Okuma have something like an accelerometer or perhaps a mic in the spindle but they use it to optimize feeds and speeds to minimize tool chatter.
> On Dec 17, 2023, at 7:14 PM, gene heskett <ghesk...@shentel.net> wrote: > > On 12/17/23 18:19, Chris Albertson wrote: >> Machine tools are a little different from 3D printers because >> 1) Printers are not built nearly are solidly are milling machines. Milling >> machines do not flex very much >> 2) the printer head moves in air and there is no resistance to movement. >> While an end mill has to have force applied to cut metal >> 3) if anything causes the mill’s spindle to vibrate it is the teeth of the >> rotating end mill, not “spring” in the machine's structure >> That said, I had planned to use accelerometers in the feet on my next robot >> project. Robot legs are very much like 3D printers or milling machines. >> Each leg has three or more axes and needs to be precisely moved and while >> moving, the foot might unexpectedly collide with some object. We can >> compute the expected acceleration on the foot and compare to the actual and >> find the difference. The robot operates in the uncontrolled real-world and >> I expect many “surprises”. The 3D printer is “bendy" and flexible so I >> would expect a difference between expected and actual. But the milling >> machine is so sturdy, I’d expect little difference. >> But still, it would be a very easy experiment. Decent accelerometers cost >> less than $20 and you could simply place one in the jacobs chuck and then >> jog the mill around and see what the accelerometer says. No software >> changes to LCNC would be needed, just put the little PCB in the chuck and >> look at some plots. > > Depends on the mill or? In the case of my G0704, the accelerometer should go > on the table for xy motion, not the relatively stationary chuck which > generally only moves vertically. In the chuck on something like the 6040, a > medium sized gantry I have. The acceleromter s/b on the moving part IOW. > > Here is one that I have >> https://www.amazon.com/HiLetgo-Gyroscope-Acceleration-Accelerator-Magnetometer/dp/B01I1J0Z7Y/ref=sr_1_1_sspa >> HiLetgo MPU9250 GY-9250 9-Axis 9 DOF 16 Bit Gyroscope Acceleration Magnetic >> Sensor 9-Axis Attitude +Gyro+Accelerator+Magnetometer Sensor Module IIC/SPI >> amazon.com >>>> On Dec 17, 2023, at 8:52 AM, gene heskett <ghesk...@shentel.net> wrote: >>> >>> One of the not so quiet revolutions taking place in the 3d printer >>> landscape over the last couple years is called input shaping, something >>> probably done best in the cards like Peter Wallace makes. >>> >>> A simplified explanation is fitting an accelerometer to to tool head, the >>> exciting each axis it turn withe an audio sweep of a small amplitude, >>> sweeping from 10 Hz to about 250 Hz while measuring the resulting movement >>> with an adxl345 recording the data it outputs for each of the axises >>> tested. Since a 3d printer works in slices, the z axis is generally much >>> slower on the 3d printer, so is left out in some versions. >>> >>> This data is then run thru a forrier or butterfly transform to develop a >>> compensating acceleration curve that does not effect the overall speed, but >>> does reduce the fine detail or boost it, to essentially cancel the machines >>> natural vibrations. On a 3d printer, given enough heat to supply the head >>> with continuous hot plastic, the use of this compensation has taken the 3d >>> printer from 50 or 60mm/second maximum speeds to 200 mm/second over the >>> last 2 years. I can now buy a printer with this built into its OS for under >>> $1000. >>> There is one obstacle, most 3d printers do not have an interpreter that >>> knows about G2/G3 and its ilk, so most slicer's converts those to tiny >>> straight line moves that look like a circle in plastic. >>> >>> This is done in the default interpreter, Marlin, but is done better by >>> klipper in the better printers but can be reflashed into 99% of the >>> controller cards out there just like we can do with Peters cards. >>> This interpreter runs on the controller cards, often stm32 based cards that >>> sell for, in the ones BTT makes for $59 for a low end octopus card, which >>> can drive up to 8 motors, 5 fans, 3 heaters and all our limit/home switches >>> and probing gizmo's. Some of these even include the G2/G3 stuffs. These >>> cards are nearly all designed to handle nema-17 motors at 24 vols and maybe >>> 3 amp max motors, but one line of the octopus family of cards has a >>> separate motor supply input that assumes 60 volt rated drivers so even >>> those tiny motors can be moved at amazing speeds. >>> >>> Top that with signal stealing plugins that fit the driver socket of these >>> boards I'm rebuilding 2 bigger printers with nema-17 versions of the closed >>> loop servo/steppers with optical encoders that use drivers like we use with >>> linuxcnc, 2m542 sized stuff, but now rated for 90 volts and up so they can >>> be driven at unreal speeds w/o losing home. The PID is in the driver, >>> linuxcnc just tells them what to do and they do it. And if they can't do >>> it, they will tell linuxcnc, stopping it by linking that signal into the F2 >>> of linuxcnc. Doing the stop quick enough on my Sheldon the I can position a >>> chuck jaw in the way, and jog a carbide chipped tool into that jaw at 20mm >>> a second, it hits the jaw, the driver shuts off the motor drive at the same >>> time it tells linuxcnc to stop, the release of the motor drive lets it >>> spring back away from the jaw by 10 thou or so. The carbide chip is not >>> damaged and the chuck jaw is not marked. Tested many times, but has never >>> occurred wile running a job on either machine where I've put those motors. >>> No PID's in the lathe config, no PID's in the 6040 config. Its all in the >>> much smarter drivers. They use the PID error to control the motor current >>> so if conditions are low load, very little current or motor heating, but it >>> it hits something, it will use every amp the supply has to prevent a step >>> loss, so home is maintained under downright abusive conditions. In short, >>> they Just Work and work well. I'm so sold I have 3 more motors, drivers, >>> and higher voltage power supplies to convert the G0704's other 3 main >>> axises to them, the A axis already is. With the PID's in the drivers, there >>> will only be one PID left in the G0704 when I'm done, in the spindle >>> circuit. >>> >>> It is the "input shaper" thing I think could improve the finish linuxcnc >>> can do, effectively driving the machine to cancel its vibrations as it >>> changes speed and directions. Doing it at ridiculous speeds. And that pays >>> the bills in a for profit shop. >>> >>> Something to investigate, for 3.1 maybe? >>> >>> 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-users mailing list >>> Emc-users@lists.sourceforge.net >>> https://lists.sourceforge.net/lists/listinfo/emc-users >> _______________________________________________ >> Emc-users mailing list >> Emc-users@lists.sourceforge.net >> https://lists.sourceforge.net/lists/listinfo/emc-users > > 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-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
