CA1040461A - Movable welding backing device - Google Patents

Abstract

Abstract of the Disclosure A movable welding backing device, which comprises guide rails laid alongside that portion of an object of welding which is going to be welded, a track traveling on the guide rails; a backing plate fitted to the track so as to be pressed against the underside that portion of the objecting welding which is going to be welded, detecting means for detecting the welding spot of the object of welding; and control means for controlling the travel of the truck so as to cause the backing plate to be always brought right below the welding spot.

Description

This invention relates to a movable welding backing device for transporting to the succes~ive welding spots of an object of welding a backing plate designed to catch molten beads dropping on the under~ide of the w~lding spot of an object of welding, when one side of 6aid object is to be welded, solidifying said welding 8pot into a desired shape through retontion of said fallen molten back beads Hitherto, an attempt ha~ been made fully to automate one side welding of an object of welding by intermittently transporting a backing plate designed to catch molten boads ~; dropping on the underside of the welding spot of the object of welding and solidify the welding spot into a desired shape through rotention of said fallen molten back beads independently of tho oporation of an automatic wolder, according as the welding spot of the object of welding i8 ~uc¢os~ively shifted The que~tion ari~ing in thi- case i- how the transport of the backing plato can be~t follow the peak point of welding by the automatic weld-r The reason i8 that unle~s the welding pot of an objoct of welding, that i8, tho arc s-ction of tho automatic welder exactly faces a backing plate, molten back bead~ fall off the underside of the wolding ~pot of the object of welding, rosulting in unsatisfactory welding ... .
It is accordingly th object of this invention to provid- an automatic welding backing device capable of alway~
locating a back$ng plato exactly at the underside of the wolding spot of an object of welding, thereby attaining the good one sid- welding of said object According to an aspoct of this invention, there iB
provid d an automatic welding backing device which comprises guide rails laid alongside a weldinq ~pot of an object of weldinqs a tradk running on the guide railss a backing plate fitted to the truck to be pres~ed against the under~ide of the welding spot of said ob~ects detection means provided on the backing plate to detect said welding spots and control means for controlling the travel of the truck 80 as to locate the backing plat- oxactly at the undersido of the welding spot upon rece~pt of an output signal from tho welding ~pot-detecting means.
Thi~ invention can be more $ully understood from the following detailed description when taken in conjunction with th accompanying drawings, in which:
Fig. 1 i~ a front view of a w ld r ~mbodying this inv ntions Fig. 2 is a ~ide olovation of the w lder of Fig. lt Fig. 3 i~ a d tail d illu-tration of a mechanism for pu~hing th- backing plate of Figs. 1 and 2~
Fig. 4 ~ a cross sectional view of a photodetoction m an- di~posed on the backing plate of Fig. 2s ~0 Fig. 5 is an obligus view of a control section of the w-lding backing d vice of the inventionS
Fig. 6 i~ a power upply circuit included in a control ~-ction of the photod tection device of Fig. 4s and Pig. 7 i8 a di~gr~m of a control circuit for controlling the travel of a backing plate which is included in the control section of Fig. 4.
Steel plates lla, llb forming, for example, the outer-most shell of a ship are placed on a ~upport table (not shown) with tho mutually facing inclined lateral odges made to abut

- 2 -.

104~)461 against each other 80 a~ to form a fusion edge 14 ~aid under tho steel plate lla are guide rails 12a, 12b extending parallel with the fu~ion edge 14 being welded An automatic welder 13 provided with two pairs 13a, 13b of wheel~ i8 movably disposed above the guide rails 12a, 12b The automatic welder 13 is ~ntonded to weld avoid space def$ned betw en the mutually facing inclined lat-ral edges, that is, the fusion edge 14 of the steel plate~ lla, llb only from the upper side thereof The auto-matic welder 13 compri~es a body 13c~ L-shaped support arm 13d fir~t oxtond~ng from the wolder body 13c in its traveling d~rection D and then b-nt to~ard the line along which the wold$ng spot of an ob~oct of weld$ng successively proceeds~
two w ldlng wire feeders 13e, 13f mountod on tho support arm 13d~
and a palr of nozzl-~ 13g, 13h f~tted to the end of the two w lding wire f-edor- 13-, 13f on- welding wiro feeder 13e co~pr~-e~ feed roller- 13e-1, 13e-2 driv n by an electr~c motor (no~ ~hown) rec-ived in the support anm 13d through gear m chan$-m At the timo of welding wire 13i of substantially th- ~a~o material as the steel plat-s lla, llb which i8 u8ed to f$11 up a void space in the fu~ion edge section 14 pas~es betw -n the f ed rollor- 13--1, 13--2 after drawn out of a torag and then into th fusion edge ~oction 14 from the tip of the nozzle 13g The other w~lding wire foeder 13f ha~ the sam arrangem nt a- tho fir~t mentioned feoder 13e A welding wire 13j pullod out of tho ~tor~ge pa~od betwoon the feed rollers 13f-1, 13f-2 into the fu~ion edge section 14 from the tip of the nozzle 13h The feed roller4 13e-1, 13e-2, l~f-l, 13f-2 concurrently act as terminal~ through which power i8 supplied to the welding wire~ 13i, 13; One terminal of a

