A Flexible Progressive Forming Method for Large Sheet Metal Parts Based on Multi-Robot Collaboration

Abstract

This invention belongs to the field of sheet metal processing technology, specifically relating to a flexible progressive forming method for large sheet metal parts based on multi-robot collaboration. The method includes the following steps: dividing the three-dimensional model of the target component into several sub-regions based on its geometric features, and determining the tool head and forming process parameters for each robot in each sub-region; performing trajectory planning and motion synchronization for each robot; performing dynamic collision detection based on the real-time position feedback of each robot, and optimizing the trajectory through coordinated planning of speed and trajectory; and dynamically adjusting the forming process parameters of each robot based on the real-time force feedback of each tool head using a force / position hybrid control algorithm. Compared with existing technologies, this invention solves the problems of limited forming range and low efficiency in existing technologies. This solution achieves both expanded forming range and ensures consistent forming accuracy and quality of the component.

Description

Technical Field

[0001] This invention belongs to the field of sheet metal processing technology, specifically relating to a flexible progressive forming method for large sheet metal parts based on multi-robot collaboration. Background Technology

[0002] The development of transportation vehicles such as aerospace and high-speed trains has led to a growing demand for large and complex curved sheet metal components. These components typically feature large dimensions and complex geometric features. Traditional mold forming methods are costly and time-consuming, making them unsuitable for small-batch or prototype manufacturing. Progressive forming technology, as a moldless flexible forming process, uses a simple tool head to locally form sheet metal point-by-point along a predetermined three-dimensional spatial trajectory, offering significant advantages in small-batch and customized manufacturing.

[0003] However, existing incremental forming equipment is mostly based on multi-axis CNC milling machines or industrial robots, which have limited forming range and are difficult to handle the forming of large components with an external dimension of more than 1m. In addition, single-point incremental forming is inefficient and can easily lead to uneven forming force distribution and large springback on large sheet metal, making it difficult to meet the forming requirements of components with complex geometric features.

[0004] Chinese patent CN120962353A proposes a multi-robot moldless forming and laser shock strengthening composite processing system and method. By having one forming robot and one forming strengthening robot work collaboratively on both sides of the workpiece, the forming performance of sheet metal can be improved and the forming accuracy increased. However, this method is essentially still an improvement on single-point incremental forming by robots, employing a vertical clamping method and not introducing a multi-robot multi-point synchronous forming mechanism. Therefore, the forming efficiency remains limited, making it difficult to meet the high-efficiency manufacturing requirements of large, thin-walled sheet metal parts.

[0005] Chinese patent CN120428648A proposes a three-point progressive forming trajectory design and forming method for sheet metal. It employs a simple support and two forming tools to create a three-point constraint on the sheet metal, significantly reducing overall skewness and wobbling during forming, thereby improving the geometric accuracy of the final part. However, this forming method requires the line connecting the two tool heads to always pass through the center point to maintain force balance, severely limiting the flexibility of trajectory planning. It is difficult to adapt to the forming of components with asymmetrical geometric features and cannot achieve asynchronous collaborative processing across multiple regions.

[0006] Chinese patent CN120862666A proposes a method and apparatus for planning vehicle grinding and polishing trajectories using multi-robot collaboration. This involves spatial accessibility analysis and collision detection within the working range of multiple robots, as well as grinding and polishing trajectory planning. However, grinding and polishing primarily aims for surface finish, and its overall processing trajectory is typically less than 0.5 mm in the normal dimension, with a small normal feed and a very low processing load, generally not exceeding 100 N. In contrast, incremental forming achieves the processing of complex-shaped sheet metal components through large plastic deformation. The total depth of the processing trajectory is typically in the range of 10 mm to 200 mm, and the forming load is generally higher than 500 N, far exceeding the load level of grinding and polishing. The two processes differ fundamentally in their technological principles, load characteristics, and control requirements.

[0007] Therefore, developing a multi-robot collaborative progressive forming method that can achieve efficient and flexible forming of large thin-walled sheet metal parts is of great engineering value for breaking through the bottleneck of single-point forming efficiency and realizing high-quality and efficient flexible manufacturing of complex components. Summary of the Invention

[0008] The purpose of this invention is to provide a flexible progressive forming method for large sheet metal parts based on multi-robot collaboration to solve at least one of the aforementioned problems, thereby addressing the issues of limited forming range and low efficiency in existing technologies. This solution achieves both an expanded forming range and ensures consistent forming accuracy and quality of the components.

[0009] The objective of this invention is achieved through the following technical solution: A flexible progressive forming method for large sheet metal parts based on multi-robot collaboration includes the following steps: The target component's 3D model is divided into several sub-regions based on its geometric features, and the tool head and forming process parameters of the robot corresponding to each sub-region are determined. Trajectory planning and motion synchronization are performed for each robot; dynamic collision detection is performed based on the real-time position feedback of each robot, and trajectory optimization is performed through coordinated planning of speed and trajectory; based on the real-time force feedback of each tool head, the molding process parameters of each robot are dynamically adjusted through a force / position hybrid control algorithm.

[0010] Preferably, the geometric features of the three-dimensional model of the target component include surface curvature and depth, and the target component is divided into several sub-regions according to different geometric features; The molding process parameters include molding trajectory, pressing amount, feed speed and trajectory spacing. By setting differentiated molding process parameters, each robot can perform asynchronous parallel processing in different sub-regions.

[0011] Preferably, the speed and trajectory coordination planning includes: speed coordination and spatial interpolation of the tool heads of adjacent robots.

[0012] Preferably, the robot is a jointed robot with at least 6 degrees of freedom; The tool head includes a hemispherical tool head, a cylindrical forming head, or a roller forming head.

[0013] Preferably, the robot has a trajectory tracking accuracy of ≤0.2 mm and a repeatability accuracy of ≤±0.05-0.1 mm; the rated load of a single robot is 16-100 kg and the arm span is 0.8-3.0 m; The tool head has a multi-dimensional force / torque sensor integrated at its end; wherein the radius of the hemispherical tool head is 5-30 mm, and the diameter of the roller-type forming head is 20-80 mm. The surface of the tool head is further provided with an elastic pad layer to form a flexible ball head; and / or, the tool head composite tool head is further integrated with a force sensor and a temperature sensor to form a composite tool head.

[0014] Preferably, the sheet material to be processed is clamped on the sheet material support device for progressive forming processing, and each robot is arranged around the sheet material to be processed. At least two robots are provided. The number of sub-regions is consistent with the number of robots.

[0015] Preferably, the sheet metal support device horizontally clamps the sheet metal to be processed through a fixed clamping assembly, with a clamping force of 5-50 kN.

[0016] Preferably, the fixing clamping assembly applies clamping force to the sheet metal to be processed through 60-80 bolts arranged circumferentially.

[0017] Preferably, the sheet metal support device is further provided with a hydraulic support pad and / or a pneumatic support pad for fine-tuning the clamping force.

[0018] Preferably, the method further includes: after completing the overall forming of the sheet material to be processed, performing local precision correction and quality inspection to obtain the target component.

[0019] Compared with the prior art, the present invention has the following beneficial effects: This invention effectively overcomes the limitations of existing technologies through a multi-robot collaborative forming method that integrates task allocation, adaptive regional planning, and real-time force / position coordination control. Addressing the issues of low efficiency and difficult springback control in single-point incremental forming, this invention employs multiple robots with various tool heads to process different areas of the sheet metal synchronously or asynchronously in parallel, significantly improving forming efficiency and suppressing overall springback through multi-point coordinated deformation. To address the problem of trajectory planning being limited by symmetry constraints and lacking flexibility, this invention decomposes the surface and divides the forming processing task into sub-regions, supporting each robot to execute asymmetric and differentiated adaptive forming paths based on the geometric characteristics of the region, achieving flexible forming of complex surfaces. Furthermore, to address the issue that light-load collaborative control strategies cannot adapt to the large load conditions of incremental forming, this invention designs a collaborative control mechanism with real-time collision avoidance and force / position hybrid feedback, ensuring stable and precise collaborative operation of multiple robots under high contact force and large deformation conditions. This expands the forming range while ensuring the forming accuracy and quality consistency of the components. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a four-robot collaborative processing system using the method of the present invention.

[0021] Figure 2 This is a schematic diagram of the structure of a three-robot collaborative processing system using the method of the present invention.

