Omron TJ2-MC64 - PROGRAMMING Programming Manual page 287

Examples and tips
system. Basically, this movement is at low speed in some direction until a
certain measuring point is reached. Such a measuring point can be scanned
from both directions to increase the precision.
At startup, the current positions of the axes using incremental encoders are
0. Because these positions do not match with the mechanical 0 of the
machine, it is necessary to execute the homing sequence. If an absolute
encoder is used, the absolute position is read at startup from the encoder
and homing is not necessary. In this case, a startup sequence must be
executed one time during the machine commissioning.
In practice there are several different origin search sequences. They are
different in these areas:
• The means used to detect limit positions of the moving part (sensors,
switches, etc.)
• Origin (home) position or reference.
• Possible positions of the moving part related to limit positions and origin
position.
Trajexia includes some pre-defined basic homing sequences:
• DATUM(0)
This is not really an origin search. This command sets DPOS=MPOS
and cancels the axis errors.
• DATUM(1)
This does an origin search in forward direction using the Z mark of an
encoder as homing switch.
• DATUM(2)
Does an origin search in reverse direction using the Z mark of an
encoder as homing switch.
• DATUM(3)
Does an origin search in forward direction using the input selected in
DATUM_IN as homing switch.
• DATUM(4)
Does an origin search in reverse direction using the input selected in
DATUM_IN as homing switch.
• DATUM(5)
PROGRAMMING MANUAL 281