Time Sequence Control Research Articles

Synchronization of Kuramoto-oscillator networks under event-triggered impulsive control with noise perturbation

This paper studies the stochastic average synchronization of Kuramoto-oscillator networks under event-triggered impulsive control (ETIC) strategies, in which the event-triggered mechanism (ETM) determines the impulsive control time sequence. The continuous ETM is designed to avoid the Zeno behavior by continuous measuring, and the periodic ETM is proposed by periodic sampling. Based on the proposed ETIC methods, several sufficient conditions for the stochastic average synchronization of Kuramoto-oscillator networks are established. Unlike time-triggered impulsive control, where the triggered instants are pre-designed, ETIC is activated only upon the occurrence of an event, so synchronization conditions are heavily dependent on the ETM. Furthermore, there is no control input between two successive triggering instants, and the control input is required only at the trigger instants. Finally, numerical simulations are shown to illustrate the effectiveness of the theoretical results. Besides, it is found that the presence of noise may favor the synchronization of Kuramoto-oscillator networks.

Trapping paramagnetic molecules in a dynamic magnetic trap

Trapping molecules in strong-field-seeking states is particularly attractive to scientists in the field of molecular optics. If the external field is strong enough, all molecules are strong-field seekers. Contrary to the weak-field-seeking states, molecules trapping in strong-field-seeking states can avoid the loss caused by the inelastic collision which is a stumbling block for evaporative and sympathetic cooling. Unfortunately, the formation of a magnetostatic maximum in free space is forbidden according to Maxwell’s equations and Earnshaw’s theory. In this paper, a dynamic magnetic trap consisting of three pairs of Helmholtz coils is proposed. The time-sequence control is given together with the distribution of the magnetic field in space. The influence of the switching frequency and electric current flowing through the wires on the number of trapped molecules is investigated. We obtain the changes in the locations and the phase-space distribution within a switching cycle by trajectory simulation. Finally, the influence of the time during which the field is off on the performance of our trap is studied.

Improved SSA‐RBF neural network‐based dynamic 3‐D trajectory tracking model predictive control of autonomous underwater vehicles with external disturbances

AbstractThis paper studies the three‐dimensional (3‐D) dynamic trajectory tracking control of an autonomous underwater vehicle (AUV). As AUV is a typical nonlinear system, each degree of freedom is strongly coupled, so the traditional control method based on the nominal model of AUV cannot guarantee the accuracy of the control system. To solve this problem, we first propose a prediction model based on a radial basis function neural network (RBF‐NN). The nonlinearity of AUV is learned and modeled offline by RBF‐NN based on previous data. This model can reflect the time sequence state and control variables of AUV. Secondly, to avoid the overfitting problem in network training based on the traditional gradient descent method, a new adaptive chaotic sparrow search algorithm (ACSSA) is proposed to optimize the network parameters, to improve the full approximation ability of RBF‐NN to nonlinear systems. To eliminate the steady‐state error caused by external interference during AUV trajectory tracking, a nonlinear optimizer is designed by updating the deviation of the NN model output layer. In each sampling period, the predictive control law is calculated online according to the deviation between the predicted value and the actual value. In addition, the stability analysis based on the Lyapunov method proves the asymptotic stability of the controller. Finally, the 3‐D dynamic trajectory tracking the performance of AUV under different external disturbances is verified by MATLAB/Simulink, and the results show that the proposed controller is more efficient and robust than the standard model predictive controller (MPC) controller and the standard NN model predictive controller (NNPC).

Time-resolved electron paramagnetic resonance spectrometer based on ultrawide single-sideband phase-sensitive detection.

