Note: Descriptions are shown in the official language in which they were submitted.
Back~round o~ the Invention
This invention relates to a portable gun welder ccntrol
system and more particularly to a digital welder control system
for the automotive industry in which the controller utilizes a
microprocessor and modular interconnections.
Portable gun welders have been used for many years in the
automotive industry, but the automation of the welding operation
for assembly line work has introduced many problems in providing
adequate control of the welding sequence~ Previously, welding
parameters such as squeeze time, weld time, heat intensity, cool
period, etc., were programmed by an operator who dialed numerous
sets of concentric switches and potentiometers on a control
panel. The dial area of this control panel became crowded as
well as introducing a possible error by the operator in setting
the numerous switches and potentiometers on the control panel.
Another problem encountered by prior art controllers was in
setting the welding heat intensity to a preselected value. The
prior art used RC time delay which was somewhat temperature
dependent so that the time delays did vary to a degree with
operating temperature. Prior art controllers also used a
continuously variable potentiometer which did not have precise
known points corresponding to small increments of heat such as
steps of 1~ increment of heat. In addition, the accuracy of the
heat settings achieved with the potentiometers often varied as
much as +10% or more depending upon the age or atmosphere in
which the potentiometers operated. Even devices which use a
stable oscillator as a timing reference and count by using
integrated circuits to generate accurate time delays, are subject
,3L~ 3t7
to erLOr because the accurlc~ of the device depends up~n a stable
and precise reference frequency.
Prior art welder control systems also did little or nothing
in the area of diagnosing malfunctions. Some malfunctions of the
controllers are obvious and can be quickly diagnosed and
remedied. However, in some instances, it is not readily apparent
what exactly is wrong with the welder control system. In
assembly line production, a problem which cannot be diagnosed
quickly can lead to costly down time if a number of the portable
gun welders are out of operation due to any number of possible
malfunctions in a welding control system. For instance, the
timing period in a sequence might extend beyond its normal
period. One or both of the SCR's in a thyristor contactor might
fail to fire causing half cycling of the welder tLansformer and
eventual saturation and destruction of the same. A rise in the
transformer temperature above its normal operating temperature
would be an important factor to know. A low water flow to the
thyristor contactor which should cause an overheating and failure
of the same would also be an important factor to know. Moreover,
a shorted SCR or an improper heat setting would be a further
malfunction and error, respectively, that must be quickly
diagnosed and remedied.
Another disadvantage in prior art welder con~rol systems is
that the circuit for the heat control used the zero crossing of
the voltage wave form as a reference for generating the time
delay signal. This technique required the controller be tuned to
the power factor of the installation. Timing in these types of
controllers was accomplished by taking the zero crossing of the
voltage wave form with a correction for a particular power factor
37
of the installation. Each time a controller is installed, a
potentiometer on the controller is adjusted to tune the
controller to the installation. Although tuning the controller
is normally an adequate remedy, the power factor often varies due
to a different gun configuration or to a dynamic change with a
different work piece in the throat of the gun; In these
instances, the heat control takes on some error because of the
welder controller's inability to account for the changes in the
power factor.
- Summary of the Invention
With-this invention, the foregoing problems are substantially
solved. The digital portable gun welder control system is
comprised of either two or three modules: a contactor module and
a sequence module or a contactor module, a sequence module, and a
junction box, respectively. The welder control system utilizes
an 8 bit microprocessor as its main control element. The
microprocessors known cycle time is used to generate a real time
delay which in turn is used to generate a phase shl~t heat
control. The random access memory ~hereinafter called RAM) of
the microprocessor is used to store constants o~ the weld
sequence previously stored in position of tap switches or
thumbwheel switches. The welder control system monitors existing
signals already in the controller to generate diagnostic messages
which indicate malfunctions in the welder control system. The
welding controller also-includes a maintenance interval counter
and compensator which is a four-step, stepper control used to
automatically increase the weld heat after a preset number of
welds to compensate for welder tip mushrooming which is most
prevalent in welding galvanized metal in the auto industry. The
~ 3~
welder control also includes programming checks that eliminate
invalid data entries to the welding sequence. Only locations in
the RAM which are used in the normal welding sequence can be
written into. The welder control system utilizes a serial
communication between the sequence module and the microprocessor
in the contactor module.
Accordingly, a principal object of the present invention is
to provide a portable gun welder control system for the
automotive industry that utilizes a digital phase shift heat
control which automatically compensates for changes in the power
factor of the installation so that the heat intensity does not
vary from the programmed setting.
Another object of the present invention is to provide a
portable gun welder control system for the automotive industry
which utilizes the ~AM in the controller's microprocessor to
store the constants of the weld sequence previously stored in the
position of tap switches, potentiometers or thumbwheel switches
that often cause reliability problems by the sheer number of
switches or potentiometers required to be set by an operator or
the possible failure of a hardware interconnection of the
switches.
A further object of the present invention is to provide a
portable gun welder control system for the automotive industry in
which common problems that are often encountered by a welder
control system but which are difficult to diagnose and remedy,
are highlighted and identified by the controller to reduce down
time and maintenance requirements of the controller.
Yet another object of the present invention is to provide a
portable gun welder control system for the automotive industry
~3'~
that inclucl~s s m.~intenance interval count~L and compensator to
automatically increase the weld heat after a preset number of
welds in each step to compensate for electrode mushrooming.
Still another object of the present invention is to provide a
portable gun welder control system for the automotive industry in
which invalid data entries into the we~ding sequence are
eliminated.
Moreover, another object of the present invention is to
provide a portable yun welder control system for the automotive
industry in which only RAM locations in the normal welding
sequence can be written into to avoid malfunctions within the
controller.
Still further, another object of the present invention is to
provide a portable gun welder control system for the automotive
industry that ùtilizes a serial communication between the
sequence module and the microprocessor in the contactor module to
reduce the requirement of additional drivers and receivers
between the sequence module and the microprocessor and to reduce
power requirements therebetween.
Another object of the present invention is to provide a
portable gun welder control system for the automotive industry in
which the controller is divided into several modules, each
containing one or more removable circuit boards and each
interconnected to its associated module by disconnect plugs so
that a malfunctioning module or one o~ its circuit boards can
easily be serviced by simply substituting another ~odule or
circuit board.
Other objects and advantages will become apparent from the
description wherein reference is made to the accompanying
~23~ 37
dL-a~ings illustrating the preferred embodiments of the invention.
Brief Description of the Drawin~s
~ Fig. 1 shows a block diagram of the module interconnections
for the welding control system embodying the principals of the
present invention;
Fig. 2 is a partial block and schematic representation of a
portion of certain electrical relationships which can exist in
the block diagram of Fig. l;
Fig. 3 is a front elevation of the sequence module front
plate of Fig. 2;
Fig. 4 is a card program work sheet carried by an operator
for the welder control system and corresponding to the address
program chart on the sequence module in Fig. 3;
Flg. 5 is a block diagram of the inputs and outputs to the
microprocessor of Fig. l;
Fig. 6 shows a circuit diagram of the power panel of Fig. l;
~ Fig. 7 shows a circuit diagram-of the thyristor contactor of
Fig. l;
Figs. 8~-C shown current and voltage versus time diagrams
which serve to explain the automatic power factor feature of the
controller of Fig. l; and
Figs. 9A-C illustrates graphically the voltage wave forms and
signal level in the embodiment of Fig. 1.
Description of_the Preferred Embodiment
Referring to Fig. 1, the digital welder control system 10
that can be used in any general, industrial or commercial
installation is connected to a power source, such as an
alternating current power source 12 having lines Ll and L2, which
are connected in any known manner through a service entrance
,f~ r~
breaker 1~. L,lne l:,~ is connected to the primary of the welding
trans~ormer and L1 is connected to the primary of the welding
transformer through thyristor eontactor 16 as sho~n in Fig. 7.
The circuit breaker side of power lines Ll and L2 are also
connected to a power panel 18 through a eable 7PL as shown in
~ig. 6. The power panel 18 is connected to the thyristor
contactor 16 through power cable 6PL. A logic panel 20 eontains
a microprocessor board 22 and an input/output board 24 whieh are
interconnected by a power cable 8PLo The microprocessor board 22
contains an 8-~it microproeessor of any known type (not shown)
such as a Motorola M6800. The 8-bit microprocessor ineludes read
only memories registers containing the executive program, random
access memories containing the program constants of the weld
sequence, port registers and various gate and amplifying cireuits
interconnecting the above mentioned integrated circuits of the
microprocessor in any known manner in the art. The
microproeessor board also ineludes a battery for retaining the
data stored in the RAM whenever the welding eontroller is
de-energized. The battery in the data retention eircuit for the
RAM is trickle charged during normal operation when the welding
controller is powered from the line and has a use~ul life of
approximately 21 days for retention of the data in the RAMs when
the welding controller is de-energized.
The input/output board (hereinafter called I/O board) 2~
serves as an I/O signal-eonditioning to interface the processor
bus. The I/O board also eontains initiation and fault relays
which energize and de-energizes the welder solenoid upon
triggering the gun or upon a fault occurring, respectively. The
I/O board also contains a solenoid amplifier for providing enough
3L;~3'~ 7
power to operat~ the selected solcnoid.
The I/O board also contains an override timer. This timer is
set so that it provides an output after approximately 70 cycles.
All timin~ periods in the welding controller are restricted to no
more than 59 cycles. During the operation of the controller and
at the beginning of each timing period in the welding sequence, a
pulse is provided to reset the override timer to zero. In normal
operation, the override timer should never time out as it is
continuously reset after each timing period/ which is less than
the time out time o~ the override timer. If one of the timing
periods goes longer than 59 cycles the override timer will time
out. The output of the override timer de-energizes the fault
relay on the I/O board which de-energizes the welder solenoid and
also provides an interrupt signal to the microprocessor which
causes the microprocessor to execute and interrupt subroutine
which locks out the welding controller. Both the microprocessor
and I/O boards communicate with the power panel through cables
4PL and 5PL, respectively. The logic panel 20, power panel 18,
thyristor contactor 16 and circuit breaker 14 are housed within
the contactor module 19.
A sequence module 26 communicates with the microprocessor
board in the contactor module through cables CPL and lPL. The
se~uence module 26 provides a means for entering the weld
schedule and interrogating the microprocessor to be described in
greater detail later. It also displays a diagnostic readout and
includes the operator controls of the welding controller.
A junction box 28 interconnects with the I/O board and the
power panel through cable JPL which branches into cables 2PL to
the IjO board and 3PL to the power panel. The junction box is a
~'~3~ 7
convenient way of hooking solenoid valve and trigger signals to
the controller at a remote location. The junction box includes
user connections, light indica~ors for initiation and solenoid
functions which indicate initiation of one of the three welding
sequences and closure of the solenoid valve, a tip maintenance
light, and a power off pushbutton for the shunt trip on the
breaker to kick it out in an emergency stop condition.
Referring now to Fig. 2, incoming power supply lines Ll and
L2 can be fused prior to entering the contactor module and
connecting with the circuit breaker 14. The welding transformer
primary 30 connects at one terminal to power supply line L~ and
its other terminal is connected to terminal Hl of the thyristor
contactor panel 16 (see Fig. 7). The core of the transformer is
grounded to the cabinet ground and its secondary 32 is connected
to the welding electrodes 34 in a manner well-known in the art.
