US2846347A - Machine for making open wire transmission line - Google Patents

Description

Aug. 5, 1958 MACHINE FOR MAKING OPEN WIRE TRANSMISSION LINE Filed April 3, 1952 EIIEE l J. D. GIULIE ET AL' 2,846,347

2 Sheets-Sheet l EIE- INVENTORS Joe 0 G/u/ie Les/le E Worcesfer ECKHOFF SLICK 1958 J. D. GIULIE ET AL 2,846,347

MACHINE FOR MAKING OPEN WIRE TRANSMISSION LINE States MACHINE FOR MAKING UPEN WIRE TRANSMISSION LINE This invention relates to an open wire transmission line, the machine on which such line can be manufactured, and to the process of manufacturing such line.

In carrying high frequency electric currents it has been long recognized that an ideal transmission line would consist of two parallel wires with only air serving to separate and insulate the wires from each other. When transmission lines having two parallel wires have a solid insulating material separating them, dielectric losses are encountered due to the material used as an insulation. In addition, when such'transmission lines are exposed to the atmosphere, dirt and moisture from the air settle on the insulation, reducing the effectiveness of the transmission line.

Of course, it is impossible to achieve a completely ideal line since some method must be used to space the wires and to support the line. One of the most effective and practical lines consists of two parallel Wires with a series of insulating spacers holding the two wires in spaced relationship. Such transmission lines are wellknown and the spacers may be made from a plastic material having good insulating properties or even from wood. However, the manufacture of such lines in the past has been slow and tedious since the spacers have ordinarily been slotted and fastened on the line by hand. An attempt has been made in the past to produce such lines using thermoplastic plastic spacers by heating the Wire to above the softening point of the plastic and pressing the wire into the unheated spacer. However, when such a method is used, the temperature of the wire must be so high that it destroys the possibility of using any corrosion resist-ant coating on the wire and an oxide film is left on the wire. Even when using parallel wires with widely separated spacers, it is highly desirable to have a corrosion resistant varnish or lacquer on the wire since, under severe operating conditions, corrosion products may be washed from the wire and onto the spacers, greatly lowering the effectiveness of the line. Further, such lines in the past have had sharp edges on the ends of the spacers so that if one attempts to roll up a section of such line, the spacers may become entangled with adjacent turns of the wire, making is diflicult to unroll the wire.

It is therefore an object of the present invention to produce an open wire transmission line having widely separated spacers wherein the ends of the spacers are smoothly rounded, are firmly bonded to the wire, and wherein the wire itself may have acontinuous film of a corrosion resistant coating on its surface.

It is another object of this invention to provide a fully automatic machine for making such transmission lines, said machine being of relatively simple construction, operating at a high rate of speed and requiring substantially no labor other than the initial set-up of the machine.

Still another object of this invention is to provide a process for making open wire transmission line wherein the wire is firmly bonded to the spacers and a protective coating on the wire is not damaged during the manufacturing process.

In general, we accomplish the objects of this invention by providing an automatic machine wherein the spacers are cut to the correct length from a length of plastic material, slot-ted, the wires inserted in the slots, the ends of the spacers heated, and the end-s sealed and rounded.

Referring now to the drawings forming -a part of this application, there is shown in 4 Figure '1 a plan view of our improved machine fo making open wire transmission line.

In Figure 2 there is shown a detailed view on the lines 22 of Figure I particularly showing the cams which control the action of the cut-off saw and feed mechanism of our improved device.

Figure 3 is a cross-section on the lines 3-3 of Figure 1.

Figure 4 is a cross-section on the lines 4--4 of Figure 3.

Figure 5 is a view, partially in cross-section, on the lines 55 of Figure 1, showing the mechanisms for heating the ends of the plastic spacers and for crimping the ends of the spacers.

Figure 6 is a cross-section on the lines 6-6 of Figure 5, showing in detail the crimping mechanism.

Figure 7 is a cross-section on the lines 77 of Figure 6, showing another view of the crimping mechanism.

Figure 8 is .an enlarged perspective view of the coacting dies which shape the/ends of the plastic spacers and crimp the spacers to the wire.

Figure 9 is a cross-section view on the lines 99 of Figure 5, showing a plasticspacer passing through the heating area of our device.

Figure 10 is a perspective view of the completed open wire transmission linemade in accordance with our invention.

