CN106683138A - Calibration method of solder paste printing machine camera - Google Patents

Abstract

The invention belongs to the technical field of image processing, and particularly relates to a calibration method of a solder paste printing machine camera. The calibration method comprises following steps of (1) by combining actual production conditions of a solder paste printing machine, establishing four coordinate systems on the solder paste printing machine; (2) establishing a system coordinate conversion relation of the coordinate systems of the solder paste printing machine; (3) acquiring images and calibrating key parameters of the coordinate systems; (4) carrying out coordinate conversion error analysis from an image coordinate system to a world coordinate system; (5) establishing a rotation module of a UVW platform; and (6) according to the movement amount, obtained through calculation, of the UVWM platform, moving the UVW platform, and checking contraposition precision so as to verify validity of calibration of the camera. According to the invention, calibration precision is greatly improved; the calibration method is simple to operate; operation complexity is reduced; calibration speed is fast; and coding realization is facilitated.

Description

A kind of scaling method of stencil printer camera

Technical field

The invention belongs to technical field of image processing, is related to a kind of scaling method of stencil printer camera, the method Calibration result is substantially improved in terms of stated accuracy.

Background technology

In PCB attachment productions, the first procedure is paste solder printing, pass of the stencil printer as PCB mounting lines One of button apparatus, the quality of its printing quality directly influences subsequent process flow and product quality.With electronic product towards Miniaturization, lightness and high reliability direction are developed so that surface adhered with electronic component is also constantly towards frivolous small height Integrated direction is developed, and the size of active components becomes less and less, and the size of passive device is also reducing.Paste solder printing is set The requirement of standby printing precision also more and more higher.An important step before accordingly, as printing, accurate contraposition is to improve entirely certainly The key of dynamic stencil printer quality, and it is the premise for aligning that accurate demarcation is carried out to stencil printer camera.

Stencil printer camera calibration just referred to during image measurement, the key parameter of geometrical model is asked for, after being It is continuous to guarantee that corresponding aperture bit alignment provides safeguard on PCB and steel mesh, fit with steel mesh subsequently to rise PCB, carry out tin cream print Brush.The scaling method of traditional stencil printer camera, due to do not account for from initially by image shot by camera to finally by The whole process of Motor drive UVW platform motion, is not set up the coordinate system of whole stencil printer, does not have systematic seat Mark conversion, so larger to the alignment method error of printing platform, contraposition result is not very accurate, and inefficiency. The requirement for improving whole printing efficiency in electronic product paste solder printing quality and printing process can not be met.

Due to there is drawbacks described above and deficiency, this area is needed badly to make and is further improved, and designs a kind of tin cream The scaling method of printing machine camera so as to the printing platform contraposition result that stencil printer occurs in use can be overcome The shortcomings of inaccurate, inefficiency, its aligning accuracy is improved, meet use demand.

The content of the invention

For the disadvantages described above or Improvement requirement of prior art, the invention provides a kind of with regard to stencil printer camera Scaling method, is processed by the Mark points to steel mesh and PCB image, asks for geometrical model key parameter, sets up UVW platforms Rotating model, according to printer platform adjustment amount mobile platform, checks aligning accuracy, verifies camera calibration effect.The method exists Stated accuracy aspect is substantially improved, and simple to operate, reduces the complexity of computing, demarcates speed fast, it is easy to which coding is realized.

For achieving the above object, according to one aspect of the present invention, there is provided a kind of demarcation side of stencil printer camera Method, it is characterised in that the bottom of the stencil printer is pcb board, the pcb board is arranged on UVW platforms, the pcb board Surface have a spectroscope for the centre of a steel mesh, the pcb board and steel mesh, be respectively arranged with a camera before and after spectroscopical With a plane mirror, the scaling method specifically includes following steps：

S1. for the structure of above-mentioned stencil printer, four coordinate systems are set up on the stencil printer, is respectively： On the image of collected by camera set up image coordinate system, on camera set up camera coordinates system, based on camera fields of view set up Reference frame and the world coordinate system set up when the motor shaft catch of stencil printer is in zero-bit；

