sup.reading encoders

8/17/2019 Sup.reading Encoders

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What is an Encoder?

Any transducer that changes a signal into a coded (digital signal) Optical Encoders

Use light & photosensors to produce digital code (ie. Lab 3 encoder ).

Most popular type of encoder.

Can be linear or rotary.


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ypes of Optical Encoders

! types of Optical Encoders"

#. $ncre%ental

Measure displace%ent relatie to a reference point.

!. Absolute

Measure absolute position.

Adantages ' A %issed reading does not affect the net reading. Only needs poer onhen ta*ing a reading.

+isadantages ' More epensie,co%ple. Cost,co%pleity proportional to

resolution,accuracy.


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-unda%ental Co%ponents ight source(s)

E+s or $/ E+s proide light source.

ight is colli%ated using a lens to %a*e the bea%s parallel.

0hotosensor(s)

Either 0hotodiode or 0hototransistor.

Opa1ue dis* (Code +is*) One or %ore 2trac*s3 ith slits to allo light to pass through.


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Optical Encoder Co%ponents


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Other Co%ponents

4tationary 2%as*ing3 dis* $dentical trac*(s) to Code +is*

Eli%inates error due to the dia%eter of the light

bea% being greater than the code dis* indo

length.


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5uadrature

o trac*s (A & 6) at

78 degrees offset.

0roide direction

infor%ation.

0roides up to 9

ti%es resolution.


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Encoder +is*sIncremental Disk Absolute Disks

Binary Gray Code


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Absolute +is* Codes

Angle Binary Decimal

0-45 000 0

45-90 001 1

90-135 010 2

135-180 011 3

180-225 100 4

225-270 101 5

270-315 110 6

315-360 111 7

Ea%ple" : bit binary code

Bit 0

Bit 0

Bit 1

Bit 1

Bit 2

Bit 2


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0roble% ith 6inary Code

One angle shift

results in %ultiple bit

changes.

Ea%ple" # ;< ! 88# (start at #)

888 (turn off bit 8)

8#8 (turn on bit #)


0-45 000 0

45-90 001 1

90-135 010 2

135-180 011 3

180-225 100 4

225-270 101 5

270-315 110 6

315-360 111 7


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0roble% ith 6inary Code

One degree shift

results in %ultiple bit

changes.

Ea%ple" # ;< ! 88# (start at #)

888 (turn off bit 8)

8#8 (turn on bit #) $t loo*s li*e e ent

fro% # ;< 8 ;< !


0-45 000 0

45-90 001 1

90-135 010 2

135-180 011 3

180-225 100 4

225-270 101 5

270-315 110 6

315-360 111 7


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=ray Code


0-45 000 0

45-90 001 1

90-135 011 2

135-180 010 3

180-225 110 4

225-270 111 5

270-315 101 6

315-360 100 7

One bit change per angle change.

Bit 0

Bit 0

Bit 1

Bit 1

Bit 2

Bit 2


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Encoder /eliability and Errors

Encoder errors

#. 5uanti>ation Error ' +ependent on digital ord si>e.

!. Asse%bly Error ' +ependent on eccentricity of rotation (is trac* center of

rotation;center of rotation of dis*)

:. Manufacturing tolerances ' Code printing accuracy sensor position and

irregularities in signal generation.


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Encoder /eliability and Errors

More encoder errors

9. 4tructural i%itations ' +is* +efor%ation physical loads on shaft.

@. Coupling Error ' =ear bac*lash belt slippage etc

B. A%bient Effects ' ibration te%perature light noise hu%idity etc


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sup.reading encoders

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