JPS61187134A - Optical head - Google Patents

Abstract

PURPOSE:To correct the optic axis of an objective to perpendicular to a recording face by impressing specified voltage to a piezo-electric element that holds the objective according to a voltage signal outputted by inclination between the recording face and optic axis of the lens. CONSTITUTION:Four piezo-electric elements 28a-28d, piezo-electric elements for correcting inclination, are attached to the lower part of the substrate 21 of an objective driving device 20. On the other hand, a difference signal E corresponding to the amount of deviation is outputted from the track deviation detector of an optical head. The signal E is supplied to the correcting section 90 of a CPU, and an average value of positive and negative peak values are calculated, and at the same time, deviation of the average value and zero is taken by a comparator circuit 95, and a signal corresponding to the deviation is outputted. The output is impressed to above-mentioned piezo-electric elements 28a..., and shifted in the direction AB or BD. Thus, optical axis of the objective can be corrected to become perpendicular to the recording face at all times.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an optical head used in, for example, an optical disk device.

[Technical Background of the Invention] Conventionally, an objective lens used inside an optical head has been driven by an objective lens drive device as shown in FIGS. 11(a) and 11(b). There is. That is, the objective lens 71 consists of two parallel plate springs 72.7.
It is supported by 3.

These leaf springs 72 and 73 are fixed to an intermediate support fitting 74, and this intermediate support fitting 74 is connected to two diaphragm springs 7.
5.76 is now supported. A magnetic circuit formed by the coil 77 and the magnet 78 causes the intermediate support fitting, that is, the objective lens 71 to move in the vertical direction (
By being driven in the direction of arrow k (1 direction), force pulling is performed. In addition, coil 79
Tracking is performed by driving the objective lens 71 in the left and right directions (directions of arrows m and n) by a magnetic circuit constituted by the iron piece 80 and the iron piece 80.

[Problems with the background art] However, with the optical head as described above, if the optical axis of the objective lens and the recording surface of the optical disc deviate from perpendicularity due to the tilt of the optical disc, it cannot be corrected. . For this reason, if the optical axis of the objective lens and the recording surface of the optical disk deviate from perpendicular, the shape of the spot focused on the optical disk by the objective lens will deteriorate.1. Clean bits could not be formed on the recording surface of the optical disc. As a result, problems such as difficulty in reading data on the optical disk occurred.

In order to solve the above problem, we adopted an optical system that is resistant to tilting of the optical disk, and by inserting a spacer between the objective lens drive device and the optical system board, we can prevent the objective lens from tilting between the optical axis of the objective lens and the optical disk. The recording surface was vertical. However, in a strict sense, the optical axis of the objective lens and the recording surface of the optical disk are not perpendicular to each other over the entire surface of the optical disk.

[Object of the Invention] The present invention has been made in view of the above circumstances, and its object is to provide an optical head that allows the optical axis of the objective lens to be always perpendicular to the entire surface of the target object. Our goal is to provide the following.

[Summary of the Invention] In order to achieve the above object, the present invention irradiates an appropriate beam of light onto a target object by moving a holding member that fixes the objective lens left and right or up and down. The amount of inclination of the optical axis of the lens and the object plane of the target object from the perpendicular axis is detected, and the optical axis of the objective lens is corrected according to this amount of inclination.

[Embodiment of the Invention] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a schematic configuration of an optical head of the present invention. That is, the optical disk (target object) 1 is rotated by a motor (not shown) with respect to the optical head 3 at a constant linear velocity. The optical disc 1 has a donut-shaped metal coating layer such as tellurium or bismuth coated on the surface of a circular substrate made of glass or plastic, for example. An optical head 3 for storing and reproducing information is provided on the back side of the optical disc 1. This optical head 3 includes a semiconductor laser oscillator 4, a convex lens 5, a deflection beam splitter 6, a λ/4 plate 7, an objective lens 8, a half mirror 9, a condenser lens 10, 11, a photodetector 12 for detecting track deviation, It is composed of a photodetector 13 for detecting defocus. Further, a front-rear light shielding plate 16 is provided between the half mirror 9 and the condenser lens 11. The photodetector 12 includes a photodetection cell 1 that converts the light imaged by the condenser lens 10 into an electrical signal.
2a and 12b. The signals output by these photodetection cells 12a and 12b are as follows:
A γ signal and a δ signal are output, respectively. The photodetector 13 includes photodetection cells 13a and 13 that convert the light imaged by the condenser lens 11 into an electrical signal.
It is composed of b. These photodetection cells 13a
, 13b are the signals output by α
signal and β signal are output.

