CH656705A5 - METHOD FOR CONTROLLING THE RECORDING OPERATION IN A RECORDING APPARATUS AND APPARATUS FOR IMPLEMENTING SAME. - Google Patents

Description

A method and apparatus for controlling the recording operation in a rotating head recording apparatus is provided.

A rotating head recording apparatus is a type of device used in particular in the field of magnetic video recording (video recorder) and its conventional embodiment comprises a rotating head assembly, on which are mounted a plurality of heads. 'recording-reproduction. The rotating head assembly is disposed in a spacing relationship to a magnetic tape recording medium. When the assembly rotates, the recording-reproduction heads mounted magnetically by recording thereon data tracks.

Some acoustic recording devices (tape recorders or tape recorders) with fixed recording heads have downstream control heads, which check the recording during playback and actually play back the entire recording . In a rotating head recording apparatus, it is much more difficult to have a particular rotating head tracked by a control system. One of the methods that could be envisaged would be to provide a second set of recording-reproduction heads mounted in a second set with rotating heads and which would in fact reproduce the entire recording. Such a process is too expensive and too ineffective to be practical. Currently, in the prior art, there is no means for economically and effectively controlling the performance of a recording arrangement or for ensuring continuous optimization of the recording process in a recording apparatus with rotating heads.

The invention aims to avoid the drawbacks indicated above.

The method according to the invention is characterized in that it comprises the operations consisting in:

applying a selected calibration signal to a rotating head during the recording operation, and thereby recording said signal on a specially provided area of an associated recording medium;

placing a stationary head downstream of said rotating head and adjacent to said intended area of the recording medium; and detecting said calibration signal recorded by said stationary head during said recording operation.

The present invention also relates to an apparatus for carrying out the method according to the invention, which is characterized in that it comprises means for generating a chosen calibration signal; means for applying said calibration signal to a rotating recording head for recording said calibration signal on an intended area of a coordinated recording medium; and an

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stationary recording head placed downstream of said rotating head and adjacent to said provided area of said recording medium for detecting said recorded calibration signal.

The invention will be better understood on reading the detailed description which follows and on examining the appended drawings, which represent, by way of non-limiting example, an embodiment.

In these drawings:

Figure 1 is a schematic representation showing the relative orientation of a rotating head assembly, a control head and a magnetic tape medium in a rotating head recording apparatus;

Figure 2 is a view taken along line 2-2 of Figure 1; Figure 3 is a view similar to Figure 2, but showing the assembly with rotating heads in a different position;

FIG. 4 is a simplified symbolic diagram of a particular embodiment of the present invention making it possible to control the performance of a recording assembly in a recording apparatus with rotating heads;

FIG. 5 is a time diagram associated with the simplified symbolic diagram of FIG. 4;

FIG. 6 represents a variant of the symbolic diagram of FIG. 4, making it possible to obtain automatic and continuous optimization of the recording arrangement in a recording apparatus with rotating heads;

Figures 7a and 7b are time diagrams associated with the assembly shown in Figure 6;

FIGS. 8a-c represent waveforms useful for describing the operation of certain parts of an apparatus according to the invention; and Fig. 9 is a characteristic curve of the type of reproduction output level as a function of the recording excitation level.

The main features of the present invention are a method and an apparatus for monitoring the performance of a recording arrangement.

The methods and apparatuses mentioned above take advantage of an area of a magnetic tape support, an area which will be designated here - under the name of "duplication area". The duplication area of the magnetic tape medium receives a recording only when two adjacent recording-reproduction heads, the first having just recorded a data track on the moving magnetic tape and the second being about to record. such a track, are both in nominal contact with the moving magnetic strip. Normal input data is recorded on a track of the moving magnetic tape when an individual recording-reproducing head scans the tape medium. When a recording-reproducing head is above the duplication area, no useful input data is recorded on the magnetic tape medium by one of the heads, but such data is recorded by the other.

A first variant of a method according to the invention comprises a cut-off of the normal input channel connected to one of the recording-reproduction heads when a head of this type is located above the duplication areas of the moving magnetic strip and the switching of a calibration signal on this head. The calibration signal is preferably periodic, of constant amplitude and of variable phase and has a wavelength the value of which is within the range of the wavelength values of the data signal. The calibration signal is recorded on the tape medium by each recording-reproducing head in turn as it passes through this duplication area. When these recorded signals are subsequently sampled or detected, they are used to reconstruct a signal proportional to the amplitude of the original calibration signal as recorded by this particular recording-reproducing head. This reconstruction results in the production of a generated signal indicative of the performance of the recording assembly. The signal generated is applied to a control means which makes it possible to use it in a form understandable to the machine or to humans. This process provides continuous and automatic verification of the performance of the recording arrangement for each recording-reproducing head of a recording device with rotating heads.

