An automatic welding machine for the outer wall of an elbow and its control method

Abstract

This invention relates to the fields of mechanical engineering and automated welding, specifically to an automatic welding machine and control method for the outer wall of an elbow; it includes a ring guide rail, a drive trolley, a welding torch adjusting arm, a magnetorheological compliant joint, and an antagonistic flexible cable net mechanism; the system drives the trolley to move in a circle along the guide rail through gear meshing, and its core is the use of the antagonistic cable net mechanism. When the trolley moves to the side welding or overhead welding position, the cam lever is deflected by gravity and pulls the closed-loop pre-tensioned steel cable, which is then converted into a full-circumferential radial contraction pre-tensioning force pointing towards the center of the circle by the tensioning wheel; this invention effectively overcomes the mechanical transmission deviation and trajectory instability caused by gravity overturning torque under complex spatial postures, avoids local jamming or swaying at the guide rail gap, and significantly improves the trajectory guidance accuracy of the equipment under gravity asymmetric interference.

Description

Technical Field

[0001] This invention relates to the fields of mechanical engineering and automated welding, specifically to an automatic welding machine and control method for the outer wall of an elbow. Background Technology

[0002] In the context of industrial pipeline manufacturing and engineering construction, metal elbows, as key pipe fittings for changing the direction of fluid transmission, directly determine the overall sealing and pressure safety of the pipeline network based on the quality of their outer wall welds. To achieve continuous automatic welding of the elbow's outer wall, automatic welding machines typically rely on guide rails and trolley mechanisms to guide the welding torch to perform continuous circumferential motion around a fixed workpiece, thus completing all-position welding operations. For continuous welding of the elbow's outer wall, existing horizontal welding equipment generally adopts a single rigid transmission or a single flexible follower architecture, that is, the welding torch is fixedly or elastically connected to a drive unit running along the guide rail through a mechanical structure. Although this solution has a certain trajectory guidance capability in conventional horizontal circumferential weld scenarios, the inevitable circumferential welding of the elbow... The process involves continuous transitions between flat welding, side welding, and overhead welding positions, and is highly susceptible to asymmetric interference from gravity. A single rigid transmission structure is prone to local mechanical jamming in areas of abrupt changes in workpiece curvature or at guide rail clearances. A single flexible follower structure, when operating in the side welding and overhead welding areas, is prone to low-frequency oscillations caused by the gravity-induced overturning torque generated by the trolley's off-center loading, resulting in severe deviation of the welding torch tip from the predetermined trajectory. Furthermore, in overhead and side welding positions, the molten pool is prone to sagging deformation due to local gravity components, causing fluctuations in the effective arc length. Existing control schemes often struggle to accurately distinguish between pseudo-disturbances caused by mechanical collisions and actual molten pool collapses, resulting in non-unique logic for arc length compensation judgment and delayed adjustment actions.

[0003] Therefore, overcoming the mechanical transmission deviation and trajectory instability caused by the gravity-induced overturning torque, and improving the timeliness and accuracy of adaptive adjustment and compensation of the molten pool in complex spatial positions, has become an urgent technical problem to be solved. Summary of the Invention

[0004] To solve the above-mentioned technical problems, the present invention provides an automatic welding machine for the outer wall of an elbow and a control method therein. Specifically, the technical solution of the present invention is as follows: An automatic welding machine for the outer wall of an elbow includes: a base fixed to the ground; and an annular guide rail fixedly connected above the base by a support column, wherein the inner diameter of the guide rail is larger than the outer diameter of the elbow to be welded. The drive trolley is mounted on the outer edge of the annular guide rail via guide wheels, and a spindle servo motor is fixed inside. The drive gear connected to the spindle servo motor meshes with the internal gear ring machined on the side of the annular guide rail. The welding torch adjustment arm is fixed at the inner side of the drive trolley at the front end and extends to the center area of ​​the inner ring of the annular guide rail at the rear end. A magnetorheological compliant joint, with its head end connected to the end of the welding torch adjustment arm and its tail end connected to the welding torch; The magnetorheological compliant joint includes an inner sleeve and an outer sleeve, with the annular gap between them filled with a magnetorheological elastomer medium, and a high-frequency electromagnetic coil wound around the outer wall of the outer sleeve. The contour roller is fixed to the side of the welding torch by a miniature bracket; The antagonistic flexible cable net mechanism includes floating tensioning wheels arranged along the periphery of the annular guide rail and slidably connected to its outer reference surface, a closed-loop pre-tensioning steel cable passing around all the floating tensioning wheels, and a cam lever hinged to the housing of the drive trolley; a high-precision absolute encoder is installed at the hinge shaft of the cam lever to collect the physical deflection angle of the cam lever under gravity in real time. A miniature dynamic tension sensor is connected in series at the closed-loop end of the closed-loop pretensioning cable to collect radial pretension data of the physical cable net in real time during operation. Both the high-precision absolute encoder and the miniature dynamic tension sensor are bidirectionally connected to the control unit. The cam lever achieves cross-zone coupling through its hinge shaft. Its hinge end is located in the transmission guide area where the drive trolley is located, while its short arm end extends axially towards the cable net pretensioning area and connects to the closed-loop pretensioning cable. Through this axially layered and radially coupled layout, the motion trajectory of the drive trolley is completely offset from that of the floating tensioning wheel in the axial direction during the circumferential feeding process, eliminating motion obstacles and collision risks. The long arm end is equipped with a counterweight.

[0005] In one embodiment, the supporting columns are evenly distributed, and the guide wheels are triangularly distributed and use V-shaped guide wheels.

[0006] In one embodiment, the output shaft of the spindle servo motor is directly connected to the drive gear via a rigid coupling, the inner sleeve is fixed to the welding torch, the outer sleeve is fixed to the welding torch adjusting arm, and the high-frequency electromagnetic coil is wrapped with an insulating and heat-conducting layer.

[0007] In one embodiment, the inner sleeve is made of non-magnetic stainless steel, and the outer sleeve is made of magnetic silicon steel.

[0008] In one embodiment, the central shaft of the floating tension wheel is slidably connected to the outer reference surface of the annular guide rail via a linear bearing, and the closed-loop pretensioning cable is an interwoven flexible steel wire rope.

[0009] In one embodiment, the outer surface of the contour roller is made of a high-temperature resistant ceramic material.

[0010] A control method for an automatic welding machine for the outer wall of an elbow includes: The spindle servo motor is controlled to drive the drive trolley to move along the annular guide rail to the elbow welding point; An initial excitation current is passed into the high-frequency electromagnetic coil to cause the ferromagnetic particles in the magnetorheological elastomer medium to form a chain-like arrangement structure, thereby controlling the magnetorheological compliant joint to exhibit a rigid locking state. The spindle servo motor is controlled to continuously drive the drive trolley to rotate around the bend, and the welding torch is controlled to perform welding operations synchronously. The gravity-induced overturning torque during the rotation of the drive trolley is obtained. The long arm of the cam lever is deflected downward by gravity and drives the short arm to pull the closed-loop pre-tensioning steel cable, converting the local gravity component into a full-circumferential radial contraction pre-tensioning force pointing towards the center of the annular guide rail. Continuously monitor the welding arc voltage and the high-frequency fluctuation rate of the welding arc voltage, as well as the time-domain fluctuation characteristics of the transient torque current of the spindle servo motor; When the welding arc voltage shows a monotonically decreasing trend and the torque current of the spindle servo motor is in a stable state, it is determined that the current liquid molten pool is sagging due to the influence of gravity. When the welding arc voltage does not show a monotonically decreasing trend or the torque current of the spindle servo motor is not in a stable state, it is determined that the current liquid molten pool has not sagged and the current welding state is maintained.

[0011] In one embodiment, after determining that the current molten pool is sagging due to gravity, the following steps are taken: Extract the arc voltage decrease curve corresponding to the monotonically decreasing trend of the welding arc voltage, and calculate the geometric offset of the molten pool sag based on the integral area enclosed by the arc voltage decrease curve and the time axis. The geometric offset of the molten pool sag is mapped to the torch lifting compensation angle required to counteract the sag. A pulse width modulation signal is sent to the high-frequency electromagnetic coil to reduce the duty cycle of the excitation current, thereby reducing the shear yield stress and elastic modulus of the magnetorheological elastomer medium to the critical yield point and controlling the magnetorheological compliant joint to enter a low stiffness compliant state.

[0012] In one embodiment, after controlling the magnetorheological compliant joint to enter a low-stiffness compliant state, the following steps are included: In the low stiffness compliant state, the spindle servo motor is controlled to finely adjust the circumferential position of the drive trolley according to the welding torch lifting compensation angle; The welding torch achieves flexible posture adaptation by relying on the contact force between the contouring roller and the outer wall of the elbow; When the posture is adjusted to the correct position, a full-load excitation current is output to the high-frequency electromagnetic coil again, which significantly increases the modulus of the magnetorheological elastomer medium and controls the magnetorheological compliant joint to return to the rigid locking state.

[0013] In one embodiment, in the step of reversely calculating the geometric offset of the molten pool sag based on the integral area enclosed by the arc voltage drop curve and the time axis, the geometric offset of the molten pool sag is calculated in reverse by combining the pre-calibrated arc voltage gradient coefficient.

[0014] The present invention has the following beneficial effects: 1. This invention employs an antagonistic flexible cable net mechanism to obtain the gravity-induced overturning torque during the rotation of the drive trolley. The long arm of the cam lever is deflected downwards by gravity, which drives the short arm to pull the closed-loop pre-tensioned steel cable. The local gravity component is converted into a full-circumferential radial contraction pre-tensioning force pointing towards the center of the annular guide rail via a floating tension wheel. This effectively overcomes the mechanical transmission deviation and trajectory instability caused by gravity-induced overturning torque under complex spatial postures, avoids local jamming or low-frequency oscillation at the guide rail fit gap, and significantly improves the trajectory guidance accuracy of the equipment under gravity asymmetric interference.

[0015] 2. This invention continuously monitors the high-frequency fluctuation rate of the welding arc voltage and the time-domain fluctuation characteristics of the transient torque current of the spindle servo motor. It determines the molten pool sagging only when the motor torque current is stable and the welding arc voltage shows a monotonically decreasing trend, thus successfully eliminating false disturbances caused by mechanical collisions. After determining sagging, it reverses the calculation of the geometric offset of the molten pool sagging and maps it to the welding torch lifting compensation angle required to counteract the sagging based on the integral area enclosed by the arc voltage drop curve and the time axis. It also controls the magnetorheological compliant joint to enter a low-stiffness compliant state and achieves flexible adaptation of the welding torch posture by relying on the contact force between the contour roller and the outer wall of the elbow. Furthermore, this invention deeply integrates the control layer software and the underlying mechanical actuator to construct a software-hardware linkage and dynamic tracking mechanism. The system software interface and underlying code are not only responsible for issuing arc compensation commands, but also directly and accurately calculate and map the mechanical tension state and trajectory correction amount of the cam lever and closed-loop pre-tensioned steel cable resisting the gravity overturning torque under different spatial postures by real-time synchronous acquisition and visualization rendering of core operating data such as the transient torque current of the spindle servo motor, the physical mechanical deflection angle transmitted back by the high-precision absolute encoder, and the real steel cable force transmitted back by the micro dynamic tension sensor. This linkage design transforms the hidden mechanical anti-interference compensation process into concrete waveform data and system screen recording dynamic logs in the software system, so that the code execution and system interface can directly confirm the motion trajectory effect of the underlying mechanical hardware. This method effectively solves the problem of non-unique logic of arc length compensation judgment conditions, and greatly improves the timeliness and accuracy of molten pool adaptive adjustment compensation. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a schematic diagram of the overall structure of the device; Figure 2 This is a schematic diagram of the drive trolley structure of the device; Figure 3 This is a schematic diagram of the magnetorheological compliant joint structure of the device; Figure 4 This is a schematic diagram of the spindle servo motor structure of the device; Figure 5 This is a flowchart of the method of the present invention.

[0017] In the diagram: 1. Base; 2. Annular guide rail; 3. Support column; 4. Drive trolley; 5. Guide wheel; 6. Main spindle servo motor; 7. Drive gear; 8. Internal gear ring; 9. Welding torch adjusting arm; 10. Magnetorheological compliant joint; 11. Welding torch; 12. Inner sleeve; 13. Outer sleeve; 14. Annular gap; 15. Magnetorheological elastomer medium; 16. High-frequency electromagnetic coil; 17. Contouring roller; 18. Miniature support; 19. Antagonistic flexible cable net mechanism; 20. Floating tension wheel; 21. Closed-loop pre-tensioned steel cable; 22. Cam lever; 23. Counterweight; 24. Rigid coupling; 25. Insulating and heat-conducting layer; 26. Linear bearing. Detailed Implementation

[0018] To enable those skilled in the art to better understand the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.

[0019] Example 1: Please see Figure 1 An automatic welding machine for the outer wall of an elbow, comprising: Base 1, fixed to the ground; The annular guide rail 2 is fixedly connected to the base 1 above by the support column 3, and its inner ring diameter is larger than the outer diameter of the elbow to be welded. The drive trolley 4 is mounted on the outer edge of the annular guide rail 2 via the guide wheel 5, and the spindle servo motor 6 is fixed inside. The drive gear 7 connected to the spindle servo motor 6 meshes with the internal gear ring 8 machined on the side of the annular guide rail 2. The welding torch adjusting arm 9 has its first end fixed to the inner side of the drive trolley 4 and its end extending to the center area of ​​the inner ring of the annular guide rail 2. A magnetorheological compliant joint 10 is connected at its head to the end of a welding torch adjusting arm 9 and at its tail to a welding torch 11. The magnetorheological compliant joint 10 includes an inner sleeve 12 and an outer sleeve 13, with a magnetorheological elastomer medium 15 filling the annular gap 14 between them, and a high-frequency electromagnetic coil 16 wound around the outer wall of the outer sleeve 13. The contour roller 17 is fixed to the side of the welding torch 11 by a miniature bracket 18; The antagonistic flexible cable net mechanism 19 includes floating tensioning wheels 20 arranged around the periphery of the annular guide rail 2 and slidably connected to its outer reference surface, a closed-loop pre-tensioning steel cable 21 passing around all the floating tensioning wheels 20, and a cam lever 22 hinged to the housing of the drive trolley 4. The short arm end of the cam lever 22 is fixedly connected to the closed-loop pre-tensioning steel cable 21, and the long arm end is equipped with a counterweight 23. Existing horizontal elbow outer wall welding equipment typically employs a single rigid transmission or a single flexible follower structure. A single rigid structure is prone to local jamming in the curvature abrupt change zone, while a single flexible structure is prone to low-frequency oscillation due to gravity-induced turning torque in the overhead and side welding zones. This embodiment adopts a combined structure of base 1, annular guide rail 2, drive trolley 4, welding torch adjustment arm 9, magnetorheological compliant joint 10, welding torch 11, contour roller 17, and antagonistic flexible cable net mechanism 19. The base 1 adopts a welded steel structure frame or a cast steel frame. The lower part of the base 1 is fixed to the concrete ground by anchor bolts. A single piece of equipment can be fixed in four-point or six-point manner. The ring guide rail 2 is supported above the base 1 by the support column 3. The inner diameter of the guide rail is larger than the maximum outer diameter of the elbow to be welded. It is preferred to reserve an installation gap of 20mm to 120mm to ensure that the structural interference inspection result is zero and to ensure that there is no interference when the elbow is clamped and the welding torch 11 rotates. Combination Figure 2 The drive trolley 4 is mounted on the outer edge of the annular guide rail 2 via the guide wheel 5. Under the drive of the main spindle servo motor 6, it makes a circumferential feed along the annular guide rail 2. The drive gear 7 directly meshes with the internal gear ring 8 on the side of the guide rail, so that the angular displacement of the motor can be directly converted into the circumferential displacement of the welding torch 11. The welding torch adjusting arm 9 transmits the motion of the drive trolley 4 to the center area of ​​the inner ring of the annular guide rail 2, enabling the welding torch 11 to approach the weld seam trajectory on the outer wall of the elbow; please refer to Figure 3A magnetorheological compliant joint 10 is located between the end of the welding torch adjusting arm 9 and the welding torch 11. The space between its inner and outer sleeves is filled with a magnetorheological elastomer medium 15. The change in the medium modulus is controlled by a high-frequency electromagnetic coil 16, which allows the welding torch 11 to switch between a rigid locking state and a low-modulus compliant state. A contour roller 17 is arranged on the side of the welding torch 11 to contact the outer wall of the elbow in the compliant state and provide posture constraints. The antagonistic flexible cable net mechanism 19 consists of floating tensioning wheel 20, closed-loop pre-tensioned steel cable 21 and cam lever 22. When the drive trolley 4 moves in a circular motion to the side welding position or overhead welding position, the gravity overturning torque formed by its eccentric mass is amplified by the cam lever 22 and then acts on the closed-loop pre-tensioned steel cable 21. The closed-loop pre-tensioned steel cable 21 is then converted into radial shrinkage prestress distributed along the circumference of the annular guide rail 2 through each floating tensioning wheel 20, so as to suppress the local deformation and gap increase of the guide rail and trolley at the gravity overturning position. When the drive trolley 4 runs to Flat welding position or When the welding position is at a dead point where the direction of gravity is collinear with the radial direction of the trolley, the pre-set position at the interface between the annular guide rail 2 and the guide wheel 5 is used. The basic assembly interference, as well as the elastic hysteresis damping of the closed-loop pre-tensioned steel cable 21 system and the floating tension wheel 20 itself, maintain the tension state before entering the dead point, thereby achieving a smooth transition in the angular displacement fluctuation of the attitude in the whole space that is less than the preset deviation value. This structural combination allows the welding torch 11 to have both trajectory compliance and vibration resistance on the same equipment, and gravity disturbance can be directly converted into preload to maintain concentricity. It is suitable for automatic welding of the outer wall of metal elbows with an outer diameter of 89mm to 1220mm and a bending angle of 45° to 180°. The preferred length ratio of the short arm end to the long arm end of the cam lever 22 is 1:5. When the drive trolley 4 moves to the side welding position, the long arm end generates a downward deflection torque under the action of gravity. After being amplified by the lever, it acts on the closed-loop pre-tensioned steel cable 21 through the short arm end, generating a circumferential tension of not less than 500N. This tension is converted into radial contraction pressure through the floating tension wheel 20, which compresses the fit gap between the annular guide rail 2 and the drive trolley 4 to within 0.05mm, thereby eliminating the mechanical deviation caused by gravity overturning. The supporting columns 3 are evenly distributed, and the guide wheels 5 are triangularly distributed and use V-shaped guide wheels 5; The meaning of the evenly distributed support columns 3 is that the support points are arranged at equal angles around the circumference of the annular guide rail 2. Preferably, four support columns 3 are distributed at 90°, but six or eight support columns 3 can also be added according to the diameter of the guide rail. The purpose of the evenly distributed support is to distribute the weight of the annular guide rail 2, the off-center load of the drive trolley 4, and the dynamic load during the welding process to each support point, thereby reducing the local deflection caused by single-point support. The triangular distribution of the guide wheels 5 means that at least three sets of guide wheels 5 form a spatially stable support relationship on the housing of the drive trolley 4, with two sets located in the lower bearing area and one set located in the upper limiting area. The three sets of guide wheels 5 together restrict the radial, axial and overturning directions of the drive trolley 4 relative to the annular guide rail 2. The V-shaped guide wheel 5 is engaged with the inclined surface of the outer edge of the annular guide rail 2. The V-shaped clamping angle is preferably 60° to 90°, which can achieve automatic centering under relatively small preload conditions. Compared with cylindrical rollers, the V-shaped guide wheel 5 can simultaneously undertake guiding and limiting functions in circular motion. Even after the guide wheel 5 is worn, it can still maintain relatively stable guiding accuracy by relying on the inclined surface contact. For the large-diameter annular guide rail 2, each set of guide wheels 5 can be made into a double-row angular contact bearing support form to improve the load-bearing capacity; by the support columns 3 being evenly distributed and the triangular V-shaped guide wheels 5 being combined, the radial movement of the drive trolley 4 during the entire circumference welding can be controlled within 0.2mm, and the swing amplitude of the welding torch 11 end is reduced accordingly, thereby improving the continuity of weld formation. Combination Figure 4 The output shaft of the main spindle servo motor 6 is directly connected to the drive gear 7 through the rigid coupling 24. The inner sleeve 12 is fixed to the welding torch 11, and the outer sleeve 13 is fixed to the welding torch adjustment arm 9. The high-frequency electromagnetic coil 16 is wrapped with an insulating and heat-conducting layer 25. The output shaft of the main spindle servo motor 6 is directly connected to the drive gear 7 through a rigid coupling 24. The purpose is to reduce the angular lag caused by intermediate reduction stages and connection gaps. The rigid coupling 24 can be a diaphragm coupling, a clamp-type rigid coupling 24, or a shrink sleeve connection. Its coaxiality control is preferably no greater than 0.05mm. The inner sleeve 12 is fixed to the welding torch 11, and the outer sleeve 13 is fixed to the welding torch adjusting arm 9. This means that the attitude change of the welding torch 11 relative to the welding torch adjusting arm 9 is only achieved by the shear deformation of the magnetorheological elastomer medium 15 in the annular gap 14. This arrangement limits the magnetic field area to the joint position and avoids functional deviation caused by magnetic interference to other parts of the welding machine body. The preset gap width is used to define the effective shear layer thickness of the magnetorheological elastomer medium 15 that can be filled between the inner sleeve 12 and the outer sleeve 13. In this embodiment, it is preferably 1 mm to 3 mm, and more preferably 2 mm. If the gap is smaller than the preset minimum value, the complexity of the medium filling and processing assembly process will exceed the preset range. If the gap exceeds the preset width threshold, the efficiency of the magnetic field will be reduced. The high-frequency electromagnetic coil 16 is wrapped with an insulating and heat-conducting layer 25. The insulating and heat-conducting layer 25 can be any of the following forms: alumina filled with silicone, polyimide insulating film combined with thermal grease, or mica insulating sheet combined with metal heat sink. It is used to simultaneously achieve electrical insulation and heat conduction to prevent the coil from overheating after long-term pulse operation. This structure enables the magnetorheological compliant joint 10 to generate repeatable modulus changes under millisecond-level current variations, and ensures that the mechanical connection stiffness between the welding torch 11 and the welding torch adjusting arm 9 is adjustable. The inner sleeve 12 is made of non-magnetic stainless steel, and the outer sleeve 13 is made of magnetic silicon steel. The inner sleeve 12 is made of non-magnetic stainless steel, preferably austenitic stainless steel such as 304 or 316L, whose relative permeability is close to 1, which can reduce the bypassing and shunting of the magnetic field in the inner sleeve 12, and allow the magnetic field to act more on the magnetorheological elastomer medium 15 in the annular gap 14. The outer sleeve 13 is made of magnetically conductive silicon steel, preferably cold-rolled non-oriented silicon steel sheets rolled into shape or integral magnetically conductive steel parts processed into shape. The purpose is to improve the magnetic circuit conduction efficiency, so that the magnetic lines of force generated by the high-frequency electromagnetic coil 16 can pass through the annular gap 14 in a concentrated manner; and to ensure that the penetration direction of the magnetic lines of force is perpendicular to the shear direction of the magnetorheological elastomer medium 15 in the annular gap 14, thereby maximizing the magnetorheological effect. Since the inner sleeve 12 is connected to the welding torch 11, the welding heat will be transferred along the structure. The non-magnetic stainless steel has good corrosion resistance and thermal stability. The outer sleeve 13 is connected to the welding torch adjustment arm 9 and needs to bear the main magnetic circuit and structural support functions. The magnetic silicon steel has both magnetic permeability and mechanical processing characteristics. This material combination increases the magnetic induction intensity in the annular gap 14 under the same coil current conditions and increases the yield stress variation range of the magnetorheological elastomer medium 15, thereby making it easier for the stiffness-flexibility switching of the joint to correspond with the welding control command. The central axis of the floating tension wheel 20 is slidably connected to the outer reference surface of the annular guide rail 2 via a linear bearing 26, and the closed-loop pre-tensioning steel cable 21 is made of interwoven flexible steel wire rope; this sliding connection means that each tension wheel can not only rotate around its own axis, but also move within a small range along the radial direction of the guide rail; The linear bearing 26 can be a linear slider with a radial guide groove, or a ball linear bearing 26 with a cylindrical guide rod; its travel is preferably 3mm to 20mm, used to absorb local length adjustments caused by tension changes in the closed-loop pre-tensioned steel cable 21; The closed-loop pre-tensioning cable 21 is made of interwoven flexible steel wire rope, preferably a stainless steel wire rope with a 7x19 or 6x37 structure, and the diameter can be selected from 2mm to 8mm according to the equipment size. The interwoven flexible steel wire rope has less bending stiffness than a single strand of steel wire, and it is easier to form a continuous tension distribution when passing through multiple floating tensioning wheels 20, thereby reducing stress concentration at each contact point. When the trolley 4 is driven into a position where gravity flips more significantly, the cam lever 22 drives the closed-loop pre-tensioned steel cable 21 to tension. The tension of the steel cable is distributed as a centripetal force on the outer periphery of the annular guide rail 2 through each floating tension wheel 20. The linear bearing 26 allows each floating tension wheel 20 to automatically adjust to the force balance position, avoiding uneven pre-tension distribution caused by geometric errors of the rigid fixed wheel seat. This arrangement makes the response of the antagonistic flexible cable net mechanism 19 to gravity disturbance dependent on geometric force transformation, and dynamic pre-tension can be formed without an independent hydraulic or pneumatic source. The outer surface of the contour roller 17 is made of high-temperature resistant ceramic material; The outer surface of the contour roller 17 is made of high-temperature resistant ceramic material. In this invention, high-temperature resistant ceramic material means a material that can maintain stable contour dimensions and is not prone to adhesion of molten metal in the environment of welding spatter, arc radiation and adjacent high-temperature workpiece. Preferred materials include alumina ceramic, silicon nitride ceramic or zirconium oxide toughened ceramic. The contour roller 17 is mounted on the side of the nozzle of the welding torch 11 by a miniature bracket 18. A predetermined angle is formed between the roller axis and the welding torch 11 axis, so that the roller contact point is located in the area adjacent to the weld without blocking the arc. The roller diameter is preferably 8mm to 30mm, and the width is preferably 3mm to 10mm; the purpose of using a high-temperature resistant ceramic outer surface is to reduce wear and thermal deformation when in contact with the outer wall of the elbow, and to reduce the change in rolling resistance caused by metal splash adhesion; When the welding torch 11 is in a low-stiffness compliant state, the contact force between the contour roller 17 and the outer wall of the elbow can be controlled within the range of 1N to 20N. This contact force is sufficient to provide an attitude reference without significantly changing the relative position between the welding torch 11 and the workpiece. Through the selection of the roller material, the attitude compliance of the compliant joint after entering the compliant state is more stable, and the trajectory error caused by roller wear or adhesion during the welding process is reduced.

