Real-time Feedback Control Research Articles

Operation results of the KSTAR far infrared interferometer.

The 2015 KSTAR experimental campaign was the first year of routine measurement with a far infrared interferometer (FIRI) utilizing 118.87 μm CH3OH lasers at maximum 200 mW CW beam power. By using rtEFIT reconstruction, the path lengths of interferometers can be calculated and so the line-averaged electron densities n¯e from the FIRI and a millimeter-wave interferometer were in excellent agreement. In this way, the number of successfully diagnosed discharges is counted: 1003 shots or 83.7% of sustained discharges, defined as shots of plasma current IP ≥ 0.3 MA with pulse lengths tf ≥ 2.0 s, have good-quality FIRI data within a few fringe jump errors. In addition, real-time H-mode density feedback control based on the FIRI was also successfully achieved with supersonic molecular beam injection as an actuator. Both constant density and controlled linear increment with a ramp-up rate of 1.0 × 1019 m-3 s-1 were achieved.

Real-Time Feedback Control System for Tuning Evanescent-Mode Cavity Filters

This paper presents a real-time feedback control system for evanescent-mode cavity filters. The control loop monitors the frequency of each cavity in the filter and adjusts the bias voltage on the tuning piezoelectric actuator based on the monitoring data, such that each resonator of the filter is at the desired frequency. The control system can tune the filter regardless of any effects from hysteresis or creep. While applicable to a variety of filter structures, the presented control system has been validated on a second-order bandstop filter built using a standard PCB process. The control system can successfully tune the filter from 0.9 to 1.45 GHz (550-MHz tuning range or 61%) without affecting the RF performance. The control system is fully electronic with a digital interface for easier integration. It also exhibits a measured frequency resolution of 33–6 MHz (or 3.5%–0.4%).

Far-infrared tangential interferometer/polarimeter design and installation for NSTX-U.

The Far-infrared Tangential Interferometer/Polarimeter (FIReTIP) system has been refurbished and is being reinstalled on the National Spherical Torus Experiment-Upgrade (NSTX-U) to supply real-time line-integrated core electron density measurements for use in the NSTX-U plasma control system (PCS) to facilitate real-time density feedback control of the NSTX-U plasma. Inclusion of a visible light heterodyne interferometer in the FIReTIP system allows for real-time vibration compensation due to movement of an internally mounted retroreflector and the FIReTIP front-end optics. Real-time signal correction is achieved through use of a National Instruments CompactRIO field-programmable gate array.

Real-time radiative divertor feedback control development for the NSTX-U tokamak using a vacuum ultraviolet spectrometer.

A radiative divertor technique is planned for the NSTX-U tokamak to prevent excessive erosion and thermal damage of divertor plasma-facing components in H-mode plasma discharges with auxiliary heating up to 12 MW. In the radiative (partially detached) divertor, extrinsically seeded deuterium or impurity gases are used to increase plasma volumetric power and momentum losses. A real-time feedback control of the gas seeding rate is planned for discharges of up to 5 s duration. The outer divertor leg plasma electron temperature Te estimated spectroscopically in real time will be used as a control parameter. A vacuum ultraviolet spectrometer McPherson Model 251 with a fast charged-coupled device detector is developed for temperature monitoring between 5 and 30 eV, based on the Δn = 0, 1 line intensity ratios of carbon, nitrogen, or neon ion lines in the spectral range 300-1600 Å. A collisional-radiative model-based line intensity ratio will be used for relative calibration. A real-time Te-dependent signal within a characteristic divertor detachment equilibration time of ∼10-15 ms is expected.

