JPS6248300B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical information reading device used in an optical video disc playback device, an audio disc playback device, etc. The present invention relates to an optical information reading device that removes an offset component from a focus error signal.

An optical information reading device that reads information from an information record carrier in which information is recorded on an optically readable medium focuses a light beam on the information record carrier and photoelectrically converts the light reflected from the information recording surface. It is configured to be detected and read by a photoelectric detector such as a means. Further, a focusing device is provided for controlling the relative position of the focus lens with respect to the information recording carrier in order to focus the light beam on the information recording surface of the information recording carrier or in the vicinity thereof.

A focusing device part in a conventional optical information reading device includes, for example, as shown in FIG. The light is projected onto the focus lens 3 via a 1/4 wavelength plate. The light beam projected onto the focus lens 3 is projected onto the information recording carrier 4 and focused near the information recording surface. A transmitted light beam or a reflected light beam (the example shown in FIG. 1 shows an example of a reflected light beam) from the information recording surface of the information recording carrier 4 is projected onto the photoelectric conversion means 5. A signal corresponding to the focal state of the light beam on the information recording surface of the information recording carrier 4 is detected.

A cylindrical lens (not shown) is placed in the middle of the reflected light beam from the information recording carrier 4 being converged by the focus lens 3, that is, between the focus lens 3 and the same point on the information recording surface with respect to the focus lens 3. , after which a photoelectric conversion means 5 is provided. The photoelectric conversion means 5 includes four divided photoelectric conversion elements _5-1 to _5-4 onto which a reflected light beam reading information from the information recording carrier 4 is projected. Further, the photoelectric conversion element 5- located on the first diagonal line
Adder _5-5 that adds the output signals of ₁ and _5-3 .
and a photoelectric conversion element 5- located on the second diagonal line.
It is provided with an adder _5-6 for adding the output signals of ₂ and _5-4 . When the focal point of the focus lens 3 is located on the emotional recording surface of the information recording carrier 4, the reflected light beam projected onto the photoelectric conversion means 5 has a circular shape that evenly covers the photoelectric conversion elements _5-1 to _5-4 . and the output signals from adders _5-5 and _5-6
S ₁ and S ₂ are equal. Now, when the distance between the information recording carrier 4 and the focus lens 3 becomes shorter than when the focus is focused, the shape of the reflected light beam projected onto the photoelectric conversion elements _5-1 to _5-4 changes from a circular shape when the focus is focused. It becomes an ellipse whose major axis coincides with the first diagonal, so that the signal S ₁ increases and the signal S ₂ decreases. Conversely, if the distance between the information recording carrier 4 and the focus lens 3 is longer than at the focused point, the shape of the reflected light beam changes from the circular shape at the focused point to an elliptical shape whose major axis coincides with the second diagonal line. becomes signal S ₁ decreases and signal S ₂
increases. Therefore adders _5-5 and 5-
₆ outputs contradictory signals centered on the focused state of the light beam on the information recording surface of the information recording carrier 4. The output signal _S1 from adder _5-5 and the output signal _S2 from adder _5-6 are sent to differential amplifier 6.
input and perform differential amplification. The output signal of the differential amplifier 6 is a focus error signal indicating the focus state of the light beam on the information recording surface. This focus error signal is amplified by an amplifier 9 via an adder 8 and then supplied to a focus lens actuator 10.
The focus lens 3 and the information recording carrier 4 are arranged so that the light beam is focused on the information recording surface of the information recording carrier 4.
It controls the relative position with the

However, in the conventional optical information reading device as described above, once the light intensity of the transmitted light beam and the light intensity of the reflected light beam from the information recording carrier 4 are determined, at the operating point at that time, the photoelectron included in the focus error signal is determined. Offset components due to optical and electrical unbalance of the conversion means 5 can be removed by setting the output voltage of the DC voltage source 7. However, when the transmittance and reflectance of the information recording carrier 4 change, the light amount of the transmitted light beam and the light amount of the reflected light beam change, and the operating point moves. In this case, if there is a difference in sensitivity with respect to the amount of light among the photoelectric conversion elements _5-1 to _5-4 constituting the photoelectric conversion means 5, an offset component will occur in the focus error signal, and this offset component will be automatically removed. There was a drawback that I couldn't do it.

The present invention has been made in view of the above, and solves the above-mentioned drawbacks, even when the transmittance and reflectance of the information recording carrier changes, the occurrence of the problem due to the optical and electrical imbalance of the photoelectric detector is achieved. An object of the present invention is to provide an optical information reading device that can automatically remove an offset component from a focusing point error signal.

The purpose of this is to modulate a projected laser beam from a projection means that projects the laser beam onto an information recording carrier via a focus lens with a predetermined signal, and to detect a signal component related to the modulation from a focus error signal. This is achieved by controlling the input signal level of one of the differential amplifiers according to the detected signal component level.

The present invention will be explained below with reference to Examples.

FIG. 2 is a block diagram showing one embodiment of the present invention.

As shown in FIG. 2, an embodiment of the present invention includes a modulation device 14 that modulates a laser beam from a laser 2 via a laser drive device 1 in the conventional optical information reading device shown in FIG. be.

Further, a variable level adjuster 15 for adjusting the level of the output signal of the adder _5-6 of the photoelectric conversion means 5;
A DC voltage source 1 is applied to the output signal of the variable level regulator 15.
An adder 16 for adding a bias voltage from 7 and an amplifier 18 for amplifying the output signal of the adder 16 are provided. The output signal of the adder 5-5 of the photoelectric conversion means ₅ and the output signal of the amplifier 18 are supplied to a differential amplifier 6 for differential amplification.

The output signal of the differential amplifier 6, ie, the focus error signal, is directly supplied to the amplifier 9. Further, a modulation signal component detection circuit 19 is supplied with the focused point error signal and the modulated signal from the modulation device 14, and performs phase detection to detect a modulated component in the focused point error signal, an adder _5-6 , and an adder 16. A level adjuster drive is inserted between the two and supplied with the output signal from the modulation signal component detection circuit 19 to control the increase/decrease rate of the variable level adjuster 15 so that the modulation signal component in the focus error signal becomes zero. A circuit 20 is provided and is configured to control the increase/decrease rate of the variable level adjuster 15 in response to the modulation signal component in the focus error signal.

In one embodiment of the present invention configured as described above, the light beam from the laser 2 passes through the beam splitter 11 and is projected onto the focus lens 3, as in the case shown in FIG. 3 is focused near the information recording surface of the information recording carrier 4. The reflected light that has read the information recorded on the information recording carrier 4 passes through the reverse path of the focus lens 3 and the beam splitter 11, is reflected by the beam splitter 11, and is projected onto the photoelectric conversion elements _5-1 to _5-4. and converted into electrical signals. The output signals of photoelectric conversion elements _5-1 and _5-3 are added by an adder _5-5 , and the output signals of photoelectric conversion elements _5-2 and _5-4 are added by an adder _5-6 , respectively. Outputs output signals S ₁ and S ₂ .

Now, when each of the photoelectric conversion elements _5-1 to _5-4 has a difference in sensitivity to the amount of light, the absolute value of the output signal _S1 | _S1 | and the absolute value of the output signal _S2 | _S2 ｜
There is also a difference in sensitivity to the amount of light. Absolute value of output signal S ₁ | S ₁ |, absolute value of output signal S ₂ |
Assume that S ₂ | is as shown in FIG. 3a with respect to the amount of light. Further, the output signal of the amplifier 18 is indicated by _S3 .

Here, if the amount of reflected light is determined to be, for example, Q _A , then if the output signals S ₁ and S ₂ are directly differentially amplified and output with respect to the amount of light Q _A , an offset _Of will occur in the focus error signal. .

Here, if the increase/decrease rate of the variable level adjuster 15 is constant, the output signal S ₂ will be the same as that of the variable level adjuster 15.
The bias voltage from the DC voltage source 17 is added by the adder 16 to the amplifier 1.
The signal is amplified at step 8 and then supplied to the differential amplifier 6. Therefore, by adjusting the bias voltage from the DC voltage source 17, the absolute value of the output signal S ₃ |S ₃
| can be made the same as the absolute value |S ₂ | of the output signal S ₂ translated to the operating point P.
Therefore, the offset _Of can be made zero.
When the modulation signal S ₀ ' from the modulation device 14 is supplied to the laser driving device 1 in this state, the laser light from the laser 1 is modulated. For example, the modulation signal is a sine wave. As a result, the amount of light incident on the photoelectric conversion means 5 also changes in proportion to the modulation signal in the modulation device 14, as shown by the sine wave _S0 in FIG. 3b. The input signal of the differential amplifier 6, that is, the output signal _S1 of the adder _5-5 and the amplifier 18 are
The output signal _S3 varies as shown by the solid and broken lines in FIG. 3c. As a result, the differential amplifier 6 outputs an output signal of (output signal S ₁ -output signal S ₃ ). Therefore, the focus error signal becomes as shown in FIG. 3d.

The modulation signal component in the focus error signal shown in FIG. 15, the increase/decrease rate of the variable level adjuster 15 is controlled in a direction such that the modulation signal component in the focus error signal becomes zero. To explain using the example in Figure 3, when the light amount exceeds the light amount Q _A , the variable level adjuster 1
The absolute value of the output signal S ₃ in FIG. _3a is reduced |S ₃ |
of the absolute value of _the output signal S ₁ |S ₁ | and the absolute value of the output signal _{S 3 |} S ₃ | The equivalent sensitivity will be adjusted to be the same. As a result,
Even if the operating point P moves, no offset will occur.

Therefore, if the offset in the focus error signal at the operating point for a predetermined amount of reflected light is removed by adjusting the bias voltage from the DC voltage source 17, the transmittance and reflectance of the information recording carrier 4 will change. offset components are automatically removed.

In addition, when the offset component is removed by adjusting the bias voltage from the DC voltage source 17 during the first adjustment, the information recording surface is adjusted to be within the depth of focus using the information recording carrier 4 with high reflectance. If this is done, even if the reflectance of the information recording carrier 4 decreases, the offset component in the focus error signal will decrease as the reflectance decreases, so the bias voltage from the DC voltage source 17 will decrease. It is good for practical use even if it is fixed.

Although the above description has been made using an astigmatic optical information reading device as an example, the present invention is not limited thereto.

As explained above, according to the present invention, the laser beam from the projection means that projects the laser beam onto the information recording carrier via the focus lens is modulated with a predetermined signal, and the laser beam related to the modulation is extracted from the focus error signal. By varying the input signal level of one side of the differential amplifier that detects signal components and outputs a focusing point error signal according to the detected signal component level, any information recording carrier can be treated as one sample. By adjusting the offset at a predetermined operating point, even if the amount of light incident on the photoelectric detector changes due to differences in the transmittance and reflectance of the information recording carrier, the optical and electrical impairments of the photoelectric detector will be maintained. No offset component based on equilibrium is generated.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a focusing device part in a conventional optical information reading device. FIG. 2 is a block diagram showing one embodiment of the present invention. Figure 3 a, b, c
and d are explanatory diagrams for explaining the operation of an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Laser drive device, 2... Laser, 3... Focus lens, 4... Information recording carrier, 5... Photoelectric detector, _5-1 to _5-4 ... Photoelectric conversion element, _5-5 and _5-6 ... Adder , 6... Differential amplifier, 10... Focus lens actuator, 14... Modulation device,
15...Variable level adjuster, 16...Adder, 17...
DC voltage source, 19... Modulation signal component detection circuit, 20
...Level adjuster drive circuit.

Claims (1)

[Claims] 1. A laser light source that projects a laser beam onto an information recording carrier through a focus lens, a plurality of photoelectric conversion elements onto which the laser beam that reads information from the information recording carrier is projected, and the output of the photoelectric conversion element is calculated. a calculation means for outputting contradictory signals centered on the focused state of the laser beam on the information recording surface of the information recording carrier; a differential amplifier for differentially amplifying the output of the calculation means; and the differential amplifier In an optical information reading device including a focus lens actuator that drives and controls the position of the focus lens to a focused state using an output signal, the laser light projected from the laser light source is modulated with a predetermined signal. modulation means; detection means for detecting a signal component related to the modulation from the output signal of the differential amplifier; and an input signal of at least one of the differential amplifiers according to the signal component level detected by the detection means. 1. An optical information reading device comprising: control means for controlling a level.