> ------------------------------ > > Message: 6 > Date: Sun, 08 Aug 2010 23:10:36 -0500 > From: Jon Elson <[email protected]> > Subject: Re: [Emc-developers] Better logic for scale feedback, > [Feature Idea] > To: EMC developers <[email protected]> > Message-ID: <[email protected]> > Content-Type: text/plain; charset=ISO-8859-1; format=flowed > > Dave wrote: > > Who really cares where your motors are at if you can accurately control > > the actual position > > via the scales? Backlash will not be compensated but the velocity > > mode stepgen won't care. The PID loop will try and compensate. > > > Yes, but with larger amounts of backlash, the motor may tend to hammer > back and forth across the backlash. > > Does anyone know if Stuart is using screw or backlash comp on that big > > horizontal mill that is setup with a dual loop and direct reading scales? > > > > I would bet that he is not. > > > I believe he was using screw compensation, and is either still using it > or has integrated it into a general 5-axis kinematics correction system, > for the 5-axis Cincinnati machine. His main goal there was to correct > some orthogonality error on the 3-axis base, as well as correct for > misalignments of the centers of rotation on the A & B axes in the head. > > I think it is his Giddings and Lewis horizontal mill that has the dual > loop control. Since Stuart's shop has a Renishaw (I think) laser > interferometer, he can measure the error on these big machines > relatively easily to build the correction tables. > > Jon > > > Gentlemen, Just to clarify the comments about my shop. On the 5-axis (XYZAB) Cinci I use the screw comp on all 5 axes. I also developed a kinematics to correct mechanical errors of the machine exactly as Jon explained. The G&L is a 4 linear axis (XYZW) horizontal machine. It is the machine with scales and encoders on X and Z and an encoder only on Y and W (the quill). It is set up to use the scales and encoders on X and Z and encoders only on Y and W. The Y axis scale is broken. I will install a new scale when we get the machine in production. We have an API laser tracker I use for machine calibration. The API is not as accurate as a Renishaw for linear calibration but the API does full 3D position capture with sub .001 accuracy in the envelope of my machines. Way closer than most anything I need to machine. www.mpm1.com:8080 has a lot of information about what my projects. You are welcome to use the info from this directory. I will try to answer questions. thanks Stuart
-- dos centavos
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