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Linear motors theory and operation

TRANSCRIPT

Dr. Adel Gastli

Electromechanical Systems & Actuators

LINEAR MOTORS

CONTENTIntroduction Types of Linear Motors Applications

Dr. Adel Gastli

Linear Motors

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INTRODUCTION Linear Motors are old motors which date from the 1970s. Were not intensively used because of their difficult

control and low performance. Advancements in Power Electronics and Microprocessors have overcome the control difficulties and have revived the use of the linear motors. Linear motors are nowadays emerging as new technologies.

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Main Types of Linear Motors Linear Synchronous Motor Permanent Magnet Wound Secondary Type Linear Induction Motor Single-Sided: Long-primary & Short Secondary Short-primary & Long-Secondary Double-Sided or Sandwich Linear Stepper Motor

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Linear Synchronous Motor (LSM)Field Yoke Field winding

I

Passive rail truck

Armature winding

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LSM (Contd)For an LSM to operate properly the control system must accurately track the position of the moving element in order to properly synchronize the moving field current in the stationary frame (stator). If synchronization is lost or interrupted the motor slips and loss of propulsion can occur. This situation is likely to be encountered by an LSM when external sensors are relied upon to handle motor synchronization. If a sensor becomes dirty or mis-aligned or if fog, smoke or other airborne obstructions are present, the system will experience problems.Dr. Adel Gastli Linear Motors 6

LINEAR INDUCTION MOTOR (LIM)Linear Induction Motors (LIMs) are significantly different than Linear Synchronous Motors (LSMs) in the way that they produce electro-motive forces or motion. In a LIM, the motor stator creates an Alternating Current (AC) field that induces currents into the reaction plate, which is typically an aluminum fin. This creates eddy currents in the moving element which react with the moving field in the stator to produce thrust. The induced currents in the aluminum plate manifest themselves in the form of heat. In cases of high duty cycles or in locked rotor conditions (where the moving element is not permitted to move) overheating can occur. In several reported cases at amusement parks, LIM fins have cracked and parts have melted.

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LIM (Contd)Cut along xy and enrollx Stator 3 winding Secondary y Primary Rotor Aluminum sheet (conductor)Traveling mmf (or Flux Density) Wave

v vs

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Traveling mmf waveLINEAR INDUCTION MOTOR

FNi/2/20

Fundamental F1

/2

-Ni/2

zg

Fundamental H1

HNi/20 0

Ni/2g

Fundamental F1 F

F: mmf H: Field

/2

-Ni/2

/2

-Ni/2g

z

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Traveling mmf waveLINEAR INDUCTION MOTOR

Same Analogy as that of Rotary Machines

2z 3 ib = I m cos(t 120 ) F ( z , t ) = Fmax cos t 2 ib = I m cos(t + 120 ) ia = I m cos t Fmax =v=Dr. Adel Gastli

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kw

N ph I m 2m

Nph : Number of turns distributed over a length m . kw : winding factor.

dz dz d = = = 2Tp f dt d dt 2Linear Motors

Tp : Pole pitch f : Exciting frequency.

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LIM PerformanceLINEAR INDUCTION MOTOR Slip

s=

vs v vs

v s = 2 Tp f [m / sec]

Thrust

3 I'22 R '2 / s F= = [N] synchronous velocity, v s vs air gap power, PgR1 l1 M l2 R2/s

Thrust, F

vsDr. Adel Gastli Linear Motors

Speed, v 11

Different Types of LIMLINEAR INDUCTION MOTOR

DOUBLE-SIDED LIM (DLIM)Secondary Primary

SINGLE-SIDED LIM (SLIM)Short Primary Long Primary

Long Secondary

Short Secondary

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End EffectLINEAR INDUCTION MOTOR

There is secondary current and secondary loss which is not

associated with a corresponding amount of useful thrust. There are reactive volt-amperes drawn from the supply which cannot be accounted for either as being due to magnetization or leakage reactance. The physical nature of this phenomena is thought to be due to the continual removal of magnetic energy at the exit edge of a machine. The exit edge produces a backward thrust on the secondary which subtracts from the thrust performance in the region of a speed-thrust curve.Dr. Adel Gastli Linear Motors 13

End Effect on Speed-Thrust CurveLINEAR INDUCTION MOTOR

The LIM cannot run lightThrust, F

at the synchronous speed vs=2pf. Generally, the running light

Short-Primary LIM Equivalent Rotary IMvs

speed is lower than vs.

Speed, v

Effect of the exit edge loss on the speed-thrust curve of a LIM.

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APPLICATIONS Transportation (Trains) Robotics & Material Handling Elevators Compressors & Pumps Catapults and Launchers Sliding Doors Closer Cartain pullers etc...

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Transportation (Trains)

Japan: Linear Chuo ShinkansenDr. Adel Gastli Linear Motors 16

Superconducting Magnetically Levitated Linear Motor Car The superconducting Magnetically-levitated

Linear Motor Car is a most promising high speed transportation system in the 21st century. It is a vehicle befitting the requirements of the

high speed and massive transportation age, as it operates at a stunning 500 Kmph, and has the transportation capacity equivalent to the existing shinkansen. It is a most advanced traffic system, which has

less noise and vibration and promises a safe and comfortable ride.

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Train Depot

Tunnel

Control Center Turnout switches Test platform

Vehicle Via duct

Information cables

Feeding section switchgears Feeder Guideway Power conversion substation Dr. Adel Gastli Linear Motors Power converter 18

Panel-type Side wall

LCX (Leaky coaxial cable)

Levitation and guidance coils

Feeding cable

Propulsion coils

Cross-inductive cable

Power/ communication cables

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What is Superconductivity? When certain metals are cooled below a specific temperature, their

electric resistance vanishes. This phenomenon is known as "superconductivity". Once current is applied to a coil made of superconductive metal, it

continues to flow permanently and without loss. This coil can generate dozens of times stronger magnetic field than that of permanent magnets. For the Maglev, a bundle of extremely fine niobium-titanium alloy

(superconductive metal) wire is embedded in a copper matrix in order to improve the stability of superconductivity. This wire is cooled with liquid helium (ca-269C) to be in a superconductive state.

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How does it advance forwards? (Propulsion System) By passing current through propulsion coils on the ground,

a magnetic field (north and south poles) is produced, thus the train is propelled forward by the force of attraction between opposite poles and the repulsive force of same poles acting between the ground coils and the superconducting magnets built into the vehicles.

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How is it levitated ? (Levitation System) When the superconducting magnets on the vehicles pass

through at high speed current flows through levitation and guidance coils on the ground producing electrodynamic levitating force to the vehicles.

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Why doesn't it collide with the wall? (Guidance System) The levitation and guidance coils on either side are

connected with electric power cables. They keep the vehicles in the center of the guideway at all times by exerting an attractive force on the further side of the vehicle and a repulsive force on the nearer side should the train move off center to either side.

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Other Types of Levitation Systems

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One-shaft Multicar Ropeless ElevatorsMoving part of linear Synchronous motor Stationary armature coil of motor

Elevator car Elevator path

Elevator Car

Elevator Hall

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Decentralized Elevator Cars Group Control Means maximum operating time. Each elevator controller can act as the

group controller. If one controller is taken out of service

temporarily, the remaining controllers continue to operate efficiently.

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Permanent magnets Yoke Armature coils Suspension bar

Rollers

Magnet holder

Elevator car

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38-story tower of terror in Australia

38-story tower of terror in Australia

Ramp

A state-of-the-art linear motor system propels the ride to reach unprecedented speeds of up to 160 km/hour, making it the most technologically-advanced ride in the world. To generate these intense speeds, an incredible 2,200,000 watts (2.2 megawatts) of power, enough to power a small town, is applied for six or seven Linear Motors Dr. seconds. Adel Gastli 28

Linear CompressorA linear compressor

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