Dynomotion Forum

Hay Tom,
Think I got a new Board Index category. What about one for tuning Servos? Would make it easier to find working examples. That's why iam posting this here instead of my CNCzone thread.

Anyhow here is what I got...
Machine....SouthBend Magnaturn Lathe(Dovetail slantbed lathe).https://www.cnczone.com/forums/dynomoti ... rofit.html
Servos.... DMM-TECH 750watt AC servos and Dyn4 drives configured to Analog Torque Mode.
Ballscrews... 25MM diameter,5mm pitch
Control Boards.... KFLOP/Kanalog/Konnect.

Current drive settings resolution and ballscrew pitch = 20320 counts per inch. (Drive resolution of 4000).
Attached are plots and screenshots of configuring windows.
Any idea what I need to change? I did get some better results when I had the drive resolution configured to 2000. But thought I could get better resolution than that.

Troy

So any ideas what i should change to get the plot smooth?

Thanks,
Troy

Hi Troy,

Torque mode servos are unlikely to work well with only P Gain. Please read this wiki article.

Hay Tom,
A couple of times I did try adding some "I" value of .001 and got runaway conditions. Also tried a value of .0001 which cause some oscillation. But, am going to start over with tuning and follow the steps in link. For some reason i always forget where that tuning info is.

In step 4 it talks about Reducing Max Following Error Limit to small value. Is this the parameter on the Config&Flash window? Or, the Max Limits Error on the Step Response window?

Thanks again,
Troy

Hi Troy,

A couple of times I did try adding some "I" value of .001 and got runaway conditions. Also tried a value of .0001 which cause some oscillation.

That article attempts to explain that a Torque Mode system like yours is inherently unstable with just P gain. If it weren't for some mechanical friction somewhere it wouldn't be stable at all. I Gain makes the system less stable so no surprise that doesn't help. The first thing to do is to add the D Gain with a helpful Low Pass filter to stabilize the system

In step 4 it talks about Reducing Max Following Error Limit to small value. Is this the parameter on the Config&Flash window? Or, the Max Limits Error on the Step Response window?

Max Following Error on the Configuration Screen triggers a Fault/Disable if the following error ever exceeds the specified value.

Max Limit Error on the Step Response Screen causes the servo to treat errors larger than the Limit as if they were only the value of the Limit.

BTW if you ever want to see a description of any parameter click "Help" and then click the Parameter.

HTH

When servo is not moving i can rotate ballscrew by hand and move table about .007" before i can feel any holding of servo. What parameter setting am i missing?

Troy

Hi Troy,

Well it more like all the parameters work together to reduce error ASAP.

But the I gain (Integrator) is what can create huge correction forces for tiny errors if they persist over time.

For example with any I gain if you push the axis off by 0.001 inches the output will continuously increase until the error is driven to zero.

HTH

Just to compare things. I tried step,dir signal. But have a issue. in closed loop step, the green output line in plot stays flat. I show encoder counts.
Any idea?
Troy

tmday7 wrote: ↑

Fri Sep 21, 2018 10:58 am

Just to compare things. I tried step,dir signal. But have a issue. in closed loop step, the green output line in plot stays flat. I show encoder counts.
Any idea?
Troy

Tom will correct me if I'm wrong, but I don't think any output is shown in step/dir mode. I think output only applies to modes that use analogue output.

In fact, just fired up the CMM, and output is shown in all the plots, however I had to ensure the correct settings had been uploaded to KMotion (aka enable the machine via KMCCN, then click Upload on the Config & Flash screen in KMotion) before trying a move. If I didn't the default KMotion settings were used, which did mean a move happened, but no output was shown.

Hi Troy,

Just to compare things. I tried step,dir signal. But have a issue. in closed loop step, the green output line in plot stays flat. I show encoder counts.
Any idea?

In "CL Step" there should be servo Output (green) for whatever the correction to the commanded position is. Were your PID gains all zero? Max Limits Zero? Please Post your settings from the Step Response, Config/Flash, and Filters Screens.