Closed-loop Feedback Control Research Articles

Design and control of the first foldable single-actuator rotary wing micro aerial vehicle

The monocopter is a type of micro aerial vehicle largely inspired from the flight of botanical samaras (Acer palmatum). A large section of its fuselage forms the single wing where all its useful aerodynamic forces are generated, making it achieve a highly efficient mode of flight. However, compared to a multi-rotor of similar weight, monocopters can be large and cumbersome for transport, mainly due to their large and rigid wing structure. In this work, a monocopter with a foldable, semi-rigid wing is proposed and its resulting flight performance is studied. The wing is non-rigid when not in flight and relies on centrifugal forces to become straightened during flight. The wing construction uses a special technique for its lightweight and semi-rigid design, and together with a purpose-designed autopilot board, the entire craft can be folded into a compact pocketable form factor, decreasing its footprint by 69%. Furthermore, the proposed craft accomplishes a controllable flight in 5 degrees of freedom by using only one thrust unit. It achieves altitude control by regulating the force generated from the thrust unit throughout multiple rotations. Lateral control is achieved by pulsing the thrust unit at specific instances during each cycle of rotation. A closed-loop feedback control is achieved using a motion-captured camera system, where a hybrid proportional stabilizer controller and proportional-integral position controller are applied. Waypoint tracking, trajectory tracking and flight time tests were performed and analyzed. Overall, the vehicle weighs 69 g, achieves a maximum lateral speed of about 2.37 m s−1, an average power draw of 9.78 W and a flight time of 16 min with its semi-rigid wing.

System-Level Modelling and Simulation of a Multiphysical Kick and Catch Actuator System

This paper presents a system-level model of a microsystem architecture deploying cooperating microactuators. An assembly of a piezoelectric kick-actuator and an electromagnetic catch-actuator manipulates a structurally unconnected, magnetized micromirror. The absence of mechanical connections allows for large deflections and multistability. Closed-loop feedback control allows this setup to achieve high accuracy, but requires fast and precise system-level models of each component. Such models can be generated directly from large-scale finite element (FE) models via mathematical methods of model order reduction (MOR). A special challenge lies in reducing a nonlinear multiphysical FE model of a piezoelectric kick-actuator and its mechanical contact to a micromirror, which is modeled as a rigid body. We propose to separate the actuator–micromirror system into two single-body systems. This step allows us to apply the contact-induced forces as inputs to each sub-system and, thus, avoid the nonlinear FE model. Rather, we have the linear model with nonlinear input, to which established linear MOR methods can be applied. Comparisons between the reference FE model and the reduced order model demonstrate the feasibility of the proposed methodology. Finally, a system-level simulation of the whole assembly, including two actuators, a micromirror and a simple control circuitry, is presented.

Reliable and safe blood–brain barrier opening by closed-loop feedback control of focused ultrasound

Real-time cavitation monitoring and feedback controller is critical to safe and effective brain drug delivery by focused ultrasound (FUS)-mediated blood-brain barrier disruption (FUS-BBBD). However, existing controllers were either open-loop or using a generalized target cavitation level (TCL). This study aimed to develop a closed-loop feedback controller with TCL defined based on the baseline stable cavitation level (SCL) of each subject. A single-element FUS transducer with a coaxially aligned passive cavitation detector (PCD) was used. PCD signals were first acquired with “dummy” sonication to determine TCL defined to be 0.5, 1, 2, 3, or 4 dB above baseline SCL. A custom closed-loop feedback controller was developed to control SCL to be at each TCL. After sonication, wild-type mice were intravenously injected with Evans Blue (EB) to quantify FUS-BBBD using ex vivo fluorescence imaging. The fluorescence intensity of delivered EB increased in an average of 1.4-fold, 2.6-fold, and 3.9-fold at 1, 2, and 3dB respectively compared to the 0.5-dB group. No apparent hemorrhage was found in lower TCLs, and hemorrhage was consistently found in the 4-dB group. This study demonstrated that the individualized feedback controller achieved reliable and safe FUS-BBBD at selected TCL.

