Elector Craft

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Handbook and ApplicationGuide for High-Performance

Brushless Servo SystemsThis updated handbook provides a

technical overview of the components,

theory, and interaction of brushless

motion control systems plus a

helpful guide outlining the design

considerations, calculations and

application of brushless servo sytems,

including helpful engineering formulas

and conversion tables.

This engineering handbook can also be

used to complement the ElectroCraft

motion control guide, DC Motors-

Speed Controls-Servo Systems.


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Handbook and Application Guide for

High-Performance Brushless Servo Systems

ContentsPart One: Theory of brushless motion control

Comparison of DC servomotors and brushless servomotors ......................... 3

Sinusoidal and trapezoidal brushless servos...............................................................5

Trapezoidal and sinusoidal EMF and square wave current ................................5

Sinusoidal EMF and sinusoidal current ..........................................................................6

Sinusoidal control for brushless and induction motors ........................................7

Closed-loop control for high performance .................................................................9

Current regulation and tuning guidelines .................................................................... 11

Part Two: Sizing and application guidelines

Mechanical considerations ...................................................................................................14

Motion profile considerations.............................................................................................18

Sinusoidal brushless motor specifications ...............................................................20

Electrical noise and its causes .........................................................................................20

Filtering, grounding, shielding, and segregation....................................................22

ElectroCraft Incorporated: Company information ...........................................26

Figure 1: Block diagram of a typical motion control system

PLC orhost

computer

Positioncontroller

Driveamplifier

Motor Load

Feedback

A simple representationof a typical motion control

system is shown in Figure

1. Each of the primary

components will be reviewed.


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Your Genius. Our Drive. 7

vious technologies, the primary difference for the sinu-soidal servo drive is a more complex control algorithm,while the motor, feedback, and power electronics remain

the same. In recent years, the advancement of high-per-formance microcontrollers and Digital Signal Processors(DSPs) that now can handle complex calculations has in-creased the capability of the sinusoidal brushless servosystem. The control hardware’s capability combined withthe decreasing cost of these components has driven fur-ther development of this control methodology aboveothers previously described.

The sinusoidal back EMF motor excited with threephase sinusoidal currents (in the proper relationship tothe back EMF at every rotor position) produces a constanttorque. An explanation of this phenomenon at a steady-state speed and torque is illustrated in Figure 9.

The three-phase sinusoidal quantities — which are dis-placed spatially by 120° — represent the magnetic fieldand current. The three-phase quantities produce a resultant vectorwith constant amplitude that rotates at the sinusoidal frequency. Therotor position sensor tracks the back EMF position and allows the cur -rent vector command to be generated perpendicular to the magneticeld vector at any instant. A pulse width modulated (PWM) currentamplifier is necessary to ensure the ability to control the current am-

plitude, frequency, and phase with sufficient dynamic performance.At this point, the fixed magnitude magnetic field vector, which is per-pendicular to the adjustable magnitude current vector, is analogousto the operation of a DC motor.

There are many brushless servo drives and brushless positioningdrives that are designed to produce sinusoidal currents with incre-mental encoder feedback. This type of servo system combines theoptimum motor design with a sinusoidal current PWM drive to pro-duce the best low-speed and high-speed performance. The Elec-troCraft CompletePower TM Plus digital servo drive takes this controlcapability one step further. True sinusoidal current control can be ac-

complished in these drives without the need for high-resolution in-cremental encoder feedback. Only the lower resolution commutationfeedback is required. In some applications, this reduces the need andcost of the additional encoder.

Other benefits resulting from the microprocessor-based drive designinclude the capability of operating induction motors using field orientedcontrol and of sharing the motor mounted encoder with the positioncontroller. This maximizes flexibility and performance and minimizes cost.

Sinusoidal control for permanent magnetbrushless motors and induction motors

The mechanical commutator of the DC servomotor ensures thatthe armature current vector is kept perpendicular to the permanent

Figure 9: Sinusoidal three-phase principle of operation

FtotalFT

γ = 60°

FR Ftotal

FT

γ = 90°

FR

FS

FR FSFT

γ 1 2 0 °

0

γ = 60°

2 4 0 °

FR FSFT

γ 1 2 0 °

0

γ = 90°

2 4 0 °

Magnetic field vector

The magnetic field vector and

current vector are of constant amplitudeand rotate at a constant speedin a steady-state condition.

Current vector


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magnet field at all speeds and torques. This pro-vides for control of torque by simply adjusting thearmature current level and makes using the DC

servomotor very straightforward. Using input com-mands analogous to those for a DC servomotor, auniversal control computes the torque producingsinusoidal currents for permanent-magnet brush-less motors. (Otherwise, for induction motors, itcomputes the torque and field-producing sinusoidalcurrents.) This universal control strategy, known asfield-oriented or vector control, is shown in Figure10. Field-oriented control ensures that the torque-producing current vector is perpendicular to thefield vector at any torque or speed. Some form ofthis control is used with all sinusoidal back EMF andsinusoidal current brushless servo drives. From theservo user’s perspective, the torque, velocity, andposition control is then analogous to the traditionalDC servomotor.

Also shown in Figure 10 is an optional phaseadvance angle. The phase advance angle can beused to optimize the amplifier/motor performancecharacteristics. The most common use of the phaseadvance angle is to compensate for the inductance

effect that causes a torque reduction as speed (fre-quency) increases. A less common use of the phaseadvance angle is to allow permanent magnet brush-less motors to operate to a higher speed than wouldnormally be possible without the phase advanceangle. If the phase advance angle is used, the mag-nitude of the angle as a function of torque and/orspeed is normally determined by the servo drivemanufacturer and is not user adjustable.

Incremental encoders and resolvers

The most commonly used motor-mounted position feedbackdevices for sinusoidal brushless servos are either incremental opti-cal encoders or brushless resolvers. The primary advantages of theresolver are that the position information is absolute and it is robust— because it is similar in construction to the motor. However, otherfactors favor the encoder over the resolver, including lower overallcost, digital feedback, higher resolution and accuracy, and easy linecount exibility (binary or decimal). The advancement of magneticand capacitance-based incremental encoder technology further en-hances the position of encoder based feedback design. However, theuse of both encoder and resolver feedback will likely continue into

the foreseeable future as both solutions service the need of specificapplications and operating environments.

