US3078383A - Arc chamber - Google Patents

Description

Feb. 19, 1963 H. J. LINGAL 3,078,383

' ARC CHAMBER Filed April 29. 1960 I 8 6 Sheets-Sheet 1 Fig. I

Feb. 19, 1963 H. J. LINGAL 3,078,383

ARC CHAMBER Filed April 29. 1960 6 Sheets-Sheet 2 H. J. LINGAL ARC CHAMBER Feb. 19, 1963 6 Sheets-Sheet 3 Filed April 29. 1960 Feb, 19, 1963 H. J. LINGAL 3,678,383

ARC CHAMBER Filed April 29. 1960 6 Sheets-Sheet '4 H. J. LlNGAL Feb. 19, 1963 ARC CHAMBER 6 Sheets-Sheet 5 Filed April 29. 1960 Feb. 19., 1963. H. J. LINGAL 3,078,383

ARC CHAMBER Filed April 29. 1960 e Sheets-Sheet 6 United States Patent 3,673,333 ARtC CHAMBER Harry J. lLingal, Pittsburgh, Pa, assignor to Westinghouse Electric (Corporation, East Pittsburgh, Pin, a corporation of Pennsylvania Filed Apr. 29, 1950, Ser. No. 25,762 9 Claims. (Q. 313-452) The present invention relates generally to are chambers and more particularly to a mechanism for drawing an arc in a pressurized arc chamber.

In a pressurized gas chamber for hypersonic wind tunnel testing or the like, which uses an electric are for heating and expanding the gas, it is desirable upon start-up to develop the are gradually to its full length to avoid developing steep front mechanical shock waves which might cause rupture of the arc chamber walls. Depending upon the power in the arc, the desirable time to develop the arc to its full length may vary between one and several cycles. For this reason it is undesirable to start an arc by melting a short circuiting fuse wire connecting the power electrodes.

The principal object of the present invention is to provide a new and improved arc chamber.

Another object of the present invention is to provide an are drawing mechanism which starts the are by parting electrodes at a controlled rate of movement, thereby avoiding the development of severe shock waves.

Another object of the present invention is to provide an arc drawing mechanism which transfers the arc to stationary electrodes upon development of the proper length arc.

Another object of the present invention is to provide an are drawing mechanism wherein the actuating and controlling part of the mechanism is located externally to the are chamber.

Further objects and advantages of the present invention will be readily apparent from the following detailed description taken in conjunction with the drawing in which:

FIGURE 1 is an elevational view of an illustrative embodiment of the present invention;

FIG. 2 is a fragmentary assembly view, partly in section, of a portion of H6. 1;

FIG. 3 is an enlarged detailed view of a portion of FIG. 2;

P16. 4 is a fragmentary view, partly in section, talren along the line lVlV in FIG. 6;

FIG. 5 is an end elevational view of PEG. 4;

FIG. 6 is an elevational view of another portion of the present invention;

P16. 7 is an elevational view, partly in section, of still another portion of the present invention; and,

FIG. 8 is a sectional view taken along the line Vlll VIII in FIG. 7.

A hypersonic wind tunnel using an arc chamber as a generator depends upon electrically increasing the internal energy of the emitted gas and utilizing Brownian movement to obtain directed kinetic energy for the desired gas ve.ocity. Because of the necessarily tremendous power involved, it is desirable to strike an electric are within the chamber and gradually increase its length so as to avoid excessive shock waves which might cause rupture of the arc chamber walls. The present invention provides apparatus for drawing an electric are between a pair of spaced stationary electrodes in the desirable manner.

For purposes of clarity, all like parts have been given the same reference characters throughout the several figures.

With reference to FIG. 1, the arc chamber 2 is illus trated mounted on a structural rack i. Admission of the gas to be heated in the arc chamber 2 is accomplished by "ice the gas inlet pipe 6. Exit means for the heated gas at the desired velocity is provided by the vent 8, which vent is provided with an exhaust cooling jacket 10 with input and output pipes 12 for a cooling medium.

Electrical connection to the upper electrode 30 (FIG. 2) is made by the upper connectors 14 encased in an insulation barrier 16. The lower connectors 18 provide electrical power to the lower electrode 32 (FIG. 2). Both the upper connectors 14 and the lower connectors 18 also provide conduit means for a cooling medium which flows in heat transfer relationship within the electrodes 30 and 32 to reduce the hot spot temperature of the electrode surfaces.

The actuating and controlling portion of the apparatus for drawing an electrical are between the upper and lower electrode is secured to the arc chamber 2 and rack 4. An arc starter assembly 59 is slidably mounted within a gas tight container 20 and is actuated by the motion transfer mechanism 3% which is driven by the driving apparatus 104). The gas pressure within the electrode container 20 and within the motion transfer mechanism 3% is substantially equal to the pressure within the arc chamber 2 providing an additional advantage of the present invention. The actuating and controlling part of the apparatus is located externally to the pressurized arc chamher 2. Therefore, the pressurized arc chamber 2 need not be opened between tests to insert a starting fuse wire or to adjust the length and speed of travel of the starting electrode as is necessary with apparatus of the prior art.

REG. 2 is a fragmentary assembly view, partly in section, of the arc chamber 2. The present invention provides apparatus for drawing an electric arc in the arc chamber 2; which arc chamber is claimed and more fully described in the copending patent application, Serial No. 19,528 dated April 4, 1960, by Werner S. Emmerich and assigned to the same assignee. As more fully described therein, the arc chamber 2 comprises an upper and lower ring electrode 3% and 32, respectively, fixedly mounted and adapted to have an ionizing potential connected thereacross by means of the upper connectors 14 and lower connectors 18 respectively. Cooling coils 3d are embedded within the stationary electrodes to conduct heat away from the electrodes during operation of the arc chamber. A ceramic cylinder 36 encloses the volume between the stationary electrodes, forming an envelope which allows the admission of incoming gases through slots 38. A magnetic field is established transverse to the electric arc by means of the magnetic coils it? so that the electric arc is forced along the ring electrodes 36 and 32 by precession due to the action of the magnetic field.

The are starter assembly 50 is mounted within the arc starter guide 44 and actuated by an electrical conducting rod 46 which in turn is connected to on electrical insulating rod 48 and thence to a driving rod or gear rack 49 which extends through the bottom of the arc chamber 2, through the motion transfer mechanism 300 and into the sealed rod container 2%. A gear rack or connecting rod 203 provides driving force to the motion transfer mechanism 3% which in turn advances and retracts the arc starter assembly St) to initiate and draw the arc to its proper length within the arc chamber 2.

Tracing the electrical circuit, the arc starter makes electrical connection to the conducting rod 46 and hence to the arc starter guide .4 through a roller contact assembly 6h. The are starter guide 44 is secured to a lower manifold 4'7 which is at the same potential as the lower connectors 18.

Referring to FIG. 3, the arc starter 50 comprises a plurality of contact fingers 51, each pivotally mounted on individual pins 52. While two contact fingers are shown for the purposes of illustration, it is to be understood that any suitable number of contact fingers may be used. A shunt 53 electrically connects the contact finger 51 to a piston member 54 and is secured at both ends by securing means such as set screws 55. A resilient member or spring 56 urges the contact finger 51 to make good electrical contact with the top and bottom electrodes 39 and 32, respectively, as the starter assembly St) advances and retracts between the two stationary electrodes.

A ceramic disc or shield 57 is secured to the piston member 54 by means of a formed receiving member 58. The ceramic insulator 57 assists the transfer of the are between the upper electrode 3% and the contact fingers 51 to the upper electrode 319 and the lower electrode 32 by wiping the arc onto the lower electrode 32 as the arc starter assembly 42 is retracted past the lower electrode when completing its cycle of operation. The ceramic shield 57 provides a heat insulating barrier for the arc starter assembly 50. Thus, the high temperatures generated within the arc chamber are contained within the desired envelope. The piston member 54 is secured to the conducting rod 46 which in turn makes electrical contact with the roller contact assembly 69.

The roller contact assembly 60 comprises a plurality of electrical contacts 61 Which are disposed to straddle the conducting rod 46 and roll along the conducting rod 46 as it advances and retracts the arc starter assembly. The contacts 61 are urged into electrical contact with the conducting rod 46 by means of a compression member or spring 62, rigidly positioned at one end by means of a plate 63. The opposite end of the spring 62 abuts a bearing 64, separated by a washer 65 on each side. The spring 62 applies force against a shoulder 66 urging the contact 61 to make contact with the conducting rod 46. Roller bearings 67 allow the contact '61 to rotate in the assembly 60 as the are starter assembly 42 advances and retracts.

Electrical connection from the roller contact assembly 60 to the arc starter guide 44- is obtained through the roller bearings 67. Where desirable, additional electrical contact may be secured by use of pigtails (not shown) which are secured to the rolling contact 61 at one end by means of the mounting hole therein and the opposite end of the pigtails secured to the arc starter guide 44 in any suitable manner.

The driving mechanism 1% and latching mechanism 260 to advance and retract the arc starter assembly 51) is illustrated in FIGS. 4, and 6 The driving means 100 comprises a pair of 'L-shaped brackets 1011 and 102 welded together or secured by bolts or other suitable means to form a cradle. A wind-up shaft 104 is rotatably mounted in the bracket 102 by means of a bushing bearing 106. A driving shaft 168 is rotatably mounted in the end bracket 101 in a similar manner with the bushing bearing 110. The shafts 104 and 108 are independently rotatable and aligned on the same axis by means of a dowel pin 112 integral with the wind-up shaft 104 and a dowel opening 11-4 within the driving shaft 1&8 forming a running fit therebetween allowing each shaft to rotate independently of the other.

The shafts 104 and 108 extend through a tension storage means or torsion spring 116 which is enclosed in a metal guard 118, in turn secured to the bracket 102. The guard 118 contains the torsion spring 116 as a safety precaution should the torsion spring fatigue and rupture.

An index plate 120 secured by suitable means, such as welding, to the wind-up shaft 104 and adapted to rotate therewith engages a spring end 122 of the torsion spring 116 by means of a pin 124. To hold the driving mechanismin assembly at a desired preloading, a number of pins are located in the index plate 129. The opposite spring end 126 engages a driving plate 123 which is secured to the driving shaft 1%.

Initially, both the index plate 12:) and the driving plate 123 are secured against rotation. The driving plate 123 is secured against rotation by means hereinafter to be described. The index plate is secured by the holding latch or pawl 130 which is pivotally mounted by means of a pin 132 secured in an extension 134 secured to the end bracket 1G2. The pawl 130 is urged against the index plate 12s by a spring member 136 secured at one end to the pawl 13th and at the opposite end to the extension 134. The pawl 13d engages a slot in the index plate 120 to prevent rotation of the index plate in the reverse direction.

H nce, by rotating the crank or operating handle 133 which is secured to the Wind-up shaft 104, the torsion spring 116 provides a tension storage of energy, the magnitude of which, it will be shown, controls the speed with which the arc starter assembly 59* advances and retracts between the stationary electrodes in the arc chamoer 2. By torsionally winding up the spring 116 a potential driving force is available to act upon the driving plate 1123 upon release of the drivingshaft 1%.

From FIG. 6, a lever arm 291 is rotatably mounted on the driving shaft 1% and is secured from rotating in a counterclockwise direction by means of the latching mechanism The power potential stored in the torsion spring 116 will be released when the lever arm 201 is uniatched.

The lever arm 261 has a slot 2&2 formed in the free end of the lever arm 291 wherein is secured the opposite end of the gear rack or connecting rod 61 by means or" a bolt 2% and castle nut It is to be noted that the effective length of the lever arm 221 is readily adjustable by sliding the secured end of the gear rack 233 within the slot 2&2 thereby altering and allowing selection of the limit of advance and retraction of the starting electrode within the arc chamber 2.

Securing the lever arm 221 from rotation is a latch 22! pivotally mounted at one end to the base plate 221 by means of a pin 222. The opposite end of the latch 22% is urged into engagement with a shoulder of the lever arm 2611 by a compression spring 223 secured at one end by a pin 224 integral with an angle 225. The opposite end of the compression spring 223 is secured to the latch 22% by means of a pin 226 inserted in the latch. To release the lever arm 2111 a solenoid plungertype tripping relay 227 is mounted to the latching frame 221 and adapted, upon an electrical signal, to attract the link 228 with sufficient force to disengage the latch 229 from the shoulder of the lever arm 291. A latch guide 223 provides a track for the latch 22% to engage and disengage.

Since it is desirable that the arc starter assembly 50 advance and retract only once the compression spring 223 and the magnetic relay 227 are so chosen that the latch 22% will reassume its initial position and reengage the lever arm 201 after a single rotation of the arm.

