On Tue, 2 Mar 2021 at 20:44, Thaddeus Waldner <thadw...@gmail.com> wrote:
> What I would like to do is mount the spindle directly to the z-axis (as one > normally would). Then have a collar that surrounds the engraving bit rub with > spring pressure against the top surface of the workpiece. This collar would > be mounted to a linear axis with an encoder, in the same orientation as the > z-axis, and thus track the surface of the workplace relative to the spindle > position. That certainly ought to work. Two coaxial sliding tubes is a capacitor. So you can actually measure the displacement with an LC bridge circuit. (I actually did this once, when I needed to measure displacement on a _very_ fast moving thing) On the scale you are talking about it might be hard to get enough resolution, and there is a susceptibility to electrical noise. I imagine the travel distance is tiny? I would be looking at (analogue) inductive sensors. Or possibly laser triangulation sensors, if I could find one cheap on eBay. Or, actually, something that is really cheap, effective and accurate... Use a thin leaf spring to hold the collar against the work (a simple C-shaped one, maybe two at 180 degrees around the Z axis) Bond strain-gauges to the inside and outside of the curve of each in a Wheastone Bridge, and take to a simple Op-amp amplifier circuit. I used to use these all the time in a previous job, and was getting sub-micron accuracy over a 5 mm range. Strain gauges are about $1 from eBay and can be bonded on with ordinary super-glue. (After abrading and de-greasing the surface, pick up the strain gauge with Sellotape (Scotch tape) and tape it down in place. Then peel up one end of the tape, lifting the gauge, put a drop of glue under it, and tape it back down.) -- atp "A motorcycle is a bicycle with a pandemonium attachment and is designed for the especial use of mechanical geniuses, daredevils and lunatics." — George Fitch, Atlanta Constitution Newspaper, 1912 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
