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4. CONTROL OF VIX DRIVES 83
Final Direction of Travel
Note that no matter where motion starts from, that is from positive side of the home switch, in
the home switch region or from the negative side of the home switch, or in which direction it
goes from its starting point (positive or negative), its final direction of travel towards a
nominated home switch edge is always the same. Direction of travel towards the positive
edge of the home switch is always negative and the direction towards the negative edge of
the home switch is always positive. This minimises variations in the home switch operating
point between separate homing moves.
Example of Homing (Datum) Routine
1START: ; start label definition
1DECLARE(MOVE3) ; declare label
1LIMITS(0,1,0) ; configure limits (enabled, normally closed, stop when hit).
1HOME1(+,1,-15,100,1) ; configure the home parameters
1GOTO(MOVE3) ; transfer to label move 3
1END ; end of label definition
1MOVE3: ; define program label move 3
1O(0) ; turn off o/p 1
1GH ; execute the go home move
1O(1) ; turn on o/p 1 after go home complete
1A100 ; set acceleration to 100rps
2
1V25 ; set velocity to 25 rps
1D4000 ; distance to 1 motor rev
1G ; execute move
1END ; end of program move 3 definition
Interaction Between Homing and Limits
In certain applications a limit switch may be used to define the home position, in which case
one switch can be used for both a limit and the home position. This requires the
consideration of two possible situations:
1. Where home and limit switches are wired separately
2. Where home and one of the limit switches are shared
In the first case, where home and limit are wired separately, the following interactions are
possible:
When the load is already on a limit and it is commanded to go home, the initial direction of
motion will be away from the limit and this may not be the direction set in the HOME
command.
If a limit is enabled and hit whilst going home, direction of travel will be reversed (bounce off
a limit) and motion will continue until the home position is reached. If a second limit is hit or
the first limit is hit for the second time, the user fault ‘homing failed’ will be set and the