Method for controlling tip dressing of an electrode tip

Abstract

A computer-implemented method for controlling tip dressing of at least one electrode tip (111, 112) of a welding gun (110) using a rotating cutter (151), the method comprising: - instructing a drive device (113) to apply a pressing force to press the at least one electrode tip (111, 112) into the rotating cutter (151) in a tip dressing procedure; - varying the pressing force stepwise over time in a series of time steps during the tip dressing procedure, wherein the pressing force applied during each time step is controlled to a set value associated with that time step, wherein the series of time steps comprises alternating primary and secondary time steps, the pressing force applied during each primary time step being at least twice the pressing force applied during each secondary time step.

Description

[0001] METHOD FOR CONTROLLING TIP DRESSING OF AN ELECTRODE TIP

[0002] TECHNICAL FIELD

[0003] The technology disclosed herein relates generally to tip dressing of electrode tips of welding guns. In particular, it relates to means and methods for controlling tip dressing of at least one electrode tip of a welding gun using a rotating cutter. It further relates to a welding robot comprising a welding gun.

[0004] BACKGROUND

[0005] Industrial welding robots are typically used for spot welding in e.g. the automotive industry. During spot welding, two metal sheets are joined together by applying pressure and heat using a welding gun of the robot. The welding gun comprises two opposite electrodes configured to clamp the two metal sheets together as an electric current is passed between the electrodes. To obtain high-quality welds, it is important that the electrode tips are sharp. However, the electrodes tend to degrade over time as a result of deformation due to heat, wear, oxide scale formation, and welding waste material deposited on the electrode tips. Therefore, tip dressing is regularly carried out to sharpen the electrode tips. During the tip dressing procedure, the electrode tips are pressed into a rotating cutter, removing the outer layers from the electrode tips and recreating the original electrode tip shape.

[0006] During the tip dressing procedure, material removed from the electrode tips form chips that are dispersed from the cutter via an opening provided therein. Chips may however become stuck in the opening, causing material to build up in the cutter. Such material build-up may prevent efficient grinding and it may also cause damages to the welding gun and / or the rotating cutter. To avoid production stops, it is therefore desirable to keep the opening of the cutter clear during operation.

[0007] SUMMARY

[0008] A primary objective of embodiments herein is to provide in at least some aspects improved methods and means for controlling tip dressing of at least one electrode tip of a welding gun. A specific objective is to provide means and methods for controlling the tip dressing procedure such that material removed from the at least one electrode tip may be prevented from building up within the cutter. In particular, it is an objective to provide such means and methods that may reduce the risk of material building up within the cutter without excessive use of compressed air.

[0009] According to a first aspect, at least the primary objective is accomplished by a computer-implemented method for controlling tip dressing of at least one electrode tip of a welding gun using a rotating cutter. The welding gun may comprise a pair of clamping devices configured to be positioned on opposite sides of the cutter. The at least one electrode tip may be disposed on at least one of the clamping devices. The welding gun may further comprise a drive device configured to move the clamping devices relative to one another, i.e., towards and away from one another. The method comprises:

[0010] - instructing a drive device to apply a pressing force to press the at least one electrode tip into the rotating cutter in a tip dressing procedure; and

[0011] - varying the pressing force stepwise over time in a series of time steps during the tip dressing procedure, wherein the pressing force applied during each time step is controlled to a set value associated with that time step, wherein the series of time steps comprises alternating primary and secondary time steps, the pressing force applied during each primary time step being at least twice the pressing force applied during each secondary time step.

[0012] By varying the pressing force in a series of time steps such that the pressing force applied during the primary time steps is at least twice the pressing force applied in the secondary time steps, a size of chips formed during the tip dressing procedure may be reduced in comparison with a process in which a constant pressing force is applied. In particular, this is applicable when the pressing forces are selected such that the rotating cutter is only able to remove a substantial amount of material from the at least one electrode tip during the primary time steps and not during the secondary time steps. During the secondary time steps, the chip maybe broken. With every second time step being a secondary time step, the chip size may be significantly reduced. The smaller chips may more easily be dispersed via an opening in the rotating cutter, such as by gravity. Hence, material build-up in the cutter may be prevented, which in turn may reduce the amount of production stops and improve efficiency.

[0013] The welding gun may be a welding gun for spot welding, comprising two electrode tips. Each electrode tip is disposed on a respective one of the clamping devices. In such a welding gun, both the electrode tips may be dressed simultaneously during the tip dressing procedure.

[0014] It is beneficial that the pressing force during the secondary time steps is a positive force, ensuring that the cutter remains in contact with the surface of the at least one electrode tip. This reduces the risk of forming an uneven electrode tip surface during the tip dressing procedure.

[0015] Optionally, the pressing force applied during each primary time step is at least 3 times the pressing force applied during each secondary time step, such as at least 4, 5, 6, 7, 8 or 10 times the pressing force applied during each secondary time step. For example, the pressing force applied during each primary time step may be 3-8 times the pressing force applied during each secondary time step, such as 5-7 times the pressing force applied during each primary time step. This may contribute to a smaller chip size and reduced material build-up in the cutter. In some embodiments, the pressing force applied during each primary time step is 6-8 times the pressing force applied during each secondary time step.

[0016] Optionally, the series of time steps comprises an initial primary time step having a longer duration than each one of the subsequent primary time steps. This maybe useful to initially reform the at least one electrode and make it fit within the cutter for subsequent machining throughout the tip dressing procedure. The duration of the initial primary time step may be set to achieve matching contact surfaces between the electrode tip and the cutter at the end of the initial primary time step.

[0017] Optionally, the method further comprises controlling the cutter to rotate. Alternatively, rotation of the cutter may be controlled independently of the proposed method.

[0018] Optionally, the controlling of the cutter to rotate may comprise controlling the cutter to rotate at a fixed rotational speed throughout the tip dressing procedure. This may facilitate the cutter control and the tip dressing procedure. In some embodiments, the cutter maybe of a type that does not allow controlled variation of the rotation speed. For example, it maybe driven by a direct online electric motor. The actual rotational speed of the cutter may vary during the tip dressing procedure, as a result of the varying pressing force, although the cutter is controlled to rotate at a set speed.

[0019] Optionally, the varying of the pressing force during the tip dressing procedure comprises successively increasing the set value of the pressing force applied during the primary time steps until a first condition is fulfilled.

[0020] Hence, in each primary time step, the pressing force may be controlled to a higher value than during the preceding primary time step until the first condition is fulfilled. In this way, it maybe ensured that the cutter is able to engage with the at least one electrode tip at the beginning of each primary time step during rough machining, removing material from the at least one electrode tip.

[0021] Optionally, the first condition is fulfilled after a predetermined number of time steps, or when a predetermined time has elapsed, or when the cutter has rotated a predetermined number of revolutions, or when a predetermined amount of material has been removed from the at least one electrode tip. In this way, the first condition may be set such that it is considered fulfilled once the rough machining of the at least one electrode tip is finished, i.e., when oxide scale and welding waste material has been removed and the electrode tip has assumed an approximate target shape.

[0022] Optionally, when the first condition has been fulfilled, the varying of the pressing force during the tip dressing procedure comprises successively reducing the set value of the pressing force applied during the primary time steps. The successive reduction of the pressing force after fulfilment of the first condition may allow a fine-tuning of the at least one electrode tip, i.e., fine machining thereof to remove irregularities.

[0023] Optionally, the set value of the pressing force applied during the secondary time steps is the same for all of the secondary time steps. This may facilitate the tip dressing procedure. Since no material removal from the at least one electrode tip is intended during the secondary time steps, it may typically not be necessary to vary the pressing force applied during those time steps. Optionally, for a major part of the tip dressing procedure, a duration of each time step is set to be smaller than the time it takes the cutter to rotate one revolution at the pressing force applied in that time step. In this way, the chip maybe broken between each revolution of the rotating cutter, ensuring a sufficiently small chip size. The major part of the tip dressing procedure herein refers to at least 50% of the tip dressing procedure as measured in terms of time. It is not necessary that all time steps have the same duration. Instead, a variable time step maybe used. For example, the primary time steps may vary in duration. Since the actual time it takes the cutter to rotate one revolution may be affected by the pressing force applied to the electrode tip, an estimated or measured rotational speed at the applied pressing force in that time step may be used to determine the time rather than a nominal rotational speed of the cutter.

