ROTATABLE HEAD TYPE DIGITAL MAGNETIC RECORDING AND REPRODUCING DEVICE

Abstract: A digital magnetic recording and reproducing device of rotatable magnetic head type comprises a rotary drum, first and second recording and reproducing heads situated at opposite positions on the circumference of the rotary drum with reversed azimuth angles, and a third recording and reproducing head adjacent to the second recording and reproducing head, with an azimuth angle reversed to the azimuth angle of the adjacent first or second head. In the normal reproduction, the first and second heads are used but in the long time reproduction, the second and third heads are used with the same rotation speed of the rotary drum, whereby an equalizer for reproducing the signal can be commonly used for the normal reproduction and long time reproduction.

Description: The present invention relates to a magnetic recording and reproducing device, and more particularly to a magnetic recording and reproducing device for recording and reproducing data signals in different tape feeding speeds respectively. Fig. 1 shows a block diagram of a conventional magnetic recording and reproducing device. Analogue signals to be recorded which are entered from an input terminal 1 are applied to a record signal processing unit 2, wherein the analogue signals are converted into digital signals. The converted digital record signals are added by one or more synchronizing bits and parity bits and converted into an array of digital signals of a predetermined recording format. The converted digital signal array as mentioned above is modulated into high frequency signals having a frequency appropriate for recording on a magnetic tape 4 such as a frequency f₀ for a logic "0" bit and a frequency f₁ for a logic "1" bit, subsequently, the modulated high frequency signals are entered in amplifiers 5a and 5b. The modulated signals entered in the amplifiers 5a and 5b are amplified in current and the outputs thereof are respectively applied to coils A1 and B1 which are provided in a fixed drum SD. Coils A2 and B2 which are provided in a rotary drum RD are magnetically coupled to the coils A1 and B1 respectively so as to constitute rotary transformers. The output signals of the amplifiers 5a and 5b which are frequency modulated are transmitted to the coils A2 and B2 through the coils A1 and B1 by induction and are recorded on the magnetic tape 4 through magnetic heads A and B respectively. The magnetic heads A and B are disposed on the rotary drum RD so as to oppose each other with an angle of 180° as shown in Fig. 2. When the magnetic head A or B traces a track of the magnetic tape 4 in order to detect a signal, if one of the magnetic heads A and B comes to contact with an adjacent track, there occurs a cross talk with the adjacent track, resulting in that there occurs a noise in the reproduced signals. Therefore, the magnetic heads A and B are attached to the drum RD with different azimuth angles in order to reduce the cross talk. For example, the magnetic head A is attached to the rotary drum RD with an azimuth angle of plus 20° and the magnetic head B is attached to the rotary drum RD with a reversed azimuth angle of minus 20°. Herein "azimuth angle" means an inclination angle between a line perpendicular to the track and a head gap. The azimuth angle is defined in order to reduce the cross talk between two adjacent tracks. As shown in Fig. 2, the magnetic tape 4 is wound on the circumference surface of the rotary drum RD along about 90° and the feeding direction of the magnetic tape 4 is coincident with the rotating direction of the rotary drum RD. Fig. 3 shows a track pattern recorded on the magnetic tape 4, wherein tracks a₁, a₂, ..., a₅, ... (represented as a hereinafter) are the tracks recorded by the magnetic head A and tracks b₁, b₂, ..., b₄, ... (represented as b hereinafter) are the tracks recorded by the magnetic head B. The signals recorded in the track patterns a and b as shown in Fig. 3 are reproduced through the magnetic heads A and B provided on the rotary drum RD. When the head gap of the magnetic head A traces on the track a₁ e.g. shown in Fig. 3, the magnetic lines of force of the head gap of the magnetic head A are varied in response to the record signals. The variation of the magnetic lines of force thereof is transmitted to the coil A1 provided in the fixed drum SD, wherein the coil A1 is magnetically coupled with the coil A2 provided in the rotary drum RD, thereby varying the induced voltage in the coil A1. Also, the recorded signals on the track b1 are similarly transmitted to the coil B1 as the induced voltage variation. The reproduced signals output from the coils A1 and B1 are respectively applied to amplifiers 6a and 6b through a signal selecting switch 7. The reproduced signals are not continuous signals but intermittent signals generated from the coils A1 and B1 every time during which the magnetic heads A or B trace any one of the tracks on the magnetic tape 4 as shown in Fig. 2. Accordingly, one of the amplifier 6a or 6b is selected by switching the signal selecting switch 7 in response to a switching signal sent from a reproduction signal processing unit 10 so as to transmit the reproduced signal from the magnetic head A or B which is now tracing the track and reproducing the signal. Both of the reproduced signals sent from the coils A1 and B1 are applied to equalizers 8a and 8b. The equalizer 8a is selected when the rotation number of the rotary drum RD is e.g. 2000 r.p.m., and the equalizer 8b is selected when the rotation number of the rotary drum RD is e.g. 1000 r.p.m.. An equalizer selection switch 9 is switched in response to a recording time selection signal which is entered from an input terminal 3. If the rotation number of the rotary drum RD is different, the property of the magnetic head is different depending on the frequency of the reproduced signal. Therefore, any one of the equalizers 8a and 8b is selected corresponding to the rotation number of the rotary drum RD so as to recover the frequency property and the phase property of the reproduced signals sent from the coils A1 and B1. Fig. 4 shows timing charts of an input signal of the reproduction signal processing unit 10, wherein Fig. 4(1) is a timing chart in a period when the rotation number of the rotary drum RD is 2,000 r.p.m. and the feeding speed of the magnetic tape 4 is 8.15 mm/sec., at a normal recording and reproducing operation, and Fig. 4(2) is a timing chart in a period when the rotation number of the rotary drum RD is 1,000 r.p.m., and the feeding speed of the magnetic tape 4 is 4.075 mm/sec., at a long time recording and reproducing operation. In Fig. 4(1), the time a₁ represents the time for reproducing the signal recorded on the track a₁ sent through the magnetic head A, and also the time b₁ represents the time for reproducing the signal recorded on the track b₁ sent through the magnetic head B. In Fig. 4(2), since the feeding speed of the magnetic tape 4 is half of the tape feeding speed of the case shown in Fig. 4(1), it takes twice of the recording or reproducing time in the case shown in Fig. 4(1) for recording and reproducing the signal through each of the heads. The reproduction signal processing unit 10 demodulates the output signals of the equalizer 8a or 8b selected by the equalizer selection switch 9 to the digital signal array so as to obtain digital signals synchronized with the synchronizing bit. After errors of the digital signals are corrected with reference to the parity bit, there are obtained digital reproduced signals. The obtained digital reproduced signals are converted to analogue signals, whereby the reproduced analogue signals are output from the output terminal 11. In the conventional digital magnetic recording device as described above, since the rotation speed of the rotary drum RD is different between the normal recording and reproducing operation and the long time recording and reproducing operation, it is necessary to provide two sets of the reproduction equalizer unit, therefore there has been a problem that the size of the magnetic recording and reproducing device becomes large. US-A-4 466 026 describes a magnetic recording and reproducing device comprising two normal reproducing heads with different azimuth angles, and a special reproducing head positioned adjacent to one of the normal heads. The heads are fixed to a rotary drum and the signals of the heads are supplied to a static circuit section having a change-over means for alternately switching the signal from the special reproducing head and the signal from the remote normal reproducing head. The signal delivered by the change-over means is fed to a feedback type amplifier. There are two feedback-type amplifiers, one for the first normal reproducing head and one for both, the second normal reproducing head and the special reproducing head. During one reproducing mode, both normal reproducing heads are used and, during the other reproducing mode, the first normal reproducing head is used in combination with the special reproducing head that is positioned adjacent the second normal reproducing head. It is an object of the present invention to provide a magnetic tape recording and reproducing device having a simpler circuit arrangement and assuring a uniform property of the output signal for both, the normal recording and reproducing operation and the longtime recording and reproducing operation. The magnetic tape recording and reproducing device of the invention is defined by claim 1. The recording and reproducing device of the invention is operable in both, the normal and longtime recording/reproducing operations with one equalizer only for equalizing the output signals of the magnetic heads. Fig. 1 is a block diagram showing a conventional magnetic recording and reproducing device, Fig. 2 is a schematic diagram for explaining a position of magnetic heads in Fig. 1, Fig. 3 is a schematic diagram for explaining a track pattern recorded on a magnetic tape in Fig. 1, Fig. 4 is a timing chart showing input signals of a reproduction signal processing unit in Fig. 1, Fig. 5 is a block diagram showing an embodiment of a magnetic recording and reproducing device according to the present invention, Fig. 6 is a schematic diagram for explaining positions of magnetic heads according to the present invention, Fig. 7 is a schematic diagram for explaining a track pattern recorded on a magic tape according to the present invention, and Fig. 8 is a timing chart showing input signals of a reproduction signal processing unit according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of a magnetic recording and reproducing device according to the present invention will be explained with reference to Figs. 5 to 8. In Fig. 5, analogue signals to be recorded entered from an input terminal 31 are applied to a record signal processing unit 32. The analogue signals applied to the record signal processing unit 32 are converted into a digital form in the record signal processing unit 32. The converted digital recording signals are added by one or more synchronising bits and parity bit and are converted into an array of digital signals according to a predetermined recording format. The digital signal array as mentioned above is modulated into high frequency signals having two frequencies appropriate for recording on a magnetic tape 34 with a frequency f₀ for the logic "0" bit of the digital signal array and a frequency f₁ (f₁ f₀) for the logic "1" bit of the digital signal array, subsequently, the modulated high frequency signals are entered in amplifiers 35a and 35b. The modulated signals entered in the amplifiers 35a and 35b are amplified in terms of current. The output signals of the amplifier 35a are applied to any one of coils C1 and D1 of the transformer of the recording heads in accordance with the selection by a switching operation of a head selection switch 42 switched in response to a recording time selection signal sent from an input terminal 33. The output signals of the amplifier 35b are applied to a coil E1. The coils C1, D1 and E1 which are provided in a fixed drum SD1 are magnetically coupled with the coils C2, D2 and E2 respectively to constitute a rotary transformer. The frequency modulated output signals of the amplifiers 35a and 35b are induced in the coils C2 or D2 and E2 through the coils C1 or D1 and E1 and are recorded on the magnetic tape 34 through magnetic heads C, D and E respectively. The magnetic heads C, D and E are provided on the rotary drum RD1 in such a manner that the head gaps face the cylindrical surface of the rotary drum RD1 in a known manner, wherein the heads C and E are disposed at opposite positions with an angle of 180° and the magnetic head D is provided at the position adjacent to the the magnetic head E as shown in Fig. 6. The magnetic heads C and E are attached to the drum RD1 with different azimuth angles in order to prevent occurrence of a noise due to a cross talk. For example, the magnetic head C is attached to the rotary drum RD1 with an azimuth angle of plus 20° and the magnetic head E is attached to the rotary drum RD1 with a reversed azimuth angle of minus 20°. Also, the magnetic head D is attached to the rotary drum RD1 with an azimuth angle of plus 20° e.g. different from that of the magnetic head E. Herein the azimuth angles are defined in order to reduce noise due to a cross talk with an adjacent track. The magnetic head C is selected by switching a head selection switch 42 in the case of the normal recording and reproducing operation and the magnetic head D is selected in the case of the long time recording and reproducing operation. The rotation number of the rotary drum RD1 is regulated to be constant 2,000 r.p.m. in both of the normal recording and reproducing operation and the long time recording and reproducing operation and only the tape feeding speed in both of the operations is different. For example, the tape feeding speed in the long time recording and reproducing operation is half of the tape speed in the normal recording and reproducing operation. As shown in Fig. 6, the magnetic tape 34 is wound on the cylindrical surface of the rotary drum RD1 over an angle about 90° and the feeding direction of the magnetic tape 34 is coincident with the rotating direction of the rotary drum RD1. Fig. 7 shows a track pattern recorded on the magnetic tape 34 in the case where the recording and reproducing head C or D is selected by switching the head selection switch 42, wherein tracks a₁, a₂, ..., a₅, ... are the tracks recorded by the magnetic head C or D and tracks b₁, b₂, ..., b₄, ... are the tracks recorded by the magnetic head E. The signals recorded in the track pattern as shown in Fig. 7 are also reproduced through the magnetic heads C or D and E provided on the rotary drum RD1. The signals reproduced through the magnetic heads C or D and E are respectively applied to amplifiers 36a and 36b. The reproduced signals are not continuous signals but intermittent signals generated from the coils C1 and E1 during the period of tracing the tracks on the magnetic tape 34 with the magnetic heads C or D and E as shown in Fig. 6. Accordingly, the amplifier 36a or 36b, which is now generating the reproduced signals, is selected by switching the signal selecting switch 37 which is operated by a switching signal sent from a reproduction signal processing unit 40, so that the output signals of the amplifier 36a or 36b are applied to an equalizer 38. The equalizer 38 is provided in order to compensate the frequency property and phase property of the magnetic head and the output signals of the equalizer 38 are applied to the reproduction signal processing unit 40. Since the rotation number of the rotary drum RD1 is the same in both of the normal recording and reproducing operation through the magnetic heads C and E and the long time recording and reproducing operation through the magnetic heads D and E, the frequency property and the phase property of the magnetic heads can be compensated by providing only one equalizer 38. Fig. 8 shows a timing chart of input signals of the reproduction signal processing unit 40. Fig. 8(1) is a timing chart at the time of normal recording and reproducing operation, and Fig. 8(2) is a timing chart at the time of long time recording and reproducing operation. In Fig. 8(1), the time a₁ represents the time period for reproducing the signal sent from the magnetic head C and also the time b₁ represents the time for reproducing the signal sent from the magnetic head E. In Fig. 8(2), the time a₁ also represents the time for reproducing the signal sent from the magnetic head D and the time b₁ represents the time for reproducing the signal sent from the magnetic head E. Since the magnetic heads D and E are provided in the adjacent positions on the rotary drum RD1, the magnetic head can be switched every one rotation of the rotary drum RD1. The reproduction signal processing unit 40 demodulates from the output signals of the equalizer 38 to the digital signal array so as to obtain digital signals on the basis of the synchronizing bit. With respect to the obtained digital signals, errors of the digital signals are corrected with reference to the parity bit so as to obtain digital reproduction signals. The obtained digital reproduction signals are converted into the analogue form, whereby reproduction signals of analogue form are output from the output terminal 41. In the present embodiment, when the normal time recording/reproducing operation is set, the magnetic heads C and E are used with 2,000 r.p.m. of the rotation speed of the rotary head RD1. On the other hand, when the long time recording/reproducing operation is set, the magnetic heads D and E are used with the same rotation speed 2,000 r.p.m. of the rotary head RD1. By changing the magnetic heads for the normal recording/reproducing operation and long time recording/reproducing operation, it becomes possible to use the same rotation speed of the rotary head RD1 for the normal recording/reproducing operation and the long time recording/reproducing operation. Thus, in the magnetic recording and reproducing device as described above, only one equalizer can be used in common for both of the normal recording and reproducing operation and the long time recording and reproducing operation, there is an advantage that the number of the circuit elements can be reduced and the production process thereof can be simplified. As described above, according to the present invention, there is provided a third magnetic head on the rotary drum, whereby the recording and reproducing operations can be performed at the same rotation speed of the rotary drum for both of the normal recording and reproducing operation and long time recording and reproducing operation, therefore, the rotation speed of the rotary drum can be easily adjusted. Moreover, the reproduced signals can be equalized by only one equalizer circuit for both of the normal reproducing operation and the long time reproducing operation, therefore, the constitution of the magnetic recording and reproducing device can be simplified.

Claims: A magnetic recording and reproducing device for recording and reproducing signals comprising; equalizer means, a rotary drum (RD1), a first recording and reproducing head (C) having an azimuth angle provided on said rotary drum (RD1), a second recording and reproducing head (D) having an azimuth angle reversed to that of said first head, provided at a position opposite to the first head on the rotary drum in terms of the circumferential direction thereof, a third recording and reproducing head (E) adjacent to said second head (D), having an azimuth angle reversed to that of the adjacent second head, means (37) for selecting an operation mode from a plurality of operation modes including a first mode using said first and second heads (C,D) and a second mode using another combination of two heads, characterized in that said first and second operation modes are performed at the same rotation speed of the rotary drum (RD1), the tape feeding speed in the second operation mode being lower than that in the first operation mode, the combination of heads used in the second operation mode comprises the second head (D) and the third head (E); and the equalizer means comprises only one equalizer (38) to equalize the signals reproduced during the first and second operation modes. A magnetic recording and reproducing device for recording and reproducing signals characterized in that the tape feeding speed in the second operation mode is half as high as the tape feeding speed in the first operation mode.

Inventors: HAIKAWA, YUKIHIKO
Applicants: SHARP KABUSHIKI KAISHA
Application year: 1988
Main classification: G11B5
IPC codes: G11B5, G11B15