JPS6228486B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotary head position control device for controlling the position of a rotary head that records or reproduces signals by slidingly contacting a recording medium such as a magnetic tape.

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. Therefore, 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 control signal to the electromechanical transducer. Brush and slip rings have been used as conventional control signal transmission means. However, since brushes and slip rings transmit signals through mechanical contact between the two, they have poor durability and unstable contact, resulting in poor reliability, and poor contact can cause electrical problems. There were drawbacks such as generation of noise.

Furthermore, it has been proposed that the control signal for the electromechanical transducer described above be chopped, converted into a high frequency signal, and transmitted via a rotary transformer. According to this device, since control signals are transmitted without contact, durability is improved and generation of electrical noise and noise due to poor contact can be prevented. However, because high-voltage pulses are transmitted and their amplitudes change significantly, spurious waves such as high-order harmonics can pass through the rotating transformer, between wiring lines, etc., or be picked up by the rotating head, causing the video signal to be distorted. There was a problem with the contamination of the system. In order to solve this problem, it is necessary to strictly shield the control signal transmission system, which has the drawback of complicating the configuration of the device.

The present invention aims to obviate the above-mentioned conventional drawbacks. In the present invention, a sine wave with the least amount of spurious is modulated by a drive signal and transmitted.

The present invention will be described below as a helical scan type VTR.
An example applied to this will be described. FIG. 1 shows a mechanical section including a rotating magnetic head. 1 is
The drum shaft 1 has a belt pulley 2, a flywheel 3, a squirrel cage rotor 4 for brakes, and a flange 5a fixed to the drum shaft 1, and is driven by a belt at 30 revolutions per second. 6 is a brake coil. A fixed upper drum 7 and a lower drum 8 are disposed above and below a rotating drum 5 fixed to a flange 5a, respectively, and a bracket 9 defines a predetermined positional relationship between the two drums. A housing 10 is provided in which a bearing for the drum shaft 1 is housed, and a lower drum 8 (not shown) is fixed on a mechanical chassis. Magnetic heads 11a and 11b are arranged on the lower surface of the rotating drum 5 facing the lower drum 8 with an angular interval of 180 degrees. The magnetic heads 11a, 11b are connected to the rotating drum 5 by head mounting devices 12a, 12b, respectively, consisting of electromechanical transducer elements, such as piezoelectric elements.

The head mounting devices 12a, 12b are shown enlarged in FIG. Reference numeral 13 denotes two piezoelectric elements 14 and 15 each having electrodes adhered to both sides by plating or the like.
This shows a bimorph board made by pasting together. One end of the bimorph plate 13 is fixed to a head substrate 17 with an adhesive 16, and a magnetic head 11a or 11b is attached to the free end of the bimorph plate 13. 18 is a damper for absorbing vibrations of the bimorph plate 13. By applying a control voltage between both electrodes through lead wires connected to electrodes 19 and 20 on both sides of the bimorph plate 13, the magnetic head 11a or 11b is rotated in its rotational direction as shown by the arrow in FIG. 2B. It can be moved perpendicular to.

Further, 22a and 22b are a rotor and a stator that constitute a rotary transformer 21 for supplying a recording signal to the magnetic head 11a or 11b or for taking out a reproduction signal from the magnetic head 11a or 11b. The rotor 22a, which rotates integrally with the rotating drum 5, and the stator 22b, which is attached to the lower drum 8, are disk-shaped, and coils are arranged in two concentric grooves formed on mutually opposing surfaces. ing.

Further, a cylindrical boss 23 is fixed to the flange 5a. A rotor 25a of a rotary transformer 24 for transmitting a drive signal to the bimorph plate is placed at the end of the cylindrical boss 23. The stator 25b is
A ring-shaped substrate 26 provided on the upper surface of the upper drum 7
The rotor 25a is supported by the support member 27 erected from
It is supported in a position opposite to. The rotor 25a and the stator 25b are pot-shaped cores having a cylindrical projection at the center, and a coil is wound around each of the pot-shaped cores.

FIG. 3 shows the electrical configuration of this embodiment. A recording signal is supplied to a terminal indicated by 29, and is supplied to the magnetic heads 11a and 11b through the recording amplifier 3a, the recording side terminal r of the recording/reproducing switch 31, and the rotary transformer 21. 32
The switches a and 32b are also recording/reproduction changeover switches, which are turned off during recording and turned on during playback, so that the playback signals from the magnetic heads 11a and 11b are transferred to the playback amplifiers 33a and 33b, the changeover switches 32a and 32b, and the rotary transformer 21. and the playback side terminal p of the selector switch 31, and the playback amplifier 34.
is supplied to the terminal 35, and a reproduced signal is taken out at the terminal 35. When recording a color video signal, a recording signal is formed in which an FM modulated luminance signal obtained by FM modulating a luminance signal component and a low-frequency converted color signal obtained by frequency-converting a carrier color signal are mixed. FIG. 5 shows the frequency spectrum of the recording signal (reproduction signal). The low frequency conversion color signal Sc is located on the low frequency side of the transmission band of the VTR shown by the broken line, and the FM modulated luminance signal Sy is located on the high frequency side.
The reproduced signal is processed so as to demodulate the FM modulated luminance signal Sy, and to return the low-frequency converted color signal Sc to the original carrier frequency.

The position of the magnetic heads 11a, 11b is moved by the head mounting device when reproducing the recording track formed on the magnetic tape.
11b to scan accurately. In order to detect a so-called track deviation between the recording track and the scanning locus during reproduction, the magnetic heads 11a and 11b are oriented by head mounting devices 12a and 12b. 36 is an oscillator that generates a sine wave for orb ringing. The frequency of this sine wave is 450
Selected from [Hz] to 1 [KHz]. Addition circuit 37
A sine wave is superimposed on the correction voltage formed as described below, and the control voltage obtained from the adder circuit 37 is passed through an amplifier 38 to an FM modulator 39 converted into an IC.
was supplied to. The control voltage is FM modulated by the FM modulator 39 so that the center frequency becomes several +KHz, for example, 20 [KHz]. The modulated output of the FM modulator 39 includes upper sideband components distributed up to about 40 KHz, and has a frequency distribution as shown by diagonal lines in FIG. Indicated by the dashed line in Figure 5.
The modulated output is located outside the transmission band of the VTR.

Since the modulated output of this FM modulator 39 has a pulse waveform, it is converted into a sine wave by passing through a bandpass filter 40, and is passed through a rotary transformer via a class B amplifier 41 and a recording/reproduction changeover switch 42 that is turned on during reproduction. 24 primary coils 28a. The primary coil 28a is connected to the stator 25
b, and the secondary coils 28b, 28c
is wound around the rotor 25a. The modulated signal taken out from the tap of the secondary coil 28b is supplied via the limiter 43 to the FM demodulator 44 which is integrated into an IC, and the sinusoidal control voltage obtained from the FM demodulator 44 is supplied via the drive amplifier 45 It is added to the bimorph plate 13 of the head mounting devices 12a, 12b. The power supply voltage (for example, 10
(about [V]) is formed by the rectifier circuit 46 connected to the secondary coil 28b. Secondary coil 28
A rectifier circuit 47 is connected to c, and a relatively high power supply voltage of about 150 [V] generated by the rectifier circuit 47 is applied to the drive amplifier 45.

In order to detect track deviation, the reproduced signal obtained at the terminal 35 is supplied to a sampling and holding circuit 49 via a tuning circuit 48. Since the magnetic heads 11a and 11b are oblique, the amplitude of the reproduced signal also changes. The reproduced signal may be simply envelope-detected, but in order to eliminate factors other than track deviation, only the frequency component (for example, 3.5 [MHz]) corresponding to the horizontal synchronization signal component is extracted by the tuning circuit 48. A horizontal synchronizing signal separated from the reproduced video signal is applied from a terminal 50 and sampled and held, and the output of the sampling and holding circuit 49 is further supplied to a tuning circuit 51 tuned to the orb ring frequency.
The output of the tuning circuit 51 is supplied to a synchronous detection circuit 52, and synchronously detected by the output of the oscillator 36.
The output of the synchronous detection circuit 52 is passed through the low pass filter 53
A correction voltage is formed by smoothing the voltage. This correction voltage, whose level changes depending on the track deviation, is applied to the above-mentioned adder circuit 37.

With the above configuration, the magnetic head 11a or 11b accurately scans the recording track formed on the magnetic tape, thereby eliminating track deviation. In this case, the center value of the meandering scanning locus is made to coincide with the center of the recording track by the level of the correction voltage. Furthermore, during still motion image playback in which the magnetic tape is stopped during playback, or slow motion image playback in which the running speed of the magnetic tape is different from that during recording, the slopes of the recording track and the center value of the scanning locus may differ. Become something. Therefore, track deviation cannot be corrected simply by using a DC voltage as a correction voltage. Therefore, a correction voltage generation circuit 54 that generates a sawtooth wave (or triangular wave) voltage and a mode switch 55 that is turned on only during still and slow operations are provided.
During still and slow operations, a sawtooth (or triangular wave) voltage is supplied to the adder circuit 37.

