Re: [Emc-users] Engraver Depth Control
> > 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. Travel distance is a the max cutting depth of a single flute 1/4” engraving tool, which is about 1/2”, plus a bit of headroom. The tool needs to first engrave the material, then contour cut. The material can theoretically be up to 1/2” thick. So a 1000ppr encoder with a reasonably small gear meshing with a linear rack or even a gt2 belt would let me get to within 1 thou, which is plenty precise for this application. An encoder is also easier for me to integrate because I have an unused encoder input on the Mesa board. ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
Re: [Emc-users] Engraver Depth Control
On Tue, 2 Mar 2021 at 20:44, Thaddeus Waldner 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
[Emc-users] Engraver Depth Control
Hi, I have an engraving spindle that rides on a spring-loaded carrier. The carrier rubs against the workpiece being engraved. The depth of cut is controlled by adjusting the distance that the engraving bit protrudes from the rub contact face of the carrier. The advantage of this tool is that it is not dependent on the thickness of the workpiece, so it works well for inconsistent material. It also holds down flexible materials as it’s being engraved. The problem is that the depth of cut is manually adjusted via a screw on the carrier. This is particularly cumbersome, for example, when engraving and cutting multiple pieces on the same job. I’m looking to design an engraving tool that measures and compensates for depth of cut in real time. 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. The LinuxCNC output to the motor drivers is step-direction I’m thinking that with appropriate PID limits, I don’t need to do anything special in the control logic other than setting this up as a regular servo axis with encoder feedback. Comments? Insights? Thaddeus Waldner ___ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
