A lightweight, automatically focusing LIBS online inspection device and method

Abstract

The application belongs to the technical field of spectral detection, and particularly relates to a light-weight LIBS online detection device and method with automatic focusing, wherein the device sequentially comprises a photoelectric switch, a pre-detection system, a controller, a delay timer, a pulse laser, a mirror, a zoom unit, an ellipsoidal mirror, a displacement adjustment platform, a transmission window sheet, a fiber coupling unit, a spectrometer and a signal strength detector according to a control logic and an optical propagation path. The application can easily realize zooming through the synchronous movement of the ellipsoidal mirror and the fiber coupling unit driven by the zoom lens and the displacement adjustment platform, can adapt to objects with different heights and shapes, solves the problem of large movement load in the zooming process, realizes light weight, and can judge the focusing range in advance through the telecentric lens imaging pre-detection system, so that the detection analysis efficiency is improved.

Description

Technical Field

[0001] This invention relates to the field of spectral detection technology, specifically to a lightweight online LIBS detection device and method with automatic focusing capability. Background Technology

[0002] Laser-induced breakdown spectroscopy (LIBS) is an elemental analysis method based on laser-induced breakdown spectroscopy. Its basic principle is to use a high-energy pulsed laser focused on the sample surface, causing a sudden increase in the local temperature of the sample, leading to material evaporation and the formation of a high-temperature plasma. The excited-state atoms and ions in the plasma emit characteristic radiation spectra when they return to their ground state. These spectra can be detected and analyzed by a spectrometer to determine the types and amounts of elements in the sample.

[0003] A typical LIBS analysis system consists of a pulsed laser, an optical system (focusing and acquisition lens group, optical fiber) for focusing the laser beam and collecting the plasma emission spectrum, a spectrometer, and a control platform. LIBS analysis systems can monitor raw materials, semi-finished products, and finished products in real time during the production process, rapidly obtaining elemental composition information. By adjusting process parameters in a timely manner, production processes can be optimized, improving product quality and production efficiency. This is particularly important for industrial processes requiring rapid feedback and adjustment, such as metallurgy, ore processing, and environmental monitoring. Furthermore, LIBS technology is a non-destructive testing method, requiring no sample pretreatment or damage. It can also simultaneously detect multiple elements, meaning that it can obtain multiple elemental composition information of a sample in a single measurement.

[0004] Most existing LIBS analysis systems employ a fixed-focus approach, which has poor adaptability to samples of varying heights and shapes. Furthermore, the optical systems used to collect the radiation spectrum during the plasma cooling process are fixed, often collecting only from one side with a relatively small aperture, resulting in limited energy acquisition of the radiation spectrum and a low signal-to-noise ratio. While some LIBS analysis systems with focusing capabilities have emerged, these systems require overall equipment adjustment during operation, making them bulky, cumbersome, and inefficient.

[0005] Therefore, this application aims to provide an online LIBS detection device that can automatically adjust focus and determine the surface focal point according to the sample conditions, thereby improving the application range of the detection device and the collection efficiency of radiation spectra. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned shortcomings of the prior art and provide a lightweight LIBS online detection device and method with automatic focusing, which can automatically focus to perform LIBS detection on objects of different heights and shapes, and has a high signal-to-noise ratio. The device has a simple and compact structure and high adjustment efficiency.

[0007] The technical solution of the present invention is as follows: The present invention provides a lightweight LIBS online detection device with automatic focusing, which includes, in sequence according to the control logic and light propagation path, a photoelectric switch, a pre-detection system, a controller, a delay unit, a pulsed laser, a reflector, a zoom unit, an ellipsoidal reflector, a displacement adjustment stage, a transmission window, an optical fiber coupling unit, a spectrometer, and a signal intensity detector.

[0008] The photoelectric switch is used to control the operation of the entire detection device. Its start signal serves as the starting point for timing control. When the object to be tested passes through the photoelectric switch, the remote pre-detection system starts working.

[0009] The pre-detection system is used to detect whether the height and shape of the object to be tested have changed relative to the initial set height and shape. It uploads the height and shape information of the object to be tested to the controller to determine the zoom adjustment range in advance.

[0010] The controller is connected to the pre-detection system, the timer, the displacement adjustment stage, the spectrometer, and the signal strength detector. The controller is used to send and receive signals.

[0011] The delay unit is connected to the pulsed laser and the spectrometer, and is used to control the output time of the pulsed laser and the acquisition time of the spectrometer.

[0012] The pulsed laser is used to provide pulsed laser light; the reflector is used to guide the pulsed laser light emitted by the pulsed laser light into the zoom unit; the zoom unit is used to focus the pulsed laser light onto the surface of the object being tested.

[0013] The ellipsoidal reflector is mounted on the first displacement adjustment stage; the ellipsoidal reflector is used to collect and reflect the radiation spectrum signal of the plasma cooling process on the surface of the object being measured;

[0014] The transmission window is used to reflect a portion of the radiation spectrum signal reflected from the ellipsoidal mirror onto the signal intensity detector, while the other portion of the radiation spectrum signal passes through the transmission window and is focused at the fiber coupling unit. The signal intensity detector is used to detect the intensity of the radiation spectrum signal, thereby determining whether the pulsed laser is focused on the surface of the object being measured. The radiation spectrum signal is transmitted to the controller, and the position corresponding to its signal peak is the focusing position.

[0015] The fiber optic coupling unit is used to receive the radiation spectrum signal collected by the ellipsoidal reflector. The fiber optic coupling unit is connected to the spectrometer through an optical fiber and transmits the radiation spectrum signal to the spectrometer for analysis.

[0016] Furthermore, the fiber optic coupling unit is mounted on the second displacement adjustment platform. When the first displacement adjustment platform causes the position of the ellipsoidal reflector to change, the second displacement adjustment platform synchronously moves the fiber optic coupling unit, so that the fiber optic coupling unit always remains at the position of the second focal point of the ellipsoidal reflector.

[0017] Furthermore, the pre-inspection system employs a telecentric lens imaging system, including an object-side telecentric lens and a detector. Besides using the object-side telecentric lens to determine if the morphology of the sample has changed, it can also use dual telecentric lenses, stereo vision, and other methods to determine if the sample has changed, thereby deciding whether refocusing is necessary.

[0018] Furthermore, the signal strength detector can be a linear array detector or a planar array detector. Of course, any detector that can linearly detect the intensity of the corresponding spectral signal can be used as a signal strength detector.

[0019] Furthermore, the controller uses a computer or PLC.

[0020] Furthermore, the displacement adjustment stage is an electric displacement stage, but other displacement adjustment stages that can be automatically controlled by signals such as light, electricity, and magnetism can also be used.

[0021] Another aspect of the present invention provides an online LIBS inspection method with automatic focusing, which uses the above-mentioned inspection device and specifically includes the following steps:

[0022] S1. When installing and debugging the testing device, set an initial position for the ellipsoidal reflector and the fiber optic coupling unit as the zero position of the two displacement adjustment stages. At this time, the testing device will be suitable for measuring the object to be measured at a certain height, and this height will be used as the initial calibration height.

[0023] S2. The object to be tested passes through the first photoelectric switch, triggering the detection device to start running.

[0024] S3. When the object to be measured passes through the pre-inspection system, the pre-inspection system transmits the measured image results to the controller. The controller processes the image, calculates the height of the object to be measured, and compares it with the initial calibration height to obtain the height difference.

[0025] S4. The object to be tested continues to move forward to the area below the ellipsoidal reflector and becomes the object to be tested. It is then sensed by the second photoelectric switch. The controller sends a control command, which drives the pulse laser to emit a pulse laser through the delay unit. The pulse laser is focused onto the surface of the object to be tested through the reflector and zoom unit. The ellipsoidal reflector then collects the light emitted by the surface during the cooling process, and part of it is reflected onto the signal intensity detector to record the intensity.

[0026] S4-1. If the height of the object to be measured is different from the initial calibration height, that is, the height difference is not 0, zoom scanning is required. At the same time as the zoom unit starts scanning, the two displacement adjustment stages move synchronously, driving the ellipsoidal reflector and the fiber optic coupling unit to move up and down. The light intensity received by the signal intensity detector will change. After the scan is completed, the position where the light intensity is at its maximum value is found as the best fixed position of the ellipsoidal reflector and the fiber optic coupling unit.

[0027] S4-2. If the height of the object to be measured is the same as the initial calibration height, that is, the height difference is not 0, then zoom scanning is not required, and the formal measurement can begin directly.

[0028] S5. The formal test begins. The pulsed laser is focused onto the surface of the object under test, exciting the plasma on the surface. Under the timing control of the delay, the light emitted by the surface of the object under test during the cooling process is collected by the ellipsoidal reflector. This part of the light is focused by the transmission window to the other focal point of the ellipsoidal reflector and enters the fiber coupling unit.

[0029] S6. The fiber optic coupling unit guides the collected light into the spectrometer via an optical fiber, where the spectrometer performs spectral analysis.

[0030] Furthermore, in step S4-1, during zoom scanning, scanning is performed within a height difference range of ±10%. That is, with the initial calibration height as point 0, if the height difference is 1, scanning can be performed within the range of 0.9 - 1.1. This allows for faster and more accurate focusing on the surface of the object being measured (i.e., the location of point "1"). Preferably, during zoom scanning, scanning can be performed within a height difference range of ±20%.

[0031] Furthermore, in some specific operations, step S3 can be omitted, that is, the height information of the object to be measured is no longer collected; and in step S4, the scanning is performed from the minimum focal length to the maximum focal length each time, and the two displacement adjustment stages move synchronously. The laser is focused on the surface of the object to be measured based on the extreme value of the light intensity received by the signal intensity detector, so as to determine the optimal fixed position of the ellipsoidal reflector and the fiber optic coupling unit.

[0032] The advantages of this invention compared to the prior art are as follows:

[0033] 1. This invention uses an ellipsoidal reflector as a collecting device, which, compared with using a lens, allows for a larger angle of radiation spectrum collection and less absorption loss, resulting in a better signal-to-noise ratio.

[0034] 2. The automatic focusing and adjustment scheme adopted in this invention utilizes the energy feedback received by the linear array detector to control the zoom unit, which can focus the incident light onto the surface of the test object of different sizes and shapes. At the same time, adjusting the position of the fiber optic coupling unit and the ellipsoidal reflector can ensure the collected radiation coupling efficiency. Since only the position of the fiber optic coupling unit and the ellipsoidal reflector needs to be adjusted, the motion load is small, which is beneficial to the lightweight design.

[0035] 3. The present invention is equipped with a telecentric lens imaging pre-inspection system, which can know the surface height, shape and other information of the object to be measured in advance, thereby pre-determining the focusing range without having to change from the maximum focusing range to the minimum focusing range, thus shortening the scanning time and improving the detection efficiency. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the overall structure of the lightweight LIBS online detection device with automatic focusing capability in an embodiment of the present invention;

[0037] It should be noted that the structures, proportions, sizes, etc., shown in the accompanying drawings of this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to specific embodiments. Methods or functional components not specifically described in the embodiments are all prior art. Example

[0039] As attached Figure 1 As shown, this embodiment provides a lightweight LIBS online detection device with automatic focusing, which includes, in sequence according to the control logic and light propagation path, a photoelectric switch, a pre-detection system, a controller, a delay unit, a pulsed laser, a reflector, a zoom unit, an ellipsoidal reflector, a displacement adjustment stage, a transmission window, an optical fiber coupling unit, a spectrometer, and a signal intensity detector.

[0040] The photoelectric switch is used to control the operation of the entire detection device. Its start signal serves as the starting point for timing control. When the object to be tested passes through the photoelectric switch, the remote pre-detection system starts working.

[0041] The pre-detection system is used to detect whether the height and shape of the object to be tested have changed relative to the initial set height. It uploads the height and shape information of the object to be tested to the controller to determine the zoom adjustment range in advance.

[0042] The controller is connected to the pre-detection system, the timer, the displacement adjustment stage, the spectrometer, and the signal strength detector. The controller is used to send and receive signals.

[0043] The delay unit is connected to the pulsed laser and the spectrometer to control the output time of the pulsed laser and the acquisition time of the spectrometer; that is, to control when to excite the surface plasma on the surface of the object under test and when to start acquiring spectral signals.

[0044] The pulsed laser is used to provide pulsed laser light; the reflector is used to guide the pulsed laser light emitted by the pulsed laser light into the zoom unit; the zoom unit is used to focus the pulsed laser light onto the surface of the object being tested.

[0045] The ellipsoidal reflector is mounted on the first displacement adjustment stage; the ellipsoidal reflector is used to collect and reflect the radiation spectrum signal of the plasma cooling process on the surface of the object being measured;

[0046] The transmission window is used to reflect a portion of the radiation spectrum signal reflected from the ellipsoidal mirror onto the signal intensity detector, while the other portion of the radiation spectrum signal passes through the transmission window and is focused at the fiber coupling unit. The signal intensity detector is used to detect the intensity of the radiation spectrum signal, thereby determining whether the pulsed laser is focused on the surface of the object being measured. The radiation spectrum signal is transmitted to the controller, and the position corresponding to its signal peak is the focusing position.

[0047] The fiber optic coupling unit is used to receive the radiation spectrum signal collected by the ellipsoidal reflector. The fiber optic coupling unit is connected to the spectrometer through an optical fiber and transmits the radiation spectrum signal to the spectrometer for analysis.

[0048] In this embodiment, the fiber optic coupling unit is mounted on the second displacement adjustment platform. When the first displacement adjustment platform causes the position of the ellipsoidal reflector to change, the second displacement adjustment platform synchronously moves the fiber optic coupling unit, so that the fiber optic coupling unit always remains at the position of the second focal point of the ellipsoidal reflector.

[0049] In this embodiment, the pre-detection system employs a telecentric lens imaging system, including an object-side telecentric lens and a detector. The signal strength detector is a linear array detector; the controller is a computer; and both displacement adjustment stages are electrically adjustable height stages.

[0050] The method of using the detection device in this embodiment includes the following steps:

[0051] S1. When installing and debugging the testing device, set an initial position for the ellipsoidal reflector and the fiber optic coupling unit as the zero position of the two displacement adjustment stages. At this time, the testing device will be suitable for measuring the object to be measured at a certain height, and this height will be used as the initial calibration height.

[0052] S2. Place the object to be tested upstream of the conveyor belt. The conveyor belt drives the object to be tested to move forward. When the object to be tested passes the first photoelectric switch, the detection device is triggered to start running.

[0053] S3. When the object to be tested continues to move forward and passes through the pre-inspection system, the pre-inspection system detects the object to be tested and transmits the image results obtained after detection to the controller. The controller processes the image, calculates the height of the object to be tested, and compares it with the initial calibration height to obtain the height difference.

[0054] S4. When the object to be tested continues to move forward and becomes the object under the ellipsoidal reflector, and is sensed by the second photoelectric switch, the conveyor belt stops, the controller issues a control command, drives the pulse laser to emit pulsed laser through the delay unit, and focuses it onto the surface of the object under test through the reflector and zoom unit; then the ellipsoidal reflector collects the light emitted by the surface during the cooling process, and part of it is reflected onto the signal intensity detector to record the intensity.

[0055] S4-1. If the height of the object to be measured is different from the initial calibration height, that is, the height difference is not 0, zoom scanning is required. During zoom scanning, the scanning is performed within the range of ±10% of the height difference. At the same time as the zoom unit starts scanning, the two displacement adjustment stages move synchronously, driving the ellipsoidal reflector and the fiber optic coupling unit to move up and down respectively. The light intensity received by the signal intensity detector will change. After the scan is completed, the position where the light intensity is at its maximum value is found, which is taken as the optimal fixed position of the ellipsoidal reflector and the fiber optic coupling unit.

[0056] S4-2. If the height of the object to be measured is the same as the initial calibration height, that is, the height difference is 0, then zoom scanning is not required and formal measurement can begin directly.

[0057] S5. The formal test begins. The pulsed laser is focused onto the surface of the object under test, exciting the plasma on the surface. Under the timing control of the delay, the light emitted by the surface of the object under test during the cooling process is collected by the ellipsoidal reflector. This part of the light is focused by the transmission window to the other focal point of the ellipsoidal reflector and enters the fiber coupling unit.

[0058] S6. The fiber optic coupling unit guides the collected light into the spectrometer via optical fiber, where it performs spectral analysis and displays the corresponding records on the host computer. The conveyor belt continues to transfer the detected object.

[0059] The above are only some embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various combinations and modifications of the aforementioned technical features. Any improvements, modifications, equivalent substitutions, or applications of the structure or method of the present invention to other fields to achieve the same effect without departing from the spirit and scope of the present invention shall fall within the protection scope of the present invention.

Claims

1. An automatic focusing light weight LIBS online detection device, characterized in that: According to the control logic and the light propagation path, the photoelectric switch, the pre-detection system, the controller, the delay timer, the pulse laser, the mirror, the zoom unit, the ellipsoidal mirror, the displacement adjustment platform, the transmission window piece, the fiber coupling unit, the spectrometer and the signal intensity detector are sequentially arranged; the pre-detection system is used for detecting whether the height and shape of the object to be detected change relative to the initial setting height and shape, and uploading the height and shape information of the object to be detected to the controller to judge the zoom adjustment range in advance; the controller is connected with the pre-detection system, the delay timer, the displacement adjustment platform, the spectrometer and the signal intensity detector, and is used for sending and receiving signals; the delay timer is connected with the pulse laser and the spectrometer, and is used for controlling the output time of the pulse laser and the acquisition time of the spectrometer; the pulse laser is used for providing the pulse laser; The mirror is used for guiding the pulse laser emitted by the pulse laser to the zoom unit; the zoom unit is used for focusing the pulse laser on the surface of the measured object; the ellipsoidal mirror is installed on the first displacement adjustment platform; the ellipsoidal mirror is used for collecting and reflecting the radiation spectrum signal of the plasma cooling process of the surface of the measured object; the transmission window piece is used for reflecting part of the radiation spectrum signal reflected by the ellipsoidal mirror to the signal intensity detector, and the other part of the radiation spectrum signal is focused on the fiber coupling unit after passing through the transmission window piece; the signal intensity detector is used for detecting the intensity of the radiation spectrum signal, and judging whether the pulse laser is focused on the surface of the measured object by real-time recording; The fiber coupling unit is used for receiving the radiation spectrum signal collected by the ellipsoidal mirror, and the fiber coupling unit is connected with the spectrometer through an optical fiber, and the radiation spectrum signal is transmitted to the spectrometer for analysis; The fiber coupling unit is installed on the second displacement adjustment platform, and when the position of the ellipsoidal mirror changes with the first displacement adjustment platform, the second displacement adjustment platform drives the fiber coupling unit to move synchronously, so that the fiber coupling unit always remains at the position of the second focal point of the ellipsoidal mirror.

2. The automatic focusable LIBS online detection device of claim 1, wherein: The pre-detection system adopts a telecentric lens imaging system, which includes an object-side telecentric lens and a detector. 3.The auto-focusing LIBS online detection device of claim 1, wherein: The pre-detection system adopts a double-telecentric lens imaging system, or a stereo vision system. 4.The auto-focusing LIBS online detection device of claim 1, wherein: The signal intensity detector adopts a linear array detector or a planar array detector. 5.The auto-focusing LIBS online detection device of claim 1, wherein: The controller adopts a computer or a PLC; and the displacement adjustment platforms are all electric displacement platforms.

6. An automatic focusing LIBS online detection method, using the detection device of any one of claims 1-5, characterized in that, The method comprises the following steps: S1, when installing and debugging the detection device, an initial position is set for the ellipsoidal mirror and the fiber coupling unit as the zero position of the two displacement adjustment platforms, so that the detection device is suitable for measuring an object to be detected at a certain height, and the height is taken as the initial calibration height; S2, the object to be detected passes through the first photoelectric switch, and triggers the detection device to start running; S3, when the object to be detected passes through the pre-detection system, the pre-detection system transmits the measured image result to the controller, the controller processes the image, calculates the height of the object to be detected, and compares the height with the initial calibration height to obtain a height difference; S4, the object to be measured continues to advance to the ellipsoidal mirror below becomes the measured object, when the second photoelectric switch is sensed, the controller sends control instructions, through the delay timer drive pulsed laser to emit pulsed laser, through the mirror, zoom unit focus to the surface of the measured object; again by ellipsoidal mirror to collect the light emitted by the surface during cooling, a part of the reflection to the signal intensity detector, record the intensity; S4-1, if the height of the object to be measured is different from the initial calibration height, zoom scanning is needed, the zoom unit starts scanning at the same time, the two displacement adjustment tables move synchronously, driving the ellipsoidal mirror and the optical fiber coupling unit to move up and down, the light intensity received by the signal intensity detector will change, after scanning, the position of the maximum light intensity is found, which is the best fixed position of the ellipsoidal mirror and the optical fiber coupling unit; S4-2, if the height of the object to be measured is the same as the initial calibration height; then no zoom scanning is needed, and the formal measurement is directly started; S5, start formal test, pulsed laser is focused on the surface of the measured object, exciting the surface plasma; under the time sequence control of the delay timer, the light emitted by the surface of the measured object during cooling is collected by the ellipsoidal mirror, this part of light is focused on the other focal point of the ellipsoidal mirror through the transmission window piece, and enters the optical fiber coupling unit; S6, the optical fiber coupling unit guides the collected light into the spectrometer through the optical fiber, and the spectrometer performs spectral analysis.

7. The method of claim 6, wherein: In step S4-1, when zoom scanning is performed, scanning is performed within the range of ±10% of the height difference.

8. The method of claim 6, wherein: In step S4-1, when zoom scanning is performed, scanning is performed within the range of ±20% of the height difference.

9. The method of claim 6, wherein: Step S3 is omitted, that is, the height information of the object to be measured is no longer collected; and in step S4, each time scans from the minimum focal length to the maximum focal length, the two displacement adjustment tables move synchronously, and whether the laser is focused on the surface of the measured object is judged according to the light intensity extreme value received by the signal intensity detector, so as to determine the best fixed position of the ellipsoidal mirror and the optical fiber coupling unit. In step S4-1, when zoom scanning is performed, scanning is performed within the range of ±10% of the height difference. In step S4-1, when zoom scanning is performed, scanning is performed within the range of ±20% of the height difference. Step S3 is omitted, that is, the height information of the object to be measured is no longer collected; and in step S4, each time scans from the minimum focal length to the maximum focal length, the two displacement adjustment tables move synchronously, and whether the laser is focused on the surface of the measured object is judged according to the light intensity extreme value received by the signal intensity detector, so as to determine the best fixed position of the ellipsoidal mirror and the optical fiber coupling unit.

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