Efficient Computation of Inverse Dynamics and Feedback Linearization for VSA-Based Robots

We develop a recursive numerical algorithm to compute the inverse dynamics of robot manipulators with an arbitrary number of joints, driven by variable stiffness actuation (VSA) of the antagonistic type. The algorithm is based on Newton-Euler dynamic equations, generalized up to the fourth differential order to account for the compliant transmissions, combined with the decentralized nonlinear dynamics of the variable stiffness actuators at each joint. A variant of the algorithm can be used also for implementing a feedback linearization control law for the accurate tracking of desired link and stiffness trajectories. As in its simpler versions, the algorithm does not require dynamic modeling in symbolic form, does not use numerical approximations, grows linearly in complexity with the number of joints, and is suitable for online feedforward and real-time feedback control. A Matlab/C code is made available.

Service-oriented mobile multimedia cooperative storing and delivery scheme based on opportunistic cloud coding and content-centric cloud compression

In order to improve the quality of multimedia communication and mobile users, the work efficiency of the cloud platform, the service-oriented mobile multimedia cooperative storing, and the delivery scheme were proposed based on opportunistic cloud coding and content-centric cloud compression. Firstly, according to the video frame and the multimedia content centric, the multimedia data compression algorithm was established based on time domain and frequency domain, which combined the image pixel scale and the component. Then, the opportunity cloud encoding program was proposed through the distortion scattering and the opportunity to cooperate with the cloud device control. Finally, the real-time transmission and cooperative feedback control of mobile multimedia streaming video content was proposed based on user requirements and service-driven demands. Experimental results show that the proposed scheme can provide high peak signal-to-noise ratio (PSNR) for large scale video frame transmission and keep high consistency and robustness from subjective experience to objective experience. In addition, the proposed scheme can significantly reduce the failure rate and improve the end-to-end communication performance.

Effectiveness of Delayed Feedback Control Applied to a Small-Size Helicopter with a Suspended Load System

[abstFig src='/00280003/11.jpg' width=""250"" text='A small-size helicopter with a suspended load' ] In this study, a cable-suspended transportation system using a small-size helicopter was investigated. For a secure flight, it is necessary to suppress the swing of the suspended load. For this purpose, a cable angle feedback system was adopted because it is easy to mount the corresponding measuring device on a helicopter. Delayed feedback control was applied for efficient swing damping. The control parameters were obtained using a simple planar double pendulum model that takes into consideration the coupled dynamics of the helicopter and the load. To build the model, the system parameters were identified through frequency response flight tests. In this paper, an appropriate design strategy is reported for a trade-off relationship between vibration damping and piloted handling qualities; the robustness of the control method against disturbances and signal noise was verified by comparing the delayed feedback control method with the real-time angular velocity feedback control method. The damping effect was verified by performing flight tests with three cable lengths.

Design, development and testing of real time control and data acquisition system for R&D IC H&CD source

One of the important auxiliary heating and current drive systems for ITER experiment is Ion Cyclotron Heating & Current Drive (IC H&CD) system. ITER requires 1 prototype and 8 independent RF Sources, each having capability to deliver constant output power of 2.5MW at VSWR 2 in the frequency range of 35–65MHz. To meet the ITER requirement, an R&D program has been launched to identify the final stage tube (Tetrode/Diacrode) for MW level RF amplifier, along with other critical components. Under this R&D program, single chain of RF cascaded amplifiers, consisting of low & high power RF sections, auxiliary power supply, Anode power supply and test bench simulating ITER requirement, are being developed. To ensure reliable and safe operation of the entire system, PLC/PXI based Local Control Unit (LCU) is developed. PLC based sequential control system is developed for sequential biasing of electrodes of high power vacuum tubes (Tetrode/Diacrode). To protect the RF Source against critical fault condition, local protection logic is developed using PXI-7841R, which will ensure fast shut off (<10μs) of RF and power supplies. Constant and stable power output even with variable load condition (up to VSWR 2) is achieved by employing two real time feedback control loops-one for making constant output power and the other one for optimizing anode & screen grid dissipation. For fault/offline analysis, event based acquisition and logging functionality is provided that acquires and logs data at 1μs sampling rate for 100ms pre and post time. During the RF Shot, normal acquisition and logging for all channels are provided with 1ms sampling rate. Further, online display for user selectable 8 channels is provided. All the operational and monitoring parameters are continuously updated on Main screen to give the real time status of the system. In this paper, salient feature of R&D LCU and test results are discussed in detail.

