ME 445 INTEGRATED MANUFACTURING TECHNOLOGIES EXPERIMENT 1 "PROXIMITY SENSORS"

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1






ME 445 INTEGRATED MANUFACTURING TECHNOLOGIES

EXPERIMENT 1

"PROXIMITY SENSORS"


OBJECTIVE


Increasing automation of complex production systems necessitates the use of components
which are capable of acquiring and transmitting information relating to the
production
process. Sensors fulfill these requirements and have therefore in the last few years become
increasingly important components in measuring and in open and closed loop technology.
Sensors provide information to a controller in the form of individ
ual process variables.


Proximity sensors are the most basic data acquisition devices in automation. They measure /
detect physical input such as temperature, pressure, force, length, and proximity of an object.
Transducers are typically a sensorial system

capable of signal processing, equipped with
electronic instrumentation
.

Position sensors give a

yes


or

no


response according to the
place of the object.


The aim of this experiment is to illustrate the aspects of different types of proximity sensors,
their properties, and to compare them. For this, a setup table
containing Magnetic,
Inductive,
Capacitive, and Optical
sensors is used. A positioning slide cou
pled with a vernier caliper is
used to measure switching distances.


Figure: Proximity sensors setup table

2






GENERAL INFORMATION

Sensors are the first of the four milestones of Automation:

1.

Sensing

2.

Signal Processing

3.

Planning and Response

4.

Memory


They usuall
y convert some physical data into a voltage difference for further processing by a
Computer, PLC or I/O Card. The advantages of proximity sensors are:



They determine the geometrical positions automatically and sensitively.



They do not need of a direct cont
act with the workpiece.



They do not have movable parts that can wear out.



They are usually equipped with electronic circuits for failure protection.



They have various types that can be used under different situations.



They provide the secure working of the

process.



They
are used for the system failure
analysis.


Their typical usage areas are:



Automotive industry,



Packaging industry,



Printing and paper industry



Ceramic industry



Wood
-
working industry



Food processing industry


CATEGORIES

According to I/O proce
ssing:



Binary: Convert a physical measurement value to a binary code (in the form of ON/OF
F

signals in a selected voltage range)



Analog: Co
nvert a physical measurement in
to an analog signal (e.g. temperature readings
to variable voltage differences)


Accor
ding to physical considerations:



Mechanical switches



Magnetic (with/without contacts, pneumatic output)



Inductive (inductive sensors)



Capacitive (capacitive sensors)



Optical (light barriers, reflection sensors)



Ultrasonic (ultrasonic barriers, ultrasonic
sensors)



Pneumatic (back
-
pressure nozzles, air reflection sensors, air barriers)



3






TYPICAL USAGE


Detecting whether an object exists in a defined position:




Positioning of an object:





Counting the number

of parts:




4






Determining the rotational speed
:




Determining the linear speed
:





5






TYPES


1. Mechanical switches:

Mechanical switches are simple GO/NoGO
indicators. They have physical contact with the
object, usually coupled with relays and contactors to drive a circuit. Widely used in the
industry to mark the end
-
start point
s of cylinders, pistons, linear

and rotary drives, to sense
doors. They are less s
ensitive and have lower maximum switching frequency compared to
proximity switches. Because of the physical contact with the object, they require maintenance
and replacement.


2. Magnetic Proximity Switches:

Magnetic switches (also called as Reed
-
contacts)

use the distortion of the magnetic field. If a
ferromagnetic material (Fe
-
Ni compound) comes in the vicinity, the magnetic field distorts
and gives an input to the switch. Thus, they are only sensitive to ferromagnetic materials and
magnetic fields. Dirt
and humidity is of little import
ance. They preserve high hystere
sis
(undefinite range of physical input). They are widely used in pairs of machine parts such as
piston
-
cylinder arrangements.


3. Inductive Proximity switches:

Inductive proximity switches a
lso work on the principles of magnetic fields and induction.
They response to conductive materials, typically metals. The tabular data on switching
distance

depends on mild steel (usually Fe37); thus, a reduction coefficient must be defined
for different m
etals. For the metals such as Cr
-
Ni, brass, aluminum, and copper this value
must be modified with the experimental reduction coefficient found usually in the range of
0.25
-
0.9. Also the reduction coefficient depends on the size of the measured object. They

are
widely used in the mass production lines and conveyors to detect metallic workpieces,
moving parts of
machinery, for measuring linear
, rotational speeds, presses, and encoders.


4. Capacitive Proximity switches:

Unlike the magnetic and inductive types
, capacitive proximity switches response to all types
of materials. The reduction coefficient is determined experimentally in the range of 0.1 to 1
(metals =1 and water =1). Note that liquids can also be detected by capacitive switches. They
are very sensi
tive to environmental factors such as dust, dirt and humidity. Therefore they can
be used to distinguish object properties such as color, thickness, water column height, and
vibration. Sample application areas are in production lines and conveyors to count

workpieces, sense packaging defects etc.


5. Optical Proximity switches:

Optical proximity switche
s

use the presence of visible (with wavelength of 660nm
-
red
-
) or
invisible (with wavelength of 880nm
-
ultra
-
red
-
), light for input. They give a NPN or PNP

output to the circuit. Here, instead of the reduction coefficient the
operation reserve

is defined
as the ratio of signal intensity in the input of the sensor to the required intensity for switching.
Note that in correct working conditions, operation rese
rve must have a value of greater than
one. The operation reserve depends on ambient conditions such as dust, dirt, ambient light
color and intensity, distance from part, reflect
-
angle etc.

Optical sensors are divided into two main parts:

6








Light sensors (can

be equipped with fiber
-
optic cabling for long distance transmission,
may use ambient light or the light produced in a coupled unit)



Reflected light sensors (can be equipped with fiber
-
optic cabling for long distance
transmission, uses the reflected light
produced in the same unit from the part or a reflector
sheet)


Optical sensors have a relatively greater switching distance. Therefore they may be used in
detecting surface irregularities, failure detection, detection of transmissive surfaces, colors
etc.
Fiber optic cabling for transmission also gives a flexibility to use small units at difficult
locations.


6. Ultrasonic Proximity switches:

They use the reflected sound power for input. Note that above the sensors stated here,
ultrasonic proximity
switches have the greatest switching distance and frequency. Therefore,
they are used to detect distant objects with very high speeds. They are usually insensitive to
ambient conditions and should be preferred in very extreme conditions, while they are ver
y
expensive.


7. Pneumatic Proximity switches:

They use the reflected back
-
pressure supplied from a nozzle at or distant from the switch unit.
Generally preferred in the areas of:




Very dirty and dusty places,



At high temperatures,



In the vicinity of explo
sive materials where electrical currents may be dangerous,



At places where intensive magnetic fields are present, in the vicinity of big motors,
pumps, turbines etc.



The sensor unit and nozzle unit may be built in one package or as different units. Can be
used to drive a pneumatic piston directly.



7






SELECTION CRITERIA


8






PROTECTION CLASSES


The protection classes of the mechanical elements are defined in DIN 40050. For example,
IP67 represents a device with protection against contact and foreign material acc
ording to 6
(Table A1) and against water and humidity
according to
7

(Table A2).


First
digit

Protection Class

0

No special protection

1

Protection against solid objects larger than 50 mm diameter. Unprotected against
forced contacts (eg. via hand).
Should be kept apart from the body

2

Protection against solid objects larger than 12 mm diameter. Should be kept apart
from the fingers

3

Protection against solid objects larger than 2.5 mm diameter. Should be kept apart
from the devices (wire, hand
tools etc.)

4

Protection against solid objects larger than 1 mm diameter. Should be kept apart
from the devices (wire, hand tools etc.)

5

Protection against hazardous dust accumulation. Dust protection is not totally
achieved, but inner dust accumulation

does not affect functioning of the device. Full
protection against forced contact.

6

Full protection against dust accumulation. Full protection against forced contact.

Table

A1
: Protection against dust & forced contact.


Second
digit

Protection Class

0

No special protection

1

Protection against vertically tipping water. The water has no hazardous effects
(tipping water).

2

Protection against vertically tipping water at 15


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9






DEFINITIONS


Object material
: The material of t
he object to be sensed. Note that

under non
-
ideal
circumstances reduction factors ar
e defined. All tabular data about the properties of the sensor
are based on identifying the indicated object under ideal circumstances.


Switching Voltage
: The operating supply/output voltage of the sensor. The sensor must
definitely be operated at the per
mitted voltage range. For most industrial applications
typically 5V DC, 12
-
24V DC
, 110
-
220
V AC.


Switching Distance
: The maximum distance of the object to be sensed from the head of the
sensor. Reduction factors about the environment and object properties
not applied.


Max. Current
: The maximum allowable current at the sensor output. To avoid excess
currents a protection circuit may be necessary.


Protection Class
: The physical protection of the industrial device against foreign material,
dust, water and humidity. Defined in DIN 40050. Generally related with the construction.


Life
: The theoretical life of the device. Indicated as time or in operating cycles.


Swit
ching Frequency
: The maximum occurrence of the object material at the switching
distance of the sensor in one second.


Reduction factor
: The ratio of switching dist
ance of metals (typically Fe37) to other
materials

at the same ambient conditions. Some gui
de values are given in the table:


Material

Reduction factor

All metals

1.0

Water

1.0

Glass

0.3 to 0.5

Plastic

0.3 to 0.6

Cardboard

0.3 to 0.5

Wood (depends on humidity)

0.2 to 0.7

Oil

0.1 to 0.3


Table: Reduction factor of some materials


Hysteresis
: The distance between swi
t
ch
-
on and switch
-
off position of a sensor.





