CN100398983C - Double-camera video frequency large-deformation measurement method and video frequency extension device based thereon - Google Patents
Double-camera video frequency large-deformation measurement method and video frequency extension device based thereon Download PDFInfo
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- CN100398983C CN100398983C CNB2006100338210A CN200610033821A CN100398983C CN 100398983 C CN100398983 C CN 100398983C CN B2006100338210 A CNB2006100338210 A CN B2006100338210A CN 200610033821 A CN200610033821 A CN 200610033821A CN 100398983 C CN100398983 C CN 100398983C
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Abstract
The present invention relates to a deformation measuring method and a deformation measuring apparatus in experiments of mechanics of materials. The purpose is to provide a measuring method and a measuring apparatus of a non-contact type, which enable a measuring range to be multiplied. Two cameras are adopted to form a picture shooting part of a video frequency extensometer, and an overlapped region of the sight angles of the two cameras is ensured to exist. During a tension test, when two mark lines on a sample are simultaneously positioned in the measuring range of the first camera, the distance between the two mark lines is determined by a picture acquired by the first camera. When the mark lines on the sample move to the overlapped region of the sight angles of the two cameras, image switching is carried out. Then, the distance between the lower mark line and the switching position is determined by the image acquired by the first camera, the distance between the upper mark line and the switching position is determined by an image acquired by the second camera, and the distance between the two mark lines is determined by adding the two distances. When the lower mark line of the sample moves over the switching position, the distance between the two mark lines is determined by the picture acquired by the second camera.
Description
Technical field
The present invention relates to the method and the instrument of distortion measurement in the materials mechanics experimental, a kind of double-camera video frequency large-deformation measurement and adopt the video tens(i)ometer of this method of saying so more specifically.
Technical background
Some material is rubber for example, and plastics etc. have very big deflection.In tension test, measure this class distortion of materials amount and be a difficult problem of failing fine solution for a long time.Adopted following several measuring method at present, and the method for the most extensive employing both at home and abroad is so-called contact type measurement.
1. contact type measurement technology
Contact type measurement will be drawn two graticules earlier on tested sample, use two chucks that stretch out from measuring mechanism to clamp this two graticules respectively then.When these two graticules moved, chuck was promptly driven together and is moved in tension test.When each chuck moves, its other end is by a silk thread, adopt metal or non-metal wire, drive the rotation of a potentiometer or photoelectric encoder, thereby mobile the changing into of chuck measured the required electric potential signal or the position signalling of electric impulse signal or scrambler.Contact type measurement mainly contains following shortcoming:
A) measuring accuracy of influence power
The gravity of chuck component, force measurement precision when the friction force that produces when chuck moves and the chuck edge of a knife can influence tension test to sample institute applied pressure.Although the gravity of chuck component can roughly be eliminated by balance, friction force is difficult to balance.The edge of a knife that the more important thing is chuck can produce stress in the contact site to sample institute applied pressure and concentrate, and sample is ruptured and the appreciable impact test findings in advance.
B) regular meeting skids during the edge of a knife
Especially true to film sample, the edge of a knife is neither programmable too sharp keen again can not be too slick and sly, and too sharp keen then stress is concentrated obviously, and too slyness may be skidded again, therefore often makes the deviser turn round and look at this and lose that.
C) the low and difficult maintenance of precision
Because temperature, humidity, wearing and tearing and the tension and relaxation variation of the caused silk thread of reason such as aging and the variation that length variations can cause measuring accuracy, the therefore low and difficult maintenance of this measuring method precision.
B) life-span is short fragile
Directly act on chuck because the energy when sample is broken discharges the great impact power that is produced, make measuring mechanism damage easily by the edge of a knife.
For addressing the above problem, adopting non-contact measurement is the direction that this field is made great efforts for a long time.
2. non-contact measuring technology
The non-contact measuring technology that is adopted in the large-deformation measuring field of material at present mainly contains three kinds.Be photoelectric tracking, laser scanning and the video tens(i)ometer that began one's study in recent years.
2.1 photoelectric tracking technology
Photoelectric tracking large-deformation measuring instrument is the technology of early developing, and it has two parts that are called as photometer head, and each photometer head is followed the tracks of a graticule.Graticule can be drawn on sample with reflectorized material, but mostly be to make graticule with reflectorized material to be attached to then on the graticule position of sample.Each photometer head can send light beam and receive the light that reflects, the light that reflects is converted into electric signal and handles, thereby the tracking direction and the amount of movement of decision photometer head, and the variable in distance between sample two graticules has just been represented in the relative displacement between two photometer heads.
Photoelectric tracking large-deformation measuring instrument has been developed out a lot year, but fails to obtain widespread use all the time, mainly is because it has following shortcoming:
A) reliability is relatively poor
When graticule was drawn on sample, along with sample is stretched, graticule became more and more wideer and color becomes more and more lighter, thereby influences its reflecting power.In order to address this problem, people have adopted the way of decals line.But along with sample is stretched, the accompanying that part of material of graticule is drawn longer and longer, and graticule usually can come off.Both just do not come off, might move yet, therefore influenced measuring reliability.In addition, the variation of the reflective and illumination of surrounding environment also can influence the reliable rows of its work, usually with losing graticule.
