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.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html
Reply to
Tim Wescott
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I've seen them, clearance to the shaft is, um, slip fit. Something, somewhere, has to sorta float. Coilspring couplers? Bigger clearances at the "other" end of the shaft? Backlash really the only concern with slop... Bit of grease in the D will also help with clearance vs. backlash. /m

Reply to
Mark F

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Can you design so that the sensor is soldered on to the PCB *after* the shaft is installed? That would remove most of your tolerance buildup.

--Winston

Reply to
Winston

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

--
Depends on the thickness of the board, the finished diameter of the
hole (which depends on the tolerance on the diameter of the hole and
the tolerance on the plating) and the tolerance on the diameter of
the shaft.
Reply to
John Fields

The data sheet states "Rotational Life" 1M cycles.....

On page 61:

Rotational Life : The adjustment rotor should be continuously rotated within ±160° of effective electrical rotational angle, at the rate of one cycle for

6 seconds for 1 Million cycles under the condition of +25±2°C of temperature without loading.

I think this is used only in slow hand operated applications.

Let us know how it works for you.

donald

Reply to
donald

Why is everyone always picking on me?

Reply to
Backlash

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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parts 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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You 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

Reply to
Mark F

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