Multiple Sensor Detection of Process Phenomena in Laser Powder Bed Fusion.

Laser powder bed fusion (LPBF) is an additive manufacturing (AM) process in which a high power laser melts metal powder layers into complex, three-dimensional shapes. LPBF parts are known to exhibit relatively high residual stresses, anisotropic microstructure, and a variety of defects. To mitigate these issues, in-situ measurements of the melt-pool phenomena may illustrate relationships between part quality and process signatures. However, phenomena such as spatter, plume formation, laser modulation, and melt-pool oscillations may require data acquisition rates exceeding 10 kHz. This hinders use of relatively data-intensive, streaming imaging sensors in a real-time monitoring and feedback control system. Single-point sensors such as photodiodes provide the temporal bandwidth to capture process signatures, while providing little spatial information. This paper presents results from experiments conducted on a commercial LPBF machine which incorporated synchronized, in-situ acquisition of a thermal camera, high-speed visible camera, photodiode, and laser modulation signal during fabrication of a nickel alloy 625 AM part with an overhang geometry. Data from the thermal camera provides temperature information, the visible camera provides observation of spatter, and the photodiode signal provides high temporal bandwidth relative brightness stemming from the melt pool region. In addition, joint-time frequency analysis (JTFA) was performed on the photodiode signal. JTFA results indicate what digital filtering and signal processing are required to highlight particular signatures. Image fusion of the synchronized data obtained over multiple build layers allows visual comparison between the photodiode signal and relating phenomena observed in the imaging detectors.

Prediction of density limit disruptions on the J-TEXT tokamak

Disruption mitigation is essential for the next generation of tokamaks. The prediction of plasma disruption is the key to disruption mitigation. A neural network combining eight input signals has been developed to predict the density limit disruptions on the J-TEXT tokamak. An optimized training method has been proposed which has improved the prediction performance. The network obtained has been tested on 64 disruption shots and 205 non-disruption shots. A successful alarm rate of 82.8% with a false alarm rate of 12.3% can be achieved at 4.8 ms prior to the current spike of the disruption. It indicates that more physical parameters than the current physical scaling should be considered for predicting the density limit. It was also found that the critical density for disruption can be predicted several tens of milliseconds in advance in most cases. Furthermore, if the network is used for real-time density feedback control, more than 95% of the density limit disruptions can be avoided by setting a proper threshold.

Real-time monitoring of focused ultrasound blood-brain barrier opening via subharmonic acoustic emission detection: implementation of confocal dual-frequency piezoelectric transducers

Burst-tone focused ultrasound exposure in the presence of microbubbles has been demonstrated to be effective at inducing temporal and local opening of the blood-brain barrier (BBB), which promises significant clinical potential to deliver therapeutic molecules into the central nervous system (CNS). Traditional contrast-enhanced imaging confirmation after focused ultrasound (FUS) exposure serves as a post-operative indicator of the effectiveness of FUS-BBB opening, however, an indicator that can concurrently report the BBB status and BBB-opening effectiveness is required to provide effective feedback to implement this treatment clinically. In this study, we demonstrate the use of subharmonic acoustic emission detection with implementation on a confocal dual-frequency piezoelectric ceramic structure to perform real-time monitoring of FUS-BBB opening.A confocal dual-frequency (0.55 MHz/1.1 MHz) focused ultrasound transducer was designed. The 1.1 MHz spherically-curved ceramic was employed to deliver FUS exposure to induce BBB-opening, whereas the outer-ring 0.55 MHz ceramic was employed to detect the subharmonic acoustic emissions originating from the target position. In stage-1 experiments, we employed spectral analysis and performed an energy spectrum density (ESD) calculation. An optimized 0.55 MHz ESD level change was shown to effectively discriminate the occurrence of BBB-opening. Wideband acoustic emissions received from 0.55 MHz ceramics were also analyzed to evaluate its correlations with erythrocyte extravasations. In stage-2 real-time monitoring experiments, we applied the predetermined ESD change as a detection threshold in PC-controlled algorithm to predict the FUS exposure intra-operatively.In stage-1 experiment, we showed that subharmonic ESD presents distinguishable dynamics between intact BBB and opened BBB, and therefore a threshold ESD change level (5.5 dB) can be identified for BBB-opening prediction. Using this ESD change threshold detection as a surrogate to on/off control the FUS exposure in stage-2 experiments, we demonstrated both excellent sensitivity (92%) and specificity (92.3%) in discriminating BBB-opening occurrence can be obtained in animal treatments, while concurrently achieving a high positive predicted value (95.8%). Wideband ESD was also highly correlated with the occurrence and level of erythrocyte extravasations (r 2 = 0.81).The proposed system configuration and corresponding analysis based on subharmonic acoustic emissions has the potential to be implemented as a real-time feedback control structure for reliable indication of intact FUS-BBB opening for CNS brain drug delivery.

