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
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