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