AU3369578A - Resistance welding - Google Patents

Description

C O M O N WE APPL

We E E LD.QNG INSTITUTE, a British Body Corporate, of Abingt ton Hall, Abington, Cambri dge CBI 6AL, England, 33 6 5 m

hereby apply for the grant of a Patent for an invention entitled:

"RESISTANCE WELDING"

which is described in the accompanying gcompe specification. complete

The application is a convention application and is based ,o the application(s) for patent or similar protection made

in GREAT BRITAIN on 28th. February, 1977 under No. 08338/77

on under No. 0*0 0

00 0 S *s Saddress for service is care of DAVIES Our COLLISON, 0 Patent Attorneys, of 1 Little Collins Street, Melbourne, in the State of Victoria,.Commonwealth of Australia.

0 00 0 DATED this 27th. day of February, 1978. 00

0 0 0 a-- 00

00 28FEB 0 0 0 PA h^'1 (a member of the firm of DAVIES COLLISON) 0 00 00 00* O for and on behalf of the applicant

0

TO: The Commissioner of Patents WODEN ACT 2606 q

ii.-

AUMTALIA FORK 7 DwMCARATION FOR CONVENTiO-N PATEN APPLICATION (Ne: To beigned by te umont(), f ndidaVs). If applicntbaGiuanp, to be sgned by a Person on hIts bL Iib a comprehensive form, and parts inapproprite to a particular applition abould be

CONMON WEALTH OF AUSTRALIA Patents Act 19.52-1966i 3 36 95 n8 DECLARATION IN SUPPORT OF A CONVENTION APPLICATION 09Mucxs FOR A PATENT OR PATENT OF ADDITION ia) Enaewt No. If avalbbh In support of the Convention application No. Jusert tull name(s) Vf evolcant(s) mnade by (b).TH.-WELDING INSTITUTE,

Invert ti of for a atent HIMfor an invention entitled (c)..ReS±BAtAT1eA Y ding

(d)lbut full nam(n) of &nLaftratfs) I/Vft Michaae.. 'Lrrthnny... AlJlf latt

Invert Madre"s(") r. de~lcinrent(,) of 9....Joiner RoadI C ~~ridgehIre., n. aI. do solemnly and sincerely declare as follows:

*0 e (or, in the case of rcm application by. a bodyi e, 1. 1 ax/VWe authorized by the aboveientioned applicant ror the patent/spgbW 00 ok~dktbhx to make this declaration on itastkltKbehalf. 2. The basic applicationg as defined by Section 141 of the Act wassm made in the following country dxxmu~ds on the following date by the following applicant (p nianely: 0 1 oov daeo0is in QeAt...ATi.a on 251)i j~~ray. 19-77.

0 0 in on 19 by

ofwhse tat a in on 19 by aINA cca 3 1-jb (or, where a person other than the inventor is the applicant) 3. Vaer.on Ro~yc. BrItlaihzub~je.ct Me 0.

Batit.Ute..r.Q. Jifg..20 te-signhets..o. I

4. The basic application referred to in paragraph 2 of this Declar.ntion was/Maw the anrt applicationfp) made in at Convention country in respect of the invention the subject of the application. (hI of Declared at C V&,40 this d.C da~oof of F 19 78.

(11) AU-Al 33695/78

(12) PATENT SPECIFICATION ABSTRACT (19) AU

(21) 33695/78 (22) 28.2.78 (23) 28.2.78 (24) 28.2.77 (31) 08338/77 (32) 28.2.77 (33) GB (43) 6.9.79 (51)2 B23K 11/24 (54) RESISTANCE WELDING (71) WELDING INSTITUTE (72) BOYD V. (74) DM (57) CLAIM 1. A weld-termination control unit, for use

with a resistance welding machine which includes

switching means controlling the application of a

succession of cycles of alternating current to

welding electrodes and having an internal timer which, in

the absence of a prior termination of the weld by the control

unit, operates the sitching means to terminate the

weld current after a predetermined number of cycles,

the control unit comprising: means responsive to the

voltage between the electrodes at a first time point

in relation to each cycle of the welding current waveform

to detect a predetermined fall in the resistance of the

material between the electrodes and, upon such detection,

to operate the switching means to stop the application

of weld current to the electrodes; a suspect weld

(11)AUA1 33695/78 2 indicator; and means responsive to the supply current waveform between the switching means and the electrodes at a second time point in relation to each cycle of the waveform, earlier in relation to the cycle than the said first time point, to detect terminationcf that supply waveform and to actuate the suspect weld indicator if the resistance-responsive means has not yet operated, whereby the suspect weld indicator is operated only when termination of the weld is brought about by the machine timer.

33-1

I- p~ yr".

COMMONWEALTH OF AUSTRALIA

PATENTS ACT 1952

COMPLETE SPECIFICATION

(Original) 3 3 69 FOR OFFICE USE

Class Int. Class

Application Number: Lodged:

Complete Specification Lodged: Accepted: Published:

Priority: C: Related Art:

:.*:Name of Applicant: THE WELDING INSTITUTE S...0

.*0:0 *S0

:::Address of Applicant: Abington Hall, Abington, Cambridge CBl 6AL,' England. :Atul nenors

Addes fo*erie VERNON BOYD

DAVIES COLLISON, Patent Attorneys, I Little Collins Street, Melbourne, 3000.

:*-Compl-ate specification for the invention entitled: S

5* "RES ISTANCE WE LDING"

*The following statement is a full description of this invention, including the best method of performing it known to .up

In the control of resistance welding processes, one of the methods which has been proposed for determining

when to terminate the welding current passing between the

welding electrodes depends on the electrical resistance

between the electrodes. This resistance falls during a weld,

I and one method of controlling the quality of the weld

c has been to monitor the resistance between the electrodes

Cq and then to terminate the welding current when this

resistance has fallen by a predetermined amount.

O In our British No. 1,446,652, we have described and shown a control unit for carrying out such a

method inwkich the peak to which the voltage across

the welding electrodes rises is detected and held, the subsequent lower cyclic peaks of the monitored

voltage are compared with a voltage which is lower .0 by a predetermined proportion han the first-mentioned peak voltage, and the weld is terminated as soon as

the subsequent cyclic peaks fall to the lower voltage S' level.

Welding machines to which such a ~cntronl n-ni+

may be connected have an internal timer which operates after

a predetermined interval, Thus, when the control .9.

e g unit is connected to such a welding machine, the 0r 0* 00 internaltimer operates to terminate the weld if the 00

resistance-responsive control unit has not previously

0 terminated it within the predetermined interval as *e

a consequence of a re.duction in resistance and therefore a fall in voltage between the electrodes, the predetermined interval being the maximum time expected for a weld of acceptable qualityi If the weld is terminated by the machine's internal timer

4 at the end of such an interval, it is dasirable to indicate C that it is a suspect weld. This means th, t the

suspect weld indication system must be able to distinguish between welds terminated by the resistance-responsive unit and welds terminated by the internal machine timer; this is made more difficult by the fact that when welding current is cut off by the internal machine timer the voltage between the electrodes falls, i.e. it brings about the condition for operation of the resistance-

S responsive unit. To ensure that the suspect weld indicator

operates only when the welding current has been cut off by the operation of the internal machine timer in Patent

No. 1,446,652 we have shown in the control unit an

auxiliary timer, set to operate after the same

interval as the internal machine timer, the auxiliary timer energising a warning light at the end of the

predetermined interval. 00 o. 00 00 uiir iesttooeaeatrtesm

00 o

000*

o 1 w i

IY,. l .III YLx ii- 1 -14 1 L

The present invention enables the auxiliary timer to

be dispensed with.

