JPS6252372B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for detecting a track deviation of a scanning center of a rotating head with respect to a data track center in a width direction scanning rotating head type magnetic tape recording mechanism.

FIG. 1 shows a block diagram of this type of track deviation detecting device conventionally used. In this figure, 1 is a magnetic tape, and 2 is a servo on which signals of different frequencies ₁ and ₂ are recorded alternately at intervals equal to the track pitch, and the boundary between frequencies ₁ and ₂ coincides with the center of the data track. 3 is a data track, 4 is a head rotor, 5 is a rotary head for recording or reproducing installed in the head rotor 4, 6 is a head rotor motor, 7 is a read amplifier for reading out the signal of the servo track 2; 8 and 9 are band pass filters whose center frequencies are frequencies ₁ and ₂ , respectively; 10 is a rectifier circuit for detecting the level;
11 is a subtracter that calculates the level difference between both inputs.

To operate this, the servo track 2 recorded on the magnetic tape 1 is scanned by the rotary head 5, and the signal from the rotary head 5 is read and the amplifier 7
Amplify with. The amplified signal is separated into frequency 1 component and frequency ₂ components by band pass filters 8 and 9, respectively, and frequency ₁ , frequency 1 and frequency 2 components are separated by rectifier circuit ₁₀ .
Detect the level of _{the second} component. These levels are input to the calculator 11 to obtain the level difference between frequencies ₁ and ₂ . This level difference is proportional to the deviation between the center of the rotary head 5 and the boundary between frequencies ₁ and ₂ , that is, the amount of track deviation. Therefore, if the control is performed so that the above-mentioned level difference is eliminated, positioning without track deviation can be achieved.

However, since this method uses the amplitude difference between the two frequencies ₁ and ₂ , factors that cause the amplitude to fluctuate, such as fluctuations in the flying height between the magnetic tape 1 and the rotating head 5, noise in the read amplifier 7, and the rotating head. If there is a variation in the sensitivity of each head rotor 4, a fluctuation in the rotational speed of the head rotor 4, a detuning of the center frequency of the bandpass filters 8, 9, a drift, etc., the track deviation detection accuracy is easily affected. Furthermore, since it is necessary to use a rectifier circuit with low frequency response, the track width of the servo track 2 has to be increased, which reduces the media usage efficiency and reduces the storage capacity per roll of the magnetic tape 1. It has the following disadvantages.

The present invention was made to eliminate the above-mentioned drawbacks, and attempts to detect track deviation by using the number of servo bits instead of the difference in amplitude of the servo track signal. Hereinafter, the present invention will be explained in detail based on the drawings.

FIG. 2A is a diagram showing the structure of a magnetic tape on which servo signals are recorded for use in the track deviation detection device of the present invention. In this figure, 2A is a first servo track, 2B is a second servo track, and 3 is a data track. 12 is a servo signal area where servo signals are recorded, and 13 is a demagnetized area where servo signals are not recorded.

FIG. 2B is an enlarged view of the first servo track 2A. In this figure, 14 is a servo bit having a constant magnetization reversal interval, and 15 is a sync bit having a magnetization reversal interval different from that of the servo bit 14.

In the servo signal area 12, a servo bit 14 of a constant frequency is recorded in the tape width direction, and a sync bit 15 of a different frequency is recorded near the center of the servo bit 14. In the first servo track 2A, parallelogram-shaped servo signal areas 12 and demagnetizing areas 13 having the same shape are alternately arranged at every track pitch P. The second servo track 2B in FIG. 2A corresponds to the first servo track 2A shifted by a pitch P in the longitudinal direction of the track. In addition, in order to make the amount of track deviation detected by the second servo track 2B equal to the amount of track deviation detected by the first servo track 2A, the servo signal area 12 of the first servo track 2A is replaced with the servo signal area of the second servo track 2B. It is located on the extension line of 12.

