JPS6226092B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic recording/reproducing device (VTR) that uses a bimorph composed of a piezoelectric element to change the mechanical height position of a rotating magnetic head. To provide a method for solving the difficulty of height adjustment between both heads that occurs when assembling a rotating cylinder in a head type VTR, and also solving the problem of height deviation between both heads due to the hysteresis characteristic of the bimorph. It is something to do.

In a helical scan rotating two-head VTR,
The mechanical height positions of both heads A and B must be the same. For example, when the tape speed and gap width of the magnetic heads are selected so that the magnetization trajectories recorded by heads A and B, which have opposite azimuth angles, are recorded adjacent to each other, the mechanical If the height positions are the same, the recorded magnetization trajectory will be as shown in FIG. 1a. 1 in the figure is a magnetic tape T
_A is the magnetization trajectory recorded by the A head, and T _B is the magnetization trajectory recorded by the B head. If for some reason the mechanical height positions of both heads A and B are different, the recorded magnetization trajectory will be as shown in Figure 1b, for example, A.
Since the B head records and reproduces a portion of the magnetization trajectory recorded by the head, a pairing phenomenon occurs in which a portion of the magnetization trajectory T _A is erased. Therefore, during reproduction, the output signal obtained from the A head decreases, and since the A head simultaneously scans the magnetization locus T _B for reproduction, the S/N of the reproduced output signal deteriorates due to the crosstalk signal.

One of the main causes of the pairing phenomenon is the height adjustment error between the heads A and B that occurs during cylinder assembly, and the other is the hysteresis characteristic of the piezoelectric element.

The height error between heads A and B that occurs when assembling the cylinder is usually kept to about 3 (μm), although it depends on the recording magnetization trajectory width. In the case of mechanical height adjustment, the limit is about 2 to 3 (μm), and conversely, if the height error is allowed to be about 10 (μm), the mass production effect will be great. The present invention has the advantage that precision is not required for the height adjustment between the two heads when assembling the cylinder because the height between the two heads is electrically adjusted as will be described later.

One of the other factors that causes pairing is due to the hysteresis characteristic of the bimorph made of piezoelectric elements. In a rotating head type VTR, a method of displacing the mechanical height position of a rotating magnetic head in the direction of the rotation axis using a bimorph composed of a piezoelectric element is already known. This method is applied to a method in which a playback head faithfully on-tracks and follows a recording track during special playback during slow, slow, or double-speed playback.

As shown in FIG. 2, the bimorph 2 composed of piezoelectric elements has two piezoelectric elements 3 and 4 polarized in the direction shown by the arrow P bonded together so as to have a common electrode 5, and electrodes 6 on both sides, 7 is formed by a method such as vapor deposition. When displacing the bimorph 2, a terminal 8 drawn out from the common electrode 5,
A voltage may be applied between the electrodes 6 and 7 on both sides and a terminal 9 drawn out from a lead wire that electrically connects them.
For example, when + voltage is applied to terminal 8 and - voltage is applied to terminal 9, piezoelectric element 3 extends in its longitudinal direction, piezoelectric element 4 contracts, and as a result, bimorph 2 bends and is displaced. It is well known that the bending direction depends on the polarity of the voltage applied between the terminals 8 and 9 and the polarization direction of the piezoelectric elements 3 and 4.

A magnetic head movable device using a bimorph having such a configuration is shown in FIG. 10 in Figure 3
is a bimorph composed of piezoelectric elements 11 and 12, and a magnetic head 13 is fixed to one end by a method such as adhesive, and the other end is attached to a mounting member 1 by an adhesive 14.
It is fixed on 5. The mounting member 15 is fixed onto the rotary disk by screws or the like. The magnetic head mover shown in FIG. 3 therefore rotates with the rotating disk.

