JPH0624070B2 - Optical disk device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk device having a large capacity and a high-speed access function, which is used for a computer external memory or the like.

Structure of Conventional Example and Problems Thereof In recent years, high-speed access of information in an optical disk device is strongly desired. There are two minimum conditions for realizing high-speed access: high-speed operation of the optical pickup and highly accurate positioning. In order to enable high-speed operation of the optical pickup, the design and development focusing on the downsizing and weight reduction of the optical pickup and the improvement of the optical pickup driving device are currently most actively carried out.

However, in addition to the high-speed operation of the optical pickup,
It also plays a large role in contributing to the high-speed access of the highly accurate positioning ability to access the target track without error. This is because when a track other than the target track is accessed, the optical pickup must be moved again to access the track even if the track is separated from the target track by several tracks. Because it makes the

Incorrect access to target track (seek error)
Most of the causes are due to track miscounting caused by eccentric rotation of the disk. That is,
Many optical disc devices move (traverse) the optical pickup while counting the number of crossed tracks until the target track is reached.
Since the conventional optical disc device (especially recordable one) cannot detect the relative movement direction of the optical pickup with respect to the optical disc surface as described later, the eccentricity of the disc overtakes the optical pickup during traverse, resulting in the optical disc. Even if the optical pickup moved in the opposite direction to the surface, the track was counted in the positive direction. Such seek error adversely affects high-precision positioning of the optical pickup, that is, high-speed access.

The drawbacks of the conventional optical disk device will be described in detail below. FIG. 1 is a partial perspective view and a block diagram of a conventional optical disk device. In FIG. 1, 1 is a laser emission source, 2 is a collimator lens, 3 is an objective lens, and these are provided on the same optical axis. Reference numeral 4 denotes a focus error detection device, which includes a light receiving optical member 41, a light receiving element 42, and a focus error voltage conversion device 4
It is composed of three. 11 and 12 are spectral members,
The spectroscopic member 11 is used to disperse the light reflected by the optical disk 6 and passed through the objective lens 3 again to the light receiving side. The spectroscopic member 12 has a function of distributing the light incident on the light receiving side to the focus error detection device 4 and the light receiving element 5, respectively. The objective lens 3 is held by an objective lens driving device 30 that moves it in the focus control direction. The objective lens driving device 30 is electrically connected to the output of the focus error detection device 4.

Although not specifically shown in the drawing, there is a traverse driving means for moving at least the objective lens 3 horizontally with respect to the surface of the optical disk 6.

The conventional optical disk device configured as described above will be described below.

The coherent light emitted from the laser emission source 1 is collimated by the collimator lens 2 and then focused on the optical disk 6 by the objective lens 3. The light reflected by the optical disk 6 passes through the objective lens 3 again, and a part of the light is sent to the light receiving side by the spectral member 11, and further passes through the spectral member 12 and then enters the focus error detection device 4. The focus error detection device electrically outputs the defocus of the objective lens 3 with respect to the optical disk 6, and many excellent methods have been realized up to the present day, but FIG. The focus error detection device by the method is described. However, the astigmatism method is well known and will be described later, so it will not be described here.

When the defocus of the objective lens 3 with respect to the optical disk 6 is detected, the voltage (or current) conversion value is detected.
Is fed back to the objective lens driving device 30 supporting the. As a result, the defocus can be corrected to zero. In this way, at least, the light emitted from the objective lens 3 is always optical by the focus control means (loop) (not particularly numbered) composed of the objective lens 3, the objective lens driving device 30, and the focus error detection device 4. It is focused on the reflecting surface of the disk 6.

At this time, a value obtained by performing convolution integration with the Fourier transform image of the track of the optical disk 6 and the initial light flux is projected on the light receiving element 5. This is shown in FIG. 3a. P
1, P2, P3 are optical discs 6 of the light (spot) focused by the objective lens 3 as shown in FIG.
It is a symbol corresponding to the position above. The reflected light of the disk projected on the light receiving element 5 is the 0th order light (
₀ ) and the −1st-order light ( ₋₁ ) and the + _1st- order light ( ₊₁ ) that are symmetrically generated with respect to the 0th-order light.
The phase of the ± first-order light with respect to the 0th-order light is determined by the position of the spot with respect to the track. When the spot is on the convex part of the track, P1 is ± π for the ± first-order light with respect to the zero-order light.
P3 is + π / 2 when it has a phase difference of / 2 and is in the concave portion.
It has a phase difference of (Fig. 4). When 0th order light and ± 1st order light are added, reflected light having a symmetrical intensity distribution as shown by P1 and P3 in FIG. 3 (a) is obtained. When the spot is at the track edge, the phase of the −1st order light is π with respect to the 0th order light.
Since the phase of the + 1st order light becomes 0, the reflected light is strengthened on the + 1st order light side.

Here, the light receiving element 5 is provided with the element pieces 5a, so that the portions interfered by the −1st order light and the + 1st order light can be detected respectively.
If the output is divided into 5b and the outputs a ou _T and b ou _T are seen, Fig. 3 (b)
become that way. In FIG. 3, the horizontal axis represents the spot position and the vertical axis represents the output. The outputs of the element pieces 5a and 5b have a maximum value or a minimum value at one track edge. Therefore, if the changes in these outputs are counted during the traverse, that is, the crossed tracks are counted.

However, it is very difficult or impossible to detect the moving direction of the spot from the output of the light receiving element 5.
This is clear from FIGS. 3 (a) and 4, but the combined light of the 0th-order light and the ± 1st-order light when the spot is on the convex portion P1 of the track and on the concave portion P3 is This is because even if the phase distributions are different, the intensity distributions are exactly the same, and therefore, even if the output of the light receiving element 5 that detects the intensity of the incident light is seen, it is not possible to detect the difference in the unevenness of the track.

Generally, in an optical disc, one of the concave and the convex of the track is used for information recording, and the other is used as a buffer area.Therefore, the unevenness of the track is discriminated depending on the presence or absence of a recording signal. Although it is possible to detect the moving direction, such a method cannot be used as it is for an optical disc in an initial state in which no information is written. Therefore, in the initial state, it is necessary to write a signal for discriminating the unevenness of the track on the optical disc in advance. However, this method not only significantly reduces the productivity of the optical disc, but conversely, when recording a signal on the optical disc,
Since the track discrimination signal and the recording signal may influence each other, a good result cannot be expected.

As described above, since it was extremely difficult to detect the moving direction of the spot with respect to the track on the optical disk in the conventional optical disk device, a seek error frequently occurs when searching for the target track, which causes the search time (access It was hindering the shortening of (time).

An object of the present invention is to solve the above-mentioned conventional drawbacks and to detect the moving direction of the spot with respect to the optical disk, and as a result, to reduce the frequency of seek error during track access. Is.

The present invention has a light emitting device, an objective lens for condensing light emitted from the light emitting device onto an optical disk, and a light receiving means for converting light reflected or transmitted through the optical disk into an electric signal. Among the light receiving means, an objective lens, a focus error detecting device for producing an electric output according to a distance between a focus of the objective lens and a recording surface on the optical disk, that is, a focus error, and an output of the focus error detecting device. An optical disk device having a focus control means composed of at least three of an objective lens driving device for moving the objective lens in the optical axis direction in accordance with the above. And a focus control unit having a target value for the focus error of zero and a focus control unit having a target value for the focus error of an appropriate finite value.
When reading or writing information, an operation equivalent to that of a conventional optical disc is performed by forming a focused spot on the optical disc by using a focus control unit whose target value for the focus error is zero. When the optical disc surface is traversed for track access, a focus control means having an appropriate finite value as a target value for the focus error is used to form a slightly defocused spot on the optical disc surface. The direction of movement of the spot during traverse with respect to the track on the optical disk can be detected from one output of the light receiving means.

Description of Embodiments A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 5 is a partial perspective view and a block diagram of the optical disk device according to the first embodiment of the present invention.

In FIG. 5, reference numeral 7 denotes a DC offset addition device provided between the focus error detection device 4 and the objective lens drive device 30, and has a DC offset changeover switch 71 and an addition device 72 as its constituent elements. The DC offset changeover switch 71 is controlled by the read / write and traverse changeover signal R / T. The other components are the same as in the conventional example.

