JPS6321262B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic storage device that reads and writes data while helical scanning a magnetic tape medium with a rotating magnetic head, and particularly relates to a skew correction method.

In this type of magnetic storage device, servo signals are written in several locations (usually four locations) on the magnetic tape medium, and by reading these servo signals, the trace (trajectory) of the rotating magnetic head becomes a data track. I'm trying to match it correctly. However, it is well known that some degree of skew occurs due to mechanical tolerances, runout of the rotating magnetic head, media positioning errors, and the like. The skew referred to here is the deviation between the trace and the data track, excluding static parallel deviation (offset).

In conventional magnetic storage devices, when data reading fails, the skew is corrected by receiving a predetermined skew correction value from the host device and controlling the feeding of the magnetic tape medium accordingly. There is. However, with this skew correction method, it is difficult to always obtain a satisfactory correction effect.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an improved skew correction scheme, particularly one suitable for autonomous management in a magnetic storage device.

Another object of the present invention is to provide a skew correction method suitable for further improving the track density (stripe density) in this type of magnetic storage device.

The skew correction method of the present invention is characterized by reading the servo signals provided at both ends of the stripe each time a stripe is scanned, measuring the amount of off-track at both ends of the stripe, and measuring the amount of off-track at both ends of the stripe. Based on the difference in the amount, the skew amount excluding the off-track component is calculated, and a predetermined correction coefficient is given to the skew amount obtained during multiple past scans to obtain the skew correction value. The object of the present invention is to control movement of a magnetic tape medium according to a skew correction value. Thereby, the skew value at the next scan can be predicted, and the skew can be automatically corrected by the apparatus itself. With this method of calculating the skew correction value from the past skew amount and correcting the skew sequentially, the desired correction effect can be achieved even if the formula for calculating the skew amount and the skew correction value is greatly simplified.
Hereinafter, the present invention will be specifically described with reference to the accompanying drawings.

FIG. 1a shows the servo signals S ₁ to _{S 4} on the magnetic tape,
FIG. 1 is a diagram schematically showing the state of tracing of a data track and a circuit magnetic head, and FIG. 1b is an enlarged view of any one of the servo signals S ₁ to _{S 4} shown in FIG. 1a. The servo signals S ₁ to _{S 4} consist of a long-period 2f signal and a short-period f signal, as shown in FIG. 1b. Now, when the magnetic head correctly traces the data track, the center of the head trace passes through the position shown in FIG. 1b, and the servo signal read waveform at that time becomes as shown in FIG. 1c. In other words, the central peak of the servo signal read waveform and the 2f signal are in phase. The head trace is
When it deviates from the track (when an off-track occurs), the read waveform of the servo signal becomes as shown in FIG. Therefore, the amount of off-track can be easily measured using, for example, a measuring circuit as shown in FIG.

In FIG. 2, 1 is a rectifier circuit, and 2 is an envelope generation circuit, both of which generate a signal corresponding to the envelope of the servo signal read waveform A, and supply it to one input of the comparator 3. The other input of comparator 3 is given a slice level. This slice level is set to, for example, half the peak level of the output of the envelope generating circuit 2. Comparator 3
The output of is given to the enable input of counter 4. The flip-flop 7 is set by a 2f signal F detected by a circuit not shown, and its output c switches the counter 4 between counting up and counting down. It is preferable to use a signal (frequency 2f) obtained by rectifying the servo signal as the count input of the counter 4, that is, the clock E, but if some error is allowed, a constant period signal (frequency 2f to 10f) generated by an appropriate oscillator is preferable. )
may also be used. The contents (output) D of the counter 4 are stored in a memory (register) 6 via a gate circuit 5. Gate circuit 5 receives timing signal Load
The timing signal is stored in the memory 6.
An address that is updated in synchronization with Load is given.

