JPS5953613B2 - Automatic focus control device in optical reproducing device for information recording medium disk - Google Patents

Description

[Detailed Description of the Invention] An information recording medium disk (hereinafter referred to as a disk) in which pits are formed in accordance with an information signal.

In a disc optical reproducing device ι that is designed to optically reproduce information signals, the distance between the disc surface and the reading lens is adjusted by driving and controlling the reading lens by an automatic focus control device. It is always kept at a normal value. In other words, while it is unavoidable that disks experience surface wobbling during playback operations, signals in the required frequency range cannot be reproduced well unless the distance between the reading lens and the disk is maintained at a predetermined value. It is from. Conventionally, an automatic focus control device in an optical playback device for a disk is generally equipped with a differential type detector (differential detector) that receives reflected light from the surface of the disk. Obtain information on the amount and direction of deviation of the distance between the disk and reading lens from the normal state from the output of
In order to maintain a regular distance between the reading lens and the disk, the position of the reading lens can be moved by, for example, an electrodynamic driving device.

By the way, if the error detection sensitivity of the above-mentioned automatic focus control device is increased, the range of change in the distance between the reading lens and the disk that corresponds to the controllable range becomes narrow. If the automatic focus control device is configured to have high error detection sensitivity, even if there is a slightly large surface runout in the 6-disk, information regarding the distance between the 6-disc and the reading lens can be obtained from the 6-differential detector. Otherwise, the automatic control system may not lose its original function, and in some cases, the reading lens may collide with the disk surface, causing damage to the disk surface. , it was necessary to apply some kind of preventive measures to prevent the above-mentioned problems from occurring. 6 In order to solve the above problems, 6 conventionally, for example, in the optical path from the 6 disk to the differential detector, a special type of lens was used in which there was no lens effect at the center and only at the periphery. Using a lens. It is possible to expand the range of change in the distance between the disk and the reading lens that can be detected by a differential detector (Japanese Unexamined Patent Publication No. 51-43948), or, for example, to use a reading lens in addition to a normal differential detector. A new detector is installed at a position where it can receive the reflected light from the disk when the distance between the disk and the disk is close.
Proposals have been made to forcibly separate the reading lens from the disk using the detection output from this new detector, but the former of the above-mentioned proposals is difficult to implement. In addition, a special shaped lens is required for this purpose, and the state in which the reflected light from the 6 disks no longer passes through the finite aperture of the lens creates a lightless state for the detector, so it is difficult to use the 2 disks. Also, it is not possible to completely eliminate the collision of the reading lens with the board surface. The latter of the above-mentioned proposals is based on the premise that a certain amount of reflected light is provided to the newly installed detector when the reading lens approaches the surface of the disk. In order to increase the detection sensitivity of the automatic focus control system. If the incident position of the auxiliary beam on the reading lens is moved far away from the optical axis, this may occur depending on the configuration of the optical path of the reflected light from the disk to the newly installed detector mentioned above. Since the reflected light may not be provided to the newly installed detector, there is less freedom in configuring the optical path of the reflected light from the disk to the detector. There were drawbacks such as the need for a new detector in addition to the detector.

The present invention is. The distance between the reading lens and the disk for reading the information signal of the disk is such that the reading lens and the disk have an overlapping part in a part of each other's detection area so that they can output the same detection force in a normal state. A first detecting element that produces the maximum detecting force when the distance between the reading lens and the disk is closer than the normal state, and a second detecting element that produces the largest detecting force when the distance between the reading lens and the disk is farther than the normal state. The state of the signal obtained based on the detection force when the distance between the reading lens and the disk in the differential detector configured to include two detection elements is closer than the normal state, and The moving direction of the reading lens is determined based on the correlation with the state of the signal obtained based on the detection force from the first detection element in the detector, and the distance between the reading lens and the disk is determined from the normal state. The upper limit of the drive signal voltage given to the read lens drive system is limited so that the read lens is forcibly separated from the disk surface when it deviates from the detection area in the approaching direction. The present invention provides an automatic focus control device for an optical playback device for discs, which eliminates the drawbacks of the previously proposed devices mentioned above, and the contents thereof will be explained in detail with reference to the attached drawings. .

