Dynomotion

Group: DynoMotion Message: 774 From: judrandom Date: 12/6/2010
Subject: Motor not moving correctly
Hi Tom
Its been awhile but my machine is finished and all motors are running.
I have had good results with the motion on axis 0 and 2. The axis 1 motor is causing me some issues. I believe this is the one i had to have repaired. Whats happening is the motor will move a number of counts and then not move back the same distance in the reverse direction. It is that way on the step response screen and the g-code screen. When I try to turn the shaft with motor on it acts very funny. The motor will sometimes act as if its trying to fight me then jerk a quarter to a half turn out of position but still read as if the encoder counts never changed. Sometimes it will just turn a couple revs but still show the same encoder count and think its in the correct position.
I thought maybe the encoder but when I disable motor power the encoder counts perfectly when turning by hand. Then I thought wiring but that seems correct also. So here we go. ]
Could it be the motor?
Maybe the axis is losing count or has an error at the board?
Can I use the 4th axis in place of the 1st and still call it Y in the g-code screen?
That is just to test the motor axis.
Could it be a setting?
The motion is not consistantly off it verys greatly.
Maybe something I havent thought of?
I know nothing is slipping mechanically.
Thanks again Tom.

Judleroy
Group: DynoMotion Message: 775 From: Tom Kerekes Date: 12/6/2010
Subject: Re: Motor not moving correctly
Hi Judleroy!
 
Well it definitely appears to be an encoder position measurement problem.  A motor or amplifier problem can not cause such a problem.  A bad motor or amplifier would cause the motor to not move or move too much and then the DRO would be way off.  Either the encoder itself, the wiring, noise, or the KMotion encoder input are possibilities to cause a position measurement problem.  From the way you describe it sounds like the quadrature counts just drop out for a while.  If you were to plot the Commanded and measured Position on the Step Response Screen if you see "flat line" conditions where the encoder suddenly stops changing for a while that would be a big clue.  Sometimes the encoder read head alignment for is very marginal such that it works ok under no load (when turning by hand), but under torque it goes out of alignment.  A simple test would be to swap the x and y axis motor/encoders to see if the problem moves with the physical encoder.  Or yes you can use amplifier #3 (instead of #1) and encoder input #3 (instead of #1).  Just move the wiring and change the input and output channels for axis #1 (Y) from 1 to 3.
 
Regards
TK