Nonlinear error control method by changing machining speed of five-axis machine tool

Abstract

The invention discloses a nonlinear error control method by changing the machining speed of a five-axis machine tool, and relates to the technical field of precision machining. Setting a nonlinear error threshold value; performing forward and inverse kinematics derivation according to a machine tool structure; cutter location information of the head and tail positions of a cutter path is obtained, the corresponding movement amount of each axis is calculated, and a starting point, the number of times of deceleration and the expected feeding speed are set; calculating fine interpolation points between the sums; calculating a nonlinear error; if so, recalculating after adjusting the feeding speed; and if yes, updating the speed between the sums, resuming and resetting, and circulating the operation until the execution is finished. For the five-axis machine tool with the RTCP function, the number of interpolation points and the distance between the interpolation points are controlled by setting an error threshold value and adjusting the machining speed between cutter location points, and the nonlinear error is effectively controlled while the machining efficiency is guaranteed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of precision machining, and particularly relates to a nonlinear error control method by changing the machining speed of a five-axis machine tool. BACKGROUND

[0002] A multi-axis linkage machine tool can adjust the tool tilt angle in real time during machining, and completes multiple processes on one device, which is suitable for various machining scenes, and has a significant advantage in machining complex parts such as impeller blades and free curved surfaces. With the development of technology, the machining precision requirement is higher and higher, and the nonlinear error of the five-axis linkage machine tool is an indispensable key factor when considering the machining precision, which has a great influence on the machining quality.

[0003] The five-axis linkage machine tool adds two rotary axes (A and C axes) on the basis of three linear axes, and the machine tool only considers the X, Y and Z three linear axes when interpolating, which leads to the actual trajectory of the tool tip deviating from the ideal trajectory due to the movement of the rotary axes during interpolation, thereby causing nonlinear error.

[0004] In this case, the machine tool needs to compensate for the nonlinear error to avoid overcutting and undercutting to reduce the machining quality. At present, the economic machine mainly adopts the post-processing method to reduce the nonlinear error, and the high-end machine adopts the RTCP function to reduce the nonlinear error. Compared with the post-processing method, the RTCP function reduces the nonlinear error in the interpolation period, and the effect is more significant. However, the current RTCP function and post-processing function only reduce the nonlinear error during machining without considering the size of the nonlinear error, and how to control the size of the nonlinear error during machining is very important.

[0005] At present, there are calculation methods and influencing factors of nonlinear error, and the size of the nonlinear error can be approximately obtained during machining. Among them, how to control the nonlinear error through the machining parameters during machining becomes an important problem.

[0006] The Chinese invention patent with the publication number CN108983704B, the authorization date of February 9, 2021, and the name of a five-axis double-turntable online nonlinear error compensation method, the disclosed nonlinear error method is characterized in that the maximum nonlinear error of the path is calculated through two known programming points, if it exceeds the set nonlinear error threshold, an interpolation point located between the two points is added, the nonlinear error between the first point and the interpolation point is calculated, and the next segment is processed. The invention scheme is stable, does not need to depend on the maximum error vector, but it does not control the nonlinear error on the machine tool with the RTCP function.

[0007] CN119369174A, the disclosure date is January 28, 2025, and the name is a nonlinear error compensation device and compensation method for a five-axis machine tool. The disclosed nonlinear error method is characterized in that the X-axis compensation assembly is installed on the bottom fixed plate, the Y-axis compensation assembly is installed on the X-axis slider, the Z-axis compensation assembly is installed on the Y-axis slider, and the workbench is installed on the Z-axis slider. For AB, BC, AC double swing head form, AC, BC double rotary table form and A swing head C rotary table, B swing head C rotary table form five-axis machine tool, nonlinear error calculation is made. The invention scheme also realizes the compensation of nonlinear error for machine tools without RTCP function, but does not control the nonlinear error of machine tools with RTCP function.

[0008] In summary, for five-axis machine tools with RTCP function, there is an urgent need for a control method that can reduce nonlinear error by adjusting machining parameters to maximize machining efficiency while meeting nonlinear error requirements. SUMMARY

[0009] To solve the problems in the background art, the present application provides a nonlinear error control method by changing the machining speed of a five-axis machine tool. For five-axis machine tools with RTCP function, by setting an error threshold, adjusting the machining speed between tool position points, controlling the number of interpolation points and the distance between interpolation points, the machining efficiency is guaranteed while the nonlinear error is effectively controlled.

[0010] To achieve the above-mentioned purpose, the present application adopts the following technical scheme: a nonlinear error control method by changing the machining speed of a five-axis machine tool, comprising the following steps:

[0011] S1, for a five-axis machine tool with RTCP function, set the maximum nonlinear error threshold allowed during machining ;

[0012] S2, analyze the structure of the five-axis machine tool, establish the machine tool kinematic chain and derive the forward and inverse kinematic models, define the tool position information for the tool tip coordinates and the tool axis vector combination ;

[0013] S3, for the part to be machined, obtain the tool position information of the first and last positions of the first tool path by processing the CAM software and , , , and import it into the five-axis machine tool according to the inverse kinematic model to calculate the movement amount of each axis corresponding to the first and last positions and , set the starting point to record The coordinates of the knife tip Set the number of decelerations. , set the first Duan Daolu Expected feed rate ;

[0014] S4. Based on the interpolation period and the Feed rate of the toolpath , Indicates the desired feed rate slow down The size after that, if This is the desired feed rate. Then calculate the starting point. and the end point The first fine interpolation point coordinates ;

[0015] S5, Calculation Corresponding movement of each axis Turntable corner , combined coordinates Obtained through inverse kinematics model The corresponding three linear axis displacements This allows us to obtain the actual motion of each axis of a five-axis machine tool over time. Substituting this into the forward kinematics model, we obtain the actual trajectory of the blade tip over time. ,Will The tool tip point is set at the location of the maximum nonlinear error, and the result is obtained. The actual tip of the blade coordinates Calculate its relationship with the line. The distance between them is the nonlinear error. ;

[0016] S6, will and If a comparison is made, If so, proceed to step S7; Then proceed to step S8;

[0017] S7, Order ,like Adjust the feed rate to And return to step S4; if Adjust the feed rate to and return to step S4;

[0018] S8, will and the speed between the two points is set to , let , reset , if , return to step S4 to process the next tool path; if , the execution is completed.

[0019] Further, in the step S2, the forward and inverse kinematics model is derived as follows:

[0020] The derivation result of the forward kinematics model is:

[0021]

[0022]

[0023] The derivation result of the inverse kinematics model is:

[0024]

[0025]

[0026] wherein X, Y, Z, A and C are the movement amounts of each axis of the five-axis machine tool, is the offset of the origin of the workpiece coordinate system relative to the machine tool coordinate system, is the offset of the program origin relative to the machine tool coordinate system, is the distance of the AC axis perpendicular line.

[0027] Further, in the step S4, the coordinate of the fine interpolation point is calculated as follows:

[0028]

[0029] wherein is the coordinate of the end point .

[0030] Further, in the step S5, the calculation formula of the rotation angle of the rotary table is as follows: .

[0031] Further, in the step S5, the expression of the nonlinear error is as follows:

[0032]

[0033] wherein , , .

[0034] Compared with the prior art, the present application has the beneficial effects that: the present application is on a five-axis precision machine tool with RTCP function, through kinematic modeling analysis of the machine tool structure, non-linear error calculation and compensation method is obtained, on this basis, by setting error threshold, the machining speed between tool position points can be adjusted, the number of interpolation points and the distance between interpolation points are controlled, and then the non-linear error is controlled, the size of the non-linear error is controlled by modifying the machining speed, while ensuring effective control of the non-linear error, the machining efficiency is improved. BRIEF DESCRIPTION OF DRAWINGS

[0035] Fig. 1 is a flowchart of the method of the present application;

[0036] Fig. 2 is a schematic diagram of a five-axis machine tool structure model;

[0037] Fig. 3 is a schematic diagram of five-axis machine tool motion. DETAILED DESCRIPTION

[0038] The technical solutions in the present application will be described clearly and completely below in combination with the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0039] The control method of non-linear error is mainly used to solve the deviation between the actual path and the theoretical path of the tool tip point during machining due to the existence of the rotating shaft in multi-axis linkage machining, and the control method of this kind of deviation, i.e. non-linear error. In precision and ultra-precision machining, non-linear error has a very great influence on machining quality, which may cause overcutting or undercutting, etc., resulting in waste pieces that do not meet the machining indicators. In traditional three-axis machine tool machining, three linear axes are linear axes, and there is no non-linear error in the real-time interpolation process of the machine tool, while in five-axis machine tool machining, the tool position information in the workpiece coordinate system is generally generated by CAM software, if the machine tool does not have RTCP function, the tool position information will be post-processed to obtain the actual command of the machine tool; while the machine tool with RTCP function directly inputs the tool position information, the machine tool will automatically analyze into the movement amount of each axis, and both of these two ways will have non-linear error, resulting in overcutting or undercutting, affecting the machining quality. At present, most of the researches generally control and study the non-linear error of machine tools without RTCP function, therefore, the present application proposes a kind of five-axis machine tool with AC rotary table type RTCP function, which adjusts the machining parameters to reduce the non-linear error.

