JPH0261829A - Focusing servo circuit - Google Patents

Abstract

PURPOSE:To detect the step out of focusing servo by employing constitution in which an offset is added on a signal related to a difference signal based on the output of a level comparator. CONSTITUTION:When a sum signal Y goes within the range of reference level L of the level comparator 15, the output of the comparator 15 is sent to an offset part 19, and a prescribed offset is supplied to an adder 18. Thereby, the adder 18 adds the offset on a focusing error signal X' from a divider 14, and inputs the output of the divider to a phase compensation circuit 16. An actuator 7 is driven corresponding to the offset, and a convergence lens 4 is moved, which changes the incident light quantity of a quadripartite detector 9. When level change occurs after the offset is added, the out of focusing servo is not detected erroneously by deciding the change as the one due to the reduction of the optical reflectance of an optical disk 6 even when the level of the sum signal Y is lowered. Also, when no level change occurs, the level change of the signal X' is detected, and correction by the pull-in of a lens 4 is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a focus servo circuit for obtaining a focused point of coherent light on the surface of an optical disk.

[Conventional technology]

FIG. 7 is a block diagram of a conventional focus servo circuit of this type. The laser beam from the laser diode 1 passes through a convex lens 2. The light is projected onto an optical disk 6 rotated by a motor 5 through a half mirror 3 and a focusing lens 4, and the focusing lens 4 is movable in the optical axis direction by an actuator 7. The reflected light of the laser beam projected onto the optical disk 6 passes through a focusing lens 4 and is reflected by a half mirror 3, and then passes through a cylindrical lens 8 and enters a four-part detector 9. The outputs of the four-division detector 9 are input to amplifiers 10 and 11, respectively. The output of the amplifier 10 is connected to the positive input terminal 12 of the differential amplifier 12.
a and one side input terminal 13a of the summing amplifier 13. The output of the amplifier 11 is input to the negative input terminal 12b of the differential amplifier 12 and the other input terminal 13b of the summing amplifier 13. Both the difference signal X and the sum signal Y, which are the outputs of the differential amplifier 12 and the summing amplifier 13, are input to the divider 14, and the sum signal Y is input to the level comparator 15.

The level comparator 15 outputs a focus servo out-of-focus signal S when the level of the input sum signal Y is within a reference level range. The output of the divider 14 is sent to a phase compensation circuit 16 that stabilizes the focus servo.
The output is inputted to the actuator driving amplifier 17, and the output is given to the actuator 7.

Next, the operation of this focus servo circuit will be explained. A laser beam emitted by a laser diode 1 is turned into parallel light by a convex lens 2, passes through a half mirror 3, and is focused onto the surface of an optical disk 6 by a focusing lens 4. The laser beam reflected by the optical disk 6 passes through a cylindrical lens 8 and is focused on a four-part detector 9. The output of the four-division detector 9 is amplified by an amplifier 10.11 and input to a differential amplifier 12 and a summing amplifier 13. As a result, the differential amplifier 12 outputs a difference signal X between the outputs of the amplifiers 10 and 11, and the summing amplifier 13 outputs a difference signal X between the outputs of the amplifiers 10 and 11.
A sum signal Y, which is the sum of each of the 11 outputs, is output. These difference signal X and sum signal Y are input to the divider 14, and the divider 1
4 outputs a normalized focus error signal X' by dividing the difference signal X by the sum signal Y in order to remove level changes in the difference signal . In order to stabilize the servo system, this focus error signal
The output of the amplifier 17 corresponding to ' is applied to the actuator 7 to move the focusing lens 4, thereby performing focus servo so that the laser beam is always focused on the surface of the optical disk 6.

Also, the level of N(f number y is determined by the level comparator 15
When the level falls within the reference level range set in , the level comparator I5 outputs a focus servo out signal S0, which is given to, for example, a display unit to notify that the focus servo is out.

Note that the levels of the difference signal X and the sum signal Y are based on the optical disc 6.
FIG. 8(a)
, as shown in (b), the voltage level of the difference signal X linearly increases toward the positive or negative voltage side as it deviates from the in-focus distance, and the voltage level of the sum signal Y gradually decreases in a curved manner. do.

