Technical data

Configuration
CPU 317T: Technology Functions
A5E00251798-03
4-41
The current position of the axis upon reaching the HW limit switch is saved. Only
when this position, plus a safety range, has been overrun is the axis considered to
have left the limit switch.
Warning
Once the HW limit switch has been overrun, the controller must not
be switched off
in order to avoid a conflict between the polarity monitoring of the HW limit switches
and the overrun monitoring of the HW limit switches in the direction of the
permissible range. In this case, the axis must be moved into the permitted range
without hardware limit switch monitoring. There, monitoring can be enabled again.
At power on of the PLC, the axis must be located in the permissible traversing
range.
Internal states are lost if the axis overruns the HW limit switch and the configuration
is reloaded. The relevant data can only be reloaded without loss of the approach
information if the axis is positioned within the valid range.
Exception: Disabling of limit position monitoring after a polarity error.
Safety range
The safety range of the HW limit switches is calculated based on the configured
resolution of the physical unit system of the axis.
Safety range = 1000 / (increments / position)
Example: A linear axis is assigned the position unit "mm" and an accuracy
(increments / position) of "1000/unit" in the "Configure units" dialog box, i.e. the
axis position is calculated with an accuracy of 0.001 mm. The safety range in this
example is a multiple of 1000 of the accuracy: 1 mm.
4.5.6.3 Software limit switches
Open the Axis > Limits dialog box, then select the "Position and velocity" tab to
configure the SW limits switches and enable monitoring. Software limit switches
should lie within the range of the HW limit switches with reference to the traversing
range in order to limit the working range of an axis, for example.
The response of software limit switches is determined by the axis configuration with
respect to the homing function. The software limit switches of an axis configured for
the execution of absolute motion commands in homed mode ("Homing required:
Yes" in the Axis > Homing dialog box) are not monitored if the axis is not homed.
However, if those commands can be executed when the axis is not homed
("Homing required: No" in the Axis > Homing dialog box), all software limit switches
are monitored, irrespective of the homing state of the axis.