Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OE THE INVENTION
1. Field of the Invention
This invention relates to document storage and retrieval systems.
In a primary application the invention relates to storing information by
using a modulated light source to redistribute the material of a deformable
film coating.
2. Description of Pr:lor Art
A variety of file systems have been considered for storing many
documents onto a high resolution material. Microfilm systems optically re-
duce the original and photograph it on a high resolution emulsion. Photo-
graphic systems of this type, including scanned photographic systems, require
time-consuming wet photography.
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Thus new entries to the file take considerable time to be made available. In
addition portions of a photographic film storage medium cannot be separately
addressed at different times because the development process normally encom-
passes the entire film. Thus new documents cannot be added to an existing
photographic storage medium. Photographic storage appears best-suited to ap-
plications where the entire plate is exposed in a single interval such as
United States Patent 3,198,880 Photographic Disc Reproduction System for Tel-
evision Signals" issued to P.M.G. Toulon on August 3, 1965.
One solution to the problem of having the stored information immed-
iately available is described in United States Patent 3,314,073 "Laser Re-
corder with Vaporizable Film" issued to Carl H. Becker on October 20, 1964.
In this system a thin thermally vaporizable film is coated onto a plastic sub-
strate. An intense laser, focused on the coating, is used to vaporize the
coating and produce arrays of transparent holes representing the information
being stored. These can be immediately read out using light sources imaged
at the holes.
This system, however, has a number of practical problems. Firstly,
the large energies required to vaporize the film can only be realized by very
expensive, high power lasers at the desired writing speeds. Secondly the
strip format of the recording material, in the form of motion picture film,
results in relatively slow accessing times to specific regions. Also the lack
of an accurate tracking method results in relatively low resolution and thus
inefficient use of the area in recording data.
Rapid accessing times can be achieved using the disc format where
the radial motion is used to find the desired document and the circumferential
motion is used to rapidly read it out. Disc recording is normally used in ap-
plications where the entire disc is written on a single sequence. For example
in the recording of television programs, as is done in the MCA Disco-Vision
system, the entire disc is written at one time and copies are made from it.
In document storage systems, however, where individual documents are added at
different times, the disc presents serious tracking problems. If the disc is
removed and then remounted, the resultant
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eccentricities of the tracks from a slightly off-center mounting can cause
the tracks to cross and thus be destroyed. If large guard spaces are used to
avoid track crossing, the storage area is used inefficiently and a limited
number of documents can be stored. In addition to eccentricities, various
warping and distortions of the recording media can also cause the subsequently
recorded tracks to cross with previously recorded tracks and thus destroy the
stored information.
In the MCA Disco-Vision system, as with other disc recording sys-
tems, the information is recorded and played back at constant angular veloc-
ity. This makes inefficient use of the area of the disc and results in re-
cording power problems. Much greater recording power is needed in the outer
diameter parts of the disc because of the increased relative motion between
the disc and the modulated recording light source. In addition, the inner di-
ameters have resolution problems because the information is packed more close-
ly together. A given data rate, at the reduced relative motion, results in
greater packing density. A relatively large inner region of the disc is often
unused because of this consideration.
SUMMARY OF THE INVENTION
An object of this invention is to provide an information storage
system which allows rapid writing from relatively low-power sources in a for-
mat which can be immediately read.
It is also an object of this invention to provide a document storage
and retrieval system where the documents are rapidly scanned, stored on a rel-
atively ~nexpensive media using a low power source, and are capable of being
immediately and rapidly accessed, read out and printed.
It is a further object of this invention to provide a method of
high-density recording on a disc without the recorded tracks overlapping due
to distortion of the disc or a lack of concentricity during each recording
interval.
It is a further object of this invention to provide a method of ef-
ficiently utilizing the area of the disc and the recording power by recording
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at a constant linear velocity.
Briefly, in accordance with the invention, a recording medium is
used consisting
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of a deformable film deposited on a disc-shaped substrate. A
modulated liqht beam causes local redistributions of the material
of the deformable film resulting in information storage. To
insure that the recorded tracks do not overlap, yet have a high
packing density, a tracking light beam is used, having a fixed
radial distance with respect to the modulated light beam, so
that the tracks are accurately recorded with respect to the
previously recorded track. For optimum use of the area of the
disc, and to provide constant recording power requirements, the
disc is rotated so as to maintain a constant linear velocity of
the modulated light beam with respect to the rotating disc.
