Delay Control Research Articles

Intelligent Time Delay Control of Telepresence Robots Using Novel Deep Reinforcement Learning Algorithm to Interact with Patients

Telepresence robots are gaining more popularity as a means of remote communication and human–robot interaction, allowing users to control and operate a physical robot remotely. However, controlling these robots can be challenging due to the inherent delays and latency in the communication systems. In this research paper, we propose a novel hybrid algorithm exploiting deep reinforcement learning (DRL) with a dueling double-deep Q-network (DDQN) and a gated recurrent unit (GRU) to assist and maneuver the telepresence robot during the delayed operating signals from the operator. The DDQN is used to learn the optimal control policy for the telepresence robot in a remote healthcare environment during delayed communication signals. In contrast, the GRU is employed to model the control signals’ temporal dependencies and handle the variable time delays in the communication system. The proposed hybrid approach is evaluated analytically and experimentally. The results demonstrate the approach’s effectiveness in improving telepresence robots’ tracking accuracy and stability performance. Multiple experiments show that the proposed technique depicts improved controlling efficiency with no guidance from the teleoperator. It can control and manage the operations of the telepresence robot during the delayed communication of 15 seconds by itself, which is 2.4% better than the existing approaches. Overall, the proposed hybrid approach demonstrates the potential implementation of RL and deep learning techniques in improving the control and stability of the telepresence robot during delayed operating signals from the operator.

A dual-loop active vibration control technology with an RBF-RLS adaptive algorithm

Active control strategies have been widely used in micro-vibration isolation with higher performance requirements. Aiming at the problem of insufficient vibration isolation performance due to time delay in feedback control, the ground-based feedforward active control is introduced to compensate in advance for higher pursuit. However, the inaccuracy of the feedforward control reference model severely restricts the vibration isolation performance. With the assistance of RBF neural network algorithm for accurate real-time identification of online model, a feedforward-feedback dual-loop active hybrid control (DAHC) strategy based on the RBF-RLS adaptive algorithm is proposed in this paper. The adaptive feedforward control uses the RBF neural network algorithm to identify the accurate model of the system online, and input it to the transverse filter of the RLS adaptive control algorithm for recursive calculation, which can effectively reduce the system error caused by the inaccuracy of the model. The experimental results show that the accuracy of online model affects the amplitude attenuation performance by 57.1%. DAHC strategy can greatly reduce the resonance peak by 25.02 dB in micro-vibration. Real applicative experiment further proves the effectiveness of our proposed algorithm.

Model-free super-twisting terminal sliding mode controller using sliding mode disturbance observer for n-DOF upper-limb rehabilitation exoskeleton with backlash hysteresis

This paper proposes a model-free super-twisting terminal sliding mode controller (MF-STTSMC) for the n-DOF upper-limb rehabilitation exoskeleton in the presence of external disturbance and backlash hysteresis. This ultra-local model-based control scheme consists of a sliding mode disturbance observer (SMDO) and a super-twisting non-singular fast terminal sliding mode controller (ST-NFTSMC). The ultra-local model is used to approximate the origin complex exoskeleton system in a short sliding time window, which avoids the requirement for accurate modelling and decreases the difficulty of controller design. To compensate for the lumped uncertainties, the SMDO is constructed to achieve finite-time observation and zero estimation error. Besides, to realise finite-time convergence of sliding surface and tracking error with less chattering, the ST-NFTSMC is proposed by employing a super-twisting algorithm. Furthermore, the stability of a closed-loop system with MF-STTSMC is ensured by using the Lyapunov theorem. Finally, to validate the proposed strategy, co-simulations of 7-DOF iReHave upper-limb exoskeleton are realised by using SolidWorks, SimMechanics, and Matlab/Simulink. Compared to time-delay estimation-based intelligent proportional-derivative control (TDE-iPD), α-variable adaptive model-free controller (α-AMFC), and inclusive and enhanced time delay controller (IETDC), the higher performances of the proposed MF-STTSMC are demonstrated.

Enhanced Dispersive Waves Generation via Sinusoidally Spectral Phase‐Modulated Pulses

AbstractThe dispersive waves (DWs) emitted from a Gaussian pulse with an initial sinusoidally spectral phase (SSP) modulation are investigated. By tailoring the modulation depth and frequency, the SSP results in complex pulses shape with a multipulses structure ranging from Airy‐like to pulse sequences having controllable delay and phase. These salient features are able to control and enhance the radiation frequency and energy conversion efficiency of the DWs. The resonant frequencies based on a modified phase‐matching condition are given, which agree with the numerical results obtained by solving the nonlinear Schrödinger equation directly. The results not only further extend the application of the pulse shaping technology in fiber optics, but also provide an alternative approach to manipulate the process of DWs emission which is relevant to the generation broadband supercontinuum as well as frequency comb.

Adverse events are not increased by controlled delay in surgery of acute upper extremity fractures

Management of the operative treatment of fractures is challenged by daily variation in patient flow. For upper limb fractures there has recently been an increasing tendency to temporarily discharge the patient to wait for a daytime operation to be performed during the next few days. The objective of this study was to study the safety of controlled delay in surgery. Upper limb fractures (N = 1 944) treated in a level 2 trauma center from 2010 to 2016 were identified and included in this retrospective cohort study with 5-year follow-up. Delay in surgery, inpatient time, readmissions, ED revisits and mortality were analyzed. Depending on the nature of the injury, controlled delay to surgery was implemented. Urgency of surgery was coded as green (2 days to 2 weeks) yellow (8–48 h) or red (less than 8 h). Harms and benefits to the groups were compared. Controlled delay of surgery (median delay of 5 days 7 h) was applied in 1 074 out of 1 944 fractures. The number of revisits to the emergency department (11.1% vs. 17.9–24.1%, p < 0.001) or hospital readmissions for any reason (0.99 per 100 person years in the delayed group vs. 3.74 and 4.35 in the non-delayed groups, p < 0.001) was no higher in patients with delayed (green) compared to those with non-delayed (yellow and red) operations. Inpatient time was significantly lower in the delayed group than other groups (IRR 2.31–3.36, (p < 0.001)). The standardized mortality ratio was 0.83 (CI 0.57–1.22) in the delayed group vs. 1.49 (CI 1.17–1.90) and 1.61 (CI 1.16–2.23) in the non-delayed groups. Controlled delay in upper limb trauma surgery did not lead to increased readmissions or mortality and was associated with reduced inpatient time.

Controllability of retarded semilinear systems with control delay

Controllability of retarded semilinear systems with control delay

Kinetics of interaction of myosin-nucleotide complex and actin.

In the actomyosin cycle myosin hydrolyses ATP and binds actin, initially weakly and then strongly. The timing of myosin ATP hydrolysis and binding to actin remains elusive. We performed double-mixing transient experiments to characterize the kinetics of actomyosin interaction shortly after ATP binding to myosin. In the experiment we first rapidly pre-mixed rabbit skeletal myosin S1 and stoichiometric ATP and after a controlled delay rapidly added unregulated F-actin to the mixture. The first mixing produces mainly complexes of myosin.ATP and myosin.ADP.Pi, we expected to have small quantity of unreacted myosin and complex of myosin.ADP in the mixture. In the second mixing myosin binds actin. We detected transient fluorescence of pyrene labeled actin and changes in the light scattering after the second mixing. It is accepted that the change of fluorescence of pyrene labeled actin reflects strong actomyosin binding due to the conformational change of actin induced by bound myosin. One can suggest that light scattering reflects the formation of weakly bound actomyosin, since light scattering is sensitive to the size of the protein complex, and not the strength of binding. In our experiments we varied protein concentrations and the time of the delay between the first and the second mixing, which is the myosin-nucleotide incubation time. We fitted obtained transients to the solution of the system of differential equations, describing the evolution of this composite protein system. We discuss models of actomyosin interaction that correspond to the observed transient kinetics and the possible cooperativity of myosin interaction with unregulated actin.

Adaptive quasi-proportional resonant control with parameter estimation for PMSM sensorless control

Conventional sliding mode control (SMO) utilizes a sign function and a low-pass filter (LPF) to achieve sensorless control of a permanent magnet synchronous motor (PMSM). However, the introduction of the sign function generates a large number of high harmonics, resulting in a significant system output chattering, whereas the addition of the LPF generates control delays and phase shifts. These degrade the PMSM speed and the position estimation accuracy and reduce the system control performance. To improve the performance of the PMSM, adaptive quasi-proportional resonant sensorless control with parameter estimation (AQPR_PE) is proposed. In this control model, an adaptive quasi-proportional resonance controller is used reduce the system output error and to weaken the chattering phenomenon. Meanwhile, the system PMSM parameters are estimated online and fed back to the control model to improve the system parameter robustness and the control accuracy. The Bode diagram, Popov theory, and root trajectory are used to analyze the stability of AQPR, parameter estimation, and AQPR_PE, respectively. Finally, the effectiveness of the proposed method is demonstrated by experimental validation.

