JPS6152531B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a position control circuit for a rotating magnetic head that controls the position of a magnetic head that records or reproduces signals in sliding contact with a magnetic recording medium.

Generally, in a VTR (video tape recorder), a magnetic head is attached to a predetermined position on a rotating part, and therefore the magnetic head rotates in a fixed trajectory. However, it would be effective in various respects if the position of the magnetic head could be arbitrarily changed during rotation. For this reason, it is necessary to attach the magnetic head to an electromechanical transducer such as a piezoelectric element or a solenoid, and to supply a predetermined drive signal to the electromechanical transducer. Brush and slip rings have been used as conventional drive signal transmission means. However, the brush and slip ring
Because the two devices are in mechanical contact to transmit signals, the durability is poor, and the contact is unstable, resulting in poor reliability, and poor contact may generate electrical noise and noise. There were flaws.

The present invention provides a position control circuit for a rotating magnetic head that can transmit a drive signal to the electromechanical transducer mentioned above without contact and has improved durability and reliability. That is, the present invention supplies the drive signal to the electromechanical transducer without contact through the rotary transformer by chopping the drive signal. Further, in the present invention, it is sufficient to use a rotary transformer for one channel in order to supply drive signals to two electromechanical transducers attached to two magnetic heads.

A preferred embodiment of the present invention will be described below. FIG. 1 shows a mechanical section including a rotating magnetic head. 1 indicates a shaft rotated by a motor at 30 revolutions per second, 2 indicates one lower drum of the tape guide drums, and 3 indicates the other upper drum. The lower drum 2 is fixed to a substrate 4, the shaft 1 is inserted through the center of the lower drum 2, and the two are connected by a bearing 5. An upper drum 3 is fixed to the shaft 1. 6 is shaft 1 and upper drum 3
The flange for fixing is shown. Upper drum 3
Magnetic heads 7a and 7b are arranged at an angular interval of 180° on the lower surface facing the lower drum 2. The magnetic heads 7a and 7b each have a head mounting device 8 made of a piezoelectric element, which is one of the electromechanical transducer elements.
It is attached to the upper drum 3 by a, 8b.

FIG. 2 shows an enlarged view of the head mounting devices 8a and 8b. Reference numeral 11 denotes a bimorph plate formed by bonding together two piezoelectric elements 12 and 13, each of which has electrodes adhered to both surfaces by plating or the like. One end of the bimorph plate 11 is fixed to a head substrate 15 with an adhesive 14, and a magnetic head 7a or 7b is attached to the free end of the bimorph plate 11. 16 is a damper for absorbing vibrations of the bimorph plate 11. By applying a voltage between the two electrodes through the lead wires connected to the electrodes 17 and 18 on both sides of the bimorph plate 11, the magnetic head 7a or 7b is rotated in the direction of rotation as shown by the arrow in FIG. 2B. It can be moved vertically.

Further, 9 is for supplying a recording signal to the magnetic head 7a or 7b, or taking out a reproduction signal from the magnetic head 7a or 7b, and transmitting a drive signal to the bimorph plate 11 of the head mounting device 8a or 8b together with this. It is a rotating transformer. Third
As shown enlarged in the figure, the rotary transformer 9 has a cylindrical shape and is fixed to the lower drum 2 in a case 1.
9 and a ring-shaped stator 20 in the case 19.
a, 20b, and 21c are attached in a stacked state. Further, rotors 21a and 2 are arranged concentrically with each stator with a gap therebetween and are fixed to the shaft 1.
1b and 21c are housed in the case 19. Grooves are formed on opposing surfaces of each stator and each rotor, and coils are wound along these grooves.
That is, the stators 20a and 20b each have a coil 22.
coils 22b and 23b are wound on the rotors 21a and 21b, respectively, a primary coil 24 is wound on the stator 20c, and a secondary coil 25 is wound on the rotor 21c. . The stators 20a, 20b and rotors 21a, 21b are used to transmit recording signals or reproduction signals for the magnetic heads 7a, 7b, and the stators 20c and rotor 21c are used to connect the electrodes of the bimorph plates 11 of the head mounting devices 8a, 8b, respectively. This is for transmitting the drive signal applied to the terminals 17 and 18.

As an example of the rotary transformer 9, a small one with a diameter of 15 [mm] and a height of about 15 [mm] can be used, and the primary coil 24 has 60 to 100 turns with a center tap, and the secondary coil 25 has a center tap. The number of turns is 30 to 50.

FIG. 4 is a block diagram of an embodiment of the present invention, in which 31 is a recording signal input terminal to which a composite color video signal to be recorded is supplied, 32 is a reproduction output terminal from which a reproduced composite color video signal is obtained; 33 is a recording/reproduction changeover switch.

During recording when the switch 33 is connected to the recording side terminal r, the color video signal from the terminal 31 is supplied to the band pass filter 34 and the low pass filter 35, and the carrier color signal generated at the output of the band pass filter 34 is transferred to the frequency conversion circuit. 36 and the luminance signal generated at the output of the low pass filter 35 is
The signal is supplied to the FM modulation circuit 37. The frequency conversion circuit 36 is for converting the carrier color signal into a converted color signal S _c having a carrier frequency f _c lower than the original carrier frequency, for example, 688 [KHz]. The FM modulation circuit 37 generates a modulated luminance signal S _y that is FM-modulated such that its sync chip level is 3.6 [MHz] and its white peak level is 4.5 [MHz]. Then, the converted color signal S _c and the modulated luminance signal S _y are added by an adding circuit 38 and supplied to a recording amplifier 39 . The recording signal generated at the output of the recording amplifier 39 has a frequency spectrum shown in FIG. This recording signal is sent to the switch 33.
Coils 22a, 23a of rotating transformer 9 via
The magnetic head 7a connected to the coil 22b and the magnetic head 7b connected to the coil 23b cause the tape to be applied to the circumferential surface of the tape guide drum by approximately 180 degrees.
Recording signals are recorded on a magnetic tape T that runs while being wound around an angle range of . magnetic tape T
is wound diagonally, so that one field of recording signals alternately recorded by the magnetic head 7a or 7b becomes one inclined magnetization track.

During reproduction, the reproduction signals alternately taken out by the magnetic heads 7a and 7b are sent to the reproduction amplifier 4 through the rotary transformer and the reproduction side terminal p of the switch 33.
0. Output signal S _p of the reproduction amplifier 40
are low pass filter 41 and high pass filter 4
2. A converted color signal S _c appears at the output of the low-pass filter 41, and the high-pass filter 4
A modulated luminance signal S _y appears at the output of No. 2. The converted color signal S _c is returned to the carrier color signal of the original carrier frequency in the frequency conversion circuit 43, and the modulated luminance signal S _y is
The FM demodulation circuit 44 demodulates the signal into a luminance signal. These carrier color signals and luminance signals are added by an adder circuit 45 to obtain a reproduced color video signal at the reproduction output terminal 32.

In this embodiment, the magnetic tape, which is normally running at a constant speed, is stopped by a carburetor and a pinch roller, and in this state, during still image reproduction in which the magnetic head scans the magnetic tape T, the magnetic head 7
This is to correct track deviations caused by changes in the inclinations of the scanning trajectories a and 7b.

