Variable stiffness laminated plate laying track generation method fusing stress evaluation function

Abstract

The invention discloses a variable stiffness laminated plate laying track generation method fusing a stress evaluation function. Specifically, the invention provides a variable stiffness laminated plate automatic fiber placement path generation method based on stress information, and the method comprises the following steps: (1) carrying out static strain analysis on a composite material laminated plate by adopting finite element software to obtain bearing information of a component; (2) establishing a tow placement head motion model, and limiting a feasible region of a robot speed sampling interval by limiting a tow curvature threshold value and an initial laying direction of a laying layer; (3) aiming at an evaluation function of a composite material automatic fiber laying improved dynamic window method, introducing a main stress direction and path direction deviation, a path local curvature threshold value and a target direction evaluation function; (4) generating an optimal laying track of the laminated plate by using a dynamic window method of an improved evaluation function, and fully laying the track; the problems that an existing variable-stiffness laminated plate laying track is simple in design, and the performance of tows cannot be exerted through a single initial path are solved.

Description

Technical Field

[0001] The invention relates to a method for generating a wire laying path for a composite material variable-rigidity laminate, and belongs to the field of composite material parts manufacturing. Background Art

[0002] Fiber-reinforced composite variable stiffness components with light weight and high strength have the advantages of fast manufacturing and good mechanical properties, and are widely used in engineering fields such as transportation, aerospace, etc. Since the engineering application environment of composite variable stiffness components is relatively complex and diverse, problems such as insufficient bearing capacity and stability are prone to occur in the actual process, especially since composite components correspond to more working conditions, it is necessary to pursue light weight and high strength performance during design.

[0003] At present, the design ideas of composite laminates include two models: constant stiffness and variable stiffness. The existing performance optimization ideas of composite laminates include ply angle optimization of fixed-angle tow paths and path optimization of variable-angle tow paths, both of which can improve the mechanical properties of composite laminates. Based on different working conditions, laminates with different optimization results can be produced to match the load-bearing requirements and working conditions.

[0004] The composite material ply is laid out by a number of prepreg tows, and the centerline trajectories of these prepreg tows can be obtained by translating or parallelizing the centerline of a tow path, and the centerline of this path is called the reference path. Conventional reference paths usually use straight lines, and the ply obtained by the straight path cannot design the fiber orientation within the ply, resulting in a small design space for the laminate structure composed of straight plies. In order to make full use of the directionality of composite materials in the process of laminate optimization, there are also variable angle laminates based on regular curves such as linear variable angles, sine curves, and Bezier curves. Whether it is a conventional straight fixed angle path or a variable angle path based on various curves, none of them makes fine use of the full performance of the fiber, and the determining factors of the path generation algorithm are too single. Therefore, a new initial path algorithm is currently needed to improve the quality of fiber laying.

[0005] Investigations have shown that the automatic wire placement path for traditional large composite laminates is relatively simple, and the laminates produced do not fully demonstrate the advantages of fiber-reinforced composite materials. There is also no wire placement path design that can finely utilize the variable angle of the fiber to adapt to different working conditions. Summary of the invention

[0006] In order to overcome the technical defects of existing composite laminates, such as the simple automatic wire laying path, the inability to fully exert the advantages of fiber-reinforced composite materials, and the difficulty in fully exerting the mechanical properties of fiber bundles, the present invention invents a new automatic wire laying path generation algorithm for composite variable-angle laminates. The method includes: establishing a mechanical simulation model of composite variable-angle laminates, establishing an actual load-bearing information model for each layer; establishing a discrete grid model for the layer; establishing an automatic wire laying initial path algorithm; and establishing a full-lay laying path generation method that takes into account global load-bearing performance.

[0007] The present invention develops a laying path generation method for variable stiffness laminates based on an improved dynamic window method, and the specific steps are as follows:

[0008] S1: Extract the composite laminate and import it into the finite element for meshing, apply boundary conditions to it, set initial values ​​and submit it for finite element analysis calculation;

[0009] S2: Obtain the node information and unit information of the laminate ply, and establish the topological relationship of points, lines and surfaces; wherein the node information includes the node number, node coordinates and the unit number to which the node belongs, the edge information includes the two points of the edge and the unit number to which they belong, and the unit information includes the unit number and the node number corresponding to the unit;

[0010] S3: Obtain the stress information of the laminate plies, import the ply mesh and node stress information into Matlab, establish a unified relationship between nodes, units, and stress, first calculate the maximum principal stress of each node, and then obtain the maximum principal stress direction of any point inside the unit through interpolation processing.

