Linear Encoders anyone?

[smackaay]

 So, I've been trying to design some measuring instruments in quantities of say 100 or so and I'm finding that getting linear encoders that meet my specifications are difficult to find. I was wondering if anyone has stumbled across something that might be useful because it's been an arduous journey thus far. I have found glass scales and stuff but they draw way too much power, are too large and are difficult to implement mechanically.

My criteria are:

Current draw 20ma or less
good resolution/accuracy (.0005" inches or even .0001")
Reasonably small size so its easier to implement since this is a handheld tool.
a bit of environmental protection or resilience.

I've found some stuff from austria microsystems that might fit the bill in the form of a magnetic encoder but the error on the magnetic strips is pretty high.

Has any found, let's say, some excellent solutions, kind of like digital caliper sensors that are really low power, perhaps absolute or that meet the criteria? Any help is greatly appreciated.

[AlfBaz]

All I can think of for precision linear position measurement are Linear Variable differential transformers (LVDT)

[AlfBaz]

I remember reading an app note in an old National Semi Linear Applications Handbook that I have and just found it its AN-301

May be a little dated but gives you an idea of how to drive one

[elCap]

You might find something here http://www.renishaw.com

As for LVDT there ones available with built in signal conditioner. Very easy to use, just apply voltage and read out a voltage prop to position.

this from NI that might be useful: http://www.ni.com/white-paper/3436/en

[fcb]

I've used the AS5304 from Austria Microsystems (www.ams.com) in something similar. 

[DenzilPenberthy]

I'd second having a look at Renishaw, they make all kinds of amazing encoders.

http://www.renishaw.com/en/position-encoders--6331

(But then I used to work for them so I would say that, wouldn't I?)

 

[Hypernova]

Another vote for Renishaw from work too (linear servo motor), their sub micron resolution scales are pretty $$$ though.

[robrenz]

digital caliper sensors that are really low power, perhaps absolute or that meet the criteria? Any help is greatly appreciated.

I have built hundreds of units using the guts of the Mitutoyo absolute calipers to be used in an industrial environment. I build custom cases to house the electronics that are air purged and I just cut the scale bar off of standard calipers. In my case the customer wanted the visual display just like the caliper but if you need to interface you can use the SPC output versions and access the positional data.  The other great thing about these is they only need to be absolute zeroed once. Rezero is only needed when you change a battery which is about 2 years life.

[N2IXK]

LVDTs are excellent for precision linear measurements, and there are single-chip signal conditioning solutions available. Check out the AD598 and AD698 from Analog Devices.

[smackaay]

I looked at a lot of solutions, but never Renishaw. They have some good encoders. Thanks everyone!

[AlfBaz]

I have built hundreds of units using the guts of the Mitutoyo absolute calipers to be used in an industrial environment. I build custom cases to house the electronics that are air purged and I just cut the scale bar off of standard calipers. In my case the customer wanted the visual display just like the caliper but if you need to interface you can use the SPC output versions and access the positional data.  The other great thing about these is they only need to be absolute zeroed once. Rezero is only needed when you change a battery which is about 2 years life.

What a fantastic and cheap (if you dont use Mitutyo) idea... Filed away for future reference 

[jeroen74]

MicroE Systems is another one. At work we use one of their sensors for micrometer precise positioning. Expensive stuff.