A time-resolved electron paramagnetic resonance (TREPR) method with 40ns time resolution and a high sensitivity suitable for the detection of short-lived radicals under thermal equilibrium is developed. The key is the introduction of a new detection technique named ultrawide single sideband phase sensitive detection (U-PSD) to the conventional continuous-wave EPR, which remarkably enhanced the sensitivity for the detection of broadband transient signals compared with the direct detection protocol. By repeatedly triggering a transient kinetic event f(t) (e.g., by laser flash photolysis) under a 100kHz magnetic field modulation with precise phase control, this technique can build an ultrawide single sideband modulated signal. After single sideband demodulation, the flicker noise-suppressed signal f(t) with wide bandwidth is recovered. A U-PSD TREPR spectrometer prototype has been built, which integrated timing sequence control, laser flash excitation, data acquisition systems, and the U-PSD algorithm with a conventional continuous-wave EPR. It exhibited excellent performance in monitoring a model transient radical system, laser flash photolysis of benzophenone in isopropanol. Both the intense chemically induced dynamic electron polarization signals and the much weaker thermal equilibrium EPR signals of the generated acetone ketyl radical and benzophenone ketyl radical were clearly observed within a wide timescale ranging from sub-microsecond to milliseconds. This prototype validated the feasibility of the U-PSD technique and demonstrated its superior performance in studying complex photochemical systems containing various transient radicals, which complements the established TREPR techniques and provides a powerful tool for deep mechanistic understandings, such as in photoredox catalysis and artificial photosynthesis.

The fixed-time consensus of leader-following nonlinear multi-agent systems under event-triggered impulsive control

This paper studies the leader-following fixed-time consensus problem for a class of first-order nonlinear multi-agent systems via event-triggered impulsive control where the communication topologies are general undirected. For each agent, the controller is updated only when some state-dependent errors exceed a tolerable bound, and the impulsive control time sequence is produced by the event triggered mechanism. This original control protocol can substantially improve the convergence speed, obtain the lower energy consumption and reduce the update times of the controller. Also, it is shown that continuous communication of neighboring agents can be avoided and there is no Zeno-behavior. The results are verified by a numerical simulation.

Hybrid Event-Triggered Intermittent Control for Nonlinear Multi-Agent Systems

A novel hybrid event-triggered intermittent control problem for a class of nonlinear multi-agent systems is addressed. The system dynamics are reconstructed to describe the nonlinear multi-agent systems via the intermittent control method and a hybrid event-triggered mechanism. This study represents the first attempt at designing a control time sequence determined by the hybrid event-triggered mechanism to replace the predesigned control time sequence. Moreover, a consensus tracking control strategy is presented for the reconstructed multi-agent systems, and the results are extended to the case involving multiple leaders. The control strategy can solve the problems associated with the artificial selection of the control time sequence and unnecessary control input consumption. There are two simulation examples presented to demonstrate the effectiveness and feasibility of the control strategies.

A Fuzzy Controller for PFN Trigger Time Sequence in Electromagnetic Railgun System

For the electromagnetic launch system, how to realize the wide pulse, fast rise, and small fluctuation of pulse forming network output current is a core problem. A trigger time sequence control method based on fuzzy theory for the pulse forming network is proposed in this paper. First, circuit models of pulse forming unit, pulse forming network, and electromagnetic rail launcher is established. Second, a fuzzy trigger time sequence controller model for pulse forming network is designed by using Simulink. Third, fixed time sequence discharge tests consisting of 20 pulsed forming units on the linear simulation load are carried out to verify the accuracy of the simulation model. Finally, discharge tests on the linear simulation load and launch tests on the electromagnetic railgun are carried out to verify the precision of the fuzzy controller output respectively. The results show that the designed fuzzy trigger time sequence controller can obtain the ideal trigger time sequence, which demonstrates the pragmatic and reliability of fuzzy control algorithm.

Universal epitaxy of non-centrosymmetric two-dimensional single-crystal metal dichalcogenides

The great challenge for the growth of non-centrosymmetric 2D single crystals is to break the equivalence of antiparallel grains. Even though this pursuit has been partially achieved in boron nitride and transition metal dichalcogenides (TMDs) growth, the key factors that determine the epitaxy of non-centrosymmetric 2D single crystals are still unclear. Here we report a universal methodology for the epitaxy of non-centrosymmetric 2D metal dichalcogenides enabled by accurate time sequence control of the simultaneous formation of grain nuclei and substrate steps. With this methodology, we have demonstrated the epitaxy of unidirectionally aligned MoS2 grains on a, c, m, n, r and v plane Al2O3 as well as MgO and TiO2 substrates. This approach is also applicable to many TMDs, such as WS2, NbS2, MoSe2, WSe2 and NbSe2. This study reveals a robust mechanism for the growth of various 2D single crystals and thus paves the way for their potential applications.

