Actuators

Mechanical process and

information processing
develop towards a
mechatronic
system

Rolf Isermann
Mechatronic Systems: Fundamentals, Springer Science & Business Media, Oct 26, 2005
Actuators
• An actuator is a component of a machine that is responsible for
moving and controlling a mechanism or system, for example by
opening a valve.
• In simple terms, it is a "mover".

• Hydraulic
• Pneumatic
• Electric
Electromagnetics—Magnetic Field
• Electromagnetic is the most widely utilized method of energy
conversion for electromechanical actuators.
• One of the reasons for using magnetic fields instead of electric fields
is the higher energy density in magnetic fields.
Electromagnetics—Magnetic Field
• Lorentz’s law of electromagnetic forces and Faraday’s law of
electromagnetic induction are the two fundamental principles that
govern electromagnetic actuators.
 Electromagnetics—Magnetic Field
• Lorentz’s Law of Electromagnetic Force
• When a current carrying conductor is placed in a
magnetic field, it will be subjected to an induced
force given by

• Where 𝐹Ԧ is the force vector, 𝑖Ԧ is the current vector,

and 𝐵 is the magnetic flux density.
Electromagnetics—Magnetic Field
• Faraday’s Law of Electromagnetic Induction
• The motion of a conductor in a magnetic field will produce an
electromotive force (emf), or electric potential, across the conductor
given by

• where φ is the magnetic flux.

Boit–Savart Law

• A long (infinite), straight, current carrying conductor induces a

magnetic field around the conductor.
• The flux density at a perpendicular distance r from the conductor is

• where i is the electric current.

solenoid
• If we bend the straight current carrying
conductor into a helical coil (solenoid) with N
turns, it will induce a corresponding magnetic
field.
• If the length of the coil L is much greater than
its diameter D , the flux density follows the
right-hand rule and the magnitude inside the
coil is approximately

is the permeability of the material inside the

coil and I is the current through the winding.
Solenoid Type Devices
• Solenoids are the simplest electromagnetic
actuators that are used in linear as well as
rotary actuations for valves, switches, and
relays.
• Solenoid consists of
• a stationary iron frame (stator), a
• coil (solenoid), and a
• ferromagnetic plunger (armature) in the center of
the coil
 Pull-type Linear Solenoid Construction
• Most electromagnetic solenoids are linear
devices producing a linear back and forth force
or motion.
• Linear solenoids are available in two basic
configurations called a “Pull-type” as it pulls
the connected load towards itself when
energised, and the “Push-type” that act in the
opposite direction pushing it away from itself
when energised.
• Both push and pull types are generally
constructed the same with the difference being
in the location of the return spring and design
of the plunger.
 Rotary Solenoids
• rotational solenoids are also available which produce an
angular or rotary motion from a neutral position in either
clockwise, anti-clockwise or in both directions (bi-
directional).
• Rotary solenoids can be used to replace small DC motors
or stepper motors were the angular movement is very
small with the angle of rotation being the angle moved
from the start to the end position.
Solenoid Switching
• Solenoid switches are used to
switch high power circuits on and
off using a much smaller electrical
control signal to actuate the
switching.
• This allows extensive logic and
decision making circuitry to be
performed on inexpensive
microchips and small electronic
parts, with the actual switching of
the high power signals being
limited to the very last step.
inductive devices
Solenoids are “inductive” devices so
some form of electrical protection is
required across the solenoid coil to
prevent high back emf voltages from
damaging the semiconductor
switching device.
In this case the standard “Flywheel
Diode” is used, but you could equally
use a zener diode or small value
varistor (semiconductor diode with
resistance dependent on the applied
voltage.).
Electric Motors
• Electric motors are the most widely used
electromechanical actuators.
• Electric Motor Classification:
• DC motors
• AC motors
• Stepper Motors
• Brushless DC motors
 The DC Motor
• All conventional electric motors consist of
a stationary element and a rotating
element, which are separated by an air
gap.
• In dc motors, the stationary element
consists of salient “poles,” which are
constructed of laminated assemblies with
coils wound round them to produce a
magnetic field.
• The rotating element is traditionally called
the “armature” and this consists of a
series of coils located between slots
around the periphery of the armature.
DC motor
• In 1827, Hungarian physicist Ányos Jedlik
started experimenting with electromagnetic
coils. After Jedlik solved the technical
problems of continuous rotation with the
invention of the commutator, he called his
early devices "electromagnetic self-rotors".
Although they were used only for teaching,
in 1828 Jedlik demonstrated the first device
to contain the three main components of
practical DC motors: the stator, rotor and
commutator. The device employed no
permanent magnets, as the magnetic fields
of both the stationary and revolving
components were produced solely by the
currents flowing through their windings.
simple form of dc motor
 DC motors
Brushed DC motors are generally
available in two types, depending
on the construction of the stator:
• permanent magnet
• wound field.
Both motor types use current and
windings to produce a magnetic
field in the rotor.
Stator magnetic field is produced:
via permanent magnets inside the
stator or with electromagnetic
windings.
 Series wound motors
• When the armature windings and field windings
are connected in series, the motor is referred to
as a “series wound” DC motor.
• Series wound motors have high starting torque
but poor speed control — series wound DC
motors are often used as starter motors for large
equipment with high inertia loads, such as cranes
and elevators.
• They’re also found in consumer products that
require only coarse speed control, such as
blenders and hand tools.
 Shunt wound DC motors
• When the armature and field windings are
connected in parallel, the motor is referred
to as a “shunt wound” DC motor.
• The shunt (field) windings have a high
resistance, preventing them from drawing
high current at startup. But unlike series
motors, shunt motors provide very good
speed regulation.
H-Bridge
• An H-bridge is a simple circuit that lets
you control a DC motor to go
backward or forward.
• used with a microcontroller, such as
an Arduino, to control motors.
 H-Bridge
• If you close switch 1 and 4, you have
plus connected to the left side of the
motor and minus to the other side.
• The motor will start spinning in one
direction.
• If you instead close switch 2 and 3,
you have plus connected to the right
side and minus to the left side.
• The motor spins in the opposite
direction.
 H-Bridge demo

https://youtu.be/GGvbnXi6yI8 Mechatronics Fun

 The H-Bridge circuit PNP transistors on the top

• One can build an H-bridge with four

transistors.
• Since the transistor can be a switch, you’ll be
able to make the motor spin in either
direction by turning on and off the four
transistors in the circuit above.
• Usually, you control the transistors from a
microcontroller, such as Arduino.

NPN transistors on the bottom

• A side-effect of how a motor works is that the motor will also
generate electrical energy. When you disable the transistors to stop
running the motor, this energy needs to be released on some way.
• If you add diodes in the reverse direction for the transistors, you give
a path for the current to take to release this energy. Without them,
you risk that the voltage rises and damages your transistors.

The H-Bridge
circuit
L293D

• L293D devices is
quadruple high-current
half-H drivers
 L293D example
/*
Bi-directional Motor
*/

int enablePin = 11;

int in1Pin = 10;
int in2Pin = 9;
int switchPin = 7;
int potPin = 0;

void setup()
{
pinMode(in1Pin, OUTPUT);
pinMode(in2Pin, OUTPUT);
pinMode(enablePin, OUTPUT);
pinMode(switchPin, INPUT_PULLUP);
}

void loop()
{
int speed = analogRead(potPin) / 4;
boolean reverse = digitalRead(switchPin);
setMotor(speed, reverse);
}

void setMotor(int speed, boolean reverse)

{
analogWrite(enablePin, speed);
digitalWrite(in1Pin, ! reverse);
digitalWrite(in2Pin, reverse);
}

https://learn.adafruit.com/adafruit-arduino-lesson-15-dc-motor-reversing/
L293D example
 Control DC motor with NPN
transistor & Arduino PWM

A small transistor like the PN2222 can be

used as a switch that uses just a little
current from the Arduino digital output to
control the much bigger current of the
motor.
When you turn the power off to a motor,
you get a negative spike of voltage, that
can damage your board or the transistor.
The diode protects against this, by
shorting out any such reverse current
from the motor.

