WO2024110056A1

WO2024110056A1 - Spot welding gun and associated spot welding method

Info

Publication number: WO2024110056A1
Application number: PCT/EP2022/083351
Authority: WO
Inventors: Hermann Janning; Peter LADWIG
Original assignee: Framatome Gmbh
Priority date: 2022-11-25
Filing date: 2022-11-25
Publication date: 2024-05-30
Also published as: CN120152811A; KR20250093536A

Abstract

This spot welding gun (12), comprises a frame (18) and a movable group (20), movable along a welding direction (W-W') within the frame (18) and comprising: - an outer unit (28) comprising a proximal electrode (34) and an outer actuation flange (38), - an inner unit (30) comprising a distal electrode (44) and an inner actuation flange (48), - a clamping actuator (32) being connected to the inner actuation flange (48) and to the outer actuation flange (38), and configured for displacing said flanges (38, 48) to displace the proximal electrode (34) relatively to the distal electrode (44) along the welding direction (W-W'), the gun (12) comprising a compensation actuator (21), arranged between the frame (18) and the movable group (20), the compensation actuator (21) being configured to exert a biasing force to compensate the weight of the movable group (20) depending on an orientation of the welding direction (W-W').

Description

Spot welding gun and associated spot welding method

The present invention relates to a spot welding gun. The invention further relates to a spot welding method implemented by such a spot welding gun.

In the domain of nuclear power plants construction, and for example for pressurized water reactor nuclear power plants, it is critical to ensure a proper welding of parts that need to be welded. Such parts are for example structural parts of fuel element cages. Ensuring a controlled and reliable welding of such parts is thus critical to ensure durability and safety of these cages and more generally of the entire reactor comprising such cages.

In order to weld such parts, it is known to use spot welding guns mounted on robotic arms. Spot welding guns rely on electric resistance welding to weld parts together. Such guns generally comprise opposed electrodes that are intended to generate an electrical current conducted in the parts to be welded. In particular, parts to be welded are arranged between the opposed electrodes so that they are resistively heated by the current generated between the electrodes, resulting in a local welding of the parts.

The electrodes of such parts are generally mounted on units that are movable one relatively to another. Movement of such units, intend for example at pressing the electrodes around the parts to be welded, to ensure a proper welding of the parts. However, accuracy of robotic arms is not sufficient to allow for a proper centering of the parts to be welded between the electrodes, or in other words between the units that are moved one relatively to another, if said units are directly controlled from the robotic arm or the a frame of the gun.

In order to cater for such a deficiency, it has been proposed to use spot welding guns comprising a frame and a movable group, movable within the frame, which itself comprises the units that can be moved one relatively to another, the units comprising the electrodes.

Such spot welding guns are especially advantageous since the entire movable group can be moved relatively to the parts to be welded, within the frame. This ensures an “automatic centerin ’ of the group relatively to the parts to be welded. In particular, since the entire movable group can be moved within the frame, interaction of an electrode on one side of the parts to be welded can generate a displacement of the entire movable group, until the opposed electrode is pressed around the parts to be welded.

Such spot welding guns are however not entirely satisfactory. In particular, and since the whole movable group can be moved relatively to the frame, the weight of the movable group is not supported by the robotic arm, unless the movable group abuts parts of the frame in which the movable group can be moved. As a consequence, weight of the movable group is often supported by the parts to be welded, through the electrodes. This results in strain in the parts to be welded and also in an unbalanced welding effort between the opposed electrodes. This in terms leads to a poor welding quality.

It is therefore an aim of the present invention to propose a spot welding gun improving the quality of welding.

To this end, the subject matter of the invention relates to a spot welding gun for a welding robotic arm, comprising a frame and a movable group, movable along a welding direction within the frame, the movable group comprising:

- an outer unit comprising:

+ a proximal electrode,

+ a guiding element, elongated along an elongation axis parallel to the welding direction, the proximal electrode being attached to said guiding element, and

+ an outer actuation flange, the outer actuation flange being attached to the guiding element,

- an inner unit comprising:

+ a distal electrode,

+ a guided element, elongated along the elongation axis and movable in translation within the guiding element along the welding direction, the distal electrode being attached to the guided element,

+ an inner actuation flange, the inner actuation flange being attached to the guided element,

- a clamping actuator, defining a clamping actuation axis parallel to the welding direction, the clamping actuator being connected to the inner actuation flange and to the outer actuation flange, and configured for displacing said flanges to displace the proximal electrode relatively to the distal electrode along the welding direction, the spot welding gun further comprising a compensation actuator, arranged between the frame and the movable group, the compensation actuator being configured to exert a biasing force to compensate the weight of the movable group depending on an orientation of the welding direction.

The use of a movable group and of a compensation actuator configured to exert a biasing force to compensate the weight of the movable group is especially advantageous since it allows centering the electrodes around the parts to be welded while preventing any unbalanced efforts on the electrodes or induced strain in the parts to be welded. This results in a high quality of welding.

According to specific embodiments of the invention, the spot welding gun further comprises one or several of the features mentioned below, considered independently or along any technically possible combination: - the compensation actuator connects the frame and one of the outer unit and inner unit;

- the frame comprises a transversal flange, located between the outer actuation flange and the inner actuation flange, the movable group defining :

- a rest configuration, in which the transversal flange is pressed between both the inner and the outer actuation flange and in which the movable group is immobilized within the frame,

- an active configuration, in which at least one of the inner and outer actuation flange is spaced apart from the transversal flange and in which the movable group is movable along the welding direction, the movable group being reconfigurable between the rest and the active configuration by actuation of the clamping actuator to displace the inner actuation flange relatively to the outer actuation flange;

- the compensation actuator is actuated to exert a biasing force to compensate the weight of the movable group only when the movable group is in the active configuration;

- the frame comprises two guiding rails parallel to the welding direction, said guiding rails being configured to guide the movable group along the welding direction within the frame;

- one of the inner and outer units comprises at least one plastic spacer, said spacer being configured to guide the guided element within the guiding element;

- the clamping actuator comprises a flat cylinder;

- the distance between the clamping actuation axis and the elongation axis is inferior to 50 mm;

- the movable group further comprises a force sensor defining a sensor axis and configured to measure a welding force applied between the electrodes, the force sensor being connected to the clamping actuator, the sensor axis being aligned to the clamping actuation axis;

- the spot welding gun comprises a welding control module, connected to the force sensor and to the electrodes, and configured to activate the electrodes for welding only if a force measurement of the force sensor reaches a predetermined threshold; and

- wherein the spot welding gun comprises a compensation control module, the compensation control module being configured to detect a gravitational field to determine the orientation of the welding direction and to control the compensation actuator as a function of said determined orientation. According to some embodiments the invention further relates to a spot welding method implemented by a spot welding gun as above-mentioned, wherein the method comprises the following steps:

- providing of the spot welding gun and of at least one part to be welded ;

- displacing of the spot welding gun, so that the electrodes of the spot welding gun face the at least one part to be welded ;

- actuation of the clamping actuator to displace the electrodes one relatively to another along the welding direction ; and

- actuation of the compensation actuator to exert a biasing force to compensate the weight of the movable group of the spot welding gun, depending on an orientation of the welding direction.

In some embodiments, the invention further relates to a spot welding gun for a welding robotic arm, comprising a frame and a movable group, movable along a welding direction within the frame, the movable group comprising:

- an outer unit comprising:

+ a proximal electrode,

- an inner unit comprising:

+ a distal electrode,

- a clamping actuator, defining a clamping actuation axis parallel to the welding direction, the clamping actuator being connected to the inner actuation flange and to the outer actuation flange, and configured for displacing said flanges to displace the proximal electrode relatively to the distal electrode along the welding direction, the spot welding gun comprising a clamping actuator stopper, configured to limit the actuation of the clamping actuator so that the distance between the inner actuation flange and the outer actuation flange is limited to a predetermined value, the spot welding gun further comprising an abortion module, configured to command an abortion of a welding if the distance between the inner actuation flange and the outer actuation flange exceeds the predetermined value.

According to specific embodiments of the invention the predetermined value is inferior to a distance between the inner actuation flange and the outer actuation flange corresponding to a configuration of the movable group in which the electrodes are in contact.

According to some embodiments the invention further relates to a spot welding method implemented by a spot welding gun as above-mentioned, wherein the method comprises the following steps:

- providing of the spot welding gun and of at least one part to be welded ;

- limiting of the actuation of the clamping actuator by the clamping actuation stopper and subsequent welding abortion.

Other features and advantages of the invention will become apparent from a detailed description which is given thereof below, as an indication and by no means as a limitation, with reference to the appended figures, wherein:

- figure 1 is a schematic top view of a robotic arm comprising a spot welding device according to the invention, wherein the movable group of the welding device is in an active configuration ;

- figure 2 is schematic side view of the spot welding device of figure 1 ; and

- figure 3 is a view of the spot welding device as figure 1 , wherein the movable group of the welding device is in a rest configuration.

In the following description, the terms distal and proximal are understood in relation to a position on the spot welding gun relatively to where the spot welding gun is being held, for example by a robotic arm. A distal element is for example further away from an element holding the spot welding gun than a proximal element.

Referring to figure 1 , a robotic arm 10 comprises a spot welding gun 12.

The robotic arm 10 is for example 6-axis robotic arms, the spot welding gun 12 being arranged at an end 14 of said robotic arm 10. One understands that the spot welding gun 12 is for example mounted on the robotic arm 10 on a tooling port of the robotic arm 10, so that the robotic arm 10 comprise the spot welding gun 12 (non illustrated).

The spot welding gun 12 is preferably configured to weld parts 16 of a nuclear power plant such as a pressurized water reactor of a nuclear power plant. The parts 16, also referred to as “parts to be welded” hereinafter, are for example parts of fuel element cages for a pressurized water reactor.

