Re: [CAD_CAM_EDM_DRO] Laser mouse based DRO

Peter Reilley wrote:

>That is only part of what you need to know. Is it linear over
>the movement range? Do you get one pulse for exactly .0005
>inches movement over the entire distance? The word "about"
>should tell you what you need to know.
>
>If you move it exactly 4 inches and move it back 4 inches
>to the counts cancel? Not likely.
>
>Interference is used all the time to measure distance. That is how
>the step and repeat type integrated circuit production equipment position
>the exposure masks. Interference works very well at those
>resolution. It does not work accurately at the price of a laser mouse.
>
>Pete.
>
>

This doesn't work on interferometry - it's an optical image sensor that
processes successive images to find displacement. They're probably just
using a laser to get higher intensity illumination and less divergence.
It's a 30x30 pixel array, and it looks like it has 64 gray levels. The
data returned is a displacement since the last data frame, and the frame
rate is programmable (they have charts that show it as high as about 7.1
KHz)

The displacement measurement was actually the maximum error (difference)
between the two axes, when the mouse was being moved at a 45 degree
angle, and it looks like the maximum was around 10 counts (ignoring the
photo paper test they did).

I'd bet that the real problem (other than the mouse effectively being
useful for a single axis) is that the laser and sensor aren't meant to
be powered continuously. Mice usually go into low power mode after a
few seconds, and then turn on once they detect motion. I'm not sure if
the detected motion gets passed to the computer or not, and even if it
is, is it at at the same resolution / response speed.

- Steve