US2363270A - Facsimile telegraph system - Google Patents

Description

Nov, 21, 1944, y L. A. SMITH 2% FACSIMILE TELEGRAPH SYSTEM Filed Oct. 3, 1942 2 Sheets-Sheet 1 PIC-3.2 FIG. 3

RELATIVE INTENSITY SENSITIVITY OF TUNGSTEN LIGHT PHOTO CELL E 0 400 e 0 e00 400 600 sec VlSlBLE- -'INFRA RED F VlSlBLE- 4-INFRA RED WAVELENGTH-'MILLIMICRONS WAVELENGTH-MILLIMICRONS FIG. 4 I FIG. 5

TRANSMISSION RELATIVE RERLECTON CHARACTERISTICS FROM E PAPER 5 DYE v B O 400 800 800 VlSlBLE INFRA RED V|$|BLE 4-1NFRA RED WAVELENGTH-MILLHMCRONS WAVELENGTHPM'LLIMCRONS INVENTOR 1.. A. SMITH BY W W V ATTORNEY NOV. 21, 1944. L, sMlTH I 2,363,27@

FACSIMILE TELEGRAPH SYSTEM Filed Oct. 3, 1942 2 Sheets-Sheet '2 FIG. l0

A- FROM AER B-FROM INK RELATIVE RELATIVE REFLECTION OUTPUT INK AREA NO FILTER ON PAPER 400 6 o VISIBLE L,INFRARED F-VISIBLE INFRA RED WAVELENGTH-MILL! M IQRONS WAVELENGTH-MILLIM ICRONS FIG. 6 FIG. 9

RELATIVE AFRoM PAPER RELATIVE OUTPUT TRANSMISSION FIBFER W'TH F'LTER B-FBOM INK I I 400 600 a 0 400 600 500 v|s|aLE- -|NF A RED |-v|s|BLE -!NFRA RED WAVELENGTH-MILLIMICRONS WAVELENGTH-MILLIMICRONS INVENIOR L. A. SMI'TH ATTORNEY Patented Nov... 21, 1944 2,303,210 FACSIMILE mnscaarn SYSTEM Leonard A. Smith, Nutley, N. 1., asslznor to The 4 Western Union Telegraph Company, New York, N,- I. a corporation of New York,

' Application October 3, 1942, Serial No. 460,604

v 4 Claims. (Cl. 178'6.6)

The present invention relates to photoelectric scanning systems, and more particularlygto an improved system for deriving the maximum useful response from a photocell employed in a facsiniile telegraph scanner.

A major difiiculty encountered in providing facsimile communicationservice to the general 'public with facsimile telegraph equipment employing a photosensitive cell at the transmitter is that little or no control may be had over the writing medium employed by a prospective patron of such a service when inscribing a message. Special writing materials may be provided by the concern offering the service for the patron's use, but business reasons mak it preferable to encourage the patron to use his own writing materials. This applies to typewriter ribbons, mimeogr aph inks, special drawing inks,

writing inks, and pencils. One important object of the present invention ,is to make it unnecessary to ofier special writing materials to prospectivepatrons of a facsimile communication service. Facsimile communication service to the public is thereby rendered more flexible in that it will suit the more varied needs of prospective patrons.

- In carrying out the invention, the optical arrangement, which illuminates the subject matter to be transmitted and which collects light transmitted through or reflected from the sheet or support bearing this subject matter, is provided with a device having selective radiant energy. transmission properties, thereby providing an improved result which will be pointed out-in the description of two illustrative embodiments appearing hereinafter.

' Another object of this invention is to provide for improving the useful response of a photo- Figs. 2 mt are curves illustrating the results obtained by a photoelectric scanning system having the several components thereof selected for the accomplishment of the purpose of the invention; and

Fig. 10 is a diagrammatic representation of 9.

- facsimile telegraph system in which the present invention may be advantageously employed.

The principle'of the invention and its application to a pickup system useful in a facsimile telegraph scanner or other signal generating device will be explained with reference to Fig. 1 and the curves of Figs. 2 to 9. In Fig. 1, in designates a source of radiant energy, preferably luminous, and H designates a radiation sensitive device having. more or less selective sensitivity to portions of the radiant energylying within the spectrum emitted by the source Hi. The radiation sensitive device ll may be any of the well knowntypes of photo or radiation sensitive cells or. tubes heretofore proposed in the art and will be referred to hereinafter as a photocell. The source i0 is usually a tungsten filament lamp vwhich has a white light output composed of the various colors of the visible spectrum plus invisible components extending into the infra-red region. The term light will be used hereinafter as synonymous with the total radiation- Y. from the source "Land the source ID will be referred to as the light source. The photocell H .issensitive to thesediiferent colored components which make up-the scanning light and is employed to translate the reflected light into n electrical energy in the form of signals appearing electric tube or cell exposed to variations in radivide improved response of a photoelectric cell or tube by removing components of radiant energy impinging on-the photocell or tube-to which the photocell ortube is most responsive.

