CN109389997B - Method and apparatus for reading magnetic recording medium, and storage medium - Google Patents
Method and apparatus for reading magnetic recording medium, and storage medium Download PDFInfo
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- 238000003379 elimination reaction Methods 0.000 abstract description 5
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- G—PHYSICS
- G11—INFORMATION STORAGE
- G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
- G11B5/00—Recording by magnetisation or demagnetisation of a record carrier; Reproducing by magnetic means; Record carriers therefor
- G11B5/48—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed
- G11B5/58—Disposition or mounting of heads or head supports relative to record carriers ; arrangements of heads, e.g. for scanning the record carrier to increase the relative speed with provision for moving the head for the purpose of maintaining alignment of the head relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
- G11B5/60—Fluid-dynamic spacing of heads from record-carriers
- G11B5/6005—Specially adapted for spacing from a rotating disc using a fluid cushion
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- G11B5/6029—Measurement using values derived from the data signal read from the disk
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Abstract
The invention provides a method and device for reading a magnetic recording medium, and a program, which can reliably read data from a magnetic recording medium with reduced magnetism without being influenced by noise by a simple circuit structure. The reading method uses a differentiating circuit to generate a digital signal which takes any one of two values according to increase and decrease in a magnetic reproduction waveform, and recovers recorded data based on the digital signal, wherein the following processing is performed: an estimation process of regarding a switching interval between two values in the digital signal as an interval section, and estimating at least a bit corresponding to the current interval section by comparing a length of the current interval section with a first threshold value; judging, namely comparing the length of a subsequent interval of the current interval with a second threshold value, and judging the subsequent interval as noise when the length of the subsequent interval is lower than the second threshold value; and a noise elimination process for executing a process of eliminating the noise when the noise is determined.
Description
Technical Field
The present invention relates to a reading method and a reading apparatus for reading data from a magnetic recording medium such as a magnetic card, and a program.
Background
In a magnetic recording medium such as a magnetic card, a bit sequence including binary bits of "0" and "1" is recorded using the direction of magnetization in a magnetic stripe. As a method of recording bit string data in a magnetic stripe, FM modulation is known, and one of them is F2F modulation. In the F2F modulation method, an area in which 1-bit data is recorded on a magnetic stripe is recorded as a bit unit so as to satisfy the following conditions: (a) reversing the direction of magnetization at the boundary of adjacent bit cells; (b) the direction of magnetization is not inverted inside the bit cell corresponding to "0" (i.e., F signal); (c) the bit cell corresponding to "1" has its magnetization direction reversed at a substantially central position (i.e., 2F signal). When the magnetic head is slid relative to the magnetic stripe on which recording is performed, a signal having a peak at a position where magnetization is inverted is output from the magnetic head, and thus the bit string data recorded in the magnetic stripe is reproduced by demodulating the signal. Such a signal output from the magnetic head is referred to as a magnetic reproduction waveform.
In demodulation of a magnetic reproduction waveform, as described in patent document 1 or patent document 2, a peak detection circuit composed of a differential circuit is generally used. The magnetic reproduction waveform is ideally a signal that forms a peak when the magnetization direction is inverted and changes monotonously to the next magnetization direction inversion. This signal is digitized by a peak detection circuit, i.e., a differential circuit, and further by a comparator, thereby obtaining a digital signal that takes any one of two values corresponding to the direction of magnetization in the magnetic stripe. Therefore, the time interval corresponding to the bit cell is extracted from the digital signal, and it is determined whether or not the polarity is inverted in the extracted time interval, thereby restoring the original bit string composed of "0" and "1". However, when there is a flaw in the magnetic stripe, the magnetic force on the magnetic stripe is reduced, or the data recording of the magnetic stripe is incomplete, hump-like noise is superimposed on the signal output from the magnetic head, and the differential circuit erroneously recognizes this noise as a regular polarity inversion, and as a result, the erroneous data may be restored. In order to prevent this erroneous recognition, patent document 3 discloses using an integrating circuit instead of the differentiating circuit, or restoring the recording data based on the result obtained from the differentiating circuit and the result obtained from the integrating circuit. In a digital signal obtained using a differentiating circuit or an integrating circuit, an interval of switching between one level (e.g., a low level) and another level (e.g., a high level) should indicate an inversion interval of the magnetization direction. Patent document 3 also describes a technique of detecting an error when a switching interval between binary levels is different from an originally predicted time interval.
Patent document 4 discloses a technique of providing an oscillation unit that generates a clock as a reference for noise removal, removing a predetermined pulse width component in digital data as noise based on the clock, and correcting a variation within a predetermined width in the middle of the digital data so as to have continuity.
Documents of the prior art
Patent document
Patent document 1: japanese patent laid-open No. 2001-135034
Patent document 2: japanese laid-open patent publication No. 2015-49914
Patent document 3: japanese patent laid-open No. 2007-95117
Patent document 4: japanese laid-open patent publication No. 8-172345
Disclosure of Invention
Technical problem to be solved by the invention
The integration circuit has an effect of smoothing the entire waveform including also a noise component. Therefore, as described in patent document 3, when the magnetic force is weakened and the magnetic recording medium whose amplitude of the magnetic reproduction waveform is originally small is read using the integrating circuit, the amplitude of the magnetic reproduction waveform is further reduced, and there is a possibility that good reading cannot be performed. In addition, when the differentiating circuit and the integrating circuit are used in combination, these two circuits must be mounted, and the circuit configuration becomes complicated. Although many conventional magnetic recording medium reading devices include a differential circuit and no integral circuit, such reading devices are required to be capable of reliably reading data without being affected by noise.
An object of the present invention is to provide a reading method and a reading apparatus for a magnetic recording medium, which can reliably read data from a magnetic recording medium or the like with a reduced magnetic force without being affected by noise, with a simple circuit configuration, and a program for executing such a reading method.
Means for solving the problems
The present invention provides a method for reading a magnetic recording medium, which generates a digital signal having any one of two values according to increase and decrease in a magnetic reproduction waveform by acquiring the magnetic reproduction waveform using a magnetic head that slides relative to the magnetic recording medium and inputting the magnetic reproduction waveform to a differentiating circuit, processes successive intervals by setting intervals between two values in the digital signal as intervals, and recovers recorded data in the magnetic recording medium based on the length of each interval, the method comprising: an estimation step of estimating at least a bit in the recording data corresponding to the current interval section by comparing the length of the current interval section with a first threshold value; a determination step of comparing the length of a subsequent interval section subsequent to the current interval section with a second threshold value, and determining that the subsequent interval section is noise when the length of the subsequent interval section is lower than the second threshold value; and a noise removal step of, when the determination step determines that the noise is generated, performing a process of removing the noise.
The present invention provides a reading device for reading recorded data from a magnetic recording medium, comprising: a magnetic head that performs relative sliding movement with respect to a magnetic recording medium; a differentiating circuit to which a magnetic reproduction waveform obtained by the magnetic head is input; a signal generation circuit that generates a digital signal that takes any one of two values according to an increase and decrease in a magnetic reproduction waveform, based on an output of the differentiation circuit; an arithmetic unit that processes successive intervals by using intervals between two values in the digital signal as intervals, and recovers recorded data in the magnetic recording medium based on the length of each interval, the arithmetic unit executing: an estimation process of estimating at least a bit in the recording data corresponding to a current interval section by comparing a length of the current interval section with a first threshold value; judging, namely comparing the length of a subsequent interval after the current interval with a second threshold, and judging the subsequent interval as noise when the length of the subsequent interval is lower than the second threshold; and a noise elimination process for executing a process of eliminating the noise when the determination process determines that the noise is generated.
The present invention provides a program for causing a computer provided in a reading device to execute processing, wherein the reading device reads recording data from a magnetic recording medium, and the program includes: a magnetic head that performs relative sliding movement with respect to a magnetic recording medium; a differentiating circuit to which a magnetic reproduction waveform obtained by the magnetic head is input; a signal generation circuit that generates a digital signal having any one of two values according to increase and decrease in a magnetic reproduction waveform based on an output of the differentiation circuit, wherein the computer processes a continuous interval section with an interval between two values in the digital signal as an interval section, and recovers recorded data in the magnetic recording medium based on a length of each interval section, the computer executing: an estimation process of estimating at least a bit in the recording data corresponding to a current interval section by comparing the length of the current interval section with a first threshold value; judging, namely comparing the length of a subsequent interval after the current interval with a second threshold, and judging the subsequent interval as noise when the length of the subsequent interval is lower than the second threshold; and a noise elimination process for executing a process of eliminating the noise when the determination process determines that the noise is generated.
When hump-like noise is superimposed on the magnetic reproduction waveform, erroneous recognition may be caused when recording data is restored from the magnetic reproduction waveform using a differentiating circuit, but according to the present invention, the noise can be removed by processing only the digital signal of the F2F waveform, for example, without providing an integrating circuit. In addition, since the digital signal is processed, noise removal can be realized only by software modification, and modification of the existing hardware structure is not required. In particular, in the reading apparatus of the present invention, the signal generation circuit may be constituted by a comparator connected to an output of the differentiation circuit, or may be constituted by a first comparator connected to an output of the differentiation circuit, a second comparator to which a magnetic reproduction waveform is input, and a timing generator which outputs a signal which changes in timing to switch between binary levels in an output signal of the first comparator to a level of an output signal of the second comparator. The reading apparatus of the present invention can remove the influence of noise superimposed on the magnetic reproduction waveform using a circuit having a simple structure in the related art.
In the present invention, when estimating a bit in the recording data, it can be estimated that the current interval section is an interval section corresponding to a bit "0" in the recording data when the length of the current interval section is equal to or greater than the first threshold value, and the current interval section and the subsequent interval section are interval sections corresponding to a bit "1" in the recording data when the length of the current interval section is less than the first threshold value. Thus, according to the present invention, recovery of recorded data from the magnetic recording medium recorded by the F2F modulation method can be performed without being affected by noise.
In the present invention, at the time of noise cancellation, it can be set that at least the current interval section and the subsequent interval section are interval sections constituting bit "0" in the recording data, regardless of the estimation result when estimating the bit in the recording data. In the case of the F2F modulation scheme, since the influence of noise is characteristic of influencing the interval section corresponding to the bit "0", it is possible to more reliably remove the influence of noise in the interval section corresponding to the bit "0" by setting at least the current interval section and the subsequent interval section to be the interval section constituting the bit "0" in the recorded data in the noise elimination processing. When it is estimated which interval section constitutes the bit "0" or "1", an interval section belonging to a bit unit may be estimated. In particular, in the present invention, it is preferable that, in the noise removal processing, when the sum of the lengths of the current interval section and the subsequent interval section is less than the third threshold value, the next interval section of the current interval section, the subsequent interval section, and the subsequent interval section is set to be an interval section constituting a bit "0" in the recorded data, and when the sum is equal to or greater than the third threshold value, the current interval section and the subsequent interval section are set to be an interval section constituting a bit "0" in the recorded data, so that the interval sections belonging to the bit unit are appropriately estimated and the subsequent bit determination is appropriately performed. With this configuration, it is possible to correct the recording data so as to have continuity including the interval section directly affected by the noise and the interval section adjacent to the interval section, and it is possible to accurately recover the recording data while excluding the influence of the noise.
In the present invention, it is preferable that the sum of the lengths of the interval sections set to constitute the bit "0" by the noise removal processing is subjected to a jitter check by obtaining the rate of change with respect to the previous bit cell length. By performing the jitter check, it is possible to determine the rationality of the noise removal processing even when misreading or error correction occurs by the noise removal processing.
In the present invention, the first threshold value is set to 70% of any one of the previous bit cell length, the average bit cell length, and the bit cell length determined according to the standard, for example, and the second threshold value is set to 25% of any one of the previous bit cell length, the average bit cell length, and the bit cell length determined according to the standard, for example. By setting these threshold values based on the actual bit cell length, it is possible to perform determination corresponding to the transport speed, and by setting these threshold values based on the bit cell length specified according to the standard, it is possible to perform determination based on the standard. In particular, regarding the second threshold value, when set to 25% of the bit cell length, since it is larger than the tolerance of the interval section of the 2F signal, the risk of erroneous determination can be suppressed.
Effects of the invention
According to the present invention, when data is read from a magnetic recording medium such as a magnetic card, the data can be reliably read from a magnetic recording medium or the like with a reduced magnetic force without being affected by noise, with a simple circuit configuration.
Drawings
Fig. 1 is a block diagram showing a configuration of a reading apparatus according to an embodiment of the present invention.
Fig. 2 is a block diagram showing a configuration of a reading apparatus according to another embodiment.
Fig. 3 is a waveform diagram showing a relationship between noise and recovered data.
Fig. 4 is a flowchart showing processing in a reading method according to the present invention.
Description of the symbols
10 … magnetic card; 12 … a magnetic head; 21 … read circuit, 22 … band pass filter; 23, 27 … amplifier; 24 … differentiation circuit; 25, 28 … comparator; 26 … calculation unit; 29 … timer generator.
Detailed Description
Next, embodiments of the present invention will be described with reference to the drawings. Fig. 1 shows a configuration of a reading apparatus according to an embodiment of the present invention. The illustrated reading device reads recorded data from a magnetic card 10 as a magnetic recording medium, and includes a motor 11 that transports the magnetic card 10, a magnetic head 12 that slides relative to a magnetic stripe (not shown) of the magnetic card 10 transported by the motor 11, and a reading circuit 21 that recovers recorded data from a magnetic reproduction waveform obtained by the magnetic head 12.
