US3562575A

US3562575A - Electron beam tube containing a multiple cathode array employing indexing means for cathode substitution

Info

Publication number: US3562575A
Application number: US856415A
Authority: US
Inventors: Lloyd J Derr
Original assignee: National Aeronautics and Space Administration NASA
Current assignee: National Aeronautics and Space Administration NASA
Priority date: 1969-09-09
Filing date: 1969-09-09
Publication date: 1971-02-09
Anticipated expiration: 1988-02-09

Abstract

An indexing mechanism for an electron beam tube having many electron guns arranged on a turret, which rotates the turret to replace the gun being used when it fails, and to rotate the turret to serially activate the cathodes of the guns during construction of the tube. One indexing apparatus employs an indexing wheel fixed to the turret, a stack of bimetallic washers, and a heater for making the washers buckle to move a pawl member toward the indexing wheel to advance it. Another indexing apparatus includes an indexing wheel fixed to the turret, a thermal motor that can rotate a shaft, a latch arm on the shaft that pivots out of engagement with the indexing wheel during the first few degrees of shaft rotation, and a pair of driving members that rotate the wheel after the latch arm disengages from it.

Description

United States Patent [56] References Cited UNITED STATES PATENTS 11/1963 Burnett........................

Primary Examiner-David Schonberg Assistant Examiner-Paul A. Sacher I72] Inventors T. O. Paine m n t at r o th at nal ronauti s and Space Administration, with respect to an invention of Lloyd J. Derr, Los Angeles, Calif.

Appl. No. 856,415

[ I [22] Filed Sept. 9, 1969 Attorneys-J. H. Warden, Monte F. Mott and G. T. McCoy l45| Patented Feb. 9, 1971 ABSTRACT: An indexing mechanism for an electron beam tube having many electron guns arranged on a turret, which rotates the turret to replace the gun being used when it fails, and to rotate the turret to serially activate the cathodes of the ELECTRON BEAM TUBE CONTAINING A guns during construction of the tube. One indexing apparatus MULTIPLE CATHODE ARRAY EMPLOYING employs an indexing wheel fixed to the turret, a stack of INDEXING MEANS FOR CATHODE bimetallic washers, and a heater for making the washers SUBSTITUTION buckle to move a pawl member toward the indexing wheel to 10 Claims, 7 Drawlng 8 advance it. Another indexing apparatus includes an indexing wheel fixed to the turret, a thermal motor that can rotate a shaft, a latch arm on the shaft that pivots out of engagement with the indexing wheel during the first fewdegrees of shaft rotation, and a pair of driving members that rotate the wheel after the latch arm disengages from it.

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LLOYD J. DERR IN VIENTOR.

ATTORNEYS ELECTRON BEAM TUBE CONTAINING A MULTIPLE CATHODE ARRAY EMPLOYING INDEXING MEANS FOR CATI'IODE SUBSTITUTION ORIGIN OF INVENTION The invention described herein was made in the performance of work under a NASA contract and is subject to the provisions of Section 305 of the National Aeronautics and Space Act of I958, Public Law 85-568 (72 Stat. 435; 42 USC 2457).

BACKGROUND OF THE INVENTION l. Field of the Invention This invention relates to an indexing mechanism which is especially useful for multicathode electron tubes.

2. Description of the Prior Art Unmanned space craft which are sent on extended missions often employ electron beam tubes such as power amplifier tubes, klystrons, and traveling wave tubes, which employ cathode structures, or electron guns. The electron guns have a limited lifetime, and there is a high possibility of gun failure prior to the end of the mission. One way of obtaining an extended life for the electron tubes is to provide many electron guns on a turret, and to provide a mechanism for advancing the turret when a gun fails, to bring the next gun into use. Such an indexing mechanism must be capable of operating reliably and accurately in a vacuum environment at long-spaced intervals.

OBJECTS AND SUMMARY OF THE INVENTION An object of the present invention is to provide an indexing mechanism of high reliability and long life, which can operate in a vacuum environment.

Another object is to provide an electron tube which is highly reliable. I

In accordance with the present invention, an indexing mechanism is provided which is especially suitable for use in an electron tube with many electron guns mounted on a turret, to index the turret when a gun fails to operate. The mechanism includes an indexing wheel coupled to the turret and a thennal motor for advancing the wheel, to replace a gun that fails, or to serially activate the cathodes of the guns during construction of the tube.

In one embodiment of the invention, a stack of bimetallic washers is used which is heated to cause the washers to buckle. A pawl member positioned against the stack is moved by the buckling washers, to advance the indexing wheel which is fixed to the turret, to thereby index the turret. The pawl member includes a ring-shaped portion that lies against the top washer of the stack for back and forth movement by the stack, and a stiff spring arm that extends to the indexing wheel to index it as the arm moves back and forth. A bimetallic locking member positioned near the heater has arms that engage the housing of the mechanism to lock the pawl member in a position away from the indexing wheel. However, when the locking member is heated as the washers are heated, its arms expand to a position where they are clear of the housing to allow the pawl member to move toward the indexing wheel.

In another embodiment of the invention, a spiral bimetallic band is used to operate a latch that holds the indexing wheel, and to move wheel-driving members that rotate the wheel to a new position. A shaft moved by the bimetallic band is fixed to a latching arm so that the first few degrees of shaft rotation pivot the latching arm out of engagement with the indexing wheel. The wheel-driving members are also fixed to the shaft at a position whereby they engage the wheel and rotate it only after the latching arm has become disengaged from the wheel.

The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional side view of electron tube apparatus constructed in accordance with the invention;

FIG. 2 is a sectional view of the electron tube apparatus of FIG. 1;

FIG. 3 is a sectional view of the actuator mechanism of the apparatus of FIG. 1;

FIG. 4 is a sectional front'view of electron tube apparatus constructed in accordance with another embodiment of the invention;

FIG. 5 is a sectilonal view taken on the line 5-5 of FIG. 4;

FIG. 6 is a sectional view taken on the line 6-6 of FIG. 5; and

FIG. 7 is a broken partial perspective view of the apparatus of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. I illustrates the cathode portion of a linear beam tube,-

such as a klystron or traveling wave tube. The tube includes a vacuum housing 10 with a cathode means or electron gun 18' for generating an electron beam, and an input region. I2 through which the beam passes and a signal is received which is amplified. A vacuum is established through an exhaust tube 14 which in pinched to seal it. and activation of the tube prior to use is accomplished with an activation screen 13 located in front of the exhaust tube I4. A holding wheel or turret I6 rotatably mounted on the housing carries twelve electron guns 18, any one of which can operate the tube when it is positioned in front of the input region 12. Each gun has a lead 20 mounted on the turret. The leads are positioned so that they are contacted by a conductive element 22 when their gun is positioned in front of the input region, and by another conductive element 23 when their gun is positioned in front of the activation screen I3.

During use of the tube, only the electron gun I8 which is positioned in front of the input region I2 is energized, the energization being accomplished by current carried through conductive element 22. When the electron gun being used fails, the turret is rotated'by one-twelfth revolution to bring the next gun into position in front of the input region.

Each of the electron guns 18 including a cathode, and a filament for heating the cathode. During manufacture of the tube, the cathodes must be activatedto break down carbonates on the cathode surface into oxides, and thereby ready the cathode surfaces for use. This is accomplished by conducting current to the guns to heat them in the same manner as they will later be heated during actual use. The initial heating during activation results in various contaminating substances being driven from the cathode surfaces. If the cathodes were activated while they were in front of the input region l2 of the tube, the substances initially driven off from the cathodes would contaminate the input region. To prevent this, the activation screen 13 is provided, and it is positioned at a location spaced from the input region 12. During cathode activation, current in is conducted to that cathode which lies adjacent to the activation screen through conductive element 23, while a positive voltage is applied to the wire mesh screen 13. As a result, the contaminating material from the cathode settles in the exhaust tube 14, on the screen 13, or at regions around the screen, instead of primarily at the input region 12. In order to activate all of the cathodes, the turret is repeatedly indexed to bring each electron gun opposite the activation screen where its cathode is activated. Once all cathodes are activated, the activation screen 13 and conductive element 23 are no longer used. 1

