JPS6145427A - Driving device of objective lens - Google Patents

Abstract

PURPOSE:To reduce the titled device at its size, to simplify its constitution and to improve response by applying a voltage to piezo-electric elements to rotate a supporting shaft on the basis of the expansion/contraction of the piezo-electric elements. CONSTITUTION:A cylindrical holding frame 22 having a hollow shaft vertical to a substrate 21 is mounted on the substrate 21 and the supporting shaft 23 is arranged along the center shaft and supported by the frame 22 through the piezo- electric elements 24a-24d. Bimorph elements 25, 26 are projected from the upper and lower end parts of the shaft 23 in parallel with each other in the same direction and a holding frame 27 for an objective lens 8 is fitted to the leading end parts of the bimorphs 25, 26. When the elements 24a, or the like contracted by the change of the applied voltage, the shaft 23 is rotated, and thereby the objective lens 8 on the frame 27 is moved through the element 25.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an objective lens driving device for an optical head used, for example, in 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. 8(a) and 8(b). There is. That is, the objective lens 61 consists of two parallel plate springs 62 and 63.
It is supported by

These leaf springs 62 and 63 are fixed to an intermediate support fitting 64, and this intermediate support fitting 64 is connected to two diaphragm springs 6.
It is now supported by 5.66. A magnetic circuit formed by the coil 67 and the magnet 68 causes the intermediate support fitting, that is, the objective lens 61 to move in the vertical direction (
Forcing is performed by driving in the direction of arrow Q1h). In addition, the coil 69
Tracking is performed by driving the objective lens 61 in the left-right direction (in the direction of arrows 1 and j) by a magnetic circuit constituted by the iron piece 70 and the iron piece 70.

[Problems with the background art] However, in the objective lens driving device as described above,
Intermediate support metal fittings have large buying interest.

For this reason, the optical head having the objective lens drive device has a drawback of poor responsiveness to follow the tracks of an optical disk rotating at high speed. Further, since the objective lens 61 is driven using a magnetic circuit, the entire device becomes large, a large phase delay occurs, and the response is poor as described above.

[Object of the Invention] This invention was made in view of the above circumstances, and its purpose is to provide an objective lens driver vJ that is lightweight, has a simple structure, and can improve responsiveness. The goal is to provide equipment.

[Summary of the Invention] In order to achieve the above object, the present invention provides a lens support frame for supporting an objective lens at the tip of a lever member extending in parallel with each other in the same direction from both ends of a support shaft, The support shaft is supported by a piezo element in a cylindrical holding frame provided on the substrate with a center support axis perpendicular to the support shaft, and a voltage is applied to the piezo element to expand and contract the piezo element. The lens holding frame, that is, the objective lens is moved by rotating the support shaft.

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

FIG. 1 schematically shows the essential parts of an optical disk device using an optical head having an objective lens driving device of the present invention. That is, the optical disc 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, condensing lenses 10 and 11, a photodetector 12 for detecting track deviation, It is composed of a photodetector 13 for detecting defocus. Further, a triangular prism 14 for wide-angle projection is provided between the half mirror 9 and the condensing lens 10. The light beam extracted by the triangular prism 14 is irradiated onto a photodetector 15 for detecting the position of the objective lens. Further, a light shielding plate 16 for widening the front is provided between the half mirror 9 and the condensing lens 11. The photodetector 12 is composed of photodetection cells 12a and 12b that convert light focused by the condenser lens 10 into electrical signals. 124 of these photodetection cells,
12L), a T signal and an ε signal are output, respectively. The photodetector 13 is composed of photodetection cells 13a and 13b that convert light focused by the condenser lens 11 into electrical signals. These photodetection cells 13a, 13b
The signals output by are α signal and β signal, respectively.
A signal is now output. The photodetector 15
is composed of photodetection cells 15a and 15b that convert light guided by a triangular prism 14 into electrical signals. The signals outputted by these photodetection cells 15a and 15b are an ε signal and a ζ signal, respectively.

The objective lens 8 is driven by an objective lens driving device 20 shown in FIGS. 2 to 4. 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 includes piezo elements (piezoresistance effect elements) 24a, 24b, which will be described later, as piezoelectric elements.
It is supported by the holding frame 22 by 24C and 24d.

From both upper and lower ends of this support shaft 23, bimorph elements 25 and 26, which will be described later, are arranged parallel to each other in the same direction.

It is extended and provided. This bimorph element 26.2
A lens holding frame 27 in which the objective lens 8 is held is attached to the tip of the lens 6 .

Support the above! 23, as shown in FIGS. 5(a), 5(b), and 5(c), four piezo elements 24a, 24b, 24G, and 24d are installed (1) at equal angles from the center. , and the support shaft 23 is supported by the holding frame 22I by these piezo elements 24a1, . . . If the piezo elements 24a, . As shown in b), the same figure (a
) The support shaft 23 rotates by a slight angle in the direction of arrow a from state hX of ) to 1/).

