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

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 position without additional control ● No sensor or feedback loop ○ 2

Parts of a Stepper Motor Stator - Stays Static Rotor - Rotates the motor shaft https://phidgets.files.wordpress.com/2014/06/stepper_back_web.jpg 3

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

Advantages of Stepper Motors Has high holding torque (maintains its position) ● Moves in discrete amounts ● Inexpensive ● Brushless (can last longer than brushed motors) ● 5

Disadvantages of Stepper Motors 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 ○ 6

How Stepper Motors Work 7

How a Stepper Motor Works Unpowered Bar with Electromagnets magnetic ends A basic stepper motor consists of a series of electromagnets surrounding a magnetically charged bar 8

How a Stepper Motor Works S Powering a pair of the electromagnets causes the middle bar to align with the electromagnets S 9

How a Stepper Motor Works Changing which electromagnets are powered and unpowered S causes the plate to realign, turning the motor S 10

How a Stepper Motor Works Changing which electromagnets are powered and unpowered S causes the plate to realign, turning the motor S 11

How a Stepper Motor Works This can be repeated to cause the motor to turn in any S direction S 12

How a Stepper Motor Works S Two groups can be powered to cause the plate to land between S the two in a process called half stepping S S 13

How a Stepper Motor Works Increasing the number of bars on the rotor can increase the S granularity of the movement. S 14

How a Stepper Motor Works S Increasing the number of bars on the rotor can increase the granularity of the movement. S 15

How a Stepper Motor Works S Continuing with this concept results in the rotor having dozens of rotor teeth S 16

How a Stepper Motor Works Slightly Offset S The electromagnets also have stator teeth . Powering the electromagnets cause the tips of the teeth to align. Aligned S 17

How a Stepper Motor Works Aligned Powering a different pair of electromagnets cause a new S group of teeth to align, causing the whole rotor to slightly shift. S Slightly Offset 18

How a Stepper Motor Works Great video demonstration of stepper motors! https://youtu.be/eyqwLiowZiU 19 Credit: Wikipedia for Stepper Motors

(Electro)magnets. How do they work? 20

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

Stator Magnet Needs 1. Must be turned on/off Electromagnets - Allows motor movement do these! 2. Must be able to change magnet direction - Allows us to both push and pull rotor - Greater torque and speed 22

Start with a Solenoid Current flowing through a solenoid coil induces a magnetic field ● Right Hand rule points to North (conventional current flow) ● I 23

Start with a Solenoid Current flowing through a solenoid coil induces a magnetic field ● Right Hand rule points to North (conventional current flow) ● I 24

Start with a Solenoid Current flowing through a solenoid coil induces a magnetic field ● Right Hand rule points to North (conventional current flow) ● I S N 25

Magnetic Field Direction Depends on conventional current flow around solenoid core ● I S N I N S 26

Magnetic Field Direction Depends on conventional current flow around solenoid core ● I S N I N S 27

Changing Direction on Demand Switch direction of current using an H-bridge ● S H-Bridge N 28

Changing Direction on Demand Switch direction of current using an H-bridge ● N H-Bridge (Reverse Current) S 29

Bipolar Control Bipolar because each coil can alternate ● its polarity Requires current reversal ● (which typically means an H-Bridge) www.pololu.com 30

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 ● www.pololu.com solenoids 31

But H-Bridges are hard... gearbest.com 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

But H-Bridges are hard... adafruit.com 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? Use more solenoids! 33

Stacking Solenoids 34

Stacking Solenoids I S N 35

Stacking Solenoids N S I 36

Unipolar Control Unipolar because each coil has one polarity ● (and can only be switched on or off) N No H-Bridge! ● Requires at least 3 wires per solenoid set ● (2 to control direction, 1 common ground) S Smaller coils mean weaker magnetic fields! ● I 37

Differences in 2-Phase Stepper Motors Bipolar Unipolar Fewer wires (4) More wires (5-8) ● ● Higher torque Lower torque ● ● Current reversal No current reversal ● ● Advanced controller and/or Much simpler controller ● ● H-Bridge 38

Stepper Motors in Industry 39

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

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

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

Interfacing with Stepper Motors 43

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

Interfacing (Option 1) Buy a controller ● Tell the controller when to step and in which direction ● (Good for bipolar) ● 45 https://www.hobbyist.co.nz/?q=stepper-motor-controller-A4988

Interfacing (Option 2) Do it ourselves! ● Must drive signals at correct times ● Remember waving and half-stepping? ● Easy to use GPIO pins (unipolar) ● 46 https://upload.wikimedia.org/wikipedia/commons/8/85/Drive.png

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

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

Half step: https://www.rs-online.com/designspark/stepper-motors-and-drives-what-is-full-step-half-step-and-microstepping 49

Microstepping: 50 https://www.rs-online.com/designspark/stepper-motors-and-drives-what-is-full-step-half-step-and-microstepping

Motor: Specs of the 5014-020 - NEMA 14 51 https://www.applied-motion.com/products/stepper-motors/5014-020

Controller: Specs of the STR2 - DC Powered Advanced Microstep Drive https://www.applied-motion.com/products/stepper-drives/str2 52

Questions? 53

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