CN114964056A - Self-calibration method for micro-assembly equipment - Google Patents
Self-calibration method for micro-assembly equipment Download PDFInfo
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- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/26—Measuring arrangements characterised by the use of optical techniques for measuring angles or tapers; for testing the alignment of axes
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/26—Measuring arrangements characterised by the use of optical techniques for measuring angles or tapers; for testing the alignment of axes
- G01B11/27—Measuring arrangements characterised by the use of optical techniques for measuring angles or tapers; for testing the alignment of axes for testing the alignment of axes
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Abstract
The invention belongs to the technical field of automatic assembly of precise micro parts, and relates to a self-calibration method for micro assembly equipment. Based on a machine vision system in the micro-assembly equipment, a calibration plate with simple characteristics is matched, planned movement is completed by controlling a corresponding linear guide rail, the coordinate change of characteristic points on the calibration plate in the camera visual field before and after the movement is observed, the movement information and the coordinate information are brought into a solution model for calculation, and the calibration tasks of all calibration parameters are completed in sequence. The invention can complete the calibration work of a plurality of parameters at one time, does not need to use an external precision measuring tool, has low cost, easy operation, high precision and high efficiency, and the calibrated parameters can be used for compensation in subsequent motion control, thereby laying a good foundation for assembly precision.
Description
Technical Field
The invention belongs to the technical field of automatic assembly of precise micro parts, and relates to a self-calibration method for micro assembly equipment.
Background
With the continuous development of technologies such as aviation and aerospace, the requirement on the assembly precision of the tiny parts is higher and higher. The micro-assembly equipment is nonstandard automatic equipment specially designed for assembly tasks of certain micro parts, the interior of the equipment can be divided into different modules according to different functions, and the interior of each module mostly comprises a plurality of orthogonal linear guide rails as a movement mechanism. Because the linear guide rails are manually installed, the linear guide rails in the corresponding directions of different modules cannot guarantee strict parallel relation, and the orthogonal linear guide rails in the modules cannot guarantee strict vertical relation. Therefore, when the assembly task is performed, the sliding table on the linear guide rail cannot accurately reach the designed position, which causes a loss of assembly accuracy. Therefore, in order to improve the assembly accuracy, the micro-assembly equipment needs to be calibrated, and the calibration result is used for subsequent motion compensation.
The essential problems of the calibration of the micro-assembly equipment are the perpendicularity measurement problem of an orthogonal linear guide rail and the parallelism measurement problem of a parallel linear guide rail, but the existing calibration method mainly discusses the two problems separately. For verticality measurement, standard parts such as a square and a prism and special equipment such as a ball rod instrument, a theodolite and a laser interferometer are mostly needed. For example, the invention patent number 201610650107.X Pengzhuang discloses a method for measuring the perpendicularity of an orthogonal linear guide rail by using an optical square brick, which has high precision, but has a very complicated measuring process and high requirements on the installation precision of an externally-added displacement sensor and the levelness of the optical square brick. The method for measuring the perpendicularity of the large-size three-dimensional linear guide rail based on the theodolite is mentioned in the 'method for measuring the perpendicularity of the large-size three-dimensional guide rail by using the theodolite' by the university of Harbin industry, has large arrangement space and is only suitable for the measurement task of the perpendicularity of the large-size linear guide rail. For parallelism measurement, currently, an indicator method is mainly adopted for measurement, but certain requirements are required for the distance between the linear guide rails, and the parallelism measurement is easily influenced by the inclination angle of the standard component. The Wangming university of the great-connectivity organization proposes a method for measuring the parallelism of a linear guide rail based on a biaxial level meter and a pentagonal prism in 'research and application of a guide rail linearity and parallelism measuring system', but a reference rail and a measuring tool need to be respectively subjected to a complicated calibration process during measurement, and the time cost is high.
In the calibration method, an external precise measurement device is mostly needed, higher requirements are imposed on the measurement environment and operators, but the space of the micro-assembly equipment is compact, and the arrangement of external equipment is difficult; the operation process is complicated, the time cost is high, and the requirement of regular and quick calibration of the micro-assembly equipment cannot be met; if the verticality error and the parallelism error of the micro-assembly equipment are calibrated simultaneously, different measuring tools are needed to be matched, and the measuring cost is increased.
In summary, in order to overcome the disadvantages of the above calibration method, a self-calibration method for a micro-assembly device is provided, in which calibration is performed in the micro-assembly device quickly, accurately and easily, and measurement tasks of various parameters in the device are completed simultaneously by using a simple tool.
Disclosure of Invention
The invention mainly solves the technical problems that: aiming at the problems of parallelism errors of linear guide rails in the corresponding directions of different modules and perpendicularity errors of orthogonal linear guide rails in the modules caused by manual installation in the existing micro-assembly equipment, self-calibration of the micro-assembly equipment is carried out based on a machine vision system in the equipment; meanwhile, the machine vision system is used as an important measuring tool in equipment, and the torsion error of the machine vision system is also used as a calibration object. The calibration principles of different calibration parameters are similar, and the basic idea is as follows: based on a machine vision system in the micro-assembly equipment, by means of a calibration plate with simple characteristics, a sliding table on a linear guide rail is moved to enable patterns on the calibration plate to appear in a camera visual field, and coordinate information of characteristic points on the calibration plate is obtained through an image processing technology; and controlling the linear guide rail to generate corresponding motion, recording the coordinate change of the characteristic points on the calibration plate in the camera visual field after the motion, and substituting the coordinate information and the linear guide rail motion information into a solving model for calculation to obtain parameter values.
The technical scheme of the invention is as follows:
a self-calibration method for micro-assembly equipment is characterized in that a calibration plate is matched based on a machine vision system in the micro-assembly equipment, planned movement is completed by controlling a corresponding linear guide rail, coordinate changes of characteristic points on the calibration plate in a camera visual field before and after movement are observed, movement information and coordinate information are brought into a solution model for calculation, and calibration tasks of all calibration parameters are completed in sequence; wherein:
the micro-assembly equipment is nonstandard automatic equipment for performing precision assembly on certain micro parts, and the structure related to a calibration task in the equipment comprises a vision measurement module, an execution module, a portal frame and an optical platform. The optical platform is a foundation built by equipment and used for placing a portal frame, a vision measuring module and an execution module; the portal frame is fixed on the optical platform along the X direction and used for raising the installation height of the vision measurement module.
The vision measuring module comprises X 1 Linear guide rail, Z 1 The device comprises a linear guide rail, a machine vision system, a guide rail fixing plate and a camera fixing plate; said X 1 Linear guide and Z 1 The linear guide rails are linear guide rails capable of generating precise displacement, each linear guide rail comprises a guide rail and a sliding table, and the X part is a linear guide rail capable of generating precise displacement 1 A guide rail in the linear guide rail is fixed on the portal frame along the X direction, and the sliding table can generate linear motion along the X direction; the guide rail fixing plate is right-angled, and one side of the guide rail fixing plate is horizontally fixed on the X 1 The sliding table in the linear guide rail moves along with the sliding table, and the other side of the sliding table is vertically arranged in front of the portal frame; z is 1 A guide rail in the linear guide rail is fixed on the vertical edge of the guide rail fixing plate along the Z direction, and the sliding table can generate linear motion along the Z direction; the camera fixing plate is in an open C shape, and one side of the camera fixing plate is fixed at Z 1 The sliding table in the linear guide rail moves along with the sliding table, and the inner side of the opposite side of the sliding table is used for fixing a machine vision system; the machine vision system comprises a camera, a telecentric lens and an annular light source which are sequentially connected from top to bottom and used as a real-time image acquisition task,the observed image can be transmitted to an upper computer for image processing; an image coordinate system is artificially established in a camera visual field, the upper edge and the left edge of the visual field are respectively defined as a U axis and a V axis, and the U axis and the V axis of the image coordinate system are mutually vertical due to the fact that the visual field is in a rectangular shape; the pixel size is obtained before the calibration task starts, the U-direction pixel size is Px, and the V-direction pixel size is Py.
The execution module represents a series of modules for executing different functions, and comprises a movement mechanism and a tail end execution mechanism inside, wherein the movement mechanism needs to carry out calibration work; the motion mechanism comprises an X 2 Linear guide, Y 2 Linear guide and Z 2 A linear guide rail; said X 2 A guide rail in the linear guide rail is fixed on the optical platform along the X direction, and the sliding table can move along the X direction; said Y 2 The guide rail of the linear guide rail is fixed on the X direction along the Y direction 2 The sliding table in the linear guide rail moves along with the sliding table, Y 2 The sliding table in the linear guide rail can generate Y-direction movement; z is 2 The guide rail of the linear guide rail is fixed on the Y direction 2 On the slide table in the linear guide rail, moving with the slide table, Z 2 The sliding table in the linear guide rail can generate Z-direction movement; the end actuating mechanism is fixed at Z 2 On a sliding table in a linear guide rail, by X 2 Linear guide, Y 2 Linear guide and Z 2 The linear guide rail realizes three-dimensional motion.
