Electric Monorail System with magnetic

levitations and linear induction motors for

contactless delivery applications
Akshay Kumar Yadav
Department of Mechanical Engineering
Global Institute of Technology
Jaipur,Rajasthan, India - 302022
yadav.akshay345@gmail.com

Abstract— In recent semiconductor and display manufac- overhead guide-ways. To eliminate sliding contacts, the
turing processes, high clean-class delivery operation is required levitation control coils and control circuit was supplied
more and more for short working time and better product from an onboard battery, and the propulsion force was
quality. Traditionally single-sided linear induction motor
(SLIM) is widely used in the liner drive applications because of
provided by 3-phase primary stators mounted along the
its simplicity in the rail structure. A magnetically levitated guide-way, with copper reaction plates mounted on each
(Maglev) unmanned vehicle with SLIM traction, which is carrier vehicle. To reduce the normal component of
powered by a contactless power supply (CPS) can be a high reaction force, which could lift the vehicle to produce
precision delivery solution for this industry. In this paper binding under light loads, no steel backing plate was used
unmanned carrier vehicle, which can levitate without in the secondary. The drag forces produced by eddy
contacting the rail structure, is suggested for high cleanclass
currents in the guide-way were very small, and it was found
FPD delivery applications. It can be more acceptable for the
complex facilities composed with many processes which require necessary only to have stators at intervals along the guide-
longer rails, because of simple rail structure. The test setup way. Vehicles were accelerated under the stators to
consists of a test vehicle and a rounded rail, in which the vehicle sufficient velocity to reach the next stator. Synchronous
can load and unload products at arbitrary position commanded speeds of 5.8 m/s at 60 Hz was used for propelling stators,
through wireless communications of host computer. The while lower values of 2 m/s were used for direction
experimental results show that the suggested carrier vehicle has controlling stators. Four types of stator on the rail was used
traction servos and robust electromagnetic suspensions without
any contact. This type of automated delivery vehicle is expected
in the prototype : positioning and acceleration at loading
to have significant role in the high clean-class delivery stations, ղ accelerating and decelerating on straight guide-
applications. way sections, ճ thrust production on curved guide-way
Sections (with shorter core length), and the last type for
Index Terms— Electric Monorail System (EMS), Linear rotating switch sections used to remove vehicles from one
Induction Motor (LIM), Magnetic Levitation (MagLev), guide-way to another. A complete guide-way system was
Contactless Power Supply (CPS), Barcode Positioning
controlled by a supervisory minicomputer and
System (BPS)
microprocessor control circuit. Control of vehicles was
achieved by a closed loop position and velocity feedback
I. INTRODUCTION
microprocessor control circuit using a variable frequency
The conventional delivery robots are supported by rigid PWM inverter. Positioning accuracy of the 8 kg loaded
contact bearings, and driven by the rotary motor and ball vehicle was to within 0.5 mm. The control system was
screw in order to achieve high acceleration and precision capable of operating with decelerations of less than 0.01 G
motion. However, because of friction, abrasion, mass and was therefore suitable for transporting delicate loads.
inertia of the driven parts, clearance between the connected [3]
parts and so on, the positioning accuracy and the response In this paper, another type of carrier system for clean
frequency is limited. Magnetically suspended system, room transportation of semiconductor materials is shown.
compared with linear driven system directly, has the Electric monorail systems (EMS), which has been used in
advantages of non-contact motion which is free of particle railways, can be adapted to clean factory automation with
generation and mechanical friction problem, therefore no the help of magnetic levitations. Anywhere the long-
abrasion and long lives. Moreover, the separation of a wearing barcode band can be attached it is possible to use
moving object from a stationary part almost eliminate heat the BPS to determine the position to within a millimeter.
generation problem that is caused by the rubbing activity Traditional vector control method which is common to the
of the mechanical components. This contact movement has rotational induction motors Guide tolerances of the system
been a main obstacle to performance improvement of the play no role as the permitted separation between band and
conventional mechanical system. A carrier system for BPS allows for large deviations in distance Contactless
clean room transportation of semiconductor materials has propulsions can be made with LIM and bar code
been developed 2 decades ago by Toshiba Corporation of positioning reading system. The magnetic levitation
Japan.[1][2] At that time, the carrier vehicles was provides the vehicle noncontracting bearings. And
suspended by a permanent magnet control system from contactless power supplies (CPS), which is moving
transformers with first coils in the rails and second coils on propulsions for the EMS, a single-sided linear induction
the vehicle, can supply sufficient power up to hundreds kilo motor (SLIM) is designed, made and tested under system
watts for LIMs, Levitation Controllers, loading/unload specifications shown in table I. Recent Space Vector Pulse
robots. A CPS system with a synchronous rectifier using a Width Modulation (SVPWM) techniques and fieldoriented
digital phaselocked loop (PLL) technique miniaturize the control scheme can be also reasonable controller for linear
rectifier unit to be mounted on the back of the secondary propulsions. [7]
coils and can achieve 92% maximum direct current-direct
current efficiency at 5-mm gaps. [4] The suggested EMS is B. Non-contacting sensors for linear propulsions
shown in Fig. 1 and side view of the vehicle is shown in Fi. In addition to mechanical measurement sensors, optical