Therefore, the reproduced signal S _p obtained at the output of the reproducing amplifier 40 is supplied to the envelope detection circuit 51, and its detection output S _d is supplied to the sampling hold circuit 52a.
and 52b. A sampling pulse generation circuit 53 generates sampling pulses P _a and P _b for sampling hold circuits 52 a and 52 b, respectively. The sampling pulse P _a is
The sampling pulse P b is generated at the beginning of one field (1V) period of the reproduction signal, and the sampling pulse P _b is generated at the end of one field period. Therefore, detection pulses corresponding to the rotational phases of the magnetic heads 7a, 7b are supplied from the detection pulse generation circuit 54 to the sampling pulse generation circuit 53. The output voltage V _a of the sampling hold circuit 52 a and the output voltage V _b of the sampling hold circuit 52 b are supplied to a voltage comparison circuit 55 , and the voltage comparison circuit 55 generates a DC voltage V _c determined by the magnitude relationship between the two. Further, 56 is a sawtooth wave generating circuit. This sawtooth wave generation circuit 56 is the detection pulse generation circuit 5
In synchronization with the detection pulse from 4, a sawtooth wave S _p of constant amplitude is generated with the reference voltage V _p set to a DC level. The sawtooth wave S _p is separated into positive and negative waves by the waveform separation circuit 57 with the DC voltage V _c from the voltage comparison circuit 55 as the center. The two waveforms from the waveform separation circuit 57 are supplied to a drive circuit 58, which will be described later, and are chopped. A pulse oscillation circuit 59 is provided as this chopping pulse. The frequency f _p of this chopping pulse is determined so as not to interfere with the recording signal and the reproduction signal. That is, when recording and reproducing a color video signal, the carrier color signal is converted to a carrier frequency f _c as shown in Fig. 5, so the frequency f _p of the chopping pulse is indicated by diagonal lines in Fig. 5. As shown, the band of the converted color signal S _c (e.g. f _c ±500 [KHz])
be selected as the lower one. Also, in this example,
Since the frequency of the sawtooth wave S _p is as low as 60 [Hz], the frequency f _p of the chopping pulse is 10
[KHz] or above is sufficient for chopping.

The output signal of the drive circuit 58 is applied between the electrodes of the bimorph plates 11 of the head mounting devices 8a and 8b via the primary coil 24 and secondary coil 25 of the rotary transformer 9. The drive circuit 58 is provided with a switch means for supplying a drive signal to the bimorph plate 11 only when reproducing a still image.

Correction of track deviation during still image reproduction using the above-described configuration will be described with reference to FIGS. 6 to 8. Figure 6A, Figure 7A and Figure 8A
, when the magnetic tape T is running at a constant speed in the direction of the arrow, respectively, the magnetic head 7a or 7b
one magnetized track 62 formed by;
This figure shows the mode of track deviation between the magnetic head 7a or 7b and the scanning locus 63 shown by the broken line during still image reproduction. The inclination of the magnetization track 62 and the inclination of the scanning locus 63 are different, and when they coincide at the center as shown in FIG. 6A,
The reproduction signal S _p from the reproduction amplifier 40 is as shown in FIG. 6B.
As shown in the figure, the amplitude is small at the beginning of one field period 1V, then increases, becomes large in the middle, and changes to a small amplitude again at the end. At this time, the detection output S _d of the envelope detection circuit 51 is as shown in FIG.
By being sampled by sampling pulses P _a and _{P b} that occur at equal timing _from the beginning and end of one field as shown in FIGS. . (V _a = V _b ), the DC voltage V _c generated from the voltage comparison circuit 55
becomes equal to the reference voltage V _p . Therefore, Figure 6F
Since the sawtooth wave _Sp has the reference voltage _Vp at the DC level as _shown in FIG. Among these separated positive and negative waveforms, the negative waveform causes a downward displacement in the bimorph plate 11 that gradually decreases from the start end to the center of the scanning locus 63, and the positive waveform gradually increases from the center to the end. An upward displacement occurs. In FIG. 6A, the amount and direction of displacement of the bimorph plate 11 are shown by arrows perpendicular to the scanning locus 63. By controlling the displacement of the bimorph plate 11 in this manner, the scanning locus 63 of the magnetic head 7a or 7b perfectly matches the magnetization track 62, and track deviation is corrected.

Further, as shown in FIG. 7A, when the vicinity of the starting end of the scanning locus 63 coincides with the magnetization track 62 and the track deviation becomes large at the end, the reproduced signal S _p shown in FIG. 7B is obtained. , envelope detection circuit 51
The detection output S _d is shown in Figure 7C, and the sampling pulses P _a and P _b (Figure 7 D and E)
As a _result of being sampled by
A sampling output V _b is generated from . In the case shown in FIG. 7, since (V _a >V _b ), the DC voltage V _c generated by the voltage comparator circuit 55 is smaller than the reference voltage V _p as shown in FIG. 7F. Since the sawtooth wave S _p caused by this DC voltage V _c is separated into positive and negative waves, the downward displacement of the bimorph plate 11 at the starting end of the scanning locus 63 is small corresponding to this negative waveform, and then the displacement becomes zero. , the upward displacement increases toward the end. The arrows in FIG. 7A indicate the amount and direction of displacement of the magnetic head 7a or 7b at the start and end of the scanning locus 63. Track deviation is corrected by such position control.

Furthermore, as shown in FIG. 8A, the vicinity of the end of the scanning locus 63 coincides with the magnetization track 62, and even if the track deviation becomes large at the starting end, the track deviation can be corrected. That is, FIG. 8B shows the reproduced signal S _p at this time, and FIG _. 8C shows _the detection output S _d of the envelope detection circuit 51. _{When sampled with}
A DC voltage V _c of <V _c ) is generated from the voltage comparator circuit 55. Since the sawtooth wave S _p is separated into positive and negative waves by this DC voltage V _c , as is clear from FIG. It is controlled so that it is largely displaced downward, then the displacement gradually becomes smaller, and conversely it is displaced upward near the terminal end.

An example of the drive circuit 58 is shown in FIG. When the DC voltage V _c supplied from the comparator circuit 55 to the waveform separation circuit 57 is equal to the DC level of the sawtooth wave _Sp as shown in FIG. 10A, a positive waveform signal shown in FIG. 10B, which is symmetrical to each other, is generated. The signal is separated into S _p1 and a negative waveform signal S _p2 shown in C of the same figure. Negative waveform signal S _p2
is further supplied to the polarity inverting circuit 60 and shown in FIG. 10D.
It is converted into a positive signal S _p3 having the waveform shown in FIG.

The signals S _p1 and S _p3 shown in FIG. 10B and D
are supplied to amplifiers 61a and 61b, respectively. Switches SW a and _{SW b that} turn on the output signals of these amplifiers 61a and 61b only when playing still images
modulation transistors 62a and 62 through respectively
added to the base of b. Modulation transistor 6
The collectors and emitters of switching transistors 2a and 62b are inserted between the emitters and ground of switching transistors 63a and 63b. Damper diodes 64a and 64b form a current path between the respective collectors and ground of switching transistors 63a and 63b when the switching transistors are off.
and resonance capacitors 65a and 65b are inserted in parallel. A chopping pulse having a frequency _fp , for example, a horizontal frequency, is supplied from the pulse oscillator 59 to the bases of the switching transistors 63a and 63b via emitter follower transistors 66a and 66b, respectively.

The primary coil 24 of the rotating transistor is provided with a center tap, which is grounded via a capacitor and connected via a resistor to a power supply terminal to which a power supply voltage (+V _cc ), for example, 10 [V] is applied. Ru. One end and the other end of this primary coil 24 are connected to the anodes of diodes 67a and 67b, and the cathodes of these diodes 67a and 67b are connected to the collectors of switching transistors 63a and 63b, respectively. Both ends of the secondary coil 25 of the rotating transformer are connected to both electrodes 17 and 18 of the bimorph plate 11 of the head device 8a. Bimorph plate 1 of the other head mounting device 8b
1 are connected in parallel.

