US3275748A

US3275748A - Electron beam-defining device and method for producing the same

Info

Publication number: US3275748A
Application number: US332348A
Authority: US
Inventors: Marvin E Knoll; William H Nicklas
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1963-12-23
Filing date: 1963-12-23
Publication date: 1966-09-27
Anticipated expiration: 1983-09-27

Description

p 1966 M. E. KNOLL ETAL 3,275,748

ELECTRQN BEAM-DEFINING DEVICE AND METHOD FOR PRODUCING THE SAME Filed Dec. 25, 1965 INVENTORS MARVIN E. KNOLL, WILLIAM H. NICKLAS,

THEIR ATTORNEY.

United States Patent 3 275,748 ELECTRON BEAM-EEFINING DEVICE AND METHOD FOR PRODUCING THE SAME Marvin E. Knoll, Central Square, and William H. Niclrlas,

North yracuse, N.Y., assignors to General Electric Company, a corporation of New York Filed Dec. 23, 1963, Ser. No. 332,348 3 Claims. (Cl. 1787.87)

The present invention relates to an electron beamdefining device and, more specifically, to an electron beam-defining apertured plate suitable for use in a light valve tube and to a method for producing such a plate.

One form of a light valve tube comprises an evacuated envelope in which is positioned an electron beam-producing gun and a rotatable disc bearing a light-modulating fluid. The electron beam is scanned across a portion of the light-modulating fluid, the beam being selectively controlled to deform the surface of the fluid to form a diffraction grating thereon. The diffraction grating in conjunction with a light source and a Schlieren optical system controls the passage of light from the source to a screen. An electron beam-defining apertured plate is positioned between the gun and the light-modulating fluid in the path of the electron beam to provide a beam of optimum size and shape.

It is found that free molecules of the light-modulating fluid dislodged by the electron beam or present because of the finite vapor pressure of the fluid will, over a period of time, pass through the beam-defining aperture and condense on the side of the beam defining plate closest to the electron gun. When the deposit thus formed is irradiated by the electron beam, an insulating layer is formed on the beam-defining plate which will accumulate a charge and cause erratic operation and ultimately failure of the tube. One way to prevent the formation of such an insulating layer is by causing the electron beam to heat the beam-defining plate to an elevated temperature as described and claimed in the co-pending application of V. C. Campbell, S.N. 332,354, filed December 23, 1963, and assigned to the assignee of the present invention.

Due to the requirement that the beam-defining plate be relatively thin so as to be heated to a sufliciently elevated temperature by the electron beam, thermal expansion may cause buckling of the plate, resulting in misalignment of the electron beam and erratic operation of the light valve tube.

The present invention eliminates charge accumulation on the beam-defining plate by heating the plate to an elevated temperature while at the same time preventing buckling of the plate from thermal expansion.

Accordingly, an object of the present invention is to provide an improved electron beam-defining apertured plate suitable for use in a light valve tube.

Another object is to provide an electron beam-defining apertured plate capable of operating at an elevated temperature without electron beam misalignment.

Still another object is to provide an electron beam-defining apertured plate wherein buckling of the plate at elevated temperatures is eliminated.

These and other objects are achieved in one embodiment of the invention through the use of an electron beamdefining apertured plate which is retained in radial tension between a pair of annular retaining members. The tensile stresses in the plate are sufficient to prevent buckling of the plate by preventing the development of compressive stresses during operation at elevated temperatures.

One way of fabricating such a plate is to attach the plate in a taut condition to a first annular member having a relatively high thermal expansion with respect to the plate. The plate is then brazed to a second annular member having a relatively low thermal expansion with respect to the plate. Tensile stresses are imparted to the plate during heating to the braze temperature due to the difference in thermal expansion between the plate and the first annular member. Further tensile stresses are imparted to the plate during cooling down from the braze temperature due to the difference in thermal expansion between the plate and the second annular member.

The novel and distinctive features of the invention are set forth in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following description and accompanying drawings in which:

FIGURE 1 is a simplified cross-sectional view of a representative light valve tube having a heated, electron beam-defining apertured plate in accordance with the present invention.

FIGURE 2 is a perspective view of the electron beamdefining plate of the present invention.

FIGURES 3 and 4 are cross-sectional views of an apparatus for fabricating the stressed beam defining plate of FIGURE 2.

Referring to FIGURE 1, there is shown a light valve tube 1 located between a light source 2 and a screen (not shown) for the projection of an image to the screen, the light source 2 being provided with a suitable reflector 3.

