CN103292578B - An automatic control method for a microwave dryer - Google Patents

Abstract

The invention discloses an automatic control method of a microwave dryer. The method includes: adjusting the height and angle of a thermal imaging camera to allow the thermal imaging camera to be seen in a conveyer belt area; pre-setting a target drying temperature T<target> and an allowed temperature deviation delta T of material by a computer according to the drying requirements of the material; calculating an average drying temperature T<average> of the material according to a thermal image of the material; comparing the calculated average drying temperature T<average> to the pre-set target drying temperature T<target>; automatically keeping the average drying temperature of the material in the set range, namely T<target> - delta T </= T<average> </= T<target).

Description

An automatic control method for a microwave dryer

technical field

The invention belongs to the technical field of microwave drying, and in particular relates to an automatic control method of a microwave drying machine.

Background technique

Traditional drying methods, such as flame, hot air, steam, electric heating, etc., are all external heating and drying. After the surface of the material absorbs heat, the heat penetrates into the interior of the material through conduction, and the moisture inside the material diffuses outward to the surface and leaves the material, so that The material is dried. Microwave drying is completely different. It is a method of internal heating, and its heat conduction direction is the same as that of moisture diffusion. Compared with traditional drying methods, microwave drying has the advantages of high drying rate, energy saving, high production efficiency, uniform drying, and good product quality, so it has been paid more and more attention in various fields.

In the microwave drying process, it is very important to grasp the drying condition of the material in time and dynamically adjust the drying parameters to ensure the drying effect of the material. At present, there are two main types of sensing methods for the drying of materials in microwave drying equipment: one is the sight glass method, which opens an observation port on the microwave drying equipment, and then equips with auxiliary lighting sources and shielding measures, relying on manual naked eyes to observe the materials in the equipment. of dryness. This type of method is labor-intensive, and it is difficult to sense the dryness of the material in real time and accurately. At the same time, if the shielding measures are not in place, it is easy to affect the health of the workers. The second type of method is as described in patents (200720031024.9, 201020616615.4). The image of the material in the equipment during the drying process is obtained through the monitor, and the image of the material is displayed on the monitor in real time. Although this type of method can keep workers away from radiation sources and monitor the drying condition of materials in real time, the interpretation of material images on the display still depends on the subjective experience of workers, making the entire monitoring accuracy poor and inefficient; at the same time, this type of method cannot According to the monitoring results, the parameters of the microwave dryer are automatically adjusted in time.

Contents of the invention

The invention proposes an automatic control method of a microwave drying machine, which is used for accurately sensing the drying state of materials and automatically adjusting the parameters of the microwave drying machine, so as to realize the automatic control of microwave drying.

In order to solve the above technical problems, the specific technical scheme adopted in the present invention is as follows:

An automatic control method for a microwave dryer, characterized by comprising the following steps:

Step 1, the higher the signal strength of the pixel point is, the higher the temperature of the material at the pixel point is, adjust the height and angle of the thermal imaging camera so that the field of view of the thermal imaging camera is located on the conveyor belt area;

Step 2, according to the drying requirements of the material, the target drying temperature _{T_target} and the allowable temperature deviation of the material are set on the computer in advance;

Step 3: When the microwave dryer is working normally, the thermal imaging camera acquires the thermal imaging image of the material on the conveyor belt at the outlet in real time, and the image acquisition card sends the thermal imaging image to the computer, and the computer calculates the material according to the thermal imaging image of the material. The average drying temperature _{T_average} ;

Step 4, the computer constantly compares the calculated average drying temperature _{T_average} with the preset target drying temperature _{T_target} , if _{T_average} > _{T_target} +?T, that is, the current average drying temperature is greater than the target drying temperature and When the temperature deviation is allowed, the computer sends a control signal to the microwave generator and the conveyor belt drive motor through the programmable controller to reduce the power of the microwave generator or increase the speed of the conveyor belt, thereby reducing the microwave drying intensity of the material;

Step five, if _{T_average} < _{T_target-} ?T, that is, when the current average drying temperature is less than the difference between the target drying temperature and the allowable temperature deviation, the computer sends a control signal to the microwave generator and the conveyor belt drive motor through the programmable controller , increase the power of the microwave generator or reduce the speed of the conveyor belt, thereby increasing the microwave drying strength of the material;

Step 6. Finally, _the average drying temperature of the material is automatically kept within the set range, that is, _{T_target-} ? _{T≤T_average≤T_target} +?T.

The average drying temperature _{T_average} calculation process of the material is as follows:

Process 1: Calibrate the thermal imaging camera to determine the corresponding relationship between the thermal imaging image signal G and the actual temperature T, the corresponding relationship is represented by a function f, that is, T=f(G);

Process 2, determine the _segmentation threshold G_segmentation of the material area and the conveyor belt area in the thermal imaging image of the material:

When the microwave dryer is in working condition but the conveyor belt does not put materials, calculate the average signal intensity G_conveyor _belt of the thermal imaging image under this condition, and assign the _current threshold G_current to G_conveyor _belt ;

When the microwave dryer is in working condition and the conveyor belt is put into the material, the thermal imaging image of the conveyor belt and the material is obtained, and the thermal imaging image is segmented with the _current threshold G_current. If the segmentation effect is not satisfactory, enter the step ; If the segmentation effect is satisfactory, enter the step ;

Amend the current threshold _{G_current} value, and return to step ;

Determining the _current threshold G_current as the segmentation threshold _{G_segmentation} ;

Process three, using the segmentation threshold _{G_segmentation} to segment the thermal imaging image of the material, and calculating _the average signal intensity G_average of pixels in other areas of the thermal imaging image outside the conveyor belt area;

In process four, according to the corresponding relationship between the signal intensity of the thermal imaging image and the actual temperature in process one, the average signal intensity in process three is converted into the average drying temperature, that is, _{T_average} =f( _{G_average} ).

The beneficial effects of the present invention are: use thermal imaging camera, acquisition card and computer to accurately perceive the drying temperature of materials, and automatically adjust the power of microwave generator and the speed of conveyor belt drive motor according to the set target drying temperature, which improves the efficiency of microwave drying. level of automation and intelligence.

Detailed ways

The present invention will be described in detail through various embodiments below. However, these embodiments do not limit the present invention, and any structural, method, or functional changes made by those skilled in the art according to these embodiments are included in the protection scope of the present invention.

The automatic control method of the microwave dryer is:

(1) According to the drying requirements of the material, set the target drying temperature _{T_target} =80°C and the allowable temperature deviation?T=5°C on the computer in advance.

(2) When the microwave dryer is working normally, the thermal imaging camera acquires the thermal imaging image of the material on the conveyor belt at the outlet in real time, and the image acquisition card sends the thermal imaging image to the computer, and the computer calculates the material according to the thermal imaging image of the material. average drying temperature.

(3) The computer can quickly calculate the average drying temperature _{T_average} of the material according to the thermal imaging image of the material;

The calculation process of the average drying temperature _{T_average} of the material is as follows:

1) Calibrate the thermal imaging camera to determine the corresponding relationship between the thermal imaging image signal G and the actual temperature T; after setting the aperture and exposure time of the thermal imaging camera, thermal imaging is performed on objects at different temperatures, and the thermal imaging image signal G Carry out regression analysis with the actual temperature T to obtain the corresponding relationship between them and express it with the function f, that is, T=f(G)=0.363G+7.07.

2) Determine _{the segmentation} threshold G_segmentation of the material area and the conveyor belt area in the thermal imaging image:

When the microwave dryer is in working condition but the conveyor belt does not put materials, calculate the average signal intensity of the thermal imaging image of the conveyor belt obtained by the thermal imaging camera under this condition G_conveyor _belt =60, and assign the _current threshold G_current to G_ _{conveyor belt} ;

When the microwave dryer is in working condition and the conveyor belt is put into the material, the thermal imaging image of the conveyor belt and the material is obtained, and the thermal imaging image is segmented with the _current threshold G_current. If the segmentation effect is not satisfactory, enter the step ; If the segmentation effect is satisfactory, enter the step ;

Amend the current threshold _{G_current} value, and return to step ;

Determine the _current threshold G_current as the segmentation threshold _{G_segmentation} , and finally determine the segmentation threshold _{G_segmentation} =80;

3) Use the segmentation threshold _{G_segmentation} to segment the thermal imaging image of the material, and calculate the average signal intensity _{G_average} of the pixels in the thermal imaging image other than the conveyor belt area;

4) According to the corresponding relationship between the signal intensity of the thermal imaging image and the actual temperature in step (1), convert the average signal intensity in step 3) into the average drying temperature, that is, _{T_average} =f( _{G_average} )= _{0.363G_average} +7.07 .