The operation of the optical disc device of the present embodiment having the above-described configuration will be described below. When the DC offset changeover switch 71 is connected to the ground side S1 in order to execute a normal read / write operation with respect to the optical disk 6, the output of the adder 72 becomes the same as the output of the focus error detector 4, and Result The operation of this embodiment is exactly the same as the operation of the conventional example.

Next, consider a case where the DC offset changeover switch 71 is connected to the DC bias side S2 when the read / write operation is terminated or interrupted and the operation shifts to the traverse (movement between tracks) operation. At this time, a DC offset is added to the focus control loop. That is, in the state of S1, the optical disc 6
If the control is performed so that the focus error of the objective lens 3 becomes zero with respect to, the control is performed so that the focus error has a finite value in the state of S2.
However, this is under the condition that the DC offset value determined in S2 is within the control range of the focus control loop.

When the objective lens 3 has a finite focus error with respect to the optical disc 6, the image projected on the light receiving element 5 is a fold of the Fourier transformed image of the track of the optical disc 6 and the wavelet aberration added to the initial light beam. Integral value. The results are shown in Fig. 6 (a). The difference between FIG. 6 (a) and FIG. 3 (a) is that in FIG. 6 (a), the reflection image obtained by P1 when the spot is on the convex portion of the track and P3 when it is on the concave portion. Is different.

This will be explained a little using the concept of wavefront aberration. FIG. 7 shows the objective lens 3, the optical disk 6, and the wavefront W1 of light formed by the objective lens 3. if,
If the wavefront is W2, the light emitted from the objective lens 3 is focused on the optical disk 6, and as a result, the reflected light observed by the light receiving element 5 has the intensity and phase distribution described in the conventional example. Become.

However, the light actually emitted from the objective lens 3 is condensed at a point P which is separated from the optical disk 6 by a finite distance foff, and its wavefront is represented by W1. Since W1 and W2 are wavefronts formed on a spherical surface centered on the point P and one point on the optical disk 6, respectively, W1 is relative to W2. Can be considered to have a wavefront aberration. Here, h represents the distance between one point on the objective lens 3 and the optical axis, and f represents the focal length of the objective lens 3. This means that W1 is It means that they propagate only with different phases.

Thus, when the image when W1 is reflected on the surface of the optical disk 6 and reaches the light receiving element 5 is considered in accordance with the conventional example, it becomes as shown in FIG. 4 (b).

From the viewpoint of wavefront aberration, the reflected image at the time of defocus is simply the Fourier transform image of the track and the wavefront aberration ωp (h).
Can be expressed as a convolution integral with the initial light flux having. That is, in Fig. 4 (a), the phase of every part was uniform in each interference light, whereas in Fig. 4 (b), each phase changed at ωp (h) with respect to the distance from the center. is doing.

What should be noted here is that the spot is the convex portion P of the track.
This is the difference between the case of 1 and the case of the concave portion. Fig. 4
In (b), in the case of P1, the 0th order light and the ± 1st order lights are almost in opposite phases near the center of the 0th order light, and in the case of P3, they are almost in phase. That is, in P1, the vicinity of the center of the 0th-order light becomes darker than the surroundings, and in P3, it becomes brighter. This feature is shown in FIG. 6 (a).

Here, FIG. 6 (b) shows a state in which the outputs a ou _T and b ou _T of the element pieces 5a and 5b of the light receiving element 5 are observed as in the conventional example. Since two outputs are obtained as two-phase signals that are neither in-phase nor in-phase, the moving direction of the spot can be determined by looking at the phase relationship between them. In other words, it is possible to determine the directionality by whether or not a ou _T leads the phase with respect to b ou _T.

It should be noted that the description of the present embodiment is only for the case where the traverse is being performed while the track is being searched and the number of traversed tracks is being counted. When performing the reading and writing of information, the DC offset changeover switch 71 is set to the ground side S1. It has to be switched on to keep the focus on the optical disc 6.

