Position based data acquisition using up down counter

[vprab]

Hi

I need to implement angular position based data acquisition. The air bearing spindle has a A, B and index output so I am guessing I need some circuit to count pulses and when the number reaches a specified value (specified by me) to output some kind of trugger signal that I can use for my Data acquisition device.

Is that correct and is there off the shelf hardware that I can get to do this?

Thanks

 

[itsmoked]

vprab; While not hard what you ask is not "simple" as the A and B indexes must both be monitored so the counter knows which direction the spindle is turning. If you don't care about direction then one will do.

Google "pulse counters".

You will need to know the voltages, and the pulse rate at your rotational speed.

What kind of display?
Does it need to be absolute?
Resettable?
Panel mounted?
What available power do you have?
Viewing ambient?

 

[cswilson]

Many full-fledged servo controllers (including ours) can do this easily, usually as an adjunct to the actual servo control. That may not be what you had in mind (or in your budget), however.

You are asking for three functions: quadrature decode, pulse counting, and "position compare". There are many chips that can do some of these. The HCTL-2016 (which I worked on many years ago) is a quadrature decoder & counter IC, so it does the first two. It does not provide a good solution for the third.

The Genapta GEN-2212-5 is also a quadrature decoder and counter chip, but it permits you to use just the decoder portion, outputting "pulse-up" and "pulse-down" signals. You can put these into standard counter chips (cascaded as necessary to get enough bits to cover your range) that can be set up for transparent output of their count value.

Next, you will have circuitry that you can write to that will hold and latch the numerical count value where you want your measurement. Each bit of the latched output is "exclusive-ORed" to the corresponding bit of the counter output, and the outputs of all of these XOR gates are ANDed or NANDed together to create your acquisition signal.

Your biggest decision is what level of integration you want. It is not hard to put all of this logic into a single CPLD or FPGA.

Curt Wilson

 

[vprab]

First thanks itsmoke and Curt appreciate your help.
I am a mechanical guy as you can tell from my description of the task at hand.

Curt: I think you got the jist of what I wanted to do. Budget is not a huge issue. I saw plenty of CPLD's that can decode but I need it to go one step beyond meaning I need it to output a pppulse when the targeet number of counts is met

Genapta GEN-2212-5 is a chip that decodes and usually what happens to the output of the chip, it goes into some kind device right?
I dont even care if it is absolute as long as I can set it relative to the index, for e.g when the position is set to say encoder count # 1000 relative to the index.
When that happens I need some kind of trigger pulse that I can use as a trigger input for data acquisition.

Thanks

 

[cswilson]

The GEN-2212-5 has an internal counter like the HCTL-2016, but it also produces signal outputs directly from the decoder circuitry. The internal counter is not of much use to you, because you cannot get direct access to it for "compare" purposes. However, if you take the "pulse-up" and "pulse-down" signals it outputs from the decoder and feed these into a compatible TTL or CMOS up/down counter IC (I don't have a databook handy to suggest a particular part number, but it should be easy to find), you can use the counter IC's output to compare to your desired value as I suggested.

A couple of points:

If you want the position relative to the encoder's index pulse, you can use the index signal to reset the counter.

As itsmoked pointed out, if you are going only in one direction (and you do not mind only one count per encoder line instead of four), you can dispense with the quadrature decoder and just feed one of the lines directly into a counter IC.

I might not have made it clear that putting all of this logic into some kind of programmable logic IC is an alternative strategy to the above. The digital logic is not difficult, but it does take someone who is familiar with the discipline.

Curt Wilson

 

[Barry1961]

http://www.redlion.net/Products/DigitalandAnalog/Counters.html

These people have a good selection of counters and rate meters that take encoder input.

Barry1961