Any device like a CD or DVD player already has the needed chips to capture laser feed back. Since a laser is already in use why cant the parts be stripped and mounted with a laser, captured by the reader and then the slower speed items like a Prop chip use the info?
Laser range finders work by timing how long the laser pulse takes to fly to the target and return (time of flight). Light travels about a foot in one nanosecond. The distance that the laser pulse travels in a CD player is a fraction of that. It is not important for a CD player to know how long the pulse is in flight, only if it is reflected or not.
I could imagine encoding a time signal onto a laser beam using AM or PWM. In theory you could read that value out of the signal that is back scattered. With a high speed clock you diff the time between now and the value of the signal to determine distance.
I imagine the back scattered light would be really faint and had to detect. It would also seem that short distances you would need a really accurate clock and fast electronics to detect time differences and hence the distances.
Acroname has a web page which describes how IR distances sensors work and they use triangulation of the back scattered light and not time at all.
I had a crazy thought earlier today. If you put the laser beam through a diffraction grating it will make a set of bars. I would think the bar spacing would be proportional to the distance to the target. So a line scan camera aligned with the beam might be able to detect the bar spacing and infer the distance.
I wish I had time to try this with my line scan camera as it sounds like a cool project.
I had a crazy thought earlier today. If you put the laser beam through a diffraction grating it will make a set of bars. I would think the bar spacing would be proportional to the distance to the target. So a line scan camera aligned with the beam might be able to detect the bar spacing and infer the distance.
I wish I had time to try this with my line scan camera as it sounds like a cool project.
I think you are on to something. Phil either built or talked about a way to use the Parallax line scan camera as a laser range finder. He did this by measuring where the dot was. Same physics but your idea is self calibrating.
If you put the laser beam through a diffraction grating it will make a set of bars. I would think the bar spacing would be proportional to the distance to the target. So a line scan camera aligned with the beam might be able to detect the bar spacing and infer the distance.
Yes, the farther away the bars are, the farther apart they will be. But distant objects also look smaller to an imager, by the same factor, thus canceling any discernable difference in the spacing.
However, you could do that with two parallel laser beans, which will appear closer together the farther the reflection gets from the scanner. This technique is actually used in underwater inspection, where both subject distance and size need to be determined.
The info you provide shows advances in IR technology.
The basic concern I have is that IR and Lasers function differently. One of the basic problems with IR used in changing light enviroments is that it won't be consisantly accurate. IR has also has proven to be unreliable in any situation of real speed because accuracy starts to degrade. Because IR can be affected by different light levels, IR and Sonar are often used together.
There is no instance that comes to mind of getting IR to function accurately in an uncontrolled enviroment at speeds even of those of an RC car. This aside the links provided also show that the IR range finders have a blind spot outside of the predetermined ranges which indicates that if IR is to be used several must be used together. Not neccesarily a bad thing but rather cumbersome. More to the point, the speed of my RC airplane is to fast for Sonar and IR to accuratly work when power is cut for landing.
Example of what I am saying is this - if you put IR and sonar on something - say a gokart - and simply let it go at jogging speed down a typical bike path accurate scanning starts to break down. By 30 MPH things are really falling apart, if they even work, and by 50 are little more then decoration. Laser doesn't have the problems of IR being affected by light and doesn't breakdown as Sonar does with sudden loud noise, like a car backfiring.
Sonar and IR most certainly have their place, but for scanning while dealing with any sort of speed they fall short and typically they don't work well above a few MPH. By contrast Laser works becaue of its speed and brightness. Also note that Phil referenced underwater lasers which is interesting in itself.