The objective lens 8 is driven by an objective lens driving device 2o shown in FIGS. 2 to 7. That is, a cylindrical holding frame 22 is provided above the substrate 21 with a central axis perpendicular thereto. A support shaft 23 is arranged along the central axis within this holding frame 22, and this support shaft 23 is made of piezoelectric resin and includes piezo elements (piezoresistance effect elements) 24a, 24b, which will be described later.
24C124d is supported by the holding frame 22.

Bimorph elements 25 and 26, which are piezoelectric resins to be described later, are provided extending parallel to each other in the same direction from both upper and lower ends of the support shaft 23. This bimorph element 25
．． A lens holding frame 27 in which the objective lens 8 is held is attached to the tip of the lens 26 . On the side of this lens holding frame 27, there is a rectangular prism-shaped bobbin 6 with a hollow inside.
o, 60 are provided parallel to the substrate 21. A coil 61 is wound around this bobbin 60, and this coil 6
A coil 62 is fixed to the upper surface of the coil 61 perpendicularly to the coil 61. Further, a U-shaped yoke 63, 63 is fixed on the substrate 21. This yoke 63.
In the middle part of 63, there is a permanent magnet 64.6 in the shape of a rectangular prism.
4 is provided, and this magnet 64 is loosely inserted into the cavity of the bobbin 60. The ends 65 and 66 of the yoke 63 are arranged to face the ends of the bobbin 60, respectively.

As a result, both the coils 61 and 62 are located in the magnetic field Bq generated by the permanent magnet 64 and the yoke 63. For example, as shown in FIG. 5, when a current is applied to the coil 62 in the Q direction, the coil 62 receives a force in the h direction, and this force is transmitted to the lens holding frame 27 via the bobbin 60. As a result, the objective lens 8 is moved in the directions of arrows e and f, thereby performing force-shinging. Further, as shown in FIG. 4, when a current is applied in one direction to the coil 61, the coil 61 receives a force in the j direction, and this force is transmitted to the lens holding frame 27 via the bobbin 60.

As a result, the objective lens 8 is moved in the direction of the arrow cSd, thereby performing tracking. In this way, the objective lens 8 can be driven in two directions, up and down and left and right, by the same magnetic circuit.

The bimorph elements 25 and 26 are shown in FIGS. 6(a) and 6(b).
As shown in (c), two piezo elements 25a each
, 25b, 26a, and 26b are pasted vertically.One of the two piezo elements contracts and the other expands, so that the lens holding frame 27 follows the movement up and down, that is, in the directions of arrows e and f. It is now possible to do so. For example, the lens holding frame 27, that is, the objective lens 8 is shown in FIG. 6(b).
As shown in FIG. 2, the bimorph elements 25 and 26 are bent downward by moving in the direction e from the state shown in FIG.
Piezo elements 25a and 26a contract, piezo element 25b,
26b is designed to extend. Further, as shown in FIG. 6(C), the lens holding frame 27, that is, the objective lens 8,
By moving in the direction f from the state shown in FIG.
5a.

26a extends, and piezo elements 25b and 26b contract.

As a result, by outputting the voltage values of the upper piezo elements 25a, 26a and the lower piezo elements 25b, 26b of the bimorph element 25, e% of the lens holding frame 27 is
It outputs a detection signal according to the movement position in the f direction, that is, the movement position of the objective lens 8. These upper piezo elements 25a, 26a, lower piezo elements 25b, 26
The signals output by b are the η signal and
A θ signal is output.

