Method for determining an estimated value of an arc voltage

Abstract

To improve the estimation of the arc voltage for use in the welding process, it is proposed that for estimating the arc voltage, the welding line (4) is modeled as a transfer system of an order greater than one with a welding line model (13), and the estimated value of the arc voltage is determined as the difference between the measured voltage at the measurement location (19) and the line voltage drop as derived.

Description

Technical Field

[0001] This invention relates to a method for determining an estimated value of the arc voltage of an electric arc burning between a welding electrode and a workpiece. The method involves using a welding circuit model with model parameters to determine the line voltage drop of the welding circuit between a measurement position on the welding circuit and the arc. The welding circuit model is modeled as a transmission system that takes the welding current flowing through the welding circuit or the measurement voltage applied at the measurement position as input parameters and the line voltage drop as output parameters to determine a current estimated value for the line voltage drop for the current welding current or the current measurement voltage. The estimated value of the arc voltage is determined using a known relationship between the line voltage drop and the arc voltage. The invention also relates to a welding power source in which such a welding circuit model is implemented. Background Technology

[0002] The primary task of a welding power source used to perform the welding process is to generate, control, and regulate process parameters—namely, welding current and / or welding voltage, and, if necessary, wire feed—according to the welding task, so as to ultimately produce a good welding result with the desired weld quality and thus a good weld joint. Regulation of the welding current plays a particularly important role here, as it provides power to the welding process. Arc voltage is also required for regulating the welding process, as it is a crucial parameter. The arc voltage, which decreases at the arc, is related to the arc length and therefore also to the distance between the welding electrode and the workpiece (or molten pool). However, arc voltage cannot be directly measured in practice; therefore, it is reconstructed from indirect measurements.

[0003] A welding circuit, consisting of a welding current line (the line leading from the welding power source to the welding torch or welding electrode) and a grounding line (the line leading back from the workpiece to the welding power source), connects the welding power source to the welding torch, i.e., to the welding electrode and the workpiece. The welding circuit is typically connected to the welding power source in a connector. The connector voltage between the connectors, i.e., between the welding current line and the grounding line, and the connector current flowing through the welding circuit, can be easily measured at the welding power source. The connector current can be the same as the welding current, since the current in parallel with the arc during welding is largely negligible. However, due to the voltage drop across the welding circuit, the connector voltage does not correspond to the arc voltage. To reconstruct the arc voltage from the connector voltage, a circuit model is used in known prior art. This circuit model models the welding circuit as a series circuit of line resistance and line inductance (R / L model) to determine the voltage drop across the welding circuit. Then, using the measured connector voltage and measured connector current, along with the circuit model, an estimate of the arc voltage can be obtained. Therefore, the circuit model compensates for the voltage drop across the welding circuit to obtain an estimate of the arc voltage. This is known, for example, from WO2000 / 74888A1 or DE102005005771B4. Because the hose bundle (line inductance L) is described by only one accumulator or dynamic component in this model, the model is first-order.

[0004] The parameters of the R / L circuit model, namely the circuit resistance and circuit inductance, are known or identified. Parameter identification can be performed during welding or during welding intervals. For example, the welding electrode (or the contact tube of the welding torch) can be short-circuited to the workpiece. The circuit resistance is then determined while the current is constant. A current pulse can then be applied, and the circuit inductance determined accordingly. For example, during welding, a current pulse that does not interfere with the welding process can be modulated onto the welding current, and the model parameters can be determined based on the response. Model parameters can also be continuously determined by formulaic relationships of existing measurements, as in, for example, DE102005005771B4.

[0005] Therefore, the arc voltage can be estimated during the operation of the welding power source. However, in practice, it has been shown that using a general R / L circuit model can lead to significant estimation errors when reconstructing the arc voltage, which may negatively impact the welding process.

[0006] The applicant's research indicates that the placement of welding lines has a significant impact on the reconstruction of arc voltage. It has been observed that welding lines are frequently placed near conductive components / parts / structures. These could be the robotic arm of a welding robot, a steel structure on a construction site or in a workshop, a metal component (e.g., in shipbuilding), a steel reinforcement in reinforced concrete, a metal cable conduit, or the like. The highly dynamic welding current flowing through the welding line (with steep edges and a high-frequency, time-varying current) can induce electromagnetic interactions with these components. The time-varying welding current generates a time-varying magnetic field around the welding line. It is known that an electric field strength is induced in a conductor within a changing magnetic field, which, due to conductivity, directly leads to a current density in that body. This current density, in turn, causes its magnetic field to be oriented against the original field, further leading to interactions between the current-guiding components. The time-varying welding current in the welding line induces this phenomenon in adjacent conductive materials. Traditional R / L line models cannot describe this coupling, and therefore cannot provide a sufficiently accurate reconstruction of the arc voltage in such cases.

[0007] This effect is particularly strong in ferromagnetic materials, such as iron or steel, because the magnetic flux density can be strongly expressed in such materials. However, this effect can also be observed in paramagnetic materials, such as aluminum, but it is weaker than in ferromagnetic materials.

[0008] Because in practical applications, welding circuitry must always be laid near this conductive material—since this material must also be welded—this effect always affects the execution of the welding process. This effect cannot be detected by the currently used R / L circuit model, which consists of series-connected circuit resistance and circuit inductance, thus making the reconstruction of the arc voltage inaccurate, which can adversely affect the achievable weld quality.

[0009] Arc voltage is not only an important parameter for regulating the welding process, but it is also necessary for determining important known characteristics of the welding process, such as the heat or streckenenergie (also known as arc energy) input to the workpiece to be welded. Therefore, it is necessary to estimate the arc voltage as accurately as possible. Summary of the Invention

[0010] The purpose of this invention is to improve the estimation of arc voltage used in welding processes.

