A two-dimensional positioning method for light source markers based on mask cross projection

Abstract

The present invention discloses a two-dimensional positioning method of a light source mark based on mask cross projection, comprising the following steps: fixing a light emitting element on a positioning target, replacing the optical lens of a traditional camera with two dot matrix masks with different focal lengths and shooting with the replaced camera; projecting the dot matrix pattern etched on the mask onto the image plane under the illumination of the light emitting element and performing distortion correction to obtain a low-frequency moiré pattern, and constructing a moiré pattern function based on the moiré pattern; periodically labeling and internally calibrating the moiré pattern function to solve a waveform function, determining the light source position based on the waveform function, and obtaining the positioning target position according to the light source position. The positioning target can be accurately positioned by the above method.

Description

Technical Field

[0001] The invention belongs to the field of positioning technology, and in particular relates to a two-dimensional positioning method of a light source mark based on mask cross projection. Background Art

[0002] One of the existing technologies is precision motion measurement based on computer micro-vision. After the digital image sequence is captured by the microscopic vision system, the image processing algorithm used for precision motion measurement can track the target at the micro-scale / nano-scale. There are two main types:

[0003] (1) Optical microscopic vision system: An optical microscopic vision system is constructed based on OMs to observe the target through transmitted light. All OMs are composed of the same basic optical path components, namely, a visible light source, a focus knob, a stage, a wheel, and an optical lens system. Combined with an image sensor, a digital image sequence can be obtained and then sent to a computer for further processing.

[0004] (2) Electron microscopic vision system: Compared with the optical microscopic vision system, the electron microscopic vision system has no optical diffraction limit. The electron microscopic vision system includes EM, which uses a shaped magnetic field to form an electron optical lens system and an accelerated electron beam as an illumination source to generate images.

[0005] However, the targets that can be observed by the microscopic vision system are limited, and there are problems with noise interference and time delay. The speed and noise robustness of the small-scale motion measurement algorithm are still insufficient. Summary of the invention

[0006] In order to solve the above technical problems, the present invention proposes a two-dimensional positioning method of a light source mark based on mask cross projection to solve the problems existing in the above prior art.

[0007] To achieve the above object, the present invention provides a two-dimensional positioning method for light source marks based on mask cross projection, comprising the following steps:

[0008] Fix the light-emitting element on the positioning target, replace the optical lens of the traditional camera with two dot matrix masks with different focal lengths, and take pictures through the replaced camera;

[0009] The dot matrix pattern etched on the mask is projected onto the image plane under the illumination of the light-emitting element and distortion correction is performed to obtain a low-frequency moiré pattern, and a moiré pattern function is constructed based on the moiré pattern;

[0010] The moiré pattern function is periodically labeled and internally calibrated to obtain a waveform function, the light source position is determined based on the waveform function, and the positioning target position is obtained according to the light source position.

[0011] Preferably, the expression for the bright spot array obtained by projecting the etched dot pattern on the mask onto the image plane is:

[0012]

[0013] Where F is a function with a period of 2π, e g To align the error, ω M is the angular velocity of the bright spot array, ψ M1 is the phase of the bright spot array in the x direction, ψ M2 is the phase of the bright spot array in the y direction.

[0014] Preferably, the relationship between the etching point on the mask and the image point on the image plane is expressed as:

[0015]

[0016] Where, d L is the coordinates of the light source to the first mask, x1, x2 are the projection coordinates, x L is the light source coordinate, s represents the distance between the front dot matrix mask and the rear dot matrix mask, and h is the distance from CCD to the rear mask.

[0017] Preferably, the projection pattern function is obtained by combining the expression of the bright spot array and the relationship between the etching points on the mask and the image plane points on the image plane. The projection pattern function is:

[0018]

[0019] In the formula, ω M is the angular velocity of the bright spot array, ψ M1 is the phase of the bright spot array in the x direction, ψ M2 is the phase of the bright spot array in the y direction, Z L is the distance from the light source to the CCD.

[0020] Preferably, the expression of the moiré pattern function is:

[0021]

[0022] Where I is the moiré function expression, ω A is the angular velocity of the moiré pattern function, u is the coordinate in the image, Ψ Ax is the phase of the moiré pattern function in the x direction, Ψ Ay is the phase of the moiré pattern function in the y direction.

[0023] Preferably, in the periodic numbering process, a control point is set at the m+m2th phase zero point of the front mask, and control points are set at the m+m2th and m+m3th phase zero points of the rear mask, respectively, and the control points satisfy the following expression:

[0024]

[0025] In the formula, k∈[0,1),X i Indicates the coordinate position.

[0026] Preferably, the method for internal reference calibration includes:

[0027] The image data of the light source is collected at different positions by using a grating ruler, and the image data is converted into an optimization objective function. The optimization objective function is differentiated to obtain the extreme points and converted into a matrix form; the expression in matrix form is solved by the least squares method to obtain the parameter value.

[0028] Preferably, the expression for obtaining the extreme value point by derivation is:

[0029]

[0030] In the formula, w n is the angular velocity w of the moiré pattern function A The subscript is replaced by the sampling number n, and u is the coordinate position in the image. ψ n is the phase of the moiré pattern function with sampling number n.

[0031] Compared with the prior art, the present invention has the following advantages and technical effects:

[0032] The present invention discloses a two-dimensional positioning method of light source marking based on mask cross projection, in which the optical lens of a traditional camera is replaced with two dot matrix masks with slightly different focal lengths, and the light-emitting element is fixed on the positioning target. The dot matrix pattern etched on the mask is projected onto the image plane under the illumination of the light-emitting element, and the mask cross projection produces a low-frequency moiré pattern. The change in the position of the light source causes the two dot matrix patterns with similar frequencies generated by the projection of the two masks to be superimposed and produce a rapidly changing moiré interference pattern. An imaging model is established based on the light source position and the dot matrix mask projection, and then the waveform function is periodically labeled to solve the waveform function to determine the light source position. The introduction of moiré acceleration to amplify the movement of the object for two-dimensional spatial positioning, and the introduction of periodic labeling to analyze the waveform function to locate the light source position can accurately locate the positioning target. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0034] Figure 1 An imaging model diagram of an embodiment of the present invention;

[0035] Figure 2A refraction model diagram of a mask according to an embodiment of the present invention;

[0036] Figure 3 The figure is a flow chart of a method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0037] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0038] It should be noted that the steps shown in the flowcharts of the accompanying drawings can be executed in a computer system such as a set of computer executable instructions, and that, although a logical order is shown in the flowcharts, in some cases, the steps shown or described can be executed in an order different from that shown here.

[0039] Embodiment 1

[0040] like Figure 1-3 As shown, this embodiment provides a two-dimensional positioning method for light source marks based on mask cross projection, including:

[0041] 1. Hardware configuration;

[0042] 1. Fix the light-emitting element on the object to be tested;

[0043] 2. If Figure 1 As shown, the optical lens of a conventional camera is replaced with two amplitude or phase masks with slightly different focal lengths;

[0044] 3. The periodic pattern etched on the mask is projected onto the image plane under the illumination of the light-emitting element, and overlaps with each other to produce a low-frequency moiré pattern.

[0045] 2. Imaging model:

[0046] The magnification and displacement ratio of a single-layer mask projection depends on the focal length (or image distance) and the object distance. Due to the focal length difference between the two masks, the light emitted by the target point will pass through the holes in the mask and a pair of bright spot arrays with different periods and displacements will be superimposed on the imaging surface, resulting in Moore acceleration, which is manifested as an interference waveform composed of bright spot arrays with rapidly changing phases. Replace the lens with two dot matrix masks. The light emitted by the target point will pass through the holes in the mask and project a bright spot array on the imaging surface. Analyze the horizontal and vertical waveforms separately:

[0047]

[0048] F is a function with a period of 2π, e g To align the error, ω M is the angular velocity of the bright spot array, ψ M1 is the phase of the bright spot array in the x direction, ψM2 is the phase of the bright spot array in the y direction, Φ M2 =Φ M1 + ω M e g .

[0049] The light source projects the front and rear mask points x onto the image plane points x1 and x2, respectively, with the following relationship:

[0050]

[0051] d L is the distance from the light source to the first mask, x i is the projection coordinate i=1, 2, x L is the light source coordinate, s is the distance between the front and rear dot matrix masks, h is the distance from the CCD to the rear mask, Z L is the distance from the light source to the CCD.

[0052] Substituting into the above formula, we can get the function of the projection pattern:

[0053]

[0054] ω M is the angular velocity of the bright spot array, ψ M1 is the phase of the bright spot array in the x direction, ψ M2 is the phase of the bright spot array in the y direction, Z L is the distance from the light source to the CCD.

[0055] In actual situations, the mask pattern is attached to the substrate in the form of a coating, and there is refraction during the projection process. This refraction will cause the ideal projection point of mask1 to Mapped to the distorted position x1, we have The ideal projection point of mask2 Mapped to the distorted position x2, we have Transformed into:

[0056]

[0057] Substitute the above formula into We can get the refraction function, and transform it to get:

[0058] S A =F(Φ A ),

[0059]

[0060] The data obtained by the camera is S A For the image I, the function can be written as:

[0061]

[0062] Where I is the moiré function expression, ω A is the angular velocity of the moiré pattern function, u is the coordinate in the image, Ψ Ax is the phase of the moiré pattern function in the x direction, Ψ Ay is the phase of the moiré pattern function in the y direction, u x =x / T S ,u y =y / T S , in pixels, pixel circular frequency w A =ω A T S =2πT s / T A =2π / τ, where τ A For S A The pixel period.

[0063] 3. Positioning method:

[0064] 1. For function I x , I y To label the cycle, take one of the functions as an example:

[0065] Set control points at the phase zero points on the front and rear masks respectively. The front mask is at the m+m2th phase zero point, and the rear mask is at the m+m2th and m+m3th phase zero points. The projection of these control points on the image plane satisfies:

[0066]

[0067] There are the following relationships:

[0068]

[0069] Further launch:

[0070]

[0071] where Φ A (x1) is the unwrapped phase of the aliased waveform at the first control point, which can be written as:

[0072] Φ A (x1)=2(n+κ)π

[0073] in, κ∈[0,1). At this time, the control point relationship can be written as:

[0074]

[0075] 2. Internal reference calibration:

[0076] w A x L +Ψ A =-ψ M , converted to the image as ω A u L +Ψ A =-ψ M . Using the grating ruler to collect N light source positions at equal intervals, we have (ω A 、u L ,Ψ A The subscripts of are replaced by the sampling numbers):

[0077]

[0078] Consider the optimization problem:

[0079]

[0080] Derivative each optimization object separately to find the extreme point:

[0081]

[0082] ω n is the angular velocity of the moiré pattern function with sampling number n, u is the coordinate position in the image, Ψ n is the phase of the moiré pattern function with sampling number n.

[0083] Writing Matrix Form:

[0084]

[0085] The inverse solution can be used to obtain u1, Δu, Ψ in the least squares optimal sense. M , due to ψ M ∈[0,2π), M By removing the integer periods in the M , after completing the positioning of the light source position, the positioning target position can be obtained.

[0086] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A two-dimensional positioning method for light source markers based on mask cross projection, characterized in that: The following steps are involved: Fix the light-emitting element on the positioning target, replace the optical lens of the traditional camera with two dot matrix masks with different focal lengths, and take pictures through the replaced camera; The dot matrix pattern etched on the mask is projected onto the image plane under the illumination of the light-emitting element and distortion correction is performed to obtain a low-frequency moiré pattern, and a moiré pattern function is constructed based on the moiré pattern; The expression of the moiré pattern function is: Where I is the moiré function expression, ω A is the angular velocity of the moiré pattern function, u is the coordinate in the image, Ψ Ax is the phase of the moiré pattern function in the x direction, Ψ Ay is the phase of the moiré pattern function in the y direction; Performing periodic labeling and internal parameter calibration on the moiré pattern function to solve the waveform function, determining the light source position based on the waveform function, and obtaining the positioning target position according to the light source position; In the cycle numbering process, a control point is set at the m+m2th phase zero point of the front mask, and control points are set at the m+m2th and m+m3th phase zero points of the rear mask, respectively. The control points satisfy the following expression: Where, κ∈[0,1), Xi represents the coordinate position; The method for internal reference calibration comprises: The image data of the light source is collected at different positions by using a grating ruler, and the image data is converted into an optimization objective function. The optimization objective function is derived to obtain the extreme value points and converted into a matrix form. The expression in the matrix form is solved by the least squares method to obtain the parameter value. The expression for obtaining the extreme point by derivation is: In the formula, ω n is the angular velocity of the moiré pattern function with sampling number n, u is the coordinate position in the image, Ψ n is the phase of the moiré pattern function with sampling number n.

2. The method for two-dimensional positioning of light source marks based on mask cross projection according to claim 1, characterized in that: The expression of the bright spot array obtained by projecting the etched dot pattern on the mask onto the image plane is: Where F is a function with a period of 2π, e g To align the error, ω M is the angular velocity of the bright spot array, ψ M1 is the phase of the bright spot array in the x direction, ψ M2 is the phase of the bright spot array in the y direction.

3. The method for two-dimensional positioning of light source marks based on mask cross projection according to claim 1, characterized in that: The relationship between the etching point on the mask and the image point on the image plane is expressed as: Where, d L is the distance from the light source to the first mask, x i is the projection coordinate i=1, 2, x L is the light source coordinate, s is the distance between the front and rear dot matrix masks, h is the distance from the CCD to the rear mask, Z L is the distance from the light source to the CCD.

4. The method for two-dimensional positioning of light source marks based on mask cross projection according to claim 1, characterized in that: The projection pattern function is obtained by combining the expression of the bright spot array and the relationship between the etching points on the mask and the image points on the image plane. The projection pattern function is: In the formula, ω M is the angular velocity of the bright spot array, ψ M1 is the phase of the bright spot array in the x direction, ψ M2 is the phase of the bright spot array in the y direction, Z L is the distance from the light source to the CCD.

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