To cushion the shock of the lever arm 261 striking the latch 22%) upon completion of one rotation, a decelerator 236 is mounted on the base plate 221. The clecelerator 239 comprises a lug 231 and a step 232 rigidly secured together and pivotally mounted on a pin 233. The lug 231 has a strike surface 239 adapted to receive a roller 207 mounted on the lever arm Ztlll by means of an integral pin 288. As the lever arm completes one complete revolution, the roller 207 rolls along the strike surface 239 of the lug 231 to decelerate the lever arm as it completes one revolution and reengages the latch 220. To adjust the decelerator 236 a set bolt 234 and engaging nut 235, secured to a third leg 236, rigidly secured to the lug 231 and stop 232 and pivotally mounted on the pin 233, engages a stationary stop 237. A spring 238 secured at one end to the stationary stop 237 and at its opposite end to the third leg 236 provides resilient means for urging the lug 231 to resist the "lever arm rotation as the roller 2 97 rolls along the strike surface 239 of the lug The set screw 234 provides means for adjust ing the force with which the decelerator will oppose the lever arm as it completes one revolution.

As the lever arm 261 makes a complete revolution it can be seen that the gear rack 293 will make a reciproeating motion which motion is transferred by the motion ransfer mechanism Silt? to the gear rack 49 of the arc starter assembly 59. The driving rack 293 engages a driving gear 3% within the motion transfer mechanism 3th).

The motion transferring mechanism 3% comprises a driving gear 331 and a driven gear 3492 secured by Woodruff keys 3&3 to a shaft 364 which is rotatably mounted by thrust bearings 3% secured in a bushing 3%. The bushing 3% is in turn threaded into the housing 3%.

It is to be recalled that the pressure within the housing 368 of the motion transfer mechanism 3% is equal to the pressure within the arc chamber. To contain the high pressure within the mechanism 3% a bushing pressure plate 310 is secured to the bushing 3% compressing a packing seal 312 and an Q-ring 314 of suitable material. Additional O-rings 316 seal the bushing 3% to the housing 3%. Thus, it can be seen that the high pressure gas within the motion transfer mechanism is contained along the bushing 366 and along the shaft 3% while at the same time allowing connection between the internal and exte nal parts of the mechanism.

A hanger guide 32d is adapted to pivot around the shaft 3% and forces the gear racl'; 2% into engagement with the driving gear 3531. Washers 318 separate the hanger guide 320 from the driving gear 3M to allow the free motion of the hanger guide. The hanger guide utilizes a pair of rollers 32?; mounted therein to allow the gear rack 2b? to make its reciprocating motion while engaging the driving gear Sill. The driven gear 3492 is rotated in the same motion. The driven gear engages the gear rack 49 of the are starter assembly 42 with the result that the conducting rod 46 advances and retracts during a rotation of the lever arm Ziil. A guide screw 139 secured by a nut 332 to the frame 30% engages a vertical slot extending along the gear rack 49 to position the gear rack so as to engage the driven gear From FIG. 7 it can be seen that the opposite end of the gear rack 49 advances and retracts within the gas sealed container 245 which is also under the same pressure as the arc chamber 2. Suitable sealing means such as O-rings 334 maintain the gas tight seal between the motion transfer mechanism housing Ell-S and the bottom side of the are chamber 2, to which it is secured by suitable means such as bolts through the bolt holes 336.

It is a feature of the present invention that the actuating and controlling elements of the apparatus for drawing an electric are between the stationary ring electrodes are located externally to the pressurized arc chamher 2. The operating connection between elements located inside the pressurized chamber and those located outside the chamber is made through a gas tight seal. The scaling is not accomplished by the use of a sliding seal with its attendant disadvantages but by means of a compression seal of the motion transfer mechanism housing 398, which seal is most efiicient.

In accordance with the present invention, upon startup of the arc chamber 2, the crank or operating handle 13% is rotated so as to wind-up the tension storage means to a desired torsional load. The further the tension spring is Wound up, the faster the arc starter assembly 5d will be advanced and retracted within the arc chamber 2. Upon release of the lever arm 201 by a suitable electric signal, the gear rack or connecting arm 2% will undergo an essentially reciprocating motion of one cycle. The hanger guide 32% compensates for any sidewise motion of the gear rack 20% and causes the gear rack 2% to engage the driving gear 301. Accordingly, the driven gear 362 transfers the motion of the gear rack 2&3 to the gear rack 49 and the arc starter assembly will advance and retract within the arc chamber 2. It is to be noted that the limit of advance of the arc starter assembly 50 may be preset by adjusting the eifec-tive length of the lever arm 201. As the arc starter assembly 50 reaches its maximum advancement and starts to retract, the electric power to the upper connectors 14 and lower connectors 13 are energized so that an ionizing potential appearing across the stationary electrodes 30 and 3-2 will initially appear between the upper electrode 30 and the contact fingers 51. As the arc starter assembly ss retracts the are between the upper electrode 36? and the contact finger 51 is gradually lengthened over a desirable preset time with a controlled rate of movement thereby avoiding development of severe shock waves.

