Maximum Sampling Time Research Articles

Asynchronous sampled-data control for connected vehicles with heterogeneous delays

This study investigates an asynchronous sampled-data control problem of vehicular platoons, with heterogeneous sampling, subjected to actuator delays. Without a synchronized clock, a completely asynchronous sampled-data controller is designed for each follower, where the state of the ith follower itself and its neighboring vehicles are sampled at their own sampling time instants. The caused closed-loop tracking error dynamics for the entire platoon considering the effect of the nonuniform sampling time intervals, heterogeneous vehicle dynamics, inter-vehicle topology and heterogeneous time delays. To simplify the stability analysis and controller design, the tracking-error dynamics of the entire platoon are decomposed into individual subsystems with reduced-order dynamics. Based on Lyapunov stability theory, the optimal conditions are explored to design an asynchronous sampled-data controller to guarantee the desired stability performance. Moreover, the exact values for the maximum allowable sampling interval and time delay are calculated for each follower using the designed feedback controller gain. The proposed asynchronous sampled-data control method is extended to a vehicular platoon using an event-based sampling scheme. Numerical examples are used to verify the effectiveness of the proposed sampled-data control method.

Consensus of double integrator multiagent systems under nonuniform sampling and changing topology

<abstract><p>This article considers a consensus problem of multiagent systems with double integrator dynamics under nonuniform sampling. In the considered problem, the maximum sampling time can be selected arbitrarily. Moreover, the communication graph can change to any possible topology as long as its associated graph Laplacian has eigenvalues in an arbitrarily selected region. Existence of a controller that ensures consensus in this setting is shown when the changing topology graphs are undirected and have a spanning tree. Also, explicit bounds for controller parameters are given. A sufficient condition is given to solve the consensus problem based on making the closed loop system matrix a contraction using a particular coordinate system for general linear dynamics. It is shown that the given condition immediately generalizes to changing topology in the case of undirected topology graphs. This condition is applied to double integrator dynamics to obtain explicit bounds on the controller.</p></abstract>

A modified sampling plan by variables with an adjustable mechanism for lot sentencing

Acceptance sampling has been used as a method of determining if submitted product lots meet required quality standards. Recently, several sampling plans with different strategies have been developed to tackle various types of situations and requirements, and to increase their performance and efficiency. In particular, repetitive group sampling plan (RGSP) has been proposed and proven to be an efficient sampling scheme. However, it has its drawbacks that occur when the sampling is repeated until the lot can be successfully determined as either accepted or rejected; in theory, the number of sampling times might be infinite. Therefore, this paper proposes a modified version of variables RGSP (VRGSP) with an adjustable mechanism for lot sentencing (Adj-VRGSP), i.e., by setting a maximum allowable sampling time. The operating characteristic (OC) and average sample number (ASN) functions of the proposed plan are derived along with the step-by-step operating procedure. The determination of plan parameters is formulated as an optimization model with nonlinear constraints related to quality and risk requirements. Additionally, the performance of the proposed plan is examined, discussed, and compared with that of the conventional sampling plans. An application is also presented as an example illustrating the effectiveness of the proposed plan.

Time-dependent gas distribution modelling

Artificial olfaction can help to address pressing environmental problems due to unwanted gas emissions. Sensor networks and mobile robots equipped with gas sensors can be used for e.g. air pollution monitoring. Key in this context is the ability to derive truthful models of gas distribution from a set of sparse measurements. Most statistical gas distribution modelling methods assume that gas dispersion is a time-constant random process. While this assumption approximately holds in some situations, it is necessary to model variations over time in order to enable applications of gas distribution modelling in a wider range of realistic scenarios. Time-invariant approaches cannot model well evolving gas plumes, for example, or major changes in gas dispersion due to a sudden change of the environmental conditions. This paper presents two approaches to gas distribution modelling, which introduce a time-dependency and a relation to a time-scale in generating the gas distribution model either by sub-sampling or by introducing a recency weight that relates measurement and prediction time. We evaluated these approaches in experiments performed in two real environments as well as on several simulated experiments. As expected, the comparison of different sub-sampling strategies revealed that more recent measurements are more informative to derive an estimate of the current gas distribution as long as a sufficient spatial coverage is given. Next, we compared a time-dependent gas distribution modelling approach (TD Kernel DM+V), which includes a recency weight, to the state-of-the-art gas distribution modelling approach (Kernel DM+V), which does not consider sampling times. The results indicate a consistent improvement in the prediction of unseen measurements, particularly in dynamic scenarios. Furthermore, this paper discusses the impact of meta-parameters in model selection and compares the performance of time-dependent GDM in different plume conditions. Finally, we investigated how to set the target time for which the model is created. The results indicate that TD Kernel DM+V performs best when the target time is set to the maximum sampling time in the test set.

Design of Precise Synchrone Mechanism in Multiaxial Laser Measurement

Precision measurement is the premise of precision motion control. When a worktable is operating, the synchronization of multiaxial sampling will directly affect the precision of table position conversion. In this paper, a precise synchrone mechanism for multiaxial laser measurement was proposed. Tests showed that the maximum synchronous sampling time error from 6 laser axes was 0.404 ns. When the table was moving at 1 m/s, the induced maximum displacement conversion error was 0.202 nm, which satisfied the strict nanometer-scale requirement imposed by ultra-precise motion control for position measurement.

Continuous adaptive observer for state affine sampled‐data systems

SUMMARYIn this paper, a hybrid adaptive observer is designed for a class of nonlinear sampled‐data systems with constant unknown parameters. The proposed observer uses a predictor of the output between the sampling times. This predictor is re‐initialized at each sampling time. This observer is very simple to implement and converges exponentially under some sufficient conditions. An explicit relation between the bound of the maximum allowable sampling time (τMASP) and the parameters of the observer is also given. Copyright © 2012 John Wiley & Sons, Ltd.

정상 에르고드성을 가지는 확률과정 스펙트럼에 대한 합리적 시계열 데이터 확보

The fatigue damages in structural details of offshore plants can be accumulated due to various environmental loadings such as swell, wave, wind and current. It is known that load histories acting on mooring and riser systems show stationary and ergodic bimodal wide-banded process. This paper provides refined approach to obtain time signals representing stress range histories from wide-banded bimodal spectrum which consists of ideally narrow-banded and fully separated two spectrums. Variations of the probabilistic characteristics for time signals according to frequency and sampling time increments are compared with the reference data to be the probabilistic characteristics such as zero-crossing period, peak period, and irregularity factor obtained from an assumed ideal spectrum. It is proved that the sampling time increment more affects on the probabilistic characteristics than frequency increment. The fatigue damages according to the frequency and sampling time increments are also compared with the ones with minimum increment condition which are thought to be exact fatigue damage. It is concluded that the maximum sampling time increment to obtain reliable time signals should be determined that ratio of applied maximum sampling time increment and minimum period is less than approximately 0.08.

Adopting a Robotic pH Instrument for Soil and Soil-Buffer pH Measurements in a Soil Test Laboratory

Optimum software settings were evaluated to minimize time of analysis without sacrificing data quality on an AS-3010D LabFit robotic instrument. There was little to no difference between soil and soil-buffer pH values measured via manual methods and LabFit analysis with four software settings. A setting for routine laboratory analysis was determined by evaluating r2 values from a comparison of LabFit versus manual measurements. Settings for routine analysis were adopted as follows: 5 s for sample delay time, 60 s for maximum sample time, 10 readings for stability, 0.02 for pH stability, 0 s for buffer run delay, and probe rinsing after every 40 samples. These settings were evaluated on 2933 Kentucky soil samples where robotic versus routine analysis of soil and soil-buffer pH resulted in r2 values of 0.94 and 0.82 for soil pH and soil-buffer pH, respectively. The results validated the utility of robotic instruments for soil pH analysis.

Asynchronous networked control of linear systems via L 2 -gain-based transformations: analysis and synthesis

This study presents a method to analyse the stability of the feedback interconnection of a class of systems, when the signals associated with the feedback interconnection are sampled asynchronously. A transformation based on L2-gain is designed and introduced on both sides of the interconnection. This transformation enlarges the maximum sampling time such that the interconnection remains stable. The transformation is designed in such a way that both systems have finite L2-gain and verifies the small-gain theorem. This design method makes easier the migration of wired continuous-time control loops to unwired asynchronous ones by just adding this transformation to both sides of the interconnection. The analysis is performed by using the concept of maximum sampling time that preserves small gain (MASG), starting from the continuous-time definition of the property. Finally, a synthesis method is included to obtain the transformation, assuming that the minimum sampling time available in the communication channel is given as a constraint. The synthesis method follows an iterative procedure and solves a set of matrix inequalities. We report on real experiments applied to the remote control of the rotor speeds of a quadrotor.

Defining the sampling space in multidimensional NMR experiments: What should the maximum sampling time be?

Efficient sampling of signals is a key issue for multiple-dimensional NMR experiments to establish the best ratio between experiment time and spectral quality. Focussing on the most widely used sampling strategy using standard rectangular sampling and data analysis by Fourier transformation, a central question is concerned with determining the optimal maximum sampling time in the individual dimensions. The spectral resolution depends directly on this choice, as do the overall experiment times when addressing the indirect dimensions. We present a theoretical, numerical, and experimental analysis of the sampling space problem and propose approaches to efficient sampling for typical cases.

Passivity of Interconnected Asynchronous Discrete-Time Systems

This paper presents a constructive algorithm to design local controllers for feedback systems that are interconnected via time-varying and asynchronous sampling. These systems result in many application fields such as remotely-operated systems, interconnected vehicle control loops, and more generally in component-based control design where synchronous exchange of information is not feasible. The design is based on the (MASP) MAximum Sampling time preserving Passivity, and uses discrete-time passivity considerations. The paper first explores several ways to compute the MASP for linear systems, and then proposes a numerical algorithm to compute local feedback loops providing a MASP compatible with the maximum sampling-time upperbound of each sub-system. This results in a exponentially stable interconnection. The paper also presents a simulation example of this design.

Measurement of airborne cyanoacrylates

The behaviour of common alkyl-2-cyanoacrylates in air has been investigated. Increasing humidity was found to increase the rate of polymerisation, although polymerisation is not instantaneous, even at high humidities. Sampling methods for these compounds have been studied and we are able to recommend a pumped Tenax sampling tube, although certain sampling limitations apply, notably that specified flow rates must be applied and that a maximum sampling time of four hours is recommended. Significant errors can occur if sampling is performed outside the range of conditions specified. Upon completion of sampling the tube is desorbed into 0.2% phosphoric acid in acetonitrile. The resulting solution is analysed by HPLC.

Measurement of Airborne Cyanoacrylates

The behaviour of common alkyl-2-cyanoacrylates in air has been investigated. Increasing humidity was found to increase the rate of polymerisation, although polymerisation is not instantaneous, even at high humidities. Sampling methods for these compounds have been studied and we are able to recommend a pumped Tenax sampling tube, although certain sampling limitations apply, notably that specified flow rates must be applied and that a maximum sampling time of four hours is recommended. Significant errors can occur if sampling is performed outside the range of conditions specified. Upon completion of sampling the tube is desorbed into 0.2% phosphoric acid in acetonitrile. The resulting solution is analysed by HPLC. Crown Copyright © 1998 Published by Elsevier Science Ltd on behalf of British Occupational Hygiene Society

Effect of Sampling Time on the Collection Efficiency of All-Glass Impingers

The changes in the physical collection efficiencies of all-glass impingers were studied experimentally with an aerodynamic particle sizer by dynamically measuring the particle concentrations upstream and downstream of AGI-4 and AGI-30 impingers. Monodisperse PSL particles of aerodynamic sizes ranging from 0.3 to 2.0 μm were used in the tests. The inner diameter of the impingement nozzle was found to be the most critical dimension affecting the collection efficiency. Significant variations were found in the performance of individual impingers due to the variations in the critical dimensions of the impingers tested. About 1% of the initial amount of impinger liquid is evaporated per minute of normal operation. On depletion to a critical minimum volume, the collection efficiency decreases drastically due to insufficient impingement into the liquid and particle bounce from the bottom surface. Particles already collected may be entrained by the air bubbles passing through the liquid and be reaerosolized, thus decreasing the overall collection efficiency. The number of reaerosolized particles increases with sampling time, but is less than 10% within the first hour of sampling with either the AGI-4 or the AGI-30. A graph has been developed for selecting the maximum sampling time for a given initial liquid volume so that the collection efficiency is approximately constant throughout the entire sampling period. The graph also indicates the limits where significant particle bounce, reaerosolization, or liquid splashing occur. The AGI-4 was found to be more efficient in collecting submicrometer particles and to be less particle-size dependent than the AGI-30.

Sampling-time effects of higher-order digitisations and their applications in digital redesign

A study is made of the sampling-time effects of higher-order digitisations (i.e. the Madwed and Boxer-Thaler digitisations) to convert a continuous-time system into a discrete-time system. A general expression for the denominator and numerator of the digitised system is proposed, and used to predict precisely the computational stability and sampling-time effects of these types of digitisation. The 'polynomial root locus' is introduced to describe the pole variations of the digitised system when the sampling time is varied from zero to infinity. The maximum sampling time of a particular digitisation can also be found by a new algorithm which is proposed. The transient behaviour of the digitised system is further studied by defining a new set of transient terms for discrete-time systems. In this way, the effects of sampling-time can be studied thoroughly. It is shown that the appropriate sampling times obtained via these approximate methods play a meaningful role in selecting appropriate sampling times for real problems. Several examples are illustrated.

Basic theory for the diffusive sampling of radon.

From the closed-form solution of the Fickian equation describing the uptake of radon by a diffusive sampler, the following are calculated: 1) the optimal estimate of the time-weighted average radon concentration; 2) the effect of the geometry of the diffusive sampler on performance; 3) the maximum sampling time consistent with a predetermined maximum error in the estimated time-weighted average concentration of radon; and 4) the effects of temperature and pressure on the performance of the sampler. It is shown that the maximum sampling error can be greatly reduced by dividing the adsorbent bed into two layers placed in series and by using a weighted average of the uptakes on the two layers.

Application of Nonlinear Quadratic Stochastic Control to a Position Servomechanism

Nonlinear Quadratic Stochastic control is applied to a position servomechanism. A method for estimating the maximum sampling time of a digital implementation of the technique is given. Additionally, a technique for improving on Gaussian statistics is shown. Non-Gaussian statistics are especially useful for the precise control of servomechanisms with granular nonlinearities such as coulomb friction and backlash.

A Non-Toxic Diffusional Dosimeter for Sulfur Dioxide

Diffusional (passive) dosimeters are often required for the determination of time-weighted average concentrations of sulfur dioxide under relatively severe workplace conditions. The method developed here combined the use of a diffusional dosimeter and a relatively non-toxic buffered formaldehyde absorbing solution. The dosimeter was found to give reproducible results using two lots of General Electric single-backed dimethyl silicone membranes; sampling times from 1 to 7 hr; sampling temperatures from 25°C to 38°C; and at face velocities from 0–600 ft/min (0–3 m/s). Concentrations as low as 0.05 ppm were determined over a maximum sampling time of 7 hr, yielding a sensitivity better than 0.35 ppm·hr. Fluctuating concentrations from 0.5,1.0 or 2.0 ppm background to 10.0 ppm for 1/2 hr were shown to result in no significant error.

A Non-Toxic Diffusional Dosimeter for Sulfur Dioxide

Diffusional (passive) dosimeters are often required for the determination of time-weighted average concentrations of sulfur dioxide under relatively severe workplace conditions. The method developed here combined the use of a diffusional dosimeter and a relatively non-toxic buffered formaldehyde absorbing solution. The dosimeter was found to give reproducible results using two lots of General Electric single-backed dimethyl silicone membranes; sampling times from 1 to 7 hr; sampling temperatures from 25°C to 38°C; and at face velocities from 0–600 ft/min (0–3 m/s). Concentrations as low as 0.05 ppm were determined over a maximum sampling time of 7 hr, yielding a sensitivity better than 0.35 ppm·hr. Fluctuating concentrations from 0.5,1.0 or 2.0 ppm background to 10.0 ppm for 1/2 hr were shown to result in no significant error.

A multiple head tissue sampler drill for regional myocardial studies

A multiple head myocardial tissue sampling drill is described. This drill allows one to simultaneously obtain up to 29 independent transmural tissue samples from the ventricular wall of large mammalian hearts. Each biopsy core can be rapidly and simultaneously frozen. Sufficient material can be obtained for radioactive microsphere flow studies and for extensive biochemical analysis. Each sample may be further subdivided into epicardial and endocardial components. Using multiple biopsy sample, the rate of decay of adenosine triphosphate and creatine phosphate in tissue at room temperature has been characterized and related to the maximum permissible sampling time for obtaining meaningful tissue samples.