A method for precision assembly of an electrospray thruster

Abstract

The present application relates to the technical field of propeller, and particularly relates to a precision assembling method of an electrospray thruster. The present application provides a precision assembling method of an electrospray thruster, comprising: aligning the electrospray thruster from above by using a zoom measurement system, moving the zoom measurement system up and down to obtain a plurality of clear imaging pictures including the upper surface of an extraction pole and the tip of an emitter pole, and each clear imaging picture is marked with height information of the zoom measurement system; generating a depth map representing surface topography information according to the plurality of clear imaging pictures and the corresponding height information; calculating an adjustment distance according to the depth map, and adjusting the positions of the emitter pole and the extraction pole according to the adjustment distance. The present application provides a precision assembling method of an electrospray thruster, which can accurately assemble the positional relationship between the extraction pole slot hole and the tip of the emitter pole.

Description

Technical Field

[0001] This invention relates to the field of propulsion technology, and in particular to a precision assembly and adjustment method for an electro-spray thruster. Background Technology

[0002] An electrospray thruster is a micro-electric propulsion device for space, consisting of an emitter, an extractor, and a storage and supply unit. It uses an ionic liquid composed entirely of positive and negative ions as the propellant. The emitter is typically made of porous materials such as porous ceramics or porous silicon with pore sizes of 2-5 μm, and its shape is often an array of elongated prisms or cones. The extractor is made of conductive metal plates such as stainless steel or tungsten, with multiple elongated or circular grooves and holes machined corresponding to the positions of the emitters. During operation, the extractor and emitter are connected to the positive and negative terminals of a power source, respectively, to create an electric field. Under the influence of this electric field, the propellant is transported from the storage tank to the emitter, where it is extracted into charged droplets or ions, which are then ejected from the emitter surface, generating thrust. Electrospray thrusters offer advantages such as small size and high specific impulse, making them suitable for missions such as orbit adjustment and formation flying for microsatellites. The relative positional relationship between the emitter and extractor is a key factor affecting thruster performance. This includes the alignment deviation between the slot on the extractor and the tip of the emitter, as well as the distance between the emitter and extractor. However, machining and assembly errors are unavoidable during the processing and assembly of various parts of the electro-spray thruster. To improve the overall performance of the thruster, it is necessary to adjust the relative position of the emitter and extractor.

[0003] Existing assembly and adjustment methods are mostly manual: first, a stereo microscope is used to observe the alignment of the emitter tip and the extractor slot in the horizontal plane, and the alignment of the two in the horizontal plane is roughly achieved by adjusting the assembly gap between the emitter and the thruster housing; however, there is no effective method to measure the distance between the emitter tip and the extractor, and it can only be guaranteed by the precision of the parts, and it is impossible to further adjust it according to the actual assembly and adjustment error.

[0004] Therefore, an efficient and accurate assembly and adjustment method is urgently needed to address the above problems. Summary of the Invention

[0005] This invention provides a precision assembly and adjustment method for an electro-spray thruster, which can accurately adjust the positional relationship between the extraction pole slot and the emitter tip.

[0006] This invention provides a method for precision assembly and adjustment of an electro-spray thruster, comprising: Using a zoom measurement system aligned with the electrospray thruster from above, the zoom measurement system is moved up and down to obtain multiple clear imaging images including the upper surface of the extractor pole and the tip of the emitter pole. Each clear imaging image is marked with the height information of the zoom measurement system. A depth map representing surface topography is generated based on multiple clear imaging images and their corresponding height information. The distance to be adjusted is calculated based on the depth map, and the positions of the emitter and extractor are adjusted according to the distance to be adjusted.

[0007] Optionally, the measurement range of the clear image acquired by the zoom distance measurement system is from 1 mm above the extractor tip to 0.5 mm below the emitter tip.

[0008] Optionally, the objective lens of the zoom measurement system has a magnification of 10x.

[0009] Optionally, after obtaining the depth map and before calculating the distance to be adjusted based on the depth map, the method further includes: Invalid points are removed using an invalid point removal algorithm.

[0010] Optionally, the invalid point removal algorithm includes: For each pixel, a set of focus evaluation function values ​​are obtained along the moving direction of the zoom measurement system, and a focus curve is obtained based on the focus function values ​​and the position of the zoom measurement system. To determine whether the focus curve of a pixel is reliable, first select the N largest values ​​from multiple focus function evaluation values, calculate the maximum span between the N values, and compare the maximum span with a set threshold. If the maximum span is greater than the set threshold, the pixel is determined to be an invalid point.

[0011] Optionally, N is 6, and the set threshold is 20.