Closed-Loop Position Control of a Self-Sensing 3-DoF Origami Module With Pneumatic Actuators

This letter presents closed-loop position control of a pneumatically actuated modular robotic platform “pneumagami” that can be stacked to enlarge work and design space for wearable applications. The module is a 3 degrees of freedom (DoF) parallel robot with two rotational and one translational motion, which is actuated by three antagonistic pneumatic pouch motor pairs attached to three leg joints. To control the pouch motors, we utilize miniature proportional valves. As for the sensing, we introduce a novel embedded resistive sensor mechanism utilizing rotary-to-translational transmission. The sensor's transmission is modeled and verified by experiments. Furthermore, we study analytic forward and inverse kinematic models of the pneumagami module. Utilizing the models, we design a closed-loop feedback controller to track two different trajectories. The experimental results show that the module follows the desired trajectories successfully. Thus, we report that the proposed pneumagami modules can be utilized for achieving a controllable robotic third arm with higher DoFs and range of motion (RoM) when connected in series.

Localization and Control of Magnetic Suture Needles in Cluttered Surgical Site with Blood and Tissue.

Real-time visual localization of needles is necessary for various surgical applications, including surgical automation and visual feedback. In this study we investigate localization and autonomous robotic control of needles in the context of our magneto-suturing system. Our system holds the potential for surgical manipulation with the benefit of minimal invasiveness and reduced patient side effects. However, the nonlinear magnetic fields produce unintuitive forces and demand delicate position-based control that exceeds the capabilities of direct human manipulation. This makes automatic needle localization a necessity. Our localization method combines neural network-based segmentation and classical techniques, and we are able to consistently locate our needle with 0.73 mm RMS error in clean environments and 2.72 mm RMS error in challenging environments with blood and occlusion. The average localization RMS error is 2.16 mm for all environments we used in the experiments. We combine this localization method with our closed-loop feedback control system to demonstrate the further applicability of localization to autonomous control. Our needle is able to follow a running suture path in (1) no blood, no tissue; (2) heavy blood, no tissue; (3) no blood, with tissue; and (4) heavy blood, with tissue environments. The tip position tracking error ranges from 2.6 mm to 3.7 mm RMS, opening the door towards autonomous suturing tasks.

Serial correlated–uncorrelated concurrent space method for process monitoring

Due to the closed-loop feedback control system, the data collected in the industry process is always temporal serial correlated. Moreover, different types of sensor data (such as temperature, pressure, liquid level, flow and so on) would show different temporal serial correlations. Meanwhile, the current process monitoring method considers all types of sensor data equally, ignoring the difference in temporal serial correlations caused by various sensor types. In response to this, serial correlated–uncorrelated concurrent space method is proposed in this work, where process variable original space is divided into serial correlated space and serial uncorrelated space via the degree of temporal serial correlations. In addition, the proposed method not only considers the local monitoring within space via principal component analysis and slow feature analysis respectively, but also monitors the information between-space based on the moving window and the mutual information. Finally, on the basis of the monitoring statistic within space and between-space, the comprehensive monitoring indicator is constructed via the local outlier factor method. The advantage and superiority of the proposed method is illustrated via testing on Tennessee Eastman process and Continuous Stirred Tank Reactor process.

Zero drift suppression method of a distributed feedback fiber laser hydrophone.

A zero drift suppression method of a distributed feedback (DFB) fiber laser hydrophone is studied. The working principle of the DFB fiber laser hydrophone and the cause, phenomenon, and influence of zero drift are briefly introduced. The design idea and implementation method of the zero drift suppression method are described in detail. The differential cross-multiplication demodulation method is improved by adding closed-loop feedback control to the appropriate stage, and the zero drift problem is solved without any hardware modification. Simulation analysis and experiments are performed to verify the feasibility and effectiveness of the method. The experimental results show that the zero drift suppression method can effectively stabilize the static operating point of the DFB fiber laser hydrophone.