This rotation causes the lens holding frame 27, that is, the objective lens 8, to move in the direction of arrow C via the bimorph element 25. Furthermore, when the piezo elements 24a1... expand due to a change in the applied voltage, as shown in FIG.
) The support shaft 23 rotates by a slight angle in the direction of the arrow from the state force \ to zero.

This rotation causes the lens holding frame 27, that is, the objective lens 8, to move in the direction of arrow d via the bimorph element 25. In the above case, although the amount of rotation of the support shaft 23 is minute, the bimorph element 25h (-1) acts as a lever arm,
The amount of movement (displacement) of the objective lens 8 is large.

Therefore, the bimorph element 25 transmits a small displacement of the piezo element 24 as a large displacement of the objective lens 8. Tracking of the optical disc 1 is performed by moving the objective lens 8 in the c and d directions. In addition, the piezo chord 24.25
For example, if the applied voltage changes by 700 volts, then 1
The displacement is about 0 micron.

The bimorph elements 25 and 26 shown in FIG. 6 (a>(b)
As shown in (C), two piezo elements 25a each
, 25b, 126a, and 26b are pasted together vertically, and by applying a voltage to each piezo element so that one of the two piezo elements contracts and the other expands, the lens holding frame 27 moves up and down, that is, arrow e, It is designed to move in the f direction. For example, when the piezo elements 25a and 26a are contracted and the piezo elements 25b and 26b are extended, the bimorph elements 25 and 26 are bent downward, and the lens holding frame 27
That is, as shown in FIG. 6(b), the objective lens 8 is moved in the direction of arrow e from the state shown in FIG. 6(a). In addition, when the piezo elements 25a and 26a are extended and the piezo elements 25b and 26b are shortened, the bimorph element 25
．． 26 is bent upward, and the lens holding frame 27, that is, the objective lens 8, is moved in the direction of arrow f from the state shown in FIG. 6(a), as shown in FIG. 6(C). Focusing on the optical disc 1 is performed by moving the objective lens 8 in the e and f directions.

The output of the optical head 3, that is, each photodetection cell 12a, 1
2b, 13a, 13b, 15a, 15b are supplied to amplifiers 30, 31.32.33.34.35, respectively. The outputs of the amplifiers 30 and 31 are respectively connected to the subtracting circuit 3.
6, is supplied to the adder circuit 37. The above amplifier 32.33
The output of is supplied to a subtraction circuit 38. The amplifier 34.
The outputs of 35 are supplied to a subtraction circuit 39 and an addition circuit 40, respectively. The subtraction circuit 36 includes the photodetection cell 12a,
By taking the lower detection signal (γ signal - δ signal) from 12'b, a signal corresponding to the track deviation during normal tracking is output.

The adder circuit 37 adds up the detection signals from the photodetection cells 12a112b and outputs the sum as a read signal. The subtraction circuit 38 includes the photodetection cell 15a.
, 15b (ε signal - ζ signal), a signal corresponding to the track deviation during high-speed access is output. 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 13a113b. The addition circuit 40 includes the photodetection cell 13a.
, 13b and outputs it as a read signal.

Output of the above subtraction circuit 36.39 and addition circuit 37.4
The output of 0 is supplied to the CPU 41.

This CPU 41 controls the entire optical disc 1. At initialization, the CPU 41 outputs an initial signal to the switching circuit 42 and also outputs an initial pull-in signal. Also,
The CPU 41 outputs a switching signal to the switching circuit 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 36 is shaped by a waveform shaping circuit 45 and supplied to the switching circuit 43. Thereby, the switching circuit 42 outputs the initial pull-in signal supplied from the CPU 41 to the bimorph element drive circuit 46 when the initial signal is supplied from the CPU 41, and the switching circuit 42 outputs the initial pull-in signal supplied from the CPU 41 to the bimorph element drive circuit 46, and the signal supplied from the waveform shaping circuit 44 at times other than the initial time. is output to the bimorph element drive circuit 46. In addition, the switching circuit 43 normally outputs the signal supplied from the waveform shaping circuit 45 to the piezo element drive circuit 47, and when the switching signal is supplied from the CPLJ 41, the switching circuit 43 outputs the signal supplied from the subtraction circuit 38. A track deviation detection signal is output to the piezo element drive circuit 47.

The bimorph element drive circuit 46 drives each piezo element 25a125b, 26a of the bimorph element 25.26,
2eb1. :, the corresponding t le fi is applied. The piezo element drive circuit 47 is adapted to apply a corresponding electric wire to the piezo elements 24a124b and 24C124d in accordance with a signal supplied from the switching circuit 43.

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 light reflected from the optical disc 1 with respect to this reproduction beam light is converted into a parallel light beam by an objective lens 8 and guided to a polarizing beam splitter 6 via a 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 10, and is also transmitted via a triangular prism 14 to a photodetector 15,
In other words, the photodetection cells 15a, 15bk: Be irradiated.
3a and 13b are irradiated. Therefore, photodetection cell 1
Signals corresponding to the irradiated light are output from 2a, 12b, 13a, 13b, 15a, and 15b, and these signals are output via amplifiers 30.31, 3''2.33゛, and 34.35, respectively. Accordingly, the addition circuit 37 sums the detection signals from the photodetection cells 12a and 12b and outputs the sum as a read signal to the CPU 41.As a result, C
The PU 41 reads data using a read signal from the adder circuit 37.

