JPS6313264B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a disc-shaped recording medium on which signals are recorded (hereinafter referred to as a recording disc), and a signal track recorded on the recording disc (hereinafter referred to as a track). a converting means for reproducing the recording disk, a rotating means for rotating the recording disk at a substantially constant angular velocity, and a scanning movement for moving the scanning position of the converting means on the recording disk in a direction substantially perpendicular to the track direction. and control means for controlling the scanning movement means so that the scanning position of the conversion means is on the track.

Devices of this type include optical playback devices, magnetic disk devices, etc., and an overview of the optical playback device will be explained below.

On the recording disk, signals are recorded in shading or unevenness with a track pitch of less than 2 μm and a track width of less than 1 μm. The tracks on the recording disk can be either concentric or spiral, but concentric tracks generally record still images, and spiral tracks record images, audio signals, or image signals. Since the signals recorded on the recording disk are reproduced by rotating the recording disk at a predetermined angular velocity, for example, if a signal with a constant frequency is recorded over the entire surface of the recording disk. The spatial frequency of the recorded signal differs depending on the radius of the recording disk, and the signals recorded on the outer periphery have a lower spatial frequency and a longer recording wavelength. Therefore, even when image or audio signals are recorded, the signals recorded on the outer periphery have longer recording wavelengths on average. In the case of a recording disk with a diameter of 30 cm, and the part where the signal is recorded is between 10 cm and 30 cm in diameter, the average recording wavelength of the signal recorded in the vicinity of 10 cm in diameter is generally about 1 μm, and the signal recorded in the vicinity of 30 cm in diameter is generally about 1 μm. The average recorded wavelength of the signal is approximately 3 μm.
In order to reproduce signals from a recording disk that is recorded at such a high density, a light beam generated from a light source is focused onto the recording disk through an optical system to a diameter of about 1 μm, and the signal is then emitted from the recording disk. The reflected light or its transmitted light is received by a photodetector to detect the signal, and is focused on the recording disk in order to always obtain a high quality signal regardless of eccentricity caused by replacing the recording disk or vibration of the device. The optical beam is controlled so that it accurately scans the track (hereinafter, this control will be referred to as tracking control).
In order to obtain the control signal for this tracking control (signal representing the deviation between the light beam focused on the recording disk and the track), the main light beam for reading the signals recorded on the recording disk must be input from the recording disk. There are methods to obtain the reflected light or its transmitted light, or methods to focus and irradiate another tracking auxiliary light beam onto the recording disk and obtain the reflected light or the transmitted light. Obtained from the signal envelope recorded above. The envelope output of the reproduced signal varies depending on the recording wavelength of the signal recorded on the recording disk, and the envelope output of the signal on the outer circumference where the average recording wavelength is long is large, and the envelope output of the signal on the inner circumference where the average recording wavelength is short is large. The envelope output of is small. Therefore, the loop gain of the tracking control system is large when the outer circumference of the recording disk is being reproduced, and small when the inner circumference is being reproduced. Therefore, in conventional devices, if the loop gain is appropriately adjusted at the outer circumference, the loop gain of the tracking control system becomes smaller at the inner circumference, resulting in poor tracking accuracy and an instantaneous transition from track to track. (hereinafter referred to as "jumping"), there were also disadvantages such as instability.

SUMMARY OF THE INVENTION An object of the present invention is to provide a reproducing apparatus that can eliminate the above-mentioned drawbacks, perform stable tracking control over the entire recording area of a recording disk, and obtain a high-quality reproduced signal.

An embodiment of the present invention will be described below based on the drawings. Note that the same symbols are used for the same objects in the explanation of the drawings. In FIG. 1, a recording disk 1 on which signals are recorded in a spiral manner is attached to a rotating shaft 3 of an electric motor 2 rotating at a substantially constant angular velocity, and a light source driven by a light source driving circuit 55. The light beam 5 generated by the optical system 4 passes through a semi-transparent mirror 6 and a total reflection mirror 7 attached to a driving element (not shown) such as a piezoelectric element or a galvano mirror, and is converged onto the recording disk 1 by a converging lens 8.
The reflected light 9 passes through a converging lens 8, is reflected by a total reflection mirror 7 and a semi-transparent mirror 6, and is irradiated onto a photodetector 10 having two divided areas. Photodetector 1
A differential amplifier 11 obtains a difference output between the outputs from each of the divided areas of 0, and the difference output is passed through a drive circuit 13 to drive a total reflection mirror 7 attached to a drive element, and is applied onto a recording disk 1. Tracking control is performed by scanning the light beam 5 converged on the track in a direction substantially perpendicular to the tracking direction. The movable parts of the light source 4, the semi-transparent mirror 6, the total reflection mirror 7, the converging lens 8, and the position detector 14 that detects the radial position of the signal being reproduced on the recording disk 7 are connected to the transfer table 1.
5, and a gain control circuit 56 changes the gain according to the output of the position detector 14. The transfer table 16 is attached to the transfer motor 16,
The difference output of the differential amplifier 11 is passed through the low pass filter 17.
and is applied to the transfer motor 16 via a drive circuit 18. Therefore, the transfer motor 16 is a total reflection mirror 7
The light beam 6 reflected by the converging lens 18 is driven so as to be incident on the converging lens 18 almost perpendicularly on the average.

Details of the position detector 14 are shown in FIG. That is, the movable plate 21 is attached to the transfer table 15, and moves according to the movement of the transfer table 15 by the arrow 22.
It is starting to move in the direction of. A light beam generated from a light source 23 such as a filament lamp passes through the gap between the fixed plates 24 and irradiates the photodetector 25. The movable plate 21 shields the light beam generated by the light source 23, and the amount of shielding changes approximately linearly according to the movement of the movable plate 24, so the amount of light irradiated to the photodetector 25 also approximately linearly changes. The position of the transfer table 15 can be detected.

Next, it will be explained with reference to FIG. 3 that the envelope output of the reproduced signal is different when reproducing a signal on the inner circumference and when reproducing a signal on the outer circumference. 3A shows a signal recorded in shading on the outer circumference of the recording disk 1, and FIG. 3B shows a signal recorded in shading on the inner periphery. Reference numeral 31 indicates a recording bit, and the recording bits 31 are concentrically connected to form a track. a is the track width, b is the track pitch, and c and c' are the recording wavelengths of the signals recorded on the outer circumference and the inner circumference. longer than the recording wavelength c′ of the recorded signal. 32,3
2', 33 and 33' represent the beam spots of the light beam 5 converged on the recording disk 1, 32 and 32' represent the state on the recording pit 31, and 33 and 33' represent the beam spots of the light beam 5 converged on the recording disk 1. This shows the state on the unrecorded area between the pit and the recording pit.
It is assumed that the reflectance of the recording pit 31 is greater than that of the unrecorded area, and the beam spots 32 and 3
When comparing the amount of reflected light 9 in each state of beam spot 32, the amount of reflected light is larger in the state of beam spot 32 because the area irradiated to the unrecorded area is smaller. Furthermore, when comparing the amount of reflected light 9 in each state of the beam spots 33 and 33',
Since the beam spot 33' is irradiating a part of the recording pit 31, the beam spot 33'
The amount of reflected light is smaller in state 3'. Therefore, the difference between the amount of reflected light in the state of beam spot 32 and the amount of reflected light in the state of beam spot 33 is larger than the difference between the amount of reflected light in the state of beam spot 32' and the amount of reflected light in the state of beam spot 33'. Record disc 1
Reading the signal recorded on the reflected light 9
This is done by changing the amount of reflected light, so when a signal recorded on the outer circumference of the recording disk 1 is being reproduced, the envelope output of the signal is large, and when a signal recorded on the inner circumference is being reproduced. The envelope output of the signal is small when

Next, we will discuss the detection of the tracking control signal in the fourth section.
This will be explained with a diagram. The photodetector 10 consists of photodetectors 10' and 10'', and 41 is the photodetector 1 of the reflected light 9.
The beam spot on 0 is shown. center dividing line 42
roughly divides the beam spot 41 into two, and the direction of the dividing line 42 is the track direction on the photodetector 10. The light beam spot 41 consists of reflected light 43 from the recording pit 31 and reflected light 44 from the unrecorded area between the recording pits. The envelope output of the signals from the photodetectors 10' and 10'' is large when the recording pit 31 is long.
When the recording pit 31 is short, it is small. Since the tracking control signal is the difference in the output of the photodetector 10' by 10'', the larger the envelope output is, the larger the loop gain of the tracking control system is. The loop gain of the tracking control system is large when the signal is being played back, and it is small when the signal from the inner circumference is being played back. 4
If the loop gain of the tracking control system is controlled to be always constant by changing the amount of light beam 5 generated by the optical system, tracking will always be stable and a high quality reproduction signal can be obtained.