Rotorcraft Dynamic Platform Landings Using Robotic Landing Gear

Abstract Articulating landing gear that use closed-loop feedback control are proven to expand the landing capabilities of rotorcraft on sloped and rough terrain. These systems are commonly referred to as robotic landing gear (RLG). Modern RLG systems have limitations for landing on dynamic platforms because their controllers do not incorporate fuselage roll and roll rate feedback. This work presents a proven crashworthy cable-driven RLG system for the commercial S-100 Camcopter that expands static landing zone limits by a factor of three and enables dynamic platform landings in rough sea state (SS) conditions. A new roll and foot-force feedback fused control algorithm is developed to enable ship deck landings of an RLG equipped S-100 without the need for deck lock or advanced vision-based landing systems. Multibody dynamic simulations of the aircraft, landing gear, and new control system show the benefits of this combined roll and force feedback approach. Results include experimental dynamic landings on platforms rolling under sinusoidal motion and simulated SS conditions. The experiments demonstrate, in a limited fashion, the usability of the RLG through ground experimentation, and the results are compared to simulations. Additional simulations of landings of the S-100 with rigid and active landing gear with more challenging landing conditions than experimentally tested are presented. Such results aid in understanding how RLG with this new roll and contact force fused controller prevent dynamic rollover.

Active impulsive disturbance rejection and oscillation control of robot manipulator, using nonclassical rod models and proportional integral derivative controller

Micro-electro-mechanical-systems scale robots are prone to impulsive disturbances during operation. Such disturbance leads to adverse oscillations of the robot manipulator. So, it is essential to mitigate and control such unwanted oscillations. On the other hand, to capture size dependencies of such robot elements, it is required to adopt nonclassical models. To address these cases, robot manipulator is modeled as a mechanical rod, comprehensive rod models are utilized, proportional integral derivative (PID) controller is designed, and the time-domain response of the system is simulated in MATLAB. Results show that adopting proper gain values of the PID controller leads to total rejection of the pulsive disturbances. However, findings conceal the importance of the nonclassical rod model such that strain gradient (SG) model shows less oscillatory amplitude than the classical theory (CT) model. While considering the nonlocal model effects (NL), such undesired vibrations are bigger than CT model. In other words, meanwhile, a simple PID controller can reject the disturbance for SG models; a stronger controller should be adopted to reject such pulsive disturbances with NL models. Eventually, it is valuable to note that to suppress unwanted oscillations in small-sized robots, PID closed-loop feedback controller is a decent choice because of the simplicity and less costs. Application of successful control design alongside the proper nonclassical theory leads to neutralizing the disturbances and increases the robot manipulator precision.

Flagellated Janus particles for multimodal actuation and transport.

Catalytic Janus particles rely on chemical decomposition to self-propel and have displayed enormous potential for targeted drug delivery and cellular penetration. Catalytic propulsion mechanisms are limiting, however, with fuel requirements and specialized fluid properties being necessary to achieve propulsion. We have improved the dynamic propulsion of catalytic Janus particles by functionalizing flagellar filaments to one of their hemispheres. Flagellated Janus particles, torqued by rotating magnetic fields, swim along their rotation axis using the explicit chirality and flexibility of flagella, mimicking flagellar rotation of live bacteria. Depending on the working fluid, flagellated Janus particles can propel using either catalytic or swimming propulsion. We demonstrate experimentally that flagellated Janus particles behave predictably under the two actuation modes and can precisely follow trajectories under closed-loop feedback control. Flagellated Janus particles were demonstrated to swim in both Newtonian and shear-thickening fluids. These are the first Janus particles developed that can be propelled interchangeably between catalytic and flagellar swimming propulsion, allowing two distinct propulsion mechanisms for future use within in vivo operations.