If no voltage is applied to the piezoelectric element, the magnetic head 13 only performs circular motion in a plane perpendicular to the rotation axis, similar to the magnetic head used in conventional rotary head type VTRs. When a voltage is externally applied to the lead wire 16 connected to each electrode via a slip ring-brush or the like, the magnetic head 13 moves along the circular motion indicated by the arrow 17.
Displaced in the direction indicated by (rotation axis direction). A method of faithfully reproducing already recorded video signals from a tape running at a tape speed different from that at the time of recording by using this displacement is described in Japanese Patent Application Laid-Open No. 53-45509 and many other published patents. There is.

In the magnetic head moving device shown in FIG. 3, when a positive voltage is applied to the bimorph, the magnetic head 13
When the direction of displacement is upward on the paper and the direction of displacement is positive, the amount of displacement of the magnetic head 13 with respect to the voltage applied to the bimorph changes as shown in FIG. In the figure, the horizontal axis represents applied voltage [V], and the vertical axis represents displacement μm. The intersection of the coordinate axes is set to zero, the right side on the paper is set as the positive applied voltage, and the top side is set as the positive direction of displacement. The position of the free end of the bimorph when the applied voltage is zero is defined as zero displacement, and the applied voltage is
When applying up to V ₁ [V], the displacement amount is 18 to 1
9 increases according to the curve shown in FIG. Apply voltage to V ₁ [V]
When the voltage is changed from to zero [V], the displacement changes along the curves shown in 19-20, and when the voltage is applied from zero to -V ₁ to V ₁ , the displacement changes to the curve 20-21-22-19. change along. When the voltage cycle of _V1 to _-V1 is applied repeatedly in the same manner, the displacement amount repeats the cycle of 19 to 20 to 21 to 22 and does not return to the starting point 18. The starting point 18 depends on the history of what voltage was applied before the displacement. For example, when a bimorph with a voltage of V ₁ [V] applied and the applied voltage made zero is used for the next purpose, the next starting point of the bimorph will be a point 20 with a residual hysteresis amount h. As shown in FIG. 5, the value of the residual hysteresis amount h varies depending on the maximum applied voltage.

When performing special playback by applying a predetermined voltage to the bimorph, if the voltages applied to the bimorph that move heads A and B are the same, the effect of the amount of residual hysteresis after the special playback mode is canceled is Since both the A and B heads appear equally, there is no pairing problem, but in reality, different voltages must be applied to the bimorphs that move each head. For example, during still playback, voltage changes as shown in FIG. 6 must be applied to the bimorph. In the figure, the solid line shows the voltage applied to the A head, and the broken line shows the voltage applied to the B head.
Voltage waveform common to both A and B heads, i.e. 23-2
Normal still playback can be obtained even if a voltage waveform of 5 to 26 to 28 is applied, but in that case, the voltage waveform of 25 to 26
This sudden change causes the head to vibrate at the resonance frequency unique to the piezoelectric element, degrading the quality of the reproduced image. Therefore, the voltage waveform actually applied to the A head is a triangular wave of 23-24-26-27, and the voltage waveform of 24-25-27-28 is used for the B head. Therefore, when the still playback mode is stopped at an arbitrary time, the final voltage applied to the bimorphs moving the A and B heads is different, so the amount of residual hysteresis of each bimorph is also different, causing a pairing problem. It turns out. The above pairing problem is not limited to still playback, but also applies to slow playback, double speed playback, etc., although the details are omitted. In order to solve this problem, we have an auxiliary device that detects the mechanical height position of the magnetic head fixed on the bimorph, and the position signal obtained from this device drives the bimorph even during recording. Either the mechanical height positions of the recording heads must be controlled so that they are always the same, or a new recording-only magnetic head fixed on the rotating disk without the use of a bimorph must be installed.

The present invention provides a novel method for solving the pairing problem during recording, without the use of an extra dedicated recording head, and without the mechanical height of the magnetic head fixed on the bimorph. Without using any auxiliary equipment to detect the position,
The present invention provides a method for solving the pairing problem.

The details of the present invention will be explained below.

