JPS62107442A - Optical head - Google Patents

Abstract

PURPOSE:To attain high-speed access with high accuracy by fixing an optical system and a magnetic circuit member, moving an objective lens holder in the radial direction and the focus direction and rotating it in a prescribed rotation direction to make the moving part small in size and light in weight. CONSTITUTION:An optical head is arranged in opposition to an optical disc 8, the optical system 20 is fixed to the periphery of the disc 8, and a focus track error and signal detector is provided to the optical system 20. Further, a couple of magnetic circuit members 21-1, 21-2 are fixed in the radial direction of the disc 8. The objective lens holder 30 is provided to bridge over a couple of the yoke members 24-1, 24-2 constituting the magnetic circuit. Further, a cylindrical member 31 is provided nearly perpendicularly to the face of the disc 8 nearly at the center of the holder 30, the lens 32 is fitted to one end of the member 31 and also a hole 33 passing through the light beam is provided. Further, focus and track control coils 34-1, 34-2, 35-1, 35-2 are provided at the periphery of the holder 30. Then the moving part is made small in size and light in weight to attain high-speed access with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical head in an optical disc device.

(Prior Art) An optical disc device is a device that records information on an optical disc according to instructions from a computer, etc., and also reads and reproduces the recorded information. , and their control devices.

Generally, in this type of optical disk device, a laser beam such as a semiconductor laser is focused on an optical disk, and information is recorded on the track by scanning minute tracks (e.g., with an interval of about 1.Etpm). Perform the action to read the above information. Therefore, in the optical head, the light beam is adjusted to an appropriate convergence shape 8 (for example, spot diameter IJ
Lm), track control to keep the convergence spot on track,
and access control to search for a desired track.

Conventionally, as for the technology in this field, ■IEICE Technical Report, 84
[203] (1984-11-22) P, 11-1
8, (1) JP-A No. 58-133640, and (2) Hitachi Hyoron, Hoku [101 (1983-10) P. 28. The configuration will be explained below using figures.

FIG. 2 is a side view of a main part showing an example of the structure of the optical head described in the above-mentioned document (2), and FIG. 3 is a front view of the main part.

In this optical head, an optical system 1 is fixed, a pair of guides 2, 2 are arranged in parallel with the laser beam emitted from the optical system 1, and a base 3 that is slidable on the guides 2, 2 is further provided. Supported. At both ends of the base 3,
A coil-wound pobbin 4.4 is attached, which pobbin 4,4 is located in the magnetic gap of the external fixed magnetic circuit members 5,5. Further, on the base 3, a 45° mirror 6 and an objective lens drive function 7 containing an objective lens 7d are mounted at a position facing the optical disc 8.

Here, as the objective lens driving function 7, there is one described in the above-mentioned document (2), for example. The objective lens 7a supported by the support is supported by an elastic member, and current is passed through two windings arranged in a magnetic circuit configured inside the drive mechanism. It has a structure that performs two-dimensional minute drive such as focus control by vertical movement of the support, and track control by rotation of an eccentric objective lens from the rotation center axis of the support.

In the above configuration, the laser beam emitted from the optical system 1 has its optical path changed by the 45° mirror 6, and enters the optical disk 8 through the objective lens 7a in the objective lens drive function 7. The reflected light from the optical disk 8 passes through the objective lens 7a and the 45° mirror 6 and returns to the optical system l. At this time, the objective lens drive function 7 performs focus control and track control, and access control is performed by passing current through the windings of the pobbins 4, 4 to move the base 3 along the guides 2, 2.

In this type of optical head, access control is performed by fixing the optical system 1 and moving the objective lens drive mechanism 7, which reduces the weight of the movable part and enables high-speed access.

However, when track control is performed by driving the objective lens 7a supported by a support, if the optical disc 8 is eccentric, the optical disc will move in proportion to the amount of movement δ of the objective lens 7a, as shown in FIG. The optical axis of the reflected light from 8 is at a distance D (=
26), causing an error in the track deviation detection by the optical system 1, which causes a deviation (track offset) between the track and the convergence spot of the light beam, and as a result, the signal-to-noise ratio (hereinafter referred to as A problem arises in that the signal-to-noise ratio (S/N) is reduced.

In this way, if one actuator (i.e., objective lens moving mechanism) is used to deal with the track deviation due to eccentricity of the optical disk 8, the above-mentioned problem will occur. This is handled with one actuator.

That is, the optical head in FIG. 5 includes a semiconductor laser 1a, a photodetector 1b, a beam splitter 1c, which constitute an optical system, an objective lens 7a, and a fine actuator 18 consisting of a galvanometer mirror for changing the optical path, and a coarse actuator. 17, the optical disc is moved in the radial direction. In this optical head, a photodetector 1b detects a track deviation, and the detected signal is band-separated into a low frequency component and a high frequency component. Then, the low frequency component is transferred to the coarse actuator 1.
7, the high-frequency components are distributed to the fine actuators 16, respectively, and they are jointly operated to follow. In particular, the movement of the optical axis is kept small by providing a galvanometer mirror with an operating range of approximately ±10 gm.

(Problems to be Solved by the Invention) However, in the optical heads shown in FIGS. 2 and 3,
Since the support supporting the objective lens 7a is supported by an elastic member, high-speed access may cause unnecessary vibrations in the objective lens 7a, causing the optical spot to vibrate.
Furthermore, there is a problem in that a large track offset occurs due to the movement of the optical axis.

Furthermore, the optical head shown in FIG. 5 requires two actuators 113 and 17, which increases the size of the optical head. Furthermore, since the coarse actuator 17 that performs access moves while carrying the fine actuator 16 on its back, there is a problem in that the weight becomes large and high-speed access is not possible.

The present invention provides an optical head that solves the problems of the prior art, such as difficulty in accurate high-speed access and large track offset.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention provides an optical head for an optical disc device that reproduces or records information on an optical disc, in which a light beam to be irradiated onto the surface of the optical disc is emitted. a fixedly disposed optical system that emits light and receives reflected light from the optical disk surface; a fixedly disposed magnetic circuit member that includes a magnet and a yoke member; and an optical path converting means that changes the optical path of the light beam and the reflected light. a carriage that is slidably supported by the guide member in a radial direction of the optical disk surface; and an objective that is loosely fitted to the carriage and that is slidably slidable in the radial and focus directions. It includes a lens holder and a control coil wound around the objective lens holder. Moreover, the control coil cooperates with the magnetic circuit member to move the control coil in the radial direction.
The arrangement is such that electromagnetic force is generated in the focus direction and in the rotation direction about an axis substantially perpendicular to both directions.

(Function) Since the optical head of the present invention is configured as described above, the carriage functions as a guide when moving the objective lens in the radial direction of the optical disk surface and in the focus direction.

Further, the control coil serves to move the objective lens holder and the sheep carriage in the radial direction and a predetermined rotational direction, and also to move the objective lens holder in the focus direction. This allows highly accurate and high-speed focus control, trunk control, and access control.

Therefore, the above problem can be eliminated.

(Embodiments) (I) First Embodiment FIG. 1 is a perspective view of essential parts of an optical head showing a first embodiment of the present invention, and FIG. 6 is a sectional view taken along line X--X of FIG. fJIJ1.

This optical head is arranged to face the optical disc 8 shown in FIG. 2, and an optical system 20 is fixedly arranged around the outer periphery of the optical disc 8. The optical system 20 includes a semiconductor laser, a focus tracking error detector, a signal detector, and the like.

Furthermore, a pair of magnetic circuit members 21 - 1 and 212 are fixedly arranged in the radial direction of the optical disk 8 .

One magnetic circuit member 21-1 includes a plate-shaped magnet 22-1 arranged in the radial direction of the optical disk 8, and the magnet 22-1.
Yoke member 23-1.2 surrounding 1 to form a closed magnetic path.
4-1, and a magnetic gap 25-1 formed between the magnet 22-1 and the yoke member 24-1.

Similarly, the other magnetic circuit member 21-2 also has a plate-shaped magnet 22.
-2, a yoke member 23-2, 24-2, and a magnetic gap 25-2. These optical system 20 and magnetic circuit members 21-1 and 21-2 are each fixed to a frame (not shown). In addition, magnet 22-1.22-
2, a pair of tip-shaped guide members 2G-1, 2
8-2 is fixedly arranged.

An objective lens holder 30 is attached to the opposing yoke members 24-1 and 24-2 so as to straddle them. A cylindrical cylindrical member 31 is provided approximately at the center of the objective lens holder 30 in a direction substantially perpendicular to the surface of the optical disc 8, and an objective lens 32 is attached to one end of the cylindrical member 31. A hole 33 for light beam passage is provided in a part of the cylindrical member 31. Furthermore, the objective lens holder 30
Focus control coils 34-1.34-
2 and the track control coil 35-1.35-2 are wound so as to be substantially perpendicular to each other within the magnetic gap 25-1.25-2.

A carriage 40 is provided adjacent to the objective lens holder 30 to engage with it. carriage 40
The moving table 41 is slidably supported by a pair of guide members 2Ef-1 and 28-2 via sliding bearings, etc., and the movable table 41 is provided protruding from the moving table 41 and is slidable inside the cylindrical member 31. A cylindrical body 42 is inserted into the cylindrical body 42. Furthermore, a bin 43 for preventing rotation of the objective lens holder 30 is mounted on the moving table 41, and a hole 44 for passing the light beam is bored in the cylinder 42. Further, an optical path converting means, for example a mirror 45, is attached within the cylinder 42 at an angle of approximately 45° with respect to the surface of the optical disk 8.

FIG. 7 is a diagram showing the state in which the focus control coils 34-1 and 34-2 provided on the objective lens holder 30 are wound. The focus control coils 34-1 and 34-2 are arranged substantially parallel to each other on the upper surface of the objective lens holder 30, and are arranged so as to partially overlap on both sides of the objective lens holder 30.

Next, the operation will be explained.

(1) The parallel light beam emitted from the focus control optical system 20 is directed to the objective lens holder 30 as shown by the broken line in FIGS. 1 and 6.
The light passes through the hole 33 of the carriage 40 and the hole 44 of the carriage 40, is reflected at a right angle by the mirror 45, and is focused onto the recording surface of the optical disk 8 by the objective lens 32.

On the other hand, the reflected light from the optical disk 8 returns to the optical system 20 via the objective lens 32 and mirror 45, and returns to the optical system 20 via the objective lens 32 and mirror 45.
Track error detection and signal detection are performed.

When a focus error is detected in the optical system 20, a current flows through the focus control coils 34-1 and 34-2 from a control circuit (not shown) based on this focus error signal.

The objective lens holder receives an electromagnetic force due to the action of the radio waves flowing through the focus control coil 34-1.34-2 and the magnetic field within the magnetic gap 25-1.25-2 in each magnetic circuit member 21-1.21-2. 30 moves up and down along a cylindrical body 42 of a carriage 40. That is, when the focus control coil 34-1, 34-2 is energized in the direction of arrow a in FIG. 1, the objective lens holder 30 moves upward,
In addition, when electricity is applied in the direction of the arrow, the objective lens holder 3
0 moves downward.

In this way, by controlling the direction of energization to the focus control coil 34-1, 34-2, the value of the energizing current, or the energizing time, the objective lens 32 approaches or moves away from the optical disk 8, and a predetermined focus control is performed. be exposed.

(2) Track Control When a track error is detected, a control circuit (not shown) causes current to flow in the same direction in each of the track control coils 35-1 and 35-2 based on this track error signal. The objective lens holder 30 receives an electromagnetic force due to the action of the current flowing through the track control coil 35-1.35-2 and the magnetic field within the magnetic gap 25-1.25-2, and the objective lens holder 30 moves along with the carriage 40 to the guide member 2f3-1, Move along 2Ei-2. That is, track control coil 35-1.
35-2 is energized in the direction of arrow C in FIG. 1, the objective lens holder 30 and carriage 40 move in the direction of arrow e, and when energized in the direction of arrow d, the objective 40 moves in the direction of arrow f.

In this way, the objective lens 32 is controlled by controlling the direction in which the current is applied to the track control coil 35-1.
The optical disc 8 is moved in the radial direction of the optical disc 8, and predetermined track control is performed.

