Electrical and electronic Actuator.ppt ‏.ppt

 Hydraulic
 Pneumatic
 Electric.
 There are three basic types of actuators:
Actuators and Drives
Actuators and Drives

Elements of the Final Control Operation
Interface control signal to actuator,
Amplifier, DAC, I/P conversion, etc.
Solenoid, stepper motor, AC & DC
motors, electronic switches, solid-state
relays (SCRs, TRIACS), pneumatic
and hydraulic actuators.
Motor-driven conveyor, belts, paper
thickness roller assemblies, heating
systems, control valve.

 Hydraulic Actuators
• Provide movement by pumping fluid (usually oil) through pipes and hoses
to hydraulic cylinders or motors.
• Flow of the fluid is controlled by electric valves. As fluid is pumped into the
cylinder the extends; as it is pumped out, the rod retracts. Similarly. as fluid
is pumped into a hydraulic motor the output shaft rotates.
• A major advantage of hydraulic actuators is their ability to lift loads of up
to
30.000 pounds.
• Another advantage is that they do not generate sparks like electric motors
and can therefore be used in explosive environments such as found in spray
painting.

 Pneumatic Actuators
• Work on the same principle as hydraulic actuators but
com- pressed air is used instead of fluid.
• Especially useful when quick movements are required.
• Pneumatic grippers are good at holding objects because
of the "springiness" caused by the gas under pressure.
• Pneumatic manipulator arms are inaccurate because
the "springiness' causes the arm to droop under load.

A Solenoid Controlled 5 Ported, 4 Way 2 Position Valve.
solenoid
solenoid
power in
exhaust out
power in exhaust out
The solenoid has two positions and when
actuated will change the direction that
fluid flows to the device. The symbols
shown here are commonly used to
represent this type of valve.

IN
EX
One-Way Restrictor
Double-Acting
Cylinder
4-Way 2-position Solenoid Valve
Typical Pneumatic System

ENGR415. MECHATRONICS
Dr. Ricardo Valverde
15
A Typical Pneumatic System

Pressure limiting/relief valve
Relief V/V’s are used to ensure that
the receiver TK or line pressure do
not exceed predetermined values

19
The air pushes against the piston inside the cylinder and causes it to
outstroke. When the piston has fully outstroked it is said to be positive.
If we stop the supply of air then the spring inside the cylinder
causes the piston to instroke to its starting position and the piston is
said to be negative.
As this happens, the air inside the cylinder is pushed back out.
Single-acting cylinders are easy to use and control but they do
not produce very big forces.
Single-acting cylinder
positive
Air in
negative
Air out

20
A double-acting cylinder has no spring inside to return it to its
original position. It needs two air supplies, one to outstroke the piston
and the other to instroke the piston.
Double-acting cylinders are used more often in pneumatic
systems than single-acting cylinders. They are able to produce
bigger forces and we can make use of the outstroke and instroke
for pushing and pulling.
Double-acting cylinder
positive
Air in Air out
negative
Air in
Air out

22
Pneumatic & Hydraulic Actuators
 Large manipulators in industry frequently employ
hydraulic drives, since such drives provide a higher
torque-to-weight ratio than electric motors
 However, because of the maintenance problems
associated with pressurized oil (including leaks),
hydraulic motors are not used in smaller mobile
robots
 Pneumatic drives have been used as actuators in the
past but are not currently popular.
 Air is compressible, resulting in nonlinear behavior
of the actuator.

Servo Motors
3- Electrical Servomotors
1- Hydraulic Servomotors
2- Pneumatic Servomotors

26
Pneumatic Servo Motor

28
 The axial piston pump with rotating swashplate.
 In hydraulic systems with a working pressure above aprox. 250 bar
the most used pump type is the piston pump.
 The pistons move parallel to the axis of the drive shaft. The swashplate
is driven by the shaft and the angle of the swashplate determines the
stroke of the piston.
 The valves are necessary to direct the flow in the right direction. This
type of pump can be driven in both directions.
THE AXIAL PISTON PUMP:

29
The Axial Piston P/P with Rotating Barrel:
• This axial piston P/P consists of a non rotating swashpla(green) te and a rotating barrel (light blue).
• The advantage of this construction is that the P/P can operate without valves because the rotating
barrel has a determined suck and pressure zone.
• The animation shows the behaviour of only one piston; normally this P/P h as 5, 7, 9 or 11 pistons.
• The P/P in the animation can also be applied as a hydraulic motor.

