JPS6244332B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for reading a reproduced signal from a hologram disk device in which holograms are arranged in a spiral pattern on a disk.

Holograms are often used for signal recording because they can perform high-density recording and have redundancy in signal recording.

Hologram disks are used especially when recording large-capacity signals such as image signals and audio signals. In many cases, holograms with recorded signals are arranged in a spiral pattern on a disk, and the reproduced signals are read out one after another. A description of such a hologram disk can be found, for example, in 1972 IEICE General Conference Proceedings 4-72, "768 Editable Voice Response Hologram Disc." When reading a signal, the readout light illuminates the outermost hologram, then sequentially illuminates the inner holograms, and after illuminating the innermost hologram, it illuminates the outermost hologram again. In this case, the disk rotates at a constant speed, the readout light advances at a constant speed from the outer circumference to the inner circumference, and returns from the innermost circumference to the outermost circumference at a faster speed.

In such a reading method, since the reading light moves on the hologram disk, it is necessary to align the reading light and the hologram.
In particular, when moving the readout light to the position of the first hologram after reading the signal of the final hologram, the return speed must be as high as possible to shorten the time required for return. The alignment of the readout light and the first hologram is
Not only does this make the control system complicated, but in order to create a stable system, it is necessary to use elements with little delay in operation, which makes the control system expensive. The difficulty in controlling both position and velocity simultaneously is similar to controlling the read head of a magnetic disk.

With conventional hologram disks that record video signals, etc., it is acceptable that it takes some time for the initial alignment of the hologram and the readout light, but with hologram disks for voice response, it is possible to It is necessary for the readout light to return from the last hologram to the first hologram where information is written in the few tens of microseconds between the two phrases, and the hologram and readout light must be aligned in a short time. No. As a conventional alignment method, there is a method in which the position of the readout light is slightly vibrated in the radial direction of the disk, so that a signal can always be detected even if the position of the hologram is shifted. In this case, the readout light movement mechanism becomes complicated.

In addition, some devices use an alignment hologram to align the hologram disk and the readout light. In this case, the hologram is divided into two halves, the position of the reproduced image reproduced from each hologram is changed, and when the intensity of both reproduced images becomes equal, it is determined that the readout light and the hologram have been aligned. make a judgment. It is also possible to multiplex record the alignment hologram and the signal recording hologram on the same hologram track, and always maintain the position of the readout light on the track during signal readout. (Patent Application No. 52-70129 "Hologram Memory Readout Device") However, in this case, photographing the hologram becomes complicated, and since a reconstructed image for positioning is obtained during signal readout, the readout contents cannot be changed. The intensity of the reconstructed image is reduced accordingly.

The purpose of the present invention is to use the characteristics of a hologram to
The purpose is to easily control the position and speed of the readout light. In the present invention, the moving speed of the readout light is set to a value for aligning the readout light and the hologram, and a value for reading a signal from the hologram.
Furthermore, it is controlled to three types of values, including the return value of the readout light, and each value is switched according to the value of the reproduction signal, but the end of the return state of the light is not determined by the value of the reproduction signal, but the value of the reproduction signal. This is done over time. In other words, when the readout light is moving at a high speed, the reproduction signal is not detected and alignment is performed. A characteristic of holograms is that even if the readout light and the hologram are slightly misaligned, the reproduced image itself will only have a slight decrease in intensity and will not have any decisive adverse effect. Therefore, once the readout light and the hologram are aligned, if the disk is rotating at a constant speed, the hologram and readout light can be separated by moving the readout light from outside to inside at a constant speed. There is no major deviation and there is no problem in reading the signal. However, when starting to read the outermost hologram, that is, when starting to read a new signal, or when the readout light returns from the innermost circumference to the outermost circumference, it is necessary to align the readout light and the hologram. be.

In the present invention, the position of the readout light is detected, but the servo for the position of the readout light is not performed based on the detected value, but only the servo for the speed is performed. Performing servo for both position and velocity makes control complicated and difficult to perform well. Further, in order to reduce the blank time for signal readout, it is necessary to control the return speed of the readout light when the readout light returns, so speed control is necessary. Therefore, controlling the readout light using only speed servo simplifies the control system.

A feature of the present invention is that the control regarding the movement of the readout light is simplified, and instead of using a new special signal for positioning, a signal of the same form as the information to be recorded is used for positioning. By using the same detector used for hologram writing and reading information, the hologram writing device and reading device can be simplified. Furthermore, other features of the present invention include:
The purpose is to shorten the time required for alignment.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of an apparatus for explaining a hologram disk reading method according to the present invention. 101 is a motor for rotating a hologram disk, and 102 is a disk on which a hologram is recorded. The holograms are recorded in a spiral shape on the disk, but one of them is
Signals for track positioning are recorded in the outermost part indicated by 03, and the remaining part of the spiral indicated by 104 is a signal recording section, in which signals to be stored except for the positioning signals are recorded. are recorded in order from the beginning of 104.

Reference numeral 105 is a readout light that illuminates the hologram, reference numeral 106 is a coherent light source, and reference numeral 107 is a moving head, to which the light source is attached, and the head and the readout light move at the same speed. The speed of light 115 reproduced from the hologram is detected by the photodetector array 11
4, and after being amplified and smoothed by the electrical processing circuit 113, the signal is divided into two, one signal passes through the delay circuit 112, and the other signal directly passes through the comparator 11.
1 and their sizes are compared. In other words, whether the reproduced signal increases or decreases over time is cut in half. A signal corresponding to this determination is sent from the voltage generation circuit 110 to the linear motor control circuit 109 to control the moving speed of the head by the linear motor 108. Further, information such as the start point and end point of the signal recording section of the reproduced signal is amplified and sent directly to the voltage generation circuit 110.

The operation of the disk and linear motor when reading signals from the hologram disk will be explained. The rotation speed of the disk is M rotations per unit time, and the pitch of the spiral of the hologram on the disk is P (the distance from the center of the disk decreases by P per revolution of the spiral).
Then, in order for the readout light to illuminate the hologram in accordance with the rotation of the disk, the moving speed V of the head must be V=MP. Furthermore, if this relationship holds when the readout light is illuminating the hologram track, the readout light will not deviate from the hologram track.

Let the position of the starting point of the head be the farthest position from the rotation axis, and the moving speed of the optical head by the linear motor 108 be Vs. If the speed at which the head moves from the outside of the disk in the direction of the rotating shaft is set to 1/2 of the speed V, the read light also moves at the same speed as the head as it moves from the outside of the disk toward the inside. When the readout light illuminates the hologram on the outermost spiral, the detector 114 detects a reconstructed image. Outermost circumference 103 of the spiral of the hologram track
The above hologram is designed so that the alignment bit in the reconstructed image is always "1", that is, the bit at a certain position in the reconstructed image consisting of many bits is "1". Record. Vs=V/2
Therefore, the readout light illuminates the outermost circumference 103 of the hologram track at least once. In this case, the intensity of the detection signal of the alignment bit in the reproduced image changes as shown by the solid line 201 in FIG.
The output of the filtered result is as shown by the dotted line 202, and the delay circuit 112 and comparator 111 output 2
Look for the peak time of 02. In other words, the time at which the processed reproduced signal begins to become smaller than its previous value by the delay time Δt of the delay circuit is found.
The time when the smoothed detection signal reaches its maximum is the time when the readout light and the hologram are aligned, and from then on, if Vs=V, the readout light will not deviate from the hologram track. Eventually, the readout light illuminates the leading hologram of the signal recording section 104. When the signal of the last hologram on the hologram track is read, the electric processing circuit 113 starts the linear motor control circuit 1.
09, in response to which the control circuit reverses the direction of the linear motor current and returns the head to its starting position outside the disk. The position of the starting point only needs to be outside the outermost hologram, and does not have to be exactly the same position. In other words, the control circuit only needs to flow a constant current for a certain period of time, and the time is set to be longer, taking into consideration the influence of the difference in the transient time until the current becomes constant.

This embodiment will be explained using the time chart shown in FIG. The horizontal axis is time, 301 indicates the moving speed of the readout light, and 302 indicates the position. When a start signal is issued at time _t1 , the linear motor control circuit 109 sends a constant current to the motor to move the head.The readout light, which was stopped at the starting point outside the disk, moves along with the head to the disk at a speed of V/2. begins to move inside. Eventually, at time _t2 when the reproduced signal reaches its maximum, the readout light and the hologram track coincide. The speed of the optical head is set to V to move the readout light in line with the hologram track. The reconstructed image from the last hologram of the track includes an end signal indicating the end of the track, and at time _t3 when this signal is detected, the direction of the current flowing through the linear motor is reversed.
The head is again returned to the outside of the disk near its starting point. The time _t4 at which the return of the head ends is the time when a certain period of time t has elapsed since the end signal was detected, and T is the time when the readout light is outside the outermost circumference of the disk, considering the return speed. Choose a value like this.

