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

Transcription

1 tepper Motors By Brian Tomiuk, Jack Good, Matthew Edwards, Isaac nellgrove November 14th,

2 What is a tepper 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

3 Parts of a tepper Motor tator - tays tatic Rotor - Rotates the motor shaft 3

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

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

6 Disadvantages of tepper 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

7 How tepper Motors Work 7

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

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

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

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

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

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

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

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

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

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

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

19 How a tepper Motor Works Great video demonstration of stepper motors! Credit: Wikipedia for tepper Motors 19

20 (Electro)magnets. How do they work? 20

21 tator 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

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

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

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

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

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

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

28 Changing Direction on Demand witch direction of current using an H-bridge H-Bridge N 28

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

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

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 31

32 But H-Bridges are hard... ometimes an H-Bridge cannot be used gearbest.com 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

33 But H-Bridges are hard... ometimes an H-Bridge cannot be used adafruit.com 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

34 tacking olenoids 34

35 tacking olenoids I N 35

36 tacking olenoids N I 36

37 Unipolar Control 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) maller coils mean weaker magnetic fields! N I 37

38 Differences in 2-Phase tepper 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

39 tepper Motors in Industry 39

40 Industrial 40

41 Medical 41

42 Cameras 42

43 Interfacing with tepper Motors 43

44 Ease of interfacing stepper motor: Rotation is proportional to number of input pulses peed 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

45 Interfacing (Option 1) Buy a controller Tell the controller when to step and in which direction (Good for bipolar) 45

46 Interfacing (Option 2) Do it ourselves! Must drive signals at correct times Remember waving and half-stepping? Easy to use GPIO pins (unipolar) 46

47 tep 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 (!) 47

48 Full step:

49 Half step: 49

50 Microstepping: 50

51 Motor: pecs of the NEMA

52 Controller: pecs of the TR2 - DC Powered Advanced Microstep Drive 52

53 Questions? 53

54 References