Simpliest route to programmable single axis scanning

[wseaton]

A friend of mine thinks he's the next Spielberg, and has been begging me to come up with some low power options and provide some portable 'liquid sky' type effects for some films he wants to shoot. Actually, he's not half bad and I'm willing to help his concepts, but being he's on a college budget. Besides, I've been interested in tinkering with some DIY galvo based scanning for awhile. I have a pile of stepper based laser units and plenty of diode modules lying around, and we don't need much power. However, steppers aren't smooth enough for the look he wants while lens based splitters that mimmick the liquid sky didn't provide the look he wanted either. A dumb scanning mirror doesn't provide enough control.

Since we just need single axis scanning with some degree of control or preset program I'm thinking the kits on goldenstarlaser would be good for what we need, but try as I can I can't find the exact details to get from the galvos and drivers to what is required to provide basic functional input and control for single axis scanning. I'd think this would be far simplier since we don't need full 3-d, multiple colors or modulation, but not sure where to start. Lots of links, but confusing details. Advice appreciated.

[Galvonaut]

I'm a newby to lasers, but a couple of years ago built my first 'I haven't got any money to spend on lasers but want one-laser'. I used a DC computer fan with a bit of broken mirror glued to it and an old hard drive galvo with a simple mono audio amp to drive it from an audio input. It was cheap and although not exactly safe or particularly controlable, it was fun.
Where abouts do you live wseaton and can you do electonic tinkerization? I think I have some cheap and nasty galvos and amps laying about which 'might' work with a bit of tinkering (UK). Too slow for what I am doing but might suit you. If you are further afield you may find some cheap lasers on ebay - you just need something with an ILDA input (uses a DB25 connector).
You also need a way of controlling the laser (Digital to analogue converter). You could build a sound card DAC which would save you a lot of money in comparison to an off the shelf product.
Software - I'm not sure but there is some shareware available.
I'm pretty sure others with more experience than me will come up with better suggestions and more details but hope I have helped a little.

Keith

[kecked]

vibrating speaker with mirror glued or bounced off it.

[The_Doctor]

I think even stepper motors would work if you had the right type of controller.

That's true. I was going to suggest it last night but thought better of it because of the discontinuous motion. But when you mentioned it (and maybe having slept well), I remembered that there is half-stepping, and even the possibility of proportional interpolation to get very fine graduation. Digital signal generation can definitely handle that. In a lumia, I bet there may be a lot of scope for the easy recall of certain patterns. Finding really cool ones is hard enough, but worth it if specific and reliable recall can be had. Steppers definitely allow that. The main weakness of these methods is the holding torque is severely compromised, so expect to spend on big motors.

[The_Doctor]

Just to clarify... I thought I was replying to the lumia motor thread. Sorry..

One other idea: small handheld barcode scanners, the type that point at stuff from a foot or so. They're likely slow, with weak mechanisms. But they might be very cheap if you find old tattered ones on eBay. Just beware the shysters who overvalue them, there are a few like that on eBay. The advantage is you get the mirror already mounted, and it will be a good small front surface mirror too. I doubt you can control speed independently of scan angle but they're ok if simple oscillator speed is all you want to use to control that angle. If filming, the main problem could be that it's all too slow to register a complete scan or two per frame of movie.

[The_Doctor]

Nice. Got a maker's name and number? I always thought they used a weak galvo method. Sounds like you got something interesting.

There is the other type, that stand still while stuff gets waved in their general direction. Those have a rigidly fixed angle set by the polygonal mirror that spins on an axis. Those are driven by some small synchronous motor, like a miniature of the sort of thing in a direct drive record deck. THose are cool for very fast clean flat scans, but it's pretty much on or off from then on. (Although it may be possible to hack the electreonics to change scan rate. Angle is totally fixed though, unless you slide a limiting shutter across part of it, wasting light. Even that might be ok, the intensity of what's left will be nicely constant with angle change that way...

[sugeek]

I was going to point you to the polygonal mirrors but you mentioned them... You can leave them on all the time just modulate the laser diode .

-Adam

[The_Doctor]

I was going to point you to the polygonal mirrors but you mentioned them... You can leave them on all the time just modulate the laser diode.

Indeed. Beats my idea of a sliding shutter... Probably worth having another very low power laser or even an LED pointing at the mirror from some angle that doesn't get projected out, but is sensed back off the mirror by a fast photodiode, to get a sync signal to make some cool modulations that stay locked to the spin speed.

[kecked]

line generator......no moving parts. or line generator and you rotate the optic. for a cone. add a sliding aperture to make the line / cone larger or smaller.

[The_Doctor]

line generator......no moving parts.

I forgot those. Actually got one somewhere, out of an old photocopier I think. I must find it again.. They don't usually make a nice consistent intensity though. The angle wasn't all that, either. Not entirely related, is a good cheap diffraction grating. Someone asked, and someone sold, just this last week, but I think I missed the boat. I imagine that a diffraction grating might allow some small AC-driven solenoid coil, a magnet (best ripped out of cheap window-open burglar alarm sensors) and a bungy mounting of some kind, to draw a flat scan too, yet another fairly cheap and simple way to get two effects at once, and a way to merge between them too. It's still moving parts, but less of them.

EDIT. Where a cheap line generator really would excell is with a multimode diode that was single-mode fine in one axis. LOTS of light and a surprisingly high quality plane of light too. Even cheap acrylic might stand a watt of that.