S2. coordinate transformation will be carried out between the above-mentioned coordinate system of stencil printer：To four coordinates set up in step S1 System is analyzed, the coordinate transformation relation set up successively between each coordinate system, including：Image coordinate is tied to camera coordinates system Conversion, camera coordinates are tied to the conversion that the conversion of reference frame, reference coordinate are tied to world coordinate system；

S3. image is gathered, the key parameter in coordinate system is demarcated, obtain the conversion between each coordinate system Formula；

S4. the conversion formula obtained between each coordinate system in step S3, turns to the coordinate in image coordinate system Change the error produced during the coordinate to world coordinate system to be analyzed, and the error information during coordinate transformation is quantified Process；

S5. the rotating model of UVW platforms is set up, when UVW platforms are in zero-bit, in calculating the rotation of UVW platform models The heart, that is, obtain the rotating model of UVW platforms；

S6. based on the UVW platform rotating models set up in step S5, the amount of movement of UVW platforms is calculated, and to UVW platforms Contraposition adjustment is carried out, camera calibration is completed.

It is further preferred that in step S1, described image coordinate system is the coordinate system set up on the image shot in camera, Its origin of coordinates is located at the image upper left corner, and coordinate unit is pixel；

The camera coordinates system is built upon the coordinate system on camera, and coordinate unit is pixel；

The reference frame is the coordinate system set up with camera fields of view, and the coordinate system is set up in the face of pcb board, regarded with camera Wild lower limb is coordinate system X-axis, and with camera fields of view right hand edge as coordinate system Y-axis, coordinate unit is mm；

The coordinate system that world coordinate system is set up when being and being in zero-bit according to three motor shaft catch of stencil printer, works as electricity When machine catch returns to zero-bit, it is considered as motor zero；Using the line of Y1 zero-bits and Y2 zero-bits as X-axis, X zero-bits and vertical are crossed In X-axis straight line as Y-axis, set up world coordinate system, coordinate unit is mm.

It is further preferred that in step S2, coordinate transformation being carried out between the coordinate system and being comprised the following steps：

S21. camera coordinates system (O is arrived from image coordinate system (U, V)_ccd, X_ccd, Y_ccd) coordinate transformation, its conversion formula For:

In formula, W is picture traverse, and (U, V) is the coordinate of the point in image coordinate system, (X_ccd,Y_ccd) it is camera coordinates system The coordinate of middle respective point；

S22. from camera coordinates system (O_ccdX_ccdY_ccd) arrive reference frame (O_R, X_R, Y_R) coordinate transformation, noteThen its conversion formula is：

In formula, (X_R,Y_R) for the coordinate of the point in reference frame, (X_ccd,Y_ccd) for the seat of respective point in camera coordinates system Mark；

S23. from reference frame (O_R, X_R, Y_R) arrive world coordinate system (O_w, X_w, Y_w) coordinate transformation, its conversion formula For：

In formula, (X_W,Y_W) for the coordinate of the point in world coordinate system, (X_R,Y_R) for the seat of respective point in reference frame Mark,

S24. simultaneous formulaAnd formulaObtain：

In above formula, parameter l_x,l_y, θ, a, b needs demarcation acquisition.

It is further preferred that to l in conversion formula_x、l_y, θ, a, b these key parameters demarcated, its concrete steps It is as follows：

S31. using the camera on stencil printer shoot Mark points on PCB not moving, along the movement of X-axis positive direction, Along three width images of Y-axis positive direction movement, Mark point central coordinate of circle is recorded, using the l obtained in step S2_x、l_yDemarcation it is public Formula calculates l_x、l_yValue：

S32. the value of θ is calculated using the calibration formula of the θ obtained in step S2：

θ=atan2 (Y_ccd1-Y_ccd2,X_ccd2-X_ccd1)；

S33. to the demarcation of parameter a, b, often rotate stencil printer UVW platforms once, shoot the Mark point diagrams of one group of PCB Picture, so rotation several times, obtain the Mark dot images of several PCB, and the Mark points center of circle is tried to achieve in the coordinate system set up Coordinate, is carried out justifying fitting with least square method, obtains the pivot coordinate (X under camera coordinates system_ccdr,Y_ccdr), sit in the world In mark system, platform pivot (X_R,Y_R), it is known that calculating the value of a, b using the calibration formula of a, b for obtaining in step S2：

