A milling cutter path optimization method for a numerical control milling machine

Abstract

The application 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; acquiring a corner angle, the length of a shorter straight line segment, and a matrix M of a tool-spindle system; constructing a vibration suppression target function, solving the transition arc radius of the corner points; calculating a basic transition feed speed; calculating the weighted influence factor of each corner point in an N continuous corner point sequence and summing the weighted influence factors to obtain a comprehensive influence coefficient, and calculating a modified transition feed speed; planning a speed transition zone; constructing an S-shaped acceleration and deceleration speed curve; determining the feed speed on the speed transition zone and the transition arc according to the S-shaped acceleration and deceleration speed curve; and generating an optimized milling cutter path. The application can comprehensively and uniformly plan the speed for a complex path containing many continuous corners, and improve the surface machining quality and machining efficiency of a workpiece.

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:

[0007] Obtain the initial cutter path consisting of straight line segments and identify adjacent straight line segments. and Corner points between ;

[0008] 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 ;

[0009] 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 ;

[0010] 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.

[0011] 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 ;

[0012] in, Corner point The radius of the transition arc, For the maximum allowable transition radius, Calculated using the following formula:

[0013] wherein, is the length of the shorter straight line segment of the two straight line segments adjacent to the corner point , and is the corner angle of the corner point ;

[0014] solving the minimum value of the vibration suppression objective function , and taking the minimum value as the transition arc radius .

[0015] Preferably, the basic transition feed speed is calculated by the following formula:

[0016] wherein, is the maximum allowable centripetal acceleration, is the transition arc radius.

[0017] Preferably, the weighted influence factor of each corner point in the N continuous corner point sequence on the corner point is calculated by calculating the path distance between the end point of the transition arc of the corner point and the start point of the transition arc of the subsequent corner point . The weighted influence factor is calculated by the following formula:

[0018] wherein, is the corner angle of the subsequent corner point , and C is a preset normalization coefficient.

[0019] Preferably, the modified transition feed speed is calculated by the following formula:

[0020] wherein, is the basic transition feed speed, and a is a preset dimensionless influence decay coefficient, is the comprehensive influence coefficient.

[0021] Preferably, the S-shaped acceleration and deceleration speed curve includes a uniform acceleration segment, a uniform acceleration segment, a uniform acceleration and deceleration segment, a uniform speed segment, a uniform acceleration and deceleration segment, a uniform deceleration segment, and a uniform deceleration and deceleration segment.

[0022] Preferably, the S-shaped acceleration and deceleration speed curve includes a uniform acceleration segment, a uniform acceleration segment, a uniform acceleration and deceleration segment, a uniform speed segment, a uniform acceleration and deceleration segment, a uniform deceleration segment, and a uniform deceleration and deceleration segment. ​​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.

[0023] Preferably, the rotation angle Calculated in the following way:

[0024] 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. .

[0025] Preferably, the maximum permissible jerk The maximum allowable rate of change of acceleration over time.

[0026] 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 .

[0027] 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 also 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

[0028] 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

[0029] 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.

[0030] 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:

[0031] S1: Obtain the initial milling cutter path composed of straight line segments and identify adjacent straight line segments. and Corner points between .

[0032] 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 .

[0033] 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 .

[0034] In one embodiment, the rotation angle Calculated in the following way:

[0035] 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. .

[0036] 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.

[0037] 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 .

[0038] 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.

[0039] 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.

[0040] 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.

[0041] Based on the corner point and the transition arc radius The center position of the circle and the tangent points on the straight line segment and are calculated. The original straight line segment and is truncated by the two tangent points, and a circular arc path with a radius of is inserted between the tangent points, and a G02 or G03 circular arc interpolation instruction is generated, with a feed speed of . For the speed transition zone, the S-shaped acceleration and deceleration speed curve is discretized according to the interpolation period of the numerical control system, the average speed and displacement in each period are calculated, and a series of micro straight line segment G01 instructions with continuously changing feed speed are generated to approximate the S-shaped acceleration and deceleration speed curve. Finally, these micro straight line segment instructions, circular arc interpolation instructions and truncated straight line segment instructions are combined in order to form a smooth and efficient optimized milling tool path G code.

[0042] In order to balance the two core needs of machining smoothness and vibration suppression, in an optional embodiment, the construction of the vibration suppression objective function with , and M as input, solving the vibration suppression objective function to obtain the transition arc radius of the corner point , includes: taking the transition arc radius as an optimization variable, determining the weight coefficients and based on the matrix M of the tool-spindle system, and constructing the vibration suppression objective function ; wherein, is the transition arc radius of the corner point , is the maximum allowed transition radius, calculated by the following formula:

[0043] wherein, is the length of the shorter straight line segment of the adjacent two straight line segments of the corner point , is the corner angle of the corner point ;

[0044] Solving the minimum value of the vibration suppression objective function , the minimum value obtained is taken as the transition arc radius .

