Commanded Speeds Vs Actual Spindle Speed

[RJS100]

I recently upgraded the spindle motor on my benchtop mill to a JMC 2.6KW AC servo motor. The servo motor is rated at 2500 rpm with a max rpm of 3000. JMC recommends running it at no more than 2800 for extended periods.

The spindle is belt driven with a 1:8 to 1 ratio. For a max spindle speed of 5000 rpm, the servo would then need to turn 2778 rpms. The servo has an analog instruction gain of 10 rpm/V. Since I want the servo to turn 2778 rpms when Acorn pulls out +10V, I programmed the parameter to 278.

For the Acorn Wizard spindle settings, I set the minimum high speed rpm to 0, and the maximum high speed rpm to 5275 rpm (Since I don't know the actual max rpm).

I then issued the following commands and recorded the actual rpm:

Command Speed ----Actual Speed
m3 S640 ---> 640 rpm
m3 s1000 --> 985 rpm
m3 s2000 --> 1985 rpm
m3 s4000 --> 3845 rpm
m3 s5000 --> 4800 rpm
m3 s5500 --> 5050 rpm

As you can see, while the m3 s640 resulted in an actual rpm of exactly 640 rpms, the actual rpms are incorrect as the rpms increase. So I went back to the Wizard and changed the max high speed rpm to 5050 rpm as observed above. Now all the commanded speeds at 1000 rpm and above are almost spot on, but when I command a speed of S640, the actual rpm is 670.

I tried adjusting the min and max speeds in the Wizard, but no luck. Any idea as to how to fix this?

Thanks... Richard

[suntravel]

Hi Richard,

The fast fix is do not care about it, since it has no significant influence on the parts you are milling.

With M3 S0 is the spindle not turning?

If yes run AF_oF1 on the servo driver.

You also could play with P06-41 P06-42

I also have not the full rpm range spot on with Acorn, same Servo with Acorn6 is max 5 rpm deviation

Most elaborate way is to edit the PLC to correct specific rpm ranges.

Uwe

[RJS100]

Thanks for your quick response!

I agree that the difference of two hundred RPM will have no effect on the parts I am milling. My goals is to have the lower commanded rpm as accurate as possible as I am getting ready to start rigid tapping. I think for now I will leave everything as is and try to do some rigid tapping

Just for my understanding, the JMC manual describes parameter P06-42 as a "Velocity analog instruction offset". This command appears to offset the rpms across the operating range.

P06-41 says "Speed analog command filter constant". It says it sets the time factor of analog instruction filtering for CN1 input. What does this "time factor" mean?'

Best... Richard

[suntravel]

Yes P06_42 is the offset you can use it also to make sure M3/4 will result in same rpm, or misuse for finetuning low rpm in one direction ...
P06-41 is filtering fluctuation from the +10V signal

In rigid tapping Z is tied to the encoder input from the spindle, not to the commanded spindle speed, so if you command 640 and the spindle turns 670 it will work perfectly too.

All default settings for rigid tapping are way to slow for my taste. I have attached my settings, on my mill tested up to 3000rpm with M3

Uwe