Position "Sensing"

[Jon Slaughter]

Anyone know of any reference that discusses the methods of measuring
distances both small and large and the electronics behind them? I want a
method to measure with mil to sub mill accuracy over a few inches. My
initial thought was to use high freq sound pulses since this would be a
cheap way but after doing some calculations it seems that it might be
impossible, or at least very difficult without precise sensors(piezo's might
work but still a problem of determining when the sound is "heard"). Speed in
measuring is not really an issue either(can take a few seconds if
necessary).

I'm a bit afraid of using light because it seems it would require relatively
expensive devices and techniques. BTW, I need a wireless method but the
device itself can be wired(so it can compare the speed with that of a wired
EM signal).

Any ideas where I can look for more info on this? The main reason for this
is to get around having to manufacture very precise positioning parts.
Obviously if the cost of "remote" position sensing is more than that of just
manufacturing the parts then its not worth it.

Also note that I suppose that I could have many sensors(I was thinking 4 to
6) that have super-mil accuracy but take some statistical average to get a
better result.

In fact I don't care much about the relative position but only the change in
position.

I just found this site:

http://electronics.sensorsmag.com/s...Sensing/ArticleStandard/Article/detail/320838

Which seems to say that the ultrasonic method might work... It also gives
two other methods. I'm going to read more about it but a book would probably
be much nicer.

Thanks,
Jon

 

[Charles]

Laser interferometry?

 

[Jon Slaughter]

Laser interferometry?

I'll look into it but my guess was that it would be too complicated for my
setup. Maybe for the accuracy I need it can be done easier than I think.
I'll see what I can learn about it. (if it can be done easy and cheaply then
it probably would be the best bet. I really know nothing about it except for
the basic physics behind it so I guess its time to learn more.

Thanks,
Jon

 

[Charles]

I'll look into it but my guess was that it would be too complicated for my
setup. Maybe for the accuracy I need it can be done easier than I think.
I'll see what I can learn about it. (if it can be done easy and cheaply
then it probably would be the best bet. I really know nothing about it
except for the basic physics behind it so I guess its time to learn more.

Yes, it probably is too expensive but I am amazed at the positioning
accuracy that it can achieve. I had some experience with it, 12 years ago,
and hoped that the cost has come down. Good luck.

 

[[email protected]]

Anyone know of any reference that discusses the methods of measuring
distances both small and large and the electronics behind them? I want a
method to measure with mil to sub mill accuracy over a few inches. My
initial thought was to use high freq sound pulses since this would be a
cheap way but after doing some calculations it seems that it might be
impossible, or at least very difficult without precise sensors(piezo's might
work but still a problem of determining when the sound is "heard"). Speed in
measuring is not really an issue either(can take a few seconds if
necessary).

I'm a bit afraid of using light because it seems it would require relatively
expensive devices and techniques. BTW, I need a wireless method but the
device itself can be wired(so it can compare the speed with that of a wired
EM signal).

Any ideas where I can look for more info on this? The main reason for this
is to get around having to manufacture very precise positioning parts.
Obviously if the cost of "remote" position sensing is more than that of just
manufacturing the parts then its not worth it.

Also note that I suppose that I could have many sensors(I was thinking 4 to
6) that have super-mil accuracy but take some statistical average to get a
better result.

In fact I don't care much about the relative position but only the change in
position.

I just found this site:

http://electronics.sensorsmag.com/sensorselectronics/Manufacturing+Au...

Which seems to say that the ultrasonic method might work... It also gives
two other methods. I'm going to read more about it but a book would probably
be much nicer.

As Paul Hovnanian says, you will have to be a lot more specific about
the items whose separation you want to measure. Heidenhain has a lot
of postion-measuring products

http://www.heidenhain.com/index.php?WCMSGroup_2238_177=479

but it is by no means obvious that you can fix a moving sensor to the
object whose position you want to monitor, and have it travel along a
fixed scale, reading off where it is as it goes.

High frequency sound pulses may not be a good idea - the speed of
sound in air does vary.

For precision interferometry, the speed of light in air can vary
enough to disturb very accurate measurements.

 

[Paul Hovnanian P.E.]

Anyone know of any reference that discusses the methods of measuring
distances both small and large and the electronics behind them? I want a
method to measure with mil to sub mill accuracy over a few inches. My
initial thought was to use high freq sound pulses since this would be a
cheap way but after doing some calculations it seems that it might be
impossible, or at least very difficult without precise sensors(piezo's might
work but still a problem of determining when the sound is "heard"). Speed in
measuring is not really an issue either(can take a few seconds if
necessary).

