JPH0439151B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a digital optical disk, and more particularly to an optical disk device that performs highly accurate positioning of several μm and shortens access time.

Currently, laser light is irradiated onto a vapor-deposited metal film on a rotating disk, narrowed down to a spot of about 1 μm.
By modulating the irradiation power, information is recorded by thermally making a hole in the metal film, and during playback, the metal film is focused and irradiated with a weak laser beam, and the information hole (called a bit) is created. An information processing device called a digital optical disk has been proposed, which reads information using changes in the amount of light reflected from the disk. A proposal of this type is Electronics magazine (Nov.23,
1978, P75, “Ten Buillion Bits Fit onto Two
A typical configuration example of this type of system is shown in FIG.

Here, a digital optical disk (hereinafter abbreviated as optical disk) 3 having a diameter of 30 cm is rotated in the direction of the arrow by a rotary motor 5 around a rotating shaft 4. As shown in FIG. An optical head 2 composed of a laser light source and an optical system is mounted on a swing arm actuator 1 conventionally used for magnetic disks, etc., and is driven in the radial direction of the optical disk 3.

The surface of the optical disk 3 is covered with a transparent protective film 6 made of glass or the like, and in the same figure, a portion of the protective film 6 is further cut away to show a pit 12, which will be described later.

In this case, information is recorded/reproduced using the structure shown in FIG. 2, which is an enlarged view of portion A of the optical disk 3.

That is, a glass or plastic substrate 1
1, a guide groove 13 having a concave cross-sectional structure with a certain width and depth is provided using an ultraviolet curing resin or the like,
After a metal film 10 is deposited thereon, a protective film 6 is provided. For recording again, the focusing spot of the optical head is guided from above the transparent protective film 6 along the guide groove 13, and the pit 12 is formed by the above-described method. Further, during reproduction, a light spot is similarly irradiated along the guide groove 13, and the amount of reflected light is read.

Here, a signal for controlling the light spot is also detected from the amount of reflected light. The signals that control this light spot consist of two types: a focus shift detection signal that detects a shift in focus due to vertical vibration of the optical disk, and a track shift detection signal that detects a shift between the center of the light spot and the center of the guide groove. All of these signals use the amount of light reflected from the metal film.

This optical disc has a track pitch of 1.6μm.
Assuming this, approximately 50,000 tracks are provided on one side of an optical disk with a diameter of 300φ, and the data stored per track is approximately 4,000 bytes.

Each of these tracks is provided with a plurality of sectors in advance in the rotational direction for each track to indicate data divisions. To record and play back external information at any location, first find one track on the disk surface,
An access operation is required to find one sector on this track. Conventionally, magnetic disks have been used as this type of recording and reproducing apparatus, but these have a track pitch of about 150 .mu.m to 30 .mu.m, which is one or two orders of magnitude larger than that of optical disks. Therefore, since the access means used for magnetic disks has an extremely low stopping accuracy of about 10 μm, there is a problem in that optical disks cannot be positioned using access operations similar to those for magnetic disks. .

In connection with the present invention, there is JP-A-57-181436.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above problems and provide an optical disk device that performs highly accurate positioning.

First, a conventional magnetic disk access method will be explained with reference to FIG. This figure shows a seek control circuit block B and a follow-up control circuit block C. First, in the seek control circuit block B,
A signal 20 indicating the number of tracks from the current track to the target track is set in the differential counter 21. The differential counter receives track pulse 2, which will be described later.
2 is input, and the set number of tracks is sequentially decreased each time a track pulse is input. The counted down output 23 of the differential counter is input to an optimum speed generation circuit 24 to output a target speed curve for speed control, and is input to a speed comparator 25. An actual operating speed signal 26, which will be described later, is input to the other input of the speed comparator 25, and the difference between the target speed and the actual operating speed is output. This output is input to a logic circuit 27 that switches between seek control and follow-up control, and drives a positioner, that is, a positioning drive circuit 29 via a current amplifier 28.

For example, when a voice coil type linear motor is used as a positioner, the current flowing through the coil is 30
is input to the integrator 31 and integrated, and since this represents the actual operating speed at which the positioner is actually moving, the actual operating speed signal 26 is detected and is input to the speed comparator 25 as described above. On the other hand, a position signal 33 read from a servo head 32 mounted on the positioner is input to a track pulse generation circuit 34 that generates track pulses 22, and one track pulse 22 is generated every time the positioner passes one track. Output.

By the above seek control circuit block B, speed control is performed according to the optimum speed curve until the target track is reached. When the target track is reached, follow-up control circuit block C performs follow-up control.

Here, the difference between the deflection X _T of the center of the track and the displacement X _H of the center of the magnetic head is calculated by the position signal generating circuit 3.
5 and generates a position signal 33'.
This position signal 33' is input to the power amplifier 28 of the seek control circuit block B through a compensation system consisting of a phase lead circuit 36 and a phase delay circuit 37. In the same block B, differential counter 2
1 is a switching signal 21 when the content is subtracted and becomes zero.
a to the logic signal 27. As a result, the logic circuit 27 is switched from seek control to follow control, and the positioner is controlled by the position signal 33'.

In this case, as the magnetic head moves on the radius of the magnetic disk, the positive
A negative output is output from the magnetic head and the position signal 3
3' has a triangular waveform as shown in FIG.
Here, black circles E represent odd-numbered tracks, and white circles O represent even-numbered tracks. The track pulse generation circuit 34 in FIG.
A track pulse 22 is generated each time the vehicle passes through. Note that the half period Δ of the triangular wave shown in FIG. 4 is approximately equal to the track interval, that is, the track width, and is approximately 35 μm in recent high-density magnetic disks.

The positioner 29 is activated by the above-mentioned position signal 33'.
When this is controlled, a deviation (deviation from the target position) of about 5 to 10 μm occurs regularly, although it varies depending on the configuration and performance of the positioner. This is caused by friction and the like, and in a transient state of position control, overshoot may occur with respect to the target position, and this value is also about 5 μm.

As mentioned above, the track spacing of optical discs is
At present, the minimum thickness is about 1.6 μm, so it is difficult to position the optical disk using the magnetic disk control described above. To solve this problem, another actuator that can position the track center with high precision but has a narrow tracking range is mounted on the positioner 29, and the actuator is mounted on the positioner 29.
Positioning accuracy that cannot be achieved using only the actuator 9 can be achieved by interlocking two actuators.

Furthermore, when positioning is performed using only one positioner with a small steady-state deviation without using the above configuration, the following problems occur. That is,
When the positioner is subjected to maximum acceleration and maximum deceleration, there is a risk that the positioner itself vibrates on the μm order, and therefore information cannot be read from the disk during seek control.

In order to solve the above problems, the present invention provides a scale in the optical head as described in the following embodiments, uses this scale to detect the accurate position of the positioner, performs rough positioning, and then sends a tracking signal. Fine positioning is performed by Embodiments of the present invention will be described below with reference to FIGS. 5 and 6.

In this embodiment, seek control and follow-up control are performed by one positioner, and the optical head mounted on this positioner is lightweight and small. As an example, the structure can be used by mounting an optical head on the arm portion of the swing arm described in FIG. 1 above.

Unlike magnetic disks, optical disks do not have a positioning disk or servo head.
The exact position of the optical head cannot be detected. Therefore, in this embodiment, a scale for detecting the rotation angle of the swing arm is provided externally. Examples of this scale include, for example, a scale based on moire fringes,
Alternatively, a magnetic scale can be used. Here, as an example, a case will be described in which a moire scale is used.

As shown in FIG. 5, this moire scale 40
is attached to the drive part of the swing arm 1, and outputs a position signal based on moire (hereinafter referred to as a moire signal).
42 (shown in FIG. 7B) is sent out from the moiré detection circuit 41. The pitch spacing of moiré scales that can be created at present is very coarse compared to the track pitch spacing, for example, the minimum pitch is about 10 μm, typically about 50 μm.

Next, the access process from the track currently being read by the optical head to the desired target track will be described.