A second variant of a method according to the invention uses the system described above. Essentially, the recording excitation level of a particular recording head is varied according to a determined program, which intervenes exclusively during the time during which this recording head crosses the zone of duplication of the magnetic tape. in motion and records the calibration signal in this area. The resulting generated signals previously described can then be used to locate certain points on the characteristic curve of the recording system obtained by bringing the reproduction output level as a function of the recording excitation level and, more particularly, to determine the optimal recording excitation level, which ensures that a reproduction output level chosen for current head / tape conditions is obtained. Once the desired recording excitation level is determined for a particular recording-reproducing head, the recording excitation level during the active part (data) of the passage of this head is made equal. at this value. Meanwhile, during the calibration part of the head passage, the tests to determine the optimal value continue. This process takes place separately and continuously for each individual recording-reproduction head and ensures continuous and automatic optimization of the recording excitation level for each head.

30 Reference will now be made to FIGS. 1-3, in which a set of rotating heads 10, a magnetic strip support 12 and a control head 14 are shown. The set of rotating heads 10 comprises a plurality of heads. recording-repro-duction 16a-f and rotates in the direction indicated by the arrow 18. The magnetic tape support 12 has a plurality of tracks 20a-f, which repeat for each complete revolution of the assembly 10, defining a sequence of tracks 22. Each of the tracks 20a-f is associated with one of the heads 16a-f, respectively. Safety margins separate tracks 20a-f to prevent overlap and dia-40 speech. The support 12 further comprises a pair of duplication zones 24a and 24b defined when two of the heads 16a-f are adjacent to the support 12 (FIG. 3), while the latter moves in the direction indicated by the arrow 26. As described below, the control head 14 has a gap 28 oriented perpendicular 45 to the longitudinal movement of the strip.

Each of the heads 16a-f records on that of the tracks 20a-f which> is associated with the head in question, or else the latter reproduced from said associated track. Although the assembly shown in Figures 1-3 shows a set of transverse rotating heads 10, 50 the principles of the invention are equally applicable to a recording device with rotating heads of any type, in which the heads are not necessarily oriented transversely to the strip support 12 and can define a plurality of helical tracks thereon. Of course, if helical tracks 55 are produced, the orientation of the control head 14 is modified correspondingly.

We will now refer to FIG. 4, on which are represented a data source 30, a calibration signal generator 32, a phase shift means 34, a first set of switches 60 S1-6, a second set of switches S7-12, a plurality of recording excitation amplifiers 36a-f, a reproduction means 38, a multiplier 40, a plurality of sampling and blocking circuits 42a-f and a control means 44 Each of the sampling and holding circuits 42a-f comprises an inter-switch 65 S13-18, a resistor 46a-f, a capacitor 48a-f and a buffer amplifier 50a-f, respectively.

Each of the amplifiers 36a-f and each of the sampling and blocking circuits 42a-f are associated with one of the recording heads

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very reproducing 16a-f. The data source 30 applies electrical data to each of the switches S1-6. The switches S1-6 are successively closed to apply this electrical data to the amplifiers 36a-f each time that one of the recording-r ~ production heads 16a-f crosses the support 12 (FIGS. 1-3). The calibration signal generator 32 generates a calibration signal of constant amplitude and frequency and applies this signal by means of phase shift 34. As described below, the phase shift means 34 periodically modifies the phase of the calibration signal . The phase shifted calibration signal leaving the phase shifting means 34 is applied to each of the switches S7-12 of the second set. Each of these switches S7-12 switches the calibration signal to one of the amplifiers 36a-f when the head associated recording-reproduction 16a-f passes over the duplication area 24a. Thus, each time that one of the recording-reproduction heads 16a-f crosses the support 12, it describes or reads data in its respective track among the tracks 20a-f between the duplication zones 24a and b. Immediately after writing data, each of the recording-reproducing heads records the calibration signal in the duplication area 24b within its respective track 20a-f. When reading data from tracks 20a-f, each recording-reproducing head 16a-f generates an electrical signal intended to be applied to the reproduction means 38. The operations of writing and reading the heads of recording-reproduction 16a-f are determined by a conventional control circuit (not shown), which selectively activates one of the two bodies comprising the data source 30 and the reproduction means 38.

The control head 14, which is placed in the immediate vicinity of the duplication zone 24b, generates an electrical signal determined from the calibration signal as it is recorded in said zone. This electrical signal is applied to the multiplier 40, which converts it into a second electrical signal determined from the unidirectional scalar quantity of the first signal. The second signal is applied to each of the sampling and blocking circuits 42a-f. Each of the switches S13-18 of a third set, respectively associated with the sampling and blocking circuits 42a-f, closes when the control head 14 is located above one of the tracks 20a-f defined by a associated recording-reproduction head 16a-f. The time constants R (resistance-capacitance), each defined by one of the resistors 46a-f and one of the capacitors 48a-f, are chosen so as to establish an average of the second signals applied to the various sampling and blocking circuits 42a -f. The average signal thus obtained, stored on each of the capacitors 48a-f, is applied to the control means 44, via one of the buffer amplifiers 50a-f. The control means 44 uses the average signal in a form understandable to humans or to machines.

We will now, with reference to FIG. 5, examine in more detail the operation of the assembly described above concurrently with FIG. 4.

FIG. 5 represents a time diagram 52. The operating sequence of the first set of switches Sl-6 is represented on line 54, that of the second set of switches S7-12 on the second line 56, and that of the third set of switches S13-17 on the third line 58. Line 54 indicates that the switches Sl-6 are closed sequentially once per complete revolution of the rotary head assembly 10, so that the data coming from the data source 30 are continuously applied to one of the recording-reproducing heads 16a-f. Line 56 indicates that immediately after each of the recording-reproducing heads 16a-fa has recorded data, it records part of the calibration signal in the duplication area 24b, by closing the appropriate switch of the second set S7 -12. The hatched areas of line 56 indicate that, during the times they represent, all of the S7-12 switches in the second set are open. The third line 58 indicates that the switches S13-18 of the third set are momentarily closed successively for -.

reproducing the parts of the calibration signal recorded in the duplication zone 24b from the respective respective tracks 20a-f. Line 58 further shows that there is an unknown delay due to the tape running time between a rotating head and the control head, for example between the time when track 20a is recorded when the track is closed. switch S1 and the time of its subsequent reproduction when the switch S13 is closed.

The delay between the recording of a calibration signal on a determined track and its subsequent detection by the control head 14 io being unknown, conventional means are necessary to determine which signal corresponds to such or such track. One of the possible methods would be not to periodically record the calibration signal on one or more selected tracks and to start recording it on a next track by means of a predetermined recording head. When this absence of signal is detected by the timing means associated with the operation of the control arrangement according to the invention, this means is informed of the identity of the recording head producing the signal on the aforementioned next track. In addition, a conventional phase control loop or the like can be provided to detect signal transitions at the output of control head 14, which correspond to transitions between adjacent tracks, so that has means for determining whether or not the control head 14 is above the axis of a specific track.

In a particular embodiment of the invention, the calibration signal has a frequency which is an integer multiple of the speed of rotation of the rotary head assembly 10. After each complete revolution of this assembly 10, the means phase shift 34 dephases the calibration signal to a selected extent after each sequence of tracks 22 has been recorded. In this regard, the phase shifting means 34 can establish, according to one embodiment of the invention, three paths or passages for the calibration signal, namely a first path which does not modify its phase by 120 * and a third path which modifies its phase of 240; (figure 8). The phase change can be ensured by timing and phase shift amplifiers. The switching between the paths can be delayed in relation to the closing of the switch S7, for example to modify the phase of the calibration signal once per complete revolution of the rotating head assembly 10. Any uniformly spaced phase shift 40 is possible since more than two phase shifts occur per cycle at the frequency of the calibration signal.

The control head 14 produces a series of bipolar voltage levels proportional to, or commensurate with, the instantaneous amplitude of the calibration signal recorded in the duplication area 24b of each of the tracks 20a-f. This series of voltage levels is applied to the multiplier 40, which multiplies each voltage level by itself to produce a series of squared high voltage levels which then become unidirectional. Having the air gap 28 of the control head 14 perpendicular to the recorded tracks 20a-f and, in particular, so that it is strictly parallel to the respective gaps of the recording-reproduction heads 16a-f ensures that a valid sample of the recorded track is obtained. As can be seen in the time diagram in FIG. 5 and more particularly on its line 55 58, the high squared voltage levels are applied to the sampling and holding circuits 42a-f; thus a part of the voltage which was present when one of the tracks 20a-f recorded by an associated recording-reproduction head 16a-f can be applied to these circuits is passed under the control head 14, after elevation-60 tion of this squared voltage. The effective time constant of the RC network (resistance-capacitance) formed by the resistors 46a-f and the capacitors 48a-f is chosen such that the DC voltage accumulated at the terminals of each of the capacitors 48a-f is a smoothed average of the individual measurements the calibration signal as recorded by a recording-reproducing head 16a-f on the associated track 20a-f.

Each of the buffer amplifiers 50a-f generates at its output a signal proportional to the average power of the calibration signal

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recorded by one of the recording-reproducing heads 16a-f respectively associated with the sampling and holding circuits 42a-f. The average signals are proportional to the power of the fact that all the recorded voltage levels are squared by the multiplier 40.

The average signal generated by each of the buffer amplifiers 50a-f can be applied to the control means 44, which can be any controller device, which presents the average signal in a form understandable to humans or machines. As described below, the average signal, as a function of the recorded level (in this case proportional to the power level) is useful for determining the optimal gain or the optimal excitation level of the amplifiers 36a-f.

The simultaneous optimization and verification of the recording process of each of the recording-reproduction heads 16a-f is carried out as described below.

We will now refer to FIG. 6, on which a variant of the assembly of FIG. 4 is represented, this variant aiming more particularly at replacing the amplifiers 36a-f and the sampling and blocking circuits 42a-f by the networks. associates shown in Figure 6.

More specifically, FIG. 6 represents a plurality of pairs of sampling and blocking circuits 60a-f, a plurality of first variable gain amplifiers 62a-f, a plurality of second variable gain amplifiers 64a-f and a plurality of differential amplifiers 68a-f. An input I is applied from the first set of switches S1-6 and from the second set of switches S7-12 (FIG. 4) and an output o is coupled with the recording-reproduction heads 16a-f. A reaction path is also provided between the multiplier 40 and each of the pairs of sampling / blocking circuits 60a-f comprises a first electrical path coupled with the inverting input of that of the differential amplifiers 68a-f to which it is associated and a second electrical path coupled with the non-inverting input of the same differential amplifier. The first path of each of the pairs of sampling / blocking circuits 60a-f comprises a switch S19-24, a resistor 70a-f and a capacitor 72a-f, respectively. The second path includes a switch S25-30, a resistor 74a-f and a capacitor 76a-f, respectively. The output of each of the differential amplifiers 68a-f is coupled with a variable gain determination input of that of the first variable gain amplifiers 62a-f with which it is associated. A variable gain determination input of each of the second variable gain amplifiers 64a-f is coupled with a first voltage source V! via a respective switch of a plurality of switches S31-36 with a second voltage source V2 via a respective switch S37-42 and with a third voltage source V3 via a respective switch S43-48. The voltage source Vj, when coupled with the variable gain determination input of the variable gain amplifiers 64a-f, determines a gain of 0 dB in these amplifiers. The voltage source V2, when coupled with the variable gain determination input of the amplifiers 64a-f, determines for example a negative gain of 1.5 dB in these amplifiers. The voltage source V3, when coupled with the variable gain determination input of the amplifiers 64a-f, to keep the same example, determines a gain of 3 dB in these amplifiers. The gains indicated in this example are chosen from the characteristic curve representative of the reproduction output level as a function of the recording excitation level, as shown in FIG. 9, on which it can be seen that, when the recording excitation level is lowered or raised under the action of V2 or V3, the reproduction output level is reduced by 2 dB from the optimal level. As described later, the optimal level is the maximum reproduction output level of the calibration signal as recorded in the duplication area, and it may not necessarily be the optimal reproduction output level of the electrical data. generated by the data source 30. The corresponding point of the characteristic curve of Figure 9 for the optimal level of electrical data reproduction output can be determined.

The characteristic curve of FIG. 9 is a curve of the reproduction voltage as a function of the recording current. The curve of the reproduction voltage, as a function of the reproduction power, is in fact that which is controlled by the control means 44, since the multiplier 40 produces a square of voltage which has a generally similar curve appearance.

If we now also refer to FIG. 7a, we see that the switches S1-S6 are successively closed and that the switches S31-36 are also successively closed, as shown, respectively, on lines 80 and 86. Consequently , data from the data source 30 is always applied to the recording-reproducing heads 16a-f with a gain of 0 dB through the respective amplifier associated among the amplifiers 64a-f. However, when each of the heads 16a-16f passes over the duplication zone 24b to record the calibration signal, the switches S37-S42 each close at the same time as the corresponding switch S7-S12, as shown in lines 82 and 88, to record the calibration signal at a lower level, this lower level being a lowered level of 1.5 dB, as shown in FIG. 9. When the recorded tracks pass in front of the control head 14 , the switches S19-S24 close to accumulate the average voltage on the corresponding capacitor 72a-f of an associated sampling and holding circuit of pairs 60a-f. At least three, but preferably more, passes of each of the recording-reproducing heads 16a-f are required through the duplicating area 24b to produce an average power at the lowered recording excitation level. Line 84 indicates that there is an unknown delay, as described above.

