FIELD OF THE INVENTION
The present invention generally relates to an End of arm tool including a pair of
templates for a robot to sandwich lamination sheets. More particularly the
invention relates to a device for automated robotic spot welding of ventilation
spacers over lamination sheets for turbo generators.
BACKGROUND OF THE INVENTION
Spot welding of ventilation spacers over lamination sheets is recognized to be
benefited heavily from automation, focusing on automatic robotic welding
process.
Ventilation Spacers are required for cooling the core of the stator of generator of
a thermal power plant. A lamination sheet is made up of Silicon steel, having
generally a thickness of 0.65 mm. The ventilation spacers are made up of Mild
Steel. The prior art process in the industry to weld space bars on a lamination
sheet is performed manually. It takes approximately 60 minutes to weld spacer
bars onto one lamination sheet manually. Automating this process can reduce
this time to as low as 15 minutes thereby increasing the production rate by at
least 400%. Also, for mass production, it is already established that the running
cost of an automated process is much lower than a manual process.
In one prior art (Refer Patent No. US20140001165), a spot welding system has
been proposed using a 6 axis robot fitted with a spot welding gun.

In another prior art (Refer Patent No. US 20090001056), the method of
positioning of a spot welding robot having a moving welding gun has been
disclosed.
In yet another prior art (Refer Patent No. US 4842451), a spot welding robot
system is disclosed, which comprises a spot welding gun unit fixed to an
articulated general-purpose robot or the like, and having a servo motor as the
open/close drive source of spot welding chips, a robot controller, a welding
current control section and a main controller has been proposed.
In a still another prior art (Refer US patent US 20050263496), there is provided a
system comprising a spot welding system including first and second spot welding
robots, and a communication line connecting the first and second spot welding
robots with each other so as to permit communication there between.
OBJECT OF THE INVENTION
It is therefore an object of the invention to propose a device for automated
robotic spot welding of ventilation spacers over lamination sheets for turbo
generators.
SUMMARY OF THE INVENTION
Accordingly, there is provided a device for automated robotic spot welding of
ventilation spacers over lamination sheets for turbo generators. The device
having a pair of templates to allow sandwiching of the lamination sheets
between them, the end of the arm tool fitted with a flange to hold the lamination
sheet along with bars sandwiched between a pair of templates and allow the

complete assembly to move through a pre programmed path for precise welding;
the upper template for precisely holding the space bars in their defined positions,
the lower template for supporting the weight of the lamination sheet with the
space bars with a minimum deflection of the upper template; wherein, the
templates are positioned such that the movement of the robot including the
welding operation is not obstructed.
The automated process according to the application area disclosed in the present
disclosure, employs a robot to move the lamination sheet through a precise path
which corresponds to the location of the weld-spots. As the lamination sheet
needs to be suspended off the robot’s flange for the entire duration of the
process, it becomes necessary to provide a rigid support to the lamination sheet.
Also, the space bars need to be held in their defined position before they are
welded. The lamination sheet is very thin and undergoes considerable deflection
under its own weight. While supporting the lamination sheet, the welding
operation, it is essential that should not be suspended intermittently.
BRIEF DESCRIPTION OF THE ACCOMPANING DRAWINGS
Figure 1 Shows a distal member of an Arm Tool of the welding machine
according to the invention.
Figure 2 Shows an Upper Template of a pair of template forming the device
of the invention.
Figure 3 Shows a Lower Template of the pair of template forming the device
of the invention.
Figure 4 Shows the ventilation spacer bars of the generator.
Figure 5 Shows Holding Cups of the device of the invention.

As shown in figure 1, the End Arm Tool consists of a flange [1] made of
Aluminum alloy. The inner and outer diameter of this flange (1) varies according
to the design of the lamination sheet. M8 holes [2] are drilled to this flange (1)
through which the device is fitted to a robot wrist. Two L channels [3] are
attached to the flange (1). Six pneumatic clamps [8] are fitted to the L channels
(3) on each side. Through these channels (3), the lamination sheet and other
supporting templates are lifted. The End of the arm tool is fitted with the robot
flange (1) through said M8 holes [2] which in turn hold the lamination sheet
along with a plurality of ventilation spacer bars [7] sandwiched between a pair of
templates [5,6] and cause the assembly of spacers and lamination sheets to
move through a pre programmed path for precise welding.
The pair of templates (5,6) is required to enable mounting of the lamination
sheet onto the robot for automatic spot welding operation. Also, the Space bars
(7) to be welded are held in desired position by the upper template [5]. The
weight of the sub assembly of the upper templates (5) and the lamination sheet
along with the space bars (7) has to be supported by the lower template [6].
The weight of the device (which includes both of the templates, lamination sheet
alongwith the space bars, channels including grippers) must be safely below the
maximum pay load of the robot. The size of the templates (5,6) must be big
enough to allow grapping of the spacers without obstructing the path of the
robot in anyway.
The upper template [5] always hold the space bars [7] in place without hindering
the welding process. The spacebars [7] are disabled to slide around too much or
topple over while the robot is moving.

The lower template [6] allows the electrode of a spot welding machine to come
in full contact with the lamination sheet.
The templates [5,6], therefore, are formed with minimum possible weight
permitted by the other associated requirements.
The clamps [8] do not obstruct the path of the robot or the electrodes of the
spot welding machine during welding operation is performed. Therefore, the
clamps [8] hold the template beyond the outermost space bar. Hence the
templates [5,6] have been made wide enough to enable the clamps (8) to hold
them firmly in place. Therefore, at the narrowest gripping point, there is almost
15-20 mm free width available for the clamps [8].
Slots have been cut in the upper template [5] according to the size and position
of the space bars [7]. For the space bars [7] to remain in place there should be
sufficient material towards the ends of the slots and material from the middle
portion of the slot can be removed. The thickness of the upper template [5] also
has been maintained at minimum for minimum weight enough for convenient
manual handling of the template during set up.
Initially, an identical configuration was selected for both the templates by the
inventors, which revealed that the width of slots required for the lower template
[6] is greater than that of the upper template as it needs to allow the electrode
of the welding machine to reach the lamination sheet, wherein the entire length
of the slots was not required in the lower template [6] for allowing welding.
Thus, the slots were required only at the location of weld spots. Consequently,
slots in the lower templates have been replaced by holes to provide much
greater clearance for the electrode as they could be made much larger without
comprising the strength constraint. As a result, the design for the lower template
(6) consists of a plurality of holes of 20 mm diameter at the location of weld

spots. In the lower template [6] material has been removed from the position of
the weld spot.
The disclosed device configuration ensures that none of the holes are covered
up. Therefore, the material around the holes can be removed without affecting
the compatibility constraint.
The lamination sheet is provided with two holes. These holes can be used to
accurately align the templates (5,6) with the lamination sheet before mounting
the assembly on to the grippers. For this purpose, two aluminium cups [4] of
required thickness and diameter, same as that of the hole in the lamination sheet
with very little tolerance are used. These cups (4) are fixed on the lower
template (6); The lamination sheet and the upper template (5) can now be
aligned by simply aligning the holes with the aluminium cups (4).

WE CLAIM :
1. A device for automated robotic spot welding of ventilation spacers over
lamination sheets for turbo generators, comprising :
- a distal member provided at the end of arm tool of an automated robotic
machine, the turbo generator having a plurality of ventilation spacers (7)
formed of steel and disposed at the core of stator for cooling, wherein a
plurality of lamination sheets made up of silicon steel is spot-welded on
said spacers by the welding machine, the device further comprising :
- a flange (1) having inner and outer diameter corresponding to that of the
lamination sheet, including a plurality of drilled holes (2), the distal
member releaseably connected to the arm tool via said drilled holes (2) of
the flange to up-lift the robot;
- at least one each L-shaped channel (3) disposed on either side of said
flange (1) and rigidly held by at least six pneumatic clamps (8);
- one upper templates (5) having slots allowing the laminated sheets
mounted on the robot and enable the assembly of the ventilation spacers
(7);
- one lower template (6) with plurality of holes allows the electrode of the
robotic welding machine to carry-out the spot welding between the
spacers (7) and the laminated sheets. The lamination sheets get
sandwiched between the two templates once the end of arm tool of the
robotic machine is actuated and moved along a programmed path for
spot-welding.

2. The device as claimed in claim 1, wherein the lamination sheet is provided
with two holes to align with the templates (5,6) for mounting, and
wherein two cups (4) are provided to hold the assembly of spacers and
lamination sheet onto the grippers of the machine.