In order to prevent pairing during recording, the present invention uses one head, for example, the A head, as a reference, and controls the mechanical height of the B head so that it is always equal to the A head. Mechanical height positional deviation between the heads is detected by reproducing and scanning the B head on the magnetization locus recorded by the A head.

The principle of the present invention will be explained using FIGS. 7 and 8. In FIG. 7, the center lines of the recorded magnetization locus on the magnetic tape 29 are indicated by T _A1 , T _B1 , T _A2 . . . . The tape 29 is transported in the direction shown by arrow 30, and the rotating magnetic head scans a still trajectory 31 in the direction of arrow 32. Therefore, if the mechanical height positions between both heads A and B are the same, and no voltage is applied to the bimorph, T _A1 , T _B are spaced at the regular track pitch T _P during recording.
₁ , T _A2 . . . Draw a magnetization trajectory centered on . The recording magnetization trajectory width is determined by the width of the magnetic head, and when performing azimuth recording, the magnetization trajectory width and track pitch T _P are made equal so that each track is recorded adjacent to each other as shown in FIG. 1a. There is. When azimuth recording is not used, a guard band is provided between each track to prevent stroke signals from adjacent tracks, so the recording magnetization trajectory width is selected to be narrower than the track pitch _TP . It is. Now, if we consider the output when the magnetization trajectory recorded by the A head is reproduced by the B head, in azimuth recording, high frequency luminance signals are not output due to azimuth loss, but low frequency converted color signals are output. Since the azimuth loss is small, an output signal can be obtained even at the B head. On the other hand, in the guard band recording method in which the magnetic head does not have an azimuth angle, a brightness signal and a color signal are output from the B head. That is, in any of the above methods, when the B head performs reproduction scanning on the magnetization locus recorded by the A head, a reproduction output signal corresponding to the on-track amount of the B head can be obtained.

Now, assuming that the recording mode is started from point 33 shown in FIG. 7, the A head draws a magnetization locus for one field shown at 33-38. Normally, the B head would then draw the magnetization trajectory shown by 34-39, but at this time, the B head should be set to playback mode and the B head should be set so that the still trajectory becomes 34-36.
Change the mechanical height position of the head. This is B
It is sufficient to apply a voltage change as shown in FIG. 841 to the bimorph for driving the head. Therefore, the actual scanning trajectory of the B head on the tape is a trajectory 40 shown at 34-37, taking into account the tape speed.
At this time, the B head reproduces data across the magnetization locus recorded by the A head, and its envelope detection output becomes a waveform 42 shown in FIG.
If the mechanical height positions of both heads A and B are the same, the maximum playback output obtained from head B is 4.
3 is located in the middle of one field period, and the voltage applied to the bimorph at the maximum point is the value shown by 44, but if the mechanical height positions of both heads are different, it will be obtained from head B. The output signal becomes 45 or 46, and the voltage applied to the bimorph at the maximum point 47 or 48 becomes 49 or 50.

The amount of displacement of the bimorph, ie, the amount of displacement of the mechanical height position of the magnetic head, is approximately proportional to the voltage applied to the bimorph. Therefore, by reproducing the magnetization trajectory recorded by the A head while tilting the B head,
If the voltage applied to the bimorph for driving the B head when the reproduction output of the B head is at its maximum is known, the relative mechanical height difference between the A and B heads can be detected. Note that the detection of the relative mechanical height deviation between both heads is not essential to knowing the voltage applied to the bimorph, but rather to detect the maximum output signal obtained when performing the above-mentioned reproduction scan of the B head from a predetermined point in time. It goes without saying that this is possible by knowing the time up to the point.

A specific example using the above principle is shown in FIG. Figure 9 shows a specific circuit example using a rotating two-head VTR as an example, and Figure 10 shows a 9-head VTR.
The waveforms of each part of the figure are shown. In the figure, 51 is the A head, 5
Reference numeral 2 denotes a B head. Although not shown, each head is fixed on the bimorph, and its mechanical height position can be independently displaced. 53,5
5 is a recording amplifier, and 54 and 56 are reproduction amplifiers, which can be switched to recording or reproduction mode by switches SW ₁ and SW ₂ as necessary. switch
SW ₁ and SW ₂ are actually electronic switches composed of transistors, and are operated in conjunction with each other.
If the point in time when the VTR is put into recording operation mode and the control of the rotary cylinder and capstan motor becomes stable is t ₀ shown in FIG. 10, then the period after t ₀ when the A head is in contact with the tape, During the period when the head switching signal is "1" as shown in FIG. 10a, both switches SW ₁ and SW ₂ are connected to the recording side R. It is clear from the tape running system of a rotating two-head VTR that the B head is not in contact with the tape at this time. If overlap recording is ignored, the B head starts contacting the tape at time _t1 . At time _t1 , both switches _SW1 and _SW2 are connected to the playback side P. At the same time, the B head driving bimorph receives a sawtooth wave voltage (10th
A voltage waveform shown in Figure b) is applied. In FIG. 9, 58 is a sawtooth wave shaping circuit, the output of which is supplied to a bimorph drive circuit 59 for driving the B head via switch _SW3 . The switch _SW3 is connected to the P terminal side at time _t1 . As explained with reference to FIG. 7, the sawtooth wave b is set to a voltage value that causes the B head to scan across the magnetization locus recorded by the A head. At this time, the playback output obtained from the B head is the envelope detection circuit 6.
0 and obtains an output signal c. The output signal c is input to the peak hold circuit 61, and the output signal d
and the value of c is input to the comparator 62. The output of the comparator 62 is configured to output a "1" signal when the signal at c becomes smaller than the signal at d, and its output waveform is indicated by e. A sample pulse shaping circuit 63 shapes the sample pulse at the rising edge of the signal e, and samples and holds the sawtooth wave signal b. Note that the circuit 64 is a sample and hold circuit. Since it is difficult for a sample and hold circuit composed of an analog circuit to hold an arbitrary constant voltage for a long period of time, the voltage is once input to the memory circuit 65 composed of a digital circuit via the switch _SW4 . At this time, switch _SW4 is connected to the P terminal side. For example, as shown in FIG. 11, the memory circuit 65 receives a hold signal f input from a terminal 66.
A variable oscillator 67 whose frequency changes depending on the voltage of
The counter 68 counts the output for a certain period of time and stores it in memory, and the DA converter 69 converts it back into an analog signal and outputs it from a terminal 70. Note that the terminal 71 is an input terminal for a command signal to operate the counter 68, for example, from t ₂ to
Operate the counter only for a period of t ₃ . circuit 72
is a read pulse generator that operates the DA converter, and is configured so that the output of the DA converter can be taken out continuously. The output of the memory circuit 65 shown in FIG. 9 is input to the drive circuit 59 of the B head drive bimol from time _t3 onwards. Note that after time _t3 , all switches _SW1 to _SW4 are connected to the R terminal, and this is maintained until the end of the recording operation mode. Also, although the details are omitted, the memory circuit 65
It is possible to output zero voltage if the output is the voltage value shown at 44 in FIG. 8, and to output negative and positive voltages if the output is the voltage value shown by 49 and 50.

As is clear from the above explanation, when the control of the rotary cylinder and capstan motor becomes stable after the VTR is put into the recording operation mode, only one field period from t ₁ to _{t 2} shown in FIG. Switches SW ₁ to _{SW 4} are connected to the P terminal side, and the B head crosses and scans the magnetization locus recorded by the A head, until the maximum point of the reproduction output obtained from the B head is reached. After converting the required time to a predetermined voltage value, the voltage is applied and held to the B-head driving bimorph to keep the relative mechanical height position of the A-head and B-head constant at all times. is possible.