The calibration parameters are obtained in the analysis and assembly process and comprise an image coordinate system U axis and a vision measurement module X 1 Error angle alpha of parallelism of linear guide 1 Execution module X 2 Linear guide rail and vision measuring module X 1 Error angle alpha of parallelism of linear guide 2 Execution module X 2 Linear guide rail and execution module Y 2 Linear guide vertical error angle beta and execution module Z 2 Linear guide rail and vision measuring module Z 1 The linear guide is parallel to the error angle gamma.
The calibration plate at least comprises the following characteristics that two square blocks are arranged at two ends of a pattern of the calibration plate, the centroid coordinates of the square blocks in the visual field of the camera can be obtained through image processing, and the distance between the centroids of the two square blocks is d; a long straight line is arranged between the squares, the connecting line of the centroids of the squares is parallel to the edge of the long straight line, and the edge of the square centroids is fitted through image processing to obtain the inclination angle of the calibration plate relative to the U axis of the image coordinate system.
After the above conditions are known, the specific steps of self-calibration are as follows: :
the method comprises the following steps: fixing the calibration plate placing table to the execution module Z 2 On the sliding table in the linear guide rail, the calibration plate is placed on the calibration plate placing table along the X direction, the sliding tables in the visual measurement module and the execution module linear guide rail are moved, so that the square block at the left end of the calibration plate clearly appears in the visual field of the camera, and the coordinate (U) of the centroid of the square block in the image coordinate system is obtained through image processing 1 ,V 1 )；
Step two: the executive module is kept still and moves the vision measuring module X rightwards 1 The sliding table in the linear guide rail enables the middle long straight line of the calibration plate to appear in the visual field of the camera, and the inclination angle theta of the long straight line is obtained through image processing 1 ；
Step three: continue moving to the right by X 1 The sliding table in the linear guide rail enables the square block at the right end of the calibration plate to appear in the visual field of the camera, records X 1 Distance sum L of two-time movement of sliding table in linear guide rail 1 Obtaining the coordinates (U) of the centroid of the square block in the image coordinate system through image processing 2 ,V 2 ) (ii) a The information is brought into an error angle calculation model formula (1), and an image coordinate system U axis and a vision measurement module X can be obtained 1 Error angle alpha of parallelism of linear guide 1 ：
Step four: visual measurement module remains stationary and moves execution module X to the right 2 A sliding table in the linear guide rail enables a square block at the left end of the calibration plate to appear in the visual field of the camera, records X 2 Distance L of linear guide rail movement 2 Obtaining the coordinates (U) of the centroid of the square block in the image coordinate system through image processing 3 ,V 3 ) (ii) a Bringing information into error angle calculation modelIn the formula (2) and the angle conversion relation formula (3), the execution module X can be obtained 2 Linear guide rail and vision measuring module X 1 Error angle alpha of parallelism of linear guide 2 ：
α 2 ＝α 1 -ω 1 (3)
Step five: the calibration plate is placed on the calibration plate placing table again along the Y direction, the sliding tables in the linear guide rails of the vision measuring module and the execution module are moved, so that the front square block of the calibration plate appears in the field of view of the camera, and the coordinates (U) of the centroid of the square block in the image coordinate system are obtained through image processing 4 ,V 4 )；
Step six: the vision measuring module is kept still, and the execution module Y is moved forwards 2 The sliding table in the linear guide rail enables a long straight line in the middle of the calibration plate to appear in the visual field of the camera, and the inclination angle theta of the long straight line relative to the V axis of the image coordinate system is obtained through image processing 2 ；
Step seven: continue to move forward Y 2 The sliding table in the linear guide rail enables the rear square block of the calibration plate to appear in the visual field of the camera and records Y 2 Distance sum L of two-time movement of sliding table in linear guide rail 3 Obtaining the coordinates (U) of the centroid of the square block in the image coordinate system through image processing 5 ,V 5 ) (ii) a The information is substituted into an error angle calculation model formula (4) and an angle conversion model formula (5), and an execution module X can be obtained 2 Linear guide rail and execution module Y 2 Linear guide vertical error angle β:
step eight: control execution module Z 2 Sliding table in linear guide rail moves downwards L 5 Distance, control vision measuring module Z 1 The sliding table in the linear guide rail moves downwards until the square on the calibration plate clearly appears in the visual field of the camera again, and the vision measuring module Z is recorded 1 Distance L of moving sliding table in linear guide rail 4 Obtaining the coordinates (U) of the centroid of the square block in the image coordinate system through image processing 6 ,V 6 ) (ii) a The information is brought into an error angle calculation model formula (6), and an execution module Z can be obtained 2 Linear guide rail and vision measuring module Z 1 Linear guide parallelism error angle γ:
the invention has the following beneficial effects:
(1) the invention carries out self-calibration of the micro-assembly equipment by means of a machine vision system in the micro-assembly equipment, does not need to be matched with an external precision measurement tool, and has simple pattern of the used calibration plate and easy finding of alternative characteristics, so the whole calibration cost is very low; meanwhile, the non-contact type calibration mode does not damage the movement mechanism and the calibration plate.
(2) The invention can finish the calibration work of a plurality of parameters at one time, and only the coordinate difference, the inclination angle and the movement distance of the characteristic point are needed to be obtained in the calibration process of each parameter, thereby being simple and easy to implement and having low requirement on operators; the used calculation models are strictly derived and verified by mathematics and can be directly substituted for use; meanwhile, mature and simple image processing algorithms are used, and the method is easy to realize by means of a digital image processing tool;
(3) the image processing algorithm and the motion control in the invention are both rapid, the measurement efficiency is high, and the time cost is very low; the manufacturing precision of the adopted calibration plate is in the micron level, the motion precision of the linear guide rail is generally in the micron level range, meanwhile, the image processing technology is mature, the overall error is small, and the calibration precision is effectively improved.
Drawings
FIG. 1 shows a schematic view of aIs a schematic diagram of the calibration process of the method of the invention, wherein: 1 an optical platform; 2X 2 A linear guide rail; 3Y 2 A linear guide rail; 4Z 2 A linear guide rail; 5 calibrating a board placing table; 6, a portal frame; 7X 1 A linear guide rail; 8, fixing a guide rail; 9 a camera; 10 camera fixing plate; 11 a telecentric lens; 12 an annular light source; 13Z 1 A linear guide rail; the plates are calibrated 14. Wherein, the vision measuring module (including 7, 8, 9, 10, 11, 12, 13) is fixed on the portal frame 6, and the machine vision system (including 9, 11, 12) follows the vision measuring module Z 1 The sliding table in the linear guide rail 13 moves, the execution module (comprising 2, 3 and 4) is fixed on the optical platform 1, and the calibration plate placing table 5 is fixed on the execution module Z 2 On the slide table in the linear guide 4, the calibration plate 14 is placed on the calibration plate placing table 5.
FIG. 2 is a schematic diagram of establishing an image coordinate system in a camera field of view, where the origin is in the upper left corner of the camera field of view and the U and V axes are along the upper and left edges, respectively.
FIG. 3 is a schematic diagram of a calibration plate pattern used in the calibration process, in which the left and right ends of the calibration plate are respectively provided with a square A and a square B, and the centroid distance between the two squares is d; the long straight line is positioned between the two square blocks, and the upper edge and the lower edge of the long straight line are parallel to the connecting line of the centroids of the two square blocks.
FIG. 4 is a block diagram of the image coordinate system U axis and the vision measuring module X 1 Error angle alpha of parallelism of linear guide 1 Calculating a model diagram, wherein U-O-V is an image coordinate system before movement; AB is a simplified graph of the calibration plate style, A is the centroid of the left square of the calibration plate, whose coordinates in the image coordinate system are (U) 1 ,V 1 ) B is the centroid of the right square block of the calibration plate, AB length is d, theta 1 The included angle between the AB and the U axis of the image coordinate system is obtained by fitting the edge of the long straight line of the calibration plate; camera with X 1 Sliding table movement L in linear guide rail 1 Distance, change of origin of image coordinate system from O point to O point 1 Point AA 'is a line which is parallel to and equal in length to OO' and passes through point A; after the movement, the coordinates of the centroid B of the square in the image coordinate system are (U) 2 ,V 2 ) (ii) a The point C is a parallel line of a U axis passing through the point A and a passing through point A, and the U axis is vertical to the V axis, so that AC (inverted T) A' C is formed; alpha is alpha 1 Namely the U axis of the image coordinate system and the vision measuring module X 1 The angle between the linear guides can be derived from the geometric relationship in Δ AA' C.
