Danaher Motion 06/2005 Single-Axis Motion
M-SS-005-03 Rev E 91
4.1.8.1. POSITION FINAL AND INCREMENTAL VERSUS
ABSOLUTE MOVES
POSITIONFINAL (the end of a move), is always specified in MOVE. The
meaning of PFINAL depends on ABSOLUTE (ABS). This allows point-to-
point moves to be specified two ways:
Absolute Moves (Absolute = TRUE)
Final position is specified as actual motor position at the end of the
move. The final position is equal to PFINAL.
Incremental (Absolute = FALSE)
Final position is referenced to the start position. The final position is
equal to the sum of PFINAL and PCMD from the start of the move. So:
CutAxis.Absolute = TRUE
Move CutAxis 100
moves CutAxis to position 100. On the other hand:
CutAxis.Absolute = FALSE
Move CutAxis 100
moves CutAxis a distance of 100 units from the current position.
ABSOLUTE defaults to FALSE. You can change ABSOLUTE at any time,
although the effect does not take place until you issue the next MOVE.
4.1.8.2. SETTLING TIME
The MC actively watches to see if axes are settled into position. In almost all
applications, the motor position feedback is slightly delayed from the position
command. After a move is complete, some time is required for the actual
position to settle out to the commanded position; this time is called settling
time.
Consider the point-to-point move shown below. The VELOCITYCOMMAND
(VCMD) is shown in solid line and VELOCITYFEEDBACK (VFB) is shown
in thin line. The area between the two curves is the following error. As you
can see, it takes a small amount of time at the end of the move for VFB to
settle out to zero. The actual amount of time required for this varies from one
system to another. Higher bandwidth systems have shorter settling times, but
all systems need some time to settle. Typical times range from a few
milliseconds to tens of milliseconds.
