Encoders

as per APJ KTU.. module 1 mechatronics

1. ME407
MECHATRONICS
SUKESH O P
Assistant Professor
Dept. of Mechanical
Engineering
JECC
10/16/18
1SUKESH O P/ APME/ME407- MR-2018

2. SYLLABUS
Introduction to Mechatronics, sensors,
Actuators, Micro Electro Mechanical Systems
(MEMS), Mechatronics in Computer Numerical
Control (CNC) machines, Mechatronics in
Robotics-Electrical drives, Force and tactile
sensors, Image processing techniques, Case
studies of Mechatronics systems.
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3. MODULE-I
Introduction to Mechatronics: Structure of
Mechatronics system. Sensors -
Characteristics -Temperature, flow, pressure
sensors. Displacement, position and proximity
sensing by magnetic, optical, ultrasonic,
inductive, capacitive and eddy current
methods. Encoders: incremental and absolute,
gray coded encoder. Resolvers and synchros.
Piezoelectric sensors. Acoustic Emission
sensors. Principle and types of vibration
sensors.
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4. Module 1
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Encoders: incremental and absolute, gray
coded encoder.

5. CNC System
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6. Encoders
An encoder is a device, circuit, transducer,
software program, algorithm or person that
converts information from one format or code
to another, for the purposes of
standardization, speed, secrecy, security, or
saving space.
A device used to change a signal or data to a
code.
Encoder is a digital optical device that
converts motion into a sequence of digital
pulses.
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12. Incremental Encoders
Magnetic
Contact
Optical

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Incremental Encoders

14. Digital Readout (DRO)
7-segment display

15. Rotary Absolute Encoders

16. Rotary Absolute Encoders

17. Rotary Absolute Encoders

18. ROTARY ABSOLUTE ENCODERS

19. Linear Absolute Encoders
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20. Opaque black is 1 and transparent glass
represents 0.
The absolute encoder provides exact rotational
position of the shaft whereas the incremental
encoder gives relative position of the shaft in
terms of digital pulses.
The outmost track has an equivalent value of 1.
(2
0
= 1).
 Similarly, other tracks 2
1
=2 , 2
2
=4, 2
3
=8, 2
4
=16
The sum of shaded area sensed by scanner
gives the displacement value.
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21. Limit Switch

22. LINEAR ENCODERS

23. LINEAR ENCODERS

24. Module 1
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Resolvers and synchros..

25. Resolver
It is also used to measure the angular position
of lead screw thereby to measure the position
of machine slide.
The resolver consist of stator and rotor
windings which are mounted at right angles to
each other.
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26. In a resolver, the output signal as a function of
rotation is obtained by inductive coupling
between the stator and rotor. If an A/C voltage
is applied to one of the stator coils, a
maximum voltage will appear at the rotor coil,
when these two coils are in line and the
voltage will disappear for 90degrees shift.
When the shaft is rotated, the induced voltage
in one rotor coil follows a sine curve and the
voltage induced in the other follows a cosine
curve. So the phase angle depends on the
angular position of the rotor shaft.
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28. A resolver is a type of rotary
electrical transformer used for measuring
degrees of rotation

29. The most common type of resolver is the
brushless transmitter resolver.
On the outside, this type of resolver may look like
a small electrical motor having a stator and rotor.
On the inside, the configuration of the wire
windings makes it different.
The stator portion of the resolver houses three
windings: an exciter winding and two two-phase
windings (usually labeled "x" and "y") (case of a
brushless resolver).
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30. The exciter winding is located on the top; it is in
fact a coil of a turning (rotary) transformer. This
transformer induces current in the rotor without a
direct electrical connection, thus there are no wires
to the rotor limiting its rotation and no need for
brushes.
The two other windings are on the bottom, wound
on a lamination. They are configured at 90 degrees
from each other.
 The rotor houses a coil, which is the secondary
winding of the turning transformer, and a separate
primary winding in a lamination, exciting the two
two-phase windings on the stator.

31. Resolvers can perform very accurate analog
conversion from polar to rectangular coordinates.
Shaft angle is the polar angle, and excitation
voltage is the magnitude.
The outputs are the [x] and [y] components.
 Resolvers with four-lead rotors can rotate [x] and
[y] coordinates, with the shaft position giving the
desired rotation angle.
Types of resolver
Receiver resolvers
Differential resolvers
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32.  Synchros
In function, the synchro is an electromechanical
transducer.
A mechanical input such as a shaft rotation is
converted to a unique set of output voltages, or
a set of input voltages is used to turn
a synchro rotor to a desired position.
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33. The complete circle represents the rotor.
The solid bars represent the cores of the windings next to
them. Power to the rotor is connected by slip rings and
brushes, represented by the circles at the ends of the rotor
winding.
The rotor induces equal voltages in the 120° and 240°
windings, and no voltage in the 0° winding. [Vex] does not
necessarily need to be connected to the common lead of the
stator star windings.

34. A synchro is, in effect, a transformer whose
primary-to-secondary coupling may be varied by
physically changing the relative orientation of the
two windings. Synchros are often used for
measuring the angle of a rotating machine such
as an antenna platform. In its general physical
construction, it is much like an electric motor.
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35. The primary winding of the transformer, fixed to
the rotor, is excited by an alternating current,
which by electromagnetic induction, causes
currents to flow in three Y-connected secondary
windings fixed at 120 degrees to each other on
the stator.
The relative magnitudes of secondary currents
are measured and used to determine the angle of
the rotor relative to the stator, or the currents can
be used to directly drive a receiver synchro that
will rotate in unison with the synchro transmitter.

36. Synchro - Eight functional Categories
Torque Transmitter (TX)
Control Transmitter (CX)
Torque Differential Transmitter (TDX)
Control Differential Transmitter (CDX)
Torque Receiver (TR)
Torque Differential Receiver (TDR)
Control Transformer (CT)
Torque Receiver-Transmitter (TRX)
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37. Acoustic emission sensor
An AE sensor is a type of sensor, which
converts the surface movement caused by an
elastic wave into an electrical signal, which ca
be processed by the measuring instrument.
The piezoelectric element of Acoustic
Emission (AE) sensor should have high
sensitivity and it should convert the surface
movement most efficiently to an electrical
voltage.
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38. Acoustic emission sensor
Acoustic emission (AE) is the phenomenon of
radiation of acoustic (elastic) waves in solids
that occurs when a material undergoes
irreversible changes in its internal structure,
for example as a result of crack formation or
plastic deformation due to aging, temperature
gradients or external mechanical forces.

39. Acoustic emission

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41. AE sensors are used in a wide range of fields,
including the inspection of manufactured products,
monitoring the safety of structures, and the
development of new materials.
Acoustic Emission (AE) is the sound emitted as an
elastic wave by a solid when it is deformed or struck.
The use of AE sensors to detect these elastic waves
and to non-destructively test on materials is called the
AE method. 
Quite some time before failure occurs, tiny
deformations and minute cracks will appear and
spread in materials. By picking up the trends in AE, the
AE method can detect and predict flaws and failures in
materials and structures.
Typical non-destructive testing methods
Ultrasonic Testing (UT)
Radiographic Testing (RT)
Eddy Current Testing (ET)
Acoustic Emission Testing (AET)

42. The AE method offers the following advantages.
Can observe the progress of plastic deformation
and microscopic collapse in real time. 
Can locate a flaw by using several AE sensors. 
Can diagnose facilities while they are in
operation

44. Types of AE sensors
AE sensors are broadly classified into two types:
 Resonance models (narrow-band) that are
highly sensitive at a specific frequency.
Wide bandwidth models that possess a
constant sensitivity across a wide band of
frequencies.
The choice of model depends on the goal of the
application. 
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45. Resonance model
The mechanical resonance of the detector
element is used to obtain high sensitivity.
Generally, these types of sensors have
resonant frequencies in the range of 60 kHz to
1 MHz .
AE sensors having a piezoelectric
accelerometer design are used if lower
resonance characteristics are required.

46. Wide bandwidth model
A damper is bonded on top of the detector
element to suppress the resonance.

47. The application of AE sensors
Product testing
Tool monitoring
Facility diagnosis
Safety monitoring in civil engg. projects
Diagnosis of the integrity of large structures.
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48. Product testing
a)Detecting event of "head touch" in magnetic
discs
AE sensors are used in the quality control
management of magnetic discs. The sensors can
detect the sounds of tiny prominences on a
rapidly spinning magnetic disc striking the
magnetic head.

49. b) Detection of abnormal sounds in small electric
motors
The passing or failure of the product can be decided based on the
level of abnormal sounds coming from motors and fans.
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50. c) Inspection of the bonding of laminated boards
An AE sensor can tell by the acoustic emissions
generated when a load is applied to a laminated board
whether there is poor bonding between laminations or
not.

51. d) Detection of sub-standard pipe welds
When pipes, etc., are improperly welded, the substandard
welding can be detected by the AE that are generated.

52. e) Detection of tiny hole in drum cans
The passing or failure of the drum can be decided by
leak detection when air is pumped into the drum.

54. The term vibration relates with the
displacement, velocity and acceleration. So
vibrations can be measured by using the
transducers which are sensitive to
displacement, velocity and acceleration.
A vibration is measured by its frequency and
amplitude.
Every vibrating body/element has mass and
frequency of vibration is a function of this
mass.
The amplitude of vibration is a function of this
mass.
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63. An accelerometer is a vibration measuring device which
uses a piezoresistive or capacitive effect for
measurement.

67. working

68. Vibration sensors
Vibrations are measured by measuring the
displacement, velocity or acceleration of the
vibrating body with the help of vibration
measuring instruments.
The vibration measuring instrument having
mass, spring and dash pot etc, is known as
seismic instrument or seismic transducer.
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69. Vibrometer (seismometer)
Accelerometer
Laser Doppler Vibr0meter (LDV)
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70. Vibrometer (seismometer)
It is designed with low natural frequency and
hence it is known as low frequency
transducer.
The relative motion between the mass and
vibrating body is converted into proportional
voltage and it can be recorded.
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71. Accelerometer
It is designed with high natural frequency and
hence it is known as high frequency
transducer.
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