Hi, Just need to pick someones brains on a problem I have.
I'm in the process of a mill servo conversion and have completed the X axis.
I spent some time tuning the Gecko G320 and started tweeking the Mach3 accel and
velocity settings. I calculated that I'd need to set the kernal speed at 100k as my
max theoretical pulse speed being 128kHz
I set the required "steps per" and the velocity to a brave but safe setting and tryed
it out jogging from the keyboard arrow keys. The servo drive faulted and so half an hour
fiddling with the accel and velocity settings, I got the servo working a treat using the
jog keys.
Then using the MDI, I commanded a few G0 X50 and then G0 X0 and every time the drive
faulted right at the end of the move.
Even moderate velocity settings and accel setting of less than 1.5 seconds faulted the drive.
I then reduced the kernal speed to 75k and started tuning the servo again using a looping
code G0 X50 , G0 X0. I found that the max settings that worked without faulting the drive
are:
velocity setting of 2800 and an accel of 200
This setting is about half the max rapid traverse I wanted and planned for so I'm scratching
my head right now.
The one thing I noticed is that the drive only faults on the end of a move and only when
using the MDI or running code, To see how far from the end I reduced the accel settings
until I could hear the motor winding down and it faults about halfway in the decel stage.
Question 1, Is this what you would expect to see from just an out of tune servo. Is more tuning required.
I got to thinking that maybe there just isn't enough power in the servo so I reset the
velocity and accel to those mentioned above and ran the looping code for about 5 minutes
just to see that everything is running fine.
Still having the axis locks attached to the machine I used them to increase the friction on
the table ways, I didn't want to go too mad but to a point where I couldn't turn the 90mm
timing pulley on the end of the ballscrew by hand. I used the MDI to command a G0 X50 and
expected the drive to fault straight away.
It didn't. I could hear that the servo was working harder but it went to X 50 just fine.
So I commanded a G0 X0 and it went back again ok.
Not wanting to stress anything too much I declared that theory well and truly unfounded.
The servo,power supply is more that capable of driving a heavier load.
More head scratching and so I kept the same settings and changed the kernal speed to 100k.
Faulted every time.
So I am now thinking that the problem may be the computor is the culprit, it is only a
1.2ghz Athlon.
Question 2, If I can set high velocitys and jog using the keys without faulting the
drive, but when using the MDI or running code I have to set lower velocitys without
faulting, basicly the computer is doing more work and not keeping up. Could this be the problem.
I have noticed that the gain setting on the drive doesn't seem to do much visually to the
motor although some settings are better than others, I have it set just over half way.
I'm under the illusion that more velocity will require more gain. Is that right?
The damping setting however, if I reduce the pot counter clockwise from it's
position (about 1/3 way round) sets the axis vibing like a table being dragged across
a polished wood floor.
If anyone has an idea where I should be looking to achieve higher velocities or answer the few questions above I'd be grateful. Relevant specs of the axis below.
Computer;
Athlon 1.2ghz ,256m memory, 200FSB Running latest version of Mach3 only.
Drive Gecko G320
Powersupply Dc 74v 750W
Motor PM ordinary motor
Motor Max V 96v
Motor Max speed 5000 rpm
Motor power 8A - 500W
(Note max speed from motor using 74v power supply is 3854rpm)
Encoder QEDS type
Resolution 500 ppr
Drive reduction 4-1
Ballscrew 25mm dia 5mm pitch
Axis table 800mm x 240mm x 60mm
Cheers
John