CN101650156B - Device and method for measuring geometric parameter of superplastic non-spherical free bulge - Google Patents

Abstract

The invention relates to a device and a method suitable for measuring a geometric parameter of a superplastic non-spherical free bulge in a superplastic non-spherical free bulge experiment and also suitable for measuring a shape change geometric parameter of an axisymmetric rotating curved surface. The device comprises a measured bulging part, an annular light source, a video camera, a PC machine and an adjustable holder, wherein the annular light source is coaxial with a lens of the video camera and is positioned between the measured bulging part and the video camera; the annular light source and the video camera are arranged on the adjustable holder; and the PC machine controls the video camera to continuously acquire images of the measured bulging part and processes the acquired images to measure and calculate the geometric parameter of the measured bulging part. Compared with other measuring methods, the measuring method takes the measured bulging part images as information carriers and extract available information by analyzing and processing the measured bulging part images, thereby achieving the purpose of measurement; in addition, the invention has the advantages of non-contact, abundant obtained information, high measuring precision and measuring speed and the like; and the invention can realize on-line real-time measurement.

Description

Geometric parameter of superplastic non-spherical free bulge measurement mechanism and method

Technical field:

Patent of the present invention belongs to the modern advanced Instrument technology field of making, specifically relate to a kind of device that is specially adapted to bulging spare geometric parameter measurement in the superplastic non-spherical free bulge experiment, also be suitable for the measurement of rotational symmetry surface of revolution change of shape geometric parameter.

Technical background:

Superplastic bulging is one of important process of superplasticforming, all occupies an important position in carrying out superplasticity theoretical research and application and development.Super real geometry of moulding free bulge is the rotational symmetry surface of revolution, in order to set up mechanical analysis theory accurately, just must accurately measure the appearance profile of bulging spare surface of revolution.And in the bulging process test specimen temperature higher and the distortion in the flanging bucket, carry out, present experimental provision can only be measured the height change at test specimen limit place, measurement for its profile profile, be after stopping bulging and test specimen taken out from the flanging bucket, to measure again, like this, once want to obtain the geometric parameter of test specimen under differing heights in the experiment, the row measurement again to the height that requires of just several test specimens must being expanded.And the method for measuring, be earlier test specimen to be crossed central shaft to cut open in early days, its profile is imprinted on the paper, measure its warp-wise radius-of-curvature and broadwise radius-of-curvature then, this measuring method is difficult for recording the low-angle Δ θ of broadwise very accurate, the author has designed the non-spherical measuring instrument for this reason, and obtains Chinese invention patent.Use this instrument, test specimen need not be cut, as long as record any data at 2 along warp-wise and broadwise, can try to achieve corresponding warp-wise radius-of-curvature and broadwise radius-of-curvature, but this method must contact with test specimen, also certainly exists artificial random deviation of measurement, and can not on-line measurement.Utilize three-coordinates measuring machine to measure, though be non-cpntact measurement, and the data of gained are more accurate, the equipment manufacturing cost height, institute takes up space big, also is difficult for on-line measurement.With three-dimensional structure photoscanner (as 3DSS), the profile of scanning bulging spare also can record its warp-wise radius-of-curvature and broadwise radius-of-curvature then, but the price of 3DSS scanner is also higher, and real-time can't satisfy Testing requirement in the experiment earlier.

Summary of the invention:

Technical matters to be solved by this invention provides a kind ofly can be measured bulging spare geometric parameter online, in real time and write down geometric parameter of superplastic non-spherical free bulge measurement mechanism and the method that geometric parameter changes super moulding in the free bulge experiment.

Above-mentioned purpose of the present invention is achieved in that accompanying drawings is as follows.

The geometric parameter of superplastic non-spherical free bulge measurement mechanism, this device is made up of tested bulging spare, annular light source, video camera, PC and adjustable The Cloud Terrace, described annular light source 2 is coaxial with the camera lens of video camera 3, and between tested bulging spare 1 and video camera 3, annular light source 2 and video camera 3 are installed on the adjustable The Cloud Terrace 5, PC 4 is controlled tested bulging spare 1 image of video camera 3 continuous acquisition, and the image of gathering is handled, and calculates the geometric parameter of tested bulging spare 1.

Adjustable The Cloud Terrace 5 table tops of described installation video camera 3 can also can move along Z-direction, and measure the distance that moves by grating displacement sensor around X, Y and three axle rotations of Z.

Adopt the bulging spare image measuring method of described geometric parameter of superplastic non-spherical free bulge measurement mechanism, it is characterized in that may further comprise the steps based on vision:

1, adjusts video camera 3 visual angles;

2, calibrating camera 3 intrinsic parameters;

3, tested bulging spare 1 object plane of measuring and calculating to the distance of video camera 3 photocentres is an object distance;

4, gather tested bulging spare 1 image, and to Flame Image Process, determine the coordinate of each point on the contour edge of tested bulging spare 1 in the image;

5,, calculate the actual coordinate of corresponding each point on the object plane in conjunction with video camera 1 intrinsic parameter of demarcating;

6, the actual coordinate that calculates gained is revised, tried to achieve the true coordinate of tested bulging spare 1 rotary body edge each point.

Described video camera 3 visual angle adjustment comprise the following steps:

1, utilize the square of a known dimensions as demarcating module, with one of them side as demarcating reference surface, be placed on the residing position of tested object plane of tested bulging spare 1 in the bulging experiment, video camera 3 is gathered its image after being tested object plane over against the demarcation reference surface;

2, use gradient operator, from images acquired, detect and demarcate foursquare edge on the reference surface;

3, adopt the sub-pix algorithm, the length of side on four limits of square in the computed image;

4, adjust video camera 3 visual angles by adjusting adjustable The Cloud Terrace 5, make two groups of parallel edges directions in the image parallel with change in coordinate axis direction on the image planes, and the equal and opposite in direction of every group of parallel edges.

Described video camera 3 intrinsic parameter timing signals according to the ratio of imaging on the square length of side and the tested object plane, are tried to achieve each pixel in the presentation video at the video camera 3 intrinsic parameter k of the true geometric size of x axle and y direction of principal axis representative _Xd, k _Yd

When described object distance is measured, come mobile camera 3 by moving adjustable The Cloud Terrace 5, and the distance that moves of record, according to the size of imaging before and after moving, calculating tested object plane to the distance of video camera 3 photocentres is object distance.

Measurement result is revised: after the correction of error correction formula, try to achieve the true coordinate of rotary body bulging spare edge each point.

Beneficial effect of the present invention:

With bulging spare image as information carrier, by to its analyzing and processing of image, therefrom extract Useful Information, reach the purpose of measurement, have advantages such as noncontact and acquired information be abundant.

2. measuring accuracy height, speed is fast, can realize that online in real time measures.

3. the control system with the bulging experimental provision combines, and shared same PC control has the advantages that to integrate control, measurement and Flame Image Process.

Description of drawings:

Accompanying drawing 1 is a measuring system hardware composition diagram;

Accompanying drawing 2 (a) is the camera calibration synoptic diagram;

Accompanying drawing 2 (b) is measured synoptic diagram for the measuring system object distance;

Accompanying drawing 2 (c) is a rotary body imaging projection error analysis chart;

Accompanying drawing 3 rotational symmetry surface of revolution bulging instrumentation plans;

The bulging spare contour curve that accompanying drawing 4 experiments record.

Among the figure: 1 is that image planes 2 are projected outline for object plane 3 for test specimen profile 4

Embodiment:

Below in conjunction with accompanying drawing embodiment, further specify particular content of the present invention and using method thereof.

Be shaped as with measurement the rotational symmetry surface of revolution bulging spare be example, as shown in Figure 4, the measurement content of its geometric parameter mainly records among the figure coordinate of each point on the bulging spare contour curve, can simulate the equation of this contour curve with this, further finds the solution the broadwise radius-of-curvature ρ of each point on the curved surface _θWith warp-wise radius-of-curvature ρ _s

Fig. 1 has provided the composition diagram of entire measuring device, is made up of tested bulging spare, annular light source, video camera, PC and adjustable The Cloud Terrace.

Wherein digital camera is selected and can be required to select according to the range of size and the measuring accuracy of test specimen.Owing to the size restrictions of sample and blank holder in the test, the full-size of its bulging spare profile is in 120mm * 120mm scope among Fig. 4.Therefore, when to select resolution be 1280 * 1024 video camera, the Pixel-level precision of its width and short transverse was respectively 120/1280=0.09mm and 120/1024=0.12mm, can further improve measuring accuracy in conjunction with the sub-pix algorithm.This patent selects to have the DH-HV1302UC industry colorful digital video camera of USB2.0 standard interface, and its resolution is 1280 * 1024, and the acquisition frame rate under the highest resolution was 15 frame/seconds, and the outfit focal length is that the general of 50mm focuses apart from camera lens;

The annular LED light source is adopted in illumination in the shooting process;

Adjustable The Cloud Terrace is after being transformed on the basis of commercial general holder, and commercial The Cloud Terrace generally has in level and vertical both direction swing function, increases on this basis after the rotation of optical axis and the function that moves along optical axis direction just can use.TG110 grating micrometer sensor is adopted in the measurement of adjustable The Cloud Terrace optical axis direction moving displacement.

Because the bulging experiment is to offer a view window at the flanging bucket sidewall at the expansive forming experimental provision, digital camera is over against view window, so that observation and record bulging process, in the bulging experimentation, by processing, and then calculate the geometric parameter of bulging spare to the view data of being gathered.Main process is as follows:

Carrying out at first must carrying out the adjustment of video camera visual angle before bulging spare measures, make its optical axis with by lateral vertical, describe in conjunction with Fig. 2 (a).Get the known square of a length of side size and use template as demarcating, place it in the residing position of bulging spare in the bulging experiment, a cubical side is overlapped with bulging spare centre section present position, with this side as tested surface and imaging, if camera optical axis with by lateral vertical, then have after the imaging | A ' B ' |=| C ' D ' |, | A ' D ' |=| B ' C ' |, otherwise, can adjust the video camera visual angle by adjusting adjustable The Cloud Terrace, it is around X-axis or Y-axis rotation, vertical with tested surface until its optical axis; Then adjustable The Cloud Terrace is rotated around the Z axle, all parallel until A ' B ' limit with the U axle with C ' D ' limit.

Carry out camera calibration then, determine each pixel on the image and the corresponding relation between physical size, in Fig. 2 (a),, can try to achieve camera parameters according to the length of side (true geometric size) on each limit on the tested surface and the length (pixel value) of pairing picture:

$k_{\mathrm{xd}}=\frac{\left|\mathrm{AB}\right|}{\left|A^{\′}{B}^{\′}\right|},$ $k_{\mathrm{yd}}=\frac{\left|\mathrm{BC}\right|}{\left|B^{\′}{C}^{\′}\right|}$

Calculate tested object plane and and the camera lens photocentre between distance (being object distance), video camera is moved to position II along optical axis direction by initial position I, grating displacement sensor detects mobile apart from k, CD limit imaging before and after moving on the demarcating module is respectively C ' D ' and C " D ", as Fig. 2 (b), have according to the geometric relationship of imaging:

$\frac{\left|C^{\′}{D}^{\′}\right|}{\left|\mathrm{CD}\right|}=\frac{\mathrm{\υ}}{u}$

$\frac{\left|C^{\′\′}{D}^{\′\′}\right|}{\left|\mathrm{CD}\right|}=\frac{\mathrm{\υ}}{u-k}$

υ and u represent image distance and object distance respectively in above-mentioned two formulas, | C ' D ' | and | C " D " | be the picture length on diverse location CD limit, can adopt image processing algorithm, obtain corresponding pixel count n ' and n "; and the size of each pixel is known as its hardware parameter in the video camera; be of a size of 5.2 μ m * 5.2 μ m as DH-HV1302UC type camera pixel; therefore; | C ' D ' |=0.0052 * n ' mm, | C " D " |=0.0052 * n " mm, and | CD| and k are known, so simultaneous two formulas after the substitution, try to achieve the image distance υ and the object distance u of imaging system, video camera visual angle adjustment so far and demarcation are all finished, and measurement next just can experimentize.

Experiment measuring carries out in two steps: only measure the variation of sample limit height in the experimentation, and preserve view data according to the frequency of setting; Profile detections etc. are further handled, and are to finish the back in experiment the image of preserving is carried out, below the main process of measuring for the experiment back.

Test specimen image such as Fig. 4 of gathering, application image is handled rim detection and sub-pix algorithm when carrying out image measurement, the accurate marginal point of test specimen in the positioning image, try to achieve the O ' among the relative Fig. 2 of point (a) on the test specimen edge coordinate (u, υ), (u ₀, υ ₀), O ' is the intersection point of optical axis and image planes, the central point of desirable image planes.

As Fig. 2 (c), on the object plane at tested profile 3 places, set up illustrated coordinate system at the intersection point Ow place of optical axis, then in this coordinate system, (u, υ), the coordinate of trying to achieve on the object plane is (k according to the coordinate at picture point edge _XdU, k _Ydυ).

Because the object in the three dimensions is to determine that by imaging model desirable projection imaging model is the central projection in the optics, also claims little pore model to the projection relation as the plane.Because the true profile of bulging spare is the rotational symmetry surface of revolution, monocular imaging system imaging based on little pore model is not to be the projection of the profile on the test specimen centre section, in Fig. 2 (c), A, B are 2 points at test specimen contour edge place in the image planes epigraph, straight line AO _CAnd BO _CBe tangential on an A ' and B ' with surface of revolution, intersect at A " and B " point with tested object plane, hence one can see that, and some A is the picture of A ', according to A on the image planes (u, the coordinate (k of corresponding point on the object plane that coordinate υ) is tried to achieve _XdU, k _Yd" therefore the coordinate of point must be revised measurement result υ) to be A.The parallel radius of a circle ξ at A ' place is exactly in Fig. 2 (c) | O ' A ' | and, during actual measurement,, can suppose parallel circle and the O of A ' because object distance is bigger _CA ' is tangent, and then geometric relationship shown in the basis has

$\mathrm{\ξ}=\left|O^{\′}{A}^{\′}\right|=\left|\mathrm{Ow}{C}^{\′}\right|=\frac{\left|O_C\mathrm{Ow}\right|\×\left|\mathrm{Ow}{C}^{\′\′}\right|}{\sqrt{{\left|O_C\mathrm{Ow}\right|}^2+{\left|\mathrm{Ow}{C}^{\′\′}\right|}^2}}=\frac{u\×{\mathrm{\ξ}}^{\′\′}}{\sqrt{u^2+{\mathrm{\ξ}}^{\′\′2}}}---\left(1\right)$

U represents that photocentre is an object distance to the distance of object plane in the formula, and the Xw coordinate of ξ " for A " is k _XdU.The Yw coordinate that A ', B ' place parallel circle are gone up point is among the figure | O ' Ow|, promptly

Yw＝|O′Ow|＝|A′C′|

A ' C ' is parallel to A " C " among the figure, so $\left|A^{\′}{C}^{\′}\right|=\frac{\left|\mathrm{Oc}{C}^{\′}\right|}{\left|\mathrm{Oc}{C}^{\′\′}\right|}\×\left|A^{\′\′}{C}^{\′\′}\right|,$ The substitution following formula gets