B) complex structure costs an arm and a leg
Because photometer head need be followed the tracks of moving of graticule, therefore must there be accurate servo control mechanism to go accurately to control moving of photometer head.This makes that its structure is very complicated, thereby costs an arm and a leg.
2.2 laser scanning
Laser scanner technique scans tested sample repeatedly by a rotary laser source.Post the reflector marking reflector laser on the sample, the laser extensometer receives the light reflect and calculates distance between graticule according to mistiming of sweep velocity and two graticule reflector lasers.
The advantage of laser scanning extensometer is accurately, but because it also needs to use reflector marking, the problem that therefore also has aforementioned reflector marking and brought.Equally, it also is a complex structure, costs an arm and a leg.
2.3 video tens(i)ometer
In recent years, computer image processing technology and image sensor technologies begin to be applied to the large-deformation measuring field, have caused the birth of video tens(i)ometer.The video tens(i)ometer utilizes video camera or digital camera continuously apace, can reach per second 50 width of cloth, takes the photo of tested sample and imports computing machine by image pick-up card.Special measurement software in the computing machine to the image of input handle with determine two graticules in image the position and be the distance of unit with the pixel between them.Follow again according to the physical length of each pixel representative and determine two actual ranges between graticule.Because the captured image of pick-up lens exists parallax and torsional deformation, causes the physical length difference of each pixel at the diverse location representative, this need install the back at the video tens(i)ometer and determine or correction with means for correcting.
Compare with the laser extensometer with photoelectric tracking large-deformation measuring instrument, the video tens(i)ometer has the following advantages:
A) simple in structure
The video tens(i)ometer does not have servo tracking control without any moving-member, and structure is greatly simplified.
B) reliability greatly improves
The video tens(i)ometer is not abutted against the reflective work of receiving graticule, as long as light is suitable, can takes distinct image and get final product work.Its measurement reliability depends primarily on software to treatment of picture.Because without any moving-member, any problem of being brought of wearing and tearing not, its hardware reliability only depends on the reliability of electronic devices and components.
C) precision is high and stable
The measuring accuracy of video tens(i)ometer depend on imageing sensor along the pixel count of direction of measurement and software to the processing of border pixel grey scale, improve this pixel count and can correspondingly improve the precision of measurement.
D) life-span is long
The life-span of video tens(i)ometer depends primarily on the life-span of electronic devices and components, therefore is particularly suitable for the king-sized occasion of experiment work amount.
E) easy to operate
Can seek graticule automatically.
3. the existing limitation of single-lens video tens(i)ometer on large-deformation measuring
The measurement range of video tens(i)ometer depends on the visual angle of camera lens and the camera lens distance to sample.Because must maintaining a certain distance just with sample, the restriction at camera lens visual angle, video tens(i)ometer can reach certain measurement range when operation.This requirement (＜400 millimeters) when measurement range is not too big does not have problem, but along with the expansion of measurement range, this problem becomes and surfaces.After enlarging, the distance between sample and camera lens can bring two problems:
The first, thus the decline of taken image resolution ratio influences measuring accuracy.Though can adopt more high-resolution camera lens and imageing sensor to go to remedy this loss, but this not only can cause the rapid rising of cost, for high-resolution camera lens and imageing sensor, resolution doubles, the lifting of price will be much larger than one times, but also is subjected to the restriction of device availability.
The second, distance add the increasing that conference causes installing inconvenience and testing machine overall dimensions, compare with contact type measurement, this can be a significant disadvantages.
Want not only to enlarge measurement range but also do not increase distance between camera lens and sample, the visual angle that just must increase camera lens, however the increase at visual angle also has certain limit.Along with the increase at camera lens visual angle, the picture quality of off-center area part can significantly descend, and resolution descends, and torsional deformation increases.Thereby measuring accuracy is significantly descended.
Summary of the invention
The object of the present invention is to provide a kind of distance that neither increases camera lens to sample, do not increase measuring method that the measurement range that makes the video tens(i)ometer under the condition at visual angle of camera lens is multiplied and the instrument that adopts this method again.
The present invention is achieved through the following technical solutions its goal of the invention.
The present invention at first provides a kind of double-camera video frequency large-deformation measurement, has comprised following steps:
1. adopt two cameras to constitute the image taking part of video tens(i)ometer, and guarantee that there is the overlapping region in the visual angle of two cameras;
2. sample is installed, and is guaranteed that two graticules on the sample are positioned at the measurement range of first camera simultaneously;
3. tensile sample;
4. when two graticules on the sample are positioned at the measurement range of first camera, the distance that the image one that is obtained by first camera is determined between two graticules;
5. when the last graticule of sample moves to the overlapping region, visual angle of two cameras, carry out image switching, and be defined as switching position two captured image one and positions in the image two of camera going up graticule this moment;
6. then, the image one that is obtained by first camera is determined the distance between the graticule and switching position down, and the image two that is obtained by second camera determines to go up the distances between graticules and the switching position, determines two distances between the graticule with two apart from addition;
7. when the following graticule of sample moved switching position, carry out the image switching second time, the distance that the image two that is obtained by second camera is determined between two graticules.
