Patent US3946367 - Three dimensional electro-optical retrieval system

THREE DIMENSIONAL ELECTRO-OPTICAL
RETRIEVAL SYSTEM

BACKGROUND OF THE INVENTION

This is a continuation-in-part of application Ser. No. 316,661 filed Dec. 20, 1972.

This invention relates to electro-optical systems which track information on a multi-layered or multidepth recording medium to provide an output of the information contained in the recording medium. More particularly, the system relates to the continuous playback of audio/video information for home and professional use. This system is especially compatible with individual home black and white, or color television sets, utilizing the sets to continuously display the information contained in the multi-layered recording medium.

Electro-optical technology which records and retrieves information on two dimensional recording medium, such as conventional film or rotating discs, is well known in the art. However, many prior art electro-optical devices which deal with high density or high frequency information are hampered by the problems of the accuracy of placement of a pick up head, or the like, and synchronizing different types of information. Further, to achieve electro-optically a continuous playback with accuracy for a substantial length of time, a great amount of two dimensional recording medium is required.

By recording information in an electro-optical form in two dimensions on a medium, in any of a number of conventional manners, and by stacking the resulting recordings, it will be apparent that storage density will dramatically increase if a reliable electro-optical system for retrieving this information can be provided.

Assuming that the recording medium used is a conventional rotating plate which consists of discs stacked one on top of the other, it is apparent that the recording density on any disc need not be as great (e.g., for a stack of five discs it may be approximately five times less) as in present systems. With a spiral like track or a plurality of tracks recorded on each disc, in any form such as digital or analog, an electro-optical unit can be provided as described herein which can electrooptically track and electro-optically sense each and every layer and follow any desired track thereupon to achieve sensing and playback, or retrieval, of the information. This information may be discretely retrieved from a particular location in the multi-layered medium or may be continuously retrieved from each and every layer of the medium.

The ability to select a layer or depth from which information is to be retrieved allows the first information layer to be located below the surface of the plates thus making the system insensitive to dirt located on the surface of the plate.

Thus, the electro-optical retrieval of information, especially continuously, in a stack of two dimensional recording medium or recorded at various depths in a single medium will provide a reasonable playing time in a relatively small volume of the recording medium.

By the practice of this invention, information may be continuously retrieved in a reasonable playing time and in three dimensions with a high degree of accuracy.

The advantages inherent in a three-dimensional electro-optical retrieval system may be realized by providing a preferred embodiment of this invention a multi

layered recording medium which contains information. The image of the data plane of interest is projected by a lens means having a depth of field less than the separation between alternative data planes to a detector

5 means. A sensing electro-optical system which includes the lens means and detector means is thereby either electro-optically focused on the projected image of the desired information or the image is focused on the detector. A tracking electro-optical system tracks the

10 desired information located in the recording medium in the lateral and normal (or depth) directions, and thereby controls the positioning and focusing of the sensing system on the desired information. Tracking in the third dimension on a given track is achieved by the

15 desired track passing the tracking and sensing electrooptical systems or by both electro-optical systems scanning to compensate for the relative motion between the systems and the desired track.

20 SUMMARY OF THE INVENTION

It is an object of this invention to provide electro-signal track following in three dimensions.

It is also an object of this invention to provide a system for electro-optically retrieving information in three 25 dimensions.

It is another object of this invention to provide an accurate electro-optical retrieval system for continuously tracking and sensing information from a multilayered recording medium. 30 It is a further object of this invention to achieve an electro-optical retrieval system which results in a reasonable playing time with a relatively small volume of recording medium. It is still a further object of this invention to provide 35 an electro-optical retrieval system to track and sense desired information in radial and normal directions in a multi-layered recording medium or in a medium having information recorded at different depths. It is still another object of this invention to provide a 40 three dimensional retrieval system including a lens means having a depth of field less than the separation between alternative data planes.

BRIEF DESCRIPTION OF THE DRAWINGS

45 The invention both as to its organization and principles of operation together with further objects and advantages thereof may better be understood by referring to the following detail description of an embodiment of the invention when taken in conjunction with

50 the accompanying drawings in which:

FIG. 1 is a block diagram illustrating an exemplary embodiment of the basic concepts of a three dimensional electro-optical retrieval system for a multi-layered recording medium in accordance with this inven

55 tion.

