JPH0349038A - Optical disk device - Google Patents

Abstract

PURPOSE:To shorten access time by storing a velocity offset value corresponding to an access range in an offset value storage means in advance, and adding or subtracting the velocity offset value to or from the table value of control target velocity generated with a velocity generating means corresponding to the position error of an optical head when making coarse access. CONSTITUTION:When track pull-in to make the optical beam of the optical head 10 follow a track is performed after the coarse access is completed, a tracking error signal detected with the optical head 10 is supplied to a tracking control circuit 18. The circuit 18 performs the track pull-in by amplifying the error signal, also, performing position compensation on the signal, supplying the signal to an actuator driving circuit 17 and a linear motor driving circuit 8, respectively, and driving an objective lens and the optical head 10. After that, the optical head 10 is jumped to a target track, however, at this time, an acceleration/deceleration pulse is generated at a jump control circuit 19 with the command of a CPU 5, and is added on a control signal generated at the tracking control circuit 18.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical disc device for recording/and/or reproducing various types of optical discs, and more specifically, for making an optical head access a target track on an optical disc. This is related to access control.

[Conventional technology]

In an optical disk device that records information on an optical disk or reproduces recorded information using a laser beam generated by a semiconductor laser, etc., track access to move the optical head to a desired track is usually divided into two sequences. It will be done.

That is, if the target track is quite far away from the current position of the optical head, first find the positional error in the radial direction between the current position detected by the position detection sensor installed on the optical head and the target track, Next, the optical head is moved to the vicinity of the target track using a moving means such as a linear motor while controlling the speed according to a predetermined speed profile so that the access distance is approximately equal to the positional error.

Next, track pull-in is performed by following the track with the light beam of the optical head, and while reading the track number, only the objective lens of the optical head is jumped from track to track and moved to the target track. In this specification, the former access is called coarse access, and the latter access is called fine access.

[Problem to be solved by the invention]

By the way, in the case of the access method described above, it is impossible to read the track number during rough access, so the number of tracks to the target track can be calculated by calculating the number of tracks between the optical beam detected by the position detection sensor and the target track. However, due to variations in the accuracy of the position detection sensor and expansion of the optical disk in a thermal environment, the accuracy of coarse access deteriorates, resulting in a longer time required for fine access. This has the problem of increasing the overall access time.

[Means to solve the problem]

In order to solve the above problems, an optical disc device according to the present invention includes an optical head, a moving means for moving the optical head in the radial direction of the optical disc, a position detecting means for detecting the position of the optical head, and a position detecting means for detecting the position of the optical head. A speed detection means for detecting the speed, a calculation means for calculating the position error of the optical head to the target track, and a control B corresponding to the position error of the optical head.
a speed generating means for generating a table value of the target speed; a speed offset value storage means for storing a speed offset value corresponding to the position error; is the control target speed obtained by adding or subtracting the speed offset value stored in the speed offset value storage means to the table value of the control + TH target speed generated by the speed generation means, and the actual speed detected by the speed detection means. a first control means that causes the optical head to be driven by the moving means based on the error signal, and sets the control target speed to "0''' after passing the speed switching position; and after the rough access is completed, the optical head is on the target track. and second control means for determining whether or not the optical head is on the target track, and causing the moving means to move the optical head to the target track to perform air access when the optical head is not at the target track.

In this case, if the position error between the optical head position and the target track at the end of rough access exceeds a predetermined value, correction is made by correcting the speed offset value corresponding to the access distance in the previous rough access. It is preferable to provide speed offset value correction means for storing a subsequent speed offset value in the speed offset value storage means.

[For production]

According to the above configuration, in consideration of the fact that an error may occur in the access distance of the optical head due to variations in the accuracy of the position detection sensor, expansion of the optical disk in a thermal environment, etc.,
A speed offset value corresponding to the access distance is stored in the offset value storage means, and the speed offset value is added to a table value of the control target speed that is generated by the speed generation means according to the position error of the optical head during rough access. Alternatively, since the optical head is driven in accordance with the control target speed determined by subtraction, the rough access accuracy is improved, thereby making it possible to shorten the overall access time.

