Sup.reading Encoders
Transcript of 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 #)
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
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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 ;< !
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
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=ray Code
Angle Binary Decimal
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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