﻿There are three ways to tune the LS Electric Servo Systems.
Off-line tuning issues three-position commands to the motor and from that it can estimate the
inertia of the load and calculate all the needed feedback loop gains and related parameters.
This is the one you will use most often because it’s super quick and easy
and it does a great job with minimal hassle. It’s called off-line tuning because it
doesn’t require an external controller to generate position commands – that is,
it tunes off-line from the external controller that may or may not be connected to the servo.
On-line tuning is the exact same thing, but it can use the external controller to generate the
position commands. It can also use the drive's internal indexer to generate move commands.
This allows you to tune to the actual motion profile your system will be using.
Manual tuning allows you to manually adjust the tuning gains yourself.
No one in their right mind would ever do a manual tune from scratch of course,
there are just too many things to keep in mind. But it does allow you to tweak the auto-
tune results or just take a peek behind the curtain for educational purposes.
In this video, we’ll cover the off-line auto-tune and we’ll take a quick look
at how to access the manual tuning stuff. We’re not going to do a manual tune – that
would require a whole series of videos all by itself and frankly, manual tuning just isn’t
necessary because auto-tune does a great job and is quick and easy to do. Here we go.
Let’s go to Setup, and Return to Factory Setting just so you know exactly where I am starting from.
Yes, we really want to reset the drive. Give it a few seconds … and it’s done. Hit this guy
to reset the drive's controller – you could also power cycle the drive. Yes, we want to do that.
Ok, we have a clean drive. Now we just click on this tuning
fork button to go to the tuning dialog. In off-line tuning, you have three controls - rigidity,
direction and distance. Rigidity determines how aggressive you want
to make the tuning gains. It’s a 1 to 20 scale and I usually like to start with a mid-range rigidity,
so we’ll set that to a 10. Direction determines which way
you want the motor to start spinning. Remember, the positive direction is determined by how you
set things up – we did that in the quick start videos, so watch those if you need a refresher.
Distance determines how large the position command is. This slider goes from 1 to 10. The max move is
400,000 user units. You will usually want to start with a small move and then gradually increase it.
So, let’s set that to a 2 for starters. Now we just make sure our machine is clear
so nothing gets hurt when it starts to move and hit this tuning button. But,
before I do that I have the scope set up to monitor the actual position of the motor,
with auto-scale off and the vertical scale set to 400,000 user units which I know is the max move. The X-Axis
tab is set to continuous trigger and 20ms is fine. I’ll go back to the Y-Axis tab and hit start.
Hit the tuning button. Stop the scope. We see the drive issued three position commands
and from that, it estimated the inertia ratio and calculated the loop gains and related parameters.
These are just the main ones – there are a lot more you don’t see here.
That’s it! Were done! If you want a larger move command,
just move this slider. How about a mid-level move of oh maybe 5? Start the scope, hit tuning.
Stop the scope. We saw the motor move a lot farther and the move commands on
the scope are also larger. The inertia and gains didn’t really change much.
So just for fun, let’s push the distance out to 10. Start the scope, hit tune,
and stop the scope. Yep, the motor moved a lot farther, and the position command looks
a lot larger. But, the inertia is still the same and the loop gains didn’t really change much.
All of which means the drive has a pretty good idea of the load it has to handle.
Since the distance doesn’t really seem to have any impact let’s reduce the distance to 5
and increase the rigidity to the max. In a more rigid system we expect to see more aggressive
gains - right? Let’s see what happens. Start the scope, hit tuning,
and stop the scope. And sure enough,
the gains are much larger when we compare them to the gains we got with a rigidity set to 5.
And that’s all there is to it. Think about it – we just tuned this system multiple times
in the span of about 30 seconds. It doesn’t get much easier than that!
And all of these parameters are already in the drive.
If you ever want to see what’s in the drive, just hit the read button.
Keep an eye on this inertia mismatch. I put an oversized load on the motor and you can see it
maxed out the allowable 3000% or 30:1 mismatch this system can handle. And the
position waveform got wonky. Another clue things aren’t optimal. The closer the mismatch is to a
perfect 100% or a 1-to-1 mismatch, the better. But realistically, a goal of 10 to 1 or 1000% mismatch
will give you a very responsive system that’ll get you accurate and reliable positioning.
One side note – our scale went from zero to 400,000 because the position register was
set to zero when we reset the drive. If you are doing tuning on a system that has been running,
this max number will be 400,000 away from whatever position you start at.
If you want to force the starting position to be near zero, just go to homing, select Mode 35
and hit home. That doesn’t move anything, it just resets the position register to zero.
What if you want to manually tweak things? Easy!
Just click this guy and you see all of the tuning-related parameters
at a glance. Over here you are just seeing the main parameters and can’t manually change them.
Here you see and can tweak everything! And of course, you can also view all of
those parameters in a flow chart format so you can visualize how they impact each other.
You can also do on-line tuning with this full parameter set – we’ll talk about that in the next
video. Just know that this is a little confusing. The gray block here means this is off, and on
means click this to turn it on. The green bar says it is on and click here to turn it off.
Why would you want to do on-line tuning? Because you can tune to the actual position commands your
system will be using and not just these three internal commands created by the drive.
And you will be able to see the difference between the commanded and actual positions
on the scope which makes it easy to visualize how the gains are impacting your system's performance.
Again, this off-line tuning is really all you’ll need for most applications.
But if you want to try on-line tuning, join me in the next video where we’ll walk through it.
It’s identical to what we just did, except you now have control over the speed
and will be able to see the difference between the actual and commanded waveforms on the scope.
Meanwhile, click here to learn more about the LS Electric Servo Systems. Click here to learn
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