Next, the accuracy with which the mechanical height position between the A and B heads can be detected will be explained with reference to FIG. 12.
FIG. 12 is a partial drawing of FIG. 8, where 73 is the voltage waveform applied to the B head driving bimorph, and 74 is the envelope output reproduced by the B head. The envelope output 74 is generated when the B head scans according to the trajectory 40 shown in FIG.
The ideal reproduction output obtained from the B head is depicted. The period from t ₁ to _{t 2} shown in FIG. 12 is 1/60 second, and as is clear from FIG. 7, the amount of movement of the B head during this period is twice the track pitch T _P . For example, when the track pitch T _P is 30 μm, t ₁ to _{t 2}
The period corresponds to a B head movement of 60 μm. On the other hand, suppose that the envelope output 74 is passed through a suitable amplifier to obtain a voltage value of 10V at the maximum point 75. The sensitivity of the comparator 62 shown in FIG.
If it is 100mV, ΔV shown in Figure 12 is 100mV.
Therefore, by simple proportional calculation, the detection error for the position of the maximum point 75 is ±0.3 μm. In other words, A
B The mechanical height position between both heads can be adjusted with an accuracy of ±0.3 μm. In reality, the accuracy is somewhat lower than the above because the amount of displacement of the bimorph is not exactly proportional to the applied voltage, but it is still possible to adjust the accuracy to within ±1 μm. Therefore, by using the present invention, it is possible to solve the pairing problem during recording due to the residual hysteresis characteristic of the bimorph, and in particular, it is possible to solve the problem of pairing during recording due to the residual hysteresis characteristic of the bimorph. It becomes possible to reduce the accuracy of height adjustment.

Although the present invention has been explained using a rotating two-head type VTR as an example, it is also possible to use a rotating two-head type VTR as an example.
It is obvious that in a VTR as well, the mechanical height position of each head can be detected by reproducing and scanning a magnetization trajectory recorded by an arbitrary head so that the other heads intersect with each other.

[Brief explanation of the drawing]

FIGS. 1a and 1b are diagrams showing changes in the recorded magnetization locus due to changes in the mechanical height positions of both heads A and B, respectively; FIG. 2 is a perspective view showing an example of a bimorph composed of voltage elements; Figures 3a and 3b are plan and side views showing an example of a magnetic head moving device using a bimorph, Figures 4 and 5 are diagrams for explaining the hysteresis characteristics of the bimorph, and Figure 6 is a still reproduction. Figure 7 is a diagram showing an example of the voltage waveform applied to the bimorph at a given time, Figure 7 is a magnetization locus for explaining the principle of the present invention, and Figure 8 is an envelope detection output and an example of the voltage applied to the bimorph to explain the principle of the present invention. A diagram showing applied voltages, FIG. 9 is a specific circuit diagram showing an embodiment of the present invention, FIG. 10 is a waveform diagram of each part of FIG. 9, and FIG. 11 is a block diagram showing an example of the configuration of a memory circuit. , and FIG. 12 are diagrams for explaining the height detection accuracy between both heads when the present invention is used. 10...Bimorph, 13,51,52...Magnetic head, 56...Reproduction amplifier, 58...Sawtooth wave shaping circuit, 60...Envelope detection circuit, 6
1...Peak hold circuit, 62...Comparator, 6
3...Sample pulse shaping circuit, 64...Sample hold circuit, 65...Memory circuit.

Claims (1)

[Claims] 1 comprises a plurality of magnetic heads that move relative to a magnetic recording medium, the magnetic heads are fixed on a bimorph composed of a piezoelectric element, and the magnetic In a magnetic recording/reproducing device configured so that the mechanical height position of the head can be varied, when the tape is running, the magnetization locus recorded by any magnetic head is moved once from one side of the tape to the other in its width direction. The relative mechanical height between the arbitrary magnetic head and the other magnetic heads can be determined by scanning the other magnetic heads in an intersecting manner and detecting the maximum point of the reproduction signal obtained by the other magnetic heads. A magnetic recording/reproducing device characterized by detecting a positional shift.