(3) Problems with track offset in track control Track deviation components due to eccentricity of the optical disk 8, etc.
Generally, there are a large amplitude low frequency component and a small amplitude high frequency component. As in this embodiment, the carriage 40 is
When moving along B-1, 26-2, the guide member 213-1, 28-
2, a phase shift between the control signal and the actual movement becomes a problem.

Therefore, in this embodiment, the focus control coils 34-1 and 34-2 are also energized in accordance with the high frequency component with a small amplitude, and by creating a current difference between the two, the objective lens holder 30 is moved slightly. tilt to This operates in the same manner as the conventional galvano mirror of the fine actuator 16 shown in FIG. 5, and makes it possible to move the light spot on the optical disk 8 in the radial direction, for example, by about ±20JL11. Therefore, the track offset becomes very small.

(3) Access Control In access control, a current flows through the track control coils 35-1 and 35-2 by a control circuit (not shown) based on the difference between the designated position and the current position. The objective lens 32 receives an electromagnetic force from the action of the current flowing through the track control coils 35-1' and 35-2 and the magnetic field within the magnetic gap 25-1, 25-2, and the objective lens 32 moves against the mirror 45 in the same manner as during track control. Access control is performed by moving the optical disc 8 in the radial direction accordingly. These position detection means may be by counting the number of tracks crossed, or by using an external scale or the like.

The focus control and track control described above are performed in a complex manner at the same time as necessary; however, when performing access control, the track control is set to the 07 state and the objective lens 3 is
2 is turned on again after it has moved the desired amount.

The advantages of this embodiment can be summarized as follows.

■ The magnetic circuit for focus control and the magnetic circuit for track access control are shared, and these magnetic circuit members 21-1 and 21-2 are fixed outside the movable part, which reduces the weight of the movable part and increases high speed. Access is movable and high-speed followability of track control can be ensured.

(2) Since the optical head is a bridge structure that directly drives the objective lens 32, the objective lens 32 does not vibrate even during high-speed access, making it possible to accurately search for a desired track.

■ Objective for track access control〉'32
When the optical disk is driven in the radial direction, the objective lens 32 moves together with the mirror 45, so the optical axis of the light beam basically passes approximately through the center of the objective lens 32. Moreover, for minute access or track control, the objective lens 32 is also tilted together with the mirror 45. Therefore, compared to the conventional case where only the mirror 45 is tilted, the occurrence of track offset caused by the movement of the reflected optical axis from the optical disk 8 can be extremely reduced, and it is possible to always obtain stable read and reproduced signals.

(4) Since the movement and tilting operations of the objective lens holder 30 are performed using electromagnetic force by the control coils 33-1.34-2.35-1.35-2, it is possible to provide a small, lightweight, and low-cost optical head.

(II) Second Embodiment FIG. 8 is a perspective view of essential parts of an optical head showing a second embodiment of the present invention. In FIG. 8, the same elements as those in FIG. 1 are given the same reference numerals.

The difference between this embodiment and the first embodiment is that a focus control coil 45--
1. The winding state of 45-2 is different. That is, the focus control coils 45-1 and 45-2 are arranged substantially parallel on the upper surface of the objective lens holder 30, and the coils 45-1 and 45-2 are arranged substantially orthogonally on both sides of the objective lens holder 30. , and about 4 to the optical axis
It is wound with a 5" slant.

FIGS. 9(1) and 9(2) are schematic diagrams of the focus control coils 45-1 and 45-2 on one side Y of the objective lens holder 30. Focus control based on the current direction of the focus control coils 45-1 and 45-2 will be explained based on FIG. 9.

FIG. 9(1) shows a case where control coil 45-1 is energized in the direction of arrow g, and control coil 45-2 is energized in the direction of arrow i. When energized in this manner, an electromagnetic force F1 is generated in the control coil 45-1 and an electromagnetic force F2 is generated in the control coil 45-2, and the combined force F causes the objective lens holder 30 to move upward.