In a document storage and retrieval system the document is
scanned with the resultant signal modulating the writing light
beam. On readout, the readout light beam produces a recording
signal which is applied to a printer.
According to one broad aspect of the present invention,
there is provided an apparatus for recording information as
variations in reflectance comprising: a metallic deformable
film deposited on a substrate in a disc format; a modulated
light beam representing the information to be recorded focused
onto the metallic deformable film having an intensity which is
sufficient to liquefy but not vaporize the material of the
metallic deformable film resulting in a redistribution of the
material of the metallic deformable film which changes the
reflectance of a readout light beam; and means for rotating the
disc with respect to the modulated light beam and radially
translating the modulated light beam to produce a pattern of
recorded reflectivity information.
According to another broad aspect of the present
invention, there is provided a method for recording information
as variations in reflectance the steps of: modulating a light
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beam with the information to be recorded; focusing the modulated
light beam on a metallic deformable film deposited on a rotating
disc; radially translating the modulated light beam with respect
to the disc; and redistributing the material of the metallic
deformable film in the region of the focused modulated light
beam to change its reflectance with the modulated light beam
having sufficient energy to liquefy but not vaporize the material.
For a more complete disclosure of the invention,
reference can be made to the following detailed description of
several illustrative embodiments thereof which is given in con-
junction with the accompanying drawings, of which:
Figure 1 is a schematic representation of an embodiment
of the invention using a rotating disc;
Figure 2 is a cross-sectional representation of an
embodiment of the storage medium;
Figure 3 is a schematic representation of a tracking
system; and
Figure 4 is a schematic representation of an embodi-
ment of the storage medium using electrical energy for addressing.
It is often desired to store information from documents
and subsequently read them out in an automatic fashion to
replace manual files. A convenient method of storage is the
disc configuration shown in Figure 1 where the data from the
documents become tracks on the disc such as track 27 on disc 10.
The original document, not shown, is scanned on document scanner
14. This can be a conventional facsimile scanner having the
document on a rotating drum or a flatbed structure. The resultant
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scanned signal, in an appropriate form, is used to modulate the light from
laser 12. This appropriate form can be the analog signal itself, or pref-
erably a frequency modulated form of the signal where different values of
reflectance on the document represent different frequencies in the signal.
Alternatively, the scanned signal can be a digital representation of the doc-
ument information. In this form it is convenient to use various forms of
bandwidth compression, if desired.
The scanned signal is applied to modulator 13 which modulates the
light from laser 12. The resultant modulated light beam 28, in reasonably
collimated fashion is directed so as to be focused on the surface of disc 10.
It goes through partially silvered mirror 22, is reflected by mirror 23, and
goes through linear actuator 20 and pickup arm 26 to the recording region.
Linear actuator 20 is used to move the pickup arm 26 radially with respect
to rotating disc 10 while allowing the modulated light beam 28 to pass
through. The modulated light beam is reflected by mirror 24 onto air bear-
ing assembly 25 which includes the objective lens. The air bearing maintains
the objective lens at a fixed distance from the surface of disc 10 to insure
that the beam will be focused and produce a diffraction-limited spot.
Previous recording systems have used photographic emulsions. Al-
though these are very sensitive, having modest light requirements, they re-
sult in a very limited and inconvenient system. The stored document infor-
mation cannot be immediately read out since an awkward photographic develop-
ment operation is required. Systems such as United States Patent 3,314,073
described in the description of prior art, have used a vaporizable film
where the laser power renders the film into the gaseous state and removes the
material. These systems require very high laser powers and are thus awkward,
expensive, and have limited data writing rates. In the system described
here, a novel approach is used where the laser power causes a local deforma-
tion on a film by redistributing the material. Significantly reduced power
is required since the material is not brought to the gaseous state. Also,
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since these redistributions are of a form which can be optically read out,
the stored infor~ation is immediately available without any further proces-
sing. The size of the redistribution regions can be carefully controlled,
using this reduced power, so as to provide high storage density.
Disc 10 consists of coating 31 on substrate 30. The coating can
be a thin metallic film such as a 400 Angstrom film of tellurium. Coatings
in the thickness range from 100 to 500 Angstroms would appear to be suit-
able. The material should be such that, with modest energies, it is brought
momentarily to the liquid state. In this state, through surface tension,
the material redistributes itself in a manner which allows it to be subse-
quently read out.
