CN109345521B - LED free-form surface array based on leather surface defect detection - Google Patents

Abstract

The invention discloses an LED free-form surface array based on leather surface defect detection, belonging to the field of machine vision detection LED lighting. By constructing a theoretical model of the off-axis illuminance distribution of the array on a spatial LED free-form surface; introducing a particle swarm optimization algorithm based on simulated annealing and setting constraints, constructing a uniformity evaluation function, and optimizing the simulation to obtain an off-axis uniform illumination on one side. Optimal solution of LED freeform surface array. The LED array can realize uniform illumination, and the illumination uniformity reaches 91.86%. The LED free-form surface array of the invention can be used for the detection of the monochromatic texture leather printing process, can be highlighted and easy to be directly detected online, and achieves the purpose of detecting printing and dyeing defects by a single-side off-axis uniform illumination method. The LED free-form surface array illumination of the present invention can accurately and quickly detect dark lines on the leather surface.

Description

A LED Freeform Surface Array Based on Leather Surface Defect Detection

technical field

The invention relates to an LED free-form surface array based on leather surface defect detection, belonging to the field of machine vision detection LED lighting.

Background technique

Artificial leather has been widely used in our lives due to its low price and rich colors. People have higher and higher quality requirements for leather products. Not only are there obvious bubbles, white spots, dark lines, scratches, stains, etc. on the leather surface. The defects must be detected, and some printing and dyeing defects such as uneven color that can only be seen at certain angles or special lighting cannot be ignored. In order to improve production efficiency and product quality stability, machine vision inspection has become a development trend. Lighting source is an important part of machine vision system. The choice of light source will affect the imaging quality, which in turn affects the performance of the entire system. The role of the light source is to obtain a contrasting image, increase the difference between the gray value of the part of interest and other parts, try to eliminate the part of interest, improve the signal-to-noise ratio, and facilitate image processing.

In the detection of leather surface, the existence of the texture of the leather itself will affect the detection results. It is particularly important to use a reasonable lighting method to increase the contrast between the defects and the texture of the leather itself. For the printing and dyeing defects of the monochromatic leather texture surface, it can only be highlighted by uniform lighting at a low angle in one direction. The existing solution is to make the image obtained by uneven illumination meet the detection requirements through image processing, but the image processing will not only increase the operation time, but also have poor stability. The use of a light source capable of realizing uniform illumination off-axis on one side reduces the operation time of image processing, improves the stability of the system, and further improves the success rate and efficiency of the detection system.

SUMMARY OF THE INVENTION

In order to solve the above technical problems, the present invention provides an LED free-form surface array based on leather surface defect detection. By constructing a theoretical model of LED off-axis illuminance distribution, a set of optimal solutions is obtained by using particle swarm optimization algorithm, and an LED array that can achieve uniform illumination on the target surface is obtained.

Technical scheme of the present invention:

An LED free-form surface array based on leather surface defect detection, by (1) constructing a theoretical model of off-axis illumination distribution of the array on a spatial LED free-form surface; (2) introducing a particle swarm optimization algorithm based on simulated annealing and setting constraints , Construct a uniformity evaluation function, and optimize the simulation to obtain the optimal solution of the LED free-form surface array that can achieve uniform illumination on one side off-axis; obtain an LED free-form surface array.

In one embodiment, the LED array can achieve uniform illumination, and the illumination uniformity reaches 91.86%.

A LED free-form surface array based on leather surface defect detection, the LED array illumination distribution is

Where (X, Y, Z) are the coordinates of the LED in the space coordinate system, n ₁ is the total number of LED rows, n ₂ is the total number of LED columns, where x, y are any point on the target surface on the x, y axis Coordinates, in which I ₀ is the light intensity of the LED, θ _1/2 is the half-angle width of the LED, Z is the distance from the position of the LED to the target surface, α is the angle between the optical axis and the normal of the target surface, and β is the target surface. The angle between the light irradiation angle at any point and the normal of the target surface, i is the row number of an LED in the LED array, and j is the column number of an LED in the LED array.

