Servo motors buzzing when mill is stopped

you need to "tune" your servo amps to match the system (aka "plant") - if you drag yourself through a discussion of the nyquest stability criteria, the reason for doing so will be clear

It is not loud, but it is bad for the servo, the ballscrew, encoder, pretty much everything.

Your method of turning the gain pot clockwise until buzzing starts, and then backing out 3 turns, works very well.

i

Their tech support is awesome.

I saw some resources on current loop tuning, but I have a velocity loop.

I will call them today to see what they got.

My attempts to tune the positioning loop ended up with a general failure.

i

I think that it actually would, but what can I do.

Right

I have two ways of exciting the system. One is just to apply some force to the servo motor pulleys, and another is to make the axis go back and forth a bit using keyboard. The last one usually makes it vibrate.

Servo motor is belted down 2:1

sounds complicated. I am not sure where to start. I removing hum and vibrations by turning gain down on the amps. Attempts to change gain (P, I, D) in EMC configs did not bring on any sensible results. Changing P does affect vibrations, but changing I does not, and it should.

I spent about 1.5 hours yesterday on this and the result was not satisfactory. In the end, I turned down gain on servo drives, and restored original defaults for Pi, I, D.

i i

Ive been working with AMC amps for 14 yrs....

Gunner

One could not be a successful Leftwinger without realizing that, in contrast to the popular conception supported by newspapers and mothers of Leftwingers, a goodly number of Leftwingers are not only narrow-minded and dull, but also just stupid. Gunner Asch

Are you sure there isn't some facilities in the software to read back what the software is seeing? Ideally it should be able to throw up a graph of the command and the response vs. time. Then you can jog the thing from the keyboard and look at how well it follows. If you can do this it can make your job a _lot_ easier.

If that's the only gearing (and if the servo motors aren't internally geared) then the lead screw moment of inertia matters, and you need to do the tuning with the lead screw in place. Since you probably have ball screws, you probably need to do it with the whole assembly in place, oh joy.

("Oh joy" because that means you have to worry about crashing an axis while tuning, which complicates things. Oh joy.)

One of the nice things about PID tuning schemes that separate the P, I and D gains is that these gains act more or less independently. So it's not surprising that turning down the integrator gain would not affect anything, where turning down the proportional gain would.

Where to start:

At the innermost loop. That's the motor drive, and where you're working already.

You don't have a scope and a signal generator?

You have to set up a particular signal to trigger the scope. I use velocity (ppmc.0.encoder.00.delta) as the trigger, it works well.

You have to pump up the gain to something like 1m (.001 or 1 milli) on signals such as the following error to see useful information.

I think there is a halscope section in one of the manuals on the wiki. You need to start using these manuals as the first place to look. When it is not there, then you can ask for answers elsewhere. But, mostly, it works like a digital scope.

Jon

Yes, it is called HalScope, and is basically a digital storage scope in software, that has available any signal routed through HAL, EMC2's Hardware Abstraction Layer.

There are also signal generators and all manner of hal "components" that perform logical and arithmetic functions.

Jon

This is something I've used for PID loops at times. I don't know where I grabbed it but I've used it for various PID loops. I've had this note in my PDA for years.

### PID Tuning

A basic idea of what the three parameters do for you is a first step:-

1) with the integral and differential set to zero, wind up the proportional gain. Keep increasing until you begin to see instability occurring. Note the gain, somewhere just over half of this gain will do for starters.

2) Wind up the diff. This will has a damping effect on the response of your system. Don't go mad on the diff. just yet, get the response a little damped.

3) With the integral (be gentle with Int.) apply just a little. Note the steady state error will decrease, you should increase the Int. until you find either (i)the system can't take any more and starts to oscillate, back off! or (ii) You achieve the required response time for steady state.

4) Go back a "tweak" Kp and Kd.

Remember, PID is an experimenters paradise.

Morgan

###

HTH,

Wes