CN112069611A - Complete machine modeling method for swing angle milling head based on block modeling and experimental parameter identification - Google Patents
Complete machine modeling method for swing angle milling head based on block modeling and experimental parameter identification Download PDFInfo
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Abstract
The invention discloses a complete machine modeling method for a swing angle milling head, which belongs to the technical field of modeling and is used for modeling in blocks and identifying experimental parameters. The method comprises the steps of determining module division according to the structure and the junction surface distribution of the swing head, establishing an equivalent dynamic model by taking non-consolidated connection structures such as junction surfaces, bearings and the like as boundaries among modules, and solving a dynamic equation. Then, the machine tool is split according to the divided modules, excitation experiments are respectively carried out on the modules, frequency response functions are collected, finite element models corresponding to the modules are established, joint surface parameters which can enable the error between the theoretical value and the measured value of the frequency response functions to be minimum are searched through an optimization algorithm, and the searched joint surface parameters are added to the finite element models of the modules. And finally integrating the finite element models of all the modules into a model of the whole head swinging machine, solving a tail end frequency response function, comparing the tail end frequency response function with the actually measured frequency response function, and verifying the reliability of the model and the feasibility of the modeling method.
Description
Technical Field
The invention belongs to the technical field of modeling, and particularly relates to a complete machine modeling method for a swing angle milling head, which is used for block modeling and experimental parameter identification.
Background
The swing angle milling head (for short, the swing head) is a core component on a multi-axis linkage numerical control machine tool, the swing angle milling head has a complex internal structure, various loading conditions and a plurality of motion poses, great difficulty is brought to research and design work, but the precision of the swing angle milling head basically directly determines the machining precision, so the swing angle milling head is also a difficult-to-avoid research focus. Effective and accurate complete machine modeling of the machine tool has great significance for characteristic research and structure optimization of the machine tool, but the complete machine modeling of the machine tool has the difficulties of large modeling workload, more parameters and difficult result verification due to complex structure and numerous joint surfaces of the machine tool.
The finite element method is the most effective and most simple method for researching the dynamic and static characteristics of the structure at present, in recent years, China has a great deal of research on finite element modeling, and basic research aiming at the dynamic characteristics of machine tools mainly focuses on the following aspects: the dynamic characteristic analysis of key parts (such as tool sharp points of a machine tool), the finite element analysis of large structural parts (a cross beam and a main spindle box of the machine tool), the acquisition of dynamic characteristics and dynamic parameters of a joint surface (a column-main spindle joint surface), the dynamic characteristic analysis of a servo feeding unit and the like.
Regarding finite element complete machine modeling direction, there are still three problems in general: (1) basic research is not yet sufficient: the research on modeling in foreign countries is established on a large number of related experiments, the setting of important parameters such as bearing rigidity, joint surface rigidity and the like is supported by a large amount of data, and the research in domestic countries is purely based on experience or directly uses the parameters provided by manufacturers, so that accurate identification cannot be carried out. (2) The accuracy of the model is low: in order to reduce the operation amount of simulation and save the function of a computer, finite element simulation needs to simplify a model by some simplifying methods (joint surface fixing, bearing simplification and mechanism simplification), but the methods are more ideal, influence on the model is difficult to examine, and finally, the simulation result is lack of experimental verification. And (3) the research on the dynamic characteristics is insufficient, and due to the limitation of finite element software functions and the insufficiency of a modeling theory method, the research on the dynamic characteristics of the machine tool still stays at a relatively shallow stage, and the boundary conditions of the machine tool under the motion condition are not set to have a convincing quantitative standard. Therefore, there is also a relatively large distance to move from finite element modeling research to practical guided design optimization.
Disclosure of Invention
In order to solve the problems, the invention provides a complete machine modeling method of a swing angle milling head, which comprises the following steps of:
1) carrying out module division on the whole swing angle milling head, and respectively establishing finite element models;
2) splitting the swing angle milling head according to the divided modules, and respectively carrying out an excitation experiment on the split modules to obtain a frequency response function;
3) and (4) fitting according to experimental parameters to obtain finite element models of all modules, and integrating the finite element models into a model of the whole swing angle milling head.
And the experimental parameters comprise joint surface parameters which are obtained by searching through an optimization algorithm when the error between the theoretical value and the measured value of the frequency response function is minimum, and the joint surface parameters are added to the finite element models of the modules.
The module division is based on the non-fixed connection structure as a boundary; the non-consolidation connecting structure comprises an inter-structure joint surface and a bearing.
The module comprises a part which is fixedly connected with the fixed plane and does not rotate, a part which rotates along with the swinging shaft but does not rotate along with the electric main shaft, and a part which rotates along with the electric main shaft.
The part which is fixedly connected with the fixed plane and does not rotate comprises a swinging head shell and a swinging shaft motor stator; the part which rotates along with the swing shaft but does not rotate along with the electric spindle comprises a swing shaft motor rotor, an electric spindle shell and an electric spindle electronic stator; the electric spindle motor rotor, the electric spindle shaft body, the cutter and the cutter handle are partially rotated along with the electric spindle.
The step 3) of integrating process is specifically as follows: and establishing a complete machine model of the swing angle milling head with different poses according to the parameters obtained by fitting, and respectively comparing with an excitation experiment to obtain a frequency response function so as to verify the model.
The invention has the beneficial effects that:
1. the method for modeling the whole head swing machine by using the block modeling and the experimental parameter identification obtains a more accurate joint surface and structural rigidity by using the experimental simulation and the parameter identification, accurately predicts a frequency response function, and provides effective reference for further structural optimization and part selection.
2. The invention applies the method of coupling the block modeling and the RCSA to the complete machine tool modeling with complexity and larger volume, and the modeling of each part is combined with the verification of the experiment, so the precision is higher, and two models, namely a dynamic model and a static model, are established according to the particularity of the head swinging model. Can be applied to the research of machine tools with similar structures and provides more accurate guidance for the production design in reality
Drawings
FIG. 1 is a schematic flow diagram of the process of the present invention;
FIG. 2 is an equivalent kinetic model of a swing angle milling head;
FIG. 3 is a finite element model of a swing angle milling head;
FIG. 4a is an I-th structural embodiment; FIG. 4b is a finite element model of the I-th structure;
FIG. 5a is a second embodiment; FIG. 5b is a finite element model of a structure II;
FIG. 6 is an electric spindle finite element model of structure III;
FIG. 7 is a comparison of frequency response functions for a dynamic case and a static case of a swing angle milling head;
FIG. 8 is a comparison of an experimental curve of an end frequency response function under static conditions with a simulated predicted curve;
FIG. 9 is a comparison of an experimental curve of a dynamic condition end frequency response function with a simulated predicted curve;
wherein:
1-structure I; 2-structure II; 3-structure III; k1-a crossed roller bearing; k2-an electric spindle bearing; points-1 a, 1b, 2a, 2b, 2c, 3a, 3 b.
Detailed Description
The invention is described in further detail below with reference to the following figures and specific examples:
according to the process shown in the method flow chart of FIG. 1, module division and sampling points are determined by taking a joint surface between structures and a bearing as an interface according to the structure of a swing head;
respectively establishing three-dimensional finite element models according to the divided modules, and properly simplifying the complex structure;
splitting the machine tool according to the condition of the division module, and respectively carrying out excitation experiments on corresponding models to obtain a frequency response function and a transfer function between sampling points;
according to the frequency response function acquired through the experiment, an optimization module of the Ansys is utilized, and the solution of the joint surface parameter, which can enable the error between the theoretical value and the measured value of the frequency response function to be minimum, is searched by taking the joint surface rigidity parameter as a variable.
Establishing a spring-damping model of the joint surface according to the joint surface parameters obtained by solving;
integrating the established models of the module and the joint surface into a model of the whole machine, performing dynamic response calculation in Ansys, and predicting a frequency response function;
and comparing the predicted frequency response function with the whole machine frequency response function acquired by the excitation experiment, and verifying the accuracy of the model.
The most difficult in the whole machine modeling is a combined surface with complex structure and various loads on a machine tool, and key combined parts in the model are a connecting piece crossed roller bearing of a swinging head and a swinging head shell, and an electric main shaft bearing, namely a pair of angular contact ball bearings and a cylindrical roller bearing. Based on a response coupling substructure analysis (Rceptaceutraling coupling substructure analysis) method proposed by Schmitz and the like, the three bearing structures are simplified into a spring and damping system, and an equivalent dynamic model is shown in a figure 2, wherein the structure I1 comprises a swing head shell, a swing shaft motor stator and the like which are fixedly connected with a fixed plane and do not rotate; the II structure 2 comprises a part of a swing shaft motor rotor, an electric spindle shell, an electric spindle electronic stator and the like which rotate along with the swing shaft but do not rotate along with the electric spindle at a high speed; the III structure 3 comprises parts, such as an electric spindle motor rotor, an electric spindle shaft body, a cutter handle and the like, which rotate at a high speed along with the electric spindle. The overall finite element model is shown in figure 3.
