Why Does My Motion Controller Fail to Find Index?
Hardware: Motion Control>>Controllers
Problem: Everything on my motion controller works fine but when I execute a Find Index, the motor moves and eventually stops but never finds the Index signal. Why is this?
Solution: The Find Index VI initiates a search sequence to find the index (marker) signal of the incremental feedback encoder. There are a number of things that could cause the motion controller to miss the index.:
- Check to see that you have loaded the correct counts per revolution value with the Load Counts/Steps per Revolution VI. This is necessary for the Find Index VI to operate properly. At this point your motor should turn and stop on the index signal. If the index is not found, the motor will stop a few counts after one revolution.
- Use an oscilloscope to verify that the index is normally high and a low pulse is output by the encoder for the index.
- To tell if the problem is with the board or the encoder, try shorting the index signal leads to simulate an index low pulse. When this occurs the motor should stop and report that the index is found. If this works, then the problem is most likely related to the encoder or the wiring of the encoder.
- The Find Index VI requires the index signal to appear when both phases (A and B) of the encoder are low. If the index pulse occurs when either phase is high, the index will never be found. You can verify this condition by hooking up all 3 channels to the oscilloscope. Another quick test is to simply switch the leads of one of the phases, for example A and A~. This will cause the motor to go in the reverse direction, however, this should allow the index to be found. If you are able to find the index this way, you simply need to swap the two phases (A and B) to have your motor travel in the right direction.
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Report Date: 03/07/2001
Last Updated: 09/15/2003
Document ID: 276AA4OA
