CN102126162B - Numerical control machine processing online measurement method - Google Patents

Abstract

An on-line measurement method for CNC machine tool processing, which can realize on-line measurement of large workpieces. The invention combines a binocular stereo vision measurement system with a numerical control machine tool, and is pulled by the numerical control machine tool to complete the overall measurement of a large workpiece. This method first calibrates the internal and external parameters of the camera, and combines the measurement system with the CNC machine tool; then performs translation calibration and rotation calibration, and calibrates the direction vectors of the X-axis and Y-axis of the CNC machine tool, and the rotation matrix R and translation vector T of the measurement system after rotation; Then, the traction measurement system of the CNC machine tool moves to perform single-field scanning until the entire surface of the workpiece to be measured is traversed; finally, the overall splicing is performed according to the point cloud data of all the field of view and the readings of the spindle of the CNC machine tool, and the overall measurement of the workpiece is completed. The invention has the characteristics of flexible use, convenience, high precision, etc., and can be used for on-line measurement of large workpieces in industrial sites.

Description

An online measurement method for CNC machine tool processing

technical field

The invention relates to a method for on-line measurement of CNC machine tool processing, which can be used for non-contact on-site measurement of industrial processed products at industrial sites. The invention belongs to the field of machine vision.

Background technique

Large workpieces, especially integral parts, are increasingly used in many occasions due to their relatively light weight and high strength. However, due to their large dimensions and many features to be measured, it is difficult to measure them in practice. . If contact measurement is used, not only can high-density data point clouds not be obtained, but also the measurement efficiency is low, and it is difficult to measure the entire workpiece due to its large size. With the development of science and technology, non-contact measurement, especially the measurement method based on vision technology, has been widely used due to its simple structure, low price and high measurement efficiency. Due to the high efficiency of non-contact measurement and simple equipment, it is very suitable for application in industrial sites.

There are many branches of measurement methods based on vision technology. Among them, the processing online measurement method based on binocular stereo vision technology has high precision, non-contact, dense point cloud, etc.

The shortcomings of the existing online measurement system are:

(1) It is generally necessary to use external mechanical equipment, such as a mechanical arm, to move the vision system, thus increasing the cost of the measurement system, and adding external machinery at the work site may affect the performance of the lathe itself.

(2) Existing measurement methods for large workpieces need to paste marking points, and the automation of large-scale measurement has not been realized.

Contents of the invention

The technical solution of the present invention is to propose an online measurement method for CNC machine tool processing, which greatly increases the utilization efficiency of the CNC machine tool and solves the problem of large-scale splicing by combining with the machine tool.

The technical solution of the present invention is: an online measurement method for CNC machine tool processing, which is characterized in that it includes the following steps:

The preparatory work includes calibrating the internal and external parameters of the two cameras, debugging and preparing the upper computer measurement software, etc. The measurement software refers to the data processing software developed for this online measurement method.

(1) Measurement system installation: Remove the tool of the machine tool spindle, install the measurement system, that is, the binocular stereo vision measurement system, on the spindle, connect the data line, and combine it with the CNC machine tool.

(2) Translation calibration: machine tool translation, calibrate the direction vectors V _x and V _y of the X-axis and Y-axis of the CNC machine tool in the coordinate system of the measurement system.

Place a pair of marker rods glued with marker points on the side of the workpiece to be measured. Place the two marker poles along the X-axis and Y-axis of the CNC machine tool respectively; control the CNC machine tool to move several times along the X-axis and Y-axis respectively, and take pictures of the two marker poles during the movement interval, each movement interval is fixed and each movement direction unanimous. in accordance with

(Mx _i -Mx _i-1 )V _x ＝Px _i -Px _i-1

(My _i -My _i-1 )V _y ＝Py _i -Py _i-1

Among them, Mx _i and My _i are the X-axis and Y-axis readings of the machine tool when the i-th shot is taken, and Px _i and Py _i are the coordinates of the reappeared mark point after the i-th shot.

Solve the optimal solutions of the equations respectively, that is, the direction vectors V _x and V _y of the X-axis and Y-axis of the CNC machine tool in the coordinate system of the measurement system.

(3) Rotation calibration: the machine tool is rotated, and the rotation matrix R and translation vector T after the measurement system is calibrated are calibrated.

According to the path planning results, control the rotation of the machine tool, respectively reproduce the circular marker points in the reference field of view and the rotated field of view in three dimensions, including circle center extraction, epipolar line matching and three-dimensional reproduction, and perform three-dimensional point matching, using the four-element method, Calculate the rotation matrix R _j and the translation vector T _j , R _j and T _j are the rotation matrix and translation vector of the jth rotation of the measurement system during rotation calibration.

(4) Pull the spindle of the CNC machine tool, move the measurement system to the part to be measured, and after the spindle is stable, scan the workpiece in a single-view field to obtain the point cloud data of the single-view field;

(5) Repeat step (4) until the surface of the workpiece to be measured is traversed to obtain all field of view point cloud data and complete the full field of view scanning;

(6) According to the point cloud data obtained in steps (4) and (5), stitching is performed.

Take the coordinate system of the first field of view of the measurement system as the world coordinate system, and stitch the point cloud data of each field of view according to the following formula:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; W</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$

Among them, P _i , Xi , _and Y _i are the point cloud data of the i-th measurement field of view, the readings of the X-axis of the CNC machine tool, and the readings of the Y-axis of the CNC machine tool, and R _j and T _j are the rotations of the j-th rotation measurement field of view Matrix and translation vector, V _x and V _y are the marked direction vectors, P _W is the scanned point cloud data in the world coordinate system.

The advantage of the present invention compared with prior art is:

(1) The present invention provides an online measurement method, which improves the processing and detection efficiency of the entire workpiece by combining it with a numerically controlled machine tool. Due to the online measurement, the workpiece does not need to be unloaded from the machine tool after processing, which greatly reduces the deformation of the workpiece due to assembly, and does not need to transport the parts to the measuring room, which greatly improves the measurement efficiency.

(2) The measuring system involved in the present invention has a simple structure and a simple on-site calibration method, and can fully adapt to the industrial on-site environment. Combining with CNC machine tools, making full use of the advantages of machine tools, the splicing speed is fast, and there is no need to paste marker points on the measured workpiece, and dense point cloud data can be obtained.

Description of drawings

Fig. 1 is a flow chart of the online measurement method of the present invention.

Fig. 2 is a schematic diagram of the process of calibrating the movement direction of the CNC machine tool according to the present invention. The single camera in the figure represents the measurement system, and the dotted line with the arrow in the figure is the calibration route of the traction measurement system of the CNC machine tool.

Fig. 3 is a measurement roadmap of the present invention. The single camera in the figure represents the measurement system, and the dotted line with the arrow in the figure is the measurement route of the traction measurement system of the CNC machine tool.

Detailed ways

In order to better understand the present invention, the technical solutions of the present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

With reference to accompanying drawing 1, a kind of CNC machine tool processing online measurement method comprises the following steps:

Before combining the measurement system with the CNC machine tool, make necessary preparations for the measurement system. The measurement system refers to a binocular stereo vision sensor, including two cameras and a projector; the necessary preparations include calibrating the internal and external parameters of the two cameras , debug and prepare the host computer measurement software, etc.;

1. The installation of the measurement system, remove the spindle tool of the CNC machine tool, install the measurement system on the spindle, connect the data line, and combine it with the CNC machine tool.

2. Translation calibration, machine tool translation, calibration of the direction vectors V _x and V _y of the X-axis and Y-axis of the CNC machine tool in the coordinate system of the measurement system.

Place a pair of marker rods glued with marker points on the side of the workpiece to be measured. Refer to the accompanying drawing 2 for the placement method. The placement directions of the two marker rods are along the X-axis and Y-axis of the CNC machine tool respectively, and the origins of the two marker rods are at the same angle of the workpiece to be measured.

According to the translation calibration path, control the CNC machine tool to move several times along the X-axis and Y-axis respectively. Refer to Figure 2 for the movement method. Two marker poles are photographed during the movement interval. The interval between each movement is fixed and the direction of each movement is the same. The movement interval should not be too large, and should be kept at about 100mm. Record the X-axis direction and Y-axis direction readings of the machine tool as _Mxi and My _i for each shooting, and the center coordinates of the three-dimensionally reproduced mark points are _Pxi and Py _i (there may be multiple points in a field of view, Px _i and Py _i may be a collection of multiple points).

According to the measurement data can be obtained:

(Mx _i -Mx _i-1 )V _x ＝Px _i -Px _i-1

(My _i -My _i-1 )V _y ＝Py _i -Py _i-1

The calculation is performed using the common points existing in _Pxi and Pxi _-1 . Take i=2, 3, 4..., then the above two formulas can form a group of equations respectively, and they all have optimal solutions V _x and V _y , that is, in the coordinate system of the measurement system, the X-axis and Y-axis of the CNC machine tool direction vector.

3. Rotation calibration, machine tool rotation, and calibration of the rotation matrix R and translation vector T after the measurement system is rotated.

According to the rotation calibration path, control the rotation of the machine tool, take pictures, and obtain the rotated image. Three-dimensional reproduction of the circular marker points in the reference field of view and the rotated field of view, including center extraction, epipolar line matching and three-dimensional reproduction, three-dimensional point matching, using the four-element method to calculate the rotation matrix R _j and translation vector T _j , take j=2, 3, 4..., R _j and T _j are the rotation matrix and translation vector of the jth rotation of the measurement system during rotation calibration.