Further, a speed offset value correction means as described above is provided,
If an error of more than a predetermined value occurs during rough access, by correcting the speed off-sensitivity, it is possible to reduce the error of rough access during subsequent accesses, so as the number of accesses increases, access time can be reduced.

(Example) An example of the present invention will be described below based on FIGS. 1 to 7.

FIG. 2 shows a block diagram of the access control system in the optical disc device of this embodiment. This access control system includes an optical head 10, a linear motor 9 as a moving means for moving the optical head 10 in the radial direction of an optical disk (not shown), and an optical head position control system that generates a position pulse according to the radial position of the optical head 10. sensor 11 and optical head position sensor 11
optical head 1 by counting position pulses from
a position detection circuit 12 as a position detection means for detecting the position of 0; a speed detection circuit 13 as a speed detection means for detecting the speed of the optical head 10; a speed table 20 serving as a speed generation means; It includes a speed offset memory 21 as an offset value storage means, and a CPU 5 that functions as a calculation means, a speed offset value correction means, and first and second control means.

This access control system includes a tlN access control system including a speed control jn system that moves the optical head 10 according to a speed profile corresponding to the access distance (acceleration/deceleration pattern of the optical head 10 during coarse access); a dense access control system consisting of a track pull-in and jump access control system;
・When SW2 is connected to the contact a side, the above coarse access control system is configured, and the first and second switches SWI・
The dense access control system is configured when SW2 is connected to each contact point.

First, a rough access control system in which the first and second switches 5WI-3W2 are connected to the contact a side will be explained.

This N11 access control system has a control target that decreases as the positional error Xe between the current position of the optical head lo and the target track and ri decreases during rough access, as shown by the solid line in FIG. The speed of the optical head 10 is controlled according to the speed Vref, and when the position error Xe determined by the position detection circuit 12 has decreased to Xo, the control target speed is set to "°0'".
', and control is performed so that the moving distance of the optical head 10 after speed switching is approximately X9.

In that case, the speed table 20 stores a table value ■tbl of the control target speed shown by the dotted line in FIG. 4, and the speed offset memory 21 stores a speed offset for adjusting the error in the access distance. The value Voff is stored and the control target speed Vref can be obtained from the difference between the two. If the position error Xe before the start of access is, for example,
By reading this and setting (1) as the initial value of the control target speed, the moving distance of the optical head 10 by rough access is determined.

In addition, the coarse access distance can be adjusted using the speed offset value Vof
By changing the magnitude of f as necessary, the value (■) of the control target speed at the time when the optical head 10 reaches the speed switching position WXo. This is done by changing the moving distance of the optical head IO after passing through the speed switching position X0.

The coarse access control system will be explained in detail below. This coarse access control system has a reference speed signal generation circuit l, and the reference speed signal generation circuit l is connected to first and twentieth A (digital/analog) converters 2 and 3 and a differential circuit 4. As will be described in detail later, the reference speed signal generation circuit 1 generates a control target speed table value vtbl supplied from a speed table 20 and a speed offset memory 21 based on an instruction from a CPU (central processing unit) 5. After the speed offset value Voff as the offset value to be calculated is subjected to D/A conversion, subtraction is performed, and a reference speed signal Eref is output.

The reference speed signal Eref is sent to the comparator circuit 6, where:
A speed error signal is generated by determining the difference between the speed detection signal corresponding to the actual speed (2) of the optical head 10 sent from the speed detection circuit 13 that detects the speed of the optical head 10 and the reference speed signal Eref.

The speed error signal from the comparison circuit 6 is amplified by the amplifier circuit 7 and supplied to the linear motor drive circuit 8. The linear motor drive circuit 8 generates a drive current according to the signal from the amplifier circuit 7. This drive current is supplied to a linear motor 9 as a moving means, and the optical head lO coupled to the linear motor 9 is shown in the figure. Not driven in the radial direction of the optical disc.