Oh, you want 30-50 MPH outdoors; you hadn't mentioned that previously. That's even easier! Just spend a few million and copy the Stanford, CMU, and Virginia Tech cars from DARPA's Urban Challenge. But don't skimp on your lasers; pass on recycled lasers from CD or DVD players; go straight for the SICK laser scanners and lidar for 3D mapping. Here's one on Ebay now for $3300: http://cgi.ebay.com/SICK-Proximity-Laser-Scanner-PLS101-312-NEW-/170551697857?pt=BI_Control_Systems_PLCs&hash=item27b5ac61c1
Robotics and Automation, 2008. ICRA 2008. IEEE International Conference on
Issue Date: 19-23 May 2008
On page(s): 3002 - 3008
Location: Pasadena, CA
ISSN: 1050-4729
Print ISBN: 978-1-4244-1646-2
INSPEC Accession Number: 10014692
Digital Object Identifier: 10.1109/ROBOT.2008.4543666
Date of Current Version: 13 June 2008
It basically lays out the NEATO 2D LIDAR unit. I am trying to work on this myself. If you don't have an IEEE membership, I can forward you a PDF copy.
All IR sensors are not necessarily slow, the LDR-M10 can respond in 10 mSec and work outside. It is a true time of flight HOBBY LIDAR that samples at 1 million samples per second.
It does not use a Laser, instead it uses a IR LED and looks at a whole "scene" of +/- 20 degree and gives you distance to the closest object within that scene.
All IR sensors are not necessarily slow, the LDR-M10 can respond in 10 mSec and work outside. It is a true time of flight HOBBY LIDAR that samples at 1 million samples per second.
It does not use a Laser, instead it uses a IR LED and looks at a whole "scene" of +/- 20 degree and gives you distance to the closest object within that scene.
Soon is a few months, and the company is in the US. There will be a demo video showing capabilities of the prototype unit in a few weeks. Stay tuned ......
Any device like a CD or DVD player already has the needed chips to capture laser feed back. Since a laser is already in use why cant the parts be stripped and mounted with a laser, captured by the reader and then the slower speed items like a Prop chip use the info?
The simple answer to your question is yes, you can use parts from a CD player to make a laser range finder. However, it's rather like trying to make a Formula 1 racing car out of parts from a Combine Harvester - all the pieces are there but somehow they just don't work so well in the new application.
The reason for this difficulty is that the components in the CD player have been manufactured to work in a specific way and can't easily be reconfigured to work differently. For example, the laser has a focusing lens that produces a very small spot at a distance of a few millimeters. For a range finder it is better to use a lens arrangement that produces a collimated (parallel) beam. It turns out that every part of the CD player will need some major or minor modification to get them to work in a laser range finder - it can be done but this process will take considerably more knowledge and skill than designing the range finder from scratch.
If you're interested, I may soon be putting an open source TOF LRF design online. You can have a look at the draft documents before they go live.
Comments
Any device like a CD or DVD player already has the needed chips to capture laser feed back. Since a laser is already in use why cant the parts be stripped and mounted with a laser, captured by the reader and then the slower speed items like a Prop chip use the info?
Laser range finders work by timing how long the laser pulse takes to fly to the target and return (time of flight). Light travels about a foot in one nanosecond. The distance that the laser pulse travels in a CD player is a fraction of that. It is not important for a CD player to know how long the pulse is in flight, only if it is reflected or not.
Rich H
I imagine the back scattered light would be really faint and had to detect. It would also seem that short distances you would need a really accurate clock and fast electronics to detect time differences and hence the distances.
Acroname has a web page which describes how IR distances sensors work and they use triangulation of the back scattered light and not time at all.
http://www.acroname.com/robotics/info/articles/sharp/sharp.html#e5
The parts may or may not work, but in the end whatever captures the return light needs to be able to read the info at a rate of around a nano second.
Correct?
That's pretty much how I understand it.
Rich H
I wish I had time to try this with my line scan camera as it sounds like a cool project.
This one is from the Seattle Robotics club
http://www.seattlerobotics.org/encoder/200110/vision.htm
http://www.eng.buffalo.edu/ubr/ff03laser.php
http://sites.google.com/site/todddanko/home/webcam_laser_ranger
http://blog.makezine.com/archive/2008/02/diy_laser_range_finder.html
I think you are on to something. Phil either built or talked about a way to use the Parallax line scan camera as a laser range finder. He did this by measuring where the dot was. Same physics but your idea is self calibrating.
