JPS628848B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an optical video disk player or the like in which the readout device (focus lens) is correctly positioned within the control range of a focus servo device for keeping the readout device (focus lens) at a predetermined distance from the disk. The present invention relates to an in-focus detection device that detects whether or not the user is in a focused state.

In conventional such devices, for example,
Like the device described in Publication No. 3201, it reads the video carrier wave signal recorded on the disk, detects whether the output level of the signal has reached a predetermined value, and outputs it as an in-focus or out-focus signal. there was. However, in such a device,
The output level of the video carrier signal varies depending on the disk, light source,
Because the output level changes depending on the state of the light receiving element, etc., and because the output level does not necessarily correspond exactly to the focus state of the readout device, the in-focus state may occur even though the readout device is not within the control range of the focus servo device. There were cases where malfunctions such as signals being detected occurred. Furthermore, when obtaining an in-focus or out-focus signal from the output end of the focus control amplifier, there is a drawback that a signal delay occurs from the light receiving element to the focus control amplifier.

It is an object of the present invention to eliminate such drawbacks and provide an in-focus detection device with less malfunction and signal delay.

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. In other words, when the focus is at the top, a circular beam spot is formed, and when the focus is shifted vertically, a horizontally or vertically elongated elliptical beam spot is formed on each photodetector. Focus servo is possible by comparing the magnitude of one and the other of the sum of the signals. When the focus lens approaches the disk from above the disk, one of the two sum signals (the first sum signal) first gradually increases, reaches one extreme value, and then gradually decreases again. The other sum signal (second sum signal) is out of phase with the first sum signal and gradually becomes larger, reaching the same level as the first sum signal at the position where the focus reaches its peak, and the focus lens Furthermore, as it approaches the disk, it increases further, reaches one extreme value, and then gradually decreases. In an embodiment of the present invention, the first sum signal is connected to the terminal 1, and the second sum signal is connected to the terminal 1.
The following description will be made assuming that the sum signals of 2 and 3 are respectively applied to terminal 2. Terminals 1 and 2 are differential amplifier 3
The output of the differential amplifier 3 is applied to the inverting terminal of the amplifier 19 and the comparator 4, respectively. The output of the amplifier 19 is connected to a differentiating circuit 20, a diode 21 and a switch 16A.
or to the non-inverting terminal of focus control amplifier 22 via switch 15A. The inverting terminal of focus control amplifier 22 is connected to negative constant potential line 18 via switches 16B 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 route including the speed-up capacitor 5, is connected to the differentiating circuit 6, the diodes 7 and 8, and the inverter 9.
Flip-flop switch 13 through NAND
It is supplied to the input terminal of circuit 13A. The output of the NAND circuit 13A is connected to the non-inverting terminal of the amplifier 15 and other terminals.
It is supplied to the input terminal of the NAND circuit 13B.
Other input terminals of the NAND circuit 13B include terminal 10.
A part of the signal supplied from the inverter 12 to the inverting terminal of the amplifier 14 is supplied from 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 and 15.
A, 16A, and 16B are connected to turn on and off, respectively.

Terminal 2 is further connected via the non-inverting terminal of amplifier 30 and the inverting terminal of comparator 31 to the bases of transistors Q ₁ and Q ₂ . The collector Y of Q ₂ is connected to the 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 the terminal 10 by a control device (not shown), and the inverter 1
The output of switch 2 becomes a low level signal (hereinafter referred to as L signal), which is applied to the inverting terminal of amplifier 14, so that the output terminal of amplifier 14 supplies an H signal and turns on switch 14A. On the other hand, since the NAND circuit 13B outputs an H signal at this time, the amplifier 1
6 supplies an H signal to turn on switches 16A and 16B. On the other hand, no output appears in the differential amplifier 3 yet, and the output of the comparator 4 is an H signal, but since the differentiating circuit 6 is involved, the input of the inverter 9 is an L signal, and its output is an H signal. becomes. Therefore, the inputs of the NAND circuit 13A are both H signals, and the output thereof is an L signal. Therefore amplifier 15
outputs an L signal 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 1
Focus control amplifier 22 via 4A and 16B
A negative potential is supplied to the inverting terminal of the inverter, 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 (toward the disk) while receiving a slight upward driving force (toward 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, NAND circuits 13A and 13B forming a flip-flop are inverted, and NAND circuit 13A outputs an H signal and NAND circuit 13B outputs an L signal. Therefore, the switch 15A is turned on via the amplifier 15, and the switch 15A is turned on via the amplifier 16.
6A and 16B are turned off. As a result, the amplifier 19
The output is directly supplied to the amplifier 22 via the switch 15A, and the focus servo of the focus lens is activated. Since the comparator 4 has a hysteresis characteristic, the focus servo is applied to the focus lens just before the time when the focus reaches its peak (at a position slightly farther from the disk than the reference position). Therefore, when the focus lens approaches the disk from the reference position, an H signal (focus lens up signal) is supplied to the terminal 23, and when it moves away from the disk, an L signal (focus lens down signal) is supplied to the terminal 23. The cast lens vibrates up and down centering on the reference position.

On the other hand, as the reading lens descends and approaches the reference position, the first sum signal decreases and the second sum signal begins to increase. compared to a reference voltage. And when it becomes higher than the reference voltage, comparator 3
The output of 1 changes from an H signal to an L signal. Therefore, transistor _Q1 is turned off and the output at terminal 24 is L.
Since the signal (out-focus signal) changes to the H signal (in-focus signal), a focus signal representing the distance relationship between the focus lens and the disk can be obtained from the terminal 24. Furthermore, comparator 3
By appropriately selecting the reference voltage 1, the timing when the output of the comparator 4 changes from the L signal to the H signal,
It is preferable to match the timing at which the output of the comparator 31 changes from the H signal to the L signal. 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. Therefore, when out-of-focus (transistor Q ₂ turns on), the amplifier 19 increases in the negative direction, and therefore the outputs of the amplifier 19 and the focus control amplifier 22 increase in the positive direction,
The focus lens is driven upward (away from the disk). 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, since the signal representing the focus state is detected directly from the output end of the light receiving element, there is little delay in the signal. In addition, rather than detecting a specific signal included in the output from the light-receiving element and detecting the level of that detection signal, the level of the output from the light-receiving element itself is detected, so the actual position of the reading device A corresponding focus signal can be obtained, and in that sense it is not affected by changes in the states of the disk, light source, light receiving element, etc.

[Brief explanation of the drawing]

The figure represents a circuit diagram of an embodiment of the invention. 1, 2... terminal, 3... differential amplifier, 4, 31
... Comparator, 9, 12 ... Inverter, 13 ...
Flip-flop switch, 14, 15, 16,
19, 30...Amplifier, 22...Focus control amplifier, _Q1 , _Q2 ...Transistor.

Claims (1)

[Claims] 1. An in-focus detection device for detecting whether or not the focus lens is correctly positioned within the control range of a focus servo device for holding the focus lens at a predetermined distance from the disk, the focus lens A first received light output whose level begins to gradually increase according to the distance from the disk and decreases after passing through one extreme value;
differential amplification means for outputting a focus error signal according to the difference between the level of the received light output and the second received light output whose level starts to increase and decreases after passing through one extreme value when the level of the received light output starts to decrease; Comparing means for comparing the level of the second light receiving output with a reference level, detecting that the level of the second light receiving output has become equal to or higher than the reference level, and generating a detection output; and switch means whose opening and closing are controlled by the detection output, and detects that the focus lens is located within the control range of the focus servo device according to the open/close state of the switch means. Orcus detection device.