- 3 -welding power source (not 8hown ) i~ connected to the feed rollers 13e-1, 13e-2, 13f-1, 13f-2, and the other terminal of said power source i~ connected to the steel plates lla, llb being welded At the time of welding, sintoring type flux F
is supplied to the fusion edge section 14 80 as to cover the whole of it It is pos~ible to apply the flux F all along the fusion edge section 14, as shown in Fig 2, befor- welding is ~tarted, or let the flux F be ~uccessively thrown into the fu-ion edge section 14 from a flux ~torage (not shown) provided in the automatic welder 13 through the end of the support arm ; 13d as welding procQeds The sintering type flux is powder formed of a mixture of a deoxidant and ritreous material, and melted by welding heat, thereby pr-venting tho surface of tho molten t-el plat-~ lla, llb from being nitrogonizod A p~ir of aluminium pipe guide rail- 15a, 15b are laid bolow th Jteel plates lla, llb being welded alongside the fu~ion odge ~-ction 14 These aluminium pipe rails 15a, 15b aro fitted to perman nt magnet~ 17a, 17b magnetically adhered to the underside of the corre~ponding steel platos lla, llb being weld~d by moans of L-shaped support members 16a, 16b A
truck 18 i~ mounted on the aluminium pipe ra~ a, 15b The truck 18 is provided with 4 pairs of wheels l9a-19b, 20a-20b, 21a-21b, 22a-22b and carried forward by a D C motor 32 with the aid of the~e wheels Disposed above the truck 18 is a backing plate 24 made of, for example, copper or aluminium The backing plate 24 is pre~sed against the underside of the steel plates lla, llb being welded by meanJ of a spring mechani m 23 through a glass fiber tape 25 bridging the butt joint of the fusion edge section 14 of the steel plates lla, llb 104~461 The ~pring mechanism 23 is constructed, for example, as shown in Fig 3, and compri~es a round hollow cylindrical member 23a mounted on the truck 18 a round pillar 23c projeeting downward from a support plate 23b fitted to the underside of the baeking plate 24 and inserted into the hollow eylindrical m~mber 23as a pair of links 23d, 23e flexibly eonneeted between the outer wall of the eylindrical member 23a and support plate 23bs and a ten~ion pring 23h ~tretched aeros- the intermediate pivotal section 23f, 23g of the links 23d, 23- The ten~ion spring 23h of the spring mechanis~ 23 con-trueted as described above always pulls the intermediate pivotal ~ections toward eaeh other, ther by causing the backing plate 24 di~po-ed abovo the truek 18 to be pu~hed upward The for~ard nd of the baeking plato 24 a~ viewed from the trav ling diroetion (indieated by tho arro~ E) of the wolding a~-o~bly i~ providod, if noe---ary, with a bent portion 24a d-parting from the gla~s fiber tapo 25, onabling the baeking plate 24 to be earried moothly without frietionally rolling up the glas~ fiber tape 25 Further, a welding spot detector a6 i~ provided noar the forward end of the baeking plate 24 The welding pot dot~etor 26 eo~priso-, as shown in Flg 4, a hole 27 bored in the baeking plate 24s a photo-eloetrie eonvor~ion el-ment 28 sueh as a phototran~istor or Cd8 eoll roeoived in the hole 27s and a transparent heat-in~ulating plate 29 sueh a8 a piece of miea provided to close a light-reeeiving opening provided on that ide o$ tho hole 27 whieh faees the glass fiber tape 25 The welding spot deteetor 26 dotoets are flashe~ or a light emittod fro~ molten metal oceurring during welding acro~s the tip of the welding wires 13i, 13; pulled out of the end of the nozzles 139, 13h and the fusion edge ~ection 14 of the steel plates lla, llb being welded, and supplies a deteetion signal to a truck travel-controlling means 31 (Fig. 5) through a cord 30. Said truck travel-controlli~g means 31 instructs the D.C. motor 32 fitted to the underside of the truek 18 to produce a prescribed driving output through a cord 33 to control the travel of the traek 18, thereby always bringing the baeking plate 24 right below the welding spot of the ~t-el plates lla, llb. The circuit arrangement of the truck travel-controlling means 31 will be later described.