The operation of the measuring circuit shown in FIG. 2 will be explained with reference to the time chart shown in FIG. When a certain servo signal is read and the level of its waveform A exceeds the slice level, the output B of the comparator 3 becomes low level,
Counter 4 starts counting lock E. The counter 4 counts up until the 2f signal F of the servo signal is detected. When the 2f signal F is detected, the flip-flop 7 is set and the counter 4 starts counting down. Therefore, the count value D of the counter 4 (which is a digital quantity, but is shown as an analog quantity in FIG. 3 for convenience) increases and decreases as shown. If the amount of off-track is zero, the count-up and count-down times will be equal, so the count value D at the end of counting will be zero. However, if a certain amount of off-track exists, the count-up and count-down times will be changed accordingly. A difference occurs in time, so that the final value of the count value D becomes a certain value Δn (n is the number 1 to 4 of the servo signal track). This Δn indicates the amount of off-track. This off-track amount Δn is written to a certain address in the memory 6 via the gate circuit 5. In this way, the off-track amount Δn (n=1, 2, 3, 4) for each servo signal S ₁ to _{S 4} is written into the memory 6 for each scan.

The skew correction value Cn is calculated from the off-track amount during past scanning obtained in the memory 6 using the calculation formula described later, and the feeding of the magnetic tape is controlled using this value to sequentially correct the skew. to correct.

An example of a skew correction circuit is shown in FIG. The above skew correction value Cn is set in register 8. The contents of the register 8 are converted into an analog signal by the D/A converter 9, and are then connected to the operational amplifier 10, capacitor _C1 , resistors _R1 to _R3 and analog switch.
Input to the ramp waveform generation circuit (integrator circuit) consisting of SW ₁ . The analog switch SW ₁ closes after observing the off-track amount Δ ₄ for the servo signal S ₄ to discharge the capacitor C ₁ and opens before tracing the servo signal S ₁ in the next scan. In this way, a ramp voltage (skew correction function waveform) with a slope proportional to the skew correction value _Co is obtained at the output terminal of the operational amplifier 10, and this is obtained by the summing amplifier circuit consisting of the operational amplifier 11 and resistors _R4 to _R7 . The signal is then added to and amplified with the servo control signal generated within the storage device. The output of this summing amplifier is supplied to a power amplifier (not shown) that drives a capstan motor.

An example of the above skew correction function waveform is shown in FIG. 5 in correspondence with a scan. In the same figure, 55
is a track containing actual skew traced by a rotating magnetic head, 56 is a true data track, and 57 is a skew correction function waveform. In addition, T ₀ to _{T 4} are the times at which the servo signals S ₁ to _{S 4} are scanned, T ₅ is the time at which the analog switch SW ₁ is closed,
T ₆ is the time to open analog switch SW ₁ .

In addition to the above-mentioned skew correction circuit, a circuit that generates a number of clock pulses corresponding to the skew correction value _C within a certain period of time (within the time for scanning a data track), such as a rate multiplier circuit, may be used. may be used, and its output may be added (subtracted) to the tacho pulse counter input of the servo circuit.

Next, a method for creating the above skew correction value C _o will be explained. The skew correction value C _o is basically
Process of calculating skew amount W from off-track Δn and skew correction value from past skew amount
It is created by the process of calculating C _o .

First, to find the skew value W from Δn (n=1, 2, 3, 4), there is generally no problem in approximating the skew as a linear value, so if you execute one of the following three sets of equations, good.

W=Δ1−Δ3, W=Δ2−Δ4 (1) Formula If Δ1 or Δ3 is abnormal, the latter is used.

W=Δ1+Δ2/2−Δ3+Δ4/2 (2) Formula W=(Δ1−k・ΔS ₁ )−(Δ3−k・ΔS ₃ ) W=(Δ2−k・ΔS ₂ )−(Δ4−k・ΔS ₄ )(3) If Δ1 or Δ3 is abnormal, use the latter.
ΔS _o is the time T _o at which the servo signal S _o is traced
This is the error in the servo system, that is, the contents of the tacho pulse counter. Also, Δ1 to Δ4 are the amount of positional deviation of the tape, and ΔS ₁ to ΔS ₄ are the amount of rotational deviation of the capstan motor, so the units are different, so the conversion coefficient k
ΔS _o is converted to Δ _o by multiplying by .
Note that the size of the conversion coefficient k, which converts the amount of rotational deviation to the amount of tape positional deviation, changes depending on the amount of tape wrapped around the capstan, but if k varies only within a certain range, there will be some error. It is also possible to ignore and regard it as a constant. According to equation (3), known errors due to servo system overshoot can be removed from the observed off-track amount.

