Small Optical Encoder Modules
Technical Data
Features
· Small Size
· Low Cost
· Multiple Mounting Options
· Wide Resolution Range
· Linear and Rotary Options
Available
· No Signal Adjustment
Required
· Insensitive to Radial and
Axial Play
· -40
°
C to +85
°
C Operating
Temperature
HEDS-9700 Series
· Two Channel Quadrature
Output
· TTL Compatible
· Single 5V Supply
· Wave Solderable
Description
The HEDS-9700 series is a high
performance, low cost, optical
incremental encoder module.
When operated in conjunction
with either a codewheel or
codestrip, this module detects
rotary or linear position. The
Package Dimensions
Mounting Option #50 - Standard (Baseplane Mounting)
Contact Factory for Detailed Package Dimensions
ESD WARNING; NORMAL HANDLING PRECAUTIONS SHOULD BE TAKEN TO AVOID STATIC DISCHARGE.
A
2
module consists of a lensed LED
source and a detector IC enclosed
in a small C-shaped plastic pack-
age. Due to a highly collimated
light source and a unique photo-
detector array, the module is
extremely tolerant to mounting
misalignment.
The two channel digital outputs
and 5V supply input are accessed
through four solder-plated leads
located on 2.54 mm (0.1 inch)
centers.
The standard HEDS-9700 is
designed for use with an 11 mm
optical radius codewheel, or
linear codestrip. Other options
are available. Please contact
factory for more information.
Applications
The HEDS-9700 provides
sophisticated motion detection at
a low cost, making closed-loop
control very cost-competitive!
Typical applications include
printers, plotters, copiers, and
office automation equipment.
Note: Agilent Technologies
encoders are not recommended
for use in safety critical
applications. Eg. ABS braking
systems, power steering, life
support systems and critical care
medical equipment. Please
contact sales representative if
more clarification is needed.
Theory of Operation
The HEDS-9700 is a C-shaped
emitter/detector module. Coupled
with a codewheel, it translates
rotary motion into a two-channel
digital output. Coupled with a
codestrip, it translates linear
motion into a digital output.
As seen in the block diagram, the
module contains a single Light
Emitting Diode (LED) as its light
source. The light is collimated
into a parallel beam by means of
a single lens located directly over
the LED. Opposite the emitter is
the integrated detector circuit.
This IC consists of multiple sets
of photodetectors and the signal
processing circuitry necessary to
produce the digital waveforms.
The codewheel/codestrip moves
between the emitter and detector,
causing the light beam to be
interrupted by the pattern of
spaces and bars on the code-
wheel/codestrip. The photodiodes
which detect these interruptions
are arranged in a pattern that
corresponds to the radius and
count density of the codewheel/
codestrip. These detectors are
also spaced such that a light
period on one pair of detectors
corresponds to a dark period on
the adjacent pair of detectors.
The photodiode outputs are fed
through the signal processing
circuitry. Two comparators
receive these signals and produce
the final outputs for channels A
and B. Due to this integrated
phasing technique, the digital
output of channel A is in
quadrature with channel B (90
degrees out of phase).
Block Diagram
3
Pulse Width (P): The number of
electrical degrees that an output
is high during one cycle. This
value is nominally 180
°
e or 1/2
cycle.
Pulse Width Error (
P): The
deviation, in electrical degrees, of
the pulse width from its ideal
value of 180
°
e.
State Width (S): The number of
electrical degrees between a
transition in the output of channel
A and the neighboring transition
in the output of channel B. There
are 4 states per cycle, each
nominally 90
°
e.
State Width Error (
S): The
deviation, in electrical degrees, of
each state width from its ideal
value of 90
°
e.
Phase (
): The number of
electrical degrees between the
center of the high state of channel
A and the center of the high state
of channel B. This value is
nominally 90
°
e for quadrature
output.
Phase Error (
): The deviation
of the phase from its ideal value
of 90
°
e.
Direction of Rotation: When the
codewheel rotates counterclock-
wise, as viewed looking down on
the module (so the marking is
visible), channel A will lead
channel B. If the codewheel
rotates in the opposite direction,
channel B will lead channel A.
Optical Radius (Rop): The
distance from the codewheel's
center of rotation to the optical
center (O.C.) of the encoder
module.
Absolute Maximum Ratings
Parameter
Symbol
Min.
Max. Units
Notes
Storage Temperature
T
S
-40
85
°
C
See Note
Operating
T
A
-40
85
°
C
See Note
Temperature
Supply Voltage
V
CC
-0.5
7
V
Output Voltage
V
O
-0.5
V
CC
V
Output Current per
I
O
-1.0
5
mA
Channel
Soldering Temperature
260
°
C
t
5 sec.
Output Waveforms
Definitions
Count (N) = The number of bar
and window pairs or counts per
revolution (CPR) of the
codewheel, or the number of lines
per inch of the codestrip (LPI).
1 Shaft Rotation = 360
mechanical
degrees
= N cycles
1 cycle (c) = 360 electrical
degrees (
°
e)
= 1 bar and
window pair
4
Encoding Characteristics
Encoding Characteristics over Recommended Operating Range and Recommended Mounting Tolerances.
These characteristics do not include codewheel/codestrip contributions.
Case 1
Case 2
Parameter
Symbol
Typ.
Max.
Max.
Units
Notes
Pulse Width Error
P
7
30
40
°
e
Logic State Width Error
S
5
30
40
°
e
Phase Error
2
10
15
°
e
Case 1: Module mounted on tolerances of
±
0.13 mm (0.005"). Case 2: Module mounted on tolerances of
±
0.25 mm (0.010")
Note: See Figures in Mounting Considerations for details on Case 1 and Case 2 mounting tolerances.
Recommended Operating Conditions
Parameter
Symbol
Min.
Max.
Units
Notes
Temperature
-40
85
°
C
Supply Voltage
V
CC
4.5
5.5
V
Ripple < 100 mV
p-p
Load Capacitance
C
L
100
pF
3.2 k
pull-up
Count Frequency
20
kHz
(Velocity (rpm) x N)/60
Note: The module performance is guaranteed to 20 kHz but can operate at higher frequencies. Contact factory for more information.
Electrical Characteristics
Electrical Characteristics over Recommended Operating Range, Typical at 25
°
C.
Parameter
Symbol
Min.
Typ.
Max.
Units
Notes
Supply Current
I
CC
17
40
mA
High Level Output Voltage
V
OH
2.4
V
I
OH
= -40
µ
A
Low Level Output Voltage
V
OL
0.4
V
I
OL
= 3.2 mA
Rise Time
t
r
200
ns
C
L
= 25 pF, R
L
= 11 k
Fall Time
t
f
50
ns
C
L
= 25 pF, R
L
= 11 k
5
Recommended Codewheel and Codestrip Characteristics
Mounting Option #51 Rounded Outline (Baseplane Mounting)
Parameter
Symbol
Min.
Max.
Units
Notes
Window/Bar Ratio
Ww/Wb
0.7
1.4
Window Length (Rotary)
Lw
1.80
2.30
mm
(0.071)
(0.091)
(inch)
Absolute Maximum Codewheel
Rc
Rop + 3.40
mm
Includes eccen
Radius (Rotary)
(Rop + 0.134)
(inch)
tricity errors
Center of Post to Inside
W1
1.04
mm
Edge of Window
(0.041)
(inch)
Center of Post to Outside
W2
0.76
mm
Edge of Window
(0.030)
(inch)
Center of Post to Inside Edge
L
3.60
mm
of Codestrip
(0.142)
(inch)
Optional Packages Available
A
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