Light-weight LIBS (laser-induced breakdown spectroscopy) online detection device and method capable of automatically focusing

Abstract

The invention belongs to the technical field of spectrum detection, and particularly relates to a light LIBS (laser-induced breakdown spectroscopy) online detection device and method capable of automatically focusing, and the device sequentially comprises a photoelectric switch, a pre-detection system, a controller, a delayer, a pulse laser, a reflector, a zooming unit, an ellipsoidal reflector, a displacement adjusting table and a transmission diaphragm according to a control logic and a light propagation path, an optical fiber coupling unit, a spectrometer and a signal intensity detector. According to the telecentric lens imaging pre-detection system, zooming can be easily achieved in the mode that the zoom lens and the displacement adjusting table drive the ellipsoidal reflector and the optical fiber coupling unit to move synchronously, the telecentric lens imaging pre-detection system can adapt to objects of different heights and forms, the problem that the motion load is large in the zooming process is solved, light weight is achieved, and the imaging precision is improved through the telecentric lens imaging pre-detection system. The focusing range can be judged in advance without changing from the maximum focusing range to the minimum focusing range, so that the detection and analysis efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of spectrum detection, and in particular to a lightweight LIBS online detection device and method capable of automatic focusing. Background Art

[0002] Laser Induced Breakdown Spectroscopy (LIBS) is an elemental analysis method based on laser-induced breakdown spectroscopy. Its basic principle is to use high-energy pulsed laser to focus on the sample surface, causing the local temperature of the sample to rise instantly, causing the material to evaporate and form a high-temperature plasma. The excited atoms and ions in the plasma emit characteristic radiation spectra when they return to the ground state. These spectra can be detected and analyzed by the spectrometer to determine the type and content of the elements in the sample.

[0003] The LIBS analysis system is generally composed of a pulsed laser, an optical system for focusing the laser beam and collecting the plasma emission spectrum (focusing and collection lens group, optical fiber), a spectrometer, a controller system control platform, etc. The LIBS analysis system can monitor the raw materials, semi-finished products and finished products in the production process in real time and quickly obtain elemental composition information. By adjusting the process parameters in a timely manner, the production process can be optimized, and product quality and production efficiency can be improved. This is especially important for industrial processes that require rapid feedback and adjustment, such as metallurgy, ore processing, and environmental monitoring. In addition, LIBS technology is a non-destructive testing method that does not require pretreatment or destruction of the sample. It can also detect multiple elements at the same time, that is, it can obtain multiple element composition information of the sample in one measurement.

[0004] Most of the LIBS analysis systems in the prior art use a fixed focus method, which has poor adaptability to samples of different heights and shapes. At the same time, the optical system for collecting the radiation spectrum of the plasma cooling process is fixed, and is often collected only on one side, and the collection aperture is relatively small. The radiation spectrum collected during the plasma cooling process is limited, and the signal-to-noise ratio is not high. Although some LIBS analysis systems that can achieve focusing functions have also appeared, these systems require overall adjustment of the equipment during operation, the equipment is relatively bulky, the adjustment operation is cumbersome, and the work efficiency is low.

[0005] Therefore, the present application aims to provide a LIBS online detection device that can automatically adjust the focus and automatically determine the surface focal point according to the sample situation, thereby improving the use range of the detection device and the collection efficiency of the radiation spectrum. Summary of the invention

[0006] The purpose of the present 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, a simple and compact device structure, and high adjustment efficiency.