[0022] Figure 3 This is a schematic diagram of the structure of a robot used in the method of the present invention.

[0023] Figure 4 This is a flowchart illustrating the method of the present invention.

[0024] In the diagram: 1-Sheet metal; 2-Fixing and clamping assembly; 3-Sheet metal support device; 4-Support platform; 5-Robot; 6-Turntable; 7-Transmission section; 8-Tool head. Detailed Implementation

[0025] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0026] Example like Figure 1The illustration shows an example of a collaborative processing device using four robots 5 employing the method of the present invention, which is generally suitable for moldless progressive forming of rectangular or elongated sheet metal parts. In use, the sheet metal 1 to be processed is laid flat and positioned and clamped onto the sheet metal support device 3 in a predetermined manner. It is horizontally clamped by the fixed clamping assembly 2 (the sheet metal 1 is fixedly clamped to the platform of the sheet metal support device 3), with a clamping force ranging from 5-50 kN, applied through 60-80 circumferentially distributed bolts. If necessary, hydraulic / pneumatic support pads can be added at multiple points on the sheet metal support device 3 for fine-tuning of the clamping force. The four robots 5 are respectively mounted on the support columns or foundation around the worktable via a support platform 4. The support platform 4 is a rigid structure, positioned to the worktable by bolts and locating pins. The height and rigidity of the support platform 4 should be configured according to the size of the target component to ensure the stability of the robot 5's end effector during movement. Four processing robots 5 are distributed along the four rectangular sides of the sheet metal support device 3. One robot 5 is positioned on each of the two shorter sides, responsible for the end geometry and corner forming of that side; one robot 5 is positioned on each of the two longer sides, responsible for the continuous forming of the middle section of the longer side. This flexible progressive forming system prioritizes an adaptive partitioned parallel strategy based on multi-objective optimization. This strategy first extracts geometric features, including curvature changes, normal vector distribution, and contour boundaries, from the 3D digital model of the target component. Combined with mechanical parameters such as forming force prediction and material flow characteristics, a dynamic mapping relationship between geometric features and processing parameters is established through a multi-objective optimization algorithm, achieving adaptive partitioning of the processing area. Based on the geometric complexity and forming requirements of different partitions, differentiated driving modes and trajectory planning strategies are matched. For example, position control and planar expansion trajectories are used in high-load areas to ensure forming accuracy, while force control and layer-cutting contour trajectories are used in flat areas to improve forming efficiency, thereby achieving refined customization of the processing strategy for each partition. Each robot 5 performs progressive forming processing according to its assigned local trajectory. The trajectory type is adaptively selected based on the characteristics of the partition, including but not limited to: general layer-cutting trajectories, planar trajectories suitable for high-load areas, helical trajectories suitable for continuous curved surfaces, and combined trajectory modes for complex feature areas. Furthermore, a specific width of overlapping transition zone is set at the boundary between each partition, where trajectory transition coordination is implemented.The width of the overlapping transition zone is dynamically determined based on the geometric gradient of adjacent zones, material thickness variations, and robot kinematic constraints. The overlapping portion does not exceed 20% of the total projected area of ​​the forming region. Within the transition zone, a real-time optimization algorithm based on a dynamic response surface model is used. A multi-objective model is established using a support vector machine algorithm. This model comprehensively considers multiple factors such as the continuity of the target component's morphology, surface quality requirements, obstacle avoidance by multiple robot motion postures, and interference avoidance by the end effector. The feed rate, tool head posture, and forming force in the trajectory overlapping area are coordinated to ensure continuous material flow and smooth transition of surface indentations in the transition zone. Ultimately, this achieves seamless connection of the zone boundaries, and the uniformity of sheet 1 thickness remains within the allowable tolerance range.

[0027] like Figure 2 The illustration shows an example of collaborative processing using three robots (5) according to the method of the present invention. This method is suitable for processing annular or centrally symmetrical sheet metal components. The composition and function of each part in this example are as follows: Figure 1 The four robots 5 shown are identical, differing only in that each robot 5 covers its assigned sector area along a 120° equally spaced working range, suitable for the progressive forming of components such as circular cavities, discs, or annular skins. By varying the number of robots 5, the continuity of the processing area coverage and the system footprint can be effectively balanced. Figure 1 , Figure 2 Based on the structure shown, the method proposed in this invention can also be expanded to an array of 5, 6 or more robots as needed, thereby improving the parallelism of molding processing and the molding accuracy of sub-regions.

