KR20070099334A - Method and apparatus for recording/playbacking data - Google Patents

Abstract

A method and an apparatus for recording/reproducing data are provided to control intervals between a head and a recording medium by judging the interference or transformation of a gap error signal on the basis of the max/min value of the gap error signal. A method and an apparatus for recording/reproducing data comprise the steps of outputting a signal based on the detected light to detect the reflected light by irradiating the light to a recording medium, judging(S63) the max/min value of the output signal, and controlling intervals between the recording medium and a head of the recording and/or reproducing apparatus according to the max/min value.

Description

Method and device for recording / playing data {Method and Apparatus for recording / playbacking data}

1 is a view showing an optical system of a conventional near field recording / reproducing apparatus;

2 is a diagram illustrating an example of a tracking error signal and a gap error signal;

3 is a diagram showing the configuration of a data recording / reproducing apparatus of the present invention;

4 is a view showing the head of FIG.

5 is a diagram showing a data recording / reproducing method according to the first embodiment of the present invention;

6 is a view showing a change in the distance between the head and the recording medium according to the first embodiment;

7 is a diagram showing a data recording / reproducing method according to the second embodiment of the present invention;

FIG. 8 is a view showing a change in the distance between the head and the recording medium according to the second embodiment.

* Description of the symbols for the main parts of the drawings *

11: head 12: head transfer unit

13 control unit 14 signal detection unit

100: recording medium 111: objective lens

112: near-field generating lens 113: lens holder

The present invention relates to data recording / reproducing, and more particularly, to a method and apparatus for recording / reproducing data using near field recording (NFR).

In general, an optical recording / reproducing apparatus is a device for reproducing data recorded on a disc such as a compact disc (CD) or a digital versatile disc (DVD), or recording data on the disc. As consumer preferences require high quality video processing and video compression technology develops, high density recording media are required. One of the key technologies necessary for developing a high density recording medium is a technology related to an optical head.

In such a recording medium, the recording density depends on the spot diameter of the light used for recording and reproduction. That is, the smaller the spot size of the focused light irradiated onto the recording medium, the higher the recording density. The size of the spot of the focused light is largely determined by two factors. One is the Numerical Aperture (NA), which is the performance of the lens used for focusing, and the other is the wavelength of light focused to the lens. Therefore, short wavelength light is used as a method for increasing the recording density. However, in the case of a far field recorder head using a general lens, there is a limit in reducing the spot size because there is a diffraction limit of light. Accordingly, near field recording (NFR) devices using near field optics capable of storing or reading information in units smaller than the wavelength of light have been developed.

1 is a diagram showing an optical system of a conventional near field recording / reproducing apparatus. As shown in Fig. 1, the head of the near field recording / reproducing apparatus includes an objective lens 1 and a near field generating means 2, which is located in close proximity to the recording medium 3. As shown in FIG. Here, the near field generating means 2 includes a fine light output portion having a size smaller than the wavelength of light used, and the light output portion is located very close to the recording medium 3.

The light emitted from the light source is focused by the objective lens 1 and is converted into an evanescent wave by the near field generating means 2. The optical recording by the dissipation wave is called near field optical recording, and the size of the recording mark in the near field optical recording is not limited to the wavelength of light and is determined by the size of the light output unit. In addition, in the remote field, it is assumed that there is air having a refractive index of 1 between the light output unit and the focal point. However, in the case of near field optical recording, the lens and the recording medium 3 are brought close to each other as described above, so that the air refractive index between the optical output and the focus of the lens is ignored. In this case, since the spot size is determined by the refractive index of the lens, a small spot size can be obtained by increasing the refractive index of the lens.

In the case of the conventional near field recording / reproducing apparatus, it is very important that the near field generating means 2 maintain proper spacing without collision or contact at a position very close to the recording medium 3. For example, when a gap error signal (GES) is not accurately detected during a gap servo process in which the near field generating means 2 approaches the recording medium 3, the near field generation occurs. The means 2 and the recording medium 3 may collide / contact or the distance between the near field generating means 2 and the recording medium 3 may be farther apart. In particular, as shown in FIG. 2, a tracking error signal detected to determine whether the near field generating means 2 has left the track of the recording medium 3 interferes with the gap error signal. If a predetermined area of the gap error signal is amplified due to the interference component, it is wrongly determined that the distance between the near field generating means 2 and the recording medium 3 is far. Therefore, when the distance is adjusted, the near field generating means 2 impinges on or comes into contact with the recording medium 3.