Another trudk 34 constructod in substantially tho same manner a- the truck 18 is provid-d, as ~hown in Flg. 2, ahead of said truek 18 as viewed from it~ traveling direetion E. Said anoth r trud~ 34 al-o runs on th aluminiu~ pipe guide rails 15a, 15b. Both trucks 18, 34 are eonneeted together by a conn-etion rod 35.
A support plate 37 of substantially the same type a~ tho baeking plate 24 i8 disposed above ~aid another truck 34 through a ~pring mechanism 36 constructed in the same manner a~ th afore~aid ~pring mechanism 23. Said support plate 37 is intendod to prevent tho glass fibor tape 25 from aagging and al~o the flux po~der suppli d to the fu~ion edge soetion 14 from falling off th efrom before welding is sta~ted.
The backing plate 24 i~ provided, if nece~sary, with cooling pipes 39, 40 (Pig. 5). Pa~sage of water through the cooling pipes 39, 40 prevents the backing plate 24 fro~ becoming unduly hot by welding heat.
There will now be described by reference to Figs. 6 104~461 and 7 the truck travel-controlling circuit 31 Fig 6 presents a circuit for supplying po~er to the D C motor 32, and Fig 7 shows a circuit for controlling said power ~upply circuit in re-ponse to an output signal from the photoelectric con~ersion element 28 included in the welding spot detector 26 RefOEring to Fig 6, referential numeral 41 denotes an A C source. First to third transformers 44 to 4S are connected in parallel to the A C source 41 through a power supply s~itch 42 and fu~e 43 A rectification smoothing circuit consi-ting of a d~ode 47 and capacitor 48 i8 connected to tho ocondary side of the firJt transformer 44 An avalanche diode 50 i- connected directly to one end of the capacitor 48, and through a re~istor 49 to tho other ond theroof ~o a~ to impro~- a pro~crib-d ~oltage acros~ the ~unction- P Q A roctiflcation moothing circuit consi~ting of a full-wave roctifier 51 and capacitor 52 i- connectod to tho -condary ~ide of the ~econd tran former 45 The positive pol- ido of the capacitor 52 i- connected to one of the input t-rminal~ of the D C motor 32 through fir~t power ~upply-controlling ~P~ typo tran~i~tor 53, re-i~tor 54, diode 55, _ etor 56, normally clo~ed terminal of the first contact momber 57-1 of a te~t chang over ~witch 57 (Fig 7) and nonmally closod terminal of the first contact m~ber 58-1 of a to-t changeover switch 58 (Fig 7) Tho n gative pole side of a capacitor 52 i8 connected to the othor input terminal of the D C motor 32 ~erie~ circuit consisting of a ~ocond power ~upply-controll~ng NP~ type tran~istor 59 and resistor 60 is connected in p~rallel betwe-n both end ~unctions M, N of a series eireuit consisting of the transistor 53 and resistor 54. The bases of the transi~tors 53, 59 are eonnected to the junetion N through a resistor 61 Said junetion N i8 conneeted to the ~unction Q Diodes 62, 63 are connected in seri-s between the e~itters of the transistor~ 53, 59 in mutually facing relationship to connect the cathodes of said diodes 62, 63. The ~unetion of said eathode~ is eonneeted to the negative pole side of the eapaeitor 52 through a serie~
eireuit eonsisting of a resistor 64, potentiomoter 65 and re~i~tor 66. NPN type transistors 67, 68 ~ointly eonstitute an amplifier of the Darlington eonneetion The eolleetors of the~e transistors 67, 68 are ~ointly eonneeted to the junetion M The em~tter of the transistor 68 i8 eonneeted to the base of the tr nsi~tor 59, and the base of the tran~istor 67 is eonneet-d to tho ~unet~on P through a resistor 69 and also to an output terminal X of the later described eomp~rator a~plifier A protective NP~ type transistor 70 is conneeted between the output tenminal X of the comparator amplifier and junetion N The base of the transistor 70 i~ connected to a slider of the potentiometer 65. A ripple-absorbing eapaeitor 71 i8 eonneeted between the negative pole side of the eapaeitor 52 and ~unetion ~ A voltmeter 72 i8 eonn eted between the negative pole side of the eapaeitor 52 and the positive pole side of the ammeter 56. The normally open terminal of the first eontaet member 57-1 of the test ehangeover switeh 57 and the normally open terminal of the first contact member 58-1 of the test ehangeover switeh 58 are connected to the other input terminal of the D C motor 32, that is, the negative pole side of the eapacitor 52 through a resistor 7~.

