JPS6248298B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus servo device for maintaining a focus lens of an optical information reading device used in a video disk playback device or a digital audio disk playback device at a predetermined distance from the disk.

A conventional focus servo device was constructed as shown in FIG. 1, for example. That is, the optical information reading device 1 optically reads the recorded information from the disk 2 which is being rotated, and the reflected light is
It is received by the divided photoelectric conversion means, and the output of the photoelectric conversion means is sent to the matrix circuit 3 to obtain a focus error signal _FE and a recording information signal _RF . The focus error signal F _E is supplied to the servo amplifier 5 via the changeover switch circuit 4, subjected to phase compensation and gain adjustment, and then sent to the actuator drive circuit 6.
supply to. The output signal of the actuator drive circuit 6 is supplied to a focus actuator that drives the focus lens to maintain the focus lens at a predetermined distance from the disk 2. On the other hand, the recording information signal R _F is supplied to a detection circuit 7 for detection, and the output of the detection circuit 7 is supplied to a level comparator 8 and compared with a reference voltage to determine the presence or absence of the recording information signal R _F , that is, the recording information Dropout, etc. is detected. The output of the level comparator 8 is supplied to a changeover switch circuit 4, and when the dropout or the like occurs, the changeover switch 4 is configured to be switched to the focus search signal generator 9 side.
As a result, in the above-mentioned focus servo device, if there is a dropout or the like on the disk 2, it is determined whether the focus servo is applied only by the presence or absence of the output signal H _F of the detection circuit 7.
The focus servo loop is cut off by the changeover switch 4 at a portion where a dropout or the like has occurred, and the focus search operation is started. However, the operation of the focus servo does not immediately become unstable in a portion where a dropout or the like occurs. For this reason, countermeasures have been taken, such as adjusting the level comparator 8 or adding an integrating circuit 10 after the level comparator 8.

However, in the conventional focus servo device as described above, the adjustment of the level comparator 8 and the integration circuit 1
It is difficult to set a time constant of 0. Furthermore, due to variations in the output signal level of the detection circuit 7, it is difficult to set the reference voltage of the level comparator 8.

The present invention has been made in view of the above, and it is an object of the present invention to provide a focus servo device that eliminates the above-mentioned drawbacks.

The present invention will be explained below using examples.

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

In one embodiment of the present invention, the focus error signal F _E output from the matrix circuit 3 in the focus servo device shown in FIG. The signal is supplied to the determination circuit 13 to determine that the focus is off. On the other hand, the changeover switch circuit 4 is connected to analog switches 4-1 and 4.
-2, analog switches 4-1 and 4
A negative voltage -V is supplied to the gate of -2 through a pull-down resistor. The output signal of the level comparator 8 is sent to the analog switch 4 via the switch circuit 11.
-1 and 4-2 to switch and drive the changeover switch circuit 4. Here, the changeover switch circuit 4, that is, the analog switch 4
When the high potential signal from the level comparator 8 is supplied to the gates of the analog switches 4-1 and 4-2 via the switch circuit 11, the analog switches 4-1 and 4-2
is controlled to be on, and the changeover switch circuit 4 is switched to the search signal generator 9 side.

In addition, the output signal of the level comparator 8 is determined by the time period for determining whether the level comparator 8 has continuously detected that the output signal H _F of the detection circuit 7 is below the reference voltage for a certain period of time or more. The signal is supplied to the discrimination circuit 12. The output signals of the time discrimination circuit 12 and the servo operation determination circuit 13 are supplied to a logic circuit 14 that performs an AND operation, and the output of the logic circuit 14 is supplied to the switch circuit 11. When the output is a high potential output, the switch circuit 11 is driven to the on state.

FIG. 3 is an explanatory diagram showing an example of the optical information reading device 1, and FIG. 4a is a block diagram showing an example of the matrix circuit 3. In FIG.

The optical information reading device 1 includes a laser light source 111, a beam splitter 112, and a tracking mirror 11.
3. It is equipped with a focus lens 114, a focus actuator 115, a cylindrical lens 116, and a photoelectric conversion means 117, and the light beam from the laser light source 111 is transmitted through a collimator lens (not shown), a beam splitter 112 (not shown), The light is projected onto a focus lens 114 via a tracking mirror 113 and a quarter-wave plate, and is focused near the information recording surface of the disk 2 by the focus lens 114. The reflected light beam modulated by the information recorded on the disk 2 returns to the beam splitter 112 through the reverse path and returns to the beam splitter 112.
12 and projected onto photoelectric conversion means 117, where it is converted into an electrical signal. Focus lens 114 and focus lens 1 of disk 2
A cylindrical lens 116 is disposed between the yoke point and the yoke point with respect to 14. On the other hand, the photoelectric conversion means 117
Photoelectric conversion element 117 divided into four parts as shown in Figure a
-1 to 117-4.

Matrix circuit 3 is photoelectric conversion element 117-1
an adder 31 that adds the output signals of and 117-3;
An adder 32 that adds the output signals of the photoelectric conversion elements 117-2 and 117-4, a differential amplifier 33 that receives the output signals of the adders 31 and 32, and an adder 3.
It consists of an adder 34 that adds the output signals of 1 and 32. The adders 31, 32 and the differential amplifier 33 constitute a focus error detection section, which outputs a focus error signal F _E corresponding to the projected image of the reflected beam on the photoelectric conversion means 117, as is well known. That is, when the projected light is focused on the information recording surface of the disk 2 by the focus lens 114, the projected image of the reflected beam on the photoelectric conversion means 117 is the same as that of the photoelectric conversion elements 117-1 to 117.
-4, and the differential amplifier 33
The output signal of is zero. Further, the focus lens 114 moves from the position where the focus lens 114 is in the above-mentioned convergent state to the disk 2.
If the image is too close to the side, the projected image will be an ellipse as shown in a, and if it is moving away, the image will be an ellipse as shown in b. Therefore, the focus error signal F _E is 0 when the focus is on, as shown in Figure 4b.
(V), when the focal point is out of focus, the signal is shifted in the positive or negative direction and exhibits a so-called S-shaped characteristic. In FIG. 4b, the horizontal axis indicates the distance D between the focus lens 114 and the disk 2 with reference to the position of the focus lens 114 at the time of focusing. On the other hand, the adders 31, 32, and 34 constitute a recorded information detection section, and output a recorded information signal R _F corresponding to the recorded information read out from the information recorded on the disk 2, as is well known.

The servo operation determination circuit 13 is configured as shown in FIG. 5, for example. That is, the servo operation determination circuit 13 is a preamplifier 13 consisting of a non-inverting amplifier 131-1 that amplifies the focus error signal _FE .
1, a diode 132-1 for rectifying the positive output signal of the preamplifier 131, and a diode 132-1.
A low-pass filter consisting of a capacitor 132-3 and a resistor 132-4 that receives the output of
2-2, a rectifier circuit 132 consisting of a low-pass filter consisting of a capacitor 132-5 and a resistor 132-6, which inputs the output of the diode 132-2.
and an inverting buffer 133 consisting of an inverting amplifier 133-1 that inverts and amplifies the output of the low-pass filter consisting of a capacitor 132-5 and a resistor 132-6.
, diodes 134-1 and 134-2, a capacitor 132-3 and a resistor 132-
a signal selection circuit 134 that selects and outputs the higher level of the output signal level of the low-pass filter consisting of 4 and the output signal level of the inversion buffer 133;
, a non-inverting amplifier 135-1 and a reference voltage source 135
-2, and a comparator 135 that compares the output signal level of the signal selection circuit 134 with the voltage of a reference voltage source 135-2. Note that the voltage of the reference voltage source 135-2 is set to such a voltage that the focus error signal does not exceed when the focus servo device is operating stably.

When the focus servo device is operating stably, the DC component of the focus error signal F _E is 0 (V), and the amplitude of the low frequency component is also suppressed to a small level. However, when the focus is off, the focus error signal F _E
The DC component becomes large in the positive or negative direction, or the amplitude of the low frequency component becomes large due to surface vibration of the disk 2 or the like.

This focus error signal F _E is applied to a preamplifier 131 and amplified. Preamplifier 13
The focus error signal F _E amplified by 1 is rectified by diodes 132-1 and 132-2 to distinguish positive and negative focus error signals. The output of diode 132-1 is capacitor 1
The low frequency component is output through a low pass filter consisting of a capacitor 132-3 and a resistor 132-4, and the low frequency component is output through a low pass filter consisting of a capacitor 132-5 and a resistor 132-6. be done. capacitor 13
The output of the low pass filter consisting of resistor 2-5 and resistor 132-6 is inverted by inverting buffer 133. Therefore, capacitor 1 of rectifier circuit 132
The polarity of the output signal of the low-pass filter consisting of 32-3 and resistor 132-4 and the polarity of the output signal of the inverting buffer 133 are aligned, and the level of each output signal is on the positive side of the focus error signal _FE . It corresponds to the amplitude level of the DC component and low frequency component, and to the amplitude level of the negative side DC component and low frequency component of the focus error signal _FE . Both output signal levels are connected to diodes 134-1, 13
The signal selection circuit 134 consisting of 4-2 selects the one with the higher level and outputs it. The output signal of the signal selection circuit 134 is sent to the comparator 1.
35 and is compared with the voltage of a reference voltage source 135-2. Here, when the focus servo device is not operating stably, the output signal level of the signal selection circuit 134 exceeds the voltage of the reference voltage source 135-2, the comparator 135 generates a high potential output, and the focus is lost. Indicate that the Conversely, when the focus servo device is operating stably, the comparator 135 generates a low potential output to indicate this fact.

Further, the time discrimination circuit 12 is configured as shown in FIG. 6, for example.

The time discrimination circuit 12 is an inverter 121-1, 1
21-2, NAND gate 121-3, resistor 121
-4, 121-6, a multivibrator 121 consisting of a capacitor 121-5 and which oscillates only when the output of the level comparator 8 is at a high potential, and a D flip-flop circuit 122-1, 122-2,..., 12
2- _o , the output of the comparator 8 is inverted and the D flip-flop 122-1, 122-2,..., 122- _o
an n-stage shift register 122 that shifts the output of the multivibrator 121 and is reset when the output of the level comparator 8 becomes a low potential; 122, and an AND gate 123 whose input is the output of 122. Therefore, when the output of level comparator 8 is at a high potential, multivibrator 121 oscillates, and the oscillation output of multivibrator 121 is supplied to shift register 122 as a clock signal. Furthermore, when the output of the level comparator 8 is at a low potential, the D flip-flops 122-1, 122-2, . . . , 1
The data supplied to 22- _o becomes L, and the reset terminal becomes H. Therefore, when the output pulse of the multivibrator 121 continues for n periods and the output of the level comparator 8 is at a high potential, a high potential output is generated from the shift register 122. During this time, if the output of the level comparator 8 becomes low potential, the D flip-flops 122-1, 122-2,..., 12
2 _o is reset. Therefore, the level comparator 8
The time discrimination circuit 12 generates a high potential output to the logic circuit 14 only when the output of the multivibrator 121 becomes a high potential over a period in which n output pulses are output.

Returning to FIG. 2, when the focus is off, the servo operation determination circuit 13
is generating a high potential output. On the other hand, when the focus is off, the recording information signal R _F output via the matrix circuit 3 is not output.
For this reason, the detection circuit 7 does not generate the output signal H _F and the level comparator 8 generates a high potential output. When the high potential output of the level comparator 8 continues for a predetermined time or longer, the time discrimination circuit 12 generates a high potential output. Therefore, only when the servo continues to be out of alignment for a predetermined period of time, that is, while both the time discrimination circuit 12 and the servo operation determination circuit 13 are generating high potential output, the logic circuit 14 generates a high potential output and turns on the switch circuit 11. state. Therefore, the high potential output from the level comparator 8 is supplied to the changeover switch circuit 4 via the switch circuit 11, and the changeover switch circuit 4 is switched to the search signal generator 9 side. By switching the changeover switch circuit 4 to the signal generator 9 side,
The sawtooth wave output from the signal generator 9 is supplied to the servo amplifier 5, and the focus servo device enters a focus search state. By this focus search, the focus lens 114 is sequentially moved, and during the movement, the recording information signal R _F
occurs. As the recording information signal R _F is generated, the output signal H _F is output from the detection circuit 7, and the output signal of the level comparator 8 becomes a low potential output. When the output signal of the level comparator 8 becomes a low potential output, the output of the logic circuit 14 becomes a low potential output and the switch circuit 1
1 is turned off, the changeover switch circuit 4 is switched, and the focus error signal output from the matrix circuit 3 is supplied to the servo amplifier 5.
A focus servo loop is formed. Then, when the focus servo operation becomes stable, the output signal of the servo operation determination circuit 13 becomes a low potential output.

Further, unless the recording information signal R _F does not exist for a predetermined period of time or more and the servo operation determination circuit 13 detects instability of the servo operation, the switch circuit 11 is in the OFF state and the changeover switch circuit 4 is in the matrix state. It is switched to the circuit 3 side and a servo loop is formed.

Therefore, when the focus servo device is operating stably, the level of the output signal H _F of the detection circuit 7 changes due to dirt, scratches, etc. on the information recording carrier, and the output signal of the level comparator 8 changes. Even if the potential is temporarily high within a predetermined time range, the switch circuit 11
is switched to the off state, the changeover switch circuit 4 is not switched to the signal generation circuit 9 side, and the focus servo loop is not cut off.
The focus servo is stabilized.

Furthermore, even if the focus servo loop becomes unstable due to oscillation or the like, as long as the output signal H _F of the detection circuit 7 is output, the focus servo loop is formed.

As explained above, according to the present invention, when the focus is not lost and the dropout does not exceed a predetermined time, the focus servo loop is not interrupted, and the focus servo loop is not interrupted more easily than the conventional focus servo device. also works stably.

In addition to making it easy to set the reference voltage of the detection means for detecting dropout, it is also easy to set the reference voltage due to differences in the amplitude of the recorded information signal due to the photoelectric conversion efficiency of the optical information reading device, variations in disks, etc. become.

Furthermore, by adding a time discrimination circuit, if the focus continues for a predetermined time or more, it is possible to shift to a focus search operation.

Furthermore, even if the focus servo device becomes unstable due to oscillation, etc., the switch means is switched by a signal that has been subjected to a logical operation, so as long as the signal detected by the recording information signal is output, the focus servo device will remain in focus. The servo loop can remain closed.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional focus servo device. FIG. 2 is a block diagram showing one embodiment of the present invention. FIG. 3 is an explanatory diagram of an optical information reading device. Fourth
Figure a is a block diagram of a matrix circuit. Figure 4b
4 is a characteristic diagram of a focus error signal output from the matrix circuit of FIG. 4a. FIG. 5 is a circuit diagram showing a servo operation determination circuit used in an embodiment of the present invention. FIG. 6 is a circuit diagram showing a time discrimination circuit used in an embodiment of the present invention. 1... Optical information reading device, 2... Disc, 3...
Matrix circuit, 4... Selector switch circuit, 5...
Servo amplifier, 6... Actuator drive circuit, 7
...Detection circuit, 8. Level comparator, 9. Signal generator for search, 11. Switch circuit, 12. Time determination circuit, 13. Servo operation determination circuit, 14. Logic circuit.

Claims (1)

[Claims] 1. In a focus servo device of an optical information reading device that optically reads a recorded information signal and a focus error signal from a rotationally driven information recording carrier, a first signal obtained by detecting the recorded information signal is used as a reference voltage. a detection means for comparing and detecting the presence or absence of the first signal; a time discrimination circuit that is supplied with the output signal of the detection means and detects that the first signal does not exist continuously for a predetermined period; and a focus a servo operation determination circuit that detects that the first signal is out of focus; and the servo operation determination circuit detects that the focus is out of focus, and the time determination circuit detects that the first signal is not present continuously for a predetermined period of time. A focus servo device comprising: switching means for switching the focus error signal to a focus search signal only during a period during which the focus servo device is in use.