Dual optical path spectrometer and color measurement device and calibration method

Abstract

The application discloses a double-optical-path spectrometer, a color measurement device and a calibration method, and relates to the field of color measurement devices. The color measurement device obtains reflected light of a measured sample and reflected light of a test light source, and inputs the reflected light into a first incident slit and a second incident slit of a spectrometer through a Y-shaped light path unit; the reflected light is incident on a grating through a lens; diffracted light spots returned by the grating are incident on a photosensitive surface of a sensor on the side of the incident slit through the lens; the photosensitive surface is provided with an aperture stop with a dislocation opening; and the photosensitive surface at each dislocation opening only receives light signals of one light path, so that the short-term repeatability of spectrophotometry is improved. When wavelength calibration is performed, light signals of a calibration light source are obtained through the Y-shaped light path unit; pixel position information of the collected light signals is obtained according to a sensor of the spectrometer; a fourth-order polynomial is used to fit wavelength data and the pixel position information; the correspondence between the pixels and the wavelengths is adjusted; and the wavelengths are calibrated, so that the short-term repeatability of spectrophotometry is improved.

Description

Technical Field

[0001] This invention relates to the field of colorimetry technology, particularly to dual-path spectrometers, as well as colorimetry devices and wavelength calibration methods based on dual-path spectrometers. Background Technology

[0002] A colorimeter calculates the tristimulus values ​​and other color parameters by obtaining the spectral reflectance curve of the sample surface within the visible light range. Measurement repeatability is a crucial indicator for evaluating the performance of a colorimeter. A colorimeter mainly consists of a light source and illumination system, a spectrophotometer system, a photoelectric receiving system, and a control and data processing system. The spectrophotometer system decomposes mixed light into monochromatic light, and the photoelectric receiving system receives the monochromatic light and performs photoelectric conversion; these two parts together are called the spectrometer. The spectrometer is the core component of a colorimeter, not only meeting a series of performance requirements but also playing a decisive role in the overall performance and structure of the colorimeter. Most colorimeters use pulsed xenon lamps as the light source. During measurement, the spectral energy of the pulsed xenon lamp changes significantly each time it is lit. A dual-path design is typically used to eliminate the impact of light source fluctuations on instrument repeatability. One optical path sensor detects the spectral reflectance signal from the surface of the object being measured, while the other optical path sensor detects the energy fluctuations of the light source. By comparing the signals from the two sensors, the influence of light source fluctuations on the measurement can be eliminated, ensuring measurement repeatability.

[0003] Existing dual-beam path designs all employ two spectrometers to detect signals from two separate optical paths. One measures the spectral information of the sample being tested, called the sample detection branch spectrometer, while the other measures the energy fluctuations of the light source, called the light source monitoring branch spectrometer. In other words, a dual-beam path system contains two gratings and two sensors. Even if the two spectrometers are of the same brand and model, inconsistencies in the gratings, optical path mechanical structures, and sensor performance parameters can introduce errors into the colorimeter. These differences cannot be offset even with a dual-beam path, leading to inconsistent changes in ambient temperature and humidity, resulting in poor short-term and long-term repeatability of the colorimeter. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies and improve the short-term and long-term repeatability of colorimeters, the present invention adopts the following technical solution:

[0005] A dual-path spectrometer includes an entrance slit, a lens, a grating, a sensor, and an aperture. The entrance slit includes a first entrance slit and a second entrance slit. The grating is a concave grating, and the lens is a plano-convex lens. The concave surface of the concave grating and the convex surface of the plano-convex lens are configured to cooperate. Two optical paths, the reflected light from the sample under test and the reflected light from the test light source, pass through the first entrance slit and the second entrance slit respectively, and are incident on the grating through the lens. The two diffracted light spots returned by the grating are then passed through the lens and misaligned on the photosensitive surface of the sensor on the side of the entrance slit, thereby optimizing the spectrometer structure. An aperture with a misaligned opening is configured on the photosensitive surface to intercept light outside 370-730nm, so that the photosensitive surface at each misaligned opening receives the light signal from only one optical path. This achieves the function of a dual-path spectrometer with a single grating and a single sensor, reducing costs. For the two optical paths, the changes in the grating, optical path structure, and sensor are consistent, effectively reducing short-term measurement repeatability.

[0006] Furthermore, the wavelength range corresponding to the width dl of the photosensitive surface of the sensor receiving a single optical signal is dλ = 730-370nm. Based on the dispersion rate of the spectrometer dλ / dl = 56.25 ± 10% nm / mm, the width of the misaligned aperture of the aperture is set to dl, and the optimal width range of the misaligned aperture is limited by the dispersion rate.

[0007] Furthermore, dl = 6.4 mm is the optimal misalignment aperture width for the aperture.

[0008] Furthermore, the aperture has two misaligned openings, which correspond to the two diffraction spots that return from the aperture beam. The two misaligned openings are rectangular openings that are arranged horizontally, misaligned vertically, and parallel to each other. The acute angle formed by the horizontally arranged rectangular openings and the line connecting the first and second incident slits is within ±30 degrees.

[0009] Furthermore, the entrance slit is equipped with a 370nm long-pass filter to eliminate the influence of second-order diffraction light on the acquisition of light signals with wavelengths less than 370nm in the specified band (370-730nm) entering the spectrometer.

[0010] Furthermore, the sensor is a linear array sensor. Through the staggered opening of the aperture, a single pixel on the photosensitive surface of the linear array sensor receives only the light signal from one optical path.

[0011] Furthermore, a stray light elimination unit is provided for the grating. The stray light elimination unit is a set of wave-shaped light cones that are tilted toward the concave grating side, thereby eliminating other diffracted light generated by the grating.

[0012] A spectrophotometric device based on a single-grating, single-sensor, dual-optical-path spectrometer includes a light signal acquisition unit. This unit is connected to the dual-optical-path spectrometer via two Y-shaped optical path units. Each Y-shaped optical path unit has two input terminals and one output terminal. The first Y-shaped optical path unit's input terminal is connected to the light signal acquisition unit to acquire the reflected light from the sample under test, its other input terminal is connected to a calibration light source, and its output terminal is connected to the entrance of the first entrance slit. The second Y-shaped optical path unit's input terminal is connected to the light signal acquisition unit to acquire the reflected light from the test light source, its other input terminal is connected to a calibration light source, and its output terminal is connected to the entrance of the second entrance slit. The calibration light source is used for the calibration and testing of the device.

[0013] A wavelength calibration method for a spectrophotometric device based on a single-grating, single-sensor, dual-optical-path spectrometer includes the following steps:

[0014] Step S1: Acquire the optical signals of the calibration light source through two Y-shaped optical path units respectively;

[0015] Step S2: The sensor acquires the light signal from the calibration light source;

[0016] Step S3: Obtain the pixel position information of the light signal collected by the sensor. The light signal contains two channels of two optical paths. Take the data of one channel.

[0017] Step S4: Fit the wavelength data and pixel position information using a fourth-order polynomial, adjust the correspondence between pixels and wavelengths, and thus calibrate the wavelength. The fourth-order polynomial is as follows:

[0018] y = C4x 4 +C3x 3 +C2x 2 +C1x+C0 (5)

[0019] y represents wavelength data, and x represents the pixel position information corresponding to the wavelength. The coefficients C4, C3, C2, C1, and C0 calculated from multiple sets of data yield the relationship between wavelength and pixel position.

[0020] Furthermore, a pixel is a photosensitive unit of a linear array sensor. Several photosensitive units are arranged one by one in a straight line to form the photosensitive surface of the linear array sensor. They are numbered according to their arrangement to form a pixel sequence number. The pixel position information is represented by the pixel sequence number that receives the light signal on the photosensitive surface of the linear array sensor.

[0021] The advantages and beneficial effects of this invention are as follows:

[0022] This invention employs a grating as the spectrometer and a linear array sensor as the sensor element to simultaneously sample the main and secondary channels of the system. Compared to existing technologies, the sampling results significantly reduce the impact of temperature variations on the short-term measurement repeatability of the instrument, while saving costs and optimizing the spectrometer structure. Furthermore, this invention designs a colorimeter and its calibration method, using wavelength calibration to calibrate the sampling data changes caused by temperature variations, thus reducing the impact of temperature changes on the long-term measurement repeatability of the instrument. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the dual-path spectrometer structure in an embodiment of the present invention.

[0024] Figure 2 This is a schematic diagram of the aperture blockage of the dual-path spectrometer in an embodiment of the present invention.

[0025] Figure 3 This is a wavelength sensitivity curve of the CMOS linear array image sensor in an embodiment of the present invention.

[0026] Figure 4 This is the optical path diagram of the dual-path spectrometer in this embodiment of the invention.

[0027] Figure 5 This is a side view of the optical path of the dual-path spectrometer in an embodiment of the present invention.

[0028] Figure 6a This is a spot pattern of the dual-path spectrometer in an embodiment of the present invention.

[0029] Figure 6b This is a spectral resolution diagram of the dual-path spectrometer in this embodiment of the invention.

[0030] Figure 7 This is a schematic diagram of the aperture structure of the photosensitive surface of the linear array sensor in an embodiment of the present invention.

[0031] Figure 8 This is a schematic diagram of the stray light elimination unit in an embodiment of the present invention.

