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From: krw on 31 Jul 2010 21:39
On Sat, 31 Jul 2010 16:17:02 -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?
>
>There is an upper limit that you ignore at your peril. The ones with
>open-collector outputs have, I think, a more severe speed limit* than
>ones with totem-pole or CMOS output.

Obviously there is an upper limit, but I wouldn't have thought it would be in
the range of encoder mechanics.
>
>* And, obviously, more sensitivity to your supporting circuitry.
From: E on 1 Aug 2010 05:42

"Tim Wescott" <tim(a)seemywebsite.com> kirjoitti
viestiss�:DvSdneYALrk1M8nRnZ2dnUVZ_gWdnZ2d(a)web-ster.com...
> 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.
>

Melexis also have them.

-ek


From: Tim Wescott on 1 Aug 2010 22:41
On 07/31/2010 04:26 PM, John Larkin 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 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.

That's the Inductosyn. Electrically it's just a resolver with lots and
lots of poles, although there are enough detail differences that the
'just' needs to be taken with a grain of salt.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html
From: John Larkin on 1 Aug 2010 23:17
On Sun, 01 Aug 2010 19:41:22 -0700, Tim Wescott <tim(a)seemywebsite.com>
wrote:

>On 07/31/2010 04:26 PM, John Larkin 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 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.
>
>That's the Inductosyn. Electrically it's just a resolver with lots and
>lots of poles, although there are enough detail differences that the
>'just' needs to be taken with a grain of salt.

Synchros and resolvers are cool. Analog Devices has s/d converter
chips for about $12.

John

From: Tim Wescott on 1 Aug 2010 23:45
On 08/01/2010 08:17 PM, John Larkin wrote:
> On Sun, 01 Aug 2010 19:41:22 -0700, Tim Wescott<tim(a)seemywebsite.com>
> wrote:
>
>> On 07/31/2010 04:26 PM, John Larkin 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 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.
>>
>> That's the Inductosyn. Electrically it's just a resolver with lots and
>> lots of poles, although there are enough detail differences that the
>> 'just' needs to be taken with a grain of salt.
>
> Synchros and resolvers are cool. Analog Devices has s/d converter
> chips for about $12.

It's not that difficult to measure the outputs directly and do the math
in a processor, either.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html
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