摘要:

One of the principal reasons that noisy measurements in the robot forward dynamics problem have not been analysed is the lack of an appropriate model. A dynamics formulation introduced by Rodriguez, J. R. (1981,I.E.E.E. J. Robotics Autom.,3, 30) and extended by Ko, K. S., and Read, R. K. (unpublished) provides a suitable framework for investigating the class of spatially distributed noise sources. The resulting solution of the forward dynamics problem has the form of a Kalman filter with smoothing for a spatially distributed system. Two measurement noise models are investigated: the uncorrelated white gaussian model and the correlated first-order markovian models. A modified Kalman filter solution is obtained in each case. Simulation experiments demonstrate the improvement in system response.

ISSN:0020-7721    

DOI:10.1080/00207729308949498

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Complex developmental systems are constructed, the different parts of which develop simultaneously due to parallel programming of their respective developments.

ISSN:0020-7721    

DOI:10.1080/00207729308949499

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

In distributed discrete event simulation, accelerating the simulation time by accelerating or warping time is a means of speeding up the execution time of the simulation. One method of accelerating time is the time warp or virtual time methodology, where processors advance their local clocks at will, communicating with other processors using messages. A processor must rollback to recover when inconsistent or unsafe states occur, using antimessages. Problems associated with accelerating time in a distributed simulation include large buffer spaces for saving state information, and the potential for ripple effects, which occur when one rollback triggers others. In addition, simulations that must produce irrevocable actions cannot allow a rollback to occur that nullifies the action. This research presents a methodology for synchronizing event-driven simulations in a distributed environment where processors can be arranged into a logical token ring. This methodology, known as event jumping, prevents non-local rollbacks and reduces the amount of buffer space used for state saves. This paper also shows the results of implementing this algorithm using both a network simulator and an actual distributed environment.

ISSN:0020-7721    

DOI:10.1080/00207729308949500

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Based on Lyapunov stability theory associated with transformation techniques, theD-stability robustness problem is first discussed for discrete large-scale systems subjected to interconnections and perturbations. Three classes of perturbation are treated: (1) unstructured parametric perturbations; (2) highly structured parametric perturbations; and (3) nonlinear perturbations. If all the eigenvalues of each nominal subsystem are located inside the specified discs Di(∝i, ri), respectively, sufficient conditions forD-stability are presented to guarantee that all the eigenvalues of each perturbed subsystem remain inside the same discs. Furthermore, the proposedD-stability criteria ensure that the whole discrete large-scale system isD-stable irrespective of perturbations and interconnections if the eigenvalues of each nominal subsystem lie within the same diskD(∝,r). By these conditions, the allowable perturbation bounds that ensure theD-stability of discrete large-scale perturbed system can be estimated. Finally, numerical examples are given for illustration.

ISSN:0020-7721    

DOI:10.1080/00207729308949501

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A decentralized model-based control method for stabilization and tracking control of a class of large-scale interconnected nonlinear uncertain systems is proposed, following a generalized model-based control approach for robot manipulator control. The subsystem interconnections satisfy the ‘matching conditions’, and may be nonlinear and uncertain. Three controllers are derived, with a built-in trade-off between simplicity of implementation on the one hand and accuracy of tracking/stabilization on the other. In the independent servo control method, the subsystem interactions are treated as disturbances, so possibly large gains are required under purely local feedback. In the offline feedforward compensation method, feedforward compensation is applied for nominal interactions, so much lower local feedback gains are required. In the online feedforward compensation method, the compensation is made online, improving closed loop system performance further. Local bounded stability of the interconnected system under the proposed controllers is shown. Simulation results are presented to illustrate the effectiveness of the proposed method.

ISSN:0020-7721    

DOI:10.1080/00207729308949502

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The objective of this study is to explore the consequences of market power for optimal stockholding and price variations in the world coffee economy. Optimal storage decision rules which incorporate risk aversion under several market scenarios are considered. These generate a set of price and quantity series that can be compared with the historical data and to test the hypothesis proposed by Newbery that a monopolistic producer tends to undertake more storage than a competitive producer and hence price stability may increase in proportion to the dominant role played by the monopolist. Our study reveals that the world coffee market has been rather close to the competitive regime since the 1960s. As far as price variations are concerned, results are not always consistent with the Newbery hypothesis.

ISSN:0020-7721    

DOI:10.1080/00207729308949503

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Frequently manufacturers of industrial products sold through a channel of distribution maintain large finished goods inventories. On the average, these inventories amount to 23% of a firm's current assets. The situation can also be expressed as an average one month supply of product available for sale. This may understate the problem. Some firms have as much as 52% of their current assets invested in finished goods inventory. In the firm studied here, the average inventory was 37% of current assets and a related three months of supply. But some items had as many as several hundred months of supply. But some items had as many as several hundred months worth of inventory on hand. The research reported here hypothesizes two structural equation models in order more clearly to understand the causes of finished goods inventory imbalances. The model is tested and coefficients are estimated based on actual conditions prevailing at a large Fortune 500 firm.

ISSN:0020-7721    

DOI:10.1080/00207729308949504

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Liveness is one of the most important properties of the Petri net analysis. This property is concerned with a capability for firing of transitions. On the other hand, place-liveness is another notion related to liveness, which is concerned with a capability for having tokens in places. Concerning these liveness and place-liveness problems, this paper suggests a new subclass of Petri net, ‘POC nets’, as a superclass of AC nets and DC nets. For this subclass, the equivalence between liveness and place-liveness is shown and a sufficient condition for liveness for this POC net is derived. Then the results are extended to liveness problem of timed Petri nets which have transitions with finite firing durations and the earliest firing rule. Although liveness of a (non-timed) Petri net is neither necessary nor sufficient condition for liveness of a timed Petri net, it is shown that liveness is preserved if the net has POC structure. Furthermore, it is pointed out that if a POC net satisfies some additional condition, Petri net liveness is equivalent to timed Petri net liveness. Finally, it is shown that liveness of timed POC nets with TC structure and the earliest firing rule is decidable with deterministic polynomial time complexity.

ISSN:0020-7721    

DOI:10.1080/00207729308949505

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A model suitable for evaluating the performance of n-unit priority standby systems is developed. The modelling approach is fairly general and applies to most commonly used priority strategies including pre-emption. The results are employed to develop a profit analysis as a measure of system performance. An example system operating under a particular pre-emptive priority strategy is treated so as to demonstrate the modelling approach.

ISSN:0020-7721    

DOI:10.1080/00207729308949506

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The fuel-optimal control problem in aeroassisted non-coplanar orbital transfer is addressed. The equations of motion for the atmospheric manoeuvre are non-linear and the optimal )nominal) trajectory and control are obtained. In order to follow the nominal trajectory under actual conditions, a neighbouring optimum guidance scheme is designed using linear quadratic regulator theory for onboard real-time implementation. One of the state variables is used as the independent variable in preference to the time. The weighting matrices in the performance index are chosen by a combination of a heuristic method and an optimal modal approach. The necessary feedback control law is obtained in order to minimize the deviations from the nominal conditons. The results are presented to a typical aeroassisted non-coplanar orbital transfer problem.

ISSN:0020-7721    

DOI:10.1080/00207729308949507

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor