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Posted by Curt Welch on November 6, 2006, 11:35 pm
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> A robot control system requires a shaft velocity measurement in the
> range 60-3600 rev/min with a resolution of 10%. The handshaking
> protocol allows communication to the computer only every 10 ms. I have
> to calculate the minimum number of lines required on the encoder disk
> if an optical incremental encoder is to be used? Please tell me how to
> do? & if you would be able to tell me and flow diagram as well to
> understand the system?
I can't tell what needs to be done based on what you have written.
The minimum number of lines is 1 which gives you one pulse per revolution
unless there are hidden requirements not made clear to me by what you
wrote.
What is the 10 ms limit for example? Is that how often the system can
check the encoder pulse output? Or, maybe are you building an encoder
which will count pulses and send a report of the number of pulses once
every 10 ms.
If the shaft velocity is to be calculated based on the number of pulses
reported each 10 ms and you need 10% accuracy then that could be used to
determine the minimum number of lines needed. Since the error in the count
is +- 1 pulse per count you would need at least 10 pulses for each 10 ms
window to produce that accuracy. Which means you would need 1000 pulses
per second when the shaft was turning at it's slowest speed. The slow
speed is 1 revolution per second (60 rpm) so you would need a minimum of
1000 lines on the encoder to produce 1 pulse per ms.
Or, you could argue that the average error was +- 1/2 pulse, making the
needed count 500 lines to produce an average error of 10%.
But, if you were producing a device to accurately measure the time between
each encoder pulse, you could calculate a new velocity with each pulse. If
you wanted to be able to produce a new updated shaft velocity value each 10
ms, then you need 100 pulses per second or 100 lines on the encoder wheel.
But if the lines to non-line spacing on the encoder is 50%/50% then you
don't need 100 lines, you only need 50 lines which would give you 100 state
changes.
In short, you didn't tell me enough to know what it is you are really
asking. The answer could be somewhere from 1 to 1000 lines.
--
Curt Welch http://CurtWelch.Com/
curt@kcwc.com http://NewsReader.Com/
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> range 60-3600 rev/min with a resolution of 10%. The handshaking
> protocol allows communication to the computer only every 10 ms. I have
> to calculate the minimum number of lines required on the encoder disk
> if an optical incremental encoder is to be used? Please tell me how to
> do? & if you would be able to tell me and flow diagram as well to
> understand the system?