JP2000242904A - Thermal asperity measuring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure selectively and quantitatively thermal asperity by providing a means detecting the thermal asperity caused at the time of reproducing using a reproducing magnetic head using a magneto-resistive effect element from a magnetic recording medium and a totalizing means totalizing the number of occurrence times of the thermal asperity. SOLUTION: A thermal asperity detection means 12 cuts a high frequency component of an input 2 from an MR head with a low-pass filter 16, and compares the input 2 of only a low frequency component with a prescribed slice level by +side, -side comparators 18a, 18b. An occurrence time setting circuit 20a delays the output signal of the +side comparator 18a by a prescribed delay time to output it to a counter 14 through an inversion circuit 22a and an AND circuit 24a. The output signal of the -side comparator 18b is processed similarly also. The slice level and the delay time are made to be set optionally, and the thermal asperity is detected selectively and quantitatively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phenomenon in which the output voltage of a reproduced signal fluctuates when reproducing information recorded on a magnetic recording medium by a reproducing magnetic head using a magnetoresistive effect element. The present invention relates to a thermal asperity measuring device that detects thermal asperity.

[0002]

2. Description of the Related Art In recent years, a reproducing magnetic head (hereinafter, referred to as an MR) using a magnetoresistive element has been used for reproducing information recorded on a magnetic recording medium such as a hard disk or a backup magnetic tape used in a computer. A fixed head storage system using a head is often used. In particular, many magnetic disks are employed. The MR head is a head in which a current called a sense current is passed through a resistor, and when magnetism is induced therein, the resistance value changes and the current changes, and the change in the current is read.

[0003] The recording density of the MR head is very high, that is, 5 to 10 times that of the conventional induction type head. On the other hand, the MR head has a drawback that it is vulnerable to temperature rise, and the resistance value changes when the temperature rises, and as a result, the current value also changes. for that reason,
During reproduction, when the head comes into contact with a protrusion existing on a magnetic recording medium moving at high speed, heat is instantaneously generated, the resistance value increases, and the output voltage level of the reproduction signal fluctuates (this is called thermal asperity). ).

[0004] Since thermal asperity causes an error when reproducing information from a magnetic recording medium, it is necessary to prevent thermal asperity. For this reason, various methods for preventing or reducing thermal asperity have been conventionally proposed.

For example, Japanese Patent Application Laid-Open No. 10-162306 discloses a method in which a signal simulating thermal asperity is generated, and this signal is subtracted from the reproduced signal to cancel the thermal asperity to reduce the thermal asperity. Things are disclosed. Also, Japanese Patent Application Laid-Open
JP-A-320216 discloses a track / sector position where thermal asperity occurs before recording / reproducing data, and prevents the position from being used for recording / reproduction, thereby preventing erroneous reading of data when there is thermal asperity. What is disclosed is disclosed.

[0006]

However, the above-mentioned countermeasures against the thermal asperity are to avoid the influence of the actually generated thermal asperity and to compensate for the thermal asperity. It analyzed the cause of thermal asperity and did not try to remove it fundamentally. In other words, it was said that the contact of the head with the protrusion of the magnetic recording medium was the cause of the thermal asperity.However, it has not been possible to specify exactly where the protrusion exists, what the shape of the protrusion is, etc. There was no.
For example, the height of the projections was thought to be about 50 nm, but since the recording density has been steadily increasing recently, how many projections have what kind of effect and how many It is desired to obtain information such as how much there is, and to analyze the cause. However, at present it has not been investigated about these problems. Thermal asperity is the relative speed of the magnetic recording medium and the head, the shape of the head,
Since it varies with the sense current and also varies with the type of magnetic recording medium, and the time and magnitude of occurrence vary, it was necessary to quantitatively measure the thermal asperity.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems. In order to eliminate the thermal asperity from the fundamental, the thermal asperity is selectively removed so that more information about the cause of the thermal asperity can be obtained. An object of the present invention is to provide a thermal asperity measuring device capable of quantitatively measuring asperity.

[0008]

In order to solve the above-mentioned problems, the present invention provides a means for detecting a thermal asperity generated when reproducing from a magnetic recording medium using a reproducing magnetic head using a magnetoresistive element. And a counting means for counting the number of occurrences of the thermal asperity.

The means for detecting the thermal asperity includes a low-pass filter for inputting a signal reproduced from the magnetic recording medium by a reproducing magnetic head using a magnetoresistive element, and a predetermined signal for outputting an output signal of the low-pass filter. A comparator for comparing with a slice level, a delay circuit for delaying an output signal of the comparator for a predetermined time, and an AND circuit for calculating a logical sum of the delayed signal and an output signal of the comparator; The counting means preferably counts the number of high-level outputs from the AND circuit for a predetermined time.

Further, it is preferable that the slice level and the delay time can be arbitrarily set.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a thermal asperity measuring apparatus according to the present invention will be described in detail based on a preferred embodiment shown in the accompanying drawings.

FIG. 1 is a block diagram schematically showing a thermal asperity measuring apparatus according to one embodiment of the present invention. In FIG. 1, the thermal asperity measuring apparatus 10 of the present embodiment has a thermal asperity detecting means 12 and a counter 14 for counting the number of detected thermal asperities.

As described above, the thermal asperity is such that an MR head comes into contact with a projection on a magnetic recording medium to generate heat and the output voltage changes due to a change in the resistance value of the head. It is known that there is a case where not only a change to the + side but also a change to the − side. Therefore, it is necessary to detect the thermal asperity not only on the positive side but also on the negative side.

The thermal asperity detecting means 12 has a low-pass filter 16 for cutting high-frequency components of a reproduced signal obtained by reproducing information recorded on a magnetic recording medium by an MR head. For detecting the thermal asperity on the + side of the reproduced signal of
In order to detect the negative-side thermal asperity, a comparator (+ side comparator 18a,-side comparator 1
8b), generation time setting circuits 20a and 20b, inversion circuit 2
2a and 22b, and two AND circuits 24a and 24b. Further, another inverting circuit 22c is provided on the side for detecting the negative thermal asperity.

A comparator (+ side comparator 18a and-
The side comparator 18b) compares the reproduced signal of only the low frequency component with a predetermined slice level. The generation time setting circuit 20a delays one of the output signals of the + side comparator 18a by a predetermined delay time. As will be described later in detail, the delay time designates the size of the thermal asperity to be detected (time width, thermal asperity generation time). Inverting circuit 22a
Is for inverting the output signal of the generation time setting circuit 20a, and the AND circuit 24a outputs the inverted signal
The logical sum with the output signal of the + side comparator 18a is obtained.

On the other hand, the output signal of the negative comparator 18b is once inverted by the inverting circuit 22c. By inverting in this way, it is possible to handle the case exactly as in the case of the + side.
b, the inverting circuit 22b, and the AND circuit 24b operate in the same manner as those described above for the + side thermal asperity. That is, the generation time setting circuit 20b includes the inverting circuit 2
2c is delayed by a predetermined delay time, and the inversion circuit 22b inverts the delayed signal, and
4b calculates the logical sum of the inverted signal and the output signal of the inverting circuit 22c.

AND indicating occurrence of thermal asperity
The number (number) of high-level outputs of the circuit 24a and the AND circuit 24b is counted by the counters 14a and 14b, respectively.

Hereinafter, the operation of the present embodiment will be described. MR
FIG. 2 shows a waveform of input 2 which is a signal read from the magnetic recording medium by the head. In the graph of FIG. 2, the horizontal direction represents time, and the vertical direction represents voltage. As shown in FIG. 2, the waveform of the input 2 has a sudden change in voltage due to thermal asperity. When this input 2 is passed through a low-pass filter 16 to cut high-frequency components, a signal as shown by a waveform 1 in FIG. 2 is obtained. At this time, a true output as shown by a waveform 1, for example, an output in the case of reproducing only without writing anything on the magnetic recording medium, does not need to pass through the low-pass filter 16, so that it is input from the input 1 in FIG. To

The waveform 1 is input to the plus side comparator 18a and the minus side comparator 18b. Since the processes on the + and-sides are the same, only the + side will be described. The + side comparator 18a compares the waveform 1 with the slice level indicated by the dashed line in the waveform 1 of FIG.
Is output. Waveform 2 is generated by generating time setting circuit 20a and
The signal is input to the D circuit 24a. Occurrence time setting circuit 20a
Outputs a waveform 3 having a width of the delay time b from the rise of the waveform 2 in order to indicate the magnitude (time width) of the thermal asperity to be detected. The inversion circuit 22a
The waveform 3 is inverted and the waveform 4 is output to the AND circuit 24a.

