JP6898171B2 - Magnetic recording medium reading method, reading device and program - Google Patents

Description

The present invention relates to a reading method, a reading device, and a program for reading data from a magnetic recording medium such as a magnetic card.

In a magnetic recording medium such as a magnetic card, a bit string consisting of binary bits of "0" and "1" is recorded using the direction of magnetization in the magnetic stripe. The FM modulation method is widely known as a method for recording bit string data in a magnetic stripe, and one of them is an F2F modulation method. In the F2F modulation method, the region in which one bit of data is recorded in the magnetic stripe is used as a bit cell, and (a) the direction of magnetization is reversed at the boundary between adjacent bit cells, and (b) the inside of the bit cell corresponding to “0”. Then, record so as to satisfy the conditions of not reversing the magnetization direction (that is, F signal) and (c) inverting the magnetization direction at a position approximately in the center of the bit cell corresponding to “1” (that is, 2F signal). I do. When the magnetic head is slid relative to the magnetic stripe recorded in this way, a signal that peaks at a position where the magnetization is reversed is output from the magnetic head. By demolating the above, the bit string data recorded on the magnetic stripe will be reproduced. Such a signal output from the magnetic head is called a magnetic reproduction waveform.

As described in Patent Document 1 or Patent Document 2, a peak detection circuit composed of a differentiating circuit is generally used for demodulation of the magnetically reproduced waveform. Ideally, the magnetically regenerated waveform is a signal that peaks when there is a reversal of the magnetization direction and changes monotonically until the next reversal of the magnetization direction. By digitizing this signal through a peak detection circuit, that is, a differentiating circuit, and further through a comparator, a digital signal having either binary value corresponding to the direction of magnetization in the magnetic stripe can be obtained. Therefore, the original bit string consisting of "0" and "1" is restored by extracting the time interval corresponding to the bit cell from this digital signal and determining whether or not there is polarity reversal in the extracted time interval. To. However, if the magnetic stripe is scratched, the magnetic force on the magnetic stripe is weakened, or the data recording on the magnetic stripe is incomplete, the signal output from the magnetic head is hump-like. The noise of the above may be superimposed and the differential circuit may mistakenly recognize this noise as a normal polarity inversion, and as a result, the wrong data may be restored. In order to prevent such misrecognition, Patent Document 3 discloses that an integrator circuit is used instead of the differentiating circuit, and that the recorded data is restored based on the result obtained from the differentiating circuit and the result obtained from the integrator circuit. doing. In a digital signal obtained using a differentiating circuit or an integrating circuit, the interval of switching between one level (for example, low level) and the other level (for example, high level) represents the interval of reversal of the direction of magnetization. Should be. Patent Document 3 also describes that when the interval of switching between binary levels is different from the time interval originally predicted, it is detected as an error.

Patent Document 4 is provided with an oscillator that generates a clock that serves as a reference for noise removal, and based on the clock, a component having a predetermined pulse width in the digital data is removed as noise, and a component in the middle of the digital data is removed in advance. It is disclosed to correct fluctuations within a defined range to be continuous.

Japanese Unexamined Patent Publication No. 2001-135034 JP-A-2015-49914 JP-A-2007-95117 Japanese Unexamined Patent Publication No. 8-172345

The integrator circuit has the effect of smoothing the entire waveform, including the noise component. Therefore, when an integrating circuit is used as described in Patent Document 3, the amplitude of the magnetically reproduced waveform becomes even smaller when reading a magnetic recording medium in which the magnetic force is weakened and the amplitude of the magnetically reproduced waveform is originally small. Good reading may not be possible. Further, when the differentiating circuit and the integrating circuit are used together, both of these circuits must be mounted, which complicates the circuit configuration. Many conventional magnetic recording medium readers do not have an integrator circuit but have a differentiating circuit, but even such a reader is required to be able to read data reliably without being affected by noise. Has been done.

An object of the present invention is a reading method and a reading device for a magnetic recording medium capable of reliably reading data from a magnetic recording medium having a reduced magnetic force without being affected by noise by a simple circuit configuration. The purpose is to provide a program for executing the reading method.

