JPS598144A - Optical information reader - Google Patents

Abstract

PURPOSE:To eliminate automatically offset components of a focus error signal, by modulating a laser light and controlling a differential amplifier by components of the focus error signal which are related to modulation. CONSTITUTION:When photoelectric transducers 5-1-5-4 are different from one another in sensitivity to the quantity of light, output signals S1 and S2 are different from each other by sensitivity. The bias voltage from a DC voltage source 17 is adjusted to set the offset of the focus error signal to 0. In this state, a modulAtion signal S0' is supplied to a laser driving device 1 to modulate the laser light. Modulation signal components in the focus error signal are detected by a modulation signal component detecting circuit 19 and are controlled through a level adjustment driving circuit 20 and etc. in such direction that modulation signal components become zero. Consequently, even if the transmission factor and the reflection factor of a recording carrier 4 are changed, offset components are eliminated automtically.

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,
It is configured to focus a light beam on the information recording carrier, and detect and read the reflected light from the information recording surface with a photoelectric detector such as photoelectric conversion means.

Further, a focusing device is provided that controls 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 its vicinity.

The focusing device part in a conventional optical information reading device is
For example, as shown in FIG. 1, a light beam from a laser 2 driven by a laser driving device 1 is transmitted through a collimator lens (not shown), a beam splitter 11 (not shown), a beam splitter 11 (not shown),
The light is projected onto the focus lens 3 via a four-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, and then photoelectric conversion is performed. Means 5 is provided. The photoelectric conversion means 5 includes four divided photoelectric conversion elements 5-1 to 5-4 onto which reflected light beams that read information from the information recording carrier 4 are projected. Furthermore, an adder 5-5 that adds the output signals of the photoelectric conversion elements 5-1 and 5-3 located on the first diagonal, and photoelectric conversion elements 5-2 and 5- located on the second diagonal. and an adder 5-6 for adding the four output signals. When the focal point of the focus lens 3 is located on the information 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 applies to the photoelectric conversion elements 5-1 to 5-4. Yes, output signal S1 from adders 5-5 and 5-6
and S2 are equal. If the distance between the information recording carrier 4 and the focus lens 3 is now shorter than that at the focused point, the shape of the reflected light beam projected onto the photoelectric conversion elements 5-1 to 5-4 changes from the circular shape at the focused point. It becomes an ellipse whose major axis coincides with the first diagonal, the signal S1 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. The signal S1 decreases and the signal S2 increases. Therefore, the adders 5-5 and 5-6 output 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 the adder 5-5 and the output signal S2 from the adder 5-6 are input to the differential amplifier 6 and differentially amplified. 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 sent to a focus lens actuator 10.
the focus lens 3 and the information recording carrier 4 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. The offset component due to the 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 amount of transmitted light beam and the amount of reflected light beam change, and the operating point moves. In this case, if there is a difference in sensitivity to the amount of light among the photoelectric conversion elements 5-1 to 5-4 constituting the photoelectric conversion means 5,
There is a drawback that an offset component occurs in the focus error signal, and this offset component cannot be automatically removed.

The present invention has been made in consideration of the above K, and eliminates the above-mentioned drawbacks, even when the transmittance and reflectance of the information recording carrier change, the problem occurs due to the optical and electrical imbalance of the photoelectric detector. An object of the present invention is to provide an optical information reading device that can automatically remove an offset component in 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. , 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 using 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 is such that the conventional optical information reading device shown in FIG. be.

Further, a variable level adjuster 15 adjusts the level of the output signal of the adder 5-6 of the photoelectric conversion means 5, and an adder 16 adds a bias voltage from the DC voltage source 17 to the output signal of the variable level adjuster 15. , and an amplifier 18 for amplifying the output signal of the adder 16. 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, that is, the focus error signal, is directly supplied to an 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 accordance with 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. It is focused near the information recording surface of the record 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, and then reaches the beam splitter 1.
1 and projected onto photoelectric conversion elements 5-1 to 5-4, where it is converted into an electrical signal. Photoelectric conversion element °5-1 and 5-
The output signals of photoelectric conversion elements 5-2 and 5-4 are added together by an adder 5-6, and output signals S1 and S2 are respectively output.

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 is 1s11. The absolute value l521 of the output signal S2 also has a difference in sensitivity with respect to the amount of light.

Absolute value 1811 of output signal S1. It is assumed that the absolute value l521 of the output signal S2 is as shown in FIG. 3(a) with respect to the amount of light. Further, the output signal of the amplifier 18 is indicated by 83.

Here, if the amount of reflected light is determined as, for example, QA, then the amount of light QA
On the other hand, if the output signals S1 and S2 are directly differentially amplified and output, the focus error signal will have an offset Of
occurs.

Here, if the rate of increase/decrease of the variable level regulator 15 is constant, the output signal S2 is increased/decreased at the constant rate of increase/decrease of the variable level regulator 15, and the bias voltage from the DC voltage source 17 is added by the adder 16. The signal is amplified by the amplifier 18 and then supplied to the differential amplifier 6. Therefore, the DC voltage source 17
By adjusting the bias voltage from the output signal S3
The absolute value +831 of the output signal S2 is the absolute value l5 of the output signal S2.
21 can be translated in parallel to the operating point P. Therefore, the offset Or can be made zero. When the modulation signal SJ from the modulation device 14 is supplied to the laser drive 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 of the modulation device 14, as shown by the sine wave So in FIG. 3(b). When the amount of incident light changes as shown in FIG. 3(b), the output signal sl of the differential amplifier 6, that is, the output signal sl of the adder 5-5 and the output signal S3 of the amplifier 18, correspond to the solid line and the output signal S3 of the amplifier 18 shown in FIG. It fluctuates as shown by the broken line. As a result, the differential amplifier 6 becomes (output signal S1 - output signal Sa
) output signal. Therefore, the focusing point error signal becomes as shown in FIG. 3(d).

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 of FIG. 3, when the light amount exceeds the light amount QA, the increase/decrease rate of the variable level adjuster 15 is decreased, and when the light amount is less than the light amount QA, the increase/decrease rate of the variable level adjuster 15 is increased. Well, the third
It acts so that the slope of the absolute value 1831 of the output signal S3 in FIG. This will cause the isometric sensitivity to be adjusted the same. As a result, even if the operating point P moves, no offset occurs.

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, even if the transmittance and reflectance of the information recording carrier 4 change. Offset components are automatically removed.

In addition, when removing the offset component 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 from the DC voltage source 17 will decrease. Even though the voltage is fixed, it is good for practical use.

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 through the focus lens is modulated with a predetermined signal, and the signal related to the modulation is selected from the focus error signal. By detecting the component and varying the input signal level of one side of the differential amplifier that outputs the focused 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 given operating point,
Thereafter, even if the amount of light incident on the photoelectric detector changes due to differences in transmittance and reflectance of the information recording carrier, an offset component based on optical and electrical imbalance of the photoelectric detector will not occur.

[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. FIGS. 3(a), 3(b), 3(c) and 3(d) are explanatory diagrams for explaining the operation of one embodiment of the present invention. 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. Patent applicant Trio Co., Ltd. Agent Patent attorney Nobuo Sunako No. 6 (C) <d>

Claims (1)

[Claims] A laser light source that projects laser light onto an information recording carrier through a focus lens, a plurality of photoelectric conversion elements onto which laser light that has read information from the information recording carrier is projected, and an output of the photoelectric conversion elements that 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 an output of the differential amplifier. An optical information reading device including a focus lens actuator that drives and controls the position of the focus lens to a focused state based on a signal, comprising: a modulation means that modulates a laser beam projected from the laser light source with a predetermined signal; a detection means for detecting a signal component related to the modulation from an output signal of the differential amplifier; and controlling an input signal level of at least one of the differential amplifiers according to the signal component level detected by the detection means. An optical information reading device comprising a control means.