JPH0237576A - Accessing device for optical head - Google Patents

Abstract

PURPOSE:To stabilize the pull-in of a light spot to a track by controlling a second driving means based on a high frequency component outputted from the displacement detecting means of the light spot and a low frequency component outputted from a relative speed detecting means. CONSTITUTION:The differential signal of the quantity of displacement of the light spot 3 detected by a displacement detector 42 and a displacement targeted value from a fine actuator displacement targeted value generator 45 is supplied to a coarse actuator 5 as a driving signal. Also, displacement detected by the displacement detector 42 is set as a velocity signal at a displacement speed change circuit 44, and a high-pass area component is taken out by a high-pass filter 47, and also, the low-pass area component of the speed signal generated from a tracking error signal by a relative speed detector 8 is taken out by a low-pass filter 40, and both signals are added 41, and a false relative speed signal vc is obtained, and difference between a speed targeted value v0 is detected by an error amplifier 9, and is supplied to a fine actuator 6 via a gain compensation circuit 11 as the driving signal.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an access device for an optical head.

[Conventional technology]

As a conventional access speed control device for an optical head, there is one shown in FIG. 4, for example. This access speed control device moves a light spot 3 in the radial direction of an optical disc 2 that is rotationally driven by a spindle motor 1 to access a desired information track on the optical disc 2.
The optical head 4 for forming the optical spot 3 is driven in the radial direction of the optical disc 2 by a coarse actuator 5, and the optical spot 3 is further driven by a fine actuator 6 mounted on the optical head 4 to drive the optical disc 2 in the radial direction of the optical disc 2. It is designed to be driven precisely and at high speed in the direction. In this conventional example, the reflected optical signal of the optical spot 3 from the optical disk 2 is supplied to the tracking error detector 7 to obtain a tracking error signal indicating the positional deviation of the optical spot 3 with respect to the information track. A relative velocity detector 8 detects the relative velocity between the optical spot 3 and the information track, and supplies the detected signal to one input terminal of an error amplifier 9. The other input terminal of the error amplifier 9 receives the light spot 3 from the speed target value generator 10.
and the information track, and detect the difference between the speed target value and the actually detected relative speed,
The output is supplied to the coarse actuator 5 via a gain compensation circuit 11 that improves the characteristics of the servo loop.

In this way, a speed control loop is formed to target the optical spot 3 by controlling the drive of the optical head 4 by the coarse actuator 5 so that the optical spot 3 and the information track have a predetermined relative speed during access. The light spot 3 is moved close to the track and then switched to a position control loop (not shown) to limit the speed at which the light spot 3 enters the target track to a relatively small value, thereby causing the light spot 3 to enter the target track.

Here, the information track on the optical disk 2 is constantly displaced in the disk radial direction due to the eccentricity of the disk and the vibration of the spindle motor 1, and this displacement is the cause of fluctuations in the relative speed between the optical spot 3 and the information track. Become. The speed control loop shown in FIG. 4 operates to suppress the influence of the fluctuation, but in this configuration, the relative speed is obtained over the entire band in the relative speed detector 8 based on the tracking error signal. Therefore, when the track crossing speed is small, the nonlinearity of the tracking error signal increases the phase delay in the high frequency region, which impairs the stability of the speed control loop.

In order to eliminate such drawbacks, for example, in the Optical Memory Symposium '86 Proceedings P191-196,
By adding an observer 20 that simulates the transfer characteristics of the coarse actuator 5 as shown in FIG. proposed in which the drive of the coarse actuator 5 is controlled based on the speed signal estimated by the observer 20. Furthermore, as shown in FIG. 6, Japanese Patent Laid-Open No. 61-267976 discloses that a speed signal is obtained in a synthesis circuit 21 based on a relative speed signal detected by a tracking error signal and a drive current of the precision actuator 6. A system has been proposed in which the drive of the precision actuator 6 is controlled based on this speed signal.