In the above-described configuration, switches SW _a and SW _b are turned on in conjunction with the VTR's still image playback operation. A stepping pulse is constantly applied from a pulse oscillator 59 to the bases of switching transistors 63a and 63b. In this case, when the modulation transistors 62a and 62b are off, the switching transistors 63a and 63b remain off even if a chopping pulse is applied, and therefore the switching transistors 63a and 63b remain off in the primary coil 24. No resonant pulse voltage is generated when the switch turns from on to off. However, as described above, since the impedance of the modulation transistor 62a is modulated by the signal S _p3 , in the first half of one field where this signal S _p3 is generated, the change in peak value of the signal S _p3 is at most 100 ~
A high frequency signal shown in FIG. 10E modulated to about 300 [V] is generated. Further, the impedance of the modulation transistor 62b is modulated by the signal S _p1 generated in the second half of one field, so that the high frequency signal shown in FIG. 10F is generated. Since the center tap of the primary coil 24 of the rotating transformer is grounded in terms of AC, the polarity of the voltage induced in the secondary coil 25 is different from that of the secondary coil 25.
If one end of 5 is used as a reference, Figure 10 E and Figure 10 F
The high-frequency signals have opposite polarities, and therefore, as shown in FIG. The displacement of the bimorph plate 11 is reversed for each of the positive and negative directions. Furthermore, while the signal S _p3 is being generated, the diode 67a
Transistor 63a, diode 64
A, by disconnecting the circuit system such as the capacitor 65a, a high frequency signal with a sufficient peak value is generated, and similarly, while the signal S _p1 is being generated, the diode 67b causes the transistor 63b, the diode 64b, The circuit system such as the capacitor 65b is disconnected.

The response speed of the bimorph plate 11 is 15.75
Since it is not fast enough to follow the pulse voltage of [KHz], the displacement roughly follows the envelope curve,
There is no particular need to connect an amplitude detection circuit to the secondary coil 25. Furthermore, when the polarity of the voltage applied between the electrodes of the bimorph plate 11 changes from negative to positive, the charge accumulated in the bimorph plate 11 due to its capacitive nature is immediately discharged through the secondary coil 25. It is not necessary to provide a resistor for discharge.

Another example of the drive circuit 58 is shown in FIG. In this example, switching transistors 63a and 63b are driven by pulse oscillator 59 without using emitter follower type transistors. In addition, for the secondary coil 25 with the same number of turns, two with opposite polarity are used.
Two primary coils 24a and 24b are provided, one
One ends of the secondary coils 24a and 24b are connected to the collectors of switching transistors 63a and 63b via diodes 67a and 67b, respectively;
The other end is the modulation transistor 68a and 68b.
Connected to the power supply terminal via the emitter and collector of the These modulation transistors 68a and 68b
Amplifiers 61a and 61b and a switch are attached to the base of
Signals S _p3 and S _p1 are supplied via SW _a and SW _b .

In the configuration shown in FIG. 11, the impedance of the modulation transistors 68a and 68b is determined by the signal S.
The modulation by _p3 and S _p1 causes the value of the power supply voltage applied to the collectors of switching transistors 63a and 63b to vary in the same way as signals S _p3 and S _p1 . Even with such a configuration using power modulation, the bimorph plates 11 of the head mounting devices 8a and 8b can be vertically displaced in the same manner as the drive circuit shown in FIG. 9 described above.

