Machine vision system based on tunable laser light source

Abstract

The utility model relates to a machine vision system based on a tunable laser light source. The machine vision system comprises a tunable laser, a light beam shaping module, a light beam reflection module and a detection module. After the tunable laser emits laser to the beam shaping module, the laser is shaped by the beam shaping module, and the shaped beam is reflected to a detection target object through the beam reflection module to provide a detection light source; a lens surface of the detection module detects a detection target object; the beam shaping module comprises a spatial filter formed by a first lens and a pinhole, laser of the tunable laser is focused through the first lens, passes through the pinhole, then is expanded to a proper size through a second lens, and passes through a 1 / 2 wave plate to change the polarization state of the beam, so that the beam shaping module is formed. And the point-to-line conversion device converts the point light beam of the 1 / 2 wave plate into a linear light beam and outputs the linear light beam to the light beam reflection module.

Description

Technical Field

[0001] The utility model relates to a visual detection system, in particular to a machine vision system based on a tunable laser light source. Background Art

[0002] The existing multi-spectral light source of LED multi-lighting is a common lighting method. Multi-spectral light sources usually consist of a group of LED lights, each of which emits light of a specific wavelength. The machine vision system can achieve image acquisition under different spectral conditions by controlling the brightness and on-off time of the LED lights. LED multi-spectral light sources use LED lights of different wavelengths to illuminate the observed object to highlight or enhance specific features or attributes of the object.

[0003] The machine vision system based on multi-spectral light source of LED light source is widely used in agriculture, food quality inspection, medical imaging, material inspection, semiconductor manufacturing and security monitoring. For example, it can be used to monitor the growth status of crops, detect defects in food, improve the quality of medical images, etc.

[0004] However, the wavelength range of color LED light sources is relatively wide, and its resolution is limited relative to some application scenarios that need to distinguish very close colors. Generally, the spectrum of LED light sources is wide, usually exceeding 100 nanometers, so it can be classified as a wide-spectrum light source. In addition, the wavelength of LED light sources cannot usually be adjusted at will. In order to obtain a specific wavelength of narrow-linewidth illumination, it is necessary to use a narrow-band filter to filter the LED light source, which will significantly reduce the brightness of the light source. The light energy absorbed by the filter is converted into heat, causing more heat dissipation problems. In some application scenarios that need to distinguish subtle color differences, monochrome LED light sources still have difficulty in achieving good color distinction due to their large luminous bandwidth, resulting in insufficient color contrast in the captured image, which is easy to cause misjudgment. Utility Model Content

[0005] The utility model aims to provide a machine vision system based on a tunable laser light source, which is used to solve the misjudgment problem of a monochromatic LED light source in tasks of high resolution and color difference recognition.

[0006] The utility model discloses a machine vision system based on a tunable laser light source, comprising: a tunable laser, a beam shaping module, a beam reflection module and a detection module; after the tunable laser emits laser light to the beam shaping module, the laser light is shaped by the beam shaping module, and the shaped light beam is reflected to a detection target object by the beam reflection module to provide a detection light source; the lens of the detection module detects the detection target object; the beam shaping module comprises: a first lens and a pinhole forming a spatial filter, the laser light of the tunable laser is first focused by the first lens, passes through the pinhole and then passes through the second lens to expand the light beam to an appropriate size, then passes through a 1 / 2 wave plate to change the polarization state of the light beam, and then passes through a point-line conversion device to convert the point-shaped light beam of the 1 / 2 wave plate into a line-shaped light beam, and then outputs it to the beam reflection module.

[0007] According to an embodiment of the machine vision system based on a tunable laser light source of the utility model, the first lens is a short focal length, double cemented achromatic lens or an achromatic microscope objective lens.

[0008] According to an embodiment of the machine vision system based on a tunable laser light source of the utility model, the pinhole is a small hole aperture with a diameter of 0.1 to 0.2 mm.

[0009] According to an embodiment of the machine vision system based on a tunable laser light source of the utility model, the light beam reflection module is a separate reflection mirror.

[0010] According to an embodiment of the machine vision system based on a tunable laser light source of the utility model, the 1 / 2 wave plate is an achromatic wave plate.

[0011] According to an embodiment of the machine vision system based on a tunable laser light source of the utility model, the point-to-line conversion device is a single cylindrical lens, and the focal length is determined according to the size of the illumination area and the distance from the light source to the target object.

[0012] According to an embodiment of the machine vision system based on a tunable laser light source of the utility model, the point-to-line conversion device is a Powell prism.

