CN115042015B

CN115042015B - Measuring head on-machine measuring method for key characteristic parameters of complex parts

Info

Publication number: CN115042015B
Application number: CN202210385978.9A
Authority: CN
Inventors: 张星; 马昂扬; 胡玉玲; 赵万华
Original assignee: Xian Jiaotong University
Current assignee: Xian Jiaotong University
Priority date: 2022-04-13
Filing date: 2022-04-13
Publication date: 2023-10-20
Anticipated expiration: 2042-04-13
Also published as: CN115042015A

Abstract

An on-machine measuring method of a measuring head of key characteristic parameters of a complex part comprises the steps of firstly determining a single measuring point contact path plan, planning a measuring path in a single characteristic, planning measuring paths among a plurality of characteristics, and connecting an optimal overall measuring path; measuring by a measuring program to obtain the coordinate value of the real measurement point of the mark point, and calculating key characteristic parameters; developing a measuring point mark, a measuring track generation, a measuring program generation and a characteristic parameter calculation function module based on a CAD kernel through CATIA CAA secondary development to form an on-machine measuring system; in the measurement planning stage, firstly, measuring point marking is carried out on a software platform, a measurement track is generated, a measurement program is derived, then actual measurement is carried out on a machine tool, and a measurement result is led into an on-machine measurement system to carry out characteristic parameter calculation and display. The invention realizes the on-machine quick measurement of the dimension parameters and the error parameters of the key features of the complex parts, has better operability and applicability, and is convenient for application in the processing field of enterprises.

Description

Measuring head on-machine measuring method for key characteristic parameters of complex parts

Technical Field

The invention belongs to the technical field of processing-measuring integration, and particularly relates to an on-machine measuring method for measuring key characteristic parameters of complex parts.

Background

With the rapid development of manufacturing industry, there is an increasing demand for less or even no human intervention in the cutting process. When the parts with high precision are processed, on-machine detection is needed between finishing working procedures and after working procedures, whether the working procedures are out of tolerance or not is judged, the working procedure quality is ensured, but the working time of a machine tool is occupied by the part of working, and the processing efficiency is reduced. Therefore, the method reduces manual intervention, improves the automation degree of the processing process, and thus improves the processing quality, improves the inspection level and accelerates the production efficiency, which is an important challenge facing the manufacturing industry in China at present.

At present, three main modes exist for detecting the quality of a workpiece: the first is manual measurement, which means that a worker uses a caliper and a dial indicator to carry out manual measurement, the measurement process is faster, but the measurement accuracy is lower, the machine tool is required to be stopped, the starting time of the machine tool can be occupied, and only some simple part characteristics can be measured; the second is measurement by a three-coordinate measuring machine, the method has high precision, does not occupy the starting time of a machine tool, but needs to repeatedly disassemble a workpiece, consumes more time, and can cause clamping errors and clamping deformation; the third is that the measuring head measures on-machine, this method utilizes the motion system of the lathe itself to replace the motion axis of the three-coordinate measuring machine, in theory, the on-machine measurement is the measurement demand of the complete and qualified complex work piece, it has saved the work piece and clamped many times, will raise too much in the measurement efficiency.

At present, from the application of abroad, a learner has introduced an on-machine measurement system into a machining center of the learner, so that the machining time is greatly shortened, and the measurement accuracy can be ensured. The on-machine measurement technology in China is generally developed and is relatively narrow in application, and some machine tools are provided with measuring heads, but the machine tools are only used for tool setting when in use, and are not used for measuring part characteristics; in addition, the measuring head is often moved in a hand-operated hand wheel mode when in use, and the sensing function of the measuring head is only utilized, so that the degree of automation is very low. Therefore, development of practical on-machine measurement systems, especially automatic generation of complex part measurement programs and calculation of characteristic parameters, is particularly urgent.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide an on-machine measuring method for measuring the key characteristic parameters of the complex parts, which can realize on-machine rapid measurement of the dimension parameters and the error parameters of the key characteristic parameters of the complex parts, has better operability and applicability, and is convenient for application in the processing field of enterprises.

In order to achieve the above purpose, the invention adopts the following technical scheme:

an on-machine measuring method for measuring key characteristic parameters of complex parts comprises the following steps:

Step 1) aiming at different areas and a plurality of characteristics of a complex part, firstly, determining a single measuring point contact path plan, then planning a measurement path in the single characteristic, then planning a measurement path among the plurality of characteristics, and finally connecting an optimal overall measurement path;

step 2), measuring by a measuring program to obtain the coordinate value of the real measurement point of the mark point, and further calculating key characteristic parameters, wherein the key characteristic parameters comprise characteristic parameters and error parameters; the characteristic parameters comprise pore diameter, pore distance and other pore characteristic parameters, wall height, wall thickness and other thin wall characteristic parameters, and web thickness characteristic parameters; the error parameters comprise dimension errors, hole coaxiality errors, hole perpendicularity errors, plane flatness errors and plane contour errors;

step 3) developing a module of CATIA through CATIA CAA for the second time, and developing functional modules of measuring point marks, measuring track generation, measuring simulation, measuring program generation, data reading, error calculation, characteristic parameter calculation and the like by means of the CAD kernel of CATIA to form an on-machine measuring system;

step 4) in the measurement planning stage, firstly, marking measuring points on a software platform, then, generating a measurement track, and deriving a measurement program; then, performing actual measurement on the machine tool; and finally, introducing the measurement result into an on-machine measurement system, and calculating and displaying the characteristic parameters.

