NORD Drivesystems BU0210 - Manual (Page 47)

6 Synchronous control
BU 0210 GB Subject to technical amendments 47
6.6 Achievable precision / Position monitoring
The achievable precision, i.e. the deviation of the master and slave drives depends on several factors. Here, in
addition to the settings of the speed control and the position control, the path, i.e. the drive or the mechanics of
the system,play a decisive role. The minimum value of the achievable precision is however determined by the
type of transmission. A deviation of at least 0.1 rotations should be expected. In practice, a value of more than
0.25 motor rotations should b planned for. The deviation between the master and the slave can be monitored
by the relay function "Position Reached" with the slave. The relay switches off if the set value in P625 "Output
Hysteresis" is exceeded or the difference between the specified and the actual speed 2Hz + the set value in
P104 "Minimum Frequency" is exceeded. The minimum frequency for the slave can be calculated with the
following formula:
P104 = 0.25 ... 1,0 * (P625 [Rotation] * 4.0Hz * P611 [%]) – 2Hz
For a permissible deviation of one rotation and a position control P of 5% this results in a speed component for
the position control of 20Hz. If P104 "Minimum Frequency" is set to a considerably lower value, the relay
message is determined by the exceeding of the speed by the slave and not by the maximum deviation in
position. This especially applies, the shorter the ramp times are set for the slave.
6.7 Significance of P630 for synchronous operation
Alternatively, the slip error monitoring P630 "Slip Error Pos" can also be enabled for the slave device. If the
synchronous control is enabled, the error between the position estimated from the speed and the actual
position will not be compared, but rather the difference between the setpoint position and the actual position
as long as synchronous operation is enabled.
The monitoring is only valid if the device is enabled and the position control is activated. If the slave is not
enabled, the position of the master may deviate from the position of the slave.
6.8 Notes on reference point runs with synchronous operation
If the slave axis is to be referenced independently from the master axis, the following must be noted: The slave
receives its setpoint speed as a specification from the master. If the master is not running, the slave does not
have a setpoint value for the reference point run. For a reference point run of the slave, an independent
parameter set must be used, in which the speed during the reference point run is determined by Fmin (P104)
and Fmax (P105) [Fmin = Fmax = Fref]. The frequency addition in P546 "Function Bus Setpoint" should be
switched off. The slave must always be referenced after the master.
For synchronous systems, where the master and the slave cannot be operated separately, a different strategy
must be developed for the case of a deviation. With incremental position detection the actual position cannot
be used in order to detect a deviation. If there is no deviation, the entire system is referenced, i.e. the slave in
synchronous operation. The reference point run should therefor be performed via the external control unit
according to the following sequence (all steps with a minimum time difference of 20ms):
4. Move entire system to reference point
5. Remove enablement for the master
6. Remove enablement for the slave
7. Perform "Reset Position" for the master (P601
Master
= 0, P602
Slave
jumps by P601
alt
-P601
neu
)
8. Perform "Reset Position" for the slave (P602
Slave
= 0, P601
Slave
= 0)