[0020] Example 2: Please see Figure 5 A control method for an automatic welding machine for the outer wall of an elbow includes: The spindle servo motor 6 drives the trolley 4 to move along the annular guide rail 2 to the elbow welding point; the initial excitation current is passed to the high-frequency electromagnetic coil 16, so that the ferromagnetic particles in the magnetorheological elastomer medium 15 form a chain-like arrangement structure, and the magnetorheological compliant joint 10 is controlled to present a rigid locking state. The spindle servo motor 6 continuously drives the drive trolley 4 to rotate around the bend, and controls the welding torch 11 to perform welding operations synchronously; the gravity overturning torque during the rotation of the drive trolley 4 is obtained, and the long arm end of the cam lever 22 is deflected downward by gravity and drives the short arm end to pull the closed-loop pre-tensioning steel cable 21, converting the local gravity component into a full-circumferential radial contraction pre-tensioning force pointing towards the center of the annular guide rail 2; Meanwhile, the software program of the control system captures in real time the algebraic sum of torque and load smoothing fluctuation characteristics generated by the spindle servo motor 6 under the intervention of this mechanical tensioning mechanism, and simultaneously reads the mechanical structure deflection displacement data output by the high-precision absolute encoder and the actual force data of the steel cable output by the micro dynamic tension sensor. Through software code algorithm, the measured gravity deflection displacement of the cam lever 22 and the cable net pretension force are converted into digital state parameters synchronized with the spatial running trajectory of the drive trolley 4. The force and motion trajectory correction mapping waveform of the mechanical mechanism are dynamically generated in the monitoring log area of ​​the operating system screen recording interface, thereby realizing the deep software and hardware linkage of pure mechanical hardware anti-gravity flipping and anti-jamming and software system data real-time tracking. Continuously monitor the high-frequency fluctuation rate of welding arc voltage and the time-domain fluctuation characteristics of transient torque current of spindle servo motor 6; when the welding arc voltage shows a monotonically decreasing trend and the torque current of spindle servo motor 6 is in a stable state, it is determined that the current liquid pool is sagging due to gravity. When the welding arc voltage does not show a monotonically decreasing trend or the torque current of the spindle servo motor 6 is not in a stable state, it is determined that the current liquid pool has not sagged and the current welding state is maintained; this control method is applicable to constant current source welding mode, and the welding power source can be a tungsten inert gas shielded welding power source or a plasma arc welding power source; When the spindle servo motor 6 drives the trolley 4 to move along the annular guide rail 2 to the elbow welding point, the circumferential target position can be calculated based on the pre-input elbow center coordinates, outer diameter, bending radius and welding angle. The spindle servo motor 6 operates in position control mode, and the positioning accuracy is preferably no more than 0.1 degrees. When the initial excitation current is applied to the high-frequency electromagnetic coil 16, the initial excitation current can be set to 60% to 100% of the rated current, which corresponds to making the magnetorheological compliant joint 10 reach a rigid locking state that can withstand the pulsating reaction force of the welding wire feed and the cantilever gravity of the welding torch 11; when the spindle servo motor 6 continuously drives the drive trolley 4 to rotate around the bend, the circumferential speed can be set to 20mm / min to 600mm / min according to the welding line energy requirements. When the system moves to the side welding or overhead welding position, the long arm end of the cam lever 22 is passively deflected downward under the action of gravity, and the short arm end pulls the closed-loop pre-tensioned steel cable 21. The tension of the steel cable is converted into radial shrinkage prestress distributed circumferentially on the annular guide rail 2 by the floating tension wheel 20, thereby reducing the deformation of the guide rail when it is subjected to eccentric load. When continuously monitoring the high-frequency fluctuation rate of welding arc voltage and the time-domain fluctuation characteristics of transient torque current of spindle servo motor 6, the sampling frequency of arc voltage is preferably not less than 5kHz, and the sampling frequency of torque current of spindle servo motor 6 is preferably not less than 2kHz. When the welding arc voltage shows a monotonically decreasing trend and the torque current of spindle servo motor 6 is in a stable state, it indicates that the arc length is shortening and the mechanical operation is not stuck. This combination of characteristics is used to determine that the molten pool is sagging due to gravity. If the arc voltage does not show a monotonically decreasing trend or the torque current has an abnormal peak, it indicates that the current change may be caused by workpiece morphology fluctuations, mechanical interference, or servo disturbances. In this case, the current welding state is maintained and the compliance compensation command is not executed. This method uses both the arc physical quantity and the mechanical transmission state as criteria, which helps to reduce the probability of misjudgment. In this embodiment, the high-frequency fluctuation rate of the welding arc voltage is used to characterize the activity of small changes in arc length near the molten pool. Its input source is the original arc voltage signal collected by the welding power source. The control first performs DC mean removal processing on the original arc voltage signal with a continuous time window, and then extracts the high-frequency components related to the molten pool disturbance. Preferably, the voltage fluctuation in the frequency band from 200Hz to 2000Hz is extracted. Specifically, this embodiment uses a second-order Butterworth bandpass filter to perform real-time filtering on the original arc voltage signal in order to accurately extract... to High-frequency AC components within the frequency band eliminate power frequency interference and DC substrate; The peak-to-peak value of the high-frequency component is calculated within each time window and compared with the average arc voltage within the current time window to obtain a normalized result characterizing the intensity of the fluctuation. The specific calculation formula is as follows: in, This is the normalized result for high-frequency volatility. This represents the peak-to-peak value of the high-frequency components. The average arc voltage is used; the preferred time window is 20ms to 100ms, and adjacent time windows can overlap by 50% to balance response speed and noise resistance; the welding arc voltage shows a monotonically decreasing trend, which means that in multiple consecutive judgment time windows, the average arc voltage after low-pass smoothing decreases sequentially, and the cumulative decrease exceeds the preset decrease threshold. The preset drop threshold can be obtained based on no-load calibration and stable flat welding calibration, preferably 0.05V to 0.5V; the number of continuous judgment time windows is preferably 3 to 8; the purpose of adopting this definition is to eliminate the influence of random fluctuations of a single sampling point on the judgment, so that the downward trend corresponds to a continuous arc length shortening phenomenon. The spindle servo motor's torque current is in a stable state, meaning that within a judgment time window that is the same as or synchronized with the arc voltage, the average torque current variation is within the allowable range and no mechanical jamming characteristic peak appears; the controller can first establish a reference fluctuation value before welding or in the initial stage of stable welding. The reference band consists of the average torque current and the natural fluctuation range under this operating condition; The torque current root mean square fluctuation value within the current time window is compared with the reference band in real time. When it is not greater than 1.2 to 1.8 times the reference fluctuation value and there are no abnormal spikes with a duration greater than 2 ms to 10 ms, it is determined to be in a stable state. The discrete calculation formula for the torque current root mean square fluctuation value is as follows: In the formula, This represents the root mean square ripple value of the torque current. This represents the total number of sampling points within the current time window. For the first Transient torque current value at each sampling point The average torque current within this time window; abnormal spikes in this embodiment represent transient mechanical load surges caused by partial guide rail jamming, gear meshing impact, or external friction; the determination process is executed in the following order: Step 1: Acquire the raw signals of arc voltage and torque current; Step 2: Perform synchronous time window segmentation and noise reduction on the two signals respectively; establish a dynamic tracking and verification mechanism for hardware and software motion trajectories. The controller calls the torque current compensation baseline generated by the mechanical pre-tightening of the bottom cable net when the spindle servo motor 6 enters gravity asymmetric areas such as side welding and overhead welding through built-in software code in real time. The electrical baseline characteristics are then aligned in the time domain and fitted with the physical cable tension change waveform captured by the micro dynamic tension sensor and the mechanical rod deflection curve recorded by the high-precision absolute encoder. The anti-sway trajectory correction process generated by the mechanical traction of the drive trolley 4 is mapped in real time to a visual data map of the system operation interface. Thus, through the strict physical binding of the system code log and multi-source physical hardware sensor data, the actual physical execution effect of the cam lever 22 and cable net mechanism in resisting gravity overturning and trajectory change is intuitively fed back and verified. Step 3: Extract the average value change trend and high-frequency fluctuation rate from the arc voltage signal, and extract the mean, fluctuation value and abnormal peak information from the torque current signal; Step 4: First check if the torque current is stable. If not, attribute the current state to mechanical disturbance and maintain the current welding state. Step 5: Only when the torque current is in a stable state, further check whether the arc voltage meets the continuous decrease condition. If it does, output the molten pool sag judgment result and pass the result to the subsequent compensation angle calculation and compliant joint modulus reduction control steps. By using this mechanical-then-arc discrimination sequence, false triggering caused by mechanism disturbance can be reduced. In this embodiment, the logic model used to determine molten pool sagging is a dual-channel state discrimination model. Its purpose is to distinguish between the actual arc length shortening caused by the gravity sagging of the molten pool and the pseudo arc length change caused by mechanical jamming, guide rail impact, or local geometrical change of the workpiece. This model does not rely on a single electrical signal to draw conclusions, but couples the arc-side information and mechanical-side information in a sequential manner to improve the consistency between the judgment result and the actual welding state. The dual-channel state discrimination model logically includes a mechanical state screening unit, an arc state analysis unit, and a result output unit. The mechanical state screening unit receives the raw torque current signal of the spindle servo motor 6 and outputs the intermediate result of whether the machine is stable. The arc state analysis unit receives the raw arc voltage signal and outputs the average voltage change trend and the degree of high-frequency fluctuation activity. The output unit only reads the output of the arc state analysis unit and forms the final determination of whether the molten pool is sagging or not when the mechanical state screening unit gives a stable conclusion. This forms a continuous data stream from original sampling, window processing, feature extraction, state screening to result determination, avoiding any intermediate quantity being directly used as the final control command. In this model, the high-frequency fluctuation rate of welding arc voltage mainly serves as an auxiliary constraint on the reliability of the arc signal, rather than determining sag independently of the average voltage trend. The reason is that when the molten pool begins to sag due to gravity, in addition to the gradual shortening of the average arc length, the changes in the surface tension of the molten pool and the shape of the liquid bridge will also cause small fluctuations in the arc. If the average arc voltage decreases but the high-frequency fluctuation rate is abnormally amplified at the same time, it is more likely to correspond to interference