A weld-termination control unit according to the

present invention,, for use with a resistance welding

machine including switching means controlling the application

of a succession of cycles of alternating current to welding

CD electrodes and having an internal timer which, in the

CO absence of a prior termination of the weld by the control unit, operates the switching means to terminate the weld

current after a predetermined number of cycles, comprises.

means responsive to the voltage between the electrodes at

a first time point in relation to each cycle of the welding

current waveform to detect a predetermined fall in the

resistance of the material between the electrodes and,

15 upon such detection, to operate the switching means to

stop the application of weld current to the electrodesl a suspect weld indicator; and means responsive to the supply

current waveform between the switching means and the

electrodes at a second time point in relation to each cycle of the waveform, earlier in relation to the cycle than the

said first time point, to detect termination of that supply

waveform and to actuate the suspect weld indicator if the resistance-responsive means has not yet operated, whereby the suspect weld indicator is operated only when termination

of the weld is brought about by the internal machine timer.

L~il~ iL- i i .CI-._I~YI.IJL ~i_I

The elimination of the auxiliary timer from the

os trol unit simplifies the setting up procedure when

changing from one welding job to another. With the

arrangement described in British Patent No. 1,446,652

both the welding machine internal timer and the

auxiliary timer in the control unit had to be

adjusted with virtually every change of job, because weld

0h time has to be adjusted with change of material,

thickness and configuration of the components to be welded. In a system embodying the present invention, only the machine timer has to be altered. A further

disadvantage of the earlier arrangement was that its

Pliability depended on the accuracy of the two weld

timers being adjusted. If the welding machine timer was

i. set at a shorter time than the auxiliary timer (either

0* l inadvertently or through malfunction) the suspect warning

light would never be activated even at undersized or

no weld conditions. The elimination of the auxiliary timer from the control unit therefore increases the

reliability of the system.

In the preferred form, the means responsive to the

resistance between the electrodes includes a ramp 3* generator which is reset once in each cycle of the

electrode waveform if the peak of that waveform exceeds a

reference level, together with a comparator operative

when the ramp output exceedsa further reference level, o*

i.e. when the ramp is not reset, to terminate the weld; and the means responsive to the supply waveform between

the switching means and the electrodes comprises a further

ramp generator and a circuit

IT I

for resetting this further ramp generator twice in each

cycle while the supply waveform continues, together with a

comparator responsive to the ramp output exceeding a

reference level to operate the suspect weld indicator. Thus,

because the first ramp- generator is reset every mains cycle

and the second ramp generator is reset every mains half Scycle the second comparator will operate the suspect weld

C indicator when the supply waveform is terminated by the machine t0 C weld timer before the output of the first ramp. generator can

reach the reference level at which it would provide a belated

weld-termination signal.

In order that the invention may be better understood,

an example of apparatus embodying the invention will now

be described with reference to the accompanying drawings, 15 in which:-

Figure 1 shows diagrammatically the supply circuit *0

of a welding machine 10 to which the control unit is 0 6 S* connected; and

Figure 2 is a circuit diagram of the control

unit.

In Figure 1, the supply voltage is applied to a *6 C.

*0

0 0

eC

6

.i YIICII1LYI Y lli-I ILC l l C~ thyristor or ignitron circuit 12 in series with the primary winding of a transformer 14. Firing circuits 16 and 18 control the operationof the thyristor or ignitron circuit. The secondary winding of the welding transformer

14 is a single turn connected through copper barsto electrodes 19.

An internal machine timer 24 prevents firing of the

thyristor or ignitrbn control if the resistance-responsive

control unit.has not terminr-ed the weld within a

1Q predetermined number of cycles of the welding current. o Figure 2 is a block diagram of an auxiliary control unit

C embodying the present invention. The voltage across the S.

electrodes (Figure 1) is taken through a lo'pass filter 26

to a mains compensator in the form of a divider circuit 28. *e sO S* The object of the mains compensator is to ensure that the

subsequent circuit for measuring the fall in electrode

voltage is not misled by a variation in the mains voltage.

The compensation is achieved as follows.