Accordingly, the present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a data recording / reproducing method and apparatus capable of accurately adjusting a distance between a head and a recording medium of a data recording / reproducing apparatus. There is.

The data recording / reproducing method of the present invention for achieving the above object comprises the steps of: detecting light reflected by irradiating light onto the recording medium, and outputting a signal based on the detected light; Determining a minimum value and a maximum value of the output signal; Adjusting the distance between the head of the recording and / or reproducing apparatus and the recording medium according to the minimum and maximum values.

The signal output based on the detected light may include: an RF signal indicating an amount of light incident on the recording medium; A gap error signal indicating whether an optical spot incident on the recording medium is focused, and a gap between the head and the recording medium; And a tracking error signal indicating whether the head is eccentric.

Adjusting a distance between the head of the recording and / or reproducing apparatus and the recording medium according to the minimum value and the maximum value comprises: comparing the minimum value with a lower reference value and comparing the maximum value with an upper reference value; And adjusting the distance between the head and the recording medium according to the comparison result. Here, in the adjusting of the distance between the head and the recording medium according to the comparison result, if the minimum value is less than the lower reference value, the distance between the head and the recording medium is widened, and if the maximum value is larger than the upper reference value The gap between the head and the recording medium is narrowed.

The data recording / reproducing method of the present invention further includes adjusting a distance between the head and the recording medium based on the vertical symmetry of the output signal. The vertical symmetry of the detected signal is determined based on whether the difference between the maximum value and the average value of the output signal and the difference between the average value and the minimum value is the same, and if the output signal is asymmetric, the output signal is The distance between the head and the recording medium is adjusted until it is symmetrical.

The recording / reproducing apparatus of the present invention includes: a signal output unit which outputs a signal based on light reflected by irradiating light onto the recording medium; A head feeder for moving the head of the recording and / or reproducing apparatus in the vertical and horizontal directions; And a controller configured to determine a minimum value and a maximum value of the output signal and to adjust a distance between the head and the recording medium according to the minimum value and the maximum value.

The controller compares the minimum value and the maximum value with a lower reference value and an upper reference value, respectively, and adjusts a gap between the head and the recording medium according to the comparison result. If the minimum value is smaller than the lower reference value, the gap between the head and the recording medium is widened. If the maximum value is larger than the upper reference value, the gap between the head and the recording medium is narrowed. The controller may further adjust a distance between the head and the recording medium based on the vertical symmetry of the output signal.

According to another aspect of the present invention, there is provided a recording / reproducing method comprising: setting an interval reference value between a head of a recording and / or reproducing apparatus and a recording medium; Irradiating light onto the recording medium to detect the reflected light, and outputting a signal based on the detected light; Determining whether noise is present in the detected signal; And adjusting the interval reference value according to the determination result.

In the determining of whether or not noise exists in the output signal, the presence of the noise is determined based on the difference between the maximum value and the minimum value of the output signal. If noise is present in the detected signal, the interval reference value is adjusted based on the maximum and minimum values of the detected signal. If the minimum value is smaller than the lower reference value, the interval reference value is widely adjusted. If the maximum value is larger than the upper reference value, the interval reference value is narrowly adjusted.

According to another aspect of the present invention, there is provided a recording / reproducing apparatus, comprising: a signal output unit for outputting a signal representing a distance between a head and a recording medium; And a controller for initially setting a gap reference value between the head and the recording medium, and adjusting the gap reference value according to whether noise is present in the signal output by the signal output unit.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Fig. 3 briefly shows an example of the data recording / reproducing apparatus of the present invention, and shows only the configuration necessary to explain the technical gist of the present invention without omitting general elements. As shown in Fig. 3, the data recording / reproducing apparatus of the present invention includes a head 11, a head conveying section 12, a control section 13, and a signal detecting section 14.

4 illustrates an example of the head 11, an objective lens 111 mounted on the top of the head 11, a near field generating lens 112 positioned below the objective lens 111, and the objective. The lens 111 and the near-field generating lens 112 includes a lens holder 113 for fixing to maintain a constant interval. When the head 11 is a flying type, the head 11 moves by itself in the vertical direction, thereby enabling high-speed recording / playback like a hard disk.

The objective lens 111 receives a laser beam output from a light source through a light transmitting means such as an optical fiber, and condenses the laser beam to transmit to the near field generating lens 112.

The near field generating lens 112 is configured to have a higher refractive index than the objective lens 111. The light passing through the objective lens 111 is refracted by the near field generating lens 112 to form a spot of focus on an inner bottom surface, and the formed spot diameter decreases in inverse proportion to the refractive index of the near field generating lens 112. do. As a result, a spot below the diffraction limit can be obtained, and the spot propagates to the recording medium 100 in the form of dissipation wave to store high-density bit information. The near field generating lens 112 is a solid immersion lens (SIL) made of a material having a high refractive index such as glass, or a hemisphere or a super hemisphere having a conical bottom. In addition, a coil is further disposed around the near field generating lens 112. The coil is used to invert the magnetic field around the near field generating lens 112 to form a recording mark.

The head conveying part 12 is used to adjust the distance between the head 11 and the recording medium 100 and to accurately perform tracking. Vertical vibration of the surface of the recording medium may occur due to distortion of the recording medium due to heat generated during manufacturing of the recording medium or eccentricity due to machining error of the center hole, and surface vibration due to the weight of the recording medium or the inclination of the recording / reproducing apparatus. This can happen. The servo technology is required in order to accurately space and track the head 11 and the recording medium 100 for these various factors. To this end, the head transfer unit 12 may be configured in the form of a floating slider for moving the head 11 in the vertical direction and the horizontal direction.

The signal detector 14 detects an RF signal, a gap error signal, a tracking error signal, and the like based on the light reflected from the recording medium 100. Here, the RF signal indicates the amount of light incident on the recording medium 100, and the gap error signal indicates whether the light spot incident on the recording medium 100 is focused and whether the head 11 and the recording medium ( 100). The tracking error signal indicates whether the head 11 is eccentric, that is, whether the incident light is off the track. The signal detector 14 is composed of one or more photo detectors.

The controller 13 generates an interval between the head 11 and the recording medium 100, in particular, a near field of the head 11, based on the RF signal and the gap error signal detected by the signal detector 14. A gap servo (focus servo) for adjusting the distance between the lens 112 and the recording medium 100 is performed, and the head (a) along the track of the recording medium 100 is based on the detected tracking error signal. 11) Perform tracking servo to move. In addition, as another example of the present invention, the recording / reproducing apparatus may include a dual servo system (control unit). For example, the dual servo system may include a first servo unit configured to perform a tracking servo and a coarse gap servo, and a first servo unit embedded in the head 11 to perform a fine gap servo. Can be.

First Example

5 is a flowchart showing a data recording / reproducing method according to the first embodiment of the present invention. Referring to Fig. 5, the recording / reproducing method according to the first embodiment is as follows. In particular, a description will be given focusing on a gap servo performed in the process of recording or reproducing data.

When a recording command or a reproduction command is input, first, the controller 13 sets a gap reference value R (for example, 20 nm) between the head 11 and the recording medium 100 (S61). The gap reference value R is an interval determined to be suitable for recording or reproducing data. The gap reference value R is set based on a reference value set at the time of manufacture of the data recording / reproducing apparatus, or is an interval (reference value) used at the time of recording / reproducing before. It can be set on the basis of.

Then, as shown in FIG. 6, the controller 13 records the head 11 at a constant speed (for example, several mm / sec) while rotating the recording medium 100 at a constant rotational speed. Begin the first approach process (I) of accessing the medium (100). The first approach I is called an approach.

When a predetermined time has elapsed or a predetermined interval A before reaching the gap reference value R reaches, the controller 13 ends the first approach process I and the first approach process I A secondary approach (II) is initiated, in which the head 11 approaches the recording medium 100 at a speed relatively slower than the approaching speed. As such, the secondary approach process II in which the head 11 approaches the gap reference value R is referred to as hand-over or pull-in. In addition, the signal detector 14 detects a gap error signal during the secondary access process II (S62).

Referring to FIG. 6, the position A of the head 11 at the end of the first approach process I and the position B at the start of the second approach process II are illustrated differently. The positions A and B may be set to match.

When the secondary access process (II) is started, the control unit 13 is the minimum value (minimum voltage value), maximum value (maximum voltage value), average value, etc. of the gap error signal detected by the signal detector 14 Determine / calculate (S63). In this case, the controller 13 determines the minimum, maximum, and average values of the gap error signal obtained while the recording medium 100 is rotated a predetermined number of times. The controller 13 compares the detected minimum value of the gap error signal with a lower reference level (S64). Here, the lower reference level may be a value obtained by converting a minimum interval capable of recording / reproducing data in voltage units or a position (C) at which the head 11 may contact the recording medium 100. Is a value converted into a voltage unit, or a value arbitrarily set in a unit of voltage (for example, 10 nm). Obviously, the lower reference level can be set to various values not presented in the present invention.

