US2615947A - Impedance matching apparatus - Google Patents

Description

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Oct. 28, 1952 MACALUSO 2,615,947

IMPEDANCE MATCHING APPARATUS Filed Nov. 30, 1948 2 Sl-lEETSSHEET 1 Fig.|.

8 |9 1 Motor V I7 Motor Control R.F. I 4

ll l Motor Motor Generator f I 7' Control i ls |s lej i F q 24 33 4 Fig.5. 2 9 138/36 35 34 3| I? --4s 34 36 I7 35 39 46 4| 49 WITNESSES: INVENTOR Oct. 28, 1952 F. MACALUSO 2,615,947

IMPEDANCE MATCHING APPARATUS Patented Oct. 28, 1952 UNITED STATES PATENT oFFicE;

IMPEDANCE MATCHING ABPARATUS Francis L..Macaluso, Baltimore, Md-., assignorto.

Westinghouse. Electric Corporation, East. Pitt's.- burgh, Pa., a corporation of. Pennsylvania:

ApplicationNovember 30, 1948; serial No. 62,755.

(Cl. 17-3 32.(l.)

7 Claims. 1

This invention relates to: radio. frequency generators, and more particularly" to matchingxof impedances of the loadsv of such generators to transmission lines which connect thegenerators to the. loads.

In most dielectric heating applications in which vacuum tube oscillators supply radio frequency energy to electrodes between which load articles are heated in. succession, as: being passed on a conveyor between the electrodes, the

changes" in the impedances of the'articles during heating; or the differences in the impedance of different articles, causes mis-match. of impedance between the transmission lines and the loads, resulting in ineifici'ent operation,. and may result in the loss of quality in. some articles. This is due to the fact that the heating load is usually a low capacitive impedance whereas the vacuum tube oscillators represent: a high impedance.

Transmissionlines are commonly'usedfor connecting the loads of dielectric heating? systems to radio frequency generators. Tuning: stubs consisting of a shorted section of a parallel two Wire transmission line. are: used as variable inductive elements to match the impedance of the load to the line; The inductance of the: tuning stubs may be varied by moving a shorting'b'ar or slider along the length of the stubs, by means such as electric motors which respond automatically to changes in impedance. This adjustment ofthe positions of the. sliders on the tuning stubs corrects for impedance mis-matches and enables optimum. power transfer; to the load articles.

A typical construction has. used motor driven sliders, each consisting. of apair ofv semi-circular collars on the opposite sides: of: a metal tube,.the collars being. rigidly connected to cross-bars, which are drawn together. by interconnecting bolts, for providing contact pressure between the collars and the tubes. A disadvantage of such aconstruction is that when. the cross-bars are tightened to provide sufficient contact? pressure, the collars bind on the tubes, due toirregularities therein, and this interferes with the adjustment of; the. collars by the motors. Such: irregularities are due to variations in the tube diameters, departures from straightness, drawing. burrs. and other imperfections in. the tubes... The tubesare usually mounted on: insulators which arenot constructed. or installed, to very close. tolerances, so that it is difficult to achieve exact parallelism between the tubes. Since the collars are-rigidly attached. to the cross-bars, the mounting; holes 2. and the assembly have to be located very accurately inorderthat the longitudinal axes of the two pairsof collars are exactly parallel.

This invention overcomes the disadvantages of prior tuning stub assemblies'by providing sliding contactors for tuning stub tubes, which are soresiliently mounted and supported. that they are movable radially of the tubes for compensating; for any irregularities: therein, wherebythey can be moved lengthwise of the tubes; without bind-- ing, while providing the necessary contact pres-- sure.

An obj ect' of the invention is to: prevent binding between a connector slidable along. a conductor. and the conductor;

Another object of" the. invention is to. prevent binding between tuning. stubs having connectors slidable along tubes.

Another object of the invention is. to eliminate the necessity for" close tolerances in tuning, stub assemblies The invention will now be described. with refs erence to the. drawings of which:

Fig. 1 is a diagrammatic view of a typical cir cuit in which thisinvention is designed for. use;

Fig. 2 is a side" elevation of a tuning. stub as'-- sembly embodying this invention;

Fig.3 is aplan view looking downwardly upon the: assembly of Fig. 2

Fig, 4 is an end elevation oi the assembly,-. and

Fig. 5 is an enlarged view; in cross. section, of.

one of the tuning stubs, slidable connectors on I a feeder tube, and of portions of the shorting cross-bars used.