In actual usage, the transformer is mounted on a counter weight
balanced off the ceiling beams and its secondary is a concentric
cable hanging from the transformer and terminating in a gun
having solenoid operated electrodes that close on the workpiece
when a trigger on the gun is pulled.
Water lines 36 flow to the thyristor contactor for cooling
the same in any manner which is also well-known in the art.
The sequence module 26 has a front panel 38 including address
and data thumbwheels 40 and 42, respectively to be described in
greater detail later, a-key operated run/program switch 44, and
an LED data display 46 and a number of operator switches 48 all
to be described in greater detail later. Also shown in Fig. 2 is
the front panel 49 of the junction box which contains the
initiations and valve output indicators 50 and 52, respectively,
ln
~23~
for t-l~' thr.~e weldin~ sequenc~s alon~3 with the maintenance
interval counter and compensa-tor indcator 54. On the lower
portion of the panel are three indicators 56, 58, and 60 for
indicating the operation of sequence 1, sequence 1 and 2, and
sequence 3, respectively. Below the junction box face 49 is its
terminal board 62 which can be wired directly onto the contactor
module if the junction box is omitted as shown in phantom. The
terminal strip 62 can be wired for the following; at terminals Al
and A2, a remote maintenance interval counter an`d compensator
(hereinafter called MICC) switch 64; at terminals TSl and TS2 a
transformer over temperature thermostat switch 66; at terminals 1
and 2 a remote MICC output indicator 68; at terminals SVl, SV2,
SV3, SV4, solenoid valves ], 2 and 3; and at terminals POl and
PO2, a power off switch 70 (circuit breaker shunt trip).
Turning now to Fig. 3, the sequence module front plate 38 is
shown in greater detail and the method of programming the welding
controller will be discussed. The controller provides the
capability of generating three weld sequences with the following
timing periods:
squeeze delay 0-59 cycles (common to all sequences)
squeeze 0-59 cycles
weld 1 - 0-59 cycles
cool 2 0-59 cycles
hold 0-59 cycles
off 3-59 cycl~es
The percent current for both weld 1 and weld 2, corresponding to
heat 1 and heat 2 respectively, can be set independently from
50-99~. The reason for three weld sequences, is that, in a
typical assembly line in the automotive industry, an operator of
the wel~er control of ten has a situation ~7here theLe are three
different weld schedules (sequences) reauired at his particular
station on the assembly line. On one gun, there may be two
triggers which allows two of the three sequences to be run. On
another gun, which is on another secondary cable connected to the r;
same welding transformer, he has one trigger; the operator is ,
able to make the welds for two of -the three sequences using the
dual trigger gun, put it down, pick up the second gun and get the
third weld sequence.
Sequences 1 and 2, at the operator's option, can be under the
control of the four-step, stepper called the maintenance interval
counter/compensator (hereinafter called MICC). The MICC is a
fully programed, four-step, stepper control used to automatically
increase the weld heat after a preset number of welds. This f
feature is used to compensate for electrode mushrooming, most
prevalent in welding galvanized metal in the automotive
industry. When the MICC is on, the percent heat for both weld 1
and weld 2 are identical and are under control of the program set
in the MICC schedule. In the top left hand portion of the module
front plate 38 is an address program chart for the three welding
sequences including the MICC and a diagnostics and MICC status
numeral listing.
Now, a brief description of the function and operation of the
controls on the sequence module front plate 38 used in
conjunction with an address program chart 72 on front plate 38
will be presented. First, an operator selects a particular
memory location (address~ on the address program chart and dials
the address thumbwheel 40 to that particular address number to
examine or alter the data stored in this RAM location in the
~;34~87
microprocessor. Next, if -the operator intends to enter or alter
the data (timing period cycles, percent current, etc.,) in the
particular address selected by the address thumbwheels, the data
to be entered is dialed on the data thumbwheels 42 and is
actually entered into the RAM memory by depressing an enter/reset
switch 74. The LED data display 46 displays the data currently
stored in the memory location set on the address thumbwheels. So
the operator can check to see if indeed the dialed data on the
data thumbwheel 42 has been entered or not. During this period
if a fault is detected by the diagnostics of the welding
controller, the data display-46 preempts the address thumbwheel
settings and flashes a number indicating a particular fault
corresponding to one of the numbers found on diagnostics portion
of the address program chart. The run/program switch 44 is a two
position switch. In the run position, the welding controller may
be initiated by closing one of the initiation switches such as a
trigyer on a portable welding gun. In the run position, the
memory locations cannot be altered, however, they may be
displayed by using the address thumbwheels and by viewiny the
data display 46. In the program position, the R~M memory
locations may be altered, but the welding controller cannot be
initiated by triggering the welding gun. The switch 4~ is key
operated and the key can only be removed in the run position. As
stated above, the enter/reset switch 74 is operated when the
run/program switch 44 is in the program posi-tion. By depressing
and releasing the enterjreset switch 74 the data settings on the
data thumbwheels is entered into the RAM's location of the
microprocessor for the ~unction set on the address thumbwheels.
