The 2225 actuators are the main and key control devices for the deformation control of FAST (Five-hundred-meter Aperture Spherical radio Telescope) reflector. The control behavior of the reflector deformation such as tracking and scanning, is implemented by the central coordination of the actuators. For each actuator, various operation state data should be uploaded to the monitoring center on time. The actuators are controlled from the upper computer in the control center and by the PLC in the relay room. OPC protocol is used in the acquisition and control process. OPC protocol is configured to set related variables. There are significant importance for the data acquisition of the actuators of FAST main reflector. The results can be used to analyze the life of the components of the actuator. They can also be used to monitor the operation status and to analyze the reason of failure, which may be of great help to the function extension, improvement and upgrading.
Five-hundred-meter Aperture Spherical radio Telescope (FAST) is a Chinese mega-science project to build the largest single dish radio telescope in the world.
Being the most sensitive single dish radio telescope. It was completed and put into use in September 2016. Its innovative engineering concept and design pave a new road to realize a huge single dish in the most effective way. The idea of sitting a large spherical dish in a karst depression is rooted in Arecibo telescope. FAST is an Arecibo-type antenna with three outstanding aspects: the karst depression used as the site, which is large to host the 500-meter telescope and deep to allow a zenith angle of 40 degrees; the active main reflector correcting for spherical aberration on the ground to achieve a full polarization and a wide band without involving complex feed systems; and the light-weight feed cabin driven by cables and servomechanism plus a parallel robot as a secondary adjustable system to move with high precision. The common feature of the latter two innovations is the transformation of large scale rigid structures into large scale flexible structures. To realize precise real-time control, the challenge of measurement and control technology is very challenging. This review intends to introduce the implementation methods, the recent progress, results, problems and future development of FAST measurement and control.
As the most important feedback source of the FAST telescope control system, the measurement system directly determines the overall performance and observing efficiency of FAST. High-precision total station measurement equipment is used in real-time measurement of the FAST reflector and the feed cabin. Because the measurement accuracy of total station is easily influenced by the atmospheric environment, in this paper, we established the distribution model of temperature, humidity and pressure through the meteorological information collected by the weather stations evenly distributed in the reflector. We analyzed the changes of atmospheric environment caused by FAST topography and calculated the real-time atmospheric correction at each location within the coverage of the weather station based on the formula. Finally, according to the variation of the atmospheric correction value in the measurement path, the optimal atmospheric correction parameter of the path is obtained, so as to improve the measurement accuracy of the FAST reflector.
Proc. SPIE. 9913, Software and Cyberinfrastructure for Astronomy IV
KEYWORDS: Human-machine interfaces, Reflectors, Telescopes, Telescopes, Data storage, Databases, Receivers, Control systems, Control systems, Space telescopes, Telecommunications, Control systems design
FAST is the largest single dish radio telescope in the world. During observation, part of spherical reflector forms paraboloid to the source direction, meanwhile the feed is placed to instant focus. The control of telescope is difficult and complicated. An autonomous central control system is designed and implemented for methodically and efficiently operation. The system connects and coordinates all subsystems including control, measurement and health monitoring for reflector, feed support and receiver respectively. The main functions are managing observation tasks, commanding subsystems, storing operating data, monitoring statuses and providing the uniform time standard. In this paper, the functions, software and hardware of FAST central control system are presented. The relative infrastructures such as power, network and control room arrangement are introduced.
In photogrammetry, an approach of automatic detection and recognition on reference points have been proposed to meet the requirements on detection and matching of reference points. The reference points used here are the CCT(circular coded target), which compose of two parts: the round target point in central region and the circular encoding band in surrounding region. Firstly, the contours of image are extracted, after that noises and disturbances of the image are filtered out by means of a series of criteria, such as the area of the contours, the correlation coefficient between two regions of contours etc. Secondly, the cubic spline interpolation is adopted to process the central contour region of the CCT. The contours of the interpolated image are extracted again, then the least square ellipse fitting is performed to calculate the center coordinates of the CCT. Finally, the encoded value is obtained by the angle information from the circular encoding band of the CCT. From the experiment results, the location precision of the CCT can be achieved to sub-pixel level of the algorithm presented. Meanwhile the recognition accuracy is pretty high, even if the background of the image is complex and full of disturbances. In addition, the property of the algorithm is robust. Furthermore, the runtime of the algorithm is fast.
With the camera internal parameters known, to calculate the external parameters is to solve a set of highly nonlinear over-determined equations. In this paper, an improved hybrid genetic algorithm is adopted to obtain external parameters. It combines the advantages of genetic algorithm and Newton method, making it possible to obtain results with high accuracy and a faster convergence.
To determine the relative pose between an object and a single camera using correspondences between 3D feature points of the object and their corresponding 2D projections in the image, this paper proposes a target’s pose measurement algorithm based on the bundle adjustment method. This iterative algorithm can be divided into two steps: first, a reliable initial pose is computed by using only three non-collinear points; second, the optimal rotation and translation matrix of the target is estimated based on the bundle adjustment method. Experiments on simulated data and real data show that this method can get high precision with its rotation angles error within 20 arc-second and the translation error within 20 micron in ideal occasions.
The paper proposed a large field of view (FOV) measurement with calibrating the camera and measuring simultaneously.
In the measurement, the whole FOV was divided into several smaller ones with overlapping areas between each other.
The overlapping areas should contain at least 4 noncollinear feature points in each for computing external parameters
and at least 4 noncollinear control points in one of them to start the calculation. To obtain the measurement of the whole
large FOV, 2 images (or more) of each small fields of view needed to be taken from different angles. In the process of
calculation, theoretical values of the camera were used as the initial values of the internal parameters and the initial
values of external values were obtained from a new solution for P4P problem. So, the internal parameters of the camera,
the external parameters for each image, and the 3D coordinates of the feature points in the large field of view could be
acquired by adjustment method. In our experiment, the large field of view range was 500mm×500mm, the smaller ones
corresponding to each image was 200mm×200mm, and the ultimate measurement accuracy was 12μm.
During the experimental process of the spatial point's position detection, we analyze the advantages
and disadvantages of the classical method, and propose an improved method. First, we interpolate the
point's data to increase the size of the image. Then use the Zernike moment to detect the edge of the
point. Finally, we obtain a coordinate of the center of the point by using the ellipse fitting algorithm,
and take this coordinate as the position of the spatial point. Experimental results in laboratory show
that, the proposed detection method on sub-pixel level is realized to detect the spatial point's position
with high-accuracy. And experimental results of relative measurement with 100 meters outdoor show
that, the repeatable accuracy of this method can reach 0.12 pixel during the day and 0.05 pixel at night.
The method of 3D reconstruction from multi-view of the object with single camera is proposed in this paper. The images
of the planar pattern from different views are captured by the single camera. The internal and external parameters of the
camera are calculated precisely with Two-stage camera calibration method. On this basis, the image points of calibration
pattern can be matched and reconstructed. Experimental results show that: the flatness of reconstructed planar pattern is
about 0.006mm; the position error of sign is about 0.012mm. The proposed method is high-accuracy, simple, flexible and
A new method of attitude measurement of the calibration target based on machine vision is proposed in this paper.
Firstly, the internal parameters and external parameters of the CCD camera are calibrated by using the feature points on
the calibration target. Secondly, shoot the calibration target in different positions and gather any different image
information. Finally, measure the calibration target's attitude through reconstructing the positions of those feature points
which on the calibration target. Experiment results show that the standard deviation of the attitude measurement errors is
less than 10 arc-second. This method is an effective high-precision space attitude measurement algorithm which can
meet the engineering requirements.
FAST is an Arecibo type large radio telescope with 500 meters aperture reflector, which is composed of about 4600
triangle panels. The panels and back structures are installed on the spring cable meshes. FAST adopts the active
reflection structure to change the spherical difference, which will form a simultaneous parabola with aperture of 300
meters. To test the feasibility of this new type reflector structure, a FAST model of 30 meters aperture was constructed in
2005. In this paper, the structure of the model is introduced, which includes a circle supporting girder of 30 meters in
diameter, 252 panel back structures, 472 main cables, and 145 sets of control cables, nodes, actuators and anchors. The
structural design and analysis are processed for these compositions, and the test results of the model reflector are given.
The work of the paper will provide a significant reference for the primary design of FAST reflector.
China has embarked on a project to build the world's largest radio telescope, the Five hundred meter Aperture
Spherical Telescope (FAST), in a karst depression in southwest Guizhou Province. The telescope is of a
modified Arecibo type. We suggest an active main reflector that is spherical in the neutral state but the
illuminated aperture of 300m in diameter would be adjusted into a proper paraboloid such that a simple feed
could be used at its focus, since the "spherical correction" has be done on the ground. The feed cabin at the
focus is supported and driven directly by cables controlled by computer, which avoids a heavy and expensive
feed supporting system. Newly developed method and technology for determining the spatial position of 2400
nodes on the main reflector of the FAST are introduced in this paper. Base on the measurements of the position
of node under which the down cable are linked, a loop feedback control enables accurately driving the spherical
reflector deformed to paraboloid. The key technique of this implementation is the precise measurement of
2400 nodes. In this article, we introduce the scheme of simplified photogrammetry aiming at no lateral shift
situation; we analyse the influence of lateral shift; and considering lateral shift, we propose a scheme using
rotation platform plus double-eye camera to accomplish the dynamic measurement of the reflector. The result
of analysis and testing shows the feasibility and effectivity of the scheme of measurement.
To meet the need of feed control, Cable Tension Real-time Measure System based on RTLinux was established. And the
system is used to keep those cables healthy and safe. Resistance tension sensors are used in the system, and differential
holodesmosomes are also used in the system to raise system performance. Bad data checking in software raised the
performance of anti-interference.
The metrology system to measure position and orientation of the cabin for FAST model consists of three Leica laser total stations. An innovative way was involved to test the performance of the metrology system. Large numbers of experiment data were obtained, including 116 groups of dynamic data and 62 groups of static data. There are many problems to be solved from experiment. 240ms delay time was found and characteristic frequency was detected. The dynamic capability of this metrology system was tested. The metrology system will work in the quasi static in FAST and FAST down scale model.The static position RMS error is less than 0.4mm and orientation RMS error less than 0.08°. Results of the total station examination indicate that this system can meet the requirement of the model. In spite of some dissatisfactory aspects, e.g. sampling rate, the total station will play an important role in the FAST.
Newly developed method and technology for determining the spatial position of the feeds of the FAST are introduced in this paper. Base on the measurements of the position and orientation of cabin in which the feeds are mounted, a loop feedback control enables accurately driving the feeds along desired tracks. The key technique of this implementation is the precise measurement of 6-freedom coordinates of the cabin in air with high sampling rate. An innovated way for this purpose is put forward and tested, combining data by different type of sensors. The errors of measurements and their influences on the control accuracy are analyzed theoretically, and checked by model tested. The experiment shows the feasibility and effectivity of the scheme of measurement and control for the telescope.