What's inside a Digital Micrometer?

Lots of info about how digital calipers work but I cannot find any description of the internals of a digital micrometer.

Do they have a rotary encoder in conjunction with a conventional screw or is there a high resolution linear encoder?

Just curious.

Ian P

My guess is a rotary encoder of some kind.

Hopefully someone who's dissected a broken one will be along in a minute.

Neil

My mitutoyo has a screw and must have a rotary encoder I think. I used to work for a company that developed the first digital micrometer for Moore & Wright - it used sliding glass moire scales, and no screw. Created a bit of a sensation at the time but proved to be a damp squib, rather unreliable I think.

My digital mic had actual numbers on 3 rings that counted (like a speedo) so was purely mechanical!

Alan

mitatoyu or whatever...

normal micrometer screw with shaft encoder built round [splines]

encoder does pulse generation asic does count and display

The micrometers that I have seen use a capacitative encoder like the digital caliper but circular, not an opto or magnetically coupled encoder which would use a lot more power. The stator has many electrodes that capacitativly couple to a rotating pcb .

With this scheme the counting circuits are powered all of the time so that the device "remembers" the number of turns from zero to save the user having to mechanically reset the micrometer to the anvils together position.

So turning the device on only powers up the display but it will draw a very small current when switched off, Mitutoyo's have a very low standby current compaired with some other brands.

Billy.

Billy

That make sense, thanks for the explanation.

I wonder if the tolerance and fit of the threaded components is considerably better than a normal mechanical micrometer? to get a 0.001mm resolution implies an encoder with better than 1000 counts per revolution. Whilst the encoder can easily resolve 1/1000th of a turn the thread has moved forward so little distance, that any play, or even the lubricating oil thickness, might have an influence on the measurement.

Ian P