Is it possible to run encoders not in quadrature?

[Cold Fusion]

Due to some mislabeled encoders, I've ended up with some 1000cpr and some 2048cpr encoders. This means that I'm very limited as far as speeds because my pulses per inch is in the 80,000 range. Is it possible to run encoders not in quadrature with Gecko 320 drives? This would solve all of my problems and give me a decent feedrate.


PS, if anyone needs some cheap high resolution encoders, give me an email

[gar]

050728-2036 EST USA

Cold Fusion:

Since you have received no responses I have some comments.

A quadrature encoder is one with two encoder channels, one phase shifted 90 deg relative to the other. This provides a means to sense direction.

If channel A is high and B is low, and one step makes B high and A unchanged, then you moved in direction F. If on the next step B remains high and A goes low, then the direction is still F.

Starting again with A high and B low, and one step makes A low and B unchanged, then the direction is R.

Also many times quadrature encoders have a once per revolution channel. This can be very useful.

A quadrature encoder can have any one or more of its channels used, that is your choice depending upon what you want to do.

I think that the question you wanted to ask was whether the Gecko drive would work with with a non-quadrature encoder. I can not answer that question. But maybe moving this to the top will get someone familiar with Gecko to give you an answer. One possibility is that Gecko does not care and rather it is your controlling software that uses the quadrature encoder information.

With appropriate hardware and/or software you can divide down a high resolution encoder to make it a lower resolution unit. Alternatively, for some applications where a low resolution encoder is used at known speed you can get higher resolution by interpolation. We have done this in a gear ratio measuring system.

.

[Mariss Freimanis]

You are kind of behind the rock and the hard place I'm sorry to say, particularly with the 2048-line ecoder.

Almost all servodrives use quadrature inputs. This is necessary because quadrature coding carries 'direction of rotation' information. Also most drives use 'X4' quadrature decoding because this gives the position best resolution for a given line-count.

In your case too much of a good thing is not a good thing. Here's why:

A 2048-line encoder requires 8,192 step pulses for one revolution. If your motor goes to 6,000 RPM (100 revs / sec.) then you would need 819,200 step pulses per second.

Mach3 tops out at 45,000 pulses per second, our G320 drive tops-out at 250,000 per second. Why so low with our drives? Because inexpensive (under $250) encoders use photo-transistors in the encoder. These transistors have a frequency response that goes to 30kHz at best. In quadrature that works out to 120,000 counts per second.

With a 2048-line encoder that works out to a rather low 880 RPM before the encoder quits. With mach2 it's a depressing 330 RPM. If you use our G340, it only gets you the 880 RPM number.

Best bet: Go to www.usdigital.com and replace your encoders with 250 to 500-line encoders. It'll set you back about $40-$50 per motor. That is the best cure for your problem.

Mariss

[ynneb]

I guess you could also just go out and buy some Rutex cards with step multiplier switches on them.
Sorry Mariss, it was a setup I just couldnt resist

EDIT: Actually dont your new drivers also have step multipliers on them now?

[Mariss Freimanis]

Not quite so funny when you come up with a unique idea and someone else copies it. Philosophically you have to brush it off because you know dogs get fleas. It also helps to know there is always another new idea percolating. :-)

Mariss

[ynneb]

Originally Posted by Mariss Freimanis Not quite so funny when you come up with a unique idea and someone else copies it. Philosophically you have to brush it off because you know dogs get fleas. It also helps to know there is always another new idea percolating. :-) Mariss

Hmm, a very cryptic answer.
Maybe there is a story I am unaware of?

I dont know who copied who or what this all means. But in defence of copying ideas, I think if there is a good idea out there then so long as it isnt patented or copyrighted then fair is fair. That is how we all evolve.

Just think, if car manufactures didnt copy Volvo we wouldnt now have seat belts and there would be a lot more injured people. Lucky they didnt copy every thing about volvlos though

I would love to know the story though. ?

[Xerxes]

Some encoders have bandwidth of 1 MHz and some cheaper ones may not even reach 100 kHz. So its better to check the encoder specs before making any decisions on drives.

[gcz]

no no no!!!!
don't have to buy more motors to get lower encoder rates at all!!
get a darn 74ls193 or something binary counter and just prescale it down
jeez= 10 cent fix per axis!

[Cold Fusion]

You guys tell me this after I buy new encoders...

[gcz]

oh man, i'm sorry - i only just saw the post...

[gcz]

get another mill to go with the new motors!

[Mariss Freimanis]

You are much better off getting new encoders. The pre-scale circuit is more involved than just a "74LS193 or something".

Mariss