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1.
This paper proposes a method for increasing capture range of a phase-locked loop (PLL). The behavior of PLL in the initial condition is nonlinear. This nonlinearity phenomenon is caused by phase detector (PD). A method using neural network as controller in PLL is proposed for overcoming this problem. In the proposed method, the reference frequency and frequency of VCO converted to voltage by FTV. Frequency tracking is achieved by neural network. The circuit has been fabricated in a standard 0.13 μm CMOS process. Simulation results show a tracking range of 110 MHz, and a capture range of 90 MHz while operating from a 2 V supply with maximum 2.18 mW power consumption.  相似文献   

2.
The acquisition of information and the search interaction process is influenced strongly by a person’s use of their knowledge of the domain and the task. In this paper we show that a user’s level of domain knowledge can be inferred from their interactive search behaviors without considering the content of queries or documents. A technique is presented to model a user’s information acquisition process during search using only measurements of eye movement patterns. In a user study (n = 40) of search in the domain of genomics, a representation of the participant’s domain knowledge was constructed using self-ratings of knowledge of genomics-related terms (n = 409). Cognitive effort features associated with reading eye movement patterns were calculated for each reading instance during the search tasks. The results show correlations between the cognitive effort due to reading and an individual’s level of domain knowledge. We construct exploratory regression models that suggest it is possible to build models that can make predictions of the user’s level of knowledge based on real-time measurements of eye movement patterns during a task session.  相似文献   

3.
In this paper, an iterative learning control strategy is presented for a class of nonlinear pure-feedback systems with initial state error using fuzzy logic system. The proposed control scheme utilizes fuzzy logic systems to learn the behavior of the unknown plant dynamics. Filtered signals are employed to circumvent algebraic loop problems encountered in the implementation of the existing controllers. Backstepping design technique is applied to deal with system dynamics. Based on the Lyapunov-like synthesis, we show that all signals in the closed-loop system remain bounded over a pre-specified time interval [0,T]. There even exist initial state errors, the norm of tracking error vector will asymptotically converge to a tunable residual set as iteration goes to infinity and the learning speed can be easily improved if the learning gain is large enough. A time-varying boundary layer is introduced to solve the problem of initial state error. A typical series is introduced in order to deal with the unknown bound of the approximation errors. Finally, two simulation examples show the feasibility and effectiveness of the approach.  相似文献   

4.
A procedure is presented whereby the control volume equations for one-dimensional, compressible gas dynamics are cast into first-order, state variable form. These equations are interpreted using causal bond graphs. The resulting bond graph is shown to reduce to the classic I-C chain under acoustic constraints and to a more recently developed model of low speed thermal energy transport subject to associated constraints.Through example it is demonstrated that the control volume bond graph is easily coupled to an overall system model and thus can be digitally simulated as part of the overall nonlinear state space representation. The result is that a very accurate gas dynamic model can be coupled with an overall dynamic system model without requiring a prohibitively large number of equations.  相似文献   

5.
In this paper, we investigate the problem of leaderless consensus control for the multiagent systems whose nonlinear dynamics satisfying incremental quadratic constraints. A distributed dynamic consensus protocol, decided by communication among neighboring agents, is presented to render nonlinear agent consensus with appropriate coupling weights. Next, an observer-based distributed protocol is considered to ensure consensus of nonlinear system without knowing full state information. Further, extensions to consensus strategies with nonlinear dynamics for the leader-following fashion are also addressed. By comparison to the traditional nonlinear consensus control methodologies, the proposed approach generalizes the Lipschitz nonlinearity as well as the combined nonlinearity of one-sided Lipschitz condition and quadratic inner-boundness condition towards a more generalized type of nonlinearity, which shows us a less conservative result in the Lyapunov proof. Finally, the numerical simulations for six agents are illustrated to show the feasibility and performance of the proposed control protocol with or without the presence of the observer.  相似文献   

6.
This paper discretizes the states, a method introduced in [18] for constant delayed systems, not only in constructing the Lyapunov-Krasovskii (L-K) functional but also in designing the integral inequality technique [17] and [19] for time-varying delayed systems, which increase the order of uncorrelated augmentation [5], [21] and [22]. Based on the discretized state, [10] and [27]'s piecewise analysis method is applied to confirm the system stability in whole delay bound. Asymmetric variation of the delay derivative is assumed so that direct extension to all constraints of the delay derivative can be achieved. Examples show the resulting criteria improve the allowable delay bounds over all existing ones in the literature.  相似文献   

7.
With the rapid evolution of the mobile environment, the demand for natural language applications on mobile devices is increasing. This paper proposes an automatic word spacing system, the first step module of natural language processing (NLP) for many languages with their own word spacing rules, that is designed for mobile devices with limited hardware resources. The proposed system uses two stages. In the first stage, it preliminarily corrects word spacing errors by using a modified hidden Markov model based on character unigrams. In the second stage, the proposed system re-corrects the miscorrected word spaces by using lexical rules based on character bigrams or longer combinations. By using this hybrid method, the proposed system improves the robustness against unknown word patterns, reduces memory usage, and increases accuracy. To evaluate the proposed system in a realistic mobile environment, we constructed a mobile-style colloquial corpus using a simple simulation method. In experiments with a commercial mobile phone, the proposed system showed good performances (a response time of 0.20 s per sentence, a memory usage of 2.04 MB, and an accuracy of 92–95%) in the various evaluation measures.  相似文献   

8.
This paper proposes an adaptive data-driven fault-tolerant control scheme using the Koopman operator for unknown dynamics subjected to nonlinearities, time-varying loss of effectiveness, and additive actuator faults. The main objective of this method is to design a virtual actuator to hide actuator faults from the view of the system’s nominal controller without having any prior knowledge about the system’s underlying dynamics. The designed virtual actuator is placed between the faulty plant and the nominal controller of the system to keep the dynamical system’s performance consistent before and after the occurrence of actuator faults. Based on the Koopman operator theory, an equivalent Koopman predictor is first obtained using the process data only, without knowing the governing equations of the underlying dynamics. Koopman operator is an infinite-dimensional, linear operator which takes the nonlinear process data into an infinite-dimensional feature space where the dynamic data correlations have linear behavior. Next, based on the approximated system’s Koopman operator, a virtual actuator is designed and implemented without knowing the system’s nominal controller. Needless to use a separate fault detection, isolation, and identification module to perform fault-tolerant control, the current method leverages the adaptive framework to keep the system’s desired performance in facing time-varying additive and loss of effectiveness actuator faults. Finally, the approach’s efficacy is demonstrated using simulation on a two-link manipulator benchmark, and a comparison study is presented.  相似文献   

9.
The notion of dominant designs refers to dominance in the market, hence the literature on dominant designs ignores the selection process that already takes place in pre-market R&D stages of technological innovation. In this paper we address the question to what extent pre-market selection takes place within an industry and how this may lead to dominance of one design over others before the market comes into play. Furthermore we study what selection criteria apply in the absence of actual market criteria. We do so through a historical analysis of design paths for hydrogen passenger cars.We argue that prototypes are used by firms in their internal search process towards new designs and at the same time as means of communicating technological expectations to competitors and outsiders. In both senses, prototypes can be taken as indicators of design paths in the ongoing search process of an industry.We analyzed the designs of prototypes of hydrogen passenger cars from the 1970s till 2008. A database is compiled of 224 prototypes of hydrogen passenger cars, listing the car's manufacturer, year of construction, hydrogen conversion technology, fuel cell type, and capacity of its hydrogen storage system. The analysis shows to what extent one design gained dominance and which strategies were adopted by the firms in their search processes.We conclude that indeed a dominant prototyping design has emerged: the fuel cell combined with high pressure gaseous storage. Actual and expected performance acted as selection criterion, but so did regulation and strategic behaviour of the firms. Especially imitation dynamics, with industry leaders and followers, is a major explanatory factor. Our main theoretical claim is that the selection of a dominant prototyping design is based on an interaction of sets of expectations about future performance of technological components and regulatory pressure that results in herding behaviour of the firms.  相似文献   

10.
This paper provides a quantitative study (N = 268) of patterns of free revealing of firm-developed innovations within embedded Linux, a type of open source software (OSS). I find that firms, without being obliged to do so, contribute many of their own developments back to public embedded Linux code, eliciting and indeed receiving informal development support from other firms. That is, they perform a part of their product development open to the public—an unthinkable idea for traditionally minded managers. Such openness obviously entails the challenge of protecting one's intellectual property. I find that firms address this issue by revealing selectively. They reveal, on average, about half of the code they have developed, while protecting the other half by various means. Revealing is strongly heterogeneous among firms. Multivariate analysis can partly explain this heterogeneity by firm characteristics and the firm's purpose behind revealing. An analysis of reasons for revealing and of the type of revealed code shows that different types of firms have different rationales for openness. Implications for management are that the conflict between downsides and benefits of openness appears manageable. Provided selective revealing is practiced deliberately, the opportunities of open development dominate.  相似文献   

11.
In this paper, a novel adaptive control scheme is investigated based on the backstepping design for a class of stochastic nonlinear systems with unmodeled dynamics and time-varying state delays. The radial basis function neural networks are used to approximate the unknown nonlinear functions obtained by using Ito differential formula and Young?s inequality. The unknown time-varying delays and the unmodeled dynamics are dealt with by constructing appropriate Lyapunov–Krasovskii functions and introducing available dynamic signal. It is proved that all signals in the closed-loop system are bounded in probability and the error signals are semi-globally uniformly ultimately bounded (SGUUB) in mean square or the sense of four-moment. Simulation results illustrate the effectiveness of the proposed design.  相似文献   

12.
Bond graph methods are used to derive a nonlinear model of a U-tube steam generator like those used in pressurized water reactor (PWR) power plants. A major advantage of bond graph modeling is the ease with which different subsystem models can be interconnected; this feature is demonstrated in the steam generator modeling. Individual models of primary water cooling, generator tube heat capacity, secondary and downcomer fluid mass and energy flows, the feedwater supply system, and the main steam control valve are developed. The complete bond graph model is validated using data from a test reactor steam generator.  相似文献   

13.
In this paper I present the architecture of system that can be used for real time exploration and management of large medical volumetric datasets. The new state of the art solution presented in this paper is an example of visual data management system. System prototype evaluation proved that it is possible to use low-powered (and cheap) up-to-date mobile devices with programmable GPUs as the remote interfaces for exploration of large volumetric medical data. The implementation was done with high-level programming language that enables portability between different hardware models. The lack of lossy compression enables to display high quality medical images visualizations without any simplifications and noises in frequency domain. The prototype of system is capable to remotely render and send to a client (for example cell phone or tablet) rendered data with frequency 30 fps with limited resolution during interaction. One second after the interaction is finished client machine receives full resolution image. The evaluation of the system was performed on volumetric computed tomography angiography image with approximate size 5123 voxels.  相似文献   

14.
This paper proposes a new scheme for ensuring data consistency in unstructured p2p networks where peers can subscribe to multiple content types (identified by labels) and are rapidly informed of content updates. The idea is based on using a static tree structure, the Cluster-K+ tree, that maintains most of the structural information about peers and labels. A label denotes a set of replicated or co-related data in the network. The Cluster-K+ tree provides efficient retrieval, addition, deletion and consistent updates of labels. Our proposed structure guarantees a short response search time of O(H + K), where H denotes the height of the tree and K the degree of an internal tree node. We present theoretical analytic bounds for the worst-case performance. To verify the bounds, we also present experimental results obtained from a network simulation. The results demonstrate that the actual performance of our system is significantly better than the theoretical bounds.  相似文献   

15.
A novel variable structure controller is investigated for satellite attitude control. This novel controller does not lead to a sliding mode, which avoids the chattering problem, making it suitable for practical implementation. Detailed formulation of the controller is presented along with analytical stability analysis for a second order system. The system having this nonlinear controller is homogeneous, which leads to a similar response at large and small deviations from the equilibrium. A procedure for tuning homogeneous controllers for all initial conditions is proposed. A detailed model of the satellite attitude dynamics, actuator dynamics, and delays in the system is utilized to optimize controller gains numerically. A comparative analysis shows the superiority of the proposed controller over a conventional PID controller in terms of better transients and lower energy consumption.  相似文献   

16.
An Antilock Braking System (ABS) is characterized by nonlinear dynamics, which render more difficult the design of a controller for high performance. The problem is even harder due to the uncertainties on the parameters appearing in its dynamics. In this paper, an ABS laboratory setup is considered, which mimics a quarter car model. A super–twisting controller is proposed to overcome the problem due to parameter uncertainties. This controller is designed in order to impose a reference value of the tire slip. Two cases are considered: in the first, nominal ABS parameters are used in the controller, whereas in the second the controller embeds an estimator of the tire–road friction coefficient, which is one of most critical parameters. The friction coefficient is estimated in finite–time by means of a high–order sliding mode differentiator. The original contributions of the paper are the real–time implementation of the super–twisting controller for the laboratory setup under study, and the use of a super–twisting estimator to provide a finite–time estimation of the friction coefficient between the tire and the road, along with a comparison with classical PI–like and super–twisting controllers, available in the literature. The ABS laboratory setup allows checking experimentally the performance of the proposed nonlinear dynamic controller, showing a considerable increase of the efficiency of the control system.  相似文献   

17.
The results of a human-in-the-loop experiment are used to investigate the control strategies that humans use to interact with nonlinear dynamic systems. Two groups of human subjects interact with a dynamic system and perform a command-following task. The first group interacts with a linear time-invariant (LTI) dynamic system. The second group interacts with a Wiener system, which consists of the same LTI dynamics cascaded with a static output nonlinearity. Both groups exhibit improved performance over the trials, but the average of the linear group’s performance is better on more than three-fourths of the trials. A new nonlinear subsystem identification algorithm is presented and used to identify the feedback and feedforward control strategies used by the subjects in both groups. The identification results for the linear group agree with prior studies suggesting that adaptive feedforward inversion is a primary control strategy used by humans for command-following tasks. The main results of this paper address an open question of whether a similar control strategy is used for nonlinear systems. The identification results for the nonlinear group suggest that those subjects also use adaptive feedforward inversion. However, the static output nonlinearity inhibits the human’s ability to approximate the inverse.  相似文献   

18.
In this paper, we consider the consensus problem of a class of heterogeneous multi-agent systems composed of the linear first-order and second-order integrator agents together with the nonlinear Euler–Lagrange (EL) agents. First, we propose a distributed consensus protocol under the assumption that the parameters of heterogeneous system are exactly known. Sufficient conditions for consensus are presented and the consensus protocol accounting for actuator saturation is developed. Then, by combining adaptive controller and PD controller together, we design a protocol for the heterogeneous system with unknown parameters (in the nonlinear EL dynamics). Based on graph theory, Lyapunov theory and Barbalat's Lemma, the stability of the controllers is proved. Simulation results are also provided to illustrate the effectiveness of the obtained results.  相似文献   

19.
This paper studies the problem of composite synchronization and learning of multiple coordinated robot manipulators subject to heterogeneous nonlinear uncertain dynamics under the leader-follower framework. A new two-layer distributed adaptive learning control scheme is proposed, which consists of the first-layer distributed cooperative estimator and the second-layer decentralized deterministic learning controller. The first layer aims to enable each robotic agent to estimate the leader’s information. The second layer is responsible for not only controlling each individual robotic agent to track over desired reference trajectory, but also accurately identifying/learning each robot’s nonlinear uncertain dynamics. Design and implementation of this two-layer distributed controller can be carried out in a fully-distributed manner, which do not require any global information including global connectivity of the communication network. The Lyapunov method is applied to rigorously analyze stability and parameter convergence of the resulting closed-loop system. Numerical simulations on a team of two-degree-of-freedom robot manipulators have been conducted to demonstrate the effectiveness of the proposed results.  相似文献   

20.
Accurate and effective state estimation is essential for nonlinear fractional system, since it can provide some vital operation information about the system. However, inevitably missing measurements and additive uncertainty in the gain will affect the performance of estimation result. Thus, in this paper, in order to deal with these problems, a novel robust extended fractional Kalman filter (REFKF) is developed for states estimation of nonlinear fractional system, by which the states can be estimated accurately even with missing measurements. Finally, simulation results are provided to demonstrate that the proposed method can achieve much better estimation performance than the conventional extended fractional Kalman filter (EFKF).  相似文献   

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