The light valve tube 1 comprises an evacuated envelope 4 in which is located a rotatable disc 5 having a transparent conductive layer 6 positioned on one surface thereof. The disc 5 is rotated through a reservoir 7 of light-modulating fluid by any suitable means. Rotation of the disc 5 on its plane about the center through the reservoir 7 causes a continuously replenished layer of modulating fluid 8 to form on the conductive layer 6. An electron gun 9 is positioned in a necked-down portion of the envelope opposite the layer of light-modulating fluid 8. The electron gun 9 might also be a separate structure which is aflixed to the envelope 4 as described and claimed in the co-pending application of V. C. Campbell and E. F. Schilling, S.N. 313,693, filed October 3, 1963, and assigned to the assignee of the present invention. The electron gun 9 comprises an electron-emitting cathode electrode 11 in conjunction with an electron lens comprising a first electrode 12 and a second electrode 13. An apertured plate 14 is positioned in the path of the electron beam 15 generated by the cathode 11, the aperture in the plate 14 defining the size and shape of the electron beam.

The electron beam 15 impinges upon the layer of lightmodulating fluid 8 and deposits charges thereon. The charges are attracted to the conductive layer 6 to cause deformations 16 in the layer of light-modulating fluid 8. The electron beam 15 is swept across the layer of modulating fluid 8 by any suitable means to define a raster area, the beam being controlled to selectively deform the light-modulating fluid to form a diffraction grating thereon.

Light rays from the source 2, as reflected by the reflector 3, are directed by a lenticular lens system 17 formed on the rear wall of the envelope 4 to the raster area as described and claimed in the co-pending application of W. E. Good, M. Graser, Jr., and L. A. Juh-lin, Jr., S.N. 316,606, filed October 16, 1963, and assigned to the present invention. By modulating the electron beam 15 through the use of suitable deflection elements the diffraction grating formed by the deformations 16 in the layer of modulating fluid 8 is selectively controlled. Through the use of a Schlieren optical system an image representative of the electron beam modulating intelligence is projected upon the screen.

In the light valve tube, as shown in FIGURE 1, the electron-beam-defining plate 14 can be heated to an elevated temperature to prevent free molecules of lightmodulating fluid which pass through the aperture in the beam-defining plate from forming an insulative coating on the side of the plate closest to the cathode. If such an insulative coating is allowed to form, charges will be collected thereon resulting in erratic behavior and ultimately failure of the tube. This problem is overcome by designing the beam-defining plate in such a manner that the electron beam heats the plate to an elevated temperature, as described in the aforementioned co-pending application S.N. 332,354. However, since the plate 14 is necessarily thin in order to be raised to the required elevated temperature, it has been found that buckling of the plate and thus severe misalignment of the electron beam 15 may occur due to thermal expansion of the plate. To prevent such buckling, the beam-defining plate 14 is so constructed in accordance with the present invention that the plate is under radial tensile stress when cold so that when the plate is heated to the elevated operating temperature the resultant thermal expansion will not reduce the tensile stress ,to zero or cause compressive stresses in the plate. In this manner the plate is prevented from buckling and accuratae alignment of the electron beam is maintained.

It will be appreciated that although particularly directed toward light valve tubes the present invention would find application in other devices wherein similar problems arise.

Referring to FIGURE 2, there is shown a perspective liew of a stressed beam-defining plate and associated reaining members in accordance with the present invention :uitable for use in the light valve tube of FIGURE 1. Qike reference numerals are given to those elements of FIGURE 2 corresponding to elements of FIGURE 1. A aeam-defining plate or membrane 14 having a centrally ocated beam-defining aperture 18 therein is positioned aetween a pair of

annular retaining members

19 and 20. in accordance with the present invention, as outlined above, the plate 14 is fixedly retained between the

aniular members

19 and 20 in such a manner that initial 'adial tensile stresses are set up in the plate 14 so that vhen the plate 14 is heated to an elevated temperature luring normal operation, any thermal expansion of the late which occurs will be insufficient to cause buckling hereof.

One method of fabricating the device of FIGURE 2 is hoWn in FIGURES 3 and 4. Referring to FIGURES 3 1nd 4, there are shown cross-sectional views of an apparaus for fabricating a beam defining plate under radial ensile stress sufficient to prevent buckling at elevated perating temperatures. As shown in FIGURE 3, a eam-defining plate 21 is initially spot-welded to an nnular member 22. The assembled plate 21 and antular member 22 are then placed in coaxial alignment with a second annular member 23, the annular member 3 having an outer diameter slightly smaller than the aner diameter of the annular member 22. Pressure is hen applied to draw the plate 21 taut over the annular iember 23. The plate 21 is spot-welded to the annular iember 23 while in the taut condition. The plate 21 is ien cut between the weld points to annular members 22 nd 23 so as to remove the annular member 22.

Referring now to FIGURE 4, the assembly of FIG- IRE 3 is utilized to attach the beam-defining plate to its ssociated retaining members, like reference numerals eing given to like elements. The beam-defining plate 1 is positioned between a pair of annular members 24- nd 25, suitable braze material 26 being sandwiched beveen the

annular rings

24 and 25 and the plate 21. he assembled elements are positioned between a fixture 7 and a cap 28, a load being applied in the direction f the arrows as shown.

The entire assembly and the fixture are then heated in vacuum or inert atmosphere to the braze temperature. .fter brazing, the assembly is removed from the fixture 1d the plate 21 is cut between the outer diameter of re

annular members

24 and 25 and the spot weld to the 27, annular member 23, thereby allowing the annular member 23 to be removed. The outer diameter of the assembly is then machined to size. The aperture can be formed in the plate 21 either before or after machining.

The desired tensile stress in the plate 21 is achieved by proper choice of materials for the

annular members

23, 24, and 25 and plate 21. The annular member 23 is chosen to have a relatively high thermal expansion with respect to the plate 21 so that the plate 21 will have tensile stresses imparted thereto during heating to the brazing temperature because of the differential in the thermal expansivities of the two materials. The

annular members

24 and 25 are chosen to have a low thermal expansion with respect to that of the plate 21, a tensile stress thus being imparted to the plate 21 after brazing of the

annular members

24 and 25 thereto and during cool down of the assembly. The two stresses thus imparted to the plate 21 are additive so that the plate is stressed during heating to the brazing temperature and is further stressed during cooling down therefrom. In this manner sufficient tensile stress can be imparted to the beam-defining plate to prevent buckling at elevated operating temperatures.

It will be appreciated that although a device has been shown employing a pair of annular retaining members, in some applications a single annular retaining member might be employed. Further it will be appreciated that sufiicient stress for a particular application might be imparted to the plate 21 by choosing the

annular members

24 and 25 to have a thermal expansion substantially the same as that of the plate 21 and relying on the difference in thermal expansion between the annular member 23 and the plate 21 to produce the desired stress.

In one particularly effective embodiment of the apparatus shown in FIGURES 3 and 4 the following materials were utilized:

Beam defining plate 21tantalum (moderate thermal expansion) Annular members 24 and 25molybdenum (low thermal expansion) Annular member 23-304 stainless steel (high thermal expansion) The approximate stress in the beam-defining plate 21 of such an embodiment can be calculated in the manner outlined below. The approximate thermal expansion of each of the elements is as follows:

Thermal expansion a n n u l a r member 23 18.0 10* in./in./ C. Thermal expansion beam-defining plate 21 Difference in thermal expansion of beam defining plate 21 and annular member 23 1O.O 10- in./in./ C.

Thus, the resultant difference represents the stretching of the beam-defining plate 21 during heating to the braze temperature.

Similarly: Thermal expansion beam defining plate 21 8.O 10 in./in./ C. Thermal expansion

annular members

24 and 25 5.8 10" in./in./ C.

Difierence of thermal expansion between beam-defining plate 21 and

annular m e m b e r s

24 and 25 2.2 10 in./in./ C.

The resultant difference represents the stretching of the beam-defining plate 21 during the cooling after the

annular members

24 and 25 have been attached thereto. The total stretching of the beam-defining plate 21 then can be calculated as follows: Stretch of beam-defining plate 21 during heating 10.0 10 in./in./ C.

Stretch of beam-defining plate 21 during cooling Total stretch of beam defining plate 21 122x10 in./in./ C.

Thus, for a braze temperature of 753 C. the beamdefining plate 21 is strained 0.0092 in./in. From a study of the stress strain curve of tantalum, it is noted that 0.0092 in./in. strain is beyond the yield point of tantalum so that the beam-defining plate 21 is actually strained to approximately 0.005 in./in. which corresponds to a stress of approximately 47,000 lbs/in. Since the elevated temperature at which the beam-defining plate will be operated in the light valve tube is less than the brazing temperature utilized to assemble the

annular members

24 and 25 to the plate 21, it is clear that tensile stresses will be maintained in the plate 21 during operation thereof. Testing of the above-described structure resulted in no observable buckling of the beam defining plate even when the electron beam was caused to melt the area around the beam-defining aperture which corresponded to a temperature of 2995 C. for tantalum.

Although the invention has been described with respect to certain specific embodiments, it will be appreciated that modifications and changes may be made by those skilled in the art without departing from the spirit and scope of the invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. A light valve apparatus for positioning between a light source and a screen for the projection of an image on the screen, said apparatus comprising:

(a) an evacuated envelope,

(b) a light-modulating fluid positioned in said envelope and arranged to control the passage of light from the source to the screen,

(c) cathode means positioned in said envelope and arranged to emit a beam of electrons impingent upon said light-modulating fluid to form a diifraction grating thereon for selectively controlling the passage of light from the source to the screen in accordance with the image being projected,

(d) electron beam-defining means including a membrane having an aperture to pass one portion of said beam of electrons, the portion of said membrane about said aperture being adapted in operation to intercept and be heated by a second portion of said beam, said heating in normal operation being sufficient to produce buckling of said membrane if said membrane is untensioned, and

(e) means to maintain said membrane in radial tension about said aperture *suflicient to prevent buckling of said membrane when said membrane is heated during normal operation of said apparatus.

2. A beam-defining electrode for use in the electron gun structure of electron beam apparatus, said electrode 5 comprising:

(a) a membrane having an aperture to pass one portion of the electron beam produced in said electron gun structure,

(b) the portion of said membrane about said aperture being adapted in operation to intercept and be 10 heated by a second portion of said beam,

(0) said heating in normal operation being sufiicient to produce buckling of said membrane if said membrane is untensioned, and

(d) means to maintain said membrane in radial tension about said aperture sufiicient to prevent buckling of said membrane when said membrane is heated during normal operation of said apparatus.

3. A beam-defining electrode for use in the electron gun structure of electron beam apparatus, said electrode comprising:

(a) a disk-shaped membrane having an aperture to pass one portion of the electron beam produced in said electron gun structure,

(b) the portion of said membrane about said aperture being adapted in operation to intercept and be heated by a second portion of said beam,

(c) said heating in normal operation being sufficient to produce buckling of said membrane if said membrane is untensioned, and

(d) means to prevent buckling of said membrane when said membrane is heated during normal operation of said apparatus,

(e) said means including an annular member secured to said membrane about the periphery thereof and imparting substantial tensile stress to said membrane,

(f) said tensile stress being of suflicient magnitude to prevent the developing of compressive stresses in said plate at said elevated temperature.

References Cited by the Examiner 50 DAVID G. REDINBAUGH, Primary Examiner, R. L. RICHARDSON, Assistant Examiner,

Claims

1. A LIGHT VALVE APPARATUS FOR POSITIONING BETWEEN A LIGHT SOURCE AND A SCREEN FOR THE PROJECTION OF AN IMAGE ON THE SCREEN, SAID APPARATUS COMPRISING: (A) AN EVACUATED ENVELOPE, (B) A LIGHT-MODULATING FLUID POSITIONED IN SAID ENVELOPE AND ARRANGED TO CONTROL THE PASSAGE OF LIGHT FROM THE SOURCE TO THE SCREEN, (C) CATHODE MEANS POSITIONED IN SAID ENVELOPE AND ARRANGED TO EMIT A BEAM OF ELECTRONS IMPINGENT UPON SAID LIGH-MODULATING FLUID TO FORM A DIFFRACTION GRATING THEREON FOR SELECTIVELY CONTROLLING THE PASSAGE OF LIGHT FROM THE SOURCE TO THE SCREEN IN ACCORDANCE WITH THE IMAGE BEING PROJECTED, (D) ELECTRON BEAM-DEFINING MEANS INCLUDING A MEMBRANE HAVING AN APERTURE TO PASS ONE PORTION OF SAID BEAM OF ELECTRONS, THE PORTION OF SAID MEMBRANE ABOUT SAID APERTURE BEING ADAPTED IN OPERATION TO INTERCEPT AND BE HEATED BY A SECOND PORTION OF SAID BEAM, SAID HEATING IN NORMAL OPERATION BEING SUFFICIENT TO PRODUCE BUCKLING OF SAID MEMBRANE IF SAID MEMBRANE IS UNTENSIONED, AND (E) MEANS TO MAINTAIN SAID MEMBRANE IN RADIAL TENSION ABOUT SAID APERTURE SUFFICIENT TO PREVENT BUCKLING OF SAID MEMBRANE WHEN SAID MEMBRANE IS HEATED DURING NORMAL OPERATION OF SAID APPARATUS.