Automatic laser focusing system and method based on intensity modulation

Abstract

The invention discloses a laser automatic focusing system and method based on intensity modulation, and relates to the technical field of automatic focusing, and the system comprises a laser emission unit which is used for emitting a laser beam to a target object, the laser beam irradiates the surface of a measured object to form a laser spot, and the laser emission unit is connected with an objective lens which is used for observing the measured object; the intensity modulation unit is located in a light path of the laser emission unit, and the intensity modulation unit is configured to divide the intensity of the laser beam into at least two areas with distinguishable intensity differences on the cross section; the imaging unit is used for acquiring a laser spot to obtain a spot image; the focusing executing mechanism is used for adjusting the distance between a measured object and the objective lens, and the processing control unit is used for judging the defocusing direction according to intensity distribution of different areas in a light spot image, calculating the defocusing amount according to morphological parameters of the light spot image and further outputting a control signal to drive the focusing executing mechanism. According to the invention, the defocusing amount can be accurately calculated, and the focusing performance is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of automatic focusing, in particular to a laser automatic focusing system and method based on intensity modulation. BACKGROUND

[0002] The existing laser focusing system distinguishes the defocusing direction of the system through the upper and lower semicircles of the light spot, and usually uses a semicircular baffle to generate a semicircular light spot. When the light spot received by the image sensor is in a focused state, the beam baffle will generate a diffraction spot, affecting the focusing accuracy. The semicircular collimated laser is generated by passing through the beam baffle, and the baffle will also generate straight edge diffraction, causing serious diffraction stray light of the light spot at the focal point position, affecting the calculation of the defocusing amount, reducing the focusing accuracy, increasing the focusing time, and affecting the focusing performance. The prior art introduces a focal point offset lens to make the light spot reflected by the focal point position of the objective lens in a divergent state at the image sensor, reducing the influence of the diffraction spot on the focusing at the focal point. However, the prior art does not truly eliminate the diffraction influence caused by the beam baffle, and the diffraction spot still exists. When the light spot reflected by the objective lens is in a focused state on the image sensor, the diffraction spot will also appear, and the defocusing amount calculation will still be distorted, affecting the focusing performance. SUMMARY

[0003] The present application aims to solve at least one of the technical problems existing in the prior art. To this end, the present application proposes a laser automatic focusing system and method based on intensity modulation, which can accurately calculate the defocusing amount and improve the focusing performance.

[0004] The laser automatic focusing system based on intensity modulation according to an embodiment of the present application comprises: A laser emitting unit for emitting a laser beam to a target object, the laser beam irradiating the surface of the measured object to form a laser spot, and the laser emitting unit being connected with an objective lens for observing the measured object; An intensity modulation unit located in the optical path of the laser emitting unit, the intensity modulation unit being configured to divide the intensity of the laser beam into at least two regions with distinguishable intensity differences in the cross section; An imaging unit for acquiring the laser spot to obtain a spot image; A focusing execution mechanism for adjusting the distance between the measured object and the objective lens, A processing control unit for judging the defocusing direction according to the intensity distribution of different regions in the spot image, calculating the defocusing amount according to the morphological parameters of the spot image, and then outputting a control signal to drive the focusing execution mechanism.

[0005] According to an embodiment of the present invention, a laser autofocus system based on intensity modulation has at least the following advantages: The processing and control unit determines the defocus direction based on the intensity distribution of different regions in the laser spot image, calculates the defocus amount based on the morphological parameters of the laser spot image, and then outputs a control signal to drive the focusing actuator. An industrial computer is selected as the processing and control unit. The imaging unit acquires laser spot images in real time, and the processing and control unit calculates the defocus amount based on the image morphological parameters and automatically drives the focusing actuator to adjust, thus realizing a fully automated focusing process, reducing manual intervention, and improving focusing efficiency.

[0006] According to some embodiments of the present invention, the intensity modulation unit is a filter whose surface is coated with a film layer with different transmittance in different areas.

[0007] According to some embodiments of the present invention, the intensity modulation unit is configured to cause the laser beam to form a region with a step change in intensity across its cross-section.

[0008] According to some embodiments of the present invention, the intensity modulation unit is configured to form a region of gradually varying intensity across the cross-section of the laser beam.

[0009] According to some embodiments of the present invention, the processing control unit is configured to: Identify the region of highest brightness in the light spot image; Defocus direction is determined based on the position information of the highest brightness region on the imaging unit; Calculate the morphological parameters of the entire or selected region of the spot image, wherein the morphological parameters include at least one of the spot radius, diameter, area, and centroid. The current defocus amount is calculated based on the pre-calibrated mapping relationship between the morphological parameters and the defocus amount.

