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'[EE] Methods for tracking finger position'
2006\05\31@130133 by Randy Boulter

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I have been tasked with doing a conceptual design for a device that tracks finger movement using a sensor device mounted to the finger.  Does anyone have experience with this or something similar?  Or thoughts or ideas?  For now, I only have to worry about one finger - but need to track position in 3 dimensions with a resolution of about 5mm over an area of 1 cubic meter.  Also, the device cannot use a reflective method (such as ir or ultrasonic).    So far, I have investigated using accelerometer chips, but these are still fairly expensive and I would like a lower-cost alternative.

Thanks,

Randy

2006\05\31@131302 by Marcel Birthelmer

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Randy Boulter wrote:
>
> I have been tasked with doing a conceptual design for a device that tracks finger movement using a sensor device mounted to the finger.  Does anyone have experience with this or something similar?  Or thoughts or ideas?  For now, I only have to worry about one finger - but need to track position in 3 dimensions with a resolution of about 5mm over an area of 1 cubic meter.  Also, the device cannot use a reflective method (such as ir or ultrasonic).    So far, I have investigated using accelerometer chips, but these are still fairly expensive and I would like a lower-cost alternative.
>
> Thanks,
>
> Randy

How about strings from  3 different points that are all tied to the
finger via pulleys. You can use the position of the pulleys to calculate
the finger position.
- Marcel

2006\05\31@133506 by Alan B. Pearce

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>For now, I only have to worry about one finger - but
>need to track position in 3 dimensions with a resolution
>of about 5mm over an area of 1 cubic meter.  Also,
>the device cannot use a reflective method (such as ir
>or ultrasonic).    So far, I have investigated using
>accelerometer chips, but these are still fairly expensive
>and I would like a lower-cost alternative.

I suspect that accelerometers will have long term drift. What sort of long
term accuracy do you need?

One thought I had was to use one of those sensory gloves that are used for
virtual reality type things. You would need to have the person sitting to
get a reference point, or some other method of reference.

2006\05\31@155041 by Randy Boulter

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Yes, I believe drift would be  a problem (using accelerometers) over time.
I need to stay within 5mm over 15 minutes or so.  As for the virtual reality
type gloves, do you know what type of sensor technology they use?

Randy
{Original Message removed}

2006\05\31@155739 by Randy Boulter
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----- Original Message -----
From: "Marcel Birthelmer" <spam_OUTmarcelb.listsTakeThisOuTspamgmail.com>
To: "Microcontroller discussion list - Public." <.....piclistKILLspamspam@spam@mit.edu>
Sent: Wednesday, May 31, 2006 12:16 PM
Subject: Re: [EE] Methods for tracking finger position


> How about strings from  3 different points that are all tied to the
> finger via pulleys. You can use the position of the pulleys to calculate
> the finger position.
> - Marcel
> --

This would be great for one finger, which is what I said I needed.  But the
application will eventually need to track 10 fingers, so I need to keep this
in mind.

Thanks,

Randy

2006\05\31@164943 by Mike Hord

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> I have been tasked with doing a conceptual design for a device
>  that tracks finger movement using a sensor device mounted to
> the finger.  Does anyone have experience with this or something
> similar?  Or thoughts or ideas?  For now, I only have to worry
> about one finger - but need to track position in 3 dimensions
> with a resolution of about 5mm over an area of 1 cubic meter.
>  Also, the device cannot use a reflective method (such as ir or
> ultrasonic).    So far, I have investigated using accelerometer
> chips, but these are still fairly expensive and I would like a
> lower-cost alternative.

I'm not certain this is a feasible project within the parameters given.
Particularly, the fact that you're feeling accelerometers are too
costlly gives me pause.  If you can't handle US$6-12 per finger,
which is the cost of many MEMS accelerometers these days, you
are not likely to find a non-reflective method for tracking ten fingers
for less than that.

That said, I believe one of the ways VR gloves do their thing is by
using strain-sensitive or flex-sensitive resistors to measure the
degree to which the fingers are bent.  Not sure that's what you need.

Are you trying to track the tip of the finger, then, or the whole finger,
so that a model of the finger can be reconstructed later?

Mike H.

2006\05\31@170232 by Gus S Calabrese

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You said you cannot use reflective technology.
Do you ultimately want to track 10 fingertips ?
Or the entire finger profile ?
POD

On 2006-May 31, at 13:54hrs PM, Randy Boulter wrote:


{Original Message removed}

2006\05\31@172504 by Sergey Dryga

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Randy Boulter <wrb <at> isp.com> writes:

>
>
> I have been tasked with doing a conceptual design for a device that tracks
finger movement using a sensor
> device mounted to the finger.  Does anyone have experience with this or
something similar?  Or thoughts or
> ideas?

How about using a (ultra)-sound source at the finger and 3 microphones to
triangulate the position.  Something like this was used for DNA sequence
readout from autoradiographs using a pen as pointing device. The resolution was
in sub-mm range (IIRC).

Another option is to use 3 sound transducers and microphone on the finger to
find position, similar to GPS, only with ultrasound.

Sergey  

2006\05\31@180149 by Robert Rolf

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Alan B. Pearce wrote:
>>For now, I only have to worry about one finger - but
>>need to track position in 3 dimensions with a resolution
>>of about 5mm over an area of 1 cubic meter.  Also,
>>the device cannot use a reflective method (such as ir
>>or ultrasonic).

Why not? Ultrasonic emitters on the tips of the fingers would be
tiny and using time-of-flight measurements, and 4 receivers,
easy to decode.
Use multiple frequencies if you need simultaneous multiple tracking.

What sample rate do you need?

>>    So far, I have investigated using
>>accelerometer chips, but these are still fairly expensive
>>and I would like a lower-cost alternative.

HUH? $25 for 3 axis 1G (ADXL 303JE) is pretty darned cheap.
But they probably won't give you the kind of accuracy you want.
And you've said nothing about tracking orientation.


> I suspect that accelerometers will have long term drift. What sort of long
> term accuracy do you need?
>
> One thought I had was to use one of those sensory gloves that are used for
> virtual reality type things. You would need to have the person sitting to
> get a reference point, or some other method of reference.

These gloves use magnetics, (Flock of birds, 6 DOF) for gross position
and fibre optics to detect bending of the fingers.

Stay away from the Polhemous stuff. It's AC and suffers from big issues
with reflections (eddie currents).

Robert

2006\05\31@180759 by Robert Rolf

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Sergey Dryga wrote:

{Quote hidden}

This method works quite well. We had an old 3-d digitizer that used
a pen that snapped (electric arc) and 3 mics with about a 0.5 meter
spacing, and it covered the 1/2 meter cube quite well.

With 4 external sources, (to get better closure on the RMS position
error), and phase measurements, one could get very good accuracy,
if a continuos high sample rate was required.

Sounds to me like you're looking to do performance art, so there is
no budget available to use the optimal technology.

Robert

2006\05\31@191146 by Randy Boulter

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Forgive me for not providing a more complete description.  The intended
applicaton is a type of "virtual keyboard".  For now, I need to simulate,
using a finger-mounted sensor, the action of reaching out and touching a key
with one finger.  And then be able to track the finger as it is lifted and
moved to another key. This will eventually be expanded to 10 fingers.   I
located some information on the sensors you mentioned - these could be used
to determine if the finger is bent (i.e pressing a key), but that still
leaves the problem of locating the finger in space.  BTW, $6-12 per finger
is not a show-stopper - I would just like to do it for less if possible.

Thanks,

Randy

{Quote hidden}

> -

2006\05\31@191704 by Zik Saleeba

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Look at the Nintendo Wii's controller. It uses an infrared LED in the
controller and for a base station has two cheap IR cameras a certain
distance apart. Position is read off the cameras and distance is
measured using triangulation. This method seems to give pretty
accurate absolute positioning for a very cheap price point.