[0011] The objective is achieved by modeling the welding circuit as a transmission system of order greater than one using a welding circuit model, and determining the estimated arc voltage as the difference between the measured voltage at the measurement location and the obtained line voltage drop. It is known that when estimating the line voltage drop using a welding circuit model of order greater than one, the magnetic coupling between the welding circuit and the conductive components surrounding the welding circuit can also be taken into account. Therefore, the estimation of the arc voltage also takes into account the layout of the welding circuit and can be achieved more accurately than before. The estimated arc voltage can be used to regulate the welding process, such as adjusting the welding current or the wire feed rate. More accurate arc voltage estimation can also improve the achievable weld quality, as it provides a more accurate estimate of the arc voltage for regulation. The arc voltage estimation can also be used to determine characteristic values ​​of the welding process, such as segment energy, resistance, power, or heat input. These characteristic values ​​can also be obtained more accurately by more accurately estimating the arc voltage.

[0012] If the model parameters of the welded circuit model are not known, parameter estimation methods can be used to identify them. Various parameter estimation methods are known and easy to apply, making it easy to determine the model parameters.

[0013] Model parameters can also be identified during the short-circuit phase of welding, allowing for continuous re-determination of these parameters within a specific welding method. This enables responses to changes in the welded circuit layout. Furthermore, model parameters can be identified prior to welding using pre-defined time profiles of the input and matching output parameters. This allows for the selection of input parameter profiles that are favorable for parameter identification, thereby improving the identification process.

[0014] It has been shown that it is particularly advantageous to use a time-varying curve of the input parameter with multiple rising edges, wherein the slope of at least two edges varies, and the output parameter is measured here. This enables good excitation of the transmission system in the form of a welded circuit, so as to obtain good measurements and good estimates of the output parameter used for parameter estimation. Attached Figure Description

[0015] The following is a reference to the appendix. Figures 1 to 5 To elaborate on the invention in more detail, Figures 1 to 5 Advantageous embodiments of the invention are illustrated, illustratively, and non-limitingly. In the figures:

[0016] Figure 1 The welding power source used to regulate the welding process is shown.

[0017] Figure 2 This shows the laying of welding lines near conductive components;

[0018] Figure 3 A welding circuit model with an order greater than one is shown;

[0019] Figure 4 The time-varying curve of the welding current is shown as an excitation for parameter identification of model parameters used in the welding circuit model; and

[0020] Figure 5 The time-varying curves of the arc voltage are shown under a given welding current, using a circuit model of order greater than one according to the invention and a conventional R / L circuit model. Detailed Implementation

[0021] Figure 1 A welding power source 1 for performing a welding process is described. The welding power source 1 includes a power component 2 for generating a welding current. The power component 2 is shown as a power source 3, which provides a socket voltage u at the connection ports A+ and A- of the welding power source 1. B and socket current i B The power unit 2 is a circuit that converts an input voltage, such as from an AC mains (which is also multiphase) or from a DC voltage (e.g., from a battery), into a current-time variation curve (of the welding current). This circuit is, for example, a transformer, an AC / DC converter, or a DC / DC converter. The current variation curve is related to the welding method and is adjusted by the welding adjustment unit 11. The welding adjustment unit 11 can be integrated into the welding power supply 1, but it can also be implemented separately from the power unit 2 or the welding power supply 1. The desired current variation curve is used as a rated parameter SG for the welding adjustment unit 11 to control the power unit 2 to achieve the welding process. Similarly, a voltage variation curve can, of course, be pre-defined as a rated parameter SG. A welding line 4, including a welding current line 5 and a grounding line 6, is connected to the connection ports A+ and A- of the welding power supply 1. Generally, but not necessarily, the grounding line 6 is separately led to and connected to the workpiece 7 to be welded.

[0022] The welding current line 5 is typically guided within the flexible hose bundle to the welding torch 8, which has a (melted or unmelted) welding electrode 9. It is known that other lines, such as cooling medium lines, shielding gas lines, lines for the welding electrode used for melting, control lines, etc., may also be integrated within the flexible hose bundle. The grounding line 6 may also be guided within the flexible hose bundle.

[0023] The welding torch 8 can be mounted on a welding robot (not shown) or can be manually guided. The welding torch 8 may have a contact tube connected to the welding current line 5 and contacted by a welding wire 18 that also functions as a welding electrode 9. Figure 1(As shown in the diagram), for example in metal inert gas welding (MIG) or metal active gas welding (MAG). However, a non-consumable welding electrode 9 may also be arranged in the welding torch 8, which is connected to the welding current line 5, for example in tungsten inert gas welding (WIG). Welding filler is supplied via welding wire 18. Welding wire 18 can be supplied to the welding site using welding wire feed unit 17.

[0024] During welding, the electric arc 10 burns between the welding electrode 9 and the workpiece 7. The arc voltage u decreases across the electric arc 10. LB However, the implementation scheme and welding method of the welding torch 8 are not important to this invention. To control the welding process, it is important to understand the welding current (which is equivalent to the socket current i with sufficient accuracy). B That is, the current flowing through the electric arc 10 and the arc voltage u. LB That is, the voltage that drops across the arc 10. Although the socket current i can be easily measured in the welding power source 1 using appropriate measurement techniques. B However, it is impossible to directly measure the arc voltage u. LB .

[0025] To regulate the welding process, the power component 2 of the welding power supply 1 is regulated by a welding regulation unit 11. This unit generates adjustment parameters S for the power component 2, such as the duty cycle of the converter's PWM (Pulse Width Modulation) control, to generate the desired welding current and / or desired welding voltage. For this purpose, a welding process regulation unit 12 can be incorporated into the welding regulation unit 11, which implements, monitors, and controls the configured welding process. The welding process regulation unit 12 is pre-given a rated parameter SG, such as the rated time variation curve of the welding current or welding voltage. This rated parameter SG can be pre-given, for example, by setting the welding process, selecting a welding program, or setting welding parameters on the I / O interface of the welding power supply 1. For this purpose, the welding regulation unit 11 and / or the welding process regulation unit 12 can also obtain input parameters from the welding process as the actual parameters for regulation, such as the arc voltage u. LB Current socket current i B,ist (as welding current) or wire feed speed v D .

