| Author |
Message |
Eric Meurville
Guest
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 Posted:
Fri Nov 04, 2005 5:35 pm Post subject:
How to measure contactlessly position of a spinning miniatur |
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Hello,
We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).
All propositions and comments are welcome.
Thanks.
--
Eric Meurville
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Jerry Avins
Guest
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| Posted:
Fri Nov 04, 2005 5:35 pm Post subject:
Re: How to measure contactlessly position of a spinning mini |
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Eric Meurville wrote:
| Quote: | Hello,
We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).
All propositions and comments are welcome.
|
Can you paint marks on it?
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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Guest
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| Posted:
Fri Nov 04, 2005 5:35 pm Post subject:
Re: How to measure contactlessly position of a spinning mini |
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Eric Meurville wrote:
| Quote: | We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).
|
What's the minimum speed at which you need to monitor the position?
Can you use a pickup coil to make an AC generator and watch the phase?
Are there fast enough hall effect devices, that you could use one or
several of and interpolate position under an assumption of no abrupt
changes in speed?
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Yukio YANO
Guest
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| Posted:
Fri Nov 04, 2005 5:35 pm Post subject:
Re: How to measure contactlessly position of a spinning mini |
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Eric Meurville wrote:
| Quote: | Hello,
We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).
All propositions and comments are welcome.
Thanks.
Use two sensors |
a Hall effect sensor for angular data and use a photo sensor and a spot
of white paint to index reference the rotor.
I have seen Hall Sensors used to monitor Centrifuges to 36,000 RPM !
Yukio YANO |
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John Fields
Guest
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| Posted:
Sat Nov 05, 2005 1:32 am Post subject:
Re: How to measure contactlessly position of a spinning mini |
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On Fri, 04 Nov 2005 16:17:43 +0100, Eric Meurville
<eric.meurville@epfl.ch> wrote:
| Quote: | Hello,
We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).
|
---
1. Is the rotor spinning about its cylindical axis or radially,
somewhere along its length?
2. What is the strength of the rotor's magnetic field?
3. How closely can the sensor approach the spinning cylinder?
4. I don't understand the +/-45° requirement. Do you mean that if,
in one instance, the sensor is located +45° off axis and, in the
next it's located -45° off axis it should still report the
absolute position of the rotor with respect to some arbitrary
reference?
5. Assuming that you want to know the angular position of the rotor
relative to some reference, how accurately do you need that
position to be known?
--
John Fields
Professional Circuit Designer |
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CWatters
Guest
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| Posted:
Sat Nov 05, 2005 1:35 am Post subject:
Re: How to measure contactlessly position of a spinning mini |
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"Eric Meurville" <eric.meurville@epfl.ch> wrote in message
news:436B7B97.2080008@epfl.ch...
| Quote: | Hello,
We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).
All propositions and comments are welcome.
|
What's making it spin? Can you monitor that or do you expect some slip?
Modern brushless DC permanant magnet motor controllers monitor the position
of the rotor using unpowered windings as a sensor coil. |
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bhauth
Guest
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| Posted:
Sat Nov 05, 2005 9:35 am Post subject:
Re: How to measure contactlessly position of a spinning mini |
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If it's in a motor, use the windings. If not, use a hall effect sensor.
Phase will tell you angle; intensity will tell you distance. If you
don't know distance in 2 dimensions, you can use a second hall sensor.
If you don't know alignment, you can use another hall sensor. A BASIC
stamp can do any math you need if you don't have a computer connected.
http://en.wikipedia.org/wiki/Hall_effect_sensor |
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Eric Meurville
Guest
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| Posted:
Mon Nov 07, 2005 5:35 pm Post subject:
Re: How to measure contactlessly position of a spinning mini |
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CWatters wrote:
| Quote: | "Eric Meurville" <eric.meurville@epfl.ch> wrote in message
news:436B7B97.2080008@epfl.ch...
Hello,
We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).
All propositions and comments are welcome.
What's making it spin? Can you monitor that or do you expect some slip?
Modern brushless DC permanant magnet motor controllers monitor the position
of the rotor using unpowered windings as a sensor coil.
The rotor is excited by an external rotating magnetic field generator |
composed of a 3-Phi coil and 3 PWM generators.
--
Eric Meurville |
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Eric Meurville
Guest
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| Posted:
Mon Nov 07, 2005 5:35 pm Post subject:
Re: How to measure contactlessly position of a spinning mini |
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John Fields wrote:
| Quote: | On Fri, 04 Nov 2005 16:17:43 +0100, Eric Meurville
eric.meurville@epfl.ch> wrote:
Hello,
We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).
---
1. Is the rotor spinning about its cylindical axis or radially,
somewhere along its length?
The rotor spins around its cylindrical axis.
2. What is the strength of the rotor's magnetic field?
The rotor is made of SmCo and the typical energy product is around 200 |
kJ/m3.
| Quote: |
3. How closely can the sensor approach the spinning cylinder?
10 mm.
4. I don't understand the +/-45° requirement. Do you mean that if,
in one instance, the sensor is located +45° off axis and, in the
next it's located -45° off axis it should still report the
absolute position of the rotor with respect to some arbitrary
reference?
No, the capsule enclosing the rotor is implanted and after implnattion |
in the body, it is not supposed to move. The question is the tolerance
of the position sensor to a misalignment between the rotor and the sensor.
| Quote: |
5. Assuming that you want to know the angular position of the rotor
relative to some reference, how accurately do you need that
position to be known?
It would be great if the position sensor output could toggle every |
360/2^N°, with e.g. N=6 (that means every 5.625°). More would be better.
--
Eric Meurville |
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Eric Meurville
Guest
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| Posted:
Mon Nov 07, 2005 5:35 pm Post subject:
Re: How to measure contactlessly position of a spinning mini |
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cs_posting@hotmail.com wrote:
| Quote: | Eric Meurville wrote:
We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).
What's the minimum speed at which you need to monitor the position?
Can you use a pickup coil to make an AC generator and watch the phase?
Are there fast enough hall effect devices, that you could use one or
several of and interpolate position under an assumption of no abrupt
changes in speed?
|
Typically, the measurement is performed between from 300 to 1 Hz.
--
Eric Meurville |
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Eric Meurville
Guest
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| Posted:
Mon Nov 07, 2005 5:35 pm Post subject:
Re: How to measure contactlessly position of a spinning mini |
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Jerry Avins wrote:
| Quote: | Eric Meurville wrote:
Hello,
We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300
Hz. The solution must not be too sensitive to misalignment of rotor
and sensor (e.g. up to +/-45°).
All propositions and comments are welcome.
Can you paint marks on it?
Jerry
Hello Jerry, |
No I can't as this rotor is a part of an implanted biosensor.
--
Eric Meurville |
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Jerry Avins
Guest
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| Posted:
Mon Nov 07, 2005 5:35 pm Post subject:
Re: How to measure contactlessly position of a spinning mini |
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Eric Meurville wrote:
| Quote: | Jerry Avins wrote:
|
...
| Quote: | Can you paint marks on it?
|
...
| Quote: | No I can't as this rotor is a part of an implanted biosensor.
|
Implanted, magnetically driven rotor! Implanted into what? Wow!
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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Jerry Avins
Guest
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| Posted:
Mon Nov 07, 2005 5:35 pm Post subject:
Re: How to measure contactlessly position of a spinning mini |
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Eric Meurville wrote:
| Quote: | CWatters wrote:
"Eric Meurville" <eric.meurville@epfl.ch> wrote in message
news:436B7B97.2080008@epfl.ch...
Hello,
We are seeking a solution to monitor contactlessly (up to 10-15mm or
more if possible) the position of a small cylindrical rotor (diameter
1.6 mm, length 2 to 4mm) diametrically magnetized spinning up to 300 Hz.
The solution must not be too sensitive to misalignment of rotor and
sensor (e.g. up to +/-45°).
All propositions and comments are welcome.
What's making it spin? Can you monitor that or do you expect some slip?
Modern brushless DC permanant magnet motor controllers monitor the
position
of the rotor using unpowered windings as a sensor coil.
The rotor is excited by an external rotating magnetic field generator
composed of a 3-Phi coil and 3 PWM generators.
|
It seems that you can know the position of the magnetic field by
measuring the coil currents. A knowledge of the viscosity on the medium
that embeds the rotor and the velocity of the field should allow you to
calculate the power angle between the field and the magnet. If
accelerations are small enough, a static calculation will do. Otherwise,
the rotor's inertia will need to be accounted for.
What you have is essentially a synchronous motor. It must either spin at
the same rate as the magnetic field or stall. When spinning, the angle
between magnet and field must be less than 90 degrees.
Jerry
--
Engineering is the art of making what you want from things you can get.
ŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻŻ |
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Eric Jacobsen
Guest
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| Posted:
Mon Nov 07, 2005 11:56 pm Post subject:
Re: How to measure contactlessly position of a spinning mini |
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On Mon, 07 Nov 2005 10:50:15 -0500, Jerry Avins <jya@ieee.org> wrote:
| Quote: | Eric Meurville wrote:
The rotor is excited by an external rotating magnetic field generator
composed of a 3-Phi coil and 3 PWM generators.
It seems that you can know the position of the magnetic field by
measuring the coil currents. A knowledge of the viscosity on the medium
that embeds the rotor and the velocity of the field should allow you to
calculate the power angle between the field and the magnet. If
accelerations are small enough, a static calculation will do. Otherwise,
the rotor's inertia will need to be accounted for.
What you have is essentially a synchronous motor. It must either spin at
the same rate as the magnetic field or stall. When spinning, the angle
between magnet and field must be less than 90 degrees.
Jerry
|
I think Jerry's on to a good idea. If you're using external coils to
excite it then you should have everything you need to measure it as
well. Whether there are other objects within the fields which may
interfere with the measurements may be an issue, but you may be able
to calibrate or sense those and work around them.
Depending on the amount of power involved I think this may preclude
the use of a Hall effect sensor, anyway, which I think was the next
best idea. If this thing is small, though, and you can't get closer
than 10mm a Hall effect device may not have worked, anyway.
Eric Jacobsen
Minister of Algorithms, Intel Corp.
My opinions may not be Intel's opinions.
http://www.ericjacobsen.org |
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CWatters
Guest
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| Posted:
Tue Nov 08, 2005 12:35 am Post subject:
Re: How to measure contactlessly position of a spinning mini |
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"Eric Meurville" <eric.meurville@epfl.ch> wrote in message
news:436f53ec$1@epflnews.epfl.ch...
| Quote: | It would be great if the position sensor output could toggle every
360/2^N°, with e.g. N=6 (that means every 5.625°). More would be better.
|
If the rotor is a two pole magnet, perhaps you could surround the rotor with
say 64 hall effect sensors. Scan and convert the analog value of each sensor
many times a second and "plot" a graph. Do averaging to improve S/N ratio
and curve fitting to look for the maximium and minimium flux positions
(indicating where the north and south poles are).
However I think I would investigate using something else in the rotor -
perhaps a directional antenna/coil that's externally excited? It's usually
better to start with an AC signal rather than a DC signal if you think you
are going to have S/N ratio problems. |
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