[Problem to be solved by the invention]

As mentioned above, the conventional focus servo circuit uses the fact that the level of the sum signal Y decreases when a focus shift occurs to determine if the focus servo is off, and the level of the sum signal Y is determined by the level comparator. When the value falls within the reference level L of No. 15 (see FIG. 8(b)), a focus servo out signal S0 is output to notify abnormality in the focus servo operation.

Incidentally, the light reflectance of an optical disc differs among individual optical discs made by the same manufacturer, and also varies greatly depending on the manufacturer of the optical disc. Therefore, when a laser beam is projected onto an optical disk with extremely low light reflectance, the amount of reflected light decreases, so the sum signal level Y
For example, the signal is as shown by the broken line in FIG. 8(b), and is significantly lower than the level of the high-level sum signal Y shown by the solid line. When the level of the sum signal Y falls within the range of the reference level L of the level comparator 15, there is a problem in that the focus servo out signal SD is output and focus servo out is erroneously detected. Therefore, as mentioned above, when the optical reflectance of the optical discs differs, there is the trouble of having to perform an operation to lower the reference level L of the level comparator 15 to correspond to the optical reflectance each time the optical disc is replaced. .

In view of such problems, the present invention aims to provide a focus servo circuit that does not erroneously detect focus servo failure due to differences in light reflectance of optical disks, and does not require the troublesome operation of changing the reference level of a level comparator. purpose.

[Means to solve the problem]

A focus servo circuit according to a first aspect of the present invention includes an offset setting section for setting a required offset, and a sum signal obtained in relation to reflected light from an optical disk, and when the level is within a predetermined level range. and a level comparator that emits an output, and based on the output of the level comparator, an offset is added to a signal related to a difference signal obtained in relation to the reflected light from the optical disk.

A focus servo circuit according to a second aspect of the invention includes an offset setting section capable of outputting a required offset, and a level comparator to which a signal related to a difference signal obtained in relation to reflected light from an optical disk is manually input, When the offset error is added to a signal related to the difference signal, if the input signal of the level comparator is within a predetermined level range, an output indicating that the focus servo is off is generated.

A focus servo circuit according to a third aspect of the invention includes an offset general constant section capable of outputting a required offset, and a level comparator to which a signal related to a difference signal obtained in relation to reflected light from an optical disk is input. In addition, when the offset is added to a signal related to the difference signal, if the human input signal of the level comparator is outside a predetermined level range, an output indicating that the focus servo is off is generated.

A focus servo circuit according to a fourth aspect of the invention is provided with an address detection circuit that receives a track address reproduction signal of an optical disc and outputs an output when the track address reproduction signal is not detected, and detects reflected light from the optical disc based on the output. The configuration is such that an offset is added to a signal related to the difference signal obtained based on.

A focus servo circuit according to a fifth aspect of the invention includes an offset setting section capable of outputting a required offset, a level comparator to which a sum signal related to reflected light from an optical disk is input, and/or a track address reproduction signal of an optical disc. and a control section to which the output of the level comparator and/or the output of the address detection circuit is input, and the output of the level comparator and/or The control unit is configured to add an offset to a signal related to a difference signal based on reflected light from the optical disk when the output of the address detection circuit is input.

[Effect]

In the first invention, a required offset is set in the offset setting section. Input the sum signal to the level comparator. The level comparator provides an output when the sum signal is within a predetermined level range. Adding an offset to the signal related to the difference signal based on the output of the level comparator.

In the second invention, a required offset is set in the offset setting section. Input the difference signal to the level comparator. An offset is added to the signal related to the difference signal, and when the input signal of the level comparator is within a predetermined level range, the level comparator outputs an output indicating that the focus servo is off.

In a third aspect of the invention, a required offset is set in the offset setting section. Input the difference signal to the level comparator. An offset is added to the signal related to the difference signal, and when the input signal of the level comparator is outside a predetermined level range, the level comparator outputs an output indicating that the focus servo is off.

In a fourth aspect of the invention, a track address reproduction signal of an optical disc is input to an address detection circuit. The address detection circuit generates an output when the track address reproduction signal is not detected.

An offset is applied to a signal related to the difference signal based on the output of the address detection circuit.