However, the microprocessor checks the incoming data to the
~ ~3f~
RAMs so that invalid data entries are eliminated. As previously
stated, timing periods are limited to the range of 0 to 59
cycles, and heats are limited to the range of 50 to 99~. When an
entry of data is made, before it is written into or stored in the
working location of the RAM, it is checlced to determine whether
it is within the above mentioned limits. If the data is not
within the above limits the entry is re]ected. Communication
between the microprocessor and the sequence module results in the
data from the sequence module being -temporarily stored in three
RAM locations. These locations are then examined to determine
whether or not the data is valid and within the limits set in the
executive program found in the ROMs of the microprocessor. If
the data is valid, then it is transferred from the temporary
storage location to the actual active memory location of the RA*I
which is accessed during the normal welding sequence. If the
data is invalid, this transer to an active R~M location does not
occur. The advantage of this checking technique is that wrong
pieces of data which could cause malfunction of the welding
controller cannot be entered. Thus the possibility of human
error is eliminated. Prior art controllers require mechanical
stops in thumbwheel switches or the like when they are used as a
storage mediumO This technique eliminates special thumbwheels in
order to keep the data entry within the limits. As stated above,
the data is compared against the limits set in the e~ecutive
program in the ROMs of the microprocessor. If it falls within
the limits, it is valid and used. If it does not Eall within the
limits the entry is just rejected, requiring the operator to
change and re-enter the data in order to successfully program the
controller.
1'1
Another advantage of this technique over the prior art, is
that many more pieces of information can be stored than would be
practical with tap switches or thumbwheels for each piece of data
in a welding sequence as on the old welding controllers. Such a
number of thumbwheels or tap switches would cause reliability
problems in the number of interconnection points required, not to
mention the problems of cost, space and complexity. The
microprocessor is by far a more e~ficient way of storing
information than mechanical tap and thumbwheel switches. The
only slight drawback is that the RAM is a volatile storage
medium, which means it must be continuously powered to retain its
information. This is provided, however, by the previously
mentioned battery which is trickle charged during the period the
welding controller is powered from the line. The ba-tter~
provides the energy to retain the data in the RAM of the
microprocessor for a minimum of 21 days which is more than an
adequate safety margin.
Should one of the six diagnostic faults occur which are
listed on the address program chart on module front plate 38, the
welding controller will not initiate when the operator triggers
the gun. After maintenance is carried out to correct the
malfunction, depressing the enter/reset switch 74 will reset the
welding controller after a fault. Then the data display 46 again
displays the data for the address set on the address thumbwheels,
and the welding controller may be initiated if desired.
A MICC on/oEf switch 76 on front panel 38 is a two position
switch. With this switch in the off position, the MICC is
disabled. The MICC is precluded from counting welds, the tip
maintenance required light on the junction box 28, if on or
~3'~
flashing is extinguished, and both the remote (iE used) and local
MICC step advance switches are inoperative. In the on position,
the MICC is operative, welds are counted, the tip maintenance
required light is operative, and the MICC may be manually
advanced.
A MICC step advance switch 78 on front panel 38 causes the
MICC to advance to the next step in the stepping program by
depressing the switch when the MICC on/off switch 76 is on. If
the welding controller is currently in step 4, the MICC step
advance switch will return it to step one. The remote MICC step
advance switch 64 (Fig. 2) corresponds to the step advance switch
78. It may be connected to the user's terminal as previously
described and performs the same function.
A repeat/non-repeat switch 80 on the front panel 38 is also a
two position switch. In the repeat position, the control will
continue to perEorm the weld sequence as long as the initiation
switch is held closed. In the non-repeat position, closing any
of the initiation switches will result in one weld sequence
only. The initiation switch must be released and reclosed to
perform another weld sequence.
A weld/no-weld switch 82 on the front panel 38 is also a two
position switch. With this switch in the weld position, a
welding current will be passed during the weld one and weld two
timing periods. In the no-weld position, the welding controller
can be sequenced but no weld current is passed.
Referring further to Fig. 3, the programming of the
maintenance interval counter and compensator will be discussed.
The MICC is basically a Eour-step, stepper that operates
sequences one and two. The MICC is used to automatically
37
increase the weld heat after a program~ed number of welds to
compenate for electrode mushrooming. What happens in a typical
commercial usage is that on some coated metals the electrode tips
deteriorate very fast and the operators are continually replacing
tips several times a shift. But each time the operators replace
the tips they are still interested in trying to get the most life
out of the tips, which is done by upping the heat periodically
during the welds as the tips deteriora-te and the current density
at the spot weld goes down. Also, when the MICC reaches step
four, the light indicator 54 on the junction box 28 and/or the
remote MICC output light 68 flashes, which is an indication that
we are at the end of step four, and tip maintenance is required.
With the MICC on/off switch 76 in the on position, the
welding controller ignores the percent current data entered for
weld one and weld two for sequence one and two (addresses 12, 15,
22, 25 on the program chart). The percent current is controlled
by the program entered in the MICC addresses.
Address 50 is the weld count times ten for step one. In
address 50, the operator enters the number of welds divided by 10
to be made in step one. For example, if 80 welds are desired,
the operator sets the address thumbwheel to 50 and sets the data
thumbwheel to 0~, depresses the enter switch 74 to enter 0~ in
address 50 in the RAM. The welding controller will perform 80
weld sequences at the s~ep one percen~ heat and then
automatically index to step 2. A dual pulse weld is considered
to be one weld for the MICC purposes.
Normally, the programming of the MICC is done by the operator
experimentally. The resultant program will depend Oll the weld
schedules selected and on the different types of material to be
` ~34~37 ~:
welded. So after some experimentation, the operator would be
able to determine an optimal program which would track the
mushrooming o-E the welding tips with the number of welds and the
amount of current required in each step, and also when the tips
changes are required.
So for programming sequence 1, the operator enters in address
60, the percent current at which these 80 welds are to be made.
This percent current applies to both the weld one and weld two
timing periods. That is, a dual pulse weld under MICC control
will have the same percent current for both pulses. ~owever, the
weld one and weld two times may be adjusted differently. In
address 70, the operator enters the percent current for sequence
two. Steps two, three, and four are programmed in a similar
manner, with the exception that the program weld count is times
100 for these steps.