The present invention also provides another kind of double-camera video frequency large-deformation measurement, has comprised following steps:
1. adopt two cameras to constitute the image taking part of video tens(i)ometer, and guarantee that there is the overlapping region in the visual angle of two cameras;
2. when when calibration, below the visual angle of each camera, determine a datum line respectively, and make second datum line in the visual angle of second camera be positioned at the overlapping region to have known fixed range between two datum lines;
3. sample is installed, and is guaranteed that two graticules on the sample are positioned at the measurement range of first camera simultaneously;
4. tensile sample;
5. when two graticules on the sample are positioned at the measurement range of first camera, the distance that the image one that is obtained by first camera is determined between two graticules;
6. when the last graticule of sample moved second datum line, carry out image switching, the image one that is obtained by first camera is determined the distance between the graticule and first datum line down, the image two that is obtained by second camera determines to go up the distances between the graticules and second datum line, and the distance between the last graticule and second datum line is added that distance between two datum lines deducts down distance between the graticule and first datum line and is distance between two graticules;
7. when the following graticule of sample moved switching position, carry out the image switching second time, the distance that the image two that is obtained by second camera is determined between two graticules.
The present invention adopts two cameras or digital camera, and the visual angle of two cameras can be identical or different.The measurement range that should guarantee two cameras when mounted has a bit of overlapping scope, the size of overlapping scope should be taken into account the parameter dispersiveness at camera lens visual angle, Survey Software makes under worst situation, also to have enough overlapping scopes, so that can realize image switching.When measuring, two cameras are taken pictures simultaneously continuously, captured image or handle by being inserted in the Survey Software that image pick-up card in the computing machine is input to computing machine, perhaps handle, then measurement result is sent to the testing machine TT﹠C software in the computing machine by Flame Image Process and measuring system that hardware and firmware constituted.Image processing software is by determining two graticule present positions and the pixel count between them, and the physical length apart from representative between per two pixels of determining during then according to calibration both can calculate two distances between the graticule.Ultimate principle of the present invention be the image that obtains by two cameras in addition amalgamation enlarge the scope of its measurement.Adopt the inventive method both to need not to increase distance between camera and the measured sample, also need not to enlarge the angular field of view of camera, thereby guaranteed the compactedness of whole surveying instrument structure.Owing to need not to adopt high-quality camera to reduce degree of distortion, greatly reduce cost.And can derive the method that adopts a plurality of cameras to enlarge measurement range according to said method, only need obtain successively after the image of each camera according to the present invention all images amalgamation, and by two graticules present position and the pixel count between them in obtaining image, both confirmable actual range between them.
Because phtographic lens exists parallax and torsional deformation, and the used wide-angle lens of large-deformation measuring is particularly remarkable, and therefore, the video tens(i)ometer is calibration earlier after installation.The purpose of calibration is the physical length apart from representative that will determine along between per two pixels of direction of measurement.
May further comprise the steps at first kind of its calibration process of measuring method:
1. a calibrated ruler with two kinds of alternate formation of color lump of certain contrast is installed in the sample installation site, be provided with in the middle of the calibrated ruler one with other two kinds of special blocks that color lump is different, this special blocks must be positioned at the overlapping region at two camera visual angles when mounted;
2. the separatrix of color lump in the image that definite camera obtains, determine the pixel count of the vertical width of each color lump thus, and compare with the developed width of the corresponding color lump of calibrated ruler respectively, can obtain the physical length between per two pixels of this upper edge, color lump present position direction of measurement in the image apart from representative;
3. the bottom of the image one that is obtained by first camera begins from bottom to top to calibrate, and when being calibrated to special blocks, switching to the image two that is obtained by second camera and calibrates, and ends to image two tops.
May further comprise the steps at second kind of its calibration process of measuring method:
1. a calibrated ruler with two kinds of alternate formation of color lump of certain contrast is installed in the sample installation site, be provided with in the middle of the calibrated ruler one with other two kinds of special blocks that color lump is different, this special blocks must be positioned at the overlapping region at two camera visual angles when mounted;
2. the separatrix of color lump in the image that definite camera obtains, determine the pixel count of the vertical width of each color lump thus, and compare with the developed width of the corresponding color lump of calibrated ruler respectively, can obtain the physical length between per two pixels of this upper edge, color lump present position direction of measurement in the image apart from representative;
3. the bottom of the image one that is obtained by first camera begins from bottom to top to calibrate, and will enter article one color lump separatrix of camera lens as first datum line;
4. when being calibrated to special blocks, switch to the image that obtains by second camera, and the following color lump separatrix of special blocks as second datum line, continue to calibrate to image two tops and end.
In above two kinds of calibration processes, in the position relation of determining between image one and the image two, be to determine that by the horizontal color lump separatrix on the special blocks lengthwise position of image one and image two is poor, determine that by the vertical color lump separatrix on the special blocks lateral attitude of image one and image two is poor.
Two kinds of calibrated ruler that existing video tens(i)ometer adopts when calibration usually or calibration rods.A kind of upward drawing has parallel lines, and when taking the image of calibrated ruler with camera, these lines promptly are divided into many sections to an image that photographed along direction of measurement.Because the distance between parallel lines is known, Survey Software only need be determined each section along the pixel count on the direction of measurement, can calculate in the physical length apart from representative between per two pixels on that section.The circular array pattern is adopted in another kind of calibrated ruler design, and this calibrated ruler can be calibrated simultaneously along a plurality of directions, but here institute at large-deformation measuring only need the calibration of a direction, adopt this calibrated ruler and inconvenience.More than the function of two kinds of calibrated rulers design two measuring basis lines indicating image one and image two of all not possessing in the second method to be mentioned.The calibration steps of the present invention's design not only can be realized above-mentioned functions simply, also the parallel lines calibrated ruler has been done improvement, makes calibration software more simple.
The present invention adopts the pane with certain color contrast to replace parallel lines to remove separate image, generally adopts the bigger black and white color lump of contrast, makes software design more simple.When with the parallel lines separate image, software needs to determine earlier the center of each parallel lines, determines the pixel count between two parallel lines then.After adopting the design of black and white piece, software only need determine that the black and white separatrix can determine the pixel count in each section.Determine the black and white separatrix than the center of determining a line come simple.The segmentation of this calibration steps is more accurate, and the lines of parallel lines segmentation must have certain width, and software is identification accurately.The segmentation of black and white piece does not then have this requirement, and the separatrix that only needs to determine color lump gets final product.Image switching when having realized calibration to the simplicity of design of special black block, the functions such as correction of the horizontal level difference of definite and the image one and the image two of second datum line.
Calibrated ruler of the present invention also can be made following modification: the black and white piece of following the characteristic distributions of the torsional deformation that produces according to camera lens to adopt width not wait; Adopt panes different colours or different gray scales to replace the black and white piece; Adopt the special black block of other pattern or use the pane different to replace special blocks etc. with other color.
For reducing the workload of computing machine or single-chip microcomputer, improve the speed of measuring, the image one of two cameras output of the present invention and image two only constitute by being positioned at 1～200 middle pixel line of the horizontal visual angle of camera.Because in the process of measuring, camera obtains image p.s. can be up to tens or even frame up to a hundred, and every width of cloth image all must be sent to computing machine or single-chip microcomputer is handled, and certainly will require very high to the computing power of computing machine or single-chip microcomputer.For the large-deformation measuring instrument, mainly be the fore-and-aft distance of measuring graticule, only need the middle image information of image promptly can determine.Existing single camera video tens(i)ometer also is to obtain to choose Useful Information after the image in the middle of image and handle.But, therefore very high to the processing power requirement of computing machine because it is that entire image is transmitted, and single-chip microcomputer is inefficient substantially.The present invention directly controls the intermediate information of a camera output image, therefore need not entire image and transmits, and greatly reduces the treatment capacity of data, even single-chip microcomputer also can obtain between the image for twice at camera and finish treatment of picture.Therefore, the frequency that camera image is obtained can further improve, and helps further improving the precision of measuring.
For using above-described inventive method, the invention provides a kind of design of video tens(i)ometer, structure-improved is that two cameras are installed on the camera installation base surface of video tens(i)ometer, the position of installing makes the visual angle of two cameras have the overlapping region, is used for can carrying out amalgamation in this zone after two cameras obtain image.The maximum magnitude of measuring is that the measurement range addition of two cameras deducts overlapping areas.In order to obtain big as far as possible measurement range and to consider the parameter dispersiveness at camera lens visual angle, make under worst situation, also to have enough overlapping scopes, overlapping generally speaking scope be controlled at the camera visual angle 10% in.In the process of measuring, the two ends of the clamp clamps sample by Material Testing Machine, and stretch; Two cameras on the measurement mechanism obtain the image of whole drawing process, and the picture signal of obtaining can be carried out following two kinds of transmission:
First kind is directly image to be sent to computing machine after obtaining image at every turn, is carried out Flame Image Process and is calculated as stated above by computing machine.The hardware configuration that adopts this mode is that described two cameras directly are connected with installation image pick-up card on computers, and the image that obtains by the image pick-up card acquisition camera also is sent to and handles in the computing machine and calculate.Second kind is directly to carry out Flame Image Process at every turn after obtaining image and calculate as stated above on measurement mechanism, and result of calculation is sent to computing machine does subsequent treatment and output.The hardware configuration that adopts this mode is that two cameras and image acquisition hardware and single-chip microcomputer are integrated, is connected with computing machine by communication interface.The image that camera obtains is directly handled in single-chip microcomputer and is calculated after storage, and last result of calculation is sent in the computing machine.This mode is installed more simple, and helps and different user's Survey Software compatibilities, has wider application surface.
The present invention has following outstanding substantive distinguishing features and obvious improvement with respect to prior art.
1. the inventive method and instrument provide bigger measurement range, can measure the bigger material of deflection, and neither increase the distance of camera lens to sample, do not increase the visual angle of camera lens again;
2. adopt the apparatus structure compactness of the inventive method, need not to adopt high resolving power, high-precision camera lens also can reach high precision;
3. the production cost of instrument is low, is easy to promote;
4. the calibration steps that adopts of the present invention makes that the design of computer measurement software is more simple, calibrates more precisely, and helps the amalgamation of image;
5. the present invention's center image of output lens only in measuring process greatly reduces data processing amount, has improved the processing speed of computing machine or single-chip microcomputer, helps more high-precision measurement;
6. camera and the direct-connected mode of image pick-up card of installing on computers, hardware configuration is simple, is easy to realize low production cost;
7. adopt camera and image acquisition hardware and the integrated mode of single-chip microcomputer, use simply, but the instrument independent operation, thereby can be applicable to the measuring system and the Survey Software of different user, application surface is extensive.
Description of drawings
Fig. 1 is for enlarging the synoptic diagram of measurement range to the distance of sample by the expansion camera;
Fig. 2 is for enlarging the synoptic diagram of measurement range by the visual angle that enlarges camera;
Fig. 3 is the structural representation of video tens(i)ometer of the present invention;
Fig. 4 is the synoptic diagram of measuring process of the present invention;
Fig. 5 is the synoptic diagram of calibrated ruler of the present invention;
Fig. 6 is a hardware configuration synoptic diagram of the present invention;
Fig. 7 A measures process flow diagram first for the present invention;
Fig. 7 B measures the process flow diagram second portion for the present invention;
Fig. 7 C measures the process flow diagram third part for the present invention;
Fig. 8 calibrates process flow diagram for the present invention.
Embodiment
The present invention will be further described below in conjunction with accompanying drawing.
The measurement range of video tens(i)ometer depends on the visual angle of camera lens and the camera lens distance to sample.Because must maintaining a certain distance just with sample, the restriction at camera lens visual angle, video tens(i)ometer can reach certain measurement range when operation.This requirement (＜400 millimeters) when measurement range is not too big does not have problem, but along with the expansion of measurement range, what this problem became surfaces, for this problem is described, please referring to Fig. 1.
Suppose that when the visual angle of camera lens was α, its maximum measurement range was A, if adopt the camera lens at same visual angle, want maximum measurement range is expanded to A1 from A that the distance between sample and camera lens just must expand L1 to from L, this can bring two problems:
The first, thus the decline of taken image resolution ratio influences measuring accuracy.Though can adopt more high-resolution camera lens and imageing sensor to go to remedy this loss, but this not only can cause the rapid rising of cost, for high-resolution camera lens and imageing sensor, resolution doubles, the lifting of price will be much larger than one times, but also is subjected to the restriction of device availability.
The second, distance add the increasing that conference causes installing inconvenience and testing machine overall dimensions.Compare with contact type measurement, this can be a significant disadvantages, has caused the not compact of structure.
Want not only to enlarge measurement range but also do not increase distance between camera lens and sample, the visual angle that just must increase camera lens is referring to Fig. 2.When the visual angle when α is increased to β, measurement range is increased to A1 from A.Yet the increase at visual angle also has certain limit.Along with the increase at camera lens visual angle, the picture quality of off-center area part can significantly descend, and resolution descends, and torsional deformation increases, thereby measuring accuracy is significantly descended.
So how could neither increase the distance of camera lens to sample, do not increase again under the condition at visual angle of camera lens the measurement range of video tens(i)ometer be multiplied? this problem to be solved by this invention just.
Fig. 3 is a dual camera large deformation video tens(i)ometer structural representation proposed by the invention.This instrument is improved on existing single camera video tens(i)ometer, mainly comprises measurement mechanism 1 and computing machine 3, and the visual angle that two cameras or digital camera 11 and 12, two cameras have been installed on measurement mechanism 1 can be identical or different.The measurement range A1 and the measurement range A2 that should guarantee two cameras when mounted have a bit of overlapping scope d, as shown in Figure 3.The size of overlapping scope should be taken into account the parameter dispersiveness at camera lens visual angle, makes also to have enough overlapping scopes under worst situation, so that Survey Software can realize image switching.Sample is installed on the plane 21 of stretching device 2.When measuring, adopt the clamp clamps sample two ends on the stretching device 2 to stretch, two cameras 11 and 12 are taken pictures simultaneously continuously, captured image or handle by being inserted in the Survey Software that image pick-up card in the computing machine is input to computing machine 3, perhaps handled by Flame Image Process and measuring system 13 that hardware and firmware constituted, the user's TT﹠C software that is sent to computing machine 3 is then handled.
The maximum measurement range Amax of this video tens(i)ometer can be obtained by Fig. 3, supposes that the measurement range of two cameras 11,12 is respectively A1 and A2, and overlapping scope is d, then Amax=A1+A2-d.If A1=A2=A, then Amax=2A-d.Because d is very little with respect to A, therefore, the measurement range of this video tens(i)ometer approximately is the twice of single camera.
The measuring method of video tens(i)ometer of the present invention can be explained by Fig. 4.In explanation after this, be called as image one by camera 11 captured images, and be called as image two by camera 12 captured images.Inferior 1 and 2 is represented the graticule position in image one and image two respectively among the figure.A among the figure is divided into (a) to view, and (b), (c), (d) four kinds of situations are represented sample 4 four kinds of situations that graticule moves in tension test respectively.
Measuring available following two kinds of methods carries out:
When measuring beginning, two graticule a1 on the sample 4 and a1 ' must be positioned at the measurement range A1 of camera 11, i.e. situation (a).In the initial period of tension test, graticule only appears in the image one, and Survey Software is only determined the distance of two graticules by image one, i.e. line segment a1a1 ' is in last graticule moves to overlapping scope d.
When last graticule moves to overlapping scope, i.e. situation (b), Survey Software will be carried out image switching, and promptly the position of determining to go up graticule by image one changes into by image two and determining.Switching can be carried out when any position in graticule moves to overlapping scope d.Software determine to be gone up the position of graticule in image one and image two simultaneously during switching, i.e. b1 ' and b2 ', and this position is defined as the image switching position.After this, b1 ' and b2 ' promptly become the image switching position in image 1 and image 2 respectively, till graticule moves to the image switching position down.
After the switching, i.e. situation (c), Survey Software is determined the position of graticule up and down respectively by image of taking simultaneously two and image one, and calculates the length of line segment c1b1 ' and b2 ' c2 ' respectively.Distance between two graticules then equals this two line segments sum, that is: graticule distance=line segment c1b1 '+line segment b2 ' c2 '.
Along with further stretching, following graticule also enters or has surmounted switching position, i.e. situation (d).Software carries out the image switching second time.After this, the position of two graticules is all obtained by image two, and the distance between two graticules is recorded by image two fully, i.e. d2d2 '.
When situation (a), two graticules obtain by image one, the distance between graticule equal graticule to the O1 line apart from a1 ' O1 deduct down graticule to the O1 line apart from a1O1.
When in last graticule moves to overlapping scope d, surpassing the O2 line, i.e. situation (b), Survey Software will be carried out image switching, and promptly the position of determining to go up graticule by image one changes into by image two and determining.Switching can surpass any position of O2 line and carry out in overlapping scope d.
After the switching, i.e. situation (c), Survey Software is determined the position of graticule up and down respectively by image of taking simultaneously two and image one.Distance between two graticules then can followingly be calculated: graticule distance=c2 ' O2+O2O1-c1O1, and wherein graticule is to the distance of O2 line in c2 ' the O2 representative, and graticule is to the distance of O1 line down in the c1O1 representative, and O2O1 represents the O2 line to the fixed range between the O1 line.
Instantly graticule also moves to when surpassing the O2 line in the overlapping scope d, i.e. situation (d), and software carries out the image switching second time.After this, two graticules are all determined by image two, the distance between two graticules equal graticule to the O2 line apart from d2 ' O2 deduct down graticule to the O2 line apart from d2O2.
The calibration of video tens(i)ometer of the present invention
Because phtographic lens exists parallax and torsional deformation, and the used wide-angle lens of large-deformation measuring is particularly remarkable, and therefore, the video tens(i)ometer is calibration earlier after installation.The purpose of calibration is the physical length apart from representative that will determine along between per two pixels of direction of measurement (Pixel).
Calibrated ruler (calibration rod) is adopted in calibration usually.The calibrated ruler that existing video tens(i)ometer is adopted when calibration has two kinds, and a kind of upward drawing has parallel lines, and when taking the image of calibrated ruler with camera, these lines promptly are divided into many sections to the image that photographed along direction of measurement.Because the distance between parallel lines is known, Survey Software only need be determined each section along the pixel count on the direction of measurement, can calculate in the physical length apart from representative between per two pixels on that section.Circular pattern is adopted in another kind of calibrated ruler design, and this calibrated ruler can be calibrated simultaneously along a plurality of directions, but here institute at large-deformation measuring only need the calibration of a direction, adopt this calibrated ruler and inconvenience.
More than the design of two kinds of calibrated rulers all do not possess measuring basis line O1 that indicates image one and image two that said method 2 mentioned and the function of O2.The present invention has designed a kind of new calibration steps, not only can realize above-mentioned functions simply, also the parallel lines calibrated ruler has been done improvement, makes the calibration software design more simple.
As shown in Figure 5, new calibrated ruler adopts chequered with black and white pane to replace parallel lines to remove separate image.A special black block that has white gap is arranged in the middle part.Special color lump has two effects, and the one, when being installed, the video tens(i)ometer helps to adjust overlapping scope; The 2nd, the black and white separatrix below this color lump promptly is the measuring basis line O2 of image two, sees the B enlarged drawing of Fig. 5.The measuring basis line O1 of image one sees the C enlarged drawing of Fig. 5 by article one black and white separatrix representative of the measurement range that enters camera 11.
Take the photo of calibrated ruler during calibration earlier simultaneously with two cameras 11 and 12, then image is sent to Survey Software.Software is begun to calibrate by the bottommost of image one, when running into article one black and white separatrix, just it is asserted the O1 line.When calibration software runs into special black block, to the calibration end of image one.Software transfers to be calibrated image two, and that black and white separatrix below the special black block, just enters article one black and white separatrix of the measurement range of camera 12, is asserted the O2 line.
Black block is not run through in white gap in the middle of special black block, but stays one section black, forms " U " type that lies low.It is poor that the bottom vertical line of " U " type of being somebody's turn to do can be used to the horizontal level of correcting image one and image two.But the correction of horizontal level difference helper applications when specimen width is narrower is being determined the position of graticule in image two fast after the image switching.
New calibrated ruler has the following advantages:
1. adopt chequered with black and white pane to replace parallel lines to remove separate image, make software more simple.When with the parallel lines separate image, software needs to determine earlier the center of each parallel lines, determines the pixel count between two parallel lines then.After adopting the design of black and white piece, software only need determine that the black and white separatrix can determine the pixel count in each section.Determine the black and white separatrix than the center of determining a line come simple.
2. segmentation is more accurate.The lines of parallel lines segmentation must have certain width, and software is identification accurately.The segmentation of black and white piece does not have this requirement.
3. image switching when having realized calibration to the simplicity of design of special black block, the functions such as correction of the horizontal level difference of definite and image one and the image two of measuring basis line O2.
Must be pointed out that calibrated ruler of the present invention also can be made following modification:
The black and white piece of following the characteristic distributions of the torsional deformation that produces according to camera lens to adopt width not wait.
Adopt panes different colours or different gray scales to replace the black and white piece.
Adopt the special black block of other pattern or use the pane different to replace special black block etc. with other pane color.
The present invention has following two kinds of schemes on hardware configuration:
The simplest embodiment be adopt general binary channels image pick-up card with two with its camera of compatibility mutually.Image pick-up card is inserted the expansion slot of computing machine and the driver that provides with card is installed.Two cameras are installed makes it have overlapping scope described in the invention.Remaining task is write software exactly and is carried out Flame Image Process, to realize measuring method described in the invention.
The hardware design of scheme 1 need be opened user's computer and insert image pick-up card and the corresponding driving program is installed.This is not too convenient in the use, and is difficult to incorporate the existing testing machine measurement and control program of user.
Figure 6 shows that the hardware structure diagram of scheme 2.Camera must be selected the camera with digital signal output for use.The output image of two cameras is deposited in video memory one and two respectively.The address generates and latchs part in order to generate required address signal of memory image and the address signal that latchs from single-chip microcomputer.In the beginning of each width of cloth image output, width of cloth signal pulse is made as the address " 0 ".After this, under the effective condition of the signal of being expert at, each pixel pulse adds 1 with the address in order, thereby deposits value one every trade of each pixel in the image in storer.The capable signal of two cameras is transfused to single-chip microcomputer to determine whether image output finishes.After image storage was finished, single-chip microcomputer then can be chosen image 1 or image 2 is handled by address latch signal and data bus strobe signal.
The shooting of two cameras is passed through I by single-chip microcomputer
2The C bus is controlled fully.Because the Single-chip Controlling camera is only exported centre tens row of each width of cloth image, therefore between the output of two width of cloth images, single-chip microcomputer has time enough to handle the image of being stored.
The measurement process flow diagram of single-chip microcomputer or computer realization the inventive method is shown in Fig. 7 A, 7B and 7C.Measuring process begins, and shown in Fig. 7 A, the RS232 interface between first initialization survey instrument and the computing machine is carried out the preparation that data transmit.Two cameras 11 of initialization and 12 are carried out the preparation of image acquisition and measurement then.Next judge that the order of receiving is measuring command or calibration command or other orders, enters respectively in the subroutine separately.If be process of measurement, survey mark M is set to 1, and image switching sign S1 and S2 are initialized as 0, begins to take and memory image.When the piece image storage finishes, judge whether to carry out image switching for the first time earlier, promptly whether image switching sign S1 is 1.If image switching sign S1 is not 1, enter modules A, in image one, determine the position of graticule up and down, judge then whether surpass second datum line O2, the words that surpass then are set at 1 with image switching sign S1 if going up graticule.Next calculate the distance of graticule up and down, the output result finishes C.
If image switching sign S1 is 1 in the said process, then enter module B, judge earlier whether the sign of image switching for the second time S2 is 0.If be 0, in image one, determine the subscript line position, judge again whether graticule surpasses O2 down.Following graticule surpasses O2 and then switching mark S2 is made as 1.But no matter descend graticule surpass the O2 line whether all in image two definite on the position of graticule.Next calculate the distance of graticule up and down, the output result finishes C.If judge that the sign of image switching for the second time S2 is not 0, then in image two, determine next to calculate the distance of graticule up and down in graticule position up and down, the output result finishes C.
If receive calibration command, then enter module D.At first two cameras are taken the image of calibrated rulers, and the initial position from image one begins to seek the black and white separatrix then, and record article one black and white separatrix is the first datum line O1.Next order is sought the black and white separatrix in image, if be the separatrix, and the exact position that then defines boundaries, and the calibration value of definite pixel.When running into special black and white piece, the black and white separatrix below it is recorded as the second datum line O2.In image two, stride across white gap then and begin to seek the black and white separatrix.If be the separatrix, calibration until last pixel, is finished in the exact position that then defines boundaries, and the calibration value of definite pixel, gets back to master routine by E and waits for Next Command.
