JPS6313261B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus servo device for maintaining a readout device (focus lens) at a predetermined distance from a disc in an optical video disc player, etc., and particularly relates to servo activation.

In such a conventional device, a video carrier wave signal recorded on a disk is read out, and the focus servo is activated when it is detected that the output level of the signal has reached a predetermined value. However, in such a device, the output level of the video carrier wave signal varies depending on the conditions of the disk, light source, light receiving element, etc., and the output level does not necessarily correspond exactly to the focus state of the readout device. This method has disadvantages such as the case that the cass servo device does not start correctly.

In addition, as described in Japanese Patent Application Laid-open No. 51-89444, there is a device that uses an electronic clock to determine when to start the focus servo, but due to variations in mechanical friction,
Due to factors such as changes in the characteristics of the electrical system in response to temperature changes and changes in both over time, it has been difficult to stably obtain an appropriate startup timing for the focus servo. If the time to start the focus servo deviates from the appropriate time, the focus servo may not be able to be pulled in or the actuator may oscillate.

It is an object of the present invention to eliminate such drawbacks and provide a focus servo device that can be activated accurately.

Examples of the present invention will be described below. To terminals 1 and 2, signals generated due to changes in the shape of a beam spot formed on a light-receiving element divided into four, for example, are applied. For example, as shown in Japanese Patent Application Laid-Open No. 104539/1983, the shape of the beam spot obtained by the astigmatism method is circular when the beam is in focus (in-focus state), but becomes horizontally long when it is out of focus. Alternatively, it is known that a vertically elongated elliptical beam spot is formed. By this astigmatism method, a beam spot is made incident on the four-divided light-receiving element shown in FIG. 3, and a focus error signal can be obtained by comparing the sum signals of the light-receiving elements on each diagonal.

Figure 4a shows the shape of the beam spot that enters the light receiving element when the lens position is farther than the focal point position, Figure 4b shows the shape of the beam spot when the lens position is in focus, and Figure 4c shows the shape of the beam spot when it is closer. . According to the figure, when the lens is farther from the in-focus position, the sum signal (the first
The sum signal (sum signal of becomes.

This first sum signal is transferred to the differential amplifier 3 shown in FIG.
By inputting the second sum signal to the non-inverting input terminal 1 and the inverting input terminal 2 of the differential amplifier 3, the output from the differential amplifier 3 has a so-called S-shaped characteristic as shown in FIG. 2A. The reason why there is a pair of peaks in the same figure is because when the lens position moves away from the in-focus position to a certain extent, defocus occurs and the output signal obtained from each light receiving element decreases. This is to get closer to.

In this way, the differential amplifier 3 receives the sum signal of each diagonal light-receiving element of the four-divided light-receiving element.
As a result, the lens position becomes zero at the in-focus position,
It is possible to obtain a focus error signal in which signals with different polarities are generated before and after the focal point, and the focus error signal approaches an extreme value and approaches zero as it moves away from the in-focus point.

It goes without saying that if the first sum signal is input to the inverting input terminal 2 of the differential amplifier 3, and the second sum signal is input to the non-inverting input terminal 1, the polarity of FIG. 2A will be reversed. However, in the following description of the embodiment, a case will be described in which the first sum signal is input to the non-inverting input terminal 1 and the second sum signal is input to the inverting input terminal 2. Terminals 1 and 2 are connected to the non-inverting terminal and the inverting terminal of differential amplifier 3, respectively, and the output of differential amplifier 3 is applied to the inverting terminal of amplifier 19 and comparator 4, respectively. The output of the amplifier 19 is sent to the differentiating circuit 2
0, via diode 21 and switch 16A, or via switch 15A to the non-inverting terminal of focus control amplifier 22. The inverting terminal of the focus control amplifier 22 is connected to the switch 1
It is connected to the negative constant potential line 18 via 6B and 14A. One end of the switch 14A is grounded via a capacitor 17. On the other hand, the output of the comparator 4, which has hysteresis characteristics due to the positive feedback loop including the speed-up capacitor 5, is sent to the input terminal of the NAND circuit 13A of the flip-flop switch 13 via the differentiating circuit 6, diodes 7 and 8, and inverter 9. Supplied. NAND circuit 1
The output of 3A is the other non-inverting terminal of amplifier 15.
It is supplied to the input terminal of the NAND circuit 13B.
Other input terminals of the NAND circuit 13B include terminal 1.
A part of the signal supplied from the amplifier 14 to the inverting terminal of the amplifier 14 is supplied from the amplifier 14 via the inverter 12. Terminal 10 is also connected to the non-inverting terminal of comparator 4 via diode 11. The output terminals of the amplifiers 14 to 16 are connected to switches 14A, 1
5A, 16A, and 16B are connected to turn on and off, respectively.

The output terminal 23 of the focus control amplifier 22 is connected via a capacitor 25, a diode 26, and a resistor 29 to the bases of transistors Q ₁ and Q ₂ . Anode of diode 26 and transistor
The bases of Q ₁ and Q ₂ are grounded via a capacitor 27 and a diode 28, respectively. The collector Y of the transistor Q ₂ is connected to a terminal Y which is connected to the inverting terminal of the amplifier 19 .

Next, the operation will be explained. When the power is turned on, a high level signal (hereinafter referred to as H signal) is supplied to terminal 10, and the output of inverter 12 becomes a low level signal (hereinafter referred to as L signal).
4, the output terminal of amplifier 14 supplies an H signal, turning on switch 14A. On the other hand, since the NAND circuit 13B outputs an H signal at this time, the amplifier 16 supplies the H signal and turns on the switches 16A and 16B. On the other hand, the differential amplifier 3 does not yet have an output, which has the same polarity as the focus error signal that occurs when the lens position is located farther than the in-focus position, and the extreme value of the focus error signal. The output of the comparator 4, in which the reference voltage V having an absolute value smaller than the absolute value of , its output becomes an H signal. accordingly
Both inputs of the NAND circuit 13A are H signals,
Its output becomes an L signal. Therefore, the amplifier 15 is L
A signal is output, and switch 15A is turned off. Note that when the H signal is supplied to the terminal 10, the reference voltage of the comparator 4 becomes high via the diode 11, so there is no risk that noise will be supplied to the inverting terminal of the comparator 4 and the comparator 4 will malfunction. Since line 18 is connected to a predetermined negative potential, switch 14A
A negative potential is supplied to the inverting terminal of the focus control amplifier 22 through 16B and 16B, and a positive DC voltage is generated at its output. Therefore, the focus lens connected to the terminal 23 becomes in an up state and moves away from the disk.

Next, the disk moves and is positioned below the focus lens, and a signal is sent to bring the focus lens closer to the disk (lower).
0 is supplied with an L signal. Therefore, inverter 1
2, the output of the amplifier 14 becomes an L signal, and the switch 14A is turned off. Then, the charge that has been stored in the capacitor 17 starts to discharge, and the discharge potential drives the focus control amplifier 22 via the switch 16B. Therefore, the focus lens gradually descends and approaches the disk.

Since the first and second sum signals are respectively supplied to the non-inverting terminal and the inverting terminal of the differential amplifier 3, the output of the differential amplifier 3 gradually becomes a positive potential as the focus lens descends and approaches the disk. begins to increase, passes through one extreme value, then decreases, and reaches zero when the focus is removed. When the focus lens is further lowered, the second sum signal level becomes higher than the first sum signal level, so the differential amplifier 3
A negative potential appears in the output, gradually increases in the negative direction, decreases after passing through one extreme value, and becomes zero as the focus lens approaches the disk.
If it continues to fall, there is a risk that the focus lens will come into contact with the disk. That is, at the output end of the differential amplifier 3, a signal having a so-called S-curve characteristic appears.

As the focus lens descends from the up position and approaches the disk, a positive potential gradually appears at the output terminal of the differential amplifier 3 and its value increases. Its output is amplified by an amplifier 19,
Differential circuit 20, diode 21, switch 16A
The positive AC component is passed through the focus control amplifier 2
2, the focus lens moves downward (towards the disk) while receiving a slight upward driving force (towards the disk). This force in the opposite direction makes it easier for the focus servo of the focus lens to be applied. On the other hand, since the output of the differential amplifier 3 is also applied to the comparator 4, the comparator 4 outputs an L signal instead of an H signal when a voltage greater than the reference voltage is supplied.
The change is differentiated by the differentiating circuit 6, but the diode 8 is turned on and the input terminal of the inverter 9 remains essentially an L signal and does not change. However, the focus lens further descends, and the input of comparator 4 passes through a certain extreme value, and then gradually decreases, and the input of comparator 4
When the output reaches a predetermined value (comparator 4 has hysteresis characteristics) which is lower than the value when the H signal is inverted to the L signal, the comparator 4 starts outputting the H signal from the L signal again. . This change is differentiated by the differentiating circuit 6 and applied to the inverter 9, so that the inverter 9 outputs an L signal corresponding to the change. Therefore, the NAND circuits 13A and 13B forming the flip-flop are inverted, and the NAND circuits 13A and 13B forming the flip-flop are inverted.
The circuit 13A outputs an H signal, and the NAND circuit 13B outputs an L signal.
Output a signal. This situation is shown in FIGS. 2B to 2E, in which waveform diagrams are shown corresponding to the symbols given in FIG. 1.

That is, the focus error signal shown in FIG. By comparing the reference voltage V, which has an absolute value smaller than the absolute value, by the comparator 4, the output of the comparator 4 shows the magnitude relationship between the focus error signal and the reference voltage, as shown in FIG. 2B. It is possible to obtain an output signal that changes from one state to another state or from said other state to one state depending on the state. The output obtained by differentiating this output with the differentiating circuit 6 is the waveform shown in FIG. 2C. The differential output generated at the change point (falling point) from the H signal to the L signal in FIG. is L
Only the differential output generated at the point of change (rising point) from the signal to the H signal is applied. That is, the differentiating circuit 6 and the diode 8 can detect a point at which the output signal changes at a position closer to the in-focus position than the extreme value of the focus error signal. As a result, the inverter 9 outputs an L signal at a position closer to the in-focus position than the lens position where the focus error signal has an extreme value, as shown in FIG. 2D. This L signal output is the NAND circuit 13A that constitutes the flip-flop 13.
The NAND circuit 13A outputs an H signal control signal. Therefore, switch 15A is turned on via amplifier 15, and switches 16A and 16B are turned off via amplifier 16. As a result, the output of the amplifier 19 is the switch 15A.
The signal is supplied as is to the amplifier 22 via , and the focus servo of the focus lens is activated. A comparator 4 compares the focus error signal with a reference voltage V, and uses a differentiating circuit 6, a diode 8, and an inverter 9 to detect a change when the comparison output is closer to the in-focus position than the extreme value of the focus error signal. Since a point is detected, focus servo is applied near the in-focus point (at a position slightly farther from the disk than the in-focus point). Therefore, when the focus lens approaches the disk from the reference position, terminal 2
3 is H signal (focus lens up signal)
However, when the object moves away again, an L signal (focus lens down signal) is supplied, and the focus lens vibrates up and down about the reference position.

Normally, the transistor Q ₁ is on, so an L signal is supplied to its collector terminal 24. However, when the readout lens starts to vibrate around the reference position, the output from the terminal 23 has its negative AC component. The capacitor 27 is charged via the capacitor 25 and the diode 26, and a negative voltage is applied to the transistor _Q1 via the resistor 29, so the transistor _Q1 is turned off and an H signal (in-focus signal) is supplied to the terminal 24. be done. If the focus lens is too close to or too far away from the disk and no AC output appears at terminal 23, the charge stored in capacitor 27 is quickly discharged via resistor 29 and diode 28, and transistor Q ₁ is turned on, and an L signal (out-focus signal) is obtained at the terminal 24. Therefore, a focus signal representing the distance relationship between the focus lens and the disk can be obtained from the terminal 24. The focus signal is supplied to, for example, a microcomputer (not shown), and is used as a signal for starting the next predetermined operation of a video disc player or the like.

Transistor Q ₂ turns on and off at the same time as transistor Q ₁ , and its collector Y is connected to terminal Y, which is connected to the inverting terminal of amplifier 19, so it is out of focus (transistor Q ₂ is on).
, the potential at the inverting terminal of the amplifier 19 increases in the negative direction, the outputs of the amplifier 19 and the focus control amplifier 22 increase in the positive direction, and the focus lens moves upward (in the direction away from the disk). Driven. Therefore, if the focus lens and the disk come too close together, the focus lens will be forced upward and will not come into contact with the disk.

As described above, in the present invention, the timing to start the focus servo loop can be accurately determined near the in-focus position (slightly further away from the in-focus position) using the focus error signal itself having S-shaped characteristics and one comparator. The focus servo can be reliably pulled in without being affected by the state of the disk, light source, light receiving element, etc.

[Brief explanation of the drawing]

Fig. 1 shows a circuit diagram of an embodiment of the present invention, Fig. 2 A to E are waveform diagrams at the main connection points in Fig. 1, and Fig. 3 shows a circuit diagram for generating a focus error signal used in the present invention. Connection diagrams of the light receiving element, FIGS. 4a to 4c are diagrams showing the shape of a beam spot incident on the light receiving element. 1, 2... terminal, 3... differential amplifier, 4... comparator, 9, 12... inverter, 13... flip-flop switch, 14, 15, 16, 19...
...Amplifier, 22...Focus control amplifier, Q ₁ ,
Q ₂ ...transistor.

Claims (1)

[Scope of Claims] 1. A focus servo device for converging light emitted from a light source onto a disk via a focus lens, which becomes zero when the lens is at a focused position; A focus having a characteristic that signals of different polarities are generated when located before and after the in-focus position, and each of the signals of different polarity passes through one extreme value and approaches zero as it moves away from the in-focus position. means for generating an error signal; an absolute value having the same polarity as a focus error signal generated when the lens is positioned at a point farther from the disk than the in-focus position and smaller than the absolute value of the one extreme value; comparing means for comparing the focus error signal with a reference voltage of the lens and generating an output signal changing from one state to another state or from said other state to said one state; detection means for detecting a point at which the output signal changes at a position closer to the in-focus position than the position when the error signal shows the one extreme value; and generating a control signal in response to the output of the detection means. What is claimed is: 1. A focus servo device comprising: control signal generating means for generating a control signal; and switch means for closing a focus servo loop in response to the control signal.