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  • 1
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    State variable representations in digital control systems with MA-prefiltered measurements (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: This paper derives three discrete state variable representations for a continuous-time plant driven by a zero-order hold with a combination of instantaneous measurements and measurements prefiltered by a multiinput/multioutput moving average (MA) process. These representations allow the control system engineer to model plants of this type accurately in a form which permits him to use standard techniques to design digital feedback controllers for them. An example is presented which illustrates how to obtain the coefficient matrices in each representation. Guidelines are presented for choosing the best representation to use for any given plant of this type.
    Keywords: CYBERNETICS
    Type: International Journal of Control (ISSN 0020-7179); 47; 1683-169
    Format: text
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  • 2
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    New method for scanning spacecraft and balloon-borne/space-based experiments (1991)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A new method is presented for scanning balloon-borne experiments, free-flying spacecraft, and gimballed experiments mounted to the space shuttle or the space station. It uses rotating-unbalanced-mass (RUM) devices for generating circular, line, or raster scan patterns and an auxiliary control system for target acquisition, keeping the scan centered on the target, and producing complementary motion for raster scanning. It is ideal for applications where the only possible way to accomplish the required scan is to physically scan the entire experiment or spacecraft as in X-ray and gamma ray experiments. In such cases, this new method should have advantages over prior methods in terms of either power, weight, cost, performance, stability, or a combination of these.
    Keywords: ENGINEERING (GENERAL)
    Type: Journal of Guidance, Control, and Dynamics (ISSN 0731-5090); 14; 548-553
    Format: text
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  • 3
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    Modelling and designing digital control systems with averaged measurements (1988)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: An account is given of the control systems engineering methods applicable to the design of digital feedback controllers for aerospace deterministic systems in which the output, rather than being an instantaneous measure of the system at the sampling instants, instead represents an average measure of the system over the time interval between samples. The averaging effect can be included during the modeling of the plant, thereby obviating the iteration of design/simulation phases.
    Keywords: CYBERNETICS
    Type: International Journal of Control (ISSN 0020-7179); 48; 161-177
    Format: text
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  • 4
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    Ideal state reconstructor for deterministic digital control systems (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A state reconstructor for deterministic digital systems is presented which is ideal in the following sense: if the plant parameters are known exactly, the output of the state reconstructor will exactly equal the true state of the plant, not just approximate it. Furthermore, this ideal state reconstructor adds no additional states or eigenvalues to the system. Nor does it affect the plant equation for the system in any way; it affects only the measurement equation. While there are countless ways of choosing the ideal state reconstructor parameters, two distinct methods are described here. An example is presented which illustrates the procedures to completely design the ideal state reconstructor using both methods.
    Keywords: CYBERNETICS
    Type: International Journal of Control (ISSN 0020-7179); 49; 2001-201
    Format: text
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  • 5
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    Pointing and Scanning Control of Optical Instruments using Rotating Unbalanced Masses (1996)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Correct pointing direction and scanning motions are essential in the operation of many flight payloads, such as balloon-borne telescopes and space-based X- ray and gamma-ray telescopes. Rotating unbalanced mass (RUM) devices have been recently proposed, implemented and successfully tested to produce a variety of scanning motions. Linear scans, raster scans, and circular scans have been successfully generated on a gimbaled payload using pairs of RUM devices. Theoretical analysis, computer simulations, and experiments have also been used to study the feasibility of using RUM devices to control instrument pointing direction, in addition to generating scanning motion. Dynamic modeling of a gimbaled payload equipped with a pair of RUM devices has been studied, and preliminary testing indicates that the pointing control is indeed feasible. However, there is also great potential for significant performance improvements through more advanced control system analysis, modeling and design. In this paper, modeling and control methods are described to achieve simultaneous scanning and pointing control of a gimbaled payload using rotating unbalance mass (RUM) devices. The model development work builds upon the results of Polites et al. and also some modeling approaches from robotics research. Results of some preliminary experiments are discussed and some nonlinear control methods will be proposed.
    Keywords: Mechanical Engineering
    Type: NASA-TM-112521 , NAS 1.15:112521 , AAS-97-065
    Format: application/pdf
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  • 6
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    Rotating Unbalanced-Mass devices for scanning: Results from the proof-of-concept test (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Rotating unbalanced-mass (RUM) devices are a new way to scan space-based, balloon-borne, and ground-based gimbaled payloads, like x-ray and gamma-ray telescopes. They can also be used to scan free-flying spacecraft. Circular scans, linear scans, and raster scans can be generated. A pair of RUM devices generates the basic scan motion and an auxiliary control system using torque motors, control moment gyros, or reaction wheels keeps the scan centered on the target and produces some complementary motion for raster scanning. Previous analyses and simulation results show that this approach offers significant power savings compared to scanning only with the auxiliary control system, especially with large payloads and high scan frequencies. However, these claims have never been proven until now. This paper describes a laboratory experiment which tests the concept of scanning a gimbaled payload with RUM devices. The test results are compared with those from a computer simulation model of the experiment and the differences are discussed.
    Keywords: Spacecraft Instrumentation
    Type: NASA-TM-111239 , AAS-94-002 , NAS 1.15:111239
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  • 7
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    Variable stiffness torsion springs (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: In a torsion spring the spring action is a result of the relationships between the torque applied in twisting the spring, the angle through which the torsion spring twists, and the modulus of elasticity of the spring material in shear. Torsion springs employed industrially have been strips, rods, or bars, generally termed shafts, capabable of being flexed by twisting their axes. They rely on the variations in shearing forces to furnish an internal restoring torque. In the torsion springs herein the restoring torque is external and therefore independent of the shearing modulus of elasticity of the torsion spring shaft. Also provided herein is a variable stiffness torsion spring. This torsion spring can be so adjusted as to have a given spring constant. Such variable stiffness torsion springs are extremely useful in gimballed payloads such as sensors, telescopes, and electronic devices on such platforms as a space shuttle or a space station.
    Keywords: PHYSICS (GENERAL)
    Format: application/pdf
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  • 8
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    Means for Positioning and Repositioning Scanning Instruments (1996)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A method is presented for positioning a scanning instrument to point toward the center of the desired scan wherein the scan is achieved by rotating unbalanced masses (RUMs) rotating about fixed axes of rotation relative to and associated with the instrument, the RUMs being supported on drive shafts spaced from the center of the mass of the instrument and rotating 180 degrees out-of-phase with each other and in planes parallel to each other to achieve the scan. The elevation and cross-elevation angles of the instrument are sensed to determine any offset and offset time rate-of-change, and the magnitude and direction are converted to a RUM cycle angular velocity component to be superimposed on the nominal velocity of the RUMs. This RUM angular velocity component modulates the RUM angular velocity to cause the speed of the RUMs to increase and decrease during each revolution to drive the instrument toward the desired center of the scan.
    Keywords: Instrumentation and Photography
    Format: application/pdf
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  • 9
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    Exact state reconstruction in deterministic digital control systems (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A state reconstructor for deterministic digital systems is presented which is ideal in the following sense: if the plant parameters are known exactly, the output of the state reconstructor will exactly equal the true state of the plant, not just approximate it. Furthermore, this ideal state reconstructor adds no additional states or eigenvalues to the system. Nor does it affect the plant equation for the system in any way; it affects only the measurement equation. While there are countless ways of choosing the ideal state reconstructor parameters, two distinct methods are described here. An example is presented which illustrates the procedures to completely design the ideal state reconstructor using both methods.
    Keywords: ENGINEERING (GENERAL)
    Type: NASA-TP-2757 , NAS 1.60:2757
    Format: application/pdf
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  • 10
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    A new approach to state estimation in deterministic digital control systems (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The paper presents a new approach to state estimation in deterministic digital control systems. The scheme is based on sampling the output of the plant at a high rate and prefiltering the discrete measurements in a multi-input/multi-output moving average (MA) process. The coefficient matrices in the MA prefilter are selected so the estimated state equals the true state. An example is presented which illustrates the procedure to follow to completely design the estimator.
    Keywords: ENGINEERING (GENERAL)
    Type: NASA-TP-2745 , NAS 1.60:2745
    Format: application/pdf
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