ch4 actuators
TRANSCRIPT
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
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
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.
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.
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
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
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 )()(
Chapter 4Actuators
Block diagram of the hydraulic system with proportional feedback control scheme
Schematic of a spool valve in neutral position.
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
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
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.
Chapter 4Actuators
DC motor operating principles
Chapter 4Actuators
Component of DC motor(brush-type)
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.
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
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.
Chapter 4Actuators
Operation of unipolar stepper motor
Full step phase sequence
Half step phase sequence
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Configuration of stepper motor
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.
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
Chapter 4Actuators
PWM velocity feedback control
PWM voltage and motor current
PWM feedback control
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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.
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