Figure 11: Resolver feedback for brushless motors

High-frequencyrotor excitation

R o t o r e x c i t a t i o n

R e s o l v e r s c h e m a t i c

High-frequencymodulated sine

High-frequency

modulated cosine



Figure 10: Field-oriented control for induction motors

and permanent-magnet brushless motors

Motor

Field coodinates (X-Y) Stator coodinates (α−β) (R,S,T)

Field command(induction motor only)

D C

m o t o r

t y p e c o m m a n d s i g n a l s

Torquecommand

Coordinatetransformation

IR* sin θ

IS* sin (θ − 120°)

IS* sin (θ − 240°)

Sensor

Three-phasecurrent regulatorSlip

constant

sin/cosgenerator

Optical phase advance angle

θM

θ

θS

θPA

Slip angle(induction motor only)

Rotor electrical position


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The resolver used in brushless servo drives is il-lustrated in Figure 11. The high-frequency excitationsignal is transferred to the rotor via a circular trans-

former. The raw resolver feedback is a high-frequen-cy AC signal modulated by the sine and cosine ofthe rotor angle. The raw resolver feedback is not veryuseful, so some form of external circuitry is requiredto create usable information. In brushless servo driveapplications the resolver feedback is usually pro-cessed by commercial resolver-to-digital-convertersthat add significant cost. The output of the resolverto digital converter is an absolute digital positionword and analog velocity.

The incremental encoder used in brushless servodrives is illustrated in Figure 12. The raw encoderfeedback, already in digital format, is typically pro-cessed with low-cost commercial circuitry to producea digital position word. The posi-tion information interfaces directlyto the microcontroller of digitaldrives. If the velocity loop is analog,then an additional circuit processesthe encoder feedback to producean analog tachometer signal. No-

tice that encoder feedback signalsare differential, for high noise im-munity, and for locating the encod-er at long distances from the drive.

Permanent-magnet servomo-tors also use a low-resolutionabsolute signal in addition to theincremental encoder. This is usedto locate the magnetic field vec-tor at startup. The low-resolutionabsolute signal is often built into

the incremental encoder (usu-ally called commutation signals)or is generally provided from aseparate Hall-effect, or commu-tation, encoder. In some cases,these commutation signals areincorporated into the incrementalencoder and are provided by asingle device, thus eliminating the separate commutation feedbackdevice, reducing the cost and complexity of the servomotor design.Induction motors do not require an additional low-resolution abso-

lute encoder because they do not use permanent magnets to estab-lish the magnetic field vector.

Figure 12: Incremental encoder feedback for brushless motors

Once per revolution:Marker of index pulse

Optical encoder construction

Encoder

Mounting surface

Light sensor

Coded disk

LED

Gap

Lens

Electronics Shaft

Coded disk

A+

A-

B+

B-

I+

I-

Figure 13: Closed-loop control for high-performance motion

POSITION CONTROLLER SERVO DRIVE

MOTORand

SENSOR

Position controller

Positioncommand

Position feedback

- - -

ddt

Ve lo city c ontrolle r Cu rre nt c on tro ller Power amplifierMotor

SensorCurrent feedbackSpeed feedback

Closed-loop frequency response

G a i n

( d B )

20

10

0

-10

-20

-30

-40

0

-20-40

-60

-80

-100

-120

-140

-160

-180

P

h a s e an gl e

( D e gr e e s )

-45° phase shift

bandwidth-3 dB bandwidth

Log frequency (Hz)

Gain

Phase angle


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10

Closed-loop control for high performance mo-tion control, the most common structure for high-performance motion controllers, is illustrated in

Figure 13. This cascade control structure has aninnermost current loop, a velocity loop aroundthe current loop, and a position loop around thevelocity loop. The sequence of current (torque),velocity, and position is natural as it matches thestructure of the process to be controlled.

This multi-loop control structure functionsproperly only if the bandwidths of the loops havethe proper relationship.

Bandwidth is the measure of how well thecontrolled quantity tracks and responds to thecommand signal. Figure 13 shows a closed-loop

frequency response and definitions for the two most common band-widths— -3 dB bandwidth and -45° phase-shift bandwidth. The cur -rent loop must have the highest bandwidth, then the velocity loop;finally, the position loop has the lowest bandwidth. Therefore, tuningcontrol-loop regulators is accomplished by starting with the inner-most loop and working outward.

Current regulationThe current control for three-phase brushless servomotors is usu-

ally performed with a PWM power amplier and closed-loop controlof the current in each phase. A block diagram of the current loop andpower amplifier is shown in Figure 14.

The power devices must be able to withstand high voltages, switchhigh currents, and exhibit low conduction and switching losses. Tradi-tionally, the bipolar transistor and power eld effect transistors (FETs)have been the most common output devices for high performanceservo systems. However, these switches are being replaced with inso-lated-gate, bipolar transistors (IGBTs) and intelligent power modulesas these devices have lower losses and can operate at higher powerlevels. These devices combine the rugged output of a bipolar tran-

sistor with the gate drive and fast turn-off times of a power FET. ThePWM frequency of modern servo drives is typically between 5 and 20kHz. The high PWM frequency allows for a high current loop gain andkeeps the current ripple frequency and audible noise to a low level.

The current feedback sensor is critical and must provide an exactrepresentation of the actual current. The current feedback signal iscompared to the current command to generate a current error sig-nal. The current regulator processes current error to create a motorvoltage command. The voltage command signal is compared to atriangle wave to create the PWM signal that commands the powerdevices to turn on and off at the proper time. There is additional

circuitry that provides lockout to ensure that the upper and lowerdevices are never on at the same time, even during turn-off and

Figure 14: Three-phase current loop for a PWM power amplifier

IR-

Current errorVoltage

command

Current feedback

I*R

IS

I*T

-IT

PHASE T CURRENT CONTROLLER

On/Offcommand

VTriangle

Motor

PHASE S CURRENT CONTROLLER

PHASE R CURRENT CONTROLLER

-

I*S




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turn-on transitions. Too much lockouttime results in excessive deadband in thecurrent loop while too little lockout time

results in short-circuit or “shoot-through”current flowing through upper and lowerdevices. The PWM technique results inthe most efficient conversion of DC tovariable AC power.

Because the current controller tuningis very important for proper drive perfor-mance, most drive manufacturers do notallow users to perform this adjustment. In the past, to eliminate theneed for current controller adjustments by the drive user, specificamplifier model numbers were matched with specific motor modelnumbers, or plug-in personality modules matched an amplifier witha motor. The next generation of ElectroCraft CompletePower TM Plusbrushless servo motors and drives will self-detect the motor and drivecombination and automatically determine the correct current controlgain settings eliminating the possibility of incorrect setting. The endresult of a properly tuned current controller is an actual current thatfollows the commanded current with -3-dB bandwidths commonly inexcess of 1 kHz. To the outer velocity loop, a properly tuned currentcontroller can be approximated by a fixed gain and first order lagsuch that the low frequency characteristics (up to frequencies of con-

cern to the velocity loop) approximate the low frequency characteris-tics of the more complicated actual transfer function.One limitation of the current loops is gain, phase, and offset errors

that occur due to imperfect sensors and other circuitry. These errorsare one source of torque ripple so it is important to keep these errorsto an absolute minimum. Another limitation of the properly designedcurrent controller is insufficient voltage to generate the necessary cur-rent. This situation occurs for large value current commands at highermotor speeds when the back EMF of the motor begins to approachthe motor supply voltage. In applications requiring high torque athigh speeds, careful observation of the motor/drive system peak

torque envelope is required.

Velocity regulation and tuning guidelinesThe most common velocity controller structure is the proportional

plus integral (PI) regulator. A block diagram of a simple velocity loopappears in Figure 15. The choice of the P gain and I gain for thedesired response are based upon the application requirements. Pro-portional gain is always used with higher bandwidths resulting fromhigher P gain values. The integral gain provides “stiffness” to loadtorque disturbances and reduces the steady-state velocity error to azero value. However, integral gain does add phase shift to the veloc-

ity controller closed-loop frequency response and can lengthen set-tling time. Therefore, a low or zero-value integral gain is sometimes

Figure 15: Velocity loop block diagram

Currentcontroller

Velocitycommand

PROPORTIONAL PLUS

INTEGRAL CONTROLLER

-ω*m

IGAIN

S

PGAIN

I*1

TS + 1

I T

TL

Load torquedisturbance

KT1

JS

1

S

ωm θm

Inertialload

Motor velocity


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used with very high bandwidth positioncontrollers in point-to-point positioningapplications, while a significant integral

gain value is used with contouring applica-tions to provide high stiffness.

In practice, the velocity controller tuningis rarely determined solely by calculation.Often tuning is done manually through trial-and-error, with the motor connected to theactual load. This tuning is simplified thoughthe use of sophisticated set-up softwareand a PC connected to the servo drive.The ElectroCraft CompletePower TM Set-UpSoftware Utility provides the user a manualtuning mode that allows a small step ve-locity command to be applied to the drivewhile the motor is attached to the actual

load. Within the software utility, real-time adjustment of the velocityloop gains can then be made while observing oscilloscope waveformson the PC to optimize the velocity loop tuning for the application. Atypical example of velocity responses to the step changes in veloc-ity command and load torque for a poorly tuned velocity loop and awell-tuned velocity loop are shown in Figure 16. Tuning should be per-formed with “small signal” responses—which means that the current

stays away from the current limit at all times.

Position regulatorand tuning guidelines

Position control applications typically fall into two basic catego-ries: contouring and point-to-point. Contouring applications requirethat the actual position follow the commanded position in a verypredictable manner — with high stiffness to reject external torquedisturbances. Notice that predictability is required, but this does notnecessarily mean that position error must be zero at all times.

The other type of position control—point-to-point positioning—

is typically defined by move time, settling time, and velocity profile,not paths.Independent of the positioning application, the form of a simple

position controller is shown in Figure 17. The velocity controller hasbeen approximated by a unity gain and a first-order lag with a timeconstant equal to the velocity loop -45° phase shift bandwidth.

A position controller with only proportional gain K is very com-mon (particularly for contouring applications), and the position loopresponse can be easily calculated for a certain crossover frequency orgain. The open-loop frequency response for the proportional positioncontroller is shown in Figure 18. The crossover frequency is related to

the common method of expressing gain:2.65 Hz = 16.66 rad/sec = 1 inch/min./mil = velocity/position error

Figure 17: Position controller block diagram

VELOCITYCONTROLLERPOSITION COMMAND

ACTUAL POSITION

θ*

-

1

TS + 1

K1

S

θ



Figure 16: Velocity responses to poorly tuned and well-tuned velocity loops

Well tuned

V e l o c i t y

TACH RESPONSETO VELOCITY COMMAND

Poorly tuned

Well tuned

Poorly tuned

TACH RESPONSETO TORQUE DISTURBANCE


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Where 1 inch/min./mil also equals 1meter/min./mm. In most position control-lers, the Kp gain is related to position loop

gain as shown in Figure 18. A general po-sition loop regulator is more complicatedthan the simple proportional gain-onlytype. The general position loop regula-tor is Proportional-Integral-Derivative withfeed-forward (velocity and acceleration)and is illustrated in Figure 19. Following isa brief explanation of the purpose for thefive adjustment terms.

The proportional gain Kp is the mostimportant term and generates a velocitycommand proportional to position error.In other words, if just Kp gain is present,motion is only possible if a position errorexists. In fact, higher velocities result inproportionally higher position followingerror. Only increasing Kp gain can reducethe position following error. However, be-cause the velocity loop has a given -45°phase-shift bandwidth, Kp gains that pushposition-loop bandwidth above about 1/3

of this velocity loop -45° phase-shift band-width cause actual position to overshootthe commanded position — which is usu-ally undesirable.

The feed-forward gain Kff generates a velocity com-mand signal proportional to the derivative of the positioncommand. Therefore, if there is no change in the posi-tion command, then the feed-forward command is alwayszero. Ideally, 100% feed-forward provides the exact veloc-ity command without the need for any position error. Inpractice, actual systems including loads are not ideal, so

a more conservative setting of feed-forward gain is oftentaken (100% or less) because too much feed-forward gaincauses actual position to overshoot the commanded position. Be-cause the feed-forward command is generated open loop, there is noeffect on the position loop stability. The function of the feed-forwardcommand is to significantly reduce the constant velocity followingerror even though the Kp gain is maintained at a proper level for sta-bility. Figure 20 shows an example of the feed-forward velocity com-mand effect on position following error when making a trapezoidalvelocity profile move.

The derivative gain Kd as shown in Figure 19 creates a command

signal that is proportional to the derivative of actual position feedback.The derivative term is used in two different situations. One situation

Figure 18: Position controller response and Kp gain

Crossover = K

Rad/sec

POSITION CONTROLLER OPEN-LOOPFREQUENCY RESPONSE

r = K

Radsec

rossov

1m/min.

mm=1

in./min.

mil=16.66

rad

sec≅ 2.65 Hz

D e c i b e l s

m/min.

mm=

in./min.

mil= Counts ×

rpm

Volt

×

Volts

bit

×

K p

60×16.66

Typically four times thenumber of encoder lines

per revolution

. .

