Presentation on Actuators

Prepared by:Kaan Ayberk Uçum

Neptun Kode:Q1WG1L

What is an actuator?Actuators are devices used to produce action or motion.

Input(mainly electrical signal , air, fluids)

Electrical signal can be low power or high power.

Actuators output can be position or rate i. e.linear displacement or velocity.

Actuation can be from few microns to few meters

Actuator functional diagram

APower

amplification & modulation

Energy conversion

Control signal

Actuator

Output

Unmodulate Energy source

ACTUATORSElectromechanical Actuators

Electrical Machines

Piezoelectric Actuators

Hydraulic and Pneumatic Actuation Systems

Electromechanical Actuators

1) Electromagnetics—Magnetic Field- Solenoid Type Devices- Voice-Coil Motors (VCMs)- Electric Motors

* 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.

Solenoid Type Devices

Solenoids,is the simplest electromagnetic actuators that are used in linear as well as rotary actuations for valves, switches, and relays.

As the name indicates, a solenoid consists of a stationary iron frame (stator), a coil (solenoid), and a ferromagnetic plunger (armature) in the center of the coil

Solenoid:A solenoid is a coil wound into a tightly packed helix.

A second actuator that is often used is known as a solenoid

In physics, the term solenoid refers to a long, thin loop of wire, and wrapped around a metallic core.

which produces a magnetic field when an electric current is passed through it.

Type of solenoids

How a selenoid works?

Voice-Coil Motors (VCMs)

- As the name indicates, the voice-coil motor was originally developed for loudspeakers

-It is now extensively used in moving read/write heads in hard disk drives

-Since the coil is in motion, VCM is also referred to as a moving-coil actuator.

How Does a Voice Coil Motor Work?

Electric Motors

Electric motors are the most widely used electromechanical actuators.

They can either be classified basedon functionality or electromagnetic characteristics.

The differences in electric motors are mainly in therotor design and the method of generating the magnetic field

How a electric motor work?

Electrical Machines-The utilization of electric motors as the power source in a mechatronic application is substantial.

-Electric motors, therefore, often feature as the prime mover in a variety of driven systems.

Electrical actuatorElectrically actuated system are very widely used in control system

There are three types of motor used in control system

D.C. motor

A.C. motor Stepper motor

Every motor works on the principle that when a current-carrying conductor is placed in a magnetic field, it experiences a mechanical force.

Working Principle of motor

A.C. motor

Stepper motor

Permanent magnet type

Variable reluctance type

Hybrid type

A stepper motor is an electromechanical device which converts electrical pulses into discrete mechanical movements.

DC MOTORS

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.

DC Motor The interaction between two magnetic

fields produces the movement.

They are the most used due to: Facility to control it. Major power. Performance. Price.

A very simple form of dc motor is illustrated in Fig. 20.56.

• A DC motor or Direct Current Motor converts electrical energy into mechanical energy.

• A direct current (DC) motor is a fairly simple electric motor that uses electricity and a magnetic field to produce torque, which turns the rotor and hence give mechanical work.

DC MOTOR

PRINCIPLE OF DC MOTORS• In any electric motor, operation is

based on simple electromagnetism.

• When a current-carrying conductor is placed in an external magnetic field, it will experience a force i.e. Lorentz force.

• Due to this force torque is produced which rotates the rotor of motor and hence a motor runs.

WORKING OF DC MOTORS

TYPES OF DC MOTORS• DC motor are of 3 types they are…..

1. DC SHUNT MOTOR

2. DC SERIES MOTOR

3. DC COMPOUND MOTOR

1. DC SHUNT MOTOR

Armature

• The parallel combination of two windings is connected across a common dc power supply.

• The resistance of shunt field winding (Rsh) is always higher than that is armature winding.

• This is because the number of turns for the field winding is more than that of armature winding.

• The cross-sectional area of the wire used for field winding is smaller than that of the wire used for armature winding.

2. DC SERIES MOTOR• The field winding is connected in

series with the armature.• The current passing through the

series winding is same as the armature current .

• Therefore the series field winding has fewer turns of thick wire than the shunt field winding.

• Also therefore the field winding will posses a low resistance then the armature winding.