FIG. 5 shows an execution block X 2 Linear guide rail and vision measuring module X 1 Error angle alpha of parallelism of linear guide 2 Calculating a model diagram, wherein AB is the position of the calibration plate before movement, and the included angle between AB and the U axis of the image coordinate system is theta 1 And the coordinate of the point B in the image coordinate system is (U) 2 ,V 2 ) (ii) a A 'B' is an execution module X 2 Sliding table in linear guide rail moves rightwards L 2 The position of the calibration plate is calibrated after the distance, and the coordinate of the point A' in the image coordinate system is (U) 3 ,V 3 ) (ii) a The point D is the intersection point between the parallel lines of the U axis passing through the point A and the parallel lines of the V axis passing through the point A ', and is AD inverted T A' D; omega 1 For the image coordinate system U-axis and the execution module X 2 The included angle between the linear guide rails can be obtained by the geometric relation in delta AA' D, and the execution module X is further obtained according to the angle relation 2 Linear guide rail and vision measuring module X 1 Error angle alpha of parallelism of linear guide 2 。
FIGS. 6(a) and 6(b) show the execution block X 2 Linear guide rail and execution module Y 2 A linear guide vertical error angle beta calculation model diagram, wherein in the diagram of FIG. 6(a), AB is the position of the calibration plate before movement, and the included angle between AB and the V axis of the image coordinate system is theta 2 The coordinate of the point A in the image coordinate system is (U) 4 ,V 4 ) (ii) a A 'B' is an execution module Y 2 Sliding table in linear guide rail moves forwards L 3 After the distance, the position of the calibration plate is calibrated, and the coordinate of the point B' in the image coordinate system is (U) 5 ,V 5 ) (ii) a Point E is the intersection point between the parallel line passing through the U axis made by point B and the parallel line passing through the V axis made by point B ', and is inverted T to B' E; f is the intersection point of the parallel line of the V axis passing through the point A and the extended line of the BE, and is AF ^ BF; omega 2 For the image coordinate system V-axis and the execution module Y 2 The angle between the linear guides can be obtained from the geometric relationship in Δ BEB', and further from the angular relationship in fig. 6(b), the execution module X is obtained 2 Linear guide rail and execution module Y 2 Straight lineRail vertical error angle beta.
FIG. 7 is an execution block Z 2 Linear guide rail and vision measuring module Z 1 A linear guide rail parallel error angle gamma calculation model diagram, wherein U-O-V is an image coordinate system before motion, and the coordinate of a square centroid B point in the image coordinate system is B 1 (U 5 ,V 5 ) (ii) a Vision measuring module Z 1 Downward movement L of sliding table in linear guide rail 4 Distance, change of origin of image coordinate system from O point to O point 2 Point, execution module Z 2 Downward movement L of sliding table in linear guide rail 5 Distance, the coordinate of the B point of the centroid of the square in the image coordinate system is B 2 (U 6 ,V 6 ) (ii) a Knowing B from the geometrical relationship 1 B 2 And Z 2 The linear guide rails are parallel in direction, and B 1 B 2 ＝L 5 (ii) a G point is passing B 1 Dot-done with OO 2 Parallel and equal length lines; gamma is the execution module Z 2 Linear guide rail and vision measuring module Z 1 Error angle of parallelism of linear guides, which can be defined by Δ B 1 B 2 The geometric relationship in G is obtained.
Detailed Description
The following further describes a specific embodiment of the present invention with reference to the drawings and technical solutions.
A self-calibration process for a micro-assembly device is shown in figure 1, a calibration plate 14 placed on an execution module is observed by means of a machine vision system in the device, and an image coordinate system U axis and a vision measurement module X axis are sequentially completed by controlling the movement of different linear guide rails 1 Parallel error angle alpha between linear guides 7 1 Execution module X 2 Linear guide rail and vision measuring module X 1 Parallel error angle alpha between linear guides 7 2 Execution module X 2 Linear guide rail 2 and execution module Y 2 Vertical error angle beta between linear guides 3 and actuator module Z 2 Linear guide 4 and vision measuring module Z 1 The task of calibrating the parallelism error angle y between the linear guides 13. An image coordinate system U-O-V as shown in FIG. 2 is established in the visual field of the camera 9 for facilitating coordinate reading, and the pixel sizes in two directions are Px and P respectivelyy; the calibration plate 14 is shown in fig. 3, and the centroid coordinates and the inclination angles of the long straight lines of the squares in the image coordinate system can be obtained by image processing technology.