와이어 송급 레이저 금속 3차원 적층 연구동향

Recent developments of Laser metal 3D deposition with wire feeding are reviewed which provide an alternative to powder feeding method. The wire feeding direction, angle and position as well as laser power, wire feeding rate, and deposition speed are found to be key parameters to make quality deposition with high throughput. When compared with the powder feed, the wire feed shows higher material efficiency, higher deposition rate, and smoother surface. Large elongated columnar grains which have epitaxial growth across deposit layers are observed in deposit cross sections. The growth direction is parallel to the thermal gradient during the deposit process. Tensile properties are found to be dependent on the direction due to the anisotropic deposit property. A real-time feedback control is demonstrated to be effective to improve the deposition stability. Key words: Wire feeding, Laser, Metal deposition, Microstructure, Mechanical properties, Feedback control

The three-wave laser polarimeter-interferometer on J-TEXT tokamak

Motivated by increasing demands on high-quality measurement of interior magnetic field in tokamak plasma, a far-infrared laser-based polarimeter-interferometer system has been developed on J-TEXT. Three formic acid lasers separately pumped by three CO2 lasers are used as sources, providing more than 90 mW output power in total. High laser power along with usage of newly developed planar Schottky diode mixer enable high phase resolution < 1 mrad. Collinearity and polarization calibrations have been carefully done to improve the measurement reliability. Meanwhile, real-time feedback control of three-wave laser source has been realized for the first time, to fulfill the system stability. Based on three-wave technique, Faraday angle and integrated density phase along the laser path are simultaneously measured with high temporal resolution. In addition, the laser beam is expanded to cover the entire cross-section of the plasma to provide high spatial resolution measurement. With this system, MHD equilibrium of the J-TEXT plasma has been reconstructed. Obscure perturbations on magnetic topology and electron density associated with MHD instabilities, e.g. sawteeth and tearing modes have also been observed. In particular, some interesting features of disruptions in high-density discharges are identified by carefully interpreting the measured polarimeter-interferometer data. In the density ramp-up phase of a high density discharge, asymmetry in both electron density and current density profiles between the Low-Field-Side (LFS) edge (r > 0.8a) and the High-Field-Side (HFS) edge (r < −0.8a) would appear and extend gradually toward the center region. At the same time, a low-frequency (< 1 kHz) density perturbation suddenly occurs at the HFS edge and also gradually propagates into the center region. The disruption takes place when the electron density asymmetry/perturbation reaches the location nearly the m/n = 2/1 (where m and n are the toroidal mode number and the poloidal one, respectively) resonant surface. Evolution of the reconstructed electron density and current density profiles present the details on the asymmetrical behaviors and provide a possible explanation for the high density disruption.

