overall turns ratio and encoder line count questions

[Commotion]

Your ppr setting will be 10,000 for a 2500 line encoder however you will probably have the same problem I was having.

It’s in my build thread but the back story is: My servos are 10,000ppr and the drives were rated to 600kHz but anything above 200kHz and my servo drives were not capturing all the pulses and it was losing steps. I was trying to run them at full resultion and they would get close to 300kHz without completely failing to respond but I had to keep lowering rapid speeds to get it to stop missing steps. I then found in the servo drive u can set a “gear ratio” which scales the actual pulses per revolution of the servo, ie with a ratio of 4, which is what I am now running, giving the servo one pulse will rotate the servo 4 pulses of the encoder. This allowed me to get the servos running at their max rpm of 3000 without exceeding 200kHz but because of my turns ratio still had a resolution of 0.001mm/step.

I would suggest trying the same thing, see if you can change the ratio in the servo drive and then divide the 10,000 by the ratio you choose. In my acorn settings im running 2500 (10,000/4). I work in metric so I’m not familiar with how the turns ratio works for you whether it’s inches per revolution or revolutions per inch.

[TRM]

thanks for the report. the report shows Z axis overall turns ratio is set to 5 should be 5.08 if screw is 5mm pitch and you are using inches.

what counts per rev settings do you the drives set for? most closed loop drives have a "gear number/ratio" or "multiplier" "dividing" parameter.. what do you have these set to? and what is the native resolution set to?

most closed loop drives have several steps per rev settings
- the steps per rev that it will expect to receive from Acorn
- the steps per rev that it will use to command one rotation of the motor (gear numebr/multiplier)
- the Encoder counts per rev (resolution of the encoder attached to the motor.

here is examples of setups of Yaskawa, Delta and Estun for reference.
http://www.centroidcnc.com/dealersuppor ... ds/306.pdf
http://www.centroidcnc.com/dealersuppor ... ds/303.pdf
http://www.centroidcnc.com/dealersuppor ... ds/297.pdf

I'm working with the X axes only for the moment.
I put 10000 in the wizard and got 2.5 turns per inch 20000 give me 5 turns per inch. Well just a tad more than 5
This is the thing that gets me is I can run it back and forth as many times as I want with the wireless MPG and it is dead nuts every time.
Put G0 X1.00 and G0 X0.00 in the MDI box toggle between the two moving the axes back and forth and it starts accumulating error.

The encoder on the X axes motor.

[cnckeith]

the manual link posted says the drive and motor run on 10,000 steps per rev

set Acorn wizard steps per rev to 10,000 for X and Z

also these drives appear not to have a "gear number" or divider etc.. like Yaskawa, and Delta etc.. so 10,000 is it.

[cnckeith]

I'm working with the X axes only for the moment.
I put 10000 in the wizard and got 2.5 turns per inch 20000 give me 5 turns per inch. Well just a tad more than 5

what to you mean by "got 2.5 turns per inch" overall turns per inch is a physical constant and has nothing to do with steps per rev.

if you rotate the ballscrew ONE revolution BY HAND with POWER OFF, how far does the axis move? that is the overall turns per inch. nothing more , nothing less. make that measure first.

[cnckeith]

please read this. viewtopic.php?f=63&t=1801

[TRM]

I tell it to move 1" and I get 2.5 turns of the motor shaft if I use 10000 in the steps/rev box. 20000 gets me 5 turns per inch.
I took the coupler out and put tape on the motor shaft to see what I would get before I let it move the axes. I marked the screw and used a indicator turning the screw buy hand to find the pitch. I knew it was a touch over 5 turns.

[Commotion]

Only have x and z axis I’m assuming you are controlling a lathe. The x works off diameter so it will not be a 1:1 scale to your commanded moves.

So it sounds about right then. You command a move of 5mm it will move 2.5mm because that 2.5 is off the radius resulting in 5mm diameter

[TRM]

please read this. viewtopic.php?f=63&t=1801

I'll read it tonight when I close up shop. Even if the steps/rev was or is incorrect it should repeat. If you command 1" and get some odd number it should return to it's staring place and go back the that odd number. Just like shooting a rifle at the range, It's not hitting the bulls eye has nothing to do with accuracy. Accuracy is the rifles ability to but the bullet in the same place if aimed at the same place. Putting the bullet on the bulls eye is sighting in the rifle.

If I'm wrong please let me know

[TRM]

Only have x and z axis I’m assuming you are controlling a lathe. The x works off diameter so it will not be a 1:1 scale to your commanded moves.

So it sounds about right then. You command a move of 5mm it will move 2.5mm because that 2.5 is off the radius resulting in 5mm diameter

Ok that makes since! I completely over looked that. So it is 10000 that needs to be but in the counts per rev box.
What about it repeating?

[Commotion]

Try it again with 10,000 to see if it’s still not repeating. Even at 20,000 and 50ipm (1270mm/min) it’s still only about 85kHz by my calculations.

At 200kHz and 10,000ppr the motor will be limited to 1200rpm but 5mm/rev that’s still 6000mm/min (236ipm). You will need to pay very careful attention to signal noise once going above 200kHz.