This webinar reviews some of the basic parameters necessary to properly select and apply stepper motor technology to motion applications. Topics included in this discussion review basic stepper speed-torque behavior including the stepper over-voltage ratio, a stepper in constant current operation vs. a stepper in voltage drive region, thermal ratings, the impact of winding changes on dynamic behavior, calculations and considerations for intermittent duty operation, motor/system accuracy, failure modes, and the application of all these criteria when applying stepper-based linear actuator products. Engineers currently using stepper technology in their motion applications that want to understand how to apply stepper motor technology will benefit from this webinar. In this webinar you will learn: -Basic parameters necessary to properly select and apply stepper motor technology -How to understand the stepper motor speed-torque curve and how to apply this to the application -The main factors to consider when trying to optimize a stepper motor in a variety of applications

1. Applying Stepper Motors:
Application Questions You Must Answer
& Things to Watch Out For

2. Before We Start
 This webinar will be available afterwards at
designworldonline.com & email
 Q&A at the end of the presentation
 Hashtag for this webinar: #DWwebinar

3. Moderator
Presenter
Miles Budimir
Tim Burke
Design World
ElectroCraft

4. Applying Steppers

5. Applying Steppers
6
Application Variables
 Mechanical Load reflected to motor
 Maximum system speed reflected to motor
 Available Voltage
 Available Current
 Ambient temperature conditions
 Position increment & accuracy
 Time to execute move

6. Applying Steppers
7
Stepping Motor Catalog Data

7. Applying Steppers
8
Torque-Speed Curves
 “Typical” Limits for stepper:
Torque-Speed, Various Overvoltage Ratios
TPP23-90A30
• 3000 RPM (10K steps/s) for Size 17
• 1500 RPM (5K steps/s) for Size 34
80
70
 Overvoltage Ratio:
Ratio of Drive Supply voltage
to Motor Voltage
• Desirable to have this at least 15
Torque (oz.-in)
60
50
40
30
20
10
0
 Torque Margin: Utilize 70 %
of available torque at any speed
0
2000
4000
6000
8000
10000
Speed (Full Steps/s)
OV 15:1
OV 20:1
OV 30:1
OV 40:1

8. Applying Steppers
9
Constant Current Drives
& Motor Current Rise
Electrical Equation
of Motor Winding:
Current (Amps)
Vs=i*R+L*di/dt+Kb*w*sinA,
A=Elec Angle, w=rotor speed
i=Vs/R (eg i=15Vm/R)
i=Vm/R
Area between curves is
where the extra torque
comes from
High
Step Rate
Med
Step Rate
Time (mS)
Low
Step Rate

9. Applying Steppers
10
Current Profiles at Speed
Phase Currents
Low Speed, Half Stepping
Medium Speed, Half Stepping
Half Step Phase Energization
Phase A
Phase B
1
Off
On, + Current
2
On, + Current
On, + Current
3
On, + Current
Off
No Current Regulation, Half Stepping
4
On, + Current
On, - Current
5
Off
On, - Current
6
On, - Current
On, - Current
7
On, - Current
Off
8
On, - Current
On, + Current
1
Off
On, + Current
High Speed, Half Stepping

10. Applying Steppers
11
Stepper Torque-Speed Curves
2 Regions
Stepper Torque-Speed
• Current Regulation
• Voltage Drive,
current does not reach set point
• Low speed torque 70% of holding torque
• Knee scaled by overvoltage ratio
(volt-amps if changing winding)
• Maximum speed scaled by overvoltage ratio
(volt-amps if changing winding)
1
Knee
Normalized Torque
Scaling
1.2
0.8
0.6
0.4
Current
Regulation
0.2
Voltage
Drive
0
0
5000
10000
Speed (Full Steps/s)
15000

11. Applying Steppers
12
Scaling Stepper Torque-Speed Curves
 Comparison of test data
against scaled curves
Stepper Torque-Speed
• 48V scaled from 24V straight line
approximation
40
35
Torque (oz.-in)
30
25
20
15
40
10
5
0
0
5000
10000
15000
Speed (Steps/s)
24V Actual
48V Predicted
24V Estimated
48V Actual

12. Applying Steppers
13
Connection
Torque-Speed
Fixed Drive Current
Diagrams
Various Connections
450
Series
Parallel
½ Cu
Phase A
400
Phase B
350
2R
Power
Loss
2I2R
Torque
2N*I
R/2
I2R/2
R
I2R
300
Torque (oz-in)
Terminal
Resistance
250
Phase A
200
Phase B
150
N*I
N*I
100
50
Inductance
L
L/4
L/4
Phase A
0
0
Elec. Time
Constant
2000
4000
6000
L/2R
L/2R
L/4R
Series
Parallel
8000
Phase B
Speed (Full Steps/s)
1/2 Cu

13. Applying Steppers
14
Thermal Ratings
 Typically conservative rating
 ElectroCraft motors rated for 130 °C
Size 17 Stepper
120.00
100.00
Temperature (deg C)
• NEMA ICS16 spec describes procedure
• Motor Hanging in free air
• Motor held in stall condition with full
current in both phases
Temperature Rise
80.00
60.00
40.00
20.00
0.00
0.00
20.00
40.00
60.00
Time (min)
80.00
100.00

14. Applying Steppers
15
Thermal Model
 Simple Model
Temperature Rise
Size 17 Stepper
• 2 Node: Winding Temp & Ambient Temp
• Some manufacturers publish data
• Thermal Resistance
C
• Thermal Time Constant
120.00
w
Tw
Ta
 More Complex Model
• 3-Node Model
• Winding temp
C
• Case temp
• Ambient temp T
w
w
Temperature (deg C)
100.00
80.00
60.00
40.00
20.00
0.00
0.00
Cc
Tc
20.00
40.00
60.00
80.00
Time (min)
Ta
Data
2 Node
3 Node
100.00

15. Applying Steppers
16
Intermittent Duty and
Overdriving Motor
 Can overdrive motor as long as
thermal limit not exceeded
60
50
40
Torque (oz-in)
• Thermal model allows calculation of
allowable duty cycle
• Torque falls off after rated current
• Note: Torque-speed curves are continuous
rated operation
Torque vs. Current
2x Rated
30
Rated Current
20
10
0
0.0
0.5
1.0
1.5
2.0
Current (amps)
2.5
3.0
3.5

16. Applying Steppers
17
Mechanisms of Loss
 I2R Loss (Joule Heating)
Stepping Motor Losses
• Dominant at Low Speed
40
10
9
35
 Core Loss
25
6
20
5
4
15
Power Loss (W)
7
Torque (oz.-in)
• Primarily in stator lamination
• Both hysteresis and eddy current
• Hysteresis is f(step rate)
• Eddy Current is f(step rate)2
8
30
3
10
2
5
1
0
0
2000
4000
6000
0
8000
Speed (Steps/s)
Torque-Speed
I*I*R
Core Loss
Total Loss

17. Applying Steppers
18
Angle Accuracy
 Resolution:
• 360o/(# steps/rev.)
 Accuracy:
• Typically 3-5%
• Non-cumulative
• Influenced by:
• Friction (Application)
• Stiffness of motor
(Motor Design)
 Hysteresis
• Error found when
approaching
same position from
either direction
• Typically 3%

18. Applying Steppers
19
Microstepping
 Full Step, Half Step &
Microstepping
Torque Vectors – Full, Half & Microstep
(Position shown in Electrical Degrees)
1.6
1.4
Full Step
1.2
Microsteps
1
0.8
Half Step
0.6
Microsteps
0.4
0.2
Full Step
0
0
0.5
1
1.5
• Microstepping accomplished by regulating
phase currents
• Tq=Kt*Isin(wt)*sin(Q)+Kt*Icos(wt)*cos(Q)

19. Applying Steppers
20
Microstepping
 Be careful if used
for positioning
1.5
0.5
0.4
1
0.3
0.5
-1.5
0.2
0
-1
-0.5
0
0.5
1
1.5
2
2.5
-0.3
-0.5
0.1
Torque
Torque
• Friction band leads to
high error, may result in
motor not moving
• Harmonics in torque
profile lead to additional
errors (cogging or detent
torque)
1/16th Microstepping
Full Step
0
-0.1
0.1
-0.1
-0.2
-1
-0.3
-1.5
Mechanical Degrees
Step 1
Step 2
-0.4
Mechanical Degrees
Step 1
Step 2
0.3