[0024] Optionally, the time series is determined such that a combined duration of one of the primary time steps and the subsequent secondary time step is less than or equal to the time it takes the cutter to rotate one revolution at the pressing force applied in the primary time step. This may lead to desirable chip size. It may be applied for the entire tip dressing procedure, or over a part of the tip dressing procedure, such as over the major part of the tip dressing procedure as defined above. In the same way as above, an estimated or measured rotational speed may be used.

[0025] Optionally, an average duration of the secondary time steps is shorter than an average duration of the primary time steps. The secondary time steps only need to be long enough to break the chip since no substantial material removal takes place during the secondary time steps. Hence, this may shorten the total duration of the tip dressing procedure in comparison with equally long primary and secondary time steps. It is possible, but not necessary, that all secondary time steps have the same duration.

[0026] Optionally, each one of the secondary time steps is interleaved between two successive primary time steps. This ensures that the chip is broken between each two successive primary time steps.

[0027] Optionally, the varying of the pressing force stepwise over time during the tip dressing procedure comprises varying the pressing force based on a predetermined schedule. This allows selection of a preset schedule based on, e.g., welding material, welding process parameters, electrode tip type, etc.

[0028] Optionally, the method further comprises:

[0029] - obtaining measurement data relating to the tip dressing procedure, wherein the varying of the pressing force stepwise over time further comprises adjusting at least one set value of the pressing force and / or a duration of at least one of the time steps and / or a total number of time steps in dependence on the obtained measurement data.

[0030] The measurement data may relate to, e.g., material removal rate, amount of material removed, rotational force, load on electric motor, etc. In this way, the duration and pressing force of each time step may be adjusted in real time in dependence on, e.g., material removal rate, amount of material removed, material type, rotational force, etc.

[0031] Optionally, the pressing force applied during each primary time step is sufficient to remove material from the at least one electrode tip, and the pressing force applied during each secondary time step is insufficient to remove material from the at least one electrode tip. Hence, the pressing force applied during the secondary time steps may be sufficient to ensure contact, but insufficient to result in substantial material removal from the at least one electrode tip.

[0032] According to a second aspect, an electronic control unit comprising processing circuitry configured to perform the method of the first aspect is provided.

[0033] According to a third aspect, a welding robot is provided. The welding robot comprises:

[0034] - a welding gun comprising a pair of clamping devices configured to be positioned on opposite sides of a workpiece, at least one electrode tip being disposed on at least one of the clamping devices, and a drive device configured to move the clamping devices relative to one another

[0035] - a rotatable cutter for tip dressing of the at least one electrode tip, and

[0036] - the electronic control unit of the second aspect. The welding robot may be an industrial welding robot, such as a spot-welding robot.

[0037] The welding gun may be a welding gun for spot welding, comprising two electrode tips. Each electrode tip is disposed on a respective one of the clamping devices.

[0038] According to a fourth aspect, a computer program comprising computer code which, when run on processing circuitry of a control unit, causes the control unit to perform the method of the first aspect, is provided.

[0039] According to a fifth aspect, a computer program product comprising a computer program of the third aspect, and a computer readable storage medium on which the computer program is stored, is provided.

[0040] Other objectives, features and advantages of the enclosed embodiments will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the drawings.

[0041] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / an / the element, apparatus, component, means, module, action, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, module, action, etc., unless explicitly stated otherwise. The actions of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated.

[0042] BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The inventive concept is now described, by way of example, with reference to the accompanying drawings, in which:

[0044] Fig. i is a schematic diagram illustrating a spot-welding robot;

[0045] Fig. 2 is a perspective view of a cutter used in a method according to embodiments;

[0046] Figs. 3 is a flowchart illustrating methods according to embodiments;

[0047] Fig. 4 is a schematic diagram showing pressing force as a function of time during a tip dressing procedure according to embodiments of the disclosed method; Fig. 5 is a flowchart illustrating methods according to embodiments;

[0048] Fig. 6 is a schematic diagram showing functional units of a control unit according to an embodiment;

[0049] Fig. 7 is a schematic diagram showing functional modules of a control unit according to an embodiment; and

[0050] Fig. 8 shows one example of a computer program product comprising computer readable means according to an embodiment.

[0051] The drawings are schematic and not drawn to scale.

[0052] DETAILED DESCRIPTION

[0053] The inventive concept will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the inventive concept are shown. This inventive concept may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the inventive concept to those skilled in the art. Like numbers refer to like elements throughout the description.

[0054] Fig. 1 schematically illustrates a welding robot loo for spot welding. In Fig. 1, the welding robot 100 is set up for a tip dressing procedure. A welding gun no of the welding robot 100 comprises a pair of clamping devices 114, 115. On the clamping devices 114, 115, electrodes comprising electrode tips 111, 112 are disposed. The clamping devices 114, 115, and hence the electrode tips 111, 112, are configured to, during spot welding, be positioned on opposite sides of a workpiece, such as on opposite sides of a pair of metal sheets that are to be joined together. An electrode drive device 113 configured to move the clamping devices 114, 115 relative to one another is further provided. The electrode drive device 113 may be configured to move one or both of the clamping devices 114, 115 to achieve the relative movement. It is thereby configured to apply a pressing force to press the electrode tips 111, 112 toward one another. During spot welding, the welding gun no presses both the electrode tips ill, 112 against the workpiece, such as the two metal sheets, while passing an electric current between the electrode tips 111, 112, thereby heating the workpiece under pressure to form a weld in the area of the electrode tips 111, 112. The electrode drive device 113 may, by way of example, comprise an electric motor enabling precise positioning of the electrode tips 111, 112.

[0055] The welding robot 100 further comprises a tip dressing device 150, comprising a rotatable cutter 151. The rotatable cutter 151 is configured to be positioned between the clamping devices 114, 115, and hence between the electrode tips 111, 112, for tip dressing of the electrode tips 111, 112. It may hence be configured to rotate about an axis of rotation A, defining an axial direction. An electronic control unit 1 is further provided, being in communicative connection with the tip dressing device 150 as well as with the drive device 113. The tip dressing device 150 may, e.g., be disposed on a pivotable arm or similar of the welding robot, such that it maybe inserted between the electrode tips 111, 112 during the tip dressing procedure, and removed therefrom during spot welding. The tip dressing device 150 may, apart from the rotatable cutter 151, comprise a cutter drive device (not illustrated) configured to rotate the cutter 151 during the tip dressing procedure. The cutter drive device may, by way of example, comprise an electric motor or another type of motor, such as a pneumatic or hydraulic motor. It may be configured to rotate the cutter at a fixed rotational speed or at a variable rotational speed, depending on motor type. Although the tip dressing device 150 is herein illustrated as a part of the welding robot 100, it may also be separate from the welding robot 100 and controlled independently of the welding robot 100.

[0056] Fig. 2 illustrates a cutter 151 according to an embodiment. The cutter 151 comprises a cutting insert 152 removably mounted on a tool body 153. The tool body 153 is configured to be secured to a tool holder (not shown) of the tip dressing device 150. The cutter 151 is configured for simultaneous tip dressing of a pair of electrodes 111, 112 as illustrated in Fig. 1. During tip dressing, chips removed from the electrode tips 111, 112 are dispersed via an opening 154 provided next to the cutting insert 152.

[0057] In a standard tip dressing procedure, the clamping devices 114, 115 are controlled to apply a set pressing force, pressing the electrode tips 111, 112 into the cutter 151 while rotating the cutter 151 at a constant speed. For example, a pressing force of 1200 N maybe applied for a time period of 3.5 seconds, with the cutter 151 rotating at a speed of 200 rpm. The cutter 151 will typically remove a major part of an intended amount of material to be removed within 1-2 revolutions of the cutter. The actual force applied will thereafter decrease slightly as a result of the removed material, reducing the material removal rate. As a result, the chips become relatively long.

[0058] If the chips become too long during the tip dressing procedure, they may get stuck in the opening 154 and cause damage to the cutter 151 or to the electrode tips 111, 112 during continued machining. It is therefore desirable to keep the chips short enough to ensure that they can be efficiently disposed via the opening 154. According to the present disclosure, a method for controlling tip dressing is proposed that aims at reducing the chip size during the tip dressing procedure, such that the risk of chips getting stuck in the cutter 151 is reduced in comparison with the standard tip dressing procedure described above.

[0059] Fig. 3 illustrates a computer-implemented method for controlling tip dressing of at least one electrode according to an embodiment of the disclosure. The method may be used in a welding robot 100 as illustrated with reference to Figs. 1 and 2. Although reference is made to a welding gun comprising two electrodes 111, 112, the method as proposed herein may also be used for tip dressing of a single electrode tip in a welding gun adapted for single electrode welding.

[0060] The method comprises the following actions, which may be carried out by the electronic control unit 1:

[0061] Action 301: Controlling the cutter 151 to rotate, such as at a fixed speed, throughout the tip dressing procedure.

[0062] Action 302: Instructing the electrode drive device 113 to apply a pressing force to press the at least one electrode tip, such as the electrode tips 111, 112, into the rotating cutter 151 in a tip dressing procedure. The pressing force may be an axial pressing force, or a force having at least one component along the axis A.

[0063] Action 303: Varying the pressing force stepwise over time in a series of time steps during the tip dressing procedure, wherein the pressing force applied during each time step is controlled to a set value associated with that time step. The series of time steps comprises alternating primary and secondary time steps. The pressing force applied during each primary time step is at least twice the pressing force applied during each secondary time step. Preferably, the pressing force applied during each primary time step may be at least 3 times the pressing force applied during each secondary time step, such as at least 4, 5, 6, 7, 8 or 10 times the pressing force applied during each secondary time step. In some embodiments, the pressing force applied during each primary time step may be up to 12-15 times the pressing force applied during each secondary time step. For example, the pressing force applied during each primary time step may be such 3-12 times the pressing force applied during each secondary time step, or 5-10 times the pressing force applied during each secondary time step. The pressing force applied during each primary time step should preferably be sufficient to remove material from the at least one electrode tip 111, 112, and the pressing force applied during each secondary time step should be insufficient to remove material, or at least any substantial amount of material, from the at least one electrode tip 111, 112.

[0064] Material removal from the electrode tips 111, 112 hence at least primarily takes place during the primary time steps, whereas during the secondary time steps, no substantial material removal takes place. During a primary time step, a chip will start to form as a result of the material removal. During the subsequent secondary time step, the chip is likely to break due to the continued rotation of the cutter 151, with the pressing force being insufficient to remove any substantial amount of material from the electrode tips 111, 112. The broken chip may hence be disposed via the opening 154, such as by falling out, by using suction, compressed air, etc.

[0065] The set value of the pressing force is the pressing force which is applied initially in each time step. During machining in the primary time steps, the actual pressing force will decrease slightly as a result of material removal during the time step. For example, the electrode drive device 113 may at the beginning of each time step bring the at least one electrode tip 111, 112 to a position at which the pressing force corresponds to the set value, and thereafter keep the at least one electrode tip 111, 112 in that position until the end of the time step. In some embodiments, the electronic control unit 1 is not configured to control the cutter 151 to rotate. Instead, the tip dressing device 150 comprising the cutter 151 may be controlled by a control unit different from the electronic control unit 1, or manually by an operator.

[0066] Fig. 4 is a diagram that schematically illustrates a force profile during a tip dressing procedure controlled using the method according to an example of the disclosure. In the tip dressing procedure, two opposite electrode tips 111, 112 are reformed and fine machined. Prior to the tip dressing procedure, the electrode tips 111, 112 are worn and have a deformed shape that does not fit perfectly in the cutter 151. The cutter 151 is rotated at a nominal speed of about 200 rpm, i.e., about 3.3 revolutions per second. An actual rotational speed is however lower due to the load applied during the machining. In the example, in an initial primary time step intended to reform flanks of the electrode tips 111, 112 to make them fit in the cutter 151, a first pressing force Fl is applied. This force is sufficient to remove material from the flanks of the deformed electrode tips 111, 112. The force Fl herein corresponds to about 1200 N. Following upon the initial primary time step is a series of 14 alternating primary and secondary time steps, during which the electrode tips 111, 112 are machined to resume an original shape and surface finish. During the primary time steps, material is removed not only from the flanks, but also from a foremost part of each electrode tip 111, 112. In the example, a first primary time step of the series follows immediately upon the initial primary time step. Over the four first primary time steps of the series, the pressing force is successively increased to a maximum pressing force Fmax, herein corresponding to about 1600 N. By successively increasing the pressing force, it is ensured that the cutter 151 engages with the electrodes 111, 112 at the beginning of each primary time step. In the following three primary time steps, the pressing force is successively reduced to a value between the first force Fl and the maximum force Fmax. During these primary time steps, fine machining is performed, removing irregularities and providing a fine surface. In each secondary time step, interleaved between two successive primary time steps, the pressing force is reduced to a minimum force Fo, insufficient to remove any substantial amount of material but sufficient to ensure contact. The force Fo herein corresponds to about 200 N. Hence, the pressing force applied in the primary time steps is in this example varied in the range of 6-8 times the pressing force applied in the secondary time steps. During the secondary time steps, the chips formed during the primary time steps are broken.

