Plastic material identification method based on slopes of two sides of wave trough of near infrared spectrum

Abstract

The invention relates to the field of material identification, and discloses a plastic material identification method based on slopes of two sides of a near infrared spectrum trough, and the method comprises the following steps: S1, preparing a plurality of plastic sample groups made of different materials; s2, acquiring a change curve of the reflectivity of the plastic sample group of each material along with the wavelength through a near-infrared spectrometer; s3, analyzing the change curve of the reflectivity of the plastic sample group of each material along with the wavelength to obtain a representative curve of each material; s4, selecting a specified material through a specified module; s5, analyzing the representative curve of each material and the specified material to obtain a characteristic wavelength range and a corresponding characteristic wavelength; s6, judging whether the to-be-detected plastic is a specified material or not by obtaining the slopes of the two sides of the corresponding characteristic wavelength in the characteristic wavelength range of the to-be-detected plastic; in the detection process, whether the plastic is the plastic made of the specified material or not can be quickly judged only by obtaining the infrared spectrum in the characteristic wavelength range of the plastic to be detected; and the detection efficiency is improved.

Description

Technical Field

[0001] The invention relates to the field of material recognition, and in particular to a plastic material recognition method based on slopes on both sides of a near-infrared spectrum trough. Background Art

[0002] Plastic recycling is an important way to reduce plastic waste and reduce the burden on the environment. Since different plastics require different treatment methods and processes, recycled plastics need to be identified and classified.

[0003] At present, plastics can be identified and classified by using near-infrared spectroscopy technology. Since the main components of different plastics are different, the infrared spectra of each plastic obtained by the near-infrared spectrometer are different. The main components in the plastic to be tested can be analyzed based on the near-infrared spectrum, and then the type of plastic can be determined based on the main components in the plastic.

[0004] However, during the detection process, in order to improve the accuracy of recognition, a near-infrared spectrum of the entire near-infrared wavelength range needs to be obtained for each plastic to be detected, and it takes a long time to obtain a complete near-infrared spectrum. When the number of plastics to be detected is large, a complete near-infrared spectrum needs to be obtained for each plastic to be detected, which wastes a lot of time and reduces the efficiency of plastic recognition. Summary of the invention

[0005] The purpose of the present invention is to provide a plastic material identification method based on the slopes on both sides of the near infrared spectrum trough to solve the following technical problems:

[0006] How to improve the recognition efficiency of plastics to be tested.

[0007] The purpose of the present invention can be achieved through the following technical solutions:

[0008] A plastic material identification method based on the slopes on both sides of a near infrared spectrum trough comprises the following steps:

[0009] S1: Prepare several plastic sample groups of different materials;

[0010] S2: Obtain the reflectivity curve of each plastic sample group with wavelength through near infrared spectrometer;

[0011] S3: by analyzing the curves of reflectivity variation with wavelength of the plastic sample groups of each material, a representative curve of each material is obtained;

[0012] S4: Select the specified material through the specified module;

[0013] S5: Obtain a characteristic wavelength range and a corresponding characteristic wavelength by analyzing the representative curve of each material and the specified material;

[0014] S6: Determine whether the material is a specified material by obtaining the slopes on both sides of the corresponding characteristic wavelength within the characteristic wavelength range of the plastic to be detected.

[0015] As a further solution of the present invention: the process of obtaining the characteristic wavelength range includes the following steps:

[0016] S10: Identify the representative curve of the specified material through the identification unit to obtain the wavelength corresponding to each trough of the specified material on the representative curve of the specified material;

[0017] S20: Obtaining a first reference wavelength range corresponding to each trough according to a preset rule based on the wavelength corresponding to each trough of the specified material by an analysis unit;

[0018] S30: Obtaining the slopes of both sides of the troughs of each designated material of each representative curve within each first reference wavelength range through an analysis unit; and performing analysis based on the slopes of both sides of the troughs of each designated material of each representative curve to obtain a slope difference index of the designated material; and selecting a second reference wavelength range based on the slope difference index of the designated material;

[0019] S40: Obtain the slope distribution index on both sides of the specified material by analyzing the reflectivity variation curve of the plastic sample group of each material within the second reference wavelength range versus wavelength; and obtain the characteristic wavelength range according to the slope distribution index on both sides of the specified material.