The read circuit 21 is a commonly used circuit having a differentiating circuit 24, and includes a Band pass filter (Band pass filter)22 for extracting a desired frequency component from a magnetic reproduction waveform from the magnetic head 12 and an amplifier 23 for amplifying the magnetic reproduction waveform having passed through the Band pass filter 22, and the magnetic reproduction waveform amplified by the amplifier 23 is input to the differentiating circuit 24. The reading circuit 21 further includes a comparator 25 that determines the polarity of the output of the differentiating circuit 24 and outputs a digital signal represented by a binary level, and an arithmetic unit 26 that executes processing for restoring the recording data based on the digital signal output from the comparator 25. The processing performed by the arithmetic unit 26 will be described later. In the magnetic reproduction waveform, when the instantaneous value changes in a decreasing manner, the output value of the differentiating circuit 24 is negative, so the output of the comparator 25 is at a low level, and in the magnetic reproduction waveform, when the instantaneous value changes in an increasing manner, the output value of the differentiating circuit 24 is positive, so the output of the comparator 25 is at a high level. Therefore, the output of the differentiating circuit 24 corresponds to a peak in the magnetic reproduction waveform, having a zero-cross point. The output of the comparator 25 is switched from a high level to a low level or from a low level to a high level in accordance with the peaks in the positive and negative directions in the magnetic reproduction waveform. The digital signal output from this comparator 25 is referred to as an F2F waveform.
Fig. 2 shows another embodiment of the reading apparatus according to the present invention. The reading apparatus shown in fig. 2 is different from the reading apparatus shown in fig. 1 in the internal structure of the reading circuit 21. The read circuit 21 shown in fig. 2 is the read circuit 21 shown in fig. 1, and further includes another amplifier 27 provided in parallel with the amplifier 23 and inputting the magnetic reproduction waveform output from the band-pass filter 22, a comparator 28 to which the output of the amplifier 27 is input, and a timing generator 29. The read circuit 21 shown in fig. 2 is a circuit that is generally used and has a differentiating circuit 24, as shown in fig. 17 of patent document 1, fig. 1 of patent document 2, and fig. 11 of patent document 3, for example. The comparator 28 outputs a digital signal corresponding to the polarity of the magnetic reproduction waveform itself. The timing generator 29 outputs a signal whose timing changes between a high level and a low level in the output signal of the comparator 25 to the level of the output signal of the comparator 28 as an F2F waveform. Since the F2F waveform is generated based on not only the positive and negative of the output of the differentiating circuit 24 but also the positive and negative of the magnetic reproduction waveform itself, the reading apparatus shown in fig. 2 has improved resistance to noise as compared with the reading apparatus shown in fig. 1. The F2F waveform obtained by the read circuit 21 shown in fig. 2 is basically a waveform obtained by logically inverting the F2F waveform obtained by the read circuit 21 shown in fig. 1, given the same magnetization reproduction waveform. The reading method according to the present invention recovers the recorded data only based on the timing of switching between the low level and the high level in the F2F waveform, and therefore there is no substantial difference in the processing for recovering the recorded data regardless of which reading circuit is used.
Next, the influence of noise when the reading apparatus shown in fig. 1 or 2 is used will be described with reference to fig. 3. Fig. 3 shows a magnetic reproduction waveform obtained from a magnetic stripe in which a bit string "110101" is recorded as recording data and an F2F waveform obtained from the magnetic reproduction waveform. The interval between the high level and the low level in the F2F waveform, which is switched to the next switching, is referred to as an F2F interval. When there is no possibility of misunderstanding, the F2F interval is simply referred to as an interval. Since the F2F modulation scheme is used, if there is no influence of noise or the like, the bit cell corresponding to data "0" is constituted by one F2F interval section corresponding to the F signal, and the bit cell corresponding to data "1" is constituted by two consecutive F2F interval sections corresponding to the 2F signal. Here, with the reading apparatus shown in fig. 1, the output of the amplifier 23 is represented as a magnetic reproduction waveform, and the output of the comparator 25 is represented as an F2F waveform.
As shown in fig. 3, the F2F waveform is switched between a low level and a high level at the position of the peak in the positive direction and the negative direction of the magnetic reproduction waveform. In the 5 th bit (bit of "0") in the recording data, a hump-like noise is superimposed on the magnetic reproduction waveform as shown by X in the figure. Since this bit is "0", it is an F signal, and the level of the F2F waveform should not be switched during the bit cell period. However, the noise X is differentiated to cause the level switching in the F2F waveform, and the F2F interval corresponding to the original F signal interval is divided into a long interval a, an extremely short interval B having a different level from the interval a, and an interval C having the same level as the interval a. When the next bit of the bit on which the noise X is superimposed is set to "1", the subsequent F2F interval section D of the interval section C is about one-half of the bit cell length and is therefore shorter than the interval section a but longer than the interval section B or the interval section C.
