On Monday 10 September 2018 19:37:32 Christopher wrote: > > On 2018-Sep-10, at 18:02, Chris Albertson <albertson.ch...@gmail.com > > <mailto:albertson.ch...@gmail.com>> wrote: > > > > You can actually make good measurements with a larger spot. This > > assumes you are using software and not just eyeball estimates. > > Typically you can do about 1/10th pixels position estimates. With > > micro-meter scale pixels this become way-overkill for machine work. > > I would not bother to do more then roughly align the laser. > > > > Yes you need a sensor. A $10 webcam with the lens replaced by a > > welding glass filter would work but you'd need to experiment with > > different filter and laser power. > > Alternately you could use a quad optical diode array and read the > currents through the four diodes: > https://www.mouser.com/datasheet/2/414/OPR5911_RevD-1145186.pdf > <https://www.mouser.com/datasheet/2/414/OPR5911_RevD-1145186.pdf>
This would work, but first find out if camview will run on the pi. It is a bit of a cpu pig and frame rates on the pi with its teeny usb2 bandwidth already being a problem. And it seems to me to need fairly accurate laser alignment in order to stay within a diode quad of that size. I'll plug in a camera, and see if cheese will run sometime today. After I get a new air compressor installed under a workbench that I just barely got assembled before the rain started again yesterday, and which my back is still complaining about this morning. Camerawise, the laser will overpower the camera, so I'm thinking I should mount the camera at a 90 degree angle to the laser beam, and set a piece of glass at a 45 degree angle to steer a fraction of the laser beam to the chip in the camera, but that would need a thick glass to separate the reflections so that only one surface of the glass would hit the camera. Humm, ISTR the pi has a separate connector for a camera, but it takes a special camera to connect to it, and that cable would need to be about 5 feet long to reach the pi from the lathes carriage. But from the available cable lengths, I'd have to setup a 2nd pi and put it all on the carriage. Which would make it a lot more insulated from lcnc. So I'd need a pi which I have, the camera $4.37(ebay, but unk if lens removable, maybe even a pinhole?), a psu I have and some sort of a display. $25(or less, ebay) for color tft touch screen. Hummmm...... Thinking out loud. > Years ago I built a rig to measure the spacing of dots on a slide > using a HeNe laser and an optical diode array like that and was able > to get sub-micron precision doing so. > > > I would not adjust anything r "zero". between measurements. leave > > the target and laser bolted down solid. Just record the numbers and > > when you are done cal the smallest number "zero" > > > > To get the center point, just use the "centroid" the same math if > > looking for the balance point of the laser spot. > > > > You should be able to make a measurement at least once per lead > > screw revolution, maybe many times more per revolution. > > > > On Mon, Sep 10, 2018 at 12:09 PM Gregg Eshelman via Emc-users < > > > > emc-users@lists.sourceforge.net <mailto:emc-users@lists.sourceforge.net>> wrote: > >> I have a LASER that is made to mount in a chuck or collet. It has > >> alignment screws and adjustable focus. Aim it at a wall far away > >> and adjust the focus for as small a dot as possible. > >> Make a target to mount on the carriage, chuck and center the body > >> of the LASER then use the alignment screws and adjusting the target > >> and rotating the spindle until the spot no longer describes a > >> circle when the spindle is rotated. > >> > >> Move the carriage to the right end as far as possible. Move the > >> cross slide intil the dot is on the target. There's your zero. > >> Advance the carriage toward the bed until the dot moves off the > >> target. Adjust the carriage until the dot is back on target, at > >> least in the X axis. A really good way to map the bed would be to > >> have a sensor as the target so the carriage could be moved by the > >> control and read a continuous stream of how far off X it gets. > >> Barring that, stop every X distance then adjust to re-zero and > >> interpolate slopes between adjustment points. > >> If you put the target on a vertical slide to re-zero Y at each > >> stop, the error map (with appropriate math) could compensate for > >> that too. Perfectly straight cutting even with a very worn bed, as > >> long as the vertical error doesn't drop the cutting tools too low. > >> > >> On Monday, September 10, 2018, 1:55:36 AM MDT, Chris Albertson < > >> albertson.ch...@gmail.com <mailto:albertson.ch...@gmail.com>> > >> wrote: The lasers are easy to find on Amazon but be warned the > >> laser is not perfectly aligned with the housing. But as I said, > >> this does not matter if you spin the spindle. > >> > >> I think a laser is the only option. If you are measuring the bed > >> your reference needs to be at least 10X straighter then the bed. > >> Precsion rods are not good enough but a $20 laser is literally > >> perfect (as long as you rotate the spindle.) > >> > >> With effort you can use the same laser to measure the error with > >> the lead screw pitch. Use it as a laser range finder or laser > >> inferometer > >> > >> But all this measurement may be moot if the lathe is not reputable. > >> The error might be random. Maybe the carriage moves like a tuck > >> on a dirt road? > >> _______________________________________________ > >> Emc-users mailing list > >> Emc-users@lists.sourceforge.net > >> <mailto:Emc-users@lists.sourceforge.net> > >> https://lists.sourceforge.net/lists/listinfo/emc-users > >> <https://lists.sourceforge.net/lists/listinfo/emc-users> > > > > -- > > > > Chris Albertson > > Redondo Beach, California > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > <mailto:Emc-users@lists.sourceforge.net> > > https://lists.sourceforge.net/lists/listinfo/emc-users > > <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) Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
