Milling cutter path optimization method of numerical control milling machine

Abstract

The invention relates to the technical field of numerical control machining, and discloses a milling cutter path optimization method of a numerical control milling machine, which comprises the following steps: acquiring an initial milling cutter path, and identifying corner points between adjacent straight line segments; obtaining a corner angle, the length of a relatively short straight line segment and a matrix M of a tool-spindle system; constructing a vibration suppression objective function, and solving the transition arc radius of the corner point; calculating a basic transition feeding speed; calculating a weighted influence factor of each corner point in the N continuous corner point sequences, performing summation to obtain a comprehensive influence coefficient, and calculating a correction transition feeding speed; planning a speed transition area; constructing an S-shaped acceleration and deceleration speed curve; and according to the S-shaped acceleration and deceleration speed curve, the speed transition area and the feeding speed on the transition arc are determined, and an optimized milling cutter path is generated. According to the method, comprehensive and unified speed planning can be carried out on a complex path comprising a plurality of continuous corners, and the surface machining quality and machining efficiency of the workpiece are improved.

Description

Technical Field

[0001] This invention relates to the field of CNC machining technology, and more specifically to a method for optimizing the cutter path of a CNC milling machine. Background Technology

[0002] In CNC milling, the cutter path is generated by CAM software based on the CAD model of the part and output in G-code. These paths are typically composed of numerous tiny straight line segments, forming sharp corners at their intersections. When the machine tool is running at high speed, if these corners are not addressed, the cutter must stop abruptly at the corners and then accelerate sharply again. This abrupt start and stop not only affects the surface finish of the machined part but also damages the lifespan of both the cutter and the machine tool, thus limiting overall machining efficiency.

[0003] To address this issue, a common technique in existing technologies is to use a smooth arc to transition at sharp corners. However, this alone is insufficient; precise control of the tool feed rate is also necessary. Existing speed control strategies often only consider ensuring that the centripetal acceleration of the tool on the transition arc does not exceed a limit, but this can cause a sudden change in tool speed at the junction of the straight line and the arc, resulting in impact. To eliminate speed abrupt changes, researchers introduced "trapezoidal acceleration / deceleration" technology. While this technology smooths the speed change, the acceleration itself changes instantaneously, and this "abrupt movement" can cause machine tool vibration. To address the vibration problem, researchers introduced a more advanced "S-shaped acceleration / deceleration" technology, which solves the vibration problem by ensuring a continuous and smooth change in acceleration.

[0004] However, most current S-shaped acceleration and deceleration applications only perform local optimization for a single corner, and cannot perform comprehensive and unified speed planning for complex paths containing many continuous corners, resulting in low surface finish and processing efficiency of the workpiece. Summary of the Invention

[0005] This invention provides a milling cutter path optimization method for CNC milling machines to solve the problem in the prior art that it is impossible to perform comprehensive and unified speed planning for complex paths containing many continuous corners, resulting in low surface machining quality and machining efficiency of the workpiece.

[0006] The milling cutter path optimization method for CNC milling machines of the present invention includes the following steps: Obtain the initial cutter path consisting of straight line segments and identify adjacent straight line segments. and Corner points between ; Get the corner point Turning angle The length of the shorter of two adjacent line segments And the matrix M of the tool-spindle system; constructing with , Let M be the input vibration suppression objective function. Solving the vibration suppression objective function yields the corner point. transition radius ; based on and maximum permissible centripetal acceleration Calculate the basic transition feed rate ; Obtain the corner point Given a sequence of N consecutive corner points, calculate the relationship between each corner point and the next corner point in the sequence. The weighted influence factors are calculated; the comprehensive influence coefficient is obtained by summing the N weighted influence factors. and utilize Adjustment Obtain the corrected transition feed rate ; Plan the speed transition zone on the straight segment where the start and end points of the transition arc are located; within the speed transition zone, adjust the transition feed rate according to the feed rate of the straight segment. Maximum permissible acceleration and maximum permissible jerk Construct an S-shaped acceleration / deceleration curve; use a transition arc radius... The generated transition arc replaces the corner points in the initial milling cutter path. Based on the S-shaped acceleration and deceleration speed curve, the speed transition zone and the feed speed on the transition arc are determined, and an optimized milling cutter path is generated.

