Solution concentration real-time detection method based on cylindrical lens focusing offset

Abstract

The invention provides a solution concentration real-time detection method based on cylindrical lens focusing offset, which comprises the following steps: step A, laser emitted by a laser diode is collimated into parallel light through a plano-convex lens, the parallel light is emitted into a sample cell through a glass window, and the sample cell is used for detecting the concentration of a sample; and then the light is emitted by the cylindrical lens and is imaged on the image sensor. B, the parallel light is imaged into a light spot on the image sensor after being emitted by the cylindrical lens, the image sensor is driven by the stepping motor to move, the minimum light spot is found, the moving distance of the image sensor is recorded, and the solution concentration change is inversed through the moving distance; by introducing a cylindrical lens light path amplification mechanism, the detection precision is remarkably improved, the temperature drift is effectively inhibited, and the defect of insufficient sensitivity in the prior art is overcome.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical detection technology, and in particular to a solution concentration real-time detection method based on focusing shift of cylindrical lens. BACKGROUND

[0002] The existing solution concentration measurement technology has significant limitations. The contact sensor (such as conductivity meter) is easy to be corroded and contaminated by the solution, and is only suitable for ionic solution. The traditional refractometer requires complex optical path and precise displacement detection, and is high in cost. The spectral analysis method requires complex spectral equipment, and is difficult to adapt to industrial site environment, especially dynamic production process (such as pharmaceutical reaction kettle and food fermentation tank), and lacks reliable non-contact online monitoring scheme. The light spot analysis method detects the change of light spot size, moves the CMOS sensor to find the minimum light spot to realize concentration detection, and has the advantages of simple structure and low cost, but the existing technology has defects such as insufficient sensitivity and large temperature drift, and the practical application is limited. The present application introduces the amplification mechanism of cylindrical lens optical path, significantly improves the detection accuracy, and effectively suppresses the temperature drift. SUMMARY

[0003] In order to solve the above technical problems, the present application provides a solution concentration real-time detection method based on focusing shift of cylindrical lens, which comprises the following steps:

[0004] Step A: the laser emitted by the laser diode is collimated into parallel light by the plano-convex lens, the parallel light is injected into the sample cell through the glass window, and then is imaged on the image sensor by the cylindrical lens;

[0005] Step B: the parallel light is imaged as a light spot on the image sensor after being emitted by the cylindrical lens, the image sensor is moved by the stepping motor, the minimum light spot is found, and the moving distance of the image sensor is recorded , the moving distance is used to inverse the change of solution concentration;

[0006] The calculation steps of inverse solution concentration change are as follows:

[0007] Let the parameters of the cylindrical lens be: the convex curvature radius of the cylindrical lens is R, the refractive index of the cylindrical lens is , and the lens thickness is L; let the parallel light incident beam diameter be D, and the edge light height of the cylindrical lens is calculated as ±D / 2;

[0008] Initial state: when the concentration to be measured is , the solution refractive index is , the angle between the light ray and the optical axis is when the light propagates in the cylindrical lens, and the exit light height is , at this time, the position of the image sensor when the light spot is the smallest is The zero displacement point of the stepper motor;

[0009] The first refraction occurs at the convex incident point of the cylindrical lens after the laser passes through the solution to be measured:

[0010] Let the incident angle be The calculation formula is when the angle is small;

[0011] According to the law of refraction: ; wherein, is the refractive index of the solution to be measured, is the refractive index of the cylindrical lens;

[0012] The refraction angle in the cylindrical lens is The calculation formula is ;

[0013] When the laser propagates in the cylindrical lens, the angle between the light and the optical axis is The calculation formula is ;

[0014] The second refraction occurs at the plane exit point of the cylindrical lens when the laser exits to the air:

[0015] Let the height of the exit light be The calculation formula is ;

[0016] The incident angle in the cylindrical lens is The angle between the light and the optical axis when propagating in the lens is ; according to the law of refraction: ; wherein, the refractive index of air is 1, is the refractive index of the cylindrical lens;

[0017] Let the intersection point of the edge light and the optical axis be point A, and the intersection point of the exit surface of the cylindrical lens and the optical axis be point O. The distance between points OA is s. The calculation formula is

[0018] when the angle is small;

[0019]

[0020] After unfolding:

[0021] ;

[0022] ;

[0023] Among them:

[0024] ;

[0025] calculated image sensor movement distance The relationship with the refractive index is:

[0026] ;

[0027] ;

[0028] .

