A robotic static shoulder friction stir welding thermodynamic mixing control system

Abstract

This invention discloses a thermo-mechanical hybrid control system for robot static shoulder friction stir welding, relating to the field of robot static shoulder friction stir welding technology. This invention utilizes thermocouples to directly obtain the temperature of the weld nugget area, and then uses a temperature control system to regulate the weld temperature online. It employs multi-dimensional force sensors to detect the magnitude of anisotropic forces, especially the upsetting force, in real time, and then sends the upsetting force magnitude to a computer for precise control. The upsetting force is further regulated to an ideal value by controlling the robot's movement. Vibration characteristics are used to characterize the stability of the system's regulation, and an accelerometer is used to collect vibration signals for processing and analysis. This invention addresses complex application scenarios such as robot friction stir welding of complex spatial curved surfaces. Based on the accurate acquisition of weld nugget temperature and anisotropic force signals during the welding process, and combined with a thermo-mechanical hybrid control strategy, it uses active control of heat input and applied force during the welding process as the main technical means to improve the weld performance of static shoulder friction stir welding.

Description

Technical Field

[0001] This invention belongs to the field of robotic static shoulder friction stir welding technology, and more specifically, relates to a thermal mixing control system for robotic static shoulder friction stir welding. Background Technology

[0002] Static shoulder friction stir welding is a new solid-state joining technology developed by the Welding Institute in the UK based on traditional friction stir welding. The static shoulder friction stir welding tool consists of a non-rotating shoulder and an internally rotating stirring tool.

[0003] During the welding process, the rotating stirring pin is first inserted into the test plate to be welded, so that the stationary shoulder is in close contact with the surface of the test plate. The rotating stirring pin rubs against the surrounding material and generates heat at the interface between the two. Under the frictional heat, the material in a certain range around the stirring pin softens and becomes viscoplastic. Subsequently, the stirring pin moves along the welding direction and the stationary shoulder slides on the surface of the test plate. The material in front of the stirring pin undergoes severe plastic deformation under the squeezing action of the stirring pin and forms a weld.

[0004] Robotic static shoulder friction stir welding is a friction stir welding system that integrates an industrial robot with a dedicated static shoulder welding spindle. It can improve the flexibility of welding operations, especially when used with serial robots, making it more suitable for the mass welding manufacturing of products with complex spatial structures, thereby improving the degree of welding automation and production efficiency.

[0005] The force and heat involved in the friction stir welding process are closely related to the weld quality. Among these, the upsetting force and the temperature of the weld nugget are the main factors affecting the weld quality. According to the forming mechanism of friction stir welding on the stationary shoulder of a robot, temperature affects the degree of plasticization of the workpiece material, and the degree of plasticization of the welded metal often plays a decisive role in the weld quality. Plasticized metal is mainly formed by upsetting force, therefore, upsetting force is also one of the key factors in welding formation.

[0006] During friction stir welding, high upsetting force can easily lead to defects such as flash in the weld, resulting in weld thinning and reduced mechanical properties. Conversely, low upsetting force can cause defects such as loose weld structure and porosity, leading to weld failure. At low welding temperatures, the weld is prone to forming grooves and voids; at higher temperatures, material softening intensifies, reducing weld mechanical properties and strength. Furthermore, static shoulder friction stir welding, as a thermo-coupling welding technology, is particularly evident when using weak-stiffness serial robots for static shoulder friction stir welding, where temperature and multi-dimensional force signals in the weld nugget area are mutually coupled and influence each other. Therefore, integrating online monitoring of temperature and force during the welding process and achieving thermo-coupling control represents a significant breakthrough in improving the quality of robotic static shoulder friction stir welding. In addition, forward resistance and lateral force are also process parameters during welding. Although they do not directly affect welding performance, synchronous control during the welding process will further improve welding performance.

