JP3225672B2 - Recording medium and recording / reproducing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording medium having concentric or spiral tracks in which access codes for access are discretely recorded, and an access means for accessing a target track in the recording medium. The present invention relates to a recording and reproducing apparatus having the same.

[0002]

2. Description of the Related Art In recent years, as recording / reproducing apparatuses have been used in advanced ways, the speeding up of access has been promoted. In particular, to enable advanced control to move the head to the target track at high speed,
There has been proposed a recording medium in which an access code (eg, a gray code) for access is discretely recorded in advance on a track.

Hereinafter, an example of the above-described conventional recording medium will be described with reference to the drawings. FIG. 6 is a conceptual diagram showing an access code of a conventional optical recording medium (optical disc). In FIG. 6, reference numeral 1 denotes a virtual center line of the track. Reference numeral 2 denotes an access code area, and reference numeral 3 denotes a tracking area. An access code that changes while circulating in an eight-track cycle is provided in the access code area 2, and a control mark for tracking control and a clock are synchronized in the tracking area 3. The access code area 2 and the tracking area 3 partially overlap each other to form a control area 4.
Reference numeral 5 denotes a data area in which information to be recorded is recorded.

The details of the optical disk constructed as described above and the operation of a recording / reproducing apparatus using the same will be described below.

First, tracking control when using this optical disc will be described. In tracking, sampling control is performed based on a tracking error detected from a control mark recorded in the tracking area 3. The track pitch is about 1.5 μm, and the allowable tracking error is about 0.1 μm. If the eccentricity of the optical disk is 100 μm and the rotation frequency is Fr (Hz), the track is displaced at the frequency Fr and the amplitude of 100 μm. On the other hand, in order for the head to follow an error of 0.05 μm, which is half of the allowable value, the control system needs a gain of 2000 times at the frequency of Fr. At this time, the gain intersection frequency of the control system is
It must be about 60 times Fr. The tracking control is a sampling control, and it is desirable that the sampling frequency be about 20 times the gain intersection frequency in order to stably perform the tracking control. Therefore, it is desired that the control area 4 has 1200 or more locations in one round. In the conventional example, about 1600 control areas 4 are provided. If this is rotated at 30 revolutions per second, the sampling period will be about 20 μs.

An access code represented by 7 bits is recorded in the access code area 2. In this access code, a mark is formed in 2 bits out of 7 bits, and between adjacent tracks, one of the 2 bit marks is at the same bit position and the other mark is shifted by one bit. To form a gray code. The access code composed of the gray code is assigned to each track so as to cycle around eight tracks.

When a recording / reproducing apparatus using such an optical disk accesses a predetermined track, an access control means for controlling a head for recording / reproducing information to access a target track uses the head for the target track. Move toward. At this time, when the head crosses the portion of the access code area 2, the track can recognize the access code. From the difference between the access code at a certain sampling point and the access code at the next sampling point, the number of tracks traversed can be determined. You can also know how many tracks have been crossed since the start. By doing so, the head can be stably moved to the target track while controlling the moving speed (for example, JP-A-3-46126).

[0008]

However, in the above configuration, if the repetition period of the access code is short, the number of tracks that traverses at least half of the repetition period of the access code during the sampling period of the access code is reduced. When moving at the speed, the head is erroneously recognized as having moved in the opposite direction, so the upper limit of the moving speed of the head is limited to a low value. There is a problem that the probability of reaching the track is increased. Further, if the repetition period of the access code is lengthened, there is a problem that the number of bits of the access code increases and the redundancy increases.

SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a recording medium having a long repetition period of an access code without increasing the redundancy of the access code, and a recording / reproducing apparatus for effectively using the same. .

[0010]

In order to solve the above-mentioned problems, a recording medium of the present invention uses a first access code and a second access code defined for each track for recording information, respectively. The data area is sandwiched so as not to be adjacent to each other at a plurality of predetermined rotation angle positions of the track
In discretely arranged, the first access code and the second access code is cyclically varied with different number of tracks from each other as a cycle, the first access code
Track by the combination of and the second access code
Configure each access code .

