JPS61258337A - Detector for position of optical head - Google Patents

Abstract

PURPOSE:To detect the position of an optical head with no contact nor change with time and with high accuracy and high responsiveness. CONSTITUTION:A mirror 41 is set on an optical head 33 which moves by means of a part of the parallel luminous flux used for record/reproduction of an optical disk 31 and at a position where an incident window is formed for the flux (d). Then the mirror 41 reflects a part of the flux (d) in the direction having a fixed angle against the moving direction of the head 33. A photoelectric detector 34 serving as a photodetecting element is set at a fixed position for detection of the position where the parallel luminous fluxes reflected by the mirror 41 are irradiated. Thus it is possible to detect the position of the head 33 with no contact nor change with time and with high accuracy and high responsiveness. Furthermore no special light source is needed for detection of the head 33 and therefore the reduction of cost is attained for a no-contact position detector for optical head.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a position detection device for an optical head that records and reproduces information on an optical disc.

2. Description of the Related Art In recent years, optical disk devices have been commercialized and applied to image files, document files, or data files as personal storage devices.

Optical disk devices have a storage capacity more than 10 times that of magnetic disk devices, which are mainly used as external storage devices for computers, and can record and reproduce information without contact, making them a large-capacity alternative to magnetic disks. It is seen as a promising storage device.

However, optical disk drives require 5 to 10 times the time required to save information, that is, access time, as compared to magnetic disk drives, which is one of the obstacles to replacing magnetic disk drives with optical disk drives. optical disc V
In order to achieve high-speed access in a device, it is necessary to make the optical head lighter, to improve the torque of the optical head transfer system, and to detect the moving position of the optical head with high precision.

The state of high-speed access in a conventional optical disc device will be explained below with reference to FIG. FIG. 5 is a circuit block diagram showing an access mechanism of an optical disc device. Light is irradiated onto an optical disc 2 rotated by a spindle motor 1 from an optical head 4 driven by a linear motor 3 to record and reproduce information. will be carried out. Usually, spiral or concentric tracks are formed on the optical disc 2, and an address is assigned to each track.

In such an optical disk device, the access operation is as follows.
It is controlled by three types of control signals given by the CPU 5 for access control, namely, an access command (a), a target address (b), and a track jump command (C). The access command <a> is the target address (
b), in the access mechanism of FIG. 5, switch 6 is open and switch 7 is closed, and the control circuit:
The recording/playback state can be switched to the access state. In the access state, the control circuit performs two modes of access operations. One is rough access in which the beam near motor 3 is moved to move the entire optical head 4 near the target address, and the other is to correct the error with the target address that remains after the rough access is completed. This is fine access in which the lens 8 in the optical head 4 is caused to jump every track or every few tracks by a track jump command (0) to bring it closer to the target track. In the rough access mode, the control system receives the signal from the optical head position detector 9 and the target address (b
) is compared with the target position signal converted into an analog value by the D/A conversion circuit 10, and the linear motor 3 is driven so that the difference becomes zero.

In the fine access mode, after the optical head 4 is moved by the rough access, the tracking coil 11 moves the lens 8 in the optical head 4 by the difference between the address read from the optical disk 2 and the target address. A drive pulse is applied to the track jump, and the playback position is moved to the track of the target address.

Therefore, in this control system, the access time is determined by the movement time of the optical head 4 and the detection accuracy of position detection of the optical head 4. If the optical head 4 is made lighter, the torque of the linear motor 3 for transporting the optical head 4 is increased, and the position of the optical head can be detected with high precision, high-speed access can be realized. In addition, in FIG. 5, 12 to 14 are amplifiers, 15 is a differential amplifier, and 16.17
1 is an adder circuit, and 18 is a differential circuit.

