This article presents an applicable real-time thermal model for the temperature prediction of permanent magnet synchronous motors. The load capacities of most permanent magnet synchronous motors are usually limited by the temperature, and overheating is one of the main reasons for permanent magnet synchronous motors breakdown, so an applicable temperature prediction approach is helpful to improve motor utilization and protect permanent magnet synchronous motors from thermal distortion. Compared with embedding temperature sensors into motor structures, implementing real-time thermal model in motor controllers is a cost-effective and rapid response protection method, but it still faces the challenges on the temperature estimation accuracy, the complexity of the model parameters and the computational efforts. To balance every aspect of these challenges, this article tries a simple real-time thermal model to accurately predict the thermal behavior by elaborately modeling stator core losses and considering motor itself cooling ability. The affections of the motor current and speed on the core losses are analyzed and a polynomial equation is adopted to deal with their dependencies. To simulate the motor speed impact on the cooling ability, motor speed is involved in the variable thermal conductance of the motor housing inside the surroundings by another polynomial equation. This article describes how to get the most parameters of the proposed real-time thermal model through motor basic dimensional information and introduces the test methods employed to determine the parameters of the above two polynomial equations. In the experiments, first the thermal model building process is provided by an actual permanent magnet synchronous motor with two simple tests, and then the online analytical expressions with the obtained parameters are implemented in the drive controller to verify the performance of the proposed real-time thermal model. The results of the performance tests show that the real-time thermal model has a good agreement between estimated and measured temperature values, and its performance can satisfy the most actual applications.
The proportional throttle cartridge valve has been widely used in heavy machine due to its fast response and huge flow rate. However, large flow impact could occur at the instant of proportional throttle cartridge valve opening, which is harmful to system stability and service life of machines. A variable flow gain–proportional throttle cartridge valve was proposed in this study to reduce the vibration of hydraulic drive system caused by the flow impact. Nevertheless, the variable flow gain introduced a strong nonlinearity, as well as a big flow force disturbance, a friction force disturbance, a flow–pressure nonlinear relationship, and a variable load stiffness which are challenges for high accurate control of spool position. Therefore, a third-order active disturbance rejection controller was developed to enhance the antidisturbance ability and improve the control precision of the variable flow gain–proportional throttle cartridge valve as well. First, the mathematical model of the variable flow gain–proportional throttle cartridge valve was established by identification of system parameters. Second, the active disturbance rejection controller was designed, and its parameters were tuned in simulation environment. And third, relevant experiments on a DN80 variable flow gain–proportional throttle cartridge valve test system were conducted to validate the proposed control strategy. The experimental results approved that compared with the well-tuned proportional–integral–derivative controller, the response time and the overshoot were almost cut to half, and the hysteresis error decreased by 75% using active disturbance rejection controller. The experiment results also indicated that variable flow gain–proportional throttle cartridge valve with active disturbance rejection controller increased the robustness of the variable flow gain–proportional throttle cartridge valve in the presence of nonlinear and uncertain disturbance and improved the control precision and dynamic response greatly.
Nonminimum phase output tracking has been addressed for a fixed-wing micro aerial vehicle. Nonminimum phase characteristics in an aircraft result from the fact that the process of generating upward vertical motion produces an initial downward force, causing the aircraft to lose altitude momentarily, and vice versa. This phenomenon leads to unstable internal dynamics in the plant model. A dynamic sliding-surface-based sliding mode control is chosen to stabilize the internal dynamics and to provide asymptotic output tracking error convergence to zero with desired eigenvalue placement. The control is designed in such a way that the output of the plant model should track a nonlinear time-varying reference trajectory generated at every time instant with a finite number of nonzero time derivatives. Design of second-order sliding-mode-based super twisting controller which ensures finite-time stability of the internal dynamics is proposed in this work. The proposed control methodology is applied in the design of an autolanding controller for a micro aerial vehicle with nonminimum phase behavior. MATLAB-based simulation results and discussions are presented to evaluate the performance of the controller and robustness of the sliding mode with respect to matched and unmatched disturbances. The proposed control algorithm has been successfully implemented in hardware-in-the-loop simulation and results are given.
In this work, a repulsive torque control of a robot-assisted surgery system using a 4-degree-of-freedom haptic master which is operated using the properties of magnetorheological fluid is undertaken. The proposed haptic master can generate a repulsive torque along 4-degree-of-freedom motion and provide command signals to the slave robot. This is possible due to controllability of the torque by applying the magnetic field (or current) to magnetorheological fluid domain of the clutch system. For the realization of the master-slave robot-assisted minimally invasive surgery system, an encoder is integrated with the haptic master, and the motion command of the haptic master is realized by the surgical slave robot in the robot-assisted minimally invasive surgery architecture. The haptic master–slave system is then established by incorporating the slave robot with the master device, in which the repulsive torque and position commands are transferred to each other. In order to demonstrate superior performance of the proposed haptic master in terms of torque-tracking controllability between the master and surgical positions, a sliding mode controller is designed and experimentally implemented. It is validated via tracking experiment that superior torque-tracking control performance can be achieved by commanding dynamic motions of the haptic master featured by the inherent characteristics of magnetorheological fluid.
Passivity analysis provides a convenient measure to assess the stability of haptic systems interacting with virtual environments. Passivity analysis of haptic sampled-data systems coupled with virtual environments requires knowledge of parameters of the employed environment model. Kelvin–Voigt models have been popularly used to describe viscoelastic behavior of soft tissues being simulated in a virtual environment. This paper employs a standard linear solid model that has been recently shown to be better suited to represent the behavior of the actual soft tissues, and provides passivity analysis of the haptic systems interacting with virtual viscoelastic soft tissues based on the standard linear solid model. The analysis results in a new criterion for design and control of passive haptic interfaces. The effect of the employed discretization method on passivity is also discussed. Experimental results show that the new passivity criterion is less conservative. This criterion increases the domain of soft-tissue environments that can be interacted with passively by the haptic interface.
This article focuses on the high-performance motion control problem of the hydraulic press. Smooth and precise motion control of the hydraulic press is hardly achieved due to the complex external disturbances which typically consist of the deformation force and friction force. An extended fuzzy disturbance observer is first constructed to estimate and compensate the hardly modeled deformation force. The proposed extended fuzzy disturbance observer differs with the fuzzy disturbance observer on parameter adaptation; the fuzzy disturbance observer is commonly driven by the disturbance observer error, while the designed extended fuzzy disturbance observer is driven by the disturbance observer error and the motion tracking error together. The nonlinear cascade controller is further applied to synthesize the motion controller considering the particular work principle of the separate meter-in separate meter-out drive system adopted in the hydraulic press. The outer motion tracking loop of the nonlinear cascade controller is designed based on the sliding mode control with the desired driving force as control output, and the inner pressure control loop of the nonlinear cascade controller uses the backstepping technique to make the separate meter-in separate meter-out drive system track the desired driving force precisely. The minimum equivalent load criterion is proposed to act as the bridge linking the outer and inner loop. The stability of the overall closed-loop system is proved based on the Lyapunov theory. The performance of the proposed scheme is verified through the simulations and experiments. The results demonstrate that the nonlinear cascade controller together with the extended fuzzy disturbance observer provides an excellent motion tracking performance in the presence of complex external disturbances.
A novel disturbance rejection control scheme is proposed to address the robust attitude control problem for the air-breathing hypersonic vehicle with actuator dynamics and disturbances based on predictive sliding mode control and nonlinear disturbance observer. To achieve attitude control subtly and precisely, the attitude control system is decomposed into two subsystems: the outer-loop subsystem and inner-loop subsystem. Different control schemes are taken to attenuate or reject model uncertainties and external disturbances, whose influences on the two subsystems are different. The predictive sliding mode control is first utilized to attenuate model uncertainties imposed on the outer-loop subsystem. Then, a novel nonlinear disturbance observer–based predictive sliding mode control is proposed to tackle the mismatched disturbances with remarkable influence on the inner-loop subsystem. Afterward, both the effectiveness and stability of the proposed nonlinear disturbance observer–based predictive sliding mode control disturbance rejection control scheme are demonstrated from the theoretical prospective. Finally, simulation results are given to present the effectiveness and robustness of the proposed disturbance rejection control scheme.
Cable-suspended robots are categorized as a style of parallel manipulator that has appealed interest for manipulation jobs. This article presents a design for a cable-suspended robot system with oscillation suppression control. The major benefits of the system design are as follows: modular, transportable, reconfigurable, and easy to install. This robotic system consists of the main object, which is a suspended platform and a cable winch that maneuvers the main object by regulating cable lengths. Furthermore, this study presents a combined control module to serve as an associate controller to stabilize the system. The associate controller positions and oscillates the suppression properties by integration feedback control with the shaping signals. The fuzzy controller is rule based and constructed based on associate controller performance-related knowledge to act as a controller. Accordingly, the proposed control scheme effectively reduces cable oscillation, especially when fuzzy control methodology is applied. The broad variety of problems deliberated in this study can be applied to assembly, automation, and large-scale manufacturing that requires a cable-suspended system.
In this article, a practical method named feedback nonlinear robust control with disturbance compensation is proposed for a hydraulic system with matched and mismatched generalized uncertainties (e.g. parameter derivations, external disturbances, modeled errors and/or unmodeled dynamics), in which a finite-time disturbance observer and a nonlinear robust controller are integrated together by backstepping method. The finite-time disturbance observer is used to estimate matched and mismatched generalized uncertainties. The design of the nonlinear robust controller is to make the closed-loop system stable. Not only the nonlinearities (e.g. nonlinear flow features of servo-valve) but also matched and mismatched generalized uncertainties are considered by the proposed controller. Furthermore, asymptotic output tracking performance after a time T0 is theoretically ensured by the proposed controller. The high-performance nature of the proposed control strategy is verified by extensive comparative experimental results.
This article presents the development of a novel artificial potential field technique for a haptic controller of an underwater remotely operated vehicle to assist the pilot to avoid obstacles. The artificial potential field technique is used to replicate potential risks presented by underwater obstacles in the vicinity of the remotely operated vehicle. A risk avoidance vector is calculated based on the artificial potential field then transmitted to a haptic joystick to generate the tactile feedback, which enables the remotely operated vehicle pilot to be alerted to potential dangers due to surrounding obstacles and prompt the pilot through the joystick to avoid the dangers and safely navigate the vehicle. The novel artificial potential field technique can deal with both stationary and moving obstacles as it is combined with an obstacle motion detection algorithm based on fuzzy C-means and Kalman filter algorithms. These algorithms are applied to process raw data from the scanning sensor to identify the relative positions and velocities between the remotely operated vehicle and the obstacles, which are employed within the artificial potential field calculations. To validate the proposed technique, the haptic joystick and the novel artificial potential field formula were applied to control a simulated remotely operated vehicle within a virtual reality environment.
Affected by discontinuous nature of the discrete controller and patients’ different characteristics, the stability analysis in servo pneumatic rehabilitation systems remains a challenge. Hence, the authors propose an approach to obtain stability boundaries of the admittance controller parameters so that a compliant interaction can be ensured. As the zero-order hold function adds nonlinear exponential terms to the continuous transfer function of the system, a discrete closed-loop root-locus analysis is presented describing how the changes in patients’ characteristics and system parameters shift the stability boundaries. The reasonable matches between the analytical and experimental stability boundaries demonstrate that the presented approach is reliable.
The leakage problem, which occurs due to the high hydrostatic pressure values of the fluid inside the pipes, is a serious issue in most of the pipeline systems. Therefore, the leak tightness test is required in different standards for verification of almost every kind of pipes used in both academic researches and industrial applications. The behavior of the hydrostatic pressure parameter in the test pipe has to be as smooth as possible during the leak tightness test. The conventional control loops of the servo mechanisms used for pumping the test fluid into the test pipe are weak to provide the minimum overshoot, the rise time and the steady-state error. In this situation, hydrostatic pressure tests are not capable of giving meaningful results. In this study, a leak tightness test machine working with a servo control loop to provide the optimum hydrostatic pressure pattern is designed. The efficacy of the designed leak tightness test machine and proposed optimized servo control loop have been shown with both simulation and experimental results.
Dynamics of assembly automation systems involve the interaction of discrete-event and continuous-variable dynamics. Hence, a hybrid model is a natural framework for scheduling tasks in assembly automation processes. This study indicates that a weighted scheduling problem can be transformed into a weighted time-optimal problem for hybrid systems. In particular, it shows that the problem can be cast as a constrained optimization problem with inequalities quantifiers. In order to obtain quantifier-free inequalities, quantifier elimination techniques are used. Based on the quantifier-free inequalities, the scheduling problem of the assembly manufacturing process can be solved using linear programming methods. Applicability and simulation results are provided to illustrate the performance of the developed algorithms.
Feedback linearization is widely used for the purpose of quadrotor control. Unfortunately, feedback linearization is highly sensitive to any quadrotor model uncertainties. This paper provides feedback linearization-based control with robustness by integrating it with a disturbance observer. The proposed approach maintains the simplicity of the control structure without ignoring the high nonlinearities existing in the model by considering these nonlinearities as disturbances to be attenuated by the disturbance observer. Thus, the requirement to include complex high-order Lie derivatives in the controller is eliminated even in the presence of the high nonlinearities. Simulation results show that the proposed controller successfully force the quadrotor to follow the desired position and heading trajectories in the presence of different types of disturbances including ignored nonlinear dynamics, wind disturbances and partial actuator failure.
This article studies the energy-saving performances of the independent metering system with pressure compensation for excavator’s manipulator. Compared to the electro-hydraulic pressure compensation method, the hydro-mechanical pressure compensation method is commonly applied in the conventional load-sensing systems as it reacts directly and rapidly. Independent metering system has more controllability, because meter-in and meter-out orifices are decoupled. In this study, the hydro-mechanical pressure compensation method is adopted in the designing of independent metering system for excavator’s manipulator. According to the demand forces and velocities of the cylinders in the excavator’s manipulator part, the pressure compensation independent metering control blocks of boom, arm, and bucket are completely designed. The most energy-efficient manner of opening the meter-in and meter-out orifices for proportional output velocity has been obtained by quasi-static behaviors’ analysis. The excavator’s manipulator virtual prototype model, the conventional load-sensing system model, and pressure compensation independent metering system model are built. The system parameters are kept as consistent values, and the energy consumptions of the two systems are compared in the simulations. The comparison results indicated that the pressure compensation independent metering system offers more significant energy savings than the conventional load-sensing system when the system is steady.
Bionics researchers identify muscle–tendon unit to be effective in producing human-like walking, but seldom real actuators have same property like muscle–tendon unit. Here, a muscle–tendon control scheme for electrohydraulic cylinder is proposed. To achieve this goal, we develop a model of electrohydraulic cylinder to clarify the relationship between the input current and output force. Additionally, a controller based on muscle–tendon unit model is applied to realize compliant control. The results of muscle–tendon unit control scheme and conventional force–position control scheme are compared. By applying the proposed one, we find that the electrohydraulic cylinder generates compliant behavior and self-adapts to load disturbances, without scarifying its fast response property and stiffness. Besides, various compliances can be accomplished by simply changing maximum muscle–tendon unit force. The results suggest that hydraulic actuators with this bionic control scheme can meet the demand of robot applications, especially for legged robots and manipulators.
Most commercial servo systems utilize cascaded proportional–integral–derivative controller due to its simplicity and robustness. Under this control structure, motion performances such as single-axial tracking and multi-axial contour following are completely determined by the controller parameters. In real applications, current loop controller parameters usually remain unchanged while velocity loop and position loop ones should be tuned as the mechanisms including inertia and resonant frequency vary. This article focuses on such cascaded proportional–integral–derivative controller parameters tuning for contour following performance improvement. It first describes the servo system dynamics under the cascaded proportional–integral–derivative control structure and identifies the model parameters via relay feedback technology. Then, the effects of the closed-loop dynamics on contour following are analyzed to gain that the matched axial dynamics is preferable. In order to match the axial dynamics, the controller parameters are tuned loop by loop through setting all the axes to have the same bandwidths. Based on the identified results, feedforward controller parameters including nonlinear coulomb friction compensation are also tuned to further improve the contour following performance. At last, the proposed tuning method is verified through the ellipse and diamond following experiments carried out on an X-Y motion stage. The results show that it can match the axial dynamics effectively and thus reduce the contour error greatly.
Magnetic levitation systems are able to provide frictionless, reliable, fast and economical operations in wide-range applications. The effectiveness and applicability of these systems require precise feedback control designs because the magnetic levitation is an unstable process and have highly nonlinear dynamics. In this article, a robust sliding mode–based cascade control approach is proposed for effectively tracking the reference position of a magnetic levitation system. The magnetic levitation plant is described with electrical and mechanical models, and the control problems of these parts are treated with cascade controllers. An integral sliding mode and an output feedback sliding mode controllers are designed for use in the cascade loops. The performance of the sliding mode controllers is compared with a proportional–integral–velocity plus proportional–integral control structure. It is shown that the proposed control structure is able to provide a highly satisfactory tracking performance and can eliminate the effects of the inductance-related uncertainties and operating point originated disturbances. The experimental results are provided to validate the efficacy and feasibility of the approach.
This article presents a nonlinear motion controller based on an extended piecewise disturbance observer to track desired motion trajectory for the hydraulic press. The proposed extended piecewise disturbance observer accounts for external load by applying the double-drive parameter adaptation. Considering the special work principle of the separate meter-in separate meter-out drive system adopted in the hydraulic press, the nonlinear cascade controller is extended to synthesize the motion controller. The outer motion tracking loop uses the sliding mode control to compensate for load estimation error with desired driving force as control output. The inner pressure control loop is designed based on the backstepping technique. The minimum equivalent load criterion is proposed to function as the bridge linking the outer and inner loops. The stability of the overall close-loop system is proved based on the Lyapunov theory. Both simulation and experiment results demonstrate that the proposed nonlinear cascade controller, together with the extended piecewise disturbance observer, provides an excellent motion tracking performance for the hydraulic press in the presence of complex external load, which typically consists of the deformation force and the friction.
Inside labyrinth piston compressor, the piston/piston rod system is main moving part. They suffer from very large periodically varying loads caused by gas force and inertia force. This may result in the piston rod’s bending and vibration. Therefore, the piston is always running eccentrically inside cylinder. It is difficult to calculate and predict the piston’s eccentricity accurately by the traditional analytical method. However, an accurate radial clearance between the piston and the cylinder wall must be calculated in the early design of the labyrinth piston compressor. Thus, this article proposes a new numerical method of studying the piston’s dynamic behavior, which is based on flexible body dynamics and finite element method. The method overall considers the piston rod’s characteristics of bending and vibration, effect of the radial clearance between the piston rod and the guide bearing, as well as crosshead and slideway. Through the model, the piston’s radial eccentric path can be better predicted. In addition, this article also introduces a new idea for realizing piston/piston rod system’s centering and utilizing an electromagnetic guiding system instead of traditional mechanical structure. The new centering technology will simplify greatly the inner structure of the compressor by removing the guide bearing. We have designed theoretically the structure of an electromagnetic guiding system and built its control model. Simulation verifies the effectiveness of this method, and good control result is obtained.
A tracking problem for a group of multiple unmanned aerial vehicle (Multi-UAV) systems with agent faults is investigated. A neighbouring rule-based cooperative control algorithm is proposed such that the Multi-UAV systems can follow the common reference signals in a fault free situation. Once in the presence of faults that change the dynamics of the agents, a fault tolerant cooperative control strategy based on the plugging operations (with a minor adjustment of connection) is employed in order to make each agent continue to follow the reference signals without increasing the number of weak points. Moreover, the utilised plugging operations do not need to reconfigure any individual’s self control law or stop the faulty agents. Simulation results show the effectiveness of the proposed methods.
A bond graph model for a closed-loop linear time invariant multiple input multiple output system with singular perturbations is presented. This system is formed by a plant, an observer and the feedback. Hence, the storage elements that represent the slow dynamics of the observer determine the feedback control. Also, a junction structure of the bond graph model for the closed-loop system with singular perturbations is proposed. A new bond graph to obtain the observer and controller gains of the closed-loop system is presented. This new bond graph has the characteristic that storage elements of the fast dynamics and slow dynamics have a derivative and integral causality assignment, respectively. Thus, a quasi-steady state model of a singularly perturbed system with a slow state estimated feedback is obtained. Finally, the proposed methodology is applied to an illustrative example.
Sensor bias faults and sensor gain faults are two important types of faults in sensor. Simultaneous estimation of these sensor faults in nonlinear systems in the presence of input disturbance and measurement noise is challenging and has not been adequately addressed in literature. Hence, this article develops an observer-based sensor fault estimation method for generalized sector-bounded nonlinear systems in the presence of input disturbance and measurement noise. A generalized sector-bounded nonlinearity was chosen because it encompasses a wide range of nonlinearities including Lipschitz, positive real, and dissipative. This article presents necessary and sufficient conditions to achieve a suboptimal cost for a cost function consisting of the sum of the square integrals of the estimation errors to the square integrals of the disturbances in the form of linear matrix inequality. The linear matrix inequality can be solved offline to explicitly calculate observer gain, and the resulting observer simultaneously estimates the system states as well as both bias and gain faults in the sensors. Compared to previous literature, the proposed methodology is designed to work in the presence of both input disturbance and measurement noise. Additionally, this article considers a generalized sector-bounded nonlinearity which encompasses a variety of different physical nonlinearities. Furthermore, the observer does not require the online solution of the Riccati equation and is thus computationally less intensive compared with the methods of extended Kalman filtering. The observer design procedure is demonstrated through two illustrative examples consisting of a fourth-order double spring–mass system and a third-order wind turbine power transmission mechanism.
This study presents a model-following positioning control system based on modified sliding mode control. In the proposed method, a robust gain matrix prevents the dependence on the plant parameters by applying the switching function to an error dynamics equation. Simulation studies are applied to a nominal plant with stable and unstable terms, and a plant with a modeling error and an input-side disturbance. Simulation and experimental results indicate the effectiveness of this method in determining a robust gain matrix. The proposed method further demonstrates positioning control with superior performance.
Cavitation is one of the important elements influencing the performance of sea water hydraulic axial piston pump. To understand the working performance of sea water hydraulic axial piston pump under cavitation effects, a fully dynamic numerical model was developed in this article, which has taken into account the fluid compressibility effect, dynamic processes of gaseous, vaporous, pseudo-cavitation and cavitation damage, and the simulation was conducted through a three-dimensional computational fluid dynamics code PumpLinx. The cavitation characteristics of the pump were presented with a set of working conditions, as well as the cavitation damage power, dynamic gas volume fraction and vapor volume fraction inside the intake, piston and port plate chamber. A test rig was developed to validate the computational fluid dynamics simulations for the case of sea water hydraulic axial piston pump. Comparisons between the measured and simulated instantaneous discharge pressure, average flow as well as the vibration characteristics under different extents of cavitation by varying the inlet pressure and rotational speed of the pump were presented.
This paper proposes an L1 fuzzy adaptive controller for a class of uncertain continuous-time single-input single-output nonaffine nonlinear systems. The structure of this controller is derived based on L1 adaptive control design methodology and integrates a fuzzy system. The latter is used to approximate as best as possible a function of an unknown ideal implicit controller, which provides good results and improves the performance significantly. The L1 fuzzy adaptive controller consists of a predictor, a control law and its adaptive laws. The major advantage of the proposed control scheme is its ability to guarantee uniformly bounded transient and tracking performance for the controlled system. These performance bounds can be rendered arbitrarily small by the systematic choice of design parameters. The effectiveness and feasibility of the proposed L1 fuzzy adaptive controller are examined experimentally in the position control of a pneumatic actuator system.
Electrodynamic bearings exploit repulsive forces due to eddy currents to produce positive stiffness by passive means. Such a feature would make this type of bearing a viable alternative to active and permanent magnet bearings. Although electrodynamic bearings do not violate Earnshaw’s theorem, the open issue remains the stabilization system that is needed to make the rotating body stable, due to the low rotational speeds. Stabilizing solutions proposed in the literature are partially effective and not totally convincing. This limits real industrial applications.
The present paper proposes a combination of electrodynamic and active magnetic bearings. At low speed the active part behaves as a conventional active magnetic bearing, while at high speed it provides damping. The readiness of the proposed solution is demonstrated by experimental results obtained using a dedicate test rig.
This article presents an eddy current damper of a passive reaction force compensation mechanism for a linear motor motion stage. The reaction force compensation mechanism with a movable magnet track and eddy current damper resolves problems with the existing spring-based reaction force compensation mechanism such as resonance, design freedom, and difficulty of assembly and manufacturing. A simplified mathematical model of the eddy current damper is derived considering the sinusoidal magnetic flux density distribution and effective width of the eddy current damper, which shows important design factors of the eddy current damper–based reaction force compensation mechanism. Then, force of the eddy current damper according to the constant speed motion of the magnet track is investigated using multi-physical finite element analysis and is verified by experiments. Finally, the passive reaction force compensation with movable magnet track and eddy current damper is identified by experiments, and the finite element analysis of the eddy current damper is verified with free and forced vibration responses.
In the harmonic gear servo system, friction is associated with not only the velocity of the input shaft but also its angle position. Traditional friction compensation based on the velocity cannot guarantee the high motion accuracy. To address this problem, this article proposed a new friction model of harmonic gear servo system, which is related to both its velocity and position. The new model includes two parts: in the presliding region, the static friction is determined by the maximum elastic deformation recovery angle of the input shaft, and in the sliding region, the friction not only has Stribeck effect from velocity but also has harmonic series relative to the input shaft’s position. In this article, the parameters of friction model were obtained by preliminary experiments. A control diagram based on this model was established for friction compensation and the proposed control algorithm showed its superiority in the experiments.
In this paper, fractional-order controller designs for integer first-order plus time delay systems are investigated. Based on Bode’s ideal transfer function as a reference model, a new structure of the fractional-order controller is proposed. The internal model control principle is used to design the controllers. The effectiveness of the controllers is demonstrated through simulations and their efficiency is validated through experimentation on a heat flow platform.
Optimization of nonlinear controller design for thermal management in polymerase chain reaction amplification
Owing to errors made by the author(s), Arman Sehat Nia and Hamed Kharrati, the article is incorrect. The names of Manizhe Zakeri and Vahid Azimirad were omitted:
Optimization of nonlinear controller design for thermal management in polymerase chain reaction amplification
Arman Sehat Nia1 and Hamed Kharrati1
Proceedings of the Institution of Mechanical Engineers, Part I: Journal of Systems and Control Engineering, April 2015 229: 334–341, first published December 23, 2014 as DOI:
The authors apologise for this error. The correct author listing should be as follows:
Optimization of nonlinear controller design for thermal management in polymerase chain reaction amplification
Manizhe Zakeri1, Vahid Azimirad1, Arman Sehat Nia1 and Hamed Kharrati2 Proceedings of the Institution of Mechanical Engineers, Part I: Journal of Systems and Control Engineering, April 2015 229: 334–341, first published December 23, 2014 as DOI:
1School of Engineering Emerging Technologies, University of Tabriz, Tabriz, Iran 2Electrical and Computer Engineering Department, University of Tabriz, Tabriz, Iran
The dynamic system simulation and the control design process of the new developed bearingless rotating-field axial-force/torque motor (AFTM) requires an augmented state-space framework for mathematical system description. After a short summary of this framework, the main focus of this paper concentrates on the model parameterization using state-of-the-art drive gauging procedures. A direct comparison features minor deviations between magnetostatic finite element analysis simulation results and available measurement data. Moreover, a closed-loop control concept for concurrent axial position stabilization and vector drive control of AFTMs is proposed. The quality of the closed-loop control system simulation is reviewed using relevant measurements of the functional prototype. A presentation of the disassembled prototype and a summary of its performance data concludes this paper.
A robot system would inevitably cause unpredictable collisions in an unknown or unstructured environment. In this paper, the controllability conditions of a general robot system with compliant actuators are proposed to judge and assess the contact constraints based on Port-based Hamiltonian. In order to satisfy the proposed controllability conditions, one fuzzy coordinated control method inspired from the pathfinding of a blind or normal person in dark environment is proposed to deal with the problem of contact constraint. This method achieves velocity–torque combined control without using force or vision sensors compared with conventional methods. Finally, the experiments validate the feasibility of the controllability conditions to deal with contact constraint problems. The results show that the fuzzy coordinated controller can work more efficiently and effectively to detect and respond to contact constraints compared with the proposed proportional control.
Single stage compressors supported in magnetic bearings are known to exhibit compromised capacity to handle loads associated with compressor surge and stall – generally in a frequency range from about 10 Hz to 100 Hz. The present work explores the premise that this reduced capacity is an artifact of the choice of PID control for the magnetic bearings, rather than something fundamental to magnetic bearing physics. A case study of a machine similar to a chiller compressor was used to compare performance achieved with two kinds of PID control (local control versus tilt/translate control) to that achieved with a generalized, multiple-input multiple-output control approach, such as H-infinity. It was found that H-infinity could readily achieve between two and three times the load rejection of PID in the frequency range associated with surge and stall, nearly reaching the theoretical capacity limit in that range. The more common approach of simply increasing the physical size of the bearings was also examined, and it was found (as expected) that a 40 percent increase in bearing size yielded roughly a 40 percent increase in capacity. More importantly, it was found that the smaller bearing with the better control algorithm substantially outperformed the larger bearing with conventional PID control. These observations provide motive to more strongly consider advanced MIMO control methods for active magnetic bearings.
A five-axis computer numerical control hybrid machine tool composed mainly of a three-RPS parallel spindle head with one translation and two rotations is investigated; because of its unique machining characteristics, this machine tool has been applied to high-efficiency aerospace monolithic component processing, and its trajectory control is one of the core technologies underpinning its efficacy. This research investigates a new type of five-axis hybrid machine tool which is loaded with a three-RPS parallel spindle head and finds a cutter orientation interpolation algorithm which can ensure its high-precision, and high-speed, operation in machining processes. First, the kinematic model of the hybrid machine tool is established using the vector chain method. Using this model, the virtual reality mapping relationship between the control axis space and the operating space is established. Then a control algorithm governing two interpolation strategies in the operation and joint spaces is proposed; this method disperses the cutter vector in the workspace. Through the mapping relationship, the point data array in the joint space can be obtained from the machining data which are calculated from the mapping model, and then the improved three B-spline interpolation method is used in the joint space. Thereafter, the post-machining module outputs the interpolation data to the motor, and the moving platform can realise the desired tool path. Finally, using the hybrid machine tool for the machining of an ‘S’ test-piece, the results prove the feasibility and effectiveness of the interpolation algorithm. The experiment indicates that the interpolation algorithm can be used in this kind of parallel machine tool control system.
For commercial aircraft, real-time fault detection is essential for condition monitoring of rotating engine components, which can improve aviation safety and reduce maintenance cost for airline companies. In this article, based on the adaptive kernel principal component analysis method, a real-time fault detection algorithm is proposed for turbine engine disk condition monitoring. A sample reduction strategy based on the k-nearest neighbors method is presented to speed up the kernel principal component analysis approach while still guaranteeing correct results. To efficiently detect fault, the fault detection model is updated timely to suit the working process of turbine engine disk. Sample clusters are obtained through the k-mean method, and the parameter of the kernel function is adaptively adjusted by minimizing the within-cluster distance and maximizing the between-cluster distance in the feature space. Experiments have demonstrated the superiority of the proposed approach in fault detection for turbine engine disk.
The objective of this work is the development of an innovative actuator for Velan ABV S.p.A., which is mainly used for control and special on/off applications where high efficiency and linear behaviors are desirable specifications. The main performances of the proposed actuator, which has been protected by a patent, have been compared with a conventional scotch yoke one, using both the simulation results and the experimental data. In order to measure the efficiency and the dynamical response of the actuators, the authors have designed a hydraulic test rig, configured to fulfill different testing procedures. In this way, it is possible to perform both static tests to identify actuator efficiency and dynamic hardware-in-the-loop tests in which an assigned load or valve impedance function is simulated to verify the response of the tested object in realistic operating conditions. Finally, the proposed test rig has been successfully used to perform reliability and fatigue tests in which the actuator is stressed with realistic and repetitive loads. Moreover, the integrated development of both innovative actuator and testing devices is explained introducing interesting concepts whose applications are normally limited to robotics (e.g. impedance and force control) or vehicular technology (e.g. smart suspensions and suppression of vibrations).
This article investigates the problem of designing robust guidance laws for intercepting maneuvering targets with desired terminal line-of-sight angle constraint. Based on generalized model predictive control for the nominal system, the discontinuous and continuous integral sliding mode control laws are, respectively, developed. Stability analysis shows that the proposed guidance law can ensure the optimal tracking characteristic of generalized model predictive control algorithm and the line-of-sight angle tracking error as well as the line-of-sight angular rate can converge to zero asymptotically. The effectiveness of the proposed guidance law is validated by applying it to a surface-to-air missile for intercepting a head-on maneuvering target under different scenarios.
This article focuses on the operational behaviours of two novel bearingless reluctance slice motor prototypes. After a brief introduction of the two systems, we present our experience with both bearingless drives. On this basis, commonalities and differences in terms of construction, geometric constraints, winding systems, force-to-torque ratio, power electronic utilization and efficiency are outlined in order to demonstrate the suitability of the reluctance slice motor concepts for industrial applications.
In recent decades, flexible manipulators have been studied by many researchers from robotics, solid mechanics, and control fields. Flexible manipulators have many advantages, including low weight because of the slenderness of the links of the robot. Although the original objective was to take advantages of the slenderness or flexibility in real robots, the challenging dynamics of the systems intrigued interests to employ an experimental flexible manipulator as a test bed to evaluate different modelling or control methods. With such a vast and various literatures, a review is indispensable for researchers who want to adapt their interests with the area. Some valuable review articles have been published, referencing numerous articles on single-link or multi-link flexible arms. This article pays an inclusive focus on trends of the research on modelling and control of multi-link flexible-link manipulators. The scope of this review article is particularly on two-link flexible manipulators, relevant models presented for closed-loop applications, and model-based control. Recent and historical contributions in the modelling and control of flexible-link manipulators are presented and discussed. As regular industrial manipulators normally have multiple links with two long links, that is, upper arm and forearm, this review can introduce advances in considering elasticity effects to robotic researchers.
