Rope-driven laser welding robot based on quaternion joint and control method thereof

Abstract

The application belongs to the technical field of mechanical arms, and discloses a rope-driven laser welding mechanical arm based on a quaternion joint and a control method thereof, which comprises an executing mechanism for performing laser welding work, wherein the executing mechanism mainly comprises a laser welding head and an executing part connecting piece; the application can enhance the stiffness and load capacity of a continuum configuration through the quaternion joint, can carry a heavy executing component such as a laser welding head, and can complete a complex welding task which is difficult or impossible for a traditional robot to complete in a non-structured environment with a narrow working space and many obstacles. The quaternion joint is introduced on the basis of the continuum configuration, the stiffness and load capacity of the mechanical arm are enhanced on the basis of ensuring the flexibility of the mechanical arm, a heavy executing component such as a laser head can be carried, and the complex operation task which is difficult or impossible for a traditional robot to complete in a non-structured environment with a narrow working space and many obstacles can be completed.

Description

Technical Field

[0001] The present invention belongs to the technical field of robotic arms, and in particular relates to a rope-driven laser welding robotic arm based on quaternion joints and a control method thereof. Background Art

[0002] Laser welding robots are industrial robots specialized in laser welding operations. They have the advantages of high efficiency, intelligence, and environmental protection. They can stabilize welding quality, improve product qualification rate, and reduce workers' labor intensity. They are the key to supporting high-quality, efficient, and intelligent manufacturing of high-end products and major equipment in the fields of machinery, shipbuilding, aerospace, rail transportation, automobiles, etc.

[0003] With the development of technology, welding tasks have gradually involved irregularly shaped workpieces, such as curves, curved pipes, hulls, etc., and the types of welds have gradually expanded from simple straight lines and arcs to complex spatial curves such as the intersection line of steel pipes and the intersection line of shell surfaces, which puts higher demands on the flexibility and adaptability of the robot arm. Traditional rigid laser welding robots usually use multi-axis joints and connecting rod structures to perform welding tasks and have become the main tools for automated welding. However, rigid laser welding robots usually require the workpiece to have a fixed position and orientation on the welding table, which limits their application to irregular or large workpieces and makes it difficult to cope with more complex welding environments and welding tasks.

[0004] In recent years, continuum robots have gained increasing attention in various fields due to their excellent compliance, flexibility, and human-machine safety, demonstrating promising application prospects. Both the motion body and actuator of a continuum robot are constructed of flexible components, lacking rigid joints. The bendable portion consists of multiple flexible segments, whose deformation controls the shape of the continuum robot. Like traditional articulated robots, continuum robots can be equipped with end effectors. They are capable of performing complex manipulation tasks that are difficult or impossible for traditional robots in unstructured environments with confined workspaces and numerous obstacles, making them more adaptable to diverse welding tasks and workpiece shapes. However, due to their continuum configuration, the robot's body stiffness and load capacity are relatively poor, and control accuracy decreases as the end load increases. The application of continuum robots in laser welding also places higher demands on their anti-interference capabilities and load capacity. Based on this, we propose a tether-driven laser welding robot arm based on quaternion joints and its control method.

[0005] Through the above analysis, the problems and defects of the existing technology are as follows:

[0006] Existing laser welding robots have low welding freedom and poor environmental adaptability, making it difficult to meet the problems of complex welding conditions and complex trajectory welding; the existing continuum configuration has poor body stiffness and load capacity, and as the end load increases, the control accuracy will gradually decrease, which does not meet the requirements of industrial production. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides a rope-driven laser welding robot arm based on quaternion joints and a control method thereof.

[0008] The present invention is achieved in that a rope-driven laser welding robot arm based on quaternion joints comprises:

[0009] An actuator is used to perform laser welding operations, and the actuator mainly includes a laser welding head and an actuator connecting piece;

[0010] The main body of the robot arm is used to carry the actuator and can achieve different trajectory movements, driving the actuator to complete the welding operation or reach the welding operation position. The main body of the robot arm includes an end plate, a spacer plate, a base plate, and several drive ropes, tension weights, connectors, connecting shafts, and support rods; the end plate, spacer plate, and base plate are collectively referred to as the end plate;

[0011] The driving mechanism is used to control the movement of the robot arm body. The driving mechanism includes a driving mechanism connector, an adapter plate, a screw transmission mechanism, a power supply, and a terminal controller.

[0012] Furthermore, the screw transmission mechanism includes a motor, a screw, a linear guide rail, a coupling, a slider, and a drive rope fixing member.

[0013] Furthermore, the end plate, spacer plate, base plate, and drive mechanism connector all have a central through hole, and six wire holes are evenly distributed at equal intervals on the edge of the disc; three lifting ears are evenly distributed on the surface of one side of the end plate and base plate, and the lifting ears are fixedly connected to the connecting shaft; there are lifting ears on both sides of the spacer plate, which are cross-distributed.

[0014] Furthermore, the main body of the robotic arm has two joints, which are connected end to end by a spacer disk. From the drive mechanism to the actuator, there are joints 1 and 2 in order. Both ends of the support rod are fixedly connected to the connecting shaft. The support rod is connected to the end disk through a connector. The three support rods and the end disk together constitute a quaternion joint. The first joint is composed of a base disk, a spacer disk, and a quaternion joint. The second joint is composed of an end disk, a spacer disk, and a quaternion joint.

[0015] The driving mechanism connecting member is fixedly connected to the base plate.

[0016] Furthermore, the drive ropes can pass through the wire holes and penetrate the joints, and are connected to the drive rope fixing members in the screw transmission mechanism through the drive mechanism connector and the base plate; three evenly distributed drive ropes form a group, respectively used to drive the bending movement of the two joints, namely the first drive rope group and the second drive rope group;

[0017] The first driving rope group passes through the base plate of the joint one, and the other end is fixedly connected to the spacer plate; the second driving rope group passes through the spacer plate, the base plate, and the driving mechanism connector, and the other end is fixedly connected to the end plate of the joint two.

[0018] Furthermore, the screw transmission mechanism is fixedly connected to the drive mechanism connecting member through the adapter plate;

[0019] Among them, the motor is connected to the terminal controller, and the motor is connected to the screw through a coupling, driving the slider and the drive rope fixing part to complete linear motion, and finally driving the drive rope to complete the bending motion of the joint; the drive rope fixing part is fixedly connected to the slider.

[0020] Another object of the present invention is to provide a control method for a rope-driven laser welding robot arm based on quaternion joints, comprising:

[0021] Step 1: Calculate the change in the length of the driving rope when any joint angle is reached according to the driving formula;

[0022] Step 2: Input the rope length change of each joint on the terminal controller;

[0023] Step 3: The controller drives the motor and the driving rope to complete linear motion;

[0024] Step 4: Different drive ropes coordinate to make the robotic arm reach the corresponding position;

[0025] From the spatial geometric relationship, it can be obtained that the lengths of each driving rope in the bending plane satisfy the following relationship:

[0026]

[0027] Among them, l j is the length of the jth driving rope, ψ is the bending angle of the joint, and h is the vertical distance between the two end discs of the joint, which remains unchanged during the bending process of the joint;

[0028] O0 point: the center point of the base plate;

[0029] Point O': the intersection of the extended projections of the base plane and the end plane in the bending plane;

[0030] O'A j ': From point O' to point A in the bending planej 'The distance between points;

[0031] O′O0: distance from point O′ to point O0 in the bending plane;

[0032] O0A j ′: From point O0 to point A in the bending plane j ′ point distance.

[0033] The following relationships can be obtained from spatial geometric relationships:

[0034]

[0035] Wherein, D is the distance between the connection point of the drive rope on the end disc and the center of the end disc, α is the angle between the X0 axis of the coordinate system O0 and O0A1, is the angle between the X0 axis of the coordinate system O0 and the joint bending plane, j is the jth driving rope;

[0036] Based on the joint kinematic model, the change in the length of the driving rope when any joint angle is reached is calculated as follows:

[0037]

[0038] According to the driving formula, the change in the length of the driving rope when reaching any joint angle can be calculated, and the robot arm can reach any posture by controlling the change in the driving rope.

[0039] Another object of the present invention is to provide a computer device, which includes a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the rope-driven laser welding robot arm control method based on quaternion joints.

[0040] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, which, when executed by a processor, causes the processor to execute the steps of the quaternion joint-based rope-driven laser welding robot control method.

[0041] Another object of the present invention is to provide an information data processing terminal, which is used to implement the rope-driven laser welding robot arm based on quaternion joints.

[0042] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0043] First, the present invention is a rope-driven laser welding robot arm based on quaternion joints and a drive control method thereof, which has the following advantages:

[0044] Quaternion joints are introduced on the basis of continuum configuration, which enhances the stiffness and load capacity of the robot arm while ensuring its flexibility. It can carry heavy actuators such as laser heads, and can complete complex operation tasks that are difficult or impossible for traditional robots to complete in unstructured environments with narrow working spaces and numerous obstacles. There are channels in the middle of the joints, so that components such as optical fibers and wires can be built into the robot arm, avoiding mechanical failures or other safety problems caused by exposed wires during actual operation. The robot arm adopts a rope drive method, with three drive ropes for each joint, each of which is controlled by a separate motor, which has a simple structure, while improving the stability of the drive and reducing the drive error. For this structure, a drive control method is proposed to realize the movement of the robot arm in different positions, filling the gap in this technical field.

[0045] The purpose of the present invention is to provide a rope-driven laser welding robot arm based on quaternion joints and a drive control method thereof, which can enhance the stiffness and load capacity of the continuum configuration through quaternion joints, can carry heavy actuators such as laser welding heads, and can complete complex welding tasks that are difficult or impossible for traditional robots to complete in unstructured environments with narrow working spaces and numerous obstacles.

[0046] Quaternion joints are introduced on the basis of continuum configuration, which enhances the stiffness and load capacity of the robot arm while ensuring its flexibility. It can carry heavy actuators such as laser heads, and can complete complex operation tasks that are difficult or impossible for traditional robots to complete in unstructured environments with narrow working spaces and numerous obstacles. There are channels in the middle of the joints, so that components such as optical fibers and wires can be built into the robot arm, avoiding mechanical failures or other safety problems caused by exposed wires during actual operation. The robot arm adopts a rope drive method, with three drive ropes for each joint, each of which is controlled by a separate motor, which has a simple structure, while improving the stability of the drive and reducing the drive error. For this structure, a drive control method is proposed to realize the movement of the robot arm in different positions, filling the gap in this technical field.

[0047] Second, in actual production, most of the welding of complex workpieces is still done manually by welders. The present invention can complete the welding of some complex workpieces, replace manual operations to a certain extent, improve production efficiency and yield rate, and reduce labor costs.

[0048] The present invention can replace the six-axis rigid welding robot on the domestic automated welding production line. By utilizing its multi-degree-of-freedom characteristics, it can complete the welding of multiple load workpieces and complex trajectories. It can enable a single robot to complete welding operations at multiple workstations, greatly improving the automation level and work efficiency of the welding production line and reducing production costs.

[0049] The introduction of quaternion joints based on the continuum configuration enhances the rigidity and load capacity of the robot arm while maintaining its flexibility. This allows it to carry heavy actuators such as laser heads and complete complex operations that are difficult or impossible for traditional robots to complete in unstructured environments with narrow workspaces and numerous obstacles. This fills a technological gap in the field of high-load continuum laser welding robot arms.

[0050] In the present invention, a channel is provided in the middle of the joint, so that components such as optical fibers and wires can be built into the robotic arm, thereby avoiding mechanical failures or other safety issues caused by exposed wires during actual operation, thus providing a new technical solution. Based on this structure, a drive control method is proposed to realize the movement of the robotic arm in different postures, thus filling the gap in this control technology field. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 1 is a schematic diagram of the overall structure of a rope-driven laser welding robot arm based on quaternion joints provided by an embodiment of the present invention;

[0052] Figure 2 This is a front view of the overall structure of a rope-driven laser welding robot arm based on quaternion joints provided by an embodiment of the present invention;

[0053] Figure 3 1. This is a top view of the overall structure of a rope-driven laser welding robot arm based on quaternion joints provided by an embodiment of the present invention;

[0054] Figure 4 This is a side view of the overall structure of a rope-driven laser welding robot arm based on quaternion joints provided by an embodiment of the present invention;

[0055] Figure 5 1 is an overall schematic diagram of an actuator of a rope-driven laser welding robot arm based on quaternion joints provided in an embodiment of the present invention;

[0056] Figure 6 1 is an overall schematic diagram of a main body of a rope-driven laser welding robot arm based on quaternion joints provided by an embodiment of the present invention;

[0057] Figure 7 This is a main view of a robot arm of a rope-driven laser welding robot arm based on quaternion joints provided by an embodiment of the present invention;

[0058] Figure 8 Schematic diagram of the spacer disk structure of a rope-driven laser welding robot based on quaternion joints provided by an embodiment of the present invention;

[0059] Figure 9 This is a schematic structural diagram of the connection between the end plate and the support rod of a rope-driven laser welding robot arm based on quaternion joints provided by an embodiment of the present invention;

[0060] Figure 10 1 is a cross-sectional view of a joint of a rope-driven laser welding robot arm based on quaternion joints provided by an embodiment of the present invention;

[0061] Figure 11 2 is a cross-sectional view of a joint of a rope-driven laser welding robot arm based on quaternion joints provided by an embodiment of the present invention;

[0062] Figure 12 1 is an overall schematic diagram of a driving mechanism of a rope-driven laser welding robot arm based on quaternion joints provided in an embodiment of the present invention;

[0063] Figure 13 1 is an overall schematic diagram of a screw transmission mechanism of a rope-driven laser welding robot arm based on quaternion joints provided in an embodiment of the present invention;

[0064] Figure 14 Schematic diagram of an ideal spherical rolling motion model of a rope-driven laser welding robot based on quaternion joints provided by an embodiment of the present invention;

[0065] Figure 15 1 is a diagrammatic projection of a curved plane of a rope-driven laser welding robot based on quaternion joints provided by an embodiment of the present invention;

[0066] Figure 16 1 is a bottom plane projection diagram of a rope-driven laser welding robot arm based on quaternion joints provided by an embodiment of the present invention;

[0067] Figure 17 This is a driving control flow chart of a rope-driven laser welding robot arm based on quaternion joints provided by an embodiment of the present invention;

[0068] Figure 18 is a general deformation diagram provided by an embodiment of the present invention;

[0069] Figure 19 is an equivalent stress diagram provided by an embodiment of the present invention;

[0070] Figure 20 This is a diagram showing the total deformation and equivalent stress results of a single joint under different loads provided by an embodiment of the present invention;

[0071] Figure 21 This is a diagram showing the total deformation and equivalent stress of two joints under different loads provided by an embodiment of the present invention;

[0072] Figure 22 is a motion experiment posture graph provided by an embodiment of the present invention;

[0073] Figure 23 1. It is a diagram of a method for measuring joint angles in a motion experiment provided by an embodiment of the present invention;

[0074] In the figure: 1. Actuator; 2. Robot arm body; 3. Drive mechanism; 4. Laser welding head; 5. Actuator connector; 6. End plate; 7. Spacer plate; 8. Base plate; 9. Drive rope; 10. Tension code; 11. Support rod; 12. Connecting shaft; 13. Connector; 14. Lifting ear; 15. Joint 1; 16. Joint 2; 17. First drive rope group; 18. Second drive rope group; 19. Drive mechanism connector; 20. Adapter plate; 21. Screw transmission mechanism; 22. Screw; 23. Slider; 24. Drive rope fixing part; 25. Coupling; 26. Motor; 27. Linear guide. DETAILED DESCRIPTION