30
 The animation shows how the displacement of an axial piston P/P can be adjusted. In this
example we use an axial piston P/P with a rotating cylinder barrel and a static' swashplate.
 The cylinder barrel is driven by the drive shaft which is guided through a hole in the
swashplate. The position (angle) of the swashplate determines the stroke of the pistons and
therefore the amount of displacement (cm3/omw) of the pump.
 By adjusting the position of the swashplate the amount of displacement can be changed. The
more the swashplate turns to the vertical position, the more the amount of displacement
decreases.
 In the vertical position the displacement is zero. In that case the P/P may be driven but will
not deliver any oil. Normally the swashplate is adjusted by a hydraulic cylinder built inside
the P/P housing.
The Axial Piston P/P With Variable Displacement:

31
C. There are common operating problems in a pump.
(1) Pressure Loss. Pressure loss means that there is a high leakage path in a system.(relief
valve, cylinders, motors, & A badly worn pump).
(2) Slow Operation. This can be caused by a worn pump or by a partial oil leak in a system.
Pressure will not drop, however, if a load moves at all. Therefore, hp is still being used
and is being converted into heat at a leakage point.
(3) No Delivery. If oil is not being pumped, a pump-
 Could be assembled incorrectly.
 Could be driven in the wrong direction.
 Has not been primed. The reasons for no prime are usually improper start-up, inlet
restrictions, or low oil level in a reservoir.
 Has a broken drive shaft.
(4) Noise. If you hear any unusual noise, shut down a pump immediately. Cavitation noise
is caused by a restriction in an inlet line, a dirty inlet filter, or too high a drive speed. Air in
a system also causes noise. Noise can be caused by worn or damaged parts, which will
spread harmful particles through a system, causing more damage if an operation continues.

Process Control Valve: Valve sizing

Electric Actuators
Electric Actuators
 Electric Actuators
• Cause motion when electrical current flows through them.
• An electric motors which fall into two basic categories:
 Continuous rotation motors
 keep turning until the power is turned off and can be only crudely
controlled.
 stepper motors.
 give highly accurate movements because they move in precise steps of
a few degrees rotation at a time.
 commonly used in smaller and medium sized robots.

 Motors
• Three broad classes
AC motors
 Primarily used in high-power applications.
DC motors
 Used in precision position-control applications.
Stepper motors
 A digital actuator used in position control applications

43
Components Of An Electric Motor
 The principle components of an electric motor are:
• A stator north and south magnetic poles to provide a strong
magnetic field, made of ferrous material they traditionally
forming the outer casing of the motor.
• An armature, which is a cylindrical ferrous core rotating within
the stator and carries a large number of windings.
• A commutator, which rotates with the armature and consists of
copper contacts attached to the end of the windings.
• Brushes in fixed positions and in contact with the rotating
commutator contacts. They carry direct current to the coils,
resulting in the required motion.

44
Components Of An Electric Motor (cont…)
(Rotating)
Commutator
Stator
Brushes
Armature

45
How Do Electric Motors Work?
 The classic DC motor has a rotating armature in the form of
an electromagnet.
 A rotary switch called a commutator reverses the direction of the
electric current twice every cycle, to flow through the armature so
that the poles of the electromagnet push and pull against the
permanent magnets on the outside of the motor.
 As the poles of the armature electromagnet pass the poles of
the permanent magnets, the commutator reverses the polarity
of the armature electromagnet.
 During that instant of switching polarity, inertia keeps the
motor going in the proper direction.

46
How Do Electric Motors Work? (cont…)
A simple DC electric motor: when the coil is powered, a magnetic field is
generated around the armature. The left side of the armature is pushed away
from the left magnet and drawn toward the right, causing rotation.

47
The armature continues to rotate

48
When the armature becomes horizontally aligned, the commutator
reverses the direction of current through the coil, reversing the magnetic
field. The process then repeats.

