NORD Drivesystems BU0710 - Manual (Page 16)

NORDAC SK 700E manual Posicon special extension
16 BU 0710 GB
With the "minimum position" (P616) and "maximum position" (P615) parameters, limits for the allowable
working range can be defined. When the actual position is found to have exceeded these limits, the "E147"
error message (actual position exceeding maximum position) or the "E148“ error message (actual position
below minimum position) will be generated.
Encoder monitoring is completely deactivated by setting the option to "0". Monitoring is not available either in
the "position increment array" position setpoint mode (displacement increments), nor in the mode for
incremental position recognition. If position setpoints are defined which are less than the set minimum or
greater than the set maximum positions, inverter control will take care of that by limiting them accordingly.
3.2.4 Positioning with single-turn absolute value encoders and incremental shaft
encoders used in absolute mode
With turntables where the individual positions to be approached are distributed along the circumference, there
is a certain problem : If a multi-turn absolute value encoder was fitted to the output end of the gearbox or an
incremental shaft encoder to the motor or to the output face of the gearbox, with the setpoint position to be
changed from – 0.375 to + 0.375 the drive would adopt the longer displacement route – "go the long way
round" (see fig. a) – while typically the displacement from one position to the next ought to be ensured via the
shortest possible, in other words the optimal, route.
This effect can be prevented if operation of a single-turn absolute value encoder or of an incremental shaft
encoder is governed by the "absolute 1 revolution" mode setting (P606 options 16-31). As a result the drive
will follow the shorter displacement route, and in doing so pass the "overflow point" of the shaft encoder type
used (as shown in fig. b).
0.5/-0.5
-0.375 0.375
-0.125 0.125
0
-0.5 -0.5
0.5/-0.5
-0.375 0.375
-0.125 0.125
0
-0.5 -0.5
The point of origin (zero) of a single-turn absolute value shaft encoder depends on the position in which it is
installed and can be varied by providing an offset value. If an incremental shaft encoder is mounted on the
output face of a gearbox and operated in the "absolute 1 revolution" mode, with this encoder, too, the point of
origin is determined by the zero track. With each zero pulse the count is automatically reset (cf. P606 settings
16-23). Thus the incremental shaft encoder is automatically referenced with every complete turn. Likewise the
location of zero can be varied by providing an offset value. Automatic referencing is not possible however
when the incremental encoder is mounted on the motor (P606 setting 24-31).
P605 setting P606 setting Automatic referen.
Absolute shaft
encoder on
gearbox output 0…3
0: SSI Single-Turn 512 marks
1: SSI Single-Turn 1024 marks
2: SSI Single-Turn 2048 marks
3: SSI Single-Turn 4096 marks
--- yes
Incremental shaft
encoder on
gearbox output --- 16…23
16: 500 marks absolute 1 revolution
.....
23: 5000 marks absolute 1 revolution
no
a) Normal displacement route b) Displacement route with single-turn absolute encoder