US2010543A - Electrooptical system - Google Patents

Description

Aug. 6, 1935. F. GRAY ELECTROOPTICAL SYSTEM 3 Sheets-Sheet l ATTORNEY INVENTOR F GRAY Filed Jan. 10, 1931 Aug. 6, 1935. F. GRAY 2,010,543

ELECTROOPTICAL SYSTEM Filed Jan. 10, 1931 3 Sheets-Sheet 2 A TTORNEV Aug. 6, 1935. F. GRA Y 2,010,543

ELECTROO-PTICAL SYSTEM Filed Jan. 10, 1931 3 Sheets-Sheet 3 FIG. 3

FIG. 4

IIIIIIIIII INVENTOR FGRAK BY ATTORNEY Patented Aug. 6, 1935 ELECTROOPTICAL SYSTEM Frank Gray, New York, .N. Y., assignor. to Bell Telephone Laboratories, Incorporated, 'New York, N. Y., a corporation of New York r Application January 10, 1931,, Serial No. 507,799

10 Claims. ((3-1. 178 6) This invention relates to electro-optical systems and more particularly to an image scanning mechanism. a 1

It has been proposed to use abelt provided with slots for projecting an image of successive unit lines of a field of view to be transmitted upon a selenium plate and to scan the elemental areas of each illuminated line by a commutating device, which comprises a pair of selenium elements connected in series with each elemental area of the selenium plate and a moving beam of light which simultaneously illuminates the pairs of elements'in succession, to releaseto a transmission circuit image currents varying in amplitude with the tone values of the successive ele mental areas'of the image. 7

.A system of the type just described possesses the disadvantage that sel'enium presents a finite resistance whether illuminated or not; and it does not respond to rapid changes in light values. As a result, leakage current will flow through the circuit including the seleniumplate and commutator when a voltage is applied thereto even if the plate andcommutator are not illuminated, the system cannot be operated at high speed, because of the lag of the selenium plate and commutating elements, and the image currents will be distorted by the residual resistance of the commutatorv elements when they are illuminated.

The present invention provides a scanning mechanism which operates in a manner similar to that described above, but which does not embody the disadvantages hereinbefore noted. -An object'of the invention isto efiect high speed scanning in a system of the typedescribed above, by using a commutating device comprising light sensitive. devices activated by a beam of lightof constant intensity.

Another object is to produce undistorted image currents. g i j fAn additional object is to;prevent theflow of leakage currents. g In accordance with one embodiment of the invention, an image of a subject, or field of view, ispro'jected upon a ,group of photoelectric cells each of which is connected in series with another photoelectric cell. The series-connected cells are arranged to constitute a second group, which are Ysuccessively illuminated by a beam of light of constant intensity to release image currents, producedinthe respective cells of the first group, to ,a communicating channel. j The second group consists of photoelectric .cells, each having a current carrying capacity which is greater than the maximum currentcaused by the activation any cell of thefirst group. a

An image maybe projected upon a bank .of photoelectric cells constituting alcomplete image field,'or successive lines of the image maybe 5 caused to traverse a row of cellslcorresponding to a'unit line of the image. V I? A description of the invention follows and is illustrated in the attached drawings, inwhich i Fig. 1 diagrammatically illustrates a system embodying the invention; J 1

Fig. 2 illustrates a difierentform of scanning means which may be used in place of that shown in Fig. If and Figs. 3'and 4 show scan'ning means which may 15 be substituted'for that of Fig. 2.

u Referring to Fig. 1, there is shown a subject or field of view i, a lens 2 for projecting animage of the subjectupon'photoelectric cells 3 correspending in numberto the-elemental areas of 0 the image and arranged to constitute a bank} of rectangular form, and a second setof photo electric cells 5, which correspondv in number to those of the bank 4. Cells 5" are of such character that no current flows between their electrodes when they are dark, i. e., when they are not'illuminated, and are of such current carrying capacity that, when illuminated by a. beam of light of predetermined constant intensity, they are activated to cause the production of a current 36 greater than the largest current ever produced .by any cell a or the first bank when illuminated by an image of the field of view.' Each of the cells 5 is connected in series with one of the cells 3 and through a common circuit to fan 35 amplifier 6 included in a transmission circuit 1.

A source of light 8 cooperates with an optical system including lens 9; a rotating disc l0 provided with a row of apertures l l arrangedin a spiral lineQand a lens 12 to produceia moving 40 beam of light of the desired/constant intensity which successively illuminates the cells 5 which are thereby renderedconductiva flmag "currents, corresponding in amplitude to the tone l4 over which transmission is effected to a receiving station.

At the receiving station, the incoming image currents are amplified in the device [5 and applied toglow lamp l6 associated with a rotating disc I! provided with a row of apertures I8 arranged in a spiral line. In accordance with more or less standard practice, the lamp and disc cooperate to produce an image which may be directly viewed by an observer 0 or may be projected by a suitable optical system on a screen for audience viewing.

To permit production of the image, the disc and I1, driven by the motors l9 and 20, must operate in synchronism and in phase with each other and are driven at such a rate that a complete image field is scanned and an image thereof is produced during each complete revolution thereof and within the period of persistence of vision. A suitable system which may be used to maintain synchronous operation of the discs 10 and I1 is disclosed in U. S. Patent 1,999,376 of H. M. Stollenissued April 30, 1935. Lamp 16 may be of any suitable type adapted to supply light varying in accordance with the amplitudes of the incoming image currents, for example, it may be a glow lamp of the type disclosed in U. S. Patent 1,918,309 of H. W. Weinhart, issued July 18, 1933.

The apparatus of Fig. 2 comprises a lens 2| for producing an image of a field of view in the plane of disc 22 provided with slots 23 which successively sweep across a series of photoelectric cells 2 1 each equal in length to a unit line of the image. Cells 24 are each connected in series with a photoelectric cell 25 having a current carrying capacity greater than the maximum current produced by any of the cells 24.

As described in connection with Fig. 1, the cells 25 are non-conductive in the dark, and they are traversed by a moving beam of light of the desired constant intensity to activate them by the optical system 8, 9, l0 and l 2, whereby image currents corresponding in amplitude to successive elemental areas of the image are released to the amplifier 6. The image is completely scanned during each revolution of the disc I0 and it is driven by a motor activating the disc 22 to which it is coupled by a gear, indicated at 50, to cause the beam of light to be swept across cells 25 at such a rate that complete scannings occur within the period of persistence of vision. The gearing 50 is of such ratio that the disc I0 is operated at the proper relative speed with respect to the disc 22.

Fig. 3 illustrates a disc 26 provided with a series of lenses which serve to move an image of a field of view across a stationary slot 21 provided in a screen or mask 28 having associated therewith a row of photoelectric cells 29, corresponding in number to the unit lines of the image. Connected in series with each of the cells 29 is a cell 30 whichis non-conductive in the dark. Cells 30 are adapted to be illuminated in succession as described above by a movable beam of light of the desired constant intensity supplied through the optical system 8, 9, l8 and [2. As the disc 26 rotates, light from successive unit lines of the image illuminates the cells 29, which are thereby activated to cause the production of image currents corresponding in amplitude to the tone values of elemental areas of the lines. The disc I0 is rotated and the beam of light sweeps across cells 30 at such a rate that image currents cor responding to elemental areas of the complete field of view are released to the amplifier 6 within the period of persistence of vision. The gear 50 serves tocouple the motor to the disc I0 so that it is rotated at the desired speed with respect to the disc 26.

As shown in Fig. 4, the lensed disc 26 of Fig. 3 may be replaced by a system of rotating mirrors 3! to sweep successive unit lines of the image across the stationary slot 21. The gearing 5| serves to couple the driving motor for the mirror system to the disc iii, which is thereby rotated at the desired rate relatively to the mirrors.

If desired, a pair of rotating prisms could be used, as disclosed in U. S. Patent 1,647,631 of H. E. Ives, dated November 1, 1927, to cause light derived from successive elemental areas of the image to illuminate corresponding photoelectric cells 3 of the first group of Fig. 1 while those of the second group 5 are successively illuminated by a moving beam of light of the desired constant intensity provided by the optical system 8, 9, l0 and I2, to release image currents, corresponding to the complete field, to the amplifier 6 at a rate within the period of persistence of vision.

In the apparatus of Figs. 2 to 4, the traversal of the movable beam of light should be controlled by the disc ID to operate in synchronism and in phase with the disc I? at the receiving station. The synchronizing system disclosed in the above mentioned Stoller application may be used for this purpose.

