An automatic focusing device and method for a visible light detection system

Abstract

The application discloses a visible light detection system automatic focusing implementation device and method, and belongs to the technical field of photoelectric detection. The device comprises a gas-tight packaging box body, a control system, an optical lens, a photoelectric sensor, an image processing system, a temperature sensor, a gas charging and discharging valve and an absolute position sensor which are installed in the gas-tight packaging box body. The optical lens, the temperature sensor, the absolute position sensor and the image processing system are electrically connected with the control system. The photoelectric sensor is connected with the image processing system. The gas charging and discharging valve is mechanically connected without electricity. The optical lens has a focusing function. The image processing system receives data sent by the temperature sensor, the absolute position sensor and the photoelectric sensor, performs real-time calculation and detection on the defocus value of a target image, and sends the defocus value of the target image to the control system to control the optical lens to focus. The application can automatically obtain a clear image of a target in real time.

Description

Technical Field

[0001] This invention belongs to the field of photoelectric detection technology, specifically relating to an automatic focusing device and method for a visible light detection system. Background Technology

[0002] In the field of photoelectric detection technology, detection systems operating in the visible light band play a crucial role in photoelectric equipment, often referred to as the "eyes" of the device, and are an important means of acquiring target image information. Visible light detection systems include optical lenses (including optical systems), photoelectric sensors, image processing, and displays. To obtain clear image information of the target, they also feature manual or manually controlled electric distance and temperature-controlled focusing functions.

[0003] The reason for setting up focusing is that during the optical and mechanical assembly of the visible light detection system, the optical lens is typically positioned at room temperature so that the imaging surface of the target at infinity is focused onto the receiving surface of the photoelectric sensor. At this point, focusing is successful, and the target image is optimal. When the imaging distance changes, the target's imaging surface deviates from the photoelectric sensor's receiving surface. When this deviation exceeds the depth of focus of the detection system, the image becomes blurred, affecting subsequent detection of the target. Distance-based focusing ensures the target remains focused on the photoelectric sensor's receiving surface. Under different ambient temperatures, the refractive index of the optical elements changes with temperature, causing variations in the system's optical path length and resulting in defocusing. Simultaneously, differences in the thermal expansion coefficients of the optical element materials and the mechanical materials such as the lens barrel and base plate cause axial displacements, exacerbating the defocusing phenomenon and causing the target's imaging surface to deviate from the photoelectric sensor's receiving surface. Therefore, temperature-based focusing is used to compensate for temperature-induced defocusing and obtain a clear image of the target. Most existing detection technologies do not consider the internal drying of the system. In complex environments, condensation occurs due to the lack of drying methods, which ultimately affects the image quality. Some products use desiccants to keep the system dry, but desiccants have an expiration date, are prone to failure, are inconvenient to maintain, and the amount of desiccant is limited by volume, which cannot meet the drying requirements of large-volume optical detection systems.

[0004] With the widespread application of visible light detection systems, the demand for real-time, automatic, and clear imaging of moving targets from near (e.g., within 100m) to far (e.g., greater than 100km) or from far to near is increasing under different operating ambient temperatures. Existing technologies include manual or hand-controlled electric distance focusing and temperature focusing, which do not meet the requirements for real-time, automated focusing. They are time-consuming and labor-intensive, and only consider a single factor. There is little research on multi-factor combined focusing, which cannot meet the requirements for real-time, fully automatic combined focusing under changes in distance and temperature. In addition, the existing automatic focusing methods based on temperature models or theoretical analytical functions with set step compensation for defocusing do not meet the accuracy requirements for clear imaging. This is because: (1) To obtain clear imaging, the glass refractive index accuracy must reach 10. -6The above shows that the theoretical model cannot meet the focusing accuracy requirements; (2) the step compensation is in an open-loop state and the compensation effect cannot meet the focusing accuracy requirements.

[0005] After distance-temperature focusing, errors in distance and temperature measurements may cause a small shift in the final focus. To achieve optimal focusing, fine-tuning using image autofocus is necessary. During image autofocus, the focusing mechanism is guided by the detection value. Existing image autofocus methods typically involve multiple optimization oscillations, affecting image quality. Furthermore, existing image-based autofocus methods lack focusing guidance (target distance change trend), making them prone to getting stuck in local optima when far from the optimal focusing position, failing to adjust to the truly optimal focus location. Additionally, image noise can significantly impact the detection value under different weather and environmental conditions, leading to optimization errors in the focusing mechanism. Summary of the Invention

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0007] An automatic focusing device for a visible light detection system includes: an hermetically sealed enclosure and a control system, an optical lens, a photoelectric sensor, an image processing system, a temperature sensor, an inflation / deflation valve, and an absolute position sensor installed inside the hermetically sealed enclosure; wherein the photoelectric sensor is installed inside the hermetically sealed enclosure with the target surface position coinciding with the optical image plane of the infinity target of the optical lens as a reference.

[0008] The optical lens, temperature sensor, absolute position sensor, and image processing system are all electrically connected to the control system; the photoelectric sensor is connected to the image processing system; the inflation and deflation valves are mechanical and have no electrical connection.

[0009] The optical lens has a focusing function, which is achieved by the control system driving the motor to move the focusing element linearly along the optical axis via a mechanical transmission pair; the control system collects the corresponding data from the temperature sensor and the absolute position sensor, and transmits the corresponding data to the image processing system; the image data obtained by the photoelectric sensor is also sent to the image processing system.

[0010] The image processing system receives data from the temperature sensor, absolute position sensor, and photoelectric sensor, performs real-time calculations and detects the defocus value of the target image, and sends the defocus value of the target image to the control system to control the optical lens to focus.

[0011] A method for achieving autofocus in a visible light detection system, used in the aforementioned autofocus device for the visible light detection system, comprising:

[0012] Step 1: At room temperature, adjust the photoelectric sensor receiving target surface of the visible light detection system autofocus device to be located on the imaging surface of the optical lens for the infinitely distant target, and obtain a clear image of the infinitely distant target to complete focusing; take the position of the focusing element of the optical lens at this time as the focusing zero point.

[0013] Step 2: The automatic focusing device of the visible light detection system is sealed with nitrogen through the filling and venting valves;

[0014] Step 3: Place the visible light detection system autofocus device into the high and low temperature test chamber, set the temperature inside the high and low temperature test chamber, read the temperature value of the temperature sensor and the corresponding position of the focusing element, and form a temperature-focusing element position relationship table.

[0015] Step 4: Based on the temperature-focusing element position relationship table recorded in Step 3, fit the temperature-focusing curve; obtain the temperature compensation position of the focusing element based on the temperature-focusing curve.

[0016] Step 5: Calculate the distance-focusing amount based on the target distance and focus relationship. ;

[0017] Step 6: Based on the temperature compensation position of the focusing element obtained in Step 4 and the distance focusing amount obtained in Step 5, the position of the focusing element is obtained, and preliminary focusing is achieved.

[0018] Step 7: Use the image processing system to calculate the image focus value and determine whether the image sharpness has reached the optimal image plane position. If it has not reached the optimal position, guide the focusing element to focus the image until the image sharpness meets the requirements, and the focusing is completed.

[0019] The present invention has the following beneficial effects:

[0020] (1) The visible light detection system autofocus device of the present invention uses a gas-tight enclosure filled with nitrogen to keep the inside dry and prevent condensation from occurring inside the device when the temperature changes from low to high in the high and low temperature chamber, which would affect the clear imaging of the target and improve the accuracy of the temperature-focusing curve.

[0021] (2) The present invention uses the temperature-focusing curve of the detection system obtained by testing in a high and low temperature chamber, which saves time and labor costs compared with obtaining the ambient temperature change in the external natural environment.

[0022] (3) The visible light detection system autofocus device of the present invention realizes real-time and accurate compensation for defocus caused by temperature by setting a built-in temperature sensor to detect the temperature of the optical lens in real time.