FIG. 1 is a block diagram showing one embodiment of an automatic focus control device in an optical disc reproducing apparatus according to the present invention. In FIG. 1, 1 is a laser light source and 2 is a beam splitter. A laser light beam 3 emitted from the laser light source 1 is split into a main beam 3a for reading the main information signal and an auxiliary beam 3b by the beam splitter 2. It is divided into
The main beam 3a is passed through the magnifying lens 4j up to one aperture of the reading lens 6, the beam diameter of which is expanded, and the beam is incident on the reading lens 6. Also. The auxiliary beam 3b is incident on the reading lens 6 at a position away from the optical axis.

In the illustrated example, the main beam 3a and the auxiliary beam 3b are applied to a reading lens 6 through a half mirror 5, and this half mirror 5 receives the main beam projected onto the surface of the disk D through the reading lens 6. The spot reflected by the auxiliary beam and the reflected light from the spot by the auxiliary beam are applied to a main information signal detection detector DETml and a differential detector DETd, respectively. Note that 7 is a lens provided in the optical path between the half mirror 5 and the detector DETrIl. The differential detector DETd, which receives the reflected light from the disk surface caused by the projection of the spot by the auxiliary beam onto the disk surface, is a 16th second detection element Dl, I) consisting of a photoelectric conversion element. 2, a differential amplifier DA, etc.

A state E in which the distance l between the reading lens 6 and the surface of the disk D (the distance l between the reading lens 6 and the disk D) is normal. , the reflected light from the board surface of the spot by the auxiliary beam is applied to both the first and second detection elements Dl and D2 in the differential detector DETd, and
The second detection elements Dl and D2 are configured to obtain detection forces of equal magnitude, and the distance l between the reading lens 6 and the disk D is in the normal state 1 described above. 6 when the interval l changes from
At the same time as the detection force from the second detection element D2 decreases, the detection force from the first detection element D1 increases, but as the reading lens 6 and the disk D gradually approach each other, As time progresses, the state goes through a state in which the detected force is output only from the first detection element D1, and then a state in which no detected force is output from either the first or second detection element D1 or D2. Contrary to the above case, the distance l between the reading lens 6 and the disk D is in the normal state 1. When the distance 2 changes from 2 to 2, the first detection element D1
At the same time as the detection force from the second detection element D2 decreases, the detection force from the second detection element D2 increases. After passing through a state in which a detection output is output only from the detection element D2, a state is reached in which no detection force is output from either the first or second detection element. Changes in the detection forces Sdl, S, 2 from the first and second detection elements Dl, D2 due to changes in the distance l between the reading lens 6 and the disk D, and the changes in the first and second detection forces described above. The output signal Sda from the differential amplifier DA (the detection power Sda of the differential detector DETd) to which the detection forces Sdl and Sd2 from the detection elements Dl and D2 are given as inputs is shown in Figures 2B and a, respectively. In FIGS. 2A and 2B, the horizontal axis is the distance 2 between the reading lens 6 and the disk D, and 10 indicates that the distance 1 between the lens 6 and the disk D is normal. ing.

In FIG. 1, arrow 6 Y indicates a change in the distance between reading lens 6 and disk D, and arrow X
As the distance l between the reading lens 6 and the disk D in the direction of the arrow Y changes, how does the light reflected from the surface of the disk D at the spot by the auxiliary beam affect the differential detector DETd? This shows whether the situation is in a state where the situation is affected.

The detection force Sda from the differential detector DETd mentioned above is:
5 through a drive amplifier DRA to a drive mechanism DRU configured as, for example, a street wheel type, which drives the reading lens 6 to be displaced in the direction of the disk D, thereby controlling the automatic focus control device. is operating within the normal control operating range, the distance 2 between the disk D and the reading lens 6 is always in the normal state 1.

It performs auto-focusing operation so that the focus is maintained at the same level. The portion constituted by the differential detector DETd, the drive amplifier DRA, the l drive mechanism DR[J, etc., which have already been described in FIG. However, an automatic focus control device having only the above-mentioned components shown in FIG. When the reading lens 6 and the disk D approach each other outside the above-mentioned normal automatic control range, it is impossible to avoid the reading lens 6 colliding with the surface of the disk D. next. 1st
The portion of block AD indicated by a broken line frame in the figure will be explained.

The detection power Sda from the differential detector DETd is applied to a first comparator COMa, where a certain threshold value is determined. a
{see FIG. 2 a1}, a signal S as shown in FIG.
It is applied to the J input terminal.

Also. The detection output Sdl from the first detection element D1 in the differential detector DET described above is . Second comparator COM
b, where a certain threshold value V. d {second
The signal Scd as shown in FIG. 2D is obtained by comparing it with FIG. The master/slave mentioned above
It is applied to flip-flop MSFF as its clock signal, and it is also applied to flip-flop FF as its reset signal. The output signal Sca from the first comparator COM and the output signal Scd from the second comparator COMb are based on the threshold values Vca and VO set in the respective comparators COMa and COMb. By appropriately selecting the values, the distance between the reading lens 6 and the disk D can be controlled by the automatic focus control device depending on the relationship between the high level and low level states of both the output signals SOa and SO6. 6, and in a direction in which the reading lens 6 and the disk D approach each other, deviating from the normal control range. : Information for determining whether the re-lens is moving or vice versa, that is, determining the moving direction of the reading lens 6, can be obtained. A more specific explanation will be given below with reference to figures a to f.

From a state in which the distance ' between the reading lens 6 and the disk D is larger than that in the normal state 110, to a normal state 2.

After that, it becomes the regular state 1. If we consider the case where the distance l between the reading lens 4 and the disk D changes to a state smaller than First, in the former case described above, the first detection element D shown in FIG.
, the detected power Sdl from the second comparator COMb exceeds the threshold value Vcd set in the second comparator COMb.
The output signal S from b. b {Fig. 2 d} changes from a high level state to a low level state, and then the detection force Sda shown in Fig. 2 a from the differential detector DETd becomes the first
The output signal Sca from the first comparator COMa exceeds the threshold value Vca set in the comparator COMa of
Figure c) changes from a low level state to a high level state, and then the detection force Sd from the first detection element D,
is the threshold value Vc set in the second comparator COM6.
b or less, the output signal S from the second comparator COM6
O, changes from a low level state to a high level state, and the detection force Sd from the six differential detectors DET,
is the threshold value Vc set in the first comparator COMa.
From a to T, the output signal S from the first comparator COMa
ca changes from a high level state to a low level state. It is clear from the explanation with reference to FIGS. 2a to 2d above that the distance between the reading lens 6 and the disk D is outside the normal control range of the automatic focusing device, and the distance between the reading lens 6 and the disk D is When the reading lens is moving so that D approaches. Output signal S from the second comparator COM6.

The output signal Sc from the first comparator COMa when b changes from a low level state to a high level state
a is always at a high level. On the other hand, in the latter case described above, that is, when the distance between the reading lens 6 and the disk D gradually increases from a very small state, the output signal Sca from the first comparator COM is
The level change state is as shown in Figure 2 e,
Furthermore, since the state of change in the level of the output signal Sc6 from the second comparator COMb is as shown in FIG. The second comparator C when going
The first comparator C when the output signal Scb from OMb changes from a low level state to a high level state
The output signal Sca from OMa is always at a low level.

In this way, the output signal Sc from the second comparator COMb
The output signal Sca from the first comparator COMa at the time when the level of b changes from low level to high level.
, it is possible to determine whether the reading lens 6 is approaching abnormally close to the disk D according to whether the level of the reading lens 6 is at a high level or a low level. When the lens 6 and the disk D are abnormally close to each other, the upper limit value of the drive signal voltage supplied from the drive amplifier DRA to the drive mechanism DRU is limited so that the reading lens 6 is forcibly separated from the disk D. We are trying to make this possible. That is, in FIG. 1, the master-slave flip-flop MSFF has a low level applied to the K terminal (not shown), and a low level Q due to the reset at the time of starting the device (when the power is turned on).
Since the output terminal is set to low level, the output signal Sca from the first comparator COM is applied to the J terminal,
Also, the output signal S from the second comparator COM6 is connected to the second clock terminal.