[0011]

According to the present invention, since the first and second access codes are paired to form an access code for each track as a whole with the above-described configuration, the sampling cycle of the access code is twice as long as that of the prior art. Since the cycle is a common multiple of the repetition cycle of each of the first and second access codes, the cycle can be made twice as long as that of the related art,
The upper limit of the detectable moving speed of the head can be made higher than before.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a recording medium according to one embodiment of the present invention will be described.
This will be described with reference to the drawings.

FIG. 1 is a conceptual diagram showing a format of a recording medium according to a first embodiment of the present invention. In FIG. 1, 1 is a virtual center line of a track, 3 is a tracking area, and 5 is a data area, which are the same as the conventional example. Reference numeral 11 denotes a first access code area, 12 denotes a second access code area, in which a first access code and a second access code that change at different repetition periods are recorded, respectively, and these first and second access codes are recorded. The two access codes are paired to form an access code for each track. Reference numeral 14 denotes a first control area, which includes the first access code area 11 and the tracking area 3, and reference numeral 15 denotes a second control area, which includes the second access code area 12 and the tracking area 3.

The details of the recording medium configured as described above will be described below with reference to FIGS. 1, 2 and 3.

FIG. 2 is a conceptual diagram showing in detail the access code portion of the format of the recording medium in the present embodiment. The first and second access code areas 11 and 12 recorded in the first access code area 11 and the second access code area 12 respectively. One cycle of the second access code is shown. Each of these access codes has eight kinds of codes that change cyclically. The second access code is 1 as in the case of the conventional access code.
While changing for each track, the first access code does not change during one cycle of the second access code, but changes for every eight tracks, and circulates with a cycle of 64 tracks. Further, the first control area 14 and the second control area 15 are arranged at 800 locations in one round so that the intervals between them are equal. Therefore, when the recording medium is rotated 30 times per second, the interval between the timing of sampling the first access code and the timing of sampling the second access code is about 20 μs, and the pair of the first and second access codes is about 20 μs. The period for recognizing the access code of the track from is about 40 μs.

Next, an embodiment of a recording / reproducing apparatus using the recording medium of FIG. 1 will be described with reference to the drawings.

FIG. 3 is a block diagram of a recording / reproducing apparatus using a recording medium according to the present embodiment. 4, reference numeral 21 denotes a recording medium having the format shown in FIG. 1, and reference numeral 22 denotes a head. The head 22 reproduces information from or records information on the recording medium 21. A preamplifier 23 functions as a buffer amplifier that amplifies an output signal from the head 22 and performs impedance conversion. 24 is an access code reading means, which is a preamplifier 2
The access code is read from the reproduced signal from the head 22 amplified in step 3. Reference numeral 25 denotes a track address estimating means for estimating the address of the track from which the access code was read this time from the access code read by the access code reading means 24 and the number of the track from which the access code was read last time. A track address memory 26 sequentially stores track addresses calculated by the track address estimating means 25. Reference numeral 27 denotes a speed calculating means for reading a change in the track address for each sampling cycle of the access code from the track address memory 26 and calculating the moving speed of the head 22 during the reading. 28 is a control means, 29 is a speed profile memory, and the control means 28 shows the relationship between the number of remaining tracks to the target track stored in the speed profile memory 29 and the reference movement speed of the head 22 at that time. While referring to the table, the track address estimating means 25
The current track address and speed calculation means 27
And outputs a control signal based on the calculated moving speed of the head 22. Reference numeral 30 denotes a drive circuit, and 31 denotes an actuator. The drive circuit 30 power-amplifies the control signal output from the control means 28, and the actuator 31 generates a thrust by the signal output from the drive circuit 30 to move the head 22.

The operation of the recording / reproducing apparatus configured as described above at the time of access will be described below with reference to the drawings.

In the following description, the second access code recorded on the recording medium 21 circulates in an eight-track cycle, and the values from 0 to 7 obtained by decoding this code are the lower three bits of the track address. Shall match the value. Further, it is assumed that the second access code changes every eight tracks and circulates at a period of 64 tracks, and the value obtained by decoding the code coincides with the value of the upper three bits of the lower three bits. The track spacing is 1 μm, and the rotation speed of the recording medium is
1800 rpm and the first and second access codes are 20
It is assumed that sampling is performed alternately every μs.

First, before starting access, the head 22 is tracking a certain track, and the information reading means (not shown) reads a track address from this track and transfers it to the control means 28. The control means 28 stores this track address. Further, the control means 28 transfers the track address to the track address memory 26. The track address memory 26 has a capacity to store eight track addresses, and stores the address of the current track sent from the control means 28 in all of them as described above. This track address is represented as A (0).

Next, when a command is given from the outside to the control means 28 so as to access a predetermined track having a track address larger than the current one, the control means 28 transmits the address of the current track and the address of the target track. Calculate the difference between Control means 2
8 further refers to the speed profile memory 29 to obtain the reference speed of the head 22 according to the difference between the track addresses. Since the head 22 is relatively stationary with respect to the track until the access is started, the speed calculation means 2
The detection speed of 7 is zero. Therefore, the control means 28
Outputs a signal such that the head 22 accelerates to reach the reference speed. At this time, the head 22 is accelerated at the maximum acceleration, and the acceleration is about 10 G (G is the gravitational acceleration and 1 G is about 9.8
m / s ² ). The time from the start of movement to the first reading of the access code is at most 40 μs, and the distance traveled during this time is at most 0.08 μm. This distance is less than one tenth of the track interval, and the value m (1) of the first access code and the value n (1) of the second access code read at this time do not change. Therefore, the track address A (1) calculated by the track address estimating means 25 does not change. Hereinafter, the value of the first access code read i-th is m (i), the value of the second access code is n (i), and the value of the track address calculated based on these is A (i). Shall be represented. Assuming that the read access code first changes after the moving distance of the head 22 exceeds half the track interval, the time required for moving 0.5 μm, which is half the track interval, is 100 μs.
, The second access code n to be read for the third time
(3) increases by one. However, when n (0) is 7, it increases by 1 and returns to 0. In general terms, if x tracks are traversed between the time when the second access code is read i-th and the time when the second access code is read i + 1-th, then n
(i + 1) is the remainder obtained by dividing n (i) + x by 8, that is, n (i + 1) = n (i) + x mod 8. On the other hand, if the user traverses y tracks between the time when the first access code is read i-th and the time when the first access code is read i + 1, m (i + 1) is obtained by adding y to m (i). The remainder obtained by dividing the value obtained by adding the integer part divided by 8 to 8, that is, m (i + 1) = m (i) + [y / 8] mod 8 (where [] is a Gaussian symbol and Represents the largest integer that does not exceed the value). At this time, the value of the lower 6 bits of the address A (i + 1) of the track from which the second access code n (i + 1) has been read is: A (i + 1) = m (i + 1) × 8 + n ( It cannot be operated like i + 1). Because the first
Is read 20 μs before the time when the second access code n (i + 1) is read. Therefore, when the moving speed of the head 22 exceeds a certain speed, this 20 μs Move some trucks during the
This is because the second access code and the second access code are for different tracks. Therefore, the track address estimating means 25 estimates the first access code in the track from which the second access code n (i + 1) has been read, as the first access code closest to the one predicted linearly from a change in the past track address. I do. That is, the i + 1-th track address predicted from the track address A (i-1) estimated from the (i-1) th read access code and the track address A (i) estimated from the i-th read access code A '(i + 1) is expressed as A' (i + 1) = A (i) + {A (i) -A (i-1)} = 2A (i) -A (i-1) Calculate. When the value n (i + 1) of the (i + 1) -th second access code is read, the track address estimating means 25
A '(i +
The first access code m (i + 1) is estimated so as to be the track address closest to 1), and the (i + 1) -th track address A (i + 1) is calculated based on this. If the i-th second access code n (i) cannot be read, the track address A (i) cannot be estimated. Stores information indicating that this could not be estimated. In this case, i + 1-th second access code n
When (i + 1) is read, the address A (i +
1) can be estimated using the track addresses A (i-1) and A (i-2) for which the estimated values are known.

