CN113406122A - Double-mechanical-arm digital ray detection device and automatic detection method - Google Patents
Double-mechanical-arm digital ray detection device and automatic detection method Download PDFInfo
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- CN113406122A CN113406122A CN202110661543.8A CN202110661543A CN113406122A CN 113406122 A CN113406122 A CN 113406122A CN 202110661543 A CN202110661543 A CN 202110661543A CN 113406122 A CN113406122 A CN 113406122A
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Abstract
The invention relates to a double-mechanical-arm digital ray detection device and an automatic detection method, belongs to the field of ray nondestructive detection, and solves the problems that a movement mechanism in an existing workpiece detection system is complex in design, high in control difficulty and incapable of realizing automatic detection and vertical transillumination detection of a complex curved surface workpiece. The application provides a double-mechanical-arm digital ray detection device and an automatic detection method based on the detection device. The device has the advantages that the two mechanical arms are arranged on the two sides of the workpiece to drive the ray source and the detector to move, so that the control difficulty of a moving mechanism is reduced, and meanwhile, the detection of any position, any angle and any amplification rate of the workpiece can be realized; meanwhile, based on the device, automatic detection of the workpiece is realized by compiling a mechanical arm control program, and automatic detection of vertical transillumination of the complex curved surface is realized by acquiring scanning path points through computer graphics based on a three-dimensional model of the workpiece. The device and the method can be widely applied to the field of nondestructive testing of workpieces, the control difficulty is reduced, and the automation of testing is improved.
Description
The invention relates to the field of digital ray nondestructive testing, in particular to a double-mechanical-arm digital ray detection device and an automatic detection method.
Background
Nondestructive testing is an indispensable tool in industrial development, and reflects the national industrial development level to a certain extent. X-ray detection has been used in industry for nearly a hundred years as a conventional non-destructive detection method. In the early and some current industrial fields (such as military manufacturing field), the X-ray detection usually uses film photography as the main detection method, and the detection method has the problems of long detection period, low detection efficiency, high detection cost, environmental pollution caused by darkroom waste liquid treatment and the like, and is not suitable for the non-destructive detection development trend of the information age. At present, the digital ray nondestructive testing technology is widely applied in the industrial field. On the premise of ensuring the detection quality of products, the digital ray nondestructive detection technology has the characteristics of high detection speed, low detection cost, easiness in image storage, easiness in realization of remote analysis and diagnosis and the like, and is the development direction of ray detection. By adopting the digital ray nondestructive testing technology, the image contrast can be improved and the identification power of the defects can be improved through the digital image processing methods such as gray level adjustment, enhancement, sharpening and the like, and the automatic screening, positioning and classification of the defects are further realized by adopting a defect identification algorithm, so that the intelligent film evaluation is realized, and the accuracy of defect identification and the film evaluation efficiency are greatly improved.
At present, in a digital ray detection scheme, a workpiece is usually placed on an object stage, and the object stage is located between a ray tube and a detector, so that transillumination imaging of the workpiece by X-rays is realized. In order to meet the transillumination requirements of different workpiece sizes, different workpiece positions, different transillumination angles and different amplification ratios, a plurality of freedom degrees of motion are required to be added on a ray tube, a detector and a workpiece stage. Because the imaging field of view of digital ray detection is limited by the factors such as the plane size of the detector, the radiation angle of the ray, the imaging magnification ratio and the like, in order to meet the requirement of full-coverage detection of a large-size workpiece, a plurality of degrees of freedom of linear motion are usually added to a ray tube and the detector (or a workpiece stage), so that the detection range is expanded. In order to meet the requirement of detecting different angles of the workpiece, the scheme of rotating a workpiece stage or rotating a ray tube detector (such as a C-shaped arm) is generally adopted.
For the above-mentioned general workpiece detection system, in order to satisfy the transillumination requirements for different workpiece sizes, different workpiece positions, different transillumination angles, and different amplification ratios, it is necessary to add a plurality of degrees of freedom of motion to the radiation source, the detector, and the workpiece stage, usually about 10 degrees of freedom of motion are necessary, for the detection of different angles, especially when the multi-angle detection is required to be performed to a plurality of rotation axis directions, or when the detection is required to be performed along the normal direction of the workpiece surface, the mechanical movement mechanism of the system is very complex to design, so that the movement control also becomes abnormally complex, and meanwhile, the detection device based on the complex movement mechanism cannot realize automatic detection.
In addition, for a workpiece with a complex curved surface, the conventional digital ray detection method cannot realize vertical transillumination on any surface position of the workpiece, while oblique transillumination increases the penetrating wall thickness of rays, so that the imaging sensitivity and the imaging quality are also influenced, and the specific position of the surface of the workpiece where the defect is located cannot be positioned.