However, you could do that with two parallel laser beans, which will appear closer together the farther the reflection gets from the scanner. This technique is actually used in underwater inspection, where both subject distance and size need to be determined.
-Phil
Typ unit: http://www.junun.org/MarkIII/Info.jsp?item=9
The basic concern I have is that IR and Lasers function differently. One of the basic problems with IR used in changing light enviroments is that it won't be consisantly accurate. IR has also has proven to be unreliable in any situation of real speed because accuracy starts to degrade. Because IR can be affected by different light levels, IR and Sonar are often used together.
There is no instance that comes to mind of getting IR to function accurately in an uncontrolled enviroment at speeds even of those of an RC car. This aside the links provided also show that the IR range finders have a blind spot outside of the predetermined ranges which indicates that if IR is to be used several must be used together. Not neccesarily a bad thing but rather cumbersome. More to the point, the speed of my RC airplane is to fast for Sonar and IR to accuratly work when power is cut for landing.
Example of what I am saying is this - if you put IR and sonar on something - say a gokart - and simply let it go at jogging speed down a typical bike path accurate scanning starts to break down. By 30 MPH things are really falling apart, if they even work, and by 50 are little more then decoration. Laser doesn't have the problems of IR being affected by light and doesn't breakdown as Sonar does with sudden loud noise, like a car backfiring.
Sonar and IR most certainly have their place, but for scanning while dealing with any sort of speed they fall short and typically they don't work well above a few MPH. By contrast Laser works becaue of its speed and brightness. Also note that Phil referenced underwater lasers which is interesting in itself.
Instead of buying a laser range finder I want to build one.
Have you seen this paper?
Robotics and Automation, 2008. ICRA 2008. IEEE International Conference on
Issue Date: 19-23 May 2008
On page(s): 3002 - 3008
Location: Pasadena, CA
ISSN: 1050-4729
Print ISBN: 978-1-4244-1646-2
INSPEC Accession Number: 10014692
Digital Object Identifier: 10.1109/ROBOT.2008.4543666
Date of Current Version: 13 June 2008
It basically lays out the NEATO 2D LIDAR unit. I am trying to work on this myself. If you don't have an IEEE membership, I can forward you a PDF copy.
Rick
All IR sensors are not necessarily slow, the LDR-M10 can respond in 10 mSec and work outside. It is a true time of flight HOBBY LIDAR that samples at 1 million samples per second.
It does not use a Laser, instead it uses a IR LED and looks at a whole "scene" of +/- 20 degree and gives you distance to the closest object within that scene.
http://www.miremadi.com/styled/LDR-M10.html
THE UNIT IS NOW ON SALE ON MIREMADI.COM !
Second time you promoted this device, but "Available Soon". How soon?
Website shows no location. USA?
The LDR-M10 HOBBY LIDAR Video is posted on line:
https://www.youtube.com/watch?v=nk2xY3usY0k
THE UNIT IS NOW ON SALE ON MIREMADI.COM !
The simple answer to your question is yes, you can use parts from a CD player to make a laser range finder. However, it's rather like trying to make a Formula 1 racing car out of parts from a Combine Harvester - all the pieces are there but somehow they just don't work so well in the new application.
The reason for this difficulty is that the components in the CD player have been manufactured to work in a specific way and can't easily be reconfigured to work differently. For example, the laser has a focusing lens that produces a very small spot at a distance of a few millimeters. For a range finder it is better to use a lens arrangement that produces a collimated (parallel) beam. It turns out that every part of the CD player will need some major or minor modification to get them to work in a laser range finder - it can be done but this process will take considerably more knowledge and skill than designing the range finder from scratch.
If you're interested, I may soon be putting an open source TOF LRF design online. You can have a look at the draft documents before they go live.