Not a circle.

**keeperx** · 04-12-2009, 08:48

ok here is teh deal.. my balistic circle looks fine (ilda test pattern) but if im just scanning a circle, it looks like this.

its not digital clipping, already checked that.

it does not matter how big or small the circle is, they all look like this.
notice the flat-ish edges

**mixedgas** · 04-12-2009, 08:50

Either the frequency is too high, or you have a PD linearity issue. Which galvos?

Steve

**allthatwhichis** · 04-12-2009, 09:30

I got a quick fix for that...

**keeperx** · 04-12-2009, 09:42

yeah i bet you do

...

SP20s Steve

**Agent C** · 04-13-2009, 14:16

Not to thread jack, but I've got a linearity pot on my amp boards. What exactly does that change, and at what step during tuning is it appropriate to adjust that? Additionally, I have an o-scope so if it's something that's easier tuned with the help of a scope I can look at that too.

**mixedgas** · 04-13-2009, 16:50

Originally Posted by Agent C

Not to thread jack, but I've got a linearity pot on my amp boards. What exactly does that change, and at what step during tuning is it appropriate to adjust that? Additionally, I have an o-scope so if it's something that's easier tuned with the help of a scope I can look at that too.

Whose amps?

I have only seen that on geometric correction boards, finding that on a scan amp seems unusual.

if you want the classical definition of linearity in laser, it means if you command one unit of deflection, you get one unit of deflection, Some systems deflect a little in the middle and much more at the edges as the image gets bigger, this is poor linearity.

Linearity is one of the things the 16 x16 grid of lines test pattern is for. Lets learn about Bow, Pincushion, Shear, Linearity, radial Linearity etc:

GOOD READING, but this is no longer manufactured:

www.jrbtechnical.com/pdf/ugcmanual.pdf

The concept is not lost, I know how,and have schematics, of how a similar unit works. In most cases these days, you do it in software, its very simple math.
Steve

DZ · 04-13-2009, 17:15

For some reason I think I've seen a problem like that before, I just can't remember what the cause was. Have you looked at the X/Y signals from your DAC on an o'scope?

**keeperx** · 04-13-2009, 17:35

yes i have.. it looks fine..

could it be a position sensor? its on both sides so i doubt it..

**mixedgas** · 04-13-2009, 17:41

Originally Posted by keeperx

yes i have.. it looks fine..

could it be a position sensor? its on both sides so i doubt it..

yeah, if done in manufacturing or design. Common on the low end stuff. can also be board component level stuff, but I'd bet on the sensors.

Does it stay the same if you take exactly the same points and move them up and down in the field of view?

Steve

**keeperx** · 04-13-2009, 17:58

yes it does.. no matter where i have a circle.. and even if there are more than one circle, they all have this strange shape..

a ballistic circle looks fine of course..

i would like to know what the deal is because i plan to unload these scanners for cheap as that are still fine for most things like beam shows etc...

they even do abstracts and most graphics quite well...

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