JPS6089834A - Optical information recording and reproducing device - Google Patents

Abstract

PURPOSE:To attain accurate focus control by detecting a middle value between positive ad negative peak values, correcting a focus error signal so as to take the value as the center of control and applying focus control of an optical beam via an error detection circuit. CONSTITUTION:An optical beam is irradiated to an information track 3 comprising pits formed intermittently via a condenser lens 6, the optical spot is moved relatively to the information track, the reflected beam from the information track is irradiated to photoelectric converting elements 9, 10 and the focus control of the optical beam is conducted by using a phase difference between output signals of the photoelectric converting element as a focus error signal. When the optical spot is converged into a proper diameter, the output signal is made in-phase by shifting the phase of the signal from the photoelectric converting elements 9, 10 and the condenser lens 6 is moved to an information medium 1 so as to zero the phase difference at all times based on the phase difference of both the output signals. Thus, accurate focus control is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical information recording/reproducing device 9, and particularly to a focus control device thereof.

Hitherto, various types of focus control devices of this type have been provided for a long time, and an example is the Japanese Patent Laid-Open No. 51
For example, there is a claw control device disclosed in Japanese Patent No. 87588. This focus control device irradiates a diffractive information track recorded on an information medium with a light beam as a light spot, and moves this light spot relative to the information track to at least reduce the reflected beam from the information medium. 2
It irradiates one photoelectric conversion element and detects the phase difference between the output signals of each photoelectric conversion element. Focusing on the fact that this phase difference is a function of the distance between the focal point of the light beam and the reading surface on the information medium, focus control is performed by changing this phase difference.

By the way, the above-mentioned phase difference cannot necessarily be caused only by a change in the distance mentioned above. In other words, even the most appropriately focused light spot has an optical diameter, so Naturally, a phase difference of 11j of about 5° to 15° occurs,
In this case, it suffices to shift the phase by a certain value to make them in phase, but what is particularly problematic is that the phase difference differs due to the roughness 1 in the manufacturing of the information track of the information medium. , simply shifting the constant value phase I7 will not solve the problem. As described above, the technical idea disclosed in Japanese Patent Application Laid-Open No. 51-8758'8 does not take into account the manufacturing errors of the information track, and therefore cannot perform accurate focus control.

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, it is an object of the present invention to provide an optical information recording/reproducing apparatus that can perform accurate focus control in response to any information medium.

An embodiment of the present invention will be described below with reference to the drawings.

The information carrier 1 has on its surface - for example a diffractive element.

, and 7 consecutively form an information track 8. However, the present invention can be applied to any information track formed by optically and intermittently recorded bits. A light beam 4 from a light source (not shown) passes through a beam splitter 5 and is focused as a light spot 7 by a focusing lens 6. As is well known, this light spot 7 needs to be kept at an appropriate constant diameter narrowed down to the information track 8. Part 1. The reflected beam 8 after irradiating the information medium 1 passes through the focusing lens 6, is reflected by the beam splitter 5, and is transmitted to a pair of light zone conversion elements -r-9,
10 irradiation.

This pair of photoelectric conversion elements 9 and lO are the information track 8
The front IK, 75, is arranged so as to be optically perpendicular to the optical axis of the light beam 4 (reflected beam 8) with respect to the traveling direction T, and from this pair of photoelectric conversion elements 9.10, , the presence or absence of the bit 2 can be checked all at once, and an information reproduction signal can be obtained as is known in the art. This news reproduction signal appears as a change in amplitude, but independent of this change, there is a change in amplitude converted from each photoelectric conversion element 9, 1O in the form of an alternating current signal indicating a phase shift. This phase shift is a function of the distance between the focal point 0 of the light beam 4 and the follow-up point M on the information blunt medium, and corresponds to the focusing error.

In other words, two light beams '
The conversion elements 9 and 1O are irradiated with the same illuminance, but when the light beam 4 is focused on a zero point other than point M, the two photoelectric conversion elements 9 and 10 are irradiated with different illumination intensities. .

For example, Fig. 42 and Fig. 8 show cases where the focal point 0 is too high or too low relative to the position of bit 2, and also show the time of the intensity of light received by the photoelectric conversion elements 9 and 10. Curves representing the change as a function of are shown in Figures 4!4 and d45. Figure 4 shows the convergence point O for bit 2 digit i+2.
If is too high, 1+J5 diagram shows that if the focal point O is above the ice surface of the information medium l, the intensity of the light incident on the photoelectric conversion element lO is first changed, and then a certain delay time 'f
, 4-, the intensity of light incident on the optical tV conversion element 9 is changed. When the information medium 1 moves in the direction of arrow B during the delay time T+, the beam 4a at the side end of the light beam 4 is tilted A.
The time when 1. and time t2 when the beam 1.4b at the other side end of the light beam 4 reaches the same slope A.

Conversely, if the focal point 0 is below the surface of the information medium l, the time 1. when the beam 4C at the side end of the light beam 4 reaches the slope A. After an elapsed time T2 from time t4 when the beam 4d at the other side end of the light beam 4 reaches the slope A, the photoelectric conversion element 9 is reflected from the slope A before the photoelectric conversion element 10. subject to changes in light.