[0075] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0076] like Figure 1 As shown, an embodiment of the present invention provides a rope-driven laser welding robot arm based on quaternion joints, comprising:

[0077] like Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 As shown, the rope-driven laser welding robot arm based on quaternion joints of the present invention includes three parts: an actuator 1, a robot arm body 2, and a driving mechanism 3;

[0078] like Figure 5 As shown, the actuator 1 mainly includes a laser welding head 4 and an actuator connecting part 5, which are used for performing laser welding operations; the actuator connecting part 5 is used to connect the actuator 1 and the robot arm body 2, and can accommodate wires passing through; the laser welding head 4 can be any laser welding head on the market. What is described in the present invention and shown in the figures are only examples for explaining the structural principles of the present invention.

[0079] The rope-driven laser welding robot based on quaternion joints in the embodiment of the present invention is composed of three parts: an actuator 1, a robot body 2 and a driving mechanism 3 (such as Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 The robot arm 2 utilizes a quaternion joint design, enabling precise posture adjustment within space. The drive mechanism 3 utilizes a rope drive method to efficiently drive the joints of the robot arm 2. The actuator 1, mounted at the end of the robot arm 2, is responsible for completing the laser welding operation.

[0080] The actuator 1 is mainly composed of a laser welding head 4 and an actuator connecting piece 5 (see Figure 5 The laser welding head 4 can be any mature product on the market. Its function is to output a stable and high-energy laser beam to achieve the welding task. The execution part connector 5 is used to firmly connect the laser welding head 4 to the robot arm body 2. At the same time, a wire channel is reserved to ensure stable power and signal transmission during the welding process, thereby ensuring welding quality.

[0081] The robotic arm's main body 2 utilizes a quaternion joint design, overcoming the universal joint lock issue common with traditional joints and enabling smooth, flexible spatial motion. The drive mechanism 3 utilizes a rope drive mechanism, precisely controlling rope tension to drive the joints of the robotic arm 2, enabling precise positioning. The collaborative work of these two mechanisms ensures high responsiveness and precision during the robotic arm's motion, meeting the stringent position and posture requirements of laser welding.

[0082] During the welding process, the controller generates control instructions for each joint based on the preset welding path and process requirements. These instructions are transmitted to the FPGA via the processor. The drive mechanism 3 then adjusts the rope tension according to these instructions, achieving real-time posture adjustment of the robot arm 2. Simultaneously, the laser welding head 4 in the actuator 1 outputs a laser beam according to the controller's instructions, performing the welding operation along a predetermined trajectory. The entire system forms a closed loop of virtual and real interaction, collecting sensor data feedback in real time and dynamically updating the motor and joint status, thereby ensuring high precision and stability during the welding process.

[0083] like Figure 6 、 Figure 7 、 Figure 8 、 Figure 9 、 Figure 10 、 Figure 11 As shown, the robot arm body 2 includes an end plate 6, a spacer plate 7, a base plate 8, a plurality of drive ropes 9, a tension code 10, a support rod 11, a connecting shaft 12, and a connecting piece 13; the end plate 6, the spacer plate 7, and the base plate 8 can be collectively referred to as an end plate; the robot arm body 2 is used to carry the actuator, can realize the movement of different trajectories, and drive the actuator 1 to complete the welding operation or reach the welding operation position;

[0084] Specifically, the robot arm body 2 has two joints, which are connected end to end through a spacer disk 7. From the driving mechanism to the actuator, there are joint 15 and joint 2 16.

[0085] Among them, the end plate 6, the spacer plate 7, the base plate 8, and the drive mechanism connector 19 all have a central through hole, and six wire holes are evenly distributed at equal intervals on the edge of the disc; three lifting ears 14 are evenly distributed on one side of the end plate 6 and the base plate 8, and the lifting ears 14 are fixedly connected to the connecting shaft 12; Figure 8 As shown, the lifting ears 14 are distributed on both sides of the spacer plate 7 in a cross-distribution; both ends of the support rod 11 are fixedly connected to the connecting shaft 12; Figure 9 As shown, the support rod 11 is connected to the end plate through a connecting piece 13, and the two connecting shafts 12 pass through the two through holes of the connecting piece 13 respectively, and the axes of the two through holes of the connecting piece 13 are perpendicular to each other; the three support rods 11, the connecting shaft 12 and the connecting piece 13 and the two end plates together constitute the quaternion joint; the joint 15 is composed of a base plate 8, a spacer plate 7, a support rod 11, a connecting shaft 12 and a connecting piece 13; the joint 2 16 is composed of a spacer plate 7, an end plate 6, a support rod 11, a connecting shaft 12 and a connecting piece 13; the quaternion joint can perform approximate spherical rolling in three-dimensional space, ensuring the motion stability of the continuum configuration without a central main rod under high load, and improving the load capacity and stiffness of the continuum configuration.

[0086] like Figure 6 、 Figure 7 、 Figure 8 、 Figure 9 、 Figure 10 、 Figure 11 As shown, the main body 2 of the robotic arm consists of an end plate 6, a spacer plate 7, and a base plate 8 (collectively referred to as the end plates). It is also equipped with several drive ropes 9, tensioning weights 10, support rods 11, connecting shafts 12, and connectors 13. This main body supports the actuator 1 and, through its own structure, enables movement along different trajectories, thereby driving the actuator 1 to complete the welding operation or reach the specified welding position. The entire system design ensures stable motion and high-precision positioning even under high loads.

