Find Forward and Reverse Limits
Setting the Find Reference search type to Forward Limit initiates a search sequence to find the forward limit. Setting the search type to Reverse Limit initiates a search sequence to find the reverse limit. Attributes you can specify include the Initial Search Direction and the Final Approach Direction (for when the search encounters each of the limits).
The search is performed at the maximum find velocity specified by Max Find Velocity or Max Find RPM. The velocity of the axis is set to this value during the find operation. The velocity is then restored to its previous value after the search completes.
When the search operation initiates the axis starts moving in the direction of the limit. When the axis encounters the limit in that direction the search completes and the Wait Reference VI or function returns a true value.
A fine-tuning operation is performed when the limit is reached. This provides for a more accurate search. To smoothly approach the edge, this portion of the sequence is executed at a fixed low velocity of 1/4 RPS unless the maximum find velocity is slower. This approach direction feature is used to minimize the effects of motion system windup, backlash, and/or home sensor hysteresis. If the final approach direction is the opposite to the direction of travel into the limit (true), the axis then slowly backs off the limit until the limit becomes inactive again. If the final approach direction is the same as the direction of travel into limit (false), then the axis slowly backs off the limit and re-approaches it. You also can set the active state of the limit with the Set Limit Input Polarity VI or function.
If Smart Enable is disabled National Instruments recommends you disable the home input before performing a Find Forward Limit or Find Reverse Limit. If the home input is enabled and encountered during a Find Center, the search stops at the home input and generates a modal error.
With the Smart Enable feature enabled the limit you are searching for is enabled, the opposite limit is left as-is, and home input is disabled prior to initiating the search. After the search completes, the limits are returned to their previous states. If you use Smart Enable, National Instruments recommends setting the default in MAX to enable the forward and reverse limits and disable the home input.
After the limit is located, an offset move is performed. Offset Move specifies the amount and direction of the offset. This offset move is performed at the maximum find velocity specified by Max Find Velocity or Max Find RPM. Usually the Offset Move is negative for a Find Forward Limit and positive for a Find Reverse Limit. By default Offset Move is 0, resulting in no offset move.
After the offset move is performed, the position is reset if Reset Position? is true. The position is set to the values indicated by Reset Primary Position and Reset Secondary Position.