The project of much-anticipated LAMOST (Large sky Area Multi-Object fibre Spectroscopic Telescope) has
successfully been inspected and accepted at national-level evaluation. It will become the world's most powerful
meter-class level ground astronomical optical survey telescope. The ever-ambitious project throughout the development
history of Chinese astronomical optics telescopes has brought an extraordinary challenge to its control system from
all-round aspects. Painstaking effort has been made to the R&D of the control system from its design strategy,
functionality analyses to most subtle technical solutions, and of course efficient engineering management is also
included. A number of papers highlighting the anticipated LAMOST control system have previously been published
during the course of the project evolving. However, much lesson and experience have been learned since 10 years ago.
Now the telescope with all its facilities and observation chamber has been put into trial observation. This is the time to
review the past and ponder over the future of the control system as a whole against the functional telescope in current
reality. Lesson and experience are discussed. Some considerations for improving the system efficiency and the
accessibility are presented too in this paper.
Large astronomical optical telescopes are badly needed in order to learn more remote universe. There exist some key
problems of the control systems of large astronomical optical telescopes. Since they have voluminous bodies that would
encounter heavy external disturbance, one of the key problems is focused on how to accurately control them.
Additionally, in order to get nicer ultra-low velocity performance and a steady field of view, friction drive is widely
applied in contemporary large optical telescopes. One serious disadvantage of friction drive is that it will cause some
nonlinear uncertainties to influence telescope controls because of the mechanical characteristics between the principal
and subordinate friction wheels. These two aspects of external and internal disturbances will make a telescope very
difficult to be controlled. In this paper, we introduce a method of higher order sliding modes (HOSM) to control
telescopes, which overcome these two disadvantages of traditional Proportional-Integral-Derivative approach and can
achieve excellent control performance. Conventional sliding mode approach has been applied in many other mechanical
control systems owing to its high accuracy in anti-jamming. By discontinuous switching, it is invariable to disturbances
based on keeping some constraints with a sufficiently energetic effort. However, such conventional sliding mode
approach may cause dangerous high-frequency vibrations in the corresponding control system, which may influence
systemic control performance or even lead the system unstable. In this work, we use the newly developed HOSM
approach in the control systems of the large astronomical optical telescopes. The HOSM approach inherits the dominant
merits of conventional sliding mode. Moreover, it acts on the higher order time derivatives of the system deviation from
the constraint. And the discontinuous dynamics are restricted to the highest state while the counterpart in standard sliding
mode is in first derivative. Thus the HOSM approach can mostly removes high-frequency vibration effects on telescope
control. This control approach needs all states of the system to be observable. We use robust exact differentiator to
estimate the immeasurable state. Simulations have been done in the environment of MATLAB language. The results
show that this approach can realize the tracking performance of accurate ultra-low velocity for telescope control.
The workshop test of mount drive for Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) was completed in June of 2005. Now the giant mount has just been erected on Xinglong station, and is due to test in the summer of 2006. LAMOST mount mechanism features friction drive on both axes, and oil pad is employed specifically for the azimuth. For further improving the tracking accuracy in worse surroundings some nonlinear phenomena in the drive chain have to be addressed. Moreover, external uncertainties on Xinglong site, wind buffeting in particular, could affect load variation on the drive. The control system parameters would change with time, thus eventually degrade the tracking performance. All these reasonable assumptions call for a more robust controller than conventional PID approach to cope with. This is where H-Infinity controller comes in. This paper focuses on the mount drive of LAMOST by using H-Infinity technique and comparison with the PID servo. The load disturbance rejection is discussed, as well as transmission rigidity improvement is analyzed. Study and simulation are done in Matlab. The model test in our friction drive lab is presented.
Proc. SPIE. 6274, Advanced Software and Control for Astronomy
KEYWORDS: Telescopes, Control systems, Global system for mobile communications, Astronomy, Mobile communications, Astronomical telescopes, Lithium, Astronomical imaging, Information technology, Cell phones
The R and D of the Chinese 4-m ever-ambitious telescope, Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST), has advanced towards a new stage, and first light is expected by the end of 2006. As one of national scientific and engineering projects the telescope will become national facility and accommodate maximum accessibility for public reach in general and for the astronomical community in particular. Thus remote or even robotic control of the telescope is put under careful exploration. With the rapid development of IT technology one of the fashions is the mobile telephone carried around by average people mainly for daily communication, and mobile notes application has become a real hit. This paper presents GSM based remote wireless application adapted to telescope control, which can be utilized for greatly enhancing LAMOST' accessibility. The novel technique has recently been developed in LAMOST control lab. Test has demonstrated successful execution of Monitor and Control (M and C) commands for LAMOST through remote wireless mobile. The hardware and software configuration with techniques involved for reliable and secure communication is outlined in this paper too.
The concept for Chinese Future Giant Telescope (CFGT) with 30-m aperture has been around for several years, although
the requirements for control system are still far from completed and conclusive at this stage. Since the project was
proposed more study on a number of key issues relevant to the control system has been conducted. In particular the
mount control system for the giant telescope has been put forward under exploration. With our ongoing 4-m LAMOST
telescope just underwent a successful mount drive test the LAMOST control group has become more knowledgeable
with hands on experience that would be quite useful for mount drive design of even large telescope. This paper focuses
on the mount control system design for CFGT telescope in general. Particular aspects such as the effect of large moment
of inertia with ultra low-speed and multi-disturbance are included. Friction drive is opted for both historical and
economical reasons. Drive stiffness and servo control parameters optimization are discussed based on the workshop test
with LAMOST mount that could possibly be mapped to CFGT.
KEYWORDS: Control systems, Servomechanisms, Computer programming, Motion controllers, Control systems design, Telescopes, Astronomical imaging, Astronomical telescopes, Feedback signals, Analytical research
Taking as an example the focal plane control system for the largest optical telescope being built in our country, the paper focuses on Universal Motion and Automation Controller (UMAC) based servo control system with high accuracy, and analyzes its design scheme. The scheme analysis and preliminary test demonstrate a broad outlook of UMAC based application in complex control systems with high precision, real time, fast action, easy adaptation and open architecture.
A brief research summary and a preliminary test of the Focal Plane Control System (FPCS) are presented. The FPCS is one of components for the control system of Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST), which is a national large scientific project. The design scheme features distributed, hierarchical and expansible network architecture with UMAC based control technology. A number of advanced techniques are integrated with some control software and hardware, which presents a solution to requirements of precision, real time and open architecture for the
FPCS in the design of large optical astronomical telescopes.
The ongoing Chinese ever-ambitious project of Large Sky Area
Multi-Object Fiber Spectroscopic Telescope (LAMOST) has brought about a tremendous challenge for the control engineers. To the bottom line the giant 4-meter class ground telescope is a comprehensive optomechatronic platform to achieve high performance and functionality, such as its capability of observing 4000 stars simultaneously, which will set a world record in contemporary ground survey telescopes. This paper outlines the R&D stages of the control system for the project along with its integrated strategy of
optomechatronic components in general and network control framework in particular. The approach is to make a careful investigation with respect to the time crucialness for execution of different tasks so as to utilize different networks. However, the overall network framework is based on a distributed platform, hierarchical structure and open architecture to boost the flexibility. Vigorous study has been invested and a number of cutting edge techniques have been applied to meet the tough network control requirements, such as
real-time database, powerful interfaces, sophisticated controllers,
remote control, etc.
The behavior of future LAMOST mount tracking is one of crucial issues for the telescope's overall performance. In order to demonstrate and to sense the real situation to some degree, the LAMOST team has set up a model mount at the camps of Nanjing Institute of Astronomical Optics & Technology. Painstaking effort has been made during the course of the interim outdoor test to improve the accuracy of the model mount tracking. The major test progress, starting from scratch to date, has been recorded in this paper, such as the anti-disturbance measures taken, the cascaded feedback application, the two-motor-differential drive till the overhaul of the model mount in its drive mechanism, etc. The tracking accuracy has been dramatically improved up to 0.35"-0.42" RMS, promising the future LAMOST tracking requirement will be met given more reliable mount and sophisticated control system.
The Chinese ever-ambitious project of 30 meter-class telescope, Chinese Future Giant Telescope (CFGT), has brought about an extraordinary challenge for the control system's robustness. Various severe factors that we have never experienced before, will impact on our considerations for the control system. With the practice in our ongoing LAMOST project plus an investigation and a reasonable prediction the paper tries to deal with, at very preliminary stage, the control system configuration in general and a number of extreme difficulties in particular, such as the drive system and analysis of wind torque disturbance rejection, etc.
Active optics is the most difficult part in LAMOST project. Especially for the segmented reflecting Schmidt plate Ma, in which both segmented mirror active optics and thin mirror (or deformable mirror) active optics are applied. To test and optimize the thin mirror active optics of Ma, and to approach the reality of operating environment of the telescope, an outdoor experiment system has been established. This experiment system is also a 'small LAMOST' with one sub-mirror of the primary mirror Mb and one sub-mirror of the Schmidt plate Ma, and with full scale in spacing (40 meters) between Ma and Mb. many parts of LAMOST were tested in the experiment system except segmented mirror active optics. Especially for force actuators, thin mirror support system, friction driving of the alt-azimuth mounting and its control system, wave front test along such a long optical path. This paper presents the experiment system, research and developments, and some experiment results.
The QNX based real time database is one of main features for Large sky Area Multi-Object fiber Spectroscopic Telescope's (LAMOST) control system, which serves as a storage and platform for data flow, recording and updating timely various status of moving components in the telescope structure as well as environmental parameters around it. The database joins harmonically in the administration of the Telescope Control System (TCS). The paper presents methodology and technique tips in designing the EMPRESS database GUI software package, such as the dynamic creation of control widgets, dynamic query and share memory. The seamless connection between EMPRESS and the graphical development tool of QNX’s Photon Application Builder (PhAB) has been realized, and so have the Windows look and feel yet under Unix-like operating system. In particular, the real time feature of the database is analyzed that satisfies the needs of the control system.
Based on an unconventional design concept the LAMOST telescope will become the world's most powerful meter-class level ground astronomical optical survey telescope when it is completed. From technical perspective the goal with such a high profile has brought an extraordinary challenge to its control system. For better image quality the telescope's segmented reflecting Schmidt mirror has to be actively controlled by nanometer technique. At the same time the mirror is driven on both azimuth and altitude axes in subarcsecond accuracy for tracking the star. Vigorous study has been done and a number of cutting edge techniques are applied to meet the tough requirements. This paper gives the overview of LAMOST control system, outlines its distributed, real time, reliable and expansible configuration and the simulation approach. The current status of the control system is briefly reported in this paper too.
The control system of LAMOST telescope is highly distributed real time system, and the time base is crucial. During the motion tracking for 4000 celestial objects being simultaneously observed the alt-azimuth mount has to be driven on two axes in a servo loop to follow the motion of the objects in a timing system that has to be precise to the level of a few milliseconds. The GPS-based timing system has been developed in the lab of Nanjing Institute of Astronomical Optics & Technology (NIAOT). This paper describes a Net Time Server (NTS) that maintains the Coordinated Universal Time (UTC) derived from GPS, and distributes the time to precisely synchronize the client computer clocks across a network. The NTS is built on real time OS QNX4.25 platform. With help of a GPS receiver at hand, the NTS reaches the precision of 0.1 millisecond, and the time precision across LAN computers served by the NTS can meet the requirements for different time critical tasks in LAMOST control.
The Chinese ever-ambitious project of Large sky Area Multi-Object fiber Spectroscopic Telescope (LAMOST) has brought about a tremendous challenge for the software engineers. This paper describes the strategy of software simulation for the telescope control system as a whole, which is vital before the actual integration at the telescope with electronics, and mechanics. The development process of the simulator itself is envisioned from level-0 upgrade to level-2, and a demonstration of such a simulator at its level-0 phase is illustrated in detail in this paper.
The first two telescopes of the Infrared-Optical Telescope Array (IOTA) project are now in place and yielding data at the Smithsonian Institution's F. L. Whipple Observatory on Mt. Hopkins, near Tucson, Arizona. The IOTA collectors are 45 cm in diameter, and may be moved to various stations in an L-shaped configuration with a maximum baseline of 38 m. A third collector will be added as soon as funding permits. Each light-collector assembly consists of a siderostat feeding a stationary afocal Cassegrain telescope that produces a 10-X reduced parallel beam, which is in turn directed vertically downward by a piezo-driven active mirror that stabilizes the ultimate image position. The reduced beams enter an evacuated envelope and proceed to the corner of the array, where they are turned back along one arm for path compensation. The delay line, in one beam, consists of two parts: one dihedral reflector positioned in a slew-and-clamp mode to give the major part of the desired delay; and a second dihedral mounted on an air-bearing carriage to provide the variable delay that is needed. After delay, the beams exit from the vacuum and are directed by dichroic mirrors into the infrared beam-combination and detection system. The visible light passes on to another area, to the image-tracker detectors and the visible-light combination and detection system. The beams are combined in pupil-plane mode on beam splitters. The combined IR beams are conveyed to two cooled single-element InSb detectors. The combined visible-light beams are focussed by lenslet arrays onto multimode optical fibers that lead to the slit of a specially-designed prism spectrometer. For the visible mode, the delay line is run at several wavelengths on one side of the zero- path point, so that several cycles of interference occur across the spectrum. First results were obtained with the IR system, giving visibilities for several K and M stars, using 2.2 micrometers radiation on a N-S baseline of 21.2 m. From these measurements we obtained preliminary estimates of effective stellar diameters in the K band.