An Improved Radio Pointing Model for SHARC II of the Caltech Submillimeter Observatory Telescope

Chen, Weirui; Wang, Zheng; Zhou, Xiaojun

doi:10.1088/1538-3873/ac94f7

Cited by 6 publications

(6 citation statements)

References 33 publications

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“…Chen et al introduced the axial displacement of the secondary refector of the telescope to the radio pointing model for SHARC II. Te results show that the reconstructed radio pointing model can improve the accuracy of estimating the pointing error [8]. Gawronski Gawronski et al show that the pointing error in the elevation direction is reduced from 16.2″ to 5″, and the pointing error in the azimuth direction is reduced from 52.2″ to 11.2″ [9,10].…”

Section: Introductionmentioning

confidence: 93%

Measuring Antenna Elevation Mechanism Pointing Errors with Multiencoder Information Sources

Wang

et al. 2023

Advances in Astronomy

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There are many factors that cause pointing errors in radio telescopes. As one of the motion positioning mechanisms of the radio telescope, the error caused by the elevation mechanism cannot be ignored. The source of error in the elevation mechanism comes mainly from the key transmission components and the support structure. Accurate measurement of the errors caused by them is the key to analyzing their law of change. Aiming at the main error factors in the antenna elevation mechanism, this study builds a scaled-down experimental platform for the elevation mechanism and proposes an error measurement method based on multiencoder information sources. The method compares the error law of change of the antenna elevation mechanism under different driving modes, different centerline deviations of the bearings, and different backlashes and designs error measurement experiments for the abovementioned operating conditions. The results show that the error measurement method based on multiencoder information sources can accurately measure the error of the antenna elevation mechanism under different driving modes. The method can also accurately reflect the law of change in transmission error when the backlash of the elevation mechanism and the centerline deviation of the bearings increase. The final experimental measurement shows that the driving mode of the dual-motor can eliminate about 70% of the mechanism error caused by the backlash. The average value of the error increases by a factor of 1.9 when the backlash increases from 0.1 mm to 1.26 mm. The average value of the error increases by a factor of 5 when the centerline deviation of the bearings increases from 0 to 1.5 mm. This has a good reference value to correct for the pointing error of a radio telescope.

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Section: Introductionmentioning

confidence: 93%

Measuring Antenna Elevation Mechanism Pointing Errors with Multiencoder Information Sources

Wang

et al. 2023

Advances in Astronomy

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“…An accurate model of LCT's pointing control system is very important to the design of the position controller. LCT's pointing control system model was constructed in our previous work (Chen & Wang 2022), which consists of the position controller, the DC motor, the reducer box, and the antenna. There are two major vibration modals of the LCT antenna, which are the low-frequency flexible modal (i.e., the first-order vibration modal of the antenna), and the main structural vibration modal of the main reflector (i.e., the second-order vibration modal of the antenna).…”

Section: Model Of Lct's Pointing Control System With Structural Vibra...mentioning

confidence: 99%

“…Therefore, it is important to construct a good model for wind gust. To better describe wind gust, the Davenport filter is introduced, which is designed by following the instructions in Section 3 of Chen & Wang (2022). The power of the white noise (i.e., the source of the Davenport filter) and the average wind speed are adjustable for generating wind disturbances of different average speeds and fluctuation amplitudes.…”

Section: Experiments Designmentioning

confidence: 99%

“…The Caltech Submillimeter Observatory (CSO) telescope was decommissioned in 2015 and will be moved to its new site at Chajnantor Plateau, Chile from its old site at Maunakea, Hawaii in 2023. After the completion of the relocation, the CSO telescope will be refurbished at the new site and renamed as the Leighton Chajnantor Telescope (LCT) (Vial et al 2020;Chen et al 2022). However, the relocation and refurbishment of LCT will face with new challenges for its pointing control system, because it is expected to resist strong wind disturbance at the new site, which has an average wind speed of 10 m s −1 , a maximum instantaneous wind speed of 30 m s −1 , and more frequent wind speed fluctuation (ALMA 2010).…”

Section: Introductionmentioning

confidence: 99%

“…However, this pointing accuracy is very difficult to achieve when LCT is working with a strong wind load. By testing the existing proportional feedback controller of LCT on its simulation model (Chen & Wang 2022), the rms of the azimuth angle error of LCT's antenna is greater than 3″ when the wind with a speed above 10 m s −1 is introduced. Obviously, the performance of the existing feedback controller cannot satisfy the requirement on the pointing accuracy when the telescope is fully exposed to high-speed wind.…”

Section: Introductionmentioning

confidence: 99%

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Disturbance Observer-based Pointing Control of Leighton Chajnantor Telescope

Chen,

Wang

2023

Res. Astron. Astrophys.

Self Cite

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Leighton Chajnantor Telescope (LCT), i.e., the former Caltech Submillimeter Observatory (CSO) telescope, will be refurbished at the new site in Chajnantor Plateau, Chile, in 2023. The environment of LCT will change significantly after its relocation, and the telescope will be exposed to large wind disturbance directly because its enclosure will be completely open during observation. The wind disturbance is expected to be a challenge for LCT’s pointing control since existing control method cannot reject this disturbance very well. Therefore, it is very necessary to develop a new pointing control method with good capability of disturbance rejection. In this research, a disturbance observer - based composite position controller (DOB-CPC) is designed, in which an H∞ feedback controller is employed to compress the disturbance, and a feedforward linear quadratic regulator is employed to compensate the disturbance precisely based on the estimated disturbance signal. Moreover, a controller switching policy (CSP) is adopted, which applies the proportional controller to the transient process to achieve a quick response and applies the DOB-CPC to the steady state to achieve a small position error. Numerical experiments are conducted to verify the good performance of the proposed pointing controller (i.e., DOB-CPC) for rejecting the disturbance acting on LCT.

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Effect of Panel Misalignment Error Distribution on the Radiation Pattern of Leighton Chajnantor Telescope’s Antenna

You,

Wang,

Reeves Díaz

2024

PASP

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The Leighton dish formerly at the Caltech Submillimeter Observatory will be reassembled to become the Leighton Chajnantor Telescope (LCT). It will be required to demonstrate high surface accuracy and controlled radiation patterns at high frequency, which are largely limited by surface error due to panel misalignment on the primary reflector. Not only the surface rms error but also the error distribution has effect on the radiation pattern of the antenna. Therefore, analyzing the effect of error distributions resulting from various panel misalignments on the radiation pattern of the antenna will facilitate better compensation of surface errors during the reassembly process. To acquire the radiation pattern of LCT’s antenna with panel misalignments, we first propose a simulation method based on physical optics and the physical theory of diffraction, which offers precise results but is time-consuming, especially at high frequencies. Then, we propose a rapid computation method that combines the method of calculating the optical path difference (OPD), the OPD fitting method, and the aperture integration method for segmented reflectors. Experimental results demonstrate that the rapid computation method is highly efficient and accurate compared to the simulation method. In order to show the effect of error distributions due to two typical panel misalignments (i.e., piston and tip-tilt) on radiation patterns, experiments are conducted using the two proposed methods for various error distributions. These experiments indicate that for the same surface rms error, smaller panel errors at smaller normalized aperture radii are more conducive to achieving improved characteristics of the radiation patterns, such as reduced peak gain losses and lower sidelobe levels. Additionally, comparison experiments also reveal that variations in piston error have a greater impact on the radiation patterns than variations in tip-tilt error under the same surface rms error.

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An Improved Radio Pointing Model for SHARC II of the Caltech Submillimeter Observatory Telescope

Cited by 6 publications

References 33 publications

Measuring Antenna Elevation Mechanism Pointing Errors with Multiencoder Information Sources

Measuring Antenna Elevation Mechanism Pointing Errors with Multiencoder Information Sources

Disturbance Observer-based Pointing Control of Leighton Chajnantor Telescope

Effect of Panel Misalignment Error Distribution on the Radiation Pattern of Leighton Chajnantor Telescope’s Antenna

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