[0010] The present invention also provides a laser autofocus method based on intensity modulation, comprising the following steps: An intensity-modulated laser beam is emitted toward the object being tested, the cross-sectional intensity of the laser beam being divided into at least two regions with distinguishable differences; Receive the laser beam reflected by the object under test and acquire the spot image; The mapping relationship between calibrated morphological parameters and defocus amount; Determine the defocus direction based on the intensity distribution of different regions in the light spot image; Based on the morphological parameters of the light spot image, and combined with the pre-calibrated mapping relationship between the morphological parameters and the defocus amount, the defocus amount is calculated. Based on the defocus direction and defocus amount, a control command is generated to drive the focusing actuator to complete focusing.

[0011] According to some embodiments of the present invention, the step of determining the defocus direction includes: When a high-brightness area in the light spot image is located in the positive defocus area on the image sensor, it is determined to be positive defocus; When a high-brightness area in the light spot image is located in a negative defocus area on the image sensor, it is determined to be negative defocus.

[0012] According to some embodiments of the present invention, the mapping relationship between the calibration morphological parameters and the defocus amount includes the following steps: The focusing system is driven to move near the focal point in fixed steps; Acquire images of light spots at different locations and calculate their morphological parameters; Set the shape parameter corresponding to the clear focus position as the focus zero point; The relationship between the defocusing amount Y and the morphological parameter X was fitted.

[0013] According to some embodiments of the present invention, the defocusing amount is calculated by adaptively selecting a specific energy region in the spot image based on the reflectivity of the object being measured.

[0014] According to some embodiments of the present invention, the step of calculating the defocus amount includes: Set a grayscale threshold; If the gray values ​​of two regions in the spot image are both higher than the threshold, then the region with lower brightness is selected to calculate the defocus amount; If only one region in the spot image has a gray value higher than the threshold, then the region with higher brightness is selected to calculate the defocus amount.

[0015] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0016] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 This is an overall schematic diagram of a laser autofocus system according to an embodiment of the present invention; Figure 2 This is a schematic diagram of an intensity modulation unit with a strong-to-weak step distribution according to an embodiment of the present invention. Figure 3 This is a schematic diagram of a gradually increasing intensity modulation unit distributed from strong to weak according to an embodiment of the present invention; Figure 4 This is a schematic diagram of laser spots distributed from strong to weak according to an embodiment of the present invention; Figure 5 This is a schematic diagram of a weak-strong-medium distributed step intensity modulation unit according to an embodiment of the present invention; Figure 6 This is a schematic diagram of a gradually increasing intensity modulation unit with a weak-strong-medium distribution according to an embodiment of the present invention; Figure 7 This is a schematic diagram of a laser spot generated in a weak-strong-medium configuration according to an embodiment of the present invention; Figure 8 This is a flowchart of a focusing method according to an embodiment of the present invention.

[0017] Icon labels: Laser emitting unit 100, laser 110, first lens 120, beam splitter 130; Objective lens 200; Intensity modulation unit 300; Imaging unit 400, second lens 410, reflector 420, image sensor 430. Detailed Implementation

[0018] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0019] In the description of this invention, it should be understood that the orientation descriptions, such as up, down, etc., are based on the orientation or positional relationship shown in the drawings and are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0020] In the description of this invention, "multiple" refers to two or more. The use of "first" and "second" is for distinguishing technical features only and should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features or their sequential relationship.

[0021] In the description of this invention, unless otherwise explicitly defined, terms such as "set up," "install," and "connect" should be interpreted broadly, and those skilled in the art can reasonably determine the specific meaning of the above terms in this invention in conjunction with the specific content of the technical solution.

[0022] Reference Figure 1As shown, an embodiment of the present invention provides a laser autofocus system based on intensity modulation, comprising: a laser emitting unit 100, an intensity modulation unit 300, an imaging unit 400, a focusing actuator, and a processing control unit. The laser emitting unit 100 emits a laser beam toward a target object. The laser emitting unit 100 includes a laser 110, a first lens 120, and a beam splitter 130. The laser 110 emits a laser beam, and the first lens 120 straightens the laser beam emitted by the laser 110 into a parallel laser beam. An aperture is disposed between the laser 110 and the first lens 120 to block light, ensuring that the laser 110 can only illuminate the first lens 120. The beam splitter 130 reflects the parallel laser beam onto an objective lens 200, which focuses the parallel laser beam onto the surface of the object being measured to form a laser spot. A laser beam illuminates the surface of the object being measured, forming a laser spot. The laser emitting unit 100 is connected to an objective lens 200 for observing the object. An intensity modulation unit 300 is located in the optical path of the laser emitting unit 100, between the first lens 120 and the beam splitter 130. The intensity modulation unit 300 is configured to divide the intensity of the laser beam across its cross-section into at least two regions with distinguishable intensity differences, allowing the intensity distribution in the spot image to clearly indicate the defocus direction. This enables rapid and accurate determination of the focusing direction, improving the system's response speed and positioning accuracy. An imaging unit 400 acquires the laser spot and obtains a spot image. The imaging unit 400 includes a second lens 410, a reflector 420, and an image sensor 430. The second lens 410 collects the light emitted from the laser spot. The light collected by the second lens 410 passes through the beam splitter 130 and the reflector 420, and finally forms an image on the image sensor 430. The image sensor 430 transmits the measured image to the processing and control unit. A stepper motor or a servo motor is selected as the focusing actuator. The specific structure of the focusing actuator is existing technology and is therefore not shown in the accompanying drawings. The focusing actuator can drive the laser emitting unit 100, intensity modulation unit 300, and imaging unit 400 to move up and down. The focusing actuator is used to adjust the distance between the object being measured and the objective lens 200. The processing and control unit is used to determine the defocus direction based on the intensity distribution of different areas in the laser spot image, calculate the defocus amount based on the morphological parameters of the laser spot image, and then output a control signal to drive the focusing actuator. An industrial computer is used as the processing and control unit. The imaging unit 400 acquires laser spot images in real time. The processing and control unit calculates the defocus amount based on the image morphological parameters and automatically drives the focusing actuator to adjust, realizing a fully automated focusing process, reducing manual intervention, and improving focusing efficiency.

[0023] Reference Figure 1As shown, in some embodiments, the intensity modulation unit 300 is a neutral density filter. The neutral density filter divides the beam cross-section into regions by smoothly attenuating the intensity through its uniform material, rather than physically blocking it, thereby significantly reducing the generation of diffraction spots. This effectively overcomes the diffraction effect introduced by traditional semi-circular baffles. This results in clear edges and a regular intensity distribution in the spot image acquired by the imaging unit 400, significantly reducing image distortion and noise caused by diffraction. It provides a more accurate image data basis with a higher signal-to-noise ratio for the processing control unit to calculate the defocus amount, thus improving focusing accuracy.

[0024] Reference Figure 1 As shown, in some embodiments, the intensity modulation unit 300 is a filter with different transmittance films coated on different areas of its surface. The filter substrate is made of optical glass or quartz. By sputtering and coating different areas separately, arbitrary-shaped regions with precise and significantly different transmittance can be divided on the filter surface. The difference in beam intensity can be the minimum value that the image sensor 430 can recognize, such as a 1% intensity difference, where the left side of the filter surface has 99% transmittance and the right side has 98% transmittance. This allows for the design of more complex intensity modulation patterns. For example, a multi-level stepped center density filter can be designed to divide the beam energy region into more than three parts, thereby embedding more specific defocus direction information in the spot image. Both neutral density filters and coated filters can achieve filters with different transmittance in different areas, producing the same technical effect. The intensity modulation unit 300 can also be replaced with other components that can achieve variable stepped filtering or gradient filtering.

[0025] In some embodiments, the intensity modulation unit is configured to create a region of intensity step change in the cross-section of the laser beam.

[0026] In some embodiments, the intensity modulation unit 300 is configured to create regions of gradually varying intensity across the cross-section of the laser beam. The transition between regions of different transmittance can be precisely controlled by the coating process, avoiding hard-edge diffraction caused by mechanical obstruction. Figure 2 and Figure 3 As shown, the energy distribution in a region of gradually changing intensity can be from strong to weak. For example... Figure 5 and Figure 6 As shown. The energy distribution in the region of gradual intensity change can also be strong-weak-medium or weak-strong-medium, etc. For example, using a weak-strong-medium distribution, the light spot received on the image sensor 430 is as follows: Figure 7 As shown, the processing control unit first determines the region with the strongest energy of the image sensor 430, then calculates the energies A and B on both sides respectively, and then compares the energy magnitudes. If A > B, the system needs to move in the positive direction; if A < B, the system needs to move in the negative direction.

[0027] The shape of the intensity modulation unit 300 can be either a step distribution as shown in the figure or a gradual distribution as shown in the figure.

[0028] In some embodiments, the processing control unit is configured to: Identify the region of highest brightness in the spot image; the region of highest brightness can also be a certain brightness region.

[0029] The defocusing direction is determined based on the position information of the highest brightness area on the image sensor 430 of the imaging unit 400; Calculate the morphological parameters of the entire or selected region of the spot image, including at least one of the spot radius, diameter, area, and centroid. The current defocus amount is calculated based on the pre-calibrated mapping relationship between morphological parameters and defocus amount.

[0030] By directly identifying the brightest region in the spot image and comparing its position with the reference position of the image sensor 430, the determination of the defocus direction is simplified into a fast logical operation, improving overall focusing efficiency. The spot radius, diameter, and area are insensitive to global changes in the reflectivity of the measured object's surface and slow drift of ambient light. Based on the calibration mapping calculation method, in actual operation, the processing unit only needs to calculate one or a few intuitive morphological parameters such as the spot radius or area to quickly obtain the defocus amount by looking up a table. This significantly reduces the complexity of real-time calculations and the dependence on the processing unit's performance while maintaining accuracy. It also enhances the system's focusing accuracy when dealing with objects of different materials, colors, and lighting conditions.

[0031] like Figure 8 As shown, the present invention also provides a laser autofocus method based on intensity modulation, comprising the following steps: The laser emitting unit 100 emits an intensity-modulated laser beam toward the object being measured. The cross-sectional intensity of the laser beam is divided into at least two regions with distinguishable differences by the intensity modulation unit 300. The imaging unit 400 receives the laser beam reflected by the object under test and acquires the spot image; The mapping relationship between the morphological parameters and the defocus amount is processed and calibrated by the control unit; The processing and control unit determines the defocus direction based on the intensity distribution of different regions in the spot image, as shown in the spot image. Figure 4 As shown; The processing and control unit calculates the defocus amount based on the morphological parameters of the spot image and the pre-calibrated mapping relationship between the morphological parameters and the defocus amount. The processing and control unit generates control commands based on the defocus direction and defocus amount, driving the focusing actuator to complete focusing. Before actual focusing, the system pre-establishes and stores a precise mapping relationship between the light spot morphology parameters, such as radius and area, and the actual physical defocus amount. Only the morphology parameters of the current light spot need to be calculated, and the defocus amount can be quickly obtained with high precision through table lookup or interpolation. This improves focusing efficiency, reduces real-time calculation time delay, and effectively overcomes errors introduced by factors such as assembly tolerances.

[0032] Reference Figure 8 As shown, in some embodiments, the specific steps for determining the defocus direction are as follows: when a higher brightness area in the spot image is located in a positive defocus area on the image sensor 430, it is determined to be positive defocus; when a higher brightness area in the spot image is located in a negative defocus area on the image sensor 430, it is determined to be negative defocus. The positive and negative defocus areas are obtained through pre-calibration.

[0033] By directly associating the defocus direction with the fixed position of the high-brightness area on the image sensor 430, the defocus direction can be quickly determined, reducing the computational load of image recognition.

[0034] Reference Figure 8 As shown, in some embodiments, calibrating the mapping relationship between morphological parameters and defocus amount includes the following steps: The focusing actuator drives the entire laser autofocus system to move near the focal point in fixed steps; Acquire images of light spots at different locations and calculate their morphological parameters; Set the shape parameter corresponding to the clear focus position as the focus zero point; The relationship between the defocus amount Y and the morphological parameter X is fitted, and the formula for the relationship is Y = k1*X + k2X. 2 +...+k n *X n +b. Where k is the fitting coefficient, b is the compensation value, and n is a positive integer. For ease of calculation, n is usually taken as 1 or 2. Under the ideal optical model, the defocus amount is directly proportional to the area of ​​the spot, and the proportional relationship is determined by the value of k. Here, b, as the compensation value, can effectively correct the fixed offset caused by system adjustment, aberrations, or algorithm reference definition.

[0035] The calibration process employs an active scanning method, ensuring that the calibration data covers a sufficient range before and after the focal point. Since the defocus amount is proportional to the area of ​​the light spot, it has better predictive reliability and stability between calibration points and outside the limited calibration range, significantly improving the system's calculation accuracy throughout the entire working range.

[0036] Reference Figure 8As shown, in some embodiments, the defocus amount is adaptively selected from specific energy regions in the spot image for calculation based on the reflectivity of the object being measured. An overly dark spot image results in insufficient signal, reducing calculation accuracy. Conversely, an overly bright spot image automatically avoids potentially overexposed areas for high-reflectivity objects, selecting the next highest energy region for analysis. For low-reflectivity objects, an energy region with a relatively high signal-to-noise ratio is selected. This adaptive selection ensures that the image region used to calculate the defocus amount always contains clear intensity distribution characteristics under different reflection conditions, improving the accuracy of the defocus amount calculation.

[0037] Reference Figure 8 As shown, in some embodiments, the step of calculating the defocus amount includes: Set a grayscale threshold; specifically, the grayscale threshold can be set to 120. If the gray values ​​of two regions in the spot image are both higher than the threshold, the region with lower brightness is selected to calculate the defocus amount. If only one region in the spot image has a grayscale value higher than the threshold, the region with higher brightness is selected to calculate the defocus amount. This low-complexity real-time decision significantly reduces the performance requirements on the processor.

[0038] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A laser autofocus system based on intensity modulation, characterized in that, include: A laser emitting unit (100) is used to emit a laser beam toward a target object. The laser beam illuminates the surface of the object being measured to form a laser spot. The laser emitting unit (100) is connected to an objective lens (200) for observing the object being measured. An intensity modulation unit (300) is located in the optical path of the laser emitting unit (100), and the intensity modulation unit (300) is configured to divide the intensity of the laser beam into at least two regions with distinguishable intensity differences in cross-section; An imaging unit (400) is used to acquire the laser spot and obtain a spot image; A focusing actuator is used to adjust the distance between the object being measured and the objective lens (200). The processing and control unit is used to determine the defocus direction based on the intensity distribution of different regions in the light spot image, calculate the defocus amount based on the morphological parameters of the light spot image, and then output a control signal to drive the focusing actuator.

2. The intensity-modulated laser autofocus system according to claim 1, characterized in that: The intensity modulation unit (300) is a filter with different transmittance films coated on different areas of its surface.

3. The intensity-modulated laser autofocus system according to claim 1, characterized in that: The intensity modulation unit (300) is configured to create a region of intensity step change in the cross-section of the laser beam.

4. The intensity modulation-based laser autofocus system according to claim 1, characterized in that: The intensity modulation unit (300) is configured to create a region of gradually varying intensity across the cross-section of the laser beam.

5. The intensity-modulated laser autofocus system according to claim 1, characterized in that: The processing control unit is configured to: Identify the region of highest brightness in the light spot image; The defocus direction is determined based on the position information of the highest brightness area on the imaging unit (400); Calculate the morphological parameters of the entire or selected region of the spot image, wherein the morphological parameters include at least one of the spot radius, diameter, area, and centroid. The current defocus amount is calculated based on the pre-calibrated mapping relationship between the morphological parameters and the defocus amount.

6. A laser autofocus method based on intensity modulation, using the laser autofocus system based on intensity modulation as described in any one of claims 1-5, characterized in that, Includes the following steps: An intensity-modulated laser beam is emitted toward the object being tested, the cross-sectional intensity of the laser beam being divided into at least two regions with distinguishable differences; Receive the laser beam reflected by the object under test and acquire the spot image; The mapping relationship between calibrated morphological parameters and defocus amount; Determine the defocus direction based on the intensity distribution of different regions in the light spot image; Based on the morphological parameters of the light spot image, and combined with the pre-calibrated mapping relationship between the morphological parameters and the defocus amount, the defocus amount is calculated; Based on the defocus direction and defocus amount, a control command is generated to drive the focusing actuator to complete focusing.

7. The laser autofocus method based on intensity modulation according to claim 6, characterized in that, The steps for determining the defocus direction include: When a high-brightness area in the light spot image is located in the positive defocus area on the image sensor, it is determined to be positive defocus; When a high-brightness area in the light spot image is located in a negative defocus area on the image sensor, it is determined to be negative defocus.

8. The laser autofocus method based on intensity modulation according to claim 6, characterized in that, The mapping relationship between the calibrated morphological parameters and the defocus amount includes the following steps: The focusing system is driven to move near the focal point in fixed steps; Acquire images of light spots at different locations and calculate their morphological parameters; Set the shape parameter corresponding to the clear focus position as the focus zero point; The relationship between the defocusing amount Y and the morphological parameter X was fitted.

9. The laser autofocus method based on intensity modulation according to claim 6, characterized in that, The defocus amount is calculated by adaptively selecting a specific energy region in the light spot image based on the reflectivity of the object being measured.

10. The laser autofocus method based on intensity modulation according to claim 9, characterized in that: The steps for calculating the defocus amount include: Set a grayscale threshold; If the gray values ​​of two regions in the spot image are both higher than the threshold, then the region with lower brightness is selected to calculate the defocus amount; If only one region in the spot image has a gray value higher than the threshold, then the region with higher brightness is selected to calculate the defocus amount.

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