Block Diagram
Output Waveforms
of multiple sets of photodetectors
and the signal processing
circuitry necessary to produce the
digital waveforms.
The codewheel/codestrip passes
between the emitter and detector,
causing the light beam to be
interrupted by the pattern of
spaces and bars on the code-
wheel. The photodiodes which
detect these interruptions are
arranged in a pattern that
corresponds to 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 then fed
through the signal processing
circuitry resulting in A, A, B, and
B. 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).
Definitions
Count (N):
The number of bar
and window pairs or counts per
revolution (CPR) of the
codewheel.
1 cycle (C):
360 electrical degrees
(°e), 1 bar and window pair.
1 Shaft Rotation:
360 mechanical
degrees, N cycles.
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 (
∆
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 elec-
trical 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 (
∆φ
):
The deviation
of the phase from its ideal value
of 90°e.
Direction of Rotation:
When the
codewheel rotates in the direction
of the arrow on top of the
module, channel A will lead
channel B. If the codewheel
rotates in the opposite direction,
channel B will lead channel A.
Optical Radius (R
op
):
The dis-
tance from the codewheel’s center
of rotation to the optical center
(O.C.) of the encoder module.
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HP [ AGILENT(HEWLETT-PACKARD) ]
