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Comment by anxman | Hacker News Reader

Yeah IMO the Compass appears to be a more convenient design

The reason Origin uses tape is to maintain precise, absolute registration over large distances - so that you can for example machine a pattern the size of a kitchen table.

I am very skeptical you can have that level of registration with mouse-style sensors that can only measure relative motion. I might be wrong, but it seems unlikely.

Yeah mouse sensors actively throttle update frequency at slow speed to mitigate drift, as they appear to suffer pretty much random walk steps of sort each time they generate an update. Exceptions are probably limited to zero-motion deltas.

Mouse sensors also only output x/y displacements, not rotations-- even though their mechanism of operation would allow it. I assume that's why this device uses four of them.

There are inexpensive mouse sensors which are made for long distances for use on drones. Sadly they're also still limited to x/y... might be useful for compass to have some upward facing sensors to track the ceiling, but maybe losing track isn't that big of an issue in practice.

The issue isn't an instant loss of tracking, but gradual accumulation of quantization errors from subpixel-alignment of features and similar "drift" sources.

Don't get me wrong: mouse sensors are great for use in closed-loop control of business ends that don't require stiffness to work (compare to CNC mill chatter) like 3D printers or these handheld wood routers. You just want some way to anchor back to absolute coordinates or drift will be painful. Note mouse sensors are more accurately described as measuring visual rotation than translation: focal plane distance in gaming mice has a linear influence on reported distance/"effective dpi".

It shouldn't need to be fast to anchor the drift if you track the drift rate/scaling coefficients appropriately. Maybe they are using a mouse sensor there in bitmap camera mode, possibly rotating through their fleet of 4, together with a sufficiently-beefy computing system that keeps a map/atlas of the object's surface texture to find/match the captured bitmaps in.

The Origin also talks about repeatability. They sell a fixture that has an image of the tape fixed along with positive stops. The idea is that you can batch out parts quickly by setting up a workspace and swapping parts in. No idea if these sensors would be able to do something similar.

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