Cavity component trajectory planning method based on wall thickness data

Abstract

The invention discloses a cavity component trajectory planning method based on wall thickness data, particularly relates to a method for completing a thin-walled workpiece digital-analog tool path trajectory planning task by taking the wall thickness of a thin-walled workpiece as a constraint condition based on 3D scanning point cloud data and a digital-analog registration comparison result, and belongs to the technical field of CAD / CAPP / CAM. Comprising the following steps: step 1, carrying out point-by-point thickness measurement on a cavity model, firstly calibrating a key measurement area, grading and planning thickness measurement points according to geometric characteristics and importance of the model, ensuring that the points are uniformly distributed at key structure positions of the model, and carrying out point-by-point measurement and data recording by using an ultrasonic thickness measurement instrument; 2, judging the position adjustment of the current point; and step 3, the thickness measuring point generates brand new point cloud data after being adjusted according to the compensation value, and a processing track is generated based on an equal residual height method. The method effectively solves the problems that in the machining process, due to the fact that the position of a theoretical model is not uniform with the position of an actual workpiece, the idle feeding phenomenon is caused, and the service life of a tool is shortened due to the too large cutting amount of a local area.

Description

Technical Field

[0001] The present invention relates to a cavity component trajectory planning method based on wall thickness data, and specifically to a method for completing a thin-walled component digital model tool path trajectory planning task based on 3D scanning point cloud data and digital model registration and comparison results, taking the wall thickness of the thin-walled component as a constraint condition, and belongs to the field of CAD / CAPP / CAM technology. Background Art

[0002] Thin-walled parts processing based on 3D scanning point cloud data and digital model registration is a key technology in advanced manufacturing, which involves multiple complex links such as point cloud data collection, data processing, digital model registration, trajectory planning, etc. This technology has broad application prospects in the processing of high-precision thin-walled structural parts in the fields of aerospace, automobile manufacturing, etc.

[0003] In the process of thin-walled parts processing, due to the inherent structural characteristics of the workpiece and the deformation during processing, the traditional tool path generation method based on the ideal CAD model is often difficult to meet the processing accuracy requirements. To this end, a tool path trajectory planning method based on 3D scanning point cloud data and digital model registration comparison results, with the wall thickness of thin-walled parts as the constraint condition, is proposed. This method first obtains the actual geometric shape of the workpiece through a high-precision 3D scanning device, and then aligns the obtained point cloud data with the ideal CAD model to obtain the actual deformation state of the workpiece. On this basis, the wall thickness of the thin-walled part is used as the main constraint condition to optimize the tool path.

[0004] This method can not only effectively control the deformation during the machining process, but also ensure the uniformity of the wall thickness of thin-walled parts in various areas. This tool path planning method based on actual geometric shapes, combined with the flexibility and high precision of multi-axis CNC machine tools, can significantly improve the machining accuracy and surface quality of thin-walled parts, providing strong support for high-end manufacturing in the fields of aerospace, automobile manufacturing, etc. Summary of the invention

[0005] In order to solve the above technical problems, the first aspect of the present invention provides a method for obtaining tool position point information of a complex surface which is simple in calculation and practical.

[0006] A second aspect of the present invention provides a tool path planning method for solving the problem of uneven wall thickness in machining cavity parts.

[0007] In view of the defects in the prior art, the object of the present invention is to provide a cavity component trajectory planning method based on wall thickness data, comprising:

[0008] Step 1: Measure the thickness of the cavity model point by point. First, calibrate the key measurement area, plan the thickness measurement points according to the geometric characteristics and importance classification of the model, ensure that these points are evenly distributed in the key structural positions of the model, and use an ultrasonic thickness gauge to measure point by point and record the data.

[0009] Step 2: Determine the current point position adjustment;

[0010] Step 21: Scan the cavity point cloud model with a 3D scanner. Due to the limitations of the scanner and parts, the inner surface of the part is an incomplete model, and the model needs to be completed according to the thickness measurement points in step 1.

[0011] Step 22: Record the wall thickness at the i-th point of the thickness gauge as ε i .

[0012] Step 23: Calculate the mean wall thickness

[0013] Step 24: Calculate the wall thickness value ε at the current point i The thickness measuring point is offset toward the inside of the model cavity along the thickness measuring point vector direction, and then step S3 is executed to update the wall thickness mean.