$\mathrm{Yw}=\frac{\sqrt{u^2-{\mathrm{\ξ}}^2}}{\sqrt{u^2+{\mathrm{\ξ}}^{\′\′2}}}\×{\mathrm{Yw}}^{\′\′}---\left(2\right)$

The Yw coordinate of Yw in the formula " for A " is k _Xdυ, just so far try to achieve each point on the bulging spare profile true coordinate (ξ Yw), just can make contour curve such as Fig. 4 (b) with this, but the further just broadwise radius-of-curvature ρ of each point on the curved surface _θWith warp-wise radius-of-curvature ρ _s

Claims (6)

1. geometric parameter of superplastic non-spherical free bulge measurement mechanism, this device is made up of tested bulging spare, annular light source, video camera, PC and adjustable The Cloud Terrace, it is characterized in that, described annular light source (2) is coaxial with the camera lens of video camera (3), and be positioned between tested bulging spare (1) and the video camera (3), annular light source (2) and video camera (3) are installed on the adjustable The Cloud Terrace (5), PC (4) the control tested bulging spare of video camera (3) continuous acquisition (1) image, and the image of gathering handled, calculate the geometric parameter of tested bulging spare (1).

2. one kind is adopted the described device of claim 1 to carry out the geometric parameter of superplastic non-spherical free bulge measuring method, it is characterized in that may further comprise the steps:

1) adjusts video camera (3) visual angle;

2) calibrating camera (3) intrinsic parameter;

3) measuring and calculating tested bulging spare (1) object plane to the distance of video camera (3) photocentre is an object distance;

4) gather tested bulging spare (1) image, and to Flame Image Process, determine the coordinate of each point on the contour edge of tested bulging spare (1) in the image;

5), calculate the actual coordinate of corresponding each point on the object plane in conjunction with video camera (1) intrinsic parameter of demarcating;

6) actual coordinate that calculates gained is revised, tried to achieve the true coordinate of tested bulging spare (1) rotary body edge each point.

3. geometric parameter of superplastic non-spherical free bulge measuring method according to claim 2 is characterized in that, described video camera (3) visual angle adjustment comprises the following steps:

1) utilize the square of a known dimensions as demarcating module, with one of them side as demarcating reference surface, be placed on the residing position of tested object plane of tested bulging spare (1) in the bulging experiment, video camera (3) is gathered its image after being tested object plane over against the demarcation reference surface;

2) use gradient operator, from images acquired, detect and demarcate foursquare edge on the reference surface;

3) adopt the sub-pix algorithm, the length of side on four limits of square in the computed image;

4) adjust video camera (3) visual angle by adjusting adjustable The Cloud Terrace (5), make two groups of parallel edges directions in the image parallel with change in coordinate axis direction on the image planes, and the equal and opposite in direction of every group of parallel edges.

4. geometric parameter of superplastic non-spherical free bulge measuring method according to claim 2, it is characterized in that, described video camera (3) intrinsic parameter timing signal, according to the ratio of imaging on the square length of side and the tested object plane, try to achieve each pixel in the presentation video at video camera (3) the intrinsic parameter k of the true geometric size of x axle and y direction of principal axis representative _Xd, k _Yd

5. geometric parameter of superplastic non-spherical free bulge measuring method according to claim 2, it is characterized in that, when described object distance is measured, come mobile camera (3) by moving adjustable The Cloud Terrace (5), and the mobile distance of record, according to the size of imaging before and after moving, calculating tested object plane to the distance of video camera (3) photocentre is object distance.

6. geometric parameter of superplastic non-spherical free bulge measuring method according to claim 2 is characterized in that, measurement result is revised: after revising, try to achieve the true coordinate of rotary body bulging spare edge each point.

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