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Old February 7th, 2019, 06:01 PM   #1
phuz
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Help with Logix 5000 motion camming / jerkiness

Setup: Kinetix 5700 servo w/ MPM motor, CompactLogix L33ERM
Was Yaskawa now AB.

I'm working with a mill that has a longitudinal axis with an MPM motor. This axis tracks an incoming material via a 2500ppr encoder and mills slots into the material as it traverses through the mill. The machine that feeds the incoming material is belt-driven and pneumatically squeezed so that it can't slip. The material is also clamped in the mill during the "milling" part of the sequence. After the milling, a simple MAM instruction moves the axis back to waiting position for the next trigger.

The problem: I am getting jerkiness during testing without even having the piece clamped in the mill. I am simply letting it pass through while rolling over the encoder. I am also wondering how I can activate a camming profile successfully while the piece is essentially clamped in both machines. I feel like there will be a lot of stress from the feeder machine trying to push the material while it is clamped in the mill.
Current camming profile attached, too.

Thanks in advance.
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Old February 7th, 2019, 11:46 PM   #2
Peter Nachtwey
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The motion profile does not look like it is using cubic splines. The ramp is linear. It is not using s-curves.


Notice that I used the same locations you did but I have s-curves in my ramps.
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Old February 8th, 2019, 02:55 PM   #3
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Is it "jerky" during the linear phase or just around the speed transitions?

Are you able to trend your encoder to see what it looks like?
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Old February 8th, 2019, 02:58 PM   #4
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The accel & decel are smooth, but the linear phase is jerky. I can only assume this has to do with the encoder positioning. Any way to help alleviate this without swapping encoders? I will try to get a trend. I just got to the site to do some more testing.
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Old February 8th, 2019, 02:59 PM   #5
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For testing you can create an imaginary axis that runs at steady speed and try camming to it instead of the encoder. If it is still jerky, then your servo is the issue - not the camming to the encoder. If it is smooth, then the encoder is suspect.
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Old February 8th, 2019, 03:00 PM   #6
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Great point. I'll certainly give this a shot.
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Old February 8th, 2019, 03:09 PM   #7
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I am doing a somewhat similar thing with a very similar cam to what you show.

I am using an "AB 842HR sine cosine serial encoder - size 25 High Resolution Auxiliary Servo Feedback". It feeds into a Kinetix 7000 auxiliary port.

Mine seems to be steady, but my process is probably more forgiving than yours, so I don't know that I would notice a little jerkiness.

How are you getting the encoder - via aux port or from an ethernet encoder?
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Old February 8th, 2019, 03:18 PM   #8
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This is from a wired encoder to the Aux port of the Servo drive. When I trend position vs. time, it "appears" to be linear, but I have only trended it in FTView, which has a limit of 50ms polling. I have recommended to the customer to invest in a high-resolution ethernet encoder. We'll see.
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Old February 8th, 2019, 03:22 PM   #9
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I forget why right now, but I think you will struggle to cam a servo to an ethernet encoder. I know I tried and couldn't do it but I don't remember the details. I think the RSL software just wouldn't let me cam to it??? (sucks to get old and forget stuff). Aux port is the way to go. Not sure if the sine/cosine encoder would help (suspect it might).
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Old February 8th, 2019, 03:51 PM   #10
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So far running the cam with a master axis of a virtual position is performing very smooth. Doesn't look good for the encoder. So how did it perform better when the Yaskawa system was in place? Was it less picky about noise?
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Old February 8th, 2019, 04:20 PM   #11
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Here's a capture of the Encoder.ActualVelocity
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Old February 8th, 2019, 04:49 PM   #12
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FWIW, this is the encoder that's installed.
https://www.automationdirect.com/adc...rd-n2500-rzvwd
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Old February 8th, 2019, 05:13 PM   #13
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Here's a Logix 5000 sample of position vs. time.
It looks really smooth, despite the actualvelocity bouncing around as much as it does.
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Old February 8th, 2019, 10:08 PM   #14
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Quote:
Originally Posted by phuz View Post
Here's a capture of the Encoder.ActualVelocity
Look at the way the velocity changes in discrete levels.
It look like the encoder is changing by 2 counts most of the time with sometimes changing by 1 count and other times changing by 3 times. This is not enough resolution to gear to.

Also, the cam profile issue seems to be ignored. The cam profile shown looks like the acceleration rate is constant during the ramp. It is impossible to change the acceleration instantly as show in the cam profile.

Ditto the comments about gearing to an Ethernet encoder.
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Old February 8th, 2019, 11:35 PM   #15
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I have had similar plots with an AB servo and ethernet encoder. After a few days I finally figured out that the feed forwards in the axis setup were at 100%. I didn't put them there, it happens when tuning the loop. Once I lowered them down, it settled down. A word of caution, the axis tuning section has a slider for adjusting the loop bandwidth. When you move that slider, it puts the feed forwards back to 100%.

Also, I know in the setup of the ethernet encoder, you can filter out some noise which cleans up the master signal, but if you apply too much the resolution is not real good.

Last edited by Kev77; February 8th, 2019 at 11:45 PM.
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