Gearing a Kinetix 5500 to an non-CIP IP encoder

[capsuleguy]

We are pretty new at servo motion and control. We have used a Kinetix 300 controlled by an absolute encoder wired directly to the drive, but have now moved to a 5500. We have a seemingly simple task. We have a encoder mounted to a shaft on an existing machine. We need the servo motor to be electronically geared to the movement of the shaft. If the shaft starts to rotate, we need the servo motor to rotate at the same speed/position. I know the simple solution is to use an ethernet CIP encoder and set it up as an axis. Then use logix to gear the two axis together. But our Compactlogix PLC only allows two motion axis, and we want to keep one availble for a follow on project. So we want to use an ethernet absolute encoder like a AB 842E-SIP10BA
Is it possible to do this? I am being told that it won't work and you can only gear a 5500 to a CIP encoder.

Thanks!

 

[Ken Roach]

Welcome to the PLCTalk forum community !

Unfortunately I think you've correctly identified the limitations of the Kinetix 5500 (built for CIP motion so it doesn't have a secondary encoder input) and the smallest CompactLogix controller you're using for that project.

You can't run CIP features like Gearing with an encoder that doesn't support CIP motion. There's no "do your best estimate of velocity by using the available position update period from a counter or other input" function.


In theory you could use a non-CIP-Motion encoder and calculate velocity and then feed that to a Virtual axis that you can gear from, but that would be a coarse and inaccurate method, and would exceed your Axis capacity of the controller.

That is to say nothing of the stout pummeling from whoever had to work on the machine next and figure out your method. I had a mentor who would say "a crocodile will never fly, no matter how low or how slow".

So you're right that is *is* a simple task, and your controller can do it. But it can't both do that simple task and have resources available for future expansion.

As painful as it is to switch to a bigger controller (because you probably have POINT I/O on that L18 CPU), I think you have to do it if you want to expand the control system in the future.

 

[kekrahulik]

Ken,

Are you saying that there exists an encoder that supports CIP motion that could be used for gearing a 5500 to?

I seem to recall that I set up an AB Ethernet encoder as an axis - but still couldn't gear to it. That was right when 5500's came out, so the memories are fogging.

 

[Ken Roach]

The A-B 842E-CM encoders act like a feedback-only axis. You can gear or motion-cam or output-cam to their actual position.

I haven't used an 842E-CM with a Kinetix 5500, so I can't say definitively that they work together. They should, and I've never heard of a bug or incompatibility that would prevent them from doing so.

While checking the Knowledgebase, I've found that I gave bad advice initially, because of how the CIP Motion Axis support limits work.

Our new member /capsuleguy mentioned a controller with only two CIP Axis, so that implies the 1769-L18ERM controller.

I found RA Knowledgebase Article 565025, which says that the limit of two CIP axes only applies to position axes, like a Kinetix 5500 or 350 drive. But the 842E-CM is a Feedback-only axis and doesn't use up that Position axis resource.

The 1769-L1 family Product Profile backs this up, showing that it's limited to 2 CIP Position axes but supports 8 Feedback axes.

So I'll reverse my original advice and say "you can use an 842E-CM encoder as a Feedback axis in this gearing application and preserve your other Position axis for future use".

 

[jstolaruk]

We are pretty new at servo motion and control. We have used a Kinetix 300 controlled by an absolute encoder wired directly to the drive, but have now moved to a 5500. We have a seemingly simple task. We have a encoder mounted to a shaft on an existing machine. We need the servo motor to be electronically geared to the movement of the shaft. If the shaft starts to rotate, we need the servo motor to rotate at the same speed/position. I know the simple solution is to use an ethernet CIP encoder and set it up as an axis. Then use logix to gear the two axis together. But our Compactlogix PLC only allows two motion axis, and we want to keep one availble for a follow on project. So we want to use an ethernet absolute encoder like a AB 842E-SIP10BA
Is it possible to do this? I am being told that it won't work and you can only gear a 5500 to a CIP encoder.

Thanks!

I just mistakenly purchased the CIP version instead of the non-CIP version you've mentioned, but the good thing for you (if you haven't already purchased it) is that the CIP version is only $50 list more then the non-CIP version.

 

[kekrahulik]

At the time, I recall my AB guy agreeing with me that I couldn't MAG a 5500 to an encoder. However, goofing around right now, the software seems to let me. Maybe the CIP encoders weren't out the last time I tried.

Thanks - good stuff to know!

 

[capsuleguy]

Great information. Thanks! I would be great news if I would not use a motion axis with the CIP encoder. I actually have the AB 5069-L306ERM unit. In the product profile it just says 2 motion axis and nothing about feedback axis, so I am not sure. We did get some sample code from our AB rep that may work. But I have not opened it yet since it is in a "new version" than I have on my laptop at the moment. I will ask him about the feedback axis. Thanks again!

 

[Ken Roach]

Oh, shoot, I can't verify if the 5069 platform accounts for non-Position loop axes the same way as the 1769-L1x platform did.

Let us know what you find out from Rockwell !

 

[Jobbe9000]

Oh, shoot, I can't verify if the 5069 platform accounts for non-Position loop axes the same way as the 1769-L1x platform did.

Let us know what you find out from Rockwell !

I think Ken is right about 2 "position closed looå axis" and up to "256 non position closed feedback loop axes".

See picture attached.

Rockwell do have an AOI called FlexGear, which does what Ken states in his previous post

In theory you could use a non-CIP-Motion encoder and calculate velocity and then feed that to a Virtual axis that you can gear from, but that would be a coarse and inaccurate method

I agree with Ken, that the best solution would be the CIP-encoder, but this AOI actually do work decently.

 

[capsuleguy]

I got confirmation today from RA that the CIP encoder does not take a motion axis. You guys were spot on! Our local supplier specialist did not know this, hence the mess we got into with the non-CIP encoder. But they are making it good and taking back the encoder even though we did power it up and configure it. Now I have to wait about two more weeks to get the correct one. Grrr.