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Old September 15th, 2006, 06:41 AM   #1
United States

kenschunk is offline
Join Date: May 2006
Location: Saratoga Springs, NY
Posts: 53
Question AB MO2AE & Yaskawa SGM drive

I'm wondering if anyone here has used these two devices together? I've got a system that is in startup testing that is exhibiting some rather odd behaviour. The MO2AE card (1756, in a ControlLogix chassis with a L61 CPU) is connected to two Yaskawa SGM drives. The connection is set for velocity mode, and the servo cards are configured for that. There are encoders (8192 PPR) connected to the drives, and the drives send the position signal to the servo card.

Everything worked pretty much as I expected for the first axis on the card. When I powered up the second axis, however, things went south. The system acts like there is a cross connection between the two servo drives on the velocity signal. If I home one of the drives both drives will move towards the home position. The drive that shouldn't have moved will travel the same distance as the homing drive, and then will slowly (over 30 seconds or so) return to the correct position (with position faults which I disabled while looking for this). If I execute a MAM command on one axis the second axis will follow. It doesn't matter which axis is commanded - the other tries to follow.

Direction seems to matter - both move together towards positive positions (which, with the motor connections, is produced by a negative voltage output). Negative positions, however, are a different matter. If one drive is a -3.0, the second drive can be moved to -3.0 quickly. Moving it to -4.0, however, causes it to get to -3.0 or so quickly, and then slowly drift up towards -4.0 (over 10's of seconds). What is odd there is that the MAM instruction reports that it's in position when in fact it is not. Moving a drive that is at -4.0 to -3.0, with the other at -3.0, results in both drives moving positive 1.0, and then the uncommanded drive slowly returning to the proper position.

The axis aren't linked in software in any way (other than being in the same motion group), and I've checked the wiring a few times. Hooking up to one of the drives with Yaskawa's software shows me that the drive that isn't being commanded sees the velocity voltage signal change when the commanded drive moves.

I've swapped MO2AE's (on the remote chance it was bad), checked the wiring twice, tied the SG on both drives together (which, from the prints, appears that it connects to the OUT- on the MO2AE), disconnected the SG's from each other, and tried one drive at a time. With only one drive powered up it works fine - as soon as I power up the second drive the problems start. I've even tried lifting the OUT+ wire from the servo card - that makes no difference. I'm suspecting some type of isolation problem, since if I lift both the OUT+ and OUT- wires the other drive works fine, and doesn't change if I command the drive with the disconnected wires (which, to me, eliminates the chance that the card or software is causing this).

So, my question after this long winded explanation, is anyone have any idea's here? I doubt it's software, since all that is in the current test program are two MAH and two MAM instructions, and I ensured they all used different variables.
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Old September 23rd, 2006, 08:25 PM   #2
United States

kenschunk is offline
Join Date: May 2006
Location: Saratoga Springs, NY
Posts: 53
Just in case anyone else is looking to use this hardware I'll answer my own question.

They work just fine together. I checked the wiring twice, but to the electricians list of signals on the multiconductor cable. He wired it like he wrote it - too bad what he wrote didn't match reality. Once I wired the OUT+ to the signal input, and the OUT- to the signal ground (vs. the other way around) it worked fine.

Oh, and it's a SGDF drive - the SGM is the motor.
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