Achieving smooth and efficient slew movements on telescope mounts is crucial for minimizing structural stress, reaching maximum velocities, and ensuring efficient operation. Traditional slew trajectory generation methods often fall short in optimizing trajectories for time, resulting in unnecessarily long slew times that reduce telescope efficiency and potentially affect observation opportunities. Additionally, traditional methods often fail to converge smoothly to tracking velocities, leading to abrupt changes in motion that can compromise settling time. This paper presents a novel time-optimal jerk-limited trajectory generator algorithm for slew movements and its current implementation at the SOAR telescope as part of the Mount Control Upgrade Project. This algorithm effectively addresses these limitations by simultaneously optimizing for user-defined constraints on position, velocity, acceleration, and jerk while achieving minimum time. The algorithm produces a jerk-constrained trajectory that converges to a constant velocity reference specified by position, velocity, and time (PVT) commands, ensuring smooth and efficient convergence to tracking velocities while minimizing structural stress and settling time. The proposed algorithm is simple to implement and can be used to generate smooth slew trajectories in telescopes and actuators in general.
KEYWORDS: Telescopes, Control systems, Sensors, Amplifiers, Field programmable gate arrays, Computer programming, Data acquisition, Observatories, Control systems design
The Southern Astrophysical Research (SOAR) Telescope is a 4.1 meter aperture telescope situated in Cerro Pachon, IV Region, Chile. The telescope works from the atmospheric cut-off in the blue (320 nm) to the near infrared and has been designed to deliver the highest possible angular resolution at optical wavelengths. The telescope has an altazimuth mount which is controlled by the Mount Control Unit (MCU) system.
The SOAR Mount Control Unit Upgrade Project seeks to replace the current MCU in the SOAR telescope. The new control unit will be based on the National Instruments cRIO-9039 controller, which will allow to improve the telemetry, improve fault detection and use new digital control techniques.
This will allow a more compact and robust MCU. This paper introduces the project, shows the control architecture and the current status of the new MCU implementation.
Since the CTIO 4m Blanco Telescope was successfully upgraded, commissioned, and integrated with the DECam Instrument in Sept 2012, the performance of the telescope mount tracking has been excellent, with a median tracking jitter of 0.025”, and 0.06”rms, for the declination, and right ascension axes respectively. Any occasional increase in mount tracking jitter, has been associated with wind induced torque disturbances, affecting both axes simultaneously, especially during high speed wind conditions, combined with dome, and wind direction alignment.
In order to investigate the response to the telescope mount servo control, to wind induced disturbances, we have instrumented the 4m Blanco Telescope mount, upper secondary ring, with a novel 2-axis direct wind force sensor, sampled at 200 Hz, using inexpensive pocket digital scale type load cells, this combined with a small surface area of 0.00375 m2, we have obtained wind pressure noise values of 0.4 Pa-rms.
Our investigation will compare the Power Spectral Density (PSD) of the wind disturbance forces, with the expected Kolgomorov model, and explore the correlation between wind disturbance forces, and mount tracking jitter.
Also we will establish under what dome, wind direction, and wind speed conditions the increased mount tracking jitter, could affect science image results, and cause an increase in image ellipticity, and FWHM. This information should help observers, in taking appropriate measures, to minimize the wind induced image degradation in the future.
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