[0020] As a further solution of the present invention: by formula:

[0021]

[0022] Calculate the slope difference index D of the nth trough of the specified material and the mth non-specified material on both sides nm ;

[0023] Where N is the total number of troughs of the specified material, n∈N; W n is the wavelength corresponding to the nth trough of the specified material; W0 is the preset wavelength interval; F i (W n ) is the wavelength W on the representative curve of the specified material n Corresponding reflectivity; F Z (W n -W0) is the wavelength W on the representative curve of the specified material n -Reflectivity corresponding to W0; F Z (W n +W0) is the wavelength W on the representative curve of the specified material n +W0 corresponding reflectivity; M is the total number of non-specified materials in all materials, m∈M; F m (W n) is the representative curve of the mth non-specified material with a wavelength of W n Corresponding reflectivity; F m (W n -W0) is the wavelength W on the representative curve of the mth non-specified material n Corresponding reflectivity; F m (W n +W0) is the wavelength W on the representative curve of the mth non-specified material n +W0 corresponds to the reflectivity.

[0024] As a further solution of the present invention: the selection process of the second reference wavelength range includes the following steps:

[0025] S100: Analyze the difference index of the slopes on both sides of each trough of the designated material and each non-designated material to obtain a difference judgment index;

[0026] S200: Determine a second reference wavelength range through a difference judgment index.

[0027] As a further solution of the present invention: in step S100, by formula:

[0028]

[0029] Calculates the comprehensive slope difference index C of the nth valley of the specified material n ;

[0030] Where f(X) is the judgment function. When X>0, f(X)=1; when X≤0, f(X)=0; D a is the first preset value; D L is the second preset value; D ns It is the minimum slope difference index between the two sides among M non-specified materials.

[0031] As a further solution of the present invention: in step S200, the process of determining the second reference wavelength range is:

[0032] Screen out T comprehensive slope difference indexes C n The preset wavelength range corresponding to the selected trough is determined as the second reference wavelength range.

[0033] As a further solution of the present invention: in step S40, the process of acquiring the characteristic wavelength range further includes the following steps:

[0034] S1000: By analyzing the curve of the change of reflectivity of the plastic sample group of each material with the wavelength, the curve of the change of reflectivity of each plastic sample group with the wavelength is obtained within the second reference wavelength range of the t segment, and the wavelength is W t The slope values ​​on both sides of ;

[0035] S2000: According to the reflectivity variation curve of each plastic sample group with wavelength W in the tth second reference wavelength range t The slope values ​​on both sides of are plotted as the central scatter plots of the t-th slope values ​​on both sides;

[0036] S3000: Analyze the central scatter plot of the t-th slope value on both sides through the recognition module to obtain a dispersion index, and determine the characteristic wavelength range according to the dispersion index.

[0037] As a further solution of the present invention: by formula:

[0038]

[0039] Calculate the dispersion index S of the second reference wavelength range of the tth segment t ;

[0040] Among them, S tm It is the area value of the overlapping part of the distribution area of ​​the mth non-specified material and the distribution area of ​​the specified material on the central scatter plot of the second reference wavelength range of the tth segment.

[0041] Beneficial effects of the present invention:

[0042] The present invention first prepares a plurality of plastic sample groups of different materials; obtains a reflectivity variation curve of the plastic sample group of each material with a wavelength through a near-infrared spectrometer; specifically, selects a specified material through a specified module; obtains a characteristic wavelength range and a corresponding characteristic wavelength by analyzing a representative curve of each material and the specified material; then obtains a characteristic wavelength range and a corresponding characteristic wavelength by analyzing a representative curve of each material and the specified material; finally, determines whether the plastic is of the specified material by obtaining the slopes on both sides of the corresponding characteristic wavelength within the characteristic wavelength range of the plastic to be detected; during the detection process, it is only necessary to obtain an infrared spectrum within the characteristic wavelength range of the plastic to be detected to quickly determine whether the plastic is of the specified material; thereby improving the recognition efficiency of the plastic to be detected. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The present invention will be further described below in conjunction with the accompanying drawings.

[0044] Figure 1 A method flow chart of an embodiment of the present invention;

[0045] Figure 2 The representative curves of the plastic sample groups of various materials according to an embodiment of the present invention are as follows: Figure 1 ;

[0046] Figure 3 The representative curves of the plastic sample groups of various materials according to an embodiment of the present invention are as follows: Figure 2 ;

[0047] Figure 4 A central scatter plot of the second reference wavelength range in the first section of an embodiment of the present invention;

[0048] Figure 5 A central scatter plot of the second reference wavelength range of the second section in an embodiment of the present invention;

[0049] Figure 6 It is a central scatter plot of the second reference wavelength range of the third section in one embodiment of the present invention;

[0050] Figure 7 It is a central scatter plot of the second reference wavelength range of the fourth section of an embodiment of the present invention;

[0051] Figure 8 It is a central scatter plot of the second reference wavelength range of the fifth section of an embodiment of the present invention;

[0052] Fig. 9 This is a central scatter plot of the sixth section of the second reference wavelength range in an embodiment of the present invention. DETAILED DESCRIPTION

[0053] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] See also Figure 1-Figure 2 As shown, in one embodiment, a method for identifying plastic materials based on the slopes on both sides of a near infrared spectrum trough is provided, comprising the following steps:

[0055] S1: Prepare several plastic sample groups of different materials;

[0056] S2: Obtain the reflectivity curve of each plastic sample group with wavelength through near infrared spectrometer;

[0057] S3: by analyzing the curves of reflectivity variation with wavelength of the plastic sample groups of each material, a representative curve of each material is obtained;

[0058] S4: Select the specified material through the specified module;

[0059] S5: Obtain a characteristic wavelength range and a corresponding characteristic wavelength by analyzing the representative curve of each material and the specified material;

[0060] S6: Determine whether the material is a specified material by obtaining the slopes on both sides of the corresponding characteristic wavelength within the characteristic wavelength range of the plastic to be detected;

[0061] Through the above technical scheme, the present embodiment first prepares several plastic sample groups of different materials; the number of plastic materials prepared in the present embodiment is seven, and the seven plastic materials are PET, PE, HDPE, PS, PVC, ABS, and PP; a reflectivity variation curve of the plastic sample groups of each material with wavelength is obtained by a near-infrared spectrometer; specifically, the near-infrared spectrometer used in the present embodiment is NIRQuest Spectrometers, whose wavelength range is from 900nm-2500nm, and whose optical resolution is 2.8nmFWHM; the reflectivity is obtained after processing by the spectrometer, and then the spectral data is saved to a computer for subsequent analysis. Before the experiment starts to obtain plastic spectral data, the reflection effect needs to be corrected, that is, a PTFE material calibration white board is used for correction. The PTFE white board spectrum is collected once in a bright environment, and then the PTFE white board dark spectrum is collected again in a dark environment. After the collection is successful, the spectrum correction before the experiment is completed; each plastic sample group includes 10 samples, and the color and thickness of the 10 samples are different. Each sample obtains 40 spectral data, so each plastic sample group obtains a total of 400 sets of spectral data. The average value of the spectral data of each plastic sample group is taken to obtain the representative curves of the seven materials of plastic; the representative curves of the seven materials of plastic are as follows Figure 2 As shown; the designated material is selected through the designated module; in this embodiment, the designated material is PET; by analyzing the representative curves of each material and the designated material, the characteristic wavelength range and the corresponding characteristic wavelength are obtained; finally, by obtaining the slopes on both sides of the corresponding characteristic wavelength within the characteristic wavelength range of the plastic to be detected, it is determined whether it is the designated material; during the detection process, it is only necessary to obtain the infrared spectrum within the characteristic wavelength range of the plastic to be detected to quickly determine whether it is a plastic of the designated material; thereby improving the recognition efficiency of the plastic to be detected.

[0062] As an embodiment of the present invention, the analysis module includes an identification unit and an analysis unit;

[0063] The recognition unit is a trained neural network model; the recognition unit recognizes the representative curve of the specified material and obtains the wavelength corresponding to each trough of the specified material on the representative curve of the specified material;

[0064] It should be noted that the training process of the recognition unit is a prior art and will not be described in detail here.