Hydraulic control with switching valves can excite undesirable hydraulic and mechanical oscillations; hence, control performance is inadequate. There are different ways to cope with such oscillations. One way is to change the design or to add some damping elements which improve the attenuation of the oscillations. Another way is to actuate the system in an appropriate way – so that almost no unwanted oscillations are excited. This article illustrates that optimal feed-forward control theory can be used to obtain a realisable switching valve command which avoids ongoing oscillations for the case of a fast position step. A system composed of a dual-stroke cylinder with its piston chamber connected to the switching valves by some pipeline and its rod chamber to pre-pressurised accumulators for counterbalancing is modelled as a discrete dynamical system of order 9. The optimal control problem is conditioned such that the resulting valve signals can be approximately realised by the existing switching valves. For this realisation, the so-called ballistic mode of switching valves plays an important role. The theoretical results are tested experimentally on a proper test rig.
Magnetic levitation technology, for magnetic bearings and magnetically suspended motors, is a cutting edge technology to produce artificial hearts and higher performance blood pumps. A wider blood gap and the elimination of the contacting parts in the device based on the maglev technology provide better blood compatibility and higher durability of the device. Several maglev pumps developed at Ibaraki University are introduced in this article. Maglev pumps have been designed for different medical requirements and for different magnetic suspension systems. All pumps have sufficient suspension and pump performance as blood pumps. The axial suspension system with a double biased hybrid magnetic bearing is explained in detail as one example of maglev blood pumps.
This article documents a new output feedback guidance scheme for autonomous spacecraft rendezvous in the presence of actuator faults. The proposed approach is essentially a compound control methodology, which consists of higher order sliding mode observer and fast nonsingular terminal sliding mode technique. More specifically, the higher order sliding mode observer is used to estimate the relative velocity between two spacecraft while the fast nonsingular terminal sliding mode controller is used to regulate the relative position and the relative velocity to a small region around zero in finite time. The stability and performance of the closed-loop system are also analyzed using finite-time bounded function and Lyapunov function methods. Finally, numerical simulations are performed to demonstrate the robustness and effectiveness of the proposed method.
The sliding-mode (SLM) control for a servo-solenoid valve (SSV) has been employed before to achieve better performance compared to traditional PID control. However, there still exists some improvement potential for the previous SLM control, such as the static accuracy, the response to ramp or sinusoidal input, and the extra cost of sensors to get full-state feedback. Through effective analysis, this paper develops four practical improvements for the SLM control of a SSV, which can obviously achieve better control performance and not increase the implementation difficulties from the existing controllers. Specifically, the modeling, identification, and the standard SLM control strategy for SSVs are introduced first. The improvements of the SLM control include: the integral element is used to eliminate steady-state error; the tracking control strategies by the velocity feedforward are developed to enhance the trajectory tracking ability; the switch of power supply is employed to improve dynamic response; and the circuit modification of linear variable differential transformer (LVDT) is designed to obtain displacement, velocity, and acceleration signals together. The experiments are carried out and the results reveal that the transient and steady-state performances of SSVs are significantly improved by these improvements to the SLM control.
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Kurita N, Timms D, Masuzawa T. Design and fundamental performance of a magnetically suspended system for the BiVACOR total artificial heart. Proceedings of the Institution of Mechanical Engineers, Part I: Journal of Systems and Control Engineering 2016; published online ahead of print on 29 February 2016. doi: 10.1177/0959651816631908
In this article, an explicit pitch command governor for a kind of proportional–integral–derivative attitude control system is proposed based on the model predictive control philosophy to avoid the dynamic rate saturation in the elevator. In this command governor, the control horizon of the model predictive controller is selected as 1 such that the predicted saturations can be represented by a set of linear inequalities, which can significantly reduce the computational complexity, and the optimal solution can be calculated in real-time. The effectiveness of the proposed method is validated via numerical simulations. In addition, the limitations of this pitch governor are also revealed through investigating its scope of application in terms of uncertainties, nonlinearities and coupling effects.
Commonly, a non-cooperative space target is tracked using angle-only data. An approach utilised in many tracking problems is to perform an initial orbit determination (IOD) step and then transition to sequential estimation. In this paper, a space-based passive tracking strategy is proposed that combines IOD and sequential estimation. For the space-based IOD problem, a modified Laplace’s method is derived, in which the non-spherical effect of Earth is considered and more than three pairs of angle measurements are fused. For the sequential estimation, a robust filtering algorithm, termed the robust square-root cubature Kalman filter, is developed. An adaptive factor is introduced in the developed algorithm, to ensure robustness to measurement malfunctions. Simulation results demonstrate that the proposed strategy can be used in actual engineering applications.
This article addresses mainly questions about the roles of fluid systems, in particular of digital ones, in an "Industrie 4.0 (I4.0)" environment. There are three roles: the general machines’ subsystems/components’ role in machines of an I4.0 production system, the role of subsystems/components of machines which are produced under I4.0 conditions, and the manufacturing of fluid systems’ components in an I4.0 setting. These roles are discussed and examples of digital hydraulic solutions which fulfill these roles excellently are presented. They feature simplicity and robustness of hardware components and transfer of functionality to software. It is concluded that components and subsystems can support the successful realization of I4.0-type production systems decisively.
The physical model of an electrohydraulic actuation system with pressure-reducing cylinder end cushioning has been obtained. In order to arrive at the closure of the model, experimental models for actuator friction and the characteristics of the relief, non-return and proportional valves have been constructed. The variation in discharge through the proportional valve with both pressure and command signal has been modeled by training a neural network with experimental data. For the characterization of the discharge through the proportional valve, besides square root of the pressure drop in each metered orifice, polynomial forms of command signal for the discharge coefficients have been used. Such a direct characterization of the discharge with the command signal eliminates the orifice opening as an intermediate variable. A simple friction model that retains all the features of the existing complex models has been developed. Parameters such as maximum dynamic friction and the corresponding velocity have been introduced for this purpose. All these nonlinear subsystem models have been integrated together in MATLAB/Simulink frame to predict the actuation dynamics. The variations in the predicted and experimental displacements of the piston against different command signals have been found to be quite close to each other.
This article presents the flight control problem of a flexible air-breathing hypersonic vehicle under input constraint and aerodynamic uncertainty. First, a control-oriented model is derived and decomposed into velocity subsystem and altitude subsystem, in which compounded disturbances are included to consider aerodynamic uncertainty and the effect of the flexible modes. Second, nonlinear disturbance observer technique is employed to estimate the compounded disturbance, where the estimation error converges to a compact set if the observer design parameters are chosen appropriately. Then, based on disturbance observer, a robust controller and a dynamic surface controller are developed, respectively, for the velocity subsystem and the altitude subsystem. Third, novel robust first-order filters are designed to overcome the "explosion of terms" problem induced by backstepping method. Additional systems are constructed to tackle input constraints. By rigorously Lyapunov stability proof, the designed control strategy can assure that tracking error converges to an arbitrarily small neighborhood around zero. Finally, simulations are performed to show the effectiveness of the presented control strategy.
An electronic control unit for a fuel control system of two-shaft gas turbine engines plays an undisputable role in providing the required fuel flow to the engine as well as satisfying engine’s operational characteristics. One of the main challenges in designing such unit is the accuracy of its performance and the control strategy implementation on an electronic hardware via repeatable and comprehensive tests. In this article, a hardware-in-the-loop simulation is presented for testing of the electronic control unit for a two-shaft gas turbine engine. For this purpose, the engine is first presented and modeled by the use of Wiener block structure method. The fuel controller with Min–Max structure is then explained. Finally, the controller is implemented on a PC/104 hardware and tested in an hardware-in-the-loop simulation in order to verify its correct performance. The results show that the fuel controller satisfies all of the engine’s physical constraints, confirming the controller competence and successful implementation of the engine control algorithm on the PC/104 hardware.
In this article, a novel control scheme is proposed to solve the problem of robust and fast tracking control for the longitudinal model of a dual-control missile steered by a combination of aerodynamic fins and reaction jets in the presence of model uncertainties and external disturbances. The control scheme contains two aspects, one is the observer-based adaptive sliding mode control law of the control moment and the other is the fuzzy allocation method which assigns the control moment to the fins and the reaction jets. The main contributions of the article are as follows: (1) to compensate the disturbances and uncertainties on the sliding mode surface and enhance the system robustness, an observer-based sliding mode surface is designed; (2) an adaptive sliding mode control scheme is proposed by introducing an adaptive term derived from radical basis function network, which does not require knowledge of the bound of the system uncertainties and external disturbances. Meanwhile, it eliminates the chattering phenomenon without deteriorating the system fast-response characteristic and robustness; (3) a control-moment allocator based on fuzzy reasoning is designed to make the system respond fast while avoiding wasting of the reaction jets. Simulation results demonstrate that the proposed control scheme is effective in improving control robustness and response rapidity.