As shown in FIG. 2, the turret is fixed to a shaft 24 that extends through a bearing plate 26 of the housing. A ratchet or indexing wheel 28 is fixed to the opposite side of the shaft. A detent 30 mounted on the housing engages the indexing wheel to tend to retain it at any of twelve rotational positions, although it allows the wheel to be advanced. The detent includes a piston 40 biased toward the indexing wheel by a spring 42, and carrying a detent rod 44 which is rotatably mounted thereon. An actuator 32 constructed in accordance with the invention and to be described in detail below, advances, or indexes the indexing wheel whenever the electron gun being used fails. The turret and indexing wheel are supported against the bearing plate by

ball bearings

34 and 36 to take up thrust. In addition, the shaft 24 is rotatably mounted on a bearing 38 fixed to the housing.

FIG. 3 illustrates the actuator 32 which indexes the indexing wheel 28. The actuator includes an actuator housing 46 with a heat-insulating base 48 for mounting on the vacuum housing 10. A stack of bimetallic washers 50 is disposed against the base, and a heating cylinder 52 extends through the stack. An activating member, or pawl-activating means 54 includes an inverted cup-shaped part 56 with a rim or ring-shaped portion disposed against the upper washer, a holder 58 extending from the cup-shaped part and slidably engaged with a bearing aperture 59 in the housing, and a pawl 60 extending from the holder to the indexing wheel. The pawl is a strip of stiff spring material, and its end normally engages'one of twelve recesses 62 formed in the indexing wheel. When the stack of bimetallic washers is heated, the washers become convex and push the pawl means 54 toward the indexing wheel, so that the pawl 60 advances the wheel. A return spring 57 urges the pawl means toward its original position when the washers cool, to return the pawl means to its original position.

A bimetallic lock member 64 has a central portion 66 mounted on the pawl means 54 and a pair of arms 68 extending on either side therefrom. Each arm is normally in the position shown in solid lines, wherein it extends through an aper ture 70 in the cup-shaped member and its end is in line to abut a shoulder portion 72 on the actuator housing. In this position, the lock member prevents the pawl means 54 from accidentally moving toward the indexing wheel to advance it. However, when the lock member is heated, the arms pivot outward to the positions indicated at 68A, where they are in line with apertures 74 in the housing. The pawl means is then free to move toward the indexing wheel to index it.

The heating cylinder 52 includes a heating element 76 extending about a core member 78, at positions near the lock member 64 as well as within the stack of washers 50. Electrical leads 80 to the heating element extend through the base of the actuator housing and through the vacuum housing to an energizing circuit. A sensing circuit 82, shown in FIG. 2, for sensing when the electron gun being used fails, controls the flow of current to the heating element. Such a circuit can include, for example, an amplifier for sensing the voltage drop across the filament of the gun to close a switch that allows current to flow through the heating element, when the voltage across the filament rises above a predetermined level indicating failure. Such sensing means are known and therefore are not described in detail herein.

When the heating element 76 is energized, the heat-responsive lock member 68 is heated and its arms move outwardly and reach a position to clear housing apertures 74. The

washers in the stack 50, which require somewhat more time to heat, then deform into cone shapes, pushing the pawl means 54 toward the indexing wheel. The pawl 60 then pushes against the indexing wheel to index it. When the heating element 76 is deenergized, the washers again assume a fiat or less convex conical shape, and the pawl means and pawl 60 thereon return to their original position. The pawl 60 must deflect slightly in order to return, and it tends to drag back the indexing wheel, although with a lesser force than it advanced it. However, the latch described above holds the indexing wheel in its new position. The indexing of the wheel brings a new electron gun in position for operation.

FIGS. 47 illustrate another embodiment of the invention wherein a turret 90 which is rotatably mounted within a housing 92 is advanced by a spiral bimetallic motor 94. The turret carries eight electron gu'ns 96. The gun at the upper position 96' is aligned with an input region of an electron beam tube so its beam operates the tube. The turret is mounted on one end ofa shaft 98 that extends through a hole in a bearing plate 100. The opposite end of the shaft 98 is fixed to an indexing wheel 102. A pair of ball-

type bearings

104 and 106 serve as radial and thrust bearings to rotatably mount the turret and indexing wheels on the bearing plate.