In the method for reading a magnetic recording medium of the present invention, a magnetic reproduction waveform is acquired by using a magnetic head that slides relative to the magnetic recording medium, and the magnetic reproduction waveform is input to a differential circuit to obtain a magnetic reproduction waveform. A digital signal that takes one of the two values according to the increase or decrease of is generated, and the interval of switching between the two values in the digital signal is used as an interval, and continuous intervals are processed based on the length of each interval. In a reading method for restoring recorded data on a magnetic recording medium, an estimation step of estimating bits in the recorded data corresponding to at least the current interval by comparing the length of the current interval with the first threshold, and the current estimation process. A determination step in which the length of the subsequent interval following the interval is compared with the second threshold value, and the subsequent interval is determined to be noise when the length of the subsequent interval is less than the second threshold value, and noise in the determination step. It is characterized by having a noise canceling step of executing a process of canceling the noise when it is determined.

The reading device of the present invention is a reading device that reads recorded data from a magnetic recording medium, and is a differential input between a magnetic head that slides relative to the magnetic recording medium and a magnetic reproduction waveform obtained by the magnetic head. Interval between the signal generation circuit that generates a digital signal that takes either of two values according to the increase or decrease in the magnetic reproduction waveform based on the output of the circuit and the differential circuit, and the switching interval between the two values in the digital signal. It has a calculation unit that processes continuous intervals and restores the recorded data in the magnetic recording medium based on the length of each interval, and the calculation unit sets the length of the current interval as a first threshold value. The estimation process that estimates the bits in the recorded data corresponding to at least the current interval by comparing with the second threshold for the length of the subsequent interval following the current interval, and the length of the subsequent interval. A determination process for determining the subsequent interval as noise when is below the second threshold value and a noise cancellation process for executing a process for canceling the noise when the determination process determines that the noise is generated are executed.

The program of the present invention is based on a magnetic head that slides relative to a magnetic recording medium, a differential circuit that inputs a magnetic reproduction waveform obtained by the magnetic head, and an output of the differential circuit, and uses a magnetic reproduction waveform. It is provided in a reading device that has a signal generation circuit that generates a digital signal that takes either of two values according to an increase or decrease and reads recorded data from a magnetic recording medium, and an interval of switching between the two values in the digital signal. To a computer that processes successive intervals and restores the recorded data on the magnetic recording medium based on the length of each interval, at least by comparing the length of the current interval with the first threshold. The estimation process for estimating the bits in the recorded data corresponding to the current interval is compared with the second threshold for the length of the subsequent interval following the current interval, and the length of the subsequent interval is less than the second threshold. Occasionally, a determination process for determining the subsequent interval as noise and a noise cancellation process for executing a process for canceling the noise when the determination process determines that the interval is noise are executed.

When hump-like noise is superimposed on the magnetically reproduced waveform, erroneous recognition may occur when trying to restore recorded data from this magnetically reproduced waveform using a differentiating circuit. Noise can be removed only by processing a digital signal which is, for example, an F2F waveform without providing it. Further, since the processing is for a digital signal, noise can be removed only by changing the software without changing the conventional hardware structure. In particular, in the reader of the present invention, the signal generation circuit can be configured by a comparator connected to the output of the differential circuit, or a first comparator connected to the output of the differential circuit and a magnetic reproduction waveform are input. It is composed of a second comparator and a timing generator that outputs a signal that changes to the level of the output signal of the second comparator at the timing of switching between the binary levels of the output signal of the first comparator. be able to. Such a reader of the present invention can eliminate the influence of noise superimposed on the magnetic reproduction waveform by using a conventional circuit having a simple configuration.

In the present invention, when estimating the bits in the recorded data, it is estimated that the current interval is the interval corresponding to the bit "0" in the recorded data when the length of the current interval is equal to or greater than the first threshold value. Then, when the length of the current interval is less than the first threshold value, it can be estimated that the current interval and the subsequent interval are the intervals corresponding to the bit "1" in the recorded data. In this way, according to the present invention, it is possible to restore recorded data from a magnetic recording medium recorded by the F2F modulation method without being affected by noise.

In the present invention, at least the current interval and the subsequent interval constitute bit "0" in the recorded data, regardless of the estimation result when the bits in the recorded data are estimated when performing noise cancellation. can do. In the case of the F2F modulation method, the influence of noise is characteristic of the interval corresponding to the bit “0”, so that at least the current interval and the subsequent interval form the bit “0” in the recorded data in the noise canceling process. By doing so, the influence of noise at the interval corresponding to the bit "0" can be more reliably removed. Estimating which interval constitutes the bits "0" and "1" is also estimating the interval belonging to the bit cell. In particular, in the present invention, in the noise canceling process, the sum of the lengths of the current interval and the subsequent interval is a third so that the interval belonging to the bit cell can be appropriately estimated and the subsequent bits can be appropriately determined. When it is less than the threshold value, the current interval, the subsequent interval, and the next interval of the subsequent interval shall constitute bit "0" in the recorded data, and when the sum is equal to or more than the third threshold value, It is preferable that the current interval and the subsequent interval constitute a bit "0" in the recorded data. With this configuration, it is possible to correct the interval so that it is continuous including the interval directly affected by noise and the interval adjacent to that interval, and it is possible to eliminate the influence of noise and restore the recorded data accurately. become.

In the present invention, it is preferable to perform a jitter check by obtaining the rate of change from the immediately preceding bit cell length with respect to the sum of the lengths of the intervals that constitute the bit “0” by the noise canceling process. By performing the jitter check, it is possible to judge the validity of the noise canceling process even if the noise canceling process causes misreading or erroneous correction.

In the present invention, the first threshold value is set to 70% of any one of, for example, the immediately preceding bit cell length, the average bit cell length, and the standard bit cell length, and the second threshold value is, for example, the immediately preceding bit cell. It is set to 25% of any one of the length, the average bit cell length, and the bit cell length specified in the standard. By setting these thresholds based on the actual bit cell length, it is possible to make a judgment according to the transport speed, and by setting these thresholds based on the bit cell length specified in the standard, the judgment based on the standard can be made. It will be possible to do. In particular, when the second threshold value is set to 25% of the bit cell length, this is larger than the permissible standard of the interval for the 2F signal, so that the risk of erroneous determination can be suppressed.

According to the present invention, when reading data from a magnetic recording medium such as a magnetic card, the simple circuit configuration ensures that the data can be reliably read from a magnetic recording medium having a reduced magnetic force without being affected by noise. You will be able to read it.

It is a block diagram which shows the structure of the reading apparatus of one Embodiment of this invention. It is a block diagram which shows the structure of the reading apparatus of another embodiment. It is a waveform diagram which shows the relationship between noise and restored data. It is a flowchart which shows the process in the reading method based on this invention.

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the configuration of a reading device according to an embodiment of the present invention. The reading device shown is for reading recorded data from a magnetic card 10 as a magnetic recording medium, and is formed on a motor 11 that conveys the magnetic card 10 and a magnetic stripe (not shown) of the magnetic card 10 that is conveyed by the motor 11. It includes a magnetic head 12 that slides relative to the magnetic head 12 and a reading circuit 21 that restores recorded data from the magnetic reproduction waveform obtained by the magnetic head 12.

The reading circuit 21 is a generally used circuit having a differentiating circuit 24, and is a bandpass filter (bandpass filter) 22 that extracts a desired frequency component from the magnetic reproduction waveform from the magnetic head 12 and a bandpass filter. An amplifier 23 that amplifies the magnetically reproduced waveform that has passed through the filter 22 is provided, and the magnetically reproduced waveform amplified by the amplifier 23 is input to the differentiating circuit 24. Further, the reading circuit 21 performs a process of determining the polarity of the output of the differentiating circuit 24 and outputting a digital signal represented by a binary level, and a process of restoring recorded data based on the digital signal output from the comparator 25. It is provided with a calculation unit 26 for executing. The processing in the calculation unit 26 will be described later. Since the output value of the differentiating circuit 24 is negative when the instantaneous value is changing so as to decrease in the magnetic reproduction waveform, the output of the comparator 25 is low level and changes so as to increase the instantaneous value in the magnetic reproduction waveform. At this time, the output value of the differentiating circuit 24 is positive, so that the output of the comparator 25 is at a high level. Therefore, the output of the differentiating circuit 24 has a zero cross point corresponding to the peak in the magnetically reproduced waveform. The output of the comparator 25 switches from high level to low level or from low level to high level corresponding to the positive and negative peaks in the magnetically reproduced waveform. The digital signal output by such a comparator 25 is referred to as an F2F waveform.