[0065] As an embodiment of the present invention, the process of obtaining the characteristic wavelength range includes the following steps:

[0066] S10: Identify the representative curve of the specified material through the identification unit to obtain the wavelength corresponding to each trough of the specified material on the representative curve of the specified material;

[0067] S20: Obtaining a first reference wavelength range corresponding to each trough according to a preset rule based on the wavelength corresponding to each trough of the specified material by an analysis unit;

[0068] S30: Obtaining the slopes of both sides of the troughs of each designated material of each representative curve within each first reference wavelength range through an analysis unit; and performing analysis based on the slopes of both sides of the troughs of each designated material of each representative curve to obtain a slope difference index of the designated material; and selecting a second reference wavelength range based on the slope difference index of the designated material;

[0069] S40: Analyzing the curve of the reflectivity of the plastic sample group of each material within the second reference wavelength range as a function of wavelength, obtaining the slope distribution index on both sides of the specified material; and obtaining the characteristic wavelength range according to the slope distribution index on both sides of the specified material;

[0070] Through the above technical scheme, this embodiment first identifies the representative curve of the specified material through the identification unit to obtain the wavelength corresponding to each specified material trough on the representative curve of the specified material; then the analysis unit obtains the first reference wavelength range corresponding to each trough according to the preset rules based on the wavelength corresponding to each specified material trough; then the analysis unit obtains the slopes on both sides of the trough of each specified material of each representative curve within each first reference wavelength range; and analyzes the slopes on both sides of the trough of each specified material of each representative curve to obtain the slope difference index of the specified material; and selects the second reference wavelength range according to the slope difference index of the specified material; finally, by analyzing the reflectivity change curve of the plastic sample group of each material within the second reference wavelength range with the wavelength, the slope distribution index on both sides of the specified material is obtained; and the characteristic wavelength range is obtained according to the slope distribution index on both sides of the specified material.

[0071] As an implementation mode of the present invention, by formula:

[0072]

[0073] Calculate the slope difference index D of the nth trough of the specified material and the mth non-specified material on both sides nm ;

[0074] Where N is the total number of troughs of the specified material, n∈N; W n is the wavelength corresponding to the nth trough of the specified material; W0 is the preset wavelength interval; F i (W n ) is the wavelength W on the representative curve of the specified material n Corresponding reflectivity; F Z (Wn -W0) is the wavelength W on the representative curve of the specified material n -Reflectivity corresponding to W0; F Z (W n +W0) is the wavelength W on the representative curve of the specified material n +W0 corresponding reflectivity; M is the total number of non-specified materials in all materials, m∈M; F m (W n ) is the representative curve of the mth non-specified material with a wavelength of W n Corresponding reflectivity; F m (W n -W0) is the wavelength W on the representative curve of the mth non-specified material n Corresponding reflectivity; F m (W n +W0) is the wavelength W on the representative curve of the mth non-specified material n +W0 corresponding reflectivity;

[0075] Through the above technical solution, this embodiment The left slope of the nth trough on the representative curve of the specified material; The wavelength on the representative curve of the mth non-specified material is W n Position left slope; The slope on the left side of the nth trough on the representative curve of the specified material and the wavelength W on the representative curve of the mth non-specified material n The absolute value of the difference in slope to the left of the position; The right slope of the nth trough on the representative curve of the specified material; The wavelength on the representative curve of the mth non-specified material is W n Position right slope; The slope of the right side of the nth trough on the representative curve of the specified material and the wavelength W on the representative curve of the mth non-specified material n The absolute value of the difference in slope to the right of the position; The slope on the left side of the nth trough on the representative curve of the specified material and the wavelength W on the representative curve of the mth non-specified material n The absolute value of the difference between the slope on the left side of the position and the slope on the right side of the nth trough on the representative curve of the specified material and the wavelength on the representative curve of the mth non-specified material is W n The sum of the absolute values ​​of the differences in the slopes on the right side of the position, the slope on the left side of the nth trough on the representative curve of the specified material and the wavelength on the representative curve of the mth non-specified material is W nThe absolute value of the difference between the slope on the left side of the position and the slope on the right side of the nth trough on the representative curve of the specified material and the wavelength on the representative curve of the mth non-specified material is W n The sum of the absolute values ​​of the differences in the slopes to the right of the position The larger the value, the greater the slope difference index D between the nth trough of the specified material and the mth non-specified material. nm The bigger;

[0076] It should be noted that the preset wavelength interval W0 is a preset value, which is obtained based on experience and will not be described in detail here.