The optical head 10 is provided with an optical head position sensor 11 made of, for example, an optical scale. The optical position sensor 11 is connected to a position detection circuit 12, and the position detection circuit 12 detects the radial position of the optical head IO by counting position pulses generated by the optical position sensor 11. It has become.

The speed detection circuit 13 generates the speed detection signal by, for example, converting the position pulse from the optical position sensor 11 into F/V (frequency/voltage). Further, the speed detection circuit 13 detects the optical head 1 from the optical head position sensor 11 consisting of, for example, an optical scale.
The speed may be detected by differentiating two analog signals having a phase difference of 90 degrees corresponding to the zero position.

The optical head 10 is provided with an actuator 14 for driving an objective lens included in the optical head 10.
An objective lens position sensor 15 is attached to the actuator 14 to detect the position of the objective lens. The position signal generated by the objective lens position sensor 15 is supplied to the objective lens aperture/trick control circuit 16 to generate an error signal subjected to phase compensation and the like. This error signal is supplied to the actuator drive circuit 17, and when the light beam of the optical head 10 follows the track at the end position of the rough access and the track is pulled in, the objective lens is moved so that the objective lens does not have residual vibration. Long lens control is now possible.

Next, the above reference speed signal generation circuit 1 will be described in detail.

The first and second D/A converters 2 and 3 in the reference speed signal generation circuit 1 depend on whether the direction of movement of the optical head 10 is from the inner circumference side to the outer circumference side of the optical disk or vice versa.
For example, either one of the
A table value vtbz of the control target speed recorded in a speed table 20 consisting of a ROM (Read Only Memory) is sent, and the other of the first and second D/A converters 2 and 3 is provided with a RAM (Rando Memory), for example.
A speed offset value Voff corresponding to the position error Xe detected by the position detection circuit 12 is sent from a speed offset memory 21 consisting of a (n+Access Memory).

For example, when moving the optical head 10 from the inner circumferential side to the outer circumferential side of the optical disk, the table value vtbz of the control target speed is sent from the speed table 20 to the first D/A converter 2, and the table value vtbz of the control target speed is sent to the first D/A converter 2. 3, the speed offset value Voff from the speed offset memory 21 is sent. Then, the analog conversion value ELbI of the table value vtbl by the first D/A converter 2! and the analog conversion value Eoff of the speed offset value Voff by the second D/A converter 3 are supplied to the differential circuit 4.
Accordingly, the reference speed signal Eref =, Etbl-
Eoff (moving direction: from the inner circumferential side to the outer circumferential side of the optical disk) is output. Also, when moving the optical head 10 from the outer circumferential side to the inner circumferential side of the optical disk, contrary to the above, the second D/A converter 3, the table value v of the control target speed from the speed table 20
tbz is sent, while the speed offset value Voff is sent from the speed offset memory 21 to the first D/A converter 2, and the differential circuit 4 outputs the reference speed signal Eref =E.
off -ELbf=-(Btbl-Eoff)
(Movement direction: from the outer circumference side to the inner circumference side of the optical disc) is output. In this way, the direction of movement of the optical head 10 can be controlled by obtaining the base velocity signal E ref of different polarity depending on the direction of movement of the optical head 10 .

Next, the speed offset memory 21 will be explained based on FIG.

T" shown in (a) in FIG. 3 is the access distance, that is, the number of trunks between the target track to be accessed and the track where the optical head IO is currently located.
r and A are access distances when accessing from the innermost circumference to the outermost circumference of the optical disc, or vice versa, from the outermost circumference to the innermost circumference. 'ro is the jump accessible distance, and the access distance Tr is 1. In the following cases, access is possible only by close access in which only the objective lens jumps from track to track without moving the optical head 10 itself.

The speed offset memory 21 stores, for example, the range of access distance Tr required for rough access, To<Tr<
Each range T0 in which T r and IAw are divided into N equal parts
It has N memories M, , M2, . . . , M8 corresponding to ˜T + , T + ˜T, , T,=T, .