[0045] The first part of the vibration suppression objective function, i.e. , improves the smoothness of the path and reduces the impact by selecting the largest possible transition radius. The second part of the vibration suppression objective function, i.e. , is to avoid the resonance region of the machine tool, because smaller radius usually results in higher cutting force frequency, which is more likely to excite the natural frequency of the tool-spindle system and thus cause vibration. The weight coefficient and are determined according to the frequency response characteristics of the tool-spindle system matrix M, if the system is sensitive to small radius machining, the value of will be relatively large.

[0046] For example, assuming that the turning angle of a turning point = 90°, the length of its adjacent shortest straight line segment is 10 mm, then the maximum allowable transition radius . Through the analysis of the system matrix M, the weight coefficient is determined to be 0.5, and

[0047] At this time, the vibration suppression objective function , by solving the minimum value of the function, for example, let its derivative equal to zero, the optimal transition arc radius can be obtained.

[0048] In order to determine a safe and efficient basic turning speed according to the physical performance constraints of the machine tool, in an optional embodiment, the basic transition feed speed is calculated by the following formula:

[0049] , wherein, is the maximum allowable centripetal acceleration, is the transition arc radius. is a fixed value set in the numerical control machine tool parameters.

[0050] Through the reverse deduction of the centripetal acceleration formula, the maximum feed speed that the machine tool can stably withstand under the given transition arc radius can be calculated as the basic transition feed speed.

[0051] In an optional embodiment, the calculation of the weighted influence factor of each turning point on the turning angle of the turning point includes: calculating the path distance between the endpoint of the transition arc of the turning point and the starting point of the transition arc of the subsequent turning point ; the weighted influence factor is calculated by the following formula ;

[0052] , wherein, is the turning angle of the subsequent turning point , and C is a predetermined normalization coefficient.

[0053] 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.

[0054] In an optional embodiment, the modified transition feed rate Calculated using the following formula:

[0055] ,in, The base transition feed rate is given by α, which is a preset dimensionless attenuation coefficient. This is the comprehensive impact coefficient.

[0056] 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 reduction. The influence of the attenuation coefficient a is then taken as an adjustment knob to control the severity of deceleration, whose value needs to be calibrated through experiments to achieve the best processing effect. By replacing the higher speed originally calculated based on a single corner point with a conservative but adaptive continuous small segment processing scenario speed, vibrations and shocks caused by frequent rapid acceleration and deceleration in dense corner areas are avoided.

[0057] In order to realize the smooth transition of speed, the modified transition feed speed , the maximum allowable acceleration and the maximum allowable jerk , the S-shaped acceleration and deceleration speed curve is constructed, including: according to the straight line segment feed speed, the modified transition feed speed , the maximum allowable acceleration and the maximum allowable jerk , the duration of the uniform acceleration acceleration segment, the uniform acceleration segment, the uniform deceleration acceleration segment, the uniform speed segment, the uniform acceleration deceleration segment, the uniform deceleration segment and the uniform deceleration deceleration segment are calculated in turn, and the speed value of each discrete time point is integrated to form a continuous and smooth S-shaped acceleration and deceleration speed curve.

[0058] The S-shaped acceleration and deceleration speed curve introduces the control of jerk, processes the acceleration change process into a smooth slope, so that the entire speed change curve is not only continuous, but also its derivative is continuously changing, which can effectively reduce the flexible impact and ensure the stability of the machine tool movement.

[0059] For example, assume that the machine tool needs to be decelerated from a straight line segment feed speed of 100 mm / s to a modified transition feed speed of 43.43 mm / s. Assume that the maximum allowable acceleration of the machine tool is 2000 mm / s2, and the maximum allowable jerk is 40000 mm / s3. At the beginning of deceleration, enter the uniform acceleration deceleration segment, and the acceleration increases linearly from 0 to -2000, and the duration of this stage is 0.05 s. If the speed difference is large enough, it will enter the uniform deceleration segment to decelerate at a constant maximum acceleration. When approaching the target speed, enter the uniform deceleration deceleration segment, and the acceleration decreases linearly from -2000 to 0. By calculating the duration of each of the seven stages, it can be ensured that the speed change during the entire deceleration process is smooth, which improves the quality of the machined surface and the running stability of the machine tool.

