1Table of Contents

Introduction .......................................................................................2Totally Integrated Automation ........................................................4

Motion Control .................................................................................5

Mechanical Basics .........................................................................13

Servomotor Construction ............................................................. 25Servomotor Ratings ...................................................................... 33

Speed-Torque Characteristics ..................................................... 39

Siemens Servomotors .................................................................. 44

Servomotor Accessories .............................................................. 46Encoders and Resolvers .............................................................. 49

Pulse Width Modulation .............................................................. 55

Siemens MASTERDRIVE MC Family ........................................ 63

MASTERDRIVE MC Compact PLUS ......................................... 64MASTERDRIVE MC Compact and Chassis .............................. 73

Technology Options ...................................................................... 78

Cables ............................................................................................. 87Applications ................................................................................... 88

Selection ........................................................................................ 95

SIMODRIVE ................................................................................... 97

Review Answers ........................................................................... 99Final Exam.................................................................................... 100

2Introduction

Welcome to another course in the STEP 2000 series, SiemensTechnical Education Program, designed to prepare our salespersonnel and distributors to sell Siemens Energy &Automation products more effectively. This course coversBasics of General Motion Control and related products.

Upon completion of Basics of General Motion Control youshould be able to:

Explain the concepts of force, inertia, speed, and torque

Explain the difference between work and power

Describe the construction of a servomotor

Identify the nameplate information of a servomotornecessary for application to a MASTERDRIVE MC

Describe the operation of a three-phase rotating magneticfield

Describe the relationship between V/Hz, torque, andcurrent

Describe the operation of an encoder

Describe the basic construction and operation of a PWMtype MASTERDRIVE MC

Describe features and operation of the SiemensMASTERDRIVE MC

Describe basic motion control applications

3This knowledge will help you better understand customerapplications. In addition, you will be able to describe products tocustomers and determine important differences betweenproducts. You should complete Basics of Electricity and Basicsof AC Drives before attempting Basics of General MotionControl. An understanding of many of the concepts covered inBasics of Electricity and Basics of AC Drives is required forBasics of General Motion Control.

If you are an employee of a Siemens Energy & Automationauthorized distributor, fill out the final exam tear-out card andmail in the card. We will mail you a certificate of completion ifyou score a passing grade. Good luck with your efforts.

SIMOVERT is a registered trademark of Siemens AG.MASTERDRIVES is a trademark of Siemens AG.

Other trademarks are the property of their respective owners.

National Electrical Manufacturers Association is located at 2101L. Street, N.W., Washington, D.C. 20037. The abbreviationNEMA is understood to mean National ElectricalManufacturers Association.

4Totally Integrated Automation

Totally Integrated Automation (TIA) is more than a concept. TIAis a strategy developed by Siemens that emphasizes theseamless integration of automation products.

The TIA strategy incorporates a wide variety of automationproducts such as programmable controllers, computernumerical controls, Human Machine Interfaces (HMI), anddrives which are easily connected via open protocol networks.

This course focuses on the MASTERDRIVES MC which arean important element of the TIA strategy. MASTERDRIVE MCdrives are designed for motion control applications that requireprecise control. In addition, MASTERDRIVE MC drives caneasily communicate with other control devices such asprogrammable logic controllers (PLCs) and personal computers(PCs) through the PROFIBUS-DP communication system andother various protocols.

5Motion Control

Motion control is an industry term used to describe a range ofapplications that involve movement with varying degrees ofprecision. Many motion control applications require only that anobject be moved from one place to another with limited concernfor acceleration, deceleration, or speed of motion. On theopposite extreme are machine tool applications which requirethe precise coordination of all aspects of motion, including ahigh degree of coordination for multiple simultaneousmovements.

Axis Single-axis motion involves controlling one rotational axis. Thisis typically a motor shaft that can be driven forward or reverse.Mechanisms are often used to translate the rotational motioninto linear motion. Multi-axis control involves control of multiplerotational axes, each of which could be converted into linearmotion. Some applications require the control of multiple axes,with each axis operating independently. Other applicationsrequire varying degrees of coordination for multiple axes rangingfrom synchronizing the start of motion control for multiple axesto the highly coordinated multiple-axis control required formachine tool applications.

6Motion Control Examples The following illustration is an example of basic single-axismotion. This illustration shows an object moving on a conveyor.The conveyor is driven by a Siemens AC motor which turns inone direction at a relatively constant speed. The sensing andcontrol circuit for this application consists of a Siemens limitswitch or sensor, a Siemens S7-200 PLC, and a Siemens SiriusType 3R full-voltage starter. Additional control and safetycircuits would be required, but are not important for thisexplanation.

In this example, the motor will move the object along theconveyor until the sensor is reached. At that point the sensorwill change the state of a PLC input. The PLC will respond tothis change of the input state by de-energizing the motorstarter, thereby stopping the motor.

This application did not require that the acceleration anddeceleration of the motor or the speed of the motor becontrolled. In addition, the control over the final position of theobject is not precise, but these conditions are often acceptablein many applications.

7Another application might involve the use of an AC drive, suchas a Siemens MICROMASTER, MIDIMASTER, orMASTERDRIVE. In this example a PLC is used to control atrimming cycle for a continuous roll. A sensor, connected to aPLC input, is used to detect a reference mark on the roll. An ACdrive, controlled by the PLC, is used to control the acceleration,deceleration, and speed of an AC motor.

In this application the motor drives a belt which feeds the rollthrough a cutter. When the sensor detects the mark it changesthe state of a PLC input. The PLC signals the drive to stop themotor long enough for the cut to be made. The motor is thenrestarted. This application involves control over motoracceleration, deceleration, and speed, but only moderateposition control.