Let K1、K2Each being a matrix of coupling stiffness between the structures, i.e. crossed roller bearings K1And an electric spindle bearing K2The stiffness matrix of (a). Let TijIn a free state for the structureWhen the excitation is applied at the j point, the response matrix at the i point expands by the expression:
wherein Xi、θiAs a response of displacement and rotation angle at point i, Fj、MjInput excitations for forces and moments at the j point. In the matrix, XiThe method can be measured through experiments, because the existing method for measuring the rotation angle has larger error and complicated operation, after an Euler beam or an Ferumoco beam simplified model is generally used, a differential equation of displacement and the rotation angle is established, and the response theta of the rotation angle is obtained through measuring the displacementi. The difference equation can be expressed as:
where i, j, k are three points separated by s.
GijFor the response matrix of the structure at point i when excitation is applied at point j in the coupled state, according to the coupling theory:
G3a3a＝T3a3a-T3a3b(T3b3b+G2c2c+K2)-1T3b3a (3)
wherein G is2c2cTo remove the frequency response function matrix at the end 2c of the structure II 2 after the electrical principal axis is removed, the structure I1 can be considered as symmetrical, and therefore has:
G2c2c＝T2c2c-T2c2a(T2a2a+G1c1c+K1)-1T2a2c-T2c2b(T2b2b+G1b1b+K1)-1T2b2c (4)
G1c1c＝G1b1b (5)
T2a2a＝T2b2b (6)
in order to obtain the frequency response function of the tail end of the whole machine model, the frequency response function needs to be measured through experimentsT in the formulae (3) and (4)ijAnd find the stiffness matrix K1、K2The expression developed is:
where k and c represent the stiffness and damping of the displacement and corner responses, respectively, when subjected to M or F. The parameters for solving K can be obtained by an inverse matrix solving method, that is:
K2＝(T3b3a(G3a3a-T3a3a)-1T3a3b-T3b3b-G2c2c)-1 (8)
K1＝(T2b2cT2a2c(G2c2c-T2c2c)-1T2c2aT2c2b-T2a2a-G1c1c)-1 (9)
the fitting method takes parameters in the matrix as variables, uses an optimization algorithm in Ansys, and obtains a value which can minimize the error of the simulation curve and the experimental curve.
The main objective of the experiment is to measure the frequency response function of each part and the transfer function in a free state. The method comprises the steps of using a PCB modal force hammer to knock a measuring point to generate excitation, starting a three-way acceleration sensor and the excitation synchronously to collect data, transmitting the data to a case, then integrating the collected data, and identifying and sorting the data by using LMS test.
Firstly, carrying out excitation experiment and numerical simulation on the I-th structure 1, wherein the experimental environment and the corresponding finite element model are as shown in fig. 4a and 4b, and the boundary condition of the model simulation is that the lower bottom surface is fixed.
Four measuring points 1a, 1b, 2a and 2b are taken on an inner ring of the crossed roller bearing, each measuring point is knocked 10 times and output to LMS test. Then in Ansys, the transfer function measured by experiments is taken as an objective function, and the rigidity of each part, namely the matrix K, is identified through an optimization algorithm1And solving to obtain a frequency response function, a II structure 2 and a III structure3, the experimental and simulation processes are the same as above, and the model is shown in fig. 5a, fig. 5b and fig. 6. In order to further verify the accuracy of the identified parameters, a simplified finite element model of the bearing is extracted independently in Ansys, the rigidity value is substituted into the model, and the radial rigidity of the bearing is obtained through a static loading test.
The radial stiffness of the angular contact ball bearing model obtained through testing is 890N/um, the radial stiffness obtained through calculation according to the experimental result is 840N/um, and the stiffness given by a manufacturer is 770N/um; the radial rigidity simulated by the cylindrical roller bearing model is 440N/um, the experimental calculation value is 450N/um, and the rigidity given by a manufacturer is 400N/um.