FIG. 3 is a block diagram of a track deviation detection device according to the present invention. In this figure, 16 is a servo bit detection circuit that detects magnetization reversal of servo bits 14 in a servo signal that is above the slice level, 17 is a reversible counter that counts the servo bits 14, 18 is a sync bit detection circuit, and 19 is a servo bit detection circuit that is above the slice level. A blank detection circuit that is sandwiched between the servo bit signals and detects an area below this level, that is, a blank; 20 is a counting controller that controls the counting state of the reversible counter 17 by detecting the sync bit 15 and the blank; 21 is a code converter for converting the result of the reversible counter 17 into a positive/negative sign and the absolute value of the track deviation; 22 is a register for taking in the output of the code converter 21; and 23 is a register between the sync bit 15 and the blank. This is a polarity converter that changes the polarity of the most significant bit (MSB) of the counting result depending on the order of occurrence. Note that symbols a to h in FIG. 3 indicate signals,
The symbols correspond to those in Figures 10 to 12.
Each will be described later.

Moreover, FIGS. 4 to 7 each show waveforms obtained by double-wave rectification of the servo signal output.

FIG. 4 shows a state in which the rotary head 5 is just inserted into the degaussing area 13, that is, in FIG.
Since the first servo track 2A has a parallelogram shape, the amplitude of the servo signal starts from zero and ends at zero.
Sync bit 15 will appear in the center. Although the rotary head 5 rotates as shown in FIG. 1, for convenience of explanation, one rotary head 5 is shown in an expanded state.

Further, FIG. 5 shows the servo signal output when scanning the broken line arrow B, which starts from the maximum amplitude, becomes zero at the center, and ends at the maximum amplitude.

Similarly, in FIGS. 6 and 7, dashed arrow C
This is the waveform obtained when the servo signal is double-wave rectified when scanning is performed along the lines D and D. V _S in FIGS. 4 to 7 is a reference level for detecting the servo bit 14. As shown in FIG. 5, it is sandwiched between servo bits 14 having an amplitude greater than the slice level, that is, the reference level V _S , and the reference level V _S
The following amplitude regions are blank. In addition, hereafter V
_S is unified at the slice level.

Next, the relationship between the servo signal waveform and the amount of track deviation will be described. When a servo signal as shown in FIG. 4 is reproduced, the number of servo bits 14 up to sync bit 15 at slice level _VS or higher is compared with the number of servo bits 14 at slice level _VS or higher after sync bit 15. This result is the same because the reproduced waveform is symmetrical with respect to the sync bit 15. Also, in the case of FIG. 5, the slice level V _S up to the blank is similar to FIG. 4.
The number of servo bits 14 above is compared with the number of servo bits 14 after the blank. This result is also the same because the reproduced waveform is symmetrical with respect to the blank. However, in the case of FIG. 6, the number of servo bits 14 above the slice level V _S is different before and after the sync bit 15, and there is a difference in the number of servo bits 14 between the two. This difference is proportional to the deviation from the scanning position A, that is, the track deviation. Therefore, as explained above, if the number of servo bits 14 equal to or higher than the slice level V _S before and after the sync bit 15 is determined and the difference between the two is calculated, the result will represent the amount of track deviation. The same can be said of blanks. In other words, if you find the number of servo bits 14 that are equal to or higher than the slice level V _S before and after blanking, and calculate the difference between the two, the result is sync bit 1.
As in case 5, it is proportional to the amount of track deviation.

Next, a specific method for calculating the difference in the number of sync bits 15 or servo bits 14 before and after blanking and determining the amount of track deviation will be explained using a reversible counter.