The gain control circuit 56 and light source drive circuit 55, which are configurations for changing the amount of light beam 5 generated from the light source 4, will be described below. The output signal of the reproduction position of the position detector 14 is applied to a gain control circuit 56, the output of the gain control circuit 56 is applied to a light source drive circuit 55 that drives the light source 4, and the light source drive circuit 55 receives the output of the gain control circuit 56. Light source 4 according to
The amount of light beam 5 emitted from the recording disk 1 is controlled to be small at the outer circumference of the recording disk 1 and large at the inner circumference. Therefore, the amount of reflected light 9 input to the photodetectors 10 and 10' changes depending on the reproduction position, and the envelope output of the signal from the photodetectors 10 and 10' remains constant and stable regardless of the reproduction position. and tracking control becomes stable.
Furthermore, even when special images such as slow motion images and quick motion images are obtained by performing jumping, the operation can be made extremely stable. This will be explained with reference to FIG. The outputs of the photodetectors 10' and 10'' are applied to envelope detection circuits 52 and 52'. Tracking control is performed by driving the reflecting mirror 7. Therefore, since the inputs of the envelope detection circuits 52 and 52' are always constant, for example, when detecting with a diode, the influence of the characteristics of the diode can be removed, and the tracking Control is stabilized.Jumping puts the tracking control system in an inoperable state, applies a jumping signal to the drive circuit 13, and controls the total reflection mirror 7.
to detect the target track and simultaneously apply tracking control. The target track is detected by envelope detection circuits 52 and 5.
A sum signal of 2' is obtained by a combining circuit 53, and further waveform-shaped by a waveform circuit 54, and the processing is performed using this signal. Since the output of the combining circuit 53 does not change depending on the radius of the recording disk 1, the target track can be detected reliably, and the light beam 5 converged on the recording disk 1 can be detected on the target track. Since the timing of detecting and applying tracking control is also constant, jumping is extremely stable.

Further, instead of driving the total reflection mirror 7 to perform tracking control, tracking control can also be performed by driving the transfer motor 16 and moving the transfer table 15 attached to the transfer motor 16.

In the above, we have explained the case of reproducing a signal recorded in shading, but even when reproducing a signal recorded in unevenness, the longer the recording wavelength is, the larger the envelope output of the reproduction symbol will be, and if the present invention is applied, it will be extremely stable. It becomes a device. Furthermore, the present invention can be applied to capacitive disk devices and magnetic disk devices.

Further, as a tracking method, there are a wobbling method, a meandering track method, etc., but the present invention can be applied to any tracking method. It goes without saying that the present invention can also be applied to a device for reproducing a concentric recording disk.

We have also explained how to optically detect the position detector, but there are methods such as attaching a rotary encoder or linear encoder and counting the pulses, and a differential transformer method.
Any device that can detect the playback position may be used.

As explained above, since the present invention changes the amount of light depending on the radial position of the recording disk at the scanning position of the conversion means, it is possible to obtain a high quality tracking control signal. In other words, when changing the circuit gain according to the radial position of the recording disk at the scanning position of the conversion means, the amount of reflected light that contributes to the tracking control signal decreases, and to prevent this, the circuit gain is increased, so the amount of light changes. However, according to the present invention, the amount of light emitted from the light source is increased so that the amount of reflected light contributing to the tracking control signal is constant depending on the radial position. Therefore, the quality of the tracking control signal does not deteriorate.

Further, according to the present invention, the apparatus can operate extremely stably even when obtaining a special image by jumping or searching by jumping.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
The figure is a detailed explanatory diagram of the scanning position detector, Figure 3 is an explanatory diagram of the recording state of signals recorded on the outer and inner circumferences of the recording disk, and Figure 4 is the reflected light irradiated onto the photodetector. FIG. 5 is a block diagram illustrating a case where a tracking control signal is detected using an envelope detection circuit. DESCRIPTION OF SYMBOLS 1... Recording disc, 4... Light source, 5... Light beam, 10... Photodetector, 11... Differential amplifier, 1
3... Drive circuit, 14... Scanning position detector, 15
. . . Transfer table, 55 . . . Light source drive circuit, 56 . . . Gain control circuit.

Claims (1)

[Claims] 1. A disk-shaped recording medium, a conversion means for reading a signal from a signal trajectory recorded by irradiating the recording medium with a light beam generated from a light source, and rotating the recording medium at a substantially constant angular velocity. a rotating means for moving the scanning position of the converting means on the recording medium in a direction substantially perpendicular to the signal trajectory direction; tracking control means for controlling the scanning movement means; scanning position detection means for detecting the position of the scanning position in the radial direction of the recording medium; A reproducing device comprising a light amount control means for changing the amount of light.