The specific process of the step 1) is as follows:

1.1 Single station contact path planning:

the speed of the measuring head is reduced before the measuring head contacts the measuring point, the measuring head returns to the measuring point after triggering, and the measuring head is accelerated again, and the measuring head is the speed changing point;

the point of the measuring head contacting the workpiece is a contact point, the contact point is a position marked on the CAD model, an offset point is defined at the lagging position of the marked measuring point, and the offset point is used as the measuring point to be contacted by the actual measuring head;

when the measurement program is written, the coordinates of the offset point are used as measurement points, and finally, the contact path of the single measurement point is the starting point p _s Decelerating, turning on a probe trigger switch, feeding the probe along the normal direction of the measuring point, and at the actual contact point p _c Stopping and then accelerating back to the starting point;

1.2 Inter-feature inter-station path planning:

the paths among the measuring points in the single feature are required to be planned according to the specific distribution of the measuring points, interference is not considered when the measuring points in the feature move, only the quantity of the measuring points is different, so that the paths in the feature are fixed after the determination, and the paths are directly applied when the paths of the same feature are planned each time, and re-planning is not required; when each feature is planned, planning is carried out by using the minimum measurement points, and then the path is copied according to the number of the measurement points;

1.2.1 Aperture measurement path planning):

when the aperture of the single hole feature is measured, the measuring points are on the same plane, and the aperture can be measured only by at least 3 measuring points; after the path of a single measuring point is fixed, only one inlet is needed to be selected from the measuring points, namely, the measuring head enters the position of the aperture from the safety plane, then the rest measuring points are measured in sequence, the starting position of the last measuring point is defined as an outlet, and the measuring head exits from the outlet position to the safety plane;

1.2.2 Hole pitch measurement path planning:

the measurement of the hole distance needs to obtain the circle center coordinates of the two holes, if the circle center of each hole needs to be determined, each hole needs at least 3 measuring points, so the hole diameters of the two holes are divided into two parts for planning paths after the measurement of the hole distance, the path of the two holes exits to a safety plane after the measurement of one hole is completed, and the hole cross sections of the two holes need to be the same plane when the hole distance is measured;

1.2.3 Hole perpendicularity measurement path planning:

when the perpendicularity of the hole is measured, the axis of the hole is required to be measured, so that at least two hole sections are selected in the hole, the center of the circle of each section is measured to obtain the axis, and therefore, the two sections also plan paths according to the aperture measurement, and each section has at least 3 points; in addition, a base surface is required to be measured, at least 3 points are required to determine a plane according to a surface equation, and the scattering of measuring points is ensured as much as possible during taking the points;

1.2.4 Thin wall thickness and wall height measurement path planning:

obtaining a plane by least square, and calculating the thickness or the height by the average value of the distances from a plurality of measuring points on the other surface to the surface, so that at least 3 measuring points are selected on the plane, and 3 points on the reference surface are dispersed as much as possible;

1.2.5 Web thickness measurement path planning:

when the thickness of the web is measured, two planar measuring paths are separated, and each path is a single planar measuring path;

1.2.6 Curved surface measurement path planning:

the curve profile measurement requires marking measuring points along the curve direction, the number of the marking measuring points depends on the size of the curve, and at least two sections are required to be marked;

1.3 Inter-feature path planning:

the inter-feature path is regarded as a path plan in a two-dimensional plane, each feature in the two-dimensional plane is regarded as a feature point, and the intra-feature path plan has no interference, so that the basis of the plan is to find the shortest measurement path between the features, the planning of the inter-feature path is converted into a TSP problem, and the shortest path is expressed as follows:

wherein: t is time; i, j and s are points on the path;the information element on the paths of the point i and the point j at the moment t; />Heuristic factors of a point i and a point j at the moment t; alpha is the relative importance of tau; beta is the relative importance of eta; allowed _k A set of points selectable for ant k at time t;

analyzing the distribution characteristics of all the features contained in the workpiece in space, marking all the features to be measured by circles, and projecting the marks on a plane, wherein the plane is the feature point which the measuring head needs to pass through on a safety plane; optimizing the marked feature points by using an ant colony algorithm to obtain the shortest path between features;

1.4 Overall measurement path planning):

and connecting paths in a plurality of single features in series by using the inter-feature paths to obtain the whole measurement path.

The specific process of the step 2) is as follows:

2.1 Calculation of pore characteristics:

(1) Calculation of pore diameter:

the aperture is obtained by calculating the average value of the distances from all measuring points to the circle center, and the aperture is shown in the following formula:

wherein: n is the number of measuring points; (x) _i ,y _i ) Is the coordinates of the ith measuring point; (x) ₀ ,y ₀ ) Is the empty center coordinates;

(2) Calculation of hole distance:

on the basis of aperture calculation, calculating the distance between the circle centers of the cross sections of the two holes, wherein the cross sections of the two holes are in the same plane; assume that two center coordinates are (x) ₀₁ ,y ₀₁ ,z ₀₁ )，(x ₀₂ ,y ₀₂ ,z ₀₂ ) Obtaining the distance between two circle centers according to a distance formula;

2.2 Calculation of thin-wall characteristic parameters:

the calculation method of the two parameters is the same, firstly, an equation of one surface is determined through coordinates, then, the distance from a point on a second surface to a first surface is calculated through the distance from the point to the surface, and the average value of the multipoint distances is the parameters of the wall height and the wall thickness of the thin-wall feature, wherein the average value is shown in the following formula;

Wherein: (x) _i ,y _i ,z _i ) The coordinates of the ith measuring point; n is the number of measuring points; (a, b, c, d) is a coefficient of the first plane equation ax+by+cz+d=0;

2.3 Web characteristic parameters are calculated:

when the thickness of the web is measured, coordinate transformation is needed to be carried out on measurement points after the measurement of two stations is completed, the measurement points are converted to the lower surface of a workpiece coordinate system, and a calculation method of a thin wall is referred to after the conversion is completed, so that a calculation formula of the thickness of the web is obtained as follows:

wherein: d, d _j For the thickness parameter of the ith measuring point, see formula (4); n (N) _j The number of the measuring points is;