[0026] The parameter S is adjusted to be converted into a specific socket current i by power component 2. B Or the socket voltage u B Therefore, the welding adjustment unit 11 may include a current regulator that adjusts the actual socket current i according to a pre-defined regulator rule (e.g., a PI regulator or a PID regulator). B,ist With the pre-given rated socket current i B,sollThe adjustment parameter S is obtained by calculating the difference. The adjustment parameter S can also be the rated socket current i. B,soll Or the rated socket voltage u B,soll In this case, such a current regulator is implemented in power component 2. The type of regulation parameter S depends, of course, on the implementation of power component 2.

[0027] The welding adjustment unit 11 can also control and monitor additional or other components of the welding power source 1 to adjust the welding process, such as the wire feed unit 17 (in Figure 1 (Shown in dashed line), which is used to feed the welding wire 18 (also serving as the welding electrode 9) at the desired or required wire feed speed v. D (Also presented as a time-varying curve) supplied to the welding area, such as in Figure 1 As shown in the figure. Therefore, the welding adjustment unit 11 can also obtain additional or other adjustment parameters S in order to adjust the welding process.

[0028] The required adjustment parameters, such as welding current or socket current, are as follows: B Socket voltage u B Or the wire feed speed v D The arc voltage u can be measured using suitable measuring sensors or, for example, pre-given based on the welding procedure to be performed. However, the arc voltage u cannot be directly measured using conventional welding power sources 1 and conventional welding torches 8. LB However, for reconstruction purposes, the arc voltage u is estimated using the welding circuit model 13 implemented in the estimation unit 16. LB Arc voltage u LB The estimated value is represented by "^", that is, by express.

[0029] All or some of the "regulation units" or "units" can be implemented as microprocessor-based hardware, wherein the functionality of these regulation units or units is implemented as software. Here, a common microprocessor-based hardware can also be used for multiple functions. However, regulation units or units can also be implemented in hardware in the form of field-programmable gate arrays (FPGAs), programmable logic devices (PLDs), application-specific integrated circuits (ASICs), or other integrated circuits. Here, multiple regulation units and / or units can also be integrated on such hardware. However, regulation units or units can also be implemented as analog circuits or analog computers. Of course, these implementations can be arbitrarily mixed.

[0030] The main requirement for welding circuit model 13 is to take the line voltage drop u on welding circuit 4, such as welding current circuit 5 and grounding circuit 6. S And from this, the estimated value of the arc voltage can be obtained. Line voltage drop u SThis is the sum of all voltage drops along the welding line 4 from measurement position 19 to the arc 10 and back to the measurement position. This also includes the corresponding current conduction portion from the welding torch 8 to the arc 10 and from the arc 10 to the workpiece 7 via the grounding line 6. At measurement position 19, the voltage u between the welding current line 5 and the grounding line 6 is measured. M .

[0031] In principle, the measuring position 19 can be set at any position between the connection sockets A+ and A- of the welding power source 1 and the welding torch 8. For example, as Figure 1 As shown, the connection ports A+ and A- can be considered as measurement positions 19. However, as... Figure 1 As indicated by the dashed line, measurement position 19 can be set at any location in the welding line 4 or at the connection point of the hose bundle. Multiple measurement positions 19 can also be set. The measurement voltage u between the welding current line 5 and the grounding line 4 is measured at measurement position 19. M .exist Figure 1 In the middle, the voltage u of the socket is measured. B As the measured voltage u M Then, at each moment, the voltage u can be measured. M The line voltage drop u obtained using welding line model 13 S To determine the arc voltage For example, as a measurement voltage u M and line voltage drop u S The difference. Here, the known voltage drop over the length of the idle welding wire electrode can also be considered in a known manner. It is not necessary to specifically calculate the line voltage drop u as an intermediate step. S Alternatively, the estimated value of the arc voltage can be obtained directly. The welding circuit model 13 should simulate the line voltage drop u on the welding circuit 4 between the measurement position 19 and the arc 10. S .

[0032] For this purpose, welding circuit model 13 can obtain, for example, the actual measured socket current i. B,ist welding current i S and / or measuring voltage u M For example, the actual socket voltage u B,ist As input parameters, these input parameters can be measured using measurement sensors and provided as analog or digital measurements, for example, in a time-continuous or time-discrete manner.

[0033] The welding circuit model 13 can also be implemented as software on microprocessor-based hardware, which can also be shared with the control unit, or can be implemented entirely or partially as hardware in the form of FPGA, PLD, ASIC or analog circuit.

[0034] Welding line 4, grounding line 6, and / or welding current line 5 may be arranged near a paramagnetic or ferromagnetic conductive component, hereinafter referred to as conductive component 14, such as in Figure 2 As shown. In Figure 2 The welding current line 5 is, for example, guided through a conductive member 14a (e.g., a conductive profile or robotic arm), laid on a conductive member 14b (which could also be the workpiece 7 to be welded) (also in the form of a return line 15), or laid on a reinforced concrete member 14c. In practice, of course, not all of them need to be laid on... Figure 2 The exemplary laying methods shown are all present, and other laying methods may also appear in the area of ​​conductive member 14. The return line 15 may also be constructed around conductive member 14 and form a coil, for example. Electromagnetic interaction may occur between conductive member 14 and solder line 4.

[0035] According to the present invention, the welding circuit model 13 should not only address the line voltage drop u caused by the welding circuit 4 itself, as has been done so far with a simple R / L circuit model, but also... S Modeling should be performed, and the influence of the surrounding environment of the welding line 4 and the laying of the welding line 4 should also be modeled. To achieve this, it has been recognized that a welding line model 13 of order two or higher is required.