Addresses 88 and 89 when dialed display the status of the
MICC. When an operator dials address 89, the LED data display 46
displays the step number (1 through 4) in which the MICC is in at
that time. When the operator dials address 88, the LED data
display 46 displays the number of welds completed in that step
(since a 2 digit display is used, the number shown must be
multiplied by 10 for step 1 and by 100 for step 2 thru 4). Each
time the MICC enters a new step, the weld counter is zeroed.
When the MICC enters step 4, the red light 54, labeled, tip
maintenance required, on the junction box 28 is lit. This is an
indication to maintenance personnel that the MICC is in its last
step and the tips will need attention soon. If an additional
remote indication is desired, a 40 watt maximum light
corresponding to light 68 in Fig. 2 can be connected to terminals
18
1 and 2 on the user's terminal strip in the contactor module or
in the junction box as previously described. When the number of
welds in step 4 are completed, the tip maintenance required light
will flash on and off. IE additional welds are mde after the
tip maintenance required light starts flashing, they will be made
at the step 4 percent currents.
Theory of Operation
As previously stated, the controller utilizes an 8-bit
microprocessor as its main control element. The software program
to do the welding controller function resides in the programmabl2
read-only memory (PROM). This memory is non-volatile, that is,
the executive program is permanent, even with the memory
unpowered. The constants for the weld schedule
(squeeze-weld-hold-off times, percent heats, MICC counts, etc.)
are stored in the programmable memory re~ister (RAM). This RAM
is volatile and requires standby power in the form of the
previously mentioned battery to retain its data when the welding
controller is de-energized. All control signals are interfaced
to microprocessor via its input-output structure. Fig. 5 shows
the input and output signàls of the microprocessor. When power
is applied to the welding controller, the microprocessor
initializes itself as well as its supporting circuitry. Once the
welding controller is initialized and is in a standby mode, there
is communication betwee~ the sequence module 26 and the
microprocessor. The mi~roprocessor sends out 24 clock pulses,
waits for approximately a millisecond, and repeats the series of
24 clock pulses. During the one millisecond break, shi~t
registers in the sequence module are in a load mode. Tha-t is,
information from enter/reset switch 74, MICC on/off switch 76,
19
MICC step advance switch 78, repeat/non-repeat switch ~0, and
weld/no weld switch 82, and run/program switch 4~ is entered into
one of the registers called a switch register. The address and
data thumbwheel settings are also entered and held in their
respective shift registers. The 24 clock pulses, each in turn,
shift one bit of data from the shift registers made up by the
switch, address and data registers to the microprocessor. This
information is retained in temporary locations in the RAMs.
During the transfer of the data information from the sequence
module to the microprocessor, the microprocessor also is
generating display information for the LED data display 46 on the
sequence module, which is captured by another shift register.
This shift register feeds the binary coded decimal (hereinafter
called BCD) to a pair of 7 segment decoder/drivers. These drive
the shift registers of the 7 segment LED display. During a fault
situation the nornal job of displaying the contents of the
location dialed on the address thumbwheel is preempted and the
display 46 is used for displaying the error numbers. This
communication is done by the microprocessor and it sends out the
error code to be displayed for a second, and then blanks the
display 46 for a second and then repeats with the error code.
This alternating display and blanking of error code number gives
the display a flashing action.
The shifting of one bit of information oE each clock pulse
from the sequence module to the microprocessor is a serial
communication. The advantages of serial communication over
parallel communication is that parallel communication requires
many more wires and additional drivers and receivers between the
sequence module and the microprocessor. This results in a
savings of wire, connector points, and drivers and receivers, and
power. Time constraints do not preclude using serial
communication in the welding controller case, which means there
is enough time to serialize and send one bit at a time between
the sequence module and the microprocessor.
After initialization and the communication between the
sequence module and the microprocessor, the welding controller
remains in a standby mode until an initiation switch is closed
such as a trigger on the portable welder gun. In the standby
mode, the microprocessor continuously communicates with the
sequence module as stated above.
On the triggering of the portable gun welder, the welding
controller leaves the standby mode and starts to generate a weld
sequence. As it starts the squeeze delay time it starts the
override timer. The override timer is started at the beginning
of each timing period in a sequence. If any timing period
exceeds 59 seconds, the override timer times out. This causes
the solenoid to drop out and the microprocessor to diagnose an
override time-out as one of the six malfunctions of any welding
controller. If after generating a fault signal for displaying a
flashing 99 on the LED data display 46 to indicate an override
time-out condition is not required, the microprocessor then
examines the three input signals as shown in Fig. 5 which are
used to generate fault indications if a malfunction has
occurred. These inputs are the automatic power factor
(hereinafter called APF), SCR over-ternperature, and transformer
over-temperature signals. During all times except weld times,
there should be a voltage present across the SCRs in the
thyristor contactor. If there is not, a shorted SCR is indicated
21
!37
by a flashing 95 in the data display 46. If either of the
thermostats is open, a corresponding fault is indicated by either
a flashing number 96 or 97 in the LED data display 46.
If no fault conditions are present, the microprocessor
generates an output signal for ener~izlng the solenoid air
valve. The welding controller remains in the squee~e delay
routine for the number of cycles equal to the contents of memory
address location 40 in the RAM. I'he AC line reference input is
examined in order to count the line cycles.
Next, the s~ueeze mode is checked, which is the same as the
squeeze delay mode except the solenoid is energized if the
squeeze mode was entered as a result of a repeat weld. In the
case of a repeat weld, no squeeze delay time is generated.