[0060] The implementation principle of the milling cutter path optimization method of the numerical control milling machine is that: the optimal transition arc radius is determined by constructing a target function based on the corner angle, the adjacent path length and the tool-spindle system characteristics, so that the selection of the arc parameters is more scientific, thereby effectively suppressing the vibration in the machining process and improving the surface machining quality and contour accuracy of the workpiece. In addition, the transition feed speed is corrected by comprehensively evaluating the influence of the subsequent continuous corners on the current point, so that the overall feed speed can be maintained at a high level and be stable, and the machining efficiency is significantly improved. Finally, by planning an S-shaped acceleration and deceleration speed curve, the continuous and smooth change of the acceleration is ensured, thereby effectively protecting the machine tool components and prolonging the service life of the equipment.

[0061] Although the embodiments of the present application have been shown and described above, it should be understood that the above-described embodiments are exemplary and are not to be construed as limiting the present application, and those of ordinary skill in the art can make changes, modifications, replacements and variations to the above-described embodiments within the scope of the present application.

Claims

1. A method of optimizing a milling tool path for a numerical control milling machine, characterized by, The method comprises the following steps: An initial milling tool path consisting of straight line segments is acquired and corner points between adjacent straight line segments are identified With 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 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 If the system is sensitive to small-radius machining, then The value of will be relatively large; 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 rotation angle; solving the vibration suppression objective function. The minimum value is used as the radius of the transition arc. ; based on and the maximum allowed centripetal acceleration , calculate the basic transition feed rate ; obtain the N continuous corner point sequence after the corner point , calculate the weighted influence factor of each corner point in the N continuous corner point sequence on the corner point ; sum the N weighted influence factors to obtain the comprehensive influence coefficient , and use to adjust to obtain the modified transition feed rate ; A speed transition zone is planned on the straight line segment where the start and end points of the transition arc are located; in the speed transition zone, according to the straight line segment feed speed, the corrected transition feed speed , the maximum allowable acceleration , and the maximum allowable jerk , an S-shaped acceleration and deceleration speed curve is constructed; a transition arc generated with a transition arc radius is used to replace the corner point in the initial milling tool path , and the feed speed on the transition arc and in the speed transition zone is determined according to the S-shaped acceleration and deceleration speed curve, to generate an optimized milling tool path.

2. The method of claim 1, wherein, the base transition feed rate is calculated by the equation: wherein, is the maximum allowed centripetal acceleration, is the transition circular arc radius.

3. The method of claim 1, wherein, The calculation of each corner point in a sequence of N consecutive corner points... The weighted influence factors include: the path distance between the end point of the transition arc of a corner point to the start point of the transition arc of a subsequent corner point ; the weighted influence factor is calculated by the following formula ; the weighted influence factor is calculated by the following formula ; the weighted influence factor is calculated by the following formula wherein, is the corner angle of the subsequent corner point C is a preset normalization coefficient.

4. The method of claim 1, wherein, the modified transition feed rate is calculated by the equation: wherein, is the base transition feed rate, a is a preset dimensionless influence decay coefficient, is the overall influence coefficient.

5. The method of claim 1, wherein, The S-shaped acceleration and deceleration speed curve comprises a uniform acceleration acceleration segment, a uniform acceleration segment, a uniform deceleration acceleration segment, a uniform speed segment, a uniform acceleration deceleration segment, a uniform deceleration segment and a uniform deceleration deceleration segment.

6. The method of claim 5, wherein, The method comprises the following steps: constructing an S-shaped acceleration-deceleration speed curve according to a linear segment feeding speed, a corrected transition feeding speed , a maximum allowed acceleration , and a maximum allowed jerk . According to the straight line segment feed speed, the corrected transition feed speed , the maximum allowable acceleration , and the maximum allowable jerk , the durations of the uniform acceleration segment, the uniform acceleration segment, the uniform deceleration segment, the uniform speed segment, the uniform acceleration-deceleration segment, the uniform deceleration segment, and the uniform deceleration-deceleration segment are sequentially calculated, and the speed values at each discrete time point are integrated to form a continuous and smooth S-shaped acceleration-deceleration speed curve.

7. The method of claim 1, wherein, the turn angle by the following: The straight line segment is calculated first With The dot product of the direction vectors, and the included angle between the two direction vectors is obtained using the inverse cosine function, and then the included angle is subtracted by 180 degrees to obtain the turning angle .

8. The method of claim 1, wherein, the maximum allowed jerk the maximum rate of change of the allowed acceleration over time.

9. The method of claim 1, wherein, The initial milling tool path composed of straight line segments is acquired, and the corner points between adjacent straight line segments are identified With The corner points between adjacent straight line segments are identified , including: sequentially processing each program segment in the numerical control machining G code file by the parser, when detecting two continuous G01 linear interpolation instructions, if the end point coordinates of the previous G01 instruction and the start point coordinates of the subsequent G01 instruction are coincident, then the coincident coordinate points are identified as corner points , and the vectors defined by the two G01 instructions are identified as adjacent straight line segments And .

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