JPS5960739A - Optical reader - Google Patents

Abstract

PURPOSE:To prevent unstable operation with a simplified circuit in an optical reader which is disposed with a photodetector having a photodetection surface divided to multiple parts on the optical axis of a focusing lens and is disposed with a knife edge for shielding a part of the light transmitting the focusing lens by projecting the knife edge up to the position inclusive of the optical axis. CONSTITUTION:A knife edge 11 is projected up to the position inclusive of the optical axis 12 of a focusing lens L. Then, the light (the light reflected by a disc 10 in the positions A, B, C) focusing on the optical axis is always partly shielded by the outside of the knife edge 11 and the light (the light reflected by the disc 10 in the position D) focusing between the edge 11 and the lens L is mostly shielded by the edge 11 so that the output difference of the photodetector 7 is made to 0 voltage only at A where the micro-spot light is formed and an S- shaped characteristic intersecting with the 0 voltage at a large gradient is obtd. A focusing position is therefore detected only by the zero cross detection circuit and a drawing control circuit is simplified. Since the edge 11 is required merely to be projected so as to include the optical axis, the assembly and adjustment are easy.

Description

TECHNICAL FIELD The present invention relates to an apparatus for optically reading data written on a recording medium, and more particularly to a control signal detection mechanism for maintaining a constant distance between an optical system and a recording medium.

BACKGROUND/TECHNICAL BACKGROUND Video recording devices and digital audio disk devices use optical reading devices that optically read codes written in digitized form on disk-shaped recording media.

This reading device generally uses a laser light source and focuses it on the track of the Dinuk to read the code on the Dinuk, but the laser light is guided to the 1-rack + by following the warpage and eccentricity of the disc. It is equipped with a focusing mechanism and a tracking device 1'7& that is necessary.

Figure 1 shows an example of the optical system of an optical reader.
In the figure, 1 is a semiconductor laser light source, 2 is a collimator lens that collimates the diffused laser light, 3 is a beam splitter that transmits the incident laser light in a straight line and reflects the reflected laser light laterally, and 4 is a polarizing prism. 1/wavelength plate that converts the polarization plane of light; 5 is a focusing lens (objective lens) that focuses the laser beam; 6 is 1/- which is reflected by the beam splitter 2;
7 is a photodetector that divides the light-receiving surface into two and has a light-receiving element arranged on each divided surface; 8 is arranged between the second focusing lens 6 and the photodetector 7; A knife 9 for blocking a part of the light transmitted through the lens 6 arranges the laser light source l and the objective lens 5 at predetermined intervals on the same optical axis J-, and also includes the lens 6, the photodetector 7, and the knife. Optical system supports arranged at predetermined intervals and supported and fixed on the side of the beam splitter 2 and the Cσ liner are shown. In addition, 10 is a disk, and the spy "i /l/ direction (/Chi, l-(
A recess) is provided using digital IF code 1~.

Although not shown, the optical system support 9 is supported by an arm that moves in the radial direction of the disk 10 so as to be able to move minutely in the Y and Z directions. This Y-Z direction moving means is a 1-racking mechanism and focusing device 171j, which is formed by a magnetic circuit having, for example, an i4J moving coil at an angle of 11°7c.

This operation will be explained in No. 71. A straight laser beam emitted from the conductor laser beam with a polarization plane of ~1f line with the optical axis enters the collimator lens 2 while being diffused, and is converted into parallel light by the collimator lens 2. ,
The light passes through the beam splitter 3 and is further converted from linearly polarized light into, for example, right-handed circularly polarized light by a 1/4 beam length 4, and is focused onto a disk 10 by an objective lens 5. disk 10
The laser beam focused upward is diffracted by Pino], and the amount of reflected light changes depending on the presence or absence of Pino l-. The laser beam reflected on the disk 10 travels backward through the lj object lens 5, the 1/4 wavelength plate 4, and the beam splitter 2 [ffi. Here, the circularly polarized light of the laser beam is reflected by the disk 10 while being circularly rotated, so that the direction of rotation of the reflected light is reversed with respect to the direction of travel, and it becomes circularly polarized light with a left-handed rotation. Therefore, the reflected light passing through the quarter-wave plate 4 is converted into linearly polarized light having a plane of polarization perpendicular to the optical axis, and this light enters the beam splitter 3. The reflected light incident on the beam splitter 3 is reflected to the side of the optical system support 9, condensed by the focusing lens "6, and partially blocked by the knife 8, and projected onto the photodetector 7.

Here, focusing control signal detection using the Pouifuenosi method will be explained with reference to FIG. 2. In FIG. 2, the beam splitter and 31/4 wavelength plate 4 are omitted to simplify the explanation, and the objective lens 5 and the focusing lens 6 are represented by two lenses [J]. f indicates the focal point of lens I. Assume that the optical system is fixed (1 to disk) and that O is close to and separated from the optical system. Further, when the disc 10 is focused at the Δ position, that is, the laser light emitted from the laser light source 1 is focused at the Δ position.
It is assumed that the optical system is focused to the minimum diameter at 0, the optical system is too close at the B position, and the optical system is too fast at the C position. When the disk 10 is at position A, the light that has traveled backward through the lens L is focused on the photodetector 7. Similarly, when the disk 10 is at the B position and the C position, it is reflected as shown by the dashed line and the dashed double dotted line in the figure, respectively, and the lens 1 is turned upside down to reach the point b outside the photodetector 7 and the outside of the photodetector 7. Focuses on 6 points in front.

In the absence of the knife 8, the projected image on the photodetector 71 shows that the disk 1o is A (<'1.
At the 3rd position and at the C position, the shape is circular, but since the knife 8 shields the light that passes through the peripheral edge of the lens L, the projection image of the photodetector 7'' is different at the disk position.

That is, when the disk 1o is at position A, the state shown in FIG.
), the shape is dot-like, and since the diameter of the knob 1 is small, the shape does not change regardless of the presence or absence of the knife 8. However, when the disk 10 is at position B, the light is focused at point b outside the photodetector 7, as shown by the dashed line in FIG. The lower half becomes darker and becomes semicircular. Further, when the disk 10 is at position C, the photodetector 7
Since the light that is once converged in front of and further diffused is projected onto the photodetector 7, it forms a semicircular shape with a dark upper half, as shown in FIG. 3(C).

Therefore, if we take the difference in the output voltages of each detection element of the photodetector 7, we can obtain a figure-8 characteristic in which the voltage is at the midpoint at the focus position, as shown in Fig. 4, and based on this focus error voltage, the optical system is adjusted. Focusing control is performed.

In the Naifetsu method, the photodetector 7 is moved to the focusing position (Fig. 2a).
It is also possible to arrange the knife 8 at the focusing position (6 points) by shifting it backward from the point), and in this case, the inner end of the knife 8 is made to protrude to the optical axis position.

Focusing using these conventional knife techniques has the following drawbacks.

That is, as shown in FIG. 5, when the disc 1o is located further outward than the position C at which it has been moved to the in-focus position,
The laser beam reflected at position 1) is indicated by the three-dot chain line 7j':
, the light is focused between the knife 8 and the lens, and is further diffused and projected onto the photodetector 7, but the entire light flux passes through the inside of the knife 8 and is not blocked by the knife 8.

Therefore, the amount of light received by each detection element of the photodetector 7 is equal, and the differential voltage becomes zero.

When the disk surface is further outward than the position, lens 1.
The light that has passed through is blocked by the knife 8 again. Therefore, as shown in Fig. 6, the flue force error 7L pressure is an inverted S-shaped rare where the electric current becomes 1 - o at the position Δ (with an opposite gradient to the A C slope and the electric current becomes Leto at the position). Indicates °.

In general, when moving the optical system on the disc controller 0, the focusing system ii<i A
), but at this time, in the focusing control operation state, the movement of the optical system stops at position D. However, the stability at this position was poor, and when subjected to minute noises or vibrations, the lens would fall to the in-focus position, which was undesirable because of transient unstable operation.

Therefore, in general, it is necessary to detect the output of the photodetector 7 with a zero-cross detection circuit and to detect the difference between the position and the position A with a polarity discrimination circuit, and since focusing control is performed only in the vicinity of position A, the control The drawback was that the range was limited. Since the position varies depending on the amount of protrusion of the knife, there is a drawback that assembly and adjustment are complicated.

DISCLOSURE OF THE INVENTION The present invention has been proposed in view of the above-mentioned drawbacks, and provides a focusing control signal detection mechanism using the Knifezi method that eliminates the above-mentioned drawbacks.

The present invention arranges a photodetector having a multi-divided light-receiving surface on the optical axis of a focusing lens, and detects the light passing through the focusing lens.
The apparatus is characterized in that the knife is arranged to extend to a position that includes the optical axis.

The present invention has the following effects as described in (1-).

1 Obtained from the output of the photodetector] A-cass error voltage is the midpoint only at in-focus i\”f, !iif?tj: LL
This is the character 8 characteristic of O.

2 (sub-), the zero-crossing detection circuit is connected to the durability discriminating circuit (1).
No. 1: There is no need to throw, and the control circuit becomes simple.

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to FIG. 7, in which it is applied to the optical system shown in FIGS. 1 and 2. Figures 1 and 2 and
The focusing lens is made to protrude as far as 1 yen including the optical axis 12 of the lens.

As a result, light is focused on the optical axis outside the knife 11 (light reflected by the disk 1o at positions Δ, B, and C).
Most of the light that is focused between the knife 11 and the lens (which is reflected at the position of the disk 1o) is blocked by the knife 11, and is formed into a minute spot as shown in Fig. 8. Only in the case of A, which is light, the output difference of the photodetector 7 becomes a voltage of 0, resulting in a figure-8 characteristic in which the voltage intersects with the voltage O at a large slope.

Therefore, the in-focus position can be detected using only the zero-cross detection circuit.
The retraction control circuit becomes simple.

Further, since the knife 11 need only be protruded to include the optical axis, assembly and adjustment are easy.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view showing an example of an optical reading device, FIG. 2 is a side sectional view illustrating the operation of the focusing control signal detection mechanism of the device shown in FIG. 4 is a characteristic diagram of the focus error voltage obtained from the output of the photodetector, FIG. The figure is a characteristic diagram of the focus error voltage obtained from the output of the photodetector, Figure 7 is a side sectional view of a focusing control signal detection mechanism for explaining the present invention, and Figure 8 is the focus obtained from the device shown in Figure 7. A characteristic diagram of error voltage is shown. L, 6... Focusing lens, 7... Photodetector,
]1... Naifetsuji, 12... Optical axis.

Claims (1)

[Claims] A photodetector having a multi-divided light-receiving surface is arranged on the optical axis of a focusing lens, and a knife is arranged to block a part of the light that passes through the focusing lens, and the knife is located at a position that includes the optical axis of the focusing lens. Optical type % type % characterized by protruding with a sword