Messages

11

General Mach Discussion / Re: Timing

« on: June 25, 2009, 06:12:15 PM »

Thanks for the helpful responses, I'll try later.  Son arrived yesterday asking that I take him and wife for 'jolly' driving a Ferrari so today's playing in the workshop is out!

Ian H

hello, did you get anywhere further with this issue yet?

12

General Mach Discussion / Re: motor tuning for vfd spindle

« on: September 16, 2008, 03:52:44 PM »

i increased the acceleration rate on the vfd side,  by around double, and also the acceleration in motor tuning to nearer top end.    it seems to have further improved the accuracy of the spindle calibration and the dro.  I'm to within 5rpm open loop now all the way through  from 500-2490 rpm, does it get much better on a light weight drive? . 

at s500/400/300 it jumps plus to around 40rpm out.  funny thing is , when i command 100rpm, it jumps right upto top speed, perhaps someone can pick up on that issue.

I shall continue testing!.  I notice alot of others have had similar experience by doing a search on spindle calibration.  I wonder if its the board im using to convert step to volts if its a linear increase at the bottom end.

13

General Mach Discussion / Re: motor tuning for vfd spindle

« on: September 15, 2008, 06:22:41 PM »

i have now tried changing the p.i.d values, it seems to hunt about too much like that, i checked closed loop feedback that also takes too long to settle, although it hunted out the commanded value for once!.  Averaging is more like pulling the wool over your eyes..!   

Im on 45khz , have one slot in my index pulse plate 10mm wide on a 94mm diamater plate.   On my inverter 10V = top speed @ 50hz = 2790, through 1.1:1 pulley = 2536.   Ive calibrated the spindle in at 1-2-3-4-5-6 ~ us.
 i can get good results for commanded in the mid to high range 750-2500,  within target to 5-8 rpm, (thats adeqaute for sure on a low inertia pint sized drive)   but for some reason still in the lower rev range when calibrating mach just dosent pick up the index pulse properly below 750. it can be anything upto 100rpm out, its non linear also,  just to be even more of a figure out!.


when initiating auto-calibration it starts the spindle around 125rpm,    and my motor spins at around 44,
mach has to increase to around 250 before the spindle starts to register steady speed at around 75-100rpm, before that its not registering properly in mach. 

by the time it gets to around 750rpm the spindle speed actual has caught up with mach calibration commanded, and from then on upto 2500 its better.  why when mach is calibrating does it not wait for the actual speed to catch up with the commanded before the commanded moves onto the next reference point up the graph* etc!.   perhaps its an acceleration thing, i'll try that next. 

14

General Mach Discussion / Re: motor tuning for vfd spindle

« on: September 13, 2008, 05:54:11 PM »

5 emc's, very interested to see that box.  
 did you remain with the origonal motor frame size?.   I just managed to squeeze the next up into the space giving me a massive power increase of 180w  (0.55Kw from origonal 0.37) .   still, the inverter will give a programmed torque boost of another 50%, the top end was sacrificed for 1.1:1 pulley reduction to give some more gain at the epxense of some top end.




I took out the index plate and turned that down to get rid of the 100 slots,  milled in a 10mm square, now it works  better for pick up, it still fluctuates around 10rpm quickly in the dro. after calibrating further 2490 = 2490 actual,  and 1000 = 1010 actual, and  600 = 605 actual. so its close!

but there is still some discrepancy at the very low speeds / 200=305 actual or so.  for some, and it may be my oversight and inexperience, mach has difficulty calibrating/syncing the low speeds in for step tuned spindle motor?.  I'll give it another go. thanks for the help so far its working out well

15

General Mach Discussion / Re: motor tuning for vfd spindle

« on: September 12, 2008, 06:48:30 PM »

im aiming for nuts then i guess, big target!. if anyone had confirmation of electronic rpm fluctuation for the dro on a set machine i would be obliged, i've just turned mach on so im looking for a standard to work from.

 I appreciate what you say about the mechanical machine is driving the dro.  Tell me you have a modbus controlling different clutches inside the gearbox, thats pretty smart, i did not know a cnc could effectively change gears!, i have hope for a machine with torque yet then! was it a conventional mahcine or a cnc to start with?

16

General Mach Discussion / Re: motor tuning for vfd spindle

« on: September 12, 2008, 06:11:50 PM »

can you give me a target discrepancy to aim for between actual and commanded spindle speed please!,  whats the general results people have, should it be a stable speed reading? few rpm, or better still none at-all with no load!?

17

General Mach Discussion / Re: motor tuning for vfd spindle

« on: September 12, 2008, 05:51:35 PM »

sure can, i'll give that a go and see if it helps, |I have faith in a wider slot.  does having 100 slots not make it more accurate for screwcutting, forgive me for thinking traditionally of dropping it on an ainjest /multi-starts..?  i guess mach can cope with accuracy using timing alone? , i worry too much, but its good to know !

18

General Mach Discussion / Re: motor tuning for vfd spindle

« on: September 12, 2008, 05:42:17 PM »

 at the same time came across another problem,

  I cannot sync the commanded or actual speeds together no-matter what I tried.  I tired various pulse widths, calibrating the spindle, trimming some millivolts on my analogue output card.  Best I could get was 2490 for 2490rpm! but..  at the lower end of the scale betwen 2-300rpm its as much as 100rpm out. for some reason , i think it may be the 100 hole timing plate. 

I noticed that below 2-300rpm the actual spindle speed read/displayed jumped about wildly in the dro when calibrating, it took a long time to move on as the speed would not settle. Sometimes leaping upto 3300 then next increment would be 65 rpm , it was just going haywire.
   The Index pulse plate has 1 ring of 100 holes as displyed in the link, and note the single notch at the top.  The index pulse for mach is taken off the top notch and a proximity sensor as norm, and signals to mach when the notch passes the sensor, its active low. Then the other 100 pulse holes, i had picked up through the other proximity and serial interface but havent plugged them into mach yet, i'm not sure if i could use them for anything.  any more ideas, very grateful :-)   i wonder if a wider slot will help,  what seems odd is i thought it would have problemswith top end speed reading not bottom end where it has a longer time frame to read the pulse.  So far my spindle has broken mach law twice!.  the slots are 2mil.

19

General Mach Discussion / Re: motor tuning for vfd spindle

« on: September 12, 2008, 05:35:33 AM »

i guess then that the spindle pulse time period is directly related to the output speed ,  how then if the pulse time period is increased does the motor speed up in the same time frame?   

is it like an inertia thing? it pulses power on and off, with the off period staying the same and the on period increasing? 
how can this be applied to different motors for tuning...

20

General Mach Discussion / Re: motor tuning for vfd spindle

« on: September 11, 2008, 02:39:35 PM »

I checked the kernel speed out sure enough it was set at 25000.  how can it run at 2500rpm then?, it sure did!.  I have now changed it over to 45Khz, so all's theoretically fair.
 
I changed the motor pulse time to see if that made a difference on the vibration, it pretty much didnt, all that happened was to increase or decrease the spindle speed,  it didnt change the vibration.

I took off the drive belt from between spindle and motor and tried again,  behold it was deathly quiet, apart from the inverter whistle!.  I think I can concllude that the belt was tracking off and up the side of the timing pulley flange, the lumpy profile of the 5MM HTD belt was just 'biting'  on entry to the pcd form on the pulley, if you get what i mean, a case of mis-alignment.   Its caused from the OEM motor mount plate bieng fixed in only two places, which is quite lame, but then I guess it wasnt intended for a heavier motor and drive, and also was driven by a plain old V belt so there were no notches  or teeth to mis-bite.

The OEM motor mount plate is 4mm thick, it's thick enough but it only has two points of contact inside the machine, one to pivot on and the other one slot/bolt to nip up once you have taken up the belt slack.  I could physically move the motor if i pushed it hard and it wasnt sitting parrallel to the spindle, so the belt was just running off to the edge without the 3rd point of contact to guarantee parrallel.

So next stop is to machine up a larger plate, so I can fix in three place at least, where arrow is!.  I wasnt oblivious to the flexing issue,  i just wanted to check the software side, thanks very much for the advice :-) .
suprising they got away with it before!