JPH0349037A - Access controller for optical disk device - Google Patents

Abstract

PURPOSE:To stably pull in an optical head on an allowable target track by suppressing velocity deviation by using a velocity profile in which acceleration/ deceleration can be decreased as approaching a target track. CONSTITUTION:When the access instruction of the optical head for the target track is inputted, the number of tracks from the current track position to a target track position is counted with a CPU 2, and the moving direction of the optical head is decided. The CPU 2 outputs a control signal corresponding to a decided moving direction to a polarity setting circuit 4, and sets the polarity of a reference velocity signal V'ref, and an operation is migrated to a velocity control loop after the number of times of the velocity control loop at a memory not shown in figure. In the loop, the current position of the optical head is read in from a position detecting means 10, and a position error to the target track is calculated, and size decision between the position error and a velocity switching position is performed, and when the error exceeds the switching position, the velocity profile corresponding to the error is read in, and the V'ref is outputted from a reference velocity signal output means 12.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an access control device for moving an optical head to a target track on an optical disc in an optical disc device.

[Prior Art] Optical disc devices that record information on an optical disc or reproduce recorded information using a semiconductor laser have been known. In such an optical disc device, track access for moving the optical head to a target track on the optical disc is constituted by two sequences V', coarse access and fine access.

That is, when the target track is far away from the current track, first, the optical head is moved to a position near the target track, that is, close access, while controlling the speed according to a predetermined speed profile using a head moving means such as a linear motor. The optical head is positioned within the tolerance required for the transition (hereinafter referred to as the permissible target track) (coarse access), and the optical head is moved to the target track while jumping from track to track (fine access). ing.

The conventional coarse access method uses a near motor and its control circuit to drive the optical head, as shown in Figure 8 (a').
As shown in FIG. 2, a method has been adopted in which the optical head accesses the target track using a speed profile 20 in which the actual speed of the optical head is constant at deceleration and acceleration. In addition,
If the actual speed of the optical head changes to completely follow the speed profile, the actual speed and the speed profile will match.

However, when such a speed profile 20 is used, a speed deviation (difference between the actual speed and the speed profile) proportional to the deceleration acceleration occurs in a general speed control system, and the desired deceleration is not achieved. The stopping time of the optical head is correspondingly delayed (as a result, a distance error occurs, and it becomes uncertain to position the optical head on the permissible target track (hereinafter referred to as track pull-in), resulting in a longer track pull-in time. When the optical head stops, a sudden change in acceleration occurs, which makes the optical head unstable and the tracking servo by the objective lens drive device unstable.In order to reduce the speed deviation mentioned above, the loop gain of the speed control system must be adjusted. It would be possible to increase the loop gain, but the control system becomes unstable due to mechanical resonance, etc., so it is not possible to increase the loop gain.

In order to improve this drawback, the optical head is made to access the target track using a speed profile 21 in which the deceleration acceleration decreases as it approaches the target track at the actual speed of the optical head, as shown in FIG. There is something like this. According to this, it is possible to reduce the speed deviation when the permissible target track is reached, reduce the distance error, and stabilize the track pull-in control without extremely increasing the loop gain of the speed control system. Further, since drastic changes in acceleration, which occur when the optical head is stopped, are prevented, the tracking servo is also stabilized.

[Problem to be solved by the invention]

However, if the speed profile 21 described above is used, the time during which the speed is controlled at a low speed becomes longer as the target track approaches, and the seek time becomes longer.
Since the speed before reaching the target track is quite slow, the optical head may stop short of the allowable target track due to the effects of friction and the like. Since the transition from coarse access control to fine access control is performed after the optical head reaches the permissible target track, there will be no switch to fine access control in the above case.

[Means for Solving the Problems] In order to solve the above problems, an access control device for an optical disk device according to the present invention includes a moving means for moving an optical head in the radial direction of the optical disk, and a moving means for moving the optical head in the radial direction of the optical disk, and a moving means for moving the optical head in the radial direction of the optical disk. A position detection means for detecting the speed of the optical head, a speed detection means for detecting the speed of the optical head, a calculation means for calculating a position error from the current position of the optical head to the target track, and a deceleration acceleration decreases as it approaches the target track. a reference speed signal output means for outputting a reference speed signal for generating a reference speed corresponding to the position error based on a speed profile having a predetermined switching point speed at a speed switching position in front of the track; Reference speed switching means for determining the position and outputting a fixed reference speed signal for generating the speed OJ instead of the reference speed for a predetermined time when the position reaches the speed switching position. and a driving means for driving the moving means based on an error signal between the actual speed signal of the optical head obtained by the speed detecting means and the reference speed signal.

[For production]

According to the above configuration, since a speed profile is used in which the deceleration acceleration decreases as the target track approaches,
It is possible to suppress speed deviation and stably draw the optical head onto an allowable target track.

The increase in seek time that becomes a problem when using the above speed profile is caused by moving the optical head at a somewhat higher speed and changing the speed to a fixed standard of "0" instead of the reference speed at the speed switching position before the target track. By outputting the speed and causing a sudden deceleration, it is possible to shorten the seek time while obtaining the travel distance necessary for access.

Furthermore, if the speed switching position, speed at the time of switching, and duration are set in consideration of the gain characteristics of the control system, rough access accuracy can be improved, and further,
If each of the above specifications is set in consideration of the gain characteristics of the control f'llll system so that the actual speed of the optical head becomes less than the tracking servo possible speed when the optical head reaches the allowable target track, the above In addition, the effects of deceleration are suppressed, the tracking servo becomes stable, and access time can be significantly shortened.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS. 1 to 7.

Access control j′J in the optical disk device according to the present invention
In the E device, as shown in FIG. 1, the speed profile is stored, for example, in the ROMI in the form of speed data corresponding to the position error Xe to the target track, and its contents are The deceleration and acceleration become smaller as the vehicle approaches the truck, and a predetermined switching point speed is maintained at the speed switching position before the target track.

The relationship between the reference speed Vref based on the speed profile and the position error Xe is shown in FIG. 3. Here,
Xo is the speed switching position, ■0 is the speed at the time of switching, and the position error Xe is the reference speed Vr when the speed switching position is X00.
e f becomes the speed ■0 at the time of switching.

The CPU 2 serves as a calculation means for calculating the position error Xe from the current position of the optical head to the target track based on the output of the position detection means 10 that detects the position of the optical head (not shown), and also serves as a calculation means for calculating the position error Xe from the current position of the optical head to the target track. This speed switching position WX is determined by determining the switching position Xo.

In addition to serving as a reference speed switching means for outputting a fixed reference speed signal for generating the speed "o" instead of the reference speed signal V'ref, which will be described later, for a predetermined time To when reaching the reference speed signal V'ref, various other functions are also used. It is for controlling.

The reference speed signal output means 12 outputs a reference speed signal V'ref for generating a reference speed ref corresponding to the position error Xe based on the speed profile, and converts the speed data from the CPLI 2 into a voltage signal. It is comprised of a D/A-2 inverter 3 for conversion, and a polarity setting circuit 4 for setting the polarity of the voltage signal based on a signal from the CPU 2 according to the moving direction of the optical head.

The comparator circuit 5 inputs the reference speed signal V'ref and calculates the difference between the reference speed signal V'ref and the optical head actual speed signal V'deL detected by the speed detecting means 11, which will be described later, to generate a speed error signal Verr. It has become.

The speed error signal Verr from the comparator circuit 5 is amplified by an amplifier 6 and then output to a driving means 7. The drive means 7 drives a linear motor (moving means) 8, which will be described later, based on the speed error signal Verr, and generates a drive current according to the amplified speed error signal Verr, which is then transferred to the 5.7 motor. 8.

The linear motor 8 receives a drive current from the drive means 7 and moves an optical head (not shown) in the radial direction of the optical disk.

The position sensor 9 outputs a signal related to the current position of the optical head, and uses, for example, an optical scale attached to the optical head. Then, the position detection means 10
The current position of the optical head is detected by counting position pulses from the position sensor 9.

The speed detection means 11 converts the position pulse from the position sensor 9 into F/V to obtain an actual speed signal V'de.
1 is generated and outputted to the comparison circuit 5 mentioned above. Note that the actual speed signal V'deL can also be generated by differentiating two analog signals with a phase difference of 90 degrees corresponding to the position from the optical scale.

In the above configuration, the access operation of the optical head to the target track will be explained with reference to FIG.

When an access command for the optical head to the target track is input, the CPU 2 calculates the number of tracks T from the current track (position) of the optical head to the target track (31).
, it is determined whether the number of tracks Tr is, for example, 100 or more (S2). If there are 100 or more, the moving direction of the optical head is determined from the target track and the current track (S3
). Then, the CPU 2 outputs a control 7J signal to the polarity setting circuit 4 in accordance with the determined moving direction. The polarity setting circuit 4 receives the reference speed signal V' ref by the above control signal.
(S4).

Next, after setting the number n of speed control loops in a memory (not shown) (S5), the process moves to the speed control loop. In this speed control loop, the CPU 2 first reads the current position of the optical head from the position detection means 10 (S6), and calculates the position error Xe to the target track (S7). Then, it is determined whether the calculated position error Xe and the speed switching position Xo are large or small (S8), and the position error Xe is
.

If it is larger than Xe, that is, if the optical head has not yet reached the speed switching position Xo, a speed profile corresponding to the position error Xe is read (S9). Then, based on this speed profile, the reference speed signal output means 12
outputs a reference speed signal V'ref (S10).

Next, read the speed control loop number n from memory and
l” (Sll). At this time, it is determined whether n is "0" (312), and if it is "0", it is determined that there is an access error, while if it is not "0", the process returns to step 6 and the speed control loop is continued.

In step 2, if the number of tracks T' up to the target track is 100 or less, that is, if the optical head is on the permissible target track, then jump access is performed.
Close access is made to the target track (S18).

Further, in step 8, when the position error Xe is equal to or less than the speed switching position Xo, that is, when the optical head reaches the speed switching position xo, the reference speed signal output means 12 outputs the reference speed Vr.
The CPU 2 sends a predetermined signal to the D/A converter 3 so as to output a fixed reference speed signal corresponding to the speed rQJ instead of er. As a result, the reference speed signal output means 12 outputs a fixed reference speed signal corresponding to the speed "0" (313). Next, a holding time To, which is the time until the optical head stops, is set (314). When the holding time To has elapsed and the optical head has settled down, the tracking servo by the objective lens driving device (not shown) in the optical head is started. (S15),) The racking servo reads the track number from the ID section of the track pulled in (316), and determines whether the track being followed by the optical head is the target track (517).
, if it is the target track, the access ends normally, but if it is not the target track, the process returns to step knob 1.

In the above control contents, the settings for the speed vO1 at the time of switching the speed switching position XO1 and the duration To will be described in detail below.

As shown in FIG. 4, in the transfer function of the control system in the access control device, Vref is the reference speed, ■ is the actual speed, A is the sensitivity of the speed sensor consisting of the position sensor 9 and the speed detection means-11, and K is Amplification degree of amplification amplifier 6, R
s is a current feedback resistance of the driving means 7 based on current control, KF is a force constant of the linear motor 8, M is the mass of the optical head, and S is a Laplace operator.

At the speed switching position XO, the response of the actual speed V when the reference speed Vref switches from the switching point speed ■0 to the speed "0" is expressed by the following equation 1, where L is the time from the switching point. be done.

In addition, the reference speed Vref changes from speed ■0 at the time of switching to speed "
Distance Xv that the optical head moves from the time it switches to "0"
is expressed by the following second equation, where t is the time from the time of switching.

Therefore, as shown in FIG. 5, the actual speed ■ from the time of speed switching shows a response that converges to rQJ as time passes, and the moving distance xv of the optical head from the time of speed switching is
As shown in FIG. 6, the response converges to a constant value.

To set the speed switching position Xo, the switching point speed ■0, and the holding time TO which is the optical head stop time, first determine the switching point speed ■0, find the convergence value of the optical head moving distance Xv at that time, and This is defined as the speed switching position XO. and,
If the holding time T o is temporarily selected within the range where the optical head moving distance 1rIJ If not, select a longer To so that the actual speed (■) is less than the tracking servo possible speed.

Regarding the track access control device explained above,
The relationship between the reference speed Vref and the actual speed Vdet is shown in FIG. 7, and a series of movements of the optical head will be explained based on this diagram. In the second section, the first speed Vref and the actual speed V
Since the difference between d and e t is large, the optical head is fully accelerated by the near motor 8, and in the Lt section, the optical head is decelerated while following the reference speed Vref. and,
In the Lz section, when the optical head comes to the speed switching position Xo in front of the target track, that is, when the reference speed Vref becomes equal to the switching point speed ■0, the reference speed ■ref switches to speed "0" and the remaining time T.