[0077] As an embodiment of the present invention, the process of selecting the second reference wavelength range includes the following steps:

[0078] S100: Analyze the difference index of the slopes on both sides of each trough of the designated material and each non-designated material to obtain a difference judgment index;

[0079] S200: determining a second reference wavelength range through a difference judgment index;

[0080] Through the above technical solution, this embodiment first analyzes the difference index of the slopes on both sides of each trough of the designated material and each non-designated material to obtain a difference judgment index; then determines the second reference wavelength range through the difference judgment index; performs a preliminary screening of the troughs to reduce the amount of subsequent calculations;

[0081] As an implementation of the present invention, in step S100, by formula:

[0082]

[0083] Calculates the comprehensive slope difference index C of the nth valley of the specified material n ;

[0084] Where f(X) is the judgment function. When X>0, f(X)=1; when X≤0, f(X)=0; D a is the first preset value; D L is the second preset value; D ns It is the smallest difference index of slopes on both sides among M non-specified materials;

[0085] Through the above technical solution, this embodiment It is the difference index of the average slopes on both sides of the nth trough of the specified material and M non-specified materials; is the difference between the average slope difference index of the nth trough of the specified material and the M non-specified materials and the first preset value; in the formula In the judgment function f(X), X refers to when When , it means that the difference index between the nth trough of the specified material and the average slopes on both sides of the M non-specified materials is small, so when When , it means that the difference index between the nth trough of the specified material and the average slopes on both sides of the M non-specified materials is large, so D ns -D L is the difference between the minimum slope difference index on both sides of the M non-specified materials and the second preset value; in the formula f(D ns -D L ), the X in the judgment function f(X) refers to D ns -D L When D ns -D L When ≤0, it means that the smallest slope difference index on both sides of M non-specified materials is small, so f(D ns -D L )=0; when D ns -D L When > 0, it means that the smallest slope difference index on both sides of the M non-specified materials is large, so f(D ns -D L )=1;

[0086] It should be noted that the first preset value D a and the second preset value D L It is a preset value obtained based on experience and will not be described in detail here.

[0087] As an implementation manner of the present invention, in step S200, the process of determining the second reference wavelength range is:

[0088] Screen out T comprehensive slope difference indexes C n The preset wavelength range corresponding to the selected trough is determined as the second reference wavelength range;

[0089] Through the above technical solution, this embodiment screens out T comprehensive slope difference indexes C n The trough of 1, therefore, has T second reference wavelength ranges, t∈T; the preset wavelength range corresponding to the nth trough is [W n -W0,W n +W0]; therefore, the second reference wavelength range of the tth segment is recorded as [W t -W0,W t +W0]; Specifically, in this embodiment, 6 comprehensive slope difference indexes C are screened out. n The trough of 1; Figure 3As shown, the wavelengths corresponding to the six troughs are 1210nm, 1393nm, 1660nm, 1720nm, 2130nm and 2290nm, respectively. W0 is 10nm in this embodiment. Therefore, the six second reference wavelength ranges correspond to (1200nm, 1220nm), (1383nm, 1403nm), (1650nm, 1670nm), (1710nm, 1730nm), (2120nm, 2140nm), (2280nm, 2300nm), respectively.

[0090] See also Figure 4-Figure 9 As shown, as an implementation of the present invention, in step S40, the process of acquiring the characteristic wavelength range further includes the following steps:

[0091] S1000: By analyzing the curve of the change of reflectivity of the plastic sample group of each material with the wavelength, the curve of the change of reflectivity of each plastic sample group with the wavelength is obtained within the second reference wavelength range of the t segment, and the wavelength is W t The slope values ​​on both sides of ;

[0092] S2000: According to the reflectivity variation curve of each plastic sample group with wavelength W in the tth second reference wavelength range t The slope values ​​on both sides of are plotted as the central scatter plots of the t-th slope values ​​on both sides;

[0093] S3000: Analyze the central scatter plot of the t-th slope value on both sides through the recognition module to obtain a dispersion index, and determine the characteristic wavelength range according to the dispersion index;

