HEDS-9730, HEDS-9731
Small Optical Encoder Modules 480lpi Digital Output
Data Sheet
Description
The HEDS-973X is a high performance incremental
encoder module. When operated in conjunction with
either a codewheel or codestrip, this module detects
rotary or linear position. The encoder consists of a lensed
LED source and a detector IC enclosed in a small C-
shaped plastic package. Due to a highly collimated light
source and a unique photodetector array, the module is
extremely tolerant to mounting misalignment.
The two channel digital outputs and 3.3V supply input
are accessed through four solder plated leads located on
2.54mm (0.1inch) centers.
The standard HEDS-973X is designed for use with an ap-
propriate optical radius codewheel or linear codestrip.
Other options are available. Please contact the factory for
more information.
Features
•
Small Size
•
High Resolution
•
Two Channel Quadrature Output
•
Linear and Rotary Applications
•
No Signal Adjustment required
•
TTL or 3.3V/5V CMOS Compatible
•
Wave Solderable
•
Lead-free Package
•
-40°C to 85°C Operating Temperature
•
Single 3.3V Supply
Applications
The HEDS-973X provides sophisticated motion detection,
making closed loop control very cost competitive. Typical
applications include printers, plotters, copiers and office
automation equipment.
Note:
Avago Technologies’ encoders are not recommended for use in safety
critical applications, e.g., ABS braking systems and critical-care medical
equipment. Please contact a sales representative if more clarification is
needed.
Block Diagram
RESISTOR
LENS
PHOTO-
DIODES COMPARATORS
A
+
A -
B
+
VCC
3
CHANNEL A
2
CHANNEL B
4
LED
B -
SIGNAL
PROCESSING
CIRCUITRY
GND
1
EMITTER SECTION
CODE
WHEEL
DETECTOR SECTION
Figure 1
ESD WARNING: NORMAL HANDLING PRECAUTIONS SHOULD BE TAKEN TO AVOID STATIC DISCHARGE.
Theory of Operation
A HEDS-973X 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 digital outputs.
As seen in Figure 1, the module contains a single Light
Emitting Diode (LED) as its light source. The light is col-
limated into 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 photo-
detectors and a 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 codewheel/
codestrip. The photodiodes, which detect these interrup-
tions, are arranged in a pattern that corresponds to the
radius and count density of the codewheel/ codestrip.
These photodiodes are also spaced such that a light
period on one pair of detectors corresponds to a dark
period on the adjacent pairs of detectors. The photodiode
outputs are fed through the signal processing circuitry.
Two comparators receive these signal and produce the
final outputs for Channels A and B. Due to this integrated
phasing technique the output of channel A is in quadra-
ture with Channel B (90 degrees out of phase).
Definitions
Note: Refer to Figure 2
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 degrees
= N cycles
1 cycle (c) = 360 electrical degree, equivalent to 1 bar and
window pair.
Pulse Width (P):
The number of electrical degrees that an
output is high during one cycle, nominally 180°e or 1/2
a cycle.
Pulse Width Error
(DP): 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 neigh-
boring transition in the output of channel B. There are 4
states per cycle, each nominally 90°e.
State Width Error (DS):
The deviation in electrical degrees of
each state width from its ideal value of 90°e.
Phase (f):
The number of electrical degrees between the
center of the high state on channel A and the center of
the high state on channel B. This value is nominally 90°e
for quadrature output.
Phase Error (Df):
The deviation in electrical degrees of the
phase from its ideal value of 90°e.
Direction of Rotation:
When the codewheel rotates in the
counter-clockwise direction (as viewed from the encoder
end of the motor), channel A will lead channel B. If the
codewheel rotates in the clockwise 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.
Angular Misalignment Error (E
A
):
Angular misalignment of
the sensor in relation to then tangential direction. This
applies for both rotary and linear motion.
Mounting Position (R
M
):
Distance from Motor Shaft center of
rotation to center of Alignment Tab receiving hole.
Output Waveforms
Figure 2.
Mounting Considerations
5.32 MAX.
(0.209)
4.40 ± 0.13
0.17 ± 0.005
SEE NOTE 1
Rm
IMAGE SIDE OF
CODEWHEEL/CODESTRIP
Rop
C OF ALIGNMENT TAB
L
6.30 MAX.
(0.248)
6.50 MIN.
(0.256)
CENTER OF ROTATION
MOTOR SHAFT CENTER
-A-
2.03 MIN.
(0.080)
1.0 DEEP MIN.
(0.039)
2X R
EA
Rm = Rop - 0.14 (0.006)
ALIGNMENT TAB RECEIVING HOLE
½
2.03 HOLE MIN.
(0.080)
1.0 DEEP MIN.
(0.039)
A 0.13 mm (0.005")
DIMENSIONS IN MILLIMETERS (INCHES).
Note: These dimensions include shaft end play and codewheel warp.
For both rotary and linear motion, angular misalignment, EA must be * ± 1 degrees to achieve Encoding Characteristics.
All dimension for mounting the module and codewheel/codestrip should be measured with respect to two mounting posts, as shown above
Recommended Codewheel and Codestrip Characteristics
MAX 3.4 (0.134)
Wb
Lw
Ww
Rc
Rop
W1
W2
Ww
Wb
L
Parameter
Window/bar Ratio
Window Length (Rotary)
Absolute Maximum Codewheel Radius (Rotary)
Center of Post to Inside Edge of Window
Center of Post to Outside Edge of Window
Center of Post to Inside Edge of Codestrip
Symbol
Ww/Wb
LW
Rc
W
W
L
Min.
0.9
.80
(0.07)
Max.
.
.
(0.09)
Rop + .40
(Rop + 0.4)
Unit
mm
(inch)
mm
(inch)
mm
(inch)
mm
(inch)
Notes
Includes eccentricity errors
.04
(0.04)
0.76
(0.06)
.60
(0.4)
mm
(inch)
4
Embedded System
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