Audio calibration

[mike_biddell]

I should imagine, calibrating the printer for various audio inputs could be challenging. Presumably an amplifier with AGC must be used, or the size of your print would depend on where you set your volume control. Even with an automatic gain control amplifier, there could be issues at low volume and high volume. At high volume, there is risk of clipping and hence inaccurate x and y due to clipping distortion. At low volume, the same applies (detail could be lost). I presume the Peachy must have some LED style VU meter, so that you turn the volume up until the LED goes green?? Maybe !!!!

You could achieve calibration manually by feeding Peachy with a calibration signal which creates a laser pattern against a calibration measure floating in the tank. Then adjust the volume until the laser just strikes the points on the measure.

[harpo99999]

it has been said that the peachy uses AM signal modulation, so probably does have an agc circuit after the band pass filter(s) for switching on and off of the laser.

[mike_biddell]

it has been said that the peachy uses AM signal modulation, so probably does have an agc circuit after the band pass filter(s) for switching on and off of the laser.

I do have some concerns about absolute printed dimensions in relation to the designed dimensions i.e. will the peachy output dimensions exactly match the design input dimensions. Since the base level Peachy is analogue, calibration becomes critical. It's no good printing a set of gears, if the dimensions are out, they wont mesh !!!! There are a lot of variables and the software will have to be quite clever to calibrate against mirror angle. A small change in the mirror angle when the beam is at a large deflection represents a much larger dimension than when the beam is vertical to the surface. So deflections will have to be progressively mathematically weighted (a reduction) as the deflection increases. I presume it is this factor which has dictated that all the example prints so far have had small deflections (small x and y). It's quite a complicated bit of maths to do the off axis deflection compensation to maintain absolute dimensions.

[mike_biddell]

I do have some concerns about absolute printed dimensions in relation to the designed dimensions i.e. will the peachy output dimensions exactly match the design input dimensions. Since the base level Peachy is analogue, calibration becomes critical. It's no good printing a set of gears, if the dimensions are out, they wont mesh !!!! There are a lot of variables and the software will have to be quite clever to calibrate against mirror angle. A small change in the mirror angle when the beam is at a large deflection represents a much larger dimension than when the beam is vertical to the surface. So deflections will have to be progressively mathematically weighted (a reduction) as the deflection increases. I presume it is this factor which has dictated that all the example prints so far have had small deflections (small x and y). It's quite a complicated bit of maths to do the off axis deflection compensation to maintain absolute dimensions.

X and Y are proportional to tan theta multiplied by the height above the resin, where theta is the angle with the vertical. This is reasonably sensible for +/- 45 degrees, but above that deflection, tan theta goes a bit wacky......... +/- infinity at 90 degrees. So you would probably want to limit mirror movement to +/- 45 degrees for the function to remain sensible.

[Slatye]

The off-axis correction isn't really a very complicated calculation, but it does have limits. If you let the beam go off at 90 degrees to the vertical then it's travelling parallel to the surface of the resin - which is a problem (especially because the resin curves around with gravity and the beam mostly doesn't, so they'll actually get further apart). Much better to just limit it to a small deflection (I was thinking more like +/- 15 degrees) and increase the Z height to get a larger printable region. The mirrors will also have mechanical limits, of course, which will prevent really large angles.

Getting absolute dimensions right will be a matter of calibration and fiddling, as it always is. I'm not sure, but I suspect that if you set up the Peachy just about anywhere, have it build a 1" cube, and measure the edge lengths exactly then you'd be able to fully calibrate the system in software. Obviously a larger cube or running the same test multiple times will help, but at the end of the day you'll have to live with "good enough" accuracy (which is probably limited by how accurately you can measure the cube).

[Chayat]

...especially because the resin curves around with gravity and the beam mostly doesn't, so they'll actually get further apart.

What kind of print are you doing where you're taking the curvature of the earth into account?!

[mike_biddell]

What kind of print are you doing where you're taking the curvature of the earth into account?!

As a matter of passing interest for the purists reading this thread and apropos of nothing....... the laser light is bent by gravity. I spent a bit of time looking at the maths and absolute accuracy will not be attainable without a tangent of theta correction. Depends how accurate you want the device to be.

[mike_biddell]

Just looked it up...... there's a 1% error at 10 degrees.

[Anuvin]

In Slatye's defense, he says light mostly doesn't bend to gravity. On Earth, that is absolutely true, if he means it doesn't bend much.

1% error at 10 degrees is not really a big deal, is it? If the height of the printer is 12" above the resin, a 10 square inch print is more than 99% accurate, and smaller prints suffer even less error. Seems good to me.

[mike_biddell]

In Slatye's defense, he says light mostly doesn't bend to gravity. On Earth, that is absolutely true, if he means it doesn't bend much.

1% error at 10 degrees is not really a big deal, is it? If the height of the printer is 12" above the resin, a 10 square inch print is more than 99% accurate, and smaller prints suffer even less error. Seems good to me.

It's not at all bad, but it's not too difficult to put a tan theta correction in the software. I think if you want to print really large stuff, it would be significant. That sort of stuff can evolve as it is nothing to do with the design of the printer, it's in the conversion software.