such as splashing, protective gas turbulence or tungsten electrode contamination. Therefore, the controller prefers to use the high-frequency fluctuation rate to identify abnormal noise windows and suppress misjudgments, and uses the continuously decreasing average arc voltage and stable torque current as the main triggering conditions. The physical relationship represented by the above model is as follows: when the mechanical relative position between the welding torch 11 and the workpiece is basically stable, if the liquid molten pool shifts downward due to gravity, the upper surface of the molten pool will be closer to the welding torch 11, the effective length of the arc will be shortened, and the average arc voltage will continue to decrease. If there is jamming, rubbing, or meshing impact in the mechanical system, the torque current of the servo motor will first show an abnormal average value or a spike disturbance. At this time, even if the arc voltage changes, it will not be primarily attributed to the molten pool sagging. This control logic covers both the thermal arc process and the mechanical transmission process, and can clearly establish the correspondence between the structural state, detection signals, and control actions. After determining that the current liquid molten pool is sagging due to gravity, the process includes: extracting the arc voltage drop curve corresponding to the monotonically decreasing trend of the welding arc voltage; calculating the geometric offset of the molten pool sagging based on the integral area enclosed by the arc voltage drop curve and the time axis; and mapping the geometric offset of the molten pool sagging to the lifting compensation angle of the welding torch 11 required to counteract the sagging. A pulse width modulation signal is sent to the high-frequency electromagnetic coil 16 to reduce the duty cycle of the excitation current, thereby reducing the shear yield stress and elastic modulus of the magnetorheological elastomer medium 15 to the critical yield point and controlling the magnetorheological compliant joint 10 to enter a low stiffness compliant state. Once the molten pool is determined to be sagging, the controller integrates the arc voltage drop curve within the sampling time window. The integration time window is preferably 10ms to 300ms. The integrated area enclosed by the arc voltage drop curve and the time axis represents the cumulative amount of arc length shortening within the time window. Combined with the pre-calibrated relationship between arc voltage and arc length, the geometric offset of the molten pool sagging can be calculated in reverse. The predetermined mapping relationship can be linear mapping, piecewise linear mapping, or lookup table mapping; for example, under specific welding current and shielding gas flow conditions, a calibration table between geometric offset and welding torch 11 lifting compensation angle can be established, and when the offset increases, the corresponding compensation angle increases synchronously. When a pulse width modulation signal is sent to the high-frequency electromagnetic coil 16, the modulation frequency is preferably 1kHz to 20kHz, and the duty cycle is reduced from the higher value of the rigid locked state to 20% to 60%, so that the ferromagnetic particle chain structure inside the magnetorheological elastomer medium 15 is partially dissociated. In this invention, the critical yield point refers to the modulus state that allows the welding torch 11 to undergo controlled posture changes under the action of small external contact forces without collapsing freely due to its own weight; in this state, the joint still retains a certain damping, which can absorb the impact when the drive trolley 4 is finely adjusting its position. Through this step, the molten pool morphology change is converted into an executable compensation angle command, and the joint stiffness has been adjusted to a range suitable for attitude reconstruction before compensation execution; the processing flow for inversely calculating the molten pool sagging geometric offset based on the integral area enclosed by the arc voltage drop curve and the time axis includes: Step 1: Read the arc voltage drop segment confirmed by the judgment process, and use the starting voltage of the drop segment as the reference voltage; Step two: Within the selected integration time window, the decrease in voltage relative to the reference voltage at each sampling point is accumulated to obtain the area (S) characterizing the trend of cumulative arc length shortening. Its discrete calculation formula is as follows: in, For area quantity, For reference voltage, For the first Real-time voltage at each sampling point The sampling point number, The sampling period is The number of samples; Step 3: Divide the area by the integration time window length to obtain the equivalent voltage drop, calculated using the following formula: in, This represents the decrease in equivalent voltage. , , Same as above; Step four: Combine the pre-calibrated relationship to convert the equivalent voltage drop into the geometric offset of the molten pool sag; the purpose of this step-by-step processing method is to enable the controller to first identify the degree of continuous drop and then convert it into geometric compensation requirements, thereby avoiding mistaking instantaneous spikes for real sag. When mapping the geometric offset of the molten pool sag to the lifting compensation angle of the welding torch 11 required to counteract the sag, a calibration table can be established according to the equipment specifications, the overhang length of the welding torch 11, and the outer diameter of the elbow. This calibration table is preferably obtained through offline test welding. Specifically, a known arc length offset is artificially applied under elbows of different outer diameters and different welding positions, and the lifting angle of the welding torch 11 that can restore the arc voltage to the target range is recorded to form the correspondence between the offset and the compensation angle. For small offset intervals, linear mapping can be used; for the transition zone between side welding positions and overhead welding positions, piecewise linear mapping or table lookup interpolation can be used; the lifting compensation angle of welding torch 11 is preferably in the range of 0.1° to 5°, so that the compensation action is sufficient to suppress sagging without causing a sudden change in weld reinforcement height. The critical yield point can be determined by joint calibration after assembly. During calibration, the welding torch 11 and the contour roller 17 are kept in the actual installation posture. The excitation current duty cycle of the high-frequency electromagnetic coil 16 is gradually reduced, and it is observed whether the welding torch 11 can produce a repeatable small-angle deflection under the contact force of the contour roller 17 from 1N to 20N. At the same time, it is monitored whether the welding torch 11 will continue to fall due to its own weight when there is no external force. The modulus state corresponding to the duty cycle is defined as the critical yield point when the following two conditions are met: First, the joint can produce a controlled deflection of 0.1° to 3° under the action of external contact force; Second, the additional drift caused by the self-weight of the welding torch 11 is no greater than 0.2° within the observation time of 100ms to 500ms. This definition clarifies the role of the critical yield point in the control logic, namely, it is both a prerequisite for the activation of compliant compensation and a lower limit constraint to prevent the welding torch 11 from becoming unstable during the compensation stage; the control steps of sending pulse width modulation signals to the high-frequency electromagnetic coil 16 and reducing the excitation current duty cycle can be executed in a graded descent manner. The controller first drops from the rigid lock state to the intermediate duty cycle to check whether the arc voltage and torque current are still stable within a judgment time window; if stable, it continues to drop to near the critical yield point; if unstable, it returns to the previous duty cycle level; the effect of the graded descent is to prevent the welding torch 11 posture from overshooting due to excessive one-time modulus reduction, thereby improving the repeatability of the compensation action. In addition, to ensure system safety, when the magnetorheological compliant joint 10 is in a low stiffness compliant state, the controller continuously monitors the angular acceleration of the welding torch 11 through the differential of the servo motor encoder or an independent accelerometer. If the welding torch 11 is detected to have an angular acceleration exceeding [a certain value] due to severe external mechanical interference, The accelerated descent triggers the safety hard-lock logic, forcibly interrupting the modulus reduction command and immediately outputting a full-load excitation current to the high-frequency electromagnetic coil 16, causing the magnetorheological compliant joint 10 to... The welding torch 11 instantly returns to a rigid locking state to prevent physical collision between the welding torch 11 and the workpiece. The logic model used in this embodiment to calculate the geometric offset from the voltage change and generate the compensation action can be called the droop compensation decision model. Its purpose is to convert the droop of the molten pool, which is difficult to measure directly, into the attitude correction requirements that the welding torch 11 can perform. The model does not directly output the movement of the welding torch 11, but instead outputs intermediate results at three levels: geometric offset, compensation angle, and joint modulus state. This allows for logical separation of detection, decision-making, and execution, facilitating phased verification by the controller. The sag compensation decision model logically includes at least a cumulative quantity extraction unit, a geometric conversion unit, an angle mapping unit, and a joint state switching unit; the cumulative quantity extraction unit reads the confirmed effective descent segment and generates the equivalent voltage drop; the geometric conversion unit converts the equivalent voltage drop into the molten pool sag geometric offset according to the pre-calibrated relationship. The angle mapping unit converts the geometric offset into a welding torch 11 lifting compensation angle based on the current welding position, the overhang length of welding torch 11, and the elbow specifications. The joint state switching unit determines the duty cycle reduction of the high-frequency electromagnetic coil 16 according to the following model calculation logic based on the compensation angle and the current stability check results: in, This represents the decrease in the duty cycle of the high-frequency electromagnetic coil 16. The pre-calibrated stiffness-angle adjustment ratio coefficient has the following dimensions: , For the lifting compensation angle of welding torch 11, This is a stability adjustment coefficient, set when the current stability check result is stable. When in a non-stationary critical fluctuation state, the stability adjustment coefficient The value is determined based on the current root mean square fluctuation of the torque current. Compared with the benchmark fluctuation value The ratio dynamic linear mapping: when When, set ;when At that time, set This terminates the modulus reduction action, thereby allowing for precise calculation of the control parameters of the electromagnetic coil; The magnetorheological compliant joint 10 is brought into a low-stiffness compliant state that allows for attitude reconstruction; this constitutes a data flow that transitions step by step from the detected quantity to the executed quantity, ensuring the accuracy and reliability of the attitude compensation command generation; the integral area enclosed by the arc voltage drop curve and the time axis in this embodiment is used to characterize the cumulative trend of arc length shortening, rather than simply characterizing the drop amplitude at a certain instantaneous sampling point. The technical basis is that the actual molten pool droop usually has a duration and cumulative effect. If it is judged only based on the instantaneous minimum voltage, it is easily affected by spatter, arc oscillation and local surface roughness disturbance. However, after accumulating the continuous descent over time, it can better reflect the actual process of the molten pool gradually approaching the welding torch 11 during this period. Therefore, it is more suitable as a preliminary characterization of geometric offset. The physical relationship represented by mapping the molten pool sagging geometric offset to the torch 11 lifting compensation angle is as follows: Given the torch 11 overhang length and installation posture, the greater the downward offset of the molten pool, the greater the equivalent intrusion degree of the torch 11 relative to the local tangential plane of the workpiece. Therefore, it is necessary to restore the target arc length and molten pool heat distribution by appropriately lifting the torch 11. The controller preferably first calculates the angle correction amount, and its calculation formula is: in, Same as above; This is the geometric offset; The effective rotation radius of the welding torch adjustment arm 9 is then achieved by the fine adjustment of the drive trolley 4 and the contact of the contour roller 17, rather than directly equating the geometric offset to a single-axis linear displacement. After the magnetorheological compliant joint 10 is controlled to enter the low stiffness compliant state, the following steps are taken: in the low stiffness compliant state, the spindle servo motor 6 is controlled to finely adjust the circumferential position of the drive trolley 4 according to the lifting compensation angle of the welding torch 11; the welding torch 11 is flexibly adapted to the posture by relying on the contact force between the contour roller 17 and the outer wall of the elbow. When the attitude is adjusted to the correct position, a full-load excitation current is output to the high-frequency electromagnetic coil 16 again, which significantly increases the modulus of the magnetorheological elastomer medium 15 and controls the magnetorheological compliant joint 10 to return to the rigid locking state. After the magnetorheological compliant joint 10 enters the low stiffness compliant state, the spindle servo motor 6 performs a small angular displacement correction according to the lifting compensation angle of the welding torch 11; this fine adjustment can be converted into the circumferential displacement of the drive trolley 4 on the annular guide rail 2, and the fine adjustment angle is preferably 0.05° to 3°. Since the joint stiffness has decreased, the welding torch 11 is no longer completely constrained by the rigid posture of the welding torch adjusting arm 9. At this time, the normal reaction force and tangential rolling force generated by the contact between the contour roller 17 and the outer wall of the elbow become important constraint sources for the adaptive posture of the welding torch 11. When the contour roller 17 rolls on the outer wall of the elbow, the welding torch 11 deflects at a small angle around the magnetorheological compliant joint 10 to satisfy the local geometric relationship between the end of the welding torch 11 and the surface of the workpiece. The posture adjustment can be determined by two conditions: first, the arc voltage recovers to the target range; second, the arc voltage fluctuation rate falls back to within the set threshold. Once the conditions are met, a full-load excitation current is output to the high-frequency electromagnetic coil 16 again. The rated excitation effect causes the internal particle chain structure of the magnetorheological elastomer medium 15 to be rapidly reconstructed, the modulus to increase, and the joint to return to the rigid locking state. This step allows the compensation action to be completed in parallel with the welding process, and the duration of the compliance window can be controlled within the range of tens of ms to hundreds of ms, thereby reducing the impact of the compensation action on the continuous formation of the weld. In the step of reverse calculation of the geometric offset of molten pool sag based on the integral area enclosed by the arc voltage drop curve and the time axis, the geometric offset of molten pool sag is calculated in reverse by combining the pre-calibrated arc voltage gradient coefficient. The pre-calibrated arc voltage gradient coefficient refers to the change in arc voltage caused by the change in unit arc length under the conditions of setting welding current, shielding gas type, shielding gas flow rate, tungsten electrode extension length and welding torch angle. During calibration, a standard flat plate sample can be used. The distance between the tungsten electrode and the workpiece surface can be adjusted in steps of 0.05 mm to 0.2 mm using a precision lifting platform. The voltage value under a stable arc is recorded, and the arc voltage gradient coefficient is obtained by fitting using the least squares method. The unit can be V / mm. During the welding process, after the controller obtains the integral area enclosed by the arc voltage drop curve and the time axis, it divides the area by the corresponding time window length to obtain the equivalent voltage drop, and then combines it with the pre-calibrated arc voltage gradient coefficient to convert it into the equivalent arc length shortening. Since mechanical jamming has been eliminated under the condition that the torque current of the spindle servo motor 6 is stable, the amount of arc length shortening can be used as an approximate value of the geometric offset of the molten pool sagging or an estimated value after correction by a correction factor. For elbows made of different materials and welding current settings, multiple sets of arc voltage gradient coefficient tables can be established. The controller can automatically call the corresponding coefficients according to the current process parameters. By using pre-calibrated arc voltage gradient coefficients, the voltage change can be converted into a geometrically meaningful offset, so that the subsequent compensation angle calculation has a clear physical basis and improves the consistency of the method implementation. The logical role of the arc voltage gradient coefficient in the control system is to convert the arc voltage change in the electrical signal domain into the arc length change in the geometric domain, and to serve as the conversion medium in the process of calculating the geometric offset of the molten pool sag; this coefficient is not an arbitrary empirical value, but a calibration parameter that corresponds one-to-one with the current welding process window. Before calling this coefficient, the controller first selects the corresponding parameter group based on the current welding current level, shielding gas type, shielding gas flow rate, tungsten electrode extension length, and torch angle. If the process parameters exceed the calibrated range, it preferentially calls the nearest parameter group and provides a recalibration prompt. The pre-calibration process for the arc voltage gradient coefficient includes: Step 1: Establish a stable arc under the same or equivalent current, gas, and torch posture conditions as in actual welding. Step 2: Use a precision lifting platform to change the distance between the tungsten electrode and the workpiece surface in fixed steps. After each change of distance, wait for the arc to stabilize and then record the corresponding voltage value. Step 3: Organize the distance changes and voltage changes of each group into a calibration data table in chronological order, and remove outliers caused by unstable arc initiation or abnormal splashing. Step four: Obtain the arc voltage gradient coefficient under this operating condition based on the remaining data and store it in the controller parameter library; through this step-by-step calibration process, the source of input data, intermediate processing steps and final output results can be clearly defined, ensuring the reliability of the arc voltage gradient coefficient. In the actual welding process, the controller first obtains the equivalent voltage drop through an integral step. Then, convert it to the equivalent arc length shortening using the following formula: in, Indicates the amount of shortening of the equivalent arc length; Same as above; This represents the arc voltage gradient coefficient. If the molten pool shape correction coefficient has been obtained through trial welding under the same working condition, the controller can further multiply the equivalent arc length shortening by this correction coefficient to obtain a geometric offset estimate that is closer to the actual molten pool sagging. The correction coefficient is preferably 0.8 to 1.2, used to compensate for the deviation caused by the arc contraction effect under different materials and different heat input conditions. The validity verification of the arc voltage gradient coefficient can be performed after each power-on or each change of welding process. During the verification, the controller makes one or more trial adjustments to the height of the welding torch 11 with a small amplitude and a known displacement, and compares the deviation between the theoretical voltage change and the actual measured voltage change. When the deviation is no greater than 10% to 15%, the coefficient is deemed valid and can continue to be used; when the deviation exceeds the above range, the controller prompts for recalibration; by adding this verification step, the accuracy of the arc voltage gradient coefficient can be kept within an acceptable range after long-term use. The arc voltage gradient coefficient calling model involved in this embodiment is designed to enable the same set of integral judgment logic to adapt to different welding process windows, rather than applying the voltage change law obtained under a certain working condition to all working conditions indiscriminately. The model directly selects, verifies and converts the coefficient group calibrated in the parameter library based on the current process parameters, thereby ensuring that the transition from the voltage domain to the geometric domain has clear boundary conditions. The arc voltage gradient coefficient calling model logically includes a working condition identification unit, a parameter matching unit, a validity verification unit, and a geometric conversion unit; the working condition identification unit reads the current welding current, shielding gas type, shielding gas flow rate, tungsten electrode extension length, and welding torch angle. The parameter matching unit searches for the corresponding or nearest gradient coefficient group in the controller parameter library based on the operating condition information. Specifically, when searching for the nearest gradient coefficient group, the parameter matching unit uses a weighted deviation calculation method to calculate the difference between the current detection operating condition and the preset operating condition in the parameter library. The calculation logic for the difference is as follows: in, For the degree of difference, These are the sequence numbers of the parameters for continuous operating conditions. This represents the total number of parameters for continuous operating conditions. For the first Preset weights for continuous parameters, preset weights The parameters are pre-assigned based on a priori empirical matrix of their sensitivity to the arc morphology. For example, in this embodiment, the preset weights for welding current, shielding gas flow rate, and tungsten electrode extension length are respectively assigned constant values. , , And must meet , For the currently read number Continuous parameter values, The parameter values ​​are preset to correspond to the operating conditions in the parameter library. and These are the upper and lower limits of the parameter's calibration within a reasonable process window; the parameter matching unit selects the calculated degree of difference, provided that discrete parameters such as the protective gas type are consistent. The minimum preset operating condition calls its corresponding gradient coefficient group; The validity verification unit confirms whether the coefficient still meets the allowable error range through a short-term verification after a trial displacement or process change; the geometric conversion unit converts the obtained equivalent voltage drop into the geometric offset of the molten pool sag only after the verification is passed; this data flow illustrates the complete path of the coefficient from storage and matching to actual use. The physical relationship represented by the model is as follows: Under given welding current, gas environment and torch posture, the change in arc length will cause the average arc voltage to change approximately according to a certain gradient. Therefore, the voltage change can be regarded as the equivalent physical quantity of the arc length change. However, when the process window changes, the degree of arc column contraction, plasma conductivity and the constraint effect of shielding gas on arc shape also change. Therefore, the arc voltage gradient coefficient needs to be rematched according to the working conditions. By adding working condition matching and validity verification, the physical mapping relationship between voltage change, arc length change and molten pool sag offset can be kept clear and logically consistent, realizing an accurate correspondence between the reverse calculation process and the actual welding physical state. To verify the effectiveness of the technical solution of the present invention, a comparative welding test was conducted on a stainless steel elbow with a pipe diameter of 114 mm and a wall thickness of 6 mm. The test results show that after adopting the antagonistic flexible cable net mechanism of the present invention, the maximum radial runout of the drive trolley in the overhead welding position is reduced from 0.45 mm to 0.08 mm, which effectively avoids trajectory instability caused by mechanical jamming. In the step disturbance test simulating the drooping of a molten pool, the dual-channel state discrimination model and the droop compensation decision model reduced the response time for the identification and decision of arc length shortening to less than 40ms. Compared with the average response time of 120ms of the traditional control system that relies solely on arc voltage feedback, the compensation timeliness was improved by 66.7%. The experimental data fully demonstrates that the present invention significantly improves the timeliness of adaptive adjustment compensation of molten pool under complex spatial positions and the accuracy of trajectory guidance.

