US3364373A - Electron discharge device having a cathode element with a renewable electron emissive surface - Google Patents

Description

3,364,373 ENT WITH Jan. 16, 1968 E. ATTI ELECTRON DISCHARGE DEVICE HAVING A CATHODE ELEM A RENEWABLE ELECTRON EMISSIVE SURFACE Original Filed March 23. 1964 ATTORNEY United States Patent 3,364,373 ELECTRON DISCHARGE DEVICE HAVING A CATHUDE ELEMENT WITH A RENEWABLE ELECTRON EMISSIVE SURFACE Eros Atti, Horseheads, N .Y., assignor t0 Westinghouse Electric Corporation, East Pittsburgh, Pa., 21 corporation of Pennsylvania Original application Mar. 23, 1964, Ser. No. 353,683, now Patent No. 3,311,774, dated Mar. 38, 1967. Divided and this application Sept. 14, 1966, Ser. No. 584,303

12 Claims. (Cl. 313-149) ABSTRACT OF THE DISCLOSURE This invention relates to electron discharge devices with cathode assemblies capable of renewing the emissive portion of the cathode element and illustratively takes the form in one embodiment of a cathode element with a layer of electron emissive material disposed beneath an aperture of a control element, an eccentric member having an opening therein, and suitable means such as a bimetallic member for rotating the eccentric member. Illustratively, the cathode element may be mounted upon an insulting dis which is disposed within the opening of the eccentric member so that when the eccentric member is rotated, the cathode element may be orbited with respect to the aperture of the control element without rotating the cathode element about its own axis. As a result, an electrical connection may be made directly to the cathode element.

This application is a division of copending application Ser. No. 353,683, filed Mar. 23, 1964, now Patent No. 3,311,774, issued Mar. 28, 1967, entitled, Electron Discharge Device, by Eros Atti, and assigned to the assignee of this invention.

This invention relates to improved electron device structures and more particularly to cathodes in which the cathode emissive portion may be renewed.

A problem has existed in cathode ray tubes and other similar electronic devices where after a short period of operation, the drawing of current from the cathode ultimately deteriorates the emissive surface of the cathode. In time the emissive surface is thereby impaired and the intensity of emission decreases thus affecting the concentration of the cathode beam. Such deterioration tends to occur more readily when the current drawn from the cathode is in excess of the current emission capabilities of the cathode, namely under severe cathode loading conditions. It also tends to occur when the environment in which the cathode operates is unfavorable such as under poor vacuum conditions.

It has been suggested that the cathode element could be rotatably mounted with respect to a screen member having an aperture therein, whereby the cathode element is rotated with respect to the aperture thereby changing the portion of the cathode from which the current is drawn and thereby increasing the life of the cathode. However, these devices have involved rather complicated means for rotating the cathode element. In particular, these devices have used complicated motor induction means to rotate the cathode. Besides being more complex and expensive, these devices have necessitated mounting means exterior to the vacuum tube envelope to properly position the induction means with respect to the cathode element within the envelope of the vacuum tube. They also create problems due to stray magnetic and electric fields associated with the induction means.

It is therefore an object of the present invention to provide an improved and longer lasting discharge device.

Another object is to provide an improved cathode assembly with an emissive portion of the cathode which can be changed from time to time to effect a longer life of the discharge device.

Still another object of this invention is to provide an improved electrode assembly and a means for changing the relative position of one of the elements of the assembly which is inexpensive to manufacture and which can be installed within the envelope of the discharge device.

A further object of this invention is to provide a slim plified mechanism for motivating an electrode comprising either a thermal-responsive or magnetically-responsive stepping mechanism.

A still further object is to provide a simplified mechanism for rotating or orbiting an electrod automatically as the discharge device is turned off and on.

Brieflly, the present invention accomplishes the abovecited objects by providing a movably mounted electrode and a simple inexpensive means for moving said electrode. More specifically, a grid or control element which has been positioned between the cathode and an anode surface is provided with an aperture over-shadowing a portion of the cathode. Thus by rotating or displacing transversely the cathode, the various emissive portions of the cathode may be positioned beneath the aperture, thereby replacing a worn or dissipated portion with a new portion. In particular, this invention teaches the use of very simple thermal responsive elements for rotating or displacing the surface of the cathode, and additionally, the use of thermal responsive elements to lock the cathode in a fixed position as long as it is desired to keep a given cathode emitting surface supplying the electron beam required for the operation of the device.

Further objects and advantages of the invention will become apparent as the following description proceeds and features of novelty which characterize the invention will be pointed out in particularity in the claims annexed to and forming a part of this specification.

For a better understanding of the invention reference may be had to the accompanying drawing, in which:

FIGURE 1 illustrates an electron tube embodying the teachings of this invention;

FIG. 2 is a sectional view of the cathode assembly which is incorporated into the electron tube of FIGURE 1; and

FIG. 3 is a cross-sectional view of FIG. 2 taken along the line lIL-III of FIG. 2.

FIGURE 1 shows a cathode ray tube 10 as a particular embodiment of this invention. The cathode ray tube It) comprises an evacuated envelope 11 of a suitable material such as glass with an elongated portion 122 and a flared portion 13. An electron gun It is mounted axially within the elongated portion 12 so that a beam of electrons emanating from the electron gun 14 will strike a target 17 coated upon the end portion of the envelope ll. Through the enclosed base portion 12 of the envelope 11, there are mounted terminals 18 for providing electrical signals to the various elements within the envelope 11. The electron gun 14 includes accelerating and focusing elements 15 and 1-6 and also a cathode assembly 20 which comprises the essence of applicant's invention. A deflection means of either the electromagnetic or the electrostatic variety may be mounted outside or inside the envelope 11 respectively so as to control the deflection of the electron beam emitted from the electron gun 14.

Referring now in detail to FIGS. 2 and 3, the cathode assembly 20 has a hollow cylindrical grid cup or central element 22 made of a suitable material such as stainless steel. Disposed within the grid cup 22 and oifset from the center axis of the grid cup 22 there is provided a hollow cathode shell or cylinder 24 made of a suitable material such as nickel. A cathode heater 36 is provided 3 within the hollow cathode shell 24 to heat the cathode shell. 24 and to excite the emission of electrons. A plurality of protrusions 25 are provided to firmly secure a ceramic disc 28 positioned about the cathode shell 24. The cathode shell 24 is spaced from the closed end of the grid cup 22 by a spacer 30. On the opposite side of the ceramic disc 28 from the spacer 30, there is positioned a support member 26 which is secured in a fixed position as by Welding to the inner side of the grid cup 22. On the outside of the closed end of the cathode shell 24, there is provided an electron emissive layer 23 as a means for producing an electron beam. Such a layer may be made of any of the Well known electron emissive oxides such as those of barium, strontium and calcium. Through the enclosed end of the grid cup 22 there is centrally located a grid aperture 34 which overshadows a portion of the emissive layer 23. In one embodiment to be used in a typical cathode ray tube, it has been found practical to make the diameter of the cathode shell 24 about .125 inch and the grid aperture 34 about 0.025 inch; further, the emissive coating 23 is spaced approximately .003 inch to .005 inch from the enclosed end of the grid cup 22.

As shown in FIGS. 2 and 3, the ceramic disc 28 and the cathode shell 24 are caused to rotate beneath the grid aperture 34 by an annular eccentric washer 60 which may be made of any suitable material such as stainless steel. The eccentric washer 60 is placed between a bimetal Washer 50 and the spacer 30; the ceramic disc 28 is placed within the eccentric washer 66 in an offset hole 61. As can be more clearly seen in FIG. 3, the eccentric washer 60 has a plurality of ratchet teeth 63. The motivating means for the eccentric washer 60 and the ceramic disc 28 comprises a bimetallic spiral coil 66 and its thermally associated coil heater 70. The spiral coil 66 is secured on its inwardmost end to a heater tube 64, which is in turn supported by' supports 62 to the grid cup 22. The coil heater 70 is located within the heater tube 64. An engaging end 68 of the spiral coil 66 projects through a slot 41 Within the grid cup 22 and engages the ratchet teeth 63 located on the periphery of the eccentric washer 60. Further, a window 74 is provided through which a dog member 72 may extend to mesh with the ratchet teeth 63 of the eccentric washer 60; one end of the dog member 72 is secured to the outer surface of the grid cup 22.