Information Fusion Tracking Control for a Class of Discrete-Time Systems With Delays

In this article, the optimal tracking control problem for a class of discrete time-delay systems with disturbance is studied using the information fusion control methodology. First, the disturbance estimation is regarded as a minimization problem, and an information fusion disturbance observer (IFDO) is designed. Second, combining the soft constraint requirement of the output tracking error contained in the performance index function, a fusion filter is constructed to estimate the system co-state and its information weight under system state and input delays. Finally, the obtained co-state and its information weight, the soft constraint requirement of the control input contained in the performance function, as well as the system delay dynamics, are all transformed into the information equations about the control input, and then the information fusion delay controller (IFDC) is directly obtained by fusing these information equations. As a result, the negative effects caused by disturbance and time delays can be effectively compensated at the same time. The convergence of the tracking errors of the closed-loop system is guaranteed by the Lyapunov stability theory. Numerical simulation results have been provided to demonstrate the effectiveness and robustness of the proposed control algorithm.

Magneto-electric self-powered electrical output and ignition performance of a multifunctional projectile under impact loading

To meet the requirements of miniaturized multifunctional ammunition with force-thermal-electromagnetic, a new concept is adopted to develop a small-caliber ammunition, which uses a magneto-electric self-powered ignition system with high overload generated by penetrating the target to ignite the active material inside the ammunition. In this paper, the force and motion of the magnet during projectile penetrating into the target under different impact loads are analyzed by joint simulation of ABAQUS/Explicit and Maxwell softwares, and the ignition reliability and relative motion velocity of magnet and coil are evaluated by the ignition system. The results show that the self-powdered ignition system can be ignited reliably when the geometric size of the magnet is Φ × L = 8 × 12 mm2, the turn number of the coil is 350 and the relative motion speed of the magnet and the coil is higher than 40 m/s. The ignition threshold energy of the military electric ignition head used in experiment is calculated between 0.29∼0.35 mJ. The maximum and minimum ignition delay times are 139 μs and 485 μs in experiments, respectively, and the corresponding relationship is determined by adjusting the relative position of the coil, magnet and magnet's geometric size, which can provide a controllable ignition delay time for penetrating targets with different natural characteristics.

Effect of Chitosan nanoparticles on quality indices, metabolites, and vase life of Rosa hybrida cv. Black magic

BackgroundChitosan nanoparticles (CTS-NPs) protect the active ingredients from the environment for a specific period and reduces sweating, control weight loss, delay ripening, and increase vase life. So, a factorial experiment was carried out as a randomized complete design in three replications to investigate the efficiency of CTS-NPs in quality improvement and longevity extension of cut rose flowers.ResultsThe 15-day maximum vase life was attained by the rose placed in a preservative solution containing 10 mg L−1 CTS-NPs. CTS-NPs also reduced microbial growth as compared to controls. Total phenolics, total flavonoids, and amount of anthocyanin in treated petals were dramatically increased. CTS-NPs solutions especially at 10 and 15 mg L−1 concentrations, markedly reduced the H2O2 and malondialdehyde at the end of 15th day and maintained the membrane index. The protein and carbohydrate and petals anthocyanin content and enzymatic activities such as superoxide dismutase, polyphenol oxidase, peroxidase, catalase and ascorbate peroxidase increased in cut roses placed in 10 mg L−1 CTS-NPs vase solution which in turn caused to increase in vase life.ConclusionCTS-NPs especially at a level of 10 mg L−1 can assist plants to enhance light usage efficiency, as well as promote photosynthetic carbon fixation and the production of additional carbohydrate products for plant growth and development.Graphical

The processes with fractional order delay and PI controller design using particle swarm optimization

In this study, the stability analysis of systems with fractional order delay is presented. Besides, PI controller design using particle swarm optimization (PSO) technique for such systems is also presented. The PSO algorithm is used to obtain the controller parameters within the stability region. As it is known that it is not possible to investigate the stability of systems with fractional order delay using analytical methods such as the Routh-Hurwitz criterion. Furthermore, stability analysis of such systems is quite difficult. In this study, for stability testing of such systems, an approximation method previously introduced in the literature by the corresponding author is used. In addition, the unit step responses have been examined to evaluate the systems' performances. It should be noted that examining unit step responses of systems having fractional-order delay is not possible due to the absence of analytical methods. One of the aims of this study is to overcome this deficiency by using the proposed approximation method. Besides, a solution to the question of which controller parameter values should be selected in the stability region, which provides the calculation of all stabilizing PI controllers, is proposed using the PSO algorithm.