The demarcation of a, b under camera situation of movement is tried to achieve by calibration formula：

It is further preferred that in step S4, according to the conversion formula tried to achieve, according to image coordinate system coordinate (U, V) generation is arrived Boundary coordinate system coordinate (X_W,Y_W) transforming relationship formulaError information during coordinate transformation is entered Row quantification treatment.

It is as follows the step of set up the rotating model of UVW platforms it is further preferred that in step S5：

S51. UVW platforms are rotated, the mark points center of circle of several pcb boards is obtained；

S52. carried out justifying fitting with least square method, obtain the central coordinate of circle (X under camera coordinates system_ccdr,Y_ccdr)；

S53. the central coordinate of circle under camera coordinates system is changed to world coordinate system, that is, obtains the rotating model of UVW platforms.

It is further preferred that in step S6, camera calibration is comprised the following steps that：

S61. according to the rotating model of the UVW platforms obtained in step S5, the platform based on pcb board is adjusted, is put down Platform adjustment includes the translational movement amount and amount of rotational movement of three motor shafts of UVW platforms；

S62. UVW platforms, checking contraposition are moved according to the translational movement amount and amount of rotational movement of calculated UVW platforms Precision；

If S63. aligning accuracy meets and requires, illustrate to demarcate effective, camera calibration terminates；Otherwise, failure is demarcated, this Shi Jixu repeat steps S3-S6 are required until calibration result meets.

In general, by contemplated above the technical scheme of the present invention compared with prior art, with advantages below with Beneficial effect：

(1) stencil printer camera calibration method proposed by the present invention, it is contemplated that from initially by image shot by camera to most The whole process moved by Motor drive UVW platform eventually, sets up the coordinate system of whole stencil printer, and the present invention is being demarcated Precision aspect is substantially improved, the characteristics of the calibration result of original printing machine inaccurate and inefficiency can be overcome, so as to Meet required precision of the stencil printer when miniature electronic components and parts are produced.

(2) scaling method of the invention can realize the demarcation to camera only with 6 steps, and in calibration process In, the view data of needs collection is few, and operating process is simple, and calculating process is simple, reduces the complexity of computing, speed Hurry up, and be easy to coding and realize.

Description of the drawings

Fig. 1 is spectroscopic structure and light path schematic diagram；

Fig. 2 is that PCB aligns schematic diagram with steel mesh；

Fig. 3 is each coordinate system locus schematic diagram；

Fig. 4 is that schematic diagram is regarded under camera；

Fig. 5 is camera upper schematic diagram；

Fig. 6 is image coordinate system schematic diagram；

Fig. 7 is camera coordinates system schematic diagram；

Fig. 8 is reference frame schematic diagram；

Fig. 9 is world coordinate system schematic diagram one；

Figure 10 is world coordinate system schematic diagram two；

Figure 11 is X-motor zero-bit schematic diagram；

Figure 12 is Y1 motor zero-bit schematic diagrames；

Figure 13 is Y2 motor zero-bit schematic diagrames；

Figure 14 is image coordinate system coordinate；

Figure 15 is camera coordinates system coordinate；

Figure 16 is image coordinate system and camera coordinates system corresponding relation schematic diagram；

Figure 17 is camera coordinates system and reference frame corresponding relation schematic diagram；

Figure 18 is reference frame and world coordinate system corresponding relation schematic diagram；

Figure 19 is that the Mark points center of circle translates schematic diagram on PCB in world coordinate system；

Figure 20 is to correspond to mark point schematic diagrames in translation motion in camera coordinates system；

Figure 21 is A1 to A2 schematic diagrames in world coordinate system；

Figure 22 is A1 to A2 schematic diagrames in camera coordinates system；

Figure 23 is that mark points rotate schematic diagram on PCB in world coordinate system；

Figure 24 is mark points rotation schematic diagram in camera coordinates system；

Figure 25 is camera movement schematic diagram；

Figure 26 is the camera calibration method flow diagram of the present invention.