In the fifth invention, a required offset is set in the offset setting section. Input the sum signal to the level comparator. A track address reproduction signal of the optical disc is input to the address detection circuit. Level comparator output and/or
Or input the output of the address detection circuit. An offset is added to the signal related to the difference signal when the output of the level comparator and/or the output of the address detection circuit is input.

This prevents erroneous detection of focus servo failure even if the optical discs have different light reflectances.

〔Example〕

The present invention will be described in detail below with reference to drawings showing embodiments thereof.

FIG. 1 is a block diagram of a focus servo circuit according to the present invention. A laser beam from a light source, for example a laser diode 1, is transmitted through a convex lens 2. An optical disk 6 is rotated by a motor 5 through a half mirror 3 and a focusing lens 4.
The focusing lens 4 is movable in the optical axis direction by an actuator 7. The reflected light of the laser beam projected onto the optical disk 6 and reflected by the optical disk 6 passes through the condenser lens 4 and is sent to the half mirror 3.
After being reflected, the light passes through a cylindrical lens 8 and enters a four-part detector 9 .

The outputs of the four-division detector 9 are input to amplifiers 10 and 11, respectively. The output of the amplifier 10 is input to the positive input terminal 12a of the differential amplifier 12 and the one side input terminal 13a of the summing amplifier 13. The output of the amplifier 11 is connected to the negative input terminal 12b of the differential amplifier 12 and the other input terminal 1 of the summing amplifier 13.
3b, respectively. Both the difference signal X and the sum signal Y, which are the outputs of the differential amplifier 12 and the summing amplifier 13, are input to the divider 14, and the output of the divider 14 is input to the adder 1.
8 and a second level comparator 20. Further, the sum signal Y is input to the first level comparator 15, and this level comparator 15 has an eighth
As shown in Figure (b), a reference level L is set at which the focus servo range can be detected. The output of this level comparator 15 is input to an offset setting section 19 that can set and output a required offset (DC voltage) in advance. The output of this offset setting section 19 is input to an adder 18, and the output is input to a phase compensation circuit 16 that compensates for the phase lead in order to stabilize the focus servo, and the output is input to an amplifier 17 for driving the actuator. I am typing. The second level comparator 20 has a level change range as shown in FIG. 8 (al) of the focus error signal
Reference level LF as shown in .

LP is set. and level comparison 20
A normal signal Su, which is output when the level of the focus error signal The abnormality signal S, which is output when The output of the pull-in control section 2I is input to the amplifier 17. The output of the amplifier 17 is applied to the actuator 7 which moves the focusing lens 4.
is given to.

Next, the operation of the focus servo circuit configured as described above will be explained. The laser light emitted by the laser diode I is turned into parallel light by a convex lens 2, passes through a half mirror 3, and is focused onto the surface of an optical disk 6 by a focusing lens 4. The laser beam reflected by the optical disk 6 passes through a cylindrical lens 8 and is focused on a four-part detector 7.

The output of the four-division detector 7 is amplified by an amplifier 10.11 and input to a differential amplifier 12 and a summing amplifier 13, respectively. As a result, the differential amplifier 12 has an amplifier 10°If
outputs a difference signal X, which is the difference between the respective outputs of
3 outputs a sum signal Y which is the sum of the respective outputs of the amplifiers 10 and 11. These difference signal X and sum signal Y are input to the divider I4, and the divider 14 sums the difference signal A focus error signal XL normalized by dividing by the signal Y, that is, a signal related to the difference signal X, is output.

This focus error signal X' is input to the phase compensation circuit 16 via the adder 18 to perform phase advance compensation to stabilize the servo system, and then input to the amplifier 17 where it is amplified to an output capable of driving the actuator 7. be done. Then, the output of the amplifier 17 is applied to the actuator 7, and the focusing lens is moved in accordance with the focus error signal X', thereby performing focus servo to always obtain a focused point of the laser beam on the optical disk 6.

However, if the optical disc 6 currently in use is replaced with an optical disc 6 made by a different manufacturer and having a lower light reflectance, for example, the amount of light incident on the four-split detector 9 will decrease. Therefore, the level of the sum signal Y decreases as shown by the broken line in FIG. When the level is within the L range, the level comparator 15 outputs an output and inputs it to the offset setting section 19. Then, the offset setting section 19 outputs the offset (DC voltage) set in advance to it and inputs it to the adder 18. As a result, the adder 18 receives the focus error signal X' from the divider 14.
An offset is added to the output signal and the output thereof is input to the phase compensation circuit 16. Therefore, the actuator 7 is driven in accordance with the offset, the focusing lens 4 is moved, and the amount of light incident on the four-split detector 9 is changed. Also, as a result, both the difference signal X and the sum signal Y change, and if the focus servo is not out of focus, the level of the focus error signal X' changes in accordance with the added offset, and the level of the focus error signal X' changes. When the reference level LP of the level comparator 20 becomes out of the LP range, the level comparator 20 gives a normal signal SIJ to the offset setting section 19 to stop outputting the offset, and focus servo is properly performed. That is, by adding an offset to the focus error signal X', the focus error signal
When the level change occurs, even if the level of the sum signal Y decreases, the focus servo failure will not be erroneously detected as being caused by a decrease in the light reflectance of the optical disk 6.

On the other hand, even if an offset is added to the focus error signal X', the level of the focus error signal X' does not change, and the reference levels LF and L of the level comparator 20
If it is within the P range, the level comparator 20 outputs an abnormal signal S. is applied to the retraction control unit 21, and the retraction control unit 21 inputs a control signal to the amplifier 17 to cause the focusing lens 4 to be retracted a predetermined distance. This causes actuator 7
is driven, and the focusing lens 4 moves to perform retraction. In other words, if the level of the focus error signal X' does not change after adding an offset to the focus error signal X', a drop in the level of the sum signal Y and no change in the level of the focus error signal X' means that the focus servo is off. will be detected. Thereby, the focusing lens 4 is retracted in order to eliminate focus servo deviation.

Therefore, with this focus servo circuit, even if the optical discs have different light reflectances, there is no false detection of focus servo failure, and even if the optical disc is replaced with an optical disc with a different light reflectance, focus servo can always be performed properly. obtain. Furthermore, there is no need to change the reference level of the level comparator to which the sum signal is input in order to detect focus servo deviation every time the optical disk is replaced, and the troublesome operation is eliminated.

FIG. 2 is a circuit diagram of a focus servo circuit according to the second invention. An offset addition command unit 25 is provided to output a command to add an offset at an appropriate time, for example, at the beginning of driving the focus servo circuit, and is configured to provide the output to the offset setting unit 19. The other circuit configuration is the same as the circuit shown in FIG. 1 except that only the level comparator 15 is removed. Therefore, after inputting the offset to the adder 1, if the level of the focus error signal By inputting this into the retraction control section 21 and retracting the focusing lens 4, the same effect as described above can be obtained.

FIG. 3 is a block diagram of a focus servo circuit according to the third invention. In the focus servo circuit of the third invention, the input side of the level comparator 20 in FIG.
This is a circuit in which the connection is changed to the output side of the circuit, and the other circuit configuration is the same as that in FIG. FIG. 4 is an explanatory diagram when out-of-focus is detected by the focus servo circuit of FIG. 3.

In this focus servo circuit, when the focus is out of focus, the actuator 7 that pulls the focus does not operate even if an offset is applied, as in the case where the input side of the level comparator 20 is connected to the input end of the adder 18. It's the same. However, the output signal of the adder 18 after adding an offset to the level comparator 20, or the output signal of the phase compensation circuit 16, the divider 14, or the amplifier 17, depending on the connection position on the input side of the level comparator, which will be described later. signal is input. therefore,
The condition for out-of-focus is when the input signal level of the level comparator 20 is outside the reference level LP and the LP range (see FIG. 4). When the focus is retracted, the actuator 7 moves to cancel the added offset, and the output of the adder 18 becomes zero, that is, the reference level LP, within the LP range, and the input side of the adder 18 becomes zero. Out-of-focus is detected in the same way as when the input side of the level comparator 20 is connected.