[0023] (4) The image processing system of the visible light detection system autofocus realization device of the present invention calculates the position of the focusing element corresponding to the target distance based on the externally input target distance value and the optical system parameters. The position information is acquired in real time by an absolute position sensor, realizing real-time and automatic compensation for defocus caused by distance changes.

[0024] (5) The automatic focusing method of the visible light detection system of the present invention adopts a pre-fitted temperature-focusing curve, combined with the real-time temperature feedback of the built-in temperature sensor, and uses the distance-focusing correspondence value and the position information of the real-time absolute position sensor to obtain the position of the focusing element at different temperatures and distances: Temperature / distance focusing position = Temperature-compensated focusing position + Distance focusing amount.

[0025] (6) The automatic focusing method of the visible light detection system of the present invention combines the fine focusing hybrid method based on the image processing system on the basis of (5) above, realizes the real-time and automatic acquisition of clear images of the target, solves the defect of pure image focusing getting trapped in local optima, and improves focusing efficiency.

[0026] (7) The image processing system of the visible light detection system autofocus realization device of the present invention uses the Tenengrad (based on Sobel gradient) method to calculate the focus value, which has advantages in effectiveness and calculation speed compared with the local variance method, entropy-based detection, Brenner gradient method, Laplacian method, etc. In particular, regarding the influence of noise on the detection result, it is removed by calculating the gradient of the image and then selecting an appropriate threshold. Attached Figure Description

[0027] Figure 1 This is a top view of the automatic focusing device of the visible light detection system of the present invention, wherein 1-optical lens, 2-control system, 3-photoelectric sensor, 4-image processing system, 5-temperature sensor, 6-inflation / expansion valve, 7-absolute position sensor, and 8-hermetically sealed packaging box.

[0028] Figure 2 This is a schematic diagram of the component connection relationship of the visible light detection system autofocus realization device of the present invention. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0030] like Figure 1 As shown, the visible light detection system autofocus device of the present invention includes: an optical lens 1, a control system 2, a photoelectric sensor 3, an image processing system 4, a temperature sensor 5, an inflation / deflation valve 6, an absolute position sensor 7, and an airtight packaging box 8.

[0031] The optical lens 1, equipped with focusing functionality, is housed within an hermetically sealed enclosure 8. The photoelectric sensor 3 is positioned within the enclosure 8 with the target surface aligning with the infinity optical image plane of the optical lens 1. The temperature sensor 5 is also housed within the enclosure 8, positioned close to the optical lens 1 according to the specific spatial layout. The control system 2 and image processing system 4 are also housed within the enclosure 8 according to their spatial layout. The enclosure 8 also includes an inflation / deflation valve 6 and an absolute position sensor 7. The inflation / deflation valve 6 is positioned within the enclosure 8 for easy operation; in this example, it is located at the rear of the enclosure 8. The optical lens 1, temperature sensor 5, absolute position sensor 7, and image processing system 4 are all electrically connected to the control system 2. The photoelectric sensor 3 is connected to the image processing system 4. The inflation / deflation valve 6 is a mechanical, non-electrical connection used to fill the automatic focusing device of the visible light detection system with nitrogen to maintain internal dryness.

[0032] like Figure 2 As shown, the component connections and functional descriptions of the automatic focusing device in the visible light detection system are as follows:

[0033] The optical lens 1 with focusing function includes a motor, a mechanical transmission pair, and a focusing element. Its focusing function is achieved by the control system 2 driving the motor to move the focusing element linearly along the optical axis via the mechanical transmission pair. At the same time, the control system 2 collects relevant data from the temperature sensor 5 and the absolute position sensor 7, and transmits the relevant data to the image processing system 4.

[0034] Temperature sensor 5 is used to monitor temperature changes inside the hermetically sealed enclosure 8 in real time.