Similarly, as can be seen in Figure 7b, the calibration signal is recorded at a higher excitation level when switches S43-S48 close at the same time as switches S7-S12, as shown on lines 94 and 100. Here again, the switches S31-S36 close successively at the same time as the respective switches S1-S6, as shown on lines 92 and 98, to ensure a gain of 0 dB in the amplifiers 64a -f when recording data. The switches S25-S30 are closed to accumulate the average voltages on the capacitors 76a-f at the upper excitation level, the line 96 indicating the delay previously described.

If one of the recording excitation levels provided by the series combination of amplifiers 62a-f and 64a-f are at a height different from the optimum level as shown in FIG. 9, the inputs of the differential amplifiers respective 68a-f are unbalanced and generate a voltage proportional to this imbalance and apply it to the variable gain determination input of the respective variable gain amplifiers 62a-f.

Repeating the recording of the calibration signal at the lower and higher recording excitation levels ultimately determines a balanced recording excitation level and produces a zero output from each of the differential amplifiers 68a-f.

It can be seen from the above that, thanks to the invention, a new method and apparatus are obtained which makes it possible to control the performance of each recording arrangement in a rotating head recording apparatus comprising a plurality of recording heads.

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Claims (12)

656,705 2 1. Method intended to allow the control of the recording operation in a recording device with a rotating head, characterized in that it comprises the operations consisting in: applying a selected calibration signal to a rotating head during the recording operation, and thereby recording said signal on a specially provided area of an associated recording medium; placing a stationary head downstream of said rotating head and adjacent to said intended area of the recording medium; and detecting said calibration signal recorded by said stationary head during said recording operation. 2. Method according to claim 1, characterized in that it further comprises the operation of providing an output signal proportional to the amplitude of said detected signal. 3. Method according to claim 1, characterized in that the operation of applying said calibration signal comprises the operation of cutting off an information signal applied to said rotating head and of connecting said calibration signal to said rotating head when it is adjacent to said provided area of said recording medium. 4. Method according to claim I, characterized in that said calibration signal is a periodic signal with a known amplitude and frequency and that said calibration signal is offset by a chosen phase angle not divisible by 180 before apply it to each of the rotating heads. 5. Apparatus for implementing the method according to claim 1, characterized in that it comprises: means (32) for generating a selected calibration signal; means (34) for applying said calibration signal to a rotating recording head for recording said calibration signal on an intended area (24b) of a coordinated recording medium (12); and a stationary recording head (14) placed downstream of said rotating head (16a-f) and adjacent to said intended area (24b) of said recording medium (12) for detecting said recorded calibration signal. 6. Apparatus according to claim 5, characterized in that it further comprises means (40) connected with said stationary head (14) for the reception of said detected signal and for the generation of an output signal proportional to the amplitude of said detected signal. 7. Apparatus according to claim 5, characterized in that it comprises a plurality of rotating heads (16a-f) mounted on a rotating drum (10) and that each of the rotating heads is connected so as to record said calibration signal in an overlap area of said recording medium (12). 8. Apparatus according to claim 7, characterized in that it is a magnetic tape recording apparatus (12) with rotating head with transverse scanning and that the air gap (28) of said stationary head (14) is oriented substantially. parallel to the respective air gaps of said rotating heads (16a-16f). 9. Apparatus according to claim 5, characterized in that it further comprises means for cutting off an information signal to be recorded at said rotating head and for connecting said calibration signal to said rotating head when it is adjacent to said overlap area. 10. Apparatus according to claim 5, characterized in that said calibration signal is a periodic signal with a known amplitude and frequency. 11. Apparatus according to claim 6, characterized in that said means connected for receiving said calibration signal comprises means for raising said calibration signal squared connected to an output of said stationary head (14) and means for obtaining a signal average, connected to an output of said means for raising said calibration signal squared. 12. Apparatus according to claim 10, characterized in that it further comprises: means (S37-S48) for varying the signal connected to said means (32) for generating said calibration signal chosen to alternately lower and increase one of its amplitudes for predetermined values periodically during successive passages of said rotating head (10) above said recording medium (12); means (60a-f) for accumulating the respective output signals in proportion to respective amplitudes of said recorded signals with said amplitude values lowered and increased; means (68a-f) for comparing said respective accumulated output signals and for generating an error signal in response; and means (62a-f) for applying said error signal to control an amplitude of an information signal to be recorded by said rotating head (10) to obtain an optimal amplitude of the recording signal.