NORDAC SK 530E with PosiCon funktion
3 Function description
BU 0510 EN
Subject to technical changes
11
3 Function
description
3.1 Introduction
Numerous positioning and position control tasks can be resolved with the positioning function. To facilitate the
decision about which configuration the task can be best resolved with, the various methods for setpoint
specification and actual value acquisition are presented below.
The setpoint specification can be provided as an absolute or relative position. An absolute position specification is
recommend for applications with fixed positions, for instance with transfer carriages, elevators, shelf access
equipment, etc. The relative position specifications are suitable for all axes operating incrementally, especially for
endless axes such as rotary tables and cycled compartmented conveyor belts. The setpoint specification can also
be implemented via bus (Profibus, CAN bus, Interbus, DeviceNet or USS interface). The position can be specified
here as value or bit combination as position number or increment.
If there is need to change between positioning and speed specification, this can be implemented via parameter
switching. To do this, the position control in parameter P600 "Position control" is parameterised to "ON" in one
parameter set and "OFF" in another parameter set. The parameter sets can be switched at any time, including
during operation.
3.2 Actual position value acquisition
3.2.1 Position
acquisition
with incremental encoder
A reference point is required for an absolute actual position, this helps to determine the zero position of the axis.
The position acquisition works as long as the frequency inverter is supplied with voltage. The impulses of the
incremental encoder are counted in the inverter and added to the actual position value. Parameter P301
"Incremental encoder pulse number“ is used to set the resolution or pulse number of the incremental encoder. The
rotation direction can be adapted according to the installation position of the encoder by using negative pulse
numbers. After switching on the inverter voltage supply, the actual position = 0 (P604 "Encoder type" without the
option "Save position") or it is set at the value present during switch-off (P604 "Encoder type" with the option "Save
position").
The position acquisition works independently of the inverter enable signal and the parameter P600 "Position
control". The inverter records the actual position as long as it is supplied with voltage. Position changes that are
implemented when the frequency inverter is switched off do not lead to any changes in the actual position. A
reference point run is therefore generally required after every "Mains on".
If the inverter is not operated in servo- mode P300 "Servo mode", the incremental encoder can also be mounted
elsewhere than on the motor shaft. In this case, the ratiofrom the motor to incremental encoder must be
parameterised. The incremental encoder revolutions are converted into motor revolutions in the encoder with the
aid of the parameters P607 "Ratio" and P608 "Reduction ratio“.
n
M
: Motor
revolution
n
M
= n
G
* Ü
b
/ U
n
n
G:
: Incremental
encoder
revolution
Ü
b
:
Ratio (P607 [01])
U
n
:
Reduction ratio (P608 [01])
Example: The incremental encoder is attached to the gear output side, the gear has a ratio of i = 26.3. The following values are
parameterised:
P607 ratio: 263;
P608 reduction ratio: 10
NOTE :
The rotation direction of the incremental encoder must correspond to that of the motor. With a
positive output frequency (rotation right), the position actual value must be larger. If the rotation
direction does not correspond, this can be corrected with a negative value in P607 "Ratio".
With the help of a parameterisable value in parameter P609 [01] "Offset position", the zero point can be moved to
another position than the position determined by the reference point. The offset is taken into account after the
conversion of the encoder revolutions into motor revolutions. After changes to the ratio/reduction ratio in P607 [01]
and P608 [01], the offset position value must be entered again.