[0007] For temperature monitoring and control during welding, conventional temperature measurement systems only measure the surface temperature of the weld and then perform data simulation, resulting in low data reliability. Furthermore, creating blind holes in the welding plate requires additional processing, making it unsuitable for large-scale welding. Patent CN112743222A addresses this by creating blind holes and grooves in the welding plate and a through hole in the center of a temperature-sensing pad. The thermocouple wire is passed through the through hole and the measuring end is placed at the bottom of the blind hole along the groove for friction stir welding and data recording. However, this requires creating blind holes in the workpiece, and reassembling the thermocouple is necessary for each workpiece replacement, making the process cumbersome and inefficient. Patent CN215545765U connects the temperature-sensing thermocouple to the top of the stirring needle, with a temperature sensor working in conjunction with the thermocouple to monitor the temperature change of the stirring needle in real time. However, it does not consider the possibility of the thermocouple wire becoming entangled when the stirring needle rotates, potentially causing measurement problems. Patent C... Patents N110653483A and CN110640298A primarily utilize infrared thermal imaging equipment to achieve precise online monitoring of the temperature of the stirring head and the base material during friction stir welding. This data is transmitted to an industrial control computer via a data cable, displaying infrared temperature images in real time. This enables long-distance real-time detection of temperature distribution and processing into temperature field data, which is then input into the process control auxiliary computer for matching with a database. Temperature control is achieved by correcting process parameters. However, this infrared imaging method can only measure the temperature of the workpiece surface and cannot obtain the accurate temperature of the weld nugget. Furthermore, the low sampling frequency of infrared camera acquisition methods makes it unsuitable for closed-loop control, and the high cost of infrared temperature measurement equipment makes it impractical for industrial applications. Patent CN106624337A mounts thermocouples and infrared temperature sensors on a stationary shoulder to measure the welding temperature in real time and feed it back to the machine tool control unit. However, when welding complex curved panels, interference can easily occur between the sensor and the workpiece, and machine tool welding is not suitable for welding complex curved surfaces in space. Although current temperature control systems can detect and control weld temperature to some extent, they cannot accurately obtain the temperature of the weld core area, thus failing to further improve the influence of weld microstructure.

[0008] For the detection and control of multi-dimensional force signals in the welding process, patent CN113118616A uses a mechanical pressure control mechanism with a constant pressure telescopic component to respond in real time to pressure changes during welding and achieve pressure control. However, it only focuses on the magnitude of the upsetting force and does not simultaneously analyze and collect force signals in other dimensions. Although the upsetting force in static shoulder friction stir welding is one of the process parameters affecting welding performance, adjusting other mechanical parameters in a synchronous manner will also improve weld performance. Patent CN104400214A collects the upsetting force and forward resistance during the welding process by evenly distributing four pressure sensors between the spindle and the spindle housing, and controls them with a PLC and servo motor. This method uses machine tool welding and can only complete simple weld trajectories. It is not suitable for serial industrial robots with high degrees of freedom and flexibility. The relationship between the trajectory and force signal of serial robots is non-linear, especially in complex trajectories. Traditional multi-dimensional mechanical signal acquisition and analysis methods for Cartesian coordinate robots or machine tools cannot be used for serial robots. Patent CN114951953A uses a force sensor and a force control module to achieve force control of the spatial weld, avoiding welding failure caused by excessive upsetting force; however, it only uses the force signal as a protective measure for threshold adjustment, without relating it to the regulation of weld performance. It only maintains a constant position by maintaining a constant pressure, ignoring the thermo-coupling relationship. For curved welds with poor heat dissipation or heat-sensitive materials, the constant force control alone makes the weld prone to failure.

[0009] For the static axis thermo-mechanical hybrid control system of robots, there are currently only friction stir welding systems that control force and temperature separately. Force-controlled friction stir welding systems have only initially solved the control of the welding process but have not yet achieved the control of welding performance. At the same time, the cost of force and temperature monitoring equipment is high, and the control strategy usually only adopts the control of a single influencing factor, which cannot handle the thermo-mechanical coupling relationship to improve the weld formation quality in complex spaces. There is a lack of research on the impact of thermo-mechanical coupling control on weld formation quality. Summary of the Invention

[0010] This invention addresses complex application scenarios such as friction stir welding of complex spatial curved surfaces in robots. Based on the accurate acquisition of temperature in the weld nugget area and force signals in all directions during the welding process, and combined with a thermo-mechanical hybrid control strategy, it improves the performance of static shoulder friction stir welds by actively controlling the heat input and applied force during the welding process.

[0011] This invention addresses the shortcomings of existing equipment and control technologies for robotic static shoulder friction stir welding. Starting with static shoulder design and flexible assembly, it provides a device capable of real-time monitoring of temperature and multi-dimensional force signals. Based on this device, a robotic static shoulder friction stir welding system is implemented that actively controls heat input and force application. This invention can monitor the temperature and magnitude of forces in all directions during the welding process in real time in the weld core area. By controlling heat input and force, optimal process parameters are obtained, ultimately improving weld performance and one-time forming quality.

[0012] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a robot static shoulder friction stir welding thermal mixing control system, including a six-axis robot system, an electric spindle system, a static shoulder tool, a cooling system, a multi-dimensional force detection device, a temperature detection device, an acceleration sensor, and a computer;

[0013] The six-axis robot system includes a six-axis robot body and a robot controller; the electric spindle system includes an electric spindle and an electric spindle driver; the stationary shoulder tool includes a stationary shoulder, a connecting device, and a stirring needle; the cooling system includes a cooling pipe and a cooler; the multi-dimensional force detection device includes a multi-dimensional force sensor and a force acquisition card; and the temperature detection device includes a thermocouple and a temperature acquisition card.

[0014] The robot controller is mounted on the six-axis robot body, and the electric spindle driver is mounted on the electric spindle. A multi-dimensional force sensor is fixedly connected between the six-axis robot body and the electric spindle, and is electrically connected to a force acquisition card to collect the upsetting force during the welding process. The computer displays the upsetting force during the welding process and controls the upsetting force to an ideal and stable pressure in real time by adjusting process parameters. An accelerometer is bonded to the electric spindle and connected to the computer to collect vibration signals during the welding process. The connecting device is fixed to the bottom end cap of the electric spindle with bolts. The upper part of the stirring needle is fitted inside the connecting device and fixed to the tool holder of the electric spindle with bolts. The stationary shoulder is adjustablely connected to the lower part of the connecting device. The end face of the tip of the stirring needle is flush with the end face of the shoulder of the stationary shoulder. A thermocouple is set at the tip of the stirring needle and is electrically connected to a temperature acquisition card. The temperature acquisition card is connected to the computer for real-time temperature control of the weld nugget area. A cooling fan is mounted on the six-axis robot body, and a cooling pipe is fixed next to the electric spindle and connected to the cooling fan. Cooling is controlled by adjusting parameters via the computer.

[0015] Preferably, a multi-dimensional force sensor coordinate system and a tool coordinate system also need to be established. During the assembly process, the multi-dimensional force sensor coordinate system is made to coincide with the tool coordinate system, and the direction of the multi-dimensional force sensor coordinate system is calibrated. The gravity of the electric spindle is compensated, and the zero point of the multi-dimensional force sensor is calibrated.

[0016] Preferably, to perform gravity compensation on the electric spindle, the weight of the electric spindle must first be obtained. The weight of the electric spindle is measured using the following method:

[0017] First, install the multi-dimensional force sensor on the end flange of the robot's six axes. Do not install the electric spindle yet. Manually adjust the robot so that the Z-axis of the multi-dimensional force sensor is perpendicular to the ground. At this time, set the multi-dimensional force sensor to zero.

[0018] Then the electric spindle is mounted on the measuring surface of the multi-dimensional force sensor. Since the Z-axis of the multi-dimensional force sensor is perpendicular to the ground, ;

[0019] By rotating the robot's six axes one revolution and recording the force signals measured at that time, a series of results can be obtained. The relationship between the gravity of the electric spindle and the measurements from the multi-dimensional force sensor is as follows: ;

[0020] The measured values ​​were obtained using the averaging method. Averaging, the gravity of the electric spindle is obtained as follows: .