Referring now to the drawings by reference characters, the machine proper consists of an elongated tablelike structure which is composed of two side members 12 and 14 suitably spaced apart and held firmly by a U-shaped center section 16. The table portions 12 and 14 are supported by a suitable framework which has not been illustrated for purposes of clarity. The members 12 and 14 may each be made from a single piece of suitable metal, such as steel, which extends the length of the machine, or they can be made in several sections and fastened together. On the inner edges of members 12 and 14 are slots 18 and 20 which serve to guide the workholders 22. The workholders 22 have a fiat base member 24 which extends into the slots 18 and 20, ensuring that the workholders will be supported in the proper relationship to the rest of the machine. The workholders 22 have a pair of upwardly extending arms 26 and 28 attached to the basemember 24. The arms 26 and 28 each have a slot 32, which provides a recess of the proper size to hold a plastic spacer. The slot 32 is defined by arms 34 and 36 and arm 34 is higher than arm 36 for reasons which will be subsequently apparent. The base 24 of the workholder 22 is attached to a suitable drive device such as an endless roller chain 38, in order that the workholder may be propelled 'along'the table members 12 and 14. The chain 38 is driven by a prime mover, not shown. I

The endless chain 38 not only serves to convey the work-holders 22-along the bed of the machine, but also serves to operate two cams 40 and 42 in timed relationship with the work-holders, said cams serving to control the feed and cut-off of the plastic rod from which the spacers for the line are made. As can be seen from Figure 1, the cams 40 and 42 are on a common shaft 44 which is driven by the chain 38 by means of gear 46 on shaft 44.

Turning now to the feed mechanism for the plastic red, the cam 40 is provided with a cam follower 48 which is held in contact with the cam by means of spring 50. A slider 52 is mounted on track 53 and given a reciprocating motion by the action of the cam follower 48 on the cam 40. The slider 52 is provided with a detent 54 which is held in contact with the plastic rod 56 by means of spring 58. The end of detent 54 is sharpened as shown, and is set at an angle, so that as the slider 52 moves forward, i. e., toward the bed of the machine, the rod 56 is engaged by the detent 54 and advanced towards the machine. On the other hand, as the slider 52 moves away from the machine, the detent 54 exercises little friction on the plastic rod 56 and slides freely over it. A second detent 60 of similar construction and biased by spring 62 is fastened to the body of the machine proper and offers substantially no resistance to the plastic rod 56 as it advances, but engages the rod 56 and prevents it from moving away from the machine. Thus, as the slider 52 moves forward the plastic rod is engaged by detent 54 and brought forward and as the slider 52 moves away from the machine, the plastic rod 56 is engaged by the detent 60 and is prevented from moving.

As will be seen in Figure l, the cam 40 has a relatively steep slope in the portion which serves to advance the rod so that the rod moves forward quite rapidly and the slider moves'to the rear relatively slowly.

The cam 42 is provided with a cam follower 64 which serves to control the position of the motor 66 and the circular saw 68, which is directly connected thereto. The motor 66 is pivotally mounted on the bed of the machine by shaft 67. It will be noted that the cam 64 raises the saw 68 very rapidly and lowers it slowly so that the saw cuts slowly through the plastic rod and is then raised rapidly to an inoperative position.

In the position of the parts shown in Figures 1, 2 and 3, the saw has just completed its cut and is starting to rise. The synchronization of the parts is such that the rod 56 is advanced, while the saw is in a raised position, the slider 52 is withdrawn as the saw starts its cut, and just as the saw completes its cut, the arm 34 of Workholder 22 is presented to the cut-off plastic rod to carry it to the subsequent operations. Mounted adjacent to the saw is a ramp-like structure 70 having a shoulder 72 thereon. The shoulder 72 serves to hold the rod in position as it is being sawed and a spring 74 further serves to hold the rod against the shoulder 72. As the workholder 22 moves forward the higher or trailing arm 34 of the workholder 22 engages the rod and pulls it along the ramp 70. Since the spring 74 is pressing downward on the rod, as the workholder advances the severed rod 78 is brought down into the recess 32 of the workholder into proper position for the subsequent operations.

Mounted adjacent to the cut-oif device and ramp described, are two saw blades 74 and 76 mounted at an acute angle to the path of travel of the workholder, as is shown in Figure 1. As the workholder advances, the plastic spacer 78-is brought in contact with the two saw blades so that a slot of suitable depth is cut in both ends of the spacer.

A source of wire is provided, not illustrated, and two wires 80 and 82 are passed over rollers 84 and 86 and onto the body of the machine. Two angular blocks 88 and 90 are provided to guide the wire into the bed of the machine, and covers 92 and 94 serve to hold the wire down into the proper position. The wire is further held in position by holders 96 and 98 which are pivotally mounted slotted members. It will be noted that the wires are introduced into the path of the grooved spacers 78 in a line which would be a continuation of the saw blades 74 and 76. As the spacer 78 passes over the end of the saw blades 74 and 76, the wires fall into the slots of the spacer and the holders 96 and 98 are pushed to each side. After the spacer 78 has passed the holders 96 and 98, they spring back into the position illustrated.

, After the wires have been inserted in the slots of the spacers, it is necessary to heatthe spacers in order that .4 they may be pressed down over the wire. It has been found that if the wire is cold it will not form a solid bond with the plastic spacers and the construction which we employ serves to heat both the wire and the spacers so that the spacer is rendered soft enough to be readily deformed at its ends and the wire is hot enough to form a solid bond with the plastic. However, the wire is not heated to the extent that it would'destroy the thin, varnishlike insulation on the wire.

The wire and the spacers are heated by passing them through the heaters designated generally as 100 and 102 of the machine. As can be seen from Figures 1 and 5, these heaters are of some length so that the plastic rods are heated slowly. The thermoplastic spacers, have rather low thermal conductivity and it is important that the heating be applied slowly. As is shown in Figure 9, the heaters, in cross-section comprise an outer U-shaped housing 104 with a strip of heat resistant insulating material, such as asbestos board 106 on the interior thereof. The heating elements themselves consist of electrical resistance elements 108, which run substantially the length of the housing 104 and which are provided with suitable wiring 110 for connection to a source of electricity not shown. Preferably the elements 108 are of the enclosed type, commonly known as Calrod elements although they may consist of open coils of resistance wire. It is apparent that any form of heating may be used so that the heating elements 100 and 102 could be gas-fired, for instance.

After the spacers have passed through the heating elements designated 100 and 102, the plastic spacers are heated to the softening point of the plastic in each end area and the wire itself has been heated to a sufliciently high temperature to insure its being bonded to the plastic material. It is now only necessary to crimp the ends of the spacers to produce the finished line.

The crimping mechanism has a frame generally indicated as 112 which consists of two upright arms designated 114, one of which is located on each side of the path of travel of the workholders 22. Mounted between the two arms 114 is a rod 116 which is free to rotate and which has at its center a second rod 118 which passes through a hole 120 in rod 116. The hole 120 is sufiiciently large that the rod 118 slips freely therein. The frame members 114 have located thereon an arm 122 to which is fastened a spring 124 which biases the rod 118 to the left in Figure 5, i. e. opposite to the direction of travel of the workholders 22. A second pair of arms 126 is mounted on the frame 122 and these arms 126 extend on either side of the path of travel of the workholders as shown. Connecting the two arms 126 is a stop member 128 which extends at a right angle to the path of travel of the workholders, and slightly above them. The stop 128 serves to limit the forward motion of the arm 118 and the mechanism carried by this arm.

Mounted on the rod 118 are a pair of U-shaped members designated 130 and 132. U-shaped member 132 is rigidly connected to the arm 118 while member 130 is slideably mounted on arm 118. Between the two members 130 and 132 is a compression spring 134 which fits over rod 118 and tends to keep the two members separated.

Mounted on the arms 126 are flat cams 136 which are shaped as shown in Figure 5. The cams 136 each have both an upper cam surface and a lower cam surface. The member 130 has mounted at its lower extremities a pair of rollers 138 each of which contacts a bottom surface of one of the cams 136 while the member 132 has near its upper extremities rollers 140 each of which contacts an upper surface of one of cams 136. Mounted near the lower extremities of member 130 are two dies 142, and mounted near the lower extremities of member 132 are corresponding dies 144. As can be seen from Figure 8, the die members have a depression 146 cut therein each of said depressions corresponding to one-fourth of a sphere. Thus when a die pair 142 and 144 are brought together the combined dies have a depression therein constituting substantially one-half of a sphere. It is apparent that when these dies are pressed upon the ends of a heated spacer passing through the machine, the ends of the spacers will be rounded.

Mounted on member 132 is member 148 which is of such a height that it will clear arm 36 of the workholder 22 but will be engaged by arm 34 of the Workholder. Thus, as the workholder comes through the machine, the member 148 will be engaged by the arm 34, causing the members 130 and 132, and associated equipment to be drawn along the machine with the workholder 22. As the members 130 and 132 are drawn along the machine, the spring 134 causes the members 130 and 132 to follow the paths on the cam 136 so that these members are brought closer together and the dies located thereon engage the heated ends of the spacer 78. In the center of the cams, the dies 142 and 144 will be brought completely into engagement with each other which serves to squeeze the ends of the plastic spacers and to bond them firmly to the wire. After passing through the center points of the earns, the arms are again separated by the action of the cams, releasing the dies from the separators. At about the end of the travel of the cam, the member 148 will become disengaged from the arm 34, permitting the crimping mechanism to return against stop 128 and be in a position to repeat the cycle on the next spacer passing through the machine. It is apparent of course, that the path of travel of the dies must be slightly shorter than the distance between the adjacent workholders on the endless chain.

The transmission line is now finished, and it is only necessary to remove it from the machine and coil it into rolls of suitable lengths. A convenient method of removing the wire from the machine consists of a ramp-like member similar to that designated 70 but turned in the opposite direction to the path of travel of the separators. Of course, the ramp should not have a shoulder such as that designated 72.

It will be noted from Figure that the completed transmission line, which has been generally designated 150 has spacers which are uniformly placed along the wires and which have smoothly rounded ends 154. The Wire itself preferably has a coating of a thin, insulating varnish or lacquer material designated 156. A suitable coating material is Formvar which is a polyvinyl methylal resin. It has been found that formvar lacquered wire will not be injured by the heat to which it is exposed in our device and that the Formvar protects the wire from corrosion.

In the use of the process and the machine described herein, any thermoplastic material may be used as the spacer material. However, we prefer to use polystyrene because of its good insulating properties, high mechanical strength and relatively low cost. The wire which may be used is preferably copper wire, although cooperclad steel wire or wires of other metals may be used.

In one typical operation, the polystyrene rod was inch in diameter and was cut into sections about 1% inches long and the wires were spaced one inch between centers by the machine. With'No. 18 wire a transmission line having a surge impedance of slightly over 400 ohms is produced which is suitable for many uses such as television lead-in wire. Of course, other wire spacing may be used, as Well as dilferent wire sizes to produce transmission lines having substantially any desired impedance. Normally the spacers are located six inches apart upon the wire although a shorter or longer distance may be used, depending upon the use to which the wire is to be put.

It will be understood that our invention is not limited to the specific embodiment illustrated and that many variations are possible. For instance, instead of the feed and cut-off mechanism shown, the spacers may be cut to lengths in a separate operation and fed into the workholders from a hopper.

We claim:

1. In a machine for making open wire transmission line wherein are provided a-bed, an endless straight line conveyor extending longitudinally of said bed, drive means for continuously advancing said conveyor, a series of Work holders fixedly secured at spaced intervals along said conveyor, each of said work holders having a leading armand a trailing arm forming a slot therebetween for receipt of a short plastic'rod, said slot being normal to the path of travel of said work-holders, the leading arms of said work-holders being shorter than the trailing arms, means for cutting a slit in either end of each of said plastic rods,. means for inserting a Wire in each of said slits, means positioned thereafter for heating the ends of said plastic rods, and means for crimping the ends of said plastic rods whereby to envelope said wires while said ends of said plastic rods are in a heated condition, the improvements comprising: means for frictionally engaging an extended length of said plastic rod and means for severing said rod into individual rods each of a length equivalent to the distance between said end-crimping means; means for reciprocating said rodengaging means normal to the bed of said machine, said rod-engaging means frictionally engaging said rod only when said engaging means advances toward the bed of said machine, said rod-engaging means serving to ad vance an end of said extended length of rod into a position transverse to said conveyor and directly over said conveyor at a height sufiicient that the leading arm of saidwork holder will pass therebeneath but the trailing arm of said work holder will engage said rod, said severing means being positioned about said conveyor and to one side thereof between said conveyor and said rod engaging means, said severing means comprising a circular saw having drive means therefor and means associated therewith synchronized with said engaging means whereby said saw is lowered into contact with a length of rod after said rod is advanced over said conveyor; support means positioned at either side of said conveyor directly beneath the area occupied by said length of rod after said feed means has advanced said rod, said support means being at least as high as the leading arms of said work holders but lower than the trailing arms of said work holders; resilient means positioned directly above said support means for urging said length of said rod downwardly into contact with said support means, said support means having ramps leading downwardly in the direction of movement of said conveyor, said ramps having resilient means positioned thereabove for urging rods supported by said ramps into close engagement therewith whereby a length of rod is first severed by said cutting means and thereafter the trailing arm of a work holder mounted on said continuously moving conveyor engages said length of rod and advances it down said ramps while said resilient means mounted above said ramps urges said length of rod into the slot between the arms of said work holder.

