WO2012049130A1

WO2012049130A1 - Methods of and apparatuses for balancing electrode arms of a welding device taking into account spatial orientation

Info

Publication number: WO2012049130A1
Application number: PCT/EP2011/067659
Authority: WO
Inventors: Florian Braun; Thomas Halach; Frank Schnur; Thomas Laubacher
Original assignee: Norgren Gmbh
Priority date: 2010-10-14
Filing date: 2011-10-10
Publication date: 2012-04-19
Also published as: DE112011103453T5

Abstract

A method of balancing electrode arms (101, 102) of a welding device (100) is provided. The welding device (100) includes a first electrode arm (101) and a second electrode arm (102) movable with respect to one another. The first and second electrode arms (101, 102) are coupled to a reference arm (30). The welding device (100) further includes a compensation actuator (106) coupled to the first electrode arm (101) and the reference arm (30) to balance a weight of the electrode arms (101, 102). The compensation actuator (106) includes first and second fluid chambers. The method of balancing the electrode arms (101, 102) includes a step of determining a balance force between the first electrode arm (101) and the reference arm (30) when the welding device (100) is in a first spatial orientation. The welding device (100) is then moved into at least a second spatial orientation and a differential pressure between the first fluid chamber and the second fluid chamber of the compensation actuator (106) is adjusted to maintain the balance force.

Description

METHODS OF AND APPARATUSES FOR BALANCING ELECTRODE ARMS OF

A WELDING DEVICE TAKING INTO ACCOUNT SPATIAL ORIENTATION

TECHNICAL FIELD

The present invention relates to, welding devices, and more particularly, to a method and apparatus for balancing electrode arms of a welding device.

BACKGROUND OF THE INVENTION

Welding devices, such as resistance spot welding devices, ultrasound welding devices, etc., are known in the art such as from European Patent 1 830 979, which is assigned on its face to the present applicants and is hereby incorporated by reference. Spot welding devices typically include two opposing electrode arms that are moved into position using two fluid operated actuators. One of the electrode arms is generally considered a "static" arm and movement is generally limited while the other electrode arm, called the "dynamic" arm moves a much greater distance to move into position to perform a welding operation. The first fluid operated actuator, often called a clamping actuator, is coupled to both electrode arms. The clamping actuator controls the general movement of the arms in order to contact the sheets to be welded. The second fluid operated actuator, often called a compensation actuator, is coupled to a stationary component, such as a robot arm and to the static electrode arm. The compensation actuator is actuated to maintain a constant force on the arms to avoid damaging the sheets. In other words, the compensation actuator counters the weight of the static arm to prevent the clamping action from bending the sheets being welded. This so-called "weight compensation" is often maintained using the double acting actuator through a variable differential pressure between the two chambers of the compensation actuator.

As can be appreciated, the differential pressure required to maintain an appropriate weight balance of the static electrode arm changes for each weight force depending on the spatial orientation of the electrode arms. For example, if the robot arm moves the electrode arms such that the arms extend in a vertical orientation, the majority of the weight of the arms will not act to close the electrodes towards one another and thus, a smaller differential pressure is required to counter the weight of the electrode arms. Conversely, if the electrode arms extend in a horizontal direction, the weight of the arms acts to close the arms towards one another or rotate about the robot arm and thus, a larger differential pressure may be required to maintain a weight balance. Because of the change in weight compensation with respect to the spatial orientation, the differential pressure required varies based on the spatial orientation of the electrode arms.

The prior art welding devices have attempted to maintain the proper force by accounting for the weight of the electrode arms in various spatial positions. However, the prior art approaches often require complex systems or provide systems that perform inadequately. It is not only the weight of the electrode arms that needs to be accounted for, but also the force provided by the clamping actuator and the compensation actuator.

Therefore, there is a need in the art for a system and method for properly balancing the electrode arms of a welding device. Further, there is a need in the art for a system and method that accurately and reliably checks proper balancing of the electrode arms of a welding device. The present invention overcomes these and other problems and an advance in the art is achieved.

SUMMARY OF THE INVENTION

A method for balancing electrode arms of a welding device is provided according to an embodiment of the invention. The welding device includes a first electrode arm and a second electrode arm movable with respect to one another and coupled to a reference arm. The welding device further includes a compensation actuator, including first and second fluid chambers, coupled to the first electrode arm and the reference arm to balance a weight of the electrode arms. According to an embodiment of the invention, the method comprises determining a balance force between the first electrode arm and the reference arm when the welding device is in a first spatial orientation. According to an embodiment of the invention, the method further comprises a step of moving the welding device into at least a second spatial orientation. According to an embodiment of the invention, the method further comprises a step of adjusting a differential pressure between the first fluid chamber and the second fluid chamber of the compensation actuator to maintain the balance force.

A method for balancing electrode arms of a welding device is provided according to an embodiment of the invention. The welding device includes a first electrode arm and a second electrode arm movable with respect to one another and coupled to a reference arm. The welding device further comprises a compensation actuator, including first and second fluid chambers, coupled to the first electrode arm and the reference arm to balance a weight of the electrode arms, and a clamping actuator coupled to the first and second electrode arms. According to an embodiment of the invention, the method comprises a step of determining a spatial orientation of the welding device. According to an embodiment of the invention, the method further comprises a step of determining a clamping pressure required by the clamping actuator to actuate the first and second electrode arms with a predetermined clamping force at the determined spatial orientation.

A welding device is provided according to an embodiment of the invention. The welding device includes a first electrode arm and a second electrode arm movable with respect to one another and coupled to a reference arm. According to an embodiment of the invention, the welding device further includes a compensation actuator, including first and second fluid chambers, coupled to the first electrode arm and to the reference arm to balance a weight of the electrode arms. According to an embodiment of the invention, the welding device further includes a force sensor coupled to the first electrode arm and to the reference arm.

A welding device is provided according to another embodiment of the invention. The welding device includes a first electrode arm and a second electrode arm movable with respect to one another and coupled to a reference arm. The welding device further comprises a compensation actuator, including first and second fluid chambers, coupled to the first electrode arm and to the reference arm to balance a weight of the electrode arms. According to an embodiment of the invention, the welding device further comprises a spatial position sensor for determining a spatial orientation of the welding device and coupled to the first electrode arm and a clamping actuator coupled to the first and second electrode arms. According to an embodiment of the invention, the welding device further comprises a control system including a processing system configured to determine a spatial orientation of the welding device and determine a clamping pressure required by the clamping actuator to actuate the first and second electrode arms with a predetermined clamping force at the determined spatial orientation. ASPECTS

According to an aspect of the invention, a method for balancing electrode arms of a welding device including a first electrode arm and a second electrode arm movable with respect to one another and coupled to a reference arm, and a compensation actuator, including first and second fluid chambers, coupled to the first electrode arm and the reference arm to balance a weight of the electrode arms comprises steps of: determining a balance force between the first electrode arm and the reference arm when the welding device is in a first spatial orientation; and adjusting a differential pressure between the first fluid chamber and the second fluid chamber of the compensation actuator to maintain the balance force when the welding device is in at least a second spatial orientation.