[0036] The welding circuit model 13 consists of interconnected electrical components, such as resistors, inductors, and capacitors, which include multiple energy storage devices, such as inductors and / or capacitors. Figure 3 The diagram shows an advantageous welding circuit model 13. A line voltage drop u caused by the welding line 4 is applied to the input terminal of the circuit of the welding circuit model 13. S And the welding current i S In the line model, the voltage drop u in the line is... S and welding current i S The relationship between them can be described by the transfer function G as the quotient of the output parameter and the input parameter, where the line voltage drop u S Indicates the output parameter y and the welding current i. S This represents the input parameter u. However, the welding circuit model 13 can also be implemented such that the measured voltage u... M Used as an input parameter, while the line voltage drop u SIt is also used as an output parameter. The order of the transfer function G, i.e., the time derivative that appears most frequently in the fundamental differential equation, or equivalently, the order of the fundamental difference equation, determines the order of the welding circuit model 13. According to the present invention, a welding circuit model 13 is used, which describes the line voltage drop u by a transfer system of order greater than or equal to two. S With welding current i S Or measure voltage u M The relationship between them is equivalent to a transfer function G of order two or higher. The structure of the welded circuit model 13 (i.e., how the electrical components are interconnected) is only secondary here. By using a higher order than in the traditional R / L circuit model (order one), the influence of the surrounding environment can be fully described.

[0037] Physical systems such as welding circuit model 13 can be described by differential equations in the continuous time domain, or equivalently by difference equations in the discrete time domain, which can also serve as a set of coupled differential equations or difference equations. As is known from system theory, a first-order coupled differential equation or difference equation set can be transformed into a higher-order differential equation or difference equation, and vice versa. For example, a set of n coupled first-order differential equations can be transformed into an nth-order differential equation, and vice versa. This also applies to difference equations. Therefore, welding circuit model 13 of order two or greater can be mathematically described in various equivalent ways.

[0038] Reference Figure 3 The welding circuit model 13 and its mathematical description are explained exemplarily. The welding circuit 4 is modeled using a series circuit on the input side consisting of an ohmic resistor R1 and a line inductance L1 (as done so far with a first-order R / L line model). Furthermore, the coupling inductance L... m Describe the coupling with the conductive component 14 in the environment surrounding the welded line 4. In the model, coupling with the coupling inductor L can also be considered. m The resistor R is set in parallel. F The resistor describes the iron loss and eddy current loss. To depict the possible current i2 in the conductive member 14, another branch can be provided, consisting of a series circuit of an ohmic resistor R2 and an inductor L2. It can be seen that this welded circuit model 13 is based on a known transformer equivalent circuit diagram with a short-circuited secondary side.

[0039] The conductive member 14 can also be modeled non-linearly, for example, as a line inductance L1, in order to depict possible magnetic saturation in the conductive member 14. Therefore, the line inductance L1 could, for example, be the socket current i. B The function, namely L1(i B In this case, the welding circuit model can be mathematically described using nonlinear system theory.13

[0040] It should also be noted that the structure of the welding circuit model 13 is not critical, and therefore can be related to... Figure 3 The difference shown is that the welding circuit model 13 can be described by an n-order transmission system (where n>1).

[0041] according to Figure 3 The welding circuit model 13 can be described by applying Kirchhoff's rules through a transfer system with a system of first-order differential equations as follows:

[0042]

[0043] y(t)=i S (t)

[0044] Wherein, the state vector x(t) = [i S (t) i m (t) i2(t)] T And the model parameter p M =[R1,R2,R F ,L1,L2,L m According to the known rules of linear system theory, the transfer function G(s) is thus used as the output parameter y (here, i). S ) and input parameter u (in this case, u) S The quotient of ) yields G(s) = [1 0 0](sI-A) -1 b, where I is the identity matrix and s is the Laplace operator. This is applied to systems with the aforementioned transfer characteristics. Figure 3 On the welding circuit model 13, the transfer function is obtained. That is, a third-order transmission system (n=3). Therefore, based on the line voltage drop u... S The input parameters in the form of welding current i are given. S The output parameter y is in the form of [formula missing]. Similarly, the transmission system can also replace the welding current i. S And to measure voltage u M The input parameter is u. The transmission system (system of differential equations) can also be represented by the welding current i. S To describe the input parameters, and using the line voltage drop u S As an output parameter, this will yield the transfer function. In the transfer function G, the order is determined by the highest power of the Laplace operator s. This leads to the method used to determine the order based on... Figure 3 The coefficients of welding circuit model 13 are, for example:

[0045] b0 = R2R F ,

[0046] b1=(L m R2+(L2+Lm )R1),

[0047] b2=L2L m ,

[0048] a0=R1R2R F ,

[0049] a1=(L m R1R2+(L2+L m )R1+(L1+L m )R2)R F ,

[0050] a2=L2L m R1+L2(L1+L m )R F +L1L m (R2+R F ),

[0051] a3=L1L2L m .

[0052] The coefficients b0, b1, b2, a0, a1, a2, a3 of the transfer function G(s) and the basic model parameters p M (For example, R1, R2, R) F L1, L2, L m Either the parameters p are known or must be determined in order to enable the use of welding circuit model 13 in welding power source 1. M If the parameters are unknown, they can be determined using known parameter estimation methods. Here, the coefficients b0, b1, b2, a0, a1, a2, a3 of the transfer function G can be determined, and the model parameters p can be indirectly determined from there. M Or directly determine the model parameter p. M .

[0053] Although the coefficients b0, b1, b2, a0, a1, a2, a3 are known, the transfer function G(s) is derived from known parameters (here, for example, the welding current i). S Or measure voltage u M The desired line voltage drop u can be obtained in the continuous time domain. SHowever, this is costly in practice. It requires solving differential equations, which is often not feasible analytically and must be performed numerically. Given the associated computational workload, this often cannot be performed online in a sufficiently short time. Therefore, it is advantageous to sample time-continuous signals at a sampling time T and establish a sampling system with an equivalent difference equation (instead of a differential equation), which calculates the current value of the output parameter from the past values ​​of the input and output parameters. This sampling system is significantly better suited for practical implementation in welding power source 1.

[0054] According to system theory, sampling t = k·T can be used. a (T a A sampling system is created for the sampling time, where k describes the corresponding sampling time point. Therefore, the welding current i... S (t) and line voltage drop u S The continuous-time function of (t) yields the discrete-time function i. S (k)(or written as i) S,k and line voltage drop u S (k)(or written as u) S,k ), where k here briefly represents k·T a The time-discrete transfer function G can also be determined by using the known z-transform. z (z) is the quotient of the output and input parameters. The time-discrete transfer function G. z The order n of (z) is similar to that of a time-continuous function, i.e., it is also greater than one. Input parameter u k (e.g., welding current i) S,k Or measure voltage u M,k and output parameter y k (e.g., line voltage drop u) S,k Here it is also used as having a z-operator and coefficient a i b i The polynomial is included in the transfer function G. z In (z), the order n is determined by the highest power of the z-operator. Therefore, a difference equation can be established using the rules of the z-transform, which is based on the welding current i at the current sampling time k. S,k (or measure voltage u) M,k The value of ) and the value of (kj)·T at past time a welding current i S,k-j (or measure voltage u) M,k-j The value of ) and from the past time (kj)·T a Initial line voltage drop u S,k-j The value of k(k·T) at the current time is obtained. a The abbreviation for T aLine voltage drop u (for sampling time) S,k .

[0055] According to Figure 3 Taking the welding circuit model 13 as an example, for instance, the transfer function of order n>1 (n=3) can be obtained in a general form. From the transfer function G z (z) The line voltage drop u at the current time k can be derived using the rules of the z-transform. S,k The difference equation has the following general form:

[0056]

[0057] According to welding circuit model 13, some terms can be omitted or other terms or additional terms can be included in the difference equation.

[0058] Discrete-time transfer function G z The coefficients b0, b1, b2, a0, a1, a2, a3 of (z) naturally have values ​​different from those in the time-continuous transfer function G(s), which are either known or to be determined, for example, using a sufficiently known parameter estimation method. However, these coefficients b0, b1, b2, a0, a1, a2, a3 also differ from the model parameters p of the welding circuit model 13. M This is relevant, and thus the model parameters p can be obtained from these coefficients. M .

[0059] The difference equation is applicable to the online determination of the line voltage drop u at the current time k. S,k Therefore, the output parameter y only needs to be stored at the required time point (kj). k-j Past values, such as line voltage drop u S,k-j Past values, and input parameter u k-j Past values, such as welding current i S,k-j (or measure voltage u) M,k-j The past values ​​of ) are obtained, and the input parameter u is obtained, for example, by measuring and sampling the corresponding parameters. k For example, welding current i S,k (or measure voltage u) M,k The current value of ).

[0060] As mentioned above, the transfer function G(s) or G can be obtained. z The coefficients b0, b1, b2, a0, a1, a2, and a3 of (z) can be used to obtain the model parameters p of the welding circuit model 13. M Alternatively, the model parameters p can be obtained directly. M Therefore, the model parameter p M For example, it is based on Figure 3 In the welding circuit model 13, R1, R2, R F L1, L2, L m Or indirectly, it is the transfer function G(s) or G z The coefficients b0, b1, b2, a0, a1, a2, a3 in (z).

[0061] In order to identify model parameter p M A well-known parameter estimation method can be used, which is suitable for models with a finite number of model parameters p. M The model, as previously discussed in the transfer function G(s) and G... z (z) or in accordance with Figure 3 As described in the mathematical description of welding circuit model 13. Generally, the model parameters p are determined indirectly or directly using parameter estimation methods. M This ensures that the welded line model 13 matches the identified road segment (here, welded line 4) as closely as possible to the specified quality standards. Numerous known parameter estimation methods exist for this purpose, frequently employing least squares or cost function optimization. Both methods are largely well-known and will therefore be briefly discussed below.

[0062] The parameter estimation method is based on the existence of an output parameter y (here, the line voltage drop u). S The N actual measured values ​​of the welding current i are used as input parameters u (here, welding current i). S The function of ). Preferably, the measurement starts from this: the welding electrode 9 is short-circuited, i.e., the arc voltage u LB =0V. When welding electrode 9 is short-circuited, the line voltage drop u S Corresponding to the measured voltage u at measurement position 9 M For example, the socket voltage u B Therefore, a predetermined welding current i can be generated by welding power source 1. S As an input parameter u, and the resulting measured voltage u is measured. M For example, the socket voltage u B As the output parameter y. In this way, the input parameter u can be used as the output parameter y. i and matching output parameter y i Generate any number of measurements i = 1, ..., N.

[0063] Based on these measurements, it is evident that the estimated welding circuit model 13, which provides the measurement voltage u, is suitable for estimating the welding circuit model 13. M The line voltage drop u between measurement position 19 and arc 10 S .

[0064] Using a parameter estimation method, the actual measured value of the output parameter y is compared with the output parameter provided by the welding circuit model 13 for the current input parameter u. The estimate (which is related to the model parameter p) M The deviation between (related to) should be minimized in order to determine the optimal model parameters.

[0065] In the least squares method, the measured value u i y i To establish a system of linear equations, and then solve the system of linear equations, we can obtain the model parameters p. M Therefore, the parameters to be determined (either directly the model parameters p) M Either the transfer function G(s) or G z The coefficients b0, b1, b2, a0, a1, a2, a3 of (z) are summarized in the parameter vector c. In a transfer function with numerator and denominator polynomials... In the case of obtaining the parameter vector c T =[a n-1 ...a0b n b n-1 ...b0], where a is usually set as n =1 and n is the order of the transfer function, where some coefficients can of course be zero. The output parameter of the i-th measurement. The estimated value was then written as Where the data vector h i This is a data vector containing measured values. Data vector h i The dimension is determined by the parameter vector c. i The dimensions are derived from this. Typically, a data vector can be written as... And therefore includes the output parameter y i-N N measured values ​​and matching input parameter u i-N And the new input parameter u i For the new input parameters, an estimate of the output parameters is sought. Current error e i Due to the deviation between estimation and measurement The form is derived. Then, using the available N measurements, the overdetermined linear equation system is obtained. Wherein, the data matrix H = [h0...h N Error vector In this formula, y = [y0...y N ], e = [e0...e N ],and The least squares method uses the square norm of the error e, i.e. Its square is minimized, i.e. Therefore, it is possible The solution is given analytically in the form of G(s) or G(s), from which the corresponding transfer function G(s) or G(s) can be obtained. z The parameter vector of coefficients b0, b1, b2, a0, a1, a2, a3 of (z). The parameters (correct estimation of the coefficients) are used to derive the underlying model parameters p. M (Correct estimation of model parameters).

[0066] In the optimization method for the cost function J, the cost function is established as the model parameters p M We find a function of (a vector with parameters), and then minimize that function. This can be mathematically written as... In the form of, for example, when using model parameters p M When directly estimating the component values ​​of welding circuit model 13, the additional condition pM>0 is considered. The cost function J can be arbitrarily set here and can include multiple cost items to track different optimization objectives. The cost items in the cost function J can also be weighted differently, for example, by using weighting factors. Various cost items are generally added together in the cost function J. In a commonly used implementation, the measured cost items, based on the input parameter u, are... i The N actual output parameters y that appear i Compared with the welding circuit model 13 for input parameter u i The estimated value The sum of the squared errors between these errors is defined as the cost function J. Therefore, the cost function J can be mathematically expressed as: Then, the optimization is typically solved numerically, for example using known iterative methods such as Newton's method or gradient methods, or evolutionary methods. During optimization, the model parameters p are chosen or pre-given at the beginning. M Then, following the rules of the optimization method, the model parameters are iteratively changed until the cost function J approaches its minimum. A termination criterion is usually defined, and the optimization ends when this criterion is reached. The model parameters p at the point where the termination criterion is reached are... M It is used as an optimization model parameter.

[0067] For example, according to Figure 3 The model parameters p of the welding circuit model 13 M The specific laying of welding line 4 is achieved by using a cost function. The optimization is estimated using the following component values: L M =28.841μh, L1=16.373μH, L2=67.27μH, R F =56mΩ, R1=2.3mΩ, R2=60.9mΩ.

[0068] In addition to these, there are many other methods that can be considered for parameter estimation, and methods that can also take measurement noise into account. Autoregressive methods are generally used, which are based on known model structures, such as ARX or ARMAX structures (essentially a system of difference equations with a specific structure), and can also take measurement noise into account. Such model structures are often solved using maximum likelihood estimation or least squares methods.

[0069] Either directly estimate the values ​​of the components in welding circuit model 13, or estimate the time-continuous transfer function G(s) or the time-discrete transfer function G. z The coefficients b0, b1, b2, a0, a1, a2, a3 of (z). If the continuous-time transfer function G(s) or the discrete-time transfer function G... z The coefficients b0, b1, b2, a0, a1, a2, and a3 of (z) can be used to directly calculate the values ​​of the components in the welding circuit model 13, as described above. If the time-discrete transfer function G is estimated... z If the coefficients b0, b1, b2, a0, a1, a2, a3 of (z) are given, then the time-discrete transfer function can be transformed back into the continuous time domain by means of the inverse z-transform, and thus the values ​​of the components in the welding circuit model 13 can be obtained.

[0070] To estimate the parameters, input parameters u (welding current i) of number i = 1, ..., N are needed. S Or measure voltage u M ) and output parameter y (line voltage drop u) S The measured value of ). Here, the input parameter u should be chosen such that as much information as possible about the system to be identified can be derived from the output parameter y. Welding current i often occurs during welding. S A current change curve with a steeply rising current edge, for example, in pulsed arc welding or short arc welding. Welding current i S The attenuation characteristics cannot be directly affected because the power generated by the current can only be removed by ohmic power loss, which occurs due to the ohmic losses in welding line 4, and also due to the power loss generated by arc 10 in the case of arc combustion. Therefore, in order to estimate the parameters, it is preferable to generate the input parameter u (welding current i). S Or measure voltage u M The following is a time-varying curve, which has multiple rising edges, for example, a slope |Δi. S The current edge is / Δt|, where the slope of each rising edge is different. Taking the welding current i as an example... S The time-varying curve of the input parameter u in this form is Figure 4This is illustrated exemplarily. It can be seen that the rising edge F1 of the first rising section is steeper than the rising edge F2 of the second rising section. Between the temporally successive edges F1 and F2, the input parameter u, such as the welding current i, is... S attenuation.

[0071] To estimate the model parameters p of welding circuit model 13 M It has proven advantageous that the different slopes of the at least two edges F1, F2 are selected within the range of 100 A / ms to 10000 A / ms. Preferably, the slope |Δi| of the first edge F1 is... S / Δt| is between 800 A / ms and 1000 A / ms, particularly preferably 900 A / ms, while the slope |Δi| of the second edge F2 S / Δt| is between 200 A / ms and 400 A / ms, particularly preferably 300 A / ms. The absolute value of the slope is given because the welding current i used for parameter identification is... S It can be positive and negative (DC), or it can be alternating (AC).

[0072] Here, input parameter u (e.g., welding current i) S The value of ) is at the minimum input value u min (e.g., minimum welding current i) S,min ) and the maximum input value u max (e.g., maximum welding current i) S,max The welding current i is generated between these two, which can be configured and can also differ for different risers. S When used as input value u, the maximum welding current i S,max Preferably, the welding current i that can be provided by welding power source 1 is used. S Choose between 90% and 100%. Minimum welding current i S Preferably, the welding current i that can be provided by welding power source 1 is used. S Choose between 0% and 40%.

[0073] Parameter identification can also be performed in two stages. Figure 3 As can be seen in the welding circuit model 13, when a pulse of input parameter u is applied, such as welding current i, S At that time, inductors L1, L2, L m The voltage or current on it decays. If a sufficiently long pulse is applied until these voltages or currents completely decay, then L m It functions like a short circuit and can be controlled by input parameters u (e.g., the applied welding current i). S ) and output parameter y (e.g., the measured voltage u measured at measurement position 9) M For example, the socket voltage u BThe ohmic resistance R1 can be directly calculated, for example, using R1 = u M / i S This simplifies the method used to determine the remaining model parameters p. M The parameter estimation method is used because the resistance R1 is known.

