No contact encoder

[jim bcp]

I'm an inventor not an electronic engineer. I have a prototype using a slotted spring loaded reel with a cable and optical coupler as an encoder. I would like to change this encoder for a no contact encoder similar to what is in an electronic tape measure. It has to be low priced in order to keep the cost low enough to be able to market the finished product. I am working in approximately 12" range and have to have accuracy of approximately 1/16 of an inch.
Is there any thing on the market that will do this at a reasonable cost?

 

[KrisBlueNZ]

An "optical coupler" _is_ a non-contact device. Have a look inside an old mouse - the type with a ball. The ball rubs against two axles, each of which has a slotted wheel, with LEDs shining through the slots and two offset phototransistors detecting the light. A simple microcontroller performs quadrature decoding to work out the speed and direction of rotation of each wheel. Google how does a ball mouse work for more details. This might give you some ideas that you can use.

Otherwise give us more information and you might get a more helpful response.

P.S. Welcome to Electronics Point

 

[shrtrnd]

Yeah, it's a little difficult to visualize your application.
It sounds to me like you want an optical encoder wheel assembly.
It's a wheel with slots in it, the optical reader counts the slots that pass through it.

 

[davenn]

An "optical coupler" _is_ a non-contact device

Yeah, it's a little difficult to visualize your application.

what Kris and Duke said

you already have a non contact system ... why isn't it good for you in your application?

give us all some more clarification

cheers
Dave

 

[jim bcp]

I tried to keep my first post brief, I guess I kept it too brief.

I am using an optical coupler in the prototype and it works real well. I can understand that the optical coupler is considered a non contact in itself, but as I'm using it, the cable that turns the slotted reel is connected to another part of the machine. This is what I want to eliminate. The product is an aftermarket item to be installed possibly by the owner of the machine so installation has to be simple.

The other problem is for me to realize any income from it, I have to license it to a manufacturer. The people I've talked to won't license it with the cable encoder. There is a good chance they would license it if there were no moving parts. So what I'm trying to do is replace the optical coupler encoder with a sensor similar to what is used in the electronic measuring devices like you can measure a room with. I know I'll need a more refined sensor to get shorter distance and much more accuracy. It has to be low cost in order to keep the overall cost low enough to sell the end product.

The encoder has to be mounted on a moveable lever and use a fixed part of the machine for a target. The range would be approximately 12" and we need a signal sent to the processor at approximately every 1/16" of movement.

 

[shrtrnd]

Hmmm,
Your assembly already uses what I was thinking, it's just cable-operated, and you
want to eliminate that. My thinking is that the original design used the cable because
that was the cheapest way to do the job.
I suspect you're worried about somebody stealing your idea, so you're not saying much
about the details. I have a lot of questions running trhrough my mind about your physical
configuration. So that confounds me.
I was thinking proximity sensor or hall effect switch, but those don't sound like they'd
work for this, and they might be more expensive than what you've got.
I'll think some more about this, but maybe somebody else will get back to you with
better ideas later.
I guess what throws me the most, is the cable/slotted wheel encoder. Is the reason
for the cable is that the cable itself measures a physical distance?

 

[shumifan50]

Have a look at this design.
PIC based tape measure

 

[jim bcp]

I have a patent on my project but if I change the encoding portion of it I'll have to apply for a new patent. So, I'm trying not to expose the whole project. I have a large company interested if I can make it work without the cable. If I could find a good reliable company that I could work with and they would sign a non-disclosure agreement, I'd reveal the whole project to them.

Visualize a machine with a moveable lever. We mount the encoder portion of our device on the moveable lever and anchor the cable to a fixed portion of the machine. Then we have all the rest of the electronics (display, switches, etc) in another case also mounted to a fixed portion of the machine. The whole objective is to know where the lever is at all times.

The PIC based tape measure is along the lines I have in mind. Is it possible to get this to work in a range from near zero up to approximately 12" with accuracy of approximately 1/16"?

I don't need a lot of what is in the tape measure. We already have a processor, display, switches, etc. Is there any off the shelf items that would work or is there any manufacturer that would build a custom unit? As is now, the cable driven slotted reel with the Honeywell optical coupler is all there is in one case. All the rest of the electronics is in another case with wires between them. It needs to stay this way.

Thanks for all the help.

 

[shrtrnd]

I'm still thinking.
Optical seems like the best way to go, but;
Look up LVDT (Linear Variable Differential Transformers), and see if that might work?
Still thinking of possible Hall Effect Switches, or even microswitches, but you want
accuracy at 1/16". Still thinking, ....

 

[shumifan50]

Found another idea that could be set up to be more accurate, but it needs reflection from the lever, so the surface it is aimed at cannot be too small and has to reflect the IR. Sensitivity can be adjusted by moving the transmitter IR LED and the receiver further apart. Instead of the Atmel with a separate ADC you could use a PIC with the ADC built in.

Have a look here:
IR Distance meter

They do not specify its accuracy, but as it measures the reflected IR intensity, this can be adjusted as described above and adjusting the brightness of the transmitter and by using transmitters with different focus. Also the lever tilting will cause more deflection for less movement which can also be used to increase sensitivity.

 

[jim bcp]

It looks like the LVDT, Hall Effect and micro switches all would require connecting to the fixed part of the machine. This is what we are trying to get away from.
The IR distance meter looks promising.
I think it has to be some type of optical or laser.?
What does a digital camera use for auto focus?

 

[shumifan50]

It is infra red which is 'light' at a wavelength we can't see. It will not work where there is lots of light around as light has an IR component that could confuse it.

 

[jim bcp]

Bright light should not be a problem in our application.

 

[(*steve*)]

What does a digital camera use for auto focus?

There are many methods.

One of the simplest early methods was to have a sensor that was essentially a pair of optical detectors. When the difference in intensity between them was the greatest, the image is in focus. This doesn't lend itself to an exact measurement of distance, rather it tells you if you're in focus or (if close) moving closer or further from it.

Incidentally, this is why early cameras might be able to focus on vertical lines, but not horizontal ones. or vice versa.