Was looking online for a way to control mirrors for a laser. Closed loop feedback would be ideal, but I'd be willing to try no feedback like a speaker or meter movement. How can I build something to experiment with? Can I use a brushless R/C motor to move 5 degrees with many analog steps in between poles? A linear actuator? Hard drive linear motor? Where can I find these or an old HDD? I've tried a stepper but with gears it's not fast enough I'd like 1-2kpps. Without gears it can move back and forth 1.8 degrees quickly, but not in between. Any ideas to help me brainstorm?
How about spinning your mirror (mirror B) at high speed on a shaft (with position feedback). Then pulsing the laser on and off at the correct times so that mirror B directs the laser to your target. Or alternatively bouncing the laser off a second spinning mirror (mirror A) such that the laser beam from mirror A only strikes mirror B at the correct time to hit the target.
I suggest you look at how Faraday or Oersted or somebody like that made their little moving coil instruments, it wasn't that high tech, you can try it that way.
I've used mirror galvos in the past and one of the problems you come up against is frequency response. The mirror has both mass and surface area. The former creates inertia and the latter "wind resistance" so frequency response is low and there is a time lag between signal and mirror movement.
If you have good mechanical construction skills, build your own mirror galvos, as Chan did: http://elm-chan.org/works/vlp/report_e.html
@jackrae- I tried pulsing my laser while the mirror is spinning. At a slow RPM I cannot make a dot, but a line nearly 1 degree long. With a shorter pulse the line is dim. Any idea why?
Chan's tutorial sounds like the best solution for someone who has a lot of time on their hands. Can anyone think of a shortcut? Something to buy for cheap? An experiment to try? I wouldn't mind learning something along the way.
Could you mount the mirror on a pivot and use a solenoid on either side? I believe that’s how the resonant scanners work on confocals, the noise can be an issue though.
A solenoid is all or nothing right? I have read of a few people using a stepper motor with one coil energized at 50% then you modulate the adjacent one to achieve an analog movement. This will give you a maximum of one step, which may be enough. What type of stepper would I use for this? I am familiar with many steppers, but never for this application.
Hi, I have seen somewhere, might even be makers or instructibles site, where the mirror was mounted on a speaker cone and deflection signal sent to speaker coil. Found it.... http://www.instructables.com/id/Arduino-Laser-Show-with-Full-XY-Control/
Tom....... 8) (32DegC here today, going to get hotter, 41DegC by Tuesday)
Has anyone done it with a Stepper Motor? What type is best?
a stepper is way too slow. too get fast you need low mass, i would start with a speaker and glue some foil on top of it, use a high tone speaker as a woofer is only good for 100 Hz. as soon as you move you will see the line dim, as it is only a small point.
MAybe an etalon would do the job
Not sure how to use one. I tried Google. Any more links? What is the lowest cost?
ebay -- $14 to $950
do a bing with keywords 'Laser' and 'etalon' -- lots of info
SolarPanels: do a bing with keywords 'Laser' and 'etalon' -- lots of info
From what I can see:
...an "etalon" is -not- anything that will help sbright33 do what he wants to do - which is to steer a beam (since he is asking about galvos and such).
shooter: too get fast you need low mass, i would start with a speaker and glue some foil on top of it
Foil is not your best option here (won't reflect well enough). The low cost option would be to use a piece of thin acrylic mirror, or try to get a small thin piece of first-surface mirror (perhaps out of an old laser printer). Mount that to a cone...
Sometimes on ebay you'll also see people occasionally (getting more and more rare as the years go by) selling x/y steering units from old laser-disc players; these were also open-loop control (well - open-loop to extent; as-is they are open-loop, but in a laser-disc player, the system would close the servo-loop by using the tracks on the laser-disc surface and special control circuitry to keep the beam aligned properly).
Ultimately, though, for precise steering of the beam, you are going to need a feedback mechanism. That is what a laser galvo is - it's a low-mass, high-speed limited rotation servo motor capable of positioning a small bit of mirror precisely, quickly, and at the same commanded angle every time.
Common galvos typically use extremely low-mass rotors (air core) to keep overshoot/undershoot/ringing to a bare minimum, and will use capacitance or optical methods for the feedback system. It would be extremely difficult (but not impossible - as has already been linked) to build your own galvos. Using a stepper motor is not advised because the mass of the rotor will likely be too high.
What might be possible (stressing "might") would be to use a coreless motor of some type; for example, if you could find a coreless "in-runner" BLDC hobby motor, then somehow set thing up to gain feedback from the system (maybe energize one or two of the coils with a custom driver, and monitor the back EMF from the remaining coil(s) for position information?) - that might just be a doable and cheap method to make your own galvo (without needing all of the minute custom machining that seems needed for most custom galvo systems). I'll have to think on this option further...
Or - if you could somehow use a coreless servo motor, and change the gear and feedback system on it to something closer to a regular galvo - that might be possible as well. The capacitance method is actually fairly simple to do, as it just uses a couple of half-plates (one stationary, one connected to the shaft of the rotor), seperated by a small air-gap - and they form an air-gap capacitor (not unlike the variable tuning caps in old radios) as the plates turn to increase or decrease the capacitance.
Optical methods use a means of reflecting IR light (or passing it through polarized filters) onto a photo-transistor, photo-diode, etc, and measuring the amount of voltage generated or current let through.
One idea I've toyed with in my head (but never tried - I've been told it isn't practical) would be to take a small mirror, and mount it to a piezo-disc transducer; again, it would be "open-loop", but maybe it could be made to move by a small amount (maybe too small to even use the shift?). Another option would be to use - instead of large speakers - small headphone speakers (and very small, low-mass mirror pieces).
Thanks for all the ideas! Please anyone let me know if you have success building one of them. For the moment I'm working on our Flying Robot...
I know it's an old topic, just wanted to say to people interested in beam steering that i'm pretty sure you'll find a galvano mirrors in laser printers. So if you go to the scrap yard you might be able to find one by dissecting an old printer...
A mirror galvanometer is simply a coil with a magnet. They are very easy to make. For the most sensitivity use a neodymium magnet and fine copper wire. 55 awg is manageable. You want a laith or some way to wind it. Thicker wire you can wind by hand but much less sensitive. The one i made with wood hot glue and a little glass bowl to block drafts is sensitive enough to to detect electricity on the surface of rocks when clamping an aluminum and copper electrode to them. I've had interesting results measuring the resistance of plants with it like George H. Lawerance. Someday ill set it up to measure the beam with a light sensitive diode and log experiment data to a raspberry. Excellent device for finding electricity everywhere.
Something like an indicator dial mechanism on a piezo slab might work at low speed? Glue lightweight mirror to the pointer...
Loudspeakers are severely limited by air-resistance and don't rotate anyway.
A small servomotor is what you really need, small so the moment of inertia is low, servomotors hold position accurately (because they have high-resolution encoders). A servomotor is built from a motor, an encoder or other angle-sensor, and a control loop.
A small coreless/slotless motor would be impressively fast to respond, but I can't see it being easy to find a small enough high-res encoder for something quite that small.
In all cases, use a front-surfaced mirror. Otherwise you get a reflection from both sides of the glass.