[0021] Preferably, after obtaining the gravity of the electric spindle, the force is obtained through formula... Obtain the representation of the electric spindle gravity in the force sensor coordinate system. To eliminate the influence of the electric spindle on the force sensor measurement, the following can be subtracted from the force sensor measurement data: ,Right now: ,in This provides a representation of the contact force between the static shoulder friction stir welding robot and the environment in the force sensor coordinate system, thus completing the zero-point calibration of the multi-dimensional force sensor.

[0022] Preferably, the lower part of the stationary shoulder is a hollow frustum-shaped shell, the upper part is provided with an internal thread, and a hexagonal operating part is provided outside the internal thread. The internal thread is screwed into the external thread of the connecting device. A circular hole is provided at the center of the lower bottom surface of the stationary shoulder, and the tip of the stirring needle extends out of the circular hole. Several thermocouple temperature probe protrusion holes are provided around the circular hole, and the thermocouple temperature probes extend out of the thermocouple temperature probe protrusion holes.

[0023] Preferably, the connecting device has a hollow internal structure, and several through holes are provided on the side wall of the connecting device, through which the thermocouple connecting wires extend to connect to the temperature acquisition card.

[0024] The beneficial effects of adopting the above technical solution are as follows:

[0025] (1) In this invention, the temperature of the weld nugget area is directly obtained through a temperature measuring device. The collected data is analyzed, and the temperature of the weld nugget area is actively adjusted during the welding process to accurately control the heat input during the welding process and improve the welding performance.

[0026] (2) This invention improves the quality of welds by directly measuring temperature and multidimensional force signals and actively controlling heat input and force during the welding process through thermo-mechanical mixing and regulation.

[0027] (3) The present invention has a simple static shaft shoulder tool, which is easy to assemble and has strong applicability. It effectively solves the processing and assembly of stirring needles and is easy to attach temperature sensors.

[0028] (4) The present invention has a simple and compact structure, wide applicability and low cost. It can collect multidimensional mechanical and temperature signals at the end during the welding process of spatial load curve welding. It can be used in actual industrial applications and is especially suitable for traditional serial robot static shoulder friction stir welding system. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the overall structure of the present invention;

[0030] Figure 2 This is a schematic diagram of the assembly structure of a multi-dimensional force sensor, an electric spindle, and a static shoulder.

[0031] Figure 3 This is a schematic diagram of the assembly structure of the stationary shaft shoulder and the connecting device;

[0032] Figure 4 This is a three-dimensional structural diagram of the static shaft shoulder;

[0033] Figure 5 This is a schematic diagram of the cross-sectional structure of the stationary shoulder and the stirring needle;

[0034] Figure 6 This is a schematic diagram of the welding principle of robot static axis shoulder friction stir welding;

[0035] Figure 7 Macroscopic cross-sectional morphology of a friction stir welded butt joint on the stationary shoulder of a robot.

[0036] Figure 8 A schematic diagram of a multi-dimensional force sensor calibration tool;

[0037] Figure 9 This is a schematic diagram of the calibration of a multi-dimensional force sensor.

[0038] Figure 10 This is a schematic diagram of the welding process of the present invention;

[0039] Figure 11 This is a schematic diagram of the welding thermal control process of the present invention;

[0040] In the diagram: 1. Six-axis robot body; 2. Robot controller; 3. Air conditioning pipe; 4. Air cooler; 5. Electric spindle; 6. Electric spindle driver; 7. Multi-dimensional force sensor; 8. Force acquisition card; 9. Temperature acquisition card; 11. Welded workpiece; 12. Static shoulder; 13. Connecting device; 14. Through hole; 15. Thermocouple temperature probe through hole; 16. Connecting thread; 17. Stirring needle; 18. Thermocouple; 19. Weld nugget area; 20. Accelerometer; 21. Multi-dimensional force sensor calibration box. Detailed Implementation

