On Friday, 6 May 2022 03:58:20 EDT andy pugh wrote: > On Fri, 6 May 2022 at 00:51, gene heskett <ghesk...@shentel.net> wrote: > > But they all, better ones anyway, use an inductive sensor to measure > > bed flatness. That sensor is uber cheap as a service part. What sort > > of drive does it use > > Most of them just need a supply voltage (typically a minimum of 9V up > to 30V) and then connect the output wire to the 0V wire (NPN) or to > the +V wire (PNP) > > For interfacing with 5V logic you need NPN, but for Mesa cards with > 24V IO it is typically best to use PNP.
Good to know. But this machine is using 12 volt field power but PNP is still good. I'll get a bag of those ordered. 4mm range. Found bags of 5 shielded PNP's for 15 USD, onshore seller, bought two. Spares... > There are two types, shielded and unshielded. You can tell them apart > by whether the threaded outer comes right to the end. > Shielded can be buried in a metal part and still work. Unshielded will > detect the part they are mounted in, if it extends into the unthreaded > area. > > I tend to bury them right in the machine frame and so use shielded. > > My Y and Z ones on the mill can be seen here: > https://photos.app.goo.gl/U6L92r7ndpda9ALL8 (well, you can see one of > them, and guess the other) > > They come in a range of diameters between 4mm and 30mm and a range of > detecting distances. How do the shielded ones work when the frame is alu? I would think the presense of alu would also detune them above their normal 800 hz resonance point. Where iron, being ferrous, would likely slow them off resonance quicker because its lossier, alu would detune them upwards. One could always glue on some snippets of sheet steel for a target I guess. The other thing that surprises me is the low frequencies they use, I'd have to assume search speeds would be limited if a direct approach, as opposed to a slide-by, for no other reason than to have room to overshoot w/o a damaging crash. Although one switch I currently use is a button, mounted on a leaf of this springy hard alu whose anchor screw is about 2" away, and that I can use a decent search speed because the whole leaf just springs away about 1.5mm while the gantry is getting stopped, then it seeks away to open, and calls that home when its found. That one has a steel screw to activate the button about 2mm from a crash, which the 4mm version would detect. Currently, the rotary has a bump of glued on plastic hitting a roller. But my plastic harmonic drive is too high a ratio, and to get a useable turn speed takes a higher motor armature speed, over 1000 rpm and running nearly continuously at more than about 3 rpm apparently overheats the bb's used for balls in its printed bearings, causing the bearing races to flow and loosen rapidly. So at 8 rpm, I'm getting one test stick per drive. Hence something different for the drive, enter a 3mn motor, turning a 5/1 worm from stage right. Currently its brand new and I think its too stiff to drive with a 1nm motor, but may loosen with some run time on it. OTOH, its not a motor I have targeted for another use. I found some adaptors from an 8mm motor shaft to the 11mm input to a 90 degree worm drive, so I ordered a bag of those from fleabay but arrival times from China leaves much to be desired, earliest estimated delivery is June 9th. So that problem of interfaceing to the motor is solved. The output will be solved by modifying the stick chuck I use in a 3 jaw now, by fitting the back end to the 14mm shaft. Its not a problem to add the keyway to the printed part. And the shaft hole, about .2mm undersized, s/b a hammer drive fit, so make the keyway come all the way to the end of the shaft with a dremel, and just drive it on with a printed in key. I'm doing that with the present drives sprocket on the axle shaft with zero play. Works well. Thanks Andy. Take care and stay well. Cheers, 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, 1940) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis _______________________________________________ Emc-developers mailing list Emc-developers@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-developers
