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VIX IM MICROSTEPPER INDEXER DRIVE USER GUIDE
84
system will respond as if a limit has been hit in the ‘normal’ manner, that is, whilst not
performing a homing move.
In the second case, where home and limit are wired together, the following interaction is
possible:
If the load is commanded to go home in a direction away from the home switch and hits a
limit, then the move will be automatically started in the opposite direction. When the load
reaches the combined limit/home switch, the home function will terminate in the normal
manner.
Limits
End-of-travel limits are used to restrict the movement of the load to a safe operating
distance. The placement of limit switches defines the direction of motion, since positive
motion is always regarded as moving towards the positive limit.
Two of the drive’s user inputs (I/O 4 & 5) can become dedicated limit inputs (negative and
positive) when enabled by the LIMITS command. From start-up, both limits are enabled
(default setting) and can only be disabled by issuing a disable limits command. For fail-safe
operation the limit switches must be normally closed, although this can be re-configured
within the LIMITS command.
Limit Switch Placement
Limit switches need to be placed such that when a limit switch is hit sufficient travel is still left
for the load to be decelerated to a stop before hitting the hardware limit or end stop. Hitting
a limit is defined as changing the state of a limit switch when that limit is enabled and the
direction of motion is appropriate, that is, you would only expect to hit the positive limit switch
when travelling in the positive direction.
Hitting a Limit
When a limit is hit, an error signal is generated (*E), the user fault bit ‘end of travel limit hit’ is
set and the status bit ‘+limit’ or ‘-limit seen during last move’ is set. Motion decelerates at the
rate set in the LIMIT command, which needs to bring motion to a stop before any hardware
limit is reached. If motion is requested whilst the load is already on the limit no motion will
take place and the drive will respond as if the limit had just been hit, although no
deceleration will take place.
A fault label can be made to run once a limit is hit, subject to the following conditions:
• No fault label is already running
• ARM command is armed and has the fault label enabled (ARMX1)
• Within the LIMIT command the mode is set to ‘Stop motion when a limit is hit and abort
program’
• A fault label has been defined
If no fault label is defined, or fault is not armed (within the main ARM), the program will be
aborted, that is motion will be stopped at limit deceleration, the program is halted and all