[0087] The end plate 6, spacer plate 7, base plate 8, and drive mechanism connector 19 are all designed with a central through-hole. Six cable holes are evenly spaced around the edges of the discs, facilitating the routing of the drive rope 9 and ensuring uniform force transmission. Furthermore, three lifting lugs 14 are evenly spaced on one side of the end plate 6 and base plate 8, and are also arranged in a cross pattern on either side of the spacer plate 7. These lifting lugs 14 are rigidly connected to the connecting shaft 12 through a fixed connection, providing a key load-bearing node for the subsequent joint construction.

[0088] Both ends of the support rod 11 are fixedly connected to the connecting shaft 12 and connected to the end plate through the connecting piece 13. Figure 9 As shown, two connecting shafts 12 pass through two perpendicular through-holes in the connecting member 13, ensuring that the connecting member 13 can accurately transmit motion and load under the action of the support rods 11. The three support rods 11, the connecting shafts 12, the connecting member 13, and the end plate together form the basic structural unit of the quaternion joint, providing the necessary rigidity and stability for the entire robotic arm.

[0089] The main robotic arm 2 features two joints: Joint 1 15 (composed of a base plate 8, spacer plates 7, support rods 11, connecting shafts 12, and connectors 13) and Joint 2 16 (composed of spacer plates 7, end plates 6, support rods 11, connecting shafts 12, and connectors 13). These quaternion joints enable near-spherical rolling motion in three-dimensional space, ensuring high load capacity and motion stability despite the continuum configuration lacking a central main rod. This design not only improves the load capacity and rigidity of the continuum configuration but also meets the stringent requirements for high precision and stability required for laser welding operations.

[0090] like Figure 6 As shown, the drive ropes 9 can all pass through the wire holes and penetrate the joints, and are all connected to the drive rope fixing members 24 in the screw transmission mechanism 21 through the drive mechanism connector 19 and the base plate 8; three evenly distributed drive ropes form a group, which are respectively used to drive the bending movement of the two joints, namely the first drive rope group 17 and the second drive rope group 18;

[0091] Specifically, such as Figure 10 As shown, six drive ropes 9 of the first and second drive rope groups 17, 18 pass through the joint 15. The thread holes of the six drive ropes 9 are evenly distributed, and the axes of the three thread holes form a 60° angle with the axis of the central through hole of the base plate 8. One end of the three drive ropes of the first drive rope group 17 is fixedly connected to the tension weight 10 of the spacer plate 7, and the other end is fixedly connected to the drive rope fixing member 24 of the screw transmission mechanism 21. The first drive rope group 17 can control the joint 15 to achieve two-degree-of-freedom bending motion.

[0092] like Figure 11 As shown, the three drive ropes 9 of the second drive rope group 18 pass through the second joint 16. The thread holes of the three drive ropes 9 are evenly distributed, and the axis of the three thread holes forms an angle of 120° with the axis of the central through hole of the spacer disk 7. Three tension weights 10 are evenly distributed on the spacer disk 7 for fixing the drive ropes of the first drive rope group 17. The axes of the drive ropes 9 of the second joint 16 and the tension weights 10 are on the same circle and concentric with the central through hole.

[0093] The second driving rope group 18 only passes through the joint 15 and does not affect the control of the joint 15 by the first driving rope group 17, so that the motion control of the two joints can be independent of each other.

[0094] like Figure 12 、 Figure 13As shown, the drive mechanism 3 includes a drive mechanism connector 19, an adapter plate 20, a screw transmission mechanism 21, a power supply and a terminal controller, and is used to control the movement of the robot arm body 2; the drive mechanism connector 19 is fixedly connected to the base plate 8; the screw transmission mechanism 21 includes a screw 22, a slider 23, a drive rope fixing member 24, a coupling 25, a motor 26, and a linear guide rail 27; the drive rope fixing member 24 is fixedly connected to the slider 23;

[0095] Specifically, such as Figure 12 As shown, the screw transmission mechanism 21 is fixedly connected to the drive mechanism connecting member 19 through the adapter plate 20, and is evenly spaced around the central axis of the drive mechanism connecting member 19; each joint is controlled by three of the screw transmission mechanisms, and the motor 26 is connected to the terminal controller. The motor 26 is connected to the screw 22 through the coupling 25, converting the rotation of the motor into linear motion, driving the slider 23 and the drive rope fixing member 24 to complete the linear motion, and finally driving the drive rope 9 to complete the bending motion of the joint.

[0096] The rope-driven laser welding robot arm based on quaternion joints of the present invention adopts a new type of continuum configuration robot arm design, which controls the retraction and extension of multiple drive ropes through a driving mechanism to achieve flexible movement of the robot arm. The main body of the robot arm is composed of an end disk, a spacer disk and a base disk. The quaternion joints are formed between the disks through support rods and connecting shafts, so that it can achieve approximately spherical rolling motion in three-dimensional space. The driving mechanism is installed on the base disk of the robot arm and consists of a motor, a screw transmission mechanism, a slider, a linear guide rail and a drive rope fixing. The drive rope is connected to the screw transmission mechanism. By controlling the rotation of the motor to drive the movement of the screw, the slider moves along the linear guide rail, thereby adjusting the tension of the drive rope, and finally controlling the joint movement of the robot arm to achieve precise positioning of the laser welding head.