Position loop gain

Velocity loop scalingmotor rpm per command volts

Full-scale velocitycommand divided by 2n

where n = DAC resolution

Figure 20: Effect of velocity feedforward

on position error profile

2.0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4

Time (sec)

P o s i t i o n

e r r o r

( r a d s )

No velocity feedforward

75% velocity feedforward

Figure 19: General structure of position loop

Positioncommand

Fgain • S

Kd S

1

S

S

θ*

Velocity loopActual position

θ

S

KI

KP

Kff

Derivative gain = Kd


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occurs when the normal velocity servo isreplaced by a torque (current) servo, whichrequires that the derivative term be used to

provide the necessary damping in the formof a velocity feedback signal. The other sit-uation occurs with a normal velocity servoto reduce overshooting of the position ifa higher-than-normal Kp gain is necessary.

The next gain term is the acceleration feed-forward gain, Fgain,which scales the second derivative of position command. This termallows position following error to be reduced when the velocity ischanging. The acceleration feed-forward term is useful in combina-tion with the velocity feed-forward term when trying to maintain a lowfollowing error at all times — which can be useful in tracking applica-tions, or if a fast settling time is required.

The last term is the integral gain, Ki, which can provide a velocitycommand signal to reduce static position errors to zero. Integral gainprovides stiffness against torque disturbances and friction torquesand is usually handled in the velocity controller. Therefore, integralgain in the position controller is normally avoided except for specialsituations. Because integral gain causes overshooting, some positioncontrollers with integral gain allow the integrator to only be activeduring certain conditions — such as when the position command isnot changing, and when the actual position is very close to the com-

manded position.

Application guidelines for sinusoidal brushlessservomotors and drive amplifiers

The trapezoidal or square wave current brushless servo is char-acterized the same as a brush-type servo drive and is generally wellunderstood. The principles of sizing the sinusoidal brushless servodrive are similar, but there are some differences which merit review.Therefore, this section provides the guidelines for applying and sizinga servo drive using the sinusoidal brushless servo drive as an exam-ple. The basic structure of the servo system to be sized is illustrated

in Figure 21.Many laborious calculations are made in the typical sizing process.Calculations include reected load inertias, RMS and peak torques,average and peak currents, RMS maximum speeds, and so on.

Mechanical transmissions, gearing,and torsional resonances

The most commonly encountered mechanical transmissions canbe analyzed for many applications and are shown in Figure 22. Thechoice of mechanical transmission is determined by application re-quirements. Useful equations in Figure 22 characterize the various

transmission types.Another important decision is the choice of rotary gearing (if any)



Figure 21: Components of a basic servo system

F r o m A

C

s u p p l y

5 0 / 6 0 H z Mandatory

NEC branchcircuit

protection

Optionaltransformer

VL2

VL1

VL3

+

-Motor

Rectifier

Dissipativeshunt

regulator

VBUS

PWM inverter

VS

VR

VT


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between the motor shaft andthe mechanical transmission/load to be moved. There are

many reasons for consideringgear reduction in a motioncontrol application such as:

Reducing inertial mismatchbetween motor and load. Inertial mismatch should beminimized for high-perfor-mance applications, and is 1:1for best results. Gearing re-duces the reflected inertia bythe square of the reduction ra-tio. For example, a 10:1 gearratio reduces reflected loadinertia by 10 squared or 100.However, do not fail to includethe extra inertia of couplings,pulleys, or gears, as these canbe significant and offset theinertia reduction. The addi-tion of couplings or thin drive

shafts will increase the compli-ance of the system as the mo-tor winds up the transmissionlike a spring, this will result inresonances as the load movesand the spring is unwound. Also note that adding a gearbox will addbacklash to the system, effectively removing the load from the mo-tor within the backlash angle. This can lead to motor high frequencyinstability at standstill, causing excess motor heating and failure toaccurately track contoured moves.

• High torque and low-speed applications. Most conventional brush-less servomotors can operate at high speeds, such as 3,000 to 6,000rpm. The torque increase due to the gear reduction (motor torque ismultiplied by the gear ratio) is used to keep the motor physical size assmall as possible. This is because the continuous torque rating (and nothorsepower) determines the motor size and cost. Horsepower is equalto torque x speed. Therefore, for minimum motor size and inertia, mo-tor speed should be as high as possible.

• Limited space. If there are space constraints, the use of gearingcan allow a smaller overall package or it can allow the motor to be

repositioned in a different location or orientation.Many different factors need to be taken into account when select-

Figure 22: Classification of common mechanical transmissions

GEARBOX OR BELT DRIVE TRANSMISSION

Motorθm, ωm, Jm, Tm




I l l u s t r a t i o n s c o u r t e s y M

o t i o n S y s t e m D e s i g n m a g a z i n e

Load

Load m

Load

LEAD SCREW TRANSMISSION

BELT-AND-PULLEY, CONVEYOR, TANGENTIAL, OR RACK-AND-PINION TRANSMISSION

Force

Gear ratio = N = Motor velocity

Load velocity

θm = N θ L and ωm = N ω L1

NT L = Load torque reflected to motor

One revolution = 2π ⋅ radians

θ = Angular distance (rad)

ω = Angular velocity (rad/sec)

J = Moment of inertia (lb- in.- sec2)

T = Torque

Velocity = v (in./min.)

Distance = x (in.)

Pitch = P =Revolutions

Leadscrew length

Reflected load inertia = J L

= m1

2πP

⎛

⎝⎜

⎞

⎠⎟

2

= W

g

1

2πP

⎛

⎝⎜

⎞

⎠⎟

2

Load torque = T L = F

2πP

θ L = 2πPx and ω L =

2πPv

60

RPM = n = Pv

W = Weight

Gravity constant = g = 386 in./sec2

ForceLoad m Drive radius r

Drive radius r

θ L = x

r and ω L =

v

60r

rpm = n = v

2πr

J L = Reflected load inertia = mr2

= W

gr

2 = m( v

2πn)2

T L = Load torque = Fr

Acceleration torque = T = J α

Where α = rad

sec2

1 hp= 746 Watts

Power (Watts) = T (Nm)×ω (rad/sec)

Power (hp) = T (lb- in.)× n (rpm)

63,024


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16

ing gearing technology. The first step for a high-performance servoapplication is to determine which gearing technology best fits theapplication—by answering the following questions:1. What are thephysical limitations for the application? For example, into what en-

velope must the motor/gearing fit, and must the motor be positionedat a right angle to the load? The three basic orientations are parallel,in-line, and right angle gearing.

