As for how often does it need to be measured, well if I go for my 'no doubt high enough' scenario of 10 microns perifferal movement, at a modest machine speed (30 feet per minute), then for the various cylinders:For all cylinder A, B and C: 10 microns pass in 0.0000656 seconds approx.D which is actually just a drive shaft (treated as a cylinder earlier to try to make it easier), has an RPM relative to A of about 1:4 (A:D).PeterH I hope that this is clearer now but if it is still not clear enough, please just say.Thanks a lot 2Tricky
In fact the printed imperfections can be around 6mm (@ 30 fpm = 0.039 approx. seconds).
Quote..I get the impression that this is more like jitter / backlash / play rather than slip (sustained gradual difference in position).If that's correct, then over what sort of timescale does this jitter occur and how small a jitter are you aiming to measure?I think you are right to think that this is the likely problem. The 6mm approx max printed imperfection is how the error shows to the naked eye and should not be taken as testimony to either the distance or duration during which the positional error exists. The trouble is, these cylinders intersect a bit i.e. the surfaces (as in plate particularly and paper to an extent) are soft, their natural relationship is never simply tangential and cannot be so because paper is not mill pond smooth and the same goes for ink with its varying viscosities and the need for a certain surface tension to the substrate (which can be synthetic) for instance. Therefore any momentary angular blip in what might otherwise be perfect motion, can appear protracted. This is very difficult to quantify because as you have mentioned, eccentricity also has a part to play. Cylinders A and C have gears that mesh directly and already use sprung anti-backlash gears and cylinder B has natural resistance caused by drag. The rest of the machine is really pretty tight I believe.QuoteI'm starting to imagine a solution based on a couple of optical mice pointed at a test pattern attached to the surface of each roller, but I'm still not sure I have understood the problem correctly, and every time you mention 10 microns it worries me.I believe that the source and duration of the mechanical error as opposed to the size of visible artifacts, is as long as a bit of string (but short!) and so if 10 microns doesn't do it, then I'm not sure what will. It's funny, I came across Arduino whilst looking for ways to hook up mice/mouses but in the end wondered whether I was asking too much when I had 10 microns in mind - I'm open minded and have become aware of the optical versus laser versus encoder rs232 debate but am aware that there are some 'pretty high' resolutions available but at what cost - I don't know.QuoteOnce you have got a number that shows there is jitter, what are you going to do with it?I would really like to view the data in real time as superimposed waves on an oscilloscope because I would like to apply 'influence' here and there and monitor the effect. If I have data, I'll simply plot it until something emerges that indicates where to next focus.N.B. Radial play is not going to exist in cylinder 'A' which is under highish radial load and has exceptional TIR or much for 'B' which I guess has no more than 1/2 thou but is also under load anyway. That said, for a small cylinder 'C' with a big solid plate mounted on it, there is likely to be no radial play whilst a bigger one with fine print might have around 1/2 thou.Thanks peterH for your interest - 2Tricky
..I get the impression that this is more like jitter / backlash / play rather than slip (sustained gradual difference in position).If that's correct, then over what sort of timescale does this jitter occur and how small a jitter are you aiming to measure?
I'm starting to imagine a solution based on a couple of optical mice pointed at a test pattern attached to the surface of each roller, but I'm still not sure I have understood the problem correctly, and every time you mention 10 microns it worries me.
Once you have got a number that shows there is jitter, what are you going to do with it?
I would be grateful for your view on hardware requirements for the 'Arduino OptiMouse library' route and hardware requirements for your preferred route too. Would they both need an Arduino board or...and which board might that be?
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