LINEAR ENCODERS ISKRA
Iskra TELA d.d.
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Different types of linear encoders by used technology: LINEAR ENCODERS
OPTOELECTRONIC
MAGNETIC
MAGNETIC BAND Features: Long length Low accuracy Low resolution Low repetability Excellent for hard enviroment (dust, liquids, …) Used in: Wood & Stone cutting machine; Iskra TELA d.d.
NON-MAGNETIC BAND Features: Long length Low accuracy Low resolution High repetability Excellent for hard enviroment (dust, liquids, …) Used in: Wood & Stone cutting machine;
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METAL TAPE: Features: Long length Good accuracy Low resolution High repetability Sensitive to dust, … Used in: Machine tool;
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GLASS SCALE Features: Length to 3m High accuracy High resolution High repetability Sensitive to dust, … Used in: Machine tool; Semiconductor industry
Different types of optoelectronic linear encoders by application: Optoelectronic glass linear encoders
DRO linear encoders For use on manualy controlled machine tool; Retro fitting of old machine tool
NC linear encoders: For use on NC controlled machine tool; For new builded machine, and for retrofitting .
Features: Good accuracy; Good interpolation error Good reliability;
Features: High accuracy Low interpoaltion error High reliability
Iskra TELA d.d.
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Optoelectronic linear encoders – theory of operation (scanning):
Iskra TELA d.d.
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9D/4 3D/2 3D/4
A
D
=INTERVAL
B RI
INDEX PLATE
A
B GLASS SCALE
Ia SI
Ia
OUTPUT SIGNALS
Iri
A DS OUTPUT SIGNALS
B RI
D/4=r
=RESOLUTION
Optoelectronic linear encoders – theory of operation (interpolation): Iskra TELA d.d.
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sin(x)
D sin(x+18)
Ia
sin(x+36)
A
sin(x+54) sin(x+72) cos(x)
Ib DIGITISING
LOGIC
CIRCUIT
CIRCUIT
B
B
cos(x+18)
cos(x+36)
A
D/I =OUTPUT PERIOD
RI
cos(x+54)
D/I/4=r =RESOLUTION
cos(x+72)
I=5
-sin(x)
Optoelectronic linear encoders – functional structure (DRO encoders): Iskra TELA d.d.
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GLASS SCALE
D
2) DIGITIZED OUTPUT SIGNALS GLASS SCALE LIGHT SOURCE
LIGHT SOURCE
INDEX PLATE SENSORS
OUTPUT RESOLUTION r = D/4 r = D/4
Ia
DIGITISED CIRCUIT
Ib
RS 422 LINE DRIVER
Iri
INDEX PLATE
RI RI
INDEX PLATE
3) INTERPOLATED AND DIGITIZED OUTPUT SIGNALS GLASS SCALE LIGHT SOURCE
SENSORS
INDEX PLATE SENSORS
OUTPUT RESOLUTION: r = (D/4)/int factor int factor=2,5,10
Ia
INTERPOLATION
Ia
CIRCUIT
A A
Ib
Ib
DIGITISED CIRCUIT
B B
Iri
Iri
RS 422
RI RI
Optoelectronic linear encoders – functional structure (NC encoders): Iskra TELA d.d.
B B
LIGHT SENSOR
1) SINUSOIDAL CURRENT OUTPUT GLASS SCALE LIGHT SOURCE
A A
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LINE DRIVER
1) SINUSOIDAL VOLTAGE OUTPUT (SV) GLASS SCALE
SENSORS
INDEX PLATE
a
Ua+ Ua-
GLASS SCALE
LIGHT SOURCE (LED)
b
AMPLIFIER
D CONDENSER LENS
ri
LIGHT SOURCE
Ub+ UbUri+ Uri-
2) INTERPOLATED AND DIGITIZED OUTPUT SIGNALS MIRROR
GLASS SCALE
INDEX PLATE
SENSORS
a INDEX PLATE
LIGHT SENSOR
b
AMPLIFIER
ri
LIGHT SOURCE
Optoelectronic linear encoders Reference Marks Positions: Iskra TELA d.d.
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OUTPUT RESOLUTION: r = (D/4)/int factor int factor=,5,10,50
INTERPOLATION
CIRCUIT
A A
DIGITISED CIRCUIT
B B
RS 422
RI RI
LINE DRIVER
1. Standard Reference Marks: TGM111 (every 100mm available), TGM113, 115, 130, 170 (available every 50mm) 2. Distance Coded Reference Marks: TGM131, TGM133, TGM173 • 20mm maximum traverse for re-establishing absolute position: (TGM131, TGM133, TGM173) • 80mm maximum traverse for re-establishing absolute position: (TGM190) • Incremental track
10,02
9,98 20
10,04
9,96 20
10,06
9,94
10,08
20
Reference track
Optoelectronic linear encoders – mechanical structure (DRO encoders):
Iskra TELA d.d.
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Optoelectronic linear encoders – mechanical structure (NC encoders):
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Optoelectronic linear encoders – features ACCURACY: Iskra TELA d.d.
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• Accumulative accuracy The extreme value of the postion error with reference to their mean value lie within +a um for a position within any max. 1m section of the measuring length. If measuring length is shorter the 1m , extreme value aplies to that measuring length.
POSITION ERROR
+a -a Measuring length or 1m
Type DRO NC
Iskra TELA d.d.
Availble grades of a 5um; 10um 3um; 5um
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Permissible change of postion error +5um/50mm +3um/50mm
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+a
Signals
Interpolation error
POSITION ERROR
• Interpolation accuracy The position error within one signal period .
-a +IE
Measuring length
-IE
Type DRO NC
Max Interpoaltion error + 1um + 0,4 um
Average Interpoaltion error + 0,5 um + 0,2 um
• Return error Iskra TELA d.d.
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+a -a
Measuring length
Measuring length
Type DRO NC
Return error
POSITION ERROR
Return error
Difference between positioning from the difference directions.
Max Return error + 3,0 um +1,5 um
Average Return error 1,5 um 0,8 um
Optoelectronic linear encoders – features OUTPUT SIGNALS: Iskra TELA d.d.
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• Output signals SV : 360o C
uo
A
A/2 A/2
B
fi
uo
D H E
uo
F
G
LINEAR ENCODER
0
SUBSEQUENT ELECTRONIC C1
47Ohm A+
C
A 22 pF
A/2 A/2
A47ohm
fi
0
Marcation Incr. Signal amplitude A, B Incr. Signal DC offset C, D Amplitude unbalance (A+B)/(A+B) Phase shift Fi Reference signal width G Reference signal ampl E Ref. Signal peak H position Ref. Sign. Secondary F amplitude
R2 120 Ohm R2
B
+
Ua R1
uo
• Output signals SI : H
G
E 167248709.docF
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V o
V
-0,5
+0,25
-3dB limit cca 450kHz
C1
0 TELA d.d. Iskra
o
Tolerances + 0,2 +0,03 + 10 + 10 +90 +0,25 +45
Ua = (A+ - A-)* (R1/R2)
2x220pF
D
o
Nominal 1 0 0 90 360 0,5 135
R1 = 10kOhm R2 = 10kOhm C1 =10pF C2 = 220pF U0 = 2,5 + 0,5 V
R1 -
Unit V V %
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360o
Marcation Incr. Signal amplitude A, B Incr. Signal DC offset C, D Amplitude unbalance (A+B)/(A+B) Phase shift Fi Reference signal width G Reference signal ampl E Ref. Signal peak H position Ref. Sign. Secondary F amplitude
LINEAR ENCODER
SUBSEQUENT ELECTRONIC C1 R1
Ia-
-
I a+
+
Ua R1
uo
uA o
-5
+3
uA
-3dB limit cca 60kHz
• Output signals DS (RS 422-A EIA):
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o
Tolerances +3 +0,3 + 10 + 10 +90 +3 +45
Ua = 2*Ia*R1
C1
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o
Nominal 11 0 0 90 360 5 135
R1 = 56kOhm R2 = 56kOhm C1 = 27pF C2 = 220pF U0 = 2,5 + 0,5 V
2x220pF
Iskra TELA d.d.
Unit uA uA %
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Unit V
Signal levels
A
Transition times Rise and fall time B Maximum load current
ns
Nominal UH > 2,5V at IH = -20 mA UL < 0,5V at IL = 20 mA <50
mA
20
HIGH IMPENDANCE STATE
A
B RI RI E*
LINEAR ENCODER A A
SUBSEQUENT ELECTRONIC
Zo
R1 R2 E R1
Line reciever: DS26LS32C Z0 = 120 Ohm R1 = 5,1kOhm R2 = 1,8 kOhm
Optoelectronic linear encoders – features DEGREE OF PROTECTION: • IP 53 (IEC 529) • IP 64 (IEC 529) if encoder is pressurized
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1) Connection on linear scale body:
2) Connection on reading head:
Compressed air requirements: Item Pressure range Filteration grade Working fluid Working fluid temperature
Specifications 20 to 200kPa Air filter 5um; Mist separator: 0,3um Air 20oC
Optoelectronic linear encoders – features ELECTRICAL CONNECTION:
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• Sensor lines SUBSEQUENT ELECTRONIC
V
Iskra TELA d.d.
LINEAR ENCODER
5V
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Optoelectronic linear encoders – features DEFINED THERMAL BEHAVIOR: • Reason of temperature influence on wrong measurment can be different thermal expansion between Scale Aluminimum housing (alfa = 25 ppm/k) and base plate made from Cast Iron (alfa = 11 ppm/K) At 20 oC Screw
At 30 oC
Due to different thermal expansion scale's Al body expand more than Base plate. Because Scale is rigidly fixed on both ends it became Scale bended. Bending of the scale cause Abbe error.
Scale Screw
Base plate Base plate
• This problem is solved by usage of fixture mechanism which compensate different thermal expansion coeficient (availible on TGM 173 and TGM 133 whith mounting bar). Connected to scale
Iskra TELA d.d.
Connected to base plate
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Optoelectronic linear encoders – ACCURACY CONSIDERATIONS : • Abbe error Lcutter
d Approximation:
Lcutter - Lscale = d* 2h / Lo
Lscale
h Lo
Examples: h =0,2mm; Lo= 620mm d (mm) 50 100 200 400
Iskra TELA d.d.
Lcutter - Lscale (um) 32 64,5 129 258
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Examples: h =0,05mm; Lo= 620mm d (mm) 50 100 200 400
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Lcutter - Lscale (um) 8 16 32 64
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