With this configuration, when the lens holding frame 27 is in a proper position, that is, when the upper piezo elements 25a, 26a and the lower piezo elements 25b, 26b are located parallel to the substrate 21, the upper piezo elements 25a, 26a and the lower piezo elements 25b and 126b each have the same value η.
signal and θ signal are output. Furthermore, if the lens holding frame 27 is shifted downward from the proper position, the upper piezo element 25a126a and the lower piezo element 25b126
The η signal and θ signal in the relationship “η signal × θ signal” are output from the signal b. Furthermore, if the lens holding frame 27 is shifted upward from the proper position, the upper piezo elements 25a, 26a and the lower piezo elements 25b, 26b
The η signal and the θ signal are output from the above, respectively, in the relationship “η signal>θ signal”.

The support shaft 23 is provided with four piezo elements 24a, 24b, 24c, and 24d arranged at equal angles from the center, as shown in FIGS. 7(a), 7(b), and 7(C). , these piezo elements 24a, . . .
3 is supported by the holding frame 22. As a result, when the piezo elements 24a1... contract as the lens holding frame 27, that is, the objective lens 8 moves in the direction of arrow C,
As shown in FIG. 71(b), the support shaft 23 rotates by a slight angle in the direction of arrow a from the state shown in FIG. 71(a). Due to this rotation, the piezo elements 24a1... output a voltage signal, that is, an ε signal according to the amount of movement thereof. Moreover, the piezo element 24a1...
When the lens holding frame 27, that is, the objective lens 8 moves in the direction of arrow d and extends, as shown in FIG. 7(C), the support shaft moves from the state of FIG. 23 is adapted to rotate by a minute angle. In the above case, although the amount of movement (displacement) of the objective lens 8 is large, the bimorph element 25 acts as a kind of lever arm, and the amount of rotation of the support shaft 23 is minute. Therefore, the bimorph element 25 transmits a large displacement of the objective lens 8 as a small displacement to the piezo element 24. Due to the movement of the piezo elements 24a in the directions a and b,
Movement in the tracking direction with respect to the optical disc 1 is detected. Thereby, by outputting the voltage values of the piezo elements 24a1, . . . , a detection signal corresponding to the movement position of the lens holding frame 27 in the C and d directions, that is, the movement position of the objective lens 8, is output.

Further, between the lower part of the substrate 21, that is, the optical head 3, and a linear motor 29 serving as a moving mechanism for moving the optical head 3 in the radial direction of the optical disk 1, there are four piezoelectric elements for tilt correction, such as piezo elements 28a, 28b, 28c, and 28cl. is provided. These piezo elements 28a, 28b, 2
By applying a predetermined voltage to 8c and 28d, they expand or contract individually, thereby tilting the substrate 21 in directions A, B or C, D, and aligning the optical axis of the objective lens 8 with the recording surface of the optical disc 1. It can be corrected so that it is perpendicular to . For example, ° piezo elements 28a, 2
8b expands due to a change in the applied voltage, and the piezo elements 28c,
When 28d shrinks due to changes in applied voltage, Fig. 3 (b
), the right side of the substrate 21 moves in the direction of the arrow, that is, upward, and the left side of the substrate 21 moves in the direction of the arrow, that is, downward, from the state shown in FIG. Furthermore, if the piezo elements 28a and 28b contract due to a change in the applied voltage, and the piezo elements 28c and 28d expand due to a change in the applied voltage, as shown in FIG. 3(C), the substrate changes from the state shown in FIG. The right side of the substrate 21 moves in the direction of arrow B, that is, downward, and the left side of the substrate 21 moves in the direction of arrow C, that is, upward.

Note that the piezo elements 24a..., 25a, 25b,
When the voltages 26a, 26b, 28a, 28b, 28c, and 28C1 are displaced by about 10 microns, for example, the voltage changes by 700 volts.

The output of the optical head 3, that is, each photodetection cell 12a, 1
The outputs of 2b, 13a, 13b are connected to the sohr amplifier 30.
．． Supplied to 3L34.35.

In addition, each piezo element 2 of the bimorph elements 25 and 26
5a, 26a and 25b, 26b (7) outputs are fed to amplifiers 32, 33, respectively. Furthermore, the outputs of the piezo elements 24a... are supplied to an amplifier 52. The outputs of the amplifiers 30 and 31 are supplied to a subtraction circuit 36 and an addition circuit 37, respectively.

The outputs of the amplifiers 32 and 33 are supplied to a subtraction circuit 38. The outputs of the amplifiers 34 and 35 are supplied to a subtraction circuit 39 and an addition circuit 40, respectively.

The output of the amplifier 52 is supplied to a comparison circuit 53.

The subtraction circuit 36 outputs a signal corresponding to the track deviation during normal tracking by taking the difference (γ signal - δ signal) between the detection signals from the photodetection cells 12a112b. The addition circuit 37 includes the photodetection cell 12
The sum of the detection signals from a and 12b is output as a read signal. The subtraction circuit 38 is
Piezo elements 25a, 26a and 25b, 26b
By taking the difference between the detection signals (η signal - θ signal @), the positional deviation of the objective lens 8 during high-speed access (
e, f direction).

The comparison circuit 53 outputs a signal corresponding to the positional deviation (c, d direction) of the objective lens 8, depending on whether the value from the amplifier 52 is larger or smaller than a predetermined value. This predetermined value is determined by the amplifier 52 when the objective lens 8 is in a fixed position.
It is equal to the value obtained from . The subtraction circuit 39 outputs a signal corresponding to defocus by taking the difference (α signal - β signal) between the detection signals from the photodetection cells 13a and 13b. The addition circuit 40 is
The sum of the detection signals from the photodetection cells 13a and 13b is output as a read signal.

Output of the above subtraction circuit 36.39 and addition circuit 37.4
The output of 0 is supplied to CPLJ41.

This CPU 41 controls the entire optical disc 1. At the time of initialization, the CPU 41 outputs an initial pull-in signal to the switching circuit 42 and switches the switching circuit 42 so that the initial pull-in signal is output. Also, C.P.
U41 outputs a switching signal to switching circuits 42 and 43 when determining high-speed access.

The output of the subtraction circuit 39 is shaped by a waveform shaping circuit 44 and supplied to the switching circuit 42. The output of the subtraction circuit 39 is shaped by a waveform shaping circuit 54 and supplied to the switching circuit 42. The above subtraction circuit 36
The output is shaped by a waveform shaping circuit 45 and supplied to the switching circuit 43. The output of the comparison circuit 53 is shaped by a waveform shaping circuit 51 and supplied to the switching circuit 43. As a result, the switching circuit 42
is determined by the switching signal from the CPU 41 at the initial time.
The initial pull-in signal supplied from the CPU 41 is output to the drive circuit 46, the signal supplied from the waveform shaping circuit 44 is outputted to the drive circuit 46 during normal times, and the signal from the waveform shaping circuit 54 is outputted during high-speed access. The signal is output to a drive circuit 46. Moreover, the switching circuit 43 is
Normally, the signal supplied from the waveform shaping circuit 45 is
When a switching signal is supplied from the CPU 41 (during high-speed access), the signal supplied from the waveform shaping circuit 51 is output to the drive circuit 47.

- The drive circuit 46 is configured to supply a corresponding current to the coils 62 . . . in response to a signal supplied from the switching circuit 42. The drive circuit 47 operates according to the signal supplied from the switching circuit 43.
A corresponding current is supplied to the coils 61.

Further, the output (E signal) of the subtraction circuit 36 is supplied to a correction section 90 that corrects the optical axis of the objective lens 8. This correction section 90 corrects the optical axis of the objective lens 8 by expanding or contracting the piezo elements 28a, . . . individually by changing the applied voltage. That is, as shown in FIG. 8, a positive peak detection circuit 91 detects the positive peak value of the tracking difference signal (E signal) supplied from the subtraction circuit 36, and a tracking difference signal supplied from the subtraction circuit 36. a negative peak detection circuit 92 that detects a negative peak value of a signal; and a pressure peak detection circuit 91
an average value calculation circuit 93 that calculates the average value of the peak values supplied from the corner peak detection circuit 92; an average value calculation circuit 94 that calculates the average value of the peak values supplied from the corner peak detection circuit 92; and the average value calculation circuit 93. A comparison circuit 95 calculates the average value of each average value supplied from 94, calculates the deviation between the calculated average value and "0", and outputs a signal corresponding to this deviation.
, a drive circuit 96 applies a voltage corresponding to each of the piezo elements 28a1 by a signal corresponding to the deviation supplied from the comparison circuit 95.

