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Hi Guys
A question hass been raised during a risk assessment about the suitability of using scanners not fitted with a torsion bar , for audience scanning under mpe levels.
Any one care to comment?
Please , no arguments about the audience scans !! This is a CTI question.
The 6210 don't have a torsion bar. How would this effect a scanners behaviour when it fails ? What difference does having a torsion bar make?
Thanks
Fluff
Hi mark
Im guessing that their argument is that under a no power situation to the scan amps the GS120 mirrors always return to a zero (safe) position ( that can be fixed above the audience )
sounds a bit petty, as we all know that torsion bars are more prone to breaking and could leave the beam anywhere under those circumstances
an alternative would to be to fit a failsafe beam shutter in series with the cambridge PSU so if it fails the beam is shut off and then it does not matter where the mirrors end up
the only other route is a scanner safety board ..... and we all know that these have there shortfalls as well
is it someone with a little bit of information making these comments or someone with a high reputation ?
all the best .... Karl
Thanks Karl , you are right about the reasons and my take on the real world situation is the same as yours.
The projector in the lastest Neo Matrix 3000mW with 6210's , so the shutter is fitted .
The person involved is a qualified LSO and experienced , just doesn't like using scanners without the torsion bar.
I was just curious to see other opinions. I prefer the long term reliability of the CTI's
By the way , do you know when rob's back?
All the best
Fluff
I too am curious regarding scanner failure.
I have seen a couple of boards that monitor the scanners and in the event of some failure it will shut the unit down.
One I've found can be found at this URL:
http://www.laservisuals.com/scanfail.htm
My question is, does this sit between the scanner amp and the scanner itself or does it monitor it some other way? Also - is this required to implement into a projector if you are trying to get a variance or does it just help a little more when applying for one?
Thanks,
Phil
My CT8600hp fitted with mechanical shutters. If there is no scanning they close (have to type a command on controller to force open them) . If there is no signal they close.... malfunction in galvos...they close
Fluff said ...
its not just reliability its speed as well, the only time i have seen scanners with torsion bars get close to the speed of CT6210s is at a LOBO demo when they used g120s with their digital scanner amps and i think that the amps are some extortionate amount like £5000 but hey did they perform !:eek:, first time i had seen quality raster scanning on G120s .... also the Guy at LOBO told me that they use algorithms that run the scanners way over there rated specQuote:
The person involved is a qualified LSO and experienced , just doesn't like using scanners without the torsion bar.
I was just curious to see other opinions. I prefer the long term reliability of the CTI's
its also strange to knock back CT6210s when they are the prefered scanner in the industry and used by nearly every major laser event company in europe, it also knocks value off the quality of the show produced, not that i am dismissing the safety reasons but i would like to see some evidence otherwise .....
im sure Rob should be back sunday as he said to me he was on holiday for a week ..... thats if he hasnt broken any bones ( on the Ski slopes you see )
all the best ... Karl
Hi Karl,
You wrote:
Well, there are two separate schools of thought here. First school of thought is -- yes, if power is COMPLETELY removed from the scanner, and if the event which removed the power from the scanner in the first place didn't break (or stress!!) the torsion rod, then yes, theoretically the scanner will point a static beam in a direction that you generally know.Quote:
Originally Posted by Banthai
Note that in my discussion above, there are no absolutes. Even under normal circumstances, the G-120 will not return PRECISELY to the center, because there is magnetic hysteresis involved. So we can only predict the general direction the beam will be pointing, which is hopefully above the heads of the audience.
Also, if power is removed from the scanner while a show is playing, then we would have to examine the event which caused the failure. Think about this. Lets say the G-120 was under hard acceleration, from the far end of the scan field, headed toward the other far end. In the center, the G-120 picks up acceleration nearly 5 million radians per second squared. Now lets "break" the coil connection. In this case, its like you going down hill in your car under hard acceleration, then removing the brakes. When the scanner reaches the other far end, the only thing slowing it down is the spring (torsion rod). Such an event might very well be enough to break the torsion rod. So then, where are you?
I am not sure about other governments, but within the walls of the CDRH, the older scanners with torsion bars are only known for one thing -- broken torsion bars... In the bad old days, lightshow folks used to break torsion bars all the time. So this scanner has a reputation for doing that, even though such breakage is through no fault of the scanner...
On the flip side of this, lets talk about the 6215 (not the 6210). Of all of the lightshow scanners produced by Cambridge, the 6215 has the highest inertia. Not "high inertia", but still the highest of all of the low inertia scanners. For audience scanning applications, we might make the argument (and in fact, I personally did) that higher inertia scanners are better for audience scanning, for obvious and semi-obvious reasons. Also, the 6215 can dissipate 4 times the amount of heat as a 6800, and 30 times as much as a G-120. Basically, the 6215 is the only scanner that I personally would recommend for any application, especially audience scanning. We also use the 6215 in conjunction with PASS.
And in any event and every event, as Godfrey wrote, you should always have some kind of scan fail interlock whenever you are doing Audience Scanning.
One thing to keep in mind is that ANYTHING can stop the scanning. We are not just talking about failure of the scanners, when we say "Scan fail". It could be that a power supply craps out, or that someone trips over the cable going from your projector to the computer, thereby PARTIALLY disabling the projector (i.e. only disconnecting the scanner signals and not the laser color drive signals), or even a failure of the software driving the whole projector.
This is the kind of thing that always makes me laugh. Well, we can discuss the space shuttle or MIG 25 or other really expensive items that none of us will ever own, and thus, none of us can really verify the true performance...Quote:
Originally Posted by Banthai
There are physics involved in laser scanning, and those physics can not be beat. The system can be optimized to deliver the best performance, but not "way over the rated spec" -- at least not doing so while lasting for a very long time.
