In servo control applications, the Command
and Actual Positions for an Axis are generally used for position
error calculations. On each sample, the XMP controller reads
the new Actual Positions from the feedback devices and calculates
the new Command Positions.
To determine the relationship between Command
and Actual Positions for an Axis and physical positions on
the machine, you can use the Origin variable (which can be
set by the host).
If it is important to set the Command or Actual
Position to an exact value, you should use the mpiAxisOriginSet(...)
function. Calling mpiAxisOriginSet(...) will modify
both Command and Actual Positions by the same amount.
The Origin variable can be set in two different
ways depending on the desired result. For example, assume
the Command and Actual Positions are 10,000 and 10,024 counts
respectively and that the axis is not moving.
Setting the Origin variable to 10,000 will result in Command
Position = 0 and Actual Position = 24. Setting the Origin
variable to 10,024 will result in Command Position = -24 and
Actual Position = 0.
This second method is the most frequently used method for
setting the new Origin after homing. Refer to the next table.