2.4 Calculation of dimensional error of feature thickness:

after the dimension thickness measurement value of the part characteristic is obtained, the dimension thickness measurement value is differenced from the design value, namely, a dimension error is obtained, and the dimension error is shown in the following formula;

e _l ＝l _m -l ₀ (6)

wherein: l (L) _m Is a measurement; l (L) ₀ Is a design value;

2.5 Hole coaxiality error parameter calculation:

pore diameter measurement is carried out at different sections of the pore to obtain N _k Center coordinates of individual cross-sectional circles (x _c,k ,x _c,k ,x _c,k ) Calculating the axis z=c of the hole according to the circle centers of the plurality of cross-section circles _a x+c _a y+c _a Then calculate the distance d from the center of each cross-section circle to the straight line _c,k Finally, calculating the average value of the two errors, namely coaxiality errors, wherein the calculation formula is as follows;

2.6 Hole perpendicularity error parameter calculation:

According to the definition of verticality, a reference plane equation is set asMeasuring point P _i (x _i ,y _i ,z _i ) Tie bias of reference section in normal directionThe difference is the hole perpendicularity error, and the calculation formula is as follows;

wherein: n (N) _i Counting the number of the measuring points; i is the number of the measuring point; (x) _i ,y _i ,z _i ) The coordinates of the ith measuring point; (v) _a ,v _b ,v _c ) Coefficients for the reference plane equation;

2.7 Surface flatness error:

obtaining the coordinates P of the point on the actual workpiece plane by measurement _i (x _i ,y _i ,z _i ) Obtaining N by least square method _i The plane equation of each measuring point is z=p _a x+p _b y+p _c And further, the minimum variance of the actual workpiece plane and the measuring point is calculated as follows:

wherein: (p) _a ,p _b ,p _c ) The coefficients of the plane equation of the measuring point;

2.8 Surface profile error:

obtaining the coordinates P of the point on the actual workpiece plane by measurement _i (x _i ,y _i ,z _i ) And calculate the distance d from the design surface _i Further, the profile error of the surface is calculated by the following formula:

the specific process of the step 3) is as follows:

3.1 The measurement point marking and the path generation are carried out in the measurement planning stage, then the actual measurement head measurement is carried out on the machine tool, and finally the measurement data are imported into the measurement system software to calculate and display key characteristic parameters;

3.2 A measuring point marking module:

the measuring point marking module is used for carrying out hierarchical nesting by using two options of characteristics and parameters, wherein the characteristics are a first level, and the parameters are a second level; the characteristics comprise holes, thin walls, ribs, upright posts, lugs and cambered surfaces, parameters to be measured of each characteristic are different, the characteristics are single-choice when the measuring points are marked, but the parameters can be multiple-choice, and the final effect is that the characteristics comprise the parameters to be measured; different measurement parameters have different measurement point numbers, so that the number of measurement points required by different parameter combinations and the position sequence of the marked measurement points need to be analyzed independently, and prompts need to be given when the measurement points are marked each time; in terms of operation logic, after a feature is selected, parameters which can be measured by the feature are in an enabled state, the rest are in a disabled state, then a mark measuring point button is in an enabled state, an adding button is in a disabled state, after the mark measuring point button is clicked, the number of marked measuring points is prompted, the mark measuring point button is placed in the disabled state, the adding button operates normally after the mark is completed, but the mark measuring point button cannot be clicked, the next group of operation can be performed only by adding the marked measuring points into a measuring point list, and a right side list box can give the marked feature, the matched parameters and the marked number information;

3.3 A measurement trajectory generation module):

the measuring track generation module is divided into two parts, for the fixed path in the characteristic, after the measuring point marking part is completed, the path in the characteristic is generated, the measuring track generation module mainly points to the position of the specified lifting tool and generates the path between the characteristics, normal vector information in the figure is used for displaying normal vector information of the measuring point relative to the surface in the CAD model, the safety plane button is used for specifying the height of the lifting tool, the measuring track button is used for generating the final measuring track, and the generated track can be displayed in the CAD model; automatically generating a starting point and an offset point in track generation, wherein the starting point is displayed in a CAD model, the starting point is also a variable speed point in measurement, and the offset point is not displayed in the CAD model but is seen through a list box on the right side of a window;

3.4 A measurement simulation module):

the measurement simulation module simulates a measurement process in a CAD model, the measuring head is also Part type digital-analog in CATIA, the simulation process can be stopped and stopped at any time, and if the measuring head collides with a workpiece in the motion process, the simulation can be automatically stopped; the volume collision in CATIA is utilized to judge interference, and the coordinates of the interference position are directly recorded and displayed in a window;

3.5 A measurement program generation module):

the measurement program generation module firstly considers the setting of the allowance, sets the corresponding allowance for each procedure to generate the actual positions of the measuring points in different procedures aiming at the measurement among the procedures; the principle is that the measuring point moves along the normal vector direction relative to the plane where the measuring point is located, and the moving distance depends on the allowance set by the working procedure; the second key set parameter is the set of the coordinate system, the set coordinate system is the measurement coordinate system, the measuring point position in the measuring procedure can be subjected to coordinate transformation according to the set coordinate system, and the generated measuring procedure is the procedure of transforming the coordinates; the program head and the program tail in the window are set with default values, the default values are changed by a craftsman, the craftsman adjusts the position of the measuring program through the program tail, and the program head is used for setting the information such as the replacement of the measuring head, the measuring speed and the like; the generated measurement program is displayed on the right side of the window, and the file is stored locally in a txt file type;

3.6 Data read-in module):

the data reading-in module reads in the actually measured coordinate information into the measuring system, the read-in file types are xls and xlsx, the measuring point display button displays the measured measuring point in the CAD model, and the coordinate information of the actual measuring point is displayed on the right side of the interface;

3.7 Error calculation module):

the error calculation module is used for calculating the deviation between the actual measurement point and the ideal measurement point, specifically, the distance between the actual measurement point and the plane to which the actual measurement point belongs, judging whether the error exists or not through the distance, displaying the error result in a right list frame of the window, and marking the error in the CAD model; if an upper error limit is established, judging where the error exists according to the error size;

3.8 A characteristic parameter calculation module):

the feature parameter calculation module is used for calculating the size to be measured, the value of the feature parameter to be calculated is preset when the feature marking module is used, the algorithm is translated into codes and written into the background according to the feature calculation method, the input value is the measured coordinate point, and the output value is the feature parameter value at the calculation position.

The specific process of the step 4) is as follows:

4.1 Marking measuring points on the workpiece digital model):

when the software is used for marking, the measuring point marking operation is carried out in the Product environment of CATIA, and the software is carried out from the Product level for the indexing of the workpieces; the method comprises the steps that the information of a measuring head needs to be obtained in advance by marking the measuring point, the measuring distance and the offset distance need to be set in advance, and the information of a single characteristic parameter measuring point, an offset point related to the single characteristic parameter measuring point and a starting measuring point is generated immediately when the measuring point is marked; when a measuring point is marked, firstly, selecting a feature to be marked, then selecting parameters measured by the feature, and then clicking a measuring point marking button, namely marking the measuring point on a model, wherein the feature outside a hole is marked on a surface, and the number of the measuring points is required to be set for manual pointing;

4.2 Generating a measurement trajectory:

generating a measuring track to directly generate the whole measuring track, wherein the measuring track inside a single feature and among a plurality of features is directly displayed on a digital model through a straight line and an arrow after the background program calculation is completed; an important step in the measurement track is to set the height of the cutter lifting, and the height of the cutter lifting is finished by selecting a safety plane distance set in advance;

4.3 Generating a measurement program:

the measurement procedure needs to be provided with allowance, the procedures are different, and the allowance is also different, so that the measurement procedure for generating a plurality of procedures is provided; in addition, a measurement coordinate system needs to be set, and the measurement coordinate system is consistent with the processing coordinate system; the transfer speed and the measurement speed are customized, the transfer speed is increased, the measurement time is reduced, the measurement speed is reduced, and the measurement precision is improved; the file name of the measuring point is used for automatically acquiring the file name set by the coordinate of the measuring point in numerical control, the custom of the program head and the program tail is modified, and a txt file is obtained by clicking a measurement program;

4.4 Machine tool gauge head on-machine measurement:

when actual measurement is carried out on a machine tool, a measurement program is firstly opened on a numerical control system interface, and if the measurement is carried out in a working procedure, the measurement program is directly operated; after the measurement is completed, a subroutine file with a measuring point coordinate is generated, and the subroutine file contains all measuring point coordinates and is used for directly checking or subsequently calculating characteristic parameters;

4.5 Post-processing calculation of characteristic parameters and error parameters:

and importing the acquired coordinate file into software, calculating the characteristic parameters and the error parameters in an error analysis module, and displaying the calculated results on a digital-analog window.

The beneficial effects of the invention are as follows:

(1) The invention provides an on-machine measuring method for the key characteristic parameters of the complex part, which has better applicability and can realize on-machine automatic measurement of the characteristics of the complex part.

(2) The invention has the functions of measuring point marking, measuring track generation, measuring program generation, characteristic parameter calculation, measuring process motion simulation, interference check, data display and the like, and can systematically solve the problem of on-machine measurement of the measuring head.

(3) The invention can realize measurement, calculation and display of various characteristic parameters and error parameters of complex parts, wherein the characteristic parameters comprise hole characteristic parameters such as hole diameter, hole distance and the like, thin-wall characteristic parameters such as wall height, wall thickness and the like, and web thickness characteristic parameters, and the error parameters comprise dimension errors, hole coaxiality errors, hole perpendicularity errors, plane flatness errors and plane profile.

(4) When the measuring path is generated, the single characteristic internal track and the multiple characteristic tracks are generated step by step, the whole measuring path is optimized, the global shortest path can be finally obtained, and the measuring efficiency is improved.

(5) The invention has better compatibility with the existing commercial cata software, can realize the import of any complex part number model, the export of a measuring program and the import of the actual measuring data of a machine tool, can be deployed on a process personnel computer, has the advantages of flow and standardization in operation, and is convenient for enterprise application.

Drawings

FIG. 1 is a single station contact path plan.

Fig. 2 is a single intra-feature measurement path planning procedure.

Fig. 3 is an aperture measurement path.

Fig. 4 is a path of pitch measurement.

Fig. 5 is a hole perpendicularity measurement path.

FIG. 6 is a thin wall thickness and wall height measurement path, where (a) is the wall thickness measurement path; (b) is a wall height measurement path.

Fig. 7 is a web thickness measurement path.

Fig. 8 is a curved profile measurement path.

FIG. 9 is a schematic diagram of an inter-feature path plan, wherein (a) is a plurality of measured feature points on a workpiece; (b) the shortest measurement path after optimization for the ant colony algorithm.

Fig. 10 is an overall measurement path on a part.

Fig. 11 is a functional architecture of an on-machine measurement system for a probe.

FIG. 12 is a station marking module, wherein (a) is a measurement marking module software interface; (b) is the effect of the measurement point marking.

FIG. 13 is a measurement trajectory generation module, wherein (a) is a measurement trajectory generation module software interface; (b) generating effects for the measurement trajectory.

FIG. 14 is a measurement simulation module, wherein (a) is a measurement simulation module software interface; (b) measuring simulation effect.

