DESCRIPTION
ROBOT SYSTEM CONTROL METHOD
TECHNICAL FIELD
The present invention relates to a control method of a robot system when
two industrial robots (two sets) that work according to a predetermined
program are used and are applied to one object.
BACKGROUND ART
Conventionally, in a production site where a welding process is
performed, for example, an industrial robot including a welding robot for
performing welding work is introduced, and automation and manpower-saving
are promoted. Here, "industrial robot" is a generic name for a configuration
where a manipulator, a controller, a tool for work, and the other peripheral
devices are interconnected. "Welding robot" is a generic name for a
configuration where apparatuses and components such as a manipulator, a
controller, a welding machine, a welding torch, and a welding electrode, and the
other peripheral devices are interconnected. Recently, for improving the
efficiency of the welding work, for example, for reducing the time for the
welding work, a plurality of industrial robots are used for one object
(hereinafter referred to as "work piece" in response to the generic name), and a
plurality of industrial robots are apt to be operated simultaneously and
collectively.
In such a case, the following coordinative control between robots is often
used: a handling robot that grips a work piece firstly changes the attitude of the

work piece to a coupling attitude that allows appropriate welding, and a
welding robot operates a welding torch to perform welding in coordination with
the handling robot. In such an example, it is important to control the
relationship in the relative position and relative attitude (hereinafter referred
to as "relationship") between a tool for work (for example, a gripping
mechanism for gripping a work piece) of the handling robot that grips the work
piece and a tool for work (the tip of a welding electrode in the welding torch) of
the welding robot. For example, when the robot that grips the work piece is
operated manually, the control is performed so that a robot that grips the
welding torch is operated while the relationship is kept. Such control is the
so-called "associative movement control", and is widespread (for example,
Patent Literature 1).
Alternatively, an example is known where, one of two robots carries a
tungsten inert gas (TIG) electrode, the other robot carries a filler wire, and the
electrode is made close to the filler wire and is TIG-welded to it by coordination
operation (for example, Patent Literature 2). In this case, the positional
relationship between the TIG electrode, filler wire, and a weld line under
welding is important. Therefore, Patent Literature 2 discloses the example
where the operation trajectory is shifted in response to a signal from the outside
while the relative position is kept, and further the relative position is finely
adjusted. Such control is also a type of "associative movement control".
In a considered method of performing the efficiency improvement such as
time reduction of the welding process, two welding robots each of which has one
electrode are used, and two-electrode welding is performed for one weld line.
A general welding condition for welding includes many parameters such
as "welding current", "welding voltage", "welding speed", "weaving method",
and "aiming position for welded joint". Here, "aiming position for welded joint"

indicates the position of the tip of the welding electrode for a welded joint and
the angle of the welding electrode with respect to the welded joint.
In the welding by two welding robots, the welding result depends on the
relationship between two welding robots. The relationship between two
welding robots is specifically the relative position between the tips of two
welding electrodes of the two welding robots and the relative attitude between
the tips of two welding electrodes. In this case, in addition to "aiming position
for welded joint", "relationship" is also one of parameters constituting the
welding condition. In order to perform welding for forming a desired bead with
stable arcs without making two arcs generated by two welding electrodes
interfere with each other, an appropriate relationship is required.
As the welding condition including many parameters, an appropriate
combination is often determined by performing welding many times by try and
error while each parameter is changed. The operation is referred to as
"welding conditioning work". For performing "welding conditioning work",
generally, an actual work piece to be welded is not used but a test piece formed
by reproducing only the welded joint is used. In the welding by two welding
robots, "relationship" is also determined through "welding conditioning work".
The welding work for an actual work piece to be welded is performed by
execution of the predetermined program by the welding robots. The welding
work by the welding robots includes many sequential operations, and is
performed by controlling an apparatus such as a welding machine as necessary
in response to the operations. Therefore, a sequence of commands and data
that indicate respective operations required for the welding work and a
command and parameter that are required for controlling an apparatus such as
the welding machine are registered in the program.
When the program is created, these commands, data, and parameters are

stored in a storage medium such as a memory of the controller of the welding
robot. The command and data indicating each operation include data
indicating the coordinate and attitude for each operation. The welding robot is
actually moved to the coordinate and attitude, and the program is created so as
to teach the welding robot the work. This operation is referred to as "teach".
Generally, this program creating work is referred to as "teaching work". The
means of the coordinate and attitude of the welding robot is described later.
In the teaching work for the welded joint of the welding part of the work
piece, the welding condition obtained by the welding conditioning work is
reflected to the program. As numerical parameters such as welding current
and welding voltage, of the welding condition, the values obtained by the
welding conditioning work are set in the program. Thus, the welding obtained
by the welding conditioning work can be relatively easily reproduced. While,
regarding "relationship" during welding, the relationship between two robots in
the target welding part of the work piece is reproduced and taught by actually
operating two welding robots for each operation during the actual welding.
In a considered method for teaching the relationship, "aiming position for
welded joint" of one robot is firstly reproduced, and then "relationship" is
reproduced by operating the other. Another method may be used where
"relationship" is reproduced near the welded joint and then "aiming position for
welded joint" is reproduced by operating both robots while the relationship is
kept (here, "associative movement control" is used). Among them, as a
considered method for reproducing the relationship, the coordinate and attitude
in the coordinate system of each welding robot during the welding conditioning
work are noted, and the coordinate and attitude are reproduced referring to the
note during teaching of the target welding part of the actual work piece.
Generally, at that time, the position in the coordinate system of the welding