[0029] In a preferred embodiment, the detection method further comprises a solution concentration measuring device, the solution concentration measuring device comprising a laser diode, a plano-convex lens, a sample cell, a cylindrical lens, a stepper motor and an image sensor arranged in sequence along an optical path, the stepper motor being connected to the image sensor;

[0030] The sample cell is provided with a glass window on the side close to the plano-convex lens, the cylindrical lens is arranged on the side of the sample cell away from the plano-convex lens, the sample cell contains the solution to be measured, and the convex surface of the cylindrical lens faces the solution to be measured;

[0031] The laser emitted by the laser diode passes through the plano-convex lens, the sample cell and the cylindrical lens in sequence, and forms a light spot on the image sensor, the stepper motor can drive the image sensor to move, thereby changing the size of the light spot, and the stepper motor can real-time position the displacement of the image sensor.

[0032] In a preferred embodiment, the stepper motor is a high-precision stepper motor integrated with an absolute encoder; the image sensor is a linear array CMOS image sensor.

[0033] In a preferred embodiment, the stepper motor drives the image sensor to perform displacement compensation, and the minimum displacement is ≤ 0.1 μm.

[0034] In a preferred embodiment, the bottom of the sample cell is provided with a temperature sensor and a pressure sensor; the temperature sensor and the pressure sensor are respectively used to detect the temperature and pressure of the solution to be measured.

[0035] In a preferred embodiment, the temperature and pressure of the solution to be measured are detected by the temperature sensor and the pressure sensor, and the influence of temperature and pressure on measurement is compensated by an algorithm.

[0036] In a preferred embodiment, the temperature sensor comprises a thermistor, and the resistance value of the thermistor changes with temperature;

[0037] According to the change of the resistance value of the thermistor, the measured value of the refractive index of the solution is compensated in real time; the calculation formula is as follows:

[0038] ;

[0039] wherein is the temperature, is the pressure value, is the salinity parameter, is the light source wavelength.

[0040] In a preferred embodiment, the measured value of the refractive index of the solution is compensated in real time according to the pressure variation measured by the pressure sensor; the calculation formula is as follows:

[0041] ;

[0042] wherein is the temperature, is the pressure value, is the salinity parameter, is the light source wavelength.

[0043] In a preferred embodiment, the pressure sensor comprises a pressure balancing device, which comprises a gas pressure regulating valve or a liquid pressure stabilizer.

[0044] Compared with the prior art, the technical scheme of the present application has the following beneficial effects:

[0045] 1. The present application provides a solution concentration measuring device, the laser emitted by the laser diode passes through the plano-convex lens, the sample cell and the cylindrical lens in turn, and is imaged as a light spot on the image sensor. The stepping motor can drive the image sensor to move, thereby changing the size of the light spot, and the stepping motor can real-time position the displacement of the image sensor. Through the light spot shape analysis and inversion algorithm based on the cylindrical lens, the whole optical measurement is realized without contacting the solution, which is suitable for non-contact rapid measurement of liquid concentration, especially for concentration detection of transparent to semi-transparent liquids such as alcohol and sugar solution.

[0046] 2. The present application significantly improves the sensitivity and accuracy by introducing the cylindrical lens light path amplification mechanism, and sets temperature sensor and pressure sensor to compensate the influence of temperature and pressure on measurement through algorithm, thereby effectively inhibiting temperature drift. BRIEF DESCRIPTION OF DRAWINGS

[0047] Figure 1 is the structure distribution diagram of the solution concentration measuring device in the preferred embodiment of the present application;

[0048] Figure 2 is the first refraction and second refraction of the laser light in the cylindrical lens in the preferred embodiment of the present application;

[0049] Figure 3 is the relationship diagram of alcohol concentration and refractive index in the preferred embodiment of the present application;

[0050] Figure 4 A curve of the moving distance of the CMOS image sensor and the refractive index of alcohol in the preferred embodiment of the present application;

[0051] Figure 5 A curve of the moving distance of the CMOS image sensor and the alcohol concentration in the preferred embodiment of the present application;

[0052] Figure 6 A curve of the temperature and the refractive index compensation in the preferred embodiment of the present application;

[0053] Figure 7 A curve of the pressure and the refractive index compensation in the preferred embodiment of the present application.

[0054] The reference signs are explained as follows: 1, a laser diode; 2, a plano-convex lens; 3, a cylindrical lens; 4, an image sensor; 5, a temperature sensor; 6, a pressure sensor; 7, a glass window; 8, a stepping motor; 9, a sample cell. DETAILED DESCRIPTION

[0055] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application; obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application, and all other embodiments obtained by those skilled in the art based on the embodiments in the present application without creative efforts fall within the scope of protection of the present application.

[0056] In the description of the present application, it should be noted that the terms "upper", "lower", "inner", "outer", "top / bottom end" and the like indicate the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0057] In the description of the present application, it should be noted that unless otherwise explicitly specified and limited, the terms "mounting", "provided with", "sleeved / connected", "connected" and the like should be understood broadly, for example, "connected" can be wall-mounted connection, can be detachable connection, or integral connection, can be mechanical connection, can be electrical connection, can be direct connection, can be indirect connection through an intermediate medium, can be the communication between two elements, and those skilled in the art can understand the specific meaning of the above terms in the present application according to the specific circumstances.

[0058] Reference Figures 1-7The embodiment provides a solution concentration real-time detection method based on column lens focusing offset, which is used for non-contact rapid measurement of liquid concentration, and is especially suitable for concentration detection of transparent to semi-transparent liquids such as alcohol and sugar solution.

[0059] The solution concentration real-time detection method comprises a solution concentration measuring device, such as Figure 1 The solution concentration measuring device comprises, in sequence along an optical path, a laser diode 1, a plano-convex lens 2, a sample cell 9, a column lens 3, a stepping motor 8 and an image sensor 4, the stepping motor 8 is connected with the image sensor 4, the sample cell 9 is provided with a glass window 7 on a side close to the plano-convex lens 2, the column lens 3 is arranged on a side of the sample cell 9 away from the plano-convex lens 2, the sample cell 9 contains a solution to be measured, and a convex surface of the column lens 3 faces the solution to be measured, laser emitted by the laser diode 1 passes through the plano-convex lens 2, the sample cell 9 and the column lens 3 in sequence, and is converged into an image of a light spot on the image sensor 4, the stepping motor 8 can drive the image sensor 4 to move, so that the size of the light spot is changed, and the stepping motor 8 can real-time position displacement of the image sensor 4, and the minimum light spot position is accurately captured.

[0060] The stepping motor 8 is a high-precision stepping motor 8 integrated with an absolute encoder, and the image sensor 4 is a linear array CMOS image sensor 4. The stepping motor 8 drives the image sensor 4 to perform displacement compensation, the minimum displacement of the image sensor 4 is less than or equal to 0.1 μm, and concentration measurement is realized by accurately positioning the minimum light spot position.

[0061] As shown in Figure 1 The bottom of the sample cell 9 is provided with a temperature sensor 5 and a pressure sensor 6, which are used for real-time monitoring of environmental parameters, and the temperature sensor 5 and the pressure sensor 6 are respectively used for detecting the temperature and pressure of the solution to be measured. The temperature and pressure of the solution to be measured are detected by the temperature sensor 5 and the pressure sensor 6, and the influence of temperature and pressure on measurement is compensated by an algorithm.

[0062] The detection method comprises the following steps:

[0063] In step A, laser emitted by the laser diode is collimated into parallel light by the plano-convex lens, the parallel light is injected into the sample cell through the glass window, and then is imaged on the image sensor by the column lens;

[0064] In step B, the parallel light is imaged into a light spot on the image sensor after being emitted by the column lens, the change of the solution concentration will cause the change of the refractive index, the change of the refractive index will affect the size of the light spot, the image sensor is moved by the stepping motor, the minimum light spot is found, and the moving distance of the image sensor is recorded , by moving distance Inversion solution concentration changes;

[0065] The calculation steps of inversion solution concentration changes are as follows:

[0066] As Figure 2 , the parameters of the cylindrical lens are: the convex curvature radius of the cylindrical lens is R, the refractive index of the cylindrical lens is , and the lens thickness is L; the diameter of the parallel light incident beam is D, and the edge light height of the cylindrical lens is calculated as ±D / 2.

[0067] Taking alcohol concentration and refractive index as an example (the relationship between alcohol concentration and refractive index is as follows Figure 3 ), the light parameters: the edge light height D / 2 (beam diameter D).