The delay time T, s Tt is the phase shift described above,
Alternatively, it corresponds to a phase difference.

Therefore, when the optical spot 7 is focused to an appropriate diameter, the phases of the output signals from each photoelectric conversion element 9 and 1O are shifted to have the same phase, and the phase difference between the Ryokawa power signals (in this case, the difference is zero) ), and shift focus control is performed by moving the focusing lens 6 relative to the information medium 1 so that the phase difference is always zero.

However, since the shape and depth of the bit 2 differ depending on the information medium 1, the phase difference between the output signals from each photoelectric conversion element 9 and 1O when the optical spot 7 has an appropriate diameter differs. Therefore, if the constant value phase is simply shifted, the focus error signal created from the double phase difference will have various waveforms (point F is the appropriate radius point) as shown in FIGS. 6(a) to (0). The location where the phase difference is zero does not necessarily mean that the diameter is appropriate.

However, the midpoint between the positive peak value and the negative peak value of the focus error signal created from the above-mentioned phase difference is an appropriate diameter.

Therefore, as shown in FIGS. 7(a) to 7(C), focus control may be performed with the center of control set as the zero point between the positive peak value and the negative peak value IP of the focus error signal. Specifically, as shown in the block diagram of the focus control circuit shown in FIG. 8, the output from each photoelectric conversion element 9.10 is sent to a phase difference detection circuit 12.4Jl via a signal processing circuit 11 that obtains information signals, etc. It is manually input to the focus error detection circuit 18 connected to the phase difference detection circuit 12 again through the switch 13, the positive peak value hold circuit 14, the positive peak value hold circuit 15, the addition circuit 16, and the hold circuit 17 connected in parallel. . That is, the pressure/negative peak value holding circuits 14 and 15 hold the positive and negative peaks, and the adder circuit 16, which is an intermediate value detection circuit, detects the intermediate value between the peak values. Detection circuit 1
In order to enable holding at a position where the offset is shifted so that the midpoint between the positive peak value and the negative peak value of the output signal from 2 becomes the zero point shown in FIG. It is conceivable to add it to the phase difference detection circuit 12. By doing this, focus control can be performed based on the value of the phase difference that actually occurs, using the intermediate value as the center of control. .

The focus error signal thus obtained is input to the differential motion circuit 22 via the 42 switch 19, the phase compensation circuit 20, and the eighth switch 21, and operates the lens driving device 28 that moves the focusing lens 6. By this operation, the focal point O relative to the position of the information medium 10 pit 2 is maintained at a position where the optical spot 7 has an appropriate diameter.

As described above, focus control is controlled, but as shown in FIG. 7, with the above means, there are many cases where a DC component is applied when there is no signal (waveforms B and c). ,
If the signal is lost due to a scratch on the information medium 1, the focusing lens 6 will move and become out of control.

However, by using variable phase means in the above-mentioned means, more effective focus control can be achieved. Suwachi,
In other words, as shown in FIG. 9, a variable phase shifter 38 is provided in the focus error detection circuit 18 to change the phase so that the center of the positive and negative peak values of the focus error signal becomes zero. Phase correction value hold circuit 1
7, and hold the focus error signals from various information media in waveform A shown in Figure 7 so that the absolute values of the positive and negative signal values are the same, so that the DC component described above is present. It is possible to solve the problem.

The method for detecting this phase difference is that the information medium l is not near the position where the optical spot 7 has an appropriate diameter ↓ Since no signal is output, a special circuit is initially installed to detect the positive and negative peak values mentioned above. Requires. Furthermore, before the commonly used i
48 Since the depth of focus of the focusing lens 6 is narrow, even if the light beam 4 passes through the focal point on the information base once during one rotation of the information medium, it does not necessarily occur when the center of the information track 8 is detected. Since the above-mentioned appropriate diameter is not necessarily the correct diameter, in order to correctly detect the above-mentioned positive and negative peak values,
It is necessary to cross many focal points.

A specific method will be explained with reference to a block diagram of the lens drive circuit 24 shown in FIG. That is, the first oscillator 25 is connected to the drive circuit 22, and the first oscillator 25 is vibrated so that a large amplitude of several H2 is generated in the lens drive device 28, and when an information signal is generated, the drive voltage to the lens drive device 28 is changed to circuit 2
Hold at 6. This information signal is generated because there is a position near the position of the focusing lens where the optical spot 7 has an appropriate diameter. Next, the drive circuit 22
Connect the f4s2 oscillator 27 to the lens drive device 28 so that a relatively small amplitude of several hundred H2 is generated around the held drive voltage, and vibrate it so that it passes through a proper secret position. As a result, a state is reached in which a focus error signal input to the focus error detection circuit 18 can be obtained.

After the hold action in the focus error detection circuit 18 is completed, the second
The vibration of the lens driving device 28 caused by the oscillator 27 is stopped, and focus control is performed based on the aforementioned held correction value. However, when pulling in the control, with a general drive device, the focusing lens 6 cannot be pulled in unless it is within a few micrometers from the position where the appropriate optical spot diameter is generated. It may not be possible to do so.

