Real-time Feedback Control System Research Articles

Frontiers in construction 3D printing: self-monitoring, multi-robot, drone-assisted processes

AbstractTo overcome productivity issues and revolutionize the stagnating construction industry, a large amount of research efforts has been devoted to robot-assisted construction technology. The advancements in robotics including mechanical system design, tool design, digital system design, and numerical control systems design enabled engineers to create complex geometries that are infeasible for conventional construction methods. In addition, innovative robotic systems that utilize mobile platforms, multiple robots, and unmanned aerial vehicles have demonstrated significant promise in fully automating the construction process. This work will provide a perspective on the state-of-the-art applications of robotics in the revolution of construction, where a comprehensive review of the current development of the relevant software and hardware, 3D concrete printing (3DCP), robot-assisted assembly of discrete prefabricated blocks, real-time quality monitoring and feedback control systems, and typical innovative robot-assisted structural designs are conducted. Finally, the limitations of existing robot-assisted construction technology are identified, which leads to several recommendations for future research toward fully automatic construction.

Study on penetration depth in laser welding: A process information database-based control strategy and OCT measuring verification

Penetration depth acts as a crucial indicator reflecting laser welding quality, thus the control of its stability and the perception of its fluctuation state are increasingly garnering attention. This paper proposes a process information database-based control strategy for penetration depth, and the control validity is verified through penetration depth detection utilizing optical coherence tomography (OCT). The process information database stores diverse expected penetration depth knowledge formed by a substantial quantity of varying welding speeds with fixed other process parameters under undisturbed welding conditions. In the database, the stable average values inside the standard penetration depth information and the corresponding heat input (HI) values are connected and mapped via an artificial neural network (ANN). In response to abnormal variations in the penetration depth curve caused by interferences during welding, according to the HI gap predicted by the trained ANN from the penetration depth gap arising from the curve deviation, the control unit can calculate the new welding speed required to feed the penetration depth curve back to within the steady fluctuation range. Based on OCT, the keyhole depth signal is acquired, and a deep belief network is built to predict the penetration depth curve via the correlation between the reconstructed keyhole depth obtained by ensemble empirical mode decomposition and the penetration depth. This detection method demonstrates that the penetration depth curve can be controlled accurately. Finally, a closed-loop real-time feedback control system for penetration depth is established.

Real-time quality control of dripping pill’s weight based on laser detection technology

The present work reports developing the first process analytical technology (PAT)-based real-time feedback control system for maintaining the Ginkgo biloba leaf dripping pills weight during manufacturing. The opening degree of the drop valve and the weight of dripping pills were chosen as the manipulated variable and as the controlled variable, respectively. A proportional-integral controller was programmed to automatically reach the desired dripping pills weight by adjusting the opening degree of the drop valve. The closed-loop feedback control system could automatically compensate for the disturbances and ensure a predefined weight of the dripping pills with excellent robustness, high accuracy, and high efficiency during manufacturing. Furthermore, the closed-loop feedback control system improved the process capability of the dripping process, and the process capability index was > 1.67. This study provides a new approach to real-time control of the weight of dripping pills and improves the process capability during Ginkgo biloba leaf dripping pills manufacturing.

Feedback Control Strategy for Transient Stability Application

Power systems are subjected to a wide range of disturbances during daily operations. Severe disturbances, such as a loss of a large generator, a three-phase bolted fault on a generator bus, or a loss of a transmission line, can lead to the loss of synchronism of a generator or group of generators. The ability of a power system to maintain synchronism during the few seconds after being subjected to a severe disturbance is known as transient stability. Most of the modern methods of controlling transient stability involve special protection schemes or remedial action schemes. These special protection schemes sense predetermined system conditions and take corrective actions, such as generator tripping or generation re-dispatch, in real time to maintain transient stability. Another method is the use of a real-time feedback control system to modulate the output of an actuator in response to a signal. This paper provides a fundamental evaluation of the use of feedback control strategies to improve transient stability in a power system. An optimal feedback control strategy that modulates the real power injected and absorbed by distributed energy-storage devices is proposed. Its performance is evaluated on a four-machine power system and on a 34-machine reduced-order model of the Western North American Power System. The result shows that the feedback control strategy can increase the critical fault clearing time by 60%, thereby improving the transient stability of the power system.

Real-time density feedback control in ADITYA-U Tokamak

A real-time density feedback control system with a 100 GHz heterodyne interferometer has been designed, developed, and commissioned in ADITYA-U tokamak. It consists of three subsystems i.e. density measurement, feedback control, and gas fuelling. A proportional feedback controller is configured in voltage amplitude mode to operate the piezo valve for gas injection. Experiments are performed during plasma discharges to achieve a predefined density evolution as well as constant density. Stickiness of the piezo valve restricts the temporal response of the valve. It is required to minimize during the plasma discharge for a fast density response which is achieved by a short preceding voltage pulse known as a stick pulse. This paper describes the implementation of a real-time density feedback control system which is successfully validated using another existing 140 GHz interferometer system in ADITYA-U. Moreover, the developed system consumes low power, is cost-effective and re-programmable, can be easily upgraded, and provides interlock with plasma parameters.

The Electronics Design of Real-Time Feedback Control System in KTX

A feedback control system has been designed for Keda Torus eXperiment (KTX) to achieve the following goals: 1) 3-D plasma stability control and 2) improvement of plasma discharge quality. The real-time electronics system which is the key unit of this feedback control system helps to resolve the lack of high-speed transmission and real-time processing capability of the previous data acquisition (DAQ) system. The electronics system is implemented in PXI Express using a modular, distributed architecture. Field-programmable gate array (FPGA) is the core component of the electronics system. This article describes in detail the reasons for the choice in the hardware components. Optical communication has been evaluated for real-time communication by using the Aurora protocol. Measurements have been executed on a prototype system. Results from several tests comparing the performance of different solutions are also provided. 2-D spatial Fourier analysis based on FPGA is first used on the reversed field pinch (RFP) fusion device. Results indicate that the system can control the whole process and calculation in low latency.

Real-Time Image-Based Feedback Control of Laser Powder Bed Fusion

Abstract This letter presents the design and experimental validation of a real-time image-based feedback control system for metal laser powder bed fusion (LPBF). A coaxial melt pool video stream is used to control laser power in real-time at 2 kHz. Modeling of the melt pool image response to changes in the input laser power is presented. Based on this identified model, a real-time feedback controller is implemented experimentally on a single track and part scales. On a single-track scale, the controller successfully tracks a time-varying melt pool reference. On a part-level scale, the controller successfully regulates the melt pool image signature to the desired reference value, reducing layer-to-layer signal variation and eliminating within-layer signal drift.

Influences of powder characteristics and recoating conditions on surface morphology of powder bed in metal additive manufacturing

Metal additive manufacturing technology requires a real-time monitoring and feedback control system to assure the quality of the final products. In particular, it is essential to reveal the phenomena of recoating and melting-solidification processes in laser powder bed fusion using a real-time monitoring system because they influence strongly the occurrence of defects. This study was conducted to elucidate the correlation among the powder characteristics, recoating conditions, and surface morphology of a powder bed in the recoating process to determine the relationship between the surface morphology of the powder bed and the final product quality. To this end, a surface morphology measurement system composed of a powder recoating test bench and a layer surface morphology measurement apparatus was first designed and fabricated. Then, it was used to quantify the surface morphology of the powder bed. Specifically, the influences of the different powder characteristics and the recoating parameters of the powder supply ratio and recoating speed on the surface morphology of the powder bed were investigated using various powders of Al-10Si-0.4Mg (AlSi10Mg) alloy and Inconel 718 (IN718) alloy. The surface morphology of the powder bed was measured as the value of 2σ at a resolution of 30 μm in height. It was found that the angle of repose and the basic flow energy of the bulk powder are promising parameters for evaluating the surface morphology. The surface morphology was significantly affected by the powder characteristics and recoating speed. The value of 2σ for the AlSi10Mg powder increased rapidly over a recoating speed of 50 mm/s for all powders. The value of 2σ for the irregularly shaped AlSi10Mg powder was approximately 19 μm, and the 2σ values for the other powders were approximately 17 μm at a recoating speed of 15 mm/s. However, at a recoating speed greater than 300 mm/s, the irregularly shaped powder exhibited better surface morphology than did the spherical powder. The recycling process deteriorated the flowability of the new powder. However, the surface morphology of the spherical recycled powder was similar to that of the spherical powder. Consequently, the correlation among the powder characteristics, recoating conditions, and surface morphology of the powder bed was revealed by employing the surface morphology measurement system. Quantification of the surface morphology of the powder bed using the monitoring system facilitates control of the recoating process to prevent the occurrence of defects.

Parameter dependencies of the experimental nitrogen concentration required for detachment on ASDEX Upgrade and JET

• An experimental scaling law to predict the threshold nitrogen concentration required for detachment is presented based on spectroscopic measurements of N II emission. • A least squares regression show that the threshold nitrogen concentration required for detachment depends strongly on the midplane separatrix density, with an exponent of −2.7 on AUG and −2.4 on JET, and approximately linearly with the power crossing the separatrix. • These two parameter dependencies are consistent with measurements on both ASDEX Upgrade and JET. • Equivalent predictions based on the well-known Lengyel model over-predict the absolute measured nitrogen concentration and show a weaker dependence on the separatrix density. While current tokamak experiments are beginning to use real-time feedback control systems to manage the plasma exhaust, future tokamaks still require validation of theoretical models used to predict the threshold impurity concentration required to sufficiently reduce the power and particle fluxes to the divertor. This work exploits new spectroscopic measurements of the divertor nitrogen concentration, c N , in partially detached N 2 -seeded H-mode plasmas on ASDEX Upgrade (AUG) and JET with the ITER-Like Wall (JET-ILW) to test the parameter dependencies of the power flowing to the outer divertor, P div , outer , and the separatrix electron density, n e , sep . A least-squares regression of the AUG measurements demonstrates that the threshold c N required for detachment scales as c N ∝ P div , outer 1.19 ± 0.32 n e , sep - 2.77 ± 0.36 . This scaling of n e , sep is also consistent with the measurements from JET which, at constant P div , outer , show c N ∝ n e , sep - 2.43 ± 0.27 . The dependencies of P div , outer and n e , sep is demonstrated over at least a factor of two change in both parameters and indicates a stronger dependence on n e , sep in comparison to the Lengyel model, which could be due to the assumption in this model that the heat flux channel width is independent of density. This first assessment of detachment scaling with impurity seeding highlights the need for further analysis of the systematic uncertainties of the measurement and more consistent scenarios from more tokamaks to investigate the machine size scaling.

Effective age of information in real-time wireless feedback control systems

Ultra-reliable and low-latency communication (URLLC) is one of the most important scenarios in forthcoming fifth generation (5G) cellular networks to ensure timely exchange of information and realize real-time wireless control. In URLLC, timely information update needs to be guaranteed since control performance, e.g., control cost and stability, is directly determined by timely control information update. In this paper, we introduce an effective age of information (EAoI) to evaluate the timeliness of information update in control process. We consider the control process with two phases: sensor to controller phase and controller to actuator phase. We adopt first-generate-first-serve (FGFS) M/M/1/1 → M/M/1/2 and FGFS M/M/1/1* → M/M/1/2* tandem queuing models to represent control process and we use finite-state Markov chains to describe control information updates. By studying state transitions, we calculate the average EAoI for both tandem queuing models. More importantly, we analyze throughput of wireless control systems and its relationship with average EAoI, which provides a guideline for URLLC system design in real-time feedback control systems. Simulation results show the advantage of using EAoI.

Applying a 6-axis Mechanical Arm Combine with Computer Vision to the Research of Object Recognition in Plane Inspection

The study of a robotic arm copied with 3D-printer combines computer vision system with tracking algorithm is proposed in the paper. Moreover, the designing to the intelligent vehicle system with the integration of electromechanical for planning to apply it to the operations in various fields is presented too. The main purpose of this work tries to avoid the complicated process with traditional manual adjustment or teaching. It is expected to achieve the purpose that the robotic arm can grab the target automatically, classify the target and place it in the specified area, and even accurately realize the classification through training to distinguish the characteristics of the target. Eventually, the mechanical arm's movement behavior is able to be corrected through a real-time image data feedback control system. In words, with the experiment that the computer vision system is used to assist the robotic arm to detect the color and position of the target. By adding color features for algorithm training as well as through human-machine collaboration, which approves that the proposed algorithm has well known that the accuracy of target tracking definitely depends on both of two parameters include “object locations” and the “illustration direction” of light source. The difference will far from 75.2% to 89.0%.

High-quality quantum process tomography of time-bin qubit’s transmission over a metropolitan fiber network and its application

We employ quantum state and process tomography with time-bin qubits to benchmark a city-wide metropolitan quantum communication system. Over this network, we implement real-time feedback control systems for stabilizing the phase of the time-bin qubits, and obtain a 99.3% quantum process fidelity to the ideal channel, indicating the high quality of the whole quantum communication system. This allows us to implement field trial of high performance quantum key distribution using coherent one way protocol with average quantum bit error rate and visibility of 0.25% and 99.2% during 12 hours over 61 km. Our results pave the way for the high-performance quantum network with metropolitan fibers.

Reliable Guaranteed Cost Control of Uncertain Systems with Nonlinear Perturbations

Network control system (NCS) is a distributed real-time feedback control system with the continuous development of network technology. It is generally composed of network, controller, actuator and sensor. It has brought great convenience to people in many fields, but it also has many problems, which makes the research of control system more complicated. Recently, there have been some efforts to tackle the reliable guaranteed cost controller design problem, and some good results have also been obtained for the continuous-time and for the discrete-time. However, there have been few results in the literature of an investigation for the reliable guaranteed cost controller design of nonlinear uncertain systems with time-varying state delay and actuator failure. This paper concerns the reliable guaranteed cost control problem of uncertain systems with time-varying state delay and nonlinear perturbations for a given quadratic cost function. The problem is to design a reliable guaranteed cost state feedback control law which can tolerate actuator failures, such that the closed-loop system is asymptotically stable and the closed-loop cost function value is not more than a specified upper bound. Firstly, the existence condition of reliable guaranteed cost control law is given by constructing Lyapunov stability function and using linear matrix inequality (LMI). Secondly, the design method of the optimal reliable guaranteed cost controller is given by solving the convex optimization problem with LMI constraints, which minimizes the upper bound of guaranteed cost for closed-loop systems. In the end, the numerical simulation result illustrates the effectiveness of the proposed method.

Optical surface measurements of a wavelength-tuned Fizeau interferometer based on an optical power, real-time feedback and compensation system

The wavelength-tuned Fizeau interferometer achieves the desired phase for interferograms based on the use of a phase-shifting technique. It can then use it to measure the surface and thickness of a parallel transparent object. However, phase errors occur owing to the inherent changes of the power of the tunable laser diode induced upon laser wavelength changes. To improve the measurement accuracy, we propose an optical power, real-time feedback control system, and a synchronous calibration scheme. The significance of the proposed method relies on the fact that the laser intensity variation can be detected quickly and compensated by adjusting the bias voltage. To verify the effectiveness of the proposed system, we incorporated it into the optical system of the wavelength-tuned, phase-shifting interferometer for experimentation. The control principles and the experimental validation of the proposed system are described in this letter.

Novel evaluation method for electrosurgical ablation by monopolar hot biopsy forceps for colonoscopy.

AimThis study evaluates tissue injury, which results from electrosurgical ablation, by correlating lesion depth to tissue impedance, and introduces a newly developed real-time feedback control system that can be applied for preventing excessive tissue injury. Although some previous studies had evaluated such tissue injuries in other ways, a specific mechanism is necessary to actually prevent excessive tissue injury.Materials and methodsAblation tests were performed by using an impedance bridge circuit and gel block that have been developed in two previous studies. Depth of the ablation site was measured with the use of a laser displacement measurement device. To simplify the programing work, voltage was used, as a substitution of tissue impedance, to evaluate tissue injury.ResultsThe depth of the ablation site was found to increase with either increased power setting or ablation duration, and the depth was analyzed to investigate correlation with measured voltage. The real-time feedback control system was developed by achieving communication between LabVIEW and an Arduino microcontroller.ConclusionIt is concluded that the depth of the ablation site modestly correlates with the measured voltage under specific conditions, and the newly developed system fulfills the goal of the design.

A Real-Time Feedback System to Stabilize Laser Intensity on Wavelength Modulation Interferometer

The phase of an interferogram carries the desired information for various applications such as 3-D profilometry. It can be obtained with a wavelength tuning interferometer by acquiring a series of interferograms while changing the laser wavelength. The phase achieved by the interferometer, however, has severe error due to the laser output power change, which is produced inherently from changing the laser wavelength. To eliminate such phase error, we propose a real-time closed-loop feedback control system to keep the laser output power stable during the wavelength tuning. The control system integrates a photodetector, a data acquisition card, and an electro-optic amplitude modulator with our software to achieve the purpose. The experimental result of the system can steadily output a desired intensity value and the measurement speed is up to 600 KHz. Both its control principles as well as its experimental validation are depicted in this letter.

An implementation of real-time feedback control of cured part height in Exposure Controlled Projection Lithography with in-situ interferometric measurement feedback

Exposure Controlled Projection Lithography (ECPL) is an in-house additive manufacturing process that can cure microscale photopolymer parts on a stationary transparent substrate with a time sequence of patterned ultraviolet beams delivered from underneath. An in-situ interferometric curing monitoring and measurement (ICM&M) system has been developed to measure the ECPL process output of cured height profile. This study develops a real-time feedback control system that utilizes an empirical process model and an online ICM&M feedback to automatically and accurately cure a part with targeted height. Due to the nature of photopolymerization, the total height of an ECPL cured part is divided into exposure cured height and dark cured height. The exposure cured height is controlled by a closed-loop feedback on-off controller. The dark cured height is compensated by an empirical process model obtained from the ICM&M measurements for a series of cured parts. A parallel computing software application is developed to implement the real-time measurement and control simultaneously. The experimental results directly validate the ICM&M system’s real-time capability in capturing the process dynamics and in sensing the process output. Meanwhile, it evidently demonstrates the feedback control system’s satisfactory performance in achieving the setpoint of total height, despite the presence of ECPL process uncertainties, ICM&M noises and computing interruptions. A comprehensive error analysis is reported, implying a promising submicron control with enhanced hardware. Generally, the study establishes a paradigm of improving additive manufacturing with a real-time closed-loop measurement and control system.

Double-null divertor configuration discharge and disruptive heat flux simulation using TSC on EAST

The tokamak simulation code (TSC) is employed to simulate the complete evolution of a disruptive discharge in the experimental advanced superconducting tokamak. The multiplication factor of the anomalous transport coefficient was adjusted to model the major disruptive discharge with double-null divertor configuration based on shot 61 916. The real-time feed-back control system for the plasma displacement was employed. Modeling results of the evolution of the poloidal field coil currents, the plasma current, the major radius, the plasma configuration all show agreement with experimental measurements. Results from the simulation show that during disruption, heat flux about 8 MW m−2 flows to the upper divertor target plate and about 6 MW m−2 flows to the lower divertor target plate. Computations predict that different amounts of heat fluxes on the divertor target plate could result by adjusting the multiplication factor of the anomalous transport coefficient. This shows that TSC has high flexibility and predictability.

Hybrid neural network for density limit disruption prediction and avoidance on J-TEXT tokamak

Increasing the plasma density is one of the key methods in achieving an efficient fusion reaction. High-density operation is one of the hot topics in tokamak plasmas. Density limit disruptions remain an important issue for safe operation. An effective density limit disruption prediction and avoidance system is the key to avoid density limit disruptions for long pulse steady state operations. An artificial neural network has been developed for the prediction of density limit disruptions on the J-TEXT tokamak. The neural network has been improved from a simple multi-layer design to a hybrid two-stage structure. The first stage is a custom network which uses time series diagnostics as inputs to predict plasma density, and the second stage is a three-layer feedforward neural network to predict the probability of density limit disruptions. It is found that hybrid neural network structure, combined with radiation profile information as an input can significantly improve the prediction performance, especially the average warning time (). In particular, the is eight times better than that in previous work (Wang et al 2016 Plasma Phys. Control. Fusion 58 055014) (from 5 ms to 40 ms). The success rate for density limit disruptive shots is above 90%, while, the false alarm rate for other shots is below 10%. Based on the density limit disruption prediction system and the real-time density feedback control system, the on-line density limit disruption avoidance system has been implemented on the J-TEXT tokamak.

基于空间光调制的光束聚焦实时反馈控制方法及系统

基于空间光调制的光束聚焦实时反馈控制方法及系统