Dynamic performance of linear electromagnetic actuators in a stray magnetic field:theoretical analysis and experimental verification

Linear electromagnetic actuators(LEAs) are widely used in tokamaks,but they are extremely sensitive to and are prone to fail in a high-strength stray magnetic field(SMF),which is usually a concomitant with tokamaks.In this paper,a multi-physics coupling analysis model of LEA,including magnetic field,electric circuit and mechanical motion,is proposed,and the dynamic characteristics of LEAs in SMFs are studied in detail based on the proposed model.The failure mechanism of LEAs in SMFs is revealed,and the influence of SMFs on the dynamic performance of LEAs is studied and quantified.It is shown that the failure threshold of the LEA selected in this work under the rated condition is 27 mT and 14 mT in the positive and negative direction,respectively.Under a typical SMF of 10 mT in the negative direction,the closing time of the LEA will be extended by 40%,while its opening time will be shortened by about 10%.Experimental tests are also conducted,which verify the validity of the proposed model and the analysis results.This paper provides a basis for the diamagnetic optimization design of LEA,and it is of great significance to ensure the reliable operation of the tokamak.

Model Identification and Control of Electromagnetic Actuation in Continuous Casting Process With Improved Quality

This paper presents an original theoretical framework to model steel material properties in continuous casting line process. Specific properties arising from non-Newtonian dynamics are herein used to indicate the natural convergence of distributed parameter systems to fractional order transfer function models. Data driven identification from a real continuous casting line is used to identify model of the electromagnetic actuator device to control flow velocity of liquid steel. To ensure product specifications, a fractional order control is designed and validated on the system. A projection of the closed loop performance onto the quality assessment at end production line is also given in this paper.

Design and fabrication of a bistable electromagnetic microactuator

An electromagnetic microactuator with two stable positions is presented. The actuator consists of a cantilever beam with two free ends, a torsional beam with two fixed ends, planar coils and permanent magnets. The cantilever beam has two stable positions due to the use of permanent magnets. With electromagnetic actuation arising from the planar coils, the cantilever beam will switch from one stable position to the other. Mechanical and magnetic analysis are carried out on the actuator, and the device with a size of 2.2 mm × 2.5 mm is fabricated with the UV-LIGA technology. The test results show that a current pulse with an amplitude of 70 mA is needed for actuator＇ s switching between the two stable states, and the switching time is no more than 6 ms. Displacement of the end of cantilever is about 15 μm.

EMC design for actuators in the FAST reflector

An active reflector is one of the three main innovations incorporated in the Five-hundredmeter Aperture Spherical radio Telescope（FAST）.The deformation of such a huge spherically shaped reflector into different transient parabolic shapes is achieved by using 2225 hydraulic actuators which change the position of the 2225 nodes through the connected down tied cables.For each different tracking process of the telescope,more than 1/3 of these 2225 actuators must be in operation to tune the parabolic aperture accurately and meet the surface error restriction.This means that some of these actuators are inevitably located within the main beam of the receiver,and Electromagnetic Interference（EMI）from the actuators must be mitigated to ensure the scientific output of the telescope.Based on the threshold level of interference detrimental to radio astronomy described in ITU-R Recommendation RA.769 and EMI measurements,the shielding efficiency（SE）requirement for each actuator is set to be 80 d B in the frequency range from 70 MHz to 3 GHz.Therefore,Electromagnetic Compatibility（EMC）was taken into account in the actuator design by measures such as power line filters,optical fibers,shielding enclosures and other structural measures.In 2015,all the actuators had been installed at the FAST site.Till now,no apparent EMI from the actuators has been detected by the receiver,which demonstrates the effectiveness of these EMC measures.

Electromagnetic control of the instability in the liquid metal flow over a backward-facing step

The tile-type electromagnetic actuator(TEA)and stripe-type electromagnetic actuator(SEA)are applied to the active control of the perturbation energy in the liquid metal flow over a backward-facing step(BFS).Three control strategies consisting of base flow control(BFC),linear model control(LMC)and combined model control(CMC)are considered to change the amplification rate of the perturbation energy.CMC is the combination of BFC and LMC.SEA is utilized in BFC to produce the streamwise Lorentz force thus adjusting the amplification rate via modifying the flow structures,and the magnitude of the maximum amplification rate could reach to 6 orders.TEA is used in LMC to reduce the magnitude of the amplification rate via the wall-normalwise Lorentz force,and the magnitude could be decreased by 2 orders.Both TEA and SEA are employed in CMC where the magnitude of the amplification rate could be diminished by 3 orders.In other words,the control strategy of CMC could capably alter the flow instability of the liquid metal flow.

