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Switch Contact Design Help

Switch Contact Design Help

Switch Contact Design Help

(OP)
Howdy:

Not sure if this is the right forum.

I am working on a product with a motor that has an encoder and a gearhead.  The encoder is an incremental type so I need some kind of sensor to signal every time the output shaft reaches a specific angle.  Unfortunatly this sensor must fit around a .125 inch shaft inside a .195 inch hole.

My thought is to design some kind of wiper that makes and breaks contact with the shaft.  From what I have read the biggest concern in wiper design is the effect of corresion on the contact resistance.  I am also concerned about wear because the wiper needs to last 3 million shaft rotations.

Fortunately I only need maybe 1 mA of current and also it only needs to average about 60 rpms (1Hz).

For corrosion resistance I have heard Gold plating recomended for switch wipers.  However I don't think Gold will have enough wear resistance.  Right now I am thinking maybe electroless nickel against hard bronze.

Any suggestions for wiper contact materials?  Are there any other factors that I am not considering?

RE: Switch Contact Design Help

Why not a hall effect IC and a small magnet?

RE: Switch Contact Design Help

(OP)
The problem with the hall effect sensor is that it would have to fit in an envelope of about .025 X .070 inch.  Thats smaller than the typical SMD resistor.

RE: Switch Contact Design Help

An optical switch?  You really need to stay away from contact.
I still like the Hall effect idea.  I have seen HE sensors on integrated circuits.  they can make them small.

= = = = = = = = = = = = = = = = = = = =
Plymouth Tube

RE: Switch Contact Design Help

(OP)
Wow.  The Allegro A1172 is a hall effect sensor that is .015 X .078 X .078 inch.  That is incy winchy!  I think I can make this work.  I will have to put it on a flex pcb.

RE: Switch Contact Design Help

(OP)
Just kidding.  I found three hall effect sensor manufacturers with chip scale packages, and every single sensor in a chip scale package sleeps for 50ms in between readings.  My the pulse train I am trying to catch has a pulse width of 350 us so this will not work at all.

How frustrating!

RE: Switch Contact Design Help

Have you considered a slip ring assembly and brushes?

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