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 <les.new...@fastmail.co.uk> 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 > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