The mains voltage is applied through a transformer

'to alow-pass filter 22 having the same characteristics as 00 0

thelow-pass filter 26, The filtered output is taken to a

peak detector Z4 which Is provided with a discharge path

Spermitting the output voltage to droop between successive

cycles. The peak voltage is fed to the uivider circuit 28

where it acts as a divisor for the electrode voltage. The

output voltage is the true quotient at the peak of an

input cycle. 'Thde'ains-compensated peak to which

the cFectrode voltage -7

rr~CYI-YL- ^r ~~L builds at the commencement of a weld is detected by the peak detector 30 whose output is applied across the potentiometer 32. The wiper is set to tap off a predeter- mined proportion of this peak voltage and to apply it to the comparator 34. The comparator 34 also receives the actual output of the divider circuit 28 during the course of the weld. At the beginning of the weld, once in.each

M cycle the divider output will rise above the tapped voltage to O from the potentiometer 32 and the comparator 34 will provide a corresponding pulse. This pulse is applied to a missing- pulse detector 36 to reset a ramp generator 38. The

S ramp voltage is fed to a comparator 40 in which it is

compared with a reference voltage from potentiometer 42, the reference level being above the level reached by the

ramp when it is reset at every cycle. When tre resistance of the weld decreases by a

predetermined amount, corresponding to the voltage drop

selected at the potentiometer 32, the divider output no

longer rises above the output of potentiometer 32 and the 3*

comparator 34 fails to' supply the resetting pulse for the,

ramp generator. When this happens the ramp output continues to rise until it exceeds the erference level of the

comparator 40. The comparator 40 then acts through a

circuit 44 and an amplifier 46 to operate a relay 48. The

relay 48 opens contacts 50 and 52 (Figure1) in the thyristor or ignitron firing control circuits and thereby terminates the weld. The circuit 44 is a timer which ensures that the

171 oil

4. -4s A

welder' cannot operate again for a predetermined number of

cycles, for example 30 cycles.

The output of lowpass filter 22 is also applied to a Schmitt trigger circuit 54 of a kihd operating on'both the

positive and the negative half of the incoming waveform

and therefore supplying pulses at twice the mains frequency.

These pulses are applied as resetting pulses to a 'amp 0 generator 56 of a further missing Pulse detector 58; the

COZ ramp output goes to a comparator 60, the combination acting in the same manner as the ramp generator and comparator 38

and 40 respectively. However, while the ramp generator 38

was reset every 20 milliseconds (on a 50 Hz supply), the vaimp generator 56 is reset every 16 milliseconds.

Thus when the is .terminated by the internal machine timer 24 (Figure 1) there is in effect a "race" condition a a

oaf)* 0O between the two missing-pulse detectors and the output of 0O a0O

ramp generator 56 reaches the reference l.vel of its 0

6 comparator before the ramp generator 38 attains its S

corresponding reference level, owing to the fact that the 0

lack of a reset pulse affects thb: ramp generator 56 before

the ramp generator 38 is affected in this way. Consequently before the missing-pulse detector 36 has operated, the

0 missing-pulse detector 58 actuates a timer circuit 62

(having the same function as the timer circuit 44) and 0

simultaneously gives an audible warning through bleeper 64

and a visible warning through light source 66. The timers 44 and 62 are in fact two halves of a single circuit and are 0 cross-coupled so that they can never be actuated together.

9

If---

Consequently when the timer 44 has been operated by the

resistance-responsive unit, the suspect weld indicator

cannot be actuated through timer 62 and vice-versa.

The output of low-pass filter circuit 26 is applied

through a Schmitt trigger circuit 68 to a four-stage shift

register 70. The Q output of the th'rd stage operates

a switching circuit connected to the peak detector to

prevent the detector from being effective in the first CP CID two cycles of operation of the unit, thereby avoiding false peaks due to transient conditions. The Q output of

the fourth stage enables the timer circuits 44 and 62.

When the missing-pulse detector 58 detects the termination

of the welding supply, a reset signal is applied to the

shift register

:15 The second stage of the shift register 70 also supplies

a signal to an amplifier 72 connected to a light source 74.

If after the second cycle there is no light from the source

74, it indicates that the electrodes are connected in the

wrong phase. The four stage shift register comprises

three lines of information:- data, 'clock an.' reset.

Data is supplied from the Schmitt trigger circuit 54

and the clock is supplied from Schmitt trigger 68. Thus

the shift register will only function when the data is

high during the leading edge of the clock pulse, and the

reset enabled. These conditions ensure the correct

operation of the shift register.

10

1' lii

It will be seen that when a control unit as described with reference to Figure 2 is connected to a welding machine having an internal timer,

the operation of- sw.tching off the machine if

the resistance-responsive control unit has not

reacted within the normal period is left to the Sinternal timer in the welding machine; the

missing-pulse detector 58 operates to detect when

C* the machine has been switched off by the internal

timer and causes the suspect weld indication.

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Claims (1)

1. THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:-

   1. A weld-termination control unit, for use with a resistance welding machine which includes switching means controlling the application of a succession of cycles of alternating current to welding electrodes and having an internal timer which, in

   the absence of a prior termination of the weld by the control

   Sunit, operates the switching means to terminate the

   weld current after a predetermined number of cycles,

   Sthe control unit comprising: means responsive to the C#Z eC 10 voltage between the electrodes at a first time point in relation to each cycle of the welding current waveform

   to detect a predetermined fall in the resistance of the

   material between the electrodes and, upon such detection,

   to operate the switching means to stop the application

   15 of weld current to the electrodes; a suspect weld

   indicator; and means responsive to the supply current

   waveform between the switching means and the electrodes

   at a second time point in relation to each cycle of

   the waveform, earlier in relation to the cycle than the said first time point, to detect terminationf that supply

   waveform and to actuate the suspect weld indicator if the

   resistance-responsive means has not yet operated, whereby *0

   the suspect weld indicator is operated only when termination 0*

   of the weld is brought about by the machine timer.

   2. A control unit in accordance with claim 1, in which the means responsive to the voltage between the electrodes includes a ramp generator and means operative to reset the ramp generator once in each cycle of the electrode waveform if the peak of that waveform exceeds a reference level, together with a comparator operative when the ramp output exceeds a further reference level, indicative of the absence of resetting of the ramp generator, to terminate the weld; and in which the means responsive to the supply current waveform between the switching c means and the electrodes comprises a further fmg s 10 generator and a circuit for resetting this further ramp generator twice in each cycle while the supply waveform to continues, oogether with a comparator responsive to the output of the further ramp generator exceeding a reference level, to operate the suspect weld indicatocr.

   15 3. A control unit in accordance with claim 4, including a*

   first and second cross-coupled circuits respectively *0 connected to the outputs of the means for terminating the

   weld as a consequence of a fall in resistance between

   S* the electrodes and the means for operating the suspect weld indicator, the cross-coupling being such as to prevent

   the operation of the resistaace-responsive means after

   the suspect weld indicator has been actuated and vice versa.

   4. A control urit in accordance with claim 2, further

   comprising a circuit connector to receive the

   supply waveform and operative on both the positive and

   negative halves of the incoming waveform to supply

   resetting pulses to the said second ramp generator.

   *1*

   13

   r ,ll, I

   A control unit in accordance with any one of

   claims 1 to 4, in which the means responsive to the

   voltage between the electrodes at the first time point

   comprises a peak detector operative to detect and

   hold the peak voltage across the welding electrodes

   and a comparator operative to compare a predetermined

   portion of the said peak voltage with subsequent

   cyclic peaks of the voltage across the welding electrodes,

   the comparator providing a signal change to terminate

   the weld when the said subsequent cyclic peaks fall

   Lfy to the level of the said predetermined proportion of the

   0p first-mentioned peak voltage. e 6. A control unit in accordance with claim 5, comprising @9 electrically connected between the electrddes and the said

   peak detector, a mains compensation circuit operative to

   divide the electrode voltage by a voltage representative of the level of the mains voltage. 7. A weld-termination control unit, substantially c

   as herein described with reference 'to'othe accompanying' drawings.::

   8. The steps or features disclosed herein or any combination

   thereof.

   Dated this 27th. day of February, 1978

   THE WELDING INSTITUTE *S.by its Patent Attorneys DAVIES COLLISON.

   14

   *0

   33 695/1

   I

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   Suspect