JPH0377571B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to tracking control for magnetic recording and reproducing devices, particularly VTRs, and in VTRs that use four types of pilot signals for tracking control and an electro-mechanical conversion element to move the head. This realizes variable speed playback at any playback tape speed. Conventional configuration and its problems Pilot signal for tracking control (hereinafter referred to as
In a VTR that uses a pilot signal (simply referred to as a pilot signal), a magnetic head is mounted on an electro-mechanical transducer such as a piezoelectric element, and in order to perform noiseless playback at a desired tape speed, it is necessary to
A preset waveform (a type of sawtooth waveform) is generated, the magnetic head is displaced according to the waveform, and the type of pilot signal is sequentially switched according to the tape speed. At this time, the tape transport may be controlled using a tracking error signal obtained by processing the signal obtained from the head. This brings the tape transport speed to the desired speed.
This allows the tape and head to be in phase, allowing for noiseless playback. This principle will be explained in more detail below. First, an overview of the four-frequency pilot system will be described. FIG. 1 shows the recorded magnetization locus of the pilot signal. In the figure, A ₁ , B ₁ , A ₂ , . . . are magnetization trajectories recorded by the A head and B head, respectively, and each recording track records one field's worth of video signals. The pilot signals f ₁ to _{f 4} are recorded superimposed on the video signal, and are recorded in order for each field as shown in the figure. Table 1 shows the frequencies of the pilot signals.

[Table] Note that _fH shown in Table 1 is the horizontal synchronization signal frequency. As shown in FIG. 1, the frequency difference in the pilot signals between adjacent tracks is f _H and 3f _H. Therefore,
By extracting these frequency differences and comparing their levels, a tracking error signal corresponding to the track deviation can be obtained. FIG. 2 is a circuit block diagram for obtaining a tracking error signal. In the same figure, a reproduced RF signal is supplied from terminal 1, and low-pass filter 2
Only the pilot signal is extracted. Circuit 3 is a balanced modulation circuit (hereinafter referred to as BM circuit), which outputs a difference signal between the input pilot signal and the reference signal supplied from terminal 4. For example, the pilot signal that is reproduced when the head reproduces and scans _A2 shown in Figure 1 is a composite signal of _f3 that is reproduced from the main scanning track, and _f2 and _f4 that are reproduced as a crosstalk signal. be. The reference number at this time is the pilot signal _f3 recorded on the main scanning track. The output of the BM circuit 3 at this time is a signal having a frequency difference between the f ₂ , f ₃ , f ₄ signals and f ₃ and includes the f _H and 3f _H signals.
These difference signals are sent to a tuning circuit 5 which extracts _fH.
3f _H is extracted by the tuning circuit 6 which extracts H, and then the comparator circuit 9 passes through the detection rectifier circuits 7 and 8.
is supplied to Circuit 10 is an analog inverting circuit and circuit 11 is an analog electronic switch.
A head switching signal is inputted from the terminal 12, and the output of the comparator circuit 9 and the inverted output thereof are taken out to the terminal 13 alternately for each field. The reason for this inversion is that the polarities of the tracking error signals extracted from the A head and B head are reversed. Therefore, a tracking error signal whose polarity is not affected by the reproduction head can be taken out from the terminal 13. Next, variable speed playback will be explained. Figure 3 shows the recorded magnetization locus on the magnetic tape,
f ₁ to f ₄ indicate pilot signals. The head scans in the direction of arrow 14 and the tape is transported in the direction of arrow 15. A ₁ , B ₁ , A ₂ , B ₂ , . . . are magnetization trajectories recorded by the A head and the B head. Reference numerals 16 and 17 show the scanning locus of the head when the tape is transported at a speed three times the tape speed during recording, that is, the scanning locus of the head in the triple speed reproduction mode. 18 and 19 are the scanning trajectories of the head in the triple speed playback mode in the reverse direction. In either the forward or reverse direction, the head scans the recording track in ascending order of number. In order to perform variable speed playback without noise,
The head must scan on one of the tracks. For this purpose, it is necessary to displace the head in the width direction of the recording track, and this displacement is usually achieved by mounting the head on an electromechanical transducer such as a piezoelectric element. FIG. 4 shows the voltage waveform supplied to the electromechanical transducer, which is necessary for triple-speed playback in the forward direction. Figure a
is a head switching signal (hereinafter referred to as H.SW signal), and f ₁ , f ₄ , f ₃ , and f ₂ are reference signals necessary for each field. The sawtooth wave shown in FIG. 1B is a voltage waveform applied to the electromechanical transducer, and the vertical axis represents the applied voltage in units of track pitch (indicated by the symbol T _p ). The polarity of the applied voltage is shown as positive polarity in the same direction as the tape transport direction shown by arrow 15 (FIG. 3), and negative polarity in the opposite direction. If the voltage shown in Figure 4b is supplied to the electromechanical transducer, the head scan in the first field will be on track _A5 shown in Figure 3, and the scan in the next field will be on track _B6 as shown in Figure 3. Then, playback scanning will be performed. FIG. 5 shows the reference numbers necessary for the triple speed mode in the reverse direction and the voltage waveforms applied to the electromechanical transducer. If the tape transport is controlled using the tracking error obtained using the above applied waveform and reference signal, the phase of the tape and the head will match, and noiseless reproduction will be realized. Next, this principle will be generalized and explained. First, it is assumed that the applied waveform and reference signal on the track currently being scanned are known. First, let the tape speed during recording be TS _t , the voltage required to displace the head by one track pitch be V _t , the center value of the slope of the applied waveform be V _o , the type of reference pilot signal be RE _o , and the current Tape speed TS _o
Let V _o+1 be the center value of the slope of the applied voltage waveform required for the next head scan, and let the amount of slope of the applied voltage waveform be
Assuming that SL _o+1 is the type of reference pilot signal and RE _o+1 is the type of reference pilot signal, the following relationship exists. V _o+1 /V _t =V _o /V _t +TS _o /TS _t −K …(1) SL _o+1 /V _t =TS _o /TS _t −1 …(2) RE _o+1 =RE _o +K-4m...(3) Here, K and m are integers and satisfy the following conditions. In equation (1), K is an integer that satisfies |V _o+1 /V _t |≦1/2, and m is an integer that satisfies 1≦RE _o+1 ≦4. Therefore, in this way, V _o+1 , SL _o+1 ,
By determining RE _o+1 for each scan and switching the applied voltage generation and reference signal, the head can scan the track at any tape speed, achieving so-called noiseless playback. It becomes possible. This tape speed does not need to be an integral multiple of the recording speed and can be set freely. Also, if you want to change the tape speed, do the following: For example, FIG. 6 shows an example of changing the speed from 1x speed to 2x speed. Instantaneous changes in tape phase velocity are difficult due to the time constants of the tape transport control system. For this reason, a method is adopted in which the speed is gradually changed for each head scan. FIG. 6 shows an example in which the speed is changed in 0.1 times the speed step. That is, the time required for the change is 10 head scanning periods. This is, for example, an NTSC VTR.
In this case, it is approximately 1/6 second, which is considered to be a sufficiently short period. Now, when determining the applied voltage waveform using such a calculation formula, noiseless reproduction is possible, but there are the following problems. That is, in the above equation (1), the value V _o+1 of the center value of the slope portion of the applied voltage waveform is not necessarily zero. For example, even at 1x speed, if V _o is not zero, V _o+1 cannot be made zero.
This corresponds to the head H _i (i=
1, 2, 3...) is not at the center of the tracks A ₁ , B ₁ , A ₂ , B ₂ . . . when no voltage is applied. This is the value V _o , which means that the center of the track is displaced so as to scan.
In other words, a DC component is applied to the electro-mechanical conversion element. In general, applying a DC component for a long time to electromechanical conversion elements such as piezoelectric elements and voice coils not only has a negative effect on the lifespan and performance of the element, but also reduces the energy efficiency of the drive unit. Often. Therefore, application of such a DC component must be avoided. OBJECTS OF THE INVENTION The present invention provides a magnetic recording/reproducing device that can prevent direct current components from being applied to electromechanical conversion elements for a long time using a simple method. Structure of the Invention The present invention records and reproduces information signals onto the magnetic tape as a group of discontinuous recording tracks by winding a magnetic tape diagonally around a cylinder equipped with a rotating magnetic head mounted on an electro-mechanical transducer. ,and,
During recording, four types of pilot signals for tracking control are superimposed on the information signal to be recorded and are sequentially recorded cyclically, and during reproduction, each pilot signal is reproduced from recording tracks that are adjacent to the recording track before and after the recording track to be reproduced. It is configured to obtain a tracking error signal corresponding to the level difference of the crosstalk signals, and uses the signal as a fine adjustment signal for the tape feed control means, and also sets the magnetic tape transfer speed during recording to TS _t and the electric - Let Vt be the voltage required to displace the mechanical transducer by one track pitch, and let the current tape speed be _Vt .
TS _o is the slope amount of the preset voltage waveform applied to the electromechanical conversion element, SL _o is the center value of the slope part of the pulsed waveform, and _{RE o is} the type of reference pilot signal.
The slope of the preset voltage waveform required for the next head scan is SL _o+1 , the center value of the stepped slope is V _o+1 ,
The type of reference pilot signal used for tracking control during playback corresponds to the four types of pilot signals during recording, where RE _o is expressed as an integer from 1 to 4, K and m are V _{o +1.} /V _t =V _o /V _t +TS _o /TS _t −K However |V _o+1 /V _t |≦1/2 SL _o+1 /V _t =TS _o /TS _t −1 RE _o+1 = _{RE o +} K−4m However, _{electricity −}
While driving the mechanical conversion element, j (j≧1)
Check the value of V _{o+1 for} each head scan, and
If _{the value of}
By replacing the value of V _o+1 with the value of δ, it is possible to prevent a DC component from being applied to the electro-mechanical conversion element for a long time. DESCRIPTION OF EMBODIMENTS Next, specific embodiments of the present invention will be described. FIG. 8 is a circuit configuration diagram showing an embodiment of the present invention. In the figure, the element designated by 20 is an electromechanical transducer, and is constructed by bonding piezoelectric elements, for example. Reference numeral 21 denotes a reproducing head mounted on the electromechanical transducer, and although not shown, it rotates together with the rotating cylinder. The signal regenerated by the head 21 is amplified by a regenerative amplifier circuit 22,
The signal is supplied to the video signal processing circuit 23. circuit 23
The output is processed so that it becomes a video signal that can be input to a regular television receiver. On the other hand, the output of the regenerative amplifier circuit 22 is supplied to the BM circuit 25 via a low-pass filter 24. The reference signal output from the reference signal generation circuit 37 is also input to the BM circuit 25 . The circuit 26 is a circuit for extracting a tracking error signal. A circuit 27 surrounded by a broken line and including circuits 25 and 26 performs the signal processing already explained in FIG. By supplying a tracking error signal, which is the output of the circuit 26, to the capstan control circuit 28, the tape feeding phase can be controlled. The tracking error signal is input to the comparison circuit 29 and compared with the error signal of one frame before, which is fed back to one terminal. The output of the circuit 29 is input to a piezo error signal processing circuit 31. circuit 29
Although details of the circuit 31 will be described later, the signal output from the circuit 31 is a tracking error signal corresponding to a DC component of track deviation or track bending. The circuit 32 is a preset voltage generating circuit and outputs, for example, a sawtooth wave as shown in FIG. The preset voltage changes depending on the reproduction speed, the details of which will be described later. The tracking error signal for the piezo and the preset signal are added together, and then passed through a D/A converter and an electromechanical transducer drive circuit 36, so that the electromechanical signal is transferred so that the head 21 on-tracks and reproduces the main scanning track. The conversion element 20 is driven. Next, a specific configuration example of the circuit 31 will be explained. FIG. 9 shows a block diagram related to the circuit 31, and a circuit block 38 surrounded by a broken line corresponds to the circuit 31. The circuit 40 is a level comparison circuit, and is the same circuit as the comparison circuit 29 shown in FIG. The level of the tracking error signal inputted from the terminal 39 is compared with the tracking error signal of one frame before. The circuit 41 is a circuit for slightly modifying the content of the tracking error signal of one frame before by +1 or -1 according to the output of the circuit 40. The corrected error signal is delayed by one frame in delay circuits 42 and 43, and then the data is fed back to minute correction circuit 41. The circuit 43 corrects the delay time of the control circuit required until a signal is obtained at the terminal 39 as a tracking error signal after outputting the signal delayed by (1 frame time) - (ΔT) from the circuit 42. This is a delay circuit for The output of circuit 43 is D/A
The signal is supplied to a comparator circuit 40 via a converter 44 .
The output of the circuit 42 is added to the output of the preset waveform generation circuit 45, and then sent to the terminal 4 via the D/A converter 46.
7 is output. The above is an example of the specific configuration of the piezo error signal processing circuit 31. Next, processing during variable speed playback will be explained. In FIG. 8, circuit 33 is a speed command circuit. The circuit 33 processes a signal input from, for example, a key operation 38 and outputs a speed command signal. This command signal is supplied to the capstan control circuit 28 to determine the tape feed rate. The signals inputted to the arithmetic processing circuit 34 are the speed command signal, the center value of the preset voltage, and the current reference signal stored in the arithmetic processing circuit.
The signals output as a result of processing these input signals are command signals for determining the slope amount and center value of the preset waveform, and the reference signal necessary for the next scan. This command signal is sent to the reference signal generation circuit 37 in 2 bits.
It is supplied with a signal of f ₁ to f ₄ and commands which signal to generate. Next, the processing contents of the arithmetic processing circuit 34 will be explained. In the following description, the type of reference signal will be simply written as a reference signal. 10 to 12 are flowcharts showing the processing procedure. FIG. 10 shows the procedure for determining the value of the next field (n+1), assuming that the preset waveform in the n-th field is known. It is now assumed that the n field is being scanned with the B head. At this time, the center value BV _o of the preset waveform, the reference signal
Assume that BRE _o is known. Therefore, find the values AV _o+1 and ARE _o+1 of the next field. First, block 48 reads the current tape speed _TSO . This is read from the speed command circuit 33, for example.
Next, the slope SL _o+1 of the preset waveform is determined by block 49.
As shown in , it can be calculated as SL _o+1 = TS _o -1.
Note that the unit used here is the track pitch equivalent voltage. For example, during normal playback, TS _o = 1
(track pitch), the slope SL _o+1 is zero, the slope SL _o+1 is 2 during triple speed playback, and -4 during reverse triple speed playback. Of course, the tape speed TS _o is not limited to an integer, and may be any real number. After 1 field, i.e. (n+1)
The center voltage AV _o+1 of the preset waveform in the th field can be considered to be the sum of the center voltage BV _o of the n field plus the tape speed TS _o . That is, since the (n+1) field is scanned by the A head, the tentative value V=BV _o +TS _o is obtained via block 50. At the same time, a temporary reference signal RE=BRE _o is also set. Now, if this value is used as it is, as the field is repeated many times, V will gradually increase in value, so by processing block 52, V will be
Processing is performed to change the reference signal so that it is within 0.5 track pitch. This is the reason why it is called "temporary". The value V processed in this way is the center value of the next field (n+1th) by RE.
Obtain AV _o+1 and reference signal type ARE _o+1 . And slope SL _o+1 is (n+1) field slope ASL _o+1
shall be. This is the processing of block 53. From the center value BV _o in the nth field (assumed to be B head scanning) and the reference signal BRE _o , (n
This is a procedure for determining the center value AV _o+1 and the reference signal ARE _o+1 in the +1)th field (A head scanning). Next, the case where the nth field is A head scanning will be explained. In this case, block 50 indicates that the (n+1)th field is a B head scan, so block 54 indicates that
(AV _o +TS _o ) is entered in the tentative center value V, ARE _o is entered in the tentative reference signal RE, and by the processing of block 55 (exactly the same processing as 52), V is ±0.5.
Change the reference signal so that it is within the track pitch. With the values V and RE processed in this way,
Next field ((n+1)th field,
B head scanning) center value BV _o+1 , reference signal
Get BRE _o+1 . Note that it is possible to determine whether A head scanning or B head scanning is performed by looking at the value of the head switching signal, but it can also be determined by knowing whether the value of n is an odd number or an even number (which is A or B). (Determine first.) The above is (n+1) from the value of the nth field
This is the procedure for finding the value of the th field (center value, slope, reference signal). This procedure may be performed for each field. Next, the "track change" processing shown in blocks 52 and 55 will be explained. FIG. 11 shows the processing contents of the subroutine. In the figure, block 57 is a block for determining whether the tape speed is forward or reverse, and the processing content is branched depending on forward playback and reverse playback. Blocks 58 and 59 are blocks for correcting the preset center voltage so that it does not exceed 0.5 track pitch. If V is 0.5 or more, subtract 1 from V until it becomes 0.5 or less. Also, the reference signal is incremented by 1 each time. Blocks 60 and 61 are blocks for processing so that the number of reference signals does not exceed five. Reference signal f ₁ ~
f ₄ corresponds to RE 1 to 4, so if the RE value is 5 or more, by subtracting 4,
It is processed so that it falls within the value of 4. Reverse playback is also processed using the same concept, and V and RE are obtained. The above is the explanation of the arithmetic processing circuit 34 shown in FIG. In FIG. 8, all circuit blocks 30 surrounded by broken lines are capable of digital signal processing, and can be processed using a microprocessor. The explanation so far has been based on a 2-head helical scan VTR, but 4
VTR using different types of pilot signals, e.g.
Head-type VTR and 4-head type with small diameter cylinder
The present invention is also applicable to VTRs. Now, V _o+1 obtained in this way has 1/2
Since there is a possibility that a DC component below the track pitch remains, the process 67 in FIG. 10, "DC component reduction", is added. The contents of this process are shown in FIG. That is, in FIG. 12, in block 70, it is checked whether it is every j times. That is, if it is every j-th time, the process moves to block 71; otherwise, the process moves to block 74 and ends. Note that j is an integer of 1 or more. Next, in block 71, the value of AV _o+1 or BV _o+1 (represented by V _o+1 here) is determined in FIG.
Check if is zero. If the value of V _o+1 is zero, the process moves to block 74 and the process ends. If the value of V _o+1 is not zero, block 73
Move to. In block 73, a minute value δ is added to V _o+1 obtained in the process shown in FIG. 10 to obtain V _o+1 again.
In other words, V o ₊₁ +δ is used instead of V o ₊₁ . This ends the process. By adding the process shown in FIG. 12, the value of V _o+1 becomes zero in a finite time. This process also results in modulation of the tape transport,
This means that the head and tape transport are synchronized. That is, in FIG. 13, the head H _o
Suppose that scans track n. At this time, the center of the head and the center of the track are offset by an amount corresponding to V _o . For this reason, a voltage V _o is applied and V _o
The head is displaced by an amount corresponding to . The same holds true for track n+1 and head H _o+1 . V _o+1 corresponds to the displacement of head H _o+1 .
At this time, the processing in Figure 12 is performed instead of V _o+1.
This corresponds to switching to a head displacement amount of V _o+1 +δ. At this time, the head position after applying the voltage is shifted by δ from the track center, as shown by H'o ₊₁ . Therefore, the tracking error signal obtained at this time is shifted by an amount corresponding to δ. The tracking error signal is sent to the capstan control circuit as shown in FIG. 8, and the tape feed is controlled, so the tape feed speed changes by an amount corresponding to δ, and finally,
The head scanning center is controlled so that the track center coincides with the center of the track. In addition, since δ is minute, even if there is a track shift corresponding to δ until the tape feed control system responds, the signal level will hardly drop and no problems will occur. do not have. Further, the polarity of δ may be selected so that it approaches zero after the change with respect to the value of V _o+1 . In this case, the maximum time it takes for the polarity to approach zero can be halved compared to when the polarity is fixed. Effects of the Invention The present invention can remove the DC component in the amount of electricity applied to the electro-mechanical conversion element in continuously variable speed noiseless reproduction with simple processing.