[0011] S4: Establish the robot motion model of the wire laying head: The motion trajectory of the wire laying head is reflected by the horizontal and vertical coordinates, velocity and acceleration of the wire laying head robot, combined with time t. Since the displacement of the wire laying head in adjacent moments (ms) is small, the motion of the wire laying head robot can be approximately regarded as uniform linear motion.

[0012] S5: Establish velocity sampling: The velocity vector space of the dynamic window algorithm consists of allowable velocities, which are subject to restrictions such as the maximum and minimum linear and angular velocities of the robot.

[0013] S7: Initialization: Import the constructed simulation map, i.e. the laying area, and set the initial position of the laying head as well as the speed and acceleration range.

[0014] S8: First, for the velocity vector space v r The linear velocity v and angular velocity ω in are discretized to obtain a series of discrete velocities (v, ω). Then, the paths corresponding to all velocities within a period of time are simulated according to the robot kinematic model.

[0015] S9: Improved algorithm evaluation function: introduce the deviation between the principal stress direction and the path direction, and the path local curvature threshold as the evaluation function. Use the improved evaluation function to score the path at the simulation point; obtain the optimal path point speed distribution and use it as the next moment's wire laying head moving speed.

[0016] S10: The fiber placement head runs according to the optimal path calculated in real time until it reaches the map boundary, that is, the placement head reaches the fiber placement boundary and stops. This path is evaluated based on the improved evaluation function to have a small curvature and a smooth path, and the path is relatively consistent with the principal stress direction of the local position, which can give full play to the performance of the fiber bundle.

[0017] S11: The normal direction of the optimal path trajectory is used as the path offset direction, and the product of the number of tow placements and the tow width is used as the offset distance to offset the optimal path until the laminate is completely covered.

[0018] S12: According to the obtained movement trajectory of the wire laying head, the positions of the entry point, the wire feeding point, the cutting point and the retraction point in the automatic wire laying process are determined.

[0019] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the present invention is described in detail below with drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the laying path generation framework of variable stiffness laminates;

[0021] Figure 2 It is a schematic diagram of the simulation calculation results of the laminate model;

[0022] Figure 3 It is a schematic diagram of stress state analysis of plane elements;

[0023] Figure 4 It is a schematic diagram of the placement head velocity vector space;

[0024] Figure 5 It is a schematic diagram of the establishment of the laminate model and algorithm map;

[0025] Figure 6 It is a schematic diagram of the instantaneous sampling path of the wire laying head;

[0026] Figure 7 It is a schematic diagram of the azimuth evaluation function;

[0027] Figure 8 This is a schematic diagram of the optimal result of the wire laying head path;

[0028] Fig. 9 It is a schematic diagram of the full laying path of the tow; DETAILED DESCRIPTION

[0029] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the specific embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific implementation disclosed below.

[0030] The present invention develops a laying path generation method for variable stiffness laminates based on an improved dynamic window method. The algorithm framework is as follows: Figure 1 As shown, the following steps are included:

[0031] S1: Extract the composite laminate and import it into the finite element for meshing. Apply boundary conditions to it, set initial values ​​and submit it for finite element analysis. The calculation results are as follows: Figure 2 As shown;

[0032] S2: Obtain the node information and unit information of the laminate ply, and establish the topological relationship of points, lines and surfaces; wherein the node information includes the node number, node coordinates and the unit number to which the node belongs, the edge information includes the two points of the edge and the unit number to which they belong, and the unit information includes the unit number and the node number corresponding to the unit;

[0033] S3: Obtain the stress information of the laminate plies, import the ply mesh and node stress information into Matlab, establish a unified relationship between nodes, units, and stresses, first calculate the maximum principal stress of each node, and then obtain the maximum principal stress direction of any point in the unit by interpolation. The interpolation method is as follows: Figure 3 shown.

[0034] S4: Establish the robot motion model of the wire laying head: The motion trajectory of the wire laying head is reflected by the horizontal and vertical coordinates, velocity and acceleration of the wire laying head robot, combined with time t. Since the displacement of the wire laying head in adjacent moments (ms) is small, the motion of the wire laying head robot can be approximately regarded as uniform linear motion. The robot motion model of the wire laying head is as follows:

[0035] S5: Establish velocity sampling: The velocity vector space of the dynamic window algorithm consists of the permissible velocity, which is subject to the robot's maximum and minimum linear velocity and angular velocity. The velocity sampling vector space is as follows: Figure 4 shown. The white area is the feasible area V s , subject to the trajectory curvature threshold and laying direction restrictions, must meet: V s ={(v,ω)|Dmin ≤D≤D max , K min ≤K≤K max} D=|v-θ| Where: D is the deviation between the laying speed direction and the principal stress direction, K is the turning radius of the laying head, i.e. the curvature radius of the laying path, θ is the principal stress direction at the current position of the laying head, It is the current linear acceleration of the wire laying head. V a The maximum speed range of the wire laying head must meet the following requirements: V a ={(v,ω)|v min ≤v≤v max ,ω min ≤ω≤ω max} Where: v min With v max is the minimum and maximum achievable linear speed of the wire laying head, ω min With ω max are the minimum and maximum achievable angular velocities of the wire laying head. V d The speed range of the wire laying head at the next moment must meet the following requirements: Where: is the maximum linear deceleration of the wire laying head; is the maximum linear acceleration of the wire laying head; The robot's maximum angular deceleration; The maximum angular acceleration of the robot. The final speed sampling range of the fiber placement head is the intersection of the following three values: V r =V a ∩V s ∩V d

[0036] S7: Initialization - importing the constructed simulation map, i.e. the laying area, and setting the initial position, speed, acceleration range, and initial laying direction of the wire laying head.

[0037] S8: First, for the velocity vector space v r The linear velocity v and angular velocity ω in are discretized to obtain a series of discrete velocities (v, ω). Then, the paths corresponding to all velocities within a period of time are simulated according to the robot kinematic model.

[0038] S9: Improved algorithm evaluation function: Introduce the deviation between the principal stress direction and the path direction, and the path local curvature threshold as the evaluation function. And change the original Heading target evaluation function to the target direction evaluation function. The improved angle Heading evaluation function is as follows: Figure 7 As shown. The improved evaluation function is used to score the path at the simulation location to obtain the optimal path point speed distribution, which is used as the robot moving speed at the next moment. The calculation formula of the Heading evaluation function is: Heading i (v,ω)=90°-θ,i=1,2 Where: θ is the deviation between the speed direction and the initial direction when the wire laying head moves to the sub-target point and the current position at a certain speed

[0039] S10: The wire placement head runs according to the optimal path calculated in real time until it reaches the map boundary, that is, the placement head stops at the wire placement boundary. The optimal path is as follows: Figure 8 As shown, this path is evaluated as a path with a small curvature and a smooth path based on the improved evaluation function, and the path is relatively consistent with the principal stress direction at the local position, which can give full play to the performance of the fiber tow.

[0040] S11: The normal direction of the optimal path trajectory is used as the path offset direction, and the product of the number of tows placed and the tow width is used as the offset distance. The optimal path is offset until the laminate is completely covered. The schematic diagram of the full-laying path is shown in Fig. 9 shown.

[0041] S12: According to the obtained movement trajectory of the wire laying head, the positions of the entry point, the wire feeding point, the cutting point and the retraction point in the automatic wire laying process are determined.

Claims

1. A method for generating a laying path for a variable stiffness laminate based on an improved dynamic window method, characterized in that: The method comprises the following steps: S1: Extract the composite laminate and import it into the finite element for meshing, apply boundary conditions to it, set initial values ​​and submit it for finite element analysis calculation; S2: Obtain the node information and unit information of the laminate ply, and establish the topological relationship of points, lines and surfaces; wherein the node information includes the node number, node coordinates and the unit number to which the node belongs, the edge information includes the two points of the edge and the unit number to which they belong, and the unit information includes the unit number and the node number corresponding to the unit; S3: Obtain the stress information of the laminate plies, import the ply mesh and node stress information into Matlab, establish a unified relationship between nodes, units, and stress, first calculate the maximum principal stress of each node, and then obtain the maximum principal stress direction of any point inside the unit through interpolation processing. S4: Establish the robot motion model of the wire laying head: The motion trajectory of the wire laying head is reflected by the horizontal and vertical coordinates, velocity and acceleration of the wire laying head robot, combined with time t. Since the displacement of the wire laying head in adjacent moments (ms) is small, the motion of the wire laying head robot can be approximately regarded as uniform linear motion. S5: Establish velocity sampling: The velocity vector space of the dynamic window algorithm consists of allowable velocities, which are subject to restrictions such as the maximum and minimum linear and angular velocities of the robot. S7: Initialization - Import the constructed simulation map, i.e. the laying area, and set the initial position of the laying head as well as the speed and acceleration range. S8: First, the linear velocity v and angular velocity ω in the velocity vector space vr are discretized to obtain a series of discrete velocities (v, ω). Then, the paths corresponding to all velocities within a period of time are simulated according to the robot kinematic model. S9: Improved algorithm evaluation function: introduce the deviation between the principal stress direction and the path direction, and the path local curvature threshold as the evaluation function. Use the improved evaluation function to score the path at the simulation point; obtain the optimal path point speed distribution and use it as the next moment's wire laying head moving speed. S10: The fiber placement head runs according to the optimal path calculated in real time until it reaches the map boundary, that is, the placement head reaches the fiber placement boundary and stops. This path is evaluated based on the improved evaluation function to have a small curvature and a smooth path, and the path is relatively consistent with the principal stress direction of the local position, which can give full play to the performance of the fiber bundle. S11: The normal direction of the optimal path trajectory is used as the path offset direction, and the product of the number of tow placements and the tow width is used as the offset distance to offset the optimal path until the laminate is completely covered. S12: According to the obtained movement trajectory of the wire laying head, the positions of the entry point, the wire feeding point, the cutting point and the retraction point in the automatic wire laying process are determined.

2. The method for generating a laying path for a variable stiffness laminate based on an improved dynamic window method according to claim 1, characterized in that: In step S3, the average direction of the element principal stress is obtained by interpolation method, and the specific steps are as follows: S3: Obtain the stress information of the laminate plies, import the ply mesh and node stress information into Matlab, establish a unified relationship between nodes, units, and stress, first calculate the maximum principal stress of each node, and then obtain the maximum principal stress direction of any point in the unit through interpolation.

3. The method for generating a laying path for a variable stiffness laminate based on an improved dynamic window method according to claim 1, characterized in that: In step S5, the feasible domain of the fiber placement head speed sampling space is subject to the fiber bundle curvature threshold limit and the placement direction limit. The specific steps are as follows: S51: Establish velocity sampling: The velocity vector space of the dynamic window algorithm consists of permissible velocities, which are subject to the robot's maximum and minimum linear and angular velocities. The feasible velocity range is subject to the trajectory curvature threshold and placement direction, and must satisfy the following requirements: V s ={(v,ω)|D min ≤D≤D max ,K min ≤K≤K max } D=|v-θ| Where: D is the deviation between the laying speed direction and the principal stress direction, K is the turning radius of the laying head, i.e. the curvature radius of the laying path, θ is the principal stress direction at the current position of the laying head, It is the current linear acceleration of the wire laying head. S52: Va is the maximum speed range of the wire laying head, which must meet the following requirements: V a ={(v,ω)|v min ≤v≤v max ,ω min ≤ω≤ω max } Where: v min With v max is the minimum and maximum achievable linear speed of the wire laying head, ω min With ω max are the minimum and maximum achievable angular velocities of the wire laying head. S53: Vd is the speed range of the wire laying head at the next moment, which must meet the following requirements: Where: is the maximum linear deceleration of the wire laying head; is the maximum linear acceleration of the wire laying head; The robot's maximum angular deceleration; The maximum angular acceleration of the robot. S54: The final speed sampling range of the fiber placement head is the intersection of the following three values: V r =V a ∩V s ∩V d。 4. The method for generating a laying path for a variable stiffness laminate based on an improved dynamic window method according to claim 1, characterized in that: In step S7, the preset laying range is the laminate expansion area, and the specific steps are as follows: S7: Initialization - importing the constructed simulation map, i.e. the laying area, and setting the initial position, speed, acceleration range, and initial laying direction of the wire laying head.

5. The method for generating a laying path for a variable stiffness laminate based on an improved dynamic window method according to claim 1, characterized in that: In step S9, the dynamic window method evaluation function is improved, and the specific steps are as follows: S9: Improved algorithm evaluation function: Introduce the deviation between the principal stress direction and the path direction, and the path local curvature threshold as the evaluation function. And change the original Heading target evaluation function to the target direction evaluation function. Use the improved evaluation function to score the path at the simulation, obtain the optimal path point speed distribution, and use it as the robot moving speed at the next moment. The calculation formula of the Heading evaluation function is: Heading i (v,ω)=90°-θ,i=1,2 Where: θ is the deviation between the speed direction and the initial direction when the wire laying head runs to the sub-target point and the current position at a certain speed.

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