Specific embodiment

In order that the objects, technical solutions and advantages of the present invention become more apparent, it is right below in conjunction with drawings and Examples The present invention is further elaborated.It should be appreciated that specific embodiment described herein is only to explain the present invention, and It is not used in the restriction present invention.As long as additionally, technical characteristic involved in invention described below each embodiment Not constituting conflict each other just can be mutually combined.

As shown in figure 1, the device of the stencil printer camera calibration of the embodiment of the present invention includes, steel mesh, PCB, light source 1, Camera, spectroscope, plane mirror used by light source 2, collection image.Steel mesh is located at the surface of camera, and PCB is located at camera Underface.It is light source 2 that Mark dot images on collection steel mesh are the light sources for using, and gathers the light source used by the Mark points on PCB It is light source 1.During collection image, light source 1 and light source 2 are opened successively, gather PCB and the Mark dot images on steel mesh.By image Capture card passes data to computer, computer by the image processing software write based on the algorithm of the present invention, to image Processed accordingly, obtained the result for needing, such as Mark point central coordinate of circle etc..

(1) stencil printer coordinate system establishment step

As shown in Figure 1, Figure 2, Figure 3 shows, with reference to stencil printer structure and practical condition, build on stencil printer 4 coordinate systems are found, is respectively image coordinate system, camera coordinates system, reference frame, world coordinate system.

Light path when pcb board is regarded under camera is as shown in Figure 4.Wherein, O_R,X_R,Y_RCoordinate system midpoint A, B, C, O_RSit in camera Mark system O_ccd,X_ccd,Y_ccdCorresponding points be A ", B ", C ", O_ccd, image coordinate system (U, V) corresponding points be A ', B ', C ', O′_ccd.A ', B ', the coordinate of C ' are obtained in image coordinate system, camera coordinates system O is transformed into_ccdX_ccdY_ccdIn, then convert To reference frame O_RX_RY_RIn, finally it is transformed into world coordinate system O_wX_wY_w。

Light path when steel mesh is regarded on camera is as shown in Figure 5.Wherein, point A, B, the C on steel mesh is in camera coordinates system O_ccdX_ccdY_ccdCorresponding points be A ", B ", C ", be A ', B ', C ' in the corresponding points of image coordinate system (U, V).With what is regarded under camera Coordinate system is converted, by the coordinate transformation of image coordinate system to world coordinate system, to the point on steel mesh in world coordinate system The coordinate put on coordinate and PCB is compared.

As shown in fig. 6, the image shot for camera, sets up image coordinate system (U, V), origin of coordinates O_IIn the upper left of image Angle.Coordinate unit：pixel.

Camera coordinates system is set up as shown in Figure 7, and camera coordinates system unit is still pixel.

Reference frame is set up as shown in Figure 8, and reference frame is the coordinate system set up with camera fields of view, and coordinate unit is mm.In the face of pcb board, with visual field lower limb as X-axis, right hand edge is Y-axis, and lower right corner intersection point is origin.

As shown in Figure 11,12,13, when motor catch returns to zero-bit, it is considered as motor zero.When the right hand edge of catch When touching X zero-bits, it is considered as X-motor zero.When the lower limb of catch touches Y1 zero-bits, it is considered as motor Y1 zeros.Work as gear When the lower limb of piece touches Y2 zero-bits, it is considered as motor Y2 zeros.The line of Y1 zero-bits and Y2 zero-bits as X-axis, cross X zero-bits and Used as Y-axis, world coordinate system O is set up in such as Fig. 9,10 to straight line perpendicular to X-axis_WX_WY_W。

(2) stencil printer coordinate system coordinate transformation step

4 coordinate systems to setting up in step (1) are analyzed, the coordinate transformation relation set up successively between coordinate system, Include 3 coordinate system conversions altogether：Image coordinate is tied to camera coordinates system conversion, camera coordinates and is tied to reference frame conversion, ginseng Examine coordinate and be tied to world coordinate system conversion.From Figure 14,15,16, image coordinate system is with the conversion formula of camera coordinates system：

In formula, W is picture traverse.(U, V) be image coordinate system in point coordinate, (X_ccd,Y_ccd) it is camera coordinates system In point coordinate.

