We've seen this problem in the past. We found the cause to be the combining of motor drive signals in the same cable bundle as encoder feedback wires. Noise was being coupled onto these wires and was cousing erroneous feedback signals. The drive cables should be seperated from the feedback cables.
Michael Aivaliotis >Wireworkers, > I'm having a flaky problem with a motion system that I'm trying to > pinpoint, and I thought I'd ask if anyone has seen something similar. > I'm using 3 NI 7344 motion boards, UMI interfaces, and MOOG servo > controllers (don't know the model) that provide a synthetic AB > signal for my NI board encoder inputs. Once every few hours of system > operation I'll see my motion system make a radical move, because one > of the encoders is "suddenly" off by 32768 counts i.e. 2^15. I put > suddenly in quotes because I don't know if a MOOG is deciding to > give me a burst of bogus steps that an NI board is counting, or if > an NI board is getting lost. Most of the incidents occur on one of the > axes, but I've seen it less often on a few other axes. Also, there is > no single set of circumstances where this occurs in terms of what my > software is doing at the time. > Thanks for the FREE tech support, > --David Moore