The indexing wheel 102 has sixteen ratchet or indexing members 108 spaced uniformly about its center, or axis of rotation. Indexing of the wheel is accomplished by driving members 110, 112 on a drive wheel 114. The drive wheel 114 is mounted on the same shaft 116 as the thermal motor 94. The indexing wheel 102 is maintained at one of eight precise rotational positions bya latching member 118 that engages recesses l 20 formed at eight positions spaced about the circumference of the indexing wheel. The latching member 118 is also mounted on the shaft 116 which is fixed to the thermal motor 94 and drive wheel 114.

Current to the electron gun 96' being used is coupled thereto through an electrical conductor 122. As shown in FIG. 6, a sensing of the state of the gun being used is made by a sensing circuit 124 which is coupled to the element by a lead 126. When the sensing circuit detects a failure, it must rotate the turret 90 by one-eighth of a revolution to bring the next gun in line with the input region of the electron tube. Such rotation is accomplished by the sensing circuit which generates a current delivered through

leads

128, 130 to the thermal motor 94.

The thennal motor 94 is constructed of a bimetallic band wound in a spiral, as shown in FIG. 7, with the outer turn 94 0 fixed to a mount 132 that is fixed to the housing 92. The inner turn 941 of the bimetallic band is fixed to the shaft 116. When current flows through the bimetallic band of motor 94, the spiral band unwinds. Inasmuch as the outer turn 94 0 is fixed in position, the inner turn 941 rotates considerably in the direction of arrowl 34, thereby turning the shaft 116.

Rotation of the shaft 116 by the thermal motor causes the latching member 1 18, which is fixed to the shaft, to be rotated in a direction to disengage from the indexing wheel 102. As the shaft 1 l6 continues to rotate in the direction of arrow 134, the driving members and 112 engage indexing members 108 on the indexing wheel to rotate the wheel in the direction of arrow 136 by one-eighth of a revolution. After the indexing wheel rotates by one-eighth of a revolution, the sensing circuit 124 ceases to provide current through leads 128, to the thermal motor 94 and it cools. As the motor cools, the shaft 116 returns to its original position. In returning, the driving members 110, 112 pass over indexing members 108, and the latching member 118 falls into the next recess 120 in the indexing wheel to hold it in its new position.

A detector 138 is provided to sense the position of the indexing wheel 102, to indicate to the sensing circuit when it may terminate the fiow of current to the thermal motor. The detector 138 comprises a roller 140 mounted on the end of a leaf spring arm 142 whose other end is fixed at 144 to the bearing plate 100. The leaf spring carries a contact assembly 146 including an insulating mount with a contact thereon, the contact being arranged to touch the contact of another assembly 148 that is fixed to the bearing plate. When the detector roller 140 is in an indexing wheel recess 120, the contacts of

assemblies

146, 148 are separated. However, when the roller 140 is not in a recess, it pushes the contacts together and a detecting current can flow through the contacts and detector leads 150 to the sensing circuit 124.

When the sensing circuit 124 detects a contact-opening pulse over lines 150 from the detector, indicating that the indexing wheel has rotated by one-eighth turn, the circuit ceases to supply current .to the thermal motor 94, thereby allowing it to cool. The sensing circuit 124, is constructed to start delivering current to the thermal motor 94 as soon as the electron gun failure is detected. It continues to supply current until the contacts at 146, 148 have been closed and then opened again, signifying that the indexing wheel 102 has rotated by oneeighth turn. The sensing circuit 124 then ceases to deliver current to the thermal motor, allowing it to cool and move back to its original configuration. A highly simplified sensing circuit, shown in H0. 6, comprises an AC flip-flop 125 whose output 127 is turned on by a negative-going pulse received at its T input and whose output is turned off by a negative-going pulse received at its F input. A negative-going pulse at T is received when a gun fails, while a negative-going pulse at F is received when the contacts at 146 and 148 are opened. Generally, a more complex sensing circuit is employed to detect many kinds of gun failure and to more closely control the thermal motor.

The bimetallic band which forms the thermal motor 94 is split into two narrow bands that are joined only at the inner turn 941 of the spiral. Thus, current supplied through lead 128 on the motor, passes around one-half of the band to the center turn 941 and then through the other half of the band to the lead 130. This allows the moving portion of the thermal motor and the means for heating the moving portion to be incorporated in a single structure, instead of employing a separate heating element for heating a bimetallic band, which would increase the complexity and response time of the motor.