After the squeeze time is completed, a weld 1 time mode is
entered. On entering this mode, the microprocessor again resets
the override timerO It then generates a delay so that the first
half cycle of the weld is fired at the delayed firing angle, 85,
because that is the natural power factor angle for the welding
transformer magnetizing current. The subsequent half cycle
firing is according to an unique automatic power factor
compensation feature to be described in greater detail later. If
the control is in weld, the SCRs are fired. After the SCRs are
fired, the voltage across them is examined to deter~ine whether
or not the SCRs actually did fire. If a voltage is present, it
indicates a misfire and the fault code 98, half cycling is
indicated in the data display g6. The voltage across the SCRs is
again examined to determine if conduction did cease. If voltage
across SCRs is not re-established after a period of time, a
shortedlSCR fault code 95 is indicated on data display gG. If
22
Li37
the welding controller is in no weld, firing portion o-f this
routine is by~p~ssed. The line reference signal is used again to
count weld cycles. If the weld is not complete, the
microprocessor generates the proper heat control angle determined
by the percent heats entered in the memory location. Note that
if the MICC switch 76 is on, the heat control angle is determined
by the percent heats entered in the MICC RAM locations. A
cooling time, a second weld time, and a hold time are the next
functions performed by the microprocessor. The COOL and HOLD and
the WELD 2 sequences follow the same routines as the squeeze time
and weld 1 respectively. Briefly, the hold time is the time
where the welding tips still apply pressure to the weld nugget
but no current is flowing. This pressure is applied long enough
for the molten material between the tips to solidify somewhat.
Then an off time is generated in which the solenoid is
de-energized moving the welding tips apart. If the welding
controller switch 80 is in a non-repeat position, off time is not
generated. The solenoid is de-energized and the control will
hold at that point until all initiation switches are recognized
as open. When this occurs, the controller goes back to the
standby mode and again communicates continuously with the
sequence module.
IE the controller is in a repeat mode, off time is generated.
Because of the delays i~ the relay isolated initiation circuit,
off time must be at least 3 cycles or else the control will
continuously cycle. This is because the controller would examine
the initiation switches before they had a chance to drop out and
re-initiate the sequence again. Because of this, if the off time
is programmed to something less than 3 cycles in the RAM
23
87
location, the microprocessor will automatically execute 3 cycles
of off time. Also the off time gives an operator time to move
the gun to a new location on the body of a car for example and to
establish a rhythmic motion in working the gun. After the off
time is completed, initiation switches are rè-examined. If one
of the initiation switches (triggers) that started the sequence
is still closed, the controller will execute another complete
sequence at the squeeze time. This continues as long as the
initiation switch is held closed. When the trigger is opened,
the welding controller will revert back to its standby mode.
After weld 2 time is completed, the MICC counter is updated.
This counter is incremented only if the following conditions are
met:
1) MICC is on;
2) weld/no weld switch is in the weld position and
3) the welding controller is not executing the sequence
three.
Referring now to the diagnostic portion of the address
program chart of Fig. 3 and the diagnostic portion of card
program work sheet in Fig. 4, it can be seen that the welding
controller circuit is designed to monitor six of the following
malfunctions: 1) override timeout; 2) half cycling; 3)
transformer temperature; 4) low water flow; 5) shorted SCR; and
6) check heat setting. .I-f any of these six malfunctions is
detected, the welding controller will immediately abort the weld
sequence, de-energize the solenoid, and return to a standby
mode. The data display 46 on the sequence module will flash the
number corresponding to the particular malfunction~ The
controller cannot be re-initiated until the enter/reset
24
3L87
pushbutton 7~ on the sequence module is depressed and released or
the controller power is turned off and then on again.
Briefly, prior art devices did little or nothing in ~he area
of diagnosing malfunctions. Some malunctions of the welding
controllers are obvious and can be quickly diagnosed and
remedied. However, in some instances it is not readily apparent
what is wrong with the welding controller. Six common problems
encountered by welding controllers which are often difficult to
diagnose were chosen and circuitry was designed to highlight and
identify each of these problems for the operator or electrician.
The welding controller senses the existing signals in the control
to generate the diagnostic messages. Thus, the diagnostics
depend on monitoring already present signals for known states at
specific times in the weld sequence. If the signals are in the
states as expected no diagnostic is indicated. If, however,
something is different than expected, the diagnostic is
generated. The problems solved by this feature are eliminating
or greatly reducing the time it takes to find and cure a problem
which previously required a great deal of time and experienced
personnel to correct the problem in order to keep the assembly
line running. An explanation of each of these diagnostic
messages follows.
There is an RC timer circuit external to the microprocessor
and found on the I/O board which serves a watch dog function.
Each timing period sequence is monitored by this circuit. The
circuit times independent of the microprocessor. If there is a
malfunction and any one of the timing periods exceeds 59 cycles,
the watch dog timer circuit will time out, signaling the
microprocessor that the override time-out condition has
~L~3'~ 37
occurred. The microprocessor generates an output signal that
stops the welding sequence, and resets the controller to a
standby mode, and also generates a fault signal which preempts
the current data on the LED data display and substitutes a
display of a flashing 99 to indicate an override time-out.
If half-cycling of the welding controller occurs, a flashing
98 is displayed by the LED data display 46 and the previous data
display is preempted as it is in the remaining diagnostic faults
infra. For this fault, the microprocessor senses whether or not
after a firing signal from the microprocessor to one or both of
the SCRs of the thyristor contactor is given, did the SCRs, in
fact, fire. If the SCRs failed to fire, the half-cycling
malfunction is indicated by the flashing 98 to the data display
46 on the sequence module.
A transformer temperature malfunction is indicated by a
flashing error numeral 97 on the data display 46. Some welding
transformers have an over-temperature switch built into the
transformer. If the user desires, this thermostat can be
connected to the terminals marked TS1 and TS2 on Fig. 2 as
previously described. The thermostat protects the transformer
against a misapplication where the transformer could possibly get
too hot. This thermostat is sensed by the rnicroprocessor and if
the thermostat opens indicatiny that the transformer is too hot,
the microprocessor responds with the flashing error numeral 97.