In order to reduce the friction of the ceramic disc 28 against the spacer 30 and the support member 26, a suitable locking means such as the bimetal washer 50 is provided to release thec eramic disc 28 and the eccentric washer 60 to allow the emissive portion to be renewed. In particular, the support member 26 has been spaced at a sufficient distance from the spacer 30 to permit the annular bimetal Washer 50 to be inserted between the ceramic disc 28 and the support member 26. In determining the metals of which to make the bimetal washer 50 (or the bimetallic element 38), one skillled in the art would choose one metal with a very low thermal coefiicient of expansion and the other metal with a high thermal coefiicient of expansion. For example, one of the metals could be chosen as invar and the other metal could be chosen from brass, stainless steel (l88), or silver. The ceramic disc 28, the spacer 36, the bimetal washer 50 and support member 26 have been arranged with respect to each other to provide a small but sufficient play so that when the tube is in an inoperative condition the ceramic disc 28 and cathode shell 24 are free to be rotationally moved. The thermal energy emitted from heater element 36 is normally sufiicient to cause the bimetal washer S to expand or warp, thereby taking up the small allowed play between the disc 28 and the support members 30 and 26. The pressure exerted by the bimetal washer 50 tends to prevent any further movement of the cathode shell 24- which is thereby locked in a fixed position relative to the grid cup 22. To release the cathode shell 24, the heater element 36 is tie-energized to allow the bimetal washer 50 to reassume a fiat or unfiexed condition. In this condition, the electron emissive portion beneath the grid aperture 34 can be renewed by allowing substantially frictionless rotation of the cathode shell 24- by the bimetallic element 66.

One advantage of providing the eccentric washer 60 is that the sliding or brush type of connections (not shown) which would normally be necessary to make electrical contact with the cathode shell may be eliminated. Normally, a wire or connector could not be fixedly secured to the cathode shell 24 because during the changing of the emissive portion, the cathode shell 24 would be rotated about its axis. The emissive portion of layer 23 is renewed by rotating the eccentric Washer 66. The rotation of the eccentric Washer 60 orbits the cathode shell 24 about the axis of the grid cup 22 thereby placing the various portions of layer 23 beneath the aperture 34. However, the cathode shell 24 does not revolve about its own axis, but remains unrotated as it moves about the center axis of the grid cup 22. Thus, a sliding contact is not needed and a wire 24a may be directly secured to the cathode shell by any suitable means known in the art such as welding.

The embodiment disclosed in FIGS. 2 and 3 can be operated so as to renew the cathode emissive portion in any of several modes. In one mode, while the electron tube 10 is in an inoperative condition, i.e., the cathode heater 36 is de-energized, the coil heater 70 is energized thereby causing the spiral coil 66 to flex and its engaging end 68 to move downward (as seen in FIG. 3) to engage the ratchet teeth 63 thereby rotating the eccentric washer 60. As a result of the rotational movement (which is only a fraction of a revolution) undergone by the washer 60, the ceramic disc 28 will take a new position previously occupied by the eccentric hole 61 and consequently a ditferent portion of the surface of emissive layer 23 will be facing the grid aperture 34:. While the spiral coil 66 is contracting on being cooled, dog member 72 prevents the eccentric washer 60 from moving in a counterclockwise motion. The dog member 72 could in principle be omitted since the operator could prevent the eccentric washer 60 from rotating clockwise or counterclockwise by energizing the cathode heater 36 and causing the bimetal washer 50 to lock the ceramic disc 28 in place. In a second mode, an automatic operation could be achieved by connecting the coil heater 7d and the cathode heater 36 in parallel so that both heaters may be switched on at the same time. The basic consideration in this mode would be to predetermine that the spiral coil 66 reacts before the bimetal washer 50 flexes to lock the ceramic disc 28 and the eccentric washer 60 in place. This could be achieved by varying the rate: tive heating capacity of the cathode heater 36 and the coil heater 70 or by selecting the constituent metals at the bimetal members so that the spiral coil 66 responds at a faster rate than the washer 50. In operation, 3. voltage would be applied simultaneously to both the cathode and the coil heaters 36 and 70 respectively; the spiral coil 66 would respond first thereby rotating the eccentric washer 60 in a clockwise direction and causing the ceramic disc 28 to move laterally as described above (see FIG. 3). As the bimetal washer 56 responds to the heat gen erated by the cathode heater 36, it will lock the ceramic disc 28 in a new position. The coil heater 70 may then be turned off after the ceramic disc 28 has been locked in place or it may simply be left on. When the cathode heater 36 and the coil heater 70 are de-energized, the dog member 72 would prevent the spiral coil 66 from rotating the eccentric washer 60 in a counterclockwise direction. In a third mode, the cathode shell 24 could be rotated during the period in which the cathode heater 36 is warming up. The basic consideration in this mode would be to design the bimetal washer 50 so as to have a prefiexed or biased condition. Therefore, when the bimetal washer St) is in a cold condition, it would be flexed so as to lock the ceramic disc 28 into position. Further, the washer 50 while being heated will go from a fiexed condition in one direction to a flexed condition in the other passing through a relatively fiat or unfiexed condition. It is during this transitional unfiexed condition of the bimetal washer 50 that the coil heater 70, which has been energized in advance, will cause the spiral coil 66 to rotate the eccentric washer 60. Further, the washer 50 could be maintained in an unfiexed condition for any desired length of time by applying a suitably reduced voltage to the cathode heater 36. The renewing of the emissive portions could be determined by external circuitry involving counters or timers without the need of an operator manually switching the circuits on.