8Motion control applications are often more complex than thosedescribed in the previous examples, involving precisepositioning and synchronized control of one or more axes. Forexample, a four-color printing process is used when printingcolor material such as brochures or magazine covers. In a four-color process, a separate printing stage is used for each color. Inthis example a continuous roll of paper is fed through a four-color printing press. Four servomotors are connected to four MCdrives. The drives control the speed and position of each motor.Each drive knows the exact speed and position of its associatedmotor. Fine adjustments are made to ensure the images line upexactly at each printing stage.

9Machine Tool Applications Before continuing with our discussion of motion control as itrelates to the MASTERDRIVE MC, it is worthwhile to brieflydescribe machine tool motion control applications. This isessential to highlight the differences with MASTERDRIVE MCmotion control.

Machine tools are designed to perform a series of specific taskssuch as milling, drilling, grinding, or turning that require a highdegree of coordination over multiple axes. For example, the inand out movement of a cutting tool on a lathe must besimultaneously coordinated with the side-to-side movement ofthat tool. This is necessary to precisely machine the part beingturned. In more complex machine tool applications, many moreaxes of motion may need to be controlled in a coordinatedfashion to machine a part quickly and precisely.

Essentially, it is this precise coordination of mulitple axes by acontrol system, called a Computer Numerical Control (CNC),that characterizes machine tool control applications. This coursedoes not focus on machine tool motion control applications, butinstead covers the single-axis or multiple axes applicationsappropriate for MASTERDRIVE MC drives.

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Linear and Rotational Axes Motion control can operate on a linear or rotational axis. Alinear axis application, such as a traversing car, has a definedtraversing range with end stops. An item may simply bemoved from one station to the next, or it may make severalstops where different manufacturing process are performed.

A rotational axis application has an endless traversing range.A rotary table, for example, travels along the shortest pathfrom one point to the next. A rotary table may also haveselectable or predefined directions of rotation to move fromone point to the next.

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Siemens MC Drives The range of applications in motion control is more specializedthan many other manufacturing applications. Motion controldrives, and their associated motors must be capable of:

Zero-speed holding torque Quick start/stop cycles High accelerating torque Repeatable velocity and torque profiles Synchronization Positioning capabilities Precise speed control

Controlling the starting, stopping, and speed of an AC motor ina motion control system is the job of a variable speed drive, likethe Siemens SIMOVERT MASTERDRIVE MC. SIMOVERT isa Siemens trade name which refers to SIemens AC MOtorinVERTers. Although an inverter is only one part of an AC drive,it is common practice to refer to an AC drive as an inverter. TheSiemens MASTERDRIVE MC (motion control) drive belongs tothe SIMOVERT MASTERDRIVES product family. Siemens alsomanufactures a complete line of servomotors to complimentthe drive family.

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Review 11. The Siemens ____________ MC is specifically designed

for general motion control applications.

2. Motion control can operate on ____________ or____________ axis.

3. Which of the following characteristics are required of amotion control drive?

a. Zero-speed holding torqueb. Quick start/stop cyclesc. High accelerating torqued. Repeatable velocity and torque profilese. Synchronization with other drivesf. Positioning capabilitiesg. Precise speed controlh. All of the above

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Mechanical Basics

Before discussing Siemens MASTERDRIVE MC drives andmotors, it is necessary to understand some of the basicterminology associated with the mechanics of motion controland drive operation. Many of these terms are familiar to us insome other context. Later in the course we will see how theseterms apply to motion control.

Units of Measurement There are two units of measurement commonly used. TheInternational System of Units, known as SI (SystmeInternationale dUnits), is used throughout the world. The SIsystem is more recently used in the United States. The Englishsystem, which most of us are more familiar with is usedprimarily in the United States. Both systems of measurementwill be referenced throughout this course. To avoid confusion,the SI system will be given first followed by the English systemin parenthesis. In some tables and charts both systems will beshown side-by-side.

Force In simple terms, a force is a push or a pull. Force may be causedby electromagnetism, gravity, or a combination of physicalmeans. The SI unit of measurement for force is Newtons (N).The English unit of measurement for force is pounds (lb).

Net Force Net force is the vector sum of all forces that act on an object,including friction and gravity. When forces are applied in thesame direction they are added. For example, if two 10 lb44.482 N (10 lb) forces were applied in the same direction thenet force would be 88.964 N (20 lb).

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If 44.482 N (10 lb) of force were applied in one direction and22.41 N (5 lb) of force applied in the opposite direction, the netforce would be 22.41 N (5 lb) and the object would move in thedirection of the greater force.

44.482 N (10 lb) of force were applied equally in both directions,the net force would be zero and the object would not move.

Torque Torque is a twisting or turning force that tends to cause anobject to rotate. A force applied to the end of a lever, forexample, causes a turning effect or torque at the pivot point.

Torque ( ) is the product of force and radius (lever distance).

Torque ( ) = Force x Radius

The SI unit of measurement is Newton-meters (Nm). In theEnglish system torque is measured in pound-feet (lb-ft) orpound-inches (lb-in).If 44.482 N (10 lbs) of force were applied toa lever 0.3048 meters long (1 foot), for example, there would be13.56 Nm (10 lb-ft) of torque.

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An increase in force or radius would result in a correspondingincrease in torque. Increasing the radius to 0.6096 meters(2 feet), for example, results in 27.12 Nm (20 lb-ft) of torque.

Speed An object in motion travels a given distance in a given time.Speed is the ratio of the distance traveled to the time it takes totravel the distance.

Linear Motion The linear speed of an object is a measure of how long it takesthe object to get from point A to point B. Linear speed is usuallygiven in a form such as meters per second (m/s). For example,if the distance between point A and point B were 10 meters,and it took 2 seconds to travel the distance, the speed would be5 m/s.

Rotational Motion The angular speed of a rotating object is a measurement of howlong it takes a given point on the object to make one completerevolution from its starting point. Angular speed is of a rotatingobject is an example where it is more common to use theEnglish system of revolutions per minute (RPM) versus the SIunit of revolutions per second (RPS). An object that makes tencomplete revolutions in one minute, for example, has a speedof 10 RPM.

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Acceleration An object can change speed. An increase in speed is calledacceleration. Acceleration only occurs only when there is achange in the force acting upon the object. An object can alsochange from a higher to a lower speed. This is known asdeceleration (negative acceleration). A rotating object, forexample, can accelerate from 10 RPM to 20 RPM, or deceleratefrom 20 RPM to 10 RPM.

Law of Inertia Mechanical systems are subject to the law of inertia. The law ofinertia states that an object will tend to remain in its currentstate of rest or motion unless acted upon by an external force.This property of resistance to acceleration/deceleration isreferred to as the moment of inertia.

The SI unit for inertia is kilogram-meter squared (kgm2). TheEnglish system of measurement is pound-feet squared (lb-ft2).

If we look at a continuous roll of paper, as it unwinds, we knowthat when the roll is stopped, it would take a certain amount offorce to overcome the inertia of the roll to get it rolling. The forcerequired to overcome this inertia can come from a source ofenergy such as a motor. Once rolling, the paper will continueunwinding until another force acts on it to bring it to a stop.

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Friction Because friction removes energy from a mechanical system,a continual force must be applied to keep an object in motion.The law of inertia is still valid, however, since the force appliedis needed only to compensate for the energy lost. In thefollowing illustration a motor runs a conveyor. A large amount offorce is applied to overcome the inertia of the system at rest tostart it moving.

Once the system is in motion, only the energy required tocompensate for various losses need be applied to keep it inmotion.

These losses include:

Friction within motor and driven equipment bearings Windage losses in the motor and driven equipment Friction between conveyor belt and rollers

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Inertia Ratios One aspect of motion control systems which must beconsidered is that the driven machine and the servo motordriving the machine are physically interdependent. It isimportant to ensure that the inertia of the servo motor ismatched to the inertia of the driven machine. Ideally it isdesirable to have a 1:1 inertia ratio between the load and themotor. However, inertia ratios of 1:10 or greater are notuncommon.

Typically, it is desirable to reach a new speed quickly whenchanging speeds in a motion control system. When changingfrom a lower speed to a higher speed, for example, the motoraccelerates the connected load quickly, resulting in a slightovershoot before settling into the new speed. If there is toogreat a mismatch between the motor and the load the systemcan become unstable. Oscillations can occur which contributeto system instability.

When the inertia of a system is properly matched the systemwill settle into a new speed quickly. This provides a stablesystem with quick response.

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Work Whenever a force of any kind causes motion, work isaccomplished. For example, work is accomplished when anobject on a conveyor is moved from one point to another.

Work is defined by the product of the net force (F) applied andthe distance (d) moved. If twice the force is applied, twice thework is done. If an object moves twice the distance, twice thework is done.

W = F x d

Power Power is the rate of doing work, or work divided by time.

In other words, power is the amount of work it takes to movethe package from one point to another point, divided by thetime.

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Power Power in an electrical circuit is measured in watts (W) orkilowatts (kW). AC drives and motors manufactured in theUnited States are generally rated in horsepower (HP), however,it is becoming common practice to rate equipment using the SIunits of watts and kilowatts.

Torque vs Power When considering motors and drives for a given application wetypically think in terms of power. We have learned that power isa function of speed. No work is accomplished unless there ismotion. Therefore, power is zero when the system and itsassociated motor is at rest (zero speed).

On the other hand, a characteristic of motion control systems isthe ability to deliver full torque at zero speed. For this reason itis more common to base motion control systems on torquerather than power.

Acceleration Torque The torque required to accelerate a machine should bedetermined first. The following information is needed:

Inertia of the m achinein kgm 2 (SI) or lb ft2 (English) (J) Amount of change of speed in RPM ( n) Time taken to change speed in seconds ( t)

A simple formula can be used to determine the requiredacceleration torque (a).

The torque required to accelerate a system with a total inertia of0.005 kgm2 (0.1187 lb ft2) from rest to 3000 RPM in 0.2 secondswould be 7.85 Nm(5.78 lb ft).

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Effective (RMS) Torque Accelerating torque is usually required on an intermittent basisonly. Due to the cyclic nature of motion control applications,servomotors have both continuous and intermittent ratings. Toselect the correct continuous rating it is also necessary to knowthe effective torque, also referred to as RMS (root-mean square)torque.

The value of effective torque is actually a means of expressingthe equivalent of varying values of torque required during acycle of operation. Effective torque is determined by looking atall the operating points of a torque-time curve during acomplete cycle.

Three operating points are used during a cycle in the followingexample. The load requires 7.85 Nm (5.78 lb ft) of torque toaccelerate the load (T1) in 0.2 seconds. During constant staterun the load requires 1 Nm (.737 lb ft) of torque to overcomelosses due to friction and maintain speed (T2) for 1 second. Todecelerate the load and stop requires 2 Nm (1.474 lb ft) of torque(T3) for 0.2 seconds. The system will remain stopped for 1second before repeating the cycle. The total cycle time is2.4 seconds (Tt).

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Calculating Effective Torque The following formula can be used to calculate effective torqueusing either SIor English units. Effective torque (eff) is thesquare root of the summation ( ) of the square of torquerequired (2) by the motor at each increment (Mot i) and timeperiod ( ti) divided by the total cycle time (Tt).

Using the values for the three time periods in the previousexample, effective torque can be calculated.

CycleIncrement

Torque(Nm)

Torque(lb ft)

Time(seconds)

1 7.85 5.78 0.22 1 0.737 13 2 1.474 0.2

12.4

Time Between CyclesTotal Time

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SimoSize Calculating the correct torque for a motion control system iscomplex, requiring a thorough understanding of the systeminvolved. SimoSize is a PC tool which allows the user toaccelerate the design process by providing the necessary toolsin a Windows 95/98/NT format. SimoSize is available throughyour sales representative at no charge and may be freely copiedand distributed.

SimoSize allows the user to select components such as gearboxes, rotary tables, and belt-pulleys. The user can also specifythe profile needs such as acceleration, run speed, and run time.A report generator in SimoSize performs calculations for speed,torque, and inertia to properly select a servomotor.

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Review 21. A ____________ is a push or a pull.

2. An object has 10 N of force applied in one direction and5 N of force applied in the opposite direction. The netforce is ____________ .

3. A twisting or turning force that causes an object torotate is known as ____________ .

4. If 20 N of force were applied to a lever 0.3 meters long,the torque would be ____________ Nm.

5. The law of ____________ states that an object will tendto remain in its current state of rest or motion unlessacted upon by an external force.

6. Ideally it is desirable to have a ____________ inertia ratiobetween the load and the motor.

7. ____________ is accomplished when force causesmotion.

8. A characteristic of motion control systems is the abilityto deliver full torque at zero speed. For this reason it ismore common to base motion control systems on____________ rather than ____________ .

9. ____________ is a Siemens software program designedto help calculate the speed, torque, and inertia of amotion control system.

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Servomotor Construction

There are two types of AC servomotors used with motioncontrol drives: synchronous and induction. Induction motors arealso referred to as asynchronous motors. The two basicelements of all AC motors are the stator and rotor. The principleof operation of a stator is the same in asynchronous andsynchronous motors. There are, however, differences in rotorconstruction.

Stator and a Rotating A rotating magnetic field must be developed in the stator of anMagnetic Field AC motor in order to produce mechanical rotation of the rotor.

Wire is coiled into loops and placed in slots in the motorhousing. These loops of wire are referred to as the statorwindings. The following drawing illustrates a three-phase stator.Phase windings (A, B, and C) are placed 120 apart. In thisexample, a second set of three-phase windings is installed. Thenumber of poles is determined by how many times a phasewinding appears. In this example, each phase winding appearstwo times. This is a two-pole stator. If each phase windingappeared four times it would be a four-pole stator.

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Magnetic Field When AC voltage is applied to the stator, current flows throughthe windings. The magnetic field developed in a phase windingdepends on the direction of current flow through that winding.The following chart is used here for explanation only. It assumesthat a positive current flow in the A1, B1 and C1 windings resultin a north pole.

It is easier to visualize a magnetic field if a time is picked whenno current is flowing through one phase. In the followingillustration, for example, a time has been selected during whichphase A has no current flow, phase B has current flow in anegative direction, and phase C has current flow in a positivedirection. Based on the above chart, B1 and C2 are south polesand B2 and C1 are north poles. Magnetic lines of flux leave theB2 north pole and enter the nearest south pole, C2. Magneticlines of flux also leave the C1 north pole and enter the nearestsouth pole, B1. A magnetic field results as indicated by thearrow.

Positive NegativeA1 North SouthA2 South NorthB1 North SouthB2 South NorthC1 North SouthC2 South North

Winding Current Flow Direction

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The amount of flux lines ( ) the magnetic field produces isapproximately equal to the voltage (E) divided by the frequency(F). Increasing the supply voltage increases the flux of themagnetic field. Decreasing the frequency increases the flux.

If the field is evaluated at 60 intervals from the starting point, atpoint 1 it can be seen that the field will rotate 60. At point 1phase C has no current flow, phase A has current flow in apositive direction and phase B has current flow in a negativedirection. Following the same logic as used for the startingpoint, windings A1 and B2 are north poles and windings A2 andB1 are south poles. At the end of six such intervals themagnetic field will have rotated one full revolution or 360.

Synchronous Speed The speed of the rotating magnetic field is referred to assynchronous speed (NS). Synchronous speed is equal to 120times the frequency (F), divided by the number of poles (P). Ifthe applied frequency of the two-pole stator used in theprevious example is 60 hertz, synchronous speed is 3600 RPM.

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Synchronous Rotor Synchronous motors are not induction motors. They are calledsynchronous because the rotor operates at the same speedas the rotating magnetic field. There are different methods toachieve synchronization between the rotor and the rotatingmanetic field. The most common method in servomotorapplications is the use of a permanent magnet rotor. Permanentrare-earth magnets are glued onto the rotor. This type of rotor isfound on smaller synchronous motors. A synchronous motor ofthis design is relatively small with low rotor inertia. The smaller,low inertia rotor provides fast acceleration and high overloadtorque ratings.

When the stator windings are energized, a rotating magneticfield is established. The permanent magnet rotor has its ownmagnetic field that interacts with the rotating magnetic field ofthe stator. The north pole of the rotating magnetic field attractsthe south pole of the permanent magnet rotor. As the rotatingmagnetic field rotates, it pulls the permanent magnet rotor,causing it to rotate.

