JPS5928254A - Focus servo device - Google Patents

Abstract

PURPOSE:To ensure stable working to an applied dropout, by avoiding the cutoff of a focus servo loop in case the focus gets out of its position and the dropout does not exceeds a prescribed period. CONSTITUTION:When a focus has a shift, a servo action deciding circuit 13 delivers a high level of potential. While no wave detecting signal HF is produced since no record information signal RF is delivered, and a level comparator 8 delivers a high level of potential. When this output of high potential continues longer than a prescribed period of time, a time discriminating circuit 12 delivers a high level of potential. Only in this period, a logical circuit 14 delivers a high level of potential to turn on a switch 11. Then the high potential output of the comparator 8 is switched and supplied to the side of a signal generator 9 for search by means of a changeover switch 4. This output is supplied to a servo amplifier 5 to obtain a search mode. When the signal RF is produced owing to the search mode, the signal HF is delivered. Thus the outputs of the comparator 8 and the circuit 14 are set at a low level of potential respectively to turn off the switch 11. Then the switch 4 is switched to supply the error signal given from a matrix circuit 3 to the amplifier 5 to form a servo loop.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus sensor 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 focuser device is constructed as shown in FIG. 1, for example. That is, the optical information reading device 1 optically reads recorded information from the disk 2 which is being rotated, and the reflected light is received by the photoelectric conversion means divided into four parts, and the output of the photoelectric conversion means is received by the matrix circuit 3. A focus error signal FB and a recording information signal R are obtained.

The focus error signal F8 is supplied to the amplifier 5 via the changeover switch circuit 4, subjected to phase compensation and gain adjustment, and then supplied to the actuator drive circuit 6. 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, 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, that is, the presence or absence of the recording information. Dropouts, etc. are 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 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 of the detection circuit 7; In the portion where there is an out, etc., the focus search operation is interrupted by the changeover switch 4 and the focus search operation is started. However, the operation of the focus sensor IF does not immediately become unstable in a portion where dropout or the like exists. 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 sensor device as described above, it is difficult to adjust the level comparator 8 and set the time constant of the integrating circuit 10. 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 80.

The present invention has been made in view of the above, and an object of the present invention is 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 FE output from the matrix circuit 3 in the focus servo device shown in FIG. to determine that the focus is off.

On the other hand, the changeover switch circuit 4 consists of analog switches 4-1 and 4-2, and analog switches 4-1 and 4-2.
A negative voltage -■ is supplied to dart -2 through the Soldown resistor. The output signal of the level comparator 8 is supplied to the analog switches 4-1 and 4-2 (f-) via the switch circuit 11 to drive the selector switch circuit 4. Here, when a high potential signal from the level comparator 8 is supplied to the changeover switch circuit 4, that is, the analog switches 4-1 and 4-2 (f-) of the analog switch 4-1 and 4-2, the high potential signal from the level comparator 8 is supplied via the switch circuit 11. 4-2
is controlled to be on, and the selector switch circuit 4 is switched to the search signal generator 9 side.

In addition, the output signal of the level comparator 8 is the output signal H of the detection circuit 7 which continues for a certain period of time or more.
, is supplied to a time determination circuit 12 that determines whether or not it has detected that the voltage is below the reference voltage. Time discrimination circuit 1
The output signals of 2 and the servo operation determination circuit 13 are supplied to a logic circuit 14 that performs an AND operation, the output of the logic circuit 14 is supplied to the switch circuit 11, and the time determination circuit 12 and the servo operation determination circuit 13 output signals. When 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. A photoelectric conversion means 117 is provided, and the light beam from the laser light source 111 is projected onto a focus lens 114 via a collimator lens (not shown), a beam sinter 112, a 174 wavelength plate (not shown), and a tracking mirror 113. The light is focused near the information recording surface of the disc 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, is reflected by the beam splitter 112, and is projected onto the photoelectric conversion means 117, where it is converted into an electrical signal. be done. Focus lens 114 and focus lens 11 of disk 2
A cylindrical lens 116 is disposed between the yoke point and the yoke point regarding 4. On the other hand, the photoelectric conversion means 117 includes photoelectric conversion elements 117-1 to 117- divided into four as shown in FIG. 4(a).
It consists of 4.

M) IJ Lux path 3 connects photoelectric conversion elements 117-1 and 1
an adder 31 that adds the output signals of the photoelectric conversion elements 117-3, an adder 32 that adds the output signals of the photoelectric conversion elements 117-2 and 117-4, and a differential amplifier 33 that receives the output signals of the adders 31 and 32 as input. and an adder 34 that adds the output signals of adders 31 and 32. Adders 31 and 32 and differential amplifier 33 constitute a focus error detection section,
As is well known, a focus error signal F8 is outputted corresponding to the projected image of the reflected beam on the photoelectric conversion means 117. Sunawachi, p disk 2 with focus lens 114
When the projected light is converged on the information recording surface of the photoelectric conversion means 117, the projected image of the reflected beam on the photoelectric conversion means 117 is circular evenly applied to the photoelectric conversion elements 117-1 to 117-4.
The output signal of differential amplifier 33 is zero. Further, when the focus lens 114 is too close to the disk 2 side from the above-mentioned convergence state position, an elliptical projected image is formed as shown in a, and when it is far away, an elliptical projected image is formed as shown in b. Therefore, as shown in FIG. 4(b), the focus error signal F becomes 0 (g) when the focus is in focus, and becomes a signal shifted in the positive or negative direction when the focus is out of focus, exhibiting the so-called character-eight characteristic. It turns out. In No. 41), the horizontal axis indicates the distance between the focus lens 114 and the disk 2 based on 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 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 includes a non-inverting amplifier 131 that amplifies the focus error signal FIl.
-1, a diode 132-1 that rectifies the positive output signal of the preamplifier 131, and a capacitor 132 whose input is the output of the diode 132-1.
-3 and a resistor 132-4, and a diode 132 that rectifies the negative output of the preamplifier 131.
-2, a rectifier circuit 132 consisting of a low-pass filter consisting of a capacitor 132-5 and a resistor 132-6, which receives the output of the diode 132-2, and a capacitor 132-2.
5 and a resistor 132-6; an inverting buffer 133 consisting of an inverting amplifier 133-1 that inverts and amplifies the output of the filter; diodes 134-1 and 134-2; a capacitor 132-3 and a resistor 132; −
a signal selection circuit 134 that selects and outputs the larger of the output signal level of the low-pass filter 1 and the output signal level of the inverting buffer 133, and the non-inverting amplifier 1;
35-1 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 the reference voltage source 135-2. Note that the voltage of the reference voltage source 135-2 is set to a voltage that does not exceed the focus error signal when the focuser is operating stably.

When the focuser is operating stably, the DC component of the focus error signal F is 0 (V), and the amplitude of the low frequency component is also suppressed to a small level. However, when the focus is out of focus, the DC component of the focus error signal F8 has a large value in the positive or negative direction, or the amplitude of the low frequency component due to surface vibration of the disk 2 or the like becomes large.

The focus error signal F8 is applied to the preamplifier 131 and amplified. Focus error signal F8 amplified by preamplifier 131 Positive side and negative side focus error signals are distinguished and rectified by diodes 132-1 and 132-2. The output of the diode 132-1 passes through a low-frequency filter consisting of a capacitor 132-3 and a resistor 132-4, and its low frequency component is output, and the output of the diode 132-2 consists of a capacitor 132-5 and a resistor 132-6. The low frequency components are output through a loaf nine filter. Capacitor 132-5 and resistor 1
The output of the low-pass filter consisting of 32-6 is inverted by an inverting buffer 133. Therefore, rectifier circuit 1
The polarity of the output signal of the low-pass filter consisting of 32 capacitors 132-3 and resistors 132-4 and the inverting buffer 1
The polarities of the output signals of 33 are aligned, and the level of each output signal is the amplitude level of the positive side DC component and low frequency component of the focus error signal FE, and the negative side DC component and the amplitude level of the focus error signal FE. It corresponds to the amplitude level of the low frequency component. This Ryokawa power signal level is connected to the diode 134-1.

The signal selection circuit 134 starting from 134-2 selects and outputs the signal with the higher level. The output signal of the signal selection circuit 134 is input to a comparator 135 and compared with the voltage of a reference voltage source 135-2. Here, when the focuser is not operating stably, the output signal level of the signal selection circuit 134 is set to the reference voltage source 135.
-2 voltage is exceeded, comparator 135 produces a high potential output, indicating out of focus. Conversely, when the focuser is operating stably, the comparator 1
35 indicates this by generating a low potential output.

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

The time discrimination circuit 12 is an inverter 121-1.121-2
, Nant Gate 121-3, Resistor 121-4.121-
6. A multivibrator 1 consisting of a capacitor 121-5, which oscillates only when the output of the level comparator 8 is at a high potential.
21 and D fritzoflotsuno circuit 122-1゜1222
,-. 122-n, inverts the output of the comparator 8 and inverts the D flip-flop 122-1.122-2. ....

122-n;
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, and receives the output of the level comparator 8 and the output of the shift register 122 as inputs. It consists of AND gate 123. Then, when the output of the level comparator 8 is at a high potential, the multivibrator 121 oscillates, and the oscillation output of the multivibrator 121 is supplied to the shift register 122 as a clock signal.

Further, when the output of the level comparator 8 is at a low potential, the D fritz floats 7'122-1, 122-2. −． 122-n
The data supplied to the terminal becomes L, and the reset terminal becomes H. Therefore, when the output pulse of the multivibrator 121 continues for a period of n times 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 a low potential, the D flip 70 knob 122-1.122-2. ...,
122-n is reset. Therefore, the level comparator 8
The output pulse of the multivibrator 121 is n
The time discrimination circuit 12 generates a high potential output to the logic circuit 14 only when the potential becomes high beyond the period in which the signal is output.

Returning to FIG. 2, when the focus is off, the servo operation determination circuit 13 generates a high potential output as described above. On the other hand, when the focus is off, the recording information signal R is outputted via the matrix circuit 3.
, is not output. For this reason, the detection circuit 7 outputs a signal H.
, 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 order for a predetermined time or longer, that is, when both the time discrimination circuit 12 and the servo operation determination circuit 13 are generating a high potential output, the logic circuit 14
generates a high potential output and the switch circuit 11 is turned on. 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 amplifier 5, and the focus servo device enters a focus search state.

By this focus search, the focus lens 114 is sequentially moved, and in the middle of the movement, the recording information signal R2 is
occurs. As the recording information signal R2 is generated, the detection circuit 7 outputs the output signal H2, 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, the switch circuit 11 is turned off, the changeover switch circuit 4 is switched, and the output is output from the matrix circuit 3. A focus error signal is supplied to the servo amplifier 5, and a focuser 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, as long as the recording information signal R2 does not exist for a predetermined period of time or longer and instability of the sensor operation is not detected by the operation determination circuit 13, the switch circuit 11 is in the off state and the changeover switch circuit 4 is in the off state. M) Since the IJ Lux route is switched to the 3 side, a loop will be formed.

Therefore, when the focus servo device is operating stably, the level of the output signal H 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 temporarily changes for a predetermined period of time. Even if the potential becomes high within the range of The sensor is applied stably.

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

As explained above, according to the present invention, when the focus is not lost and the dropout does not exceed a predetermined period, the focuser loop is not interrupted. The servo equipment also operates stably.

In addition to making it easier to set the reference voltage of the detection means for detecting dropout, it is also easier 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 the disc, etc. It gets easier.

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 loop will be closed. You can leave it as soon as you complete it.

[Brief explanation of drawings]

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. FIG. 4(a) is a block diagram of a matrix circuit. FIG. 4(b) is a characteristic diagram of the focus error signal output from the matrix circuit of FIG. 4(a). 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... Disk, 3...
・Matrix circuit, 4... Changeover switch circuit, 5.
・Servo amplifier, 6 ・Actuator drive circuit, 7
...Detection circuit, 8.Level comparator, 9.Search signal generator, 11.Switch circuit, 12.Time determination circuit, 13.Servo operation determination circuit, 14.Logic circuit. . Patent Applicant Trio Co., Ltd. Patent Attorney Nobuo Dosa Figure 3 Figure 4 Figure 55 Figure 6

Claims (1)

[Claims] A focuser 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 compares a first signal detected from the recorded information signal with a reference voltage. a detection means for detecting the presence or absence of the first signal by detecting the presence or absence of the first signal; a time determination 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; The sensor that detects this is an operation judgment circuit,
Switching to switch the focus error signal to a signal for focus search only during a period in which the servo operation determination circuit detects an out-of-focus state and the time determination circuit continuously detects the absence of the first signal for a predetermined period of time. A focus servo device characterized by comprising means for applying force.