2. What reduction ratio is required? After deciding on the basicclassification, the next factor to consider is the reduction ratio—il-lustrated in Figure 23 for the most common gearing technologies.For example, timing belts are generally not used for ratios above 3:1,while harmonic type gearing is usually not available with ratios belowabout 40:1.

At this point in the selection process, the performance param-

eters of the gearing technologies are examined to further narrow thechoice. Figure 23 includes the most important performance param-eters and their relative ranking. These are only approximate rankingsand variations do exist.

For high-performance servo applications, three of the perfor -mance parameters are of particular importance and need additionalexplanation: accuracy, torque-carrying capability, and reliability.

Accuracy is often equated to backlash but there is more that mustbe considered. Backlash is the space between mating parts orgears and it is usually specified in degrees or arc minutes. Normal-

ly, gears need backlash to run reliably because space is needed toaccommodate lubrication, manufacturing errors, and eccentricities

Figure 23: Classification of common mechanical transmissions

Gearing

orientaation

Technology Physical parameters Performance Typical applications

Ratio range Compactness Backlash Stiffness Torquerange

Smoothness Effic iency Maximuminput rpm

Inertia Price

Parallel

Timing bel t


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in the gears and other components.The tradeoff is to keep the backlash aslow as possible without sacrificing ef-

ficiency or other performance features.Excessive backlash can cause position-ing error and instability so low-back-lash gearing is generally preferred withbrushless servo drives.

Other components of accuracy in-clude stiffness (compliance), transmissionerror, and output smoothness. Stiffness is the amount of deflectionmeasured when a load is applied to the reducer. Insufficient stiffnesswill result in positioning errors or torsional resonance problems. Trans-mission error is a measure of how accurately the motor input shaft po-sition is translated through the reducer. Gear ratios are seldom exactand positional inaccuracies are also caused by gear imperfections. Thetorque and speed output must also be smooth and free from ripple ifthe input speed and torque is smooth and ripple-free. Eccentric-typereducers (such as harmonic or cycloidal gears) typically have outputripple under some operating conditions; timing belts and spur, bevel,planetary, or worm gearing are less susceptible to this characteristic.

The torque-carrying capability varies among the different types ofreducers and is usually related to the frame size within any one type

of technology. The objective is to ensure that the chosen reductionmethod has ample torque-carrying capability for the application.Some applications are light-duty and do not place heavy torque de-mands on the reducer. The torque-carrying capability of the reducershould have a 25 to 50% safety margin to ensure a long life.

Finally, reliability is primarily a function of the reducer componentquality, efciency, and the life expectancy for the reducer type. Forexample, timing belts usually wear out faster than spur gears. Wormgears, due to their sliding gear action, also usually wear out fasterthan spur gears. Preloaded contact members, as found in harmonic

and cycloidal gearing, wear out faster than the other forms of gear-ing. Timing belt gearing should only be of the HTD type to ensurehigh stiffness while V belts, non-HTD type timing belts, and chainsshould be avoided with high performance servo drives.

High performance servo drives typically are applied with high-velocity loop bandwidths. In practice, a torsional resonance existsdue to mechanical compliance between the load inertia and the mo-tor inertia. A model of this mechanical system and the open-loop fre-quency response is shown in Figure 24. The compliance is modeledas a torsional spring with its inertia and damping neglected. Bestresults are obtained if the torsional resonant frequency is kept as

high as practical. Torsional stiffness K of a solid round shaft is propor-tional to the fourth power of the diameter and inversely proportional

Figure 24: Mechanical model of motor and load with compliant connection and open-loop frequency response

MOTOR LOAD


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18

to the length. Therefore, torsional stiffness is dramaticallyimproved by selecting a motor and other mechanical trans-mission element with the largest shaft diameter.

A common torsional problem is improper coupling ofthe motor to the load. A key-type coupling should be avoid-ed if possible; a compression-type coupling that is clampedas close as possible to the motor flange is best. Axial shaftloading due to impact shocks as a result of hammering thecoupling on the shaft is absolutely not allowed, as this candamage the motor bearings or break the encoder disc.

Finally, if some torsional resonance is unavoidable and isaffecting the servo system performance, many suppliers canprovide electronic damping schemes in the servo drives thathelp minimize the torsional resonance effect.

Motion profile considerationsWith the load defined, the worst-case velocity-time or

velocity-distance prole (as in Figure 25) is analyzed to de-termine the following significant information:

• RMS and peak torque requirement of the motor• RMS and maximum speed requirement of the motor• Average and peak current requirement of the amplier• Average and peak motoring power• Average and peak generating power

Arbitrary motion profiles can be defined and, alongwith the mechanical system information, are used to calcu-late the significant sizing information. Different mechanicalparameters (such as gearing), motion proles, and motorchoices can be quickly and easily analyzed for the optimumselection of a motor/amplifier combination.

Sinusoidal brushless motor specificationsElectroCraft specifies the important motor constants for

a three-phase sinusoidal back-EMF motor as:Ke = line-to-line peak volts/KRPMKt = in-lb/peak phase amps

R = line-to-line resistance (Ohms)L = line-to-line inductance (Henrys)The peak value of the line-to-line voltage or phase amps is de-

ned as the zero to peak value of the sine wave. For reference, theRMS value of a sine wave is the peak value divided by the square rootof two. Also, Kt is related to Ke:

Kt = Ke/11.834 for a DC motorKt = Ke/13.662 for a sinusoidal current with a sinusoidal-EMF

brushless motor.The torque-speed curve of a brushless servo system is shown in

Figure 26. The continuous operating region is defined by operating

the motor to the maximum allowable winding temperature at variousspeeds and recording the output torque. The continuous torque rat-

Figure 26: Torque-speed curve of brushless system

Figure 25: Example of velocity and torque profile

for incremental motion application

G e

n e r a t i n g

M o t o r i n g

Torque profile

Motor shaft power profile

Velocity profile RMS velocity

RMS torque

Time

Time

Time

Averagemotoring power

Averagegenerating power

Peak motoring power

Peakgenerating power




19/26


ing is worst case if the motor is in free air during thetest. ElectroCraft brushless motors are normally ratedmounted to an aluminum plate of a specified dimen-

sion. Notice that the continuous torque output of themotor decreases as the speed is increased. Eventu-ally the continuous torque is reduced to zero, this oc-curs when the BEMF voltage and winding inductancelimit the current to a level where the motor generatedtorque matches the motors internal drag torque frombearing friction and windage. The low-speed portion of the peakcurve is usually limited by the amplifier peak current rating; avail-able amplifier voltage usually limits the high-speed portion ofthe peak torque curve. As the speed increases, a voltage limit isreached which causes peak torque to roll off at higher speeds.