Other and more specific objects of the invention are defined by the terms .of the appended claims and will be apparent from the following description taken in connection with the accompanying drawings, in which:

Fig. 1 is a diagrammatic representation of an e s nmn system utilizing the presentm ventionr 1 the drawings.

in the output circuit of an amplifier l2.

A light source of the tungsten filament type .has its maximum energy in the invisible infrared region, as shown by the curve of Fig. 2 of In Figs. .2 to 9, the curves are plotted with wave lengths in millimicrons as abscissae and with relative. values of light intensity as ordinates. The approximate limits of the visible portion of the spectrum ar indicated for each curve. Fig. 3 shows the responsiveness to variouswave lengths of the total spectrum of the light source I 0 oiv the type of photocell normally employed. A caesium cellwas selected ;for illustrative purposes as such a cell is usually used in pickup devices. A sheet of paper l4 hearing markings l5, such as characters of a message for transmission by the facsimile process, is arranged so that relative movement between the source It and the sheet l4 is produced in any known' manner wherebylight from the source It "is projeeted'successively onto elemental areas of] the sheet ll. In areas or the sheet ll which do not contain markings I! the light is reflected onto the photocell throughout the entire i'requency range of light from an ideal uniform source assumed to be substituted for the practical source In, as shown by the curve of Fig. 4 01' the drawings. This curve or relative reflection assumes equal intensity or allcomponents in the light source.

Assuming that the subject matter for transmission by the facsimile process is composed of black characters on white paper, the result of the scanning process may be described in the following terms. when the incident light falls on the unmarked background of the sheet I, a high percentage of this incident light is reflected from the paper and collected by the photocell ll, causing a relatively large change in the output of the amplifier H, from the minimum incident light condition. If the relative movement between the sheet H and the light source it causes the light to be incident on a black area forming a part of one of the markings IS, a large portion of the light is absorbed by the black area and only a small percentage is reflected onto the photocell. Since the output of the photocell is dependent upon the amount of light directed onto its collecting element, and the quantity of light reflected from the black area is small, the change in the output of the amplifler i2 is small in comparison to the minimum incident light condition. Where writing or printing materials, such as black India ink, black lead pencil, black printers ink or black typewriter ribbon, are provided for the purpose of inscribing or otherwise marking a message sheet, a pickup system of the kind shown in Fig. l produces signals in facsimile in the output circuit of the photocell and hence in the output circuit of the amplifier i2 in the manner just described. If the subject matter to be transmitted con sists of a colored ink on the reflective surface oi a paper sheet and this colored ink has the prop= erty of absorbing only a relatively small portion of the incident light, the electrical output of the photocell, when the light is incident on one of the characters of the subject matter, will not differ greatly from the electrical output of the photocell when the'light is incident on the reflective surface of the'paper sheet. The resulting record produced at a recorder supplied with signals generated by the photocell it will not have sufficient contrast between the two levels.

Many substances such as fountain pen inks derive their characteristic color from dye stuffs. To the eye, a character written, or printed or otherwise impressed on the reflective surface of a paper sheet with such inks may appear to be quite dark as compared to the paper background because a large proportion of the visible light falling on the character is absorbed and only a small'proportion of the visible light corresponding to the characteristic color oi the dye is reflected to affect the eye. The infra-red content of the incident light, even if it is reflected from the area in question, is not visible and therefore does not affect the eye.

Substantially all known dye stuffs have the property of freely transmitting wave lengths corresponding to the invisible infra-red rays which will be reflected by the paper underneath the dye marking, and will be retransmitted back through the dye marking to be incident on the radiation sensitive portionof a photocell. If the visible components of the incident light are negaseaavo lected and only the infra-red components considered, it will be round that there is very little difference in the total energy containedin the light reflected from unmarked areas of the paper sheet and areas of visually dark characters produced by the dye.

It should be pointed out that ink normally consists of a vehicle being merely a means of retaining the dye stuff in a form suitable for writing or printing purposes. In general, the radiant energy absorption characteristics of the vehicle used may be neglected and the dye stufl' considered as the controlling factor. Color as is well known is the result of a selective absorption and reflection of light rays. A writing fluid composed of a dye stuiI and a vehicle which produces a visible record of some definite color reflects a large percentage of the light rays of this color. In addition, however, the reflected light contains a very large percentage of infra-red rays present in the incident light. As previously pointed out, these infra-red rays are reflected from the paper underneath the ink with little or no absorption by the dye stufl. contained therein. In accordance with the invention, a selectively absorbent screen or fllter i6 is placed either, as shown, in the light path from the source it to the sheet I or, if desired, in the light path from the sheet it to the photocell M.