As a result, when a symmetric track difference signal as shown in FIG. 9(a) is supplied, the average of positive peak values and the average of negative peak values are the same, and the drive circuit is no longer supplied. Furthermore, when a track difference signal biased toward the positive side is supplied as shown in FIG. 9(b), the average value of the average of positive peak values and the average of negative peak values becomes positive, and this A positive deviation between the average value and rOJ is determined, and a signal corresponding to this deviation is output to the drive circuit 96. Furthermore, Fig. 9 (C
), when a track difference signal biased toward the negative side is supplied, the average value of the average of positive peak values and the average of negative peak values becomes negative, and this average value and "0" A negative deviation is determined, and a signal corresponding to this deviation is output to the drive circuit 96.

Next, the operation in such a configuration will be explained.

For example, the laser beam emitted from the semiconductor laser oscillator 4 is made into a parallel beam by the convex lens 5 and guided to the deflection beam splitter 6. The light beam guided to the deflection beam splitter 6 is reflected, then enters the objective lens 8 via the λ/4 plate 7, and is focused onto the optical disk 1 by the objective lens 8. In this state,
When storing information, bits are formed on tracks on the optical disk 1 by irradiation with a laser beam of high intensity (storage beam), and when reproducing information, a laser beam of low intensity (storage beam) is irradiated. (reproduction beam light) is irradiated. The reflected light from the optical disc 1 for this reproduction beam light is converted into a parallel light beam by the objective lens 8 and guided to the polarizing beam splitter 6 via the λ/4 plate 7 . At this time, the laser beam guided to the deflection beam splitter 6 is directed to the λ/4 plate 7
The plane of polarization is rotated by 90 degrees compared to when it is reflected by the polarization beam splitter 6. This results in
The laser beam passes through the deflection beam splitter 6 without being reflected, and is guided to the half mirror 9. The laser beam passing through this half mirror 9 is irradiated onto a photodetector 12, that is, photodetection cells 12a and 12b, via a condensing lens 1o, and is also transmitted via a triangular prism 14 to a photodetector 15,
In other words, the light detection cells 15a and 15b are irradiated with light. Also,
The laser beam reflected by the half mirror 9 passes through a condenser lens 11 to a photodetector 13, that is, a photodetection cell 13a.
, 13b. Therefore, the photodetection cell/L, 1
Signals corresponding to the irradiation light are output from 2a, 12b, 13a, and 13b, and these signals are sent to amplifiers 30 and 31, respectively.
, 34.35. Thereby, the addition circuit 37 sums up the detection signals from the photodetection cells 12a and 12b, and outputs the sum to the CPU 41 as a read signal. As a result, the CPtJ 41 reads data using the read signal from the adder circuit 37.

In the above state, the force pulling operation will be explained. That is, at the initial time, the CPU 41 supplies an initial pull-in signal to the drive circuit 46 via the switching circuit 42. Thereby, the drive circuit 46 supplies a predetermined current to the coil 62, and moves the lens holding frame 27, that is, the objective lens 8, in the e or f direction. Then, the CPU 41 determines that the subtraction result of the subtraction circuit 36 is "±0".
When this happens, it is determined that the objective lens 8 corresponds to the proper focal position, and the switching circuit 42 is switched.

As a result, the signal corresponding to the defocus output from the subtraction circuit 39, that is, the signal obtained by taking the difference between the detection signals from the photodetection cells 13a and 13b, is transmitted via the waveform shaping circuit 44 and the switching circuit 42. and is supplied to the drive circuit 46. Thereby, the drive circuit 46 supplies a predetermined current to the coil 62 according to the signal from the waveform shaping circuit 44, and the lens holding frame 27, that is, the objective lens 8
Alternatively, move in the f direction and perform normal force tweezing.

Next, the tracking operation will be explained.

That is, the signal corresponding to the track deviation during normal tracking from the subtraction circuit 36, that is, the photodetection cell 12a,
A signal obtained by taking the difference between the detection signals from 12b is supplied to the drive circuit 47 via the waveform shaping circuit 45 and the switching circuit 43. As a result, the drive circuit 47 supplies a corresponding current to the coil 61 in accordance with the signal from the waveform shaping circuit 45, and the lens holding frame 27, that is, the objective lens 8, is moved in the direction C or d, and normal tracking is performed. be exposed.

Next, the operation during high-speed access will be explained. That is, when high-speed access is determined by the CPLI 41, the CPU 41 switches the switching circuit 43.

As a result, a signal corresponding to the positional deviation (c, d direction) of the objective lens 8 from the comparator circuit 53, that is, the piezo element 24
A signal depending on whether the signal obtained from a1... is larger or smaller than a predetermined value is supplied to the drive circuit 47 via the switching circuit 43. Thereby, the drive circuit 47 supplies a corresponding current to the coil 61 in accordance with the signal from the comparison circuit 53, and the lens holding frame 27, that is, the objective lens 8,
Move in direction C or d so that it is in the fixed position. For example, when the output of the comparison circuit 53 is positive, the lens holding frame 27
is moved in the C direction, and when the output of the comparison circuit 53 is negative, the lens holding frame 27 is moved in the d direction.

Furthermore, when the CPU 41 determines that high-speed access is required, the CPU 41 switches the switching circuit 42 . As a result, a signal corresponding to the positional deviation (e%f direction) of the objective lens 8 from the waveform shaping circuit 54, that is, the piezo elements 25a, 26a1 and 25b of the bimorph element 25, 26,
A signal obtained by taking the difference from 26b is supplied to the drive circuit 46 via the switching circuit 42. As a result, the drive circuit 46 supplies a corresponding current to the coil 62 in accordance with the signal from the waveform shaping circuit 54, and moves the lens holding frame 27, that is, the objective lens 8, in the e or f direction so as to be in a home position. do.

For example, when the output of the waveform shaping circuit 54 is large, the lens holding frame 27 is moved in the direction f, and when the output of the waveform shaping circuit 54 is small, the lens holding frame 27 is moved in the direction C.

Therefore, if the lens holding frame 27, that is, the objective lens 8 is vibrating during high-speed access, the objective lens 8
Movement control (c, d directions, e, f directions) to appropriate positions is performed. In other words, residual vibrations caused by track jumps can be attenuated (stabilized) in a short time.

Next, correction of the optical axis of the objective lens 8 will be explained.

That is, the positive peak value of the tracking difference signal (E signal) supplied from the subtraction circuit 36 is detected by the positive peak detection circuit 9.
1, and a negative peak value is detected by a negative peak detection circuit 92. For these detection results, average values of peak values are calculated by average value calculation circuits 93 and 94, respectively, and these results are supplied to a comparison circuit 95. Thereby, the comparator circuit 95 calculates the average value of each average value supplied from the average value calculation circuit 93.94, and combines this calculated average value with rO
The deviation from J is calculated and a signal corresponding to this deviation is output to the drive circuit 96. As a result, the drive circuit 96 uses the supplied signal corresponding to the deviation to drive the piezo elements 28a1...
・Apply the corresponding voltage to each individual. As a result, each of the piezo elements 28a128b, 28C, and 28d individually expands or contracts in accordance with the applied voltage, thereby tilting the substrate 21 in the A, B or C, D direction, and tilting the objective lens 8.
is corrected so that its optical axis is perpendicular to the recording surface of the optical disc 1.

For example, when a symmetric track difference signal as shown in FIG. 9(a) is supplied, the average of positive peak values and the average of negative peak values are the same, and the drive circuit is not supplied. For this reason, each piezo element 28a, 28b
, 28c, and 28d do not change, and the optical axis of the objective lens 8 is not corrected.

Furthermore, when a track difference signal biased toward the positive side is supplied as shown in FIG. 9(b), the average value of the average of positive peak values and the average of negative peak values becomes positive, and this A positive deviation between the average value and "0" is determined, and a signal corresponding to this deviation is output to the drive circuit 96. As a result, the drive circuit 96
The piezo elements 28a and 28b expand due to changes in the applied voltage, and the piezo elements 280, 28d contract due to changes in the applied voltage, and as shown in FIG. 3(b), the right side of the substrate 21 changes from the state shown in FIG. moves in the direction indicated by the arrow, that is, upward, and the left side of the substrate 21 moves in the direction indicated by the arrow, that is, downward.