One advantage of the present system is that it reduces the speed of moving parts and hence permits'large images to be scanned at high speed, Without causing the flow of leakage currents and without distortion of the image currents supplied to the transmission circuit. As a result large aperture lenses can be used to effect 2. corresponding gain in the amount of light available to produce image currents.

What is claimed is:

1. A television system comprising a group of photoelectric cells, a second group of photoelectric cells each of greater current carrying capacity than those of the first group and respectively connected in series with a cell of the first group, means for projecting an image of a field of view upon said first group of cells, and means for successively activating the cells of the second group.

2. A television system comprising a group of photoelectric cells, a second group of photoelectric cellseach of greater current carrying capacity than those of the first group and respectively connected in series with a cell of the first group, means for projecting an image of a field of view upon said first group of cells, and means for producing a moving beam of light of constant intensity for successively activating the cells of the second group.

3. A television system comprising light sensitive devices, means for projecting an image of a field of View upon said devices, other light sensitive devices each connected in series with one of said first mentioned devices and of greater current carrying capacity than the device with which it is connected, and means for successively activating said other devices.

4. A photoelectric cell assembly for use in a television system comprising a bank of photoelectric cells, the number of cells being equal and their arrangement similar to the desired number and arrangement of elemental areas in a field of view, and a group of photoelectric cells equal in number to those in said bank of cells, each cell of said group having greater current carrying capacity than the cells of said bank and each respectively connected in series with a cell of said bank.

5. A television system compring a bank of photoelectric cells, the number of cells being equal and their arrangement similar to the desired number and arrangement of elemental areas in a field of view, a group of photoelectric cells equal in number to those in said bank of cells, each cell of said group having greater current carrying capacity than the cells of said bank and each respectively connected in series with a cell of said bank, means to illuminate each cell of said bank with light from the corresponding elemental area of the field of view, and means to successively activate the cells of said group of cells, each cell being activated while the corresponding cell of the bank is illuminated;

6. A television system comprising a, bank of photoelectric cells, the number of cells being equal and their arrangement similar to the desired number and arrangement of elemental areas in a field of view, a group of photoelectric cells equal in number to those in said bank of cells, each cell of said group having greater current carrying capacity than the cells of said bank and each respectively connected in series with a cell of said bank, and means to successively illuminate the cells of said group with a moving beam of light of constant intensity.

'7. A television system comprising a plurality of elongated photoelectric cells equal in number to the elemental lines of a field of view, means to simultaneously illuminate an elemental portion only of each of said cells, which. portions correspond to elemental areas of said elemental lines, a second group of photoelectric cells equal to the number of elongated cells, each cell of this group having a current carrying capacity greater than the maximum current produced by any of said elongated cells and each respectively connected in series with one of said elongated cells, and means for successively activating the cells of said second group.

8. An electro-optical system comprising two cellular structures each having the same number of compartments, a photoelectric cell positioned in each compartment each of said cells having two electrodes one a cathode and the other an anode, a connection common to all of the electrodes of one kind of the cells in one structure, another connection common to all of the electrodes of the other kind of the cells in the other structure, conductors individual to pairs of cells one of which is in each structure, each said con-- ductor joining the not commonly connected electrodes of the said pairs of cells, a source of current energizing said cells through said common connections, and means to energize the cells of one structure in succession with an energy carrying beam.

9. An electro-optical system comprising two cellular structures each having the same number of compartments, a photoelectric cell positioned in each compartment each of said cells having two electrodes one a cathode and the other an anode, a connection common to all of the electrodes of one kind of the cells in one structure, another connection common to all of the electrodes of the other kind of the cells in the other structure, metallic conductors individual to pairs of cells one of which is in each structure, each said conductor joining the not commonly connected electrodes of the said pairs of cells, a source of current energizing said cells through said common connections, and means to ener gize the cells of one structure in succession with a moving beam of light.

10. An electro-optical system comprising two cellular structures each having the same number of compartments, a photoelectric cell positioned in eachrcompartment each of said cells having two electrodes one a cathode and the other an anode. a connection common to all of the electrodes of one kind of the cells in one structure, another connection common to all of the electrodes of the other kind of the cells in the other structure, conductors individual to pairs of cells one of which is in each structure, each conductor joining the not commonly connected electrodes of the said pairs of cells, a source of current energizing said cells through said common connections, and means to energize the cells of one structure in succession with an energy carrying beam, the cells in the successively energized structure each having a greater current, carrying capacity than the corresponding cell in the other structure.

FRANK GRAY.

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