Wednesday, April 11, 2007
Monitoring the x-axis drift
A few days ago I put in firmware code that kept track of the absolute value (in pulses) of the end points of the line segment extrusions that Tommelise was putting down. The idea was to get a look at this x-axis drift that I had been seeing.
It's important to know that I am not attempting to recalibrate the start point for the layers with each new layer, so errors are additive to an extent.
The pulses are right at 0.007 mm. I got up to layer #4 before the the line last line segment forming to square on the -x side fell off. This meant that the extrusion thread was 0.13 mm off centre. At first blush, considering that the thread as put down is right at 1 mm wide one wouldn't think that this should have caused a problem. I am, however, putting down a bit more polymer flow that I probably should. That seems to create a side thrust in the extruded HDPE from observation. It would appear that that makes alignment a bit more critical than one would ordinarily expect.
Note also the sudden shift to the left at layer 8. I'm still trying to figure out what that is about. My first impression is that it is a firmware coding problem associated with trying to figure out when to stop the gearmotors when one of the xy axis gearmotors exceeds its boundary goal.
Both the shifts and the degree of shifts match what the print layers actually look like.