Anyone with experience with this sensor?

[Tim Wescott]

http://www.murata.com/catalog/r50/r50e15_l0595.pdf

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

 

[Mark F]

http://www.murata.com/catalog/r50/r50e15_l0595.pdf

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.

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

 

[Winston]

http://www.murata.com/catalog/r50/r50e15_l0595.pdf
(...)

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?

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

 

[John Larkin]

http://www.murata.com/catalog/r50/r50e15_l0595.pdf

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.

John

 

[James Waldby]

http://www.murata.com/catalog/r50/r50e15_l0595.pdf

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 [snip]

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.

 

[John Fields]

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.

 

[donald]

http://www.murata.com/catalog/r50/r50e15_l0595.pdf

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

 

[Backlash]

Why is everyone always picking on me?

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

 

[Mechanical Magic]

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.

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.
http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=623

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:
http://www.usdigital.com/products/e4p/
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.
http://www.drillspot.com/products/36865/Dayton_1F560_28_28_Washdown_Uhmw-PE_Bearing
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

 

[John Larkin]

---
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.

Thanks. That was very helpful.

John

 

[Mark F]

We have clearance to do so... /m

Why is everyone always picking on me?