104046~
A rectification ~moothing circuit consisting of a full-wave rectifier 7~ and capacitor 75 i8 connected to the secondary side of the third transistor 46. Connected to both ends of the capacitor 75 is a constant voltage power supply circuit consisting of a pair of NPN type transistors 76, 77, resistors 78, 79, 80, 81 avalanche diode 82, potentiometer 83, and capacitor 84. A variable referential voltage-presetting circuit i8 connected between the output terminal of the constant voltage power supply circuit, that is, both end junctions V, W of the capacitor 84 through a series circuit consisting of resistors 85, ~6 and potentiometer 87. The junction G of the resistors 85, 86 of said series circuit is connected to an output terminal Tl of the laSer described control circuit of Fig. 7. The slider of the potentiometer 87 is connected to an output termin l T2 of said control circuit.
Connected betwoen the junction~ V, W is a comparator amplifier (differential amplifier) consisting of a pair of NPN type transi~tors 88, 89, NPN type transistor 90, another pair of transistors 91, 92 constituting an amplifier and resistors 93, 9~, 95, 96, 97, 98. The referential voltage input terminal of the comparator amplifier, namely, the base of the transistor 88 is connected to the ~unction G. A load voltage input ~- terminal of the comparator amplifier, that is, a base of the transistor 89 is connected to a slider of a potentiometer 101 connected between the junctions N, W through a series circuit consisting of resistors 99, 100. Connected between the junctions V, W is a transistor-transistor logic (abbreviated as ~TTL") power supply circuit consisting of an NPN type transistor 102 and capacitors 105, 106, 107. The output _ g _ terminals of said TTL power supply c;rcuit, namely, both ends of capacitor 107 are connected to the power supply input terminals 21, 22 of the control cireuit of Fig 7 The junction V is conneeted to the negative pole end of the capaeitor 52 includod in the rectifie~tion smoothing circuit connected to the s-eond transformer 45 R ferontial numeral 28 of Fig 7 denotes the previou~ly mentioned photoel-etric conversion elemont ~hen xpo-ed to are fla~he- oeeurring durinq welding, the photo-leetrie conver~ion olement 28 i~ ~o operated aJ to reduee itsinternal re-istanee one nd of the photoel-etrie convorsion lem nt 28 is grounded and th oth r nd thereof is conneetod to a po~er Jupply input t-rminal ~1 through a resistor 108 ~n ~P~ typ- tr n-i~tor 109 (Fig 7) i~ a ~witehing typ-, who-o colle¢tor i- eonneet~d to the po~er upply input te~min-l Zl, ~ho-- mitt r i~ grounded through a r~ tor 110 and ~hos~ ba-o iJ eonn-et~d to the ~unetion ~ of th- reJistor 108 and photo-el-etrie conver~ion ~ ent 28 Th output of t~r~inal or ~itter of th transi~tor 109 is eonn et d to a base of an ~P~ typo po~ r ~upply-eontrolling transi-tor 112 through a re-i-tor 111 A eolleetor of ~id tran~i~tor 112 i~ eonn eted to the output terminal T2 and an emitter thereof is grounded - An mitt r of the ~witehing transistor 109 i~ eonneet-d to a ba~- of an ~P~ typ- flip-flop r-versing transi~tor 114 through a r-sistor 113 A eolleetor of said transistor 114 is eonneeted to the power supply input ter~inal ~1 through a re~i~tor 115 and an emitt r thereof i8 grounded An output tenminal or oolleetor of the transistor 114 i8 eonnected to the set input ter~inal S of a flip-flop eireuit FF (Big 7) 104046~;
consi~ting of four NA~D gates 116 117 118 119 A reset input terminal R of the flip-flop circuit FF i8 connected to an emitter of an NPN type flip-flop circuit-resetting transistor 120 A collector of ~aid transi~tor 120 is connected to the power supply input terminal Zl, and an e~itt r thereof is grounded through a resistor 124 A
capacitor 122 i~ connected b-tween the base and collector of the transistor 120 The base of the tran~i~tor 120 i~
grounded through a re~istor 123 The Q of the flip-flop circuit FF i~ connected to a base of a po~er ~upply-controlling transi~tor 125 through an output terminal redstor 124 A
collector of the po~er ~upply-controlling tr nsistor 125 is connected to ~he output ter~inal Tl, and an ~itter th reof i~ connected to the normally closed t-rminal of the second contact ~ember 58-2 of the t-~t changeover witch 58 A
nor~ally ope~l torminal of the ~econd contact ~ber 58-2 is connect~ to th ba-e of th pow r ~upply-controlling ~iran~i~tor 125 A c~on t-rminal of the second contact ~ber 58-2 i8 conn~cted to a normally clos d terminal of the ~-cond contact m~ber 57-2 of the test changeover ~witch 57 Tho nor lally open terminal of the ~econd contact m~ber 57-2 ~f the te~t changeover #~itch 57 is connect-d to a base of the tran-i~tor 112, and the ca_on terminal of the second contact m~bqr 57-2 i~ groundod The ~P~ transistor 126 of Fig 7 is a fir~t di~play transistor A collector of this display tran-istor 126 is connected to the pow r upply input terminal Sl through a re-i-tor 127 and light-emitting diode 128 usea as a di~play lamp An emitter of said display transistor 126 i8 grounded, and a base thereof is connected to an emitter of the 104046~
switching transistor 109 through a resistor 129 An NPN
transistor 130 i~ a second display transistor A collector of this display transistor 13a $a eonnected to the ~pwer ~upply in~ut terminal Zl through a light-emitting diode 132 used a~ a di~play lamp An emitter of said display transistor 130 is grounded, and a base thereof i8 eonnected to a Jet input terminal S of the flip-flop eireuit PF through a resistor 133 There will now be de-cribod the operation of a ~ovabl- wolding baeking device aeeording to thi~ invention which 1~ con~tructed a~ deseribed above First, tho power supply witeh 42 of the truek trav l-eontrolling eircuit 31 is thrown in Then a pr-~cribed voltage i8 impre-J d on the s-condary ~ld of th fir-t to third tr~n~formers 44 to 46, rendering the re~pectivo eireuit- r-ady for operation R ferring to the TTL