[0007] Preferably, the construction is based on , Let M be the input vibration suppression objective function. Solving the vibration suppression objective function yields the corner point. transition radius This includes: adjusting the radius of the transition arc. As optimization variables, weighting coefficients are determined based on the matrix M of the tool-spindle system. and Construct the vibration suppression objective function ; in, Corner point The radius of the transition arc, For the maximum allowable transition radius, Calculated using the following formula: ,in, Corner point The length of the shorter of two adjacent line segments. Corner point The angle of rotation; Solve the vibration suppression objective function The minimum value is used as the radius of the transition arc. .

[0008] Preferably, the basic transition feed rate Calculated using the following formula: ,in, For the maximum permissible centripetal acceleration, The radius of the transition arc.

[0009] Preferably, the calculation of each corner point in the sequence of N consecutive corner points... The weighted influence factors include: calculating the corner points The end point of the transition arc to the subsequent corner point Path distance between the starting points of the transition arc The weighted influence factor is calculated using the following formula. ; ,in, For subsequent corner points The turning angle is C, which is a preset normalization coefficient.

[0010] Preferably, the corrected transition feed rate Calculated using the following formula: ,in, The base transition feed rate is given by α, which is a preset dimensionless attenuation coefficient. This is the comprehensive impact coefficient.

[0011] Preferably, the S-shaped acceleration / deceleration curve includes a uniform acceleration segment, a uniform acceleration segment, a uniform deceleration segment, a uniform speed segment, a uniform acceleration / deceleration segment, a uniform deceleration segment, and a uniform deceleration / deceleration segment.

[0012] Preferably, the step of adjusting the transition feed rate based on the straight segment feed rate is... Maximum permissible acceleration and maximum permissible jerk Constructing an S-shaped acceleration / deceleration curve includes: adjusting the transition feed rate based on the feed rate of the straight segment. Maximum permissible acceleration and maximum permissible jerk The durations of the uniform acceleration segment, uniform acceleration segment, uniform deceleration segment, uniform velocity segment, uniform acceleration and deceleration segment, uniform deceleration segment, and uniform deceleration segment are calculated sequentially, and the velocity value at each discrete time point is generated by integration, forming a continuous and smooth S-shaped acceleration and deceleration velocity curve.

[0013] Preferably, the rotation angle Calculated in the following way: First calculate the line segment and The angle between the two direction vectors is obtained by taking the dot product of their direction vectors and then using the inverse cosine function. Finally, the angle is obtained by subtracting the angle from 180 degrees. .

[0014] Preferably, the maximum permissible jerk The maximum allowable rate of change of acceleration over time.

[0015] Preferably, the step involves obtaining the initial milling cutter path composed of straight line segments and identifying adjacent straight line segments. and Corner points between This includes: sequentially processing each program segment in the CNC machining G-code file through a parser; when two consecutive G01 linear interpolation instructions are detected, if the endpoint coordinates of the previous G01 instruction coincide with the starting coordinates of the subsequent G01 instruction, then the coincident coordinate point is identified as a corner point. Furthermore, it identifies the vectors defined by these two G01 instructions as adjacent line segments. and .

[0016] The beneficial effects of this invention are as follows: This invention determines the optimal transition arc radius by constructing an objective function based on the rotation angle, adjacent path length, and tool-spindle system characteristics. This makes the selection of arc parameters more scientific, effectively suppressing vibrations during machining and improving the surface finish and contour accuracy of the workpiece. Furthermore, this method corrects the transition feed rate by comprehensively evaluating the impact of subsequent continuous rotation angles on the current point. This ensures that the overall feed rate remains both high and stable, significantly improving machining efficiency. Finally, by planning an S-shaped acceleration / deceleration curve, this invention ensures continuous and smooth changes in acceleration, effectively protecting machine tool components and extending the equipment's service life. Attached Figure Description

[0017] Figure 1 This is a flowchart illustrating the milling cutter path optimization method for a CNC milling machine provided in an embodiment of the present invention. Detailed Implementation

[0018] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0019] like Figure 1 As shown, an embodiment of the CNC milling machine cutter path optimization method provided by the present invention includes the following steps: S1: Obtain the initial milling cutter path composed of straight line segments and identify adjacent straight line segments. and Corner points between .

[0020] Specifically, the parser sequentially processes each program segment in the CNC machining G-code file. When two consecutive G01 linear interpolation instructions are detected, if the endpoint coordinates of the previous G01 instruction coincide with the starting coordinates of the next G01 instruction, then the coincident coordinate point is identified as a corner point. Furthermore, it identifies the vectors defined by these two G01 instructions as adjacent line segments. and .

[0021] S2, Obtain the corner point Turning angle The length of the shorter of two adjacent line segments And the matrix M of the tool-spindle system; constructing with , Let M be the input vibration suppression objective function. Solving the vibration suppression objective function yields the corner point. transition radius .

[0022] In one embodiment, the rotation angle Calculated in the following way: First calculate the line segment and The angle between the two direction vectors is obtained by taking the dot product of their direction vectors and then using the inverse cosine function. Finally, the angle is obtained by subtracting the angle from 180 degrees. .

[0023] Specifically, the matrix M of the tool-spindle system is obtained in advance through modal experiments on the CNC milling machine. The modal experiments use a force hammer and an acceleration sensor to obtain the frequency response function of the system, and then use a parameter identification algorithm to fit the natural frequencies, damping ratios and mode parameters of the system, thereby constructing the matrix M.

[0024] S3, based on and maximum permissible centripetal acceleration Calculate the basic transition feed rate ; Obtain the corner point Given a sequence of N consecutive corner points, calculate the relationship between each corner point and the next corner point in the sequence. The weighted influence factors are calculated; the comprehensive influence coefficient is obtained by summing the N weighted influence factors. and utilize Adjustment Obtain the corrected transition feed rate .

[0025] S4, plan the speed transition zone on the straight segment where the start and end points of the transition arc are located; within the speed transition zone, adjust the transition feed rate according to the feed rate of the straight segment. Maximum permissible acceleration and maximum permissible jerk Construct an S-shaped acceleration / deceleration curve; use a transition arc radius... The generated transition arc replaces the corner points in the initial milling cutter path. Based on the S-shaped acceleration and deceleration speed curve, the speed transition zone and the feed speed on the transition arc are determined, and an optimized milling cutter path is generated.

[0026] Specifically, the change in speed is first determined, namely the feed speed on the straight section and the corrected transition feed speed. The difference. Then, based on the machine tool's preset maximum allowable acceleration. and maximum permissible jerk Calculate the time required for each stage in the S-shaped acceleration / deceleration curve. Specifically, the S-shaped acceleration / deceleration curve includes a uniform acceleration segment, a uniform acceleration segment, a uniform deceleration segment, a constant velocity segment, a uniform acceleration / deceleration segment, a uniform deceleration segment, and a uniform deceleration / deceleration segment.

[0027] Specifically, jerkiness is the rate of change of acceleration over time. By integrating the velocity function over each stage of time, the displacement required to complete the entire acceleration / deceleration process is calculated; this displacement length is the length of the velocity transition zone. The velocity transition zone is defined as the straight segment preceding the starting point of the transition arc. and the straight segment after the endpoint superior.

[0028] Based on the corner point and transition arc radius Calculate the position of the center of the circle and its position on the straight line segment. and The point of tangency on the line. The original line segment. and It is cut off by these two tangent points, and a segment is inserted between the tangent points. A circular path with radius [radius] is generated, and a G02 or G03 circular interpolation command is created, with a feed rate of [feed rate]. For the speed transition zone, the S-shaped acceleration / deceleration curve is discretized according to the interpolation cycle of the CNC system. The average speed and displacement within each cycle are calculated, generating a series of G01 commands for continuously varying feed rates, representing tiny linear segments, to approximate the S-shaped acceleration / deceleration curve. Finally, these tiny linear segment commands, circular interpolation commands, and truncated linear segment commands are sequentially combined to form G-code for a smooth and efficient optimized milling cutter path.

