question about scanners

[nighttower]

Hello everyone.Im new to lasers.
Ive read many forum posts and articles on the internet, but i still have some questions i couldnt find anywhere.

I know the 'power' of scanners is determined on how many points they can show each second (kpps).
What ive also learned is the kpps depends on the scan angle and you can get more or less if you change it.

Lets take the DT40 scanners for example. They say they can display 40,000 points each second. Lets say the projector runs at 30 hz, so it would be able to display 1333 points each second at most.

But the specs of the scanners say 40,000 pps when the scan angle is 8 degrees. Thats not very impressive to me, its about 1 square meter projection from 7 meter distance from projector to wall.
How can i calculate how many points per second or frame (if running at 30 hz) i can get if i change the scan angle to somethign else, like 20 degrees?

[andyf97]

it is a guide / reference that the scanners can address that many points at 8 degrees, like a standard to which everyone refers.

It always reminds me of companies selling internet connections, they always use bits per second, actually we all use bytes but 250k bits per second sounds much faster than 32 bytes per second even tho in principle they are the same.

[nighttower]

Thx for the explanation.But how can i found out the how much the kpps rate changes as you change the scan angle.
Also ive heard people say the max scan rate for some 40k scanners is actually 60 kpps. What does 'max scan rate' mean?
I think theres a lot more for me to learn about this subject.

[absolom7691]

Max scanrate is like advertising the top speed of a car. How often would you drive that car at top speed? It is the absolute max speed the scanner can run while displaying images correctly at 8°. Most laser shows run at 30K. It is pretty standard. It also depends on what you're scanning and how you're scanning it. If you are just wanting a wide spread of beams, you can run these scanners pretty wide at 30k because accuracy is a little less important with beams. If you want to scan really wide, you can lower the scanrate to 25K or even 20K and I don't think you would see too much difference.

If you're scanning graphics, 30k should be able to achieve 12~14° depending on how good your tuning is and how well you cool your amps and galvo block.

You mentioned 30hz, what is it that you're trying to scan? What effect are you trying to achieve?

[mixedgas]

Thx for the explanation.But how can i found out the how much the kpps rate changes as you change the scan angle.
Also ive heard people say the max scan rate for some 40k scanners is actually 60 kpps. What does 'max scan rate' mean?
I think theres a lot more for me to learn about this subject.

That is image size and shape dependent, which is why you will not see a chart. Scanner mirrors and shaft have inertia, and inertia in this case acts like a complex, second order, low pass filter with some added sharp resonances.

Older scanners came with a sine wave response chart, like a speaker, but that is pretty much useless for laser images which contain large amounts of square waves.

The ILDA test pattern, among other things, measures the small sine wave 3db response in terms of frequency, 30 Kpps ~ 2400 Hz, small angle. But again, that only helps with small circles :-)

I design images for 750 -850 points typical.

Steve

[nighttower]

Max scanrate is like advertising the top speed of a car. How often would you drive that car at top speed?

To things:
1. i wouldnt drive my car at top speed usualy because i dont have a need to
2. i also wouldnt because of speed limit laws

But i cant see this being good analogy to lasers. With lasers ill
1. usualy need most possible detail (speed), for graphics
2. there are no external limits like laws.

It is also weird that they advertise speed of lasers for tiny 8 degree angle to make it seem higher but dont use the same logic by not saying 60 kpps is normal, but 'max scan rate'. Sounds contradicting.
Maybe there is something else that needs to be taken into account about that 'max scan rate' number?

And i said 30hz only because ive read some people using that for graphics. I think 24hz and over are considered realtime so i thought that was a good number.

And thank you for telling me 30 kpps is standard for most shows. I want to create my own animations and i want to squeeze as much points from the scanners as i can without breaking them.

btw, is it true that if you try to run an animation with too many points, you might brake your scanners?

thanks for the help

[absolom7691]

Here is the deal with points on scanners. The more points you put in, the longer it takes the scanners to draw them. It really comes down to simple math. If you have scanners that are running at 30K, that means that in 1 second, the scanners will draw 30K points. So, if you have an image with 3000 points, which is insane, it will take the galvos 1/10 of a second to draw them. To only way to draw the image faster is to raise the scan speed but even if you set the scan speed to 60K, 3000 point will still take 1/20, which is still terrible flicker. You can't really get too complex with images.

You can break the scanners but not instantly. They can get hot if you push them too hard and that may cause a breakdown over a short period of time but most scanner amps will power limit if they are push pushed too hard. At least, they should power limit.

From experience, the more points you throw at a scanner, the worse the graphic is going to look. You could have 120K galvos and still not be able to draw super complex images that don't flicker like crazy. If you want complex images, you are going to need multiple scan-heads, each drawing a portion of the graphic. Some companies out there use this trick but then you are talking about multiple DACs and software that can handle it.