II. DESIGN OF LINEAR INDUCTION MOTOR PROPULSIONS methods are particularly well suited for determining
For the design of the magnetic suspensions, please refer positions as they operate without mechanical wear and
to the references [5] and [6]. For the design of the slippage. Unlike other optical measurement methods, the
barcode positioning system (BPS) is not restricted to linear
movements. It can also be used flexibly in curved systems.
Anywhere the long-wearing barcode band can be attached
it is possible to use the BPS to determine the position to
within a millimeter. Guide tolerances of the system play no
role as the permitted separation between band and BPS
allows for large deviations in distance. The BPS uses
visible red laser light to determine its position relative to
the barcode band.
It takes there steps:
1. Reading a code on the barcode band
2. Determining the position of the read code in the
scanning area of the laser beam
3. Calculating of the position to within a millimeter
using the code information and the code position
The position value is then passed on via the standardized
Synchronous Serial Interface (SSI) to the main DSP of the
vehicle for which the position to be determined. Using this
BPS, it is possible to exactly determine positions from A. Experimental test setup
distances of 10,000 m and the using the wireless blue-tooth For the arbitrary movement of materials, the vehicle
communications, positioning of each vehicle can be should start to move from any position of the closed path
detected easily. The installation of the BPS is shown on of the rail to another position. For the test of the electric
Fig. 5. monorail system with magnetic levitations and linear
induction motors, a closed loop type rail with length of
26m is constructed as shown in Fig. 7. For the proof of
feasibility for contactless delivery applications, the test
vehicle started to run from station A and passed by two
curved rails, B and C, and finally arrived another arbitrary
station D. On the straight-line rails, the vehicle is
accelerated and decelerated at its maximum rate.

Fig. 5. Installation of the BPS on the Maglev EMS

With the exact position information of the test vehicle,

the vehicle positioning controller can calculate the speed of
the vehicle and calculate the slip of the linear induction
motors. Fig. 6 shows the control block diagram of the
traction control. Two LIMs which located on the front and
rear is controlled by the inverter power stack which is
controlled by the vehicle controller. Traditional vector
control method which is common to the rotational Fig. 7. Test setup for Maglev EMS
induction motors is used again to control the LIMs. All
B. Response of the test vehicle
traction control algorithms are made up with a high speed
Digital Signal Processing (DSP) controller, TMS320F2812 The trajectory of position and velocity and control toque
from Texas Instrument Corporation. The controller is is displayed on Fig. 8 as the vehicle moves from A to D.
commanded by a host computer via wireless On Fig. 9 the position controller is activated at 25 seconds.
telecommunications. For the tests, two DSP controllers, The levitation control response on each magnetic
propulsion and levitation controllers are equipped in the suspension is presented on Fig. 10.
vehicle.
 IV. CONCLUSIONS
In recent semiconductor display manufacturing processes,
high clean-class delivery operation is required more and
more for short working time and better product quality.
Traditionally single-sided linear induction motor (SLIM)
is widely used in the liner drive applications because of
its simplicity in the rail structure. A magnetically levitated
(Maglev) unmanned vehicle with SLIM traction, which is
powered by a contactless power supply (CPS) can be a
high precision delivery solution for this industry. In this
paper unmanned delivery vehicle, which can levitate
without contacting the rail structure, is suggested for high
clean-class delivery applications. It can be more
acceptable for the complex facilities composed with many
processes which require longer rails, because of simple
rail structure. The test setup consists of a test vehicle and
a rounded rail, in which the vehicle can load and unload
products at arbitrary position commanded through
wireless communications from host computer. The
experimental results show that the suggested vehicle and
rail have reasonable traction servo and robust
electromagnetic suspensions without any contact. The
resolution of point servo errors in the SLIM traction
system is accomplished under one mm. The maximum
gap error is s0.25mm with nominal air gap length of
4.0mm in the electromagnetic suspensions. This type of
automated delivery vehicle is expected to have significant
role in the clean delivery applications.

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