Conventionally, a method using a contact type linear potentiometer has been used to detect the position of this optical head. An example of such a conventional optical head position detection device will be explained with reference to FIGS. 6 and 7. 6 is a perspective view of a direct type potentiometer, and FIG. 7 is a perspective view of a conventional optical head position detection device using the potentiometer shown in FIG.
0 is the conductor, 21 is the contact moving on the potentiometer, 2
2 and 23 are terminals at both ends of the resistor, and 24 is a terminal representing a variable resistance value detected by the contactor 21. Further, 25 is a direct type potentiometer, a 2G linear linear motor, 27 is an optical head placed on the linear motor 26, and 28 is a moving body that is moved by the linear motor 26 together with the optical head. A contactor 21 is attached. When the linear motor 2G moves, the contactor 21 attached to the moving body 2B changes to the linear potentiometer 25.
move while touching the surface. At this time, if a constant voltage is applied between the terminals 22 and 23 of the linear potentiometer 25, the voltage generated at the contact 21 changes as the contact 21 moves, and this voltage
a to the other end 21tl, further transmitted to the conductor 2G of the linear potentiometer 25, taken out from the detection terminal 24 of the linear potentiometer 25, and becomes a position detection signal.

Problems to be Solved by the Invention However, in the conventional configuration described above, since a contact type detector called a linear potentiometer 25 is used, the resistor 19 is worn out due to friction between the contactor 21 and the resistor 19, and the resistor 19 wears out over time. There is a risk of change. This is particularly dangerous in applications that require high-speed access hundreds of times a day, such as magnetic disks connected to computers.Also, detection accuracy is determined by the trimming accuracy of the resistance value of the potentiometer. In reality, it is about ±0.3%, which means that there is an error of about ±60μ in terms of position accuracy.This error can be absorbed by the track jump of the 7-fin access described above. This increases the number of jumps and slows down the access time.Also, regarding the responsiveness of the position detection signal, in the case of the linear potentiometer 25, it is only about a few 108 Z due to the vibration characteristics of the contactor 21. Therefore, the response characteristics of the control system of the linear motor 2a are suppressed by the detection system.Furthermore, in the linear potentiometer 25, the contact 21 is connected to the resistor 19.
Since the optical head 21 is pressed against the optical head 21, the movement of the optical head 21 deteriorates due to friction caused by this contact.

As described above, position detection using the conventional linear potentiometer 25 has problems in that it is not suitable for high-speed access in terms of aging, accuracy, and high-speed drive of a responsive optical head.

The present invention solves the above conventional problems, and aims to provide a position detection device that is non-contact, does not change over time, is highly accurate, has sufficiently high responsiveness, and is suitable for high-speed access of an optical head. shall be.

Means for Solving the Problems In order to solve the above problems, the optical head position detection device of the present invention includes a light source placed at a fixed position, and a parallel beam of light emitted from the light source at the fixed position. The first to convert to
and an optical system that is on a moving body that moves parallel to the traveling direction of the parallel light beam obtained by the first optical system and focuses the parallel light beam onto an optical disk and records a signal on the optical disk, or a second optical system for reproducing signals from an optical disk; The apparatus includes a reflecting means forming an entrance window for the parallel light beam on the body, and a photoelectric detector located at a fixed position and detecting the irradiation position of the parallel light beam reflected by the reflecting means.

According to the above configuration, a part of the parallel light beam used for recording a signal on an optical disk or reproducing a signal from an optical disk is reflected by the incident window for the parallel light beam formed on the moving optical head. By utilizing the change in the irradiation position of the reflected parallel light beam as the optical head moves, the position is detected by a photoelectric detector, and from this, the position of the optical head is detected. Therefore, since it is optical non-contact position detection, it has a long life and quick response, and as a photoelectric detector, it is easier to obtain high precision compared to a potentiometer. A good position detection device can be obtained.

In addition, since a part of the light used for recording and reproducing optical discs is used as a light source for position detection, the parallelism of the parallel light beam,
It has excellent stability of light intensity and can perform highly accurate position detection, and since there is no need to prepare a separate light source for position detection, it is possible to realize high precision position detection at low cost. Furthermore, since the reflection means that reflects the parallel light beam is used as an entrance window for the parallel light beam formed on the moving optical head, the optical head is sealed by this reflection means, and the optical It is possible to prevent dust from entering the head and fluctuations in the luminous flux due to this dust.

Embodiments Hereinafter, embodiments of the present invention will be explained based on FIGS. 1 to 4.

FIG. 1 is a schematic configuration diagram of an optical head position detection device according to a first embodiment of the present invention, in which 31 is an optical disk, 32 is a fixed optical system, 33 is an optical head, 34 is a charging detector, 35
is the spindle motor. The fixed optical system 32 is
It is composed of a light source 36, a condensing lens 37, a beam splitter 38, and a detection system 39 for detecting signals from the optical disk 31. The optical head 33 is composed of an objective lens 40 and mirrors 41 and 42.

