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Crane has been one of the most vital material-handlingequipment in all manufacturing sectors for many years.Variants of this lifting equipment used by industry, ranges fromIn-door crane like E.O.T., Chain Hoists, Stackers, Outdoorcranes like Goliath Crane, Mobile cranes etc.

Traditionally for all electrically operated cranes various optionhas emerged with time starting from Standard cage rotormotor, wound rotor motor, conical rotor motor, DC motors etc.

Major contributing factors for the selection of these motoroptions were hovering around Capital cost, Maintenance cost,Starting Current vis-a-vis Starting Torque, Power consumption,Critical load handling parameters like positioning accuracy,jerks, load sharing etc.

Cage rotor motor along with DOL contactors gives low capital& maintenance cost but the disadvantages with this controlsystem are that it requires more parking time since it has nooption of creep-speed, start and stop are jerky leading to heavyload sway and increased wear and tear of brake shoe. It alsodemands high starting current which makes a big impact onsystem electricals when handling large nos. of start andstops.

For achieving better positioning accuracy, motors are requiredto be operated in creep speed. The options with caged rotormotor to achieve this creep speed are either all motions werepowered with dual speed motor or an additional planetarygeared motor which will be selected thru electric contactorfor low speed operation.

This is little crude way of achieving low speed operation sinceit calls for an additional motor, gearbox etc. Such system alsorequires extra mounting space on crane and also leads tooverall poor system efficiency due to more components,cables, hardware etc.

Next option for crane control is use of Slip-ring motor withRotor Resistor Control (RRC) or solid state Variable VoltageControl (VVC) for stator supply or DC motor.

Compared to dual speed option of caged rotor motor, Slip-ring, Motor Control or DC motor control provides increasedflexibility in terms of speed steps, consumes lower startingcurrent for producing high starting torque. This benefits ofslip-ring motor and DC motor control comes along withdisadvantages like slip-ring, carbon brushes maintenance,arching, bigger size and bulkiness of motor puts extra load ontrolley and bridge.

These control systems also have regular maintenance ofcurrent carrying contacts of contactor which requires regularmaintenance / replacement due to frequent braking andreversal involved.

Many company-encountered problems with Slip-Ring & DCMotor are the difficulty and high cost involved in protectingthese motors to necessary IP 54 class of protection.

Additionally if Slip ring motor is used along with VVC controlthen Techogenerator is must for the VVC control.

In all above cases since brake are operated at relatively higherspeed, brake shoe wears off faster and it also requiresfrequent adjustment to ensure safe operation of crane.

Slip-ring motor or DC motor were preferred choice for craneapplication even when application not requiring accuratepositioning. This was merely due to the apprehension thatcaged rotor motor may not be able to lift the large rating load.

Introduction of Variable Voltage Variable Frequency (VVVF) ACdrive combined with advantages of Caged rotor motor makesan ideal combination for many variable speed applicationincluding complex vertical transportation applications likeCranes and Elevators.

A Variable Speed AC Drives essentially works on the principalof keeping V/F or Flux level constant in the motor. This simpleV/F control by varying the Voltage V and Frequency Fsimultaneously maintains peak torque level produced bymotor.

Standard V/F scalar control or less precise vector control facestough challenges when it comes handling vertical loads likecranes and elevators.

These loads unlike other loads ask for more accurate andstable low speed control since it has to work againstgravitational force. The crucial areas in these types of verticaltransportation equipment are starting torque, accuratecalculation of motor flux to achieve stable low speed operation,proper brake coordination, electric braking to controlregenerative load.

The challenges faced in low speed area are accuratecalculation of motor flux & it varies dynamically with change ofload and speed. Slightest variation in the amount of voltagecompensation more than actually required will make motordraw either more current or create saturation leading to motorheating. Contrary if less compensation is given then it produceless torque, which will lead to slippage of load or may bepulsating revolution of motor for horizontal movements.

L&T-Yaskawa Crane Control Solution enhancescrane performance without Worries

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In addition to this accurate vector calculation, externalmechanical brake needs to be tightly coordinated with CraneHoisting and Lower sequences when Caged rotor motor areused with VVVF control. Logic sequence should ensure:

z Enough torque is produced by motor before brake isreleased to avoid slippages of load Safety Factor.

z They provide jerk free start and stop by getting released atthe low speed or ideally at zero RPM - Positioning Factor.

z Motor, Brake shoe and overall Crane structure shouldexperience minimum possible stress Maintenance andDown time Factor.

z Completion of required tasks in reduced number of Start-Stops and Optimization of Power Operational EfficiencyFactor.

In order to achieve these crucial performance parameters ofVertical transportation, L&T-Yaskawa offers their state of artmodel 616 G7 drives combined with special embeddedCRANE Control Software.

L&T-Yaskawas 616-G7 model is the worlds FIRST and theONLY drive offering 3 level Architecture in 200V / 400 V classVVVF segment. This not only provides superb servo likeperformance from standard caged rotor motor but also helps

in mitigating many of the previous drawback of 2-level VVVFdrive without use of any external components.

This unique 3 level technology of G7 drive along with standardcaged rotor motor provides ideal solution for crane control.Special embedded crane software in G7 drives makes L&T-Yaskawa G7 drive as the First choice of crane users andmanufacturers.

L&T-Yaskawas crane control software along with caged rotormotor provides numerous benefits to the crane users.

Caged Rotor Motor Benefit factor

z Caged rotor motor by virtue of its rotor construction ismechanically more robust than slip-ring or DC motor. Alsoperiodic maintenance of the slip-ring and carbon brushesis eliminated.

z Caged rotor can be offered in IP 54 or even betterenclosure protection as a standard helping to serve harshdusty environment.

z Caged rotor motor are compact, economical and havefaster availability then any other type of motor.

(Fig.1) How Yaskawa G7 drives unique Crane Control Software improves Safety?

RUN command(from Controller)

Torque ForcingValue

(Set by parametersanalog input)

Inverter OutputFrequency

Brake ReleaseRequest

(From inverter)

Brake Answer(From Controller)

During run(From inverter) Brake Close Point

- Inverter Output Freq > Brake Release Freq. (S1-01 or S1-02) AND- Inverter Output Current > Brake Release Current (S1-05 or S1-06) AND- Inverter Torque >Torque Forcing Value (S1-07 or S1-08)

Brake Close Point- Inverter Output Freq < Breake Close Freq (S1-12 or S1-13)

OFF ON

Time ConstantC4-02

S1-01 (S1-02)

S1-04

OFF (Brake Closed

OFF (Brake Closed

S1-03 S1-12 (S1-13)

S1-15

smaller value:B2-01 or E1-09

ON (Brake Open)

ON (Brake Open)

ON (During Run)

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Yaskawas special Crane Control SoftwareBenefit Factor:This software handles fundamental requirements of craneapplication as follows.

z Safety Brake sequence, Independent Hoisting /Lowering torque compensation. Over speed protection.

z Minimum down time Torque / Current - limit, Stallprevention during acceleration, Power supply protection,Major and Minor fault classification, Ultra high reliability ofYaskawas drive. Input/output phase failure.

z Dedicated crane functions Brake sequence, Travel limit,Light load acceleration, Impact Stop, Zero Servo, Multi-Stepspeed, S curves

z Cost performance Due to dedicated crane function andinbuilt protection for drives and motors, external hardwareand associated wiring are reduced leading to reliableperformance at minimum cost.

How L&T-Yaskawa G7 drives unique CraneControl Software improves Safety?One of the most vital roles of this crane software is takingcontrol of opening and closing of external Mechanical Brakethru its multifunction outputs. Timing diagram explains thedecision making of drive for brake control in Open Loop systemwithout any encoder feedback. (shown in fig. 1)

Drive releases brake after having three important feedback ofoutput frequency, motor current and internal torque referenceand comparing them with preprogrammed values. Thisensures maximum safety in brake co-ordination.

These parameters for forward and reverse direction can beset independent of each other making it possible to use onload with or without counterweight.

Other Advantages of Yaskawas CraneControls are:z Electric Braking:

Drive will bring the motor to zero speed thru electricalbraking and mechanical brake is applied just in the end tohold it. This reduces sway in the load. Also since themechanical brake is opened and closed in low speedzone, wear and tear of brake, reduces substantially.

Application having higher regenerative load cycle thenYaskawa Drives with Regenerative front end can beprovided. This will feed back regenerated energy to themains supply instead of dissipating it into DynamicBraking Resistor Bank.

z Zero Servo Control (Hold operation without mechanicalbrake):

Zero Servo feature is possible with Encoder feedback. Thisenables to hold the load without applying the mechanicalbrake. The purpose of the zero servo function is to provideposition control capability at zero speed. The shaft positionis maintained by monitoring the Encoder feedback pulses,and correcting the position error.

z Light Load Acceleration (Express):

Motors can be made to run at speed higher then its basespeed if crane is lightly loaded. The sensing of light loadis automatically done by measuring load current. Thisreduces cycle time and in-turn improves operationalefficiency.

RUN

ZeroServo

ZeroServo Rotor Postion

is kept

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Other special Crane control features arez Travel limit Function Management of extreme position

limit switches.

z Impact Stop function - Stops the operation if drive sensesthe feeder is impacted thru current and torque sensing.

z Load sensing based starting torque compensation.

z Droop Control for the equal load sharing of motor drivingcommon loads.

z Slip Compensation during motoring and regeneration -Keeps Hoisting / Lowering speed nearly same evenwithout encoder speed feedback.

Speed holding accuracy of 0.2 % in open loop and 0.02 %in closed loop can be achieved.

G7- 3 level topology benefit factors:616-G7 is the only model in the world to offer 3-level technologyfor 400 V class motor in the world. Output voltage wave form ofthis 3-level technology is shown in fig. below. G7 Inverter hassmaller line-to-line voltage steps than the 2-level inverter.

This technology helps in mitigating some problem associatedwith 2 level inverters without the use of external componentse.g,

z Lesser surge voltage seen by motor terminals ascompared to 2-level control. Making it possible to use orupgrade existing old Crane with VVVF drive.

z Reduction of bearing pitting due to reduced bearingcurrent.

G7s Open Loop Vector control mode with the new dual fluxobserver results in excellent torque control characteristics.

Feed-forward control in the speed control block assures afast response even in the Open Loop Vector control mode.The use of an encoder for actual motor speed feedbackprovides even better control and higher response in bothspeed and torque control.

Other benefits associated with L&T-YaskawaInverters are:z User friendly 5 line *16 Character Alphanumeric display

for programming and monitoring drive parameters. Thiscan even store last fault history which will be useful introuble shooting the faults.

z G7 offers three different control methods: ElectronicPotentiometer function (EP) for two step push buttoncontrollers, Potentiometer (PO) for analog joy-stick type ofcontroller interfacing with Radio remote control, On BoardCommunication option for automated cranes. G7 can beused with any or all of these control modes. This versatilitymakes it easy to apply G7 to application requiring severalcontrol places.

z Common Control card for the entire G7 range of drive.High Dynamic performance of G7 drivecombined with 3-level technology andembedded crane control softwareprovides solution to all apprehensionsrelated to capability of using cagedrotor motor in Crane applications.

Credentials of crane control are manyin India and abroad.

L&T in India has installation base ofover 400 drives which are aimed ateliminating human errors, repetitivetasks, saving time, improvingproductivity and increasing safety.

These drives offer more functions with faster response time,which maximizes crane performance.

Benefits accrued to user after using L&T-Yaskawa drives withrespect to older traditional system are tangible in terms ofmaintenance cost , operational safety and efficiency. This hasnot only benefited user who are buying new crane but also theusers who have opted for modernization of their existing cranesystem.

Many Crane user and manufacturer have reposed their faithin L&T-Yaskawa drives system for quality and safer cranecontrol.

L&T-Yaskawas reference in Crane OEM segment includesbrands like Mukund, WMI, Unique, Reva, AVON, Anupam,Saico, Meeka, Tisco and many more

End user segment includes name like L&T, Ambuja Cement,Tube products of India, BHEL, COFMOW, Indal, Steel majorslike Essar Steel, SAIL - Bhilai Steel, Jindal Iron & Steel , BhushanSteels, Uttam Galva and many more ..

In years to come L&T-Yaskawa with its leadership position inthe segment of vertical transportation will providetechnologically more and more advanced product to industry.Users will benefits in terms of Safety, Higher Performance toCost ratio and gentle to the environments.

Line-to-line inverter output waveforms

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