Another feature of the present invention is that at the end of the are starter assembly travel, the terminal of the arc will transfer to the bottom fixed electrode 32. The ceramic disc 57 will assist in transferring the are by wiping the arc to the bottom electrode. The are starter '50 is retracted sufficiently to position the ceramic disc 57 to protect the starter from heat damage.

Thus, it is readily apparent that the present invention has provided apparatus for drawing an electric are between a pair of spaced stationary electrodes in an arc chamber or the like which is subjected to great pressure and temperature extremes. Conventional starting fuse wires have been eliminated. The extent of travel and the speed of advance and retraction of the arc starter assembly .is controlled by external means. The pressurized arc chamber 2 need not be opened between tests.

Although this invention has been described with a particular degree of exactness for the purpose of illustration, it is to be understood that all equivalents, alterations, and modifications within the spirit and scope of the invention are herein meant to be included. For instance, the present invention provides apparatus for drawing an electric arc in an arc chamber which is applicable to many uses besides hypersonic wind tunnels. Such an arc chamber may be used for the magnetohydrodynamic generation of electric power. Additional applications include fixation and synthesis of various chemical compounds wherein extreme heat generation is required.

I claim as my invention? 1. Apparatus for drawing an electric are between a pair of spaced stationary electrodes within a pressurized arc chamber comprising, in combination: a starting electrode adapted to travel from one stationary electrode to the opposite stationary electrode and return transferring the arc therebetween; means for connecting an ionizing potential across said electrodes; a rotatably mounted lever arm; means for rotating said lever arm at a predetermined speed; means responsive to an input signal for allowing the lever arm to rotate one revolution; a link member pivotally mounted at the free end of said le ver arm; and motion transfer means connecting said link member to said starting electrode for transferring he motion of said link member to said starting electrode to advance and retract said starting electrode.

2. Apparatus for drawing an electric are between a pair of spaced stationary electrodes within .a pressurized arc chamber comprising, in combination: a starting electrode adapted to travel from one stationary electrode to the opposite stationary electrode and return transferring the are therebet-ween; means for connecting an ionizing potential across said electrode; a rotatably mounted lever arm; means for rotating said lever arm at a predetermined speed; means responsive to an input signal for allowing the lever arm to rotate one revolution; a link member pivotaily mounted at the free end of said lever arm; means for adjusting the effective length of said lever arm; and motion transfer means connecting said link member to said starting electrode for transferring the motion of said link member to said starting electrode to advance and retract said starting electrode.

3. Apparatus for drawing an electric are between a pair of spaced stationary electrodes within a pressurized epvaass are chamber comprising, in combination: a starting electrode adapted to travel from one stationary electrode tothe opposite stationary electrode and return transferring the arc therebetween; means for connecting an ionizing potential across said electrode; a rotatably mounted lever arm; means for rotating said lever arm at a predetermined speed; said last-mentioned means comprising tension storage means and means for establishing a predetermined amount of energy in said tension storage means; a lever arm rotatably mounted and connected to said tension storage means for receiving stored up energy urging rotation of said arm upon release of said lever arm; release means responsive to an input signal for allowing the lever arm to rotate one revolution; a link member pivotally mounted at the free end of said lever arm; means for adjusting the effective length of said lever arm; and motion transfer means connecting said link me iber to said starting electrode for transferring the motion of said link member to said starting electrode to advance and retract said starting electrode.

4. Apparatus for drawing an electric arc between a pair of spaced stationary electrodes within a pressurized a'rc chamber comprising, in combination; a starting electrode adapted to travel from one stationary electrode to the opposite stationary electrode and return transferring the arc therebetween; means for connecting an ionizing potential across said electrodes; a rotatably mounted lever arm; means for rotating said lever arm at a predetermined speed; said last-mentioned means comprising an index plate and a driving plate rotatably mounted on first and second independently rotatable shafts respectively; a torsion spring secured at its opposite ends to the index plate and the driving plate respectively and peripherally spaced from said first and second shafts; said lever arm connected to rotate with said second shaft; means responsive to an input signal for allowing the lever arm to rotate one revolution; a link member pivotally mounted at the free end of said lever arm; means for adjusting the eiiec tive length of said lever arm; and motion transfer means connecting said link member to said starting electrode for transferring the motion of said link member to said starting electrode to advance and retract said starting electrode.

