A flexible intelligent manufacturing unit for car body laser welding and trajectory optimization method

Abstract

A flexible intelligent manufacturing unit for laser welding of a car body and a trajectory optimization method, the unit includes a workstation, a robot and a laser device, an electric control cabinet, and a robot control cabinet; the electric control cabinet communicates with a PLC controller; a robot and a laser device that can execute corresponding operation processes according to the instructions of the PLC controller are arranged inside the workstation, and are used to weld the workpiece according to the program of the control system; a rotating worktable is arranged on the workstation, and a fixture for clamping the workpiece is respectively arranged at both ends above the rotating table, so that one of the fixtures is located inside the workstation and the other is located outside the workstation; workpiece in-place detection sensors are arranged at multiple points of the fixture to identify the type of the workpiece being processed; the workpiece in-place detection sensor sends a signal to the PLC controller after detecting that the workpiece is in place, and the PLC controller identifies the type of the workpiece after receiving the signal, and retrieves the program data for producing the product. The flexibility of the production process is increased.

Description

Technical Field

[0001] The present invention belongs to the technical field of laser welding of new energy vehicle bodies, and specifically relates to a flexible intelligent manufacturing unit for laser welding of vehicle bodies and a trajectory optimization method. Background Art

[0002] Car body welding is a critical step in the manufacturing process of new energy vehicles. In order to improve production efficiency and welding quality and increase flexibility in the manufacturing process, laser welding automation equipment with robots and laser equipment as the core is widely used.

[0003] At present, most of the laser welding automation equipment are highly customized non-standard products, which require a lot of manpower and material resources in the configuration process of the production site. CN 114669918 A discloses a robot welding workstation and a multifunctional welding control method, which can make the single-axis and double-axis positioners flexibly convert by replacing some parts, and can effectively reduce the cost for some occasions of welding simple workpieces. However, it is a typical non-standard customized equipment, and the process is cumbersome during the configuration process, which will cause a lot of waste of manpower and material resources, resulting in increased costs. When performing large-scale welding work, the automation level of existing laser processing equipment is low, and technicians are required to perform targeted robot trajectory teaching according to the characteristics of the processed parts, which not only causes waste of manpower, but also leads to low production efficiency. CN 111344102 discloses a welding trajectory tracking method, device and system, which are mainly composed of a laser scanner, a photosensitive element and a laser welding device, and can generate a welding control signal according to the welding trajectory. However, the system described is not only complex in structure, but also difficult to implement in terms of control technology, and is accompanied by high costs. In addition, the existing products are not convenient for realizing flexible production of small batches and multiple batches of different models and flexible production of different parts of the same model. In addition, the laser welding process of the car body includes laser deep fusion welding, laser brazing, laser wire welding, etc. Different processes have different requirements for the impact, time, energy consumption and other indicators of the robot arm during the operation trajectory, and the trajectory parameters need to be optimized according to different processes. CN 106563900 A discloses a method for the optimal welding trajectory of automobile interior and exterior trims, providing a path with the minimum moving distance under the condition of multiple welding points of different welding parts. However, the method described is only for spot welding process, and is not applicable to a variety of laser welding processes. Summary of the invention

[0004] The purpose of the present invention is to provide a new energy vehicle body laser welding flexible intelligent manufacturing unit and trajectory optimization method, which can automatically select the production process, improve production efficiency, and increase the flexibility of the production process.

[0005] The technical solution to achieve the purpose of the present invention is:

[0006] A flexible intelligent manufacturing unit for laser welding of a car body, comprising a workstation, a robot and laser equipment, an electric control cabinet, and a robot control cabinet;

[0007] Robot control cabinet, used for controlling the operation of the robot;

[0008] The electric control cabinet communicates with the PLC controller and stores the models and brands of the robot and laser equipment for selection;

[0009] Inside the workstation are robots and laser equipment that can execute corresponding operation processes according to the instructions of the PLC controller. The robots and laser equipment are used to perform welding operations on the workpiece according to the program of the control system;

[0010] The workstation is provided with a rotating worktable, and a fixture for clamping the workpiece is respectively provided at both ends above the rotating worktable. When the rotating worktable rotates, it can pass through the feed hole on the workstation, and it satisfies that when one of the fixtures is located inside the workstation, the other fixture is located outside the workstation;

[0011] Workpiece arrival detection sensors are arranged at multiple points on the fixture to identify the type of workpiece being processed;

[0012] The workpiece arrival detection sensor sends a signal to the PLC controller after detecting that the workpiece is in place. After receiving the signal, the PLC controller identifies the type of workpiece and retrieves the program data of the robot and laser equipment used to produce the product.

[0013] Compared with the prior art, the present invention has the following significant advantages:

[0014] (1) Modular configuration: Through the control system with a programmable logic controller as the core, various brands and types of subsystems (laser sources, laser processing tools, robot subsystems, etc.) can be integrated into a complete intelligent manufacturing unit.

[0015] (2) High degree of automation: Through the program settings of sensors and control systems, this intelligent manufacturing unit can automatically identify the type of the current workpiece and call the corresponding robot trajectory and process parameters, greatly reducing the waste of human resources.

[0016] (3) Flexible production capabilities: Through mechanical design, different tooling fixtures can be equipped on the turntable to achieve flexibility in the workpiece being processed; through the switching of process equipment and parameters and the targeted optimization of the robot's motion trajectory, the flexibility of the processing technology can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a structural schematic diagram of the present invention;

[0018] Figure 2 It is the flow chart of automated processing;

[0019] Figure 3 Flowchart for targeted optimization of robot motion trajectory for different laser welding processes;

[0020] Figure 4 This is an example of the Pareto optimal solution set obtained after multi-objective optimization of trajectories.

[0021] Figure 1 Middle: 1-laser source, 2-water cooler, 3-electric control cabinet, 4-robot controller, 5-inspection door, 6-bottom plate, 7-laser protection room wall, 8-rotating workbench, 9-dust collector, 10-air duct, 11-robot. DETAILED DESCRIPTION

[0022] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0023] This embodiment is a flexible intelligent manufacturing unit for laser welding of vehicle bodies, such as Figure 1 As shown: including workstation, robot and laser equipment, rotary table, water cooler, dust removal equipment, electric control cabinet, robot control cabinet;

[0024] The workstation includes a bottom plate 6, a laser protection room wall 7 made of aluminum alloy profiles is spliced ​​and fixed on the top of the bottom plate 6, and a top plate is fixed on the top of the laser protection room wall 7. The bottom plate 6, the laser protection room wall 7 and the top plate form a square studio. The wall is a spliced ​​wall with laser protection capability, which is not only easy to install, flexible in size, but also highly safe.

[0025] In order to facilitate maintenance, an inspection door 5 is installed on one side wall of the workstation.

[0026] Robot and laser equipment: A robot 11 and a laser equipment are arranged inside the workstation, which can perform corresponding operation processes according to the instructions of the PLC controller. The laser equipment includes a laser head arranged on the industrial robot 11 and a laser source 1 for providing laser. The robot and the laser equipment can perform welding operations on the workpiece according to the program of the control system.

[0027] A rotating workbench is provided with a feeding hole on one of the walls of the workstation, and a rotating workbench 8 is fixed on the base. A flexible clamp for clamping the workpiece can be respectively provided at the two ends above the rotating table. The rotating workbench 8 can pass through the feeding hole when rotating, and it can satisfy that one of the flexible clamps is located inside the workstation while the other flexible clamp is located outside the workstation. The use of double clamps can enable the workpiece to be loaded and unloaded on the other side while the workpiece is being processed on one side, thereby improving work efficiency.

[0028] Workpiece arrival detection sensors are arranged at multiple points on the flexible fixture. By combining the output results of multiple sensors, the control system can identify the type of the workpiece being processed.

[0029] The water cooler 2 is arranged outside the workstation and is used to provide water cooling for the laser device when the workpiece is welded.

[0030] The dust removal equipment includes a dust collector 9 and an air duct 10. The exhaust fan 9 is arranged outside the workstation. The input end of the exhaust fan 9 is connected to the air duct 10. The air duct 10 is connected to the inside of the workstation. The dust generated during the welding process inside the workstation is extracted by the exhaust fan 9 to achieve the dust removal effect.

[0031] The electric control cabinet 3 is embedded in the outer wall of the workstation and has all the electrical accessories for controlling the workstation. An LCD screen is arranged on the outside to display the UI user interface.

[0032] The robot control cabinet 4 is embedded in the external wall of the workstation and is used in conjunction with the robot 11 to control the operation of the robot 11 .

[0033] Introduction to automated processing:

[0034] The automated processing flow mentioned in this embodiment is as follows Figure 2 As shown:

[0035] S1. Select the model and brand of the robot and laser equipment in the UI user interface. The PLC controller accesses the electronic data of the corresponding robot and laser equipment in the GSD electronic equipment database according to the product type for matching;

[0036] S2, fix the workpiece to be processed on the rotating worktable 8 through a flexible fixture, and the infrared sensor on the flexible fixture sends a signal to the PLC controller after detecting that the workpiece is in place. After receiving the signal, the PLC controller can distinguish the type of workpiece according to the sensor point signal and retrieve the program data of the robot and laser equipment used to produce the product;

[0037] S3, the robot and the laser equipment produce products according to the program data retrieved in S2, and after the production is completed, a feedback signal is given to the PLC controller to control the rotation of the rotary table 8 so that the processed workpiece is transferred to the outside of the workstation, and the operator removes the processed workpiece.

