FORM-2
THE PATENTS ACT, 1970
(39 of 1970)
&
The Patents Rules 2003
COMPLETE SPECIFICATION
(SECTION 10 & Rule 13)
TITLE "A Spot Welding Robotic Gun System"
APPLICANT
We, Bajaj Auto Limited, an Indian Company, incorporated under the Indian Companies Act, 1956, having its registered office at Akurdi, Pune - 411 035, State of Maharashtra, India.
The following specification describes and ascertains the nature of this invention and the manner in which it is to be performed:-

A Spot Welding Robotic Gun System
I FIELD OF INVENTION
The present invention relates to spot welding robotic gun system.
II BACK GROUND OF THE INVENTION
Resistance welding, or spot welding, is used to join metal members, such as sheets or structures. The members to be welded are typically held together between a pair of electrodes. As the electrodes contact outer surfaces of the members, electric current passes through the members between the electrodes. The resistance of the members creates heat, which melts a portion of the members between the electrodes to form a spot weld. When a spot weld gun is used in robotic applications, the electrodes are commonly supported by pivoting arms actuated with a pneumatic cylinder or a servo actuator. Because of mounting restraints and inertia the electrodes of the weld gun do not actuate evenly, causing the electrodes to contact one of the metal members before the other. When the electrodes contact members are off centered or unequal force is caused on them, the electrodes will bend the assembly due to non alignment thereby causing indentations on the member and resulting weld is also weak.
Some of the prior arts are:
(1) WO 2008/110635 Al
The invention relates to a spot weld gun (1) comprising a base unit (20 arranged to be attached to a tool holder, a movable gun unit (4) with first (5) and a second electrode carrying arm (6). The spot weld gun further comprising an equalizing means (25) for balancing the movable gun unit (4) in relation to the fixed base unit (2) during welding operations. The base unit (2) comprises linear guide means (12, 13). The equalizing means (25) is arranged connecting the base unit (2) and the gun unit (4). The first (5) and the second electrode carrying arm (6) are sliding along the linear guide means (12,13) during balancing of the movable gun unit (4).
(2) US 8076604 B2
A plurality of linkages, preferably a robot holding either a spot welder with welding guns or the workpiece. The plurality of linkages move a spot welder with open tongs toward a first spot

weld position. The welding guns are then closed on the workpiece and welding is performed at the first spot weld position. While the welding is being performed, parts of the plurality of linkages are advanced toward a second weld position while the welding guns remained closed at the first spot weld position. When the welding at the first position is finished, parts of the linkages are already advanced towards the second position, and the remaining linkages are then advanced to the second position. This allows the linkages or robot to move faster from one spot welding position to another.
(3) US 2008/0272092 Al
A spot weld gun with thereto belonging power transmission being achieved by means of a rotating transformer including one primary side and one secondary side for transporting electrical power over a rotating joint. The one secondary side is adapted to provide both required power to weld current and any required auxiliary power.
III OBJECT OF THE INVENTION
The present invention relates generally to a welding assembly. More specifically the present invention relates to a spot welding assembly capable of creating two weld spots by using two weld guns.
The object of the invention is to provide a novel robotic system with twingun system but without increasing pay load capacity of an existing conventional single gun robotic system.
The objective of the invention is to increase the productivity of the process and reduce the cost of welding process.
Yet another objective is to reduce the capital cost or expenditure of spot welding machine.
This and other objects, features, and advantages of this invention will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, which are a part of this disclosure and which illustrate, by way of example, the principles of this invention.
IV Summary
The invention provides a spot welding robotic gun system for spot welding of work pieces. It has a robot which is a movable arm (118) around the workpieces. As per the invention a common

base plate means (110) has been designed to be mounted on to the said robot. The movable weld gun assemblies (119), preferably two of them are mounted onto the common base plate means (110). Each gun assembly (119) shall include a parallel set of electrodes (109), a gun cylinder (122) and also gun equalization means (114). A weld transformer (101, 102) is provided to each assembly. The transformers (101, 102) are operably associated with the gun assembly (119). The said transformer (101, 102) assemblies shall supply current controllably to the electrodes (109) from their secondary windings. These transformers (101, 102) as per the invention are novel to the extent that they are displaced and disposed away from the gun assembly (119). They are preferably mounted on mounting rails (105, 106) and spaced away from the associated gun assembly (119), thereby, reducing the load on the robotic system. A weld controller (not shown) is also part of the system which comprises of a logic control system. It further includes programmable software for interfacing the two guns and the welding cycle of the system. Through the programmable software the sequencing of the electric current between the pairs of electrode is managed selectively.
V Detailed Description of the Invention
The improvement according to the present invention is that the system comprises the transformers (101,102) are arranged to be spaced away the gun unlike an integral transformer. The system as per invention is an assembly including a robot. The robotic arm (118) is movable around the workpieces. As per the invention a common base plate means (110) has been designed to be mounted on to the said robot. The said movable weld gun assemblies, preferably two of them are mounted onto the common base plate means (110). Each gun assembly (119) shall include a parallel set of electrodes (109), a gun cylinder (122) and also gun equalization means (114). The said weld transformers (101, 102) are provided to each gun assembly. The transformers (101, 102) are operably associated with the gun assembly (119). The said transformers (101, 102) assemblies shall supply current controllably to the electrodes (109) from their secondary windings. These transformers (101, 102) as per the invention are novel to the extent that they are displaced and disposed away from the gun assemblies (119). It is preferably mounted on mounting rails (105, 106) and spaced away from the associated gun assembly (119), thereby, reducing the load on the robotic system. The said weld controller is also part of the system which comprises of a logic control system. It further includes programmable software for interfacing the two guns and the welding cycle of the system.

Through the programmable software the sequencing of the electric current between the pairs of electrode is managed selectively.
In another aspect of the invention, the gun assembly (119), i.e., both the guns are mounted on the common base plate (110) to be in alignment with the robot axis (125) such that the centre of gravity (124) of the gun assembly (119) mounted on base plate (110) is so aligned with the centre of gravity of the robot axis (125) which is achieved by arranging the two gun assemblies (119) in a manner as illustrated in the accompanying drawings. Thus the robot axis (125) and the gun assembly axis (126) are made to coincide with each other.
This has done by removing the transformers (101, 102) and mounting them separately on rails (105, 106). The existing centre of gravity (124) of the guns which would necessarily have been disturbed is hence adjusted/ compensated suitably. Both the guns are mounted on a common base plate (110) and manually weight of both the guns is balanced by hanging on hoist. From center of base plate X and Y co-ordinates are measured and entered into robot memory to arrive at the aligned arrangement.
The system in another aspect shall comprise of the gun equalization means (114) which is a set of springs, each spring having one end fixed on the common base plate (110) and other end fixed to the gun cylinder (122) of the gun assembly (119).
In another aspect of the invention, the gun cylinder (122) is pneumatically operable.
In another aspect of the invention, the gun cylinder (122) is pneumatically operable and further comprising of an auxiliary cylinder (132).
In another aspect of the invention the said auxiliary cylinder (132) is also pneumatically operable and shall comprise of reed switch. The said auxiliary cylinder shall have two positions. It can be held at forward position and a high lift position (111). When it is in the forward position, it restricts the piston down stroke movement. When it is in high lift position, the cylinder (132) is actuated backwards thereby enabling the gun cylinder (122) to reach BDC thereby allowing the gun tips to open fully.
In another aspect of the invention the guns comprising in the above assembly is selected from any conventional or manual spot welding system.
In another aspect of the invention the gun may be heavy in weight.

In another aspect of the invention the guns shall be light in weight. Typically weight of a conventional gun with transformer (2) is 120 Kg and whereas weight of a conventional gun without transformer (101,102) is 70Kg with this arrangement as disclosed in the invention.
In another aspect of the invention the weld controller with the logic control system comprises interfacing logic for essentially moving the guns with respect to each other and with specific reference to the welding cycle such that the logic is characterized in enabling simultaneous operation of the two guns or independent operation of the two guns. It also further enables operation of the one of the selected two guns.
VI While the invention has been described by reference to certain preferred embodiments, it should be understood that numerous changes could be made within the spirit and scope of the inventive concepts described. Accordingly, it is intended that the invention not be limited to the disclosed embodiments, but that it shall have the full scope permitted by the language of the claims.
VII These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.
VIM Fig. 1 illustrates a Conventional Gun Welding Arrangement.
Fig. 2 and 2A illustrates side view of the system as shown in Fig. 1.
Fig. 3A and 3B illustrates the side view of the system as shown in Fig. 1 with a portion marked for better view.
Fig. 4 illustrates front view of the robotic system of the invention.
Fig. 5 illustrates top view of the robotic system of the invention.
Fig. 6 illustrates the various views of Robotic twin gun (two guns mounted on common base plate) according to the invention
IX The present invention relates generally to a welding assembly but more specifically, the present
invention relates to a spot welding assembly that provides spaced welds on weldable members with the novel system of weld assembly.

X Thus, the need for a welding device that can provide simultaneous two spot-welds on members without moving the members. The present invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art with this disclosure.
XI An additional and specific aspect of the software is known by those skilled in the art as "equalization". The process of equalization in this invention ensures that the pressure generated additionally by the pair of weld tips is equal on both sides of the workpieces. The software of the present invention provides methods for equalization, even when the weld gun has to make adjustments for uneven tip wear.
The software with required inputs is enabling equalization on twin gun electrodes (109) by actuating the components like arm cylinder.
The software may or may not do automatic managing of tip wear but essentially atleast generates an alarm as per predetermined specified frequency for dressing or tip replacement. The software includes the above referred logic.
XII By using welding guns with non integral transformers (101, 102) on its programmable welding robots, it has been found that it can make those robots more efficient and versatile.
XIII In conventional robot welding installations, where heavy cabling is required because the transformer (2) is mounted overhead, the secondary electrical requirements are cumbersome, and do not allow the robots to make smoothly all the moves they are capable of making, but this invention overcomes this problem also with the arrangement as described above
XIV It can thus be appreciated that the objectives of the present invention have been fully and effectively accomplished in the invention. The foregoing specific embodiments have been provided to illustrate the structural and functional principles of the present invention and are not intended to be limiting. To the contrary, the present invention is intended to encompass all modifications, alterations, and substitutions within the spirit and scope of the appended claims.

XV Description of Numerals:
Sr. No. Part Name And Number For Figures 1, 2, 2A, 3A and 3B
1 Longitudinal Rail
2 Conventional Transformer
3 Kickless Cable
4 Jumper Cable
5 Cross Rail
6 Movable Gun Arm Of Gun Unit
7 Fixed Gun Arm Of Gun Unit
8 Balancer
9 Electrode
10 Cytinder
11 Handle
12 Stopper

14 Gun Bracket
15 Robot Arm
16 Robot Axis
17 Centre Of Gravity Of Gun Structure
18 Gun Axis In Longitudinal Direction
19 Gun Assembly Axis In Vertical Plane

21 High Lift Cylinder
22 Gun Cylinder
23 Gun Bracket
24 Robotic Arm
30 Equilising Springs
Sr. No. Part Name And Number For Figures 4,5 and 6
101 Transformer 1
102 Transformer 2
103 Kickless Cable 1
104 Kickless Cable 2
105 Cross Rail
106 Longitudinal Rail
107 Movable Gun Arm
108 Fixed Gun Arm
109 Electrode
110 Common Base Plate
111 High Lift Cylinder
112 Jumper Cable
113 Cylinder

114 Spring
115 Pivot
116 Pivot Pin
117 Robot Base
118 Robot Arm
119 Gun Assembly
120 Robot Controller
121 Axis Of Robot Base
122 Gun Cylinder
123 Gun Axis
124 Centre of Gravity
125 Robot Axis
126 Gun Assembly Axis
127 Gun Bracket

131 Axis of Base Plate 110
132 Auxiliary Cylinder

WE CLAIM:
1. A spot welding robotic gun system for spot welding a work piece comprising of:
a. A robot movable about the workpiece
b. a common base plate (110) mounted to the said robot
c. a pair of moveable spot weld gun assembly (119) mounted on the common base plate
(110) and each gun assembly (119) comprising atleast of a pair of parallel electrodes
(109), a gun cylinder (122) and a gun equalization means,
d. a weld transformer (101, 102) assembly operably associated with each of the said pair
of gun assembly (119), said transformer (101, 102) assembly supplying current
controllably to the electrodes (109) by secondary winding of the transformers (101,
102), said transformers (101,102) characterized in that the transformers (101,102) are
disposed on mounting rails (105,106) spaced away from the said pair of associated gun
assemblies (119),
e. a weld controller with a logic control system comprising of interfacing the two guns and
the welding cycle of the system by selective sequence of the electric current between
said pairs of electrodes (109), and
f. Cables preferably electrically coupling the transformers (101, 102) to the weld
controller.
2. The spot welding robotic gun system as claimed in claim 1 wherein each of said gun assembly (119) is mounted on common base plate (110) in alignment with robot axis (125) such that the C.G. (124) of the gun assembly (119) mounted on base plate (110) is aligned with C.G. of the robot axis (125).
3. The spot welding robotic gun system as claimed in claim 1 wherein said gun equalization means (114) comprises of springs, one end of each spring being fixed on common base plate (110) and other end fixed to the gun cylinder (122) of the gun assembly (119).
4. The spot welding robotic gun system as claimed in claim 1 wherein the said gun cylinder (122) is pneumatically operable and comprising of an auxiliary cylinder (132).

5. The spot welding robotic gun system as claimed in claim 5 wherein said auxiliary cylinder (132) is pneumatically operable and comprising of reed switch; the said auxiliary cylinder having two positions a forward position and high lift position, such that when in forward position it restricts the piston down stroke movement and in high lift position the auxiliary cylinder is actuated backwards enabling gun cylinder (122) to reach BDC allowing gun tips to open fully.
6. The spot welding robotic gun system as claimed in claim 1 wherein said pair of guns selected from conventional or manual spot welding system.
7. The spot welding robotic gun system as claimed in claim 1 wherein said pair of guns may also be selected from conventional or manual spot welding system
8. The spot welding robotic gun system as claimed in claim 1 wherein said pair of guns is selected from conventional or manual spot welding system which are light in weight.
9. The spot welding robotic gun system as claimed in claim 1 wherein the logic control system comprises an interfacing logic for moving the guns with respect to each other and with reference to the welding cycle, the said logic characterized in that it enables simultaneous or independent operation of the said two guns.
10. A method for spot welding a work piece with a spot welding robotic gun system comprising of
a. providing a movable robo around the work piece.
b. mounting a common base plate (110) on the said movable robo.
c. mounting a pair of movable spot welding guns on the said base plate means and
providing each gun assembly (119) with atleast a pair of parallel electrodes (109), a gun
cylinder (122) and a gun equalization means (114).
d. operably associating a weld transformer (101, 102) assembly with each of the said pair
of gun assembly (119) wherein the transformer (101, 102) assembly supplying current
controllably to the said electrodes (109) by secondary winding of the transformer (101,
102) and the said transformer (101, 102) characterized in being spaced away from the
said pair of associate gun assemblies (119) and disposed on a distanced mounting rails
(105,106).

e. providing a logic control system in a weld controller for interfacing the two guns and the
welding cycle of the system by selectively sequencing the electric current between the
pairs of electrodes (109), and
f. coupling the said transformer (101,102) to the weld controller preferably with electrical
cables.