US2300591A - Electronic scanning device - Google Patents

Description

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" STATE nnncm'omc s'csNNmGnEvlcE I Juichi'O'sawa, Tokyo, Japan, assigner to International Standard Electric Corporation, New

York, N. Y., a corporation of'Delaware :une s, me, serai No. sacos Application In Japan AUM 3,1935

scams.. (onus-1.a) l j 'rms invention relates t'o'scanmng of the und" e employed in Vtelevision or similar systems and more particularly to electronic beam' scanning.

The obiect of this invention is to providcan improved device for the transmission of' images utilizing anjelectronic beamscanning means.

In television or similar systems requiring electronic scanning, certain methods have been used i tube is used as a photoelectric piane, the photoelectrons `generated therefrom being accelerated in a, proper direction and th'ephotoelectrons rav heretofore, an example of which is a method in i. which the electron generating source in a Braun age and the number of repetitions ci the image.

Also. in the device-of this invention; as there is diated from elemental areas thereof being 'projectedupon an 4electron collector inl succession, and the current generated thereby beingl amplined and transmitted. Another method heretofore used involves the use of a photoelectric plane composed of a large number of minute photoelectric elements, saidl elements being scanned by the electron current in the Braun tube, discharge bejing eected in succession between said minute photoelectric elements and a metallic plate provided oppositely and'l capacitively to said' lclements, and the discharging current which is generated at that time being transmitted as an out- #In thedevice of this invention as hereinafter described as anV illustrative embodiment, a means is provided in a vessel which is so arranged that it successively sets up a space charge when it is scanned by an electron means, a control electrode having a plurality of minute elements which are photoelectrically sensitiveis arrangedso that it liesvin an operative position with respect to said charge, the control electrode is illuminated by the image light from a body, and the potential which la to be generated due to the difference in illumination of each minute element controls the space. current due to the space `charge which is successivelyv generated as above described. As the potential upon each minutephotcelectric element is changed corresponding to the brightness of each part of the object, thel current which is to be controlled by saidpotential is caused to form no sudden bombardment oi electrons upony the l acting surface which is phctoelectrically sensitive, as is thecase 4in the so-call iconosccpe, there is noV probability ofcausing the 'breakdown'.of the photoelectric plane, and as it is not of the nature which utilizes a transient phenomenon, it' lhas an advantage in that it is possible to'obtain an image having 4less distortion. -1

,The invention will be more readily understood `by'reierring tothe following description taken l in' connection with the accompanying drawing forming a part thereof, in which:

Fig. 1 is an arrangement of the device of this invention; and

Figs. 2, 3 and 4 show a number of practical L types o! an opposed electrode and s control elecan image 4current proportional tothe illumination j due tothe scanning of the radiated electron current.

A feature of the devicefofk this invention .lies in the' fact' thatvthe energy necessary i'or the image control is almost sera-as only a balancing potential yis ,utililed. The scanning efficiency of lthis device is made entirely independent of the" number of picture elements constituting the lm '55 maintained at'a deiinite potential by a suitable -at any given time oteach'part of the image plane Y upon a 'silver foil. The' central conductor it is` trede.

Referring more particularly to the drawing,v

Fig. 1 shows a practical example ci the device of this invention. In thel figure. i isa cathode which generates an electron current, .9, is a flux collecting electrode which serves to concentrate and project the electron flux into an opposed electrode t by means oi devising battery i3, t 'is an accelerating anode having a small hole in the-center, t, s are the deilecting plates for pro,

ducing scanning, and ii is a vessel which maintains the electrode in vacuum. The electron current emitted by the cathode l is concentrated and projected into a point upon the 'opposed electrode 8,4 its position being made to change by the `action of the two sets o! deflecting plates which cause the electrode t to be scanned in the wellknown manner.

The opposed electrode B. is a met-al sheet made of, for example, aluminum having a thickness of the order of a few'microns. The electrons of high speed which have beenemitted from i are `allowed to shoot electrode t which lessens their speed to practically zero so that vthe electrons.

Just manage to pass through plate 6 where 4they form a space charge in the rear thereof. The element 1V isa grid shaped control electrode which has a surface composedof minute pieces of phoisoelectric` material' insulated from each other,

'for onrarnple'-,` Ait haslthe construction shownln Fig. 2.'

With reference to 'an insulating illm, and Ila layer of photoelectric material arranged at ilxed intervals upon il, such as, for examplera thin'lm of ca'esium mounted Fig'.-2. i6 is a conductor, I'Il Achange of illumination.

NNUU@ means, auch as the battery 25. When light is proiected upon the elemental pieces |18 of the electrode 1, these pieces radiate photoelectrons. and the potential `of these pieces will be brought up until it becomes almost equal to the maximum point of potential of the electrode 6 lying in the neighborhood thereof. 'I'he potential which is l r nnally reached at each elemental point depends moon the amount of the radiation of the photoelectrons and hence it is proportional to the iliuminationof the light and is higher as the light intensity becomes greater. Moreover, said pbtential depends upon the radiationl of pnotoelectrons and the influence of the leakage pathat that portion as well as the potential distribution of each electrode, and it is not influenced by the increase or decrease of the number of image points. When the potential of the conductor It is taken properly the potential of the photoelec- -tric pieces I8 becomes negative with respect to plate l. Electrons emitted from the cathode l shoot at the plate I, and the electrons of low speed which appear from the rear of said plate Y are thus not caused to bombard the small pieces at a point of the plate 6; an electron current of low speed is radiated from a point of the same position at the rear of said plate, which causes a current to be produced in the output circuit. The rays of light from the image plane are projected upon the plane of control electrode 1 by meansl of a lens 9. The plate 6 is placed close to the i electrode 1. and the scanning is done by the electron current'as mentioned above. 4

'I'he space current and hence the current of the l' output circuit is caused to successively change its value according to the magnitude of potential of each photcelectric piece I 8 upon the control electrode 1, or in otherwords, the current of the l output circuit is to be controlled by the-potentials of each photoelectric piece which is changed from time to 'time -and hence by theillumination of each point of electrode 1. As 'the diiference of potential at each point is caused to vary according to its change in illumination, it is clear that the change of said :current is sensitive to thel 4As the output current is produced continuously in proportion tothe illumination at eachpoint of the limage which had been projected upon -the electrode' 1. this output current may be amplified.

if desired, and .transmitted into a transmission circuit.

vThe constructions and actions of the control electrode and the opposed electrode of this invention shown in Fig. 3 will now be explained.` It is possible to have. them operate similar to that above described by arranging it so as to put a net shaped member 20 insteadl ofthe opposed electrode plate 64 in Fig. 1, to give a proper negative potential to said member and to dampen the electrons of. high speed which had been emitted from the cathode I and acceleratedV by the accelerating anode I, said net shaped member 2l charge in me Vmathberhcoci or each point of the control electrode 1.

`The device shown in Fig. 4 is an example of a construction using the plate 8 and the electrode 1 of Fig. i in combination. In this figure. a core 2l is covered with an insulating substance 22 upon which a photoelectric substance 23 is applied at suitable intervals only at one side surface and a potential is givento the core 21|. This arrangement permits the suppression-oi the striking electron current and performs the control of the space charge by the photoelectric potential of the photoelectrlc spot 23.

Although it is' not specifically shown in the drawing, the plate 6 may be made of a substance which is especially susceptible to secondary electron radiation, such as for example, a sheet of aluminum which had been properly treated. "With this arrangement a concentrated electron current which has the most suitable speed for secondary electron radiation is transmitted from the cathode l which bombards the plate 6 .to produce a sufilcient space charge due to the secondary electrons, the primary electrons being caused the thickness of said sheet metal being' so small that. as a result of said moving stream of electrons striking one side of said sheet metal, a

lstream of electrons passes from the other side of said sheet of metal to' said anode. photoelectrlc means for controlling the flow of electrons between said electrode iirst mentioned and said anode. and an output circuit interconnected between said electrode and said anode.

2. A cathode ray tube having an envelope, a

separating member adapted to emit secondary electrons dividingsaid envelope into two chambers, the ilrst chamber containing means for producing a cathode ray beam and means for causing the cathode ray beam to scan said separating member, the second chamber containing a photosensitive member and an anode and means responsive to projection of light upon said phot-o- `sensitive member for causing the secondary electrons emitted by the separating member to be modulated by the change on 'the photosensitive member.

43. Cathode beam scanning means for a telef vision camera, comprising an evacuated vessel containing a plate-like element having an extended surface capable of emitting electrons, a

second plate-like element having a photo-emissaid first surface-and parallel thereto, means for sive surface coating, spaced a small distance from to cause #mission of electrons therefrom and thereby place different' charges 'upon different elemental areas spectivelyjof said second element.' whereby a free electron emittedA from said ilrst sur face into said space will travel toward said second surface under control of said charges, and means for causing electrons to be emitted into said space from said rst surface element by element there-.

of in succession.

thereby changing said electrons into a space 4. Cathode beam scanning means acccrdingto.

cansan minis claim 3, 'whe-rein second .plate-like ,element -comprisedan apertured screen, said. photo-'emissive coating beinson the surface of said screen remote from said extended surface whereby electrons 4emitted. from lsaid rst surface travel through said apertures 'of said screen in acordance with the said charges. t

5. yCathode beam scanning means accordingtoclaim 8 5 Awherein said means for causing electrons to be emitted comprises means I or scanning said rst plate-like element to produce secondaryelec- U tron from said element.

-6. Cathode beam scanning means according to claim 3, wherein said second plate-like element comprised an apertured screen, said photo-emissive coating being onthe surface of said'screen y remote from-said extended surface whereby electrons emitted from said first surface travel through said apertures of said screen in accord- -ance with the said charges, wherein said means for causing electrons to be emitted comprises 1 lmeans for scanning said first plate-like element to produce secondary electron from said element.

.- JUICHE OSAWA.

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