Arc temperature measurement system and method based on moiré fringe

Abstract

The embodiment of the present invention discloses an arc temperature measurement system based on moiré fringes, comprising: a laser, a first plano-convex lens, a second plano-convex lens, a first Ronchi grating, a second Ronchi grating, a third plano-convex lens, an aperture, a fourth plano-convex lens and a camera arranged in sequence along an optical path; and an arc generated at any position in the optical path between the second plano-convex lens and the first Ronchi grating, wherein an AC arc generation system applies an adjustable voltage to two electrodes so that the air gap between the two electrodes is broken down to generate the arc, and the two electrodes are placed opposite to each other in the vertical direction. The embodiment of the present invention discloses an arc temperature measurement method based on moiré fringes. The present invention solves the problem that the contact diagnosis method causes interference to the plasma and the spectral diagnosis method has weak anti-interference ability.

Description

Technical Field

[0001] The present invention relates to the technical field of plasma temperature measurement, and in particular to an arc temperature measurement system and method based on moiré fringes. Background Art

[0002] Air arc plasma is common in power scenarios such as photovoltaic power generation systems, offshore wind power systems, high-speed rail functional systems, and medium and low voltage distribution systems. Its combustion process is often accompanied by physical phenomena such as high temperature and strong light, which can easily cause accidents such as insulation damage to power equipment and burning of power lines, and even cause personal safety liability accidents. Arc temperature is one of the most important parameters to describe the thermodynamic state of arc plasma. By studying the arc temperature level and arc temperature distribution law, we can learn about the physical properties inside the plasma, which is of great significance for a deeper understanding of the arc generation mechanism and the prevention of arc hazards.

[0003] For arc plasma, AC power and switching power supplies are currently used to generate air arcs. The arcs generated by this method have problems such as small arc current, mild arcing, and the arc cannot burn continuously, which is not conducive to further temperature measurement research using the generated arc.

[0004] In addition, the temperature measurement using arc plasma is currently mainly divided into contact diagnosis method and non-contact diagnosis method. The contact diagnosis method is simple to operate, but due to the direct contact between the temperature sensor and the plasma, it will produce certain interference and large errors. The non-contact diagnosis method mainly uses the spectral diagnosis method, which has the disadvantages of being sensitive to the vibration of the surrounding environment and weak anti-interference ability. Summary of the invention

[0005] The object of the present invention is to provide an arc temperature measurement system and method based on moiré fringes, which generates an arc by controlling the control signal of an AC arc generating system, and performs non-contact temperature measurement based on the generated arc, so as to solve the problems of interference to plasma caused by contact diagnosis method and weak anti-interference ability of spectral diagnosis method.

[0006] An embodiment of the present invention provides an arc temperature measurement system based on moiré fringes, the system comprising:

[0007] A laser, a first plano-convex lens, a second plano-convex lens, a first Ronchi grating, a second Ronchi grating, a third plano-convex lens, an aperture, a fourth plano-convex lens and a camera are sequentially arranged along the optical path; and,

[0008] An arc is generated at any position in the optical path between the second plano-convex lens and the first Ronchi grating, wherein an AC arc generating system applies an adjustable voltage to two electrodes so that an air gap between the two electrodes is broken down to generate the arc, and the two electrodes are placed opposite to each other in a vertical direction;

[0009] The light beam generated by the laser is expanded by the first plano-convex lens and focused by the second plano-convex lens to become a parallel light beam. The parallel light beam is sequentially passed through the arc, the first Ronchi grating and the second Ronchi grating to interfere and generate a plurality of moiré fringes. The plurality of moiré fringes are focused by the third plano-convex lens and then filtered out by the aperture except for the +1 or -1 spectrum. The filtered light beam is focused by the fourth plano-convex lens and then received by the camera, so as to determine the temperature of the arc at the horizontal position of any moiré fringe according to the degree of distortion of the moiré fringe image taken by the camera.

[0010] As a further improvement of the present invention, the AC arc generating system comprises an arc generator,

[0011] The arc generator includes the two electrodes and two insulating resin workpieces for fixing the two electrodes.

[0012] One end of each electrode is conical, the conical ends of the two electrodes are placed opposite to each other and the air gap between the two conical ends is adjustable, so that when the adjustable voltage is applied to both ends of the two electrodes, the air gap is broken down to generate the arc, wherein the arc is in the shape of a vertical cylinder.

[0013] As a further improvement of the present invention, the AC arc generating system further comprises: a rectifier, a filter, an inverter, a transformer, a resistor and a signal monitor.

[0014] The rectifier rectifies three-phase AC power into DC power, and the DC power is output to the inverter after being stabilized and filtered by the filter. The inverter inverts the DC power into voltage-adjustable sinusoidal AC power and outputs it to the low-voltage side of the transformer. The resistor and the arc generator are connected in series to the high-voltage side of the transformer, and the signal monitor displays the voltage across the filter and the voltage output by the inverter.

[0015] As a further improvement of the present invention, the inverter includes two IGBT modules, each IGBT module includes two IGBT devices on the same bridge arm, one end of the two IGBT modules serves as an output end, respectively connected to the positive and negative poles of the direct current, and the other end of the two IGBT modules serves as an output end, respectively connected to the low-voltage side of the transformer.

[0016] As a further improvement of the present invention, the AC arc generating system further comprises: an inverter output controller,

[0017] The inverter output controller includes a control board and an IGBT drive board.

[0018] The control board outputs a control signal to the IGBT driving board, and the IGBT driving board drives the IGBT device to turn on and off at a specific frequency according to the control signal. The inverter is controlled by the control signal to adjust the voltage output by the inverter according to the control signal.