[0097] In this system, the realization of quaternion joints depends on the connection method between multiple end plates. The edges of the base plate, spacer plate and end plate are evenly distributed with wire holes for driving ropes to pass through and connect each joint structure. The first drive rope group and the second drive rope group are used to control the movement of joint one and joint two respectively, wherein each drive rope group contains three drive ropes and is fixed to the base plate and spacer plate respectively. The first drive rope group is responsible for the two-degree-of-freedom movement of joint one, while the second drive rope group only passes through joint one and does not affect its movement, thereby realizing independent control of the two joints. This design ensures that the robotic arm still has a high load capacity without a central main rod, and maintains the stability of movement through precise force transmission.

[0098] The drive mechanism's lead screws are evenly spaced across the drive mechanism connector, with each joint independently controlled by three lead screws. A motor drives the lead screw through a coupling, rotating the slider along the linear guide. This in turn drives the drive rope fixture to retract and release the drive rope, thereby changing the joint angle and achieving bending motion. Due to the lead screw's high linear motion precision, this drive method ensures the robot's precise motion. To further optimize the robot's force profile, the axis of the drive rope's through hole is aligned at a specific angle to the axis of the central through hole in the end plate. This ensures more even force distribution, improves force transmission efficiency, and enhances the overall stability of the system.

[0099] During the operation of the robotic arm, the terminal controller calculates the required joint motion trajectory based on the welding task requirements and adjusts the drive rope length via the motor-driven lead screw to achieve the desired posture. Through the coordinated control of the three drive ropes, the position of the welding head can be precisely adjusted in three-dimensional space, allowing welding operations to proceed along the set trajectory. Furthermore, the structural design of the system enables the robotic arm to adapt to various welding environments, making it particularly suitable for complex welding tasks requiring high flexibility and high precision. At the same time, due to its rope drive, the robotic arm is lighter and more energy-efficient than traditional rigid robotic arms, thereby improving the overall efficiency of welding operations.

[0100] According to the present invention, a driving control method of a rope-driven laser welding robot arm based on quaternion joints is proposed.

[0101] The present invention's rope-driven laser welding robot control method, based on quaternion joints, relies on a kinematic model of the joints. By calculating the change in the length of the drive rope, the robot's motion is precisely controlled. During the control process, the robot's target position is first determined, and a mathematical model of the joints is established based on spatial geometric relationships. This mathematical model calculates the change in the length of the drive rope based on the robot's joint angles, the geometric parameters of the end plate, and the distribution of the fixed points of the drive rope. By leveraging the kinematic relationship between the drive rope and the joints, the robot's trajectory in three-dimensional space can be precisely controlled, thus meeting the requirements of welding operations.

[0102] During control execution, the terminal controller inputs the change in drive rope length, calculated from the joint kinematic model, into the control system based on the target pose. After receiving these input parameters, the controller drives the motor, which drives the lead screw mechanism, causing the slider to move along the linear guide, thereby adjusting the drive rope length accordingly. Because the drive rope is fixed to the end plate, changes in its length cause the corresponding joint to bend around its center of rotation. The synergistic effect of different drive rope combinations enables high-precision adjustment of the joint along the preset direction, ensuring that the laser welding head follows the set trajectory.

[0103] During the robot's motion, the joint's bending angle and the change in the length of the drive rope meet specific geometric constraints. Based on this spatial geometry, a formula can be derived to calculate the change in the length of the drive rope within the joint's bending plane. Parameters such as the joint angle, the vertical distance between the end plates, and the distance from the drive rope's fixed point to the end plate's center determine the amount of stretch or contraction of the drive rope. Based on these parameters, the terminal controller calculates the actual adjustment value for each drive rope and adjusts the motor control signal in real time to ensure that the rope retraction and extension conform to the expected changes, thereby allowing the robot to move smoothly along the target trajectory.

[0104] The entire control process is based on joint kinematic calculations and precise control of the drive rope, enabling the robotic arm to efficiently and stably achieve complex welding motion trajectories. Due to the flexible nature of the rope drive method, the robotic arm can maintain precise motion stability under high loads, while also possessing good shock resistance and energy consumption optimization capabilities. In addition, the control method can adapt to different welding conditions by adjusting the drive parameters, and can be combined with the sensor feedback mechanism to further optimize motion control and improve the accuracy and reliability of welding operations. The present invention mainly relies on the coordinated motion of the drive rope to control the bending of the robotic arm. First, it is necessary to determine the change in the length of the drive rope at any joint angle of the robotic arm;

[0105] like Figure 14 As shown, a single joint of the robotic arm can perform approximately spherical rolling in three-dimensional space, and an ideal spherical rolling motion model can be established;

[0106] Specifically, the center of the base circle is the origin of the spatial coordinate system O0, and the spatial coordinate system O0 is established; the center of the end circle is the origin of the spatial coordinate system O e , establish the space coordinate system O e Coordinate system; the Z0 axis of the coordinate system O0 is perpendicular to the base plane, and the Y0 axis is in the bending plane of the joint; the coordinate system O e Z e Axis perpendicular to the end plane, Y e The axis is in the plane of flexion of the joint;

