Results 1 to 7 of 7

Thread: Scanner resolution

  1. #1
    Join Date
    May 2008
    Posts
    4

    Default Scanner resolution

    Hi Folks !

    I'm Morgan Heijdemann (aka NoXQS) from Singapore.

    Since a week or 2 the laser bug has caught me and I -like many before me- have some questions. I've read Chan's design (which site is now offline), contacted Norm and checked out Joey's designs and decided to skip the DIY of the laser scanner and get one off the shelf.

    The real fun will come when I loop back the laser images through a webcam to the software that controls the laser. I want to do 3d scanning.


    First the simple questions:

    In order to generate a pattern on the wall , some would need:

    2 galvos with their power supply, which is
    a device that converts x/y/blanking to pulses for the galvos
    and finally a device that listens to the computer using a protocol (forgot the name of this communication standard).

    I am a bit confused how you would connect your scanner to your pc. By usb or network ? I don't see that in the packages on LaserShowParts.
    Where do you get those ?

    Second question I have is about the resolution.
    Because the resolution of the scanner is important to me, I would like to know the scanning resolution of the kids (LaserShowParts or any other), but they are not mentioned (Dave?). I've seen 16 and 8 bit.

    Do you know if there are some API or example C++ code snipped to get started writing your own application ?

    Cheers,
    Morgan

  2. #2
    Join Date
    May 2008
    Posts
    4

    Default DMX

    The device that connects the PC to the scanner driver, is that a DMX ?

    Could someone direct me to the laser scanner faq ?

  3. #3
    Join Date
    Dec 2006
    Location
    Pflugerville, TX, USA
    Posts
    1,977

    Default

    The interface from the PC to the galvos is a DAC (digital to analog converter). You could just about use any DAC (National Instruments for instance) but there are some made specifically for laser galvos. Examples are EasyLase, Moncha, Riya, Lumax etc. Pangolin also makes some but I am not sure of the names.

    The first 4 I mentioned are easy to control via your own code. I have written some laser show software and have been able to easily communicate with those. Pangolin DACs are a little trickier.

    Moncha has 16 bit resolution. EasyLase has 12. I can't remember off the top of my head the resolution of the other 2 (16 or 12 for sure). Norm also makes a USB DAC now but it is only 8 bits with only TTL modulation. Unfortunately, I don't recommend that DAC for those reasons.

    There are also devices that communicate to the PC via DMX. They are a bit of a different beast, however. You probably don't want to mess with that in your application.

    Anyway, that's what I know off of the top of my head. I hope that gets you started in the right direction.

  4. #4
    mixedgas's Avatar
    mixedgas is offline Creaky Old Award Winning Bastard Technologist
    Infinitus Excellentia Ion Laser Dominatus
    Join Date
    May 2007
    Location
    A lab with some dripping water on the floor.
    Posts
    9,012

    Default

    You can assume that mechanically the scanners have infinite resolution.
    Actaully they dont, but laser show purposes you'll never reach the resolution limit.
    Hold out until you can get at least 30,ooo point per second scanners. The limiting factor is the time per jump, which is angle dependant.

    Norm's has the best bang for the buck for a start, if you insisnt on coding your own, you should start there, skip popplescan and the other 8 bit dacs. This way you have a minimum known performing program for testing and aligning your scanners etc. Besides, Norms is pretty good to learn from. For actual use you want at least 10 bits, because morphing, changing image size, and rotating a image all burn up bits. A 8 bit image rotating is downgraded to say 6 bits in reality.

    My friend has posted his source code at http://sourceforge.net/projects/lfiplayer3d

    Steve Roberts

  5. #5
    Join Date
    May 2008
    Posts
    4

    Default

    Thanks Carmangary to share your practical knowledge !

    You're right about the res on Norm's DAC, that's 8 bit which is too bad cos I liked his design.
    So the resolution is not linked to the scanner but to the DAC ? That's interesting. Means that the scanner needs to be of a decent quality to maintain the same resolution , I guess.

    Another question that I have after reading the blanking doesn't come from the scanner but from the laser driver, how do you sync the blanking signal with the xy signals for the scanner ?
    A laser driver mend for a scanner should have a special blank control channel ?