[0068] Initial state: when the concentration to be measured is , the refractive index of the solution is , the angle between the light and the optical axis when the light propagates in the cylindrical lens is , and the exit light height is , at this time the position of the smallest light spot on the image sensor is , which is located at the zero displacement point of the stepper motor.

[0069] The first refraction occurs when the laser is incident into the convex surface of the cylindrical lens after passing through the solution to be measured:

[0070] Let the incident angle be , and the calculation formula is (approximation of small angle);

[0071] According to the law of refraction: ; wherein, is the refractive index of the solution to be measured, is the refractive index of the cylindrical lens;

[0072] The refraction angle in the cylindrical lens is , and the calculation formula is ;

[0073] When the laser propagates in the cylindrical lens, the angle between the light and the optical axis is , and the calculation formula is ;

[0074] The second refraction occurs when the laser exits the plane of the cylindrical lens to the air:

[0075] Let the exit light height be , and the calculation formula is ;

[0076] The incident angle in the cylindrical lens is the angle between the light and the optical axis when the light propagates in the lens ; according to the law of refraction: ; wherein the air refractive index is 1, is the refractive index of the cylindrical lens;

[0077] Let the intersection of the edge light and the optical axis be point A, the intersection of the cylindrical lens exit surface and the optical axis be point O, and s be the distance between points OA.

[0078] (small angle approximation);

[0079]

[0080] After unfolding:

[0081] ;

[0082] ;

[0083] wherein:

[0084] ;

[0085] The calculated image sensor movement distance and the refractive index (such as Figure 4 ) are as follows:

[0086] ;

[0087] ;

[0088] .

[0089] According to the above calculation, the relationship diagram of alcohol concentration and movement distance is as follows: Figure 5 .

[0090] In this embodiment, temperature compensation is achieved by adding a temperature compensation element, such as a thermistor, in the solution concentration measuring instrument, which is used in conjunction with the sensor. As Figure 6 , the resistance value of the thermistor will change with temperature, and by measuring the resistance value change of the thermistor, the temperature change can be known, and then according to the pre-established temperature compensation model, the measured value of the solution refractive index is compensated in real time. The calculation formula is as follows:

[0091] ;

[0092] wherein is the temperature, is the pressure value, is the salinity parameter, is the light source wavelength.

[0093] In the present embodiment, pressure compensation is to add pressure balancing devices, such as installing gas pressure regulating valve or liquid pressure stabilizer, etc., so that the pressure in the measurement environment remains relatively stable, reducing the influence of pressure changes on the measurement of the refractive index of the solution. As Figure 7 , according to the pressure change of the pressure sensor, the measured value of the refractive index of the solution is compensated in real time; the calculation formula is as follows:

[0094] ;

[0095] Wherein is the temperature, is the pressure value, is the salinity parameter, is the wavelength of the light source.

[0096] The above description is only the preferred specific embodiment of the present application, but the design concept of the present application is not limited to this, any person skilled in the art within the technical range disclosed by the present application, using this concept to make non-essential changes to the present application, all belong to the act of infringing the protection scope of the present application.

Claims

1. A method for real-time detection of solution concentration based on cylindrical lens focus offset, characterized by: The detection method comprises the following steps: Step A: The laser light emitted by the laser diode is collimated into parallel light by a plano-convex lens. The parallel light is incident on the sample cell through a glass window and then emitted by a cylindrical lens to form an image on the image sensor. Step B: After the parallel light is emitted by the cylindrical lens, it is imaged as a light spot on the image sensor. The image sensor is driven to move by a stepper motor to find the minimum light spot, and the movement distance Δs of the image sensor is recorded. The change in solution concentration is inverted by the movement distance Δs; The calculation steps for inverting the solution concentration change are as follows: Assume that the parameters of the cylindrical lens are: the radius of curvature of the convex surface of the cylindrical lens is R, the refractive index of the cylindrical lens is n L , the lens thickness is L; let the incident parallel light beam diameter be D, calculate the edge light height of the cylindrical lens ±D / 2; Initial state: When the concentration to be measured is c0, the refractive index of the solution is n0, the angle between the light and the optical axis when propagating in the cylindrical lens is γ0, and the height of the emitted light is y0. At this time, the position of the image sensor when the light spot is minimized is s0, which is located at the zero displacement point of the stepper motor; The first refraction occurs when the laser passes through the solution to be measured and enters the convex incident point in the cylindrical lens: Assume that the incident angle is α, and the calculation formula is as follows when the angle is small: According to the law of refraction: nsinα=n L sinβ; where n is the refractive index of the solution to be measured, n L is the refractive index of the cylindrical lens; The internal refraction angle β of the cylindrical lens is calculated as follows: When the laser propagates in the cylindrical lens, the angle between the light and the optical axis is γ, and the calculation formula is: The second refraction occurs at the plane exit point where the laser exits the air through the cylindrical lens: Assuming the height of the outgoing light is y, the calculation formula is The incident angle α in the cylindrical lens is the angle γ between the light and the optical axis when propagating in the lens; according to the law of refraction: n air sinδ=n L sinγ; where n is the refractive index of air air is 1, n L is the refractive index of the cylindrical lens; Assume that the intersection of the marginal ray and the optical axis is point A, the intersection of the exit surface of the cylindrical lens and the optical axis is point O, and s is the distance between points OA. When the angle is small, the calculation formula is: After expansion: in: The calculated relationship between the image sensor moving distance Δs and the refractive index is:

2. The method for real-time solution concentration detection based on cylindrical lens focus offset according to claim 1, characterized in that: The detection method further includes a solution concentration measuring device, which includes a laser diode, a plano-convex lens, a sample cell, a cylindrical lens, a stepping motor, and an image sensor arranged in sequence along the optical path, wherein the stepping motor is connected to the image sensor; A glass window is provided on a side of the sample cell close to the plano-convex lens, the cylindrical lens is provided on a side of the sample cell away from the plano-convex lens, the sample cell contains a solution to be tested, and the convex surface of the cylindrical lens faces the solution to be tested; The laser light emitted by the laser diode passes through the plano-convex lens, the sample cell, and the cylindrical lens in sequence, and is imaged as a light spot on the image sensor. The stepper motor can drive the image sensor to move, thereby changing the size of the light spot, and the stepper motor positions the displacement of the image sensor in real time.

3. The method for real-time solution concentration detection based on cylindrical lens focus offset according to claim 2, characterized in that: The stepper motor adopts a high-precision stepper motor integrated with an absolute encoder; the image sensor adopts a linear array CMOS image sensor.

4. The method for real-time solution concentration detection based on cylindrical lens focus offset according to claim 3, characterized in that: The stepping motor drives the image sensor to perform displacement compensation, and the minimum displacement is ≤0.1 μm.

5. The method for real-time detection of solution concentration based on cylindrical lens focus offset according to claim 2, characterized in that: A temperature sensor and a pressure sensor are provided at the bottom of the sample pool; the temperature sensor and the pressure sensor are used to detect the temperature and pressure of the solution to be tested respectively.

6. The method for real-time solution concentration detection based on cylindrical lens focus offset according to claim 5, characterized in that: The temperature and pressure of the solution to be measured are detected by the temperature sensor and the pressure sensor, and the influence of temperature and pressure on the measurement is compensated by an algorithm.

7. The method for real-time solution concentration detection based on cylindrical lens focus offset according to claim 6, characterized in that: The temperature sensor includes a thermistor, and the resistance value of the thermistor changes with temperature; According to the resistance change of the thermistor, the measured value of the refractive index of the solution is compensated in real time; the calculation formula is as follows: n(T,P r =10.13dbar,S=35psu,λ=635nm)=1.339522-0.3255·10 -4 ·T-0.2623·10 -5 ·T 2 +3.3269·10 -8 ·T 3 -2.0863· 10 -10 ·T 4 ； Where T is temperature, P r is the pressure value, S is the salinity parameter, and λ is the wavelength of the light source.

8. A method for real-time detection of solution concentration based on cylindrical lens focus offset according to claim 6, characterized in that: According to the pressure change of the pressure sensor, the measured value of the refractive index of the solution is compensated in real time; the calculation formula is as follows: Where T is temperature, P r is the pressure value, S is the salinity parameter, and λ is the wavelength of the light source.

9. The method for real-time solution concentration detection based on cylindrical lens focus offset according to claim 8, characterized in that: The pressure sensor includes a pressure balancing device, and the pressure balancing device includes a gas pressure regulating valve or a liquid pressure stabilizer.

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