A specific connection example of the configuration provided on the secondary side, that is, the rotating part, of the rotary transformer 24 in the above-described configuration is shown in FIG. In FIG. 4, instead of providing a tap on the secondary coil 28b of the rotating transistor 24, resistors 56a and 56b are connected in parallel, and the modulated signal obtained at the connection point of both resistors is transmitted without passing through the limiter 43.
It is supplied to the FM demodulator 44. diode 57
and a capacitor 58 constitute a rectifier circuit 46 that forms a low voltage power supply. In addition, the secondary coil 28c
diodes 59a, 59b and capacitor 60
A rectifier circuit 47 configured as a voltage doubler rectifier circuit consisting of circuits a and 60b is provided. If the number of turns of the primary coil 28a is 50 turns, the secondary coil 2
The number of turns of 8b is selected to be 50 turns, and the secondary coil 2
The number of turns of 8c is selected to be 500 turns. The drive amplifier 45 is composed of NPN transistors 61 and 62 with emitters grounded, and an NPN transistor 63a and a PNP transistor 63b in the output stage, and the DC component of the control voltage corresponding to the correction voltage is transmitted through a variable resistor 64 and a PNP transistor 65. It is adjustable. transistor 63
The respective bases and respective emitters of a and 63b are commonly connected via a resistor, a control voltage is applied from the collector of the transistor 62 to the common connection point on the base side, and a control voltage is applied to the common connection point on the emitter side via a capacitor 66. One electrode 1 of bimorph plate 13
9 is connected, and the other electrode 20 is connected to the collector of the transistor 63b. Further, a discharge resistor 67 with a large value is provided, and this discharge resistor 6
The residual charge on the bimorph plate 13 is discharged through the bimorph plate 7. During a period of the sinusoidal control voltage that is greater than the correction voltage (DC component), the transistor 63a becomes conductive, causing the electrode 19 to be positive and the electrode 2 to be positive.
A voltage in the direction that makes 0 negative is applied to the bimorph plate 13, and the capacitor 66 is charged, and the transistor 63b becomes conductive for a period smaller than the correction voltage, so that the voltage in the direction that makes the electrode 19 negative and the electrode 20 positive is applied. is applied to the bimorph plate 13. Since the direction of displacement of the bimorph plate 13 differs depending on the direction of the voltage applied between the two electrodes, the center value of the reproduction scanning locus moves in parallel according to the value of the correction voltage.

In order to drive the bimorph plates 13 of each of the head mounting devices 12a and 12b, both may be connected in parallel, or control voltages may be applied to each via separate transmission systems.

According to the present invention described above, since the sine wave is transmitted through the rotary transformer 24, spurious waves such as high-order harmonics are significantly less than in the chopping method, and there is no possibility that spurious waves will be mixed into the video signal system. can be avoided. In addition, since power can be obtained in the rotating part by rectifying a modulated signal with a constant amplitude, a drive amplifier can be placed inside the rotating part, and if a small amplitude modulated signal is transmitted. Furthermore, the reproducing amplifier can be disposed within the rotating section, and the reproduced signal once amplified by the reproducing amplifier can be sent out via the rotary transformer 21, thereby improving the S/N ratio of the reproduced signal. In addition to this, there are great advantages in that an arbitrary value of DC voltage can be obtained in the rotating part, such as making it possible to form an erase signal within the rotating part.

Note that the present invention can be applied to things other than correction of track deviation, and the control signal may be transmitted using a modulation method other than FM modulation such as PM modulation or PWM modulation.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view of a mechanical part of an embodiment of the present invention, FIG. 2 is an enlarged view of a head mounting device, and FIGS. 3 and 4 are a block diagram and a portion thereof of an embodiment of the present invention. FIG. 5 is a frequency spectrum diagram used to explain the present invention. 1 is a drum shaft, 5 is a rotating drum, 11a, 11
b is a magnetic head, 12a, 12b are head mounting devices, 13 is a bimorph plate, 21, 24 are rotary transformers, 39 is an FM modulator, 44 is an FM demodulator, 4
6 and 47 are rectifier circuits.

Claims (1)

[Claims] 1. A rotating head for recording or reproducing information signals;
An electromechanical transducer element constituting a mounting means for coupling the rotary head to the rotary part, a rotary transformer consisting of coils provided in the rotary part and the fixed part, respectively, and a control signal for controlling the position of the rotary head. a modulation circuit provided in the fixed portion and modulating a predetermined frequency signal using the control signal; a circuit provided in the rotating portion and configured to make the output signal of the modulation circuit a sine wave; and a demodulation circuit for demodulating the output signal of the modulation circuit supplied via a rotary transformer, and the output signal of the demodulation circuit is applied to the electromechanical conversion element to control the position of the rotary head. Position control device for rotating head. 2. The device according to claim 1, characterized in that it has a rectifier circuit that rectifies the output signal of the modulation circuit via a rotary transformer, and the output of this rectification circuit is used as a power source for the demodulation circuit. Position control device for rotating head.