It will therefore be apparent that there has been disclosed a very simple and inexpensive means for rotating the cathode assembly to renew that portion of the electron emissive layer beneath the aperture of the grid face. By simply rotating or displacing the cathode shell about an ofiset axis with respect to the grid aperture 21 new portion of the electron emissive layer may be employed as a source of an electron beam. Another means for renewing a cathode emissive portion employing an elongated filament is shown in a copending application Ser. No. 360,268, now US. Patent No. 3,290,540, entitled Electronic Tube Device, to Eros Atti, and assigned to the assignee of this invention.

It is noted that though all of the electron emissive layer 23 is being excited by the cathode heater element 36, it is principally the portion of the layer 23 beneath the apertures 34 that will be dissipated. This results from the fact that the current drawn from the cathode shell 24 to form the electron beam emanates from that portion of the layer 23 facing the aperture 34.

While the present invention has been described with a degree of particularity for the purpose of illustration, it is to be understood that all modifications, alterations and substitutions within the spirit and scope of the present invention are herein meant to be included.

I claim as my invention:

1. An electron discharge device comprising a cathode element for providing an electron beam, said cathode element including at least first and second portions capable of emitting electrons, a control element having an aperture therein, said aperture so positioned with respect to said cathode element that said first portion emanates substantially all of said electron beam, and means for translating said cathode element in an orbital path with respect to said aperture of said control element without imparting a rotational motion to said cathode element about the axis of said cathode element so that said second portion emanates substantially all of said electron beam rather than said first portion.

2. An electron discharge device as claimed in claim 1, wherein an electrical connection may be secured directly to said cathode element.

3. An electron discharge device as claimed in claim 1, wherein said means for translating includes a first member having an opening therein offset from the axis of said first member, and means for imparting a rotational motion to said first member, said cathode element being disposed within said opening of said first member in a slipping relationship.

4. An electron discharge device as claimed in claim 3, wherein an electrical connector is secured directly to said cathode element.

5. An electron discharge device as claimed in claim 3, wherein there is included means for fixing the position of said first member and said cathode element with respect to said aperture of said control element and for releasing said first member and said cathode element to allow said first member and said cathode element to be moved.

6. An electron discharge device as claimed in claim 3, wherein said cathode element takes the form of a second tubular member having an enclosed end with an emissive surface thereon, said second tubular member supported by a third insulating member, said third insulating member disposed within said opening of said first member.

7. An electron discharge device as claimed in claim 3, wherein said cathode element is supported by an insulating member, said insulating member disposed within said opening of said first member, said first member having a plurality of teeth on the periphery thereof adapted to receive said means for imparting the rotational motion.

8. An electron discharge device as claimed in claim 3, wherein said cathode clement takes the form of a second tubular member having an enclosed end with an emissive surface thereon, said second tubular member supported upon a third insulating member of approximately circular configuration, said. third insulating member disposed within said opening of said first member in such a relation that when said first member is rotated said third insulating member and said cathode element are orbited about the axis of said first member.

9. An electron discharge device as claimed in claim 8, wherein said first member is of approximately circular configuration and has a plurality of teeth for receiving said means for imparting a rotational motion.

10. An electron discharge device as claimed in claim 9, wherein said means for imparting a rotational motion takes the form of a bimetal member having one end fixed with regard to said control element and the other end adapted to engage said plurality of teeth of said first member.

11. An electron discharge device as claimed in claim 10, wherein said control element takes the form of a fourth tubular member having an enclosed end with said aperture therein; said emissive surface of said cathode element disposed beneath said aperture; a fifth spacing member disposed between said third insulating member and said first member, and said enclosed end of said fourth tubular member, and a sixth mounting member disposed upon the opposite side of said third insulating member from said fifth spacing member and secured to the inner periphery of said fourth tubular member.

12. An electron discharge device as claimed in claim 1, wherein said means for translating includes a first member rotatable about an axis and having a cam surface associated with said cathode element in a slipping rela tionship, and means for rotating said first member about said axis, said cam surface disposed to impart an orbital motion to said cathode element when said first member is rotated so that said second portion substantially emits all of said electron beam rather than said first portion.

References Cited UNITED STATES PATENTS 2,175,582 10/1939 Vogel 3l3149X 3,213,318 10/1965 Glenn 313-151X STANLEY D. SCHLOSSER, Primary Examiner. JAMES w. LAWRENCE, Examiner.

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