RE: following error / Angular axis

[rehenry-at-up.net]

Granville wrote

> It looks like my motors are moving the wrong way, or my encoders where
> hooked up backwards.  I reversed the a/b on the encoders and have it 
moving
> all the axis.  

Reversing the leads works or you can also change the sine of the 
relevant ini file lines.

> The new problem is that if I try to move real fast I get
> following errors

I posted some stuff on this recently.  You will need to make max 
velocity larger in the [TRAJ) section than it is in any of the [AXIS] 
sections.  By doing this you allow the motion stuff to feed in pulses 
stored up as following error during acceleration.

>, and it's not doing rectangular to polar conversions.  ( IS
> EMC SUPPOSE TO? )  

Yes the EMC will do non cartesian motion planning.  I do it with the 
hexapod kinematics but I donīt know how to ask it to do do it with a 
robot.  The latest stuff from sourceforge includes some modifications 
to tkemc that allows you to switch from joint motion to world motion.  
This sounds like what you want to do.  To access world coordinates, you 
first home out each joint and then in manual mode switch to world 
coordinates and it should provide xyzabc or xyzrpw motion. 

>It seems like if the axis are defined as angular, and you
> move x, it should move both axis to make the x move.

Defining an axis as angular only tells the EMC that this one goes 
around rather than along.  It does not tell anything about the 
cartesian or non_cartesian nature of the relationship between that 
single axis and the world beyond it.  This is done in the kinematics 
files and they may well need to be changed for your machine geometry.


> --
> Granville Barker

Hope this helps.

Ray

 
> -----Original Message-----
> From: Chris Stratton [stratton-at-mdc.net]
> Sent: Saturday, June 23, 2001 2:17 PM
> To: Multiple recipients of list
> Subject: Re: following error / Angular axis
> 
> 
> 
> Maybe try increasing the minimum following error parameter - the
> following error limit gets scaled (by velocity?) and as a result the
> effective limitmight at times be unreasonably low, so you can set a
> minimum value.
> 
> You may also need to do some servo loop tuning, and check for
> something like an offset error on your amps (assuming this is a servo
> system).
> 
> > I just finished the hard part, getting Mandrake linux, rtlinux, and 
emc up
> > and running with my hardware.  Now I have emc reportin the arm's 
position,
> > and moving the arm.  I am getting the "following error" whenever I 
move
> > either axis.  The robot also has two polar axis, but EMC is 
reporting the
> > X,Y positions as direct reads from the controller rather than 
trying to
> > interpolate the x,y based on the movement of both encoders.  
> > 
> > I'm sure there are alot of things in the ini file that aren't quite 
right
> > yet, but I don't understand enough yet to get them set right.  
> > 
> > One oddity that i notice, is joggin the x, y axis in one direction 
moves
> > very slowly, while the other direction takes off like a racecar.  ( 
any
> > particular setting that effect this)?
> > 
> > Anyone have a good Angular sample ini file?
> > 
> > --
> > Granville Barker
> > 
> > 
> 
> 
> -- 
> Christopher C. Stratton, stratton-at-mdc.net
> Instrument Maker, Horn Player & Engineer
> 22 Adrian Street, Somerville, MA 02143
> http://www.mdc.net/~stratton
> NEW PHONE NUMBER: (617) 628-1062 home, 253-2606 MIT
> 
> 
> 
> 


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