FIG. 2 shows another form of the reader according to the present invention. The difference between the reading device shown in FIG. 2 and the reading device shown in FIG. 1 is the internal configuration of the reading circuit 21. The reading circuit 21 shown in FIG. 2 is further provided in parallel with the amplifier 23 in the reading circuit 21 shown in FIG. 1, and another amplifier 27 for inputting a magnetic reproduction waveform output by the bandpass filter 22 and an amplifier 27. A comparator 28 for inputting the output of the above and a timing generator 29 are provided. The reading circuit 21 shown in FIG. 2 also has a differentiating circuit 24 and is generally used, for example, as shown in FIG. 17 of Patent Document 1, FIG. 1 of Patent Document 2, and FIG. 11 of Patent Document 3. It is what has been done. The comparator 28 outputs a digital signal according to the polarity of the magnetic reproduction waveform itself. The timing generator 29 outputs a signal that changes to the level of the output signal of the comparator 28 as an F2F waveform at the timing of switching between the high level and the low level of the output signal of the comparator 25. Since the F2F waveform is generated based not only on the positive and negative of the output of the differentiating circuit 24 but also on the positive and negative of the magnetic reproduction waveform itself, the reader shown in FIG. 2 has improved resistance to noise as compared with the reader shown in FIG. doing. Assuming that the same magnetization reproduction waveform is given, the F2F waveform obtained by the reading circuit 21 shown in FIG. 2 is basically a logical inversion of the F2F waveform obtained by the reading circuit 21 shown in FIG. Since the reading method based on the present invention restores the recorded data only based on the timing of switching between the low level and the high level in the F2F waveform, the recorded data can be read regardless of which reading circuit is used. It does not make a substantial difference in the process for restoration.

Next, the influence of noise when the reading device shown in FIG. 1 or 2 is used will be described with reference to FIG. FIG. 3 shows a magnetic reproduction waveform obtained from a magnetic stripe in which the bit string “110101” is recorded as recorded data, and an F2F waveform obtained from the magnetic reproduction waveform. The section from the switching between the high level and the low level in the F2F waveform to the next switching is called the F2F interval. When there is no risk of misunderstanding, the F2F interval is simply called an interval. Since the F2F modulation method is used, if there is no influence such as noise, the bit cell corresponding to the data "0" is composed of one F2F interval corresponding to the F signal, and the bit cell corresponding to the data "1" is 2F. It will consist of two consecutive F2F intervals corresponding to the signal. Here, assuming that the reader shown in FIG. 1 is used, the output of the amplifier 23 is shown as a magnetic reproduction waveform, and the output of the comparator 25 is shown as an F2F waveform.

As shown in FIG. 3, switching between the low level and the high level in the F2F waveform occurs at the positions of the peaks in the positive and negative directions of the magnetic reproduction waveform. Here, at the fifth bit (“0” bit) in the recorded data, as shown by X in the figure, hump-like noise is superimposed on the magnetic reproduction waveform. Since this bit is "0", it is an F signal, and the level switching in the F2F waveform should not occur during the period of the bit cell. However, by differentiating the noise X, the level of the F2F waveform is switched, and the F2F interval corresponding to the original F signal interval is a relatively long interval A and an interval that is different from the interval A and extremely short. It will be divided into B and interval C at the same level as interval A. Assuming that the bit next to the bit on which the noise X is superimposed is "1", the F2F interval D following the interval C is about half the length of the bit cell, so that it is shorter than the interval A, but the interval B and the interval C Will be longer.

In the conventional reading method, if the length of the current F2F interval is equal to or longer than the bit determination threshold determined by the length of the immediately preceding bit cell, that is, the first threshold, the current F2F interval is bit "0" in the recorded data. If it is less than the bit determination threshold value, it is determined that the current F2F interval and the subsequent F2F interval correspond to the bit “1”. The bit determination threshold is, for example, 70% of the immediately preceding bit cell length. Such a bit determination method is called a bit tracking method. When the bit tracking method is applied to the F2F waveform shown in FIG. 3, it is erroneously recognized that the interval A alone represents the bit “0” and the interval B and the interval C represent the bit “1”, or the interval A and It is erroneously recognized that the interval B represents the bit "1" and the interval C and the interval D represent the bit "1".

Such misrecognition due to the hump-like noise superimposed on the magnetically reproduced waveform occurs when the change in the magnetically reproduced waveform is gentle, that is, when the peak and peak due to the reversal of the magnetization direction are relatively long. It occurs and is characteristically generated when the recording bit is "0". Although the reader shown in FIG. 2 has higher noise immunity than the reader shown in FIG. 1, noise is generated as a result of hump-like noise superimposed at a position where the signal level in the magnetic reproduction waveform is close to 0. When the positive / negative of the magnetically reproduced waveform changes in the vicinity, the occurrence of the above-mentioned erroneous recognition cannot be prevented.

Therefore, in the reading method based on the present invention, when an F2F interval extremely shorter than the length of the immediately preceding bit cell is detected based on the above-mentioned characteristics of the F2F waveform that causes erroneous recognition, the reading device shown in FIG. 1 or FIG. The calculation unit 26 of the above determines that the F2F interval is due to noise, and performs a process of canceling the noise. After canceling the noise, the calculation unit 26 restores the recorded data based on the bit tracking method. Since the extremely short F2F interval generated by noise in the F2F waveform is characteristic of the recording bit, that is, the F signal, which is “0” as described above, the extremely short interval (FIG. 6) is used in the noise canceling process. In the example of 3, it is determined that the interval B) and the intervals before and after the interval (interval A and interval C in the example of FIG. 3) constitute the recording bit “0”. Whether or not the F2F interval is extremely short is determined by using the noise determination threshold value, which is the second threshold value. The noise determination threshold value needs to be set so that the normal F2F interval in the original recording bit “1” (that is, the 2F signal) is not mistaken for noise. Given that JIS X6302-2 and -6 specify that the margin of error for the F2F interval at the recording bit "1" is ± 20%, 25% of the average bit cell length with a slight margin added to this margin of error. Can be used as the noise determination threshold. The average bit cell length is the average bit cell length for the last few bits. Alternatively, for example, 25% of the bit cell length of the immediately preceding 1 bit may be used as the noise determination threshold value. 25% of the bit cell length defined in the standard value for writing data to the magnetic recording medium may be used as the noise determination threshold value.

By the process described above, it is possible to prevent erroneous recognition due to the hump-like noise and to estimate that the portion including the noise corresponds to the recording bit “0”. However, this process adds anomalous properties to the reading of magnetic data, and there is a risk that erroneous recognition will occur in the F2F interval after the noise cancellation interval. Therefore, the sum of the lengths of the extremely short interval B, which is the target of noise cancellation, and the intervals A and C before and after the interval B is obtained, and the rate of change (that is, bits) with respect to the length of the immediately preceding bit cell with respect to this sum. Inter-jitter (BBJ): Bit to Bit Jitter) may be obtained, and a so-called jitter check may be performed to determine whether or not the BBJ is within the expected range (for example, ± 40%) including various variations. .. In the jitter check, if the BBJ is within the expected range, it is judged to be normal, and if not, an alarm is generated as there is a possibility of erroneous recognition. Alternatively, the sum of the lengths of the extremely short interval B targeted for noise cancellation and the interval A immediately before it is calculated so that the interval belonging to the bit cell can be appropriately estimated and the subsequent bits can be appropriately determined. When it is equal to or higher than a predetermined bit cell determination threshold value (that is, a third threshold value), the interval C following the extremely short interval B is not subject to noise cancellation processing, that is, the interval C belongs to the subsequent bit cell. It may be assumed. This process is called bit cell determination because it determines whether the interval C belongs to the current bit cell or a subsequent bit cell. For the bit cell determination threshold value, for example, the average bit cell length may be used, or the length specified in the standard for the F signal may be used as it is.