In Fig. 6, the difference between the current track and the target track is measured by the upper control unit (not shown).
A signal 43 is obtained which indicates the direction and the number of moiré pitches corresponding to the track difference. This signal 43 is taken into the present device by a latch circuit 44 and set in a down counter 45. A moiré pulse 46, which will be described later, is input to the other input of the down counter 45, and the set value of the down counter 45 is subtracted. In addition, Moire Pulse 46
The moire signal 42 is transmitted to the moire pulse generation circuit 47.
, and generate one pulse per moiré pitch.

The output of the down counter 45 represents the number of remaining moiré pitches up to the moiré position near the target track, and this is input to an optimum speed generation circuit 48 to generate an optimum speed signal for seek control. This optimum speed signal is applied as one input to speed comparator 49. The other input of the speed comparator 49 receives an actual operating speed signal. There are various means for detecting this actual operating speed, but in this embodiment, the moiré pulse 46 is input to an F/V (frequency-voltage) converter 50 to detect the actual operating speed. Note that another method is to integrate the current that drives the swing arm.

The speed comparator 49 compares the difference between the optimum speed signal and the actual operating speed, and outputs the difference. This output is input to a first switching circuit 51 that switches between seek control and follow-up control, and switches according to a logic sequence to be described later.
2 to drive the swing arm.

The moiré signal 42 is further input to a second switching circuit 53, selected according to a logic sequence described later, and sent to an adder 5 by a phase compensation circuit 54.
5 is input. The other input of the adder 55 has
A jump signal (c) from a jump counter, which will be described later, is input for skipping tracks one by one. For details on jump operation, please refer to
I am familiar with Philips Technical Review, Vol. 33, P178, so I will omit it here.

The output of the adder 55 is sent to the first switching circuit 5.
1 and is selected in the case of follow-up control to drive the swing arm via the power amplifier 52. In addition, the second switching circuit 5
Since the output of No. 3 also serves as a signal representing the tracking accuracy when tracking control is performed, the output of the sequence circuit 56 that generates the timing of the logic sequence is
is input.

The other input of the second switching circuit 53 receives a tracking signal 57 representing the deviation between the center of the track where the optical head is detected and the center position of the optical spot.
2 is input, and is used when one track is selectively followed by the second switching circuit 53.

In this embodiment, fine positioning to the target track is performed by jump operation, so after coarse positioning by moiré, the number of the nearby track is read once, and the difference to the target track is calculated by the upper control unit. , the difference therebetween and the direction thereof, a signal 58 is set in the jump counter 59. The jump counter 59 generates pulses of a certain period for the set number of jumps, activates the jump signal generation circuit 60 that generates a jump signal with this pulse, and sends the output to the adder 55 as described above. Enter.

Next, the operation of this embodiment will be explained using the time chart shown in FIG. 7 and the trajectory chart of the light spot shown in FIG. When the number of moiré pitches corresponding to the difference between the target track and the current track is set in the latch circuit 44 as a signal 43, the swing arm moves at a time t ₀
The moire pulse generation circuit 47 detects the moire signal 42 and applies a moire pulse 46 to the down counter ₄₅ during this time. When the set value of the down counter 45 reaches zero, it generates a signal 45a indicating that it has approached the moiré closest to the target track, and inputs the signal 45a to the sequence circuit 56.

In the sequence circuit 56, the second switching circuit 53
The first switching circuit 5 generates a switching signal A for positioning based on the moire signal from the moiré signal 42 inputted through the signal 45a and the signal 45a.
Add to 1. The generation timing of this switching signal A is preferably such that it occurs when the moire signal enters a linear portion with the zero point of the moire signal as a symmetrical point, taking into consideration the conditions for stable pull-in of the servo system. most appropriate. Due to this timing, the locus of the light spot shown in FIG. 8 is drawn to the moiré target _X0 . In the figure, the half period of the moiré pitch is δ, and the eccentricity of the optical disk is η.
It is expressed as Whether or not the moire positioning has reached a certain accuracy can be determined by detecting in the sequence circuit 56 that the voltage level of the moire signal is within a certain set value. After this time t ₂ , a switching signal E for positioning based on the tracking signal is generated and applied to the second switching circuit 53.

At that moment, the optical head is drawn into the encountered track 71 and reads out the address information recorded on this track. By reading this address information, the upper control section calculates the number of remaining tracks and the moving direction, and sets the values in the jump counter 59. The time required for this is _t3 . Next, the optical head reaches the target track 72 while jumping over the tracks one by one in accordance with the jump signal outputted from the jump signal generating circuit 60. Here, in order to correct errors in the jump operation, it is desirable to read out the address information of the currently reached track when jumping over a plurality of tracks, and perform the jump operation while checking it again.

In addition, in the explanation of the above embodiment, the optical spot is once drawn to the zero point of the moiré signal, but if the final velocity at the time when the content of the down counter 45 becomes zero by seek control is small, the eccentricity will be changed again. is small and the speed due to eccentricity of the track is small, it becomes possible to position the swing arm within the detection range of the tracking signal. Therefore, tracking control can be performed using only the tracking signal. In this case, the settling time t ₂ becomes unnecessary.

Furthermore, since this example describes the case where a swing arm is used, if equally spaced moire scale pitches are attached to the coil part of the swing arm, an error will occur between the position on the optical disk surface and the count number of the moire pitches. . In order to absorb this error, the pitch of the moiré scale may be changed depending on the angle, or correction may be performed during calculation by the upper control section.

The above problems do not occur with actuators that linearly drive optical heads, such as linear motors. Further, this embodiment can also be applied to a structure in which an optical head is mounted on an actuator that moves in a straight line, such as a linear motor.

Next, FIG. 9 shows another embodiment of the present invention, in which another actuator that can position the track center with high precision but has a narrow tracking range is attached to the optical head 2'. is mounted on an actuator that can move over the entire radius of the optical disk, although the stopping accuracy is not good, and highly accurate positioning over the entire surface of the optical disk is performed.

In this embodiment, a linear motor 80 is used, and is composed of a coil 81, a support section 82 that supports the coil 81 and transmits force to the linear carriage 83, and rollers 86 that roll the carriage 83 along a base 84. In addition, the optical head 2' mounted on this is
It consists of an objective lens 88 that focuses light from a light source (not shown) onto an optical disk, a mirror 85 that moves a light spot within the field of view of the lens, and known optical components, a light source and a photodetector 87. There is.

Furthermore, as an actuator for tracking a limited area, a two-dimensional actuator that performs focusing by moving the objective lens 88 parallel to the optical axis and in the radial direction of the optical disk perpendicular to the optical axis is used. There are also things like.

FIG. 10 shows its rotation configuration, and the configuration and access procedure for performing seek control and position control of the linear motor using a moiré scale are the same as in FIG. 6. Next, the different points will be explained.

After positioning the linear carriage 83 using the moiré signal, it is confirmed that the position has reached a certain level (5 to 10 .mu.m), and a switching signal ``H'' is input to the switch circuit 89 to put the tracking servo device into an operating state. Note that a tracking signal 87a is input to the switch circuit 89 from a photodetector 87 that detects a tracking signal. Due to the switching signal E, the tracking signal 87a passes through the compensation circuit 90 via the switch circuit 89 and is applied to one input of the adder 55. The jump signal C is input to the other input of the adder 55, and the adder 55
The output is applied to the mirror drive circuit 91, and its mechanical output F deflects the mirror 85 to perform tracking.

As explained above, according to the present invention, the position of the optical head being accessed can be reliably known using an external scale without reading out the track recorded on the optical disk, and seek control and tracking control can be performed. It can be done reliably. Also,
This method has many advantages, such as being able to accurately position the optical disk by using an actuator whose stopping accuracy is higher than the track pitch.

