hobbit@topaz.rutgers.edu ($ *Hobbit*) (12/06/88)
Well, by "light show" you apparently mean oscillators-talking-to-some-kind- of-deflection-system. This is really only part of a decent full-blow show.. anyway, the canonical [albeit expensive] route is to find General Scanning galvanometers and drive them with some kind of amplifier. I don't know about the commercial unit you mentioned [if you have more info on it, could you send it along? The price seemed awfully low] but I do know about the "Laser F/X" thing being marketed by your local yuppie stores -- it isn't a laser, they're using *one* bouncing mirror for deflection, and you could throw one together for about $5. Don't buy it. Anyway, speaker-based kludges will work but will never give you the linearity and repeatibility that real galvos will. An alternative is small stepper motors, 90-degree if you can get 'em, with a holding voltage on one coil and your signal going to the other. [You also might want some form of mechanical restraint so it doesn't "wrap around" on strong pulses.] Check for loose bearings... Professional shows use multiple x-y pairs of GS's better positional-feedback galvos -- they're not only fast as hell, they provide exact feedback about where they are, and you can build your driver accordingly. They also cost something like $700 per. Since GS is apparently still the only company making these things [someone please correct me if I'm wrong] they can get away with this pricing scheme. I've always been generally irked at the prices these manufacturers are getting for laser equipment. They *can't* cost that much to build... _H*
cbell2@orion.cf.uci.edu (Chris Bell) (12/07/88)
In article <Dec.6.06.33.54.1988.4315@topaz.rutgers.edu> hobbit@topaz.rutgers.edu ($ *Hobbit*) writes: >Professional shows use multiple x-y pairs of GS's better positional-feedback >galvos -- they're not only fast as hell, they provide exact feedback about >where they are, and you can build your driver accordingly. They also cost >something like $700 per. Since GS is apparently still the only company >making these things [someone please correct me if I'm wrong] they can get >away with this pricing scheme. > Yes. I do work for a company called LOGIC+ (logic plus) which does portable laser graphics shows. We use GS galvonometers. They are pretty good, but not as good as we would like. All of the feedback in the world won't do you any good if the thing just won't slew fast enough. We have, with our own custom amplifiers, a bandwidth of about 1500hz from these guys. Eventually, we will be adding a digital control feedback control system with a very large power ampilfier to coax more bandwidth. However, even 1500hz does not give you very much bandwidth to scan a vectored x-y image that has a lot of corners. (I mean a picture, not an abstract art work). As a result, we use multiple coordinated scanners. (We do a piece from the Star Wars trench scene that is very busy. 1 scanner gets the trench, 2 others handle Skywalkers x wing and vaders tie.) Fun stuf ;-) Later. Guy ~The Interrupt Master~
hedley@imagen.UUCP (Hedley Rainnie) (12/08/88)
> Questions about laser positioning hardware Here is an article I saw about 2 years ago on net.analog: -------- From: agn@unh.cs.cmu.edu (Andreas Nowatzyk) Date: 5-Aug-86 18:52 EDT Subject: Re: Laser beam positioning anyone??? > > .... There is no known way to > do this positioning of laser beams without using mechanical positioners. > Sweeping statements like this are usually wrong. To wit: Philips used an all-solid state, digital laser beam delector for their Holographic memory research. That was more than 10 years ago. The scheme is pretty neat, so a brief description might be in order: +-+ ^ +-+ ^ +-+ ^ Leaser Beam in ------->|K|---/P\---|K|---/P\---|K|---/P\------> out +T+ / 1 \ +T+ / 2 \ +T+ / 3 \ | ----- | ----- | ----- A0 A1 A2 The linear polarized laser beam enters this 3bit delector from the left. The K-Boxes are Kerr-cells that can rotate the polarization plane of the beam. These are essentialy capacitors with some optical active medium. If a voltage is applied, the polarization plane is rotated. The voltages A0-A1 are set so that a '1' rotates the beam by 90 degrees and a '0' does not rotate the beam at all. The prisms P1-P3 are made of CaCO3 crystals. These crystals have 2 distinct difraction indices that depend on the polarization plane of the light with respect to a certain crystal orientation. Say that this difference is 1degree for P1, 2 for P2 and 4 for P3. Optical prisms can be manufactured with very tight tolerance, so you can continue this scheme for 10 or more bits (Philips used either 10 or 16 stages - weak memory). Assume that the unrotated beam has the lower deflection and A0=A1=A2=0 is said to be 0 deflection. So you get: A0 A1 A2 Beam defelction ----------------------------------- 0 0 0 0 1 1 0 1 0 1 1 2 1 0 1 3 0 0 1 4 1 1 1 5 0 1 0 6 1 0 0 7 This type of deflector can be made very fast (sub 100 ns) and precise (10-16 bit). In addition, you can build 2dimensional defelctors by adding a second deflector at the output, rotated by 90degrees. -- Andreas Usenet: ...!seismo!unh.cs.cmu.edu!agn --------------- -- {decwrl!sun}!imagen!hedley
paul@hpldola.HP.COM (Paul Bame) (12/13/88)
I once thought about laser-deflection using electrostatically deflected mirrors in a vacuum. You could really reduce mass and air friction. I think I calculated some poor performance numbers though (e.g., size of mirror/plate Vs. driving voltage Vs. deflection) but maybe I was wrong. Just an idea.. -Paul Bame
jbn@glacier.STANFORD.EDU (John B. Nagle) (12/23/88)
In article <10960009@hpldola.HP.COM> paul@hpldola.HP.COM (Paul Bame) writes: >I once thought about laser-deflection using electrostatically deflected >mirrors in a vacuum. You could really reduce mass and air friction. It could be done even in air. Kynar (tm) film, which is an electret, can be deflected at high speed with about 2mm separation from a conductive plate, 400VDC, and microamps of current. This is how the Polaroid sonar transducers work. One could probably build a deflection system this way. But it's not clear that there is any fundamental advantage over magnetic or piezoelectric techniques. John Nagle