galvo mirror mounting theory question

[norty303]

Nicely put Mr Planters. It will be interesting to see what sort of mirror solution Mr Benner will use with the much anticipated Pangolin scanners.

[planters]

I've been thinking the same thing. And because it is such an Achilles's heel, I will be disappointed if P. does not address this. However, Bill said at SELEM in Aug that the mirrors were waiting/done? and if so I'm afraid that they may be the simple/default design.

[tribble]

the all important "propeller" has been under engineered by all but the top end manufacturers.

Fascinating post, planters! Thanks for that. :-)

I'm wondering if a mirror too thin to maintain its integrity under the accelerations of the galvo could be mated to a light composite-based back webbing for support. Sort of like the plastic ribs we see in thin moldings to provide rigidity; the I-beam principle. Perhaps this would be lighter than a sheet of glass other material strong enough to support itself internally. Perhaps such a thing could be extruded from a 3D printer, though I'm not sure if the materials they can extrude are necessarily superior in the weight-to-strength metric.

[james]

Another reason for making both scanners equal in mass and rotational inertia is the math that goes into optimizing images for those scanners. If X and Y are the same then any vector in any direction would be optimized the same. If one scanner is a lot faster than the other, there is really no advantage if you are drawing typical vector art. There might be a lot of advantage if you are using scanners to laser etch text or other high speed industrial applications.

[dkumpula]

There was a great detailed discussion on this topic from Bill Benner, The Doctor, and others waaaay back in 2007 that I enjoyed reading recently. You can find it here: http://www.photonlexicon.com/forums/...n-mirror-specs

-David

[tribble]

There was a great detailed discussion on this topic from Bill Benner, The Doctor, and others waaaay back in 2007 that I enjoyed reading recently. You can find it here: http://www.photonlexicon.com/forums/...n-mirror-specs

OK, now there's some excellent discussion... lots to chew on there. Sounds like they didn't quite agree on whether mirror mass was making an impact or not. I was surprised to hear that tidbit about manufacturers of scanner amps not knowing what the pots did or why! Going to do some more reading... and maybe look at re-aligning my cheap chinese galvos.

[dkumpula]

OK, now there's some excellent discussion... lots to chew on there.

I always enjoy those types of documented discussions from really smart people, even when they occurred nearly 6 years ago. :-)

[ArcDevilz]

I always enjoy those types of documented discussions from really smart people, even when they occurred nearly 6 years ago. :-)

I was taken back to some good 'ol days. Thanks for bringing that post up. I know Yaddatrance got into many a good post back then. Look at the one where he discusses color theory with Bill Benner. Some good info there as well.

[planters]

I went through that discussion and there are some good descriptions of the relative importance of galvo mass, mirror mass, size and shape. But firstly, I am a little skeptical of Bill's claim that the mirror's rotational inertia is on the order of 1/10 that of the rotor. Having seen the new Pangolin scanner motor, I was impressed with its small diameter and this combined with their approach to accommodate larger diameter (diode array) beams... I don't know. At least in my experience with the EMS 4000 series amps and motors, running with the large aperture 14mm minor diameter mirrors, I begin to see significant performance compromise above 18K. I believe, but I don't know this for a fact, that the 7mm and 5mm mirrors with these same motors and amps as an example, do not preform the same in terms of speed (by a large margin).

As far as the design of the mirror goes, the first approach should be to minimize inertia and maximize stiffness by optimizing it's shape and dimensions and second to choose the best material that is practical for fabrication. That is why I described a mirror that tapers in thickness as you move to its outer edge. This is an established method of maintaining stiffness at the axis where it is needed and where the mass contributes little to the rotational inertia. At the same time the reduced mass at the edge contributes less inertia than a full thickness slab of glass and unlike the axis of the mirror the edge is only required to support itself. Depending on the fabrication the overall mass of the mirror can be reduced toward 1/2 of a monolithic slab and the bulk of the reduction is where it counts; at the high velocity edge.

Once the shape is right then I would avoid composite material in such small structures. I don't know enough about precision molded then coated over a near net composite part, but oh boy... I would rather sapphire or silicon carbide. Both are currently fabricated for small scanner optics. They are both superior to glass or fused silica. And the cost of the sapphire at least, would be almost entirely in the fabrication rather than the material. I am less familiar with SiC.

http://optics.org/article/34451

Once I am done with a DPSS project that is sucking up all my time, I think I will look into sourcing some super light weight mirrors for my big and slow scanner and asking Fred at OSLS if he would be willing to install them and comparatively test them. Yes, I think I will definitely do that.

[dkumpula]

Once I am done with a DPSS project that is sucking up all my time, I think I will look into sourcing some super light weight mirrors for my big and slow scanner and asking Fred at OSLS if he would be willing to install them and comparatively test them. Yes, I think I will definitely do that.

Definitely looking to seeing how this pans out after you geniuses are done with Big Green!


ArcD - thank you for the pointer to old the Yaddatrance discussion! I'll definitely look that one up - assuming PL search cooperates of course . . .