Inertia Matching Steppers - Tollerance for "Matched"?
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Morning all,
If you are going to the point of using closed loop drivers then I guess the inertia matching needs to be addressed first.
Ideally the motor's inertia should match the reflected inertia of the load, along with matching the required performance characteristics.
Questions:
- What sort of tollerance is there for matched for motor to load inertia, are we talking broad like 0.5-2:1, within a 1/10th, or just close as you can from supplier x?
- How does friction effect innertia matching? Guess a high drag taught belt drive on a bed will reduce sensitivity?
- Anyone gone through the inertia matching exercise and seen a significant posative benefit with either open or closed loop stepper drive?
This is just getting the lay of the land at the moment. I appreciate closed loop drive is expensive. I was considering it for a large router like the work bees for cutting foam profiles.
Cheers,
Wes.
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https://www.automate.org/industry-insights/understanding-the-mysteries-of-inertia-mismatch
My understanding of the above:
In essense inertia matching is in an attempt to avoid a situation where a standard motor control loop would cause the motor, or the load entering into a state of significant resonance.
The motor:load (/reflected load inertia) ratios are rules of thumb. If anything mismatches are more likely to show their head in a closed loop system. We already aware that with some systems specific rates of motion can cause resonances and so we work to identify these troublesome rates and avoid them.
As suspected the springyness of belts and and damping introduced due to frictions or drag in bearings from lubrication will have an effect on these resonances.
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@DocTrucker that sounds like what Input Shaping helps to reduce.
For the closed loop Duet 3 expansion 1HCL board, there is a tuning plug in to get that correct too. See https://docs.duet3d.com/en/User_manual/Tuning/Duet_3_1HCL_tuning
If you’re talking about a different feature you’d like considered for RRF, probably best to tag @dc42 into the conversation, to get his view.
Nice to see you’re still around. I think I remember you visiting us at RepRapPro, about 10 years ago!
Ian
TronXY X5S with Duet 3 MB6HC and Roto toolboard : Cartesian bed-slinger with Duet 3 Mini 5+ WiFi and 1LC : RRP Fisher Delta v1 with Duet 2 Maestro : Polargraph with Duet 2 WiFi
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@droftarts Thanks, I had a glimpse at that and thought that looked very interesting. But having worked closely with folk responsible for servo drives from PLC systems I thought I'd try to do my homework with regards to setting up the sizing of the steppers for more than "has enough torque" before I looked at it - perhaps while I got used to one of the mini duet 3s.
Recolection is hazy but I think I chatted over email a fair bit with you while setting up my RepRapPro Ormerod 2 from RS Components around 2014. Didn't come to visit RepRapPro, but did attend a presentation at either Solid Freeform Fabrication Symposium in Texas, or a presentation at an inugural conterence that was run by loughborough by Adrian, but to be fair it was a few more years before I really understood open source. That would have been sometime between 2003 & 2006. A happy accident may have me returning to my roots tinkering with the software running metal laser pricessing machines after a ~10 year break!
