CN112525096A - Double-telecentric-lens video extensometer based on field segmentation - Google Patents
Double-telecentric-lens video extensometer based on field segmentation Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/16—Measuring arrangements characterised by the use of optical techniques for measuring the deformation in a solid, e.g. optical strain gauge
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/02—Details
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06T—IMAGE DATA PROCESSING OR GENERATION, IN GENERAL
- G06T7/00—Image analysis
- G06T7/60—Analysis of geometric attributes
Abstract
The invention discloses a double-telecentric-lens video extensometer based on field segmentation, which comprises double-telecentric lenses, a video camera and an upper computer, wherein the double-telecentric lenses are adopted to shoot a to-be-tested piece, the video camera is used for collecting a video image of the to-be-tested piece, and the video image is transmitted to the upper computer for data processing; the two plane reflectors of the second group are symmetrically arranged on two sides of the vertical optical axis, and two field light rays divided by the two plane reflectors of the first group are reflected and then aligned to a piece to be tested. The invention utilizes 4 plane reflectors to divide the view field of the double telecentric lens, effectively enlarges the gauge length of the test piece which can be measured by the double telecentric lens, thereby improving the measurement precision of the double telecentric lens video extensometer and enabling the method to be used for wider measurement objects.
Description
Technical Field
The invention discloses a double telecentric lens video extensometer based on field segmentation. The video extensometer increases the gauge length of a test piece which can be observed by the double telecentric lenses through a field-of-view segmentation method, thereby expanding the application range of the video extensometer based on the double telecentric lenses and improving the measurement precision of the method, and belongs to the field of photoelectric detection.
Background
The mechanical property test of the material is a basic test before the material is applied and is also a basic condition for the development of material science and technology, and the strain is an important parameter for analyzing the mechanical property of the material. Extensometers, as a system for measuring trace line deformation, have been widely used in scientific research and testing in various fields. The existing extensometers can be roughly divided into two types, one is a contact extensometer, and the other is a non-contact video extensometer.
The contact extensometer is divided into a mechanical extensometer and an electronic extensometer, both of which need to fix a device on a to-be-tested member for strain acquisition, and the difference is that the former amplifies and displays deformation through a lever, a gear and the like, for example, a dial indicator and the like is adopted, and the latter processes an electric signal transmitted from a sensor and converted from the deformation through a processor to obtain a strain indication. The device has the advantages of simple structure, low price, convenient assembly and the like, and has the defects of easy slipping, incapability of eliminating the bending influence of eccentric stretching due to the fact that the extensometer needs to be removed before a sample is broken, incapability of being applied to a large-strain sample test, incapability of directly measuring the elastic-plastic stress and strain behaviors of the sample in a post-yielding stage, a necking stage and a breaking stage, high requirements on the rigidity of a test piece and the like.
In recent years, video extensometers have been developed rapidly to overcome the defects of contact extensometers, and the principle thereof is mainly to calculate the amount of deformation by tracking the positions of specific points before and after deformation by an image processing technique. A video extensometer generally consists of an illumination source, a digital CCD camera, a lens, an image acquisition card, and a computer including a video image tracking program. Comparing contact extensometer, video extensometer need not contact with the test piece, consequently can avoid the damage to the test piece, and in addition, to some small test pieces, contact extensometer just can't the centre gripping at all, and at this moment video extensometer has just become only selection. The video extensometer is also more convenient to operate relative to a contact extensometer.
However, the conventional video extensometer usually uses a common optical lens, and the common optical lens imaging is a process of central projection, so when a measured object is displaced along the direction of the optical axis of the camera, a false displacement of the object imaged in an imaging plane is caused, thereby causing a measurement error of the video extensometer. The double telecentric lens has the imaging characteristic of parallel projection, so that even if the object to be measured moves along the optical axis direction of the camera, the displacement of the object in the imaging plane can not be caused, and further the measurement error caused by using the common lens can be effectively eliminated. However, due to the difficulty of the imaging principle and the manufacturing process, the imaging field of view of the double telecentric lens is usually within 50mm, and the double telecentric lens with larger field of view is expensive and bulky and inconvenient to use. As shown in fig. 1, two observation mark points are preset on the piece to be tested, and the length between the two observation mark points is the gauge length; before the test piece to be tested is subjected to tensile deformation, the gauge length is D; after the test piece to be tested was stretched, the gauge length was changed to D ', and the strain ∈ ═ [ (D' -D)/D ] × 100% of the test piece to be tested was calculated. The imaging field of view of the double telecentric lens in the prior art is limited, and the gauge length of the test piece which can be measured by the video extensometer based on the double telecentric lens is also limited due to the limitation of the field of view, so that the application range and the measurement precision which can be achieved by the method are limited. This is a technical problem to be solved.
Disclosure of Invention
In order to solve the problem of limited precision of a double telecentric lens video extensometer in the prior art due to limited field of view, the invention aims to overcome the defects in the prior art, and provides the double telecentric lens video extensometer based on field of view segmentation, wherein the field of view of the double telecentric lens is segmented by using 4 plane mirrors, so that the gauge length of a test piece which can be measured by the double telecentric lens is effectively enlarged, the measurement precision of the double telecentric lens video extensometer is improved, and the method can be used for measuring objects more widely.
In order to achieve the purpose of the invention, the invention adopts the following technical scheme:
the utility model provides a two telecentric mirror video extensometers based on field of view are cut apart, including two telecentric mirrors, video camera and host computer, adopt two telecentric mirrors of two telecentric mirrors to just treating the test piece, utilize video camera to gather the video image of treating the test piece, carry out data analysis processing with video image signal transmission to host computer, output the mechanical properties test result of treating the test piece, two plane reflectors of first group are placed to upper and lower or bilateral symmetry in two telecentric mirror fronts, divide into two parts with the field of view of two telecentric mirrors, make the field of view direction of two telecentric mirrors perpendicular to the optical axis direction, and in two plane reflectors of second group of bilateral symmetry of perpendicular optical axis, aim at the test piece after reflecting two field of view light rays that two plane reflectors of first group cut apart.
Preferably, the first group of two reflectors arranged in front of the double telecentric lenses are mutually in a right angle, the two mirror surfaces are connected at a right-angle edge, and a right-angle bisector is collinear with the optical axes of the double telecentric lenses, so that the two reflectors and the optical axes of the double telecentric lenses form an included angle of 45 degrees; the first group of two reflectors divide the view field of the double telecentric lens into two parts, and the view field directions of the double telecentric lens are perpendicular to the optical axis and point to the two sides of the optical axis respectively.
Preferably, the two plane reflectors of the second group, which are symmetrically arranged perpendicular to the optical axis of the double telecentric lens, and the two plane reflectors of the first group are positioned on the same straight line perpendicular to the optical axis and form 45-degree included angles with the optical axis, so that the light rays of the two view fields divided by the two plane reflectors of the first group are reflected and then face the to-be-tested piece along the direction of the optical axis.
Preferably, the video camera collects images shot by the double telecentric lenses, the images are transmitted to the upper computer in real time, and the image analysis software of the upper computer realizes the identification and tracking of the gauge length points on the piece to be tested, so as to complete the strain measurement of the piece to be tested; as shown in fig. 1, two observation mark points are preset on the piece to be tested, and the length between the two observation mark points is the gauge length; before the test piece to be tested is subjected to tensile deformation, the gauge length is D; after the test piece to be tested was stretched, the gauge length was changed to D ', and the strain ∈ ═ [ (D' -D)/D ] × 100% of the test piece to be tested was calculated.
Preferably, after the field of view is divided, the field of view originally aligned with the middle portion of the test piece to be tested is divided into an upper block, a lower block, or a left block and a right block, which are aligned with the upper block, the lower block, or the left block and the right block of the test piece to be tested,the observable gauge length is changed from D to D1，D1Greater than D. Under the condition of the same image recognition accuracy, the larger the gauge length is, the smaller the strain which can be measured is, and the higher the accuracy is. By the method of field division, the length of the gauge length which can be measured can be enlarged, thereby improving the measurement precision. As shown in fig. 2, after the field division, the field area originally aligned with the middle part of the test piece is divided into an upper field area and a lower field area, which are respectively aligned with the upper part and the lower part of the test piece, and the observable gauge length is changed from D to D1Due to D1Greater than D, the strain measurement accuracy is improved.
Preferably, the video camera is a CCD or CMOS camera.
Preferably, a first group of two plane reflectors, namely a first reflector and a second reflector, which form an included angle of 45 degrees with the horizontal line, are symmetrically arranged in front of the double telecentric lens from top to bottom, so that the field of view of the double telecentric lens is divided into two parts; and a second group of two plane reflectors are symmetrically arranged on two sides of the vertical optical axis, namely a third reflector and a fourth reflector which form an included angle of 45 degrees with the horizontal line respectively, the third reflector and the fourth reflector are vertically aligned with the first reflector and the second reflector, and the 4 reflectors are arranged to divide the view field of the double telecentric lens into an upper part and a lower part which are separated from each other.
Preferably, in the two divided fields of view, two marking points are respectively marked on the piece to be tested, images of the two marking points are imaged by a parallel projection system consisting of 4 reflectors and double telecentric lenses and are finally imaged on a target surface of the video camera, and the video camera transmits the acquired images to an upper computer for processing in real time.
Preferably, the upper computer tracks the mark points by a digital image correlation method according to the collected images; the calculated gauge length in the initial image is noted as D1And the calculated gauge length in the subsequent image is recorded as D1', so as to obtain the real-time strain epsilon' in the process of stretching the tested piece [ (D)1'-D1)/D1]*100％。
Preferably, the observable specimen gauge length is at least 3 times greater than the width of the double telecentric lens imaging field of view.
Compared with the prior art, the invention has the following obvious and prominent substantive characteristics and remarkable advantages:
1. compared with the traditional video extensometer, the double telecentric lens video extensometer based on field segmentation divides the observation field of view of the double telecentric lenses by adopting the four plane reflectors, and enlarges the test piece scale distance which can be measured by the double telecentric lenses while keeping the advantage of parallel projection imaging of the double telecentric lenses, thereby effectively improving the application range and the measurement precision of the double telecentric lens video extensometer;
2. under the condition of the same image recognition precision, the larger the gauge length is, the smaller the strain which can be measured is, and the higher the precision is; the invention can enlarge the length of the gauge length which can be measured by a view field segmentation method, thereby improving the measurement precision;
3. the double telecentric lens video extensometer based on field segmentation can not only eliminate errors caused by the movement of a common optical lens in the direction of the optical axis of a camera, but also overcome the problem of limited measuring specimen gauge length caused by limited field of view of the double telecentric lens by a field segmentation method, and increase the length of the measurable gauge length, thereby improving the measuring precision.
Drawings
FIG. 1 is a schematic view of a strain observation of a test piece prior to field segmentation or a prior art test piece.
FIG. 2 is a schematic view of a strain observation of a test piece after field segmentation by the apparatus of the present invention.
Fig. 3 is a schematic diagram of the structure and strain observation principle of the double telecentric lens video extensometer based on field segmentation in the invention.
Fig. 4 is a schematic view of strain observation in the third embodiment of the present invention.
Detailed Description
The above-described scheme is further illustrated below with reference to specific embodiments, which are detailed below:
the first embodiment is as follows:
in this embodiment, referring to fig. 2 and 3, a double telecentric lens video extensometer based on field segmentation comprises a double telecentric lens 7, a video camera 8 and an upper computer 9, wherein the double telecentric lens 7 is adopted to shoot a to-be-tested piece 5, the video camera 8 is used to collect a video image of the to-be-tested piece 5, a video image signal is transmitted to the upper computer 9 for data analysis and processing, and a mechanical property test result of the to-be-tested piece 5 is output; a first group of two plane reflectors are symmetrically arranged in the upper and lower directions or in the left and right directions in front of a double telecentric lens 7, the view field of the double telecentric lens 7 is divided into two parts, the view field direction of the double telecentric lens 7 is perpendicular to the optical axis direction, a second group of two plane reflectors are symmetrically arranged on two sides of the perpendicular optical axis, and two view field rays divided by the first group of two plane reflectors are reflected and then aligned to a piece to be tested 5.
The double-telecentric-lens video extensometer based on field division of the embodiment adopts 4 plane reflectors to divide the observation field of view of the double-telecentric lens 7, so that the test piece gauge length which can be measured by the double-telecentric lens 7 is enlarged while the advantage of parallel projection imaging of the double-telecentric lens 7 is kept, and the use range and the measurement precision of the double-telecentric-lens video extensometer are effectively improved.
Example two:
this embodiment is substantially the same as the first embodiment, and is characterized in that:
in this embodiment, referring to fig. 2 and 3, the first two reflectors arranged in front of the double telecentric lens 7 are mutually at right angles, the two mirror surfaces are connected at the right-angle edge, and the right-angle bisector is collinear with the optical axis of the double telecentric lens 7, so that the two reflectors and the optical axis of the double telecentric lens 7 form an included angle of 45 degrees; the first group of two reflectors divide the view field of the double telecentric lens 7 into two parts, and the view field directions of the double telecentric lens 7 are perpendicular to the optical axis and respectively point to the two sides of the optical axis.
In this embodiment, the two plane mirrors of the second group, which are symmetrically disposed perpendicular to the optical axis of the double telecentric lens 7, and the two plane mirrors of the first group are on the same straight line perpendicular to the optical axis and form an included angle of 45 degrees with the optical axis, so that the light rays of the two fields of view divided by the two plane mirrors of the first group are reflected and then face the to-be-tested piece 5 along the direction of the optical axis.
In this embodiment, as shown in fig. 2, after the apparent field of view is divided, the field of view area originally aligned with the middle portion of the to-be-tested piece 5 is divided into an upper portion, a lower portion, or a left portion and a right portion, which are aligned with the upper portion, the lower portion, or the left portion and the right portion of the to-be-tested piece 5, respectively, and the observable gauge length is also changed from D to D1Due to D1Greater than D, the strain measurement accuracy is improved.
In this embodiment, the video camera 8 is a CCD or CMOS camera.
The extensometer of the embodiment can not only eliminate errors caused by the movement of a common optical lens in a measured object along the optical axis direction of the camera, but also overcome the problem of limited measuring specimen gauge length caused by limited field of view of the double telecentric lens by a field-of-view segmentation method, thereby increasing the measurable gauge length and improving the measurement precision.
The examples are as follows:
this embodiment is substantially the same as the above embodiment, and is characterized in that:
in this embodiment, referring to fig. 2-4, a first group of two plane reflectors, namely a first reflector 1 and a second reflector 2, which both form an included angle of 45 ° with the horizontal line, are symmetrically disposed in front of the double telecentric lens 7 from top to bottom, so as to divide the field of view of the double telecentric lens 7 into two parts; and a second group of two plane reflectors are symmetrically arranged on two sides of the vertical optical axis, namely a third reflector 3 and a fourth reflector 4 which form an included angle of 45 degrees with the horizontal line respectively, the third reflector 3 and the fourth reflector 4 are vertically aligned with the first reflector 1 and the second reflector 2, and the 4 reflectors are arranged to divide the view field of the double telecentric lens 7 into an upper part and a lower part which are separated from each other.
In the present embodiment, referring to fig. 2-4, in two divided fields of view, two marking points 6 are respectively marked on the to-be-tested piece 5, the images of the two marking points 6 are imaged by a parallel projection system consisting of 4 reflectors and a double telecentric lens 7 and finally imaged on the target surface of a CCD or CMOS camera, and the acquired images are transmitted to an upper computer 9 for processing in real time.
In the present embodiment, referring to fig. 2-4, the upper computer 9 tracks the marker points 6 by a digital image correlation method according to the collected images; the calculated gauge length in the initial image is noted as D1And the calculated gauge length in the subsequent image is recorded as D1', so as to obtain the real-time strain epsilon' ═ D in the process of stretching the piece 5 to be tested1'-D1)/D1]*100％。
In the embodiment, a double telecentric lens 7 with an object space field of view of 40 × 30mm and a working distance of 142mm is adopted, and a large constant photoelectricity GCO-232103 is adopted. As shown in fig. 4, in the case of an undivided field of view, the maximum observable gauge length is 40mm as shown by the dotted line in the figure, and the maximum observable gauge length after division reaches 240 mm. Compared with the original field of view, after the field of view segmentation method is adopted, the mark distance length of the observable test piece to be tested is increased by 6 times, and the minimum strain capable of being measured is 1/6 of the original scale distance, so that the strain measurement precision is improved. The length of the observable specimen scale distance is at least 6 times larger than the width of the imaging field of view of the double telecentric lens 7. In the embodiment, under the condition of the same image recognition accuracy, the larger the gauge length is, the smaller the strain which can be measured is, and the higher the accuracy is. By the method of field division, the length of the gauge length which can be measured can be enlarged, thereby improving the measurement precision.
The embodiments of the present invention have been described with reference to the accompanying drawings, but the present invention is not limited to the embodiments, and various changes and modifications can be made according to the purpose of the invention, and any changes, modifications, substitutions, combinations or simplifications made according to the spirit and principle of the technical solution of the present invention shall be equivalent substitutions, as long as the purpose of the present invention is met, and the present invention shall fall within the protection scope of the present invention without departing from the technical principle and inventive concept of the present invention.
