HEDL-64 HP [Agilent(Hewlett-Packard)], HEDL-64 Datasheet - Page 3

• Manufacturer Part Number: HEDL-64
• Description: Optical Incremental Housed Encoders
• Manufacturer: HP [Agilent(Hewlett-Packard)]

Theory of Operation
The HEDL- 64XX translates
rotary motion of a shaft into a
two or three channel digital
output. The HEDL- 64XX series
has four key parts: a single light
emitting diode (LED) light
source, a photodetector IC with
a set of uniquely configured
photodiodes , a line drive IC
and a pair of lenses. The lens
over the LED focuses light onto
the codewheel. As the codewheel
rotates, an alternating pattern of
light and dark corresponding to
the pattern of the codewheel
falls upon the photodiodes.
This light is used to produce
internal signals A and A’, and B
and B’.
As part of this “push- pull”
detector system, these signals
are fed through comparators and
line driver that are part of the
signal processing circuitry to
produce the final outputs for
channels A and B and index.
LED
RESISTOR
LENS
CODEWHEEL
PHOTODIODE
Definitions
Count (N): For rotary motion,
the number of bar and window
pairs or counts per
revolution(CPR) of the
codewheel. For linear motion,
the number of bar and window
pairs per unit length (lines per
inch[LPI] or lines per mm
[LPmm]).
One Cycle(C): 360 electrical
degree(
pair.
One Shaft Rotation: 360
mechanical degrees, N cycles
(rotary motion only).
Line Density: The number of
reflective and non- reflective
pairs per unit length, expressed
as either lines per inch(LPI) or
lines per mm (LPmm).
Cycle error(
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
°
e), 1 bar and window
SIGNAL
PROCESSING
CIRCUITY
∆
C):: An indication
Gnd
Ch A
I
Ch A
Ch B
Ch B
I
Vcc
Pulse Width (P): The number of
the electrical degrees that an
output is high during one cycle,
nominally 180
Pulse Width Error(
deviation in electrical degrees of
the pulse width from its ideal
value of 180
State Width (S): The number of
the electrical degrees between a
transition in the output of the
channel B. There are 4 states
per cycle, each nominally 90
State Width Error (
deviation in electrical degrees of
each state width from its ideal
value of 90
Phase (f): The number of
electrical degrees between the
center of the high state on the
channel A and the center of the
high state of channel B. This
value is nominally 90
Phase error (
in electrical degrees of the phase
from its ideal value of 90
Position error (
normalized angular difference
between the actual shaft position
and the position indicated by
the encoder cycle count.
Index Pulse Width (Po): The
number of electrical degrees that
an index is high during one full
shaft rotation. This value is
nominally 90°e or ¼ cycle.
°
e.
°
e.
∆
°
f): The deviation
e or 1/2 a cycle.
∆
q):: The
∆
∆
P): The
S): The
°
e.
°
e.
°
e.
3