Levitation Control Research Articles

Design of Ultrasonic Levitation Control System Based on FPGA

As a method to achieve containerless processing, the object levitation technique has a broad application prospect in vital research fields. However, the levitation distance of Electromagnetic levitation, near-field acoustic levitation is not far enough to complete cantainerless processing, and the stability of ultrasonic levitation that use single emitter or single transductor array is still needed to be improved. Therefore, this paper proposes a new embedding electronic system based on FPGA controller to drive a construction of transducer arrays that perpendicularly formed by uniaxial concave sphere and uniaxial biplane. A phase delay algorithm is used on this system to change the position of the stand wave points to move the object smoothly. Furthermore, through experimental validation, this system has a stable signal output to reach the goal of levitation and control.

Modeling and Characteristic Investigation of Axial Reluctance Force for Bearingless Switched Reluctance Motor

Combining the advantages of switched reluctance motors and magnetic bearings, bearingless switched reluctance motors (BSRMs) have the potential value for industrial applications, such as turbine generators and compressors, because of their high reliability and low friction. In order to ensure the axial levitation of a rotor coping with loading in the axial direction, the axial reluctance force is essential to be considered for the BSRM. In this article, the analytical model of the axial reluctance force is proposed for BSRMs to investigate the axial levitation ability of the studied BSRM. The operational characteristics of the axial reluctance force are revealed by electromagnetic analysis for the BSRM. The factors affecting the axial reluctance force are explained, and the principle of output characteristics with the change of parameters is obtained. The analytical model is applicable for the calculation of the axial reluctance force under different motor parameters, i.e., axial displacement, current, and some mechanical parameters. After that, the finite-element method is adopted to verify the proposed analytical model. Then, the torque and radial levitation control and corresponding power converters are implemented in experiments to test the performance of the studied BSRM on the axial levitation in practice.

Suspension Regulation of Medium-Low-Speed Maglev Trains Via Deep Reinforcement Learning

This article studies the suspension regulation problem of medium-low-speed maglev trains (mlsMTs), which is not well solved by most model-based controllers. We propose a sample-based controller by reformulating it as a continuous Markov decision process (MDP) with unknown transition probabilities. Then, we propose a reinforcement learning algorithm with actor-critic neural networks to solve the MDP. To reduce estimation errors in the Q-function, we adopt a double Q-learning scheme and propose a novel initialization method to accelerate the convergence by exploiting the PID controller. Finally, we illustrate that the proposed controllers outperform the existing PID controller with a real dataset from the mlsMT in Changsha, China, and are even comparable to model-based controllers, which, however, assume that the complete information of the model is known, via simulations. <p xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><i>Impact Statement</i>—The control problem of levitation systems is essential for maglev trains. The advanced control methods require an exact dynamical model, which is difficult to establish in practice due to uncertainties and complex dynamics. Reinforcement learning (RL), as a model-free method, learns a controller directly from data. We are the first to propose deep RL algorithms to address the levitation control problem. By learning the real dataset provided by CRRC, the proposed algorithms outperform the well-known PID controller significantly. In particular, our controller responses 50 times faster than PID even without additional efforts on modeling. Moreover, the proposed initialization method can be applied in a variety of RL-based control problems to improve performance.

Analysis of electrostatic levitation control system and oscillation method for material properties measurement.

Electrostatic levitation is an important method of studying material properties. Without using a container, a physical object is levitated between electrostatic plates and melted to the liquid state using a laser. Then, measurements are made via fast cooling or oscillation. Control technology is critical to the electrostatic levitation system. Uncertainty regarding the sample charge during the start-up and laser-melting periods often causes disturbances or causes levitation to fail. In this paper, we design a two-step adaptive control strategy with charge estimation and feed-forward control. This method can better adapt to charge uncertainty during the initial stage. In addition, we propose an innovative new method of superimposing oscillation signals via software to measure the material surface tension and viscosity. Unlike the traditional method, this approach does not require extra hardware resources and is flexible with regard to regulating the frequency and amplitude. A control system model with an accurate electric field model is established and used to simulate control progress in order to illustrate the advantage of our control method. Experiments based on a high-speed vision-servo system also validate the effectiveness of the adaptive and oscillation control strategies.

Design and characteristics of a new aerostatic bearing stylus sensor for surface measurement

Stylus profilometry is extensively employed in practice due to its wide measurement range and praiseworthy stability. However, its lever structure will cause nonlinear errors and mitigated precision. Given this context, this paper proposes a new aerostatic bearing stylus sensor (ABSS) for surface measurement, which inherits the stability and large-scale measuring range while avoiding the structural nonlinear errors of the conventional stylus profilometry. The designed ABSS is composed of a magnetic levitation control system and an aerostatic bearing device in the vertical and horizontal directions, respectively. Furthermore, the bearing capacity and the radial dynamic characteristics are analyzed to ensure stylus’ scanning stability and rapid response. Template experiments with different scanning velocities of the stylus are performed to verify the natural frequency and obtain the critical velocity. Finally, the surface two/three-dimensional topographies reconstruction validates the repeatability and accuracy of the proposed ABSS compared to a commercial conventional stylus profilometry.

Vertical direction conveyance control of the magnetic levitation control system using the electromagnet with the embedded displacement sensor

Vertical direction conveyance control of the magnetic levitation control system using the electromagnet with the embedded displacement sensor

Simulation and Test of Energy Consumption of High-Tc Superconducting Coils in Electromagnetic Levitation System

In order to evaluate the energy consumption of the superconducting magnetic levitation system with real-time control, the methods of simulation and test were used to study the AC plus DC loss of the superconducting coil. The simulation established a 2D finite element model in COMSOL, which was based on the H equations method with simple form and fast calculation speed. The test was carried out on a new type of measurement system, which adopted the electrical method with high sensitivity, simple operation and easy implementation. The results of simulation and test showed that, under normal working conditions, the levitation current in the form of AC plus DC produced a relatively small energy loss below $1mW$ per meter. This conclusion is helpful for the promotion and application of superconducting magnetic levitation control system.

Stability and control of maglev vehicle–girder coupled system considering torsional vibration of the girder

The EMS (Electro-Magnetic Suspension) maglev vehicle uses controlled electromagnetic forces to achieve stable levitation; however, the interactions between the vehicle and the flexible girder may induce strong coupled resonances. Recently, a new type of girder resonance has been encountered, and field measurements indicate that this resonance is caused by torsional vibration of the girder. However, up to now, the principle of the girder torsional resonance has not been studied, and related control strategies have not been developed either. In this paper, a typical maglev girder with a steel track is investigated through finite element analysis, and a searching algorithm is proposed to obtain a best fit of the girder transfer function. Then, a maglev vehicle with twenty levitation control units is considered, and together with the girder model, the vehicle–girder coupled system is established. Factors that affect the coupled resonances are analyzed, and it is found that the velocity feedback of the electromagnet, which is effective to suppress the bending resonance of the girder, may lead to torsional resonance of the girder. This conclusion is validated by experiments in a real maglev system. To solve this problem, a distributed virtual tuned mass damper scheme is discussed, and suggestions to avoid the torsional resonances are also presented. This work not only interprets the principle underlying the vehicle–girder coupled torsional resonance, but also presents a methodology for dealing with the maglev vehicle–girder coupled resonance problems.

Research on two-dimensional external magnetic drive method of maglev ball based on force imbalance.

In this paper, an external magnetic driving method of a maglev ball based on force imbalance is first proposed to meet the requirement that the maglev ball is moved linearly in the axis direction of the electromagnetic actuator in the non-liquid environment. This method is expected to be better applied in the fields of industrial and medical miniature curved tube. The maglev ball is a magnetic levitated object. Based on the interpolation algorithm, the two-dimensional stepwise levitation motion trajectory of the maglev ball is designed as the target curve of the motion. The maglev ball can be driven with a large range along a specified motion path. Compared with the 1.0 mm step input, the overshoot of a 0.2 mm step input is decreased by 73.7% and 73.6% in the descending phase and the ascending phase, respectively. Therefore, fluctuation of the step response of the maglev ball is improved by smaller step control. However, the larger the step input, the faster the speed and the larger the levitation gap. Under the condition of a 1.0 mm step input, the maximum levitation gap can be up to 20.487 mm, and the speed of the maglev ball can reach 3.086 mm/s. Compared with static levitation control, the position of the maglev ball is fluctuated severely due to radial runout under motion control conditions, and the position accuracy can reach ±0.03 mm.