[0107] like Figure 15 、 Figure 16 As shown, the projection views of the ideal spherical rolling motion model in the joint bending plane and the base plane are obtained;

[0108] like Figure 15 As shown, from the spatial geometric relationship, it can be obtained that the lengths of each driving rope in the bending plane satisfy the following relationship:

[0109]

[0110] Among them, l jis the length of the jth driving rope, ψ is the bending angle of the joint, and h is the vertical distance between the two end discs of the joint, which remains unchanged during the bending process of the joint;

[0111] like Figure 16 As shown, the following relationships can be obtained from the spatial geometric relationship:

[0112]

[0113] Wherein, D is the distance between the fixed point of the drive rope on the end disc and the center of the end disc, the spatial coordinate system O0 is established with the center of the base as the origin of the spatial coordinate system O0, α is the angle between the X0 axis of the coordinate system O0 and O0A1, is the angle between the X0 axis of the coordinate system O0 and the joint bending plane, j is the jth driving rope;

[0114] Based on the joint kinematic model, the change in the length of the driving rope when any joint angle is reached is calculated as follows:

[0115]

[0116] like Figure 17 As shown, according to the driving formula, the change in the length of the driving rope when reaching any joint angle can be calculated, and the change in the length of the rope of each joint can be input into the terminal controller; each driving rope 9 is controlled by a separate motor 26; the controller drives the motor 26 and drives the driving rope 9 to complete linear motion at the same time; different driving ropes 9 coordinate with each other to enable the robotic arm to reach the corresponding posture.

[0117] This paper proposes a control method for a rope-driven laser welding robot arm based on quaternion joints. The method first calculates the change in the driving rope length for each joint at any angle using a driving formula. The mathematical model of quaternion joints accurately describes any rotation and posture of the robot arm in three-dimensional space, enabling it to adapt to complex motion trajectories. This calculation determines the required rope length change for each joint, providing a precise parameter basis for subsequent control.

[0118] Through the terminal controller, the user inputs the calculated rope length changes for each joint into the control system. The terminal controller features a human-machine interface that monitors the accuracy of input parameters in real time and ensures that the target length of each drive rope matches the robot's pose. This step effectively reduces the complexity of manual adjustments and improves control efficiency.

[0119] The control system's built-in processor drives multiple motors synchronously based on input rope length change data. Each drive rope is controlled by an independent motor. The precise rotation of the motor enables the drive rope to complete position adjustment in the form of linear motion, thus ensuring the stability and responsiveness of the robot arm.

[0120] Each joint of the robotic arm is controlled by three independent drive cables, which are coordinated through a control algorithm to ensure that the robotic arm can accurately adjust to the target position in three-dimensional space. This multi-drive cable collaboration mechanism increases the flexibility of the robotic arm, enabling it to handle complex manipulation tasks in unstructured environments.

[0121] Compared to traditional robotic arms, this invention significantly improves stiffness and load capacity while enhancing flexibility by introducing quaternion joints. This design allows the robotic arm to carry heavier actuators, such as laser heads, and complete complex welding tasks in confined spaces or in environments with numerous obstacles, expanding the possibilities for robotic applications.

[0122] Each quaternion joint is designed as a hollow structure, allowing components such as optical fibers and wires to be built into the robotic arm. Compared to traditional robotic arms with exposed wires, this invention effectively avoids mechanical failures or safety issues caused by exposed wires, significantly improving the reliability and operational safety of the device.

[0123] This invention utilizes a rope drive system, with each joint equipped with three independent drive ropes, each controlled by a separate motor. This results in a simple and easy-to-maintain drive system. Compared to complex gear or hydraulic drives, rope drive significantly reduces system errors while improving stability and responsiveness during the drive process.

[0124] The control method of this invention is applicable to robotic arm designs with varying numbers of joints, drive cables, and motors. Users can flexibly adjust the number of joints or drive cable configurations based on specific application requirements, thereby achieving robotic arm designs with varying motion ranges and functions. This flexibility not only expands the scope of robotic arms but also fills a gap in current laser welding robotic arm control technology.

[0125] Simulations were conducted on the load capacity of single and double joints of the robotic arm to analyze the deformation of the joints under gravity and load conditions. The gravity was set to 9806.6 mm / s. 2 The end load is set to 50 / 100 / 150 / 200 N. The material settings of each part of the robot arm joint are shown in the following table.

[0126] Table material settings

[0127]

[0128]

[0129] Figure 18 Total deformation;

[0130] Figure 19 Equivalent stress;

[0131] Figure 20 Result diagram of total deformation and equivalent stress of a single joint under different loads;

[0132] Figure 21 Result diagram of total deformation and equivalent stress of double joints under different loads;

[0133] Under the combined action of gravity and a 200N load, the maximum deformation of a single joint is 0.5mm, with the deformation concentrated in the end plate and the drive rope. The maximum equivalent stress is 388.76MPa, with the stress concentrated in the support rod, shaft, and drive rope.

[0134] Under the combined effects of gravity and a 200N load, the maximum deformation of the dual joints was 0.98mm, with a maximum equivalent stress of 272.82MPa. Deformation was concentrated in the end plate and drive rope, while stress was concentrated in the support rod and drive rope. Under high loads, the overall deformation of the robotic arm was minimal, meeting practical operational requirements.

[0135] 1. Joint Posture Experimental Plan

[0136] like Figure 22 , set the three postures of the robotic arm, calculate the control parameters of the robotic arm in these three postures through the driving formula, and verify the execution accuracy of the robotic arm mechanism and the accuracy of the control formula by comparing the error between the actual angle and the theoretical angle.

[0137] Robotic arm pose parameters

[0138]

[0139] 2. Joint angle measurement methods, such as Figure 23 ;

[0140] Before measurement, each joint reference plane needs to be calibrated. The calculation formula for the robot arm joint posture motion error is:

[0141]

[0142] The angle between the reference plane and the horizontal ground is the calibration angle The angle between the reference plane and the end surface of the joint is the joint angle θ i , the theoretical angle of joint i is θ i 0

[0143] Joint reference plane calibration angle

[0144]

[0145] 3. Experimental Results

[0146] The results of the drive control experiment are shown in the table below. The average error of joint 1 is 0.97%, the average error of joint 2 is 0.57%, and the average error of the entire robotic arm is 0.42%. The execution accuracy of the robotic arm mechanism meets the work requirements, verifying the correctness of the drive formula.

[0147] Drive control experiment results

[0148]

[0149]

[0150] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with this technical field within the technical scope disclosed by the present invention and within the spirit and principles of the present invention should be covered by the scope of protection of the present invention.

Claims

1. A control method for a rope-driven laser welding robot based on quaternion joints, characterized in that: The robotic arm comprises an actuator, a robotic arm body and a driving mechanism; The actuator is mounted on the end plate of the robot arm body and is used to connect to the laser welding head; The robot arm body is connected to the end plate and the base plate through a spacer plate, and includes a plurality of drive ropes, support rods and connecting shafts; The driving mechanism is mounted on the base plate of the robot arm body through a driving mechanism connector and is connected to the driving rope; The end plate, spacer plate and base plate in the main body of the robotic arm form a quaternion joint through a support rod and a connecting shaft. The edges of the disks of the end plate, spacer plate and base plate are provided with wire holes at equal intervals for the driving rope to pass through. The driving rope passes through the through hole on the base plate, penetrates the joint 1, and is fixed on the spacer plate; another set of driving ropes passes through the through hole on the spacer plate, penetrates the joint 2, and is fixed on the end plate; The control method includes: Step 1: Calculate the change in the length of the driving rope when any joint angle is reached according to the driving formula; Step 2: Input the rope length change of each joint on the terminal controller; Step 3: The controller drives the motor and the driving rope to complete linear motion; Step 4: Different drive ropes coordinate to make the robotic arm reach the corresponding position; From the spatial geometric relationship, it is found that the lengths of each driving rope in the bending plane satisfy the following relationship: Among them, l j is the length of the jth driving rope, ψ is the bending angle of the joint, and h is the vertical distance between the two end discs of the joint, which remains unchanged during the bending process of the joint; The following relationships are obtained from spatial geometric relationships: Wherein, D is the distance between the fixed point of the drive rope on the end disc and the center of the end disc, the spatial coordinate system O0 is established with the center of the base as the origin of the spatial coordinate system O0, α is the angle between the X0 axis of the coordinate system O0 and O0A1, is the angle between the X0 axis of the coordinate system O0 and the joint bending plane, j is the jth driving rope; Based on the joint kinematic model, the change in the length of the driving rope when any joint angle is reached is calculated as follows: According to the driving formula, the change in the length of the driving rope when reaching any joint angle can be calculated, and the robot arm can reach any posture by controlling the change in the driving rope.

2. The control method of the rope-driven laser welding robot arm based on quaternion joints according to claim 1 is characterized in that: The driving mechanism is fixedly connected to the driving mechanism connecting member through an adapter plate. The driving mechanism includes a motor, a screw rod, a coupling, a slider, a linear guide rail and a driving rope fixing member. The slider and the driving rope fixing member are assembled together.

3. The control method of the rope-driven laser welding robot arm based on quaternion joints according to claim 1 is characterized in that: A through hole is provided in the center of the end plate, the spacer plate and the base plate, and the optical fiber and the wire pass through the entire robot arm body through the central through hole and avoid crossing the drive rope.

4. The control method of the rope-driven laser welding robot arm based on quaternion joints according to claim 1 is characterized in that: The two ends of the support rod are respectively assembled on the end plate and the spacer plate through the connecting shaft, and the three support rods are evenly distributed at equal angles to form the joints of the robot arm body.

5. The control method of the rope-driven laser welding robot arm based on quaternion joints according to claim 1 is characterized in that: The driving mechanism is fixedly connected to the base plate, and the two ends of the driving rope are respectively fixed between the driving mechanism and the end plate. The slider is driven to move through the screw transmission mechanism, so that the driving rope completes the bending action of each joint of the robotic arm.

6. A computer-readable storage medium storing a computer program, wherein when the computer program is executed by a processor, the processor executes the steps of the control method of a cable-driven laser welding robot based on quaternion joints according to any one of claims 1 to 5.

7. An information data processing terminal, characterized in that: The information data processing terminal is used to execute the steps of the rope-driven laser welding robot arm control method based on quaternion joints as described in any one of claims 1 to 5.

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