[0074] Here, the pulse is continuously applied until the measured voltage u is reached. M Constant, that is, until the inductors L1, L2, L m The voltage on it has decayed. This can be achieved by measuring the voltage u. M The measured value can be easily determined when to measure voltage u. M It is constant. The pulse height is constant with the welding current i. S In the case of welding current i that can be provided by welding power source 1, it is preferable to use welding current i S Choose between 40% and 60%.

[0075] It should be noted that, in order to identify the parameters, the order of the edges F1, F2, and pulses if necessary is not important for estimating the resistance R1 and can be chosen arbitrarily.

[0076] For example, the input parameter u selected for parameter estimation, such as welding current i S The temporal variation (also time-discrete) is assigned to the welding process control unit 12 as a rated parameter SG, and the corresponding output parameter y is measured by means of the pre-given input parameter u, for example, when the welding electrode 9 is short-circuited, by the line voltage drop u. S The form of measurement is preferably performed at a specific sampling time point T. a Time-discrete measurements are taken to obtain measurement values ​​for quantities i = 1, ..., N. The choice of the temporal variation trend of the input parameter u affects the quality of parameter identification and thus advantageously matches the objective.

[0077] Using the known model parameters p of welding circuit model 13 M For example, in identifying model parameters p as described above M This model can then be applied to welding power source 1 so that the measured parameters of the input parameter u, such as the current welding current i, can be used. S,ist (It corresponds to the measured socket current i) B,ist The measured parameter or the current measured voltage u at measurement position 19. M,ist (e.g., the current socket voltage u) B,ist The measured parameters are used to obtain the estimated value for the arc voltage. This estimate The measured voltage u M,ist The line voltage drop u obtained from the welding line model 13 SThe known relationship between them is obtained, optionally taking into account the known voltage drop on an idle welding electrode. This relationship is, for example, simply a measurement of voltage u. M,ist The obtained line voltage drop u S The difference between them.

[0078] Model parameter p of welding circuit model 13 M The determination of the welding current can be performed once before welding begins. For this purpose, welding electrode 9 is short-circuited on workpiece 7, and an input parameter u (welding current i) is generated. S Pre-defined or configured time-varying curves are used to identify model parameters p. M Here, the voltage u is measured at measurement location 19. M In the case of a short circuit, it corresponds to the line voltage drop u. S Therefore, the model parameters p can be obtained as described above. M .

[0079] A welding process exists in which short-circuit stages are regularly incorporated, such as a so-called CMT (cold metal transition) welding process or a short-arc welding process. Here, the molten welding electrode moves towards the workpiece 7 until a short circuit is formed upon contact with the molten pool. Then, the welding electrode moves back in the opposite direction. Before the short circuit occurs, the molten droplet of the welding electrode melts during the arc stage and is subsequently discharged into the molten pool during the short-circuit stage. The arc stage and the short-circuit stage alternate periodically.

[0080] Such a short-circuit phase can also be used to continuously update the weld circuit model 13 during welding, for example by redetermining the model parameters p as described above during the short-circuit phase. M .

[0081] Repeatedly redetermine the model parameters p M This can help ensure that the welding circuit model 13 continuously matches the actual welding situation, for example, when the welding torch 8 is guided by a welding robot and the welding circuit 4, grounding circuit 6, and / or welding current circuit 5 are at least partially arranged on the welding robot. This magnetic interaction can be taken into account in this way because the movement of the welding robot's joints may result in alternating magnetic interactions between the welding circuit 4 and the welding robot (conductive member 14). The position of the welding circuit 4 relative to the conductive member 14 may also change due to the movement of the welding robot, which could also lead to alternating interactions. A similar situation could, of course, occur during manual welding.

[0082] exist Figure 5 The figure shows the arc voltage u measured for comparison. LBAn exemplary time-varying curve of the arc voltage over time t, wherein the arc voltage is in response to welding current i S In the case of a current pulse with a steep rising current edge (in Figure 5 The upper middle part (including the conductive component 14 near the welding line 4) is shown in dashed lines. The arc voltage u estimated using the simple R / L circuit model commonly used to date is shown in dashed lines. LB,RL The order n>1 (specifically, the third order, as described above) according to the invention is indicated by a dashed line. Figure 3 The arc voltage obtained from the welding circuit model 13 (as described) It follows the measured arc voltage u with a small deviation. LB A small deviation can be observed between these two curves. For clarity, in Figure 5 The lower part shows the estimated arc voltage (one estimated using an R / L line model, u). LB,RL The other is the arc voltage obtained according to the present invention. ) and the measured arc voltage u LB The corresponding error e between them. The arc voltage obtained according to the present invention. The obtained error The arc voltage u is less than that obtained using the R / L circuit model to date. LB,RL The obtained error e.

[0083] Therefore, it is evident that the existing R / L circuit models, especially in highly dynamic welding processes (steep current edges), are less suitable than the welding circuit model 13 of the present invention with order n>1. It can be seen that this welding circuit model 13 is significantly closer to the arc voltage u. LB Estimation of arc voltage In some cases, nonlinear modeling of the inductance L1 in the welding circuit model 13 can be used, for example, modeling it as the welding current i. S The function, namely L1(i S ( ) to further improve.

[0084] As mentioned above, the model parameters p are estimated through parameter estimation. M The value of p. If the process is repeated regularly and at least one model parameter p is recorded. M As time progresses, from the at least one model parameter p M The value of p can also be used to infer the state of the welding line over time. If at least one model parameter p... M For example, if there are too many variations in successive estimates (corresponding limit values ​​can be set), damage in the welding circuit can be inferred and corresponding outputs can be made on welding power supply 1, such as outputting visual displays and / or audible warning signals.

[0085] The model parameters or at least one model parameter p M It can also be used to obtain conclusions regarding the laying of welded line 4. If the model parameter p M (It determines the coupling with conductive member 14, for example, as) Figure 3 The coupled inductor L in the welding circuit model 13 m If the value becomes too large (which can be preset or configured by a corresponding limit value), an indication can be given, for example, acoustically or visually, that the location of solder line 4 should be checked.