b-, the reading lens 6 reads the disk D.
The output signal S from the first comparator COM, abnormally approaches 6. When the state of a is high level, the second comparator COM
When the state of the output signal Scb from 6 changes from low level to noq level, a high level control signal is sent from the Q output terminal to the drive signal voltage upper limit limit circuit ULC, and the upper limit is set by the control signal. Operate the limiter provided in the value limiting circuit ULC. Thereby, the maximum voltage value of the drive signal to be supplied from the drive amplifier DRA to the drive mechanism DRU is limited so that the reading lens 6
can be prevented from approaching. In addition, the limiter provided in the above upper limit value limiting circuit ULC changes the mode of limiting the maximum voltage value of the drive signal by the limiter 6, so that when the limiter operates to limit the drive signal voltage, the limiter It is also possible to apply a drive signal to the drive mechanism DRU from the drive amplifier DRA so as to drive the drive mechanism DRU in the direction of moving the disk 6 away from the disk D.

FIG. 3 is a block circuit diagram showing an example of the configuration of a six upper limit value limiting circuit ULC and its related parts. In this FIG. is applied to the base via a resistor Ra, a capacitor C is connected between the collector and emitter of the above transistor T, and a resistor R is connected between the collector and the positive voltage source +B. l! :． It consists of an amplifier A1 with low output and impedance, and a diode Dl, and the emitter of the transistor T is connected to a negative voltage source -B.
is connected at a point in the drive amplifier DRA exhibiting a relatively high impedance.

The connection polarity of the tie auto Dl is determined by the polarity of the drive signal supplied to the drive mechanism U and the reading lens 6 by the drive mechanism DRU.
In the illustrated example, the connection polarity of the diode D2 is such that the reading lens 6 is moved in the direction closer to the disk D by the drive mechanism DRU when the 6 drive signal or the polarity is positive. An example is shown in which the maximum value of the positive polarity of the drive signal voltage is limited by a limiter formed by a diode Dl and an amplifier A1 having a low output impedance. In the example shown in FIG. 3, the drive amplifier DRA consists of six amplifiers A2 to A
The detection force Sda from the differential detector DA is applied to the drive mechanism DRU via an amplifier A2, a resistor R66, an amplifier M, etc. The drive signal voltage supplied to the first drive mechanism DRU is limited by the limiter means of the upper limit limit circuit LILC described above, and the output signal from the flip-flop FF is The configuration is such that a drive signal can also be generated by the system. Now, when the device is turned on and the disk D, which has a static surface distortion, starts rotating, a large surface deflection occurs on the disk D until it reaches high speed rotation. As described above, unless the reading lens 6 is separated from the disk D at the start of rotation of the six disk D, collision between the surface of the six disk D and the reading lens 6 is likely to occur.

Then, when disk D starts rotating at high speed,
The flatness of the disk D is improved by the action of centrifugal force and the action of air flow between the disk D and the stabilizing plate, so when the rotation of the take D starts, the reading lens 6 is moved toward the disk D. It is desirable that the automatic focus control system start operating when the 6-disc D reaches normal high-speed rotation by moving it away from the disk surface. Referring to FIGS. 1 and 3, the operation of the apparatus when power is turned on will be described as follows.

When the power is turned on. Since the potential of the capacitor C in the upper limit limiting circuit ULC is negative, when the power is turned on, the negative potential of the capacitor C is applied to the drive amplifier DRA via the amplifier A1 and the diode De, and the drive signal becomes negative polarity, and the drive mechanism DRU drives and displaces the reading lens 6 in a direction to separate it from the surface of the disk D, thereby separating the reading lens 6 from the surface of the disk D. The potential of the capacitor C mentioned above is determined by the resistance R configured between the +B power supply and the -B power supply.
The potential of the upper limit limiting circuit ULC, which is applied to the cathode side of the diode Dl, is higher than that of the anode of the diode Dl. The upper limit limiting circuit ULC and the drive amplifier DRA are electrically disconnected by the diode Dl being turned off at that time. The condition shall be maintained.

In addition. The discharging operation of the capacitor C of the time constant circuit described above is performed when the transistor T is conducting. The drive signal given to the drive mechanism DRU from the drive amplifier DRA by the operation of the upper limit limit circuit ULC as described above at the time of power-on is also given to the third comparator COMc, and this third comparison The device COMO obtains information that the reading lens 6 has been separated from the disk D by comparing the signal level of the drive signal described above with the threshold value set in the third comparator COMO, and outputs the information. A signal is given to the master/slave flip-flop MSFF and flip-flop FF.

The master-slave flip-flop MSFF is set by the output signal from the third comparator COMe, and the flip-flop FF is set by the output signal from the third comparator COMO.

The aforementioned master-slave flip-flop MSFF
Due to the reset operation, its Q output terminal is brought to a low level state. Further, the setting operation of the flip-flop FF is performed by applying the output signal from the flip-flop FF to the drive amplifier DRA, thereby controlling the drive signal supplied from the drive amplifier DRA to the drive mechanism DRU. The driving of the reading lens 6 by the drive mechanism DRU allows the reading lens 6 to approach the surface of the disk D, thereby making it possible to carry out a device force phase movement return operation. That is, the upper limit limit circuit ULC. and its related circuits, the reading lens 6 is moved to the disk D.
When the upper limit limit circuit LC is electrically disconnected from the drive amplifier DRA after the disk D is greatly separated from the disk surface, the light reflected from the disk D of the spot by the auxiliary beam is detected by differential detection. Since it is outside the detection area of the differential detector DETd, the detection force Sd from the differential detector DETd
a has a polarity and size preset for the detection elements Dl, D and the differential amplifier DA, and is usually set to have a polarity in a direction that moves the reading lens 6 away from the disk D. A lot. Therefore, in such a case, simply electrically disconnecting the upper limit value limiting circuit ULC from the drive amplifier DRA as described above will leave the automatic focus control device in a state where it cannot perform normal automatic focusing operation. This is because it will be done. So 6 third comparator COM
The flip-flop FF is set by the output signal from O. The output of the flip-flop FF is driven by the amplifier DRA.
The drive amplifier DRA supplies the drive signal to the drive mechanism DRU so that the reading lens 6 can approach the surface of the disk D.

As the reading lens 6 gradually approaches the disk D from the position where it is largely separated from the disk D by the above operation, the normal detection force Sda is applied from the differential detector DETd. , then the second comparator COM
The output signal Scb from the output terminal Scb changes from a high level state to a low level state as shown in FIG. 2d. As mentioned above, when the output signal Scb from the second detector COMb changes from a high level state to a low level state, the flip-flop FF is reset and the automatic focus control device 6 adjusts the automatic focus in the normal control operation range. It is used to perform control operations. and. Reading lens 6
is abnormally close to disk D, and the second comparator COMb
When the output signal Scb from the 6 master-slave flip-flop MSFFOQ changes from low level to high level, the output terminal of 6 master-slave flip-flops MSFFOQ becomes high level.
Upper limit value 111 The transistor Tr in the limiting circuit ULC becomes conductive, thereby discharging the capacitor C, and at the same time -
The voltage of the B power supply is applied to the cathode side of the diode Dl via the amplifier A1. The drive signal of the drive amplifier DBA is limited in its upper limit 6, and the operation of the drive mechanism DRU thereby prevents the reading lens 6 from colliding with the disk D, and then the output from the third comparator COMO is When a signal occurs, the master/slave
At the same time that flip-flop MSFF is reset, flip-flop FF is also set, and the automatic return operation as described above is performed.

Figures 4a to 4f are diagrams for illustrating and explaining the above-mentioned series of operating states in the automatic focus control device of the present invention, in which the horizontal axis is time and Figure 4a is The vertical axis in is the distance l between the reading lens 6 and the disk D (in the upper part of the figure, the interval l is small, and in the lower part of the figure, the interval j is large), and the fourth
The vertical axis in Figures b to f is the voltage value. In Figure 4, as an example, the distance between the reading lens 6 and the disk D changes from a normal state (l = 10) to a state where l < 10.
>10 (Fig. 4a) Change in the detection force Sda from the differential detector DETd (Fig. 4b)
Changes in the outputs S and l of the detection element D1 {Figure 4 c} 6th
Changes in the output signal SOa of the second comparator COMa {Fig. 4 d}, changes in the output signal SO6 of the second comparator COMb {Fig. 4 e}, and the Q output of master-slave flip-flop MSFF (7). Terminal potential change {Fig. 4 f}
are shown respectively. As is clear from the detailed explanation above, in the automatic focus control device of the present invention, the detection force of one detection element in the differential detector is related to the detection force of the other detection element. By comparing, it is possible to accurately detect the point at which the reading lens deviates from the detectable area and enters a dangerous area close to the disk surface, and based on the detection result, it is possible to forcibly change the reading lens. It is possible to prevent the reading lens from colliding with the disk surface by driving it away from the disk surface, and by controlling the retraction using a time constant circuit, it is possible to use a servo system with high sensitivity and a narrow detection range. According to the present invention, it is possible to perform a stable retracting control operation even in the case of 6, and it is also possible to perform an automatic return operation after the distance between the reading lens and the disk is forcibly separated. All the problems in the existing proposals are successfully solved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one embodiment of the automatic focus control device of the present invention, FIGS. 2 a-f and 4 a-f are operational characteristic diagrams for explanation, and FIG. FIG. Dl, D2...First and second detection elements. DET
d. ．． ．． ...Differential detector, DA...Differential amplifier, COMa, COMb, COMO...1st.
Second and third comparators, DRA...drive amplifier.
DRLI...Drive mechanism, MSFF...1...Master slave ●Flip-flop, FF...
Flip-flop, Dl...Diode, A,
~A4...Amplifier. ULC...Upper limit limit circuit, T,...Transistor, R, Ra,
Rb...Resistor, C...Capacitor. 1
... Laser light source, 2 ... Beam splitter, 5 ... Half mirror. 6...Reading lens.

Claims (1)

[Scope of Claims] 1. The distance between the reading lens for reading the information signal of the information recording medium disc and the information recording medium disc is a part of each other's detection area so that the same detection force can be exerted in a normal state. a first detection element that has an overlapping portion and produces the maximum detection force when the distance between the reading lens and the information recording medium disc is closer than in a normal state; and the reading lens and the information recording medium disc. A state in which the distance between the reading lens and the information recording medium disc in the differential detector is configured to include a second detection element that produces the maximum detection force when the distance is more distant than in the normal state. Due to the interaction between the state of the signal obtained based on the detection force in a state closer than The direction of movement of the reading lens is determined, and when the reading lens and the information recording medium disk deviate from the detection area in a direction where the distance between the reading lens and the information recording medium disk becomes closer than in the normal state, the reading lens is forced to move away from the information recording medium disk surface. An automatic focus control device in an optical reproducing device for an information recording medium disk, which limits the upper limit value of a drive signal voltage applied to a drive system of a reading lens so that the reading lens moves away from the drive system. 2. The reading lens for reading the information signal of the information recording medium disk and the information recording medium disk have an overlapping part in a part of their detection areas so that the distance between the information recording medium disk and the information recording medium disk is equal to each other in a normal state. , a first detection element that produces the maximum detection force when the distance between the reading lens and the information recording medium disc is closer than the normal state; When the distance between the reading lens and the information recording medium disk in a differential detector including a second detection element that produces the maximum detection force when they are separated from each other is closer than in the normal state. The direction of movement of the reading lens is determined by the correlation between the state of the signal obtained based on the detected force of the sensor and the state of the signal obtained based on the detected force from the first detection element in the differential detector. If the distance between the reading lens and the information recording medium disk deviates from the detection area in a direction that is closer than the normal state, the reading lens is forced to move away from the information recording medium disk surface. In an automatic focus control device in an optical reproducing device for an information recording medium disc, which limits the upper limit of the drive signal voltage given to the drive system of the Based on the signal indicating the separated state, a drive signal is given to the drive system of the reading lens to forcibly bring the reading lens closer to the information recording medium disc surface, and the reading lens and the information recording medium disc are connected. An automatic focus control device in an optical reproducing device for an information recording medium disc, which restores the spacing to a normal state.