Claims (10)
1. The utility model provides a two telecentric mirror head video extensometers based on visual field is cut apart, including two telecentric mirror head (7), video camera (8) and host computer (9), adopt two telecentric mirror head (7) of two telecentric mirror head just to treat test piece (5) and shoot, utilize video camera (8) to gather the video image of treating test piece (5), carry out data analysis processing with video image signal transmission to host computer (9), the mechanical properties test result of output treating test piece (5), its characterized in that: the method comprises the steps of symmetrically placing a first group of two plane reflectors up and down or left and right in front of a double telecentric lens (7), dividing a view field of the double telecentric lens (7) into two parts, enabling the view field direction of the double telecentric lens (7) to be perpendicular to the optical axis direction, symmetrically placing a second group of two plane reflectors on two sides of the perpendicular optical axis, reflecting two view field rays split by the first group of two plane reflectors, and aligning the two view field rays to a piece to be tested (5).
2. The field segmentation-based double telecentric lens video extensometer of claim 1, wherein: a first group of two reflectors arranged in front of the double telecentric lens (7) are mutually in a right angle, the two mirror surfaces are connected at the right-angle edge, and a right-angle bisector is collinear with the optical axis of the double telecentric lens (7), so that the two reflectors and the optical axis of the double telecentric lens (7) form an included angle of 45 degrees; the first group of two reflectors divide the view field of the double telecentric lens (7) into two parts, and the view field directions of the double telecentric lens (7) are perpendicular to the optical axis and respectively point to the two sides of the optical axis.
3. The field segmentation-based double telecentric lens video extensometer of claim 1, wherein: the second group of two plane reflectors symmetrically arranged perpendicular to the optical axis of the double telecentric lens (7) and the first group of two plane reflectors are positioned on the same straight line perpendicular to the optical axis and form an included angle of 45 degrees with the optical axis, so that the light rays of two view fields divided by the first group of two plane reflectors are reflected and then face the to-be-tested piece (5) along the direction of the optical axis.
4. The field segmentation-based double telecentric lens video extensometer of claim 1, wherein: the video camera (8) collects images shot by the double telecentric lens (7), the images are transmitted to the upper computer (9) in real time, and the identification and tracking of the gauge length points on the piece to be tested (5) are realized by the image analysis software of the upper computer (9), so that the strain measurement of the piece to be tested (5) is completed.
5. The field segmentation-based double telecentric lens video extensometer of claim 1, wherein: after the division of the view field, the view field area originally aligned with the middle part of the piece to be tested (5) is divided into an upper part, a lower part or a left part and a right part which are respectively aligned with the upper part, the lower part or the left part and the right part of the piece to be tested (5), so that the observable gauge length is changed from D to D1，D1Greater than D.
6. The field segmentation-based double telecentric lens video extensometer of claim 1, wherein: the video camera (8) adopts a CCD or CMOS camera.
7. The field segmentation-based double telecentric lens video extensometer of claim 1, wherein: a first group of two plane reflectors, namely a first reflector (1) and a second reflector (2) which form an included angle of 45 degrees with a horizontal line, are symmetrically arranged up and down in front of the double telecentric lens (7), and the view field of the double telecentric lens (7) is divided into two parts; and a second group of two plane reflectors are symmetrically arranged on two sides of a vertical optical axis, namely a third reflector (3) and a fourth reflector (4) which form an included angle of 45 degrees with a horizontal line respectively, the third reflector (3) and the fourth reflector (4) are vertically aligned with the first reflector (1) and the second reflector (2), and the field of view of the double telecentric lens (7) is divided into an upper part and a lower part which are separated from each other through the arrangement of the 4 reflectors.
8. The field segmentation-based double telecentric lens video extensometer of claim 1, wherein: in the two divided fields of view, two marking points (6) are respectively marked on a piece to be tested (5), images of the two marking points (6) are imaged by a parallel projection system consisting of 4 reflectors and a double telecentric lens (7) and are finally imaged on a target surface of a video camera (8), and the video camera (8) transmits the acquired images to an upper computer (9) for processing in real time.
9. The field segmentation-based double telecentric lens video extensometer of claim 1, wherein: the upper computer (9) tracks the mark points (6) by a digital image correlation method according to the collected images; the calculated gauge length in the initial image is noted as D1And the calculated gauge length in the subsequent image is recorded as D'1So as to obtain real-time strain epsilon ' ═ D ' of the piece to be tested (5) in the stretching process '1-D1)/D1]*100％。
10. The field segmentation-based double telecentric lens video extensometer of claim 1, wherein: the length of the observable specimen scale distance is at least 3 times larger than the width of the imaging field of view of the double telecentric lens (7).
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Application publication date: 20210319 |