[0014] Step 25, execute the next point, repeat steps 23 and 24, until the average value of the planned thickness measurement point after adjustment remains within the controllable range, and the thickness measurement point compensation adjustment is completed.

[0015] Step 3: The thickness measurement points are adjusted according to the compensation value to generate new point cloud data, and the processing trajectory is generated based on the equal residual height method.

[0016] Step 31, residual height calculation;

[0017] After determining the initial tool contact point trajectory, the first line of tool position trajectory can be obtained through it. Before calculating the next line of tool position, the residual height point of the current tool position needs to be calculated. The residual height point is calculated by creating a local coordinate system of the current tool position, calculating the intersection of the data point and the cutting plane, and calculating the residual height point based on the intersection.

[0018] Step 32, calculating the tool position points of adjacent tool paths;

[0019] For residual height points Establish local coordinate system O S X S Y S Z S As shown in the figure, is the origin, X S , Y S , Z S The positive direction unit vector of the axis is i S ={x x ,y x ,zx}、j S ={x y ,y y ,z y}, k S ={x z ,y z ,z z}, the coordinate transformation between the world coordinate system and the local coordinate system can be performed, and the point P in P i The coordinates in the local coordinate system can be obtained by the following formula 1-1.

[0020]

[0021] Select a part of the points in P to form a subset P i ' ,j As the calculation of adjacent cutting positions Adjacent candidate knife contact point, according to formula 1, P can be calculated i ' ,j The point is O S X S Y S Z S The coordinates are obtained in the coordinate system. i ' ,j The point is O S X S Y S Z S The coordinates in the coordinate system must meet the following conditions:

[0022] P i ' ,j = {P i ∈P|-R≤P i ·x s ≤2R&-R≤P i ·y s ≤R} (2)

[0024] According to the adjacent tool position points, the intersection point of the tool circle with the center as the circle is obtained. At the same time, the two tool position points are also located on a circle with the residual height point as the center and R as the radius. The adjacent tool position points can be obtained according to the tangent relationship between the tool position point and the point cloud.

[0025] Step 33, calculating the tool position point that satisfies the equal bow height error;

[0026] The tool position points in the step direction do not necessarily satisfy the bow height error, and there may be redundant tool position points. In order to make the error between tool position points less than the allowable value and remove unnecessary redundant tool position points, the tool position bow height error calculation method and related processing methods are given.

[0027] For the method of equal bow height error of the surface model, the bow height error is approximately expressed by the distance from the intersection of the tangent line of the tool contact point to the connection line of the tool contact point. The bow height error e can be calculated by Equation 3.

[0028]

[0029] For the cavity complex point cloud model, the tool contact point is actually a set of points constrained by the wall thickness. The bow height error e in formula 3 needs to be considered as the maximum distance between the point set and the P1P2 connection line. Since the part to be processed is a cavity type, it is necessary to solve the maximum distance with uniform wall thickness as the constraint. The tool position point corresponds to the wall thickness λ. Let the point set is a point in the point set, then The distance to P1P2 is shown in the following formula.

[0030]

[0031] If the requirement in formula 4 is not met, a new tool position point needs to be added between the two tool position points to reduce the error. To add a new tool position point, the above step 3 needs to be repeated, and new tool position points need to be added until the requirement is met.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] The present invention proposes a cavity component trajectory planning method based on wall thickness data and provides a new trajectory adjustment strategy, which effectively solves the "empty tool walk" phenomenon caused by the inconsistency between the theoretical model and the actual workpiece position during the machining process, as well as the problem of reduced tool life caused by excessive cutting amount in local areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Model completion based on ultrasonic thickness measurement.

[0035] Figure 2 Machining trajectory adjustment based on wall thickness.

[0036] Figure 3 Tool point adjustment based on wall thickness.

[0037] Figure 4 The bow height distance between two tool positions is uniformly solved with the wall thickness as constraint.

[0038] Figure 5 Flowchart of trajectory planning with wall thickness as constraint. DETAILED DESCRIPTION

[0039] The embodiments of the present invention are described in detail below with reference to the accompanying drawings:

[0040] In view of the defects in the prior art, an object of the present invention is to provide a cavity component trajectory planning method based on wall thickness data.

[0041] The cavity component trajectory planning method based on wall thickness data provided by the present invention includes:

[0042] Step 1: Measure the thickness of the cavity model point by point. First, mark the key measurement area, plan the thickness measurement points according to the geometric characteristics and importance of the model, and ensure that these points are evenly distributed in the key structural positions of the model. Use an ultrasonic thickness gauge to measure point by point and record the data, such as Figure 1 shown.

[0043] Step 2: Determine the current point position adjustment;

[0044] S1. Scan the cavity point cloud model with a 3D scanner. Due to the limitations of the scanner and parts, the inner surface of the part is an incomplete model and needs to be completed according to the thickness measurement points in step 1.

[0045] S2. Record the wall thickness at the i-th point of the thickness gauge as ε i .

[0046] S3. Calculate the average wall thickness

[0047] S4. Calculate the wall thickness value ε at the current point i The thickness measuring point is offset toward the inside of the model cavity along the thickness measuring point vector direction, and then step S3 is executed to update the wall thickness mean.

[0048] S5. Execute the next point and repeat S3 and S4 until the average value of the planned thickness measurement point is kept within the controllable range after adjustment, and the thickness measurement point compensation adjustment is completed.

[0049] Step 3: The thickness measurement points are adjusted according to the compensation value to generate new point cloud data, and the processing trajectory is generated based on the equal residual height method.

[0050] S1. Residual height calculation;

[0051] After determining the initial tool contact point trajectory, the first line of tool position trajectory can be obtained through it. Before calculating the next line of tool position, the residual height point of the current tool position needs to be calculated. The residual height point is calculated by creating a local coordinate system of the current tool position, calculating the intersection of the data point and the cutting plane, and calculating the residual height point based on the intersection.

[0052] S2, calculation of tool position points of adjacent tool paths;

[0053] For residual height points Establish local coordinate system O S X S Y S Z S As shown in the figure, is the origin, X S , Y S , Z SThe positive direction unit vector of the axis is i S ={x x ,y x ,z x}、j S ={x y ,y y ,z y}, k S ={x z ,y z ,z z}, the coordinate transformation between the world coordinate system and the local coordinate system can be performed, and the point P in P i The coordinates in the local coordinate system can be obtained by the following formula 1-1.

[0054]

[0055] like Figure 2 and Figure 3 As shown, a part of the points in P is selected to form a subset P i ' ,j As the calculation of adjacent cutting positions Adjacent candidate knife contact point, according to formula 1, P can be calculated i ' ,j The point is O S X S Y S Z S The coordinates are obtained in the coordinate system. i ' ,j The point is O S X S Y S Z S The coordinates in the coordinate system must meet the following conditions:

[0056] P i ' ,j = {P i ∈P|-R≤P i ·x s ≤2R&-R≤P i ·y s ≤R} (2)

[0058] According to the adjacent tool position points, the intersection point of the tool circle with the center as the circle is obtained. At the same time, the two tool position points are also located on a circle with the residual height point as the center and R as the radius. The adjacent tool position points can be obtained according to the tangent relationship between the tool position point and the point cloud.

[0059] S3. Calculation of tool position points that meet the equal bow height error

[0060] The tool position points in the step direction do not necessarily satisfy the bow height error, and there may be redundant tool position points. In order to make the error between tool position points less than the allowable value and remove unnecessary redundant tool position points, the tool position bow height error calculation method and related processing methods are given.

[0061] For the method of equal bow height error of the surface model, the bow height error is approximately expressed by the distance from the intersection of the tangent line of the tool contact point to the connection line of the tool contact point. The bow height error e can be calculated by Equation 3.

[0062]

[0063] As shown in the figure, for the cavity complex point cloud model, the tool contact point is actually a set of points constrained by the wall thickness. The bow height error e in formula 3 needs to be considered as the maximum distance between the point set and the P1P2 connection line. Since the part to be processed is a cavity type, it is necessary to solve the maximum distance with uniform wall thickness as the constraint. The tool position point corresponds to the wall thickness λ. Let the point set is a point in the point set, then The distance to P1P2 is shown in the following formula.

[0064]

[0065] If the requirement in formula 4 is not met, a new tool position point needs to be added between the two tool position points to reduce the error. To add a new tool position point, the above step 3 needs to be repeated, and new tool position points need to be added until the requirement is met.

[0066] The present invention effectively solves the problem of "empty tool movement" caused by the inconsistency between the theoretical model and the actual workpiece position during the machining process, and the problem of reduced tool life caused by excessive cutting volume in a local area.

Claims

1. A cavity component trajectory planning method based on wall thickness data, characterized in that: include: Step 1: Measure the thickness of the cavity model point by point. First, mark the key measurement area, plan the thickness measurement points according to the geometric characteristics and importance classification of the model, ensure that these points are evenly distributed in the key structural positions of the model, and use an ultrasonic thickness gauge to measure point by point and record the data; Step 2: Determine the current point position adjustment; Step 3: The thickness measurement points are adjusted according to the compensation value to generate new point cloud data, and the processing trajectory is generated based on the equal residual height method.

2. The cavity component trajectory planning method based on wall thickness data according to claim 1 is characterized in that: Step 2 includes: Step 21, scan the cavity point cloud model through a 3D scanner. Due to the limitations of the scanner and parts, the inner surface of the part is an incomplete model, and the model needs to be completed according to the thickness measurement points in step 1; Step 22: Record the wall thickness at the i-th point of the thickness gauge as ε i ; Step 23: Calculate the mean wall thickness Step 24: Calculate the wall thickness value ε at the current point i The thickness measuring point is offset toward the inside of the model cavity along the thickness measuring point vector direction, and then step S3 is executed to update the wall thickness mean value; Step 25, execute the next point, repeat steps 23 and 24, until the average value of the planned thickness measurement point after adjustment remains within the controllable range, and the thickness measurement point compensation adjustment is completed.

3. The cavity component trajectory planning method based on wall thickness data according to claim 1 is characterized in that: Step 3 includes: Step 31, residual height calculation; After determining the initial tool contact point trajectory, the first line of tool position trajectory can be obtained through it; before calculating the next line of tool position, the residual height point of the current tool position needs to be obtained first; by creating a local coordinate system for the current tool position, calculating the intersection of the data point and the cutting plane, and calculating the residual height point based on the intersection; Step 32, calculating the tool position points of adjacent tool paths; For residual height points Establish local coordinate system O S X S Y S Z S As shown in the figure, is the origin, X S , Y S , Z S The positive direction unit vector of the axis is i S ={x x ,y x ,z x }、j S ={x y ,y y ,z y }, k S ={x z ,y z ,z z }, that is, coordinate transformation between the world coordinate system and the local coordinate system, point P in P i The coordinates in the local coordinate system are obtained by the following formula 1-1: Select a part of the points in P to form a subset P i ' ,j As the calculation of adjacent cutting positions Adjacent candidate knife contact point, according to formula 1, P can be calculated i ' ,j The point is O S X S Y S Z S Coordinates obtained in the coordinate system; P i ' ,j The point is O S X S Y S Z S The coordinates in the coordinate system must meet the following conditions: P i ′ ,j ={P i ∈P∣-R≤P i ·x s ≤2R&-R≤P i ·y s ≤R} (2) According to the adjacent tool position points, the intersection point of the tool circle with the center as the circle is obtained. At the same time, the two tool position points are also located on a circle with the residual height point as the center and R as the radius; the adjacent tool position points can be obtained according to the tangent relationship between the tool position point and the point cloud; Step 33, calculating the tool position point that satisfies the equal bow height error; The tool position points in the step length direction do not necessarily meet the bow height error, and there may be redundant tool position points. In order to make the error between tool position points less than the allowable value and remove unnecessary redundant tool position points, the tool position bow height error calculation method and related processing methods are given. For the method of equal bow height error of the surface model, the bow height error is approximately expressed by the distance from the intersection of the tangent line of the knife contact point to the connection line of the knife contact point. The bow height error e can be calculated by formula 3; For the cavity complex point cloud model, the tool contact point is actually a set of points constrained by the wall thickness. The bow height error e in formula 3 is considered to be the maximum distance between the point set and the P1P2 connection line. Since the part to be processed is a cavity type, the maximum distance is solved with uniform wall thickness as the constraint. The tool position point corresponds to the wall thickness λ. Let the point set is a point in the point set, then The distance to P1P2 is shown in the following formula; If the requirements in formula 4 are not met, it is necessary to add a new tool position point between the two tool position points to reduce the error. To add a new tool position point, repeat the above step 3 and continue to add new tool position points until the requirements are met.

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