CN110773738B - Laser scanning path regional planning method based on polygon geometric feature recognition - Google Patents

Abstract

The laser scanning path sub-regional planning method based on polygon geometric feature recognition, takes the single-layer slice of the part as the object, identifies and extracts each polygonal connected area in the current slice, obtains the principal axis direction of the polygonal connected area, and then uses the projection method to obtain the The span of the polygon connected area in the direction of the main axis and the direction perpendicular to the main axis. The polygon connected area whose span in both directions is greater than the user-set threshold is planned by the island scanning method, and the polygonal connected area that is not satisfied is planned by the parallel scan method. scan path. The invention can avoid island scanning path planning for small connected areas, improve calculation efficiency, processing efficiency and forming quality of small connected areas; effectively avoid the appearance of excessively long scanning lines, reduce part deformation; Temperature field; reduce the idle stroke of laser jump in actual processing, and improve processing efficiency.

Description

Subregional planning method of laser scanning path based on polygon geometric feature recognition

technical field

The invention belongs to the technical field of laser selective melting and additive manufacturing, and in particular relates to a laser scanning path sub-regional planning method based on polygon geometric feature recognition.

Background technique

In recent years, laser selective melting technology has received extensive attention and rapid development, showing broad application prospects and technical advantages in aviation, aerospace, mold, medical and other fields. It slices and stratifies the three-dimensional model of the part through special software, obtains the profile data of each section, and uses a high-energy laser beam to selectively act on the metal powder according to a certain scanning method, so that the scanned powder is melted and solidified. , to manufacture 3D solid parts.

For the laser selective melting technology, the heat generated by the powder during the rapid melting and solidification process and its transfer have a direct impact on the stress concentration and the deformation and cracking of the parts. Therefore, a reasonable laser scanning path can effectively manage and control the heat, so as to balance the temperature field of the formed parts, reduce the stress concentration, prevent deformation and cracking, and improve the forming quality of the parts. For example, the island scanning strategy proposed by Concept Laser divides the processing area of each layer of the model into multiple island regions, and uses the random exposure strategy to process each island in turn, which greatly reduces the generation of internal stress during processing. However, if island scanning is used in small areas, it will not only reduce the calculation efficiency of the scanning path and the processing efficiency of the parts, but also easily form too short scanning lines, resulting in frequent switching of the laser, and it is difficult to control the overlap between the islands, which will affect the final forming. quality.

With the expansion of the application range of laser selective melting technology, the processed parts are becoming more and more complex. The size and number of polygonal connected areas of each layer slice of the part model are constantly changing. A single scanning method is no longer suitable for the processing and manufacturing of the entire model. Therefore, It is necessary to use an appropriate scanning method to plan the scanning path according to the geometric feature information of the polygonal connected area of each slice to ensure the final forming quality of the part.

SUMMARY OF THE INVENTION

Aiming at the deficiencies in the prior art, the present invention provides a laser scanning path sub-regional planning method based on polygon geometric feature recognition. The method can identify and extract polygonal connected regions in slices, and then decide the appropriate scanning method for path planning according to the geometric information of the connected regions, which can effectively ensure the calculation efficiency of the scanning path and the processing efficiency of the parts, and can balance the temperature field in the forming process of the parts. , to ensure the forming quality of parts.

To achieve the above object, the present invention adopts the following technical solutions:

The laser scanning path sub-regional planning method based on polygon geometric feature recognition is characterized in that it includes the following steps:

Step 1: Input the slice information of all layers of the 3D model of the part, and determine the scanning distance d and the island side length L according to the actual manufacturing needs;

Step 2: Read the minimum span _Sp required by the island scanning method for the connected region defined by the user;

Step 3: Read the contour polygons in the single-layer slice, determine the inclusion relationship between the contours, and construct a contour tree structure according to the inclusion relationship between the contours and the number of times they are included, where the number of times the outer contour is included by other contours is an even number , the number of times the inner contour is contained by other contours is odd;

Step 4: Use the contour tree structure to extract each polygonal connected area, each polygonal connected area contains an outer contour and N inner contours, N ≥ 0, and the outer contour in each polygonal connected area is contained more frequently than its inner contour. contains less than 1;

Step 5: Taking the polygon connected area as the object, obtain the main axis direction of the current polygon connected area;

Step 6: Call the outer contour of the connected area of the current polygon, use the projection method to obtain the projection values of all contour vertices in the main axis direction and the direction perpendicular to the main axis, and calculate the span S ₁ and S ₂ , by comparing S ₁ and S ₂ with _Sp respectively, carry out scanning path planning of the polygonal connected area;

Step 7: Read the connected regions of each polygon in turn, and complete the scanning path planning of the current slice layer;

Step 8: Traverse the slice information of the entire part model, complete the planning of the laser scanning path of the part, and output the scanning path.

In order to optimize the above technical solutions, the specific measures taken also include:

Further, in step 3, the ray method is used to determine the inclusion relationship between the contours.

Further, in step 5, the covariance matrix is used to obtain the principal axis direction of the connected region of the current polygon.

Further, in step 6, the spans S ₁ and S ₂ of the connected region of the current polygon in two directions are obtained by the difference between the maximum and minimum values of the projection values, and S ₁ and S ₂ are compared with S _p respectively, if both are greater than S _p , then For the polygonal connected area, use island scanning to plan the path, otherwise use parallel scanning to plan the path; when planning the scanning path, the scanning direction is determined by the spindle direction.

Further, when using the parallel scanning method to plan the path, after the slice of the odd-numbered layer obtains the principal axis direction of the polygonal connected region, the rotation angle θ is used as the scanning direction; after the slice of the even-numbered layer obtains the principal axis direction of the polygonal connected region, the The rotation angle (180°-θ) is then used as the scanning direction, so as to ensure that the scanning directions of adjacent layers cross each other.

Further, when planning the path using the island-type scanning method, each island adopts parallel scanning path planning, and the scanning directions of adjacent islands are perpendicular to each other; after the slice of the odd-numbered layer obtains the main axis direction of the polygonal connected area, it is rotated by the angle θ. As the scanning direction of one of the basic islands, the scanning direction of this basic island is used to derive the scanning directions of other islands; after the slice of the even-numbered layers obtains the main axis direction of the polygonal connected area, it is rotated by an angle (180°-θ) As the scanning direction of one of the basic islands, the scanning directions of the other islands are derived from the scanning direction of this basic island, thereby ensuring that the scanning directions of adjacent layers intersect each other.

The beneficial effects of the present invention are:

1. The present invention takes the polygonal connected region as the object to carry out scanning path planning, and after obtaining the main axis direction of the connected region, the projection method is used to obtain the span of the polygonal connected region in the main axis direction and the vertical direction of the main axis, respectively, and the span threshold defined by the user is used. It is possible to avoid island scanning path planning for small connected areas, and improve computing efficiency, processing efficiency and forming quality of small connected areas;

2. The present invention takes the polygonal connected area as the object to carry out scanning path planning, and determines the scanning direction by obtaining the main axis direction of the polygonal connected area, which can effectively avoid the appearance of excessively long scanning lines and reduce the amount of deformation of parts;

3. The present invention regards the rotation angle θ of the main axis direction of the polygonal connected area of odd-numbered layers as the scanning direction, and the rotation angle of the main axis direction of the polygonal connected area of even-numbered layers (180°-θ) as the scanning direction to ensure that the scanning directions of adjacent layers are mutually Cross, can ensure the overlap between layers and balance the temperature field;

4. The present invention takes the polygonal connected area as the object for scanning path planning, which reduces the idle travel of laser jumping in actual processing and improves the processing efficiency.

Description of drawings

FIG. 1 is a schematic flowchart of scanning path planning according to the present invention.

FIG. 2 is an exemplary diagram of a model for scanning path planning according to the present invention.

3a to 3b are schematic diagrams of scanning paths obtained by using the method of the present invention for the model shown in FIG. 2, wherein FIG. 3a shows island scanning for large-area bases, and FIG. 3b shows parallel scanning for lattice filling parts.

4 is a schematic diagram of a scanning path obtained by using the method of the present invention for a slice including a large-area polygonal connected area and a small-area polygonal connected area.