2. The structure of claim 1 wherein said crimping means comprises a pair of separable dies on each side of the path of travel of said work holders, said dies being pivoted from a support member positioned over said conveyor and means whereby movement of said dies is synchronized with movement of said work holders whereby each of said separable dies is moved toward its cooperating die to engage and squeeze the ends ofa plastic rod after said rod has been heated, said dies traveling along with said rod as the Work holder advances and thereafter moving apart whereby to release the ends of said plastic rods, said dies thereafter returning to a rest position for receipt of the next of said plastic rods carried by said work holders.

(References on following page) 7 8 References Cited in the file of this patent 2,529,863 Bowen Nov. 14, 1950 Z 577 005 Giacomo Dec. 4 1951 PATENT 1 UNITED STATES S 2,579,487 Frankwich Dec. 25, 1951 988,616 Anderson Apr. 4, 1911 1,421,168 Charm June 27, 1922 r FOREIGN PATENTS 1,440,492 Rankin Jan. 2, 1923 9 920,880 France Apr. 21, 1947 1,783,997 Burden Dec. 9, 1930 2,158,496 George May 16, 1939 OTHER REFERENCES 2,272,850 Poole Feb, 10, 1942 Modern Plastics, October 1951, page 182. 2,471,592 Thomson May 31, 1949

Claims (1)

1. IN A MACHINE FOR MAKING OPEN WIRE TRANSMISSION LINE WHEREIN ARE PROVIDED A BED, AN ENDLESS STRAIGHT LINE CONVEYOR EXTENDING LONGITUDINALLY OF SAID BED, DRIVE MEANS FOR CONTINUOUSLY ADVANCING SAID CONVEYOR, A SERIES OF WORK HOLDERS FIXEDLY SECURED AT SPACED INTERVALS ALONG SAID CONVEYOR, EACH OF SAIOD WORK HOLDERS HAVING A LEADING ARM AND A TRAILING ARM FORMING A SLOT THEREBETWEEN FOR RECEIPT OF A SHORT PLASTIC ROD, SAID SLOT BEING NORMAL TO THE PATH OF TRAVEL OF SAID WORK-HOLDERS, THE LEADING ARMS OF SAID WORK-HOLDERS BEING SHORTER THAN THE TRAILING ARMS, MEANS FOR CUTTING A SLIT IN EITHER END OF EACH OF SAID PLASTIC RODS, MEANS FOR INSERTING A WIRE IN EACH OF SAID SLITS, MEANS POSITIONED THEREAFTER FOR HEATING THE ENDS OF SAID PLASTIC RODS, AND MEANS FOR CRIMPING THE ENDS OF SAID PLASTIC RODS WHEREBY TO ENVELOPE SAID WIRES WHILE SAID ENDS OF SAID PLASTIC RODS ARE IN A HEATED CONDITION, THE IMPROVEMENTS COMPRISING: MEANS FOR FRICTIONALLY ENGAGING AN EXTENDED LENGTH OF SAID PLASTIC ROD AND MEANS FOR SEVERING SAID ROD INTO INDIVIDUAL RODS EACH OF A LENGTH EQUIVALENT TO THE DISTANCE BETWEEN SAID END-CRIMPING MEANS; MEANS FOR RECIPROCATING SAID RODENGAGING MEANS NORMAL TOP THE BED OF SAID MACHINE, SAID ROD-ENGAGING MEANS FRICTIONALLY ENGAGING SAID ROD ONLY WHEN SAID ENGAGING MEANS ADVANCES TOWARD THE BED OF SAID MACHINE, SAID ROD-ENGAGING MEANS SERVING TO ADVANCE AN END OF SAID EXTENDED LENGTH OF ROD INTO A POSITION TRANSVERSE TO SAID CONVEYOR AND DIRECTLY OVER SAID CONVEYOR AT A HEIGHT SUFFICEINT THAT THE LEADING ARM OF SAID WORK HOLDER WILL PASS THEREBENEATH BUT THE TRAILING ARM OF SAID WORK HOLDER WILL ENGAGE SAID ROD, SAID SEVERING MEANS BEING POSITIONED ABOUT SAID CONVEYOR AND TO ONE SIDE THEREOF BETWEEN SAID CONVEYOR AND SAID ROD ENGAGING MEANS, SAID SEVERING MEANS COMPRISING A CIRCULAR SAW

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