DC Motor Comparison A permanent magnet synchronous motor can be compared to astandard DC motor. A DC motor consists of a stator and rotor.The rotor windings are made up conductors that terminate at acommutator. DC voltage is applied to the rotor thru carbonbrushes which ride on the commutator.

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A permanent electromagnet with north and south poles isestablished when DC voltage is applied to the stator. Theresultant magnetic field is static (non-rotational).

The DC voltage applied to the rotor conductors causes currentto flow. This current reverses direction twice per revolution.Voltage polarity is such that during one half of a revolutioncurrent flows through half the conductors in one direction andhalf of the conductors in the opposite direction.

Current flow momentarily decreases to zero in a conductorwhen a brush is in direct contact with it. Polarity of the appliedvoltage is reversed. This is known as commutation. Current flowthrough the conductor increases in the opposite direction. Theresultant magnetic field reverse polarity for the second half of arevolution.

The resultant magnetic armature fields are of opposite polarityto the main stator field. The north pole of the rotor is attracted tothe south pole of the stator and rotation results.

conductor..

There are weak points with this design. The commutator addssignificant weight to the rotor, increasing inertia and reducingacceleration capability. The design of the commutator also limitsthe maximum speed of the motor. Current flow through rotorwindings generates heat in the center of the motor that requiressome method of cooling, such as intenal ventilation. In addition,there are added maintanance cost, such as brushes, whichmust be checked and replaced regularly.

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Synchronous Servomotor Permanent magnet synchronous servomotors offer manyadvantages over DC motors. The permanent magnetic field isgenerated by the rotor instead of the stator. There is no currentflow to generate heat in the rotor. Instead, heat is generated inthe stator windings which are close to the surface of the motor.In many applications natural convection cooling is all that isrequired. In some more demanding applications an externalblower provides sufficient cooling. Since no internal ventilationis required, servomotors can be built to higher degrees ofprotection. Servomotors have a higher efficiency since there areno losses in a rotor/armature winding.

In addition, there is no commutator to limit speed oracceleration. Instead of switching rotor current mechanically toestablish the correct polarity of the rotors magnetic field, theMASTERDRIVE MC commutates the magnetic field of thestator electronically. In order to accomplish this the drive mustmonitor the position of the permanent magnet rotor withrespect to the rotating magnetic field of the stator. Thisinformation is provided to the drive by a feedback device knownas an enccoder. On permanent magnet type synchronousmotors, the encoder must give the absolute position of the rotorwithin one revolution.

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Asynchronous Rotor Siemens also offers asynchronous (induction) servomotors. Themost common type of rotor used with asynchronous motors isthe squirrel cage rotor. The construction of the squirrel cagerotor is reminiscent of the rotating exercise wheels found incages of pet rodents. The rotor consists of a stack of steellaminations with evenly spaced conductor bars around thecircumference. The conductor bars are mechanically andelectrically connected with end rings. A slight skewing of thebars helps to reduce audible hum. The shaft is an integral part ofthe rotor construction.

There is no direct electrical connection between the stator andthe rotor or between the power supply and the rotor of anasynchronous motor. When a conductor, such as a conductorbar of the rotor, passes through a magnetic field, a voltage (emf)is induced in it. The induced voltage causes current flow in theconductor.

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Current flow in the conductor bars produces magnetic fieldsaround each rotor bar. The rotor becomes an electromagnet withalternating north and south poles. It must be remembered thatcurrent and magnetic fields of the stator and rotor are constantlychanging.The following drawing illustrates one instant in timeduring which current flow through winding A1 produces a northpole. The expanding field cuts across an adjacent rotor bar,inducing a voltage. The resultant magnetic field in the rotortooth produces a south pole, which is attracted to the statorsnorth pole. As the stator magnetic field rotates the rotor follows.

Asynchronous Slip There must be a difference in speed between the rotor of anasynchronous motor and the rotating magnetic field. This isknown as slip. If the rotor and the rotating magnetic field wereturning at the same speed, no relative motion would existbetween the two and no lines of flux would be cut. With no fluxlines cut no voltage would be induced in the rotor. Thedifference in speed is called slip. Slip is necessary to producetorque.

Slip is dependent on load. An increase in load will cause therotor to slow down, that is to increase the slip. A decrease inload will cause the rotor to speed up or decrease slip. Thefollowing formula is used to calculate slip. For example, a four-pole motor operated at 60 Hz has a synchronous speed of 1800RPM. If rotor speed at full load were 1765 RPM, slip is 1.9%.

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Servomotor Ratings

Siemens Servomotors Servomotors, like the Siemens servomotor shown below, arehigh-performance motors specifically designed for use with thehigh demand of variable speed drives and motion controlapplications.

Nameplate The nameplate of a motor provides important informationnecessary when applying a motor to an AC drive and motioncontrol application.

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Catalog and Serial Number The catalog number gives important information about themotor. The first four digits of the catalog number are the modelnumber. In this case it is a 1FT6 synchronous servomotor. Inaddition to the 1FT6 Siemens also manufactures a 1FK6synchronous servomotor. There is also the 1PH7, 1PL6, and1PH4 asynchronous servomotors.

1FT6082-8AF71-1AG1

The serial number (Nr) is used to identify the motor.

E J899 1745 01 001 EN 60034

Voltage The example motor, like all 1FK6 and 1FT6 motors, is rated for380 to 460 VAC, which correlates to an effective voltage in thestator windings of 240 VAC. Induction motors are designed tooperate on a voltage source that supplies a smooth sinusoidalsine wave, such as the one shown below.

