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Positioning
10.1.2 Functional Description
This section includes a brief description of the IP 240's method of operation in "positioning"
mode and provides explanations of terms used in subsequent sections.
Configuring the IP, data interchange
The IP 240 is a two-channel module. You can configure one or both channels for "positioning"
mode using configuring function block FB 167. The configuring FB is invoked in the restart organi-
zation blocks.
After configuring, you can initiate data interchange between the S5 CPU and the IP 240 to read
the actual value, the status bits and the interrupt bits, and to specify the new position using
control function block FB 168. For special applications, you can also program direct data inter-
change yourself.
Both standard function blocks require a data block for data interchange. You must generate the
data block prior to the first FB call.
Controlled positioning
For controlled positioning, the approach to the position is defined on a time-dependent or path-
dependent basis. When the cut-off point is reached, the positioning drive is stopped and the
actual value is no longer corrected. Fig. 10-2 illustrates a typical positioning sequence with a mo-
tor designed for two speeds:
•
Switch on motor, rapid traverse
•
Switch to creep speed
•
Switch off motor.
Starting
position
v
Controlled positioning with the IP 240
In order to control this positioning sequence with the IP 240, the module requires:
•
An incremental encoder for generating the path-dependent signals,
•
Synchronization of the actual value,
•
The position value of the target position and
•
The distance of the switching point and the cut-off point from the position value.
The synchronization of the actual value determines the zero point (reference point) of the actual
value range. The actual value and the position values relate to this point.
Because the positions can be approached from both directions, the IP 240 computes range BEE1
from the distance of the switching point and range BEE2 from the distance of the cut-off point
(
Fig. 10-3). The module firmware compares these ranges with the computed actual value.
Depending on the result of the setpoint/actual-value comparison:
•
Status bits are set and reset,
•
Outputs are switched and
•
Interrupts are generated on the IP 240.
10-2
Rapid traverse
Fig. 10-2. Controlled Positioning with Two Speeds
Target
position
Creep
speed
Switching
Cut-off
point
point
IP 240
EWA 4NEB 811 6120-02a
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