JPH04321942A - Distributed optical head device - Google Patents

Abstract

PURPOSE:To prevent the influence exerted by an optical axis movement of a reflected light which follows a movement of a movable optical system by a simple constitution without using an exclusive actuator for correcting an optical axis. CONSTITUTION:A fixed optical system 27 emits an emitted light as parallel rays to a movable optical system 31, and also, photodetects a reflected light from an optical disk 32 by a detecting optical system 25 through the movable optical system 31. In this case, an optical axis 45 of said parallel rays is displaced by a galvanomirror 24, and a rotation angle of the galvanomirror 24 is detected by a deflection angle detector 26. Subsequently, the sum of an error of an output of the deflection angle detector 26 to a deflection angle target value S1 from a controller 35 and a tracking error signal detected by the detecting optical system 25 is supplied to said galvanomirror 24, and also, the tracking error signal is supplied to a linear motor 30 for driving the movable optical system 31.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a separate optical head device for recording and reproducing information by forming a light spot on a recording medium such as an optical disk.

0002

2. Description of the Related Art An optical head device used in an optical disk device records information by irradiating a minute light spot onto a track provided on an optical disk using a condensing lens, or uses reflected light reflected by an optical disk. It is a device that reads information from. The tracks of an optical disc are
Since the condensing lens is provided over a certain range in the radial direction of the disk, it is necessary to move the condensing lens in order to record and reproduce information on any track. At this time, if the entire optical head device including the light source and photodetector is moved, the moving mass becomes large and it is difficult to move it at high speed, so a separate type optical head device that moves only the condensing lens is being considered. has been done.

However, in the separation type optical head device, the movement axis of the movable part and the optical axis emitted from the fixed optical system toward the movable part may deviate from each other due to the limit of mechanical precision. If there is such a shift, the optical axis of the light beam reflected by the disk and returned to the fixed optical system will be displaced depending on whether the movable part is on the inner circumference of the disk or on the outer circumference, and the tracking error signal will be affected. A problem has arisen in that the offset fluctuates.

[0004] In order to solve the above-mentioned problems,
62735, a separate type optical head device as shown in FIG. 8 has been proposed. This optical head device includes a fixed optical system 9 having a semiconductor laser 1, a collimating lens 2, a beam splitter 3, an optical axis shift actuator 4, and a detection optical system 8, and a movable part 10 having a raising mirror 5 and a condensing lens 6. It is equipped with The optical axis shift actuator 4 is supported such that a parallel glass plate is rotatable about an axis perpendicular to the plane of the paper, and can tilt the parallel glass plate according to an input current.

FIG. 9 shows a method for detecting fluctuations in the movable part 10. An auxiliary beam 13 is emitted from a fixed optical system 9 and received by a two-split photodetector 14 provided on the movable part 10. Based on the difference between the two outputs of the two-split photodetector 14, the movable part 1
Detect 0 fluctuations.

With the above configuration, the optical axis shift actuator 4 is controlled by a signal that detects a change in the movable part 10.
By controlling the current input to the mirror and tilting the parallel glass plate to move the optical axis of the emitted light in parallel, it is possible to compensate for fluctuations in the movable part 10 and prevent the influence of the optical axis movement of the reflected light.

[0007]

However, the above-described separated optical head device requires an optical axis shift actuator exclusively for optical axis correction in addition to the actuator for following the disk track. Therefore, the fixed optical system becomes large and complicated, making it difficult to downsize and simplify the entire optical disc device. Further, there arises a problem of high cost.

The present invention has been made in view of these circumstances, and eliminates the need for an actuator dedicated to optical axis correction and eliminates the influence of optical axis movement of reflected light due to movement of a movable optical system with a simple configuration. It is an object of the present invention to provide a separate type optical head device that can prevent such problems.

[0009]

[Means for Solving the Problems] A separate optical head device according to the present invention includes: a light source means for emitting emitted light as parallel light; a reflecting mirror rotatably disposed in the optical path of the parallel light; A fixing device having a first actuator that drives a mirror to displace the optical axis of the parallel light, an angle detection means that detects a rotation angle of the reflection mirror, and a light detection means that receives reflected light from a recording medium. an optical system; a movable optical system that is movably provided relative to the fixed optical system and that focuses the emitted light onto a recording medium and causes reflected light from the recording medium to enter the fixed optical system; a second actuator that drives the movable optical system; a sum of an error in the output of the angle detection means with respect to a preset target value of the rotation angle of the reflection mirror; and a tracking error signal detected by the light detection means; and a tracking control system that supplies the tracking error signal to the second actuator.

0010

[Operation] The light source means of the fixed optical system emits the emitted light as parallel light. The movable optical system focuses the emitted light onto the recording medium and causes the reflected light from the recording medium to enter the fixed optical system. The light detection means of the fixed optical system receives the reflected light from the recording medium. At this time, a first actuator drives a reflection mirror rotatably arranged in the optical path of the parallel light to displace the optical axis of the parallel light, and an angle detection means detects the rotation angle of the reflection mirror. . Then, the sum of the error in the output of the angle detection means with respect to the target value of the rotation angle of the reflection mirror set in advance by the angle control system and the tracking error signal detected by the light detection means is sent to the first actuator. At the same time, a tracking control system supplies the tracking error signal to a second actuator that drives the movable optical system.

[0011]

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 to 3 relate to a first embodiment of the present invention, in which FIG. 1 is a configuration explanatory diagram showing the configuration of a separation type optical head device, and FIG. 2
is an explanatory diagram showing the operation of the separate optical head device, and FIG. 3 is similar to FIG. 1.
3 is a flowchart showing the operation of the separate optical head device of FIG.

As shown in FIG. 1, the separated optical head device includes a semiconductor laser 21, a collimating lens 22, a beam splitter 23, a galvanometer mirror 24 as a reflecting mirror and a first actuator, and a detection optical system as a light detection means. 25. A fixed optical system 27 composed of a deflection angle detector 26 as an angle detection means, a rising mirror 28,
a movable optical system 31 that includes a condensing lens 29 and moves substantially parallel to the optical axis of the parallel light flux emitted from the fixed optical system 27 by a linear motor 30 as a second actuator to form a light spot on the optical disk 32; It is equipped with

The output of the detection optical system 25 is supplied to a controller 35, from which a deflection angle target value S1 for controlling the angle of the galvanometer mirror 24 is inputted to the positive input terminal of a subtracter 36. It has become. The deflection angle detector 26 is connected to the negative input terminal of the subtracter 36 . The output end of the subtracter 36 is connected to one input end of an adder 38 via a first phase compensation circuit 37. Further, the output of the detection optical system 25 is also supplied to a second phase compensation circuit 39 and a low-pass filter 40. The output terminal of the second phase compensation circuit 39 is connected to the other input terminal of the adder 38 via the first switch 41. The output of the adder 38 is input to the galvanomirror 24 via the first amplifier 42, which includes a controller 35, a subtracter 36, phase compensation circuits 37, 39, an adder 38, and a first switch 41. , and the first amplifier 42 constitute an angle control system. The output of the low-pass filter 40 is connected to a second switch 43
, and is input to the linear motor 30 via a second amplifier 44, and the low-pass filter 40, second switch 43, and second amplifier 44 constitute a tracking control system.

Next, the operation of this embodiment will be explained. In this embodiment, as shown in FIG.
is parallel to the moving direction 46 of the movable optical system 31, and the angle of the galvanometer mirror 24 is slightly varied in the vicinity of the adjusted angle, so that the light spot focused on the optical disc 32 is focused on the optical disc 32. Control to follow the track.

The light emitted from the semiconductor laser 21 is converted into a parallel beam by a collimating lens 22, passes through a beam splitter 23, and enters a galvanometer mirror 24. The galvanometer mirror 24 consists of a mirror supported so as to be rotatable about an axis perpendicular to the plane of the drawing, and a mechanism for driving this mirror, such as a magnet and a coil. The direction of reflection of the light flux incident on the galvanometer mirror 24 is controlled by the current flowing through the coil. The parallel light beam reflected by the galvanometer mirror 24 is reflected by the rising mirror 28 of the movable optical system 31 and enters the condenser lens 29 to form a light spot on the optical disk 32.

Then, the light reflected by the optical disk 32 passes through the condenser lens 29 and the raising mirror 2 again.
8, enters the fixed optical system 27, and enters the galvano mirror 24.
and is reflected by the beam splitter 23, and detected by the detection optical system 25.
incident on . The detection optical system 25 detects the amount of deviation between the light spot on the optical disc 32 and the information track from the reflected light from the optical disc 32, and outputs it as a tracking error signal. Further, the deflection angle detector 26 detects the rotation angle of the galvanometer mirror 24 and outputs a deflection angle signal. The rotation angle of the galvanometer mirror 24 can be detected by, for example, detecting the capacitance between the back surface of the mirror and an electrode placed opposite to the fixed part, or by detecting light emitted from a light source such as an LED. A method is used in which the light is reflected by a mirror surface or its back surface, and the reflected light is received by a two-split photodetector to detect a change in the optical axis.

The deflection angle target value S1 output from the controller 35 and the deflection angle signal are input to a subtracter 36, and the difference between them is determined. The obtained difference signal is subjected to phase lead compensation in order to stabilize the servo system by the first phase compensation circuit 37, and then sent to the adder 38 and the first amplifier 42.
The signal is inputted to the galvano mirror 24 via the galvano mirror 24, and an angle control loop for the galvano mirror 24 is formed. Within the frequency band determined by the characteristics of this angle control loop, the angle of the optical axis 45 of the light beam emitted from the fixed optical system 27 is maintained at an angle corresponding to the deflection angle target value S1 output from the controller 35. The tracking error signal is subjected to phase lead compensation for stabilizing the servo system by a second phase compensation circuit 39, and then inputted to the adder 38 via the first switch 41, and then inputted to the adder 38 by the first amplifier. At the same time, the low frequency component of the tracking error signal is inputted to the galvano mirror 24 via the signal filter 42, and the low frequency component of the tracking error signal is extracted by the low pass filter 40, and then sent to the second switch 43 and the second amplifier 4.
4 and is input to the linear motor 30, forming a position control loop for the light spot. In this optical spot position control loop, the linear motor 30 is driven in the low frequency region determined by the characteristics of the low-pass filter 40, and the galvanometer mirror 24 is driven in the high frequency region, so that the optical spot follows the track on the optical disk 32. controlled by.

Next, the operation of the controller 35 will be explained with reference to FIG. First, in step 1 (hereinafter, step is omitted and simply referred to as S1), the first switch 41 and the second switch 43 are opened to put the optical spot position control loop in an inactive state, and step S2 After setting the deflection angle target value S1 to zero, the controller 35 detects the amount of change in the offset of the tracking error signal between when the movable optical system 31 is on the inner circumference side of the optical disk 32 and when it is on the outer circumference side. Here, in S3, the movable optical system 3
1 to the inner circumference of the optical disk 32, in S4, the offset of the tracking error signal on the inner circumference is detected and set as B1, and in S5, the movable optical system 31 is moved to the inner circumference of the optical disk 32.
In S6, the offset of the tracking error signal at the outer circumference is detected and set as B2. Then, in S7, the deflection angle target value S1 is determined by setting S1 = C.(B1 - B2).

Optical axis 4 of the light beam emitted from the fixed optical system 27
5 and the moving direction 46 of the movable optical system are not parallel, and the amount of offset change in the tracking error signal is proportional to the degree of deviation from parallelism, so the amount of change in offset is multiplied by a constant coefficient C. By holding the deflection angle target value S1 in the controller 35 and outputting it to the angle control loop of the galvano mirror, the angle of the galvano mirror 24 is controlled so that the optical axis 45 is precisely parallel to the moving direction 46. It becomes like this. The operation of determining the deflection angle target value S1 may be performed only once at the stage of assembling and adjusting the optical disc device, or may be performed each time the power is turned on to use the optical disc device. Next, in S8, the first switch 41 and the second switch 43 are closed to put the optical spot position control loop into an operating state, so that the galvano mirror 24 is configured such that the optical axis 45 of the emitted light is aligned at the center angle. While being maintained parallel to the moving direction 46, the light spot is controlled to vibrate slightly in the vicinity of the center angle in the high frequency range, so that the light spot follows the track.

In this way, by using the galvano mirror 24 as an actuator for correcting the angle of the optical axis emitted from the fixed optical system and as an actuator for making the light spot follow the track on the optical disk, the optical axis can be particularly corrected. It is possible to prevent offset fluctuations in the tracking error signal due to movement of the movable optical system with a simple configuration without requiring a dedicated actuator. Further, since the offset of the tracking error signal is kept constant regardless of the position of the movable optical system 31, it can be easily corrected electrically.

FIGS. 4 and 5 relate to a second embodiment of the present invention, and FIG. 4 is a configuration explanatory diagram showing the configuration of a separate type optical head device;
FIG. 5 is an explanatory diagram showing the configuration of the optical axis position detector.

As shown in FIG. 4, the second embodiment is an example in which the fixed optical system of the first embodiment is modified.
2, is reflected by a galvanometer mirror 24, and is configured to be reflected and transmitted by a beam splitter 23. Further, an optical axis position detector 52 is provided so that the light transmitted through the beam splitter 23 is incident thereon, and is connected to the negative input terminal of the subtracter 36 . The optical axis position detector 52
As shown in FIG.
4, and the position of the incident light beam is detected by inputting the output of each light receiving area of the two-split photodetector 53 to a subtracter 54 and outputting the difference therebetween. . The rest of the structure is the same as that of the first embodiment.

The light emitted from the semiconductor laser 21 is turned into a parallel beam by the collimating lens 22 and is incident on the galvanometer mirror 24 . A part of the parallel light beam reflected by the galvanometer mirror 24 passes through the beam splitter 23 and enters the optical axis position detector 52 . Optical axis position detector 5
2 inputs the output of each light receiving area of the two-split photodetector 53 to a subtracter 54 and outputs the difference therebetween. This output signal indicates the position of the light flux incident on the two-split photodetector 53, and corresponds to the angle of the galvanometer mirror 24, and corresponds to the deflection angle signal in the first embodiment, so here also the deflection This will be referred to as an angle signal.

On the other hand, the light beam reflected by the beam splitter 23 enters the movable optical system 31, is reflected by the raising mirror 28, enters the condenser lens 29, and forms a light spot on the optical disk 32. And optical disc 3
The reflected light reflected by the condenser lens 29,
The light enters the fixed optical system 51 via the raising mirror 28, passes through the beam splitter 23, and enters the detection optical system 25. The detection optical system 25 detects the amount of deviation between the light spot on the optical disc 32 and the information track from the reflected light from the optical disc 32, and outputs it as a tracking error signal.

The galvanometer mirror 24 is maintained at an angle corresponding to the deflection angle target value S1 by the angle control loop, so that the optical axis 45 of the light beam emitted from the fixed optical system 51 is precisely parallel to the moving direction 46. At the same time, the galvano mirror 24 is slightly vibrated near the center angle by the position control loop of the light spot, and the light spot is controlled so as to follow the track on the optical disk 32.

In this way, in this embodiment, since the angle of the galvano mirror 24 is detected using a part of the light beam used for recording and reproducing information, the electrodes and the like are used as elements for detecting the angle. Since no LED or the like is required, the apparatus can be simplified, and the output of the two-split photodetector 53 can also be used for monitoring the power of the light emitted from the semiconductor laser 21.

Other functions and effects are similar to those of the first embodiment.

FIGS. 6 and 7 relate to a third embodiment of the present invention, and FIG. 6 is a configuration explanatory diagram showing the configuration of a separate type optical head device;
FIG. 7 is an explanatory diagram showing the configuration of the movable measuring optical system.

As shown in FIG. 6, the third embodiment is a modification of the second embodiment, and a target value setting circuit 61 is provided in place of the controller 35. The target value setting circuit 61 includes, for example, a reference voltage source and a variable resistor. The rest of the structure is the same as that of the second embodiment.