[0094] Through the above technical solution, this embodiment analyzes the reflectivity variation curve of the plastic sample group of each material with the wavelength, and obtains the reflectivity variation curve of each plastic sample group with the wavelength within the second reference wavelength range of the t segment, and the wavelength is W t The slope values ​​on both sides of the reflectivity of each plastic sample group are calculated based on the reflectivity curve of each plastic sample group with wavelength W in the tth second reference wavelength range. t The slope values ​​on both sides of are plotted as the central scatter plots of the t-th slope values ​​on both sides; Figure 4-Figure 9 They are the central scatter plots of the slope values ​​on both sides of the 6 second reference wavelength ranges; the horizontal axis represents the left slope of each plastic, and the vertical axis represents the right slope; the characteristic points of the slope values ​​on both sides of the 400 groups of spectral data of each plastic sample group are marked on the central scatter plot, and each plastic sample group is marked with a different color; Figure 4-Figure 9, it can be seen that the distribution of each plastic has obvious differences under the characteristics of the left slope and the right slope; finally, the central scatter plot of the t-th slope value on both sides is identified by the recognition module, and the distribution areas of various color marking points are obtained according to the color. The distribution area of ​​a color marking point is the distribution area of ​​the slope values ​​on both sides of a plastic sample group, and then the dispersion index is obtained based on the distribution area of ​​each color marking point. The second reference wavelength range with the most obvious distribution of the specified material and the non-specified material is obtained as the characteristic wavelength range through the dispersion index.

[0095] As an implementation mode of the present invention, by formula:

[0096]

[0097] Calculate the dispersion index S of the second reference wavelength range of the tth segment t ;

[0098] Among them, S tm It is the area value of the overlapping part of the distribution area of ​​the mth non-specified material and the distribution area of ​​the specified material on the central scatter plot of the second reference wavelength range of the tth segment;

[0099] Through the above technical solution, this embodiment is the cumulative value of the area values ​​of the overlapping parts of the distribution areas of M kinds of non-specified materials and the distribution areas of the specified materials on the central scatter plot of the second reference wavelength range of the tth segment; the cumulative value of the area values ​​of the overlapping parts of the distribution areas of M kinds of non-specified materials and the distribution areas of the specified materials The larger the value, the more difficult it is to select the specified material from various plastic materials, and the lower the accuracy. The dispersion index S of the second reference wavelength range of the tth segment t The smaller the value, the cumulative value of the overlapping area of ​​the distribution area of ​​M non-specified materials and the distribution area of ​​the specified material. The smaller it is, the easier it is to select a specific material from various plastic materials, and the higher the accuracy. The dispersion index S of the second reference wavelength range of the tth segment t The bigger; when When , the distribution area of ​​M non-specified materials does not overlap with the distribution area of ​​the specified material; therefore, the dispersion index S is selected t =0 is the characteristic wavelength range; the corresponding wavelength of the trough of the representative curve of the specified material within the characteristic wavelength range is the corresponding characteristic wavelength; the dispersion index S of the first section of the second reference wavelength range (1200nm, 1220nm) of this embodiment is t =0; therefore, (1200nm, 1220nm) is the characteristic wavelength range; therefore, 1210nm is the corresponding characteristic wavelength;

[0100] It should be noted that obtaining the distribution area according to each color marking point and obtaining the area value of the overlapping part of each distribution area is a prior art and will not be described in detail here.

[0101] The above is a detailed description of an embodiment of the present invention, but the content is only a preferred embodiment of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A plastic material identification method based on the slopes on both sides of the near infrared spectrum trough, characterized in that: The following steps are involved: S1: Prepare several plastic sample groups of different materials; S2: Obtain the reflectivity curve of each plastic sample group with wavelength through near infrared spectrometer; S3: by analyzing the curves of reflectivity variation with wavelength of the plastic sample groups of each material, a representative curve of each material is obtained; S4: Select the specified material through the specified module; S5: Obtain a characteristic wavelength range and a corresponding characteristic wavelength by analyzing the representative curve of each material and the specified material; S6: Determine whether the material is a specified material by obtaining the slopes on both sides of the corresponding characteristic wavelength within the characteristic wavelength range of the plastic to be detected.

2. The method for identifying plastic materials based on the slopes on both sides of the near infrared spectrum trough according to claim 1 is characterized in that: The process of obtaining the characteristic wavelength range comprises the following steps: S10: Identify the representative curve of the specified material through the identification unit to obtain the wavelength corresponding to each trough of the specified material on the representative curve of the specified material; S20: Obtaining a first reference wavelength range corresponding to each trough according to a preset rule based on the wavelength corresponding to each trough of the specified material by an analysis unit; S30: Obtaining the slopes of both sides of the troughs of each designated material of each representative curve within each first reference wavelength range through an analysis unit; and performing analysis based on the slopes of both sides of the troughs of each designated material of each representative curve to obtain a slope difference index of the designated material; and selecting a second reference wavelength range based on the slope difference index of the designated material; S40: Obtain the slope distribution index on both sides of the specified material by analyzing the reflectivity variation curve of the plastic sample group of each material within the second reference wavelength range versus wavelength; and obtain the characteristic wavelength range according to the slope distribution index on both sides of the specified material.

3. The method for identifying plastic materials based on the slopes on both sides of the near infrared spectrum trough according to claim 2 is characterized in that: By formula: Calculate the slope difference index D of the nth trough of the specified material and the mth non-specified material on both sides nm ; Where N is the total number of troughs of the specified material, n∈N; W n is the wavelength corresponding to the nth trough of the specified material; W0 is the preset wavelength interval; F Z (W n ) is the wavelength W on the representative curve of the specified material n Corresponding reflectivity; F Z (W n -W0) is the wavelength W on the representative curve of the specified material n -Reflectivity corresponding to W0; F Z (W n +W0) is the wavelength W on the representative curve of the specified material n +W0 corresponding reflectivity; M is the total number of non-specified materials in all materials, m∈M; F m (W n ) is the representative curve of the mth non-specified material with a wavelength of W n Corresponding reflectivity; F m (W n -W0) is the wavelength W on the representative curve of the mth non-specified material n Corresponding reflectivity; F m (W n +W0) is the wavelength W on the representative curve of the mth non-specified material n +W0 corresponds to the reflectivity.

4. The method for identifying plastic materials based on the slopes on both sides of the near infrared spectrum trough according to claim 3 is characterized in that: The selection process of the second reference wavelength range comprises the following steps: S100: Analyze the difference index of the slopes on both sides of each trough of the designated material and each non-designated material to obtain a difference judgment index; S200: Determine a second reference wavelength range through a difference judgment index.

5. The method for identifying plastic materials based on the slopes on both sides of the near infrared spectrum trough according to claim 4 is characterized in that: In step S100, by formula: Calculates the comprehensive slope difference index C of the nth valley of the specified material n ; Where f(X) is the judgment function. When X>0, f(X)=1; when X≤0, f(X)=0; D a is the first preset value; D L is the second preset value; D ns It is the minimum slope difference index between the two sides among M non-specified materials.

6. The method for identifying plastic materials based on the slopes on both sides of the near infrared spectrum trough according to claim 5, characterized in that: In step S200, the process of determining the second reference wavelength range is as follows: Screen out T comprehensive slope difference indexes C n The preset wavelength range corresponding to the selected trough is determined as the second reference wavelength range.

7. The method for identifying plastic materials based on the slopes on both sides of the near infrared spectrum trough according to claim 6, characterized in that: In step S40, the process of acquiring the characteristic wavelength range further includes the following steps: S1000: By analyzing the curve of the change of reflectivity of the plastic sample group of each material with the wavelength, the curve of the change of reflectivity of each plastic sample group with the wavelength is obtained within the second reference wavelength range of the t segment, and the wavelength is W t The slope values ​​on both sides of ; S2000: According to the reflectivity variation curve of each plastic sample group with wavelength W in the tth second reference wavelength range t The slope values ​​on both sides of are plotted as the central scatter plots of the t-th slope values ​​on both sides; S3000: Analyze the central scatter plot of the t-th slope value on both sides through the recognition module to obtain a dispersion index, and determine the characteristic wavelength range according to the dispersion index.

8. The method for identifying plastic materials based on the slopes on both sides of the near infrared spectrum trough according to claim 7 is characterized in that: By formula: Calculate the dispersion index S of the second reference wavelength range of the tth segment t ; Among them, S tm It is the area value of the overlapping part of the distribution area of ​​the mth non-specified material and the distribution area of ​​the specified material on the central scatter plot of the second reference wavelength range of the tth segment.

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