Nippon Pulse Stepper Motor Basics Presentation

Stepper Motors

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What is a Stepper Motor?

• The stepper motor is a motor which takes input pulses and then takes proportional steps to input these signals. You can use for positioning and/or speed control for most any applications. The stepper motor needs a power circuit and a sequence circuit for changing phase.



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What is a Stepper Motor? <Stepper with Peripheral Construction>

Sequencer

Power Tr.

CPU or

Motion- Control-Chip

Vm (Motor Power)<Driver><Controller>

<Motor>

Vcc (Logic power) ELECTROMATE

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What is a Stepper Motor? <Applications>• Medical: Infusion Pump, Brad Test, X-ray,

Dialysis, DNA Extraction, Pump• Semiconductor: Masking, Etching, Wafer

Handling, Test-equipment, Die-Bonder• FA: Pick & Place, NC Machine, X-Y-Z stage • OA: Printer, Fax, Scanner• HA: HVAC, Cleaner Robot• Other: Vending machine ELECTROMATE


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Stepper and Synchronous MotorsMovement Generation• Step Mode• Torque Generation• Characteristics• Reduced Duty Cycle• Synchronous Motor



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N S

N

S

S

NN S

S

N

S

NS N

S

N

SN

S N

N

S

S

NN S

N

S

S

NN S

S

N

S

NS N

S

N

SN

for the next step invert magnetic field in the other coilone step ⇒ invert magnetic field in 1 coilrotor follows the stator field

Movement Generation

S N

N

S

S

N

A stepper motor always needs electronic control.step angle depends on number of poles -> fixed by construction



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PhA1 (=GND) PhA2 (=open)+

SN

PhA1 (=open) PhA2 (=GND)+

NS

Movement Generation Unipolar Principle

• every coil end has only one polarity (”+” or ”ground (-)”)

• motor coils are unipolar



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PhA1 PhA2

S

GND+

N

Movement Generation Bipolar Principle

• every coil end will be positive (”+”) or ground (”-”)

• motor coils are bipolar

S

GND +

N ELECTROMATEToll Free Phone (877) SERVO98


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Movement Generation Unipolar Drive

• low side switches

+

GND

I

+

GND

I

• 4 switches for the whole motor



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Movement Generation Bipolar Drive

• 2 full bridges (or H-bridges) are needed = 8 switches

• switches in bridge configuration

+

GND

I

+

GND

I



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Movement Generation Tin Can Motor



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NS

N

S

N

S

N

SN

SN

S

N

S

N

S NS

N

S

N

S

N

S

NS

N

S

N

S

N

S

Movement Generation Tin Can Motor - Step Generation

N

N

N N

S S

S SS

S

S S

N N

N N

front side teethback side teeth

if there is only 1 magnetic system...N

SN

SNS

N

S N

SN

SN

SN

SN

SN

S

N

S

N

S

N

N

N N

S S

S SS

S

S S

N N

N NN

N

N N

S S

S SS

S

S S

N N

N N

NS

N

S

N

S

N

S

NS

NS

NS

NS

NS

NSN

S

N SN

SN

S

N

S

N

S motor is able to start in both directionsdirection is undefined



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CoilStator Core

Shaft

Permanent Magnet

Bobbin

Movement Generation Tin Can Motor



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N

N

N N

S S

S S

Movement Generation Tin Can Motor - Step Generation

2 magnetic systems = 2 stators...electrical phase shift 90 °direction is defined by coil control sequencing

coil 1coil 2

coil 1coil 2 direction CW

direction CCW

control pattern (bipolar motor):N

S

NS

NS

NS

N

N

N

N

S

S

S

SS

S

S S

N N

N N

N S

NS

NSN

S

S

S

S

S

N

N

N

N

N

SN

SN

SN

S

N

N

N N

S S

S S

N

SN

SNS

N

S

S

S

S S

N N

N N

N

SN

SN

SN

S

N

N

N

N

S

S

S

S

N S

NS

NSN

S

N

N

N N

S S

S S

NS

NS

NS

NS

S

S

S

S

N

N

N

N

N

SN

SNS

N

S

front side teethback side teeth

stator 1 stator 2ELECTROMATE


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Old Technology, No Longer Used

Movement Generation VR - Step Generation



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• Hybrid Motor Bobbin Teeth

Coil

ShaftP.M.

RotorStatorB.B. P.M.

Coil

StatorFlame

Rotor

Bracket

Movement Generation Hybrid - Step Generation



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S N

S

N

SN

Rotor follows the stator field

Rotor reaches the end stop noise

Rotor is not able to follow the stator field

Rotor swings back

Movement Generation Step Loss

S N

N

S

SNN S

N

S

S

NN S

S

N

S

NS N

S

N

S

NS N

N

S

SNN S

N

S

S

NN S

S

N

S

NS N

S

N

S

NS N

N

S

SN

Motor will always loose n·4 steps



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S N

S

N

SN

Rotor follows the stator field

Rotor reaches the end stop noise

Rotor is not able to follow the stator field

Rotor swings back

Movement Generation Step Loss

S N

N

S

SNN S

N

S

S

NN S

S

N

S

NS N

S

N

S

NS N

N

S

SNN S

N

S

S

NN S

S

N

S

NS N

S

N

S

NS N

N

S

SN

Motor will always loose n·4 steps



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Stepper and Synchronous Motors

• Movement Generation• Step Mode• Torque Generation• Characteristics• Reduced Duty Cycle• Synchronous Motor



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Step Mode Full Step Mode

• Step angle = catalogue value

N S

N

S

S

NN S

S

N

S

NS N

S

N

S

N

S N

N

S

S

NN S

N

S

S

NN S

S

N

S

NS N

S

N

S

N

S N

N

S

S

N

0

-1

1

I1 / I1max

I2 / I2max

1

0

-1

coil current in a bipolar motor



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Step Mode Half Step Mode

• Step angle = half catalogue value

NN S

NN

S

S

NNN SS NNN S

S

NN

S

N

S

NN

S

NS NN

S

NN

S

N

S NNSNS NN

NN

S

S

N

NN

S

S

N

0

-1

1

I1 / I1max

I2 / I2max

1

0

-1

coil current in a bipolar motor



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Step Mode Half Step vs. Compensated Half Step

0

-1

1

I1 / I1max

I2 / I2max

1

0

-1

0

-1

1

I1 / I1max

I2 / I2max

1

0

-1

1/√2

1/√2

-1/√2

-1/√2 ELECTROMATEToll Free Phone (877) SERVO98


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Torque Generation Torque vs. Angle

Mel(torque)

Sαα1 2 3-1-2 4

MH(holding torque)

-MH

N

N

N N

S S

S S

N S

NS

NS

NS

N

N

N

N

S

S

SS

N

N

N N

S S

S S

N

SN

SN

SN

S

N

N

N

N

S

S

S

S

N

N

N N

S S

S S

N

SN

SN

SN

S

N

N

N

N

S

S

S

S



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Mel(torque)

Sαα1 2 3-1-2 4

MH(holding torque)

-MH

Mel

Torque Generation Positioning Accurancy

Δα...Step Angle Tolerance

(torque)

Sαα

2 Δα

Friction

Tolerance exists at every position, but it will not sum up!Accuracy depends on friction and motor tolerances (5-7% of step angle). ELECTROMATE


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α

M(torque)

M

α

(torque)

friction

step no. 1 2 3 4 5 6

Torque Generation Micro Step Modus

• micro step only for smoother travel at low frequencies

• with tin can motor:

• Current in coils increases/decreases in small increments



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Characteristics Torque

with chopper(pull out graph)

reduced duty cycle = increased power consumption (pull out graph)

pull-out

fA fB

pull-in

torq

ue

frequencyf2f1

Resonances may influence application!



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Characteristics Influence of Inertia

Load inertia reduces start-stop-range.

torq

ue

f

f

FI

Inertia Factor FI = JROTOR

JLOAD + JROTOR



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Characteristics Output Power

torq

ue

frequency

pow

er

Motor output power : P = M · ω

with

M...torque

ω...angular velocity

zf⋅Π⋅

=2ω

f...step frequencyz...steps per revolution



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Characteristics Resonance

• Step motors are resonant because in short their rotors behave much like a classic “mass on a spring”.