Experimental investigation on using the piezoelectric and electromagnetic vibration absorbers in milling

The paper presents an active control system that counteracts the development of chatter vibration. The vibration amplitude depends on the dynamic properties of the machine tool, cutting tool and work-piece. In the paper we analyze the case when the loss of machining stability is caused by the work-piece. The proposed active control system employs electromagnet or piezoelectric actuator to suppress vibration during milling. The active control introduces damping into the system, thereby raising the critical depth of cut and reducing forced vibration amplitude. It enables stable cutting under a much wider range of cutting parameters that for the uncontrolled system. Cutting tests are performed on JAFO FYN-50 machine with mill DIN 845 B-25 K-N HSS to demonstrate an effectiveness of the proposed systems.

Design and Optimization of the Electromagnetic Actuator in Active-Passive Hybrid Vibration Isolator

The design and optimization of actuators are difficult andcritical for the active-passive hybrid vibration control system. Inthis paper, an electromagnetic actuator model is establishedbased on Ohm’s Law for magnetic circuit considering theleakage flux. The 600N electromagnetic actuators are designedand optimized based on ANSYS simulation according to theengineering request. Its transient characteristics are studied. Theeffects of different structural parameters on its output force areanalyzed. The experimental results show that the structureparameters and output force characteristics of the designedelectromagnetic actuators satisfy the practical requirement.

Loss Analysis of Electromagnetic Linear Actuator Coupling Control Electromagnetic Mechanical System

As an energy converter,electromagnetic linear actuators(EMLAs)have been widely used in industries.Multidisciplinary methodology is a preferred tool for the design and optimization of EMLA.In this paper,a multidisciplinary method was proposed for revealing the influence mechanism of load on EMLA’s loss.The motion trajectory of EMLA is planned through tracking differentiator,an adaptive robust control was adopted to compensate the influence of load on motion trajectory.A control-electromagnetic-mechanical coupling model was established and verified experimentally.The influence laws of load change on EMLA’s loss,loss composition and loss distribution were analyzed quantitatively.The results show that the data error of experiment,and simulation result of input energy,mechanical work,and iron loss is less than 3%.The iron loss accounts for less than 54.9%of the total loss under no-load condition,while the iron loss increases with the increase of load.For iron loss distribution,only the percentage of inner yoke keeps increasing with the increase of load.The composition and distribution of loss are the basis of thermal analysis and design.

Vacuum Switching Technology for Future of Power Systems

Even though switching in vacuum is a technology with almost 100 years of history,its recent develop-ments are still changing the future of power transmission and distribution systems.First,current switch-ing in vacuum is an eco-friendly technology compared to switching in SF 6 gas,which is the strongest greenhouse gas according to the Kyoto Protocol.Vacuum,an eco-friendly natural medium,is promising for reducing the usage of SF 6 gas in current switching in transmission voltage.Second,switching in vacuum achieves faster current interruption than existing alternating current(AC)switching technolo-gies.A vacuum circuit breaker(VCB)that uses an electromagnetic repulsion actuator is able to achieve a theoretical limit of AC interruption,which can interrupt a short-circuit current in the first half-cycle of a fault current,compared to the more common three cycles for existing current switching technologies.This can thus greatly enhance the transient stability of power networks in the presence of short-circuit faults,especially for ultra-and extra-high-voltage power transmission lines.Third,based on fast vacuum switching technology,various brilliant applications emerge,which are benefiting the power systems.They include the applications in the fields of direct current(DC)circuit breakers(CBs),fault current lim-iting,power quality improvement,generator CBs,and so forth.Fast vacuum switching technology is promising for controlled switching technology in power systems because it has low variation in terms of opening and closing times.With this controlled switching,vacuum switching technology may change the“gene”of power systems,by which power switching transients will become smoother.

Clawed Miniature Inchworm Robot Driven by Electromagnetic Oscillatory Actuator

In this research we propose a novel inchworm robot, which is composed of an Electromagnetic Oscillatory Actuator （EOA） and claws. The EOA consists of a yoke, a magnet, and a coil. The overall robot size is 12.2 mm x 11 mm x 9 mm （length x height ~ width）. The locomotion of the robot is achieved by different amounts of slips when the robot stretches and contracts its front leg. To realize locomotion, the working conditions were calculated theoretically and the calculated input signal was applied to the robot. The performance of the inchworm robot was evaluated experimentally with varying input voltages and frequencies. A simple op-amps based driving circuit was used to provide a square-wave input. Travel speed, average distance per step of the robot, and moving distance of the leg and body at each step were measured. The maximum travel speed was 36 mm-s-1 at 30 Hz, which validates our simple locomotion strategy experimentally.

A Miniaturized Tadpole Robot Using an Electromagnetic Oscillatory Actuator

In this paper, we propose a miniaturized tadpole-like robot using an electromagnetic oscillatory actuator. The electro- magnetic actuator has a simple structure with a moving-magnet type and the body size is 13 mm （length） × 11 mm （height） ×10 mm （width）. A tail has the thickness of 100 μm and the length of 20 mm which is twice of the body-length （BL）. The tail attached to the oscillatory actuator generates undulatory propulsion for the forward swimming. Moreover, the tadpole robot enables the change of the direction by controlling input signal pattems applied to the oscillatory actuator. Prototypes of the tadpole robot have been manufactured and the thrust force and swimming speed are measured to evaluate the performance of the biomimetic robot in water at various tail-beat frequencies. The maximum thrust force is 42 mN at the tail-beat frequency of 30 Hz with voltage of 3 V, enabling the tadpole robot to swim at the speed of 210 mm·s^-1 （6 BL·s^-1）. The tadpole robot can also change its moving direction with the angular velocity of 21 deg·s^-1 at the half pulse pattem of 30 Hz.

A Sub-100 mg Electromagnetically Driven Insect-inspired Flapping-wing Micro Robot Capable of Liftoff and Control Torques Modulation

Inspired by the unique,agile and efficient flapping flight of insects,we present a novel sub-100 mg,electromagnetically driven,tailless,flapping-wing micro robot.This robot utilizes two optimized electromagnetic actuators placed back to back to drive two wings separately,then kinematics of each wing can be independently controlled,which gives the robot the ability to generate all three control torques of pitch,roll and yaw for steering.To quantify the performance of the robot,a simplified aerodynamic model is used to estimate the generated lift and torques,and two customized test platforms for lift and torque measurement are built for this robot.The mean lift generated by the robot is measured to be proportional to the square of the input voltage amplitude.The three control torques are measured to be respectively proportional to three decoupled parameters of the control voltages,therefore the modulation of three control torques for the robot is independent,which is helpful for the further controlled flight.All these measured results fit well with the calculated results of the aerodynamic model.Furthermore,with a total weight of 96 mg and a wingspan of 3.5 cm,this robot can generate sufficient lift to take off.

Miniaturized Twin-legged Robot with an Electromagnetic Oscillatory Actuator

There have been many studies on the moving mechanism of micro robots, such as stick-slip, inchworm like motion, and impact drive. Novel actuators like lead zirconate titanate （PZT）, Shape Memory Alloy （SMA）, magnetostrictive materials, electromagnetic actuators, electoractive polymers, ultrasonic linear motors, and dielectric elastomers are utilized to realize the moving mechanism. The use of a conventional electromagnetic actuator is unfavorable, because of a few drawbacks, such as generation of stray magnetic fields, hard to miniaturize to the millimeter scale because of 3D integration and a scaling law, and power consumption to maintain a certain position. This research presents a micro robot that uses an electromagnetic actuator customized and developed for micro robot. The electromagnetic actuator is designed from a Brushless Direct Current （BLDC） motor to overcome the drawbacks mentioned above. The developed robot is composed of two electromagnetic actuators. The overall size of the robot is 20 mm × 11 mm× 9 mm （length × height × width） and the weight is 3 g. The developed robot is able to move bidirectionally with a maximum moving speed of 15.76 mm·s︿-1 （0.79 body-length per second）. The optimal conditions of an input signal are calculated theoretically and verified with experiments.

Comparison of smart panels for tonal and broadband vibration and sound transmission active control

This paper presents a comprehensive overview of the principal features of smart panels equipped with feed-forward and feedback systems for the control of the flexural response and sound transmission due respectively to tonal and to stochastic broadband disturbances.The smart panels are equipped with two types of actuators:first,distributed piezoelectric actuators formed either by small piezoelectric patches or large piezoelectric films bonded on the panels and second,point actuators formed by proof-mass electromagnetic transducers.Also,the panels encompass three types of sensors:first,small capacitive microphone sensors placed in front of the panels;second,distributed piezoelectric sensors formed by large piezoelectric films bonded on the panels and third point sensors formed by miniaturized accelerometers.The proposed systems implement both single-channel and multi-channel feed-forward and feedback control architectures.The study shows that,the vibration and sound radiation control performance of both feed-forward and feedback systems critically depends on the sensor-actuator configurations.

Moving Mechanism of a High-speed Insect-scale Microrobot via Electro-magnetically Induced Vibration

This paper presents the moving mechanism of a high-speed insect-scale microrobot via electromagnetically induced vibration of two simply supported beams.The microrobot,which has a body length of 12.3 mm and a total mass of 137 mg,can achieve reciprocating lift motion of forelegs without any intermediate linkage mechanisms due to the design of an obliquely upward body tilt angle.The gait study shows that the body tilt angle prevents the forelegs from swinging backward when the feet contact the ground,which results in a forward friction force applied on the feet.During forward movement,the microrobot utilizes the elastic deformation of the simply supported beams as driving force to slide forward and its forelegs and rear legs work as pivots alternatively in a way similar to the movement of soft worms.The gait analysis also indicates that the moving direction of the microrobot is determined by whether its body tilt angle is obliquely upward or downward,and its moving speed is also related to the body tilt angle and as well as the body height.Under an applied AC voltage of 4 V,the microrobot can achieve a moving speed at 23.2 cm s1(18.9 body lengths per second),which is comparable to the fastest speed(20 cm s-1 or 20 body lengths per second)among the published insect-scale microrobots.The high-speed locomotion performance of the microrobot validates the feasibility of the presented actuation scheme and moving mechanism.