Each memory M+, M2, . . . , M has its own access distance range T0 to T I , T I ”-
Speed offset values 8, D2, . . . , DN corresponding to TZ, T2 to 1゛3, . . . are stored. In addition,
When starting up the device, each speed offset value DI, Dz,
..., a speed offset value Voff shown in FIG. 4 is stored as DH.

Next, the speed table 20 will be explained using FIG. 4.

In the speed table 20, as shown by the dotted line, a table value vtb1 of the control target speed of the optical head 10 corresponding to the reference speed signal Ere4 is set to a position between the current position of the optical head IO and the target track. It is stored in correspondence with the magnitude of the error Xe. As shown by the solid line, the actual control n target speed V ref is the value obtained by subtracting the speed offset value Voff stored in the speed offset memory 21 from the above table value vtb1, and the deceleration acceleration decreases as it approaches the target track. At the same time, when the position error Xe from the target track is Xo, the control target speed Vre
f is set to be the switching speed ■o. As described above, during rough access, the control target speed of the optical head 10 is Vref, which is the switching speed (2).

At the point when the control target speed Vref reaches °“0°
“It is now possible to switch to

FIG. 5 is a professional diagram showing the transfer function of the coarse access control system. As mentioned above, Vref is the control target speed of the optical head IO, ■ is the actual speed of the optical head 10, A is the sensitivity of the speed detection circuit 13, K1 is the amplification degree of the amplifier circuit 7, and Rs is the linear motor drive circuit 8 using current control. current feedback resistance, K
, the force constant of the linear motor 9, M the weight of the optical head 10, and S the Laplace operator. At the above speed switching position X0, the control target speed Rref is the switching speed ■
.

The response of the actual speed after switching from 0 to 0 is calculated by the following formula, where L is the elapsed time from the time of switching. The distance Xv that the head 10 moves is given by the following formula (2)
It is expressed as

FIG. 6 shows the response of the actual speed (■) after switching the control target speed to °"0"', and FIG. Curve 1 in is the response when access is performed for the first time after the device is started, and the actual speed ■ when the optical head stop time to゛ has elapsed converges to 0%, and the optical head moving path jdtX
v converges to a certain value. If the convergence value of Xv is made equal to Xo corresponding to the speed switching position when setting the control target speed, the speed of the optical head 10 at the end position of the rough access will be lower than the speed at which it can pull in the track. , Also, if you pull in the truck here,
Positioning near the target track can be performed with high accuracy.

Further, the control target speed Vref is the switching speed -■. However, the above is a case where ideal rough access is performed, and due to variations in the sensitivity of the optical head position sensor 11, thermal expansion of the optical disk, etc., the position of the optical head 10 at the end of the rough access may be different from the target I- It is possible that it may be slightly off the rack.

Therefore, in this embodiment, in the first access, if the optical head 10 is positioned in front of the target track by a certain amount or more at the end of the coarse access, the speed offset value VoH is decreased and the speed switching position is adjusted. Control target speed at X0 ■. On the other hand, if the optical head IO passes the target track by a certain amount or more at the end of the coarse access and is positioned, the speed offset value ■
Control target speed ■ at speed switching position X0 by increasing off. This reduces the Figures 6 and 7
Curves ■ and m in the figure show the response of the actual speed ■ of the optical head 10 and the moving distance Xv after passing the speed switching position X0 when access is performed again over approximately the same distance. Curve 2 shows the case where the speed offset value Voff is made small, and curve 2 shows the case where the speed offset value Voff is made large.

As can be seen from the curve ■, if the optical head 10 is positioned a predetermined amount or more ahead of the target track at the end of the first coarse access, in the second access, after passing the speed switching position Xs in the coarse access, The optical head movement distance Xv after the optical head stop time L0 has elapsed is Xo
The rough access ends at a position closer to the target track than at least the first access.

On the other hand, if the Hikari Rad 10 is positioned at a position where it has passed the target track by a predetermined amount or more at the end of the coarse access in the first access, as shown by curve ■, in the second access, the speed switching position is After passing X0, the optical head moving distance X when the optical head stop time L0 has elapsed
v becomes smaller than Xo, and the coarse access ends at a position closer to the target track than the first access.

As described above, the speed offset value Voff is set so that the coarse access accuracy improves as the number of accesses increases.
is changed, and as shown in Figure 3, for example,
Speed offset value V according to the access distance divided into N
Since each off is set optimally, coarse access accuracy is improved regardless of the length of the access distance, and the time required for fine access is shortened, thereby shortening the overall access time.

Next, based on FIG. 2, a fine access control system for performing fine access by track pull-in and jump access after coarse access is completed will be explained. During secret access, as described above, the first and second switches SWI-S
W2 is connected to the contact side.

After the coarse access is completed, when the optical head 10 pulls in a track to make the optical beam follow the track, a tracking error signal T er detected by the optical head 10 is detected.
r is supplied to the tracking control circuit on the 1st. In the tracking control circuit 18, the supplied tracking error signal Terr is amplified and subjected to phase compensation to produce a control signal 5act and a control signal SI! , m are generated. The control signal 5act and the control signal S1- are supplied to the actuator drive circuit 17 and the linear motor drive circuit 8, respectively, thereby driving the objective lens and the optical head 10 to perform track pull-in.

Thereafter, a jump access to the target track is performed while reading the track number from the ID section of the optical disc. At the time of this jump access, acceleration pulses and deceleration pulses are generated in the jump control circuit 19 according to instructions from the CPU 5. Acceleration pulses and deceleration pulses are added to the control signal 5act generated by the tracking control circuit 18, thereby -actuator drive circuit 1
Actuator 14 is driven via 7 to jump the objective lens from track to track.

Hereinafter, the access operation will be explained in more detail with reference to the flowchart shown in FIG.

When a command to access the target track is supplied from an external device (not shown), the current position of the optical head 10 detected by the position detection circuit 12 and the target track are
The PU 5 compares and detects the positional error to the target track, and based on it, the access distance 14Tr is determined (Sl).

Next, the CPU 5 uses the obtained access distance ^II
It is determined whether the Tr is at least a distance that can be accessed only by jump access, for example, at least 100 tracks (S2).

If it is more than 100 hours, coarse access using the coarse access control system described above is required, so first, the moving direction of the optical head 10 is determined by comparing the target track and the track where the optical head 10 is currently located. is determined (S3).

That is, the CPU 5 determines whether the moving direction of the optical head 10 during rough access is from the inner circumferential side to the outer circumferential side of the optical disk (S4), and if so, stores the current access distance Tr from the speed offset memory 21. The corresponding speed offset value is read, and the speed offset value is output to the second D/A converter 3 (S6).

Next, the CPU 5 switches the first and second switches SW1 and SW2.
are connected to the contact a side, and the phase access control system (speed control system) is turned on (S7), and the number of speed control loops described later is set according to the current access distance A1fTr determined by Sl, After storing data in the internal memory (S8), the speed control loop is entered.

Here, first, the position of the optical head IO is determined by the position detection circuit 1.
2 (S9), and calculates the position error Xe to the target track (310). Then, it is determined whether the calculated position error Xe is larger than the value of the speed switching position X0 (Sll).

The position error Xe is larger than the value of the speed switching position X0,
Therefore, if the optical head 10 has not yet reached the speed switching position X0, the table value vtbp of the control target speed corresponding to the remaining position error Xe is read from the speed table 20 (S12), and the read table value vtbl is output to the first D/A converter (first DAC) 2 (S13).

Next, the number of speed control loops is read from the internal memory, and °''1'' is subtracted (S14).Then, it is determined whether the number of speed control loops is "0°°" (515), and the number of speed control loops is If it is not 0°, the process returns to S9 and the speed control loop is executed again. On the other hand, if the number of speed control loops is "O°" in S15, the rough access has not been completed even though the predetermined number of loops have passed, so it is determined that an access error has occurred and the access is started again. do.