    MixedGas: I agree, Norm seems like a nice guy and is a great learning experience. I've asked him when he's going to do 8bits but not anywhere soon

    So I prob go ahead with a ScanPro 20Kpps and a Moncha DAC and a low end green laser (with a blanking channel).

    The next problem would be syncing the camera framerate with the laser frame rate, but that's going to be a problem because the scanner framerate is variable, right ?

    Does an increase of Kpps means the accuracy would be better ?

    Sorry about all the questions. I shall combine all the facts and write a laser scanner FAQ !

  6. #6
    Join Date
    Dec 2006
    Location
    Pflugerville, TX, USA
    Posts
    1,977

    Default

    No, an increase in kpps means more accuracy at higher speeds.

    If you get the Moncha, make sure that he will give you the API. It doesn't come as part of the normal deal. You have to ask for it. I like Moncha because it doesn't require an external power supply and is 16 bit. It's downfall is that it doesn't have any DMX or TTL capabilities.

    As far as blanking goes, your software has to know to turn on/off the laser at the right time. Roughly speaking, that is a no brainer. But, in order to compensate for the lag between scanner movement and laser blanking you'll have to come up with some tricks. For instance, you may want to pause the galvos for a moment when turning the lasers on/off. If you don't you will end up with little comet tails.

  7. #7
    mixedgas's Avatar
    mixedgas is offline Creaky Old Award Winning Bastard Technologist
    Infinitus Excellentia Ion Laser Dominatus
    Join Date
    May 2007
    Location
    A lab with some dripping water on the floor.
    Posts
    9,012

    Default

    [QUOTE=MorganH;48957]Thanks Carmangary to share your practical knowledge !

    You're right about the res on Norm's DAC, that's 8 bit which is too bad cos I liked his design.
    So the resolution is not linked to the scanner but to the DAC ? That's interesting. Means that the scanner needs to be of a decent quality to maintain the same resolution , I guess.

    Your missing the point, I want you to look at the software that comes with norm's dac, its hard to achive results with new code without ever seeing a workinmg system, and is best to have a working tool to see what scanners do. I've helped several people start from scratch, and I'm trying to help you avoid " reinventing the wheel"


    Another question that I have after reading the blanking doesn't come from the scanner but from the laser driver, how do you sync the blanking signal with the xy signals for the scanner ?
    A laser driver mend for a scanner should have a special blank control channel ?

    Ah, you ahve now hit the classical thing called "double buffering" The basic idea is that you have your analog outputs wired in such a way that they all update at the same time, ie
    in hardware you write red,green,blue, x and y to seperate data latches, then update the dac chips all at the same time using the same control signal using the data stored in the latches. M

    mixedGas: I agree, Norm seems like a nice guy and is a great learning experience. I've asked him when he's going to do 8bits but not anywhere soon

    his par port system is 8 bits, you can geta used 500 mhz Pii for what, 20 bucks?
    So I prob go ahead with a ScanPro 20Kpps and a Moncha DAC and a low end green laser (with a blanking channel).

    The next problem would be syncing the camera framerate with the laser frame rate, but that's going to be a problem because the scanner framerate is variable, right ?

    why would you want to do that? Scanners are vector and only scan whats illuminated in the drawing, like a oscilloscope.


    Does an increase of Kpps means the accuracy would be better ?

    No, you have two types of accuracy, position accuracy, and time accuracy, position accuracy is a function of the scanner manufacturer, time accuracy is basically defined by the scanner tuning (a typical scanner amp has 4-6 ten turn potentiometers for tuning) and
    and then mainly by the software/harware combination you use. You cant control the hardware, your buying it, so it comes down to your software smoothly and consistanly delivering thepoint data in real time. Now the hardware will have a buffer in it to smooth things out, norms has a buffer of 1 point pair, better hardware will have a bigger buffer that holds more points so your software can "think" more. Windows is very unstable in the time domain, so you eiher need a simple system and a fast computer (norms) or a smart hardware board and a slower computer, ie pangolin.




    start with a working system, or at least a board that comes with demo software and you can be scanning out of the box, (warning there are a few dacs out there that dont come with a demo program, just a api or dll) you'll be much happier.

    you could try lissajous.exe or laserboy, they are freeware/lowcost ware that use a sound card, that could get you started. Do you have a laser yet?

    Keep asking questions!

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •