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Jerky motion
« on: April 21, 2019, 07:43:44 PM »
Setting up a manual knee mill with Allen Bradley servos, all are connected and functioning.
When I setup each axis using the DSPMC/ip axis setup/tuning screen, I get smooth motion, but when I try to jog or do a G00 x6 y6 move from with in Mach, my motion is jerky.

Motors will run at speed, pause, then run at speed, pause, run at speed….

This happens with either the X or Y axis (only 2 axis configured)

Motors MPL-A320P
Servo Amp Ultra 3000
Motion controller DSPMC/ip

Any ideas out there?
Thanks

Offline reuelt

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Re: Jerky motion
« Reply #1 on: April 21, 2019, 10:41:19 PM »
The polling frequency should  be set at 100Hz or higher.
"the gift of God is eternal life through Jesus Christ our Lord"
Re: Jerky motion
« Reply #2 on: April 22, 2019, 12:09:33 AM »
Hi,

Quote
The polling frequency should  be set at 100Hz or higher

Firstly the 'Polling Frequency' is a new one to me. I know the Ethernet SmoothSteper has a 'Refresh Rate' set at
40Hz (default). That is the rate at which the controller and Mach swap data packets.

Each outgoing Mach data packet will contain as many as 50 PVT (Position Velocity Time) data lines. Each time slice is
1 millisecond wide. These time slices get stacked up in the controller buffer. Any given time slice will contain position
data for ALL axes of the machine and ALL axes will move simultaneously. There should be none of this 'one axis moves
a bit and then the next axis moves a bit'

Quite frankly I think the Refresh Rate (I'm assuming its synonymous Polling Frequency) is a red herring. It has no bearing
on the granularity of the PVT time slices.

The Ethernet SmoothStepper has a buffer of 180 ms (default) of motion. I've never seen it drop below 150ms. If the buffer
runs out Mach crashes. May I suggest you find the comparable spec data for your controller and monitor the buffer. The ESS
plugin has a live diagnostic to monitor the buffer and would guess your controller has a similar feature.

Craig

My wife left with my best friend...
     and I miss him!

Offline reuelt

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Re: Jerky motion
« Reply #3 on: April 22, 2019, 02:38:35 AM »
'Polling Frequency' just exist in DSPMC plug-in config.
See attached:-

From DSPMC plug-in manual:-
"Polling Frequency – This parameter sets the update and data exchange frequency of the DSPMC plugin. A higher value will speed up the plugin processes and exchange data faster with the DSPMC, but it will also significantly increase network traffic and add more strain on the CPU.
Valid values are 2 – 250Hz. Although Mach3 used a Frequency of 10Hz with every plugin to exchange data with devices, the recommended value for Mach4 is 100Hz."
"the gift of God is eternal life through Jesus Christ our Lord"
Re: Jerky motion
« Reply #4 on: April 22, 2019, 03:20:03 AM »
Hi,
well that is exactly the same interpretation that the ESS attaches to 'refresh Rate' as I had supposed.

That does not explain OPs problem. Lets say the Polling frequency is as the manual suggest ie 100 Hz. Then every 10ms
Mach will dispatch something like 10 one millisecond time slices of movement data.  Any one slice of data contains the
movement information for ALL axes.

It sounds to me as if the controller is just plain running out of data. My recommendation stands, use the diagnostic to
observe and understand the buffer.

Craig
My wife left with my best friend...
     and I miss him!

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Re: Jerky motion
« Reply #5 on: April 22, 2019, 04:06:59 AM »
The problem is that the default was left at 10 (because of Mach3) and 10 causes trouble with Mach4.
In this forum, someone changed from 10 to 100 and his problem got fixed.

We learn from the experiences of others.

"No one need to try eating every mushroom to know that some are poisonous." Just read..
"the gift of God is eternal life through Jesus Christ our Lord"
Re: Jerky motion
« Reply #6 on: April 22, 2019, 01:17:18 PM »
Thank you joeaverage

As soon as I read your reply I remembered I had to do the same for my other machine

Adjusting the poll rate fixed the problem.

Thank you again