As described above, according to this embodiment, since the DC offset adding device 7 is provided between the focus error detecting means 4 and the objective lens driving device 30, the moving direction of the spot with respect to the optical disc can be detected. As a result, seek errors at the time of searching for the target track can be reduced, and faster access can be realized.

Here, a supplementary explanation will be given for the light receiving element 5. In the conventional example or the present embodiment, when the focus error is controlled to zero, the light receiving element 5 is used as a tracking error signal detecting means. However, when the traverse is executed in this embodiment, the traveling direction of the spot can be identified from the output of the light receiving element 5, that is, it serves as the moving direction detecting means described in the claims.

Next, another embodiment of the present invention will be described with reference to the drawings.

FIG. 8 shows a partial perspective view and a block diagram of an optical disk device according to a second embodiment of the present invention.

In FIG. 8, reference numeral 41 is a first focus error detection device,
42 is a second focus error detection device. Reference numeral 13 is a spectral member that distributes the reflected light from the optical disk 6 to the first and second focus error detection devices 41 and 42. Reference numeral 8 denotes a focus control changeover switch that connects the objective lens driving device 30 to the output of either one of the first and second focus error detecting devices 41 and 42.

The operation of the optical disc device of the present embodiment having the above-described configuration will be described below.

When the focus control changeover switch 8 is connected to the S1 side,
A focus control loop composed of the objective lens 3, the first focus error detection device 41, and the objective lens drive device 30
When the focus control changeover switch 8 is connected to the S2 side, the focus control loop constituted by the objective lens 3, the second focus error detection device 42 and the objective lens drive device 30 operates. If the former is used to focus the objective lens 3 on the optical disk 6 (focus error is zero), and the latter is used to focus on a point at a finite distance from the optical disk 6, the first embodiment is performed. The same effect as described in the example can be obtained.

Further, in the first embodiment, the offset applied to the focus control loop must be within the focus controllable range, and the focus error detection device 4 must also have a sufficiently wide detection range. Since separate control loops are used for reading and writing information and for track retrieval, this consideration is not necessary.

As described above, according to this embodiment, the first and second focus error detecting means 41 and 42 are connected to the focus control changeover switch 8.
By configuring the control loops by selecting in the above, even if the control range of each control loop is not as wide as that required in the first embodiment, the same effect as that described in the first embodiment can be obtained. be able to.

FIG. 9 (a) is a plan view of an essential part of an optical disk device according to the third embodiment of the present invention, and FIG. 9 (b) is a block diagram of the same.

In FIG. 9 (a), 42a, 42b, 42c, 42d
Is an element piece constituting the light receiving element 42, and 44a, 44
Reference numeral b is an element piece that constitutes the auxiliary light receiving element 44. Fig. 9
In (b), 43 is a focus error voltage conversion device that outputs the sum or difference of the outputs of the element pieces. Reference numeral 9 denotes a focus control changeover switch provided between the output and the objective lens driving device 30.

The operation of the optical disc device having the above-described configuration according to this embodiment will be described below. Now, it is assumed that the astigmatism method is used to detect the focus error. When the focus of the objective lens 3 is on the optical disc 6, the disc reflected light projected on the light receiving element 42 becomes circular (FIG. 10 SP).
1). When the focal point is defocused, the reflected light extends in the diagonal direction of the light receiving element 42 (SP2). Therefore, from the outputs A, B, C, D from each element piece of the light receiving element 42 (see FIG. 9 (b)) A + C By obtaining the amount of − (B + D) (3), an electrical output proportional to the focus error can be obtained (FIG. 10 (b)).

However, when the focus error becomes large and the light reflected from the disk exceeds the range of the light receiving element 42 (SP3), the focus error detection device 4
Misses its linear region and, in some cases, becomes impossible to control. Therefore, if stray light mixes in S /
When the size of the light receiving element 4 is limited for reasons such as prevention of N drop, it becomes difficult to control the focus in the state where the DC offset is added as described in the first embodiment.

