Stuart Stevenson wrote: > Gentlemen, > I have the lead screw compensation working - finally. > It seems as if the compensation is applied differently depending on > which side of the nominal value the machine is on. > > I have comp in my machine as follows: > > in the X axis comp file I have > > -0.5 -0.502 -0.4972 > 0.0 0.000 0.0043 > 0.5 0.5005 0.5052 > > all the rest of the numbers from -61.5 to 61.5 have the triplets equal > - no compensation > > I am working around the point X zero > > there is about .0042/.0046 backlash in the X axis ballscrew. I have > been told by a longtime maintenance man that a ballscrew this size > will be built to have .003/.004 backlash. I don't like it but that is > another story. Maybe my experience of rebuilding a ballscrew of this > size was not the dismal failure I thought it was. > > set the machine to jog the X axis .0001 or .001 > position the X axis to -.0002 or more negative > using the + or - buttons in AXIS or a handwheel - jog the axis > positive or negative one unit of motion > the axis motion is smooth and accurate - very nice > > set the machine to jog the X axis .0001 or .001 > position the X axis to -.0001 or more positive > per above - jog the axis in the negative direction one unit and then > one unit positive > > the compensation is immediate and harsh - the table is moved (bounced) > farther than the unit - jogging the axis farther positive reveals the > ballscrew catches up with the table and the compensation is accurate. > On axis reversal you can feel the 'hit' of the compensation. > > per above - jog the axis in the positive direction one or more units > and then one unit negative - the table is moved smooth and accurate to > the indicated position - no 'hit' or impulse is felt during axis > reversal in the negative direction. > > when the X axis is -.0001 or more positive - oscillating the jog one > unit will reveal a 'hit' for every jog (axis reversal) positive and > smooth motion for every jog (axis reversal) negative. > > the compensation magnitude seems to be accurate for all motion > directions and positions > > the compensation seems to implement the tuning for all negative jog motions > > the compensation seems to be immediate and harsh (not per the tuning > of the axis) for positive jog motions on the positive side of the > nominal compensation location > > further testing reveals the exact same results when using MDI > > I will add another triplet on each side (-1.000 and 1.000) and check > the motion at -.500 and .500 > thanks > Stuart >
This calls for halscope. There are three items of interest: axis.0.backlash-corr : this is the total amount of correction to be applied. It will instantly change when you reverse direction (if the forward and reverse comp values differ, which they do in your case). axis.0.backlash-file : this is the above value, after being subjected to velocity and acceleration limits. This is the value that is actually added to the position and goes to the motor. It should never jump abruptly, if it does it points to a bug in the accel limiting code. axis.0.backlash-vel : I believe this is an internal variable of the accel limiting code, and would be usefull for debugging. Since axis.0.backlash-corr should jump abruptly on a direction reversal, it is probably the easiest thing to trigger on. If you can capture scope screenshots of a "good" and "bad" direction reversal, and post them maybe we can figure out what is going on. Regards, John Kasunich ------------------------------------------------------------------------- This SF.Net email is sponsored by the Moblin Your Move Developer's challenge Build the coolest Linux based applications with Moblin SDK & win great prizes Grand prize is a trip for two to an Open Source event anywhere in the world http://moblin-contest.org/redirect.php?banner_id=100&url=/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