https://learn.adafruit.com/adafruit-arduino-lesson-13-dc-motors/transistors
 motor controller based on high-current operational
amplifiers
• LM12, OPA548, L165, L2720
The power path of this motor driver circuit is based on the
LM12 high power operational amplifier that can be used
in some other power applications like : motor controller ,
audio amplifiers or some other power applications

This damaging condition can be avoided with clamp diodes

(D1,D2) from the output terminal to the power supplies.
Schottky rectifier diodes with a 5 A or greater continuous
https://www.electroniq.net/motor-control-
circuits/lm629-lm628-dc-motor-driver.html rating are recommended
AC Machines Synchronous Motors
• Synchronous motors are so called because
they operate at only one speed, i.e., the
speed of a rotating magnetic field.
• The production of the rotating magnetic field
may be actioned using three, 120° displaced,
stator coils supplied with a three-phase
current.
• The rotational speed of the field is related to
Simple synchronous motor.
the frequency of current.
 Induction Motors
• The stator of an induction motor is much like that of an alternator and in
the case of a machine supplied with three-phase currents, a rotating
magnetic flux is produced.
 Induction Motors
• In an AC motor, there's a ring of electromagnets
arranged around the outside (making up the stator),
which are designed to produce a rotating magnetic
field. Inside the stator, there's a solid metal axle, a
loop of wire, a coil, a squirrel cage made of metal
bars and interconnections (like the rotating cages
people sometimes get to amuse pet mice), or some
other freely rotating metal part that can conduct
electricity. Unlike in a DC motor, where you send
power to the inner rotor, in an AC motor you send
power to the outer coils that make up the stator. The
coils are energized in pairs, in sequence, producing a
magnetic field that rotates around the outside of the
motor.
 Induction Motors
• In synchronous AC motors, the rotor turns at exactly
the same speed as the rotating magnetic field; in an
induction motor, the rotor always turns at a lower
speed than the field, making it an example of what's
called an asynchronous AC motor.
• The theoretical speed of the rotor in an induction
motor depends on the frequency of the AC supply
and the number of coils that make up the stator and,
with no load on the motor, comes close to the speed
of the rotating magnetic field. In practice, the load
on the motor (whatever it's driving) also plays a
part—tending to slow the rotor down. The greater
the load, the greater the "slip" between the speed of
the rotating magnetic field and the actual speed of
the rotor.
 Induction Motors
• The biggest advantage of AC induction motors is
their sheer simplicity.
• They have only one moving part, the rotor, which
makes them low-cost, quiet, long-lasting, and
relatively trouble free.
• DC motors, by contrast, have a commutator and
carbon brushes that wear out and need replacing
from time to time.
• The friction between the brushes and the
commutator also makes DC motors relatively noisy
(and sometimes even quite smelly)
 Induction Motors
• constant speed unless you use a variable-frequency
drive
• Though relatively simple, induction motors can be
fairly heavy and bulky because of their coil windings.
• Unlike DC motors, they can't be driven from
batteries or any other source of DC power
Who invented the induction motor?
• Nikola Tesla's original design
for the AC induction motor.
 The Stepper Motor
• A stepper motor is a device that converts a dc
voltage pulse train into a proportional
mechanical rotation of its shaft.
• In essence, stepper motors are a discrete
version of the synchronous motor.
• The discrete motion of the stepper motor
makes it ideally suited for use with a digitally
based control system such as a
microcontroller.
Types of Steppers
Permanent Magnet or Hybrid
steppers, either 2-phase
bipolar, or 4-phase unipolar
• A stepper motor may have any number of coils. Unipolar drivers, always energize
the phases in the same way. One
• But these are connected in groups called "phases". lead, the "common" lead, will
always be negative. The other
• All the coils in a phase are energized together lead will always be positive.
Unipolar drivers can be
implemented with simple
transistor circuitry. The
disadvantage is that there is less
available torque because only
half of the coils can be energized
at a time.

