Five-axis linkage machine tool motion model construction method

Abstract

The invention relates to the technical field of numerical control machine tools, in particular to a five-axis linkage machine tool motion model construction method, which comprises the following steps of: determining a kinematics solving sequence of five axes of a machine tool, namely a B axis, a C axis, a Z axis, a Y axis and a C20 axis in sequence; constructing a motion mathematical model of the B axis and the C axis; constructing a motion mathematical model of the Z axis; constructing motion mathematical models of a Y axis and a C20 axis according to a cutter location track source file of the machine tool, the B-axis motion mathematical model and the cutter length; according to machining of a workpiece in the-Y direction of a machine tool coordinate system, a linkage mathematical model of all axes is constructed; and compiling a post-processing program of the machine tool. According to the method, the kinematic model of the machine tool is reconstructed, an iterative algorithm is not used, a calculation method for the position of the linkage shaft of the machine tool is directly deduced, the post-processing program of the machine tool is programmed according to the deduced calculation method, the numerical control machining program capable of being recognized by the machine tool is efficiently and accurately generated, operation is simple, and the data size is small.

Description

Technical Field

[0001] The invention relates to the technical field of numerically controlled machine tools. Background Art

[0002] Five-axis CNC machine tools usually have two rotary axes and three linear axes linked together. Their post-processor algorithms are very mature and are used as standard post-processors in Siemens NX software. However, in the field of large propeller CNC machining, five-axis linkage milling machines with large turntables and double swing angle heads are used to achieve linkage machining through three rotary axes and two linear axes. The post-processor that comes with Siemens NX cannot meet the needs and must be developed separately for this type of CNC machine tools. The post-processor currently developed can achieve linkage between three rotary axes and two linear axes, and its calculation is mainly achieved through iterative algorithms.

[0003] The iterative algorithm gradually approaches the target result by repeatedly executing calculations. It may fall into a local optimal solution, resulting in poor versatility and slow convergence. Faced with the complex tool paths and large data volumes of the precision machining program, it can be clearly felt that the calculation time of the post-processing program has become longer. Summary of the invention

[0004] In order to solve the technical problems of poor versatility, slow convergence speed, complex tool paths and large data volume caused by realizing the linkage of three rotary axes and two linear axes of a machine tool through an iterative algorithm in the prior art, the present invention provides a method for constructing a five-axis linkage machine tool motion model.

[0005] The technical solution adopted by the present invention to achieve the above-mentioned purpose is:

[0006] A method for constructing a five-axis linkage machine tool motion model comprises the following steps:

[0007] S1. According to the motion law of the five-axis machine tool, the kinematic solution order of the five axes of the machine tool is determined to be B axis, C axis, Z axis, Y axis and C20 axis;

[0008] S2. Construct the mathematical model of the motion of the B-axis and C-axis according to the Rodriguez formula;

[0009] S3. Constructing a mathematical model of motion of the Z axis based on the mathematical model of motion of the B axis;

[0010] S4. Constructing the motion mathematical model of the Y axis and the C20 axis according to the (X1, Y1) coordinate value in the tool path source file of the machine tool, the B axis motion mathematical model and the tool length;

[0011] S5. Based on the constructed motion mathematical models of the B-axis, C-axis, Z-axis, Y-axis and C20-axis, the mathematical models of the linkage of each axis are constructed according to the processing of the workpiece in the -Y direction of the machine tool coordinate system.

[0012] The step S2 obtains the calculation formula of the rotation of the tool vector V around the reference vector U according to the Rodriguez formula:

[0013] V'=V×cosθ+(U×V)×sinθ+U×(U·V)×(1-cosθ)

[0014] Where: V is the vector (i, j, k) of the tool in the tool path source file, the reference vector U is the Z axis (0, 0, 1) of the machine tool coordinate system, and the rotated vector V' is (i×cosθ, i×sinθ+j×cosθ, k);

[0015] Construct the angle calculation formula between the B axis and the C axis based on the vector V':

[0016] B = arcos(k)

[0017] C=arctg((i×sinθ+j×cosθ) / (i×cosθ))

[0018] Expand the angle calculation formula of the C axis to get:

[0019] C = arctg(j / i)+θ.