If a low water flow occurs to the thyristor contactors (Fig.
2) a flashing error 96 will be displayed in the data display 46
on the sequence module. There is a thermostat mounted on the
heat-sink assembly which mounts the two SCR packages of the
thyristor contactor. If for some reason the water flow to the
26
., .
~;~3~ 37
thyristor contactor is insufficient or absent, the heat-sink
temperature will rise and eventually get too hot. The thermostat
will trip when the temperature gets too ho-t, and the
microprocessor senses this tripping and shuts down the controller
and returns it to standby and generates a signal for flashing 96
in the LED data display ~6.
In the case of the shorted SCR, a flashing error numeral 95
is displayed in the data display 46 on the sequence module. The
microprocessor again looks at the APF signal to sense a shorted
SCR. In each of the timing periods, the thyristor contactor SCRs
are monitored for a shorted condition. During the times when the
SCR should be non-conducting, the APF signal should be a zero.
This indicates voltage across the SCRs. If one of the SCRs is
shorted, the APF signal will never go to a zero, as shown in Fig.
9C. If this happens, the microprocessor generates an error
signal 95 to indicate that a shorted SCR has occurred.
The microprocessor monitors all of the heat settings in the
RAM. These are locations 12, 15, 22, 25, etc. The
microprocessor will detect if the percent current addresses
contain a number other than 50-99, and a flashing error signal 93
will be displayed in the data display 46 on the sequence module.
If an operator attempts to trigger a gun welder having a weld
sequence which contains a percent current other than 50-99~, the
sequence will abort and.flash the 93 in the display 46. This
check also pertains to percent current addresses associated with
the MICC. Even though the controller prevents the entry of a
number other than 50~99, it is possible that a particular address
was never programmed, in which case that address would contain a
random number not necessarily between 50-99. The flashing 93 is
27
~3'~18t7
an indication to a maintenance man that there is an illegal heat
setting somewhere in one of the RAM locations. The maintenance
man or operator could remedy this by looking at the heat
locations and putting in the proper heat setting in that location
which contains the illegal one.
Referring now to Figs. ~A-C, the au-tomatic power factor (APF)
and the unique digital phase shift heat control feature for the
welding controller will be explained. Fig. 8A shows the AC line
voltage ~ and the line current I for a 100% weld heat current
setting having no time delay gaps between firing of the SCRs as
shown in Fig. 8A. The natural power factor angle for a typical
gun welding transformer load is approximately 354-60O as shown in
Fig. 8A. Fig. 8B shows a manual power factor set-up where a -
potentiometer or the like is tuned to the installation power
factor. In the manual power factor set-up as in the automatic
power factor set-up to be described infra, the first half cycle
in any welding period is always fired at the natural power factor
angle of 85 of the magnetizing current for a welding
transformer. Subsequent half cycles of welding current are fired
at various phase shifted angles to select the optimum welding
current for the work piece. Now, in the manual power factor
setting, the timing for the heat control is done from the zero
crossing of the voltage wave form as indicated by reference
numeral 84. So the zero crossing of the voltage wave form is the
timing point for heat control in a manual power factor welding
controller in which a potentiometer or the like is used to tune
the welding controller to the power factor of the installation.
Since the timing is fixed to a fixed reference point, the zero
crossing of the voltage wave form, if the power factor varies the
~Z~ 7
time delay gap between current loads will vary and the bottom
line is that the heat setting is going to vary also. This system
works fine if the power factor of installation remains constant.
But in the real world this is usually not the case since a change
of the work in the throat of the gun also changes the overall
power factor of the installation along with it. Normally, the
change of work pieces in the throat of the gun do not affect the
power factor to a great degree, but there are measurable changes
in the weld heat current because of it.
Since the phase shift heat control is essentially a timing
function, the features of the welding controller, in the present
invention are ideally suited for providing an automatic power
factor correction scheme. Timing for the digital phase shift
heat control of the welding controller proceeds from the end of
current conduction of the previous half cycle of we~ding current
to the firing point for the next half cycle of current as shown
in Fig. 8C. The first half cycle of the weld is always fired at
85~ after the zero crossing of the voltage wave form. After the
first half cycle, all succeeding half cycles are referenced to
the end of the current conduction of the previous half cycle. In
this application, the microprocessor îs a digital timer. This
digital phase shift heat control for the welding controller is
done by taking advantage of the fact that the time it takes for
the microprocessor to execute a particular instruction is both
fixed and known. The time delay is made by placing the
microprocessor in a program loop immediately after the end of
current conduction of the previous half cycle. The number of
times the microprocessor goes through this loop determines the
actual time delay before the next half cycle of welding cllrrent
.
29
is initiated. The n~.~ber of times the microprocessor enters this
loop is stored in a location in the microprocessor's memory.
The user when setting up the weld sequence will enter the
desired percent current in the RAM location of the
microprocessor. The percent current, as discussed supra, has a
range available between 50 and 99%. If the user desires a low
heat setting and enters 50~ for example, the delay between the
end of the conduction of one-half cycle and the beginning of
conduction of another will be long. The microprocessor will go
through its delay loop the maY~imum number of times. The higher
the heat setting desired, the smaller the number of times the
delay loop is executed. In the present invention, the maximum
delay required is 3.24 milliseconds. This corresponds to 70 on
a 60 Hz. supply voltage. In the present invention, an operator
can set the percent current between 50 and ~9~ in 1~ increments.
hus each 1% increment is:~ 1% = 3.24 MS = 66.1 us. A fixed
49
program delay loop of approximately 66.1 microseconds will be
constructed in the ROM memory. The number of times this loop is
executed is determined by the heat settings the user makes. For
example, a 64~ setting would cause the loop to be executed 36
times (100 64 = 36). Note that the higher the heat setting the
smaller the delay required, hence the subtraction from 100.
The advantage of using a digital phase shift heat control is
that the real time delays generated are very accurate. As shown
in Fig. 8C, the first half cycle of the welding time period is
fired at the natural power factor angle of 85, but each
subsequent time delay gap is measured at the end of current
conduction in each preceeding half cycle as indicated by
reference numbers 86 and 88, respectively. Thus, the timing
~L~2;~
point is not fixed and varies with changes in the power ~actor so
that the current heat settings are always accurate. The cycle
time of the microprocessor is based on a crystal clock reference
whieh is very stable. The prior art uses the ~C time delay which
is somewhat temperature dependent so that the `delays would vary
to a degree with temperature. The digital phase shift heat
control also allows more precise setability of the percent
current. For instance, there is a definite detent on each
position of the data thumbwheel address 42 for a 1~ incrernent in
current heat. The prior art uses a continuously variable
potentiometer which lacks precise known points corresponding to
each 1% increment of heat the user might desire~ Another
advantage to the digitally generated delay is that when a logic
panel is replaced and the setting duplicated, the percent current
heat is exaetly the same as it was with the old logic panel. In
the prior art welding controllers using the RC timing, the
inherent tolerance of the potentiometer could eause the same
setting on the pot to produce as much as a ~ 10% error on the
aetual percent current heat obtained.
The microprocessor generates the gap angles, or the delay
angles between the current lobes digitally, and produces a weld
signal whieh is fed from the microproeessor board to the power
panel on ineoming line ~PL7, as shown in Fig. 6. The weld signal
is amplified by an amplifier eircuit 90 whieh takes the weld
signal from the microprocessor and provides a pulse voltage for
the gates of the power SCRs. This pulse voltage is isolated from
the logie by pulse transformers 4T and 5T. This voltage is a 20
microseeond wide pulse to the gates of the SCRs in the thyristor
contactor as shown in Fig. 7 through plug connections 6PI.3 and
~3~
6PI.4 or 6PL5 and 6PL6, depending upon which half cycle is
conduction, with a pulse occurring at every half cycle of weld
current. The current in the gate of the SCRs during the 20
microsecond time rises to about 1 ampere and, once an SCR is
gated, it stays on for the rest of the half-cycle. One SCR
conducts in one direction and the other SCR conducts in the other
direction to fire each one in order to get a complete weld cycle.
Referring now to Figs. 9A-C, the microprocessor senses the
voltage across the SCRs as an indication of an end of current
conduction. When the current stops, the SCRS recover and the
voltage across them snaps back to line voltage at that instant,
as shown in Fig. 9B. When the SCRs are conducting and a weld
heat is occurring, the voltage across the SCRS drops to zero.
This transition from zero voltage back to line voltage across the
SCRS is tapped off of the Hl terminal in the thyristor contactor,
as shown in Fig. 7 on 6PL8 cable connection and is fed to a full
wave bridge rectifier 92 in the power panel circuit as shown in
Fig. 6. The signal which is across the line 1 and ~1 terminals
of the thyristor contactor serves as an input to an opto-isolator
circuit ~2 on the power panel. The opto-isolator is saturated
when there is voltage present across the SCRs. The output of the
op~o-isol~tor circuit is fed to the I/O board, which in turn
feeds the microprocessor. Upon receiving the signal, the
microprocessor starts tbe digitally generated delay in the
control at the end of which the next half cycle of current is
fired. This sequence continues for all of the half cycles in the
weld, each referenced from the end of current conduction from the
previous half-cycle. This technique is very accurate, and also
allows complete interchangeability of panels ~lithout any set-up
32
3L~3'~
by electricians. The power factor referred to in the above
discussion relates to the power factor presented to the control
by its secondary circuit. The secondary circuit includes the
secondary cable, the gun, and the work within the throat geometry
o~ the gun. Referring now to Fig. 9C, when the opto-isolator
circuit is saturated when there is voltage present across the
SCRs, the logic signal for the automatic power factor to the
microprocessor is a logic zero. Conversely, when the SCRs have
fired and are conducting the opto-isolator is off and the signal
at cable 5PL14 in Fig. 6 is at the logic 1 to the microprocessor,
hence the wave form shown in Fig. 8C.
Referring back to Fig. 4, a card program work sheet is
shown. An operator can use this card as a guide in programming
the welding controller. The programming work sheet card with the
desired times and heats for the weld sequences to be used can be
filled out by an operator supervisor or the like. Steps used to
enter the work sheet information into the controller is as
follows: 1) set the run/program key switch 44 to the program
position; 2) set the address thumbwheels 40 to the address number
to which data is to be entered (in Fig. 4, address 10 corresponds
to the squeeze time for sequence l); 3) set the data thumbwheels
42 to the number that is to be entered into location dialed by
the address thumbwheels; and 4) press and release the enter/reset
button 74. The data display 46 will change to correspond to the
number on the data thumbwheels 42. This indicates that the data
was successfully entered into the RAM memory of the
microprocessor. This procedure is repeated until all entries are
made. If a dual pulse weld schedule is not required, the user
programs t~e cool and weld 2 timing periods to zero cycles. The
:~23~ 37
controller is designed so tha~ certain data entries that are not
allowed are rejected, as previously stated. If such a data entry
is attempted, the display will not change to match the data
thumbwheels. Summarizing once again the rejected data entries
are as follow: 1) a number greater than S9 in one of the timing
periods; 2) a number less than 50 in one of the percent heats;
and 3) any alteration of any address not shown on the programming
work sheet.
