Stepper Motors By Brian Tomiuk, Jack Good, Matthew Edwards, Isaac - - PowerPoint PPT Presentation

▶
stepper motors
SMART_READER_LITE
LIVE PREVIEW

Stepper Motors By Brian Tomiuk, Jack Good, Matthew Edwards, Isaac - - PowerPoint PPT Presentation

Feb 21, 2023 151 likes •711 views

Stepper Motors By Brian Tomiuk, Jack Good, Matthew Edwards, Isaac Snellgrove November 14th, 2018 1 What is a Stepper Motor? A motor whose movement is divided into discrete steps Turn 10 steps clockwise Holds its

slide-1
SLIDE 1

Stepper Motors

By Brian Tomiuk, Jack Good, Matthew Edwards, Isaac Snellgrove November 14th, 2018

1

slide-2
SLIDE 2

What is a Stepper Motor?

  • A motor whose movement is divided into discrete “steps”

○ “Turn 10 steps clockwise”

  • Holds its position without additional control

○ No sensor or feedback loop

2

slide-3
SLIDE 3

Parts of a Stepper Motor

Stator - Stays Static Rotor - Rotates the motor shaft

3 https://phidgets.files.wordpress.com/2014/06/stepper_back_web.jpg

slide-4
SLIDE 4

Different Types of Torque

Holding torque - How much load can the motor hold in place when the coils are energized Detent torque - The torque the motor produces when the windings are not energized, sometimes call residual torque

4

slide-5
SLIDE 5

Advantages of Stepper Motors

5

  • Has high holding torque (maintains its position)
  • Moves in discrete amounts
  • Inexpensive
  • Brushless (can last longer than brushed motors)
slide-6
SLIDE 6

Disadvantages of Stepper Motors

6

  • Uses the same amount of power regardless of load

○ Lower power efficiency

  • Torque decreases rapidly as speed increases
  • No internal feedback

○ Cannot tell when a step was missed ○ Must step slowly to ensure accuracy

  • Low torque to inertia

○ Cannot accelerate loads very rapidly

slide-7
SLIDE 7

How Stepper Motors Work

7

slide-8
SLIDE 8

How a Stepper Motor Works

Unpowered Electromagnets Bar with magnetic ends

A basic stepper motor consists

  • f a series of electromagnets

surrounding a magnetically charged bar

8

slide-9
SLIDE 9

How a Stepper Motor Works

Powering a pair of the electromagnets causes the middle bar to align with the electromagnets

9

S S

slide-10
SLIDE 10

How a Stepper Motor Works

Changing which electromagnets are powered and unpowered causes the plate to realign, turning the motor

10

S S

slide-11
SLIDE 11

How a Stepper Motor Works

Changing which electromagnets are powered and unpowered causes the plate to realign, turning the motor

11

S S

slide-12
SLIDE 12

How a Stepper Motor Works

This can be repeated to cause the motor to turn in any direction

12

S S

slide-13
SLIDE 13

How a Stepper Motor Works

Two groups can be powered to cause the plate to land between the two in a process called half stepping

13

S S S S

slide-14
SLIDE 14

How a Stepper Motor Works

Increasing the number of bars

  • n the rotor can increase the

granularity of the movement.

14

S S

slide-15
SLIDE 15

How a Stepper Motor Works

Increasing the number of bars

  • n the rotor can increase the

granularity of the movement.

15

S S

slide-16
SLIDE 16

How a Stepper Motor Works

Continuing with this concept results in the rotor having dozens of rotor teeth

16

S S

slide-17
SLIDE 17

How a Stepper Motor Works

The electromagnets also have stator teeth. Powering the electromagnets cause the tips of the teeth to align.

17

S S

Slightly Offset Aligned

slide-18
SLIDE 18

How a Stepper Motor Works

S

Powering a different pair of electromagnets cause a new group of teeth to align, causing the whole rotor to slightly shift.

18

S

Aligned Slightly Offset

slide-19
SLIDE 19

How a Stepper Motor Works

Great video demonstration of stepper motors! https://youtu.be/eyqwLiowZiU

Credit: Wikipedia for Stepper Motors

19

slide-20
SLIDE 20

(Electro)magnets. How do they work?

20

slide-21
SLIDE 21

Stator Magnet Needs

  • 1. Must be turned on/off
  • Allows motor movement
  • 2. Must be able to change magnet direction
  • Allows us to both push and pull rotor
  • Greater torque and speed

21

slide-22
SLIDE 22

Stator Magnet Needs

  • 1. Must be turned on/off
  • Allows motor movement
  • 2. Must be able to change magnet direction
  • Allows us to both push and pull rotor
  • Greater torque and speed

22

Electromagnets do these!

slide-23
SLIDE 23

Start with a Solenoid

  • Current flowing through a solenoid coil induces a magnetic field
  • Right Hand rule points to North (conventional current flow)

23

I

slide-24
SLIDE 24

Start with a Solenoid

  • Current flowing through a solenoid coil induces a magnetic field
  • Right Hand rule points to North (conventional current flow)

24

I

slide-25
SLIDE 25
  • Current flowing through a solenoid coil induces a magnetic field
  • Right Hand rule points to North (conventional current flow)

Start with a Solenoid

25

I

S N

slide-26
SLIDE 26
  • Depends on conventional current flow around solenoid core

Magnetic Field Direction

26

I I

S N N S

slide-27
SLIDE 27
  • Depends on conventional current flow around solenoid core

Magnetic Field Direction

27

I I

S N N S

slide-28
SLIDE 28

Changing Direction on Demand

  • Switch direction of current using an H-bridge

28

S N

H-Bridge

slide-29
SLIDE 29

Changing Direction on Demand

  • Switch direction of current using an H-bridge

29

N S

H-Bridge (Reverse Current)

slide-30
SLIDE 30

Bipolar Control

  • Bipolar because each coil can alternate

its polarity

  • Requires current reversal

(which typically means an H-Bridge)

www.pololu.com

30

slide-31
SLIDE 31

Bipolar Control

  • Bipolar because each coil can alternate

its polarity

  • Requires current reversal

(which typically means an H-Bridge)

  • Only two wires for each set of

solenoids

www.pololu.com

31

slide-32
SLIDE 32

But H-Bridges are hard...

  • Sometimes an H-Bridge cannot be used

○ They can (potentially) be larger than the motor in some cases ○ They generate a lot of heat ○ You can’t be bothered

  • How do you change the magnetic direction of a solenoid without

changing the current direction?

32 gearbest.com

slide-33
SLIDE 33

But H-Bridges are hard...

  • Sometimes an H-Bridge cannot be used

○ They can (potentially) be larger than the motor in some cases ○ They can generate a lot of heat ○ You can’t be bothered

  • How do you change the magnetic direction of a solenoid without

changing the current direction?

33

Use more solenoids!

adafruit.com

slide-34
SLIDE 34

Stacking Solenoids

34

slide-35
SLIDE 35

Stacking Solenoids

35

I

N S

slide-36
SLIDE 36

Stacking Solenoids

36

S N

I

slide-37
SLIDE 37

Unipolar Control

37

S N

I

  • Unipolar because each coil has one polarity

(and can only be switched on or off)

  • No H-Bridge!
  • Requires at least 3 wires per solenoid set

(2 to control direction, 1 common ground)

  • Smaller coils mean weaker magnetic fields!
slide-38
SLIDE 38

Differences in 2-Phase Stepper Motors

Bipolar

  • Fewer wires (4)
  • Higher torque
  • Current reversal
  • Advanced controller and/or

H-Bridge Unipolar

  • More wires (5-8)
  • Lower torque
  • No current reversal
  • Much simpler controller

38

slide-39
SLIDE 39

Stepper Motors in Industry

39

slide-40
SLIDE 40

Industrial

https://www.pcworld.com/article/2069020/from-android-to-automations-rubins-robots-are-googles-next-moonshot.html 40

slide-41
SLIDE 41

Medical

41 https://www.youtube.com/watch?v=4WqaadMqTRA&feature=youtu.be

slide-42
SLIDE 42

Cameras

42 http://www.pngmart.com/image/14730

slide-43
SLIDE 43

Interfacing with Stepper Motors

43

slide-44
SLIDE 44

Ease of interfacing stepper motor:

  • Rotation is proportional to number of input pulses
  • Speed is proportional to frequency of input pulses
  • Quick response to starting, stopping, and reversing
  • Very precise

○ 3-5% and error does not accumulate from one step to the next

44

slide-45
SLIDE 45

Interfacing (Option 1)

  • Buy a controller
  • Tell the controller when to step and in which direction
  • (Good for bipolar)

https://www.hobbyist.co.nz/?q=stepper-motor-controller-A4988

45

slide-46
SLIDE 46

Interfacing (Option 2)

  • Do it ourselves!
  • Must drive signals at correct times
  • Remember waving and half-stepping?
  • Easy to use GPIO pins (unipolar)

https://upload.wikimedia.org/wikipedia/commons/8/85/Drive.png 46

slide-47
SLIDE 47

Step modes:

  • Full step

○ 200 teeth / 360° = 1.8° per step

  • Half step

○ One winding energized, other two alternate

■ Half the distance per step (0.9°) and smoother operation, but 30% less torque

  • Microstepping

○ Newer technology that divides each step up to 256 microsteps, resulting in a step angle of 0.007° (!)

47

slide-48
SLIDE 48

Full step:

https://www.rs-online.com/designspark/stepper-motors-and-drives-what-is-full-step-half-step-and-microstepping https://www.rs-online.com/designspark/stepper-motors-and-drives-what-is-full-step-half-step-and-microstepping

48

slide-49
SLIDE 49

Half step:

49

https://www.rs-online.com/designspark/stepper-motors-and-drives-what-is-full-step-half-step-and-microstepping

slide-50
SLIDE 50

https://www.rs-online.com/designspark/stepper-motors-and-drives-what-is-full-step-half-step-and-microstepping

Microstepping:

50

slide-51
SLIDE 51

Motor:

Specs of the 5014-020 - NEMA 14

51

https://www.applied-motion.com/products/stepper-motors/5014-020

slide-52
SLIDE 52

Controller:

Specs of the STR2 - DC Powered Advanced Microstep Drive

52

https://www.applied-motion.com/products/stepper-drives/str2

slide-53
SLIDE 53

Questions?

53

slide-54
SLIDE 54

References

https://www.youtube.com/watch?v=eyqwLiowZiU https://learn.adafruit.com/all-about-stepper-motors/what-is-a-stepper-motor https://en.wikipedia.org/wiki/Stepper_motor https://www.youtube.com/watch?v=0qwrnUeSpYQ https://www.linengineering.com/industries/medical/ https://www.elprocus.com/stepper-motor-types-advantages-applications/ https://www.linengineering.com/industries/security-surveillance/ https://photo.stackexchange.com/questions/24109/what-does-stm-mean-on-a-canon-lens http://www.machinetoolhelp.com/Automation/systemdesign/stepper_dcservo.html

54