[0020] The motion mathematical model of the Z axis in step S3 is:

[0021] Z=Z1+HC+(HB+CL)×k

[0022] Where: Z1 is the position of the coordinate point in the tool trajectory source file of the machine tool, HC is the distance from the end face of the machine tool slide to the B-axis rotation center, HB is the distance from the B-axis rotation center of the machine tool's double-swing milling head to the end face of the milling head, and CL is the tool length.

[0023] The motion mathematical model of the Y axis in step S4 is:

[0024]

[0025] The motion mathematical model of the C20 axis is:

[0026] C20=arctg((X1+(HB+CL)×i) / (Y1+(HB+CL)×j)).

[0027] The mathematical model of the axis linkage in step S5 is:

[0028]

[0029] C20=arctg((X1+(HB+CL)×i) / (-1)×(Y1+(HB+CL)×j))

[0030] C = arctg (j / i) - C20.

[0031] The method further includes step S6 of using the post-processing constructor Post Builder of Siemens NX to convert the obtained mathematical model into an expression of TCL language, and compile a post-processing program of the machine tool.

[0032] The advantages of the present invention compared with the prior art are:

[0033] The present invention aims at a 3-rotational 2-linear five-axis linkage machine tool used in the field of large propeller CNC machining. The kinematic model of the machine tool is reconstructed, and a calculation method for the position of the linkage axis of the machine tool is directly derived without using an iterative algorithm. A post-processing program of the machine tool is compiled according to the derived calculation method, so as to achieve efficient and accurate generation of a CNC machining program that can be recognized by the machine tool, with simple calculation and small data volume. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flow chart of a method for constructing a five-axis linkage machine tool motion model of the present invention.

[0035] Figure 2 It is a diagram of the B-axis and C-axis analysis process in a method for constructing a five-axis linkage machine tool motion model of the present invention.

[0036] Figure 3 It is an analysis diagram of the coordinate system of the Z axis in a method for constructing a five-axis linkage machine tool motion model of the present invention.

[0037] Figure 4 It is a diagram of the analysis process of the Y-axis and C20-axis in a method for constructing a five-axis linkage machine tool motion model of the present invention. DETAILED DESCRIPTION

[0038] The invention provides a method for constructing a five-axis linkage machine tool motion model. Figure 1 As shown, the following steps are included:

[0039] S1. According to the motion law of the five-axis machine tool, the kinematic solution order of the five axes of the machine tool is determined to be B axis, C axis, Z axis, Y axis and C20 axis;

[0040] The CNC machine tool used for processing large propeller blades in this scheme is a gantry vertical milling machine, whose rotary table center is concentric with the ram center. During processing, the propeller is placed at the center of the rotary table. Through the double-swing milling head, beam, ram, rotary table and other components, a five-axis processing mode with three rotary axes and two linear axes is realized. In order to improve processing efficiency, the X-axis is eliminated during the design of this machine tool, that is, the huge gantry frame is avoided from repeatedly moving short distances in the X-axis direction during processing, and the rotation of the rotary table is used to convert the feed in the X-axis direction. Thus, this five-axis processing mode with three rotary axes and two linear axes is formed. Common five-axis CNC machine tools, whether they are double-swing head structures, double-turntable structures, or swing head and turntable structures, all belong to the linkage mode of 2 rotary axes and 3 linear axes. Their kinematic calculation relationships have long had mature calculation methods, which are used as a standard template in the post-processing constructor of Siemens NX. However, this type of motion form with 3 rotary axes and 2 linear axes linked requires the calculation method to be rebuilt and expressed in the command language TCL used by the post-program constructor of Siemens NX, in order to convert the tool trajectory source file into a CNC code file that can be recognized by the machine tool.

[0041] In this scheme, the machine tool structure consists of three rotary axes and two linear axes. The three rotary axes are:

[0042] C20 axis (the rotary table rotates around the Z axis and can rotate N*360°);

[0043] C axis (double swing angle milling head rotates around the Z axis and can rotate N*360°);

[0044] B axis (double swing angle milling head rotates around the Y axis, ±95° rotation);

[0045] Its two linear axes are:

[0046] Y-axis (horizontal machine tool beam linear axis);

[0047] Z axis (vertical machine slide linear axis).

[0048] The calculation method of the kinematics of each linkage axis is essentially to build a mathematical model that can convert the coordinate points and tool vector points in the tool path source file into the motion positions of each CNC axis in the linkage of the CNC machine tool. Due to the particularity of this 3-rotary axis 2-linear axis linkage method, the RTCP function in the CNC system cannot be used, that is, the size of the swing milling head and the tool size cannot be automatically calculated and compensated by the CNC system. Therefore, these sizes must be calculated in the process of building the mathematical model to obtain the precise motion position of each CNC axis.

[0049] The kinematic model of the common double-swing angle five-axis linkage machine tool is easier to establish and understand. It is processed through the linkage of 2 rotary axes and 3 linear axes. For any point that needs to be cut in space, the B-axis and C-axis of the double-swing angle milling head are rotated to make the tool installed on the end face of the milling head move to the specified angle. The angles of the B-axis and C-axis are calculated by the tool vector in the tool path source file. At the same time, the X-axis, Y-axis and Z-axis of the gantry frame of the machine tool are linked to enable the double-swing angle milling head to reach the specified position. The positions of the X-axis, Y-axis and Z-axis are calculated by the coordinate points and the rotation angle of the double-swing angle milling head in the tool path source file. However, the motion mode of the linkage of 3 rotary axes and 2 linear axes in this scheme does not have an X-axis. Instead, the double-swing angle milling head is linked to the C20 axis of the rotary table, the Y-axis of the beam and the Z-axis of the ram to reach the specified position. The rotation of the C20 axis of the rotary table causes the problem of the coordinate point and the vector point rotating around the Z-axis in this motion process. According to the tracking relationship between these five linked axes, the changes in the C20 axis, Y axis, and Z axis will drive and affect the positions of the B axis and the C axis. Therefore, it is necessary to first analyze the changes in the tool vector that affect the angles of the B axis and the C axis, that is, the analysis process from the end of the tool along the double-swing angle milling head to the machine tool body.

[0050] S2. Construct the mathematical model of the motion of the B-axis and C-axis according to the Rodriguez formula; the change of vector rotation can be regarded as the process of any vector V in space rotating around the reference vector U by an angle θ. According to the Rodriguez formula, the calculation formula of the tool vector V rotating around the reference vector U is obtained:

[0051] V'=V×cosθ+(U×V)×sinθ+U×(U·V)×(1-cosθ)

[0052] Where: V is the vector (i, j, k) of the tool in the tool path source file. The tool path source file mainly contains the coordinate points (x, y, z) of the tool path in the machining coordinate system and the tool axis vector (i, j, k). In the tool path source file generated in Siemens NX, GOTO / is followed by the coordinate value and tool vector value of the tool movement, the reference vector U is the Z axis (0, 0, 1) of the machine tool coordinate system, and the rotated vector V' is (i×cosθ, i×sinθ+j×cosθ, k);

[0053] It can be seen that no matter how much the rotary table C20 axis rotates, the vector component k that determines the angle of the double-swing milling head B axis remains unchanged.

[0054] Construct the angle calculation formula between the B axis and the C axis based on the vector V':

[0055] B = arcos(k)

[0056] C=arctg((i×sinθ+j×cosθ) / (i×cosθ))

[0057] Expand the angle calculation formula of the C axis to get:

[0058] C = arctg(j / i)+θ.

[0059] It can be seen that the position of the C-axis angle is composed of the angle calculated by the vector in the tool path source file and the angle of the rotary table. The B-axis and C-axis analysis process is as follows: Figure 2 (The size structure of the double-swing milling head and the installed tool are simplified to straight line segments).

[0060] S3. After determining the angles of the B-axis and C-axis of the double-swing milling head, the position of the Z-axis can be analyzed, such as Figure 3 As shown in the figure, because the position of the Z axis follows the angle change of the B axis, by analyzing the positional relationship between the milling head and the tool in space, the motion mathematical model of the Z axis is constructed according to the motion mathematical model of the B axis:

[0061] Z=Z1+HC+(HB+CL)×k

[0062] Where: Z1 is the position of the coordinate point in the tool trajectory source file of the machine tool, HC is the distance from the end face of the machine tool slide to the B-axis rotation center, HB is the distance from the B-axis rotation center of the machine tool's double-swing milling head to the end face of the milling head, and CL is the tool length.