Claims (7)
1. double-camera video frequency large-deformation measurement is characterized in that may further comprise the steps:
1. adopt two cameras to constitute the image taking part of video tens(i)ometer, and guarantee that there is the overlapping region in the visual angle of two cameras;
2. sample is installed, and is guaranteed that two graticules on the sample are positioned at the measurement range of first camera simultaneously;
3. tensile sample;
4. when two graticules on the sample are positioned at the measurement range of first camera, the distance that the image one that is obtained by first camera is determined between two graticules;
5. when the last graticule of sample moves to the overlapping region, visual angle of two cameras, carry out image switching, and be defined as switching position two captured image one and positions in the image two of camera going up graticule this moment;
6. then, the image one that is obtained by first camera is determined the distance between the graticule and switching position down, and the image two that is obtained by second camera determines to go up the distances between graticules and the switching position, determines two distances between the graticule with two apart from addition;
7. when the following graticule of sample moved switching position, carry out the image switching second time, the distance that the image two that is obtained by second camera is determined between two graticules.
2. double-camera video frequency large-deformation measurement according to claim 1 is characterized in that also comprising calibration process, and calibration process may further comprise the steps:
1. a calibrated ruler with two kinds of alternate formation of color lump of certain contrast is installed in the sample installation site, be provided with in the middle of the calibrated ruler one with other two kinds of special blocks that color lump is different, this special blocks must be positioned at the overlapping region at two camera visual angles when mounted;
2. the separatrix of color lump in the image that definite camera obtains, determine the pixel count of the vertical width of each color lump thus, and compare with the developed width of the corresponding color lump of calibrated ruler respectively, can obtain the physical length between per two pixels of this upper edge, color lump present position direction of measurement in the image apart from representative;
3. the bottom of the image one that is obtained by first camera begins from bottom to top to calibrate, and when being calibrated to special blocks, switching to the image two that is obtained by second camera and calibrates, and ends to image two tops.
3. double-camera video frequency large-deformation measurement is characterized in that may further comprise the steps:
1. adopt two cameras to constitute the image taking part of video tens(i)ometer, and guarantee that there is the overlapping region in the visual angle of two cameras;
2. when when calibration, below the visual angle of each camera, determine a datum line respectively, and make second datum line in the visual angle of second camera be positioned at the overlapping region to have known fixed range between two datum lines;
3. sample is installed, and is guaranteed that two graticules on the sample are positioned at the measurement range of first camera simultaneously;
4. tensile sample;
5. when two graticules on the sample are positioned at the measurement range of first camera, the distance that the image one that is obtained by first camera is determined between two graticules;
6. when the last graticule of sample moved second datum line, carry out image switching, the image one that is obtained by first camera is determined the distance between the graticule and first datum line down, the image two that is obtained by second camera determines to go up the distances between the graticules and second datum line, and the distance between the last graticule and second datum line is added that distance between two datum lines deducts down distance between the graticule and first datum line and is distance between two graticules;
7. when the following graticule of sample moved switching position, carry out the image switching second time, the distance that the image two that is obtained by second camera is determined between two graticules.
4. double-camera video frequency large-deformation measurement according to claim 3 is characterized in that also comprising calibration process, and calibration process may further comprise the steps:
1. a calibrated ruler with two kinds of alternate formation of color lump of certain contrast is installed in the sample installation site, be provided with in the middle of the calibrated ruler one with other two kinds of special blocks that color lump is different, this special blocks must be positioned at the overlapping region at two camera visual angles when mounted;
2. the separatrix of color lump in the image that definite camera obtains, determine the pixel count of the vertical width of each color lump thus, and compare with the developed width of the corresponding color lump of calibrated ruler respectively, can obtain the physical length between per two pixels of this upper edge, color lump present position direction of measurement in the image apart from representative;
3. the bottom of the image one that is obtained by first camera begins from bottom to top to calibrate, and will enter article one color lump separatrix of camera lens as first datum line;
4. when being calibrated to special blocks, switch to the image that obtains by second camera, and the color lump separatrix below the special blocks as second datum line, continue to calibrate to image two tops and end.
5. according to claim 2 or 4 described double-camera video frequency large-deformation measurements, it is characterized in that in the calibration process, determine that by the horizontal color lump separatrix on the special blocks lengthwise position of image one and image two is poor, determine that by the vertical color lump separatrix on the special blocks lateral attitude of image one and image two is poor.
6. according to claim 1 or 3 described double-camera video frequency large-deformation measurements, it is characterized in that the image one of two camera outputs and image two constitute by being positioned at 1～200 middle pixel line of the horizontal visual angle of camera.
7. video tens(i)ometer, it is characterized in that on the camera installation base surface of video tens(i)ometer, installing two cameras, the position of installing makes the visual angle of two cameras have the overlapping region, described overlapping region be controlled at the camera visual angle 10% in, two cameras and image acquisition hardware and single-chip microcomputer are integrated, are connected with computing machine by RS232 or USB communication interface.
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