[0019] As a further improvement of the present invention, the control signal is an SPWM signal, and a plurality of buttons are provided on the control panel.

[0020] Controlling the output of the SPWM signal and the duty cycle of the SPWM signal by the multiple buttons to adjust the voltage output by the inverter includes:

[0021] By resetting the control button, the control board outputs the SPWM signal to make the IGBT driver board drive all IGBT devices to turn off, and the voltage output by the inverter is 0 at this time;

[0022] Through the boost control button, the control board outputs the SPWM signal to increase the on-time of the IGBT device driven by the IGBT drive board, so that the voltage output by the inverter increases;

[0023] Through the step-down control button, the control board outputs the SPWM signal to increase the off time of the IGBT driving board driving the IGBT device, so as to reduce the voltage output by the inverter;

[0024] Wherein, each time the boost control button or the buck control button is pressed, the duty cycle of the SPWM signal increases or decreases once according to a predetermined value until it increases or decreases to a target duty cycle, so that the on time or off time of the IGBT device changes according to the same gradient, so that the inverter output voltage increases or decreases according to the gradient.

[0025] As a further improvement of the present invention, the first Ronchi grating and the second Ronchi grating are respectively mounted on two oscillators, and the two oscillators are adjusted so that the inclination angles of the two oscillators are the same and the inclination directions are different, so that the multiple moiré fringes generated by interference are horizontal fringes.

[0026] As a further improvement of the present invention, the system further comprises a Z-axis optical lifting platform and a lens bracket placed on a plane.

[0027] The laser and the camera are placed on the Z-axis optical lifting platform.

[0028] The first plano-convex lens, the second plano-convex lens, the first Ronchi grating, the second Ronchi grating, the third plano-convex lens, the aperture and the fourth plano-convex lens are fixed on the lens holder,

[0029] One of the two electrodes is fixed on a plane, the other electrode is fixed on the Z-axis optical lifting platform, and the one electrode is located below the other electrode.

[0030] The embodiment of the present invention further provides a method for measuring arc temperature based on moiré fringes, the method comprising:

[0031] S1, placing two electrodes generating an electric arc at the position of the measured object, adjusting the optical path and the positions of the two electrodes, so that a plurality of moiré fringes generated by the interference of the first Ronchi grating and the second Ronchi grating and the two electrodes are simultaneously presented in the field of view of the camera, wherein the plurality of moiré fringes are clearly visible in black and white, and the black shadows of the two electrodes are located at the center of the field of view in the vertical direction;

[0032] S2, applying an adjustable voltage to both ends of the two electrodes through an AC arc generating system, so that the air between the gaps of the two electrodes is broken down to generate the arc;

[0033] S3, using a camera to shoot a video to obtain an original image of a moiré fringe image, wherein the electric arc changes the refractive index of air around the electric arc to generate distorted moiré fringes;

[0034] S4, processing the original image, and determining the temperature of the arc at a horizontal position where any moiré fringe is located according to the processed image.

[0035] As a further improvement of the present invention, the S4 comprises:

[0036] S41, performing cropping processing on the original image, cropping out left and right areas of the original image that are not related to the moiré fringes and top and bottom areas of the original image that are not related to the black shadows of the two electrodes, to obtain a first image;

[0037] S42, performing grayscale processing, binarization processing and thinning processing on the first image to obtain a second image;

[0038] S43, obtaining positions of all pixel points of each moiré fringe in the second image, for the same moiré fringe, deleting white points in the vertical direction due to the large fringe width and retaining pixel points at the center of the fringe to obtain retained pixel points, re-aggregating the retained pixel points and presenting them in the form of single point lines to obtain multiple single point lines;

[0039] S44, for each horizontal position of each single-point line, obtain the pixel height y1 of the single-point line at the horizontal position, and the pixel height y0 of the single-point line when it is not distorted at the horizontal position, obtain the distorted pixel height l of the single-point line at the horizontal position, and convert the distorted pixel height into the actual distorted height h of the moire fringe according to the ratio k:

[0040] h=kl,l=y1-y0,

[0041] Wherein, k is the gap length L between the two electrodes and the gap pixel length L between the two electrodes in the original image. / The ratio between them, k = L / L / ;

[0042] S45, for each horizontal position of each single point line, determine the deflection angle of the light in the y-axis direction according to the actual distortion height of the single point line at the horizontal position

[0043]

[0044] Wherein, θ is the angle between the grating lines, d is the distance between the first Rangchi grating and the second Rangchi grating, h is the actual distortion height of each single point line at each horizontal position, p is the grating constant, and p is / is the distance between two adjacent moiré fringes;

[0045] S46, performing an inverse Abel transform on the deflection angle obtained at each horizontal position of each single point line to obtain the air refractive index n at each horizontal position of each single point line, and determining the temperature of the arc corresponding to each horizontal position on each single point line by using the relationship between temperature and air refractive index:

[0046]

[0047] Wherein, T0 is the on-site ambient temperature, n0 is the on-site air refractive index, and n is the air refractive index obtained by the Abel inverse transformation.

[0048] The beneficial effects of the present invention are:

[0049] The optical platform based on moiré fringes collects images of the reaction arc temperature, and controls the generation and extinction of the arc through the control signal of the AC arc generation system. After coupling the optical platform and the AC arc generation system, the moiré fringes images in the arc starting, burning and arc extinction processes can be recorded, the distortion of the moiré fringes can be processed and calculated, and non-contact arc temperature measurement can be realized. The generated plasma does not require direct contact, will not cause interference, and has a small error. In addition, the non-contact measurement is insensitive to the vibration of the surrounding environment and has a strong interference ability. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the prior art descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention, and for ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor.

[0051] Figure 1 A schematic diagram of an arc temperature measurement system based on moiré fringes according to an exemplary embodiment of the present invention;

[0052] Figure 2 A schematic diagram of an AC arc generating system in an arc temperature measurement system based on moiré fringes according to an exemplary embodiment of the present invention;

[0053] Figure 3 A schematic diagram of a spectrum of light spots appearing on an aperture in an arc temperature measurement system based on moiré fringes according to an exemplary embodiment of the present invention;

[0054] Figure 4 A schematic diagram showing the comparison of moiré fringes captured by a camera before and after distortion in an arc temperature measurement system based on moiré fringes according to an exemplary embodiment of the present invention;

[0055] Figure 5 This is a first image of a moire fringe image according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0056] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0057] It should be noted that if the embodiments of the present invention involve directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0058] In addition, in the description of the present invention, the terms used are only for illustrative purposes and are not intended to limit the scope of the present invention. The terms "include" and / or "comprise" are used to specify the existence of the elements, steps, operations and / or components, but do not exclude the existence or addition of one or more other elements, steps, operations and / or components. The terms "first", "second" and the like may be used to describe various elements, do not represent the order, and do not limit these elements. In addition, in the description of the present invention, unless otherwise specified, the meaning of "multiple" is two and more than two. These terms are only used to distinguish one element from another element. In conjunction with the following drawings, these and / or other aspects become apparent, and it is easier for a person of ordinary skill in the art to understand the description of the embodiments of the present invention. The accompanying drawings are used to describe the embodiments of the present invention for illustrative purposes only. Those skilled in the art will easily recognize from the following description that, without departing from the principles of the present invention, alternative embodiments of the structures and methods shown in the present invention can be adopted.

[0059] An arc temperature measurement system based on moiré fringes according to an embodiment of the present invention is as follows: Figure 1 As shown, the system comprises:

[0060] A laser S, a first plano-convex lens L1 with a focal length of f1, a second plano-convex lens L2 with a focal length of f2, a first Ronchi grating G1, a second Ronchi grating G2, a third plano-convex lens L3 with a focal length of f3, an aperture V, a fourth plano-convex lens L4 with a focal length of f4, and a camera C are sequentially arranged along the optical path; and,

[0061] An arc X is generated at any position in the optical path between the second plano-convex lens L2 and the first Ronchi grating G1, wherein an AC arc generating system applies an adjustable voltage to two electrodes so that an air gap between the two electrodes is broken down to generate the arc, and the two electrodes are placed opposite to each other in a vertical direction;

[0062] The focal length of the selected lens should satisfy the requirement that the light beam generated by the laser becomes a parallel light beam after being sequentially expanded by the first plano-convex lens L1 and converged by the second plano-convex lens L2. The parallel light beam sequentially passes through the arc, the first Ronchi grating G1 and the second Ronchi grating G2 to interfere and generate a plurality of moiré fringes. The plurality of moiré fringes are converged by the third plano-convex lens L3, and the light beam outside the +1 or -1 spectrum is filtered out by the aperture V. The filtered light beam is converged by the fourth plano-convex lens L4 and received by the camera C, so as to determine the temperature of the arc at the horizontal position where any moiré fringes are located according to the degree of distortion of the moiré fringe image taken by the camera C.

[0063] The optical platform of the present invention collects images of reaction arc temperature based on moiré fringes, and controls the generation and extinction of the arc through the control signal of the AC arc generation system. After coupling the optical platform and the AC arc generation system, the moiré fringes images in the arc starting, burning and arc extinction processes can be recorded, the distortion amount of the moiré fringes is processed and calculated, and non-contact arc temperature measurement is realized. The generated plasma does not need direct contact, does not generate interference, has a small error, and the non-contact measurement is insensitive to the vibration of the surrounding environment and has a strong interference ability.

[0064] Before using the system to measure temperature, the optical path needs to be adjusted to ensure that the moiré fringes received by the camera C are clearly black and white and usable. It is also necessary to adjust the AC arc generation system, including two electrodes and the voltage applied across the two electrodes, to ensure that the arc X is generated and located in the center of the camera C field of view.

[0065] Among them, adjusting the optical path mainly includes adjusting the relative distance of each plano-convex lens so that the light beam passing through the two Ronchi gratings is parallel light with good parallelism. It is also necessary to adjust the distance between the two Ronchi gratings and the angle between the grating lines so that the moiré fringes observed in the camera field of view are distinct in black and white and clearly visible. Ronchi grating refers to a grating with a ratio of 1:1 between transparent and opaque lines. The focal length of each lens in the system can be adaptively designed as long as it can meet the requirements of the grating to generate parallel light and form an image.

[0066] After the optical path is adjusted, a row of light spots will be generated at the aperture V, such as Figure 3 As shown. Among them, the light spot at the center has the highest brightness. This light spot is formed by focusing the light of the 0th order spectrum. If this light beam is used to generate moiré fringes, the image received by the camera will have ghosting. Therefore, it is necessary to control the position of the aperture V and the size of the light hole of the aperture V, so that only one light spot next to the brightest light spot passes through the aperture V, even if the light spot of the +1 or -1 spectrum passes through the aperture, to eliminate ghosting in the image.

[0067] Wherein, adjusting the AC arc generating system includes moving the positions of the two electrodes in the horizontal direction so that the shadows of the two electrodes can be clearly seen in the field of view of the camera C, and the shadows of the two electrodes are located in the center of the field of view in the vertical direction. It also includes adjusting the output voltage of the AC arc generating system (for example, gradually increasing to a voltage that can break through the air gap between the two electrodes) until the air gap between the two electrodes (i.e., the air breakdown distance) is broken down, so that the arc X can be generated.

[0068] It can be understood that when the two Ronchi gratings and the two electrodes are located in the center of the field of view, the generated arc X is also located in the center of the field of view of the camera C, and the fringe distortion around the arc X will also be fully displayed.

[0069] The laser S may be, for example, a solid-state laser or other light source with low divergence. It is understood that the laser S should meet the requirements of strong directionality and low divergence. After the adjustment is completed, the laser S is turned on, and the laser emitted by the laser S is expanded by the first plano-convex lens L1 and converged by the second plano-convex lens L2 to become a parallel beam. The parallel beam passes through the arc X, the first Ronchi grating G1 and the second Ronchi grating G2 in sequence, and then interferes to generate multiple moiré fringes, and then converges through the third plano-convex lens L3, and the aperture V installed at the focus filters out the light outside the +1 or -1 spectrum. The light passing through the aperture V is converged by the fourth plano-convex lens L4 and received by the camera C. The camera C records the video, takes a screenshot of the video, obtains the change in the refractive index of the air around the arc column caused by the high-temperature arc column, and then obtains the original image of the moiré fringes. After a series of image processing is performed on the original image, the arc temperature at the horizontal position where all the moiré fringes are located can be calculated.

[0070] If the camera C cannot completely present the moiré fringe image after the laser S is turned on, it means that the two Ronchi gratings are not parallel to the optical path, or the Ronchi gratings and the camera C are not at the center of the optical path. At this time, it is necessary to adjust the relative positions of the two Ronchi gratings or the camera C and the optical path again so that the moiré fringe is completely presented in the center of the field of view of the camera C, that is, the edges and internal fringes of the two Ronchi gratings can be seen in the camera C, so that as much fringe information as possible can be obtained after the moiré fringe image is cropped. After the complete moiré fringe is observed in the field of view, the distance between the two Ronchi gratings is adjusted so that the moiré fringe observed in the field of view is clearly visible in black and white.

[0071] When the camera C only shoots static stripes, a suitable ordinary camera can be selected; when it is necessary to shoot the arc starting and arc extinction process or more arc details, a high-speed camera with a frame rate of more than 1000fps should be selected.

[0072] In one embodiment, the system further comprises a Z-axis optical lifting platform and a lens holder placed on a plane.

[0073] The laser and the camera are placed on the Z-axis optical lifting platform.

[0074] The first plano-convex lens, the second plano-convex lens, the first Ronchi grating, the second Ronchi grating, the third plano-convex lens, the aperture and the fourth plano-convex lens are fixed on the lens holder,

[0075] One of the two electrodes is fixed on a plane, the other electrode is fixed on the Z-axis optical lifting platform, and the one electrode is located below the other electrode.

[0076] like Figure 1 As shown, the laser S and the camera C are placed on a Z-axis optical lifting platform, all plano-convex lenses, all Ronchi gratings and the aperture V are fixed on a lens holder, and the height of the Z-axis optical lifting platform and the lens holder are adjusted so that the center lines of the components in the system are at the same horizontal height, ensuring that the optical path can pass through the center position of each component. And one electrode is fixed on a plane, and the other electrode is fixed on the Z-axis optical lifting platform, so that the arc X generated by the air gap between the two electrodes can be located in the optical path, and the distance between the two electrodes, that is, the air gap between the two electrodes, can be adjusted (changed) by the Z-axis optical lifting platform to test the arc temperature at different air breakdown distances. In the above system, the plane where the electrodes are placed can be the same plane as the plane of the Z-axis optical lifting platform and the lens holder, or different planes. It is only necessary to adjust the arc between the electrodes so that the arc can be recorded by the camera in the optical path.

[0077] In one embodiment, the AC arc generating system comprises an arc generator 7,

[0078] The arc generator 7 includes the two electrodes and two insulating resin workpieces for fixing the two electrodes.

[0079] One end of each electrode is conical, the conical ends of the two electrodes are placed opposite to each other and the air gap between the two conical ends is adjustable, so that when the adjustable voltage is applied to both ends of the two electrodes, the air gap is broken down to generate the arc, wherein the arc is in the shape of a vertical cylinder.

[0080] like Figure 2 As shown, the arc generator 7 is composed of a pair of electrodes and two insulating resin workpieces fixing them. The pair of electrodes are cylindrical copper electrodes, the copper column is tapped on the outside, one end is conical, and the other end is cylindrical. The pair of electrodes are fixed to two workpieces with through holes drilled inside with nuts, and the two workpieces are placed so that the electrodes are located in the vertical direction and the conical ends of the electrodes are placed opposite to each other. The side of the workpiece located above is fixed to the Z-axis optical lifting platform to adjust the length of the air gap between the pair of electrodes so that an arc is generated when a voltage is applied between the two electrodes. The voltage is applied by connecting the cylindrical end of the copper column to the external circuit. The tips (conical ends) of the upper and lower electrodes should be aligned as much as possible so that the generated arc is as cylindrical as possible in the vertical direction to reduce the error in arc image processing.

[0081] In one embodiment, the AC arc generating system further comprises: a rectifier 1, a filter 2, an inverter 4, a transformer 5, a resistor 6 and a signal monitor 9.

[0082] The rectifier 1 rectifies three-phase AC power into DC power, and the DC power is output to the inverter 4 after being stabilized and filtered by the filter 2. The inverter 4 inverts the DC power into voltage-adjustable sinusoidal AC power and outputs it to the low-voltage side of the transformer 5. The resistor 6 and the arc generator 7 are connected in series to the high-voltage side of the transformer 5. The signal monitor 9 displays the voltage across the filter 2 and the voltage output by the inverter 4.

[0083] like Figure 2 As shown, the rectifier 1 rectifies the input three-phase AC mains, and its DC output end is connected in parallel with a filter 2 composed of a capacitor bank, which plays a role in voltage stabilization and filtering after charging the capacitor bank, thereby achieving the purpose of stable DC output. The stabilized DC power is output to the inverter 4. Under the control of the control signal, the inverter 4 inverts the DC power into a voltage-adjustable sinusoidal AC power.

[0084] The transformer 5 is, for example, a transformer of model D11-70 / 0.3-10, with a tap voltage of 300V at the input voltage end and two tap positions at the output load end, and the tap corresponding voltages are 5000V and 10000V, that is, the transformer 5 transforms the inverter output voltage to a maximum of 10kV, and the rated frequency of the transformer 5 is 50Hz. The sinusoidal alternating current output by the inverter 4 is connected to the input end of the transformer 5, and the output end is connected to the load. The 50Hz alternating current output by the inverter 4 is connected to the low-voltage side of the transformer 5, and the monitoring signal of the signal monitor 9 is taken from the input and output ends of the inverter 4. The monitor displays the charging voltage of the capacitor bank, the output voltage of the inverter 4, and the current size on the low-voltage side in real time. The resistor 6 and the arc generator 7 are connected in series on the high-voltage side of the transformer 5. The function of the resistor 6 is to limit the current size within the tolerance range of the low-voltage side line when the arc generator 7 generates an arc.

[0085] In one embodiment, the inverter 4 includes two IGBT modules, each IGBT module includes two IGBT devices on the same bridge arm, one end of the two IGBT modules serves as an output end, respectively connected to the positive and negative poles of the direct current, and the other end of the two IGBT modules serves as an output end, respectively connected to the low-voltage side of the transformer 5.

[0086] like Figure 2As shown, the inverter 4 is composed of two high-power IGBT modules, each of which includes two IGBT devices on the same bridge arm. The two high-power IGBT modules constitute a full-bridge inverter. Taking the Infineon FF1200R121E5 IGBT module as an example, the positive and negative poles of the direct current are respectively connected to the 10th and 9th terminals of the two IGBT modules, and the No. 3 terminals of the two IGBT modules are respectively led out as output terminals. The two IGBT modules constitute a full-bridge inverter.

[0087] In one embodiment, the AC arc generating system further comprises: an inverter output controller,

[0088] The inverter output controller includes a control board and an IGBT drive board.

[0089] The control board outputs a control signal to the IGBT driving board, and the IGBT driving board drives the IGBT device to turn on and off at a specific frequency according to the control signal. The inverter is controlled by the control signal to adjust the voltage output by the inverter according to the control signal.

[0090] In one embodiment, the control signal is an SPWM signal, and a plurality of buttons are provided on the control panel.

[0091] Controlling the output of the SPWM signal and the duty cycle of the SPWM signal by the multiple buttons to adjust the voltage output by the inverter includes:

[0092] By resetting the control button, the control board outputs the SPWM signal to make the IGBT driver board drive all IGBT devices to turn off, and the voltage output by the inverter is 0 at this time;

[0093] Through the boost control button, the control board outputs the SPWM signal to increase the on-time of the IGBT device driven by the IGBT drive board, so that the voltage output by the inverter increases;

[0094] Through the step-down control button, the control board outputs the SPWM signal to increase the off time of the IGBT driving board driving the IGBT device, so as to reduce the voltage output by the inverter;

[0095] Wherein, each time the boost control button or the buck control button is pressed, the duty cycle of the SPWM signal increases or decreases once according to a predetermined value until it increases or decreases to a target duty cycle, so that the on time or off time of the IGBT device changes according to the same gradient, so that the inverter output voltage increases or decreases according to the gradient.

[0096] like Figure 2As shown, it also includes an inverter output controller 8 for controlling the inverter 4. Under the control signal of the inverter output controller 8, the inverter 4 inverts the direct current into a voltage-adjustable sinusoidal alternating current. The inverter output controller 8 is composed of a control board and an IGBT driver board. It can be understood that the inverter 4 is composed of IGBT devices, and the inverter output controller 8 is a programming circuit board. The inverter output voltage is increased or decreased by a certain step value by controlling the buttons. The output voltage and current signal is displayed in real time by the signal monitor 9. The IGBT driver board controls the on and off of the IGBT device to achieve the function of changing the inverter voltage. For example, the core of the control board is an stm32 chip, which is programmed to output an SPWM control signal to the IGBT driver board to control the conduction and disconnection of the inverter 4. And the duty cycle of the SPWM control signal is controlled by the key interrupt to realize the function of adjusting the output voltage of the inverter 4. The arc generator 7 (two electrodes and two workpieces) is connected in series with the resistor 6 as a load. When the inverter output voltage reaches a certain value, the air gap between the copper column electrodes will be broken down, generating a measured arc that can be used by the system.

[0097] When the control board is in the reset state, the control board outputs a signal to turn off all IGBT devices, and the inverter output voltage is 0 at this time;

[0098] When the boost control button of the control board is pressed, the boost indicator light (such as a red LED) of the control board lights up, and the control board outputs an SPWM control signal to increase the conduction time of the IGBT device. At this time, the inverter outputs sinusoidal AC power. After the button is pressed, the duty cycle of the SPWM signal of the control board increases, and the output voltage and current increase.

[0099] When the step-down control button of the control board is pressed, the step-down indicator light (e.g., green LED) of the control board lights up, which increases the off time of the IGBT device. After the step-down control button is pressed, the duty cycle of the SPWM signal of the control board decreases, and the output voltage and current decrease.

[0100] Each time the boost or buck button is pressed, the target duty cycle value of the SPWM signal output by the control board increases or decreases by the same value, and slowly changes from the current duty cycle to the target duty cycle. At this time, the on-time or off-time of the IGBT device changes according to the same gradient (the gradient is the same value mentioned above), so that the inverter output voltage increases or decreases according to the gradient, that is, the inverter output voltage slowly increases or decreases by a certain value.

[0101] In one embodiment, the oscillator of the first Ronchi grating and the oscillator of the second Ronchi grating have the same inclination angle and different inclination directions, so that the multiple moiré fringes generated by interference are horizontal fringes.

[0102] like Figure 1As shown, the two oscillators installed with the first Rangchi grating G1 and the second Rangchi grating G2 are respectively set to the same inclination angle and different inclination directions to ensure that the moiré fringes generated after interference are horizontal fringes. In order to make the moiré fringes image in the field of view easy to identify (that is, the moiré fringes are fully presented in the camera field of view), the angles of the oscillators are respectively set to 2° and -2° in this embodiment. If the angle is too large, the moiré fringes in the field of view are too dense and it is difficult to extract the distortion amount. On the contrary, the moiré fringes are too sparse and the degree of distortion of the moiré fringes cannot be fully displayed. The two oscillators tilt the two gratings in opposite directions, and there is an angle between the grating lines, which is twice the inclination angle of a single oscillator.

[0103] The arc temperature measurement method based on moiré fringes described in the embodiment of the present invention adopts the arc temperature measurement system based on moiré fringes described in the above-mentioned embodiment, and the system is not described in detail here. The arc temperature measurement method based on moiré fringes includes:

[0104] S1, placing two electrodes generating an arc at the position of the measured object, adjusting the optical path and the position of the two electrodes, so that a plurality of moiré fringes generated by the interference of the first Ronchi grating and the second Ronchi grating and the two electrodes are simultaneously presented in the field of view of the camera, wherein the plurality of moiré fringes are distinct in black and white and clearly visible, and the black shadows of the two electrodes are located in the center of the vertical direction of the field of view.

[0105] S2, applying an adjustable voltage to both ends of the two electrodes through an AC arc generating system, so that the air between the gaps of the two electrodes is broken down to generate the arc.

[0106] S3, using a camera to shoot a video to obtain an original image of the moiré fringe image, wherein the electric arc changes the refractive index of air around the electric arc to generate distorted moiré fringes.

[0107] S4, processing the original image, and determining the temperature of the arc at a horizontal position where any moiré fringe is located according to the processed image.

[0108] In the above step S1, it can be understood that the following adjustment process is included:

[0109] S11, adjusting the relative distance between each plano-convex lens so that the light beams passing through the two Ronchi gratings are parallel light with good parallelism.

[0110] S12, adjusting the distance between the two Ronchi gratings and the angle between the grating lines so that the plurality of moiré fringes observed in the field of view are distinct in black and white and clearly visible.

[0111] S13, moving the positions of the two electrodes in the horizontal direction so that the black shadows of the two electrodes can be clearly seen in the field of vision, and the black shadows of the two electrodes are located in the center of the field of vision in the vertical direction.

[0112] In the above step S2, it can be understood that: a voltage is applied to both ends of the two electrodes, and the voltage is adjusted (for example, gradually increased) until the air gap between the two electrodes is broken down to generate an arc.

[0113] In one implementation, the S4 includes:

[0114] S41, the original image is cropped to remove the left and right areas of the original image that are not related to the moiré fringes (i.e., the areas outside the Ronchi grating overlap area) and the upper and lower areas of the original image that are not related to the shadows of the two electrodes (part of the fringes blocked by the electrodes will affect the calculation results, so the blocked areas need to be removed), to obtain a first image, which only contains the completed fringes, such as Figure 5 shown.

[0115] In the above steps, the size of the original image is first calibrated using the distance between the two electrodes in the original image, such as Figure 4 As shown, the size of the original image can be obtained as: length X, width Y. Taking the lower left corner of the original image as the coordinate origin, the pixel coordinates of the upper and lower electrode tips are read as (X0, Y0) and (X1, Y1) respectively, and the pixel length of the gap between the two electrodes is L. / =Y1-Y0 (i.e. the pixel length is L / ), the gap length between the two electrodes is measured as L (that is, the actual length is L), and the ratio of the actual length to the pixel length in the corresponding image is k = L / L / After the calibration process is completed, the original image is cropped.

[0116] S42, performing grayscale processing, binarization processing and thinning processing on the first image to obtain a second image.

[0117] S43, obtaining the positions of all pixel points of each moiré fringe in the second image, for the same moiré fringe, deleting the white spots in the vertical direction caused by the large stripe width and retaining the pixel points in the center of the stripe to obtain the retained pixel points, reaggregating the retained pixel points and presenting them in the form of single-point lines to obtain multiple single-point lines.

[0118] S44, for each horizontal position of each single-point line, obtain the pixel height y1 of the single-point line at the horizontal position, and the pixel height y0 of the single-point line when it is not distorted at the horizontal position, obtain the distorted pixel height l of the single-point line at the horizontal position, and convert the distorted pixel height into the actual distorted height h according to the ratio k.

[0119] h=kl,l=y1-y0,

[0120] Wherein, k is the gap length L between the two electrodes and the gap pixel length L between the two electrodes in the original image. / The ratio between them, k = L / L / .

[0121] like Figure 4 As shown, for example, the pixel height of the topmost moiré fringe at the horizontal position x0 is y1, and the pixel height y0 of the moiré fringe when it is not distorted at the horizontal position x0 is subtracted from the pixel height y1 to obtain the distorted pixel height l=y1-y0 of the moiré fringe at the horizontal position x0, and the distorted pixel height is converted into the actual distorted height h=kl of the moiré fringe according to the ratio k. The calculation of other moiré fringes is the same as the above process and will not be repeated here.

[0122] It is understandable that, despite the thinning process, the moiré fringe itself has a certain width. For the same moiré fringe, there are multiple pixel points with different ordinates under the same horizontal coordinate. When calculating the moiré fringe distortion, different distortions will be obtained by selecting pixel points with different ordinates, which will inevitably affect the calculation results. Therefore, the average ordinate value of multiple pixel points under the same horizontal coordinate is extracted, that is, the coordinates of the pixel point located at the center of the fringe are obtained, the coordinates of the center point of all the horizontal coordinate positions of the fringe are extracted, and the coordinates of the obtained points are reconstructed, and finally a moiré fringe image composed of a single pixel is obtained.

[0123] For a certain moiré fringe, the ordinate of each pixel point in the horizontal coordinate direction is subtracted from the ordinate of the point when the fringe is not distorted, and the distorted pixel height of the moiré fringe at the horizontal coordinate position is obtained. According to the image pixel height corresponding to the air gap length between electrodes, the pixel length corresponding to the actual unit length can be obtained, and the obtained fringe distortion pixel height is converted to the actual distortion height according to this ratio.

[0124] S45, for each horizontal position of each single point line, determine the deflection angle of the light in the y-axis direction according to the actual distortion height of the single point line at the horizontal position

[0125]

[0126] Wherein, θ is the angle between the grating lines (the grating lines are the angle between the first Rangchi grating and the second Rangchi grating, which is twice the tilt angle of the oscillator), d is the distance between the first Rangchi grating and the second Rangchi grating, h is the actual distortion height of each single point line at each horizontal position, p is the grating constant (i.e., the constant of the first Rangchi grating and the second Rangchi grating), p / is the distance between two adjacent moiré fringes (the distance is Figure 4 shown);

[0127] S46, performing an inverse Abel transform on the deflection angle obtained at each horizontal position of each single point line to obtain the air refractive index n at each horizontal position of each single point line, and determining the temperature of the arc corresponding to each horizontal position on each single point line by using the relationship between temperature and air refractive index:

[0128]

[0129] Wherein, T0 is the on-site ambient temperature, n0 is the on-site air refractive index, and n is the air refractive index obtained by the Abel inverse transformation.

[0130] It can be understood that the above steps S44-S46 are the calculation of the arc temperature corresponding to each horizontal position point on each single point line, and the horizontal position is the x-axis position. For each single point line, through multiple calculations of steps S44-S46, the arc temperature corresponding to different horizontal positions of each single point line can be obtained, that is, the arc temperature corresponding to all horizontal coordinate positions on a moiré fringe can be obtained. Figure 4 As shown, there are multiple moiré fringes, and the arc temperatures corresponding to the horizontal positions of other moiré fringes refer to the above process. Among the multiple moiré fringes, since each moiré fringes corresponds to a vertical coordinate position, the arc temperatures corresponding to different horizontal coordinate positions at different vertical coordinate positions can be obtained through the above steps. According to the ratio of the actual length to the corresponding pixel length, the temperature distribution of the arc and the air in a certain range around the arc can be converted.

[0131] In the description provided herein, a large number of specific details are described. However, it is understood that embodiments of the present invention can be practiced without these specific details. In some instances, well-known methods, structures and techniques are not shown in detail so as not to obscure the understanding of this description.

[0132] In addition, it will be understood by those skilled in the art that although some embodiments described herein include certain features included in other embodiments but not other features, the combination of features of different embodiments is meant to be within the scope of the present invention and form different embodiments. For example, in the claims, any one of the claimed embodiments can be used in any combination.

[0133] It will be appreciated by those skilled in the art that, although the present invention has been described with reference to exemplary embodiments, various changes may be made and equivalents may be substituted for its elements without departing from the scope of the present invention. In addition, many modifications may be made to adapt specific circumstances or materials to the teachings of the present invention without departing from the essential scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed, but the present invention will include all embodiments falling within the scope of the appended claims.

Claims

1. An arc temperature measurement system based on moiré fringes, characterized in that: The system comprises: A laser, a first plano-convex lens, a second plano-convex lens, a first Ronchi grating, a second Ronchi grating, a third plano-convex lens, an aperture, a fourth plano-convex lens and a camera are sequentially arranged along the optical path; and, An arc is generated at any position in the optical path between the second plano-convex lens and the first Ronchi grating, wherein an AC arc generating system applies an adjustable voltage to two electrodes so that an air gap between the two electrodes is broken down to generate the arc, and the two electrodes are placed opposite to each other in a vertical direction; The light beam generated by the laser is sequentially expanded by the first plano-convex lens and converged by the second plano-convex lens to become a parallel light beam. The parallel light beam sequentially passes through the electric arc, the first Ronchi grating and the second Ronchi grating to interfere and generate a plurality of moiré fringes. The plurality of moiré fringes are converged by the third plano-convex lens, and the light beams other than the +1 or -1 spectrum are filtered out by the aperture. The filtered light beams are converged by the fourth plano-convex lens and then received by the camera. The camera takes a video to obtain an original image of the moiré fringes image, and the original image is cropped to crop the left and right areas of the original image that are not related to the moiré fringes and the upper and lower areas of the original image that are not related to the black shadows of the two electrodes to obtain a first image. Performing grayscale processing, binarization processing, and thinning processing on the first image to obtain a second image; Obtaining positions of all pixel points of each moiré fringe in the second image, for the same moiré fringe, deleting white points in the vertical direction due to the large fringe width and retaining pixel points at the center of the fringe to obtain retained pixel points, reaggregating the retained pixel points and presenting them in the form of single-point lines to obtain multiple single-point lines; For each horizontal position of each single-point line, obtain the pixel height y1 of the single-point line at the horizontal position and the pixel height y0 of the single-point line when it is not distorted at the horizontal position, obtain the distorted pixel height l of the single-point line at the horizontal position, and convert the distorted pixel height to the actual distorted height h according to the ratio k: h=kl,l=y1-y0, Wherein, k is the gap length L between the two electrodes and the gap pixel length L between the two electrodes in the original image. / The ratio between them, k = L / L / ; For each horizontal position of each single-point line, determine the deflection angle of the light in the y-axis direction according to the actual distortion height of the single-point line at that horizontal position. Wherein, θ is the angle between the grating lines, d is the distance between the first Rangchi grating and the second Rangchi grating, h is the actual distortion height of each single point line at each horizontal position, p is the grating constant, and p is / is the distance between two adjacent moiré fringes; The deflection angle obtained at each horizontal position of each single point line is subjected to an inverse Abel transformation to obtain the air refractive index n at each horizontal position of each single point line, and the temperature of the arc corresponding to each horizontal position on each single point line is determined using the relationship between temperature and air refractive index: Wherein, T0 is the on-site ambient temperature, n0 is the on-site air refractive index, and n is the air refractive index obtained by the Abel inverse transformation.

2. The system of claim 1, wherein: The AC arc generating system comprises an arc generator, The arc generator includes the two electrodes and two insulating resin workpieces for fixing the two electrodes. One end of each electrode is conical, the conical ends of the two electrodes are placed opposite to each other and the air gap between the two conical ends is adjustable, so that when the adjustable voltage is applied to both ends of the two electrodes, the air gap is broken down to generate the arc, wherein the arc is in the shape of a vertical cylinder.

3. The system of claim 2, wherein: The AC arc generating system further comprises: a rectifier, a filter, an inverter, a transformer, a resistor and a signal monitor. The rectifier rectifies three-phase AC power into DC power, and the DC power is output to the inverter after being stabilized and filtered by the filter. The inverter inverts the DC power into voltage-adjustable sinusoidal AC power and outputs it to the low-voltage side of the transformer. The resistor and the arc generator are connected in series to the high-voltage side of the transformer, and the signal monitor displays the voltage across the filter and the voltage output by the inverter.

4. The system of claim 3, wherein: The inverter includes two IGBT modules, each IGBT module includes two IGBT devices on the same bridge arm, one end of the two IGBT modules serves as an output end, respectively connected to the positive and negative poles of the direct current, and the other end of the two IGBT modules serves as an output end, respectively connected to the low-voltage side of the transformer.

5. The system of claim 3, wherein: The AC arc generating system further comprises: an inverter output controller, The inverter output controller includes a control board and an IGBT drive board. The control board outputs a control signal to the IGBT driving board, and the IGBT driving board drives the IGBT device to turn on and off at a set frequency according to the control signal. The inverter is controlled by the control signal to adjust the voltage output by the inverter according to the control signal.

6. The system of claim 5, wherein: The control signal is an SPWM signal, and a plurality of buttons are provided on the control panel. Controlling the output of the SPWM signal and the duty cycle of the SPWM signal by the multiple buttons to adjust the voltage output by the inverter includes: By resetting the control button, the control board outputs the SPWM signal to make the IGBT driver board drive all IGBT devices to turn off, and at this time the voltage output by the inverter is 0; Through the boost control button, the control board outputs the SPWM signal to increase the on-time of the IGBT device driven by the IGBT drive board, so that the voltage output by the inverter increases; Through the step-down control button, the control board outputs the SPWM signal to increase the off time of the IGBT driving board driving the IGBT device, so as to reduce the voltage output by the inverter; Wherein, each time the boost control button or the buck control button is pressed, the duty cycle of the SPWM signal increases or decreases once according to a predetermined value until it increases or decreases to a target duty cycle, so that the on time or off time of the IGBT device changes according to the same gradient, so that the inverter output voltage increases or decreases according to the gradient.

7. The system of claim 1, wherein: The first Ronchi grating and the second Ronchi grating are respectively mounted on two oscillators, and the two oscillators are adjusted so that the inclination angles of the two oscillators are the same and the inclination directions are different, so that the multiple moiré fringes generated by interference are horizontal fringes.

8. The system of claim 1, wherein: The system also includes a Z-axis optical lifting platform and a lens holder placed on a plane. The laser and the camera are placed on the Z-axis optical lifting platform. The first plano-convex lens, the second plano-convex lens, the first Ronchi grating, the second Ronchi grating, the third plano-convex lens, the aperture and the fourth plano-convex lens are fixed on the lens holder, One of the two electrodes is fixed on a plane, the other electrode is fixed on the Z-axis optical lifting platform, and the one electrode is located below the other electrode.

9. An arc temperature measurement method using the arc temperature measurement system according to any one of claims 1 to 8, characterized in that: The method comprises: S1, placing two electrodes generating an electric arc at the position of the measured object, adjusting the optical path and the positions of the two electrodes, so that a plurality of moiré fringes generated by the interference of the first Ronchi grating and the second Ronchi grating and the two electrodes are simultaneously presented in the field of view of the camera, wherein the plurality of moiré fringes are clearly visible in black and white, and the black shadows of the two electrodes are located at the center of the field of view in the vertical direction; S2, applying an adjustable voltage to both ends of the two electrodes through an AC arc generating system, so that the air between the gaps of the two electrodes is broken down to generate the arc; S3, using a camera to shoot a video to obtain an original image of a moiré fringe image, wherein the electric arc changes the refractive index of air around the electric arc to generate distorted moiré fringes; S4, processing the original image, and determining the temperature of the arc at a horizontal position where any moiré fringe is located according to the processed image.

Images