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Control Systems, IEEE

Issue 3 • Date April 1991

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Displaying Results 1 - 10 of 10
  • Real-time monitoring and control in plasma etching

    Page(s): 3 - 10
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (631 KB)  

    Process control strategies have been developed for plasma etching of silicon (Si) and silicon dioxide (SiO/sub 2/) in a CF/sub 4//O/sub 2/ plasma. The analysis considered four measured variables, four manipulated variables, and up to seven performance variables. Empirical input-output models were developed by regression analysis. Relative gain array analysis and singular value decomposition were used to select manipulated/process variable control loop pairings and to evaluate potential difficulties in control system performance. Singular value decomposition was also used to determine process/performance variable pairings. Block relative gain analysis of multivariable interactions in the process indicated that partial decoupling was necessary for adequate control, and this was verified by simulation.<> View full abstract»

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  • Time optimal contour tracking for machine tool controllers

    Page(s): 11 - 17
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (500 KB)  

    A decomposition procedure was used to optimize feedrate and voltage control of biaxial contouring systems. The optimization procedure takes into account the contour-error, voltage, and current constraints while tracking the contour in minimum time. The tracking time is first minimized with respect to the feedrate profile using a nominal linear-quadratic-regulator type of controller. Using the feedrate profile obtained, the controller is tuned by minimizing a certain objective function with respect to the Q and R weighting matrices. The process is repeated until no further improvements can be obtained in tracking time. The use of iterative decomposition avoids mismatch in sensitivity since the feedrate profile has significant effects on the constraints and tracking time, while the weighting matrices have significant effects only, on the constraints. The procedure was tested and evaluated using a model of a representative biaxial DC motor system.<> View full abstract»

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  • An expert system to perform on-line controller tuning

    Page(s): 18 - 23
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (498 KB)  

    An expert system that tunes a proportional-integral-derivative (PID) controller online for a single-input-single-output multiple-lag process with dead time is described. The expert system examines features of each transient response and the corresponding controller parameters. It determines a new set of controller gains to obtain a more desirable time response. This technique can be used to determine and implement a different set of PID gains for each operating regime, and once in steady state, the system can be used to find optimal parameters for load disturbance rejection. The expert system can be applied to any system of the specified form (aerospace, industrial, etc.) and can be expanded to include additional process models.<> View full abstract»

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  • Control of a six-degree-of-freedom flexible industrial manipulator

    Page(s): 24 - 30
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (511 KB)  

    A controller design is proposed for manipulators modeled with joint and link compliances. First, nonlinear feedforward and PID state feedback components are used in the controller, and manipulator dynamics are converted into error-driven system dynamic equations. Then, the error-driven dynamic equations are stabilized using the second method of Lyapunov. The special structure of the Lyapunov matrix equation is exploited, and an explicit solution to this equation is presented. The analysis shows that controller performance can be enhanced through the modulation of this solution. The controller was numerically implemented on the model of a six-degree-of-freedom Cincinnati Milacron T3-776: industrial manipulator that is modeled with three joint and four link flexibilities. The simulations show satisfactory path tracking and oscillation rejection properties.<> View full abstract»

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  • Radial basis function networks for classifying process faults

    Page(s): 31 - 38
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (720 KB)  

    It is shown that under certain conditions the backpropagation network classifier can produce nonintuitive, nonrobust decision surfaces. These result from the inherent nature of the sigmoid transfer function, the definition of the training set, and the error function used for training. The backpropagation network has no mechanism in the standard training scheme for identifying regions not in any known classes. The radial basis function network overcomes these difficulties by using a nonmonotonic transfer function based on the Gaussian density function. While producing robust decision surfaces, the radial basis function also provides an estimate of how close a test case is to the original training data, allowing the classifier to signal that a test case potentially represents a novel class while still presenting the most plausible classification. For applications where this type of behavior is important, such as fault diagnosis, the radial basis function network is shown to offer clear advantages over the backpropagation network. The radial basis function is also faster to train because the training of the two layers is decoupled.<> View full abstract»

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  • Nonlinear adaptive control of a twin lift helicopter system

    Page(s): 39 - 45
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (467 KB)  

    The tracking control of a twin-lift helicopter system in the presence of parametric uncertainty is considered. A nonlinear model is used to describe the dynamics of a twin-lift helicopter configuration in the lateral/vertical plane, and a controller is synthesized using an input-output feedback linearization technique in conjunction with an adaptation algorithm. The control scheme does not require any knowledge of the bound of uncertainties present and drives the output tracking error to zero asymptotically. The performance of the controller is illustrated by simulating the nonlinear model of the twin-lift system.<> View full abstract»

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  • Precision pointing control for an orbital Earth observing system

    Page(s): 46 - 52
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (570 KB)  

    The design concept developed for the pointing system of the High-Resolution Imaging Spectrometer (HIRIS) which will be flown on one of NASA's Earth observing system platforms is presented. The instrument is an F 5.4-aperture spectrometer with a focal length of 1222 mm, and it uses a precision two-axis gimballed mirror pointing system to image and track targets. Pointing accuracy of better than 585 arcsec (peak-to-peak), and pointing jitter of less than 2.65 arcsec in 33 ms are ensured through the use of gimbal position and basebody rate sensors. A state-space controller implemented with a digital computer is used to provide a position loop bandwidth of 1 Hz and a rate loop bandwidth of 7 Hz. An overview of the system design and flight hardware is given, the development of the controller architecture is addressed, and a simulation assessment of the pointing system that takes into consideration issues such as nonlinear effects, sensor noise, and noncollocated sensors and actuators in a flexible structure is discussed.<> View full abstract»

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  • An expert system for automated highway driving

    Page(s): 53 - 61
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1435 KB)  

    The applicability of expert systems to the task of guiding an automobile on a limited-access highway is studied. The vehicle is assumed to be equipped with sensors detecting the surrounding traffic, road signs, and road geometry as well as control logic and actuators governing the throttle, steering angle, and brakes. The goal of the expert system is to issue commands to the controllers, given the traffic situation, traffic signals, road signs, and the strategy chosen by the driver. The system presented consists of a rule base providing the required driving knowledge, a backward chaining inference engine that performs the reasoning, a knowledge-base compiler that optimizes the reasoning process, and a highway-traffic simulator that simulates vehicles on a highway, either controlled by a preset strategy or by instance of the expert system. The implementation and the testing environment, including the highway traffic simulator and simulation results, is described. The benefits associated with the use of the system are summarized.<> View full abstract»

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  • Robust decentralized control laws for the ACES structure

    Page(s): 62 - 70
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (665 KB)  

    Control system design for the Active Control Technique Evaluation for Spacecraft (ACES) structure at NASA Marshall Space Flight Center is discussed. The primary objective of this experiment is to design controllers that provide substantial reduction of the line-of-sight pointing errors. Satisfaction of this objective requires the controllers to attenuate beam vibration significantly. The primary method chosen for control design is the optimal projection approach for uncertain systems (OPUS). The OPUS design process allows the simultaneous tradeoff of five fundamental issues in control design: actuator sizing, sensor accuracy, controller order, robustness and system performance. A brief description of the basic ACES configuration is given. The development of the models used for control design and control design for eight system loops that were selected by analysis of test data collected from the structure are discussed. Experimental results showing that very significant performance improvement is achieved when all eight feedback loops are closed are presented.<> View full abstract»

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  • Active vibration control using fixed order dynamic compensation with frequency shaped cost functionals

    Page(s): 71 - 78
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (564 KB)  

    An approach for the design of controllers for active suppression of helicopter vibration that combines recent developments in the design of fixed-order dynamic compensators with the frequency-shaped cost functional approach is presented. A robust compensator that provides loop shaping at the plant input is used in conjunction with frequency-shaped cost functionals to arrive at a controller for vibration reduction. The effectiveness of this technique is demonstrated by a detailed case study for the design of an active vibration controller.<> View full abstract»

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