CH634433A5 - Apparatus for automatic track setting for a signal reproducing device - Google Patents

Description

634433

PATENT CLAIMS

1. Automatic tracking device for a signal reproducing apparatus in which information-carrying signals recorded on a track (t) of a recording medium (T) are reproduced with a transducer (1) which is for reproducing the signals carrying the information along the track (t) is movable, a deflectable holder (2) for this transducer (1), with which the transducer (1) is deflected in a direction transverse to the track (t) in accordance with an electrical actuation signal (Sf), one Control circuit (6,9), which delivers a tremor motion signal (Sc) which, when applied to the deflectable holder (2) of the transducer (1), causes the transducer (1) to oscillate in the transverse direction about a zero position, an envelope rectifier (5) for rectifying the envelope (Sa) of the output of this converter (1) when it moves along the track (t) and oscillates in the direction transverse thereto, a device (22) z Ur synchronous demodulation of the envelope rectified by the envelope rectifier (5) by means of a signal (Sg) which has the frequency component of the signal frequency of the jitter motion signal, so that a tracking error signal (S ^) is achieved which, with respect to the transverse direction, resets the converter (1) from the center of the track (t), and with an adding circuit (8), which adds the tracking error signal (Sk) with the jitter motion signal (Sc), so that it delivers an electrical drive signal (Sf), characterized that a deflection signal generator (11,

12 or 11 ', 29) is present, which generates the deflection signal (Sg) in accordance with the deflection of the transducer (1) with respect to a rest position, and that the device (22) for synchronous demodulation is designed so that it detects that of the Envelope rectifier (5) rectified envelope (Sb) synchronously demodulated with respect to the deflection signal (Sg), so that the control signal (Sf) of the adding circuit (8) can keep the zero position of the converter (1) in precise alignment with the center of the track (t) .

2. Device according to claim 1, characterized in that the device for synchronous demodulation of the envelope signal rectified by the envelope rectifier (5) has a multiplier circuit (22), at the inputs of which the envelope curve rectifier (5) rectified envelope signal (Sb) and the deflection signal (Sg) are created.

3. Device according to claim 2, characterized in that the multiplier circuit is formed by a push-pull modulator (22).

4. Device according to one of claims 1 to 3, characterized in that the control circuit further comprises a first bandpass filter (21) via which the envelope signal (Sb) rectified by the envelope rectifier (5) to the device (22) for synchronous demodulation thereof Signal and that it has a second bandpass filter (19), via which the deflection signal (Sg) is applied to the device (22) for synchronous demodulation of the rectified envelope signal, both the first and the second bandpass filter (21 and 19 ) have a pass band in which the lower limit frequency is a fraction of the frequency (fc) of the jitter motion signal (Sc) and in which the upper limit frequency is less than twice this frequency (fe) of the jitter motion signal.

5. Device according to one of claims 1 to 4, characterized in that the control circuit further comprises a bandstop filter (23) through which the tracking error signal (Sk) is applied to the adding circuit (8), to which the dither motion signal is also applied , wherein the bandstop filter serves to eliminate a predetermined frequency band, the center of which is twice the frequency (fc) of the jittering motion signal (S0).

6. The device according to claim 1, characterized in that the deflectable holder of the transducer has a support arm (2) carrying the transducer (1), which can be deflected in the transverse direction, the deflection signal generator (11, 12 or 11 29) with this Support arm (2) is connected to generate the deflection signal (Sg) in accordance with the deflection of the support arm.

7. The device according to claim 6, characterized in that the deflection signal generator has a capacitive sensor (12) which has a fixed electrode (12a) and a movable electrode (12b) located on the support arm (2), and that it has an amplifier circuit ( 11) which has a high input impedance and which is connected to the capacitive sensor (12) in order to generate the deflection signal (Sg) in accordance with the capacitance changes which result from the displacement of the movable electrode (12b) with respect to the fixed electrode ( 12a).

8. The device according to claim 7, characterized in that the deflection signal generator further comprises an electrical shield (20) which the amplifier circuit (11)

surrounds it in order to shield it from the electrical field which results when the control signal (Sf) is applied to the deflectable holder of the converter.