[0029] To balance the two core requirements of smooth processing and vibration suppression, in an optional embodiment, the construction is based on... , Let M be the input vibration suppression objective function. Solving the vibration suppression objective function yields the corner point. transition radius This includes: adjusting the radius of the transition arc. As optimization variables, weighting coefficients are determined based on the matrix M of the tool-spindle system. and Construct the vibration suppression objective function ;in, Corner point The radius of the transition arc, For the maximum allowable transition radius, Calculated using the following formula: ,in, Corner point The length of the shorter of two adjacent line segments. Corner point The angle of rotation; Solve the vibration suppression objective function The minimum value is used as the radius of the transition arc. .

[0030] The first part of the vibration suppression objective function is... By selecting the largest possible transition radius, the smoothness of the path is improved, reducing impact. The second part of the vibration suppression objective function is... This is to avoid the machine tool's resonance zone, because a smaller radius typically generates a higher cutting force frequency, making it easier to excite the natural frequency of the tool-spindle system and thus induce vibration. Weighting coefficient and The frequency response characteristics of the tool-spindle system are determined based on matrix M analysis. If the system is sensitive to small-radius machining, then... The value will be relatively large.

[0031] For example, suppose the corner of a turning point =90°, the length of its adjacent shortest straight segment If the value is 10 mm, then the maximum allowable transition radius is... By analyzing the system matrix M, the weighting coefficients are determined. It is 0.5. It is 12.5.

[0032] At this time, the vibration suppression objective function By finding the minimum value of the function, for example by setting its derivative to zero, the optimal transition arc radius can be obtained.

[0033] To determine a safe and efficient base turning speed based on the physical performance constraints of the machine tool, in one optional embodiment, the base transition feed speed... Calculated using the following formula: ,in, For the maximum permissible centripetal acceleration, The radius of the transition arc. These are fixed values ​​set in the parameters of the CNC machine tool.

[0034] By deriving the centripetal acceleration formula in reverse, the maximum feed rate that the machine tool can stably withstand under a given transition radius can be calculated as the basic transition feed rate.

[0035] In an optional embodiment, the calculation of each corner point in a sequence of N consecutive corner points... The weighted influence factors include: calculating the corner points The end point of the transition arc to the subsequent corner point Path distance between the starting points of the transition arc The weighted influence factor is calculated using the following formula. ; ,in, For subsequent corner points The turning angle is C, which is a preset normalization coefficient.

[0036] In practical applications, if a sharp turn follows the current turning point, the machine tool needs to decelerate in advance when entering the current turning point. The angle of the subsequent turning point... The larger it is, or the greater its distance from the current corner point. The closer it is, the better it is for the current corner point. The greater the impact of speed planning, the better. A preset normalization coefficient C is used to adjust the overall magnitude of the influencing factors. For example, assume we are currently at a turning point. The next corner point is Assuming The corner Approximately 2.094 radians. and path distance The value is 20mm. Let the normalization factor C = 10mm. Then... right The impact factor is approximately 1.047. If there is another turning point further along the path... Its corner It is 60°, or approximately 1.047 radians. and path distance If it is 50mm, then right The influence factor is approximately 0.209. This indicates that closer and sharper turning points have a far greater impact on the current speed decision than farther and gentler turning points.

[0037] In an optional embodiment, the modified transition feed rate Calculated using the following formula: ,in, The base transition feed rate is given by α, which is a preset dimensionless attenuation coefficient. This is the comprehensive impact coefficient.