The driving members 110, 112 that are mounted on the driving wheel 114 are thin flexible spring members with one end fixed to the wheel 114 and the other end extending to a position against a face of the indexing wheel 102. When the driving wheel 114 begins to turn in the direction of arrow 134, and latching member 118 has moved out of a recess 120, the first driving member 110 contacts an indexing member 108 on the indexing wheel. After the member 110 has pushed an indexing member 108 a small fraction of a turn, the other driving member 112 engages an indexing member 108 and pushes it along the rest of the one-eighthturn by which the indexing wheel must be rotated.

The reason for the use of the first driving member 110 is to start the indexing wheel. The member 1 must overcome the initially high resistance which is partly due to the fact that the roller 140 of the detector 138 must be moved out of the recess into which it has fallen. When the driving member 110 first contacts an indexing member 108, it moves the indexing member in a direction almost tangent to the path of the driving member 110. This, combined with the fact that the first driving member 110 is closer to the axis of the driving wheel 114 than the other member 112, allows it to exert a larger force against an indexing member. After the first member 110 has advanced the indexing wheel by several degrees, the second member 112 contacts an indexing member to advance the indexing wheel the rest of the one-eighth turn. When the thermal motor cools and the driving members move in the reverse direction, they deflect when they reach an indexing member 108, and pass over it. The small dragging force that they tend to apply to the indexing wheel is resisted by the roller 140 of the detector. During the last portion of rotation of the thermal motor back to its original position, the latching member 1 l8 enters a recess 120 in the indexing wheel to accurately fix the position of the indexing wheel.

During the actual use of thermal motor to advance the indexing wheel 102, the shaft 116 may rotate only about onequarter turn. However, during production, when the tube may have to be heated to a very high temperature during outgasing, the bimetallic band of the thermal motor 94 may be heated to a very high temperature which causes the shaft 116 to rotate by considerably more than one-quarter turn. This excess rota-.

tion (up to about three-quarters turn) can be tolerated without damage to the thermal motor or any of the driving mechanism.

Although particular embodiments of the invention have been described and illustrated herein. it is recognized that modifications and variations may readily occur to those skilled in the art, and consequently, it is intended that the claims be interpreted to cover such modifications and equivalents.

lclaim:

I. An electron tube device comprising:

a housing;

a holding wheel rotatably mounted within said housing;

a plurality of cathode means mounted on said holding wheel;

indexing wheel means coupled to said holding wheel;

pawl means mounted for reciprocation to advance said indexing wheel means;

heat-responsive washer means for deformation when heated, mounted adjacent to said pawl means to move it in a first direction to advance said indexing wheel means;

spring means for urging said pawl means in a direction opposite to said first direction; and

means for heating said washer means.

2. The electron tube device described in claim 1 including: heat-responsive means mounted adjacent to said means for heating, for changing between a first configuration wherein it interferes with the movement of said pawl means in said first direction, and a second configuration wherein it is clear of interference with said movement of said pawl means.

3. The electron tube device described in claim 1 wherein said pawl means comprises a ring-shaped portion disposed against a face of said washer means.

4. The electron tube device described in claim 1 wherein:

said washer means comprises a stack of bimetallic washers;

and i said heating means comprises a heating element disposed within the holes of said washers.

5. The electron tube device described in claim 1 including:

means for carrying current to one of said cathode means which is in a predetermined position; and

means responsive to the operation of said cathode means in said predetermined position for energizing said means for heating.

6. An electron tube device comprising:

a housing;

a holding wheel rotatably mounted within said housing;

a plurality of cathode means mounted on said holding wheel;

an indexing wheel coupled to said holding wheel;

a thermal motor including a shaft for rotation in first and second directions when said motor is heated and cooled, respectively;

a latching member coupled to said shaft for rotation between a position in engagement with said indexing wheel when said thermal motor is cool, and a position out of engagement with said indexing wheel when said motor is heated; and

driving means coupled to said shaft for engaging said indexing wheel and rotating it after said shaft has moved past a position out of engagement with said indexing wheel as said motor is heated.

