[Robotgroup] RoboSPInArt - Design issues revealed.. :)

[Gray Mack]

If you want to keep the printing system on the main 
platter then the hall effect or magnet sensing coil
seems best since it would not be affected if it got
hit by stray paint like an optical system would.
If the motor has enough free spin then you could
accelerate it past the point of rotational speed
desired then let it free spin down a few revolutions
until it was at the desired speed and print. You could
even use multiple magnets for more accuracy than
timing one full rev. Then you wouldn't have to change
the speed that the print system works.

If there was a separate spinner that you put the paper
in then a slow stepper motor system could allow you to
reprint several times from the exact same place for a
bold or custom font maybe?

> 
> Vern Graner <vern at txis.com> wrote:
>   Ok, so now that we've run the unit with Ink Arm in
> place, it seems we 
> need to find a more accurate way to control the
> turntable motor, or 
> failing that, find a way to discover the RPM and
> position of the platter.
> 
> Since we are using an analog control to vary the
> turntable speed, there 
> is a lot of leeway in how fast it actually is
> turning. This is a bad 
> thing when we're trying to print a perfect circle of
> text. If the 
> turntable is moving slightly fast, the text gets
> stretched out longer 
> and overlaps (i.e. the first few letters of the
> sentence get overwritten 
> by the last few characters).
> 
> If, on the other hand, the turntable is going to
> slow, we get text that 
> doesn't fill the entire circle (i.e. a large gap
> between the first 
> character and the last character in the sentence).
> 
> I was thinking that if we had a hall-effect sensor,
> or maybe a visible 
> light interrupter, we could determine exactly where
> the turntable is, 
> read a timing value for one revolution of the
> turntable to get a speed 
> rate, then print the text using a variable to alter
> the inter-columnar 
> delay. :)
> 
> Or, if we could find a digital speed controller that
> had a tach input 
> that could drive the motor, we could tell the
> controller to reach and 
> hold a specific speed so we would get consistent
> printing...
> 
> Frankly, I'm a bit disappointed by the Ink Jet arm
> as the text intensity 
> is pretty weak since it doesn't print in "bold" or
> "NLQ" but only in 
> simple , single dot, dot-matrix characters...
> 
> Maybe time to get Paul to look at making a custom,
> BOLD font for the 
> inkjet...? :)
> 
> Anyway, so Ideas for speed controllers or alternate
> methods to deal with 
> this issue would be appreciated. :)
> 
> Vern
> 
> -- 
> Vern Graner CNE/CNA/SSE | "If the network is down,
> then you're
> Senior Systems Engineer | obviously incompetent so
> why are we
> Texas Information Services | paying you? Of course,
> if the network
> http://www.txis.com | is up, then we obviously don't
> need
> Austin Office 512 328-8947 | you, so why are we
> paying you?" ©VLG
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