As a result of comparing the minimum value with the lower reference level, if the minimum value of the gap error signal is smaller than the lower reference level, the controller 11 may come into contact with or collide with the recording medium 100. (13) is reset by raising the gap reference value (R) (S65). On the contrary, if the minimum value of the gap error signal is greater than or equal to the lower reference level, the controller 13 maintains or lowers the gap reference value R as it is (S66).

In addition, the controller 13 compares the maximum value of the detected gap error signal with an upper reference level (S67). Here, the upper reference level is a value obtained by converting the maximum interval in which data can be recorded / reproduced in voltage units, or the position B of the head 11 at the beginning of the secondary access process II in voltage units. It is a value converted into a value, or the value which converted the arbitrarily set interval (for example, 50 nm) by the voltage unit. Obviously, the higher reference level can be set to various values not presented in the present invention.

As a result of comparing the maximum value with the upper reference level, if the maximum value of the gap error signal is larger than the upper reference level, the control unit 13 is a position where the head 11 cannot record / reproduce data accurately. If it is determined to be at and the gap reference value (R) is lowered and reset (S68). On the contrary, if the maximum value of the gap error signal is less than or equal to the upper reference level, the controller 13 maintains or increases the gap reference value R as it is (S69).

When the gap reference value R is adjusted based on the minimum value and the maximum value of the gap error signal, the gap reference value (a) within the range that the minimum value and the maximum value do not deviate between the lower reference level and the upper reference level ( R) must be adjusted. When the minimum value and the maximum value do not deviate between the lower reference level and the upper reference level, the head 11 does not touch the recording medium 100 and does not go to such an extent that data recording / reproducing is impossible.

As an optional process, the controller 13 determines the up and down symmetry of the gap error signal (S70). In general, when the head 11 contacts the recording medium 100, the gap error signal is detected in an asymmetrical form. Accordingly, in order to determine whether the head 11 and the recording medium 100 are in contact with each other, the controller 13 determines whether the gap error signal is vertically symmetrical.

In order to determine whether the gap error signal is vertically symmetrical, the control unit 13 determines the difference between the maximum value and the average value of the gap error signal (maximum value-average value) and the difference between the average value and the minimum value of the gap error signal (average value). -Minimum value) and determine whether the two difference values are the same. If the two difference values are the same, the gap error signal is vertically symmetrical, and thus the controller 13 maintains the gap reference value R reset based on the minimum value and the maximum value. On the contrary, since the gap error signal is asymmetric when the two difference values are not the same, the controller 13 adjusts the reset gap reference value R again. For example, if the two difference values are not the same, the control unit 13 adjusts the gap reference value R based on the minimum and maximum values of the gap error signal as described above, or the gap error. The gap reference value R is increased until the signal is vertically symmetrical (S71).

Then, when the gap reference value R is not changed, the control unit 13 approaches the head 11 until reaching the initially set gap reference value R (S72), and the gap reference value R is If changed, the head 11 is approached until the changed gap reference value R is reached. Then, the control unit 13 records data on the recording medium 100 or reproduces the recorded data. The above-described gap reference value R adjustment process may be repeatedly performed during the secondary access process II and may also be performed while recording or reproducing data.

2nd Example

7 is a flowchart showing a data recording / reproducing method according to the second embodiment of the present invention. Referring to Fig. 7, the recording / reproducing method according to the second embodiment is as follows.

First, the control unit 13 sets the gap reference value R in the same manner as in the first embodiment (S81), and rotates the recording medium 100 at a predetermined rotational speed as shown in FIG. (11) is approached to the recording medium 100 at a constant speed (e.g., several mm / sec). At this time, the signal detector 14 detects a gap error signal (S82), and the controller 13 determines a minimum value, a maximum value, an average value, and the like of the gap error signal detected by the signal detector 14 /. Calculate (S83).

In addition, the controller 13 determines whether noise is included in the detected gap error signal (S84). Here, noise refers to deformation / damage of the gap error signal due to interference components caused by other signals or various factors of the data recording / reproducing apparatus or the recording medium 100. To determine whether noise is included in the gap error signal, the controller 13 uses a difference between the maximum value and the minimum value of the gap error signal.

The controller 13 compares the difference value (maximum value-minimum value) with a reference value or determines whether it is within a set range, and determines whether the gap error signal includes noise according to the result, and determines the gap. Reset the reference value (R). Here, the reference value and the setting range may be set based on the difference between the maximum value and the minimum value of the normal gap error signal that does not include noise, that is, the peak-to-peak, or may be set to any other value. Can be.

For example, when the difference value (maximum value-minimum value) is compared with the reference value, and the difference value (maximum value-minimum value) is greater than the reference value, the controller 13 includes noise in the gap error signal. And the gap reference value R is reset based on the maximum value and the minimum value.

When it is determined whether the difference value (maximum value-minimum value) falls within the setting range, if the difference value (maximum value-minimum value) is out of the setting range, the control unit 13 generates noise in the gap error signal. Is determined to be included and resets the gap reference value R based on the maximum value and the minimum value.

When noise is included in the gap error signal, a method of resetting the gap reference value R based on the maximum and minimum values of the gap error signal is as follows.

The controller 13 compares the minimum value of the detected gap error signal with a lower reference level (S85). Here, the lower reference level is a value obtained by converting the minimum distance that the head 11 can access the recording medium 100 in units of voltage, or the head 11 is in contact with the recording medium 100. It is a value obtained by converting the contact level (C) into voltage units or a value of a randomly set interval (for example, 10 nm) into voltage units.

As a result of comparing the minimum value with the lower reference level, if the minimum value of the gap error signal is smaller than the lower reference level, the controller 11 may come into contact with or collide with the recording medium 100. (13) is reset by raising the gap reference value (R) (S86). On the contrary, if the minimum value of the gap error signal is greater than or equal to the lower reference level, the controller 13 maintains or lowers the gap reference value R as it is (S87).

In addition, the controller 13 compares the maximum value of the detected gap error signal with an upper reference level (S88). Here, the upper reference level is a value obtained by converting a maximum interval for recording / reproducing data in voltage units or a value in which arbitrarily set intervals (for example, 50 nm) are converted into voltage units.

As a result of comparing the maximum value with the upper reference level, if the maximum value of the gap error signal is larger than the upper reference level, the control unit 13 is a position where the head 11 cannot record / reproduce data accurately. If it is determined to be at and the gap reference value (R) is lowered and reset (S89). On the contrary, if the maximum value of the gap error signal is less than or equal to the higher reference level, the controller 13 maintains or increases the gap reference value R as it is (S90).

If noise is not included in the gap error signal, the controller 13 maintains the gap reference value R as it is and approaches the head 11 until it reaches the gap reference value R (S91). .

In addition, as a process that can be selectively added, the controller 13 determines the vertical symmetry of the gap error signal to determine whether the head 11 and the recording medium 100 are in contact with each other. Here, in order to determine whether the gap error signal is vertically symmetrical, the controller 13 determines a difference between the maximum value and the average value of the gap error signal (maximum value-average value) and the difference between the average value and the minimum value of the gap error signal. (Mean value-minimum value) is calculated and it is determined whether the two difference values are equal.

If the two difference values are the same, the gap error signal is symmetrical up and down, and thus the controller 13 maintains the gap reference value R initially set. On the contrary, since the gap error signal is asymmetric when the two difference values are not the same, the controller 13 adjusts the gap reference value R. For example, if the two difference values are not the same, the control unit 13 adjusts the gap reference value R based on the minimum and maximum values of the gap error signal as described above, or the gap error. Raise the gap reference value R until the signal is up-down symmetrical.

The rights of the present invention are not limited to the embodiments described above, but are defined by the claims, and those skilled in the art can make various modifications and adaptations within the scope of the claims. It is self-evident.

According to the present invention, the gap between the head and the recording medium can be stably controlled by adjusting the gap (gap reference value) between the head and the recording medium based on the minimum and maximum values of the detected gap error signal. In addition, since the gap error signal can be judged on the basis of the minimum and maximum values of the gap error signal, the gap between the head and the recording medium can be adjusted more accurately.

In addition, since the contact between the head and the recording medium can be determined based on the symmetry of the gap error signal, the stability of the recording / reproducing apparatus can be maximized.

