Telescope control research projects











Green Bank Telescope (GBT), National Radio Astronomy Observatory (NRAO), WV, USA
















Giant Meterwave Radio Telescope (GMRT), National Centre for Radio Astrophysics (NCRA), Tata Institute of Fundamental Research (TIFR), India




Project 1: High-performance control of multi-motor systems with cogging torque. Application to the Green Bank Telescope

Abstract: This project develops: (1) a novel load-sharing control system design methodology, based on an iterative, self-tuning model-based harmonic identification to achieve high-performance control specifications in systems with multiple motors affected by cogging torque, nonlinear characteristics, model uncertainty and low-speed specifications, including a reliable and easy-to-use controller implementation; and (2) the implementation and experimental validation of the new methodology, controlling the azimuth (16 motors) and elevation (8 motors) axes of the large flexible structure of the Green Bank Radio Telescope (GBT-NRAO, National Radio Astronomy Observatory), West Virginia, US, the largest fully steerable radio telescope in the world, for low speed and very high precision tracking and pointing, with the objective of extending the frequency range of operation of the telescope.


Project 2: Quantitative robust control methodologies for high-performance active vibration control in large mechanical structures with model uncertainty. Application to the Green Bank Telescope

Abstract: In last few decades use of large flexible structures for space based applications like space robotics, space based telescopes, space stations and ground based radio telescopes have become a routine. The request of larger, lighter and faster mechanical structures --more susceptible to vibrations-- along with the necessity of more demanding motion control specifications have greatly challenged the existing vibration control design methodologies. The principal objective of this research project is to develop new quantitative robust control techniques for active vibration control in large mechanical structures with high-performance control specifications and practical limitations in the location and number of sensors and actuators. The research includes theoretical analysis, computer simulation, controller implementation and experimental verification in the extra-large Green Bank Radio Telescope (GBT-NRAO, National Radio Astronomy Observatory) in West Virginia, US --the world's largest fully steerable radio telescope and the world's largest land based movable structure--, with the objective of (1) extending the frequency range of operation of the telescope and (2) increasing the time available for astronomical observations by suppressing wind induced vibrations.


Project 3: High-Performance Quantitative Robust Switching Control for Optical Telescopes

Abstract: This project introduces an innovative robust and nonlinear control design methodology for high-performance servo-systems in optical telescopes. The dynamics of optical telescopes typically vary according to azimuth and altitude angles, temperature, friction, speed and acceleration, leading to nonlinearities and plant parameter uncertainty. The methodology proposed in this project attenuates the effect of friction and combines robust Quantitative Feedback Theory (QFT) techniques with nonlinear switching strategies that achieve simultaneously the best characteristics of a set of very active robust controllers and very stable robust controllers. It is also proven that the nonlinear/switching controller is stable for any switching strategy and switching velocity, according to described frequency conditions based on common quadratic Lyapunov functions (CQLF) and the circle criterion.


Project 4: Advanced nonlinear robust MIMO control systems for high precision tracking and pointing in large optical and radio telescopes. Application to the Giant Meterwave Radio Telescope

Abstract: This project proposes (1) develop a new advanced nonlinear and robust multi-input multi-output control methodology to design high performance servo systems for extremely large telescopes and antennas, and (2) validate it experimentally in the GMRT, Giant Meterwave Radio Telescope, National Centre for Radio Astrophysics (NCRA), Tata Institute of Fundamental Research (TIFR), India. The facility has 30 fully steerable radio antennas, each of diameter 45 meters. GMRT operates in frequency range of 50 MHz to 1500 MHz. It is the largest radio telescope in Asia and largest in the world at this frequency range. The radio dishes of GMRT are made using SMART (Stretch Mesh Attached to Rope Trusses) concept. This allows construction of light weight, low cost dishes. But such structure also lowers the fundamental frequency of the dish making it more challenging to control under windy conditions.


Selection of publications

[1]. Garcia-Sanz,M., Ranka,T., Joshi,B.C. (2011). Advanced nonlinear robust controller design for high-performance servo-systems in large radar antennas. 63th National Aerospace & Electronics Conference, IEEE-NAECON, Dayton, Ohio, USA.

[2]. Garcia-Sanz,M., Ranka,T., Joshi,B.C. (2012). High-performance switching QFT control for large radio telescopes with saturation constraints. 64th National Aerospace & Electronics Conference, IEEE-NAECON, Dayton, Ohio, USA.

[3]. Garcia-Sanz,M., Franke,T., Ranka,T., Adams,M.L., Adams,M., Ford,J., Weadon,T., McCullough,R., Ray,J. (2013). Advanced control solutions to extend the operational frequencies of the Green Bank Radio Telescope: from control theory to experimental validation. CWRU ShowCase, Cleveland, Ohio, USA.

[4]. Franke,T., Weadon,T., Ford,J., Garcia-Sanz,M. (2014). An Iterative Model-Based Cogging Compensator for the Green Bank Telescope Servo System. Montreal, Quebec: 2014 SPIE Astronomical Telescopes and Instrumentation Conference, SPIE, Ground-based and Airborne Telescopes V.

[5]. Lounsbury,W., Garcia-Sanz,M. (2014). High-Performance Quantitative Robust Switching Control for Optical Telescopes. Montreal, Quebec: 2014 SPIE Astronomical Telescopes and Instrumentation Conference, SPIE, Software and Cyberinfrastructure for Astronomy III.

[6]. Ranka,T., Garcia-Sanz,M., Weadon,T., Ford,J. (2014). System Identification and Interval Analysis of the Green Bank Telescope structure and servo system. Montreal, Quebec: 2014 SPIE Astronomical Telescopes and Instrumentation Conference, SPIE, Ground-based and Airborne Telescopes V.

[7]. Ranka,T., Garcia-Sanz,M., Weadon,T., Ford,J. (2014). System identification of The Green Bank Telescope structure and servo system. Portland, Oregon: American Control Conference, ACC-2014. (Best presentation in session award).

[8]. Ranka,T., Garcia-Sanz,M., Ford,J. (2015). Extended state observer based controller design for the Green Bank Telescope servo system. Columbus, Ohio: ASME 2015 Dynamical Systems and Control Conference.

[9]. Franke,T., Weadon,T., Ford,J., Garcia-Sanz,M., (2015). Correcting Encoder Interpolation Error on the Green Bank Telescope Using an Iterative Model-Based Identification Algorithm. Journal of Astronomical Telescopes, Instruments and Systems, 1(4), 044005-2015. DOI: 10.1117/1.JATIS.1.4.044005.

[10]. Ranka,T., Garcia-Sanz,M., Symmes,A., Ford,J., Weadon,T. (2016). Dynamic analysis of the Green Bank Telescope structure and servo system. Journal of Astronomical Telescopes, Instruments and Systems, 2(1), 014001. DOI: 10.1117/1.JATIS.2.1.014001.

 

 


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