Disclosure of Invention
In view of the above analysis, in order to solve the problems that the conventional workpiece detection system has a high control difficulty of a movement mechanism, cannot realize automatic detection, and cannot realize vertical transillumination detection of a workpiece with a complex curved surface, embodiments of the present invention provide a double-mechanical-arm digital ray detection apparatus and an automatic detection method based on the apparatus.
On one hand, the embodiment of the invention provides a double-mechanical-arm digital ray detection device, which comprises a ray source, a detector, a workpiece rotary table, a first mechanical arm, a second mechanical arm, a control system and a data acquisition system;
the first mechanical arm and the second mechanical arm are arranged on two sides of the workpiece rotary table, and the ray source and the detector are respectively arranged on the first mechanical arm and the second mechanical arm;
the workpiece to be measured is arranged on the workpiece rotary table;
the data acquisition system is used for acquiring imaging data of the detector;
the control system changes the positions and the directions of the detector and the ray source by adjusting the motion axes of the first mechanical arm and the second mechanical arm, so as to realize the detection of the workpiece; the central beam of the ray source is always vertical to the surface of the detector and passes through the central point of the detector in the scanning process.
Furthermore, the control system keeps the direction of the central beam of the ray source unchanged by adjusting the movement axes of the first mechanical arm and the second mechanical arm, so that the detector and the ray source perform synchronous translation movement along a certain direction, and the detection of different positions of the workpiece is realized.
Furthermore, the control system keeps the position of the central point of the detector unchanged by adjusting the motion axes of the first mechanical arm and the second mechanical arm, so that the detector rotates along the bisector of the horizontal or vertical direction of the detector, and simultaneously, the ray source rotates in an arc track by taking the central point of the detector as the center of a circle and the distance between the central point of the detector and the focus of the ray source as the radius, so that the detection of different angles of the workpiece is realized.
Furthermore, the control system adjusts the movement axes of the first mechanical arm and the second mechanical arm, so that the detector and the radiation source rotate along an arc track in opposite directions by taking a certain point to be measured in the workpiece as a circle center, taking the distance from the center point of the detector to the point to be measured as a radius, taking the distance from the point to be measured to the focus of the radiation source as a radius, and thus, the detection of different angles of the workpiece is realized.
Furthermore, the control system enables the detector or the ray source to move along the connecting line direction of the ray source and the detector by adjusting the movement axes of the first mechanical arm or the second mechanical arm, so that the distance between the ray source and the detector is changed, and the detection of different amplification ratios of the workpiece is realized.
Furthermore, the detection of different angles of the workpiece in the circumferential direction is realized through the rotation of the workpiece rotary table.
On the other hand, the embodiment of the invention provides an automatic detection method based on a double-mechanical-arm digital ray detection device, which is characterized by comprising the following steps of:
s1, the control system runs a mechanical arm control program;
s2, the control system controls the ray source and the detector to move to the ith scanning path point, and the initial value of i is 1;
s3, the control system outputs a signal acquisition starting instruction to the data acquisition system, then executes an input waiting instruction, and waits for the data acquisition system to finish data acquisition;
s4, after receiving the instruction of starting to collect signals, the data collection system starts the ray source and the detector, collects data output by the detector, and outputs a collection completion signal to the control system after collection is completed;
and S5, after receiving the acquisition completion signal, the control system judges whether the program is finished, if so, the detection is completed, if not, the value i is added by 1, and the step S2 is returned.
Further, scanning path points are obtained through manual teaching, specified offset or a mode of extracting path points through computer graphics based on a three-dimensional model of the workpiece.
Further, the method for extracting the path points through computer graphics based on the three-dimensional model of the workpiece comprises the following steps:
s21, acquiring a three-dimensional model of the workpiece;
s22, dividing the surface of the workpiece to be detected into a plurality of areas to be detected;
s23, acquiring the position and normal direction of the central point of each area to be detected on the surface of the workpiece based on computer graphics;
s24, determining the position and the normal direction of the central point of the detector according to the position and the normal direction of the central point, wherein the normal direction of the detector is consistent with the normal direction of the area;
s25, obtaining a focal point position of a ray source and a central beam direction according to the position and the normal of the central point of the detector, wherein the central beam direction is consistent with the normal of the detector;
the central position and normal direction of the detector, the focal position of the ray source and the direction of the central beam corresponding to each region to be measured are the acquired scanning path points.
Further, the robot arm control program is specifically as follows:
s1, creating a mechanical arm control program;
s2, inserting a movement instruction in the program to enable the ray source and the detector to move to the scanning path point;
s3, inserting a signal acquisition starting instruction in the program, and informing a data acquisition system to start data acquisition;
s4, inserting an input waiting instruction in the program, and waiting for the data acquisition system to finish acquisition;
and S5, judging whether the scanning path is planned or not, if not, returning to the step S2, and if so, ending the process.
Compared with the prior art, the invention can realize at least one of the following beneficial effects:
1. according to the invention, the detector and the ray source are driven to move by adopting the double mechanical arms, so that the movement structure is simplified, and the movement control of the mechanical arms is easy to realize; the device drives the detector and the ray source to do synchronous translation motion along a certain direction through the control and adjustment of the control system on each motion axis of the mechanical arm, the detector can keep the position of a central point unchanged to do rotary motion, and the detector and the ray source can do reverse rotation along an arc track, so that the detection of different positions, different angles and different amplification ratios of the workpiece is finally realized.
2. By adopting three-dimensional modeling of the workpiece, the position and the normal direction of the central point of the region to be detected on the surface of the workpiece are obtained by utilizing computer graphics, the position and the normal direction of the central point of the detector, the position and the normal direction of the focal point of the ray source and the central beam direction corresponding to each detection region are obtained according to the position and the normal direction of the central point, the normal direction of the detector and the central beam direction of the ray source are consistent with the normal direction of the region to be detected, and the vertical transillumination detection of the complex curved surface can be realized according to the scanning path point obtained by the method, so that the imaging quality and the detection precision are improved.
3. Three control instructions corresponding to each path point are inserted into a program by compiling a mechanical arm control program, and according to the instructions, the control system controls the motion of each motion axis of the mechanical arm, so that the detector and the ray source reach positions corresponding to the scanning path points, and controls the acquisition system to complete data acquisition, thereby realizing automatic detection.
In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and drawings.
Drawings
FIG. 1 is a schematic diagram of a digital ray detection device with two mechanical arms;
FIG. 2 is a schematic view of a robotic arm configuration;
FIG. 3 illustrates a coordinate system definition and reference relationship of a dual robot linkage;
FIG. 4 is a schematic view of a detector scanning position adjustment;
FIG. 5 is a schematic view of the adjustment of the scanning angle of the detector;
FIG. 6 is a comparison graph of imaging results of different transillumination angles for an overlapped defect;
FIG. 7 is a schematic view of scanning focus adjustment;
FIG. 8 is a flow chart of an automatic detection method based on a dual-robot digital ray detection device;
FIG. 9 is a flowchart of a robot program;
FIG. 10 is a schematic diagram illustrating the division of the inspection area on the surface of the workpiece;
FIG. 11 is a schematic view of a world coordinate system in the inspection apparatus.
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.
Detailed Description
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate preferred embodiments of the invention and together with the description, serve to explain the principles of the invention and not to limit the scope of the invention.
Example 1
The invention discloses a double-mechanical-arm digital ray detection device,
the device comprises a ray source, a detector, a workpiece rotary table, a first mechanical arm, a second mechanical arm, a control system and a data acquisition system;
the first mechanical arm and the second mechanical arm are arranged on two opposite sides of the workpiece rotary table, and the ray source and the detector are respectively arranged on the first mechanical arm and the second mechanical arm; the workpiece to be measured is arranged on the workpiece rotary table; the data acquisition system is used for acquiring imaging data of the detector;
the control system changes the positions and the directions of the detector and the ray source by adjusting the motion axes of the first mechanical arm and the second mechanical arm, so as to realize the detection of the workpiece; the central beam of the ray source is always vertical to the surface of the detector and passes through the central point of the detector in scanning, and particularly, the central beam of the ray source is always vertical to the surface of the detector and passes through the central point of the detector through the linkage of the first mechanical arm and the second mechanical arm.
The device adopts the double mechanical arms to drive the detector and the ray source to move, thereby simplifying the movement structure and easily realizing the movement control of the mechanical arms; the device drives the detector and the ray source to do synchronous translation motion along a certain direction through the control and adjustment of the control system on each motion axis of the mechanical arm, the detector can keep the position of a central point unchanged to do rotary motion, and the detector and the ray source can do reverse rotation along an arc track, so that the detection of different positions, different angles and different amplification ratios of the workpiece is finally realized.