The AND circuit 24a calculates the logical sum of the waveform 2 and the waveform 4, and outputs the waveform 5. Waveform 5 corresponds to the occurrence of thermal asperity. Each time a high-level signal of the waveform 5 is output, a flag is set, and the number is counted by the counter 14a. Here, the operator can arbitrarily set the slice level in the + side comparator 18a and the delay time b in the generation time setting circuit 20a. For example, when the slice level is increased, a thermal asperity having a large amplitude, that is, a large voltage fluctuation can be detected. Also, the delay time b
When the logical sum of the waveform 2 and the waveform 4 is calculated by the AND circuit 24a, all the high-level portions of the waveform 2 disappear, and fluctuations having a smaller time width than the width b are not caught, and a thermal expansion having a large time width is prevented. Only asperities can be captured. By appropriately setting these values, it is possible to selectively perform quantitative detection of thermal asperity.

The signal which has risen in the AND circuit 24a (24b) is input to a switch of the recording AMP and recorded to be used as a marker. When the magnetic recording medium is a magnetic tape, by magnetically developing the magnetic tape on the magnetic tape, the nucleus of the thermal asperity can be detected later by returning the delay time b from that position.

Next, the results of actually measuring the number of generated thermal asperities for seven magnetic tapes A to G while changing the slice level and the delay time b are shown. The running system is 1/2 inch wide, the relative speed is 1 m / s, the tape tension is 100 g, the tape used is a metal tape, and the reproducing head is an MR head. Table 1 below,
2 is 1/2 (from peak to peak) when recording / reproducing a frequency of 1 MHz, the recording current is ORC (optimum recording current), and Tables 3 and 4 are (from peak to peak) when recording / reproducing a frequency of 1 MHz. At 3/4 of the peak) the recording current is OR
C, and in each case, the number of generated thermal asperities per 60 m was measured.

[0023]

[0024]

[0025]

[0026]

As can be seen from these results, the frequency 1
MHz when recording / reproducing (peak to peak)
In either case of お よ び and ／, the number of occurrences of thermal asperity is particularly concentrated on a delay time (thermal asperity generation time) of 2 μs or less. As described above, according to the present embodiment, by variously changing the setting of the slice level (amplitude) and the delay time (occurrence time), it is possible to selectively and quantitatively determine the size of the grain that causes the thermal asperity. By detecting, the cause of thermal asperity and its influence can be analyzed from various angles.

The signals of the inputs 2 and 1 are converted to a high-speed A signal.
It is also possible to count the number of occurrences of thermal asperity by taking in with a / D converter and performing the processing described above in software. Further, as described above, the flag for counting by the counter 14a (14b) is taken out, the recording / reproducing AMP is switched by the flag, and the mark is put on the magnetic tape as described above, so that the mark is obtained. It is possible to search for the core of thermal asperity.

Although the thermal asperity measuring apparatus of the present invention has been described in detail above, the present invention is not limited to the above examples, and the scope of the present invention does not depart from the gist of the present invention.
Of course, various improvements and changes may be made.

[0030]

As described above, according to the present invention, thermal asperity can be selectively measured quantitatively, more information can be obtained on the cause of the occurrence of thermal asperity, and thermal asperity can be fundamentally measured. The analysis of thermal asperity becomes possible to solve the problem. The counting means for counting the number of occurrences of thermal asperity takes out a flag for counting and records / records the flag.
When the reproduction AMP is switched to put a mark on the magnetic tape, it becomes possible to search for a core of thermal asperity by using the mark. Further, the input signal reproduced by using the reproducing magnetic head is converted into a high-speed A /
If the data is captured by a D converter, the number of occurrences of thermal asperity can be counted by software processing.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing a thermal asperity measuring device according to an embodiment of the present invention.

FIG. 2 is a diagram showing signal waveforms showing the operation of the present embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Thermal asperity measuring device 12 Thermal asperity detecting means 14 Counter 16 Low pass filter 18a + side comparator 18b-side comparator 20a, 20b Generation time setting circuit 22a, 22b, 22c Inverting circuit

Claims (2)

[Claims] A means for detecting a thermal asperity generated when reproducing from a magnetic recording medium using a reproducing magnetic head using a magnetoresistive element; and a totaling means for totalizing the number of occurrences of the thermal asperity. A thermal asperity measuring device, comprising: 2. A low-pass filter for inputting a signal reproduced from the magnetic recording medium by a reproducing magnetic head using a magneto-resistive element, and a means for detecting an output signal of the low-pass filter. A comparator for comparing with a slice level, a delay circuit for delaying an output signal of the comparator for a predetermined time, and an AND circuit for calculating a logical sum of the delayed signal and an output signal of the comparator; 2. The thermal asperity measuring device according to claim 1, wherein the counting means counts the number of high-level outputs from the AND circuit for a predetermined time.