po~-r Jupply elrcuit, a D C voltag of 5 volt~ is i~pre-~ d on an output termin~l of the T~L po~er supply cireuit, that i-both nd- of the eapacitor 107 ~na ~upplied to the pow r supply tenminal- ~ 2 At this timo, the tran istor 120 of Fig 7 i~ t-~porarily rend red eonducting by a ri-ing eo~ponent of the D C voltage ~ely, tho tran-i-tor 120 i8 bia~ed for ;~ op-ration by a time con-tant of the eapaeitor 122 and re~istor 123 until the eapaeitor 122 i- fully eharged Sin¢e the reset input t-r~inal R of the flip-flop eircuit FF is supplied ~ith a re~et pul~e, aid flip-flop circuit FP never fails to be r-set, ~hen po~r i~ introdueed As the reJult, the ~ output of the flip-fl~p eireuit presents a logic level of ~1~ to render the tran-i~tor 125 condueting, causing the output terminal Tl to be greund~d Since a voltag at the junction G of the referenti~l voltage-preJetting eireuit drop~ to a zero level, the transistor 88 of the comparator is turned off, whereas the transistor 91 thereof i8 turned on. At this time, the output terminal x of the comparator amplifier has a sufficiently low voltage to render the transistors 67, 68 of the Darlington connection inoperative. A~ the result, the transistors 53, 59 have the base voltage brought to zero, and become inoperative, thus preventing power supply to the D.C. motor 32. At the initial stage therefore, the truck 18 of the sub~ect movable welding backing device stands at rest right under the automatic welder 13.
Now let it be assumed that the steel plates lla, llb have begun to be welded by the automatic welder 13. The automatic welder 13 i8 carried forward in the direction of the indioated arrow D (Fig. 2) as welding proceeds. When the automatic weld-r 13 i8 brought to a prescribed position, then the ~elding spot detector 26 detects welding arc flashes. Upon recoipt of the arc flashes, the photoelectric conversion element 28 has 1ts internal resistance reduced. As the result, a voltage at the ~unction ~ of Fig. 7 drops to render the transi~tor 109 nonconducting, and the transistor 112 is turned off to open the output terminal T2. Since the transistor 114 becomes inoperative, the voltage of the set input terminal S
of the flip-flop circuit FF is changed from ~OH to "1", causing said flip-flop circuit FF to be brought to a set condition.
Since, at this time, the Q output is shifted from HlH to "~, the transistor 12~ is ~rned off to open the output terminal Tl.
When both output terminals Tl, T2 are opened, a prescribed referential voltage is supplied to the referential voltage input terminal of the comparator amplifier, that i8, the base 1040461:
of the transistor 88. Since, at this time, the other input terminal of the comparator amplifier, that i8, the base of the transistor 89 is not supplied with any input, a prominent differential output appears at the output tenminal of the comparator amplifier. Said large differential output i8 amplified by the transistors 67, 68 of the Darlington connection, and donducted to the base of the transistors 53, 59, which in turn are rendered conducting, causing the D.C.
motor 32 to be supplied with D.C. power appearing at both ends of the capacitor 52, and in consoquence to be rotated at high spoed for the quick travel of the truck 18 in the direction of the indicated arrow E. When the truck 18 travels, the welding spot detector 26 is carried ahead of the welding spot of the tcel plate~ lla, llb. When the welding pot detector a6 coa-e~ to detcct welding arc fla~hes, then tho photoelectric converaion elemcnt 28 ha~ its internal resistance increased and regainod the original condition. The transistor 109, and in con~ quence the tran~i~tor 112 are renderod conducting, cau~ing the output torminal T2 to be grounded. Since the transistor 114 i~ also turned on, the voltage at the set input terminal of tho flip-flop circuit PF i~ changod from ~1~ to ~0~. Ho~ever, the Q output of the flip-flop circuit retains a level of ~0", and the output terminal Tl is left open. As the result, a voltage impressed on the referential input terminal of the comparator amplifier, that is, the base of the transistor 88 is slightly decreased by tho extent that the output terminal T2 is grounded. At this time, thc load vol~age input terminal of the comparator amplifier is impressed with a pre~cribed level of voltage resulting from division of load voltage. As 104~)461 the result, the output terminal X of the comparator amplifier is impressed with a voltage obtained by amplifying the differential voltage Said amplified voltage is further amplified by the transi~tors 67, 68 and later conducted to the base of the transistors 53, 59 At this time, however, the voltage of the transistor base is considerably lower than the transistor base voltage impressed i~mediately after power upply Therefore, power ~upply to the transistors 53, 59 drops, leading to the slow rotation of the D C motor 32, and in conseguence the slow travel of the trudk 18 The potentiometor 87 is previously 80 ad~usted as to cause the truck 18 to travel at a lower speea than the automatic welder 13, thereby enabling the automatic w lder 13 to catch up with tho backing plate truck 18 aftor lap-e of a certain length of tim When the welding spot detector 26 again detects arc fla-he- emitted from the welding spot of the steel plates lla, llb, then tho tran-istor 109 and in conseguence the tran~istor 112 are turned off to open the terminal T2 Though the tran~istor 114 also becomes inoperative, the flip-flop circuit FP still r~mains set, and the output terminal Tl is left opon Accordingly, a voltage at the referential input terminal of the comparator amplifier, that i8, the baso of the transistor 88 is slightly increased by the extent that the output terminal T2 is openod, enabling more power to be introduced through the transistors 53, 59 Thus, the D C motor 32 runs at a higher speed to carry the truck 18 ahead of the automatic welder 13 ~hen the welding spot detector 26 ceases to detect welding arc flashes, then the travel of the truck 18 slows down as previously described ~hereafter the truck 18 is carried forward 104~461 alternately at a higher and a lower speed 80 as to move ~ointly with the welder 13 running at a constant rate of, for example, 400 to 600 mm/min. In this caQe, a maximum di~tance between the truck 18 and welder 13 is defined by, for example, the responsiveness, or inertia of the truck 18. With this invention, the backing plate 24 is chosen to have ~uch a length as can dover the welding spot of the steel plates lla, llb, even when the truck 18 is spaced from the automatic welder 13 at the above-mentioned maximum distance, thereby enabling the intermittently traveling backing plate 24 to be always po-itioned exactly below the welding spot.
During the high speed run of the truck 18, the light-~itting diode 132 gives forth a light, but tho light-emitting - dlode 128 remains inoperative. When the photoelectric conver~ion element 128 receiveJ welding arc flashes, the tran-i-tor 109 and in conseguence transistor 114 are turned off.
AJ the re-ult, the diJplay transistor 130 i8 rendered conducting to cau-e the light-emitting diode 132 to send forth a light.
Since, however, the display transistor 126 is turned off when the tranJistor 109 becomes inoperative, the light-emitting diode 128 iJ prevented from producing a light. Conversely, where the truck 18 i8 moved at a low Jpeed, the display transistor 126 i8 turned on and the display transistor 130 is turned off. In this case, the light-emitting diode 128 generates a light, but the light-emitting diode 132 remains inactive.
Where excess load current happen~ to be introduced during the above-mentioned operation, a voltage across both end~
of the resistors 54, 60 respectively prominently drop~ and the protective transistor 70 is more noticeably biased, leading to 104046~
the passage of more rent through said transistor 70. A8 the result, a voltage at the output terminal X of the comparator amplifier is forcefully reduced, giving rise to a docline in the base ~oltage of the transistors 67, 68 of the Darlington connection and decreasing current passage through the transistors 53, 59, thereby restricting the introduction of excess current. Accordingly, the circuit elements of the movable w lding backing device of this invention are saved fro~ d~mage causod by oxce~s current.
~hile the high speod of the truck 18 can be varied by ad~ustment of the potentiometer 101, the faster run of the truck 18 than the automatic weldor 13 generally attains the ob~ect. ~herefore, a maximum voltage impressQd on the D.C.
motor 32 i- chosen to be 24 volts. Tho low ~peed of the truck 18 can also be varied by ad~u~tment of the potentiometer 87.
~ here the speed of the auto~atic welder 13 i8 varied according to the thickne~s of ~t-el plat 8 lla, llb, being weldod, the ob~ect is attained by ad~usting the potentiometer 87 according to aid thickness, and causing the truck 18 to bo carried forward at a lower speed than the automatic welder 13.
~ he truck travel-controlling circuit 31 of the movablo welding backing device of this invention can be tested without actual w lding by actuating test switche~ 57, 58.
When the to~t switch 5? is thrown in, operation of the first contact member 57-1 and second contact member 57-2 are both changed over. As the result, the transistor 112 of Fig. 7 is turned off, enabling the control terminal æ to be opened in the same manner as when the photoelectric conversion element 28 i8 exposed to weldîng arc fla~hes. Since the grounding of the emitter of the transistor 125 i~ relea~ed, the control terminal Tl i8 also opened. Namely, the conditions occurring during the high speed run of the trudk 18 are ~upplied to the referential voltage input terminal of the comparator ampli-fier. Since the operation of the first contact member 57-1 of the test switch 57 (F~g. 6) is changed over to the normally open terminal, the re~istor 73 having an eguivalent resistance to the coil re~istance of the D.C. motor 32 is connected instead of said motor 32. The load current can be detected by the ammeter 56 and the load voltage can be detected by the voltmeter 72, thereby attaining the ad~ustment of the potentiometer 101.
Where the different test switch 58 is actuated, then the operation of the first and second contact members 58-1, 58-2 is changed over. AB the result, the transistor 125 of Fig. 7 is rendered i perative, and the control terminal Tl alone is opened. The control terminal T2 is grounded, because the transistor 109 and in consequence the tran~i~tor 112 are turned on due to the high resistance of the photoeleotric conversion element 28. The above-mentioned operation causes the slow run condition of the truck 18 to be supplied to the referential voltage input terminal of the compar~tor amplifier. The resi~tor 73 is connected, a8 mentioned above, in place of the winding of the D.C. motor 32 due to the changed over operation of the fir~t contact member 58-1 of the test switch 58 (Fig. 6).
In this case, it is poss~ble to examine load voltage and load current and adjust the potentiometer 87.

