7 Additional settings
The time interval for the current controller can be configured. If the time interval is too
short, an internal overflow may occur as in this case the processor does not have a
sufficient amount of computing time. If the time interval is too long, the dynamic response
will deteriorate, i.e. disturbances will be compensated only very slowly.
The speed controller is subordinate to the current controller. Normally, it is requested
during every second current controller cycle. If the factor is increased, the dynamic
response will also decrease as the speed controller request rate will be reduced. If the
factor is increased, the computing time reserves will be increased.
The position controller, on the other hand, is subordinate to the speed controller. Normally,
it is requested during every second cycle. The information provided above applies in this
case, too, including the last point "Interpolation calculation".
Variable cycle times became necessary in order to be able to support functions requiring,
for example, a synchronisation of the current controller intervals of several devices via a
fieldbus system. In this case, the cycle time of the current controller is set to a certain
value based on experience. During operation, the cycle time will be automatically and
continuously adapted within a very narrow correction range.
To extend the computing time reserve, we recommend changing the cycle time of the
current controller in the range of a few µs. This is sufficient in most cases. The factors
should be increased only for special applications, e.g. for the "Interpolated Position Mode"
under CANopen.
Operation in an interpolated operating mode
When using the servo drive in an interpolated operating mode (e.g. 7 or 8 under
CANopen/EtherCAT), the interpolator cycle t
p
must be adapted to the cycle time of the
external bus system. The following table includes possible combinations for reaching the
bus cycle time with 1 ms.
t
i
Factor t
n
Factor t
x
Factor t
p
t
p
31,2 µs
2
3
8
998.4 µs
33,3 µs
2
3
5
999.0 µs
35,7 µs
2
2
7
999.6 µs
37,0 µs
3
3
3
999.0 µs
41,7 µs
2
2
6
1000.8 µs
47,7 µs
2
3
4
1000.8 µs
50,0 µs
2
2
5
1000.0 µs
Product manual BL 4000-C
Page 188 of 298
