HEDM-55xx/560x & HEDS-55xx/56xx
Quick Assembly Two and Three Channel Optical Encoders
Data Sheet
HEDM-55xx/560x HEDS-550x/554x, HEDS-560x/564x
Description
The HEDS-5500/5540, HEDS-5600/5640, HEDM-5500/5540
and HEDM-5600 are high performance, low cost, two
and three channel optical incremental encoders. These
encoders emphasize high reliability, high resolution, and
easy assembly.
Each encoder contains a lensed LED source, an integrated
circuit with detectors and output circuitry, and a codewheel
which rotates between the emitter and detector IC. The
outputs of the HEDS-5500/5600 and HEDM-5500/ 5600
are two square waves in quadrature. The HEDS-5540/5640
and HEDM-5540 also have a third channel index output in
addition to the two channel quadrature. This index output
is a 90 electrical degree, high true index pulse which is
generated once for each full rotation of the codewheel.
The HEDS series utilizes metal codewheels, while the
HEDM series utilizes a film codewheel allowing for resolu-
tions to 1024 CPR.
These encoders may be quickly and easily mounted to a
motor. For larger diameter motors, the HEDM-5600, and
HEDS-5600/5640 feature external mounting ears.
The quadrature signals and the index pulse are accessed
through five 0.025 inch square pins located on 0.1 inch
centers.
Standard resolutions between 96 and 1024 counts per
revolution are presently available. Consult local Avago
sales representatives for other resolutions.
Features
Two channel quadrature output with optional index
pulse
Quick and easy assembly
No signal adjustment required
External mounting ears available
Low cost
Resolutions up to 1024 counts per revolution
Small size –40°C to 100°C operating temperature
TTL compatible
Single 5 V supply
Applications
The HEDS-5500, 5540, 5600, 5640, and the HEDM-5500,
5540,5600 provide motion detection at a low cost, making
them ideal for high volume applications. Typical applica-
tions 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 representa-
tive if more clarification is needed.
ESD WARNING:
NORMAL HANDLING PRECAUTIONS SHOULD BE TAKEN TO AVOID STATIC DISCHARGE.
Theory of Operation
The HEDS-5500, 5540, 5600, 5640, and HEDM-5500, 5540,
5600 translate the rotary motion of a shaft into either a
two- or a three-channel digital output.
As seen in the block diagram, these encoders contain a
single Light Emitting Diode (LED) as its light source. The
light is collimated into a parallel beam by means of a
single polycarbonate 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 rotates between the emitter and detector,
causing the light beam to be interrupted by the pattern
of spaces and bars on the codewheel. The photodi-
odes 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 photo-
diode outputs are then fed through the signal processing
circuitry resulting in A, A, B and B (also I and I in the HEDS-
5540/5640 and HEDM-5540). 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-5540/5640 and HEDM-5540, the output of
the comparator for I and I is sent to the index processing
circuitry along with the outputs of channels A and B.
The final output of channel I is an index pulse PO which
is generated once for each full rotation of the codewheel.
This output PO is a one state width (nominally 90 electri-
cal degrees), high true index pulse which is coincident
with the low states of 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 (ΔΘ):
The normalized angular difference
between the actual shaft position and the position
indicated by the encoder cycle count.
Cycle Error (ΔC):
An indication of cycle uniformity. The
differ¬ence 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 1 cycle. This value is nominally 180°e
or 1/2 cycle.
Pulse Width Error ( ΔP):
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 neighbour-
ing transition in the output of channel B. There are 4 states
per cycle, each nominally 90°e.
State Width Error ( ΔS):
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 the high state of channel A and the center of the
high state of channel B. This value is nominally 90°e for
quadrature output.
Phase Error (Δφ):
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.
Index Pulse Width (P
O
):
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.
Block Diagram
RESISTOR
PHOTO
DIODES
LENS
VCC
COMPARATORS
A
+
A
−
B
+
B
−
I
+
I
−
SIGNAL PROCESSING
CIRCUITRY
EMITTER
SECTION
CODE
WHEEL
DETECTOR SECTION
INDEX-
PROCESSING
CIRCUITRY
GND
CH. A
LED
CH. B
CH. I
Note: Circuitry for CH I is only for HEDS-5540, 5640 and HEDM 5540 Three Channel Encoder
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