The X and Y axes of my system have a step by revolution of 5mm.X axis two rails 500 mm, 5 mm / rev, direct drive, each shaft an motor.
Y axis one rail 500 mm, 5 mm / rev, direct drive
Z axis one rail 250 mm, 4 mm / rev, drive with reduction 10: 1
The Z axis has a 4mm revolution step, but it has a 10: 1 reduction.
therefore the precision in the X and Y axes is 0.025 (5mm / 200 step motor) and 0.002 (4 / (200 * 10) micrometers in the Z axis.
I advise you to install these reducers in all axes, in fact I am about to do it. Not because more resolution is necessary, but because you will have less vibrations.Accuracy X axis = 5/200 = 0.025m
Accuracy Y axis = 5/200 = 0.025mm
Accuracy Z axis = 4 / (200 * 10) = 0.002mm
Although the vibrations only occur when they move from one point to another. My program after each displacement, and before taking the picture, stops the time I want in order to eliminate the residual vibration of the movement.
I have more problems with the trains that pass near my house than with the vibrations of my system.
In my program, I always attack movements in the same direction in order to eliminate backlash problems in X and Y axes. But for these axes is not important: what does a change in the overlap of a few microns or so in a field of 5 or 6 mm matter ?.
No, I have not detected that kind of problem. Yes on the Z axis, but I think it's because I had an accident when I was assembling the robot. The table, in which the robot was, collapsed and the Z axis was hit against a nearby shelf that started the bearings of their guides ... and the same I think the screw was deformed.Despite this I can work perfectly in the range of the magnifications in which I work.mawyatt wrote: With your setup do you notice any backlash or wobble (side to side tilt or motion) of the rails, and what pitch are the screw threads?
Here I show you the error that produces the displacement of the Z axis. What you see is the trace that makes a bad pixel in the set of photos of the stacking of the Bryozoa. The HFOV is 8mm. They are 25 pixels in one direction and 68 pixels in the other. this represents an error of 0.04mm and 0.11mm. On the right side you can see the artifact generated by Zerene when making the automatic adjustments (X, Y)
Since the robot can withstand relatively high weights, you may feel more comfortable if you mount a double guide on the Z axis.
Put in any search engine "cnc Z axis slide" and you will see many options.
Just as an example: