Method for operating a spot welding gun and spot welding gun

Abstract

This invention relates to a method for operating a spot welding clamp, the clamp including a clamp control device, a valve device, a fluid actuator, and a sensor assembly. The method comprises the following steps: receiving and processing a fieldbus signal into a control signal; providing the control signal to the valve device by the clamp control device; influencing the fluid flow to the fluid actuator according to the control signal; detecting at least one operating pressure at the fluid actuator using the sensor assembly; and providing a sensor signal from the sensor assembly to an operating pressure regulator of the clamp control device for adjusting the operating pressure to the fluid actuator according to the control signal. According to the invention, a supply pressure signal from a supply pressure sensor disposed at an output connector of the valve device connected to the fluid actuator is provided to the supply pressure regulator for adjusting the supply pressure supplied at the output connector according to the control signal.

Description

Technical Field

[0001] This invention relates to a method for operating a spot welding clamp, the clamp including a clamp control device, a valve device, a fluid actuator, and a sensor assembly. The method comprises the following steps: receiving a fieldbus signal at a fieldbus connector of the clamp control device and processing the fieldbus signal into a control signal for the valve device within the clamp control device; providing the control signal to the valve device by the clamp control device; influencing the fluid flow to the fluid actuator according to the control signal provided to the valve device; detecting at least one operating pressure at the fluid actuator using the sensor assembly; providing a sensor signal to the clamp control device by the sensor assembly; and processing the sensor signal in a working pressure regulator of the clamp control device for adjusting the working pressure to the fluid actuator according to the control signal. Furthermore, this invention relates to a spot welding clamp. Summary of the Invention

[0002] The objective of this invention is to provide a method for operating a spot welding clamp and a spot welding clamp, thereby optimizing compressed air consumption using the method and the spot welding clamp.

[0003] The task is solved by the method of the type mentioned at the beginning in the following manner: A supply pressure signal from a supply pressure sensor located at the output connector of the valve device connected to the fluid actuator is provided to a supply pressure regulator belonging to the valve device and connected to a clamp control device. The supply pressure regulator is configured to adjust the supply pressure provided at the output connector according to a control signal, preferably to one of at least two preset supply pressure levels, particularly to the minimum supply pressure level necessary to execute the corresponding motion command. Preferably, the corresponding supply pressure level is selected such that only such a supply pressure is always provided at the output connector, i.e., at a supply pressure that is just sufficient to execute the desired adjustment or working motion for the spot welding clamp. Therefore, a minimum supply pressure level adapted to the corresponding operating state of the spot welding clamp is provided, which is lower than the network pressure or feed pressure provided to the valve device.

[0004] This motion command can be understood not only as a command that should cause a change in the electrode spacing of the welding electrodes, but also as a command that should cause a force to be built between the two welding electrodes.

[0005] Here, the supply pressure is understood as the fluid pressure provided at the output connection of the valve device, wherein the output connection is connected to the fluid actuator either directly (i.e., without any other intermediate fluid component, such as a valve and / or throttling device), or indirectly (i.e., with at least one intermediate fluid component, such as a valve or throttling device). The pressure of the working fluid, especially compressed air, supplied to the valve device by a working fluid source, particularly a compressed air source, is called the input pressure. Within the scope of the method execution, the input pressure is set to be constant except for possible fluctuations (such as those that may occur in the fluid supply system due to time-alternating loads). In contrast, according to this method, the supply pressure is limited to a correspondingly suitable supply pressure level according to the different functions of the spot welding clamp, such as the opening process, closing process, or welding process, in order to ensure the minimum possible consumption of the working fluid.

[0006] The purpose of the method is to influence the supply pressure to the fluid actuator as needed, so that a lower supply pressure level can be used, for example, during the simple movement of the fluid actuator, compared to the force build-up required for welding (in which a higher supply pressure level is needed for the fluid actuator).

[0007] Here, in particular, one can proceed from the following: the fluid actuator acts directly or via a transmission mechanism, especially a lever transmission mechanism, on at least one welding electrode of the spot welding clamp. Exemplarily, it can be configured to increase the spacing between the normally two oppositely arranged welding electrodes in preparation for the execution of the welding process, so that movement around the contour of the sheet metal part to be processed can be achieved, for example, without contact. A low supply pressure level is sufficient for this, as only the frictional and inertial forces of the spot welding clamp need to be overcome. This relative movement of the first welding electrode relative to the second welding electrode is called a traversing motion. Furthermore, it can be configured to first complete the approach of the oppositely arranged welding electrodes upon reaching the welding position until the welding electrodes reach mechanical contact with the sheet metal part to be processed, which also involves traversing motion. A high supply pressure level is only required when electrical energy is supplied to the at least two welding electrodes so that the welding force required during the welding process can be applied between the at least two welding electrodes.

[0008] According to the invention, the adjustment of the required supply pressure level is performed in parallel with the original fluid control operation of the fluid actuator. The limitation of the supply pressure is performed by a supply pressure regulator, which is directly coupled to the valve device and is specifically parameterized with respect to the valve device. Here, the supply pressure regulator accesses the sensor signal of the supply pressure sensor and is further configured to preset a corresponding appropriate supply pressure level based on the control signal provided to the supply pressure regulator by the clamp control device.

[0009] In contrast, the clamp control device adjusts the working pressure based on sensor signals from the sensor assembly associated with the fluid actuator and on the arriving fieldbus signals (which are converted into control signals in the clamp control device).

[0010] Preferably, the clamp control device with the working pressure regulator is configured such that the adjustment movement of the spot welding clamp, i.e., the change in the distance between the two welding electrodes, is performed without regard to the sensor signals of the first and second working pressure sensors. Instead, the adjustment movement is performed by the clamp control device as an adjustment process (closed loop), particularly as a position adjustment process, using the position signal of the position sensor. In contrast, the working process of the spot welding clamp, i.e., the execution of the spot welding process, can be configured to be force-regulated (closed loop) by the working pressure regulator using the sensor signals of the first and second working pressure sensors. This can be achieved by storing all the parameters required for the corresponding welding force at the electrodes, such as the geometry of the fluid actuator and / or the first and second welding electrodes, in the working pressure regulator.

[0011] In practice, this simply means, exemplarily, that the clamp control receives a sequence of fieldbus signals at its fieldbus interface and first determines from these fieldbus signals the motion commands set for the fluid actuator. In subsequent processing steps, if working pressure regulation is required (as is the case when performing a welding process), then, in the case of a working pressure regulator configured as part of the clamp control, the clamp control determines from the motion commands a suitable control signal for the valve and provides it to the valve. Furthermore, the clamp control also provides the control signal to a supply pressure regulator, which determines from the control signal the supply pressure level necessary to execute the corresponding motion command and performs the corresponding operation of the valve at that supply pressure level.

[0012] Advantageous improvements of the invention are the subject of the dependent claims.

[0013] Suitablely, the supply pressure is at most 50 percent greater than the operating pressure, preferably at most 30 percent, particularly preferably at most 20 percent, and especially at most 10 percent. The purpose of this method is to provide the supply pressure so that only minimal, and especially minimal, measures are required when operating the valve device to limit the operating pressure. If, for example, the required operating pressure is known for the movement of a fluid actuator, the supply pressure is adjusted by the supply pressure regulator so that the supply pressure is only slightly greater than the required operating pressure. Furthermore, by adjusting the supply pressure to a pressure level slightly higher than the required operating pressure, unnecessary consumption of the working fluid, especially compressed air, is avoided, because the small difference between the supply and operating pressures keeps throttling losses in the valve device minimal.

[0014] In an improved embodiment of the method, a first supply pressure level is selected such that the fluid actuator can induce an adjustment movement against the welding electrode, and a second supply pressure level is selected such that the fluid actuator can apply welding force to the welding electrode used in the welding process. Simply exemplarily, this can be achieved at a working pressure of 2 bar for the adjustment movement of the welding electrode, while the supply of welding force for performing the welding process requires a working pressure of 5 bar. Accordingly, a supply pressure regulator is configured, for example, to limit the supply pressure used to perform the adjustment movement to 2.2 bar, where the input pressure can simply exemplarily be 6 bar. For example, a supply pressure of 5.5 bar can be provided to perform the welding process. Simply exemplarily, it can be configured such that different supply pressures, sequentially occurring, must be provided to different weld positions constructed in different times during the welding process. Accordingly, the supply pressure levels are adapted accordingly.

[0015] Preferably, the working pressure regulator is configured as a processing device of the clamp control device, particularly a regulation algorithm in a microcontroller or microprocessor, and configured to provide a control signal to the valve device according to a control signal. The supply pressure regulator is configured as a processing device of the valve device, particularly a regulation algorithm in a microcontroller or microprocessor, and configured to provide or determine and provide the required supply pressure level according to the control signal. Here, the working pressure regulator belonging to the clamp control device regulates the working pressure to be supplied to the fluid actuator in a closed regulation loop (closed loop) based on the arriving motion command and the sensor signal from a sensor assembly associated with the fluid actuator to determine the working pressure. Furthermore, the supply pressure regulator belonging to the valve device provides or determines and provides the supply pressure level required for executing the motion command (based on the control signal) according to the control signal arriving from the clamp control device and the supply pressure signal from the supply pressure sensor, and (particularly for the duration of the execution of the corresponding motion command) regulates the supply pressure in a closed regulation loop, which is provided at the output connector of the valve device.

[0016] The objective of this invention, according to a second aspect, is achieved by a spot welding clamp for welding sheet metal components. Here, the spot welding clamp comprises: a clamp interface configured for attachment to an industrial robot, the clamp interface including a fieldbus connector, a compressed air connector, and a current connector; a clamp control device connected to the fieldbus connector; a valve device connected to the clamp control device and to the compressed air connector; and a fluid actuator connected to the valve device, the fluid actuator having a sensor assembly configured to detect operating pressure at the fluid actuator and to provide a sensor signal related to the operating pressure to the clamp control device, wherein the clamp control device has an operating pressure regulator for adjusting the operating pressure at the fluid actuator, characterized in that the valve device has a supply pressure sensor at an output connector connected to the fluid actuator, the supply pressure sensor configured to provide a supply pressure signal, and the valve device includes a supply pressure regulator connected to the clamp control device, the supply pressure regulator being electrically connected to the supply pressure sensor and configured to adjust the supply pressure provided at the output connector to one of at least two preset supply pressure levels according to a control signal.

[0017] The clamp interface is used for the mechanical connection between the spot welding clamp and the arm of an industrial robot. Alternatively, the clamp interface can also be used to secure the spot welding clamp to a fixed machine frame. Preferably, the clamp interface is configured such that the mechanical connection between the spot welding clamp and the industrial robot establishes a connection between the fieldbus connector, compressed air connector, and current connector and their corresponding connectors on the industrial robot, even without other assistance. With the clamp interface and the corresponding interfaces on the industrial robot configured in this way, the spot welding clamp can be received and placed in a fully automated manner by the industrial robot. The clamp control device is connected to the fieldbus connector and the current connector and is used to determine motion commands for the fluid actuator from the fieldbus signals arriving via the fieldbus connector, so as to determine control signals for the valve device therefrom. Furthermore, the clamp control device is simply exemplarily configured to influence the current flow between the current connector and the welding electrode according to the arriving fieldbus signals. Alternatively, the welding current is provided by a separately constructed welding transformer and transmitted to the welding electrode by the clamp interface without the clamp control device. Furthermore, the clamp control device is connected to the sensor assembly and configured to process sensor signals from the sensor assembly (which can determine the operating pressure at the fluid actuator) to form a closed regulating loop for adjusting the operating pressure based on the arriving motion command and the control signal determined therefrom. For this purpose, the clamp control device (which may in particular be a computer) includes an operating pressure regulator by means of which the operating pressure can be regulated.

[0018] The valve assembly includes at least one valve, which may be configured as a switching valve or a continuous valve, and is configured for electrical operation. Valve operation is performed via a supply pressure regulator, which is an integral part of the valve assembly and is electrically connected to a supply pressure sensor and a clamp control device. The supply pressure regulator has the following functions: determining a supply pressure level (required for executing a corresponding motion command) based on a control signal from the clamp control device and maintaining that supply pressure level during the execution of the motion command. Here, the supply pressure regulator utilizes a supply pressure signal from a supply pressure sensor configured to detect the supply pressure at the output connector of the valve assembly. Simply by example, the supply pressure regulator can be configured to adjust the supply pressure to a low first supply pressure level when the motion commands "open welding clamp" and "close welding clamp" arrive, and to a high second supply pressure level when the motion command "execute welding process" arrives.

[0019] Advantageously, the fluid actuator is constructed as a dual-acting pneumatic cylinder having a first working joint, a first pressure sensor coupled with a sensor assembly, and a second working joint, a second pressure sensor coupled with a sensor assembly. Both the first and second pressure sensors are electrically connected to a clamp control device. Here, the first working joint is used for ventilation and exhaust of a first working space within the pneumatic cylinder, while the second working joint is used for ventilation and exhaust of a second working space within the pneumatic cylinder. Both the first pressure sensor located at the first working joint and the second pressure sensor located at the second working joint are electrically connected to the clamp control device so that first and second working pressure signals can be provided to a working pressure regulator in the clamp control device based on a first working pressure at the first working joint and a second working pressure at the second working joint.