Referring first to: Fig. 1, theradiofrequency generator H), which maybe a20kilowatt-vacuum. tube oscillator operating at a frequency of 1 3.6- megacycles, is-connected by the transmission line H to' a load 13, which-maybe a dielectricload to be heated byradio frequency energy. A. pair: of tuning stubs, one in series with. the load and one in parallel with the load, are. pI'OVldGd for matching the impedance of. the load [3 to the transmission line H. slidable connectors M of, the series tuning stub are in contact with the parallel conductors 16 of the stub and areconnected together by a short-circuiting cross-bar ll. The cross-bar I1 is connected to an electric motor 18, which, in"turn,.is connected through a motor control t9 t0 theload. l.3-.. Slidablecon-- nectors W of the parallel tuning stub are in contact with the parallel conductors I6 of. the. stub and are connected. together by' a short-cincuiting. cross-barilfl. Thecross-bar ll" isconnected to an electric motor l8 which, i i-turn,

3 is connected through a. motor control 19' to the load [3.

In operation, impedance changes in the load l3 cause the motor controls I9 and I9 to operate the motors l8 and [8' to slide the connectors l4 and M in one direction or the other along the parallel conductors I 6 and I6, until the load impedance is restored to normal.

In prior constructions, irregularities in the parallel conductors l6 and I6 forming the tuning stubs and lack of close tolerances in the manufacture and assembly of the other components of tuning stub assemblies, have caused the slidable connectors to bind, making it difficult for v the automatic controls to properly position the connectors along the parallel conductors. While close tolerances in the manufacture of the tun-' ing stubs and their components, and care in their installation will avoid some of the difficulties, this would add greatly to the cost of an installation.

The construction embodying this invention, and which will now be described in connection with Figs. 2 to'5 of the drawings, avoids the difficulties of the prior tuning stub assemblies, and can be manufactured and installed at a relatively low expense.

The parallel conductors 16 which may be straight copper tubes, are attached at their ends to the supports 20 which, in turn, are attached to the upper ends of the insulators 2!, the lower ends 'of which are attached to the structural I- beams 22. The supports 20 for one of the tubes I6 is connected by the metal strap 23 at one end of the assembly, the left hand end facing Figs. 2 and 3 of the drawings, to one of the I-beams when it is desired to ground one side of the tuning stub. The supports 20 for both feeder tubes are interconnected at the other end of the assembly by the metal strap 24.

The inner ends of the tubular insulators 25 are attached to the bars I! and extend parallel to the tubes equal distances therebetween. These insulators are provided for attaching the crossbars I! to the motor driven mechanism described in the foregoing, for adjusting the position of the cross-bar I'i along the parallel conductors.

As illustrated most clearly by Fig. 5, each connector M comprises the upper and lower collars with inner surfaces formed as circular segments, with the diameters of the inner surfaces equal to the outer diameters of the tubes Hi. The upper and lower collars are flattened at 3! at the centers of their outer surfaces.

The short circuiting cross-bars ll contact the collars 30 at their flattened portions 3|, and are secured thereby to the machine screws 33 which have their ends 34 threaded into the collars. The screws 33 have the body portions 35 which have larger diameters than the threaded ends 34, and which have the flat shoulders 36 which contact the flattened portions 3| of the collars.

The bars ll have the circular openings 38 through which the body portions 35 of the screws 33 extend, which openings have substantially larger diameters than those of the screw body portions. The washers 39 around the screws 33, contact the outer surfaces of the bar 1?, and the similar washers '30 around the screws 33 contact the inner surfaces of the heads thereof. The coil springs M are compressed between the washers 39 and 4B, and serve to press the inner surfaces of the bars H tightly against the outer flattened surfaces 3! of the collars 30.

The springs 4| provide resiliency which permits vertical movement of the bars ii, relative 4 their associated collars, when irregularities in the upper and lower outer surfaces of the tubes II appear during the sliding of the collars along the tubes.

The differences between the diameters of the circular openings 38 in the bars, and of the body portions 35 of the screws 33, which extend through the openings 38, and the resiliences of the spring 4| permit side movement of the collars relative to the bar ll when irregularities in their side surfaces appear, and when the tubes depart from parallelism during the sliding of the collars along the tubes.

The springs il provide good contact pressure between the cross bars i1 and the collars 30 during their motion relative to each other, thus permitting the elimination of the flexible copper straps which have been used heretofore for electrlcally connecting the collars to the cross-bars.

The bolts 45 extend vertically through the bars H intermediate the tubes E6. The washers 46 extend around the bolts 45 in contact with the lower surface of the lower bar 1?. The nuts 4'! are threaded onto the bolts 45, and the washers 48 extend around the bolts and in contact with the inner surfaces of the nuts 41. The coiled springs 49 are compressed between the washers 46 and 48. The nuts 58 threaded onto the lower ends of the bolts are look nuts. The bolts 45 pull the bars together for pressing the collars 30 against the tubes Iii, the springs 49 providing resiliency whereby the bars i! are able to move vertically relative to each other for additionally compensating for any irregularities in the upper and lower surfaces of the tubes 16 when the collars 38 are moved therealong.

