Instruction Manual PSx3xxPN
27
motor power has to be in a valid range at the time when this transition
happens (e.g. Bit 4 in the status word is being set). If the motor power is
missing at that time, the readjustment fails
and bits10 (“positioning error”)
and 13 (“motor power was missing”) will become active. If later the motor
power comes back again (after leaving the positioning window), there will
be
no
further attempt to readjust. This is to prevent a situation that
suddenly a drive begins to run if motor power is being switched on.
If an ongoing positioning run or manual run is aborted (relaese bit in the control word
to 0), the drive readjusts the position not before a new run is being sent and finished
successfully.
Deasserting the release bit and/or disabling the readjustment function can completely
disable the readjustment process.
Drives with a brake generally don’t have a readjustment function.
3.4
Positioning sequence with loop
The length of loop (Par. 45) has the effect of ensuring that a target value is always
approached from the same direction. This allows, for example, to eliminate the lash in
a driven spindle. The diagram below illustrates the function of the length of loop:
If the target value is above the current position (actual value 1) and the length of loop
is > 0, the drive runs past the target value by the specified length of loop (run 1a) and
then runs to the target value (run 1b).
If the target value is below the current position and the actual value (actual value 2) is
outside the length of loop, the drive approaches the target value directly (run 2).
If the position always should be approached from the left, the length of loop must be <
0.
Hence the PSx3xxPN differs between the following steps of a positioning sequence
(Presumption: the target position is always approached through backward motion, i.e.
the length of loop is > 0, which corresponds to the drawing above):
1. New position value is larger than the current value: The device overruns the target
position by 5/8 of one rotation, then approaches the exact position in backward
motion.
2. New position value is smaller than the current value: The position will be
approached directly.
3. New position value is smaller than the current value, but before there was a
forward run without loop (e.g. a manual run): Because the loop length is > 0, the
device by all means approaches the position by moving in backward direction.
The distance in backward direction is at least the length of loop. To achieve this,
the device first will run in forward direction, if necessary (i.e. in opposite to the
actually desired direction). The maximum length of this run is the length of loop.