[0020] In another embodiment of the invention, the valve assembly includes an electrically operated first proportional valve having a first supply pressure regulator and a first supply pressure sensor, the first proportional valve being coupled to a first working connector, and an electrically operated second proportional valve having a second supply pressure regulator and a second supply pressure sensor, the second proportional valve being coupled to a second working connector. In this embodiment, both the first and second proportional valves have dual functions, as they directly affect both the supply pressure and the working pressure. This is particularly relevant to the fixed relationship between the supply pressure and the working pressure, which relates especially to the characteristics of the fluid connection between the output connector of the respective valve assembly and the working connector of the respective fluid actuator. The electrically operated first and second proportional valves are responsible for consistently influencing the network pressure or feed pressure supplied to the valve assembly such that a supply pressure level exists at the corresponding output connector of the respective proportional valve, but this supply pressure level is also chosen to be as low as possible so that the desired motion command can still be reliably executed. If possible, the supply pressure level can be adjusted during the execution of motion commands, for example, by increasing the supply pressure level if it can be determined that the desired function of the spot welding clamp is not being ensured.

[0021] Preferably, the valve assembly includes: an electrically controlled supply pressure valve, particularly configured as a proportional valve, connected to a compressed air connector, having a supply pressure regulator and a supply pressure sensor; and an electrically controlled working pressure valve, particularly configured as a proportional valve, disposed between the supply pressure valve and the fluid actuator, configured to selectively ventilate and exhaust the first and second working connectors, and having an input connector connected to the output connector of the supply pressure valve. Here, the supply pressure valve and the working pressure valve form a fluid series connection extending between the compressed air connector of the clamp interface and the fluid actuator. The supply pressure valve with the corresponding supply pressure regulator has the function of providing a supply pressure level determined according to the control signal of the clamp control device during the execution of a motion command, while the working pressure valve with the corresponding working pressure regulator has the function of supplying working fluid to the fluid actuator in a suitable manner for executing the motion command. This is achieved by separating the valve assembly into at least one supply pressure valve and at least one working pressure valve: the at least one working pressure valve (which is used to directly influence the fluid flow to or from the fluid actuator) can be operated in such a way that optimal fluid supply to the fluid actuator is ensured without regard to limitations on the supply pressure, as this task is undertaken by the supply pressure valve, in order to ensure the most efficient use of the working fluid.

[0022] In an advantageous improvement of the invention, the working pressure regulator is configured as a processing device of a clamp control device, in particular a regulation algorithm in a microcontroller or microprocessor, and configured to provide a control signal to the valve device and / or supply pressure regulator according to a control signal.

[0023] Advantageously, the fluid actuator is equipped with a position sensor configured to determine the position of the actuator element relative to the actuator housing and to provide a position signal to a clamp control device, which is selectively configured for position adjustment or force adjustment of the fluid actuator. Attached Figure Description

[0024] Advantageous embodiments of the invention are shown in the accompanying drawings. In the drawings:

[0025] Figure 1 A strongly schematic connection diagram showing a first embodiment of a spot welding clamp, and

[0026] Figure 2 A strongly schematic connection diagram is shown for a second embodiment of the spot welding clamp. Detailed Implementation

[0027] Figure 1 The first embodiment of the spot welding clamp 1, strongly illustrated in the diagram, is constructed, purely exemplarily, on a sheet metal part (not shown) for performing a spot welding process. Typically, for performing the spot welding process, the spot welding clamp 1 is coupled to the arm of an industrial robot (not shown), whereby the spot welding clamp 1 can move at least one dimension in one spatial direction, preferably two dimensions in two mutually perpendicular spatial directions, and particularly preferably three dimensions in three mutually perpendicular spatial directions. Exemplarily, such a spot welding clamp 1 can be used in body manufacturing for the automotive industry.

[0028] The spot welding clamp 1 includes a clamp interface 2 configured for mechanical coupling with an industrial robot (not shown). Exemplarily, the clamp interface 2 includes a fieldbus connector 3, a current connector 4, and a compressed air connector 5. Preferably, the clamp interface 2 is configured such that, through coupling with the industrial robot (not shown), a connection is automatically established between the fieldbus connector 3 and a fieldbus present in the industrial robot, between the current connector 4 and a current supply device present in the industrial robot, and between the compressed air connector 5 and a compressed air supply device present in the industrial robot.

[0029] The use of the spot welding clamp 1 can be described as follows: the spot welding process is independently executed by the spot welding clamp 1 when fieldbus signals are provided to the fieldbus connector 3, electrical energy is provided to the current connector 4, and compressed air is provided to the compressed air connector 5. The spatial orientation of the spot welding clamp 1 is achieved by an industrial robot (not shown). Furthermore, coordination between the spatial orientations of the spot welding clamp 1 is achieved by the industrial robot, and the execution of the spot welding process (triggered by the corresponding fieldbus signals) is achieved by a machine control device (not shown), which can in particular be configured as a robot control device for an industrial robot.

[0030] The spot welding clamp 1 includes a clamp control device 6, which is connected to a fieldbus connector 3 and, exemplarily, to a current connector 4. Furthermore, the spot welding clamp 1 includes a first proportional valve 7 and a second proportional valve 8, which together form a valve assembly 14. The fluid actuator 11 of the spot welding clamp 1 (which is exemplarily configured as a pneumatic cylinder) is equipped with a first working pressure sensor 9 and a second working pressure sensor 10, which together form a sensor assembly 13. Exemplarily, the fluid actuator 11 is equipped with a position sensor 12 for detecting the position of the working piston 15 relative to the actuator housing 16, wherein the position sensor 12 is also part of the sensor assembly 13 in this case. A piston rod 17 connected to the working piston 15 acts via a lever transmission mechanism 18 on a first welding electrode 19 and a second welding electrode 20, which are pivotally supported on the actuator housing 16 and can perform correspondingly opposite movements to increase or decrease the welding gap 24.

[0031] The clamp control device 6 has a communication area 21 and a working pressure regulator 22 and, if possible, an end stage 23, which is shown only as a purely schematic functional block. In one embodiment of the spot welding clamp (not shown), the end stage may be arranged entirely outside the clamp control device, particularly next to the spot welding clamp.

[0032] The communication area 21 and the working pressure regulator 22 can, for example, run as an algorithm on a microcomputer incorporated in the clamp control device 6 in a manner not shown in detail. The algorithm is correspondingly a computer program in which the communication area 21 is configured to analyze and evaluate arriving fieldbus signals and to determine motion commands from the fieldbus signals. The computer program for the working pressure regulator 22 is configured to determine control signals from the motion commands, if possible, taking into account the sensor signals of the first working pressure sensor 9 and the second working pressure sensor 10. If a position sensor 12 is also provided, the working pressure regulator 22 may also consider the sensor signal of the position sensor 12 to determine the control signal. The control signal is provided to the first proportional valve 7 and the second proportional valve 8 via signal lines 26, 27. Further processing of the control signal for the working pressure regulator 22 is performed in the first proportional valve 7, while in the second proportional valve 8, the control signal for the working pressure regulator 22 is directly converted into a change in the control state for the second proportional valve 8. For example, the adjustment process of the spot welding clamp 1 is configured such that the sensor signals of the first working pressure sensor 9 and the second working pressure sensor 10 are not considered. Instead, the adjustment movement is performed by the working pressure regulator 22 as a position adjustment process (closed loop) using the position signal of the position sensor 12. In contrast, the operation of the spot welding clamp 1, i.e., the execution of the spot welding process, can be configured to be force-regulated (closed loop) using the sensor signals of the first working pressure sensor 9 and the second working pressure sensor 10. This can be achieved by storing in the working pressure regulator 22 all the parameters required to determine the corresponding welding force at the electrodes 19, 20, such as the geometry of the fluid actuator 11 and / or the first and second welding electrodes 19, 20.

[0033] In a variant of the clamp control device (not shown), the current connector and final stage in the clamp interface are omitted because these components are incorporated into a separate welding current control device.

[0034] The first proportional valve 7 has an input connector 29, which is connected to the compressed air connector 5 of the clamp interface 2 via a compressed air piping assembly 30. The first proportional valve 7 further includes: a processing unit 32 configured as a microprocessor, which is connected to the clamp control unit 6 via a signal line 26; and a supply pressure sensor 33 electrically connected to the processing unit 32, which is fluidly connected to the output connector 30 and provides a supply pressure signal to the processing unit 32 based on the supply pressure at the output connector 30. A computer program runs on the processing unit 32, which analyzes and evaluates the arriving control signal and the arriving supply pressure signal, and thereby determines an adjustment signal for the electro-pneumatic pre-control device 34 of the continuous valve 35, which is exemplarily configured as a fluid pre-control 2 / 2-way valve. Thus, the processing unit 32 with the subordinate computer program forms a supply pressure regulator 36. The task of the first proportional valve 7 is to ensure a supply pressure level based on the control signal received by the clamp control device 6. This supply pressure level can be provided at the output connector 30 of the first proportional valve 7 so that, in the case of the second proportional valve 8, the clamp control device 6 can fluidly manipulate the fluid actuator 11 to execute the corresponding motion command to be satisfied.

[0035] The second proportional valve 8 is simply exemplarily constructed as a pre-controlled 5 / 3-way valve via electro-pneumatic means. The supply connector 52 of the second proportional valve 8 is fluidly connected to the output connector 30 of the first proportional valve 7 via a supply line 40. Furthermore, the second proportional valve 8 is connected to the first muffler 43 via a first exhaust line 41 and to the second muffler 44 via a second exhaust line 42. Additionally, the second proportional valve 8 is fluidly connected to the first working connector 47 of the fluid actuator 11 via a first working line 45 and to the second working connector 48 of the fluid actuator 11 via a second working line 46.

[0036] The first working pressure sensor 9 is in fluid communication with the first working conduit 45 and provides an electrical sensor signal to the clamp control device 6 via the first sensor line 49. The second working pressure sensor 10 is in fluid communication with the second working conduit 46 and provides an electrical sensor signal to the clamp control device 6 via the second sensor line 50. The position sensor 12 is simply and exemplary disposed directly on the actuator housing 16 and configured to detect the magnetic field of a permanent magnet (not shown) disposed on the working piston 15 and provide a sensor signal related to the relative position of the working piston 15 with respect to the actuator housing 16 to the clamp control device 6 via the third sensor line 51.

[0037] The working principle of the spot welding clamp 1 can be described as follows: First, a machine control device or robot control device (not shown) of an industrial robot (the spot welding clamp 1 is coupled to the industrial robot by its clamp interface 2) provides compressed air via compressed air connector 5, current via current connector 4, and a supply of fieldbus signals via fieldbus connector 3. The fieldbus signals are provided to the clamp control device 6 by fieldbus connector 3 and analyzed and evaluated in the communication area 21. During the analysis and evaluation process, instructions are extracted from the fieldbus signals; these instructions are also called motion instructions and are intended to change the welding gap 24 by inducing relative movement about the two welding electrodes 19, 20 when using a fluid actuator 11.

[0038] For example, motion commands can be provided to a working pressure regulator 22 via a communication area 21, which takes into account sensor signals from a first working pressure sensor 9 and a second working pressure sensor 10. In the working pressure regulator 22, the motion commands are converted into control signals for a second proportional valve 8 within a closed regulation loop (closed loop). Here, the working pressure regulator 22 is configured to provide the control signals to the second proportional valve 8 via a second signal line 27.

[0039] Alternatively, the motion command can be provided by the communication area 21 to the working pressure regulator 22 and processed there as an adjustment signal without taking into account the sensor signals of the first working pressure sensor 9 and the second working pressure sensor 10, so as to induce the desired adjustment motion of the welding electrodes 19, 20.

[0040] Furthermore, a control signal is provided via a first signal line 26 to a supply pressure regulator 36 of the first proportional valve 7. The supply pressure regulator 36 is configured as an algorithm within the processing unit 32 of the first proportional valve 7. Exemplarily, the supply pressure regulator 36 may be configured to determine a supply pressure level based on the arriving control signal, particularly using reference data stored in a memory (not shown in detail) of the processing unit 32. This supply pressure level is necessary for the execution of the motion command represented by the control signal and must be supplied by the first proportional valve 7 (which is connected via a compressed air connector 5 to a compressed air source (not shown in detail)) to the second proportional valve 8 and from there to the fluid actuator 11.

[0041] Alternatively, the supply pressure regulator 36 may be configured to obtain information about the supply pressure level to be provided solely based on the incoming control signal, and the determination of the supply pressure level, particularly when using reference data from a memory (not shown in detail) from the clamp control device 6, may be performed in the clamp control device 6.

[0042] For example, the system is configured to provide a pressure level via compressed air connector 5, which may also be referred to as the network pressure or feed pressure of the compressed air network to which an industrial robot (not shown) is connected. Simply exemplarily, the network pressure is 6 bar.

[0043] The task of the first proportional valve 7 is currently to provide a suitable supply pressure level at the output connector 30 according to the corresponding motion command. Exemplarily, it can be configured such a supply pressure level is sufficient for the execution of the motion command (which aims to change the welding gap 24, particularly increasing or decreasing the welding gap 24) where no force is applied to the workpiece (not shown) by the welding electrodes 19, 20, i.e., the supply pressure level is less than 50 percent of the network pressure. Simply exemplarily, it can be configured such that the supply pressure level for this motion of the welding electrodes 19, 20 is in the range of 2 bar. Correspondingly, the supply pressure regulator 36, using the sensor signal from the supply pressure sensor 33, thus controls the electro-pneumatic pre-control device 34 of the continuous valve 35 to provide a supply pressure of 2 bar at the output connector 30.

[0044] If the execution of a motion command intended to apply force to a workpiece (not shown) by welding electrodes 19, 20 is configured, the supply pressure regulator can be configured to provide a supply pressure level at output connector 30 that is only slightly less than the network pressure, for example, no more than 20 percent less than the network pressure, based on the arriving control signal, particularly when using reference data stored in a memory (not shown in detail) of the processing device 32. Exemplarily, the supply pressure regulator 36, when using the sensor signal from the supply pressure sensor 33, operates the electro-pneumatic pre-control device 34 of the continuous valve 35 such that a supply pressure of 5 bar is provided at output connector 30.

[0045] Preferably, the supply pressure regulator 36 maintains the corresponding supply pressure level until a new control command is provided by the clamp control device 6.

[0046] According to Figure 2 In an alternative embodiment of the spot welding clamp 71, it is used for components with the same function and in Figure 1 The same reference numerals are used in the accompanying drawings. The difference between spot welding clamp 71 and spot welding clamp 1 is that the first proportional valve 77 and the second proportional valve 78 (the first proportional valve and the second proportional valve form valve device 84) are constructed in the same way and are electronically connected to clamp control device 6 via corresponding signal lines 96, 97 respectively.

[0047] Both the first proportional valve 77 and the second proportional valve 78 have a similar structure to the first proportional valve 7 provided in the first embodiment of the spot welding clamp 1. The difference between the proportional valves 77 and 78 and the proportional valve 7 is that the corresponding continuous valve 105 is constructed as an electromagnetically operated 3 / 3-way valve. Accordingly, each continuous valve 105 is provided with not only an input connector 99 connected to the compressed air line 31 and an output connector 100 connected to the working connector 47 or 48, but also an exhaust connector 107 connected to the muffler 113 via a corresponding exhaust line 111.

[0048] Each of the proportional valves 77 and 78 is thus fluidly connected to the compressed air connector 5 via compressed air line 101. Each of the two proportional valves 77 and 78 further includes a processing unit 32, a supply pressure sensor 33, and an electromagnetic control device 104. Furthermore, a computer program serving as a supply pressure regulator 36 is implemented in the processing unit 32.

[0049] In the spot welding clamp 71, each of the two proportional valves 77, 78 serves a dual function, not only for adjusting or limiting the respective required supply pressure levels but also for providing fluid flow necessary to meet the motion tasks of the fluid actuator 11 as defined by the corresponding motion commands, which can be achieved through ventilation and exhaust of the corresponding working joints 47, 48.

[0050] Here, the working pressure regulator has the task of adjusting the working pressure, taking into account the available supply pressure provided by the corresponding proportional valves 77, 78, so as to meet the desired motion task. The supply pressure regulator 36 in the corresponding proportional valves 77, 78 has the task of adjusting the supply pressure to the level required to meet the corresponding motion task. Accordingly, the regulating functions of the working pressure regulator 22 and the supply pressure regulator 36 for the corresponding proportional valves 77, 78 are superimposed, wherein the working pressure regulator 22 is only indirectly connected to the electro-pneumatic pre-control device 34, because the supply pressure regulator 36 is connected between the working pressure regulator 22 and the electro-pneumatic pre-control device 34.

Claims

1. Method for operating a spot welding gun (1; 71) comprising a gun control device (6), a valve device (14; 84), a fluid actuator (11) and a sensor assembly (13), the method comprising the steps of: The clamp control device (6) receives a fieldbus signal at its fieldbus connector (3) and processes the fieldbus signal into a control signal for the valve device (14; 84); the clamp control device (6) provides the control signal to the valve device (14; 84); the control signal provided to the valve device (14; 84) affects the fluid flow to the fluid actuator (11); at least one operating pressure at the fluid actuator (11) is detected using the sensor assembly (13); the sensor assembly (13) provides a sensor signal to the clamp control device (6); and the operating pressure regulator (22) of the clamp control device (6) is activated. The sensor signal is processed for adjusting the working pressure for the fluid actuator (11) according to the control signal, characterized in that the supply pressure signal of the supply pressure sensor (33) disposed at the output connector (30) of the valve device (14) connected to the fluid actuator (11) is provided to a supply pressure regulator (36) belonging to the valve device (14) and connected to the clamp control device (6), the supply pressure regulator being configured to adjust the supply pressure provided at the output connector (30) to one of at least two preset supply pressure levels according to the control signal, which is the minimum supply pressure level necessary to execute the corresponding motion command.

2. The method according to claim 1, characterized in that, The supply pressure is up to 50 percent greater than the working pressure.

3. The method according to claim 2, characterized in that, The supply pressure is up to 30 percent greater than the working pressure.

4. The method according to claim 3, characterized in that, The supply pressure is up to 20 percent greater than the working pressure.

5. The method according to claim 4, characterized in that, The supply pressure is up to 10 percent greater than the working pressure.

6. The method according to claim 1, characterized in that, The first supply pressure level is selected such that the fluid actuator (11) can cause adjustment movement for the welding electrodes (19, 20), and the second supply pressure level is selected such that the fluid actuator can apply welding force to the welding electrodes (19, 20) used in the welding process.

7. The method according to claim 1, characterized in that, The working pressure regulator (22) is configured as a regulation algorithm in the processing device of the clamp control device (6) and is configured to provide the control signal to the valve device (14; 84) according to the control signal, and the supply pressure regulator (36) is configured as a regulation algorithm in the processing device (32) of the valve device (14; 84) and is configured to provide or determine and provide the corresponding required supply pressure level according to the control signal.

8. The method according to claim 7, characterized in that, The processing device of the clamp control device (6) is a microcontroller or microprocessor.

9. The method according to claim 7, characterized in that, The processing device (32) of the valve device (14; 84) is a microcontroller or microprocessor.

10. A spot welding clamp (1; 71) for welding sheet metal components, the spot welding clamp having: a clamp interface (2) configured for attachment to an industrial robot, and the clamp interface including a fieldbus connector (3), a compressed air connector (5), and a current connector (4); a clamp control device (6) connected to the fieldbus connector (3); a valve device (14; 84) connected to the clamp control device (6) and to the compressed air connector (5); a fluid actuator (11) connected to the valve device (14; 84) and having a sensor assembly (13) configured to detect the operating pressure at the fluid actuator (11) and to provide a sensor signal related to the operating pressure to the clamp control device (6), wherein, The clamp control device (6) has a working pressure regulator (22) for adjusting the working pressure at the fluid actuator, characterized in that the valve device (14) has a supply pressure sensor (33) at an output connector (30) connected to the fluid actuator (11), the supply pressure sensor being configured to provide a supply pressure signal, and the valve device (14) includes a supply pressure regulator (36) connected to the clamp control device (6), the supply pressure regulator being electrically connected to the supply pressure sensor (33) and the supply pressure regulator being configured to adjust the supply pressure provided at the output connector (30) to one of at least two preset supply pressure levels according to a control signal for the valve device (14; 84).

11. The spot welding clamp (1; 71) according to claim 10, characterized in that, The fluid actuator (11) is configured as a dual-acting pneumatic cylinder, the pneumatic cylinder having a first working connector (47) with a first pressure sensor (9) of the sensor assembly (13) associated with the first working connector, and the pneumatic cylinder having a second working connector (48) with a second pressure sensor (10) of the sensor assembly (13) associated with the second working connector, wherein the first pressure sensor (9) and the second pressure sensor (10) are electrically connected to the clamp control device (6).

12. The spot welding clamp (71) according to claim 11, characterized in that, The valve assembly (84) includes an electrically controlled first proportional valve (77) having a first supply pressure regulator (36) and a first supply pressure sensor (33), the first proportional valve being coupled to the first working connector (47), and the valve assembly (84) includes an electrically controlled second proportional valve (78) having a second supply pressure regulator (36) and a second supply pressure sensor (33), the second proportional valve being coupled to the second working connector (48).

13. The spot welding clamp (1) according to claim 11, characterized in that, The valve assembly (84) includes: an electrically operated supply pressure valve (7) connected to the compressed air connector (5), the supply pressure valve having a supply pressure regulator (36) and a supply pressure sensor (33); and an electrically operated working pressure valve (8) disposed between the supply pressure valve (7) and the fluid actuator (11), the working pressure valve being configured to selectively ventilate and exhaust the first working connector (47) and the second working connector (48), and the working pressure valve having a supply connector (52) connected to the output connector (30) of the supply pressure valve (7).

14. The spot welding clamp (1) according to claim 13, characterized in that, The supply pressure valve (7) is constructed as a proportional valve.

15. The spot welding clamp (1) according to claim 13, characterized in that, The working pressure valve (8) is constructed as a proportional valve.

16. The spot welding clamp (1; 71) according to any one of claims 10 to 15, characterized in that, The working pressure regulator (22) is configured as a regulation algorithm in the processing device of the clamp control device (6) and is configured to provide the control signal to the valve device (14; 84) according to the control signal and / or the supply pressure regulator (36) is configured as a regulation algorithm in the processing device (32) and is configured to determine the corresponding required supply pressure level according to the control signal.

17. The spot welding clamp (1; 71) according to claim 16, characterized in that, The processing device of the clamp control device (6) is a microcontroller or microprocessor.

18. The spot welding clamp (1; 71) according to claim 16, characterized in that, The processing device (32) is a microcontroller or microprocessor.

19. The spot welding clamp (1; 71) according to any one of claims 10 to 15, characterized in that, The fluid actuator (11) is equipped with a position sensor (12) configured to determine the position of the actuator element (15) relative to the actuator housing (16) and to provide a position signal to the clamp control device (6), and the clamp control device (6) is selectively configured for position adjustment or force adjustment of the fluid actuator (11).

Images