20. Applying Steppers
21
Stepper Start-Stop Rate
and Acceleration
 Steppers capable of very
high acceleration rates
(high Torque/inertia ratio)
Stepper Move Profile
18 Step Move, Constant Acceleration
2500
 Start-Stop Rate – Step rate at which
motor will pull into synchronism
• Speeds above start-stop
will require acceleration
• Function of total system inertia
• Proportional to sqrt(1/total inertia)
Velocity (Full Steps/s)
2000
1500
1000
Start-Stop Rate
Start-Stop Rate
500
0
0
0.005
Time (sec)
0.01
0.015

21. Applying Steppers
22
Common Failure Mode
 Stepping at motor’s natural
frequency
Low Frequency Resonance
450
400
350
300
Torque (oz-in)
• wn=sqrt(Kt*I*A/J), Kt=Torque Constant,
I=operating current, A=# of pole pairs,
J=inertia
• Typically found at 150 to 450 steps/sec
• Influenced by reflected inertia of load
Torque-Speed
250
200
150
 Remedies
• Add mechanical damping or friction
• Microstepping
100
50
0
0
500
1000
1500
2000
Speed (Full Steps/s)
2500
3000

22. Applying Steppers
23
Common Failure Mode
 Mid-Frequency Resonance
 Electronic damping
found in many
newer drives will
quiet this behavior
Mid Frequency Resonance
40
35
30
Torque (oz-in)
• Less severe, but occurs at much
higher step rates
• Traced to oscillation of BEMF (amplitude
and frequency modulation) leading to
unstable torque
Torque-Speed
25
20
15
10
5
0
0
2000
4000
6000
8000
Speed (Full Steps/sw)
10000
12000

23. Applying Steppers
24
Stepping Motor Linear Actuators
 Linear Actuators
• Conversion of rotary to linear
done within motor envelope
• Requires external hardware
to guide screw & support loads
• Features
• Low cost linear motion
• High resolution
• High force

24. Applying Steppers
25
Types of Actuator
 Translating Screw
• Screw must be prevented from
rotating. For “long” travel must
allow clearance behind motor
for screw
 Translating Nut
• Must provide guide or rail
for nut to prevent rotation.

25. Applying Steppers
26
Types of Screw
 Lead Screw
• ACME Thread Design
• Efficiency Range from 0.3 to 0.7
• Function of coefficient of friction
• Backlash range from .002” to .007”
 Ball Screw
• Efficiency Range from 0.8 to 0.95
• Lower friction leads to better accuracy
• Backlash from 0.000” to 0.010”

26. Applying Steppers
27
Force Speed Curves
• A-thread: 0.0625” lead
(16 Threads/in.)
• B-thread: 0.125” lead
 Efficiency of
lead screws
• A-thread: 42%
• B-thread: 58%
• C-thread: 68%
(8 Threads/in.)
• C-thread: 0.25” lead
(4 Threads/in.)
Formula:
Eff=L/(dm*p)*((L+p*m*sec(a))/(p*dm-m*L*sec(a)))
• m = Coef. of Friction
• L = Thread Lead
• dm = Pitch diameter • a = Thread angle/2
Size 17S - Force vs. Linear Speed
48V, 2A RMS
100
90
80
70
Force (lb.)
 Lead of screw is
another variable to
tailor performance
60
50
40
30
20
10
0
0
5
10
15
Linear Speed (in/s)
A-Thread Tested
B-Thread Tested
C-Thread Tested
20
25

27. Questions?
Design World
Miles Budimir
mbudimir@wtwhmedia.com
Phone: 440.234.4531
Twitter: @DW_Motion
ElectroCraft
Tim Burke
tburke@electrocraft.com
Phone: 603.516.1255

28. Thank You
 This webinar will be available at
designworldonline.com & email
 Tweet with hashtag #DWwebinar
 Connect with
 Twitter: @DesignWorld
 Facebook: facebook.com/engineeringexchange
 LinkedIn: Design World Group
 YouTube: youtube.com/designworldvideo
 Discuss this on EngineeringExchange.com

29. Applying Steppers