The apparatus is described in detail below with reference to fig. 1 to 7, and as shown in fig. 1, the apparatus includes: the device comprises a ray source, a detector, a first mechanical arm, a second mechanical arm, a workpiece rotary table, a data acquisition system and a control system. And a rectangular coordinate system is established at the center of the workpiece turntable, and the Z axis is vertically upward. The end effector of the second mechanical arm is a detector, the end effector of the first mechanical arm is a ray source, and a workpiece to be detected is placed on the workpiece rotary table. The control system controls the movement axes of the first mechanical arm and the second mechanical arm to enable the detector and the ray source to translate along the Y axis or the Z axis, so that scanning detection of different transillumination positions in the same transillumination direction is realized; the detector and the ray source are enabled to move horizontally along the X axis, and the adjustment of the focal length, the object distance, the image distance and the magnification ratio of the imaging system is realized. By controlling the movement axes of the second mechanical arm and the first mechanical arm, the detector and the ray source rotate along the Y axis and reversely move along the Z axis, so that the multi-angle detection of the detected workpiece along the Y axis rotation direction is realized. The detector and the ray source rotate along the Z axis and reversely move along the Y axis by controlling the movement axes of the second mechanical arm and the first mechanical arm, so that the multi-angle detection of the detected workpiece along the Z axis rotation direction is realized. The limitation of the motion range of the mechanical arm is considered, and the multi-angle detection of the detected workpiece along the Z-axis rotation direction is realized through the rotation of the workpiece turntable.
The control system completes the scanning detection of any position, any transmission angle and any focal length amplification ratio of the detected workpiece through the cooperative control of the first mechanical arm, the second mechanical arm, the workpiece rotary table, the ray source switch and the detector acquisition.
Specifically, the first mechanical arm and the second mechanical arm are six-degree-of-freedom mechanical arms, and comprise a base, a shoulder joint assembly, a large arm structural member, an elbow joint assembly, a small arm structural member and a wrist joint assembly which are sequentially connected, as shown in fig. 2.
The workpiece to be detected can be a workpiece which can be penetrated by rays and has any material and any shape, and specifically can be a casting, a welding piece, a composite material and the like; the workpiece turntable is a mechanical mechanism which can satisfactorily support the weight of a workpiece and can rotate clockwise or anticlockwise. Specifically, the rotary part of the rotary table adopts a precise annular guide rail, the upper part of the rotary table adopts an annular product support, the outer part of the rotary table is provided with teeth, and the rotary table is driven by a servo motor driving gear.
In the scanning detection process of different positions and different angles of a workpiece, a ray source is required to be always opposite to a detector plane, namely a central beam of the ray source always passes through the center of the detector and is vertical to the surface of the detector. Therefore, the radiation source requires coordinated control when adjusting the detector position or angle. Here, the second mechanical arm corresponding to the detector is used as a main control mechanical arm, and the first mechanical arm corresponding to the ray source is used as a linkage mechanical arm for description.
The dual-robot linkage coordinate system definition and reference relationship are shown in fig. 3. The base coordinate system is a reference point of the position of the mechanical arm, and the position relation of the flange coordinate system and the reference base coordinate system can be calculated through a mechanical arm kinematics forward solution algorithm according to the geometric dimension of each joint and the rotation angle of each shaft of the mechanical arm.
Wherein, PFAAnd PFBIs the flange coordinate system position, P, of the second robot arm and the first robot armBAAnd PBBIs the base coordinate system position of the second robot arm and the first robot arm,
and
is a position transformation matrix (mechanical arm kinematics positive solution algorithm) of the flange coordinate system of the second mechanical arm and the first mechanical arm relative to a base coordinate system,
for each of the shaft positions of the second robot arm,
the position of each axis of the first robot arm.
The position relation of the base coordinate system B and the reference base coordinate system A can be calibrated by a base coordinate system calibration method.
Wherein the content of the first and second substances,
is a position transformation matrix of the base coordinate system B relative to the base coordinate system a.
By the tool coordinate system calibration method, the position relation of the tool coordinate system B with reference to the flange coordinate system B and the position relation of the workpiece coordinate system B with reference to the flange coordinate system A can be calibrated.
Wherein, PTBIs the position of the tool coordinate system B, PWBIs the position of the object coordinate system B,
is a position transformation matrix of the tool coordinate system B relative to the flange coordinate system B,
is a matrix of positional transformations of the workpiece coordinate system B relative to the flange coordinate system a.
The motion plan of the first robot arm can be expressed as a movement of the tool coordinate system B into a certain coordinate system position Q of the object coordinate system B, Q being understood as a transformation matrix of the position of the tool coordinate system B relative to the object coordinate system B.
PTB＝PWB·Q (6)
The positional transformation relationship of the flange coordinate system B with respect to the base coordinate system B is obtained from the equations (1) to (6)
First of allThe linkage of the robot arms may be described as when given the position of the axes of the second robot arm
Then, the position of each axis of the first mechanical arm is calculated
So that Q remains unchanged. In the formula (7), the first and second groups,
constant is obtained by a calibration method, and Q is constant in order to achieve the linkage effect, so when each shaft of the second mechanical arm moves to a certain position
When it is, can calculate
Then obtaining the position of each axis of the mechanical arm B according to the inverse kinematics calculation method of the first mechanical arm
How to adjust the scanning position, how to adjust the scanning angle, and how to adjust the scan magnification ratio will be explained below by way of several specific examples.
(1) Adjusting scanning position
The scanning position is adjusted in such a way that the full-coverage detection of the workpiece is realized by synchronously translating the ray source and the detector under the condition that the scanning angle (the angular relation between the central beam of the ray source and the workpiece) is not changed. Because the detector and the ray source are always in direct alignment linkage, the adjustment of the scanning position only needs to be considered in the section. The manual motion control of mechanical arms is divided into two types, axis space motion control and cartesian space motion control. The axis space motion control can be described as controlling one joint axis at a time individually, and enabling the detector to reach the target position through multiple control adjustments. The position of the detector is adjusted in such a way relatively complicated, a plurality of joint shafts need to be adjusted in sequence, and the precision cannot be guaranteed. The Cartesian space motion control is controlled in a track planning mode, a reference coordinate system is selected firstly, and then the motion control is performed by planning a straight track according to XYZ axes of the reference coordinate system. The detector position is typically adjusted using cartesian spatial motion control. Fig. 4 shows several common scanning position adjustment modes of the detector. The diagram (a) is a vertical motion track of a horizontal incident angle, and is suitable for the detection of a workpiece which is vertically placed, and the normal direction of the surface of the workpiece is horizontal or approximately horizontal; the diagram (b) is a vertical movement track of an oblique incident angle, for the case that horizontal reinforcing ribs exist in the workpiece, rays cannot penetrate through thicker reinforcing ribs by using the method (a), and the detection of the reinforcing ribs in the workpiece is realized by using the oblique incident angle; and (c) an oblique incident angle is an oblique movement track, for a workpiece with a workpiece surface which is inclined in a normal direction, in order to achieve the optimal imaging effect, the detector is required to be opposite to the workpiece surface, the plane of the detector is approximately perpendicular to the normal direction of the workpiece surface through the oblique incident angle, and the optimal imaging effect is achieved through movement detection in the oblique direction.
Besides the two manual motion control modes, a more complex motion track can be planned through a multi-point teaching or off-line programming mode. An arc track, a spline track and the like can be planned through multi-point teaching; a track which is always vertical to the normal direction of the surface of the workpiece and has a constant distance with the surface of the workpiece can be planned through an off-line programming mode based on the three-dimensional model of the workpiece.
(2) Adjusting the scanning angle
Just the adjustment of the scanning angle of the detector needs to be considered, similar to the adjustment of the scanning position. The adjustment of the scanning angle is also realized by the control of the spatial motion of the mechanical arm shaft and the control of the Cartesian spatial motion. The control of the spatial motion of the shaft is not intuitive and the precision cannot be controlled. The Cartesian space motion control can plan a motion track rotating along an X axis, a Y axis or a Z axis according to the selected reference coordinate system, and the effect of fixed point posture changing is achieved. Fig. 5 shows the effect of two fixed point poses.
FIG. 5(a) is a view showing that the scanning angle can be changed by fixing a point along the center point of the detector and changing the posture, i.e. keeping the position of the center point of the detector constant, and rotating the detector along the X-axis or Y-axis, and the scanning modes of FIGS. 4(b) and 4(c) can be realized by combining the adjustment of the scanning position in (1); FIG. 5(b) shows that the position of the object is changed along a certain point of the workpiece, i.e. the position of the object is changed along the center, the detector and the radiation source are respectively centered on the center, the distance between the center of the detector and the center is a radius, the distance between the center of the detector and the center of the detector is a radius, the radiation source rotates along the arc track along the opposite direction, and the detector and the radiation source rotate along the arc track along the opposite direction; by the method, the detection of different angles of the point can be realized, and the influence of image overlapping on the detection result can be eliminated. As shown in fig. 6, two horizontal defects, one large defect and one small defect, exist in the workpiece, and when horizontal angle transillumination is adopted, the imaging result is only a large defect, and a small defect cannot be seen; by changing the transillumination angle, both large defects and small defects can be seen on the imaging result.
In general, the scanning angle of the X-axis rotation of fig. 5 is adjusted by means of fixed-point posture change, and the scanning angle of the Y-axis rotation is adjusted in a small range, and the adjustment of the scanning angle of the Y-axis rotation in a large range is realized by rotating the workpiece turntable. No adjustment of the scan angle of the Z-axis rotation is required.
(3) Adjusting scan magnification
The distance from the focal point of the ray source to the surface of the detector is defined as a focal distance, the distance from the workpiece to the surface of the detector is defined as an image distance, and the distance from the workpiece to the focal point of the ray source is defined as an object distance. As shown in fig. 7, the second mechanical arm is controlled to move the detector along the Z-axis of the tool coordinate system a, so that the image distance is adjusted, and the object distance is changed along with the change of the focal distance due to the linkage of the radiation source and the detector; when the linkage control is cancelled, the image distance and the focal distance can be changed without changing the object distance. And controlling the first mechanical arm to enable the ray source to move along the Z axis of the tool coordinate system B, so as to realize the adjustment of the object distance and the focal length.
By executing the method flow of embodiment 2, the workpiece is automatically detected by adopting any optional implementation manner of the embodiment.
Compared with the prior art, the double-mechanical-arm digital ray detection device provided by the embodiment has the advantages that the two mechanical arms are arranged on the two sides of the workpiece, the detector and the ray source are driven to move through the mechanical arms, the detection of different positions, different angles and different amplification ratios of the workpiece is realized, the complexity of the movement mechanism is simplified by adopting the two mechanical arms, and the movement control process is simple and easy to realize.
Example 2
Another embodiment of the present invention provides an automatic detection method based on a dual-robot digital ray detection apparatus, including the following steps:
s1, the control system runs a mechanical arm control program;
s2, the control system controls the ray source and the detector to move to the ith scanning path point, and the initial value of i is 1;
s3, the control system outputs a signal acquisition starting instruction to the data acquisition system, then executes an input waiting instruction, and waits for the data acquisition system to finish data acquisition;
s4, after receiving the instruction of starting to collect signals, the data collection system starts the ray source and the detector, collects data output by the detector, and outputs a collection completion signal to the control system after collection is completed;
and S5, after receiving the acquisition completion signal, the control system judges whether the program is finished, if so, the detection is completed, if not, the value i is added by 1, and the step S2 is returned.
The automatic detection method will be described in detail with reference to fig. 8 to 11.
The method realizes the automatic scanning process by compiling a control program for operating the mechanical arm to control the movement positions of the detector, the ray source and the workpiece and combining a data acquisition system. The detection method comprises the following steps, see fig. 8.
S1, the control system runs a mechanical arm control program;
the robot arm control program flow is shown in fig. 9. For each automated scanning process, a robot arm control program needs to be created. The instruction block of each scanning path point is inserted in the control program of the mechanical arm in turn, and each instruction block comprises 3 instructions:
motion instructions are inserted to move the source and detector to the designated scan path point.
And inserting a signal acquisition starting instruction, transmitting the instruction to the data acquisition system, and informing the data acquisition system of starting acquisition.
And inserting an input waiting instruction, and waiting for the data acquisition system to finish acquisition.
And when all the scanning path points are inserted into the mechanical arm program, finishing the programming process and saving the program.
Specifically, the robot arm control program is as follows:
s11, creating a mechanical arm control program;
s12, inserting a movement instruction in the program to enable the ray source and the detector to move to the scanning path point;
s13, inserting a signal acquisition starting instruction in the program, and informing a data acquisition system to start data acquisition;
s14, inserting an input waiting instruction in the program, and waiting for the data acquisition system to finish acquisition;
and S15, judging whether the scanning path is planned or not, if not, returning to the step S2, and if so, ending the process.
S2, the control system controls the ray source and the detector to move to the ith scanning path point, and the initial value of i is 1;
the scanning path points can be obtained through a manual teaching mode, a mode of specifying offset, and a method of extracting path points through computer graphics based on a three-dimensional model of a workpiece.
Preferably, the method for extracting the path points through computer graphics based on the three-dimensional model of the workpiece comprises the following steps:
s21, acquiring a three-dimensional model of the workpiece;
the three-dimensional model is a grid representation of the workpiece, and exists in the form of a file, and records position coordinates of each grid point in the model (e.g. stl file) and topological information of edges, faces, bodies, and the like (e.g. stp file) included in the model, and is usually displayed and edited by a computer or other video equipment. Anything that exists in physical nature can be represented by a three-dimensional model. The three-dimensional model of the workpiece can be obtained by: the method comprises the following steps that (1) a 3D model is created through 3D modeling software, generally, a workpiece to be detected is created before production, and production and processing are carried out according to a drawing generated by the 3D model; and modeling is carried out through a three-dimensional laser scanning modeling instrument.
S22, dividing the surface of the workpiece to be detected into a plurality of areas to be detected;
specifically, to realize the full-coverage detection of the workpiece surface, the workpiece surface may be divided into a series of quadrilateral mesh regions, as shown in fig. 10 (a); to achieve the detection of the vertical weld on the workpiece, the surface of the workpiece where the weld is located may be divided into a plurality of quadrangular lattice regions in the direction of the weld of the workpiece, as shown in fig. 10 (b).
