7.8 Absolute Encoders
7.8.7 Multiturn Limit Setting
7-36
7.8.7
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 revolutions
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 motor revolutions and the number of turntable revolutions.
For a machine with a gear ratio of n:m, as shown above, the value of m minus 1 will be the set-
ting for the multiturn limit setting (Pn205).
Multiturn limit (Pn205) = m - 1
The relationship between the number of turntable revolutions and the number of motor revolu-
tions is shown in the following graph for when m is 100 and n is 3.
Set Pn205 to 99.
Pn205 = 100 - 1 = 99
Note: This parameter is enabled when you use an absolute encoder.
The data will change as shown below when this parameter is set to anything other than the
default setting.
•
If the motor operates in the reverse direction when the multiturn data is 0, the multiturn data
will change to the value set in Pn205.
•
If the motor operates in the forward direction when the multiturn data is at the value set in
Pn205, the multiturn data will change to 0.
Set Pn205 to one less than the desired multiturn data.
If you change the multiturn limit in Pn205, an A.CC0 alarm (Multiturn Limit Disagreement) will be
displayed because the setting disagrees with the value in the encoder. Refer to the following
section for the procedure to change the multiturn limit settings in the encoder.
Multiturn Limit Disagreement Alarm (A.CC0)
Pn205
(2205h)
Multiturn Limit
Setting Range
Setting Unit
Default Setting
When Enabled
Classification
0 to 65,535
1 Rev
65,535
After restart
Setup
Turntable
Gear
Motor
0
1
2
3
4
5
6
7
8
9
100
200
300
0
100
50
Number of table rotations
Multiturn data
Number of table rotations
Multiturn data
Setting of Pn205 = 99
Number of rotations
Speed
Position
Torque