[Problem to be solved by the invention]

In the conventional examples shown in FIGS. 5 and 6, a drive signal for the coarse actuator 5 or the fine actuator 6 is input to an electric circuit having the same transmission characteristics as the actuator,
The output is treated as the speed of the actuator, but since it is difficult to accurately simulate the high-order mechanical resonance of the actuator, the transfer characteristics in the electric circuit described above are considered to be accurate even if there is no mechanical resonance. It matches the assumed characteristics. Therefore, the speed signal obtained from such an electric circuit is different from the true speed of the actuator, and even when external disturbances such as frictional force or inertial force due to acceleration act on the actuator, the speed signal obtained is different from the true speed of the actuator. The speed will be different. For this reason, it is no longer possible to accurately control the relative speed between the light spot and the information track, and when the target track is reached, the relative speed exceeds the limit speed that allows stable retraction, resulting in failure in retraction. be.

In addition, especially in the conventional example shown in FIG. 6, the fine actuator 6 is controlled after the coarse actuator 5 has moved to the vicinity of the target track in advance, and it is necessary to switch the control mode in the middle of the access operation. The problem is that the system becomes complicated.

The present invention has been made in view of these conventional problems, and it is an object of the present invention to provide an access device for an optical head that is appropriately configured to be able to stably draw a light spot to a desired track with a simple configuration. With the goal.

[Means to solve the problem]

In order to achieve the above object, the present invention provides an optical head access device that positions a light spot on a desired information track by moving a light beam in a tracking direction perpendicular to the information track of an optical recording medium. a first drive means for moving the optical head over a wide range in the tracking direction; a second drive means for moving the light spot over a minute range in the tracking direction; and a first drive means for moving the optical head over a small range in the tracking direction; a relative speed detecting means for detecting a relative speed in the direction; and a displacement detecting means for detecting a displacement of the light spot caused by the second driving means; The second driving means is controlled based on a high frequency component of the output of the displacement detecting means and a low frequency component of the output of the relative speed detecting means.

[For production]

FIG. 1 shows a conceptual diagram of the present invention, showing a speed target value signal v0 and a pseudo relative speed signal ν. A difference signal between the two is processed by an appropriate gain compensation circuit 25 and used as a drive signal for the second drive means 26. The displacement of the light spot caused by the second driving means 26 is detected by a displacement detector 27, and this is passed through an appropriate phase compensation circuit 28 to be used as a driving signal for the first driving means 29. 1st. The displacements of the second driving means 29 and 26 are added to obtain the displacement of the light spot, which is differentiated by the differentiating means 30 and converted into a velocity, and from this velocity the velocity V in the tracking direction of the recording medium is subtracted. The relative velocity Vc between the light spot and the information track is obtained. This relative velocity V. is detected by the relative velocity detection means 31, and its reduced component is extracted via the low-pass filter 32. On the other hand, the output of the displacement detector 27 is supplied to a displacement speed conversion circuit 33 and converted into a speed signal.

This displacement velocity signal is supplied to a bypass filter 34 to extract its high-frequency components, which are then filtered to a low-pass filter 32.
A pseudo relative speed signal vc is obtained by adding it to the low frequency component of the relative speed from , and this is added to the speed target value signal v0 to form a speed control loop.

In this way, in a high frequency band that the first driving means 29 cannot follow, the second driving means 26 is made to respond, and the displacement velocity at that time is made into a high frequency component of the speed signal, and in a low frequency band, the second driving means 26 is made to respond. The driving means 29 is made to respond so that the entire recording medium can be accessed, and the signal detected by the relative velocity detecting means 31 at this time is taken as a low-frequency component of the velocity signal.

〔Example〕

FIG. 2 shows a first embodiment of the invention. This access device accesses a desired information track on the optical disk 2 by moving a light spot 3 in the radial direction of the optical disk 2, which is rotationally driven by a spindle motor 1, as shown in FIGS. 4 to 6. The optical head 4 for forming the optical spot 3 is driven by a coarse actuator 5 over a wide range in the radial direction of the optical disk 2, and the optical spot 3 is further mounted on the optical head 4. The precision actuator 6 drives the disc precisely and at high speed in a minute range in the radial direction of the disc. In this embodiment, the reflected optical signal of the optical spot 3 from the optical disk 2 is supplied to the tracking error detector 7 to obtain a tracking error signal indicating the positional deviation of the optical spot 3 with respect to the information track. A relative velocity detector 8 detects the relative velocity between the optical spot 3 and the information track, and supplies the signal to a low-pass filter 40 to extract a low frequency component, which is supplied to one input terminal of an adder 41.

Further, the optical helad 4 is provided with a displacement detector 42 for detecting the displacement of the optical spot caused by the precision actuator 6, and its output is supplied to one input terminal of the error amplifier 43.
It is supplied to the displacement speed conversion circuit 44.

The other input terminal of the error amplifier 43 is supplied with the target value of the displacement of the optical spot 3 by the precision actuator 6 from the displacement target value generator 45, and the output of this error amplifier 43 is supplied with a phase value for stabilizing the servo loop. The signal is supplied to the coarse actuator 5 as a drive signal via a compensation circuit 46. Also,
The displacement speed conversion circuit 44 converts the displacement of the optical spot 3 caused by the precision actuator 6 detected by the displacement detector 42 into a speed signal, supplies this to a bypass filter 47 to extract a high frequency component, and sends this to the adder 41. Supplied to the other input terminal. As a result, the adder 41 adds the low frequency component of the relative velocity and the high frequency component of the displacement velocity of the light spot 3 by the precision actuator 6 to obtain a condensed relative velocity valley, which is input to one side of the error amplifier 9. Supply to the terminal.

The other input terminal of the error amplifier 9 is supplied with the target value v0 of the relative velocity between the optical spot 3 and the information track from the velocity target value generator 10, and the velocity target value ν is supplied thereto. A speed control loop is formed by detecting the difference between the relative speed signal and the pseudo relative speed signal, and supplying the output as a drive signal to the fine actuator 6 via a gain compensation circuit 11 that improves the characteristics of the servo loop.

The operation of this embodiment will be explained below.

When the difference signal between the speed target v0 and the pseudo relative speed signal is supplied to the fine actuator 6 via the gain compensation circuit 11,
The precision actuator 6 controls the lens, so that the relative speed between the light spot 3 and the information track matches the speed target value v0.
The light spot 3 is moved by driving a mirror or other means.

From the reference position fixed to the light nozzle 4, the light spot 3
When the displacement detector 42 detects how much displacement has occurred due to the action of the fine actuator 6, and the difference signal between the amount of displacement and the displacement target value from the fine actuator displacement target value generator 45 is input to the coarse actuator 5, A position servo system for the displacement of the optical spot 3 by the coarse actuator 5 is formed, and if the displacement target value is set equal to the output of the displacement detector 42 at the reference position of the optical head 4, the optical spot 3 will be displaced by the optical head. The coarse actuator 5 is controlled so that it is always in the reference position with respect to 4.

Here, since the band of the position servo system is relatively low due to the properties of the coarse actuator 5, the high frequency component of the speed of the optical spot 3 is caused by the relative speed between the optical head 4 and the optical sub-node 3 caused by the fine actuator 6. almost equal.

In addition, the frequency characteristics of the disturbance velocity due to the influence of disk eccentricity etc. also decrease as the frequency increases, so the
The relative speed between the throat 4 and the optical spot 3 is approximately equal to the relative speed between the optical spot 3 and the information track in the high frequency region. On the other hand, in the low frequency region, the influence of the above-mentioned disturbance speed is large, so it is necessary to detect the relative speed from the tracking error signal. Therefore, in this embodiment, as described above, the displacement detected by the displacement detector 42 is converted into a speed signal by the displacement speed conversion circuit 44, the high frequency component of the signal is extracted by the bypass filter 47, and the tracking error signal is The low-frequency components of the speed signal generated by the relative speed detector 8 are passed through the low-pass filter 4.
0 and add both signals to obtain a pseudo relative speed signal, and the difference signal between this pseudo relative speed signal and the speed target value v0 is sent to the precision actuator 6 as a drive signal via the gain compensation circuit 11. supply

With this configuration, the accuracy of the speed control system regarding the relative speed between the light spot and the information track during access can be increased, and therefore the relative speed when the light spot enters the target track can be made smaller than the limit speed. Therefore, the optical spot can be stably drawn to the target track. In addition, the coarse actuator 5
moves in conjunction with the precision actuator 6 (therefore, the light spot can be made to reach the target track without switching the control mode midway, and the control system can therefore be simplified. In addition, in the above configuration, the displacement detector 42 can be configured with a sensor that detects the displacement and angle of the movable part of the precision actuator 6, and the displacement speed conversion circuit 4.
4 can be configured with, for example, a differential circuit.

