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-   -   Kinetix 5500 and the MSF/MSO Instruction Behaviour (http://www.plctalk.net/qanda/showthread.php?t=113724)

robw53 January 12th, 2018 05:09 AM

Kinetix 5500 and the MSF/MSO Instruction Behaviour
 
Hi,

Just after some help with the following issue we are having.

On the Kinetix 5500, if the servo is in motion and the MSF is executed, what does this cause?

We have an issue onsite with a Kinetix 5500 and VPL motor configuration. When the drive goes into fault the code appears to execute this instruction and the load it is moving free wheels for maybe 300mm. When we execute the MSO instruction the drive does an absolute move (MAM) to 0, but now has a physical offset of 300mm but displays 0mm on the faceplate of the drive.

My understanding of this is that the MSF opens the feedback loop and allows the load to be moved by hand, but doesn't track the positioning. And then when the MSO instruction is executed then this closes the loop. If the new position when the MSO is executed is different from when the MSF was executed does this error get corrected when a MAM is executed or would the offset remain?

Looking at what is happening on site, I believe that this is correct and that the offset would remain and not be corrected causing a discrepancy between the physical and software position.

The SI who did the upgrade is looking into this, but I thought I would reach out and try get some further information for them.

Regards

Rob

daba January 12th, 2018 06:54 AM

From the MSF instruction "help"

"Important: If you execute an MSF instruction while the axis is moving, the axis coasts to an uncontrolled stop."

Perhaps it would be better to use MAS, and leave the servos holding the position of the drive.

kekrahulik January 12th, 2018 08:10 AM

MSF turns the servo off - you're freewheeling.

MSO turns the servo on - back in control. To answer your question about "offset" really depends on the programming. Assuming the servo doesn't rehome or redefine position, the servo should still know it's actual position.

Will a MAM correct things? If the MAM is absolute, probably. If the MAM is relative - no. very programming dependent.

Gomez_ January 12th, 2018 12:29 PM

Quote:

Originally Posted by kekrahulik (Post 764839)
MSF turns the servo off - you're freewheeling.

MSO turns the servo on - back in control. To answer your question about "offset" really depends on the programming. Assuming the servo doesn't rehome or redefine position, the servo should still know it's actual position.

Will a MAM correct things? If the MAM is absolute, probably. If the MAM is relative - no. very programming dependent.

Well said.

I will also add, @rob that the axis itself will have some settings for what action to take during a fault/stop/overload, so double check those as well.

https://i.imgur.com/XFq8Mwo.png

robw53 January 12th, 2018 04:47 PM

Hi,

Thanks for you responses.

Your suggestion to use an MAS is valid, and this is something I will bring up with them.

The system doesn't rehome afterwards, it executes the MSO and does an absolute move to 0.

What our engineers have witnessed is that when the fault occurs, the servo position value to the faceplate stops changing and holds the last value before the fault. so the coast/ramp down from that point isn't changing the value and this gives an offset against mechanical position vs electrical position.

This has been confirmed with the measurements been taken at the time the fault occurs and is consist with the amount the mechanical part is out when the servo has done an absolute move MAM to 0.

This is definitely not a mechanical issue as in slip, as the mechanical part would have to advance the electrical part of the system and that's impossible on this application.


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