1. Literature Survey on Sensors and Actuators Topic: Stepper Motor
Prepared by:
Michael Wood
3/4/2009

2. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Outline
Reference list
To explore further
When to use
Stepper vs Servo
Applications
Advantages and Disadvantages
How stepper motors work
Types of Stepper Motors
Winding Arrangements
Controlling
How to pick
Where to buy
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

3. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
To explore further
Handbook of Small Electric Motors
William H. Yeadon and Alan W, Yeadon, eds. McGraw-Hill, c LC number: TK2537 .H
Stepping motors: a guide to modern theory and practice
Acarnley, P. P. P. Peregrinus on behalf of the IEE, 1984, c LC number: TK2537 .A
Stepping motors and their microprocessor controls
Kenjo, Takashi Oxford University Press, c LC number: TK2785 .K4 1984
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

4. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
When to Use
Whenever discrete steps are required
High torque at low speeds
When precision positioning is required
If torque needs to be held
To eliminate closed loop control (stepper motors can operate in open loop)
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

5. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Stepper Vs Servo
Motion Characteristics
Servo Motors
Stepper Motors
High Torque, Low Speed
Can be considered if cost/ complexity is not an issue.
Continuous duty applications requiring high torque and low speed.
High Torque and high speed (>2000 rpm)
A DC servomotor can deliver greater continuous shaft power at high speeds compared to steppers. High speed up to rpm is possible.
If speeds are less than 2000 rpm stepper may be economical. Stepper becomes bulky at high torque.
Short, Rapid Repetitive Moves
Use servo if you need high dynamic requirements.
Stepper will offer more economic solution when requirements are more modest.
Positioning Applications
Servo can handle effectively when load is mostly inertia instead of friction. The ability to overdrive servo motor in intermittent duty allows a smaller motor to be used. If positioning is critical in micron level use servo.
Use stepper motor if torque is lower than 500 oz-in, less 2000 rpm, low to medium acceleration rates.
Applications in Hazardous Environments
Use brushless servo motor.
Use step motor.
Low Speed, High Smoothness
Use DC servo.
Use microstepping.
Control Method
Closed loop.
Preferred to be used in open loop applications.
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

6. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Example Applications
Machine Tools
X-Y and X-Y-Z Positioning
Process Control
Main Conveyor Drive
Assembly Line parts positioning
Business Machines
Copy Machine- lens positioning and paper feed
Computer Peripherals
Printer- positioning the matrix print head
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

7. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Advantages
Rotation angle is proportional to input pulse
Motor has full torque at standstill
Precise positioning and repeatability of movement
Excellent response start/stop/reverse
Open loop control possible
Achieve low speed with a directly couple load
Realize a wide range of speeds
Inexpensive relative to other motion control systems
Easy to set up and use
Overload safe. Motor cannot be damaged by mechanical overload
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

8. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Disadvantages
Low efficiency. Motor draws substantial power regarldess of load.
Torque drops rapidly with speed (torque is the inverse of speed).
Low accuracy. 1:200 at full load, 1:2000 at light loads.
Prone to resonances. Requires microstepping to move smoothly.
No feedback to indicate missed steps.
Low torque to inertia ratio. Cannot accelerate loads very rapidly
Motor gets very hot in high performance configurations.
Motor will not “pick up” after momentary overload
Motor is audibly very noisy at moderate to high speeds.
Low output power for size and weight.
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

9. How stepper motors work
Current flows through the coil creating a magnetic field A metallic core channels the field perpendicular to the rotor Depending on the polarity of the field an attraction or repulsion drives the rotor
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

10. How stepper motors work
Current pulses are applied to the motor, and this generates discrete rotation of the motor shaft
By controlling the pulses the rotation speed can be controlled
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

11. How stepper motors work
If a coil is energized the closes rotor edges will be attracted to that coil. As long as the coils remain energized the rotor will remain stagnant.
By energizing coils the correct sequence the motor will discretely rotate
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

12. Types of stepper motors
Variable-reluctance
Permanent-magnet
Hybrid
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

13. Variable-reluctance (VR)
Variable-reluctance motors are not very common but easy to understand
Rotor – made of soft iron
and has multiple teeth
Stator – wound type stator
If the stators are energized
with DC current the poles
are magnetized and the
rotor is attracted to the stator
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

14. Permanent-magnet (PM)
Rotor – magnetized with alternating north and south poles situated in a straight line parallel to the shaft
Stator – wound type stator
Characteristics
Low Cost
Low Precision
High Torque
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

15. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Hybrid
Like the name implies the hybrid motor is a combination of VR and PM motors. The rotor has teeth and axially concentric magnets around its shaft.
More Expensive
Better step resolution
Better torque
Better speed
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

16. Unipolar Winding Arrangement
Has two windings for each phase (one for each direction of current).
Each winding has one common wire and two coil-end wires
Current does not need to be reversed to change the magnetic pole
Easily controlled with a
Stepper motor controller
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

17. Bipolar Winding Arrangement
Has only one winding per phase
Current must be reversed to change the magnetic pole
More difficult to control than the unipolar winding
Each phase has two leads (there is no common)
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

18. Controlling a two phase Stepper Motor
Half Stepping there are 8 stages
Assume two coils are A and B
Coil A is set high
Both coils A and B are high
Only B is high
B is high A is low
Only A is low
Both A and B are low
Only B is low
A is high B is low
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

19. Controlling a Stepper Motor With a HCS12 Microcontroller
Microcontrollers are often used to control stepper motors because:
Compatible with the discrete movements of steppers
Fast
Can easily be programmed to work with steppers of other types
Can produce the waveform used to drive small stepper motors
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

20. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
How to pick
Determine the resolution needed
- "step angle”(number of degrees the shaft turns per input signal)
Choose a winding scheme
- unipolar or bipolar stator winding
Determine the torque required for your application
4. Factor in the size, weight and power requirements
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

21. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Where to buy
(search stepper motor)
(search stepper motor)
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

22. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators
Cost
The cost of Stepper motors varies greatly depending on the required specifications. Lower end hobby stepper motors are under $2 while larger high end motor can be hundreds of dollars. For a better feel for the costs of different stepper motors go to
8/30/2018
ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators