Upload
others
View
7
Download
0
Embed Size (px)
Citation preview
D R . T A R E K A . T U T U N J I
P H I L A D E L P H I A U N I V E R S I T Y , J O R D A N
2 0 1 3
Actuators: DC Motors Overview
Mechatronics Diagram
[Ref]. George Chiu
Actuator Functional Diagram
[Ref]. George Chiu
Electrohydraulic & Electromechanical Actuators
[Ref]. George Chiu
Actuators
Actuators (or drives) are essential elements of mechatronic systems. They are the muscles that provide the mechanical movements .
Actuation is the result of a direct physical action upon the process, such as the application of a force.
Actuators take low power signals transmitted from the computer and produce high power signals which are applied as input to the process
Actuators
Electr0-Mechanical
DC motors
Stepper motors
AC motors
Electro-Magnetic
Solenoids and relays
Hydraulic and Pneumatic
Smart Materials
DC Motors
Introduction
The electric motor is based on the principle that a current-carrying conductor will experience a physical force when in the presence of a magnetic field.
The DC motor consists of a rotating armature and a stationary magnetic field.
The current in the armature, which must come through brushes, causes the rotating forces.
The stationary magnetic field is provided by either electromagnets (in which case, it is called a wound-field motor) or by permanent magnets.
Theory of Operation
[Ref] Kiliani
DC Motor Types
Wound-field The series motor has the armature and field windings connected in
series. This type of motor is characterized by a high starting torque and a high no-load speed but poor speed regulation (the speed changes considerably if the load changes).
The shunt motor has the armature and field windings connected in parallel. This type of motor has much better speed regulation than does the series motor.
The compound motor has both series and shunt-type field windings and combines the good characteristics of both the series and shunt motors.
Permanent magnet (PM) motors use permanent magnets to provide the stationary magnetic field. This results in a very linear torque-speed curve, which makes it easy to
calculate the motor speed for various load conditions and thus attractive for control system a applications.
Series-Motor
[Ref] Kiliani
Shunt-Motor
[Ref] Kiliani
Compound Motor
[Ref] Kiliani
PM Motors
[Ref] Kiliani
PM Motors
[Ref] Kiliani
Torque-Speed Curves
[Ref] Kiliani
Use the torque-speed curve to find the motor speed and current for: no-load, stall conditions, and lifting a 10-oz load with a 2-in radius pulley
Example
Torque-speed curves shift by changing the supply voltage
[Ref] Kiliani
DC Data Sheets
Data Sheets provide all the needed information about the DC motor to be used.
It is important for engineers to able to read the data sheets and find the needed information
The following two slides provide examples of two data sheets
DC Motor Control Circuits
DC Motor Control
There are two ways to control the speed of a DC motor: Analog drive uses linear amplifiers to provide a varying DC voltage to
the motor. Although simple and direct, this method is very power-inefficient and is usually used only with smaller motors.
Pulse-width modulation (PWM), a more efficient method, provides the motor with constant voltage pulses of varying widths: the wider the pulse, the more energy transferred to the motor.
For larger DC motors, SCRs power the motor with pulses taken directly from the AC waveform. This is a form of PWM, and it eliminates the need for a large DC-power supply.
Speed Control
[Ref] Kiliani
Analog-Drive
Power Transistors
[Ref] Kiliani
Power Op-Amp
Darlington Pair
Reversing Direction using Relay
[Ref] Kiliani
Reversing Direction using H-Bridge
IC’s
[Ref] Kiliani
DC Motor Control
[Ref] Kiliani
DC Motor from AC Source
[Ref] Kiliani
Silicon Control Rectifier (SCR)
[Ref] Kiliani
DC Braking
Brushless DC Motors
The newest type of DC motor is the brushless DC motor (BLDC).
This motor uses permanent magnets instead of coils in the armature (called the rotor) and so does not need brushes.
The field coils are switched on and off in a rotating sequence that pulls the rotor around.
BLDCs have built-in sensors that direct when the individual field coils are to be switched on and off.
Brushless DC Motors
[Ref] Kiliani
Stepper Motors
Stepper Motors
A unique type of DC motors that rotate in fixed steps as related to number of degrees.
They do not require feedback sensors and can be used in control applications for exact positioning.
They usually have low velocity and can be used without gear reductions.
Two-Phase (Bipolar) Stepper Motor
[Ref] Kiliani
Four-Phase (Unipolar) Stepper Motor
[Ref] Kiliani
Modes of Operation
Single Step Slew
[Ref] Kiliani
Data Sheets
Drive Circuits for Bipolar
[Ref] Kiliani
Drive Circuits for Unipolar
[Ref] Kiliani
Example: Hard Drive Application
[Ref] Kiliani
Electrical Motors: DC Motors Summary
[Ref]. George Chiu
Summary
DC Motors can be divided into: Wound-field and Permanent magnet
Wound field motors. The series motor The shunt motor The compound motor
PM motors use permanent magnets to provide the stationary magnetic field.
Stepper motors are type of DC motors that do not require
a feedback sensor
Summary
There are two ways to control the speed of a DC motor: Analog drive uses linear amplifiers to provide a varying DC
voltage to the motor. Although simple and direct, this method is very power-inefficient and is usually used only with smaller motors.
Pulse-width modulation (PWM), a more efficient method, provides the motor with constant voltage pulses of varying widths: the wider the pulse, the more energy transferred to the motor.
For larger DC motors, SCRs power the motor with pulses taken directly from the AC waveform