FIG. 15 is a measurement program generation module software interface.

FIG. 16 is a data read-in module, wherein (a) is a data read-in module software interface; (b) reading in display effects for data.

FIG. 17 is an error calculation module, (a) an error calculation module software interface; (b) calculating the display effect by error.

FIG. 18 is a feature parameter calculation module software interface.

Detailed Description

The invention is described in detail below with reference to the drawings and examples.

1.1 Single station contact path planning:

the measuring head is likely to collide when contacting a workpiece, so that the measuring head is damaged, and the measuring head needs to have higher speed to ensure the measuring efficiency when moving between measuring points, so that the speed is required to be reduced before contacting the measuring points, and the measuring head returns to the point to accelerate after triggering, namely the speed changing point;

The point of the measuring head contacting the workpiece is a contact point, the contact point is a position marked on the CAD model, however, the position on the workpiece in actual processing may be advanced or retarded, the measuring head automatically returns to and records the coordinates of the center point of the ball at the starting position only after triggering, so that in order to ensure that the measuring head can trigger, an offset point is defined at the retarded position of the marked measuring point, and the offset point is used as the measuring point to be contacted by the actual measuring head;

as shown in FIG. 1, the coordinates of the offset point are used as measurement points when the measurement program is written, and finally, the contact path of the single measurement point is that of the starting point p _s Decelerating, turning on a probe trigger switch, feeding the probe along the normal direction of the measuring point, and at the actual contact point p _c Stopping and then accelerating back to the starting point;

1.2 Inter-feature inter-station path planning:

the paths among the measuring points in the single feature are required to be planned according to the specific distribution of the measuring points, interference is not considered when the measuring points in the feature move, only the quantity of the measuring points is different, so that the paths in the feature are fixed after the determination, and the paths are directly applied when the paths of the same feature are planned each time, and re-planning is not required; when each feature is planned, the minimum measurement points are firstly planned, and then the path is copied according to the number of the measurement points, so that the single intra-feature measurement path planning flow can be represented as shown in fig. 2;

1.2.1 Aperture measurement path planning):

when the aperture of the single hole feature is measured, the measuring points are on the same plane, and the aperture can be measured only by at least 3 measuring points; after the path of a single measuring point is fixed, only one inlet is needed to be selected from the measuring points, namely, the measuring points enter the position of the aperture from the safety plane, then the rest measuring points are measured in sequence, the starting position of the last measuring point is defined as an outlet, and the measuring point exits from the outlet position to the safety plane, as shown in fig. 3;

1.2.2 Hole pitch measurement path planning:

as shown in fig. 4, the hole pitch measurement needs to obtain the center coordinates of two holes, if the center of each hole is to be determined, at least 3 measuring points are needed for each hole, so that the hole pitch measurement divides the hole diameters of the two holes to carry out planning paths, the track which exits to the safety plane after one hole is measured is seen from the hole pitch measurement, and the hole cross sections of the two holes are ensured to be the same plane when the hole pitch is measured;

1.2.3 Hole perpendicularity measurement path planning:

when the perpendicularity of the hole is measured, the axis of the hole is required to be measured, so that at least two hole sections are selected in the hole, the center of the circle of each section is measured to obtain the axis, and therefore, the two sections also plan paths according to the aperture measurement, and each section has at least 3 points; in addition, a base surface needs to be measured, at least 3 points are required to determine a plane according to a surface equation, the scattering of measuring points is ensured as much as possible during taking the points, and a measuring path of the perpendicularity of the available holes is shown in figure 5;

1.2.4 Thin wall thickness and wall height measurement path planning:

as shown in fig. 6, the thickness and the height of the thin wall are two characteristic parameters to be measured, and in theory, the two parameters are measured by only calculating the distance between two measuring points along the thickness or height direction, but taking the measurement accuracy into consideration, a plane is obtained by least square, and the thickness or the height is calculated by the average value of the distances from a plurality of measuring points on the other plane to the plane, so that at least 3 measuring points are selected on the plane, and 3 points on the reference plane are scattered as much as possible, especially when the height is measured;

1.2.5 Web thickness measurement path planning:

when the thickness of the web is measured, if the paths of the web are the same as those of the thin-wall thickness measurement from the perspective of parameter calculation, but since two planes cannot be measured at one time because two surfaces on the web are not positioned at the same station, the measurement paths of the two planes need to be separated, and each path is a single plane measurement path, as shown in fig. 7;

1.2.6 Curved surface measurement path planning:

the curved surface contour measurement needs to mark the measuring points along the curved surface direction, the number of the marking measuring points depends on the size of the curved surface, and in order to measure a relatively accurate curved surface error, at least two sections are taken for marking, as shown in fig. 8;

1.3 Inter-feature path planning:

the inter-feature path can be regarded as a path plan in a two-dimensional plane, each feature in the two-dimensional plane can be regarded as a feature point, the path plan in the feature has no interference, so the planning is based on finding the shortest measurement path between the features, the planning of the inter-feature path can be converted into a TSP problem, the description of the TSP problem is that a shortest path which can lead a traveller to pass through all cities at one time and return to a starting city is found, and the shortest path can be expressed as follows:

wherein: t is time; i, j and s are points on the path;the information element on the paths of the point i and the point j at the moment t;heuristic factors of a point i and a point j at the moment t; alpha is the relative importance of tau; beta is the relative importance of eta; allowed _k A set of points selectable for ant k at time t;

all the features to be measured are marked with circles as shown in fig. 9 (a), and these marks in the drawing are projected onto a plane, i.e., the feature points that the probe needs to pass through on the safety plane. Optimizing the marked feature points by using an ant colony algorithm to obtain shortest paths among features as shown in fig. 9 (b);

1.4 Overall measurement path planning):

the paths in a plurality of single features are connected in series by using inter-feature paths, so that an overall measurement path is obtained; as shown in fig. 10, is the final overall measurement path planned on the CAD model.

