JPS6227454B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a focus lens protection device for preventing a readout device (focus lens) from coming too close to a disk and coming into contact with the disk in an optical video disk player or the like.

Conventional optical video disk players are equipped with a focus servo device that maintains the focus lens at a predetermined distance from the disk, but the focus servo device may malfunction for some reason or the control may fail. If a change beyond the possible range occurred, there was a risk that the focus lens would come into contact with the disk. Further, when a protection device for this is provided using the output of the focus control amplifier, there is a drawback that a signal delay occurs between the light receiving element and the focus control amplifier.

The present invention eliminates such drawbacks and protects the focus lens (disc) by forcibly and quickly driving the focus lens away from the disk when the focus lens gets too close to the disk. The purpose is to provide equipment.

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 parts, 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, 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 terminal 1, and the second sum signal is connected to 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 connected 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 is supplied from the inverter 12 to the inverting terminal of the amplifier 14. 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 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, 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. It becomes a signal. 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 1
5A 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, a negative potential is supplied to the inverting terminal of focus control amplifier 22 via switches 14A and 16B, producing a positive potential DC voltage at its output.
Therefore, the focus lens connected to the terminal 23 is 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 in the same way as transistor Q ₁ , and its collector Y is connected to terminal Y, which is connected to the inverting terminal of amplifier 19, so when it becomes out-of-focus (transistor Q ₂ turns on), The potential at the inverting terminal of amplifier 19 increases in the negative direction, and therefore the outputs of amplifier 19 and 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, when the focus lens comes too close to the disk beyond the controllable range of the focus servo device, the output of the focus control amplifier to drive the focus lens upward becomes small. Also, since the focus lens is forcibly driven in a direction away from the disk, there is no risk of the focus lens coming into contact with the disk. Furthermore, the focus lens can be protected more quickly than when the protection device is driven using the output of the focus control amplifier.

[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)

[Scope of Claims] 1. A focus lens that focuses a light beam onto a disk having a reflective surface carrying information to be read; a light-receiving element that is divided into four parts and forms an observation surface from which the information is read; first and second sum signals from which a light receiving element outputs a signal corresponding to the distance between the disks due to a change in the shape of the light beam spot; and a differential circuit that extracts a difference between the first and second sum signal outputs. , a comparator that compares the output of the differential circuit with a reference potential, a switch means controlled by the output of the comparator, and a signal to which each output signal of the switch means is applied to output a signal for starting a focus servo. a focus control amplifier, when the distance between the focus lens and the disk approaches by a predetermined distance or more due to the value of either the first or second sum signal increasing (or decreasing) from a predetermined value; a focus lens controlled by the output of the focus control amplifier is driven in the opposite direction by the output of the comparison means. Cas lens protection device.