In FIG. 3, the reproduced signal amplified by the read amplifier 7 is divided into three parts and input to a servo bit detection circuit 16, a sync bit detection circuit 18 and a blank detection circuit 19. First, the servo bit detection circuit 16 double-wave rectifies the input reproduced signal and converts the servo signal exceeding the slice level V _S into pulses. This servo pulse is converted into a reversible counter 17.
and count the number of pulses. Further, the sync bit detection circuit 18 detects the sync bit 15 in the servo signal having a slice level V _S or higher, and converts it into a sync pulse a. In this case, the sync bit 15 can be detected by utilizing the fact that the magnetization reversal interval of the sync bit 15 is different from that of the servo bit 14, for example, by discriminating the time interval during servo signal reproduction using a monostable multivibrator. Further, in the blank detection circuit 19, when the servo signal amplitude is below the slice level _VS and servo signals above the slice level _VS are reproduced on both sides, it is considered as a blank, and during the period when the servo signal is below the slice level _VS , a blank pulse b is generated. Output. This circuit can be configured as follows, for example. When the slice level V _S is set to 30%, the servo signal is below the slice level V _S for 30% of the scanning time _of the servo track width. A vibrator is driven to generate a gate signal delayed by about 15% of the scanning time. If no servo pulse enters this gate, it can be determined that it is blank.

The sink pulse a and the blank pulse b are input to a counting controller 20, and the state of the flip-flop (F/F) is inverted every time the blank pulse b or the blank pulse a occurs. This counting controller 2
The output of 0 causes the reversible counter 17 to switch between up-counting and down-counting. The counting result of the reversible counter 17 is inputted to the code converter 21 excluding the most significant bit (MSB) e of the output of the reversible counter 17, and each bit is changed to "1" or "1" depending on the sign of the MSB.
Invert “0”. Thereby, the counting result is converted into a positive/negative sign (track deviation direction) and an absolute value (track deviation amount). This converted track deviation amount is input to the register 22, and the rotation head 5
The result at the time when the servo track 2 has been scanned is taken into the register 22. Further, the MSB of the count result of the reversible counter 17 is input to the polarity converter 23, and the sign of the MSB is changed depending on the order in which the blank pulse b and the sink pulse a are generated. Specifically, when blank pulse b and sync pulse a are detected in that order, and when only blank pulse b is detected, MSB is
Reverse the polarity of

FIG. 8 shows the track deviation detection characteristics of the detection device of the present invention. The horizontal axis represents the servo signal reproduction waveform of FIG. 4, that is, the amount of track deviation with respect to the track pitch centered on the case where the scanning position is A. The vertical axis is the output of the register 22 expressed in bits when the total number of bits is 100. As shown in this figure, the track deviation amount is -70~
It shows linear characteristics over a wide range of +70%. The detection method of the present invention explained above can be summarized as follows.

Slice level of reproduced signal after double-wave rectification V _S
Count the above servo bits.

The up and down states of the reversible counter 17 are reversed every time a sink pulse a or a blank pulse b is detected. (Figures 6 and 7 show the up and down areas of the servo bit.) However, if only blank pulse b is detected, or if blank pulse b and sink pulse a are detected in this order, the polarity bit of the counting result will change. Reverse the sign of .

FIG. 9 shows the track deviation detection characteristics when a detection method different from the above method is applied only when the sync pulse a and the blank pulse b are detected in that order. This method is a case in which the following items are added to the above-mentioned items.

If the sync pulse a and the blank pulse b are detected in this order, take the multiple of the total number of bits,
Reverse the polarity bits.

An embodiment of the circuit used in the present invention is shown in FIGS. 10 to 12 below.

FIG. 10 shows an embodiment of the circuit of the reversible counter 17, code converter 21 and register 22. When the total number of bits is 100, two ICs 17a and 17b of the 4-bit up-down counter function as reversible counter 1.
7 can be configured. Further, the code converter 21 can be realized by five exclusive OR gates.

FIG. 11 shows an embodiment of the counting controller 20.
In this figure, a and b are the aforementioned sync pulse and blank pulse, and c is a reset pulse. first or second servo track 2A,
2B (FIG. 2), the flip-flop F/F is reversed by the reset pulse c. Next, with the appearance of sink pulse a and blank pulse b, the flip-flop F/F is inverted. That is, the counting state (up, down) of the reversible counter 17 changes. Note that d is an inversion control signal.

FIG. 12 shows an embodiment of the polarity converter 23.
Here, e is the input polarity signal, that is, the MSB signal of the reversible counter, f is the clock pulse generated after the end of the servo track, and g is the polarity signal of the output of the polarity converter 23.

This circuit recognizes two cases: a case in which only the blank pulse b is detected, and a case in which the blank pulse b and the sync pulse a are detected in that order, and inverts the polarity of the input at that time and outputs it.

Note that h in FIG. 3 indicates a write signal. Also,
Although two servo tracks are used in FIG. 2A, there is no limit to the number of servo tracks. Furthermore, if it is desired to detect track deviation on the upper edge side of the tape, it may also be placed on the upper edge. Furthermore, although the track width of the rotary head 5 has been described as being equal to the track pitch, it is not necessarily limited to this.

Furthermore, the servo signal area and demagnetization area have a base length P
Although it has been described that the two regions are isomorphic parallelograms, the base lengths P of both regions do not necessarily have to be the same.

As explained in detail above, the present invention provides a width direction scanning rotary head type magnetic tape recording mechanism.
Since the amount of track deviation can be detected as the number of servo bits, detection errors do not occur due to fluctuations in the flying clearance between the magnetic tape and the rotating head, variations in sensitivity between heads, fluctuations in rotation speed, etc., and highly accurate and reliable track deviation can be achieved. It has the advantage of being able to provide signals. If a positioning control loop is constructed using this track deviation signal, highly accurate track positioning becomes possible. Furthermore, if this invention is applied to a VTR, the amount of track deviation can be detected by the rotary head itself that records and plays back signals, which eliminates the conventional problems of mounting errors in the control head and increases in track following errors due to expansion and contraction of the tape. There are advantages to avoiding it.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional track deviation detection circuit, FIG. 2A is a diagram showing the recording pattern of the magnetic tape used in the present invention, FIG. 2B is an enlarged view of the first servo track, and FIG. A block diagram showing an embodiment of the present invention, FIG. 4 is a double-wave rectified waveform diagram of the reproduced signal at scanning position A in FIG. 3, and FIG. 5 is a double-wave rectified waveform diagram of the reproduced signal at scanning position B in FIG. 6 and 7 are double rectified waveform diagrams of reproduced signals at scanning positions C and D, respectively. FIG. 8 is a track deviation detection characteristic diagram showing an embodiment of the present invention. A track deviation detection characteristic diagram showing another embodiment, FIG. 10 is a circuit diagram showing an embodiment of the reversible counter, code converter, and register used in the present invention, and FIG. 11 is an implementation of the counting controller. FIG. 12 is a circuit diagram showing an example of the polarity converter. In the figure, 1 is a magnetic tape, 2 is a servo track,
2A is the first servo track, 2B is the second servo track, 3 is the data track, 4 is the head rotor, 5 is the rotating head, 6 is the head rotor motor, 7 is the read amplifier, 12 is the servo signal area, and 13 is the degaussing area. , 14 is a servo bit, 15
is a sync bit, 16 is a servo bit detection circuit,
17 is a reversible counter, 18 is a sync bit detection circuit, 19 is a blank detection circuit, 20 is a counting controller, 21 is a code converter, 22 is a register, and 23 is a polarity converter.

Claims (1)

[Claims] 1 In a width direction scanning rotary head type magnetic tape recording mechanism, a plurality of magnetization reversal signal portions are recorded at regular intervals in the tape width direction, and a sync signal with a magnetization reversal interval different from the above-mentioned intervals is placed in the center of the magnetization reversal signal portions. A servo signal area having a parallelogram shape with two sides parallel to the longitudinal direction of the tape and a degaussing area having the same shape as the servo signal area are arranged alternately along the longitudinal direction. a magnetic tape having servo tracks formed to be arranged in the same direction; a servo signal reproducing circuit for reading the servo tracks with a rotating head; and a reversible counter for counting the number of magnetization reversals of the reproduced servo signals. a sync bit detector for detecting the sync signal portion; a blank detector for detecting that the core width portion of the rotary head is in a demagnetized region; and a sync bit detector for detecting the sync signal portion; 1. A track deviation detection device comprising a counting controller that changes the counting direction of a counter.