Anyone with experience with this sensor?

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I want to use this in an application where I have this on a PC board,
engaging a shaft. My problem is one of tolerancing: I'd like to have a
tolerance stack-up that just lets me just assemble the whole unit and
have it work, without adjusting and without the shaft binding up on the
pot. But the part doesn't come with any mechanical specifications for
the radial tolerance of the shaft, nor does it come with any guidelines
for using the pot as a bearing (so I assume that's a big no-no).
I got samples and looked at one under a microscope -- it appears that the
rotor can move about 0.005" in any direction before it touches the case.
Using "don't touch" as a guideline, I end up with tolerances that drive
my mechanical assembly costs through the roof. I can't imagine that's
the intended way to use this -- it's for consumer products, so there's
got to be a way to make it happen.
So, how do people make these things work as rotary position sensors? Is
there a mechanical specifications document buried on the MuRata web site
that I'm missing? Is there a cost-effective shaft coupler to be had
that'll couple the angle without coupling off-axis motion?
Comments, advise, brickbats -- all are appreciated.
Reply to
Tim Wescott
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Is there only one on the board? If so, keep the pcb mounting screws loose, insert the shaft, tighten screws.
What's the application?
Hmmm, I wonder how good a plated-through hole works as a bearing.
John
Reply to
John Larkin
Interlocks and sensors like this that I've seen on printers and disk drives typically depend on cheap and accurate injection-molded plastic parts. E.g, item is at end of wire, mounted in a molded pocket; or item is on a little PCB that sits in molded grooves or is located by molded pins and fastened by a screw, a plastic catch, a metal spring, or a live (molded plastic) spring. Molded plastic parts for your purpose aren't off-the-shelf items. You probably could hold a small PCB in place good enough with extension springs at each corner.
Reply to
James Waldby
>> >>
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>>I want to use this in an application where I have this on a PC board, >>engaging a shaft. My problem is one of tolerancing: I'd like to have a >>tolerance stack-up that just lets me just assemble the whole unit and >>have it work, without adjusting and without the shaft binding up on the >>pot. But the part doesn't come with any mechanical specifications for >>the radial tolerance of the shaft, nor does it come with any guidelines >>for using the pot as a bearing (so I assume that's a big no-no). >> >>I got samples and looked at one under a microscope -- it appears that the >>rotor can move about 0.005" in any direction before it touches the case. >>Using "don't touch" as a guideline, I end up with tolerances that drive >>my mechanical assembly costs through the roof. I can't imagine that's >>the intended way to use this -- it's for consumer products, so there's >>got to be a way to make it happen. >> >>So, how do people make these things work as rotary position sensors? Is >>there a mechanical specifications document buried on the MuRata web site >>that I'm missing? Is there a cost-effective shaft coupler to be had >>that'll couple the angle without coupling off-axis motion? >> >>Comments, advise, brickbats -- all are appreciated. > >Is there only one on the board? If so, keep the pcb mounting screws >loose, insert the shaft, tighten screws. > >What's the application? > >Hmmm, I wonder how good a plated-through hole works as a bearing.
Reply to
John Fields
Tim, I'd fab the board using the thru hole pot. Keep the PCB mounting holes loose.
Assemble bearings, shaft, etc, and loose PCB.
Attach alignment fixture, this fixture has 2 dial indicators one measuring X the other Y.
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Move the board by hand to the middle of the travel, tighten screws. Should take under 30 seconds and be within .001" of perfect position.
Remove alignment fixture.
I have used these:
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are very intolerant of misalignment, it's all important to have the correct alignment tools and fixtures.
Also, if you use flange mount bearings, with loose mounting holes, it's easy to have +-.015 tolerances on your parts, while having assembled accuracy of .002" with ease. Like these.
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could do this in Rulon, with positional accuracy of .010", and a reamed hole for next to nothing. Then, when it's time to secure the bearings, you use a fixture to hold the shaft in the exact location tighten fasteners. Remove fixture. Now attach PCB as above.
Dave
Reply to
Mechanical Magic
Thanks. That was very helpful.
John
Reply to
John Larkin
I concur.
Gunner
Reply to
Gunner

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