Basics of Positioning
2-2
FM 351 Positioning Module
C79000-G7076-C351-02
2.1 Controlled Positioning
Each positioning operation is characterized by the following:
• a start position
• a target to which the tool will move, and
• parameters determining how the positioning operation is executed.
The target position is first approached at high speed (rapid speed).
At a specified distance from the target position the speed is reduced to a lower
speed (creep speed). Shortly before the axis reaches the target position, again at a
specified distance from the target position, the drive is switched off. The module
then monitors the final target approach.
The drive is controlled via digital outputs that set the rapid or creep speed and the
required direction (see Section 8.3, page 8-6).
2.2 Ranges and Switching Points of the FM 351
Target
The target is the absolute or relative position on the axis that is approached during
a positioning operation.
Definition of the Switching Points and Ranges
The following ranges and positions can be set for each positioning operation:
Range Explanation
Working range Defines the range that you set for your task using the software limit
switches or the end of the rotary axis.
Switchover
difference
Defines the distance to the target at which the drive switches from rapid
speed to creep speed.
Switchover point Defines the position at which the drive changes from rapid speed to
creep speed.
Switch-off
difference
Defines the distance to the target at which the drive is turned off.
Switch-off point Defines the position at which the drive is turned off. From this point
onwards, the FM 351 activates monitoring functions.
Target range Defines the positioning accuracy of your application and is located
symmetrically either side of the target.
Stationary range Defines a symmetrical range around the target that is monitored by the
FM 351.
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