After obtaining accurate rigidity value, integrating all parts into a whole machine model, and solving in the model to obtain G3a3a. And then carrying out an excitation experiment of the whole machine, carrying out an excitation experiment under static conditions (the swing head swing shaft is stopped, the motor is locked) and dynamic conditions (the swing head swings between minus 10 degrees and 10 degrees, and the swing head is knocked once at a zero-crossing point every time), wherein specific parameters are shown in tables 1 and 2, a response curve measured under the static and dynamic conditions is shown in a graph 7, a dynamic and static frequency response function curve obtained by model simulation is respectively compared with an actually measured frequency response function curve (a graph 8 and a graph 9), and the reliability of the model is verified.
The implementation of the invention has the following beneficial effects: compared with the existing modeling method of the whole machine of the swing head and the machine tool, the modeling of each step of the method is compared with the experimental result, the accuracy is higher, the prediction error under the dynamic condition is not more than 10 percent, and a basis is provided for further research and design optimization of the dynamic and static characteristics of the swing head.
TABLE 1 comparison of static Experimental curves with simulation curves
TABLE 2 comparison of dynamic Experimental curves with simulation curves
Claims (6)
1. A complete machine modeling method for a swing angle milling head based on block modeling and experimental parameter identification is characterized by comprising the following steps:
1) carrying out module division on the whole swing angle milling head, and respectively establishing finite element models;
2) splitting the swing angle milling head according to the divided modules, and respectively carrying out an excitation experiment on the split modules to obtain a frequency response function;
3) and (4) fitting according to experimental parameters to obtain finite element models of all modules, and integrating the finite element models into a model of the whole swing angle milling head.
2. The method according to claim 1, wherein the experimental parameters comprise a joint surface parameter obtained by searching through an optimization algorithm when the error between the theoretical value and the measured value of the frequency response function is minimum, and the joint surface parameter is added to the finite element model of each module.
3. The method of claim 1, wherein the modules are divided based on an unconsolidated interconnect structure; the non-consolidation connecting structure comprises an inter-structure joint surface and a bearing.
4. The method according to claim 1, wherein the module comprises a non-rotating part fixed to the fixed plane, a part which follows the swing shaft but does not follow the rotation of the electric spindle, and a part which follows the rotation of the electric spindle.
5. The method of claim 4, wherein the non-rotating portion fixedly connected to the fixed plane comprises a swing head housing, a swing shaft motor stator; the part which rotates along with the swing shaft but does not rotate along with the electric spindle comprises a swing shaft motor rotor, an electric spindle shell and an electric spindle electronic stator; the electric spindle motor rotor, the electric spindle shaft body, the cutter and the cutter handle are partially rotated along with the electric spindle.
6. The method of claim 1, wherein the step 3) integration process is specifically: and establishing a complete machine model of the swing angle milling head with different poses according to the parameters obtained by fitting, and respectively comparing with an excitation experiment to obtain a frequency response function so as to verify the model.
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113357349A (en) * | 2021-06-18 | 2021-09-07 | 中国第一汽车股份有限公司 | Prediction method for sealing pressure of joint surface of speed reducer shell |
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| CN108268745A (en) * | 2018-03-30 | 2018-07-10 | 华中科技大学 | A kind of binary tree robot milling system frequency response Forecasting Methodology based on RCSA |
| CN108334722A (en) * | 2018-04-19 | 2018-07-27 | 大连理工大学 | Consider micro- milling cutter point frequency response function modeling method of main shaft rotation |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20070088456A1 (en) * | 2005-04-07 | 2007-04-19 | University Of Florida Research Foundation, Inc. | System and method for tool point prediction using multi-component receptance coupling substructure analysis |
| CN108268745A (en) * | 2018-03-30 | 2018-07-10 | 华中科技大学 | A kind of binary tree robot milling system frequency response Forecasting Methodology based on RCSA |
| CN108334722A (en) * | 2018-04-19 | 2018-07-27 | 大连理工大学 | Consider micro- milling cutter point frequency response function modeling method of main shaft rotation |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN113357349A (en) * | 2021-06-18 | 2021-09-07 | 中国第一汽车股份有限公司 | Prediction method for sealing pressure of joint surface of speed reducer shell |
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Application publication date: 20201211 |