Event-Triggered Impulsive Control for Stochastic Networked Control Systems Under Cyber Attacks

The event-triggered impulsive control (ETIC) problem is studied for stochastic networked control systems (NCSs) under random cyber attacks. The random cyber-attacks model is proposed to integrate denial-of-service (DoS) attacks and deception attacks into a unified framework by means of two independent Bernoulli random sequences. In ETIC systems, the impulsive control time sequence is generated by the event-triggered mechanism (ETM). Both continuous ETM and periodic ETM are developed by continuous measuring and periodic sampling, respectively. In order to exclude the Zeno behavior, an easy and effective method is provided to choose the waiting time of continuous ETM and the sampling period of periodic ETM. According to the proposed ETMs, sufficient conditions of the mean-square exponential stability are derived for stochastic NCSs. An example of Chua’s circuits is given to explain our ETIC schemes.

Event-Triggered Impulsive Control for Nonlinear Stochastic Systems.

We study the stabilization problem for nonlinear stochastic systems via an event-triggered impulsive control (ETIC) scheme, where the impulsive control time sequence is generated by the event-triggered mechanism (ETM). Both continuous ETM and periodic ETM are developed by continuous measuring and periodic sampling, respectively. The continuous ETM with time regularization is proposed to exclude the Zeno behavior. The upper bound of the sampling period is given for the periodic ETM. By means of the continuous ETM and periodic ETM, sufficient conditions are given to guarantee the p th moment uniform stability and the p th moment exponential stability of related systems. Moreover, LMI-based conditions of exponential stability in the mean square are established for linear stochastic systems under ETIC. Finally, two examples are presented to illustrate the proposed ETIC schemes, in which an example of the consensus of linear stochastic multiagent systems is considered.

Study on timing sequence control fracture blasting excavation of deep rock masses with filled joints

During the blasting excavation of deep underground caverns, the effects of the structural surface on crack propagation are usually considered in addition to the clamping effects of high in situ stress. Based on the notched borehole and timing sequence control (TSC) fracture blasting method, this paper studies the effects of different borehole shapes on the degree of damage of the surrounding rock and profile flatness of the rock anchor beams and the effects of different filled joint characteristics on the blasting crack propagation rules. The results show that the damage depth of the surrounding rocks by round hole smooth blasting is approximately twice that by notched hole smooth blasting, by which the profile formed is flatter. The notched primary borehole (PBH) remains a strong guidance for crack propagation in a rock mass with filled joints, while the stress concentration effects of the round target borehole (TBH) cannot fully guide the cracks until they fall within a certain distance between the PBH and TBH. It is favourable for cracks to propagate along the lines between boreholes with larger filled joint strengths and larger angles between boreholes.

Analysis and Optimization of Dynamic Performance for Resonant Integrated Optical Gyroscope

In this article, a closed-loop signal detection method is proposed to improve the dynamic performance of the resonant integrated optical gyroscope. We firstly establish a closed-loop error model of the angular velocity tracking system with optical nonlinearity and parameter uncertainty based on triangular phase modulation technology. Then, we optimize the loop gains of the signal processing to improve the signal-to-noise ratio of the closed-loop error signal about angular velocity tracking. Secondly, we design a timing sequence control method to effectively eliminate the time-delay of signal processing for optimizing the dynamic performance of the angular velocity tracking system. Finally, a control algorithm is designed to suppress the influence of the optical nonlinearity and parameter uncertainty for improving the dynamic tracking performance of resonant integrated optical gyroscopes. The experimental results demonstrate that the resonant integrated optical gyroscope has a rise time less than 36 μs, a high frequency response with the bandwidth 13.1 kHz, and a low scale factor nonlinearity less than 269.2 ppm, which verifies the effectiveness of the proposed closed-loop signal detection method for the resonant integrated optical gyroscope.

