actuators: dc motors overview - philadelphia university · dc motors can be divided into:...

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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