[0086] As mentioned, multiple measurement locations 19 can also be set. This allows the model parameter p to be estimated separately using measurements taken at different measurement locations 19. M To determine the welding circuit model 13 for different measurement positions 19, at least two different estimates of the arc voltage can be obtained. Therefore, for example, the reliability of an estimate can be verified by another estimate in such a way that if the two estimates do not differ excessively from each other (where corresponding limits can be configured or pre-defined), the estimate is considered valid. However, at least two different estimates of the arc voltage can also be used. The average value is calculated, and then this average value is used as an estimate of the arc voltage. However, different estimates of arc voltage This can be used to limit the error in welding line 4 at a specific location. If multiple estimates of the arc voltage are needed... The same estimate of the arc voltage is provided from a specific measurement position 19 (i.e., towards the welding torch 9). However, if these estimates differ from those prior to that particular measurement position 19, this could indicate damage to the soldered line 4 prior to that particular measurement position 19.

[0087] Estimated arc voltage It can be used to adjust the welding process implemented by welding power source 1, as described above for... Figure 1 As stated above. However, the estimated arc voltage... It can also be used to determine other characteristic values ​​that are important for the welding process. For example, the arc voltage can be used. And other process parameters, such as welding current i, when necessary. STo determine the characteristic values ​​of the welding process, such as the heat and / or arc energy (also known as the electric arc energy) introduced into the workpiece 7 to be welded. Arc energy is, for example, a measure of the energy delivered to the welding process. For quality assurance and for subsequent welding error tracking, the heat input and / or arc energy can be recorded as recorded values. Other characteristic values ​​of the welding process are the resistance or power values ​​at the welding position, which can be determined based on the estimated arc voltage. This can be determined and stored as a recorded value. The recorded value can be stored at the welding power source or other location, or it can be output in real time (or synchronously with the welding process cycle) via an (analog or digital) interface.

Claims

1. An estimate of the arc voltage of an electric arc (10) burning between a welding electrode (9) and a workpiece (7). LB The method, in which, With model parameters p M The welding circuit model (13) is used to calculate the line voltage drop u of the welding circuit (4) between the measurement position (19) and the electric arc (10) on the welding circuit (4). S And the welding circuit model (13) uses the welding current i flowing through the welding circuit (4) S Or the measuring voltage u applied at the measuring position (19) M As input parameter u and with line voltage drop u S The welding circuit (4) is modeled as a transmission system as an output parameter y, so that it can be applied to the current welding current i. S Or the current measured voltage u M Find the voltage drop u used for the line. S The current estimated value, and in the case of line voltage drop u S With arc voltage u LB The estimated value of the arc voltage is obtained by using the known relationship between them. LB The feature is that, in order to estimate the arc voltage u LB The welding circuit (4) is modeled as a transmission system of order greater than one using the welding circuit model (13), and the estimated value of the arc voltage is û LB The measured voltage u at the measurement position (19) is determined. M The obtained line voltage drop u S The difference between them.

2. The method according to claim 1, characterized in that, The transfer system is represented by the transfer function G(s) and G(u), which is the quotient of the output parameter y and the input parameter u. z (z) Modeling.

3. The method according to any one of claims 1 to 2, characterized in that, During a short circuit between the welding electrode (9) and the workpiece (7) or the molten pool on the workpiece (7), a corresponding output parameter y is measured for N input parameters u, and model parameters p are identified based on these N input parameters u and output parameters y using a parameter estimation method. M .

4. The method according to claim 3, characterized in that, Identify model parameters p during the short-circuit phase of welding. M .

5. The method according to claim 3, characterized in that, Identify model parameter p before welding based on the pre-given time variation curves of the input parameter u and the matching output parameter y. M .

6. The method according to claim 3, characterized in that, Generate the following time-varying curve for the input parameter u, wherein the time-varying curve has multiple rising edges, and at least two edges have different slopes.

7. The method according to claim 6, characterized in that, The welding current i used as an input parameter S The different slopes of the at least two edges are selected in the range of 100 A / ms to 10000 A / ms.

8. The method according to claim 3, characterized in that, The model parameters of the weld circuit model are determined by minimizing the deviation between the measured values ​​of the output parameters and the estimates of the output parameters obtained using the weld circuit model for the input parameters using a parameter estimation method.

9. The method according to claim 3, characterized in that, The model parameters are identified multiple times, and the value of at least one of the model parameters is investigated over time in order to draw conclusions about faults in the welded circuit or about unfavorable layout of the welded circuit.

10. The method according to claim 1 or 2, characterized in that, The welding current i S The pulse is continuously applied to the welding line (4) until the measuring voltage u at the measuring position (19) is reached. M The value is constant, and the ohmic resistance R1 of the welding circuit model (13) is determined by the measured voltage u. M With the applied welding current i S They came to the merchants to seek it.

11. A welding power source for performing a welding process, the welding power source having a welding adjustment unit (11), wherein, The estimation unit (16) of the welding adjustment unit (11) implements the model parameter p. M The welding circuit model (13) describes the welding current i flowing through the welding power source (1) as an input parameter u in the form of a transmission system. S Or the measuring voltage u applied at the measuring position (19) of the welding line (4) M The line voltage drop u on the welding line (4) is the output parameter y. S The relationship, and the welding circuit model (13) for the current welding current i S Or the current measured voltage u M Find the voltage drop u used for the line. S The current estimated value, and the welding adjustment unit (11) thereby reduces the voltage drop u in the line. S With arc voltage u LB The estimated value of the arc voltage is obtained from the known relationship between them. LB The feature is that the welding circuit model (13) is modeled as a transmission system of order greater than one in the estimation unit (16), and the estimation unit (16) is implemented to convert the estimated value of the arc voltage into a transmission system of order greater than one. LB The measured voltage u at the measurement position (19) is determined. M The obtained line voltage drop u S The difference between them.

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