9. The device according to claim 6, characterized in that the support arm (2) consists of a bimorph crystal, which is clamped at one end and at the other end of the transducer (1) is attached, wherein the electrical control signal (Sf) on the bimorph crystal (2) is applied in order to bend it and thus cause a deflection in the transverse direction.

10. Device according to one of claims 6 and 9,

characterized in that the deflection signal generator has a strain gauge (29) which is attached to the support arm (2) so that it is stretched in accordance with the deflection of this arm, and in that it has a circuit (36,37) which has a deflection signal (Sg) generated according to the strain of the strain gauge.

11. The device according to claim 10, characterized in that the strain gauge (29) is constructed with a resistance wire so that it provides a resistance varying with its elongation, and that the circuit for generating the deflection signal (Sg) has a constant current source (36) which is connected to the strain gauge (29) to generate a voltage signal which changes with the resistance, and that an amplifier (38-41) is present for amplifying this voltage signal.

12. The device according to one of claims 9 to 11,

characterized in that the bimorph crystal (2) has a first and a second piezoceramic element (2a, 2b) and a central, intermediate electrode (2c), the transducer (1) and the strain gauge (29) on the outer surface of the second Piezoceramic element (2b), which is connected to ground, and that a circuit (42a, 42b, 43a, 43b) sends the control signal (Sf) to the first piezoceramic element (2a) and to the central electrode (2c) creates.

13. The device according to one of claims 1 to 12,

characterized in that the recording medium is a magnetic tape (T) on which the track (t) extends in the oblique direction and on which follow similar tracks which are parallel to one another and in which information signals are recorded, the tape being helical over at least one Part of the periphery of a guide drum (25) extends and can be moved in the longitudinal direction and wherein at least a part (26) of the guide drum (25) is rotatable, and that the transducer is a magnetic head (1) which can be moved by means of a deflectable holder (2 ) is attached to the rotatable part of the guide drum so that it can rotate with it and in this way during the forward movement

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When the tape is scanned, the tracks are added and the oscillation or jitter signal is added near them, so it leads. cause the zero position of the transducer to the center of the

Track is aligned.

It can be seen that in the proposed automatic tracking system described above 5, the output of the envelope rectifier contains various undesirable frequency components related to mechanical; The invention relates to a device for automatic vibration of the bimorph crystal carrying the head, tracking for a signal reproducing device, such as it can be traced back to the top; Such undesirable frequency compo term of claim 1 is specified. Ions have an unfavorable effect on the accuracy of what is received

It is known to record video signals or other information-tracking error signals when the output of the envelope-matching signals along successive, parallel rectifiers with the constant dither signal in the amplitude tracks that cross or skew on a magnetic modulation -Synchronous detector is compared.

band run, as is the case, for example, in a video tape- The occurrence of difficulties caused by the mechanical

advises (VTR) according to the oblique writing method (helical scan-see 15 oscillation of the bimorph crystal, which drive) is the case. There has already been proposed a system that carries a playback head or transducer, for example in which a signal transducer for information or US Pat. No. 4,080,636 has been recognized. In the apparatus disclosed in this data, such as a rotating magnetic head, continuously, the output of the rewinder is held in a desired position which processes on the transducer or transducer in the manner described above, or the traces of the recorded signals at 20 ; the output is related to an envelope rectifier video tape recorder using the helical track method. Such a system is, for example, in the meantime that is applied to the bimorph crystal, so that published Belgian patent application 77.03797, which receives a tracking error signal, finally leads to the dither signal on U.S. Patent Application Ser. No. is added to correspond to a drive signal for the bimorph crystal 669 047. Obtained from the earlier one. In addition to the foregoing, the striking system, when scanning the track, discloses the position of the latter patent, a negative feedback circuit, with which the information signal converter or the head with respect to which an electrical damping signal is obtained, monitors the track by means of the reproduction of the recorded also applied to the bimorph crystal is so that the information signal is damped during the transducer vibrations via the transducer, in particular in the case of its gene element in the form of a piezoelectric bending element resonance frequency. In the device described, the mentes, such as a bimorph crystal, a small oscillation-electrical damping signal from a signal generator or movement or a “tremor” (dither) is given. The tremor derived from a sensor that ver with the bimorph crystal

Movement is tied to by a suitable modulation signal to produce a signal representative of the bimorph crystal, which causes the transducer to be transversely instantaneous deflection of the transducer, and which swings around its scan track using the 1 direction. The oscillation of the 35 of a differentiator into a converter speed signal converter is converted in the envelope of the reproduced informa. The converter speed signal through-tion signal, which occurs when the recorded one is sampled, then runs a low-pass filter, which produces the signals that give the track deviations. These deviations resonances of second and higher order of the bimorphic crystal

have the shape of an amplitude modulation of the envelope curve stable, dampens; this is followed by a network for the reproduced signal, the change in the size 40 phase shift with which the phase of the filter from the envelope, which is representative of the amount of the transversely received signals, is shifted such that these signals, displacement of the converter relative to its optimal or its Frequency is close to the resonance frequency of the bimorph centered position with respect to the track, and where the Rieh crystal lies, have a resulting phase shift of 0 ° towards the transverse displacement of the transducer. Finally, the output of the phase pre-optimal position is applied by the phase of the amplitude shift network to an inverting or counter-modulation of the envelope with respect to the fundamental frequency of the coupling amplifier, so that one characterizes a damping signal oscillation or jitter movement. In order to receive the information about the position of the transducer or of the control signal described above is added. That for the current deflection of the

To obtain the magnetic head, the signal representative of the transducer, which is obtained from the signal generator or sensor connected to the bimor-obtained modulated high-frequency envelope signal to a so-called crystal, is fed to the amplitude modulation envelope rectifier, and is therefore used only to obtain the feedback signal or which uses the fundamental frequency and the sidebands of the dither electrical damping signal with which the signal is recovered; the output of the envelope-like mechanical vibration of the bimorph crystal at its rectifier is damped by a synchronous detector for the amplitude-mo resonance frequency. This attenuation eliminates supply to the amplitude and polarity of the 55, but does not correct such inaccuracies that occur in the envelope rectifier's output with respect to the tracking error signal due to the fact that the original or constant oscillation or Zifter tracking error signal results from a comparison of the steady tremor

Signal, by which the head is simultaneously excited to transversal vibration signal with which obtained after envelope rectification, is determined. The amplitude-modulated reproduction signal of the head or transducer, which supplies the synchronous detector, provides a tracking error signal which is added to the oscillation-60 mechanically induced vibrations or other unions or tremors signal, so that a drive desired frequencies are compared .

signal results, with which the oscillation of the head or wall- object of the invention is accordingly a device

lers is effected. In general, the amplitude of the tracking for automatic tracking must be specified, with which error signals proportional to the transverse distance between what has been achieved so far, a higher degree of seeing the zero position of the oscillating head to the center 65 accuracy is achieved in tracking. The track, while the polarity of the track error signal on this device with a simple and easy-to-produce direction of such a displacement of the zero position relative to the arrangement, should enable precise track adjustment. Further-indicates the center of the track. If the tracking error signal is to cause interference caused by mechanically induced or

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other undesirable vibrations can occur can be avoided.

This object is achieved with a device for automatic track adjustment as specified in the preamble of patent claim 1, which is designed according to the invention in the manner specified in the characterizing part of patent claim 1.

In the case of a signal reproducing device which is provided with the device according to the invention, a transducer for reproducing the recorded signals is moved along the recording track; automatic tracking control or scanning is achieved in that a deflection device is provided, on which the reproduction transducer is mounted, and which deflects the transducer in a direction transverse to the direction of the track in accordance with an electrical control signal; the deflection device can consist of a bimorph crystal. There is also a deflection signal generator with which a deflection signal is generated in accordance with the deflection of the transducer in the transverse direction against its rest position; the deflection signal can be formed in particular in accordance with the change in the capacitance value of a capacitance which consists of a fixed electrode and an electrode attached to the deflection device, or also in accordance with the elongation of a strain gauge attached to the deflection device. Furthermore, there is a control circuit for emitting a dither signal, which is applied to the deflection device for the transducer and by which the transducer is caused to oscillate in the transverse direction about a zero position. The control circuit also includes an envelope rectifier that rectifies the envelope of the output of the transducer as it moves along the track and oscillates in the transverse direction; the control circuit may further include an arrangement for synchronous demodulation of the rectified envelope signal by means of the deflection signal, so that a tracking error signal is obtained which precisely identifies the deviation of the zero position of the transducer from the center of the recording track, with respect to the transverse direction; the device for synchronous demodulation can in particular have a multiplier circuit. Finally, the control circuit contains an adder, with which the tracking error signal is added to the oscillation signal for the trembling movement, so that this results in an electrical control signal for the transducer deflection device, by means of which the zero position of the transducer is aligned with the center of the recording track. "

