CN105953749B - A kind of optical 3-dimensional topography measurement method - Google Patents

Abstract

An optical three-dimensional shape measurement method. First, according to the actual measurement requirements, a measurement system consisting of a projection system and a camera is arranged; then a fringe pattern is designed according to the measurement requirements and projected by the projection system onto the surface of the measured object. The fringes reflected by the object The image is sampled by the camera; then the wrapped phase is demodulated from the sampled fringe image, and the real phase value of the fringe image is obtained after unwrapping; then the measured value is obtained by solving the magnification of the telecentric lens, the pixel size of the camera and the image coordinates of the sampled fringe image X and Y axis coordinates of the object; the relevant parameters of the projection system are finally calibrated, combined with the fringe phase, and the coordinates of the Z axis of the measured object are obtained according to the triangular relationship; the calibration process of the invention is simple, which not only improves the solution speed of the three-dimensional coordinates but also achieves Higher measurement accuracy; one calibration can ensure the use of all subsequent measurements, and the efficiency is very high.

Description

An optical three-dimensional shape measurement method

technical field

The invention belongs to the technical field of three-dimensional measurement, and in particular relates to an optical three-dimensional shape measurement method.

Background technique

Three-dimensional measurement has a wide range of requirements in rapid prototyping and quality inspection. At the same time, it is also widely used in reverse engineering, medical and other fields. The traditional three-dimensional measurement method is mainly contact measurement, such as three-coordinate measuring machine. With the advancement of optical technology, optical three-dimensional measurement technology has been greatly developed, and is more and more widely used in three-dimensional measurement. Typical optical three-dimensional measurement methods include laser scanning measurement, line laser scanning measurement, structured light projection measurement and interferometry. Among them, the structured light projection three-dimensional measurement method based on sinusoidal fringe projection is a very superior three-dimensional measurement method due to its advantages of convenient operation, high measurement accuracy, fast measurement speed, and good adaptability.

The sinusoidal fringe projection three-dimensional measurement profilometry needs to project the sinusoidal fringe onto the surface of the measured object, and the reflected fringe image is sampled by the camera. After solving the phase of the sampled fringe, combined with the measurement system parameters obtained by calibration, the three-dimensional shape of the measured object can be recovered from the phase. appearance. The existing sinusoidal fringe projection three-dimensional measurement profilometry has the following characteristics: the phase of the projected sinusoidal fringe pattern changes linearly along a certain direction in the entire image plane; in the measurement system composed of a single camera and a single projector, the phase to The transformation of the three-dimensional shape of the measured object always uses the triangular relationship between the projection light and the camera sampling light. In many cases, a reference surface is required, and the three-dimensional solution process is complicated.

Contents of the invention

In order to overcome the above-mentioned shortcomings of the prior art, the object of the present invention is to provide an optical three-dimensional shape measurement method, which simplifies the process of solving the three-dimensional shape, improves the speed and accuracy of solving X and Y coordinates, and makes the calibration process simple. Higher measurement accuracy, and can ensure the use of all subsequent measurements after one system calibration, improving measurement efficiency.

In order to achieve the above object, the technical scheme that the present invention takes is:

An optical three-dimensional shape measurement method, comprising the following steps:

Step 1: According to the actual measurement requirements, arrange the measurement system consisting of projection system and camera;

Step 2: Design the projected circular fringe pattern according to the measurement needs and project it onto the surface of the measured object by the projection system;

Step 3: The fringe pattern reflected by the object is sampled by the camera;

Step 4: demodulate the wrapped phase from the sampled fringe pattern, and obtain the real phase value of the fringe pattern after unwrapping;

Step 5: Obtain the X and Y axis coordinates of the measured object by solving the magnification of the telecentric lens, the size of the camera pixel and the image coordinates of the sampling fringe pattern;

Step 6: Calibrate to obtain the relevant parameters of the projection system, combine the fringe phase, and obtain the coordinates of the Z-axis of the measured object according to the triangular relationship formed by the projection light and the projection optical axis.

The projection system in step 1 is a digital projector, or a projection system composed of a point light source, a grating, and a photomask. object, and the projection optical axis and the camera optical axis need to be kept parallel.

The camera in step 1 is equipped with a telecentric lens, and the parameters of the telecentric lens are selected according to actual measurement requirements.

