Physically, a mechatronic system is composed of four prime components. They are sensors, actuators, controllers and mechanical components. Figure shows a schematic diagram of a mechatronic system integrated with all the above components. - PowerPoint PPT Presentation

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Physically, a mechatronic system is composed of four prime components. They are sensors, actuators, controllers and mechanical components. Figure shows a schematic diagram of a mechatronic system integrated with all the above components.

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Title: Physically, a mechatronic system is composed of four prime components. They are sensors, actuators, controllers and mechanical components. Figure shows a schematic diagram of a mechatronic system integrated with all the above components.


1
Physically, a mechatronic system is composed of
four prime components. They are sensors,
actuators, controllers and mechanical components.
Figure shows a schematic diagram of a mechatronic
system integrated with all the above components.
2
Actuators are broadly categorized into three
groups, namely, Electromechanical actuators,
Fluid power actuators and Active material based
actuators. Electro-mechanical actuators are used
to efficiently convert electrical energy into
mechanical energy. Magnetism is basis of their
princi-
ples of operation. They use permanent magnets,
electromagn-ets, and exploit the electromagnetic
phenomenon in order to produce the actuation.
Electromechanical actuators are DC, AC and
stepper motors. DC Motor is the most versatile
actuator and sometimes called rotating machine.
The DC motor has two parts, stator and rotor. The
stator is the outer part of the motor which
contains evenly spaced magnetic poles as shown.
3
Practically two windings are there within the
electromag-netic type motor system, namely,
stator winding (s) and rotor winding (s). The
stator winding (s) is called field coil or field
winding.
(a) Separately excited electromagnetic DC
motor (b) Self-excited wound-field shunt
configuration (c) Self-excited wound-field series
configuration
4
A DC motor converts the electrical energy to
mechanical energy. The torque is produced due to
input current. In reverse situation, the torque,
which is equivalent to mechanical energy, can
produce current that is equivalent to electrical
energy. This reverse process is utilized for the
design of DC generator. Figure-7.4 illustrates
schematic diagram of typical DC motor and DC
generator.
5
Brushed DC Motor
  • The rotor electr-omagnet at an instant
  • (b) The rotor electr-omagnet before the rotor
    current flips.
  • (c) The rotor electr-omagnet after the rotor
    current flips
  • (d) A simple brush-ed DC motor illustration
  • (e) Commutator-brush arrangement

