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Positional accuracy for opto detectors

I want to use some IR opto transmitters and receivers to detect positions of a pivoting sector plate. The transmitter is attached to the sector plate, and the receivers are attached around the fixed plate. At the interface between the (motorised) sector plate and the fixed plate, the sector plate is intended to move at approx 5mm/s. (The sector plate is approx 1000mm long.) Here's a rough sketch:

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I need to detect the position to within 1mm, preferably less. Owing to the comparatively generous beam angle of most common optos, I am therefore thinking that some thin vertical slots in front of the receivers, and also possibly the transmitter, will be necessary to obtain the required detection accuracy.

Before I go ahead and try some bits and pieces, and play around with transmitter-to-detector and device-to-slot distances, do you think this approach is viable? And if yes, what kinds of distances do you think I should be starting to experiment with?

regards Russ Elliott

Reply to
Russ Elliott
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Russ Elliott wrote: ...(clip of some details)...

Yes it's viable, depending on the sensitivity of the receptor. Distances . . . let see. You need a resolution of 1mm, right? So that's how wide the beam has to be (maximum) as the sector plate interrupts it, right? So, do some trig. How far is the sector plate going to be from the slit aperture and how far will the slit aperture be from the IR LED? And how wide is the slit aperture going to be (has to be substantially less than 1mm)?

Mark 'Sporky' Stapleton Watermark Design, LLC

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Reply to
Sporkman

Depending on the inertia of the sector arm, this should be viable. You might want a gap under 10 mm.

Or if you incorporate a laser diode instead, almost any gap would be viable.

Brian W Altus OK

Reply to
Brian Whatcott

Slots of 1mm width should be about right.

Be sure the part that's supposed to break the light, e.g., between the slots, is made of, or covered with, metal. Even black colored plastics are transparent or translucent to infrared.

Use Schmitt triggers in the detector circuits.

For finer resolution, put a disc with one slot on the motor shaft, and an emitter/detector pair straddling that. Depending on the drive ratio, this may give you more than one motor position pulse per sector slot pulse, so you may have to narrow the sector slots.

-Mike-

Reply to
Mike Halloran

Use an blade to interrupt a modular opto-interrupter. Omron ee-sx671 modules are good for around a micron repeatability if the edge is sharp and the velocity is constant.

Reply to
Jeff Lowe

Sporkman wrote in news: snipped-for-privacy@bigfootDOT.com:

I've lost the OP, but why can you not use a readily available commercial encoder? That is seemingly what you are trying to build. You can get them in a variety of resolutions, either absolute positioning or incremental with a zero pulse.

Reply to
Anthony

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