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• When a step motor takes a step, the rotor reacts to the changing stator field in the same way a mass on a spring reacts to a change in position.




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– Just like the mass on a spring, the motion of the rotor settles into position after each step.

– This settling can last as long as a second or more in worst cases!




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– If the settling doesn’t occur rapidly, or the ringing of the rotor gets worse, the motor can become unstable and lose position (stall).




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• There are two major, negative side effects of resonance.

– Rough motion• When step motors resonate they generally vibrate

excessively.• This can be bad for sensitive equipment.

– Loss of torque, which can lead to loss of position • When step motors resonate much of the torque available in

the motor is used up in keeping the rotor synchronized with the stator field, and in worst cases the motor will not have enough torque to move the load.

• Loss of torque often leads to stalling.




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• higher output power requires higher input power •-> power losses increase •-> duty cycle needs to be reduced, otherwise motor becomes too hot

Reduced Duty Cycle

•Order a Motor with reduced duty cycle,•specify cycle time,

•do not only request reduced coil resistance.

•Otherwise you get a motor with reduced coil resistance. But the winding is changed so that it will have the same maximum power

dissipation, same duty cycle and therefore the same output torque.

“We need more torque!“

M...torque ω...angular velocity = revolution_per_steps2frequency_step π⋅

P = M · ω

· [Nm · rad/s]You need more output power.



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Reduced Duty Cycle Independence from Resistance

lm

ϕαΘ

RMnIS

PCu

ϑ

coil winding area ACu

Temperature ~ PCu ~ S2

For same duty cycle same current density is needed.PCu =const. ϑ=const. Duty Cycle=const. S is the parameter, not R!

.constAV mcuCu =⋅= lcopper volume

average length of a copper wiremagnetic fluxangle current linkage

magnetic resistance no. turns (winding)currentcurrent density

consumed energy

temperature

)R,n(f≠ϕ

CuASn ⋅=⋅=Θ IMRΘ

=ϕ

mM

Cu

M

Cu

RVS

RAS

l⋅⋅

=⋅

=ϕ

αϕ

=ddM

S~ϕ

torque

2Cu S~P

Cu22

Cu VS~RP ⋅⋅= I

CuP~ϑ

temperature



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• Duty cycle is based on 5 minutes cycle time (unless otherwise specified).

Reduced Duty Cycle Operations

t

T

maxϑΔ

t

T

maxϑΔ

tStB

t

T

maxϑΔ

tStB

continuous operation

operation with reduced duty cycle

tB ...ON-time

tS ...cycle time

%100ttEDS

B ⋅=Duty CycleELECTROMATE


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Reduced Duty Cycle A Simplified Calculation

input power at 100% duty cycle:

ph

kED

RUP

2

100 =UK ...supply voltage from catalogueRph ..coil resistance

real duty cycle:

%100%100%100100

2100

•=•⎟⎠⎞

⎜⎝⎛=•=

ED

ph

S

kED

RR

UU

PPED

PED100 ... Power for 100% duty cycleUS ... supply voltage in applicationRED100 ... coil resistance for 100% duty cycle



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Synchronous Motor Schematic

U~

U~

Parallel Connection

Common, full voltage over both coils

Serial Connection

otherwise too many windings with too thin wire -> not possible

• electrical phase shift is done by capacitor instead• construction is similar to bipolar stepper motor

• stepper motorsstepper motors are used with DCDC• synchronous motorssynchronous motors are used with ACAC



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Synchronous Motor Frequencies

cloc

k

i1

i2

i1

i2 t

t

t

t

t

bipolar stepper motor

f = 200Hz

synchronous motor

f = 50Hz

Speed is equal !

f = step frequency = ff = step frequency = fss

f = frequency of coil current = ff = frequency of coil current = fii

• fs = 4·fi (for motors with identical construction)ELECTROMATE


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Synchronous Motor Operation Area

C

U

Resonance

thermal overload

min

imum

vol

tage

to s

tart

minimum capacity

operation area

UN ±10%

CN ±10%



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Competitors for Stepper MotorRotary:

