US3628076A

US3628076A - Photoconductive screen deriving light thorugh light conductor from tube filament

Info

Publication number: US3628076A
Application number: US885914A
Authority: US
Inventors: Willem Paul Weijland; Hans Georg Gerlach; Antonius Joannes Maria Va Beld; Louis Maarten Swart
Original assignee: US Philips Corp
Current assignee: US Philips Corp
Priority date: 1968-12-24
Filing date: 1969-12-17
Publication date: 1971-12-14
Anticipated expiration: 1988-12-14
Also published as: US3751703A; FR2027026A1; DE1960700B2; GB1240083A; DE1960700A1; AT291367B; CH500585A

Abstract

A television camera tube of the Vidicon type in which a photoconductive screen at one end of an evacuated envelope receives an image of a scene to be televised and is scanned by an electron beam. An auxiliary light source is provided for uniformly illuminating the screen and a light conductor, at least partly outside the path of illumination from the scene, conducts light from the auxiliary source to the screen.

Description

J'QUY JQJ. D11 1 1 SEARCH R0 KR 396253101176 OM United State I 1 1 3,628,076

1 STITUTE F0. 1111251. 1e "1 [72] Inventors Willem Paul Wellland; [50] Fleld 01' Search 3 l 3/65, 65

Hans Georg Gerlach; Antonlus Joannes A Marla Van Den Bald; Louls Mnarten Swart,

all 01 Emmaslngel, Elndhoven. Netherlands I 56] Reterences Cmd [21 1 Appl. No. 885,914 UNITED STATES PATENTS 1 1 Filed -1 2,131,185 9/1938 Knoll 3l3/65X Palemed 14, 1971 2,915,659 12/1959 Goodman 3 l 3/65 1 Assign 1 Corporation 3,002,101 9/l96l Anderson et a1... 313/65 x NCW York. 3,048,728 8/1962 Beurle 313/65 [32] Priority Dec. 24, 1968 [33} Netherlands Primary Exammer- Robert Segal Anorney- Frank R. Trifan ABSTRACT: A television camera tube of the Vidicon type in which a photoconductive screen at one end of an evacuated envelope receives an image of a scene to be televised and is [5 1 1 PHO'IO'CONDUCTIVE SCREEN DERIVING LIGHT THROUGH LIGHT CONDUCTOR FROM TUBE FILAMENT 4 cmml's Drawing Figs; scanned by en electron beam An auxihury light source 15 provlded for uniformly illuminating the screen and a light conduc- [52] U.S.C| 313/65 A, I of a[ least partly outside the Path Of illumination from 1116 1 250/227 313/65 LF scene. conducts light from the auxiliary source to the screen. 1511 lm. c1 .1101] 31/28. HOlj 3l/38,HOlj 5/16 Patented "Dec. 14,1971 j 3,628,076

2 Shoets-$heet 1 fig.1

.fig.2

INVENTORs; WILLEM P. WEIJLAND HANS G. GERLACH ANTONIUS J.M VAN DEN BELO BY 1 ou1s 11151111111111 AGENT Patented Qec. 14, 1971 T 3,628,016

2 Sheets-Sheet? AND FEW: IJ L A u fufh'Wkocu new By LOUJ M. swun NVENTORS PHOTOCONDUCI'IVE SCREEN DERIVING ucrrr morwcrr ucrrr cormuc'ron FROM runs mm The invention relates to a camera tube of the vidicon type comprising a photoconductive screen, the invention relates in particular to a Pluiiibicon.

in such a camera tube the drawback is experienced that, in the case of low-luminosity pictures, inertia phenomena may occur as a result of the high resistance of the photoconductive layer of the screen in the case of such low luminosity exposures. These inertial phenomena can be reduced by ensuring that also in case no light of a picture is incident the screen parties a given :quiescent current, the so-called dark current. This dark current can be controlled by providing a given uniform auxiliary illumination or background illumination of the screen. This could be done by incorporating a weak light source in the camera in which the tube is provided. However, in this case it is necessary to provide elements in the optical path of the tube, which may give rise to disturbances and light reflections, particularly in color cameras in which the optic are very critical. Moreover, in that case, one is not free in the choice of the color of the auxiliary light-source.

A considerable improvement is obtained if the tube according to the invention comprises one or more light-conductive members which conduct light from an auxiliary light source in the direction of the photoconductive screen. The auxiliary light source may be the filament of the cathode of the tube itself but a larger control range of the dark current can be obtained by the light of a separate light source, if desirable in combination with color filters. By conducting additional light to the photoconductive screen, while using a light conductor, this auxiliary light can be transferred, for example, to the collector space of the tube and from there distributed uniformly over the photocond uctive screen by diffuse reflection.

As is known per se, the light conductor may consist of a glass rod which is suitably bent so that the light of a light source situated in front of one end of the rod emanates at the other end from the rod. lf desirable the light-conductor may be formed entirely or partly bythe wall of the envelope of the tube itself.

The invention will be described with reference to the accompanying drawing, in which:

F I68. I, 2, Band 4 are diagrammatic longitudinal cross-secthe light guided to the screen 9 can be obtained within certain limits by varying the filament current 7. However, one is restricted to the minimum operating temperature of the cathode, while the maximum adjustable temperature may not reduce the lifetime too strongly. The limits within which the background light can be controlled therefore are comparatively narrow.

A larger control range is obtained in the embodiment shown in H68. 2 and 3.

In FIG. 2 the light conductor in bent at one end in such manner that said end can be passed out through the aperture of the exhaust tube in the bottom of the tube, and be sealed in the tip of the exhaust tube. The tip of the exhaust tube is surrounded by a sheath 13 in which a light source 14 is situated. The sheath 13 may be housed in the holder 5 of the tube. it is alternatively possible to bend the end of the light conductor tioiial views of vidicon tubes according to the invention employing light conductors having various shapes.

HO. 5 is across-section view of a light conductor.

Reference numeral 1 in the drawings denotes the cylindrical glass wall of a television camera tube which is closed at one end by a glass window portion 2 and at the other end by a botminosity of a picture projected on the screen 9 through the window 2, it is desirable to provide a low uniform background illumination of the screen 9.

As is shown in FIG. 1, this is done by means of arogll shagedr light condugtor 10 which is bent at one end in such manner msra' an of firefi h irradiated by the filament 7 is guided through the light conductor 10 to the collector space 11 inside the last electrode 12 of the electron lens of the tube and emerges there from the light-conductor. The cathode is optically open at its lower side, so as to permit the filament light to emanate. 'Ihe light-conductor 10 can be supported by electrodes of the tube bymeans of clamping

members

18, 19. The electrode 12 comprises an inner wall which is proccssed so that the light is reflected in a diffuse manner and is unifonnly distributed over the photoconductive screen 9. The control of 21 towards the inside of the sidewall of the envelope of the tube and to place a light source 20 at that area on the outside. The end of the light-conductor need not touch the sidewall (see FIG. 2). If desirable, a color filter can be arranged between the light source 14 and the photoconductive screen. The color filter can be provided between the light source and the end of the light conductor, or near the end of the light conductor. If desirable, the light conductor itself may consist of colored material. if the end of a rod-shaped light conductor ends opposite to the sidewall of the tube, the sidewall of the envelope may be manufactured from colored glass or a color filter may be provided on the wall. Naturally, the color filter may also be provided on the envelope of the light source itself.

It is alternatively possible to give the light conductor a straight construction and seal it in the bottom of the tube, preferably by means 'of a plastic material or a readily melting type of glass 15. Leading through can take place at the area of an omitted contact pin. In this case also a sheath 13 having a light source 14 may be provided in the holder 5 of the tube (HS. 3). in order to obtain a more uniform illumination of the screen 9, two light conductor are preferably used.

In the embodiment shown in FlG. 4, again the light irradiated by the filament of the cathode is used. By rounding off the edges of the bottom 3 of the tube, and in particular of the window portion 2, and by covering the rounded-offedges with the external readily reflecting layer, for example, a layer of

silver

16 and 17 respectively, it can be achieved that the light rays which have reached the bottom of the tube are conveyed through the wall 1 of the tube to the window 2 andimpinge upon the photoconductive screen 9 inv a uniformly distributed manner. The radius of the rounding off of the window portion is preferably equal to the thickness of the glass of the window portion. The layer of silver l 6 may be connected to a screening means while the layer of silver 17 may serve as an electric current supply member for the screen 9.This latter embodiment has the advantage that the construction of the electrodes can remain the same. Light conductors are known per so. instead of a single glass rod, the light conductor may also consist of a bundle of glass wires 22 which extend parallel and are adhered together.

it will be obvious that the invention is not restricted to the examples described and that many variations are possible to those skilled in the art without departing from the scope of this invention. For example, the lighbconductor may be formed differently within the scope of this invention. Alternatively,

several embodiments may be combined.

What is claimed is:

l. A television camera tube comprising an evacuated envelope having a transparent wall portion, a photoconductive screen having one surface facing said transparent wall portion for receiving an image of a scene, means to scan the opposite side of said screen with an electron beam thereby generating an electrical current corresponding to light variations in said scene, said scan means including an electron gun for generating an electron beam remote from the screen and means to deflect the electron beam before it impinges on the screen, means for uniformly illuminating said screen including a filaatone end.

3. A camera tube as claimed in claim 1 wherein the lightconductor comprises a bundle of parallel glass wires which are adhered together.

4. A camera tube as claimed in claim 1 wherein the envelope wall is the light conductor and at least the edges of the transparent wall portion are rounded ofi and are covered with a light reflecting layer so that light of the filament of the cathode is guided to the photoconductive screen through the envelope wall.

l i i i. l-

UNHED STATES PATENT @FFKQE @ERTHFECATE @i CRRETYLN batent NO. 3,628,076 Dated Decexfiber 14, 1971 inventor(s) W.P. Weij land; H.G. Gerlach; A.J.M. Van Den Beld ET AL It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 58 after "together" insert --as shown in Fig. 5

Signed and sealed this 19th day of December 1972.

(SEAL) Attest:

EDWARD MELETCHERJR; ROBERT G-OTTSCI-IALK Attesting Officer- 1 Commissioner of Patents

Claims

1. A television camera tube comprising an evacuated envelope having a transparent wall portion, a photoconductive screen having one surface facing said transparent wall portion for receiving an image of a scene, means to scan the opposite side of said screen with an electron beam thereby generating an electrical current corresponding to light variations in said scene, said scan means including an electron gun for generating an electron beam remote from the screen and means to deflect the electron beam before it impinges on the screen, means for uniformly illuminating said screen including a filament and at least one light conductor for conducting light by multiple internal reflection from filament to a point opposite the side of the screen struck by the electron beam for providing bias illumination over substantially the entire surface of the screen struck by the electron beam, at least a portion of said light conductor lying outside the path of illumination from the scene.

2. A camera tube as claimed in claim 1 wherein the light conductor is shaped as a rod and is bent towards the filament at one end.

3. A camera tube as claimed in claim 1 wherein the light-conductor comprises a bundle of parallel glass wires which are adhered together.

4. A camera tube as claimed in claim 1 wherein the envelope wall is the light conductor and at least the edges of the transparent wall portion are rounded off and are covered with a light reflecting layer so that light of the filament of the cathode is guided to the photoconductive screen through the envelope wall.