Cheers,
Zik

On 01/06/06, Randy Boulter <wrbspamKILLspamisp.com> wrote:
>
>
> I have been tasked with doing a conceptual design for a device that tracks finger movement using a sensor device mounted to the finger.  Does anyone have experience with this or something similar?  Or thoughts or ideas?  For now, I only have to worry about one finger - but need to track position in 3 dimensions with a resolution of about 5mm over an area of 1 cubic meter.  Also, the device cannot use a reflective method (such as ir or ultrasonic).    So far, I have investigated using accelerometer chips, but these are still fairly expensive and I would like a lower-cost alternative.
>
> Thanks,
>
> Randy
> -

2006\05\31@194725 by Randy Boulter

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> Sergey Dryga wrote:
>
> > Randy Boulter <wrb <at> isp.com> writes:
> >>
> >>I have been tasked with doing a conceptual design for a device that
tracks
{Quote hidden}

to
> > triangulate the position.  Something like this was used for DNA sequence
> > readout from autoradiographs using a pen as pointing device. The
resolution was
> > in sub-mm range (IIRC).
> >
> > Another option is to use 3 sound transducers and microphone on the
finger to
> > find position, similar to GPS, only with ultrasound.

Robert Rolf wrote :

{Quote hidden}

This sounds like an excellent method, but how far apart would the
microphones have to be if they were placed, say 20 feet away from the sound
source (finger), and still maintain accuracy within a few millimeters?

Randy

2006\05\31@200613 by Gus S Calabrese

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When you come up with a method for $12 per finger, let me know
I would love to help you test it.
POD
0000000000000000000000000000000000000000000000
On 2006-May 31, at 17:08hrs PM, Randy Boulter wrote:

Forgive me for not providing a more complete description.  The intended
applicaton is a type of "virtual keyboard".  For now, I need to  
simulate,
using a finger-mounted sensor, the action of reaching out and  
touching a key
with one finger.  And then be able to track the finger as it is  
lifted and
moved to another key. This will eventually be expanded to 10  
fingers.   I
located some information on the sensors you mentioned - these could  
be used
to determine if the finger is bent (i.e pressing a key), but that still
leaves the problem of locating the finger in space.  BTW, $6-12 per  
finger
is not a show-stopper - I would just like to do it for less if possible.

Thanks,

Randy


{Quote hidden}

> -

2006\05\31@204826 by Robert Rolf

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Randy Boulter wrote:
{Quote hidden}

First you say 1 meter (3 feet) and now you're asking for 20 feet.
BIG change in specifications here. Pointless for me to waste my time
suggesting solutions for a moving target.

The accuracy would be determined by noise levels, and how accurately
you measure the transit time.

Robert


'[EE] Methods for tracking finger position'
2006\06\01@035135 by Alan B. Pearce
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>That said, I believe one of the ways VR gloves do their
>thing is by using strain-sensitive or flex-sensitive
>resistors to measure the degree to which the fingers are bent.

Another method I have heard of is to use a light fibre, and measure the
change in reflected light as the fibre is bent.

2006\06\01@113229 by Robert Ammerman

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You said 'no reflective' and downchecked ultrasonic, but would this work?

small ultrasonic transmitter mounted at the tip of each finger

the transmitters 'chirp' in sequence

three ultrasonic receivers mounted appropriately to receive the signals from
the transmitters

time of flight to the receivers is used to compute the three distances

a little bit of magic math, and....

Bob Ammerman
RAm Systems

2006\06\01@131629 by Peter

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Take a look at J.M.Jarres laser organ and at how camera-equipped barcode
scanners work. By combining the two you can implement the 3rd dimension
scanning (the camera already does 2d). You would have to use a
reflective dot or fingercap (likely IR).

Peter

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