7. The electron tube device described in claim 6 including:

a detector for sensing the rotation of said indexing wheel by a predetermined amount; and V a sensing circuit for heating said thermal motor, including means responsive to said detector for terminating the heating of said thermal motor when said indexing wheel has been rotated by said predetermined amount.

8. The electron tube device described in claim 6 wherein:

said indexing wheel includes a plurality of indexing members spaced about its axis of rotation; and

said driving means includes a wheel with first and second driving members arranged to engage said indexing members in sequence as said shaft rotates during heating of said thermal motor.

9. An electron tube comprising:

a housing;

means defining an input region in said housing for receiving a stream of electrons;

a holding wheel rotatably mounted within said housing;

a plurality of activatable cathode means mounted on said wheel for sequential positioning adjacent to said input region;

means for advancing said holding wheel;

activation means spaced from said input region, for activating said cathode means;

means for driving said indexing wheel;

a latching arm for movement into said rccesses to hold said indexing wheel at each of a plurality of positions wherein one of said cathode means is opposite said input region; and

detector means for sensing the position of said indexing wheel, for controlling the operation of said means for driving said indexing wheel and the movement of said latching arm.

Claims

1. An electron tube device comprising: a housing; a holding wheel rotatably mounted within said housing; a plurality of cathode means mounted on said holding wheel; indexing wheel means coupled to said holding wheel; pawl means mounted for reciprocation to advance said indexing wheel means; heat-responsive washer means for deformation when heated, mounted adjacent to said pawl means to move it in a first direction to advance said indexing wheel means; spring means for urging said pawl means in a direction opposite to said first direction; and means for heating said washer means.

4. The electron tube device described in claim 1 wherein: said washer means comprises a stack of bimetallic washers; and said heating means comprises a heating element disposed within the holes of said washers.

5. The electron tube device described in claim 1 including: means for carrying current to one of said cathode means which is in a predetermined position; and means responsive to the operation of said cathode means in said predetermined position for energizing said means for heating.

6. An electron tube device comprising: a housing; a holding wheel rotatably mounted within said housing; a plurality of cathode means mounted on said holding wheel; an indexing wheel coupled to said holding wheel; a thermal motor including a shaft for rotation in first and second directions when said motor is heated and cooled, respectively; a latching member coupled to said shaft for rotation between a position in engagement with said indexing wheel when said thermal motor is cool, and a pOsition out of engagement with said indexing wheel when said motor is heated; and driving means coupled to said shaft for engaging said indexing wheel and rotating it after said shaft has moved past a position out of engagement with said indexing wheel as said motor is heated.

7. The electron tube device described in claim 6 including: a detector for sensing the rotation of said indexing wheel by a predetermined amount; and a sensing circuit for heating said thermal motor, including means responsive to said detector for terminating the heating of said thermal motor when said indexing wheel has been rotated by said predetermined amount.

8. The electron tube device described in claim 6 wherein: said indexing wheel includes a plurality of indexing members spaced about its axis of rotation; and said driving means includes a wheel with first and second driving members arranged to engage said indexing members in sequence as said shaft rotates during heating of said thermal motor.

9. An electron tube comprising: a housing; means defining an input region in said housing for receiving a stream of electrons; a holding wheel rotatably mounted within said housing; a plurality of activatable cathode means mounted on said wheel for sequential positioning adjacent to said input region; means for advancing said holding wheel; activation means spaced from said input region, for activating said cathode means; means for coupling currents to a cathode means in front of said input region; and means for coupling currents to a cathode means adjacent to said activation means, whereby to enable the activation of all of said cathode means by sequentially activating said cathode means as they move to a position adjacent to said activation means.

10. The apparatus described in claim 9 wherein said means for advancing said holding wheel comprises: an indexing wheel fixed to said holding wheel, said indexing wheel having recesses spaced thereabout; means for driving said indexing wheel; a latching arm for movement into said recesses to hold said indexing wheel at each of a plurality of positions wherein one of said cathode means is opposite said input region; and detector means for sensing the position of said indexing wheel, for controlling the operation of said means for driving said indexing wheel and the movement of said latching arm.