Similarly, as shown in FIG. 9(2), the control coil 45-1 is directed in the direction of the arrow, and the control coil 45-2 is directed in the direction of the arrow j.
When electricity is applied in each direction, a resultant force -F is generated and the objective lens holder 30 moves downward. In this way, a predetermined focus control can be performed by controlling the direction of energization to each control coil 45-1, 45-2, and further the value of the energizing current or the energizing time. In addition, in track control, track control coil 35-1, 35-2
At the same time, the focus control coil 45-1 or 45- is energized depending on the small amplitude frequency as in the first embodiment.
2 is energized. At this time, focus control coil 45-1
．． When the current value flowing through the lens 45-2 is small, the frictional force of the objective lens holder 30 in the optical disk radial direction is greater than in the focusing direction, so the objective lens holder 30 is tilted somewhat, producing the same effect as in the first embodiment. is obtained.

(III) Modifications The present invention is not limited to the illustrated embodiment, and various modifications are possible. Examples of variations include the following.

■ 1st. In the second embodiment, a pair of magnetic circuit members 21-
1.21 to 2 are provided, but if particularly high-speed operation is not required, it is also possible to use only one of them. Further, the guide members 2B-1 and 26-2 may be shaped like rails, or the cylindrical member 31 and the cylindrical body 42 may be shaped like square tubes, and the pin 43 for preventing rotation may be omitted.

■ 1st. In the second embodiment, magnetic gaps 25-1.
25-2 Inside, focus control coil 34-1
．． 34-2 and the track control coils 35-1 and 35-2 form a substantially right angle to each other.Similarly, the focus control coils 45-1 and 45-2 also form a substantially right angle; Even if you set it to any other angle than
．． The same functions and effects as in the second embodiment can be obtained.

■ In the first embodiment, two new control coils are added exclusively for minute track control, and the objective lens holder 30 is
It may be wrapped around.

■ 1st. In the second embodiment, the objective lens holder 30 is slightly rotated around an axis perpendicular to the access direction and the focus direction, and the mirror 45 is tilted to perform minute access control. By performing access control, access speed can be increased.

(Effects of the Invention) As described above in detail, according to the present invention, the optical system and the magnetic circuit member are fixed, and the objective lens holder is moved in the radial direction and the focus direction and rotated in a predetermined rotation direction. As a result, the movable parts can be made smaller and lighter, allowing high-precision and high-speed access operations.
Moreover, the track offset caused by the movement of the optical axis can be made very small.

[Brief explanation of drawings]

FIG. 1 is a perspective view of essential parts of an optical head showing a first embodiment of the present invention, FIG. 2 is a side view of essential parts of a conventional optical head, and FIG.
The figure is a front view of main parts of a conventional optical head, FIG. 4 is an explanatory diagram of the operations of FIGS. 2 and 3, FIG. 5 is a configuration diagram of another conventional optical head, and FIG. 6 is a - An X-ray sectional view, FIG. 7 is a winding diagram of the focus control coil in FIG. ), (2) are schematic diagrams of the focus control coil in FIG. 8... Optical disk, 20... Optical system,
21-1.21-2...Magnetic circuit member, 22-
1.22-2... Magnet, 23-1.23-2.
24-1.24-2...Yoke member. 25-1.25-2...Magnetic gap, 2f3
-1.28-2... Guide member, 30...
...Objective lens holder, 32...Objective lens,
34-1.34-2.35-1.35 to 2.45-1.
45-2... Control coil, 40... Carriage, 45... Optical path conversion means. Applicant's agent Yasushi Kakimoto Figure 3 Figure 4 X-X cross-sectional view of Figure 1 Figure 6 Coil of Figure 1 Figure 7

Claims (1)

[Scope of Claims] In an optical head of an optical disc device that reproduces or records information on an optical disc, a fixed unit that projects a light beam to be irradiated onto the optical disc surface and receives reflected light from the optical disc surface. a fixedly arranged magnetic circuit member consisting of a magnet and a yoke member; and an optical path converting means for changing the optical path of the light beam and the reflected light, the optical system being slidable in the radial direction of the optical disk surface. It has a carriage that is freely arranged, and an objective lens that irradiates the optical disc surface with a light beam from the optical path changing means and receives reflected light from the optical disc surface, and an objective lens holder loosely fitted on the carriage so as to be slidable in a substantially perpendicular focus direction; An optical head comprising: a control coil that generates an electromagnetic force in a rotational direction about an axis that is substantially perpendicular to both directions.