[0013] According to an embodiment of the machine vision system based on a tunable laser light source of the utility model, the light beam reflection module is a scanning galvanometer, and the scanning galvanometer swings at a certain frequency to form a line scanning form of illumination for the target object.

[0014] According to an embodiment of the machine vision system based on a tunable laser light source of the utility model, the detection module includes an area array camera and an analyzer, and the analyzer is arranged in front of the lens of the area array camera.

[0015] According to an embodiment of the machine vision system based on a tunable laser light source of the utility model, the tunable laser is a titanium sapphire solid laser or a ruby ​​laser.

[0016] The utility model adopts a laser light source, which has a narrower spectral line width than color LEDs and can distinguish minute color differences. At the same time, the output wavelength (spectrum) of the tunable laser light source can be adjusted in real time according to demand, thereby achieving the output of different wavelengths (colors) in the visible light band to meet the needs of various application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Shown is a schematic diagram of a machine vision system based on a tunable laser light source of the utility model;

[0018] Figure 2 Shown is a schematic diagram of the beam shaping module;

[0019] Figure 3 Shown is another principle diagram of a machine vision system based on a tunable laser light source according to the utility model. DETAILED DESCRIPTION

[0020] In order to make the purpose, content, and advantages of the utility model clearer, the specific implementation methods of the utility model are further described in detail below in conjunction with the drawings and embodiments.

[0021] Figure 1 The figure shows a schematic diagram of a machine vision system based on a tunable laser light source according to the present invention. Figure 1 As shown, the utility model is a machine vision system based on a tunable laser light source, comprising: a tunable laser 1, a beam shaping module 2, a beam reflecting module 3, and a detection module 4.

[0022] like Figure 1 As shown, after the tunable laser 1 emits laser light to the beam shaping module 2, the laser light after beam shaping is reflected to the detection target 5 by the beam reflection module 3. The lens of the detection module 4 faces the detection target 5, and the reflected laser light provides the light source required by the detection module 4.

[0023] Figure 2 The schematic diagram of the beam shaping module is shown in FIG. Figure 1 as well as Figure 2As shown, the beam shaping module 2 includes: a first lens 21 and a pinhole 22 form a spatial filter, which can remove stray light from the laser spot to make the illumination more uniform. The second lens 23 expands the light beam to an appropriate size. This size determines the width of the line light at the illuminated object. After the light beam is filtered and expanded, it passes through a 1 / 2 wave plate 24. By rotating the angle of the 1 / 2 wave plate 24, the polarization state of the light beam can be changed, which can improve the image's ability to distinguish the material of the object. The point-to-line conversion device 25 converts the point light beam of the 1 / 2 wave plate 24 into a linear light beam.

[0024] like Figure 1 As shown, the output beam of the tunable laser 1 is generally close to a fundamental mode Gaussian beam. The radius of a common fundamental mode Gaussian beam is generally on the order of 1 mm, and the divergence angle is on the order of 1 mrad.

[0025] like Figure 1 As shown, the first lens 21 can be a short focal length (10-20 mm), double-cemented achromatic lens or achromatic microscope objective lens (the aperture of the lens needs to be larger than the diameter of the light beam). Through the achromatic design, incident laser beams of different wavelengths can be accurately focused to the pinhole 22 position.

[0026] like Figure 1 As shown, the size of the focused light spot of the pinhole 22 is estimated by multiplying the beam divergence angle by the focal length of the lens. The size of the focused light spot is about 0.1 mm. The size of the pinhole 22 is slightly larger than the focused light spot to take into account the uniformity of the light spot and the higher energy utilization rate. Therefore, the pinhole 22 can use a small aperture diaphragm with a diameter of 0.1 to 0.2 mm.

[0027] like Figure 1 As shown, the second lens 23 expands the light beam to an appropriate size. This size determines the width of the line light at the illuminated object. A beam width that is too small will place greater requirements on the installation accuracy of the optical path, and increase the difficulty of subsequent camera and light source installation and adjustment. It is more appropriate to expand the light beam to a diameter of about 5mm to 10mm. The diameter of the light beam incident on the first lens 21 is 1mm, and the diameter of the light beam emitted from the second lens 23 is 5 to 10mm, so the beam expansion ratio is 5 to 10 times, and the focal length of the second lens 23 is 50 to 100mm. The aperture of the second lens 23 also needs to be larger than the diameter of the emitted light beam (recommended> 10mm). Since the beam diameter is larger after expansion, the diameter difference is small after the beam is expanded at different wavelengths. Therefore, the second lens 23 can use a plano-convex lens.

[0028] like Figure 1As shown, the detection module 4 includes an array camera 41 and an analyzer 42, and the analyzer 42 is arranged in front of the array camera 41. By rotating the angle of the 1 / 2 wave plate 24, the polarization state of the light beam can be changed, and the image can be used to improve the material distinction of the object in cooperation with the analyzer 42. Since the incident light beam is polychromatic light (different wavelengths), the 1 / 2 wave plate 24 can use an achromatic wave plate, and its size can be larger than the beam diameter.

[0029] like Figure 1 As shown, the point-to-line conversion device 25 can be a single cylindrical lens. Its focal length is determined according to the size of the illumination area and the distance from the light source to the target object. The focal length of the cylindrical lens can be estimated by dividing the "distance from the light source to the target" by the "size of the illumination area" and then multiplying by the "beam diameter after expansion". For example: if the required illumination area width is 100mm, the distance from the light source to the target is 300mm, and the beam diameter after expansion is 10mm, then the required focal length of the cylindrical lens is about 300mm / 100mm*10mm=30mm. The size of the cylindrical lens should be larger than the beam diameter after expansion.

[0030] like Figure 1 As shown, for situations where uniformity requirements are high and a more uniform straight line of light is obtained, the point-to-line conversion device 25 can use a Powell prism. The divergence angle of the Powell prism is also selected based on the "distance from the light source to the target" and the "size of the illumination area". The divergence angle of the Powell prism can be greater than the "size of the illumination area" divided by the "distance from the light source to the target". The diameter of the Powell prism can also be greater than the diameter of the light beam after expansion. For example: if the width of the illumination area is required to be 100mm, the distance from the light source to the target is 300mm, and the diameter of the light beam after expansion is 10mm, a Powell prism with a divergence angle of 20 degrees (100mm / 300mm=0.33mrad=19 degrees) and a diameter of 12.7mm (1 inch) can be selected.

[0031] like Figure 1 to Figure 2As shown, the beam reflection module 3 can be a scanning galvanometer. The laser beam shaped by the beam shaping module 2 is reflected to the target through a uniaxial scanning galvanometer to form an illumination light. The reflector of the scanning galvanometer can be an aluminum-plated or silver-plated reflector to ensure that the reflectivity is sufficiently high (>90%) under a wide range of visible light wavelengths to improve the utilization rate of the light source. The size of the reflector must also ensure that it is larger than the beam diameter after beam expansion over the entire scanning range. The scanning angle of the scanning galvanometer depends on the "illumination area size" and the "distance from the light source to the target". The scanning angle can be greater than the "illumination area size" divided by the "distance from the light source to the target". The vibration frequency of the scanning galvanometer should match the exposure time of the array camera 41. It is ensured that within a complete exposure time, the scanning galvanometer can allow the line light to scan the entire target area. For example: if the exposure time of the array camera 41 is 10ms, the vibration period of the scanning galvanometer should be 10ms / 2=5ms, that is, the vibration frequency is 200Hz. When the scanning galvanometer is not scanning, it is ensured that the width of the light source in the image captured by the area array camera 41 is greater than 10 pixels.

[0032] like Figure 1 to Figure 2 As shown, there are many types of tunable lasers 1 available for selection in the utility model. It can be an industrial camera commonly used in the field of machine vision, with a spectral response wavelength of 350nm to 1000ns, belonging to the visible light to near infrared band. In order to match the spectral response wavelength range of the camera, the wavelength of the light source should also be within this range.

[0033] like Figure 1 to Figure 2 As shown, the tunable laser 1 that can be used in this embodiment can include: a titanium sapphire solid laser, whose wavelength adjustment range is 700nm to 1000nm, and whose spectral line width is 0.01 to 0.05nm. The tunable laser 1 that can be used in this embodiment can also be a ruby ​​laser, and its output wavelength is 400 to 760nm.

[0034] When the target is relatively large, the beam expansion method will cause the optical power density to drop too much. In order to obtain a better lighting effect, the output laser of the tunable laser is filtered through the pinhole 22 and expanded into a line beam by a cylindrical lens. Then it is reflected to the target through the scanning galvanometer. The scanning galvanometer swings back and forth at a certain frequency, and the line beam will form a line scanning form of illumination for the target. By making the exposure time of the camera longer than the swing period of the scanning galvanometer, a complete and evenly illuminated image of the target can be obtained.

[0035] Figure 3 FIG. 1 is another schematic diagram of a machine vision system based on a tunable laser light source according to the present invention. Figure 3As shown, the beam reflection module 3 can also be a separate reflector. That is, the laser illumination area and the imaging area are matched by a separate reflector to maximize the use of the light source's illumination energy. The laser beam output by the tunable laser 1 is shaped to form a fan-shaped illumination. It is reflected onto the target object through the reflector to form a line illumination area. The angle of the reflector is adjusted so that the line illumination area coincides with the imaging area (linear area) of the linear array camera. In this way, the energy of the light source can be maximized.

[0036] Since the wavelength of the tunable laser 1 is adjustable in real time, for application scenarios where small color differences need to be distinguished, the following method can be used to optimize the wavelength of illumination. First, within the range allowed by the entire tunable laser 1, let the tunable laser 1 output light beams of different wavelengths for illumination, and capture images at multiple wavelength points (for example, 100 wavelength points).

[0037] For some materials, there are specific absorption peaks. By using the characteristic that the wavelength of the tunable laser can be adjusted in real time, two very close wavelength beams are generated for illumination, one wavelength is located at the absorption peak position of the material, and the other wavelength deviates from the absorption peak position. In this way, two images are taken separately and compared. For positions without material-specific absorption, the brightness of the image is almost the same because the wavelengths of the light generated twice are similar. For positions with material-specific absorption, the brightness of the two images will be quite different. Therefore, by differential operation of the two images, specific materials can be detected. Using a tunable laser light source instead of an LED light source solves the problem that the spectral range of the LED light source is not narrow enough and the wavelength cannot be finely adjusted in real time from the source. The wavelength of the tunable laser light source can be adjusted in real time, so that the machine vision system has more diverse image acquisition methods. For example: using different wavelengths of light for illumination multiple times to obtain a high-spectral image of the target object, the line width of the tunable laser light source is very narrow (~1nm), and a very high color resolution can be obtained. The problem of the illumination form of the laser as a machine vision light source is solved.

[0038] LED light source control methods (such as stroboscopic, synchronous triggering, etc.) can all be realized in the present invention. Moreover, the tunable laser light source can bring more control effects. For example, if the laser light source outputs linearly polarized light, there is no need to add additional polarizing elements, and there is no problem of energy loss caused by polarization, which greatly improves efficiency; if the narrow line width of the laser is used, the camera can be equipped with a narrow-band filter to greatly reduce the interference of ambient light and obtain a better image signal-to-noise ratio.

[0039] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A machine vision system based on a tunable laser light source, It is characterized in that include: Tunable laser, beam shaping module, beam reflection module and detection module; After the tunable laser emits laser light to the beam shaping module, the beam is shaped by the beam shaping module, and the shaped beam is reflected to the detection target through the beam reflection module to provide a detection light source; The lens of the detection module faces the detection target object for detection; The beam shaping module includes: a first lens and a pinhole form a spatial filter. The laser of the tunable laser is first focused by the first lens, passes through the pinhole and then passes through the second lens to expand the beam to an appropriate size, then passes through a 1 / 2 wave plate to change the polarization state of the beam, and then passes through a point-to-line conversion device to convert the point beam of the 1 / 2 wave plate into a line beam, and then output to the beam reflection module.

2. The machine vision system based on a tunable laser light source as claimed in claim 1, It is characterized in that The first lens is a short focal length, double cemented achromatic lens or an achromatic microscope objective lens.

3. The machine vision system based on a tunable laser light source as claimed in claim 1, It is characterized in that The pinhole is a small aperture with a diameter of 0.1 to 0.2 mm.

4. The machine vision system based on a tunable laser light source as claimed in claim 1, It is characterized in that The beam reflection module is a separate reflector.

5. The machine vision system based on a tunable laser light source as claimed in claim 1, It is characterized in that The 1 / 2 wave plate is an achromatic wave plate.

6. The machine vision system based on a tunable laser light source as claimed in claim 1, It is characterized in that The point-to-line conversion device is a single cylindrical lens, and the focal length is determined according to the size of the illumination area and the distance from the light source to the target object.

7. The machine vision system based on a tunable laser light source as claimed in claim 1, It is characterized in that The point-to-line conversion device is a Powell prism.

8. The machine vision system based on a tunable laser light source as claimed in claim 1, It is characterized in that The beam reflection module is a scanning galvanometer, which swings at a certain frequency to form a line scanning form of illumination for the target object.

9. The machine vision system based on a tunable laser light source as claimed in claim 1, It is characterized in that The detection module comprises an area array camera and an analyzer, wherein the analyzer is arranged in front of a lens of the area array camera.

10. The machine vision system based on a tunable laser light source as claimed in claim 1, It is characterized in that The tunable laser is a titanium sapphire solid laser or a ruby ​​laser.

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