FIG. 5 is a focus servo circuit diagram according to the fourth invention. A trunk address reproduction signal AD of the optical disk is input to an address detection circuit 22, and this address detection circuit 22 is configured to output an output when the trunk address reproduction signal AD is not detected. The output of this address detection circuit 22 is input to the offset setting section 19. The other circuit configuration is the same as the circuit shown in FIG. 1 except that only the level comparator 15 is removed.

In this focus servo circuit, when the track address reproduction signal AD of the optical disk is no longer detected by the address detection circuit 22 due to focus servo failure, the address detection circuit 22 emits an output, inputs the output to the offset setting section 19, and offsets is given to the adder 18. If the level of the focus error signal X' after applying the offset is within a predetermined level range set in the level comparator 20, an abnormality signal S, which is a focus servo out signal, is output and the focusing lens 4 is reactivated. It performs retraction and operates in the same manner as described above to obtain the same effect. In this case, if an optical disc that is not affected by changes in the light reflectance of the optical disc and has a very low light reflectance is used, the circuit that inputs the sum signal Y to the level comparator 15 will not be affected by the change in the light reflectance of the optical disc. Since the reference levels set in the level comparators are both low, the sum signal level is often disturbed by disturbances to the focus servo system, and an offset must be added each time. Therefore, even with the method of adding the same offset, it is more practical to determine whether a track address reproduction signal is detected than to observe the level of the sum signal Y.

FIG. 6 is a circuit diagram of a focus servo circuit according to the fifth invention. A track address reproduction signal AD of the optical disc is input to the address detection circuit 22. Address detection circuit 2
Reference numeral 2 outputs an output when the track address reproduction signal AD is not detected, and the output is input to a control section 23 consisting of, for example, a microcomputer. The output of the address detection circuit 22 and/or the level comparator 15 is input to the control section 23 . Further, the output of the control section 23 is input to the offset setting section 19 and the pull-in control section 21. The other circuit configuration is the same as the circuit shown in FIG. In this circuit, the control section 23 selects whether to use the output of the level comparator 15 and/or the output of the address detection circuit 22 and inputs the output to the offset setting section 19, and also uses the input from the level comparator 20 to input the output to the offset setting section 19. The same effect is obtained by controlling to stop the output of the offset and operating in the same manner as described above.

In this circuit, the level comparator 20 to which the focus error signal X' is inputted only needs to determine the magnitude relationship between the focus error signal X' and the predetermined level set in the level comparator 20; A level comparator 20 whose control operation can be performed by the control unit 23 and into which the focus error signal X' is input.
The circuit scale can be reduced.

Note that in this embodiment, when the focus servo is detected to be out of focus, the retraction control section 21 is operated for control, but this is merely an example and is not limited to this configuration.

Furthermore, in this embodiment, the input side of the level comparator 20, into which the signal related to the difference signal X is input, is directly connected in close proximity to the input side of the adder 18; If the conditions are met, there is no problem even if another circuit is interposed between the input terminal of the level comparator 20 and the adder 18. Further, the same effect can be obtained by locating the input side of the level comparator 20 and the adder 18 at appropriate positions in the circuit from the differential amplifier 12 to the amplifier 17. However, it is desirable to change the reference level of the level comparator 20 depending on the connection position of the input end of the level comparator 20. Furthermore, when the input side of the level comparator 20 is connected to the output side of the adder 18, the connection position can be changed in the same manner as described above, and the same effect can be obtained.

[Effects of the Invention] As described in detail above, according to the first invention, defocus can be detected by adding an offset to the signal related to the difference signal based on the level of the sum signal. According to the second invention, when an offset is added to a signal related to the difference signal, out-of-focus can be detected if the signal related to the difference signal is within a predetermined level range. According to the third invention, when an offset is added to a signal related to the difference signal, out-of-focus can be detected if the signal related to the difference signal is outside the predetermined level range. According to the fourth invention, out-of-focus can be detected by adding an offset to the signal related to the difference signal based on the output of the address detection circuit. According to the fifth invention, out-of-focus can be detected by adding offset I to a signal related to the difference signal based on the output of the address detection circuit and/or the level comparator.

Therefore, even when the level of the sum signal is low, focus servo failure is not erroneously detected. In addition, it is an excellent method that can provide a highly reliable focus servo circuit, such as eliminating the need for troublesome operations such as changing the reference level to detect focus servo deviation each time when the optical reflectance of the optical disc differs. be effective.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the focus servo circuit according to the first invention, FIG. 2 is a block diagram of the focus servo circuit of the second invention, FIG. 3 is a block diagram of the focus servo circuit of the third invention, and FIG. FIG. 3 is an explanatory diagram of detecting out-of-focus by using the focus servo circuit, FIGS. 5 and 6 are block diagrams of the focus servo circuit of the fourth and fifth inventions, and FIG. 7 is a conventional one. The block diagram of the focus servo circuit, FIGS. 8(a) and 8(b), are curve diagrams showing the relationship between the voltage levels of the difference signal and the sum signal with respect to the focal point distance. 1... Laser diode 3... Half mirror 4
...Focusing lens 6...Optical disk 9...
4-division detector 12... Differential amplifier 13...
Adding amplifier 14...X divider 15...Level comparator 17...Amplifier 18...Adder 19.
. . . Offset setting section 20 . . Level comparator 22 . . . Address detection circuit 21 . . . Pull-in control section 23 . Funeral diagram procedure amendment (method) % formula % 2, Name of the invention Focus servo circuit 3, Person making the amendment 5, Date of amendment order November 2, 1985 (Shipping mortar 63.11.29) 6.
In column 7 of “Brief explanation of drawings” of the specification to be amended, on page 27, line 13 of the specification of contents of the amendment, “Fig. 8 (a) and (b)
” is corrected to “Figure 8 is”. Representative Moriya Shiki 4, agent

Claims (1)

[Claims] 1. Obtaining a difference signal and a sum signal of signals related to reflected light of coherent light projected onto an optical disk, and obtaining a focal point of the coherent light on the surface of the optical disk in relation to the difference signal. A focus servo circuit that performs control, comprising: an offset setting section that can output a required offset; and a level comparator that receives the sum signal and outputs an output when its level is within a predetermined level range;
A focus servo circuit characterized in that it is configured to add an offset to a signal related to the difference signal based on the output of the level comparator. 2. A focus servo that obtains a difference signal and a sum signal of signals related to the reflected light of the coherent light projected onto the optical disc, and performs control to obtain a focused point of the coherent light on the surface of the optical disc in relation to the difference signal. The circuit includes an offset setting section that can output a required offset, and a level comparator to which a signal related to the difference signal is input, and when the offset is added to the signal related to the difference signal, the level A focus servo circuit characterized in that the focus servo circuit is configured to generate an output indicating that the focus servo is off when the input signal of the comparator is within a predetermined level range. 3. A focus servo that obtains a difference signal and a sum signal of signals related to the reflected light of the coherent light projected onto the optical disc, and performs control to obtain a focused point of the coherent light on the surface of the optical disc in relation to the difference signal. The circuit includes an offset setting section that can output a required offset, and a level comparator to which a signal related to the difference signal is input, and when the offset is added to the signal related to the difference signal, the level A focus servo circuit characterized in that the focus servo circuit is configured to generate an output indicating that the focus servo is off when the input signal of the comparator is outside a predetermined level range. 4. A focus servo that obtains a difference signal and a sum signal of signals related to the reflected light of the coherent light projected onto the optical disc, and performs control to obtain a focused point of the coherent light on the surface of the optical disc in relation to the difference signal. In the circuit, an address detection circuit is provided which receives a track address reproduction signal of the optical disc and outputs an output when the track address reproduction signal is not detected, and adds the offset to a signal related to the difference signal based on the output. A focus servo circuit characterized by a configuration. 5. A focus servo that obtains a difference signal and a sum signal of signals related to the reflected light of the coherent light projected onto the optical disc, and performs control to obtain a focused point of the coherent light on the surface of the optical disc in relation to the difference signal. The circuit includes an offset setting unit capable of outputting a required offset, a level comparator to which the sum signal is input, and/or a track address reproduction signal of the optical disc is input;
An address detection circuit that outputs an output when the track address reproduction signal is not detected, and a control section to which the output of the level comparator and/or the output of the address detection circuit is input, A focus servo circuit characterized in that, when an output of the address detection circuit is input, a control section adds the offset to a signal related to the difference signal.