.5. Apparatus for drawing an electric are between a pair of spaced stationary electrodes within a pressurized arc chamber comprising, in combination; an arc starter assembly adapted to travel from one stationary electrode to the opposite stationary electrode and return transferr'ing the arc therebetween; means for connecting an ionizing potential between said opposite stationary electrode and said one stationary electrode; said are starter assembly including a driving rod and contact fingers adapted to be energized at the same potential as said one stationary electrode and move between said stationary electrodes so as to develop an electric arc gradually to its full length across said stationary electrodes; said are chamber having an auxiliary chamber through which said driving rod extends; a closure member secured to said auxiliary chamber in gas tight relationship therewith for containing said driving rod as it extends out of said auxiliary chamber; and means for advancing and retracting the driving rod a predetermined distance and at a predetermined speed.

6. Apparatus for drawing an electric are between a pair of spaced stationary electrodes within a pressurized arc chamber comprising, in combination; an arc starter assembly adapted to travel from one stationary electrode to the opposite stationary electrode and return transferring the arc therebetween; means for connecting an ionizing potential between said opposite stationary electrode and said one stationary electrode; said are starter assembly including a driving rod and contact fingers adapted to be energized at the same potential as said one stationary electrode and move between said stationary electrodes so as to develop an electric are gradually to its full length across said stationary electrodes; said are chamber having an auxiliary chamber through which said driving rod extends; a closure member secured to said auxiliary chamher in gas tight relationship therewith for containing said driving rod as it extends out of said auxiliary chamber; motion transfer means including a driving gear and a driven gear; said driven gear being located within said auxiliary chamber and connected to said driving gear through a pressure tight seal; a .gear rack operably connected to said driving gear; and means for driving said gear rack in a reciprocating motion of two to three cycles duration with a predetermined length of travel and speed.

7. The apparatus of claim 6 wherein said are starter assembly includes an electrically conducting rod; a roller contact assembly including a plurality of roller contacts straddling said conducting rod and adapted to roll along the surface of said rod making electrical contact therewith; and means for-connecting said electricalroller contacts to said ionizing potential.

8. The apparatus of claim 6 in which said arc starter assembly consists of at least one electrical contact finger pivotally mounted and adapted to make electrical contact with the first and second stationary electrodes as the arc starter assembly advances and retracts; and a heat and electrical barrier secured to said are starter assembly trode and said one stationary electrode; said are chamher having an auxiliary chamber through which said starter assembly extends; a closure member secured to said auxiliary chamber in gas tight relationship'therewith for containing said starting assembly as it extends out of said auxiliary chamber; and means 'for advancing and retracting thedriving .rod a predetermined distance and at a predetermined speed.

References *Cited in the file of this patent UNITED STATES PATENTS 1,571,924 Kenyon Feb. 2, 1926 1,814,851 1931 1846,32 1 Kuntke Feb. 6, 1934 2,607,024 Marwell et .al .d Aug. 1.2, 1952

Claims (1)

1. APPARATUS FOR DRAWING AN ELECTRIC ARC BETWEEN A PAIR OF SPACED STATIONARY ELECTRODES WITHIN A PRESSURIZED ARC CHAMBER COMPRISING, IN COMBINATION: A STARTING ELECTRODE ADAPTED TO TRAVEL FROM ONE STATIONARY ELECTRODE TO THE OPPOSITE STATIONARY ELECTRODE AND RETURN TRANSFERRING THE ARC THEREBETWEEN; MEANS FOR CONNECTING AN IONIZING POTENTIAL ACROSS SAID ELECTRODES; A ROTATABLY MOUNTED LEVER ARM; MEANS FOR ROTATING SAID LEVER ARM AT A PREDETERMINED SPEED; MEANS RESPONSIVE TO AN INPUT SIGNAL FOR ALLOWING THE LEVER ARM TO ROTATE ONE REVOLUTION; A LINK MEMBER PIVOTALLY MOUNTED AT THE FREE END OF SAID LEVER ARM; AND MOTION TRANSFER MEANS CONNECTING SAID LINK MEMBER TO SAID STARTING ELECTRODE FOR TRANSFERRING HE MOTION OF SAID LINK MEMBER TO SAID STARTING ELECTRODE TO ADVANCE AND RETRACT SAID STARTING ELECTRODE.

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