Next, the skew amount W _on (m=1, 2,..., n-
1, n is the number of scans) to the skew correction value C _o
To find , you can calculate either of the following two equations.

C _o = 1/i (W _o-1 + W _o-2 +…+ W _oi ) = C _o-1 +1/i・(W _o-1 − W _oi-1 ) (4) Equation (4) is the past This is the simple average of the skew (including noise) during the i scans. Originally,
Since skew does not change frequently, this formula does not have a large error. Normally, i=4 or so is appropriate.

C _o = 1-γ/γ {γ・W _o-1 +γ ²・W _o-2 +…} = (1-γ)・W _o-1 +γC _o-1 = (1-γ)・X _{o- 1} +C _o-1 Equation (5), X _o-1 = W _o-1 −C _o-1 (the amount of skew actually observed in the previous scan), γ is 0 < γ < 1
It is.

Equation (5) is the average of the skew (including noise) observed in the i previous scan, weighted by γ ⁱ , and the skew observed value in the previous scan X _o-1
and its correction value C _o-1 only from the skew correction value C _o
This has the advantage of making calculation processing easier. For example, if γ = 1/2, [binary representation of C _o-1 ] + [previous skew observed value X _o
The value obtained by shifting the binary representation of _-1 by 1 bit to the right. Usually, it is appropriate for γ to be about 1/2 or 3/4.

The above calculations can be executed by either a hardware circuit or a microprogram control type circuit, but
In any case, since it can be easily implemented using well-known techniques, a detailed explanation of the arithmetic circuit will be omitted.

As described above, the present invention calculates a skew correction value using a simple formula from the amount of off-track observed during past scans, and controls the feeding of the magnetic tape medium based on the skew correction value, thereby eliminating the skew. are corrected sequentially. Therefore, compared to the conventional method in which the feeding of the magnetic tape medium is controlled by a fixed skew correction value given by the host device when data reading fails, it is possible to achieve a much improved skew correction effect, and the data The reliability of read/write operations can be greatly improved. In addition, by predicting the skew when scanning the next stripe and automatically correcting it, the magnetic tape media is Since scanning can be performed with less positional deviation with respect to the above servo information, compatibility can be maintained even if the core width of the rotating head is narrowed, and therefore the track density can be further improved.

[Brief explanation of the drawing]

Figure 1a is a diagram explaining the servo signals on the magnetic tape, Figure 1b is an enlarged view of one servo signal in Figure 1a, and Figure 1c is the servo when the off-track amount is zero. Signal reading waveform diagram, Figure 1d is a servo signal reading waveform diagram when the off-track amount reaches a certain value (other than zero), Figure 2 is a block diagram showing the off-track amount detection circuit, Figure 3 The figure is a time chart for explaining the operation of the circuit in Figure 2, Figure 4 is a circuit diagram showing an example of the skew correction circuit, and Figure 5 is an explanatory diagram of the skew correction function waveform generated in the skew correction circuit in Figure 4. . 1... Rectifier circuit, 2... Envelope creation circuit, 3...
...Comparator, 4...Counter, 5...Gate circuit,
6...Memory, 7...Flip-flop, 8...
Register, 9...D/A converter, 10, 11
...Operation amplifier, C ₁ ...Capacitor, SW ₁ ...
Analog switch, R ₁ to R ₇ ... Resistor, S ₁ to _{S 4} ...
...servo signal.

Claims (1)

[Scope of Claims] 1. In a magnetic storage device that reads and writes data while helically scanning a stripe on a magnetic tape medium with a rotating magnetic head, for each scan of a stripe on the magnetic tape medium, a magnetic tape is provided at each end of the stripe. The measured servo signals are read, the amount of off-track at both ends of the stripe is measured, and the amount of skew excluding the off-track component is calculated from the difference between the measured amounts of off-track at both ends of the stripe. A skew correction method characterized in that a skew correction value is determined by applying a predetermined correction coefficient to the skew amount obtained at the time of scanning, and when scanning the next stripe, the magnetic tape medium is moved based on the determined skew correction value. .