Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01D—MEASURING NOT SPECIALLY ADAPTED FOR A SPECIFIC VARIABLE; ARRANGEMENTS FOR MEASURING TWO OR MORE VARIABLES NOT COVERED IN A SINGLE OTHER SUBCLASS; TARIFF METERING APPARATUS; MEASURING OR TESTING NOT OTHERWISE PROVIDED FOR
  • G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
  • G01D5/12—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means
  • G01D5/14—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage
  • G01D5/142—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage using Hall-effect devices

Definitions

• Magnetic rotation measuring device for a magnetized ball and method for measuring the rotation of the ball
• the invention relates to a measuring device comprising at least one ball.
• a first solution found, for example, in conventional ball mice, is to measure the rotation of the ball by contact, with wheels arranged tangentially on the surface of the ball. The rotation of the rollers is then measured by various known methods such as optical measurement, electrical measurement, etc.
• Text written on a piece of paper can be scanned using a scanner. After scanning, an image file is obtained.
• digital pens have been developed that perform digital acquisition themselves while writing on a sheet of paper.
• US Pat. No. 6,479,768 describes a pen comprising a magnetic ball whose rotation is continuously measured so as to digitally transcribe what a user writes or draws on a sheet of paper.
• the magnetic ball generates a resulting magnetic field having no axis of symmetry.
• a magnetized ball 1 can be in the form of two half-balls 1a and 1b, a magnetized sheet 2 being inserted during the assembly of the two half-balls 1a and 1 b to form the magnetic ball 1.
• Figure 2 Another method, described in this document, to obtain a magnetic ball having no axial symmetry
• the invention aims a device for measuring the rotation of a magnetized ball on an easily industrializable surface.
• each ball being magnetized so as to have a dipolar magnetization, and being free to rotate in a receptacle of a frame
• the device comprises means for detecting a magnetic field created by said at least one ball, according to at least three non-coplanar axes and different directions.
• the object of the invention also aims at a method of measuring the rotation of the ball comprising the following successive steps: determining the three components of the magnetic field vector created by the ball in the mobile frame of reference of at least one magnetometer forming the magnetic field detection means,
• FIGS 1 and 2 illustrate variations of magnetized balls used in magnetic measuring devices of the prior art.
• Figure 3 illustrates, in section, a device according to the invention.
• Figure 4 illustrates the magnetization process of ferromagnetic balls.
• Figures 5 and 6 illustrate other embodiments of balls.
• Figure 7 illustrates a device according to the invention forming a surface feeler.
• Figure 8 illustrates, in section, the use according to one embodiment of a device in the form of a digital pen.
• Figure 9 illustrates an algorithm for analyzing the rotation of the ball of a measuring device.
• Figure 10 illustrates a digital pen using a ball as shown in Figure 6.
• the device for measuring the rotation comprises at least one freely rotating ball 1 in a receptacle 6 of a frame 10.
• a ball is a sphere whose outer surface is not deformable in normal use. .
• normal use is meant a rolling displacement of the ball on a flat surface or not.
• Each ball 1 is magnetized, or has temporary magnetization properties, so as to have a dipolar magnetization. In all the cases of figures, even if the ball is with temporary magnetization, it comprises at a given moment a dipolar magnetization.
• the device is intended to measure the rotation of each ball 1 by studying the evolution of the magnetic field generated by the latter.
• the variations in the magnetic field induced by the ball 1 are measured by means of detecting a magnetic field 5 along at least three non-coplanar axes and of different directions.
• the magnetic field detection means are preferably of the magnetometer type 5, and are integrated in the measuring device.
• the magnetic field detection means are preferably placed at a fixed or near-fixed distance from the center C of the ball 1.
• the ball 1 can be held in the receptacle 6 by holding means 6a and 6b ( Figure 3) disposed at the receptacle 6.
• the receptacle 6 can also be suitably shaped to maintain the ball 1 therein.
• the receptacle 6, allowing only the rotation of the ball 1, keeps the center C of the ball 1 at a quasi-fixed distance R m of the magnetometer 5.
• the ball 1 with dipole magnetization has a total axial symmetry very easy to achieve, with a uniform distribution of the magnetization. For this, it suffices, as illustrated in FIG. 4, to dive the ball 1, having ferromagnetic characteristics necessary for magnetization, in a sufficiently strong polarizing magnetic field H outside.
• the magnetic field H necessary for the magnetization of the ball 1 is generated by the air gap of a magnet.
• This type of magnetization has undeniable advantages at the level of industrialization. Indeed, depending on the size of the gap, it is possible to magnetize many balls 1 simultaneously as in Figure 4.
• the remanent magnetization of the ball 1 must be large before that of the local magnetic field if we want to perceive the rotational movements of the ball 1.
• the local magnetic field corresponds to the resultant of the Earth's magnetic field and the magnetic fields present at the place of use of the measuring device.
• the ball 1 having ferromagnetic properties, can be made of tungsten carbide comprising cobalt, or any other body ferromagnetic.
• the ball 1 may also be made of a composite or non-magnetic material in which, during molding, a magnet or particles of ferromagnetic metal, for example iron (Fe 1 ), cobalt (Co), nickel ( Ni) or their alloys, or ferrimagnetic particles.
• the magnetization of the ball 1 can be achieved by any other means for assimilating it to a magnetic dipole, for example coils placed in the ball 1 in which a magnetization is induced.
• the microbattery 12 is also integrated in the ball 1.
• This variant can generate a constant or alternating magnetic field comparable to that of a permanently magnetized ball, as long as the battery 12 feeds the coil 11. This magnetic field is as indicated above dipolar.
• the ball 1 may be too small to integrate the battery pack 12 and its electronics.
• the ball then comprises, as illustrated in Figure 6, a coil 11 is, for example, in the form of a coil. So that the coil can induce a magnetic field, it is necessary to excite the latter by generation means 13 of a magnetic field external to the ball 1, said generation means 13 being arranged, for example, in the frame 10
• the dipole obtained is not constant, and it becomes necessary to know the instantaneous current intensity in the coil to correct the values measured by the magnetometer or 5. This intensity can be determined by calculation.
• the ball may be dipole magnetized temporarily. According to a particular embodiment illustrated in FIG.
• the measuring device comprises three balls 1 of different diameters arranged to roll tangentially to a plane 8 to form a surface feeler.
• the surface feeler makes it possible to determine the asperities of the plane 8 on which the balls move in order to establish an accurate cartography of this plane.
• each ball 1 is associated with a magnetometer 5.
• the use of several balls makes it possible to obtain a plurality of different measurements and to study the values of the incident magnetic fields to map the surface of the plane 8.
• the balls 1 can also be assimilated to alternative dipoles, that is to say that the magnetic field created by each ball 1 can be magnetostatic type at a given frequency. This is obtained, for example, by coils placed in the balls 1 and powered by an alternating voltage to create an alternating excitation field H. The exciter field then induces an alternating dipolar magnetization in each ball 1. It is thus possible to determine with common magnetic field detection means the rotational movements of one or more balls by performing synchronous detections at each of the frequencies concerned. Therefore, a single magnetometer can be used to determine the movements of several balls.
• the alternative dipole principle can also be applied when the measuring device has only one ball. Thus, several separate measuring devices can operate nearby without the risk of disturbances.
• FIG. 7 is not limited to three balls, it may be adapted to the convenience of those skilled in the art depending on the desired accuracy of the mapping.
• a probe has a plurality of balls, of different diameters, arranged to roll tangentially to the same plane.
• the magnetic field detection means may be magnetometers 5 for measuring the magnetic field along at least three axes.
• the three-axis measurement provides the three components of the vector representative of the magnetic field generated by the ball 1. These axes are preferably orthogonal to each other.
• a magnetometer 5 may be of the Hall effect, fluxgate type, giant magnetoresitance (GMR), anisotropic magnetoresistance (AMR), inductive, etc. type. Some of these magnetometers have a low consumption allowing a device integrating them to be autonomous without becoming too bulky. It is also possible to use much more sensitive magnetometers, such as nuclear magnetic resonance or optical pumping magnetometers.
