FIELD OF THE INVENTION
The present invention relates to robotic welding of ventilation spacer bars on
laminations sheets of stator core in steam turbine generator adapting spot welding
process. More particularly the invention relates to a method of offline determination
of robot operating path during welding of ventilation spacer bars in steam turbine
generators.
BACKGROUND OF THE INVENTION
Ventilation laminations required for cooling the stator core of the steam turbine
generator are manufactured by welding ventilation spacer bars on lamination sheets
using spot welding process. For a typical large generator, multiple ventilation
spacers are required to be welded to a lamination sheet. Each ventilation spacer bar
requires minimum welds at different locations resulting in hundreds of weld points
on a single lamination sheet.
In one of the prior art methods of an automated process of spot welding of spacer
bars of ventilation laminations, a robot holds the assembly consisting of ventilation
lamination and ventilation spacer bars by an end arm tool that is attached to the
wrist of a robot. The robot then moves the assembly around the tip of the spot
welding gun at a stationary sport welding machine. To eliminate hours of trial and

error time to create robot paths, a method of determining the operating path for the
robot using the CAD data is preferred. Thus method is developed off line and has
many other advantages such as maximizing uptime, throughput, and work-cell
utilization.
US 2002/0038855 Al describes a method for compensating the position of a robot
using a laser measuring instrument by establishing an origin coordinate system;
irradiating laser beams onto reflectors and calculating distances to the reflectors;
converting the origin coordinate system to an established coordinate system;
generating coordinates of an end of a lower tip of a Welding gun; calculating a
position and posture of the robot; teaching the robot four o more postures;
uploading position coordinates of the robot and robot teaching program data to a
main computer; determining if an error between CAD data and data modeled '
through simulation is less than a predetermined value, revising the data if it is not or
completing compensation of positions of the Welding gun, the robot and the jigs if it
is; and downloading the robot teaching program to a robot controller.
US 6522950 teaches a method of acquisition of data from predefined information
technology media, particularly from information technology-based design
environment of CAD type, but does not describe a method of off-line determination
of robot operating path during welding of ventilation spacer bars in steam turbine .
generators.

US 5511147 teaches apparatus and methods for graphically creating and visualizing
robot positions, orientations and trajectories in space and for controlling and
moving robots in accordance with graphical information.
None of the prior arts cited above directly correlate to the present invention which
relates to a method for generating a robot off-line program from CAD drawing the
spot welding applications.
OBJECTS OF THE INVENTION
It is therefore an object of the present invention to propose a robotic welding of
ventilation spacer bars on lamination sheets of stator core in steam turbine
generator adapting spot welding process.
SUMMARY OF THE INVENTION
Accordingly, there is provided a robotic' welding of ventilation spacer bars on
lamination sheets of stator core in steam turbine generator adapting spot welding
process the method comprising providing a spot welding machine with a welding
robot having a programmable robot controller; generating a CAD model of
ventilation laminations having a plurality of circles representing spot welding
positions extracting X,Y co-ordinate data of centre of said plurality of circles,
processing said data to produce off-line robot operational data; transferring the off-
line data to the robot controller; generating data representing possible movement
of an assembly consisting of the ventilation laminations and the spacer bars along X,
Y direction based on said data from the CAD model; and determining the operating •
path of the robot during welding of said ventilation laminations and the spacer bars.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Figure 1 shows an exemplary robotic welding of ventilation spacer bars on lamination
sheets of stator core in steam turbine generator adapting spot welding process.
Figure 2 shows a generator ventilation lamination with spacer bars and spot weld
positions.
Figure 3 shows a device for generating data for determining the operational path of a
robot during spot welding of ventilation spacer bars.
DETAILED DESCRIPTION OF THE INVENTION
Ventilation laminations 21 required for cooling a stator core of a steam turbine
generator which are manufactured by welding ventilation spacer bars 23 on
lamination sheets 21 using spot welding process. For a typical large generator, many
ventilation spacers are required to be welded to the lamination sheet,. Each .
ventilation spacer bar requires minimum welds 22 at different locations totaling to
more than 100 welding locations on a single lamination sheet 21.
In one of the methods of an automated process of spot welding of spacer bars 23 of
ventilation laminations 21, a robot 36 holds and moves the assembly consisting of
ventilation lamination 21 and ventilation spacer bars 23 by an end of an arm tool
attached to the wrist of the robot at a stationary spot welding machine (not shown).
The automated process reduces the cycle time quite substantially thus improving
productivity and reduction in fatigue of the operator.

The conventional method of determining a robot path is typically carried out by using
point-to-point method for each spot weld position 22. This new method is preferred
due to elimination of hours of time to create operating path for robot movement
without wasting time on trial and error calculations, which interalia eases of creating
the robot paths from CAD data. The innovative method also has many other
advantages such as maximizing uptime, throughput, and work-cell utilization.
In the embodiment of the present invention, an off-line method 34 for X-Y movement
of the assembly consisting of ventilation lamination 21 and spacer bars 23 is
generated by using the coordinates of spot welding obtained from CAD model 11.
In the embodiment of the present invention, a CAD model 11 of ventilation lamination
with circles representing spot welding positions is prepared using a computer 31 in
CAD software 32 such as AutoCAD. From the CAD model, the X, Y of coordinate data
12 of centre of circles representing spot welds is extracted and exported to an Excel
file 13, 33. The data is processed to 14 to suit the conversion to off-line robot
operational data. The processed data is converted to off-line robot path 15, 32 fef •
using VBA 34. The off-line robot program is.then transferred 16 to a robot controller
35 by means of portable and compatible devices such as USB stick or Compact Disk.
The robot reference frame is matched to CAD reference point 24 and the off-line
robot data is verified using the robot controller 35 that controls the movement of the
robot 36.

WE CLAIM :
1. A robotic welding of ventilation spacer bars on lamination sheets of stator
core in steam turbine generator adapting spot welding process, the
method comprising :
- providing a fixed spot welding machine with a robot having a
programmable robot controller;
- generating a CAD model of ventilation laminations having a plurality of circles
- representing spot welding positions;
extracting X,Y co-ordinate data of centre of said plurality of circles,
- processing said data to produce off-line robot operational data; transferring
the off-line data to the robot controller;
generating data representing possible movement of an assembly consisting
of the ventilation laminations and the spacer bars along X, Y direction
based on said data from the CAD model;
- and determining the operating path of the robot during welding of said
ventilation laminations and the spacer bars.

2. The method as claimed in claim 1, wherein the robot reference frame is
matched to the CAD reference point before transferring to the robot
controller.
3. The method as claimed in claim 1, wherein the processed data is
converted to off-line robot operating process for application.

ABSTRACT

The invention relates to a robotic welding of ventilation spacer bars on lamination
sheets of stator core in steam turbine generator adapting spot welding process
the method comprising providing a spot welding machine with a robot
having a programmable robot controller; generating a CAD model of ventilation
laminations having a plurality of circles representing spot welding positions
extracting X,Y co-ordinate data of centre of said plurality of circles, processing said
data to produce off-line robot operational data; transferring the off-line data to the
robot controller; generating data representing possible movement of an assembly
consisting of the ventilation laminations and the spacer bars along X, Y direction
based on said data from the CAD model; and determining the operating path of the
robot during welding of said ventilation laminations and the spacer bars.