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Author Topic: ESS + Mach4 + Clearpath = Motor error input goes where?  (Read 4085 times)

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Re: ESS + Mach4 + Clearpath = Motor error input goes where?
« Reply #30 on: June 19, 2018, 03:19:58 PM »
Hi,
if you stand back a bit from your system consider this:

If you issue a step change in position to your machine it will attempt to drive to the new location. If you have set the following error window wide enough that it doesn't
fault at least! The machine will approach its new location and may overshoot and the return for another go.

In classical control engineering parlance that behavior is described by two numerical variables:
OmegaN(atural) which is a measure of the speed of the response of your axis, generally the faster the better and
Zeta the damping figure, 0 is no damping and the machine overshoots wildy, 1 is slightly overdamped and it doesn't overshoot at all, and 0.7071 damping is considered optimal.

These two figures will allow you to calculate the maximum following error for any given input. You may have seen these figures of merit when talking about a servos PID ability.
and its closely related. The dynamics of the servo will be changed by the mass and friction of the axis that the servo is bolted into. Thus if you can calculate OR measure
the dynamics of your axis you can determine the absolute error for any given input. As it turns out calculating it is not easy unless you have very good and extensive
information about your servo/axis. Measuring it is a realistic alternative but will require a sophisticated setup.

Craig
My wife left with my best friend...
     and I miss him!
Re: ESS + Mach4 + Clearpath = Motor error input goes where?
« Reply #31 on: June 19, 2018, 07:18:28 PM »
Hey Tom,

Glad to here you got it working.

Unrelated question. Assuming your fourth motor is not for a fourth axis, how did you go about tuning the slave motor? I've been considering upgrading to a dual drive for my X but was not sure how the tuning portion worked.

Thanks
Re: ESS + Mach4 + Clearpath = Motor error input goes where?
« Reply #32 on: June 19, 2018, 08:58:16 PM »
Hi,
I have a second hand Allen Bradley servo I use for a spindle motor. It has tuning software installed on my PC
to program the drives EPROM.

Amgonst the many many features of the software is a 'scope'. It allows you to follow various variables against
time for instance. Given that I use my servo as a spindle I've never really played with it. As a position
servo you can cause it to display position error (actual encoder count vs programmed position) in time.
It updates at the servo refresh rate, about 20kHz, so is hardly a 'high bandwidth oscilloscope' but none the less
provides a very useful visual indication of following error, all for the sake of a few keystrokes to program/set it up.

I don't know whether Teckincs have provided a similar facility for their Clearpath servos. Such a facility would go a long
way to answering your query about following error window verses positional accuracy. Note that such a display would
include the effects of the mass of the axis and its friction. Very useful and informative.

Years ago when I was at University studying this stuff much of the gear was analogue (resolvers, synchros, storage scopes
and some very groovy long stroke LDVT's), and while digital offer a few wrinkles of it own the principles of feedback
control remain the same. The gear was all expensive, often many many times the value of the servos and amps!

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

Offline thosj

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Re: ESS + Mach4 + Clearpath = Motor error input goes where?
« Reply #33 on: June 20, 2018, 08:11:52 AM »
Hey Tom,

Glad to here you got it working.

Unrelated question. Assuming your fourth motor is not for a fourth axis, how did you go about tuning the slave motor? I've been considering upgrading to a dual drive for my X but was not sure how the tuning portion worked.

Thanks

Sorry I can't offer up any help, my 4th axis is a 4th axis. I have a knee mill, Z is the quill and A is the knee. I simply, (well, not TOO simply), use the knee for tool length offsetting.

That said, I have seen, somewhere, something about tuning a slave axis. I can't recall where, but read it somewhere. You might try support@teknic.com, they're responsive but due to their large array of available servos they have a difficult time understanding YOUR problem!!

Tom

Offline thosj

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Re: ESS + Mach4 + Clearpath = Motor error input goes where?
« Reply #34 on: June 20, 2018, 08:46:27 AM »
I don't know whether Teckincs have provided a similar facility for their Clearpath servos.

ClearPath DOES have exactly this. Hook a USB cable to the drive, start their software, MANY, MANY selectable options for the "scope." I've discovered that this runs fine while Mach is running and controlling the servo. The problem here will be the dummy (me!) watching the software!!! I was smart enough to figure out Auto Tune, and how to set the error mode, and now, to figure out the following error setting, but the rest seems pretty complicated to me.

I got the ClearPath servos to get away from this PID tuning. The Gecko's have pots and I could never get the Z motor to not buzz all the time, over 8 years of reading posts on how to do it. I actually replaced the encoder, drive, and motor and couldn't get it. I tried CNCDrive servo drives with software PID tuning, but manual, and couldn't get the PID set AT ALL, finally returned all 4 and gave up. Bought ONE ClearPath for the Z, a PS and for future expansion, a Power4-HUB, and it worked flawlessly after Auto Tune. Thought about it for approximately 3 seconds and bought 3 more, done with buzzing servos. My system is WAY better than it's ever been, Mach acceleration higher, top speed higher, NO buzzing/screeching. I could perhaps squeeze more out of it, but I'm happy with it the way it is and I'll tell you, I'm inclined to stop chasing it and just enjoy.

OH, and the mechanics of my system did NOT change, same ball screws, same belt ratio's, everything the same since the Geckos were first installed in 2009 when I converted the machine.

Tom
Re: ESS + Mach4 + Clearpath = Motor error input goes where?
« Reply #35 on: June 20, 2018, 09:27:33 AM »
Hi,
AC servos are the next generation of servos by comparison to DC servos. The smarts provided by the manufacturer for tuning is the proof of the pudding.
Make no mistake PID tuning is in there, its just that you haven't had to concern yourself with it.

To make use of the scope what you need to do is either expand the following error window greatly or even turn it off. Go to Mach and icrease the acceleration of your X axis to something
very high, in effect infinite. Then if you issue an MDI:
G0 X100
then the X axis will attempt to move to the programmed location very quickly and will only be limited by the maximum speed the servo can accelerate. If you have the scope 'on' to
observe you will see the following error of the axis. As you decrease the acceleration of the X axis in Machs tuning page the following error will reduce. When it reduces to what you determine is
acceptable, lets say 0.05mm then you have established the maximum acceleration your X axis can achieve and you can set your following error window to just accommodate it.

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