According to the present invention described above, since the drive signal to the bimorph plate 11 is not supplied by a brush and a slip ring as in the past, durability is improved and electrical noise and noise due to poor contact are prevented. It can be prevented. Furthermore, only one channel of rotary transformer (primary coil 24 and secondary coil 25) is required for transmitting the drive signal. For example, in order to displace the bimorph plate 11 both above and below with respect to the neutral point, a reference voltage V _p which is stepped through one of the two channels of the rotary transformer is applied to one electrode 17 of the bimorph plate 11. A conceivable configuration is to transmit the chopped sawtooth wave S _p (superimposed on the DC voltage V _c ) to the other electrode 18 of the bimorph plate 11 via the other. According to the present invention, unlike this configuration, it is possible to generate displacement on both sides of the bimorph plate 11 by using only one channel of the rotary transformer. Therefore, when a cylindrical rotary transformer as shown in FIG. When using a flat plate rotary transformer in which the transformers face each other, there is an advantage that the diameter thereof hardly increases. Furthermore, since both ends of the secondary coil 25 are connected to the electrodes 17 and 18 of the bimorph plate 11, there is no need to provide an amplitude detector, and an increase in the time constant (deterioration of response) due to the provision of an amplitude detector is avoided. ) Alternatively, an increase in the number of parts can be avoided. Furthermore, by providing the diodes 67a and 67b as in the above-mentioned embodiment, when one of the two sets of high-frequency pulse generation circuits is operating, the other is isolated so that it does not become a load, thereby reducing the power supply voltage. It is possible to generate a pulse voltage with a sufficient peak value.

In addition, the present invention is not limited to correcting track deviations during still playback, but also corrects track deviations that occur during normal playback in which the running speed of the magnetic tape T is set equal to that during recording, or recording the running speed of the magnetic tape T. The present invention can also be applied to correction of track deviations that occur during slow motion image playback in which playback is performed at a slower speed than normal. Further, the head mounting device may be constructed so that it can be displaced in the same direction as the rotational direction of the magnetic head. That is, as shown in FIG. 12, if one end of the bimorph plate 11 is fixed to the head substrate 15 so that its thickness direction is in the direction of rotation of the magnetic head 7a or 7b, and the magnetic head 7a or 7b is attached to the free end of the bimorph plate 11, then Bimorph board 11
The position of the magnetic head 7a or 7b can be displaced in the same direction as its rotating direction in accordance with the driving voltage applied between the electrodes 17 and 18. Then, by detecting a time axis variation called jitter or drift and applying a drive voltage related to this detection output to the bimorph plate 11, the time axis variation can be removed. The present invention can be applied to this drive voltage transmission. Furthermore, the bimorph plates 1 of the two head mounting devices 8a and 8b
1 may be driven independently by separate drive signals instead of being connected in parallel.

[Brief explanation of the drawing]

Fig. 1 is a partial cross-sectional view of the mechanical part of an embodiment of the present invention, Fig. 2 is an enlarged view of the head mounting device, Fig. 3 is a cross-sectional view of the rotary transformer, Fig. 4 is an overall block diagram, Figure 5 is a frequency spectrum diagram of the recording (reproduction) signal, Figures 6 to 8 are diagrams used to explain track deviation correction, and Figures 9 and 10 are connection diagrams of an example of the drive circuit and their explanations. FIG. 11 is a connection diagram of another example of the drive circuit, and FIG. 12 is an enlarged view of another example of the head mounting device. T is a magnetic tape, 7a and 7b are magnetic heads, 8
a, 8b are magnetic head mounting devices, 9 is a rotary transformer, 11 is a bimorph board, 58 is a drive circuit, 62
is a magnetization track, and 63 is a scanning locus.

Claims (1)

[Claims] 1. A magnetic head that reproduces signals by slidingly contacting a magnetic recording medium, an electromechanical transducer that constitutes a mounting means for coupling this magnetic head to a rotating part, a primary coil provided in a fixed part, and a primary coil provided in the rotating part. a transformer comprising a secondary coil provided; a means for obtaining a DC voltage corresponding to a scanning position of the magnetic head with respect to a magnetic track recorded on the magnetic recording medium; It has means for separating the sawtooth wave of one field period into voltages in the positive direction and negative direction, and means for converting the two separated signals into high-frequency signals, and corresponds to the two converted high-frequency signals. A position control circuit for a rotating magnetic head, which drives the electromechanical transducer connected to the secondary coil with reverse polarity.