Repeat the same operation below.

In the embodiments described below, the coherent light source itself is attached to the optical head, but the light from the external light source is guided through an optical fiber, one end of this fiber is attached to the head, and the readout light emitted from the fiber is A reproduced image can also be obtained by moving it together with the head. In addition, in the above embodiment, the moving speed of the head when aligning the readout light and the track is the moving speed V at the time of reading.
half of that. The greater the difference between the moving speed of the head during positioning and the moving speed V during reading, the shorter the length of the hologram track for positioning. For example, the speed at the time of positioning is the signal reading speed V
If the number of rotations per unit time of the disk is halved, the hologram for positioning only needs to rotate once at most, and the time required for positioning is at most 2/M time, where M is the number of revolutions per unit time of the disk. (It varies depending on the position where the readout light returns.) On the other hand, if the speed during alignment is 2/3V, the hologram for alignment will require a maximum of 2 turns, and 3/M time will be required for alignment. It is. The rotational speed of normal disks is often about 3600 rpm or less, and the maximum time required for alignment is about 30 msec at V/2, 2V/3
When , it is approximately 50 msec. When used in a voice response device, it is necessary to keep it within several + msec, and the moving speed of the readout light during alignment is preferably slower than V/2. Furthermore, if the speed difference is too large, the control circuit, mechanism, etc. will become complicated. Of course, it is also possible to make the moving speed of the head faster than V during alignment.

In the conventional method of controlling the speed in two stages, that is, when reading the signal and when returning the head, it is necessary to control the speed and the position at the same time, making the control complicated.

According to the present invention, since alignment with the hologram is not performed at the time of return, control is easy, and the speed of the head at the time of return can be increased, so the time required for return can be shortened. can do.

As described above, in the reading method of the present invention, in addition to the normally used signal recording equipment and reading equipment, a simple device that uses a delay circuit and a comparator is used to read holograms arranged in a spiral shape. The positioning of the readout light and the readout light can be realized at low cost, and the signal can be read out stably.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of an apparatus for explaining the hologram disk reading method according to the present invention, FIG. 2 is a diagram showing temporal intensity changes of a reproduced signal from an alignment hologram, and FIG. The figure is a diagram showing temporal changes in head speed and position in an embodiment for explaining the present invention. In the figure, 101 is a motor, 102 is a hologram disk, 103 is a hologram track for positioning, 104 is a hologram track on which signals are recorded, 105 is a readout light, 106 is a coherent light source, 107 is a head to which a light source is attached, 1
08 is a linear motor, 109 is a linear motor control circuit, 110 is a voltage generation circuit, 111 is a comparator,
112 is a delay circuit, 113 is an electrical processing circuit, 11
4 is a photodetector, 115 is reproduction light, 201 is the detection intensity of the signal reproduced from the alignment hologram, and 202 is the filtered result.
301 is a graph showing the speed of the head in the embodiment of the present invention, and 302 is a graph showing the position of the head.

Claims (1)

[Claims] 1. Using a disk in which holograms are arranged in a spiral pattern, the disk is rotated at a substantially constant speed, and readout light is moved in the diametrical direction of the disk to read the reproduced signal. In this method, a hologram that generates a reconstructed image consisting of a plurality of bits is arranged on the outermost periphery of the disk as a hologram for alignment, and the moving speed of the readout light is adjusted to adjust the speed of movement of the readout light when aligning the readout light and the hologram, when reading out the signal, and when reading out the signal. A method for reading a hologram disk, characterized in that control is performed so that three different values are obtained when the reading light position returns after completion of reading. 2. The reproduced images from all the alignment holograms arranged on the outermost periphery of the disk should have at least one bit that is "1" in common, and the reading light and 2. The hologram disk reading method according to claim 1, further comprising the step of determining whether the position matches the hologram. 3 To align the readout light and the hologram, the speed of movement of the readout light in the disk diameter direction is approximately 2 times the product of the spiral pitch and the number of revolutions per unit time.
The reading method according to claim 1, wherein the reading method is more than twice as large. 4 To align the readout light and the hologram, the speed of movement of the readout light in the disk diameter direction is approximately 1/1/2 of the product of the spiral pitch and the number of revolutions per unit time.
2. The reading method according to claim 1, wherein the number is 2 or less.