Next, the operation will be explained. The light emitted from the light source 36 of the fixed optical system 32 is converted into a parallel beam (d) by the circumferential lens 31, passes through the beam splitter 38, and is emitted from the fixed optical system 32. The parallel light beam (d) is incident on the optical head 33 moving in a direction parallel to the direction of travel of the parallel light beam (d), and the optical head 3
3 is partially reflected by a mirror 41 that also serves as an entrance window, and then reflected by a mirror 42, and is reflected by an objective lens 40.
The information is focused onto the optical disc 31, and information is recorded and reproduced. On the other hand, the light reflected by the mirror 41 has its traveling direction aligned with the moving direction of the optical head 33, is bent in a direction forming a certain angle, and is incident on the upper end of the photoelectric detector 34. Next, when the optical head 33 moves to the inner circumference of the optical disk 31, the parallel light beam reflected by the mirror 41 moves from the position (ill) to the position (f), and the position where it enters the photoelectric detector 34 changes. do. Therefore, by detecting the incident position of the parallel light beam (e> or (f)) on the photoelectric detector 34, the position of the optical head 33 will be detected. It is possible to use a non-divided type semiconductor device detection element in which the photocurrent obtained from both ends of the element changes depending on the change in the photocurrent, or a divided type photodetection element such as a CCD type or MOS type linear image sensor.Also, the simplest detection element The incident position of the light can also be detected by differentially detecting the output using a two-split photodetection element.The detection accuracy is as follows.
Several μI for both semiconductor device detection element and linear image sensor
It has a positional resolution of about 1 to 20 μm, and a sufficiently fast response of several μsec can be obtained.

In this way, according to this embodiment, a part of the parallel light beam (d) used for recording and reproduction of the optical disk 31 is used to place a parallel light beam (d) on the moving optical head 33 at a position forming the incident window of the parallel light beam (d). A mirror 41 is provided that reflects the traveling direction of a part of the light beam (d') in a direction forming a certain angle with respect to the moving direction of the optical head 33, and the irradiation position of the parallel light beam reflected by this mirror 41 is provided. By providing the photoelectric detector 34 as a photodetecting element that detects the
It can be determined with high precision and responsiveness. Further, according to this embodiment, since there is no need to provide a special light source for position detection, a low-cost non-contact position detection device can be realized. Furthermore, a mirror 4 that reflects the parallel light beam ((1)
1 is a parallel light beam formed on the moving optical head 33 (
d'), the optical head 33
is sealed by this mirror 41, preventing dust from entering the optical head 33 as the optical head 33 moves;
Fluctuations in the luminous flux due to this dust can be prevented.

FIG. 2 is a schematic configuration diagram of an optical head position detection device according to a second embodiment of the present invention. This is the same as the first embodiment shown in FIG. This second embodiment differs from the first embodiment in that a mirror 41 that reflects part of the parallel light beam (d) is used to record and reproduce signals on the optical disk 31. The point is that a prism 43 with a reflective film attached to its end face is used so that it is integrated with the optical system.

Next, the operation will be explained. Similar to the first embodiment, when the parallel light beam (d) enters the optical head 33, a part of the incident light is reflected by the reflective film on the end face of the prism 43 on the incident side. Similarly, the position of the optical head 33 is detected by the photoelectric detector 34 . On the other hand, the light transmitted through the end face of the prism 43 on the incident side is transmitted through the prism 4
The light is reflected by the end face on the exit side of the optical disc 3 and is used for recording and reproducing the optical disc 31 through the objective lens 40 .

In this way, by combining the optical element that reflects part of the parallel light beam (d) and the optical element used for recording and reproducing the optical disk 31 into one using the prism 43 provided with a reflective film, The optical system within the optical head 33 is simplified, and it is possible to reduce costs, simplify adjustment, and reduce weight.

FIG. 3 is a schematic configuration diagram of an optical head position detection device according to a third embodiment of the present invention. This is similar to the first embodiment shown in FIG. This third embodiment differs from the first embodiment in that an aperture 44 is provided for the parallel light beam reflected by the mirror 41.
, and the diameter of the light beam incident on the photoelectric detector 34 is small.