The same configuration of Figure 1 can be used for reading out the
stored document and displaying it. Light beam 28 from laser 12 is now used
in an unmodulated fashion with document scanner 14 and modulator 13 not
functioning. This light beam, focused on recorded track 27 is selectively
reflected by the redistributions of material on deformable film 31 to create
a reflected light beam containing the document information. This light beam
traverses the same path as the incident light beam, in the opposite direc-
tion. Part of it is reflected by partially silvered mirror 22 and detected
by detector 15. This detector can be a photocell which produces the record-
ing signal 29. This signal can be applied to printer 16 which is a standard
facsimile printer using any of a variety of techniques to convert signal 29
into variations of reflectance on a substrate. Some of the printing methods
currently used include electrochemical, thermal, electrostatic, and mechan-
ical. These are all commercially available. Alternatively, the signal can
be applied to a television type display system where it can be viewed. An
intermediate storage system can be used to store the recording signal so
that it can be repeatedly applied to the display.
Previous disc recording systems have used constant angular veloc-
ity, with the motor speed remaining cDnstant. This results in increased
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writing power requirements at the outer radii of the disc where the linearvelocity is greatest. In addition, the area of the disc is inefficiently
used since the data is excessively packed together at the inner radii.
Usually only a limited area of the disc is used in these systems. In Fig-
ure 2, these problems are solved by recording and playing back with a cons-
tant linear velocity.
On recording a radial indicating signal 21 is derived from linear
actuator 20 which indicates the radial position of the objective lens assem-
bly 25. This radial indicating signal is applied to motor speed control 19
which controls motor ll such that the product of the radiusand the motor
speed remain a constant. This provides constant linear velocity of the foc-
used modulated light beam with respect to the surface of the disc 10.
On playback, recording signal 29 is applied to the data rate mon-
itor 17. This monitor measures the data rate of this signal 29 and applies
an error signal 18 to motor speed control 19 so as to keep the data rate
constant. A constant data rate corresponds to constant linear velocity if
the track has been recorded at constant linear velocity.
The data rate monitor can simply measure the bit rate if a digital
format is used. If a frequency modulated format is used the data rate mon-
i.tor can measure the frequency during the synchronization pulse regionswhere the frequency should be a constant. Alternatively, if a buffered sys-
tem is used with the printer 16, the data rate monitor can measure the status
of the buffer.
Figure l shows an embodiment where the recording and playback are
conveniently used in a single system. In some applications it may be more
convenient to use separate systems. For example, a disc containing a number
of stored documents could be used with a number of readout systems where
these documents are printed out or displayed. The readout-only system nor-
mally requires a lower power light source and no light modulator and is thus
less expensive.
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In many existing systems all of the information is written onto
the disc at a single time interval without ever removing the disc and re-
placing it. In these the registration of each newly written track with re-
spect to the previously recorded tracks is reasonably accurate since there
is no problem of concentricity. However, even in these systems, subtle
warpage or other distortions of the disc between recording periods can cause
problems. The newly recorded tracks can overlap previously recorded tracks,
thus destroying information. This problem is avoided by increasing track
spacing, thus reducing the storage capability.
This tracking problem is particularly aggravated in systems where
the disc is removed and then replaced, as would be the case in the desirable
versatile arrangements. Here the eccentricity caused by the replaced disc
not being exactly centered again can cause the tracks to cross and destroy
information. If guard bands are placed between recording intervals, much of
the information storage capacity is lost.
This problem is solved by the unique approach illustrated in Fig-
ure 2. Here the focused modulated light beam 42 is referenced to a prev-
iously recorded track 41 so as to insure that the tracks maintain the de-
sired spacing independent of eccentricity or distortion. Initially a refer-
ence track is written on the outer periphery of the disc. This can be doneusing a lead screw to radially drive a light source while the disc is being
rotated. A tracking light source, positioned a fixed radial distance with
respect to the modulated light source, is used to track the reference track
and thus position the writing beam. As new tracks are written, the tracking
beam tracks those to accurately position the focused modulated light beam
with respect to the previously recorded track.
In Figure 2 the modulated light beam 28 is produced by an argon
laser source 12 and modulator 13. This beam is transmitted through di-
chroic mirrors 51 and 43. These mirrors are transmissive to the shorter
wavelength of the argon laser and reflective or partially reflective to the
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longer wavelength of the helium neQn laser 46 which is the source of the
tracking light beam 52. The modulated light bea~ 28 is then reflected off
controllable mirror 24 and focused by objective lens 40 onto the surface of
rotating disc 10 to produce focused modulated light beam 42.
The tracking light beam 52 is reflected from dichroic mirror 51
and is partially transmitted by the partially reflective dichroic mirror
43. It is then also reflected off controllable mirror 24, at a slightly
different angle, and focused by lens 40 to produce a focused tracking beam
at track 41 which is displaced a fixed radial distance from the focused mod-
ulated light beam 42. The light reflected from track 41 traverses the same
optical path in the opposite direction and is partially reflected off par-
tially reflecting dichroic mirror 43. This reflected beam is focused by
lens 50 onto adjacent photocells 48 and 49. Their outputs are applied to
difference amplifier 47. This amplifier subtracts the two photocell outputs
to form error signal 53. This signal will be zero when the two outputs are
equal which corresponds to the focused tracking beam being exactly on the
previously recorded track 41. If it is off on either side, either photocell
48 or 49 will have a greater output, generating a positive or negative error
signal 53. This error signal is coupled to the mirror actuator system 45
which drives rotator 44 and thus pivots mirror 24 in response to signal 53.
The mirror actuator system 45 can be a servo-amplifier with rotator 44 a
servo-motor. As mirror 24 rotates the focused tracking light beam is brought
onto the center of previously recorded track 41 and the focused modulated
light beam 42 is simultaneously moved to remain a fixed radial distance from
the focused tracking light beam. Thus the focused modulated light beam is
kept a fixed radial distance from the previously recorded track.
The mirror 24, rotator 44 and objective lens holder 25 are all
supported by pickup arm 26 of Figure 1. This pickup arm is moved radially
by linear actuator 20 which provides the coarse radial motions which brings
the tracking system into the vicinity of the correct track. The rotating
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tracking mirror 24 has a range of a number of tracks so that the coarse
radial position provided by linear actuator 20 needn't be very accurate.
The tracking light system can also be used in the readout mode
without using the modulated light beam 28 from the argon laser 12. As the
focused tracking light beam tracks the previously recorded tracks it is
providing a readout of these tracks in addition to a tracking error signal
53. For example the output of either photocell, such as 48 as shown, can
be used for the recording signal 29 which is then applied to the display
system or printer 16. Alternatively, the sum of the two photocells 48 and
10 49 can be used for recording signal 29.
Assembly 25 in Figures 1 and 2 contains the objective lens 40
which must be kept a fixed distance from the surface of disc 10. This can
be accomplished by an air bearing system such as the one desc~ibed in United
States Patent 3,947,888 "Hydrodynamic Bearing Head Providing Constant Spac-
ing" issued to Manfred H. Jarsen On March 30, 1976.
As shown in Figure 3, a number of methods may be used to redis-
tribute the material in deformable film 31. Referring to the upper layers
only and ignoring the lower layers, the incident energy causes the material
in film 31 to become momentarily liquified. Due to phenomena such as sur-
20 face tension the material redistributes itself in a new configuration whichcan be subsequently read out. With sufficient incident power the material
in deformable film 31 will redistribute itself so as to form a void 33.
This can be read out in a number of ways. For example, the variation in
light transmission can be measured by transmitting a focused readout beam
through the film to a photocell on the other side of the substrate. Gen-
erally, however, it is more convenient to have the readout beam measure var-
iations in reflected light as shown in Figures 1 and 2.
The variations in reflection can be enhanced by the use of an ad-
ditional antireflection coating 32 placed between the deformable film 31 and
30 the light source. Firstly, however, this film has an important function in
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the writing operation by matching the modulated light beam to the deform-
able film 31. Anti-reflection coating 32 can provide matching by being a
quarter wave thick at the writing wavelength and having a refractive index
which is the geometric mean of that of free space and that of the deform-
able film. Alternatively it can be a more complex multilayer coating. The
film will thus minimize the reflections of the modulated light beam so that
most of the energy goes into deformable film 31.
The coating 31 can serve a variety of functions in the reflective
readout mode. For example it can minimize the reflections of the readout
beam from the film, and result in large reflections in the vicinity of
voids 33 because the coating 32 is intentionally not matched to the sub-
strate material 30. Alternatively, when using a readout wavelength differ-
ent from that of the writing beam, a relatively large reflection can be ob-
tained at the metal film and a small reflection at the void since, at the
readout wavelength, the coating 32 is better matched to the substrate 30
than the deformable film 31. Here the readout signal will have the opposite
polarity since it will decrease in the written regions.
The power requirements are further diminished by having the modu-
lated light beam liquefy only the upper portion of the film. Here the ma-
terial will redistribute itself in the forms shown in 34 and 35. In 34 the
material has redistributed itself into a concave region and in 35 it has
become a concave diffuse region because of the material used. These are
~lso read out due to their varying reflectivity. This variation is due to
combinations of effects. One effect is the partial destruction of the
matching between anti-reflection coating 32 and the deformable film 31 due
to the small separation. This causes increased reflections at the exposed
regions. Another effect is the spreading of the reflected light caused by
the concavity 34. This can cause an effective increase or decrease in re-
flectivity depending on the remainder of the optical system. The lens
action of the concavity can cause the reflected beam to be more or less
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concentrated on the receiving photocell as determined by the optics. The
diffuse region 35 will, in general, cause a spreading of the light beam
without lens action. This effect alone will result in an effective decrease
in reflectivity.
It is important to note that the particular mode of operation is
determined by the power level of the modulated light beam. To maintain this
at its proper value, the newly written track can be immediately read out
with the resultant signal used to control the power of the modulated light
beam. The readout should be done at some information independent portion of
the track, such as a portion corresponding to a synchronization region,
which should always produce the same readout signal.
The ability to use the anti-reflection coating 32, with its many
advantages is a result of the novel recording scheme used where the film ma-
terial is redistributed by the modulated light beam. In the prior art,
where high powers are used to vaporize the material, this coating could not
be used since it does not permit the escape of the vaporized material.
As shown in Pigure 3, both sides of the disc can be used. An ad-
ditional deformable film 31 and anti-reflection coating 32 is deposited on
the underside of the substrate 30. This can be separately written on and
read out in the same manner previously described to double the storage cap-
acity of each disc.
In the systems discussed thusfar the writing modulated light beam
itself caused the redistribution of material in the deformable film 31. An
alternate embodiment is shown in Figure 4 where the modulated light beam
acts as a control of another energy source which contributes to the process
of redistributing the material in deformable film 31. Here a photoconductor
60 and a transparent conductor 61 are deposited on the deformable film 31.
If desired, these coatings can also have some of the anti-reflection proper-
ties of coating 32 previously described. In addition, substrate 30 is made
of conductive material. A power source 62 is connected between the trans-
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parent conductor ~1 and the conducting substrate 30. The modulated light
beam 28, as before, is focused by objective lens 40 to form a focused spot
42 in the region of the photoconductive coating 60 and the deformable film
31. This focused modulated light beam changes the photoconductor from an
insulator to a conductor, thus completing the electrical path in the vicin-
ity of the focused light beam 42. This electrical energy is then applied
to that region of deformable film 31 and contributes to the process of re-
distributing the material of the film to create the writing action.
Although most of the embodiments illustrated used readout in the
reflection mode, light transmission can also be used where the readout beam
and photocell pickup are on opposite sides of the disc. This mode, how-
ever, is limited to the redistribution arrangement 33 of Figure 3 where a
void is created. It is also limited to recording the information on one
side of the substrate 30.
Formats other than the disc format illustrated can be used with
this system. The deformable film can be used in a rotating drum configura-
tion with the light sources appropriately translated along the axis of the
drum. Alternatively the deformable film can be used in a flat bed format
where the light beams are mechanical or electro-optically scanned across the
stationary deformable film. In all of the formats the tracking while writing
can be accomplished by referencing to a previously recorded track as was de-
scribed for the disc format.
The systems as described used the signal from a scanned document
to modulate the writing light beam to produce the redistributions of mate-
rail on the deformable film. The information used to modulate the light
beam can, of course, be any signal source. One important application is the
storage of digital information. Thus modulator 13 in Figure 1 can be driven
by a digital signal derived from a computer. The signal 29 read out by de-
tector 15 will then be the desired digital information.
The track format on disc 10 will generally be a spiral so that
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continuous information can be recorded over more than one track. In some
applications, however, it may be convenient to use a concentric ring format.
In this case the linear actuator 20, rather than moving continuously, moves
in radial steps following each revolution of disc 10.
Under some conditions disc 10 in Figures 1 and 2 may be subject to
excessive vibration. Under those circumstances air bearing assembly 25 may
not be able to adequately follow these variations, especially when they
occur at a relatively high frequency. This problem is solved by the use of
a forced air system, not shown, on the underside of the disc 10. This
forced air can be derived from an annular array of apertures positioned
under the disc. The air creates a force proportional to position which
both reduces the amplitude and frequency of the vibration. In addition, it
provides a viscous force which damps the vibration. These effects bring the
variations within the range of air bearing assembly 25.
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