[0012] Optionally, calculating the distance to be adjusted based on the depth map includes: A post-processing algorithm is used to extract a cross section through the emitter axis. Based on the cross section, the eccentricity value of the emitter tip in the extraction slot hole in the horizontal plane is determined, as well as the vertical distance between the emitter tip and the extraction electrode in the vertical plane is determined. This is then compared with a preset vertical distance to obtain a vertical difference value. The eccentricity value and the vertical difference value are the distance to be adjusted.

[0013] Optionally, the method is applied to the emitter and extractor at the four corner positions. Based on the depth map of the emitter and extractor at the four corner positions, four sets of distances to be adjusted are calculated respectively. First, the centering deviation of the four adjustment positions is adjusted according to the four eccentric values, and then the vertical distance of the four adjustment positions is adjusted according to the vertical difference.

[0014] Optionally, the step of first adjusting the centering deviation of the four adjustment positions according to the four eccentricity values ​​includes: First, based on the four eccentricity values, the emitter array and the extractor array are aligned by adjusting the spring set screws on the side of the thruster housing.

[0015] Optionally, the step of adjusting the vertical distances of the four adjustment positions based on the vertical difference includes: Then, based on the vertical difference, the distance between the emitter array and the extractor array is adjusted by adjusting the four fastening screws on the upper surface of the electro-spray thruster.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: This application, taking into account the structural and functional characteristics of the electro-spray thruster, uses a zoom measurement method to achieve non-contact measurement and three-dimensional reconstruction of the emitter and extractor poles. A post-processing algorithm is then used to obtain the eccentricity values ​​in the horizontal plane and the distance in the vertical plane between the emitter tip and the extractor pole slot, guiding subsequent assembly and adjustment. Accordingly, the electro-spray thruster should adopt an adjustable structure, allowing the emitter pole to move horizontally and the extractor pole to move vertically, adjusting to the required values ​​before locking and preventing loosening.

[0017] This invention effectively solves the problems of traditional manual debugging, where the alignment accuracy of the emitter and extractor can only be adjusted visually with a microscope, and the distance between the emitter tip and the extractor cannot be measured. By using a zoom measurement system and post-processing software, it can provide quantitative data for the precision assembly and adjustment of the electro-spray thruster, demonstrating good ingenuity.

[0018] Compared to the traditional manual assembly process, this method has higher measurement accuracy and work efficiency; compared to optical non-contact detection methods such as laser confocal microscopy, it is better suited for application scenarios where the sample being tested contains both specular and diffuse reflection components. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 This is a schematic diagram of a depth map creation process provided in an embodiment of the present invention; Figure 2 This is an original three-dimensional depth map obtained by scanning reconstruction according to an embodiment of the present invention; Figure 3 This is a three-dimensional depth map for removing invalid points provided in an embodiment of the present invention; Figure 4 This is a cross-sectional schematic diagram provided in an embodiment of the present invention; Figure 5 This is a schematic diagram of an electro-spray thruster provided in an embodiment of the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of the present invention, but not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0022] In the description of the embodiments of the present invention, unless otherwise expressly specified and limited, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance; unless otherwise specified or stated, the term "multiple" refers to two or more; the terms "connected," "fixed," etc., should be interpreted broadly. For example, "connected" can be a fixed connection, a detachable connection, an integral connection, or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in the present invention according to the specific circumstances.

[0023] In this specification, it should be understood that the directional terms such as "upper" and "lower" used in the description of the embodiments of the present invention are used to describe the angles shown in the accompanying drawings and should not be construed as limiting the embodiments of the present invention. Furthermore, in the context, it should also be understood that when it is mentioned that one element is connected "upper" or "lower" to another element, it can be directly connected to the other element "upper" or "lower," or indirectly connected to the other element "upper" or "lower" through an intermediate element.

[0024] This invention provides a method for precision assembly and adjustment of an electro-spray thruster, comprising: Using a zoom measurement system aligned with the electrospray thruster from above, the zoom measurement system is moved up and down to obtain multiple clear imaging images including the upper surface of the extractor pole and the tip of the emitter pole. Each clear imaging image is marked with the height information of the zoom measurement system. A depth map representing surface topography is generated based on multiple clear imaging images and their corresponding height information. The distance to be adjusted is calculated based on the depth map, and the positions of the emitter and extractor are adjusted according to the distance to be adjusted.

[0025] Because the emitter is a porous material with severe diffuse reflection, while the extractor is made of metal and exhibits specular reflection under an optical microscope, these two different optical properties make it impossible for a conventional optical microscope to simultaneously achieve clear imaging of both the emitter and extractor, let alone quantitatively measure their relative positions.