[0021] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. An elbow outer wall automatic welding machine characterized by, The utility model relates to a welding torch automatic adjusting device for pipe elbow, including: Base (1) is fixed to ground, Annular guide rail (2) is fixedly connected above base (1) through support column (3), and the inside circle aperture is greater than the outer diameter of the elbow to be welded, Driving trolley (4) is clamped to the outer side edge of annular guide rail (2) through guide wheel (5), and the inside fixed connection main shaft servo motor (6) is connected with the driving gear (7) of main shaft servo motor (6) and is engaged with the internal gear ring (8) processed in the side surface of annular guide rail (2), Welding torch adjusting arm (9) is fixed to the inside surface of driving trolley (4) first end, and the tail end extends to the inside circle center area of annular guide rail (2), Magnetorheological compliant joint (10) is connected with the tail end of welding torch adjusting arm (9) first end, and is connected with welding torch (11) tail end, and the magnetorheological compliant joint (10) includes inner layer sleeve (12) and outer layer sleeve (13), and the annular gap (14) between the two is filled with magnetorheological elastomer medium (15), and the outer wall of outer layer sleeve (13) is wound with high-frequency electromagnetic coil (16), Profiling roller (17) is fixed to the side of welding torch (11) through micro support (18), Antagonistic flexible cable net mechanism (19) includes floating tension wheel (20) arranged along the periphery of annular guide rail (2) and slidably connected to the outer reference surface thereof, closed loop pre-tightening steel cable (21) passing through all floating tension wheels (20), and cam lever (22) hinged to the shell of driving trolley (4), the hinged shaft of cam lever (22) is provided with high-precision absolute value encoder, which is used for collecting the physical deflection angle of cam lever under the action of gravity in real time, The closed loop pre-tightening steel cable (21) is connected with micro dynamic tension sensor at the closed loop end point, which is used for collecting the radial pre-tightening tension data of the entity cable net in the running process in real time, the high-precision absolute value encoder and micro dynamic tension sensor are connected with control unit in bidirectional communication, the cam lever (22) is coupled through the hinged shaft, and the hinged end is located in the transmission guide area of driving trolley (4), and the short arm end extends axially to the cable net pre-tightening area and is connected with the closed loop pre-tightening steel cable (21), through the axial layered and radial coupling layout, the movement track of driving trolley (4) is completely overlapped with floating tension wheel (20) in the axial direction in the circumferential feeding process, and the movement obstacle and collision risk are eliminated, and the counterweight (23) is arranged at the long arm end.

