Multitouch Zero Force Setup Based on IR Laser Light

Here is the setup that I’ve been working on for a while now. It is based on front IR illumination by IR laser.

Camera

For this project I’ve been using my old Orange Micro iBot firewire camera with great success. This low-cost camera generates 640x480 at 30fps uncompressed images in Y800 format. I found that because of all of this and the IR sensitivity this camera is very suitable for IR multitouch application:

After removing the original lens and mounting the new lens without IR blocking filter, I placed the double-sided tape on top of the lens and cut the opening in it:

IR Bandpass Filter

In the past I used photo negative with some success, but found that using narrow bandpass filter is by far the best in removing any unwanted IR noise and visible light:

Here is the filter mounted on the camera:

Table Setup

Currently I’m in the process of redesigning the table. Right now it is an open-frame setup:

IR Laser

And now the most important part. I use the 850nm IR Laser light to illuminate the front of the surface. When finger or any object interfere with the laser light, the camera below picks up the bright spot and runs it through the image processing algo to generate detected blob information.
Here is the view from the surface:

The laser is mounted on a tripod on a tri-point adjustable platform so that it can be positioned is a way that it generates a light beam that is parallel to the glass surface:

The IR laser is positioned just above the glass surface:

Software

Even though I could use touchlib for blob processing/tracking, having a lot of experience in image processing, I found that it was easier for me to write a highly optimized version blob tracking software. Because of this, I achieve very low latency and low CPU usage running my blob tracking software (around 3-4% on my E6600 2.4GHz system).
Here are some screenshots of my blob tracking app: 

As you can see blobs are very bright and clean:

Here is my iPhone placed on the surface:

Video

Here you can see the system in action. While using FTIR the blobs become dimer during the fast movement, using the laser method the blobs are always bright

Short video of the system:

WOW! Alex, nice setup and video. I’m interested in the IR Laser setup so that means I’m going to ask alot of questions . How does it perform with ambient light? I know that the laser is mounted parallel to the screen, but how does it create a uniform spread across the glass? I would have thought it would use something like a FTIR setup beamed into the side of some acrylic. Also, you mentioned you use glass, is it frosted or do you use a different diffuser?

Looks good!

A very interesting setup… love to see more details about it.

Taha

Looks great..
I’also wondering how you get the ir light to spread out evenly, and doesn’t the ir light get blocked by the first obstacle/finger and the 2nd won’t show up if there behind each other?

Fairlane - 28 May 2008 02:58 AM

WOW! Alex, nice setup and video. I’m interested in the IR Laser setup so that means I’m going to ask alot of questions . How does it perform with ambient light? I know that the laser is mounted parallel to the screen, but how does it create a uniform spread across the glass? I would have thought it would use something like a FTIR setup beamed into the side of some acrylic. Also, you mentioned you use glass, is it frosted or do you use a different diffuser?

Because of the high brightness and light intensity of the laser light, I found that this setup performs very well in both ambient and daylight. This is why my current test setup is in the form of the open box. The blob tracking pictures are taken in the room that was lit by a bright halogen light. As you can see there is some background IR light going through the bandpass filter. This is how you can see my hand on the other side of the glass.

Regarding the FTIR - I tried to beam the laser light into the acrylic, althought the light that was shining through was very bright, I didnt get any FTIR effect. I think this is due the high collimation of the laser light. Unless your acrylic is perfectly polished and its edges are perfectly parallel to each other, the light will escape the acrylic and you will not get enough light bounces within the acrylic panel.

In my setup I specifically use the fact that the laser light is very collimated to generate a thin plane of IR light right on top of the glass surface. I found that the closer you can get to the surface - the better. The IR light plane thickness is about 1mm throughout the glass area. When the tip of your finger touches the glass it is lit by the laser light. The blob brightness generated by this mehtod is many times higher in intensity than equivalent generated by FTIR, DI and other methods. This of course depends on the output power of laser used. In this particular setup I use a single IR laser that generates only about 3.5mW of light power. Because of its efficiency and simplicity, I prefer this mthod over the FTIR and DI.

Although I could have used frosted glass panel instead of the clear one, the difuser I’ve played with and got good results is a thin drafting/tracing paper (velum).

Because of its simplicity and small number of parts this method could be equally used in both horizontal and vertical setups. The one I’m particularly interested in is the storefront application of this method.

Great, thanks for clearing that up. Just on what Helza1 said about the shadow effect, does that come into play considering that there is only one laser beaming from a single point or is it reflected in some way? It certainly looks like there are no shadow effects from your pics/vid.

Looks very nice Alex.

How are you spreading the laser bean? as normally doesn’t it come out in a direct line.
From the Microsoft vid I think they were using 3 lasers. How wide is the IR coverage?

Just had a random thought: Have you tried fiducials? I know that the IR light is coming above the surface but maybe a clear plastic cube/puck would glow red and show the pattern.

Fairlane - 28 May 2008 02:58 AM

I’m interested in the IR Laser setup so that means I’m going to ask alot of questions

Nice Fairlane so I will only have to read the anwsers!
I’m interested too!
Chris

nice 1 !
How much mW is the laser?  5mW or more ?

gally - 28 May 2008 07:22 AM

nice 1 !
How much mW is the laser?  5mW or more ?

Alex mentions that he is getting 3.5mW. But didn’t mention in terms of cost if thats what you mean.

Hi , this is really interesting and your setup looks great.How exactly are you dispersing the laser evenly on the surface?Where did you get the laser , the diode looks preaty small and seaing you said it’s 3.5mW , is it from a CD-ROM or did you buy it separately.

Could you please try out this setup without the bandpass filter but with touchlib’s background removal function , if it works whitout the bandpass filter i think we just got a better way of building tables.

nice work!
it seems you found the way Microsoft did.
do you have any idea about the Qty of IR Laser Vs. Glass Area? what’s the size of your glass?
Hope to see more details soon!

is it possible for you to tell us the make and model of the IR laser? or did u modify it with a “filter” to generate the plane?

I decided to work with scale for a little while and I have come up with some rough dimensions of the size of his table or at least the area captured by the camera.

I got 33” wide and 24” high. or 40.8” inch diagonal ( THESE MEASUREMENTS ARE IN INCHES )

I too am interested in more info on the laser. I think AlexP said that he is using collimation to his advantage in this setup, so perhaps the beam is fanning out sufficiently by itself? I don’t know. But still, the results posted so far are phenomenal, compared to a lot of other MT setups I’ve seen, looking forward to seeing more!