P of the field switches 62 are connected to a parallel-to-serial converter 65 via amplifiers 63. The parallel-to-serial converter 64 is connected to a light emitting element 50 via a light modulator 65. The reproducing terminals P of the field switches 62, the amplifiers 63, the parallel-to-serial converter 64, the light modulator and the light emitting element 50 constitute a reproducing circuit for reproducing data stored on the magnetic tape. A controller 66 is provided for controlling the positions of the field switches 62, the serial-to-parallel converter 60, the parallel-to-serial converter 64 and the linear motor 38. Fig. 7 diagramatically and explanatorily illustrates a recording circuit in the preferred embodiment of the recording and/or reproducing apparatus. The serial-to-parallel converter 60 is connected to a data input terminal 67, such as a video input terminal, via a low-pass filter 68 and an analog-to-digital (A/D) converter 69. The outputs of the serial-to-parallel converter 60 are connected to error correction code (ECC) encoders 70. Each of the ECC encoders 70 is connected to a pair of field memories 71 and 72 via a switch 73. The field memories 71 and 72 are, in turn, connected to a modulator 75 via a switch 74. The modulator 75 is connected to its corresponding magnetic head 41, 2, 43 or 44 via an equalizer 76 and amplifier 61. Each of the field memories 71 and 72 is connected to a clock generator 89 via a selector 90. In the shown embodiment, the clock generator 89 generates different frequencies of clock signals. The selector 90 selects one of the clock signals to supply the field memories 71 and 72. The data is written in and read from the field memories 71 an 72 based on the clock signal supplied from the selector 90. Fig. 8 explanatorily depicts a reproducing circuit in the preferred embodiment of the recording and/or reproducing circuit according to the invention. Each of the magnetic heads 41, 42, 43 and 44 are respectively connected to a pair of field memories 80 and 81 via associated amplifier 63, equalizer 78, demodulator 79, error correction code (ECC) demodulator 80 and switch 83. The switch 83 selectively connects the associated magnetic head 41, 42, 43 or 44 to one of the field memories 81 or 82 for writing data read from the associated magnetic head in selected one of the field memories 81 an 82. The outputs of the field memories 81 an 82 are connected to the parallel-to-serial converter 64. The parallel-to serial converter 64 is, in turn, connected to a data output terminal 87, such as a video output terminal, via a digital-to-analog converter 85 and a low-pass filter 86. The field memories 81 and 82 are connected to the clock generator 89 via the selector 90 to be supplied therefrom the clock signal for time base correction in writing in and reading data. Operation of the preferred embodiment of the longitudinal or parallel scanning-type recording and/or reproducing apparatus, according to the present invention, will be described herebelow. The magnetic tape 10 in the magnetic tape cassette 11 is extracted from the cassette and wrapped onto the periphery of the rotary head drums 15 and 16. The magnetic tape 10 is not wrapped on the periphery of the rotary head drums 15 and 16 in helical fashion to lie the tape axis oblique to the rotating direction of the drum, but in parallel fashion to lie the tape axis in parallel to the rotating direction of the drum. As will be seen from Fig. 1, the rotary head drum 16 mates with the front surface of the magnetic tape 10. On the other hand, the rotary head drum 15 mates with the back side of the magnetic tape. Therefore, both sides of the magnetic tape 10 are scanned by means of the rotary head drums 15 and 16. As shown in Figs. 3 and 4, the magnetic heads 41, 42, 43 and 44 are arranged in alignment along the rotary axis of the rotary head drums 15 and 16. These magnetic heads 41, 42, 43 and 44 are fixedly mounted on the movement 40 which is associated with the linear motor 38 as set forth above and by which the magnetic heads 41, 42, 43 and 44 are shifted in the axial direction every scanning cycle. It shall be noted that for the purposes of this document one scanning cycle is the period that the magnetic heads 41-44 are in contact with the tape 10 during one revolution of a rotary head drum 15 or 16. Operation of the linear motor 38 is synchronized with rotation of the rotary head drums 15 and 16. Namely, the linear motor 38 is driven to cause axial shift of the magnetic heads at the time when the magnetic heads 41, 42, 43 and 44 are not in contact with the magnetic tape 10. As will be seen from Fig. 1, the magnetic heads 41, 42, 43 and 44 are not in contact with the magnetic tape 10 in angular position range S (approximately 90°). Therefore, axial shift of the magnetic heads 41, 42, 43 and 44 takes place while the magnetic heads are in this angular range S. As is well known, the rotary head drums 15 and 16 rotate at a speed of 1/60 sec. (16.6 msec.) per cycle. Therefore, the period of time that the magnetic head is within the angular range S is about 4.15 msec. In the preferred embodiment, the linear motor 38 is designed to preform the axial shift of the magnetic heads 41, 42, 43 and 44 in 2 msec. In the shown embodiment, the magnetic heads 43 and 44 forming the lower azimuth-pair-head form tracks No. 1, No. 2, No. 3 and No. 4 in sequence with an axial shift upwards occuring between every scanning cycle. Conversely while shifting downwards, the magnetic heads 43 and 44 form tracks No. 5, No. 6 and No. 7 with an axial shift downwards occuring between every scanning cycle. In summary the magnetic heads 43 and 44 scan the No. 1 track first. After one scanning cycle, the magnetic heads 43 and 44 are shifted to mate with the No. 2 track to scan No. 2 track. Similarly, the magnetic heads 43 and 44 are shifted upwards once every scanning cycle to scan the No. 3 and No. 4 tracks. After reaching the No. 4 track and after one cycle of scanning on the No. 4 track, the magnetic heads 43 and 44 are shifted downwards to mate with the No. 5 track which is formed between the No. 3 and No. 4 tracks. Similarly, between every scanning cycle, the magnetic heads 43 and 44 are shifted downward to scan the No. 6 and No. 7 tracks. Since they are rigidly mounted on the same member as magnetic heads 43 and 44 the magnetic heads 41 and 42 forming the upper azimuth-pair-head are shifted upwardly and downwardly in synchronizm with axial shifting of the lower azimuth-pair-head to scan corresponding No. 1 to No. 7 tracks formed on the upper half of the magnetic tape 10. It should be appreciated that, during every one cycle of scan performed by the magnetic heads 41, 42, 43 and 44, one field data, i.e. one field of video data, is written in or read from the corresponding tracks. As shown in Fig. 9, a high-density track pattern can be formed on the magnetic tape 10 with substantially no guard band between the adjacent tracks. In this case, since each pair of the magnetic heads 41, 42 and 43, 44 respectively have different azimuth angle in relation to each other, the azimuth pattern of the upper half in each track becomes different from that in the lower half of the same track. As a result, the upper half of one track will have different azimuth pattern to that in the adjacent lower half of the upper adjacent track. The herring bone azimuth patterns created in the adjacent tracks successfully eliminate cross-talk between adjacent tracks. By providing differently oriented azimuth patterns in each track, high-density track formation with little or no guard band becomes possible. Relationship between magnetic tape feed and the axial shift of the magnetic heads 41, 42, 43 and 44 are explanatorily illustrated in Fig. 11. In this case, the magnetic tape 10 is fed sequentially at a constant speed. Therefore, the magnetic heads 41, 42, 43 and 44 are released from the magnetic tape 10 at the angular range S of Fig. 1. At this angular range, the axial shift of the magnetic heads is executed to shift the magnetic heads to their corresponding tracks, as set forth above. On the other hand, when the magnetic tape 10 is fed intermittently, the magnetic tape 10 is intermittently stopped while the magnetic heads 41, 42, 43 and 44 mate with the corresponding tracks. Shifting of the magnetic heads in the axial direction thus intermittently occurs while the magnetic heads are in the angular range S in Fig. 1. While the magnetic heads are in the angular range S, the magnetic tape 10 is fed, as shown in Fig. 12. Furthermore, in the dual drum arrangement of Fig. 1, it would be possible to record and reproduce data on both sides of the magnetic tape alternately, as shown in Fig. 13. As will be seen from Fig. 13, in this both side recording or reproduction, the rotary head drums 15 and 16 are activated alternately during each scanning cycle. Axial shifting of the magnetic heads occurs in each rotary head drum 15 and 16 within the interval between the active cycles. Fig. 10 shows the track pattern formed in two directional recording, i.e. forward and revearse direction recording. It should be appreciated that two directional recording is possible in single sided recording or double sided recording. Single sided recording can be performed by the recording and/or reproducing apparatus of Fig. 2. As will be seen from Fig. 2, the single sided recording system will allow simple construction of the recording and/or reproducing apparatus. On the other hand, the double sided recording system will provide greater capacity of recording. For single sided recording, a single side coated magnetic tape can be used. In two directional recording, the tracks No. 1, No. 2, No. 3 and No. 4 are formed in the same manner as that discussed with respect to Fig. 9. However, the tracks No. 1 through No. 7 and No. 8 in the upper half of the magnetic tape 10 are formed symmetrical opposite to the No. 1, No. 2, No. 3 and No. 4 tracks with respect to the longitudinal center axis of the magnetic tape. As will be seen from Fig. 10, the starting points and end points of the No. 8, No. 7, No. 6 and No. 5 tracks are axially opposed to the corresponding positions to that of No. 1, No. 2, No. 3 and No. 4 tracks. This track pattern is essential for providing a high quality of video image without causing disturbance of the recorded or reproduced image. The No. 1 to No. 4 tracks are formed in the forward direction recording or reproduction mode. On the other hand, the No. 5 to No. 8 tracks are formed in the reverse direction recording or reproduction mode. Therefore, in the shown embodiment, the data is recorded in the No. 1, No. 2, No. 3 and No. 4 tracks and reproduced therefrom, while the magnetic tape 10 is fed in forward direction. On the other hand, while the magnetic tape is fed in reverse direction, recording and reproduction is performed with respect to the No. 5, No. 6, No. 7 and No. 8 tracks. As will be appreciated, in this case, the last track, i.e. No. 4 track in the forward recording is formed adjacent the first track, i.e. No. 5 track of the reverse direction recording. As set forth, the start and end points of the No. 4 and No. 5 tracks are longitudinally the same positions. This arrangement is particularly advantageous for providing a time-margin for reversing the tape feeding direction. Furthermore, this arrangement makes a servo control for the capstan easier. The track pattern of Fig. 10 is advantageously employed in the shown embodiment to perform recording and reproduction without causing disruption of the signal when reversing the tape feeding direction. Next, herein below will be discussed the relationship between the tape feeding direction and/or feeding speed, and rotating direction of the rotary head drums 15 and 16. In the shown embodiment, the rotary head drum rotates in the same direction as the tape feed direction in the forward feed. This means, that the tape feeding direction in the reverse feed becomes opposite to the rotating direction of the rotary head drum. In the forward feed of the magnetic tape, the magnetic heads 41, 42, 43 and 44 (only head 41 is shown) on the rotary head drum 16 come into contact with the magnetic tape at the position shown in Fig. 14. The magnetic head 41 maintains contact with the magnetic tape in the angular range of about 270° as shown by the arrow in Fig. 14. The magnetic head 41 separates from the magnetic tape 10 at an angular position 270° shifted from the starting position in Fig. 14. In this case, since the rotating direction of the rotary head drum 16 is same as the tape feeding direction in the forward feed mode, the relative rotation speed of the rotary head drum becomes lower to cause shortening of the track length to scan if scanning ends at 270° of the scanning start point. Therefore, the scanning end position may be angularly shifted at the angle , therefore, the scanning remains to the position angularly advanced at the angle  as shown in Fig. 15. Therefore, the scanning end point has to be advance at the corresponding angle . By advancing the scanning end points at the angle , the track length can be maintained at about 3/4 of the peripheral length (πD) of the rotary head drum. On the other hand, in the reverse direction feed of the magnetic tape, the scanning of the track starts at the head position of Fig. 16. In this case, since the tape feed direction is opposite to rotating direction of the rotary head drum, the relative speed of the rotary head drum with respect to the magnetic tape become higher than the standard speed. Therefore, scanning track length become longer than 3/4 of the peripheral length of the rotary head drum. This requires retarding of the scanning end position at the corresponding angle  from the scanning end position in Fig. 16. Therefore, at the corresponding angle  as shown in Fig. 15 so that the magnetic head 41 can fully can the track of the length of 3/4 of the peripheral length (πD) of the rotary head drum. When the scanning of the track on the magnetic tape is performed in still mode, the magnetic tape is fed intermittently, as set forth with respect to Fig. 12. Therefore, the scanning start position of the magnetic head may not be shifted either in the advancing direction and retarding direction. Therefore, the scanning start position and the scanning end position are never shifted as shown in Figs. 18 and 19. It should be appreciated, when tape feed speed is varied from normal speed to be N-times higher speed than normal speed, the shifting angle can be N in forward feed and -N in reverse feed. Based on this shifting angle  or N, wrapping angle ϑ of the magnetic tape 10 with respect to the periphery of the rotary head drum is determined. The correction angle  for causing angular shift of the scanning start position and the scanning end position can be determined according to the following equation: S = t/n where t is a track length; n is number of tracks formed by single head during one cycle; and s is a step length. In the shown embodiment, the number of tracks to be formed by one magnetic head in one cycle is 7. On the other hand, the track length t can be obtained by: t = (πD - s) x ϑ/360 On the other hand, the step length s can also be illustrated by: s = V/60 In this case, the correction angle  can be illustrated by:  = 360s/πD where V is a tape speed; and D is a diameter of the rotary head drum. Returning to Fig. 9, the signal, e.g. video signal, to be recorded on the track is transmittead through the photo coupling 47 to the rotary head drum 16. The signal is received by the circuit on the circuit board 45 and is converted into parallel data therein. This parallel data is distributed to the magnetic heads 41, 42, 43 and 44. The photo coupling 47 also transmits a control signal for the linear motor 38. The linear motor control signal transmitted through the photo coupling is picked up by the circuit on the circuit board 46. According to the control signal, the circuit board 46 controls operation of the linear motor 38. By the operation of the linear motor 38, the magnetic heads 41, 42, 43 and 44 are axially shifted to scan the tracks. Operation of the circuit on the circuit board 45 will be described herebelow in further detail. As shown in Fig. 7, the outputs of the ECC encoders 70 are written in one of their respectively associated field memories 71 or 72. At this time, the stored data in the other field memory 72 or 71 is read out in a compressed form and applied to the associated magnetic heads 41, 42, 43 and 44 through the modulators 75, equalizers 76 and the amplifiers 61. In this case, a standard clock of the clock generator 89 is selected by the selector 90 and applied to the one of the field memories 71 or 72 into which the output data from the ECC encoder 70 is written through the switches 73. On the other hand, for the other field memory 72 or 71, a clock having higher frequency than that of the standard clock is selected by the selector and applied. The frequency of the higher frequency clock is determined according to the relative speed between the magnetic tape and the magnetic heads. Adjustment of the clock frequency to be applied to the field memory from which data is read out, helps to maintain a constant track length irrespective of variation of the correction angle . On the other hand, in reproduction of the recorded data on the magnetic tape, the magnetic heads 41, 42, 43 and 44 pick-up data on the magnetic tape 10 and feed the field memories 81 and 82 via respectively associated amplifiers 63, the equalizers 78, demodulators 79 and ECC recoders 80 and through the switches 83. The switch 83 selects one of the associated field memories 81 and 82 to write in the data transmitted from the ECC recoder 80. The write-timing for the selected one of the field memories 81 or 82 is determined by the clock applied by the selector 90. Therefore, the clock is selected by the selector so that the output data of the ECC recoder 80 can be written in the selected one of the field memory 81 or 82 within a predetermined period of time. On the other hand, the other field memory 82 or 81 is connected to the parallel-to-serial converter 64 via the switch 84 to read out the stored data. Reading of the stored data in the other field memory 82 or 81 is performed in real time. Therefore, the standard clock is selected by the selector 90 and applied thereto. Therefore, according to the shown embodiment, the magnetic tape can be wrapped parallel to the rotating direction of the rotary head drum. This allows formation of the magnetic tape path in a single plane. Therefore, a simplified tape loading system and tape drive system can be employed for the recording and/or reproducing apparatus. Furthermore, since the tape guides for defining the tape path can be perpendicular to the tape run axis, rotary guides can be employed for smooth feeding of the tape. In addition, since the shown embodiment of the longitudinal recording and/or reproducing apparatus is designed for digital recording, influence in a reproduced video image of variation of bit-rate in recording and reproducing can be successfully avoided to allow high quality reproduced image in forward and reverse mode reproduction and in still mode reproduction. Furthermore, according to the shown embodiment, serial data transmission for the magnetic head can be employed. Additionally, in the serial data transmitted to the magnetic heads, the control signal for the head-shifting linear motor can be superimposed. Furthermore, the longitudinal recording and/or reproducing apparatus, according to the present invention, can be adapted not only for a single drum recording and/or reproducing system but also for a dual drum system. When longitudinal recording system according to the invention is applied in a multi-drum system, both sided recording becomes possible significantly expanding recording capacity of the magnetic tape. In addition, since the present invention allows dual direction recording and reproduction, trick-play becomes possible. Also, by allowing both direction recording and reproduction, access-time for the desired data can be drastically shortened. In the showm embodiment, since the track pattern to be formed on the magnetic tape in dual direction recording is set so that the scanning start positions and scanning end positions of the mutually corresponding tracks will have the same longitudinal position, disruption of the reproduced image upon reversing tape drive direction can be completely avoided. Also, advantages can be achieved by forming tracks by means of azimuth-pair-head consisting of a pair of magnetic heads having different azimuth angles, in that cross-talk between adjacent tracks can be successfully prevented. Furthermore, according to the invention, the first group of tracks are formed during up-shifting of the azimuth-pair-head with track-to-track intervals, each of which corresponds to the width of a track. The second group of tracks are formed during down-shifting of the azimuth-pair-head in the track-to-track intervals left in the first group of tracks. As a result, substntially high-density longitudinal recording becomes possible. This helps to make the size of the magnetic tape cassette compact without degrating recording capacity.

Claims: A parallel scanning tape recording and/or reproducing apparatus for a magnetic tape, characterised in that it comprises: a rotary head drum (16) carrying first and second magnetic heads, (41,42), said first magnetic head (41) being formed with a first gap (41a) and said second magnetic head (42) being formed with a second gap (42a) with an azimuth angle different from that of said first gap (41a), said first and second magnetic heads (41,42) are associated so as to form a block of two heads constituting an azimuth-pair-head and are cooperative in forming a portion of a single longitudinally extending track on a magnetic tape (10) in one cycle of a recording operation, said track portion having a first section formed by means of said first magnetic head (41) and having a first azimuth pattern and a second section formed by means of said second magnetic head (42) and having a second azimuth pattern which is different from said first azimuth pattern of said first section; means for guiding said magnetic tape (10) onto said rotary head drum (16) for recording and reproduction, said guiding means, in use, wrapping said magnetic tape (10) on the periphery of said rotary head drum (16) so that the longitudinal axis of said magnetic tape (10) lies perpendicular to the axis of rotation of said rotary head drum (16) and that said magnetic tape (10) mates with the periphery of said rotary head drum (16) over a predetermined angular range around the axis of the head; means, cooperating with said pair of magnetic heads (41,42) for shifting said pair of magnetic heads (41,42) relative to the tape in a direction parallel to said axis of rotation of said rotary head drum (16) for switching tracks scanned by said pair of magnetic heads (41,42) and adjusting means which, when said apparatus performs recording and reproducing both in forward and reverse driving of said magnetic tape, increases a scanning angular range over which said pair of magnetic heads scan the magnetic tape when the driving direction of said tape coincides with the direction of rotation of said rotary head drawn and decreases said scanning angular range when said driving direction and said direction of rotation do not coincide to form longitudinal tracks of equal longitudinal length both in forward and reverse recording and reproducing. An apparatus according to claim 1, wherein, in use, during rotation of said head a first group of longitudinal track portions are recorded with lateral clearances therebetween and thereafter a second group of longitudinal track portions are recorded in said clearances. An apparatus according to claim 2, wherein said shifting means is arranged to shift said pair of magnetic heads (41,42) in a first direction to form portions of said first group of longitudinal tracks (Nos 1 - 4) and in a second direction opposite to said first direction to form portions of said second group of longitudinal tracks (Nos 5 - 7), each of said longitudinal tracks of said first group (Nos 1 - 4) being formed in spaced apart relationship to the other leaving a given clearance therebetween, and each of said longitudinal tracks of said second group (Nos 5 - 7) being formed in said clearances between said longitudinal tracks of said first group. An apparatus according to claim 3, wherein said shifting means are adapted to shift said azimuth-pair-head relative to the tape in a first axial direction for forming said first group of longitudinal track portions which are separated from each other by a predetermined clearance left therebetween, and in the opposite axial direction for forming said second group of longitudinal track portions in said clearances between adjacent first tracks. An apparatus according to any one of claims 1 to 4, wherein said shifting means intermittently shifts said pair of magnetic heads (41,42) relative to said tape (10) for switching scanning tracks in synchronism with rotation of said rotary head drum (16). An apparatus according to any one of the preceding claims, wherein said shifting means intermittently shifts said pair of magnetic heads (41,42) in said axial first direction up to reaching a first end track No 4 and subsequently reversing shifting direction to shift said pair of magnetic heads (41,42) in axial second direction up to reaching a second end track No 7. An apparatus according to any one of the preceding claims, wherein said longitudinal tracks of one group (Nos 1 - 4) of track portions has a first section opposing a second section of adjacent longitudinal tracks of a second group (Nos 5 - 7) of track portions. An apparatus according to any one of the preceding claims, wherein said shifting means is operative to shift said pair of magnetic heads (41,42) during a period in which said azimuth-pair-head (41,42) is out of said predetermined angular range. An apparatus according to any one of claims 2 to 7, wherein said given clearance between said longitudinal tracks of said first group Nos 1 - 4 corresponds to the lateral width of said longitudinal tracks of said second group Nos 5 - 7 to be formed therein. An apparatus according to claim 10, wherein said tape (10) is separated into first and second halves by the longitudinal axis thereof, said first half being scanned by said pair of magnetic heads (43,44) for recording or reproduction while said tape (10) is driven in forward direction and said second half being scanned by said pair of magnetic heads (41,42) while said tape (10) is driven in reverse direction. An apparatus according to claim 10, wherein track pattern formed in said first half is symmetric to that formed in second half. An apparatus according to any one of the preceding claims which further comprises an auxiliary rotary head drum 15 with a pair of magnetic heads of different azimuth angles, said auxiliary rotary head drum (15) being designed and arranged for recording and reproducing on the back side of said tape (10). An apparatus according to any one of the preceding claims, wherein said tape (10) guiding means is designed for guiding said tape (10) onto both of rotary head drums (15,16) for sequential operation of said rotary head drums (15,16). An apparatus according to any one of the preceding claims, wherein said rotary head drum (16) is provided with first and second pair of magnetic heads with different azimuth angles which are associated with said shifting means to be axially shifted in synchronism with each other. An apparatus according to claim 14, wherein said shifting means comprises a linear motor (38) and movement (40) driven by said linear motor (38) in parallel to the rotation axis of said rotary head drum (16), said movement (40) carrying said first and second pairs of magnetic heads for simultaneously shifting both heads in axial directions for switching scanning tracks. An apparatus according to any one of the preceding claims and operative to record and/or reproduce a video signal. A method of recording and/or reproducing information on a plurality of tracks formed on a magnetic tape (10) and extending parallel to the longitudinal axis of said magnetic tape (10) using an apparatus according to any one of the preceding claims, comprising the steps of: guiding said magnetic tape (10) on said rotary head drum (16) in such a manner that said magnetic tape (10) runs in parallel to the direction of motion of said azimuth-pair-head and is wrapped onto the periphery of said rotary head drum (16) over a predetermined angular range, around the axis of the head; and shifting said azimuth-pair-head from one track to another track every cycle of rotation of said rotary head drum (16), the magnitude of the shift of said azimuth-pair-head in every shifting operation substantially corresponding to twice the axial width of a single track thereby to scan alternate tracks across the width of the tape; driving said tape recording medium along a tape path in both forward and reverse directions; and increasing a scanning angular range over which said heads scan said tape when the driving direction of said tape coincides with the direction of rotation of said azimuth-pair-head and decreasing said scanning angular range when said driving and rotation directions do not coincide whereby the longitudinal length of each of said tracks formed by said heads per rotation of said rotary head drum is equal in both forward recording and reverse recording and reproducing. A method according to claim 17, wherein shifting is caused in first axial direction and second axial direction opposite to said first axial direction, and in shifting in said first axial direction, said pair of magnetic heads scans first tracks and in shifting in second axial direction, said pair of magnetic heads scans second tracks located between said first tracks. A method according to claim 18, wherein adjacent first and second tracks are formed by means of said head assembly in such a manner that the sections of tracks opposing to each other have different azimuth patterns. A method according to any one of claims 17 to 19, which further comprises the step of guiding said magnetic tape (10) onto said auxiliary rotary head drum (15) for scanning tracks on the back of said magnetic tape (10). A method according to any one of claims 17 to 20, which further comprises a step of reversing the tape driving direction between forward and reverse directions. A method according to any one of claims 20 to 22 which further comprises a step of reversing tape driving direction between forward and reverse directions, and a first group of said first and second tracks are formed in a first half of said magnetic tape (10) during forward driving, a second group of first and second tracks are formed in a second half of said magnetic tape (10) during tape driving in said reverse direction. A method according to any one of claims 19 to 24 used for recording and/or reproducing a video signal. A video recording recorded or reproduced by apparatus as set forth in any one of claims 1 to 16 or by a method as set forth in any one of claims 17 to 23.

Inventors: SAITO ETSURO C O SONY CORPORAT, SAITO, ETSURO C/O SONY CORPORATION
Applicants: SONY CORP, SONY CORPORATION
Application year: 1987
Main classification: G11B5
IPC codes: G11B5, G11B15