Re: [Emc-users] Encoder with 5 000 000 pulses/rev

[Andre' Blanchard]

At 12:20 AM 6/6/2008, you wrote:
>  Aram,
>
>i talk to company that manufacture encoder with 5 000 000 pulses per rev.
>the problem is that that encoder has MAXIMUM rpm less than 200 rpm!!!
>so that encoder can be speen faster than 200 rpm because frequences not
>enogh to keep so much pulses.
>if you want speen faster get lower resolution incoder 1 000 000 pulses per
>rev.
>
>
>I am not sure which way you are going.
>5,000,000 pulses per rev at 200 rpm gives a 16,000,000 pulses per second 
>which means you have to handle 32 MHz signals to be able to count the pulses.
>These are (sorry for the wording) insane data rates.

One reason for such high res. encoders is to get good velocity resolution 
even if the position resolution is not needed.  In times past you would use 
the encoder you needed for position resolution and a good analog tach and 
velocity amp to do such things.  You see that kind of stuff on EDM machines.
Now days the insane digital rates are cheaper then the analog stuff and the 
people who really understand how to design good analog systems.

The 200 rpm limit is likely a bandwidth limit on the electronics in the 
encoder, but there could also be some mechanical reason.

__
Andre' B.  Clear Lake, Wi.



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Re: [Emc-users] Encoder with 5 000 000 pulses/rev

[Rob Jansen]

 Aram,

i talk to company that manufacture encoder with 5 000 000 pulses per rev.
> the problem is that that encoder has MAXIMUM rpm less than 200 rpm!!!
> so that encoder can be speen faster than 200 rpm because frequences not
> enogh to keep so much pulses.
> if you want speen faster get lower resolution incoder 1 000 000 pulses per
> rev.


I am not sure which way you are going.
5,000,000 pulses per rev at 200 rpm gives a 16,000,000 pulses per second
which means you have to handle 32 MHz signals to be able to count the
pulses.
These are (sorry for the wording) insane data rates.
This makes me wondering what you are trying to do, with a 2 inch ball screw
this gives you 0.4 micro inch resolution. 200 rpm, 2 inch == 400 inch/min or
10 meters/min (380 mph or 600 kmh). With a 0.2 inch ball screw speeds would
make sense again, and in that case I'd love a higher speed, but a 0.04 micro
inch (approx 1 micro meter) resolution on a ball screw rotation measurement
is very high, most likely much higher than the precision of all separate
components.

is this possible to build electronics "gear box" that at lover rpm will
> use encoder with 5 000 000 pulses per rev and when rpm increases
> "electronic gear box" will switch to encoder with lover resolution that is
> 1 000 000 pulses per rev?
>

You could stick two encoders together and switch from high to low(er)
precision when you reach a certain speed but you will always loose precision
while doing this.
If your design needs such high precision combined with high speeds then
you'll need to think of another way of designing your machine.

Regards,

Rob
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