[0040] As shown in Figs. 1-3 , a non-linear error control method by changing the machining speed of a five-axis machine tool, the flow is combinedFig. 1 As shown, comprising the following steps:

[0041] S1, for the five-axis machine tool with RTCP function, set the maximum nonlinear error threshold allowed during processing

[0042] S2, analyze the five-axis machine tool, for Fig. 2 As shown in the five-axis machine tool structure model, establish Fig. 3 As shown in the five-axis machine tool kinematic chain, define Located on the A-axis axis, Located on the C-axis axis, AC two-axis common perpendicular line; The origin of the machine tool coordinate system MCS, the point coincides with In the initial state of the machine tool, , And X, Y and Z axes of the machine tool coordinate system MCS, the positive direction of each axis is shown in the figure; The origin of the workpiece coordinate system WCS, , And X, Y and Z axes of the workpiece coordinate system WCS, the positive direction of each axis is shown in the figure; The movement amount of each axis of the five-axis machine tool is X, Y, Z, A and C, and the positive direction of each axis is shown in the figure; The vector In the initial state of the machine tool coordinate, expressed as , The distance between ; The offset of the origin of the workpiece coordinate system WCS Relative to the machine tool coordinate system MCS, expressed as ; The offset of the program origin relative to the machine tool coordinate system MCS, expressed as ; The combined vector of And .

[0043] Then the forward and inverse kinematics are derived, in which:

[0044] The forward kinematics model derivation result is:

[0045] (1)

[0046] (2)

[0047] The inverse kinematics model derivation result is:

[0048] ​ (3)

[0049] (4)

[0050] Define tool position information Coordinates of the knife tip and tool axis vector combination ;

[0051] S3. For the part to be processed, the first step is to obtain the result through CAM software. Tool position information at the beginning and end of the tool path and , The data is then imported into a five-axis machine tool and the movement of each axis corresponding to the first and last positions is automatically calculated according to formulas (3) and (4). and Set the starting point. Used to record The coordinates of the knife tip ,set up Record the number of decelerations, and set the number of decelerations. Duan Daolu Expected feed rate ;

[0052] S4. Based on the forward and inverse kinematics models, the interpolation period is known. and the Feed rate of the toolpath ( Indicates the desired feed rate slow down The size after that, if This is the desired feed rate. ), calculate the processing time The starting point of the segmented knife path coordinates and the end point coordinates fine interpolation points between The coordinates.

[0053] In actual machining, a five-axis machine tool will be in the first... The starting point of the segmented knife path and the end point Linear interpolation is performed between these points to obtain a series of fine interpolation points. These points are the actual points of motion for each axis of the five-axis machine tool, but there will be nonlinear errors in the paths between adjacent points. Based on the starting point... coordinates and the end point coordinates Interpolation period and the Feed rate of the toolpath Then the first fine interpolation point The following relationship is approximately satisfied:

[0054] (5)

[0055] The calculation formula is further obtained as follows:

[0056] (6)

[0057] Thus, the first fine interpolation point is obtained. coordinates ;

[0058] S5, Calculate the... Starting point of the segmented knife path With the first fine interpolation point Nonlinear error between .

[0059] Given the starting point coordinates ,end coordinates , Turntable corner as well as Turntable corner , to obtain the first The first precise insertion point in the Duan Daolu route Corresponding movement of each axis Turntable corner The calculation formula is as follows:

[0060] (7)

[0061] The first fine interpolation point Turntable corner and coordinates Substituting into formula (4) yields the corresponding movement of each axis. The displacement of the three linear axes .

[0062] Actual motion of each axis of a five-axis machine tool over time The calculation formula is as follows:

[0063] (8)

[0064] Because of the existence of the rotation axis, the actual motion of each axis will be calculated. Substituting into formula (1) yields the actual trajectory of the tool tip changing over time. for:

[0065] (9)

[0066] Because the point where the maximum nonlinear error is located is difficult to find, the tool tip point at time which is half of the interpolation period is approximately set as the point where the maximum nonlinear error is located. According to formula (9), the coordinates of the actual tool tip point at time are obtained, and the distance between the tool tip point and the straight line , i.e., the nonlinear error , is calculated. The expression is as follows:

[0067] (10)

[0068] In the formula, , , .

[0069] Because the interpolation points between adjacent tool tip points are very dense, and the information of adjacent tool positions changes little, to avoid excessive calculation, the nonlinear error of the first section of the tool path is determined as the obtained ;

[0070] S6, the calculated nonlinear error is compared with the set nonlinear error threshold :

[0071] If , step S7 is entered;

[0072] If , step S8 is entered;

[0073] S7, the number of decelerations is reduced;

[0074] If , according to the calculated nonlinear error and the set nonlinear error threshold , the feed speed is adjusted to , and step S4 is entered;

[0075] If , to avoid excessive calculation, the feed speed is adjusted to , and step S4 is entered;

[0076] After adjustment, the distance is shortened, thereby reducing the nonlinear error;

[0077] S8, the starting point and the end point​​​​ The intermediate speed is set as ;

[0078] Take , reset , if , turn to step S4 to calculate the nonlinear error of the next tool path; if , the execution is ended.

[0079] In summary, the application completes the calculation of nonlinear error on a five-axis machine tool with RTCP function, and can control the nonlinear error by adjusting the machining speed to reduce the distance between interpolation points through the information between two path points known in the machining.

[0080] It is apparent to those skilled in the art that the application is not limited to the details of the foregoing exemplary embodiments, and that the application can be implemented in other embodiments without departing from the spirit or essential characteristics of the application. Therefore, the embodiments should be considered in all respects as illustrative and not restrictive, and the scope of the application should be defined by the appended claims rather than the above description, and it is intended to include all changes falling within the meaning and scope of equivalents of the claims. Any reference signs in the claims should not be considered as limiting the claims involved.

[0081] Furthermore, it should be understood that, although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the present specification is described in this way only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be properly combined to form other embodiments that those skilled in the art can understand.

Claims

1. A method of non-linear error control by varying the machining speed of a five-axis machine tool, characterized in that: The method comprises the following steps: S1, for five-axis machine tool with RTCP function, set the maximum nonlinear error threshold allowed during processing ; S2. Perform structural analysis on the five-axis machine tool, establish the machine tool kinematic chain and derive the forward and inverse kinematic models, and define the tool position information. Coordinates of the knife tip and tool axis vector combination ; S3. For the part to be processed, the first step is to obtain the result through CAM software. Tool position information at the beginning and end of the tool path and , The data is then imported into a five-axis machine tool to calculate the movement of each axis corresponding to the initial and final positions based on the inverse kinematics model. and Set the starting point Used to record The coordinates of the knife tip point Set the number of decelerations. , set the first Duan Daolu Expected feed rate ; S4. Based on the interpolation period and the feed rate of the toolpath , Indicates the desired feed rate slow down The size after that, if This is the desired feed rate. Then calculate the starting point. and the end point The first fine interpolation point coordinates ; S5, calculating corresponding axis movement amount turntable rotation angle in , combined with coordinates obtained by inverse kinematics model corresponding three straight line axis movement amount in , and then obtain the actual movement amount of each axis of five-axis machine tool over time , and substitute into the forward kinematics model to obtain the actual trajectory of the tool tip point changing over time , set the tool tip point at as the maximum nonlinear error, and obtain the actual tool tip point at coordinates , calculate the distance between it and the straight line , that is, the nonlinear error ; S6、if with comparing, if then go to step S7; if then go to step S8; S7, let , if , the feed speed is adjusted to , and the process returns to step S4; if , the feed speed is adjusted to , and the process returns to step S4; S8, set the speed between the two points to and , let , reset , if , return to step S4 to process the next segment of the tool path;​ If then the execution ends.

2. A method of controlling non-linear error by varying the speed of a five-axis machine tool according to claim 1, characterized in that: In the step S2, the positive and inverse kinematics model is derived as follows: The derivation result of the positive kinematics model is: The derivation result of the inverse kinematics model is: In the formula, X, Y, Z, A and C are respectively the moving amount of each axis of the five-axis machine tool, is the offset of the origin of the workpiece coordinate system relative to the machine tool coordinate system, is the offset of the program origin relative to the machine tool coordinate system, is the distance of the common perpendicular of the AC axis.

3. A method of controlling non-linear error by varying the speed of a five-axis machine tool according to claim 2, characterized in that: In the step S4, the coordinates of the fine interpolation points are calculated according to the following formula: In the formula, the coordinates of the end point .

4. A method of controlling non-linear error by varying the speed of a five-axis machine tool according to claim 3, characterized in that: In the step S5, the rotation angle of the turntable The calculation formula is: .

5. A method of controlling non-linear error by varying the speed of a five-axis machine tool according to claim 4, characterized in that: In the step S5, the non-linear error is expressed as follows: In the formulae, , , .

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