On Tue, 08 Nov 2005 00:26:56 -0500, Jerry Avins wrote:> Don Kelly wrote: >> "Jerry Avins" <jya@ieee.org> wrote in message >>>Eric Meurville wrote: >>>>CWatters wrote: >>>>>"Eric Meurville" <eric.meurville@epfl.ch> wrote in message >>>>> >>>>>>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[degrees]). >>>>>> >>>>>>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. >>> >> 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).I wonder, is the guy constrained to magnetic sensing? My first thought, on reading the OP, was, "Paint a white stripe on the shaft and use a reflective sensor." Thanks! Rich
How to measure contactlessly position of a spinning miniature cylindrical magnet?
Started by ●November 4, 2005
Reply by ●November 8, 20052005-11-08
Reply by ●November 8, 20052005-11-08
The device is implanted- I assume that optical means are not valid unless the detection is also implanted. -- Don Kelly @shawcross.ca remove the X to answer ---------------------------- "Rich Grise" <rich@example.net> wrote in message news:pan.2005.11.08.17.43.49.19885@example.net...> On Tue, 08 Nov 2005 00:26:56 -0500, Jerry Avins wrote: >> Don Kelly wrote: >>> "Jerry Avins" <jya@ieee.org> wrote in message >>>>Eric Meurville wrote: >>>>>CWatters wrote: >>>>>>"Eric Meurville" <eric.meurville@epfl.ch> wrote in message >>>>>> >>>>>>>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[degrees]). >>>>>>> >>>>>>>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. >>>> >>> 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). > > I wonder, is the guy constrained to magnetic sensing? My first thought, > on reading the OP, was, "Paint a white stripe on the shaft and use a > reflective sensor." > > Thanks! > Rich >
Reply by ●November 8, 20052005-11-08
Rich Grise wrote: ...> I wonder, is the guy constrained to magnetic sensing? My first thought, > on reading the OP, was, "Paint a white stripe on the shaft and use a > reflective sensor."Read my first message in this thread and the response to it. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●November 10, 20052005-11-10
Well, you *can* use optical means: bright infrared LEDs, infrared markings, and an infrared-filtered CCD, for example. Magnetic sensing is just better.
Reply by ●November 10, 20052005-11-10
On 10 Nov 2005 14:40:39 -0800, "bhauth" <bhauth@gmail.com> wrote:>Well, you *can* use optical means: bright infrared LEDs, infrared >markings, and an infrared-filtered CCD, for example. Magnetic sensing >is just better.--- Didn't you bother to read the thread? It's _implanted_. -- John Fields Professional Circuit Designer
Reply by ●November 11, 20052005-11-11
"John Fields" <jfields@austininstruments.com> wrote in message news:0oj7n1ph3ogf50uqc4qbcn090dosiglaa0@4ax.com...> On 10 Nov 2005 14:40:39 -0800, "bhauth" <bhauth@gmail.com> wrote: > > >Well, you *can* use optical means: bright infrared LEDs, infrared > >markings, and an infrared-filtered CCD, for example. Magnetic sensing > >is just better. > > --- > Didn't you bother to read the thread? > > It's _implanted_.Only 10mm deep though. Try shining a torch through your hand. I'm sure I read that someone was trying to use light to replace some hospital x-rays. They were experimenting with using sensitive sensors similar to those used by optical telescopes. Probably wouldn't work for this application but it might not as daft as you imply.
Reply by ●November 11, 20052005-11-11
CWatters wrote:> "John Fields" <jfields@austininstruments.com> wrote in message > > > Didn't you bother to read the thread? > > > > It's _implanted_. > > Only 10mm deep though. Try shining a torch through your hand. I'm sure I > read that someone was trying to use light to replace some hospital x-rays. > They were experimenting with using sensitive sensors similar to those used > by optical telescopes. Probably wouldn't work for this application but it > might not as daft as you imply.I'm with you. I've seen strange and subtle things happen with different lighting conditions and different sensors... all in the optical or near-optical range (i.e. not X-ray). I'm not sure it WILL work, however I am certain it's worth investigating. Ciao, Peter K.
Reply by ●November 13, 20052005-11-13
["Followup-To:" header set to sci.electronics.misc.] On 2005-11-07, Eric Meurville <eric.meurville@epfl.ch> wrote:> Jerry Avins wrote: >> 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.you say diametrically magnetised meaning north pole at 0 degrees and south at 180 degrees and spinning so to that north and south swap places? what's the minimum rate of spin? will it spin backwards, if it does do you need to know it's going backwards? do you need angle information? In what environments must the sensor operate, hand-held or worn .... are momentary failures acceptable? how often and for how long? -- Bye. Jasen
Reply by ●November 13, 20052005-11-13
["Followup-To:" header set to sci.electronics.misc.] On 2005-11-07, Eric Meurville <eric.meurville@epfl.ch> 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.external to the implantee? so you have to cancel that field out before you can read its position, any nearby magnetic materials are going to muddy the water no matter how finely you tune the sensor. -- Bye. Jasen
