A three-dimensional measurement method based on amplitude modulation segmented phase encoding

Abstract

The application discloses a three-dimensional measurement method based on amplitude modulation segmented phase encoding, which comprises the following steps: firstly, four computer-generated sinusoidal fringe patterns and four amplitude-modulated segmented phase encoding fringe patterns are generated; secondly, the wrapped phase can be solved from the four computer-generated sinusoidal fringe patterns, two sets of fringe orders can be respectively solved from the four amplitude-modulated phase encoding fringe patterns, and the plane and the absolute phase of the object can be solved together with the wrapped phase; finally, the real three-dimensional information of the object can be obtained through a phase-height model conversion formula; the method can obtain two sets of fringe order information through one set of amplitude-modulated segmented phase encoding fringe patterns without adding an additional set of phase encoding projection patterns, thereby performing relationship matching to obtain complete fringe orders, more code words can be obtained, and the measurement speed and precision are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of optical three-dimensional measurement method, belongs to photoelectric detection technical field, specifically related to a kind of three-dimensional measurement method based on amplitude modulation segmented phase encoding. BACKGROUND

[0002] Structured light three-dimensional measurement is a kind of technology using structured light illumination to obtain the three-dimensional shape of object, which is widely used in industrial product detection, reverse engineering, robot vision, experimental mechanics, biomedical and other fields. It projects one or more specific coded fringe patterns onto the surface of the object, and uses an imaging device to record the deformation of these fringe patterns from different angles, thereby obtaining the three-dimensional information of the object.

[0003] With the rapid development of modern industry and information technology, the speed and accuracy of three-dimensional measurement of objects are increasingly demanding. Traditional phase encoding method requires at least six images to obtain absolute phase, but due to the fact that traditional phase encoding method is prone to errors when the number of code words is large, researchers have proposed segmented phase encoding method. For example, double-step phase encoding method requires an additional set of phase encoding fringe patterns to connect the segmented fringe orders, increasing the number of projected fringe patterns. Later, scholars proposed quantized phase encoding method to solve the problem of too few code words in traditional method, but still need to project additional fringe patterns to solve the final fringe order. Therefore, how to use fewer projected fringe frames to solve the absolute phase of the measured object has become a breakthrough.

[0004] The present application proposes a segmented phase encoding three-dimensional measurement method based on amplitude modulation, which does not require an additional set of phase encoding fringe patterns to connect the segmented fringe orders, reduces the number of projected fringe patterns, improves the measurement speed, and has potential application prospects and practical value in the field of fast measurement. SUMMARY

[0005] The purpose of the present application is to provide a segmented phase encoding three-dimensional measurement method based on amplitude modulation, which modulates the amplitude based on the traditional segmented phase encoding method, thereby eliminating the need for an additional set of phase encoding fringe patterns to connect the segmented fringe orders, generating more code words, and reducing the time and speed of measurement. It has potential application prospects and practical value in the field of three-dimensional measurement of complex objects.

[0006] To achieve the above purpose, the technical solution provided by the present application is as follows: a segmented phase encoding three-dimensional measurement method based on amplitude modulation, comprising the following steps:

[0007] Step 1: generate four sinusoidal fringe patterns and four segmented phase encoding fringe patterns with amplitude modulation using a computer;

[0008] Step two: obtain wrapped phase, segmented fringe order and modulated amplitude value by using eight fringe patterns captured by camera;

[0009] Step three: combine segmented fringe order and modulated amplitude value, connect into final continuous fringe order, and then obtain absolute phase of plane and object;

[0010] Step four: obtain real three-dimensional information of object to be measured by using phase-height conversion formula again according to obtained absolute phase.

[0011] Further, the four segmented phase-encoding fringe patterns with amplitude modulation in step one refer to embedding four-level fringe amplitude into traditional segmented phase-encoding fringe patterns as an encoding strategy on the basis of traditional segmented phase-encoding fringe patterns.

[0012] Further, the segmented fringe order in step two is two groups of fringe orders, one group of fringe orders is segmented phase-encoding information, and the second group of fringe orders is four-level fringe amplitude information, the corresponding relationship formed by the two groups of fringe orders can form the final segmented fringe order, and the modulated amplitude value in step two is the second group of fringe order information.

[0013] Further, the four sinusoidal fringe patterns generated by computer in step one are represented as I1(x,y), I2(x,y), I3(x,y) and I4(x,y) respectively, and the optical expressions of the four patterns are respectively:

[0014]

[0015] Wherein A(x,y) is background light intensity, B(x,y) is modulation intensity, is ideal phase information, which is generally expressed by the following formula:

[0016]

[0017] Wherein N is the number of fringe periods.

[0018] Further, the four segmented phase-encoding fringe patterns with amplitude modulation generated by computer in step one are represented as I5(x,y), I6(x,y), I7(x,y) and I8(x,y) respectively, and the optical expressions of the four patterns are respectively:

[0019]

[0020] Wherein B S (x,y) is the amplitude distribution along the phase shift direction, the values set by the application are 0.3, 0.5, 0.2 and 0.4, and the reason for setting in this way is that the discrimination degree between amplitudes can be increased in the experimental process, For the S-shaped coded phase, the application is set to 4-step cyclic phase coding.

[0021] Further, the wrapped phase and the segmented fringe order in step two are obtained by using eight captured fringe patterns by the camera, and the specific solving process is as follows:

[0022] Wrapped phase:

[0023] Segmented fringe order: I5(x, y), I6(x, y), I7(x, y) and I8(x, y) can be solved to obtain two groups of fringe orders K1 and K2, wherein K2 refers to the amplitude value of the modulation, wherein:

[0024]

[0025] The relationship of K1 and K2 can obtain the complete fringe order, the result of K1 solving is distributed in (-π, π), and the result of K2 solving is set to 0.3, 0.5, 0.2 and 0.4; in order to express clearly in the subsequent, since the four-step S-shaped segmented phase coding is set, K1 is quantized to (1, 4), so that it is distributed in (1, 4), and K2 is multiplied by 10, so that the result is 3, 5, 2 and 4.

[0026] Further, the segmented fringe order is connected into the final continuous fringe order in step three, and the complete fringe order K composed of K1 and K2 is shown in Table 1:

[0027] Table 1

[0028] [K1] 1 2 3 4 4 3 2 1 1 2 3 4 4 3 2 1 [K2] 3 3 3 3 5 5 5 5 2 2 2 2 4 4 4 4 K 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

[0029] The final absolute phase can be obtained from the fringe order K and the wrapped phase

[0030]

[0031] Further, the phase-height conversion formula in step four is shown as follows:

[0032]

[0033] Wherein f0 is the sine fringe frequency on the reference plane, Δφ is the absolute phase difference between the surface of the measured object and the corresponding point of the reference plane, d is the distance between the projector and the camera, and L is the distance from the projector and the camera to the reference plane; from the conversion formula, the real three-dimensional information of the measured object can be obtained.

[0034] The beneficial effects of the application are:

[0035] ​1. The present application can obtain two sets of fringe order information through a set of amplitude-modulated segmented phase-encoding fringe patterns, thereby connecting into the final continuous fringe order, reducing the number of projected fringe patterns, expanding the code word, and improving the measurement speed and accuracy.

[0036] 2. In the present application, phase is used instead of intensity to determine the code word, which is not sensitive to surface contrast, environmental light and camera noise, and has strong robustness.

[0037] 3. In the present application, only one set of amplitude-modulated phase-encoding fringe patterns can obtain two sets of fringe orders, which to some extent reduces the error rate. BRIEF DESCRIPTION OF DRAWINGS

[0038] Figure 1 A schematic diagram of a measurement system for three-dimensional measurement in the present application;

[0039] Figure 2 Four sinusoidal fringe patterns and four amplitude-modulated segmented phase-encoding fringe patterns in the present application, wherein (a) is I1-I4 and (b) is I5-I8;

[0040] Figure 3 The wrapped phase of the four sinusoidal fringe patterns and the four amplitude-modulated segmented phase-encoding fringe patterns in the present application after solving Fringe order K1 and fringe order K2;

[0041] Figure 4 Fringe order K1 and fringe order K2 and the final fringe order K in the present application.

[0042] Figure 5 The absolute phase map of the simulation plane in the embodiment of the present application.

[0043] LIST OF ELEMENTS

[0044] 1-DLP projector, 2-CCD camera, 3-computer, 4-measuring support, 5-reference plane, 6-object to be measured. DETAILED DESCRIPTION

[0045] The examples of the present application are further described in detail below in conjunction with the accompanying drawings, but the examples are not used to limit the present application, and any similar coding strategy and similar changes thereof that adopt the present application shall be included in the protection scope of the present application.

[0046] Example 1

[0047] A three-dimensional measurement system of an amplitude-modulated segmented phase-encoding three-dimensional measurement method of the present application is as follows Figure 1As shown, including DLP projector 1, CCD camera 2, computer 3, measuring support 4, reference plane 5 and the object to be measured 6.

[0048] DLP projector 1 and CCD camera 2 are placed on the measuring support 4; DLP projector 1, CCD camera 2 are connected to computer 3 through data line respectively; the object to be measured 6 is placed on the reference plane 5; computer 3 contains image acquisition card, projection software, measurement software.

[0049] DLP projector 1 projects the characteristic information of the stripe to the surface of the object to be measured 6, and the stripe information is collected by CCD camera 2, and the characteristic information is extracted after being processed by computer 3, and three-dimensional reconstruction is carried out according to a specific algorithm.

[0050] Embodiment 2

[0051] Reference Figures 2-5 The application is a segmented phase encoding three-dimensional measurement method based on amplitude modulation, and the steps are as follows:

[0052] Step one, four sinusoidal stripe images and four amplitude modulation segmented phase encoding stripe images are generated by computer, the four sinusoidal stripe images generated by computer are represented as I1(x,y), I2(x,y), I3(x,y) and I4(x,y) respectively, and the optical expressions of the four images are as follows:

[0053]

[0054] Wherein A(x,y) is background light intensity, B(x,y) is modulation intensity, is ideal phase information, which is generally expressed by the following formula:

[0055]

[0056] Wherein N is the number of stripe periods;

[0057] The four amplitude modulation segmented phase encoding stripe images generated are represented as I5(x,y), I6(x,y), I7(x,y) and I8(x,y), and the optical expressions of the four images are as follows:

[0058]

[0059] Wherein B S (x,y) is the amplitude distribution along the phase shift direction, the application sets the value to 0.3, 0.5, 0.2 and 0.4, and the reason for such setting is to increase the distinguishability in the experiment, is S-shaped encoding phase, and the application sets it as 4-step cyclic phase encoding;

[0060] Step 2: Using the eight fringe patterns captured by the camera, determine the wrapping phase, the segmented fringe order, and the modulation amplitude. The wrapping phase generated by the four sinusoidal fringes is as follows:

[0061]

[0062] The two sets of fringe orders obtained from the segmented phase-coded fringe pattern of four amplitude modulations are:

[0063]

[0064] Step 3: Due to the four-step S-shaped segmented phase encoding, K1 is quantized to (1,4), distributing it between (1,4). K2 is multiplied by 10, resulting in 3,5,2,4. The segmented fringe order and the modulation amplitude value are combined to form the final continuous fringe order. The complete fringe order K relationship formed by K1 and K2 is shown in Table 1 below:

[0065] Table 1

[0066] [K1] 1 2 3 4 4 3 2 1 1 2 3 4 4 3 2 1 [K2] 3 3 3 3 5 5 5 5 2 2 2 2 4 4 4 4 K 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

[0067] Composed of stripe order K and wrapping phase The final absolute phase can be obtained:

[0068]

[0069] The phase-height conversion formula described in step four is as follows:

[0070]

[0071] Where f0 is the sinusoidal fringe frequency on the reference plane, Δφ is the absolute phase difference between corresponding points on the surface of the object under test and the reference plane, d is the distance between the projector and the camera, and L is the distance from the projector and the camera to the reference plane. From this formula, the true three-dimensional information of the object under test can be obtained.