S23, acquiring the position and normal direction of the central point of each area to be detected on the surface of the workpiece based on computer graphics;
in the 3D modeling software, a world coordinate system is defined in the center of the bottom surface of the workpiece, and a coordinate system is established with the center of the bottom surface of the workpiece as an origin, horizontally to the right as an X-axis, and vertically upward as a Z-axis, as shown in fig. 11.
According to computer graphics, the position and normal direction of any point on the surface of the workpiece can be obtained, so that the position and normal direction of the central point of the area to be detected can be obtained.
S24, determining the position and the normal of the central point of the detector corresponding to each area according to the position and the normal of the central point, wherein the normal of the detector is consistent with the normal of the area;
specifically, the method for acquiring the position and the normal direction of the center point of the detector is as follows:
and determining the position and the normal direction of the central point D of the detector according to the position and the normal direction of the central point P of the area to be detected and the distance v between the detector and the surface of the workpiece. As shown in fig. 11, an included angle between the normal direction of the center point P and the detector center point D and the vertical direction is α, a distance between the center point P and the detector center point D is v, and the x and z coordinates of the detector center point D are respectively
Dx＝Px-v·sin(α) (8)
Dz＝Pz+v·cos(α) (9)
S25, obtaining a focal point position of a ray source and a central beam direction according to the position and the normal of the central point of the detector, wherein the central beam direction is consistent with the normal of the detector;
specifically, the method for acquiring the focal position of the radiation source and the direction of the central beam is as follows:
and determining the position and the normal direction of a focal point R of the radiation source according to the position and the normal direction of a central point P of the region to be detected, the distance v from the detector to the surface of the workpiece and the distance f from the focal point of the radiation source to the detector. As shown in fig. 11, the included angle between the normal direction of the central point P, the central beam direction of the source focal point R and the vertical direction is α, the distance between the central point P and the source focal point R is f-v, and the x and z coordinates of the source focal point R are respectively
Rx＝Px+(f-v)·sin(α) (10)
Rz＝Pz-(f-v)·cos(α) (11)。
The central position and normal direction of the detector, the focal position of the ray source and the direction of the central beam corresponding to each region to be detected are the acquired scanning path points.
The controller controls the first mechanical arm and the second mechanical arm to enable the detector and the ray source to reach scanning path points corresponding to the area to be detected.
S3, the control system outputs a signal acquisition starting instruction to the data acquisition system, then executes an input waiting instruction, and waits for the data acquisition system to finish data acquisition;
after the detector and the ray source reach the scanning path point, the control system sends a signal acquisition starting instruction to the data acquisition system, then executes an input waiting instruction, waits for the data acquisition system to finish acquisition, and the acquisition finishing mark is that the control system receives an acquisition finishing signal sent by the data acquisition system.
S4, after receiving the instruction of starting to collect signals, the data collection system starts the ray source and the detector, collects data output by the detector, and outputs a collection completion signal to the control system after collection is completed;
after the data acquisition system receives the instruction of starting to acquire signals, a radiation source switch is turned on, so that a radiation source emits rays, a detector is controlled to start working at the same time, and a ray beam which penetrates through the surface of a workpiece and reaches the detector is received and imaged; the imaging data of the detector is transmitted to a data acquisition system through a data line, and after the data acquisition system finishes acquisition, the data acquisition system outputs an acquisition completion signal to a control system and controls the ray source to be closed;
and S5, after receiving the acquisition completion signal, the control system judges whether the program is finished, if so, the detection is completed, if not, the value i is added by 1, and the step S2 is returned.
The control system needs to judge whether the program is finished after the detection of one scanning path point is finished, the end indicates that all the path points are detected, if the program is not finished, the control system indicates that undetected path points exist in the program, the value of i is added with 1 to enter the next undetected path point, and the program is finished until all the path points are detected.
According to the automatic detection method, a mechanical arm control program is compiled, three control instructions corresponding to each path point are inserted into the program, and according to the instructions, a control system controls a detector and a ray source to reach positions corresponding to scanning path points and controls an acquisition system to complete data acquisition, so that automatic detection is realized.
