Would it be difficult to update the actual position with the position from the linear encoders? The DRO position would just stomp on the actual position. Hopefully most of the time the error would be small and it would require real time DRO position... or perhaps only assign the DRO value when the axis is moving very slow or stopped.
----- Original Message ----- From: <[EMAIL PROTECTED]> To: <[email protected]> Sent: Friday, February 01, 2008 4:07 AM Subject: Re: [Emc-users] DRO Input? > >> Message: 9 >> Date: Thu, 31 Jan 2008 13:36:51 -0800 >> From: Dave Engvall <[EMAIL PROTECTED]> >> Subject: Re: [Emc-users] DRO input? > >> >> Hi Dave, >> >> It all depends on what you want to do. If you just want manual >> position then the glass scales will do your job. >> >> However, if you ever intend to control the axes then encoders mounted >> on the end of the ball screws would be my choice. USdigital or >> Automation Direct (Koyo) encoders are reasonably priced and should do >> the job. > > > With respect to you all, I know about encoders, and I know any CNC > control > software is going to need positional input many, many times per > second. > > but... sticking an encoder on an axis is not measuring the position of > anything except the leadscrew, it takes no account whatsoever of > backlash, > uneven wear or pitch errors. > > To a certain extent you can map out backlash and areas of wear on a > leadscrew, but leadscrew pitch errors are going to be tough. > > The DRO is, quite differently, measuring the *actual* X Y Z position, > if > the DRO says you are 100.000 mm from point A then you can take it to > the > bank. > > My leadscrews are ten turns to the inch, I can compensate for backlash > etc > manually, second nature, and even with less than theoretically perfect > accuracy I can still trust feeding a leadscrew in a few thou and know > and > measure that the error on that movement is very small. > > We appear to be confusing two things. > > Encoding leadscrew rotational angles and feeding this back to the > human > brain or CNC software, and factoring in mental or electronic fudge > tables > for backlash and wear, can give us fairly good accuracy of MOVEMENT. > > A DRO with proper glass scales gives us fairly good accuracy of > POSITION. > > 5 times a second is *plenty* for an accurate positional measurement > system > to update an accurate movement system, and produce a system with true > accuracy. > > While leadscrew encoders and a copy of emc and no stepper or servo > motors > will indeed give me a system that will display X Y Z co-ordinates on a > screen, the accuracy of these readings is going to be just as suspect > as > it is sans emc and encoders, only the DRO and pukka glass scales will > give > true positional accuracy. > > As someone who couldn't code "hello world" (except maybe in BASIC) > writing > the code isn't an option, so unless emc has this facility on the > roadmap > then being free as in beer isn't enough. > > Many thanks to all, hopefully there is some more meat in this subject > yet. > > end > > > > ------------------------------------------------------------------------- > This SF.net email is sponsored by: Microsoft > Defy all challenges. Microsoft(R) Visual Studio 2008. > http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------- This SF.net email is sponsored by: Microsoft Defy all challenges. Microsoft(R) Visual Studio 2008. http://clk.atdmt.com/MRT/go/vse0120000070mrt/direct/01/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
