A decent parabola would require a rather large billet to start with, and a lot of material to be removed. I agree that it would be a good test.
The proposed test came out of a discussion of quantization error, which intrinsically prevents a hexapod from cutting a smooth plane, unlike a Cartesian machine which could cut a perfect plane.
What I was curious about is how to measure the small-scale deviations from the desired shape. Isn't this property called surface roughness? What is a simple way to measure surface roughness?
-- Carl
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At 11:44 AM 9/4/2006, gran3d wrote:
Yes, a flat plane and a bowl are excellent tests for a hexapod. You
might also include a parabola. The focus point would be a good (if
analog) measurement of both the overall shape and the surface
roughness. Use it to reflect the sun onto something. The fuzzyness
would reflect the roughness. The evenness would reflect the shape
accuracy.
Carl Mikkelsen wrote:
What are good ways to measure surface smoothness? It would be
interesting
sometime to attempt to cut a plane, and see what the error actually
is, and
somehow estimate what portion is quantization related, vibration
related,
calibration related, and simple actuator error related.
One test I can think of is to try to cut a "bowl", the inside of a
hemisphere. I
would think a lot of motion artifacts would show up in that, especially
stickiness
or backlash in the struts.
Jon Elson