To better understand the torque-speed characteristics of thesinusoidal brushless motor, refer to the steady state per phasemodel shown in Figure 27. The voltage and current quantities aresinusoidal and are related as shown in Figure 28.

Notice how the voltage drop across the inductance beginsto dominate as speed (or frequency) increases, which eventuallycauses the peak torque to roll off as mentioned before.

By knowing the maximum available line-to-neutral motor ter -minal volts, the peak torque characteristic as a function of speedcan be calculated using the per phase motor model. The maxi-

mum line-to-neutral volts can be calculated using the followingrelationships. (Refer to Figure 28.) Vbus [DC volts] = 2 x V

L1-L2[volts RMS line-to-line]

Maximum VRN [peak volts] = Vbus/3Once completing the work to calculate the motor and ampli-

fier requirements, the torque-speed curves are used to select theproper ElectroCraft motor/amplifier combination.

The continuous motor torque should be available at the RMSvelocity of the motion profile. Some allowance should be made for mo-tor Kt and Ke tolerance and for voltage drop due to low line conditionsand transformer load regulation.

Figure 25 shows the motoring and generating power for this in-cremental motion profile. Only the motoring power is supplied fromthe AC power line, as ElectroCraft servo drives do not regeneratepower to the AC power line.

Actual AC power requirements are higher than the average motor-shaft power due to power losses in the motor, drive, and transformer.A multiplication safety factor of about two is used to account for thelosses and power factor. Many suppliers provide load regulation curvesfor their standard transformers; one such curve is shown in Figure 29.

In servo applications, the peak power requirements for goodtransformer voltage regulation usually require selection of a power

transformer that is oversized for continuous power requirements.Conservatively sized motor/amplifier operates longer without failure

Figure 27: Per-phase model of sinusoidal brushless motor

Figure 28: Voltage relationships

for sinusoidal brushless motors

Figure 29: Transformer load regulation curve


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20

and reduces application problems that are caused by under sizingthe motor/amplifier combination.

Up to now, it has been assumed that the motion profile cycle time

is short compared to the motor thermal time constant. The motorthermal time constant is defined as the time to reach 63.2% of therated temperature rise when rated current is supplied to the motor.The motor thermally averages the power losses and reaches a con-stant steady state temperature. Some applications apply power andremove power to the motor with cycle times that are similar to themotor thermal time constant. In these cases, the motor temperaturewill fluctuate up and down as the power is applied and removed. Toproperly size these applications, duty cycle curves can be providedfor the motors as shown in Figure 30. For example, the operatingpoint labeled A in Figure 30 allows the motor to repetitively produce200% continuous torque for about 6 minutes and no torque for about24 minutes. The amplifier has a very short thermal time constant com-pared to the motor so the amplifier must be oversized to handle thepeak motor torque on a continuous basis in these types of overloadapplications.

Brushless amplifier dissipative shuntThe final consideration in sizing the amplifier concerns the dis-

sipative shunt regulator shown in Figure 21. Braking the motor re-turns energy stored in the rotating mechanical mass to the amplifier

power supply. Because the power supply is not able to regeneratethis energy back to the AC input supply, the power supply capacitoris charged up beyond its normal level. If the excess braking energy islow, then the capacitor may be able to absorb the excess energy andsimply return it to the motor during the next motoring period. How-ever, if the excess energy is high, then a clamp circuit is used to limitthe bus voltage to a safe level and to dissipate the excess energy asheat in a power resistor.

The shunt regulator is specified to handle a peak power and acontinuous power. If the peak power is exceeded, then the clamp cir-cuit will be unable to limit the voltage to a safe level and the amplifier

turns off. In practice, if peak shunt power is being exceeded, check tosee if the current limit can be lowered or if the deceleration time canbe lengthened. Applications that frequently stop and start with highinertia and high speed should be studied closely to see if continu-ous shunt power is exceeded. Vertical applications with a gravity load(especially ones without any form of counterbalance) must be verycarefully considered as to continuous shunt power.

ElectroCraft drives have the ability to add external shunt resistorsthat extend the continuous and peak shunt power of the system. Fig-ure 25 shows the generating power for an incremental motion pro-file: Actual dissipated power is less than the regenerated motor shaft

power due to motor losses, amplifier losses, and energy absorbed bythe bus capacitor.

Figure 30: Duty cycle characteristics (motor only)

90

80

70

60

50

40

30

20

10

01 3 6 10 30 60 100

D u t y

( P e r c e n t )

ON time (Minutes)Motor thermal time constant = 47 min.

110%

120%

130%

200%

180%

160%

140%




21/26


Electrical noise considerationsPerhaps no other subject discussed so far in this handbook is

as misunderstood as electrical noise. Nothing strikes fear in the in-

dustrial equipment user more than being told by the drive vendor,“You have a noise problem.” While the subject is complex and thetheory can (and does) easily ll books, this section provides someguidelines that can minimize noise problems.

The majority of installations exhibit no noise problems. However,filtering and shielding guidelines are countermeasures if problemsarise. In contrast, grounding, bonding guidelines combined withgood panel layout are simply good practice and should be followedin all installations.

There are two characteristics to electrical noise: the genera-tion or emission of electromagnetic interference (EMI), and the re-sponse, or immunity to EMI. The degree to which a device emits noEMI, and is immune to EMI, is called the device’s electromagneticcompatibility.

Figure 31 shows the commonly used EMI model. The model con-sists of an EMI source, a coupling mechanism, and an EMI victim.Devices such as servo drives and computers (which contain switchingpower supplies and microprocessors) are EMI sources. The mecha-nisms for the coupling of energy between the source and victim areconduction and radiation. Victim equipment can be any electromag-netic device that is adversely affected by the EMI coupled to it.

Equipment immunity is primarily determined by its design, buthow one wires and grounds the device is also critical for EMI immu-nity. Therefore, selecting equipment designed and tested for indus-trial environments is paramount. Selecting equipment that is certi-fied or designed to meet industrial immunity standards is a goodstart. Laying out the electrical panel in “Clean” and “Dirty” zones tosegregate motor power wires from sensitive analog inputs etc. willcost very little in planning time compared to the cost of sending anengineer to site to nd an intermittent EMI event.

