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

[Vern Graner]

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
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Austin Office 512 328-8947 | you, so why are we paying you?" ©VLG