The forcing operation in the above state will be explained. That is, at the initial time, CPLI41
supplies an initial pull-in signal to the bimorph element drive circuit 46 via the switching circuit 42. As a result, the bimorph element drive circuit 46 drives the bimorph element 25.
．． A predetermined voltage is applied to each piezo element 26, and the lens holding frame 27, that is, the objective lens 8, is moved in the e or f direction.

Then, the CPU 41 determines that the subtraction result of the subtraction circuit 36 is "±".
0'', 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 outputted 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. The signal is then supplied to the bimorph element drive circuit 46. As a result, the bimorph element drive circuit 46 applies a voltage corresponding to each piezo element of the bimorph elements 25 and 26 in accordance with the signal from the waveform shaping circuit 44, and moves the lens holding frame 27, that is, the objective lens 8, in the e or f direction. Move to and do the normal force shinging.

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 a piezo element drive circuit 47 via a waveform shaping circuit 45 and a switching circuit 43. Thereby, the piezo element drive circuit 47 controls each piezo element 24a, 24b, 24c,
A voltage corresponding to 24d is applied to rotate the support shaft 23 in the direction a or b. As a result, the rotation of the support shaft 23 moves the lens holding frame 27, that is, the objective lens 8, in the direction C or d, and normal tracking and picking are performed.

Furthermore, when the CPU 41 determines high-speed access, the CPLI 41 switches the switching circuit 43.

As a result, one signal corresponding to the track deviation during high-speed access from the subtraction circuit 38, that is, the photodetection cells 15a, 1
A signal obtained by taking the difference between the detection signals from 5b is supplied to the piezo element drive circuit 47 via the switching circuit 43. As a result, the piezo element drive circuit 4
7 indicates each piezo element 2 according to the signal from the subtraction circuit 38.
4a, 24b, 24c, and 24d are applied to rotate the support shaft 23 in the direction a or b. For example, when the output of the subtraction circuit 38 is positive, the support shaft 23 is rotated in the direction a, and when the output of the subtraction circuit 38 is negative, the support shaft 23 is rotated in the direction b. As a result, due to the rotation of the support shaft 23, the lens holding frame 27, that is, the objective lens 8 is moved to C or d.
tracking during high-speed access.

As mentioned above, it is possible to reduce the weight of the objective lens drive device with a simple configuration, and the weight of the optical head as a whole can also be reduced, resulting in very good track following response when the optical disk rotates at high speed. .

In the above embodiment, the number of piezo cords supporting the support shaft on the holding frame was four, but the number is not limited to this, and other numbers may be used. For example, as shown in FIG. 7, it may be supported by two piezo elements 24a' and 24b'. Further, if the force shinging is not performed strictly, a leaf spring may be used instead of the bimorph element.

[Effects of the Invention] As described in detail above, according to the present invention, it is possible to provide an objective lens driving device that is lightweight, has a simple structure, and can also improve responsiveness.

[Brief explanation of the drawing]

FIG. 1 to FIG. 6 show an embodiment of this invention.
Figure 1 is a schematic configuration diagram of the optical disk device, from Figures M2 to M4.
The figure is an H diagram showing the configuration of the objective lens drive gJ device, FIG. 5 is a diagram showing the relationship between the piezo element and the support shaft, FIG. 6 is a diagram showing the relationship between the bimorph element and the objective lens, and FIG. The figure is a diagram showing a configuration example of a piezo element in another embodiment, and FIG. 8 is a diagram showing a conventional objective lens driving device. DESCRIPTION OF SYMBOLS 1... Optical disk, 3... Optical head, 6... Deflection beam splinter, 7... λ/4 plate, 8... Objective lens, 9... Half mirror 110, 11... Collection Optical lens, 12.13, 15-'/l, WA output H112
a, 12b, 13a, 13b, 15a, 15b, - photodetection cell, 20...objective lens drive device, 21...
Substrate, 22... Holding frame, 23.4 holding 1111.24a
, 24b, 24c, 24d... piezo element, 25.2
6 river bimorph elements, 25a, 25b, 26a, 26b
... Piezo element, 27... Lens holding frame, 36.3
8.39... Subtraction circuit, 37.40... Addition circuit,
41... CPU, 42.43... Switching circuit, 44.45... Waveform shaping circuit, 46... Bimorph element drive circuit, 47... Piezo element drive circuit. Atsushi Figure 6 Figure 7 Figure 8

Claims (2)

[Claims] (1) A holding frame provided on the substrate with a central support shaft perpendicular to the holding frame, a support shaft provided within this holding frame and supported by the holding frame by a piezo element, and both ends of this support shaft. A voltage is applied to a lever member extending parallel to each other in the same direction, a lens support frame provided at the tip of the lever member for supporting the objective lens, and the piezo element. An objective lens driving device comprising: a driving means that rotates the support shaft by expanding and contracting. (2) The objective lens driving device according to claim 1, wherein the lever member is composed of a bimorph element.