[0041] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0042] Based on the basic principles and forming mechanism of static shoulder friction stir welding (such as...) Figure 6 As shown, the welding process parameters affecting heat input include spindle speed and welding speed; the process parameters affecting upsetting force include spindle speed, welding speed, and downward pressure; and the process parameters affecting forward resistance include spindle speed and welding speed. Spindle speed and welding speed are related to both heat and force, but spindle speed has a greater impact on heat input. Upsetting force tends to decrease with increasing welding temperature, but is mainly affected by the depth of downward pressure. Forward resistance is mainly related to welding speed. This invention's patented control strategy first controls heat, then monitors the temperature of the weld core area in real time, the magnitude of forces in each direction during welding, then controls the upsetting force, and finally controls the forward resistance. Temperature is controlled by controlling spindle speed and the external cooling system; force is increased or decreased by controlling downward pressure; and forward resistance is controlled by adjusting the forward speed. By controlling heat input and force, optimal process parameters are obtained. Vibration signals are detected during the thermal regulation process, and the control gain ratio is adjusted to stabilize the system, ultimately improving weld performance and one-time forming quality.

[0043] The main contents of this invention are as follows: First, a threaded structure is designed on the stationary shaft shoulder, and the stationary shaft shoulder is connected to the connecting device by the thread, which has extremely high flexibility in assembly and strong adaptability to different stirring needle lengths. At the same time, the stationary shaft shoulder designed for flexible assembly provides a pre-installed installation interface for the temperature measuring device.

[0044] Secondly, in order to achieve real-time detection and control of the temperature of the weld nugget area during the welding process, this invention uses a thermocouple to measure the temperature at the tip of the stirring needle, thereby directly obtaining the temperature of the weld nugget area. Then, the temperature control system is used to control the weld temperature online, thereby improving the weld strength.

[0045] Third, to further improve the forming quality of static shoulder friction stir welding, this invention utilizes a multi-dimensional force sensor coaxially mounted with the stirring tool to detect the magnitude of forces in all directions, especially the upsetting force, in real time during the welding process. The collected upsetting force is sent to a computer via a force acquisition card. While ensuring the temperature is within a certain threshold, the upsetting force is further precisely controlled, and the robot's movement is controlled to adjust the upsetting force to the ideal value.

[0046] Fourth, the stability of the robot static shoulder friction stir welding system is a key factor in determining whether it can achieve reliable welding. As a thermo-mechanical coupling process, friction stir welding has particularly obvious vibration signals during the thermo-mechanical interaction process. Therefore, this invention uses vibration characteristics to characterize the stability of system regulation, uses an accelerometer to collect vibration signals for processing and analysis, and dynamically adjusts the regulation process of thermo-mechanical mixing control based on the vibration signals.

[0047] Specific embodiments of the present invention: such as Figure 1-5 As shown, the present invention includes a six-axis robot system, an electric spindle system, a static shoulder tool, a cooling system, an upsetting force detection device, a temperature detection device, an acceleration sensor 20, and a computer.

[0048] A six-axis robot system consists of a robot body 1 and a robot controller 2. The six-axis robot system is responsible for the execution and management of various tasks, including process flow programming, motion control programming, event and interrupt handling, logic control programming, and human-machine interaction. It employs edge computing to acquire and adjust temperature and force signals, sending the results back to the robot system to complete the control process. This improves the stability of the robot system and the versatility of the process control system.

[0049] The electric spindle system includes an electric spindle 5 and an electric spindle driver 6. The stationary shoulder tool includes a stationary shoulder 12, a connecting device 13, and a stirring pin 17. The cooling system includes a cooling air pipe 3 and a cooling fan 4. The upsetting force detection device includes a multi-dimensional force sensor 7 and a force acquisition card 8. The temperature detection device includes a thermocouple 18 and a temperature acquisition card 9.

[0050] A multi-dimensional force sensor 7 is fixed between the end of the six-axis robot body 1 and the electric spindle 5. A stirring needle 17 is fixed to the tool holder of the electric spindle 5 with bolts. A thermocouple 18 temperature probe passes through a threaded hole 15, and the thermocouple wire passes through a hole 14. A connecting device 13 is fixed to the bottom end cap of the electric spindle 5 with bolts. The stationary shoulder 12 is connected to the connecting device 13 through a connecting thread 16. The upper end of the stationary shoulder 12 is designed with an internal thread. The lower end of device 13 is designed with an external thread to facilitate the assembly and disassembly of the stationary shoulder 12. During assembly, it ensures that the end face of the tip of the stirring needle 17 is flush with the shoulder surface of the stationary shoulder 12. The cooling pipe 3 is fixed next to the electric spindle 5, with one end used to cool the workpiece 11 and the other end connected to the cooling fan 4. The acceleration sensor 20 is attached to the electric spindle. The workpiece 11 is placed on the welding fixture and is pressed tightly by pressure plates, pressure blocks, and bolts to reduce the deformation of the workpiece 11. This completes all mechanical assembly before the robot's stationary shoulder friction stir welding.