3. DC COMPOUND MOTORDC

COMPOUND MOTORLONG

SHUNT COMPO

UND MOTOR

SHORT SHUNT COMPO

UND MOTOR

CUMULATIVE COMPOUND MOTOR

DIFFERENTIAL COMPOUND MOTOR

I. LONG SHUNT COMPOUND MOTOR

• In this the series winding is connected in series with the armature winding and the shunt winding is connected in parallel with the armature connection.

II. SHORT SHUNT COMPUND MOTOR

• In short shunt compound motor the series winding is connected in series to the parallel combination of armature and the shunt winding

• This is done to get good starting torque and constant speed characteristics.

a) CUMULATIVE COMPOUND DC MOTORS

b) DIFFERENTIAL COMPOUND DC MOTORS

• If the two field windings i.e. series and shunt are wounded in such a way that the fluxes produced by them add or assist each other

• If the two field winding i.e. series and shunt are wounded in such a way that the fluxes produced by them always try to oppose and try to cancel each other.

APPLICATIONS OF DC MOTORSMOTORS.. APPLICATIONS…

D.C. SHUNT MOTORLATHES , FANS, PUMPS DISC AND BAND SAW DRIVE REQUIRING MODERATE TORQUES.

D.C. SERIES MOTOR ELECTRIC TRACTION, HIGH SPEED TOOLS

D.C. COMPOUND MOTORROLLING MILLS AND OTHER LOADS REQUIRING LARGE MOMENTARY TORQUES.

AC Motor Asynchronous Motors

Synchronous Motors

Synchronous Motors

Synchronous motors are so called because they operate at only one speed, i.e., the speed of a rotating magnetic field.

Servomotors

Conformed by:

Motor.

Reducing box.

Control circuit.

Great precision.

Servomotors

Similar to a direct current motor, with the aptitude to be located in any position inside a range of operation and to be kept stable in the mentioned position.

It is frequently used in radiocontrol systems and robotics.

It´s use is not limited to these.

Stepper Motors.

Electromagnetic device that converts a series of electric pulses into discrete angular displacements.

It advances a series of degrees (steps) depending on its imputs.

Piezoelectric Actuators

Piezoelectric actuatorsPierre and Jacques Curie discovered the piezoelectric effect in 1880.

The application of an electric field to a piezoelectric crystal leads to a physical deformation of the crystal.

Piezoelectric materials are: Quartz, Ceramics, PZT(lead zirconate titanade). Advantages

short response time.An ability to create high forces.A high efficiency and a high mechanical durability.

Disadvantage

Have small strains. (0.1-.2%)High supply voltage needed.(60-1000V)Large hysteresis.(actuator doesn’t go back to exactly where it started).

Configuration A piezo ceramic crystal is coated with silver on both sides.

Glued to a brass, nickel alloy, or stainless steel disk.

Brass: Commercial & industrial use.(not subjected to environment )

Nickel alloy:

Use where it subjected to environment.

Stainless steel: Uses where it subjected to solvent, corrosive chemical,

Underwater . Medical fields.

Types of piezoelectric actuators

Piezoelectric Stack ActuatorsProduce linear motion.

Linear motor

Piezoelectric bender actuator

Piezomotors (Ultrasonic Motors)Vibromotors find wider and wider application as

actuators based on the conversion of high frequency mechanical oscillations (dozens of kHz) into continuous motion.

Advantages of piezomotorslarge torque, high resolution, excellent controllability, small time constant, compactness, high efficiency,silent operation,no electromagnetic induction.

Hydraulic and Pneumatic Actuation Systems

The primary function of an actuation system is to influence the controlled system so as to obtain the desired movement or action.

This objective is made possible by the actuation system, which converts the primary energy with which the actuator operates into the final mechanical energy.

Fluid Actuation SystemsAn actuation system, which is part of an automatic

machine, consists of a power part and a control part as illustrated in Fig. 20.86.

The power part comprises all the devices for effecting the movements or actions.

Figure 20.87 illustrates a fluid actuation system. The power part consists of the actuator—a doubleacting cylinder in the case in the figure—the front and rear chambers of which are fed by a 4/2 distributor valve, which constitutes the fluid power adjustment interface.

Hydraulic actuator:Hydraulic systems are used to control & transmit power.

A pump driven by prime mover (electric motor) creates flow of fluid

Linear actuator (hydraulic cylinder)-Provides motion in straight line.Linear displacement depends on stroke length.Usually referred to as cylinders, rams (single acting cylinders) or jacks.

Rotary actuators (Hydraulic motors)-Produces continuous rotational motion.Pump shaft is rotated to generate flow.A motor shaft is caused to rotate by fluid being forced into the driving chambers.

Types of hydraulic actuator

Semi rotary actuators-Produces non-continuous rotational motion.Limited to less than one revolution (<360°).Used to produce oscillatory motions in mechanisms.

Applications

Hydraulic jack.

Hydraulic brake.

Hydraulic ram.

Used as sensor. Close loop velocity controlling. Highly precise positioning for heavy loads.

Hydraulic Actuation SystemsThe components of a hydraulic actuation system are the pump, that is, the hydraulic power generation system; the actuator, that is, the element which converts hydraulic

power into mechanical power; the valve, that is, the hydraulic power regulator;the pipes for connecting the various components of the

actuation system;the filters, accumulators, and reservoirs;the fluid, which transfers the power between the various circuit

elements; the sensors and transducers; the system display, measurement, and control devices.

PumpsPumps transform electrical or mechanical energy

into hydraulic energy.They constitute the fluid flow generator of the

hydraulic system, as the pressure is determined by the fluid resistance downstream from the generator.

The main types of pumps are shown in Fig. 20.90.

Gear PumpsGear pumps are subdivided into pumps with

external gears, pumps with internal gears, and screw pumps.

Rotary Vane PumpsVane pumps (Fig. 20.93) generally consist of a

stator and a rotor, which can rotate eccentrically with respect to one another. Vanes can move in special slits placed radially in the stator or in the rotor and delimit appropriate variable volumes.

Piston PumpsVolumetric piston pumps can have one or more

cylinders; that is, there may be one or more cylinders with a piston sliding in each of them.

ValvesValves are the components in hydraulic circuits that

carry out the task of regulating the hydraulic power sent to the actuator.

They are subdivided as follows on the basis of the operations they carry out:

• directional valves• on-off valves• pressure regulator valves• flow-rate regulator valves

Animation How basic hydraulic circuit works

It convert energy formed by compressed air at high pressure into ether linear or rotary motion. Quickly respond in operation.

Pneumatic actuator

CONSTRUCTIONAL FEATURES OF CYLINDER

Pneumatic Actuation SystemsJust as described for the hydraulic system, the

components of a pneumatic actuation system are:• the valve, that is, the regulator of the pneumatic

power;• the actuator, which converts the pneumatic power

into mechanical power;• the piping;• the sensors and transducers;• the system display, physical magnitude

measurement, and control devices.

CompressorsThe types of compressors used to produce

compressed air are summarized in Fig. 20.113. In volumetric compressors, the air or gas is sucked in by means of a valve in the compression chamber where its volume is reduced to cause compression of the gas.

They can be single and double acting, with one or more pistons and one or more stages (Fig. 20.114).

Pneumatic ValvesPneumatic valves are functionally similar to those

used in hydraulic systems, so that reference should be made to the general considerations described above.

-PWM (Pulse Width Modulation) Valves-Proportional Pressure Regulator Valves

ACTUATORS - COMPARISONActuator types Advantages Disadvantages

Electrical(servomotor or stepping motor)

Direct interface with computer system. Simple

design.

Low thrust. Slow speed.

No mechanical fail safe hazardous.

Electromechanical(Motors combined with gear

boxes)

High thrustHigh stiffness coefficient

Flexible adaptation

Complex designNo mechanical fail safeLarge, heavy structure

HazardousHydraulic and Electro

hydraulicHigh thrustFast speed

High stiffness coefficientSelf lubrication

Complex designLarge, heavy structure

HazardousFluid Viscosity

SensitivePneumatic and Electro-

pneumaticLow cost

Mechanical Fail safeSimple designSmall package

Suitable for highly hazardous areas also

Good control with control device

Slow speedLack of stiffness

InstabilityModerate trust

Quality air requirement