Bipolar drivers use H-bridge

circuitry to actually reverse the
current flow through the phases.
By energizing the phases with
alternating the polarity, all the
coils can be put to work turning
the motor.
Driving a Stepper
• Driving a stepper motor is a bit more complicated than driving a
regular brushed DC motor.
• Stepper motors require a stepper controller to energize the phases in
a timely sequence to make the motor turn.
 Simple Unipolar Driver
• The simplest type of driver can be built
with a handful of transistors. These are
simply switched on and off in sequence
to energize the phases and step the
motor. Unipolar drivers are relatively
inexpensive to build, but only work with
unipolar motors.
Simple Dual H-Bridge Driver
• Driving a bipolar motor
requires 2 full H-bridges so it
can reverse the current to the
phases. H-bridges can be
tricky to build from scratch.
But there are plenty of H-
bridge chips available to
simplify the task.

The L293D is one of the most

popular and economical chips.
#include <Stepper.h>

const int stepsPerRevolution = 1500; // change this to fit the number of steps per
revolution

// initialize the stepper library on pins 8 through 11:

Stepper myStepper(stepsPerRevolution, 8, 10, 9, 11);

void setup() {
// set the speed at 20 rpm:
myStepper.setSpeed(20);
// initialize the serial port:
Serial.begin(9600);
}

void loop() {
// step one revolution in one direction:
Serial.println("clockwise");
myStepper.step(stepsPerRevolution);
delay(500);

// step one revolution in the other direction:

Serial.println("counterclockwise");
myStepper.step(-stepsPerRevolution);
delay(500);
}
 DRV8825 Stepper Motor Driver Module
• NOT in your Kit!!!
• The DRV8825 stepper motor driver has output drive
capacity of up to 45V and lets you control one bipolar
stepper motor at up to 2.2A output current per coil.

• The driver has built-in translator for easy operation.

This reduces the number of control pins to just 2, one
for controlling the steps and other for controlling
spinning direction.

• The driver offers 6 different step resolutions viz. full-

step, half-step, quarter-step, eighth-step, sixteenth-step
and thirty-second-step.

https://www.ti.com/lit/ds/symlink/drv8825.pdf
DRV8825 Stepper Motor Driver Module
 DRV8825 Stepper Motor Driver Module
Step (and microstep) size

Microstep
MODE0 MODE1 MODE2
Resolution
Low Low Low Full step
High Low Low Half step
Low High Low 1/4 step
High High Low 1/8 step
Low Low High 1/16 step
High Low High 1/32 step
Low High High 1/32 step
High High High 1/32 step
To control this with the DRV8825,
connect stepper lead A to board To connect the phase coils in parallel,
output A1, stepper lead C to board you can connect it to the connect stepper leads A and C’ to
output A2, stepper lead B to board DRV8825 as a bipolar stepper board output A1, stepper
output B1, and stepper lead D to motor by making the bipolar leads A’ and C to board output A2,
board output B2. connections described in the stepper leads B and D’ to board
section above and leaving output B1, and stepper
stepper leads B’ and D to board output B2.
leads A’ and B’ disconnected. To connect the phase coils in series,
These leads are center taps to connect stepper lead A’ to C’ and
the two coils and are not used for stepper lead B’ to D’. Stepper
bipolar operation. leads A, C, B, and D should be
connected to the stepper motor driver
as normal for a bipolar stepper motor
 Stepper motor with drv8825 driver

https://youtu.be/rAIXfkRIQ5s https://lastminuteengineers.com/drv8825-stepper-motor-driver-arduino-tutorial/
 Brushless dc Motors
• These motors have position feedback
of some kind so that the input
waveforms can be kept in the proper
timing with respect to the rotor
position.
• Solid-state switching devices are used
to control the input signals and the
brushless dc motor can be operated
at much higher speeds with full
torque available at those speeds.
 Brushless dc Motors