Preferably, the welding device further includes a clamping actuator coupled to the first and second electrode arms, wherein the method further comprises a step of determining a clamping pressure required by the clamping actuator to actuate the first and second electrode arms with a predetermined clamping force.

Preferably, the clamping pressure is determined based on the differential pressure between the first and second fluid chambers of the compensation actuator required to maintain the balance force.

Preferably, the balance force is determined from a force sensor coupled to the first electrode arm and the reference arm.

Preferably, the welding device further includes a position sensor comprising a first portion coupled to the first electrode arm and a second portion coupled to the reference arm and wherein the method further comprises steps of:

determining a spatial orientation of the first electrode arm using the first portion of the position sensor;

determining a spatial orientation of the reference arm using the second portion of the position sensor; and

comparing the spatial orientation of the first electrode arm relative to the spatial orientation of the reference arm to check the weight balance of the electrode arms. Preferably, the compensation actuator further includes a magnet coupled to a first portion and a coil coupled to a second portion and wherein the method further comprises a step of determining a movement of the compensation actuator based on a voltage produced by movement of the magnet relative to the coil.

Preferably, the step of adjusting the differential pressure between the first and second fluid chambers of the compensation actuator comprises actuating a 3/2-way proportional pressure regulating valve in series with a 5/2-way valve, which are in fluid communication with a pressurized fluid source.

According to another aspect of the invention, a method for balancing electrode arms of a welding device including a first electrode arm and a second electrode arm movable with respect to one another and coupled to a reference arm, a compensation actuator, including first and second fluid chambers, coupled to the first electrode arm and the reference arm to balance a weight of the electrode arms, and a clamping actuator coupled to the first and second electrode arms comprises steps of:

determining a spatial orientation of the welding device; and

determining a clamping pressure required by the clamping actuator to actuate the first and second electrode arms with a predetermined clamping force at the determined spatial orientation.

Preferably, the spatial orientation is determined using a spatial position sensor coupled to the first electrode arm.

Preferably, the spatial position sensor comprises a digital spatial position sensor. Preferably, the method further comprises a step of determining a differential pressure required between the first and second fluid chambers to balance the electrode arms at the determined spatial orientation.

Preferably, the method further comprises a step of adjusting the differential pressure between the first and second fluid chambers of the compensation actuator to balance the electrode arms at the determined spatial orientation by actuating a 3/2-way proportional pressure regulating valve in series with a 5/2-way valve, which are in fluid communication with a pressurized fluid source.

Preferably, the welding device further includes a position sensor comprising a first portion coupled to the first electrode arm and a second portion coupled to the reference arm and wherein the method further comprises steps of: determining a spatial orientation of the first electrode arm using the first portion of the position sensor;

comparing the spatial orientation of the first electrode arm relative to the spatial orientation of the reference arm to check the weight balance of the electrode arms.

Preferably, the compensation actuator further includes a magnet coupled to a first portion and a coil coupled to a second portion and wherein the method further comprises a step of determining a movement of the compensation actuator based on a voltage produced by movement of the magnet relative to the coil.

According to another aspect of the invention, a welding device comprises:

a first electrode arm and a second electrode arm movable with respect to one another and coupled to a reference arm;

a compensation actuator, including first and second fluid chambers, coupled to the first electrode arm and to the reference arm to balance a weight of the electrode arms; and

a force sensor coupled to the first electrode arm and to the reference arm.

Preferably, the welding device further comprises a control system including a processing system configured to:

determine a balance force between the first electrode arm and the reference arm when the welding device is in a first spatial orientation using a signal from the force sensor;

move the welding device into at least a second spatial orientation; and

adjust the differential pressure between the first and second fluid chambers of the compensation actuator to maintain the balance force.

Preferably, the welding device further comprises a clamping actuator coupled to the first electrode arm and the second electrode arm, wherein the processing system is further configured to:

determine a clamping pressure required by the clamping actuator to actuate the first and second electrode arms with a predetermined clamping force. Preferably, the clamping pressure is based on the differential pressure between the first and second fluid chambers of the compensation actuator required to maintain the balance force.

Preferably, the welding device further comprises a position sensor including a first portion coupled to the first electrode arm and a second portion coupled to the reference arm.

determine a spatial orientation of the first electrode arm using the first portion of the position sensor;

determine a spatial orientation of the reference arm using the second portion of the position sensor; and

compare the spatial orientation of the first electrode arm relative to the spatial orientation of the reference arm to check the weight balance of the electrode arms.

Preferably, the welding device further comprises a magnet coupled to a first portion of the compensation actuator and a coil coupled to a second portion of the compensation actuator, and a control system including a processing system configured to determine movement of the compensation actuator based on a voltage produced by movement of the magnet relative to the coil.

Preferably, the welding device further comprises a 3/2-way proportional pressure regulating valve in series with a 5/2-way valve to selectively provide fluid communication between the first and second fluid chambers of the compensation actuator and a pressurized fluid source.

According to another aspect of the invention, a welding device comprises:

a compensation actuator, including first and second fluid chambers, coupled to the first electrode arm and to the reference arm to balance a weight of the electrode arms;

a spatial position sensor for determining a spatial orientation of the welding device and coupled to the first electrode arm; a clamping actuator coupled to the first and second electrode arms; and a control system including a processing system configured to:

determine a spatial orientation of the welding device; and

determine a clamping pressure required by the clamping actuator to actuate the first and second electrode arms with a predetermined clamping force at the determined spatial orientation.

Preferably, the spatial position sensor comprises a digital spatial position sensor. Preferably, the processing system is further configured to determine a differential pressure required between the first and second fluid chambers to balance the electrode arms at the determined spatial orientation.

Preferably, the welding device further comprises a position sensor including a first portion coupled to the first electrode arm and a second portion coupled to the reference arm and wherein the processing system is further configured to:

Preferably, the welding device further comprises a magnet coupled to a first portion of the compensation actuator and a coil coupled to a second portion of the compensation actuator wherein the processing system is further configured to determine a movement of the compensation actuator based on a voltage produced by movement of the magnet relative to the coil. BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagrammatic representation of a welding device 100 according to an embodiment of the invention.

FIG. 2 shows a diagrammatic representation of the welding device according to another embodiment of the invention.

FIG. 3 shows a compensation actuator according to an embodiment of the invention.

FIG. 4 shows a diagrammatic representation of the welding device according to another embodiment of the invention.

FIG. 5 shows a differential pressure determination routine according to an embodiment of the invention.

FIG. 6 shows a weight balancing routine according to an embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 - 6 and the following description depict specific examples to teach those skilled in the art how to make and use the best mode of the invention. For the purpose of teaching inventive principles, some conventional aspects have been simplified or omitted. Those skilled in the art will appreciate variations from these examples that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific examples described below, but only by the claims and their equivalents.