The gray value distribution of the projected circular fringe image in step 2 needs to satisfy:

f(x _p ,y _p )=a+bcos(2π·r(x _p ,y _p )/R) (1)

Among them, (x _p , y _p ) represents the pixel coordinates of the projected fringe image, a represents the fringe background item, b represents the fringe amplitude, R is the fringe period represented by the pixel distance, and

Among them, (x _p0 , y _p0 ) represents the intersection point of the projection array and the optical axis of the projection system, which is preliminarily considered to be the geometric center of the projection array.

The phase demodulation in step 4 adopts the classical phase demodulation method, and the phase unwrapping adopts the classical phase unwrapping method.

In the described step 5, the X and Y axis coordinates of the measured object are obtained by the following formula:

Where: (x _c , y _c ) is the sampled image coordinates, β is the magnification of the telecentric lens, and s is the pixel size of the camera.

The solution formula of the Z coordinate of the measured object in the described step 6 is:

Among them, R is the circular fringe period represented by the pixel distance, p is the projection system parameter, Φ(x _c , y _c ) is the phase value of the sampled image point (x _c , y _c ), d(x _c , y _c ) is the spatial distance between the point (x _c , y _c ) on the sampling image and the zero-phase point, calculated by the following formula:

Among them, s is the pixel size of the camera, (x _c0 , y _c0 ) is the pixel coordinate of the zero phase point of the sampling fringe image, and β is the magnification of the telecentric lens.

Compared with the traditional sinusoidal fringe projection three-dimensional measurement profilometry, the present invention has the following beneficial effects: no need to calibrate the camera; the solution of the X and Y coordinates of the measured object is greatly simplified compared with the traditional method, which greatly improves the X , The solution speed of the Y coordinate can also guarantee the solution accuracy; the calibration parameters involved in the solution of the Z coordinate of the measured object are less, the calibration process is simple, the source of the measurement error is less, and a higher measurement accuracy can be achieved; when the focal length of the projector is determined Finally, one calibration can ensure the use of all subsequent measurements, which is extremely efficient.

Description of drawings

Fig. 1 is a schematic structural diagram of a measurement system used in the method of the present invention.

Fig. 2 is a schematic diagram of the method of the present invention.

Fig. 3 is a circular fringe diagram used in the present invention.

Fig. 4 is the fringe pattern obtained by simulating the projection of the fringe pattern in Fig. 3 to the spherical surface to be tested.

FIG. 5 is a demodulation phase diagram of the fringe pattern in FIG. 4 .

FIG. 6 is an unwrapped phase diagram of the fringe pattern in FIG. 4 .

Fig. 7 shows the three-dimensional shape of the measured object restored by the method of the present invention.

Fig. 8 is a three-dimensional topography diagram after processing in Fig. 7 .

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

An optical three-dimensional shape measurement method, comprising the following steps:

Step 1: According to the actual measurement requirements, arrange a measurement system consisting of a projection system and a camera equipped with a telecentric lens. Referring to Figure 1, in the measurement system, the optical axis of the projection system and the optical axis of the camera are equivalently collinear through the optical path design. In actual use, the optical axis of the projection system and the optical axis of the camera do not have to be collinear. The measurement principle is shown in Figure 2, where ON is the optical axis of the projection system, point B is the intersection point between the optical axis of the projection system and the projection pixel array, from The light emitted by the light source O is projected onto the point M on the measured object through the projection pixel at A, MN is a line segment perpendicular to the projection optical axis, and point N is a virtual point, which does not need to be obtained in practice, as shown in Figure 2 The Z coordinate used in the 3D reconstruction is also indicated. Let the coordinate value of point M on the sampling image be (x _c , y _c ), and the length of the line segment MN be d(x _c , y _c ), defined in the illustration Next, the Z coordinate of point M is

Since ΔOAB∽ΔOMN,

thus,

In reality The value of is obtained by calibration, and is set in this embodiment:

Step 2: Design the projected circular fringe pattern according to the measurement needs and project it onto the surface of the measured object by the projection system. The projected circular fringe pattern used is shown in Figure 3. Unlike the traditional sinusoidal fringe pattern, its phase is not in the entire image It changes linearly along a specific direction in the plane, but radiates linearly outward from the center of the image, so it looks like a set of light and dark rings. The period of the fringe in the illustration is 10 pixels, and the projection system is used to project the fringe onto The surface of the object to be measured;

Step 3: The fringe pattern reflected by the object is sampled by a camera equipped with a telecentric lens, refer to Figure 4, which is the fringe pattern obtained by analog sampling;

Step 4: demodulate the sampled fringe phase image using the four-step phase shift method to obtain the wrapping phase of the fringe image shown in Figure 4, as shown in Figure 5, use the multi-frequency unwrapping technology to unwrap the wrapped phase shown in Figure 5, The unwrapped phase is shown in Figure 6, and its value is set to Φ(x _c , y _c );

Step 5: Solve the X and Y axis coordinates of the measured object from the magnification of the telecentric lens, the size of the camera pixel and the image coordinates of the sampling fringe pattern, set the magnification of the telecentric lens to β=0.1, and the pixel size of the camera to s= 0.005mm, then the horizontal coordinates corresponding to the sampling point M can be easily obtained:

Step 6: Calibrate to obtain the relevant parameters of the projection system, set the pixel size of the projector to 0.005mm, then there is

Combined with the fringe phase, the coordinates of the Z-axis of the measured object are obtained according to the triangular relationship,

The three-dimensional shape of the simulated measured object obtained by the final solution is shown in Figure 7. In order to see the three-dimensional shape of the measured object more clearly, subtract the data in Figure 7 from the maximum height 1990 of the simulated measured object, and the three-dimensional shape of the measured object drawn at this time is shown in Figure 8. It can be seen that The invention can realize the measurement of the three-dimensional profile of the measured object very conveniently.

The above description is only an embodiment of the present invention, and is not intended to limit the present invention. Any modification, equivalent replacement and expansion made on the basis of the present invention shall be included in the protection scope of the present invention.

Claims (5)

1. a kind of optical 3-dimensional topography measurement method, which comprises the following steps:

Step 1: being required according to actual measurement, arrange the measuring system being made of optical projection system, camera；

Step 2: needing to design projection circle bar graph according to measurement and by projection systems project to testee surface；

Step 3: the bar graph being reflected by the object is sampled by camera；

Step 4: recalling wrapped phase from sampling striped diagram, the true phase value of bar graph is obtained after unpacking；

Step 5: being solved and be tested by the image coordinate of the enlargement ratio of telecentric lens, camera Pixel size and sampling bar graph Object X, Y axis coordinate；

Step 6: calibration obtains the relevant parameter of optical projection system, in conjunction with fringe phase, according to by projection ray and projection optical axis structure At triangle relation acquire the coordinate of testee Z axis；

The solution formula of testee Z coordinate is in the step 6

Wherein, R is the circle fringe period indicated with pixel distance, and p is optical projection system parameter, Φ (x_c,y_c) it is sample graph picture point (x_c,y_c) phase value, d (x_c,y_c) it is point (x on sampled images_c,y_c) and phase zero points between space length, pass through following public Formula calculates:

Wherein, s is camera pixel dimension, (x_c0,y_c0) it is the pixel coordinate for sampling bar graph phase zero points, β is put for telecentric lens Big multiplying power.

2. a kind of optical 3-dimensional topography measurement method according to claim 1, it is characterised in that: in the step 1 Optical projection system is the optical projection system that digital projector or point light source and grating, photomask board form, and projected image is in range It inside wants that measurand can be covered but cannot too much be more than measurand, and projection optical axis and camera optical axis need to keep flat Row.

3. a kind of optical 3-dimensional topography measurement method according to claim 1, it is characterised in that: in the step 1 Camera is furnished with telecentric lens, and the parameter of telecentric lens is selected according to actual measurement demand.

4. a kind of optical 3-dimensional topography measurement method according to claim 1, it is characterised in that: in the step 2 Circle bar graph is projected, grey value profile needs to meet:

f(x_p,y_p)=a+bcos (2 π r (x_p,y_p)/R) (1)

Wherein, (x_p,y_p) indicating that projection round bar print image element coordinate, a indicate striped background item, b indicates streak amplitude, and R is with picture The circle fringe period that element distance indicates, and

Wherein, (x_p0,y_p0) indicate projected array and optical projection system optical axis intersection point, it was initially believed that the point is the geometry of projected array Center.

5. a kind of optical 3-dimensional topography measurement method according to claim 1, it is characterised in that: quilt in the step 5 Survey object X, Y axis coordinate is acquired using following formula:

Wherein: (x_c,y_c) it is sampled images coordinate, s is camera pixel dimension, and β is telecentric lens enlargement ratio.