Real Time Embedded Systems. Lecture 1 January 17, 2012

Transcription

1 Electric Motors

2 Real Time Embedded Systems Lecture 1 January 17, 2012 Topic

3 Warning! This is a work in progress. Watch out for sharp corners and slippery surfaces

4 Motors CSCI / Real Time Embedded Systems George Washington University Spring stems

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6 Motors Inductors Inductors make relays, motors, Basic Motor

7 Motors

8 Motor Types Types of motors DC Servo Stepper Others that we are not going to talk about...

9 Inside a DC motor

10 Inside a real DC motor

11 Whats that coil thing?

12 Inductor

13 Inductors

14 Inductors Make... Electromagnet Relay

15 and... Transformer Solenoid

16 Electro Magnetic Field

17 Input Protection

18 Input Protection

19 Some words/terms Torque Speed Power Torque/Speed curve Power curve

20 Torque F τ = F r r Torque A force to produce a rotation. A twisting force. SI units = N m, English units = inch-pounds, foot-pounds

21 Angular Velocity ω r V tangential = r ω Angular velocity Rate of rotation around an axis. In radians/second or rotations/minute.

22 Power Power Rate at which work is done or energy is emitted/transferred. SI units = Watts (1 watt = 1 N*m/s). English units = Horsepower or footpound/second. P = τ ω

23 Torque/Speed

24 Torque/Speed curve Mostly linear τ motor = τ s - ωt s /ω n ω motor = (τ s t s ) ω n /t s

25 Recall P = τ ω Area of rectangle under curve is power Max Power P max = ½τ s ½ω n Power Curve

26 Power curve We know P = τ ω τ motor = τ s - ωt s /ω n ω motor = (τ s t s ) ω n /t s So P motor (ω) = -(τ s /ω n )ω 2 + τ s ω P motor (τ) = -(ω n /τ s )τ 2 + ω n τ

27 Power Curve

28 Torque Pull-Out Torque - The largest torque under which a motor can operate without sharply losing speed. Pull-In Torque - The largest steady torque with which a motor will attain normal speed after accelerating from a standstill.

29 DC Motors To to control them Use a transistor (for low DC voltages) Power Mosfets How to reverse How to vary speed (PWM) Assorted circuits Transistors H-bridge

30 Some DC motors

31 DC Motor Speed Contol

32 Simple DC motor driver

33 Power MOSFETs

34 ?

35 Driving Loads

36 DC Motor Speed Control

37 DC Motor Speed Control

38 DC Motor Direction Control

39 DC Motor Direction Control

40 DC Motor Direction Control

41 DC Motor Direction Control

42 DC Motor Speed & Direction

43 DC Motor Speed & Direction

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45 Servo Motors How they work How to control them 555, uc, servo controller No H-Bridge needed

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48 Servo Motor

49 Servo Control

50 Some ready-made drivers Servo Pololu Others Directly from a z8 Can a java microcontroller control a servo?

51 Stepper Motors Unipolar Bipolar Variable Reluctance Bifilar We consider Unipolar and Bipolar A look inside, how they work

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55 Variable Reluctance Motor

56 Variable Reluctance Motor

57 Unipolar Stepper Motor

58 Unipolar Stepper Motor

59 Bipolar Stepper Motor

60 Bipolar Stepper Motor

61 Universal Stepper Motor

62 Universal Stepper Motor

63 Stepper Motors

64 Stepper Motor Control

65 How do you drive a stepper motor (what hardware)?

66 Dual H-Bridge

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68 More on Steppers Setpping Half-stepping Microstepping Friction, Dead zone, Dynamics - holding torque, running torque

69 Unipolar Stepper Motor

70 Still More Control circuits Power transistor Darlington pair H-Bridge (the real answer)

71 Real Motor Spec

72 Another

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76 Some ready-made drivers Stepper Pololu Jameco H-bridges Whats in a stepper driver board and why?

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79 An Example

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82 Motor Coupling

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84 Special Motors Threaded shaft Linear motors Solenoids Muscle Wire

85 Linear Stepper

86 Threaded Shaft

87 Muscle Wire muscle wire A shape memory alloy (smart metal, memory metal, memory alloy, smart alloy) is an alloy that "remembers" its original, cold-forged shape: returning the pre-deformed shape by heating.

88 Solenoid

89 Measuring Motor Speed or position DC Stepper

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91 Sensing Motor Position Optical Hall-effect

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93 Questions?

94 Motor Example Example_ StepperMotor Demonstrate how to control a simple stepper motor

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97 References _Electronics/Stepper_Motors