FIG. 2 is a diagram illustrating an embodiment of an electro-optical head utilized to sense information on a multi-layered recording medium in accordance with this invention.

60 FIG. 3 is a side view of a two head system in accordance with this invention.

FIG. 4 is a front view of the two head system of FIG. 3 in accordance with this invention. FIGS. 5a, 5b and 5c are representations of the light 65 pattern on a split photodetector in accordance with this invention.

FIGS. 6a, 6b, 6c, and 6d and 6e are illustrations of various waveforms which occur in the electrooptical

DESCRIPTION OF THE PREFERRED
EMBODIMENT

3 4

retrieval system in accordance with this invention. This is in distinction to many prior art systems which

FIG. la illustrates a track of a recording medium with require exact focusing on the desired information in the

binary representation thereon, FIG. lb illustrates a recorded medium. A split photodetector 17 is utilized

track of a recording medium with a series of varying in a preferred embodiment but its equivalents, such as

density bands thereon, and FIG. 7c illustrates a track of 5 a pair of positioned light responsive resistors, semi-con

a recording medium with varying width opaque lines ductors, photomultipliers, or the like, will suffice,

therein, all in accordance with this invention. The split photodetector 17 comprises halves 17a and

FIG. 8 illustrates a perspective view of an embodi- lib. Each half provides an output signal representative

ment of a multi-layered recording medium in disc form, of the amount of light impinging upon its surface from

in accordance with this invention. 10 the light source 16 as the desired information in disc 11

FIG. 9 illustrates a side view of a multi-layered re- moves past the photodetector 17. The outputs of the

cording medium, in accordance with this invention. split photodetector 17 are connected, through amplifi

FIG. 10 is a block diagram illustrating another em- ers, as inputs to a differential amplifier 18 which in turn

bodiment of the basic concepts of a three dimensional is connected through its output to a first input of a

electro-optical retrieval system for a multi-layered re- 15 servo amplifier 20. The output of differential amplifier

cording medium in accordance with this invention. 18 is also connected to a servo amplifier 22, through a

FIG. 11 is a diagram illustrating another embodiment delay unit 23, to position the second electrooptical

of an electro-optical head including various data and system 13 in the lateral direction after a predetermined

image planes, utilized to sense information on a multi- time delay as will be described subsequently. Servo

layered recording medium in accordance with this in- 20 amplifier 20 which controls the lateral positioning of

vention. the lens 14 through control apparatus 15, is also provided with a second input 21 to allow a coarse setting of the control apparatus 15 and thus a coarse positioning of the first electro-optical system 12 in the lateral direc

Referring now to FIG. 1, a multi-layered recording 25 tion.

medium or plate 11 in the form of a plurality of discs Lateral positioning of the first electro-optical system

(only a small segment of which is shown) is illustrated 12 and the second electro-optical system 13 (after a

to contain tracks of information on a plurality of its delay) is thus achieved by the relative amount of light

layers. In this embodiment, plate 11 is capable of being -striking halves 17a and lib of split photodetector 17.

driven so that the desired information will pass a first 30 Due to the positioning of the split photodetector 17,

adjustable electrooptical system 12 at a first time and halves 17a and lib receive the same amount of light

pass a second adjustable electro-optical system 13 a when the first electro-optical system is properly posi

predetermined time thereafter. Electro-optical system tioned (i.e. straddling the information track) on the

12 follows an information track on a given layer or disc desired information. When equal amounts of light

of plate 11, and controls positioning of the electroopti- 35 strike halves 17a and lib, the output of the differential

cal system 13 which retrieves information. The plate 11 amplifier 18 will be zero, and thus no signal is provided

may also be in the form of a single disc which includes to the input 19 of servo amplifier 20 and the position of

information recorded at various depths therein. lens 14 as controlled by apparatus 15 is unaltered.

Electro-optical system 12 is utilized to electro-opti- When halves 17a and lib receive different amounts

cally focus and track the desired information in the 40 of light from light source 16, the input signals to the

lateral and normal or depth directions and includes a differential amplifier 18 likewise will be different,

lens 14 which is adjustable in the lateral and normal When this occurs, an output signal from the differential

directions by control apparatus 15. The lens 14 has a amplifier 18 will command, through servo amplifier 20,

generally short focal length, i.e. a fraction of a centime- a correction of lens 14 in the appropriate lateral direc

ter, and a large enough numerical aperture to provide a 45 tion.

depth of field less than the separation between alterna- FIG. 1 is illustrative of a two head or lens system in

tive data layers or planes of plate 11. accordance with this invention, i.e. a first electro-opti

A microscope objective, for example Tiyoda cal system 12 having a lens means 14 and a second

P171755 20x lens with a numerical aperture 0.40 oper- electro-optical system 13 having a lens means 32. In the

ated without a cover glass is satisfactory. Control appa- 50 disclosed embodiment the first electro-optical system

ratus 15 may be of any readily available design or com- 12 is utilized to track in the lateral and in the normal

bination of designs such as the type utilizing speaker directions. From this disclosure it is deemed evident

type coils in a permanent magnetic field to electromag- that a three head system could be realized by providing

netically change the position of the lens 14 to a selected separate electro-optical systems for the lateral tracking

focal plane. Control apparatus 15 is a two axes posi- 55 function and the normal tracking function of the first

tionable lens system. The axes of motion are, (1) in the electro-optical system 12 and for the sensing function

disc plane transverse to the track in a direction along a of the second electro-optical system 13. A one head or

disc radius; and (2) perpendicular to the track and the lens system in which a common lens means is utilized

disc itself. The control apparatus 15 controls the lateral will be described when referring to FIGS. 10 and 11.

and vertical position of lens 14 which in turn focuses 60 Having described the lateral tracking function of the

the desired image plan on the split photodetector 17. first electro-optical system 12, the normal or depth

The light source 16 positioned beneath the plate 11 tracking function of electro-optical system 12 will be

in the first electro-optical system 12 emits light and discussed. The depth or normal tracking function of the

floods the general area of the desired information on first electro-optical system 12 utilizes lens 14, control

plate 11 through lens 14, or other focusing equipment, 65 apparatus 15, split photodetector 17, summing ampli

to a light responsive unit such as a photosensor or split fier 24, video envelope detector 50, phase detector 25,

photodetector 17. The light from the source 16 need servo amplifier 26 and oscillator 27. The outputs from

not be carefully focused on the desired information. halves 17a and lib of split photodetector 17 are fur

ther connected through amplifiers, as inputs to the summing amplifier 24. The output of summing amplifier 24 is connected through the video envelope detector 50 to a first input to the phase detector 25. The output of phase detector 25 is connected to a servo 5 amplifier 28 in the second electro-optical system 13 through a delay unit 29 and to a first input 30 of the servo amplifier 26 in the first electro-optical system 12. A second input 31 of servo amplifier 26 is provided to allow a coarse setting to be made of the control appara- 10 tus 15 in the normal direction.

Oscillator 27 provides a dither signal of a predetermined frequency such as 100 to 120 hertz to a second input of phase detector 25 and to the first input 30 of servo amplifier 26. The dither signal from the oscillator 27 applied to the first electro-optical system 12 causes the lens 14 to vibrate in the normal or depth direction at a frequency determined by the output of the oscillator 27.

The output of the phase detector 25 is applied to the first input 30 of servo amplifier 26 to ultimately retain the lens 14 at an average position (in the normal direction) to focus on the desired information. The phase detector 25 will not provide an output signal when the 25 first electro-optical system 12 is focused at this average position in the normal direction and thus, the dither signal produced by oscillator 27 is free to alone cause equal excursions in the normal or depth direction of lens 14 through a true focus to the high and low focus, 30 as will be explained in discussing FIGS. 6a through 6e.

The movement of the plate 11 in the desired track direction (or the scanning by the electrooptical systems 12 and 13 because of relative motion between the systems and the disc) and the positioning of the first elec- 35 tro-optical system 12 in the lateral and normal directions allow the second electro-optical system 13 to focus upon any desired information location and follow its track continuously.

The second adjustable electro-optical system 13, 40 which finally sense or reads the desired information for retrieval thereof is, in effect, positioned and focused on the projected image of the desired information all in response to the first electro-optical system 12 after a predetermined time delay. Electro-optical system 13 is 45 utilized to electro-optical ly focus on and sense the projected image of the desired information, and includes a lens 32 similar to lens 14, a second light source 33, a condenser lens 34, a housing 35, and a cap structure 36. The cap structure 36 may be a screw-on cap, 50 and contains a plurality of photosensors, such as light responsive diodes 37, therein.

Light from source 33 floods the volume of interest and may be focused generally by a condenser lens 34 on the general area of the desired information. The 55 light need not be carefully focused. The lens 32 focuses the projected image plane of the desired information on a detector means such as the light responsive diodes 37 in the cap structure 36.

Servo amplifier 28 controls the positioning in a nor- 60 mal direction of the second electro-optical system 13 by electromagnetically varying the position of the lens 32 or alternatively by changing the position of the diodes 37 to the correct focal plane by moving the cap 36 up and down with respect to the housing 35. Alterna- 65 tively, the diodes 37 could be mounted in a diode holder or base (not shown), which is in turn connected to the cap 36. By moving the diode holder (not the

whole cap) the diodes 37 could be moved in the focal plane thereby resulting in a light weight system.

The predetermined delay provided is the time it takes the information focused at a first time by the first electro-optical system 12 to travel to the second electro-optical system 13 and is provided by delay units 23 and 29. In the embodiment wherein the electro-optical systems 12 and 13 both are removed to scan in the desired track direction, this time is the period necessary for the second electro-signal system 13 to reach the desired information after the first electro-optical system 12 is focused thereon.

In operation, the first electro-optical system 12 is positioned to track the desired information in the lateral direction by the described circuitry and electro-optical equipment which attempts to center laterally the desired track. More specifically, when the track is centered properly, the light from source 16 falls equally on both halves 17a and lib of the split photodetector 17 by the lens 14. When the light on half 17a and half lib of the split photo-detector 17 is not equal, differential amplifier 18, through servo amplifier 19, will adjust the lateral position of the lens 14 through control apparatus 15 until both input signals from split photodetector 17 in differential amplifier 18 are equal. The action is a conventional servo action and will provide a proper input signal to servo amplifier 20 representative of the fact that the first electro-optical system 12 is properly centered in the lateral direction.

The first electro-optical system 12 also is positioned to track the desired information in the normal (or vertical as viewed in FIG. 1) direction, on the average. This is accomplished through the previous described circuitry and electrooptical equipment which in part, may be common with the lateral tracking function of the first electrooptical system 12. More particularly, the output of the phase detector 25 is applied to the servo amplifier 26 in such a manner to retain the lens 14 in focus (on the average) on the desired track image. This is accomplished by comparing in the phase detector 25 the output signal from the video envelope detector 50 with the dither signal from the oscillator 27 (as explained in more detail in conjunction with FIGS. 6a through 6e) and allowing the dither signal to cause equal excursions in the normal direction of lens 14 when average focus in the normal direction is achieved.

After a predetermined delay provided by delay units 23 and 29, the second electro-signal system 13 is positioned and focused in response to the position of the first electro-optical system 12 to sense the desired information either discretely or continuously. This three dimensional electrooptical retrieval system will thereby reduce the absolute centering requirements and the flatness requirements of the layers of recording medium sandwiched together to form a multi-layered disc.

FIG. 2 illustrates in greater detail a portion of the second electro-optical system 13; In this embodiment, the second light source 33 is generally focused through a condenser lens 34 and the plate 11 (only a small segment of which is shown). Plate 11 comprises a plurality of layers with some of the layers containing information 38 as will be explained subsequently in discussing FIGS. 7a, lb and 7c. The image by the lens 32 through the housing 35 onto diodes 37 contained in the cap structure 36. The adjustability of this second electro-optical system 13 is accomplished through adjusting the lens 32 and/or adjusting the distance from lens

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Three dimensional electro-optical retrieval system