5.24 Absolute Encoders
5.24.2 Structure of the Position Data of the Absolute Encoder
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5.24.2
Structure of the Position Data of the Absolute Encoder
The position data of the absolute encoder is the position coordinate from the origin of the
absolute encoder.
The position data from the absolute encoder contains the following two items.
•
The number of rotations from the origin of the encoder coordinate system (called the multi-
turn data)
•
The position (number of pulses) within one rotation
The position data of the absolute encoder is as follows:
Position data of absolute encoder = Multiturn data × Number of pulses within one encoder
rotation (encoder resolution) + Position (number of pulses) within one rotation.
For a single-turn absolute encoder, the multiturn data is 0.
5.24.3
Reading the Position Data from the Absolute Encoder
To read the position data from the absolute encoder, turn the power supply OFF and ON again.
5.24.4
Multiturn Limit Setting
The multiturn limit is used in position control for a turntable or other rotating body.
For example, consider a machine that moves the turntable shown in the following diagram in
only one direction.
Because the turntable moves in only one direction, the upper limit to the number of rotations
that can be counted by an absolute encoder will eventually be exceeded.
The multiturn limit is used in cases like this to prevent fractions from being produced by the
integral ratio of the number of Servomotor rotations and the number of turntable rotations.
For a machine with a ratio of n:m between the number of Servomotor rotations and the number
of turntable rotations, as shown above, the value of m minus 1 will be the setting for the multi-
turn limit setting (Pn205).
Multiturn limit (Pn205) = m
−
1
If m = 100 and n = 3 (i.e., the turntable rotates three times for each 100 Servomotor rotations),
the relationship between the number of Servomotor rotations and the number of turntable rota-
tions would be as shown below.
Set Pn205 to 99.
Pn205 = 100
−
1 = 99
S
ervomotor
Gear
Turntable
