HEDL-65xx, HEDM-65xx, HEDS-65xx Series
Large Diameter (56 mm), Housed Two and
Three Channel Optical Encoders
Data Sheet
Description
The HEDS-65xx/HEDL-65xx are high performance
two and three channel optical incremental encoders.
These encoders emphasize high reliability, high
resolution, and easy assembly. Each encoder contains a
lensed LED source (emitter), an integrated circuit with
detectors and output circuitry, and a codewheel which
rotates between the emitter and detector integrated
circuit. The outputs of the HEDS-6500 are two single
ended square waves in quadrature. The HEDL-65xx
outputs are differential.
The HEDS-6540 / HEDL-6540 also have a third channel
index output in addition to the two quadrature outputs.
This index is an active high pulse that occurs once ev-
ery full rotation of the codewheel. Resolutions up to 1024
Counts Per Revolution are available in the two and three
channel versions.
The line driver option offers enhanced performance
when the encoder is used in noisy environments, or
when it is required to drive long distances.
The line driver option utilizes an industry standard line
driver IC AM26C31Q which provides complementary
outputs for each encoder channel. Thus the outputs
–
–
of the line driver encoder are A and A, B and B, and I and
–
I for three channel versions. Suggested line receivers
are 26C32 and 26C33.
The quadrature signals are accessed through a cable
and 10-pin female connector. Please refer to the or-
dering information at the end of this data sheet for a
selection matrix.
Features
•
Two channel quadrature output with optional
index pulse
•
TTL compatible single ended outputs on HEDS Series
•
100ºC operating temperature for metal code wheel
•
70°C operating temperature for mylar code wheel
•
Industry standard AM26C31Q CMOS line driver IC on
HEDL Series
•
Easy assembly, no signal adjustment necessary
•
Resolutions up to 2048 counts per revolution
Applications
The HEDS-65xx / HEDL-65xx provide motion de-
tection to a very high resolution and accept a
variety of shaft sizes up to a maximum of 5/8 inches.
Typical applications include printers, plotters, tape
drives, positioning tables, and automatic handlers.
Note: Avago Technologies encoders are not recommend-
ed for use in safety critical applications. Eg. ABS braking
systems, power steering, life support systems and critical
care medical equipment. Please contact sales represen-
tative if more clarification is needed.
HEDL-65XX fig 1
Theory of Operation
The HEDS-65xx / HEDL-65xx translate the rotary motion
of a shaft into either a two or three channel digital
output.
The HEDS-65xx uses one of the standard HEDS-9000
or HEDS-9040 modules for encoding purposes. The
HEDL-654x uses the standard HEDL-9040 for encoding
purposes.
As seen in the block diagram, these modules contain a
single Light Emitting Diode (LED) as their light source
(emitter). The light is collimated into a single parallel
beam by means of a plastic lens located directly over
the LED. Opposite the emitter is the integrated detector
circuit (detector). This circuit consists of multiple sets
of photodetectors and the signal processing circuitry
necessary to produce the digital waveforms.
The codewheel rotates between the emitter and
detector, causing the light beam to be interrupted by a
pattern of spaces and bars on the codewheel. The pho-
todiodes which detect these interruptions are arranged
in a pattern that corresponds to the radius and design
of the codewheel. 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 then fed into the signal pro-
–
–
cessing circuitry resulting in A, A, B, and B (I and I also in
the three channel encoders). 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 that of channel
B (90 degrees out of phase).
In the HEDS-6540 / HEDL-6540 the output of the com-
parator for the index pulse is combined with that of the
outputs of channel A and channel B to produce the final
index pulse. The index pulse is generated once every
rotation of the codewheel and is a one state width
(nominally 90 electrical degrees), true high index pulse.
It is coincident with the low states on channels A and B.
Definitions
Count (N): The number of bar and window pairs or counts
per revolution (CPR) of the codewheel.
One Cycle (C): 360 electrical degrees (e), 1 bar and
window pair.
One Shaft Rotation: 360 mechanical degrees, N cycles.
Position Error (∆Θ): The normalized angular difference
between the actual shaft position and the position
indicated by the encoder cycle count.
Cycle Error (∆C): An indication of cycle uniformity. The
difference between an observed shaft angle which gives
rise to one electrical cycle, and the nominal angular
increment of 1/N of a revolution.
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 (Φ): the number of electrical degrees between the
center of 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 (∆Φ): The deviation of the phase from its
ideal value of 90 e.
Direction of Rotation: When the codewheel rotates in
a counterclockwise direction (when 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.
Index Pulse Width (P0): The number of electrical degrees
that an index output is high during one full shaft rotation.
This value is nominally 90 e or 1/4 cycle.
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