[Brief explanation of drawings]

FIG. 1 is a perspective view showing a digital optical disk system, FIG. 2 is a partially enlarged perspective view of the optical disk, FIG. 3 is a block diagram showing a seek control circuit block and a follow-up control circuit block of a magnetic disk, and FIG. 4 is a waveform diagram showing the relationship between the amount of movement and the optical head output when the optical head moves along the radius of the optical disk, FIG. 5 is an explanatory diagram showing an embodiment of the present invention, and FIG. 6 is the same circuit configuration. 7 is a time chart showing the signal waveforms of each part, FIG. 8 is an explanatory diagram showing the locus of the light spot, and FIGS. 9 and 10 are explanations showing other embodiments of the present invention. FIG. 2 is a block diagram showing the diagram and its circuit configuration. 2, 2'...Optical head, 3...Digital optical disk, 40...Moiré scale, B...Seek control circuit block, C...Following control circuit block.

Claims (1)

[Scope of Claims] 1. An optical disk device in which an optical disk having a track is irradiated with a light beam from an optical head, and the light beam is positioned on a desired track in order to record and/or reproduce information along the track. , a position detecting means having a scale with a predetermined pitch interval and generating a position signal that becomes zero each time the optical head moves by the pitch interval; a first signal generating means for reproducing a signal; and detecting the number of pitches of the scale corresponding to the difference between the track on which the light beam is positioned and the desired track based on the signal from the first signal generating means; a second signal generating means for generating a first control signal for controlling the moving speed of the optical head according to the number of the optical heads; and controlling the position of the optical head so as to position the optical head at the zero point according to the position signal. a third signal generating means for generating a second control signal for causing the optical disk to track; a fourth signal generating means for receiving the light from the optical disk and generating a tracking signal for causing the optical beam to follow the track; In response to a first control signal, the irradiation position of the light beam approaches the desired track, and the second control signal is switched to position the light beam at the zero point of the position signal, so that the position signal is within a predetermined range. an optical disk device, comprising: a drive means for detecting this and controlling the irradiation position of the light beam based on the tracking signal. 2. When the irradiation position of the light beam approaches the scale position closest to the desired track and the position reaches a linear portion with the zero point of the position signal as a symmetrical point, the first control signal 2. The optical disk device according to claim 1, wherein the second control signal is applied to the drive means instead of the second control signal. 3. The optical disk device according to claim 1 or 2, wherein the driving means includes a swing arm that moves the optical head substantially in a radial direction of the optical disk. 4. The driving means includes a first actuator that moves the optical head in a substantially radial direction of the optical disk, and a second actuator provided on the optical head, and the first actuator moves the optical head in a substantially radial direction of the optical disk. 3. The optical disk device according to claim 1, wherein the second actuator responds to the first control signal and the second control signal, and the second actuator responds to the tracking signal. 5. In an optical disk device in which an optical disk having tracks is irradiated with a light beam from an optical head and the light beam is positioned on a desired track in order to record and/or reproduce information along the track, a predetermined pitch interval is used. a position detecting means having a scale and generating a position signal that becomes zero each time the optical head moves by the pitch distance; and a first position detecting means for generating a signal each time the optical head moves by the pitch distance based on the position signal. and a signal from the first signal generating means to detect the number of pitches of the scale corresponding to the difference between the track on which the light beam is located and the desired track, and to adjust the number of pitches of the scale according to the number of pitches. a second signal generating means for generating a first control signal for controlling the moving speed of the head; and a third signal generating means for receiving light from the optical disk and generating a tracking signal for causing the optical beam to follow the track. a signal generating means; in response to the first control signal, the irradiation position of the light beam approaches the desired track, and when the moving speed at the zero point of the position signal is small, the light beam is pulled to the zero point of the position signal; driving means for controlling the irradiation position of the light beam based on the tracking signal, and for controlling the irradiation position of the light beam based on the tracking signal after pulling the position signal to a zero point when the moving speed is high. An optical disk device characterized by: 6. The optical disk device according to claim 5, wherein said driving means includes a swing arm for moving said optical head substantially in a radial direction of said optical disk. 7. The driving means includes a first actuator for moving the optical head in a substantially radial direction of the optical disk, and a second actuator provided within the optical head, and the first actuator is configured to move the optical head in a substantially radial direction of the optical disk. 6. The optical disk device according to claim 5, wherein said second actuator responds to said tracking signal in response to said first control signal and said second control signal.