2
Theory of Operation
The AEDS-964X 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
nal 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).
De nitions
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 ½ 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 neighbor-
ing 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 (): 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 (): 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 (Rop): 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.
