Time Synchronization Control Research Articles

Time-Synchronized Convergence Control for n-DOF Robotic Manipulators with System Uncertainties.

A time-synchronized (TS) convergence control method for robotic manipulators is proposed. Adversely to finite-time control, a notion of time-synchronization convergence is introduced based on the ratio persistence property, which can ensure that all system components converge simultaneously in a finite time. Firstly, a robust disturbance observer is constructed to be compatible with the time-synchronized control framework and precisely estimate system uncertainties. Furthermore, we design a (finite) time-synchronized controller to ensure that all states of the robotic manipulator simultaneously converge to an equilibrium point, irrespective of initial conditions. Stability analysis shows the feasibility of the proposed TS control method. At last, simulations are performed with a two-link rehabilitation robotic system, and the comparison results indicate its superiority.

Research on picosecond synchronization control between synchrotron radiation X-ray pulse and femtosecond laser pulse on SSRF

The laser-pumped X-ray detection method is a crucial tool for investigating molecular dynamics, allowing researchers to study ultrafast structural changes within materials. This method demands extremely high precision in the synchronization and delay timing between the pump pulse and the probe pulse. In this study, we explored picosecond (ps)-level clock synchronization control between synchrotron radiation X-ray pulses and femtosecond (fs) laser pulses at the BL05U (d-Line) of the Shanghai Synchrotron Radiation Facility (SSRF). Utilizing the X-ray pulses generated by the 40 ps/0.3 mA electron beam bunch from the SSRF and femtosecond laser pulses with high repetition rates and high emission power, we conducted synchronization experiments. A custom-developed picosecond time synchronization control system and a high dynamic range X-ray streak camera with picosecond time resolution were used as detectors, enabling ultra-precise time synchronization monitoring of X-ray and laser pulses. This setup achieves higher time resolution without the need for photodiodes and oscilloscopes. Using the X-ray pulses as a stationary reference frame, we adjusted the clock synchronization control system to delay the laser pulses and measured their relative timing changes with the X-ray streak camera. The experiments demonstrated a time resolution better than 10 ps, providing a foundation for achieving 60 ps time resolution in laser-pumped X-ray detection experiments at the SSRF.

Time-Synchronized Control for Spacecraft Reorientation With Time-Varying Constraints

Time-Synchronized Control for Spacecraft Reorientation With Time-Varying Constraints

Finite-time synchronization of fractional multi-wing chaotic system

The objective of this article is to obtain multi-wing chaotic attractors of fractional chaotic systems through computerized symbolic computation. By applying the Julia fractal technique, the different number wing attractors are constructed for proposed equations. Moreover, the dynamics of the multi-wing system are analyzed by phase diagram, Poincare mapping, etc Consequently, the system exhibits complex dynamics, and the motion states at different order can be known from the bifurcation diagram with the change of order. Additionally, aiming at multi- wing fractional chaotic system, the controllers are designed, and the finite time synchronization control of the proposed system is performed. The results prove that the proposed finite-time synchronization method has important research value in the field of engineering.

Time-Synchronized Control for an Uncertain Marine Vessel System With External Disturbance

In this paper, we focus on the tracking control problem of the unmanned marine vessel (UMV) system with uncertainty and external disturbance. In order to resist the adverse effect on each other between the UMV system states, a time-synchronized control method is proposed to handle the coupling problem, which can guarantee that all system states can achieve the convergence at the same time. In the control design, a time-synchronized estimator is designed to handle the problems of system uncertainty and external disturbance. Furthermore, the stability analysis of the UMV system is given to prove the feasibility of the proposed time-synchronized control. Finally, simulations on a practical UMV model are conducted to illustrate the advantages and effectiveness of the proposed time-synchronized control.

An Energy-Efficient MAC Protocol for Three-Dimensional Underwater Acoustic Sensor Networks With Time Synchronization and Power Control

In recent years, Underwater Acoustic Sensor Networks (UASNs) have gained considerable attention for their unique role in detecting and monitoring the underwater environment. However, due to the long propagation time, high bit error rate, and limited bandwidth of underwater acoustic systems, the design of media access control (MAC) protocols is extremely complex, especially for the power consumption of UASNs. Therefore, this paper proposes an energy-efficient MAC protocol for three-dimensional UASNs with time synchronization and power control (TDTSPC-MAC). The proposed protocol is a hybrid access scheme for three-dimensional UASN using techniques such as time synchronization, power control, clustering, layering, and sleep mechanisms. Moreover, the TDTSPC-MAC protocol uses the hierarchical concept and distributed clustering algorithm to divide the three-dimensional space, and combines time synchronization and power control strategies to avoid collisions. Besides, energy consumption is reduced through monitoring and sleep mode. Simulation results demonstrate that the proposed TDTSPC-MAC protocol has reasonable data transmission delay time, throughput, energy consumption, and other performance.

Time-Synchronized Tracking Control for 6-DOF Spacecraft in Rendezvous and Docking

For the short-rangerelative motion of the on-orbit service spacecraft during rendezvous and docking missions, this article improves control performance with the describable straight line convergence trajectory and reduces energy consumption by proposing and solving the spacecraft time-synchronized control problem. This problem requires that the closed-loop system of the spacecraft is finite/fixed-time stable, all nonzero elements converge synchronously, and the trajectory of the closed-loop system tends to be the describable straight line. Based on the time-synchronized stability (TSS) and fixed-time-synchronized stability (FTSS), this article proposes the TSS and FTSS controllers for the 6-degree of freedom (DOF) spacecraft to solve the problem. For the spacecraft closed-loop system under these optimization-free methods, the derivative of the state is always opposite to the direction of the state, then the system trajectory will tend to a straight line, and the redundant motion components in the direction orthogonal to the state are significantly suppressed (performance improvement), and the excess energy loss is reduced considerably. Conversely, redundant motion components will cause excess transient motion and more energy consumption. Furthermore, this article proposes the linear combination theorem of the ratio persistence property, which further enriches the theoretical tools for the time-synchronized control method. The rigorous theoretical proof and comparative simulation verify the rationality, effectiveness, and advantages of the controllers proposed.

A Novel Time Synchronization Method for Smart Grid Based on Improved Wolf Colony Algorithm-Cuckoo Search Optimized Fuzzy PID Controller

This paper develops a high-precision time synchronization control method based on IEEE 1588 protocol. A novel control technique based on the hybridization of the improved wolf colony algorithm and cuckoo search algorithm (hybrid IWCA-CS) is used to dynamically adjust the fuzzy PID controller parameters to reduce the error of the master-slave clock. To make better performance of conventional wolf colony algorithm (WCA), it is improved using the Bloch coordinate encoding to determine the initial population and adding inertial weights to balance the search ability of the algorithm. The proposed hybrid IWCA-CS combines the best attributes of WCA’s global search and local search of cuckoo search (CS). In optimizing benchmark function experiments, the proposed hybrid IWCA-CS presents a superior performance compared to other soft computing methods. Furthermore, the hybrid IWCA-CS optimized controllers with different structures are presented to demonstrate its dynamic response characteristics. The results show that IWCA-CS tuned fuzzy PID controller shows the best dynamic performance as compared to PID/PI controllers. And the IWCA-CS based fuzzy PID controller is less sensitive to step load disturbance and parameter changes. Finally, the effectiveness of the proposed time synchronization control method in this paper over published methods is further confirmed by employing in power information collection system (PICS).

Finite time Synchronization of Inertial Memristive Neural Networks with Time Varying Delay

Finite time synchronization control of inertial memristor-based neural networks with varying delay is considered. In view of drive and response concept, the sufficient conditions to ensure finite time synchronization issue of inertial memristive neural networks is given. Based on Lyapunov finite time asymptotic theory, a kind of feedback controllers is designed for inertial memristorbased neural networks to realize the finite time synchronization. Based on Lyapunov stability theory, close loop error system can be proved finite time and fixed time stable. Finally, illustrative example is given to illustrate the effectiveness of theoretical results.

Time-Synchronized Control for Disturbed Systems.

Finite-time control is concerned with steering a system state to the origin before a certain settling-time limit, ignoring any consideration of when each state element converges relative to the others. In this article, a control problem called time-synchronized control is investigated, where all the system state elements have to converge to the origin at the same time. To facilitate this problem formulation, we introduce the notion of time-synchronized stability together with sufficient Lyapunov conditions. Based on these, the analytical solution of a time-synchronized stable system is obtained and discussed, explicitly offering a quantitative method to preview and predesign the control system performance in prior. Following these results, a robust time-synchronized control law is designed for multivariable systems under external disturbances and model uncertainties. Finally, comparative numerical simulations between time-synchronized control and finite/fixed/prescribed-time control are conducted to showcase the time-synchronized features attained.