4. According to the path planning results, the overall measurement route refers to the attached figure 3, pull the spindle of the CNC machine tool, and move the measurement system to the part to be measured. After the spindle is stable, scan the workpiece to obtain single-field point cloud data and point cloud data Denoted as P _i , at this time the readings of the X and Y axes of the CNC machine tool are denoted as Xi and _{Y i .}

5. Repeat step 4 until the surface of the workpiece under test is traversed, and all field of view point cloud data are obtained to complete the full field of view scanning;

6. According to the point cloud data obtained in steps 4 and 5, stitching is performed.

From steps 4 and 5, the measurement system traverses the entire workpiece to obtain point cloud data of all fields of view. Transform all point cloud data into a unified coordinate system to complete the splicing. Specifically: take the coordinate system of the first field of view of the measurement system as the world coordinate system, and carry out the coordinate system 1 of the point cloud data of each field of view according to the following formula:

${\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; W</span>}}<span\; class="notranslate">\; =</span>\underset{\mathrm{<span\; class="notranslate">\; i</span>}<span\; class="notranslate">\; ,</span>\mathrm{<span\; class="notranslate">\; j</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; R</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; T</span>}}_{\mathrm{<span\; class="notranslate">\; j</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; x</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; x</span>}}<span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; i</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Y</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; the\; y</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ,</span>$

Among them, P _i , Xi , _and Y _i are the point cloud data of the i-th measurement field of view, the readings of the X-axis of the CNC machine tool, and the readings of the Y-axis of the CNC machine tool, and R _j and T _j are the rotations of the j-th rotation measurement field of view Matrix and translation vector, V _x and V _y are the marked direction vectors, P _W is the scanned point cloud data in the world coordinate system.

Then P _W is the result of the unified coordinate system of all field point cloud data, that is, the splicing is completed.

Claims (4)

1. a Digit Control Machine Tool processing On-line Measuring Method is characterized in that, may further comprise the steps:

(1) measuring system is installed: measuring system is installed on the main shaft of numerical control machine tool;

(2) translation is demarcated: the lathe translation, demarcate the direction vector V of Digit Control Machine Tool X-axis and Y-axis _x, V _y

(3) rotation is demarcated: lathe rotation, the postrotational spin matrix R of calibration measurements system and translation vector T;

(4) the traction main shaft of numerical control machine tool moves to part to be measured with measuring system, scans, and obtains the monoscopic cloud data;

(5) repeating step (4) is namely finished full-field scanning until measured workpiece surface traversal is finished;

(6) cloud data that obtains according to step (4), (5) splices;

Wherein, described (2) translation is demarcated, and the direction vector V of Digit Control Machine Tool X-axis and Y-axis is demarcated in the lathe translation _x, V _y, required marker post is placed as: a pair of marker post that is stained with index point is placed on the measured workpiece limit, and two marker post placement directions are respectively along X-axis and the Y-axis of Digit Control Machine Tool.

2. a kind of Digit Control Machine Tool processing On-line Measuring Method according to claim 1 is characterized in that: described (2) translation demarcation, lathe translation, the direction vector V of demarcation Digit Control Machine Tool X-axis and Y-axis _x, V _y, accuse Digit Control Machine Tool processed respectively along X-axis and Y-axis translation several times, take marker post in the mobile interval, each mobile certain and each moving direction unanimity at interval; Foundation

(Mx _i-Mx _i-1)V _x=Px _i-Px _i-1

(My _i-My _i-1)V _y=Py _i-Py _i-1

Wherein, Mx _i, My _iX-axis reading and the Y-axis reading of lathe when being the i time shooting index point, Px _i, Py _iIt is the index point coordinate that reappears after the i time shooting;

Difference solving equation group optimal solution V _xAnd V _y, i.e. the direction vector of Digit Control Machine Tool X-axis and Y-axis under the measuring system coordinate system.

3. a kind of Digit Control Machine Tool according to claim 1 is processed On-line Measuring Method, it is characterized in that: described (3) rotation is demarcated, the lathe rotation, the postrotational spin matrix R of calibration measurements system and translation vector T are for benchmark visual field and visual field, rotation back, three-dimensional reproduction circular index point respectively, comprise that extract in the center of circle, polar curve mates and three-dimensional reproduction, carry out the three-dimensional point coupling, utilize quaternary element method, calculate spin matrix R _jWith translation vector T _j, R _jAnd T _jSpin matrix and translation vector for the j time rotation of rotation timing signal measuring system.

4. a kind of Digit Control Machine Tool according to claim 1 is processed On-line Measuring Method, it is characterized in that: the cloud data that described (6) obtain according to step (4), (5), splice, splicing be coordinate system with first visual field of measuring system as world coordinate system, and according to following formula each visual field cloud data is spliced:

$P_w=\underset{i,j}{\mathrm{\&Sigma;}}(R_j\&CenterDot;P_i+T_j+(X_i-X_1)V_x+(Y_I-Y_1)V_y),$

Wherein, P _i, X _i, Y _iBe respectively i cloud data, Digit Control Machine Tool X-axis reading, the Digit Control Machine Tool Y-axis reading of measuring the visual field, R _jAnd T _jBe spin matrix and the translation vector of j wheel measuring visual field, V _xAnd V _yFor marking direction vector, P _WScan cloud data under the world coordinate system.

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