robot is completely different from that in the welding conditioning work, and
the direction of the weld line is not always the same. Therefore, the noted
values of the coordinate and attitude are converted into the present coordinate
and attitude, and the relationship is reproduced with the welding robot. This
operation is actually extremely troublesome. The controller of a usual welding
robot has a function of displaying the coordinate and attitude of the control
point, so that the coordinate and attitude in the coordinate system of each
welding robot can be obtained using the function. Generally, the control point
is disposed at the tip of the welding electrode.
Once the relationship is established, "associative movement control"
where one robot is moved in response to the operation of the other robot while
the relationship is established becomes a useful function. The teaching of the
welding part is performed by driving "associative movement control" of two
welding robots. However, at the start of the control, it is an issue how
"relationship" obtained in welding conditioning work is reproduced and
established. How the relationship can be easily established before "associative
movement control" is a common issue for not only the welding robots but also
all industrial robots employing "associative movement control".
Further, when a work piece to be welded has a plurality of weld lines and
a plurality of welded joints must be welded, the welding conditioning work is
performed for each welded joint. As a result, a plurality of "relationships" is
obtained. In the teaching work, it is required to select one of the plurality of
relationships correspondingly to the welded joint for each welding part. In this
case, the troublesome work must be performed a plurality of times. Once the
relationship is established, "associative movement control" where one robot is
moved in response to the operation of the other robot while the relationship is
established becomes a useful function. However, at the start of the control, it

is an issue how one "relationship" is reproduced and established from the
plurality of relationships obtained in welding conditioning work. This issue is
also a common issue for not only the welding robots but also all industrial
robots employing "associative movement control".
CITATION LIST
[Patent Literature]
[PTL 1] Unexamined Japanese Patent Publication No. H02-271402
[PTL 2] Unexamined Japanese Patent Publication No. H11-342473
SUMMARY OF THE INVENTION
The present invention provides a control method of a robot system that
can reduce the time and effort for the operation for establishing "relationship"
before "associative movement control", or select one of a plurality of
relationships and reduce the time and effort for the operation for establishing
"relationship". Especially, the present invention provides a control method of a
robot system including a welding robot.
In a control method of a robot system of the present invention, for
addressing the above-mentioned issues, two industrial robots are used, one
industrial robot is used as a master robot, and the other is used as a slave robot.
The control method includes the following steps:
a storing step of storing, as one set of information, data indicating
the relation of the relative position and relative attitude between the master
robot and the slave robot; and
a first operating step of operating the slave robot with respect to the
position of the master robot so as to reproduce the relation of the relative
position and relative attitude indicated by the one set of stored information in a

state where the master robot and the slave robot exist at any positions; or
a second operating step of operating the master robot with respect to
the position of the slave robot so as to reproduce the relation of the relative
position and relative attitude indicated by the one set of information in a state
where the master robot and the slave robot exist at any positions.
In this method, when there are two industrial robots such as welding
robots, by storing the relationship between them and reproducing them at any
time point, the time and effort for the operation for establishing the relationship
between two industrial robots before "associative movement control" can be
reduced. Thus, two arcs are generated by two welding electrodes and welding
can be performed at a predetermined position where the two arcs do not
interfere with each other, so that the bead shape can be optimized. As a result,
welding where the coupling strength is sufficient and the reliability is high can
be executed.
In a control method of a robot system of the present invention, two
industrial robots are used, one industrial robot is used as a master robot, and
the other is used as a slave robot. The control method includes the following
steps:
a storing step of storing a plurality of sets of information each of
which has data indicating the relation of the relative position and relative
attitude between the master robot and the slave robot." and
a first operating step of operating the slave robot with respect to the
position of the master robot so as to reproduce the relation of the relative
position and relative attitude indicated by one of the plurality of sets of stored
information in a state where the master robot and the slave robot exist at any
positions! or
a second operating step of operating the master robot with respect to

the position of the slave robot so as to reproduce the relation of the relative
position and relative attitude indicated by the one of the plurality of sets of
stored information in a state where the master robot and the slave robot exist
at any positions.
In this method, when there are two industrial robots such as welding
robots, by storing a plurality of relationships between them, selecting one of the
plurality of relationships, and reproducing them at any time point, the time and
effort for the operation for establishing the relationship between two industrial
robots before "associative movement control" can be reduced. Thus, two arcs
are generated by two torches and welding can be performed at a predetermined
position where the two arcs do not interfere with each other, so that the bead
shape can be optimized. As a result, welding where the coupling strength is
sufficient and the reliability is high can be performed.
BRIEF DESCRIPTION OF DRAWINGS
Fig. 1 is a diagram showing a schematic configuration of a welding
system in accordance with a first exemplary embodiment of the present
invention.
Fig. 2 is a diagram showing an operation of the welding system in
accordance with the first exemplary embodiment of the present invention.
Fig. 3 is a diagram showing an example of a program for performing the
operation of the welding system in accordance with the first exemplary
embodiment of the present invention.
Fig. 4 is a diagram showing storing processing in accordance with the
first exemplary embodiment of the present invention.
Fig. 5 is a diagram showing the positional relationship between the tips
of welding electrodes of two single-electrode welding torches of the welding

system in accordance with the first exemplary embodiment of the present
invention.
Fig. 6 is a diagram showing reproducing processing in accordance with
the first exemplary embodiment of the present invention.
Fig. 7 is a diagram showing an example of the reproducing processing
based on a master in accordance with the first exemplary embodiment of the
present invention.
Fig. 8 is a diagram showing an example of the reproducing processing
based on a slave in accordance with the first exemplary embodiment of the
present invention.
Fig. 9 is a diagram showing storing processing in accordance with a
second exemplary embodiment of the present invention.
Fig. 10 is a diagram showing reproducing processing in accordance with
the second exemplary embodiment of the present invention.
Fig. 11 is a diagram showing storing processing of a plurality of sets of
information in accordance with a third exemplary embodiment of the present
invention.
Fig. 12 is a diagram showing reproducing processing of a plurality of sets
of information in accordance with the third exemplary embodiment of the
present invention.
DESCRIPTION OF EMBODIMENTS
A welding system in accordance with exemplary embodiments of the
present invention will be described hereinafter with reference to the
accompanying drawings. Similar elements are denoted with similar reference
marks, and the descriptions of those elements are omitted.

(FIRST EXEMPLARY EMBODIMENT)
Fig. 1 is a diagram showing a schematic configuration of a welding
system in accordance with a first exemplary embodiment of the present
invention. Fig. 1 shows an example where the welding system is formed of two
welding robots having a peripheral device or the like. The connecting method
between component apparatuses depends on the specification of the component
apparatuses, and the configuration of Fig. 1 is one example.
In a practical welding system, often, the welding robot includes the
following elements: a shift moving device that has a manipulator for holding a
tool such as a welding torch and moves the position of the manipulator; a
positioner that has a base material to be welded and changes the attitude
thereof; and a fixture for mounting the base material. However, this welding
system is not directly related to the contents of the present embodiment, so that
this welding system is not drawn and described.
In Fig. 1, for purpose of illustration, one of the two welding robots is
called as welding robot A, and the number and mark of each element of welding
robot A have suffix (a). The other welding robot is called as welding robot B,
and the number and mark of each element of welding robot B have suffix (b).
Thus, the apparatuses and components constituting the two welding robots are
individually drawn and described.
First, the configuration of welding robot A is described. Welding robot A
includes manipulator 11a and welding power supply device 12a. Cable 123a is
connected to torch terminal 121a disposed in welding power supply device 12a.
Base material W is connected through cable 124a to base material terminal
122a disposed in welding power supply device 12a. Wire feeder 14a is attached
to manipulator 11a. The operation of manipulator 11a is controlled by
controller 10a. When touch sensor unit 13a shown in Fig. 1 is used, cable 123a

is connected through it to power feeding terminal 141a disposed in wire feeder
14a. When touch sensor unit 13a is not used, cable 123a is directly connected
to power feeding terminal 141a.
Wire feeder 14a is connected to single-electrode welding torch 16a
through torch cable 15a. Welding electrode 18a as a consumable welding wire
passes through torch cable 15a. Cable 124a whose one end is connected to
base material W to be welded is connected to base material terminal 122a
whose the other end is disposed in welding power supply device 12a.
In welding, an arc is generated by supplying power between welding
electrode 18a and base material W with welding power supply device 12a. By
generating the arc, a circuit of welding current connected from torch terminal
121a to base material terminal 122a through welding electrode 18a and base
material W is formed. Welding current flows in this circuit of welding current.
By controlling wire feeder 14a with welding power supply device 12a,
welding electrode 18a is continuously fed to base material W. By controlling
the operation of manipulator 11a with controller 10a, welding electrode 18a
moves along the weld line of base material W. Thus, arc welding is performed.
Controller 10a controls the operation of manipulator 11a based on an
operation program previously stored in memory 40a shown in Fig. 1, for
example. Further, controller 10a issues a command of welding current or
welding voltage to welding power supply device 12a. Welding power supply
device 12a controls the welding current or welding voltage according to the
command.
Arc sensor processing section 17a applies a predetermined processing, in
response to a demand of controller 10a, to at least one of the welding current
and welding voltage measured in one of the inside of welding power supply
device 12a and the circuit of the welding current, converts the processing result

into data equivalent to the shift from the weld line of the welding position, and
feeds the data to controller 10a. Controller 10a controls the operation of
manipulator 11a based on the received data equivalent to the shift from the
weld line, and corrects the shift from the weld line of the welding position. Arc
sensor processing section 17a is not required necessarily, and is used in the first
exemplary embodiment.
Welding robot B welds base material W common with welding robot A,
and has the same configuration with that of welding robot A. Therefore, the
descriptions of individual apparatuses constituting welding robot B are omitted.
In Fig. 1, controller 10a is connected to controller 10b through an
inter-robot communication cable X.
In the first exemplary embodiment, welding robots A and B have
single-electrode welding torches 16a and 16b, respectively, and two welding
electrodes 18a and 18b are arranged near the weld line so as to be close to each
other in the welding progressing direction as in conventional tandem arc
welding. In the state where one welding electrode progresses in advance of the
other welding electrode in the welding progressing direction on the weld line,
they generate arcs with welding electrodes 18a and 18b while moving in the
welding progressing direction. In other words, movement of the welding
electrode by the other manipulator follows movement of the welding electrode
by one manipulator. Then, welding is performed while a molten pool is formed
by two nearby arcs generated between two welding electrodes 18a and 18b and
base material W. Thus, welding such as the conventional tandem welding can
be performed. In other words, in Fig. 1, the welding is performed while one
molten pool is formed by two arcs: an arc generated between base material W
and welding electrode 18a moved by manipulator 11a! and an arc generated
between base material W and welding electrode 18b moved by manipulator lib.

The welding may be performed in two molten pool states by forming two nearby
molten pools using two arcs without forming one molten pool using two arcs.
In performing the welding, the processing described in the first
exemplary embodiment is performed mainly with the controller of one welding
robot. The one welding robot is called a master robot (hereinafter referred to
as "master"), and the other welding robot is called a slave robot (hereinafter
referred to as "slave"). The processing is performed by the master, so that the
program and the parameters such as a welding condition are stored in a
memory (not shown) of the controller of the master. Operation required for the
processing is also performed through an operation panel (not shown) of the
controller of the master.
The master and the slave play different roles, namely the master
subjectively performs control and the slave obeys the master. When which
welding robot is the master or slave is previously determined before the
processing discussed below, any of two welding robots may be set as the master
or the slave. Then, essential difference is not required between specifications
of the apparatuses constituting two welding robots. In welding control, the
master may be leading or following if it is determined.
In the following description, it is assumed that welding robot A is the
master, welding robot B is the slave, and the master is leading. In other words,
controller 10a is a leading controller of the master, and controller 10b is a
following controller of the slave.
Next, the operation of the welding system shown in Fig. 1 is described
using Fig. 2. Fig. 2 is a diagram showing an operation of the welding system
in accordance with the first exemplary embodiment of the present invention.
The welding for one weld line and the operations of welding electrode 18a and
welding electrode 18b before and after the welding are shown in Fig. 2. Here,

P210, P211, P212, and P213 surrounded with broken lines show teach points
programmed as the operation of the welding robots. Each teach point includes
data (hereinafter referred to as "positional data") required for specifying the
coordinate and attitude (hereinafter referred to as simply "position") of each of
two control points disposed at the tips of welding electrode 18a and welding
electrode 18b. Each teach point is a combination of the positions of both
welding electrodes 18a and 18b, and is formed of positional data of both welding
electrodes 18a and 18b.
Generally, there are various methods of expressing the positional data
indicating the position of the industrial robot including a welding robot. For
example, there are a method of expressing the data using the position of each
operation axis constituting the industrial robot and a method of expressing the
data using a matrix determined based on the relationship between respective
axes. Either of the methods can be converted into the other method. The
method is often used where the tip position of the welding electrode is expressed
by the coordinate value in a predetermined rectangular coordinate system, such
as coordinate value A0-'(X, Y, Z), and the attitude is expressed by the Euler
angle defined on the rectangular coordinate of the welding electrode, such as
Euler angle B0:(U, V, W). However, the rectangular coordinate is defined
according to individual industrial robot. A plurality of rectangular coordinates
can be defined. "Positional data" can be expressed uniquely when only one
rectangular coordinate system is used, or when there is a plurality of
rectangular coordinate systems but only one of them is used. However, when
there is a plurality of rectangular coordinate systems and any rectangular
coordinate system of them is used, information for specifying which rectangular
coordinate system is used is also required. There are many methods of
specifying the rectangular coordinate system. These methods do not show new

contents and do not especially concern the first exemplary embodiment, so that
the descriptions of them are omitted.
In the following description, a rectangular coordinate system (hereinafter
referred to as "robot coordinate system") disposed at the center of an attaching
section of the manipulator is used, and "positional data" of the welding robot is
expressed by a combination of position coordinate value (X, Y, Z) at the tip of
the welding electrode and Euler angle (U, V, W) of the attitude of the welding
electrode.
When the welding robot has a shift moving device and a positioner and
there are a shift axis and a positioner axis, information for specifying these
positions is also included in "positional data". However, this is not important
in the first exemplary embodiment and is not especially described.
In Fig. 2, for example, an execution start signal is input into controller
10a and controller 10b, and the start of the execution of the program is
commanded. Then, manipulator 11a whose operation is controlled by
controller 10a and manipulator 11b whose operation is controlled by controller
10b start the operations. After a while, welding electrode 18a and welding
electrode 18b reach respective positions shown by P210. These positions are
those before welding, and welding electrode 18a is not required to be close to
welding electrode 18b. The operations of manipulator 11a and manipulator
11b continue, and welding electrode 18a and welding electrode 18b reach weld
line 20 to be close to each other as shown by P211. Then, both welding
electrodes start to generate arcs (P211 is welding start point), and the welding
is performed in each specified welding condition. Welding electrode 18a and
welding electrode 18b move along weld line 20 at a welding speed specified as
the welding condition. When welding electrode 18a and welding electrode 18b
reach respective positions shown by P212, both welding robots complete the

welding (P212 is welding end point). Then, the welding electrodes evacuate
from weld line 20, the closing state between welding electrode 18a and welding
electrode 18b is canceled as shown in P213, and they move to separate positions
in air.
One example of the program for performing such operation is shown as
PRG 2 in Fig. 3. Fig. 3 shows one example of the program for performing the
operation of the welding system of the first exemplary embodiment of the
present invention. This program is stored in one of controller 10a and
controller 10b, and stored in a storage section (not shown) in controller 10a of
the master, for example.
In Fig. 3, command L201 commands that welding electrode 18a and
welding electrode 18b move to respective positions shown by P210. Command
L202 commands the welding condition used in welding. Command L203
commands that welding electrode 18a and welding electrode 18b move to
respective positions shown by P211. Command L204 commands that welding
electrode 18a as the leading electrode starts welding. Command L205
commands that welding electrode 18b as the following electrode starts welding.
Command L206 commands that two welding electrodes, namely welding
electrode 18a and welding electrode 18b, move to respective positions shown by
P212. Command L207 commands that welding electrode 18a as the leading
electrode completes the welding. Command L208 commands that welding
electrode 18b as the following electrode completes the welding. Command
L209 commands that two welding electrodes, namely welding electrode 18a and
welding electrode 18b, move to respective positions shown by P213.
As one technical characteristic of the first exemplary embodiment,
"storing processing" is performed where "positional data" of both welding robots
is stored as information showing the relationship between the control point of

the tip of welding electrode 18a and that of welding electrode 18b. "Storing
processing" of the first exemplary embodiment is described using Fig. 4. Fig. 4
shows the information processing of the first exemplary embodiment.
In "storing processing" shown in Fig. 4, predetermined operation a
discussed later is performed in a state where the master and slave have
relationship obtained by the welding conditioning work. Thus, the processing
executed in one of controller 10a of the master and controller 10b of the slave is
"storing processing". The processing may be executed by any of controller 10a
and controller 10b, but the processing is assumed to be executed by controller
10a of the master here. Operation a is assumed to be performed with the
operation panel (not shown) connected to controller 10a of the master. The
operation method and using tool do not directly concern the first exemplary
embodiment. This operation is used only for starting "storing processing", and
any operation may be employed for this purpose.
Fig. 4 shows an operation example of the welding robot during the
welding conditioning work. One of the purpose of the welding conditioning
work is to determine "relationship" required for obtaining a desired welding
result during the operation from P211 to P212 by adjusting the positional data
of both welding robots A and B constituting the teach points of P211 and P212.
When appropriate welding is obtained finally, the positional data of both
welding robots A and B constituting the teach points of P211 and P212 or the
positional data of both welding robots A and B during the operation from P211
to P212 shows the relationship required for obtaining the desired welding result.
In other words, the state where the master and slave have the relationship
obtained by welding conditioning work in starting "storing processing" shows
state 21 surrounded with the solid line shown in Fig. 4 where the operation
from P211 to P212 is stopped midway. Fig. 4 shows the example where

operation a is performed in this state and "storing processing" is started.
Positional data Pa of the master in the view from "robot coordinate
system" of the master when "storing processing" is started and positional data
Pb of the slave in the view from "robot coordinate system" of the master are
described. Positional data Pa and Pb (coordinate value or Euler angle) is
positional data in the coordinate system of the positions of the tips of welding
electrode 18a and welding electrode 18b surrounded with small rounds as
shown in Fig. 4-
Pa: (Xpa, Ypa, Zpa), (Upa, Vpa, Wpa)
Pa: (Xpb, Ypb, Zpb), (Upb, Vpb, Wpb).
Fig. 5 is a diagram showing the positional relationship between the tips
of welding electrodes 18a and 18b of two single-electrode welding torches 16a
and 16b of the welding system in accordance with the first exemplary
embodiment of the present invention. The part surrounded with the round in
the left diagram of Fig. 5 is enlarged to provide the right-side diagram. The
position in the coordinate system of positional data Pa and Pb shows coordinate
values (Xpa, Ypa, Zpa), (Xpb, Ypb, Zpb), and the angle between the coordinate
system and the straight line along the direction from the positions of positional
data Pa and Pb to the arranging part of welding electrodes 18a and 18b shows
Euler angles (Upa, Vpa, Wpa), (Upb, Vpb, Wpb).
As shown in Fig. 5, single-electrode welding torches 16a and 16b can be
made to take different attitudes according to the joint, so that convenience in
welding is improved. Fig. 5 shows the case where a fillet welding joint having
a chevron-shaped groove is welded. It is assumed that a fillet welding bead
having a certain leg length is required to be disposed on the groove part Gl. In
Fig. 5, leading welding electrode 18a performs first welding Wl of the groove
part Gl, and following welding electrode 18b performs second welding W2 of a

filler part. In this case, when the inclination of following welding electrode 18b
to leading welding electrode 18a is made large, a substantially flat bead shape
is obtained.
Not two welding systems but one welding system can weld a narrow part
that is difficult to be welded by a plurality of electrodes, so that reduction in
automation rate as the whole system can be prevented.
The welding system of the first exemplary embodiment is a typical
welding system for performing welding with a single-electrode welding torch
without using a special apparatus such as a torch for tandem welding or an
attaching mechanism for two-torch welding. Thus, the welding system is
constituted by typical apparatuses, so that replacement components are
obtained easily and inexpensively and the maintenance property is high.
The periphery of the welding torch can be more compact than that in the
case where a special apparatus such as the torch for tandem welding or the
attaching mechanism for two-torch welding is used. Thus, when the torch for
tandem welding or the attaching mechanism for two-torch welding is used, the
welding of a part which abuts on a peripheral member or the like of a welding
part to prohibit the welding is allowed, and the convenience becomes high.
In "storing processing" of the first exemplary embodiment, information
such as coordinate values and Euler angles in the coordinate system of
positional data Pa and Pb is stored in memory 40a as the storage section of
controller 10a of the master in Fig. 4, for example. The storage medium is not
necessarily limited to memory 40a of controller 10a of the master, and may be a
memory existing in another part. It is required that the information can be
stored and used in the process of "reproducing processing" discussed later. The
storage medium may be an external memory of a memory card or the like, and
may be a memory disposed in controller 10b of the slave.

As another technical characteristic of the first exemplary embodiment,
the relationship is reproduced by operating one of the master and slave robots
for the other robot. The process of "reproducing processing" of the first
exemplary embodiment is described using Fig. 6. Fig. 6 is a diagram showing
the reproducing processing in accordance with the first exemplary embodiment
of the present invention.
"Reproducing processing" is executed in a state where the master and
slave exist at any positions. This processing is started by predetermined
operation (31 or predetermined operation β2 in a state where the master or slave
exists in a place requiring reproduction of relationship or near that place, for
example. Operation β1 or operation β2 is assumed to be executed through an
operation panel (not shown) connected to controller 10a of the master. As the
apparatus of the operation panel, a teaching pendant or the like for teaching or
the like of a robot is used, for example. However, the operation method and
using tool do not directly concern the first exemplary embodiment. This
operation is used only for starting "reproducing processing", and any operation
may be employed for this purpose. Operation β1 differs from operation p2 in
which robot is used as the reference when the relationship is reproduced. For
example, in operation β1, the relationship is reproduced with reference to the
master. In operation p2, the relationship is reproduced with reference to the
slave.
At the time when "reproducing processing" is started, positional data Qa
of the master in the view from "robot coordinate system" of the master and
positional data Qb of the slave in the view from "robot coordinate system" of the
master are expressed by
Qa: (Xqa, Yqa, Zqa), (Uqa, Vqa, Wqa)
Qa: (Xqb, Yqb, Zqb), (Uqb, Vqb, Wqb).

As shown in Fig. 6, "reproducing processing" is started by performing
operation β1 or β2. In step S10, firstly, Pa and Pb of the information stored in
"reproducing processing" are read from memory 40a of controller 10a of the
master.
In step S20 of Fig. 6, the difference between positional data Pa and
positional data Pb, namely relative position difference Axyz and relative
attitude difference Auvw, are calculated. Relative position difference Axyz and
relative attitude difference Auvw are expressed by
Δxyz = (Xpb, Ypb, Zpb) - (Xpa, Ypa, Zpa)
Δuvw = (Upb, Vpb, Wpb) - (Upa, Vpa, Wpa).
Next, the process branches in step S30 according to which robot is used
as the reference when the relationship is reproduced. When "reproducing
processing" is started by operation β1, it is determined that the master is used
as the reference in step S30, the process goes to step S40. In step S40, the
slave position where the relationship to the master position is reproduced is
calculated. In other words, positional data Qab having relative position
difference Axyz and relative attitude difference Auvw to positional data Qa of
the master is calculated as follows'-
Qab : (Xqa, Yqa, Zqa) + (Xpb, Ypb, Zpb) - (Xpa, Ypa, Zpa), (Uqa, Vqa,
Wqa) + (Upb, Vpb, Wpb) - (Upa, Vpa, Wpa).
In step S50, positional data Qab determined in step S40 is converted into
the positional data of the slave in the view from "robot coordinate system" of the
slave. At this time, converting processing using a conversion matrix
expressing the positional relationship between the master and the slave is
performed, but this converting processing is a known technology and is not
especially described here.
In step S60, the slave is operated based on the positional data of the

slave determined in step S50. At this time, via inter-robot communication
cable X, processing such as a transfer of the positional data from the master to
the slave and an operation command from the master to the slave is performed.
Thus, when the master and the slave exist at any positions, the slave can
be operated to the position of the slave where the relationship is reproduced to
the position of the master. This operation is shown in Fig. 7. Fig. 7 is a
diagram showing an example of the reproducing processing based on the master
in accordance with the first exemplary embodiment of the present invention.
In Fig. 7, single-electrode welding torch 16a is the torch on the master side, and
single-electrode welding torch 16b is the torch on the slave side.
While, when "reproducing processing" is started by operation p2, it is
determined that the slave is used as the reference in step S30, the process goes
to step S80. In step S80, the master position where the relationship is
reproduced to the slave position is calculated. In other words, positional data
Qba having relative position difference Axyz and relative attitude difference
Auvw to positional data Qb of the slave in the view from "robot coordinate
system" of the master is calculated as follows:
Qba : (Xqb, Yqb, Zqb) - (Xpb, Ypb, Zpb) + (Xpa, Ypa, Zpa), (Uqb, Vqb,
Wqb) - (Upb, Vpb, Wpb) + (Upa, Vpa, Wpa).
Positional data Qba determined in step S80 is the positional data in the
view from "robot coordinate system" of the master. In step S100, the master is
operated to the positional data.
Thus, when the master and the slave exist at any positions, the master
can be operated to the position of the master where the relationship to the
position of the slave is reproduced. This operation is shown in Fig. 8. Fig. 8 is
a diagram showing an example of the reproducing processing based on a slave
in accordance with the first exemplary embodiment of the present invention.

In Fig. 8, single-electrode welding torch 16a is the torch on the master side, and
single-electrode welding torch 16b is the torch on the slave side.
In the first exemplary embodiment, when the relationship allowing a
desired welding is obtained by "welding conditioning work", information
showing the relationship at that time is stored. Then, during "teaching work",
the stored relationship is reproduced. Thus, the relative position and relative
attitude can be easily established during "teaching work".
When two welding robots having one welding electrode are used and
welding is performed while two welding electrodes are arranged close to each
other near the weld line in the welding progressing direction as in the
conventional tandem welding, the relationship which is the relative position
and relative attitude is important. Therefore, in performing such welding, the
first exemplary embodiment is especially effective.
In other words, in a control method of the robot system of the present
invention, two industrial robots are used, one industrial robot is used as a
master robot, and the other is used as a slave robot. The control method
includes a storing step, and a first operating step or second operating step. In
the storing step, data indicating the relation of the relative position and relative
attitude between the master robot and the slave robot is stored as one set of
information. In the first operating step, in a state where the master robot and
the slave robot exist at any positions, the slave robot is operated with respect to
the position of the master robot so as to reproduce the relation of the relative
position and relative attitude indicated by one set of stored information. In the
second operating step, in a state where the master robot and the slave robot
exist at any positions, the master robot is operated with respect to the position
of the slave robot so as to reproduce the relation of the relative position and
relative attitude indicated by the one set of information.

In this method, when there are two industrial robots such as welding
robots, by storing the relationship between them and reproducing them at any
time point, the time and effort for the operation for establishing the relationship
between two industrial robots before "associative movement control" can be
reduced. Thus, two arcs are generated by two torches and welding can be
performed at a predetermined position where the two arcs do not interfere with
each other, so that the bead shape can be optimized. As a result, welding
where the coupling strength is sufficient and the reliability is high can be
performed.
The following method may be used. The master robot is a welding robot
for holding one welding electrode, and the slave robot is also a welding robot for
holding one welding electrode. One set of information to be stored indicates
the relation of the relative position and relative attitude between the welding
electrode held by the master robot and the welding electrode held by the slave
robot.
In this method, the time and effort for the operation for establishing the
relationship between two industrial robots before "associative movement
control" can be further reduced.
One set of information to be stored indicates the relation of the relative
position and relative attitude between the welding electrode held by the mater
robot and that held by the slave robot when an appropriate welding condition is
determined. Here, the appropriate welding condition is determined by
performing the welding conditioning work of determining the appropriate
welding condition by performing welding many times while changing the
contents of the items of the welding condition. A method may be employed
where the relation of the relative position and relative attitude indicated by the
one set of stored information is reproduced when the teaching work of the

welding robot is performed.
This method can further reduce the time and effort for the operation for
establishing the relationship between two industrial robots before "associative
movement control".
(SECOND EXEMPLARY EMBODIMENT)
Fig. 9 is a diagram showing storing processing in accordance with a
second exemplary embodiment of the present invention. Fig. 10 is a diagram
showing reproducing processing in accordance with the second exemplary
embodiment of the present invention. A control method of a robot system of
the present invention is specifically described using Fig. 9 and Fig. 10. The
second exemplary embodiment differs from the first exemplary embodiment in
the form of the information stored by "storing processing".
The information stored by "storing processing" in the first exemplary
embodiment is used for reproducing the relationship by "reproducing
processing". This information is simply required to reproduce the relationship,
so that the information is not required to be positional data such as Pa and Pb
as shown in the first exemplary embodiment, but may be the calculation result
of relative position difference Axyz and relative attitude difference Auvw as
shown in Fig. 8 and expressed by
Δyz = (Xpb, Ypb, Zpb) - (Xpa, Ypa, Zpa)
Δuvw = (Upb, Vpb, Wpb) - (Upa, Vpa, Wpa).
In the first exemplary embodiment, relative position difference Axyz and
relative attitude difference Auvw are calculated by "reproducing processing".
In the second exemplary embodiment, however, they are calculated and stored
in "storing processing". Therefore, the process of "reproducing processing"
starts in step S25 in Fig. 10. In step S25, the calculation result of relative

position difference Axyz and relative attitude difference Auvw stored in the
memory by "storing processing" is used. The process from step S30 to step
S100 of Fig. 10 is similar to the process from step S30 to step S100 of Fig. 6 in
the first exemplary embodiment, so that the detailed description of the process
is omitted.
In the second exemplary embodiment, when the relationship allowing a
desired welding is thus obtained by "welding conditioning work", the
information showing the relationship is stored. Then, the information is
reproduced during "teaching work", and hence the relative position and relative
attitude can be easily established during "teaching work". Thus, two arcs are
generated by two torches and welding can be performed at a predetermined
position where the two arcs do not interfere with each other, so that the bead
shape can be optimized. As a result, welding where the coupling strength is
sufficient and the reliability is high can be performed.
(THIRD EXEMPLARY EMBODIMENT)
Fig. 11 is a diagram showing storing processing of a plurality of sets of
information in accordance with a third exemplary embodiment of the present
invention. Fig. 12 is a diagram showing the reproducing processing of a
plurality of sets of information in accordance with the third exemplary
embodiment of the present invention. A control method of a robot system of
the present invention is specifically described using Fig. 11 and Fig. 12. The
third exemplary embodiment differs from the first and second exemplary
embodiments in that a plurality of sets of information showing the relationship
between both robots is stored by "storing processing" and one set of information
is selected from the plurality of sets of stored information and reproduced by
"reproducing processing".

In the first exemplary embodiment and second exemplary embodiment,
one set of information indicating the relationship between both robots is stored,
and the reproduction is performed using it. Here, the information is a
combination of positional data Pa and positional data Pb, or a combination of
relative position difference Axyz and relative attitude difference Auvw. In the
third exemplary embodiment, the information showing a plurality of
relationships is stored and the relationship is reproduced using one set of
information selected from the plurality of sets of stored information.
In the following description, the positional data itself shown in the first
exemplary embodiment is stored. However, the relative position difference
and relative attitude difference shown in the second exemplary embodiment
may be stored.
Fig. 11 shows "storing processing" of the third exemplary embodiment.
Operation a for starting "storing processing" is performed together with setting
of identification code n (for example, identification number) for identifying the
information to be stored, and a plurality of sets of information is managed so as
to be specified with identification code n and stored in memory 40a of controller
10a of the master robot. Identification code n is number "1, 2, ..." for example,
and is stored in memory 40a in association with the information to be stored.
Fig. 11 shows this operation, and shows the example where n sets of
information are stored (identification code n is 1 through n).
In "reproducing processing" of Fig. 12, operation β1 or operation 02 for
starting "reproducing processing" is performed together with setting of
identification code n for identifying the information to be used. Identification
code n is described later. In step S15 of Fig. 12, one set of positional data is
selected from the plurality of sets of information in memory 40a in response to
identification code n and is used. The process from step S20 to step S100 of Fig.

12 is similar to the process from step S20 to step S100 of Fig. 6 in the first
exemplary embodiment, so that the description of this process is omitted.
In the third exemplary embodiment, information indicating a plurality of
relationships is stored, and one can be selected from them and reproduced
during "teaching work".
For example, when welding conditioning work is applied to a plurality of
different welding joints and relationships allowing a desired welding for each
welding joint are obtained, these relationships are stored in memory 40a in
association with code n associated with each welding joint. When operation |31
or operation (32 for starting "reproducing processing" is performed during
"teaching work" for a certain welding joint, the relationship appropriate to the
welding joint can be reduced by inputting identification code n associated with
the welding joint.
In other words, in a control method of the robot system of the present
invention, two industrial robots are used, one industrial robot is used as a
master robot, and the other is used as a slave robot. The control method
includes a storing step, and a first operating step or second operating step. In
the storing step, a plurality of sets of information each of which includes data
indicating the relation of the relative position and relative attitude between the
master robot and the slave robot is stored. In the first operating step, in a
state where the master robot and the slave robot exist at any positions, the
slave robot is operated with respect to the position of the master robot so as to
reproduce the relation of the relative position and relative attitude indicated by
one of the plurality of sets of stored information. In the second operating step,
in a state where the master robot and the slave robot exist at any positions, the
master robot is operated with respect to the slave robot so as to reproduce the
relation of the relative position and relative attitude indicated by one of the

plurality of sets of stored information.
In this method, when there are two industrial robots such as welding
robots, the plurality of relationships is previously stored, one relationship is
selected from the plurality of relationships, and the selected relationship is
reproduced at any time point. Thus, the time and effort for the operation for
establishing the relationship between two industrial robots before "associative
movement control" can be reduced. Thus, two arcs are generated by two
torches and welding can be performed at a predetermined position where the
two arcs do not interfere with each other, so that the bead shape can be
optimized. As a result, welding where the coupling strength is sufficient and
the reliability is high can be performed.
The following method may be used. The master robot is a welding robot
for holding one welding electrode, and the slave robot is also a welding robot for
holding one welding electrode. One set of information to be stored is
information indicating the relation of the relative position and relative attitude
between the welding electrode held by the master robot and the welding
electrode held by the slave robot.
In this method, the time and effort for the operation for establishing the
relationship between two industrial robots before "associative movement
control" can be further reduced.
One set of information to be stored indicates the relation of the relative
position and relative attitude between the welding electrode held by the mater
robot and that held by the slave robot when an appropriate welding condition is
determined. Here, the appropriate welding condition is determined by
performing the welding conditioning work of determining the appropriate
welding condition by performing welding many times while changing the
contents of the items of the welding condition. Then, when the teaching work

of the welding robot is performed, the relation of the relative position and
relative attitude indicated by one set of stored information is reproduced. The
method may be employed where information indicating the relation of the
relative position and relative attitude for each of the welding joints required for
the weld lines is stored, and information indicating the relation of the relative
position and relative attitude for each of the welding joints required for the
weld lines is reproduced.
This method allows each reproduction of the relative position and
relative attitude for each welding joint.
INDUSTRIAL APPLICABILITY
A control method of an industrial system of the present invention can
reduce the time and effort for the operation where the relationship obtained by
"welding conditioning work" when tandem welding is performed using two
welding robots discussed above is reproduced during teaching work of a
program for a welding part of an actual work piece. Further, in the work using
two industrial robots, for example when a welding robot welds a work piece
gripped by a handling robot or when one work piece is conveyed with two
handling robots, the operation load can be reduced in the case where the
relationship between two industrial robots is important for the work. This
control method is industrially useful.
REFERENCE MARKS IN THE DRAWINGS
10a, 10b controller
11a, 11b manipulator
12a, 12b welding power supply device
13a, 13b touch sensor unit

14a, 14b wire feeder
15a, 15b torch cable
16a, 16b single-electrode welding torch
17a, 17b arc sensor processing section
18a, 18b welding electrode
20 weld line
21 state
40a memory
121a, 121b torch terminal
122a, 122b base material terminal
123a, 123b, 124a, 124b cable
141a, 141b power feeding terminal

We Claim:
1. A control method of a robot system where two industrial robots are
used, one industrial robot is used as a master robot, and the other is used as a
slave robot, the control method comprising:
a storing step of storing, as one set of information, data indicating a
relation of relative position and relative attitude between the master robot and
the slave robot; and
a first operating step of operating the slave robot with respect to a
position of the master robot so as to reproduce the relation of the relative
position and relative attitude indicated by the one set of stored information in a
state where the master robot and the slave robot exist at any positions; or
a second operating step of operating the master robot with respect to
a position of the slave robot so as to reproduce the relation of the relative
position and relative attitude indicated by the one set of information in a state
where the master robot and the slave robot exist at any positions.
2. The control method of the robot system of claim 1, wherein
the master robot is a welding robot for holding one welding electrode,
and the slave robot is also a welding robot for holding one welding electrode,
and
the one set of information to be stored is information indicating a
relation of relative position and relative attitude between the welding electrode
held by the master robot and the welding electrode held by the slave robot.
3. The control method of the robot system of claim 2, wherein
the one set of information to be stored is information indicating a

relation of relative position and relative attitude between the welding electrode
held by the master robot and the welding electrode held by the slave robot when
an appropriate welding condition is determined, the appropriate welding
condition being determined by performing welding conditioning work of
determining the appropriate welding condition by performing welding many
times while changing contents of items of the welding condition, and
the relation of the relative position and relative attitude
indicated by the one set of stored information is reproduced when teaching work
of the welding robot is performed.
4. A control method of a robot system where two industrial robots are
used, one industrial robot is used as a master robot, and the other is used as a
slave robot, the control method comprising:
a storing step of storing a plurality of sets of information each of
which has data indicating a relation of relative position and relative attitude
between the master robot and the slave robot; and
a first operating step of operating the slave robot with respect to a
position of the master robot so as to reproduce the relation of the relative
position and relative attitude indicated by one of the plurality of sets of stored
information in a state where the master robot and the slave robot exist at any
positions; or
a second operating step of operating the master robot with respect to
a position of the slave robot so as to reproduce the relation of the relative
position and relative attitude indicated by one of the plurality of sets of stored
information in a state where the master robot and the slave robot exist at any
positions.

5. The control method of the robot system of claim 4, wherein
the master robot is a welding robot for holding one welding electrode,
and the slave robot is also a welding robot for holding one welding electrode,
and
the one set of information to be stored is information indicating a
relation of relative position and relative attitude between the welding electrode
held by the master robot and the welding electrode held by the slave robot.
6. The control method of the robot system of claim 5, wherein
the one set of information to be stored is information indicating a
relation of relative position and relative attitude between the welding electrode
held by the master robot and the welding electrode held by the slave robot when
an appropriate welding condition is determined, the appropriate welding
condition being determined by performing welding conditioning work of
determining the appropriate welding condition by performing welding many
times while changing contents of items of the welding condition, and
the relation of the relative position and relative attitude indicated by
the one set of stored information is reproduced when teaching work of the
welding robot is performed, information indicating the relation of the relative
position and relative attitude is stored for each of a plurality of welding joints
required for a plurality of weld lines, and information indicating the relation of
the relative position and relative attitude is reproduced for each of the plurality
of welding joints required for the plurality of weld lines.
7. The control method of the robot system of one of claims 2, 3, 5, and 6
wherein
movement of the welding electrode of one welding robot is followed

by movement of the welding electrode of the other welding robot, and the
welding electrode of the one welding robot and the welding electrode of the
other welding robot simultaneously perform welding for the same weld line in
the same direction.
8. The control method of the robot system of claim 7, wherein
welding is performed while a molten pool is formed in a welding
object by an arc generated between a welding object and the welding electrode
of the one welding robot and by an arc generated between the welding object
and the welding electrode of the other welding robot.

ABSTRACT

In a control method of a robot system of the present invention, one of two
industrial robots is used as a master robot, and the other is used as a slave
robot. Data indicating the relation of the relative position and relative attitude
between the master robot and the slave robot in welding conditioning work is
stored as one set of information. During teaching work, in a state where the
master robot and the slave robot exist at any positions, the slave robot is moved
with respect to the position of the master robot so as to reproduce the relation of
the relative position and relative attitude indicated by the one set of stored
information, or the master robot is moved with respect to the position of the
slave robot.