[0007] The technical solution of the present invention is as follows: On the one hand, the present invention provides a lightweight LIBS online detection device capable of automatic focusing, which includes a photoelectric switch, a pre-detection system, a controller, a delay device, a pulse laser, a reflector, a zoom unit, an ellipsoidal reflector, a displacement adjustment platform, a transmission window, a fiber coupling unit, a spectrometer and a signal strength detector in sequence according to the control logic and the light propagation path; The photoelectric switch is used to control the operation of the entire detection device, and its start signal is used as the starting point of the timing control. When the object to be detected passes through the photoelectric switch, the remote pre-detection system starts to work; The pre-check 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, and uploads the height and shape information of the object to be tested to the controller to determine the zoom adjustment range in advance; The controller is connected to the pre-check system, the time delay device, the displacement adjustment platform, the spectrometer and the signal strength detector, and the controller is used to send and receive signals; The time delay device is connected to the pulse laser and the spectrometer, and is used to control the output time of the pulse laser and the collection time of the spectrometer; The pulse laser is used to provide pulse laser; the reflector is used to guide the pulse laser emitted by the pulse laser into the zoom unit; the zoom unit is used to focus the pulse laser onto the surface of the object to be measured; The ellipsoidal reflector is mounted on the first displacement adjustment platform; the ellipsoidal reflector is used to collect and reflect the radiation spectrum signal of the plasma cooling process on the surface of the measured object; The transmission window is used to reflect a part of the radiation spectrum signal reflected by the ellipsoidal reflector to the signal intensity detector, and the other part of the radiation spectrum signal is focused on the optical fiber coupling unit after passing through the transmission window; the signal intensity detector is used to detect the intensity of the radiation spectrum signal, so as to determine whether the pulse laser is focused on the surface of the object to be measured; the radiation spectrum signal is transmitted to the controller, and the position corresponding to the signal peak is the focusing position; The optical fiber coupling unit is used to receive the radiation spectrum signal collected by the ellipsoidal reflector. The optical fiber coupling unit is connected to the spectrometer through an optical fiber to transmit the radiation spectrum signal to the spectrometer for analysis.

[0008] Furthermore, the fiber coupling unit is installed on the second displacement adjustment platform. When the first displacement adjustment platform drives the ellipsoidal reflector to change its position, the second displacement adjustment platform synchronously drives the fiber coupling unit to move, so that the fiber coupling unit always remains at the position of the second focus of the ellipsoidal reflector.

[0009] Furthermore, the pre-inspection system uses a telecentric lens imaging system, including an object-side telecentric lens and a detector. In addition to using the object-side telecentric lens to determine whether the shape of the sample under test has changed, it is also possible to use a dual telecentric lens, stereo vision, etc. to determine whether the sample under test has changed, thereby determining whether to refocus.

[0010] Furthermore, the signal strength detector may 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 the signal strength detector.

[0011] Furthermore, the controller adopts a computer or a PLC.

[0012] Furthermore, the displacement adjustment platform adopts an electric displacement platform, and of course other displacement adjustment platforms that can realize automatic control through optical, electrical, magnetic and other signals can also be adopted.

[0013] Another aspect of the present invention provides a LIBS online detection method capable of automatic focusing, using the above-mentioned detection device, and specifically comprising the following steps: S1. When installing and debugging the detection device, set an initial position for the ellipsoidal reflector and the fiber coupling unit as the zero position of the two displacement adjustment stages. At this time, the detection device will be suitable for measuring the object to be measured at a certain height, and the height will be used as the initial calibration height; S2, the object to be tested is placed past the first photoelectric switch, triggering the detection device to start running; S3, when the object to be measured passes through the pre-inspection system, the pre-inspection system transmits the measured image result 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; S4, the object to be measured continues to move forward to the bottom of the ellipsoidal reflector and becomes the object to be measured, and is sensed by the second photoelectric switch, when the controller issues a control instruction, drives the pulse laser to emit a pulse laser through the delay device, and focuses on the surface of the object to be measured through the reflector and the zoom unit; then the ellipsoidal reflector collects the light emitted by the surface during the cooling process, and a part of it is reflected to the signal intensity detector to record the intensity; 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. When the zoom unit starts scanning, the two displacement adjustment stages move synchronously, driving the ellipsoidal reflector and the fiber 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 with the maximum light intensity is found as the optimal fixed position of the ellipsoidal reflector and the fiber coupling unit. 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, there is no need to perform zoom scanning and the formal measurement can be started directly; S5. The formal test begins. The pulse laser is focused on the surface of the object to be tested to excite the plasma on the surface. Under the timing control of the delay device, the light emitted by the surface of the object to be tested during the cooling process is collected by the ellipsoidal reflector. This part of the light is focused to the other focus of the ellipsoidal reflector through the transmission window and enters the 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.

[0014] Further, in step S4-1, when zoom scanning is performed, scanning is performed within the range of ±10% of the height difference. 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, so that the surface of the object to be measured (that is, the position of point "1") can be focused more quickly and accurately. Preferably, when zoom scanning is performed, scanning can be performed within the range of ±20% of the height difference.

[0015] Furthermore, in some specific operations, step S3 can also be omitted, that is, the height information of the object to be measured is no longer collected; and in step S4, each time scanning is performed from the minimum focal length to the maximum focal length, the two displacement adjustment tables move synchronously, and the light intensity extreme value received by the signal intensity detector is used to determine whether the laser is focused on the surface of the object to be measured, so as to determine the optimal fixed position of the ellipsoidal reflector and the optical fiber coupling unit.

[0016] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention uses an ellipsoidal reflector as a collection device. Compared with the use of a lens, it has a larger angle to collect the radiation spectrum and a smaller absorption loss, and can have a better signal-to-noise ratio; 2. The automatic focusing and adjustment scheme adopted by the present invention uses the energy feedback received by the linear array detector to control the zoom unit, which can focus the incident light on the surface of the measured objects of different sizes and shapes. At the same time, adjusting the position of the fiber coupling unit and the ellipsoidal reflector can ensure the collected radiation coupling efficiency; since only the position of the fiber coupling unit and the ellipsoidal reflector needs to be adjusted, the motion load is small, which is conducive to lightweight; 3. The present invention is provided 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, so as to predetermine the focusing range, without changing from the maximum focusing range to the minimum focusing range, thereby shortening the scanning time and improving the detection efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the overall structure of a lightweight LIBS online detection device capable of automatic focusing in an embodiment of the present invention; It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification so as to facilitate understanding and reading by persons familiar with this technology. They are not used to limit the conditions under which the present invention can be implemented, and therefore have no substantive technical significance. Any structural modification, change in proportion or adjustment of size, without affecting the effects and purposes that can be achieved by the present invention, should still fall within the scope of the technical contents disclosed by the present invention. DETAILED DESCRIPTION

[0018] The present invention will be further described in detail below in conjunction with specific embodiments. Methods or functional components not specifically described in the embodiments are all prior art. Example

[0019] As attached Figure 1 As shown, this embodiment provides a lightweight LIBS online detection device with automatic focusing, which includes a photoelectric switch, a pre-detection system, a controller, a delay device, a pulse laser, a reflector, a zoom unit, an ellipsoidal reflector, a displacement adjustment stage, a transmission window, a fiber coupling unit, a spectrometer and a signal strength detector in sequence according to the control logic and the light propagation path; The photoelectric switch is used to control the operation of the entire detection device, and its start signal is used as the starting point of the timing control. When the object to be detected passes through the photoelectric switch, the remote pre-detection system starts to work; The pre-check 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 it uploads the height and shape information of the object to be tested to the controller to determine the zoom adjustment range in advance; The controller is connected to the pre-check system, the time delay device, the displacement adjustment platform, the spectrometer and the signal strength detector, and the controller is used to send and receive signals; The time delay device is connected to the pulse laser and the spectrometer, and is used to control the output time of the pulse laser and the acquisition time of the spectrometer; that is, to control when to excite the surface plasma on the surface of the measured object and when to start collecting the spectrum signal; The pulse laser is used to provide pulse laser; the reflector is used to guide the pulse laser emitted by the pulse laser into the zoom unit; the zoom unit is used to focus the pulse laser onto the surface of the object to be measured; The ellipsoidal reflector is mounted on the first displacement adjustment platform; the ellipsoidal reflector is used to collect and reflect the radiation spectrum signal of the plasma cooling process on the surface of the measured object; The transmission window is used to reflect a part of the radiation spectrum signal reflected by the ellipsoidal reflector to the signal intensity detector, and the other part of the radiation spectrum signal is focused on the optical fiber coupling unit after passing through the transmission window; the signal intensity detector is used to detect the intensity of the radiation spectrum signal, so as to determine whether the pulse laser is focused on the surface of the object to be measured; the radiation spectrum signal is transmitted to the controller, and the position corresponding to the signal peak is the focusing position; The optical fiber coupling unit is used to receive the radiation spectrum signal collected by the ellipsoidal reflector. The optical fiber coupling unit is connected to the spectrometer through an optical fiber to transmit the radiation spectrum signal to the spectrometer for analysis.

[0020] In this embodiment, the fiber coupling unit is installed on the second displacement adjustment platform. When the first displacement adjustment platform drives the ellipsoidal reflector to change its position, the second displacement adjustment platform synchronously drives the fiber coupling unit to move, so that the fiber coupling unit always remains at the position of the second focus of the ellipsoidal reflector.

[0021] In this embodiment, the pre-inspection system adopts a telecentric lens imaging system, including an object-side telecentric lens and a detector. The signal strength detector adopts a linear array detector; the controller adopts a computer; and the two displacement adjustment platforms both adopt electric height adjustment platforms.

[0022] The method for using the detection device in this embodiment includes the following steps: S1. When installing and debugging the detection device, set an initial position for the ellipsoidal reflector and the fiber coupling unit as the zero position of the two displacement adjustment stages. At this time, the detection device will be suitable for measuring the object to be measured at a certain height, and the height will be used as the initial calibration height; S2, placing the object to be tested upstream of the conveyor belt, and 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; S3, when the object to be measured continues to move forward and passes through the pre-inspection system, the pre-inspection system detects the object to be measured and transmits the image result obtained after the detection 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; S4, when the object to be measured continues to move forward to the bottom of the ellipsoidal reflector and becomes the object to be measured, and is sensed by the second photoelectric switch, the conveyor belt pauses, and the controller issues a control command to drive the pulse laser to emit a pulse laser through the delay device, which is focused to the surface of the object to be measured through the reflector and the zoom unit; the light emitted by the surface during the cooling process is then collected by the ellipsoidal reflector, and a part of it is reflected to the signal intensity detector to record the intensity; 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. When zoom scanning is performed, scanning is performed within the range of ±10% of the height difference. When the zoom unit starts scanning, the two displacement adjustment tables move synchronously, driving the ellipsoidal reflector and the fiber 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 with the maximum light intensity is found as the optimal fixed position of the ellipsoidal reflector and the fiber coupling unit. 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 there is no need to perform zoom scanning, and formal measurement can be started directly; S5. The formal test begins. The pulse laser is focused on the surface of the object to be tested to excite the plasma on the surface. Under the timing control of the delay device, the light emitted by the surface of the object to be tested during the cooling process is collected by the ellipsoidal reflector. This part of the light is focused to the other focus of the ellipsoidal reflector through the transmission window and enters the 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 and displays the corresponding records in the host computer. The conveyor belt continues to transfer the detected objects.

[0023] 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 may have combinations and modifications of the aforementioned various technical features. Without departing from the spirit and scope of the present invention, those skilled in the art may improve, modify, or replace the present invention with equivalents, or apply the structure or method of the present invention to other fields to achieve the same effect, which all fall within the scope of protection included in the present invention.

Claims

1. A lightweight LIBS online detection device with automatic focusing, characterized in that: According to the control logic and the light propagation path, it includes a photoelectric switch, a pre-detection system, a controller, a delay device, a pulse laser, a reflector, a zoom unit, an ellipsoidal reflector, a displacement adjustment stage, a transmission window, a fiber coupling unit, a spectrometer and a signal strength detector; The pre-check 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, and uploads the height and shape information of the object to be tested to the controller to determine the zoom adjustment range in advance; The controller is connected to the pre-check system, the time delay device, the displacement adjustment platform, the spectrometer and the signal strength detector, and the controller is used to send and receive signals; The time delay device is connected to the pulse laser and the spectrometer, and is used to control the output time of the pulse laser and the collection time of the spectrometer; The pulse laser is used to provide pulse laser; The reflector is used to guide the pulse laser emitted by the pulse laser into the zoom unit; The zoom unit is used to focus the pulse laser onto the surface of the object to be measured; The ellipsoidal reflector is mounted on a first displacement adjustment platform; 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; The transmission window is used to reflect a part of the radiation spectrum signal reflected by the ellipsoidal reflector to the signal intensity detector, and the other part of the radiation spectrum signal passes through the transmission window and is focused on the optical fiber coupling unit; The signal intensity detector is used to detect the intensity of the radiation spectrum signal and determine whether the pulse laser is focused on the surface of the object to be measured by real-time recording; The optical fiber coupling unit is used to receive the radiation spectrum signal collected by the ellipsoidal reflector. The optical fiber coupling unit is connected to the spectrometer through an optical fiber to transmit the radiation spectrum signal to the spectrometer for analysis.

2. The lightweight LIBS online detection device with automatic focusing according to claim 1 is characterized in that: The fiber coupling unit is mounted on the second displacement adjustment platform. When the first displacement adjustment platform drives the ellipsoidal reflector to change its position, the second displacement adjustment platform synchronously drives the fiber coupling unit to move, so that the fiber coupling unit always remains at the second focus of the ellipsoidal reflector.

3. The lightweight LIBS online detection device with automatic focusing according to claim 1 is characterized in that: The pre-inspection system adopts a telecentric lens imaging system, including an object-side telecentric lens and a detector.

4. The lightweight LIBS online detection device with automatic focusing according to claim 1 is characterized in that: The pre-inspection system adopts a dual telecentric lens imaging system or a stereoscopic vision system.

5. The lightweight LIBS online detection device with automatic focusing according to claim 1 is characterized in that: The signal strength detector is a linear array detector or a planar array detector.

6. The lightweight LIBS online detection device capable of automatic focusing according to claim 1, characterized in that: The controller adopts a computer or a PLC; the displacement adjustment platforms are all electric displacement platforms.

7. A LIBS online detection method capable of automatic focusing, using the detection device according to any one of claims 1 to 6, characterized in that: The following steps are involved: S1. When installing and debugging the detection device, an initial position is set for the ellipsoidal reflector and the fiber coupling unit as the zero position of the two displacement adjustment stages. At this time, the detection device will be suitable for measuring an object to be measured at a certain height, and this height will be used as the initial calibration height; S2, the object to be tested passes through the first photoelectric switch, triggering the detection device to start running; S3, when the object to be measured passes through the pre-inspection system, the pre-inspection system transmits the measured image result 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; S4, the object to be measured continues to move forward to the bottom of the ellipsoidal reflector and becomes the object to be measured. When it is sensed by the second photoelectric switch, the controller issues a control instruction to drive the pulse laser to emit a pulse laser through the delay device, which is focused to the surface of the object to be measured through the reflector and the zoom unit; the light emitted by the surface during the cooling process is then collected by the ellipsoidal reflector, and a part of it is reflected to the signal intensity detector to record the intensity; S4-1. If the height of the object to be measured is different from the initial calibration height, zoom scanning is required. When the zoom unit starts scanning, the two displacement adjustment stages move synchronously, driving the ellipsoidal reflector and the fiber 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 with the maximum light intensity is found as the optimal fixed position of the ellipsoidal reflector and the fiber coupling unit. S4-2. If the height of the object to be measured is the same as the initial calibration height, there is no need to perform zoom scanning and the formal measurement can be started directly; S5. The formal test begins. The pulse laser is focused on the surface of the object to be tested to excite the plasma on the surface. Under the timing control of the delay device, the light emitted by the surface of the object to be tested during the cooling process is collected by the ellipsoidal reflector. This part of the light is focused to the other focus of the ellipsoidal reflector through the transmission window and enters the 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.

8. The detection method according to claim 7, characterized in that: In step S4-1, when performing zoom scanning, scanning is performed within the range of ±10% of the height difference value.

9. The detection method according to claim 7, characterized in that: In step S4-1, when performing zoom scanning, scanning is performed within the range of ±20% of the height difference value.

10. The detection method according to claim 7, characterized in that: 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 the scan is performed from the minimum focal length to the maximum focal length, the two displacement adjustment stages move synchronously, and the light intensity extreme value received by the signal intensity detector is used to determine whether the laser is focused on the surface of the object to be measured, so as to determine the optimal fixed position of the ellipsoidal reflector and the optical fiber coupling unit.

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