The processing executed by the calculation unit 26 has been outlined above, but an example of the processing performed by the calculation unit 26 will be described below with reference to the flowchart shown in FIG. It is assumed that the processing up to a certain bit cell is completed and the data up to that bit cell is restored. The calculation unit 26 sets the first unprocessed F2F interval as the current F2F interval, sets the time length of the current F2F interval as T1 in step 101, and determines whether T1 is equal to or greater than the bit determination threshold value in step 102. Judge whether or not. As the first threshold value, the bit determination threshold value is a threshold value for determining whether the F2F interval corresponds to the F signal or the 2F signal, as described above. The bit determination threshold value can be set as, for example, 70% of the immediately preceding bit cell length, 70% of the average bit cell length, or 70% of the value defined in the standard as the length of the F signal. Here, if the bit determination threshold value is determined based on the bit cell length of one bit immediately before, the determination can be made according to the variation in the carrying speed of the magnetic card 10 in the reading device. When the bit determination threshold is set based on the average bit cell length, even if the length of the bit cell for the immediately preceding bit suddenly becomes an abnormal value, the abnormal value is taken into consideration with the carrying speed of the magnetic card 10. It is possible to avoid erroneous judgment due to. When the bit determination threshold value based on the length defined by the standard is used, the determination with respect to the standard can be performed. In the standard, the margin of error of the F2F interval of the 2F signal is ± 20%, but the length variation in the 2F signal is caused by using the bit cell length as the reference instead of the 2F signal length as the reference. Even when the upper limit of the standard is reached, the bit determination can be performed with high accuracy.

When T1 is lower than the bit determination threshold value in step 102, the current F2F interval and the subsequent F2F interval (that is, the F2F interval next to the current F2F interval) are "1" according to the conventional bit tracking method. This is the case when it is determined that the recording bit is configured. Also in this embodiment, if it is not affected by noise, it is estimated that the current F2F interval and the subsequent F2F interval are intervals corresponding to bit “1” in the recorded data. In step 111, the calculation unit 26 sets the length of the subsequent F2F interval to T2, and in step 112, determines whether or not T2 is equal to or greater than the above-mentioned noise determination threshold value. The noise determination threshold is the second threshold, and when T2 is equal to or greater than the noise determination threshold, it is determined that the subsequent F2F interval is not noise but a normal F2F interval. Therefore, in step 113, Based on the bit tracking method, it is determined that the current F2F interval and the subsequent F2F interval constitute a recording bit of "1", and the process ends.

On the other hand, when T2 is equal to or less than the noise determination threshold value in step 112, it is determined in step 114 that the subsequent F2F interval is noise. When it is determined to be noise, as described above, the current F2F interval (interval A in the example of FIG. 3), the subsequent F2F interval (interval B in the example of FIG. 3), and the subsequent next F2F interval (FIG. 3). In the example of, it may be estimated immediately that the interval C) constitutes a recording bit of “0”. The subsequent next F2F interval is the F2F interval that follows the subsequent interval. However, in the process shown in FIG. 4, the above-mentioned bit cell determination is incorporated, and in step 115, the calculation unit 26 determines whether or not the sum of T1 and T2 is equal to or greater than the above-mentioned bit cell determination threshold value, which is the third threshold value. judge. When the sum of T1 and T2 is less than the bit cell determination threshold, it is estimated that the current F2F interval, the subsequent F2F interval, and the subsequent next F2F interval correspond to the recording bits of "0" in step 116. And end the process. On the other hand, when the sum of T1 and T2 is equal to or greater than the bit cell determination threshold value in step 115, it is inappropriate to set the subsequent next F2F interval as a noise cancellation target. In step 117, it is estimated that the recording bit of “0” is formed by the current F2F interval and the subsequent F2F interval, and the process ends.

When T1 is equal to or greater than the bit determination threshold value in step 102, it is determined that the current F2F interval constitutes a recording bit of “0” according to the conventional bit tracking method. Also in this embodiment, it is estimated that the current F2F interval is the interval corresponding to the bit “0” in the recorded data if it is not affected by noise. Here, the calculation unit 26 sets the length of the subsequent F2F interval to T2 in step 121, and determines in step 122 whether or not T2 is equal to or greater than the above-mentioned noise determination threshold value, which is the second threshold value. When T2 is equal to or greater than the noise determination threshold value, it is determined that the subsequent F2F interval is not noise but a normal F2F interval. Therefore, in step 123, the current F2F interval is set to "" based on the bit tracking method. It is determined that the recording bit of "0" is formed, and the process is terminated.

On the other hand, when T2 is equal to or less than the noise determination threshold value in step 122, it is determined in step 124 that the subsequent F2F interval is noise. When it is determined that the noise is present, the calculation unit 26 determines in step 125 whether or not the sum of T1 and T2 is equal to or greater than the bit cell determination threshold value described above, as in the process of steps 115 to 117 described above. When the sum of T1 and T2 is less than the bit cell determination threshold, it is estimated that the current F2F interval, the subsequent F2F interval, and the subsequent next F2F interval correspond to the recording bits of "0" in step 126. And end the process. On the other hand, when the sum of T1 and T2 is equal to or greater than the bit cell determination threshold value in step 125, it is inappropriate to set the subsequent next F2F interval as a noise cancellation target. In step 127, it is estimated that the recording bit of “0” is formed by the current F2F interval and the subsequent F2F interval, and the process ends.

[effect]
In the reading method of the present embodiment, data can be reliably read from the magnetic recording medium without being affected by noise with a simple circuit configuration without providing an integrator circuit. In particular, as described with reference to FIGS. 1 and 2, the reading circuit 21 in the present embodiment has a hardware configuration similar to that of a conventionally known reading circuit having a differentiating circuit. Only the processing in the calculation unit 26 is different from the conventional one. The arithmetic unit 26 that restores the recorded data based on the F2F waveform can 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 of the present embodiment can be executed by software processing in the calculation unit 26, and the influence of the hump-like noise component on the magnetic reproduction waveform can be removed by this software processing. This software processing is relatively small, as shown in FIG. As described above, the reading method of the present embodiment can be realized by replacing the software of the arithmetic unit included in the existing reading device with one that executes the above-described processing, and the reading device based on the present invention is an existing reading device. This can be achieved only by modifying the software in the reader.

10 ... magnetic card; 12 ... magnetic head; 21 ... reading circuit, 22 ... bandpass filter; 23, 27 ... amplifier; 24 ... differentiating circuit; 25, 28 ... comparator; 26 ... arithmetic unit; 29 ... timing generator.

Claims (15)

By acquiring a magnetic reproduction waveform using a magnetic head that slides relative to the magnetic recording medium and inputting the magnetic reproduction waveform into a differential circuit, either of two values is obtained according to the increase or decrease in the magnetic reproduction waveform. A digital signal that takes one of them is generated, the interval of switching between the two values in the digital signal is set as an interval, the continuous intervals are processed, and recording in the magnetic recording medium is performed based on the length of each interval. In the reading method to restore data
An estimation step of estimating bits in the recorded data corresponding to at least the current interval by comparing the length of the current interval with the first threshold.
A determination step of comparing the length of the subsequent interval following the current interval with the second threshold value, and determining the subsequent interval as noise when the length of the subsequent interval is less than the second threshold value. ,
A noise canceling step of executing a process of canceling the noise when it is determined to be noise in the determination step,
A reading method, characterized in that it has. In the estimation process
When the length of the current interval is equal to or greater than the first threshold value, it is estimated that the current interval is the interval corresponding to the bit “0” in the recorded data.
Claim 1 that, when the length of the current interval is less than the first threshold value, it is estimated that the current interval and the subsequent interval are intervals corresponding to bit "1" in the recorded data. The reading method described in. The second aspect of the present invention, wherein in the noise canceling step, at least the current interval and the subsequent interval constitute bit "0" in the recorded data regardless of the estimation result in the estimation step. How to read. In the noise canceling step, when the sum of the lengths of the current interval and the subsequent interval is less than the third threshold value, the current interval, the subsequent interval, and the next interval of the subsequent interval Consists of bit "0" in the recorded data, and when the sum is equal to or greater than the third threshold value, the current interval and the subsequent interval are bit "0" in the recorded data. 3. The reading method according to claim 3. According to any one of claims 2 to 4, a jitter check is performed by obtaining the rate of change from the immediately preceding bit cell length with respect to the sum of the lengths of the intervals that form the bit "0" by the noise canceling step. How to read the description. The reading method according to any one of claims 1 to 5, wherein the first threshold value is 70% of any one of the immediately preceding bit cell length, the average bit cell length, and the bit cell length defined in the standard. The reading method according to any one of claims 1 to 6, wherein the second threshold value is 25% of any one of the immediately preceding bit cell length, the average bit cell length, and the bit cell length defined in the standard. A reader that reads recorded data from a magnetic recording medium.
A magnetic head that slides relative to the magnetic recording medium,
A differentiating circuit to which the magnetic reproduction waveform obtained by the magnetic head is input, and
A signal generation circuit that generates a digital signal that takes either of two values according to the increase or decrease in the magnetic reproduction waveform based on the output of the differentiating circuit.
An arithmetic unit that processes the continuous intervals and restores the recorded data in the magnetic recording medium based on the length of each interval, with the switching interval between the binary values in the digital signal as an interval.
Have,
The calculation unit
An estimation process that estimates bits in the recorded data corresponding to at least the current interval by comparing the length of the current interval with the first threshold.
A determination process in which the length of the subsequent interval following the current interval is compared with the second threshold value, and when the length of the subsequent interval is less than the second threshold value, the subsequent interval is determined to be noise. ,
A noise canceling process that executes a process of canceling the noise when it is determined to be noise in the determination process,
A reader that runs. In the estimation process, the calculation unit estimates that the current interval corresponds to the bit "0" in the recorded data when the length of the current interval is equal to or greater than the first threshold value. Then, when the length of the current interval is less than the first threshold value, it is estimated that the current interval and the subsequent interval are intervals corresponding to bit "1" in the recorded data. Item 8. The reading device according to item 8. In the noise canceling process, the calculation unit assumes that at least the current interval and the subsequent interval constitute bits "0" in the recorded data, regardless of the estimation result in the estimation process. The reading device according to claim 9. In the noise canceling process, when the sum of the lengths of the current interval and the subsequent interval is less than the third threshold value, the calculation unit performs the current interval, the subsequent interval, and the subsequent interval. It is assumed that the interval next to the interval constitutes a bit "0" in the recorded data, and when the sum is equal to or greater than the third threshold value, the current interval and the subsequent interval are the recorded data. The reading device according to claim 10, wherein the bit "0" of the above is configured. The calculation unit performs a jitter check by obtaining the rate of change from the immediately preceding bit cell length with respect to the sum of the lengths of the intervals which are supposed to form the bit "0" by the noise canceling process. The reading device according to any one item. The reader according to any one of claims 9 to 12, wherein the signal generation circuit is composed of a comparator connected to an output of the differentiating circuit. The signal generation circuit is between a first comparator connected to the output of the differential circuit, a second comparator input by the magnetic reproduction waveform, and a binary level in the output signal of the first comparator. The reader according to any one of claims 9 to 12, comprising a timing generator that outputs a signal that changes to the level of the output signal of the second comparator at the timing of switching. Based on the magnetic head that slides relative to the magnetic recording medium, the differential circuit that the magnetic reproduction waveform obtained by the magnetic head inputs, and the output of the differential circuit, depending on the increase or decrease in the magnetic reproduction waveform. A signal generation circuit that generates a digital signal that takes either of the two values is provided in a reading device that reads recorded data from the magnetic recording medium, and a switching interval between the two values in the digital signal is set. As an interval, a computer that processes the continuous intervals and restores the recorded data in the magnetic recording medium based on the length of each interval.
An estimation process that estimates bits in the recorded data corresponding to at least the current interval by comparing the length of the current interval with the first threshold.
A determination process in which the length of the subsequent interval following the current interval is compared with the second threshold value, and when the length of the subsequent interval is less than the second threshold value, the subsequent interval is determined to be noise. ,
A noise canceling process that executes a process of canceling the noise when it is determined to be noise in the determination process,
A program that executes.

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