Therefore, in this embodiment, an auxiliary light receiving element 44 is newly provided on the outer peripheral portion of the light receiving element 42, and the amount of (A + B + C + D)-(E + F) (4) is obtained from the outputs E and F of each element piece and the output of the light receiving element 42. The control range is widened by adding a new one to the focus control loop (Fig. 10 (b)). The focus control changeover switch functions to add the focus error output represented by the equations (3) and (4) to the focus control loop depending on the case of reading / writing information or searching for a track.

As described above, according to this embodiment, by providing the auxiliary light receiving element 44 in the peripheral portion of the light receiving element 42, the control range of the focus control loop can be widened.

Advantageous Effects of Invention According to the present invention, a plurality of focus control loops are provided, and each focus control loop has a different target value for the focus error so that the focus error is intentionally generated when the traverse is executed. Thus, the moving direction of the spot with respect to the track can be detected. As a result, seek errors during track access can be reduced, and as a result, high speed access is possible.

[Brief description of drawings]

FIG. 1 is a perspective view including a block diagram of a conventional optical disk device, FIG. 2 is a perspective view showing the positions of spots, and FIG.
(a), (b) are explanatory views showing the operation of the conventional example, and FIG. 4 (a),
(b) is an explanatory view showing the principle of generation of reflected light from the optical disk, FIG. 5 is a perspective view including a block diagram of the optical disk device in the first embodiment of the present invention, and FIGS. 6 (a) and 6 (b). ), FIG. 7 is an explanatory view showing the principle of the present invention, FIG. 8 is a perspective view including a block diagram of the optical disk device in the second embodiment of the present invention, and FIG. 9 (a) is the present invention. FIG. 9 (b) is a plan view of the essential parts of an optical disk device according to the third embodiment, FIG. 9 (b) is a block diagram of the essential parts including a perspective view of the essential parts of the optical disk device of the present invention, and FIGS. FIG. 9 is an explanatory diagram showing an operation of the third exemplary embodiment of the present invention. 1 ... Laser emission source, 3 ... Objective lens, 4 ... Focus error detection device, 5 ... Light receiving element, 7 ... DC offset addition device, 8, 9 ... Focus control changeover switch, 30 ...
Objective lens driving device, 42 ... Light receiving element, 44 ... Auxiliary light receiving element.

Claims (4)

[Claims] 1. A light emitting means, an objective lens for condensing light emitted from the light emitting means onto an optical disk on which continuous tracks are formed, and light reflected or transmitted by the optical disk is converted into an electric signal. A focus error detecting means having a first light receiving means, which outputs an electrical output from at least the first light receiving means according to a focus error which is a difference between the focus of the objective lens and the recording surface on the optical disc; In an optical disc device having a focus control means comprising an objective lens driving means for moving the objective lens in the optical axis direction thereof in accordance with the output of the focus error detection means, the focus control means is for recording or reproducing information. First focus control means for controlling the focus error target value to be zero, and to make the focus error target value an appropriate finite value other than zero when traversing. Substantially including at least two of second focus control means for executing control, and further having second light receiving means for converting positive and negative diffracted light generated by the continuous track into electric signals, An optical disk device, wherein a traverse direction is detected by an output signal of the second light receiving means. 2. Addition means for adding a DC offset to the electrical output of the focus error detection means is provided between the focus error detection means and the objective lens drive means, and the DC offset value is substantially switched according to the purpose. The optical disk device according to claim 1, wherein a plurality of focus control means are provided in the optical disk device. 3. A plurality of focus error detection means are substantially provided,
Each focus error detection means is configured to have a plurality of different electrical outputs for the same focus error, and the input of the objective lens drive means and one electrical output of the focus error detection means are switched. The optical disk device according to claim 1, wherein a plurality of focus control means are substantially constituted by connecting the optical disk drive and the focus control means. 4. A light receiving means and an auxiliary light receiving means are provided as means for converting a light beam incident on the focus error detecting means into an electric signal, and the light receiving means senses a change in the incident light beam due to the focus error. One electric output corresponding to the focus error is obtained, and similarly, the auxiliary light receiving means or both the light receiving means and the auxiliary light receiving means sense another light beam to obtain another electric output, and as a result, for the same focus error. The optical disc device according to claim 3, wherein the optical disc device is configured to obtain a plurality of electrical outputs.