Great description. Thanks Gene. > -----Original Message----- > From: Gene Heskett [mailto:[email protected]] > Sent: July-17-19 7:00 PM > To: [email protected] > Subject: Re: [Emc-users] Spindle control > > On Wednesday 17 July 2019 16:51:30 John Dammeyer wrote: > > > There are a number of videos out there changing up the G0704 gear > > driven spindle to belt drive. Some use toothed belts, others a double > > set of pulleys. Most of the videos explain that they will soon but > > the slotted RPM sensor disk back on but for most of them they've not > > done that yet. > > > > For LinuxCNC what sort of encoder resolution is required on the > > spindle to be able to do tapping. I know I can do it with one pulse > > per rev with my Electronic Lead Screw to cut nice threads but I also > > don't slow down the spindle at the end of a tap into a blind hole > > while tracking spindle speed. > > > > My new 1.8kW AC Servo motor with a 2500 pulse per rev encoder can echo > > the encoder pulses out of the drive so if I used a 1:1 toothed belt I > > could use that. But if I want stepped pulleys to give me extra torque > > at low speeds then I'm looking at V belts so I'll need an encoder on > > the spindle. > > > > The spindle pulley on my G3616 type mill has a tapered cone. That > > also suggests I want to stay with V belts and just mount a slotted > > disk onto it rather than try to make a similar cone that holds toothed > > GT3 belts. There's room. But how many slots? > > > > Thanks > > John Dammeyer > > > I have a G0704 John, and have not managed to damage those plastic gears > yet, but I found a 67 slot wheel replacing the original drilled tach > wheel, with slot interruptors had way too much quantization noise to be > used as spindle speed feedback. An amount to gain in a pid to hold the > average speed close enough for rigid tapping, injected so much noise > into the servo that it sounded like the spindle bearings had square > balls slowly destroying their cages. The noise was actually the servo > amp slamming the tooth clearances back and forth. > > Some background: I took the OEM control box off, and built a power supply > makeing a well filtered 126 volts dc, good for 20 amps surge. And I > took the output of the spindle PID to a pwmgen module in a 5i25, and > that PWM signal to one of Jons (Pico Systems)PWM-Servo amps which is > heavy enough to control a PSU with that sort of muscle. The motor has > a nameplate voltage of 0 at 9.7 amps for its one hp rating. So I've > power enough to reverse the spindle from 2900 revs fwd to 2900 revs > backwards in about 400 miliseconds, and back again. I have Jons amp set > to current limit at about 17 amps and you can hear it chirp as it does > this. > > But that homemade encoder was just too coarse, so without really > figureing it out ahead of time, I bought on fleabay, an Omron encoder > with a 1000 line quadrature A/B/Z output. Once it was in hand. I drilled > and tapped the top of the motor shaft and planted a 5mm extension about > 5/8" long and made a mount to put the encoder on top of the motor so it > spins at motor rpms. > > Somewhere along the line I discovered the encoder was a low voltage > differential output, so the A/B wires were interrupted by a pair of > rs-485 interfaces, about $2 each on fleabay. They turned out to be > bi-dir, so I had to jumper them for one way, and they gave me some purty > 5 volt rail to rail signals to feed a 5i25's encoder inputs. The Z still > comes from the old optical because it needs to mark zero degrees on the > spindle. Then I put a notch in the speed knob that fitted the rollers of > 2 small micro switches, and made a sandwich out of a pair of half > circles cut from .030 alu sheet with the microswitches between them and > arranged to see that notch, sending a pair of "I'm in gear so and so" > back to the 5i25. Those face a mux4 which is used to both slow the > motor to a crawl when neither switch is closed, and scale the SCALE from > the ini file for feedback to the pid and video tach. I temporarily added > some more hal to make me a scale reference, so the SCALE is scaled to > the correct values regardless of which gear its in, and rigid tapping is > correct in either gear. > > That gives me an effective scale of a bit over 7000/rev in high gear, and > something over 14000 in low gear. Quantization noise has vanished! I > won't claim its silent, but I have to either look, or listen real > carefully to make sure the spindle is turning. The 2 unused inputs to > the mux4 are fed about a 25 motor rpm offset voltage by a setp in the > hal file, and the speed response is so instant that I can reach up and > change gears while running wide open since by the time the knob has been > turned 3 degrees, the motor has slowed to a crawl, the flat faced gears > change silently and are completely engaged by the time the other switch > closes. 200 millisecs later the motor is back to top speed and the > spindle is turning at either 1500, or 3000 revs. All with zero > possibility of damaging the gears. And I can run a Pgain of about 20, > even as high as 40, but thats overkill, in the spindle PID. Worst effect > is that until Jon's servo amp regulates, making the motors magnetics > chirp, I haven't a clue how hard the motor is actually working. The > spindle doesn't slow as the load of tapping a hole comes in. Makes me > wish I could find a 15 horse motor as that would remove the need to peck > tap the bigger holes :) > > If interested John, I can pm you a tarball of that whole config dir so > you can borrow what you want. Theres also some alignment stuff that > still needs fine tuning and which is waiting on me finding a camera that > doesn't die about the time I get a good view. Teeny cameras with long > lenses have seemed to disappear from the fleabay listings over the last > 2 years. Darnit. > > Cheers John, Gene Heskett > -- > "There are four boxes to be used in defense of liberty: > soap, ballot, jury, and ammo. Please use in that order." > -Ed Howdershelt (Author) > If we desire respect for the law, we must first make the law respectable. > - Louis D. Brandeis > Genes Web page <http://geneslinuxbox.net:6309/gene> > > > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users
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