JPH0213374B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical system drive for tracking control of an optical information reading device in a video disc player, a digital audio disc player, etc. This invention relates to an optical information reading device whose purpose is to reduce the weight of the unit and increase the frequency response range of tracking control to a high frequency range.

Conventionally, this type of optical information reading device has (a) One beam astigmatism method (b) One beam faucult prizm method (c) One beam knife edge method etc. are common.

In the method (a) above, as shown in Fig. 1, when the disk 1 moves in the Z direction, the beam spot on the detector 2 moves towards the lens 3 as shown in Fig. 2 A, B, and C.
and the focus point changes due to the astigmatism of the cylinder lens 4. Therefore, the focus error signal is e _f = (B ₁ + B ₃ ) - (B ₂ B ₄ ) as shown in Figure 2.
Detected by This signal is applied to the Z-direction drive device for the focus lens 5 to move the focus lens 5 in the Z-direction and maintain it at a constant interval with respect to the surface runout of the disk 1.

On the other hand, the tracking error signal is a variation in the intensity of ±1st-order diffracted light as shown in Figure 3 (shaded area in Figure 3).
Therefore, e _t = (B ₁ + B ₄ ) - (B ₂ + B ₃ ), and this tracking error signal is applied to the X-direction drive device of the focus lens 5 to move the focus lens 5 in the radial direction of the disk 1. It is possible to track the optical beam spot with respect to the polarization of the disk 1.

Here too, if only the focus lens 5 is moved in the X direction, the light beam spot will move in the Z direction on the detector 2, and an accurate tracking error signal will no longer be generated. Therefore, conventional devices have a mechanism that moves the entire optical system in the X direction.

However, in order to increase the tracking response performance to a high frequency range, it was necessary to make the optical system smaller and lighter.

In the figure, 6a is a first lens, 6b is a second lens, 7 is a laser, 8 is a cylinder lens, 9 is a beam splitter, and 10 is a 1/4λ plate. In addition, in the above method b, as shown in FIG. 4, when the disk 1 moves in the Z direction, the beams separated by the Foucault prism 11 move in opposite directions on the detector 2, that is, as shown in FIG.
When disk 1 and focus lens 5 are far apart, the two beam spots move outward on detector 2, and when disk 1 and focus lens 5 are close, they move inward. Therefore, e _f = (b ₁ + b ₄ ) − (b ₂ +
b ₃ ) allows the focus error signal to be detected.
This is added to the Z-direction driving device for the focus lens 5, and the distance between the disk 1 and the focus lens 5 is always kept constant.

On the other hand, in the tracking error signal, the ±1st-order diffracted light (shaded area) changes as shown in Figure 6 A and B, and e _f =
It can be detected by ( _b1 + _b2 )-( _b3 + _b4 ). This signal is applied to the X-direction driving device of the focus lens 5, allowing the optical beam spot to follow the eccentricity of the disk 1. However, here too, if only the focus lens 5 is moved in the X direction, the two light beam spots will move in the same direction on the detector 2, causing disturbance to the focus error and also making it impossible to obtain accurate tracking error signals. Therefore, in the conventional example shown in this example, it was necessary to make the optical system smaller and lighter in order to move the entire optical system in the X direction.

Furthermore, in the method (c) above, as shown in Figure 7,
When the disk 1 moves in the Z direction, the beam spot on the detector 2 changes as shown in Fig. 8, A, B, and C. Therefore, the focus error signal is e _f =B ₁ −B ₂
It is obtained by On the other hand, the tracking signal is transmitted by the detector 2' as e _t =B ₃ −B ₄ as shown in FIG.
It is obtained by Here, when the tracking servo is performed by moving only the focus lens 5 in the X direction in the same way as in the method shown in FIGS. 1 to 4, the beam spot moves in the X direction on the detector 2 shown in FIG.
This will cause disturbance to the tracking error signal. Therefore, even in the conventional example shown in this example, it is necessary to move the optical system integrally in the X direction. In the figure 12
is a mirror.

As mentioned above, conventional examples a, b, and c all require optical systems to operate as one unit, and a reduction in size and weight has been desired. There were problems such as the difficulty in manufacturing the mechanism.

This invention was made in response to the above-mentioned demands, and it is designed to make the optical thread drive for tracking control independent, reduce the weight of the drive unit, and increase the frequency response range of tracking control to high frequencies. The present invention provides an optical information reading device configured as follows. In the drawings, parts and parts corresponding to those of the conventional example will be described with the same reference numerals. 1st
FIG. 0 shows an embodiment according to the present invention, in which light emitted from a laser 7 is turned into a parallel beam by a lens 6a, and is bent by a mirror 12 in the direction of a focus lens 5. The beam focused on the disk 1 by the focus lens 5 is reflected by the disk 1, returns to the beam splitter 9 again, and forms a spot on the detector 2.
The focus error signal is e _f = (B ₁ + B _{3 ) - ( because the beam spot shape changes on the detector 2 as shown in Fig. 11 A, B, and C due to the astigmatism of the lens 6a and the cylinder lens 8} . B ₂ + B ₄ ).

On the other hand, the tracking error signal can be detected by e _f =(B ₁ +B ₄ )−(B ₂ +B ₃ ) as shown in FIG. When this tracking error signal is applied to the X-direction drive device of the focus lens 5, the beam spot moves in the Z direction in FIG. 12 on the detector 2, causing disturbance to the tracking error signal. Therefore, in the present invention, a tracking error signal is applied to the X-direction drive device of the focus lens 5 and simultaneously applied to the S-direction drive device of the mirror 12, thereby moving the focus lens 5 and the mirror 12 in synchronization.

By doing so, the beam reflected back from the disk 1 is always incident on the detector 2 as a beam centered on the optical axis of the lens 6a even if the focus lens 5 moves in the X direction.

Therefore, even if the focus lens 5 moves in the X direction, the spot on the taker 2 does not move, so a correct tracking error signal can be obtained.
Furthermore, since it is only necessary to move the focus lens 5 and the mirror 12, the driving section can easily push the tracking response frequency range to a high frequency range.

FIG. 13 shows another embodiment according to the present invention, in which the beam spot shown in FIG. 15 is moved in the Z direction by moving the mirror 12 in the S direction in synchronization with the movement of the focus lens 5 in the X direction. It shows that it is not moving. Here, in FIG. 13, since the focus error signal is detected by the knife edge method, the focus error on the detector 2 appears as shown in FIG. 14 A, B, and C.

As explained in detail above, according to the present invention, a mechanism is provided to move the mirror in the S direction in synchronization with moving the focus lens in the X direction, so even if the focus lens moves in the It is possible to make the reflected light enter the detector as a beam centered on the optical axis.

Furthermore, since only the focus lens and mirror need to be moved, the drive unit is light and it is easy to extend the frequency response range of tracking control to high frequencies.

That is, by moving the focus lens in the radial direction for tracking control, the beam spot does not move on the photodetector element. Furthermore, since the drive section on each optical element is independent, the weight of the drive section can be reduced, and the frequency response range of tracking control can be extended to high frequencies. Therefore, there is no need to integrate the optical system in order to move the entire optical system in the radial direction as in the past, and the weight of the drive unit increases due to integration.
The tracking response frequency does not become low.

[Brief explanation of drawings]

Figures 1 to 3, Figures 4 to 6, and Figures 7 to 9 are block diagrams explaining the outline of conventional examples, focusing error detection diagrams, tracking error detection diagrams, and Figures 10 to 9. FIG. 12 outlines an embodiment according to the present invention. FIGS. 13 to 15 are block diagrams, focus error detection diagrams, and tracking error detection diagrams showing other embodiments according to the present invention. 1... Disk, 2... Daytector, 5...
Focus lens, 7...laser, 9...beam splitter, 12...mirror.

Claims (1)

[Claims] 1. In an optical information reading device, a focus lens that focuses a light beam onto an information recording medium is moved in parallel in the disk radial direction of the information recording medium so that the reading device follows a track on the information recording medium, and the focus lens is In synchronization with the movement of the lens, a part of the optical system such as a mirror is moved independently of the focus lens using a tracking error signal, and the beam of reflected light is controlled around the optical axis of the lens. An optical information reading device characterized by: