18,063 research outputs found
Effects of Transport Delays of Manual Control System Performance
Throughput or transport delays in manual control systems can cause degraded performance and lead to potentially unstable operation. With the expanding use of digital processors, throughput delays can occur in manual control systems in a variety of ways such as in digital flight control systems in real aircraft, and in equation of motion computers and computer generated images in simulators. Research has shown the degrading effect of throughput delays on subjective opinion and system performance and dynamic response. A generic manual control system model is used to provide a relatively simple analysis of and explanation for the effects of various types of delays. The consequence of throughput delays of some simple system architectures is also discussed
Time Domain Simulations of Arm Locking in LISA
Arm locking is a technique that has been proposed for reducing laser
frequency fluctuations in the Laser Interferometer Space Antenna (LISA), a
gravitational-wave observatory sensitive in the milliHertz frequency band. Arm
locking takes advantage of the geometric stability of the triangular
constellation of three spacecraft that comprise LISA to provide a frequency
reference with a stability in the LISA measurement band that exceeds that
available from a standard reference such as an optical cavity or molecular
absorption line. We have implemented a time-domain simulation of arm locking
including the expected limiting noise sources (shot noise, clock noise,
spacecraft jitter noise, and residual laser frequency noise). The effect of
imperfect a priori knowledge of the LISA heterodyne frequencies and the
associated 'pulling' of an arm locked laser is included. We find that our
implementation meets requirements both on the noise and dynamic range of the
laser frequency.Comment: Revised to address reviewer comments. Accepted by Phys. Rev.
Design of PID Controllers Satisfying Gain Margin and Sensitivity Constraints on a Set of Plants
This paper presents a method for the design of PID-type controllers, including those augmented by a filter on the D element, satisfying a required gain margin and an upper bound on the (complementary) sensitivity for a finite set of plants. Important properties of the method are: (i) it can be applied to plants of any order including non-minimum phase plants, plants with delay, plants characterized by quasi-polynomials, unstable plants and plants described by measured data, (ii) the sensors associated with the PI terms and the D term can be different (i.e., they can have different transfer function models), (iii) the algorithm relies on explicit equations that can be solved efficiently, (iv) the algorithm can be used in near real-time to determine a controller for on-line modification of a plant accounting for its uncertainty and closed-loop specifications, (v) a single plot can be generated that graphically highlights tradeoffs among the gain margin, (complementary) sensitivity bound, low-frequency sensitivity and high-frequency sensor noise amplification, and (vi) the optimal controller for a practical definition of optimality can readily be identified
Study on stability and rotating speed stable region of magnetically suspended rigid rotors using extended Nyquist criterion and gain-stable region theory
This paper presents a novel and simple method to analyze the absolute stability and the rotor speed stable region of a magnetically suspended rotor (MSR). At the beginning of the paper, a complex variable is introduced to describe the movement of the MSR and a complex coefficient transfer function is obtained accordingly. The equivalent stability relationship between this new variable and the two traditional deflection angles is also demonstrated in a simple way. The detailed characteristics of the open-loop MSR system with time delay are studied carefully based on the characteristics of its Nyquist curve. A sufficient and necessary condition of absolute stability is then deduced by using an extended complex Nyquist stability criterion for MSRs. Based on the relationship between the rotor speed and gain-stable region proposed in this paper, the rotor speed stable region can be solved simply and directly. The usefulness and effectiveness of the proposed approaches are validated by examples and simulations
The performance of arm locking in LISA
For the laser interferometer space antenna (LISA) to reach it's design
sensitivity, the coupling of the free running laser frequency noise to the
signal readout must be reduced by more than 14 orders of magnitude. One
technique employed to reduce the laser frequency noise will be arm locking,
where the laser frequency is locked to the LISA arm length. This paper details
an implementation of arm locking, studies orbital effects, the impact of errors
in the Doppler knowledge, and noise limits. The noise performance of arm
locking is calculated with the inclusion of the dominant expected noise
sources: ultra stable oscillator (clock) noise, spacecraft motion, and shot
noise. Studying these issues reveals that although dual arm locking [A. Sutton
& D. A Shaddock, Phys. Rev. D 78, 082001 (2008).] has advantages over single
(or common) arm locking in terms of allowing high gain, it has disadvantages in
both laser frequency pulling and noise performance. We address this by
proposing a hybrid sensor, retaining the benefits of common and dual arm
locking sensors. We present a detailed design of an arm locking controller and
perform an analysis of the expected performance when used with and without
laser pre-stabilization. We observe that the sensor phase changes beneficially
near unity-gain frequencies of the arm-locking controller, allowing a factor of
10 more gain than previously believed, without degrading stability. We show
that the LISA frequency noise goal can be realized with arm locking and
Time-Delay Interferometry only, without any form of pre-stabilization.Comment: 28 pages, 36 figure
All-propulsion design of the drag-free and attitude control of the European satellite GOCE
This paper concerns the drag-free and attitude control (DFAC) of the European Gravity field and steady-state Ocean Circulation Explorer satellite (GOCE), during the science phase. GOCE aims to determine the Earth's gravity field with high accuracy and spatial resolution, through complementary space techniques such as gravity gradiometry and precise orbit determination. Both techniques rely on accurate attitude and drag-free control, especially in the gradiometer measurement bandwidth (5-100mHz), where non-gravitational forces must be counteracted down to micronewton, and spacecraft attitude must track the local orbital reference frame with micro-radian accuracy. DFAC aims to enable the gravity gradiometer to operate so as to determine the Earth's gravity field especially in the so-called measurement bandwidth (5-100mHz), making use of ion and micro-thruster actuators. The DFAC unit has been designed entirely on a simplified discrete-time model (Embedded Model) derived from the fine dynamics of the spacecraft and its environment; the relevant control algorithms are implemented and tuned around the Embedded Model, which is the core of the control unit. The DFAC has been tested against uncertainties in spacecraft and environment and its code has been the preliminary model for final code development. The DFAC assumes an all-propulsion command authority, partly abandoned by the actual GOCE control system because of electric micro-propulsion not being fully developed. Since all-propulsion authority is expected to be imperative for future scientific and observation missions, design and simulated results are believed to be of interest to the space communit
Combined MIMO adaptive and decentralized controllers for broadband active noise and vibration control
Recent implementations of multiple-input multiple-output adaptive controllers for reduction of broadband noise and vibrations provide considerably improved performance over traditional adaptive algorithms. The most significant performance improvements are in terms of speed of convergence, the \ud
amount of reduction, and stability of the algorithm. Nevertheless, if the error in the model of the relevant transfer functions becomes too large then the system may become unstable or lose performance. On-line adaptation of the model is possible in principle but, for rapid changes in the model, necessitates \ud
a large amount of additional noise to be injected in the system. It has been known for decades that a combination of high-authority control (HAC) and low-authority control (LAC) could lead to improvements with respect to parametric uncertainties and unmodeled dynamics. In this paper a full digital implementation of such a control system is presented in which the HAC (adaptive MIMO control) is implemented on a CPU and in which the LAC (decentralized control) is implemented on a high-speed Field Programmable Gate Array. Experimental results are given in which it is demonstrated that the HAC/LAC combination leads to performance advantages in terms of stabilization under parametric uncertainties and reduction of the error signal
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