This article focuses on the high-performance motion control of an accumulator assistant fast forging hydraulic press. As the accumulator has a significant impact on the motion control performance of the fast forging hydraulic press, the dynamic and static characteristics of the accumulator are studied and a simplified mathematical model is applied in the motion controller design. To hold the nonlinear parameter uncertainty associated with the accumulator model, a nonlinear damping regulator and a nonlinear robust feedback are synthesized based on the simplified mathematical model. The virtual control law "lumped flow" is proposed to act as the equivalent input of the fast forging hydraulic press, which successfully solves the decoupling problem and makes the motion controller design feasible. And the most economical distribution scheme is finally applied to synthesize the actual control law for each fast forging valve. In consideration of the parametric uncertainties and uncertain nonlinearities appearing in the mathematical model of the accumulator assistant fast forging hydraulic press, the discontinuous projection-based adaptive robust control is extended to synthesize the motion controller. Both simulation and experiment results demonstrate that with the proposed motion controller, the transient performance and final tracking accuracy are guaranteed although the system is subjected to various model uncertainties coming from both parametric uncertainties and uncertain nonlinearities. Furthermore, with the proposed nonlinear damping regulator, the influence of the accumulator can be well compensated and the control performance is improved.
The article concerns the modelling and control of a digital hydraulic cylinder drive involving a standard differential cylinder controlled by four digital flow control units in a full bridge circuit. A special focus of the modelling lies in the compromise between the prediction accuracy of the model and the computational efficiency of the control algorithms based on the models. A physically motivated model for the static pressure-flow-characteristic of digital flow control units is derived and compared to conventional models. Based on this model, a switching algorithm is developed which finds an optimal switching combination for each DFCU, if certain dimensioning conditions are fulfilled. The algorithm forms the inner loop of a hierarchical controller for the overall system. In an outer loop, a flatness-based tracking controller is used for the independent metering control of the cylinder. The models and algorithms developed in this article are validated in experimental investigations using a laboratory test rig.
Discrete fluid power systems featuring transmission lines inherently include pressure oscillations. Experimental verification of a discrete fluid power power take off system for wave energy converters has shown the cylinder pressure to oscillate as force shifts are performed. This article investigates how cylinder pressure oscillations may be reduced by shaping the valve opening trajectory without the need for closed loop pressure feedback. Furthermore the energy costs of reducing pressure oscillations are investigated.
A disturbance observer–based multi-model soft switching tracking control design is proposed for the near-space interceptor. Initially, based on the Takagi–Sugeno modeling approach, a slow–fast loop soft switching model is employed to approximately describe the nonlinear dynamics of the near-space interceptor. Subsequently, a disturbance observer is constructed to estimate the unknown disturbance. Based on the disturbance observer, a descriptor system approach is proposed to solve the multi-model soft switching tracking control design problem. The suggested controller can not only ensure the stability of the closed-loop near-space interceptor system but also provide an upper bound of the cost function. Moreover, a robust least-squares weighted control allocation algorithm is employed to distribute the virtual control command among the redundant actuators (the aerodynamic fins and reaction jets). Finally, simulation results demonstrate the effectiveness of the proposed control scheme.
In this article, an overview of principle research works regarding control of nonlinear nonminimum-phase systems is presented. Key concepts of some research of fundamental importance that has been done in this area are discussed. The research is categorized into the five fundamental methodologies, and further work based on particular methodology is also discussed. Limitations of each concept are also highlighted at the end.
This article deals with the robust H control problem for uncertain stochastic systems with time-varying delays in state and control input. The time delay is assumed to be a time-varying continuous function varying in an interval and uncertainties are assumed to be norm bounded. New delay-dependent criteria for the existence of memoryless state feedback H controller are proposed to guarantee robust asymptotic stability in the mean square as well as the prescribed H performance level of the closed-loop systems for all admissible uncertainties. The main contribution of this article is the instrumental idea of delay decomposing, which leads the resultant conditions to be much less conservative than the existing results in the literature with the decomposing getting thinner. By using free-weighting matrices and a new technique to estimate the upper bound of the stochastic differential of Lyapunov–Krasovskii functional candidate, new delay-dependent conditions are derived by considering the relationship among the time-varying delay and its lower and upper bounds without ignoring any useful terms. The advantage of the results proposed in this article lies in their reduced conservatism, as shown via illustrative examples, which also demonstrates the effectiveness of the proposed method.
This study combines self-organizing fuzzy logic control technology with optimal control theory and presents a self-organizing fuzzy optimal controller for under-actuated systems. Instead of calibrating the control input directly, the self-organizing fuzzy optimal controller employs the self-organizing fuzzy system as a superior regulator to adjust the weighting matrix of the cost function for the optimal controller. Through this operation and the hierarchical control architecture design, self-organizing fuzzy optimal controller adaptively regulates the control strategy and manipulates the optimal control procedure according to the system dynamic behavior in real time. The optimal control law corresponding to the proposed regulator is then derived from the maximum principle for optimal control theory. The stability of the self-organizing fuzzy optimal controller is analyzed and proved through the Lyapunov stability theorem. Simulations on an under-actuated gantry crane system and a ball-and-beam system have verified that the self-organizing fuzzy optimal controller provides superior control performances as compared with the traditional linear quadratic regulating controller.
This article presents natural corner-based simultaneous localization and mapping (SLAM) using a new data association algorithm that achieves partial compatibility in a real unknown environment. In the proposed corners’ extraction algorithm, both the end points of an extracted line segment far away from the other segments and the intersection point of the two closer line segments are considered as corners. In data association, a partial compatibility algorithm obtaining a robust matching result with low computational complexity is proposed. This method divides all the extracted corners at every step into several groups. In each group, the local best matching vector between the extracted corners and the stored ones is found by joint compatibility, while the nearest feature for every new extracted corner is checked by individual compatibility. All these groups with the local best matching vector and the nearest feature candidate of each new extracted corner are combined, and its joint compatibility is checked with the linear matching time. The experimental results in an indoor environment with natural corners show the robust matching result and low computational complexity of the partial compatibility algorithm in comparison with individual compatibility nearest neighbor and joint compatibility branch and bound.
This article focuses on the nonlinear Wiener system identification of three-dimensional elliptical vibration cutting. The developed three-dimensional elliptical vibration cutting device is actuated by four piezoelectric stacks, which have hysteresis nonlinear characteristics. Our research proposes an improved memetic algorithm in order to identify the nonlinear elliptical vibration cutting model. The improved memetic algorithm displays the advantages of both particle swarm optimization and genetic algorithm, while simultaneously overcoming these programs’ shortcomings. Moreover, it can quickly and efficiently search for the global optimization. The improved memetic algorithm’s identification performance may be compared with the conventional memetic algorithm, particle swarm optimization, and genetic algorithm using two well-known test functions. Test results demonstrate that the improved memetic algorithm can search the global optimal solution more efficiently than available state-of-the-art algorithms. Based on the input–output data collected from experiments, the accuracy of the identification model can potentially reach 97.55%. This relatively small margin of error verifies the efficiency of the proposed improved memetic algorithm for system identification.
The wide range of engineering domains aggregated in mechatronic systems can cause problems for design engineers. It is important to treat the different domains in an integrated, concurrent manner during design to be able to achieve the frequently sought-for synergetic effects of mechatronic systems. Traditional design methods are usually based on the different engineering disciplines being treated separately and only integrated at a late stage of the development process. Consequently, those methods do not work sufficiently well for mechatronic systems, leading to a suboptimal product. Previous research by the authors presents a novel approach to mechatronic system design by allowing quick optimisation and evaluation of design concepts. This is done by front loading certain design activities, hence decreasing the need for time- and cost-consuming iterations in later design stages. The method is backed up by a supporting software tool prototype. This article extends the method by including the dynamic aspects of the designed systems while also implementing basic control aspects, hence creating a concurrent and holistic method for mechatronic system design. This allows the designer to take synergetic effects into account at an earlier stage of the design process, hence increasing product quality and decreasing development costs. A conceptual design case is used in this article for an initial evaluation of the method and the results show great potential for the methodology.
In this article, image-based visual servoing control of an underactuated unmanned aerial vehicle is considered for the three-dimensional translational motion. Taking into account the low quality of accelerometers’ data, the main objective of this article is to only use information of rate gyroscopes and a camera, as the sensor suite, in order to design an image-based visual servoing controller. Kinematics and dynamics of the unmanned aerial vehicle are expressed in terms of visual information, which make it possible to design dynamic image-based visual servoing controllers without using linear velocity information obtained from accelerometers. Image features are selected through perspective image moments of a flat target plane in which no geometric information is required, and therefore, the approach can be applied in unknown environments. Two output feedback controllers that deal with uncertainties in dynamics of the system related to the motion of the target and also unknown depth information of the image are proposed using a linear observer. Stability analysis guarantees that the errors of the system remain uniformly ultimately bounded during a tracking mission and converge to 0 when the target is stationary. Simulation results are presented to validate the designed controllers.
Rare earth permanent magnet brushless direct current motor is the energy conversion device between power system and propeller of high-altitude airship. Its performance has a profound effect on the overall performance of the high-altitude airship. Limited by the output torque of the permanent magnet brushless direct current motor, propeller on the ground cannot reach the rated angular speed when propeller works at high altitude, so it is difficult to carry on rotation test on the ground. In addition, performances of the permanent magnet brushless direct current motor system such as control accuracy, reliability and efficiency cannot be tested. The functional level of the motor load simulator is proposed considering the dynamic properties of the propeller and the basic functions of the propulsion system. Different loading actuators are evaluated and the conceptual design of the load simulator is accomplished. Inertia is realized by relatively small flywheel and inertia electrical emulation method. Torque is simulated by servo motor that can work at braking state and thrust is exerted on the motor by hydraulic servo valve control system. Finally, depending on the proposed scheme and design parameters, co-simulation model of the load simulator is established utilizing software MATLAB/Simulink and AMESim. After comparing co-simulation results with real propeller properties, the feasibility of the conceptual design of permanent magnet brushless direct current motor load simulator is proved, and what is more, the effectiveness of control strategies and the rationality of parameters settings for co-simulation are testified.
Realization of biologically motivated algorithms in industrial applications is becoming a new research, especially in the field of electrohydraulic systems. One of the recent innovations named brain emotional learning–based intelligent controller has been catching eyes of the researcher as a model-free adaptive controller, which has effective capabilities to handle nonlinearities and uncertainties of controlled systems. The aim of this article is to develop a so-called self-tuning brain emotional learning–based intelligent controller for tracking control of electrohydraulic actuators. Here, the main control unit brain emotional learning–based intelligent controller is used to drive the system to desired targets. Meanwhile, a fuzzy inference is designed to tune online the reward function (RF) parameter of the brain emotional learning–based intelligent controller, which enables the system robustness and stability. A test rig employing an electrohydraulic actuator is then setup to investigate the system control performance. The experimental results implied that proposed controller has strong ability to drive the system to follow different reference trajectories with minimal errors.
Control allocation can be used onboard fully electric vehicles in order to maximise the regenerative power produced during braking manoeuvres. In this study, the efficiency characteristics of an electric motor are used in conjunction with constraints from European braking regulations in an offline optimisation procedure aimed at maximising the regenerative power yielded at different motor speed and braking demand conditions. The resulting optimisation data are used in a simple online control allocation approach via a look-up table. Simulation results highlight significant motor power loss reductions and small increases in regenerative power under various levels of braking demand in comparison with a wheel torque allocation scheme in which the front axle-to-total braking force ratio is maintained at a constant level. The approach does not rely on complex online optimisation schemes and can thus be practically implemented in real time on fully electric vehicles.
Investigating the ability of a pneumatic actuator to exhibit the desired mechanical impedance is the subject of this article. Inertia, stiffness and damping are three components of mechanical impedance, and achieving the desired values of these parameters is restricted. Inappropriate compensation of friction, low bandwidth or inaccurate measurement of the external force and losing the pressure tracking ability of the inner pressure control loop are the main factors that affect quality and range of achievable mechanical impedance in pneumatic actuators. In this article, the limitations induced by pressure tracking characteristics on the range of achievable mechanical impedance in pneumatic actuators are investigated by focusing on the inertia term. The experiments show that the minimum stable achievable target inertia in pneumatic actuators is limited; for low values of target inertia, the system goes toward instability. In this condition, the actuator shows sustained oscillations whose frequency and amplitude depend on the value of target inertia. Also, the value of minimum stable achievable target inertia is a function of actuator stiffness, so that for higher values of stiffness, the minimum stable achievable target inertia increases. In other words, the stability margin decreases. Then, on the basis of the results of the pressure tracking tests and taking into consideration the new mathematical model presented in this article, the experimental results are discussed.
This article shows the controller design problem of a flexible air-breathing hypersonic vehicle in the presence of input constraint and aerodynamic uncertainty. A control-oriented model, derived from curve-fitted model, is reasonably decomposed into subsystems that include velocity subsystem, altitude and flight path angle subsystem and angle of attack and pitch rate subsystem. Then, dynamic inversion and robust adaptive control are integrated with approximate backstepping control philosophy to design the control scheme, in which the upper bounds of uncertainties are not to be known in advance and estimated by adaptive law. To tackle input constraints, auxiliary systems are constructed and the states of them are used for controller design and stability analysis. Moreover, a detailed stability analysis of the resulting rigid body system is carried out within the framework of Lyapunov theory. Finally, simulation results illustrate the property of the designed control strategy in handling input constraint and aerodynamic uncertainty.
Dynamic balance and motion control for a class of underactuated wheeled inverted pendulum vehicles that are inherent unstable are investigated in this study. The control objective is to stable the posture of the vehicle platform (longitudinal and rotational position/velocity) as well as hold upright position of the pendulum (tilt angle stability), only with two control inputs generated by the left and right motors. The overall dynamic system is separated into two decoupled subsystems: one is a one-dimensional fully actuated subsystem while the other is a two-dimensional underactuated subsystem. A new hierarchical sliding mode control methodology is first developed to resolve the underactuated problem of this kind of unstable vehicles. The first layer sliding mode surfaces are established upon tilt angle and longitudinal displacement of the vehicle body, respectively; while the second layer sliding mode surface is constructed by the first layer sliding mode surfaces. Consequently, the total control law is deduced, and then the asymptotic stabilities for the overall closed-loop control system are addressed via Lyapunov stability theorem and Barbalat’s Lemma. Numerical simulations illustrate the effectiveness of the proposed control approaches and methodologies.
This article proposes an energy-saving hydraulic servo control system to output axial tension forces under cyclical disturbances in pipe fatigue tests. A hydraulic accumulator and a single-chamber control method were utilized to recover the energy generated by the external disturbance. For the increased potential hazard of pipe fracture in the proposed system, a parameter selection method was discussed, which also considered desired force control accuracy and low energy consumption. A proportional–integral–derivative controller with a model-based feedforward compensator was designed to achieve good force control performance. The mathematical and simulation models of the proposed system were established, and the simulation results indicated that the proposed system could achieve the desired force control accuracy. The energy consumption of the proposed system could be reduced by 71.0% in contrast to that of the traditional system in a case study. Also, the simulation results indicated that the control performance was robust to uncertainties of the disturbance noises, the effective bulk modulus, the internal leakage coefficient of the cylinder and the adiabatic gas rate.
A new robust nonlinear controller is proposed to improve the performance of the atmospheric pressure simulator that has some special characteristics such as asymmetry and nonlinearity. The three major components in such systems, the chamber, the servo valve and the vacuum pump, are studied to develop a full nonlinear model which encompasses all the major nonlinearities. Based on the model expressed in the controllability canonical form, a feedback linearization controller is developed to handle the strong asymmetry and nonlinearity of the atmospheric pressure simulator. Considering the parametric uncertainties and un-modeled dynamics existing in the atmospheric pressure simulator, a self-tuning fuzzy proportional integral derivative controller integrating with feedback linearization is introduced to improve the performance of the atmospheric pressure simulator at high-altitude simulations. Simulations and experiments indicate that the proposed controller can effectively raise the dynamic response performance, and in the meantime stability can be ensured.
Relay experiment can be used to identify exact model parameters of an unstable first-order plus dead time transfer function when a limit cycle exists. This article deals with unstable processes with large time delay where the relay test is not applicable. For these processes, the conventional relay method does not induce a stable limit cycle at the output. A method to overcome the problems with inducing a sustained limit cycle output is discussed by deriving a suitable stabilizer for a feedback control. Then, a non-iterative estimation technique is given to identify the unknown parameters of a first-order mathematical model.
In this article, a fuzzy predictive control scheme is proposed for controlling liquid level in a three-tank system in the presence of disturbances and uncertainties. The three-tank system is considered as a hybrid system, and a hybrid model of the system is obtained using the mixed logical dynamical modeling approach. Nonlinear parts of the system are linearized based on a piecewise affine linear method. Then, a model predictive control is designed based on the hybrid model and applied to the three-tank system. Although the performance of the model predictive control method is satisfactory in normal condition, it suffers from the problem of bias in output in the presence of disturbance and uncertainty. In this article, a fuzzy supervisor is utilized to adjust the main predictive controller such that the effects of disturbance and uncertainties are degraded by using zero-offset tracking. The proposed fuzzy predictive control scheme has advantages of simplicity and efficiency in normal operation, and strong robustness in the presence of disturbances and uncertainties. Simulation results demonstrate the effectiveness and superiority of the method.
In this article, we propose an adaptive recurrent fuzzy wavelet neural network control strategy to improve high-accuracy position tracking for robot manipulators. In order to deal with the unknown knowledge of the robot system problems, the adaptive recurrent fuzzy wavelet neural networks are applied in the main controller to approximate the unknown dynamics without the requirement of prior knowledge. In addition, an adaptive robust control law is also developed to eliminate uncertainties that consist of estimation errors and disturbances from the robot control system. The design of the adaptive online learning algorithms is determined using the Lyapunov stability theorem. Therefore, the proposed controller proves that it can guarantee not only the stability and robustness but also the tracking performance of the robot manipulators control system. The effectiveness and robustness of the proposed method are demonstrated by comparative simulation and experimental results.
This article considers the problem of determining the complete stabilizing set of proportional–integral controllers, which is applied in a class of high-order processes with time delay in complex-frequency domain. First, we give a necessary condition for a proportional–integral controller to stabilize the process with certain constant delay using Descartes’ rule of signs. Then by employing the generalization of the Hermite–Biehler theorem applicable to quasi-polynomials, a complete set for all stabilizing proportional–integral parameters is derived to stabilize the open-loop stable and unstable systems. In the case of uncertain time delay, we provide a design approach to stabilize the related plant with a robust proportional–integral controller, where the unknown but constant time delay lies inside a known interval. Three examples illustrate the effectiveness of the proposed results.
A model reference adaptive controller for a twin rotor multiple-input multiple-output system is considered in this article. The objective is to make the twin rotor multiple-input multiple-output system move quickly and accurately to the desired attitudes specified by a reference model. Because of the coupling influence between the two axes of the twin rotor multiple-input multiple-output system and its nonlinear complexity, the controller design is performed on the vertical plane and horizontal plane separately. Thus, the nonlinear multiple-input and multiple-output model of the twin rotor multiple-input multiple-output system is decoupled into two subsystems, and the cross-couplings are considered as disturbances to each other. The obtained two models are transformed via Lie derivatives to a canonical form required for adaptive controller design. Then, a hyperstability-based adaptive control technique is applied for each subsystem. The proposed controller design is evaluated in simulations of cross-coupled condition. The obtained results show that the controlled system is robust against disturbances with high tracking performance.
This article presents the design, simulation and real-time implementation of a constrained non-linear model predictive controller for a coupled tank system. A novel wavelet-based function neural network model and a genetic algorithm online non-linear real-time optimisation approach were used in the non-linear model predictive controller strategy. A coupled tank system, which resembles operations in many chemical processes, is complex and has inherent non-linearity, and hence, controlling such system is a challenging task. Particularly important is low-level control where often instability and oscillatory responses are observed. This article designs a wavelet neural network with high predicting precision and time–frequency localisation characteristics for an online prediction model in the non-linear model predictive controller to show the effectiveness of this approach in controlling the liquid at low level. To speed up the training process, a fast global search stochastic non-linear conjugate wavelet gradient algorithm is initially used to train the wavelet neural network structure before the genetic algorithm optimisation technique is utilised to tune adaptively the wavelet neural network parameters. The non-linear model predictive controller algorithm is tested for both approaches: first, in a simulation using identified models, and second, in a real-time practical application to a single-input single-output system coupled tank system. The results show an excellent control performance with respect to mean square error and average control energy values obtained.
In applications, usually sampled data controllers are employed. If the sampling time is sufficiently small, the sampled data structure may be neglected and the system is treated quasi-continuously. If the sampling time is longer, the system is treated in discrete time neglecting the behaviour in between the sample instances and the z-transform is used. This article combines these two approaches. The plant is driven by an input which consists of a sequence of values and a function forming the actuating variable. By use of the modified z-transform, the plant is modelled by a parametric transfer function matrix, whose additional parameter discloses the behaviour between sampling instances. Thus, the output signal is calculated not only at the points of sampling. A right co-prime matrix-fraction description is derived. Building on that description, basis variables are defined in the z-domain. The corresponding basis sequences can be chosen arbitrarily and with them the input sequences and the output functions are fixed and can be calculated without solving a differential or difference equation. This mathematical fact is applied to plan trajectories in continuous time. Hence, the entire output trajectory in continuous time can be taken into account. A tracking controller may be added to ensure that the disturbed system complies with the plan.
This work focuses on the development of a pressure-loop controller for a hybrid brake-by-wire system, composed of a hydraulic link and an electro-mechanical actuator. Towards this goal, we will start by constructing a reduced model that is capable of capturing the fundamental dynamics of the actuator, which is particularly useful for control design purposes. Motivated by the large friction disturbances that affect the system, we also investigate linear-in-the-parameter models suitable for (online) model-based friction compensation. More specifically, results from the theory of function approximation, together with optimization techniques, are explored to approximate the Stribeck friction model through a linear-in-the-parameter model. This new linear-in-the-parameter model is then employed in the design of a control law for tracking the braking pressure of the hybrid brake-by-wire. The main features of this controller are the robustness to parametric uncertainties, thanks to the inclusion of a switching- adaptive mechanism, and the attenuation of non-parametric disturbances with a continuous sliding mode action. The stability and robustness properties of the closed-loop system are investigated with the help of the Lyapunov method. Finally, experimental tests demonstrate the effectiveness of the proposed approach and its ability to handle disturbances.
In this article, a fault tolerant control approach is proposed for the formation control system of unmanned aerial vehicles with bounded external disturbance and unknown fault using both adaptive sliding mode control and H control techniques. First, a linearized formation model of unmanned aerial vehicles is established under a straight and level formation flight condition. A reference model is introduced for the aim of the fault tolerant control problem. Then a sliding mode surface is designed for the deduced error dynamics, an virtual adaptive sliding mode controller and an adaptive fault estimation algorithm are proposed, which can drive the error dynamics onto the predefined sliding mode surface, and guarantee the property of asymptotical stability with a given disturbance attenuation level. On the basis of the normal proportional plus integral formation controller and the estimated fault information, a compensated control–based fault tolerant formation control scheme is proposed to ensure that the formation geometry is maintained in fault case. Finally, simulation results are given to show the effectiveness of the result obtained in this study.
The nature of digital hydraulic systems may cause severe pressure pulsation problems. For example, switched inertance hydraulic systems can be used to adjust or control flow and pressure by a means that does not rely on dissipation of power, but they have noise problems because of the pulsed nature of the flow. An effective method to reduce the noise is needed that does not impair the system performance and efficiency. This article reports on an initial investigation of an active attenuator for pressure pulsation cancellation in a switched inertance hydraulic system. Using the designed noise attenuator, the pressure pulsation can be decreased effectively by superimposing an anti-phase control signal. A high-performance piezoelectric valve was selected and used as the secondary path actuator in terms of its fast response and wide bandwidth. Adaptive notch filters with the filtered-X least mean square algorithm were applied for pressure pulsation attenuation, while a frequency-domain least mean square filter was used for secondary path identification. A ‘switched inertance hydraulic system’ in a flow booster configuration was used as the test rig. Experimental results show that excellent cancellation was achieved using the proposed method, which has several advantages over passive noise control systems, being effective for a wide range of frequencies without impairing the system’s dynamic response. The method is a very promising solution for pressure pulsation cancellation in hydraulic systems with severe noise or vibration problems.
Significant fore-and-aft tower vibrations of large wind turbines due to wind shear can be reduced using individual pitch control, in which the pitch angle of each blade is adjusted individually. A short survey of the existing individual pitch control strategies is presented, and a new architecture with preview measurements of the wind speeds at different heights is proposed in this article for the turbine tilt moment reduction. The approach includes look-ahead calculations of the desired blade loads and pitch angles as well as preprocessing algorithms for calculation of the derivative of the desired pitch angle. Wind speed measurement records, performed at two different heights with Risoe P2546 cup anemometer, are directly used in the turbine simulations. It is shown that the variations of tilt moment can be essentially reduced using the approach described in this article.
This article deals with a method for the time and space superposition of data acquired in the dynamical testing of large structures. The method permits two procedures comprising the integration of sets of measurements taken at different times and the integration of sets of measurements taken at different places. The latter is a very useful feature when dealing with huge structures, such as big buildings comprising a number of different architectural details. The validation of this method is a case study consisting of many dynamical tests performed on an ancient castle.
The gyro is an interesting and everlasting nonlinear nonautonomous dynamical system that exhibits very rich and complex behavior such as chaos. However, in recent years, modeling and control of fractional-order dynamical systems have become important and useful topics in both research and engineering applications. In this article, the dynamical behavior of a nonautonomous fractional-order gyro system is investigated. We apply the maximal Lyapunov exponent criterion to show that the fractional-order gyro system exhibits chaos. Strange attractors of the system are also plotted to validate the chaotic behavior of the system. Subsequently, in order to suppress the chaotic state of the fractional-order gyro system, a robust finite-time fractional controller is designed. The convergence time of the proposed control scheme is estimated. And the fractional Lyapunov theory is adopted to prove the finite-time stability and robustness of the proposed method. Besides, some computer simulations are given to illustrate the effectiveness and applicability of the proposed fractional controller.