[0063] S4. Finally, the Y axis and C20 axis are analyzed. If the B axis of the double-swing milling head always keeps 0 degrees, that is, it is parallel to the Z axis, which is equivalent to the linkage of the Y axis, Z axis, and C20 axis. The coordinate points X1 and Y1 in the tool path source file can be directly used to obtain the position of the slide. However, during the five-axis linkage process, the B axis of the double-swing milling head will rotate by an angle. This angle causes the length of the B axis to accumulate the length of the tool to produce an offset in the XY plane. This requires calculating the specific offsets in the X and Y directions in the XY plane, and correcting X1 and Y1 in the tool path source file to obtain the actual X and Y coordinate values, such as Figure 4 As shown in the figure, the positions of the Y axis and the C20 axis can be calculated through the actual coordinates (X, Y). Due to the rotation of the rotary table, it can be seen from the figure that the position of the Y axis is the distance from the actual coordinates (X, Y) to the center of rotation. The rotation angle of the machine tool C20 is the angle between the actual coordinates (X, Y) and the Y direction. The motion mathematical model of the Y axis and the C20 axis is constructed according to the (X1, Y1) coordinate value in the machine tool's in-place trajectory source file, the B axis motion mathematical model and the tool length:

[0064]

[0065] The motion mathematical model of the C20 axis is:

[0066] C20=arctg((X1+(HB+CL)×i) / (Y1+(HB+CL)×j)).

[0067] S5. Based on the constructed motion mathematical models of the B-axis, C-axis, Z-axis, Y-axis and C20-axis, the mathematical models of the linkage of each axis are constructed according to the processing of the workpiece in the -Y direction of the machine tool coordinate system:

[0068] B = arcos(k)

[0069] Z=Z1+HC+(HB+CL)×k

[0070]

[0071] C20=arctg((X1+(HB+CL)×i) / (-1)×(Y1+(HB+CL)×j))

[0072] C = arctg (j / i) - C20.

[0073] Where: X1, Y1, Z1, i, j, k are the coordinate points and tool vector points in the tool trajectory source file, HC is the distance from the end face of the ram to the rotation center of the B axis, HB is the distance from the rotation center of the B axis to the end face of the milling head, and CL is the tool length.

[0074] S6. Prepare the post-processing program of the machine tool based on the obtained mathematical model of the axis linkage.

[0075] The post-processing program compiled in this solution is completed in the Siemens NX post-processing builder Post Builder, which is a tool software for creating and modifying post-processing programs. It defines the format and output content of NC programs in an interactive way of a graphical interface and uses TCL language as its command language. After the kinematic model of this CNC machine tool is established, it can be converted into the expression of TCL language in Post Builder to compile a post-processing program dedicated to this machine tool.

[0076] Set the main machine parameters in Post Builder

[0077] The machine tool in this solution is not included in the standard post-processing template of Post Builder, so only the standard 5-axis double-swing milling machine template can be selected. The machine tool type in this solution needs to be converted in the kinematic relationship calculation. According to the actual structural data of the CNC machine tool and the requirements of the CNC system, the settings are made in the three main modules of the software. The machine tool structure parameter module needs to define the subordinate relationship of each linkage axis of the machine tool according to the machine tool structure and kinematic relationship, determine the limit travel of each axis, and build the digital machine tool structure; the program and tool path parameter module is the main data calculation module, which determines the running position of each linkage axis. This process will calculate the coordinate points and tool vector points in the tool path source file into the actual running position of each linkage axis according to the structural characteristics of the CNC machine tool. In this module, the kinematic calculation formula of the machine tool in this solution needs to be written into the tool path processing process as a custom command; the NC data definition module needs to define the G code and M code format, the format of the machining program output, the number of bits of the output coordinate data, the sequence number of the program segment and other specific contents.

[0078] TCL language expression of machine tool kinematics model

[0079] According to the syntax rules of TCL language, the calculation expressions of each linkage axis can be obtained:

[0080] set B[expr acos($k)]

[0081] set Z[expr{$Z1+$HC+($HB+$CL)*$k}]

[0082] set Y[expr{(-1)*sqrt(($X1+($HB+$CL)*$i)*($X1+($HB+$CL)*$i)+($Y1+($HB+$CL)*$j)*($Y1+($HB+$CL)*$j))}]

[0083] set C20[expr{atan2(($X1+($HB+$CL)*$i),(-1)*($Y1+($HB+$CL)*$j))*$RAD2DEG}]

[0084] set C[expr{atan2($j,$i)-$C20}]

[0085] Generate postprocessor

[0086] By writing the TCL language expression of the machine tool kinematic model into the Post Builder as a custom command, the post-processor for the linkage of 3 rotary axes and 2 linear axes in this solution can be generated. The software system will generate 2 files, .def and .tcl files, which will calculate and process the information and data in the tool path source file and generate the NC machining program format that the machine tool in this solution can recognize. The NC machining program generated by the post-processor can be simulated using machining simulation software to verify the correctness of the calculation of each linkage axis by the post-processor. After actual cutting, the correctness of the post-processor calculation can be verified again.

[0087] The linkage mode and calculation method of 3 rotations and 2 straight lines in this solution can be applied to five-axis CNC floor-standing boring and milling machines. The calculation method of 3 rotations and 2 straight lines in this solution can be applied in the post-processing compilation process of other CAM software. The calculation method of 3 rotations and 2 straight lines in this solution can be applied to the CNC system of machine tools, which can enable this five-axis linkage mode in this solution to have RTCP function (tool tip point following function).

[0088] The present invention is described by way of embodiments, and those skilled in the art will appreciate that various changes or equivalent substitutions may be made to these features and embodiments without departing from the spirit and scope of the present invention. In addition, under the teachings of the present invention, these features and embodiments may be modified to adapt to specific circumstances and materials without departing from the spirit and scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application belong to the protection scope of the present invention.

Claims

1. A method for constructing a five-axis linkage machine tool motion model, characterized in that: The following steps are involved: S1. According to the motion law of the five-axis machine tool, the kinematic solution order of the five axes of the machine tool is determined to be B axis, C axis, Z axis, Y axis and C20 axis; S2. Construct the mathematical model of the motion of the B-axis and C-axis according to the Rodriguez formula; S3. Constructing a mathematical model of motion of the Z axis based on the mathematical model of motion of the B axis; S4. Constructing the motion mathematical model of the Y axis and the C20 axis according to the (X1, Y1) coordinate value in the tool trajectory source file of the machine tool, the B axis motion mathematical model and the tool length; S5. Based on the constructed motion mathematical models of the B-axis, C-axis, Z-axis, Y-axis and C20-axis, the mathematical models of the linkage of each axis are constructed according to the processing of the workpiece in the -Y direction of the machine tool coordinate system.

2. The method for constructing a five-axis linkage machine tool motion model according to claim 1, characterized in that: The step S2 obtains the calculation formula of the rotation of the tool vector V around the reference vector U according to the Rodriguez formula: V'=V×cosθ+(U×V)×sinθ+U×(U·V)×(1-cosθ) Where: V is the vector (i, j, k) of the tool in the tool path source file, the reference vector U is the Z axis (0, 0, 1) of the machine tool coordinate system, and the rotated vector V' is (i×cosθ, i×sinθ+j×cosθ, k); Construct the angle calculation formula between the B axis and the C axis based on the vector V': B = arcos(k) C=arctg((i×sinθ+j×cosθ) / (i×cosθ)) Expand the angle calculation formula of the C axis to get: C = arctg(j / i)+θ.

3. The method for constructing a five-axis linkage machine tool motion model according to claim 1, characterized in that: The motion mathematical model of the Z axis in step S3 is: Z=Z1+HC+(HB+CL)×k Where: Z1 is the position of the coordinate point in the tool trajectory source file of the machine tool, HC is the distance from the end face of the machine tool slide to the B-axis rotation center, HB is the distance from the B-axis rotation center of the machine tool's double-swing milling head to the end face of the milling head, and CL is the tool length.

4. The method for constructing a five-axis linkage machine tool motion model according to claim 1, characterized in that: The motion mathematical model of the Y axis in step S4 is: The motion mathematical model of the C20 axis is: C20=arctg((X1+(HB+CL)×i) / (Y1+(HB+CL)×j)).

5. The method for constructing a five-axis linkage machine tool motion model according to claim 1, characterized in that: The mathematical model of the axis linkage in step S5 is: C20=arctg((X1+(HB+CL)×i) / (-1)×(Y1+(HB+CL)×j)) C = arctg (j / i) - C20.

6. The method for constructing a five-axis linkage machine tool motion model according to claim 1, characterized in that: The method further includes step S6 of using the post-processing constructor Post Builder of Siemens NX to convert the obtained mathematical model into an expression of TCL language, and compile a post-processing program of the machine tool.

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