Next, the operation will be explained. Similarly to the first embodiment, the parallel light beam for position detection reflected by the mirror 41 becomes a narrow light beam whose diameter is limited by the aperture 44 and enters the photoelectric detector 34. Similarly, the position of the optical head 33 is detected.

In this way, by inserting the aperture 44 into the parallel light beam for position detection whose traveling direction is bent and limiting the diameter of the light beam, the irradiation area of the light on the photoelectric detector 34 can be reduced. This makes it possible to improve the accuracy and linearity of the position detection signal.

FIG. 4 is a schematic configuration diagram of an optical head position detection device according to a fourth embodiment of the present invention. 9 as in the first embodiment shown in FIG. The difference between this fourth embodiment and the first embodiment is as follows.
The point is that an optical filter 45 with a sufficiently narrow band that includes the wavelength emitted from the light source 36 is used in front of the light receiving surface of the photoelectric detector 34.

Next, the operation will be explained. Similarly to the first embodiment, the parallel light beam for position detection reflected by the mirror 41 passes through an optical filter 45 placed in front of the charge detector 34, enters the photoelectric detector 34, and enters the first photoelectric detector 34. The position of the optical head 33 is detected in the same manner as in the embodiment.

In this way, the optical filter 45 is placed in front of the photoelectric detector 34.
By adding , the influence of stray light such as external light can be removed, and a position signal with good signal quality can be detected. On this occasion,
Normally, the light source used for the optical disc 31 is a very monochromatic laser beam, so to remove stray light, a filter that only passes the wavelength of the laser beam can be used, which can effectively remove stray light. I can do it.

Note that the first to fourth embodiments described above can be combined with each other, thereby realizing more stable and accurate position detection.

Effects of the Invention As described above, according to the present invention, the position of the optical head can be detected in a non-contact manner, so there is no change over time, and the position can be determined with high precision and good responsiveness. Furthermore, since the light source used for recording and reproducing optical discs is used as the light source for position detection, a stable and low-cost non-contact position detection device can be realized.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of an optical head position detection device in a first embodiment of the present invention, FIG. 2 is a schematic configuration diagram of an optical head position detection device in a second embodiment of the present invention, FIG. 3 is a schematic configuration diagram of an optical head position detection device in a third embodiment of the present invention, FIG. 4 is a schematic configuration diagram of an optical head position detection device in a fourth embodiment of the present invention, FIG. 5 is a circuit block diagram of an access mechanism of an optical disk device, FIG. 6 is an external perspective view of a linear potentiometer, and FIG. 7 is an external perspective view of a conventional optical head position detection device. 31... Optical disk, 32... Fixed optical system, 33.
...Optical head, 34... Photoelectric detector, 36... Light source, 41... Mirror, 43... Prism, 44...
・Aperture, 45...Optical filter representative Yoshihiro Morimoto Figure 5 Figure 6

Claims (1)

[Claims] 1. A light source located at a fixed position, a first optical system located at a fixed position that converts the light emitted from the light source into a parallel light beam, and this first optical system a second optical system, which is mounted on a moving body that moves parallel to the traveling direction of the parallel light beam obtained by the above method, and which focuses the parallel light beam onto an optical disk and records a signal on the optical disk or reproduces a signal from the optical disk; a system on the movable body that reflects part of the parallel light beam at a constant angle with respect to the moving direction of the movable body and forms an entrance window for the parallel light beam on the movable body; an optical head position detecting device comprising: a reflecting means; and a photoelectric detector located at a fixed position and detecting the irradiation position of the parallel light beam reflected by the reflecting means. 2. The optical head position detection device according to claim 1, wherein the reflecting means is arranged as a part of the second optical system. 3. The optical head position detection device according to claim 1, wherein an aperture is inserted between the second optical system and the photoelectric detector to limit the diameter of the parallel light beam. 4. The optical head position according to claim 1, wherein an optical filter is disposed in front of the light-receiving surface of the photoelectric detector to pass only wavelengths in a sufficiently narrow band including the wavelength of light emitted from the light source. Detection device. 5. The optical head position detection device according to claim 1, wherein a non-divided semiconductor device detector is used as the photoelectric detector. 6. The optical head position detection device according to claim 1, which uses a multi-divided photoelectric detector array as the photoelectric detector.