Bldg Blocks

8/17/2019 Bldg Blocks

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ME 486 - AutomationME 486 - Automation


Objectives

• To review basic building blocks for implementing automation

• To consider application conditions

• To introduce assessment criteria

• To test understanding of the material presented


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Building Blocks• Sensors

• Analyers

• Actuators

• !rives

• "ision system #integrated sensor$analyer%

Inductive proximityInductive proximity

sensorssensors


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Building Blocks – sensor features• Accuracy and repeatability

• &recision

• Range

• Response time

• 'alibration methods

• (inimum drift

• 'osts and reliability

• Sensitivity


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)e can characterie a sensor*s capability

by it*s operating fre+uency or by its

response time, Both determine how well thesensor might measure the desired property

#pro-imity. length/% of a moving object,

0sing a sensor*s specification. how might

we determine how fast a moving object

might move past the sensor and the sensorstill read the object parameter correctly1

Building Blocks – sensors & moving objects


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Building Blocks – sensor devicesSee te-t for in depth description2

• &hotoelectric sensors

• &ro-imity switches #inductive and capacitive%

• Range sensors #ultrasonic$acoustic. laser reflectors/%

• Transducers #encoders%

Inductive proximityInductive proximity

sensorssensors

Linear

encoder

Absolute rotary

encoder


7/31ME 486 - AutomationME 486 - AutomationME 486 - AutomationME 486 - Automation

Building Blocks – analyzers Encoder e-ample 3 An absolute optical encoder has 4 rings. 4 5E!

sensors. and 4 bit resolution, 6f the output pattern is 78878778. what is theshaft*s angular position1

Ring Angle #deg% &attern "alue #deg%

7 748 7 748

9 :8 8

; =,>9= 7 =,>9=

? 9,479= 7 9,479=

4 7,9= 8 Total 978,:<



Building Blocks – drives

• Stepper (otors #inde- by open@loop control%

• A'$!' servomotors #&6! feedback control. holds tor+ue

when at rest%

• inematic devices #intermittent

operation. e,g,. geneva mechanism%

• !igital drives



Building Blocks – present drives

(otion(otion

&lanning&lanning

'ontrol'ontrol

S e t & o i n t s S e t & o i n t s A m p l i f i e r s A m p l i f i e r s

Servo@loopsServo@loops

ApplicationApplication

ServocardServocard

'ontroller'ontroller



Building Blocks – digital drives

• (icroprocessors and !igital Signal &rocessors #!S&*s% are replacing

analog components with digital components #i,e,. digital drives%,

•E6A RS@



Building Blocks – digital drives

Ormec’s servowire implementation of IEEE 13!

!(A'!(A'



&)( and digital drives "binary control#$ &)( 3 &ulse )idth (odulation @ a constant fre+uency. two@valued

signal #e,g,. voltage% in which the proportion of the period for which thesignal is on and the period for which it is off can be varied,

• &ercentage of time on is called the duty cycle%

• "oltage value will depend on the application

• &)( fre+uency must be high enough so that motor cannot respond

to a single &)( signal

On On

Off Off

T 9T ;T



A$! Signal 'onversion

Resolution of A$! is represented by number of conversion bits n

C+ F number of +uantitiation levels F 9n

R F conversion resolution F "oltage range$#C+ 3 7% #G 78 "%G R

Variable

(or Voltage)

Time



A$! Signal 'onversion

Successive appro-imation method is similar to the method we usedto e-tract the encoder value from the binary output but

backwards, Here is simple e-ample

Range #G 78 "% Iuantitiations Bit #on or off% "alue>,4 " = 7 =

7,4 9,= 8

7,4 7,9= 7 7,9=

8,== 8,>9= 8

8,== 8,;79= 7 8,;79=

8,9;?= 8,7=>9= 7 8,7=>9=

8,8479= F error >,?7: "



!$A Signal 'onversion

The decoding e+uation is

Eo F Eref J8,= B7 K 8,9= B9 K 8,79= B;K/K#9n%@7BnL

where

Eo F output analog signal value

Eref F ref voltage

Mor e-ample 78878 means B7 F 7. B9 F 8. B; F 8. B



'urrent flow produces magnetic field and associated flu-,

'hanging field #flu-% through a coil induces a reactive electromotive force #emf% e

e F @C d

$dt #Maraday*s 5aw% C F N turns in coil is flu- in webers

This in turn generates an induced current in opposite direction and a resulting opposing flu-

as described by

e F @5 d $dt 5 F inductance in henrys

I

B

MM == II ll xx BBMM == II ll xx BB

Ml

I

Electromagnetism

B



A' motorsStator structure is composed of steel laminations

shaped to form poles around which are wound

copper wire coils, These primary windings connectto. and are energied by. the voltage source to

produce a rotating magnetic field, Three@phase

windings spaced 798 electrical degrees apart are

popular in industry,

Rotor #or rotating secondary% is another assemblyof laminations over a steel shaft core, Radial slots

around the laminations* periphery house rotor bars

Pcast@aluminum or copper conductors shorted at

one end and positioned parallel to the shaft #see

photo%,

The motor*s name comes from the alternating current #ac% Qinduced into the rotor by therotating magnetic flu- produced in the stator, (otor tor+ue is developed from interaction of

currents flowing in the rotor bars and the stator*s rotating magnetic field,



#new tech% 5inear motors

Slot@less refers to a special design of steel laminations where the windings go through holes in the

stator rather than slots, The result is a smoother surface facing the magnet, This design

also reduces cogging by eliminating variation in attractive force,

Tubular linear motors roll up the unit about an a-is parallel to its length, 6n one style. an outer

thrust block carrying the motor coils envelops and moves along a stationary thrust rod that

houses magnets, Another style has a central rod with magnets that moves relative to an outerstator member, Travel is limited since the thrust rod must be supported at both ends #or at one

end for the moving@rod version%,

ubular linear motor

Two basic classes 7% permanent magnet #&(% brushless.