[0038] Comprehensive influence coefficient It is obtained by summing the influence factors of the N future turning points. The larger the value, the more winding the road ahead, and the greater the need for deceleration. This is an inverse proportional adjustment model. When When it is zero, that is, the line ahead is long. It is equal to ;when When the denominator increases, the denominator increases. The corresponding decrease will occur. The attenuation coefficient α acts as an adjustment knob, controlling the degree of deceleration. Its value needs to be calibrated experimentally to achieve the best processing effect. By replacing the higher speed originally calculated based on a single corner point with a conservative speed suitable for processing continuous small line segments, vibration and impact caused by frequent rapid acceleration and deceleration in dense corner areas are avoided.

[0039] To achieve a smooth speed transition, the feed rate is adjusted based on the straight-line segment feed rate. Maximum permissible acceleration and maximum permissible jerk Constructing an S-shaped acceleration / deceleration curve includes: adjusting the transition feed rate based on the feed rate of the straight segment. Maximum permissible acceleration and maximum permissible jerk The durations of the uniform acceleration segment, uniform acceleration segment, uniform deceleration segment, uniform velocity segment, uniform acceleration and deceleration segment, uniform deceleration segment, and uniform deceleration segment are calculated sequentially, and the velocity value at each discrete time point is generated by integration, forming a continuous and smooth S-shaped acceleration and deceleration velocity curve.

[0040] By introducing control over the jerk, the S-shaped acceleration / deceleration curve treats the acceleration change process as a smooth ramp, making the entire velocity change curve not only continuous but also its derivative continuously changing. This effectively reduces flexible impacts and ensures the smoothness of machine tool movement.

[0041] For example, suppose a machine tool needs to reduce its feed rate from a linear feed rate of 100 mm / s to a corrected transition feed rate of 43.43 mm / s. Assume the machine tool's maximum permissible acceleration... The maximum permissible jerk is 2000 mm / s². The speed is 40,000 mm / s. At the start of deceleration, a uniform acceleration / deceleration phase begins, where the acceleration linearly increases from 0 to -2000, lasting 0.05 s. If the speed difference is large enough, a uniform deceleration phase begins, where deceleration occurs at a constant maximum acceleration. Approaching the target speed, a uniform deceleration phase resumes, where the acceleration linearly decreases from -2000 to 0. By calculating the duration of each of the seven phases, the speed change throughout the deceleration process is ensured to be smooth, improving the quality of the machined surface and the operational stability of the machine tool.

[0042] The implementation principle of the milling cutter path optimization method for CNC milling machines in this invention is as follows: This invention determines the optimal transition arc radius by constructing an objective function based on the rotation angle, adjacent path length, and tool-spindle system characteristics. This makes the selection of arc parameters more scientific, effectively suppressing vibrations during machining and improving the surface finish and contour accuracy of the workpiece. Furthermore, this invention also corrects the transition feed rate by comprehensively evaluating the impact of subsequent continuous rotation angles on the current point, ensuring that the overall feed rate remains both high and stable, significantly improving machining efficiency. Finally, by planning an S-shaped acceleration / deceleration curve, continuous and smooth changes in acceleration are ensured, effectively protecting machine tool components and extending the equipment's service life.

[0043] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for optimizing the cutter path of a CNC milling machine, characterized in that, Includes the following steps: Obtain the initial cutter path consisting of straight line segments and identify adjacent straight line segments. and Corner points between ; Get the corner point Turning angle The length of the shorter of two adjacent line segments And the matrix M of the tool-spindle system; constructing with , Let M be the input vibration suppression objective function. Solving the vibration suppression objective function yields the corner point. transition radius ; based on and maximum permissible centripetal acceleration Calculate the basic transition feed rate ; Obtain the corner point Given a sequence of N consecutive corner points, calculate the relationship between each corner point and the next corner point in the sequence. The weighted influence factors are calculated; the comprehensive influence coefficient is obtained by summing the N weighted influence factors. and utilize Adjustment Obtain the corrected transition feed rate ; Plan the speed transition zone on the straight segment where the start and end points of the transition arc are located; within the speed transition zone, adjust the transition feed rate according to the feed rate of the straight segment. Maximum permissible acceleration and maximum permissible jerk Construct an S-shaped acceleration / deceleration curve; use a transition arc radius... The generated transition arc replaces the corner points in the initial milling cutter path. Based on the S-shaped acceleration and deceleration speed curve, the speed transition zone and the feed speed on the transition arc are determined, and an optimized milling cutter path is generated.