• One big advantage is efficiency, as these

motors can control continuously at
maximum rotational force (torque). Brushed
motors, in contrast, reach maximum torque
at only certain points in the rotation. For a
brushed motor to deliver the same torque
as a brushless model, it would need to use
larger magnets. This is why even small BLDC
motors can deliver considerable power.
• The second big advantage—related to the
first—is controllability. BLDC motors can be
controlled, using feedback mechanisms, to
delivery precisely the desired torque and
rotation speed. Precision control in turn
reduces energy consumption and heat
generation, and—in cases where motors are
battery powered—lengthens the battery life.
 Brushless dc Motors

• An ESC or an Electronic Speed

Controller controls the brushless
motor movement or speed by
activating the appropriate MOSFETs
to create the rotating magnetic field
so that the motor rotates. The higher
the frequency or the quicker the ESC
goes through the 6 intervals, the
higher the speed of the motor will be.
servomotor
• A servomotor is a rotary actuator or linear actuator that allows for
precise control of angular or linear position, velocity and acceleration.
• It consists of a suitable motor coupled to a sensor for position
feedback.
• It also requires a relatively sophisticated controller, often a dedicated
module designed specifically for use with servomotors.
• Servomotors are not a specific class of motor, although the
term servomotor is often used to refer to a motor suitable for use in
a closed-loop control system.
servomotor

Modern servomotors use rotary encoders, either absolute or

incremental.
The type of motor is not critical to a servomotor and different types
may be used.
Small Servo
• A Servo is a small device that incorporates a three wire DC
motor, a gear train, a potentiometer,an integrated circuit, and an
output shaft bearing
• Of the three wires that stick out from the motor casing, one is
for power, one is for ground, and one is a control input line. The
shaft of the servo can be positioned to specific angular positions
by sending a coded signal.
• As long as the coded signal exists on the input line, the servo
will maintain the angular position of the shaft.
• If the coded signal changes, then the angular position of the
shaft changes.
Servos
• Servos come in different sizes but use similar control schemes
and are extremely useful in robotics.
• The motors are small and are extremely powerful for their size.
It also draws power proportional to the mechanical load.
• A lightly loaded servo, therefore, doesn’t consume much energy
• A very common use of servos is in Radio Controlled models like
cars, airplanes, robots, and puppets.
 Servo motors on Arduino
• This library allows an Arduino board to control RC (hobby) servo motors.
Servos have integrated gears and a shaft that can be precisely controlled.
Standard servos allow the shaft to be positioned at various angles,
usually between 0 and 180 degrees. Continuous rotation servos allow the
rotation of the shaft to be set to various speeds.
• The Servo library supports up to 12 motors on most Arduino boards and
48 on the Arduino Mega.
 Circuit
• Servo motors have three wires: power, ground, and signal.
• The power wire is typically red, and should be connected to
the 5V pin on the Arduino board.
• The ground wire is typically black or brown and should be
connected to a ground pin on the Arduino board.
• The signal pin is typically yellow, orange or white and
should be connected to a digital pin on the Arduino board.
• Note that servos draw considerable power, so if you need to
drive more than one or two, you'll probably need to power
them from a separate supply (i.e. not the +5V pin on your
Arduino).
• Be sure to connect the grounds of the Arduino and external
power supply together.
https://www.arduino.cc/en/Tutorial/LibraryExamples/Sweep
Piezoelectric Actuators
• The direct piezoelectric effect consists in ability of certain materials to
generate electric charge in proportion to externally applied force.
• The inverse piezoelectric effect of these materials consists in their
expansion under the action of electric field parallel to the direction of
polarization.
Piezomaterials
• Materials that exhibit a significant and useful piezoelectric effect fall
into three main groups:
• Natural (quartz, Rochelle salt) and
• synthetic crystals (lithium sulfate, ammonium dihydrogen phosphate),
polarized ferroelectric ceramics, and certain polymer films.
• The main piezomaterial for engineering applications is ferroelectric
ceramics, Lead Zirconate Titanate (PZT) especially.
 Piezoactuating Elements
• Piezoactuating elements in a wide range of sizes are produced as
squares, rectangles, rings, discs, spheres, hemispheres, bars and
cylinders, and special elements.
Piezoactuating Elements