It is possible to improve the lifespan and reliability of the element, and to optimize the efficiency of driving the element.
The effect is great.

[Brief explanation of drawings]

Figure 1 is a diagram showing the recorded magnetization trajectory of the pilot signal, Figure 2 is a circuit diagram showing a reproducing circuit for obtaining a tracking error signal, and Figure 3 is a diagram showing the reproduction circuit at 3x speed in the forward and reverse directions. Figure 4 is a waveform diagram showing the preset voltage waveform and reference signal during 3x forward playback, and Figure 5 is a waveform diagram showing the preset voltage waveform and reference signal during 3x reverse playback. , Fig. 6 is a diagram showing a method of changing from 1x speed to 2x speed, Fig. 7 is a diagram showing head scanning in which a DC component remains, Fig. 8 is a block diagram showing an embodiment of the present invention, and Fig. 9 is a diagram showing a method of changing from 1x speed to 2x speed. is a circuit diagram showing a specific configuration of a piezo error signal processing circuit in the same embodiment,
FIG. 10 is a flowchart of the processing contents of the arithmetic processing circuit, FIG. 11 is a flowchart of the processing contents of the subroutine block of FIG. 10, and FIG. 12 is a flowchart of the processing contents of the DC component reduction section of FIG. FIG. 13 is a diagram showing a reduction in the DC component. A ₁ , B ₁ ...recorded magnetization locus, f _H ...horizontal synchronization signal frequency, f ₁ to _{f 4} ... pilot signal for tracking control, 3 ... balanced modulation circuit, 5, 6 ... f _H and 3f _H tuning circuit, 7, 8...detection circuit, 10...
...Analog inversion circuit, 14...Head scanning direction,
15...Tape transport direction, 16, 17...Head scanning locus during triple speed playback, _Tp ...Track pitch, 20...Electro-mechanical conversion element, 21...Rotating video head, 41...Minute correction circuit, _H1 ,
H ₂ , H _o ... head.

Claims (1)

[Claims] 1. A magnetic tape is wound diagonally around a cylinder equipped with a rotating magnetic head mounted on an electro-mechanical transducer, and information signals are recorded and reproduced on the magnetic tape as a group of discontinuous recording tracks. In addition, during recording, four types of pilot signals for tracking control are superimposed on the information signal to be recorded and are sequentially recorded cyclically, and during reproduction, the recording track is reproduced from the recording track adjacent before and after the recording track to be reproduced. The tracking error signal is configured to obtain a tracking error signal corresponding to the level difference of the crosstalk signal of each pilot signal, and this signal is used as a signal for fine adjustment of the tape feed control means, and also controls the transport speed of the magnetic tape during recording. TS _t , the voltage required to displace the electro-mechanical transducer by one track pitch is V _t , the current magnetic tape transport speed is T _O , the center value of the slope of the preset voltage waveform is V _o , and the reproduction The type of reference pilot signal sometimes used for tracking control is set to RE o, which is an integer from 1 to 4, corresponding to the four types of pilot signals during recording, and the preset voltage waveform required for the next head operation is set as RE _o . The center value of the slope is V _o+1 ,
The slope of the preset voltage waveform is SL _o+1 , the type of reference pilot signal is RE _o+1 , K and m are integers, and V _o+1 /V _t =V _o /V _t +TS _o /TS _t − K However, |V _o+1 /V _t |
≦1/2 SL _o+1 /V _t =TS _o /TS _t −1 RE o ₊₁ =RE _o +K−4m However, by performing arithmetic processing that satisfies the condition of 1≦RE _o+1 ≦4 The electro-mechanical conversion element is driven using the calculated values of V _o+1 , SL _o+1 , and RE _o+1 , and the V _o+1 is driven every j head scans (j≧1). Examine the value,
If the value of V _o+1 is not zero, using a small value δ that is sufficiently small with respect to the absolute value of V _t , V′ _o+1 =
A magnetic recording/reproducing device characterized in that the value of V _o+1 is replaced by the value of V _{o+1 +} δ.