Another tip: In industrial environments, use encoders with differ-ential line driver outputs rather than single-ended outputs, and use

digital inputs/outputs with electrical isolation, such as those pro-vided with optocouplers.Reconsider Figure 31. This EMI model provides only three op-

tions to eliminate the emission problem. The EMI source could bereduced, which in the case of servo drives would require slowingpower semiconductor switching speeds. However, this degradesdrive performance with respect to heat dissipation and speed/torque regulation.

Another possibility is to harden the victim equipment, which maynot be possible or practical. The final and most realistic solution isto reduce the coupling mechanism between the source and victim

—with filtering, shielding, and grounding.

Figure 31: EMI soure-victim model

i i

llili i

EMI source EMI victim

EMI victim

Conducted EMI

Radiated EMI


22/26

22

FilteringAs mentioned, high-frequency energy can be coupled

between circuits via radiation or conduction. The AC power

wiring is one of the most important paths for both types ofcoupling mechanisms. The AC line can conduct noise into thedrive from other devices, or can emit conducted noise directlyinto other devices. It can also act as an antenna and transmitor receive noise between the drive and other devices.

One method of improving the EMC characteristics of adrive is to use an isolation AC power transformer to feedthe amplifier its input power. This minimizes inrush currentson power-up, and provides electrical isolation. In addition,it provides common mode filtering, though the effect is lim-ited in frequency by the inter-winding capacitance.

Note: “Common mode” noise is present on all conduc-tors referenced to ground while “differential mode” noise ispresent on one conductor referenced to another conductor.

An alternative is to use AC line filters to reduce the con-ducted EMI emitting from the drive. This allows nearby equipment tooperate undisturbed. In most cases, an AC line filter is not requiredunless other sensitive circuits are powered off the same AC branch cir-cuit. The basic operating principle is to minimize the high frequencypower transfer through the filter.

An effective filter achieves this by using capacitors and inductors

to mismatch the source impedance (AC line) and the load impedance(drive) at high frequencies.The machine builder is responsible for the suitability of the filter

selection in a specific application.Selection of the proper filter is only the first step in reducing con-

ducted emissions. Correct filter installation is crucial to achieving bothEMI attenuation and to ensure safety. All of the following guidelinesshould be met for effective filter use.

1. The filter should be mounted to a grounded conductive surface toestablish a high frequency (HF) connection to that surface. To achieve

the HF ground, the surface interface between the lter and structuremust be free of paint or any other insulator. This may require paintremoval from the inside of a cabinet. A wire should not be used toground the filter because it will act as an antenna when ground cur-rents are present.

1. The filter must be mounted close to the drive input terminals. Ifthe distance exceeds 1 ft, then a strap should be used to connect thedrive and filter, rather than a wire. 2. The wires connecting the AC source to the filter should be shieldedfrom, or at least separated from, the wires (or strap) connecting the

drive to the filter. If the connections are not segregated from each oth-er, then the EMI on the drive side of the lter can couple over to the

Figure 32: AC line filter installation

Conducted

EMI

Radiated EMI

Poor setup

DriveConductedEMI

AC line

Radiated EMI

Good setup

AC line

Drive

Radiated

EMIConducted

EMIFilter

Filter

Figure 33: Single-point ground types

Series connection Parallel connection

Circuit

One Circuit

One

Circuit

Two

Circuit

Two

Circuit

ThreeCircuit

Three




23/26


source side of the filter, thereby reducing, or eliminating the filtereffectiveness. The coupling mechanism can be radiation, or straycapacitance between the wires. The best method of achieving

this is to mount the filter where the AC power enters the enclo-sure. Figure 32 shows a good installation and a poor installation.

When multiple power cables enter an enclosure, an unfil-tered line can contaminate a filtered line external to the enclo-sure. Therefore all lines must be filtered to be effective.The situation is similar to a leaky boat. All the holes mustbe plugged in order to prevent sinking.

WARNING: The filter must be grounded for safety be-fore applying power due to the leakage currents. Failure toproperly ground the filter can be hazardous.

The only reasonable filtering at the drive output termi-nals is the use of inductance. (Capacitors would slow theoutput switching, and deteriorate the drive performance.)A common mode choke can be used to reduce the HFvoltage at the drive output to reduce emission couplingthrough the drive back to the AC line. However, the motorcable still carries a large HF voltage and current. In fact,motor cable length directly affects the amplitude and fre-quency of emissions on the AC line. Therefore, it is very im-portant to segregate the motor cable from the AC powercable, or to use a shielded motor cable. For applications

where long motor cables are required, the need for AC lineltering increases. More information on cable shieldingand segregation is contained in the section on shielding.

GroundingHigh-frequency (HF) grounding is different from safety grounding.

A long wire is sufficient for a safety ground, but is completely ineffec-tive as a HF ground due to the wire inductance. As a rule of thumb,a wire has an inductance of 20 nH/in., regardless of diameter. At lowfrequencies it acts as constant impedance; at intermediate frequen-cies as an inductor; and at high frequencies as an antenna. The use

of ground straps is a better alternative to wires. However, the lengthto width ratio must be 5:1 or better yet 3:1 to remain a good highfrequency connection.

The ground system’s primary purpose is to function as a returncurrent path. It is commonly thought of as an equipotential circuit ref-erence point, but different locations in a ground system may be at dif-ferent potentials. This is due to the return current flowing through theground systems finite impedance. In a sense, ground systems are thesewer systems of electronics and as such are sometimes neglected.

The primary objective of a high frequency ground system is to pro-vide a well-dened path for HF currents, and minimize the loop area of

the HF current paths. It is also important to separate HF grounds fromsensitive circuits’ grounds. A single-point parallel-connected ground

Figure 34: Encoder shielding method

for brushless servomotors

Brushless motor

Encoder cable

Motorcase

Amplifier

Shield

Figure 35: Motor power winding methods

to minimize noise emissions

Brushless motorAmplifier

Shield

Motor case

RS T

Chassis

R

ST

To single point —earth common

Twisted together


Chassis

R

ST

To single point —earth common

Twisted together


Motor case

RS T

Chassis

R

ST

To single point —

earth common

Twisted together

Motor case

RS T

Common mode choke(10 to 20 turns on common

ferrite toroidal core)


24/26

24

system is recommended. Figure 33 showssingle-point grounds for both series (daisychain) and parallel (separate) connections.

A ground bus bar or plane should beused as the “single point” at which circuitsare grounded. This minimizes common(ground) impedance noise coupling. Thisground bus bar (GBB) should be connectedto the AC ground, and if necessary, to theenclosure. All circuits or subsystems shouldbe connected to the GBB by separate con-nections. These connections should be asshort as possible, and straps should be usedif possible. The motor ground conductormust return to the ground terminal on thedrive, not to the GBB.

Shielding and segregationThe primary propagation route for EMI

emissions from a drive is through cabling.The EMI radiating from the drive enclosureitself drops off very quickly with distance.The cables conduct the EMI to other devic-es, and can also re-radiate the EMI. There-

fore, cable segregation and shielding canbe important to reducing emissions. Cableshielding can also increase the level of im-munity of a drive.

The following suggestions are recom-mended for all installations, because theyare inexpensive to implement.

Signal cables (encoder, serial, analog) should be routed away fromthe motor cable and power wiring. Separate steel conduit can be usedto provide shielding between the signal and power wiring. Do notroute signal and power wiring through common junctions or raceways.

Signal cables from other circuits should not pass within 1 ft of the drive.The length of parallel runs between other circuit cables and themotor or power cable should be minimized. A rule of thumb is 1 ft ofseparation for each 30 ft of parallel run. The 1-ft separation can bereduced if the parallel run is less than 3 ft. Cable intersections shouldalways occur at right angles to minimize magnetic coupling.

Do not route any cables connected to the drive directly over drivevent openings. Otherwise, the cables will pick up the higher levels ofemissions leaked through the vent slots.

If you are constructing your own motor cable, a four-conductorcable should be used, with the four conductors twisted. The ground

conductor must be attached to the motor and drive earth terminals.The encoder mounted on the brushless servomotor should be

Figure 36: Conversion tables for motion and loads

EQUATIONS FOR STRAIGHT-LINE MOTION WITH CONSTANT ACCELERATION

v t = v i + at

x t = x i +1

2(v i + v f )t

v f 2= v i

2+ 2a( x f − x i )

T rms =T

1

2t 1 + T

2

2t 2 + T 3

2t 3 + T 4

2t 4

t 1 + t 2 + t 3 + t 4

where x f = Final position

x i = Initial position

v f = Final velocity

v i = Initial velocity

a = Acceleration

t = Time

Aside = L × h

V = L × h × w

J =W

12g× h2 + w 2( )

Aend = π ⋅ r2

V = Aend × L

J =mD2

8=Wr2

2g

=π Lρ ⋅ r

4

2g

Aend =π

4× Do

2− Di

2( )V = Aend × L

J =m

8× Do

2+ Di

2( ) =W

2g× ro

2+ ri

2( )

=π Lρ

2g× ro

4− ri

4( )

AREA, VOLUME, AND INERTIA FOR COMMON SHAPES

V e l o c i t y

Time

T o r q u e

T1

T2T3

T4

t1 t2 t3 t4

LL L

H

W

D = 2r

Do = 2ro

Di = 2ri

V = Volume (in.3)

L = Length (in.)

h = Height (in.)

w = Width (in.)

J = Inertia (in./lb/sec2)

m = Mass (lb/m)

W = Weight (lb)

D = Diameter (in.)

r = Radius (in.)

g = Gravity (386 in/sec2)

ρ = Density (lb/in.3)

A = Area (in.2)

π = 3.14




25/26


connected to the amplifier with acable using multiple twisted wirepairs and an overall cable shield

Otherwise noise on the encodersignals can cause drive faults inthe drive.

If EMI problems persist, ad-ditional counter measures can beattempted. Here are several sug-gestions for system modifications.

Placing a ferrite “donut” arounda signal cable may help. The ferriteattenuates common mode noisebut does nothing for differentialmode noise. Connecting cableshields directly to the drive chas-sis instead of the cable connectorscan reduce the effect of externalEMI on the drive operation.

Use a shielded motor cableterminated at the circular sectionat both ends. The shield shouldbe connected to the drive earthterminal, or chassis at the drive

end, and the motor frame at themotor end. The coaxial configura-tion provides magnetic shielding,and the shield provides a returnpath for HF currents, which are ca-pacitively coupled from the motorwindings to the frame. If power frequency circulating currents are anissue, a 250-VAC capacitor should be used at one of the connectionsto block the 50/60 Hz currents, but pass the HF currents. Figure 35 il-lustrates all the motor cable options discussed in this section.

Suppress each switched inductive device that is near the servo

amplifier. This includes solenoids, relay coils, starter coils and AC mo-tors (such as motor driven mechanical timers). DC coils should besuppressed with a “freewheeling” diode connected across the coil inthe non-conducting direction. AC coils should be suppressed with RCfilters: A 220 ohm 1/2 watt resistor in series with a 1/2 microfarad, 600volt capacitor is commonly used.

Figure 37: Conversion tables for motion and loads — for various units

Conversion of length

Conversion of torque

Conversion of moment of inertia

Note: This handbook section presents some guidelines that can minimize noise problems.However, equipment EMC performance must meet regulatory requirements in various parts ofthe world, specically in the European Union. It is the responsibility of the machine builder toensure that a machine meets the appropriate requirements as installed.


26/26

ElectroCraft, Inc. is a global provider of fractional-horsepowermotor and motion control solutions for both industrial and com-mercial applications. Capitalizing on many years of experiencehas resulted in a broad family of motor and motion control com-ponents available. ElectroCraft products include: • Sinusoidal brushless servomotors utilizing either the high energyproduct neodymium iron boron permanent magnets for the low-est rotor inertias or the cost-effective ferrite permanent magnetsfor medium rotor inertias.

• Digital sinusoidal brushless servo ampliers designed to pro-vide today’s OEM with maximum brushless servo performance atthe lowest possible cost. The ACE500 Series utilizes the latest inDSP-based drive design architecture to provide software select-

able torque, velocity, and position mode (optional) operation.Sine wave commutation using encoder feedback provides smoothtorque at low speeds for demanding motion control requirementsfound in robotic, direct drive, and linear motor applications.

• Cost effective analog and two-quadrant brushless DC speedcontrols. These drives include ramp generator and braking func-tions for controlled acceleration and deceleration. Mode of opera-tion is set by simple DIP switches.

All of the above components can be combined from a single

manufacturer to produce high performance motion controlsystems for a variety of automation tasks. Typical applicationsinclude machine tools, EDM machines, coil winding equipment,medical equipment, press feeders, thermoforming machines,robotics, automotive assembly and machining equipment,postal sorting machines, material handling equipment, packag-ing equipment, and other types of specialty machines requiringprecise control of torque, velocity and position.

ElectroCraft is headquartered in Dover, New Hampshire withoperations in the United States, Europe, and Asia.

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