In the case of the G-120, the torque constant is 60,800 Dyne Centimeters per amp, and the Inertia is 0.028 GM*CM squared. Due to the construction of the G-120, there is a saturation torque which occurs at 2.25 amps. If you put in more current, you don't get more speed. You only reduce the life of the scanner, because you will demagnetize it (eventually). I am sure old timers on PL can tell you about failures they have seen of the G-120.
You can't get too much higher performance from a G-120 than what is achieved with a TurboTrack amp. I am not just saying that because I designed it -- I am saying that because of the electronic engineering involved in the control circuit, and the physics involved in the scanner itself. I won't get too deeply into a story of how the TurboTrack pre-dated a famous laser company's product, and how this same famous laser company purchased a TurboTrack amp, and then used it as the basis of their amp design, but I will say that the famous laser company really loves themselves, really charges high prices, and has only four letters in their name :D.
One thing about LOBO shows. In every LOBO show that I have ever seen, they use at least 2 scanners to create the graphics, and do foreground/background type image design. In most large tradeshows, they use 4 scanners to create the graphics. For laser enthusiasts, the display looks damned impressive, and there is a higher information density (lets call it, "more light to the brain"). But unless you can do an honest-to-goodness apples-to-apples comparison, I wouldn't put too much stock into what ANYONE says (even Bill Benner) :D.
I don't want to be argumentative, but, do you have statistics to back this up Karl?Quote:
Originally Posted by Banthai
As far as I can tell, the 6800 is still the "preferred" scanner in the industry, especially in Europe. But this is much to my own surprise and dismay. But the only reason why the 6800 is so popular is because of comfort level and "historical reasons".
COMFORT LEVEL: People have been using the 6800 since 1992. In the early days, Cambridge made the schematics of the CB6580 available (much against my pleading with Bruce Rohr to keep it private) and so many companies copied that scanner amp and now they make their own. Because of this long history with the 6800, people have a kind of comfort level with it. And of course, almost every Chinese scanner is a copy of the original Cambridge 6800 and the CB6580 amp.
"HISTORICAL REASONS": As a result of the popularity of the 6800, a lot of projectors in the field have these scanners. So when it comes time to replace a scanner, what are you going to do? Are you going to replace it with a completely different scanner, that requires a completely different amp (and thus have to keep two types of scanners in stock) or are you going to just have one scanner in stock?
The 6800 is not as good as the 6210, which is nowhere near as good as the 6215. The only scanner that we highly recommend is the Cambridge model 6215 and Cambridge amps. This recommendation is not only made because of my involvement with the project (technically, I also had involvement with the development and evolution of the 6800) but because it's just a damn good product.
Best regards,
William Benner
PS: It doesn't take great scanners to do raster imagery. Raster is the same waveform over and over. BUT, raster is a high-RMS application which generates a lot of heat in the scanners, particularly moving magnet scanners. But yes, G-120s can do rasters, and, when we first developed raster (in 1995, along with Lightspeed, significantly predating a certain laser company with four letters in their name) we would routinely run rasters on open-loop G-124s, just to show that it could be done.
Hi Bill
wow .... thanks for sharing you thoughts and knowledge
You show the first quote by me, :eek: but i was just replying to Marks ( fluff ) question, im sure he will really apreciate your detailed response,
its difficult when you have to comply with an LSO and even though you respect thier advise.... you still wonder the reasons why ?
your thoughts ( even though they are far more technical than mine could ever be ) are still along the same as mine,
Bill said
definately wont argue :D and no statistics, i used "CT6210s" as this was the thread topic, but i was generalising and should have just said "Cambridge"Quote:
Originally Posted by Banthai http://photonlexicon.com/forums/imag...s/viewpost.gif
its also strange to knock back CT6210s when they are the prefered scanner in the industry and used by nearly every major laser event company in europe.
I don't want to be argumentative, but, do you have statistics to back this up Karl?
I noticed the LOBO thing where they used multiple pairs to create a single image, i guess they have thier reasons but it all seems way over the top ( including the prices :D )
again thanks bill for your input .... hopefully fluff will keep us informed of the progress
all the best .... Karl
Hi Mark,
Good to see you interested in this subject. Give us a call or email me regarding the safety issues you sound like you may be having with the installation. We’re pretty experienced at putting together robust safety cases and successful legal audience scanning applications.
As for Bill and Karl’s comments on how LOBO use galvos, both views are correct to an extent, and certainly, that overdriving any galvo will cause accelerated wear. However, what you can’t take away from LOBO, whether they are simply doubling up the use of galvos, or do have some smart way of driving the galvos with an optimised control signal, the graphics and imagery used in their shows is second to none. Their style and artistic content really does stand out from the rest of the industry, with people always being able to spot a “LOBO production”. Perhaps it is no surprise that they have one so many awards for their work than any other laser production company, and continue to do so. And they do this using galvonometers that the rest of the mainstream laser business stopped using 15 years ago.
The picture on the following link http://www.laser.shows.org/drawing.htm is not a Lobo show, but it does show what was achievable at 2.5K pps many years ago, when this wonderful machine was being used http://www.laser.shows.org/interact.htm
Quality not Quantity I suppose the saying goes.
Cheers,
James Stewart
LOBO has a BIG check from government every month. They can do whatever they want and still have money. Yes I know that for a fact. I would not put LOBO as an example of anything because LOBO is NOT a profitable company.Quote:
Originally Posted by JStewart