AC variable speed drives, unfortunately, do not produce asmooth sinusoidal waveform. Modern drives produce a PWM(pulse width modulation) waveform. This technology producesvery rapid changes in voltage, resulting in high voltage spikesthat can shorten the life of a motor. In addition, motion controlapplications typically incorporate quick starts and stops whichadd further stress to a standard motor. Siemens servomotorsare specifically designed to operate with the PWM waveformproduced by modern AC variable-speed motion control drives.

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Speed and Torque Rated speed is the nameplate speed, given in RPM, where them otor develops rated torque (n) at rated voltage. This motor, forexample, is rated to develop 10.3 Nm of torque at 3000 RPMwith a supply voltage range of 380 to 460 VAC, which correlatesto an effective voltage in the stator windings of 240 VAC. Thenameplate of the 1F.6 motors also shows ratings when thesupply voltage is reduced 50%. At 50% supply voltage ratedspeed is 1500 RPM, rated torque is 11.7 Nm, and the effectivestator winding voltage is 120 VAC. This information is put inparenthesis because this supply voltage is outside the ratedvoltage of the MASTERDRIVE MC drive.

The nameplate on this motor also gives a maximum speed of4160 RPM. Maximum speed is the fastest speed the motor canoperate at and still develop enough torque to maintain thatspeed with some amount of load. Variable speed drives arecapable of running a motor at various speeds. When a variablespeed drive is set to turn a motor faster than rated speed, themotors ability to develop continuous and overload torque isdiminished. A variable speed drive should not be set to operatea servomotor above its maximum speed.

Current Stall (Stand still) current is 8.2 amps at zero speed and stalltorque (o) with 60 K rise. The Current at stall is 10.7 amps witha 100 K rise.

Stall Torque and Current Stall describes a condition where power is supplied to themotor but the rotor is at zero speed. This condition occurs whenan AC drive is causing the motor to act as an electrical brake tohold the connected load at a specific position.

Stall Current (Io) is the current drawn by the motor that isrequired to produce the given stall torque (0).

Stall torque is also a thermal limiting torque when the motor isat standstill, corresponding to 60 K or 100 K temperature rise.Stall torque is available at zero speed for an unlimited time.

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Insulation Class In an electrical circuit, current causes heat. A certain amount ofcurrent will flow in the windings of a motor as soon as it isstarted. This will cause motor temperature to rise. DIN(Deutsche Industrie Normenausschuss) is a set of Germanstandards now used in other countries. DIN VDE 0530 classifiesthe accepted amount of temperature rise. The three mostcommonly used classes are B, F, and H.

Before a motor is started its windings are at the temperature ofthe surrounding air. This is known as ambient temperature. Thestandard ambient temperature for electrical equipment is 40 C.Each insulation class has a specific allowable temperature rise.Ambient temperature and allowable temperature rise equals themaximum winding temperature in a motor. In addition, a marginis allowed to provide for a point at the center of the motorswindings where the temperature is higher. This is referred to asthe motors hot spot.

Temperature rise is always given in absolute values. Theabsolute value of Celsius is the Kelvin (K). Kelvin is the SI unit oftemperature. The degree sign () is not used with Kelvin.

The insulation or thermal class (Th. CL. F.) of the example motoris Class F. Class F insulation has a maximum temperature rise of105 K. The maximum winding temperature is 145 C (40 Cambient plus 105 K rise). The maximum steady-statetemperature of a motor with Class F insulation is 155 C.

The operating temperature of a motor is an important factor inefficient operation and long life. Operating a motor above thelimits of the insulation class reduces the motors lifeexpectancy. A 10 K increase in the operating temperature candecrease the life expectancy of a motor as much as 50%.

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Stall Torque, Current, There are two ratings for stall torque (o), stall current (Io), andand Temperature Rise temperature rise given for this motor. These ratings are related.

o = 10.4/13.0 NmIo = 8.20/10.7 ATemperature Rise = 60/100 K

The motor begins developing torque to turn the connected load.If the load is such that it only requires 10.4 Nm of torque at stall,current will be 8.20 A and the temperature rise will be 60 K. Ifthe load requires 13.0 Nm at stall, current will be 10.7 A andtemperature rise will be 100 K. This is well within Class Ftemperature limitations.

IP Protection The International Electrotechnical Commission (IEC) is anorganization that, among other things, defines the degree ofprotection provided by enclosures. IEC is associated withelectrical equipment sold in many countries, including theUnited States.

The IEC system of classification consists of the letters IPfollowed by two numbers. The first number indicates thedegree of protection provided by the enclosure with respectto persons and solid objects entering the enclosure. Thesecond number indicates the degree of protection against theingress of water. The motor indicated by the sample nameplateis dust tight and protected against splashing water (IP 64).

1st Number Description0 Not Protected1 Protected Against Objects Greater than 50 mm2 Protected Against Objects Greater than 12 mm3 Protected Against Objects Greater than 2.5 mm4 Protected Against Objects Greater than 1.0 mm5 Protected Against Dust6 Dust Tight

2nd Number0 Not Protected1 Protected Against Dripping Water2 Protected Against Dripping Water when Tilted up to 153 Protected Against Spraying Water4 Protected Against Splashing Water5 Protected Against Water Jets6 Protected Against Heavy Seas

7 Protected Against the Effects of Immersion for Specific Time and Pressure

8 Protected Against Continuous Submersion Under Conditions Specified by the Manufacturer

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Review 31. Two types of servomotors used in motion control drives

are ____________ and ____________ .

2. Phase windings in a 3-phase motor are located____________ degrees apart.

3. The speed of the rotating magnetic field is known as____________ speed.

4. The difference between rotor speed and synchronousspeed of an asynchronous motor is known as____________ .

5. The output of a PWM type drive is ____________ .

a. sinusoidalb. pulse width modulated

6. The temperature rise of insulation class F is____________ K.

7. A motor that is dust tight and protected againstsplashing water would have an IP rating of____________ .

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Speed-Torque Characteristics

Duty Cycle All motors are limited by the amount of heat that can develop inthe motor windings. Speed-torque curves are based onstandardized duty cycles which lead to the same temperaturerise. The number of possible duty cycle types is almost infinite.To help promote a better understanding, duty cycles have beendivided into nine standardized categories, which cover most ofthe applications encountered.

S1 Continuous Running DutyS2 Short-Time DutyS3 Intermittent Periodic Duty Without StartingS4 Intermittent Periodic Duty With StartingS5 Intermittent Periodic Duty with Starting and

Electric BrakingS6 Continuous Operation Periodic DutyS7 Continuous Operation Periodic Duty with Starting

and Electric BrakingS8 Continuous Operation Periodic Duty with Related

Load/Speed ChangesS9 Continuous Operation Duty with Non-Periodic Load

and Speed Variations

Duty cycle profiles can become complex. S1, S3, and S6,however, are three common duty cycles. Part 2 of the GeneralMotion Control Catalog provides speed/torque curves for S1and intermittent/periodic duty cycles where applicable.

S1 Duty Each duty cycle is characterized by cycle times, cycle durations,and load. S1 duty cycle, for example, characterizes a conditionwhere the motor operates under constant load of sufficientduration for thermal equilibrium to be established. All motorslisted in the Siemens catalog are designed for continuous dutytype S1, unless otherwise indicated.

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S3 Duty S3 duty operation is comprised of a sequence of identical dutycycles, each of which consists of a period of constant loadfollowed by an interval of no load. Starting current has nomarked effect on the temperature rise of the motor. Operatingtime is given in minutes, such as 10 minutes, 30 minutes, or 60minutes. If no time is given a 10 minute cycle time is assumed.Cycle duty is given in a percent such as 15%, 20%, 25%, 30%,or 40%. An S3 duty cycle of 40% for 10 minutes, for example,would indicate a motor load would be constant for 40% of thetime (4 minutes). A no load condition would occur for 60% ofthe time (6 minutes).

S6 Duty S6 duty operation is similar to S3 duty operation. The maindifference is that there arent any de-energized intervals. Themotor remains energized during the no load interval. Operatingtime and cycle duration are given in the same manner as for S3duty operation.

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Speed-Torque Curve A motor can be identified by its frame size, which is associatedof Synchronous with useful mounting information. The speed and torqueServomotor characteristics for a given frame size depend upon the motor

windings available. A common approach for representing therange of speed and torque characteristics available for a givenmotor frame size is the speed-torque curve.

A speed-torque curve, like the one shown in the followingillustration, shows a motor frame which can be wound forvarious speeds and duty cycles. A letter in the catalog numberis used to designate the speed of the motor. A speed-torquecurve will show the expected torque performance of a motor fora specific duty cycle at a given speed. The motor frame for apermanent magnet synchronous motor illustrated by thefollowing speed-torque curve is used on four different motorwindings: 2000, 3000, 4500, and 6000 RPM. Torque ratings inthis example are shown for S1 and S3 duty cycles.

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The speed-torque curve can be made less confusing by filteringout information so that only the applicable winding and dutycycles are shown. In the following illustration a motor with an Fwinding (3000 RPM) is used. The rated stall torque (zero speedtorque) when operating the motor in S1 duty is about 1.1 Nm(0.81 lb ft). As the motor accelerates to rated speed, torquedecreases to approximately 0.9 Nm (0.66 lb ft) due to friction(bearings) and stator losses (mainly eddy currents). Themaximum torque that the motor can supply for a short period oftime at rated speed is called limit.

If the motor speed is increased beyond rated speed (3000 RPM)continuously available torque, indicated by the S1 line,continues to decrease. The maximum speed is defined by theintersection of the S1 line with the voltage limiting curve. Thevoltage limiting curve must be followed from that point on.Higher speeds result in reduced available torque.

The maximum torque or current limiting curve indicates themaximum available short-time torque of the motor. Exceedingthe limit results in a sudden demagnetizing of the permanentmagnets, destroying the synchronous motor.

The rated stall torque when operating the motor in S3 duty isapproximately 1.5 Nm (1.1 lb ft). Torque will remain constant untilabout 2000 RPM. Torque will then decrease slightly toapproximately 1.4 Nm (1.0) at 3000 RPM. Torque will continue todecrease as motor speed is increased above the rated speed of3000 RPM.

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Speed-Torque Curve for Speed-torque curves can also be supplied for a specific motor.Specific Motors Larger motors are rated in Newton meters (Nm) and pound-feet

(lb-ft). Smaller motors are rated in Newton meters (Nm) andpound-inches (lb-in). The following speed-torque curve, forexample, shows the operating capabilities of a 1FT6082 motor.The motor associated with this curve can deliver 13 Nm (115 lb-in) at stall and 10.3 Nm (91.2 lb-in) at rated speed (3000 RPM)continuously. The region in the light grey area of the graphrepresents a continuous operating range (S1 duty cycle). Thearea represented by the dark grey region of the graphrepresents the intermittent operating region.

