Ultra 3000 step/direction setting

[glentner2000]

Hello all,
Can anyone tell me where I can change what the default rotational increment is for a step input???

Right now each step pulse is rotating the shaft more then I would like it to.

Thanks for any help,
-greg

 

[dr_cronik]

Hi Greg

The Ulta 3000 I have been working on have been frigged to work through a 1747-HSTP card on a slc 5/04. With this setup I have 2 words to control the position of the shaft MSW will provide coarse position control and LSW fine position control.
LSW 0 - 999
MSW 1000 ->

so to achieve a position of 1250 :
MSW = 1
LSW = 250

What kit are you working on? How do the drive and PLC communicate? Dnet, analog, etc.

 

[glentner2000]

The Ultra 3000 is sent the step and direction signals from a PC running Mach 3. The servo is for a new spindle motor for my DIY mill.

 

[kolyur]

Greg,
I assume you have the Ultraware software, and have set the operation mode to "Follower: Step/Direction" or "Follower: Step Up/Step Down". The setting you need to adjust is the Master:Follower Gear Ratio for Preset 0, which is under Mode Configuration > Follower in the left pane. For example, a ratio of 2:1 will reduce your step size by half. The other Presets allow you to switch to different gear ratios using the digital inputs.

 

[glentner2000]

Thanks John, I have adjusted the gear ratio. Is that the only setting in Ultraware to change the step increment??? Is there a "master step increment" setting or something similar to that?

 

[kolyur]

Is there a "master step increment" setting or something similar to that?

I don't quite understand what you're looking for. The gear ratio allows you to scale the output rotation to the input pulse signal.

Prior to the gear ratio scaling, each step pulse input corresponds to one encoder count. The rotation of one encoder count depends on the motor you're using. The TLY-series motors with incremental feedback, for example, have 2000 line (8000 count) encoders which equates to 0.045 degrees per count or step. Ultraware requires you to select a specific motor, so the Lines/Revolution setting cannot be adjusted. If you use an Auxiliary Encoder, however, the Lines/Revolution can be specified.

But why would you want to do this? Setting the gear ratio should allow any adjustment you need.

 

[glentner2000]

Well I got the ratio adjusted so the PC controller output matches the actual motor shaft output.
But now I'm getting some very un-smooth rotation once I get to about 450 RPM. 100 RPM, 200 RPM runs good, 300 starts getting a little rough, then 400 and over starts getting pretty bad. So bad that I can't run it longer then about 5 seconds before it gets so bad that I'll get an encoder follower error.

 

[kolyur]

Have you autotuned the drive in Ultraware?

What's the range of the step pulse frequency from your PC? Typically you need a frequency upwards of 1 MHz to assure smooth motion across the entire speed range.

 

[glentner2000]

Oddly enough, the auto-tune fails every time. I can manually tune the velocity and position though.

The max frequency is 35KHz, The counts per rev is 8000.

 

[kolyur]

The max frequency is 35KHz

Unfortunately this restriction is going to haunt you I think. The problem is that typical servo drives don't "microstep" like some stepper drives can. The input pulse frequency needs to be high enough so that the drive control loop isn't responding to single steps (causing the rough motion you have observed). You can't overcome this just by adjusting the gear ratio and it can even make the problem worse. You could try lowering the gains in Ultraware to slow the response time of the drive, but that may lead to other problems.

 

[glentner2000]

John,
That all makes sense to me and would explain my issues.
I may be able to add in some sort of separate controller card capable of >1 MHz just for spindle control.

This may be a dumb question, but should I be auto-tuning the motor with the spindle pulleys and spindle all connected? That way it can tune with the extra mass? I'm not sure why it won't auto-tune now (even with the pullies removed), but I will be looking into that.

Thanks for the help.

 

[kolyur]

should I be auto-tuning the motor with the spindle pulleys and spindle all connected?

Yes, tuning should be done with the full load connected. The Ultraware autotuner doesn't always seem to work, so sometimes you have to just experiment and change the values manually. Usually I only have to modify the Velocity Regulator Gains (P and I; D is rarely needed).

Just curious, but if this is for a mill spindle then why is a servo drive required, not just basic speed control? For thread tapping? Keep in mind that the Ultra 3000 has other control options available; for example in analog mode you can use a 0-10V signal to regulate the RPM of the motor. I'm not sure if the accuracy would be acceptable for tapping.

 

[glentner2000]

Next chance I get, I'll mess with the P and I. Do you just adjust values by trial and error till the movement is as smooth as you want? I've never done any fiddling with the gain before.

A spindle isn't required, but I got a free MPL servo motor and cables, so I just had to buy an ultra 3000 (~$200 off ebay) and now I have a much stronger (and quieter) motor with the ability to set the RPM via my M code (using the step / dir inputs).

BUT, since I'm having such a hard time getting the step / dir inputs to be smooth > 400 RPM, I am initially resorting to preset velocities in 500 RPM increments.

 

[kolyur]

Do you just adjust values by trial and error till the movement is as smooth as you want?

I'm sure there are more scientific ways, but trial & error is pretty much how I do it. Just to give you an idea of range, I looked back at a previous Ultra/MPL installation and I used P=800 and I=400. Your application may be way different but it's at least a starting point.

 

[glentner2000]

I've finally had some time to fiddle around more with my motor a little more.
I think I have a slightly better understanding of what's going on and I'm back to the original question I proposed:

How does the Ultra 3000 know how far one step pulse is when it step/direction follower mode?

I tried adjusting the aux. encoder counts but that doesn't change anything. The aux. encoder settings must only be used if you put the ultra in aux. encoder follower mode (makes sense). So when i put it in step/dir follower mode, is it moving one step per built-in encoder count? The encoder is 260k counts per rev, so i feel like that's pretty high.

As far as I can tell, the only settings that effect the RPM are the counts out of Mach 3 and the gearing in U-W. When I max out the pulses that Mach 3 can achieve on my system (something like 35khz), I have to gear it up 1:540 in U-W to achieve the desired RPM. This is causing my vibrations due to the course stepping of the motor.

I feel like if there was a way to tell U-W that one step pulse = 1.8deg (for example) that I could then lower my electronic gearing WAY down and achieve a smoother rotation.

As an alternative test, I set the motor mode to preset velocity mode, added a few switches, and can run the motor at 8 different preset RPMS using the digital inputs of the switches. Everything runs smooth like that so my motor tuning seems fine.

I think at this point i need to ditch the step/dir input.
It would take some programming, but I could run my spindle pulse output (from the mach 3 PC) into my A-B PLC, let it count the pulses to determine what my desired RPM is, then convert that to an analog output and feed that into the the Ultra. That should allow finite control of the RPM but not with a pulsed input into the ultra.

I wouldn't be able to rigid tap, but i probably wouldn't have done that anyway.