Effect of Signal Coordination on the Traffic Operation of Urban Corridor

The severity of traffic congestion has increased in Baghdad city and influenced the public’s perception of the community. Extended travel time is experienced by users of the urban street system, so optimal traffic operation with a coordinated traffic signal system becomes necessary. Also, it is needed to alleviate congestion and progress traffic movement along the urban corridor. This study aims to evaluate and optimize traffic signal timing for selected intersections on Palestine arterial corridor and apply the coordinated signal system to reduce the users’ travel time on the selected urban corridor. Analyzing and evaluating congested signalized intersections using Synchro (ver.9) (Al-Nakhala intersection, Al-Sakhra intersection, and Beirut intersection) were performed. Also, their adopted strategies for improving traffic performance and reducing delays were provided. The overall assessment in terms of the level of service for the current traffic states is (LOS F) with an average control delay of (197.2, 166.8, and 262.3) sec/veh. for the Al-Nakhala, Al-Sakhra, and Beirut intersections respectively. The queue length appears after two cycles, becoming more severe congestion at intersections under oversaturated traffic conditions. The performance operation efficiency improved by reducing the control delay from (197.2 to 88) sec/veh, (166.8 to 46) sec/veh, and (262.3 to 76) sec/veh for the Al-Nakhala, Al-Sakhra, and Beirut intersections respectively. Even at high volume and oversaturated conditions, the blocked intersections were effectively alleviated. Finally, it was observed that the proposed signal coordination, built on standard actuated control significantly performed along the urban corridor, reducing vehicles’ delay. However, there are still concerns regarding the flow-to-capacity ratio (v/c ratio is still greater than 1), and the level of service is still in poor conditions (LOS E) for Beirut and (LOS F) for Al-Nakhala intersections. The application of signal coordination improved traffic progression by reducing travel time, and vehicle delay and alleviating blocked intersections.

Design and analysis of higher-order repetitive sliding mode controller for uncertain linear systems with time-varying periodic disturbances

In this article, a discrete-time design of higher-order repetitive sliding mode controller (HO-RSMC) for uncertain linear systems with time-varying periodic disturbances is presented. In the design, a higher-order repetitive control (HORC) is employed to significantly suppress the periodic exogenous disturbance with period variation. The HORC-based control system offers a slow transient response due to the multiple control delays. Moreover, since the system stability is easily affected by model uncertainties, an output-feedback sliding mode controller (SMC) is added to overcome the shortcomings of HORC. Stability analysis of the resulting closed-loop system is rigorously provided. The simulation results and comparison studies confirm the effectiveness and good performance of the proposed design.

Existence of chaos in controlled first-order partial difference equations with general delay controllers

This paper is concerned with chaos in a class of controlled first-order partial difference equations with general delay controllers. Three criteria of chaos are established by applying snap-back repeller theory. All the equations are proved to be chaotic in the sense of both Devaney and Li-Yorke when they satisfy some weak conditions. Three examples are provided with computer simulations.

Explicitly incorporating surrogate safety measures into connected and automated vehicle longitudinal control objectives for enhancing platoon safety

The concepts of Connected and Automated Vehicles (CAV) and vehicle platooning have generated high expectations regarding the safety performance of future transportation systems. Existing CAV longitudinal control research primarily focuses on efficiency and control stability, by considering different inter-vehicle spacing policies. In very few cases, safety was also considered as a constraint, but not in the main control objectives. Theoretically, stability can only guarantee that CAV platoons eventually achieve an equilibrium state but is unable to promise safety along the process of achieving equilibrium. It is important to note that CAV does not mean absolutely safe, and its longitudinal or platoon control safety performance depends on how the control algorithms are designed, how accurately it can detect and predict its lead vehicle’s (could be a human-driven vehicle) next move, and other practical factors such as control and communication delays. To optimize CAV platoon safety, this study integrates surrogate safety measures (SSM) and model predictive control (MPC) into CAV longitudinal control for trajectory optimization. SSM has been widely adopted for modeling the safety consequences of various vehicle control strategies and identifying near-crash events from either simulated or field-captured traffic data. This study directly incorporates three typical SSM into the longitudinal control objectives of CAV and constructs a state-space MPC algorithm to model how these SSM vary as a result of CAV dynamics. Numerical examples are provided to show the performance of these SSM-based optimal CAV longitudinal control methods under traffic flow perturbations. To further confirm the necessity of explicitly considering SSM in CAV longitudinal control and its effectiveness in reducing rear-end collision risk, the proposed methods are compared with three classical longitudinal control models that do not consider SSM based on microscopic traffic simulation. It is noted that all SSM-based optimal control methods perform better than others as manifested by some key risk indicators, demonstrating the importance of explicitly considering SSM and safety in CAV longitudinal control.

