A high-resolution photogrammetry dynamic displacement detection platform

Abstract

The present invention provides a high-resolution photogrammetric dynamic displacement detection platform, which belongs to the field of experimental mechanics technology. The detection platform includes a vibration isolation platform, a displacement sensor, a piston-cylinder motion group, a photographic table, a mobile system and a camera system. The present invention adopts a conventional displacement sensor that is insensitive to environmental changes as a displacement detection reference, and improves the resolution of the output displacement through the pressure-motion conversion of the piston-cylinder group. According to the slope of the straight line segment measured by photogrammetry and the slope of the straight line segment of the true displacement curve, the pixel equivalent can be inverted and corrected. The platform has a simple structure, low cost and simple operation.

Description

Technical Field

[0001] The invention belongs to the technical field of experimental mechanics and relates to a high-resolution photogrammetry dynamic displacement detection platform. Background Art

[0002] Due to the advantages of non-contact measurement, high measurement accuracy, high degree of automation, applicability to dynamic measurement, and relatively low cost, photogrammetry is widely used in the fields of national defense and aerospace, industrial inspection, construction monitoring, experimental mechanics, etc. Accuracy is an eternal theme in measurement and is closely related to the various components of the measurement system. Among them, the resolution of the measurement system is an important indicator reflecting the measurement accuracy.

[0003] Resolution refers to the minimum displacement change that can be repeatedly detected during the measurement process of the displacement sensor, and is the minimum graduation value of the measurement system. For conventional linear displacement sensors based on the principle of potentiometers, infinite resolution can be achieved in theory. However, in actual use, the measurement resolution is affected by the noise on site and the resolution of the acquisition system, and it is impossible to reach infinitesimal. There is still a minimum value.

[0004] Photogrammetry systems often use pixel equivalent (physical length / pixel) to reflect the resolution of the measurement. For each known component of the measurement system, the pixel equivalent is determined, but how to accurately detect the pixel equivalent size is related to the overall accuracy of the measurement system. Using a calibration plate is a common method. By shooting a feature block of known length on the calibration plate, the pixel equivalent is obtained by processing and converting in the pixel coordinate system. For example, the pixel equivalent is (1mm) / (100 pixels), which means that 1 pixel represents 0.01mm. In other words, every change of 1 pixel captured by photogrammetry indicates that the actual physical displacement captured is 0.01mm. This is based on the ideal conversion of static images. For motion (dynamic) shooting systems, the displacement resolution needs to be calibrated by a high-resolution displacement detection platform. Grating rulers or linear displacement sensors are often used as references on the displacement detection platform. In this process, the value measured by the displacement sensor with higher resolution is considered to be the standard value (true value), and the displacement measured by the photogrammetry system is the test value (measured value). Combined with the observation of the displacement curve changes measured by the photogrammetry system, the minimum displacement can be captured. However, high-resolution displacement sensors have limited range, are expensive, difficult to manufacture, sensitive to the operating environment, and have high requirements for the operating process.

[0005] Therefore, there is an urgent need for a low-cost, low-requirement for the use environment, simple to operate, and high-resolution dynamic displacement calibration platform for photogrammetry systems. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a high-resolution photogrammetry dynamic displacement detection platform.

[0007] The technical solution of the present invention is:

[0008] 1) Basic principles

[0009] A high-resolution photogrammetry dynamic displacement detection platform uses a conventional (low) resolution displacement sensor (referred to as displacement sensor) as a reference, and improves its displacement resolution through the pressure-motion conversion of the piston-cylinder group, such as Figure 1 As shown. The implementation process is as follows: two piston cylinders with different cylinder diameters (the diameter of the large piston cylinder is D, and the diameter of the small piston cylinder is d) are connected to each other, and the cavity is filled with incompressible oil medium. According to Pascal's principle, the displacement of the two piston rods is inversely proportional to the square of the cylinder diameter ratio; the displacement of the small and large cylinder piston rods is used as the input and output of the displacement respectively. The displacement sensor measures the piston rod displacement h (input) of the small cylinder piston cylinder, and the piston rod displacement H (output) of the large cylinder piston cylinder is expressed as

[0010] H=(d / D) 2 *h

[0011] That is, the resolution of the displacement sensor is improved by (D / d) 2 For example, when the resolution of the displacement sensor is 0.1 mm, if D / d = 25, the resolution of the converted output is 0.004.

