Hi Matthew,
That FF1 is probably causing the increasing following error. Again I'd
strongly recommend using just stepgen rather than a combination of
stepgen and PID. At the moment LCNC and your drives are fighting each other.
The oscillation could be the drive tuning or the loops fighting each other.
I’d be fine with a max rapid speed of 250 IPM but I’d hope to be able to have
enough torque to cut at the full 250 IPM
From your numbers I'd say you'll have plenty of torque at 250IPM. The
motor torque should be pretty flat from 0 to 250IPM.
As far as speeds are concerned the absolute limit is the critical speed
of the screws. You can calculate it using this calculator
<https://www.lintechmotion.com/sizing/critical-speed/critical-speed-inputs.php>.
Exceeding the critical speed is a really bad idea. The next limiting
factor is the nuts. If you spin the screws too fast the balls skid in
the nuts and you get accelerated wear. Without the manufacturer's data
sheets this is much harder to estimate. About all you can do is look up
data sheets from various manufacturers and make estimates based on their
numbers for similar sized screws. By the way the Z axis screw is a bit
of an oddity. It has a very large diameter and fairly fine pitch. It's
lubricated from the central lube system. The combination of large
diameter and thick way oil means you get a lot of viscous friction
losses in the nut. If I remember correctly I limited mine to somewhere
around 2 - 3m/min 80-120IPM.
Les
On 28/06/2021 15:27, Matthew Herd wrote:
Hi Les,
I’m jogging at 60IPM, 120IPM, and 250IPM for testing purposes. Depending on
the PID parameters I was seeing increasing ferror with jog time at all three
speeds. The delay in stopping also seemed to correlate with the ferror.
Tuning eventually brought it down to constant ferror, but results were still
subpar.
The motors seem to be capable of far more than they’re currently doing because
when the ferror oscillated during a stop from 250 IPM the machine would shake.
During normal jogging moves at 60 or 120 IPM they apparently struggled to keep
up (per the ferror)
The max rated RPM for these motors is 2500 RPM, which equals 500 IPM. Max
continuous is supposed to be 2000 RPM (400 IPM). I’d be fine with a max rapid
speed of 250 IPM but I’d hope to be able to have enough torque to cut at the
full 250 IPM. I’m hoping to achieve good high speed machining performance so
I’d also like to get the accelerations up pretty high if possible. Cutting
speed isn’t too big a concern, but the NEMA 42 steppers I used to use were
quite slow to accelerate. Your max acceleration values (30 in/s/s) seem like a
good target for me.
Unfortunately, although the drives support PWM and analog, my USC boards don’t
support them. In hindsight I would have gone with PWM or analog control of the
drives, but I already had the USC boards.
Matt
On Jun 28, 2021, at 9:51 AM, Les Newell <[email protected]> wrote:
Hi Matthew,
I'd recommend setting this up as a stepper system and ignore the encoder
feedback for now. The feedback loop inside the drive is likely to fight with
the PID loop inside LinuxCNC. The encoders can be used for position feedback
but that's not essential and is just making it harder to figure out what is
going on. Later once you have the machine running you can come back to this.
You can use Halscope and monitor the axis commanded position and encoder
position to assist setting the PID values within the drive.
Alternatively if the drives can accept PWM torque commands I'd do that and have
LinuxCNC doing all of the PID work.
Extended jogs tend to result in the machine moving awhile after I release the
button and ferror is all over the place
That's a symptom of the machine not being able to keep up with the command.
Either your speed or acceleration are too high. Looking at your numbers I'd
guess you are maxing out the speed.
What is a reasonable acceleration value for a Bridgeport BOSS5 (Series 1 type
factory CNC machine) with 1kW 5Nm AC servos? Are my accelerations too low?
Raising them by orders of magnitude seemed to have no effect. I freely admit
I’ve been too lazy to try to calculate it.
It depends on a huge number of variables. I generally work on trial and error.
1kW is a bit overkill for a S1 BP so assuming your gearing is correct the
limiting factor is probably your ball screws. I'd feel a bit uncomfortable
going much over 250IPM. If you spin the screws too fast you'll damage them. How
fast will your motors be running at that speed? Could you simply be running out
of revs on your motors?
To give you a rough idea my Hurco, which is considerably bigger than a S1 CNC,
uses 750W servos and does 10m/min (~400IPM) easily. From my ini file:
MAX_VELOCITY = 166.66666
MAX_ACCELERATION = 750.0
Note these are metric so divide by 25.4 to get inches.
Looking at your ini file:
MAX_VELOCITY = 8.33
MAX_ACCELERATION = 10.0
Your velocity looks way out. That's 500IPM. While 1kW servos should be able to
run the machine this fast with the right gearing I can't see it lasting very
long.
Les
On 28/06/2021 14:08, Matthew Herd wrote:
Hi Les,
The drives accept step/direction from the USC board to command position, not
velocity. The encoders are pass-through to the USC board and then to LinuxCNC.
Thanks!
Matt
_______________________________________________
Emc-users mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/emc-users
_______________________________________________
Emc-users mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/emc-users
_______________________________________________
Emc-users mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/emc-users
