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4. CONTROL OF VIX DRIVES 85
associated flags are cleared. The program will also be aborted if you are already on a limit
and you request motion in a direction which takes you further on to that limit.
If the LIMIT command has been set to ‘stop motion when a limit is hit but continue the
program’ and you hit a limit or request motion in a direction which takes you further on to a
limit no response will be given, apart from a possible *E (depending upon the setting of the
EX variable). In this situation, program execution will continue and no fault label will be run.
This allows the limit switch to be used as both a limit and home switch.
Hitting Both Limits
If both limits are hit motion will be stopped and the drive will respond as if a single limit has
been hit, but no further motion will be possible until both limits have been cleared. The
status will report which limit was seen first (positive or negative), but if both were hit in the
same millisecond period, the positive limit will be reported as being ‘seen’ first.
Clearing a Limit
A limit is cleared as soon as a motion command is given that moves the load away from the
limit, that is, in the opposite direction to which the limit was originally hit. Once a limit has
been cleared and the limit switch has returned to its normal state (closed or open contacts)
movement can be commanded in either direction.
Following and Limits
The way the drive reacts to hitting a limit while following depends upon the setting of the
FOLLOW mode parameter.
In encoder following mode (E), it is possible to re-enable following on a limit and reverse off
the limit. The drive will prevent motion further onto the limit while allowing motion off the
limit.
In all cases, the recommended action when a limit is hit during following, is for the
application to perform an indexed move to a position between the +ve and –ve end of
travel limits, before re-enabling following.