Note that sequence S5 is executed when it is determined in S4 that the moving direction of the optical head 10 is from the outer circumferential side to the inner circumferential side.
' to S15' are for changing the polarity of the reference speed signal Eref mentioned above, and the contents can be understood by referring to the explanations for 55 to 315, so the explanation will be omitted.

When the position error Xe is less than the value of the speed switching position X0 at Sll or Sll', that is, when the optical head 10 has reached the speed switching position X, the first and second D/
A value corresponding to the speed ``0'' is written into the A converters 2 and 3, and a reference speed signal ref=o is output (S16).

Then, a waiting time is provided for a predetermined light "rad" stop time t0 until the actual speed of the optical head 10 becomes "0" (S
17).

When the optical head stop time t0 has elapsed, the CPU 5 terminates the speed control operation (coarse access) of the optical head IO, and then connects the first and second switches SWI and SW2 to their respective contact sides to perform fine access control. The system is turned on and the trunk pull-in operation begins (S18). When the trunk pull-in is completed, the track number is read from 10 of the pulled-in tracks (S19), and it is determined whether the track currently being followed by the optical head 10 is the target trunk (320).

If the currently followed track is the target j-rack, the access is completed normally, and if it is not the target track, the position error between the target track and the currently followed track, that is, the coarse access error P. Calculate err (S21). At this time, the sign of the coarse access error P err is negative (-) if the optical head IO has not reached the target track before the track is pulled in, and positive (-) if the trunk is pulled in after passing the target track.
+).

Next, the CPU 5 determines whether the coarse access error P err is larger than a positive predetermined value Po (522), and Perr
is less than the predetermined value P0, the coarse access error P
It is determined whether err is smaller than a predetermined negative value -P (S23). A predetermined value P0 with a positive rough access error Perr
If it is less than or equal to the predetermined negative value Pa, it is determined that the speed offset value Dm set in S5 is within the appropriate range, and dense access is immediately started without correcting the speed offset value Dm. .

That is, the actuator 14 performs a track jump to move the objective lens in the direction corresponding to the polarity of the coarse access error P err (S24), reads the track number again (S25), and confirms that it is currently following the target track. Determine whether the tracks are equal (3
26), and if the target track and the currently followed track are equal, the access is completed normally, and if the target track and the currently followed track are not equal, then
Return to S24 and perform track jump again.

On the other hand, if the coarse access error perr is larger than the positive predetermined value P in S22, the movement distance of the optical head 10 due to the current access is excessively large, and therefore, S
This means that the speed offset value Dk set in step 5 was too small. Therefore, in that case, the speed offset value Dk is corrected by adding "1" to the speed offset value Dk (527), and after storing the corrected speed offset value in the speed offset memory 21 (32B), S24
As a result, as mentioned above, when accessing a distance approximately equal to the access distance of the current access is performed again, the speed offset value Dk has been corrected, so that the coarse access error can be further reduced. become able to.

Similarly, if the coarse access error P err is smaller than the negative predetermined value -Po in S23, the moving distance of the optical head IO due to the coarse access of the current access is excessively small, in other words, the speed offset value D1 in S5 is It turns out it was too much. Therefore, "1" is subtracted from the speed offset value Dk to correct the speed offset value (329),
After storing the corrected speed offset value in the speed offset memory 21 (S30), the process proceeds to 324.

Note that if the access distance Tr is less than 1°O track in S2, the target track can be accessed only by close access, so the process immediately advances to S24 and processes 324 to 326 are performed in the same manner as above. .