and 9% asynchronous linear induction motors #56(s%,

&( brushless motors abound in various subclasses. such

as the moving coil and moving magnet types, 6ronless

refers to a core containing only copper coils #and epo-y

encapsulation%, Smooth cog@free motion is produced

since no attractive force e-ists between coil and magnet@@

but at the cost of lower force output,



#new tech% Switched reluctance motorReluctance @ opposition of a material to magnetic lines of force

Both stator and rotor of the switched reluctance motor have

projecting poles, 6n the image. poles 7 and 7 are energied,These are wired in series, The rotor has no permanent magnets

or windings, Thus when one of the four phases of the stator is

energied. the closest set of poles of the rotor #made up of

reluctance magnets% are pulled into alignment, By turning off

phase 7 and energiing phase 9. you can visualie how the rotor

will rotate 7= '') to align the rotor poles closest to phase 9,

A four phase converter capable of accepting feedback is used to energie the coils in order to control

the switched reluctance motor, The feedback is necessary to run the motor in self@synchronous

mode. which enables a continuous smooth speed operation, By energiing the phases in reverse

se+uence. the motor can also run '), The switched reluctance motor along with the four phaseconverter are meant to be used as a precise speed control device. and they are appro-imately 9D

more efficient than the other A' speed control systems,



6EEE 7;:



Building Blocks Assessment

7, )ho are major vendors of pro-imity switches.

servomotors1

9, )hat are the limits to sensor pro-imity distances1

;, )hat types of pro-imity accuracies might you e-pect

from pro-imity sensors1

, )hat are weight to tor+ue ratios for common

servomotors1



Building Blocks Assessment

?, )hat does tor+ue speed curve look like for the

motors typically used to control robots1

4, )hat is difference between absolute encoder and

relative encoder1 How do encoders measure

directional changes1:, )hat is difference between a resolver and digital

encoder1

78, 'osts of sensors. motors. etc,1

77, How do the new linear drives work. and what are

their response characteristics1


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ME 486 - AutomationME 486 - AutomationME 486 - AutomationME 486 - Automation

Building Blocks – mac'ine vision

(efinition 3 Q(achine vision is the capturing of an image #asnapshot in time%. the conversion of the image to digital

information. and the application of processing algorithms to

e-tract useful information about the image for the purposes of

pattern recognition. part inspection. or part positioning and

orientation/,Ed Red

Algorit#mAlgorit#m

$"


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E)uipment*

• 'omputer

• Mrame grabber

• 'amera #''! array%

• 5enses

• 5ighting

• 'alibration templates

• Algorithms

Mront

Back

Side

Structured

Strobe

Types

Building Blocks – mac'ine vision


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(achine "ision 3 structured lighting

Structured 5ighting is used in a front

lighting mode for applications re+uiring

surface feature e-traction, Structured

lighting is defined as the projection of a

crisp line of light onto an object, The

patterned light is then used to determine

the ;@! characteristics of an object fromthe resulting deflections observed,

Cote the non@typical

approach of

projecting a grid

array of light on an

object to detect

features


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(achine "ision 3 image processing

+egmentation 3 !efine and separate regions of interest

'res'olding 3 'onvert each pi-el into binary #B or )% value

by comparing bit intensities

Edge detection 3 5ocate boundaries between objects

,eature e-traction 3 !etermine features based on area and

boundary characteristics of image

.attern recognition 3 6dentify objects in midst of other objects

by comparing to predefined models or standard values #of

area. etc,%


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(achine "ision 3 applications

(imensional measurement

Object verification

.roper position/orientation

,laws and defects

0ounting

uidance and control "offsets2 tracing$


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(achine "ision 3 e-ample

• 4@bit image of metallic iron as it appears in iron

ore #lighter objects in the image represent the metallic iron%

• Histogram displays pi-el intensity distribution /

background appears at gray level


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(achine "ision 3 e-ample

Suppose we wish to calculate the areaand centroid of the selected binary

region in the last figure. how would

you do it1 Assume that you have a

camera such that the pi-els are

s+uare and you have a matri- of

pi-el values as depicted in the figure

shown,

)hat e+uations would you apply1 U

V


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(achine "ision Assessment

7, )ho are major vendors of vision systems and the various

components1

9, )hat are typical camera resolutions1

;, )hat are typical camera calibration techni+ues1

, How long does it take to process images1 As a function of image

processing function1

?, )hat are typical costs for imaging systems1 Mor frame grabbers.cameras. lenses. lighting1


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ME 486 iME 486 A t tiME 486 A t tiME 486 A t ti

Building Blocks

4'at 'ave we learned5

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