In the conventional reading method, if the length of the current F2F interval section is equal to or longer than a first threshold value, which is a bit decision threshold determined by the length of the previous bit unit, it is determined that the current F2F interval section corresponds to bit "0" in the recorded data, and if it is lower than the bit decision threshold, it is determined that the current F2F interval section and its subsequent F2F interval section correspond to bit "1". The bit decision threshold is for example 70% of the previous bit cell length. This type of bit decision is called a bit following type. When the bit following method is applied to the F2F waveform shown in fig. 3, erroneous recognition occurs in which interval section a alone represents bit "0" and interval sections B and C represent bit "1", or in which interval section a and interval section B represent bit "1" and interval section C and interval section D represent bit "1".
The false recognition caused by the superposition of the hump-like noise and the magnetic reproduction waveform is caused when the change in the magnetic reproduction waveform is smooth, that is, when the peak-to-peak distance due to the reversal of the magnetization direction is long, and is characteristically generated when the recording bit is "0". Although the reading apparatus shown in fig. 2 has higher noise resistance than the reading apparatus shown in fig. 1, when a hump-shaped noise is superimposed on a position in the magnetic reproduction waveform where the signal level is close to 0, and as a result, the positive and negative of the magnetic reproduction waveform near the noise change, the above-described occurrence of misrecognition cannot be prevented.
Therefore, in the reading method according to the present invention, when the F2F interval section that is much shorter than the length of the immediately preceding bit cell is detected based on the feature of the above-described F2F waveform that causes the erroneous recognition, the arithmetic unit 26 of the reading apparatus shown in fig. 1 or 2 determines that the F2F interval section is caused by noise, and performs the process of removing the noise. The arithmetic unit 26 performs recovery of the recorded data based on the bit-following method after removing the noise. Since the extremely short F2F interval section generated by the noise in the F2F waveform is a characteristic interval section in the F signal that is the recording bit of "0" as described above, it is determined that the extremely short interval section (interval section B in the example of fig. 3) and the preceding and following interval sections (interval section a and interval section C in the example of fig. 3) constitute the recording bit of "0" in the noise canceling process. Whether or not the interval is an extremely short F2F interval is determined using a noise determination threshold as a second threshold. The noise determination threshold needs to be set so that the normal interval of F2F in the original recording bit "1" (i.e., 2F signal) is not erroneously recognized as noise. In JISX 6302-2 and-6, the allowable error of the F2F interval for recording bit "1" is defined as ± 20%, and in view of this, 25% of the average bit cell length obtained by adding a slight margin to the allowable error may be used as the noise determination threshold. The average bit cell length is the average of the previous bit cell lengths of several bits. Alternatively, for example, 25% of the bit cell length of the previous bit amount may be used as the noise determination threshold, or 25% of the bit cell length determined in the standard value for writing data to the magnetic recording medium may be used as the noise determination threshold.
Through the above-described processing, it is possible to prevent erroneous recognition due to hump-shaped noise, and a portion including the noise is estimated to correspond to the recording bit "0". However, this process increases irregularity in the reading of the magnetic data, and may cause erroneous recognition in the F2F interval section following the interval section where the noise is removed. Therefore, the sum of the lengths of the extremely short interval B to be noise-cancelled, and the preceding and following interval a and interval C is obtained, and the rate of change of the sum with respect to the length of the preceding Bit cell (i.e., Bit-to-Bit Jitter (BBJ)) is obtained, and it is possible to determine whether or not the BBJ is within an assumed range (e.g., ± 40%) including various kinds of variations, that is, to perform a Jitter check. In the jump check, if the BBJ is within the assumed range, it is judged to be normal, otherwise, an alarm is generated as a possibility of erroneous recognition. Alternatively, in order to appropriately estimate the interval section to which the bit cell belongs and appropriately perform the subsequent bit decision, when the sum of the lengths of the extremely short interval section B to be subjected to noise cancellation and the interval section a preceding the extremely short interval section B is equal to or greater than a predetermined bit cell decision threshold (i.e., a third threshold), the interval section C subsequent to the extremely short interval section B is not a processing target of noise cancellation, i.e., the interval section C belongs to the subsequent bit cell. This process may be a process of determining whether the interval section C belongs to the current bit cell or the subsequent bit cell, and is therefore referred to as bit cell determination. The bit cell determination threshold may be, for example, an average bit cell length, or may be a length determined by the F signal according to a standard.
Although the outline of the processing performed by the arithmetic unit 26 has been described above, an example of the processing performed by the arithmetic unit 26 will be described below with reference to a flowchart shown in fig. 4. It is assumed that after the processing up to a certain bit cell is completed, the data up to the bit cell is restored. The arithmetic unit 26 sets the first interval section of the unprocessed F2F interval sections as the current F2F interval section, sets the time length of the current F2F interval section to T1 in step 101, and determines whether or not T1 is equal to or greater than a bit determination threshold in step 102. The bit decision threshold is a first threshold for determining whether the F2F interval section corresponds to the F signal or the 2F signal as described above. The bit decision threshold may be, for example, 70% of the previous bit cell length, 70% of the average bit cell length, or 70% of a value determined by a standard as the length of the F signal. Here, when the bit determination threshold is determined based on the bit unit length of the previous bit amount, it is possible to determine that the deviation of the transport speed of the magnetic card 10 in the reader device matches. When the bit determination threshold is determined based on the average bit unit length, even when the length of the bit unit of the previous bit amount suddenly becomes an abnormal value, it is possible to avoid erroneous determination by the abnormal value while increasing the transport speed of the magnetic card 10. When a bit decision threshold based on a length determined according to a standard is used, a decision with respect to the standard can be made. Further, although the tolerance of the interval of F2F of the 2F signal is ± 20% according to the standard, the bit determination can be performed with high accuracy even when the length deviation of the 2F signal reaches the upper limit of the standard by using the bit cell length as a reference instead of the length of the 2F signal.
In step 102, when T1 is lower than the bit decision threshold, it is determined that the current F2F interval section and the subsequent F2F interval section (i.e., the next F2F interval section from the current F2F interval section) constitute "1" recording bits according to the existing bit following method. In the present embodiment, if the present embodiment is not affected by noise, it is estimated that the current F2F interval section and the subsequent F2F interval section are interval sections corresponding to bit "1" in the recording data. The arithmetic unit 26 sets the length of the subsequent F2F interval section to T2 at step 111, and determines whether or not T2 is equal to or greater than the above-described noise determination threshold at step 112. When the noise determination threshold is the second threshold and T2 is equal to or greater than the noise determination threshold, it is determined that the subsequent F2F interval section is not noise but a normal F2F interval section, and therefore, in step 113, it is determined that the current F2F interval section and the subsequent F2F interval section are interval sections of recording bits constituting "1" based on the bit following method, and the process is ended.
On the other hand, when T2 is equal to or less than the noise determination threshold value in step 112, it is determined that the subsequent F2F interval section is noise in step 114. When it is determined to be noise, as described above, it can be immediately estimated that the current F2F-spaced interval (spaced interval a in the example of fig. 3), the subsequent F2F-spaced interval (spaced interval B in the example of fig. 3), and the subsequent F2F-spaced interval (spaced interval C in the example of fig. 3) constitute "0" recording bits. The subsequent F2F interval is the next F2F interval immediately following the subsequent interval. However, in the processing shown in fig. 4, the bit cell determination described above is introduced, and in step 115, the arithmetic unit 26 determines whether or not the sum of T1 and T2 is equal to or greater than the bit cell determination threshold value that is the third threshold value. If the sum of T1 and T2 is lower than the bit cell determination threshold, it is estimated that the current F2F interval section, the subsequent F2F interval section, and the subsequent F2F interval section correspond to the recording bit of "0" in step 116, and the process ends. On the other hand, in step 115, when the sum of T1 and T2 is equal to or greater than the bit cell determination threshold, it is inappropriate to set the next F2F interval section to be subjected to noise cancellation, so the arithmetic unit 26 estimates in step 117 that the recording bit is "0" constituted by the current F2F interval section and the next F2F interval section, and ends the processing.
In step 102, when T1 is equal to or greater than the bit decision threshold, it is determined that the current F2F interval section constitutes a recording bit of "0" according to the conventional bit following method. In the present embodiment, if the present embodiment is not affected by noise, it is also assumed that the current F2F interval section is an interval section corresponding to bit "0" in the recording data. Here, the arithmetic unit 26 sets the length of the subsequent F2F interval section to T2 in step 121, and determines whether or not T2 is equal to or greater than the above-described noise determination threshold value as the second threshold value in step 122. When T2 is equal to or greater than the noise determination threshold, it is determined that the subsequent F2F interval section is not noise but a normal F2F interval section, and therefore, in step 123, it is determined that the current F2F interval section is an interval section of recording bits constituting "0" based on the bit following method, and the process ends.
On the other hand, when T2 is equal to or less than the noise determination threshold value in step 122, it is determined that the subsequent F2F interval section is noise in step 124. When it is determined to be noise, the arithmetic unit 26 determines whether or not the sum of T1 and T2 is equal to or greater than the bit cell determination threshold in step 125, as in the processing of steps 115 to 117 described above. If the sum of T1 and T2 is lower than the bit cell determination threshold, it is estimated that the current F2F interval section, the subsequent F2F interval section, and the subsequent F2F interval section correspond to the recording bit of "0" in step 126, and the process ends. On the other hand, in step 125, when the sum of T1 and T2 is equal to or greater than the bit cell determination threshold, it is inappropriate to set the next F2F interval section to be subjected to noise elimination, so the arithmetic unit 26 estimates in step 117 that the recording bit is "0" constituted by the current F2F interval section and the next F2F interval section, and ends the processing.