The above-described linear prediction is based on the assumption that the moving speed of the head 22 is constant. However, an error is actually generated because an acceleration of 10 G is applied. However, this error occurs when the sampling period is 40μ.
Because it is short, it is as small as 0.3 μm, and even if a quantization error equivalent to 1.5 times the track interval (1.5 μm) caused by the access code changing stepwise in track units is added, it is less than 2 times the track interval Is the value of It is clear that the estimation of the track address A (i + 1) can be performed accurately in consideration of the fact that the cyclic error of the second access code is eight tracks, so that the prediction error is allowed up to three tracks. is there. When A (i + 1) is estimated in this manner, the head 22 is moved to the target track by the access means including the speed calculation means 27, the control means 28, the speed profile memory 29, the drive circuit 30, and the actuator 31. Access control is performed to move to The operation will be described first.
Calculates the number of tracks up to the target track, reads the reference speed according to the remaining number of tracks with reference to the speed profile memory 29. The reference speed is substantially proportional to the square of the number of remaining tracks, but when the number of remaining tracks is equal to or greater than a predetermined value, the reference speed is limited to a constant value. Immediately after the head 22 starts moving, the detected speed is lower than the reference speed, and during this time, the head 22 is accelerated by the maximum thrust of the actuator 31. During this time, the reference speed is changed in accordance with the number of remaining tracks. When the detected speed reaches the reference speed, the head 22 is decelerated while controlling the detected speed to follow the change in the reference speed.
When reaching the vicinity of the target track, the moving speed becomes about several mm / s, and thereafter, the vehicle travels toward the target track while maintaining this speed. At such a low speed, only about 0.1 μm moves during 20 μs from the time when the first access code is read until the time when the next second access code is read, and the first and second access codes on the same track are moved. The code can be easily read. Therefore, the first and second
If the target track is recognized while looking at both access codes, the target track can be accurately reached even if the track address is incorrectly estimated by about 8 or 16 tracks. When the target track is recognized, when it reaches the target track, the speed becomes an extremely small value, and it can be stopped immediately to follow the target track.
If the upper limit of the reference speed is, for example, 0.5 m / s, the moving distance during the access code sampling period of 40 μs is at most 20 μm, and the number of traversing tracks during this period is 20 or less. Therefore, the ith first first
If the difference between the value of the access code m (i) and the value of the (i + 1) -th first access code m (i + 1) becomes 3 or more, it is determined that the speed exceeds the normal value, and By reducing the speed, it is possible to prevent damage due to collision of the head 22 or the like.

As described above, according to the present embodiment, the access code is divided into two types having different cyclic periods and arranged discretely and alternately, and an access code for each track is constituted by a combination of these. Even if an access code having a relatively small number of bits is used, the cycle of circulation can be lengthened, and accurate access control can be performed even when the head 22 moves at a high speed.

A second embodiment of the present invention will be described below with reference to the drawings. FIG. 4 is a conceptual diagram showing a part of a format of a recording medium according to a second embodiment of the present invention. This embodiment is different from the first embodiment in that the first and second access codes are composed of four types of codes,
The access code composed of these pairs changes cyclically with a period of 16 tracks.

The operation of the recording / reproducing apparatus using the recording medium configured as described above at the time of access will be described below.

The recording / reproducing apparatus according to the present embodiment has the configuration shown in FIG. 3 as in the case of the first embodiment. What differs from the first embodiment is the method of estimating the access code of the traversing track by the track address estimating means 25 and the method of controlling when moving at high speed. In general, the access control requires high-precision speed control when the moving speed becomes low as the vehicle approaches the target track. In this embodiment, however, the cycle of the access code circulation is short, and the second access code is 4 times. Since the track address circulates in the track cycle, it is necessary to predict the track address at the next sampling point with an accuracy of two tracks or less. Therefore, in the present embodiment, when the moving speed of the head 22 becomes equal to or lower than a predetermined speed, the predicted value A ′ (i + 1) of the next track address is changed to A ′ (i + 1) = A (i) + The calculation is performed as {A (i) −A (ij)} / j (where j is a natural number of 2 or more). In this way, for example, when j = 4, the error in the predicted value is at most about 1 μm, even if the acceleration is about 10 G and the error due to the acceleration and the quantization error are equal to the number of tracks. Can be reduced to about one. Although the error is small enough as it is, in the present embodiment, the error is further corrected by assuming an error due to acceleration. That is, when the head 22 is accelerated at the maximum acceleration (10 G), the movement amount of the head 22 is predicted to be slightly smaller by 0.4 μm, so that the predicted value A ′ (i + 1) of the track address is corrected by this amount. Also,
Even when decelerating according to the speed profile, an error assumed from the reference acceleration of the speed profile is corrected. Assuming that the velocity profile at the time of deceleration is generated based on the acceleration of -7G, the amount of movement of the head 22 by linear prediction during the deceleration is increased by about 0.3 μm. . In this manner, the linearly predicted track address A ′ (i + 1) is corrected by the error due to the assumed acceleration, and the track address A ′ (i + 1) having the second address code having the same value as n (i + 1) is corrected. It is estimated that the track having the address closest to the predicted value of the track address is the track from which the second address code n (i + 1) has been read. Since the tracks before and after the second access code has the same value as n (i + 1) are four tracks apart, if the error of the predicted value is about one track, the track address A
(i) can be estimated very accurately.

When the difference between the second address code of the track having the corrected predicted value at the address and the actually read second address code n (i + 1) becomes 2, only 2 from the predicted value is obtained. Two tracks, a track having a larger address and a track having an address smaller by two, are candidates for estimation, and it is impossible to narrow down any one of them. In this case, the estimation is suspended and both candidates are stored in the track address memory 26.
When the first access code m (i + 2) or the second address code n (i + 2) to be sampled next is read, the likelihood of the two candidates reserved is high. Is determined as the estimated value of the track address A (i + 1).

When the moving speed detected from the change of the track address is equal to or higher than the predetermined speed, the speed control accuracy is not so required, so that the speed detection and the track counting are performed using only the first access code. . Also in this case, when the speed is detected from two consecutive first access codes, the quantization error becomes large. Therefore, the speed is detected from two further first access codes.

As described above, in the present embodiment, the second
The address of the track that read the access code
Since the prediction is performed using the track address estimated last time and the track address estimated two or more times earlier, the quantization error in predicting the track address can be reduced, and the prediction accuracy can be reduced. Go up. Therefore, sufficient performance can be obtained even if the number of bits of the access code is reduced to shorten the cycle of circulation.

Next, a third embodiment of the present invention will be described with reference to the drawings. FIG. 5 is a conceptual diagram showing a part of the format of a recording medium according to a third embodiment of the present invention. This embodiment is different from the first embodiment in that the first access code circulates in five track cycles with five types, and the second access code circulates in four track cycles with four types.

The operation of the recording / reproducing apparatus using the recording medium configured as described above at the time of access will be described below.

The recording / reproducing apparatus according to the present embodiment has the configuration shown in FIG. 3 as in the case of the first embodiment. The difference from the first and second embodiments is the method of estimating the access code of the traversing track by the track address estimating means 25. In this embodiment, the first access code is
Since the second access code changes every one track and circulates in a four-track cycle while changing every one track, the access code of each track composed of these pairs is It circulates in a cycle of 20 tracks, which is the least common multiple of the cycle. Also in this embodiment, the first and second access codes have a shorter circulation cycle than in the first embodiment, so that the prediction of the track address needs to be performed with high accuracy as in the second embodiment. is there.
This embodiment is different from the second embodiment in that the first and second embodiments are different.
Are different for each track. Therefore, in this embodiment, the track address can be estimated both when the first access code is sampled and read, and when the second access code is sampled and read. Can be estimated. Therefore, the second
When the track address at the next sampling point after 20 μs is predicted by the same arithmetic expression as that of the embodiment, the error can be reduced to about 0.8 μm. This is an error amount less than one track interval.
There is no problem even if the address code is 4 track cycles.

As described above, in this embodiment, the first
Since both the second access code and the second access code change for each track, the track address of that track can be accurately estimated each time each access code is read. Therefore, each of the first and second access codes can be configured with a small number of bits.
Moreover, the cycle of the access code of each track composed of these pairs is 20 tracks which is the least common multiple of the cycle of each of the first and second access codes. Even so, the probability of accessing the wrong track can be kept low.

In the first embodiment, the access means performs access control while performing accurate control based on the track address estimated by the track address estimation means 25. However, accurate control is particularly required. Since the moving speed of the head 22 decreases after approaching the target track, the access is performed by referring to the second address code only when the speed detected by the speed calculating means 27 is lower than a predetermined speed. Control may be performed, and when the speed is higher than a predetermined speed, coarse access control may be performed with reference to only the first access code.

In the first embodiment, the control means 28 is configured to perform precise speed control according to the profile stored in the speed profile memory 29. Only a coarse track control and a rough speed control for controlling the moving speed of the head 22 to a constant speed may be used.

Further, in the first embodiment, when the track address cannot be estimated, information indicating that the track address could not be estimated is stored in the track address memory 26, but the track address could not be estimated. Sometimes, the predicted value of the track address may be stored instead.

Furthermore, in the above embodiment, the case of an optical disk is shown, but the present invention is essentially irrelevant to the recording principle, and a magnetic disk may be used.

[0038]

As described above, according to the present invention, the access code is divided into two types which have different cyclic periods and are arranged discretely and alternately, and an access code for each track is constituted by a combination of these. Even if an access code having a small number of target bits is used, the cycle of the tour can be lengthened, and accurate access control can be performed even when the head moves at a high speed.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a format of a recording medium according to a first embodiment of the present invention.

FIG. 2 is a conceptual diagram showing in detail an access code part of a format of a recording medium in the embodiment.

FIG. 3 is a block diagram of a recording / reproducing apparatus using a recording medium in the embodiment.

FIG. 4 is a conceptual diagram showing a part of a format of a recording medium according to a second embodiment of the present invention.

FIG. 5 is a conceptual diagram showing a part of a format of a recording medium according to a third embodiment of the present invention.

FIG. 6 is a conceptual diagram showing an access code of a conventional optical recording medium.

[Explanation of symbols]

 1 virtual center line of track 3 tracking area 5 data area 11 first access code area 12 second access code area 14 first control area 15 second control area 24 access code reading means 25 track address estimating means 26 Track address memory 27 Speed calculation means 28 Control means

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinichi Kadowaki 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) References JP-A-3-23520 (JP, A) JP-A-4- 125822 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G11B 27/00 G11B 27/10 G11B 7/085

Claims (6)

(57) [Claims] A track for recording information concentrically or spirally is provided, and a first access code and a second access code defined for each of the tracks are applied to a plurality of predetermined rotations of each track. The first access code and the second access code are arranged discretely with the data area interposed therebetween so as not to be adjacent to each other at the angular positions, and the first access code and the second access code change cyclically with the mutually different number of tracks as a cycle . Access code and the second access code
Access code for each track according to the combination of
Recording medium which is characterized in that configuration. 2. The second access code changes cyclically with Q (Q is an integer greater than 1) tracks as a cycle,
The first access code changes every Q tracks N (N
2. The recording medium according to claim 1, wherein the recording medium comprises a number of types of codes, and changes cyclically with a period of Q × N tracks. 3. The method according to claim 1, wherein the first access code comprises N types of codes, and the second access code comprises M types of codes, wherein M and N have no common divisor other than 1. Item 2. The recording medium according to Item 1. 4. A head for recording information on or reproducing information from the recording medium according to claim 2, access code reading means for reading an access code from a reproduced signal from the head, and a second access code based on the access code. A track address estimating means for substantially estimating a track address having an access code, an access means for moving the head to a target track while controlling based on the track address estimated by the track address estimating means, Control means for inspecting whether the operation of the track address estimating means is normal or abnormal based on the first access code read by the code reading means, and switching the operation of the access means when detecting an abnormality. Recording and reproducing device. 5. A head for recording information on or reproducing information from the recording medium according to claim 2, access code reading means for recognizing an access code from a reproduction signal from the head, and Track address estimating means for substantially estimating a track address having an access code of 2; access means for moving the head to a target track while controlling based on the track address estimated by the track address estimating means; Control means for inspecting whether the operation of the track address estimating means is normal or abnormal based on the first access code read by the access code reading means, and switching the operation of the access means when detecting an abnormality. Characteristic recording / reproducing device. 6. A head for recording information on or reproducing information from the recording medium according to claim 2, an access code reading means for recognizing an access code of a traversing track from a reproduction signal from the head, and Speed detecting means for detecting the moving speed of the head based on the access code read by the access code reading means; and moving the head to a target track while controlling the moving speed based on the speed detected by the speed detecting means. Access means for controlling the moving speed based on only the first access code when the speed detected by the speed detecting device exceeds a predetermined speed, and when the speed detected by the speed detecting device becomes lower than the predetermined speed. A recording / reproducing apparatus for controlling a moving speed based on both a first access code and a second access code.