2. The method for optimizing the cutter path of a CNC milling machine according to claim 1, characterized in that, The construction is based on , Let M be the input vibration suppression objective function. Solving the vibration suppression objective function yields the corner point. transition radius ,include: The transition radius As optimization variables, weighting coefficients are determined based on the matrix M of the tool-spindle system. and Construct the vibration suppression objective function ; in, Corner point The radius of the transition arc, For the maximum allowable transition radius, Calculated using the following formula: ,in, Corner point The length of the shorter of two adjacent line segments. Corner point The angle of rotation; Solve the vibration suppression objective function The minimum value is used as the radius of the transition arc. .

3. The method for optimizing the cutter path of a CNC milling machine according to claim 1, characterized in that, The basic transition feed rate Calculated using the following formula: ,in, For the maximum permissible centripetal acceleration, The radius of the transition arc.

4. The method for optimizing the cutter path of a CNC milling machine according to claim 1, characterized in that, The calculation of each corner point in a sequence of N consecutive corner points... The weighted influence factors include: Calculate the corner point The end point of the transition arc to the subsequent corner point Path distance between the starting points of the transition arc The weighted influence factor is calculated using the following formula. ; ,in, For subsequent corner points The turning angle is C, which is a preset normalization coefficient.

5. The method for optimizing the cutter path of a CNC milling machine according to claim 1, characterized in that, The corrected transition feed rate Calculated using the following formula: ,in, The base transition feed rate is given by α, which is a preset dimensionless attenuation coefficient. This is the comprehensive impact coefficient.

6. The method for optimizing the cutter path of a CNC milling machine according to claim 1, characterized in that, The S-shaped acceleration / deceleration curve includes a uniform acceleration segment, a uniform acceleration segment, a uniform deceleration segment, a uniform speed segment, a uniform acceleration / deceleration segment, a uniform deceleration segment, and a uniform deceleration / deceleration segment.

7. The method for optimizing the cutter path of a CNC milling machine according to claim 6, characterized in that, The method of adjusting the transition feed rate based on the straight segment feed rate... Maximum permissible acceleration and maximum permissible jerk Construct S-shaped acceleration and deceleration curves, including: Based on the feed rate of the straight segment, the transition feed rate is corrected. Maximum permissible acceleration and maximum permissible jerk The durations of the uniform acceleration segment, uniform acceleration segment, uniform deceleration segment, uniform velocity segment, uniform acceleration and deceleration segment, uniform deceleration segment, and uniform deceleration segment are calculated sequentially, and the velocity value at each discrete time point is generated by integration, forming a continuous and smooth S-shaped acceleration and deceleration velocity curve.

8. The method for optimizing the cutter path of a CNC milling machine according to claim 1, characterized in that, The angle of rotation Calculated in the following way: First calculate the line segment and The angle between the two direction vectors is obtained by taking the dot product of their direction vectors and then using the inverse cosine function. Finally, the angle is obtained by subtracting the angle from 180 degrees. .

9. The method for optimizing the cutter path of a CNC milling machine according to claim 1, characterized in that, The maximum permissible jerk The maximum allowable rate of change of acceleration over time.

10. The method for optimizing the cutter path of a CNC milling machine according to claim 1, characterized in that, The process involves obtaining the initial milling cutter path composed of straight line segments and identifying adjacent straight line segments. and Corner points between This includes: sequentially processing each program segment in the CNC machining G-code file through a parser; when two consecutive G01 linear interpolation instructions are detected, if the endpoint coordinates of the previous G01 instruction coincide with the starting coordinates of the subsequent G01 instruction, then the coincident coordinate point is identified as a corner point. Furthermore, it identifies the vectors defined by these two G01 instructions as adjacent line segments. and .

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