Numerical Simulation Research of Smooth Wall Blasting Using the Timing Sequence Control Method under Different Primary Blast Hole Shapes

To make sure the integrity and stability of surrounding rock structure during blasting excavation of important structural planes in deep underground caverns, two kinds of fine blasting methods, timing sequence control fracture blasting network and notch blast hole, are innovatively combined and the formation of cracks between smooth blasting holes with different delay initiation and different shapes of primary blast holes (PBHs) are compared and analyzed. The results show that when the delay initiation time between the successive explosion holes is greater than or equal to the transverse wave of the PBH propagates to the target blast hole (TBH), the concentrated stress along the connection direction of the hole on the wall of the TBH is larger than the other directions of the hole wall. After the TBH is detonated, cracks will preferentially expand along the connection direction of the blast holes. If the PBH is the notch blast hole, more explosive energy will be directed to the wall of the TBH so that the hole wall along the connection direction of the blast holes will be subjected to greater tension stress before the initiation of the TBH. In this way, the interval between successive holes can be increased and the efficiency of blasting excavation of rock mass can be improved accordingly.

Design of Closed-Loop Parameters With High Dynamic Performance for Micro-Grating Accelerometer

A novel closed-loop parameter design scheme with timing sequence control method is proposed to obtain fast tracking ability of micro-grating accelerometer. Firstly, we investigate a timing sequence control method to achieve the minimum time-delay of signal processing only dependent on the response capability of sensing element, which is the same as half modulation period in the designed closed-loop accelerometer system. Considering optical sensing principle and time-delay of signal processing, we establish a dynamic equation for closed-loop micro-grating accelerometer. Then, we analyze the design principle of closed-loop parameters on the condition of system stability, which describes the relationship between time-delay and control parameters to guarantee fast tracking performance of micro-grating accelerometer system. And, through proposed parameter design principle, the closed-loop parameters of micro-grating accelerometer can be obtained with the gains of forward channel and feedback channel in closed-loop detection system. The conducted experiment results show that micro-grating accelerometer can achieve the nonlinearity within 0.28%, the fast step response time of 0.8ms and -3dB bandwidth up to 525Hz, which validate the effectiveness of our parameter design scheme and timing sequence control method.

Analysis on the Optimization of High-Frequency Performance for Optical Voltage Sensors Based on Pockels Effect

A novel closed-loop signal detection method is proposed to optimize the high-frequency performance of the optical voltage sensors (OVSs) based on Pockels effect. First, a timing sequence control method is introduced to accomplish the whole closed-loop process within one transit period of the optical propagation path, which can ensure the system high dynamic response with high-frequency signal input. Then, we investigate the frequency spectrum of closed-loop error, and design the signal processing before the closed-loop controller with a low pass filter to enhance the signal to noise ratio without reducing the system bandwidth. Furthermore, considering the optical parameter uncertainty and the unavoidable external disturbance, a closed-loop control algorithm is presented to optimize the steady state accuracy and dynamic performance of OVSs. The experimental results show that the closed-loop steady state accuracy of sine response, slope response, and acceleration measurement with the 20-kHz input signal are basically consistent with the static accuracy, and the relative measurement error of OVS is ±0.1% with the applied voltage over 100 V, which verify the effectiveness of the proposed detection scheme.

A study of smooth wall blasting fracture mechanisms using the Timing Sequence Control Method

High quality of cracking and low depth of damage in sidewall is usually required in a blasting excavation. On the contrary, large spacing of blast holes can efficiently reduce cost. Therefore Timing Sequence Control (TSC) Method can be applied, so as to meet the challenge. In the TSC method, there is a very short delay between two adjacent blast holes, i.e., the Primary borehole (PBH) and the Target borehole (TBH), in sequence. Study of the cracking process around adjacent borehole indicates, larger stress concentration on the hole wall, if the TBH initiates after the stress wave from PBH has past it. The initial crack generated on the TBH is most likely to occur along the direction of borehole attachment.Our study also shows that, keeping the borehole spacing and borehole diameter as constant, a through crack can be formed between the adjacent boreholes when the delay time, spacing of PBH and TBH, and transverse wave velocity obey a certain relationship. Keeping the hole spacing between PBH and TBH, borehole diameter and the delay time for PBH and TBH as constant, borehole through cracks between the adjacent boreholes can be formed only when the spacing of TBH equal or below 25 times of borehole diameter.

