NORD Drivesystems BU0510 - Manual (Page 28)

POSICON position control for NORD frequency inverters, SK 530E and above
28 Subject to technical alterations BU 0510 GB-3911
3.2.4.1 Optimised path positioning with a single rotation of the encoder
Rotating platform applications in which the individual positions are distributed around the circumference require
a path optimised positioning function for optimum operation. However, with a standard positioning, with a
change of the setpoint position from -0.375 to + 0.375 the drive unit would select the long movement path
"around the outside" (See Fig. 6 / a). In contrast, positioning with path optimisation automatically selects the
shortest path and therefore independently decides on the direction of rotation of the drive unit. Here, the drive
unit passes over the overflow point
2
of the relevant rotary encoder (See Fig. 6 / b).
Positioning with path optimisation can be set with all encoders (see table above).
The zero point of a single-turn absolute encoder is determined by where it is mounted and can be varied via
the parameter P609 [-02] "Offset Position". If an incremental encoder is used, either a "Reference Point Run"
or a "Reset Position" function must be performed in order to determine the zero position. The zero position can
also be varied by means of an entry in parameter P609 [-01] "Offset Position".
The following example is for a speed ratio or reduction ratio of "1". The maximum value of the position or the
overflow point is calculated as follows:
n
max
: Maximum value of motor rotation

n
max
= 0,5 * Ü
b
/ U
n
Ü
b
: Speed Ratio (P607[-02])
U
n
: Reduction ratio (P608[-02])
Example: The absolute encoder or incremental encoder is installed on the output side of the gear unit. The
gear unit has a ratio of i=26.3.
n
max
=0.5 * 263 / 10= 13.15 rotations
0.5 / -0.5
0
0.125
-0.125
0.25 -0.25
0.375 -0.375
0.5 / -0.5
0
0.125
-0.125
0.25 -0.25
0.375 -0.375
a) normal path
b) optimised path
Fig. 6: Standard a) and path optimised b) movement with a single-turn application
2
The overflow point corresponds to 1/2 of an encoder revolution