Oscillating servo motor problem

[sparkotronic 0]

Hi, I'm looking for a bit of guidance on a problem that I have on one of the machines in my workplace. I have a servo motor attached to a pusher arm which oscillates backwards and forwards when it's not in use. We are using a Logix 5000 CPU with 1756-M02AE Motion control cards. The Servo drive is a Siemens Simodrive 611 I don't have a great deal of experience with motion control but when I look atthe program when the drive is oscillating there are no MAM functions in use. I did speak to an AB engineer regarding the problem, he told me to adjust theGain setting in the Axis Properties in the motion groups. Is this tied into some sort of PID control for the drive? It was set for 20.0 1/s I took it down to 17.0 1/s. This helped a bit but I now occasionally get a feedback noise error. Any ideas on what this error is? Any help would be most appreciated Colin

[dmargineau 6]

Is it a positioning application? Is this a new install? If it not a new install and the system functioned properly in the past, the culprit seems to be a feedback device(motor encoder, transducer or the feedback cabling) or mechanical slippage. Reducing a Proportional Gain Kp will reduce the "reaction" of the drive to any positioning error; even there is no active motion instruction, the drive will try maintaining the current position presuming the power is applied and the Enable condition is declared. "Loose Gearing", a malfunctioning brake or erratic feedback values would cause the drive to "compensate". The application's proportional gains are established during commissioning and they should not be altered since they are determined by the system's proper functional characteristics; you might be able to get by for a while, however, sooner or later you will have to find the root cause. Edited 5 Feb 2013 by dmargineau

[sparkotronic 0]

Thanks for the reply. The oscillation has been coming and going for a few months now, it was mostly going but is now mostly coming! The machine in question has 6 servo's on it, this particular servo is peculiar as the encoder isn't fitted to the motor but runs on a rack and pinion attached to the pusher. I may look at new cable and encoder to rule it out. I did notice that the encoder cable isn't screened, so it could be picking up some noise. Motion stuff is another language to me, I just get by on ladder! What is a feedback noise error? Is it irregular pulses from the encoder? Is there any way in control logix that I can look for this? Thanks again. I think Mr Bradley has washed his hands on me as it is Siemens drives in the application. There was a sharp intake of breath when I mentioned this :) Colin Edited 5 Feb 2013 by sparkotronic

[dmargineau 6]

I have yet to try to motion integrate a Siemens drive with a Logix controller...But who knows...Maybe soon they will be playing nicely together...Yeah right.... I do not have a Simodrive manual (and Siemens doesn't make it easier when looking for it!), however, the error is most likely generated by the drive and then passed onto the CLX controller as status; if you have the manual, research the fault codes, establish what could be the cause and follow the mitigation recommendations. Encoder cables without properly implemented (and connected!) shielding are nothing but trouble; 5vdc "noise" pulses are extremely easy to acquire within an industrial environment; luckily, your drive's processor monitoring algorithm could discern between true pulses and errant ones.