(4) The computer continuously compares the calculated average drying temperature _{T_average} with the preset target drying temperature _{T_target} =80°C; when the current average drying temperature is greater than the sum of the target drying temperature and the allowable temperature deviation, if T _{_average} > _{T_target} +?T means _{T_average} >80℃+5℃, the computer sends control signals to the microwave generator and conveyor belt drive motor through the programmable controller to reduce the power of the microwave generator or increase the transmission The speed of the belt, thereby reducing the microwave drying intensity of the material.

(5) When the current average drying temperature is less than the difference between the target drying temperature and the allowable temperature deviation, if _{T_average} < _{T_target-} ?T, that is, _{T_average} <80°C-5°C, the computer sends The microwave generator and the conveyor belt drive motor send control signals to increase the power of the microwave generator or reduce the speed of the conveyor belt, thereby increasing the microwave drying intensity of the material.

(6) Finally, the average drying temperature _{T_average} of the _material is automatically maintained within the set range _{T_target-} ? _{T≤T_average≤T_target} +?T, that is, 80°C-5° _{C≤T_average≤80} ℃+5℃.

Claims (1)

1. an automatic control method of microwave dryer, it is characterized in that comprising the following steps: Step 1, the higher the signal strength of the pixel point is, the higher the temperature of the material at the pixel point is, adjust the height and angle of the thermal imaging camera so that the field of view of the thermal imaging camera is located on the conveyor belt area; Step 2, according to the drying requirements of the material, the target drying temperature _{T_target} and the allowable temperature deviation of the material are set on the computer in advance; Step 3: When the microwave dryer is working normally, the thermal imaging camera acquires the thermal imaging image of the material on the conveyor belt at the outlet in real time, and the image acquisition card sends the thermal imaging image to the computer, and the computer calculates the material according to the thermal imaging image of the material. The average drying temperature _{T_average} ; Step 4, the computer constantly compares the calculated average drying temperature _{T_average} with the preset target drying temperature _{T_target} , if _{T_average} > _{T_target} +?T, that is, the current average drying temperature is greater than the target drying temperature and When the temperature deviation is allowed, the computer sends a control signal to the microwave generator and the conveyor belt drive motor through the programmable controller to reduce the power of the microwave generator or increase the speed of the conveyor belt, thereby reducing the microwave drying intensity of the material; Step five, if _{T_average} < _{T_target-} ?T, that is, when the current average drying temperature is less than the difference between the target drying temperature and the allowable temperature deviation, the computer sends a control signal to the microwave generator and the conveyor belt drive motor through the programmable controller , increase the power of the microwave generator or reduce the speed of the conveyor belt, thereby increasing the microwave drying strength of the material; Step 6. Finally, the average drying temperature of the material is automatically maintained within the set range, that is, _{T_target-} ? _{T≤T_average≤T_target} +?T _; The average drying temperature _{T_average} calculation process of the material is as follows: Process 1: Calibrate the thermal imaging camera to determine the corresponding relationship between the thermal imaging image signal G and the actual temperature T, the corresponding relationship is represented by a function f, that is, T=f(G); Process 2, determine the _segmentation threshold G_segmentation of the material area and the conveyor belt area in the thermal imaging image of the material: When the microwave dryer is in working condition but the conveyor belt does not put materials, calculate the average signal intensity G_conveyor _belt of the thermal imaging image under this condition, and assign the _current threshold G_current to G_conveyor _belt ; When the microwave dryer is in working condition and the conveyor belt is put into the material, the thermal imaging image of the conveyor belt and the material is obtained, and the thermal imaging image is segmented with the _current threshold G_current. If the segmentation effect is not satisfactory, enter the step ; If the segmentation effect is satisfactory, enter the step ; Amend the current threshold _{G_current} value, and return to step ; Determining the _current threshold G_current as the segmentation threshold _{G_segmentation} ; Process three, using the segmentation threshold _{G_segmentation} to segment the thermal imaging image of the material, and calculating _the average signal intensity G_average of pixels in other areas of the thermal imaging image outside the conveyor belt area; In process four, according to the corresponding relationship between the signal intensity of the thermal imaging image and the actual temperature in process one, the average signal intensity in process three is converted into the average drying temperature, that is, _{T_average} =f( _{G_average} ).