AEDS-965X Datasheet, PDF (2/8 Pages) AVAGO TECHNOLOGIES LIMITED – Small Optical Encoder Modules 150 and 180 LPI Digital Output

Theory of Operation
The AEDS-965X 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 two-channel
digital output.
As seen in the Figure 1, the module contains a single
Light Emitting Diode (LED) as its light source. The light
is collimated into parallel beam by means of a single
lens located directly over the LED. Opposite the emitter
are the integrated detector circuits.
This IC consists of multiple sets of photodetectors 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 codehweel/
codestrip. The photodiodes that detect these
interruptions are arranged in a pattern that
corresponds to the radius and count density of the
codewheel/0codestrip.
These detectors 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 signals and produce
the final outputs for Channels A and B. Due to this
integrated phasing technique the output of channel A
is in quadrature with Channel B (90 degrees out of
phase).
Aerosol Tolerant
The AEDS-965x series uses the Transmissive Optical
Technology with specially designed photodetector IC
to reduce and compensate the errors due to ink mists
contaminations. Coupled with a brighter LED, for better
penetration through ink mists deposits, this enables
the encoder to continue operating normally in ink mists
environment.
Definitions
Note: Refer to Figure 1 for the output waveform
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 degree 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°
Phase (φ): 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.
Phase Error (∆φ): the deviation 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 (R_op): The distance from the
codewheel’s center of the rotation to the optical center
(O.C) of the encoder modules.
Angular Misalignment Error (E_A): Angular
misalignment of the sensor in relation to the 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.
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