Design of Compact Bearingless Disc Drive Systems

Inflating costs and emerging applications are spawning interests toward smaller and faster electric drives. The challenges of miniaturization make magnetic bearings more appealing, as they provide intrinsic high-speed capability and need virtually zero-maintenance. These advantages come at the cost of more sensors, which require a seamless integration especially at small geometrical scale. In the magnetic levitation domain, slice drives are particularly interesting, given their stabilizing passive characteristics that simplify the control of levitation and render the system simpler. These drives are already suitable for compressor applications, where control of all degrees of freedom is not necessary. In this article, the design process for a bearingless disc drive with a high degree of system integration is proposed. Two motor topologies, namely slotted and slotless drives, are rated by their passive stability, active properties, and power losses. Two sensor systems, fundamental for magnetic bearing commissioning, are proposed. They are simple to industrialize and offer a low footprint, thus not interfering with the drive design process. Ultimately, an optimization example is presented. For the presented scenario, drives with intermediate rotor size are the optimal contenders. Specifically among them, the slotless variant proves the best, given lower electrical losses and lighter mass compared to the slotted variant. However, the slotted becomes interesting if a stiffer magnetic bearing is needed.

Fuzzy Sliding Mode Control of Magnetic Levitation System of Controllable Excitation Linear Synchronous Motor

In order to improve the ability of magnetic levitation feed platform of controllable excitation linear synchronous motor (CELSM) to resist external disturbance, a sliding mode control method based on fuzzy switching gain adjustment is proposed. According to the operation mechanism of CELSM, the voltage equation, flux equation, magnetic levitation force equation, and state equation of CELSM are established. The sliding mode surface is designed, and the integral term is introduced to eliminate the steady-state error of the system. The reaching law is designed to reduce chattering by using the saturation function instead of the sign function. Fuzzy logic reasoning is used to estimate the switching gain, to cancel the unknown disturbance, and further weaken the chattering of the system. The sliding mode controller based on fuzzy switching gain adjustment is designed, and the system is simulated in MATLAB environment. The simulation results show that the fuzzy sliding mode control algorithm can improve the dynamic performance of the system and weaken chattering. The feasibility of this algorithm is proved. The experimental platform of CELSM magnetic levitation system is built to carry out partial experimental research on the magnetic levitation control system.

Coupled dynamic analysis of low and medium speed maglev vehicle-bridge interaction using SIMPACK

The low- and medium-speed maglev vehicle generally operates on elevated bridges with a levitation gap of only 8--10 mm, which makes it very sensitive to the vehicle--bridge coupled vibration. To conduct the corresponding modeling and simulation with common dynamics tools, an equivalent processing of the levitation system is required. Using the dynamics software SIMPACK, this paper first introduces the methods of building the multi-body vehicle system, levitation control system and the elastic bridge, respectively, in the SIMPACK railway module, levitation control module and SIMBEAM elastomer module, thus providing a modeling idea for the simulation of the active levitation and operation of low- and medium-speed maglev vehicles through multi-span bridges. It then goes on to simulate and analyze the coupled vibration of a 160 km/h low- and medium-speed maglev vehicle passing through 25 m + 25 m double-span continuous bridges. The research results show that the modeling method introduced in this paper can simulate the low- and medium-speed maglev vehicle--bridge coupled vibration phenomenon, which can be affected significantly by the low-order frequency of the elastic bridge, and can also be intensified under the bridge end impact when the vehicle enters and leaves the bridge. As the running speed of the vehicle increases and the dynamic force increases, the vertical vibration amplitudes of the elastic bridge mid-span, the car body as well as the levitation frame approximate a linear fitting with the vehicle speed. The variation amplitudes of the levitation gap and of the electromagnet current approximate a quadratic fitting with the vehicle speed.

Deep learning controller design of embedded control system for maglev train via deep belief network algorithm

The maglev train has been successful in practice as a new type of ground transportation. Owing to the inherent nonlinearity and open-loop instability of the electromagnetic suspension (EMS) system, an analogue or a digital controller is used to control the maglev trains’ stability. With the rapid development of embedded systems and artificial intelligence, intelligent digital control has begun to replace the conventional analogue control technology creating a new approach to the EMS control system. This paper proposes a hardware module for an embedded levitation controller based on digital signal processor and field programmable gate array, hence producing an open loop mathematical model of the embedded maglev control system. The deep learning controller is then developed based on a deep belief network (DBN) algorithm and a proportional integral derivative feedback controller. The simulations are conducted in the MATLAB environment after training the DBN. Simulation results are compared with those obtained from the conventional controller. Finally, experiments are implemented to examine the feasibility in practice of the application of the DBN into a maglev embedded control system. The system, with the proposed controller, can accurately track the target airgap of 8 mm. The maximum tracking error of sinusoidal trajectory is 0.17 mm and the maximum tracking error of step trajectory is 0.98 mm. Both simulation and experimental results are included in this paper to show that the proposed deep learning controller can be more robust and less complicated to implement in maglev control applications.

Levitation Stability and Hopf Bifurcation of EMS Maglev Trains

This paper analyzed the mechanical characteristics of single electromagnet system and elastic track beam of EMS maglev train and established a five-dimensional dynamics model of single electromagnet-track beam coupled system with classical PD control strategy adopted for its levitation system. Then, based on the Hurwitz criterion and the high-dimensional Hopf bifurcation theory, the stability of the coupled system is analyzed; the existence of the Hopf bifurcation is discussed and the bifurcation direction and the stability of the periodic solution are determined with levitation control feedback coefficient kp as the bifurcation parameter; and numerical simulation is conducted to verify the validity of the theoretical analysis results. The results show that the Hurwitz algebra criterion can directly determine the eigenvalues and symbols of the dynamics system to facilitate the analysis on the stability of the system and the Hopf bifurcation without the necessity of calculating the specific eigenvalues; supercritical Hopf bifurcation will occur under the given parameters, that is, when kp&lt;kp0, the real-time system is asymptotically stable, yet Hopf bifurcation occurs as kp increases gradually beyond kp0, with the stability of the system lost and a stable limit cycle branched.

Novel Bearingless Switched Reluctance Motor With Wide Flat Inductance Region to Simplify the Control of Torque and Levitation Force

In conventional 12/8 bearingless switched reluctance motors (BSRMs), the generation and control of torque and levitation forces are always coupled and interacted, which increases the complexity of the current control algorithm. In this paper, a novel BSRM with 12 stator poles and 4 rotor poles is proposed to simplify the control of torque and levitation, which has wide flat inductance region. Through allocating the generation of torque and levitation forces to different inductance regions of each phase, the levitation control can be similar as that of magnetic bearings, and the torque control can adopt the methods of conventional switched reluctance motors, e.g. current chopping control and angle position control. Accordingly, the current control algorithm of proposed BSRM becomes very easy and flexible. Extensive experiments were completed to verify the demonstrated performance of proposed motor.

Camera-based sample-position detection and control for microgravity electrostatic levitation.

This paper presents a method for high-speed sample detection and position control in an electrostatic levitator. The algorithm uses images acquired from two charge coupled device cameras and allows for robust and reliable detection of the sample position under various process conditions. The results show improvements over position sensitive detector systems especially under harsh environments and during autonomous operation under microgravity conditions. The position of samples with a radius from 0.6 mm to 1.1 mm is detected in three dimensions with an accuracy of ±40 μm inside a 7 mm × 7 mm × 7 mm levitation area. The two orthogonally arranged cameras, recording images at a resolution of 260 px × 260 px, are used to calculate the position every 5 ms. The control model and the corresponding position controller for the three axes are presented as well. The system was successfully tested in the laboratory and under microgravity conditions at the drop tower, during parabolic flights, and on the MAPHEUS sounding rocket.

Design of Interval Type-2 Fuzzy Controllers for Active Magnetic Bearing Systems

This article proposes an active levitation control system composed of an active magnetic bearing (AMB) rotor and an interval type-2 (IT2) model-based fuzzy logic controller (FLC). The controller aims to achieve fast and stable levitation by compensating for system uncertainties via proper design of IT2 membership functions. In particular, the complex nonlinear dynamics of the AMB are modeled as a set of local linear systems around multiple operating points, which can be stabilized by a parallel distributed compensation scheme. Sufficient conditions are derived to guarantee the asymptotical stability of the closed-loop system based on the linear matrix inequality approach and the Lyapunov stability theory. Moreover, input constraints are applied in an enhanced version of the controller. Experiments on a real AMB platform were conducted to demonstrate the effectiveness and superiority of the proposed IT2 FLC.

Analysis of Gap Time-Delay in Maglev Control System

In the maglev control system, signal filtering, A/D sampling and communication all bring time-delay to the gap signal, which will affect the performance of the levitation control. In order to analyze this effect, a single-degree-of-freedom maglev system model is established. The state feedback control method is used to control the maglev system, and the stability of the closed-loop system is analysed and he stable region of control parameters is studied. Gap time-delay is introduced into the closed-loop system model, and the influence of time-delay on the stability range of control parameters is analyzed. It is concluded that the gap time-delay will reduce the stability range of control parameters, the larger the time-delay of position signal is, the smaller the lower limit of the stability region of differential feedback coefficient is and the smaller the stability region is. The simulation results are used to verify the validity of the theoretical analysis.

A Robust Levitation Control of Maglev Vehicles Subject to Time Delay and Disturbances: Design and Hardware Experimentation

Maglev vehicles have become a new type of transportation system with higher speed, lower noise, and commercial appeal. Magnetic-suspension systems, which have high nonlinearity and open-loop instability, are the core components of maglev vehicles. The high-performance control of maglev vehicles has been the focus of numerous studies. Encountering challenges in the levitation control of maglev vehicles in the form of uncertain time delays and disturbances is unavoidable. To cope with these problems, this study presents the design of an adaptive robust controller based on the Riccati method and sliding-mode technology, simultaneously taking into account the influence of time delays and disturbances. The asymptotic stability of the closed-loop system with the proposed control law is proved by the Lyapunov method. Control performances of the proposed controller are shown in the simulation results. Together with the consistently stabilizing outputs, the presented control approach can handle time delays and disturbances well. Finally, experiments were also implemented to examine its practical control performance of the robust levitation-control law.

Comparison of Ziegler-Nichols and Cohen Coon tuning method for magnetic levitation control system

Magnetic levitation is an example of a nonlinear system that is naturally unstable. In the control system field, it can be also used to check the effectiveness of control methods. Unlike other researches overcoming by analytical method, this research investigates the solution of the nonlinearity of the magnetic field by placing two effect hall sensors on the top and bottom of magnetic coils. After decreasing the effect of nonlinearity, two PID control tuning methods, Ziegler Nichols (ZN) and Cohen Coon (CC), are compared to obtain an appropriate control structure and its initial parameters. The experimental result shows that the best control structure of ZN method is PID whereas its initial parameters, Kp, Ti, and Td, are 15.33, 0.036 and 0.009, respectively. The rise-time and settling time of the response are 0.54s and 0.59s. The appropriate control structure is PI control whereas Kp and Ti are 30.05 and 0.012 from CC method. The rise-time and settling time resulted are 0.8s and 0.67s. The ZN method with PID control structure has a better response with smaller rise-time and settling time than PI control from CC Method. This research is benefit for solving a problem dealing with magnetic levitation control.