Technology instructions
10.3 Motion control
S7-1200 Programmable controller
System Manual, V4.2, 09/2016, A5E02486680-AK
723
Homing refers to the matching of the axis coordinates to the real, physical drive position. (If
the drive is currently at position x, the axis will be adjusted to be in position x.) For position-
controlled axes, the entries and displays for the position refer exactly to these axis
coordinates.
Note
The agreement between the axis coordinates and the real situation is extremely important.
This step is necessary to ensure that the absolute target position of the axis is also achieved
e
xactly with the drive.
The MC_Home instruction initiates the homing of the axis.
There are 4 different homing functions. The first two functions allow the user to set the
current position of the axis and the second two position the axis with respect to a Home
reference Sensor.
● Mode 0 - Direct Referencing Absolute: When executed this mode tells the axis exactly
where it is. It sets the internal position variable to the value of the Position input of the
Homing instruction. This is used for machine calibration and setup.
The axis position is set regardless of the reference point switch. Active traversing motions
are not aborted. The value of the Position input parameter of the MC_Home instruction is
set immediately as the reference point of the axis. To assign the reference point to an
exact mechanical position, the axis must be at a standstill at this position at the time of
the homing operation.
● Mode 1 - Direct Referencing Relative: When executed this mode uses the internal
position variable and adds the value of the Position input on the Homing instruction to it.
This is typically used to account for machine offset.
The axis position is set regardless of the reference point switch. Active traversing motions
are not aborted. The following statement applies to the axis position after homing: New
axis position = current axis position + value of the Position parameter of the MC_Home
instruction.
● Mode 2 - Passive Referencing: When the axis is moving and passes the Reference Point
Switch the current position is set as the home position. This feature will help account for
normal machine wear and gear backlash and prevent the need for manual compensation
for wear. The Position input on the Homing instruction, as before, adds to the location
indicated by the Reference Point Switch allowing easy offset of the Home position.
During passive homing, the MC_Home instruction does not carry out any homing motion.
The traversing motion required for this step must be implemented by the user via other
motion control instructions. When the reference point switch is detected, the axis is
homed according to the configuration. Active traversing motions are not aborted upon
start of passive homing.
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