IR Encoder

AIman

Question on using IR with encoders.

I was looking at the options Parallax has for IR because I want to create a specific encoder for a project, however I cant find information on how fine a point the transmitter can transmit or the receiver pick up.

Taking this back to a very basic encoder I have is the best way to explain.

I have a very basic encoder that has gear teeth stamped around the edge which are supposed to interrupt the transmitters beam and indicate to the receiver a count. However to encoder I want to use is much more refined and has many more places to turn the receiver on and off. I need to be able to focus the IR beam from the transmitter to be able to work with much better refinement and / or be able to refine the location the receiver picks up the light. So far I haven't found anything and am looking at having to make a tube with one end narrowed and a slit in it and attach it to the transmitter and / or receiver.

I am looking for millisecond resolution if possible without getting into commercial grade and the fragile glass or expense. Does anyone know the speed and resolution of the IR transmitters and receivers?

erco

Numerous inexpensive break-beam or reflective encoder sensors are available. My favorite reflective type was just on Ebay: http://forums.parallax.com/showthread.php/149740-Rare-Wheel-Encoder-Sensors-Available-Strike-Now! That sensor has internal circuitry (ie, filters & Schmitt trigger) which is very useful.

I used two of those at https://www.youtube.com/watch?v=VmNc_V5jdPE with a humble BS2, which kept up fine at 394 pulses per second. But that was a quad encoder with two sensors, so each sensor was only measuring ~197 pulses per second (5 ms resolution). I'm sure the sensor can go faster, the BS2 was the limiter there.

Duane Degn

I don't think it should be hard to find an encoder capable of 1ms resolution. As erco suggests, you might have trouble reading the sensor fast enough with a Basic Stamp. What microcontroller do plan to use?

Erco got me hooked on these encoders. They're not the break beam sort (though they would probably could be made to work that way).

SparkFun sells these. They should be able to easily achieve 1ms resolution.

AIman

I am working on a project that will need encoders or steppers run through an Arduino board. I have to be able to have accuracy and repeatability coupled with smooth motion. In addition this will be entering an oven that has extreme heat (like 700 centigrade). So the need to be able to control the location is important and the need to be able to control a tong that enters the oven is critical.

I have been thinking of getting a propeller chip or a BS2 and doing everything from the ground up but I have 6 weeks to get this done and this is week one. The other item is that the budget is restricted because of the end user sales price.

Genetix

Stepper motors are very repeatable if the torque and pulse rate are below specifications. Under these conditions an encoder is not needed.
If the torque needed is too high or the pulse rate is too fast then the Stepper will "skip" steps and an encoder allows the microcontroller to detect missing steps.

Finding the maximum torque and rate that is needed will save you a lot of trouble. Then get a Stepper as far above these requirements as you can get.
Just understand that on all steppers the torque goes down as the pulse rate goes up, so slow and steady is always the best way to go.

Another thing you could do is monitor the Stepper voltage and current because if they spike suddenly then the motor has probably stalled.

Phil Pilgrim (PhiPi)

Alman wrote:

In addition this will be entering an oven that has extreme heat (like 700 centigrade).

That pretty much rules out anything with aluminum or plastic parts! And I doubt that any solid-state electronics will survive in there. Is there a way you can couple things mechanically to the outside of the oven and read them there?

-Phil

Genetix

Phil,

Read it again. A tong will go into the oven and the motor and electronics only need to control its movement.

AIman

At this point it looks like a linear actuator is the best way to go. Even though the oven gets hot it is a small space of roughly 3" x 4" and the trick is to get the stuff out as smoothly as possible without destroying the items. Some of the pieces coming out will be balancing on a point as small as a pins thickness which is why everything must be smooth. Perhaps Teflon coated rails or something along those lines.

It looks like an actuator run by an ardunio board is the best bet because I can't find anything on the propeller having done this sort of thing. Regardless of which way I go I need to learn the language...

Right now we are looking at running rails across the front with a tong just about the level of the oven. Once the oven opens the tongs extend, lifts the item a few mm and then extracts the piece.

Coupled to this is the temp problem. Thermal couples need a reference so I am staying away from that in favor of trying to find a different way to measure temp like an IR or something of that sort. One set of items will come out at 700 C and another just above 400 C.

The parts that actually go into the oven will be either 309, 310 or 330 alloys. Most likely 309 or 310 since they are easier to machine. The weight will be up to 600 grams and as indicated the movement must be very smooth.

However the hard part is trying to locate parts that aren't over budget. There are a lot of parts that work up to a few hundred degrees, but even getting something that reads up to 700 C is a trick.

erco

Genetix wrote: »

A tong will go into the oven and the motor and electronics only need to control its movement.

This sounds a bit like landing on the sun at night...

Genetix

Erco, sounds like your kind of thing. Mechatronics and Fire.