lQ4~461 It will be noted that thi~ invention i8 not limited to the above-mentioned embodiment, but may be practised in various modification~ as decribed below. $he foregoing de~cription refers to the ca~e where a pair of ~teel plate~
were welded ~traight. Obviously, this invention can be practised without any limitation regarding, for example, the shape of an ob~ect of welding or the outline of a welded ~unction. Further in the foregoing embodiment, aluminium pipe rails were used to guide a trucX by being magnetically adhered to the underside of steel plates being welded. The guide members may of course have an L-shape or channel shape cros~
~oction in placo of the circular cross section of the aluminium pipe. Attachment of the guide members to an object of welding may bo ffected by bolting or engaging means. Further according to tho abovo-mentioned embodiment, a photoelectric convorsion element wa~ fitted to the backing plate to detect the po~ition of the automatic welder. Obviously, said position-detecting means may instead be of the type using electromagnetic waves, supersonic waves, heat, vibrations, or .
static capacity. It is also possible to mount the welding spot detector not only on the backing plate, but also on the truck or welder. The bacXing plate may be cooled selectively by wator or air according to the expected amount of welding hoat. A single welding wire in~tead of two may be inserted into the fusion edge section of an ob~ect of welding.
According to this invention, the backing plate is provided separately from the welder. Yet, the bacXing plate is carried forward according to the movement of the welder by being mounted on the trucX 80 as to be always brought right under the welding spot of an ob~ect of welding, thereby reliably preventing molten welding back beads from falling downward, an event which might otherwise present difficulties when stoel plates are welded, for ex#mple, only on one side.