6
Many applications require precise positioning
control. The alternative is the stepper motor.
The stepper motor also consists of a rotor and
stator. As the name suggests, the stepper motor
steps a bit at a time. The motor can be
controlled using a microcontroller as it can
responds to digital pulse trains. The rotor of
the motor rotates a specified number of degrees
by each pulse the motor receives from its
controller. The motion caused by one pulse is
called one step.
7
There are only four possible positions of the
rotor when all the phases are excited. In this
typical case, the step size is 90o.
8
In order to have better precision, the number of
step size can be increased by building more
number of poles, phases and introducing proper
control connections within the stator circuits. A
control scheme with 45 degree step size.
9
Pneumatic actuators cause something to move by
taking the advantage of potential energy. The
actuators in their conventional form are
basically called pneumo-mechanical devices and
are used to automate industrial tasks of simple
but iterative nature. The actuator has three
components cylinder, piston and valve. The
cylinder is a hollow chamber into which the
external compressed air is allowed to enter so as
to enable the piston to move. The linear
actuators convert the potential energy in the
compressed air into mechanical energy in terms of
linear motion. Linear actuators are of four
types. Figure shows single-rod single acting type.
10
Linear single-rod double acting
The single-rod double acting actuators have one
rod (piston) two ports (Figure-7.10). Compressed
air is sent to one side of the chamber and the
air in the other side is allowed to escape. The
piston is thus pushed to one end of the cylinder.
When compressed air is allowed to enter in to the
other side and the first side is allowed to
exhaust, then the piston is pushed back.
11
Linear double-rod double acting type actuator has
two rods and two ports as illustrated in the
Figure
12
The rodless type actuator does not have a rod.
The basic operation of rodless actuators is
similar to the standard cylinders. However,
instead of an extending rod, a rodless carriage
is supported by bearings within the main
cylinder. This gives the rodless actuator the
ability to guide and support a load.
13
Valve is a device for closing or modifying the
passage through a pipe, outlet, inlet in order to
stop, allow, or control the flow of a fluid or
air. In case of pneumatic actuators valves act as
the controlling element to control the flow of
air into the chamber of the cylinder.
14
Some of the hydraulic actuator are designed to
provide rotary movement.
These types of actuators provide torque. There
are many types as far as design is concerned, but
importantly rack and pinion type and gear-motor
type actuators are employed in industrial
applications.
15
An example based on piezoelectric actuator is
given. The research group at Tempere University
of Technology, Helsinki, developed a
microtelemanipulator that facilitates remote
handling of microscopic objects. The actuation
system consists of a piezoelectric actuator, a
small tank and a bellows, as illustrated in the
figure. The bellows is a spring type of passive
component. The force required to deform the
bellows is directly proportional to the
displacement. The piezoelectric actuator is
placed in the tank filled with hydraulic oil. The
micromanipulator is controlled either using a PC.
16
The bearing is an active component that reduces
frictional losses as surfaces side past one
another. These bearings are needed whenever one
part of a machine slides against another. The
bearing facilitates linear motion between a load
and a support. It typically uses a lubricant to
reduce friction between the sliding surfaces.
17
The mechanism of journal bearing is similar to
sliding bearing but in this case, a rotating
shaft is involved. Journal bearings are two
types, dry and lubricant-based. Dry type permits
the moving surfaces to rub together as they past
one another. These bearings use low friction
rubbing materials or materials impregnated with a
lubricant in between the two surfaces, subject to
movement. The second type use lubricant. The
lubricants are oil, grease, jelly, gas film and
water.
18
Rolling element bearing is considered as one of
the very important mechanical components and is
essentially used for almost all rotary
applications. The friction reduction is achieved
by providing smooth and hard metal rollers and a
smooth inner and outer circular metal surface for
the rollers to roll against each other. Note that
rolling reduces friction related energy loss to a
minimum, ideally to zero.
19
There are many types of bearings as far as
rolling element is concerned. The geometric shape
of these rolling elements define the
classification. Commonly used rolling elements
are, Balls Cylindrical rollers Needle type
rollers Tapered rollers
20
The rolling element bearings consist of two
circular metal (usually steel) rings and a set of
rolling elements. One of the rings is larger than
the other. The smaller of the two is called inner
ring and the other one is referred to as the
outer ring. The inner ring fits well within the
perimeter of the outer ring. A fixed number of
solid rollers, depending upon the load
requirements are designed into geometric shapes
and placed at equal intervals in the open space
between the two rings.
21
The limitation of friction losses in bearings is
an engineering challenge. In magnetic bearings,
mechanical friction losses are eliminated. A
typical magnetic bearing shown in the figure
composed of four horseshoe-shaped electromagnets.
Each of the electromagnets can produce a force
that attracts the rotor iron towards them. These
bearings allow the rotating shaft to float on a
magnetic field created by the electromagnet.
22
The pulley is a simple component consists of a
plain or grooved wheel and a rope or belt wrapped
around the wheel, mainly used to change the
direction and the point of application of a
pulling force. Depending upon the system
requirements, design of several types of pulleys
are considered. Pulleys can be combined to form
double pulleys, which have at least two wheels.
There are various other combinations, which can
result in a triplex pulleys and complex pulleys.
23
Pulleys can be constructed to assure accurate
positioning, repeatability, and drive
performance. One type of pulleys are called
timing pulleys which are mainly used for
positioning applications.
24
In some applications magnetic pulleys are
employed. The prime function of a magnetic pulley
is for continuous extraction and separation of
contamination such as unwanted iron particles,
piece etc. from the mixture in order to protect
the processing machinery such as crushers,
grinders and other valuable equipment
25
Gears are important mechanical components used in
almost all machineries. They facilitate mechanism
in terms of transformation of power and motion
from one rotating shaft to another. They can help
to increase or decrease force, torque or speed
and can change the direction of the axis of
rotation. They can also change rotary motion to
linear motion.
26
The gears essentially work together at least in
groups of two or more. A single pair may be
inadequate for certain sources and loads, in
which case more complex combinations, are
necessary. More than two gears working together
is called a gear train. They can mesh in many
different ways depending upon the application
requirements.
27
The way the teeth are designed classifies the
gears. Basically, four types of gears are found
in engineering applications, however, some
derivatives from these are also designed.
Spur gears Bevel gears Helical gears
Worm gears
28
The gear ratio is related to the ratio of the
gears, as already mentioned, but usually it is
defined as the ratio of speeds. The velocity
ratio of the driver and follower does not change
by putting any number of gears between them.
29
(Courtesy Andantex USA, Inc.)
Rack and pinion driving mechanism refers to a
special type of gearing mechanism in which the
rotational motion is converted to linear one and
vice versa.
30
The ratchet is an asymmetric mechanical component
that allows something to turn in one direction
only. In conjunction with another component
called pawl, fundamentally, as if the ratchet
works like a locking system. It is designed with
suitably shaped teeth, receiving an intermittent
circular motion from another member, called
crank.
31
The slider-crank is a linkage that transforms
linear motion to circular motion or vice versa.
The crank is a lever attached to a rotating
shaft. It is really a link, which revolves
relative to a frame. The link can convert a
rotating motion into a reciprocating motion or
vice versa.
32
A cam is defined as a machine element having a
curved surface, which, by its rotational motion,
gives a predetermined specified motion to another
element called the follower which always in
contact with the cam. The irregul-arly shaped cam
rotates in an eccentricalaxis. The mechanism is
used to transmit reciprocal motion .
A typical cam and its displacement profile
33
Classification of cams
  • Circular eccentric
  • (b) Elliptical
  • (c) pear-shaped edge
  • (d) Heart-shaped
  • (e) Cylindrical