[0026] To address the aforementioned issues, this application abandons the simple measurement and comparison of two-dimensional images. Instead, it utilizes a zoom method to establish the surface morphology of the extractor and emitter regions, resulting in a three-dimensional depth map. A schematic diagram of the working process is shown below. Figure 1 As shown: First, a displacement-driven structure is used to perform a vertical scanning motion within a specified range using an objective lens or sample. Simultaneously, images are acquired, and the corresponding height coordinates are recorded, resulting in a series of images with different degrees of focus. The most focused position of different pixels in these images corresponds to different image sequence numbers, so calculating the most focused position yields the depth map, which is the surface morphology information.

[0027] After obtaining the depth map, the spatial position of the emitter tip can be calculated, and then the adjustment distance between the emitter tip and the extractor, including the eccentricity and vertical difference, can be calculated. Then, the position of the emitter or extractor can be precisely adjusted according to the adjustment distance to align them and complete the assembly.

[0028] In one embodiment of the present invention, the measurement range of the clear image acquired by the zoom distance measurement system is from 1 mm above the extractor tip to 0.5 mm below the emitter tip.

[0029] In this embodiment, to balance the integrity of the measurement data and the measurement efficiency, the measurement range is selected as 1 mm above the extraction electrode to 0.5 mm below the emitter cone tip.

[0030] In one embodiment of the present invention, the objective lens of the zoom measurement system has a magnification of 10x.

[0031] In this embodiment, to ensure measurement accuracy, the objective lens magnification is 10x. The selection of the system objective lens magnification must simultaneously consider lateral sampling resolution, axial resolution, field of view, and measurement stability. From the perspective of lateral sampling resolution, although the 5x objective lens has a large field of view, the actual size corresponding to a single pixel is large, resulting in weak lateral sampling resolution; while the 20x objective lens has stronger lateral sampling resolution, the field of view is significantly reduced, failing to cover the emitter and extractor, and is more sensitive to system focusing, sample tilt, vibration, and reflection. From the perspective of axial resolution, when the magnification is too low, the depth of field is large, the peak of the focusing curve is wide, and the height positioning sensitivity decreases; when the magnification is too high, the depth of field is too small, and although theoretically the focus changes are brighter, it is also more sensitive to noise, vibration, sample tilt, and reflection, while requiring a smaller Z-axis step size and more image frames, leading to a decrease in measurement efficiency. After comprehensively comparing the 5x, 10x, and 20x objectives, the 10x objective lens was ultimately selected as the main measurement magnification of the system. The reasons are as follows: First, the 10x objective lens has a suitable lateral sampling resolution, and its field of view covers both the emitter and extractor poles, meeting the measurement requirements. Second, the 10x objective lens offers a better balance between accuracy and stability. Zoom-based measurements rely not only on the theoretical resolution of the objective lens but also on image signal-to-noise ratio, surface texture, reflection characteristics, focusing curve quality, and scanning stability. The 10x objective lens can ensure sufficient detail resolution while also considering the field of view, scanning speed, and system stability, making it more suitable as the default measurement magnification for this system.

[0032] Please refer to Figure 2 and Figure 3 In one embodiment of the present invention, after obtaining the depth map and before calculating the distance to be adjusted based on the depth map, the method further includes: Invalid points are removed using an invalid point removal algorithm.

[0033] In this embodiment, after obtaining the sample morphology data, invalid points are removed using an invalid point removal algorithm. The invalid point removal algorithm is as follows: The invalid point discrimination algorithm of this system is designed based on the unimodality and monotonicity characteristics of the focus evaluation function. Unimodality and monotonicity can be understood as the focus evaluation function value at the most focused position being the maximum value in the sequence, which is much larger than the function value at the defocus position, and the curves on both sides have good monotonically increasing and monotonically decreasing characteristics.

[0034] Specifically, the focus evaluation function is essentially a local image sharpness measurement operator: regions in focus have large gray-level gradients and rich details, resulting in larger calculated function values; defocused, blurred regions have flat gray levels, and their function values ​​approach 0. The specific steps are as follows: Take the i-th layer image Ii and extract the grayscale data of the target pixel m and its surrounding small neighborhood (usually 3×3 or 5×5 pixel windows); Substituting the grayscale of the local window into the standard sharpness evaluation mathematical formula, a scalar is calculated, which is the focus evaluation value Fmi of the pixel at the i-th Z depth; For the same pixel m, traverse all Z layers i=1~n to finally obtain a sequence {Fm1,Fm2,…,Fmn}, which is the complete Z-axis focusing curve of the pixel.

[0035] The following pixel-local operators can be used to calculate Fmi: The Laplacian gradient operator performs second-order differential summation on local gray levels, resulting in significantly higher calculated values ​​for focus positions with rich edges and textures. The Brenner gradient function calculates the squared gray-level difference between neighboring pixels, has a fast computation speed, and is suitable for high-speed Z-scan scenarios. The gray-level variance / energy gradient function is used to statistically analyze the gray-level dispersion of a local window, resulting in uniform gray-level and small variance in the fuzzy region.

[0036] In one embodiment of the present invention, the invalid point removal algorithm includes: For each pixel, a set of focus evaluation function values ​​are obtained along the moving direction of the zoom measurement system, and a focus curve is obtained based on the focus function values ​​and the position of the zoom measurement system. To determine whether the focus curve of a pixel is reliable, first select the N largest values ​​from multiple focus function evaluation values, calculate the maximum span between the N values, and compare the maximum span with a set threshold. If the maximum span is greater than the set threshold, the pixel is determined to be an invalid point.

[0037] In this embodiment, for each pixel, a set of focus evaluation function values ​​can be obtained by scanning the sequence along the Z direction, denoted as F. m Let i = 1, 2, ..., n. To determine the reliability of the focusing curve of a pixel, the N largest points are first selected from this sequence. Then, the maximum span between these position indices is calculated, denoted as K. If K is greater than the set threshold M, it indicates that the high-response region of the pixel is relatively dispersed, and the focusing curve does not satisfy the good single-peak characteristic. Therefore, the pixel is determined to be an invalid point. In this system, parameters N=6 and M=20 are selected for invalid point removal. Using the above method, invalid points can be identified and removed, thereby enabling the upper surface of the extracted electrode and the emitter tip to be clearly reconstructed in the same 3D image.

[0038] Please refer to Figure 4 In one embodiment of the present invention, calculating the distance to be adjusted based on the depth map includes: A post-processing algorithm is used to extract a cross section through the emitter axis. Based on the cross section, the eccentricity value of the emitter tip in the extraction slot hole in the horizontal plane is determined, as well as the vertical distance between the emitter tip and the extraction electrode in the vertical plane is determined. This is then compared with a preset vertical distance to obtain a vertical difference value. The eccentricity value and the vertical difference value are the distance to be adjusted.

[0039] In this embodiment, the post-processing algorithm includes a complete set of post-geometric analytical algorithms for extracting geometric features, slicing, and quantitatively measuring the dimensions of the formed 3D model after the reconstruction of the emitter and extractor 3D models is completed. The specific process may include: 1. Three-dimensional feature fitting algorithm First, divide the complete 3D point cloud / mesh model into two types of structures to establish a baseline: The three-dimensional contour of the emitter is segmented, and the emitter central axis is solved by least squares and RANSAC cone / cylinder fitting. Segment the extraction pole slot area and fit the center reference circle / reference axis of the slot; Output: Equation of emitter axis and reference coordinates of slot center.

[0040] 2. Algorithm for Generating 3D Sectional Cross-Sections Using the fitted emitter axis as a reference, a cutting plane passing through this axis is constructed, and a three-dimensional cutting operation is performed: Calculate the intersection line between the cutting plane and the three-dimensional electrode mesh; Interpolation is used to extract the intersection profile, generating a two-dimensional cross-sectional view that includes the emitter tip and the extraction slot. Corresponding to the original text description: A cross section taken through the emitter axis.

[0041] 3. Algorithm for calculating cross-sectional geometric dimensions Extract the centroid of the profile from the generated 2D cross section, convert it to physical dimensions, and calculate two types of parameters respectively: Horizontal eccentricity: Project the center of the emitter tip and the center of the slot onto the XY horizontal plane and calculate the lateral offset distance between the two points; Vertical plane distance: Calculate the axial height difference between the tip and the slot along the emitter axis (Z-direction vertical direction).

[0042] In one embodiment of the present invention, the emitter and extractor at the four corner positions are applied. Four sets of distances to be adjusted are calculated according to the depth maps of the emitter and extractor at the four corner positions. First, the centering deviation of the four adjustment positions is adjusted according to the four eccentric values, and then the vertical distance of the four adjustment positions is adjusted according to the vertical difference.

[0043] The emitter array of the electro-spray thruster consists of hundreds of emitters, and similarly, the extractor has the same number of slots evenly distributed at the corresponding positions. However, due to manufacturing errors, it is impossible to guarantee that all emitter tips and extractor slots are in their theoretical positions. Therefore, it is difficult to ensure that all emitters are concentric with the extractors after assembly and adjustment, and the distance between the emitter tips and the extractors cannot be guaranteed to be completely consistent.

[0044] This patent proposes a method for precise assembly and adjustment by measuring the alignment deviation and distance between the emitter and extractor at four corner positions (i.e., upper left, upper right, lower left, and lower right) in a horizontal plane. Please refer to... Figure 5 During the adjustment process, firstly, the alignment deviations of the emitter and extractor at the four corners of the horizontal plane are measured. Based on these four data points, the emitter array and extractor array are aligned by adjusting the spring set screws on the side of the thruster housing. Then, based on the distance data between the emitter tip and the extractor at these four locations, the distance between the emitter array and the extractor array is adjusted by adjusting the four fastening screws on the upper surface of the electro-spray thruster. When the four distances are consistent and meet the design specifications, the overall distance between the emitter array and the extractor array is considered to be qualified.

[0045] It should be noted that during the setup and adjustment process, to prevent sample movement from affecting the measurement results, a clamp must be used to fix the electrospray thruster to the stage of the zoom measurement system. After each adjustment of the relative position between the extractor and emitter, the aforementioned zoom measurement method is used to obtain the measured values ​​of the alignment deviation and distance between them until the measured values ​​meet the design requirements.

[0046] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for precision assembly and adjustment of an electro-spray thruster, characterized in that, include: Using a zoom measurement system aligned with the electrospray thruster from above, the zoom measurement system is moved up and down to obtain multiple clear imaging images including the upper surface of the extractor pole and the tip of the emitter pole. Each clear imaging image is marked with the height information of the zoom measurement system. A depth map representing surface topography is generated based on multiple clear imaging images and their corresponding height information. The distance to be adjusted is calculated based on the depth map, and the positions of the emitter and extractor are adjusted according to the distance to be adjusted.

2. The precision assembly and adjustment method for the electro-spray thruster according to claim 1, characterized in that, The measurement range of the clear image acquired by the zoom distance measurement system is from 1 mm above the extractor tip to 0.5 mm below the emitter tip.

3. The precision assembly and adjustment method for the electro-spray thruster according to claim 1, characterized in that, The objective lens of the zoom measurement system has a magnification of 10x.

4. The precision assembly and adjustment method for the electro-spray thruster according to claim 1, characterized in that, After obtaining the depth map and before calculating the distance to be adjusted based on the depth map, the process also includes: Invalid points are removed using an invalid point removal algorithm.

5. The precision assembly and adjustment method for the electro-spray thruster according to claim 4, characterized in that, The invalid point removal algorithm includes: For each pixel, a set of focus evaluation function values ​​are obtained along the moving direction of the zoom measurement system, and a focus curve is obtained based on the focus function values ​​and the position of the zoom measurement system. To determine whether the focus curve of a pixel is reliable, first select the N largest values ​​from multiple focus function evaluation values, calculate the maximum span between the N values, and compare the maximum span with a set threshold. If the maximum span is greater than the set threshold, the pixel is determined to be an invalid point.

6. The precision assembly and adjustment method for the electro-spray thruster according to claim 5, characterized in that, N is 6, and the set threshold is 20.

7. The precision assembly and adjustment method for the electro-spray thruster according to claim 1, characterized in that, The step of calculating the distance to be adjusted based on the depth map includes: A post-processing algorithm is used to extract a cross section through the emitter axis. Based on the cross section, the eccentricity value of the emitter tip in the extraction slot hole in the horizontal plane is determined, as well as the vertical distance between the emitter tip and the extraction electrode in the vertical plane is determined. This is then compared with a preset vertical distance to obtain a vertical difference value. The eccentricity value and the vertical difference value are the distance to be adjusted.

8. The precision assembly and adjustment method for the electro-spray thruster according to claim 7, characterized in that, The method is applied to the emitter and extractor at the four corner positions. Based on the depth map of the emitter and extractor at the four corner positions, four sets of distances to be adjusted are calculated respectively. First, the centering deviation of the four adjustment positions is adjusted according to the four eccentric values, and then the vertical distance of the four adjustment positions is adjusted according to the vertical difference.

9. The precision assembly and adjustment method for the electro-spray thruster according to claim 8, characterized in that, The step of first adjusting the centering deviation of the four adjustment positions based on the four eccentricity values ​​includes: First, based on the four eccentricity values, the emitter array and extractor array are aligned by adjusting the spring set screws on the side of the thruster housing.

10. The precision assembly and adjustment method for the electro-spray thruster according to claim 8, characterized in that, The step of adjusting the vertical distances of the four adjustment positions based on the vertical difference includes: Then, based on the vertical difference, the distance between the emitter array and the extractor array is adjusted by adjusting the four fastening screws on the upper surface of the electro-spray thruster.

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