Claims (25)

A method of recording and / or reproducing data on a recording medium, the method comprising: Irradiating light onto the recording medium to detect the reflected light, and outputting a signal based on the detected light; Determining a minimum value and a maximum value of the output signal; Adjusting the distance between the head of the recording and / or reproducing apparatus and the recording medium according to the minimum and maximum values. The method of claim 1, The signal based on the detected light, An RF signal representing an amount of light incident on the recording medium; A gap error signal indicating whether an optical spot incident on the recording medium is focused, and a gap between the head and the recording medium; And a tracking error signal indicating whether the head is eccentric. The method of claim 1, Adjusting the distance between the head of the recording and / or playback device and the recording medium in accordance with the minimum value and the maximum value, Comparing the minimum value with a lower reference value and comparing the maximum value with an upper reference value; And adjusting the distance between the head and the recording medium according to the comparison result. The method of claim 3, wherein In the step of adjusting the distance between the head and the recording medium according to the comparison result, And if the minimum value is less than the lower reference value, widening the distance between the head and the recording medium. The method of claim 3, wherein In the step of adjusting the distance between the head and the recording medium according to the comparison result, And when the maximum value is larger than the upper reference value, the distance between the head and the recording medium is narrowed. The method of claim 1, And adjusting the distance between the head and the recording medium based on the up and down symmetry of the output signal. The method of claim 6, And determining the vertical symmetry of the detected signal based on whether the difference between the maximum value and the average value of the output signal and the difference between the average value and the minimum value are the same. The method of claim 6, And adjusting the distance between the head and the recording medium until the output signal is symmetrical if the output signal is asymmetrical up and down. An apparatus for recording and / or reproducing data on a recording medium, A signal output unit which outputs a signal based on the reflected light by irradiating light onto the recording medium; A head feeder for moving the head of the recording and / or reproducing apparatus in the vertical and horizontal directions; And a controller which determines a minimum value and a maximum value of the output signal and adjusts a distance between the head and the recording medium according to the minimum value and the maximum value. The method of claim 9, The signal output unit, Recording and / or reproducing apparatus, comprising one or more photodetecting elements. The method of claim 9, The signal output unit, An RF signal representing an amount of light incident on the recording medium; A gap error signal indicating whether an optical spot incident on a fraudulent recording medium is focused, and a gap between the head and the recording medium; And a tracking error signal indicating whether the head is eccentric and outputting the detected tracking error signal to the controller. The method of claim 9, The control unit, And comparing the minimum value and the maximum value with a lower reference value and an upper reference value, respectively, and adjusting a distance between the head and the recording medium according to the comparison result. The method of claim 12, The control unit, And if the minimum value is smaller than the lower reference value, the interval between the head and the recording medium is widened. The method of claim 12, The control unit, And if the maximum value is larger than the upper reference value, the interval between the head and the recording medium is narrowed. The method of claim 9, The control unit, And a distance between the head and the recording medium is further adjusted based on the vertical symmetry of the output signal. The method of claim 15, The control unit, And the symmetry of the output signal is determined based on whether the difference between the maximum value and the average value of the output signal is equal to the difference between the average value and the minimum value. The method of claim 15, The control unit, And adjusting the distance between the head and the recording medium so that the output signal is symmetric if the output signal is asymmetrical. A method of recording and / or reproducing data on a recording medium, the method comprising: Setting an interval reference value between the head of the recording and / or reproducing apparatus and the recording medium; Irradiating light onto the recording medium to detect the reflected light, and outputting a signal based on the detected light; Determining whether noise is present in the detected signal; And adjusting the interval reference value according to the determination result. The method of claim 18, In a step of determining whether noise exists in the output signal, And determining the presence or absence of the noise based on the difference between the maximum value and the minimum value of the output signal. The method of claim 18, In the adjusting of the interval reference value according to the determination result, And if the noise is present in the detected signal, adjusting the interval reference value based on the maximum and minimum values of the detected signal. The method of claim 20, And when the minimum value is smaller than a lower reference value, the interval reference value is widely adjusted, and when the maximum value is larger than the upper reference value, the interval reference value is narrowly adjusted. A signal output unit for outputting a signal representing a distance between the head and the recording medium; And a control unit for initially setting a gap reference value between the head and the recording medium, and adjusting the gap reference value according to whether noise is present in the signal output by the signal output unit. The method of claim 22, The control unit, And determining whether the noise exists based on a difference between the maximum value and the minimum value of the output signal. The method of claim 22, The control unit, And if the noise exists in the output signal, adjusting the interval reference value based on the maximum and minimum values of the output signal. The method of claim 24, The control unit, And if the minimum value is smaller than the lower reference value, the interval reference value is wider and if the maximum value is larger than the upper reference value, the interval reference value is narrowly adjusted.

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