Roughly speaking, when a track difference signal biased toward the negative side is supplied as shown in FIG. 9(C), the average value of the average of positive peak values and the average of negative peak values becomes negative, A negative deviation between this average value and "0" is determined, and a signal corresponding to this deviation is output to the drive circuit 96. As a result, the drive circuit 9
6, the piezo elements 28a and 28b contract due to a change in the applied voltage, and the piezo elements 28c and 28d expand due to a change in the applied voltage, and as shown in FIG. The right side moves in the direction of arrow B, that is, downward.
The left side moves in the direction of arrow C, that is, upward.

Therefore, as described above, when the optical axis of the objective lens 8 is tilted in the radial direction of the optical disc, regardless of the position on the optical disc, the piezoelectric sensor provided at the bottom of the substrate is By extending or contracting the element, the optical axis can be corrected to be perpendicular to the recording surface of the optical disc 1.

In the above embodiments, the case where the number of piezoelectric elements provided at the bottom of the substrate is one layer has been explained, but the invention is not limited to this. For example, as shown in FIG. 288', 28b', 280', 28
d′ may also be used. In this case, there are advantages in that a large amount of displacement and driving force can be obtained. Further, although the piezoelectric element is a piezo element, other elements such as a bimorph element may be used. Further, although the case has been described in which the inclination of the optical axis of the objective lens with respect to the radial direction of the optical disc is corrected, the present invention is not limited to this, and the case where the inclination of the optical axis of the objective lens with respect to the track direction of the optical disc is corrected may be used. In this case, the correction is made using the degree of modulation of the bit reproduction signal. Furthermore, the four piezo elements may be moved individually to perform various tilt corrections.

[Effects of the Invention] As detailed above, according to the present invention, it is possible to provide an optical head in which the optical axis of the objective lens can always be perpendicular to the entire surface of the target object.

[Brief explanation of the drawing]

1 to 9 show an embodiment of this invention,
FIG. 1 is a schematic configuration diagram of the optical head, FIGS. 2 to 4 are perspective views showing the configuration of the objective lens drive device, and FIG. 5 is a side view of the bobbin for explaining the moving direction of the lens holding frame.
FIG. 6 is a diagram showing the relationship between the bimorph element and the objective lens, FIG. 7 is a diagram showing the relationship between the piezo element and the support shaft, FIG. 8 is a block diagram showing the schematic configuration of the correction section, and FIG. The figures are diagrams for explaining the track difference signal, FIG. 10 is a perspective view showing the configuration of an objective lens drive device in another embodiment, and FIG. 11 is a diagram showing a conventional objective lens drive device. be. DESCRIPTION OF SYMBOLS 1... Optical disk, 3... Optical head, 6... Polarization beam splitter, 7... λ/4 plate, 8... Objective lens, 9... Half mirror 110, 11... Collection Optical lens, 12.13,...Photodetector, 12a, 1
2i), 13a, 13b... photodetection cell, 20...
Objective lens drive device, 21... Substrate, 22... Holding frame, 23... Support shaft, 24a, 24b, 24c, 24
d... Piezo element, 25.26... Bimorph element, 25a, 25b, 26a, 26b... Piezo element, 27... Lens holding frame, 28a, 28b, 28
c, 28 (1... piezo element, 36... subtraction circuit, 90... correction section, 91... positive peak detection circuit,
92... Negative peak detection circuit, 93.94... Average value calculation circuit, 95... Comparison circuit, 96... Drive circuit. Applicant's agent Patent attorney Takehiko Suzue See Figure 2 2 31. ! ! 1 Figure 4 Figure 5 Hum Figure 7 (a) Fu 2 (b) (c) No. 811
A Figure 9 (a) ■ Figure 10

Claims (3)

[Claims] (1) In an optical head that irradiates an appropriate beam of light onto a target object by moving the holding member that fixes the objective lens left and right or up and down, the optical axis of the objective lens is perpendicular to the target plane of the target object. An optical head comprising: a detection means for detecting the amount of inclination from the axis; and a correction means for correcting the optical axis of the objective lens according to the amount of inclination detected by the detection means. (2) The correction means corrects the optical axis of the objective lens by changing the inclination with a piezoelectric element provided at the lower part of the substrate supporting the holding member. optical head. (3) Claim 2, wherein the piezoelectric element is composed of a piezo element or a bimorph element.
Optical head described in section.