Design, Actuation, and Control of an MRI-Powered Untethered Robot for Wireless Capsule Endoscopy

Magnetic resonance imaging (MRI)-powered magnetic robotics aims to convert clinical MR scanners into a remote robotic manipulation platform to provide an alternative approach for interventional MRI procedures. The presence of the main magnetic field ( <b xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</b> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><b>0</b></sub> ) inside of MRI systems imposes magnetic constraints. Because of this static and strong magnetic field, many magnetic actuation techniques to orient or rotate magnetic objects are not feasible under MRI. Therefore, the robot design and actuation methods should consider these constraints for the intended medical applications. A free-to-rotate robot design could be utilized under MRI for providing rotational motion with magnetic pulling. However, the coupled translation with rotation induces difficulty in control of these robots, especially for camera pointing towards capsule endoscopy. In this study, we present a wireless magnetic robot that exploits a surface contact to create a rotation around a contact point with minimal translation. The proposed robot is integrated with a camera and an on-board battery for endoscopy purposes. The robot's tuned density also allows three-dimensional (3D) navigation to visually scan the workspace. We also demonstrate the open- and closed-loop actuation and control performance to explore the range of pitch angles accomplishable and closed-loop feedback control accuracy by using visual feedback. The closed-loop control experiments have shown 0.19 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">°</sup> of steady-state error with 1.9 seconds rise time and 20% overshoot. Thanks to the surface contact during orientation control, the worst-case undesired translation is found to be 6.7 mm. Such robot provides the first steps towards active capsule endoscopy actuated by MRI devices for combining physiological images from an MRI device and the auxiliary visual camera images via the capsule robot to diagnose certain diseases in the gastrointestinal (GI) tract.

The case for digital twins in metal additive manufacturing

The digital twin (DT) is a relatively new concept that is finding increased acceptance in industry. A DT is generally considered as comprising a physical entity, its virtual replica, and two-way digital data communications in-between. Its primary purpose is to leverage the process intelligence captured within digital models—or usually their faster-solving surrogates—towards generating increased value from the physical entities. The surrogate models are created using machine learning based on data obtained from the field, experiments and digital models, which may be physics-based or statistics-based. Anomaly detection and correction, and diagnostic closed-loop process control are examples of how a process DT can be deployed. In the manufacturing industry, its use can achieve improvements in product quality and process productivity. Metal additive manufacturing (AM) stands to gain tremendously from the use of DTs. This is because the AM process is inherently chaotic, resulting in poor repeatability. However, a DT acting in a supervisory role can inject certainty into the process by actively keeping it within bounds through real-time control commands. Closed-loop feedforward control is achieved by observing the process through sensors that monitor critical parameters and, if there are any deviations from their respective optimal ranges, suitable corrective actions are triggered. The type of corrective action (e.g. a change in laser power or a modification to the scanning speed) and its magnitude are determined by interrogating the surrogate models. Because of their artificial intelligence (AI)-endowed predictive capabilities, which allow them to foresee a future state of the physical twin (e.g. the AM process), DTs proactively take context-sensitive preventative steps, whereas traditional closed-loop feedback control is usually reactive. Apart from assisting a build process in real-time, a DT can help with planning the build of a part by pinpointing the optimum processing window relevant to the desired outcome. Again, the surrogate models are consulted to obtain the required information. In this article, we explain how the application of DTs to the metal AM process can significantly widen its application space by making the process more repeatable (through quality assurance) and cheaper (by getting builds right the first time).

A fuzzy CMAC learning approach to image based visual servoing system

This study presents a fuzzy robotic joint controller using a cerebellar model articulation controller (CMAC) integrating a Takagi-Sugeno (T-S) framework with an online compensator for an articulated manipulator. The proposed controller is applied to image-based visual servoing (IBVS), including closed-loop feedback control and the kinematic Jacobian calculation. This approach learns a mapping from image feature errors for each joint’s velocity instead of the classical kinematics, thereby reducing the computational complexity and improving the self-regulation ability of the control system. These connecting weights of the cerebellar model learn offline, and an online compensator that uses reinforcement learning is developed to resolve system noise and uncertainties in an unknown environment. Compared with the classical inverse kinematics model, this approach does not need an excessive computational expense so that this proportional controller can be implemented in general scenarios with an eye-in-hand configuration. Experimental results show the proposed method can outperform the classical IBVS controller.

A neoteric closed loop feedback controller based on correlative-elemental curvature algorithm

PurposeThe power framework has become a vital part in the day-to-day life and exhibits a rapid development in this current era. Due to the fact of huge power utilization, the power frameworks fall under several power transmission-related concerns. Precisely, frequency deviation has generated a huge impact during power transmission; this in turn highly reduces the power system stability as well as reliability too.Design/methodology/approachTo boost the system’s efficacy, this study proposes a neoteric closed loop feedback controller in which a control algorithm named correlative-elemental-curvature algorithm is introduced with a constant threshold.FindingsWith the aim of mitigating frequency deviation, a stability analysis technique called Retrofit Lyapunov’s method is deployed in the controller. This would simultaneously reduce the load disturbances along with tie-line synchronization issues faced with the prior controllers. Optimization is carried out with the aid of duelist optimization algorithm, which tunes the controller parameters thereby mitigating the complexities while designing a loop feedback controller power framework.Originality/valueThe efficacy of the proposed work is assessed with the aid of metrics, such as integral absolute error, accuracy and settling time. Thus, the proposed work enhances the system reliability as well as the stability by mitigating the frequency deviation related issues and guarantees reliable power transmission.

Maximal L-regularity for an abstract evolution equation with applications to closed-loop boundary feedback control problems

In this paper we present an abstract maximal $L^p$-regularity result up to $T = \infty$, that is tuned to capture (linear) Partial Differential Equations of parabolic type, defined on a bounded domain and subject to finite dimensional, stabilizing, feedback controls acting on (a portion of) the boundary. Illustrations include, beside a more classical boundary parabolic example, two more recent settings: (i) the $3d$-Navier-Stokes equations with finite dimensional, localized, boundary tangential feedback stabilizing controls as well as Boussinesq systems with finite dimensional, localized, feedback, stabilizing, Dirichlet boundary control for the thermal equation.

Automatic synchronisation of the cell cycle in budding yeast through closed-loop feedback control

The cell cycle is the process by which eukaryotic cells replicate. Yeast cells cycle asynchronously with each cell in the population budding at a different time. Although there are several experimental approaches to synchronise cells, these usually work only in the short-term. Here, we build a cyber-genetic system to achieve long-term synchronisation of the cell population, by interfacing genetically modified yeast cells with a computer by means of microfluidics to dynamically change medium, and a microscope to estimate cell cycle phases of individual cells. The computer implements a controller algorithm to decide when, and for how long, to change the growth medium to synchronise the cell-cycle across the population. Our work builds upon solid theoretical foundations provided by Control Engineering. In addition to providing an avenue for yeast cell cycle synchronisation, our work shows that control engineering can be used to automatically steer complex biological processes towards desired behaviours similarly to what is currently done with robots and autonomous vehicles.

FES Cycling and Closed-Loop Feedback Control for Rehabilitative Human–Robot Interaction

For individuals with movement impairments due to neurological injuries, rehabilitative therapies such as functional electrical stimulation (FES) and rehabilitation robots hold vast potential to improve their mobility and activities of daily living. Combining FES with rehabilitation robots results in intimately coordinated human–robot interaction. An example of such interaction is FES cycling, where motorized assistance can provide high-intensity and repetitive practice of coordinated limb motion, resulting in physiological and functional benefits. In this paper, the development of multiple FES cycling testbeds and safeguards is described, along with the switched nonlinear dynamics of the cycle–rider system. Closed-loop FES cycling control designs are described for cadence and torque tracking. For each tracking objective, the authors’ past work on robust and adaptive controllers used to compute muscle stimulation and motor current inputs is presented and discussed. Experimental results involving both able-bodied individuals and participants with neurological injuries are provided for each combination of controller and tracking objective. Trade-offs for the control algorithms are discussed based on the requirements for implementation, desired rehabilitation outcomes and resulting rider performance. Lastly, future works and the applicability of the developed methods to additional technologies including teleoperated robotics are outlined.

Intrinsically compliant parallel robot for fractured femur reduction: Mechanism optimization and control

A robotic system for the reduction of fractured femur bone is proposed in this research to help orthopedics during the labor intensive bone reduction procedures and also save them from radiation stimulated environment. Fractured femur reduction is a good candidate for robotics application owing to its elongated anatomy and strong counteracting forces from surrounding muscles. However, the robot forces should be compliant, and motions need to be accurate. Aiming to achieve these two conflicting objective, a parallel robot actuated by six intrinsically compliant actuators is being proposed here. After an initial design analysis, three performance metrics, namely, the conditioning index, actuator force index and interaction compliance index were identified and formulated. An evolutionary algorithm SPEA2 was employed to simultaneously optimize these objectives by varying the key robot design variables. Subsequent to the optimization, an optimal robot design is obtained which provides the best trade-off between the performance measures. Initial proof of concept experiments were carried out whereby the robot was tested for trajectory following accuracies while maneuvering the moving platform about the three axes. A fuzzy based closed loop feedback controller was implemented on the robot. Excellent trajectory tracking results were observed in response to the sinusoidal inputs.

Design of Half-bridge Bidirectional DC-DC Converter Control Loop

In recent years, the direct current (DC) microgrid system has received extensive attention from industrial and academic circles worldwide. As an essential part of the DC microgrid, the bidirectional DC-DC converter can realize the bidirectional flow of energy according to the needs of the DC microgrid. In this paper, the half-bridge bidirectional DC-DC converter is taken as the research object, and the double closed-loop feedback control loop of the converter in the charging and discharging mode is designed based on the intermittent and fluctuating characteristics of distributed generation. Besides, a simulation model is built using MATLAB to analyze the operation of the converter in different modes and the control effect of the double closed-loop feedback control loop. The results verify the effectiveness and feasibility of the proposed control method.

Realisation of a Novel Functionally Redundant Actuation System for a Railway Track-Switch

This paper focuses on modelling, control, realisation and performance analysis of a full-scale demonstrator for a novel railway track switch. For over a century, railway track switches (or points) have been allowing trains to safely change between routes. As they are safety-critical elements of the rail network, when they fail, the signalling system will prevent trains from using that route. This means poor reliability (or lack of availability) leads to significant delays and costs; hence there is huge interest from researchers and engineers in improving the overall reliability of track switches. This paper presents new results, which represent a meaningful first step toward a revolution in the way track switches are actuated. A “REPOINT-Light” railway track switch demonstrator is introduced which uses a new concept of locking to allow redundant actuation with three actuator bearers operating under closed-loop feedback control. The new concept, its control system and its mechanical viability are tested in experiments at the Great Central Railway in the UK. To support the design of the actuators and the control system, a dynamic simulation model is developed by co-simulation involving Simulink and Simpack. The experimental results presented are used to validate the models and the paper discusses how the models themselves are used as the vehicle for the design of feedback controllers. Virtual testing of the controllers in simulation is a vital step prior to the implementation and deployment of the controllers in the demonstrator switch. The major contribution of this work is demonstrating, for the first time at full scale on a real-world track switch, that it is possible to use one-out-of-three actuator redundancy to provide fault-tolerant operation of railway track switch.