Fig. 5 shows the light transmission characte istics of a typical dye stuff and Fig. 6 the re= flection characteristic of an area written on ordinary paper with an ink employing this dye. 'I'hesecurves assume equal intensity of all com ponent parts of the incident light used in do taining the characteristics. A purple dye was used when obtaining the curves of 5 and 6, and the curve of Fig. 4 was obtained by using a sheet of ordinary paper which may be readily obtained. However, it will be understood the underlying principle of the invention herein and illustrated by the curves of Figs. 2 to 9 applicable to dyes of all colors and to any type of paper providing the effect 01 visual com ponents is considered.

The output energy of the amplifier i2 con-= trolled by the photocell it will depend upon the magnitude of the components of difierent wave lengths contained in the light incident as the sheet I l, the percentage oi these various com" ponents contained in the reflected light, and the relative sensitivity of the photocell to the various components. Therefore, a combination of the curves of Figs. 2, 3 and 4 will produce the curve A of Fig. '2' which shows the distribution of energy produced in the output of the photocell by light, using the paper selected by way of example irom which the curve of Fig. 4 was obtained.

Similarly, a combination of Figs. 2, 3 and 6 will produce the curve B of Fig. 7 for the distribution of power resulting from light reflected from the character lb.

The ratio of the areas under the curves A and B of Fig. 7 will be an indication of the relation ship between the power outputs of areas of paper background and the markings is, respectively.

It will be seen that in the longer wave region in the neighborhood of the infra-red portion of the spectrum, there is a fairly large percentage of power both for the paper background and the character. The large amount of power due to the longer wave lengths in the infra-cod region reflected from the paper through the marklugs is detrimental, since they greatly reduce the ratios of power of the two cases, a high ra= and photocell ll.

tio being desirable. By introducing the selective optical-filter It in the beam of light which scans the message, the longerwave lengths in the infra-red region of the spectrum can be reatly reduced. The removal of the infra-red portion of the spectrum will reduce the total power output, since there wm be less total light the results of this invention. It shouldbe understood that the curve of Fig. .8 shows the transmission characteristic of a filter selected by way of example and that other filters may be employed which result in producing the desired high ratio between the power outputs of the cell.. Curves A and B of Fig. 9 show the result obtained when the optical filter having the transmission charateristic of Fig. 8 is introduced at any point in the light pathbetween the light Ill These curves are for the same combination of dye characters impressed on the paper used in obtaining the curve of Fig. 7 without a filter. It will be noted that, although the total area under each curve is considerably less for the case covered by Fig. 9 thanvforthat of Fig. '7, the ratio of the output powers for the character and the plain background of the sheet H is greatly increased. The reduction in total power is of no consequence, as it can easily be offset by increased amplification of the electrical output of the system in the amplifier I2, or

i by any other known means.

The choice oi the optical filter l6 for use in a pickup-system employing the present invention will depend upon the characteristic of the color content of. the light reflected from areas covered with the particular color of the ink being considered. fWhere, as will normally be the case, a difierent color may be used for each d if- I ferent piece of subject matter, such as signatures by diflerent persons using fountain pen ink, the color of which is not under control of the person who is to transmit a facsimile of the written of scanning may be employed in practising the light from a suitable source as. I: desired, tn

light from this source may be 'concentratedby a lens 21 upon the surface of the message sheet IS. The light incident on the sheet is re.-

fiected therefrom into a light sensitive device such as the photocell 29, the latter'being suitably supported in a housing or the like (not shown) at a proper distance from the outer periphery of the drum 2|. The spot of light pro-, Jected upon the surface of the drum by the lens 21 is caused to traverse the drum in a longitudinal direction'as the drum rotates by reason ofv the axial movement imparted by the screw means 24. In this manner the spot of light will follow a helical tpa'th as the drum 2| is rotated,

thus producing a scanning action.

The foregoing method of obtaining a seaming movement as well as various other methods of scanning a given field are wellknown', and it will be understood that any of the known methods inventiom j The light which is incident upon the photocell 29 is interrupted by a shutter or light chopper 3|, which may, as illustrated, be a disc, having a series of equally spaced openings or notches 32 adjacent its outer edge. Where the reflected .beam is to be interrupted as shown, a lens 33' serves to bring the reflected light beam to a locus substantially in the planeof the disc 9| so that it may passthrough the openings 32 in matter, a filter may bev selected which operates l to eliminate the infra-red or other unabsorbable content of the light and permits transmission of the remaining absorbable content of the light to be incident on ink of substantially any color. This also applies where both the absorbable and the unabsorbable components are incident on the ink and the filter is interposed in the path of both these components after reflection. Also, the invention is applicable to characters on a transparency which are impressed or written thereon by colored inks. In this case, the infrared or other unabsorbable component may be prevented from passing through the ink and succession. The disc 3| is secured upon a rotatable shaft 34 which is driven in any suitable .manner, either from the motor 23 or a separate source of mechanical power. 1 The number or openings in the chopper disc and the speed of rotation of the shaft may vary within wide limits,.vdepending upon the desired ,rate of scan ning, the constants of the communication circuit employed between stations and other factors. The output appearing across the terminals of the photocell 29 is supplied to the amplifier 31 for transmission over the line conductors L or any other desired communication channel to the receiving amplifier 38. The output of the amplifier 38 is inverted by a signal inverting device 39 so that a positive reproduction of the original subject matter [9 may be obtained by employing a recording stylus.