49
Electric Motors
 Electric motors usually have a small rating, ranging up to
a few horsepower.
 They are used in small appliances, battery operated
vehicles, for medical purposes and in other medical
equipment like x-ray machines.
 Electric motors are also used in toys, and in automobiles
as auxiliary motors for the purposes of seat adjustment,
power windows, sunroof, mirror adjustment, blower
motors, engine cooling fans etc.

50
Drives
Drives
 Usually used to slow down the high speed rotation of
actuators.
 Include such speed reducing mechanisms as screw drives and
gears.
 The gear is a basic mechanism which is connected by the
center hole to the rotary shaft of the actuator. Each gear is a
wheel having precise teeth that fit into a similar wheel of the
same type.
 Used in pairs, gears can reduce actuator speed.

51

52
Stepper Motors
 When incremental rotary motion is required in a robot, it
is possible to use stepper motors.
 A stepper motor possesses the ability to move a specified
number of revolutions or fraction of a revolution in order
to achieve a fixed and consistent angular movement.
 This is achieved by increasing the numbers of poles on
both rotor and stator.
 Additionally, soft magnetic material with many teeth on
the rotor and stator cheaply multiplies the number of poles
(reluctance motor).

53
Stepper Motors
 This figure illustrates the design
of a stepper motor, arranged
with four magnetic poles
arranged around a central rotor.
 Note that the teeth on the rotor
have a slightly tighter spacing
to those on the stator.
This ensures that the two sets of teeth are close to
each other but not quite aligned throughout.

54
Where pairs of teeth are least offset, the electro magnetic
pulse causes alignment and a small rotation is achieved,
typically 1-2o
Movement is achieved when power is applied for short
periods to successive magnets.

55
The top electromagnet (1) is charged, attracting the topmost
four teeth of a sprocket.
Operation

56
The top electromagnet (1) is turned off, and the right
electromagnet (2) is charged, pulling the nearest four teeth to the
right. This results in a rotation of 3.6°.

57
The bottom electromagnet (3) is charged; another 3.6°
rotation occurs.

58
The left electromagnet (4) is enabled, rotating again by 3.6°.
When the top electromagnet (1) is again charged, the teeth in the
sprocket will have rotated by one tooth position; since there are
25 teeth, it will take 100 steps to make a full rotation.

59
 Stepper motors have several advantages:
• Their control is directly compatible with digital technology
• They can be operated open loop by counting steps, with an
accuracy of 1 step.
• They can be used as holding devices, since they exhibit a
high holding torque when the rotor is stationary

• A central rotor surrounded by a number of windings.
• Opposite pairs of coils are energised in turn.
• This ‘drags’ the rotor round one ‘step’ at a time.
• Speed proportional to frequency.
• Typical motor might require 48-200 steps per revolution
 Stepper motors

Driving Stepper Motors
 Note: Signals to the stepper motor are binary, on-off
values (not PWM).
 Easy in principle :
Activate poles as A B C D A… or A D C B A…Steps
are fixed size, so no need to sense the angle!
(open loop control).
 Sequence of (3 or more) poles is activated in turn,
moving the stator in small “steps”.
 Very low speed / high angular precision is possible
without reduction gearing by using many rotor teeth.

Stepper-Motor Current Waveforms

Use a coil of wire to generate a magnetic field that attracts an
iron component toward the coil.
Often used in an ON/OFF mode. A typical solenoid as shown.
Solenoids:
 The number of turns N of the coil.
 The current I, the pole area A.
 The air gap h permeability of air.
The force generated by the solenoid is a function of:

64
Pneumatic & Hydraulic Actuators
 Large manipulators in industry frequently employ
hydraulic drives, since such drives provide a higher
torque-to-weight ratio than electric motors
 However, because of the maintenance problems
associated with pressurized oil (including leaks),
hydraulic motors are not used in smaller mobile
robots
 Pneumatic drives have been used as actuators in the
past but are not currently popular
 Air is compressible, resulting in nonlinear behavior
of the actuator

65
 Heater Actuator

Electrical and electronic Actuator.ppt ‏.ppt

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