On Friday 25 January 2013 02:37:47 dave did opine: Message additions Copyright Friday 25 January 2013 by Gene Heskett
> On Thu, 2013-01-24 at 18:51 +0200, Roland Jollivet wrote: > > On 24 January 2013 18:27, Gene Heskett <[email protected]> wrote: > > > On Thursday 24 January 2013 11:05:42 Todd Zuercher did opine: > > > Message additions Copyright Thursday 24 January 2013 by Gene Heskett > > > > > > > Add a spring to your contact, to give it a degree of compression. > > > > > > I did, in a previous design, mount the pcb on grommets so there was > > > room for crush. but found it near impossible to get a consistent > > > spring back. Or if off center, a consistent restoration to level. > > > a 4 grommet mount would have solved that, but the frame of that > > > gage didn't have room. So I wound up insulating the pcb being > > > carved in a pocket of micarta, and g38.2'd the pcb I was carving, > > > which worked very well indeed. > > > > > > Like T. Edisons & his light bulb, he found 10,000 ways it didn't > > > work. > > > > > > All my current problems regarding this would go away if the switch > > > hysteresis backup move would just do another 5 thou of back away > > > anyway if it found the switch open when it checked instead of > > > freezing in place and fussing with a big red error advisory because > > > the switch was found to be already open as it started the back away > > > move. HINT, HINT. IMO, the only error here is in the assumption > > > that the home switch is mechanical, with several tens of > > > thousandths on an inch, or in metric, possibly a whole mm of > > > hysteresis. Perhaps even a per axis keyword to make it work either > > > way? Would seem to give maximum flexibility at any rate. > > > > How about using a proper travel limit switch. The contact operates > > well within the first mm, and then you can press it a further 5mm or > > so with no ill effect. And on release the hysterisis is very short... > > > > http://www.galco.com/buy/Eaton-Cutler-Hammer/E47BMS04 > > http://www.galco.com/buy/NTE-Electronics/54-438-BP > > > > Regards > > Roland > > Hi all, > As Gene would say "there are many ways to skin this cat". Indeed there are. And its nice the cat has several lives in case it doesn't work the first time. > a. manually run the carriage up against a stop and press home for that > axis. Depending on the springiness of the mechanics probably good to > about a thou. > > b. use a home switch with a cam actuator i.e. ramp the switch on which > guarantees it will stay closed with over-travel. Then you can either > back off until it opens and use that as home or better yet back off to > the index pulse. Steppers don't have index pulses for starters unless fitted with encoders. Most drivers will go to a fixed position if disabled by a powerdown, & then repowered, I guess one could call that an index, but you would still have the ambiguity of at least a half steps motion that you would still have to measure and correct for. Thats a YAEPC, Yet Another Error Prone Complication that proper homing design removes the need for. > The homing method should match the repeatability of the machine. Like so > many things measuring to .0001" isn't very valuable if the machine will > only hold a thou. OTOH, I would rather home to a 10 thousandth even if it can't hold to 10 thousandths. It is just that much less in the error budget. By the same, simplicate the process theory, Z home should IMO reference the end of the workpiece sticking out of the chuck on a lathe, or on a mill, the sacrificial table covering the material is sitting on, or the top of the freshly mounted material. > On my cinci I give up a couple of inches to have a homing setup that is > easy. Someday I'm going to fix that. :) Love it Dave, you "grok" it well. But then you have to make test cuts, measure and 'touch off'. > HTH > > Dave Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! My views <http://www.armchairpatriot.com/What%20Has%20America%20Become.shtml> Your goose is cooked. (Your current chick is burned up too!) I was taught to respect my elders, but its getting harder and harder to find any... ------------------------------------------------------------------------------ Master Visual Studio, SharePoint, SQL, ASP.NET, C# 2012, HTML5, CSS, MVC, Windows 8 Apps, JavaScript and much more. Keep your skills current with LearnDevNow - 3,200 step-by-step video tutorials by Microsoft MVPs and experts. ON SALE this month only -- learn more at: http://p.sf.net/sfu/learnnow-d2d _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