[ Effect ]
In the reading method of the present embodiment, it is not necessary to provide an integration circuit, and data can be reliably read from the magnetic recording medium with a simple circuit configuration without being affected by noise. In particular, as described with reference to fig. 1 and 2, the reading circuit 21 of the present embodiment has the same hardware configuration as a conventionally known reading circuit including a differentiating circuit, except that the processing of the arithmetic section 26 is different from that of the conventional reading circuit. The arithmetic unit 26 for restoring the recorded data based on the F2F waveform may be configured by using a dedicated hardware circuit, but in recent years, it is generally realized by a microprocessor, a microcomputer, or the like. Therefore, the reading method according to the present embodiment can be executed by software processing of the arithmetic unit 26, and the influence of the hump-like noise component on the magnetic reproduction waveform can be removed by the software processing. As shown in fig. 4, this software process is a smaller-scale process. As described above, the reading method according to the present embodiment can be realized by replacing software of the arithmetic section included in the existing reading apparatus with software for executing the above-described processing, and the reading apparatus according to the present invention can be realized only by modifying software in the existing reading apparatus.
Claims (20)
1. A reading method for generating a digital signal having any one of two values in accordance with increase and decrease in a magnetic reproduction waveform obtained by using a magnetic head that performs relative sliding with respect to a magnetic recording medium, and inputting the magnetic reproduction waveform to a differentiating circuit, processing the continuous interval sections with an interval between the two values in the digital signal as an interval section, and recovering recording data in the magnetic recording medium based on a length of each interval section, the reading method comprising:
an estimation step of estimating at least a bit in the recording data corresponding to a current interval section by comparing a length of the current interval section with a first threshold value;
a determination step of comparing the length of a subsequent interval section subsequent to the current interval section with a second threshold value, and determining that the subsequent interval section is noise when the length of the subsequent interval section is lower than the second threshold value;
and a noise removal step of, when the determination step determines that the noise is generated, performing a process of removing the noise.
2. The reading method according to claim 1,
in the estimation step, the estimation step is performed,
estimating that the current interval section is an interval section corresponding to a bit "0" in the recording data when the length of the current interval section is equal to or greater than the first threshold value,
when the length of the current interval section is less than the first threshold value, it is estimated that the current interval section and the subsequent interval section are interval sections corresponding to bit "1" in the recording data.
3. The reading method according to claim 2,
in the noise removing step, it is set that at least the current interval section and the subsequent interval section are interval sections constituting a bit "0" in the recording data, regardless of the estimation result in the estimating step.
4. The reading method according to claim 3,
in the noise removing step, when a sum of lengths of the current interval section and the subsequent interval section is less than a third threshold value, a next interval section of the current interval section, the subsequent interval section, and the subsequent interval section is set as an interval section constituting a bit "0" in the recording data, and when the sum is equal to or greater than the third threshold value, the current interval section and the subsequent interval section are set as an interval section constituting a bit "0" in the recording data.
5. The reading method according to claim 2,
the sum of the lengths of the interval sections set to constitute bit "0" in the noise removal process is subjected to a jitter check by determining the rate of change with respect to the previous bit cell length.
6. The reading method according to claim 3,
the sum of the lengths of the interval sections set to constitute bit "0" in the noise removal process is subjected to a jitter check by determining the rate of change with respect to the previous bit cell length.
7. The reading method according to claim 4,
the sum of the lengths of the interval sections set to constitute bit "0" in the noise removal process is subjected to a jitter check by determining the rate of change with respect to the previous bit cell length.
8. The reading method according to any one of claims 1 to 7,
the first threshold is 70% of any one of a previous bit cell length, an average bit cell length, and a bit cell length determined according to a standard.
9. The reading method according to any one of claims 1 to 7,
the second threshold is 25% of any one of a previous bit cell length, an average bit cell length, and a bit cell length determined according to a standard.
10. The reading method according to claim 8,
the second threshold is 25% of any one of a previous bit cell length, an average bit cell length, and a bit cell length determined according to a standard.