[0051] Force acquisition card 8 is connected to multi-dimensional force sensor 7 via a connector. Force acquisition card 8 is connected to the computer via a fieldbus. Thermocouple is connected to temperature acquisition card 9. Temperature acquisition card 9 is connected to the computer via a fieldbus. Air cooler 4 is connected to the computer via a fieldbus. Accelerometer 20 is connected to the computer via a universal serial bus. This completes all electrical connections prior to friction stir welding of the robot's stationary shoulder.

[0052] The software design utilizes an edge computer to control the robot body 1, electric spindle 5, air cooler 4, etc., and to collect and display temperature, force signals, and acceleration signals.

[0053] Temperature acquisition card 9 is connected to a computer for real-time temperature control of welding nugget area 19 (e.g., Figure 7 As shown, this design avoids the wire entanglement problem that occurs when the stirring pin 17 is fixedly connected to the thermocouple 18, and eliminates the need to drill blind holes in the workpiece to be welded. The stationary shoulder 12 is connected to the connecting device 13 via threads, and the stationary shoulder 12 can be adjusted up and down via threads to accommodate stirring pins 17 of different lengths. The cooling pipe 3 is fixed next to the electric spindle and connected to the cooling fan 4, and the cooling is controlled by adjusting parameters via a computer. The multi-dimensional force sensor 7 is connected to the force acquisition card 8 to collect the upsetting force during the welding process. The computer displays the upsetting force during the welding process and controls it to the ideal stable pressure in real time by adjusting process parameters. The acceleration sensor 20 is connected to the computer to collect vibration signals during the welding process.

[0054] According to the requirements of the robot's stationary shoulder friction stir welding system, a multi-dimensional force sensor 7 and an electric spindle 5 need to be mounted on the robot's six-axis flange, with the electric spindle 5 serving as the tool axis. The robot's six-axis flange connects to a dedicated electric spindle, and the multi-dimensional force sensor 7 is installed between the robot's six-axis flange and the dedicated electric spindle. Figure 8-9 As shown, a multi-dimensional force sensor coordinate system (S) and a tool coordinate system (T) are established respectively. During assembly, the force sensor coordinate system and the tool coordinate system need to be aligned. However, the multi-dimensional force sensor 7, due to its mechanical connection, will inevitably have errors. To reduce the transmission error of the multi-dimensional force sensor's measurements between coordinate systems, the multi-dimensional force sensor coordinate system needs to be calibrated. Secondly, the gravity of the electric spindle will have different effects on the multi-dimensional force sensor measurement when the robot is in different poses. When the robot tool end is in different postures, the weight of the end tool will affect the multi-dimensional force sensor measurement. To accurately obtain the external force applied to the electric spindle 5, the gravity of the electric spindle 5 must be compensated. That is, the zero-point calibration of the multi-dimensional force sensor 7 is required.

[0055] To perform gravity compensation on the electric spindle 5, its gravity must first be obtained. The gravity of the electric spindle 5 is measured using the following method: First, install the multi-dimensional force sensor 7 onto the six-axis end flange of the six-axis robot body 1 using the connector. Do not install the electric spindle 5 yet. Manually adjust the six-axis robot body 1 so that the Z-axis of the multi-dimensional force sensor 7 is perpendicular to the ground. At this point, set the multi-dimensional force sensor 7 to zero. Then, install the electric spindle 5 onto the measuring surface of the multi-dimensional force sensor 7. Since the Z-axis of the multi-dimensional force sensor 7 is perpendicular to the ground, ... Rotating the six axes of the six-axis robot body 1 one revolution and recording the force signals measured at this time yields a series of results. The relationship between the values ​​measured by the electric spindle 5 (gravity) and the multi-dimensional force sensor 7 is as follows: The measured values ​​were obtained using the averaging method. The average force is calculated to be the gravitational force of the electric spindle 5. Because a multi-point measurement and averaging method was used, the obtained weight of the electric spindle 5 is relatively accurate. The advantage of this method is that when the electric spindle 5 is replaced, an automatic weighing program can be edited to repeat the measurement according to the above algorithm, finally obtaining the weight of the electric spindle 5, thus offering better versatility. After obtaining the weight of the electric spindle 5, it can be calculated using the formula... The representation of gravity of the electric spindle 5 in the force sensor coordinate system is obtained. To eliminate the influence of the electric spindle 5 on the force sensor measurement, the following can be subtracted from the force sensor measurement data: ,Right now: ,in This represents the contact force between the robot body 1 and the environment in the force sensor coordinate system. This completes the zero-point calibration of the multi-dimensional force sensor 7.

[0056] During welding, the X-direction of the multi-dimensional force sensor 7 should be aligned with the welding direction to ensure the accuracy of multi-dimensional force measurement. This is easily achieved in one-dimensional planar welds; however, when welding spatial curves, the sixth axis of the robot needs to be rotated, which increases gear backlash and reduces the rigidity of the robot body 1, affecting welding quality. Establishing the relationship between the multi-dimensional force sensor coordinate system and the robot tool coordinate system without rotating the sixth axis of the robot body 1 is also an effective and feasible method. The multi-dimensional force sensor calibration box 21 is fixed to the welding table with bolts. The robot body 1 is manually adjusted so that the electric spindle 5 is perpendicular to the ground, and the tip of the stirring needle is directly above the center point O on the calibration box. The robot body 1 is moved Lmm along the X-direction to point A, ensuring that the stirring needle 17 exerts pressure on the inner wall of the multi-dimensional force sensor calibration box 21. The force measured by the multi-dimensional force sensor 7 at this point is recorded. Then, move robot body 1 back to the origin O. Robot body 1 then moves Lmm along the Y direction from the origin to point B, and record the value measured by the multi-dimensional force sensor 7 at this point. The value is used to determine the relationship between the multi-dimensional force sensor coordinate system and the flange coordinate system. Then, the relationship between the flange coordinate system and the tool coordinate system is established. Ultimately passed Determine the relationship between the multi-dimensional force sensor 7 and the tool coordinate system. This completes the orientation calibration of the multi-dimensional force sensor 7.

[0057] like Figure 10-11 As shown, during the welding process, the electric spindle driver 6 rotates the electric spindle 5, which in turn drives the tool holder to rotate the stirring needle 17. The thermocouple temperature probe directly measures the temperature at the tip of the stirring needle 17, and the measured temperature is fed back to the computer through the temperature acquisition card 9, thus accurately obtaining the temperature of the weld nugget area. Temperature control is the primary method during the welding curve segment, with upsetting force control as a secondary method. When the temperature is low, the computer can adjust process parameters such as spindle speed and welding speed to increase the temperature; when the temperature is high, the computer can send instructions to the cooling fan 4 to blow cold air from the cooling pipe 3 to the workpiece 11 to lower the temperature; thus, the computer accurately controls the influence of temperature on the weld formation quality. When the temperature in the weld nugget area is at a set threshold, the multi-dimensional force sensor 7 directly measures the upsetting force during the welding process, and the magnitude of the upsetting force is sent to the computer through the force acquisition card 8. When the upsetting force is too large or too small, the downward pressure is adjusted to control the upsetting force, ultimately achieving constant pressure control during the welding process. Furthermore, by adjusting the forward speed to control the forward resistance, and by detecting vibration signals during the thermal regulation process, the gain ratio is adjusted to stabilize the system. By controlling the stable heat during the friction stir welding process on the robot's stationary shoulder, the one-time forming quality of the friction stir weld on the robot's stationary shoulder is improved.

