NORD Drivesystems BU0710 - Manual (Page 26)

NORDAC SK 700E Manual Posicon special extension
26 BU 0710 GB
5 System start-up
When setting up Posicon control for an application it is advisable to carry out the individual steps in the order
described below. For errors that may occur during this stage see also Section 6, Fault clearance.
1 st step: Putting the axle into operation without control
After all parameter settings have been entered as required, begin by putting the axle into operation without
position or speed control. Accordingly switch off position control in the "Positioning" parameter group, and the
servo mode in the "Control parameters" parameter group.
Important note: Make sure that emergency stop and safety circuits are operative!
With lifting gear applications take precautions before turning on the power for the first time to ensure that the
load will not suddenly drop or sag.
In speed-controlled lifting gear, set the speed controller before you optimise the moment the load is taken up
(setpoint delay parameter).
2 nd step: Putting the speed controller into operation
If no speed control is desired or no incremental encoder provided, disregard this step, otherwise set the servo
mode to ON. For operation in the servo mode, enter the exact motor data and the correct number of encoder
graduation marks.
If after the servo mode has been activated the motor runs at low speed while the current input is high, this is
caused in all probability by a wiring error or by a parameterisation error concerning the connection of the
incremental encoder. Very often the above condition results from a discrepancy between the sense of rotation
of the motor and the counting direction of the encoder. Preferably the speed controller is not optimised until
the position controller is put into operation, because the behaviour of the position control loop can be
manipulated by varying the parameters relating to the speed controller.
3 rd step: Putting the position controller into operation
When the parameters P604, P605/606 have been set, check first whether the actual position is recognized
correctly. The actual position is read out in the "Current position" parameter (P601). The value is supposed to
be stable, and to increase when the motor is activated with the "enable right" command. If the value does not
change when the axle is rotated, check on the parameter settings and the encoder connection. The same
checking should be performed if the actual position value read out is erratic although the shaft does not move.
After that a setpoint position should be parameterised next to the current position. If the axle moves away from
that position rather than towards it when the motor has been enabled, the sense of rotation of the motor does
not match the sense of rotation of the encoder. Exchange the sign of the multiplication factor to put things
right.
When actual position recognition is working correctly, the position controller can be optimised. As a rule the
axle will respond more "rigidly" as the P gain is increased, in other words there will be less deviation from the
setpoint position than with minor gain values.
The maximum P gain of the position controller that can reasonably be set depends on the dynamical
behaviour of the total system. As a rule the following principle is true: The greater the masses involved in the
system and the less the friction, the more it is prone to oscillation, and the less is the maximum allowable P
gain value. To determine the critical value, the gain is gradually increased until the drive oscillates around the
position (departing from it for an instant and returning to it again). After that set the gain to between 0.5 and
0.7 times the critical value.
As the default setting will probably not be adequate for positioning applications with cascaded controller (servo
mode) involving heavy loads, a different setting should be preferred, e.g. a value between 3% and 5% for the I
gain of the speed controller, and a value between 100% and 150% as the P gain.