11. A reading apparatus for reading recorded data from a magnetic recording medium, comprising:
a magnetic head that performs relative sliding movement with respect to the magnetic recording medium;
a differentiating circuit that inputs a magnetic reproduction waveform obtained by the magnetic head;
a signal generation circuit that generates a digital signal having any one of two values according to an increase and decrease in the magnetic reproduction waveform, based on an output of the differentiation circuit;
a calculation unit that processes the successive interval sections with the switching interval between the two values in the digital signal as an interval section, and recovers the recording data in the magnetic recording medium based on the length of each interval section,
the arithmetic unit executes the following processing:
an estimation process of estimating at least a bit in the recording data corresponding to a current interval section by comparing a length of the current interval section with a first threshold value;
a determination process of comparing a length of a subsequent interval section subsequent to the current interval section with a second threshold value, and determining that the subsequent interval section is noise when the length of the subsequent interval section is lower than the second threshold value;
and a noise removal process of, when it is determined in the determination process that the noise is generated, performing a process of removing the noise.
12. The reading apparatus according to claim 11,
in the estimation process, the calculation unit estimates that the current interval section is an interval section corresponding to a bit "0" in the recording data when the length of the current interval section is equal to or greater than the first threshold value, and estimates that the current interval section and the subsequent interval section are interval sections corresponding to a bit "1" in the recording data when the length of the current interval section is less than the first threshold value.
13. The reading apparatus of claim 12,
the arithmetic unit sets, in the noise removal processing, that at least the current interval section and the subsequent interval section are interval sections constituting a bit "0" in the recording data, regardless of an estimation result of the estimation processing.
14. The reading apparatus of claim 13,
in the noise removal processing, the calculation unit sets, when a sum of lengths of the current interval section and the subsequent interval section is lower than a third threshold value, an interval section next to the current interval section, the subsequent interval section, and the subsequent interval section as an interval section constituting a bit "0" in the recording data, and sets, when the sum is equal to or higher than the third threshold value, the current interval section and the subsequent interval section as an interval section constituting a bit "0" in the recording data.
15. The reading apparatus of claim 12,
the arithmetic unit obtains a rate of change of the sum of the lengths of the interval sections set to constitute a bit "0" by the noise removal processing with respect to the previous bit cell length, and performs a jitter check.
16. The reading apparatus of claim 13,
the arithmetic unit obtains a rate of change of the sum of the lengths of the interval sections set to constitute a bit "0" by the noise removal processing with respect to the previous bit cell length, and performs a jitter check.
17. The reading apparatus of claim 14,
the arithmetic unit obtains a rate of change of the sum of the lengths of the interval sections set to constitute a bit "0" by the noise removal processing with respect to the previous bit cell length, and performs a jitter check.
18. The reading apparatus according to any one of claims 12 to 17,
the signal generating circuit is constituted by a comparator connected to an output of the differentiating circuit.
19. The reading apparatus according to any one of claims 12 to 17,
the signal generating circuit includes a first comparator connected to an output of the differentiating circuit, a second comparator to which the magnetic reproduction waveform is input, and a timing generator that outputs a signal in which a timing of switching between binary levels in an output signal of the first comparator changes to a level of an output signal of the second comparator.
20. A medium storing a program for causing a computer provided in a reading device for reading recorded data from a magnetic recording medium to execute processing, the medium comprising: a magnetic head that performs relative sliding movement with respect to the magnetic recording medium; a differentiating circuit that inputs a magnetic reproduction waveform obtained by the magnetic head; a signal generation circuit that generates a digital signal having any one of two values according to increase and decrease in the magnetic reproduction waveform based on an output of the differentiation circuit, wherein the computer processes successive intervals, each interval being a switching interval between the two values in the digital signal, and recovers recorded data in the magnetic recording medium based on a length of each interval,
the program causes the computer to execute:
an estimation process of estimating at least a bit in the recording data corresponding to a current interval section by comparing a length of the current interval section with a first threshold value;
a determination process of comparing a length of a subsequent interval section subsequent to the current interval section with a second threshold value, and determining that the subsequent interval section is noise when the length of the subsequent interval section is lower than the second threshold value;
and a noise removal process of, when it is determined in the determination process that the noise is generated, performing a process of removing the noise.
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| Application Number | Priority Date | Filing Date | Title |
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| JP2017-153174 | 2017-08-08 | ||
| JP2017153174A JP6898171B2 (en) | 2017-08-08 | 2017-08-08 | Magnetic recording medium reading method, reading device and program |
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| CN109389997B true CN109389997B (en) | 2020-05-19 |
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| JP6169322B2 (en) * | 2012-03-30 | 2017-07-26 | 日本電産サンキョー株式会社 | Information reproducing apparatus and information reproducing method |
| JP6050059B2 (en) * | 2012-08-30 | 2016-12-21 | 日本電産サンキョー株式会社 | Data demodulating device, data demodulating method, magnetic recording data reproducing device, and program |
| US8985449B2 (en) * | 2012-09-11 | 2015-03-24 | Maxim Integrated Products, Inc. | Magnetic stripe reader |
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| JP2019032915A (en) | 2019-02-28 |
| JP6898171B2 (en) | 2021-07-07 |
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