2. The elbow outer wall automatic welding machine according to claim 1, characterized in that, The support columns (3) are uniformly arranged, the guide wheels (5) are distributed in a triangular shape and adopt V-shaped guide wheels.

3. The elbow outer wall automatic welding machine according to claim 1, characterized in that, The output shaft of main shaft servo motor (6) is directly connected with driving gear (7) through rigid coupling (24), the inner layer sleeve (12) is fixedly connected with welding torch (11), the outer layer sleeve (13) is fixedly connected with welding torch adjusting arm (9), and the high-frequency electromagnetic coil (16) is wrapped with insulating heat-conducting layer (25) outside.

4. The elbow outer wall automatic welding machine according to claim 3, characterized in that, The inner layer sleeve (12) is made of non-magnetic stainless steel material, and the outer layer sleeve (13) is made of magnetic silicon steel material.

5. The elbow outer wall automatic welding machine according to claim 1, characterized in that, The central shaft of floating tension wheel (20) is slidably connected with the outer reference surface of annular guide rail (2) through linear bearing (26), and the closed loop pre-tightening steel cable (21) adopts interlaced flexible steel wire rope.

6. The elbow outer wall automatic welding machine according to claim 1, characterized in that, The outer surface of the contour roller (17) is made of high-temperature resistant ceramic material.

7. The control method for the automatic elbow outer wall welding machine of claim 1, characterized in that, include: The spindle servo motor (6) is controlled to drive the drive trolley (4) to move along the annular guide rail (2) to the elbow welding point; An initial excitation current is passed into the high-frequency electromagnetic coil (16) to cause the ferromagnetic particles in the magnetorheological elastomer medium (15) to form a chain-like arrangement structure, thereby controlling the magnetorheological compliant joint (10) to present a rigid locking state. The spindle servo motor (6) is controlled to continuously drive the drive trolley (4) to rotate around the bend, and the welding torch (11) is controlled to perform welding operations synchronously. Obtain the gravity-induced overturning torque during the rotation of the drive trolley (4), and use the long arm end of the cam lever (22) to deflect downward under the action of gravity and drive the short arm end to pull the closed-loop pre-tensioning steel cable (21), so as to convert the local gravity component into a full-circumferential radial contraction pre-tensioning force pointing to the center of the annular guide rail (2); Continuously monitor the welding arc voltage and the high-frequency fluctuation rate of the welding arc voltage and the time-domain fluctuation characteristics of the transient torque current of the spindle servo motor (6); When the welding arc voltage shows a monotonically decreasing trend and the torque current of the spindle servo motor (6) is in a stable state, it is determined that the current liquid molten pool is drooping due to gravity. When the welding arc voltage does not show a monotonically decreasing trend or the torque current of the spindle servo motor (6) is not in a stable state, it is determined that the current liquid molten pool has not sagged and the current welding state is maintained.

8. The control method of an elbow outer wall automatic welding machine according to claim 7, characterized in that, After determining that the current molten pool is sagging due to gravity, the following steps are taken: Extract the arc voltage decrease curve corresponding to the monotonically decreasing trend of the welding arc voltage, and calculate the geometric offset of the molten pool sag based on the integral area enclosed by the arc voltage decrease curve and the time axis. The geometric offset of the molten pool sag is mapped to the welding torch (11) lifting compensation angle required to counteract the sag. A pulse width modulation signal is sent to the high-frequency electromagnetic coil (16) to reduce the duty cycle of the excitation current, thereby reducing the shear yield stress and elastic modulus of the magnetorheological elastomer medium (15) to the critical yield point, and controlling the magnetorheological compliant joint (10) to enter a low stiffness compliant state.

9. The control method of an elbow outer wall automatic welding machine according to claim 8, characterized in that, After the magnetorheological compliant joint (10) enters a low-stiffness compliant state, the following steps are taken: In the low stiffness compliant state, the spindle servo motor (6) is controlled to finely adjust the circumferential position of the drive trolley (4) according to the lifting compensation angle of the welding torch (11); The welding torch (11) achieves flexible posture adaptation by relying on the contact force between the contour roller (17) and the outer wall of the elbow; When the posture is adjusted to the correct position, a full-load excitation current is output to the high-frequency electromagnetic coil (16) again, which significantly increases the modulus of the magnetorheological elastomer medium (15) and controls the magnetorheological compliant joint (10) to return to the rigid locking state.

10. The control method of an elbow outer wall automatic welding machine according to claim 8, characterized in that, In the step of reversely calculating the geometric offset of the molten pool sag based on the integral area enclosed by the arc voltage drop curve and the time axis, the geometric offset of the molten pool sag is calculated in reverse by combining the pre-calibrated arc voltage gradient coefficient.

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