Therefore, when performing control pull-in, as shown in FIG. 6 is vibrated and the information signal is output while being attenuated by the attenuator 28. After vibrating at the frequency FG of the second oscillator 27, the information signal is sent to the lens driving device 28 when the lens cannot be retracted. The drive voltage is held and the DC drive voltage is corrected.

In addition, when detecting the positive peak value and negative peak value mentioned above,
Beak 1i1L K due to scratches etc. on information medium 1
In order to prevent errors from occurring, the information signal from the signal processing circuit 11 is detected by a detection circuit 80 as shown in FIG.
A gate pulse is generated by waveform shaping 81.

This gate pulse is input to a control circuit 82 that controls the operation of each circuit described above.

This control circuit 82 operates the first switch 18 in response to the input of the gate pulse, so that the positive peak value hold circuit 14 or the negative peak value hold circuit 1'5 detects the peak value only when the gate pulse is input. I have to. Further, the control circuit 82 operates the second switch 19 so as to pass the focus error signal only when an information signal of a certain level or higher is output.

Further, the control circuit 82 controls the eighth switch 21
．． a hold circuit 17 of the focus error detection circuit 18;
Lens drive circuit 240g1 Oscillator 25 hold circuit 2
6, switch 88, and hold circuit 2 of attenuator 28
9 and switch 84, switch 85 of ff12 oscillator 27
, the flow of signals, and the hold point.

Further, in order to determine whether the focus control performed as described above is appropriate, the signal processing circuit 11 is switched to the switch 86.
is connected to the judgment circuit 87 via the information signal, and measures the information error rate from the information signal, and if the rate is higher than the standard, sends a signal to the control circuit 82 to correct the focus error signal again. Switch 86 of circuit 87 is also control circuit 8
It is controlled by 2.

The present invention irradiates a light beam as a light spot through a converging lens onto a 1a information track of bits formed in an optical state and intermittently on an information medium, and converts this light spot into the information track. The reflected beam from the information medium is irradiated onto at least two light conversion elements that are optically arranged in front and behind with respect to the traveling direction of the information track, and the output signal of each photoelectric conversion element is In an optical information recording and reproducing apparatus that performs focus control of the light beam by using a phase difference of A peak value hold circuit and an intermediate value detection circuit that detects an intermediate value between the positive peak value and the negative peak value are provided, and a focus error detection circuit that corrects the focus error signal so that this intermediate value is the center of control. The focus control of the light beam is performed through the optical system, and this method eliminates the influence of the phase difference between the output signals of each photoelectric conversion element that differs depending on the various information media, with respect to the phase difference caused by the focus error. By using the phase difference as a focus error signal, it is possible to provide an optical information recording/reproducing device that can perform accurate focus control.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention. Figure %i1 is an explanatory diagram showing the main parts of the device, Figures 2 and 8 are explanatory diagrams showing the relationship between the information medium and the focal point of the light beam, and Figures 4 and 5 are diagrams showing the relationship between the output from the light intensity conversion element and the phase shift.
Figure 6(a), Figure 6(b), Figure 6(C) are diagrams showing focus error signals created from phase difference, Figure 7(a)
, Fig. 7 ('b), g'r (C) are diagrams showing the focus error signal tube after correction, Fig. 8 shows 10721% of the focus control circuit, Fig. 9 shows another embodiment of the focus error detection circuit. The block diagram illustrating FIG. M510 is an explanatory diagram illustrating the vibration state of the focusing lens at the time of control pull-in. j...information medium, 2...pit, 8...information track,
4.-Light beam, 6.-Focusing lens, 7.-Light spot, 8.-Reflected beam, 9.10-.Light 1u conversion element, 1
4... Positive peak value hold circuit, 15... Negative peak value hold circuit, 16... Intermediate value detection circuit, 18... Focus error detection circuit. Patent applicant: Mansei Kogyo Co., Ltd.

Claims (1)

[Claims] (Li) A light beam is irradiated as a light spot through a converging lens onto an information track such as bits that is optically and intermittently formed on an information medium.
is moved relative to the information track to irradiate the reflected beam from the information medium onto at least two photoelectric conversion elements optically disposed in front and behind with respect to the traveling direction of the information track, and each of the photoelectric conversion elements In an optical information recording and reproducing device that performs focus control of the light beam using a phase difference between output signals as a focus error signal, a positive peak value that holds each of a positive peak value and a negative peak value in the fluctuating wave of the phase difference. A hold circuit, a negative peak value hold circuit, and an intermediate value detection circuit for detecting an intermediate value between the positive peak value and the negative peak value are provided, and the focus error signal is corrected so that this intermediate value is the center of control. 7 focus control of the light beam is performed through the focus error detection circuit.(2) Before the focus error detection circuit is provided with a variable phase shift means, the positive peak value and the negative peak of the phase difference fluctuation wave are controlled. The optical information recording/reproducing apparatus according to claim 1, wherein the optical information recording/reproducing apparatus corrects the value so that the intermediate value becomes the zero point.