rus
Issue #8/2023
P. S. Zavialov, E. V. Vlasov, A. V. Beloborodov, M. S. Kravchenko, A. A. Gutschina, D. V. Skokov
Non-Contact Measurement System for Geometric Parameters of Ion Thruster Grids
Non-Contact Measurement System for Geometric Parameters of Ion Thruster Grids
DOI: 10.22184/1993-7296.FRos.2023.17.8.622.631
The most important parameter of an ion thruster, affecting its performance and service life, is the gap between the screen and the accelerating and decelerating grids of the ion optics unit. During operation of the ion thruster, the gap is changed due to the heating and thermal expansion of the grids. Awareness of this gap in the hot grid is necessary for adequate assessment of the ion thrust operating parameters and service life. The paper considers a measuring system based on the direct shadow parallel light method. To register the grid position, the pins protruding above the grid surface are placed on them. The image is recorded by a telecentric lens that lowers the requirements for positioning accuracy of the measurement object. The illumination unit and the image acquisition unit are placed in the pressure-tight housings that allow measurements to be performed in a vacuum chamber. The system has successfully passed the tests, the measurement results are given in the paper.
The most important parameter of an ion thruster, affecting its performance and service life, is the gap between the screen and the accelerating and decelerating grids of the ion optics unit. During operation of the ion thruster, the gap is changed due to the heating and thermal expansion of the grids. Awareness of this gap in the hot grid is necessary for adequate assessment of the ion thrust operating parameters and service life. The paper considers a measuring system based on the direct shadow parallel light method. To register the grid position, the pins protruding above the grid surface are placed on them. The image is recorded by a telecentric lens that lowers the requirements for positioning accuracy of the measurement object. The illumination unit and the image acquisition unit are placed in the pressure-tight housings that allow measurements to be performed in a vacuum chamber. The system has successfully passed the tests, the measurement results are given in the paper.
Теги: ion optics. ion thruster grids measurement of geometric parameters shadow method бесконтактные измерения измерение геометрических параметров ионная оптика. non-contact measurements решетки ионного двигателя теневой метод
Non-Contact Measurement System for Geometric Parameters of Ion Thruster Grids
P. S. Zavialov, E. V. Vlasov, A. V. Beloborodov, M. S. Kravchenko, A. A. Gutschina, D. V. Skokov
Design and Technology Institute
of Scientific Instrumentation SB RAS,
Novosibirsk, Russia
The most important parameter of an ion thruster, affecting its performance and service life, is the gap between the screen and the accelerating and decelerating grids of the ion optics unit. During operation of the ion thruster, the gap is changed due to the heating and thermal expansion of the grids. Awareness of this gap in the hot grid is necessary for adequate assessment of the ion thrust operating parameters and service life. The paper considers a measuring system based on the direct shadow parallel light method. To register the grid position, the pins protruding above the grid surface are placed on them. The image is recorded by a telecentric lens that lowers the requirements for positioning accuracy of the measurement object. The illumination unit and the image acquisition unit are placed in the pressure-tight housings that allow measurements to be performed in a vacuum chamber. The system has successfully passed the tests, the measurement results are given in the paper.
Key words: non-contact measurements, shadow method, measurement of geometric parameters, ion thruster grids, ion optics.
Article received: 29.09.2023
Article accepted: 24.11.2023
INTRODUCTION
The most important parameters of an ion thruster that affect its performance and service life are the gaps between the screen and the accelerating and decelerating grids of the ion optics unit. During operation of the ion thruster, the gaps are changed due to the thermal expansion of grids, thus leading to a risk of gap breakdown (or even fault of the grids), especially in the high differential heating modes, for example, when the thruster is started. Therefore, for an adequate assessment of the thruster operating parameters and service life, as well as when studying new materials for the grid production, it is necessary to dynamically measure the specified gaps directly in the running thruster.
The problem of measuring distance between the grids has already been solved previously. Thus, in paper [1] it was proposed to perform the visual measurements by observing the marks (markers) on the graduated metal pins mounted on the screen grid and passing through the holes of the accelerating grid. However, the pins were metal, i. e. they were under the same voltage as the grid, and therefore the beam generation by the thruster with installed pins was impossible. In paper [2], the metal pins were also used, and the measuring device was located at the output of the ion optics.
In paper [3], the device was located at an angle relative to the normal to the thruster grid. The measurement was performed using two long-focal microscopes observing the holes in opposite sides of the grids. However, two measurements were required to register the radial motion that led to the significant method complication. In addition, when the microscope was displaced relative to the normal, the resolution was decreased. Since the holes in the accelerating grid were much smaller than the holes in the screen grid, and the gap between the grids was rather small, the resolution was sufficient only if the measuring microscope was placed in the plume of the generated ion flow.
In publication [4], the authors described a simple dynamical measurement method for the gap between hot grids of an ion thruster operating with the ion flow generation. The gap between the grids was measured at the center of the ion optics unit using a long-focal microscope. The microscope was focused on an aluminum oxide pin that was mechanically attached to the screen grid and protruded through the central hole of the accelerating grid. The same authors have published the paper [5] a little bit later. The object illumination has been changed, and an LED has been added to the microscope objective. The pin fastening design has been improved: the device has covered only 4 holes in the accelerating grid instead of 8 holes. In papers [6, 7], the same videometrical method was used with application of a long-focal microscope. However, in this case, the authors positioned the camera away from the running thruster. The pin design was prepared in such a way that it occupied one hole in the grid. The authors placed the pins in each of the grids under study, thereby simultaneously obtaining information about the positions of all three grids.
The authors of this paper propose to use the shadow control method, in contrast to the vast majority of other systems based on the light reflected from the measurement object, to measure the gap between the ion thruster grids. It is expected that this approach will allow achieving higher accuracy due to the fact that the distance at which the measured object may be located has little effect on the measurement accuracy. In addition, it will be possible to remove the measurement system elements from the ion beam, providing it with the acceptable operating conditions. Having placed the measuring system in a sealed compartment, it is possible to ensure that the measurements are performed while the ion thruster is operated inside a thermal vacuum chamber.
MEASUREMENT PLAN
The measurement plan proposed by the authors and based on the direct shadow parallel light method [8] is shown in Fig. 1.
To register the grid positions, the pins 1 made of aluminum-oxide ceramics are placed on them while protruding above the surface of the grid or grids, if there are several of them. The distance between the grids is determined indirectly, namely by establishing the position of these pins. Aluminum oxide ceramics is a dielectric medium and can withstand the operating temperature of the ion thruster (1 000 °C), while having a minimum thermal expansion coefficient that will allow measurements of the grid positions while the thruster is running.
The measurement system (hereinafter referred to as the GPNMS, namely the geometric parameter non-contact measurement system) consists of two units: an illuminator and a recorder. The pins are illuminated by a pulsed LED 2, and the image of their shadow projections generated by a telecentric lens 3, is recorded by a digital camera 4. In this case, the light pulse from the LED is synchronized with the camera shutter.
The illuminator uses a red LED as a light source, and the receiving part contains a bandpass filter 5 (λ = 650 ± 20 nm) matched. The Ar or Xe jet stream plasma does not contain the red light absorption lines, and its own radiation lies mainly in the blue spectrum portion and is suppressed by a filter that eliminates possible interference in the measurements.
A two-axis adjustment with an intermittent drive 6 is used to compensate for temperature changes in the base and regulates the LED position in such a way that the maximum illumination on the digital camera is achieved.
DESIGN of a telecentric lens
and its calibration
To remove the GPNMS from the flame of a running ion thruster, it is necessary to design a telecentric lens with an increased front flange focal distance. Selection of such a lens makes it possible to lower the requirements for positioning accuracy of the measurement object [9]. The telecentric lens was designed in the Zemax software package by optimizing the specifications of the initial optical circuit to achieve the required image quality, ensuring the required measurement accuracy. With a given measurement error of 50 µm, the ray path telecentricity shall be no worse than 0.05%, and the image distortion shall be no more than 0.5%. Figure 2 shows the optical circuit of designed lens with the ray path and its aberration specifications. The optical performance of the designed lens is given in Table 1.
The given data shows that the lens has an increased front flange focal distance, allowing it to be used at the required distance from the object. The field of view is 40 mm, the depth of field reaches 100 mm. The wavelength range is shifted to the red region of the spectrum. The lens has low residual non-telecentricity (0.047°) and low distortion (less than 0.2%) that will ensure the required measurement accuracy.
The residual aberrations and errors occurred at the assembly stage can be compensated during the GPNMS software calibration process on the basis of a mask work, on which a pattern in the form of holes in the square grid points is applied by a circular laser recording system CLWS‑300C/M [10] based on the high-precision laser photolithographic method (about 30 nm) (Fig. 3a).
When calibrating on the basis of a mask work, the centers of mass in its image are used to determine the centers of circles, each of which is associated with a point on an ideal plane. The entire set of centers is divided into the triangles using the Delaunay triangulation. Each triangle in the image is related to an ideal triangle with an established shape and size. To adjust the position of any image point, it is enough to find the triangle containing this point and convert its coordinates from pixels to millimeters, using a conformal transformation.
Another possible method is calibration using a shadow image of a cylindrical sample with an established diameter (Fig. 3b). In this case, the shadow boundaries are determined in the image with subpixel accuracy, after which the resolution value is calculated that is about 22 μm/pixel in this system.
GPNMS and its testING
The 3D model of the system developed is shown in Figure 4, its photograph is given in Figure. 5.
The system consists of an illuminator 1 and a recorder 2. They are installed on the frame 3, and the ion thruster grid assembly 4 is placed between them. The pins 5 are installed on each of the three assembly grids. In total, the assembly has 5 installation points for the groups consisting of 3 pins; the total number of pins is up to 15.
The normal conditions required for the operation of electro-optical units are provided inside the sealed enclosures, capable of operating at an external vacuum of 10–4 Pa and in the external temperature range from –70 °C to +120 °C using a heat shield and an air conditioning system (water-heated/cooled radiators and a fan). The supply pipes for the air conditioning system coolant and the communication cables between the equipment and the control computer are laid in a vacuum-tight tube extending beyond the thermal vacuum chamber through the pipe 7.
To protect the optical windows of the illuminator and recorder from settling of the ion thruster products, the protective plane-parallel glass plates 6 are installed in front of them that can be easily dismantled for cleaning and re-installed without application of any seals.
The illuminator forms a parallel beam to illuminate one of five groups of pins. The recorder, using a telecentric lens 8, captures the resulting shadow pattern of the pins on a digital array 9 with a resolution of 2 048 × 2 048 pixels (Fig. 6).
The illuminator and recorder are moved synchronously by the step drives 10 (Fig. 5) between the measurement positions, while recording all images within 1 minute.
Special software has been developed for the GPNMS, using which calibration, measurements, and viewing of previous measurements are performed. The ability to place an additional mark related to the measurement object in the field of view of the telecentric lens has been implemented. This allows to link the received data to the coordinate system of the measurement object.
The shadow pattern can be processed in two modes: the measurement mode for changes in the distance between the grids (actual changes in the distance along the selected radial direction between the pin heads) and the measurement mode for distance from the pin located on the grid under study to a similar base pin located on a fixed support.
The grids have a spherical shape. It is believed that they are deformed along the radius. The measuring pin is located along the grid radius (normal to its surface) at a predetermined point, so that it is visible in the image at a predetermined angle. The image is cross-sectioned with a set of rays parallel to the radius (according to Fig. 6 from right to left), with an increment of 1 pixel; the intersection points of the rays with the pin shadow are found with the sub-pixel accuracy on the sections; the points obtained make up the measured pin profile. Then, the profile is used to identify the position of the individual pin axes and measure the reference pin position on each pin. Further, either any required differences in the visible heights of the pins or any distance between the reference points of the measuring and base pins are calculated.
The reference point determination can be a difficult process if the pin surface does not have any typical features. Thus, it is unclear in Fig. 6 what point of the flat top of the pin shall be taken as the reference point. It can be seen that the pin shape significantly affects the measurement accuracy and must be specially selected. Morover, the pins must be manufactured with good accuracy and surface quality that is not an easy task given their material (ceramics) properties. In this system, in addition to the flat-top pins shown in the figure, the pins with a spherical top have been tested. Such pins have been accepted as the main ones. The reference point in this case was the point of maximum profile elevation, and the profile was approximated in the vicinity of the reference point by a circular arc using the least squares method.
As a part of the successful GPNMS tests in normal climatic conditions, the following results have been obtained:
the GPNMS was operated continuously without any failures for more than 30 hours;
the measurement time in one measuring position was less than 0.1 s;
the measurement time in all measuring positions was less than 60 s;
the measurement repeatability was 2 µm;
the measurement error was less than 7 µm.
Conclusion
The system developed by us allows to control the distance between the ion thruster grids. The shadow control method used in the GPNMS and applied for this task for the first time, allows for real-time control of the gaps without affecting operation of the measured object. The resulting error equal to 7 microns shows that the system developed can be used in various fields where non-contact deformation control over the critical objects is required, for example, in the space and aviation industries. It provides and opportunity to increase the reliability and durability of thrusters being produced and improve their operating quality. Our development has the prospects of further improvement and expansion of the range of applications to achieve better results in the field of control of ion thruster grid deformation.
ABOUT AUTHORS
Zavyalov Petr Sergeevich, graduated from the Novosibirsk State Technical University (NSTU) ith a degree in Physics, Cand.of Sc. (Eng.) Works as an assistant director for scientific and technical projects at the Tecnological Design Institute of Scientific Instrument Engineering of the Siberian Branch of the Russian Academy of Sciences (TDI SIE SB RAS). Research interests: diffractive optical elements, applied optics, systems of technical vision and dimen-sional control. Author ID in RSCI 177280.
Contribution – idea, organization of work.
Vlasov Evgeny Vladimirovich, graduated from the NSTU, Master of Engineering and Technol-ogy with a degree in Optotechnics, works as a researcher at the TDI SIE SB RAS. Research interests: optoelectronic devices and complexes, development of optical installations for monitoring and measuring geometric parameters. Author ID in RSCI 677894.
Contributions: experimental design, experiment execution.
Aleksey Vadimovich Beloborodov, graduated from the Novosibirsk Electrotechnical Institute with a degree in Electrophysical Installations and Charged Particle Accelerators, works as a leading programmer at TDI SIE SB RAS. Area of interest: image processing for flaw detection and dimensional control, programming. Author ID in RSCI 177287.
Contribution – processing of results, discussions.
Kravchenko Maxim Sergeevich, graduated from NSTU, Master in Applied Informatics, works as a researcher at KTI NP SB RAS. Research interests: speckle interferometry, optoelectronic devices and complexes, thermal vacuum tests. Author ID in RSCI 825558.
Contribution – experimental design, organization of work.
Gushchina Anna Alexandrovna, graduated from the Siberian State University of Telecommunications and Informatics with a degree in Computer Engineering and Automated Systems Software, works as a leading programmer at KTI NP SB RAS. Research interests: image processing for flaw detection and dimensional control, programming. Author ID in RSCI 177286.
Contribution – processing of results, discussions.
Skokov Dmitry Vladimirovich, graduated from the NSTU with a degree in metalworking ma-chines and complexes, works as a chief designer at KTI NP SB RAS. Area of interest: 3D design. Author ID in RSCI 933269.
Contributions: experimental design, experiment execution.
P. S. Zavialov, E. V. Vlasov, A. V. Beloborodov, M. S. Kravchenko, A. A. Gutschina, D. V. Skokov
Design and Technology Institute
of Scientific Instrumentation SB RAS,
Novosibirsk, Russia
The most important parameter of an ion thruster, affecting its performance and service life, is the gap between the screen and the accelerating and decelerating grids of the ion optics unit. During operation of the ion thruster, the gap is changed due to the heating and thermal expansion of the grids. Awareness of this gap in the hot grid is necessary for adequate assessment of the ion thrust operating parameters and service life. The paper considers a measuring system based on the direct shadow parallel light method. To register the grid position, the pins protruding above the grid surface are placed on them. The image is recorded by a telecentric lens that lowers the requirements for positioning accuracy of the measurement object. The illumination unit and the image acquisition unit are placed in the pressure-tight housings that allow measurements to be performed in a vacuum chamber. The system has successfully passed the tests, the measurement results are given in the paper.
Key words: non-contact measurements, shadow method, measurement of geometric parameters, ion thruster grids, ion optics.
Article received: 29.09.2023
Article accepted: 24.11.2023
INTRODUCTION
The most important parameters of an ion thruster that affect its performance and service life are the gaps between the screen and the accelerating and decelerating grids of the ion optics unit. During operation of the ion thruster, the gaps are changed due to the thermal expansion of grids, thus leading to a risk of gap breakdown (or even fault of the grids), especially in the high differential heating modes, for example, when the thruster is started. Therefore, for an adequate assessment of the thruster operating parameters and service life, as well as when studying new materials for the grid production, it is necessary to dynamically measure the specified gaps directly in the running thruster.
The problem of measuring distance between the grids has already been solved previously. Thus, in paper [1] it was proposed to perform the visual measurements by observing the marks (markers) on the graduated metal pins mounted on the screen grid and passing through the holes of the accelerating grid. However, the pins were metal, i. e. they were under the same voltage as the grid, and therefore the beam generation by the thruster with installed pins was impossible. In paper [2], the metal pins were also used, and the measuring device was located at the output of the ion optics.
In paper [3], the device was located at an angle relative to the normal to the thruster grid. The measurement was performed using two long-focal microscopes observing the holes in opposite sides of the grids. However, two measurements were required to register the radial motion that led to the significant method complication. In addition, when the microscope was displaced relative to the normal, the resolution was decreased. Since the holes in the accelerating grid were much smaller than the holes in the screen grid, and the gap between the grids was rather small, the resolution was sufficient only if the measuring microscope was placed in the plume of the generated ion flow.
In publication [4], the authors described a simple dynamical measurement method for the gap between hot grids of an ion thruster operating with the ion flow generation. The gap between the grids was measured at the center of the ion optics unit using a long-focal microscope. The microscope was focused on an aluminum oxide pin that was mechanically attached to the screen grid and protruded through the central hole of the accelerating grid. The same authors have published the paper [5] a little bit later. The object illumination has been changed, and an LED has been added to the microscope objective. The pin fastening design has been improved: the device has covered only 4 holes in the accelerating grid instead of 8 holes. In papers [6, 7], the same videometrical method was used with application of a long-focal microscope. However, in this case, the authors positioned the camera away from the running thruster. The pin design was prepared in such a way that it occupied one hole in the grid. The authors placed the pins in each of the grids under study, thereby simultaneously obtaining information about the positions of all three grids.
The authors of this paper propose to use the shadow control method, in contrast to the vast majority of other systems based on the light reflected from the measurement object, to measure the gap between the ion thruster grids. It is expected that this approach will allow achieving higher accuracy due to the fact that the distance at which the measured object may be located has little effect on the measurement accuracy. In addition, it will be possible to remove the measurement system elements from the ion beam, providing it with the acceptable operating conditions. Having placed the measuring system in a sealed compartment, it is possible to ensure that the measurements are performed while the ion thruster is operated inside a thermal vacuum chamber.
MEASUREMENT PLAN
The measurement plan proposed by the authors and based on the direct shadow parallel light method [8] is shown in Fig. 1.
To register the grid positions, the pins 1 made of aluminum-oxide ceramics are placed on them while protruding above the surface of the grid or grids, if there are several of them. The distance between the grids is determined indirectly, namely by establishing the position of these pins. Aluminum oxide ceramics is a dielectric medium and can withstand the operating temperature of the ion thruster (1 000 °C), while having a minimum thermal expansion coefficient that will allow measurements of the grid positions while the thruster is running.
The measurement system (hereinafter referred to as the GPNMS, namely the geometric parameter non-contact measurement system) consists of two units: an illuminator and a recorder. The pins are illuminated by a pulsed LED 2, and the image of their shadow projections generated by a telecentric lens 3, is recorded by a digital camera 4. In this case, the light pulse from the LED is synchronized with the camera shutter.
The illuminator uses a red LED as a light source, and the receiving part contains a bandpass filter 5 (λ = 650 ± 20 nm) matched. The Ar or Xe jet stream plasma does not contain the red light absorption lines, and its own radiation lies mainly in the blue spectrum portion and is suppressed by a filter that eliminates possible interference in the measurements.
A two-axis adjustment with an intermittent drive 6 is used to compensate for temperature changes in the base and regulates the LED position in such a way that the maximum illumination on the digital camera is achieved.
DESIGN of a telecentric lens
and its calibration
To remove the GPNMS from the flame of a running ion thruster, it is necessary to design a telecentric lens with an increased front flange focal distance. Selection of such a lens makes it possible to lower the requirements for positioning accuracy of the measurement object [9]. The telecentric lens was designed in the Zemax software package by optimizing the specifications of the initial optical circuit to achieve the required image quality, ensuring the required measurement accuracy. With a given measurement error of 50 µm, the ray path telecentricity shall be no worse than 0.05%, and the image distortion shall be no more than 0.5%. Figure 2 shows the optical circuit of designed lens with the ray path and its aberration specifications. The optical performance of the designed lens is given in Table 1.
The given data shows that the lens has an increased front flange focal distance, allowing it to be used at the required distance from the object. The field of view is 40 mm, the depth of field reaches 100 mm. The wavelength range is shifted to the red region of the spectrum. The lens has low residual non-telecentricity (0.047°) and low distortion (less than 0.2%) that will ensure the required measurement accuracy.
The residual aberrations and errors occurred at the assembly stage can be compensated during the GPNMS software calibration process on the basis of a mask work, on which a pattern in the form of holes in the square grid points is applied by a circular laser recording system CLWS‑300C/M [10] based on the high-precision laser photolithographic method (about 30 nm) (Fig. 3a).
When calibrating on the basis of a mask work, the centers of mass in its image are used to determine the centers of circles, each of which is associated with a point on an ideal plane. The entire set of centers is divided into the triangles using the Delaunay triangulation. Each triangle in the image is related to an ideal triangle with an established shape and size. To adjust the position of any image point, it is enough to find the triangle containing this point and convert its coordinates from pixels to millimeters, using a conformal transformation.
Another possible method is calibration using a shadow image of a cylindrical sample with an established diameter (Fig. 3b). In this case, the shadow boundaries are determined in the image with subpixel accuracy, after which the resolution value is calculated that is about 22 μm/pixel in this system.
GPNMS and its testING
The 3D model of the system developed is shown in Figure 4, its photograph is given in Figure. 5.
The system consists of an illuminator 1 and a recorder 2. They are installed on the frame 3, and the ion thruster grid assembly 4 is placed between them. The pins 5 are installed on each of the three assembly grids. In total, the assembly has 5 installation points for the groups consisting of 3 pins; the total number of pins is up to 15.
The normal conditions required for the operation of electro-optical units are provided inside the sealed enclosures, capable of operating at an external vacuum of 10–4 Pa and in the external temperature range from –70 °C to +120 °C using a heat shield and an air conditioning system (water-heated/cooled radiators and a fan). The supply pipes for the air conditioning system coolant and the communication cables between the equipment and the control computer are laid in a vacuum-tight tube extending beyond the thermal vacuum chamber through the pipe 7.
To protect the optical windows of the illuminator and recorder from settling of the ion thruster products, the protective plane-parallel glass plates 6 are installed in front of them that can be easily dismantled for cleaning and re-installed without application of any seals.
The illuminator forms a parallel beam to illuminate one of five groups of pins. The recorder, using a telecentric lens 8, captures the resulting shadow pattern of the pins on a digital array 9 with a resolution of 2 048 × 2 048 pixels (Fig. 6).
The illuminator and recorder are moved synchronously by the step drives 10 (Fig. 5) between the measurement positions, while recording all images within 1 minute.
Special software has been developed for the GPNMS, using which calibration, measurements, and viewing of previous measurements are performed. The ability to place an additional mark related to the measurement object in the field of view of the telecentric lens has been implemented. This allows to link the received data to the coordinate system of the measurement object.
The shadow pattern can be processed in two modes: the measurement mode for changes in the distance between the grids (actual changes in the distance along the selected radial direction between the pin heads) and the measurement mode for distance from the pin located on the grid under study to a similar base pin located on a fixed support.
The grids have a spherical shape. It is believed that they are deformed along the radius. The measuring pin is located along the grid radius (normal to its surface) at a predetermined point, so that it is visible in the image at a predetermined angle. The image is cross-sectioned with a set of rays parallel to the radius (according to Fig. 6 from right to left), with an increment of 1 pixel; the intersection points of the rays with the pin shadow are found with the sub-pixel accuracy on the sections; the points obtained make up the measured pin profile. Then, the profile is used to identify the position of the individual pin axes and measure the reference pin position on each pin. Further, either any required differences in the visible heights of the pins or any distance between the reference points of the measuring and base pins are calculated.
The reference point determination can be a difficult process if the pin surface does not have any typical features. Thus, it is unclear in Fig. 6 what point of the flat top of the pin shall be taken as the reference point. It can be seen that the pin shape significantly affects the measurement accuracy and must be specially selected. Morover, the pins must be manufactured with good accuracy and surface quality that is not an easy task given their material (ceramics) properties. In this system, in addition to the flat-top pins shown in the figure, the pins with a spherical top have been tested. Such pins have been accepted as the main ones. The reference point in this case was the point of maximum profile elevation, and the profile was approximated in the vicinity of the reference point by a circular arc using the least squares method.
As a part of the successful GPNMS tests in normal climatic conditions, the following results have been obtained:
the GPNMS was operated continuously without any failures for more than 30 hours;
the measurement time in one measuring position was less than 0.1 s;
the measurement time in all measuring positions was less than 60 s;
the measurement repeatability was 2 µm;
the measurement error was less than 7 µm.
Conclusion
The system developed by us allows to control the distance between the ion thruster grids. The shadow control method used in the GPNMS and applied for this task for the first time, allows for real-time control of the gaps without affecting operation of the measured object. The resulting error equal to 7 microns shows that the system developed can be used in various fields where non-contact deformation control over the critical objects is required, for example, in the space and aviation industries. It provides and opportunity to increase the reliability and durability of thrusters being produced and improve their operating quality. Our development has the prospects of further improvement and expansion of the range of applications to achieve better results in the field of control of ion thruster grid deformation.
ABOUT AUTHORS
Zavyalov Petr Sergeevich, graduated from the Novosibirsk State Technical University (NSTU) ith a degree in Physics, Cand.of Sc. (Eng.) Works as an assistant director for scientific and technical projects at the Tecnological Design Institute of Scientific Instrument Engineering of the Siberian Branch of the Russian Academy of Sciences (TDI SIE SB RAS). Research interests: diffractive optical elements, applied optics, systems of technical vision and dimen-sional control. Author ID in RSCI 177280.
Contribution – idea, organization of work.
Vlasov Evgeny Vladimirovich, graduated from the NSTU, Master of Engineering and Technol-ogy with a degree in Optotechnics, works as a researcher at the TDI SIE SB RAS. Research interests: optoelectronic devices and complexes, development of optical installations for monitoring and measuring geometric parameters. Author ID in RSCI 677894.
Contributions: experimental design, experiment execution.
Aleksey Vadimovich Beloborodov, graduated from the Novosibirsk Electrotechnical Institute with a degree in Electrophysical Installations and Charged Particle Accelerators, works as a leading programmer at TDI SIE SB RAS. Area of interest: image processing for flaw detection and dimensional control, programming. Author ID in RSCI 177287.
Contribution – processing of results, discussions.
Kravchenko Maxim Sergeevich, graduated from NSTU, Master in Applied Informatics, works as a researcher at KTI NP SB RAS. Research interests: speckle interferometry, optoelectronic devices and complexes, thermal vacuum tests. Author ID in RSCI 825558.
Contribution – experimental design, organization of work.
Gushchina Anna Alexandrovna, graduated from the Siberian State University of Telecommunications and Informatics with a degree in Computer Engineering and Automated Systems Software, works as a leading programmer at KTI NP SB RAS. Research interests: image processing for flaw detection and dimensional control, programming. Author ID in RSCI 177286.
Contribution – processing of results, discussions.
Skokov Dmitry Vladimirovich, graduated from the NSTU with a degree in metalworking ma-chines and complexes, works as a chief designer at KTI NP SB RAS. Area of interest: 3D design. Author ID in RSCI 933269.
Contributions: experimental design, experiment execution.
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