10






EXPERIMENTAL DATA


The following equipment is contained on the setup table. In the experiment, you may use this
list as a reference to distinguish between equipment.


Compo
nent

Designation

Proximity Sensor, non
-
contact, inductive
-
magnetic

167055

Reed switch

167056

Optical proximity sensor with fiber optic connector, block shaped (2 pieces)

167065

Diffuse reflective optical sensor, block shaped

167068

Optical sensor with

fiber optic connector, cylindrical, M18

167166

Inductive Proximity Sensor, cylindrical, M12

177464

Inductive Proximity Sensor, cylindrical, M18

177466

Capacitive proximity switch, cylindrical, M18

177470

Ultrasonic proximity sensor, cylindrical, M18

184118


Table: List of sensors


Component

Designation

Reflector unit for reflex light barrier

150504

Optical fiber for one
-
way light barrier (2 pieces)

150505

Optical fiber for diffuse reflective optical sensor

150506

One way light barrier,
transmitter

167064

One way light barrier, receiver

167067


Table : List of optical fibers & barriers


Component

Designation

Set of test objects

034083

Graph paper, mm grid

034085

Positioning slide

034094

Adapter set

035651

Vernier caliper

035653

Digital multimeter

035681

Ruler

035697

Distributor unit

162248

Counter unit

162252

Rotary unit

167097


Table: List of auxiliary equipment



11






Part no

Material, Dimensions (mm)

1

Magnet 1

2

Magnet 2

3

Mild steel (St 37), 90 x 30

4

Stainless steel,
90 x 30

5

Aluminium, 90 x 30

6

Brass, 90 x 30

7

Copper, 90 x 30

8

Cardboard, 90 x 30

9

Rubber, 90 x 30

10

Plastic, transparent, 90 x 30

11

Mild steel (St 37), 30 x 30

12

Mild steel (St 37), 25 x 25

13

Mild steel (St 37), 20 x 20

14

Mild steel (St

37), 15 x 15

15

Mild steel (St 37), 10 x 10

16

Mild steel (St 37), 5 x 5

17

Kodak gray card, 100 x 100

18

Plastic, transparent, 100 x 100

19

Plastic, red, 100 x 100

20

Plastic, blue, 100 x 100

21

Plastic, black, 100 x 100

22

Cardboard, white, 100
x100

23

Plastic, 2.0 mm thick, 90 x 30

24

Plastic, 3.0 mm thick, 90 x 30

25

Plastic, 4.0 mm thick, 90 x 30

26

Plastic, 8.0 mm thick, 90 x 30

27

Plastic, 11.0 mm thick, 90 x 30

28

Plastic, 14.0 mm thick, 90 x 30

29

Plastic, 17.0 mm thick, 90 x 30

30

Holder for fiber optic cable

31

Base plate with gear wheels

32

Holding bracket for liquid level measurement, through
-
beam sensor

33

Beaker

34

2 test screws

35

Valve housing

36

Screw driver


Table: List of test objects

12






PART 1 (Switching
characteristics of a contacting magnetic proximity sensor)


The objective of the experiment is to learn about the switching characteristics of a contact
based magnetic proximity sensor (Reed contact) as a function of position and orientation of a
magnet.


Setup

Mount the distribution plate (1), the positioning slide (2), and the magnetic Reed sensor (3,
Designation 167056) on the assembly board. Mount the magnetic sensor laterally offset by 5
cm to the center of the positioning slide. Plug in the electrical

power supply and connect the
sensor to the distribution plate. Note that the red color represents (+24V), the blue (0 V or
natural) and the black is the sensorial output (either +24V or 0, ON/OFF). Mount the test
object (Magnet 1) on the positioning slide
. Adjust
the distance from 0 to +18 mm with 2 mm
increments and at a constant distance adjust
the str
oke from
-
50 to +
50 mm

manually to detect
on/off positions
. Enter the response points into the
data sheet

provided

in the following pages
.
Repeat the same
procedure with the test object 2 (Magnet 2).



Figure: Setup for part 1

13






Conclusion

When working with magnetic proximity sensors, one has to take into account that there may
be several switching areas. This can lead to multiple counting when counters are
employed.
This effect depends on the field strength of the permanent magnet used, and/or the distance of
the magnet to the proximity sensor.


As can be seen from the response diagram, two or even three switching areas may be
observed, depending on the orie
ntation of the axis of the magnetic poles. This ambiguity of
the output signals can be prevented by attaching the magnet with the correct orientation of the
axis and, given a specific field strength, at the correct distance.


Discussion

Which orientation
of the magnet would be appropriate if the magnet is located on a wheel and
for each rotation it should count only once? Is there a similarity of the response diagram and
magnetic field lines, why?


14






Data sheet for Part 1



Distance

Stroke (On/Off)








































































Table: Response positions

for magnet 1








Distance

Stroke (On/Off)








































































Table: Response
positions for

magnet 2

15






PART 2 (Switching characteristics of different types of sensors)


The objective of the experiment is to learn about the switching characteristics of different
types of sensors, their interaction with material, thickness, color. The reduction fac
tors and
hysteresis will be investigated.


Setup

Mount the distribution plate (1), the positioning slide (2) on the assembly board. In this
experiment you will use all other sensors (3) available:




Figure: Setup for Part 2

16






Data sheet for Part 2



Component

Workpiece

Switch
-
On
Point

Switch
-
Off
Point

Hysteresis

Inductive Proximity
Sensor, cylindrical, M12
(177464)

Mild Steel
(St 37), Part
3




Inductive Proximity
Sensor, cylindrical, M18
(177466)

Mild Steel
(St 37), Part
3






Component

Workpiece

Switch
-
On
Point

Switch
-
Off
Point

Hystere
-
sis

Reduction
Factor

Inductive Proximity
Sensor, cylindrical, M18
(177466)

Mild Steel
(St 37),

Part 3




1.0

""

Stainless
Steel,

Part 4





""

Aluminium,
Part 5





""

Brass,

Part 6





""

Copper,

Part 7








17






Component

Workpiece

Switch
-
On
Point

Switch
-
Off
Point

Hysteresis

Optical sensor with fiber
optic connector, cylindrical,
M18 (167166)

Kodak grey
card, white
side, part 17




""

Kodak grey
card, grey
side, part 17




""

Plastic,
transparent,
part
18




""

Plastic, red
part 19




""

Plastic, blue,
part 20




""

Plastic, black
part 21




""

Cardboard,
white, part 22




""

Mild steel
(St37), part 3




""

Rubber,

part 9





Component

Workpiece

Switch
-
On
Point

Switch
-
Off
Point

Hystere
sis

Capacitive proximity
switch, cylindrical, M18,
(177470)

Mild Steel (St
37), Part 3




""

Stainless Steel,
Part 4




""

Aluminium,
Part 5




""

Brass,

Part 6




""

Copper,

Part 7




""

Cardboard,
Part 8




""

Rubber,

part 9




""

Plastic,
transparent,
part 10






18






Discussion

Industrial solutions are highly problem dependent so that the selection of sensor for particular
cases is very important. Which sensor would

you prefer in an installation i
f you were to count:

1.

Automobile
tyres
,

2.

Tiny in
dustrial metallic chips,

3.

Plastic cups,

4.

Bottles to determine either filled or empty.









































19






PART 3 (Determining the rotational speeds)


The objective of the experiment is to learn about the differences and the application
criteria of
rotational speed detection with optical and inductive proximity sensors.


Setup

Mount the distribution plate (1), the counting unit (2), rotary unit (3), Optical sensor with
fiber optic c
onnector, cylindrical, M18, (4,
167166) and Inductive Pro
ximity Sensor,
cylindrical, M12 (
6,
177464) on the assembly board. Mount the Optical fiber for diffuse
reflective optical sensor (150506) to the Optical Sensor. The inductive sensor unit is to be
mounted approximately 2

mm away from the perforated disc. Yo
u will use the counting unit
to read the output pulse frequency and to determine the speed. Use the digital multimeter to
read the motor voltage. Adjust the speed such that the motor voltage is increased in 2V
intervals.


Figure 6. Setup for Part 3

20






The
rotational speed is determined by the formula:


n
f
60
RS
s




where,

RS: Rotational speed (rpm)

n: Number of actuations per rotation (=8 pulse/rpms for the disc)

f
s
: Pulse frequency of the output signal (pulse/s)


Data sheet for Part 3


Motor

Voltage

(V)

Output pulse frequency
of optical sensor (167166)
(pulse/s)

Speed RS
(rpm)

Output pulse frequency
of inductive sensor
(177464) (pulse/s)

Speed RS
(rpm)

4





6





8





10





12





14





16





18





20







21






INSTRUCTIONS FOR
THE EXPERIMENT


Before the Experiment

1.

Read your lab manual carefully.

2.

You can use the data sheets in your manual provided, or you take photocopies of the data
sheets and fill them.


During the Experiment

1.

Note that the experiment will be conducted by the gr
oup members, so be prepared and
familiar with the setup. The assistant should not answer all your questions or mount items
to help you.

2.

You should take notes in the experiment to prepare a good report.

3.

Time is short, be quick to finish everything required.


Grading

1.

Your individual contributions in the laboratory will be assessed and graded.

2.

Prepare a lab report
according to the report outline that will be provided to you as a word
document.

3.

Submit your report one we
ek after the lab date until 17:
3
0 to your
assistant.