As shown in figure 17, in each coordinate system locus schematic diagram, spectroscope is removed, camera coordinates system is sat with reference The relation of mark system can regard upper figure as.NoteThe conversion formula that then camera coordinates are tied to reference frame is：

Wherein, (X_R,Y_R) for the coordinate of the point in reference frame, (X_ccd,Y_ccd) for the seat of the point in camera coordinates system Mark.

Regulation is by X_wTurn to Y_wFor the positive direction of θ.As shown in figure 18, reference frame O_R,X_R,Y_RTo world coordinate system O_W, X_W,Y_WConversion formula be：

Wherein, (X_W,Y_W) for the coordinate of the point in world coordinate system, (X_R,Y_R) for the coordinate of the point in reference frame.

Simultaneous formulaAnd formulaCan obtain：

In above formula, there is parameter l_x,l_y, θ, a, b needs demarcation acquisition.

(3) coordinate system key parameter is demarcated

According to the coordinate transformation of step (2), need the coordinate system geometrical model parameter for solving there are 5, need to shoot PCB Picture of the upper Mark points when motor does not move, moves, moves along Y-axis positive direction along X-axis positive direction, calculates picture Mark null circles Heart coordinate, geometrical model shown with reference to the accompanying drawings, sets up solution formula, can obtain wherein 3 key parameters；Often rotate tin cream Printing machine UVW platforms once, shoot the Mark dot images of one group of PCB, and so rotation several times, obtains the Mark of some groups of PCB Dot image, processes picture and tries to achieve Mark point central coordinate of circle in the coordinate system set up, is carried out justifying fitting with least square method, obtains The pivot coordinate under camera coordinates system, in world coordinate system, printing platform pivot are obtained, it is known that passing through solution formula Can be in the hope of the value of remaining 2 key parameters a, b.The demarcation of a, b under situation of movement, in a coordinate system, moves according to camera Coordinate value, can be in the hope of the value of a, b under situation of movement.

1. key parameter l_x,l_yDemarcation

As shown in Figure 19,20, note A1, A2, A3 be on pcb board Mark points not moving, along X positive directions movement, square along Y Home position when movement.

A1 points are moved to A2 towards X positive directions, and displacement is dX=X₂-X₁；

A2 points are moved to A3 towards Y positive directions, and displacement is dY=Y1₃-Y1₂=Y2₃-Y2₂。

(X_i、Y1_i、Y2_iThe respectively reading of UVW platforms motor X, Y1 and Y2)

2. the demarcation of key parameter θ

The calculation specifications of θ：

As shown in Figure 21,22

α=atan2 (Y_ccd2-Y_ccd1,X_ccd2-X_ccd1)

∵ α=- θ

∴ θ=- α=atan2 (Y_ccd1-Y_ccd2,X_ccd2-X_ccd1)

3. the demarcation of key parameter a, b

Rotation UVW platforms, with the mark points center of circle for obtaining several pcb boards, are carried out justifying fitting with least square method, are obtained Central coordinate of circle (X under camera coordinates system_ccdr,Y_ccdr).As shown in figure 23, in world coordinate system, platform pivot (X_R, Y_R), it is known that then according to Figure 24, a, b can be tried to achieve by equation below：

As shown in figure 25, under camera situation of movement a, b demarcation：

Note：(X_ccd1,Y_ccd1)(X_ccd2,Y_ccd2) camera is respectively in shooting upper left Mark holes (reference-calibrating position) and bottom right Position coordinates during Mark holes.

(4) image coordinate is tied to the coordinate transformation error analysis of world coordinate system

Image coordinate system coordinate (U, V) arrives world coordinate system coordinate (X_W,Y_W) transforming relationship formula it is as follows：

X_W=(l_x·X_ccd·cosθ-l_y·Y_ccd·sinθ)+a₀+Δa

=[l_x·(W-U)·cosθ-l_y·V·sinθ]+X_R-l_x·X_ccdr·cosθ+l_y·Y_ccdr·sinθ

=l_x·cosθ·(W-U-X_ccdr)+l_y·sinθ·(-V+Y_ccdr)+X_R+Δa

I.e.：

X_W=f (U, V, X_ccdr,Y_ccdr,X_R, Δ a)=l_x·cosθ·(W-U-X_ccdr)+l_y·sinθ·(-V+Y_ccdr)+X_R +Δa

=g_x(U,V,X_ccdr,Y_ccdr)+X_R+Δa

Wherein,

CCDX₀Represent that the position coordinates X (camera position coordinate system) of camera calibration position, CCDX represent that camera tests the seat of position Mark X.Herein, camera position coordinate is different from camera coordinates system and world coordinate system.

Y_W=f (U, V, X_ccdr,Y_ccdr,Y_R, Δ b)=l_x·sinθ·(W-U-X_ccdr)+l_y·cosθ·(V-Y_ccdr)+Y_R+ Δb

=g_y(U,V,X_ccdr,Y_ccdr)+Y_R+Δb

Wherein,

CCDY₀Represent that the position coordinates Y (camera position coordinate system) of camera calibration position, CCDY represent that camera tests the seat of position Mark Y.

Wherein, W is picture traverse, (X_ccdr,Y_ccdr) be under camera coordinates system be fitted central coordinate of circle, (X_R,Y_R) be The pivot coordinate of UVW platforms under world coordinate system.

In addition, l_x,l_y, θ expression formulas are as follows：

θ=atan2 (Y_ccd1-Y_ccd2,X_ccd2-X_ccd1)

=atan2 (V₁-V₂,U₁-U₂)

(5) UVW platforms rotating model is set up, and when UVW platforms are in zero-bit, calculates the parameter relevant with rotating model, Obtain UVW rotation platform models.

(6) stencil printer printing platform adjustment amount is calculated

After step (5), whole stencil printer system model is set up and is completed substantially.Calculate based on the flat of PCB templates Platform is adjusted and the platform based on steel net template and PCB templates is adjusted, and platform adjustment includes that the translation of 3 motor shafts of UVW platforms is moved Momentum and amount of rotational movement.If moving UVW platforms according to the amount of movement of calculated UVW platforms, aligning accuracy is verified, such as Fruit precision meets requirement, then illustrate camera calibration effectively, and contraposition terminates.Otherwise, camera calibration failure, now continuation repetition (3), (4) till, (5), (6) are until meeting contraposition result satisfaction requirement.

The specific implementation step of the scaling method of the stencil printer camera of the embodiment of the present invention is described as follows：

By method proposed by the invention, stencil printer camera can be demarcated, lift stencil printer print Platform aligning accuracy is brushed flat, crucial geometrical model parameter is obtained.By the realtime graphic to steel mesh and PCB and the Mark of template image Point is processed, and carries out positional error compensation, realizes contraposition.The scaling method with traditional stencil printer camera is compared, this Invention is substantially improved in stated accuracy and in terms of demarcating efficiency.Meanwhile, the algorithm complex of the present invention is not high, it is easy to which programming is real It is existing.

As it will be easily appreciated by one skilled in the art that the foregoing is only presently preferred embodiments of the present invention, not to The present invention, all any modification, equivalent and improvement made within the spirit and principles in the present invention etc. are limited, all should be included Within protection scope of the present invention.