[0032] Figure 9a This is a schematic diagram of the dual-path spectrometer and Y-shaped optical fiber in an embodiment of the present invention.

[0033] Figure 9b This is a schematic diagram of the spectrophotometric device of the dual-path spectrometer in an embodiment of the present invention.

[0034] Figure 10 This is a flowchart of the calibration method for the dual-path spectrometer in this embodiment of the invention.

[0035] Figure 11aThis is a spectral diagram of mercury-argon gas lamp collected by a dual-path spectrometer in an embodiment of the present invention.

[0036] Figure 11b This is a spectral curve of channel 1 in the spectral diagram of the mercury-argon gas lamp according to an embodiment of the present invention.

[0037] Figure 12 This is a spectral calibration curve of channel 1 when fitted with a fourth-order polynomial in the wavelength calibration method of this invention.

[0038] Figure 13 is a graph showing the color difference of the spectrophotometer at a temperature of 20°C in Experiment 1 of this embodiment of the invention.

[0039] Figure 14 is a graph showing the color difference of the uncalibrated spectrophotometer in Experiment 2 of this embodiment of the invention at temperatures ranging from 10°C to 35°C.

[0040] Figure 15 This is a graph showing the color difference changes of the spectrophotometer in Experiment 3 of this invention at temperatures ranging from 10°C to 35°C.

[0041] Among them, 1. Lens, 2. First entrance slit, 3. Second entrance slit, 4. Waveform light cone, 5. Grating, 6. Offset opening, 7. Aperture, 8. Linear array sensor, 9. Filter, 10. First Y-shaped fiber, 11. Calibration light source, 12. Second Y-shaped fiber. Detailed Implementation

[0042] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0043] In existing technologies, the optical path structure of D / 8 colorimeters is commonly used. To achieve good measurement repeatability, the inner wall of the integrating sphere is usually chosen as a reference point to eliminate the influence of light source fluctuations on instrument repeatability. The light beam from the test light source illuminates the integrating sphere, and after homogenization by the integrating sphere, it diffuses illumination onto the sample being tested. The reflected light from the sample enters the main optical path spectrometer, while the light reflected from the reference inner wall of the integrating sphere enters the auxiliary optical path spectrometer. The reflectance spectrum of the sample measured by the main optical path spectrometer is P0(λ), and the spectrum of the light source measured by the auxiliary optical path spectrometer is P... s Given that the light intensity input from the light source is S(λ), due to the change in the energy of the light source, the light intensity will change to k(λ)S(λ). The reflectance spectrum of the sample obtained by the main optical path spectrometer will change accordingly to k(λ)P0(λ), and the spectrum of the light source measured by the auxiliary optical path spectrometer will change accordingly to k(λ)P. s (λ), by using the ratio of formula (1), eliminates the influence of light source fluctuation on the measurement.

[0044]

[0045] k(λ) represents the percentage change in the light intensity of the light source.

[0046] Two independent spectrometers were used as a dual-optical-path structure. In an adjustable constant temperature and humidity test chamber, the same colorimeter and the same sample were used. The sample was fixed at the measurement port and multiple measurements were performed. After obtaining the L, a, and b values ​​of each measurement, the color difference was calculated using the first measurement data as a reference value. The repeatability of the instrument was evaluated by the standard deviation of the final calculated color difference value.

[0047] Color difference is calculated using the color difference formula in the CIELAB uniform color space. The formula is:

[0048]

[0049] Where, ΔL * The lightness index L represents the difference between the reference sample and the tested sample. * The difference, Δa * Δb * This indicates the colorimetric index a between the reference sample and the tested sample. * and b * The corresponding difference.

[0050] Standard deviation of color difference S ΔE for:

[0051]

[0052] Where, ΔE i This represents the color difference value of the i-th measurement, and n represents the number of measurements. This represents the average of n color differences measured.

[0053] When ambient temperature and humidity remain constant, the short-term repeatability of the instrument deteriorates with the increase in the number of measurements. When ambient humidity is constant but temperature changes, the short-term repeatability of the instrument is poor, and the long-term repeatability is also poor. Therefore, the dual-optical-path structure with dual gratings and dual sensors cannot effectively correct for the impact of temperature changes on the instrument's measurement repeatability.

[0054] The main reasons for this phenomenon are as follows:

[0055] 1. A spectrometer is an instrument for the quantitative detection of light components. Through dispersive imaging, each pixel of the spectrometer detector receives a light intensity signal of a specific wavelength. When the temperature changes, the optical path structure of the instrument and the relative position of the grating will change. This will cause a certain misalignment in the correspondence between the wavelength and the sensor pixels, resulting in changes in the instrument's sampling data. As a result, the long-term repeatability of the instrument's measurements is poor.

[0056] 2. Temperature changes alter the spectral response and dark current of both sensors. However, because the ambient temperature changes of the two sensors are not entirely consistent, this leads to inconsistencies in the changes in spectral response efficiency and dark current. After calibration, if the temperature changes, the two sensors will produce different photocurrents for the same energy light signal. This results in poor short-term repeatability of the instrument measurements. The spectral response of a sensor reflects its sensitivity to incident light of various wavelengths, thus determining its application range. Temperature changes significantly impact spectral response characteristics. Dark current is a crucial performance indicator for sensors, determining the detector rate; a lower dark current results in a lower detector rate and better performance. Temperature changes greatly affect the magnitude of the sensor's dark current.

[0057] To reduce the impact of temperature changes on the short-term measurement repeatability of the instrument, embodiments of this invention design a dual-optical-path spectrometer. This spectrometer uses a grating as the spectroscopic device and a linear array sensor as the detector to simultaneously measure the optical signals of the main and auxiliary channels. Through optical path and structural design, a dual-optical-path structure based on a single grating and single sensor is integrated into a single spectrometer. Compared to existing dual-grating and dual-sensor dual-optical-path technologies, when the temperature changes, the grating, optical path structure, and sensor all change in the same way, effectively reducing short-term measurement repeatability.

[0058] like Figure 1 As shown, the dual-path spectrometer includes two light-incident slits, a lens 1, a grating 5, a linear array sensor 8, a stray light elimination structure, and an optical path mechanical structure. The two light signals pass through quartz optical fibers and illuminate the first entrance slit 2 and the second entrance slit 3, respectively. The light entering the spectrometer through the entrance slits passes through the lens 1 and is incident on the grating 5 at a certain angle. After being split by the concave grating 5, the light passes through the plano-convex lens 1 again and converges on the linear array sensor 8 below the entrance slit.

[0059] Different wavelengths of light diffract at different angles and are focused onto the photosensitive surface of the linear array sensor 8. The two light paths are split, producing two diffraction spots that are distributed on the left and right sides of the linear array sensor 8 and offset vertically, ensuring that each pixel of the linear array sensor 8 receives the light signal from only one light path. An aperture 7 is also placed on the surface of the linear array sensor 8 to intercept light beyond 370-730nm. Figure 2 As shown.

[0060] According to the characteristics of grating 5, light will undergo second-order diffraction on grating 5. Therefore, light in the 182.5-370nm band will generate second-order diffracted light in the 370-730nm band. In order to eliminate the acquisition of light signals in the 370-730nm band by second-order diffracted light, a 370nm long-pass filter 9 is set at the front or rear end of the entrance slit to prevent light signals with wavelengths less than 370nm from entering the spectrometer.

[0061] The linear array sensor 8 is arranged on the imaging surface of the spectrometer. After collecting the light signal, it is converted into an electrical signal and then into digital information through an AD conversion circuit, and finally uploaded to the host computer.

[0062] The photosensitive surface of the linear array sensor 8 needs to be larger than the imaging areas of the main and auxiliary optical paths. In this embodiment, a Hamamatsu CMOS (Complementary Metal Oxide Semiconductor) linear image sensor, specifically model S10121-512Q-01, is selected, and its performance parameters are shown in Table 1. The spectral response curve is shown in... Figure 3 As shown, its photodiode has a photosensitive area that meets the design requirements, high sensitivity, and is particularly suitable as a detector for colorimeters.

[0063] Table 1 Performance parameters of CMOS

[0064]

[0065] In the embodiments of this invention, a concave grating 5 with a grating constant of 1 / 750 is selected, the spectral range is 350nm-850nm, the thickness is 1cm, the radius of curvature is 95mm, and the aperture of grating 5 is 20mm. In a dual-path spectrometer with a single grating and a single sensor, the optical path of a single optical path signal is as follows: Figure 4 As shown, its side view is as follows Figure 5 As shown. The lens 1 selected in the optical path is a plano-convex lens 1 made of quartz glass with a focal length of 32mm, a thickness of 10mm, a width of 18mm, and a height of 20mm.

[0066] In the optical simulation software Tracepro, by setting it to display only the +1st order diffracted light from grating 5, and adding light in four wavelength bands (400nm, 500nm, 600nm, and 700nm) to the optical fiber, ray tracing shows that the light passes through aperture 7 and converges onto the linear array sensor 8. That is, the light incident through this slit, after being split by grating 5, ultimately strikes the photosensitive surface of the linear array sensor 8 as the +1st order diffracted light.

[0067] In the optical simulation software Tracepro, only the +1st and -1st order diffracted light of grating 5 is displayed, and the same light source as in the single-path simulation is used for fiber optic tracing. The optical paths of the two optical signals in a dual-path spectrometer with a single grating and a single sensor are simulated. From the optical path simulation diagram, it is found that the light incident from the two slits has two orders of diffracted light, +1st and -1st order, respectively. One order of the +1st and -1st order diffracted on grating 5 of each optical path converges on the linear array sensor 8, and the other order of diffracted light propagates to the left and right sides of the linear array sensor 8, respectively.

[0068] Illuminance analysis was performed using the photosensitive surface of the detector. The spot pattern and spectral resolution of the dual-path spectrometer with a single grating and single sensor are shown below. Figure 6a and Figure 6b As shown, the distribution of light spots in the four wavelength bands (400nm, 500nm, 600nm, and 700nm) on the photosensitive surface of the linear array sensor 8 conforms to the design requirements of a dual-path spectrometer with a single grating and single sensor. The spectral resolution diagram illustrates the imaging effects at three wavelengths: 400nm, 405nm, and 410nm. The diagram shows that the resolution at 405nm is approximately 5nm, and the simulation results preliminarily demonstrate the correctness of the design.

[0069] The distance dl that two spectral lines with a wavelength difference of dλ are separated on the focal plane of the image is represented by dλ / dl (mm / nm). In practical work of spectroscopy, the dispersive performance of the spectrometer is often represented by the reciprocal of the dispersion, dλ / dl, that is, the inverse linear dispersion rate. It represents the wavelength range contained per unit length (mm) when the spectrum is imaged on the focal plane. The smaller the value, the greater the linear dispersion rate.

[0070] Based on simulation results, an aperture 7 was designed on the photosensitive surface of the linear array sensor 8. The aperture 7 has two horizontally arranged rectangular, staggered openings 6, which are vertically offset and aligned at ±30 degrees with the line connecting the first and second entrance slits. The aperture dimensions are as follows: Figure 7 As shown in the aperture size diagram, the width of the photosensitive surface of the linear array sensor 8 receiving a single optical signal is dl = 6.4 mm. This width corresponds to a wavelength range of dλ = 730-370 nm. Therefore, the dispersion rate of the spectrometer designed in this embodiment is dλ / dl = (730-370) / 6.4 = 56.25 nm / mm. The dispersion rate of the spectrometer is within ±10% of 56.25 nm / mm. Therefore, based on the inverse calculation of the dispersion rate, the width of the photosensitive surface of the linear array sensor 8 receiving a single optical signal is set.

[0071] Stray light can cause excessive background noise in spectral analysis instruments, blurring the spectral edges and even introducing spurious spectral lines, thus reducing the instrument's signal-to-noise ratio and dynamic range. The main sources of stray light are: internal scattering; reflection from gratings and optical components (near-field stray light); in the single-grating, single-sensor, dual-optical-path spectrometer of this embodiment, grating 5 generates other diffracted light besides the required diffracted light. Based on simulation results, the design is as follows... Figure 8 The two symmetrical stray light elimination units shown are a set of waveform light cones 4, which are inclined towards the concave grating 5. Furthermore, the inner and outer surfaces of the spectrometer structural components are coated with black.

[0072] A dual-path spectrometer was implemented using a single grating and a single sensor, which improved the problem of poor short-term repeatability caused by inconsistencies in the grating, optical path structure, and sensor. However, under long-term temperature variations, the relative positions of the optical path structure and the grating will still change with temperature, leading to variations in the sampling data and resulting in poor long-term repeatability of the instrument.

[0073] Therefore, in this embodiment of the invention, a spectrophotometric device based on a dual-path spectrometer is designed, such as... Figure 9a , Figure 9b As shown, the instrument includes a dual-path spectrometer, a calibration light source 11, a Y-shaped optical path unit, an optical signal acquisition unit, and functional accessories such as a control circuit and a collimation optical path. In this embodiment, the detection range is approximately 370-730 nm. A mercury-argon gas lamp is used as the calibration light source 11 to test the instrument calibration and resolution. The optical signal acquisition unit acquires the reflected light from the sample under test and the reflected light from the test light source. A Y-shaped optical fiber is used as the Y-shaped optical path unit. The Y-shaped optical fiber includes two input ends and one output end. A Y-shaped optical fiber is connected to each of the two entrance slits of the dual-path spectrometer. The input end of the first Y-shaped optical fiber 10 is connected to the optical signal acquisition unit to acquire the reflected light from the sample under test, the other input end is connected to the mercury-argon gas lamp, and the output end is connected to the entrance of the first entrance slit 2. The input end of the second Y-shaped optical fiber 12 is connected to the optical signal acquisition unit to acquire the reflected light from the test light source, the other input end is connected to the mercury-argon gas lamp, and the output end is connected to the entrance of the second entrance slit 3.

[0074] Optical signal acquisition unit such as Figure 9b As shown, it includes a test light source, a test light source filter, an integrating sphere, and an observation lens. Considering the stability and lifespan of the test light source, the embodiment of the present invention uses a pulsed xenon lamp as the test light source. The integrating sphere includes a side light-passing port, a baffle, a bottom measurement port, a top observation port and light trap, and a reference light-exit port on one side of the top.

[0075] The overall control circuit includes a spectrometer control circuit and a light source control circuit. The spectrometer control circuit is connected to the linear array sensor 8 of the dual-path spectrometer, and the light source control circuit is connected to the mercury argon gas lamp and the pulsed xenon lamp, respectively.

[0076] The light source control circuit controls the pulsed xenon lamp to turn on. The light beam passes through the test light source filter and illuminates the inside of the integrating sphere. After being homogenized by the integrating sphere, it diffuses and illuminates the sample under test through the measurement port. The reflected light from the sample under test passes through the observation port and the observation port lens in sequence and is input to one end of the first Y-shaped fiber 10. The light reflected by the inner wall of the integrating sphere reference is used as the test light source reflected light through the reference light outlet and is input to one end of the second Y-shaped fiber 12. The spectrometer control circuit is connected to the linear array sensor 8.

[0077] Based on this colorimetric device, a wavelength calibration method based on a dual-path spectrometer is constructed, such as... Figure 10 As shown, the spectrometer uses a linear array sensor 8 to simultaneously receive spectral data at various wavelengths. Wavelength calibration is used to correct wavelength shifts caused by temperature changes in order to determine the specific wavelength corresponding to each pixel. The specific steps include the following:

[0078] Step S1: During wavelength calibration, the light source control circuit shuts off the test light source and turns on the mercury argon gas lamp, so that the light signal from the mercury argon gas lamp enters the spectrometer through two Y-shaped optical fibers and two incident slits, thereby obtaining the light signal of the calibration light source 11.

[0079] Step S2: Linear array sensor 8 acquires the optical signal of calibration light source 11;

[0080] Step S3: Obtain the pixel position of the light signal collected on the linear array sensor 8. The light signal contains two channels, and take the data from one of the channels.

[0081] A pixel is a photosensitive unit of a linear array sensor 8. Several photosensitive units are arranged in a straight line to form the photosensitive surface of the linear array sensor 8. They are numbered according to their arrangement to form a pixel sequence number. The pixel position is represented by the pixel sequence number on the photosensitive surface of the linear array sensor 8 that receives the light signal.

[0082] The actual spectral curve acquired by the linear array sensor 8 of the spectrometer is as follows: Figure 11a As shown, the spectral diagram consists of two symmetrically shaped spectral lines because a linear array sensor 8 simultaneously measures the mercury-argon gas lamp signals from two optical paths. This is determined by the optical path structure of the dual-path spectrometer. The data from channel 1 is used for wavelength and pixel fitting, and the spectral data of the mercury-argon gas lamp in this channel is shown below. Figure 11bAs shown, six characteristic spectral lines were identified, from left to right: 404.66 nm, 435.84 nm, 546.08 nm, 578.02 nm, 696.54 nm, and 706.72 nm. Due to instrument resolution limitations, the double peaks at 576.96 nm and 579.07 nm could not be distinguished and were merged into a single peak; therefore, the average of the two wavelengths, 578.02 nm, was taken. The pixel sequence numbers corresponding to the six characteristic spectral lines in the two channels are shown in Table 2.

[0083] Table 2. Pixel positions corresponding to the spectral lines of mercury and argon gas lamps.

[0084]

[0085] Step S4: Fit the wavelength and pixels using a fourth-order polynomial, adjust the correspondence between pixels and wavelength, and thus calibrate the wavelength. The fourth-order polynomial is as follows:

[0086] y = C4x 4 +C3x 3 +C2x 2 +C1x+C0 (5)

[0087] y represents wavelength data, and x represents the pixel position corresponding to the wavelength. By calculating coefficients C4, C3, C2, C1, and C0 from multiple sets of data, the relationship between wavelength y and pixel position x is obtained. Channel 2 is fitted using the same method.

[0088] For example, the scaling coefficients are shown in Table 3, where the fitting results for channel 1 are as follows: Figure 12 As shown.

[0089] Table 3. Spectrometer wavelength calibration coefficients

[0090]

[0091] The distance between the x and y coordinates obtained by the wavelength calibration method of this invention and the fitting curve corresponding to the calibration coefficients is the fitting error.

[0092] The fitting error between the obtained wavelength and the characteristic spectral line wavelength is shown in Table 4.

[0093] Table 4. Fitting error of wavelength calibration function

[0094]

[0095] Calibration at every measurement improves both short-term and long-term repeatability. However, it leads to excessively long measurement times. Therefore, calibration is only performed when significant temperature changes or long time intervals are detected. Embodiments of this invention configure the instrument to automatically perform wavelength calibration at regular intervals.

[0096] Energy calibration is employed to calibrate the sensor's spectral response efficiency and dark current variations caused by temperature changes. These temperature-induced changes in sensor spectral response efficiency and dark current lead to variations in pixel response values ​​over long-term use. To ensure the system's long-term measurement stability, response data from a standard white board with unchanged surface properties is collected at regular intervals. The spectral response values ​​of the standard white board are then used as a reference standard for normalization. Energy calibration is divided into black calibration and white calibration. Before each operation and after a period of operation, the white board is moved to the measurement port, and the system collects white board data for white calibration. After the white calibration data measurement is completed, the black board is moved to the sampling port, and black board data is collected for black calibration. After obtaining the black and white calibration data, normalization is performed using the following formula:

[0097]

[0098] In the formula, Φ(λ) represents the response value at wavelength λ after normalization, and Φ0(λ) represents the response value at wavelength λ before normalization. W (λ) represents the response value of the reference whiteboard at wavelength λ, Φ B (λ) represents the dark signal at the wavelength λ position after eliminating external light interference. Black-and-white calibration eliminates instrument correlation in the measurement data, improving instrument performance.

[0099] To evaluate the short-term and long-term repeatability of a colorimeter based on a single-grating, single-sensor, dual-path spectrophotometer, three sets of experiments were set up.

[0100] Experiment 1: A standard dual-path colorimeter and the dual-path colorimeter based on a single grating and single sensor, as described in this embodiment, were placed in a constant temperature and humidity chamber. The temperature was set to 20℃ and the humidity to 50%. After the instruments were left to stand for 1 hour, a calibration operation was performed, followed by measurements. The instrument was used to measure the same position on a standard white board every 3 seconds for 100 consecutive measurements. No calibration was performed during the entire measurement process. The data from the first measurement was taken as the standard data. The color difference was calculated. The color difference change of the standard dual-path colorimeter was as follows: Figure 13a As shown, calculate the standard deviation of the instrument's color difference; the standard deviation of the color difference S... ΔE =0.011, with a maximum and minimum deviation of 0.04; the color difference variation of the dual-path colorimeter based on a single grating and single sensor in this embodiment of the invention is as follows: Figure 13b As shown, the standard deviation S of the color difference ΔE =0.002, the maximum and minimum deviation is 0.01.

[0101] Experiment 2: A standard dual-path colorimeter and the dual-path colorimeter based on a single grating and single sensor, as described in this embodiment, were placed in a constant temperature and humidity chamber. The temperature was set to 10℃ and the humidity to 50%. After the instruments were allowed to stand for 1 hour, measurements were taken. After black and white calibration, the instrument was used to measure the same position on a white board every 5 seconds for 30 consecutive measurements, and the data were recorded. The temperature was then increased to 15℃, and after the instrument was allowed to stand for 1 hour, measurements were taken at the same position on the white board every 5 seconds for 30 consecutive measurements, and the data were recorded. This process was repeated, increasing the temperature by 5℃ each time, up to 35℃, for a total of 6 sets of measurements, accumulating 180 measurements.

[0102] Throughout the measurement process, without using the wavelength calibration and energy calibration described in this embodiment of the invention, the color difference change of a conventional dual-path colorimeter at temperatures ranging from 10°C to 35°C is as follows: Figure 14a As shown, the calculated instrument standard deviation S ΔE =0.09, with a maximum and minimum deviation of 0.3; the color difference change measured by the dual-path colorimeter based on a single grating and single sensor in this embodiment of the invention is as follows: Figure 14b As shown. Calculate the standard deviation S of the instrument's color difference. ΔE =0.018, maximum and minimum deviation 0.081. The measurement repeatability is also significantly better than that of colorimeters that do not use the spectrometer designed in this paper.

[0103] Experiment 3: Place the instrument in a constant temperature and humidity chamber, set the temperature to 10℃ and the humidity to 50%, and let the instrument stand for 1 hour before taking measurements. After black and white calibration, measure the same position on the white board every 5 seconds, for a total of 30 measurements and record the data. Raise the temperature to 15℃, let the instrument stand for 1 hour, and then measure the same position on the white board every 5 seconds, for a total of 30 measurements and record the data. Repeat the operation, increasing the temperature by 5℃ each time, until reaching 35℃, for a total of 6 sets of measurements, accumulating 180 measurements.

[0104] Throughout the measurement process, wavelength and energy calibrations were performed before each temperature change. The instrument's color difference variation between 10°C and 35°C is as follows: Figure 15 As shown. Calculate the standard deviation S of the instrument's color difference. ΔE =0.003, the maximum and minimum deviation is 0.015.

[0105] Experimental data show that the colorimeter using the dual-path spectrometer of this invention exhibits better short-term measurement repeatability than the colorimeter not using the spectrometer of this invention, under constant temperature and humidity. The standard deviation of the color difference, S... ΔE =0.002, maximum and minimum deviation 0.01. When humidity is constant, and temperature increases from 10℃ to 35℃, the standard deviation S of the colorimeter designed in this paper for measuring color difference is... ΔE=0.009, maximum and minimum deviation 0.015, measurement repeatability is significantly better than that of colorimeters that do not use the spectrometer designed in this paper.

[0106] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A dual-path spectrometer, comprising an entrance slit, a lens (1), a grating (5), a sensor, and an aperture (7), characterized in that: The entrance slits include a first entrance slit (2) and a second entrance slit (3). Two light paths pass through the first entrance slit (2) and the second entrance slit (3) respectively, and are incident on the grating (5) through the lens (1). The diffracted light spots returned by the grating (5) are then distributed off-center on the sensor photosensitive surface on the side of the entrance slits through the lens (1). An aperture (7) with an off-center opening (6) is provided on the photosensitive surface, so that the photosensitive surface at each off-center opening (6) receives the light signal of only one light path. The off-center opening (6) of the aperture (7) has two The two diffraction spots returned by the aperture (7) are respectively the two misaligned openings (6). The two misaligned openings (6) are rectangular openings arranged horizontally, misaligned vertically and horizontally, and parallel to each other. The sensor is a linear array sensor (8). Through the misaligned opening (6) of the aperture (7), a single pixel of the photosensitive surface of the linear array sensor (8) receives only the light signal of one optical path. The wavelength range corresponding to the width dl of the photosensitive surface of the sensor receiving the light signal of a single optical path is dλ=730-370nm. According to the dispersion rate of the spectrometer dλ / dl=56.25±10% nm / mm, the width of the misaligned opening (6) of the aperture (7) is set to dl.

2. The dual-path spectrometer according to claim 1, characterized in that: The value of dl is 6.4 mm.

3. A dual-path spectrometer according to claim 1, characterized in that: The acute angle formed by the horizontally arranged rectangular openings and the line connecting the first and second entrance slits is within ±30 degrees.

4. A dual-path spectrometer according to claim 1, characterized in that: The entrance slit is equipped with a 370nm long-pass filter (9) to eliminate the influence of secondary diffraction light on the light signals with wavelengths less than 370nm collected in the specified band entering the spectrometer.

5. A dual-path spectrometer according to claim 1, characterized in that: A stray light elimination unit is provided for the grating (5). The stray light elimination unit is a set of waveform light cones (4) that are tilted toward the grating side.

6. A colorimetric device based on the dual-path spectrometer of claim 1, comprising a light signal acquisition unit, characterized in that: The optical signal acquisition unit is connected to the dual-path spectrometer through two Y-shaped optical path units. The Y-shaped optical path unit includes two input ends and one output end. The input end of the first Y-shaped optical path unit is connected to the optical signal acquisition unit to acquire the reflected light of the sample under test. The other input end is connected to the calibration light source (11), and the output end is connected to the entrance of the first entrance slit (2). The input end of the second Y-shaped optical path unit is connected to the optical signal acquisition unit to acquire the reflected light of the test light source. The other input end is connected to the calibration light source (11), and the output end is connected to the entrance of the second entrance slit (3). The calibration light source (11) is used for the calibration and testing of the device.

7. A wavelength calibration method for the colorimetric device of a dual-path spectrometer according to claim 6, characterized in that... Includes the following steps: Step S1: Obtain the optical signal of the calibration light source (11) through two Y-shaped optical path units respectively; Step S2: The sensor acquires the optical signal from the calibration light source (11); Step S3: Obtain the pixel position information of the light signal collected on the sensor; Step S4: Fit the wavelength data and pixel position information using a fourth-order polynomial, adjust the correspondence between pixels and wavelengths, and thus calibrate the wavelength. The fourth-order polynomial is as follows: y represents wavelength data, and x represents the pixel position information corresponding to the wavelength. The relationship between wavelength and pixel position is obtained by calculating the coefficients C4, C3, C2, C1, and C0.

8. The wavelength calibration method for the colorimetric device of the dual-path spectrometer according to claim 7, characterized in that: A pixel is a photosensitive unit of a sensor. Several photosensitive units are arranged to form the photosensitive surface of the sensor. They are numbered according to their arrangement to form a pixel sequence number. The pixel position information is represented by the pixel sequence number that receives the light signal.

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