After the above preconditions are known, the specific calibration steps are as follows:
(1) placing the calibration plate 14 on the calibration plate placing table 5 along the X direction, moving the sliding tables in the linear guide rails of the vision measuring module and the execution module to ensure that the square block at the left end of the calibration plate 14 clearly appears near the center position of the visual field of the camera 9, and obtaining the coordinate (U) of the square centroid A in the image coordinate system through the image processing technology 1 ,V 1 ) (ii) a Rightward movement vision measuring module X 1 A slide table in the linear guide 7 for allowing the middle part of the long straight line in the calibration plate 14 to appear in the field of view of the camera 9, and obtaining the inclination angle theta of the long straight line by image processing technology 1 (ii) a Continue moving to the right by X 1 The coordinates (U) of the centroid B of the square block in the image coordinate system are obtained by image processing technology until the square block at the right end of the calibration plate 14 appears near the center of the visual field of the camera 9 in the sliding table in the linear guide 7 2 ,V 2 ) (ii) a Record X at the same time 1 Sum of distances L traveled by linear guide 7 1 ；
(2) As shown in fig. 4, in the right angle Δ ACA', it is obtained by the pythagorean theorem: a' C 2 +AC 2 ＝AA′ 2 Will coordinate (U) 1 ,V 1 ) And (U) 2 ,V 2 ) Long straight line inclination angle theta 1 Distance of movement L 1 And the distance d between the centroids of the two squares is taken into the formula (1), so that the U axis of the image coordinate system and the vision measuring module X can be obtained 1 Parallel error angle alpha between linear guides 7 1 ：
(3) Visual measurement module remains stationary and moves execution module X to the right 2 The sliding table in the linear guide rail 2 records X until the square block at the left end of the calibration plate 14 appears near the center of the visual field of the camera 9 2 Distance L of movement of the slide table in the linear guide 2 2 By means of a drawingThe image processing technique obtains the coordinates (U) of the centroid A' of the square in the image coordinate system 3 ,V 3 )；
(4) As shown in fig. 5, in the right angle Δ ADA', it follows from the pythagorean theorem: a' D 2 +AD 2 ＝AA′ 2 Will coordinate (U) 2 ,V 2 ) And (U) 3 ,V 3 ) Long straight line inclination angle theta 1 Distance of movement L 2 And the distance d between the centroids of the two blocks is expressed in the formula (2), so as to obtain the U axis of the image coordinate system and the execution module X 2 Angle omega between linear guides 2 1 Further obtaining an execution module X from the angle conversion relation (3) 2 Linear guide rail 2 and vision measuring module X 1 Parallel error angle alpha between linear guides 7 2 ：
α 2 ＝α 1 -ω 1 (3)
(5) The calibration plate 14 is placed on the calibration plate placing table 5 again along the Y direction, the sliding tables in the linear guide rails of the vision measuring module and the execution module are moved, so that the front end square block of the calibration plate 14 clearly appears near the center of the visual field of the camera 9, and the coordinate (U) of the square centroid A in the image coordinate system is obtained through the image processing technology 4 ,V 4 ) (ii) a Move execution Module Y forward 2 A sliding table in the linear guide 3, so that the middle part of the long straight line in the calibration plate 14 appears in the visual field of the camera 9, and the inclination angle theta of the long straight line relative to the V axis of the image coordinate system is obtained by image processing technology 2 (ii) a Continue to move forward Y 2 Until the square block at the rear end of the calibration plate 14 appears near the center of the visual field of the camera 9, the coordinates (U) of the square centroid B' in the image coordinate system are obtained by image processing technology 5 ,V 5 ) (ii) a At the same time record Y 2 Total distance L of movement of the slide table in the linear guide 3 3 ；
(6) As shown in fig. 6(a), in the right angle Δ BEB', it is obtained by the pythagorean theorem: b' E 2 +BE 2 ＝BB′ 2 Will coordinate (U) 4 ,V 4 ) And (U) 5 ,V 5 ) Long straight line inclination angle theta 2 Distance of movement L 3 And the distance d between the centroids of the two blocks is expressed in formula (4), so as to obtain the V axis of the image coordinate system and the execution module Y 2 The included angle omega between the linear guide rails 3 2 (ii) a Further, the angle transformation relation (5) in fig. 6(b) results in the execution module X 2 Linear guide rail 2 and execution module Y 2 Vertical error angle β of linear guide 3:
(7) will execute module Z 2 The slide table in the linear guide 4 moves down L 5 Distance, control vision measuring module Z 1 The slide in the linear guide 13 moves downwards until the squares on the calibration plate 14 again appear clearly in the field of view of the camera, registering the vision measuring module Z 1 Distance L of movement of the slide table in the linear guide 13 4 Obtaining the coordinates (U) of the centroid of the square block in the image coordinate system by image processing technology 6 ,V 6 )；
(8) As shown in FIG. 7, γ is the execution module Z 2 Linear guide 4 and vision measuring module Z 1 Angle of parallelism error between linear guides 13, at Δ B 1 B 2 In G, B is obtained by the cosine theorem 1 B 2 2 +B 1 G 2 -B 2 G 2 ＝2·B 1 B 2 ·B 1 G.cos gamma., coordinates (U) 5 ,V 5 ) And (U) 6 ,V 6 ) Distance of movement L 4 And L 5 The execution module Z can be obtained by carrying in the formula (6) 2 Linear guide rail and vision measuring module Z 1 Parallel error angle γ between linear guides:
the invention provides a self-calibration method for micro-assembly equipment, aiming at parallel errors and vertical errors caused by installation errors in the micro-assembly equipment, based on a machine vision system in the equipment, a simple calibration plate is matched, the coordinate changes of characteristic points on the calibration plate in the camera visual field before and after movement are observed by controlling the movement of sliding tables in different linear guide rails, and the coordinate changes are brought into an error calculation model for calculation so as to sequentially complete the solving work of each calibration parameter. The whole calibration method can complete the calibration tasks of a plurality of parameters at one time, has high efficiency, is easy to operate and has low requirement on operators; a machine vision system of the micro-assembly equipment is used, other precision measurement tools are not required to be added, and the calibration cost is low; meanwhile, the manufacturing precision of the calibration plate, the motion precision of the linear guide rail and the image processing precision reach high levels, and the calibration precision is effectively improved by combining the model in the calibration method. The method has important significance for system calibration in the field of micro-assembly equipment, and meanwhile, the method provided by the invention also provides a simple and feasible thought for measuring the parallelism and the perpendicularity between the linear guide rails.
Claims (1)
1. A self-calibration method for micro-assembly equipment is characterized in that a calibration plate is matched based on a machine vision system in the micro-assembly equipment, planned movement is completed by controlling a corresponding linear guide rail, the coordinate change of characteristic points on the calibration plate in the camera visual field before and after the movement is observed, movement information and coordinate information are brought into a solution model for calculation, and the calibration tasks of all calibration parameters are completed in sequence; wherein:
the micro-assembly equipment is non-standard automatic equipment for performing micro-miniature part precision assembly, and the structure related to a calibration task in the equipment comprises a vision measurement module, an execution module, a portal frame and an optical platform; the optical platform is used for placing a portal frame, a vision measuring module and an execution module; the portal frame is fixed on the optical platform along the X direction and used for raising the installation height of the vision measurement module;
the vision measuring module comprises an X 1 Linear guide rail, Z 1 The device comprises a linear guide rail, a machine vision system, a guide rail fixing plate and a camera fixing plate; said X 1 Linear guide and Z 1 The linear guide rails are linear guide rails generating precise displacement, each linear guide rail comprises a guide rail and a sliding table, and the X part is arranged in the linear guide rail 1 A guide rail in the linear guide rail is fixed on the portal frame along the X direction, and the sliding table can generate linear motion along the X direction; the guide rail fixing plate is right-angled, and one side of the guide rail fixing plate is horizontally fixed on the X 1 The sliding table in the linear guide rail moves along with the sliding table, and the other side of the sliding table is vertically arranged in front of the portal frame; z is 1 A guide rail in the linear guide rail is fixed on the vertical edge of the guide rail fixing plate along the Z direction, and the sliding table can generate linear motion along the Z direction; the camera fixing plate is in an open C shape, and one side of the camera fixing plate is fixed at Z 1 The sliding table in the linear guide rail moves along with the sliding table, and the inner side of the opposite side of the sliding table is used for fixing a machine vision system; the machine vision system comprises a camera, a telecentric lens and an annular light source which are sequentially connected from top to bottom and used as a real-time image acquisition task, and an observed image is transmitted to an upper computer for image processing; an image coordinate system is artificially established in a camera visual field, the upper edge and the left edge of the visual field are respectively defined as a U axis and a V axis, and the U axis and the V axis of the image coordinate system are mutually vertical due to the fact that the visual field is in a rectangular shape; the U-direction pixel size is Px, and the V-direction pixel size is Py;
the execution module comprises a motion mechanism and a tail end execution mechanism, wherein the motion mechanism needs to carry out calibration work; the motion mechanism comprises an X 2 Linear guide, Y 2 Linear guide and Z 2 A linear guide rail; said X 2 A guide rail in the linear guide rail is fixed on the optical platform along the X direction, and the sliding table can move along the X direction; said Y 2 The guide rail of the linear guide rail is fixed on the X direction along the Y direction 2 The sliding table in the linear guide rail moves along with the sliding table, Y 2 The sliding table in the linear guide rail can generate Y-direction movement; z is 2 The guide rail in the linear guide rail is fixed on the Y along the Z direction 2 On the slide table in the linear guide rail, moving with the slide table, Z 2 Sliding table in linear guide railGenerating Z-direction movement; the end actuating mechanism is fixed at Z 2 On a sliding table in a linear guide rail, by X 2 Linear guide, Y 2 Linear guide and Z 2 The linear guide rail realizes three-dimensional motion;
the calibration parameters comprise an image coordinate system U axis and a vision measurement module X 1 Error angle alpha of parallelism of linear guide 1 Execution module X 2 Linear guide rail and vision measuring module X 1 Error angle alpha of parallelism of linear guide 2 Execution module X 2 Linear guide rail and execution module Y 2 Linear guide vertical error angle beta and execution module Z 2 Linear guide rail and vision measuring module Z 1 A linear guide parallel error angle gamma;