[0035] An absolute position sensor 7 is used to measure the position information of the focusing element in real time. In this example, the sampling accuracy of the absolute position sensor 7 is 50 nanometers. The control system 2 receives the position data from the absolute position sensor 7. The control system 2 uses a PID (proportional, integral, and derivative) control algorithm to achieve a minimum movement step accuracy of less than 1 micrometer for the focusing element, which can meet the image focusing requirements of the optical system.

[0036] Photoelectric sensor 3, in this example, is a digital industrial camera. During temperature calibration (step 3 below), photoelectric sensor 3 obtains an image of the target at infinity provided by the collimator. In practical use, this is the image of the imaging target, and the image signal of the imaging target is sent to image processing system 4 for data processing.

[0037] The image processing system 4 receives temperature and position sensor data sent back by the control system 2, combines it with image data acquired by the photoelectric sensor 3, calculates and detects the defocus value of the target image in real time, and sends it to the control system 2 to control the optical lens 1 to focus.

[0038] The visible light detection system autofocus implementation method of the present invention uses the above-mentioned visible light detection system autofocus implementation device, including:

[0039] Step 1, as follows Figure 1 As shown, at room temperature, the photoelectric sensor 3 of the visible light detection system is manually adjusted to be positioned on the imaging surface of the optical lens 1 for the infinitely distant target (using a light tube to simulate the infinitely distant target) to achieve a clear image of the infinitely distant target (using a light tube to simulate the infinitely distant target). The position of the focusing element of the optical lens 1 at this time is taken as the focusing zero point. This zero point is the zero point of the absolute position sensor 7 (the zero point position will change with temperature, so it will be calibrated and corrected using a high and low temperature chamber later).

[0040] Step 2: The automatic focusing device of the visible light detection system is sealed with nitrogen through the filling and venting valve 6.

[0041] Step 3: Place the visible light detection system autofocus device into the high and low temperature test chamber. A collimator is installed outside the test chamber, its position ensuring that the optical lens 1 in the visible light detection system autofocus device can clearly image the target at infinity provided by the collimator. Set the temperature range and temperature change method within the high and low temperature test chamber, such as from -40℃ to +60℃, with data read every 10℃ intervals. Maintain the temperature at each level for 1 hour. The control system 2 controls the focusing element of the optical lens 1 to move along the optical axis until a clear target image is observed at the corresponding temperature. Read the temperature value of the temperature sensor 5 and the corresponding position of the focusing element (position information measured by the absolute position sensor 7). After recording all temperature ranges, a temperature-focusing element position relationship table is generated.

[0042] Step 4: Based on the temperature-focusing element position relationship table from Step 3, fit a temperature-focusing curve. Based on the temperature-focusing design curve provided by the optical structure design, this example currently provides one or more straight line equations: L = kT + L0, where k is the slope, L0 is a constant related to the focusing position, T is the temperature (measured by temperature sensor 5), and L is the focusing element position. Using temperature T and focusing element position L as parameters, the least squares method is used to fit the straight line equation to obtain the temperature-focusing curve. In implementation, based on the temperature-focusing curve, the corresponding temperature value is input to obtain the temperature compensation position of the focusing element.

[0043] Step 5: Calculate the distance-focusing amount based on the target distance and focus relationship. ;

[0044] The following formula represents the relationship between target distance and focus, from which the distance-focusing amount is derived. .

[0045] The object-image relationship of optical lens 1 is expressed by the Gaussian formula:

[0046] (1)

[0047] in, For object distance, Image distance, Focal length;

[0048] Therefore, the formula for calculating the image distance can be obtained:

[0049] (2)

[0050] The photoelectric sensor 3 can resolve a minimum dispersion of 1 pixel. At this point, the corresponding image plane changes along the axial direction according to the following formula:

[0051] (3)

[0052] in, For detector pixel size, For optical focal length, The aperture of the optical system (entrance pupil diameter). This refers to changes in the image plane.

[0053] Current target distance Distance focusing is no longer required when the following relationship is met:

[0054] ; (4)

[0055] Current target distance satisfy: > > At that time, distance focusing amount As shown in the following formula:

[0056] (5)

[0057] in, The optical maximum target distance. This is the closest detection distance;

[0058] Based on actual detection requirements, the stroke of the absolute position sensor 7 covering the focusing range is selected, and the corresponding focusing speed is designed to match the target movement speed.

