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Chapter 4 Actuators INTRODUCTION Actuators are the muscles of robots. Several types of actuator noteworthy… Electric motors Servomotors Stepper motors Hydraulic actuators Pneumatic actuators Shape memory metal actuators
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Page 1: Ch4 Actuators

Chapter 4Actuators

INTRODUCTION

Actuators are the muscles of robots.

Several types of actuator noteworthy… Electric motors

Servomotors Stepper motors

Hydraulic actuators Pneumatic actuators Shape memory metal actuators

Page 2: Ch4 Actuators

Chapter 4Actuators

INTRODUCTION

종류 특징 용도 비고 ( 구성 )

유압 actuator(Hydraulic actuator)

고출력누유 및 oil 관리

건설기계 , 공작기계산업용 robot

Pump, 압축원 , 배관 ,servo valve

공기압 actuator(Pneumatic actuator)

고속이동압축성 , 안전 , clean

공기압 hand전차 door

Compressor, 배관 , servo valve

전자력 motor(Electric motor)

사용이 용이clean, 제어성 좋음

용도 다수 전원 , motor driver

형상기억합금(SMA, Shape Memoried Alloy)

구조체를 겸함응답성이 조금 느림

안경 frame, joint 등 가열 , 냉각

초음파 motor(Ultrasonic motor)

경량 , 소형 , brake 불필요

camera lens 구동 등 압전 ceramics

각종 actuator 의 특징

Page 3: Ch4 Actuators

Weight, Power-to-Weight Ratio, Operating Pressure

The weight of the actuating system and Power-to-Weight Ratio is

important.

stepper motor < servomotor

pneumatic : lowest, hydraulic : highest Pneumatic and hydraulic system are composed of two system, actuating system and power system. Operating pressure

hydraulic : 55~5,000 psi pneumatic : 100~120 psi

Chapter 4Actuators

CHARACTERISTICS OF ACUATING SYSTEM

Characteristics of actuating system is criteria of selecting the kind of actuator.

Page 4: Ch4 Actuators

Stiffness

the resistance of a material against deformation

hydraulic systems : very stiff & noncompliant

pneumatic systems : easily compressed -> compliant

Chapter 4Actuators

CHARACTERISTICS OF ACUATING SYSTEM

Use of Reduction Gears

To increase the torque and make it to slow it down to manageable

speeds. It increase the cost, number of parts, backlash, inertia of the rotating body, and resolution of the system.

Page 5: Ch4 Actuators

Inertia and torque relationship between a motor and a load.

Chapter 4Actuators

)(11

1 llllmmmmmmmmm bIN

bITN

bIT

lEffective IN

I2

1 mlTotal II

NI

2

1

Effect of reduction gear

Page 6: Ch4 Actuators

It offers a high power-to-weight ratio , large forces at low speeds compatibility with microprocessor and tolerance of extreme hazardous environments.

A rotary hydraulic actuator. where, A is the effective area of the piston, p is the working pressure.

Chapter 4Actuators

HYDRAULIC ACTUATOR

drtdA

drtrpdArpTr

r

r

r 22

11

)(2

1 21

22

1

2

rrptdrrptr

r

Page 7: Ch4 Actuators

Schematic of a hydraulic system and its components.

Chapter 4Actuators

HYDRAULIC ACTUATOR

where, q is the flow rate, C is a constant, x is the spool’s displacement, y is piston’s displacement and A is the area of the piston (d/dt denoted as D).

)()vol()( dyAddtq

Cxq

xAD

Cy

dyAdtCx )()(

Page 8: Ch4 Actuators

Chapter 4Actuators

Block diagram of the hydraulic system with proportional feedback control scheme

Schematic of a spool valve in neutral position.

Page 9: Ch4 Actuators

It is very similar to hydraulic system, but power-to-weight ratio is much lower than hydraulic system. Because the air is compressible, it compressed and deforms under load.

Chapter 4Actuators

PNEUMATIC DEVICES

Page 10: Ch4 Actuators

Basic Concept of Electric Motors

Sorts of electric motors used in robotics DC motors Reversible AC motors Brushless DC motors Stepper motors

Important design factor is like below.

Dissipation of heat -> Size, Power of motors

Heat dissipation is generated from below.

Resistance of the wiring to electric current

Heat due to iron losses

Eddy current losses, hysteresis losses

friction losses, brush losses, short-out circuit

losses

Basic Principle of all electric motors;

Chapter 4Actuators

ELECTRIC MOTORS

BIF

Page 11: Ch4 Actuators

Heat dissipation path of motors.

Chapter 4Actuators

What is important is the path that the heat must take to leave the motor since if the heat is dissipated faster more generated heat can be dissipated before damage occurs.

Page 12: Ch4 Actuators

Chapter 4Actuators

DC motor operating principles

Page 13: Ch4 Actuators

Chapter 4Actuators

Component of DC motor(brush-type)

Page 14: Ch4 Actuators

The changing flux is provided by the AC current(60Hz) and commutators and brushes are eliminated. AC motors can dissipate heat more favorable than DC motors, yielding more power.

Chapter 4Actuators

AC Motors

Brushless DC Motors

This types of motors are a hybrid between AC motors and DC motors. It is not necessary that line frequency as 60Hz. For smooth operation and almost constant torque, the rotor usually has three phases in it.

Direct-Drive Electric Motors These motors are designed to deliver a very large torque at very low speeds and with very high resolution, but to be used directly with a joint without any gear reduction.

Page 15: Ch4 Actuators

Scheme of a servomotor controller.

Chapter 4Actuators

Servomotors

The back electromotive force or back-emf is most important factor for all electric motors.

Motor equivalent circuit

Page 16: Ch4 Actuators

Chapter 4Actuators

Stepper motors

Stepper motors are long-lasting, versatile and used without feedback.

Basic principle of operation of a stepper motor.

It has permanent magnet rotors and multiple winding stator housing.

Most industrial steppers run between 1.8 to 7.5 degrees at full stepping.

The number of poles means more precise resolution, but it has physical limitation.

Page 17: Ch4 Actuators

Chapter 4Actuators

Operation of unipolar stepper motor

Full step phase sequence

Half step phase sequence

Page 18: Ch4 Actuators

Chapter 4Actuators

Configuration of stepper motor

Page 19: Ch4 Actuators

Chapter 4Actuators

Hybrid Stepper Motors

These motors are made with two coils, each with four poles.

Application of unequal divisions for measuring lengths as in a caliper.

Basic operation of a hybrid stepper motor.

Page 20: Ch4 Actuators

Chapter 4Actuators

A robot is supposed to be a manipulator that is controlled by computers or microprocessor and actuated by the electric motors with controller, which is computer or microprocessor.

PWM timing. Sine wave generation with PWM.

MICROPROCESSOR CONTROL OF ELECTRIC MOTORS

Pulse Width Modulation

PWM is used for DC motor speed control with microprocessors.

It requires only high voltage(5V) and one output bit.

Average output voltage of PWM is like below.

t

tVV CCout

1

Page 21: Ch4 Actuators

Chapter 4Actuators

PWM velocity feedback control

PWM voltage and motor current

PWM feedback control

Page 22: Ch4 Actuators

Chapter 4Actuators

Application of H-bridge for motor direction control

Direction Control of DC Motors with an H-Bridge

PWM It is desirable to change the direction of current flow in a motor for changing its

direction of rotation with only two bits of information.

It means one should change the direction of the flow by changing bit information from

the microprocessor.

Page 23: Ch4 Actuators

Chapter 4Actuators

One particular metal alloy, called Biometal shortens about 4% when it

reaches a

certain temperature.

The major disadvantage of the wire is that the total strain happens within a

very small

temperature range and it is very difficult to accurately control the strain.

SHAPE-MEMORY-TYPE METALS