FIG. 1 shows a diagrammatic representation of a welding device 100 according to an embodiment of the invention. The welding device 100 includes two electrode arms 101, 102, each of which includes an electrode 12, 22 used for welding sheets 20a, 20b as is generally known in the art. The electrode arms 101, 102 can be movable relative to one another. The electrode arms 101, 102 can be coupled to and are free to rotate about a reference arm 30. The reference arm 30 may comprise a stationary component or a movable component such as a robot arm. The electrode arms 101, 102 are shown coupled to the reference arm 30 at a pivot point 31, for example. For example, the electrode arms 101, 102 may be coupled to the reference arm 30 using a pivot pin or the like. The reference arm 30 can comprise a portion of a robot (not shown) that can move the welding device 100 into various spatial orientations in order to perform a welding operation on the welding sheets 20, for example. In some embodiments, the reference arm 30 may be capable of moving the welding device 100 in three dimensions rather than simply pivoting about a single axis as in most prior art systems.

According to an embodiment of the invention, the first electrode arm 101 comprises a "static" arm in that the arm 101 is maintained in a relatively constant position. According to an embodiment to of the invention, the second electrode arm 102 comprises a "dynamic" arm that is moved into position using a clamping actuator 103. Therefore, according to an embodiment of the invention, once the reference arm 30 has moved the electrode arms 101, 102 into a desired position with respect to the sheets 20a, 20b, the electrode arm 101 can be moved into the position shown in FIG. 1 where the electrode 12 is contacting the sheet 20a. The electrode arm 101 may be moved into the position shown in FIG. 1 by actuating the clamping actuator 103, a compensation actuator 103, or a combination thereof. With the static electrode arm 101 contacting the sheet 20a, the dynamic electrode arm 102 can be actuated into a welding position by actuating the clamping actuator 103. In a welding position, the second electrode 22 may be in contact with the second sheet 20b.

The clamping actuator 103 is in the general form of a fluid operated actuator comprising a piston assembly 104 movable within a cylinder 105. The piston assembly 104 separates the cylinder 105 into a first fluid chamber 105a and a second fluid chamber 105b. The cylinder 105 is shown coupled to the first electrode arm 101 while the piston assembly 104 is shown coupled to the second electrode arm 102. According to an embodiment of the invention, the clamping actuator 103 is not coupled directly to the reference arm 30 as shown by the dashed lines in FIG. 1. Consequently, as the piston assembly 104 moves within the cylinder 105 in response to a pressurized fluid supply, the electrode arms 101, 102 pivot about point 31 to either clamp down onto the sheets 20a, 20b or move away from the sheets 20a, 20b. The pressurized fluid supplied to the clamping actuator 103 may comprise a liquid or a gas. Typically, air is used, but the present invention should in no way be limited to air. The pressurized fluid supply used to supply the clamping actuator 103 with fluid is omitted from the drawing in order to reduce the complexity. The clamping actuator 103 can be actuated from a first position shown in FIG. 1 to a second position to move the electrode 22 into contact with the sheet 20b. Actuation of the clamping actuator 103 can be accomplished by supplying pressurized fluid to the cylinder 105 as is generally known in the art in order to create a differential clamping pressure between the first and second fluid chambers 105a, 105b. The various fluid lines and valves used to actuate the clamping actuator 105 are not shown in FIG. 1 in order to simplify the drawing. Although the electrode arms 101, 102 are free to pivot about point 31, prior to and during actuation of the clamping actuator 103, the electrode arms 101, 102 are maintained in a "floating" position where the weight of the electrode arms 101, 102 are substantially balanced by the compensation actuator 106.

The compensation actuator 106 is provided to hold the electrode arm 101 in a "floating" position where the weight of the electrode arms 101, 102 are balanced and the position of the electrode arm 101 remains substantially stationary. If the position of the clamping actuator 103 is held constant, the electrode arm 102 is likewise balanced. The compensation actuator 106 can therefore, maintain the electrode arms 101, 102 in a substantially stationary position even though they can pivot about point 31. The discussion below is concerned mainly with balancing the electrode arm 101; however, it should be appreciated that because the two electrode arms 101, 102 are coupled by the clamping actuator 103, the weight of the electrode arm 102 can also be balanced for a given position of the clamping actuator 103.

As can be appreciated, with the electrode arm 101 being coupled to the clamping actuator 103, the reference arm 30, and the compensation actuator 106, various forces may be acting on the electrode arm 101. The compensation actuator 106 can advantageously account for these forces by adjusting the differential pressure within the compensation actuator 106. Therefore, according to an embodiment of the invention, the compensation actuator 106 can compensate for the imbalance of the electrode arms 101, 102 as they pivot about point 31 of the reference arm 30. The compensation actuator 106 can thus maintain a desired contact force between the electrode arms 101, 102 and the sheets 20a, 20b to prevent the sheets 20a, 20b from being bent. For example, if the weight of the electrode arm 101 is compensated, the clamping force experienced by sheets 20a, 20b as the electrodes 12, 22 contact the sheets 20a, 20b can be controlled. Furthermore, because the electrode arms 101, 102 can rotate about point 31, the clamping force can be substantially balanced with respect to the sheets 20a, 20b.

According to an embodiment of the invention, a first portion of the compensation actuator 106 is coupled to the reference arm 30 or some other fixed component while a second portion of the compensation actuator 106 is coupled to the electrode arm 101. In the embodiment shown, the cylinder 107 is coupled to the reference arm 30 while the piston assembly 108 is coupled to the electrode arm 101.

According to an embodiment of the invention, a differential pressure experienced by the compensation actuator 106 can be controlled to balance the weight of the electrode arms 101, 102. As can be appreciated, the differential pressure required to balance the weight of the electrode arm 101 will vary depending on the spatial orientation of the welding device 100. In the prior art European Patent 1 830 979 mentioned above, once the welding device was in the desired spatial orientation, the compensation actuator was set to a predetermined position and the differential pressure was measured. This differential pressure was then maintained constant throughout the balancing operation. While this procedure provided adequate results in some circumstances, the present applicants have developed improved methods for determining a desired differential pressure.

According to an embodiment of the invention, the welding device 100 may include one or more spatial position sensors 110. In the embodiment shown in FIG.l, the spatial position sensor 110 is shown coupled to the electrode arm 101. However, it should be appreciated that in other embodiments, the spatial position sensor 110 does not have to be coupled directly to the electrode arm 101 and rather, may be coupled to the electrode arm 101 through other components of the welding device 100, such as for example the compensation actuator 106. However, because the spatial position sensor 110 is provided to determine the spatial orientation of the electrode arm 101, the spatial position sensor 110 should be coupled to a component of the welding device 100 that at least provides a correlation to the spatial orientation of the electrode arm 101. According to an embodiment of the invention, the spatial position sensor 110 may be configured to determine a spatial orientation of the welding device 100, and in particular, the spatial orientation of the electrode arm 101. The spatial position sensor 110 may comprise a wide variety of known devices, such as accelerometers, gyroscopes, or rotary displacement sensors, for example. The particular type of spatial position sensor used should in no way limit the scope of the present invention.

While analog spatial position sensors are known and may be used in some embodiments, according to an embodiment of the invention, the spatial position sensor 110 comprises a digital position sensor. Digital position sensors provide a number of advantages over analog spatial position sensors. For example, precise orientation of the analog spatial position sensor on the electrode arm 101 is required in order to obtain accurate measurements. In contrast, digital spatial position sensors can easily be calibrated once coupled to the electrode arm 101. Therefore, the precise positioning of digital position sensors is not as critical as the positioning of analog position sensors. In addition, by using a digital position sensor, an analog-to-digital converter is not required, thereby reducing cost and size of the device. In some embodiments, the use of a digital position sensor may allow for faster processing by eliminating the time spent converting the analog signal to a digital signal.

In some embodiments, the spatial position sensor 110 may be configured to determine the orientation of the welding device 100 about one axis, such as movement of the welding device 100 as the reference arm 30 pivots about the z-axis. In other embodiments, the reference arm 30 may be capable of also rotating the welding device 100 about the x-axis. In these embodiments, the spatial position sensor 110 may comprise a sensor that is capable of determining the spatial orientation of the welding device 100, and in particular, the electrode arm 101 in more than one dimension. While the welding device 100 may also rotate about the y-axis, such rotation is generally not of interest in the present application because rotation about the y-axis does not alter the weight of the electrode arm 101 that needs to be balanced by the compensation actuator 106. Consequently, no change in the differential pressure is required by the compensation actuator 106 to balance the weight of the electrode arms 101, 102 due to rotation of the welding device 100 about the y-axis.

As can be appreciated, as the orientation of the welding device 100 changes, the differential pressure required in the compensation actuator 106 to balance the gravitational force, F_g, acting on the electrode arms 101, 102 in a direction parallel to movement of the compensation actuator 106 will change. One reason for the change is the asymmetrical mounting of the electrode arms 101, 102 along with the clamping actuator 103 on the reference arm 30.

Assuming the gravitational force is acting in the -y-direction as shown in the figures, a maximum differential pressure will be required in the compensation actuator 106 in the position shown in FIG. 1. This is because the weight of the electrode arms 101, 102 are acting substantially parallel to the movement of the piston assembly 108, which is in the ±y-direction in the orientation shown in FIG. 1. Conversely, if the reference arm 30 rotates the welding device 100 approximately 90° about the z-axis, the gravitational force acting on the electrode arms 101, 102 is still in the -y-direction, however, the compensation actuator 106 would be moving in the ±x-direction. Therefore, the weight of the electrode arms 101, 102 will be acting mainly perpendicular to the movement of the compensation actuator 106. Consequently, a much smaller differential pressure may be required in the compensation actuator 106. Further rotation of the welding device by another 90°, for a total of 180° would again require a maximum differential pressure; however, the pressure would require the piston assembly 108 to provide an extending force rather than a retracting force as in the orientation of FIG. 1. Likewise, starting from the position shown in FIG. 1, if the reference arm 30 rotates the welding device 100 approximately 90° about the x-axis, the weight of the electrode arms 101, 102 will once again be acting approximately perpendicular to the movement of the compensation actuator 106. Using the spatial orientation of the welding device 100 as determined by the position sensor 110, the differential pressure required by the compensation actuator 106 can easily be determined.

According to an embodiment of the invention, the differential pressure required by the compensation actuator 106 may be determined during an initial calibration for one or more spatial orientations. For example, the welding device 100 may be rotated about the z-axis between 0-90°, for example while the differential pressure required in the compensation actuator 106 to balance the weight of the electrode arms 101, 102 is determined at one or more locations between the 0-90° movement. The various differential pressures may be stored along with corresponding spatial orientations, in a storage system 352 (See FIG. 3) for later retrieval, for example. A similar calibration can be performed as the welding device 100 is rotated about the x-axis. It should be appreciated, that the calibration does not have to be limited to 90°, but rather, may be performed through a complete 360° rotation or any other desired amount.

As an alternative to the calibration described above, the differential pressure required in the compensation actuator 106 may be determined mathematically. For example, the required differential pressure may be determined at an initial reference position, such as the position shown in FIG. 1. This would give a maximum weight of the electrode arms 101, 102 acting parallel to the movement of the compensation actuator 106, thereby requiring a maximum differential pressure in the compensation actuator 106. As the welding device 100 rotates about the z-axis and/or the x-axis, the weight of the electrode arms 101, 102 that needs to be balanced by the compensation actuator 106 can be determined as cos(9_z)*cos(9_x)*maximum weight, where Θ is the angle of rotation about the z-axis and x-axis, with θ_ζ = θ_χ = 0 in the position shown in FIG. 1. Therefore, if the angle Θ is determined by the position sensor 110, the weight of the electrode arms 101, 102 that needs to be offset by the compensation actuator 106 can easily be calculated to determine a required differential pressure in the compensation actuator 106.

FIG. 2 shows the welding device 100 according to another embodiment of the invention. The welding device 100 shown in FIG. 2 is similar to the welding device 100 shown in FIG. 1; however, rather than including the spatial position sensor 110, the welding device 100 shown in FIG. 2 includes a force sensor 111. According to an embodiment of the invention, the force sensor 111 is coupled to the electrode arm 101 as well as the reference arm 30. The force sensor 111 may comprise any known type of sensor capable of determining a force between two or more components, such as a piezo-electric force sensor, an accelerometer, a strain gauge, or an electro-restrictive type sensor, for example. The particular type of force sensor used should in no way limit the scope of the present invention.

According to an embodiment of the invention, the force sensor 111 can be configured to determine a force experienced by the electrode arm 101 relative to a reference point, such as the reference arm 30. It should be appreciated that while the reference arm 30 is used as the reference point in the description that follows, the force sensor 111 can alternatively determine the force experienced between the electrode arm 101 and some other reference point. As can be appreciated, the force experienced between the electrode arm 101 and the reference arm 30 while the welding device 100 is in the position shown in FIG. 2 is a combination of the weight of the electrode arms 101, 102 acting parallel to the movement of the compensation actuator 106 and the compensation force provided by the compensation actuator 108 in the ±y-direction required to balance the electrode arms 101, 102. According to an embodiment of the invention, the force sensor 111 can advantageously, determine a balance force between the electrode arm 101 and the reference arm 30 when the electrode arm 101 is in a first position, for example. As shown, in the position shown in FIG. 2, the weight of the electrode arms 101, 102 provide a weight force F_g, which is acting in the -y-direction. Simultaneously, the compensation actuator 106 provides a compensation force, F_c acting in the +y-direction. The sum of these two forces can be determined by the force sensor 111 as a predetermined balance force. The predetermined balance force may be stored in the storage system 352, for example.

If the welding device 100 is rotated about the x-axis or the z-axis away from the position shown in FIG. 2, the gravitational force acting to pull the electrode arm 101 away from the reference arm 30 (and push the electrode arm 102 towards the reference arm 30) will decrease. Consequently, in order to maintain the balance force determined when the welding device 100 was in the position shown in FIG. 2, the differential pressure in the compensation actuator 106 can be adjusted in order to decrease the compensation force, F_c provided by the compensation actuator 106 to pull the electrode arm 101 towards the reference arm 30. According to an embodiment of the invention, the balance force can be continuously monitored to ensure that the electrode arms 101, 102 are properly balanced. Therefore, while the embodiment described in FIG. 1 adjusts the differential pressure based on a particular spatial orientation, the embodiment shown in FIG. 2 can use the force sensor 111 to maintain by the balance force by adjusting the differential pressure in the compensation actuator 106.

The clamping actuator 103 acts substantially independent from the compensation actuator 106 and the actuation of the clamping actuator 103 is generally determined by the desired welding operation. Consequently, it should be appreciated that even when the welding device 100 is maintained in a constant orientation, the compensation actuator 106 may need to be adjusted to maintain a constant balance force as the clamping actuator 103 is being actuated during a welding operation. For example, if the differential pressure in the compensation actuator 106 were maintained constant while the clamping actuator 103 was actuated from the position shown in FIG. 2 to an extended position to bring the electrode 22 into contact with the sheet 20b, the balance force could change. Advantageously, once the predetermined balance force is determined, the balance force can be maintained regardless of the spatial orientation of the welding device 100 or the clamping actuator position and without the use of the spatial position sensor 110 simply by adjusting the differential pressure in the compensation actuator 106.

FIG. 3 shows the compensation actuator 106 and a control system 350 according to an embodiment of the invention. According to an embodiment of the invention, the piston assembly 108 separates the cylinder 107 into a first fluid chamber 306a and a second fluid chamber 306b. As shown in FIG. 3, the first and second fluid chambers 306a, 306b are selectively in fluid communication with a pressurized fluid source 320 or an exhaust. The pressurized fluid source 320 may comprise a liquid or a gas. The particular fluid used to pressurize and operate the compensation actuator 106 should in no way limit the scope of the present invention. According to the embodiment shown, the first and second fluid chambers 306a, 306b are in fluid communication with the pressurized fluid source 320 via a 3/2-way proportional pressure regulating valve 321 and a 5/2-way valve 322. According to an embodiment of the invention, the 3/2-way proportional valve 321 is in fluid communication with the pressurized fluid source 320 via a fluid line 323. According to an embodiment of the invention, the 3/2-way proportional valve 321 is in fluid communication with the 5/2-way valve 322 via a fluid line 324. According to an embodiment of the invention, the 5/2-way valve 322 is in fluid communication with the first fluid chamber 306a via a fluid line 325a and in fluid communication with the second fluid chamber 306b via a fluid line 325b.

While prior art systems have required separate pressure regulating valves for each of the fluid chambers of the compensation actuator, the present invention eliminates the need for separate pressure regulating valves. Rather, the present invention utilizes a single 3/2-way proportional pressure regulating valve in series with a 5/2-way valve rather than separate pressure regulating valves. The cost of the system can be substantially reduced using this valve combination. In addition, the particular valve combination substantially reduces costs compared to the 5/3-way proportional pressure regulating valve used in EP 1 830 979 discussed above. 5/3-way proportional pressure regulating valves are currently as much as three times more expensive than the providing a 3/2-way proportional pressure regulating valve in series with a 5/2-way valve. Therefore, the particular valve combination provided in FIG. 3 can substantially reduce the costs of the system compared to prior art approaches.

According to an embodiment of the invention, the welding device 100 may further include first and second pressure sensors 316a, 316b located in fluid communication with the first and second fluid chambers 306a, 306b, for example. The first and second pressure sensors 316a, 316b may be coupled to the fluid lines 325a, 325b as shown or may be coupled directly to the first and second fluid chambers 306a, 306b. The first and second pressure sensors 316a, 316b may be in communication with the control system 350 via lines 357, 358, for example. Alternatively, the first and second pressure sensors 316a, 316b could be in communication with the control system 350 using a wireless interface. The first and second pressure sensors 316a, 316b, can advantageously determine a pressure in each of the fluid chambers 306a, 306b. Therefore, the control system 350 can use the received pressures to determine a differential pressure between the first and second fluid chambers 306a, 306b. In alternative embodiments, the first and second pressure sensors 316a, 316b can be replaced with a single differential pressure sensor that can be in fluid communication with both the first and the second fluid chamber 306a, 306b.

According to an embodiment of the invention, the control system 350 can actuate the valves 321, 322. The control system 350 can actuate the valves 321, 322 in order to adjust the differential pressure between the first and second fluid chambers 306a, 306b of the compensation actuator 106 in order to maintain a weight balance of the electrode arms 101, 102. The differential pressure between the first and second fluid chambers 306a, 306b may be adjusted by supplying the pressurized fluid to the first or the second fluid chamber 306a, 306b and/or exhausting pressurized fluid from the other fluid chamber.

The control system 350 can include an interface 353 and a processing system 351. The processing system 351 may include a storage system 352. The storage system 352 may comprise an internal memory as shown, or alternatively, may comprise an external memory. According to an embodiment of the invention, the interface 353 may perform any necessary or desired signal conditioning, such as any manner of formatting, amplification, buffering, etc. Alternatively, some or all of the signal conditioning may be performed by the processing system 351. While the interface 353 is shown in communication with the valves 321, 322 via lines 255 and 256, it should be appreciated that the interface 353 may be capable of electronic, wireless, or optical communication.

The processing system 351 can conduct operations of the control system 350. The processing system 351 can execute the data processing required to actuate the valves 321, 322. The processing system 351 can also execute the data processing required to conduct the routines 500 and 600 described below. The routines 500 and 600 may be stored in the storage system 352, for example. The processing system 351 can comprise a general-purpose computer, a micro-processing system, a logic circuit, or some other general purpose or customized processing device. The processing system 351 can be distributed among multiple processing devices. The processing system 351 can include any manner of integral or independent electronic storage medium, such as the storage system 352.

It should be appreciated that the control system 350 may include various other components and functions that are generally known in the art. These additional features are omitted from the description and figures for the purpose of brevity. Therefore, the present invention should not be limited to the specific embodiments shown and discussed.

According to an embodiment of the invention, the control system 350 can actuate the valves 321, 322 according to a user input received by the interface 353 over line 354. The line 354 may be in communication with an external device such as a computer or a separate controller, for example. Alternatively, the control system 350 can actuate the valves 321, 322 based on signals received from the spatial position sensor 110 shown in FIG. 1 or the force sensor 111 shown in FIG. 2, for example. Therefore, the position sensor 110 or the force sensor 111 may be in communication with the control system 350, for example. The communication may be via wire leads (not shown) or some type of wireless communication, for example. The wire leads between the sensors 110, 111 and the control system 350 are not shown in the drawings in order to simplify the figures. According to an embodiment of the invention, if a signal is received by the interface 353, the control system 350 can actuate the valves 321, 322 based on the orientation of the electrode arm 101 determined by the spatial position sensor 110 or the relative force between the electrode arm 101 and the reference arm 30 determined by the force sensor 111. According to an embodiment of the invention, the control system 350 can retrieve the desired differential pressure based on the spatial orientation as determined by the position sensor 110, for example. The control system 350 can therefore control the valves 321, 322 to obtain the desired differential pressure between the first and second fluid chambers 306a, 306b of the compensation actuator 106. According to another embodiment of the invention, the control system 350 can retrieve the predetermined balance force. The control system 350 can then control the valves 321, 322 to move the piston assembly 108 in order to maintain the desired balance force as determined by the force sensor 111.

While the position sensor 110 or the force sensor 111 may adequately balance the electrode arm 101, it may be desirable to provide a way to check that the electrode arm 101 is properly balanced. Therefore, in some embodiments, the welding device 100 can include one or more additional sensors to provide a check.

FIG. 4 shows the welding device 100 according to another embodiment of the invention. According to the embodiment shown in FIG. 4, the welding device 100 further includes a position sensor 410. According to an embodiment of the invention, the position sensor 410 is separated into two or more portions. A first portion 410a of the position sensor 401 is coupled to the electrode arm 101 and a second portion 410b is coupled to a reference component, such as the reference arm 30. According to an embodiment of the invention, the first and second portions 410a, 410b may each comprise spatial position sensors similar to the spatial position sensor 110 shown in FIG. 1. Other types of sensors may be used, for example, the first and second portions 410a, 410b may comprise portions of a proximity sensor.

In embodiments where the position sensor 410 comprises a pair of spatial position sensors, the first portion 410a can determine a spatial orientation of the electrode arm 101 while the second portion 410b can determine a spatial orientation of the reference arm 30. Therefore, the spatial orientation of the electrode arm 101 can be determined relative to the spatial orientation of the reference arm 30. For example, in the embodiment shown in FIG. 4, the electrode arm 101 is at an angle a with respect to the reference arm 30. According to an embodiment of the invention, the compensation actuator 106 is provided to maintain the position of the electrode arm 101 with respect to the reference arm 30 regardless of the spatial orientation of the welding device 100. The present invention can advantageously provide the position sensor 410 to check that the position of the electrode arm 101 with respect to the reference arm 30 is maintained constant. According to an embodiment of the invention, the check can be made by comparing the spatial orientation determined by the two position sensors 410a, 410b. If the compensation actuator 106 is operating correctly, the spatial orientation of the first portion 410a should remain substantially constant compared to the spatial orientation of the second portion 410b. If a change between the two portions 410a, 410b is detected, which is not due to actuation of the clamping actuator 103, the control system 350 may trigger an alarm condition. The alarm condition may indicate that the compensation actuator 106 is not performing correctly.

The control system 350 may respond to the alarm condition in a variety of ways. In one embodiment, the control system 350 may simply provide a visual and/or an audio warning to a user or operator. According to another embodiment of the invention, the control system 350 may shut the system down preventing further welding operations from being performed. The particular actions taken by the control system 350 in response to a change between the two portions 410a, 410b of the position sensor 410 should in no way limit the scope of the present invention.

According to the embodiment of the invention shown in FIG. 4, the compensation actuator 106 further comprises a piston position sensor 412. The piston position sensor 412 is in the form of a magnet/coil combination where a first portion of the compensation actuator 106 includes a magnet and a second portion of the compensation actuator 106 includes a coil. In the embodiment shown, the piston assembly 108 comprises a magnetic piston 412a or a magnet coupled to the piston assembly 108, while the cylinder 107 includes a coil assembly 412b. The coil may be internal of the cylinder 107 or wrapped around a magnetically permeable cylinder, for example. However, it should be appreciated that in other embodiments, the piston assembly 108 may include the coil assembly 412b while a magnet 412a is included in the cylinder 107.

As is generally known in the art, when a magnet moves relative to a coil, the interaction produces a voltage that can be detected. For example, the coil assembly 412b may be in communication with the control system 350. Therefore, with one portion of the compensation actuator 106 including the magnet and the other portion including a coil, a voltage will be produced if the piston assembly 108 moves relative to the cylinder 107. Advantageously, movement of the electrode arm 101 relative to the reference arm 30 can be detected. The movement of the compensation actuator 106 may be caused by an error or malfunction of the compensation actuator 106, for example. It should be appreciated that while the magnet/coil combination is shown in the compensation actuator 106, the clamping actuator 103 may also include a similar configuration to detect movement of the clamping actuator 103.

In some embodiments, the voltage produced by movement of the piston assembly 108/104 within the cylinder 107/105 can be stored, such as in a capacitor or a battery (not shown), for example. The energy can be later used to power various components of the welding device 100, such as the control system 350, for example.

The discussion above has been directed primarily to balancing the weight of the electrode arms 101, 102 in a "floating" position prior to actuation of the clamping actuator 103. However, during the welding operation, the electrode arms 101, 102 clamp down onto the sheets 20a, 20b with a predetermined desired clamping force. The clamping force is determined mainly by the differential pressure supplied to the clamping actuator 103. As can be appreciated, it is desirable to provide the same predetermined clamping force regardless of the spatial orientation of the welding device 100. Therefore, regardless of whether the position sensor 110, the force sensor 111, or some other prior art approach, is used to determine a spatial orientation of the welding device 100, the control system 350 can also adjust the differential pressure in clamping actuator 103 to account for the weight of the electrode arm 102. For example, when the welding device is in the position shown in FIGS. 1, 2, and 4, the compensation actuator 106 can maintain the electrode arm 101 in a substantially stationary position. As mentioned above, if the clamping actuator 103 remains stationary, the upper electrode arm 102 will also be balanced and remain substantially stationary. However, as the clamping actuator 103 is actuated from the position shown in the figures to a second position to bring the electrode 22 into contact with the sheet 20b and then apply a clamping force on the sheets 20a, 20b, the weight of the electrode arm 102 provides additional force acting on the sheet 20b. Prior art systems have simply ignored this additional weight because the majority of the weight is balanced by the compensation actuator 106 and the additional force of the arm 102 is ignored. However, in some situations, the weight of the electrode arm 102 may cause changes in the clamping force that are significant enough to cause variations in the weld quality.

According to an embodiment of the invention, in addition to adjusting the differential pressure in the compensation actuator 106, the differential pressure in the clamping actuator 103 can be adjusted based on the spatial orientation of the welding device 100. For example, during an initial calibration, the spatial orientation may be determined at a reference orientation, such as the orientation shown in the figures. At the reference orientation, the control system 350 or a user or operator can determine a differential pressure required by the clamping actuator 103 to obtain a desired clamping force experienced by the sheets 20a, 20b. This differential pressure may be stored as a clamping pressure. The clamping pressure may be stored in the storage system 352, for example. The welding device 100 can then be moved to at least a second spatial orientation and the differential pressure required by the clamping actuator 103 can be determined in the second spatial orientation. The calibration can obtain a clamping pressure for each of a plurality of desired spatial orientations. The plurality of clamping pressures can be stored in a look-up table, a graph, an equation, etc. If for example, the clamping pressures are stored in a look-up table, and the particular spatial orientation is not stored in the look-up table, the appropriate clamping pressure may be determined by interpolation or extrapolation, for example based on the known clamping pressures and spatial orientations.

According to an embodiment of the invention, the clamping pressure required by the clamping actuator 103 can be correlated to a compensation pressure required by the compensation actuator 106 for one or more spatial orientations. For example, if during an initial calibration it is determined that the compensation actuator 106 requires a first compensation differential pressure to balance the electrode arms 101, 102, this first compensation differential pressure can be correlated to a first clamping pressure required by the clamping actuator 103 at the first spatial orientation to obtain a desired clamping force. The calibration can then determine at least a second compensation differential pressure required by the compensation actuator 106 and a second clamping pressure required by the clamping actuator at a second spatial orientation. In some embodiments, it may be appropriate to assume that as the spatial orientation of the welding device changes, the clamping pressure will change in proportion to the change in the compensation pressure. Therefore, if the compensation pressure is determined at any particular spatial orientation of the welding device 100, the clamping pressure can likewise be determined based on the correlation between the two pressures. The correlation may be stored in a look-up table, a graph, equation, etc. The compensation pressure may be based on the spatial orientation determined by the spatial position sensor 110 or a differential pressure required to maintain the balance force determined by the force sensor 111.

FIG. 5 shows a differential pressure determination routine 500 according to an embodiment of the invention. The differential pressure determination routine 500 can be conducted by the control system 350, for example. Alternatively, the differential pressure determination routine 500 can be conducted manually by a user or operator. The differential pressure determination routine 500 provides a method for determining an ideal differential pressure between the first and second fluid chambers 316a, 316b of the compensation actuator 106 to adequately maintain a weight balance for the static electrode arm 101 of the welding device 100.

In step 501, a spatial orientation of the electrode arm 101 is determined. As discussed above, the spatial orientation may be determined by the spatial position sensor 110, for example.

In step 502, a differential pressure required by the compensation actuator 106 is determined. The required differential pressure may be determined based on the spatial orientation determined in step 501. The required differential pressure may be retrieved from a previously stored value for the determined spatial orientation. Alternatively, the required differential pressure may be determined based on a maximum differential pressure required when the electrode arm 101 is at a reference spatial orientation and the difference between the current spatial orientation and the reference spatial orientation. For example, the reference spatial orientation may comprise the spatial orientation shown in FIG. 1 where the maximum weight of the electrode arm 101 is being countered by the compensation actuator 106. Therefore, the required differential pressure can be determined based on the angle of the current spatial orientation compared to the reference spatial orientation as explained above. According to an embodiment of the invention, with the required differential pressure determined, the control system 350 can actuate the valves 221, 222 in order to obtain the desired differential pressure between the first and second fluid chambers 306a, 306b of the compensation actuator 106.

In step 503, a clamping pressure can be determined. The clamping pressure may be determined directly from the spatial orientation determined by the spatial position sensor 110. Alternatively, the clamping pressure may be determined based on a correlation between the clamping pressure and the differential pressure required by the compensation actuator 106. As explained above, the clamping pressure may vary based on the spatial orientation as determined by the position sensor 110.

In optional step 504, the balance of the electrode arms 101, 102 can be checked. The check may be performed using the position sensor 410 or the position sensor 412, for example. As explained above, if the position sensor 410 is utilized, a change in the relative spatial orientation between the electrode arm 101 and the reference arm 30 indicates an error in the balancing being maintained by the compensation actuator 106. This may indicate an error by the control system 350 or a failure in the compensation actuator 106. Appropriate action may be taken by the control system 350 if an error is detected.

FIG. 6 shows a weight balance routine 600 according to an embodiment of the invention. According to an embodiment of the invention, the weight balance routine 600 can be performed by the control system 350. Alternatively, the weight balance routine 600 can be conducted manually by a user or operator. The weight balance routine 600 can provide a method for adjusting the differential pressure between the first and second fluid chambers 306a, 306b of the compensation actuator 106 based on a signal received from the force sensor 111 shown in FIG. 2.

In step 601, a balance force between the electrode arm 101 and the reference arm 30 can be determined. The force can be determined by the force sensor 111, for example. The force can be determined while the electrode arm 101 is in a first spatial orientation, for example, the spatial orientation shown in FIG. 2.

In step 602, the electrode arm 101 can be moved to at least a second spatial orientation. The electrode arm 101 may be moved to the at least second spatial orientation using a robot (not shown) to move the reference arm 30, for example. In step 603, the control system 350 can actuate the first and second valves 221, 222 to adjust the differential pressure between the first and second fluid chambers 306a, 306b in order to maintain the balance force determined in step 601. Therefore, while the weight of the electrode arm 101 that needs to be compensated may change as the spatial orientation of the electrode arm 101 changes, the force experienced by the force sensor 111 can be maintained constant.

With the balance force maintained, the control system 350 can ensure the electrode arm 101 does not move relative to the reference arm 30 using the position sensor 410, the position sensor 412, or both. If the balance force changes despite actuation of the first and second valves 321, 322, the control system 350 may indicate an error condition exists. For example, the compensation actuator 106 may not be performing properly.

In an optional step 604, the clamping pressure may be determined. As discussed above, the clamping pressure may be determined based on the differential pressure required by the compensation actuator 106 to maintain the balance force, for example. As discussed above, the differential pressure required by the compensation actuator 106 is dependent upon the spatial orientation of the welding device 100. Likewise, the clamping pressure required to obtain a desired clamping force is dependent upon the spatial orientation of the welding device 100. Therefore, if the differential pressure required by the compensation actuator 106 is determined, the clamping pressure can be directly correlated.

The present invention as described above provides a welding device 100 and various methods for balancing the electrode arms 101, 102 of the welding device. The electrode arms 101, 102 may be balanced using a spatial position sensor or a force sensor. The balancing may be checked using a position sensor coupled to the electrode arm 101 and the reference arm 30 or a position sensor coupled to the compensation actuator 106. Further, with a spatial orientation of the welding device determined, the clamping pressure can be adjusted to obtain a desired clamping force of the welding device 100 regardless of the spatial orientation of the welding device 100.

The detailed descriptions of the above embodiments are not exhaustive descriptions of all embodiments contemplated by the inventors to be within the scope of the invention. Indeed, persons skilled in the art will recognize that certain elements of the above-described embodiments may variously be combined or eliminated to create further embodiments, and such further embodiments fall within the scope and teachings of the invention. It will also be apparent to those of ordinary skill in the art that the above-described embodiments may be combined in whole or in part to create additional embodiments within the scope and teachings of the invention.

Thus, although specific embodiments of, and examples for, the invention are described herein for illustrative purposes, various equivalent modifications are possible within the scope of the invention, as those skilled in the relevant art will recognize. The teachings provided herein can be applied to other fluid operated actuators, and not just to the embodiments described above and shown in the accompanying figures. Accordingly, the scope of the invention should be determined from the following claims.

Claims

CLAIMS We claim:

1. A method for balancing electrode arms of a welding device including a first electrode arm and a second electrode arm movable with respect to one another and coupled to a reference arm, and a compensation actuator, including first and second fluid chambers, coupled to the first electrode arm and the reference arm to balance a weight of the electrode arms, the method comprising steps of:

determining a balance force between the first electrode arm and the reference arm when the welding device is in a first spatial orientation; moving the welding device into at least a second spatial orientation; and adjusting a differential pressure between the first fluid chamber and the second fluid chamber of the compensation actuator to maintain the balance force.

2. The method of claim 1, wherein the welding device further includes a clamping actuator coupled to the first and second electrode arms, wherein the method further comprises a step of determining a clamping pressure required by the clamping actuator to actuate the first and second electrode arms with a predetermined clamping force.

3. The method of claim 2, wherein the clamping pressure is determined based on the differential pressure between the first and second fluid chambers of the compensation actuator required to maintain the balance force.

4. The method of claim 1, wherein the balance force is determined from a force sensor coupled to the first electrode arm and the reference arm.

5. The method of claim 1, wherein the welding device further includes a position sensor comprising a first portion coupled to the first electrode arm and a second portion coupled to the reference arm and wherein the method further comprises steps of:

determining a spatial orientation of the reference arm using the second portion of the position sensor; and comparing the spatial orientation of the first electrode arm relative to the spatial orientation of the reference arm to check the weight balance of the electrode arms.

6. The method of claim 1, wherein the compensation actuator further includes a magnet coupled to a first portion and a coil coupled to a second portion and wherein the method further comprises a step of determining a movement of the compensation actuator based on a voltage produced by movement of the magnet relative to the coil.

7. The method of claim 1, wherein the step of adjusting the differential pressure between the first and second fluid chambers of the compensation actuator comprises actuating a 3/2-way proportional pressure regulating valve in series with a 5/2-way valve, which are in fluid communication with a pressurized fluid source.

8. A method for balancing electrode arms of a welding device including a first electrode arm and a second electrode arm movable with respect to one another and coupled to a reference arm, a compensation actuator, including first and second fluid chambers, coupled to the first electrode arm and the reference arm to balance a weight of the electrode arms, and a clamping actuator coupled to the first and second electrode arms, the method comprising steps of:

determining a spatial orientation of the welding device; and

9. The method of claim 8, wherein the spatial orientation is determined using a spatial position sensor coupled to the first electrode arm.

10. The method of claim 9, wherein the spatial position sensor comprises a digital spatial position sensor.

11. The method of claim 8, further comprising a step of determining a differential pressure required between the first and second fluid chambers to balance the electrode arms at the determined spatial orientation.

12. The method of claim 11, further comprising a step of adjusting the differential pressure between the first and second fluid chambers of the compensation actuator to balance the electrode arms at the determined spatial orientation by actuating a 3/2-way proportional pressure regulating valve in series with a 5/2-way valve, which are in fluid communication with a pressurized fluid source.

13. The method of claim 8, wherein the welding device further includes a position sensor comprising a first portion coupled to the first electrode arm and a second portion coupled to the reference arm and wherein the method further comprises steps of:

14. The method of claim 8, wherein the compensation actuator further includes a magnet coupled to a first portion and a coil coupled to a second portion and wherein the method further comprises a step of determining a movement of the compensation actuator based on a voltage produced by movement of the magnet relative to the coil.

15. A welding device (100), comprising:

a first electrode arm (101) and a second electrode arm (102) movable with respect to one another and coupled to a reference arm (30); a compensation actuator (106), including first and second fluid chambers (206a, 206b), coupled to the first electrode arm (101) and to the reference arm (30) to balance a weight of the electrode arms (101, 102); and a force sensor (111) coupled to the first electrode arm (101) and to the reference arm (30).

16. The welding device (100) of claim 15, further comprising a control system (350) including a processing system (351) configured to:

determine a balance force between the first electrode arm (101) and the reference arm (30) when the welding device (100) is in a first spatial orientation using a signal from the force sensor (111); and

adjust the differential pressure between the first and second fluid chambers (206a, 206b) of the compensation actuator (106) to maintain the balance force when the welding device (100) is in at least a second spatial orientation.

17. The welding device (100) of claim 16, further comprising a clamping actuator (103) coupled to the first electrode arm (101) and the second electrode arm (102), wherein the processing system (351) is further configured to:

determine a clamping pressure required by the clamping actuator (103) to actuate the first and second electrode arms (101, 102) with a predetermined clamping force.

18. The welding device (100) of claim 17, wherein the clamping pressure is based on the differential pressure between the first and second fluid chambers (206a, 206b) of the compensation actuator (106) required to maintain the balance force.

19. The welding device (100) of claim 15, further comprising a position sensor (410) including a first portion (410a) coupled to the first electrode arm (101) and a second portion (410b) coupled to the reference arm (30).

20. The welding device (100) of claim 19, further comprising a control system (350) including a processing system (351) configured to:

determine a spatial orientation of the first electrode arm (101) using the first portion (410a) of the position sensor (410);

determine a spatial orientation of the reference arm (30) using the second portion

(410b) of the position sensor (410); and

compare the spatial orientation of the first electrode arm (101) relative to the spatial orientation of the reference arm (30) to check the weight balance of the electrode arms (101, 102).

21. The welding device (100) of claim 15, further comprising a magnet (412a) coupled to a first portion (108) of the compensation actuator (106) and a coil (412b) coupled to a second portion (107) of the compensation actuator (106), and a control system (350) including a processing system (351) configured to determine movement of the compensation actuator (106) based on a voltage produced by movement of the magnet (412a) relative to the coil (412b).

22. The welding device (100) of claim 15, further comprising a 3/2-way proportional pressure regulating valve (321) in series with a 5/2-way valve (322) to selectively provide fluid communication between the first and second fluid chambers (206a, 206b) of the compensation actuator (106) and a pressurized fluid source (320).

A welding device (100), comprising:

a first electrode arm (101) and a second electrode arm (102) movable with respect to one another and coupled to a reference arm (30); a compensation actuator (106), including first and second fluid chambers (206a, 206b), coupled to the first electrode arm (101) and to the reference arm (30) to balance a weight of the electrode arms (101, 102); a spatial position sensor (110) for determining a spatial orientation of the welding device (100) and coupled to the first electrode arm (101);

a clamping actuator (103) coupled to the first and second electrode arms (101, 102); and a control system (350) including a processing system (351) configured to:

determine a spatial orientation of the welding device (100); and determine a clamping pressure required by the clamping actuator (103) to actuate the first and second electrode arms (101, 102) with a predetermined clamping force at the determined spatial orientation.

24. The welding device (100) of claim 23, wherein the spatial position sensor (110) comprises a digital spatial position sensor.

25. The welding device (100) of claim 23, wherein the processing system (351) is further configured to determine a differential pressure required between the first and second fluid chambers (206a, 206b) to balance the electrode arms (101, 102) at the determined spatial orientation.

26. The welding device (100) of claim 23, further comprising a 3/2-way proportional pressure regulating valve (321) in series with a 5/2-way valve (322) to selectively provide fluid communication between the first and second fluid chambers (206a, 206b) of the compensation actuator (106) and a pressurized fluid source (320).

27. The welding device (100) of claim 23, further comprising a position sensor (410) including a first portion (410a) coupled to the first electrode arm (101) and a second portion (410b) coupled to the reference arm (30) and wherein the processing system (351) is further configured to:

(410b) of the position sensor (410); and

28. The welding device (100) of claim 23, further comprising a magnet (412a) coupled to a first portion (108) of the compensation actuator (106) and a coil (412b) coupled to a second portion (107) of the compensation actuator (106) wherein the processing system (351) is further configured to determine a movement of the compensation actuator (106) based on a voltage produced by movement of the magnet (412a) relative to the coil (412b).