Jitter-based Adaptive True Random Number Generation Circuits for FPGAs in the Cloud

In this article, we present and evaluate a true random number generator (TRNG) design that is compatible with the restrictions imposed by cloud-based Field Programmable Gate Array (FPGA) providers such as Amazon Web Services (AWS) EC2 F1. Because cloud FPGA providers disallow the ring oscillator circuits that conventionally generate TRNG entropy, our design is oscillator-free and uses clock jitter as its entropy source. The clock jitter is harvested with a time-to-digital converter (TDC) and a controllable delay line that is continuously tuned to compensate for process, voltage, and temperature variations. After describing the design, we present and validate a stochastic model that conservatively quantifies its worst-case entropy. We deploy and model the design in the cloud on 60 EC2 F1 FPGA instances to ensure sufficient randomness is captured. TRNG entropy is further validated using NIST test suites, and experiments are performed to understand how the TRNG responds to on-die power attacks that disturb the FPGA supply voltage in the vicinity of the TRNG. After introducing and validating our basic TRNG design, we introduce and validate a new variant that uses four instances of a linkable sampling module to increase the entropy per sample and improve throughput. The new variant improves throughput by 250% at a modest 17% increase in CLB count.

Controllability Criteria for Nonlinear Impulsive Fractional Differential Systems with Distributed Delays in Controls

We establish a class of nonlinear fractional differential systems with distributed time delays in the controls and impulse effects. We discuss the controllability criteria for both linear and nonlinear systems. The main results required a suitable Gramian matrix defined by the Mittag–Leffler function, using the standard Laplace transform and Schauder fixed-point techniques. Further, we provide an illustrative example supported by graphical representations to show the validity of the obtained abstract results.

BoxCARS 2D IR spectroscopy with pulse shaping.

BoxCARS and pump-probe geometries are common implementations of two-dimensional infrared (2D IR) spectroscopy. BoxCARS is background-free, generally offering greater signal-to-noise ratio, which enables measuring weak vibrational echo signals. Pulse shapers have been implemented in the pump-probe geometry to accelerate data collection and suppress scatter and other unwanted signals by precise control of the pump-pulse delay and carrier phase. Here, we introduce a 2D-IR optical setup in the BoxCARS geometry that implements a pulse shaper for rapid acquisition of background-free 2D IR spectra. We show a signal-to-noise improvement using this new fast-scan BoxCARS setup versus the pump-probe geometry within the same configuration.

Analytical and experimental validation of vibration isolation system with complementary stiffness and composite control

In the spacecraft, optical payloads are greatly disturbed by micro-vibration. Therefore, the active-passive vibration isolation system (APVIS) with stable performance and high efficiency has become the focus of many scholars, with the increasing demand for vibration isolation. The voice coil motor (VCM) is often used to verify the APVIS. However, due to processing and installation errors, noncontact and low stiffness between the mover and stator of the VCM, the normal operation of the system will be affected. An APVIS based on the complementary pair of axial and radial stiffness is proposed in this paper. Structurally, the flexible joint and the membrane are used to compensate for each other and explained and verified from the mechanism and experiment. In the control algorithm, feedback control and feedforward control are used to build an active composite control (ACC) algorithm, and the two compensate each other to solve the problems of feedback control time delay and feedforward control instability. Experimental results show that the errors of the axial force transmission and the output force of the VCM are only 1.09% and −1.5%, respectively. The designed structure can ensure the co-axiality of the mover and stator, and the VCM can work normally. After control, the ACC algorithm can achieve vibration attenuation of 95.8%, the amplitude at natural frequency is decreased by 27.53 dB, which verifies the effectiveness of the ACC algorithm.