Claims (7)

1. a kind of scaling method of stencil printer camera, it is characterised in that the bottom of the stencil printer is pcb board, institute State pcb board to be arranged on UVW rotation platforms, the surface of the pcb board has one for the centre of a steel mesh, the pcb board and steel mesh Spectroscope, before and after spectroscopical a camera and a plane mirror are respectively arranged with, and the scaling method specifically includes following Step：

S1. for the structure of above-mentioned stencil printer, four coordinate systems are set up on the stencil printer, is respectively：In camera The image coordinate system set up on the image of collection, camera coordinates system, the reference based on camera fields of view foundation set up on camera Coordinate system and the world coordinate system set up when the motor shaft catch of stencil printer is in zero-bit；

S2. coordinate transformation will be carried out between the above-mentioned coordinate system of stencil printer：Four coordinate systems to setting up in step S1 enter Row analysis, the coordinate transformation relation set up successively between each coordinate system, including：Image coordinate is tied to turning for camera coordinates system Change, camera coordinates are tied to the conversion that the conversion of reference frame, reference coordinate are tied to world coordinate system；

S3. image is gathered, the key parameter in coordinate system is demarcated, the conversion obtained between each coordinate system is public Formula；

S4. the conversion formula obtained between each coordinate system in step S3, arrives to the coordinate transformation in image coordinate system The error produced during coordinate in world coordinate system is analyzed, and the error information during coordinate transformation is carried out at quantization Reason；

S5. the rotating model of UVW platforms is set up, when UVW platforms are in zero-bit, the pivot of UVW platform models is calculated, i.e., Obtain the rotating model of UVW platforms；

S6. based on the UVW platform rotating models set up in step S5, the amount of movement of UVW platforms is calculated, and UVW platforms is carried out Contraposition adjustment, completes camera calibration.

2. scaling method as claimed in claim 1, it is characterised in that in step S1, described image coordinate system is clapped in camera The coordinate system set up on the image taken the photograph, its origin of coordinates is located at the image upper left corner, and coordinate unit is pixel；

The camera coordinates system is built upon the coordinate system on camera, and coordinate unit is pixel；

The reference frame is the coordinate system set up with camera fields of view, and the coordinate system is set up in the face of pcb board, regarded with camera Wild lower limb is coordinate system X-axis, and with camera fields of view right hand edge as coordinate system Y-axis, coordinate unit is mm；

The coordinate system that world coordinate system is set up when being and being in zero-bit according to three motor shaft catch of stencil printer, when motor gear When piece returns to zero-bit, it is considered as motor zero；Using the line of Y1 zero-bits and Y2 zero-bits as X-axis, X zero-bits are crossed and perpendicular to X The straight line of axle sets up world coordinate system as Y-axis, and coordinate unit is mm.

3. scaling method as claimed in claim 1 or 2, it is characterised in that in step S2, coordinate is carried out between the coordinate system Conversion is comprised the following steps：

S21. camera coordinates system (O is arrived from image coordinate system (U, V)_ccd, X_ccd, Y_ccd) coordinate transformation, its conversion formula is:

In formula, W is picture traverse, and (U, V) is the coordinate of the point in image coordinate system, (X_ccd, Y_ccd) in camera coordinates system The coordinate of point；

S22. from camera coordinates system (O_ccd, X_ccd, Y_ccd) arrive reference frame (O_R, X_R, Y_R) coordinate transformation, noteThen its conversion formula is：

In formula, (X_R, Y_R) for the coordinate of the point in reference frame, (X_ccd, Y_ccd) for the coordinate of the point in camera coordinates system；

S23. from reference frame (O_R, X_R, Y_R) arrive world coordinate system (O_w, X_w, Y_w) coordinate transformation, its conversion formula is：

In formula, (X_w, Y_w) for the coordinate of the point in world coordinate system, (X_R, Y_R) for the coordinate of the point in reference frame,

S24. simultaneous formulaAnd formulaObtain：

$\left\{\begin{array}{c}{X}_W=\[l_x\·X_{ccd}\·\cos \mathrm{\θ}-l_y\·Y_{ccd}\·\sin \mathrm{\θ}\]+a\\ Y_W=\[l_x\·X_{ccd}\·\sin \mathrm{\θ}+l_y\·Y_{ccd}\·\cos \mathrm{\θ}\]+b\end{array}\right.$

In above formula, parameter l_x,l_y, θ, a, b needs demarcation acquisition.

4. scaling method as claimed in claim 3, it is characterised in that to l in conversion formula_x、l_y, θ, a, b these key ginseng Number is demarcated, and it is comprised the following steps that：

S31. Mark points on PCB are shot not moving, along the movement of X-axis positive direction, along Y-axis using the camera on stencil printer Three width images of positive direction movement, record Mark point central coordinate of circle, using the l obtained in step S2_x、l_yCalibration formula meter Calculation draws l_x、l_yValue：

$\left\{\begin{array}{c}{l}_x=\frac{A1A2\·\cos \mathrm{\θ}}{A{1}^{\′\′}A{2}^{\′\′}\·\cos \mathrm{\θ}}=\frac{A1A2}{A{1}^{\′\′}A{2}^{\′\′}}=\frac{dX}{\sqrt{{(X_{ccd2}-X_{ccd1})}^2+{(Y_{ccd2}-Y_{ccd1})}^2}}\\ l_y=\frac{A2A3\·\cos \mathrm{\θ}}{A{2}^{\′\′}A{3}^{\′\′}\·\cos \mathrm{\θ}}=\frac{A2A3}{A{2}^{\′\′}A{3}^{\′\′}}=\frac{dY}{\sqrt{{(X_{ccd2}-X_{ccd2})}^2+{(Y_{ccd3}-Y_{ccd2})}^2}}\end{array}\right.;$

S32. the value of θ is calculated using the calibration formula of the θ obtained in step S2：

θ=atan2 (Y_ccd1-Y_ccd2,X_ccd2-X_ccd1)；

S33. to the demarcation of parameter a, b, often rotate stencil printer UVW platforms once, shoot the Mark dot images of one group of PCB, So rotation several times, obtains the Mark dot images of several PCB, and Mark points center of circle seat is tried to achieve in the coordinate system set up Mark, is carried out justifying fitting with least square method, obtains the pivot coordinate (X under camera coordinates system_ccdr,Y_ccdr), in world coordinates In system, platform pivot (X_R,Y_R), it is known that calculating the value of a, b using the calibration formula of a, b for obtaining in step S2：

$\left\{\begin{array}{c}a=X_R-\[l_x\·X_{ccdr}\·cos\mathrm{\θ}-l_y\·Y_{ccdr}\·sin\mathrm{\θ}\]\\ b=Y_R-\[l_x\·X_{ccdr}\·sin\mathrm{\θ}+l_y\·Y_{ccdr}\·cos\mathrm{\θ}\]\end{array}\right.;$

The demarcation of a, b under camera situation of movement is tried to achieve by calibration formula：

$\left\{\begin{array}{c}{a}_2=a_1-(X_{ccd2}-X_{ccd1})\\ b_2=b_1-(Y_{ccd2}-Y_{ccd1})\end{array}\right..$

5. scaling method as claimed in claim 4, it is characterised in that in step S4, according to the conversion formula tried to achieve, according to figure As coordinate system coordinate (U, V) arrives world coordinate system coordinate (X_W,Y_W) transforming relationship formulaTo coordinate Error information in conversion process carries out quantification treatment.

6. scaling method as claimed in claim 5, it is characterised in that in step S5, set up the step of the rotating model of UVW platforms It is rapid as follows：

S51. UVW platforms are rotated, the mark points center of circle of several pcb boards is obtained；

S52. carried out justifying fitting with least square method, obtain the central coordinate of circle (X under camera coordinates system_ccdr,Y_ccdr)；

S53. the central coordinate of circle under camera coordinates system is changed to world coordinate system, that is, obtains the rotating model of UVW platforms.

7. scaling method as claimed in claim 6, it is characterised in that in step S6, camera calibration is comprised the following steps that：

S61. according to the rotating model of the UVW platforms obtained in step S5, the platform based on pcb board is adjusted, platform is adjusted Whole translational movement amount and amount of rotational movement including three motor shafts of UVW platforms；

S62. UVW platforms, checking contraposition essence are moved according to the translational movement amount and amount of rotational movement of calculated UVW platforms Degree；

If S63. aligning accuracy meets and requires, illustrate to demarcate effective, camera calibration terminates；Otherwise, demarcate failure, now after Continuous repeat step S3-S6 is required until calibration result meets.