[0038] Repeat steps S2 to S3 to perform welding on the next workpiece.

[0039] Among them, the program data retrieved in S2 includes the process parameters for product processing and the robot trajectory parameters optimized for different processes.

[0040] like Figure 3As shown, the targeted optimization method used by the robot trajectory called by S2 in the process of realizing automated processing is as follows:

[0041] Step 1: Determine the optimization objectives and constraints;

[0042] In order to improve the robot's operating efficiency, reduce energy consumption, and protect the robot's key component drivers, it is generally expected that the robot's movement time is the shortest, the trajectory is the smoothest, the energy consumption is the lowest, and the driving torque change is the smallest. Therefore, the optimization objectives of this method are as follows:

[0043]

[0044]

[0045]

[0046] Where T is the time it takes for the robot to move from the initial position to the final position along a certain trajectory, v i ,a i ,j i are the joint velocity, acceleration and impact of the i-th point, t represents time, t i and t i+1 Represent the time of the i-th point and the i+1-th point respectively, n represents the number of path points in the trajectory planning process, m represents the number of joints, M represents the total number of joints, S 1 is the exercise time, S 2 is the average acceleration of the joint, S 3 Average impact for joints;

[0047] The planned trajectory must meet certain conditions. For example, the joint drive of each robot cannot provide infinite torque, so the torque constraint of the joint must be considered. The rated speed of each robot's joint motor and the deceleration of the joint reducer limit the maximum speed, so the speed limit must be considered. Similarly, the acceleration and even jerk limits must also be considered. At the same time, the constraints of the robot's task space must also be considered. At the same time, the robot's motion is subject to the following constraints:

[0048] Joint torque: |τ m (t)|≤τ mmax ;

[0049] Joint jerk: |j m (t)|≤j mmax ;

[0050] Joint acceleration: |a m (t)|≤j mmax ;

[0051] Joint velocity: |v m(t)|≤v mmax ;

[0052] Joint displacement: q∈Ω;

[0053] where τ m (t), j m (t), a m (t), v m (t) and q are the joint torque, joint jerk, joint acceleration, joint velocity and joint displacement of the mth joint, respectively. mmax 、j mmax 、a mmax 、v mmax , are the maximum torque, maximum jerk, maximum acceleration, and maximum velocity of the mth joint respectively, and Ω is the working space of the robot.

[0054] Step 2: Use NSGA-II algorithm to perform multi-objective optimization and obtain the Pareto optimal solution set. Figure 4 shown.

[0055] Step 3: After obtaining the optimal solution set, the normalized weight function is used to select the engineering solutions corresponding to different laser welding processes.

[0056] Common laser welding processes for new energy vehicles include: laser brazing, wire-filling fusion welding, laser deep fusion welding, etc. Due to the different characteristics of different processes, their requirements for the robot arm's motion trajectory are also different. For example, laser brazing has a large spot and low power density, and the processing equipment used for laser brazing often has an active or passive weld tracking device. Therefore, the laser brazing process has a high tolerance for impacts in the robot arm's motion trajectory, and the laser brazing welding speed is relatively low. However, for laser deep fusion welding, its spot is small and the power density is very high. At the same time, for laser deep fusion welding of thin plate parts that exist in large quantities in automobile bodies, defocus is a very important process parameter and has an extremely important impact on welding quality. Therefore, laser deep fusion welding has a low tolerance for impacts in the robot arm's motion trajectory, and the laser deep fusion welding has a faster welding speed, which is also a major advantage of laser welding.

[0057] According to the characteristics of different laser welding processes used in the bodies of new energy vehicles, the corresponding engineering solutions in the Pareto solution set are selected in a targeted manner.

[0058] Normalized weight function: f c =α 1 S 1 / N 1 +α 2 S 2 / N 2 +α 3 S 3 / N3 ;

[0059] Where: S 1 The movement time is used to measure the robot's movement efficiency;

[0060] S 2 is the average acceleration of the joint, which measures the energy consumed by the robot joint;

[0061] S 3 is the average impact of the joint, which measures the smoothness of the trajectory;

[0062] α 1 is the weight coefficient of motion efficiency;

[0063] α 2 is the weight coefficient of energy consumption;

[0064] α 3 is the weight coefficient of smoothness;

[0065] f c Used to characterize the suitability of the solution;

[0066] N 1 , N 2 , N 3 It is the maximum value of each indicator in the Pareto optimal solution set, in order to make each objective function in the same range.

[0067] Take the laser brazing process as an example. Based on the laser welding principle and referring to the on-site debugging experience, we take α 1 =0.2, α 2 =0.6, α 3 = 0.2, and the S corresponding to each point in the obtained parato optimal solution set 1 , S 2 , S 3 Substituting into the equations, we get f c The value of f c The corresponding point is the optimal engineering solution required by the robot to perform the laser brazing process.

Claims

1. A flexible intelligent manufacturing unit for car body laser welding, including a workstation, a robot and laser equipment, an electric control cabinet, and a robot control cabinet; Robot control cabinet, used for controlling the operation of the robot; The electric control cabinet communicates with the PLC controller and stores the models and brands of the robot and laser equipment for selection; Inside the workstation are robots and laser equipment that can execute corresponding operation processes according to the instructions of the PLC controller. The robots and laser equipment are used to perform welding operations on the workpiece according to the program of the control system; It is characterized in that The workstation is provided with a rotating worktable, and a fixture for clamping the workpiece is respectively provided at both ends above the rotating worktable. When the rotating worktable rotates, it can pass through the feed hole on the workstation, and it satisfies that when one of the fixtures is located inside the workstation, the other fixture is located outside the workstation; Workpiece arrival detection sensors are arranged at multiple points on the fixture to identify the type of workpiece being processed; The workpiece arrival detection sensor sends a signal to the PLC controller after detecting that the workpiece is in place. After receiving the signal, the PLC controller identifies the type of workpiece and retrieves the program data of the robot and laser equipment used to produce the workpiece. The program data includes process parameters for workpiece processing and robot trajectory parameters optimized for different processes; The robot trajectory optimization method is as follows: Step 1: Determine the optimization objectives and constraints: The robot motion time, average joint acceleration, and average joint impact are taken as optimization targets, and constraints are set for the robot's joint torque, joint jerk, joint acceleration, joint velocity, and joint displacement; Step 2: Use NSGA-II algorithm to perform multi-objective optimization and obtain the Pareto optimal solution set; Step 3: After obtaining the optimal solution set, the normalized weight function is used to select the engineering solutions corresponding to different laser welding processes; The objectives are as follows: Where T is the time it takes for the robot to move from the initial position to the final position along a certain trajectory, v i ,a i ,j i are the joint velocity, acceleration and impact of the i-th point, t represents time, t i and t i+1 Represent the time of the i-th point and the i+1-th point respectively, n represents the number of waypoints in the trajectory planning process, m represents the number of joints, M represents the total number of joints, S1 is the movement time, S2 is the average acceleration of the joint, and S3 is the average impact of the joint; Constraints: Joint torque: |τ m (t)|≤τ mmax ; Joint jerk: |j m (t)|≤j mmax ; Joint acceleration: |a m (t)|≤j mmax ; Joint velocity: |v m (t)|≤v mmax ; Joint displacement: q∈Ω; where τ m (t), j m (t), a m (t), v m (t) and q are the joint torque, joint jerk, joint acceleration, joint velocity and joint displacement of the mth joint, respectively. mmax 、j mmax 、a mmax 、v mmax , are the maximum torque, maximum jerk, maximum acceleration, and maximum speed of the mth joint, respectively, and Ω is the robot’s workspace; Normalized weight function: f c =α1S1 / N1+α2S2 / N2+α3S3 / N3; Among them: S1 is the exercise time; S2 is the average acceleration of the joint; S3 is the average impact of the joint; α1 is the weight coefficient of motion efficiency; α2 is the weight coefficient of energy consumption; α3 is the weight coefficient of smoothness; f c Used to characterize the suitability of the solution; N1, N2, and N3 are the maximum values ​​of each indicator in the Pareto optimal solution set.

2. The car body laser welding flexible intelligent manufacturing unit according to claim 1 is characterized in that: The workstation comprises a bottom plate, a laser protection room wall is spliced ​​and fixed on all sides above the bottom plate, and a top plate is fixed on the top of the laser protection room wall.

3. The car body laser welding flexible intelligent manufacturing unit according to claim 2 is characterized in that: An inspection door is installed on one side wall of the workstation.

4. The body laser welding flexible intelligent manufacturing unit according to claim 1 is characterized in that: It also includes a water cooler, which is arranged outside the workstation and is used to provide water cooling for the laser equipment when the workpieces are welded.

5. The body laser welding flexible intelligent manufacturing unit according to claim 1 is characterized in that: It also includes dust removal equipment, which includes a dust collector and an air duct. The exhaust fan is arranged outside the workstation, and the input end of the exhaust fan is connected to the air duct, which is connected to the inside of the workstation. The dust generated during the welding process inside the workstation is extracted by the exhaust fan.

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