Detailed ways

The present invention will now be described in further detail with reference to the accompanying drawings.

The invention discloses a laser scanning path sub-regional planning method based on polygon geometric feature recognition. As shown in FIG. 1 , the method includes: taking a single-layer slice of a part as an object, identifying and extracting each polygonal connected area in the current layer slice, and finding After taking the main axis direction of the polygonal connected region, use the projection method to obtain the span of the polygonal connected region in the main axis direction and the direction perpendicular to the main axis, respectively. Scanning path, the unsatisfied polygonal connected area uses parallel scanning to plan the scanning path. Wherein, when the island type scanning path planning is adopted, each island adopts parallel scanning path planning, and the scanning directions of adjacent islands are perpendicular to each other. In addition, by rotating the main axis directions of the polygonal connected regions of the parity layers by different angles as the scanning directions, it is ensured that the scanning directions of adjacent layers intersect each other. The method specifically includes the following steps:

Step 1: Input the slice information of all layers of the 3D model of the part, and determine the scanning distance d and the island side length L according to the actual manufacturing needs.

Step 2: Read the minimum span S required by the island scanning method for the user-defined connected area. .

Step 3: Read the single-layer slice contour polygon, use the ray method to determine the inclusion relationship between the contours, and build a contour tree structure according to the inclusion relationship between each contour and the number of times it is included, where the number of times the outer contour is included by other contours is Even numbers (including 0), the inner contour is included an odd number of times.

Step 4: Use the contour tree structure to extract each polygonal connected area. Each polygonal connected area contains an outer contour and N inner contours (N ≥ 0). From the perspective of the contour tree, the outer contour and its sub-contours constitute a connected region.

Step 5: Taking the polygon connected area as the object, use the covariance matrix to obtain the principal axis direction of the current polygon connected area.

Step 6: Retrieve the outer contour of the connected area of the current polygon, use the projection method to obtain the projection values of all contour vertices in the main axis direction and the direction perpendicular to the main axis, and obtain the current connected area in the two directions by the difference between the maximum and minimum values of the projection values. The spans S ₁ and S ₂ of , compare S ₁ and S ₂ with _Sp respectively, and if both are greater than _Sp , plan the path by island scanning method for the polygonal connected area, otherwise use parallel scanning method to plan the path. When planning the scan path, the scan direction is determined by the spindle direction.

Step 7: Read the connected regions of each polygon in turn, and complete the scanning path planning of the current slice layer.

Step 8: Traverse the slice information of the entire part model, complete the planning of the laser scanning path of the part, and output the scanning path.

Wherein, when the path is planned by the island-type scanning method, each island adopts parallel scanning path planning, and the scanning directions of adjacent islands are perpendicular to each other. After obtaining the principal axis direction of the connected region for the slices of odd-numbered layers, the rotation angle θ is taken as the scanning direction of the connected region or the scanning direction of the basic islands in the connected region. After obtaining the principal axis direction of the connected area from the slices of the even-numbered layers, the rotation angle (180°-θ) is used as the scanning direction of the connected area or the scanning direction of the basic island in the connected area, so as to ensure the corresponding connected area or The scanning directions of the islands cross each other.

FIG. 2 is an exemplary diagram of a model for scanning path planning according to the present invention. The slices obtained at the base part are large-area polygonal connected areas, as shown in the lower right part of Figure 2; the slices obtained at the lattice filling part are multiple small-area polygonal connected areas, as shown in the upper right part of Figure 2.

FIG. 3 is a schematic diagram of a scanning path obtained by using the method of the present invention for the model shown in FIG. 2 . For the large-area base, the island scanning method is used, as shown in Figure 3a; for the lattice filled part, the parallel scanning method is used, as shown in Figure 3b.

FIG. 4 is a schematic diagram of a scanning path obtained by the method of the present invention for a slice including a large-area polygonal connected area and a small-area polygonal connected area. Among them, A shows the small-area connected area, and the scanning path planning is carried out by using the parallel scanning method; B shows the large-area connected area, and the scanning path planning is carried out by using the island scanning method.