[0067] Each one of the secondary time steps maybe interleaved between two successive primary time steps for at least a part of the tip dressing procedure, such as in the illustrated example in Fig. 4. This means that, if the chips are broken during each secondary time step, several short chips will form during the tip dressing procedure instead of one long chip. The length of the chips will depend on the duration of the primary time steps. Typically, a duration of each time step maybe set to be smaller than the time it takes the cutter 151 to rotate one revolution at the applied pressing force in that time step. The time series may be determined such that a combined duration of one of the primary time steps and the subsequent secondary time step is less than or equal to the time it takes the cutter 151 to rotate one revolution at the pressing force applied in the primary time step. The duration of the time steps may vary over the time series. In particular, the primary time steps may have different durations. However, it is also possible that most or all primary time steps have the same duration.

[0068] An average duration of the secondary time steps should preferably be shorter than an average duration of the primary time steps, since no substantial material removal takes place during those time steps. To keep the total duration of the tip dressing procedure as short as possible, it is desirable to set the average duration of the secondary time steps to a value which is as small as possible. For a rotational speed of 200 rpm, a duration of about 0.1 s may typically be sufficient.

[0069] As illustrated in Fig. 4, the varying of the pressing force during the tip dressing procedure in the action 303 may comprise successively increasing the set value of the pressing force applied during the primary time steps until a first condition is fulfilled. For example, in each primary time step, the set value maybe slightly increased with respect to the set value of the preceding primary time step. In the example in Fig. 4, the first condition is considered fulfilled after a predetermined number of time steps. In other examples, it may be considered fulfilled when a predetermined time has elapsed, or when the cutter 151 has rotated a predetermined number of revolutions, or when a predetermined amount of material has been removed from the at least one electrode tip 111, 112. When the first condition has been fulfilled, the set value of the pressing force applied during the primary time steps maybe successively reduced, as also illustrated in Fig. 4.

[0070] In other non-illustrated examples, the set value of the pressing force applied during the primary time steps may be constant over time. In yet other examples, the set value of the pressing force applied during the primary time steps maybe successively increased over the entire tip dressing procedure.

[0071] The set value of the pressing force applied during the secondary time steps may preferably be constant, i.e., the same for all secondary time steps. It may also be varied, as long as it remains below a force necessary to result in substantial material removal from the at least one electrode tip 111, 112, and as long as it is sufficient to ensure contact between the electrode tips 111, 112 on the one hand and the cutter 151 on the other hand.

[0072] The actual values of the pressing force, the duration of the time steps, the total number of time steps, etc., maybe varied within the scope of the disclosure, as long as the series of time steps comprises alternating primary and secondary time steps, wherein the pressing force applied during each primary time step is at least twice the pressing force applied in the secondary time steps.

[0073] Fig. 5 illustrates a method for varying the pressing force stepwise over time during the tip dressing procedure according to an embodiment. The pressing force is herein varied based on a predetermined schedule. The following actions maybe carried out:

[0074] Action 501: Loading a predetermined schedule defining a series of time steps and a pressing force to be applied in each time step. The schedule may be one which is tailored to the particular type of electrode tips 111, 112, the type of cutter 151, the welding process, materials used, etc.

[0075] Action 502: Varying the pressing force stepwise over time during the tip dressing procedure based on the predetermined schedule. The varying of the pressing force stepwise over time may either strictly follow the schedule, or it may be adapted to the actual tip dressing procedure by actions 503, 504.

[0076] Action 503: Obtaining measurement data relating to the tip dressing procedure. Measurement data may be obtained continuously during the tip dressing procedure and may relate to material removal rate, amount of material removed, load on the cutter drive device, etc.

[0077] Action 504: Adjusting at least one set value of the pressing force and / or a duration of at least one of the time steps and / or a total number of time steps in dependence on the obtained measurement data. The adjustment maybe performed to adjust parameters of the schedule during the ongoing tip dressing procedure, and / or it may be performed such that the schedule is adjusted prior to a subsequent tip dressing procedure.

[0078] Fig. 6 schematically illustrates, in terms of number of functional units, the components of an electronic control unit 1 according to an embodiment. Processing circuitry 610 is provided using any combination of one or more of a suitable central processing unit (CPU), multiprocessor, microcontroller, digital signal processor (DSP), etc., capable of executing software instructions stored in a computer program product 820 (as in Fig. 8), e.g., in the form of a storage medium 630. The processing circuitry 610 may further be provided as at least one application specific integrated circuit (ASIC), or field programmable gate array (FPGA).

[0079] Particularly, the processing circuitry 610 is configured to cause the control unit 1 to perform a set of operations, or actions, as disclosed above. For example, the storage medium 630 may store the set of operations, and the processing circuitry 610 maybe configured to retrieve the set of operations from the storage medium 630 to cause the control unit 1 to perform the set of operations. The set of operations maybe provided as a set of executable instructions. The processing circuitry 610 is thereby arranged to execute methods as herein disclosed.

[0080] The storage medium 630 may also comprise persistent storage, which, for example, can be any single one or combination of magnetic memory, optical memory, solid state memory or even remotely mounted memory.

[0081] The control unit 1 may further comprise a communications interface 620 for communications with other entities, functions, nodes, and devices, over suitable interfaces. As such, the communications interface 620 may comprise one or more transmitters and receivers, comprising analogue and digital components. The processing circuitry 610 controls the general operation of the control unit 1, e.g., by sending data and control signals to the communications interface 620 and the storage medium 630, by receiving data and reports from the communications interface 620, and by retrieving data and instructions from the storage medium 630. Other components, as well as the related functionality, of the control unit 1 are omitted in order not to obscure the concepts presented herein.

[0082] Fig. 7 schematically illustrates, in terms of a number of functional modules, the components of a control unit 1 according to an embodiment. The control unit 1 of Fig. 7 comprises a number of functional modules:

[0083] - a controlling module 710 configured to control the cutter 151 to rotate;

[0084] - an instructing module 720 configured to instruct the electrode drive device 113 to apply a pressing force to press the at least one electrode tip 111, 112 into the rotating cutter 151 in a tip dressing procedure; and

[0085] - a varying module 730 configured to vary the pressing force stepwise over time in a series of time steps during the tip dressing procedure as described above with reference to Figs. 1-5.

[0086] The control unit 1 may further comprise a number of additional optional modules (not shown) configured to perform the actions described above with reference to Fig. 5. In general terms, each functional module 710-730 maybe implemented in hardware or in software. Preferably, one or more or all functional modules 710-730 may be implemented by the processing circuitry 610, possibly in cooperation with the communications interface 620 and the storage medium 630. The processing circuitry 610 may thus be arranged to from the storage medium 630 fetch instructions as provided by a functional module 710-730 and to execute these instructions, thereby performing any actions of the control unit 1 as disclosed herein.

[0087] Fig. 8 shows one example of a computer program product 820 comprising computer readable means 840. On this computer readable means 840, a computer program 830 can be stored, which computer program 830 can cause the processing circuitry 610 and thereto operatively coupled entities and devices, such as the communications interface 620 and the storage medium 630, to execute methods according to embodiments described herein. The computer program 830 and / or computer program product 820 may thus provide means for performing any actions of the control unit 1 as herein disclosed.

[0088] In the example of Fig. 8, the computer program product 820 is illustrated as an optical disc, such as a CD (compact disc) or a DVD (digital versatile disc) or a Blu-Ray disc. The computer program product 820 could also be embodied as a memory, such as a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM) and more particularly as a non-volatile storage medium of a device in an external memory such as a USB (Universal Serial Bus) memory or a Flash memory, such as a compact Flash memory. Thus, while the computer program 830 is here schematically shown as a track on the depicted optical disk, the computer program 830 can be stored in any way which is suitable for the computer program product 820.

[0089] The inventive concept has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended patent claims.

Claims

CLAIMS1. A computer-implemented method for controlling tip dressing of at least one electrode tip (m, 112) of a welding gun (no) using a rotating cutter (151), the method comprising:- instructing (302) a drive device (113) to apply a pressing force to press the at least one electrode tip (111, 112) into the rotating cutter (151) in a tip dressing procedure;- varying (303) the pressing force stepwise over time in a series of time steps during the tip dressing procedure, wherein the pressing force applied during each time step is controlled to a set value associated with that time step, wherein the series of time steps comprises alternating primary and secondary time steps, the pressing force applied during each primary time step being at least twice the pressing force applied during each secondary time step.

2. The method of claim 1, wherein the pressing force applied during each primary time step is at least 3 times the pressing force applied during each secondary time step, such as at least 4, 5, 6, 7, 8 or 10 times the pressing force applied during each secondary time step.

3. The method of claim 1 or 2, wherein the varying of the pressing force during the tip dressing procedure comprises successively increasing the set value of the pressing force applied during the primary time steps until a first condition is fulfilled.

4. The method of claim 3, wherein the first condition is fulfilled after a predetermined number of time steps, or when a predetermined time has elapsed, or when the cutter (151) has rotated a predetermined number of revolutions, or when a predetermined amount of material has been removed from the at least one electrode tip (111, 112).

5. The method of claim 3 or 4, wherein, when the first condition has been fulfilled, the varying of the pressing force during the tip dressing procedure comprises successively reducing the set value of the pressing force applied during the primary time steps.

6. The method of any one of the preceding claims, wherein the set value of the pressing force applied during the secondary time steps is the same for all of the secondary time steps.

7. The method of any one of the preceding claims, wherein, for a major part of the tip dressing procedure, a duration of each time step is set to be smaller than the time it takes the cutter (151) to rotate one revolution at the pressing force applied in that time step.

8. The method of any one of the preceding claims, wherein the time series is determined such that a combined duration of one of the primary time steps and the subsequent secondary time step is less than or equal to the time it takes the cutter (151) to rotate one revolution at the pressing force applied in the primary time step.

9. The method of any one of the preceding claims, wherein an average duration of the secondary time steps is shorter than an average duration of the primary time steps.

10. The method of any one of the preceding claims, wherein the varying (303) of the pressing force stepwise over time during the tip dressing procedure comprises varying (502) the pressing force based on a predetermined schedule.

11. The method of claim 10, further comprising:- obtaining (503) measurement data relating to the tip dressing procedure, wherein the varying (303) of the pressing force stepwise over time further comprises adjusting (504) at least one set value of the pressing force and / or a duration of at least one of the time steps and / or a total number of time steps in dependence on the obtained measurement data.

12. The method of any one of the preceding claims, wherein the pressing force applied during each primary time step is sufficient to remove material from the at least one electrode tip (111, 112), and the pressing force applied during each secondary time step is insufficient to remove material from the at least one electrode tip (111, 112).

13. The method of any one of the preceding claims, wherein the series of time steps comprises an initial primary time step having a longer duration than each one of the subsequent primary time steps.14- An electronic control unit (1) comprising processing circuitry (510) configured to perform the method of any one of claims 1-13.

15. A welding robot (100), comprising:- a welding gun (no) comprising a pair of clamping devices (114, 115) configured to be positioned on opposite sides of a workpiece, at least one electrode tip being disposed on at least one of the clamping devices, and a drive device (113) configured to move the clamping devices (114, 115) relative to one another,- a rotatable cutter (151), and- the electronic control unit (1) of claim 13.

16. A computer program (730) comprising computer code which, when run on processing circuitry (510) of a control unit (1), causes the control unit (1) to perform the method of any one of claims 1-13.

17. A computer program product (720) comprising a computer program of claim 16, and a computer readable storage medium (740) on which the computer program (730) is stored.

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