..:

Claims (10)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A movable welding backing device which comprises a pair of guide rails laid alongside a welding spot of an object of welding; a first truck traveling on the guide rails; a first backing plate fitted to the first truck to be pressed against the underside of the welding spot of the object of welding; welding spot detecting means for detecting the welding spot of the object of weldings and means for controlling the travel of the first truck to cause the first backing plate to be always positioned right under the welding spot.

2. A movable welding backing device according to claim 1 wherein the welding spotdetecting means is mounted on the first backing plate.

3. A movable backing device according to claim 1, wherein the object of welding is formed of steel plates whose welding spots jointly define a fusion edge section; and the guide rails are supported by support members fitted to permanent magnets magnetically adhered to the underside of steel plates being welded in parallel with the fusion edge section of said steel plates.

4. A movable welding backing device according to claim 1 wherein the first truck comprises a plurality of pairs of wheels rolling on the guide rails and an electric motor mounted on the truck to drive said wheels.

5. A movable welding backing device according to claim 1, wherein the first backing plate is pressed against the underside of the object of welding by a spring mechanism disposed between the truck and backing plate.

6. A movable welding backing device according to claim 1, which further comprises a second truck running on the guide rails ahead of the first truck as viewed from its travelling direction and a second backing plate fitted to the second truck to be pressed against the underside of the object of welding.

7. A movable welding backing device according to claim 1, wherein the welding spot-detecting means comprises a hole bored in the first backing plate and photoelectric conversion element received in the hole to detect are flashes or a light emitted from molten metal occurring during welding.

8. A movable welding backing device according to claim 4, wherein the welding spot-detecting means is provided in the forward position of the first truck as viewed from its travelling direction and the truck-driving means includes control means for controlling the rotating speed of the motor according to an output from the welding spot-detecting means, such that while said detecting means lies apart from the welding spot, the truck is mad to run at a low speed, and when the detecting means is brought to the welding spot, the truck is made to travel at a higher speed than that at which welding proceeds.

9. A movable welding backing device according to claim 8, wherein the truck travel-controlling moans includes display means for indicating the high and low speed advances of the truck.

10. A movable welding backing device according to claim 4, wherein the truck travel-controlling means includes a test circuit for generating, when no welding takes place, an output equivalent to a detection output delivered from the welding spot-detecting means during welding.