One output terminal of the inverter 39 is con 'nected to the stylus H, the other terminal being connected to the scanning drum 42 of the receiver which serves as a conductive platens The scanning mechanism of, the recorder is shown as being similar to that of the recorder; Any recording instrumentality may be substituted for the stylus 4|, and where a photographic recording is obtained; the inverter 39 I maybe omitted.

the transparency or the unabsorbable component may be removed after it has passed throughthe transparency by a filter selected in accordance with this invention. I

Referring to Fig. 10, which illustrates a facsimiletelegraph system embodying" the invention, a message sheet l8 having a message or 1 other subject matter l9 written, stamped or printed thereon with any kind of ink is mounted A selective optical filter 43, similar in all respects to the filter I6 of Fig. 1, is shown as being locatedin the light beam which is incident on the message sheet l8. However, as pointed. out

above, this filter may be located atany point between the message sheet and the photocell 29.

- In operation of the facsimile system disclosed in Fig. 10, that portion of the total light flux emitted by the light source 26 which will not be absorbed by the ink'composingthe characters I9 upon a drum 2|} which *is rotated through a suit-v v able driving connection 22 by a motor '23.

of the subject matter to be transmitted is absorbed by the selective filter 43. Therefore, the

- ratio of the power output of the-photocell when Screw means are provided for advancing-the message sheet bearing drum 2| axially as it ro-' tates so that the entire field will be covered by the background 01' the sheet" is 'scann'ediscon-" i siderably in excess of the power outputfrom the photocell when the subjectmatter scanned,

, to produce relative movement between said surface and said device, means to direct a beam of radiation from said source upon said directive surface, means to direct radiation from said refiective surface to said radiation sensitive device, and a selectively absorbent filter positioned between said source and said device, said source,

said filter, and said device having the respective characteristics of emitting rays of maximum intensity, maximum absorption and maximum sensitivity in a common region of the spectrum whereby the response of said device will be, primarily, in accordance with the relative absorption characteristics of said surface and said markings thereon, in the remaining portion of the spectrum of said source.

2. A photoelectric scanner for a facsimile telegraph system for generating signals in accordance with markings upon a surface in which the radiation absorption characteristics of said markings and said surface are similar in one portion of the spectrum and dissimilar in other portions of the spectrum comprising a source of radiation, a radiation sensitive device, means to direct radiation from said source upon a sheet having subject matter inscribed thereon in ink for transmission by a facsimile telegraph process, means to direct radiation from successive areas of said sheet upon said radiation sensitive device, and a filter positioned between said source and said device, said filter having high absorption characteristics in said region of the spectrum of said source in which said surface and markings aaoaaro filter having low absorption characteristics in that portion of the spectrum of said source in which the surface and markings have dissimilar absorption characteristics whereby the response of said radiation device will be, primarily, in accordance with the relative absorption characteristics of said surface and said markings in that portion of the spectrum in which said characteristics are dissimilar.

3. An optical scanning system for deriving electrical signals representative of markings in ink upon a surface of a member having reflective properties comprising a source of radiation of both visible and invisible wave length componcnts, a radiation sensitive device responsive to both said visible and invisible wave length components, means to direct a beam of radiation from said source upon said reflective surface,

.means for direct radiation from said reflective surface to said radiation sensitive device, and a selectively absorbent filter positioned between said source and said device having high absorption characteristics of the invisible wave length components radiating from said source, whereby the response ,of said device will be, primarily, in accordance with the relative absorption characteristics of said markings and said 7 surface in the visible portion of the spectrum.

s. A photoelectric scanner for a facsimile telegraph system comprising a source of radiation in both the visible and infra-red portions of the spectrum, a radiation sensitive device responsive to radiations in both said visible and, infra-red have similar absorption characteristics and said I portions of the spectrum, means to direct radiation from said source upon a sheet having subject matter inscribed thereon in ink for transmission by a facsimile telegraph process, means to direct radiation from said sheet upon said radiation sensitive device,- and a filter disposed between saidsource and said radiation sensitive device and having a high absorption characteristic in the infrared portion of the spectrum whereby the response of said device to light reflected from said surface will be substantially independent of the infrared radiation from said source,.

LEONARD A. SMEiZ-Z.

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