It should be noted that the terms such as "up", "down", "left", "right", "front", "rear", etc. quoted in the invention are only for the convenience of description and clarity, and are not used for Limiting the applicable scope of the present invention, the change or adjustment of the relative relationship shall be regarded as the applicable scope of the present invention without substantially changing the technical content.

The above are only the preferred embodiments of the present invention, and the protection scope of the present invention is not limited to the above-mentioned embodiments. For example, other features of the polygonal connected area can be identified to plan other scanning methods, all of which belong to the technical solutions of the present invention All belong to the protection scope of the present invention. It should be pointed out that for those skilled in the art, some improvements and modifications without departing from the principle of the present invention should be regarded as the protection scope of the present invention.

Claims (4)

1. a laser scanning path subregional planning method based on polygon geometric feature recognition, is characterized in that, comprises the steps: Step 1: Input the slice information of all layers of the 3D model of the part, and determine the scanning distance d and the island side length L according to the actual manufacturing needs; Step 2: Read the minimum span _Sp required by the island scanning method for the connected region defined by the user; Step 3: Read the contour polygons in the single-layer slice, determine the inclusion relationship between the contours, and construct a contour tree structure according to the inclusion relationship between the contours and the number of times they are included, where the number of times the outer contour is included by other contours is an even number , the number of times the inner contour is contained by other contours is odd; Step 4: Use the contour tree structure to extract each polygonal connected area, each polygonal connected area contains an outer contour and N inner contours, N ≥ 0, and the outer contour in each polygonal connected area is contained more frequently than its inner contour. contains less than 1; Step 5: Taking the polygon connected area as the object, obtain the main axis direction of the current polygon connected area; Step 6: Call the outer contour of the connected area of the current polygon, use the projection method to obtain the projection values of all contour vertices in the main axis direction and the direction perpendicular to the main axis, and calculate the span S ₁ and S ₂ , by comparing S ₁ and S ₂ with _Sp respectively, the scanning path planning of the connected area of the polygon is carried out; in step 6, the span of the connected area of the current polygon in two directions is obtained by the difference between the maximum and minimum values of the projection values S ₁ and S ₂ , compare S ₁ and S ₂ with _Sp respectively, if both are greater than _Sp , then use island scanning to plan the path for the polygonal connected area, otherwise use parallel scanning to plan the path; when planning the scanning path , the scanning direction is determined by the direction of the main axis; when planning the path using the island scanning method, each island is planned with a parallel scanning path, and the scanning directions of adjacent islands are perpendicular to each other; after the slice of odd-numbered layers obtains the main axis direction of the polygonal connected area, the Its rotation angle θ is used as the scanning direction of one of the basic islands, and then the scanning direction of the other island is derived from the scanning direction of this basic island; after the slice of the even-numbered layer obtains the main axis direction of the polygonal connected area, its rotation angle (180 °-θ) as the scanning direction of one of the basic islands, and then derive the scanning directions of other islands from the scanning direction of this basic island; thus ensuring that the scanning directions of adjacent layers intersect each other; Step 7: Read the connected regions of each polygon in turn, and complete the scanning path planning of the current slice layer; Step 8: Traverse the slice information of the entire part model, complete the planning of the laser scanning path of the part, and output the scanning path. 2. the laser scanning path subregional planning method based on polygon geometric feature recognition as claimed in claim 1, it is characterized in that: in step 3, at first utilize outline bounding box size to carry out presort to outline, then combine coordinate extreme value method and The ray method judges the inclusion relationship between contours. 3. The laser scanning path subregional planning method based on polygon geometric feature recognition as claimed in claim 1, characterized in that: in step 5, the covariance matrix is used to obtain the principal axis direction of the connected region of the current polygon. 4. the laser scanning path subregional planning method based on polygon geometric feature recognition as claimed in claim 1, is characterized in that: when adopting parallel scanning mode to plan path, after the slice of odd-numbered layer obtains the principal axis direction of polygonal connected area, will The rotation angle θ is used as the scanning direction; after obtaining the principal axis direction of the polygonal connected region for slices of even-numbered layers, the rotation angle (180°-θ) is used as the scanning direction, so as to ensure that the scanning directions of adjacent layers intersect each other.

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