〔Effect of the invention〕

As described above, the optical disc device according to the present invention includes an optical head, a moving means for moving the optical head in the radial direction of the optical disc, and a position detecting means for detecting the position of the optical head.
speed detection means for detecting the speed of the optical head; calculation means for calculating the position error of the optical head to the target track;
speed generating means for generating a table value of a control target speed in response to the position error of the optical head; speed offset value storage means for storing a speed offset value corresponding to the position error; Before passing the speed switching position on the near side of the target position, the control target speed is obtained by adding or subtracting the speed offset value stored in the speed offset value storage means to the control target speed table value generated by the speed generation means and the above speed detection. The optical head is driven by the moving means based on an error signal with respect to the actual speed detected by the means, and after passing the speed switching position, a first control l1 means sets the control target speed to "0°"; The optical head is on the target track after access is completed.
and second control means for determining whether or not the optical head is located at the target track, and for causing the moving means to move the optical head to the target track to perform close access when the optical head is not at the target track.

As a result, a speed offset value corresponding to the access distance is stored in advance as an offset value, taking into account that errors may occur in the access distance of the optical head due to variations in the accuracy of the position detection sensor, expansion of the optical disk in a thermal environment, etc. According to the control target speed obtained by adding or subtracting the speed offset value to the table value of the control target speed which is stored in the means and is generated by the speed generating means according to the position error of the optical head during rough access. Since the optical head is driven, the f■ access accuracy is improved, and as a result,
This makes it possible to shorten the overall access time.

Note that when the position error between the optical head position and the target track at the end of rough access exceeds a predetermined value, the speed offset value corresponding to the access distance in the previous rough access is corrected to calculate the corrected speed. If speed offset value correction means is provided to store the offset value in the speed offset value storage means, and if an error of more than a predetermined value occurs during rough access, the speed offset value is corrected. Since the error in rough access can be reduced, the access time can be gradually shortened as the number of accesses increases.

[Brief explanation of drawings]

1 to 7 show one embodiment of the present invention. FIGS. 1(a) and 1(b) are flowcharts showing the access procedure. FIG. 2 is a block diagram showing the access control system. FIG. 3 is an explanatory diagram showing the correspondence between access distance and speed offset memory. FIG. 4 is a graph showing the relationship between position error and control target speed. FIG. 5 is a block diagram showing the transfer function of the coarse access control system. FIG. 6 is a graph showing the relationship between the elapsed time after passing the speed switching position in rough access and the actual speed of the optical head. FIG. 7 is a graph showing the relationship between the elapsed time after passing the speed switching position and the moving distance of the optical head in rough access. 5 is a CPU (calculating means/offset value correction means/first
・Second control means), 9 is a linear motor (moving means), 1
0 is an optical head, 12 is a position detection circuit (position detection means),
13 is a speed detection circuit (speed detection means), and 21 is a speed offset memory (value storage means).

Claims (1)

[Claims] 1. An optical head, a moving means for moving the optical head in the radial direction of the optical disk, a position detecting means for detecting the position of the optical head, and a speed detecting means for detecting the speed of the optical head.
a calculating means for calculating a position error of the optical head to the target track; a speed generating means for generating a table value of a control target speed corresponding to the position error of the optical head; and a speed generating means for generating a table value of a control target speed corresponding to the position error of the optical head; The speed offset value storage means stores a table value of the control target speed generated by the speed generation means before passing the speed switching position on the near side of the coarse access target position during rough access. The optical head is driven by the moving means based on the error signal between the control target speed obtained by adding or subtracting the speed offset value and the actual speed detected by the speed detecting means, and after passing the speed switching position, the control target speed is a first control means that sets the speed to "0"; and a first control means that determines whether or not the optical head is on the target track after the coarse access is completed, and when the optical head is not on the target track, the moving means moves the optical head to the target track and fine-grained the optical head; An optical disc device comprising: second control means for causing access. 2. When the positional error between the optical head position and the target track at the end of rough access exceeds a predetermined value, the speed offset value corresponding to the access distance in the previous rough access is corrected to calculate the corrected speed. 2. The optical disc apparatus according to claim 1, further comprising speed offset value correction means for storing an offset value in said speed offset value storage means.