34
Broadly, the shape of the followers is of three
types pointed follower, roller-type follower and
the mushroom or flat foot follower. The pointed
follower is designed with a knifelike edge or
point. It is the simplest one and inherits
drawbacks of rapid rate of wear. Roller-type
followers incorporate rollers, a design that can
improve reliability and performance. Roller-type
followers overcomes the problem of rapid rate of
wear and can withstand higher dynamic loads.
Mushroom followers utilize a tappet that has a
larger diameter base than the diameter of the
body of the follower itself.
35
The chain and sprocket drive is another
mechanical component, which is also exploited for
power transmission. The sprocket is a toothed
wheel and the chain is a loop of loosely jointed
links (Figure-7.35). In operation, the
chain-sprocket in combination offers the means of
transmitting power between two or more rotating
shafts.
36
Geneva wheel based mechanism is used for
achieving intermittent motions. The component has
two wheels, the upper and the lower wheel. There
is a projection, called drive pin, mounted on the
lower wheel. The rotational movement of the lower
wheel is essentially continuous but the upper
wheel only rotates step-wise i.e.,
intermittently. The upper wheel makes one
complete rotation corresponding to four complete
rotations of the lower wheel, in this typical
example.
37
Four-bar linkage has four axes of rotation
connected by four rigid linkages. Four-bar
linkages have the capability of mimicking
rotation, oscillation, and translation. The
linkage is a versatile component used extensively
in many machineries and system such as steering
systems of almost all automobiles, the sewing
machines, earth movers, packaging machines and so
on.
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