Relative Position Information Research Articles

Consensus of Second-Order Multiagent Systems with Fixed Topology and Time-Delay

We are concerned with the consensus problems for networks of second-order agents, where each agent can only access the relative position information from its neighbours. We aim to find the largest tolerable input delay such that the system consensus can be reached. We introduce a protocol with time-delay and fixed topology. A sufficient and necessary condition is given to guarantee the consensus. By using eigenvector-eigenvalue method and frequency domain method, it is proved that the largest tolerable time-delay is only related to the eigenvalues of the graph Laplacian. And simulation results are also provided to demonstrate the effectiveness of our theoretical results.

A Pre-Compensation Fuzzy Logic Algorithm Designed for the Dynamic Compensation Robotic System

This paper deals with the issue of non-model-based position regulation for the dynamic compensation robotic system (DCRS), which has been proposed for cooperating with the existing main robotic systems, such as the common serial robotic arms, to accomplish high-speed and accurate manipulations. The dynamic compensation concept is realized by fusing a high-speed & light-weight compensation actuator as well as endpoint closed loop (ECL) configured high-speed cameras. Within the context of the DCRS, the coarse motion, which is realized by the main robotic system, usually gives rise to negative dynamic impact on the compensation actuator that is configured to accomplish the fine motion. Through the analysis of a simplified model for the coupled two-plant system, relative velocity information between the two plants is found to play a role in the first order derivative of the displacement error. With the use of the relative position information from high-speed visual feedback, this paper proposes a new pre-compensation fuzzy logic control (PFLC) approach for control of the compensation actuator. The PFLC method is model-independent and is realized with a cascade fuzzy inference structure that conveniently integrates the relative velocity term between the two plants into the error regulation, and therefore realizes the partial counteraction of the disturbance from the main robot easily without knowing the explicit mathematical models of the system. Comparison works between the proposed PFLC and approaches that take no consideration of the relative velocity information, such as proportional-derivative (PD) control and conventional fuzzy logic control, are conducted. Simulations and experiments show the consistent effectiveness of the proposed approach.

Observer-based consensus tracking for second-order leader-following nonlinear multi-agent systems with adaptive coupling parameter design

This paper considers the leader-following tracking problem of second-order nonlinear multi-agent systems with a reference leader. It is assumed that all following agents can only access the relative position information with its neighbors, the position and velocity information of the leader is only accessed by a subset of the following agents, and the leader׳s bounded reference input cannot be available by any following agents. To track the active leader, a distributed discontinuous observer-based consensus protocol is proposed for each following agent, whose observer is used to estimate the agent׳s unmeasured velocity. Under connected undirected interaction topology, the proposed protocol can be used to solve the second-order nonlinear multi-agent consensus problem. While the reference input of the leader is known, the proposed protocol can solve the consensus problem under a class of directed switching interaction topologies. Furthermore, to make the designed approach in fully distributed fashion, the distributed adaptive laws are provided to design the protocol coupling parameters. Finally, a numerical example is presented to illustrate our obtained result.

Robust consensus tracking for a class of heterogeneous second‐order nonlinear multi‐agent systems

SummaryThis paper deals with the robust consensus tracking problem for a class of heterogeneous second‐order nonlinear multi‐agent systems with bounded external disturbances. First, a distributed adaptive control law is proposed based on the relative position and velocity information. It is shown that for any connected undirected communication graph, the proposed control law solves the robust consensus tracking problem. Then, by introducing a novel distributed observer and employing backstepping design techniques, a distributed adaptive control law is constructed based only on the relative position information. Compared with the existing results, the proposed adaptive consensus protocols are in a distributed fashion, and the nonlinear functions are not required to satisfy any globally Lipschitz or Lipschitz‐like condition. Numerical examples are given to verify our proposed protocols. Copyright © 2014 John Wiley & Sons, Ltd.

UWB for Robust Indoor Tracking: Weighting of Multipath Components for Efficient Estimation

In a radio propagation channel, deterministic reflections carry important position-related information. With the help of prior knowledge such as a floor plan, this information can be exploited for indoor localization. This letter presents the improvement of a multipath-assisted tracking approach using information about the relevance of deterministic multipath components in an environment. This information is fed to a tracking filter as an observation noise model. It is estimated from a few training signals between anchors and an agent at known positions. Tracking results are presented for measurements in a partial non-line-of-sight environment. At a bandwidth of 2 GHz, an accuracy of 4 cm can be achieved for over 90% of the positions if additional channel information is available. Otherwise, this accuracy is only possible for about 45% of the positions. The covariance of the estimation matches closely to the corresponding Cramèr-Rao lower bound.

Formation tracking of the second-order multi-agent systems using position-only information via impulsive control with input delays

In this paper, the formation tracking problem for the second-order multi-agent system with and without input delay are investigated, respectively. The objective is to design the formation tracking algorithm such that a certain follower follows the trajectory of the leader while also maintains a certain desired geometric formation with other agents simultaneously. The impulsive algorithms are designed by using only the relative position information of the neighbors for both the cases with and without the input delay. By using properties of the Laplacian matrix and combining the stability theory of impulsive systems, necessary and sufficient conditions are derived to achieve the formation tracking of the second-order multi-agent system with and without the input delay, respectively. The numerical examples are given to illustrate the effectiveness of our theoretical results.

Beyond synchronization: String instability in coupled harmonic oscillator systems

Summary In this paper, we consider the problem of disturbance response and error amplification for a simple system of coupled harmonic oscillators. We first suppose that identical oscillators are connected in a string in which each oscillator attempts to track its predecessor by using the same control law that depends on the relative position information from its immediate predecessor. Such an oscillator string is called a homogeneous oscillator string with predecessor-following architecture. Motivated by terminology from the problem of vehicle platooning, we say that the synchronized oscillator system is string unstable if the effect of a disturbance to the lead oscillator is amplified as it propagates along the string. With the use of a new Bode-like integral relation that must be satisfied by the complementary sensitivity function, we provide sufficient conditions for string instability. The sufficient conditions show that any string of oscillators that satisfies certain time domain performance specifications and bandwidth limitations must necessarily be string unstable. We further introduce a concept of time headway for the oscillator system and extend our analysis of string instability to consider the heterogeneous oscillator string and a more general communication range. Copyright © 2014 John Wiley & Sons, Ltd.

Second-order consensus of nonlinear multi-agent systems with restricted switching topology and time delay

In this paper, a distributed protocol based on only relative position information is proposed for consensus of second-order multi-agent systems with inherent nonlinear dynamics and communication time delay. Compared with previous works, the distinguished feature of the paper lies in the directed interaction topology that is switching according to average dwell time (ADT) switching signals. Under the proposed protocol, we not only present sufficient conditions for ensuring consensus, but also explicitly give the lower bound of ADT for admissible switching signals. Numerical examples are provided to illustrate the performance of the proposed consensus algorithm.

Asymptotic Tracking Control for Spacecraft Formation Flying with Decentralized Collision Avoidance

This paper presents a tracking control scheme for spacecraft formation flying with a decentralized collision-avoidance scheme, using a virtual leader state trajectory. The configuration space for a spacecraft is the Lie group , which is the set of positions and orientations in three-dimensional Euclidean space. A virtual leader trajectory, in the form of attitude and orbital motion of a virtual satellite, is generated offline. Each spacecraft tracks a desired relative configuration with respect to the virtual leader in an autonomous manner, to achieve the desired formation. The relative configuration between a spacecraft and the virtual leader is described in terms of exponential coordinates on . A continuous-time feedback tracking control scheme is designed using these exponential coordinates and the relative velocities. A Lyapunov analysis guarantees that the spacecraft asymptotically converge to their desired state trajectories. This tracking control scheme is combined with a decentralized collision-avoidance control scheme generated from artificial potentials for each spacecraft, which includes information of relative positions of other spacecraft within communications range. Asymptotic convergence to the desired trajectory with this combined control law is demonstrated using a Lyapunov analysis. Numerical simulation results verify the successful application of this tracking control scheme to a formation maneuver with decentralized collision avoidance.

Automatic segmentation of intra-cochlear anatomy in post-implantation CT of unilateral cochlear implant recipients

A cochlear implant (CI) is a neural prosthetic device that restores hearing by directly stimulating the auditory nerve using an electrode array that is implanted in the cochlea. In CI surgery, the surgeon accesses the cochlea and makes an opening where he/she inserts the electrode array blind to internal structures of the cochlea. Because of this, the final position of the electrode array relative to intra-cochlear anatomy is generally unknown. We have recently developed an approach for determining electrode array position relative to intra-cochlear anatomy using a pre- and a post-implantation CT. The approach is to segment the intra-cochlear anatomy in the pre-implantation CT, localize the electrodes in the post-implantation CT, and register the two CTs to determine relative electrode array position information. Currently, we are using this approach to develop a CI programming technique that uses patient-specific spatial information to create patient-customized sound processing strategies. However, this technique cannot be used for many CI users because it requires a pre-implantation CT that is not always acquired prior to implantation. In this study, we propose a method for automatic segmentation of intra-cochlear anatomy in post-implantation CT of unilateral recipients, thus eliminating the need for pre-implantation CTs in this population. The method is to segment the intra-cochlear anatomy in the implanted ear using information extracted from the normal contralateral ear and to exploit the intra-subject symmetry in cochlear anatomy across ears. To validate our method, we performed experiments on 30 ears for which both a pre- and a post-implantation CT are available. The mean and the maximum segmentation errors are 0.224 and 0.734mm, respectively. These results indicate that our automatic segmentation method is accurate enough for developing patient-customized CI sound processing strategies for unilateral CI recipients using a post-implantation CT alone.

A Self-Organizing Cooperation for Autonomous Agents Based on Immune Network

In order to solve the cooperation of autonomous agent systems,an artificial immune network cooperation algorithm is proposed,which is based on Jerne's idiotypic immune network hypothesis. A sheep- dog herding problem is taken as an example. The relative position information of dogs with the sheep and sheep pen is taken as an antigen. Dogs' action is taken as an antibody. We calculate antibody concentration according to Farmer's kinetic model. By selecting the appropriate antibody according to the antibody concentration the cooperation for autonomous agent systems can be realized. Simulation of sheep-dog herding in different environment shows that a herding strategies based on immune network can not only realize sheep-dog herding but also be more robust and flexible, which shows the effectiveness of the artificial immune network algorithm in autonomous agents systems.

The Positional-Specificity Effect Reveals a Passive-Trace Contribution to Visual Short-Term Memory

The positional-specificity effect refers to enhanced performance in visual short-term memory (VSTM) when the recognition probe is presented at the same location as had been the sample, even though location is irrelevant to the match/nonmatch decision. We investigated the mechanisms underlying this effect with behavioral and fMRI studies of object change-detection performance. To test whether the positional-specificity effect is a direct consequence of active storage in VSTM, we varied memory load, reasoning that it should be observed for all objects presented in a sub-span array of items. The results, however, indicated that although robust with a memory load of 1, the positional-specificity effect was restricted to the second of two sequentially presented sample stimuli in a load-of-2 experiment. An additional behavioral experiment showed that this disruption wasn’t due to the increased load per se, because actively processing a second object – in the absence of a storage requirement – also eliminated the effect. These behavioral findings suggest that, during tests of object memory, position-related information is not actively stored in VSTM, but may be retained in a passive tag that marks the most recent site of selection. The fMRI data were consistent with this interpretation, failing to find location-specific bias in sustained delay-period activity, but revealing an enhanced response to recognition probes that matched the location of that trial’s sample stimulus.

Cooperative Inertial Navigation for GNSS-Challenged Vehicular Environments

Cooperative positioning (CP) is an approach for positioning and/or positioning enhancement among a number of participants, which communicate and fuse their position-related information. Due to the shortcomings of Global Navigation Satellite Systems (GNSSs), modern CP approaches are considered for improving vehicular positioning where the GNSS cannot address the requirements of the specific applications such as collision avoidance or lane-level positioning. An inertial navigation system (INS) has not been considered for CP in the literature. The hybrid INS/GNSS methods used for positioning enhancement in standalone nodes cannot be classified as CP because the position-related data are not communicated between at least two independent entities. In this paper, we present a novel CP technique to improve INS-based positioning in vehicular networks. This cooperative inertial navigation (CIN) method can be used to enhance INS-based positioning in difficult GNSS environments, such as in very dense urban areas and tunnels. In the CIN method that is proposed, vehicles communicate their inertial measurement unit (IMU) and INS-based position data with oncoming vehicles traveling in the opposite direction. Each vehicle fuses the received data with those locally observed and the carrier frequency offset (CFO) of the received packets to improve the accuracy of its position estimates. The proposed method is analyzed using simulations and is also experimentally verified. The experimental results show up to 72% improvement in positioning over the standalone INS-based method.

Airborne Integrated Vision/Inertial Navigation System for Landing on Aircraft Carrier

It is a very difficult task to land on aircraft carrier, because of limits of the carrier runway during rough sea. In this article, a new algorithm of aircraft carrier landing is proposed utilizing airborne infrared camera/inertial integrated system, which can provide the relative positions and orientation of the aircraft with respect to the carrier so as to help aircrafts semi-auto or auto landing. The mathematic relationship between guidance parameters and imaging information was modeled, and then the relative position and attitude information between the carrier and the aircraft were estimated through Newton iteration method. From that information, the pitching, rolling and heave movement of the carrier were estimated and compensated, so the touchdown point could be predicted and provided to the pilot so as to control aircraft landing. On the ground of the theoretic research, the field verification tests were carried out, which adopted the minification scheme to simulate the process of aircraft carrier landing. In the experiments, the runway simulator simulated the motion of the carrier runway and the land vehicle was used as the aircraft. The results verify the landing guidance system scheme is feasible and effective, and lay the technical foundation for the flight test, improving its safety.

A two-step heuristic algorithm for layout design of unequal-sized facilities with input/output points

The facility layout problem (FLP) is to arrange facilities within a given area so as to minimise the total material-handling cost. An efficient arrangement of facilities plays an important part in the achievement of high productivity in a manufacturing system. This paper focuses on the layout design of unequal-sized facilities with fixed shapes and input/output (I/O) points. A mixed-integer programming (MIP) model is developed to obtain optimal solutions. Since the MIP model is not applicable to large-sized problems, a two-step heuristic algorithm is developed to solve the FLPs. In the first step, a layout solution with moderate quality is generated by using an interconnected zone algorithm and a simulated annealing (SA) algorithm. The zone algorithm is a newly developed layout construction technique which places facilities successively within designated zones according to a placing sequence. The zone concept is introduced to reduce the solution space such that the computational effort is decreased, while SA is used to search for the placing sequences. The second step improves that solution further using the reduced MIP by employing the relative position information obtained from the first step. Computational experiments indicate that the algorithm in the first step can yield on average a 1.048% improvement on the best solutions obtained by the existing algorithms. The second step can further improve the solutions obtained in the first step by 0.484% on average. Compared to the commercial software VIP-PLANOPT 2006 (Engineering Optimization Software 2005), the proposed two-step algorithm improves the solutions by 9.113% on average.

Relative position and attitude estimation of spacecrafts based on dual quaternion for rendezvous and docking

The capacity to acquire the relative position and attitude information between the chaser and the target satellites in real time is one of the necessary prerequisites for the successful implementation of autonomous rendezvous and docking. This paper addresses a vision based relative position and attitude estimation algorithm for the final phase of spacecraft rendezvous and docking. By assuming that the images of feature points on the target satellite lie within the convex regions, the estimation of the relative position and attitude is converted into solving a convex optimization problem in which the dual quaternion method is employed to represent the rotational and translational transformation between the chaser body frame and the target body frame. Due to the point-to-region correspondence instead of the point-to-point correspondence is used, the proposed estimation algorithm shows good performance in robustness which is verified through computer simulations.

Development of ordinal sequence perception in infancy.

Perception of the ordinal position of a sequence element is critical to many cognitive and motor functions. Here, the prediction that this ability is based on a domain-general perceptual mechanism and, thus, that it emerges prior to the emergence of language was tested. Infants were habituated with sequences of moving/sounding objects and then tested for the ability to perceive the invariant ordinal position of a single element (Experiment 1) or the invariant relative ordinal position of two adjacent elements (Experiment 2). Experiment 1 tested 4- and 6-month-old infants and showed that 4-month-old infants focused on conflicting low-level sequence statistics and, therefore, failed to detect the ordinal position information, but that 6-month-old infants ignored the statistics and detected the ordinal position information. Experiment 2 tested 6-, 8-, and 10-month-old infants and showed that only 10-month-old infants detected relative ordinal position information and that they could only accomplish this with the aid of concurrent statistical cues. Together, these results indicate that a domain-general ability to detect ordinal position information emerges during infancy and that its initial emergence is preceded and facilitated by the earlier emergence of the ability to detect statistical cues.

Using head poses to control a virtual robot walking in a virtualmaze

This paper develops a game system based on head pose identification techniques to control a virtual robot walking in a virtual maze environment built with Microsoft Robotics Developer Studio. Adaboost face classifiers are used to detect a face in the image and give a rough head pose classification. Two approaches are proposed to further determine more specific head poses. The first approach adopts PCA with nose template matching method, and the second one firstly uses a nose classifier to detect the nose in a detected face region and then directly utilizes the nose’s relative position information to achieve head pose classification. A method to select the best nose area is proposed to solve the problem that multi-nose areas may be detected in one face region. Experiment results show that the two approaches have comparable time consumed, but the second approach provides more correct identification results.

Quantization effects on synchronized motion of teams of mobile agents with second-order dynamics

For a team of mobile agents governed by second-order dynamics, this paper studies how different quantizers affect the performances of consensus-type schemes to achieve synchronized collective motion. It is shown that when different types of quantizers are used for the exchange of relative position and velocity information between neighboring agents, different collective behaviors appear. Under the chosen logarithmic quantizers and with symmetric neighbor relationships, we prove that the agents’ velocities and positions get synchronized asymptotically. We show that under the chosen symmetric uniform quantizers and with symmetric neighbor relationships, the agents’ velocities converge to the same value asymptotically while the differences of their positions converge to a bounded set. We also show that when the uniform quantizers are not symmetric, the agents’ velocities may grow unboundedly. Through simulations we present richer undesirable system behaviors when different logarithmic and uniform quantizers are used. Such different quantization effects underscore the necessity for a careful selection of quantization strategies, especially for multi-agent systems with higher-order agent dynamics.

Modeling and optimal design of relative position detection sensor for high speed maglev train

The long stator track for high speed maglev train has a special tooth-slot structure. The relative position detection sensor obtains precise relative position information for the operation control system by detecting the changing coil inductance reflecting the long stator tooth-slot structure. The aluminum windings are inlaid in the stator slots, and the magnetic field due to the sensor coils induces eddy current in them, which would change the magnetic field distribution and have a significant influence on the sensor. In this paper, the multipole theory (MT) is adopted to build the analytical electromagnetic model of the sensor. Based on the electromagnetic model, the influence of the eddy current induced in the windings on the coil inductance is studied. The DC offset formula of differential voltage owing to the slight inductance difference of the coils is derived. The influence of the eddy current on the DC offset is analyzed, based on which, a method of no-load voltage compensation and an optimal sensor excitation frequency is proposed to improve the accuracy of the sensor.