A low-noise 64-channel front-end readout ASIC for CdZnTe detectors aimed to hard X-ray imaging systems

In this paper, we report on the recent development of a 64-channel low-noise front-end readout ASIC for CdZnTe detectors aimed to hard X-ray imaging systems. The readout channel is comprised of a charge sensitive amplifier, a leakage current compensation circuit, a CR-RC shaper, two S–K filters, an inverse proportional amplifier, a peak-detect-and-hold circuit, a discriminator and trigger logic, a time sequence control circuit and a driving buffer. The readout ASIC is implemented in TSMC 0.35μm mixed-signal CMOS technology, the die size of the prototype chip is 2.7mm×8.0mm. The overall gain of the readout channel is 200mV/fC, the power consumption is less than 8 mW/channel, the linearity error is less than 1%, the inconsistency among the channels is less than 2.86%, and the equivalent noise charge of a typical channel is 66 e− at zero farad plus 14 e− per picofarad. By connecting this readout ASIC to an 8×8 pixel CdZnTe detector, we obtained an energy spectrum, the energy resolution of which is 4.5% at the 59.5keV line of 241Am source.

A Fast Optical Spectrum Data Acquisition Method Based on FPGA and DSP

Abstract This paper presents a fast CCD optical spectrum data acquisition method based on FPGA, FIFO and DSP. Introduces a linear CCD timing sequence control signal generation and high speed ADC interface with FIFO and DSP in detail, publishes this design key parts FPGA logic schematic and VHDL source code, provides a general solution for universal high speed CCD optical spectrum data acquisition and analysis system.

Numerical Control Programming System for Mill-Turn Machining

To develop the numerical control program of mill-turn machine, the traditional method is to apply the computer-aided design and manufacture software to construct the geometric model, then to generate tool path and convert the path to NC program. For complex numerical control program of mill-turn machine, such as the multiple turret synchronized motion machining, because of the need to control time sequence, the NC program is highly required on using of dedicated software system. The objective of this paper is to establish a mill-turn machining system with window interface of via the language of Borland C++ Builder. The developed system can plan the machining path of simple mill-turn features, including turning shape, axial slot milling, and radial packet milling, and generate the corresponding NC program. For the milling functions, after the offset coordinates are calculated along the polygonal angle vector in the center point of cutters, the NC program is generated. For the turning functions, through importing the 2D DXF (Drawing Exchange Format) file and inputting related configurations, the entity coordinates can be retrieved and the corresponding NC program is then converted. By means of the solid cutting simulation software and practical cutting experiment for the generated numerical control program, the accuracy of the tool path generation algorithm is confirmed. Hence, the cost of purchasing commercial software can be saved and the time of generating program can also be decreased so that the working efficiency can be enhanced.

The Timing System of the Neutral Beam Injector on EAST

In order to synchronize the elements of the EAST Neutral Beam Injector (NBI) spatially located in several places, a distributed Timing System (TS) is developed in this paper. The timing system provides a clock reference for synchronization and an interlock protection of the EAST NBI system. It sends timing signals to field devices, controls the pulse widths of the timing sequences, and provides a sampling clock for the Data Acquisition System (DAS). The timing system also generates analog waveforms to control power supplies and gas supplies according to the operator's configuration. The timing system is developed on a PXI (PCI eXtensions for Instrumentation) platform consisting of a LabVIEW workstation and a timing control terminal. The timing control terminal consists of a timing node and several control interface crates. Two timing nodes are configured in one beam line. Each node is responsible for the timing sequence, analog generation and feedback control for one ion source. The architecture and implementation of the timing system are presented in this paper.