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
How to measure contactlessly position of a spinning miniature cylindrical magnet?
Started by ●November 4, 2005
Reply by ●November 4, 20052005-11-04
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 -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●November 4, 20052005-11-04
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=B0).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?
Reply by ●November 4, 20052005-11-04
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. > > 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
Reply by ●November 4, 20052005-11-04
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? 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
Reply by ●November 4, 20052005-11-04
"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.
Reply by ●November 5, 20052005-11-05
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
Reply by ●November 7, 20052005-11-07
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? > > JerryHello Jerry, No I can't as this rotor is a part of an implanted biosensor. -- Eric Meurville
Reply by ●November 7, 20052005-11-07
cs_posting@hotmail.com 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�). > > > 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
Reply by ●November 7, 20052005-11-07
John Fields wrote:> 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.> > 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.> > 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