[0058] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A robot static-axle shoulder friction stir welding thermomechanical mixing control system, characterized by, Includes a six-axis robot system, an electric spindle system, a static shoulder tool, a cooling system, a multi-dimensional force detection device, a temperature detection device, an accelerometer, and a computer; The six-axis robot system includes a six-axis robot body and a robot controller; the electric spindle system includes an electric spindle and an electric spindle driver; the stationary shoulder tool includes a stationary shoulder, a connecting device, and a stirring needle; the cooling system includes a cooling pipe and a cooler; the multi-dimensional force detection device includes a multi-dimensional force sensor and a force acquisition card; and the temperature detection device includes a thermocouple and a temperature acquisition card. The robot controller is mounted on the six-axis robot body, and the electric spindle driver is mounted on the electric spindle. A multi-dimensional force sensor is fixedly connected between the six-axis robot body and the electric spindle, and is electrically connected to a force acquisition card to collect the upsetting force during the welding process. The computer displays the upsetting force during the welding process and controls the upsetting force to an ideal and stable pressure in real time by adjusting process parameters. An accelerometer is bonded to the electric spindle and connected to the computer to collect vibration signals during the welding process. The connecting device is fixed to the bottom end cap of the electric spindle with bolts. The upper part of the stirring needle is fitted inside the connecting device and fixed to the tool holder of the electric spindle with bolts. The stationary shoulder is adjustablely connected to the lower part of the connecting device. The end face of the tip of the stirring needle is flush with the end face of the shoulder of the stationary shoulder. A thermocouple is set at the tip of the stirring needle and is electrically connected to a temperature acquisition card. The temperature acquisition card is connected to the computer for real-time temperature control of the weld nugget area. A cooling fan is mounted on the six-axis robot body, and a cooling pipe is fixed next to the electric spindle and connected to the cooling fan. Cooling is controlled by adjusting parameters via the computer. The lower part of the stationary shoulder is a hollow frustum-shaped shell, and the upper part is provided with an internal thread. A hexagonal operating part is provided outside the internal thread. The internal thread is screwed into the external thread of the connecting device. A circular hole is provided in the center of the lower bottom surface of the stationary shoulder. The tip of the stirring needle extends out of the circular hole. Several thermocouple temperature probe protrusion holes are provided around the circular hole. The thermocouple temperature probes extend out of the thermocouple temperature probe protrusion holes.

2. The robotic static shoulder friction stir welding thermal mixing control system according to claim 1, characterized in that, Establish a multi-dimensional force sensor coordinate system S and a tool coordinate system T. During assembly, the multi-dimensional force sensor coordinate system is aligned with the tool coordinate system. The direction of the multi-dimensional force sensor coordinate system is calibrated, the gravity of the electric spindle is compensated, and the zero point of the multi-dimensional force sensor is calibrated.

3. The robotic static shoulder friction stir welding thermal mixing control system according to claim 1, characterized in that, To perform gravity compensation on the electric spindle, the weight of the electric spindle must first be obtained. The weight of the electric spindle is measured using the following method: First, install the multi-dimensional force sensor on the end flange of the robot's six axes. Do not install the electric spindle yet. Manually adjust the robot so that the Z-axis of the multi-dimensional force sensor is perpendicular to the ground. At this time, set the multi-dimensional force sensor to zero. Then, the electric spindle is mounted on the measuring surface of the multi-dimensional force sensor. Since the Z-axis of the multi-dimensional force sensor is perpendicular to the ground, ; By rotating the robot's six axes one revolution and recording the force signals measured at that time, a series of results can be obtained. The relationship between the gravity of the electric spindle and the measurements from the multi-dimensional force sensor is as follows: ; The measured values ​​were obtained using the averaging method. Averaging, the gravity of the electric spindle is obtained as follows: .

4. The robotic static shoulder friction stir welding thermal mixing control system according to claim 1, characterized in that, The connecting device has a hollow internal structure, and several through holes are provided on the side wall of the connecting device. The thermocouple connecting wires extend from the through holes to connect to the temperature acquisition card.

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