As the collars are moved along the tubes I6 during impedance adjustments, the springs 4| on the screws 33, the springs 49 on the bolts 45, and the clearances in the openings 38 in the bars I 7 around the screws 33 will permit the collars to move vertically and horizontally, and in directlons therebetween, so as to ride over any irregularities in the tube surfaces without binding.

Although I have described in detail the series tuning stub, it is understood that the parallel tuning stub is constructed in identically the same manner.

I claim as my invention:

1. A transmission line for matching the impedance of a load to a radio frequency generator, comprising a pair of spaced, substantially parallel conductors, a pair of sliders formed to partially surround each of said conductors, a pair of cross-bars connecting the sliders on one of said conductors with the sliders on the other of said conductors, screws extending through said crossbars and threaded into said sliders; said crossbars having openings around said screws with diameters substantially larger than the diameters of the screws, coiled springs around said screws and compressed between the heads thereof and said cross-bars, and means for drawing said crossbars together.

2. A transmission line for matching the impedance of a load to a radio frequency generator, comprising a pair of spaced, substantially parallel conductors, a pair of sliders formed to electrically contact each of said conductors, a pair of cross-bars connecting the sliders on one of said conductors with the sliders on the other of said conductors, said cross-bars being positioned in a plane substantially perpendicular to a plane containing the conductors, screws extending through said cross-bars and threaded into said sliders, said cross-bars having openings around said screws with diameters substantially larger than the diameters of the screws, coiled springs around said screws and compressed between the heads thereof and said cross-bars, and means for drawing said cross-bars together.

3. A transmission line for matching the impedance of a load to a radio frequency generator, comprising a pair of spaced, substantially parallel conducting tubes; a pair of sliders formed as circular segments on each of said tubes, a pair of cross-bars connecting the sliders on one of said tubes with the sliders on the other of said tubes, said sliders having flattened portions contacting said cross-bars, screws extending through said cross-bars and threaded into said sliders; said cross-bars having openings around said screws with diameters substantially larger than the diameters of the screws, the portions of said screws threaded into said sliders having smaller diameters than their portions which extend in said openings in said cross-bars, and having flat shoulders contacting said flattened portions of said sliders, coiled springs around said screws and compressed between the heads thereof and said cross-bars, and means for drawing said cross-bars together.

4. A transmission line as claimed in claim 3 in which the pair of cross-bars is positioned in a plane substantially perpendicular to a plane containing said pair of conducting tubes.

5. A transmission line tuning stub comprising a pair of substantially parallel conductors, a short-circuiting member connected between said conductors, said short-circuiting member includin a first and second Sliding contact member respectively positioned on opposite sides of each conductor, a first cross-bar means, a first resilient coupling means connected between said first cross-bar means and each of said first sliding contact members, a second cross-bar means, a second resilient coupling means connected between the second cross-bar means and each of said second sliding contact members, each of said resilient coupling means comprising fastener members fixedly connected to the respective contact members and movable relative to the respective cross-bar means with resilient spring members adjacent each of said fastener members and operative therewith, and fastener means for drawing said first and second crossbar means together to hold the respective sliding contacts in position on opposite sides of each conductor.

6. A transmission line tuning stub comprising a first conductor, a second conductor spaced from said first conductor and substantially parallel thereto, a short-circuiting member connected between said conductors, said short-circuiting member including a first and a second sliding 6 contact member respectively positioned on substantially opposite sides of said first conductor, a third and a fourth sliding contact member respectively positioned on substantially opposite sides of said second conductor, a first cross-bar member, a first resilient connector means connected between the first cross-bar member and each of said first and third contact members, a second cross-bar member, a second resilient connector means connected between the second cross-bar member and each of said second and fourth contact members, each of said resilient coupling means comprising fastener members fixedly connected to the respective contact members and movable relative to the respective crossbar means with resliient spring members adjacent each of said fastener members and operative therewith, and a resilient means for drawing together said first and second cross-bar members.

7. A transmission line tuning stub comprising a pair of substantially parallel conductors, a short-circuiting member connected between said conductors, said short-circuiting member including a first and a second sliding contact member respectively positioned on opposite sides of each of said conductors, a first cross-bar member a first resilient coupling means connected between the first cross-bar member and each of said first sliding contact members, a second cross-bar member, a second resilient coupling means connected between the second cross-bar member and each of said second sliding contact members, each of said resilient coupling means comprising fastener members fixedly connected to the respective contact members and movable relative to the respective cross-bar means with resilient spring members adjacent each of said fastener members and operative therewith, said first and second cross-bar members being positioned in a plane which is perpendicular to a plane including said conductors, and a fastener for pulling together said first and second cross-bar members.

FRANCIS L. MACALUSO.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,225,227 Dunham May 8, 1917 2,123,631 Koehler July 12, 1938 2,125,900 Evans Aug. 9, 1938 2,453,994 Lappin et a1. Nov. 16, 1948 FOREIGN PATENTS Number Country Date 379,796 Great Britain Sept. 8, 1932

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