This paper describes an indoor stand for a computer-controlled model helicopter. This stand was built to verify modern multivariable controller algorithms in real-world tests rather than in simulations. A commercial r...
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This paper describes an indoor stand for a computer-controlled model helicopter. This stand was built to verify modern multivariable controller algorithms in real-world tests rather than in simulations. A commercial radio-controlled helicopter (not a scale model) is mounted on a mechanical structure allowing 6-degree of freedom flight conditions in a 2-m cube. The symmetrical geometry of the frame reduces its physical influence on the rotorcraft to be equivalent to a concentrated mass near the center of gravity. Including the dynamics of the driving motor and some unsteady aspects of the aerodynamics, an unstable 18th order mathematical model results. In addition, the radio controller causes a significant time delay. For this system, several control algorithms have been applied [channelwise proportional differential (PD) controller used for system identification, Linear Quadratic Gaussian/Loop Transfer Recovery (LQG/LTR) approaches, modal controller]. The quality of the test results and some aspects of design problems are described and compared in the second part of the paper.
Development of a feedback control law to follow an optimal path is presented concerning the deployment/retrieval phase of a subsatellite connected to the Shuttle through a tether. The optimal path to be tracked is obt...
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Development of a feedback control law to follow an optimal path is presented concerning the deployment/retrieval phase of a subsatellite connected to the Shuttle through a tether. The optimal path to be tracked is obtained numerically by solving a two-point boundary-value problem with inequality constraints on tether tension that is the control force, with fixed boundary conditions, and with an unspecified terminal time. The feedback control algorithm is designed using a Lyapunov function to asymptotically reduce the deviation of the actual trajectory from the optimal path. The Lyapunov function is defined to be positive definite and to be zero when the trajectory coincides simultaneously with the optimal path. The present method of control is simulated numerically, and the results show excellent controlled response of the tethered subsatellite system. A comparison of the present approach with the neighboring optimum feedback control is also presented and shows the superior performance of the tracking-type control using the Lyapunov function for large initial variations from the optimal path.
This paper presents a coherent methodology for robust controller synthesis for the Middeck Active control Experiment (MACE): a Shuttle program scheduled for flight on STS-67 in February 1995. The experiment has been d...
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This paper presents a coherent methodology for robust controller synthesis for the Middeck Active control Experiment (MACE): a Shuttle program scheduled for flight on STS-67 in February 1995. The experiment has been designed to investigate the extent to which the on-orbit behavior of a precision-controlled spacecraft can be predicted and controlled using analysis and ground testing prior to launch. A goal of the flight experiment is to demonstrate good payload pointing performance using active controllers designed based on the predicted structural dynamics. For systems with complicated control topologies and large model uncertainties, this requires a systematic control design methodology. The results from preliminary ground-based control experiments are used in this paper to present such st design technique and to illustrate how it can be applied to future flight experiments. This control design methodology is then used to develop controllers that obtain a 22 dB improvement in the performance metric on the current MACE hardware.
A three-channel active control system is applied to an operational turbofan engine to reduce tonal noise produced by both the fan and the high-pressure compressor. The control approach is the feedforward filtered-x le...
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A three-channel active control system is applied to an operational turbofan engine to reduce tonal noise produced by both the fan and the high-pressure compressor. The control approach is the feedforward filtered-x least-mean-square algorithm implemented on a digital signal processing board. Reference transducers mounted on the engine case provide blade passing and harmonics frequency information to the controller. Error information is provided by large area microphones placed in the acoustic far field. To minimize the error signal, the controller actuates loudspeakers mounted on the inlet to produce destructive interference. The sound pressure level of the fundamental tone of the fan was reduced using the three-channel controller by up to 16 dB over a +/- 30-deg angle about the engine axis. A single-channel controller could produce reduction over a +/- 15-deg angle. The experimental results show the control to be robust. Outside of the areas controlled, the levels of the tone actually increased due to the generation of radial modes by the control sources. Simultaneous control of two tones is achieved with parallel controllers. The fundamental and the first harmonic tones of the fan were controlled simultaneously with reductions of 12 and 5 dBA, respectively, measured on the engine axis. Simultaneous control was also demonstrated for the fan fundamental and the high-pressure compressor fundamental tones.
It has been experimentally verified that the jerk of the desired trajectory adversely affects the performance of the tracking control algorithms for robotic manipulators. In this paper, we investigate the reasons behi...
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It has been experimentally verified that the jerk of the desired trajectory adversely affects the performance of the tracking control algorithms for robotic manipulators. In this paper, we investigate the reasons behind this effect, and state the trajectory planning problem as an optimization problem that minimizes a norm of joint jerk over a prespecified Cartesian space trajectory. The necessary conditions are derived and a numerical algorithm is presented.
We have significantly simplified the IMC-PID tuning rules. These new rules cover the vast majority of control loops encountered in the chemical industry. This work is the result of a great deal of experience in succes...
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We have significantly simplified the IMC-PID tuning rules. These new rules cover the vast majority of control loops encountered in the chemical industry. This work is the result of a great deal of experience in successfully applying IMC-PID tuning rules and an effort to prepare a training course on controller tuning. The simplified rules are very similar in form to the classic open loop Ziegler-Nichols rules and use the process reaction curve method for process testing. The two differences are that these rules are based on a less aggressive performance criteria and that we adapt the rules for some commonly encountered special cases. This paper presents the relationship between the simplified IMC-PID rules, the general IMC-PID rules, the Ziegler-Nichols rules and the Cohen-Coon rules. We show that the simplified rules are less sensitive to parameter mis-estimation than other more aggressive tuning rules. We also proposed rules for a fourth action;filtering. Filtering is available in digital controllers and smart field transmitters. We report that filtering and derivative action cancel each other and therefore should not be used together. We briefly outline the contents of the tuning course and finish the paper with an industrial example where the simplified rules have been successfully applied.
Studies related to time-optimal attitude maneuvers, conducted over the past thirty years, are reviewed. Specific topics covered include flexibility effects, equations of motion, control and model development, rigid-bo...
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Studies related to time-optimal attitude maneuvers, conducted over the past thirty years, are reviewed. Specific topics covered include flexibility effects, equations of motion, control and model development, rigid-body solutions, flexible spacecraft, and specific configurations. The survey traces the development of time-optimal and near time-optimal control algorithms and includes many of the more recent advances in the field. (AIAA)
A rule-based fuzzy controller is presented and compared with an adaptive MIMO LQR controller in a low-Earth-orbit small satellite attitude control system. The attitude is passively gravity gradient stabilized and acti...
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A rule-based fuzzy controller is presented and compared with an adaptive MIMO LQR controller in a low-Earth-orbit small satellite attitude control system. The attitude is passively gravity gradient stabilized and actively three-axis magnetorquer controlled. This method insures an Earth-pointing satellite making use of a nondepletable and nonmechanical means of control. A realistic simulation environment, using a nonlinear satellite dynamic model with linear attitude estimators plus sensor measurement noise and external disturbance torques, was used to evaluate the different control techniques.
Active feedforward control algorithms have proven to be successful in the attenuation of stationary disturbances such as single frequency, multiple frequencies, and random inputs. In feedforward control the mean squar...
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Active feedforward control algorithms have proven to be successful in the attenuation of stationary disturbances such as single frequency, multiple frequencies, and random inputs. In feedforward control the mean square value of a measurable response quantity induced by the disturbance input is minimized by coherent ''secondary'' control inputs. The traditional design procedure is to choose the location/number of control forces and error sensors based on a physical understanding of the response of the uncontrolled and controlled systems. Thus, an analytical procedure for actuator and sensor design in feedforward controlled systems is nonexistent in contrast to feedback control where pole allocation, optimal control, etc., are extensively used. Recent analytical work has demonstrated that feedforward controlled systems have new eigenproperties. The controlled eigenvalues and eigenfunctions are only a function of the control input location and the error quantity to be minimized. Here, an eigenvalue assignment design methodology for feedforward controllers is presented, and it is based on designing an optimal error sensor such that the controlled system eigenvalues have predetermined values.
This article presents a two-dimensional axisymmetric combined conduction and radiation model for the prototype of the programmable multizone furnace, which is under design at NASA Lewis Research Center. The actual fur...
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This article presents a two-dimensional axisymmetric combined conduction and radiation model for the prototype of the programmable multizone furnace, which is under design at NASA Lewis Research Center. The actual furnace is intended for growing high-quality semiconductor crystals and performing other materials processing experiments in space. A novel feature of the model is a control algorithm that automatically adjusts the power in any number of independently controlled heaters to establish the desired sample temperatures during the numerical simulations. The control algorithm eliminates the need for numerous trial and error runs previously required to obtain the same results. The finite element code, FIDAP, was modified to directly incorporate the control algorithm. This algorithm, which presently uses proportional-integral-derivative (PID) control, and the associated heat transfer model are briefly discussed. Together, they have been used to predict the heater power distributions for a variety of furnace configurations and desired temperature profiles. Examples are included to demonstrate the effectiveness of the PID-controlled model in establishing isothermal, Bridgman, and other complicated temperature profiles in the sample. An example is also given to show how the algorithm can be used to change the desired profile with time according to a prescribed temperature-time evolution.
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