Active control of flexible multi-body systems and structures through utilization of smart materials is considered in this paper. Specifically, utilization of piezoceramics for sensing and actuation is investigated. Ex...
Active control of flexible multi-body systems and structures through utilization of smart materials is considered in this paper. Specifically, utilization of piezoceramics for sensing and actuation is investigated. Experimental setups have been developed at CRRL to study modeling issues and control design approaches for flexible structures with embedded (or surface-mounted) piezoceramics. In this paper, experimental results on vibration suppression for a flexible manipulator with surface mounted piezoceramics are presented. It will be shown that piezoceramics substantially improve the performance of the systems under consideration. The advocated approaches for control designs are decentralized frequency shaping and self-tuning adaptive controllers. The self-tuning controller is based on identification of the system dynamics in frequency domain utilizing Fast Fourier Transform (FFT). Addition of a self-tuning regulator enhances the performance and the robustness of the controlled system to parameter variations.
This paper deals with necessary conditions for integral and exponential-of-integral cost functions, when the signal is a controlled diffusion process, and the observations consist of continuous and discontinuous proce...
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This paper deals with necessary conditions for integral and exponential-of-integral cost functions, when the signal is a controlled diffusion process, and the observations consist of continuous and discontinuous processes. These problems are reformulated as infinite dimensional stochastic problems having full information, with state of the Zakai equation for the integral cost, and the information state for the exponential-of-integral cost. The approach is the one considered by Bensoussan (1992) for the case of integral cost with continuous observations.< >
This paper studies the ability of the exponentially weighted RLS algorithm to track a doppler shifted BPSK communications signal. This is modeled as a chirped AR1 process in Gaussian white noise. Expressions for the o...
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This paper outlines some preliminary work on the stability analysis of switched and hybrid systems. The hybrid systems considered are those that combine continuous dynamics, represented by differential or difference e...
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This paper outlines some preliminary work on the stability analysis of switched and hybrid systems. The hybrid systems considered are those that combine continuous dynamics, represented by differential or difference equations, with finite dynamics usually thought of as being a finite automaton. Here, we concentrate on the continuous dynamics and model the finite dynamics as switching among finitely many continuous systems. We introduce multiple Lyapunov functions as a tool for analyzing Lyapunov stability of such "switched systems". We use iterated function systems theory as a tool for Lagrange stability. We also discuss the case where the switched systems are indexed by an arbitrary compact set.< >
The problem of control design for robotic arms manipulating unknown flexible payloads is considered. control design based on neglecting the internal dynamics of the payload will result in degraded performance, increas...
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The problem of control design for robotic arms manipulating unknown flexible payloads is considered. control design based on neglecting the internal dynamics of the payload will result in degraded performance, increased task execution time, and even failure in performing tasks. At the same time, the characteristics of payloads to be handled vary with application. These considerations make it impractical to outfit the payload with sensors. A novel scheme utilizing a force/torque sensor at the wrist of the manipulator is introduced. A controller utilizing the wrist torque feedback from the sensor is designed as a function of parameters of the payload dynamics. An adaptive scheme for online identification of these parameters and adaptation of controller parameters is discussed. The scheme is implemented on a single-link manipulator carrying a flexible unknown payload. Experimental results validate the fact that the adaptive control maintains a robust performance for high speed slewing and varying payloads.< >
A code division multiple access detector that employs a combination of a decorrelator and a multidimensional interference canceler is considered. The weights of the canceler are adaptively controlled using a steepest ...
A code division multiple access detector that employs a combination of a decorrelator and a multidimensional interference canceler is considered. The weights of the canceler are adaptively controlled using a steepest descent algorithm. The probability of error is evaluated and compared to those of the decorrelating detector and a similar, fixed-weights scheme that requires an estimation of received signal energies. It is shown that the proposed two-stage detector provides substantial improvement over the decorrelating detector, particularly in the presence of strong interfering signals. This is especially noticeable in the high bandwidth efficiency cases. It is also observed that in the presence of weak interferers, the proposed scheme performs better than its fixed-weights counterpart.
A code division multiple access detector that employs a combination of a correlation detector and a multiuser adaptive interference canceler was previously proposed by the authors. The weights of the canceler are adap...
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A code division multiple access detector that employs a combination of a correlation detector and a multiuser adaptive interference canceler was previously proposed by the authors. The weights of the canceler are adaptively controlled by the steepest descent algorithm using the minimum power criterion of the canceler outputs. It was shown that such a canceler substantially outperforms the decorrelating detector and has almost the same error probability as a canceler that uses reliable estimates of the received signal energies. In this paper, a different weight control criterion based on minimizing the correlation between the signals at the outputs of the canceler is used, and its performance is compared to that obtained with the minimum power criterion. It is shown that both cancelers have almost the same performance, particularly when SNR is modestly high. Although it is not shown in this paper, we believe that minimizing correlation rather than power outputs is a more suitable criterion when dealing with highly dispersive channels.< >
The fidelity of a signal formed by the sequence of recalling stored digital samples from a look-up table and then converting these sample amplitudes to a waveform in a digital-to-analog converter (DAC) is affected by ...
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The fidelity of a signal formed by the sequence of recalling stored digital samples from a look-up table and then converting these sample amplitudes to a waveform in a digital-to-analog converter (DAC) is affected by the time and amplitude quantization of the process. The size of the look-up table, hence the number of bits in the addressing scheme, affects the signal's time resolution and results in time-base jitter while the number of bits in the DAC affects amplitude quantization. These errors can be reduced by using noise feedback to spectrally shape the quantization noise formed by the table's address generator and of the quantization noise of the sample values presented to the DAC.< >
The paper describes an asynchronous, network based algorithm to enforce integrity control on top of active objects. It proposes that the control of each active object be expressed as production rules, and the producti...
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The paper describes an asynchronous, network based algorithm to enforce integrity control on top of active objects. It proposes that the control of each active object be expressed as production rules, and the production rules associated with the objects be compiled into a network so that they can be evaluated collectively using databased operations. To maintain correctness and exploit all possible parallelism, each token is time stamped and can be processed asynchronously. To handle rollbacks, a lazy cancellation approach is used. It is shown that, in most cases, the performance of the network approach is superior to that of the fully distributed object oriented approach.
This paper introduces a fuzzy neural based adaptive controller for simultaneous stabilization and robust performance of a family of plants. The family of plants may be attained from linearization of a nonlinear plant ...
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This paper introduces a fuzzy neural based adaptive controller for simultaneous stabilization and robust performance of a family of plants. The family of plants may be attained from linearization of a nonlinear plant around different operating points or large parameter variations in a given plant. The main idea is to design a sequence of controllers corresponding to the different plants utilizing any standard control design. Thereafter, the obtained controllers will form the basis of the knowledge base of a fuzzy controller capable of deriving a desired crisp output through its inference engine. A neural network is utilized to derive a fuzzy model of the plant and to generate the rule base for the fuzzy logic controller through training. The effectiveness of this new scheme is verified on a smart structure with piezoceramic sensors and actuators.
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