In this embodiment, the deflection angle target value is set at the time of assembly and adjustment of the separate optical head device. With the first switch 41 and the second switch 43 open, the direction of the optical axis 45 of the light beam emitted from the fixed optical system 51 is detected, and the optical axis 45 is detected in the moving direction 46 of the movable optical system 31.
The deflection angle target value S2 is set by adjusting the variable resistor of the target value setting circuit 61 so that it is parallel to the deflection angle target value S2. here,
Whether or not the optical axis 45 and the moving direction 46 are parallel can be determined by, for example, using a movable measurement system as shown in FIG. 7 in which the condenser lens of the movable optical system is removed and a semiconductor position detection device 62 is installed instead Using the optical system 63, the light beam from the fixed optical system 51 reflected by the upright mirror 28 is made incident on the semiconductor position detection device 62, and the incident position is detected and determined. After setting the deflection angle target value S2 which is the output of the target value setting circuit 61, the normal movable optical system 31 is attached, and the first switch 41 and the second switch 43 are closed to complete the angle control loop of the galvanometer mirror. By activating the optical spot position control loop, the optical axis 45 of the light beam emitted from the fixed optical system 51 is controlled to be precisely parallel to the moving direction 46, and the optical spot is positioned on the optical disk 32. is controlled to follow the track of

As described above, in this embodiment, the target value setting circuit 61 is used instead of the controller 35, which performs complicated operations such as detecting the amount of offset change in the tracking error signal and setting the target value. Since the angle target value is set and the control is performed, the device can be simplified and the cost can be reduced.

Other functions and effects are similar to those of the first and second embodiments.

[0033]

As explained above, according to the present invention, an actuator for correcting the angle of the optical axis emitted from a fixed optical system and an actuator for making a light spot follow a track on an optical disk can be used. This has the effect that it is possible to prevent the influence of the optical axis movement of the reflected light due to the movement of the movable optical system with a simple configuration, without requiring an actuator dedicated to optical axis correction.

[Brief explanation of drawings]

FIG. 1 is a configuration explanatory diagram showing the configuration of a separate optical head device according to a first embodiment of the present invention.

[Fig. 2] An explanatory diagram showing the operation of the separated optical head device.

[Figure 3
] Flowchart showing the operation of the separate optical head device in FIG. 1

FIG. 4 is a configuration explanatory diagram showing the configuration of a separate optical head device according to a second embodiment of the present invention.

[Fig. 5] Explanatory diagram showing the configuration of the optical axis position detector

FIG. 6 is a configuration explanatory diagram showing the configuration of a separate optical head device according to a third embodiment of the present invention.

[Figure 7] Explanatory diagram showing the configuration of the movable measurement optical system

[Figure 8]
Explanatory diagram showing the configuration of a conventional separated optical head device

[Figure 9]
An explanatory diagram showing a method of detecting fluctuations in the movable part shown in FIG. 8

[Explanation of symbols]

21...Semiconductor laser 24... Galvano mirror 25...Detection optical system 26...Deflection angle detector 27...Fixed optical system 30...Linear motor 31...Movable optical system 35...Controller 36...Subtractor 37, 39...phase compensation circuit 38...Adder 40...Low pass filter 41, 43...switch 42, 44...Amplifier 52...Optical axis position detector 61...Target value setting circuit

Claims (4)

[Claims] 1. Light source means for emitting emitted light as parallel light, a reflecting mirror rotatably disposed in the optical path of the parallel light, and driving the reflecting mirror to displace the optical axis of the parallel light. a fixed optical system having a first actuator, an angle detection means for detecting a rotation angle of the reflecting mirror, and a light detection means for receiving reflected light from a recording medium;
a movable optical system that is movably provided relative to the fixed optical system and focuses the emitted light onto a recording medium and causes reflected light from the recording medium to enter the fixed optical system; and the movable optical system. and a second actuator that drives the first actuator, which calculates the sum of the error of the output of the angle detection means with respect to a preset target value of the rotation angle of the reflection mirror and the tracking error signal detected by the light detection means. A separate optical head device comprising: an angle control system that supplies the tracking error signal to the second actuator; and a tracking control system that supplies the tracking error signal to the second actuator. 2. The angle control system is characterized in that the target value is set to a value proportional to an amount of change in offset of the tracking error signal due to movement of the movable optical system when the target value is set to zero. A separate optical head device according to claim 1. 3. The angle control system sets the target value to a value adjusted so that the optical axis of the fixed optical system is parallel to the moving direction of the movable optical system. 1. The separated optical head device according to 1. 4. The separation type optical head device according to claim 1, wherein the angle detection means includes a photodetector that receives a part of the parallel light reflected by the reflection mirror.