Engineering topics

Knospe, Carl R.

Publications and source records attributed to Knospe, Carl R..

9 records

NASA NTRS1996

Design of Robust Adaptive Unbalance Response Controllers for Rotors with Magnetic Bearings

Experimental results have recently demonstrated that an adaptive open loop control strategy can be highly effective in the suppression of unbalance induced vibration on rotors supported in active magnetic bearings. This algorithm, however, relies upon a predetermined gain matrix. Typically, this matrix is determined by an optimal control formulation resulting in the choice of the pseudo-inverse of the nominal influence coefficient matrix as the gain matrix. This solution may result in problems with stability and performance robustness since the estimated influence coefficient matrix is not equal to the actual influence coefficient matrix. Recently, analysis tools have been developed to examine the robustness of this control algorithm with respect to structured uncertainty. Herein, these tools are extended to produce a design procedure for determining the adaptive law's gain matrix. The resulting control algorithm has a guaranteed convergence rate and steady state performance in spite of the uncertainty in the rotor system. Several examples are presented which demonstrate the effectiveness of this approach and its advantages over the standard optimal control formulation.

Knospe, Carl R.↗

NASA NTRS1993

Magnetic Actuators and Suspension for Space Vibration Control

The research on microgravity vibration isolation performed at the University of Virginia is summarized. This research on microgravity vibration isolation was focused in three areas: (1) the development of new actuators for use in microgravity isolation; (2) the design of controllers for multiple-degree-of-freedom active isolation; and (3) the construction of a single-degree-of-freedom test rig with umbilicals. Described are the design and testing of a large stroke linear actuator; the conceptual design and analysis of a redundant coarse-fine six-degree-of-freedom actuator; an investigation of the control issues of active microgravity isolation; a methodology for the design of multiple-degree-of-freedom isolation control systems using modern control theory; and the design and testing of a single-degree-of-freedom test rig with umbilicals.

Knospe, Carl R.↗

NASA NTRS1992

A six degree-of-freedom magnetic bearing for microgravity vibration isolation

A design for a magnetic bearing, proposed as the fine stage of a coarse-fine actuator for microgravity vibration isolation, is presented. The bearing is novel in that it uses a geometry that has just three independent flux path systems. This contrasts the twelve flux path systems (six bidirectional thrust bearings) used in conventional designs. The design results in compactness, light weight, and high performance when compared with the published designs. A control system is proposed to reject disturbances caused by an umbilical connection to the experiment.

Allan, A. Peter↗

NASA NTRS1992

Extended H2 synthesis for multiple degree-of-freedom controllers

H2 synthesis techniques are developed for a general multiple-input-multiple-output (MIMO) system subject to both stochastic and deterministic disturbances. The H2 synthesis is extended by incorporation of anticipated disturbances power-spectral-density information into the controller-design process, as well as by frequency weightings of generalized coordinates and control inputs. The methodology is applied to a simple single-input-multiple-output (SIMO) problem, analogous to the type of vibration isolation problem anticipated in microgravity research experiments.

Hampton, R. David↗

NASA NTRS1992

A microgravity vibration isolation rig

It is well known that the spacecraft environment deviates from a state of zero gravity due to various random as well as repetitive sources. Science experiments that require a microgravity environment must therefore be isolated from these disturbances. Active control of noncontact magnetic actuators enables such isolation. A one degree of freedom test rig has been constructed to demonstrate the isolation capability achievable using magnetic actuators. A cylindrical mass on noncontacting electromagnetic supports simulates a microgravity experiment on board an orbiter. Disturbances generated by an electrodynamic shaker are transmitted to the mass via dashpots representing umbilicals. A compact Lorentz actuator has been designed to provide attenuation of this disturbance.

Banerjee, Bibhuti B.↗

NASA NTRS1992

Microgravity vibration isolation research at the University of Virginia

Research at the University of Virginia on microgravity vibration isolation is reviewed. This work falls into three areas: the one degree of freedom isolation test rig and Lorentz actuator design, multiple degree of freedom active isolation system control, and innovative actuators for long stroke, non-contacting six degree of freedom isolation. Theoretical and design issues of multiple degree of freedom isolation are discussed.

Knospe, Carl R.↗

NASA NTRS1992

Extended H2 synthesis for microgravity vibration isolation

The vibration environment onboard current and planned manned orbiters requires isolation for microgravity science experiments. The disturbance frequencies are sufficiently low and the attenuation requirements sufficiently great so as to preclude a passive isolation system. Described here is a design procedure, known as extended H2 synthesis, for active isolation system controllers currently being developed by the University of Virginia.

Hampton, R. David↗

NASA NTRS1991

Control issues of microgravity vibration isolation

Active vibration isolation systems contemplated for microgravity space experiments may be designed to reach given performance requirements in a variety of ways. An analogy to passive isolation systems proves to be illustrative but lacks the flexibility as a design tool of a control systems approach and may lead to poor design. Control theory as applied to vibration isolation is reviewed and passive analogies discussed.

Knospe, Carl R.↗

NASA NTRS1991

Microgravity vibration isolation: An optimal control law for the one-dimensional case

Certain experiments contemplated for space platforms must be isolated from the accelerations of the platform. An optimal active control is developed for microgravity vibration isolation, using constant state feedback gains (identical to those obtained from the Linear Quadratic Regulator (LQR) approach) along with constant feedforward gains. The quadratic cost function for this control algorithm effectively weights external accelerations of the platform disturbances by a factor proportional to (1/omega) exp 4. Low frequency accelerations are attenuated by greater than two orders of magnitude. The control relies on the absolute position and velocity feedback of the experiment and the absolute position and velocity feedforward of the platform, and generally derives the stability robustness characteristics guaranteed by the LQR approach to optimality. The method as derived is extendable to the case in which only the relative positions and velocities and the absolute accelerations of the experiment and space platform are available.

Hampton, Richard D.↗