Fixed Time Synchronization Control for Bilateral Teleoperation Mobile Manipulator With Nonholonomic Constraint and Time Delay

In this brief, the fixed time synchronization control is investigated for nonholonomic mobile manipulator teleoperation system. The mobile manipulator is divided into two subsystems for analysis, which are nonholonomic mobile platform and holonomic constrained manipulator. Coupling terms between two subsystems are considered as disturbances. A fixed time synchronization controller is proposed to deal with the parameter uncertainties and unknown bounded disturbances. Lyapunov stability theory guarantees the stability of the closed-loop teleoperation system. Numerical simulations verify the effectiveness of the proposed results.

A JOINT CALIBRATION METHOD OF 3D IMAGES ACQUIRED BY COMMON OPTICAL PATH PAYLOAD

Abstract. The common optical path payload is a new type of imaging payload that can acquire LiDAR data and CCD images simultaneously. This new payload integrates the linear LiDAR and linear CCD images according to the common optical system, and achieves the registration of LiDAR point cloud and CCD images by the alignment of common aperture optical axis and time synchronization control in the front of hardware. Based on the fixed matching relationship between CCD probes and LiDAR probes offered by optical path of common, this paper proposes a joint calibration method, which reduces the ranging error and misalignment error. And the results verify that this method can effectively improve the quality of the three-dimensional images. The standard deviations of validation area and roof are improved from 0.54 m to 0.14 m and 1.83 m to 0.26 m respectively.

Improved Time-Synchronization Algorithm Based on Direct Compensation of Disturbance Effects.

In this paper, an improved time-synchronization algorithm is proposed. The improvement of time synchronizing performance was achieved by introducing a stochastic model-based direct compensation of the disturbance effects appearing in the IEEE 1588 Precision Time Protocol (PTP)-based time synchronization system. A dynamic model of PTP clock system was obtained by reflecting the three major sources of disturbances, i.e., clock frequency drift, clock rate offset, and network noise. With the application of the dynamic model of the PTP clock system, the effects of the disturbances can be effectively eliminated in the PTP time synchronization control loop. Computer simulations are performed to verify the performance of the proposed time synchronization algorithm by applying the various types of disturbances, including network noise and clock drift. The simulation results are compared with those of other representative time synchronization algorithms, i.e., IEEE 1588 PTP algorithm and Kalman-filter-based algorithm. It is shown that the proposed algorithm improves time synchronizing performance up to 84% with respect to that of the Kalman-filter-based synchronization algorithm when simulated with colored noise type disturbances. The proposed time synchronization algorithm is expected to contribute for the realization of future Ethernet-based industry-plant monitoring and control including IEC 61850-based digital substation.

Adaptive Fixed Time Parameter Estimation and Synchronization Control for Multiple Robotic Manipulators

In this paper, an adaptive fixed time parameter estimation and synchronization control scheme is proposed for multiple robotic manipulators with unknown parameters and lumped disturbances. A mean coupling synchronization error is defined by averaging all the tracking errors of multiple robotic manipulators, and an adaptive fixed time synchronization control scheme is proposed to guarantee that both the tracking error and the synchronization error can simultaneously converge to zero within a fixed time, which means that the upper bound of the settling time is independent of the initial conditions. Moreover, an adaptive parameter estimation law is developed through constructing auxiliary filtered variables to achieve the accurate estimation of the unknown system parameters. Comparative simulations are provided to validate the effectiveness of the proposed scheme.

Integrated Time Synchronization and Multiple Access Protocol for Underwater Acoustic Sensor Networks

Due to the limited energy and mobility of the traditional sensor nodes, autonomous underwater glider (AUG) is widely used in underwater acoustic sensor networks to achieve long-term and large-scale marine environmental monitoring. In the communication between AUGs, time synchronization (TS) and multiple access control process (MACP) both need control frames to guarantee the data transmission. However, the independent execution of these two processes causes the control frames to be sent repeatedly, resulting in more transmission delay and energy cost. In order to communicate between AUGs more efficiently, an integrated TS with multiple access (TSMA) protocol is proposed in this paper. Within the AUG group, an AUG is selected as the beacon node to provide a standard clock to complete the intra-group TS process, while inter-group TS adopts the non-beacon synchronization method. In the TS process, the effect of the relative movement between AUGs is considered to improve the accuracy of synchronization. Besides, we create a new control frame that can fuse the message exchange of TS and MACP. Simulation results show that TSMA has a better performance in terms of the packet delivery fraction, synchronization errors, and energy efficiency.

Precision time synchronization control method for smart grid based on wolf colony algorithm

Abstract In order to satisfy the high accuracy and high security requirements of time synchronization in smart grid, this paper has conducted a research on high-precision time synchronization control algorithm based on IEEE 1588 protocol. A slave clock model is built considering both phase offset and frequency drift. A novel approach using proportional–integral–derivative (PID) controller in cooperation with the wolf colony algorithm (WCA) is proposed to eliminate the offset of the slave clock with respect to the master clock. As a new swarm-intelligence algorithm, WCA is introduced for self-tuning the optimal parameters of the PID controller, which simulates the intelligent predatory behaviors and prey distribution rule of the wolf colony. The WCA-based PID control approach is compared with the method based on standard Particle Swarm Optimization (PSO) and Back-Propagation (BP) neural network. The experimental results show that the proposed WCA-based PID control approach in time synchronization for smart grid has higher precision, can adaptively adjust compensation and keep the master–slave clock synchronization effectively.

Clock Skew Estimation of Listening Nodes with Clock Correction upon Every Synchronization in Wireless Sensor Networks

Time synchronization is a significant component in Wireless Sensor Networks (WSNs) for maintaining synchrony among nodes. Most time synchronization protocols in WSNs utilize dedicated synchronization packets for clock accuracy optimization. However, in practical WSNs, the joint design of time synchronization and Media Access Control layer protocols should be considered. One approach is adding timestamps directly into data packets and the corresponding acknowledgements (ACKs). Therefore, communication and energy overhead could be saved greatly and time synchronization could be seamlessly integrated into networks. In this letter, we investigate the time synchronization scheme of listening nodes overhearing the neighboring two-way timing packet exchange based on periodical ACK mechanism and present an efficient clock skew estimation algorithm with clock correction upon every synchronization. The Maximum Likelihood Estimator (MLE) of clock skew for Gaussian random packet delay is derived, and the corresponding Cramer-Rao Lower Bound (CRLB) is obtained. In addition, the MLE shows that the clock skew could be estimated without any prior knowledge of the fixed packet delay and the time of adjustment. Simulation results verify that the MLE is efficient.

Adaptive cluster general projective synchronization of complex dynamic networks in finite time

This paper investigates adaptive cluster general projective synchronization (CGPS) of complex dynamic networks in finite time. Based on the finite time synchronization control techniques and Lyapunov stability theorem, sufficient conditions are derived to guarantee the realization of adaptive cluster general projective synchronization. Finally, numerical simulation is provided to support the theoretical results.

Stabilization of a high-order harmonic generation seeded extreme ultraviolet free electron laser by time-synchronization control with electro-optic sampling

A fully coherent free electron laser (FEL) seeded with a higher-order harmonic (HH) pulse from high-order harmonic generation (HHG) is successfully operated for a sufficiently prolonged time in pilot user experiments by using a timing drift feedback. For HHG-seeded FELs, the seeding laser pulses have to be synchronized with electron bunches. Despite seeded FELs being non-chaotic light sources in principle, external laser-seeded FELs are often unstable in practice because of a timing jitter and a drift between the seeding laser pulses and the accelerated electron bunches. Accordingly, we constructed a relative arrival-timing monitor based on non-invasive electro-optic sampling (EOS). The EOS monitor made uninterrupted shot-to-shot monitoring possible even during the seeded FEL operation. The EOS system was then used for arrival-timing feedback with an adjustability of 100 fs for continual operation of the HHG-seeded FEL. Using the EOS-based beam drift controlling system, the HHG-seeded FEL was operated over half a day with an effective hit rate of 20%–30%. The output pulse energy was $20~{\rm\mu}\text{J}$ at the 61.2 nm wavelength. Towards seeded FELs in the water window region, we investigated our upgrade plan to seed high-power FELs with HH photon energy of 30–100 eV and lase at shorter wavelengths of up to 2 nm through high-gain harmonic generation (HGHG) at the energy-upgraded SPring-8 Compact SASE Source (SCSS) accelerator. We studied a benefit as well as the feasibility of the next HHG-seeded FEL machine with single-stage HGHG with tunability of a lasing wavelength.

Cooperative distributed optimization for the hyper-dense small cell deployment

The fifth generation mobile networks will be developed to improve area spectral and energy efficiency, and provide uniform user experience. Hyper-dense small cell deployment can move devices closer to the wireless network and satisfy 5G system requirements. The main challenge of this network deployment results from the random deployment, dynamic on-off, flexible connection to cellular core networks, and flat system architecture of 5G systems. Therefore, conventional network planning and radio resource management, which depend on a central control node, cannot be applied to small cell networks. In this article some cooperative distributed radio resource management algorithms for time synchronization, carrier selection, and power control are discussed for hyper-dense small cell deployment.