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Siemens Servomotors

Siemens manufactures asynchronous and synchronousservomotors for virtually every motion control application.Selection and ordering information, as well as configuration aidssuch as speed-torque curves for specific motors, can be foundin Part 2 of the General Motion Control Catalog. This is availablefrom your local Siemens sales representative.

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Motor Protection Cooling Power Range kW (HP)

Rated Torque Nm (lb-in)

1FK6 IP64 (IP65)* Natural 0.5 - 5.2(0.7 -7.0)

0.8 - 16.5(7 - 148)

1FT6 IP64 (IP65, IP67)* Natural 0.5 - 15.5(0.7 - 20.7)

0.8 - 88(7 - 779)

Blower Vent 6.9 - 34.6(9.2 - 46.4)

17 - 160(150 - 1416)

Water 11 - 27.6(14.7 - 37)

34 - 78(300 - 690)

* Optional

Synchronous Servomotors Siemens manufactures two models of permanent-magnetsynchronous servomotors. The 1FK6 is a standard servomotor.The 1FT6 is a performance servomotor.

Asynchronous Siemens manufactures three models of squirrel-cageServomotors asynchronous servomotors: 1PH7, 1PL6, and 1PH4.

Motor Protection Cooling Power Range kW (HP)

Rated Torque Nm (lb-ft)

1PH7 IP 55 Blower Vent Surface

3.7 - 215(5 - 288)

22 - 1145(16 - 844)

1PL6 IP23 Blower Vent 24.5 - 300(32.8 - 400)

370 - 1720(273 - 1268)

1PH4 IP65 Water 7.5 - 61(10 - 81)

48 - 330(35 - 243)

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Servomotor Accessories

Holding brakes, built-on gears, and encoders are typicalaccessories for use with servomotors and motion controlsystems. Holding brakes and built-on gears will be covered inthis section. Encoders will be covered in a separate section.

Holding Brakes Many systems need a holding brake as part of an emergency-stop function, or for other reasons related to safety. Thesebrakes are electromagnetic brakes. When voltage is applied tothe brake, the brake is released and the motor is free to beturned by the AC drive. In the event of a power loss, such as apower interruption caused by initiating an emergency stop, thebrake is engaged. This will bring the motor to a standstill.

Holding brakes are available for the 1FK6, 1FT6, and 1PH7motors.

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Gear Reducer In drive systems servomotors are frequently combined withplanetary gear reducers. Planetary gears designed for use withSiemens servomotors provide a compact unit with low torsionalplay, high torsional rigidity, and low running noise.

Earlier in the course we discussed some basic mechanicalconcepts which include power, torque, and speed. One way tosee the relationship of these concepts is through a gearreducer. Power is a function of speed, and directly proportionalto both speed and torque. If torque and speed are increased,power would also increase. However, if torque is increased andspeed is decreased by a proportionate amount, power remainsconstant. This is exactly what happens in a gear reducer. Thefollowing drawing illustrates a 30:1 gear reducer. The input isdriven by a servomotor with 4.068 Nm (3 lb-ft) of torque at 1750RPM. Output speed is reduced by the gear reducer to 58.3RPM. Output torque, however, increases to 103.73 Nm(76.5 lb-ft) for use by the connected system.

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SPG, LP, and PG Series Siemens uses SPG and LP series planetary gears made byAlpha Geardrives, Elk Grove Village, IL, for 1FK6, 1FT6, andsome 1PH7 motors. Siemens uses PG series planetary gearsmanufactured by ZF Friedrichshafen, Florence, KY, for 1FK6 and1FT6 motors.

Review 41. ____________ is the duty cycle designation for

continuous running duty.

2. If no time is given for a duty cycle a ____________minute time is assumed.

3. The speed-torque curve for specific servomotors showspeed-torque ratings for ____________ and____________ operating regions.

4. The maximum rated torque of a 1PH4 asynchronousservomotor is ____________ HP.

5. 1PH7, 1PL6, and 1PH4 are examples of ____________servomotors.

SPG Gears LP Gears PG GearsTransmissionRatios, single-stage

4, 5, 7, 10 5, 10 4, 5, 7, 10

TransmissionRatios, 2-stage

16, 20, 28, 40, 50, 70, 100

25, 50, 100 16, 20, 25, 35, 40, 49, 50, 70, 100

Efficiency up to 97% >95% >95% single-stage, >97%, 2-stage

Torsional Play up to under 2 arc min

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Encoders and Resolvers

Siemens encoders and resolvers are designed for use with theSiemens servomotors discussed in previous sections. Encodersand resolvers allow the MASTERDRIVE MC to determinespeed, position, and direction of shaft rotation.

One type of encoder available for use with Siemensservomotors is an incremental encoder. An incremental encoderconsists of a transparent disk marked with lines around theradius. A photoelectric scanning device is located near the disk.The output of an incremental encoder is either a series ofpulses or a series of sinusoidal waveforms.

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Closed-Loop Control In a motion control system, precise control must be maintainedover acceleration, deceleration, velocity, and position. Thisrequires that the drive or other controlling device be providedwith commands associated with these items. The drivedetermines the signal to provide to the servomotor bycomparing the actual values with the command values. Theactual values are calculated based upon feedback received fromthe encoder. This is an example of closed-loop control.

In the following illustration an input reference signal, indicatingthe position the load is to be moved to, is applied to a counter inthe motion control drive. As the motor is accelerated pulsesfrom an encoder are returned to the counter at an increasingrate. Once the motor has reached the desired running speed thepulses are returned at a constant rate. The drive can keep trackof the rotors position and number of rotations by counting thesepulses. When the load approaches the desired location thedrive slows the motor to a stop. The load is now in the desiredlocation.