As presented in more details later, the spot welding gun 12 is configured to weld parts 16 by spot welding, that is by local resistance welding of the parts 16. The spot welding gun 12 relies on Joule heating of the parts to be welded 16 to weld such parts together.

As illustrated in figures 1 to 3 the spot welding gun 12 comprises a frame 18 and a movable group 20. As this will be exposed in more details hereinafter, the movable group 20 is movable along a welding W- direction within the frame 18.

As this will be presented later, the spot welding gun 12 further comprises a compensation actuator 21 connecting the frame 18 and the movable group 20.

Referring to figures 1 to 3, the frame 18 comprises for example a body 22, a transversal flange 24 and comprises for example two guiding rails 26.

The frame 18 is for example substantially flat and defines a frame plane P-P. In other words, a width W of the frame 18, as visible from figure 1 , is for example substantially larger than a thickness T of the frame 18, as visible from the footprint of the frame 18 illustrated with dashed lines on figure 2.

As visible from figure 1 , the body 22 is for example arranged at least partially around the movable group 20. In particular, the body for example defines an inner volume 27 in which is movable the movable group 27.

As illustrated in figures 1 to 3, the body 22 is for example elongated along the welding direction W-W’.

The transversal flange 24 extends transversally within the body 22. The transversal flange 24 extends for example in the body 22 perpendicularly to the welding direction W- W. As illustrated in figures 1 and 3, the transversal flange 24 connects for example opposed walls of the body 22.

As illustrated in figure 1 , the guiding rails 26 are parallel to the welding direction W- W. The guiding rails 26 are for example connected to opposite walls of the body 22.

As presented on figures 1 to 3, the guiding rails extend for example through the transversal flange 24.

Each of the rails 26 comprises for example a rod of a diameter comprised between 5 mm and 20 mm and for example of 10 mm.

A distance D1 between the guiding rails is for example comprised between 20 mm and 100mm, for example between 40 mm and 80 mm, and is of example of 58 mm.

The guiding rails 26 define for example together a rail plane R-R that is substantially parallel to the frame plane P-P. As this will be presented in more details later, the guiding rails 26 are configured to guide the movable group 20 along the welding direction W-W.

As illustrated in figures 1 to 3, the movable group 20 comprises an outer unit 28, an inner unit 30 and a clamping actuator 32. The movable group 20 further comprises for example a force sensor 33.

As illustrated in figures 1 to 3, the outer unit 28 comprises a proximal electrode 34, a guiding element 36 and an outer actuation flange 38.

The guiding element 36 is elongated along an elongation axis E-E’ parallel to the welding direction W-W’.

The guided element 36 is for example movable in translation relatively to the frame 18 along the welding direction W-W. The guided element 36 is for example movable through an orifice (not referenced) of the body 22.

The guiding element 36 is for example tubular and has for example a circular transversal section.

A ratio of a length of the guiding element 36, measured along the elongation axis E- E’, over a width of the guiding element 36, measured transversally to the elongation axis, is for example superior to 5.

As illustrated on figures 1 to 3, the proximal electrode 34 is attached to the guiding element 36, for example at a distal end (not referenced) of the guiding element 36. For example, the outer unit 28 comprises an electrode port 42 connecting the proximal electrode 34 to the guiding element 36, the electrode port 42 extending radially relatively to the elongation axis E-E’.

In a specific embodiment, the term proximal electrode 34 should be understood as a group of proximal electrodes 34, such as for example two proximal electrodes 34.

As illustrated from figures 1 to 3, the outer actuation flange 38 is attached to the guiding element 36, for example opposite the proximal electrode 34. As illustrated from figures 1 to 3, the outer actuation flange 38 is for example attached to the guiding element 36 at a proximal end (not referenced) of the guiding element 36.

In a non-illustrated embodiment, the outer actuation flange 38 and the guiding element 36 are for example monolithic.

The outer actuation flange 38 preferably extends radially relatively to the elongation axis E-E’.

As visible from figures 1 and 2, the outer actuation flange 38 extends for example transversally within the frame 18. The outer actuation flange 38 for example comprises two guiding orifices 51 , configured to cooperate with the guiding rails 26 and to guide the displacement of outer unit 28 along the welding direction W-W within the frame 18.

As illustrated in figures 1 to 3, the inner unit 30 comprises a distal electrode 44, a guided element 46 and an inner actuation flange 48.

The guided element 46 is elongated along the elongation axis E-E’. The guided element 46 for example concentric to the guiding element 36.

The guided element 46 is for example tubular and has for example a circular transversal section.

A ratio of a length of the guided element 46, measured along the elongation axis E- E’, over a width of the guiding element 46, measured transversally to the elongation axis, is for example superior to 5.

As visible from figures 1 to 3, the guided element 46 is for example longer that the guiding element 36.

The guided element 46 is movable in translation within the guiding element 36 along the welding direction W-W’.

As visible from figures 1 to 3 in dashed lines, the guided element 46 is for example movable through the transversal flange 24 and the outer actuation flange 38 along the welding direction W-W, for example through orifices (non represented) of the transversal flange 24 and of the outer actuation flange 38. The guided element 46 is for example further movable through the body 22.

As illustrated on figures 1 to 3, the distal electrode 44 is attached to the guided element 46, for example at a distal end (not reference) of the guided element 46. For example, the inner unit 30 comprises an electrode port 50, connecting the distal electrode 44 to the guided element 46, the electrode port 50 extending radially relatively to the elongation axis E-E’.

In a specific embodiment, the term distal electrode 44 should be understood as a group of distal electrodes 44, such as for example two distal electrodes 44.

As illustrated in figures 1 to 3, the inner actuation flange 48 is attached to the guided element 46, for example opposite the distal electrode 44. As illustrated from figures 1 to 3, the inner actuation flange 48 is for example attached to the guided element 46 at a proximal end (not reference) of the guided element 46.

In a non-illustrated embodiment, the inner actuation flange 48 and the guided element 46 are for example monolithic.

The inner actuation flange 48 preferably extends radially relatively to the elongation axis E-E’. As visible from figures 1 and 2, the inner actuation flange 48 extends for example transversally within the frame 18.

The inner actuation flange 48 for example comprise two guiding orifices 43 configured to cooperate with the guiding rails 26 and to guide the displacement of inner unit 30 along the welding direction W-W’ within the frame 18.

As visible on figures 1 to 3, the flanges 38, 48 are for example movable on opposed sides of the transversal flange 24. In other words, the transversal flange 24 is arranged between the outer actuation flange 38 and the inner actuation flange 48.

As visible from figures 1 to 3, one of the inner 28 and outer 30 unit comprises at least one plastic spacer 52 configured to guide the guided element 46 within the guiding element 36.

The plastic spacer 52 is for example a spacer known under the commercial name of IGLUDUR W300.

The spacer 52 is for example attached to an inner face 54 of the guiding element 36 and configured to guide the guided element 46 within the guiding element 36. In alternative, the spacer 52 is attached to an outer face 56 of the guided element 46 and configured to be guided by the guiding element 36.

The clamping actuator 32 defines a clamping actuation axis C-C’ parallel to the welding axis W-W’. For example, the clamping actuator 32 comprises a cylinder 58 and an actuation element 60 movable relatively to the cylinder 58 along the clamping actuation axis C-C’. The actuation element 60 is for example elongated along the clamping actuation axis C-C’.

The clamping actuator 32 is for example a pneumatic or a hydraulic actuator.

The clamping actuator 32 is for example an actuator known as a “flat cylinder”, that is an actuator comprising a cylinder 58 that is flat. The cylinder 58 is for example a prismatic cylinder such as a parallelepipeds cylinder.

The actuator 32 is for example flat along a plane that is parallel to the frame plane P- P.

The distance D2 between the actuation axis and the elongation axis is for example inferior to 50 mm and for example equal to 33 mm.

The clamping actuator 32 is for example connected to the inner unit 28 and to the outer unit 30. In particular, the clamping actuator 32 is connected to the inner actuation flange 48 and to the outer actuation flange 38.

For example, and as this will be exposed in more details later, the clamping actuator 32 is for example connected to one of the inner actuation flange 48 and outer actuation flange 38 by the force sensor 33. In the example presented in figures 1 to 3, the cylinder 58 is fastened to the outer actuation flange 38, and the actuation element 60 is fastened to the inner actuation flange 48, though the force sensor 33.

The clamping actuator 32 is configured for displacing the inner unit 28 relatively to the outer unit 30. The clamping actuator 32 is in particular configured to displace the flanges 38, 48 to which it is connected, to displace the proximal electrode 34 relatively to the distal electrode 44, along the welding direction W-W.

The clamping actuator 32 is thus configured to displace the electrodes 34, 44 relatively to the parts to be welded 16, in particular to weld these parts 16.

The movable group 20 defines in particular a rest configuration, illustrated in figure 3 and an active configuration, illustrated in figure 1.

The movable group 20 is in particular reconfigurable between the rest and the active configuration by actuation of the clamping actuator 32 to displace the inner unit 30 relatively to the outer unit 28 and in particular, to displace the inner flange 48 relatively to the outer flange 38.

In the rest configuration, and as illustrated in figure 3, the transversal flange 24 is pressed between both the inner 48 and the outer 38 actuation flanges. In other words, the distance D3 between the inner 48 and the outer 38 flanges along the welding direction W- W is substantially equal to the width of the transversal flange 24 along the welding direction W-W’.

In the rest configuration, the movable group 20 is immobilized within the frame, the inner 38 and the outer actuation flanges 38 cooperating on both sides of the transversal flange 24 to maintain the movable group 20 on a fix position on the rails 26.

In the active configuration, and as illustrated in figures 1 and 2, at least one of the inner 48 and outer 38 actuation flanges is spaced apart from the transversal flange 24. In other words, the distance D3 between the inner 48 and the outer 38 flanges along the welding direction W- is bigger that the width of the transversal flange 24 along the welding direction W-W.

In the active configuration, the movable group 20 is movable along the welding direction W-W. In particular, the movable group 20 is movable along the rails 26 between a position in which one of the inner 48 and outer 38 flanges abuts the transversal flange 24 and another position in which the other of the inner 48 and outer 38 actuation flanges abuts the transversal flange 24.

The force sensor 33 is configured to measure a force applied between the distal electrode 44 and the proximal electrode 34. To that end, the force sensor 33 is for example connected to the outer unit 28 and to the inner unit 30. In particular, and as illustrated in figures 1 to 3, the force sensor 33 is for example connected to the outer unit 28 and to the inner unit 30 through the clamping actuator 32.

The force sensor 33 is for example arranged between the clamping actuator 32, attached to one of the inner 30 and outer 28 unit, and the other of the inner 30 and outer 28 unit. The force sensor 33 is therefore configured to measure the effort applied by the clamping actuator 32 on the inner 30 and outer 28 units, and is thus configured to measure the force applied between the electrodes 34, 44, that are, as seen above, each connected to a respective actuation flange 38, 48.

As illustrated in figures 1 to 3, the force sensor defines a sensor axis S-S’, along which it is configured to measure a force. The sensor axis S-S’ and the clamping actuation axis C-C’ are for example aligned. The force sensor 33 is for example configured to measure only efforts applied by the clamping actuator 32 along the clamping axis C-C’.

As illustrated in figures 1 to 3, the compensation actuator 21 is arranged between the frame 18 and the movable group 16 to connect the frame 18 and the movable group 20.

The compensation actuator 21 connects for example the frame 18 and one of the outer 28 and inner unit 30. In the example of figures 1 to 3, the compensation actuator 21 connects the frame 18 and the outer unit 28, and more specifically, the frame 18 and the outer actuation flange 38.

The compensation actuator 21 comprises for example a cylinder 62 and an actuation element 64. In the example of figures 1 to 3, the cylinder 62 is connected to the transversal flange 24 and the actuation element 64 is connected to the frame 18.

The compensation actuator 21 is for example a pneumatic or a hydraulic actuator.

The compensation actuator 21 is configured to exert a biasing force to compensate the weight of the movable group 20 depending on an orientation of the welding direction W- W’. By depending on an orientation of the welding direction W-W’, one understands that the biasing force depends on the orientation of the welding direction W-W’ relatively to an environment in which is operated the spot welding gun 12 and in particular relatively to a gravitational field in the environment where is operated the spot welding gun 12.

In a specific embodiment, and as will be presented in more details later, the compensation actuator 21 is actuated to exert a biasing force to compensate the weight of the movable group 20 only when the movable group 20 is in the active configuration. In particular, and since the movable group 20 is immobilized within the frame 18 when the movable group 20 is in its rest configuration, no biasing force is required to compensate the weight of the movable group 20.

As visible from figures 1 and 3, the spot welding gun comprises for example a compensation control module 66 and/or a welding control module 68. The compensation control module 66 is configured to detect a gravitational field to detect the orientation of the welding direction W-W. To that end, the compensation control module 66 either comprises a gravity sensor (not illustrated), or, is connected to a gravity sensor (not illustrated).

The compensation control module 66 is further configured to control the compensation actuator 21 as a function of the determined orientation. For example, the control module 66 is provided with a mass information of the movable group 20 and is configured to control the compensation actuator 21 as a function of the determined orientation and of the provided mass of the actuator.

As an example, based on the spot welding gun 12 illustrated on figures 1 to 3, if the spot welding gun 12 is horizontal, that is if the welding direction is horizontal, or in other words perpendicular to an ambient gravitational field, the compensation control module 66 controls the compensation actuator 21 so that it does not apply any effort between the frame 18 and the movable group 20. If the spot welding gun 12 is vertical, with its distal end upwards, the compensation control module 66 controls the compensation actuator 21 so that it pulls the movable group 20 upwards relatively to the frame 18 by applying and effort to the movable group 20 equal and opposed to the weight of said movable group 20. If the spot welding gun 12 is vertical, with its distal end downwards, the compensation control module 66 controls the compensation actuator 21 so that it pushes the movable group 20 upwards relatively to the frame 18 by applying and effort to the movable group 20 equal and opposed to the weight of said movable group 20.

It is understood that control module 66 controls the compensation actuator 21 so that the effort applied by the actuator 21 compensate the weight of the movable group 20 whatever the orientation of the welding direction W-W’, a component of the weight being in some cases supported by the frame 18, such as for example the rails 26.

The welding control module 68 is for example connected to a power source (not illustrated) and configured to supply the electrodes 34, 44 with electricity.

The welding control module 68 is for example connected to the force sensor 33 and to the electrodes 34, 44.

The welding control module 68 is for example configured to activate the electrodes 34, 44 for welding, or in other words to supply the electrodes 34, 44 from the power source, only if a force measurement of the force sensor 33 reaches, or in other words, is above, a predetermined threshold.

The welding control module 68 is for example further connected to an hydraulic or pneumatic power source (not illustrated) to control the clamping actuator 32, for example depending on instructions provided by a human machine interface (not illustrated). For example, the welding control module 68 is configured to activate the electrodes 34, 44 for welding, only if a force measurement of the force sensor 33 reaches a force equal to a preset value for the force at each of the electrodes 34, 44

For example, the spot welding gun 12 comprises an information processing unit comprising, for example, a memory associated with a processor (non illustrated).

In such an example, the compensation control module 66 and the welding control module 68 are for example each produced in the form of software executable by the processor. The memory is then able to store a weight compensation software, configured to detect a gravitational field to determine the orientation of the welding direction W-W’ and to control the compensation actuator as a function of said determined orientation. The memory is then also able to store a welding control software, configured to activate the electrodes 34, 44 for welding only if a force measurement of the force sensor 33 reaches a predetermined threshold.

The processor of the information processing unit is then able to execute the acquisition software, the filtering software and the command software.

In a variant (not shown), the compensation control module 66 and the welding control module 68 are each produced in the form of a programmable logic components, such as a FPGA (Field Programmable Gate Array), or in the form of a dedicated integrated circuit, such as an ASIC (Application Specific Integrated Circuit), or in the form of any combination of ASIC, FPGA and/or software.

In another variant (not shown) the compensation control module 66 and the welding control module 68 are each implemented as analog signal processing devices.

When the processing component is made in the form of one or several software programs, i.e., in the form of a computer program, it is further able to be stored on a medium, not shown, readable by computer. The computer-readable medium is for example a medium suitable for storing electronic instructions and able to be coupled with a bus of a computer system. As an example, the readable medium is an optical disc, a magnetic-optical disc, a ROM memory, a RAM memory, any type of non-volatile memory (for example, EPROM, EEPROM, FLASH, NVRAM), a magnetic card or an optical card. A computer program including software instructions is then stored on the readable medium.

According to another aspect of the invention, and as presented in the spot welding gun 12 illustrated on figures 1 to 3, the spot welding gun 12 comprises a clamping actuator stopper 70 and an abortion module 72.

In the example presented in figures 1 to 3, the spot welding gun 12 comprising a clamping actuator stopper 70 and an abortion module 72 comprises the features previously mentioned. In other embodiments, the spot welding gun 12 comprising a clamping actuator stopper 70 and an abortion module 72 does not comprise all the features previously described and for example does not comprise a compensation actuator 21 .

As schematically illustrated on figures 1 to 3, the actuator stopper 70 is configured to to limit the actuation of the clamping actuator 32 so that the distance D3 between the inner actuation flange 48 and the outer actuation flange 38 is limited to a predetermined value.

For example, the actuator stopper 70 is an adjustable stopper, so that the predetermined value can be adjusted by a user of the spot welding gun 12.

The predetermined value is for example inferior to a distance D3 between the inner actuation flange 48 and the outer actuation flange 38 corresponding to a configuration of the movable group 20 in which the electrodes 34, 44 are in contact.

In a specific embodiment, the predetermined value is for example equal to a distance D3 between the inner actuation flange 48 and the outer actuation flange 38 corresponding to a configuration of the movable group 20 in which the electrodes 34, 44 are in contact.

Alternatively, the predetermined value is for example equal to a distance D3 between the inner actuation flange 48 and the outer actuation flange 38 corresponding to a configuration of the movable group 20 in which the electrodes 34, 44 are spaced apart by less than 5mm.

The abortion module 72 is configured to command an abortion of a welding if the distance D3 between the inner actuation flange 48 and the outer actuation flange 38 exceeds the predetermined value. To that end, the abortion module 72 is for example connected to the actuator stopper 70.

For example, the abortion module 72 is connected to the electrodes 34, 44 and/or to the welding control module 68 to prevent the electrodes 34, 44 from being supplied with electricity if the distance D3 between the inner actuation flange 48 and the outer actuation flange 38 exceeds the predetermined value.

Furthermore, the abortion module 72 is for example connected to the clamping actuator 32 and/or to the welding control module 68 to deactivate the actuator 32, for example to bring the movable group 20 into a rest configuration if the distance D3 between the inner actuation flange 48 and the outer actuation flange 38 exceeds the predetermined value.

For example, and as presented above, the spot welding gun 12 comprises an information processing unit comprising, for example, a memory associated with a processor (non illustrated).

In such an example, the abortion module 72 is for example of similar form as the compensation control module 66 and the welding control module 68 and is for example produced in the form of software executable by the processor In a variant (not shown), the abortion module 72 is produced in the form of a programmable logic components, such as a FPGA (Field Programmable Gate Array), or in the form of a dedicated integrated circuit, such as an ASIC (Application Specific Integrated Circuit), or in the form of any combination of ASIC, FPGA and/or software.

In another variant (not shown), and similarly to the compensation control module 66 and the welding control module 68, the abortion module 72 is implemented as analog signal processing devices.

A spot welding method implemented by a spot welding gun as above described will now be presented.

In a providing step, a spot welding gun 12 as previously described and at least one part to be welded 16 are provided.

In a displacing step, the spot welding gun 12 is displaced so that the electrodes 34, 44 of the spot welding gun 12 face the at least one part 16 to be welded. For example, the spot welding gun is displaced so that the spot welding gun 12 face opposed faces of the at least one part 16 to be welded.

The spot welding gun 12 is for example displaced by the robotic arm 10 on which the spot welding gun 12 is mounted.

In a first actuation step, the clamping actuator 32 is actuated to displace the proximal electrodes 34 relatively to the distal electrodes 44, along the welding direction W-W’. For example, in the first actuation step, the clamping actuator 32 is actuated to reconfigure the movable group 20 from the rest configuration to the active configuration, the inner actuation flange 48 and the outer actuation flange 38 being pushed away one relatively to the other by the clamping actuator 32, the electrodes 34, 44 being thus brought closer one to the other.

In a second actuation step, occurring for example in parallel of the first actuation step, the compensation actuator 21 is actuated.

The compensation actuator 21 is in particular actuated to exert a biasing force to compensate the weight of the movable group 20 of the spot welding gun 12, depending on an orientation of the welding direction W-W’.

Furthermore, in alternative of the second actuation step, or in complement to the second actuation step for the spot welding gun illustrated in figures 1 to 3, the spot welding method comprises a limiting step.

In the limiting step, the actuation of the clamping actuator 32 is limited by the clamping actuator stopper 70 and a welding is subsequently aborted, for example by the abortion module 72. In particular, the actuator stopper 70 limits the distance D3 between the inner actuation flange 48 and the outer actuation flange 38 to a predetermined value. The abortion module 72 then commands for example an abortion of a welding, if the distance D3 between the inner actuation flange and the outer actuation flange exceeds the predetermined value, or for example, if the actuator stopper 70 limits the distance D3 between the inner actuation flange 48 and the outer actuation flange 38 to the predetermined value.

As understood from the above description, the use of a compensation actuator 21 is especially advantageous to improve the welding quality.

The use of a compensation actuator connecting the frame 18 and one of the outer unit 28 and inner unit 30 is especially advantageous to simplify the weight compensation mechanism.

A movable group defining a rest configuration and an active configuration is especially advantageous to ensure a centering of the electrodes 34, 44 while reducing the need of energy to compensate the weight of the movable group, especially when a biasing force is only applied when the movable group 20 is in its active configuration.

The use of parallel guiding rails 26 allows having an inter rail space that can be used to reduce the thickness of the spot welding gun 12.

The plastic spacers 52 are especially advantageous since such spacers 52 allow reducing friction between the outer unit 28 and the inner unit 30, thus further improving clamping precision and welding quality.

The use of a flat cylinder 58, of a limited distance D2 between the actuation axis C-C’ and the elongation axis E-E’, and a sensor axis S-S’ aligned with the actuation axis C-C’ allows a better control of the clamping between the electrodes 34, 44.

A conditional activation of the electrodes 34, 44 depending on a force measurement ensures a proper welding of the parts 16 to be welded.

The use of a clamping actuator stopper 70 and of an abortion module 72 as previously described is especially advantageous since this allows detecting missing electrodes 34, 44 and thus prevents any defective welding and dangers associated with a lack of electrode 34, 44.

Claims

1 Spot welding gun (12) for a welding robotic arm (10), comprising a frame (18) and a movable group (20), movable along a welding direction (W-W) within the frame (18), the movable group (20) comprising:

- an outer unit (28) comprising:

+ a proximal electrode (34),

+ a guiding element (36), elongated along an elongation axis (E-E’) parallel to the welding direction (W-W’), the proximal electrode (34) being attached to said guiding element (36), and

+ an outer actuation flange (38), the outer actuation flange (38) being attached to the guiding element (36),

- an inner unit (30) comprising:

+ a distal electrode (44),

+ a guided element (46), elongated along the elongation axis (E-E’) and movable in translation within the guiding element (34) along the welding direction (W-W), the distal electrode (44) being attached to the guided element (46),

+ an inner actuation flange (48), the inner actuation flange (48) being attached to the guided element (46),

- a clamping actuator (32), defining a clamping actuation axis (C-C’) parallel to the welding direction (W-W), the clamping actuator (32) being connected to the inner actuation flange (48) and to the outer actuation flange (38), and configured for displacing said flanges (38, 48) to displace the proximal electrode (34) relatively to the distal electrode (44) along the welding direction (W-W), the spot welding gun further comprising a compensation actuator (21 ), arranged between the frame (18) and the movable group (20), the compensation actuator (21 ) being configured to exert a biasing force to compensate the weight of the movable group (20) depending on an orientation of the welding direction (W-W).

2.- Spot welding gun (12) according to claim 1 , wherein the compensation actuator (21 ) connects the frame (18) and one of the outer unit (28) and inner unit (30).

3.- Spot welding gun (12) according to claim 1 or 2, wherein the frame (18) comprises a transversal flange (24), located between the outer actuation flange (38) and the inner actuation flange (48), the movable group (20) defining : - a rest configuration, in which the transversal flange (24) is pressed between both the inner (48) and the outer (38) actuation flange and in which the movable group (20) is immobilized within the frame (18),

- an active configuration, in which at least one of the inner (48) and outer (38) actuation flange is spaced apart from the transversal flange (24) and in which the movable group (20) is movable along the welding direction (W-W), the movable group (20) being reconfigurable between the rest and the active configuration by actuation of the clamping actuator (32) to displace the inner actuation flange (48) relatively to the outer actuation flange (38).

4.- Spot welding gun (12) according to claim 3, wherein the compensation actuator is actuated to exert a biasing force to compensate the weight of the movable group only when the movable group is in the active configuration.

5.- Spot welding gun (12) according to any of the preceding claims, wherein the frame (18) comprises two guiding rails (26) parallel to the welding direction (W-W’), said guiding rails (26) being configured to guide the movable group (20) along the welding direction (W-W) within the frame (18).

6.- Spot welding gun (12) according to any of the preceding claims, wherein one of the inner (30) and outer units (28) comprises at least one plastic spacer (52), said spacer (52) being configured to guide the guided element (46) within the guiding element (36).

7.- Spot welding gun (12) according to any of the preceding claims, wherein the clamping actuator (32) comprises a flat cylinder (58).

8.- Spot welding gun (12) according to any of the preceding claims, wherein the distance (D2) between the clamping actuation axis (C-C’) and the elongation (E-E’) axis is inferior to 50 mm.

9.- Spot welding gun (12) according to any of the preceding claims, wherein the movable group (20) further comprises a force sensor (33) defining a sensor axis (S- S’) and configured to measure a welding force applied between the electrodes (34, 44), the force sensor (33) being connected to the clamping actuator (32), the sensor axis (S-S’) being aligned to the clamping actuation axis (C-C’).

10.- Spot welding gun (12) according to claim 9, wherein the spot welding gun (12) comprises a welding control module (68), connected to the force sensor (33) and to the electrodes (34, 44), and configured to activate the electrodes (34, 44) for welding only if a force measurement of the force sensor (33) reaches a predetermined threshold.

11 .- Spot welding gun (12) according to any of the preceding claims, wherein the spot welding gun (12) comprises a compensation control module (66), the compensation control module (66) being configured to detect a gravitational field to determine the orientation of the welding direction (W-W) and to control the compensation actuator (21 ) as a function of said determined orientation.

12.- Spot welding method implemented by a spot welding gun (12) according to any of the claims 1 to 1 1 , wherein the method comprises the following steps:

- providing of the spot welding gun (12) and of at least one part (16) to be welded ;

- displacing of the spot welding gun (12), so that the electrodes (34, 44) of the spot welding gun face the at least one part (16) to be welded ;

- actuation of the clamping actuator (32) to displace the electrodes (34, 44) one relatively to another along the welding direction (W-W’) ; and

- actuation of the compensation actuator (21 ) to exert a biasing force to compensate the weight of the movable group (20) of the spot welding gun (12), depending on an orientation of the welding direction (W-W).

13.- Spot welding gun (12) for a welding robotic arm (10), comprising a frame (18) and a movable group (20), movable along a welding direction (W-W) within the frame (18), the movable group (20) comprising:

- an outer unit (28) comprising:

+ a proximal electrode (34),

+ a guiding element (36), elongated along an elongation axis (E-E’) parallel to the welding direction (W-W), the proximal electrode (34) being attached to said guiding element (36), and

- an inner unit (30) comprising:

+ a distal electrode (44), + a guided element (46), elongated along the elongation axis (E-E’) and movable in translation within the guiding element (34) along the welding direction (W-W), the distal electrode (44) being attached to the guided element (46),

- a clamping actuator (32), defining a clamping actuation axis (C-C’) parallel to the welding direction (W-W’), the clamping actuator (32) being connected to the inner actuation flange (48) and to the outer actuation flange (38), and configured for displacing said flanges (38, 48) to displace the proximal electrode (34) relatively to the distal electrode (44) along the welding direction (W-W), the spot welding gun comprising a clamping actuator stopper, configured to limit the actuation of the clamping actuator so that the distance between the inner actuation flange and the outer actuation flange is limited to a predetermined value, the spot welding gun further comprising an abortion module, configured to command an abortion of a welding if the distance between the inner actuation flange and the outer actuation flange exceeds the predetermined value.

14.- Spot welding gun (12) according to claim 13, wherein the predetermined value is inferior to a distance (D3) between the inner actuation flange (48) and the outer actuation flange (38) corresponding to a configuration of the movable group (20) in which the electrodes (34, 44) are in contact.

15.- Spot welding method implemented by a spot welding gun (12) according claim 13 or 14, wherein the method comprises the following steps:

- displacing of the spot welding gun (12), so that the electrodes (34, 44) of the spot welding gun (12) face the at least one part (16) to be welded ;

- actuation of the clamping actuator (32) to displace the electrodes (34, 44) one relatively to another along the welding direction (W-W) ; and

- limiting of the actuation of the clamping actuator (32) by the clamping actuation stopper (70) and subsequent welding abortion.