FIG. 3 shows a second embodiment of the invention. In this embodiment, the speed of the precision actuator 6 is detected by a speed detector 51.
, and supplies it to the adder 41 via the bypass filter 47, and extracts the low frequency component of the drive signal of the precision actuator 6 using the low-pass filter 52.
This embodiment differs from the first embodiment in that this signal is supplied to the coarse actuator 5 as a drive signal via a phase compensation circuit 53. Therefore, according to this embodiment, in addition to being able to obtain the same effects as the first embodiment, the speed detector 5
1 can be configured to detect, for example, the back electromotive force of the actuator drive coil, which eliminates the need for a circuit that converts displacement into speed, and has the effect of simplifying the configuration.

The present invention is not limited to optical disks, but can also be effectively applied to optical head access devices when using magneto-optical disks or optical cards.

〔Effect of the invention〕

As described above, according to the present invention, the first driving means that moves the optical head over a wide range detects the displacement of the optical spot caused by the second driving means that moves the optical spot at least within a minute range. The second driving means is controlled based on the output of the displacement detecting means, and the second driving means is controlled by a high frequency component of the output of the displacement detecting means and a low frequency component of the output of the relative speed detecting means for detecting the relative speed of the optical spot and the information track. Since the control is performed based on , the accuracy of the speed control system regarding the relative speed between the optical spot and the information track at the time of access can be improved. Therefore, the relative speed at which the light spot enters the target track can be made smaller than the limit speed, and the light spot can be stably drawn into the target track. Further, since the first drive means moves in conjunction with the second drive means, the light spot can be made to reach the target track without switching the control mode midway, and the control system can therefore be simplified.

[Brief explanation of the drawing]

Figure 1 is a conceptual diagram of this invention, Figure 2 is a diagram showing a first embodiment of this invention, Figure 3 is a diagram also showing a second embodiment, and Figures 4 to 6 are conventional techniques. FIG. l...Spindle motor 2...Optical disc 3...
- Light spot 4... Optical head 5... Coarse actuator 6... Fine actuator 7... Tracking error detector 8... Relative speed detector 9... Error amplifier 10.
...Speed target value generator 11...Gain compensation circuit 25
...Gain compensation circuit 26...Second driving means 2
7...Displacement detector 28...Phase compensation circuit 2
9...First drive means 31...Relative speed detection means 33...Displacement speed conversion circuit 40...Low pass filter 42...Displacement detector 44...Displacement speed conversion circuit 46... Phase compensation circuit 51... Speed detector 53... Phase compensation circuit 30... Differentiating means 32... Low pass filter 34... Bypass filter 41... Adder 43... Error amplifier 45...・Displacement target value generator 47...Bypass filter 52...Low pass filter Patent applicant Olympus Optical Industry Co., Ltd.

Claims (1)

[Claims] 1. In an optical head access device that positions a light spot on a desired information track by moving the optical head in a tracking direction perpendicular to the information track of an optical recording medium, the optical head is moved over a wide range in the tracking direction. a first drive means for moving the light spot over a small range in the tracking direction; and a second drive means for moving the light spot over a minute range in the tracking direction.
a driving means, a relative velocity detecting means for detecting the relative velocity of the information track and the optical spot in the tracking direction, and a displacement detecting means for detecting the displacement of the optical spot by the second driving means, The second driving means is controlled based on at least the output of the displacement detecting means, and the second driving means is controlled based on a high frequency component of the output of the displacement detecting means and a low frequency component of the output of the relative speed detecting means. What is claimed is: 1. An access device for an optical head, characterized in that the access device is configured to control the optical head.