Claims

1. A three-dimensional measurement method based on amplitude modulation and segmented phase encoding, characterized in that, Includes the following steps: Step 1: Use a computer to generate four sinusoidal fringe patterns and four segmented phase-coded fringe patterns with amplitude modulation; Step 2: Use the eight fringe patterns captured by the camera to determine the wrapping phase, segmented fringe order, and modulation amplitude. Step 3: Combine the segmented fringe order with the modulation amplitude value to form the final continuous fringe order, thereby obtaining the absolute phase of the plane and the object; Step 4: Using the obtained absolute phase, the phase-height conversion formula is used to obtain the true three-dimensional information of the object under test; The four amplitude-modulated segmented phase-coded fringe patterns in step one refer to the traditional segmented phase-coded fringe patterns, in which the fringe amplitude is divided into four levels as an encoding strategy and embedded into the traditional segmented phase-coded fringe patterns. The segmented fringe levels in step two consist of two sets of fringe levels. One set of fringe levels is segmented phase coding information, and the second set of fringe levels is fringe amplitude information divided into four levels. The correspondence between these two sets of fringe levels can form the final segmented fringe levels. Furthermore, the amplitude value modulated in step two is the information of the second set of fringe levels. The four sine fringe patterns generated by the computer in step one are represented as follows: , The optical expressions for its four diagrams are as follows: (1) (2) (3) (4) in Background light intensity, For modulation intensity, For ideal phase information, it is expressed by the following formula: (5) Where N is the number of stripe periods; The four amplitude-modulated segmented phase-coded fringe patterns generated by the computer in step one are represented as follows: , The optical expressions for its four diagrams are as follows: (6) (7) (8) (9) in To represent the amplitude distribution along the phase shift direction, values ​​of 0.3, 0.5, 0.2, and 0.4 were set. This setting was chosen to increase the discriminative power between amplitudes during the experiment. The S-shaped coding phase is set to a cyclic phase coding with 4 steps; The specific solution process for obtaining the wrapping phase and piecewise fringe order using the eight fringe patterns captured by the camera in step two is as follows: Package Phase: (10) Segmented stripe levels: , , and Two sets of fringe orders K1 and K2 can be solved, where K2 refers to the modulation amplitude value, and: (11) (12) The relationship between K1 and K2 can yield the complete fringe order, and the result of solving K1 is distributed in... Between these values, the results of K2 are set to 0.3, 0.5, 0.2 and 0.4; for clarity in subsequent expressions, due to the four-step S-shaped segmented phase encoding, K1 is quantized to (1,4) so ​​that it is distributed between (1,4), and K2 is multiplied by 10 so that its result is 3,5,2,4; In step three, the segmented fringe orders are connected into a final continuous fringe order. The complete fringe order K relationship formed by K1 and K2 is shown in Table 1 below: Table 1 Composed of stripe order K and wrapping phase The final absolute phase can be obtained: (13)。 2. The three-dimensional measurement method based on amplitude modulation and segmented phase encoding according to claim 1, characterized in that: The phase-height conversion formula described in step four is as follows: (14) in For the frequency of the sinusoidal fringes on the reference plane, The absolute phase difference between corresponding points on the surface of the object under test and the reference plane. The distance between the projector and the camera. The distances from the projector and camera to the reference plane are given by the formula; from this formula, the true three-dimensional information of the object under test can be obtained.

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