According to the method, three-dimensional modeling of the workpiece is adopted, the position and the normal direction of the central point of the region to be detected on the surface of the workpiece are obtained by computer graphics, the position and the normal direction of the central point of the detector, the position and the central beam direction of the ray source corresponding to each detection region are obtained according to the position and the normal direction of the central point, the normal direction of the detector and the central beam direction of the ray source are consistent with the normal direction of the region to be detected, the vertical transillumination detection of the complex curved surface can be realized according to the scanning path point obtained by the method, and the imaging quality and the detection precision are improved.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (10)
1. A double-mechanical-arm digital ray detection device is characterized by comprising a ray source, a detector, a workpiece rotary table, a first mechanical arm, a second mechanical arm, a control system and a data acquisition system;
the first mechanical arm and the second mechanical arm are arranged on two sides of the workpiece rotary table, and the ray source and the detector are respectively arranged on the first mechanical arm and the second mechanical arm;
the workpiece to be measured is arranged on the workpiece rotary table;
the data acquisition system is used for acquiring imaging data of the detector;
the control system changes the positions and the directions of the detector and the ray source by adjusting the motion axes of the first mechanical arm and the second mechanical arm, so as to realize the detection of the workpiece; the central beam of the ray source is always vertical to the surface of the detector and passes through the central point of the detector in the scanning process.
2. The dual-robot digital radiography apparatus of claim 1, wherein the control system adjusts the axes of motion of the first robot and the second robot to maintain the direction of the central beam of the radiation source unchanged, so that the detector and the radiation source perform a synchronous translational motion in a certain direction, thereby performing the detection of different positions of the workpiece.
3. The dual-robot digital radiography apparatus of claim 1, wherein the control system adjusts the axes of motion of the first robot and the second robot to maintain the position of the center of the detector, so as to rotate the detector along the bisector of the detector in the horizontal or vertical direction, and to rotate the radiation source in an arc orbit around the center of the detector and the distance between the center of the detector and the focal point of the radiation source as a radius, thereby detecting different angles of the workpiece.
4. The dual-robot digital radiography apparatus of claim 1, wherein the control system adjusts the axes of motion of the first robot and the second robot such that the detector and the radiation source rotate along a circle centered on a point to be detected in the workpiece, the detector has a radius from a center point of the detector to the point to be detected, the radiation source has a radius from the point to be detected to a focal point of the radiation source, and the radiation source rotate along opposite directions in an arc orbit to detect different angles of the workpiece.
5. The dual-mechanical-arm digital ray detection device according to any one of claims 1 to 4, wherein the control system adjusts each motion axis of the first mechanical arm or the second mechanical arm to move the detector or the ray source along the connection line between the ray source and the detector, so as to change the distance between the ray source and the detector, thereby realizing detection of different amplification ratios of the workpiece.
6. The dual-robot digital radiography apparatus of any one of claims 1-4, wherein the detection of different angles in the circumferential direction of the workpiece is achieved by rotation of the workpiece turntable.
7. An automatic detection method based on the device of any one of claims 1-4, characterized by comprising the following steps:
s1, the control system runs a mechanical arm control program;
s2, the control system controls the mechanical arm to enable the ray source and the detector to move to the ith scanning path point, and the initial value of i is 1;
s3, the control system outputs a signal acquisition starting instruction to the data acquisition system, then executes an input waiting instruction, and waits for the data acquisition system to finish data acquisition;
s4, after receiving the instruction of starting to collect signals, the data collection system starts the ray source and the detector, collects data output by the detector, and outputs a collection completion signal to the control system after collection is completed;
and S5, after receiving the acquisition completion signal, the control system judges whether the program is finished, if so, the detection is completed, if not, the value i is added by 1, and the step S2 is returned.
8. The automatic detection method according to claim 7, wherein the scanning path points are obtained by manual teaching, specifying an offset, or extracting path points by computer graphics based on a three-dimensional model of the workpiece.
9. The automatic detection method according to claim 8, wherein the method of extracting the waypoint by computer graphics based on the three-dimensional model of the workpiece comprises:
s21, acquiring a three-dimensional model of the workpiece;
s22, dividing the surface of the workpiece into a plurality of areas to be detected;
s23, acquiring the position and normal direction of the central point of each area to be detected on the surface of the workpiece based on computer graphics;
s24, determining the position and the normal direction of the central point of the detector according to the position and the normal direction of the central point, wherein the normal direction of the detector is consistent with the normal direction of the area;
s25, obtaining a focal point position of a ray source and a central beam direction according to the position and the normal of the central point of the detector, wherein the central beam direction is consistent with the normal of the detector;
the central position and normal direction of the detector, the focal position of the ray source and the direction of the central beam corresponding to each region to be measured are the acquired scanning path points.
10. The automatic detection method according to claim 7, wherein the robot arm control program is specifically as follows:
s11, creating a mechanical arm control program;
s12, inserting a movement instruction in the program to enable the ray source and the detector to move to the scanning path point;
s13, inserting a signal acquisition starting instruction in the program, and informing a data acquisition system to start data acquisition;
s14, inserting an input waiting instruction in the program, and waiting for the data acquisition system to finish acquisition;
and S15, judging whether the scanning path is planned or not, if not, returning to the step S2, and if so, ending the process.
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