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From: John Larkin on 31 Jul 2010 19:26
On Sat, 31 Jul 2010 15:31:29 -0700 (PDT), dclist <dclist(a)gmail.com>
wrote:

>I'm looking for a way to do moderately robust angular displacement
>(and angular velocity) measurement. I was trying to use quadrature
>encoders but it appeared the sensors were occasionally missing some
>state transitions possibly due to the discs moving too quickly or some
>occasional optical occlusion. I am therefore looking for alternatives.
>
>What are commonly used alternatives to measuring angular displacement?

Absolute optical or mechanical encoders, synchro/resolvers,
inductosyns, sin/cos pots, maybe some equivalent capacitive thing.
RVDTs or pots for modest angles, less than a full rotation.

Incremental encoders are usually pretty reliable. All sorts of
printers and things use them. Maybe you have a signal conditioning
problem.

There's some sort of cool encoder that uses round PC boards, with
inductive coupling between traces.

John


From: Jamie on 31 Jul 2010 20:24
dclist wrote:
> I'm looking for a way to do moderately robust angular displacement
> (and angular velocity) measurement. I was trying to use quadrature
> encoders but it appeared the sensors were occasionally missing some
> state transitions possibly due to the discs moving too quickly or some
> occasional optical occlusion. I am therefore looking for alternatives.
>
> What are commonly used alternatives to measuring angular displacement?
We use Q encoders on fulcrums to detect position that does at times
move very quickly.. The problem i've seen is the electronics doing the
decoding.. If you don't account for chatter pulse from vibration where
it would cause a pulse to render it self off/on on channel and not the
other and depending on your coding scheme, you can see extra and fewer
pulses than expected..


Using a RS D flip flop to latch signals on each transition does remove
this problem. It seems many ready made process controllers for Q
operation that I've seen do exhibit these issues how ever, in most cases
the applied application does not lend itself to cause problems.

It would be nice to know how you are doing the actual decoding of the
A,B,Z signals?


Jamie.


From: whit3rd on 31 Jul 2010 21:16
On Jul 31, 3:31 pm, dclist <dcl...(a)gmail.com> wrote:
> I'm looking for a way to do moderately robust angular displacement
> (and angular velocity) measurement. I was trying to use quadrature
> encoders but it appeared the sensors were occasionally missing some
> state transitions

Is this about absolute angular displacement? There are
Gray-code wheel types of sensors that can give good
performance in the missing-codes sense. Quadrature
is a crude 2-bit Gray code, but the sensitivity to error
gets less as you go to higher bit counts, with more
'known-illegal' transitions between states.

Even if you miss step 12, it's comforting to know that THIS
one is step 13. Unless you're superstitious.

With 6-bit Gray code, the position only gets ambiguous if you
miss dozens of steps.
From: dclist on 31 Jul 2010 21:26
On Jul 31, 8:24 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...(a)charter.net> wrote:
> dclist wrote:
> > I'm looking for a way to do moderately robust angular displacement
> > (and angular velocity) measurement. I was trying to use quadrature
> > encoders but it appeared the sensors were occasionally missing some
> > state transitions possibly due to the discs moving too quickly or some
> > occasional optical occlusion. I am therefore looking for alternatives.
>
> > What are commonly used alternatives to measuring angular displacement?
>
> We use Q encoders on fulcrums to detect position that does at times
> move very quickly.. The problem i've seen is the electronics doing the
> decoding.. If you don't account for chatter pulse from vibration where
> it would cause a pulse to render it self off/on on channel and not the
> other and depending on your coding scheme, you can see extra and fewer
> pulses than expected..
>
>   Using a RS D flip flop to latch signals on each transition does remove
> this problem. It seems many ready made process controllers for Q
> operation that I've seen do exhibit these issues how ever, in most cases
> the applied application does not lend itself to cause problems.
>
>    It would be nice to know how you are doing the actual decoding of the
> A,B,Z signals?
>
>   Jamie.

I'm doing the decoding using a state transition table using a
microcontroller that is polling the A and B channels with a sampling
rate to be much higher than the possible state transitions rate on the
encoder. I'm not sure what a 'Z' signal refers to.

The datasheet inidicates that the encoders may have some extra logic
in them as well but it does not specify any behavior explicitly. The
encoder is an AEDS-964x.
From: krw on 31 Jul 2010 21:39
On Sat, 31 Jul 2010 16:15:26 -0700, Tim Wescott <tim(a)seemywebsite.com> wrote:

>On 07/31/2010 03:49 PM, krw(a)att.bizzzzzzzzzzzz wrote:
>> On Sat, 31 Jul 2010 15:31:29 -0700 (PDT), dclist<dclist(a)gmail.com> wrote:
>>
>>> I'm looking for a way to do moderately robust angular displacement
>>> (and angular velocity) measurement. I was trying to use quadrature
>>> encoders but it appeared the sensors were occasionally missing some
>>> state transitions possibly due to the discs moving too quickly or some
>>> occasional optical occlusion. I am therefore looking for alternatives.
>>
>> What sort of rates would an LED/photo-diode not track?
>>
>>> What are commonly used alternatives to measuring angular displacement?
>>
>> I saw a cute Hall-effect rotary encoder this week. The output was 360-degree,
>> with any sort of encoding desired (mag-dir, quadrature, binary,...).
>>
>> http://www.austriamicrosystems.com/eng/Products/Magnetic-Encoders/Rotary-Encoders
>
>If I'm not mistaken Allegro Microsystems has those, too.

Not familiar with Alegro's product. These are ICs. You add your own
mechanics on top, or bottom.

Saw some neat motion sensors this week too (all the disties were through with
their toy vendors in tow).
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