[0059] Step 6: Based on the temperature compensation position of the focusing element obtained in Step 4 and the distance focusing amount obtained in Step 5... This allows us to obtain the position of the focusing element and achieve initial focusing.

[0060] Wherein, focusing element position = focusing element temperature-compensated focusing position + distance focusing amount .

[0061] Step 7: Based on the initial focusing in Step 6, the image processing system 4 calculates the image focus detection value to determine whether the image sharpness has reached the optimal image plane position. Otherwise, it guides the focusing element to focus the image until the image sharpness meets the requirements, and the focusing is completed. In this embodiment, the focus detection value is calculated based on the image as follows:

[0062] As can be seen from formula (3), the F-number (focal length) of the detector determines the theoretical focal plane position of the optical lens 1. When the image blur is greater than one pixel of the photoelectric sensor 3, it is considered that defocus has occurred. At this time, the amount of defocus is greater than the depth of focus. Based on Shannon's sampling principle, the focusing step size S of control system 2 can be set to 2 times. .

[0063] Image focus value calculation: Commonly used autofocus focus value calculation methods include the following: local variance method, entropy-based point detection, Tenengrad (based on Sobel gradient) method, Brenner gradient method, Laplacian method, etc.

[0064] Combining the effectiveness and computational speed of the focus detection value evaluation, this invention selects the Tenengrad (based on Sobel gradient) method to calculate the focus detection value. The drawback of this method is that noise affects the results. Since most noise is a low-frequency signal, after calculating the gradient of the image, most of it is in a low-threshold state. Choosing an appropriate threshold to remove low-threshold signals can filter out most of the noise. Image noise is mainly generated by the camera. A uniform background image is acquired, its Sobel gradient is calculated, and the mean and variance at this point are statistically analyzed. Based on 3... The criteria and formula for calculating the segmentation threshold are as follows:

[0065] (6)

[0066] in, The segmentation threshold is... The mean gradient of the uniform background image. The gradient variance of the uniform background image.

[0067] Image focus value The calculation formula is as follows:

[0068] , (7)

[0069] in, and These represent the horizontal and vertical responses of the Sobel filter, respectively. The width of the image (horizontal direction). The height (vertical direction) of the image.

[0070] Image focus value The higher the value, the clearer the image. Based on this property, the focusing mechanism is guided to move, recording the position of the focusing element and its corresponding focus value information. Initially, the focusing mechanism moves towards the optical parfocal position. If the corresponding focus value continues to decrease, the focusing direction is considered incorrect, and the mechanism moves in the opposite direction. When the focus value continues to increase, the focusing direction is considered correct, and the focusing mechanism continues to move in the same direction until the peak value of the focus value is detected. The final image focusing position is the position of the focusing element corresponding to the peak value of the focus value.

[0071] The above description is merely an embodiment of the present invention and does not limit the scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification and drawings, or direct or indirect applications in other related system fields, are similarly included within the protection scope of the present invention.

[0072] The contents not described in detail in this specification are existing technologies known to those skilled in the art.

