JPH0471254B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a focus servo pull-in circuit.

(b) Prior art In optical information devices, a laser beam or the like is irradiated onto an optical disk and the reflected light or transmitted light is detected. It is necessary to converge the light.
For this purpose, such a reproducing device is equipped with a focus servo circuit.

Regarding the focus servo circuit, see Japanese Patent Application Laid-Open No. 1983
Seen in Publication No. 80835, etc. FIG. 3 shows a typical example of an information reproducing device equipped with a focus servo circuit using astigmatism, in which 30 is a semiconductor laser, 31
is a collimator lens, 32 is a beam splitter,
33 is a 1/4 wavelength plate, 34 is an objective lens, and 35 is a drive coil for moving the objective lens in the vertical direction, which has the same configuration as the voice coil of a speaker. 36 is an optical disk having an information recording surface, 37
38 is a cylindrical lens, and 39 is a 4-split optical sensor.

The light (LB) emitted from the semiconductor laser 30 passes through the collimator lens 31, the beam splitter 32, the 1/4 wavelength plate 33, and the objective lens 4, and is irradiated onto the optical disk 36, and the reflected light is reflected from the objective lens. Lens 34, 1/4 wavelength plate 33, beam splitter 32, lens 37, and cylindrical lens 38
The light is then detected by the four-split optical sensor 39. Here, the shape of the light spot on the four-division optical sensor 39 changes depending on the relative distance between the objective lens 34 and the optical disk 36, thereby obtaining a focus error signal. Focus servo is performed by operating the drive coil 35 based on the focus error signal.

Incidentally, in such a focus servo circuit, it is necessary to stably perform the focus servo start timing, that is, the focus servo pull-in.

Focus servo pull-in is preferably performed when the objective lens 34 is positioned so that the relative distance between the objective lens 34 and the optical disk 36 is near the optimum position (hereinafter referred to as a focus matching point).
Therefore, conventionally, a signal of a certain frequency is applied to the drive coil 35 to vibrate the objective lens 34 in the vertical direction, and the reflected light from the optical disk 36 is detected in such a state. This detection signal has a characteristic that it becomes maximum when the objective lens 34 is located at the focus matching point, and therefore, when it is detected that the detection signal has exceeded a certain reference level, the focus servo is activated. By starting, focus servo pull-in can be performed stably.

(C) Problems to be Solved by the Invention By the way, if the reflectance of the optical disk differs, the magnitude of the detection signal of the reflected light from the optical disk will naturally change. Therefore, even though the detection signal has reached its maximum value, there is a possibility that this value will fall below the above level and the start timing of the focus servo cannot be detected.

An object of the present invention is to perform stable focus servo pull-in.

(d) Means for Solving the Problems The present invention provides a displaceable objective lens that focuses light from a light source onto a recording medium, and a displaceable objective lens that focuses light from a light source onto a recording medium, and that displaces the objective lens to an optimal value based on the reflected light from the recording medium. a focus servo retraction circuit that energizes the focus servo circuit when the reflected light from the recording medium exceeds a certain level while the objective lens is forcibly displaced; The present invention is characterized by comprising a level adjustment circuit that changes the level based on the maximum value of a sum signal of focus signals, which is the amount of reflected light from the recording medium.

(e) Effect The present invention sets the magnitude of the reference level for determining the focus servo pull-in timing based on the sum signal of focus signals, which is the maximum amount of reflected light from the optical disk.

(f) Embodiment FIG. 1 is a block diagram showing an embodiment of the present invention. Reference numeral 1 denotes a four-part sensor for detecting reflected light from an optical disk (not shown) in the configuration shown in FIG. 3, and is composed of photoelectric conversion elements of first to fourth sensors _S1 to _S4 . 2 is (output of first sensor S ₁ + output of second sensor S ₂ ) - (output of third sensor S ₃ +
This is a difference signal calculation circuit that calculates the output of the fourth sensor _S4 ), and the output of this circuit is a focus error signal. Reference numeral 3 denotes a focus adjustment circuit that performs adjustments such as amplification of the focus error signal.

4 is an RF detection circuit that detects the high frequency component of the sum signal of each output of the 4-divided sensor 1; 5 is an RF adjustment circuit that removes noise etc. from the signal from the RF detection circuit; C is an RF signal C representing information recorded on the optical disc.

Reference numeral 6 denotes a sum signal calculation circuit that detects the low frequency component of the sum signal of each output of the four-divided sensor 1, that is, the amount of reflected light from the optical disk. The output sum signal a of the sum signal calculation circuit 6 has a mountain-shaped waveform that has a maximum value when the objective lens is located at the focus matching point. Further, the value of this signal a is proportional to the light reflectance of the optical disk. 7 is a division circuit that calculates the value of the output sum signal a to, for example, 2/3, and 8 is a division circuit that calculates a signal of a certain constant value, for example.
A constant voltage generation circuit that outputs a voltage of 1V, an addition circuit 9 that adds the output value of the divider circuit 7 and an output value of the constant voltage generation circuit 8, and 10 a peak hold that holds the maximum value of the addition circuit for a certain period of time. circuit,
11 is a comparator that compares the value of the output sum signal a and the hold value of the peak hold circuit 10, and outputs a signal b when the value of the output sum signal a is larger than the hold value; 12 is a flip-flop whose D input is It is always at a high level, and the Q output becomes a high level at the fall of the CK input. Furthermore, when the CL input becomes low level, the Q output becomes low level. 13
14 is a retrigger type monostable multi; 14 is a delay circuit that delays the output signal e of the monostable multi for a certain period of time;
15 inverts signal b and sends it to flip-flop 1
16 is an inverter that inverts the output signal f of the delay circuit 14 and uses it as the CL input of the flip-flop 12; 17 is an OR gate that receives the Q output signal d of the flip-flop 12 and the signal f; 18 is an AND gate which receives signals b, c and the output signal g of the OR gate 17 as inputs.

Further, 19 is an oscillation circuit that generates a sine wave signal of, for example, 1 to 2 Hz, and 20 is a switch that switches the output of the focus adjustment circuit 3 and the oscillation circuit 19. When the signal e is at a high level, the focus adjustment circuit 3 side connected to. 21 is a drive circuit, and 22 is a drive coil that shifts an objective lens (see FIG. 3) that focuses a light beam on an optical disk (not shown) in response to a signal from the drive circuit.

The operation of this embodiment will now be explained with reference to the signal waveform diagram in FIG.

First, in the initial state when the optical disk is mounted and rotation starts, the switch 20 is connected to the oscillation circuit 19 side. Therefore, the drive circuit 21 drives the drive coil 22 in response to the 1-2 Hz sine wave generated by the oscillation circuit 19, and as a result, the objective lens (not shown) is moved in the vertical direction, and the focus is matched. Move up and down using a point as a boundary.

In the following explanation of the operation of this embodiment, the objective lens will first be explained as being shifted so as to approach the focus matching point.

As described above, the reflected light from the optical disk is detected by the four-division sensor 1 while the objective lens is displaced, and the sum signal a is calculated by the sum signal calculation circuit 6. This sum signal a has a mountain-shaped waveform as shown in Fig. 2, and has the characteristic that as the objective lens approaches (goes away from) the focus matching point, the value of signal a approaches (goes away from) the maximum value. The maximum value is 6V.

The division circuit 7 calculates the value of the sum signal a to 2/3.

The constant voltage generation circuit 8 generates a constant voltage of, for example, 1V, and the addition circuit 9 adds this constant voltage and the output of the division circuit 7 and outputs the result to the peak hold circuit 10.

Comparator 11 compares the contents of peak hold circuit 10 and sum signal a. The content of the peak hold circuit 10 is (2/3x+1)V, where the magnitude of the sum signal a is xV. Therefore, when the sum signal a becomes larger than 3V, the comparator 11 sets the signal b to a high level.

At this time, the Q output signal d of the flip-flop 12
is at a low level, and the output signal e of the monostable multi 13 is also at a low level.Therefore, the output signal g of the OR gate 17 is at a low level, and the AND gate 18 remains closed, so the switch 20 is activated by the oscillation circuit. Stay connected to 19.

The objective lens approaches the focus match point and then moves away from the focus match point. With this transition, the sum signal a reaches its maximum value and then gradually decreases.

The peak hold circuit 10 holds the value of the adder circuit 9 when the sum signal a reaches the maximum value, that is, 5V, for a certain period of time.

After such a hold, the sum signal a becomes this hold value.
When the signal b falls from the high level due to being lower than 5V, the Q output signal d of the flip-flop 12 becomes high level, and the output signal g of the OR gate 17 becomes high level.

Thereafter, the objective lens moves away from the focus matching point and approaches the focus matching point again. At this time, the peak hold circuit 10 operates at least until the objective lens reaches the focus matching point again.
The hold value 5V is held, so when the sum signal a becomes greater than 5V, the comparator 11 sets the signal b to a high level.

On the other hand, when the objective lens approaches the focus matching point, the RF detection circuit 4 detects the high frequency component of the 4-split sensor 1, and the RF adjustment circuit 5 detects the RF signal c.
Output.

In this way, the AND gate 18 is opened by the signals b, g and the RF signal c, the monostable multi 13 is triggered, and the switch 20 is switched to the focus adjustment circuit 3 side. That is, focus servo pull-in is performed.

Note that the output signal e of the monostable multi 13 is applied to the delay circuit 14, and this signal f is applied to the inverter 1.
The signal is inputted to the CL terminal of the flip-flop 12 via the flip-flop 6, clears the flip-flop 12, and is applied to the AND gate 18 via the OR gate 17. Since the output signal b of the comparator 11 naturally remains at a high level after the servo pull-in, the AND gate 18 continues to trigger the monostable multi 13, and the focused servo state continues.

As described above, if the maximum value of the sum signal a is 6V, the objective lens is pulled into the focus servo when the value obtained by photoelectrically converting the amount of reflected light from the optical disk becomes greater than 5V.

By the way, when the maximum value of sum signal a reaches 4V,
The peak hold circuit 10 holds 11/3V, and therefore, the focus servo is pulled in when the sum signal a becomes larger than this hold value.

That is, in this embodiment, when the maximum value of the sum signal a is yV, the pull-in to the focus servo is performed when the value of the sum signal a becomes larger than (2/3y+1)V.

Note that the calculation of the division circuit 7 is not limited to 2/3, and the constant voltage generated by the constant voltage generation circuit 8 is not limited to 1V either.

(G) Effects of the Invention According to the present invention, the reference level for focus servo pull-in is changed based on the magnitude of the sum signal of focus signals that are reflected light from the optical disk, so the focus servo can be stably operated. Can be withdrawn.

[Brief explanation of drawings]

1 and 2 are a block circuit diagram and a timing chart showing one embodiment of the present invention, and FIG. 3 is a schematic configuration diagram showing a typical example of an information reproducing apparatus. 6... Sum signal calculation circuit, 10... Peak hold circuit, 11... Comparator, 20... Switch.

Claims (1)

[Claims] 1 A displaceable objective lens that focuses light from a light source onto a recording medium, and a focus servo circuit that displaces the objective lens to an optimal position based on the reflected light from the recording medium, and forcibly moves the objective lens. In a focus servo pull-in circuit that energizes the focus servo circuit when the reflected light from the recording medium reaches a certain level or more in a state where the recording medium is displaced, a sum signal of focus signals that is the amount of reflected light from the recording medium is generated. A focus servo pull-in circuit comprising a level adjustment circuit that changes the level based on the maximum value of.