Technical data

Table Of Contents
SFBs for Compact CPUs
System Software for S7-300/400 System and Standard Functions - Volume 2/2
28-14
A5E00739858-01
28.2 Positioning with Digital Output Using SFB 46
"DIGITAL"
Description
Use SFB DIGITAL ( SFB 46) to control the positioning functions via user program.
The four 24-V digital outputs are assigned fixed to drive. They control the power
stage. Dependent on the control mode configuration, the digital outputs control the
direction and speed stages (rapid/creep speed).
The distance is measured via an asymmetrical 24-V incremental transducer with
two phases offset at 90 degrees.
First, the target is approached with the speed (V
Rapid).
At the changeover point the speed is toggled to creep speed (V
Creep).
The drive is switched off at the switch-off point.
The switch-over point and the switch-off point are determined for every Step
Approach by the parameter values you have declared for changeover
difference and cut-off difference. The changeover difference and cut-off
difference can be determined differently for the forward motion (in plus
direction) and for the reverse motion (in minus direction).
The run is completed (WORKING = FALSE) when the cut-off point is reached.
A new run can then be started.
The specified target is reached (POS_RCD = TRUE) when the actual position
value has reached the home target. If the actual position value drifts off without
a new run having been started the signal "Position reached" is not reset again.