Microprocessor and Microcontroller Based Systems

1
Microprocessor and Microcontroller Based Systems
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The Islamic University of Gaza Faculty of
Engineering Electrical Engineering Department
EELE 4315 Fall 2010

• Instructor
  Eng.Moayed N. EL Mobaied

Lecture 15
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Actuators for Robots
Actuators are used in order to produce mechanical
movement in robots.

• In this lecture we will present
• Actuators types
• Control method for
• DC motor
• AC motor
• Stepper motor
• Servos motor

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Actuator Types
4
Electrical Actuator
5
DC Motor
6
AC Motor
7
AC Motor
8
Stepper Motor
9
Stepper Motor
10
Servos Motor
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Hydraulic Actuators
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Hydraulic Actuators
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Pneumatic Actuators
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Pneumatic Actuators
15
Other Actuators
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DC motor control

• Controller H-bridge
• PWM control

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DC motor control
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H-Bridge

• DC motors only have two leads. The direction it
  spins is determined by which terminal has power
  applied and which is connected to ground.
• An H-bridge consists of four switches (in our
  case BJTs) and depending on which two are closed,
  allow the motor to operate in either direction
• We chose to use an L298 chip from
  STMicroelectronics because it has two H-bridges
  in one package.

19
DC motor control PWM control

• A pulse-width modulated signal is a rectangular
  waveform with a varying duty cycle.
• A longer duty cycle means the voltage is on for
  longer and the average voltage applied to the
  motor is higher and vice versa.
• Will be implemented using the PWM generator on
  our microcontroller.

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Pulse-Width Modulation
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Stepper Motor (uni-polar)
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Stepper Motor
0001
0010
0100
1000
Stepping Sequences for Single Coil Excitation
Only one coil is active at a given instant of time
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Stepper Motor
Single Coil Excitation
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Stepper Motor (Single Coil Excitation)
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Stepper Motor (Double Coil Excitation)
1001
0011
0110
1100
Stepping Sequences for Double Coil Excitation
Two coils active at any given instant of time
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Stepper Motor (Double Coil Excitation)
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Stepper Motor (Driver circuit)
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Stepper Motor (Driver circuit)
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Stepper Motor (sequence)
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Stepper Motor (sequence)
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Servos motor
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Servos motor

• Do not confuse servos with servo motors

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Servos Motor
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Motors and Encoders
35
Feedback measurement optical encoder
- direction
- resolution

• Relative position

light sensor
decode circuitry
light emitter
grating
36
Optical Encoders
mask/diffuser
light sensor
decode circuitry
light emitter
grating
A diffuser tends to smooth these signals
Ideal
Real
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Optical Encoders

• Relative position

- direction
light sensor
- resolution
decode circuitry
light emitter
grating
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Optical Encoders

• Relative position

- direction
light sensor
- resolution
decode circuitry
light emitter
grating
A
A
A lags B
B
B
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Optical Encoders

• Relative position

- direction
light sensor
- resolution
decode circuitry
light emitter
grating
Phase lag between A and B is 90 degree
A
B
A leads B
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Design problems
Design 1 ( Stepper motor)

• Design controller for stepper motor
• Switch for on/off
• Switch for right/left rotation with single coil
  excitation method.
• Switch for right/left rotation with double coil
  excitation method.
• Switch for speed (1,2) selection.