Environmental Robust Position Control for Compact Solenoid actuators by Sensorless Simultaneous Estimation of Position and Force

This paper aims to realize compact actuation systems by sensorless approach. This study adopts solenoid actuators which have advantageous characteristics from the view point in inexpensive cost, simple structure, and high-output force in spite of difficulty in low cost position and force sensing. Some sensorless position estimation techniques for solenoid actuators were reported. However, position and force simultaneous estimation has not sufficiently been achieved. In addition, any real-time feedback control has not been reported. This paper proposes sensorless feedback position control for compact solenoid actuators. The force generation and position/force estimation are conducted by using a dc supply power superposed by an ac component. This control technique has three main features: 1) separation of the power supply into ac and dc components for the position estimation, 2) simultaneous real-time estimation of position and force, and 3) robust feedback position control. Simulations and experiments were conducted for verification of the proposed control with the above three features, and the results indicated that error between the estimation and actual positions was within 0.2 mm. This proposed system offers a new avenue for compact and inexpensive application field.

Deterministic generation of remote entanglement with active quantum feedback

We consider the task of deterministically entangling two remote qubits using joint measurement and feedback, but no directly entangling Hamiltonian. In order to formulate the most effective experimentally feasible protocol, we introduce the notion of average sense locally optimal (ASLO) feedback protocols, which do not require real-time quantum state estimation, a difficult component of real-time quantum feedback control. We use this notion of optimality to construct two protocols which can deterministically create maximal entanglement: a semiclassical feedback protocol for low efficiency measurements and a quantum feedback protocol for high efficiency measurements. The latter reduces to direct feedback in the continuous-time limit, whose dynamics can be modeled by a Wiseman-Milburn feedback master equation which yields an analytic solution in the limit of unit measurement efficiency. Our formalism can smoothly interpolate between continuous-time and discrete-time descriptions of feedback dynamics, and we exploit this feature to then derive a superior hybrid protocol for arbitrary non-unit measurement efficiency that switches between quantum and semiclassical protocols. Finally, we show using simulations incorporating experimental imperfections that deterministic entanglement of remote superconducting qubits may be achieved with current technology using the continuous-time feedback protocol alone.

Digital implementations of thalamocortical neuron models and its application in thalamocortical control using FPGA for Parkinson׳s disease

Due to the relay ability of sensory information and communication between cortical regions, the thalamocortical (TC) relay neuron plays an essential role in the therapy of Parkinson׳s disease. This paper first explores a series of efficient methods for the hardware implementation of TC relay neuron models, aiming to reproduce relevant biological behaviors and present appropriate feedback control in neural dynamics in thalamic systems. In addition, a modified two-dimensional TC neuron model is presented for convenient realization to decrease the complexity of the original model and promote the feasibility of the digital design, which shows significance for the large-scale network simulation of TC-based networks and the establishment of digital thalamus. A system-on-a-chip model-based control system is implemented on an FPGA using the modified TC neuron model, which is aimed at the real-time feedback control of tremor dominant Parkinsonian state. In this paper, the hardware syntheses and theoretical researches are given to illustrate the outstanding performance of the presented hardware implementation. The presented platform can be applied in both the brain-machine interface and the robotic control projects, and the proposed modular hardware framework can be extended to the real-time closed-loop treatments of other dyskinesia diseases.

Model-Based Transmission Control

Abstract This article presents an overview of model-based transmission control. The transmission is an integral part of the automotive powertrain and connects the engine to the vehicle via the driveline. Just as for the internal combustion engine, traditional transmission control has been conducted with extensive calibrations. This is mainly due to the lack of precise models and low cost sensors that can enable real-time model-based feedback control. However the calibration-based approach is facing more challenges as the recent trend in transmission systems has driven up the time and cost associated with the calibration process. Recently, eight and nine speed transmissions have been introduced. The increasing number of different types of transmissions and the gear ratios can drastically increase the burden for control calibration. This calls for control-oriented model development and model-based control. Transmission control is mainly concerned with the transmission shift scheduling and gear ratio shift control. This shift scheduling determines when to shift and which gear to shift.

An Optimal Real-Time Controller for Vertical Plasma Stabilization

Modern Tokamaks have evolved from the initial axisymmetric circular plasma shape to an elongated axisymmetric plasma shape that improves the energy confinement time and the triple product, which is a generally used figure of merit for the conditions needed for fusion reactor performance. However, the elongated plasma cross section introduces a vertical instability that demands a real-time feedback control loop to stabilize the plasma vertical position and velocity. At the Tokamak \`a Configuration Variable (TCV) in-vessel poloidal field coils driven by fast switching power supplies are used to stabilize highly elongated plasmas. TCV plasma experiments have used a PID algorithm based controller to correct the plasma vertical position. In late 2013 experiments a new optimal real-time controller was tested improving the stability of the plasma. This contribution describes the new optimal real-time controller developed. The choice of the model that describes the plasma response to the actuators is discussed. The high order model that is initially implemented demands the application of a mathematical order reduction and the validation of the new reduced model. The lower order model is used to derive the time optimal control law. A new method for the construction of the switching curves of a bang-bang controller is presented that is based on the state-space trajectories that optimize the time to target of the system. A closed loop controller simulation tool was developed to test different possible algorithms and the results were used to improve the controller parameters. The final control algorithm and its implementation are described and preliminary experimental results are discussed.

Mechanical characteristics of ultra-long horizontal nanocantilevers grown by real-time feedback control on focused-ion-beam chemical vapour deposition

Focused-ion-beam chemical vapour deposition (FIB-CVD) has been repeatedly proved to be a useful tool for the growth of three-dimensional (3D) micro- and nano-structures. The strategy of real-time feedback control on FIB-CVD was previously proposed and experimentally demonstrated to be effective for growing ultra-long horizontal nanocantilevers. To fabricate various nanoelectromechanical systems that consist of such types of nanocantilever structures, the mechanical characteristics of ultra-long horizontal nanocantilevers should be investigated. In this study, nanocantilevers with an overhang length of up to 35 μm were grown by using a 30 kV Ga+ FIB, a beam current of 0.50 pA and phenanthrene (C14H10) as the gas source to deposit a diamond-like carbon structure. The Young’s modulus of each nanocantilever was measured by bending the nanocantilever with a nanopillar whose Young’s modulus was known. The average density of each nanocantilever was calculated from the Young’s modulus and the measured resonant frequency. We found that the mechanical characteristics of each nanocantilever depended on the length of the nanocantilever if the strategy of real-time feedback control was applied in fabrication. The Young’s moduli and the averaged densities of the nanocantilevers with a length of 11 to 34 μm were found to be 86 to 254 GPa and 1950 to 5750 kg m−3, respectively. With the increase of the overhang length, the Young’s modulus and the average density were found to gradually increase.

Preliminary fsLIBS study on bone tumors.

The aim of this study is to evaluate the capability of femtosecond Laser Induced Breakdown Spectroscopy (fsLIBS) to discriminate between normal and cancerous bone, with implications to femtosecond laser surgery procedures. The main advantage of using femtosecond lasers for surgery is that the same laser that is being used to ablate can also be used for a feedback system to prevent ablation of certain tissues. For bone tumor removal, this technique has the potential to reduce the number of repeat surgeries that currently must be performed due to incomplete removal of the tumor mass. In this paper, we performed fsLIBS on primary bone tumor, secondary tumor in bone, and normal bone. These tissues were excised from consenting patients and processed through the UC Davis Cancer Center Biorepository. For comparison, each tumor sample had a matched normal bone sample. fsLIBS was performed to characterize the spectral signatures of each tissue type. A minimum of 20 spectra were acquired for each sample. We did not detect significant differences between the fsLIBS spectra of secondary bone tumors and their matched normal bone samples, likely due to the heterogeneous nature of secondary bone tumors, with normal and cancerous tissue intermingling. However, we did observe an increase in the fsLIBS magnesium peak intensity relative to the calcium peak intensity for the primary bone tumor samples compared to the normal bone samples. These results show the potential of using femtosecond lasers for both ablation and a real-time feedback control system for treatment of primary bone tumors.