Step 2), measuring the coordinate values of the actual measurement points of the marking points by a measuring program, and further calculating key characteristic parameters, wherein the key characteristic parameters comprise characteristic parameters (hole characteristic parameters such as hole diameter, hole distance and the like, thin-wall characteristic parameters such as wall height, wall thickness and the like, and web thickness characteristic parameters) and error parameters (dimension errors, hole coaxiality errors, hole perpendicularity errors, plane flatness errors and plane profile errors);

2.1 Calculation of pore characteristics:

(1) Calculation of pore diameter:

the aperture can be obtained by calculating the average value of the distances from all measuring points to the circle center, and the aperture is shown as the following formula:

(2) Calculation of hole distance:

on the basis of aperture calculation, the distance between the centers of two hole cross sections is calculated, and attention is paid to two empty cross section circlesShould be in the same plane; assume that two center coordinates are (x) ₀₁ ,y ₀₁ ,z ₀₁ )，(x ₀₂ ,y ₀₂ ,z ₀₂ ) The distance between two circle centers can be obtained according to a distance formula;

2.2 Calculation of thin-wall characteristic parameters:

2.3 Web characteristic parameters are calculated:

when the thickness of the web is measured, as the thickness cannot be measured in the first station and can be measured only after the second station is processed, the references of the workpiece at different stations are different, so that the coordinate transformation is required to be carried out on the measuring points respectively after the measurement at the two stations is completed, the measuring points are converted to the lower surface of a workpiece coordinate system, and the calculation formula of the thickness of the web can be obtained by referring to a thin-wall calculation method after the conversion is completed;

2.4 Calculation of dimensional error of feature thickness:

after the dimension thickness measurement value of the part characteristic is obtained, the dimension thickness measurement value is differenced from the design value, and then the dimension error can be obtained, wherein the dimension error is shown in the following formula;

e _l ＝l _m -l ₀ (6)

Wherein: l (L) _m Is a measurement; l (L) ₀ Is a design value;

2.5 Hole coaxiality error parameter calculation:

2.6 Hole perpendicularity error parameter calculation:

according to the definition of verticality, a reference plane equation is set asMeasuring point P _i (x _i ,y _i ,z _i ) And the tie deviation of the reference section along the normal direction is the hole perpendicularity error. The calculation formula is as follows;

2.7 Surface flatness error calculation

Obtaining the coordinates P of the point on the actual workpiece plane by measurement _i (x _i ,y _i ,z _i ) N can be obtained by least square method _i The plane equation of each measuring point is z=p _a x+p _b y+p _c And further, the minimum variance of the plane and the measuring point is calculated as follows:

2.8 Surface profile error:

3.1 The overall functional architecture of the on-machine measuring system of the measuring head is shown in fig. 11, the measuring point marking and the path generation are carried out in the measuring planning stage, then the actual measuring head measurement is carried out on the machine tool, and finally the measuring data is imported into the measuring system software to calculate and display key characteristic parameters;

3.2 A measuring point marking module:

the measuring point marking module is used for carrying out hierarchical nesting by using two options of characteristics and parameters, wherein the characteristics are a first stage, the parameters are a second stage, the characteristics are holes, thin walls, ribs, stand columns, lugs and cambered surfaces, the parameters to be measured of each characteristic are different, the characteristics are single options when the measuring points are marked, but the parameters can be selected more, for example, the hole characteristics can measure the aperture, the hole distance and the coaxiality, and the final effect is that the characteristics comprise the parameters to be measured; different measurement parameters have different measurement point numbers, so that the number of measurement points required by different parameter combinations and the position sequence of the marked measurement points need to be analyzed independently, and prompts need to be given when the measurement points are marked each time; in terms of operation logic, after a feature is selected, parameters which can be measured by the feature are in an enabled state, the rest are in a disabled state, then a mark measuring point button is in an enabled state, an adding button is in a disabled state, after the mark measuring point button is clicked, the number of marked measuring points is prompted, the mark measuring point button is placed in the disabled state, the adding button can normally operate after the mark is completed, but the mark measuring point button cannot be clicked, the next group of operation can be performed only by adding the marked measuring points into a measuring point list, and a right side list box can give the marked feature, the matched parameters and the marked number information. The software interface of the measuring point marking module and the marking effect of the measuring point are shown in fig. 12 (a) and (b), respectively;

3.3 A measurement trajectory generation module):

the measuring track generating module is divided into two parts, for the path in the feature is fixed, after the measuring point marking part is completed, the path in the feature is generated, the module focuses on designating the position of the lifting tool and generating the path between the features, normal vector information in the figure is used for displaying normal vector information of the measuring point relative to the surface in the CAD model, a safety plane button is used for designating the height of the lifting tool, the measuring track button is used for generating the final measuring track, and the generated track is displayed in the CAD model. In the track generation process, a starting point and an offset point are automatically generated, the starting point is displayed in a CAD model, the starting point is also a speed change point in measurement, and the offset point is used for preventing the situation that a measuring head cannot touch a workpiece due to over-cutting, and the offset point is not displayed in the model, but can be seen through a list box on the right side of a window; the measurement track generation module software interface and the measurement track generation effect are shown in fig. 13 (a) and (b), respectively;

3.4 A measurement simulation module):

the measurement simulation module is mainly used for simulating a measurement process in a CAD model, the measuring head is also Part type digital-analog in CATIA, and a user can draw the measuring head by himself; in addition, the simulation can be stopped and stopped at any time in the simulation process, and if the measuring head collides with the workpiece in the motion process, the simulation can be automatically stopped. The volume collision in CATIA is used for judging interference, and the coordinates of the interference position are directly recorded and displayed in a window. The measurement simulation module software interface and the measurement simulation effect decibels are shown in fig. 14 (a) and (b);

3.5 Measurement program generation module

The measurement program generation module firstly considers the setting of the allowance, and for the measurement among the working procedures, a CAD model cannot give a rough machining or semi-refined model, so that the corresponding allowance is required to be set for each working procedure to generate the actual positions of measuring points in different working procedures; the principle is that the measuring point moves along the normal vector direction relative to the plane where the measuring point is located, and the moving distance depends on the allowance set by the working procedure; the second parameter to be set is the setting of the coordinate system, the set coordinate system is the measurement coordinate system, the position of the measuring point in the measurement procedure will be transformed according to the set coordinate system, and the generated measurement procedure is the procedure of transforming the coordinates. The program head and the program tail in the window are set to default values, but can be changed by a craftsman, because the measuring program can be in the process or after the process, the craftsman can adjust the position of the measuring program through the program tail, and the program head can be used for setting the information such as the replacement of the measuring head, the measuring speed and the like. The resulting measurement program is shown on the right side of the window and the examination can save the file locally in txt file type. The measurement program generation module software interface is shown in fig. 15;

The common basic format and code notes for the measurement program are as follows:

N10 G54 G90

g01 F3000; initial velocity, linear motion is defined as%

N20t=cem6; the percent of the cutter is replaced by the measuring head, and the self-definition can be realized

DEF INT RESULT; % defines the shaping variable

N30X 123.581Y 79.1502Z 20; % is moved to a safe planar position above the first measurement point

N40X 123.581Y 79.1502Z-20; % is moved to the starting point position of the first measuring point

N50 meas= 1G01 F200 X116.56 Y82.9856Z-20; the method comprises the steps that a measuring head starting command is started by using a MEAS command, when the MEAS value is 1, multiple pre-strokes are deleted, and the measuring head automatically returns after being triggered

STOPERATE; % joins the command, giving time for reading the trigger value

n60deg.R1= $AA_MW [ X ] R2= $AA_MW [ Y ] R3= $AA_MW [ Z ]; the%% is used for temporarily storing the data value triggered by the measuring head through the R variable, and the $ AA_MW [ ] is used for reading the coordinate of the main shaft knife point

WRITE (RESULT, "123" < < R < 1 >); % writing the value of R variable into a subroutine file named 123 by a WRITE WRITE instruction, wherein the subroutine file and a measurement program file are in the same directory

WRITE(RESULT,"123",<<R[2])

WRITE(RESULT,"123",<<R[3])

N70F 1000X 123.581Y 79.1502Z-20; the measurement is ended in percent, and the starting point is returned

N80X 130.35Y 56.0811Z-20; the% moves to the next station, if within the same feature, then no movement to the security plane is required, otherwise, the movement to the security plane is required first

N90 meas= 1G01 F200 X126.514 Y49.0604Z-20; % of the measurement at the second measurement point is started

STOPRE

N100R1= $AA_MW [ X ] R2= $AA_MW [ Y ] R3= $AA_MW [ Z ]; the numerical value in the%R variable can be covered after being read, and can be reused, so that the use quantity of the R variable is reduced

WRITE (RESULT, "123" < < R < 1 >); the% of the coordinates of the measuring points stored in the variable memory are repeatedly written

WRITE(RESULT,"123",<<R[2])

WRITE(RESULT,"123",<<R[3])

N110F 1000X 130.35Y 56.0811Z-20; the measurement of the next point is repeated in percent until the end

N120 X153.419 Y62.8498 Z-20

……

N560X 128.268Y-7Z 20; the last point in percent is completely measured back to the security plane

M30; end of the% measurement

3.6 Data read-in module):

the data reading module reads the actually measured coordinate information into the measuring system, the readable file types are xls and xlsx, the measuring point display button displays the measured measuring point in the CAD model, and the coordinate information of the actual measuring point is displayed on the right side of the interface; the software interface of the data reading module and the data reading display effect are shown in fig. 16 (a) and (b), respectively;

3.7 Error calculation module):

the error calculation module is used for calculating the deviation between the actual measurement point and the ideal measurement point, specifically, the distance between the actual measurement point and the plane to which the actual measurement point belongs, whether the error exists or not can be judged through the distance, the error result can be displayed in a right list frame of the window, and the error can be marked in the CAD model. If an upper error limit is established in the module, judging where the error exists according to the error size; the error calculation module software interface and the error calculation display effect are shown in fig. 17 (a) and (b), respectively;

3.8 A characteristic parameter calculation module):

the characteristic parameter calculation module is used for calculating the size to be measured, the value of the characteristic parameter to be calculated is preset when the characteristic marking module is used, the algorithm is translated into codes and written into the background according to the characteristic calculation method mentioned in the section above, the input value is the measured coordinate point, and the output value is the characteristic parameter value at the calculation position; the calculated feature parameter values are displayed in a window list box, as shown in fig. 18;

step 4) in the measurement planning stage, firstly, marking measuring points on a software platform, then, generating a measurement track, and deriving a measurement program; then, performing actual measurement on the machine tool; finally, the measurement result is imported into an on-machine measurement system to calculate and display characteristic parameters;

4.1 Marking measuring points on the workpiece digital model):

when the software is used for marking, attention is paid to the fact that the measurement point marking operation needs to be performed in the Product environment of the CATIA, and the software indexes the workpieces from the Product level. The method comprises the steps that the information of a measuring head, such as a measuring sphere radius, needs to be obtained in advance by marking the measuring point, and the measuring distance and the offset distance need to be set in advance, so that the information of a single characteristic parameter measuring point, an offset point related to the single characteristic parameter measuring point and a starting measuring point can be generated in real time when the measuring point is marked; when the measuring points are marked, firstly, the characteristics needing marking are selected, then parameters which can be measured by the characteristics are selected, then, a marking measuring point button is clicked, the marking of the measuring points can be carried out on the model, the characteristics outside the holes are marked on the surface, and the number of the measuring points needs to be set for manual pointing;

4.2 Generating a measurement trajectory:

the whole measuring track can be directly generated by generating the measuring track, and the measuring track inside a single feature and among a plurality of features can be directly displayed on a digital model through a straight line and an arrow after the calculation of a background program is completed; an important step in measuring the trajectory is to set the lift height, i.e. the safety plane distance, in order to prevent interference when moving between features. The knife lifting height can be achieved by selecting a safety plane distance which is set in advance;

4.3 Generating a measurement program:

the measurement program needs to be provided with allowance, and because the workpiece is a workpiece after the final processing is finished, the working procedures are different, and the allowance is also different, and the measurement program with multiple working procedures can be generated by the arrangement; in addition, a measurement coordinate system needs to be set, and the measurement coordinate system is consistent with a processing coordinate system, so that errors caused by different origins can be avoided; the transfer speed and the measurement speed can be customized, the transfer speed can be accelerated to reduce the measurement time, and the measurement speed needs to be reduced to improve the measurement accuracy. The file name of the measuring point is a file name set for automatically acquiring the coordinates of the measuring point in numerical control. The program head and the program tail can be modified by self-definition, and a txt file can be obtained by clicking a measurement program;

4.4 Machine tool gauge head on-machine measurement:

when the actual measurement is carried out on the machine tool, a measurement program is firstly opened at a numerical control system interface, and if the measurement is carried out in a working procedure, tool setting is not needed, and the measurement program is directly operated. After the measurement is completed, a subroutine file with the coordinates of a measurement point is generated. All the measurement point coordinates are contained in the file and can be used for directly checking or subsequently calculating characteristic parameters;

Claims

1. The on-machine measuring method for the key characteristic parameters of the complex parts is characterized by comprising the following steps of:

step 2), measuring by a measuring program to obtain the coordinate value of the real measurement point of the mark point, and further calculating key characteristic parameters, wherein the key characteristic parameters comprise characteristic parameters and error parameters; the characteristic parameters comprise hole characteristic parameters of hole diameter and hole distance, thin-wall characteristic parameters of wall height and wall thickness, and web thickness characteristic parameters; the error parameters comprise dimension errors, hole coaxiality errors, hole perpendicularity errors, plane flatness errors and plane contour errors;

Step 3) developing a module of CATIA through CATIA CAA for the second time, and developing functional modules of measuring point marks, measuring track generation, measuring simulation, measuring program generation, data reading, error calculation and characteristic parameter calculation by means of the CAD kernel of CATIA to form an on-machine measuring system;

the specific process of the step 1) is as follows:

1.1 Single station contact path planning:

1.2 Inter-feature inter-station path planning:

1.2.1 Aperture measurement path planning):

1.2.2 Hole pitch measurement path planning:

1.2.3 Hole perpendicularity measurement path planning:

1.2.4 Thin wall thickness and wall height measurement path planning:

1.2.5 Web thickness measurement path planning:

1.2.6 Curved surface measurement path planning:

1.3 Inter-feature path planning:

1.4 Overall measurement path planning):

the paths in a plurality of single features are connected in series by using inter-feature paths, so that an overall measurement path is obtained;

the specific process of the step 2) is as follows:

2.1 Calculation of pore characteristics:

(1) Calculation of pore diameter:

(2) Calculation of hole distance:

on the basis of aperture calculation, the distance between the centers of the cross sections of the two holes is calculated, and the cross sections of the two holes should be In the same plane; assume that two center coordinates are (x) ₀₁ ,y ₀₁ ,z ₀₁ )，(x ₀₂ ,y ₀₂ ,z ₀₂ ) Obtaining the distance between two circle centers according to a distance formula;

2.2 Calculation of thin-wall characteristic parameters:

2.3 Web characteristic parameters are calculated:

2.4 Calculation of dimensional error of feature thickness:

e _l ＝l _n -l ₀ (6)

Wherein: l (L) _m Is a measurement; l (L) ₀ Is a design value;

2.5 Hole coaxiality error parameter calculation:

2.6 Hole perpendicularity error parameter calculation:

according to the definition of verticality, let the reference plane equation be z=v _a x+v _b y+v _c Measuring point P _i (x _i ,y _i ,z _i ) The tie deviation of the reference section along the normal direction is the hole perpendicularity error, and the calculation formula is as follows;

2.7 Surface flatness error:

obtaining the coordinates P of the point on the actual workpiece plane by measurement _i (x _i ,y _i ,z _i ) Obtaining N by least square method _i Plane of each measuring pointEquation z=p _a x+p _b y+p _c And further, the minimum variance of the actual workpiece plane and the measuring point is calculated as follows:

2.8 Surface profile error:

the specific process of the step 3) is as follows:

3.2 A measuring point marking module:

3.3 A measurement trajectory generation module):

3.4 A measurement simulation module):

3.5 A measurement program generation module):

3.6 Data read-in module):

3.7 Error calculation module):

3.8 A characteristic parameter calculation module):

the characteristic parameter calculation module is used for calculating the size to be measured, the value of the characteristic parameter to be calculated is preset when the characteristic marking module is used, the algorithm is translated into codes and written into the background according to the characteristic calculation method of the value of the characteristic parameter, the input value is the actually measured coordinate point, and the output value is the calculated characteristic parameter value;

the specific process of the step 4) is as follows:

4.1 Marking measuring points on the workpiece digital model):

4.2 Generating a measurement trajectory:

4.3 Generating a measurement program:

4.4 Machine tool gauge head on-machine measurement: