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. -- Eric Meurville
How to measure contactlessly position of a spinning miniature cylindrical magnet?
Started by ●November 4, 2005
Reply by ●November 7, 20052005-11-07
Reply by ●November 7, 20052005-11-07
Eric Meurville wrote:> Jerry Avins wrote:...>> Can you paint marks on it?...> 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. �����������������������������������������������������������������������
Reply by ●November 7, 20052005-11-07
Eric Meurville wrote:> 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. �����������������������������������������������������������������������
Reply by ●November 7, 20052005-11-07
On Mon, 07 Nov 2005 10:50:15 -0500, Jerry Avins <jya@ieee.org> wrote:>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. > >JerryI 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
Reply by ●November 7, 20052005-11-07
"Eric Meurville" <eric.meurville@epfl.ch> wrote in message news:436f53ec$1@epflnews.epfl.ch... > 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.
Reply by ●November 7, 20052005-11-07
"CWatters" <colin.watters@pandoraBOX.be> wrote in message news:h8Nbf.41815$2d7.2028640@phobos.telenet-ops.be...> > "Eric Meurville" <eric.meurville@epfl.ch> wrote in message > news:436f53ec$1@epflnews.epfl.ch... > > 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 rotorwith> say 64 hall effect sensors. Scan and convert the analog value of eachsensor> 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.I forgot to add... You will need to deal with noise produced by whatever is spinning the rotor. Hope you don't have an electric motor too close to it.
Reply by ●November 7, 20052005-11-07
On Mon, 07 Nov 2005 18:38:33 GMT, "CWatters" <colin.watters@pandoraBOX.be> wrote:> >"CWatters" <colin.watters@pandoraBOX.be> wrote in message >news:h8Nbf.41815$2d7.2028640@phobos.telenet-ops.be... >> >> "Eric Meurville" <eric.meurville@epfl.ch> wrote in message >> news:436f53ec$1@epflnews.epfl.ch... >> > 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. > >I forgot to add... > >You will need to deal with noise produced by whatever is spinning the rotor. >Hope you don't have an electric motor too close to it.--- LOL, go back and read the thread. It's _part_ of an electric motor! -- John Fields Professional Circuit Designer
Reply by ●November 7, 20052005-11-07
On Mon, 07 Nov 2005 13:51:46 +0100, Eric Meurville <eric.meurville@epfl.ch> wrote:>Jerry Avins wrote: >> 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�). >>> All propositions and comments are welcome.Questions: - The position measurement is relative to what? Displacement between the cylinder and it's container? - Which axis do you want to measure displacement along, the axis of rotation or either of the 2-axis at 90 deg to axis of rotation? Or some angular displacement from the rotation axis (i.e. precession). - Is the container transparent (i.e. could you use a light pipe combined with a light source and light sensor)? - can you post a diagram online?
Reply by ●November 7, 20052005-11-07
---------------------------- "Jerry Avins" <jya@ieee.org> wrote in message news:JrOdnd0OM80m6vLenZ2dnUVZ_vudnZ2d@rcn.net...> Eric Meurville wrote: >> 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---------------------- I think you are on to the best bet so far. However, the problem of the power angle is still there and there seems to be a demand for a position reading in the order of 5 degrees. If the motor is always lightly loaded then ignoring the power angle may be sufficient. It does appear that the problem is still not well specified beyond 1-300Hz and implanted as well as the type of drive. What is missing is the purpose of the device, the location of the device, the necessity for accurate position sensing and all in all the minimum satisfactory criteria. Depending on these factors, this may well be something for a biomedical engineering (assuming implantation is in a carbon based life form) grad student to sink his/her teeth into. There are places which have good biomedical engineering programs - the University of Alberta, Edmonton, Alberta, Canada has (or at least had) such a program. With due respect to this group, you need someone with the necessary skills who can spend time and effort on this problem. Time and effort on the definition of the problem is also required and this has, so far, been minimal. -- Don Kelly @shawcross.ca remove the X to answer
Reply by ●November 8, 20052005-11-08
Don Kelly wrote:> ---------------------------- > "Jerry Avins" <jya@ieee.org> wrote in message > news:JrOdnd0OM80m6vLenZ2dnUVZ_vudnZ2d@rcn.net... > >>Eric Meurville wrote: >> >>>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 > > ---------------------- > I think you are on to the best bet so far. > However, the problem of the power angle is still there and there seems to be > a demand for a position reading in the order of 5 degrees. If the motor is > always lightly loaded then ignoring the power angle may be sufficient. > It does appear that the problem is still not well specified beyond 1-300Hz > and implanted as well as the type of drive. What is missing is the purpose > of the device, the location of the device, the necessity for accurate > position sensing and all in all the minimum satisfactory criteria. > Depending on these factors, this may well be something for a biomedical > engineering (assuming implantation is in a carbon based life form) grad > student to sink his/her teeth into. There are places which have good > biomedical engineering programs - the University of Alberta, Edmonton, > Alberta, Canada has (or at least had) such a program. > With due respect to this group, you need someone with the necessary skills > who can spend time and effort on this problem. Time and effort on the > definition of the problem is also required and this has, so far, been > minimal.What's more, if the plane of the rotating cylinder is not normal to the axis of the rotating field, it will lope like a canted Hooke coupling (the standard -- not CV -- universal joint). Jerry -- Engineering is the art of making what you want from things you can get. ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