Claims

1. A method for automatic focusing of a visible light detection system, characterized in that, The application relates to an automatic focusing device for a visible light detection system. Step 1: at room temperature, the photoelectric sensor of the automatic focusing device for the visible light detection system receives a target surface on the imaging surface of an optical lens for an infinite distance target to obtain clear imaging of the infinite distance target, and the focusing is completed; the position of the focusing element of the optical lens at this time is taken as a focusing zero point; Step 2: the automatic focusing device for the visible light detection system is filled with nitrogen through the filling and discharging valve and is packaged; Step 3: the automatic focusing device for the visible light detection system is placed in a high-low temperature test box, the temperature in the high-low temperature test box is set, the temperature value of the temperature sensor and the corresponding focusing element position are read, and a temperature-focusing element position relationship table is formed; Step 4: according to the temperature-focusing element position relationship table recorded in step 3, a temperature-focusing curve is fitted; the temperature compensation position of the focusing element is obtained according to the temperature-focusing curve; Step 5, calculate the distance focus amount according to the distance of the target and the focus relationship ; Current target distance When the following relationship is satisfied, the distance focusing action is no longer required: ； ； Current target distance Satisfies: Distance focusing amount The following equation:​​ ； wherein, is the optical far target distance, is the optical system aperture, is the detector pixel size, is the optical focal length; is the nearest detection distance; Step 6: the temperature compensation position of the focusing element obtained in step 4 is combined with the distance focusing amount obtained in step 5 to obtain the position of the focusing element, and preliminary focusing is realized; Step 7: the image processing system is used to calculate the image focusing value, and it is judged whether the image definition reaches the best phase position; if not, the focusing element is guided to image focusing until the image reaches the image definition requirement, and the focusing is completed.

2. The method of claim 1, wherein the method further comprises: In step 1, a light pipe is used to simulate an infinite distance target.

3. The method of claim 1, wherein the method further comprises: In step 3, a parallel light pipe is arranged outside the high-low temperature test box, the position of the parallel light pipe ensures that the optical lens in the automatic focusing device for the visible light detection system can clearly image the infinite distance target provided by the parallel light pipe; the temperature range and temperature change mode in the high-low temperature test box are set, the control system controls the focusing element of the optical lens to move along the optical axis until a clear target image is observed at multiple corresponding temperatures; the temperature value of the temperature sensor and the corresponding focusing element position at this time are read, and the temperature-focusing element position relationship table is formed after all temperature segments are recorded.

4. The method of claim 1, wherein the method further comprises: In step 4, the least square method is used to fit a straight line equation with temperature T and focusing element position L as parameters, and a temperature-focusing curve is obtained.

5. The method of claim 1, wherein the method further comprises: In step 6, focus element position = focus element temperature-compensated focus position + distance focus amount .

6. The method of claim 1, wherein the method further comprises: In step 7, the image focus value The calculation formula is as follows: ， ； wherein, and are the responses of the Sobel filter in horizontal and vertical direction, respectively, is the width of the image, is the height of the image, is the segmentation threshold.

7. The method of claim 6, wherein the method further comprises: Segmentation threshold The formula for calculating the segmentation threshold is as follows: ； wherein, is the uniform background image gradient mean, is the uniform background image gradient variance.

8. An apparatus for implementing an auto-focusing method of a visible light detection system, for implementing the auto-focusing method of the visible light detection system according to any one of claims 1 to 7, characterized in that, The application relates to an automatic focusing device for a visible light detection system. The gas-tight packaging box body, the control system, the optical lens, the photoelectric sensor, the image processing system, the temperature sensor, the filling and discharging valve and the absolute position sensor are arranged in the gas-tight packaging box body; the photoelectric sensor is arranged in the gas-tight packaging box body and is set according to the position of the receiving target surface and the infinite distance target optical image surface of the optical lens; The optical lens, the temperature sensor, the absolute position sensor and the image processing system are electrically connected with the control system; the photoelectric sensor is connected with the image processing system; the filling and discharging valve is a mechanical type without electrical connection; The optical lens has a focusing function, the focusing function is realized by driving the focusing element to move linearly along the optical axis direction through a mechanical transmission pair driven by a motor of the control system; the control system collects corresponding data of the temperature sensor and the absolute position sensor and transmits the corresponding data to the image processing system; the image data obtained by the photoelectric sensor is also transmitted to the image processing system; The image processing system receives data sent by the temperature sensor, the absolute position sensor and the photoelectric sensor, performs real-time calculation and detection on the defocus value of the target image, and sends the defocus value of the target image to the control system for controlling the optical lens to focus.

9. The automatic focusing device for a visible light detection system according to claim 8, wherein The control system adopts a PID control algorithm, and the control precision of the minimum moving step of the focusing element is less than microns.

Images