In one embodiment, the position and angle of each LED in the LED array conform to:

In one embodiment, the construction of an array off-axis illuminance distribution theoretical model on a spatial LED free-form surface includes:

Ⅰ. When calculating LED coaxial illumination, the illuminance at D(x, y, 0) at any point on the target surface is formula (1). The coaxial illumination is that the LED optical axis is parallel to the normal of the target surface, As shown in Figure 1;

所示，

是图1中LED位置到目标面中任意一点的位置如

所示；Among them, formula (1) (X, Y, Z) is the coordinates of the LED in the space coordinate system, where x, y are the coordinates of any point on the target surface on the x, y axes, and I ₀ is the light intensity of the LED, m=-ln2/ln(cosθ _1/2 ), θ _1/2 is the half-angle width of the LED, and Z is the distance from the position of the LED to the target surface in Figure 1.

shown,

is the position from the LED position to any point in the target surface in Figure 1, such as

shown;

Ⅱ. Arrange formula (1) to obtain formula (2)

Ⅲ. Derive off-axis illumination. The off-axis illumination is that the LED optical axis is not parallel to the normal of the target surface, that is, when the angle α between the optical axis and the normal of the target surface is not zero, as shown in Figure 2 , the illuminance distribution model of LED on the target surface is formula (3);

图2中LED位置到目标面中任意一点的位置

where β is the angle between the irradiation angle of any point on the target surface and the normal of the target surface, as shown in Figure 2, where

The position of the LED from the position of the LED to any point on the target surface in Figure 2

Ⅳ. Derive the off-axis illuminance distribution of the LED array. Considering that the LEDs are non-correlated light sources and the superposition of light, when there are n ₁ × n ₂ LEDs spatially distributed, n ₁ is the total number of LED rows, and n ₂ is the LED column. The total number of LEDs in the target area satisfies linear superposition, and the off-axis illuminance distribution model of the LED array is formula (4):

Equation (4) shows that each LED needs 4 parameters to determine E, and the entire array needs 4n ₁ n ₂ (LED position x, y, z, angle α) parameters to determine, the number is very large.

Ⅴ. Simplify the array model, make the LEDs evenly distributed along the Y direction, the spacing is d, and they are distributed symmetrically with respect to the central axis of the array, the deflection angle of the center point of the array is α ₀ , and the angle of the adjacent LED1 is α ₁ , as shown in Figure 3 As shown, formula (5) is derived according to Figure 3:

According to formula (5), the position and angle of each LED in the n ₁ ×n ₂ LED arrays are as follows:

The distribution of the entire LED array can be constructed from equations (4) and (6). At this time, the parameters to be solved have become n ₁ +n ₂ , and the computational complexity has been greatly simplified.

In one embodiment, the optimization objective function includes: defining the illuminance uniformity μ,

为目标面照度平均值，E_max为目标面照度最大值；in,

is the average value of the illuminance of the target surface, and E _max is the maximum value of the illuminance of the target surface;

According to formula (7), using μ as the evaluation index of uniformity, taking the maximum uniformity as the optimization objective, and the maximum μ is 1, the convergent optimization objective function F is constructed:

In one embodiment, the constraints are,

In one embodiment, the optimization algorithm steps are:

S1. Randomly obtain LED position coordinate parameters x, y, z and angle α;

S2. Determine whether the obtained coordinate parameters meet the constraints, and go to step S3 if the constraints are met, otherwise go to step S1;

S3. Substitute the parameters that meet the constraints in step S2 into formulas (4), (6), (8) for calculation;

S4. Substitute the result in step S3 into formula (9) to determine whether F is the minimum value, and if F is the minimum value, it is the optimal solution, otherwise, go to step S3.

Another object of the present invention is based on the application of the above-mentioned LED array in a machine vision leather defect detection system, the system includes an image acquisition system of Mercury MER-200CCD, a detection sample, and a LTH-300 strip light source.

In one embodiment, the application of the machine vision leather defect detection system includes using Laws texture filtering to extract texture features through programming on the Halcon platform, and Gaussian mixture model classifier to perform defect detection.

In one embodiment, the test sample is a single-color textured leather with surface printing and dyeing defects provided by Benecke Changshun Company.

Another object of the present invention is to provide a method for manufacturing a lighting device with uniform illumination off-axis on one side. According to the above-mentioned LED free-form surface array, a curved frame 3D structure is designed to _fix the substrate and control the LED array device. A 10mm×1mm slot is reserved, the bottom surface of the slot is tangent to the curved surface, and the substrate is embedded in the slot to accurately control the position and angle of the LED.

In one embodiment, considering the heating of the LED and the weight of the substrate, a nylon material with tensile strength and thermal deformation resistance is selected, and a curved frame is obtained by 3D printing. Use DXP software to design a strip substrate, and install the LED lamp beads on the substrate.

By means of the above technical solutions, the beneficial effects of the present invention are:

The present invention can realize uniform illumination of one side off-axis, and the uniformity of illumination reaches 91.86%.

The invention is used in the detection of leather surface texture defects, and can detect printing and dyeing defects that cannot be identified by other lighting devices. The LED array capable of realizing one-side off-axis uniform illumination of the present invention is applied to a leather surface texture defect detection system, which can reduce the operation time of image processing, improve the stability of the system, and further improve the success rate of the detection system. and efficiency.

Description of drawings

Fig. 1 is the LED coaxial illumination schematic diagram of the present invention;

Fig. 2 is the LED off-axis illumination schematic diagram of the present invention;

3 is a schematic diagram of the distribution and illumination of a curved LED array of the present invention;

Fig. 4 is the model schematic diagram of the curved LED array used in the present invention;

Fig. 5 is the illuminance map obtained by optimization;

Figure 6 is a 3D structure diagram of the LED curved frame;

Fig. 7 is the acquisition system diagram;

Figure 8 is an illuminance diagram measured by an actual LED array;

Figure 9 is a system diagram of a leather detection platform;

Figure 10 is a leather inspection chart.

Detailed ways

The specific embodiments of the present invention will be described in further detail below in conjunction with the accompanying drawings: the present embodiment is implemented on the premise of the technical solution of the present invention, and provides detailed embodiments and processes, but the protection scope of the present invention is not limited to the following Example.

Example 1

1. Derive the theoretical model of the off-axis illuminance distribution of the LED array

Figure 1 is a schematic diagram of the coaxial illumination of the LED. The LED is located at point A (X, Y, Z), AB is the vertical distance from the target surface, and the angle between the optical axis and the normal of the target surface is α. When α=0, it is coaxial illumination, that is, Fig. 1, then the illumination at any point D(x, y, 0) on the target surface I is

这时式(1)可以改写成：In formula (1), I ₀ is the light intensity of the LED, m=-ln2/ln(cosθ _1/2 ), and θ _1/2 is the half-angle width of the LED,

Then formula (1) can be rewritten as:

式(2)仍然适用。则LED在面Ⅱ上的离轴照度分布可表示为：When α≠0, that is, Figure 2, then there is

Equation (2) still applies. Then the off-axis illuminance distribution of LED on surface II can be expressed as:

Considering the superposition principle of LEDs as non-correlated light sources and light, if there are n ₁ × n ₂ LEDs distributed in space, the illuminance of the LEDs in the target area satisfies linear superposition, and the off-axis illuminance distribution expression of the LED array is:

Equation (4) shows that each LED needs 4 parameters to determine E, and the entire array needs 4n ₁ n ₂ parameters to determine, which is very large. To achieve uniform illumination, ie E(x,y,z)→E ₀ , it is necessary to find a set of optimal parameters using a suitable algorithm and optimization objective function.

Reducing variables can effectively reduce the operation time. Let the LEDs be evenly distributed along the Y direction, the spacing is d, and they are symmetrically distributed with respect to the central axis of the array, the deflection angle of the center point of the array is α ₀ , and the angle of the adjacent LED1 is α ₁ , as shown in Figure 3, there are:

By analogy, the position and angle of each LED can be expressed

The distribution of the entire LED array can be constructed by formulas (4) and (6). At this time, the parameters to be solved have been reduced to n ₁ +n ₂ , which is greatly simplified.

2. Optimization of the theoretical model of off-axis illuminance distribution of LED arrays

Optimization objective function: defined according to the usual illumination uniformity

为目标面照度平均值，E_max为目标面照度最大值。in

is the average value of the illuminance of the target surface, and E _max is the maximum value of the illuminance of the target surface.

Take μ as the evaluation index of uniformity, take the maximum uniformity as the optimization goal, and the maximum value of μ is 1. Optimization with SimuAPSO requires the construction of a convergent optimization objective function F:

Constraints: Considering that the curved LED array should be versatile and easy to install, the selected light source is an LED chip without secondary optical design. Make the optical axis of the chip coincide with the normal direction of the surface where it is located, that is, use the curvature of this point to control α. Considering that the LED chip has a certain size, to avoid the surface array running out of control, the sudden change of curvature and the overlap between different LEDs, set the optimization constraints:

Programming optimization: ① randomly obtain the LED position coordinate parameters x, y, z and angle α; ② judge whether the obtained coordinate parameters meet the constraints, and go to step ③ if they meet the constraints, otherwise go to step ①; ③ make step ② meet the constraints Substitute the parameters into equations (4), (6) and (8) for calculation; ④ Substitute the result in step ③ into equation (9) to determine whether F is the minimum value, and if F is the minimum value, it is the optimal solution, otherwise turn to Step 3: Obtain the LED array of the optimal solution, and use the light tracking software to make the LED array as shown in Figure 4;

3. Numerical model verification of curved LED array distribution

Simulation verification: The light source is 5730SMD white LED, θ _1/2 = 70°, and the rated current is 10μA. It is assumed that Z ₀ =200mm, α ₀ =45°, and the target surface is 200mm×200mm. The LED array is shown in Figure 4. The result of Fig. 4 is simulated to follow the light, and the illuminance distribution is obtained as shown in Fig. 5, and the illuminance uniformity reaches 91.79%. The results show that the LED free-form surface array design method proposed by the present invention is reasonable and effective, and the LED free-form surface array light source can achieve the goal of uniform illumination on one side off-axis.

Physical verification: According to the results in Figure 4, a curved array light source is produced, and multi-point measurement of illuminance is performed on a two-dimensional electric translation stage. According to the LED array distribution in Figure 4, a curved frame 3D structure is designed to fix the aluminum substrate and control the LED array device, as shown in Figure 6. A 10mm×1mm slot is reserved at Y _j on the frame, the bottom of the slot is tangent to the curved surface, and the aluminum substrate is embedded in the slot to accurately control the position and angle of the LED. Taking into account the heating of the LED and the weight of the aluminum substrate, nylon materials with tensile strength and thermal deformation resistance are selected, and a curved frame is obtained by 3D printing. Use DXP software to design a strip-shaped aluminum substrate and install the LED lamp beads on it. The QJ3003H regulated power supply is used to keep the current of the LED unchanged, and the SPIC-200 illuminance meter is used to measure the illuminance. The illuminance meter is fixed on a two-dimensional electric translation stage with an accuracy of 0.05mm and a working range of 200mm×200mm. The light source is fixed on the support rod with a 45° adapter block and a pendulum adjustment slider, as shown in Figure 7. The experiments were carried out in a dark room with a measurement step of 4 mm.

Figure 8 shows the measured illuminance distribution, and the illuminance uniformity reaches 91.86%, which is in complete agreement with the theoretical results, indicating that our proposed production scheme is effective and accurate, and its illuminance value ranges from 841lx to 1144lx. According to the illuminance value >800lx required by fine lighting in industrial inspection, the designed light source fully meets the lighting requirements.

Example 2

Application of the LED array device designed according to Example 1 in machine vision leather defect detection: As shown in Figure 9, the machine vision leather defect measurement system, the image acquisition system is Mercury MER-200CCD, and the Laws texture is used by programming on the Halcon platform The texture features are extracted by filtering, and the Gaussian mixture model classifier is used for defect detection. The test samples are single-color textured leather with surface printing and dyeing defects provided by Benecke Changshun Company. For comparative analysis, two LTH-300 strip light sources were also selected. The detection was carried out with two light sources and four illumination modes, as shown in Table 1. (a) and (b) in Table 1 are the direct lighting and bilateral symmetrical lighting methods, respectively, which cannot identify the dark grain defects on the leather surface; (c) the plane light source composed of double strip light sources illuminates on one side, which can be intuitively The dark pattern defects on the surface were seen, but due to the obvious uneven illumination, the software was used to identify the defects, resulting in a misjudgment. (d) For the curved light source produced in this paper, the illumination of the target surface is uniform, and the dark pattern defects can be accurately identified by both intuition and software.

Table 1 Defect identification under different lighting methods

For the reasons for the misjudgment of (c) in Table 1, the present invention analyzes that the tested sample is a defect of uneven depth on the surface of monochrome leather, which does not change the texture structure of the leather surface itself, but only manifests in the gray level of the image. Therefore, the image processing of the present invention is mainly completed by filtering the texture and using gray level filtering. The uneven illumination will also produce changes in the gray level on the image, thereby affecting the judgment. Some scholars also make the image obtained by uneven illumination meet the detection requirements through image processing, but this will not only increase the computing time, but also have poor stability. In fact, there will still be scratches, damages, stains, indentations and other defects on the leather surface. Different lighting methods should be selected according to the actual situation during inspection.

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Anyone who is familiar with this technology can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, The protection scope of the present invention should be defined by the claims.

Claims (6)

1. The utility model provides a LED free curved surface array based on leather surface defect detects which characterized in that, the illuminance distribution of LED array is:

where (X, Y, Z) is the coordinates of the LED in a spatial coordinate system, n₁Is the total number of LED rows, n₂Is the total number of LED columns, where x, y are the coordinates of any point on the target surface on the x, y axis, where I₀Is the intensity of the LED, theta_1/2The half-angle width of the LED is shown, Z is the distance from the position of the LED to a target surface, alpha is the included angle between the optical axis and the normal line of the target surface, beta is the included angle between the light irradiation angle of any point on the target surface and the normal line of the target surface, i is the number of rows where a certain LED is located in the LED array, and j is the number of columns where a certain LED is located in the LED array.

2. The LED array of claim 1, wherein the LED arrays are uniformly distributed along the Y direction at a pitch d, each of which is symmetric about the central axis of the array, and the deflection angle of the central point of the array is α₀With adjacent LEDs at an angle alpha₁The position and angle of each LED in the LED array are matched

3. An LED array according to claim 2, wherein Y is_jAnd alpha_iConform to

4. An LED array according to any of claims 1-3, wherein the LED array provides uniform illumination with a uniformity of 91.86%.

5. Unilateral off-axis uniform illumination deviceThe lighting device is characterized in that the LED array of the lighting device is any one of the arrays of claims 1 to 4, each LED is arranged on a substrate, the substrate is fixed on a curved-surface frame 3D structure manufactured according to the LED array, and the curved-surface frame 3D structure Y_jA caulking groove with the thickness of 10mm multiplied by 1mm is reserved at the position, the bottom surface of the groove is tangent to the curved surface, and the position and the angle of the LED can be accurately controlled by embedding the substrate into the groove.

6. The lighting device as claimed in claim 5, wherein the substrate is made of nylon material with tensile strength and thermal deformation resistance, a curved frame is obtained by 3d printing, the strip-shaped substrate is designed by using DXP software, and the LED lamp beads are mounted on the substrate.

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