Adalbert wrote:For my second quick test I have chosen the step-size 10µm, 5 steps forwards and 5 steps backwards.
This graph is clearly on the path toward what we are expecting. From here, doing just the center third, with steps about 30 times smaller, should show the backlash region clearly.
As far as I can see the size of the steps depends on the direction?!
Yes, it looks that way.
Of course the appearance could be either unexpected movement or some problem with the measurement.
In this case I expect the measurements are correct. Assuming this is camera resolution at 20 megapixels, then xoffset shifts of roughly 0.01 will be a couple of hundred pixels. It is very unlikely that there is any significant error in the alignment process with such a large shift, but you could check that in ZS by putting a checkmark on "Show as adjusted" in the Input Files panel, then clicking back and forth between adjacent frames to confirm that after alignment the images match.
At this point, my guess is that the precise step size varies depending on how the gear teeth happen to be engaged at each position. For your first graph, I wrote that "the second half of the movement curve looks like what I would expect from a gear-driven system.
" Here is what I what I was referring to in that comment:
This sort of repeating pattern is typical of what happens as successive teeth engage and disengage. I expect what we're seeing with this fast/slow alternation is a more exaggerated instance of the pattern shown in the first two "cumulative movement" graphs at http://www.photomacrography.net/forum/v ... 119#170119
In your latest graph with 10 points, the two directions may be different because different faces of the gears will be engaged.
The pattern would be more obvious with more data points. But note also that when you re-run the experiment, the pattern may be different if the screw starts in a different position. You can see from the last two "Deviation From Linear Distance" graphs at http://www.photomacrography.net/forum/v ... 119#170119
that the pattern of step sizes can become very complicated depending on what scale and where in the pattern you happen to be looking.