the calibration plate at least comprises the following characteristics: two square blocks are arranged at two ends of the pattern of the calibration plate, the centroid coordinates of the square blocks in the visual field of the camera are obtained through image processing, and the distance between the centroids of the two square blocks is d; a long straight line is arranged between the squares, the connecting line of the centroids of the squares is parallel to the edge of the long straight line, and the edge of the square centroids is fitted through image processing to obtain the inclination angle of the calibration plate relative to the U axis of the image coordinate system;
the self-calibration method comprises the following specific steps:
the method comprises the following steps: fixing the calibration plate placing table to the execution module Z 2 On the sliding table in the linear guide rail, the calibration plate is placed on the calibration plate placing table along the X direction, the sliding tables in the visual measurement module and the execution module linear guide rail are moved, so that the square block at the left end of the calibration plate clearly appears in the visual field of the camera, and the coordinate (U) of the centroid of the square block in the image coordinate system is obtained through image processing 1 ,V 1 )；
Step two: the executing module is kept still and moves the vision measuring module X to the right 1 The sliding table in the linear guide rail enables the middle long straight line of the calibration plate to appear in the visual field of the camera, and the inclination angle theta of the long straight line is obtained through image processing 1 ；
Step three: continue moving to the right by X 1 The sliding table in the linear guide rail enables the square block at the right end of the calibration plate to appear in the visual field of the camera, records X 1 Distance sum L of two-time movement of sliding table in linear guide rail 1 Obtaining the coordinates (U) of the centroid of the square block in the image coordinate system through image processing 2 ,V 2 ) (ii) a The information is brought into an error angle calculation model formula (1), and an image coordinate system U axis and a vision measurement module X can be obtained 1 Error angle alpha of parallelism of linear guide 1 ：
Step four: visual measurement module remains stationary and moves execution module X to the right 2 A sliding table in the linear guide rail enables a square block at the left end of the calibration plate to appear in the visual field of the camera, records X 2 Distance L of linear guide rail movement 2 Obtaining the coordinates (U) of the centroid of the square block in the image coordinate system through image processing 3 ,V 3 ) (ii) a The information is substituted into an error angle calculation model formula (2) and an angle conversion relation formula (3), and an execution module X can be obtained 2 Linear guide rail and vision measuring module X 1 Error angle alpha of parallelism of linear guide 2 ：
α 2 ＝α 1 -ω 1 (3)
Step five: the calibration plate is placed on the calibration plate placing table again along the Y direction, the sliding tables in the linear guide rails of the vision measuring module and the execution module are moved, so that the front square block of the calibration plate appears in the field of view of the camera, and the coordinates (U) of the centroid of the square block in the image coordinate system are obtained through image processing 4 ,V 4 )；
Step six: the vision measuring module is kept still and the executing module Y is moved forwards 2 The sliding table in the linear guide rail enables a long straight line in the middle of the calibration plate to appear in the visual field of the camera, and the inclination angle theta of the long straight line relative to the V axis of the image coordinate system is obtained through image processing 2 ；
Step seven: continue to move forward Y 2 A sliding table in the linear guide rail is provided,the rear square block of the calibration plate appears in the field of view of the camera, and Y is recorded 2 Distance sum L of two-time movement of sliding table in linear guide rail 3 Obtaining the coordinates (U) of the centroid of the square block in the image coordinate system through image processing 5 ,V 5 ) (ii) a The information is brought into an error angle calculation model formula (4) and an angle conversion model formula (5), and an execution module X can be obtained 2 Linear guide rail and execution module Y 2 Linear guide vertical error angle β:
step eight: control execution module Z 2 Sliding table in linear guide rail moves downwards L 5 Distance, control vision measuring module Z 1 The sliding table in the linear guide rail moves downwards until the square on the calibration plate clearly appears in the visual field of the camera again, and the vision measuring module Z is recorded 1 Distance L of moving sliding table in linear guide rail 4 Obtaining the coordinates (U) of the centroid of the square block in the image coordinate system through image processing 6 ,V 6 ) (ii) a The information is brought into an error angle calculation model formula (6), and an execution module Z can be obtained 2 Linear guide rail and vision measuring module Z 1 Linear guide parallelism error angle γ:
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