[0028] Figure 3For the purpose of this invention, a schematic diagram of a single-arm structure of a robot 5 is provided. It is recommended that each processing robot 5 adopt at least a 6-DOF articulated robot 5, with each arm having a rotating base, shoulder, elbow, wrist, and other joints. The trajectory tracking accuracy should be ≤0.2 mm, and the repeatability should be ≤±0.05-0.1 mm. Based on the load, contact force, and workpiece mass of the tool head 8, it is recommended that the rated load of a single robot 5 be selected as 16-100 kg, and the arm span be 0.8-3.0 m to cover large-sized workpieces. The robot 5 is specifically composed of a turntable 6, a transmission section 7, and a tool head 8 connected sequentially. The turntable 6 can be a mechanical turntable 6, or a turntable 6 with an encoder (resolution ≤0.01°) can be installed as needed to improve positioning flexibility. The transmission section 7 can specifically include drive and transmission structures such as joint reducers, servo motors, and encoders. Preferably, the robot 5 (with its controller) supports closed-loop speed control and force / torque feedforward control. The forming tool head 8 is the direct contact end for achieving progressive forming. The tool head 8 can be selected from, but is not limited to, the following shapes: hemispherical tool head 8 (radius 5-30 mm), roller-type forming head (diameter 20-80 mm), flexible ball head (with elastic padding to disperse local stress), or composite tool head 8 (with force sensor, temperature sensor, and replaceable contact end), etc., integrating multiple functions. Furthermore, the tool head 8 should have a quick-change interface and be able to withstand working loads. If necessary, a multi-dimensional force / torque sensor can also be integrated at the tool head 8 at the end of the robot 5 for real-time closed-loop adjustment.

[0029] Furthermore, each robot 5 is equipped with a unified scheduling multi-arm coordination controller (communication connection). This controller not only performs hierarchical path planning based on surface discretization, but also integrates a real-time collision detection algorithm and a force closed-loop control module. During collaborative operation, the controller dynamically monitors the position and force state of the end effector (tool head 8) of each robot 5. Through online trajectory optimization and speed coordination, it ensures smooth transition and stable forming even in asynchronous processing or boundary overlapping areas. An asynchronous control and distributed execution architecture is adopted to decouple the overall collaborative problem into independent local pose control for each robot and global collaborative constraint optimization. Based on real-time monitoring of the end effector pose, force state, and spatial relationships of each robot, the controller constructs a unified objective function that includes multi-dimensional indicators such as forming quality, processing efficiency, collision avoidance, and force-position tracking accuracy. Multi-objective trade-off decisions are made through an online rolling optimization algorithm. Unlike conventional centralized synchronous control or light-load collaborative control, this strategy is specifically designed for the large load disturbance and large deformation response characteristics of incremental forming. In the detection stage, an abnormal working condition rapid identification mechanism based on force / position hybrid perception is introduced. In the judgment stage, a hierarchical conflict resolution logic is adopted. In the implementation stage, distributed instruction scheduling is used to realize the asynchronous parallelism and dynamic coordination of the actions of each robot. In this way, the efficiency of multi-machine collaborative forming is maximized while ensuring system stability, and the thickness uniformity and geometric accuracy of the formed component are ensured.

[0030] like Figure 4 The diagram shown illustrates the processing flow of the method of this invention. By arranging multiple industrial robots on a workbench and equipping them with progressive forming tool heads, and using a multi-arm coordination controller for unified trajectory planning and motion synchronization, collaborative progressive forming of large sheet metal by multiple tool heads is achieved, thereby completing the manufacturing of large and complex components with high efficiency and high quality. Specifically, it includes the following steps: Step 1: Place the sheet material to be processed horizontally on the sheet material support device and use the fixing clamping components to secure it horizontally to ensure its overall stability during the processing.

[0031] Step 2: Based on the size and forming complexity of the target component, arrange multiple industrial robots around the workbench and install appropriate progressive forming tool heads at the end of each robot to build a collaborative working system.

[0032] Step 3: Based on the 3D model (such as CAD model) of the target component, perform global planning of the overall forming trajectory, and intelligently divide the overall surface into multiple processing sub-regions according to the geometric features such as surface curvature and depth. Then, assign collaborative processing areas and task sequences to each robot.

[0033] Step four involves performing global collision pre-detection and collaborative trajectory planning for each robot, and setting forming process parameters for each sub-region, such as pressing amount and feed speed, to achieve customized processing for each region.

[0034] Step 5: Start the system. All robots synchronously execute progressive forming according to the planned path. During the processing, the controller, based on real-time observation (tool head position and acceptance information), coordinates and fine-tunes the robot's motion trajectory through a collision avoidance algorithm, and dynamically optimizes the process parameters (such as compression amount) of each robot through force feedback data to maintain a reasonable distribution of forming force and optimize unreasonable process parameters online.

[0035] Step six: After the overall forming is completed, perform local precision correction and final quality inspection on the component to ensure that it meets the design specifications.

[0036] Furthermore, multiple robots specifically include at least two or more industrial robots, and the number and layout of robots can be flexibly configured according to the component size and forming complexity. For example, robots can be arranged at different workstations around the sheet metal to achieve symmetrical or asynchronous collaborative forming paths.

[0037] Furthermore, the tool head at the end of the robot is a flexible incremental forming tool. The structural forms that can be adopted include, but are not limited to, general-purpose tool heads used in traditional single-point and double-point incremental forming, such as hemispherical or cylindrical shapes. They are made of wear-resistant materials such as tool steel or cemented carbide to ensure the stability of the forming process and the tool life.

[0038] Furthermore, multi-robot collaborative progressive forming achieves intelligent task allocation and dynamic trajectory coordination through a multi-arm coordination controller. Specifically, based on the 3D model of the component, the target surface is divided into multiple forming sub-regions. Appropriate general-purpose toolheads (such as hemispherical, cylindrical, or roller-type) are assigned to each robot according to the geometric features and forming difficulty of different regions. Differentiated parameters for pressure, feed rate, and trajectory spacing are also defined, supporting asynchronous independent forming of each robot in different sub-regions. This improves overall efficiency while ensuring local forming accuracy.

[0039] Furthermore, the multi-arm coordinated controller possesses region adaptive planning capabilities. Based on the 3D model and geometric features of the component, it intelligently decomposes the target surface into multiple forming sub-regions and independently plans the most suitable forming strategy for each sub-region. This includes assigning different types of general-purpose toolheads to different regions (e.g., using a small-radius hemispherical head for deep cavity regions and a roller head for flat regions), and setting differentiated process parameters such as pressure, feed rate, and trajectory spacing. Each robot can then perform asynchronous parallel processing, improving overall efficiency while achieving precise control over the local geometry and thickness of the component.

[0040] Furthermore, the multi-robot system employs an integrated real-time collision avoidance cooperative control mechanism. The multi-arm coordination controller performs dynamic collision detection and trajectory optimization based on the kinematic models and real-time position feedback of each robot. At the trajectory planning and execution level, speed coordination and spatial interpolation ensure interference-free operation of multiple tool heads on complex trajectories, especially at processing area boundaries or tool head path intersections, enabling smooth and continuous collaborative work.

[0041] Furthermore, this solution employs a coordination strategy based on force / position hybrid control and dynamic feedback for its multi-robot system. Each robot's end effector is equipped with a multi-dimensional force sensor, and the multi-arm coordination controller monitors and integrates the forming force information from each tool head in real time. Through a force closed-loop control algorithm, the pressing amount or position of each robot is dynamically adjusted to balance the forming force distribution at multiple points, compensate for inconsistencies in sheet deformation, and thus ensure uniform and stable sheet deformation during high-load collaborative forming, thereby guaranteeing the dimensional accuracy and surface quality of the final formed part.

[0042] In summary, the present invention has the following advantages: (1) Through multi-robot collaborative operation, the limitation of the forming range of a single device is broken, and large and even super-large sheet metal components can be manufactured efficiently; (2) Multi-tool head synchronous forming significantly improves processing efficiency and effectively alleviates the problem of large springback caused by single-point cumulative forming; (3) The system does not require large special molds and has high flexibility, making it particularly suitable for efficient processing and manufacturing of small batches and customized large components; (4) Intelligent task allocation and real-time collaborative control are achieved through a multi-arm coordination controller, resulting in high forming accuracy, good consistency, and wide applicability.

[0043] In the method of this invention, each robot can independently or collaboratively perform local or overall forming tasks according to the geometric characteristics of the component, significantly improving forming efficiency. Compared with existing single-robot or machine tool forming methods, this invention has advantages such as a large forming range, high flexibility, no need for large molds, and strong adaptability, making it particularly suitable for low-cost and rapid manufacturing of large sheet metal components.

[0044] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for flexible progressive forming of large sheet metal parts based on multi-robot collaboration, characterized in that, Includes the following steps: The target component's 3D model is divided into several sub-regions based on its geometric features, and the tool head and forming process parameters of the robot corresponding to each sub-region are determined. Trajectory planning and motion synchronization are performed for each robot; dynamic collision detection is performed based on the real-time position feedback of each robot, and trajectory optimization is performed through coordinated planning of speed and trajectory; based on the real-time force feedback of each tool head, the molding process parameters of each robot are dynamically adjusted through a force / position hybrid control algorithm.

2. The method for flexible progressive forming of large sheet metal parts based on multi-robot collaboration according to claim 1, characterized in that, The geometric features of the target component's three-dimensional model include surface curvature and depth. Based on these different geometric features, the target component is divided into several sub-regions. The molding process parameters include molding trajectory, pressing amount, feed speed and trajectory spacing. By setting differentiated molding process parameters, each robot can perform asynchronous parallel processing in different sub-regions.

3. The method for flexible progressive forming of large sheet metal parts based on multi-robot collaboration according to claim 1, characterized in that, The speed and trajectory coordination planning includes: speed coordination and spatial interpolation of the tool heads of adjacent robots.

4. The method for flexible progressive forming of large sheet metal parts based on multi-robot collaboration according to claim 1, characterized in that, The robot in question is an articulated robot with at least 6 degrees of freedom; The tool head includes a hemispherical tool head, a cylindrical forming head, or a roller forming head.

5. The method for flexible progressive forming of large sheet metal parts based on multi-robot collaboration according to claim 4, characterized in that, The robot's trajectory tracking accuracy is ≤0.2 mm, and its repeatability is ≤±0.05-0.1 mm; the rated load of a single robot is 16-100 kg, and its arm span is 0.8-3.0 m. The tool head has a multi-dimensional force / torque sensor integrated at its end; wherein the radius of the hemispherical tool head is 5-30 mm, and the diameter of the roller-type forming head is 20-80 mm. The surface of the tool head is further provided with an elastic pad layer to form a flexible ball head; and / or, the tool head composite tool head is further integrated with a force sensor and a temperature sensor to form a composite tool head.

6. The method for flexible progressive forming of large sheet metal parts based on multi-robot collaboration according to claim 1, characterized in that, The sheet material to be processed is clamped on the sheet material support device for progressive forming processing, and each robot is arranged around the sheet material to be processed. At least two robots are provided. The number of sub-regions is consistent with the number of robots.

7. The method for flexible progressive forming of large sheet metal parts based on multi-robot collaboration according to claim 6, characterized in that, The sheet metal support device horizontally clamps the sheet metal to be processed through a fixed clamping assembly, with a clamping force of 5-50kN.

8. The method for flexible progressive forming of large sheet metal parts based on multi-robot collaboration according to claim 7, characterized in that, The aforementioned fixing and clamping assembly applies clamping force to the sheet metal to be processed through 60-80 bolts arranged circumferentially.

9. A method for flexible progressive forming of large sheet metal parts based on multi-robot collaboration according to claim 7, characterized in that, The sheet metal support device is also equipped with a hydraulic support pad and / or a pneumatic support pad for fine-tuning the clamping force.

10. A method for flexible progressive forming of large sheet metal parts based on multi-robot collaboration according to claim 1, characterized in that, The method further includes: after completing the overall forming of the sheet material to be processed, performing local precision correction and quality inspection to obtain the target component.

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