• the magnetic measuring device can be used for flow measurement, rotational speed measurement of a wheel, vehicle or camshaft ball bearing, etc. It can also be used in the field of handwriting recognition.
• the frame 10 of the measuring device may, as illustrated in FIG. 8, be in the form of an elongate body 7 to form, preferably, a digital pen comprising at one of its ends the receptacle 6 in which is housed a ball 1.
• a single ball 1 is disposed at one end of said elongate body 7.
• the elongated body 7 further comprises means for detecting its inclination (not shown) to know the position of the pen when writing.
• the device then constitutes an autonomous digital ballpoint pen.
• the association of the ball 1, magnetized or temporarily magnetized dipole, and a magnetometer 5 at least three axes can scan a text and / or drawings made on a fixed plane 8 by moving the pen on it plane (by rolling ball 1).
• the data digitized by the pen (for example the measurement of the magnetic field of the ball and the inclination of the pen) can be stored in an internal memory (not shown) of the pen, then transferred to a personal computer by wired connection means. or not.
• the connection means may be in the form of a universal serial transmission port (USB for "Universal Serial Bus" in English), WIFI transceiver, etc.
• the measurements are, in practice, always made when the ball 1 is in contact with a plane 8 or a surface and rolls, without sliding, on this plane or this surface.
• the ball 1 is rotating, the probability that the latter rotates around the axis of symmetry of its magnetization is low.
• a simple dipole magnetization of the ball is therefore sufficient for use as a probe or digital pen.
• the magnetic ball 1 rolls on a fixed plane 8.
• the magnetic field lines 9, created by the ball 1 form in the space loops closing on the axis of magnetization (axis passing through the two poles).
• the rotation of the ball 1 modifies the position of the field lines with respect to the elongated body 7.
• the resulting magnetic field is measured and then analyzed to determine the movement made by the ball 1 on the plane 8. The analysis makes it possible to extrapolate what the user has written and / or drawn.
• the method for measuring the rotation of the ball of any device as described above may comprise a step of determination of the three components of the magnetic field vector created by the ball 1 in the mobile reference frame of at least one magnetometer forming the magnetic field detection means. Then, it is possible to calculate a magnetization vector in the magnetometer frame from the magnetic field vector.
• the rotation of the ball 1 can then be determined by the calculation of a rotation vector of the ball 1, from the data of the magnetization vector in the magnetometer frame, with respect to a fixed frame representative of a plane or a surface on which rolls the ball 1, considering that the pivoting of the ball 1 is zero.
• pivoting is meant that the ball rotates only about its own axis.
• the plan may for example be a sheet on which a user writes and / or draws.
• the displacement of the ball in the plane is calculated from the rotation vector of the ball 1.
• FIG. 9 A first particular calculation algorithm for translating the movements of the ball into letters and / or drawings is illustrated in FIG. 9.
• the magnetometer records the three components of the vector field.
• a magnetization vector M m (t) in the magnetometer repository is then calculated, in a step E2, from the equation
• ⁇ 0 is the magnetic permeability constant of the vacuum
• r is the representative vector of the coordinates of the center of the ball in the magnetometer frame
• Id the identity matrix
• R m the distance separating the center of the ball from the magnetometer.
• a magnetization vector M f (step E3) is then determined in a fixed frame of reference, for example the sheet or plane on which the ball rolls.
• the marker change matrix N (t) may be constant if the device is a surface feeler moving tangentially to a plane, or be determined by orientation measuring means such as accelerometers, spirit levels, etc. , if the device is a digital pen whose inclination may change during use.
• the time derivatives of the magnetization in the fixed frame of reference are calculated.
• a step E4 the rotation vector ⁇ of the ball is calculated with respect to the fixed reference frame.
• the rotation ⁇ of the ball with respect to the fixed reference is deduced by inverting the following equation:
• step E4 for calculating the rotation vector of the ball 1 From the results of the step E4 for calculating the rotation vector of the ball 1, it is possible to calculate the displacement of the ball 1 on the plane 8. Indeed, if the ball 1 rolls without sliding, then the field Magnetic is modified and the point of contact of the ball on the plane, being identified by Cartesian coordinates (x, y), is obtained by:
• R b is the radius of the ball
• CO x and ⁇ y represent the rotational components along the x and y axes, and dt the time step of the measurement.
• Such a pen or a probe associated with the algorithm described above, allows the measurement of the rotation of the ball 1 without contact other than that with the sheet or the plane 8 used, thus avoiding any parasitic measure due to the friction of the ball on roulette measuring means as in the prior art.
• This algorithm works as long as the assumptions of non-slip and non-pivoting are satisfied, which is the case when the ball or balls move in a rolling plane.
• the probe it is necessary to either move the balls constituting it to prevent a first ball disturbs the magnetometer of a second ball, or to carry out an adequate filtering of the signals. For example, taking R b1 the radius of the first ball and R b2 the radius of the second ball, if the probe moves at a speed V p , the first ball produces a magnetic signal rotating at the speed V p / R b1 and the second ball at the speed V p / R b2 .
• the chassis 10 comprises means 13 for generating an exciter field shown in FIG. the vector
• the vector H is known and the vector M is measured at each instant t. Indeed, the ball rotating in the exciter magnetic field H, the coil becomes the seat of an induced current which in turn produces an induced magnetization M generating a magnetic field B measurable by a magnetometer 5.
• the vector v of FIG. 10 is a representation equivalent to the vector of displacement of the ball during a time dt.
• I is the current flowing in the turn at time t, the surface vector of the turn at time t.
• the vector of surface S corresponds to a vector normal to the turn and of standard equal to the surface of the turn.
• the induced magnetization M is therefore always collinear with the vector 5.
• the magnetic excitation H can be constant or variable in time.
• a time-varying excitation can be a sinusoidal excitation. In both cases (constant or variable excitation), it is necessary to calibrate the magnetometers by measuring the signal H without rotating the ball 1 and subtract the latter from measurements when the ball 1 rotates.
• the magnetization vector in the magnetometer frame can be determined as in the first algorithm (step E2). This magnetization vector
• Mm (O in the magnetometer repository is also equal to / (0-5 (0, where I is the current flowing in the coil at time t, the surface vector of the coil at time t, l (t) being known using Lenz's law, then the vector rotation ⁇ of the ball in a fixed reference representative of the plane in which the ball moves is deduced by inverting the equation
• the inclination of the pen In order to make a suitable measurement at the matrix N (t), it is preferably necessary to know the inclination of the pen. This inclination can be determined by accelerometers as described above. In some cases, the accelerometers are not necessarily sufficient, it is then possible to improve the measurement using a terrestrial magnetometer, arranged for example in the frame, measuring the Earth's magnetic field. However, the terrestrial magnetometer must not be disturbed by the magnetic field generated by the ball 1. This constraint can be bypassed by using a ball 1 having a magnetic field of 10 times the terrestrial magnetic field, and the distance separating the ball 1 from the terrestrial magnetometer must be 5 times the distance separating the ball 1 of the magnetic field detection means of the ball 1.
• the induced field of the ball decreases in 1 / R b ⁇ 3 so that if one places at a distance of five times the distance separating the center of the ball magnetometer, one obtains a magnetic field 125 times lower.
• Measurements of the magnetic moment of the ball can be made at different times with a low pitch and a single magnetometer (tri-axis). It is then possible to measure with great precision the direction and the intensity of the rotation of the ball relative to the fixed plane.
• the pen can perform character recognition and generate a file compatible with known word processors.
• This recognition can either be achieved by the pen itself, which generates a text file, or, for reasons of limitation of pen consumption, by software installed on a personal computer that does not have problems of operation at reduced consumption, the data being then transmitted via appropriate connecting means.

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Citations (4)

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• 2009
  • 2009-03-19 FR FR0901285A patent/FR2943412B1/fr not_active Expired - Fee Related
• 2010
  • 2010-03-19 US US13/257,498 patent/US20120101772A1/en not_active Abandoned
  • 2010-03-19 JP JP2012500289A patent/JP2012520999A/ja active Pending
  • 2010-03-19 EP EP10713693A patent/EP2409118A2/de not_active Withdrawn
  • 2010-03-19 WO PCT/FR2010/000232 patent/WO2010106252A2/fr active Application Filing

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