LINEAR ENCODERS
ISKRA
Iskra TELA d.d.
687292358
06.02.1601
Page 1 of 20
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;
687292358
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
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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
687292358
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Optoelectronic linear encoders – theory of operation (scanning):
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
Iskra TELA d.d
687292358
=RESOLUTION
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Optoelectronic linear encoders – theory of operation (interpolation):
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)
cos(x+54)
A
D/I =OUTPUT PERIOD
RI
D/I/4=r =RESOLUTION
cos(x+72)
I=5
-sin(x)
Iskra TELA d.d
687292358
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Optoelectronic linear encoders – functional structure (DRO encoders):
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
Ib
DIGITISED
CIRCUIT
RS 422
LINE DRIVER
Iri
1) SINUSOIDAL CURRENT OUTPUT
RI
RI
3) INTERPOLATED AND DIGITIZED OUTPUT SIGNALS
GLASS SCALE
LIGHT SOURCE
INDEX PLATE
SENSORS
INDEX PLATE
SENSORS
OUTPUT RESOLUTION:
r = (D/4)/int factor
int factor=2,5,10
INTERPOLATION
Iskra TELA d.d
B
B
LIGHT SENSOR
INDEX PLATE
GLASS SCALE
LIGHT SOURCE
A
A
687292358
A
A
Ia
Ia
CIRCUIT
Ib
Ib
DIGITISED
CIRCUIT
B
B
Iri
Iri
RS 422
RI
RI
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LINE DRIVER
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Optoelectronic linear encoders – functional structure (NC encoders):
1) SINUSOIDAL VOLTAGE OUTPUT (SV)
GLASS SCALE
SENSORS
INDEX PLATE
a
Ua+
Ua-
GLASS SCALE
LIGHT SOURCE (LED)
b
AMPLIFIER
D
CONDENSER LENS
Ub+
UbUri+
ri
LIGHT SOURCE
Uri-
2) INTERPOLATED AND DIGITIZED OUTPUT SIGNALS
MIRROR
GLASS SCALE
INDEX PLATE
SENSORS
a
INDEX PLATE
LIGHT SOURCE
Iskra TELA d.d
687292358
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ri
CIRCUIT
A
A
DIGITISED
CIRCUIT
B
B
RS 422
RI
RI
INTERPOLATION
LIGHT SENSOR
b
OUTPUT RESOLUTION:
r = (D/4)/int factor
int factor=,5,10,50
AMPLIFIER
LINE DRIVER
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Optoelectronic linear encoders Reference Marks Positions:
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
Iskra TELA d.d
687292358
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Optoelectronic linear encoders – mechanical structure (DRO encoders):
Iskra TELA d.d
687292358
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Optoelectronic linear encoders – mechanical structure (NC encoders):
Iskra TELA d.d
687292358
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Optoelectronic linear encoders – features ACCURACY:
 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
687292358
Permissible change of postion error
+5um/50mm
+3um/50mm
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Signals
Interpolation error
POSITION ERROR
 Interpolation accuracy
The position error within one signal period .
+a
-a
+IE
Measuring length
-IE
Type
DRO
NC
Iskra TELA d.d
Max Interpoaltion error
+ 1um
+ 0,4 um
687292358
Average Interpoaltion error
+ 0,5 um
+ 0,2 um
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+a
-a
Measuring length
Measuring length
Type
DRO
NC
Iskra TELA d.d
Return error
POSITION ERROR
Return error
 Return error
Difference between positioning from the difference directions.
Max Return error
+ 3,0 um
+1,5 um
687292358
Average Return error
1,5 um
0,8 um
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Optoelectronic linear encoders – features OUTPUT SIGNALS:
 Output signals SV :
360o
C
A
A/2
uo
A/2
B
fi
uo
D
H
E
uo
F
Marcation
feature
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
Unit
V
V
%
o
o
V
o
V
Nominal
1
0
0
90
360
0,5
135
Tolerances
+ 0,2
+0,03
+ 10
+ 10
+90
+0,25
+45
-0,5
+0,25
G
LINEAR ENCODER
SUBSEQUENT ELECTRONIC
C1
47Ohm A+
R1
R2
22 pF
-
120
Ohm
A47ohm
R1 = 10kOhm
R2 = 10kOhm
C1 =10pF
C2 = 220pF
U0 = 2,5 + 0,5 V
Ua
Ua = (A+ - A-)* (R1/R2)
R2
+
R1
uo
-3dB limit cca 450kHz
2x220pF
C1
Iskra TELA d.d
687292358
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 Output signals SI :
360o
C
A
A/2
0
A/2
B
fi
0
D
H
E
0
F
Marcation
feature
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
Unit
uA
uA
%
o
o
uA
o
Nominal
11
0
0
90
360
5
135
Tolerances
+3
+0,3
+ 10
+ 10
+90
+3
+45
-5
+3
uA
G
LINEAR ENCODER
SUBSEQUENT ELECTRONIC
C1
R1
I a-
R1 = 56kOhm
R2 = 56kOhm
C1 = 27pF
C2 = 220pF
U0 = 2,5 + 0,5 V
Ua
Ua = 2*Ia*R1
I a+
+
R1
uo
-3dB limit cca 60kHz
2x220pF
C1
Iskra TELA d.d
687292358
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IMPENDANCE STATE
 Output signals DS (RS 422-A EIA):
A
A
Transition times
Rise and fall time
Maximum load current
mA
20
HIGH
B
Signal levels
Unit
feature
Nominal
V
UH > 2,5V at IH = -20 mA
UL < 0,5V at IL = 20 mA
ns
<50
B
RI
RI
LINEAR
ENCODER
A
E*
SUBSEQUENT ELECTRONIC
Zo
A
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)
Iskra TELA d.d
687292358
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 IP 64 (IEC 529) if encoder is pressurized
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:
Iskra TELA d.d
687292358
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 Sensor lines
SUBSEQUENT
ELECTRONIC
V
Iskra TELA d.d
LINEAR
ENCODER
5V
687292358
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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
Scale
Screw
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.
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
687292358
Examples:
h =0,05mm; Lo= 620mm
d (mm)
50
100
200
400
Lcutter - Lscale (um)
8
16
32
64
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