When I changed over from a 2HP 220VAC motor to an AC Servo for the spindle motor I knew it was also time to look at spindle encoding. Cost of the AC Servo was just under half of a 2-phase 2HP + VFD.
If I was running toothed belts it would be a no brainer to use the AC Servo drive encoder outputs (which can also be divided to create a slower pulse train). But for the moment that wasn't possible. I've probably posted some of these photos but here's the AC Servo mounted with a new dual step pulley (and no intermediate pulley). http://www.autoartisans.com/mill/SpindleMotorPulley-5.jpg Notice the 4 step pulley on the spindle. There's no room for any sort of pulley to encoder on the spindle. This pulley is driven by a tapered cone so it's also not an easy fix. I didn't want to damage the original pulley so I made a new one that was 2 step instead of 4 with a thick mounting plate on the bottom for the encoder. http://www.autoartisans.com/mill/NewPulleys-1.jpg Here's the encoder disk mounted to the pulley with LCNC for the machining including using the 4mm cutter for a G-Code program that expected a 3mm cutter. 8-( http://www.autoartisans.com/mill/ShavedEncoderDisk.jpg My 3D printer to the rescue (plus lathe for creating custom bolts to hold the bracket). http://www.autoartisans.com/mill/SensorTrialFit.jpg And the final brackets and interface board before it's all packaged into a box and the wires neatly routed. http://www.autoartisans.com/mill/SensorTestSetup.jpg The biggest mistake was that the two pulleys aren't exactly 1:1 where a toothed one would have been. (We won't talk about casting the taper backwards so the pulley is really upside down from what I wanted). Anyway I've found that my HAL file stuff and pulley speed reporting is still a bit flakey in order to scale the spindle speed to the true speed of the spindle motor which is controlled with step/dir rather than 0-10V. The V belts aren't perfectly smooth so they also contribute jitter. Until I switch to toothed belts and pulleys I'm not going to worry about that. John > -----Original Message----- > From: [email protected] [mailto:[email protected]] > Sent: April-02-22 7:05 AM > To: 'Enhanced Machine Controller (EMC)' > Subject: Re: [Emc-users] Homebuilt encoder > > Agreed about making an encoder and I have an Omron unit with A/B/Z outputs > "in the mail" from China. > > The drawbar for my R8 spindle extends out the top of the spindle. It is a > hollow shaft encoder with an 8mm through hole but that is insufficient to > accommodate a drawbar. I suppose that I could couple it to the top of the > drawbar with some sort of slip coupling but that has potential issues with > alignment and coupling backlash. Perhaps I'm not looking at things the > correctly but it seems that the simplest approach is using a pulley and belt > to offset things. Also, the encoder is rated for a maximum of 10000 rpm and > that is my max spindle speed; I could reduce with a 2:1 pulley + belt. > > Other suggestions are welcomed! > > -----Original Message----- > From: Chris Albertson <[email protected]> > Sent: April 1, 2022 11:37 PM > To: Enhanced Machine Controller (EMC) <[email protected]> > Subject: Re: [Emc-users] Homebuilt encoder > > It is hard to beat GT2. It is the current state of the art in belt-tooth > profile. (except for the identical G3) > > But if you are using a belt, then just buy a $30 Omron encoder. No need to > build one as it would be hard to make a better encoder. I doubt you could > make an encoder as small and accurate as the Omron using normal CNC > equipment. > > But if you could fit a pulley to the spindle, why can't you fit an encoder > disk? > > > > On Fri, Apr 1, 2022 at 7:28 PM <[email protected]> wrote: > > > There has been some good info on how to build an encoder on this thread. > > My concern is how to couple an encoder to my mill spindle. Due to the > > mill design it doesn't seem feasible to attach the encoder directly to > > the spindle so I will need to use a belt drive. The spindle runs at up > > to 10500 rpm. GT2 belts are readily available and the SDP-SI website > > says that they can be used at up to 7500 feet per minute. I believe > > that a 2-inch pulley spinning at 10000 rpm would move the belt at > > about 5,200 fpm so somewhat below the maximum. Is there a better belt > choice? > > > > > > > > _______________________________________________ > > Emc-users mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > > -- > > Chris Albertson > Redondo Beach, California > > _______________________________________________ > 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