The tracking error signal is thus obtained by means of a comparison of the output signal of the reproduction transducer resulting from the rectification of the curve with the control signal; Both the signal of the playback transducer and the deflection signal can contain frequency components that result from mechanical vibrations of the bimorph crystal or another carrier of the transducer, so that these undesirable frequency components that result from mechanical vibrations or the like are automatically removed from the tracking error signal by canceling each other out.

In one embodiment of this invention, the device with which the deflection signal is generated in accordance with the deflection of the transducer contains a capacitance which is formed from a fixed electrode and an electrode attached to the bimorph crystal or the carrier of the transducer, so that the Capacitance value of this capacitance changes with the deflection of the transducer in the transverse direction; it also contains an amplifier circuit which has a high input impedance and which is connected to the variable capacitance, so that it generates the desired deflection signal in accordance with the change in capacitance which is due to the

Displacement of the movable electrode with respect to the fixed electrode results.

In another embodiment of the invention, a strain gauge is provided to generate the deflection signal, which is attached to the bimorph crystal and which is stretched in accordance with the deflection of the transducer; a circuit is also provided with which the resulting change in the resistance of the strain gauge is converted into a corresponding voltage change in the output or the deflection signal.

The invention is described and explained in more detail below on the basis of preferred exemplary embodiments and the figures.

Fig. 1 shows a schematic block diagram illustrating an automatic tracking device according to the prior art;

Fig. 2 is a schematic illustration showing a part of a magnetic tape on which there is an inclined recording track, the path of the playback head or the transducer being shown in broken lines;

Fig. 3 is a graphical representation of the output of a playback head or transducer which scans the recording track in the manner shown in Fig. 2;

Fig. 4 is a schematic diagram showing an automatic tracking device according to an embodiment of this invention;

5A through 5E show waveforms referred to in explaining the operation of the system of FIG. 4;

FIG. 6 is a schematic diagram showing an automatic tracking device according to another embodiment of this invention, and FIG. 7 is a circuit diagram showing details of a part of the system shown in FIG. 6.

With reference to the individual figures, first of all to Fig. 1, it can be seen that in the known device for tracking adjustment which is disclosed in the aforementioned Belgian patent application no. 77.03797, each rotary magnetic head 1 in a video tape recorder using the helical track method the rotatable part of the usual guide drum (not shown) is mounted by means of a bimorph sheet 2, which can bend in the axial direction of the guide drum. In a known manner, video signals or other information-carrying signals are recorded in successive parallel tracks which run transversely or obliquely on the magnetic tape T, as is indicated, for example, in FIG. 2 with respect to a single recording track t. Thus, when the recorded magnetic tape T is guided in a helical track around part of the circumference of the guide drum, the magnetic head 1 can scan the recording track t.

In order to keep the magnetic head 1 continuously in a desired position with respect to the recording track t in the known device for track adjustment according to FIG. 1, the position of the head 1 is monitored during the scanning of the track by evaluating the playback signals Sa of the head 1, while a small one oscillating movement or a “tremor” is applied to the head 1 by means of a control signal Sf to the bimorph crystal 2. The resulting oscillation of the head 1, which runs according to the dashed lines la in Fig. 2 transverse to the track t, leads to fluctuations in the envelope of the reproduced video signal or another information-carrying signal Sa (see. Fig. 3) that results from the scanning of the track by head 1. These deviations take the form of an amplitude modulation of the envelope curve of the reproduction signals Sa, the change in the size of the envelope curve being characteristic of the amount of the transverse displacement of the head 1 compared to its optimum

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or centered position with respect to the track t, and being between 0.2 and 0.5 mm.

the direction of the transverse displacement of the head. The circuit 11 also contains an amplifier with high input

the phase of the amplitude modulation of the envelope curve in that of the converter 12 in relation to its optimal signal conversion position due to gearing impedance for converting the capacitance changes into a corresponding voltage signal, which is the fundamental frequency of the trembling movement. For the 5 also changes in a suitable manner to thereby

Obtaining the above-described information about the position directly and without delay the deflection of the head 1 from the development of the head are reproduced in the known device for its rest position. 1 contains the playback signals Sa of the Kop- illustrated embodiment of the invention, the circuit 11 fes 1 via a playback amplifier 3 to an output resistors 13 and 14, which are connected in series between the fixed elec processes the reproduced video signal, and io trode 12a and the gate electrode of a junction field effect are connected to an envelope rectifier 5 for the amplitude module transistor (FET) 15; the FET15 serves as an amplifier,

tion laid, which regains the fundamental and the sidebands of its source-sink circuit with the connections Vi and V2 of the signals of the trembling movement. The output signal power supply is connected via a resistor 16. A signal Sb of the envelope rectifier 5 is connected to a synchronous second FET 17, which is applied as a high resistance, for example as a detector 7 for the amplitude modulation, which is intended to serve for the resistance of more than 10 M ohms, with an output signal Sb of the envelope rectifier the amplitude of its source and sink electrodes connected to the connector and the polarity with respect to the original or constant point of extension between the resistors 13 and 14, jitter motion signal Sc, with which the head 1 is too transverse while the other sink and Source electrode is exposed to len vibrations. The synchronous electrode and the gate electrode of the FET 17 are connected to the voltage supply tector 7 for the amplitude modulation by a tracking error connection V2. The output signal falling at the resistor 16, which is applied to an adder circuit 8, drops via a capacitance 18 to a dither signal Sc there, which has a frequency fc of approximately 450 Hz bandpass filter 19. An electrical shield 20 has to be added. The resulting sum signal Se envelops the amplifier 11, and this is fed to a driver amplifier 9 in order to shield the drive electric field which is obtained for the bimorph crystal 2 when the signal Sf is applied. 25 control signal to the bimorph sheet 2, where the

In general, the amplitude of the tracking error signal Sd per head 1 is mounted.

proportional to the transverse distance between the zero position. According to the known device for tracking the oscillating head 1 and the center of the deposition, which was described with reference to FIG. 1, constant track t becomes, while the polarity of the track error signal Sd the at of the device 10 according to the invention indicates the frequency mod direction of this offset between the zero position of the playback signal or output signal Sa of the head 1 head from the center of the track. If the track error signal Sd is added to the dither motion signal Sc via a reproduction amplifier 3 to an output circuit 4, it is applied to an envelope rectifier circuit 5. This helps to align the zero position of the oscillating head 1 signal Sa is amplitude-modulated with an oscillator to the center of the track t. However, there is a detection signal Sc of the fixed frequency fc, which is provided by an oscillator, that in the system shown in FIG. 1 each mechanical mechanism is supplied and that has a frequency of approximately 450 Hz, see oscillation of the bimorph crystal 2, which carries the head 1 The amplitude fluctuations of the output of the envelope curve leads to the fact that the output of the envelope curve rectifying signal Sb (FIG. 5A) give, among other things the tracking errors again, which between 5 different undesired frequency components see the path of movement of the head 1 and the tracks t. If such an envelope envelope output signal Sb which are sampled by the head exist. However, the envelope converter 5 in the amplitude modulation synchronous detector 7 40 sense signal Sb contains, in addition to the tracking error information, with the constant dither motion signal Sc of the festoscilla- the frequency of the oscillation signal fc undesired fre tors 6, which of course is compared to this by mechanical components, for example frequency components if the oscillation does not contain the undesired frequency of the first and second resonance frequency and does not contain the anti-component, then the tracking error signal Sd obtained from the modulation resonance frequency of the bimorph crystal 2 and the various detector 7 is caused by the undesired other frequency components influenced by transient frequency components and the accuracy of the processes. Such unwanted frequency component tracking is affected. adversely affect the detection and correction of the

In Fig. 4, to which reference will now be made, tracking error between the track of the head 1 and the track t are those parts which already exist with reference to Fig. 1 of the magnetic tape.

The envelope signal Sb of the envelope demodulator 5 can be seen from FIG. 4 that a device is used to apply a bandpass filter 21 which is adapted to automatic tracking 10 according to the invention it transmits a frequency band, the center of which quickly moves when the head 1 trembles from a rest position which is determined by the frequency fc, and which is determined by the bimorph crystal 2 carrying the tracking error information. In particular, the upper limit frequency and precisely determined with the deflection signal generator circuit 11 of the bandpass filter 21 is selected so that it is somewhat lower. In the exemplary embodiment shown, the frequency 2fc, while the frequency fc around a multi-circuit 11 contains a capacitive converter 12 with a fixed elec- tricity greater than the selected lower cut-off frequency of the filter 12a, which is suitably at the free end of the bimorph ters 21. The resulting output signal S'b of the bandpass film crystal 2 is mounted and a movable electrode 12b, ters 21 is applied to an input of a multiplier circuit 22 which is mounted on the crystal 2 so that it is the fixed elec- created, for example, opposite from a push-pull modulator trode 12a; can be constructed when the head 1 is displaced and which has a further input, on which the output S'g of the bandpass filter 19 is applied in a track transverse to the track scanned by the head. The capacitance of the converter 12 thus changes in direction. The bandpass filter 19 has essentially the same inverse to the distance between the fixed electrode 12a and the characteristic as the bandpass filter 21 described above; the movable electrode 12b connected to the ground. In 55 the filter 19 is thus designed in such a way that a frequency band, the practical center of which is the center of the jitter movement frequency fc, is passed through the electrode 12a square with a side length of 3 to 4 mm. In the case of the deflection signal Sg (FIG. 5B) from the amplifier 11 and the distance between the electrodes 12a and 12b, this is the momentary deflection of the head 1 from a rest position.

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Läge corresponds, the frequency component fc, the circuit 8 applied to a drive amplifier 9 to this

Vibration of the bimorph crystal 2 corresponds to a saw-way to achieve a control signal Sf with which the bimorph tooth signal S; be superimposed, which is controlled in a slow-motion or crystal so that the zero position of the head 1,

Still image reproduction of the recorded video signals on which the bimorph crystal 2 is applied in a direction transverse to the direction of the recording track. In the absence of such a direction, the direction of the center signal Sj would correspond to the scanning path of the head 1 in one of the recording tracks.

6 are those parts that are already referring to the direction of each of which in FIG.

Head-scanned recording track t is related. 4 have been described, with the same

In any case, the filter 19 is able to provide reference numerals from the signal. FIG. 6 shows an automatic S'g (FIG. 5C) which indicates the deflection and which occurs at its exit tracking system 10 'after a further embodiment, the low-frequency component of each of such forms of the invention; remove the sawtooth waveform Si from the rotary head or transducer. The guide drum assigned to signal S'g is shown in dashed lines and still contains undesired frequency components, provided with the reference symbol 25. Such a guide play resonances of the first and second order and of drum arrangement 25 contains an upper rotatable drum anti-resonance of the bimorph crystal 2 and various 15 melteil 26 and a stationary lower drum part 27, two other frequency components, which are due to transient behavior one in the radial Direction of open slot 28 is formed along which circumference lies in addition to the components of the trembling frequency. The piezoceramic FC can be evoked. Since the deflection signal Sg or S'g bimorph crystal 2 is based with its base or its inner more the deflection of the head 1 from its rest position end on the bottom surface of the rotating upper drum part than the position of the head 1 with respect to the center 20 26 attached so that the magnetic head 1 on the free outside of the scanned track t, it can be seen that the deflection signal is fixed to the end of the bimorph crystal 2 and does not extend through the S'g applied to the multiplier 22, no slot 28; it will contain information regarding the tracking error in the vertical direction. It is to be emphasized, parallel to the axis of rotation of the upper drum part 26, that the frequency, phase and amplitude of the undesired measure of the deflection of the bimorph crystal 2 move the frequency components which occur in the deflection signal S'g when this bimorph crystal 2 the dither signal Sf is stopped, essentially the respective frequency, phase is set. A magnetic tape, not shown, is screw-shaped and the amplitude of the corresponding, undesirable streak, i.e. at an angle to the plane of the slit 28, to correspond to a sequence component which is contained in the envelope signal essential part, for example by one half of the circumference S'b, which is obtained from the filter 21. the drum 25 is wound so that when the upper

The multiplier circuit 22, which - as already mentioned 30 drum part 26 the head also rotates and has become oblique - can be a push-pull modulator, delivers the scanning from the above across the belt; at the same time creating an output signal Sj (Fig. 5D), which represents the difference or moves or oscillates the head 1 in a to -sampling-the sum of the frequencies of the signals, which is directed to the middle perpendicular direction according to the deflection of the inputs the multiplier 22 are applied. bimorph crystal 2.

The multiplier circuit 22 thus serves to compute the components 35 in a device for automatic tracking with the trembling frequency fc and with the low frequency 10 'according to this invention, a strain gauge 29 at desired frequencies, for example the resonances of the surface of the bimorph crystal 2 attached so that it and second-order and the anti-resonances of the bimorph is stretched according to its deflection. The strain crystal 2 to remove from its output signal Sj. The knife works together with an assigned circuit 11 ', the resulting output signal Sj contains the information relating to 40 to generate the deflection signal Sg, the magnitude and the amount of the tracking error and also a frequency component in the direction of the deflection of the head 1 from its rest position -with the frequency 2fc, which indicates from the multiplier circuit 22 lung. In the system 10 'shown in Fig. 6, that which is generated and which is removed in a bandstop filter 23, the deflection signal generating circuit 11' and a reproduction-The filter 23 is designed so that it is for a frequency band amplifier 3 for amplification of the output signal of the head locks, the center of which is at the frequency 2fc and 45 fes 1 are contained in a circuit 30, which suitably compared to this frequency only a fraction of the frequency within the upper rotatable drum part 26 of the frequency fc extends above and below. Thus one gets arranged from rung drum.

the band-stop filter 23 a track error signal Sk (FIG. 5E), which can be seen from FIG. 7 that the playback signal represents the deviation of the head 1 from the scanned recording track of the magnetic head 1 by the playback amplifier 3. In an alternative embodiment, the 50 can be strengthened and then, with the aid of a converter 31, replaced by the band-stop filter 23 by a low-pass filter, the circuit arrangement 30 in the upper drum part 26 of which characteristic is selected such that it is compared to the 2fc-Fre - will wear. Furthermore, the circuit sequence component is blocked according to FIG. 7. arrangement 30 provided with slip rings 32 and 33 on which

The track error signal Sk is applied via an amplifier 24 to each brush, which in turn is applied to an operating voltage adder circuit 8, in which it is connected to the jitter voltage source or to a ground line. It supply signal Sc of the oscillator 6 is added. Furthermore, further slip rings 34 and 35 can be provided, to which a sawtooth signal Sj is applied to the adding circuit; a ■ if brushes are present, which will feed or remove the deflection signal Sg and the control signal Sj in the case of a slow-motion or still picture signal Sf.

Playback mode of the video tape device applied to the The strain gauge, such as a resistance wire,

Angular deviation of the path of the rotary head 1 with respect to eo is provided in FIG. 7 with the reference number 29 and is connected with the longitudinal direction in each recording track t circle 11 '; it is also to be compensated with the reference in FIG. 7; This angular deviation results from the symbol 29 ', which is intended to show that it is based on the fact that the speed of the longitudinal front is attached to the bimorph crystal 2.

upward movement of the tape T in slow motion or still picture- The resistance wire 29 undergoes a change in its

Playback mode deviates from the normal locomotion resistance value corresponding to the deflection or bending speed of the tape when recording each take on the bimorph crystal 2 to which it is attached. The taking track t makes a difference. Finally, as in the previously known system 11, which is connected to the strain gauge 29, the output of the adder contains a field effect transistor 36 which is connected between the grinding

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ring 32 and the strain gauge 29, so that it serves as a contact to the inner end of the bimorph crystal 2 at the above-current source for the strain gauge. The change ren drum part 26 is attached. It can also be seen that that of the resistance value of the strain gauge 29, that of the magnetic head 1 and of the strain gauge, which in FIG.

Deflection of the bimorphic crystal 2 occurs, is denoted in one, attached to the top of the bimorphic crystal 2.

speaking voltage change, which are acc. 5 connected to ground. Accordingly, strengthening by an amplifier 37 forms the deflection signal Sg, the deflection signal Sg, which corresponds to the deflection of the head 1

The amplifier 37 contains an operational amplifier 38, which corresponds to its rest position and does not correspond to the control

Resistors 39 and 40 and a capacitance 41; its output signai Sf), which is assigned to the bimorphic crystal 2,

is connected to the slip ring 34. gei the circuit shown with which the drive

6 that the device 10 'signai Sf is applied to the bimorph crystal 2, the pie

Similar to the device 10 described earlier, is made with ceramic elements 2a and 2b in mutually opposite

Taking the part by which the deflection signal Sg is generated. polarized set direction, and the diodes 42a and 42b as well

In the device 10 ', the frequency-modulated re-Zener diodes 43a and 43b ensure that the control

After passing gnaj gs, the output signal Sa of the head 1 does not cause any depolarization of the elements 2a and 2b.

of the playback amplifier 3 can with the help of the converter 31 to 15 fen.

the envelope rectifier circuit 5 is applied, and the resultant It should be noted that in the case of a device output or envelope signal Sb_, the multiplication bandpass filter 21 is passed through the device 10 or 10 'according to this invention, so that a signal S'b receives the device or the push-pull demodulator 22, a comparison or the one input of the multiplier circuit or a synchronous demodulation of the envelope-type push-pull modulator 22. Furthermore, the envelope judge signal S'b developed by the judge 5 is executed with the deflection-deflection signal Sg via the slip ring 34 to a bandpass filter signal S 'g which supplies the current position of the head 1 19, and the resulting signal S'g is sent to the represents and thus all unwanted frequency components, other input of the multiplier 22 is applied. An output Sj of the multiplier 22 which is also contained in the envelope signal is closed via the band. There is a difference to the known blocking filter 23 supplied to the adder circuit 8, to which the 25 system according to FIG. 1, in which the multiplier circuit or dither motion signal Sc of the oscillator 6 and the sawtooth push-pull demodulator 7, the envelope signal Sb with the Signal Si are applied in order to compare an added signal Se to obtain a constant dither motion signal Sc which is the first one which is applied to the drive amplifier 9. The desired frequency component, which therefore supplies a drive signal Sf for vibration or the like of the bimorph sheet 2 resulting from the mechanical movement of the amplifier 9, does not contain the bimorph crystal 2. 30 hen. Because of this difference, the

As shown in detail in FIG. 7, the head 1 multiplier circuit or push-pull demodulator 22 in supporting bimorph crystal 2, preferably from an upper one of the device according to the invention, is automatically the

and a lower piezoceramic element 2a or 2b, the desired frequency components in the output signal Sj,

are provided with external electrodes and a central one so that as a result the signal Sk accurately tracks the error

Electrode 2c constructed, which is between the elements 2a 35 and is due to this relatively simple device and 2b. Furthermore, the control signal Sf is permitted via the head 1 automatically in the optimum

Hold slip ring 35 directly against the outer electrode of the lower pie-scan position.

ceramic element 2a created; it is also said that for the movable support 2 of the head 1 in a voltage divider, which has been indicated by diodes 42a and 42b and the foregoing, that it consists of a

Zener diodes 43a and 43b, to which central electrode 2c consists of 40 bimorph crystal, it goes without saying that this bimorph crystal 2 is applied. The outer electrode of the carrier 2 can also be made of any other piezoelectric element.

upper piezoceramic element 2b of the bimorphic creme, consisting of a magnetostrictive element or a stable 2, is connected to ground, for example via a carrier 44, a voice coil element can exist.

G

3 sheets of drawings