This is maintained for a period of time, and after this time has elapsed, the optical head almost stops. Next, in the L4 section, the moving speed of the optical head is controlled below the tracking servo possible speed by passing through the E3 section, and the tracking servo is stably performed, and if the track pulled in by this servo is the target track. If the track is not the target track, the access is terminated by jump access in interval t5 to reach the target track.

As described above, since the speed profile in which the deceleration and acceleration become smaller as the optical head approaches the target track is used, it is possible to suppress speed deviation and stably draw the optical head onto the permissible target track.

The increase in rough access time that becomes a problem when using the above speed profile is caused by moving the optical head at a somewhat higher speed and changing the speed to "0" instead of the reference speed Vref at the speed switching position XO before the target track. By outputting a fixed reference speed and decelerating it, it is possible to shorten the rough access time while obtaining the travel distance necessary for access.

Furthermore, as in this embodiment, if the speed switching position XO1 switching point attainment ■0 and the designation of the duration To are set in consideration of the gain characteristics of the control system, the coarse access accuracy can be improved. Furthermore, each of the above specifications should be set in consideration of the gain characteristics of the control system so that when the optical head reaches the allowable target track, the actual speed of the optical head will be below the tracking servo possible speed. If the above 2
．． 1. Suppressing the effects of deceleration. The trunking servo also becomes stable, making it possible to significantly shorten access time.

〔Effect of the invention〕

As described above, the access control device for an optical disk device according to the present invention includes 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 position detecting means for detecting the speed of the optical head. speed detection means;
A calculation means for calculating the position error from the current position of the optical head to the target track, and a speed profile that decreases deceleration and acceleration as it approaches the target track and has a predetermined switching point speed at a speed switching position before the target track. a reference speed signal output means for outputting a reference speed signal for generating a reference speed corresponding to the position error; and a reference speed signal output means for determining the speed switching position and determining a predetermined time when the speed switching position is reached. a reference speed switching means outputting a fixed reference speed signal for generating a speed "0" instead of the reference speed; and a reference speed switching means for outputting a fixed reference speed signal for generating a speed "0" in place of the reference speed; This configuration includes a driving means for driving the moving means based on the error signal.

This makes it possible to shorten seek time while stably performing track pull-in control, resulting in the effects of shortening access time and improving accuracy. Furthermore, if the speed switching position, speed at the time of switching, and duration are specified appropriately, it is possible to improve the rough access accuracy and stabilize the tracking servo.

[Brief explanation of drawings]

1 to 7 show one embodiment of the present invention. FIG. 1 is a block diagram showing a control system of an access control device. FIG. 2 is a flowchart 1 showing the access control device. FIG. 3 is a graph showing a velocity profile in relation to position error and reference velocity. FIG. 4 is an explanatory diagram showing the transfer function of the control system in the access control device. FIG. 5 is a graph showing how the actual speed of the optical head converges to "0". FIG. 6 is a graph showing how the optical head movement distance converges to a constant value. FIG. 7 is a graph showing the relationship between reference speed and actual speed over time. FIGS. 8(a) and 8(b) are graphs showing speed profiles used in conventional access control devices, respectively. l is ROM (speed profile), 2 is CPU (calculation means/reference speed switching means), 3 is D/A converter, 4
5 is a polarity setting circuit, 5 is an amplifier, 7 is a drive means, 8 (moving means), 9 is a position sensor, 11 is a speed detection means, and 12 is an output means. 6 is a comparison circuit, 6 is a linear motor 10, and position detection is a reference speed signal.

Claims (1)

[Claims] 1. 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, a speed detecting means for detecting the speed of the optical head, and a moving means for moving the optical head in the radial direction of the optical disk. a calculation means for calculating the position error; and a reference speed corresponding to the position error based on a speed profile in which deceleration and acceleration become smaller as the target track approaches and a predetermined switching point speed is reached at a speed switching position before the target track. a reference speed signal output means for outputting a reference speed signal for generating a reference speed signal; speed"
a reference speed switching means for outputting a fixed reference speed signal for generating "0", and driving the moving means based on an error signal between the actual speed signal of the optical head by the speed detection means and the reference speed signal. What is claimed is: 1. An access control device for an optical disc device, characterized in that it is provided with a drive means.