Portescap (Danaher)HSI (Haydon Switch & Instrument)

Hybrid:Lin EngineeringPortescap (Danaher)Oriental MotorSanyo Denki, Shinano

Linear: HSI (Haydon Switch & Instrument)Lin Engineering



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NPM/NPA Products• Tin-Can Rotary

<PF/PFC Series> PF20, PF25, PF25C, PF35, PF35T, PF42, PF42T, PF42HPF55, PF55H

• Tin-Can Linear: <PFL/PFCL Series> PFCL25, PFL35T

• Hybrid: <PJB Series> PJB42S, PJB56H<PR Series> (Only for North America )

PR20, PR28, PR35, PR42, PR57



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Designation – PF/PF Series• PF C 42 H – 48 C 1 Magnet Material

1: Ferrite Anisotropic2: Ferrite Isotropic4: Neodymium

Winding CodeUnipolar> B:24V, C:12V, D:5VBipolar> P:12V, Q:5V

Step/Rev24: 15deg/step48: 7.5deg/step96: 3.75deg/step

Connector Version

Motor SizeDia. (mm)25, 35, 42, 55

Motor Length or High Torque VersionBlank: StandardT: Thin stack (Avail. In 35 and 42)H: High Torque (Avail. 42 and 55) ELECTROMATE


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Designation – PF/PF Series• PFC42H–48C1 G 1/10

Gear Ratio

G: w/ gear head



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Designation – PR Series• PR 42 H -25 – 04 04 J A

A: Shingle ShaftB: Double Shaft

Step AngleJ: 1.8deg/step (=200step/rev)M:0.9deg/step (=400step/step)

Step/Rev24: 15deg/step48: 7.5deg/step96: 3.75deg/step

Size (mm)

Stack Length (mm)

H: High TorqueS: Standard

Motor Current04: 0.4Amp/phase10:1.0Amp/phase



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Weakness and Settlements Mis-step -> 1. Taking Care Margin (Chose Best)

2. Closed loop (Add Encoder)3. Use/Change Higher Current

Resonance-> 1. Use High Resolution Motor

2. Use Microstep Driver 3. Adjustment (reduce) Current



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Stepper VS Servo (Brushless)

Stepper ServoCost √Speed (600rpm) √

(3000rpm)

Power/Torque √Response √Silence √Easy to Use √



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Glossary -1Holding Torque

The holding torque is the maximum torque the stepping motor has when rated current is being supplied but the motor is not rotating (with consideration given to the permissible strength of the gear when applicable). If you are setting "automatic current down (Idle Current)" function at motor standstill, the holding torque should be less than setting rated current.

Pullout Torque Pullout torque is the maximum torque that can be output at given speed. When selecting a motor, be sure the required torque falls within this curve.

Rotor Inertia This refers to the inertia of rotor inside the motor. This is necessary when the required torque (acceleration torque) for the motor needs is calculated. ELECTROMATE


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Glossary -2

Rated Current The rated current is determined by motor temperature rise. It is the current value that can flow to the motor coils continuously at motor standstill. As a general rule, the current must be set to the rated current.

Step Angle The step angle is the angular distance (in degrees) that the motor moves at the input of one pulse from the driver. It differs depending on the motor structure and excitation system.

Gear Ratio This is the ratio in rotation speed between the input speed from the motor and the speed of the ear output shaft. For example, the gear ratio 10:1 is that when the input speed from the motor is 10rpm, the gear output shaft is 1rpm.



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Glossary -3

Allowable (Permissible) TorqueThe allowable torque represents the torque value limited by the mechanical strength of the gear.

BacklashThe play of gear output shaft when the motor shaft is fixed. When positioning in bi-direction, the positioning accuracy is affected.

Maximum Starting Frequency (fs)This is the maximum pulse speed at which the motor can start or stop instantly (without an acceleration or deceleration period) when the functional load and inertial load of the stepper motor are 0. Driving the motor at greater than this pulse speed requires gradual acceleration or deceleration. This frequency drops when there is load inertia on the motor.



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Speed

Torque

Glossary -4

Pull-Output Torque Pull-in

Torque

Max. Starting Frequency

Holding Torque



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