[0012] 2) Platform composition

[0013] A high-resolution photogrammetry dynamic displacement detection platform comprises a vibration isolation platform 1, a displacement sensor 2, a piston cylinder motion group, a photography platform 10, a moving system and a camera system, such as Figure 1 shown.

[0014] The vibration isolation platform 1 is used to carry other components of the high-resolution photogrammetry dynamic displacement detection platform. The piston cylinder motion group includes a small-diameter piston cylinder 5 and a large-diameter piston cylinder 7; the small-diameter piston cylinder 5 is installed on the vibration isolation platform 1 through a fixed base 4, and the piston rod of the small-diameter piston cylinder 5 is connected to the displacement sensor 2; the displacement sensor 2 is fixed on the vibration isolation platform 1 through a sensor flange 3; the large-diameter piston cylinder 7 is installed on the vibration isolation platform 1 through a fixed bracket 6, and is maintained in a vertical plane with the small-diameter piston cylinder 5; the cylinder bodies of the small-diameter piston cylinder 5 and the large-diameter piston cylinder 7 are connected to each other through a metal pipe 15; an oil pressure input pipe 14 is provided at the front end of the small-diameter piston cylinder 5, and the input oil pressure drives the piston of the small-diameter piston cylinder 5 to produce displacement; the moving system includes a sliding flange 9, a linear ball bearing 11 and a guide rod 12, and the large The piston rod of the cylinder piston cylinder 7 is connected to the sliding flange 9; the photographic platform 10 is fixedly mounted on the sliding flange 9; the sliding flange 9 is mounted on the linear guide rod 12 through a linear ball bearing 11, the photographic platform 10 can perform reciprocating linear motion on the guide rod 12, and the upper end surface of the photographic platform 10 is printed with a characteristic block for shooting; one end of the linear guide rod 12 is fixed on the guide rod support 8, and the other end is fixed on the base 13, and the guide rod support 8 is a support that can fine-tune the fixed height; the camera system includes a camera bracket column 16, a rotating table 17 and a camera 18, the camera bracket column 16 is fixed on the vibration isolation platform 1, the rotating table 17 is mounted on the camera bracket column 16, and the camera 18 is fixed on the rotating table 17, and is used to shoot the characteristic blocks on the photographic platform 10.

[0015] The beneficial effects of the present invention are as follows: the present invention adopts a conventional displacement sensor that is insensitive to environmental changes as a displacement detection reference, and improves the resolution of the output displacement through the pressure-motion conversion of the piston cylinder group. According to the slope of the straight line segment measured by photogrammetry and the slope of the straight line segment of the real displacement curve, the pixel equivalent can be inverted and corrected. The platform has a simple structure, low cost and simple operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a high-resolution dynamic displacement detection platform;

[0017] In the figure: 1 vibration isolation platform; 2 displacement sensor; 3 sensor flange; 4 fixed base; 5 small-diameter piston cylinder; 6 fixed bracket; 7 large-diameter piston cylinder; 8 guide rod support; 9 sliding flange; 10 photographic table; 11 linear ball bearing; 12 guide rod; 13 base; 14 oil pressure input pipe; 15 metal pipe; 16 camera bracket column; 17 rotating table; 18 camera; DETAILED DESCRIPTION

[0018] The present invention will be further described below in conjunction with the accompanying drawings.

[0019] A high-resolution photogrammetry dynamic displacement detection platform comprises a vibration isolation platform 1, a displacement sensor 2, a sensor flange 3, a fixed base 4, a small-diameter piston cylinder 5, a fixed bracket 6, a large-diameter piston cylinder 7, a guide rod support 8, a sliding flange 9, a photographic table 10, a linear ball bearing 11, a guide rod 12, a base 13, an oil pressure input pipe 14, a metal pipe 15, a camera bracket column 16, a rotating table 17 and a camera 18.

[0020] The vibration isolation platform 1 is made of cast iron, which has a better vibration isolation effect.

[0021] The displacement sensor 2 is an LVDT displacement sensor with an accuracy of 0.1% and a measuring range of 100 mm.

[0022] The small-diameter piston cylinder 5 and the large-diameter piston cylinder 7 can be selected as AirTac single-rod standard cylinders, and the specifications are selected as d=8mm (stroke 100mm) and D=32mm (stroke 25mm) respectively.

[0023] The displacement detection is carried out using the above-mentioned high-resolution dynamic displacement detection platform, including the following steps:

[0024] The first step is to adjust the shooting field of view and shooting distance of the camera 18, and fix the camera system to perform static shooting, and calculate the approximate pixel equivalent based on the static image.

[0025] The second step is to pre-adjust the flow rate of the small piston cylinder oil pressure input pipe 14 according to the pixel equivalent of the camera system and the ratio of the large and small piston cylinder diameters (i.e., the resolution conversion coefficient), and observe the displacement rate of the displacement sensor 2 to make its displacement change rate within a suitable range;

[0026] The third step is to start the camera 18 and the displacement sensor 2 at the same time and record the collected data. Observe the displacement-time curve of the photogrammetry. Once a straight line segment appears on the curve, the starting point of the straight line segment is the minimum displacement capture amount of the camera system, that is, the displacement resolution.

[0027] The fourth step is to compare the difference in the slope of the straight line segment of the displacement-time curve of the photogrammetry and the real displacement-time curve of the photography platform 10 (converted by the displacement sensor 2), and invert and correct the real pixel equivalent of the camera system according to the slope difference multiple. Repeat this process to continuously approach the most accurate pixel equivalent size and improve the accuracy of photogrammetry;

[0028] The fifth step is to repeat the third step after obtaining the accurate pixel equivalent to obtain the displacement resolution under the current flow rate of the oil pressure input pipe 14; gradually increase the flow rate, repeat the test, and obtain the resolution distribution under different displacement rates.

Claims

1. A high-resolution photogrammetry dynamic displacement detection platform, characterized in that: The vibration isolation platform (1) is used to carry other components of a high-resolution photogrammetry dynamic displacement detection platform; the piston cylinder motion group comprises a small-diameter piston cylinder (5) and a large-diameter piston cylinder (7); the small-diameter piston cylinder (5) is mounted on the vibration isolation platform (1) via a fixed base (4), and the piston rod of the small-diameter piston cylinder (5) is connected to a displacement sensor (2); the displacement sensor (2) is fixed to the vibration isolation platform (1) via a sensor flange (3); the large-diameter piston cylinder (7) is mounted on the vibration isolation platform (1) via a fixed bracket (6), and is maintained in a vertical plane with the small-diameter piston cylinder (5); the cylinder bodies of the small-diameter piston cylinder (5) and the large-diameter piston cylinder (7) are connected to each other via a metal pipe (15); an oil pressure input pipe (14) is provided at the front end of the small-diameter piston cylinder (5), and the input oil pressure drives the piston of the small-diameter piston cylinder (5) to generate displacement; the moving system comprises a sliding flange (9), a linear ball shaft The large-diameter piston cylinder (7) is provided with a bearing (11) and a guide rod (12), wherein the piston rod of the large-diameter piston cylinder (7) is connected to the sliding flange (9); the photographic table (10) is fixedly mounted on the sliding flange (9); the sliding flange (9) is mounted on the linear guide rod (12) through a linear ball bearing (11); the photographic table (10) can perform reciprocating linear motion on the guide rod (12), and a feature block for photographing is printed on the upper end surface of the photographic table (10); one end of the linear guide rod (12) is fixed to the guide rod (11) and the other end is fixed to the guide rod (12). The guide rod support (8) is fixed at one end, and the other end is fixed on the base (13); the guide rod support (8) is a support with a finely adjustable fixed height; the camera system comprises a camera support column (16), a rotating table (17) and a camera (18); the camera support column (16) is fixed on the vibration isolation platform (1), the rotating table (17) is installed on the camera support column (16), and the camera (18) is fixed on the rotating table (17) for photographing feature blocks on the photography platform (10).

Images