Non contact position sensing, I assume (otherwise the problem becomes
trivial). Can you attach a target to the object? What are its optical
and acoustic properties? Also the characteristics of the environment in
which the measurement will be performed.

How many degrees of freedom must be monitored? X, Y, and Z position?
Orientation of the object as well?

I'm a bit afraid of using light because it seems it would require relatively
expensive devices and techniques. BTW, I need a wireless method but the
device itself can be wired(so it can compare the speed with that of a wired
EM signal).

Any ideas where I can look for more info on this? The main reason for this
is to get around having to manufacture very precise positioning parts.
Obviously if the cost of "remote" position sensing is more than that of just
manufacturing the parts then its not worth it.

Also note that I suppose that I could have many sensors(I was thinking 4 to
6) that have super-mil accuracy but take some statistical average to get a
better result.

In fact I don't care much about the relative position but only the change in
position.

I just found this site:

http://electronics.sensorsmag.com/s...Sensing/ArticleStandard/Article/detail/320838

Which seems to say that the ultrasonic method might work... It also gives
two other methods. I'm going to read more about it but a book would probably
be much nicer.

Thanks,
Jon

--
Paul Hovnanian mailto[email protected]
------------------------------------------------------------------
It's easier said than done.
.... and if you don't believe it, try proving that it's easier done than
said, and you'll see that it's easier said that `it's easier done than
said' than it is done, which really proves that it's easier said than
done.

 

[Eeyore]

Anyone know of any reference that discusses the methods of measuring
distances both small and large and the electronics behind them? I want a
method to measure with mil to sub mill accuracy over a few inches. My
initial thought was to use high freq sound pulses

Since the speed of sound isn't constant it would be a lousy method.

Graham

 

[hrh1818]

Anyone know of any reference that discusses the methods of measuring
distances both small and large and the electronics behind them? I want a
method to measure with mil to sub mill accuracy over a few inches. My
initial thought was to use high freq sound pulses since this would be a
cheap way but after doing some calculations it seems that it might be
impossible, or at least very difficult without precise sensors(piezo's might
work but still a problem of determining when the sound is "heard"). Speed in
measuring is not really an issue either(can take a few seconds if
necessary).

I'm a bit afraid of using light because it seems it would require relatively
expensive devices and techniques. BTW, I need a wireless method but the
device itself can be wired(so it can compare the speed with that of a wired
EM signal).

Any ideas where I can look for more info on this? The main reason for this
is to get around having to manufacture very precise positioning parts.
Obviously if the cost of "remote" position sensing is more than that of just
manufacturing the parts then its not worth it.

Also note that I suppose that I could have many sensors(I was thinking 4 to
6) that have super-mil accuracy but take some statistical average to get a
better result.

In fact I don't care much about the relative position but only the change in
position.

I just found this site:

http://electronics.sensorsmag.com/sensorselectronics/Manufacturing+Au...

Which seems to say that the ultrasonic method might work... It also gives
two other methods. I'm going to read more about it but a book would probably
be much nicer.

Thanks,
Jon

Take a look at linear incremental optical encoders made by Gurley
Precision instruments.
See http://www.gpi-encoders.com/lininc.htm
Scale length to 125 inches, resolution to 0.5 micrometers with
incremental interpolators and non-contacting friction free.

If you do a Google search on "linear optical encoder" you will find
other companies also make them.

Howard

 

[[email protected]]

http://www.spaceagecontrol.com/selpt.htm

 

[hrh1818]

Take a look at linear incremental optical encoders made by Gurley
Precision instruments.
Seehttp://www.gpi-encoders.com/lininc.htm
Scale length to 125 inches, resolution to 0.5 micrometers with
incremental interpolators and non-contacting friction free.

If you do a Google search on "linear optical encoder" you will find
other companies also make them.

Howard

Also take a look at linear optical encoders made by Renishaw.
See http://www.renishaw.com/en/6433.aspx
and also click on their non-contact position encoder brochure.

 

[James Arthur]

Take a look at linear incremental optical encoders made by Gurley
Precision instruments.
Seehttp://www.gpi-encoders.com/lininc.htm
Scale length to 125 inches, resolution to 0.5 micrometers with
incremental interpolators and non-contacting friction free.

If you do a Google search on "linear optical encoder" you will find
other companies also make them.

Howard

1) The sensors and encoder strips used in ink jet printers are
economical & hi-res, made by one of HP's orphans.
2) For small sale use, Chinese digital calipers / (dremel + cutoff
wheel) = cheap digital scale.

Cheers,
James Arthur